Point cloud data transmission device, point cloud data transmission method, point cloud data reception device, and point cloud data reception method

Abstract

A point cloud data decoding method and device are disclosed. The point cloud data decoding method, according to the embodiments, may comprise the steps of: receiving geometry data, attribute data, and signaling information; decoding the geometry data on the basis of the signaling information; and decoding the attribute data on the basis of the signaling information.

Description

Point cloud data transmission device, point cloud data transmission method, point cloud data reception device, and point cloud data reception method

[0001] Embodiments relate to a method and apparatus for processing point cloud content.

[0002] Point cloud content is content expressed as a point cloud, a collection of points belonging to a coordinate system that represents three-dimensional space (space or volume). Point cloud content can express three-dimensional media and is used to provide various services such as VR (Virtual Reality), AR (Augmented Reality), MR (Mixed Reality), XR (Extended Reality), and autonomous driving services. However, expressing point cloud content requires tens to hundreds of thousands of point data. Therefore, a method for efficiently processing massive amounts of point data is required.

[0003] That is, transmitting and receiving point cloud data requires a significant amount of processing power. Therefore, encoding for compression and decoding for decompression are performed during the process of transmitting and receiving point cloud data. However, the large size of point cloud data makes the computations complex and time-consuming.

[0004] The technical problem according to the embodiments is to provide a device and method for efficiently transmitting / receiving a point cloud in order to solve the problems described above.

[0005] The technical problem according to the embodiments is to provide a device and method for resolving latency and encoding / decoding complexity.

[0006] The technical task according to the embodiments is to provide a device and method for efficiently providing a scalable service by performing neighbor search in subgroup units.

[0007] However, the scope of the embodiments is not limited to the technical tasks described above, and the scope of the embodiments may be expanded to other technical tasks that can be inferred by a person skilled in the art based on the entire described content.

[0008] To achieve the above-described purpose and other advantages, a point cloud data decoding method according to embodiments may include a step of receiving geometry data, attribute data, and signaling information, a step of decoding the geometry data based on the signaling information, and a step of decoding the attribute data based on the signaling information.

[0009] According to embodiments, the geometry data is divided and included in data units of a layer group structure, and the geometry data of the current data unit of the current layer group can be decoded by referring to context information of the data unit of the upper layer group stored in the memory.

[0010] According to embodiments, the memory is managed for each data unit, and the memory referenced for decoding geometry data of the current data unit is divided into a context state storage area, a reference count information storage area, and a counter information storage area, the context state storage area stores context information of a data unit of the upper layer group, the reference count information storage area stores the number of data units referencing a data unit of the upper layer group for each layer group constituting the layer group structure, and the counter information storage area can store counter information that is updated each time a data unit of the upper layer group is used for each layer group.

[0011] According to embodiments, the step of decoding the geometry data may not store context information of the current data unit of the decoded current layer group in the memory if there is no subsequent data unit that refers to context information of the current data unit.

[0012] According to embodiments, the step of decoding the geometry data may not store context information of the current data unit of the decoded current layer group in the memory if the current layer group is the last layer group in the layer group structure.

[0013] According to embodiments, the step of decoding the geometry data may not store context information of the current data unit of the decoded current layer group in the memory if the current layer group is the last layer group, excluding the layer group whose decoding is skipped in the layer group structure.

[0014] According to embodiments, the step of decoding the geometry data may determine the release of context information of the data unit of the upper layer group based on a value stored in a reference count information storage area of ​​the memory and a value stored in the count information storage area.

[0015] According to embodiments, the signaling information may include information for identifying a data unit of the upper layer group that is referenced for decoding geometry data of the current data unit.

[0016] According to embodiments, the signaling information may include information related to the number of reference data units per layer group stored in a reference count storage area of ​​the memory.

[0017] According to embodiments, a point cloud data decoding device may include a receiving unit that receives geometry data, attribute data, and signaling information, a geometry decoder that decodes the geometry data based on the signaling information, and an attribute decoder that decodes the attribute data based on the signaling information.

[0018] According to embodiments, the geometry data is divided and included in data units of a layer group structure, and the geometry decoder can decode the geometry data of the current data unit of the current layer group by referring to context information of the data unit of the upper layer group stored in the memory.

[0019] According to embodiments, the memory is managed for each data unit, and the memory referenced for decoding geometry data of the current data unit is divided into a context state storage area, a reference count information storage area, and a counter information storage area, the context state storage area stores context information of a data unit of the upper layer group, the reference count information storage area stores the number of data units referencing a data unit of the upper layer group for each layer group constituting the layer group structure, and the counter information storage area can store counter information that is updated each time a data unit of the upper layer group is used for each layer group.

[0020] According to embodiments, the geometry decoder can determine the release of context information of a data unit of the upper layer group stored in the context state storage area based on a value stored in a reference count information storage area of ​​the memory and a value stored in the count information storage area.

[0021] According to embodiments, a method for encoding point cloud data may include encoding geometry data, encoding attribute data, and transmitting the encoded geometry data, the encoded attribute data, and signaling information.

[0022] According to embodiments, a point cloud data encoding device may include a geometry encoder that encodes geometry data, an attribute encoder that encodes attribute data, and a transmission unit that transmits the encoded geometry data, the encoded attribute data, and signaling information.

[0023] The device and method according to the embodiments can provide a quality point cloud service.

[0024] The devices and methods according to the embodiments can achieve various video codec schemes.

[0025] The device and method according to the embodiments can provide general-purpose point cloud content such as autonomous driving services.

[0026] The device and method according to the embodiments can provide improved parallel processing and scalability by performing spatially adaptive segmentation of point cloud data for independent encoding and decoding of point cloud data.

[0027] The device and method according to the embodiments can improve the encoding and decoding performance of a point cloud by dividing point cloud data into tiles and / or slices to perform encoding and decoding and signaling data required for this.

[0028] The device and method according to the embodiments can divide and transmit compressed data according to certain criteria for point cloud data. Furthermore, when layered coding is used, the compressed data can be divided and transmitted according to each layer. Therefore, the storage and transmission efficiency of the transmission device is increased.

[0029] The device and method according to the embodiments can efficiently manage a context buffer when decoding a bitstream in a layer group structure composed of a plurality of data units.

[0030] The device and method according to the embodiments can efficiently manage the context buffer during partial decoding by managing the context buffer for each data unit by layer group in a layer group structure composed of a plurality of data units.

[0031] The drawings are included to further understand the embodiments, and the drawings illustrate the embodiments together with the description related to the embodiments.

[0032] Figure 1 illustrates an example of a point cloud content provision system according to embodiments.

[0033] FIG. 2 is a block diagram illustrating a point cloud content provision operation according to embodiments.

[0034] FIG. 3 illustrates an example of a point cloud encoder according to embodiments.

[0035] Figure 4 illustrates examples of octree and occupancy codes according to embodiments.

[0036] Figure 5 shows an example of a point configuration by LOD according to embodiments.

[0037] Figure 6 shows an example of a point configuration by LOD according to embodiments.

[0038] Fig. 7 illustrates an example of a point cloud decoder according to embodiments.

[0039] Figure 8 is an example of a transmission device according to embodiments.

[0040] Fig. 9 is an example of a receiving device according to embodiments.

[0041] Fig. 10 shows an example of a structure that can be linked with a point cloud data transmission / reception method / device according to embodiments.

[0042] Figures 11 and 12 are diagrams showing the encoding, transmission, and decoding processes of point cloud data according to embodiments.

[0043] FIG. 13 is a diagram illustrating an example of layer-based point cloud data configuration according to embodiments.

[0044] Fig. 14 (a) shows a bitstream structure of geometry data according to embodiments, and Fig. 14 (b) shows a bitstream structure of attribute data according to embodiments.

[0045] FIG. 15 is a diagram showing an example of a configuration of a bitstream for dividing a bitstream into layer units and transmitting it according to embodiments.

[0046] FIG. 16 illustrates an example of a bitstream alignment method when a geometry bitstream and an attribute bitstream are multiplexed into one bitstream according to embodiments.

[0047] FIG. 17 illustrates another example of a bitstream alignment method when a geometry bitstream and an attribute bitstream are multiplexed into one bitstream according to embodiments.

[0048] FIGS. 18(a) to 18(c) are drawings showing examples of symmetrical geometry-attribute selection according to embodiments.

[0049] FIGS. 19(a) to 19(c) are drawings showing examples of asymmetric geometry-attribute selection according to embodiments.

[0050] FIGS. 20(a) to 20(c) illustrate examples of a method for constructing slices including point cloud data according to embodiments.

[0051] Figures 21(a) and 21(b) illustrate single-slice and split-slice based geometry tree structures according to embodiments.

[0052] Figures 22(a) and 22(b) illustrate the layer group structure of the geometry coding tree and the aligned layer group structure of the attribute coding tree according to embodiments.

[0053] Figure 23 illustrates the layer group and subgroup structure according to embodiments.

[0054] Figure 24 illustrates an example of context references between layer groups according to embodiments.

[0055] Figure 25 illustrates an example of context reference between groups according to embodiments.

[0056] Figures 26 (a) to (c) illustrate examples of context buffer management according to embodiments.

[0057] Figures 27 (a) to (c) illustrate examples of context buffer management according to embodiments.

[0058] Figures 28 (a) to (c) illustrate examples of context buffer management according to embodiments.

[0059] Figures 29 (a) to (c) illustrate a context buffer release method according to embodiments.

[0060] Figure 30 illustrates a context buffer release method according to embodiments.

[0061] Figure 31 illustrates a context memory management method according to embodiments.

[0062] Figure 32 illustrates a bitstream containing point cloud data according to embodiments.

[0063] FIG. 33 illustrates an example of a syntax structure of a sequence parameter set (SPS) of a bitstream according to embodiments.

[0064] FIG. 34 illustrates an example of a syntax structure of a dependent geometry data unit header of a bitstream according to embodiments.

[0065] FIG. 35 illustrates an example of a syntax structure of a dependent attribute data unit header of a bitstream according to embodiments.

[0066] Figures 36a and 36b illustrate an example of a syntax structure of a layer group structure inventory (LGSI) according to embodiments.

[0067] Fig. 37 illustrates a point cloud data transmission device / method according to embodiments.

[0068] Fig. 38 illustrates a point cloud data receiving device / method according to embodiments.

[0069] Figure 39 illustrates a method for receiving point cloud data according to embodiments.

[0070] Fig. 40 illustrates a layer group-based point cloud data encoding method according to embodiments.

[0071] Figure 41 illustrates a layer group-based point cloud data decoding method according to embodiments.

[0072] Figures 42 (a) to (c) illustrate a context buffer management method according to embodiments.

[0073] Figures 43 (a) to (c) illustrate a context buffer management method according to embodiments.

[0074] Figures 44 (a) to (c) illustrate a context buffer management method according to embodiments.

[0075] Figure 45 illustrates an example of a syntax structure of a geometry data unit header according to embodiments.

[0076] Figure 46 illustrates an example of a syntax structure of a dependent geometry data unit header according to embodiments.

[0077] Figure 47 illustrates an example of the syntax structure of an attribute data unit header according to embodiments.

[0078] Figure 48 illustrates an example of the syntax structure of a dependent attribute data unit header according to embodiments.

[0079] FIG. 49 is a diagram showing an example of a layer group structure considering partial decoding according to embodiments.

[0080] Figures 50 (a) to (d) illustrate a context buffer management method according to embodiments.

[0081] Figure 51 shows an example of a syntax structure of a sequence parameter set according to embodiments.

[0082] Figure 52 illustrates an example of a syntax structure of a geometry data unit header according to embodiments.

[0083] Figure 53 illustrates an example of a syntax structure of a dependent geometry data unit header according to embodiments.

[0084] Figure 54 illustrates an example of the syntax structure of an attribute data unit header according to embodiments.

[0085] Figure 55 illustrates an example of the syntax structure of a dependent attribute data unit header according to embodiments.

[0086] Figure 56 is a drawing showing an example of compressing and serving the geometry and attributes of point cloud data.

[0087] FIG. 57 is a diagram showing another example of compressing and serving the geometry and attributes of point cloud data according to embodiments.

[0088] Figure 58 is a diagram showing the operation of the transmission and reception unit when transmitting point cloud data composed of layers.

[0089] Fig. 59 illustrates a point cloud data transmission / reception device / method according to embodiments.

[0090] Figure 60 shows a flowchart of a point cloud data transmission method according to embodiments.

[0091] Figure 61 shows a flowchart of a method for receiving point cloud data according to embodiments.

[0092] Preferred embodiments of the embodiments are described in detail, examples of which are illustrated in the accompanying drawings. The following detailed description, with reference to the accompanying drawings, is intended to illustrate preferred embodiments of the embodiments, rather than merely show embodiments that can be implemented according to the embodiments. The following detailed description includes details to provide a thorough understanding of the embodiments. However, it will be apparent to those skilled in the art that the embodiments may be practiced without these details.

[0093] While most of the terms used in the examples are commonly used in the field, some terms were arbitrarily selected by the applicant, and their meanings are described in detail in the following descriptions as needed. Therefore, the examples should be understood based on the intended meaning of the terms, not simply their names or meanings.

[0094] FIG. 1 illustrates an example of a point cloud content provision system according to embodiments.

[0095] The point cloud content provision system illustrated in FIG. 1 may include a transmission device (10000) and a reception device (10004). The transmission device (10000) and the reception device (10004) are capable of wired and wireless communication to transmit / receive point cloud data.

[0096] A transmission device (10000) according to embodiments can secure, process, and transmit a point cloud video (or point cloud content). According to embodiments, the transmission device (10000) can include a fixed station, a base transceiver system (BTS), a network, an Artificial Intelligence (AI) device and / or system, a robot, an AR / VR / XR device and / or a server, etc. In addition, according to embodiments, the transmission device (10000) can include a device that performs communication with a base station and / or other wireless devices using a wireless access technology (e.g., 5G NR (New RAT), LTE (Long Term Evolution)), a robot, a vehicle, an AR / VR / XR device, a portable device, a home appliance, an IoT (Internet of Things) device, an AI device / server, etc.

[0097] A transmission device (10000) according to embodiments includes a Point Cloud Video Acquisition unit (10001), a Point Cloud Video Encoder (10002), and / or a Transmitter (or Communication module), 10003.

[0098] A point cloud video acquisition unit (10001) according to embodiments acquires a point cloud video through a processing process such as capture, synthesis, or generation. The point cloud video is point cloud content expressed as a point cloud, which is a collection of points located in a three-dimensional space, and may be referred to as point cloud video data, etc. The point cloud video according to embodiments may include one or more frames. One frame represents a still image / picture. Therefore, the point cloud video may include a point cloud image / frame / picture, and may be referred to as any one of a point cloud image, a frame, and a picture.

[0099] A point cloud video encoder (10002) according to embodiments encodes acquired point cloud video data. The point cloud video encoder (10002) may encode point cloud video data based on point cloud compression coding. The point cloud compression coding according to embodiments may include G-PCC (Geometry-based Point Cloud Compression) coding and / or V-PCC (Video-based Point Cloud Compression) coding or next-generation coding. In addition, the point cloud compression coding according to embodiments is not limited to the above-described embodiment. The point cloud video encoder (10002) may output a bitstream including encoded point cloud video data. The bitstream may include not only encoded point cloud video data but also signaling information related to encoding of the point cloud video data.

[0100] A transmitter (10003) according to embodiments transmits a bitstream including encoded point cloud video data. The bitstream according to embodiments is encapsulated into a file or segment (e.g., streaming segment) and transmitted through various networks such as a broadcast network and / or a broadband network. Although not shown in the drawing, the transmission device (10000) may include an encapsulation unit (or an encapsulation module) that performs an encapsulation operation. In addition, the encapsulation unit may be included in the transmitter (10003) according to embodiments. According to embodiments, the file or segment may be transmitted to a receiving device (10004) through a network or may be stored in a digital storage medium (e.g., USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc.). The transmitter (10003) according to embodiments may communicate with the receiving device (10004) (or receiver (10005)) via a network such as 4G, 5G, or 6G via wired / wireless communication. Additionally, the transmitter (10003) can perform data processing operations required according to a network system (e.g., a communication network system such as 4G, 5G, or 6G). Additionally, the transmission device (10000) can transmit encapsulated data in an on-demand manner.

[0101] A receiving device (10004) according to embodiments includes a receiver (10005), a point cloud video decoder (10006), and / or a renderer (10007). According to embodiments, the receiving device (10004) may include a device, robot, vehicle, AR / VR / XR device, mobile device, home appliance, IoT (Internet of Things) device, AI device / server, etc. that performs communication with a base station and / or other wireless devices using a wireless access technology (e.g., 5G NR (New RAT), LTE (Long Term Evolution)).

[0102] A receiver (10005) according to embodiments receives a bitstream containing point cloud video data or a file / segment in which the bitstream is encapsulated, from a network or a storage medium. The receiver (10005) may perform data processing operations required according to a network system (e.g., a communication network system such as 4G, 5G, or 6G). The receiver (10005) according to embodiments may decapsulate the received file / segment and output a bitstream. In addition, the receiver (10005) according to embodiments may include a decapsulation unit (or decapsulation module) for performing the decapsulation operation. In addition, the decapsulation unit may be implemented as a separate element (or component) from the receiver (10005).

[0103] A point cloud video decoder (10006) decodes a bitstream containing point cloud video data. The point cloud video decoder (10006) can decode the point cloud video data according to how it is encoded (e.g., the reverse process of the operation of the point cloud video encoder (10002)). Accordingly, the point cloud video decoder (10006) can decode the point cloud video data by performing point cloud decompression coding, which is the reverse process of point cloud compression. The point cloud decompression coding includes G-PCC coding.

[0104] The renderer (10007) renders the decoded point cloud video data. In one embodiment, the renderer (10007) may render the decoded point cloud video data according to a viewport, etc. The renderer (10007) may render not only the point cloud video data but also audio data to output point cloud content. According to embodiments, the renderer (10007) may include a display for displaying the point cloud content. According to embodiments, the display may not be included in the renderer (10007) but may be implemented as a separate device or component.

[0105] The dotted arrows in the drawing indicate the transmission path of feedback information acquired from the receiving device (10004). The feedback information is information for reflecting the interaction with the user consuming the point cloud content, and includes information about the user (e.g., head orientation information, viewport information, etc.). In particular, when the point cloud content is content for a service requiring interaction with the user (e.g., autonomous driving service, etc.), the feedback information may be transmitted to the content transmitter (e.g., the transmitting device (10000)) and / or the service provider. Depending on the embodiments, the feedback information may be used not only by the transmitting device (10000) but also by the receiving device (10004), or may not be provided.

[0106] Head orientation information according to embodiments may refer to information about the position, direction, angle, movement, etc. of the user's head. The receiving device (10004) according to embodiments may calculate viewport information based on the head orientation information. The viewport information is information about the area of ​​the point cloud video that the user is looking at (i.e., the area that the user is currently viewing). In other words, the viewport information is information about the area that the user is currently viewing within the point cloud video. In other words, the viewport or the viewport area may refer to the area that the user is viewing within the point cloud video. In addition, the viewpoint is the point that the user is viewing within the point cloud video, and may refer to the exact center point of the viewport area. In other words, the viewport is an area centered on the viewpoint, and the size, shape, etc. that the area occupies may be determined by the FOV (Field Of View). Therefore, the receiving device (10004) may extract viewport information based on the vertical or horizontal FOV supported by the device in addition to the head orientation information. In addition, the receiving device (10004) may perform gaze analysis, etc. based on head orientation information and / or viewport information to check the user's point cloud video consumption method, the point cloud video area the user gazes at, the gaze time, etc. According to embodiments, the receiving device (10004) may transmit feedback information including the gaze analysis result to the transmitting device (10000). According to embodiments, a device such as a VR / XR / AR / MR display may extract a viewport area based on the user's head position / direction, a vertical or horizontal FOV supported by the device, etc. According to embodiments, head orientation information and viewport information may be referred to as feedback information, signaling information, or metadata.

[0107] Feedback information according to embodiments may be acquired during the rendering and / or display process. The feedback information according to embodiments may be acquired by one or more sensors included in the receiving device (10004). Additionally, the feedback information according to embodiments may be acquired by the renderer (10007) or a separate external element (or device, component, etc.). The dotted line in Fig. 1 represents the transmission process of the feedback information acquired by the renderer (10007). The feedback information may not only be transmitted to the transmitting side, but may also be consumed by the receiving side. That is, the point cloud content providing system may process (encode / decode / render) point cloud data based on the feedback information. For example, the point cloud video decoder (10006) and the renderer (10007) may use the feedback information, i.e., head orientation information and / or viewport information, to preferentially decode and render only the point cloud video for the area currently being viewed by the user.

[0108] Additionally, the receiving device (10004) can transmit feedback information to the transmitting device (10000). The transmitting device (10000) (or point cloud video encoder (10002)) can perform an encoding operation based on the feedback information. Therefore, the point cloud content providing system can efficiently process necessary data (e.g., point cloud data corresponding to the user's head position) based on the feedback information without processing (encoding / decoding) all point cloud data, and provide point cloud content to the user.

[0109] According to embodiments, the transmitting device (10000) may be referred to as an encoder, a transmitting device, a transmitter, a transmitting system, etc., and the receiving device (10004) may be referred to as a decoder, a receiving device, a receiver, a receiving system, etc.

[0110] Point cloud data processed (processed through a series of processes of acquisition / encoding / transmission / decoding / rendering) in the point cloud content providing system of FIG. 1 according to embodiments may be referred to as point cloud content data or point cloud video data. According to embodiments, point cloud content data may be used as a concept including metadata or signaling information related to point cloud data.

[0111] The elements of the point cloud content provision system illustrated in FIG. 1 may be implemented by hardware, software, a processor, and / or a combination thereof.

[0112] FIG. 2 is a block diagram illustrating a point cloud content provision operation according to embodiments.

[0113] The block diagram of Fig. 2 illustrates the operation of the point cloud content provision system described in Fig. 1. As described above, the point cloud content provision system can process point cloud data based on point cloud compression coding (e.g., G-PCC).

[0114] A point cloud content providing system according to embodiments (e.g., a point cloud transmission device (10000) or a point cloud video acquisition unit (10001)) can acquire a point cloud video (20000). The point cloud video is expressed as a point cloud belonging to a coordinate system representing a three-dimensional space. The point cloud video according to embodiments can include a Ply (Polygon File format or the Stanford Triangle format) file. If the point cloud video has one or more frames, the acquired point cloud video can include one or more Ply files. The Ply file includes point cloud data such as the geometry and / or attributes of points. The geometry includes the positions of points. The position of each point can be expressed as parameters (e.g., values ​​of each of the X-axis, Y-axis, and Z-axis) representing a three-dimensional coordinate system (e.g., a coordinate system composed of XYZ axes). Attributes include attributes of points (e.g., texture information of each point, color (YCbCr or RGB), reflectance (r), transparency, etc.). One point has one or more attributes (or properties). For example, one point may have one attribute of color, or two attributes of color and reflectance. According to embodiments, geometry may be referred to as positions, geometry information, geometry data, etc., and attributes may be referred to as attributes, attribute information, attribute data, etc. In addition, a point cloud content providing system (e.g., a point cloud transmission device (10000) or a point cloud video acquisition unit (10001)) may obtain point cloud data from information related to the acquisition process of a point cloud video (e.g., depth information, color information, etc.).

[0115] A point cloud content providing system according to embodiments (e.g., a transmission device (10000) or a point cloud video encoder (10002)) can encode point cloud data (20001). The point cloud content providing system can encode point cloud data based on point cloud compression coding. As described above, point cloud data can include geometry and attributes of points. Therefore, the point cloud content providing system can perform geometry encoding to encode geometry and output a geometry bitstream. The point cloud content providing system can perform attribute encoding to encode attributes and output an attribute bitstream. According to embodiments, the point cloud content providing system can perform attribute encoding based on geometry encoding. The geometry bitstream and the attribute bitstream according to embodiments can be multiplexed and output as a single bitstream. A bitstream according to embodiments may further include signaling information related to geometry encoding and attribute encoding.

[0116] A point cloud content providing system according to embodiments (e.g., a transmission device (10000) or a transmitter (10003)) can transmit encoded point cloud data (20002). As described in FIG. 1, the encoded point cloud data can be expressed as a geometry bitstream and an attribute bitstream. In addition, the encoded point cloud data can be transmitted in the form of a bitstream together with signaling information related to encoding of the point cloud data (e.g., signaling information related to geometry encoding and attribute encoding). In addition, the point cloud content providing system can encapsulate a bitstream that transmits the encoded point cloud data and transmit it in the form of a file or segment.

[0117] A point cloud content providing system according to embodiments (e.g., a receiving device (10004) or a receiver (10005)) can receive a bitstream including encoded point cloud data. In addition, the point cloud content providing system (e.g., a receiving device (10004) or a receiver (10005)) can demultiplex the bitstream.

[0118] A point cloud content providing system (e.g., a receiving device (10004) or a point cloud video decoder (10005)) can decode encoded point cloud data (e.g., a geometry bitstream, an attribute bitstream) transmitted as a bitstream. The point cloud content providing system (e.g., a receiving device (10004) or a point cloud video decoder (10005)) can decode the point cloud video data based on signaling information related to encoding of the point cloud video data included in the bitstream. The point cloud content providing system (e.g., a receiving device (10004) or a point cloud video decoder (10005)) can decode the geometry bitstream to restore positions (geometry) of points. The point cloud content providing system can decode the attribute bitstream based on the restored geometry to restore attributes of points. A point cloud content provision system (e.g., a receiving device (10004) or a point cloud video decoder (10005)) can reconstruct a point cloud video based on positions and decoded attributes according to the reconstructed geometry.

[0119] A point cloud content providing system (e.g., a receiving device (10004) or a renderer (10007)) according to embodiments can render decoded point cloud data (20004). The point cloud content providing system (e.g., a receiving device (10004) or a renderer (10007)) can render the geometry and attributes decoded through the decoding process according to various rendering methods. Points of the point cloud content may be rendered as vertices having a certain thickness, cubes having a certain minimum size centered on the vertex position, or circles centered on the vertex position. All or a portion of the rendered point cloud content is provided to a user through a display (e.g., a VR / AR display, a general display, etc.).

[0120] A point cloud content provision system according to embodiments (e.g., a receiving device (10004)) can obtain feedback information (20005). The point cloud content provision system can encode and / or decode point cloud data based on the feedback information. The feedback information and the operation of the point cloud content provision system according to embodiments are identical to the feedback information and operation described in FIG. 1, and therefore, a detailed description thereof will be omitted.

[0121] FIG. 3 illustrates an example of a point cloud encoder according to embodiments.

[0122] FIG. 3 illustrates an example of a point cloud video encoder (10002) of FIG. 1. The point cloud encoder reconstructs point cloud data (e.g., positions and / or attributes of points) and performs an encoding operation to adjust the quality of point cloud content (e.g., lossless, lossy, near-lossless) depending on network conditions or applications. If the total size of the point cloud content is large (e.g., point cloud content of 60 Gbps at 30 fps), the point cloud content provision system may not be able to stream the content in real time. Therefore, the point cloud content provision system can reconstruct the point cloud content based on the maximum target bitrate in order to provide it according to the network environment, etc.

[0123] As described in FIGS. 1 and 2, the point cloud encoder can perform geometry encoding and attribute encoding. Geometry encoding is performed before attribute encoding.

[0124] The point cloud encoder according to the embodiments includes a coordinate system transformation unit (Transformation Coordinates, 30000), a quantization unit (Quantize and Remove Points (Voxelize), 30001), an octree analysis unit (Analyze Octree, 30002), a surface approximation analysis unit (Analyze Surface Approximation, 30003), an arithmetic encoder (Arithmetic Encode, 30004), a geometry reconstruction unit (Reconstruct Geometry, 30005), a color transformation unit (Transform Colors, 30006), an attribute transformation unit (Transfer Attributes, 30007), a RAHT transformation unit (30008), a LOD generation unit (Generated LOD, 30009), a lifting transformation unit (Lifting) (30010), and a coefficient quantization unit (Quantize Coefficients, 30011) and / or an arithmetic encoder (30012). In the point cloud encoder of FIG. 3, the coordinate system transformation unit (30000), the quantization unit (30001), the octree analysis unit (30002), the surface approximation analysis unit (30003), the arithmetic encoder (30004), and the geometry reconstruction unit (30005) can be grouped and referred to as a geometry encoder. In addition, the color conversion unit (30006), attribute conversion unit (30007), RAHT conversion unit (30008), LOD generation unit (30009), lifting conversion unit (30010), coefficient quantization unit (30011) and / or arithmetic encoder (30012) can be grouped and referred to as an attribute encoder.

[0125] The coordinate system transformation unit (30000), the quantization unit (30001), the octree analysis unit (30002), the surface approximation analysis unit (30003), the arithmetic encoder (30004), and the geometry reconstruction unit (30005) can perform geometry encoding. The geometry encoding according to the embodiments can include octree geometry coding, direct coding, trisoup geometry encoding, and entropy encoding. Direct coding and trisoup geometry encoding are applied selectively or in combination. In addition, the geometry encoding is not limited to the above examples.

[0126] As illustrated in the drawing, a coordinate system conversion unit (30000) according to embodiments receives positions and converts them into coordinates. For example, the positions may be converted into location information of a three-dimensional space (e.g., a three-dimensional space expressed in an XYZ coordinate system, etc.). The location information of the three-dimensional space according to embodiments may be referred to as geometry information.

[0127] A quantization unit (30001) according to embodiments quantizes geometry. For example, the quantization unit (30001) may quantize points based on the minimum position value of all points (e.g., the minimum value on each axis for the X-axis, Y-axis, and Z-axis). The quantization unit (30001) performs a quantization operation of multiplying the difference between the minimum position value and the position value of each point by a preset quantization scale value, and then rounding down or up to find the closest integer value. Accordingly, one or more points may have the same quantized position (or position value). The quantization unit (30001) according to embodiments performs voxelization based on the quantized positions to reconstruct the quantized points. The minimum unit containing two-dimensional image / video information is a pixel, and points of point cloud content (or three-dimensional point cloud video) according to embodiments may be included in one or more voxels. A voxel is a combination of a volume and a pixel, and refers to a three-dimensional cubic space generated when a three-dimensional space is divided into units (unit=1.0) based on axes representing the three-dimensional space (e.g., X-axis, Y-axis, Z-axis). The quantization unit (40001) may match groups of points in the three-dimensional space to voxels. According to embodiments, one voxel may include only one point. According to embodiments, one voxel may include one or more points. In addition, in order to express one voxel as one point, the position of the center of the voxel may be set based on the positions of one or more points included in one voxel. In this case, the attributes of all positions contained in one voxel can be combined and assigned to the voxel.

[0128] The octree analysis unit (30002) according to the embodiments performs octree geometry coding (or octree coding) to represent voxels in an octree structure. The octree structure represents points matched to voxels based on an octree structure.

[0129] The surface approximation analysis unit (30003) according to the embodiments can analyze and approximate an octree. The octree analysis and approximation according to the embodiments is a process of analyzing and voxelizing an area including a large number of points to efficiently provide an octree and voxelization.

[0130] An arithmetic encoder (30004) according to embodiments entropy encodes an octree and / or an approximated octree. For example, the encoding method includes an arithmetic encoding method. The encoding results in a geometry bitstream.

[0131] The color conversion unit (30006), the attribute conversion unit (30007), the RAHT conversion unit (30008), the LOD generation unit (30009), the lifting conversion unit (30010), the coefficient quantization unit (30011) and / or the arithmetic encoder (30012) perform attribute encoding. As described above, one point may have one or more attributes. Attribute encoding according to embodiments is applied equally to the attributes of one point. However, when one attribute (e.g., color) includes one or more elements, independent attribute encoding is applied to each element. Attribute encoding according to embodiments may include color transform coding, attribute transform coding, RAHT (Region Adaptive Hierarchial Transform) coding, Interpolarization-based hierarchical nearest-neighbor prediction-Prediction Transform) coding, and lifting transform (interpolation-based hierarchical nearest-neighbor prediction with an update / lifting step (Lifting Transform)) coding. Depending on the point cloud content, the above-described RAHT coding, prediction transform coding, and lifting transform coding may be selectively used, or a combination of one or more codings may be used. In addition, attribute encoding according to embodiments is not limited to the above-described examples.

[0132] The color conversion unit (30006) according to the embodiments performs color conversion coding to convert color values ​​(or textures) included in attributes. For example, the color conversion unit (30006) may convert the format of color information (e.g., convert from RGB to YCbCr). The operation of the color conversion unit (30006) according to the embodiments may be optionally applied depending on the color values ​​included in the attributes.

[0133] The geometry reconstruction unit (30005) according to the embodiments reconstructs (decompresses) an octree and / or an approximated octree. The geometry reconstruction unit (30005) reconstructs an octree / voxel based on the results of analyzing the distribution of points. The reconstructed octree / voxel may be referred to as a reconstructed geometry (or restored geometry).

[0134] The attribute conversion unit (30007) according to the embodiments performs attribute conversion that converts attributes based on positions for which geometry encoding has not been performed and / or reconstructed geometry. As described above, since the attributes are dependent on the geometry, the attribute conversion unit (30007) can convert the attributes based on the reconstructed geometry information. For example, the attribute conversion unit (30007) can convert the attribute of a point at a position based on the position value of the point included in the voxel. As described above, when the position of the center point of a voxel is set based on the positions of one or more points included in the voxel, the attribute conversion unit (30007) converts the attributes of one or more points. When try-soup geometry encoding is performed, the attribute conversion unit (30007) can convert attributes based on the try-soup geometry encoding.

[0135] The attribute transformation unit (30007) can perform attribute transformation by calculating the average value of the attributes or attribute values ​​(e.g., the color or reflectance of each point) of neighboring points within a specific position / radius from the position (or position value) of the center point of each voxel. The attribute transformation unit (30007) can apply a weight according to the distance from the center point to each point when calculating the average value. Accordingly, each voxel has a position and a calculated attribute (or attribute value).

[0136] The attribute transformation unit (30007) can search for neighboring points within a specific position / radius from the position of the center point of each voxel based on the KD tree or the Moulton code. The KD tree is a binary search tree that supports a data structure that can manage points based on their positions to enable fast nearest neighbor search (NNS). The Moulton code represents the coordinate values ​​(e.g. (x, y, z)) representing the 3D positions of all points as bit values ​​and is generated by mixing the bits. For example, if the coordinate values ​​representing the position of a point are (5, 9, 1), the bit values ​​of the coordinate values ​​are (0101, 1001, 0001). If the bit values ​​are mixed in the order of z, y, and x according to the bit index, it is 010001000111. If this value is expressed in decimal, it is 1095. That is, the Moulton code value of the point with coordinate values ​​(5, 9, 1) is 1095. The attribute transformation unit (30007) can sort points based on the Moulton code value and perform nearest neighbor search (NNS) through a depth-first traversal process. After the attribute transformation operation, if nearest neighbor search (NNS) is also required in other transformation processes for attribute coding, a KD tree or Moulton code is utilized.

[0137] As shown in the drawing, the converted attributes are input to the RAHT conversion unit (30008) and / or the LOD generation unit (30009).

[0138] The RAHT transform unit (30008) according to the embodiments performs RAHT coding to predict attribute information based on reconstructed geometry information. For example, the RAHT transform unit (30008) can predict attribute information of a node at an upper level of an octree based on attribute information associated with a node at a lower level of the octree.

[0139] The LOD generation unit (30009) according to the embodiments generates a LOD (Level of Detail) to perform predictive transformation coding. The LOD according to the embodiments represents the level of detail of point cloud content. A smaller LOD value indicates lower detail of point cloud content, and a larger LOD value indicates higher detail of point cloud content. Points can be classified according to LOD.

[0140] The lifting transformation unit (30010) according to the embodiments performs lifting transformation coding that transforms attributes of a point cloud based on weights. As described above, lifting transformation coding may be applied selectively.

[0141] The coefficient quantization unit (30011) according to the embodiments quantizes attribute-coded attributes based on coefficients.

[0142] An arithmetic encoder (30012) according to embodiments encodes quantized attributes based on arithmetic coding.

[0143] The elements of the point cloud encoder of FIG. 3 may be implemented by hardware, software, firmware, or a combination thereof, including one or more processors or integrated circuits configured to communicate with one or more memories included in the point cloud providing device, although not shown in the drawing. The one or more processors may perform at least one or more of the operations and / or functions of the elements of the point cloud encoder of FIG. 3 described above. Furthermore, the one or more processors may operate or execute a set of software programs and / or instructions for performing the operations and / or functions of the elements of the point cloud encoder of FIG. 3. The one or more memories according to embodiments may include high-speed random access memory, or may include non-volatile memory (e.g., one or more magnetic disk storage devices, flash memory devices, or other non-volatile solid-state memory devices).

[0144] Figure 4 illustrates examples of octree and occupancy codes according to embodiments.

[0145] As described in FIGS. 1 to 3, the point cloud content provision system (point cloud video encoder (10002)) or point cloud encoder (e.g., octree analysis unit (30002)) performs octree geometry coding (or octree coding) based on an octree structure to efficiently manage the area and / or position of a voxel.

[0146] The top of Fig. 4 shows the octree structure. The three-dimensional space of the point cloud content according to the embodiments is expressed by the axes of the coordinate system (e.g., X-axis, Y-axis, Z-axis). The octree structure has two poles (0,0,0) and (2 d , 2 d , 2 d ) is generated by recursively subdividing the cubical axis-aligned bounding box defined by . 2d can be set to a value that constitutes the smallest bounding box that encloses all points of the point cloud content (or point cloud video). d represents the depth of the octree. The value of d is determined by the following equation. In the equation below, (x int n , y int n , z int n ) represents the positions (or position values) of quantized points.

[0147]

[0148] As shown in the middle of the upper part of Fig. 4, the entire three-dimensional space can be divided into eight spaces according to the division. Each divided space is expressed as a cube with six faces. As shown in the upper right of Fig. 4, each of the eight spaces is again divided based on the axes of the coordinate system (e.g., X-axis, Y-axis, Z-axis). Therefore, each space is again divided into eight smaller spaces. The divided smaller spaces are also expressed as cubes with six faces. This division method is applied until the leaf nodes of the octree become voxels.

[0149] The bottom of Fig. 4 shows the occupancy code of the octree. The occupancy code of the octree is generated to indicate whether each of the eight partitioned spaces generated by partitioning one space contains at least one point. Therefore, one occupancy code is expressed by eight child nodes. Each child node represents the occupancy of the partitioned space, and each child node has a value of 1 bit. Therefore, the occupancy code is expressed as an 8-bit code. That is, if the space corresponding to the child node contains at least one point, the node has a value of 1. If the space corresponding to the child node does not contain a point (empty), the node has a value of 0. Since the occupancy code illustrated in Fig. 4 is 00100001, it indicates that the spaces corresponding to the third and eighth child nodes among the eight child nodes each contain at least one point. As shown in the drawing, the third child node and the eighth child node each have eight child nodes, and each child node is expressed by an 8-bit occupancy code. The drawing shows that the occupancy code of the third child node is 10000111, and the occupancy code of the eighth child node is 01001111. A point cloud encoder according to embodiments (e.g., an arithmetic encoder (30004)) can entropy encode the occupancy code. In addition, the point cloud encoder can intra / inter code the occupancy code to increase compression efficiency. A receiving device according to embodiments (e.g., a receiving device (10004) or a point cloud video decoder (10006)) reconstructs an octree based on the occupancy code.

[0150] A point cloud encoder according to embodiments (e.g., the point cloud encoder of FIG. 3, or the octree analysis unit (30002)) can perform voxelization and octree coding to store the positions of points. However, points within a 3D space are not always evenly distributed, and thus, there may be specific areas where there are not many points. Therefore, performing voxelization on the entire 3D space is inefficient. For example, if there are few points in a specific area, there is no need to perform voxelization up to that area.

[0151] Therefore, the point cloud encoder according to the embodiments can perform direct coding that directly codes the positions of points included in the specific region (or nodes excluding leaf nodes of the octree) without performing voxelization for the specific region described above. The coordinates of the direct coded points according to the embodiments are referred to as a direct coding mode (DCM). In addition, the point cloud encoder according to the embodiments can perform trisoup geometry encoding that reconstructs the positions of points within the specific region (or node) on a voxel basis based on a surface model. Trisoup geometry encoding is a geometry encoding that expresses the representation of an object as a series of triangle meshes. Therefore, the point cloud decoder can generate a point cloud from the mesh surface. Direct coding and trisoup geometry encoding according to the embodiments can be selectively performed. Additionally, direct coding and tri-subtractive geometry encoding according to embodiments may be performed in combination with octree geometry coding (or octree coding).

[0152] In order to perform direct coding, the option to use direct mode for applying direct coding must be activated, the node to which direct coding is to be applied must not be a leaf node, and there must be points below a threshold within a specific node. In addition, the total number of points subject to direct coding must not exceed a preset threshold. If the above conditions are satisfied, the point cloud encoder (or arithmetic encoder (30004)) according to the embodiments can entropy code the positions (or position values) of the points.

[0153] A point cloud encoder according to embodiments (e.g., surface approximation analysis unit (30003)) can determine a specific level of an octree (when the level is smaller than the depth d of the octree) and, starting from that level, perform tri-subject geometry encoding to reconstruct the positions of points within a node region on a voxel basis using a surface model (tri-subject mode). A point cloud encoder according to embodiments can specify a level to which tri-subject geometry encoding is to be applied. For example, when the specified level is equal to the depth of the octree, the point cloud encoder does not operate in tri-subject mode. That is, a point cloud encoder according to embodiments can operate in tri-subject mode only when the specified level is smaller than the depth value of the octree. A three-dimensional cubic area of ​​nodes at a specified level according to embodiments is called a block. One block may include one or more voxels. A block or a voxel may correspond to a brick. Within each block, geometry is represented by a surface. According to embodiments, a surface may intersect each edge of the block at most once.

[0154] Since one block has 12 edges, there are at least 12 intersections within one block. Each intersection is called a vertex. A vertex existing along an edge is detected if there is at least one occupied voxel adjacent to the edge among all blocks sharing the edge. An occupied voxel according to embodiments means a voxel containing a point. The position of a vertex detected along an edge is the average position along the edge of all voxels adjacent to the edge among all blocks sharing the edge.

[0155] When a vertex is detected, the point cloud encoder according to the embodiments calculates the starting point of the edge (x, y, z), the direction vector of the edge ( x, y, z), vertex position values ​​(relative position values ​​within an edge) can be entropy-coded. When tri-subspace geometry encoding is applied, the point cloud encoder according to the embodiments (e.g., geometry reconstruction unit (30005)) can perform triangle reconstruction, up-sampling, and voxelization processes to generate restored geometry (reconstructed geometry).

[0156] The vertices located at the edge of a block determine the surface passing through the block. According to the embodiments, the surface is a non-planar polygon. The triangle reconstruction process reconstructs the surface represented by a triangle based on the starting point of the edge, the direction vector of the edge, and the position value of the vertex. The triangle reconstruction process is as follows. ① Calculate the centroid value of each vertex, ② Subtract the centroid value from each vertex value, and ③ Square the values, and then add up all the values ​​to obtain the value.

[0157]

[0158] Then, the minimum of the added values ​​is found, and the projection process is performed according to the axis with the minimum value. For example, if the x element is minimum, each vertex is projected to the x-axis based on the center of the block, and projected onto the (y, z) plane. If the value produced when projected onto the (y, z) plane is (ai, bi), the θ value is found through atan2(bi, ai), and the vertices are sorted based on the θ value. The table below shows the combination of vertices to create a triangle depending on the number of vertices. The vertices are sorted in order from 1 to n. Table 1 below shows that two triangles can be formed depending on the combination of vertices for four vertices. The first triangle may be composed of the 1st, 2nd, and 3rd vertices among the sorted vertices, and the second triangle may be composed of the 3rd, 4th, and 1st vertices among the sorted vertices.

[0159] [Table 1] Triangles formed from vertices ordered 1,… , nnTriangles3(1,2,3)4(1,2,3), (3,4,1)5(1,2,3), (3,4,5), (5,1,3)6(1,2,3), (3,4,5), (5,6,1), (1,3,5)7(1,2,3), (3,4,5), (5,6,7), (7,1,3), (3,5,7)8(1,2,3), (3,4,5), (5,6,7), (7,8,1), (1,3,5), (5,7,1)9(1,2,3), (3,4,5), (5,6,7), (7,8,9), (9,1,3), (3,5,7), (7,9,3)10(1,2,3), (3,4,5), (5,6,7), (7,8,9), (9,10,1), (1,3,5), (5,7,9), (9,1,5)11(1,2,3), (3,4,5), (5,6,7), (7,8,9), (9,10,11), (11,1,3), (3,5,7), (7,9,11), (11,3,7)12(1,2,3), (3,4,5), (5,6,7), (7,8,9), (9,10,11), (11,12,1), (1,3,5), (5,7,9), (9,11,1), (1,5,9)

[0160] The upsampling process is performed to voxelize the triangle by adding points in the middle along the edges. Additional points are generated based on the upsampling factor and the width of the block. The additional points are called refined vertices. A point cloud encoder according to embodiments can voxelize the refined vertices. The point cloud encoder can also perform attribute encoding based on the voxelized positions (or position values).

[0161] Figure 5 shows an example of a point configuration by LOD according to embodiments.

[0162] As described in FIGS. 1 to 4, the encoded geometry is reconstructed (decompressed) before attribute encoding is performed. When direct coding is applied, the geometry reconstruction operation may include changing the arrangement of direct-coded points (e.g., placing the direct-coded points at the front of the point cloud data). When trysoup geometry encoding is applied, the geometry reconstruction process includes triangle reconstruction, upsampling, and voxelization. Since attributes depend on the geometry, attribute encoding is performed based on the reconstructed geometry.

[0163] A point cloud encoder (e.g., LOD generation unit (30009)) can reorganize points by LOD. The drawing shows point cloud content corresponding to LOD. The left side of the drawing shows the original point cloud content. The second figure from the left in the drawing shows the distribution of points of the lowest LOD, and the rightmost figure in the drawing shows the distribution of points of the highest LOD. That is, points of the lowest LOD are sparsely distributed, and points of the highest LOD are densely distributed. That is, as LOD increases in the direction of the arrow indicated at the bottom of the drawing, the interval (or distance) between points becomes shorter.

[0164] Figure 6 shows an example of a point configuration by LOD according to embodiments.

[0165] As described in FIGS. 1 to 5, a point cloud content providing system, or a point cloud encoder (e.g., a point cloud video encoder (10002), the point cloud encoder of FIG. 3, or a LOD generation unit (30009)) can generate a LOD. The LOD is generated by reorganizing points into a set of refinement levels according to a set LOD distance value (or a set of Euclidean distances). The LOD generation process is performed not only in the point cloud encoder but also in the point cloud decoder.

[0166] The upper part of Fig. 6 shows examples of points (P0 to P9) of point cloud content distributed in 3D space. The original order in Fig. 6 represents the order of points P0 to P9 before LOD generation. The LOD-based order in Fig. 6 represents the order of points according to LOD generation. The points are rearranged by LOD. Additionally, a higher LOD includes points belonging to a lower LOD. As shown in Fig. 6, LOD0 includes P0, P5, P4, and P2. LOD1 includes points of LOD0 and P1, P6, and P3. LOD2 includes points of LOD0, points of LOD1, and P9, P8, and P7.

[0167] As described in FIG. 3, the point cloud encoder according to the embodiments can selectively or in combination perform predictive transform coding, lifting transform coding, and RAHT transform coding.

[0168] A point cloud encoder according to embodiments can perform predictive transformation coding to generate a predictor for points and set a predicted attribute (or predicted attribute value) for each point. That is, N predictors can be generated for N points. The predictor according to embodiments can calculate a weight (= 1 / distance) value based on the LOD value of each point, indexing information for neighboring points existing within a distance set for each LOD, and distance values ​​to the neighboring points.

[0169] According to the embodiments, the predicted attribute (or attribute value) is set as the average value of the product of the attributes (or attribute values, for example, color, reflectance, etc.) of neighboring points set in the predictor of each point and the weight (or weight value) calculated based on the distance to each neighboring point. The point cloud encoder according to the embodiments (for example, the coefficient quantization unit (30011)) can quantize and inverse quantize the residual values ​​(which may be referred to as residual attribute, residual attribute value, attribute prediction residual value, etc.) obtained by subtracting the predicted attribute (attribute value) from the attribute (attribute value) of each point. The quantization process is as shown in Tables 2 and 3 below.

[0170] int PCCQuantization(int value, int quantStep) {if( value >=0) {return floor(value / quantStep + 1.0 / 3.0);} else {return -floor(-value / quantStep + 1.0 / 3.0);}}

[0171] int PCCInverseQuantization(int value, int quantStep) {if( quantStep ==0) {return value;} else {return value * quantStep;}}

[0172] A point cloud encoder according to embodiments (e.g., an arithmetic encoder (30012)) can entropy code the quantized and dequantized residuals as described above when there are neighboring points to the predictor of each point. A point cloud encoder according to embodiments (e.g., an arithmetic encoder (30012)) can entropy code the attributes of the point without performing the above-described process when there are no neighboring points to the predictor of each point.

[0173] A point cloud encoder according to embodiments (e.g., lifting transformation unit (30010)) can perform lifting transformation coding by generating a predictor for each point, setting the LOD calculated in the predictor, registering neighboring points, and setting weights according to the distance to the neighboring points. Lifting transformation coding according to embodiments is similar to the above-described predictive transformation coding, but differs in that weights are cumulatively applied to attribute values. The process of cumulatively applying weights to attribute values ​​according to embodiments is as follows.

[0174] 1) Create an array QW (QuantizationWieght) that stores the weight values ​​of each point. The initial value of all elements in QW is 1.0. Add the value obtained by multiplying the weight of the current point's predictor by the QW value of the predictor index of the neighboring node registered in the predictor.

[0175] 2) Lift prediction process: To calculate the predicted attribute value, the weighted value of the point's attribute value is multiplied and subtracted from the existing attribute value.

[0176] 3) Create temporary arrays called updateweight and update and initialize them to 0.

[0177] 4) For each predictor, the calculated weights are multiplied by the weights stored in the QW corresponding to the predictor index, and the resulting weights are cumulatively added to the update weight array as the index of the neighboring node. The update array accumulates the values ​​obtained by multiplying the calculated weights by the attribute values ​​of the indexes of the neighboring nodes.

[0178] 5) Lift update process: For each predictor, the attribute values ​​in the update array are divided by the weight values ​​in the update weight array of the predictor index, and the existing attribute values ​​are added to the divided value.

[0179] 6) For all predictors, the predicted attribute values ​​are calculated by additionally multiplying the updated attribute values ​​through the lift update process by the weights (stored in QW) updated through the lift prediction process. The point cloud encoder according to the embodiments (e.g., coefficient quantization unit (30011)) quantizes the predicted attribute values. In addition, the point cloud encoder (e.g., arithmetic encoder (30012)) entropy-codes the quantized attribute values.

[0180] A point cloud encoder according to embodiments (e.g., RAHT transform unit (30008)) can perform RAHT transform coding that predicts attributes of upper-level nodes using attributes associated with nodes at lower levels of an octree. RAHT transform coding is an example of attribute intra coding through octree backward scan. A point cloud encoder according to embodiments scans from a voxel to the entire area, and repeats the merging process up to a root node while merging voxels into larger blocks at each step. The merging process according to embodiments is performed only for occupied nodes. The merging process is not performed for empty nodes, and the merging process is performed for the node immediately above the empty node.

[0181] The following equation represents the RAHT transformation matrix. g lx,y,z represents the average attribute value of voxels at level l. g lx,y,z can be calculated from gl+1 2x,y,z and gl+1 2x+1,y,z. g l 2x,y,z and the weights of gl 2x+1,y,z are w1=w l 2x,y,z And w2=wl 2x+1,y,z.

[0182]

[0183] g l-1 x,y,z is a low-pass value, used in the merging process at the next higher level. h l-1 x,y,z are high-pass coefficients, and the high-pass coefficients at each step are quantized and entropy coded (e.g., encoding of an arithmetic encoder (30012)). The weights are w l-1 x,y,z = w l 2x,y,z + wl is calculated as 2x+1,y,z. The root node is the last g 1 0,0,0 and g 1 0,0,1 It is generated through:

[0184]

[0185] The gDC values ​​are also quantized and entropy coded, like the high-pass coefficients.

[0186] Fig. 7 illustrates an example of a point cloud decoder according to embodiments.

[0187] The point cloud decoder illustrated in FIG. 7 is an example of a point cloud decoder and can perform a decoding operation, which is the reverse process of the encoding operation of the point cloud encoder described in FIGS. 1 to 6.

[0188] As described in Figure 1, the point cloud decoder can perform geometry decoding and attribute decoding. Geometry decoding is performed before attribute decoding.

[0189] A point cloud decoder according to embodiments includes an arithmetic decoder (7000), an octree synthesizer (7001), a surface approximation synthesizer (7002), a geometry reconstructor (7003), an inverse transform coordinates (7004), an arithmetic decoder (7005), an inverse quantize (7006), a RAHT transform (7007), a LOD generator (7008), an inverse lifting (7009), and / or an inverse transform colors (7010).

[0190] The arithmetic decoder (7000), the octree synthesis unit (7001), the surface oproximation synthesis unit (7002), the geometry reconstruction unit (7003), and the coordinate system inversion unit (7004) can perform geometry decoding. Geometry decoding according to embodiments can include direct coding and trisoup geometry decoding. Direct coding and trisoup geometry decoding are applied selectively. In addition, geometry decoding is not limited to the above examples, and is performed by the reverse process of the geometry encoding described in FIGS. 1 to 6.

[0191] An arithmetic decoder (7000) according to embodiments decodes a received geometry bitstream based on arithmetic coding. The operation of the arithmetic decoder (7000) corresponds to the reverse process of the arithmetic encoder (30004).

[0192] The octree synthesis unit (7001) according to the embodiments can generate an octree by obtaining an occupancy code from a decoded geometry bitstream (or information about the geometry obtained as a result of decoding). A specific description of the occupancy code is as described in FIGS. 1 to 6.

[0193] The surface off-axis synthesis unit (7002) according to the embodiments can synthesize a surface based on the decoded geometry and / or the generated octree when the tri-sub geometry encoding is applied.

[0194] The geometry reconstruction unit (7003) according to the embodiments can regenerate geometry based on the surface and / or decoded geometry. As described in FIGS. 1 to 6, direct coding and try-soup geometry encoding are selectively applied. Therefore, the geometry reconstruction unit (7003) directly retrieves and adds position information of points to which direct coding is applied. In addition, when try-soup geometry encoding is applied, the geometry reconstruction unit (7003) can restore geometry by performing a reconstruction operation of the geometry reconstruction unit (30005), such as triangle reconstruction, up-sampling, and voxelization operations. The specific details are the same as described in FIG. 4 and are therefore omitted. The restored geometry may include a point cloud picture or frame that does not include attributes.

[0195] The coordinate system inverse transformation unit (7004) according to the embodiments can obtain the positions of points by transforming the coordinate system based on the restored geometry.

[0196] The arithmetic decoder (7005), the inverse quantization unit (7006), the RAHT transform unit (7007), the LOD generation unit (7008), the inverse lifting unit (7009), and / or the color inverse transform unit (7010) can perform attribute decoding. The attribute decoding according to the embodiments can include RAHT (Region Adaptive Hierarchical Transform) decoding, prediction transform (Interpolaration-based hierarchical nearest-neighbor prediction-Prediction Transform) decoding, and lifting transform (interpolation-based hierarchical nearest-neighbor prediction with an update / lifting step (Lifting Transform)) decoding. The three decodings described above can be used selectively, or a combination of one or more decodings can be used. In addition, the attribute decoding according to the embodiments is not limited to the above-described examples.

[0197] An arithmetic decoder (7005) according to embodiments decodes an attribute bitstream using arithmetic coding.

[0198] The inverse quantization unit (7006) according to the embodiments inverse quantizes information about the decoded attribute bitstream or the attributes obtained as a result of the decoding and outputs the inverse quantized attributes (or attribute values). The inverse quantization may be selectively applied based on the attribute encoding of the point cloud encoder.

[0199] According to embodiments, the RAHT transform unit (7007), the LOD generator (7008), and / or the inverse lifting unit (7009) may process the reconstructed geometry and the inverse quantized attributes. As described above, the RAHT transform unit (7007), the LOD generator (7008), and / or the inverse lifting unit (7009) may selectively perform a corresponding decoding operation according to the encoding of the point cloud encoder.

[0200] The color inverse transform unit (7010) according to the embodiments performs inverse transform coding to inversely transform the color values ​​(or textures) included in the decoded attributes. The operation of the color inverse transform unit (7010) may be selectively performed based on the operation of the color transform unit (30006) of the point cloud encoder.

[0201] The elements of the point cloud decoder of FIG. 7 may be implemented by hardware, software, firmware, or a combination thereof, including one or more processors or integrated circuits configured to communicate with one or more memories included in a point cloud providing device, although not shown in the drawing. The one or more processors may perform at least one or more of the operations and / or functions of the elements of the point cloud decoder of FIG. 7 described above. Furthermore, the one or more processors may operate or execute a set of software programs and / or instructions for performing the operations and / or functions of the elements of the point cloud decoder of FIG. 7.

[0202] Figure 8 is an example of a transmission device according to embodiments.

[0203] The transmission device illustrated in FIG. 8 is an example of the transmission device (10000) of FIG. 1 (or the point cloud encoder of FIG. 3). The transmission device illustrated in FIG. 8 can perform at least one or more of the same or similar operations and encoding methods as the operations and encoding methods of the point cloud encoder described in FIGS. 1 to 6. A transmission device according to embodiments may include a data input unit (8000), a quantization processing unit (8001), a voxelization processing unit (8002), an octree occupancy code generation unit (8003), a surface model processing unit (8004), an intra / inter coding processing unit (8005), an arithmetic coder (8006), a metadata processing unit (8007), a color conversion processing unit (8008), an attribute conversion processing unit (or a property conversion processing unit) (8009), a prediction / lifting / RAHT conversion processing unit (8010), an arithmetic coder (8011), and / or a transmission processing unit (8012).

[0204] The data input unit (8000) according to the embodiments receives or acquires point cloud data. The data input unit (8000) may perform operations and / or acquisition methods identical or similar to those of the point cloud video acquisition unit (10001) (or the acquisition process (20000) described in FIG. 2).

[0205] The data input unit (8000), quantization processing unit (8001), voxelization processing unit (8002), octree occupancy code generation unit (8003), surface model processing unit (8004), intra / inter coding processing unit (8005), and arithmetic coder (8006) perform geometry encoding. Since the geometry encoding according to the embodiments is the same or similar to the geometry encoding described in FIGS. 1 to 6, a detailed description thereof will be omitted.

[0206] The quantization processing unit (8001) according to the embodiments quantizes geometry (e.g., position values ​​of points or position values). The operation and / or quantization of the quantization processing unit (8001) is identical to or similar to the operation and / or quantization of the quantization unit (30001) described in FIG. 3. The specific description is the same as that described in FIGS. 1 to 6.

[0207] The voxelization processing unit (8002) according to the embodiments voxels the position values ​​of quantized points. The voxelization processing unit (80002) may perform operations and / or processes identical or similar to the operations and / or voxelization processes of the quantization unit (30001) described in FIG. 3. Specific descriptions are identical to those described in FIGS. 1 to 6.

[0208] The octree occupancy code generation unit (8003) according to the embodiments performs octree coding on the positions of voxelized points based on the octree structure. The octree occupancy code generation unit (8003) can generate an occupancy code. The octree occupancy code generation unit (8003) can perform operations and / or methods identical or similar to those of the point cloud encoder (or octree analysis unit (30002)) described in FIGS. 3 and 4. The specific description is the same as that described in FIGS. 1 to 6.

[0209] The surface model processing unit (8004) according to the embodiments can perform tri-subject geometry encoding to reconstruct the positions of points within a specific area (or node) on a voxel basis based on the surface model. The surface model processing unit (8004) can perform operations and / or methods identical or similar to those of the point cloud encoder (e.g., surface approximation analysis unit (30003)) described in FIG. 3. The specific description is the same as that described with reference to FIGS. 1 to 6.

[0210] The intra / inter coding processing unit (8005) according to embodiments may perform intra / inter coding on point cloud data. The intra / inter coding processing unit (8005) may perform coding identical to or similar to intra / inter coding. According to embodiments, the intra / inter coding processing unit (8005) may be included in an arithmetic coder (8006).

[0211] An arithmetic coder (8006) according to embodiments entropy encodes an octree and / or an approximated octree of point cloud data. For example, the encoding method includes an arithmetic encoding method. The arithmetic coder (8006) performs operations and / or methods identical or similar to those of the arithmetic encoder (30004).

[0212] The metadata processing unit (8007) according to the embodiments processes metadata regarding point cloud data, such as setting values, and provides the metadata to a necessary processing step, such as geometry encoding and / or attribute encoding. In addition, the metadata processing unit (8007) according to the embodiments may generate and / or process signaling information related to geometry encoding and / or attribute encoding. The signaling information according to the embodiments may be encoded and processed separately from geometry encoding and / or attribute encoding. In addition, the signaling information according to the embodiments may be interleaved.

[0213] The color conversion processing unit (8008), the attribute conversion processing unit (8009), the prediction / lifting / RAHT conversion processing unit (8010), and the arithmetic coder (8011) perform attribute encoding. Since the attribute encoding according to the embodiments is the same as or similar to the attribute encoding described in FIGS. 1 to 6, a detailed description thereof will be omitted.

[0214] The color conversion processing unit (8008) according to the embodiments performs color conversion coding to convert the color values ​​included in the attributes. The color conversion processing unit (8008) can perform color conversion coding based on the reconstructed geometry. The description of the reconstructed geometry is the same as that described with reference to FIGS. 1 to 6. In addition, the color conversion processing unit (8008) performs the same or similar operation and / or method as that of the color conversion unit (30006) described with reference to FIG. 3. A detailed description thereof will be omitted.

[0215] The attribute transformation processing unit (8009) according to embodiments performs attribute transformation to transform attributes based on positions for which geometry encoding has not been performed and / or reconstructed geometry. The attribute transformation processing unit (8009) performs operations and / or methods that are the same as or similar to those of the attribute transformation unit (30007) described in FIG. 3. A detailed description thereof will be omitted. The prediction / lifting / RAHT transformation processing unit (8010) according to embodiments can code transformed attributes by using any one or a combination of RAHT coding, prediction transformation coding, and lifting transformation coding. The prediction / lifting / RAHT transformation processing unit (8010) performs at least one or more of operations that are the same as or similar to those of the RAHT transformation unit (30008), LOD generation unit (30009), and lifting transformation unit (30010) described in FIG. 3. In addition, the description of the prediction transformation coding, lifting transformation coding, and RAHT transformation coding is the same as that described in FIGS. 1 to 6, so a detailed description is omitted.

[0216] An arithmetic coder (8011) according to embodiments can encode coded attributes based on arithmetic coding. The arithmetic coder (8011) performs operations and / or methods identical or similar to those of the arithmetic encoder (300012).

[0217] The transmission processing unit (8012) according to embodiments may transmit each bitstream including encoded geometry and / or encoded attribute, metadata information, or may transmit the encoded geometry and / or encoded attribute, and metadata information as one bitstream. When the encoded geometry and / or encoded attribute, and metadata information according to embodiments are configured as one bitstream, the bitstream may include one or more sub-bitstreams. The bitstream according to embodiments may include signaling information including a Sequence Parameter Set (SPS) for sequence-level signaling, a Geometry Parameter Set (GPS) for signaling geometry information coding, an Attribute Parameter Set (APS) for signaling attribute information coding, and a Tile Parameter Set (TPS) for tile-level signaling, and slice data. The slice data may include information about one or more slices. One slice according to embodiments may include one geometry bitstream (Geom0). 0 ) and one or more attribute bitstreams (Attr0 0 , Attr1 0 ) may be included.

[0218] A slice is a series of syntax elements that represent all or part of a coded point cloud frame.

[0219] A TPS according to embodiments may include information about each tile (e.g., coordinate value information of a bounding box and height / size information, etc.) for one or more tiles. A geometry bitstream may include a header and a payload. The header of a geometry bitstream according to embodiments may include identification information of a parameter set included in GPS (geom_ parameter_set_id), a tile identifier (geom_tile_id), a slice identifier (geom_slice_id), and information about data included in the payload. As described above, a metadata processing unit (8007) according to embodiments may generate and / or process signaling information and transmit it to a transmission processing unit (8012). According to embodiments, elements that perform geometry encoding and elements that perform attribute encoding may share data / information with each other as indicated by a dotted line. The transmission processing unit (8012) according to the embodiments may perform operations and / or transmission methods identical or similar to those of the transmitter (10003). A detailed description thereof is omitted as it is the same as that described in FIGS. 1 and 2.

[0220] Fig. 9 is an example of a receiving device according to embodiments.

[0221] The receiving device illustrated in FIG. 9 is an example of the receiving device (10004) of FIG. 1. The receiving device illustrated in FIG. 9 can perform at least one of the same or similar operations and methods as the operations and decoding methods of the point cloud decoder described in FIGS. 1 to 8.

[0222] A receiving device according to embodiments may include a receiving unit (9000), a receiving processing unit (9001), an arithmetic decoder (9002), an occupancy code-based octree reconstruction processing unit (9003), a surface model processing unit (triangle reconstruction, up-sampling, voxelization) (9004), an inverse quantization processing unit (9005), a metadata parser (9006), an arithmetic decoder (9007), an inverse quantization processing unit (9008), a prediction / lifting / RAHT inverse transform processing unit (9009), a color inverse transform processing unit (9010), and / or a renderer (9011). Each component of the decoding according to embodiments may perform the reverse process of the component of the encoding according to embodiments.

[0223] The receiving unit (9000) according to the embodiments receives point cloud data. The receiving unit (9000) may perform operations and / or receiving methods identical or similar to those of the receiver (10005) of FIG. 1. A detailed description thereof will be omitted.

[0224] The receiving processing unit (9001) according to the embodiments can obtain a geometry bitstream and / or an attribute bitstream from the received data. The receiving processing unit (9001) can be included in the receiving unit (9000).

[0225] The arithmetic decoder (9002), the occupancy code-based octree reconstruction processing unit (9003), the surface model processing unit (9004), and the inverse quantization processing unit (9005) can perform geometry decoding. Since the geometry decoding according to the embodiments is identical or similar to the geometry decoding described in at least one of FIGS. 1 to 8, a detailed description thereof will be omitted.

[0226] An arithmetic decoder (9002) according to embodiments can decode a geometry bitstream based on arithmetic coding. The arithmetic decoder (9002) performs operations and / or coding identical to or similar to those of the arithmetic decoder (7000).

[0227] The occupancy code-based octree reconstruction processing unit (9003) according to embodiments can reconstruct an octree by obtaining an occupancy code from a decoded geometry bitstream (or information about the geometry obtained as a result of decoding). The occupancy code-based octree reconstruction processing unit (9003) performs the same or similar operations and / or methods as those of the octree synthesis unit (7001) and / or the octree generation method. The surface model processing unit (9004) according to embodiments can perform tri-sub geometry decoding and related geometry reconstructing (e.g., triangle reconstruction, up-sampling, voxelization) based on the surface model method when tri-sub geometry encoding is applied. The surface model processing unit (9004) performs the same or similar operations as those of the surface off-ratio synthesis unit (7002) and / or the geometry reconstructing unit (7003).

[0228] The inverse quantization processing unit (9005) according to the embodiments can inverse quantize the decoded geometry.

[0229] The metadata parser (9006) according to the embodiments can parse metadata, such as setting values, contained in the received point cloud data. The metadata parser (9006) can pass the metadata to geometry decoding and / or attribute decoding. A detailed description of the metadata is omitted as it is the same as described in FIG. 8.

[0230] The arithmetic decoder (9007), the inverse quantization processing unit (9008), the prediction / lifting / RAHT inverse transform processing unit (9009), and the color inverse transform processing unit (9010) perform attribute decoding. Since attribute decoding is identical or similar to the attribute decoding described in at least one of FIGS. 1 to 8, a detailed description thereof will be omitted.

[0231] An arithmetic decoder (9007) according to embodiments can decode an attribute bitstream using arithmetic coding. The arithmetic decoder (9007) can decode the attribute bitstream based on the reconstructed geometry. The arithmetic decoder (9007) performs operations and / or coding identical or similar to those of the arithmetic decoder (7005).

[0232] The inverse quantization processing unit (9008) according to the embodiments can inverse quantize the decoded attribute bitstream. The inverse quantization processing unit (9008) performs operations and / or methods identical or similar to the operations and / or inverse quantization methods of the inverse quantization unit (7006).

[0233] The prediction / lifting / RAHT inverse transform processing unit (9009) according to embodiments can process reconstructed geometry and inverse quantized attributes. The prediction / lifting / RAHT inverse transform processing unit (9009) performs at least one or more of the same or similar operations and / or decodings as the operations and / or decodings of the RAHT transformation unit (7007), the LOD generation unit (7008), and / or the inverse lifting unit (7009) of FIG. 7. The color inverse transform processing unit (9010) according to embodiments performs inverse transform coding for inverse transforming the color value (or texture) included in the decoded attributes. The color inverse transform processing unit (9010) performs the same or similar operations and / or inverse transform coding as the operations and / or inverse transform coding of the color inverse transform unit (7010) of FIG. 7. A renderer (9011) according to embodiments can render point cloud data.

[0234] Fig. 10 shows an example of a structure that can be linked with a point cloud data transmission / reception method / device according to embodiments.

[0235] The structure of FIG. 10 represents a configuration in which at least one of a server (1060), a robot (1010), an autonomous vehicle (1020), an XR device (1030), a smartphone (1040), a home appliance (1050), and / or an HMD (1070) is connected to a cloud network (1010). The robot (1010), the autonomous vehicle (1020), the XR device (1030), the smartphone (1040), or the home appliance (1050) are referred to as devices. In addition, the XR device (1030) may correspond to or be linked with a point cloud data (PCC) device according to embodiments.

[0236] A cloud network (1000) may refer to a network that constitutes part of a cloud computing infrastructure or exists within the cloud computing infrastructure. Here, the cloud network (1000) may be configured using a 3G network, a 4G or LTE (Long Term Evolution) network, or a 5G network.

[0237] The server (1060) is connected to at least one of a robot (1010), an autonomous vehicle (1020), an XR device (1030), a smartphone (1040), a home appliance (1050), and / or an HMD (1070) through a cloud network (1000), and can assist in at least part of the processing of the connected devices (1010 to 1070).

[0238] The HMD (Head-Mount Display) (1070) represents one of the types in which the XR device and / or the PCC device according to the embodiments can be implemented. The HMD type device according to the embodiments includes a communication unit, a control unit, a memory unit, an I / O unit, a sensor unit, and a power supply unit.

[0239] Below, various embodiments of devices (1010 to 1050) to which the above-described technology is applied are described. Here, the devices (1010 to 1050) illustrated in FIG. 10 can be linked / combined with the point cloud data transmission / reception devices according to the above-described embodiments.

[0240] <PCC+XR>

[0241] The XR / PCC device (1030) may be implemented as a HMD (Head-Mount Display), a HUD (Head-Up Display) equipped in a vehicle, a television, a mobile phone, a smart phone, a computer, a wearable device, a home appliance, digital signage, a vehicle, a fixed robot, a mobile robot, etc., by applying PCC and / or XR (AR+VR) technology.

[0242] The XR / PCC device (1030) can obtain information about surrounding space or real objects by analyzing 3D point cloud data or image data acquired through various sensors or from external devices to generate location data and attribute data for 3D points, and can render and output an XR object to be output. For example, the XR / PCC device (1030) can output an XR object including additional information about a recognized object in correspondence with the recognized object.

[0243] <PCC+XR+모바일폰>

[0244] The XR / PCC device (1030) can be implemented as a mobile phone (1040) or the like by applying PCC technology.

[0245] The mobile phone (1040) can decode and display point cloud content based on PCC technology.

[0246] <PCC+자율주행+XR>

[0247] Autonomous vehicles (1020) can be implemented as mobile robots, vehicles, unmanned aerial vehicles, etc. by applying PCC technology and XR technology.

[0248] An autonomous vehicle (1020) to which XR / PCC technology is applied may refer to an autonomous vehicle equipped with a means for providing XR images, or an autonomous vehicle that is the subject of control / interaction within an XR image. In particular, an autonomous vehicle (1020) that is the subject of control / interaction within an XR image is distinct from an XR device (1030) and can be linked with each other.

[0249] An autonomous vehicle (1020) equipped with a means for providing XR / PCC images can obtain sensor information from sensors including cameras and output XR / PCC images generated based on the obtained sensor information. For example, the autonomous vehicle (1020) can be equipped with a HUD to output XR / PCC images, thereby providing passengers with XR / PCC objects corresponding to real objects or objects on a screen.

[0250] At this time, when the XR / PCC object is output to the HUD, at least a part of the XR / PCC object may be output so as to overlap with an actual object toward which the passenger's gaze is directed. On the other hand, when the XR / PCC object is output to a display provided inside the autonomous vehicle, at least a part of the XR / PCC object may be output so as to overlap with an object on the screen. For example, the autonomous vehicle (1220) may output XR / PCC objects corresponding to objects such as a lane, another vehicle, a traffic light, a traffic sign, a two-wheeled vehicle, a pedestrian, a building, etc.

[0251] VR (Virtual Reality) technology, AR (Augmented Reality) technology, MR (Mixed Reality) technology and / or PCC (Point Cloud Compression) technology according to the embodiments can be applied to various devices.

[0252] In other words, VR technology is a display technology that provides only CG images of real-world objects or backgrounds. On the other hand, AR technology refers to a technology that shows a virtually created CG image on top of an image of an actual object. Furthermore, MR technology is similar to the aforementioned AR technology in that it mixes and combines virtual objects in the real world. However, in AR technology, the distinction between real objects and virtual objects created with CG images is clear, and virtual objects are used in a form that complements real objects, whereas in MR technology, virtual objects are considered to have the same characteristics as real objects. A more specific example is the hologram service, which is an application of the aforementioned MR technology.

[0253] However, recently, rather than clearly distinguishing between VR, AR, and MR technologies, they are often referred to as XR (extended reality) technologies. Therefore, the embodiments of the present disclosure are applicable to all VR, AR, MR, and XR technologies. These technologies can be applied to encoding / decoding based on PCC, V-PCC, and G-PCC technologies.

[0254] The PCC method / device according to the embodiments can be applied to a vehicle providing an autonomous driving service.

[0255] Vehicles providing autonomous driving services are connected to PCC devices to enable wired / wireless communication.

[0256] A point cloud data (PCC) transmission / reception device according to embodiments, when connected to a vehicle to enable wired / wireless communication, can receive / process content data related to AR / VR / PCC services that can be provided together with autonomous driving services and transmit the same to the vehicle. In addition, when the point cloud data transmission / reception device is mounted on a vehicle, the point cloud transmission / reception device can receive / process content data related to AR / VR / PCC services and provide the same to a user according to a user input signal input through a user interface device. A vehicle or a user interface device according to embodiments can receive a user input signal. The user input signal according to embodiments can include a signal instructing an autonomous driving service.

[0257] The point cloud data transmission method / device according to the embodiments is interpreted as a term referring to the transmission device (10000) of FIG. 1, the point cloud video encoder (10002), the transmitter (10003), the acquisition-encoding-transmission (20000-20001-20002) of FIG. 2, the point cloud video encoder of FIG. 3, the transmission device of FIG. 8, the device of FIG. 10, the encoding method of FIG. 25, the transmission device of FIG. 27, the transmission method of FIG. 41, etc.

[0258] The point cloud data receiving method / device according to the embodiments is interpreted as a term referring to the receiving device (10004), receiver (10005), point cloud video decoder (10006) of FIG. 1, transmission-decoding-rendering (20002-20003-20004) of FIG. 2, point cloud video decoder of FIG. 7, receiving device of FIG. 9, device of FIG. 10, decoding method of FIG. 26, receiving device of FIG. 28, receiving method of FIG. 41, etc.

[0259] Additionally, the point cloud data transmission / reception method / device according to the embodiments may be abbreviated as the method / device according to the embodiments.

[0260] According to embodiments, geometry data, geometry information, location information, etc., which constitute point cloud data, are interpreted as having the same meaning. Attribute data, attribute information, property information, etc., which constitute point cloud data, are interpreted as having the same meaning.

[0261] The method / device according to the embodiments can process point cloud data taking into account scalable transmission.

[0262] The method / device according to the embodiments describes a method for efficiently supporting selective decoding of a portion of data when transmitting / receiving point cloud data due to receiver performance or transmission speed. In particular, this document proposes a technique for increasing the efficiency of scalable coding, wherein an encoder on the transmitting side can selectively transmit information required by a decoder on the receiving side for already compressed data, and the decoder can decode the information. In this case, a coding unit can be configured as an independent slice according to the meaning of a tree level, LOD, layer group unit, etc.

[0263] In particular, this paper proposes a method for improving the efficiency of scalable coding among point cloud data compression methods. Here, scalable coding is a technology that can gradually change the resolution of data depending on the circumstances such as the request / processing speed / performance / transmission bandwidth of the receiving end, so that the transmitting end can efficiently transmit compressed data and the receiving end can decode the compressed data. To this end, in addition to the technology of the present disclosure, packing can be applied to effectively transmit point cloud data organized based on layers, and in particular, when a direct compression mode is used for position compression, a method for organizing and transmitting / receiving slice segments to be more suitable for scalable PCC services is proposed. In addition, a compression method can be used for efficient storage and transmission of large-capacity point cloud data with a wide distribution and high point density.

[0264] Referring to the point cloud data transmission / reception device (or may be abbreviated as encoder / decoder) according to the embodiments illustrated in FIGS. 3 and 7, the point cloud data is composed of a set of points, and each point is composed of geometry information (or referred to as geometry or geometry data) and attribute information (or referred to as attribute or attribute data). The geometry information is three-dimensional position information (xyz) of each point. That is, the position of each point is expressed as parameters on a coordinate system representing a three-dimensional space (for example, parameters (x, y, z) of the three axes representing the space, namely the X-axis, Y-axis, and Z-axis). In addition, the attribute information means the color (RGB, YUV, etc.), reflectance, normal vectors, transparency, etc. of the point. Point Cloud Compression (PCC) uses octree-based compression to efficiently compress distribution characteristics that are unevenly distributed in three-dimensional space, and compresses attribute information based on this. The point cloud video encoder and point cloud video decoder illustrated in FIGS. 3 and 7 can process operation(s) according to embodiments through each component.

[0265] According to embodiments, a transmitting device compresses geometric information (e.g., location) and attribute information (e.g., color / brightness / reflectivity, etc.) of point cloud data and transmits them to a receiving device. At this time, point cloud data can be organized according to an octree structure with layers or LoD (Level of Detail) depending on the level of detail, and scalable point cloud data coding and representation are possible based on this. At this time, it is possible to decode or represent only a part of the point cloud data depending on the performance or transmission speed of the receiving device, but there is currently no method for removing unnecessary data in advance.

[0266] That is, in cases where only a portion of a scalable point cloud compression bitstream needs to be transmitted (e.g., when only some layers are decoded during scalable decoding), it is not possible to selectively transmit only the required portion. Therefore, the required portion must be re-encoded after decoding at the transmitting device, as shown in Fig. 11, or the entire bitstream must be transmitted to the receiving device, as shown in Fig. 12, and then the required data must be selectively applied after decoding at the receiving device.

[0267] However, in the case of Fig. 11, there may be a delay due to the time for decoding and re-encoding, and in the case of Fig. 12, there is a disadvantage in that bandwidth efficiency is reduced because unnecessary data is transmitted to the receiving device, and when a fixed bandwidth is used, data quality must be lowered for transmission.

[0268] Accordingly, the method / device according to the embodiments provides slices so that the point cloud can be divided and processed by region.

[0269] In particular, for octree-based positional compression, entropy-based compression methods and direct coding can be used together, in which case a slice configuration is proposed to efficiently utilize scalability.

[0270] Additionally, the method / device according to the embodiments can define a slice segmentation structure of point cloud data and signal a scalable layer and slice structure for scalable transmission.

[0271] The method / device according to the embodiments can process a bitstream by dividing it into specific units for efficient bitstream transmission and decoding.

[0272] The method / device according to the embodiments enables selective transmission and decoding of point cloud data composed of layers in bitstream units.

[0273] A unit according to embodiments may be referred to as LOD, layer, slice, etc. LOD is a term similar to LOD of attribute data coding, but in another sense, it may mean a data unit for a layer structure of a bitstream. LOD according to embodiments may be a concept corresponding to one depth or binding two or more depths based on the depth (level) of a layer structure of point cloud data, for example, an octree or multiple trees. Similarly, a layer is a concept corresponding to one depth or binding two or more depths for generating a unit of a sub-bitstream, and may correspond to one LOD or corresponding to two or more LODs. In addition, a slice is a unit for configuring a unit of a sub-bitstream, and may correspond to one depth, a part of one depth, or corresponding to two or more depths. In addition, a slice may correspond to one LOD, a part of one LOD, or corresponding to two or more LODs. According to embodiments, LODs, layers, and slices may correspond to or be inclusive of each other. Furthermore, units according to embodiments may include LODs, layers, slices, layer groups, subgroups, etc., and may be referred to as complementary to each other. According to embodiments, in an octree structure, layer, depth, level, and depth level may be used with the same meaning.

[0274] Fig. 13 is a diagram illustrating an example of a layer-based point cloud data configuration according to embodiments. Fig. 13 is an example of an octree structure in which the depth level of the root node is set to 0 and the depth level of the leaf node is set to 7.

[0275] The method / device according to the embodiments can encode and decode point cloud data by configuring layer-based point cloud data as shown in FIG. 13.

[0276] Layering of point cloud data according to embodiments may have a layer structure in various perspectives such as SNR, spatial resolution, color, temporal frequency, bitdepth, etc. depending on the application field, and may form layers in the direction of increasing data density based on an octree structure or LOD structure.

[0277] That is, when generating LOD based on an octree structure, the LOD can be defined to increase in the direction of increasing detail, i.e., in the direction of increasing octree depth levels. In this document, the term "layer" can be used interchangeably with "level," "depth," and "depth level."

[0278] As an example, in Fig. 13, in an octree structure having 7 depth levels excluding the root node level (or referred to as the root level), LOD 0 is configured including from the root node level to octree depth level 4, LOD 1 is configured including from the root node level to octree depth level 5, and LOD 2 is configured including from the root node level to octree depth level 7.

[0279] Fig. 14 (a) shows a bitstream structure of geometry data according to embodiments, and Fig. 14 (b) shows a bitstream structure of attribute data according to embodiments.

[0280] The method / device according to the embodiments can generate LODs based on layering of an octree structure as in FIG. 13, and configure a geometry bitstream and an attribute bitstream as in (a) and (b) of FIG. 14.

[0281] A transmission device according to embodiments can divide a bitstream obtained through point cloud compression into a geometry bitstream and an attribute bitstream according to the type of data and transmit the bitstream.

[0282] At this time, each bitstream can be transmitted as a slice. According to embodiments, a geometry bitstream (e.g., (a) of FIG. 14) and an attribute bitstream (e.g., (b) of FIG. 14) can each be transmitted as a slice, regardless of layer information or LoD information. In this case, in order to use only a part of a layer or LoD, a process of decoding the bitstream, a process of selecting only the part to be used and removing unnecessary parts, and a process of re-encoding based only on the necessary information must be performed.

[0283] This paper proposes a method to divide the bitstream into layers (or LoDs) and deliver them to avoid these unnecessary intermediate processes.

[0284] FIG. 15 is a diagram showing an example of a configuration of a bitstream for dividing the bitstream into layer (or LoD) units and transmitting it according to embodiments.

[0285] For example, considering the case of LoD-based PCC technology, it has a structure in which a lower LoD is included in a higher LoD. That is, the upper LoD includes all points of the lower LoD. In addition, if the information of points newly added for each LoD, that is, points included in the current LoD but not in the previous LoD, is defined as R (rest or retained), the transmitting device can divide the initial LoD information and the information R newly included in each LoD into independent units (e.g., slices) and transmit them, as shown in FIG. 15.

[0286] In other words, the set of points newly added compared to the previous LoD to constitute each LoD can be defined as information R. Figure 15 is an example in which LoD1 includes LoD0 + information R1, and LoD2 includes LoD1 + information R2.

[0287] According to one embodiment, points sampled for one or more octree depth levels can be determined as data belonging to information R. That is, a set of points sampled (i.e., matching occupied nodes) for one or more octree depth levels can be defined as information R. According to another embodiment, points sampled for one octree depth level can be defined by dividing them into multiple pieces of information R according to a certain criterion. At this time, various criteria for dividing one octree depth level into multiple pieces of information R can be considered as follows. For example, when dividing one octree depth level into M pieces of information R, data in the information R can be made into M pieces of information R having consecutive Moulton codes, or M pieces of information R can be made by grouping together pieces with the same remainder when Moulton code order index is divided by M, or M pieces of information R can be made by grouping together pieces at the same position when grouped as sibling nodes. According to another embodiment, if necessary, some of the sampled points of multiple octree depth levels can be determined as information R.

[0288] Figure 15 shows an example in which a geometry bitstream and an attribute bitstream are each divided into three slices according to embodiments. Each slice includes a header and a payload (or data unit) containing actual data (e.g., geometry data, attribute data). The header may include information about the corresponding slice. In addition, the header may further include reference information related to a previous slice, a previous LoD, or a previous layer for LoD configuration.

[0289] Taking Fig. 15 as an example, the geometry bitstream is divided into a slice that carries geometry data belonging to LoD0, a slice that carries geometry data belonging to information R1, and a slice that carries geometry data belonging to information R2. And the attribute bitstream is divided into a slice that carries attribute data belonging to LoD0, a slice that carries attribute data belonging to information R1, and a slice that carries attribute data belonging to information R2.

[0290] The receiving method / device according to the embodiments can receive a bitstream divided into LODs or layers and efficiently decode only the data to be used without a complex intermediate process.

[0291] At this time, various embodiments can be applied to the method of transmitting the bitstream.

[0292] For example, the geometry bitstream and the attribute bitstream may be transmitted separately, or the geometry bitstream and the attribute bitstream may be multiplexed into a single bitstream and transmitted.

[0293] Additionally, when each bitstream includes LoD0 and one or more pieces of information R, the transmission order of LoD0 and one or more pieces of information R may be different.

[0294] Figure 15 is an example in which a geometry bitstream and an attribute bitstream are transmitted respectively, and at this time, LoD0 including a geometry bitstream and two pieces of information R(R1, R2) are transmitted sequentially, and LoD0 including an attribute bitstream and two pieces of information R(R1, R2) are transmitted sequentially.

[0295] FIG. 16 illustrates an example of a bitstream alignment method when a geometry bitstream and an attribute bitstream are multiplexed into one bitstream according to embodiments.

[0296] The transmission method / device according to the embodiments can serially transmit geometry data and attribute data as illustrated in FIG. 16 when transmitting a bitstream. At this time, depending on the type of data, the entire geometry data (or geometry information) can be transmitted first, and then attribute data (or attribute information) can be transmitted. In this case, there is an advantage in that the geometry data can be quickly restored based on the information in the transmitted bitstream.

[0297] FIG. 16 illustrates an example in which layers (LODs) including geometry data may be positioned first in the bitstream, and layers (LODs) including attribute data may be positioned after the geometry layer. Since attribute data is dependent on geometry data, layers (LODs) including geometry data may be positioned before layers (LODs) including attribute data. FIG. 16 illustrates an example in which LoD0 including geometry data and two pieces of information R (R1, R2) are sequentially transmitted, and then LoD0 including attribute data and two pieces of information R (R1, R2) are sequentially transmitted. At this time, the positions may be variously changed according to embodiments. In addition, references between geometry headers are possible, and references between attribute headers and geometry headers are also possible.

[0298] FIG. 17 illustrates another example of a bitstream alignment method when a geometry bitstream and an attribute bitstream are multiplexed into one bitstream according to embodiments.

[0299] The transmission method / device according to the embodiments can serially transmit geometry data and attribute data as shown in FIG. 17 when transmitting a bitstream. At this time, bitstreams constituting the same layer including geometry data and attribute data can also be collected and transmitted. In this case, if a compression technique capable of parallel decoding of geometry and attributes is used, the decoding execution time can be shortened. At this time, information that must be processed first (small LoD, geometry must precede attributes) can be placed first.

[0300] Figure 17 is an example in which LoD0 including geometry data, LoD0 including attribute data, information R1 including geometry data, information R1 including attribute data, information R2 including geometry data, and information R2 including attribute data are transmitted in that order. At this time, the position can be changed in various ways depending on the embodiments. In addition, references between geometry headers are possible, and references between attribute headers and geometry headers are also possible.

[0301] The transmission / reception method / device according to the embodiments can efficiently select a desired layer (or LoD) in an application field at the bitstream level when transmitting and receiving a bitstream. In the bitstream alignment method according to the embodiments, when geometry information is collected and transmitted as in FIG. 16, an empty part may appear in the middle after selecting a specific bitstream level, and in this case, the bitstream may need to be rearranged.

[0302] Meanwhile, when geometry data and attribute data are bundled and transmitted according to layers as in Fig. 17, necessary information can be selectively transmitted and / or unnecessary information can be selectively removed as in Figs. 18(a) to 18(c) or Figs. 19(a) to 19(c) depending on the application field.

[0303] FIGS. 18(a) to 18(c) are drawings showing examples of symmetrical geometry-attribute selection according to embodiments.

[0304] In cases where a part of a bitstream needs to be selected according to embodiments, taking FIGS. 18(a) to 18(c) as an example, the transmitting device selects and transmits only up to LoD1 (i.e., LoD0+R1), and removes and does not transmit information R2 (i.e., a new part among LoD2) corresponding to the upper layer from the bitstream. In the case of symmetric geometry-attribute selection, geometry data and attribute data of the same layer are selected and transmitted simultaneously, or selected and removed simultaneously.

[0305] Figures 19(a) to 19(c) are diagrams illustrating examples of asymmetric geometry-attribute selection according to embodiments. In the case of asymmetric geometry-attribute selection, only one of the geometry data and attribute data of the same layer is selected and transmitted or removed.

[0306] In embodiments where a part of a bitstream needs to be selected, taking FIGS. 19(a) to 19(c) as examples, the transmitting device selects and transmits LoD1 (LoD0 +R1) including geometry data, LoD1 (LoD0 +R1) including attribute data, and R2 including geometry data, and removes R2 including attribute data from the bitstream and does not transmit it. That is, attribute data is an example of selecting and transmitting the remaining data except for data of an upper layer (R2), and geometry data is an example of transmitting data of all layers (from level 0 (root level) to level 7 (leaf level) of an octree structure).

[0307] In cases where a portion of a bitstream needs to be selected according to embodiments, a portion of the bitstream can be selected by using the symmetrical geometry-attribute selection method of FIGS. 18(a) to 18(c) or the asymmetrical geometry-attribute selection method of FIGS. 19(a) to 19(c) or a combination of the symmetrical geometry-attribute selection method and the asymmetrical geometry-attribute selection method.

[0308] The segmentation of bitstreams and selection of some bitstreams described above are intended to support the scalability of point cloud data.

[0309] This document represents point cloud data in an octree structure and supports scalable encoding / decoding (scalability) when separated by LOD (or layer).

[0310] Scalability features according to embodiments may include slice level scalability and / or octree level scalability.

[0311] According to embodiments, a LoD may be used as a unit to represent a set of one or more octree layers. Additionally, a LoD may also have the meaning of a bundle of octree layers to be configured as a slice unit.

[0312] LOD according to the embodiments can be used in a broad sense, such as a unit for dividing data in detail, by extending the meaning of LOD when encoding / decoding attributes.

[0313] That is, spatial scalability by the actual octree layer (or scalable attribute layer) can be provided for each octree layer, but it can be selected at the LoD level when configuring scalability at the slice level before bitstream parsing.

[0314] Taking Fig. 13 as an example, in the octree structure, the level from the root level to the 4th level corresponds to LoD0, the level from the root level to the 5th level corresponds to LoD1, and the level from the root level to the 7th level (i.e., the leaf level) corresponds to LoD2.

[0315] That is, taking Fig. 13 as an example, when utilizing scalability in slice units, the scalable stages provided are three stages of LoD0, LoD1, and LoD2, and the scalable stages that can be provided in the decoding stage by the octree structure are eight stages from the root level to the leaf level.

[0316] According to embodiments, when LoD0 to LoD2 are each composed of slices, a transcoder (see FIG. 11) of a receiver or transmitter may select only LoD0, only LoD1, or LoD2 for scalable processing. In FIG. 13, LoD1 includes LoD0, and LOD2 includes LoD1 and LoD2.

[0317] For example, if only LoD0 is selected, the maximum octree level is 4, and one scalable layer among octree layers 0 to 4 can be selected during the decoding process. At this time, the receiving device can consider the node size that can be obtained through the maximum octree level (or depth) as a leaf node, and the node size at this time can be transmitted as signaling information.

[0318] For example, if LoD1 is selected, layer 5 is added, so that the maximum octree level becomes 5, and one scalable layer among octree layers 0 to 5 can be selected during the decoding process. At this time, the receiving device can consider the node size that can be obtained through the maximum octree level (or depth) as a leaf node, and can transmit the node size at this time as signaling information. According to embodiments, octree depth, octree layer, octree level, etc. mean units for dividing data in detail.

[0319] For example, if LoD2 is selected, layers 6 and 7 are added, so that the maximum octree level becomes 7, and one scalable layer among the octree layers 0 to 7 can be selected during the decoding process. At this time, the receiving device can consider the node size that can be obtained through the maximum octree level (or depth) as a leaf node, and the node size at this time can be transmitted as signaling information.

[0320] FIGS. 20(a) to 20(c) illustrate examples of a method for constructing slices including point cloud data according to embodiments.

[0321] The transmission method / device / encoder according to the embodiments may be configured by dividing a G-PCC bit stream into a slice structure. A slice may be a data unit for detailed data representation.

[0322] For example, one slice may have one or more octree layers (or depths).

[0323] A transmission method / device according to embodiments, for example, an encoder, may scan nodes (points) included in an octree in the direction of a scan order (21000) to construct a bitstream based on a slice (21001). One slice may include nodes of one or more levels in the octree structure, may include only nodes of a specific level, may include only some nodes of a specific level, or may include only some nodes of one or more levels.

[0324] Fig. 20(a) shows an example in which an octree structure is composed of seven slices. Slice (21002) may be composed of nodes from level 0 to level 4. Slice (21003) may be composed of some nodes of level 5, slice (21004) may be composed of other some nodes of level 5, and slice (21005) may be composed of still other some nodes of level 5. That is, level 5 in Fig. 20(a) is divided into three slices. Similarly, level 6 (i.e., leaf level) in Fig. 20(a) is also divided into three slices. In other words, one slice may be composed of some nodes of a specific level.

[0325] Figure 20(b) shows an example in which an octree structure is composed of four slices, with one slice composed of nodes from level 0 to level 3 and some nodes of level 4, one slice composed of the remaining nodes of level 4 and some nodes of level 5, and one slice composed of the remaining nodes of level 5 and some nodes of level 6. In addition, one slice composed of the remaining nodes of level 5 and some nodes of level 6, and one slice composed of the remaining nodes of level 6.

[0326] Fig. 20(c) shows an example in which an octree structure is composed of five slices, with one slice composed of nodes from level 0 to level 3, and four slices composed of nodes from level 4 to level 6. That is, one slice is composed of some nodes of level 4, some nodes of level 5, and some nodes of level 6. That is, one slice at level 4 or level 6 can include some data of level 4 and data of level 5 or level 6 corresponding to child nodes of that data.

[0327] In other words, as shown in FIGS. 20(b) and 20(c), when multiple octree layers are matched to a single slice, only some nodes of each layer may be included. In this way, when multiple slices constitute a single geometry / attribute frame, the information required to configure the layers at the receiving device can be transmitted to the receiving device through signaling information. For example, the signaling information may include layer information included in each slice, node information included in each layer, etc.

[0328] An encoder and a device corresponding to the encoder according to the embodiments can encode point cloud data and generate and transmit a bitstream further including signaling information (or parameter information) regarding the encoded data and the point cloud data.

[0329] Furthermore, when generating a bitstream, the bitstream can be generated based on a bitstream structure according to embodiments (e.g., see FIGS. 14-20, etc.). Accordingly, a receiving device, a decoder, a corresponding device, etc. according to embodiments can receive and parse a bitstream configured to suit a selective decoding structure of some data, thereby decoding only a portion of the point cloud data and efficiently providing it.

[0330] The following describes scalable transmission of point cloud data.

[0331] The point cloud data transmission method / device according to the embodiments can scalably transmit a bitstream including point cloud data, and the point cloud data reception method / device according to the embodiments can scalably receive and decode the bitstream.

[0332] When a bitstream having the structure described in FIGS. 11 to 20 is used for scalable transmission, signaling information for selecting a slice required by the receiving device can be transmitted to the receiving device. Scalable transmission may mean transmitting or decoding only a portion of the bitstream rather than transmitting or decoding the entire bitstream, and the result may be low resolution point cloud data.

[0333] When applying scalable transmission to an octree-based geometry bitstream according to embodiments, it should be possible to construct point cloud data with only information up to a specific octree layer for the bitstream of each octree layer (Fig. 13) from the root node to the leaf node.

[0334] To achieve this, the target octree layer must not depend on information from lower octree layers. This can be a common constraint for geometry / attribute coding.

[0335] In addition, during scalable transmission, it is necessary to transmit a scalable structure for selecting a scalable layer from the transmitting / receiving device to the receiving device. Considering the octree structure according to the embodiments, all octree layers may support scalable transmission, but scalable transmission may be enabled only for a specific octree layer or lower. For example, if some of the octree layers are included, the receiving device can determine whether the slice is necessary or unnecessary at the bitstream stage by notifying the receiving device of which scalable layer the slice is included in through signaling information. In the example of Fig. 20(a), levels 0 (i.e., the root level) to 4 (21002) do not support scalable transmission and constitute a single scalable layer, and the octree layers below can be configured to have a one-to-one matching with the scalable layer. In general, scalability can be supported for the part corresponding to the leaf node, and in the case where multiple octree layers are included in one slice, as in Fig. 20(c), the layers can be defined to form one scalable layer.

[0336] At this time, scalable transmission and scalable decoding can be used separately depending on the purpose. According to embodiments, scalable transmission can be used for the purpose of selecting information up to a specific layer without going through a decoder in a transmitting / receiving device. According to embodiments, scalable decoding can be used for the purpose of selecting a specific layer during coding. That is, scalable transmission can support the selection of required information without going through a decoder in a compressed state (i.e., at the bitstream stage), thereby enabling the identification of a specific layer in a transmitting or receiving device. On the other hand, scalable decoding can be used in cases such as scalable representation by supporting encoding / decoding only up to the required part in the encoding / decoding process.

[0337] In this case, the layer configuration for scalable transmission and the layer configuration for scalable decoding may differ. For example, the three lower octree layers including leaf nodes may constitute one layer from the perspective of scalable transmission, but from the perspective of scalable decoding, scalable decoding may be possible for each of the leaf node layer, leaf node layer-1, and leaf node layer-2 if all layer information is included.

[0338] Figures 21(a) and 21(b) illustrate single-slice and segmented-slice based geometry tree structures according to embodiments.

[0339] The method / device according to the embodiments can configure a slice for transmitting point cloud data as shown in FIG. 21(a) and FIG. 21(b).

[0340] Figures 21(a) and 21(b) are geometry tree structures included in different slice structures. According to the G-PCC technology, the entire coded bitstream can be included in a single slice. Furthermore, for multiple slices, each slice can include sub-bitstreams. The order of the slices can be the same as the order of the sub-bitstreams. The bitstreams are accumulated in breadth-first order of the geometry tree, and each slice can be matched with a group of tree layers (Figures 21(a) and 21(b)). The divided slices can inherit the layering structure of the G-PCC bitstream.

[0341] Just as higher layers in a geometry tree do not affect lower layers, following slices may not affect previous slices.

[0342] Segmented slices according to the embodiments are efficient in terms of error robustness, effective transmission, supporting region of interest, etc.

[0343] 1) Error resilience

[0344] Compared to a single-slice structure, a partitioned slice can be more error-resistant. If a slice contains the entire bitstream of a frame, data loss can affect the entire frame data. On the other hand, if the bitstream is partitioned into multiple slices, even if some slices are lost, some slices that are not affected by the loss can still be decoded.

[0345] 2) Scalable transmission

[0346] Consider supporting multiple decoders with different capabilities. If the coded data resides in a single slice, the LOD of the coded point cloud can be determined prior to encoding. Therefore, multiple pre-encoded bitstreams with different resolutions of the point cloud data can be delivered independently. This can be inefficient in terms of high bandwidth or storage space.

[0347] When a PCC bitstream is generated and included in segmented slices, a single bitstream can support different levels of decoders. From the decoder side, the receiver can select target layers and pass the partially selected bitstream to the decoder. Similarly, by using a single PCC bitstream without partitioning the entire bitstream, a partial PCC bitstream can be efficiently generated on the transmitter side.

[0348] 3) Region-based spatial scalability

[0349] In terms of the G-PCC requirements, region-based spatial scalability can be defined as follows: A compressed bitstream can be structured to have more than one layer. Certain regions of interest can have additional layers and higher density, and layers can be predicted from lower layers.

[0350] To support this requirement, it is necessary to support different detailed representations of regions. For example, in VR / AR applications, it is desirable to represent distant objects with low precision and nearby objects with high precision. Alternatively, the decoder can increase the resolution of a region of interest upon request. This can be implemented by using scalable structures of G-PCC, such as geometry octrees and scalable attribute coding schemes. Based on the current slice structure containing the entire geometry or attribute, decoders must access the entire bitstream. This can lead to bandwidth, memory, and decoder inefficiencies. On the other hand, if the bitstream is segmented into multiple slices, each slice containing sub-bitstreams according to scalable layers, the decoder according to embodiments can select a slice as needed before efficiently parsing the bitstream.

[0351] Figures 22(a) and 22(b) illustrate the layer group structure of the geometry coding tree and the aligned layer group structure of the attribute coding tree according to embodiments.

[0352] Figures 22(a) and 22(b) illustrate the layer group structure of the geometry coding tree and the aligned layer group structure of the attribute coding tree according to embodiments.

[0353] The method / device according to the embodiments can create a slice layer group using a hierarchical structure or tree structure of point cloud data, as shown in FIG. 22(a) and FIG. 22(b).

[0354] The method / device according to the embodiments can apply segmentation of geometry and attribute bitstreams contained in different slices. In addition, the coding tree structure of each slice and geometry and attribute coding contained in partial tree information can be used from a tree depth perspective.

[0355] Referring to Fig. 22(a), an example of a geometry tree structure and a proposed slice segment is shown.

[0356] For example, if there are eight layers (layer 0 to layer 7) in an octree, five slices can be used to contain sub-bitstreams of one or more layers. A group represents a group of geometry tree layers. For example, group 1 consists of layer 0 to layer 4, group 2 includes layer 5, and group 3 includes layer 6 and layer 7. In addition, a group can be divided into three sub-groups. Parent and child pairs exist in each sub-group. Group 3-1 to group 3-3 are sub-groups of group 3. When scalable attribute coding is used, the tree structure is identical to the geometry tree structure. The same octree-to-slice mapping can be used to create attribute slice segments (Fig. 22(b)).

[0357] Layer group: Represents a group of layer structure units that occur in G-PCC coding, such as octree layers and LoD layers.

[0358] Sub-group: A sub-group can be represented as a set of adjacent nodes based on location information for a single layer group. Alternatively, a group can be formed based on the lowest layer within the layer group (which can mean the layer closest to the root, for example, layer 6 for group 3). A group of adjacent nodes can be formed based on the Morton code order, a group of adjacent nodes based on distance, or a group of adjacent nodes based on coding order. Additionally, nodes in a parent-child relationship can be specified to exist within a single sub-group.

[0359] When defining a subgroup, a boundary occurs in the middle of the layer, and whether to have continuity at the boundary can be maintained by indicating whether entropy is used continuously, such as sps_entropy_continuation_enabled_flag, gsh_entropy_continuation_flag, and by indicating ref_slice_id.

[0360] The tree structure of the geometry according to the embodiments may be an octree structure, and the attribute layer structure or attribute tree structure according to the embodiments may include a structure of a level of detail (LOD). That is, the tree structure for point cloud data includes layers corresponding to depth or level, and the layers may be grouped.

[0361] The method / device according to the embodiments (e.g., the octree analysis unit (30002) or LOD generation unit (30009) of FIG. 3, the octree synthesis unit (7001) or LOD generation unit (7008) of FIG. 7) can generate an octree structure of geometry or an LOD tree structure of attributes. In addition, point cloud data can be grouped based on layers of the tree structure as shown in FIGS. 21 and 22.

[0362] Referring to Figures 22(a) and 22(b), multiple layers are grouped to form Groups 1 through 3. A group can be further divided within itself to form subgroups. Figures 22(a) and 22(b) illustrate Group 3 being divided into three subgroups.

[0363] The method / device according to the embodiments can generate geometry-based slices and attribute-based slice layers.

[0364] The attribute coding layer may have a different structure than the geometry coding tree.

[0365] To efficiently use the layering structure of G-PCC, it is possible to provide segmentation of slices paired with the geometry and attribute layering structure.

[0366] For a geometry slice segment, each slice segment may contain data coded from a layer group, where a layer group is defined as a group of contiguous tree layers, and the start and end depths of the tree layers may be a specific number within the tree depth, with the start being less than the end.

[0367] For attribute slice segments, each slice segment contains coded data from a group of layers, where the layers can be tree depths or LODs according to the attribute coding scheme.

[0368] The order of coded data within slice segments may be the same as the order of coded data within a single slice.

[0369] As parameter sets included in the bitstream, the following can be provided:

[0370] Figure 23 illustrates the layer group and subgroup structure according to embodiments.

[0371] Referring to Figure 23, point cloud data and bitstream can be expressed by being separated into bounding boxes.

[0372] Referring to Fig. 23, the subgroup structure and the bounding boxes corresponding to the subgroups are illustrated. Layer group 2 is divided into two subgroups (group2-1, group2-2) and included in different slices, and layer group 3 is divided into four subgroups (group3-1, group3-2, group3-3, group3-4) and included in different slices. Given slices of layer groups and subgroups along with bounding box information, spatial access can be performed by 1) comparing the bounding box of each slice with the ROI, 2) selecting a slice in which the subgroup bounding box overlaps the ROI, and 3) decoding the selected slice.

[0373] When considering the ROI in region 3-3, slices 1, 3, and 6 are selected as the subgroup bounding boxes of layer group 1, subgroups 2-2, and 3-3 covering the ROI area. For efficient spatial access, it is assumed that there are no dependencies between subgroups within the same layer group. For live streaming or low-latency use cases, selection and decoding can be performed upon receiving each slice segment to improve time efficiency.

[0374] The method / device according to the embodiments may represent data as a tree (22000) composed of layers (which may be referred to as depths, levels, etc.) when encoding geometry and / or attributes. Point cloud data corresponding to each layer (depth / level) may be grouped into a layer group (or groups). Four layers may be grouped to form layer group 1 (22001). Layer group 2 (22002) may be further divided (segmented) into two subgroups, and layer group 3 (22003) may be further divided (segmented) into four subgroups. Each subgroup may be composed of each slice, and a bitstream may be generated.

[0375] A receiving device according to embodiments may receive a bitstream, select a specific slice from the bitstream, and decode a bounding box corresponding to a subgroup included in the selected slice. For example, when slice 1 is selected, a bounding box (22004) corresponding to layer group 1 may be decoded. Layer group 1 may be data corresponding to the largest area. When additionally displaying a detailed area for layer group 1, a method / device according to embodiments may partially hierarchically access bounding boxes (point cloud data) of subgroup 2-2 and / or subgroup 3-3 for a detailed area included in an area of ​​layer group 1 by selecting slice 3 and / or slice 6.

[0376] Encoding and decoding of point cloud data using the layer group and subgroup of FIG. 23 can be performed by at least one of the transmitting / receiving device of FIG. 1, the encoding and decoding of FIG. 2, the transmitting device / method of FIG. 3, the receiving device / method of FIG. 7, the transmitting / receiving devices / methods of FIGS. 8 and 9, the devices of FIG. 10, the encoding device of FIG. 37, the encoding method of FIG. 39 or FIG. 40, the decoding device of FIG. 38, and the decoding method of FIG. 41.

[0377] In this way, the present disclosure divides a geometry bitstream or attribute bitstream in a layer-group / subgroup unit into slices, and efficiently compresses and restores geometry information or attribute information in slice units. In this case, the continuity of context references can be used as a method for reducing coding efficiency loss.

[0378] That is, the context table used in the process of coding one slice can be used when coding another slice. A context table is based on the correlation between nodes within a geometry tree and can be used to improve coding efficiency. At this time, as a method of considering the local correlation between layer groups, a context reference relationship can be restricted to be established when the subgroup bounding box of the referenced slice includes or is the same as the subgroup bounding box of the referenced slice. In other words, coding efficiency can be further improved by using the context table of a slice that is in a parent subgroup-child subgroup relationship or an ancestor subgroup-child subgroup relationship. Alternatively, the context table of the first slice can be used in the coding of subsequent slices as a way to reduce the burden on the buffer storing the context table.

[0379] The following describes an embodiment that applies the continuity of context reference among the criteria presented above. In order to use the continuity of context reference information, the layer group index and subgroup index of each node are determined, and the reference context reference according to each index is used as the initial value of the context table at the start of each subgroup. During the encoding process, nodes can exist regardless of the subgroup order, and the process of storing and loading the context state (encoder context state) in a buffer in the encoder can ensure the continuous use of the context table within the subgroup.

[0380] This process is done in two steps: when the depth changes, it determines whether the layer group has changed and performs different actions accordingly.

[0381] The relationship between parent nodes and child nodes included in a tree structure (e.g., an octree or LOD) according to embodiments may be expressed as a connection relationship between upper-level nodes and lower-level nodes. The transmitting and receiving device / method according to embodiments may generate a tree structure and group point cloud data into a plurality of groups based on layers of the tree structure. The groups may be layer groups, subgroups, etc., and may correspond to slices according to embodiments.

[0382] The transmitting / receiving device / method according to the embodiments may perform encoding / decoding by loading a context (or context information) stored in a buffer based on a reference layer group, reference subgroup, or reference slice when encoding / decoding point cloud data belonging to a layer group, subgroup, or slice. At this time, the reference layer group, reference subgroup, or reference slice may include nodes corresponding to parents of nodes belonging to the layer group, subgroup, or slice to be encoded / decoded.

[0383] In other words, the point cloud data transmission / reception device / method according to the embodiments encodes / decodes the second group based on context information for the first group and stores the context information of the second group in a buffer. The stored context information of the second group can be used to encode / decode the third group. In this case, the first group to the third group may be groups grouped based on arbitrary layers. Additionally, the first group may be a group corresponding to the parent layer of the second group.

[0384] In addition, the point cloud data transmission / reception device / method according to the embodiments may store the context of a parent layer group, a parent subgroup, or a parent slice in a buffer, and use the stored context when encoding / decoding a child layer group, a child subgroup, or a child slice. The parent group or slice may be located at a higher level in the tree structure than the child group or slice, and a node belonging to the parent group (layer group, subgroup) / slice may correspond to a parent-child relationship with a node belonging to the child group / slice.

[0385] Figure 24 illustrates an example of contextual references between layer groups according to embodiments. In particular, Figure 24 is an example of a fixed contextual reference, where the current subgroup references a parent subgroup.

[0386] Referring to FIG. 24, a fine-granularity slice (FGS) may represent a subgroup or slice, and the subgroup or slice may be a grouping of point cloud data according to embodiments.

[0387] In Fig. 24, FGS 1(1,0) represents subgroup 0 of layer group 1, and FGS 2(1,1) represents subgroup 1 of layer group 1. FGS N+1(2,0) represents subgroup 0 of layer group 2, and FGS N+2(2,1) represents subgroup 1 of layer group 2.

[0388] In Fig. 24, Save states indicates encoding or decoding the corresponding subgroup and saving context information, and Refer context indicates referencing the saved context information to encode or decode the corresponding subgroup.

[0389] Accordingly, in FIG. 24, it is exemplified that FGS 1 references the context information of FGS 0 (23001), and FGS N+1 (23003) references the context information of FGS 1 (23002). As in FIG. 24, a subgroup (or slice) belonging to layer group 2 can reference the context of a subgroup (or slice) belonging to layer group 1. In addition, a subgroup belonging to layer group 1 can be a parent subgroup of a subgroup belonging to layer group 2.

[0390] Context inheritance

[0391] Figure 24 illustrates a context reference structure of layer group slicing according to embodiments. In the figure, an FGS may correspond to a subgroup according to embodiments, and subgroups in the same row are considered to be in the same layer group. A subgroup may correspond to a slice. In the figure, an arrow pointing from one slice to another indicates a context reference relationship between the two slices. The context reference of the current slice may be one of the slices decoded before the current slice.

[0392] Considering the spatial random access (SRA) implementation, referencing parent subgroups can be a good choice for ensuring independence between subgroups. However, as the number of subgroups or layer groups increases, the number of context buffers can also increase. Considering the number of context buffers as the number of referenced slices, the number of context buffers can be the sum of all subgroups except those belonging to the first and last layer groups. This can be formalized as follows, where N represents the number.

[0393] N (context buffer) = 1 + N subgroup × (N (layer-group) -2)

[0394] Figure 25 illustrates an example of context references between groups according to embodiments. In particular, Figure 25 is an example of flexible context references, where all subgroups reference context information of the root subgroup (i.e., the root slice).

[0395] In Fig. 25, FGS 1 (24002) to FGS N, FGS N+1 (24003) to FGS 2N+1 refer to the context information of FGS 0 (24001). That is, all subgroups (or slices) except FGS 0 (24001) refer to FGS 0 (24001).

[0396] One way to mitigate the size of the context buffer according to embodiments may be to reduce the number of subgroups referenced by following slices. An extreme example of this method is to reference the root slice, as shown in Figure 25. This approach, based on the number of context buffers described above, results in a single context buffer because the number of subgroup slices referenced is zero.

[0397] N (context buffer) =1

[0398] That is, all slices reference the first slice. Compared to the case of Fig. 24, the number of stored context states is reduced to one, and all dependent slices reference the first slice.

[0399] Figures 26(a) to (c) illustrate examples of context buffer management according to embodiments. In particular, these are examples when referencing a parent subgroup.

[0400] Referring to (a) of FIG. 26, the transmitting and receiving device according to the embodiments processes FGS 0(0,0)(25001) and stores context information (25002) for the corresponding group (FGS 0) in the context buffer.

[0401] Referring to (b) of FIG. 26, the transceiver device according to the embodiments can load the context information (25004) of FGS 0 (0,0) stored in the context buffer to process (encode or decode) FGS 2 (1,1) (25003) (load states), and process FGS 2 (1,1) and store the context information of FGS 2 (1,1) in the context buffer (Save states). At this time, the process of loading the context information can be performed with reference to the ref_layer_group_id and ref_subgroup_id parameters.

[0402] Referring to (c) of FIG. 26, the transmitting and receiving device according to the embodiments can load context information (context states (1,1)) (25006) of FGS 2 (1,1) to process (encode or decode) FGS N+2 (2,1) (25005). Since FGS N+2 (2,1) belongs to the last layer group, context information is not stored in the context buffer.

[0403] In this way, in the case of the parent subgroup reference method, the change of the context buffer is explained in (a) to (c) of Fig. 26. When the bitstream of the slice is decoded, the context state is stored in the context buffer as shown in Fig. 26(a). If context inheritance is used, the context state of the following slices is initialized by one of the stored context states of the previous slices indicated by ref_layer_group_id and ref_subgroup_id (Fig. 26(b)). Therefore, the context state of the slice belonging to the last layer group is initialized by the stored context state of the previous slice as shown in Fig. 26(c). However, the receiving device (or decoder) according to the embodiments may decide not to store the context of FGS N+1 to 2N if there is a restriction that it does not refer to a subgroup belonging to the same layer group. Based on the previous information, the smart decoder can save the context buffer.

[0404] Figures 27(a) to (c) illustrate examples of context buffer management according to embodiments. In particular, these are examples when referencing a root layer group.

[0405] Referring to (a) of FIG. 27, the transmitting and receiving device according to the embodiments processes FGS 0(0,0)(26001) and stores context information (26002) for the corresponding group (FGS 0) in the context buffer.

[0406] Referring to (b) of FIG. 27, the transceiver device according to the embodiments can load context information (26004) of FGS 0 stored in a context buffer to process (encode or decode) FGS 2(1,1)(26003) (load states), and process FGS 2(1,1) and store context information of FGS 2(1,1) in the context buffer (Save states). At this time, the process of loading context information can be performed with reference to the ref_layer_group_id and ref_subgroup_id parameters.

[0407] Referring to (c) of FIG. 27, the transmitting and receiving device according to the embodiments can load the context information (context states (0,0)) (26006) of FGS 0 (0,0) (26001) to process (encode or decode) FGS N+2 (2,1) (26005). Since FGS N+2 (2,1) (26005) belongs to the last layer group, the context information is not stored in the context buffer.

[0408] When flexible context references are allowed, there may be context states that are not used by following slices. For example, consider a root layer group reference, where all context states of dependent slices are initialized by the context state saved from the first slice. Decoders are unaware of the overall reference structure and may use the current context of following slices. However, as expected, the context states saved from (1,0) to (1,N-1) are not used by any slice. In this example, the inefficiency arises from the lack of information on the decoder side.

[0409] Figures 28 (a) to (c) illustrate examples of context buffer management according to embodiments.

[0410] Referring to (a) of FIG. 28, the transmitting and receiving device according to the embodiments processes FGS 0(0,0)(27001) and stores context information (27002) for the corresponding group (FGS 0) in the context buffer.

[0411] Referring to (b) of FIG. 28, the transmitting / receiving device / method according to the embodiments can retrieve context information (context states(0,0))(27004) of FGS 0(0,0)(27001) from the context buffer to process (encode or decode) FGS 2(1,1)(27003). Then, the context information of FGS 2(1,1) can be stored in the context buffer based on context reference indication flag (context_reference_indication_flag) information. That is, the context information of FGS 2(1,1) may or may not be stored in the buffer depending on the context_reference_indication_flag information. The context_reference_indication_flag information can be generated and transmitted by the transmitting device / method according to the embodiments, and used in the receiving device / method according to the embodiments.

[0412] Referring to (c) of FIG. 28, the transmitting and receiving device / method according to the embodiments can retrieve context information (context states(0,0))(27006) of FGS 0(0,0)(27001) from the context buffer to process (encode or decode) FGS N+2(2,1)(27005).

[0413] Since the context buffer always stores only context information of FGS 0, the transmitting and receiving device according to the embodiments can efficiently use the memory of the buffer.

[0414] The transceiver according to the embodiments proposes a new signal to assist the decoder in indicating whether the current context of followed slices is used and deciding whether to store the context, in order to increase the efficiency of context buffer management.

[0415] A followed slice according to embodiments may represent a slice that is referenced by other slices. A following slice according to embodiments may represent a slice that references other slices.

[0416] To improve context buffer management on the decoder side, context reference information is proposed from the perspective of the current slice, i.e., context state reference indication by followed slices.

[0417] Figure 28 (b) illustrates a buffer management case of the proposed signal. Compared to previous cases without other information, storing the context state in the context buffer is determined by the context reference indication flag (context_reference_indication_flag). If the context reference indicator is on, the decoder stores the current context state in the context buffer to allow the context state to be used by followed slices. On the other hand, if the context reference indicator is off, the decoder does not store the current context state in the context buffer to save context memory. Comparing Figure 26 (c) with Figure 27 (c), the context buffer of the root layer reference case only has one context compared to the context buffer of the parent subgroup reference case. The saved context memory size is N units, where N represents the number of subgroups.

[0418] Meanwhile, the receiver can use context, phiBuffer, Planar context, and buffer continuity between slices to prevent coding efficiency reduction caused by dividing slices, and the receiver can also decide whether to store context, phiBuffer, and Planar context based on whether the context is reused.

[0419] if (_dep_gbh.context_reuse_flag) {

[0420] _refIdxToSavedArrayIdx[curLayerGroup][_dep_gbh.subgroup_id] = _ctxtMemSaved.size();

[0421] _ctxtMemSaved.push_back(cur_ctxtMem);

[0422]

[0423] if(_gps->geom_angular_mode_enabled_flag)

[0424] _phiBufferSaved.push_back(cur_phiBuffer);

[0425] if(_gps->geom_planar_mode_enabled_flag)

[0426] _planarSaved.push_back(cur_planar);

[0427] int idx = _refIdxToSavedArrayIdx[curLayerGroup][_dep_gbh.subgroup_id];

[0428] }

[0429] Figures 29 (a) to (c) illustrate a context buffer release method according to embodiments.

[0430] A method according to embodiments includes a method for determining a decoder context release time.

[0431] When indicating whether a context is reusable, it indicates whether the context used in a specific slice should be stored in the context buffer. This allows for efficient use of context buffer memory by storing only the context needed when coding subsequent slices. However, in this case, the context is stored in the context buffer until the coding for that frame is completed, which can place a burden on the context buffer as the number of stored contexts increases. To use the context buffer more efficiently, a method can be used to delete (i.e., release) stored contexts from the context buffer when they are no longer in use.

[0432] 1) List-based context memory management method

[0433] Figures 29 (a) to (c) illustrate a method for managing a list of slices / subgroups using context information stored in a buffer as a method for effectively managing context memory (i.e., a buffer). Figures 29 (a) to (c) illustrate a method for managing context memory based on a list.

[0434] (a) of Fig. 29: Whether the context used to code the current slice is stored can be indicated through the context reference indication flag (context_reference_indication_flag). That is, if the context reference indication flag (context_reference_indication_flag) is 1, it can indicate that the context of the current slice / subgroup can be used in the slice / subgroup transmitted later, and for this purpose, the context of the current slice / subgroup can be stored in the context buffer. In order to use the context later, the index of the context can be made to have the same index as the subgroup index. At this time, if information about the slice / subgroup using the current context is given as a list, the target list can be stored and compared with the list for actual use cases. The list of slices / subgroups using the context can be investigated in advance by the encoder and transmitted, or the list can be generated by estimating the context reference relationship in the decoder based on a predetermined layer group structure. For example, if fixed by referencing the context of a parent subgroup, a list of subgroups that are children of the current subgroup can be examined, which in this embodiment can be called list A.

[0435] (b) of Fig. 29: When a new slice / subgroup is passed, the context used to decode the slice / subgroup can be specified based on the context reference id. In the following example, the context corresponding to (0,0) is used, and the index of the current slice / subgroup, (1,1), can be added to the list of used subgroups. In the coding process, the list of slices / subgroups that use a specific context is called List B. If the context reference indication flag (context_reference_indication_flag) is 1, it means that the context of the current slice / subgroup will be used later, so it can be stored in the context buffer, and List B (1,1) of the context buffer (1,1) can be initialized.

[0436] (c) of Fig. 29: If List A and List B are the same for a specific context buffer, memory can be managed by releasing (i.e., releasing) the context buffer. As follows, if the context reference id is (1,1), the context state (1,1) can be used for coding in the context buffer. At this time, the index of the current slice / subgroup, (2,1), can be added to List B. At this time, since List B and List A are the same as (2,1), it can be seen that the context state (1,1) will not be used in the future. In this case, the memory of the context buffer can be effectively managed by releasing the memory that stored the context state (1,1).

[0437] The embodiments include a method for specifying a context index based on a layer group index and a subgroup index. If a unique slice index is assigned to each slice, a list of context buffers can be managed based on the slice index.

[0438] Figure 30 illustrates a context buffer release method according to embodiments.

[0439] Embodiments include a method for managing context memory based on the number of references.

[0440] Context buffers can be efficiently utilized by managing unused context states in real time based on the number of times each context state is used. Embodiments can manage context buffers using target numbers and counters for each context state in the context buffer.

[0441] Fig. 30(a): The target number indicates the number of times the context state is used, and the counter can update the number of times the context state is used. That is, the counter value increases by 1 every time the context state is used. Fig. 30(a) shows the case of the first slice / subgroup, and if the context reference indication flag (context_reference_indication_flag) is 1 or layer-group slicing is used, the context state (0,0) can be stored in the context buffer. In addition, the number of times the context state is used, N, can be stored in the target number, and this can be specified as the same value as N, the number of subgroups belonging to layer-group 1, since the case of using the context state of the parent subgroup is used as an example. In other words, the list of child subgroups of FGS 0 is FGS 1 (1,0), FGS 2 (1,1), … , can be obtained as FGS N (1, N-1), and the number of elements in the list, N, can be specified as the target number.

[0442] (b) of Fig. 30: When coding a new slice / subgroup, the context reference of the slice / subgroup can be found in the context buffer via the context reference id. The context state (0,0) will be used, and the counter number can be increased by 1. Since the context state (0,0) was already used to code FGS 1 (1,0), the counter can have the value 2. In addition, since the context reference indication flag (context_reference_indication_flag) is 1, it means that it can be used as a context reference in the following slice / subgroup, so the context state of FGS 2 (1,1) can be stored in the context buffer. At this time, the number of child slices / subgroups that use the context state (1,1) can be stored in the target number.

[0443] (c) of Fig. 30: The memory usage of the context buffer can be managed through memory release for context states whose target number and counter managed in the context buffer are the same. The context state (1,1) corresponding to the context reference id of FGS N+2(2,1) can be used, and the counter (1,1) can be increased by 1. In this case, the target number and the counter values ​​of the context state (1,1) become the same, which means that the context state (1,1) is no longer in use. Therefore, even if the context state (1,1) is deleted from the context buffer, it does not affect the coding of subsequent slices / subgroups. The memory usage of the context buffer can be minimized by deleting context states that are no longer used from the context buffer.

[0444] The following shows an example of decoder code implementation.

[0445] if (_dep_gbh.context_reference_indication_flag) {

[0446] _refIdxToSavedArrayIdx[curLayerGroup][_dep_gbh.subgroup_id] = _ctxtMemSaved.size();

[0447] _ctxtMemSaved.push_back(cur_ctxtMem);

[0448] _numSubsequentSubgroups.push_back(_dep_gbh.numSubsequentSubgroups);

[0449] if (_gps->geom_angular_mode_enabled_flag)

[0450] _phiBufferSaved.push_back(cur_phiBuffer);

[0451] if (_gps->geom_planar_mode_enabled_flag)

[0452] _planarSaved.push_back(cur_planar);

[0453] }

[0454] _numSubsequentSubgroups[refArrayIdx]--;

[0455] if (_numSubsequentSubgroups[refArrayIdx] == 0) {

[0456] _ctxtMemSaved[refArrayIdx].resetMap();

[0457] _ctxtMemSaved[refArrayIdx].reset();

[0458] }

[0459] The target number for each context state can be passed after examining the number of subsequent subgroups in the encoder. If necessary, a list of slices / subgroups used as context references can be additionally passed to verify the accuracy of the number of subsequent subgroups and determine whether to delete the context state.

[0460] Figure 31 illustrates a context memory management method according to embodiments.

[0461] Embodiments include a method for managing context memory based on a data unit coding structure.

[0462] Slices / subgroups can be delivered based on a certain order. Representative methods include breadth-first search and depth-first search. Breadth-first search is a method that codes subgroups within the same layer group before coding subgroups within child layer groups. In contrast, depth-first search is a method that first codes children within the same parent layer group after reaching the subgroup corresponding to the maximum depth.

[0463] If we consider each node as an FGS slice index, we can assume that layer group 0 belongs to slice 0, layer group 1 belongs to slices 1 and 2, and layer group 2 belongs to slices 3, 4, 5, and 6. In addition, we can assume that slices connected by solid lines represent slice pairs belonging to a parent-child relationship. If coding is based on breadth-first search, the order is 0, 1, 2, 3, 4, 5, 6, and if coding is based on depth-first search, the order is 0, 1, 3, 4, 2, 5, 6.

[0464] If the memory of the context buffer is managed based on the slice order, it can work as follows. At this time, it can be assumed that the parent context state is used as the reference context. If it is coded based on breadth-first search, the context state of the upper layer group is no longer used when the coding of the subgroup belonging to each layer group is finished. That is, context state 0 is used when coding slices 1 and 2, but context state 1 is no longer used when coding slice 2. In this case, when the layer group is switched (slice 2), the context state of the parent subgroup (the context state of slice 0) can be deleted from the context buffer.

[0465] If coding is based on depth-first search, the context state can be deleted at the point where the coding for the child subgroup is finished or when the layer group is switched (from the bottom to the root). After coding for slices 3 and 4 is finished, it moves on to slice 2. At this time, slices 3 and 4 belong to layer group 2, and slice 2 belongs to layer group 1. Slices 3 and 4 are coded using the context state of slice 1, and since context state 1 is no longer used, it can be deleted from the context buffer.

[0466] In this case, context memory can be used efficiently without additional information such as the list of subsequent subgroups or the number of subsequent subgroups.

[0467] Figure 32 illustrates a bitstream containing point cloud data according to embodiments.

[0468] An encoder according to embodiments may encode point cloud data and generate related parameter information (i.e., signaling information) to generate a bitstream. A decoder according to embodiments may receive the bitstream and decode the point cloud data based on the parameter information (i.e., signaling information).

[0469] Information about separated slices can be defined in parameter sets and SEI messages as follows. It can be defined in the Sequence Parameter Set (SPS), Geometry Parameter Set (GPS), Attribute Parameter Set (APS), Geometry Slice Header (GSH), and Attribute Slice Header (ASH). Depending on the application or system, it can be defined in a corresponding location or in a separate location to use different scopes, application methods, etc. In other words, signaling can have different meanings depending on where it is transmitted. If it is defined in the SPS, it can be applied equally to the entire sequence. If it is defined in the GPS, it can indicate that it is used for position recovery. If it is defined in the APS, it can indicate that it is applied to attribute recovery. If it is defined in the Tile Parameter Set (TPS), it can indicate that the signaling is applied only to points within a tile. If it is transmitted in slice units, it can indicate that the signaling is applied only to the corresponding slice. In addition, depending on the application or system, it can be defined in a corresponding location or in a separate location to use different scopes, application methods, etc. Additionally, if the syntax elements (or fields) defined below can be applied to multiple point cloud data streams as well as the current point cloud data stream, they can be conveyed through a higher-level parameter set, etc.

[0470] Each abbreviation stands for the following. Each abbreviation may be referred to by other terms within the same meaning: SPS: Sequence Parameter Set, GPS: Geometry Parameter Set, APS: Attribute Parameter Set, TPS: Tile Parameter Set, Geom: Geometry bitstream = geometry slice header + geometry slice data, Attr: Attribute bitstream = attribute blick header + attribute brick data.

[0471] Embodiments can generate this information independently of the coding technique or in conjunction with the coding method. A tile parameter set can be defined to support regionally varying scalability. Alternatively, bitstreams can be selected at the system level by defining a Network Abstract Layer (NAL) unit and conveying relevant information, such as a layer ID (layer_id), that allows layer selection.

[0472] Hereinafter, parameters (which may be referred to in various ways, such as metadata, signaling information, etc.) according to the embodiments may be generated in the process of a transmitter according to the embodiments described below, and may be transmitted to a receiver according to the embodiments and used in the reconstruction process.

[0473] For example, parameters according to embodiments may be generated in a metadata processing unit (or metadata generator) of a transmitting device according to embodiments described below, and may be obtained in a metadata parser of a receiving device according to embodiments.

[0474] FIG. 33 illustrates an example of a syntax structure of a sequence parameter set (SPS) of a bitstream according to embodiments.

[0475] FIG. 34 illustrates an example of a syntax structure of a dependent geometry data unit header of a bitstream according to embodiments.

[0476] FIG. 35 illustrates an example of a syntax structure of a dependent attribute data unit header of a bitstream according to embodiments.

[0477] Figures 36a and 36b illustrate an example of a syntax structure of a layer group structure inventory (LGSI) according to embodiments.

[0478] The definition of each syntax element in FIGS. 33 to 36a and 36b is as follows:

[0479] When the layer group enabled flag (layer_group_enabled_flag) is equal to 1, it indicates that the geometry and / or attribute bitstreams of a frame or tile are contained in multiple slices that match the coding layer group or its subgroups. When layer_group_enabled_flag is equal to 0, it indicates that the geometry bitstreams of a frame or tile are contained in a single slice.

[0480] The layer group slice order type (layer_group_slice_order_type) indicates the ordering type of layer group slices. If layer_group_slice_order_type is 0, it indicates a breadth-first search order of layer group slices. If layer_group_slice_order_type is 1, it indicates a depth-first search order of layer group slices. A layer_group_slice_order_type of 2 indicates that no ordering type is specified.

[0481] If the context reference indication flag (context_reference_indication_flag) is 1, it indicates that the context state of the current dependent slice is inherited by one or more followed dependent slices. If the context_reference_indication_flag is 0, it indicates that the context state of the current dependent slice is not inherited by followed dependent slices.

[0482] Decoders can manage context buffers using context_reference_indication_flag. If context_reference_indication_flag is 1, the context state of the current dependent slice is stored in the context buffer when decoding is finished. If context_reference_indication_flag is 0, the context state of the current dependent slice is not stored in the context buffer.

[0483] The number of subsequent data units (num_subsequent_data_units) indicates the number of subsequent dependent data units that use the context state of the current data unit.

[0484] If the subsequent data unit list presence flag (subsequent_data_unit_list_present_flag) is 1, it indicates that a list of subsequent data units exists. If next_data_unit_list_present_flag is 0, it indicates that a list of subsequent data units does not exist.

[0485] The number_of_layer_groups indicates the number of layer groups in the list of subsequent data units.

[0486] The subsequent layer group id (subsequent_layer_group_id) indicates the layer group index of the subsequent data unit.

[0487] The number_of_subgroups indicates the number of subgroups in the layer group of the list of subsequent data units.

[0488] The subsequent subgroup id (subsequent_subgroup_id) indicates the subgroup index within the layer group of the subsequent data unit.

[0489] Layer Group Structure Inventory Syntax

[0490] Sequence parameter set id (lgsi_seq_parameter_set_id) indicates the sps_seq_parameter_set_id value. lgsi_seq_parameter_set_id being 0 is a requirement for bitstream conformance.

[0491] lgsi_frame_ctr_lsb_bits represents the length of the lgsi_frame_ctr_lsb syntax element (or field) in bits.

[0492] lgsi_frame_ctr_lsb represents the lgsi_frame_ctr_lsb_bits least significant bits of the FrameCtr for which the group structure inventory is valid. A layer group structure inventory remains valid until it is replaced by another layer group structure inventory.

[0493] Number of slices (lgsi_num_slice_ids_minus1): This value plus 1 represents the number of slices in the layer group structure inventory.

[0494] Slice id (gi_slice_id) represents the slice ID of the sid-th slice within the layer group structure inventory. It is a bitstream conformance requirement that all values ​​of lgsi_slice_id be unique within the layer group structure inventory.

[0495] The number of layer groups (lgsi_num_layer_groups_minus1) + 1 indicates the number of layer groups.

[0496] Layer group id (lgsi_layer_group_id) indicates the indicator of a layer group. The range of lgsi_layer_group_id is from 0 to lgsi_num_layer_groups_minus1.

[0497] The number of layers (lgsi_num_layers_minus1) + 1 represents the number of coded layers in the slice of the i-th layer group of the sid-th slice. The total number of coded layers required to decode the n-th layer group is equal to the sum of lgsi_num_layers_minus1[sid][i] + 1, where i is from 0 to n.

[0498] The number of subgroups (lgsi_num_subgroups_minus1) + 1 represents the number of subgroups in the i-th layer group of the sid-th slice.

[0499] The subgroup id (lgsi_subgroup_id) indicates the indicator of the layer group. The range of lgsi_subgroup_id is from 0 to lgsi_num_subgroups_minus1.

[0500] The parent subgroup id (lgsi_parent_subgroup_id) indicates the indicator of a subgroup within the layer group pointed to by lgsi_subgroup_id. The range of lgsi_parent_subgroup_id is from 0 to gi_num_subgroups_minus1 within the layer group pointed to by lgsi_subgroup_id.

[0501] The subgroup bounding box origin (lgsi_subgroup_bbox_origin) and subgroup bounding box size (lgsi_subgroup_bbox_size) represent the bounding box of the current subgroup.

[0502] The subgroup bounding box origin (lgsi_subgroup_bbox_origin) indicates the origin of the subgroup bounding box of the subgroup indicated by lgsi_subgroup_id among the layer groups indicated by lgsi_layer_group_id.

[0503] lgsi_subgroup_bbox_size indicates the size of the subgroup bounding box of the subgroup indicated by lgsi_subgroup_id among the layer groups indicated by lgsi_layer_group_id.

[0504] lgsi_origin_bits_minus + 1 represents the length of the lgsi_origin_xyz syntax element in bits.

[0505] The origin location (lgsi_origin_xyz) indicates the origin of all partitions. The value of lgsi_origin_xyz[ k ] is equal to sps_bounding_box_offset[ k ].

[0506] lgsi_origin_log2_scale represents a scaling factor for scaling the components of lgsi_origin_xyz. The value of lgsi_origin_log2_scale is equal to sps_bounding_box_offset_log2_scale.

[0507] Fig. 37 illustrates a point cloud data transmission device / method according to embodiments.

[0508] 37 Each component of the device corresponds to hardware, software, a processor, and / or a combination thereof.

[0509] Referring to Fig. 37, an embodiment of a detailed functional configuration for encoding / transmitting point cloud data is shown. When point cloud data is input, the encoder can encode geometry information (e.g., XYZ coordinates, phi-theta coordinates, etc.) and attribute information (e.g., color, reflectance, intensity, grayscale, opacity, medium, material, glossiness, etc.) respectively. The compressed data is divided into units for transmission, and the required information can be selected from the bitstream units according to the layering structure information through a sub-bitstream generator (40010) and packed into appropriate units.

[0510] According to embodiments, when different types of bitstreams are included in one slice, the encoder can separate the generated bitstream (AEC bitstream or DC bitstream) according to the purpose. Then, each slice or adjacent information can be included in one slice according to layer group information. At this time, through the metadata generator (40006), information such as layer group information, layer information included in the layer group, number of nodes, layer depth information, number of nodes included in the sub-group, bitstream type, bitstream offset, bitstream length, and bitstream direction can be transmitted according to each slice ID.

[0511] When point cloud data is input to a transmitting device according to embodiments, a geometry encoder (40002) encodes location information (geometry data: e.g., XYZ coordinates, phi-theta coordinates, etc.), and an attribute encoder (40004) encodes attribute information (attribute data: e.g., color, reflectance, intensity, grayscale, opacity, medium, material, glossiness, etc.).

[0512] Compressed (encoded) data is divided into units for transmission, and the required information can be selected from the bitstream units according to layering structure information through the sub-bitstream generation unit (40010) and packed into appropriate units.

[0513] According to embodiments, an octree coded geometry bitstream is input to an octree coded geometry bitstream segmentation unit (octree coded geom bitstream segmentation, 40011), and a direct coded geometry bitstream is input to a direct coded geometry bitstream segmentation unit (direct coded geom bitstream segmentation, 40012).

[0514] The octree-coded geometry bitstream segmentation unit (40011) performs a process of dividing the octree-coded geometry bitstream into one or more groups and / or subgroups based on information about segmented (separated) slices generated by the layer-group structure generation unit (40014) and / or information related to direct coding.

[0515] Additionally, the direct coded geometry bitstream segmentation unit (40012) performs a process of dividing the direct coded geometry bitstream into one or more groups and / or subgroups based on information about segmented (separated) slices generated by the layer-group structure generation unit (40014) and / or information related to direct coding.

[0516] The output of the octree-coded geometry bitstream segmentation unit (40011) and the output of the direct-coded geometry bitstream segmentation unit (40012) are input to the geometry bitstream bonding unit (40013).

[0517] The geometry bitstream bonding unit (40013) performs a geometry bitstream bonding process based on information about segmented (separated) slices generated by the layer-group structure generation unit (40014) and / or information related to direct coding, and outputs sub-bitstreams to the segmented slice generation unit (40016) in units of layer groups. For example, the geometry bitstream bonding unit (40013) performs a process of bonding an AEC bitstream and a DC bitstream within one slice. The final slices are created in the geometry bitstream bonding unit (40013).

[0518] The coded attribute bitstream segmentation unit (40015) performs a process of dividing the coded attribute bitstream into one or more groups and / or subgroups based on information about segmented (separated) slices generated by the layer-group structure generation unit (40014) and / or information related to direct coding. The one or more groups and / or subgroups of attribute information may be linked to one or more groups and / or subgroups for geometry information, or may be generated independently.

[0519] The segmented slice generation unit (40016) receives the geometry bitstream bonding unit (40013) and / or the coded attribute bitstream segmentation unit (40015) based on information about the segmented (separated) slice generated by the metadata generation unit (40006) and / or information related to direct coding, and performs a process of segmenting one slice into multiple slices. Each sub-bitstream is transmitted through each slice segment. At this time, the AEC bitstream and the DC bitstream may be transmitted through one slice or may be transmitted through different slices.

[0520] The multiplexer (40008) multiplexes the output of the segmented slice generation unit (40016) and the output of the metadata generation unit (40006) for each layer and outputs them to the transmitter (40009).

[0521] When different types of bitstreams (e.g., AEC bitstream and DC bitstream) are included in one slice, the geometry encoder (40002) can separate the generated bitstreams (e.g., AEC bitstream and DC bitstream) according to the purpose. Then, each slice or adjacent information can be included in one slice according to information about the segmented (separated) slices generated by the layer-group structure generation unit (40014) and / or the metadata generation unit (40006) and / or information related to direct coding (i.e., layer-group information). According to embodiments, information about segmented (separated) slices and / or information related to direct coding (e.g., layer-group information, layer information included in the layer-group, number of nodes, layer depth information, number of nodes included in the sub-group, along with information about bitstream type, bitstream_offset, bitstream_length, bitstream direction, etc., according to each slice id) may be transmitted through the metadata generation unit (40006). Information about segmented (separated) slices and / or information related to direct coding (e.g., layer-group information, layer information included in the layer-group, number of nodes, layer depth information, number of nodes included in the sub-group, along with information about bitstream type, bitstream_offset, bitstream_length, bitstream direction, etc., according to each slice id) may be signaled in an SPS, an APS, a GPS, a geometry data unit header, an attribute data unit header, or an SEI message.

[0522] Fig. 38 illustrates a point cloud data receiving device / method according to embodiments.

[0523] The receiving method of Fig. 38 can follow the reverse process of the transmitting method of Fig. 37. Each component of the device of Fig. 38 corresponds to hardware, software, a processor, and / or a combination thereof.

[0524] Fig. 38 is an embodiment of a detailed functional configuration for receiving / decoding point cloud data (i.e., PCC data). When a bitstream is input, the receiving device according to the embodiments can distinguish and process a bitstream for position information and a bitstream for attribute information. At this time, a sub-bitstream classifier (41010) can transmit the bitstream to an appropriate decoder based on information in the bitstream header. Alternatively, the layer required by the receiver can be selected during this process. The classified bitstream can be restored into geometry data and attribute data, respectively, by a geometry decoder (41006) and an attribute decoder (41008) according to the characteristics of the data, and then converted into a format for final output by a renderer (41009).

[0525] When different types of geometry bitstreams are included, each bitstream can be decoded separately through a bitstream splitter (41014) as shown below. In an embodiment of the present invention, an arithmetic entropy coded bitstream based on octree coding and a direct coded bitstream can be distinguished and processed in a geometry decoder (41006). At this time, separation can be performed based on information about bitstream type, bitstream_offset, bitstream_length, and bitstream direction. A process of attaching (or connecting) bitstream segments of the same type for the separated bitstreams can be performed by a bitstream segment concatenation unit (41016). This can be included as a process for processing bitstreams separated by layer-group as a continuous bitstream, and bitstreams can be sorted in order based on layer-group information. If a bitstream can be processed in parallel, it can be processed in the decoder without a concatenation process.

[0526] The receiver (41002) can receive a bitstream.

[0527] The demultiplexer (41004) can output point cloud data and metadata (signaling information) included in the bitstream.

[0528] The sub-bitstream classifier (41010) can select slices, split the bitstream, and concatenate bitstream segments of the octree-coded geometry bitstream and the directly-coded geometry bitstream.

[0529] A metadata parser (41005) may provide information about slices and / or layer groups.

[0530] A slice selector (41012) can select one or more slices included in a bitstream.

[0531] The bitstream separator (41014) can split a geometry bitstream. The geometry data can be encoded based on an octree and / or directly coded.

[0532] A bitstream segment concatenation (41016) can concatenate an octree-coded geometry bitstream and a direct-coded geometry bitstream, respectively, according to the encoding type. For a layer group-based geometry bitstream, bitstream segments including multiple groups / subgroups related to the decoding area can be concatenated.

[0533] The geometry decoder (41006) can decode a geometry bitstream and output geometry data.

[0534] The attribute decoder (41008) can decode attribute data included in the selected slice.

[0535] The renderer (41009) can render point cloud data based on geometry data and / or attribute data.

[0536] Figure 39 illustrates a method for receiving point cloud data according to embodiments.

[0537] FIG. 39 illustrates in more detail the operation of the sub-bitstream classifier (41010) illustrated in FIG. 38.

[0538] The receiving device receives data in slice units, and the metadata parser transmits parameter set information such as SPS, GPS, APS, and TPS (e.g., information on segmented (separated) slices and / or information related to direct coding). Based on the transmitted information, it is possible to determine whether scalability is possible. If scalability is possible, the slice structure for scalable transmission is identified as shown in Fig. 39 (42011). First, the geometry slice structure can be identified based on information such as num_scalable_layers, scalable_layer_id, tree_depth_start, tree_depth_end, node_size, num_nodes, num_slices_in_scalable_layer, and slice_id transmitted via GPS.

[0539] If the value of the aligned_slice_structure_enabled_flag field is 1 (42017), the attribute slice structure can also be identified in the same way (for example, if the geometry is octree-based, the attribute is encoded based on scalable LoD or scalable RAHT, and the geometry / attribute slice pairs generated through the same slice partitioning have the same number of nodes for the same octree layer).

[0540] When the structure is the same, the range of geometry slice id is determined according to the target scalable layer, the range of attribute slice id is determined through slice_id_offset, and geometry / attribute slice is selected according to the determined range (42012-42014, 42018, 42019).

[0541] If aligned_slice_sturcutre_enabled_flag = 0, the attribute slice structure is separately identified based on information such as num_scalable_layers, scalable_layer_id, tree_depth_start, tree_depth_end, node_size, num_nodes, num_slices_in_scalable_layer, and slice_id transmitted through APS, and the range of attribute slice ids required according to the scalable purpose can be limited, and based on this, the required slice can be selected through each slice id before reconstruction (42020-42021, 42019). The geometry / attribute slice selected through the above process is transmitted as an input to the receiving device according to the embodiments.

[0542] The above explanation describes the decoding process according to the slice structure based on the scalable transmission or the scalable selection of the receiver. However, if scalable_transmission_enabled_flag is 0, the ranging geom / attr slice id process can be omitted and the entire slice can be selected, allowing it to be used in non-scalable processes as well. In this case, information about the preceding slice (e.g., a slice belonging to a higher layer or a slice specified via ref_slice_id) can be used through slice structure information conveyed through parameter sets such as SPS, GPS, APS, and TPS (e.g., information about segmented (separated) slices and / or information related to direct coding).

[0543] When different types of geometry bitstreams exist, all slices within the range for different bitstreams can be selected during the slice selection process. If different types of bitstreams are included in a single slice, each bitstream can be separated based on offset and length information, and the separated bitstreams can be rearranged according to the layer group order for decoding.

[0544] Fig. 40 illustrates a layer group-based point cloud data encoding method according to embodiments.

[0545] An encoder according to embodiments includes a flowchart of FIG. 40. When point cloud data is input, a layer group structure is constructed and related parameters are acquired. A reference relationship between subgroups is established based on the layer group structure (or already by external input). Encoding can be performed based on the layer group structure and the reference structure. For each subgroup / slice, whether it is used as a reference can be checked, and if so, context_reference_indication_flag can be set to 1. If not, context_reference_indication_flag can be set to 0. Whether it is used as a reference can be performed after encoding and can be obtained directly through the reference structure. If it is used as a reference, the number of times the slice / subgroup is used as a reference can be signaled as the number of subsequent data units (num_subsequent_data_units). Additionally, if a specific list of slices / subgroups that are used as references is passed, the subsequent subgroup list presence flag (subsequent_subgroup_list_present_flag) can be set to 1 and the subsequent data unit list can be passed with the layer-group index and subgroup index. The parameters required for decoding can be included in the data unit header, and the encoded compressed bit stream can be generated for each slice, and this process can be performed for every data unit / slice / subgroup.

[0546] Figure 41 illustrates a layer group-based point cloud data decoding method according to embodiments.

[0547] The decoding method of Fig. 41 can follow the reverse process of the encoding method of Fig. 40.

[0548] The decoder can prepare for decoding by analyzing the data unit header for each slice. At this time, the context state used for decoding can be retrieved from the context buffer through the reference layer group ID (ref_layer_group_id) and reference subgroup ID (ref_subgroup_id). The decoder is initialized based on the retrieved context state and then decoding is performed. Whether to store the new context state generated during the decoding process can be determined by the context_reference_indication_flag included in the data unit header. If it is used in the decoding of subsequent slices / subgroups / data units, the context_reference_indication_flag is signaled as 1. In this case, the target number of subsequent data units can be set to the number of subsequent data units (num_subsequent_data_units) to manage the memory of the context state. Additionally, if subsequent_subgroup_list_present_flag = 1, the layer group index and subgroup index of subsequent data units can be stored in the list of subsequent data units.

[0549] For a used context state, the context state counter and the list of used data units can be updated. At this time, if the target number of subsequent data units of the context state and the counter are the same, or the number of subsequent data units in the given list (list of subsequent data units (list_given)) and the updated list of used data units in the updated list (updated list of used data units (lilst_updated)) are the same, the context state can be freed from the counter buffer.

[0550] The context buffer management method can be applied equally to both the decoder and the encoder. Furthermore, it can be applied not only to slices based on layer-group slicing, but also to cases where context buffers are referenced between slices within a regular frame or between frames.

[0551] Figures 42 (a) to (c) illustrate a context buffer management method according to embodiments.

[0552] In Fine Granularity Slicing (FGS), context inheritance between slices is used to mitigate coding losses caused by discontinuities between adjacent nodes or coding layers. However, as the number of slices or layer groups increases, the number of context states in memory (also called context buffers) increases. To help decoders manage the context buffer, an indication of future use of the current context by subsequent slices is signaled.

[0553] Referring to (a) to (c) of Fig. 42, the context buffer management method of the current layer group slicing method is shown. When the bitstream of a slice is decoded and the context reference indication flag (context_reference_indication_flag) is enabled, the context state of the decoder output is stored in the context buffer as shown in (a) of Fig. 42. When context inheritance is used, the context state of the following slice can be initialized with one of the stored context states of the previous subgroups indicated by the reference layer group ID (ref_layer_group_id) and the reference subgroup ID (ref_subgroup_id) (see (b) of Fig. 42). In (c) of Fig. 42, the context state of the slice belonging to the last layer group is initialized with the stored context state of the parent slice. However, since the context_reference_indication_flag is disabled, the output context state is not stored in the context buffer.

[0554] Using the context_reference_indication_flag flag can reduce the overall size of the context buffer by selecting context states known to be used in following slices. However, decoders have a limitation: they cannot know when each stored context will be released. Therefore, all context states must be stored in the context buffer until all subgroups have been decoded.

[0555] Referring to (a) of Fig. 42, the first slice FGS 0 (0,0) represents subgroup 0 of layer group 0 of point cloud data. When encoding (or decoding) from FGS 0 (0,0), the context state (0, 0) for FGS 0 is stored in the context buffer for subsequent FGSs.

[0556] Referring to (b) of Fig. 42, the third slice FGS 2(1,1) can be sequentially encoded (or decoded). FGS 2(1,1) represents subgroup 1 of layer group 1 of point cloud data. FGS 2(1,1) may be a subgroup belonging to (or dependent on) FGS 0(0,0) (parent-child relationship). Therefore, FGS 2(1,1) can be efficiently encoded (or decoded) by referring to the context state (0, 0) for FGS 0(0,0) stored in the context buffer. And the context state (1, 1) is stored in the context buffer for the subsequent slice (FGS).

[0557] The method according to the embodiments can solve this problem as follows through a mechanism for releasing context state.

[0558] Figures 43 (a) to (c) illustrate a context buffer management method according to embodiments.

[0559] The method according to the embodiments includes a method of indicating the number of subgroups that reference the current subgroup so that the decoder can know when to release the stored context state.

[0560] Figures 43(a) to (c) illustrate a method for releasing a context buffer using the proposed signal. Compared to Figure 42(a) to (c), the context buffer has two additional columns to indicate the number of subsequent (i.e., following) subgroups that reference the current subgroup, and to count the number of subgroups whose context state has already been used in subgroup decoding. When the context_reference_indication_flag is enabled, the number of subsequent (i.e., following) subgroups (num_subsequent_subgroups) is signaled and stored together with the context state, as shown in Figure 43(a). As shown in Figure 43(b), three context states (i.e., (0,0), (1,0), (1,1)) are stored in the context buffer, which are known to be referenced N or 1 times. For example, when there are N successive (i.e., following) subgroups referencing the context state of FGS 0(0, 0), when encoding (or decoding) FGS 2(1, 1) with reference to the context state of FGS 0(0, 0), the value of the counter for the context state (0, 0) becomes 2 because the context state of FGS 0(0, 0) was referenced by FGS 1(1, 0) and FGS 2(1, 1) respectively (i.e., twice). As in (c) of Fig. 43, the context state of FGS 2 (1, 1) is released after being used in FGS N+2(2, 1). The context states (0, 0) and (1, 0) are released beforehand because there are no more successive subgroups referencing them. Releasing the context state means deleting the context state from the context buffer (or memory).

[0561] Figures 44 (a) to (c) illustrate a context buffer management method according to embodiments.

[0562] The proposed method can be equally effective when using different orders for the FGS (which can be simply referred to as slices, sub-slices, etc.). As shown in (a) to (c) of Fig. 44, the method according to the embodiments is also applicable to the case of depth first ordering. For comparison with the breadth first order case of (a) to (c) of Fig. 43, the names of each slice are the same and the transmission order is changed from FGS 0, FGS 1, FGS 2, FGS 3, ... to FGS 0, FGS 1, FGS N+1, FGS 2. As shown in (b) of Fig. 44, when the decoding of FGS2 is completed, the output context state (1, 1) is stored in the context buffer and the number of subsequent subgroups (e.g., 1) is stored. As in c) of Fig. 44, when the next slice FGS N+2 is decoded, the context state is initialized by context state (1, 1), and the corresponding counter in the context buffer is increased by 1. Then, since the number in the counter and the stored value of the number of subsequent subgroups are the same, the context state (1, 1) can be released from this point on. In this example, the maximum number of context states in the context buffer is 2, which is the number of layer groups minus 1.

[0563] At this time, the size of the context buffer can be predicted in advance at the receiver. For example, if there are N layer groups, and the size of the subgroup within the nth layer group is S[n], we can consider a case where the parent subgroup (or upper subgroup) is referenced.

[0564] In this case, the number of context states that need to be stored in memory (or called context buffer) can be estimated as follows: Since the maximum number (N-1) will not be referenced subsequently, the addition process is performed only up to N-2.

[0565]

[0566] As an extreme opposite case, if we consider the case where we reference the first slice / subgroup, then the number of context states that need to be stored in memory can be estimated as follows:

[0567] (number of subgroup in the root layer-group)=1

[0568] For example, the number of subgroups within a root layer group can be 1.

[0569] The case where the parent subgroup is referenced may be the case where context state is used the most, while the case where context state is used the least may be the case where the first slice / subgroup (e.g., the root subgroup) is referenced. Therefore, when using layer group slicing with different reference relationships, it is possible to consider a position between the maximum and minimum values.

[0570] Using the method according to the embodiments may require less space to store context states than dynamically freeing memory. For example, if FGS generated by layer group slicing are generated and / or passed based on breadth-first order and only reference parent subgroups, the context states belonging to the parent layer group can be freed when coding for a layer group is completed. Therefore, the number of context states that need to be stored in memory can be estimated as follows.

[0571] MAX(S[0],S[1],…,S[N-2])

[0572] If the FGS generated by layer group slicing is generated / transferred in depth-first order, the context memory of the parent subgroup can be released (deleted) when the coding of the child subgroup is completed by the method according to the embodiments. In this case, only the context of the parent subgroup with remaining children needs to be stored, and since leaf layer groups are excluded, the number of context states that need to be stored in memory can be estimated as follows.

[0573] N-1

[0574] If the receiver needs to estimate the memory size for storing the context buffer (or context state), it can pass related information (slice coding order type, depth first / breadth first, number of layer-groups, number of subgroups in each layer-group, context reference method, parent reference / root reference, etc.) and estimate the number of context states as in the method presented above.

[0575] In the following, based on the context memory management mechanism according to embodiments, the number of subsequent data units (num_subsequent_data_units), which is new signaling information, is signaled in the geometry data unit header and the dependent geometry data unit header.

[0576] An encoder according to embodiments encodes point cloud data and generates related signaling information. It then generates and transmits a bitstream containing the encoded point cloud data and parameter information. In reverse, a decoder according to embodiments receives the bitstream, parses the parameter information contained in the bitstream, and decodes the point cloud data based on the parameter information. Figures 45 to 47 illustrate the syntax of parameter information contained in the bitstream.

[0577] Figure 45 illustrates an example of a syntax structure of a geometry data unit header according to embodiments.

[0578] Figure 46 illustrates an example of a syntax structure of a dependent geometry data unit header according to embodiments.

[0579] Figure 47 illustrates an example of the syntax structure of an attribute data unit header according to embodiments.

[0580] Figure 48 illustrates an example of the syntax structure of a dependent attribute data unit header according to embodiments.

[0581] In FIGS. 45 to 48, the number of subsequent data units (num_subsequent_data_units) indicates the number of subsequent dependent data units referencing the current data unit or dependent data unit. The data unit may be a slice. A slice may be an FGS for a subgroup within a layer group according to embodiments.

[0582] The geometry parameter set ID (dgsh_geometry_parameter_set_id) is a geometry parameter set identifier. It may be information identifying a parameter set for a dependent geometry data unit.

[0583] The slice ID (dgsh_slice_id) is a slice identifier. It may be the slice identifier associated with a dependent geometry data unit.

[0584] The layer group ID (layer_group_id) is the layer group identifier. It can be the identifier of the layer group to which the dependent geometry data unit is associated.

[0585] The subgroup_id is the subgroup identifier. It may be the identifier of a subgroup associated with a dependent geometry data unit.

[0586] The subgroup bounding box location (subgroup_bbox_origin[i]) indicates the origin location of the subgroup bounding box.

[0587] Subgroup bounding box size (subgroup_bbox_size[i]) indicates the size of the subgroup bounding box.

[0588] The reference layer group ID (ref_layer_group_id) is the reference layer group identifier. It can be the identifier of the layer group referenced by the dependent geometry data unit.

[0589] The reference subgroup ID (ref_subgroup_id) is the reference subgroup identifier. It can be the identifier of a subgroup referenced by the layer group for the layer group identifier.

[0590] The context reference indication flag (context_reference_indication_flag) is a flag indicating whether or not a context is referenced.

[0591] The reference count (num_referenced) indicates the number of references.

[0592] Next, we will explain how to control the context buffer (or memory) considering partial decoding.

[0593] The context memory control method described in FIGS. 43 and 44 described above can efficiently manage a context buffer when a bitstream composed of multiple slices is received and all received slices are decoded. However, in the case of partial decoding (i.e., when only some slices are decoded when there is a region of interest or a resolution of interest), the number of references transmitted by the encoder (num_subsequent_data_units) may not be fully filled. In the present disclosure, slice, subgroup, and data unit may be used interchangeably with each other with the same meaning.

[0594] For example, considering a layer group structure divided into three layer groups, the decoder of the receiving device may decide not to use the last layer group. In this case, if it knows the number referenced in the second layer group, it does not need to store the context (or context state or context information) in the context buffer to decode the last layer group.

[0595] To this end, the present disclosure can enable a decoder to release context memory after a given number of times a context is used (or referenced) in a given unit (e.g., a data unit). Furthermore, the present disclosure can enable a decoder to release context memory after a given number of times by signaling the number of times a context is used (i.e., referenced) in a given unit (e.g., a data unit) by signaling it for each layer group. For example, if there are two or more layer groups referencing a current data unit, the number of subsequent data units (i.e., data units referencing the current data unit) can be signaled for each layer group. In the present disclosure, a data unit can be a subgroup or a slice.

[0596] At this time, the number of times the context is used (i.e., referenced) for each data unit can have a relationship with the number of times the entire context is used (i.e., referenced) as follows: num_subsequent_data_units = i in subsequeny layer-groupsnum_sdu_per_layer_group[i]

[0597] In the above formula, subsequent layer-groups represents layer groups that contain subgroups (i.e., data units) that reference the context of the current data unit, and num_sdu_per_layer_group can represent the number of times that the subgroups belonging to each layer group reference the context of the current subgroup. In other words, num_sdu_per_layer_group can represent the number of data units among the data units (or subgroups) belonging to each layer group that reference the context of the current data unit of the current layer group.

[0598] Assuming that FGS1 (1,0) of layer-group #1 in Fig. 49 is the current data unit, subsequent layer-groups become layer-group #2 and layer-group #3. In addition, the number of data units referencing the context of FGS1 (1,0), which is the current data unit, in layer-group #2 becomes 1. In addition, the number of data units referencing the context of FGS1 (1,0), which is the current data unit, in layer-group #3 becomes 1.

[0599] Fig. 49 is a diagram showing an example of a layer group structure considering partial decoding according to embodiments. That is, a context reference structure such as Fig. 49 can be considered for partial decoding in terms of layer groups. More specifically, a subgroup belonging to layer-group #1 can refer to the context state of a subgroup of layer-group #0 (i.e., a root subgroup), a subgroup belonging to layer-group #2 can refer to the context state of a parent subgroup belonging to layer-group #1, and a subgroup belonging to layer-group #3 can refer to the context state of a grandparent subgroup belonging to layer-group #1.

[0600] At this time, in a layer group structure divided into four layer groups as shown in Fig. 49, the decoder of the receiving device can perform partial decoding that does not use the last layer group (i.e., layer-group#3).

[0601] According to embodiments, when partial decoding is performed by skipping a specific layer group, for example, layer-group #3, the context buffer may store num_subsequent_subgroups (or num_subsequent_data_units) for each layer group, and determine whether the context reference count is satisfied for each subsequent layer group. In an example such as FIG. 49, since layer-group #3 is skipped, the counter of the context buffer does not use num_subsequent_subgroups (or num_subsequent_data_units) for layer-group #3, and does not need to be stored.

[0602] Figures 50 (a) to (d) illustrate a context buffer management method according to embodiments.

[0603] In (a) to (d) of FIG. 50, the context buffer is managed for each data unit. According to embodiments, the context buffer may be divided into three storage areas for each data unit, for example, a context state storage area (51010), a reference count information storage area (51020), and a counter information storage area (51030). At this time, the reference count information storage area (51020) and the counter information storage area (51030) may be further divided into sub-storage areas corresponding to the number of layer groups in the layer group structure.

[0604] Taking the layer group structure of Fig. 49 as an example, since it includes four layer groups (i.e., layer-group #0-layer-group #3), the reference count information storage area (51020) and the counter information storage area (51030) in the context buffer can each be divided into four sub-storage areas.

[0605] Referring to FIG. 50(a), the context state of FGS0 (0,0) (i.e., context state(0,0)) is stored in the context state storage area (51010) of the context buffer after FGS0 (0,0) is encoded or decoded. In addition, the number of data units (i.e., subgroups) that reference context state(0,0) in each layer group, i.e., four layer groups (layer-group #0-layer-group #3) is stored in the reference count information storage area (51020). At this time, since context state(0,0) only references N data units of layer-group #0 (i.e., FGS1 (1,0) to FGSN (1,N-1)) and is not referenced in other layer groups, the value of {- | N | 0 | 0} is stored in the reference count information storage area (51020). Here, ““ means no reference. That is, for context state(0,0), it indicates that there is no reference in layer-group #0, that it is referenced N times in layer-group #1, and that it is not referenced even once in layer-group #2 and layer-group #3. In addition, in Fig. 50(a), since context state(0,0) has not been referenced yet, the value of {- | 0 | 0 | 0} is stored in the counter information storage area (51030).

[0606] That is, in (a) of FIG. 50, when FGS 0 / subgroup (0,0) is decoded (FGS 0(0,0)), the context state storage area (51010) of the context buffer stores context state(0,0), and the reference count information storage area (51020) can store num_subsequent_subgroups (corresponding to num_subsequent_data_units in the signaling information of FIGS. 51 to 55) transmitted through the data unit header for each subsequent layer group. In this example, the values ​​{- | N | 0 | 0} can be stored.

[0607] In other words, when the context_reference_indication_flag is enabled, the number of subsequent (i.e., following) subgroups (num_subsequent_subgroups or num_subsequent_data_units) is signaled, and the context state (0,0) is stored in the context state storage area (51010) as shown in (a) of FIG. 50, and the corresponding number for each layer group is stored in the reference count information storage area (51020). At this time, the counter information storage area (51030) is set to {- | 0 | 0 | 0}.

[0608] These rules apply equally to other data units.

[0609] Taking FGS1 (1,0) of (b) of FIG. 50 as an example, the context state of FGS1 (1,0) (i.e., context state(1,0)) is stored in the context state storage area (51010) of the context buffer after FGS1 (1,0) is encoded or decoded. At this time, since context state(1,0) is referenced in FGS N+1 (2,0) of layer-group #2 and FGS 2N+1 (3,0) of layer-group #3, the value of {- | - | 1 | 1} is stored in the reference count information storage area (51020). That is, for context state(1,0), it indicates that there is no reference in layer-group #0 and layer-group #1, that it is referenced once in layer-group #2, and that it is also referenced once in layer-group #3. And, in Fig. 50(b), since context state(1,0) has not yet been referenced, the value of {- | 0 | 0 | 0} is stored in the counter information storage area (51030). At this time, since context state(0,0) is referenced in FGS1 (1,0), the value of {- | 1 | 0 | 0} is stored in the counter information storage area (51030) corresponding to FGS0 (0,0).

[0610] That is, in (b) of FIG. 50, when FGS 1 / subgroup (1,0) is decoded (FGS 1(1,0)), since context_reference_indication_flag is 1, the context state storage area (51010) of the context buffer stores context state (1,0), and the reference count information storage area (51020) can store num_subsequent_subgroups (corresponding to num_subsequent_data_units in the signaling information of FIGS. 51 to 55) transmitted through the data unit header for each subsequent layer group. In this example, the values ​​{- | - | 1 | 1} can be stored.

[0611] In the present disclosure, the loading process of context states (i.e., context information) can be performed with reference to the ref_layer_group_id and ref_subgroup_id parameters. In Fig. 50(b), context information (context states(0,0)) of FGS 0(0,0) can be loaded to process (encode or decode) FGS 1 (1,0). Then, context states (0,0) are used to process FGS 1 (1,0), and the counter value is increased by 1. That is, the value of {- | 1 | 0 | 0} is stored in the counter information storage area (51030) corresponding to FGS0 (0,0).

[0612] If the data unit processing order is breadth first search, then after FGS 1 (1,0) is processed, the next data unit (i.e., FGS 2 (1,1)) of the same layer group (i.e., layer-group #1) is processed. In contrast, if the data unit processing order is depth first search, then after FGS 1 (1,0) is processed, the first data unit (i.e., FGS N+1 (2,0)) of another layer group (i.e., layer-group #2) is processed. FIGS. 50(a) to 50(d) show examples of the depth first search method. This is one embodiment, and the present disclosure can also be applied to the breadth first search method.

[0613] Here, breadth-first search is a method that codes / decodes subgroups within the same layer group before coding / decoding subgroups within a child layer group. In contrast, depth-first search is a method that codes / decodes children within the same parent layer group after reaching the subgroup corresponding to the maximum depth.

[0614] The decoder can prepare for decoding by analyzing the data unit header for each data unit (i.e., subgroup or slice). At this time, the context state used for decoding can be retrieved from the context buffer through the reference layer group ID (ref_layer_group_id) and reference subgroup ID (ref_subgroup_id). Based on the retrieved context state, the decoder initializes the context buffer for the current data unit and then performs decoding.

[0615] When decoding FGS N+1 / subgroup (2, 0) in (b) of FIG. 50 (FGS N+1(2,0)), the encoder / decoder can initialize the context state of FGS N+1 / subgroup (2, 0) based on the context state (1,0) corresponding to ref_layer_group_id=0, ref_subgroup_id=0. That is, the context state can be initialized based on the context state (1,0). At this time, since the context state (1, 0) is referenced in FGS N+1(2,0) of layer-group #2, the value of the counter information storage area (51030) is changed from { - | 0 |0| 0} to { - | 0 |1| 0}. And, considering the skip layer group, since no reference will be made in layer-group #3, the number of references to each layer-group stored in the context buffer matches the number of references to the counter, so the context state (1, 0) can be released (i.e., deleted). That is, the value (=1) corresponding to layer-group #2 stored in the reference count information storage area (51020) of the context buffer corresponding to FGS (1, 0) and the value (=1) corresponding to layer-group #2 stored in the counter information storage area (51030) are the same, so the context state (1, 0), reference count information, and counter information of the context buffer corresponding to FGS (1, 0) are deleted from the context buffer. In this way, the context state and related information (i.e., reference count information and count information) of FGS 1 (1, 0) are released after being used in FGS N+1 (2, 0). Releasing the context state means deleting the context state from the context buffer (or memory).

[0616] Also, since it is assumed that decoding of layer-group #3 is skipped, FGS N+2 (2,1) belongs to the last layer group, and therefore the context state of FGS N+2 (2,1) is not stored in the context buffer. As another example, even if it is assumed that layer-group #3 is not skipped, since there is no data unit referencing layer-group #2 in FIG. 49, the context state of FGS N+2 (2,1) is not stored in the context buffer. That is, if the current data unit is a data unit of the last layer group due to a skipped layer group and / or there is no data unit referencing the current data unit, the context state of the encoded or decoded current data unit is not stored in the context buffer.

[0617] As in (c) of Fig. 50, when FGS 2 / subgroup (1,1) is decoded (FGS 2(1,1)), since context_reference_indication_flag is 1, the context state storage area (51010) of the context buffer stores context state (1,1), and the reference count information storage area (51020) can store num_subsequent_subgroups (or num_subsequent_data_units) transmitted through the data unit header for each subsequent layer group. In this example, the values ​​{- | - | 1 | 1} can be stored. For a detailed description of (c) of Fig. 50, refer to (b) of Fig. 50.

[0618] When decoding FGS 2N / subgroup (2, N-1) as in (d) of Fig. 50 (FGS 2N(2, N-1)), the encoder / decoder can initialize the context state of FGS 2N / subgroup (2, N-1) based on the context state (1, N-1) corresponding to ref_layer_group_id=1, ref_subgroup_id=N-1. That is, the context state of FGS 2N / subgroup (2, N-1) can be initialized based on the context state (1, N-1) identified by ref_layer_group_id and ref_subgroup_id.

[0619] At this time, since context state (1, N-1) is referenced in FGS 2N(2,N-1) of layer-group #2, the value of the counter information storage area (51030) changes from { - | 0 |0| 0} to { - | 0 |1| 0}. And, considering the skip layer group, since no reference will be made in layer-group #3, the number of references to each layer-group stored in the context buffer matches the number of references to the counter, so context state (1, N-1) can be released (i.e., deleted). That is, since the value (=1) corresponding to layer-group #2 stored in the reference count information storage area (51020) of the context buffer corresponding to FGS (1,N-1) and the value (=1) corresponding to layer-group #2 stored in the counter information storage area (51030) are the same, the context state (1,N-1), reference count information, and counter information of the context buffer corresponding to FGS (1,N-1) are deleted from the context buffer. In this way, the context state and related information (i.e., reference count information and count information) of FGS N (1, N-1) are released after being used in FGS 2N (2, N-1).

[0620] Also, since it is assumed that decoding of layer-group #3 is skipped, FGS 2N (2,N-1) belongs to the last layer group, and therefore the context state of FGS 2N (2,N-1) is not stored in the context buffer. As another example, even if it is assumed that layer-group #3 is not skipped, since there is no data unit referencing layer-group #2 in FIG. 49, the context state of FGS 2N (2,N-1) is not stored in the context buffer. That is, if the current data unit is a data unit of the last layer group due to a skipped layer group and / or there is no data unit referencing the current data unit, the context state of the encoded or decoded current data unit is not stored in the context buffer.

[0621] In the present disclosure, the layer group whose decoding is skipped can be determined by the decoder depending on the application.

[0622] As explained so far, in a partial decoding situation, the context memory (i.e., the context buffer) can be released early.

[0623] The following describes the signaling information required to release context memory (i.e., context buffer) in a partial decoding situation.

[0624] According to embodiments, the present disclosure can signal and transmit the entire context reference structure. In one embodiment, the encoder of the transmitting device of the present disclosure signals the entire context reference structure through SPS and transmits it to the decoder of the receiving device. In this case, the actual relationship that allows the decoder to identify the reference structure, such as information about the layer group structure and reference subgroup identification information / number of subsequent subgroups, can be transmitted. In addition, the decoder can early release the context (or context state) in the case of partial decoding based on the identified entire reference structure.

[0625] According to embodiments, the present disclosure can signal subsequent subgroup identification information (i.e., subsequent subgroup id) and directly transmit it to a decoder of a receiving device. In one embodiment, an encoder of a transmitting device of the present disclosure directly transmits subsequent subgroup identification information (i.e., subsequent subgroup id) to a decoder of a receiving device through a data unit header. In this case, a context reference structure is transmitted in units of data units. In addition, the decoder can check whether a request comes from a corresponding subgroup id in a buffer, and perform an early release if all corresponding contexts are used in subgroups used in partial decoding.

[0626] According to embodiments, the present disclosure can transmit the number of subsequent subgroups by dividing them. In one embodiment, the encoder of the transmitting device of the present disclosure divides and signals the number of subsequent subgroups by using a data unit header and then transmits the divided number of subsequent subgroups to the decoder of the receiving device. For example, for the number of subsequent subgroups N, N = N1 (the number referenced in layer-group 1) + N2 (the number referenced in layer-group 2) can be transmitted. In addition, the decoder of the receiving device that does not decode layer-group #2 can early release the context when the context has been used N1 times. In addition, in the case of full decoding, the context can be released after it has been used N1 + N2 times. Here, the subsequent subgroups can be subsequent data units.

[0627] Figures 51 to 55 illustrate the syntax of parameter information included in a bitstream. That is, Figures 51 to 55 describe a method for transmitting the number of times each data unit is referenced within each layer group and subgroup identification information (subgroup id). In the present disclosure, when multiple child subgroups exist in one parent subgroup, by adding bounding box information of the referencing subgroups, etc., the number of context references is transmitted more accurately in the case of partial decoding according to ROI, so that the decoder can release the context memory (i.e., the context buffer) at an accurate time.

[0628] Figure 51 illustrates an example of a syntax structure of a sequence parameter set (SPS) according to embodiments.

[0629] In FIG. 51, if the value of layer_group_enabled_flag is equal to 1, it can be specified that the geometry bitstream of a slice is contained in multiple slices which is matched to a group of coding layers or its subgroup. If the value of layer_group_enabled_flag is equal to 0, it specifies that the geometry bitstream is contained in a single slice.

[0630] Adding 1 to num_layer_groups_minus1 specifies the number of layer-groups where the layer-group represents a group of consecutive tree layers that are part of the geometry coding tree structure. num_layer_groups_minus1 is in the range 0 to the number of coding tree layers.

[0631] layer_group_id specifies the indicator of a layer group of a slice. layer_group_id ranges from 0 to num_layer_groups_minus1.

[0632] Adding 1 to num_layers_minus1 specifies the number of coding layers contained in the i-th layer-group. The total number of layer-groups can be derived by adding all (num_layers_minus1[i] + 1) for i equal to 0 to num_layer_groups_minus1.

[0633] If the value of subgroup_enabled_flag is 1, it indicates that the i-th layer group is divided into two or more subgroups. In this case, the set of points in the subgroups of the layer group is identical to the set of points in the layer group (subgroup_enabled_flag is equal to 1 specifies that the i-th layer group is divided into two or more subgroups where the set of points in the subgroups of a layer group is identical to the set of points in the layer group). If the value of subgroup_enabled_flag of the i-th layer group is 1, the subgroup_enabled_flag of the j-th subgroup is 1. In this case, j is greater than or equal to i. If the value of subgroup_enabled_flag is 0, it indicates that the current layer group is not subdivided into multiple subgroups but is included in a single slice.

[0634] Add 1 to subgroup_bbox_origin_bits_minus1 to express the length of the syntax elements subgroup_bbox_origin in bits.

[0635] Add subgroup_bbox_size_bits_minus1 to express the length of the syntax elements subgroup_ bbox_size in bits.

[0636] Add 1 to num_subgroups_minus1 to indicate the number of subgroups in the i-th layer group.

[0637] num_subsequent_data_units represents the number of subsequent dependent data units that refer to the j-th data unit or the j-th dependent data unit of the i-th layer group.

[0638] subsequent_data_unit_id represents the index of the kth subsequent data unit referencing the jth data unit or the jth dependent data unit of the ith layer group.

[0639] Figure 52 illustrates an example of a syntax structure of a geometry data unit header according to embodiments.

[0640] Figure 53 illustrates an example of a syntax structure of a dependent geometry data unit header according to embodiments.

[0641] Figure 54 illustrates an example of the syntax structure of an attribute data unit header according to embodiments.

[0642] Figure 55 illustrates an example of the syntax structure of a dependent attribute data unit header according to embodiments.

[0643] In FIGS. 52 to 55, dgsh_geometry_parameter_set_id is an identifier for identifying a geometry parameter set. In one embodiment, dgsh_geometry_parameter_set_id may be information for identifying a parameter set for a dependent geometry data unit.

[0644] dgsh_slice_id is a slice identifier. In one embodiment, dgsh_slice_id may be a slice identifier to which a dependent geometry data unit is associated.

[0645] layer_group_id is a layer group identifier. In one embodiment, layer_group_id may be an identifier of a layer group to which a dependent geometry data unit is associated.

[0646] subgroup_id is a subgroup identifier. In one embodiment, subgroup_id may be an identifier of a subgroup associated with a dependent geometry data unit.

[0647] subgroup_bbox_origin[i] indicates the origin location of the subgroup bounding box.

[0648] subgroup_bbox_size[i] represents the size of the subgroup bounding box.

[0649] ref_layer_group_id is a reference layer group identifier. In one embodiment, ref_layer_group_id may be an identifier of a layer group referenced by a dependent geometry data unit.

[0650] ref_subgroup_id is a reference subgroup identifier. In one embodiment, ref_subgroup_id may be an identifier of a subgroup referenced by a layer group for a layer group identifier.

[0651] context_reference_indication_flag is a flag indicating whether a context is referenced. In one embodiment, depending on the value of context_reference_indication_flag, whether a new context state generated during the decoding process of the corresponding data unit is stored in the context buffer may be determined.

[0652] num_subsequent_data_units indicates the number of subsequent dependent data units referencing the current data unit or dependent data unit. The data unit may be a subgroup or a slice. A slice may be an FGS for a subgroup within a layer group according to embodiments.

[0653] If the value of num_sdu_per_layer_group_present_flag is 1, it indicates that the number of subsequent data units in each layer-group is present. If the value of num_sdu_per_layer_group_present_flag is 0, it indicates that the number of subsequent data units in each layer-group does not exist. In other words, num_sdu_per_layer_group_present_flag is a flag to indicate whether to transmit the number of references and data_unit_id for each layer-group. If the value of num_sdu_per_layer_group_present_flag is 0, only num_subsequent_data_units are transmitted.

[0654] If the value of sdu_present_flag is 1, it indicates that the successor data unit of the current data unit exists in the i-th layer group. If the value of sdu_present_flag is 0, it indicates that the successor data unit of the current data unit does not exist in the i-th layer group.

[0655] num_sdu_per_layer_group represents the number of subsequent data units within the i-th layer group referenced by the current data unit or dependent data unit.

[0656] subsequent_data_unit_id indicates the index of the subsequent data unit referenced by the current data unit or the dependent data unit.

[0657] For syntax elements not described in FIGS. 52 to 55, refer to the descriptions in FIGS. 45 to 48.

[0658] And, taking Fig. 49 as an example, the geometry data unit to which the geometry_data_unit_header of Fig. 52 is applied corresponds to the data unit included in layer-group #0, and the dependent data unit to which the dependent_geometry_data_unit_header of Fig. 53 is applied corresponds to the data unit included in layer-group #1 to layer-group #3.

[0659] Fig. 56 is a diagram showing an example of compressing and providing a service for the geometry and attributes of point cloud data. That is, in a point cloud compression (PCC)-based service, the compression ratio or the number of data can be adjusted and transmitted depending on the receiver performance or transmission environment. However, in the case where point cloud data is bundled into a single slice unit as in Fig. 56, if the receiver performance or transmission environment changes, 1) a bitstream suitable for each environment is converted in advance and stored separately and selected when transmitting, or 2) a process of converting (transcoding) is required before transmission. In this case, if the number of receiver environments to be supported increases or the transmission environment changes frequently, storage space issues or delays due to conversion may become a problem.

[0660] FIG. 57 is a diagram showing another example of compressing and serving the geometry and attributes of point cloud data according to embodiments.

[0661] As proposed in this disclosure, when compressed data is divided and transmitted according to layers, there is an advantage in that only the necessary portions of pre-compressed data can be selectively transmitted through a bitstream selector at the bitstream stage without a separate conversion process. This is efficient in terms of storage space, as only one storage space is required per stream, and efficient transmission is also possible in terms of bandwidth, as only the necessary layers are selectively transmitted through the bitstream selector before transmission.

[0662] If we describe the effects according to the features of the present disclosure from the perspective of a receiver, in one application of the present disclosure, when layered coding is used, compressed data can be divided and transmitted according to layers, in which case the efficiency of the receiver increases. In particular, when scalable attribute coding is applied, there is a disadvantage in that a delay occurs and a burden is placed on the receiver's computation by receiving and decoding the entire coded geometry data. However, through the proposal of the present disclosure, by decoding only the geometry layer that matches the tree level used in scalable attribute coding, the delay element is reduced, and the efficiency of the decoder can be increased by saving the computing power required for decoding.

[0663] Figure 58 is a diagram illustrating the operation of the transmitting and receiving ends when transmitting point cloud data composed of layers. In this case, if information capable of restoring the entire point cloud data is transmitted regardless of the performance of the receiver, the receiver requires a process (e.g., data selection or subsampling) to restore the point cloud data through decoding and then select only the point cloud data corresponding to the required layer. In this case, since the transmitted bitstream has already been decoded, a receiver targeting low delay may experience delay or may not be able to decode depending on the receiver's performance.

[0664] However, as proposed, if only the compressed data of the required layer is received according to the layer, the receiver can selectively decode a specific layer, thereby increasing decoder efficiency and supporting decoders of various performances.

[0665] Fig. 59 illustrates a point cloud data transmission / reception device / method according to embodiments.

[0666] Multi-resolution ROIs according to embodiments may be supported when layer group slicing is used to generate a G-PCC bitstream.

[0667] Referring to Fig. 59, multi-resolution ROIs can be supported by the scalability and spatial accessibility of hierarchical slicing. In Fig. 59, the encoder (47001) on the transmitting side can generate bitstream slices of spatial subgroups of each layer group or octree layer-groups. Upon request, a slice matching each resolution ROI is selected and transmitted to the receiving end. The overall bitstream size is reduced compared to the tile-based approach because it does not include details other than the requested ROI. At the receiver, the decoder (47004) can combine the slices to produce three outputs, for example: 1) a high-level view output from the layer group; 2) a mid-level view output from selected subgroups of layer group 1 and layer group 2; and 3) a low-level view output with good detail from selected subgroups of layer groups 2 and 3 and layer group 1. Since the outputs can be generated progressively, the receiver can provide a viewing experience such as zooming in which the resolution progressively increases from the high-level view to the low-level view.

[0668] The above encoder (47001) is a point cloud encoder according to embodiments, and may correspond to a geometry encoder and / or an attribute encoder. The encoder (47001) may slice point cloud data based on a layer group (or groups). A layer may be referred to as a depth of a tree, a level of LOD, etc. As in 47002, the depth of an octree of a geometry and / or the level of an attribute layer may be divided into layer groups (or subgroups).

[0669] The slice selector (47003) can be linked with the encoder (47001) to select a divided slice (or sub-slice) and selectively transmit it partially, such as layer group 1 to layer group 3.

[0670] The decoder (47004) can selectively and partially decode transmitted point cloud data. For example, for a high-level view, it can decode layer group 1 (high depth / layer / level or index 0, closer to the root). Furthermore, for a mid-level view, it can decode based on layer group 1 and layer group 2, increasing the depth / level index slightly more than layer group 1 alone. Furthermore, for a low-level view, it can decode based on layer group 1 to layer group 3.

[0671] Referring to FIG. 59, an encoder (47001) according to embodiments can receive point cloud data as input and slice it into layer groups. That is, the point cloud data can be hierarchically structured and divided into layer groups. At this time, the hierarchical structure can mean an octree structure or LoD (Level of Detail). 47002 represents how point cloud data is divided into layer groups. A slice selector (47003) can select a layer group (or a slice corresponding thereto), and the selected slices are transmitted to a decoder (47004) of a receiving end. The decoder (47004) can combine the received slices according to a user's request to restore only layer group 1, layer groups 1 and 2, or all received layer groups. The layer groups are hierarchical and have different levels of detail. When only layer group 1 is restored, the restored range is wide but details are not expressed. When all layer groups 1 to 3 are restored, the restored range is narrow but details can be expressed in detail.

[0672] Figure 60 shows a flowchart of a point cloud data transmission method according to embodiments.

[0673] A method for transmitting point cloud data according to embodiments may include a step of acquiring point cloud data (71001), a step of encoding point cloud data (71002), and a step of transmitting encoded point cloud data and signaling information (71003). At this time, a bitstream including the encoded point cloud data and signaling information may be encapsulated into a file and transmitted.

[0674] The step (71001) of acquiring point cloud data may perform part or all of the operations of the point cloud video acquisition unit (10001) of FIG. 1 or may perform part or all of the operations of the data input unit (8000) of FIG. 8.

[0675] The step of encoding point cloud data (71002) may perform part or all of the operations of the point cloud video encoder (10002) of FIG. 1, the encoding (20001) of FIG. 2, the point cloud video encoder of FIG. 3, the point cloud video encoder of FIG. 8, the encoding device of FIG. 37, the encoding method of FIG. 39, and the encoding method of FIG. 40 for encoding geometry information and attribute information.

[0676] The step (71002) of encoding point cloud data according to embodiments may include a step of compressing geometry information of input point cloud data and a step of compressing attribute information.

[0677] According to embodiments, the step of compressing geometry information may compress geometry information in units of layer groups and / or subgroups. At this time, a context buffer for storing a context state (or context information) of an encoded data unit is managed for each data unit, as an embodiment. In the present disclosure, a data unit may mean a subgroup or a slice. The method of compressing geometry information and the method of managing a context buffer in the step of compressing geometry information will be described with reference to the descriptions of FIGS. 49 and 50, and a detailed description thereof will be omitted herein.

[0678] According to embodiments, the step of compressing attribute information compresses attribute information based on positions for which geometry encoding has not been performed and / or reconstructed geometry information.

[0679] In this specification, signaling information may include information for partial decoding and / or context buffer management.

[0680] Information for the above partial decoding and / or context buffer management may be transmitted to the receiving end as included in at least one of an SPS, an APS, a geometry data unit header (or a dependent geometry data unit header) and / or an attribute data unit header (or a dependent attribute data unit header). Detailed information included in the information for the above partial decoding and / or context buffer management is omitted here, with reference to FIGS. 51 to 55.

[0681] Figure 61 shows a flowchart of a method for receiving point cloud data according to embodiments.

[0682] A method for receiving point cloud data according to embodiments may include a step (81001) of receiving encoded point cloud data and signaling information, a step (81002) of decoding point cloud data based on the signaling information, and a step (81003) of rendering the decoded point cloud data.

[0683] The step (81001) of receiving point cloud data and signaling information according to the embodiments may be performed in the receiver (10005) of FIG. 1, the transmitter (20002) or decoding (20003) of FIG. 2, and the receiving unit (9000) or receiving processing unit (9001) of FIG. 9.

[0684] The step (81002) of decoding point cloud data according to embodiments may perform part or all of the operations of the point cloud video decoder (10006) of FIG. 1, the decoding (20003) of FIG. 2, the point cloud video decoder of FIG. 8, the point cloud video decoder of FIG. 9, the decoding device of FIG. 38, and the decoding method of FIG. 41 for decoding geometry information and attribute information.

[0685] The step (81002) of decoding point cloud data according to the embodiments includes a step of decoding geometry information and a step of decoding attribute information.

[0686] The step of decoding the above geometry information can decode (i.e., restore) the geometry information in units of layer groups and / or subgroups based on information for partial decoding and context buffer management included in the signaling information.

[0687] In the step of decoding the above geometry information, if a specific layer group (e.g., layer-group #3 in Fig. 49) is skipped and partial decoding is performed, the context buffer stores num_subsequent_subgroups (or num_subsequent_data_units) for each layer group, and it can be determined whether the context reference count is satisfied for each subsequent layer group.

[0688] In the step of decoding the above geometry information, the context buffer is managed for each data unit. According to embodiments, the context buffer may be divided into three storage areas for each data unit, for example, a context state storage area (51010), a reference count information storage area (51020), and a counter information storage area (51030). At this time, the reference count information storage area (51020) and the counter information storage area (51030) may be further divided into sub-storage areas corresponding to the number of layer groups in the layer group structure. The method of managing the context buffer in the step of decoding the above geometry information will be described in detail with reference to FIGS. 49 and 50, and will be omitted here.

[0689] The step of decoding the above attribute information decodes (i.e., decompresses) the attribute information in units of layer groups and / or subgroups based on information for partial decoding and / or context buffer management included in the restored geometry information and signaling information.

[0690] The rendering step (81003) according to the embodiments may restore point cloud data based on restored (or reconstructed) geometry information and attribute information and render it according to various rendering methods. For example, points of the point cloud content may be rendered as vertices having a certain thickness, cubes having a certain minimum size centered around the vertex position, or circles centered around the vertex position. All or part of the rendered point cloud content is provided to the user through a display (e.g., VR / AR display, general display, etc.). The rendering step (81003) of the point cloud data according to the embodiments may be performed in the renderer (10007) of FIG. 1, the renderer (20004) of FIG. 2, or the renderer (9011) of FIG. 9.

[0691] Each of the parts, modules, or units described above may be software, processors, or hardware parts that execute sequential execution processes stored in memory (or storage units). Each of the steps described in the embodiments described above may be performed by processors, software, or hardware parts. Each of the modules / blocks / units described in the embodiments described above may operate as a processor, software, or hardware. In addition, the methods presented in the embodiments may be implemented as code. This code may be written on a processor-readable storage medium and thus may be read by a processor provided by an apparatus.

[0692] Furthermore, throughout the specification, when a part is said to "include" a component, this does not exclude other components, unless otherwise specifically stated, but rather implies the inclusion of other components. Furthermore, terms such as "part" described in the specification mean a unit that processes at least one function or operation, which may be implemented using hardware, software, or a combination of hardware and software.

[0693] For convenience of explanation, this specification has been described separately in each drawing. However, it is also possible to design new embodiments by combining the embodiments described in each drawing. Furthermore, designing a computer-readable recording medium containing a program for executing the previously described embodiments, as required by those skilled in the art, is also within the scope of the embodiments.

[0694] The devices and methods according to the embodiments are not limited to the configurations and methods of the embodiments described above, but the embodiments may be configured by selectively combining all or part of each embodiment so that various modifications can be made.

[0695] Although preferred embodiments of the embodiments have been illustrated and described, the embodiments are not limited to the specific embodiments described above, and various modifications may be made by those skilled in the art to which the invention pertains without departing from the spirit or scope of the embodiments claimed in the claims, and such modifications should not be understood individually from the technical idea or prospect of the embodiments.

[0696] The various components of the devices of the embodiments may be implemented by hardware, software, firmware, or a combination thereof. The various components of the embodiments may be implemented by a single chip, for example, a single hardware circuit. The components according to the embodiments may be implemented by separate chips. At least one of the components of the devices of the embodiments may be configured with one or more processors capable of executing one or more programs, and the one or more programs may perform, or include instructions for performing, one or more of the operations / methods according to the embodiments. The executable instructions for performing the methods / operations of the devices of the embodiments may be stored in non-transitory CRMs or other computer program products configured to be executed by one or more processors, or may be stored in temporary CRMs or other computer program products configured to be executed by one or more processors. In addition, the memory according to the embodiments may be used as a concept including not only volatile memory (e.g., RAM, etc.), but also non-volatile memory, flash memory, PROM, etc. Additionally, it may include implementations in the form of carrier waves, such as transmissions via the Internet. Furthermore, processor-readable recording media may be distributed across network-connected computer systems, allowing processor-readable code to be stored and executed in a distributed manner.

[0697] In this document, " / " and "," are interpreted as "and / or". For example, "A / B" is interpreted as "A and / or B", and "A, B" is interpreted as "A and / or B". Additionally, "A / B / C" means "at least one of A, B, and / or C". Also, "A, B, C" means "at least one of A, B, and / or C". Additionally, "or" in this document is interpreted as "and / or". For example, "A or B" can mean 1) "A" only, 2) "B" only, or 3) "A and B". In other words, "or" in this document can mean "additionally or alternatively".

[0698] Various elements of the embodiments may be implemented by hardware, software, firmware, or a combination thereof. Various elements of the embodiments may be implemented on a single chip, such as a hardware circuit. In some embodiments, the embodiments may optionally be implemented on separate chips. In some embodiments, at least one of the elements of the embodiments may be implemented within one or more processors that include instructions for performing operations according to the embodiments.

[0699] Additionally, the operations according to the embodiments described in this document may be performed by a transceiver device including one or more memories and / or one or more processors according to the embodiments. One or more memories may store programs for processing / controlling the operations according to the embodiments, and one or more processors may control various operations described in this document. One or more processors may be referred to as a controller, etc. The operations according to the embodiments may be performed by firmware, software, and / or a combination thereof, and the firmware, software, and / or a combination thereof may be stored in a processor or a memory.

[0700] Terms such as "first," "second," etc. may be used to describe various components of the embodiments. However, the various components according to the embodiments should not be interpreted as limited by these terms. These terms are merely used to distinguish one component from another. For example, a first user input signal may be referred to as a second user input signal. Similarly, a second user input signal may be referred to as a first user input signal. The use of these terms should be interpreted as not departing from the scope of the various embodiments. Although a first user input signal and a second user input signal are both user input signals, they do not mean the same user input signals unless the context clearly indicates otherwise.

[0701] The terminology used to describe the embodiments is for the purpose of describing particular embodiments and is not intended to be limiting of the embodiments. As used in the description of the embodiments and in the claims, the singular is intended to include the plural unless the context clearly dictates otherwise. The expressions “and / or” are used to mean all possible combinations of the terms. The expression “comprises” or “includes” describes the presence of features, numbers, steps, elements, and / or components, but does not mean that additional features, numbers, steps, elements, and / or components are not included. Conditional expressions such as “if” or “when” used to describe the embodiments are not intended to be limited to only optional cases. When a specific condition is satisfied, a related action is performed in response to a specific condition, or a related definition is intended to be interpreted.

[0702] As described above, the relevant contents have been described in the best form for carrying out the embodiments.

[0703] As described above, the embodiments may be applied, in whole or in part, to point cloud data transmission and reception devices and systems. Those skilled in the art may variously modify or alter the embodiments within the scope of the embodiments. The embodiments may include modifications and variations, and such modifications and variations do not depart from the scope of the claims and their equivalents.

Claims

1. A step of receiving geometry data, attribute data, and signaling information; A step of decoding the geometry data based on the signaling information; and A point cloud data decoding method comprising a step of decoding the attribute data based on the signaling information.

2. In paragraph 1, The above geometry data is divided and included in data units of a layer group structure, A point cloud data decoding method in which the geometry data of the current data unit of the current layer group is decoded by referring to the context information of the data unit of the upper layer group stored in memory.

3. In paragraph 2, The above memory is managed by data unit, The memory referenced to decode the geometry data of the current data unit is divided into a context state storage area, a reference count information storage area, and a counter information storage area. The above context state storage area stores context information of the data unit of the upper layer group, The above reference count information storage area stores the number of data units referencing the data units of the upper layer group for each layer group constituting the layer group structure, A point cloud data decoding method in which the above counter information storage area stores counter information that is updated each time a data unit of the upper layer group is used for each layer group.

4. In the third paragraph, the step of decoding the geometry data A point cloud data decoding method that does not store context information of a current data unit of the decoded current layer group in the memory if there is no subsequent data unit that references context information of the current data unit.

5. In the third paragraph, the step of decoding the geometry data A point cloud data decoding method in which context information of a current data unit of the decoded current layer group is not stored in the memory if the current layer group is the last layer group in the above layer group structure.

6. In the fifth paragraph, the step of decoding the geometry data A point cloud data decoding method in which context information of a current data unit of the decoded current layer group is not stored in the memory if the current layer group is the last layer group, excluding a layer group whose decoding is skipped in the above layer group structure.

7. In the third paragraph, the step of decoding the geometry data A point cloud data decoding method for determining the release of context information of a data unit of the upper layer group based on a value stored in a reference count information storage area of ​​the above memory and a value stored in the count information storage area.

8. In the second paragraph, the signaling information is A point cloud data decoding method including information for identifying a data unit of the upper layer group referenced for decoding geometry data of the current data unit.

9. In the second paragraph, the signaling information is Contains information related to the number of reference data units per layer group stored in the reference count storage area of ​​the above memory, The above information is a method for decoding point cloud data that is signaled by dividing it by layer group.

10. A receiving unit for receiving geometry data, attribute data, and signaling information; A geometry decoder that decodes the geometry data based on the signaling information; and A point cloud data decoding device including an attribute decoder that decodes the attribute data based on the signaling information.

11. In paragraph 10, The above geometry data is divided and included in data units of a layer group structure, The above geometry decoder is a point cloud data decoding device that decodes the geometry data of the current data unit of the current layer group by referring to the context information of the data unit of the upper layer group stored in the memory.

12. In paragraph 10, The above memory is managed by data unit, The memory referenced to decode the geometry data of the current data unit is divided into a context state storage area, a reference count information storage area, and a counter information storage area. The above context state storage area stores context information of the data unit of the upper layer group, The above reference count information storage area stores the number of data units referencing the data units of the upper layer group for each layer group constituting the layer group structure, The above counter information storage area is a point cloud data decoding device that stores counter information that is updated each time a data unit of the upper layer group is used for each layer group.

13. In the 12th paragraph, the geometry decoder A point cloud data decoding method for determining the release of context information of a data unit of the upper layer group stored in the context state storage area based on a value stored in the reference count information storage area of ​​the memory and a value stored in the count information storage area.

14. Step of encoding geometry data; A step of encoding attribute data; and A point cloud data encoding method comprising the steps of transmitting the encoded geometry data, the encoded attribute data, and signaling information.

15. Geometry encoder that encodes geometry data; An attribute encoder that encodes attribute data; and A point cloud data encoding device comprising a transmission unit that transmits the encoded geometry data, the encoded attribute data, and signaling information.

Images