Mesh data encoding device, mesh data encoding method, mesh data decoding device, and mesh data decoding method

Abstract

A decoding method according to embodiments may comprise the steps of: decoding a base mesh within a bitstream; decoding displacements within the bitstream; and decoding attributes within the bitstream. An encoding method according to embodiments may comprise the steps of: encoding a base mesh of mesh data; encoding displacements of the mesh data; and encoding attributes of the mesh data.

Description

Mesh data encoding device, mesh data encoding method, mesh data decoding device, and mesh data decoding method

[0001] The embodiments provide a method for providing Point Cloud content to provide users with various services such as Virtual Reality (VR), Augmented Reality (AR), Mixed Reality (MR), and autonomous driving services.

[0002] A point cloud is a collection of points in 3D space. The sheer number of points in 3D space makes it difficult to generate point cloud data.

[0003] There is a problem that a lot of processing power is required to transmit and receive point cloud data.

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

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

[0006] However, the scope of the embodiments is not limited to the aforementioned technical tasks, 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 contents of this document.

[0007] To achieve the above-described purpose and other advantages, a decoding method according to embodiments may include a step of decoding a base mesh in a bitstream; a step of decoding a displacement in the bitstream; and a step of decoding an attribute in the bitstream. An encoding method according to embodiments may include a step of encoding a base mesh of mesh data; a step of encoding a displacement of the mesh data; and a step of encoding an attribute of the mesh data.

[0008] The point cloud data transmission method, transmission device, point cloud data reception method, and reception device according to the embodiments can provide a high-quality point cloud service.

[0009] The point cloud data transmission method, transmission device, point cloud data reception method, and reception device according to the embodiments can achieve various video codec methods.

[0010] The point cloud data transmission method, transmission device, point cloud data reception method, and reception device according to the embodiments can provide general-purpose point cloud content such as autonomous driving services.

[0011] The drawings are included to further understand the embodiments, and the drawings illustrate the embodiments together with the description related to the embodiments. For a better understanding of the various embodiments described below, reference should be made to the following description of the embodiments in conjunction with the following drawings, in which like reference numerals correspond to corresponding parts throughout the drawings.

[0012] Figure 1 illustrates a system for providing dynamic mesh content according to embodiments.

[0013] Figure 2 illustrates a V-MESH compression method according to embodiments.

[0014] Figure 3 illustrates pre-processing of V-MESH compression according to embodiments.

[0015] Figure 4 illustrates a mid-edge subdivision method according to embodiments.

[0016] Figure 5 shows a displacement generation process according to embodiments.

[0017] FIG. 6 illustrates an intra-frame encoding process of a V-MESH compression method according to embodiments.

[0018] Figure 7 illustrates an inter-frame encoding process of a V-MESH compression method according to embodiments.

[0019] Figure 8 shows a lifting conversion process for displacement according to embodiments.

[0020] Figure 9 illustrates a process of packing transformation coefficients according to embodiments into a 2D image.

[0021] Fig. 10 shows an attribute transfer process of a V-MESH compression method according to embodiments.

[0022] Fig. 11 illustrates an intra-frame decoding process of a V-MESH compression method according to embodiments.

[0023] Fig. 12 shows a V-MES and Fig. 13 shows a point cloud data transmission device according to embodiments.

[0024] Fig. 13 shows a point cloud data transmission device according to embodiments.

[0025] Fig. 14 shows a point cloud data receiving device according to embodiments.

[0026] Figure 15 shows a method for calculating normal vectors according to embodiments.

[0027] Figure 16 shows examples of triangles and plane normal vectors of triangles that constitute a mesh according to embodiments.

[0028] Figure 17 shows an example of a vertex normal vector when the mesh according to the embodiments is in the shape of a hexahedron.

[0029] Figure 18 shows an example of a vertex normal vector when the mesh according to the embodiments is in the shape of a hexahedron.

[0030] Figure 19 shows a method for calculating normal vectors according to embodiments.

[0031] Figure 20 shows the triangles that constitute the mesh according to the embodiments and the internal angles in the direction of one vertex.

[0032] Figure 21 shows an example of a vertex normal vector when the mesh according to the embodiments is in the shape of a hexahedron.

[0033] Fig. 22 shows a dynamic mesh encoding device according to embodiments.

[0034] Fig. 23 shows a dynamic mesh decoding device according to embodiments.

[0035] Figure 24 shows a mesh restoration method according to embodiments.

[0036] FIG. 25 illustrates the V-DMC extension syntax of an atlas sequence parameter set in a bitstream according to embodiments.

[0037] FIG. 26 illustrates the V-DMC extension syntax of an atlas frame parameter set within a bitstream according to embodiments.

[0038] Figure 27 shows the syntax of a mesh patch data unit in a bitstream according to embodiments.

[0039] Figure 28 shows an encoding method according to embodiments.

[0040] Figure 29 shows a decryption method according to embodiments.

[0041] 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.

[0042] 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.

[0043] Figure 1 illustrates a system for providing dynamic mesh content according to embodiments.

[0044] The system of FIG. 1 includes a point cloud data transmission device (100) and a point cloud data reception device (110) according to embodiments. The point cloud data transmission device may include a dynamic mesh video acquisition unit (101), a dynamic mesh video encoder (102), a file / segment encapsulator (103), and a transmitter (104). The point cloud data reception device (110) may include a reception unit (111), a file / segment decapsulator (112), a dynamic mesh video decoder (113), and a renderer (114). Each component of FIG. 1 may correspond to hardware, software, a processor, and / or a combination thereof. Hereinafter, the point cloud data transmission device according to embodiments may be interpreted as a term referring to the transmission device (100) or a dynamic mesh video encoder (hereinafter, referred to as an encoder) (102). The point cloud data receiving device according to the embodiments may be interpreted as a term referring to a receiving device (110) or a dynamic mesh video decoder (hereinafter, decoder) (113).

[0045] The system of Fig. 1 can perform video-based dynamic mesh compression and decompression.

[0046] Advances in 3D capture, modeling, and rendering have enabled users to consume diverse forms of 3D content, such as AR, XR, metaverse, and holograms, across multiple platforms and devices. 3D content increasingly represents objects with greater precision and realism, enabling users to enjoy immersive experiences. To achieve this, the creation and use of 3D models requires a significant amount of data. Among various types of 3D content, 3D meshes are widely used for efficient data utilization and realistic object representation. Embodiments include a series of processing steps in a system that utilizes such mesh content.

[0047] First, the method of compressing dynamic mesh data starts with the V-PCC (Video-based point cloud compression) standard technology. Point cloud data is data that contains color information at the vertex coordinates (X, Y, Z). Mesh data refers to data in which connectivity information between vertices is added to this vertex information. When creating content, it can be created in the form of mesh data from the beginning. By adding connectivity information to point cloud data, it can be converted into mesh data and used.

[0048] Currently, the MPEG standards body defines two types of dynamic mesh data: Category 1: Mesh data with texture maps as color information. Category 2: Mesh data with vertex colors as color information.

[0049] Mesh coding standards for Category 1 data are currently under development, and work on Category 2 data standards is also planned for the future. The overall process for providing mesh content services may include acquisition, encoding, transmission, decoding, rendering, and / or feedback, as shown in Figure 1.

[0050] To provide mesh content services, 3D data acquired through multiple cameras or specialized cameras can be processed into mesh data types through a series of processes and then converted into video. The generated mesh video is then transmitted through a series of processes, and the receiving end can then reprocess the received data into mesh video and render it. This allows mesh video to be presented to users, who can then interact with the mesh content according to their intended intent.

[0051] A mesh compression system may include a transmitting device and a receiving device. The transmitting device can encode mesh video to output a bitstream, which can be delivered to the receiving device via digital storage media or a network in the form of a file or streaming segment. The digital storage media may include various storage media, such as USB, SD, CD, DVD, Blu-ray, HDD, or SSD.

[0052] The transmitting device may roughly include a mesh video acquisition unit, a mesh video encoder, and a transmitting unit. The receiving device may roughly include a receiving unit, a mesh video decoder, and a renderer. The encoder may be referred to as a mesh video / video / picture / frame encoding device, and the decoder may be referred to as a mesh video / video / picture / frame decoding device. The transmitter may be included in the mesh video encoder. The receiver may be included in the mesh video decoder. The renderer may include a display unit, and the renderer and / or the display unit may be configured as separate devices or external components. The transmitting device and the receiving device may further include separate internal or external modules / units / components for a feedback process.

[0053] Mesh data represents the surface of an object as a number of polygons. Each polygon is defined by its vertices in 3D space and connection information that describes how those vertices are connected. It can also contain vertex properties such as vertex color and normal. Mapping information that allows the surface of the mesh to be mapped to a 2D planar area can also be included as a mesh property. The mapping is typically described as a set of parametric coordinates, called UV coordinates or texture coordinates, associated with the mesh vertices. Meshes contain 2D attribute maps, which can be used to store high-resolution attribute information such as textures, normals, and displacement.

[0054] The mesh video acquisition unit may include processing 3D object data acquired through a camera, etc. into a mesh data type with the properties described above through a series of processes and generating a video composed of such mesh data. The mesh video may have properties of the mesh, such as vertices, polygons, connection information between vertices, colors, normals, etc., that may change over time. A mesh video with properties and connection information that change over time can be expressed as a dynamic mesh video.

[0055] A mesh video encoder can encode an input mesh video into one or more video streams. A single video can include multiple frames, and a single frame can correspond to a still image / picture. In this document, a mesh video can include a mesh image / frame / picture, and the mesh video can be used interchangeably with the mesh image / frame / picture. A mesh video encoder can perform a Video-based Dynamic Mesh (V-Mesh) Compression procedure. A mesh video encoder can perform a series of procedures such as prediction, transformation, quantization, and entropy coding for compression and coding efficiency. The encoded data (encoded video / image information) can be output in the form of a bitstream.

[0056] The encapsulation processing unit (file / segment encapsulation module) can encapsulate encoded mesh video data and / or mesh video-related metadata in the form of a file, etc. Here, the mesh video-related metadata may be received from the metadata processing unit, etc. The metadata processing unit may be included in the mesh video encoder, or may be configured as a separate component / module. The encapsulation processing unit may encapsulate the corresponding data in a file format such as ISOBMFF, or process it in the form of other DASH segments, etc. The encapsulation processing unit may include mesh video-related metadata in the file format according to an embodiment. The mesh video metadata may be included in boxes at various levels in the ISOBMFF file format, for example, or may be included as data in a separate track within the file. According to an embodiment, the encapsulation processing unit may encapsulate mesh video-related metadata itself in a file.

[0057] The transmission processing unit can process encapsulated mesh video data for transmission according to the file format. The transmission processing unit can be included in the transmission unit, or can be configured as a separate component / module. The transmission processing unit can process mesh video data according to any transmission protocol. The processing for transmission can include processing for transmission through a broadcast network or processing for transmission through broadband. According to an embodiment, the transmission processing unit can receive not only mesh video data but also mesh video-related metadata from the metadata processing unit and process the same for transmission.

[0058] The transmission unit can transmit encoded video / image information or data output in the form of a bitstream to the receiving unit of a receiving device via a digital storage medium or network in the form of a file or streaming. The digital storage medium can include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. The transmission unit can include an element for generating a media file via a predetermined file format and can include an element for transmission via a broadcasting / communication network. The receiving unit can extract the bitstream and transmit it to a decoding device.

[0059] The receiver can receive mesh video data transmitted by a mesh video transmission device. Depending on the transmission channel, the receiver can receive mesh video data via a broadcast network, via broadband, or via digital storage media.

[0060] The receiving processing unit can perform processing on the received mesh video data according to a transmission protocol. The receiving processing unit can be included in the receiving unit, or can be configured as a separate component / module. In response to the processing performed for transmission on the transmitting side, the receiving processing unit can perform the reverse process of the aforementioned transmitting processing unit. The receiving processing unit can transfer the acquired mesh video data to the decapsulation processing unit, and transfer the acquired mesh video-related metadata to a metadata parser. The mesh video-related metadata acquired by the receiving processing unit can be in the form of a signaling table.

[0061] A decapsulation processing unit (file / segment decapsulation module) can decapsulate mesh video data in file format received from a receiving processing unit. The decapsulation processing unit can decapsulate files according to ISOBMFF, etc., to obtain a mesh video bitstream or mesh video-related metadata (metadata bitstream). The obtained mesh video bitstream can be transmitted to a mesh video decoder, and the obtained mesh video-related metadata (metadata bitstream) can be transmitted to a metadata processing unit. The mesh video bitstream may include metadata (metadata bitstream). The metadata processing unit may be included in the mesh video decoder, or may be configured as a separate component / module. The mesh video-related metadata obtained by the decapsulation processing unit may be in the form of a box or track within a file format. If necessary, the decapsulation processing unit may receive metadata required for decapsulation from the metadata processing unit. Mesh video related metadata can be passed to a Mesh video decoder for use in the Mesh video decoding process, or passed to a renderer for use in the Mesh video rendering process.

[0062] A mesh video decoder can receive a bitstream and perform operations corresponding to those of a mesh video encoder to decode video / images. The decoded mesh video can be displayed via a display unit. Users can view all or part of the rendered result via a VR / AR display or a general display.

[0063] The feedback process may include a process of transmitting various feedback information that may be acquired during the rendering / display process to the transmitter or to the decoder on the receiver. Interactivity may be provided in mesh video consumption through the feedback process. Depending on the embodiment, head orientation information, viewport information indicating the area that the user is currently viewing, etc. may be transmitted during the feedback process. Depending on the embodiment, the user may interact with things implemented in the VR / AR / MR / autonomous driving environment, in which case information related to the interaction may be transmitted to the transmitter or the service provider during the feedback process. Depending on the embodiment, the feedback process may not be performed.

[0064] Head orientation information can refer to information about the user's head position, angle, and movement. Based on this information, information about the area the user is currently viewing within the mesh video, i.e. viewport information, can be calculated.

[0065] Viewport information can be information about the area the user is currently viewing in the mesh video. This can be used to perform gaze analysis to determine how the user consumes the mesh video, which area of ​​the mesh video they are gazing at, and for how long. Gaze analysis can be performed on the receiving side and transmitted to the transmitting side through a feedback channel. Devices such as VR / AR / MR displays can extract the viewport area based on the user's head position / orientation, the vertical or horizontal FOV supported by the device, etc.

[0066] Depending on the embodiment, the aforementioned feedback information may not only be transmitted to the transmitter but may also be consumed by the receiver. That is, the aforementioned feedback information may be utilized to perform decoding, rendering, and other processes on the receiver. For example, head orientation information and / or viewport information may be utilized to preferentially decode and render only the mesh video for the area currently being viewed by the user.

[0067] This document relates to dynamic mesh video compression as described above. The method / embodiment disclosed in this document can be applied to the Video-based Dynamic Mesh Compression (V-Mesh) standard of the Moving Picture Experts Group (MPEG) or the next-generation video / image coding standard. Dynamic mesh video compression is a method for processing mesh connection information and properties that change over time, and it can perform lossy and lossless compression for various applications such as real-time communication, storage, free-view video, and AR / VR.

[0068] The dynamic mesh video compression method described below is based on MPEG's V-Mesh method.

[0069] In this document, picture / frame can generally mean a unit representing one video of a specific time period.

[0070] A pixel or pel can refer to the smallest unit that constitutes a picture (or image). Additionally, the term "sample" can be used as a counterpart to a pixel. A sample can generally represent a pixel or a pixel value, and can represent only the pixel / pixel value of the luma component, only the pixel / pixel value of the chroma component, or only the pixel / pixel value of the depth component.

[0071] A unit may represent a basic unit of image processing. A unit may include at least one of a specific region of a picture and information related to the region. In some cases, the term "unit" may be used interchangeably with terms such as "block" or "area." In general, an MxN block may include a set (or array) of samples (or sample array) or transform coefficients consisting of M columns and N rows.

[0072] The encoding process of Fig. 1 is as follows.

[0073] Video-based dynamic mesh compression (V-Mesh) compression methods can provide a method for compressing dynamic mesh video data based on 2D video codecs such as HEVC and VVC. The V-Mesh compression process receives the following data as input and performs compression.

[0074] Input mesh: Contains the 3D coordinates (geometry) of the vertices that make up the mesh, normal information for each vertex, mapping information that maps the mesh surface to a 2D plane, and connection information between the vertices that make up the surface. The mesh surface can be expressed as triangles or more polygons, and connection information between the vertices that make up each surface is stored according to a set shape. The input mesh can be saved in the OBJ file format.

[0075] Attribute map: (Hereinafter, texture map is also used in the same meaning): Contains information about the properties (color, normal, displacement, etc.) of the mesh, and stores data in the form of a mapping of the surface of the mesh onto a 2D image. Mapping which part (surface or vertex) of the mesh each data of this attribute map corresponds to is based on the mapping information contained in the input mesh. Since the attribute map has data for each frame of the mesh video, it can also be expressed as an attribute map video (or attribute for short). The attribute map in the V-Mesh compression method mainly contains the color information of the mesh, and is saved in an image file format (PNG, BMP, etc.).

[0076] Material Library File: Contains information about the material properties used in a mesh, particularly information that links the input mesh to its corresponding attribute map. It is saved in the Wavefront Material Template Library (MTL) file format.

[0077] In the V-Mesh compression method, the following data and information can be generated through the compression process.

[0078] Base mesh: The input mesh is simplified (decimated) through a preprocessing process to express the objects of the input mesh using the minimum number of vertices determined by the user's standards.

[0079] Displacement: This is displacement information used to express the input mesh as similarly as possible to the base mesh, and is expressed in the form of 3D coordinates.

[0080] Atlas information: This is the metadata required to reconstruct a mesh using base mesh, displacement, and attribute map information. It can be created and utilized as sub-mesh units (such as patches) that make up the mesh.

[0081] Referring to FIGS. 2 to 7, a method for encoding mesh position information (vertex) is described, and referring to FIGS. 6-10, etc., a method for encoding attribute information (attribute map) by restoring mesh position information is described.

[0082] Figure 2 illustrates a V-MESH compression method according to embodiments.

[0083] Fig. 2 illustrates the encoding process of Fig. 1, and the encoding process may include a pre-processing process and an encoding process. The encoder of Fig. 1 may include a pre-processor (200) and an encoder (201) as in Fig. 2. The transmitting device of Fig. 1 may be broadly referred to as an encoder, and the dynamic mesh video encoder of Fig. 1 may be referred to as an encoder. The V-Mesh compression method may include a pre-processing (200) and an encoding (201) process as in Fig. 2. The pre-processor of Fig. 2 may be located in front of the encoder of Fig. 2. The pre-processor and the encoder of Fig. 2 may be referred to as a single encoder.

[0084] The preprocessor can receive a static dynamic mesh and / or an attribute map. The preprocessor can generate a base mesh and / or displacement through preprocessing. The preprocessor can receive feedback information from the encoder and generate the base mesh and / or displacement based on the feedback information.

[0085] The encoder can receive a base mesh, displacement mesh, static dynamic mesh, and / or attribute map. The encoder can encode mesh-related data to generate a compressed bitstream.

[0086] Figure 3 illustrates pre-processing of V-MESH compression according to embodiments.

[0087] Figure 3 shows the configuration and operation of the pre-processor of Figure 2.

[0088] Fig. 3 shows a process of performing preprocessing on an input mesh. The preprocessing process (200) can be broadly divided into four steps: 1) Group of Frame (GoF) generation, 2) Mesh Decimation, 3) UV parameterization, and 4) Fitting subdivision surface (300). The preprocessor (200) can receive an input mesh, generate a displacement and / or base mesh, and transmit the generated displacement and / or base mesh to the encoder (201). The preprocessor (200) can transmit GoF information related to GoF generation to the encoder (201).

[0089] Below, each step of Figure 3 is described.

[0090] GoF Generation: This is the process of generating a reference structure for mesh data. If the number of vertices, number of texture coordinates, vertex connection information, and texture coordinate connection information of the mesh of the previous frame and the current mesh are all the same, the previous frame can be set as the reference frame. In other words, if only the vertex coordinate values ​​are different between the current input mesh and the reference input mesh, inter-frame encoding can be performed. Otherwise, the frame performs intra-frame encoding.

[0091] Mesh Decimation: This process simplifies the input mesh to create a simplified mesh, or base mesh. Vertices to be removed from the original mesh are selected based on user-defined criteria, and the selected vertices and the triangles connected to them can be removed.

[0092] In the process of performing mesh simplification (Mesh decimation), the input mesh (voxelized), target triangle ratio (TTR), and minimum triangle component (CCCount) information are passed as input, and the simplified mesh (decimated mesh) can be obtained as output. In this process, connected triangle components smaller than the set minimum triangle component (CCCount) can be removed.

[0093] UV parameterization: This is the process of mapping a 3D surface of a decimated mesh into a texture domain. Parameterization can be performed using the UVAtlas tool. This process generates mapping information, which indicates where each vertex of the decimated mesh can be mapped to on a 2D image. This mapping information is expressed and stored as texture coordinates, and through this process, the final base mesh is created.

[0094] Fitting subdivision surface: This is the process of performing subdivision on a simplified mesh. The subdivision method can be a user-defined method, such as the mid-edge method. The fitting process ensures that the input mesh and the subdivision mesh are similar to each other.

[0095] Figure 4 illustrates a mid-edge subdivision method according to embodiments.

[0096] Figure 4 illustrates the mid-edge method of the fitting subdivision surface described in Figure 3. Referring to Figure 4, an original mesh containing four vertices is subdivided to create a sub-mesh. A sub-mesh can be created by creating a new vertex midway between the edges between the vertices.

[0097] When a fitted subdivided mesh (hereinafter referred to as a fitted subdivided mesh) is generated, displacement is calculated using this result and a pre-compressed and decrypted base mesh (hereinafter referred to as a reconstructed base mesh). That is, the reconstructed base mesh is subdivided in the same way as the fitting subdivision surface. The difference in position of each vertex between this result and the fitted subdivided mesh is the displacement for each vertex. Since displacement represents the position difference in three-dimensional space, it is also expressed as a value in the (x, y, z) space of a Cartesian coordinate system. Depending on the user input parameters, the (x, y, z) coordinate values ​​can be converted to (normal, tangential, bi-tangential) coordinate values ​​of the local coordinate system.

[0098] Figure 5 shows a displacement generation process according to embodiments.

[0099] FIG. 5 illustrates in detail the displacement calculation method of the fitting subdivision surface (300) as described in FIG. 4.

[0100] An encoder and / or pre-processor according to embodiments may include 1) a subdivision unit, 2) a local coordinate system calculation unit, and 3) a displacement calculation unit. The subdivision unit may receive a reconstructed base mesh and generate a subdivided reconstructed base mesh. The local coordinate system calculation unit may receive a fitted subdivision mesh and a subdivided reconstructed base mesh, and transform a coordinate system of the mesh into a local coordinate system. The local coordinate system calculation operation may be optional. The displacement calculation unit may calculate a positional difference between the fitted subdivision mesh and the subdivided reconstructed base mesh. For example, a positional difference value between vertices of two input meshes may be generated. The vertex positional difference value becomes a displacement.

[0101] The method and device for transmitting point cloud data according to the embodiments can encode the point cloud as follows. The point cloud data (which may be referred to as a point cloud for short) according to the embodiments can refer to data including vertex coordinates and color information. The term "point cloud" includes mesh data, and in this document, point cloud and mesh data can be used interchangeably.

[0102] The V-Mesh compression (reconstruction) method according to the embodiments may include intra frame encoding (Fig. 6) and inter frame encoding (Fig. 7).

[0103] Based on the results of the GoF generation described above, intra-frame encoding or inter-frame encoding is performed. In the case of intra-encoding, the data to be compressed may be a base mesh, displacement, attribute map, etc. In the case of inter-encoding, the data to be compressed may be a displacement, attribute map, and a motion field between a reference base mesh and the current base mesh.

[0104] FIG. 6 illustrates an intra-frame encoding process of a V-MESH compression method according to embodiments.

[0105] The encoding process of Fig. 6 details the encoding of Fig. 1. That is, it shows the configuration of an encoder when the encoding of Fig. 1 is an intra-frame method. The encoder of Fig. 6 may include a preprocessor (200) and / or an encoder (201).

[0106] The preprocessor can receive an input mesh and perform the preprocessing described above. The preprocessing can generate a base mesh and / or a fitted subdivided mesh. The quantizer can quantize the base mesh and / or the fitted subdivided mesh. The static mesh encoder can encode the static mesh. The static mesh encoder can generate a bitstream including the encoded base mesh. The static mesh decoder can decode the encoded static mesh. The inverse quantizer can inversely quantize the quantized static mesh. The displacement calculation unit can receive the reconstructed static mesh and generate displacement, which is a position difference, based on the fitted subdivided mesh. The forward linear lifting unit can receive the displacement and generate lifting coefficients. The quantizer can quantize the lifting coefficients. The image packing unit can pack an image based on the quantized lifting coefficients. A video encoder can encode a packed image. A video decoder decodes the encoded video. An image unpacker can unpack a packed image. A dequantizer can inversely quantize an image. An inverse linear lifting unit applies inverse lifting to the image to generate a reconstructed displacement. A mesh restoration unit restores a warped mesh using the reconstructed displacement and the reconstructed base mesh. An attribute transfer unit receives an input mesh and / or an input attribute map, and generates an attribute map based on the reconstructed warped mesh. A push-pull padding unit can pad data in the attribute map based on a push-pull method. A color space transformation unit can transform the space of a color component, which is an attribute. A video encoder can encode an attribute. A multiplexer can generate a bitstream by multiplexing a compressed base mesh, compressed displacement, and compressed attributes.

[0107] Figure 7 illustrates an inter-frame encoding process of a V-MESH compression method according to embodiments.

[0108] The encoding process of Fig. 7 details the encoding of Fig. 1. That is, it shows the configuration of an encoder when the encoding of Fig. 1 is an inter-frame method. The encoder of Fig. 7 may include a preprocessor (200) and / or an encoder (201).

[0109] Among the encoding operations of Fig. 7, the corresponding configuration of the encoding operation of Fig. 6 refers to the description of Fig. 7. For the inter-frame-based encoding of Fig. 7, the motion encoder can encode motion based on the restored quantized reference base mesh. The base mesh restoration unit can restore the base mesh based on the restored quantized reference base mesh.

[0110] The encoder of Fig. 6 generates a bitstream by compressing the base mesh, displacement, and attributes within the frame, and the encoder of Fig. 7 generates a bitstream by compressing the motion, displacement, and attributes between the current frame and the reference frame.

[0111] The encoding method according to the embodiments includes base mesh encoding (intra encoding). When performing intra frame encoding on the current input mesh frame, the base mesh generated in the preprocessing process can be encoded using a static mesh compression technique after going through a quantization process. In the V-Mesh compression method, for example, Draco technology is applied, and the vertex position information, mapping information (texture coordinates), vertex connection information, etc. of the base mesh are compressed.

[0112] The encoding method according to the embodiments may include motion field encoding (inter encoding). Inter frame encoding may be performed when a one-to-one correspondence of vertices is established between a reference mesh and a current input mesh, and only the position information of the vertices is different. When performing inter frame encoding, instead of compressing the base mesh, the difference between the vertices of the reference base mesh and the current base mesh, i.e., the motion field, may be calculated and this information may be encoded. The reference base mesh is the result of quantizing the already decoded base mesh data and is determined according to the reference frame index determined in the GoF generation. The motion field may be encoded as a value. Alternatively, the predicted motion field may be calculated by averaging the motion fields of the restored vertices among the vertices connected to the current vertex, and this predicted motion field The residual motion field, which is the difference between the value and the motion field value of the current vertex, can be encoded. This value can be encoded using entropy coding. The process of encoding the displacement and attribute map, excluding the motion field encoding process of inter-frame encoding, is the same as the structure of the intra-frame encoding method except for the base mesh encoding.

[0113] Figure 8 shows a lifting conversion process for displacement according to embodiments.

[0114] Figure 9 illustrates a process of packing transformation coefficients according to embodiments into a 2D image.

[0115] Figures 8-9 show the process of converting the displacement of the encoding process of Figures 6-7 and the process of packing the conversion coefficients, respectively.

[0116] The encoding method according to the embodiments includes displacement encoding.

[0117] After encoding the base mesh through base mesh encoding and / or motion field encoding, a reconstructed base mesh is generated through restoration and dequantization, and the displacement between the result of performing subdivision on the reconstructed base mesh and the fitted subdivided mesh generated through the fitting subdivision surface can be calculated. For effective encoding, a data transform process such as wavelet transform can be applied to the displacement information.

[0118] Figure 8 shows the process of transforming displacement information using lifting transform in V-Mesh. The transform coefficients generated through the transform process are quantized and then packed into a 2D image as shown in Figure 9. The transform coefficients are organized into one block for each 256 (=16×16) units, and each block can be packed in z-scan order. The horizontal number of blocks is fixed to 16, but the vertical number of blocks can be determined according to the number of vertices of the subdivided base mesh. The transform coefficients can be packed by sorting them with Morton code within a block. The packed images generate a displacement video for each GoF unit, and this displacement video can be encoded using an existing video compression codec.

[0119] Referring to FIG. 8, the base mesh (original) may include vertices and edges for LoD0. The first subdivision mesh generated by dividing the base mesh includes vertices generated by further dividing the edges of the base mesh. The first subdivision mesh includes vertices for LoD0 and vertices for LoD1. LoD1 includes the subdivided vertices and the vertices (LoD0) of the base mesh. The first subdivision mesh may be generated by dividing the second subdivision mesh. The second subdivision mesh includes LoD2. LoD2 includes the base mesh vertices (LoD0), LoD1 including the vertices additionally generated from LoD0, and the vertices additionally divided from LoD1. LoD is a level indicating the degree of detail (Level of Detail), and as the level index increases, the distance between vertices becomes closer and the level of detail increases. LoD N includes the vertices included in the previous LoDN-1 as they are. When a vertex is further divided through subdivision, considering the previous vertices v1, v2 and the subdivided vertex v, the mesh can be encoded based on a prediction and / or update method. Instead of still encoding information about the current LoD N, a residual value between the previous LoD N-1 can be generated, and the mesh can be encoded using the residual value to reduce the size of the bitstream. The prediction process means the operation of predicting the current vertex v using the previous vertices v1, v2. Since adjacent subdivision meshes have similar data, efficient encoding can be achieved by utilizing this property. The current vertex position information is predicted as the residual for the previous vertex position information, and the previous vertex position information is updated using the residual.

[0120] Referring to Figure 9, the vertices have coefficients generated through the lifting transformation. The coefficients of the vertices related to the lifting transformation can be encoded by packing them into an image.

[0121] Fig. 10 shows an attribute transfer process of a V-MESH compression method according to embodiments.

[0122] Figure 10 shows the detailed operation of attribute transfer of encoding such as Figures 6-7.

[0123] Encoding according to embodiments includes attribute map encoding.

[0124] Information about the input mesh is compressed through base mesh encoding, motion field encoding, and displacement encoding. In the encoding process, the compressed input mesh is restored through base mesh decoding (intra frame), motion field decoding (inter frame), and displacement video decoding processes, and the restored result, the reconstructed deformed mesh (hereinafter referred to as Recon. deformed mesh), is used to compress the input attribute map as shown in FIGS. 6 and 7. The reconstructed deformed mesh (Recon. deformed mesh) has vertex position information, texture coordinates, and corresponding connection information, but does not have color information corresponding to the texture coordinates. Therefore, as shown in Fig. 10, in the V-Mesh compression method, a new attribute map having color information corresponding to the texture coordinates of the reconstructed deformed mesh is created through the attribute transfer process.

[0125] Attribute transfer first checks whether each point P(u, v) in the 2D texture domain belongs to a texture triangle of the reconstructed deformed mesh, and if it is in the texture triangle T, calculates the barycentric coordinate (α, β γ) of P(u, v) according to the triangle T. Then, using the 3D vertex position and (α, β γ) of triangle T, calculate the 3D coordinate M(x, y, z) of P(u, v). Find the vertex coordinate M'(x', y', z') that corresponds to the position most similar to the calculated M(x, y, z) in the input mesh domain and the triangle T' that contains this point. And in this triangle T', the center of mass coordinates (α', β', γ') of M'(x', y', z') are calculated. Using the texture coordinates corresponding to the three vertices of triangle T' and (α', β', γ'), the texture coordinates (u', v') are calculated, and the color information corresponding to these coordinates is found in the input attribute map. The color information found in this way is immediately assigned to the pixel location (u, v) of the new attribute map. If P(u, v) does not belong to any triangle, the pixel at that location in the new attribute map can be filled with a color value using a padding algorithm such as the push-pull algorithm.

[0126] The new attribute map generated through attribute transfer is grouped into GoF units to form an attribute map video, which is then compressed using a video codec.

[0127] Referring to Figure 10, the reference relationship between the input mesh, input attribute map, restored mesh, and generated attribute map can be seen.

[0128] The decoding process of Fig. 1 can perform the reverse process of the corresponding encoding process of Fig. 1. The specific decoding process is as follows.

[0129] Fig. 11 illustrates an intra-frame decoding process of a V-MESH compression method according to embodiments.

[0130] Fig. 11 shows the configuration and operation of a decoder of a receiving device such as Fig. 1.

[0131] Figure 11 illustrates the intra decoding process of V-Mesh technology. First, the input bitstream can be separated into a mesh sub-stream, a displacement sub-stream, an attribute map sub-stream, and a sub-stream containing mesh patch information, such as V3C / V-PCC.

[0132] The mesh sub-stream is decoded by the decoder of the static mesh codec used in encoding, such as Google Draco, and as a result, the connection information, vertex geometry information, vertex texture coordinates, etc. of the base mesh can be restored. The displacement sub-stream is decoded into a displacement video by the decoder of the video compression codec used in encoding, and goes through the image unpacking, inverse quantization, and inverse transform processes to restore displacement information for each vertex. Inverse quantization is applied to the restored base mesh, and this result is combined with the restored displacement information to generate the final decoded mesh.

[0133] The attribute map sub-stream is decoded through the decoder of the video compression codec used in encoding, and then restored to the final attribute map through processes such as color format conversion.

[0134] The restored decoded mesh and decoded attribute map can be utilized by the receiver as final mesh data that can be utilized by the user.

[0135] Referring to FIG. 11, the bitstream includes patch information, a mesh substream, a displacement substream, and an attribute map substream. The term "substream" is interpreted as referring to a portion of the bitstream included in the bitstream. The bitstream includes patch information (data), mesh information (data), displacement information (data), and attribute map information (data).

[0136] The decoder performs the following decoding operations within the frame. The static mesh decoder decodes the mesh to generate a reconstructed quantized base mesh, and the inverse quantizer applies the quantization parameters of the quantizer inversely to generate the reconstructed base mesh. The video decoder decodes the displacement, the unpacker unpacks the decoded video image, and the inverse quantizer inversely quantizes the quantized image. The linear lifting inverse transform applies a lifting transform in the reverse process of the encoder to generate the reconstructed displacement. The mesh restoration unit generates a warped mesh based on the base mesh and the displacement. The video decoder decodes the attribute map, and the color transformation unit transforms the color format and / or space to generate the decoded attribute map.

[0137]

[0138] Figure 12 shows the inter-frame decoding process of the V-MESH compression method.

[0139] Fig. 12 shows the configuration and operation of the decoder of the receiving device of Fig. 1.

[0140] Figure 12 illustrates the inter-decoding process of V-Mesh technology. First, the input bitstream can be separated into a motion sub-stream, a displacement sub-stream, an attribute sub-stream, and a sub-stream containing mesh patch information, such as V3C / V-PCC.

[0141] The motion sub-stream is decoded through entropy decoding and inverse prediction processes, and the reconstructed motion information is combined with the already reconstructed reference base mesh to generate a reconstructed quantized base mesh for the current frame. The result of applying inverse quantization to this is combined with the displacement information reconstructed in the same way as the intra decoding described above to generate the final decoded mesh. The attribute map sub-stream is decoded in the same way as the intra decoding. The reconstructed decoded mesh and the decoded attribute map can be utilized by the receiver as the final mesh data that can be utilized by the user.

[0142] Referring to Fig. 12, the bitstream includes motion, displacement, and attribute maps. Since inter-frame decoding is performed, a process of decoding inter-frame motion information is further included. The motion is decoded, and a restored quantized base mesh for the motion is generated based on the reference base mesh, thereby generating a restored base mesh. For a description of the operations in Fig. 12, which are identical to those in Fig. 11, refer to the description in Fig. 11.

[0143] Fig. 13 shows a point cloud data transmission device according to embodiments.

[0144] Fig. 13 corresponds to the transmitting device (100), the dynamic mesh video encoder (102), the Fig. 2 encoder (preprocessor and encoder), and / or the transmitting encoding device corresponding thereto of Fig. 1. Each component of Fig. 13 corresponds to hardware, software, a processor, and / or a combination thereof.

[0145] The operation process of a transmitter for compressing and transmitting dynamic mesh data using V-Mesh compression technology may be as shown in Fig. 13.

[0146] The mesh preprocessor receives the original mesh as input and generates a simplified mesh (decimated mesh). Simplification can be performed based on the target number of vertices or the target number of polygons that constitute the mesh. Parameterization can be performed on the simplified mesh to generate texture coordinates and texture connection information per vertex. Additionally, quantization of floating-point mesh information into fixed-point information can be performed. This result can be encoded as a base mesh through a static mesh encoding unit. The mesh preprocessor can perform mesh subdivision on the base mesh to generate additional vertices. Depending on the subdivision method, vertex connection information, texture coordinates, and texture coordinate connection information including the added vertices can be generated. The subdivided mesh can be fitted by adjusting the vertex positions to resemble the original mesh, thereby generating a fitted subdivided mesh.

[0147] When performing intra-encoding on the corresponding mesh frame, the base mesh generated through the mesh preprocessing unit can be compressed through the static mesh encoding unit. In this case, encoding can be performed on the connection information, vertex geometry information, vertex texture information, normal information, etc. of the base mesh. The base mesh bitstream generated through encoding is transmitted to the multiplexing unit.

[0148] When performing inter encoding for the corresponding mesh frame, a motion vector encoding unit is performed, which can calculate a motion vector between the base mesh and the reference reconstruction base mesh as input and encode the value. The motion vector encoding unit can perform prediction based on connection information using a previously encoded / decoded motion vector as a predictor, and encode a residual motion vector obtained by subtracting the predicted motion vector from the current motion vector. The motion vector bitstream generated through encoding is transmitted to the multiplexing unit.

[0149] The encoded base mesh and motion vectors can be used to generate a restored base mesh through the base mesh restoration unit.

[0150] The displacement vector calculator can perform mesh refinement on the restored base mesh. The displacement vector can be calculated as the difference in vertex positions between the refined restored base mesh and the fitted subdivision mesh generated in the preprocessing unit. As a result, the number of displacement vectors can be calculated equal to the number of vertices in the refined mesh. The displacement vector calculation unit can convert the displacement vector calculated in the 3D Cartesian coordinate system into a local coordinate system based on the normal vector of each vertex.

[0151] A displacement vector video generator can transform displacement vectors for effective encoding. The transformation can be performed by a lifting transformation, a wavelet transformation, etc., depending on the embodiment. In addition, quantization can be performed on the transformed displacement vector values, i.e., the transform coefficients. Different quantization parameters can be applied to each axis of the transform coefficients, and the quantization parameters can be derived according to the promise of the encoder / decoder. The transformed and quantized displacement vector information can be packed into a 2D image. A displacement vector video can be generated by bundling the packed 2D images for each frame, and the displacement vector video can be generated for each GoF (Group of Frame) unit of the input mesh.

[0152] A displacement vector video encoder can encode the generated displacement vector video using a video compression codec. The generated displacement vector video bitstream is transmitted to a multiplexer.

[0153] The displacement vector restored through the displacement vector restorer and the base mesh restored through the base mesh restorer and refined are restored through the mesh restorer, and the restored mesh has restored vertices, connection information between vertices, texture coordinates, and connection information between texture coordinates.

[0154] The texture map of the original mesh can be regenerated as a texture map for the restored mesh through the texture map video generation unit. The color information per vertex of the texture map of the original mesh can be assigned to the texture coordinates of the restored mesh. The regenerated texture maps for each frame can be bundled into GoF units to generate a texture map video.

[0155] The generated texture map video can be encoded using a video compression codec through a texture map video encoding unit. The texture map video bitstream generated through encoding is transmitted to a multiplexing unit.

[0156] The generated motion vector bitstream, base mesh bitstream, displacement vector bitstream, and texture map bitstream may be multiplexed into a single bitstream and transmitted to a receiver via a transmitter. Alternatively, the generated motion vector bitstream, base mesh bitstream, displacement vector bitstream, and texture map bitstream may be generated as a file with one or more track data or encapsulated into segments and transmitted to a receiver via a transmitter.

[0157] Referring to FIG. 13, a transmitting device (encoder) can encode a mesh in an intra-frame or inter-frame manner. A transmitting device according to intra-encoding can generate a base mesh, a displacement vector (displacement), and a texture map (attribute map). A transmitting device according to inter-encoding can generate a motion vector (motion), a base mesh, a displacement vector (displacement), and a texture map (attribute map). A texture map obtained from a data input unit is generated and encoded based on a restored mesh. Displacement is generated and encoded through the difference in vertex positions between the base mesh and the segmented mesh. The base mesh is generated by preprocessing, simplifying, and encoding the original mesh. Motion is generated as a motion vector for the mesh of the current frame based on the reference base mesh of the previous frame.

[0158] Fig. 14 shows a point cloud data receiving device according to embodiments.

[0159] Fig. 14 corresponds to the receiving device (110), the dynamic mesh video decoder (113), the decoder of Figs. 11-12, and / or the receiving decoding device corresponding thereto of Fig. 1. Each component of Fig. 14 corresponds to hardware, software, a processor, and / or a combination thereof. The receiving (decoding) operation of Fig. 14 may follow the reverse process of the corresponding process of the transmitting (encoding) operation of Fig. 13.

[0160] The bitstream of the received Mesh is demultiplexed into a compressed motion vector bitstream or base mesh bitstream, displacement vector bitstream, and texture map bitstream after file / segment decapsulation.

[0161] If the current mesh has inter-frame encoding applied according to the frame header information, the motion vector decoding unit can perform decoding on the motion vector bitstream. The final motion vector can be reconstructed by adding the previously decoded motion vector to the residual motion vector decoded from the bitstream using the previously decoded motion vector as a predictor.

[0162] If the current mesh has been encoded within the screen according to the frame header information, the base mesh bitstream can restore the connection information, vertex geometry information, texture coordinates, normal information, etc. of the base mesh through the static mesh encoding unit.

[0163] In the base mesh restoration unit, if the current mesh has inter-frame encoding applied, the current base mesh can be restored by adding the decoded motion vector to the reference base mesh and then performing inverse quantization. If the current mesh has intra-frame encoding applied, the static mesh decoding unit can perform inverse quantization on the decoded mesh to generate a restored base mesh.

[0164] The displacement vector bitstream can be decoded as a video bitstream using a video codec in a displacement vector video decoding unit.

[0165] In the displacement vector restoration unit, displacement vector transformation coefficients are extracted from the decoded displacement vector video, and the displacement vector is restored through the inverse quantization and inverse transformation processes. If the restored displacement vector is a value in the local coordinate system, a process of inverse transformation to the Cartesian coordinate system can be performed.

[0166] The mesh restoration unit can generate additional vertices by performing subdivision on the restored base mesh. Subdivision can generate vertex connection information, texture coordinates, and texture coordinate connection information, including the added vertices. The subdivided restored base mesh can be combined with the restored displacement vector to generate the final restored mesh.

[0167] The texture map bitstream can be decoded as a video bitstream using a video codec in a texture map video decoding unit. The restored texture map contains color information for each vertex contained in the restored mesh, and the color value of each vertex can be obtained from the texture map using the texture coordinates of the corresponding vertex.

[0168] The restored mesh and texture map are displayed to the user through a rendering process using a mesh data renderer, etc.

[0169] Referring to FIG. 14, a receiving device (decoder) can decode a mesh in an intra-frame or inter-frame manner. A receiving device according to intra-decoding can receive a base mesh, a displacement vector (displacement), and a texture map (attribute map), and decode the restored mesh and the restored texture map to render the mesh data. A receiving device according to inter-decoding can receive a motion vector (motion), a base mesh, a displacement vector (displacement), and a texture map (attribute map), and decode the restored mesh and the restored texture map to render the mesh data.

[0170] A point cloud data encoding device and method according to embodiments can encode mesh data and transmit a bitstream including the encoded mesh data. A point cloud data decoding device and method according to embodiments can receive a bitstream including mesh data and decode the mesh data. The point cloud data encoding / decoding method / device according to embodiments may be referred to as the method / device according to embodiments. The point cloud data encoding / decoding method / device according to embodiments may also be referred to as the mesh data encoding / decoding method / device according to embodiments. In addition, the term encoding / decoding method / device may be used in this document for short.

[0171] The encoding method / device according to the embodiments may include and perform operations such as a transmitting device (100) in FIG. 1, a mesh encoder (102), a file / segment encapsulator (103), a transmitter (104), a pre-processor in FIG. 2, FIG. 3, FIG. 4, FIG. 6, and FIG. 7, an encoder, an encoder in FIG. 13, an encoding operation in FIG. 15 to FIG. 21, an encoder in FIG. 22, syntax generation and bitstream generation in FIG. 25 to FIG. 27, and encoding in FIG. 28.

[0172] The decryption method / device according to the embodiments may include and perform operations such as a receiving device (110) of FIG. 1, a receiving unit (111), a file / segment decapsulator (112), a mesh decoder (113), a renderer (114), a decoder of FIG. 11 and FIG. 12, a decoder of FIG. 14, a decoding operation of FIG. 15 to FIG. 21, a decoder of FIG. 23 to FIG. 24, bitstream acquisition and syntax acquisition within a bitstream of FIG. 25 to FIG. 27, and decoding of FIG. 29.

[0173] The method and device according to the embodiments may include and perform an Angle Weighted Vertex Normal Generation Method of V-DMC.

[0174] The embodiments relate to Video-based Dynamic Mesh Compression (V-DMC), a method for compressing 3D dynamic mesh data using an existing 2D video codec. In the preprocessing stage of V-DMC, the step of generating a base mesh and the step of reconstructing the base mesh in the sub-decoder / decoder include the process of calculating normal vectors for several vertices of the mesh. The embodiments include a method of reflecting the sizes of the interior angles of surrounding triangles containing the vertex as weights in the process of calculating the normal vector. By applying this method, the accuracy of normal vector calculation can be improved compared to the current method, thereby generating a more accurate base mesh in the preprocessing stage, and a bit saving effect can be obtained in the process of converting displacement vectors into a local coordinate system in the direction of the normal vector of the reconstructed base mesh in the sub-decoder / decoder stage.

[0175] The embodiments relate to V-DMC (Video-based Dynamic Mesh Compression), a method for compressing 3D dynamic mesh data using an existing 2D video codec, and include an improvement method in the process of obtaining a normal vector for a vertex of a dynamic mesh and a method for generating and obtaining syntax and semantics information related thereto.

[0176] Recently, V-DMC technology has been actively standardizing since the CfP Response in April 2022.

[0177] Currently, in the preprocessing and encoding / decoding intermediate stages of the V-DMC standard, various meshes generated and restored calculate normal vector information for vertices when necessary, and the normal vector of one vertex of the mesh is calculated by simply adding all face normal vectors of all surrounding triangles containing the vertex to obtain the average of the face normal vectors of the vertex. However, this method causes that if there are multiple triangles with similar face normal vectors among the surrounding triangles containing the vertex, the normal vectors in the corresponding direction are added by that number, causing the normal vector to be biased in the corresponding direction. Therefore, the embodiments include a method of calculating a more accurate normal vector by multiplying the face normal vector by the internal angle of all surrounding triangles containing each vertex and adding them. In addition, the process of using this normal vector can be largely divided into two cases. First, there is a process of generating a base mesh in the preprocessing stage, and second, there is a process of calculating the normal vector of the reconstructed base mesh in the encoder / decoder and converting the displacement vector into the local coordinate system of the normal vector for the mesh.

[0178] The method according to the embodiments includes a method of multiplying the size of the inner angle of the surrounding triangles including the vertex by the normal vector of the corresponding plane as a weight and adding the result in the process of obtaining the normal vector for the vertex of the mesh at each step in the preprocessing process of generating the base mesh.

[0179] In the process of obtaining the normal vector for the vertex of the restored base mesh in the encoding / decoding process, a method is included of multiplying the size of the inner angle of the surrounding triangles containing the vertex by the normal vector of the plane and adding them as weights.

[0180] In the current V-DMC technology, the normal vectors for all vertices forming the 3D mesh being processed at that stage are calculated through the normal vector calculation unit in the pre-processing stage and various stages of the encoder / decoder, and the calculated vertex normal vectors can be used to increase compression efficiency or improve mesh accuracy.

[0181] In these processes, the method proposed is first described in exactly how it is performed in Figs. 15 to 21, etc., and then in Figs. 22 and 23 to 24, the part where the corresponding method is performed at each step of the dynamic mesh encoder / decoder is described.

[0182] Figures 15 to 21: A method for calculating a vertex normal vector based on an internal angle of a triangle according to embodiments (which can be performed in both an encoding device and / or a decoding device according to embodiments).

[0183] Figure 15 shows a method for calculating normal vectors according to embodiments.

[0184] Referring to FIG. 15, the method for calculating a normal vector according to the embodiments may include a plane normal vector calculation step; a vertex normal vector calculation step; and / or a vertex normal vector normalization step.

[0185] The normal vector calculation part of Fig. 15 is performed for all triangles that make up the mesh, and may be performed through the following steps depending on the embodiment.

[0186] First, the plane vector calculation unit calculates the plane vector for the triangle and stores it for each of the three vertices. Then, after calculating the plane vector for the next triangle, it adds it for the three vertices that make up the triangle, and accumulates and adds the plane normal vectors of the triangles that contain the same vertex. By adding the sum of the plane normal vectors of all surrounding triangles that contain a vertex of the mesh, the vertex normal vector of the vertex can be calculated.

[0187] Finally, normalization is performed on the vertex normal vectors for all vertices.

[0188] Figure 16 shows examples of triangles and plane normal vectors of triangles that constitute a mesh according to embodiments.

[0189] Referring to Fig. 16, the operation of the plane normal vector calculation unit of Fig. 15 is further explained.

[0190]

[0191]

[0192] (1)

[0193] Figure 16 is an example of triangles that make up a mesh and their plane normal vectors. Here, are three vertices of a 3D mesh forming a triangle, is a 3D vector corresponding to the edge connecting two vertices. And in the figure on the right, represents the plane normal vector of the triangle, and Equation 1 is How to find and This is an example of a method for obtaining .

[0194] Calculate the plane normal vector of a plane (triangle) consisting of three vertices. Using the coordinates of these three vertices, calculate the 3D vectors corresponding to two adjacent corners within the triangle, and then perform the cross product of these two vectors to calculate the plane normal vector of the triangle.

[0195] At this time, since the three vertices of the triangle are located on the same plane, the same plane normal vector value is calculated regardless of which two of the three vertices are used.

[0196] The operation of the vertex normal vector calculation unit of Fig. 15 is as follows:

[0197] (2)

[0198] By calculating the plane normal vectors of all surrounding triangles that contain a vertex in a 3D mesh and taking the average of them, we can find the normal vector of that vertex, and by applying the vertex normal vector instead of the plane normal vector to that vertex, we can use a more accurate normal vector value.

[0199] In the vertex normal vector calculation unit, the plane normal vectors of the corresponding triangles calculated by the plane normal vector calculation unit for each of the three vertices that make up the triangle are accumulated, added, and stored. Since the normal vector calculation unit is performed on all triangles that make up the mesh, in this process, the plane normal vectors of all surrounding triangles that include a vertex are accumulated and added to calculate the normal vector of the corresponding vertex.

[0200] Equation (2) is an example of a method for calculating a vertex normal vector, and n_adjacnet_triangles_of_vertex_x represents the number of surrounding triangles containing vertex x. represents the plane normal vector of the surrounding triangles.

[0201] Since the vertex normal vector whose cumulative sum is calculated is normalized to a unit vector with a size of 1 in the next normal vector normalization section, the added value while accumulating the plane normal vectors is the same as the average value of the plane normal vectors.

[0202] The operation of the normal vector normalization part of Fig. 15 is as follows:

[0203] In order to minimize numerical errors and make calculations easier, such as by omitting the process of dividing by the length of the vector during operations between vectors, it can be normalized to a unit vector with length 1 and the same direction.

[0204] Normalization can be performed on the vertex normal vectors of all vertices that make up the mesh calculated in the vertex normal vector calculation unit.

[0205] Depending on the embodiment, the entire normal vector calculation module can be performed as follows (normal vector calculation module).

[0206] for (int t_idx=0; t_idx < n_triangle; t_idx++){

[0207] p0_idx=triangles[t_idx][0];

[0208] p1_idx=triangles[t_idx][1];

[0209] p2_idx=triangles[t_idx][2];

[0210] face_normal[t_idx]=(positon[p1_idx]-position[p0_idx] X (position[p2_idx]-position[p0_idx]);

[0211] vertex_normal[p0_idx]+=face_normal[t_idx];

[0212] vertex_normal[p1_idx]+=face_normal[t_idx];

[0213] vertex_normal[p2_idx]+=face_normal[t_idx];

[0214] }

[0215] normalize(vertex_normal);

[0216] t_idx is the index of the triangles that make up the mesh and increases by the total number of triangles. The three vertex indices of the triangles based on the entire mesh expressed as p(0,1,2,)_idx are stored from the triangle connection information.

[0217] Calculate the cross product of the vector connecting points p1 and p0 and the vector connecting points p2 and p0 to calculate the plane normal vector of the triangle, face_normal[t_idx].

[0218] The calculated plane normal vector value is stored in vertex_normal[p(0,1,2)_idx], which is the vertex normal vector value for the three vertex indices.

[0219] Since the above process is repeated for all triangles, the vertex normal vector value for the vertex index is accumulated and added to the plane normal vector values ​​of the surrounding triangles including the vertex.

[0220] Iterate over all triangles, compute the vertex normal vector for all vertices, and then normalize all vertex normal vectors.

[0221] Figure 17 shows an example of a vertex normal vector when the mesh according to the embodiments is in the shape of a hexahedron.

[0222] Figure 17 is an example of a mesh in the shape of a cube, and the correct vertex normal vector of a point P of the cube. will be the direction in which the plane normal vectors of the surrounding triangles a, b, d containing the point P are reflected in equal proportions, and to calculate this, the plane normal vectors of triangles a, b, d You can add:

[0223] In this example, triangles b and c lie on the same plane, so the plane normal vectors of the two triangles have the same value:

[0224] Figure 18 shows an example of a vertex normal vector when the mesh according to the embodiments is in the shape of a hexahedron.

[0225] Figure 18 is an example of a case where the mesh is in the shape of a cube, and shows the vertex normal vector of a point Q of the cube. To calculate the plane normal vectors of the surrounding triangles a, b, c, d containing the point Q You can add:

[0226] Therefore, the plane normal vector of triangle b is added twice, which causes the vertex normal vector of point Q to be calculated incorrectly.

[0227] Figure 19 shows a method for calculating normal vectors according to embodiments.

[0228] To solve the above-described problem, the method according to the embodiments further includes a method for calculating an internal angle of a triangle as shown in FIG. 19.

[0229] As shown in Fig. 19, a triangle internal angle calculation unit process according to embodiments may be added to the normal vector calculation unit module according to embodiments. In this case, the product of the plane normal vector calculated by the plane normal vector calculation unit and the triangle internal angle calculated by the triangle internal angle calculation unit may be accumulated and added by the vertex normal vector calculation unit.

[0230] Figure 20 shows the triangles that constitute the mesh according to the embodiments and the internal angles in the direction of one vertex.

[0231] The method according to the embodiments calculates an interior angle of a plane (triangle) consisting of three vertices, as in the embodiment of Fig. 20. By calculating and normalizing three-dimensional vectors corresponding to two corners adjacent to a point inside the triangle and then performing the inner product of these two vectors, the cosine value of the interior angle of the corresponding point can be determined, and the interior angle value of the corresponding point can be calculated using the inverse cosine function.

[0232]

[0233]

[0234] (3)

[0235] (4)

[0236] Equations (3) and (4) are examples of calculating this. It is the interior angle for point p0, and this value is used as a weight. It calculates the interior angle from the cosine value obtained by calculating the inner product of two edges including the interior angle using the inverse cosine function. n_adjacent_triangles_of_vertex_x represents the number of surrounding triangles that include vertex x, represents the plane normal vector of the surrounding triangles. represents the interior angle of the corresponding vertex position of the i-th surrounding triangle.

[0237] At this time, the internal angles for the three vertices of the triangle may be different, so the weights for the three vertices multiplied by the plane normal vector of the triangle will be different.

[0238] When performing a triangle interior angle calculation unit according to an embodiment, the process of deriving a vertex normal vector of the entire normal vector calculation unit can be performed as follows (operation of the normal vector calculation unit with interior angle weight applied).

[0239] for (int t_idx=0; t_idx < n_triangle; t_idx++){

[0240] p0_idx=triangle[t_idx][0];

[0241] p1_idx=triangle[t_idx][1];

[0242] p2_idx=triangle[t_idx][2];

[0243] face_normal[t_idx]=(position[p1_idx]-position[p0_idx]

[0244] compute_angle_weight;

[0245] vertex_normal[p0_idx]+=face_normal[t_idx]*angle_weight[0];

[0246] vertex_normal[p0_idx]+=face_normal[t_idx]*angle_weight[0];

[0247] vertex_normal[p0_idx]+=face_normal[t_idx]*angle_weight[0];

[0248] }

[0249] normalize(vertex_normal);

[0250] t_idx is the index of the triangles that make up the mesh and increases by the total number of triangles. The three vertex indices of the triangles based on the entire mesh expressed as p(0,1,2,)_idx are stored from the triangle connection information.

[0251] Calculate the cross product of the vector connecting points p1 and p0 and the vector connecting points p2 and p0 to calculate the plane normal vector of the triangle, face_normal[t_idx].

[0252] Compute_angle_weight calculates the angle_weight, which is the internal angle of the triangle, and multiplies it by the plane normal vector face_normal and adds it to the vertex normal vector vertex_normal.

[0253] The calculated plane normal vector value is stored in vertex_normal[p(0,1,2)_idx], which is the vertex normal vector value for the three vertex indices.

[0254] Since the above process is repeated for all triangles, the vertex normal vector value for the vertex index is accumulated and added to the plane normal vector values ​​of the surrounding triangles including the vertex.

[0255] Iterate over all triangles, compute the vertex normal vector for all vertices, and then normalize all vertex normal vectors.

[0256] In addition, according to embodiments, the process of deriving the interior angles of the triangle interior angle calculation unit can be performed as follows (triangle interior angle calculation unit).

[0257] p0=position[p0_idx], p1=position[p1_idx], p2=position[p2_idx]

[0258] edge01=p1-p0; edge02=p2-p0;

[0259] edge12=p2-p1; edge10=p0-p1;

[0260] edge20=p0-p2; edge21=p1-p2;

[0261]

[0262] edge01.normalize(); edge02.normalize();

[0263] edge12.normalize(); edge10.normalize();

[0264] edge20.normalize(); edge21.normalize();

[0265] dot[0]=edge01[0]*edge02[0]+edge01[1]*edge02[1]+edge01[2]*edge02[2];

[0266] dot[1]=edge10[0]*edge12[0]+edge10[1]*edge12[1]+edge10[2]*edge12[2];

[0267] dot[2]=edge20[0]*edge21[0]+edge20[1]*edge21[1]+edge20[2]*edge21[2];

[0268] for (int i=0; i<3; i++){

[0269] if(dot[i]<=-1)

[0270] angle_weight[i]=acos(-1);

[0271] else if(dot[i]>=1)

[0272] angle_weight[i]=acos(1);

[0273] else

[0274] angle_weight[i]=acos(dot[i]);

[0275] }

[0276] After obtaining the coordinates of the three points of the triangle and the vector edges representing the corners through them, the vectors are normalized to a vector with a size of 1 so that the inner product can be calculated using only the coordinate values ​​of the vectors. The cosine value of the interior angle is calculated through the dot of the inner product calculation using the normalized edge vectors, and the size of the interior angle is calculated as an angle weight using the inverse cosine function.

[0277] Additionally, depending on the embodiments, a clipping operation may be used to limit the inner product calculation value to be entered into the inverse cosine function to between -1 and 1, since the inner product calculation value dot is outside the cosine range when it is less than -1 or greater than 1.

[0278] Figure 21 shows an example of a vertex normal vector when the mesh according to the embodiments is in the shape of a hexahedron.

[0279] Figure 21 is an example of a case where the mesh is in the shape of a cube, and shows the correct vertex normal vector of a point P of the cube. will be the direction in which the plane normal vectors of the surface containing the surrounding triangles a, b, d containing the point P are reflected in equal proportions, and to calculate this, the plane normal vectors of triangles a, b, c, d And the size of the interior angle including each point can be multiplied by the weight and added.

[0280]

[0281] For example, the interior angles of surrounding triangles can be used as weights.

[0282] In the above example Therefore, the sum of the plane normal vectors of triangle b and triangle c is reflected in the vertex normal vector in the same ratio as the plane normal vectors of triangle a and triangle d.

[0283] Below, the operation according to the above-described embodiments is described from the perspective of an encoding device and a decoding device.

[0284] Fig. 22 shows a dynamic mesh encoding device according to embodiments.

[0285] The encoding device of Fig. 22 can perform operations such as Fig. 1 transmitting device (100), mesh encoder (102), file / segment encapsulator (103), transmitter (104), Figs. 2, 3, 4, 6, and 7 pre-processor, encoder, Fig. 13 encoder, Fig. 15 to 21 encoding operation, Figs. 25 to 27 syntax generation and bitstream generation, and Fig. 28 encoding.

[0286] The encoding device of FIG. 22 may be composed of a memory and at least one processor. Each component of the encoding device of FIG. 22 may correspond to software, hardware, a processor, and / or a combination thereof.

[0287] The mesh simplification unit receives the original mesh as input and simplifies it to create a base mesh.

[0288] Simplification of the input source mesh can be performed by targeting the number of vertices or target number of faces.

[0289] One of the criteria for selecting vertices to be removed during the simplification process is to select the direction of the normal vector.

[0290] In some embodiments, a flag for generating normal vector angle weights (generate_angle_weight_normal_flag) may be obtained from a bitstream, and in the process of calculating the normal vector of each vertex of a mesh, the internal angles of all surrounding triangles including the vertex and the positions containing the vertex within the triangles may be reflected as weights for calculation.

[0291] The mesh parameterization unit performs parameterization to generate texture coordinates (UV coordinates) and texture connection information per vertex of the base mesh.

[0292] The mesh subdivision unit can generate additional vertices by performing subdivision on the base mesh. Depending on the subdivision method, geometric information connection information, texture coordinate connection information, and texture coordinates can be implicitly derived and generated.

[0293] Mesh refinement can be performed by user parameters or decoder / decoder commitments, and may be performed by refining the vertices of the base mesh, depending on the embodiment. , perform subdivision 1 to create a new vertex The vertices generated by performing the subdivision When defined as can be defined as follows:

[0294]

[0295] After calculating the normal vector of the mesh that has been subdivided in the n-th subdivision process, the interpolated normal vector can be used.

[0296] In an embodiment, the generate_angle_weight_normal_flag may be obtained from a bitstream and, in the process of calculating the normal vector of each vertex of a subdivided mesh, the internal angles of all surrounding triangles containing the vertex and the positions containing the vertex within the triangles may be reflected as weights for calculation.

[0297] The mesh fitting part adjusts the vertex positions so that the subdivided mesh resembles the original mesh.

[0298] In some embodiments, the generate_angle_weight_normal_flag may be parsed to calculate the normal vector of each vertex of the mesh during the fitting process, and the internal angles of all surrounding triangles that include the vertex and the positions that include the vertex within the triangles may be reflected as weights for calculation.

[0299] Depending on the embodiment, the mesh simplification unit, mesh parameterization unit, mesh refinement unit, and mesh fitting unit may be omitted, and if the processes are omitted, the original mesh may be applied as input to the mesh quantization unit.

[0300] At this time, coordinate information of the original mesh can be applied as input to the displacement vector calculation unit, and depending on the embodiment, the displacement vector encoding process (displacement vector calculation unit, displacement vector coordinate system conversion unit, displacement vector encoding unit) can be omitted.

[0301] The mesh quantization unit can quantize geometric information (x, y, z) in floating-point form or / and texture coordinates (u, v) or / and normal information (nx, ny, nz) into fixed-point form.

[0302] Depending on the embodiment, quantization for certain components may be omitted.

[0303] The static mesh encoding unit performs encoding on the connection information, vertex geometry information, vertex texture coordinates, normal information, etc. of the base mesh.

[0304] Motion vector encoding can be performed by calculating motion vectors using the reference restoration base mesh and the current base mesh as input.

[0305] The motion vector encoding unit can perform prediction based on connection information using a previously encoded / decoded motion vector as a predictor, and perform entropy encoding on a residual motion vector obtained by subtracting a predicted motion vector from a current motion vector.

[0306] Motion vector encoding can be performed on a vertex basis or a subgroup basis, depending on the embodiment.

[0307] The displacement vector calculation unit calculates the displacement vector between the fitted subdivision mesh and the reconstructed base mesh generated by the base mesh decoding unit.

[0308] The displacement vector calculation unit can calculate a number of displacement vectors equal to the number of vertices of the subdivided mesh.

[0309] The displacement vector coordinate system transformation unit can transform the vertex displacement vector of the subdivided restored base mesh calculated in the (x, y, z) space into a local coordinate system consisting of (normal, tangential, bi-tangential) by calculating the tangent and bi-tangent vectors based on the normal vector of each vertex.

[0310] At this time, the normal vector can be calculated for each subdivided vertex based on the geometric information or / and connection information of the surrounding vertices.

[0311] In some embodiments, the generate_angle_weight_normal_flag may be obtained from the bitstream and, in the process of calculating the normal vector of each vertex, the internal angles of all surrounding triangles including the vertex and the positions containing the vertex within the triangles may be reflected as weights for calculation.

[0312] Depending on the embodiment, only the normal component among the (normal, tangential, bi-tangential) coordinates may be encoded, and this may always be encoded only on the normal component when a coordinate system transformation is applied according to the encoder / decoder agreement, or the encoder may decide to signal a 1-bit flag (onlyNormFlag).

[0313] Whether or not to transform the displacement vector coordinate system is determined by the encoder / decoder agreement, or the coordinate system transformation flag (applyLocalCoord) is transmitted in units such as sequence, GOF (Group of frame), frame, and sub-mesh to determine whether or not to transform the coordinate system.

[0314] The base mesh restoration unit performs restoration of the base mesh according to the current mesh encoding type (inter-screen encoding or intra-screen encoding).

[0315] When inter-screen encoding is performed, the current base mesh can be generated by adding the restored motion vector to the reference restored base mesh.

[0316] At this time, if the motion vector is not quantized, the motion vector restoration process is omitted, and the current base mesh can be restored using the motion vector calculated by the motion vector encoding unit.

[0317] When in-screen encoding is performed, the current base mesh can be restored by performing inverse quantization on the quantized base mesh through the mesh quantization unit.

[0318] The base mesh inverse quantization unit performs inverse quantization using inputs such as restoration geometric information (x, y, z) of the restoration base mesh or / and texture coordinates (u, v) or / and normal information (nx, ny, nz).

[0319] In some embodiments, dequantization for certain components may be omitted.

[0320] The displacement vector restoration unit is packed into a 2D image / video, decodes the encoded bitstream through a 2D video encoder, and performs depacking.

[0321] The quantized transformation coefficients for which inverse packing has been performed are dequantized and inversely transformed to calculate the restored displacement vector.

[0322] The mesh restoration unit performs subdivision on the restored base mesh that has been restored by performing inverse quantization in the base mesh inverse quantization unit, thereby generating subdivided vertex position information, texture coordinates, and connection information.

[0323] Restored vertex position information is generated by adding the restored displacement vector to the detailed vertex position information.

[0324] According to an embodiment, before adding a restoration displacement vector to the subdivided vertex position information, a vertex normal vector of the subdivided restoration base mesh can be calculated and a displacement vector converted to a local coordinate system (normal, tangent, bitangent) based on this vertex normal vector can be added.

[0325] Depending on the embodiment, in the process of calculating the normal vector of each vertex by parsing the generate_angle_weight_normal_flag in the same way as in the displacement vector coordinate system transformation section, the internal angles of all surrounding triangles including the vertex and the positions containing the vertex within the triangles can be reflected as weights for calculation.

[0326] The texture map generation unit generates a texture map of the restoration mesh through the relationship between the texture coordinates and connection information of the restoration mesh and the texture map of the original mesh.

[0327] The texture map encoding unit stacks the texture maps generated by the texture map generation unit in the frame order of the mesh to form a texture map video, and encodes this through a 2D video encoder.

[0328] Depending on the embodiment, if the color space of the texture map is RGB444, encoding may be performed after conversion to a color space such as YUV420 or YUV444.

[0329] Fig. 23 shows a dynamic mesh decoding device according to embodiments.

[0330] The decoding device of Fig. 23 can perform operations such as the receiving device (110) of Fig. 1, the receiving unit (111), the file / segment decapsulator (112), the mesh decoder (113), the renderer (114), the decoder of Figs. 11 and 12, the decoder of Fig. 14, the decoding operation of Figs. 15 to 21, the bitstream acquisition and syntax acquisition within the bitstream of Figs. 25 to 27, and the decoding operation of Fig. 29.

[0331] The decryption device of Fig. 23 may be configured with a memory and at least one processor. The operation of the decryption device of Fig. 23 may follow the reverse process of the operation of the encoding device of Fig. 22.

[0332] Each component of the decryption device of FIG. 23 may correspond to software, hardware, a processor, and / or a combination thereof.

[0333] The motion vector decoding unit can perform motion vector decoding when the current mesh performs inter-screen prediction.

[0334] A residual motion vector can be decoded in units of vertices or subblocks through a motion vector bitstream, and a motion vector can be decoded by adding it to the residual motion vector by performing prediction based on connection information using a previously decoded motion vector as a predictor.

[0335] The static mesh decoding unit can restore the connection information, vertex geometry information, vertex texture coordinates, normal information, etc. of the base mesh.

[0336] The base mesh restoration unit can restore the current base mesh by adding a motion vector to the reference base mesh and then performing inverse quantization if the current base mesh is encoded based on the reference mesh.

[0337] If the current base mesh is decoded through a static mesh encoder, inverse quantization is performed to generate a restored base mesh.

[0338] Depending on the embodiment, the inverse quantization unit may be omitted.

[0339] The mesh subdivision unit can generate additional vertices by performing subdivision on the base mesh. Depending on the subdivision method, geometric information connection information, texture coordinate connection information, and texture coordinates can be implicitly derived and generated.

[0340] The mesh subdivision section can perform subdivision using methods such as mid-edge, Loop, and Catmul&Clark, depending on the embodiment.

[0341] Mesh refinement can be performed by user parameters or decoder / decoder commitments, and may be performed by refining the vertices of the base mesh, depending on the embodiment. , perform subdivision 1 to create a new vertex , …, the vertices generated by performing n-th subdivision When defined as can be defined as follows:

[0342]

[0343] Figure 24 shows a mesh restoration method according to embodiments.

[0344] Figure 24 illustrates the mesh restoration method of Figure 23 in more detail.

[0345] The displacement vector coordinate system inverse transformation part can be performed in two forms depending on the embodiment of the restored base mesh. First example: restored base mesh normal calculation step; restored base mesh refinement step; and refinement vertex normal interpolation step, Second example: restored base mesh refinement step; refinement vertex normal calculation step;

[0346] As in the first example, a normal vector per vertex can be calculated based on the restoration vertex position information of the restoration base mesh according to an embodiment, and a normal value of a newly created vertex can be assigned by interpolating the vertex normal vector of the calculated restoration base mesh for the vertex additionally created through the subdivision process.

[0347] At this time, depending on the embodiment, the normal vector can be calculated for each subdivided vertex based on geometric information and / or connection information of the surrounding vertices, and generate_angle_weight_normal_flag can be obtained from the bitstream to calculate the normal vector of each vertex by reflecting the internal angles of all surrounding triangles including the vertex and the positions including the vertex within the triangles as weights.

[0348] In this case, interpolation can be performed by averaging or distance-based weighting the normal information of the base mesh used for subdivision.

[0349] As in the second example, after performing subdivision on the restored base mesh according to the embodiment, normal vectors can be calculated for the vertices generated through the subdivision section and the vertices of the base mesh.

[0350] At this time, depending on the embodiment, the normal vector can be calculated for each subdivided vertex based on the geometric information and / or connection information of the surrounding vertices, and generate_angle_weight_normal_flag can be additionally parsed to calculate the normal vector of each vertex, and the internal angles of all surrounding triangles including the vertex and the positions including the vertex within the triangles can be reflected as weights.

[0351] The following formula can be used to inversely transform a displacement vector in a local coordinate system consisting of (normal, tangential, bi-tangential) by calculating the tangential and bi-tangential vectors perpendicular to the normal vector calculated per vertex in the (x, y, z) coordinate space. The following formula can be used to inversely transform a displacement vector coordinate system from a local coordinate system to the (x, y, z) coordinate system.

[0352]

[0353] The displacement vector coordinate system inverse transformation unit can perform inverse transformation of the restored displacement vector, which has been inversely quantized into the local coordinate system, into the (x, y, z) coordinate axes when the coordinate system transformation flag (applyLocalCoord) parsed by sequence or GoF (group of frame) or frame or sub-mesh unit is 1.

[0354] Depending on the embodiment, it is always possible to perform coordinate system inversion without sending flags.

[0355] The mesh restoration unit calculates the final vertex position information of the restored mesh by adding the displacement vector restored by the displacement vector restoration unit to the vertices generated through the subdivision process in the mesh refinement unit.

[0356] Depending on the embodiment, the vertex positions of the final restored mesh can be calculated by adding the restored displacement vector to the vertices of the refined mesh using the following formula.

[0357] recon_point_position(v)+=

[0358] The texture map decoding unit may be a process of receiving a texture map bitstream as input and decoding the texture map.

[0359] Texture map decoder types include video decoder, zero run length decoder, and arithmetic decoder.

[0360] Depending on the embodiment, color space conversion of the texture map can be performed.

[0361] The Fig. 23 encoder can encode mesh data and generate parameter information (which may be referred to as signaling information, syntax elements, etc.). The Fig. 23 encoder can generate a bitstream including the encoded mesh data and parameter information. Conversely, the Fig. 24 decoder can obtain parameter information within the bitstream and decode the mesh data based on the parameter information. Hereinafter, the syntax of the signaling information included within the bitstream will be described with reference to each drawing.

[0362] Depending on the embodiment, parameter information can be defined in units of sequence, frame, and mesh patch, and the corresponding syntax is as follows.

[0363] FIG. 25 illustrates the V-DMC extension syntax of an atlas sequence parameter set in a bitstream according to embodiments.

[0364] As shown in Fig. 25, angle weighted normal generation at the sequence level is applied to assign internal angle weights according to the sequence (Example 1), and related information can be defined in the atlas sequence parameter set of the bitstream.

[0365] FIG. 26 illustrates the V-DMC extension syntax of an atlas frame parameter set within a bitstream according to embodiments.

[0366] As shown in Fig. 26, angle weighted normal generation can be applied at the frame level to assign internal angle weights according to the frame (Example 2), and related information can be defined in the atlas frame parameter set of the bitstream.

[0367] Figure 27 shows the syntax of a mesh patch data unit in a bitstream according to embodiments.

[0368] As shown in Fig. 27, angle weighted normal generation is applied at the mesh patch level to assign internal angle weights according to the mesh patch (Example 3), and related information can be defined in the mesh patch data unit of the bitstream.

[0369] The common semantics of the syntax elements defined in Figures 25 to 27 are as follows.

[0370] generate_angle_weight_normal_flag: This flag indicates whether to calculate vertex normal vectors with internal angle weights. For example, if it is 0, internal angles are not calculated or weighted, and if it is 1, internal angles are calculated and weighted.

[0371] normalize_flag: A flag indicating whether to perform normalization on the normal vector. For example, if it is 0, normalization is not performed, and if it is 1, normalization is performed.

[0372] n_triangle: Indicates the total number of triangles that make up the mesh.

[0373] t_idx: Indicates the index of the current triangle among all triangles that make up the mesh. For example, t_idx has a value of 0 to n_triangle.

[0374] p0_idx, p1_idx, p2_idx: Indicates the indices of the three vertices of the current triangle based on the entire mesh.

[0375] triangles[t_idx][i]: The index of the i-th vertex of the t_idx-th triangle that makes up the mesh, where i has the values ​​0, 1, and 2.

[0376] face_normal[t_idx]: Represents the plane normal vector of the current triangle.

[0377] position[p_idx]: Indicates the coordinate values ​​(x, y, z) of the p_idxth vertex.

[0378] vertex_normal[p_idx]: Represents the vertex normal vector value for the p_idxth vertex, which is accumulated by adding the plane vectors of the surrounding triangles including the p_idxth vertex.

[0379] angle_weight[i]: Indicates the interior angle weight value of the ith vertex in the triangle. For example, i can have values ​​of 0, 1, or 2.

[0380] edgeij: Represents the edge vector connecting pi and pj. For example, edgeij=pj-pi, where i and j have values ​​of 0, 1, and 2.

[0381] dot[i]: The inner product of two edges. This represents the cosine value of the inner angle of a triangle. For example, i can have values ​​of 0, 1, or 2.

[0382] acos(n): Represents the value of the inverse cosine function for n. The result is angle_weight.

[0383] applyLocalCoord: A flag indicating whether to transform the displacement vector to the local coordinate system. 0 indicates the (x, y, z) coordinate system, and 1 indicates the (n, t, b) coordinate system.

[0384] onlyNormFlag: A 1-bit flag indicating whether to encode the 1D displacement vector (normal component). If 0, decoding is performed on the displacement vector of (n, t, b), and if 1, decoding is performed on the 1D displacement value of the normal component.

[0385] dispEncType: Indicates a flag or index for determining the displacement vector decoding method. Depending on the parsed dispEncType: , displacement vector decoding can be performed through a 2D video codec, zero-run length decoding, or arithmetic decoding.

[0386] profileToolIdx: The decoding method can be determined based on the profile defined in the decoder / sub-decoder. For displacement vectors, decoding can be performed using a 2D video codec, zero-run length decoding, or arithmetic decoding, depending on profileToolIdx. If the displacement vector decoding method is determined through profileToolIdx, dispEncType can be omitted.

[0387] lodCount: Indicates the number of mesh subdivision levels. For example, if lodCount=3, the mesh contains subdivision levels 0, 1, and 2.

[0388] maxLOD: Indicates the maximum mesh subdivision level. If lodCount=3, maxLOD has a value of 2.

[0389] dispCoeff[v]: Represents the displacement vector value of vertex v.

[0390] Figure 28 shows an encoding method according to embodiments.

[0391] The encoding method according to the embodiments may include a step of encoding a base mesh of mesh data (S2800); a step of encoding a displacement of mesh data (S2810); and / or a step of encoding an attribute of mesh data (S2820).

[0392] The encoding method / device according to the embodiments may include and perform operations such as a transmitting device (100) in FIG. 1, a mesh encoder (102), a file / segment encapsulator (103), a transmitter (104), a pre-processor in FIG. 2, FIG. 3, FIG. 4, FIG. 6, and FIG. 7, an encoder, an encoder in FIG. 13, an encoding operation in FIG. 15 to FIG. 21, an encoder in FIG. 22, syntax generation and bitstream generation in FIG. 25 to FIG. 27, and encoding in FIG. 28.

[0393] The step of encoding the base mesh (S2800); the step of encoding the displacement of the mesh data (S2810); and / or the step of encoding the attribute of the mesh data (S2820) may follow the description of the encoding operation described above.

[0394] Referring to Fig. 22 encoding (mesh simplification based on interior angle weights), the base mesh can be generated based on normal vectors generated based on weights related to interior angles for triangles for vertices of the mesh data.

[0395] Referring to Fig. 22 encoding (mesh refinement based on interior angle weights), the base mesh can be refined based on weights associated with the interior angles of triangles relative to the vertices of the base mesh.

[0396] Referring to Fig. 22 encoding (mesh fitting based on interior angle weights), the positions of vertices of a subdivided mesh can be adjusted based on weights associated with the interior angles of triangles for the vertices of the subdivided mesh.

[0397] Referring to Fig. 22 encoding (inner angle-based displacement coordinate system transformation), the step of encoding the displacement may include: generating a displacement based on the refined mesh and the restored base mesh, and transforming the coordinate system of the displacement based on weights related to the inner angles of triangles for vertices included in at least one of the refined mesh or the restored base mesh.

[0398] The encoding method may be performed by an encoding device. The encoding device includes a memory; and at least one processor connected to the memory; wherein the at least one processor may be configured to: encode a base mesh of mesh data; encode a displacement of the mesh data; and encode an attribute of the mesh data.

[0399] Embodiments further include a computer-readable storage medium storing a bitstream generated by the method of FIG. 28.

[0400] Embodiments further include a method comprising: obtaining a bitstream for mesh data, the bitstream being generated based on: encoding a base mesh of the mesh data; encoding a displacement of the mesh data; and encoding an attribute of the mesh data; and transmitting data including the bitstream.

[0401] Figure 29 shows a decryption method according to embodiments.

[0402] A decoding method according to embodiments may include a step of decoding a base mesh within a bitstream (S2900); a step of decoding a displacement within a bitstream (S2910); and / or a step of decoding an attribute within a bitstream (S2920).

[0403] The decryption method of Fig. 29 can follow the reverse process of the encoding method of Fig. 28.

[0404] The decoding method of Fig. 29 may include operations such as the receiving device (110) of Fig. 1, the receiving unit (111), the file / segment decapsulator (112), the mesh decoder (113), the renderer (114), the decoder of Fig. 11 and Fig. 12, the decoder of Fig. 14, the decoding operation of Figs. 15 to 21, the decoder of Figs. 23 to 24, the bitstream acquisition and the syntax acquisition within the bitstream of Figs. 25 to 27. The step of decoding the base mesh (S2900), the step of decoding the displacement (S2910), and the step of decoding the attribute (S2920) refer to the description of the decoding operation described above.

[0405] In relation to the mesh restoration part of Fig. 23 and / or the normal vector calculation (application of interpolation and surrounding triangle angle weighting) of Fig. 24, the step of decoding the base mesh (S2900) includes: generating a normal vector for a vertex based on a vertex of the base mesh, generating a new vertex for the base mesh, and generating a normal vector for the new vertex, wherein the normal vector for the new vertex is generated by interpolating the normal vector for the vertex, and the normal vector for the new vertex can be generated based on weights related to interior angle information for surrounding triangles of the new vertex.

[0406] In relation to the mesh restoration part of Fig. 23 and the normal vector calculation (surrounding triangle angle weight) of Fig. 24, the step of decoding the base mesh (S2900) includes: generating a vertex for the base mesh, and based on the weights related to the interior angle information of the surrounding triangles of the vertex in the base mesh, the normal vector of the vertex can be generated.

[0407] In relation to the mesh restoration part of Fig. 23, the coordinate system of the displacement is inversely transformed based on the normal vector, and the position of the vertex can be restored based on the displacement.

[0408] With respect to generate_angle_weight_normal_flag commonly included in FIGS. 25 to 27, the bitstream may include information indicating whether the normal vector of a vertex is generated based on a weight related to the inner angle.

[0409] With respect to the method for calculating the internal angle described in Fig. 19, the decryption method further includes a step of generating a normal vector with respect to a vertex of the base mesh; and the step of generating the normal vector may include: generating a plane normal vector of a triangle with respect to the vertex, and generating the vertex normal vector based on the plane normal vector and the internal angle of the triangle with respect to the vertex.

[0410] The decryption method may be performed by a decryption device. The decryption device includes a memory; and at least one processor connected to the memory; wherein the at least one processor may be configured to: decode a basemesh within a bitstream; decode a displacement within the bitstream; and decode an attribute within the bitstream.

[0411] The method and device according to the embodiments provide the following technical effects.

[0412] The embodiments can provide a method for improving the calculation of a vertex normal vector for a vertex of a 3D mesh performed in V-DMC. Currently, in the preprocessing process and the mesh sub / decoder, when calculating a vertex normal vector, the average of the planar normal vectors of the surrounding triangles that include the vertex is simply added together. If the triangles on a plane are divided into multiple pieces, the planar normal vector in the corresponding direction should originally be added only once to calculate the correct vertex normal vector, but if it is added multiple times, the influence of the direction on the vertex normal vector increases. The embodiments use a method of multiplying the interior angle of the position containing the vertex for which the vertex normal vector of each triangle is to be calculated by a weight and then adding it when adding the planar normal vectors of adjacent triangles. This allows for the calculation of more accurate vertex normal vectors, improves the performance of the base mesh in the preprocessing process, and reduces the bit amount of the displacement vector in the sub / decoder.

[0413] The embodiments have been described in terms of methods and / or devices, and the descriptions of methods and devices may be applied complementarily.

[0414] For the convenience of explanation, each drawing has been described separately, but it is also possible to design a new embodiment by combining the embodiments described in each drawing. In addition, designing a computer-readable recording medium having a program recorded thereon for executing the previously described embodiments, as needed by a person skilled in the art, also falls within the scope of the embodiments. 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 the embodiments so that various modifications can be made. 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 can be made by a person skilled in the art to which the present invention pertains without departing from the gist of the embodiments claimed in the claims, and such modifications should not be understood individually from the technical idea or prospect of the embodiments.

[0415] 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. According to embodiments, the components according to the embodiments may be implemented by separate chips. According to embodiments, 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.

[0416] 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”.

[0417] 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 "first user input signal" and "second user input signal" are both user input signals, they do not mean the same user input signals unless the context clearly indicates otherwise.

[0418] 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 terms. The expression “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.

[0419] Additionally, the operations according to the embodiments described in this document may be performed by a transceiver device including a memory and / or a processor according to the embodiments. The memory may store programs for processing / controlling the operations according to the embodiments, and the processor may control various operations described in this document. The processor 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 the processor or in the memory.

[0420] Meanwhile, the operations according to the embodiments described above may be performed by a transmitting device and / or a receiving device according to the embodiments. The transmitting / receiving device may include a transmitting / receiving unit for transmitting and receiving media data, a memory for storing instructions (program code, algorithm, flowchart, and / or data) for a process according to the embodiments, and a processor for controlling the operations of the transmitting / receiving device.

[0421] The processor may be referred to as a controller or the like, and may correspond to, for example, hardware, software, and / or a combination thereof. The operations according to the above-described embodiments may be performed by the processor. Furthermore, the processor may be implemented as an encoder / decoder or the like for the operations of the above-described embodiments.

[0422] As described above, the relevant contents have been described in the best form for carrying out the embodiments.

[0423] As described above, the embodiments may be applied in whole or in part to a point cloud data transmission and reception device and system.

[0424] Those skilled in the art may make various changes or modifications to the embodiments within the scope of the embodiments.

[0425] Embodiments may include modifications / changes, which do not depart from the scope of the claims and their equivalents.

Claims

1. Step of decoding the base mesh in the bitstream; A step of decoding displacement within the bitstream; and A step of decoding an attribute within the bitstream; comprising: How to decrypt.

2. In paragraph 1, The steps for decoding the above base mesh are: Generate a normal vector for the vertex based on the vertex of the base mesh, Generating a new vertex for the above base mesh and generating a normal vector for the new vertex, The normal vector for the new vertex is generated by interpolating the normal vector for the vertex, The normal vector for the new vertex is generated based on the weights related to the interior angle information of the surrounding triangles of the new vertex. How to decrypt.

3. In paragraph 1, The steps for decoding the above base mesh are: Including generating vertices for the above base mesh, Based on the weights related to the interior angle information of the surrounding triangles of the vertex in the base mesh, the normal vector of the vertex is generated. How to decrypt.

4. In paragraph 2 or 3, Based on the above normal vector, the coordinate system of the above displacement is inversely transformed, The position of the vertex is restored based on the above displacement. How to decrypt.

5. In paragraph 1, The bitstream includes information indicating whether the normal vector of the vertex is generated based on a weight related to the interior angle. How to decrypt.

6. In paragraph 1, the method: A step of generating a normal vector for a vertex of the base mesh; further comprising: The steps to generate the above normal vector are: Generate a plane normal vector of the triangle with respect to the above vertex, generating a vertex normal vector based on the plane normal vector and the interior angle of the triangle with respect to the vertex, How to decrypt.

7. Memory; and At least one processor connected to the memory; wherein the at least one processor comprises: Decode the basemesh within the bitstream; Decoding displacements within the above bitstream; and configured to decode an attribute within the above bitstream; How to decrypt.

8. Step of encoding the base mesh of mesh data; a step of encoding the displacement of the above mesh data; and A step of encoding attributes of the above mesh data; comprising; Encoding method.

9. In paragraph 8, The above base mesh is generated based on a normal vector generated based on a weight related to the interior angle of a triangle for the vertex of the above mesh data. Encoding method.

10. In paragraph 8, The above base mesh is subdivided based on the weights related to the interior angles of triangles for the vertices of the above base mesh. Encoding method.

11. In paragraph 10, Based on the weights associated with the interior angles of triangles for the vertices of the above-detailed mesh, the positions of the vertices of the above-detailed mesh are adjusted. Encoding method.

12. In paragraph 8, The steps for encoding the above displacement are: Generate displacements based on the refined mesh and restored base mesh, Including transforming the coordinate system of the displacement based on a weight related to the interior angle of a triangle for a vertex included in at least one of the refined mesh or the restored base mesh, Encoding method.

13. Memory; and At least one processor connected to the memory; wherein the at least one processor comprises: Encode the base mesh of mesh data; Encoding the displacement of the above mesh data; and Encoding attributes of the above mesh data; configured to do so; Encoding device.

14. A computer-readable storage medium storing a bitstream generated by the method according to Article 8.

15. Step of obtaining bitstream for mesh data, The bitstream is generated based on the steps of encoding a base mesh of the mesh data; encoding a displacement of the mesh data; and encoding an attribute of the mesh data; and A method comprising the step of transmitting data including the bitstream.

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