Mesh data transmission device, mesh data transmission method, mesh data reception device, and mesh data reception method

Abstract

A mesh data decoding method according to embodiments may comprise the steps of: decoding a base mesh in a bitstream; decoding displacement data in the bitstream; and decoding attribute data in the bitstream, wherein the step of decoding the base mesh includes subdividing the base mesh by the number of subdivisions corresponding to a specific LoD level, and the step of decoding the displacement data includes decoding, on the basis of a video codec, displacement data included in the bitstream up to the specific LoD level according to the number of subdivisions.

Description

Mesh data transmission device, mesh data transmission method, mesh data reception device, and mesh data reception method

[0001] The embodiments provide a method for providing 3D content to provide users with various services such as VR (Virtual Reality), AR (Augmented Reality), MR (Mixed Reality), and autonomous driving services.

[0002] Among 3D content, point cloud data and mesh data are collections of points in 3D space. However, the sheer number of points in 3D space makes it difficult to generate point cloud or mesh data.

[0003] That is, there is a problem that a lot of processing is required to transmit and receive 3D data with a large amount of points, such as point cloud data or mesh data.

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

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

[0006] A technical problem according to embodiments is to provide a device and method for efficiently performing encoding and decoding of mesh data.

[0007] 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.

[0008] 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 displacement data in the bitstream, and a step of decoding attribute data in the bitstream.

[0009] According to embodiments, the step of decoding the base mesh may perform subdivision of the base mesh a number of times corresponding to a specific LoD (Level of Detail) level.

[0010] According to embodiments, the step of decoding the displacement data may include a step of decoding displacement data included in the bitstream based on a video codec up to a specific LoD level according to the number of subdivisions, a step of depacking displacement data decoded up to the specific LoD level, a step of dequantizing displacement data depacked up to the specific LoD level, and a step of deconverting displacement data dequantized up to the specific LoD level.

[0011] According to embodiments, the method may further include a step of checking whether decoding function support is possible up to the specific LoD level.

[0012] According to embodiments, whether or not decoding function support is possible up to the specific LoD level can be determined based on information indicating whether or not decoding is possible up to the specific LoD level included in the signaling information.

[0013] According to embodiments, the signaling information may be an atlas sequence parameter set.

[0014] According to embodiments, when texture map and displacement data are packed into one frame and encoded into video and received, whether or not decoding function support is possible up to the specific LoD level can be derived based on whether or not scalability function support is possible.

[0015] According to embodiments, when the displacement data is encoded and received based on a video codec, whether or not support for a decoding function up to the specific LoD level is possible can be derived based on whether or not LoD-based displacement data can be extracted by packing each LoD level.

[0016] According to embodiments, a decoding device includes a memory and at least one processor connected to the memory, wherein the at least one processor can be configured to decode a basemesh within a bitstream, decode displacement data within the bitstream, and decode attribute data within the bitstream.

[0017] According to embodiments, the at least one processor may include a subdivision unit that performs subdivision on the base mesh a number of times corresponding to a specific LoD (Level of Detail) level.

[0018] According to embodiments, the at least one processor may further include a displacement decoding unit that decodes displacement data included in the bitstream based on a video codec up to a specific LoD level according to the number of subdivisions, a depacking unit that depacks displacement data decoded up to the specific LoD level, a dequantization unit that dequantizes displacement data depacked up to the specific LoD level, and an inverse transformation unit that inversely transforms displacement data dequantized up to the specific LoD level.

[0019] According to embodiments, the encoding method may include a step of encoding a base mesh of mesh data, a step of encoding displacement data of the mesh data, and a step of encoding attribute data of the mesh data.

[0020] According to embodiments, the encoding device includes a memory and at least one processor connected to the memory, wherein the at least one processor can be configured to encode a base mesh of the mesh data, encode displacement data of the mesh data, and encode attribute data of the mesh data.

[0021] According to embodiments, a computer-readable storage medium can store a bitstream generated by an encoding method.

[0022] According to embodiments, a transmission method may include a step of obtaining a bitstream for mesh data, the bitstream being generated based on a step of encoding a base mesh of the mesh data, a step of encoding displacement data of the mesh data, and a step of encoding attribute data of the mesh data, and a step of transmitting data including the bitstream.

[0023] The mesh data transmission method, mesh data transmission device, mesh data reception method, and mesh data reception device according to the embodiments can provide a quality 3D service.

[0024] The mesh data transmission method, mesh data transmission device, mesh data reception method, and mesh data reception device according to the embodiments can achieve various video codec methods.

[0025] The mesh data transmission method, mesh data transmission device, mesh data reception method, and mesh data reception device according to the embodiments can provide general-purpose 3D content such as autonomous driving services.

[0026] The mesh data transmission method, mesh data transmission device, mesh data reception method, and mesh data reception device according to the embodiments can support a function of performing decoding at various mesh resolutions based on LoD levels by extracting only a portion of the mesh bitstream of LoD (or resolution) suitable for the environment of the decoder and performing decoding and restoration when performing decoding in sub-mesh units.

[0027] The mesh data transmission method, mesh data transmission device, mesh data reception method, and mesh data reception device according to the embodiments can decode and restore a mesh of a resolution (or LoD) suitable for a decoder environment by taking into consideration various environments of a receiver where decoding and restoration are performed (e.g., network conditions, display characteristics, receiver performance, etc.), thereby extracting and decoding only a bitstream corresponding to a low-resolution mesh (or a low LoD level), thereby enabling the use of low-resolution mesh content with less memory required than a high-resolution mesh and with less computational effort than a high-resolution mesh.

[0028] 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.

[0029] Figures 1(a) and 1(b) are diagrams showing examples of an encoder and a decoder according to embodiments.

[0030] FIG. 2 illustrates a system for providing dynamic mesh content according to embodiments.

[0031] Figure 3 illustrates a V-MESH compression method according to embodiments.

[0032] Figure 4 illustrates pre-processing of V-MESH compression according to embodiments.

[0033] Figure 5 illustrates a mid-edge subdivision method according to embodiments.

[0034] Figure 6 shows a displacement generation process according to embodiments.

[0035] Figure 7 illustrates an encoding process of mesh data according to embodiments.

[0036] Figure 8 shows a lifting conversion process for displacement according to embodiments.

[0037] Figure 9 illustrates a process of packing transformation coefficients into a 2D image according to embodiments.

[0038] Figure 10 illustrates an attribute transfer process of a V-MESH compression method according to embodiments.

[0039] Figure 11 illustrates a decoding process of mesh data according to embodiments.

[0040] Fig. 12 is a drawing showing an example of a transmitting device according to embodiments.

[0041] Fig. 13 is a drawing showing an example of a receiving device according to embodiments.

[0042] Fig. 14 is a drawing showing another example of a transmitting device according to embodiments.

[0043] FIG. 15 is a block diagram showing an example of a displacement vector encoder that encodes a displacement vector or a quantized displacement vector transform coefficient according to the present disclosure based on a 2D video codec.

[0044] FIG. 16 is a block diagram showing an example of a displacement vector encoder that encodes a displacement vector or a quantized displacement vector transform coefficient based on a zero run length according to the present disclosure.

[0045] FIG. 17 is a block diagram illustrating an example of a displacement vector encoder that arithmetically encodes a displacement vector or a quantized displacement vector transform coefficient according to the present disclosure.

[0046] FIG. 18 is a block diagram showing another example of a displacement vector encoder that encodes a displacement vector or a quantized displacement vector transform coefficient based on a zero run length according to the present disclosure.

[0047] FIG. 19 is a block diagram showing another example of a displacement vector encoder that arithmetic encodes a displacement vector or a quantized displacement vector transform coefficient according to the present disclosure.

[0048] Fig. 20 is a flowchart showing an example of a process for converting a displacement vector in a displacement vector conversion unit according to embodiments.

[0049] Fig. 21 is a drawing showing another example of a receiving device according to embodiments.

[0050] Fig. 22 is a detailed block diagram showing an example of a displacement vector coordinate system inverse transformation unit according to embodiments.

[0051] Fig. 23 is a detailed block diagram showing another example of a displacement vector coordinate system inverse transformation unit according to embodiments.

[0052] Fig. 24 is a detailed block diagram showing an example of a displacement vector decoder according to embodiments.

[0053] Fig. 25 is a flowchart showing an example of a process of inversely transforming a displacement vector in a displacement vector inverse transform unit according to embodiments.

[0054] FIG. 26a and FIG. 26b are diagrams showing an example of a syntax structure of an atlas sequence parameter set according to embodiments.

[0055] FIG. 27 is a drawing showing another example of a receiving device according to embodiments.

[0056] FIG. 28 is a diagram showing an example of a V-DMC bitstream structure according to embodiments.

[0057] Figure 29 is a flowchart showing an example of a transmission method according to embodiments.

[0058] Figure 30 is a flowchart showing an example of a receiving method according to embodiments.

[0059] 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.

[0060] 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.

[0061] With the recent development of 3D data modeling and rendering technology, research on creating and processing 3D data is being conducted in various fields such as Virtual Reality (VR), Augmented Reality (AR), autonomous driving, Computer-Aided Design (CAD) / Computer-Aided Manufacturing (CAM), and Geographic Information Systems (GIS). 3D data can be represented as point clouds, meshes, etc., depending on the representation format. Among these, a mesh is composed of geometric information expressing the coordinate values ​​of each vertex (or point), connection information indicating the connection relationship between vertices, a texture map expressing the color information of the mesh surface as 2D image data, and texture coordinates indicating mapping information between the surface of the mesh and the texture map. In the present disclosure, a mesh is defined as a dynamic mesh if one or more of the elements that make up the mesh change over time, and a static mesh if they do not change. In other words, dynamic mesh data may refer to mesh data that has an object or movement.

[0062] Because dynamic mesh data has a large amount of data for elements that constitute the mesh compared to two-dimensional image data, technologies have been developed to efficiently compress this large amount of mesh data to store and transmit it.

[0063] Figures 1(a) and 1(b) illustrate a V-DMC-based encoder and decoder according to embodiments. In particular, Figure 1(a) illustrates an encoder, and Figure 1(b) illustrates a decoder.

[0064] The basic structure of the currently in-progress V-DMC (v-mesh) is as shown in Fig. 1(a) and Fig. 1(b). The encoder according to Fig. 1(a) and the decoder according to Fig. 1(b) perform the process of encoding and decoding media representing dynamic meshes using V3C (Visual Volumetric Video-based Coding) technology. The preprocessor converts the input dynamic mesh representation into several V3C components (base mesh, displacement set, 2D representation of attributes, and atlas). The original mesh is simplified into the base mesh. The base mesh can be encoded using any mesh codec. The displacement vector can be encoded into the V3C geometry video component using any video codec, either indicated by the profile or based on the SEI (supplemental enhancement information) message. For example, depending on the profile, the displacement vector (or displacement data) can be encoded via a video codec-based encoder, a zero-run length encoder, an arithmetic encoder, etc. The attribute data can include additional attributes. For example, texture or material information can be included as additional attributes, and can be encoded based on any video codec. The atlas data includes information on how to perform inverse reconstruction, and is provided to the V3C (or v-mesh) decoding and / or rendering system of the receiving device. For example, the atlas data can include a method for performing subdivision of the base mesh, a method for applying displacement vectors to subdivided mesh vertices, a method for applying attributes to the reconstructed mesh, etc.

[0065] An encoder according to embodiments may comprise a memory and at least one processor connected to the memory. The at least one processor may be configured to perform operations such as a pre-processor, an atlas encoding unit, a basemesh encoding unit, a displacement vector encoding unit, a video encoding unit, and a multiplexer.

[0066] The atlas encoding unit encodes an atlas of mesh data to generate an atlas bitstream. The basemesh encoding unit encodes a basemesh of mesh data to generate a basemesh bitstream. The displacement vector encoding unit encodes a displacement vector of mesh data to generate a displacement vector bitstream. The video encoding unit encodes an attribute of mesh data to generate an attribute bitstream. An encoder according to embodiments may generate parameter information (which may be referred to as signaling information, metadata, etc.) related to each encoding. An encoder according to embodiments may generate a compressed bitstream including parameter information, an atlas, a basemesh, displacement vectors, and / or attributes.

[0067] A decoder according to embodiments may comprise a memory and at least one processor connected to the memory. The at least one processor may be configured to perform operations such as a demultiplexer, an atlas decoding unit, a basemesh decoding unit, a displacement vector decoding unit, and a video decoding unit.

[0068] The atlas decoding unit decodes the atlas within the bitstream. The basemesh decoding unit decodes the basemesh within the bitstream. The displacement vector decoding unit decodes the displacement vector within the bitstream. The video decoding unit decodes the attribute within the bitstream. The decoder according to the embodiments may perform each decoding operation based on parameter information within the bitstream. In the decoder according to the embodiments, the basemesh processing unit restores the current basemesh from the decoded basemesh based on the atlas and / or parameter information. In the decoder according to the embodiments, the displacement processing unit restores the displacement vector by performing coordinate system transformation of the decoded displacement vector based on the atlas and / or parameter information. In the decoder according to the embodiments, the mesh restoration unit restores the final mesh by combining the restored basemesh and the restored displacement vector based on the atlas and / or parameter information. The restored mesh processing unit of the decoder according to the embodiments can generate and render a reconstructed dynamic mesh image by combining the decoded attribute (or texture map) with the restored final mesh. That is, the reconstructed dynamic mesh image can be displayed to the user.

[0069] Below, the operation of the V-DMC encoder and decoder of Fig. 1 is described in more detail.

[0070] FIG. 2 illustrates a system for providing dynamic mesh content according to embodiments.

[0071] The system of FIG. 2 includes a transmitting device (100) and a receiving device (110) according to embodiments. The transmitting device (100) may include a mesh video acquisition unit (101), a mesh video encoder (102), a file / segment encapsulator (103), and a transmitter (104). The receiving device (110) may include a receiving unit (111), a file / segment decapsulator (112), a mesh video decoder (113), and a renderer (114). Each component of FIG. 2 may correspond to hardware, software, a processor, and / or a combination thereof. Hereinafter, the mesh data transmitting device according to embodiments may be interpreted as a term referring to a 3D data transmitting device or transmitting device (100), or a mesh video encoder (hereinafter, referred to as an encoder) (102). The mesh data receiving device according to the embodiments may be interpreted as a term referring to a 3D data receiving device or receiving device (110), or a mesh video decoder (hereinafter, decoder) (113).

[0072] The system of FIG. 2 can perform video-based dynamic mesh compression and decompression.

[0073] 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.

[0074] First, the method of compressing dynamic mesh data starts from the V-PCC (Video-based point cloud compression) standard technology for point cloud data. Point cloud data is data that has color information at the coordinates (X, Y, Z) of a vertex (or point). In the present disclosure, the coordinates (i.e., position information) of a vertex are referred to as geometry information, the color information of a vertex is referred to as attribute information, and the geometry information and attribute information are referred to as vertex information or point cloud data. The vertex information to which connectivity information between vertices is added is referred to as mesh data. When creating content, it can be created in the form of mesh data from the beginning. Alternatively, it can be used by converting it into mesh data by adding connectivity information to point cloud data.

[0075] Currently, the MPEG standards body defines the data types of dynamic mesh data as the following two types.

[0076] Category 1: Mesh data with texture maps as color information.

[0077] Category 2: Mesh data with vertex colors as color information.

[0078] 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 2.

[0079] 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.

[0080] A mesh compression system may include a transmitting device (100) and a receiving device (110) as shown in FIG. 2. The transmitting device (100) may encode mesh video to output a bitstream, and transmit the bitstream to the receiving device (110) in the form of a file or streaming (streaming segment) via a digital storage medium or a network. The digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, and SSD.

[0081] In the above transmitting device (100), the encoder may be called a mesh video / video / picture / frame encoding device, and in the receiving device (110), the decoder may be called a mesh video / video / picture / frame decoding device. The transmitter may be included in a mesh video encoder. The receiver may be included in a mesh video decoder. The renderer (114) 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 (100) and the receiving device (110) may further include separate internal or external modules / units / components for a feedback process.

[0082] Mesh data represents the surface of an object as a number of polygons. Each polygon is defined by vertices in 3D space and connection information that describes how the vertices are connected. It can also contain vertex attributes 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 in the attributes of the mesh. The mapping can be described as a set of parameter coordinates, commonly 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 texture, normal, and displacement. Here, displacement can be used interchangeably with displacement information or displacement vector.

[0083] The mesh video acquisition unit (101) may include processing 3D object data acquired through a camera, etc. into a mesh data type having the attributes described above through a series of processes and generating a video composed of such mesh data. The mesh video may have attributes of the mesh, such as vertices, polygons, connection information between vertices, colors, normals, etc., that may change over time. A mesh video having attributes and connection information that change over time in this way may be expressed as a dynamic mesh video.

[0084] A mesh video encoder (102) can encode an input mesh video into one or more video streams. One video can include multiple frames, and one frame can correspond to a still image / picture. In this document, a mesh video can include a mesh image / frame / picture, and a mesh video can be used interchangeably with a mesh image / frame / picture. The mesh video encoder (102) can perform a Video-based Dynamic Mesh (V-Mesh) Compression procedure. The mesh video encoder (102) 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.

[0085] The file / segment encapsulator (103) 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 a metadata processing unit, etc. The metadata processing unit may be included in the mesh video encoder (102) or may be configured as a separate component / module. The file / segment encapsulator (103) can encapsulate the corresponding data in a file format such as ISOBMFF, or process it in the form of other DASH segments, etc. The file / segment encapsulator (103) 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. Depending on the embodiment, the file / segment encapsulator (103) may encapsulate the mesh video related metadata itself into a file.

[0086] 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 (104) 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 it for transmission.

[0087] The transmission unit (104) can transmit encoded video / image information or data output in the form of a bitstream to the reception unit (111) of the reception device (110) 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 (104) can include an element for generating a media file through a predetermined file format and can include an element for transmission via a broadcasting / communication network. The reception unit (111) can extract the bitstream and transmit it to a decoding device.

[0088] The receiving unit (111) can receive mesh video data transmitted by a mesh data transmission device. Depending on the channel through which it is transmitted, the receiving unit (111) can receive mesh video data through a broadcast network, through a broadband, or through a digital storage medium.

[0089] The receiving processing unit can perform processing according to the transmission protocol on the received mesh video data. The receiving processing unit can be included in the receiving unit (111) or can be configured as a separate component / module. In order to correspond to the processing performed for transmission on the transmitting side, the receiving processing unit can perform the reverse process of the aforementioned transmission processing unit. The receiving processing unit can transfer the acquired mesh video data to the file / segment decapsulator (112) and transfer the acquired mesh video-related metadata to the metadata parser. The mesh video-related metadata acquired by the receiving processing unit can be in the form of a signaling table.

[0090] The file / segment decapsulator (112) can decapsulate mesh video data in the form of a file received from a receiving processing unit. The file / segment decapsulator (112) 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 the mesh video decoder (113), and the obtained mesh video-related metadata (metadata bitstream) can be transmitted to the metadata processing unit. The mesh video bitstream may include metadata (metadata bitstream). The metadata processing unit may be included in the mesh video decoder (113) or may be configured as a separate component / module. The mesh video-related metadata obtained by the file / segment decapsulator (112) may be in the form of a box or track within a file format. The file / segment decapsulator (112) may receive metadata required for decapsulation from the metadata processing unit, if necessary. The mesh video related metadata may be passed to the mesh video decoder (113) and used in the mesh video decoding procedure, or may be passed to the renderer (114) and used in the mesh video rendering procedure.

[0091] The mesh video decoder (113) can receive a bitstream and perform a reverse operation corresponding to the operation of the mesh video encoder (102) to decode the video / image. The decoded mesh video / image can be displayed through the display unit of the renderer (114). The user can view all or part of the rendered result through a VR / AR display or a general display.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] This document relates to embodiments of 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 attributes that change over time, and it can perform lossy and lossless compression for various applications such as real-time communication, storage, free-viewpoint video, and AR / VR.

[0097] The dynamic mesh video compression method described below is based on MPEG's V-Mesh method.

[0098] In this document, picture / frame can generally mean a unit representing one video of a specific time period.

[0099] 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.

[0100] 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.

[0101] As described above, the encoding process of Fig. 2 is as follows.

[0102] That is, the video-based dynamic mesh compression (V-Mesh) compression method can provide a method of compressing dynamic mesh video data based on 2D video codecs such as HEVC (High Efficiency Video Coding) and VVC (Versatile Video Coding). The V-Mesh compression process receives the following data as input and performs compression.

[0103] Input mesh: Contains the 3D coordinates 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.

[0104] Attribute map: (Hereinafter, texture map is also used in the same meaning): Contains information about the attributes of the mesh (color, normal, displacement, etc.), and stores data in the form of mapping 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. 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.).

[0105] Material Library File: Contains information about the material attributes used in a mesh, and in particular, information that links the input mesh to its corresponding attribute map. It is saved in the Wavefront Material Template Library (MTL) file format.

[0106] In the V-Mesh compression method, the following data and information can be generated through the compression process.

[0107] Base mesh: The input mesh is simplified (decimated) through a pre-processing process, thereby expressing the objects of the input mesh using the minimum number of vertices determined by the user's standards.

[0108] 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.

[0109] Atlas information: This is the metadata required to reconstruct a mesh using base mesh, displacement, and attribute map information. Atlas information can be created and utilized as sub-mesh units (such as patches) that make up the mesh.

[0110] Referring to FIGS. 3 to 7, a method for encoding mesh position information (or vertex position information) is described, and referring to FIGS. 7 to 10, etc., a method for encoding attribute information (attribute map) by restoring mesh position information is described.

[0111] Figure 3 illustrates a V-MESH compression method according to embodiments.

[0112] Fig. 3 illustrates the encoding process of Fig. 2, and the encoding process may include a pre-processing process and an encoding process. The mesh video encoder (102) of Fig. 2 may include a pre-processor (200) and an encoder (201) as shown in Fig. 3. In addition, the transmitting device of Fig. 2 may be broadly referred to as an encoder, and the mesh video encoder (102) of Fig. 2 may be referred to as an encoder. The V-Mesh compression method may include a pre-processing process (Pre-processing, 200) and an encoding process (Encoding, 201) as shown in Fig. 3. The pre-processor (200) of Fig. 3 may be located in front of the encoder (201) of Fig. 3. The pre-processor (200) and the encoder (201) of Fig. 3 may be referred to as a single encoder.

[0113] The pre-processor (200) can receive a static of a dynamic mesh (M(i)) and / or an attribute map (A(i)). The pre-processor (200) can generate a base mesh (m(i)) and / or a displacement (d(i)) through pre-processing. The pre-processor (200) can receive feedback information from the encoder (201) and generate the base mesh and / or the displacement based on the feedback information.

[0114] The encoder (201) can receive a base mesh (m(i)), a displacement (d(i)), a static of a dynamic mesh (M(i)), and / or an attribute map (A(i)). In the present disclosure, at least one of the base mesh (m(i)), the displacement (d(i)), the static of a dynamic mesh (M(i)), and / or the attribute map (A(i)) can be referred to as mesh-related data. The encoder (201) can encode the mesh-related data to generate a compressed bitstream.

[0115] Figure 4 illustrates a pre-processing process of V-MESH compression according to embodiments.

[0116] Fig. 4 illustrates the configuration and operation of the preprocessor of Fig. 3. In Fig. 4, the input mesh may include a static of a dynamic mesh (M(i)) and / or an attribute map (A(i)). In addition, the input mesh may include three-dimensional coordinates of vertices constituting the mesh, normal information of each vertex, mapping information for mapping the mesh surface to a 2D plane, connection information between vertices constituting the surface, etc.

[0117] Fig. 4 shows a process of performing pre-processing on an input mesh. The pre-processing process (200) may largely include four steps: 1) GoF (Group of Frame) generation, 2) Mesh Decimation, 3) UV parameterization, and 4) Fitting subdivision surface (300). According to embodiments, GoF generation may be referred to as a GoF generation process or a GoF generation unit, mesh simplification may be referred to as a mesh simplification process or a mesh simplification unit, UV parameterization may be referred to as a UV parameterization process or a UV parameterization unit, and the fitting subdivision surface may be referred to as a fitting subdivision surface process or a fitting subdivision surface unit. The pre-processor (200) can generate displacement and / or base meshes from the received input mesh and transmit them to the encoder (201). The pre-processor (200) can transmit GoF information associated with GoF generation to the encoder (201).

[0118] Below, each step of Fig. 4 is described.

[0119] GoF Generation: This is the process of generating a reference structure for mesh data. If the number of vertices, the number of texture coordinates, the vertex connection information, and the 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. That is, if only the vertex coordinate values ​​are different between the current input mesh and the reference input mesh, the encoder (201) can perform inter frame encoding. Otherwise, intra frame encoding is performed for the corresponding frame.

[0120] 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.

[0121] 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.

[0122] 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.

[0123] OrthoAtlas technology generates texture coordinates using orthographic projection. OrthoAtlas technology sequentially generates patches and packs them. First, adjacent triangles are divided to generate Connected Components (CCs), and then the optimal CCs are merged using a cost function to generate patches. The cost function can measure the cost based on the degree of distortion that occurs when orthogonally projecting patches in each direction. By packing the patch that minimizes the cost function into the texture domain, the texture coordinates can be calculated. In the case of orthoAtlas technology, texture coordinates and texture connection information can be derived from the base mesh decoder without being compressed during the base mesh encoding process.

[0124] Fitting subdivision surface (300): This is a process of performing subdivision on a decimated mesh (i.e., a simplified mesh having texture coordinates). The displacement and base mesh generated through this process are output to the encoder (201). A user-defined method, such as a mid-edge method, may be applied as the subdivision method. A fitting process is performed so that the input mesh and the mesh on which the subdivision is performed are similar to each other. In the present disclosure, the mesh on which the fitting process is performed is referred to as a fitted subdivision mesh (or fitted subdivision mesh). This process is a process of performing fitting so that the mesh on which the subdivision is performed on the base mesh is similar to the surface of the input mesh. As a subdivision method, a user-defined method such as the mid-edge method (see Fig. 5), the loop method, and the LS3 method can be applied.

[0125] Figure 5 illustrates a mid-edge subdivision method according to embodiments.

[0126] Figure 5 illustrates the mid-edge method of the fitting subdivision surface described in Figure 4. Referring to Figure 5, an original mesh containing four vertices is subdivided to generate a sub-mesh. A sub-mesh can be generated by creating a new vertex in the middle of the edge between the vertices. Then, a fitting process is performed so that the input mesh and the sub-mesh become similar to each other, thereby generating a fitted sub-division mesh.

[0127] 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 decoded 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 the displacement represents the position difference in three-dimensional space, it is also expressed as a value in the (x, y, z) space of the 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.

[0128] Fig. 6 illustrates a displacement generation process according to embodiments. The displacement generation process of Fig. 6 may be performed in a pre-processor (200) or in an encoder (201).

[0129] Fig. 6 illustrates in detail the displacement calculation method of the fitting subdivision surface (300) as described in Fig. 5.

[0130] 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 perform subdivision on a restored base mesh to generate a subdivided restored base mesh. Here, the restoration of the base mesh may be performed in the pre-processor (200) or in the encoder (201). The local coordinate system calculation unit may receive a fitted subdivision mesh and a subdivided restored base mesh, and may convert a coordinate system of the mesh into a local coordinate system based on the fitted subdivision mesh and the subdivided restored base mesh. 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 restored 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.

[0131] The mesh data transmission method and device according to the embodiments can encode mesh data as follows. Mesh data is a term including point cloud data. Point cloud data (which may be referred to as point cloud for short) according to the embodiments can refer to data including vertex coordinates (or geometry information) and color information (or attribute information). In addition, geometry images, attribute images, occupancy maps, and additional information (or patch information) generated through patch generation and packing based on vertex coordinates and color information are also referred to as point cloud data. Therefore, point cloud data including connection information can be referred to as mesh data. In this document, point cloud and mesh data can be used interchangeably.

[0132] The V-Mesh compression (decompression) method according to the embodiments may include intra frame encoding and inter frame encoding.

[0133] 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.

[0134] Figure 7 illustrates a V-DMC encoding process according to embodiments.

[0135] The elements of the transmitting device illustrated in FIG. 7 may be implemented by hardware, software, a processor connected to a memory, and / or a combination thereof. That is, the elements of the transmitting device illustrated in FIG. 7 may be implemented by hardware, software, firmware, or a combination thereof, including one or more processors or integrated circuits configured to communicate with one or more memories, although not illustrated in the drawing. One or more processors may perform at least one or more of the operations and / or functions of the elements of the transmitting device illustrated in FIG. 7. In addition, one or more processors may operate or execute a set of software programs and / or instructions for performing the operations and / or functions of the elements of the transmitting device illustrated in FIG. 7. The execution order of each block in FIG. 7 may be changed, some blocks may be omitted, and some blocks may be newly added.

[0136] In the present disclosure, the operation process of a transmitter for compressing and transmitting dynamic mesh data using V-Mesh compression technology may be as shown in Fig. 7. The transmitter of Fig. 7 may support both an intra-frame encoding (or intra-encoding or intra-screen encoding) process and / or an inter-frame encoding (or inter-encoding or inter-screen encoding) process.

[0137] The encoding process of FIG. 7 details the encoding of the mesh video encoder (102) of FIG. 2. The encoder of FIG. 7 may include a pre-processor (200) and / or an encoder (201). The pre-processor (200) and encoder (201) of FIG. 7 may correspond to the pre-processor (200) and encoder (201) of FIG. 4.

[0138] The preprocessor (200) can receive an input mesh and perform the preprocessing described above. The preprocessing can generate a base mesh and / or a fitted subdivision mesh.

[0139] The quantizer (411) of the encoder (201) can quantize the base mesh and / or the fitted subdivided mesh.

[0140] According to embodiments, the base mesh quantized in the mesh quantization unit (411) may be output to a static mesh encoder (413) or a motion vector encoder (414) through a switching unit (412). According to embodiments, the base mesh is output to a motion vector encoder (414) through the switching unit (412) when inter-encoding is performed on the corresponding mesh frame, and is output to a static mesh encoder (413) through the switching unit (412) when intra-encoding is performed on the corresponding mesh frame. The motion vector encoder (414) may be referred to as a motion encoder.

[0141] For example, when performing intra encoding or intra frame encoding for the corresponding mesh frame, the base mesh can be compressed through a static mesh encoder (413). In this case, encoding can be performed on connection information, vertex geometry information, vertex texture information, normal information, etc. of the base mesh. That is, vertex coordinates, vertex connection information, texture coordinates, texture connection information, etc. of the mesh can be encoded in the static mesh encoder (413). The base mesh bitstream generated through encoding is transmitted to a multiplexer (not shown).

[0142] As another example, when performing inter-encoding (or inter-frame encoding) on ​​the corresponding mesh frame, the motion vector encoder (414) may receive the current base mesh and the reference reconstructed base mesh (or the reconstructed quantized reference base mesh) as input, calculate a motion vector between the two meshes, and encode the value. In addition, the motion vector encoder (414) may perform prediction based on connection information using a previously encoded / decoded motion vector as a predictor, and entropy-encode a differential motion vector (or residual motion vector) obtained by subtracting the predicted motion vector from the current motion vector. According to embodiments, the motion vector encoding may be performed on a vertex basis or a subgroup basis. The motion vector bitstream generated through the motion vector encoding is transmitted to a multiplexer (not shown) as a base mesh bitstream. That is, in the case of intra-frame encoding, the static mesh bitstream is input to the multiplexer as the base mesh bitstream, and in the case of inter-frame encoding, the motion vector bitstream is input to the multiplexer as the base mesh bitstream.

[0143] In FIG. 7, the base mesh restoration unit (415) can receive a base mesh encoded by the static mesh encoder (413) or a motion vector encoded by the motion vector encoder (414) to generate a reconstructed base mesh. The base mesh restoration unit (415) performs restoration of the base mesh according to the encoding type (inter-screen encoding or intra-screen encoding) of the current mesh. For example, the base mesh restoration unit (415) can perform static mesh decoding on the base mesh encoded by the static mesh encoder (413) to restore the base mesh. At this time, quantization can be applied before static mesh decoding, and inverse quantization can be applied by the inverse quantization unit (416) after static mesh decoding. That is, when intra-screen encoding is performed, the inverse quantization unit (416) can perform inverse quantization on the quantized base mesh through the mesh quantization unit (411) to restore the current base mesh. As another example, the base mesh restoration unit (415) can restore the base mesh based on the restored quantized reference base mesh and the motion vector encoded by the motion vector encoder (414). That is, when inter-screen encoding is performed, the current base mesh can be generated by decoding the motion vector using the motion vector decoding method and then applying (i.e., adding) the decoded motion vector to the reference restoration base mesh. At this time, when 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 encoder (414). The restored base mesh is output to the displacement vector calculation unit (417) and the mesh restoration unit (425).

[0144] According to embodiments, the displacement vector calculation unit (417) can perform mesh refinement on the restored base mesh. In addition, the displacement vector calculation unit (417) can calculate a displacement vector, which is a difference value in vertex positions between the restored base mesh that has been refined and the fitted subdivision (or refined) mesh generated by the pre-processor (200). That is, the displacement vector is a difference in positions between the vertices of the two meshes so that the fitted subdivision (or refined) mesh becomes similar to the original mesh. At this time, the displacement vector can be calculated as many times as the number of vertices of the subdivision mesh. That is, the displacement vector of the number of vertices of the subdivision (refined) mesh can be calculated through the displacement vector calculation unit (417).

[0145] The lifting transformation unit (418) can perform a lifting transformation on the input displacement vector to generate a lifting coefficient (or displacement vector transformation coefficient). The quantizer (419) can quantize the lifting coefficient, i.e., the displacement vector transformation coefficient.

[0146] In the present disclosure, the displacement vector or the quantized displacement vector transform coefficient can be encoded through a 2D video codec-based encoding method, and / or a zero run length encoding method, and / or an arithmetic encoding method, etc.

[0147] If an arithmetic encoding method is used, the displacement vector or the quantized displacement vector transform coefficient is encoded based on an arithmetic codec in an arithmetic encoding unit (421) after inter prediction in an inter prediction unit (420), and if a 2D video codec-based encoding method is used, the displacement vector or the quantized displacement vector transform coefficient is encoded based on a 2D video codec in a video encoding unit (423) after image packing in an image packing unit (422) and can be output as a displacement bitstream (i.e., compressed displacement bitstream). For example, the image packing unit (422) can pack an image based on quantized lifting coefficients (i.e., displacement vector transform coefficients). The video encoding unit (423) can encode the packed image. That is, the quantized lifting coefficients are packed into one frame as a 2D image by the image packing unit (422), compressed by the video encoding unit (423), and output as a displacement bitstream (i.e., compressed displacement bitstream).

[0148] The displacement vector restoration unit (424) may include a video decoder, an image unpacking unit, an inverse quantizer, and an inverse linear lifting unit. That is, the displacement vector restoration unit (424) performs decoding on an encoded displacement vector in the video decoder, performs image unpacking in the image unpacking unit, performs inverse quantization in the inverse quantizer, and then performs inverse transformation in the inverse linear lifting unit to restore the displacement vector. The restored displacement vector is output to the mesh restoration unit (425). The mesh restoration unit (425) restores the deformed mesh based on the base mesh restored by the base mesh restoration unit (415) and the displacement vector restored by the displacement vector restoration unit (424). That is, the mesh restoration unit (425) restores the reconstructed and deformed mesh through the restored displacement output from the displacement vector restoration unit (424) and the restored base mesh (or subdivided restored base mesh) output from the inverse quantization unit (416). The present disclosure refers to the reconstructed and deformed mesh as a restored deformed mesh. The restored mesh (or restored deformed mesh) has restored vertices, connection information between vertices, texture coordinates, and connection information between texture coordinates.

[0149] The attribute transfer (426) receives an input mesh and / or an input attribute map, and regenerates an attribute map based on the restored deformed mesh. The attribute map refers to a texture map corresponding to attribute information among mesh data components, and in the present disclosure, the attribute map and the texture map may be used interchangeably. The push-pull padding (427) may pad data in the attribute map based on the push-pull method. The color space conversion unit (428) may convert the space of the color component of the attribute map. For example, the attribute map may be converted from an RGB color space to a YUV color space. The video encoding unit (429, also referred to as a video encoder) may encode the attribute map and output it as a compressed attribute bitstream.

[0150] According to embodiments, the atlas encoder (430) may encode atlas information (or atlas data) to generate a compressed atlas bitstream. Then, the atlas bitstream generated through atlas information encoding is transmitted to the multiplexer (431). In the present disclosure, the atlas may be information required in a mesh reconstruction process and may mean information such as tiles and patches. In addition, the atlas information may mean data required in processes such as 2D mapping for a 3D object, texture mapping-related information, mesh decoding, and mesh restoration, and may include additional information such as a segmentation method, a transformation method, a quantization method, and the position and size of a patch within an atlas frame. In the present disclosure, the atlas information may be encoded through Exp-Golomb coding of the atlas encoder (430), etc.

[0151] According to embodiments, the multiplexer (430) can multiplex an input compressed base mesh bitstream, a compressed displacement (or displacement vector) bitstream, a compressed attribute (or texture map) bitstream, and a compressed atlas bitstream to generate a single compressed bitstream. The multiplexed bitstream can be encapsulated into one or more tracks of a file.

[0152] According to embodiments, the bitstream or file multiplexed in the multiplexer (431) may be transmitted over a network or stored in a digital storage medium. Here, the network may include a broadcasting network and / or a communication network, and the digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, and SSD.

[0153] In summary, for the base mesh, encoding can be performed in different ways depending on the base mesh type (INTRA type, INTER type, SKIP type). If the base mesh is INTRA type, it can be encoded using the static mesh encoding method. If the base mesh is INTER type, the motion field between the reference base mesh and the current base mesh can be encoded. If the current base mesh is SKIP type, the reference base mesh can be derived as the current base mesh.

[0154] After being encoded by the encoder, the decoded base mesh can be subdivided into a subdivided mesh through a subdivision process. Subdivision algorithms such as mid-point subdivision and loop subdivision can be used.

[0155] Static Base Mesh Encoding (Intra Base Mesh Encoding): When performing Intra encoding on the current base mesh, the base mesh generated during the preprocessing process can be encoded using static mesh compression technology after going through the quantization process. Static mesh compression applies MPEG EdgeBreaker (MEB) technology, and the vertex position information, mapping information (texture coordinates), vertex connection information, and normals of the base mesh are compressed.

[0156] Connection information can be encoded and compressed based on the edgebreaker algorithm. The edgebreaker algorithm sequentially traverses triangles according to rules, maps symbols based on the characteristics of each triangle, and then encodes the corresponding symbols.

[0157] A technique for compressing vertex position information can encode the residual value, which is the difference between the current vertex and the predicted value, after obtaining the predicted value based on a prediction technique such as multiple parallelogram prediction.

[0158] A technique for compressing mapping information (texture coordinates) can encode the residual value, which is the difference between the current mapping information (texture coordinates) and the predicted value, after obtaining the predicted value based on a prediction technique such as stretch.

[0159] Techniques for compressing normals can encode residual values, which are the differences between the current normal and the predicted values, after obtaining predicted values ​​based on prediction techniques such as delta coding, multiple parallelogram prediction, and cross product-based prediction.

[0160] Motion Field Encoding (Inter Basemesh Encoding): Inter basemesh encoding can be performed when a one-to-one correspondence exists between the reference mesh and the current input mesh, and only the vertex position information differs. When performing inter 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, can be calculated and this information can be encoded. The reference base mesh is the result of quantizing the already decoded base mesh data and is determined by the reference frame index.

[0161] The motion field can be encoded as a value, or the predicted motion field can be calculated by averaging the motion fields of the reconstructed vertices among the vertices connected to the current vertex, and the residual motion field, which is the difference between the predicted motion field value and the motion field value of the current vertex, can be encoded. This value can be encoded using entropy coding.

[0162] Displacement Encoding: After base mesh encoding, restoration and dequantization are performed to generate a Recon. base mesh, and the displacement between the result of performing subdivision on this and the fitted subdivided mesh can be calculated. For effective encoding, a data transform process such as wavelet transform can be applied to the displacement information, and Figure 8 shows the process of transforming displacement information using lifting transform in V-Mesh. The displacement vector transform coefficients generated through the transform process are quantized, and the quantized transform coefficients can be compressed through a video codec or through arithmetic encoding depending on the compression method.

[0163] When compressed through a video codec, it is packed into a 2D image as shown in Fig. 9. The transformation coefficients are organized into one block for each N^2(N*N) unit, and each block can be packed in z-scan order. The horizontal number of blocks is fixed to N, but the vertical number of blocks can be determined according to the number of vertices of the subdivided base mesh. Within one block, the transformation coefficients can be packed by sorting them with Morton code. The packed images generate a displacement video for each GoF unit, and this displacement video can be encoded using an existing video compression codec.

[0164] When compressed through arithmetic encoding, inter-frame prediction can be performed on the quantized displacement vector transform coefficients. When inter-frame prediction is performed on the current quantized displacement vector transform coefficients, the residual value, which is the difference between the current displacement vector transform coefficients and the reference displacement vector transform coefficients, can be encoded, and information about the reference target can be encoded. Depending on the displacement vector type, if it is an INTRA type, the quantized displacement vector transform coefficients can be arithmetic encoded, and if it is an INTER type, the residual value can be arithmetic encoded. When encoding, it can be performed based on Context Adaptive Binary Arithmetic Coding (CABAC). The CABAC process can first binarize the displacement vector data and map it to a bin string. The bin string can be a binarized output of 0 and 1, and each 0 or 1 can be a bin. Each bin can be arithmetic encoded using context information selected from a context model, and a process of updating the probability can be performed.

[0165] Figure 8 shows a lifting conversion process for displacement according to embodiments.

[0166] Figure 9 illustrates a process of packing transformation coefficients (or lifting coefficients) according to embodiments into a 2D image.

[0167] Figures 8 and 9 illustrate the process of converting the displacement of the encoding process of Figure 7 and the process of packing the conversion coefficients, respectively.

[0168] The encoding method according to the embodiments includes displacement encoding.

[0169] After 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 (417 in Fig. 7). For effective encoding, a data transform process such as wavelet transform can be applied to the displacement information (418 in Fig. 7).

[0170] FIG. 8 shows a process of transforming displacement information using a lifting transform in the lifting transform unit (418) of FIG. 7. For example, a linear wavelet-based lifting transform may be performed. The transform coefficients generated through the transform process are quantized in a quantizer (419) and then packed into a 2D image through an image packing unit (422) as in FIG. 9. The transform coefficients are organized into one block for each 256 (= 16 × 16) units, and each block can be packed in a 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 a Morton code within one 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 in a video encoding unit (423, or video encoder).

[0171] Referring to FIG. 8, a base mesh (original) may include vertices and edges for LoD (Level Of Detail) 0. A first subdivision mesh generated by dividing (or subdividing) the base mesh includes vertices generated by further dividing (or subdividing) 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 of the base mesh (LoD0). The first subdivision mesh may be further divided (or subdivided) to generate a second subdivision mesh. The second subdivision mesh includes LoD2. LoD2 includes base mesh vertices (LoD0), LoD1 including vertices further divided (or subdivided) from LoD0, and vertices further divided (or subdivided) from LoD1. LoD is a Level of Detail (LoD) that indicates the degree of detail of mesh data content. As the level index increases, the distance between vertices becomes closer and the level of detail increases. In other words, the smaller the LoD value, the lower the detail of the mesh data content, and the larger the LoD value, the higher the detail of the mesh data content. LoD N contains the vertices included in the previous LoDN-1 as is. When a mesh (or vertex) is further divided through subdivision, the mesh can be encoded based on a prediction and / or update method by considering the previous vertices v1, v2, and the subdivided vertex v. Instead of directly 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 bitstream size. The prediction process refers to the operation of predicting the current vertex v using the previous vertices v1 and v2. Since adjacent subdivision meshes have similar data, this property can be utilized for efficient encoding.Current vertex position information is predicted as a residual of previous vertex position information, and the previous vertex position information is updated through the residual. In the present disclosure, vertex, apex, and point may be used with the same meaning. In addition, LoDs may be defined during the subdivision process of the base mesh. According to embodiments, the subdivision process of the base mesh may be performed in the pre-processor (200) or in a separate component / module.

[0172] Referring to FIG. 9, a vertex has a transformation coefficient (also called a lifting coefficient) generated through a lifting transformation. The transformation coefficient of a vertex related to a lifting transformation can be packed into an image by an image packing unit (422) and then encoded by a video encoding unit (423).

[0173] Figure 10 illustrates an attribute transfer process of a V-MESH compression method according to embodiments.

[0174] According to the embodiments, FIG. 10 shows the detailed operation of the attribute transfer (426) of FIG. 7.

[0175] Encoding according to embodiments includes attribute map encoding. According to embodiments, attribute map encoding may be performed in the video encoding unit (429) of FIG. 7.

[0176] According to embodiments, in the present disclosure, the encoder compresses information about the input mesh through base mesh encoding (i.e., intra encoding), motion field encoding (i.e., inter 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 FIG. 7. The reconstructed deformed mesh (Recon. deformed mesh) has position information of vertices, 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 restored deformed mesh is regenerated through the attribute transfer process of the attribute transfer (426).

[0177] According to embodiments, attribute transfer (426) first checks whether each point P(u, v) of a 2D texture domain belongs to a texture triangle of a reconstructed deformed mesh, and if it exists in a texture triangle T, the barycentric coordinate of P(u, v) according to the triangle T ( , , ) is calculated. And the 3D vertex positions of triangle T and ( , , ) is used to compute the 3D coordinates M(x, y, z) of P(u, v). Find the vertex coordinates M'(x', y', z') and the triangle T' containing this vertex that corresponds to the most similar position to the calculated M(x, y, z) in the input mesh domain. Then, the center of mass coordinates of M'(x', y', z') in this triangle T' ( ', ', ') is calculated. The texture coordinates corresponding to the three vertices of Triangle T' and ( ', ', ') is used to calculate the texture coordinates (u', v'), 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 (u, v) pixel location in the new attribute map. If P(u, v) does not belong to any triangle, the pixel at the corresponding location in the new attribute map can be filled with a color value using a padding algorithm, such as the push-pull algorithm of the push-pull padding (427).

[0178] A new attribute map generated through attribute transfer (426) is grouped into GoF units to form an attribute map video, which is compressed using a video codec of the video encoding unit (429).

[0179] Referring to Figure 10, the reference relationship between the input mesh, the input attribute map, the reconstructed deformed mesh, and the regenerated attribute map can be seen.

[0180] The decoding process of Fig. 2 can perform the reverse process of the corresponding process of the encoding process of Fig. 2. The specific decoding process is as follows.

[0181] Figure 11 illustrates a decoding process of V-Mesh technology according to embodiments.

[0182] Fig. 11 illustrates the configuration and operation of the mesh video decoder (113) of the receiving device of Fig. 2. In addition, Fig. 11 can restore mesh data by performing the reverse process of the encoding process of Fig. 7. In the present disclosure, the receiving device of Fig. 11 may be referred to as a mesh data receiving device or decoder or a decoder of the receiving device or a V-Mesh decoder or a dynamic mesh decoder.

[0183] The elements of the receiving device illustrated in FIG. 11 may be implemented by hardware, software, a processor connected to a memory, and / or a combination thereof. That is, the elements of the receiving device illustrated in FIG. 11 may be implemented by hardware, software, firmware, or a combination thereof, including one or more processors or integrated circuits configured to communicate with one or more memories, although not illustrated in the drawing. One or more processors may perform at least one or more of the operations and / or functions of the elements of the receiving device illustrated in FIG. 11. In addition, one or more processors may operate or execute a set of software programs and / or instructions for performing the operations and / or functions of the elements of the receiving device illustrated in FIG. 11. The execution order of each block in FIG. 11 may be changed, some blocks may be omitted, and some blocks may be newly added.

[0184] Fig. 11 may largely include a demultiplexer (611), an atlas decoder (612), and a decoding unit (620).

[0185] According to embodiments, a bitstream (i.e., a compressed bitstream) of mesh data received by a receiver (not shown) may be demultiplexed into a base mesh bitstream (or a base mesh substream) after file / segment decapsulation, a displacement vector bitstream (or a displacement substream), a texture map bitstream (or an attribute map substream or a texture map substream), and / or an atlas bitstream in a demultiplexer (611). If the bitstream of mesh data is not encapsulated in a file form in the transmitter, the decapsulation process is omitted in the receiver. If the current mesh has inter-encoding applied, the base mesh bitstream may be a motion vector bitstream.

[0186] According to embodiments, an atlas bitstream is provided to an atlas decoder (612). The atlas decoder (612) can decode the atlas bitstream to restore atlas information. The restored atlas information can be used in a mesh decoding process. According to embodiments, the process in which the atlas information is used may be a segmentation process, a displacement vector restoration process, etc., and may include information such as tiles and patches.

[0187] According to embodiments, the atlas bitstream may be decoded through Exp-Golomb coding of the atlas decoder (612), etc. At this time, the atlas may be information required for the mesh reconstruction process, and may mean information such as tiles and patches. In addition, the atlas data may mean data required for the mesh decoding, mesh reconstruction, etc. processes, and may include a segmentation method, a transformation method, a quantization method, the location and size of a patch within the atlas frame, etc.

[0188] According to embodiments, the base mesh bitstream is provided to a motion vector decoder (623) via a switching unit (621) or to a static mesh decoder (622).

[0189] For example, if the current mesh has inter encoding applied, the base mesh bitstream, i.e., the motion vector bitstream, is received, demultiplexed, and then output to the motion vector decoder (623) through the switching unit (621). As another example, if the current mesh has intra encoding applied, the base mesh bitstream is received, demultiplexed, and then output to the static mesh decoder (622) through the switching unit (621). Here, the motion vector decoder (623) may be referred to as a motion decoder.

[0190] According to embodiments, the motion vector decoder (623) can perform decoding on a motion vector bitstream in units of vertices or subgroups.

[0191] According to embodiments, the motion vector decoder (623) can reconstruct the final motion vector by adding the differential motion vector (i.e., residual motion vector) decoded from the bitstream using the previously decoded motion vector as a predictor. That is, the motion vector decoder (623) decodes the differential motion vector (or residual motion vector) in units of vertices or subgroups (or subblocks) through the motion vector bitstream, and performs prediction based on connection information using the previously decoded motion vector as a predictor to decode the motion vector by adding it to the residual motion vector.

[0192] According to embodiments, the static mesh decoder (622) can decode the base mesh bitstream to restore connection information, vertex geometry information, texture coordinates (i.e., attribute geometry information), normal information, etc. of the base mesh. That is, the static mesh decoder (622) can restore a restored quantized base mesh, for example, connection information, vertex geometry information, vertex texture coordinates, etc. of the base mesh.

[0193] According to embodiments, the base mesh restoration unit (631) may restore the current base mesh based on the decoded motion vector or the decoded base mesh. For example, if the current mesh has inter-screen encoding applied, the base mesh restoration unit (631) may add the decoded (or restored) motion vector to the reference base mesh and then perform inverse quantization to generate a restored base mesh (i.e., the current base mesh). As another example, if the current mesh has intra-screen encoding applied, the base mesh restoration unit (631) may perform inverse quantization on the decoded (or restored) base mesh through the static mesh decoder (622) to generate a restored base mesh (i.e., the current base mesh). According to embodiments, inverse quantization may be omitted.

[0194] According to embodiments, the displacement sub-bitstream is provided to the arithmetic decoding unit (625) or the video decoding unit (627) through the switching unit (624) depending on the decoding method.

[0195] For example, if the decoding method is an arithmetic codec method, the arithmetic decoding unit (625) decodes the displacement sub-stream based on the arithmetic codec, and the inverse prediction unit (626) performs the inverse process of prediction on the decoded displacement information and then outputs it to the inverse quantization unit (629). As another example, if the decoding method is a 2D video codec method, the video decoding unit (627) decodes the displacement sub-stream based on the 2D video codec, and the image unpacking unit (628) unpacks the image of the decoded displacement video and then outputs it to the inverse quantization unit (629).

[0196] The displacement information provided from the above-mentioned inverse prediction unit (626) or image unpacking unit (628) is inversely quantized in the inverse quantization unit (629) and inversely transformed in the inverse linear lifting unit (630), and then restored as displacement information for each vertex (i.e., Recon. displacements).

[0197] According to embodiments, the mesh restoration unit (632) reconstructs and restores the deformed mesh (i.e., decoded mesh) using the restored displacement output from the inverse linear lifting unit (630) and the restored base mesh output from the base mesh restoration unit (631). That is, the dequantized restored base mesh is combined with the restored displacement information to generate the final decoded mesh. In the present disclosure, the final decoded mesh is referred to as a reconstructed deformed mesh.

[0198] According to embodiments, an attribute map sub-stream is decoded through a video decoding unit (633) corresponding to a video compression codec used in encoding, and then restored to a final attribute map (i.e., decoded attribute map) through a color conversion unit (634) through processes such as color format conversion and color space conversion.

[0199] According to embodiments, 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.

[0200] To summarize Fig. 11, the base mesh sub-stream can be decoded through a static mesh decoder (622) based on MEB (MPEG EdgeBreaker) technology depending on the basemesh type, for example, if it is an INTRA type, and as a result, connection information, vertex geometry information, vertex mapping information (texture coordinates), etc. of the base mesh can be restored.

[0201] In an encoder according to embodiments, when the texture parameterization method is orthoAtlas, the decoder can derive mapping information (texture coordinates) and attribute information (texture) connection information using vertex coordinates. The process of deriving mapping information (texture coordinates) and connection information can generate mapping information (texture coordinates) and attribute information (texture) connection information by calculating a homography transform of each face and then projecting the vertex based on the homography transform.

[0202] According to embodiments, when the base mesh type is INTER, motion information can be decoded through entropy decoding and inverse prediction processes. The decoded motion information is combined with a reference base mesh that has already been reconstructed and stored in a buffer to generate a reconstructed quantized base mesh for the current frame. An inverse quantization process can be performed on the reconstructed base mesh.

[0203] That is, the motion vector decoder derives the motion field of the base mesh of the current frame through motion estimation and compensation based on the base mesh in the reference frame when the mesh data in the bitstream is encoded based on inter prediction. The static mesh decoder decodes the base mesh when the mesh data in the bitstream is encoded based on intra prediction.

[0204] The displacement sub-stream is decoded into displacement video through the decoder of the video compression codec, for example, if it is compressed through a video codec, depending on the compression method used by the encoder, and then the image unpacking process is performed.

[0205] As another example, when compressed through arithmetic coding, the displacement sub-stream can be decoded into binarized syntax elements through arithmetic decoding, a contextual probability model (CPM) can be adaptively determined according to each bin of the syntax elements, and arithmetic decoding can be performed by predicting the occurrence probability of the bin through the CPM. The binarized syntax elements can be decoded through inverse binarization. Quantized displacement vector transform coefficients can be derived from the decoded syntax elements. As another example, when the displacement information type is INTER (when inter prediction is performed), an inverse inter prediction process is performed using reference information for the quantized displacement vector transform coefficients.

[0206] The quantized displacement vector transformation coefficient is restored to displacement information for each vertex through the inverse quantization, inverse transformation, and coordinate system transformation processes.

[0207] The restored base mesh and the restored displacement information are combined to generate the final decoded mesh. The attribute map substream is decoded by the decoder of the video compression codec used by the encoder, and then reconstructed into the final attribute map through processes such as color format conversion.

[0208] 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.

[0209] Fig. 12 illustrates a mesh data transmission device according to embodiments.

[0210] FIG. 12 corresponds to the transmitting device (100) or mesh video encoder (102) of FIG. 2, the encoder (preprocessor and encoder) of FIG. 3 or FIG. 7, and / or a transmitting encoding device corresponding thereto. Each component of FIG. 12 corresponds to hardware, software, a processor, and / or a combination thereof.

[0211] The operation process of a transmitter for compressing and transmitting dynamic mesh data using V-Mesh compression technology may be as shown in Fig. 12. The transmitter of Fig. 12 may perform an intra-frame encoding (or intra-encoding or intra-screen encoding) process and / or an inter-frame encoding (or inter-encoding or inter-screen encoding) process.

[0212] The pre-processor (811) receives the original mesh as input and generates a simplified mesh (decimated mesh) (or base mesh) and a fitted decimated mesh (or subdivision). Simplification can be performed based on the target number of vertices or target number of polygons that constitute the mesh. Parameterization, which generates texture coordinates and texture connection information per vertex, can be performed on the simplified mesh. For example, parameterization is a process of mapping a 3D surface to a texture domain for the decimated mesh. If parameterization is performed using the UVAtlas tool, mapping information is generated that can identify where each vertex of the decimated mesh can be mapped on a 2D image. The mapping information is expressed and stored as texture coordinates, and the final base mesh is generated through this process. In addition, the work of quantizing the mesh information in floating-point form into fixed-point form can be performed. This result can be output as a base mesh to a motion vector encoder (813) or a static mesh encoder (814) through a switching unit (812). The pre-processor (811) 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 pre-processor (811) can generate a fitted subdivided mesh by adjusting the vertex positions so that the subdivided mesh becomes similar to the original mesh.

[0213] According to embodiments, the base mesh is output to a motion vector encoder (813) via a switching unit (812) when performing inter-encoding for the corresponding mesh frame, and is output to a static mesh encoder (814) via a switching unit (812) when performing intra-encoding for the corresponding mesh frame. The motion vector encoder (813) may be referred to as a motion encoder.

[0214] For example, when performing intra-encoding (or intra-frame encoding) on ​​the corresponding mesh frame, the base mesh can be compressed through a static mesh encoder (814). In this case, encoding can be performed on 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 a multiplexer (823).

[0215] As another example, when performing inter-encoding (or inter-frame encoding) for the corresponding mesh frame, the motion vector encoder (813) can receive a base mesh and a reference reconstructed base mesh (or a reconstructed quantized reference base mesh) as input, calculate a motion vector between the two meshes, and encode the value. In addition, the motion vector encoder (813) 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 multiplexer (823).

[0216] The base mesh restoration unit (815) can receive the base mesh encoded by the static mesh encoder (814) or the motion vector encoded by the motion vector encoder (813) and generate a reconstructed base mesh. For example, the base mesh restoration unit (815) can perform static mesh decoding on the base mesh encoded by the static mesh encoder (814) to restore the base mesh. At this time, quantization can be applied before the static mesh decoding, and inverse quantization can be applied after the static mesh decoding. As another example, the base mesh restoration unit (815) can restore the base mesh based on the reconstructed quantized reference base mesh and the motion vector encoded by the motion vector encoder (813). The reconstructed base mesh is output to the displacement calculation unit (816) and the mesh restoration unit (820).

[0217] The displacement calculation unit (816) can perform mesh refinement on the restored base mesh. The displacement calculation unit (816) can calculate a displacement vector, which is a difference value in the vertex positions between the restored base mesh that has been refined and the fitted subdivision (or refined) mesh generated by the pre-processor (811). At this time, the displacement vector can be calculated as many times as the number of vertices of the refined mesh. The displacement calculation unit (816) 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.

[0218] The displacement vector video generation unit (817) may include a linear lifting unit, a quantizer, and an image packing unit. That is, in the displacement vector video generation unit (817), the linear lifting unit may transform the displacement vector for effective encoding. The transformation may be performed by a lifting transformation, a wavelet transformation, etc., according to embodiments. In addition, quantization may be performed in a quantizer on the transformed displacement vector value, that is, the transform coefficient. At this time, different quantization parameters may be applied to each axis of the transform coefficient, and the quantization parameters may be derived according to the agreement of the encoder / decoder. The displacement vector information that has undergone transformation and quantization may be packed into a 2D image in the image packing unit. The displacement vector video generation unit (817) may generate a displacement vector video by bundling the packed 2D images for each frame, and the displacement vector video may be generated for each GoF (Group of Frame) unit of the input mesh.

[0219] The displacement vector video encoder (818) can encode the generated displacement vector video using a video compression codec. The generated displacement vector video bitstream is transmitted to a multiplexer (823).

[0220] The displacement vector restoration unit (819) may include a video decoder, an image unpacking unit, an inverse quantizer, and an inverse linear lifting unit. That is, the displacement vector restoration unit (819) performs decoding on an encoded displacement vector in the video decoder, performs image unpacking in the image unpacking unit, performs inverse quantization in the inverse quantizer, and then performs inverse transformation in the inverse linear lifting unit to restore the displacement vector. The restored displacement vector is output to the mesh restoration unit (820). The mesh restoration unit (820) restores the deformed mesh based on the base mesh restored in the base mesh restoration unit (815) and the displacement vector restored in the displacement vector restoration unit (819). The restored mesh (or restored deformed mesh) has restored vertices, connection information between vertices, texture coordinates, and connection information between texture coordinates.

[0221] The texture map video generation unit (821) can regenerate a texture map based on the texture map (or attribute map) of the original mesh and the restored deformed mesh output from the mesh restoration unit (820). According to embodiments, the texture map video generation unit (821) can assign color information per vertex of the texture map of the original mesh to the texture coordinates of the restored deformed mesh. According to embodiments, the texture map video generation unit (821) can generate a texture map video by grouping the regenerated texture maps by GoF unit for each frame.

[0222] The generated texture map video can be encoded using a video compression codec of a texture map video encoder (822). The texture map video bitstream generated through encoding is transmitted to a multiplexer (823).

[0223] A multiplexer (823) multiplexes a motion vector bitstream (e.g., in case of inter encoding), a base mesh bitstream (e.g., in case of intra encoding), a displacement vector bitstream, and a texture map bitstream into a single bitstream. The single bitstream can be transmitted to a receiver via a transmitter (824). Alternatively, the motion vector bitstream, the base mesh bitstream, the displacement vector bitstream, and the texture map bitstream can be generated as a file with one or more track data or encapsulated into segments and transmitted to a receiver via the transmitter (824).

[0224] Referring to FIG. 12, 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 (or displacement), and a texture map (or attribute map). A transmitting device according to inter-encoding can generate a motion vector (or motion), a displacement vector (or displacement), and a texture map (or attribute map). The texture map obtained from the data input unit is generated and encoded based on the restored mesh. The displacement is generated and encoded through the difference in vertex positions between the base mesh and the divided (or subdivided or subdivided) mesh. More specifically, the displacement is the difference in positions between the fitted sub-divided mesh and the sub-divided restored base mesh, i.e., the difference in vertex positions between the two meshes. In addition, the base mesh is generated by simplifying and encoding the original mesh through pre-processing. Motion is generated as motion vectors for the mesh of the current frame based on the reference base mesh of the previous frame.

[0225] Fig. 13 illustrates a mesh data receiving device according to embodiments.

[0226] Fig. 13 corresponds to the receiving device (110) or mesh video decoder (113) of Fig. 2, the decoder of Fig. 11, and / or the receiving decoding device corresponding thereto. Each component of Fig. 13 corresponds to hardware, software, a processor, and / or a combination thereof. The receiving (decoding) operation of Fig. 13 may follow the reverse process of the corresponding process of the transmitting (encoding) operation of Fig. 12.

[0227] The bitstream of the mesh data received by the receiver (910) is demultiplexed into a compressed motion vector bitstream (e.g., inter decoding) or a base mesh bitstream (e.g., intra decoding), a displacement vector bitstream, and a texture map bitstream after file / segment decapsulation in the demultiplexer (911). For example, if the current mesh has inter-screen encoding (i.e., inter encoding) applied, the motion vector bitstream is received, demultiplexed, and then output to the motion vector decoder (913) via the switching unit (912). As another example, if the current mesh has intra-screen encoding (i.e., intra encoding) applied, the base mesh bitstream is received, demultiplexed, and then output to the static mesh decoder (914) via the switching unit (912). Here, the motion vector decoder (913) may be referred to as a motion decoder.

[0228] According to embodiments, if the current mesh has inter-screen encoding applied according to frame header information, the motion vector decoder (913) can perform decoding on the motion vector bitstream. According to embodiments, the motion vector decoder (913) can reconstruct the final motion vector by adding the previously decoded motion vector as a predictor to the residual motion vector decoded from the bitstream.

[0229] According to embodiments, if the current mesh has been subjected to in-screen encoding according to frame header information, the static mesh decoder (914) can decode the base mesh bitstream to restore connection information, vertex geometry information, texture coordinates, normal information, etc. of the base mesh.

[0230] According to embodiments, the base mesh restoration unit (915) can restore the current base mesh based on the decoded motion vector or the decoded base mesh. For example, if the current mesh has inter-screen encoding applied, the base mesh restoration unit (915) can generate a restored base mesh by adding the decoded motion vector to the reference base mesh and then performing inverse quantization. As another example, if the current mesh has intra-screen encoding applied, the base mesh restoration unit (915) can generate a restored base mesh by performing inverse quantization on the base mesh decoded through the static mesh decoder (914).

[0231] According to embodiments, the displacement vector video decoder (917) may decode the displacement vector bitstream as a video bitstream using a video codec or decode it using an arithmetic codec. That is, if the displacement vector bitstream is encoded using a video codec, for example, depending on the encoding codec type, a depacking process may be performed after decoding using the video codec. As another example, if encoded using arithmetic coding, arithmetic decoding may be performed on the displacement vector bitstream through a displacement vector arithmetic decoding unit, and if inter-screen prediction is performed, a residual value may be added to a reference displacement vector transform coefficient through inter-screen prediction to generate a current displacement vector transform coefficient.

[0232] According to embodiments, the displacement vector restoration unit (918) extracts displacement vector transformation coefficients from the decoded displacement vector video, and restores the displacement vector by applying inverse quantization and inverse transformation processes to the extracted displacement vector transformation coefficients. To this end, the displacement vector restoration unit (918) may include an image unpacking unit, an inverse quantizer, and an inverse linear lifting unit. If the restored displacement vector is a value in a local coordinate system, a process of inverse transformation to a Cartesian coordinate system may be performed.

[0233] The mesh restoration unit (916) can generate additional vertices by performing subdivision on the restored base mesh. Through subdivision, vertex connection information including the added vertices, texture coordinates, and texture coordinate connection information can be generated. At this time, the mesh restoration unit (916) can generate a final restored mesh (or a restored deformed mesh) by combining the subdivided restored base mesh with the restored displacement vector.

[0234] According to embodiments, the texture map video decoder (919) can decode the texture map bitstream as a video bitstream using a video codec to restore the texture map. The restored texture map has 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 each vertex.

[0235] According to embodiments, the mesh restored by the mesh restoration unit (916) and the texture map restored by the texture map video decoder (919) are shown to the user through a rendering process in the mesh data renderer (920).

[0236] Referring to FIG. 13, 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 (or referred to as displacement), a texture map (or referred to as attribute map), and render mesh data based on the restored mesh and the restored texture map. A receiving device according to inter-decoding can receive a motion vector (or referred to as motion), a displacement vector (or referred to as displacement), a texture map (or referred to as attribute map), and render mesh data based on the restored mesh and the restored texture map.

[0237] A mesh data transmission device and method according to embodiments may pre-process mesh data, encode the pre-processed mesh data, and transmit a bitstream including the encoded mesh data. A point mesh data reception device and method according to embodiments may receive a bitstream including mesh data and decode the mesh data. The mesh data transmission and reception method / device according to embodiments may be abbreviated as method / device according to embodiments. The mesh data transmission and reception method / device according to embodiments may also be referred to as 3D data transmission and reception method / device or point cloud data transmission and reception method / device.

[0238] As described above, in the present disclosure, the mesh may be composed of sub-units, for example, sub-meshes. In the present disclosure, a sub-mesh may be defined as an independently decodable region of the base mesh.

[0239] According to embodiments, the V-DMC encoder / decoder of the present disclosure may perform encoding / decoding in units of sub-mesh. In particular, the present disclosure proposes a method for decoding a sub-mesh up to a specific LoD level in a decoder of a receiving device when decoding the sub-mesh. The present disclosure can decode a sub-mesh at a specific LoD level by decoding the sub-mesh up to a specific LoD level depending on the status of the receiving device, the network environment, etc.

[0240] That is, there may be environments where high-resolution mesh content cannot be used depending on the network status of the receiver, display characteristics, receiver device performance, etc. In order to use mesh content even in a low-performance receiver environment, a technology is needed that can decode and restore only a portion of the V-DMC bitstream corresponding to the low-resolution mesh and decode and restore it as a low-resolution mesh, thereby enabling decoding and restoration with a small amount of computation and memory space. However, the current V-DMC technology has a limitation in that it cannot perform decoding and restoration of low-resolution meshes at a specific LoD level because it only performs the decoding and restoration process with a mesh of the same LoD (or resolution) as the number of subdivisions determined in the encoder. Therefore, the present disclosure proposes a method of performing decoding and restoration by extracting only a portion of the mesh bitstream of the LoD (or resolution) suitable for the decoder environment. That is, the present disclosure allows for decoding and restoring a mesh of a resolution (or LoD) suitable for the decoder environment by taking into account various environments of the receiver where decoding and restoration are performed (e.g., network conditions, display characteristics, receiver performance, etc.). Therefore, since only a bitstream corresponding to a low-resolution mesh (or a low LoD level) can be partially extracted and decoded, less memory is required compared to a high-resolution mesh, and since mesh decoding and restoration can be performed only up to a low LoD level, it is possible to enable the use of low-resolution mesh content using less computational effort compared to a high-resolution mesh.

[0241] As such, the present disclosure relates to V-DMC, a method for compressing 3D dynamic mesh data using an existing 2D video codec, and more particularly, to a method, device, and syntax and semantics information related thereto that support decoding a sub-mesh of a dynamic mesh up to a specific LoD level. In the present disclosure, each vertex constituting the mesh represents a position in 3D space, and is expressed as, for example, x, y, z coordinates (i.e., a canonical coordinate system). In addition, a polygon may be a triangle or a quadrangle. In the present disclosure, vertex, point, and point may be used with the same meaning. That is, a vertex has a coordinate in 3D space, and a triangular or quadrangle polygon can be generated through a connection between a plurality of vertices. In addition, V-DMC referred to in the present disclosure may also be referred to as V-mesh, and the two terms are expressions used with the same meaning.

[0242] The following describes in detail how the encoder of the transmitting device compresses mesh data by packing it into one frame per LoD level, and how the decoder of the receiving device decodes sub-meshes up to a specific LoD level.

[0243] Fig. 14 illustrates a transmitting device according to embodiments. The transmitting device of Fig. 14 may be referred to as a mesh data transmitting device or an encoder or an encoder of a transmitting device or a V-Mesh encoder or a dynamic mesh encoder.

[0244] FIG. 14 corresponds to the transmitting device (100) or mesh video encoder (102) of FIG. 1, the encoder (pre-processor and encoder) of FIG. 2 or FIG. 7, the transmitting device of FIG. 12, and / or the transmitting encoding device corresponding thereto. Therefore, parts not described in FIG. 14 will refer to the description of the transmitting device (100) or mesh video encoder (102) of FIG. 1, the encoder (pre-processor and encoder) of FIG. 2 or FIG. 7, and the transmitting device of FIG. 12. The elements of the transmitting device illustrated in FIG. 14 may be implemented by hardware, software, a processor connected to a memory, and / or a combination thereof. That is, the elements of the transmitting device of FIG. 14 may be implemented by hardware, software, firmware, or a combination thereof, including one or more processors or integrated circuits configured to be able to communicate with one or more memories, although not illustrated in the drawing. One or more processors may perform at least one of the operations and / or functions of the elements of the transmitting device of FIG. 14 described above. Furthermore, one or more processors may operate or execute a set of software programs and / or instructions for performing the operations and / or functions of the elements of the transmitting device of FIG. 14. The execution order of each block in FIG. 14 may be changed, some blocks may be omitted, and some blocks may be newly added.

[0245] In the present disclosure, the operation process of a transmitter for compressing and transmitting dynamic mesh data using V-Mesh compression technology may be as shown in Fig. 14. The transmitter of Fig. 14 may support both an intra-frame encoding (or intra-encoding or intra-screen encoding) process and / or an inter-frame encoding (or inter-encoding or inter-screen encoding) process.

[0246] In Fig. 14, the mesh simplification unit (11011) simplifies the input original mesh through a mesh simplification algorithm to generate a base mesh (or simplified base mesh or simplified mesh). At this time, mesh simplification can be performed based on the number of target vertices or target polygons constituting the mesh. For example, a method such as decimation can be used as a mesh simplification algorithm that simplifies the original mesh. That is, the decimation method can be a process of selecting vertices to be removed from the original mesh using a certain reference point, and then removing the selected vertices and the triangles connected to the selected vertices.

[0247] That is, the mesh simplification unit (11011) can simplify the input mesh by the target number of vertices or the target number of faces. At this time, the simplification process can be performed through various methods such as triangle collapse and edge collapse.

[0248] According to embodiments, the base mesh simplified in the mesh simplification unit (11011) is provided to the mesh parameterization unit (11012) and the mesh refinement unit (11018).

[0249] The mesh parameterization unit (11012) performs a process of mapping a 3D surface to a texture domain for a simplified mesh (decimated mesh). That is, the mesh parameterization unit (11012) generates texture coordinates and texture connection information of the input mesh. In one embodiment, the mesh parameterization unit (11012) may perform parameterization using a UV Atlas tool. Through this process, mapping information is generated regarding which location on a 2D image each vertex of the simplified mesh (decimated mesh) can be mapped to. The mapping information is expressed and stored as texture coordinates, and through this process, the final base mesh is generated. That is, the mesh parameterization unit (11012) performs parameterization to generate texture coordinates (UV coordinates) and texture connection information per vertex of the input mesh (i.e., simplified mesh or simplified base mesh).

[0250] The final base mesh (or base mesh with texture map) generated in the above parameterization unit (11012) is input to the mesh quantization unit (11013) and quantized.

[0251] According to embodiments, the mesh quantization unit (11013) may perform a task of quantizing floating-point type mesh information (e.g., geometry information (x, y, z) or / and texture coordinates (u, v), normal information (nx, ny, nz), etc.) into fixed-point type. That is, the mesh quantization unit (11013) may quantize vertex coordinates and texture coordinates of the base mesh. According to embodiments, quantization for specific components may be omitted.

[0252] The above mesh subdivision unit (11018) subdivides the base mesh simplified by the mesh simplification unit (11011). That is, the mesh subdivision unit (11018) 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. At this time, depending on the subdivision method, geometry information connection information, texture coordinate connection information, and texture coordinates can be implicitly derived and generated. According to embodiments, the mesh subdivision unit (11018) can perform subdivision through a method such as mid-edge, Loop, or Catmul&Clark.

[0253] More specifically, in the mesh refinement unit (11018), mesh refinement can be performed n times by user parameters or a promise of the encoder (i.e., transmitting device) / decoder (i.e., receiving device). According to embodiments, the vertices of the base mesh are vertices of level 0 (R0), the vertices newly generated by performing refinement once are vertices of level 1 (R1), … the vertices newly generated by performing refinement n times are vertices of level n (R n ) can be defined as vertices of level 0 (R0). For convenience of explanation, the present disclosure refers to vertices of level 0 (R0) as level 0 vertices, vertices of level 1 (R1) as level 1 vertices, …, level n (R n ) can be called level n vertices. Also, level 0 is called the 0th level (R0), level 1 is called the 1st level (R1), … level n is called the nth level (R n ) can be referred to as level 0 to level n (R0 to R n ) can be referred to as refinement level 0 to refinement level n, or segmentation level 0 to segmentation level n, or LoD level 0 to LoD level n.

[0254] According to embodiments, LoD0, LoD1, … LoDn can be defined as in the following mathematical expression 1.

[0255] [Mathematical Formula 1]

[0256] LoD0 = R0

[0257] LoD1 = R0+ R1= LoD0 + R1

[0258] …

[0259] LoDn = R0+ R1+, … , + R n = LoDn-1 + R n = R0∪ R1∪, … , ∪ R n

[0260] That is, the base mesh includes vertices for LoD0. And, the first subdivision mesh generated by subdividing the base mesh once includes vertices for LoD1. That is, LoD1 includes vertices of the base mesh (i.e., R0 vertices) and vertices of a newly generated level 1 by subdividing the base mesh (i.e., R1 vertices). In addition, the second subdivision mesh generated by subdividing the first subdivision mesh again includes vertices for LoD2. That is, LoD2 includes vertices of the base mesh (i.e., R0 vertices), vertices of a newly generated level 1 by subdividing the base mesh (i.e., R1 vertices), and vertices of a newly generated level 2 by subdividing the first subdivision mesh (i.e., R2 vertices).

[0261] In this way, LoD indicates the level of detail of mesh data content, and as the LoD (or level) index increases, the distance between vertices becomes closer and the level of detail increases. In other words, the smaller the LoD value, the less detailed the mesh data content, and the larger the LoD value, the higher the detail of the mesh data content.

[0262] According to embodiments, the mesh fitting unit (11019) can perform fitting by adjusting vertex positions so that the mesh subdivided by the mesh subdivision unit (11018) becomes similar to the original mesh, thereby generating a fitted subdivided mesh.

[0263] According to embodiments, the mesh simplification unit (11011), the mesh parameterization unit (11012), the mesh refinement unit (11018), and the mesh fitting unit (11019) may be omitted, and when these processes are omitted, the original mesh may be applied as input to the mesh quantization unit (11013).

[0264] At this time, coordinate information of the original mesh can be applied as input to the displacement vector calculation unit (11020), and according to embodiments, the displacement vector encoding process (displacement vector calculation unit (11020), displacement vector coordinate system conversion unit (11021), and displacement vector encoder (11022)) can be omitted.

[0265] The present disclosure may be referred to as a pre-processor, including a mesh simplification unit (11011), a mesh parameterization unit (11012), a mesh refinement unit (11018), and a mesh fitting unit (11019). According to embodiments, the pre-processor may further include a displacement vector calculation unit (11020).

[0266] According to embodiments, the base mesh quantized in the mesh quantization unit (11013) may be output to a motion vector encoder (11015) or a static mesh encoder (11016) via a switching unit (11014). According to embodiments, the base mesh is output to the motion vector encoder (11015) via the switching unit (11014) when inter-encoding is performed on the corresponding mesh frame, and is output to the static mesh encoder (11016) via the switching unit (11014) when intra-encoding is performed on the corresponding mesh frame. The motion vector encoder (11015) may be referred to as a motion encoder.

[0267] For example, when performing intra encoding or intra frame encoding for the corresponding mesh frame, the base mesh can be compressed through a static mesh encoder (11016). In this case, encoding can be performed on connection information, vertex geometry information, vertex texture information, normal information, etc. of the base mesh. That is, vertex coordinates, vertex connection information, texture coordinates, texture connection information, etc. of the mesh can be encoded in the static mesh encoder (11016). The base mesh bitstream generated through encoding is transmitted to a multiplexer (not shown).

[0268] As another example, when performing inter-encoding (or inter-frame encoding) on ​​the corresponding mesh frame, the motion vector encoder (11015) may receive the current base mesh and the reference reconstructed base mesh (or the reconstructed quantized reference base mesh) as input, calculate a motion vector between the two meshes, and encode the value. In addition, the motion vector encoder (11015) may perform prediction based on connection information using a previously encoded / decoded motion vector as a predictor, and entropy-encode a differential motion vector (or residual motion vector) obtained by subtracting the predicted motion vector from the current motion vector. According to embodiments, the motion vector encoding may be performed on a vertex basis or a subgroup basis. The motion vector bitstream generated through the motion vector encoding is transmitted to a multiplexer (not shown) as a base mesh bitstream. That is, in the case of intra-frame encoding, the static mesh bitstream is input to the multiplexer as a base mesh bitstream, and in the case of inter-frame encoding, the motion vector bitstream is input to the multiplexer as a base mesh bitstream.

[0269] In FIG. 14, the base mesh decoder (11017, or base mesh restoration unit) can receive a base mesh encoded by a static mesh encoder (11016) or a motion vector encoded by a motion vector encoder (11015) and generate a reconstructed base mesh. The base mesh decoder (11017) performs restoration of the base mesh according to the encoding type (inter-screen encoding or intra-screen encoding) of the current mesh. For example, the base mesh decoder (11017) can perform static mesh decoding on the base mesh encoded by the static mesh encoder (11016) to restore the base mesh. At this time, quantization can be applied before static mesh decoding, and inverse quantization can be applied after static mesh decoding. That is, when intra-screen encoding is performed, the current base mesh can be restored by performing dequantization on the quantized base mesh through the mesh quantization unit (11013). As another example, the base mesh decoder (11017) can restore the base mesh based on the restored quantized reference base mesh and the motion vector encoded by the motion vector encoder (11015). That is, when inter-screen encoding is performed, the current base mesh can be generated by decoding the motion vector using the motion vector decoding method and then applying (i.e., adding) the decoded motion vector to the reference restored base mesh. At this time, when 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 encoder (11015). The restored base mesh is output to the displacement vector calculation unit (11020) and the mesh dequantization unit (11024).

[0270] According to embodiments, the displacement vector calculation unit (11020) can perform mesh refinement on the restored base mesh. In addition, the displacement vector calculation unit (11020) can calculate a displacement vector, which is a difference value of vertex positions between the restored base mesh that has been refined and the fitted subdivision (or refined) mesh generated by the mesh fitting unit (11019). At this time, the displacement vector can be calculated as many times as the number of vertices of the refined mesh. That is, the displacement vector of the number of vertices of the refined mesh can be calculated through the displacement vector calculation unit (11020).

[0271] According to embodiments, the displacement vector coordinate system transformation unit (11021) can transform a vertex displacement vector calculated in a 3D Cartesian coordinate system (i.e., (x, y, z) space) into a local coordinate system (i.e., normal, tangential, bi-tangential coordinate system) based on the normal vector of each vertex. At this time, the normal vector can be calculated for each subdivided vertex based on the geometry information and connection information of the surrounding vertices. According to embodiments, only the normal component among the (normal, tangential, bi-tangential) coordinate systems can be encoded. This means that when the coordinate system transformation is applied according to the agreement between the encoder / decoder, encoding of only the normal component is always performed, or the encoder can decide to signal a 1-bit flag (onlyNormFlag).

[0272] In the present disclosure, whether or not to perform displacement vector coordinate system transformation is determined by an agreement between the encoder / decoder, or whether or not to perform coordinate system transformation is determined by transmitting a coordinate system transformation status flag (applyLocalCoord) in units such as sequence, GOF (Group of frame), frame, and sub-mesh.

[0273] According to embodiments, the displacement vector encoder (11022) may perform encoding on the displacement vector or displacement vector transform coefficient output from the displacement vector calculation unit (11020) or the displacement vector coordinate system transformation unit (11021). In the present disclosure, the displacement vector encoder (11022) may perform encoding through a video codec-based encoder, a zero run length encoder, an arithmetic encoder, or the like. For example, when the encoding method is video codec-based encoding, the displacement vector encoder (11022) may encode the displacement vector transform coefficients by packing them into frames. That is, in the displacement vector encoder (11022), the displacement vector transform coefficients may be packed into a 2D image and then encoded using a 2D video codec (i.e., a video compression codec), or zero run length encoded, or arithmetic encoded to generate a displacement vector video bitstream.

[0274] According to embodiments, a displacement vector video bitstream encoded and generated by a displacement vector encoder (11022) is transmitted to a multiplexer (not shown). According to embodiments, a method for selecting encoding of the displacement vector encoder (11022) may use a displacement vector encoder promised in an encoder (i.e., a transmitting side) / decoder (i.e., a receiving side), or may analyze the characteristics of a displacement vector in an encoder on the transmitting side and transmit the type of a selected displacement vector encoder to a decoder on the receiving side.

[0275] According to embodiments, the displacement vector restoration unit (11023) can restore the displacement vector by performing the reverse process of displacement vector encoding on the displacement vector or displacement vector transform coefficient encoded by the displacement vector encoder (11022). That is, the displacement vector restoration unit (11023) can perform displacement vector depacking depending on the method of encoding the displacement vector, for example, when encoding is based on a video codec. In other words, the bitstream encoded by the 2D video encoder (i.e., the video codec-based encoder) after being packed into a 2D image / video is decoded by the 2D video decoder and depacked. In addition, the displacement vector restoration unit (11023) can additionally perform inverse quantization, inverse transformation, etc. depending on whether quantization and transformation processes are performed during the displacement vector encoding process. For example, inverse quantization is performed on the quantized transform coefficients on which inverse packing has been performed, and inverse transformation is performed to calculate the restored displacement vector.

[0276] According to embodiments, the mesh dequantization unit (11024) can dequantize vertex coordinates or texture coordinates of the restored base mesh as a reverse process of quantization. More specifically, the mesh dequantization unit (11024) performs dequantization using inputs such as restored geometry information (x, y, z) and / or texture coordinates (u, v) and / or normal information (nx, ny, nz) of the restored base mesh. According to embodiments, dequantization for a specific component may be omitted. In addition, if the quantization process is omitted in the mesh quantization unit (11013), the dequantization process is also omitted in the mesh dequantization unit (11024).

[0277] According to embodiments, the mesh restoration unit (11025) can restore a mesh based on a restored displacement vector output from the displacement vector restoration unit (11023) and a restored base mesh (or a dequantized restored base mesh) output from the mesh dequantization unit (11024). More specifically, the mesh restoration unit (11025) can perform subdivision on the restored base mesh output from the mesh dequantization unit (11024) and add the restored displacement vector from the displacement vector restoration unit (11023) to generate a reconstructed deformed mesh. That is, the mesh restoration unit (11025) performs subdivision on the restored base mesh, which is restored by performing dequantization in the mesh dequantization unit (11024), to generate subdivided vertex position information, texture coordinates, and connection information. In addition, the mesh restoration unit generates restored vertex position information by adding a restored displacement vector to the subdivided vertex position information. The mesh restored by the mesh restoration unit (11025) (or referred to as restored mesh or restored deformed mesh) has restored vertices, connection information between vertices, texture coordinates, and connection information between texture coordinates. The restored mesh (or referred to as restored mesh or restored deformed mesh) generated by the mesh restoration unit (11025) is provided to the texture map generation unit (11026).

[0278] According to embodiments, the texture map generation unit (11026) can regenerate the texture map of the current mesh based on the texture map (or attribute map) of the original mesh and the mesh restored by the mesh restoration unit (11025). That is, the texture map generation unit (11026) can generate the texture map of the restored mesh through the relationship between the texture coordinates and connection information of the restored mesh and the original mesh and the texture map of the original mesh.

[0279] According to embodiments, the texture map generation unit (11026) can assign color information per vertex of the texture map of the original mesh to the texture coordinates of the restored base mesh (or the restored deformed mesh). According to embodiments, the texture map generation unit (11026) can generate a texture map (or texture map video) by grouping the regenerated texture maps by GoF unit for each frame.

[0280] The texture map generated in the texture map generation unit (11026) may be encoded in the texture map encoder (11027). For example, the texture map encoder (11027) may encode the texture map using a 2D video codec-based encoder, a zero run length encoder, an entropy coding-based arithmetic encoder, etc. That is, the texture map generated through the texture map generation unit (11026) is stacked in the frame order of the mesh to form a texture map video, and encoding is performed on the texture map video using the 2D video encoder. In addition, the texture map encoder (11027) may further perform color space conversion of the texture map. That is, when the color space of the texture map is RGB444, encoding may be performed after conversion to a color space such as YUV420 or YUV444. Then, the texture map substream (or texture map video bitstream) generated through the texture map encoding is transmitted to a multiplexer (not shown).

[0281] According to embodiments, the type of texture map encoder (11027) may include a video encoder (e.g., VVC, HEVC, etc.), an entropy coding-based encoder, etc. In addition, a method for selecting a texture map encoder (11027) may use a texture map encoder promised in an encoder (i.e., a transmitting side) / decoder (i.e., a receiving side), or may transmit the type of texture map encoder selected by the encoder on the transmitting side to the decoder on the receiving side.

[0282] According to embodiments, the atlas encoder (11029) may generate an atlas bitstream by encoding atlas information (or atlas data). Then, the atlas bitstream generated through the atlas information encoding is transmitted to a multiplexer (not shown). In the present disclosure, the atlas may be information required in a mesh reconstruction process, and may mean information such as tiles and patches. In addition, the atlas information may mean data required in processes such as 2D mapping for a 3D object, texture mapping-related information, mesh decoding, and mesh restoration, and may include additional information such as a segmentation method, a transformation method, a quantization method, and the position and size of a patch within an atlas frame. In the present disclosure, the atlas information may be encoded through Exp-Golomb coding of the atlas encoder (11029), etc.

[0283] According to embodiments, a multiplexer (not shown) can multiplex an input base mesh bitstream, a displacement vector bitstream, a texture map bitstream, and an atlas bitstream into a single bitstream and then transmit the multiplexed bitstream to a receiving device. The multiplexed bitstream can further include a V3C / V-DMC parameter set (VPC) and a packed video bitstream. The VPS can include parameter set information such as decoder configuration information related to mesh encoding / decoding and a sequence header. The packed video bitstream is data in which texture map and displacement information are packed into a single frame. In addition, the multiplexed bitstream can be encapsulated into one or more tracks of a file and transmitted to the receiving device.

[0284] According to embodiments, the bitstream or file multiplexed in the multiplexer may be transmitted over a network or stored on a digital storage medium. Here, the network may include a broadcasting network and / or a communication network, and the digital storage medium may include various storage media such as a USB, SD, CD, DVD, Blu-ray, HDD, or SSD.

[0285] The following describes in detail the process of encoding a displacement vector or displacement vector transform coefficient in a displacement vector encoder (11022).

[0286] That is, the displacement vector encoder (11022) can perform transformation and quantization on the displacement vector. In addition, the displacement vector encoder (11022) can encode the displacement vector or the quantized displacement vector transform coefficients through a 2D video codec-based encoding method, and / or a zero run length encoding method, and / or an arithmetic encoding method, etc. In this case, the displacement vector encoder (11022) can encode the displacement vector or the quantized displacement vector transform coefficients by selectively using only one of the 2D video codec-based encoding method, the zero run length encoding method, and the arithmetic encoding method, or by using one or more various combinations thereof.

[0287] FIGS. 15 to 19 are diagrams showing various examples of the displacement vector encoder (11022) of the present disclosure.

[0288] In the present disclosure, the displacement vector encoder (11022) may be referred to as a displacement vector transform coefficient encoder. Each component of FIGS. 15 to 19 corresponds to hardware, software, a processor, and / or a combination thereof. As shown in FIGS. 15 to 19, the execution order of each block may be changed, some blocks may be omitted, and some blocks may be newly added.

[0289] Fig. 15 is a block diagram showing an example of a displacement vector encoder that encodes a displacement vector or a quantized displacement vector transform coefficient according to the present disclosure based on a 2D video codec. The displacement vector encoder (11022) of Fig. 15 may include a displacement vector transform unit, a displacement vector transform coefficient quantization unit, a displacement vector transform coefficient packing unit, and a displacement vector transform coefficient image / video encoding unit.

[0290] Fig. 16 is a block diagram showing an example of a displacement vector encoder that encodes a displacement vector or a quantized displacement vector transform coefficient based on a zero run length according to the present disclosure. The displacement vector encoder (11022) of Fig. 16 may include a displacement vector transform unit, a displacement vector transform coefficient quantization unit, a restored displacement vector transform coefficient level buffer, a displacement vector transform coefficient level prediction unit, and a displacement vector transform coefficient zero run length encoding unit.

[0291] Fig. 17 is a block diagram illustrating an example of a displacement vector encoder that arithmetic encodes a displacement vector or a quantized displacement vector transform coefficient according to the present disclosure. The displacement vector encoder (11022) of Fig. 17 may include a displacement vector transform unit, a displacement vector transform coefficient quantization unit, a restored displacement vector transform coefficient level buffer, a displacement vector transform coefficient level prediction unit, and a displacement vector transform coefficient arithmetic encoding unit.

[0292] Fig. 18 is a block diagram showing another example of a displacement vector encoder that encodes a displacement vector or a quantized displacement vector transform coefficient based on a zero run length according to the present disclosure. The displacement vector encoder (11022) of Fig. 18 may include a displacement vector transform unit, a restored displacement vector transform coefficient buffer, a displacement vector transform coefficient prediction unit, a displacement vector transform coefficient quantization unit, and a displacement vector transform coefficient zero run length encoding unit.

[0293] Fig. 19 is a block diagram illustrating another example of a displacement vector encoder that arithmetic encodes a displacement vector or a quantized displacement vector transform coefficient according to the present disclosure. The displacement vector encoder (11022) of Fig. 19 may include a displacement vector transform unit, a restored displacement vector transform coefficient buffer, a displacement vector transform coefficient prediction unit, a displacement vector transform coefficient quantization unit, and a displacement vector transform coefficient arithmetic encoding unit.

[0294] According to embodiments, the displacement vector encoder (11022) may perform displacement vector encoding through a 2D video encoder such as H.264, HEVC, VVC, etc. as in FIG. 15, or may perform displacement vector encoding through a zero run length encoder as in FIG. 16 or FIG. 18, or may perform displacement vector encoding through an arithmetic encoder as in FIG. 17 or FIG. 19.

[0295] According to embodiments, the displacement vector encoding method may be determined as a specific encoding method by an agreement between the encoder / decoder, or the encoding method determined by the encoder may be signaled as a flag (dispEncType) or an index and transmitted to the receiving device.

[0296] In the present disclosure, the displacement vector encoding method may be various, and according to an embodiment, one of {video codec-based encoding method, zero run length encoding method}, {video codec-based encoding method, zero run length encoding method}, {video codec-based encoding method, arithmetic encoding method}, video codec-based encoding method, zero run length encoding method, and arithmetic encoding method may be determined through the dispEncType flag or index.

[0297] According to embodiments, a displacement vector encoding method may be determined according to a profile defined in an encoder / decoder, and an index (profileToolsetIdx) indicating profile information may be signaled and transmitted to a receiver, and a displacement vector decoding method may be determined according to profileToolsetIdx in a decoder of the receiver.

[0298] In FIGS. 15 to 19, the displacement vector transformation unit can perform transformation on the displacement vector of the (x, y, z) or (n, t, bt) coordinate system. Here, the transformation may be applied as a lifting transformation, a wavelet transformation, etc. according to embodiments. In the (n, t, bt) coordinate system, n means normal, t means tangential, and bt means bi-tangential. For example, when a lifting transformation is performed, the vertex R of the kth subdivision level k R as a predictor when performing prediction t (t <k 또는 t<=k)의 세분화 정점 변위 벡터를 통해 k번째 세분화 레벨의 변위 벡터 예측을 수행할 수 있다. 실시예들에 따라 변위 벡터의 예측 수행 시 현재 정점보다 세분화 레벨이 낮은 정점 중 연결정보를 기반으로 가까운 n개의 점을 평균 또는 거리 기반 가중평균예측을 수행할 수 있다. 실시예들에 따라 메쉬 세분화 단계에서 현재 정점을 생성하기 위해 사용한 n개의 정점의 변위 벡터를 기반으로 예측을 수행할 수 있다. 본 개시는 모두 인접 정점의 정보를 활용해 현재 정점의 값을 예측하고 보정하는 리프팅 변환 기법을 사용하며, 예측 가중치를 적용하는 방식이 사용될 수 있다.

[0299] And, when a lifting transformation is performed, a process of updating the displacement vector of the vertex used in the prediction can be performed through the residual signal generated by the prediction.

[0300] Taking Fig. 18 or Fig. 19 as an example, the restoration displacement vector transformation coefficient is stored in the restoration displacement vector transformation coefficient buffer according to the reference structure, and the displacement vector transformation coefficient prediction unit can perform prediction through the following mathematical expression 2 by using the restoration displacement vector transformation coefficient (refDispCoeff) of the reference mesh mapped to the current mesh vertex stored in the restoration displacement vector transformation coefficient buffer as a predictor of the current displacement vector transformation coefficient.

[0301] [Equation 2]

[0302] for(size t v = 0; v <N; v++){

[0303] for(size t v = 0; d <dim; d++){

[0304] dispCore[v][d] = curDispCoeff{v][d] - refDispCoeff[v][d]

[0305] }

[0306] }

[0307] And, the displacement vector transform coefficient quantization unit can perform quantization on the displacement vector value transformed by the displacement vector transform unit, that is, the displacement vector or the displacement vector transform coefficient. According to embodiments, the displacement vector transform coefficient quantization unit can perform quantization on the differential displacement vector transform coefficient (dispCoeff) obtained by subtracting the predicted displacement vector transform coefficient (refDispCoeff) from the current displacement vector transform coefficient (curDispCodff). In the present disclosure, the displacement vector transform coefficient is used interchangeably with the displacement vector coefficient or transform coefficient as having the same meaning. According to an embodiment, the displacement vector transform coefficient may be quantized through different quantization parameters for each axis, and the quantization parameter or scaling parameter may be derived by the encoder / decoder agreement to determine the quantization rate for each LoD level.

[0308] Fig. 20 is a flowchart showing an example of a process for converting a displacement vector in a displacement vector conversion unit according to embodiments.

[0309] According to embodiments, a displacement vector in the (x,y,z) or (n,t,bt) coordinate system can be transformed through a displacement vector transformation unit.

[0310] According to embodiments, when coordinate system transformation into the (n, t, bt) coordinate system is performed in the displacement vector coordinate system transformation unit (11021), a 1D scalar displacement vector of the normal (n) component may be applied as an input to the displacement vector transformation unit of the displacement vector encoder (11022), and transformation, quantization, and encoding may be performed on the displacement value of the normal component.

[0311] At this time, the transformation may be performed by lifting transformation, wavelet transformation, etc. according to embodiments. If lifting transformation is performed, transformation of the displacement vector may be performed through the embodiment of FIG. 20.

[0312] The present disclosure can determine the number of lifting transformations using the number of mesh subdivision levels (lodCount). In the present disclosure, the lifting transformation process can be performed for each mesh subdivision level. Furthermore, a lifting transformation prediction unit and a lifting transformation update unit can be performed during the lifting transformation process.

[0313] In Fig. 20, the displacement vector transformation unit can perform lifting transformation prediction and lifting transformation update for each subdivision level.

[0314] In Fig. 20, the lifting transformation prediction part is the vertex R of the kth subdivision level. k When performing displacement vector prediction, t(t <k 또는 t≤k)번째 세분화 레벨의 정점 R t Displacement vector prediction of the kth subdivision level can be performed using the displacement vector as a predictor.

[0315] According to embodiments, when performing prediction of a displacement vector, the lifting transformation prediction unit may perform an average or distance-based weighted average prediction of n points near the current vertex based on connection information among vertices having a lower level of detail than the current vertex.

[0316] According to embodiments, the lifting transformation prediction unit can perform prediction based on displacement vectors of n vertices used to generate the current vertex in the mesh refinement step.

[0317] According to embodiments, the lifting transformation prediction unit can generate a residual signal through the difference between the displacement vector of the subdivision level and the predicted displacement vector.

[0318] In Fig. 20, the lifting transformation update unit performs a process of updating the displacement vector of the vertex used for prediction through the residual signal generated by the lifting transformation prediction unit.

[0319] The following describes the process of updating based on distance between vertices or connectivity information features (curvature, slope, etc.).

[0320] According to embodiments, the lifting transformation update weight (updateWeight) in the lifting transformation update unit can be derived from the vltp_log2_lifting_update_weight syntax (or field) included in the signaling information.

[0321] According to embodiments, the lifting transformation update process in the lifting transformation update unit may perform updates by sharing the same weight for each LoD level of the mesh, or may perform updates using different weights for each LoD level of the mesh. For example, if adaptiveUpdateWeight, which indicates whether to perform adaptive updates, is 0 (i.e., false), the same update weight can be used for each LoD level, and if it is 1 (i.e., true), different adaptive updates can be performed for each LoD level according to the characteristics of the LoD level. In other words, adaptiveUpdateWeight indicates whether to perform adaptive updates.

[0322] The following is a description of a displacement vector transformation coefficient packing method when the displacement vector encoding method is video codec-based, as in Fig. 15.

[0323] That is, the displacement vector transform coefficient packing unit of FIG. 15 can pack the quantized displacement vector transform coefficient into a 2D image of size WxH. That is, if the displacement vector encoder (11022) encodes the displacement vector transform coefficients using a video codec-based encoding method, the process of packing the displacement vector transform coefficients into a frame as a 2D image is performed in the displacement vector transform coefficient packing unit. In other words, the displacement vector transform coefficient packing unit can pack the displacement vector transform coefficients into a 2D image, and the displacement vector image / video encoding unit can encode the packed 2D images using a video compression codec.

[0324] For example, assuming that the total number of displacement vector transformation coefficients is N, the number of displacement vector transformation coefficients included in LoD0 is N0 (LoD0 = R0), and the number of displacement vector transformation coefficients included in LoD1 is N1 (LoD1), then the number of displacement vector transformation coefficients of refinement level 0 (R0) is N0, and the number of displacement vector transformation coefficients of refinement level 1 (R1) is N1-N0. That is, the number of displacement vector transformation coefficients included in LoD1 (N1) is the sum of the number of displacement vector transformation coefficients of refinement level 0 (R0) (N0) and the number of displacement vector transformation coefficients of refinement level 1 (R1) (N1-N0).

[0325] According to embodiments, the displacement vector transform coefficient packing unit can pack N displacement vector transform coefficients (e.g., N quantized displacement vector transform coefficients) into an image of size W×H. In the present disclosure, W×H can be the size of a frame in which the displacement vector transform coefficients are packed as a 2D image.

[0326] According to embodiments, displacement vector transformation coefficients of all refinement levels may be packed into one image (i.e., one frame) and encoding may be performed in the displacement vector image / video encoding unit, or displacement vector transformation coefficients may be packed into each image (i.e., each frame) for each refinement level (R) and encoding may be performed separately. Alternatively, displacement vector transformation coefficients of a specific refinement level may be packed into one image, and displacement vector transformation coefficients of multiple or more different refinement levels may be packed into another image.

[0327] According to embodiments, displacement vector transformation coefficients for each refinement level may be packed into rectangular regions to support partial decoding up to a specific LoD level. At this time, padding may be performed to fit the rectangular regions for each refinement level. In the present disclosure, these rectangular regions are referred to as packing units, refinement-level-specific packing units, or subdivision-level-specific packing units.

[0328] That is, when the displacement vector encoding method is a video codec-based encoding method as in FIG. 15, the displacement vector transform coefficient packing unit can pack the quantized displacement vector transform coefficients into one frame by LoD level through the displacement vector transform coefficient quantization unit. At this time, the area packed by LoD level may be in a raster-scan order or may be in a rectangular shape depending on the embodiment. In addition, the packing method may be derived and determined in the encoder / decoder in the same way, and the packing method may be determined in the decoder by signaling.

[0329] In the present disclosure, refinement level N may refer to vertices excluding LoD (N-1) mesh vertices among mesh vertices of LoD N. For example, LoD 0 may be a set of vertices composed of refinement level 0, LoD 1 may be a set of vertices composed of refinement level 0 and refinement level 1, LoD 2 may be a set of vertices composed of refinement level 0, refinement level 1, and refinement level 2, and LoD 3 may be a set of vertices composed of refinement level 0, refinement level 1, refinement level 2, and refinement level 3.

[0330] Depending on the embodiment, the displacement information packed by LoD level may be configured for each frame, for each tile, for each patch, for each sub-patch, etc.

[0331] According to embodiments, information about an area in which displacement information (i.e., displacement vector transformation coefficients) for each LoD packed unit may be transmitted. Information about the packed area may include the width and height of the packed area, and 2D coordinates of the upper left position of the packed area within the frame. For example, if the packed area is a patch unit, the upper left position of each patch may be signaled and transmitted to the receiving device.

[0332] In this way, the displacement vector encoder (11022) based on the video codec of the present disclosure can perform encoding while taking into account support for the LoD-based scalable decoding function of the dynamic mesh.

[0333] As a method for supporting a scalable decoding function according to embodiments, displacement vector data and texture maps may be packed into one frame each for each resolution and encoded as a V3C_PVD type (see FIG. 28), and multiresolution video in which each packed displacement vector video for each multiresolution texture map and refinement level is packed may be encoded through a scalable video codec such as SHVC or multilayer VVC.

[0334] According to embodiments, as a method for supporting a scalable decoding function, displacement vector data may be packed into a rectangular shape for each LoD level, and then video encoding may be performed by restricting each LoD packing area to a unit that can be independently decoded at the video bitstream level, such as MCTS (Motion Constrained Tile Sets) or subpicture.

[0335] That is, when coding video, the packed area by LoD level can be divided into bitstream extractable units such as MCTS (Motion-Constrained Tile Sets) for each LoD level depending on the type of video codec, in the case of HEVC, and the area can be divided into bitstream extractable units such as subpictures for each LoD level, in the case of VVC.

[0336] According to embodiments, the MCTS or subpictures may be packed in a one-to-one correspondence for each refinement level, or a one-to-one correspondence may not be established. That is, displacement information for one or more refinement levels within a subpicture or MCTS may be packed.

[0337] Depending on the embodiments, the availability of decoding support up to a specific LoD level can be directly signaled via LoD_extraction_flag. That is, the decoder of the receiving device can determine whether to perform decoding up to a specific LoD level based on LoD_extraction_flag. In the present disclosure, LoD_extraction_flag can be referred to as information indicating whether decoding up to a specific LoD level is possible. A detailed description of LoD_extraction_flag will be provided later.

[0338] Fig. 21 illustrates a receiving device according to embodiments. In the present disclosure, the receiving device of Fig. 21 may be referred to as a mesh data receiving device or decoder or a decoder of a receiving device or a V-Mesh decoder or a dynamic mesh decoder.

[0339] FIG. 21 corresponds to the receiving device (110) or mesh video decoder (113) of FIG. 1, the decoder of FIG. 11, the receiving device of FIG. 13, and / or the receiving decoding device corresponding thereto. Therefore, parts not described in FIG. 21 will refer to the description of the receiving device (110) or mesh video decoder (113) of FIG. 1, the decoder of FIG. 11, and the receiving device of FIG. 13. The elements of the receiving device illustrated in FIG. 21 may be implemented by hardware, software, a processor connected to a memory, and / or a combination thereof. That is, the elements of the receiving device of FIG. 21 may be implemented by hardware, software, firmware, or a combination thereof, including one or more processors or integrated circuits configured to communicate with one or more memories, although not illustrated in the drawing. One or more processors may perform at least one or more of the operations and / or functions of the elements of the receiving device of FIG. 21 described above. Additionally, one or more processors may operate or execute a set of software programs and / or instructions for performing operations and / or functions of elements of the receiving device of FIG. 21. The execution order of each block in FIG. 21 may be changed, some blocks may be omitted, and some new blocks may be added.

[0340] FIG. 21 may largely include a base mesh decoding unit, a displacement information decoding unit, and a texture map decoding unit. According to embodiments, the base mesh decoding unit may include a switching unit (15011), a motion vector decoder (15012), a static mesh decoder (15013), a base mesh restoration unit (15014), a mesh refinement unit (15015), and a mesh restoration unit (15016). According to embodiments, the displacement information decoding unit may include a displacement vector decoder (15017) and a displacement vector coordinate system inverse transformation unit (15020). In addition, the receiving device of FIG. 21 may further include an atlas decoder (15031).

[0341] According to embodiments, a bitstream of mesh data received by a receiver (not shown) may be demultiplexed into a base mesh bitstream, a displacement vector bitstream, a texture map bitstream, and / or an atlas bitstream after file / segment decapsulation in a demultiplexer (not shown). If the bitstream of mesh data is not encapsulated in a file form in the transmitter, the decapsulation process in the receiver is omitted. If the current mesh is subjected to inter-encoding, the base mesh bitstream may be a motion vector bitstream.

[0342] According to embodiments, an atlas bitstream is provided to an atlas decoder (15031). The atlas decoder (15031) can decode the atlas bitstream to restore atlas information. The restored atlas information can be used in a mesh decoding process. According to embodiments, the process in which the atlas information is used may include a segmentation process, a displacement vector restoration process, etc., and may include information such as tiles and patches.

[0343] According to embodiments, the atlas bitstream may be decoded through Exp-Golomb coding of the atlas decoder (15031), etc. In this case, the atlas may be information required for a mesh reconstruction process, and may mean information such as tiles and patches. In addition, the atlas data may mean data required for processes such as mesh decoding and mesh reconstruction, and may include a segmentation method, a transformation method, a quantization method, the location and size of a patch within an atlas frame, etc.

[0344] According to embodiments, the base mesh bitstream is provided to a motion vector decoder (15012) via a switching unit (15011) or to a static mesh decoder (15013).

[0345] For example, if the current mesh has inter encoding applied, the base mesh bitstream, i.e., the motion vector bitstream, is received, demultiplexed, and then output to the motion vector decoder (15012) through the switching unit (15011). As another example, if the current mesh has intra encoding applied, the base mesh bitstream is received, demultiplexed, and then output to the static mesh decoder (15013) through the switching unit (15011). Here, the motion vector decoder (15012) may be referred to as a motion decoder.

[0346] According to embodiments, the motion vector decoder (15012) can perform decoding on a motion vector bitstream on a vertex-by-vertex basis or a subgroup basis.

[0347] According to embodiments, the motion vector decoder (15012) can reconstruct a final motion vector by adding a differential motion vector (i.e., a residual motion vector) decoded from a bitstream using a previously decoded motion vector as a predictor. That is, the motion vector decoder (15012) can decode a differential motion vector (or a residual motion vector) in units of vertices or subgroups (or subblocks) through a motion vector bitstream, and perform prediction based on connection information using a previously decoded motion vector as a predictor to decode the motion vector by adding it to the residual motion vector.

[0348] According to embodiments, the static mesh decoder (15013) can decode the base mesh bitstream to restore connection information, vertex geometry information, texture coordinates (i.e., attribute geometry information), normal information, etc. of the base mesh.

[0349] According to embodiments, the base mesh restoration unit (15014) may restore the current base mesh based on the decoded motion vector or the decoded base mesh. For example, if the current mesh has inter-screen encoding applied, the base mesh restoration unit (15014) may add the decoded (or restored) motion vector to the reference base mesh and then perform inverse quantization to generate a restored base mesh (i.e., the current base mesh). As another example, if the current mesh has intra-screen encoding applied, the base mesh restoration unit (15014) may perform inverse quantization on the decoded (or restored) base mesh through the static mesh decoder (15012) to generate a restored base mesh (i.e., the current base mesh). According to embodiments, the inverse quantization unit may be omitted.

[0350] According to embodiments, the mesh subdivision unit (15015) can generate additional vertices by performing subdivision on the base mesh. The present disclosure can implicitly derive and generate geometry information connection information, texture coordinate connection information, and texture coordinates according to the subdivision method.

[0351] According to embodiments, the mesh refinement unit (15015) can perform refinement through methods such as mid-edge, Loop, and Catmul&Clark.

[0352] According to embodiments, mesh refinement in the mesh refinement unit (15015) may be performed n times by a user parameter or a promise of the encoder / decoder. According to embodiments, vertices of the base mesh are vertices of refinement level 0 (R0), vertices newly generated by performing refinement once are vertices of refinement level 1 (R1), …, vertices newly generated by performing refinement n times are vertices of refinement level n (R n ) can be defined as vertices of refinement level 0. In addition, refinement level 0 is defined as the 0th refinement level (R0), refinement level 1 is defined as the 1st refinement level (R1), …, refinement level n is defined as the nth refinement level (R n ) can be called.

[0353] According to embodiments, LoD0, LoD1, …, LoDn can be defined as in the following mathematical expression 3.

[0354] [Equation 3]

[0355] LoD0 = R0

[0356] LoD1 = R0+ R1= LoD0 + R1

[0357] …

[0358] LoDn = R0+ R1+, … , + R n = LoDn-1 + R n== R0∪ R1∪, … , ∪ R n

[0359] That is, the base mesh includes vertices for LoD0. And, the first subdivision mesh generated by subdividing the base mesh once includes vertices for LoD1. That is, LoD1 includes vertices of the base mesh (i.e., R0 vertices) and vertices of a newly generated refinement level 1 by subdividing the base mesh (i.e., R1 vertices). In addition, the second subdivision mesh generated by subdividing the first subdivision mesh again includes vertices for LoD2. That is, LoD2 includes vertices of the base mesh (i.e., R0 vertices), vertices of a newly generated refinement level 1 by subdividing the base mesh (i.e., R1 vertices), and vertices of a newly generated refinement level 2 by subdividing the first subdivision mesh (i.e., R2 vertices).

[0360] According to embodiments, the mesh subdivision unit (15015) may be performed only up to a specific LOD level depending on a specific number of subdivisions determined by the decoder.

[0361] Depending on the embodiments, the availability of support for decoding functions up to a specific LoD level may be directly parsed through the LoD_extraction_flag syntax, and / or in the case of the V3C_PVD type, may be derived depending on whether scalability function support is available, and / or in the case of the V3C_GVD type, may be derived depending on whether LoD-based displacement vector data is packed for each LoD level and extracted for each LoD level. Here, the V3C_PVD type indicates that the corresponding V3C unit payload carries packed video data, and the V3C_GVD type indicates that the corresponding V3C unit payload carries displacement data coded based on a video codec. The packed video data is data in which a texture map and displacement information are packed into one frame.

[0362] The method for determining a specific LoD according to embodiments may be input from a user or may be determined by various factors such as network environment, performance of a receiving device (or receiver), display characteristics, etc.

[0363] According to embodiments, the mesh subdivision unit (15015) can perform subdivisions as many times as the number of subdivisions corresponding to a specific LoD. For example, if the LoD to be decoded is 1, the number of subdivisions to be performed can be derived as 1, and thus subdivisions can be performed once. If the LoD to be decoded is 2, the number of subdivisions to be performed can be derived as 2, and thus subdivisions can be performed twice.

[0364] According to embodiments, the displacement vector decoder (15017) may perform video codec-based decoding on the demultiplexed displacement vector bitstream as a video bitstream, or perform zero run-length decoding, or perform arithmetic decoding.

[0365] According to embodiments, the displacement vector decoder (15017) can restore the displacement vector by decoding the displacement vector in a reverse process of the displacement vector encoding method of the transmitting side.

[0366] According to embodiments, the displacement vector coordinate system inversion unit (15020) can perform a process of inverting the displacement vector decoded by the displacement vector decoder (15017) into a Cartesian (or canonical) coordinate system (x, y, z) if the displacement vector is a value of a local coordinate system (n, t, bt). The output of the displacement vector coordinate system inversion unit (15020) is provided to the mesh restoration unit (15016).

[0367] That is, in the encoder of the transmitting device, the vertex displacement vector calculated in the (x,y,z) space can be converted to a (normal, tangential, bi-tangential) coordinate system (or local coordinate system) based on the normal vector of each vertex. At this time, the normal vector can be calculated for each subdivided vertex based on the geometric information and connection information of the surrounding vertices.

[0368] Fig. 22 is a detailed block diagram showing an example of a displacement vector coordinate system inverse transformation unit (15020) according to embodiments.

[0369] Fig. 23 is a detailed block diagram showing another example of a displacement vector coordinate system inverse transformation unit (15020) according to embodiments.

[0370] More specifically, the displacement vector coordinate system inverse transformation unit (15020) parses the coordinate system transformation flag (applyLocalCoord) included in the signaling information in units of sequence or GoF (group of frame) or frame or sub-mesh, and if its value is 1, it can perform inverse transformation of the inverse quantized (or inversely transformed) restored displacement vector from the local coordinate system (n, t, b) to the canonical coordinate system (x, y, z).

[0371] In addition, a normal vector per vertex is calculated based on the restoration vertex position information of the restoration base mesh, 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 (see Fig. 22).

[0372] At this time, in the case of interpolation, interpolation can be performed by averaging or distance-based weighting the normal information of the base mesh used for subdivision. Alternatively, the normal information of the base mesh can be used as is for subdivided vertices on the same plane.

[0373] According to the embodiments, after performing subdivision on the restored base mesh, normal vectors can be calculated for vertices generated through the mesh subdivision unit (15015) and vertices of the base mesh (see FIG. 23).

[0374] And, through the calculated normal vector per vertex, the tangential and bi-tangential vectors orthogonal to the normal vector can be calculated and the displacement vector coordinate system inverse transformation can be performed. The following mathematical expression 4 disp n (0), disp n (1), disp n (2) refers to the results of normal, tangential, and bitangential components obtained by performing inverse transformation and inverse quantization.

[0375] [Equation 4]

[0376]

[0377] In some embodiments, coordinate system inversion can always be performed without flag transmission.

[0378] According to embodiments, the mesh restoration unit (15016) restores the mesh based on the mesh refined in the mesh refinement unit (15015) and the restored displacement vector output from the displacement vector coordinate system inverse transformation unit (15020).

[0379] According to embodiments, the received and demultiplexed texture map bitstream is input to a texture map decoder (15021). According to embodiments, the texture map decoder (15021) can decode the texture map through a 2D scalable decoder. That is, the texture map decoder (15021) can restore the texture map by applying 2D scalable decoding to the texture map. In this way, the texture map decoder (15021) receives the texture map bitstream as input and performs a process of decoding the texture map. At this time, the type of texture map decoder may include a video decoder, a zero run length decoder, an arithmetic decoder, etc. According to embodiments, the texture map decoder (15021) can perform color space conversion of the texture map.

[0380] When the base mesh bitstream, displacement vector bitstream, and texture map bitstream encoded by the dynamic mesh encoder of the transmitting device are transmitted in this way, the decoder of the receiving device restores the mesh by decoding each bitstream. First, the base mesh is decoded by the motion vector or static mesh decoder depending on whether it is an inter or intra frame, and the geometry information is restored along with the decoded displacement vector information through subdivision.

[0381] Fig. 24 is a detailed block diagram showing an example of a displacement vector decoder according to embodiments. The displacement vector decoder according to embodiments may include a displacement vector transform coefficient decoding unit, a displacement vector transform coefficient inverse quantization unit, and a displacement vector inverse transform unit. Each component of Fig. 24 corresponds to hardware, software, a processor, and / or a combination thereof. The execution order of each block in Fig. 24 may be changed, some blocks may be omitted, and some blocks may be newly added.

[0382] According to embodiments, the displacement vector transform coefficient decoding unit may perform displacement vector decoding through a 2D video decoder such as H.264, HEVC, VVC, etc., or may perform displacement vector decoding through a zero run length decoder or an arithmetic decoder, etc.

[0383] According to embodiments, in the displacement vector transform coefficient decoding unit, the displacement vector transform coefficient decoding method may be determined by a specific decoding method through an agreement between the encoder and the decoder, or may be determined by receiving an encoding method determined by the encoder as a flag (dispEncType) or an index.

[0384] In the present disclosure, the displacement vector transform coefficient decoding method may be various, and according to embodiments, one of {video codec-based decoding method, zero run length decoding method}, {video codec-based decoding method, zero run length decoding method}, {video codec-based decoding method, arithmetic decoding method}, video codec-based decoding method, zero run length decoding method, and arithmetic decoding method may be determined through the dispEncType flag or index.

[0385] According to embodiments, a displacement vector transformation coefficient decoding method may be determined according to a profile defined in an encoder / decoder, and an index (profileToolsetIdx) indicating profile information may be transmitted so that the decoder may determine a displacement vector decoding method according to profileToolsetIdx. Here, in one embodiment, the decoder is a displacement vector decoder (15017).

[0386] When a method of decoding displacement vector transform coefficients based on a video codec is determined according to embodiments, a displacement vector transform coefficient decoding unit and a displacement vector transform coefficient dequantization unit of a displacement vector decoder (15017) are further provided with a displacement vector transform coefficient depacking unit.

[0387] That is, the displacement vector transform coefficients decoded based on the video codec in the displacement vector transform coefficient decoding unit undergo a depacking process in the displacement vector transform coefficient depacking unit. At this time, the displacement vector transform coefficient decoding unit can perform decoding by extracting the displacement vector bitstream only up to the area corresponding to a specific LoD from the input displacement vector bitstream in order to restore the mesh with a specific LoD. In the present disclosure, the video codec-based displacement vector bitstream may be used interchangeably with a displacement vector video bitstream, a displacement information video bitstream, or a displacement information bitstream.

[0388] The following is a description of the displacement vector transformation coefficient inverse packing.

[0389] In other words, if the displacement vector decoding method is a video codec-based decoding method, the displacement vector transform coefficient depacking unit performs a process of depacking the packed displacement vector transform coefficients in a frame.

[0390] According to embodiments, the depacking method in the displacement vector transform coefficient depacking unit may be derived in the same manner in the encoder / decoder, or the depacking method may be determined in the decoder by receiving the packing method from the encoder of the transmitting device. Here, the decoder may be a displacement vector decoder (15017). In addition, the depacking method may be determined in the displacement vector transform coefficient depacking unit within the displacement vector decoder (15017).

[0391] The reverse packing method according to the embodiments may be in a raster-scan order or may be in a rectangular shape.

[0392] According to embodiments, the unit in which displacement information is packed may be a LoD level. That is, displacement information may be packed according to LoD levels, and a depacking process may be performed based on information in the area packed for each LoD (level). According to embodiments, the area packed for each LoD level on the transmitting side may be a rectangular area.

[0393] According to embodiments, the displacement vector transform coefficient decoding unit may perform decoding on the displacement vector transform coefficient only up to a specific LOD level according to a specific number of subdivisions determined by the decoder. In one embodiment, when displacement information is transmitted by being packed by LoD level at the transmitting side, the displacement vector transform coefficient decoding unit may perform decoding on the displacement vector transform coefficient only up to a specific LOD level.

[0394] In the present disclosure, the availability of support for decoding functions up to a specific LoD level may be directly parsed through the LoD_extraction_flag syntax, and / or in the case of V3C_PVD type, may be derived based on the availability of support for scalability functions, and / or in the case of V3C_GVD type, may be derived based on the availability of extraction for each LoD level by packing LoD-based displacement vector data for each LoD level.

[0395] At this time, a specific LoD may be input from the user or may be determined by various factors such as network environment, receiver performance, and display characteristics.

[0396] According to embodiments, if the V3C_PVD type (i.e., texture map and displacement vector data are packed into one frame and encoded as video) and LoD-based scalable decoding function is supported, a layer corresponding to a specific LoD can be decoded with a scalable video decoder such as SHVC or multilayerVVC.

[0397] According to embodiments, when the displacement vector data is of type V3C_GVD (i.e., when the displacement vector data is encoded into a video) and LoD-based scalable encoding is performed, the decoder of the receiving device can decode only the displacement vector video corresponding to a specific LoD, and can perform video decoding by extracting only the video bitstream corresponding to the MCTS index or subpicture index corresponding to the specific LoD.

[0398] At this time, the displacement vector transformation coefficient inverse packing unit can obtain the displacement vector transformation coefficient by performing the inverse packing process from the decoded displacement vector data video to a specific LoD.

[0399] According to embodiments, the displacement vector transform coefficient inverse quantization unit can perform inverse quantization on displacement vector transform coefficients. According to embodiments, the displacement vector transform coefficients input to the displacement vector transform coefficient inverse quantization unit may be displacement vector transform coefficients that have been subjected to zero run length decoding or arithmetic decoding in the displacement vector transform vector decoding unit, or may be displacement vector transform coefficients that have been subjected to inverse packing in the displacement vector transform coefficient inverse packing unit. At this time, the displacement vector transform coefficients may be inverse quantized through different quantization parameters for each axis, and a quantization parameter or a scaling parameter may be derived by an agreement between the encoder / decoder to determine a quantization rate for each LoD level.

[0400] At this time, the displacement vector transform coefficient inverse quantization unit can perform inverse quantization on displacement vector transform coefficients only up to a specific LOD level according to a specific subdivision number determined in the decoder.

[0401] And, whether or not the decoding function is supported up to a specific LoD level can be directly parsed through the LoD_extraction_flag syntax, and / or in the case of V3C_PVD type, it can be derived depending on whether or not the scalability function is supported, and / or in the case of V3C_GVD type, it can be derived depending on whether or not the LoD-based displacement vector data is packed by LoD level and extraction by LoD level is possible.

[0402] Depending on the embodiments, a specific LoD may be input from a user or may be determined by various factors such as network environment, receiver performance, display characteristics, etc.

[0403] In the present disclosure, vertices corresponding to a specific LoD may be vertices that have undergone a subdivision process a specific number of times.

[0404] And, the displacement vector transformation coefficient inverse quantization unit can perform inverse quantization only for the quantized displacement vector transformation coefficients of vertices corresponding to a specific LoD.

[0405] According to embodiments, the displacement vector inverse transform unit performs an inverse transform of the transform performed in the encoder of the transmitting device on the inverse quantized displacement vector transform coefficients to output displacement vectors. According to embodiments, a lifting inverse transform, a wavelet inverse transform, etc. may be performed. If a lifting inverse transform is performed in the displacement vector inverse transform unit, a process of updating the displacement vector of a vertex used for prediction in the encoder through the parsed residual signal may be performed. That is, the displacement vector inverse transform unit performs an inverse transform of the inverse quantized displacement vector coefficients. At this time, the inverse transform may be applied to a lifting inverse transform, a wavelet inverse transform, etc. according to embodiments.

[0406] At this time, the displacement vector inverse transform unit can perform lifting inverse transform on the displacement vector transform coefficients that have been inversely quantized only up to a specific LOD level according to a specific subdivision number determined by the decoder.

[0407] Depending on the embodiments, the availability of support for decoding functions up to a specific LoD level may be directly parsed through the LoD_extraction_flag syntax, and / or in the case of V3C_PVD type, it may be derived based on whether scalability function support is available, and / or in the case of V3C_GVD type, it may be derived based on whether LoD-based displacement vector data is packed for each LoD level and extraction for each LoD level is available.

[0408] Depending on the embodiments, a specific LoD may be input from a user or may be determined by various factors such as network environment, receiver performance, display characteristics, etc.

[0409] At this time, the vertices corresponding to a specific LoD may be vertices subdivided by a specific number of subdivisions.

[0410] And, the displacement vector inverse transform unit can perform lifting inverse transform on the displacement vector transformation coefficients of vertices corresponding to a specific LoD.

[0411] Fig. 25 is a flowchart showing an example of a process of inversely transforming a displacement vector in a displacement vector inverse transform unit according to embodiments. That is, when a lifting inverse transform is performed in the displacement vector inverse transform unit, the inverse transform of a displacement vector can be performed through the embodiments of Fig. 25. At this time, the number of lifting inverse transforms can be determined using the number of mesh subdivision levels (lodCount). In addition, the lifting inverse transform process can be performed in units of mesh subdivision levels. In addition, a lifting inverse transform prediction unit and a lifting inverse transform update unit can be performed during the lifting inverse transform process.

[0412] Figure 25 is an example of performing displacement vector inverse transformation for each LoD, and may include a lifting inverse transformation update unit and a lifting inverse transformation prediction unit.

[0413] In Fig. 25, the lifting inverse transformation prediction unit can perform inverse transformation prediction on a displacement vector for which lifting inverse transformation update has been performed in the lifting inverse transformation update unit.

[0414] According to the embodiments, the lifting inverse transform prediction unit performs the lifting inverse transform on the vertex R of the kth subdivision level. k R as a predictor when performing prediction t (t <k 또는 t<=k)의 세분화 정점 변위 벡터를 통해 k번째 세분화 레벨의 변위벡터 예측을 수행할 수 있다.

[0415] According to embodiments, when performing prediction of a displacement vector, an average or distance-based weighted average prediction can be performed on n points near the current vertex based on connection information among vertices with a lower level of detail than the current vertex.

[0416] According to embodiments, prediction can be performed based on the displacement vectors of n vertices used to generate the current vertex in the mesh refinement step.

[0417] Additionally, when the lifting inverse transformation is performed, the displacement vector of the vertex of the subdivision level can be restored through the sum between the predicted displacement vector and the parsed residual signal.

[0418] In Fig. 25, the lifting inverse transformation update unit performs a process of updating the displacement vector of the vertex used for prediction through the residual signal parsed by the lifting inverse transformation prediction unit.

[0419] In the lifting inverse transform update part of the present disclosure, the lifting inverse transform update weight (updateWeight) can be derived from the vltp_log2_lifting_update_weight syntax included in signaling information (e.g., vdmc_lifting_transform_parameters).

[0420] According to embodiments, the lifting inverse transformation update process may perform updates by sharing the same weights for each LoD level of the mesh, or may perform updates using different weights for each LoD level of the mesh. For example, if adaptiveUpdateWeight, which indicates whether to perform an adaptive update, is 0, the same update weight can be used for each LoD level, and if it is 1, different adaptive updates can be performed according to the characteristics of the LoD level. In other words, adaptiveUpdateWeight indicates or determines whether to perform an adaptive update.

[0421] The following are examples of the reconstruction process and related code in the decoder of the receiving device.

[0422] The restoration processes described below are applied to the syntax elements for decoded atlas frames, basemesh frames, video frames, and syntax elements associated with the same atlas ID identified by RecAtlasID.

[0423] And, the restoration process for the current mesh frame with composition time index (compTimeIdx) uses syntax elements, variables, and the following arrays as input:

[0424] submeshesPerFrameCountNF[compTimeIdx] is a one-dimensional array in nominal format specifying the number of decoded submeshes per frame.

[0425] basemeshFramesNF[ compTimeIdx ][ submeshIdx ] is a two-dimensional array of decoded basemesh structures where submeshIdx ranges from 0 to submeshesPerFrameCountNF[compTimeIdx] - 1.

[0426] geoFramesNF[0][compTimeIdx][0][y][x] is a 5-dimensional array representing the decoded geometry frames in canonical format, if vps_geometry_video_present_flag[RecAtlasID] is 1 and the profile or codec ID indicates a 2D video codec.

[0427] Here, y is in the range [0, asps_frame_height-1] and x is in the range [0, asps_frame_width-1].

[0428] dispFramesNF[ compTimeIdx ][ dispIdx ][ dispDimIdx ] is a 3-dimensional array representing the decoded displacements in canonical format, if the profile or codec indicates an arithmetic codec. Here, dispIdx is in the range [0, DispCountPerFrame[compTimeIdx]1], and dispDimIdx is in the range [0, DispDimension-1].

[0429] attrFramesNF[ attrIdx ]

[0000] [ compTimeIdx ][ compIdx ][ y ][ x ] is a 6-dimensional array representing the decoded attribute frame in canonical format when ai_attribute_count[RecAtlasID] is greater than 0.

[0430] The output of this process is a sequence of restored mesh frames prior to the post-processing step, each containing an attribute map.

[0431] The structure RecMeshFrame, which represents the restored mesh frame, contains the following members:

[0432] The variable verCoordCount represents the number of vertex coordinates within the restored mesh frame.

[0433] The 2D array verCoordsArray represents the restored vertex coordinate array (containing x, y, z values).

[0434] The variable faceCount represents the number of vertex coordinate faces.

[0435] The 2D array verCoordFaces represents an array of vertex indices that constitute each face.

[0436] The following is a 1D array of size vps_ext_bmesh_data_attribute_count[ RecAttlasID ].

[0437] The variable attrValueCountArray represents the number of values ​​for each attribute in the restored mesh frame.

[0438] The variable attrValueDimensionArray represents the dimensions of the attribute.

[0439] The 3D array attrValuesArray is a three-dimensional array that stores attribute values.

[0440] The 3D array attrFacesArray is a cubic array representing attribute linking information.

[0441] The variable submeshCount specifies the number of sub-meshes in the reconstructed mesh frame.

[0442] The 1D array submeshVerCoordCount (size submeshCount) represents the number of reconstructed vertices associated with the submesh.

[0443] The 1D array submeshLodCount (size submeshCount) represents the number of LoDs associated with the submesh.

[0444] The 2D array submeshVerCoordPerLodCount (size submeshCount × submeshLodCount[ smIdx ]) represents the number of reconstructed vertices associated with the ith LoD of the submesh with index smIdx.

[0445] The output attribute map can be expressed as follows:

[0446] The 4D array aFrame (size attrCount × attrDim × height × width) represents the attribute map associated with the reconstructed mesh, where attrCount is equal to ai_attribute_count[ RecAtlasID ], attrDim is equal to ai_attribute_dimension_minus1[ RecAtlasID ][ attrIdx ] + 1, height is equal to vps_ext_attribute_frame_height[ attrIdx ], and width is equal to vps_ext_attribute_frame_width[ attrIdx ].

[0447] The transformation of variables is performed as follows:

[0448] DisplacementDim = Min(DisplacementDim, DispDimension)

[0449] The mesh reconstruction is performed as follows. At this time, the output 4D array aFrame[ attrIdx ][ compIdx ][ y ][ x ] can be obtained as follows.

[0450] for( a = 0; a < ai_attribute_count[ RecAtlasID ]; a++ ){

[0451] for( j = 0; j < vps_ext_attribute_frame_height[ a ]; j++ ){

[0452] for( i = 0; i < vps_ext_attribute_frame_width[ a ]; i++ ){

[0453] for( c = 0;

[0454] c < ai_attribute_dimension_minus1[ RecAtlasID ][ a ] ​​+ 1; c++ ){

[0455] aFrame[ a ][ c ][ j ][ i ] = attrFramesNF[ a ]

[0000] [ compTimeIdx ][ c ][ j ][ i ]

[0456] }

[0457] }

[0458] }

[0459] }

[0460] The array gFrame[ compIdx ][ y ][ x ] can be derived as follows:

[0461] for(j = 0; j < asps_frame_height; j++ )

[0462] for( i = 0; i < asps_frame_width; i++ )

[0463] for( c = 0; c < DisplacementDim; c++ )

[0464] gFrame[ c ][ j ][ i ] = geoFramesNF

[0000] [ compTimeIdx ][ c ][ j ][ i ]

[0465] If p is 0..AtlasTotalNumMeshpatches - 1, then the following can be applied. In this case, the array dFrame[dispIdx][dispDimIdx] can be derived such that dispIdx has the same value as DisplIDToIndex[ AtlasMeshpatchDisplID[ p ] ].

[0466] for( i = 0; i < 3; i++ )

[0467] if( ( DispDimension == 1 ) && ( i > 1 ) )

[0468] dFrame[ dispIdx ][ i ] = 0

[0469] else

[0470] dFrame[ dispIdx ][ i ] = dispFramesNF[ compTimeIdx ][ j ][ i ]

[0471] If p is 0..AtlasTotalNumMeshpatches - 1, the following can be applied. In this case, the structure baseSubmeshFrame can be derived as follows, where submeshId has the same value as BaseMeshSubmeshIDToIndex[AtlasMeshpatchSubmeshID[p]].

[0472] baseSubmeshFrame.verCoordCount =

[0473] basemeshFramesNF[ compTimeIdx ][ submeshIdx ].verCoordCount

[0474] baseSubmeshFrame.faceCount =

[0475] basemeshFramesNF[ compTimeIdx ][ submeshIdx ].faceCount

[0476] baseSubmeshFrame.verCoordsArray =

[0477] basemeshFramesNF[ compTimeIdx ][ submeshIdx ].verCoordsArray

[0478] baseSubmeshFrame.verCoordFacesArray =

[0479] basemeshFramesNF[ compTimeIdx ][ submeshIdx ].verCoordFacesArray

[0480] basemeshFrame.attrIdxTexCoords = -1

[0481] basemeshFrame.attrIdxFacegroupIds = -1

[0482] for( i =0; i < vps_ext_bmesh_data_attribute_count[ RecAtlasID ]; i++ ){

[0483] basemeshFrame.attrValueCountArray[ i ] =

[0484] basemeshFramesNF[ compTimeIdx ][ submeshIdx ].attrValueCount[ i ]

[0485] basemeshFrame.attrValueDimensionArray[ i ] =

[0486] basemeshFramesNF[ compTimeIdx ][ submeshIdx ].attrValueDimensionArray[ i ]

[0487] basemeshFrame.attrValuesArray[ i ] =

[0488] basemeshFramesNF[ compTimeIdx ][ submeshIdx ].attrValuesArray[ i ]

[0489] basemeshFrame.attrFacesArray[ i ] =

[0490] basemeshFramesNF[ compTimeIdx ][ submeshIdx ].attrFacesArray[ i ]

[0491] if( vps_ext_bmesh_attribute_type[ RecAtlasID ][ i ] == ATTR_TEXCOORD )

[0492] basemeshFrame.attrIdxTexCoords = i

[0493] if( vps_ext_bmesh_attribute_type[ RecAtlasID ][ i ] == ATTR_FACEGROUP_ID )

[0494] basemeshFrame.attrIdxFacegroupIds = i

[0495] }

[0496] If p is 0..AtlasTotalNumMeshpatches - 1, then the following can be applied. Here, the array SubdivisionIterationCount[ p ] can be derived as follows:

[0497] if ( LoDExtractionEnabled )

[0498] SubdivisionIterationCount[p] = targetSubdivisionIterationCount[p]

[0499] else

[0500] SubdivisionIterationCount[p] = AtlasMeshpatchSubdivCount[p]

[0501] The array targetSubdivisionIterationCount[ p ] can be initialized with AtlasMeshpatchSubdivCount[ p ]. targetSubdivisionIterationCount[ p ] must be in the range 0 to AtlasMeshpatchSubdivCount[ p ], inclusive.

[0502] In the above, if LoDExtractionEnabled is 1, it indicates that LoD-based decoding is supported. If LoDExtractionEnabled is 0, it indicates that LoD-based decoding is not supported. LoDExtractionEnabled is a variable that plays the same role as LoD_extraction_flag described above. That is, if LoDExtractionEnabled is true (i.e., 1), SubdivisionIterationCount[p] is set to targetSubdivisionIterationCount[p], otherwise it is set to AtlasMeshpatchSubdivCount[p].

[0503] The submesh reconstruction process described below is applied using the structure baseSubmeshFrame, the array gFrame or dFrame, and the patch index p as inputs. The output is the p-th element of the 1D structure array, recSubmeshFrames[ p ]. Then, the submesh addition process described below is applied using the variable AtlasTotalNumMeshpatches and the 1D array recSubmeshFrames of size AtlasTotalNumMeshpatches as inputs, and the structure recMeshFrame as output.

[0504] Additional variables can be calculated and used after reconstructing as follows:

[0505] recMeshFrame.submeshCount = AtlasTotalNumMeshpatches

[0506] for( i = 0; i < AtlasTotalNumMeshpatches; i++ ) {

[0507] recMeshFrame.submeshVerCoordCount[i] = recSubmeshFrames[p].verCoordCount

[0508] recMeshFrame.submeshLodCount = SubdivisionIterationCount[ p ]

[0509] for( j = 0; j < SubdivisionIterationCount[ p ]; j++ ) {

[0510] recMeshFrame.submeshVerCoordPerLodCount[ i ][ j ] =

[0511] AtlasMeshpatchVertexCountPerSubdiv[ p ][ j ]

[0512] }

[0513] }

[0514] The following describes the submesh reconstruction process.

[0515] The inputs to this process are a baseSubmeshFrame structure, a 3D array gFrame if the profile or geometry codec ID indicates the use of a 2D video codec, a 2D array dFrame if the profile or geometry codec indicates the use of an arithmetic codec, an atlas patch index p, and a SubdivisionIterationCount array identifying the number of subdivision iterations to be decoded. In this disclosure, the number of subdivision iterations is used synonymously with the number of subdivisions.

[0516] The output of this process is a recSubmeshFrame structure.

[0517] The submesh restoration process according to the embodiments can be performed by applying various processes described below.

[0518] First, if the variable AtlasMeshpatchTexcoordProjectionFlag[p] is 1, the texture coordinate generation process is applied, taking the structure baseSubmeshFrame and the index p as input, and generating the structure baseSubmeshFrame with updated texture coordinates as output.

[0519] Next, the aforementioned subdivision process is applied, with the structure baseSubmeshFrame, AtlasMeshpatchSubdivMethod[p], and SubdivisionIterationCount[p] as inputs. The structure subdivSubmeshFrame, the 2D array verCoordEdges, and the 1D array levelOfDetailCounts are generated as outputs.

[0520] If the syntax element vps_geometry_video_present_flag[ RecAtlasID ] is 1, the following steps are performed:

[0521] That is, if the profile or geometry codec ID indicates the use of a 2D video codec, the aforementioned inverse transform coefficient packing process is applied, with the inputs being arrays gFrame, AtlasMeshpatch2dSizeX[ p ], AtlasMeshpatch2dSizeY[ p ], AtlasMeshpatch2dPosX[ p ], AtlasMeshpatch2dPosY[ p ], gi_geometry_2d_bit_depth_minus1[ RecAtlasID ] + 1, SubdivisionIterationCount[ p ], AtlasPatchTotalVertexCount[ atlasPatchIdx ], and the output being a 2D array dispQuantCoeffArray. Otherwise, if the profile or geometry codec indicates the use of an arithmetic codec, the output dispQuantCoeffArray will have the value of dFrame, the disparity frame.

[0522] Then, the aforementioned inverse quantization process is applied, with variables AtlasPatchTotalVertexCount[ atlasPatchIdx ], SubdivisionIterationCount[ p ], 2D array dispQuantCoeffArray, and 1D array AtlasPatchVertexCount[ atlasPatchIdx ] as input, and the output is a 2D array called dispCoeffArray.

[0523] If the profile or geometry codec ID indicates the use of a 2D video codec, the inverse transform coefficient processing described above is applied, with inputs being the variables AtlasPatchTotalVertexCount[ atlasPatchIdx ], SubdivisionIterationCount[ p ], AtlasMeshpatchTransformMethod[ p ], the 1D array AtlasPatchVertexCount[ atlasPatchIdx ], and the 2D arrays dispCoeffArray and verCoordEdges, and the output is a 2D array called dispArray. Otherwise, i.e., if the profile or geometry codec indicates the use of an arithmetic codec, the output dispCoeffArray is assumed to be dispQuantCoeffArray.

[0524] Then, the aforementioned normal, tangent, and bitangent vector generation process is applied, with the structures subdivSubmeshFrame and AtlasMeshpatchDispCoordSys[ p ] as inputs, and the outputs being normals, tangents, and bitangents. In addition, the aforementioned vertex coordinate restoration process is applied, with the structure subdivSubmeshFrame, arrays dispArray, normals, tangents, and bitangents as inputs, and the structure vertexRefinedSubmeshFrame as output. Otherwise, that is, when vps_geometry_video_present_flag[ RecAtlasID ] is 0, the structure vertexRefinedSubmeshFrame is set equal to subdivSubmeshFrame.

[0525] If the syntax element asve_attribute_subtexture_enabled_flag[ i ] is 1 for the index i of the attribute video data unit, the aforementioned texture coordinate adaptation process is applied, and the structures vertexRefinedSubmeshFrame, AtlasPatchAttribute2dSizeX[ p ][ i ], AtlasMeshpatchAttributes2dSizeY[ p ][ i ], AtlasPatchAttribute2dPosX[ p ][ i ], AtlasPatchAttribute2dPosY[ p ][ i ], asve_attribute_frame_width[ i ], asve_attribute_frame_height[ i ] are used as input, and the structure recSubmeshFrames[ p ] is output. Otherwise, recSubmeshFrames[ p ] is set to vertexRefinedSubmeshFrame.

[0526] As explained so far, SubdivisionIterationCount[ p ] is the number of subdivisions of patch index p, which can be received as input to the submesh reconstruction process, and its value can exist in the range of 0 to AtlasMeshpatchSubdivCount[ p ].

[0527] The variable targetSubdivisionIterationCount is the number of subdivisions to decode. If the variable is not initialized, it can be initialized to AtlasMeshpatchSubdivCount[ p ]. The variable targetSubdivisionIterationCount corresponds to a specific LoD or target LoD.

[0528] LoDExtractionEnabled is a variable that indicates whether LoD-based decoding is performed. If its value is 1 (i.e., true), it means that LoD-based decoding is possible, and if it is 0 (i.e., false), it means that LoD-based decoding is not possible.

[0529] In the present disclosure, LoDExtractionEnabled, i.e., whether or not decoding function support is possible up to a specific LoD level, may be derived by parsing LoD_extraction_flag at the Atlas Sequence Parameter Set (ASPS) level, and / or in the case of GVD type, may be derived depending on whether independent bitstream extraction and decoding are possible through LoD-based packing, and / or in the case of PVD type, may be derived depending on whether or not spatial scalability function support is possible.

[0530] The variable targetSubdivisionIterationCount may be input from the user, or may be determined by various factors such as network environment, receiver performance, display characteristics, application, and rendering environment. According to embodiments, targetSubdivisionIterationCount may be derived as the subdivision iteration count of the surrounding reconstructed sub-mesh of the currently decoded sub-mesh, targetSubdivisionIterationCount may be adaptively derived according to the computational requirements by considering the rendering environment, or targetSubdivisionIterationCount may be adaptively derived according to the distance between the camera and the object. In the present disclosure, the subdivision iteration count may be referred to as the subdivision count.

[0531] FIGS. 26A and 26B are diagrams showing an example of a syntax structure of an atlas sequence parameter set (ASPS) according to embodiments. In particular, FIGS. 26A and 26B show a method of defining and signaling asve_LoD_extraction_flag, which indicates whether mesh decoding based on LoD is possible in a dynamic mesh decoder, in a V-DMC extension of ASPS. That is, the present disclosure can signal and transmit asve_LoD_extraction_flag, which indicates whether mesh decoding based on LoD is possible in a dynamic mesh decoder, at the ASPS level.

[0532] That is, FIG. 26a and FIG. 26b are diagrams showing an example of the syntax structure of asps_vdmc_extension( ) according to embodiments.

[0533] asve_subdivision_iteration_count indicates the number of iterations used for subdivision in the mesh subdivision unit, i.e. the subdivision iteration count (or subdivision count).

[0534] asve_LoD_extraction_flag is information indicating whether the function of decoding a dynamic mesh to a specific LoD level is supported. For example, if the value of asve_LoD_extraction_flag is 1, it can indicate that the function of decoding a dynamic mesh to a specific LoD level is supported, and if it is 0, it can indicate that the function of decoding a dynamic mesh to a specific LoD level is not supported.

[0535] Fig. 27 is a diagram showing another example of a receiving device according to embodiments. The receiving device of Fig. 27 may be referred to as a dynamic mesh content receiving device. The receiving device of Fig. 27 may correspond to the receiving device of Fig. 1, the receiving device of Fig. 11, the receiving device of Fig. 13, or the receiving device of Fig. 21. Therefore, parts not described in Fig. 27 will refer to the description of the receiving device of Fig. 1, the receiving device of Fig. 11, the receiving device of Fig. 13, or the receiving device of Fig. 21. The elements of the receiving device illustrated in Fig. 27 may be implemented by hardware, software, a processor connected to a memory, and / or a combination thereof. That is, the elements of the receiving device of Fig. 27 may be implemented by hardware, software, firmware, or a combination thereof, including one or more processors or integrated circuits configured to communicate with one or more memories, although not illustrated in the drawing. One or more processors may perform at least one of the operations and / or functions of the elements of the receiving device of FIG. 27 described above. Furthermore, one or more processors may operate or execute a set of software programs and / or instructions for performing the operations and / or functions of the elements of the receiving device of FIG. 27.

[0536] In particular, Fig. 27 is an example of a receiving device for decoding a sub-mesh of a dynamic mesh up to a specific LoD level.

[0537] Decoding up to a specific LoD level proposed in this disclosure may correspond to the operation within the mesh data decoding module of Fig. 27, and the receiver operation according to the proposed method is as follows.

[0538] According to embodiments, a bitstream of mesh data (also referred to as a dynamic mesh bitstream or a bitstream of mesh data or a dynamic bitstream) encapsulated in a file from a transmitting device and delivered to a receiving device via a delivery module is decapsulated in a file decapsulation module. If the bitstream of mesh data is not encapsulated in a file form from the transmitting device, the decapsulation process is omitted at the receiving device.

[0539] That is, when the stored and / or received dynamic mesh content passes through the delivery module and the file / segment decapsulation module, it can be in a form similar to the V-DMC bitstream structure of FIG. 28.

[0540] FIG. 28 is a diagram showing another example of a V-DMC bitstream structure according to embodiments.

[0541] In the present disclosure, the V-DMC bitstream of FIG. 28 is, as an embodiment, generated and output by one of the encoding devices / encoding methods of FIG. 1, FIG. 2, FIG. 3, FIG. 7, FIG. 12, or FIG. 14. The V-DMC bitstream of the present disclosure can be transmitted / received in either a V3C unit stream format or a V3C sample stream format. The V-DMC bitstream of the present disclosure can follow the V3C bitstream structure defined in the V3C codec specification (ISO / IEC 23090-5). In this case, the existing V3C bitstream structure may be followed, but some V3C units may not be used, and some structures for V-DMC only, such as V-DMC extensions, may be followed. The present disclosure describes, as an embodiment, the use of a sample stream data unit used when encoding V3C content of the V3C codec specification (ISO / IEC 23090-5) as shown in FIG. 28.

[0542] A bitstream (referred to as a V-DMC bitstream, a dynamic mesh bitstream, or a bitstream of mesh data) transmitted from a transmitting device to a receiving device of the present disclosure may be composed of a sample stream DMC header and a plurality of sample stream DMC units. In the present disclosure, the sample stream DMC header may be referred to as a sample stream header, and the sample stream DMC unit may be referred to as a sample stream data unit.

[0543] At this time, if the sample stream DMC unit follows the V3C codec specification (ISO / IEC 23090-5), each sample stream DMC unit can be composed of V3C sample stream size information and a V3C unit. The V3C unit is again composed of a V3C unit header (V3C_unit_header) and a V3C unit payload (V3C_unit_payload).

[0544] The above V3C sample stream size information specifies the size of the subsequent V3C unit in bytes. At this time, the sample stream DMC header can indicate the accuracy of the V3C sample stream size information in all sample stream DMC units in bytes.

[0545] The above V3C unit header includes type information (vuh_unit_type) indicating the type of data carried by the corresponding V3C unit payload. The V3C unit payload may carry one of a V3C / V-DMC parameter set (VPC), atlas data (AD), base mesh data (BMD), displacement data / geometry video data (DD / GVD), attribute video data (AVD), and packed video data (PVD) according to the type information (vuh_unit_type). In the present disclosure, attribute video data is used interchangeably with attribute data and has the same meaning, and displacement video data is used interchangeably with displacement data or displacement information and has the same meaning.

[0546] Here, VPS may include parameter set information such as decoder configuration information related to mesh encoding / decoding and sequence header. Atlas data (AD) may include additional information such as 2D mapping or texture mapping for 3D objects. Base mesh data (BMD) is compressed base mesh data for mesh encoding / decoding. Attribute video data (AVD) is attribute or texture data (or texture map information) compressed using a video codec. Packed video data (PVD) is packed texture map and displacement information compressed using a video codec. And, DD / GVD represents displacement data (or displacement information), where DD represents displacement data that is arithmetic coded, and GVD represents displacement data that is encoded using a video codec. In the present disclosure, displacement data or displacement information may mean displacement data encoded with a video codec or displacement data encoded with arithmetic coding.

[0547] The present disclosure provides, as an embodiment, a method of distinguishing between type information (vuh_unit_type) of arithmetic-coded displacement data and displacement data coded based on a video codec. In this case, the V3C unit payload may carry one of VPC, atlas data (AD), base mesh data (BMD), video codec-based displacement video data (GVD), attribute video data (AVD), packed video data (PVD), and arithmetic codec-based displacement data (DD) according to the type information (vuh_unit_type). That is, the values ​​of type information (vuh_unit_type) of displacement data (GVD) compressed (i.e., encoded) using a video codec and displacement data (DD) compressed (i.e., encoded) based on an arithmetic codec may be assigned differently.

[0548] The V3C unit header of the present disclosure includes type information (vuh_unit_type) of the V3C unit header, and the vuh_unit_type is V3C unit type information indicating the type of data carried as the corresponding V3C unit payload.

[0549] For example, if the vuh_unit_type field indicates displacement video data (V3C_GVD) based on a video codec, the V3C unit payload includes a video sub-bitstream (video_sub_bitstream(numBytesInV3CPayload)) that carries displacement video data (or geometry video data) encoded based on a video codec. As another example, if the vuh_unit_type field indicates V3C_PVD, the V3C unit payload includes a packed video sub-bitstream (video_sub_bitstream(numBytesInV3CPayload)) that carries packed video data. In the present disclosure, the video sub-bitstream is used interchangeably with the same meaning as the video bitstream or bitstream.

[0550] For convenience of explanation, the present disclosure will refer to an atlas sub-bitstream carrying atlas data (AD) as an atlas bitstream, a base mesh sub-bitstream carrying base mesh data (BMD) as a base mesh bitstream, a displacement data sub-bitstream carrying video codec-based or arithmetic codec-based displacement data (DD / GVD) as a displacement information (or displacement vector) bitstream, an attribute sub-bitstream carrying attribute video data (AVD) as an attribute (or texture map) bitstream, and a packed video data sub-bitstream carrying packed video data (PVD) as a packed video data bitstream.

[0551] And, the base mesh bitstream, atlas bitstream, displacement vector bitstream, attribute bitstream and / or packed video data bitstream within the bitstream configured as in FIG. 28 can be separated in the mesh data decoding module and then decoded through each decoder.

[0552] According to embodiments, a bitstream parser (not shown) of a mesh data decoding module may serve to parse a V-DMC bitstream (or dynamic mesh content bitstream). That is, a V3C unit header and a V3C unit payload constituting the bitstream may be parsed to obtain a base mesh bitstream, an atlas bitstream, a displacement vector bitstream, an attribute bitstream, and / or a packed video data bitstream, respectively, and may be decoded by each decoder. In addition, the bitstream parser of the mesh data decoding module may parse a V3C unit header and a V3C unit payload to obtain data corresponding to V3C_VPS, that is, VPS data, and data corresponding to V3C_GVD, that is, a video sub-bitstream, in which the type information (i.e., vuh_unit_type) included in the V3C unit header is V3C_VPS. Alternatively, data corresponding to V3C_PVD, that is, a video sub-bitstream, may be obtained.

[0553] Additionally, the receiver (e.g., mesh data decoding module) can obtain information for partial extraction from the LoD level-specific displacement video bitstream via SEI messages.

[0554] According to embodiments, a receiver (e.g., a mesh data decoding module) may identify encoded displacement vector data information in order to perform partial extraction of displacement vector bitstreams by LoD level from the bitstream of the corresponding dynamic mesh content prior to a direct decoding process of displacement vector data through the aforementioned process.

[0555] According to embodiments, in a displacement vector video bitstream extraction process, a sub-video bitstream can be extracted by inputting an MCTS index or a sub-picture index corresponding to a user's target LoD into a bitstream extraction process according to the user's target LoD. The MCTS bitstream extraction process can extract a sub-bitstream corresponding to a specific MCTS. The sub-picture bitstream extraction process can extract a sub-bitstream corresponding to a specific subpicture. A plurality of extracted sub-bitstreams can be merged to generate a single sub-bitstream.

[0556] According to embodiments, a transmitting device of the present disclosure may transmit information (e.g., LoD_extraction_flag) indicating whether support for a decoding function is possible up to a specific LoD level in signaling information (e.g., an ASPS or SEI message) to decode a submesh up to a specific LoD level (i.e., a target LoD level), and a receiving device may parse this information from the signaling information to determine whether support for a decoding function is possible up to the specific LoD level. In this case, parsing of the signaling information may be performed in a metadata parser (not shown) of a decoder of the receiving device.

[0557] In the present disclosure, the availability of support for a decoding function up to a specific LoD level can be directly confirmed by parsing the LoD_extraction_flag syntax. As another example, the availability of support for a decoding function up to a specific LoD level can be derived based on whether scalability function support is possible when the type information (i.e., vuh_unit_type) included in the V3C unit header is of the V3C_PVD type, or can be derived based on whether LoD-based displacement vector data can be packed for each LoD level and extracted for each LoD level when the type information included in the V3C unit header is of the V3C_GVD type.

[0558] According to embodiments, a specific number of segmentations, i.e., a specific LoD, may be obtained from signaling information or input from a user, or may be determined by various factors such as network environment, receiver performance, display characteristics, etc.

[0559] According to embodiments, the mesh subdivision unit of the receiving device can perform subdivision of the base mesh only up to a specific LOD level based on a specific number of subdivisions determined by the decoder. That is, the mesh subdivision unit can perform subdivision of the base mesh only up to a specific LOD level.

[0560] According to embodiments, when the displacement information decoding method of the displacement vector decoder of the receiving device is a video codec-based decoding method, the displacement vector transform coefficient decoding unit can perform decoding of the displacement vector transform coefficient only up to a specific LOD level according to a specific subdivision number determined by the decoder.

[0561] For example, if the type is V3C_PVD and LoD-based scalable decoding is supported, a layer corresponding to a specific LoD can be decoded using a scalable video decoder such as SHVC or multilayerVVC.

[0562] As another example, if the type is V3C_GVD and LoD-based scalable encoding is performed, only the displacement vector video corresponding to a specific LoD can be decoded, and only the video bitstream corresponding to the MCTS index or subpicture index corresponding to the specific LoD can be extracted to perform video decoding.

[0563] According to embodiments, when the displacement information decoding method is a video codec-based decoding method, the displacement vector transform coefficient depacking unit of the displacement vector decoder of the receiving device can perform the depacking process for the displacement vector transform coefficient only up to a specific LOD level according to a specific subdivision number determined in the decoder.

[0564] According to embodiments, a displacement vector transform coefficient inverse quantization unit of a displacement vector decoder of a receiving device may, when a displacement information decoding method is a video codec-based decoding method, perform an inverse quantization process on displacement vector transform coefficients only up to a specific LOD level according to a specific number of subdivisions determined by the decoder. That is, inverse quantization may be performed only on quantized displacement vector transform coefficients of vertices corresponding to a specific LoD.

[0565] According to embodiments, when the displacement information decoding method is a video codec-based decoding method, the displacement vector inverse transform unit of the displacement vector decoder of the receiving device may perform an inverse transform process on displacement vector transform coefficients only up to a specific LOD level according to a specific number of subdivisions determined by the decoder. For example, a lifting inverse transform may be performed on displacement vector transform coefficients of vertices corresponding to a specific LoD.

[0566] That is, when the displacement information decoding method is a video codec-based decoding method, the displacement vector decoder can perform decoding of displacement vector transform coefficients only up to a specific LOD level according to a specific number of subdivisions determined by the decoder.

[0567] In this way, the mesh data decoding module can reconstruct a mesh (or submesh) up to a specific LOD level (i.e., target LoD) based on the reconstructed base mesh and reconstructed displacement vectors from each decoder. Here, the target LoD may be the entire LoD or a portion of the entire LoD.

[0568] According to embodiments, the mesh data processing / rendering module may render mesh data by applying a restored texture map (or attribute) to a mesh of a restored target LoD (i.e., up to the target LoD level). That is, a mesh video / image of the restored target LoD may be displayed through rendering. A user may view all or part of the rendered result through a VR / AR display or a general display.

[0569] Fig. 29 is a flowchart illustrating an example of an encoding method according to embodiments. The encoding method according to embodiments may include a step of encoding a base mesh of mesh data (S31011), a step of encoding a displacement of mesh data (S31012), and a step of encoding an attribute of mesh data (S31013).

[0570] In the step (S31011) of encoding the base mesh of the above mesh data, if intra encoding or intra frame encoding is performed on the corresponding mesh frame, the base mesh can be encoded through a static mesh encoder. In this case, encoding can be performed on connection information, vertex geometry information, vertex texture information, normal information, etc. of the base mesh. In the step (S31011) of encoding the base mesh of the above mesh data, if inter encoding or inter frame encoding is performed on the corresponding mesh frame, a motion vector encoder can calculate a motion vector between the base mesh and the reference restored base mesh (or the restored quantized reference base mesh) and encode the value. In addition, connection information-based prediction can be performed using a previously encoded / decoded motion vector as a predictor, and a residual motion vector obtained by subtracting the predicted motion vector from the current motion vector can be encoded.

[0571] The step (S31012) of encoding the displacement of the above mesh data may perform video codec-based encoding on the displacement data or arithmetic codec-based encoding. The step (S31012) of encoding the displacement of the mesh data may transform the coordinate system of the displacement data from a 3D Cartesian coordinate system to a local coordinate system before encoding the displacement data. If the displacement data is encoded based on a video codec, the displacement vector transform coefficients for each LoD level (i.e., for each refinement level) that have undergone the displacement vector transform and displacement vector transform coefficient quantization processes may be packed into a rectangular area to support partial decoding up to a specific LoD level. At this time, padding may be performed to fit the rectangular area for each refinement level.

[0572] That is, the step (S31012) of encoding the displacement of the above mesh data can be performed by taking into account the support of the LoD-based scalable decoding function of the dynamic mesh. As a method for supporting the scalable decoding function, displacement vector data and texture maps can be packed into one frame each for each resolution and encoded as a V3C_PVD type, and multi-resolution video in which each packed displacement vector video is packed for each multi-resolution texture map and refinement level can be encoded through a scalable video codec such as SHVC or multilayer VVC. In addition, as a method for supporting the scalable decoding function, video encoding can be performed by packing displacement vector data into a rectangular shape for each LoD level and then limiting each LoD packing area to a MCTS, subpicture, etc., which are units that can be independently decoded at the video bitstream level, according to an embodiment.

[0573] Additionally, the present disclosure may transmit a LoD_extraction_flag to a receiving device via signaling information (e.g., ASPS and / or SEI messages) to indicate whether decoding functionality support is available up to a specific LoD level.

[0574] The step of encoding the attributes of the above mesh data (S31013) may perform encoding based on a video codec for the attribute data (or texture map).

[0575] The above encoding method may further include a step of transmitting a bitstream including encoded basemesh, encoded displacement data, encoded attribute data, and / or atlas data. The bitstream transmitted in the above step may be transmitted to a receiving device in a structure as illustrated in FIG. 28.

[0576] The encoding method of the present disclosure can be performed by an encoding device (encoder). The encoding device includes a memory and at least one processor connected to the memory, and the at least one processor can 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.

[0577] Embodiments further include a computer-readable storage medium storing a bitstream generated by the method according to FIG. 29.

[0578] Embodiments further include a method comprising the steps of obtaining a bitstream for mesh data, the bitstream being generated based on the steps of encoding a basemesh 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.

[0579] Fig. 30 is a flowchart showing an example of a decoding method according to embodiments. The decoding method according to embodiments may include a step of decoding a base mesh in a bitstream (S32011), a step of decoding a displacement in the bitstream (S32012), and a step of decoding an attribute in the bitstream (S32013). The decoding step of Fig. 30 may further include a step of receiving a bitstream including a base mesh, displacement data, and attribute data, or a file in which a bitstream is encapsulated. When the file is received, the receiving step performs a decapsulation process to extract a bitstream, and when the bitstream is received, the decapsulation process is omitted. The bitstream is referred to as a V-DMC bitstream or a V3C bitstream, and has a structure as shown in Fig. 30. The above receiving step can separate an atlas sub-bitstream, a basemesh sub-bitstream, a displacement sub-bitstream, and an attribute sub-bitstream (or attribute video sub-bitstream) from the bitstream according to the type information of the V3C unit header.

[0580] The step (S32011) of decoding the base mesh in the bitstream may, if the current mesh has been subjected to inter-screen encoding, use a previously decoded motion vector as a predictor to restore a final motion vector by adding it to a residual motion vector decoded from the base mesh sub-bitstream. The step (S32011) of decoding the base mesh in the bitstream may, if the current mesh has been subjected to intra-screen encoding, statically decode the base mesh sub-bitstream to restore connection information, vertex geometry information, texture coordinates, normal information, etc. of the base mesh. The step (S32011) of decoding the base mesh in the bitstream may perform subdivision of the base mesh only up to a specific LOD level according to a specific subdivision number determined by the decoder. That is, subdivision of the base mesh may be performed only up to a specific LOD level.

[0581] In the present disclosure, the availability of support for a decoding function up to a specific LoD level can be directly confirmed by parsing the LoD_extraction_flag syntax. As another example, the availability of support for a decoding function up to a specific LoD level can be derived based on whether scalability function support is possible when the type information (i.e., vuh_unit_type) included in the V3C unit header is of the V3C_PVD type, or can be derived based on whether LoD-based displacement vector data can be packed for each LoD level and extracted for each LoD level when the type information included in the V3C unit header is of the V3C_GVD type.

[0582] According to embodiments, a specific number of segmentations, i.e., a specific LoD, may be obtained from signaling information or input from a user, or may be determined by various factors such as network environment, receiver performance, display characteristics, etc.

[0583] The step (S32012) of decoding displacement within the above bitstream performs decoding on the displacement sub-bitstream based on the video codec if the displacement data is encoded based on a video codec, and performs decoding based on the arithmetic codec if the displacement data is encoded based on an arithmetic codec. In the present disclosure, the displacement sub-bitstream may be referred to as a displacement vector bitstream.

[0584] The following describes the process for extracting a displacement vector bitstream up to a specific LoD level corresponding to a specific LoD (i.e., target LoD) and decoding it based on a video codec.

[0585] The step (S32012) of decoding displacement in the above bitstream performs the video codec-based decoding, depacking, dequantization, and deconversion processes on the displacement vector bitstream only up to a specific LOD level according to a specific subdivision number determined by the decoder, if the displacement data is encoded based on a video codec.

[0586] In the present disclosure, the availability of support for a decoding function up to a specific LoD level can be directly confirmed by parsing the LoD_extraction_flag syntax. As another example, the availability of support for a decoding function up to a specific LoD level can be derived based on whether scalability function support is possible when the type information (i.e., vuh_unit_type) included in the V3C unit header is of the V3C_PVD type, or can be derived based on whether LoD-based displacement vector data can be packed for each LoD level and extracted for each LoD level when the type information included in the V3C unit header is of the V3C_GVD type.

[0587] According to embodiments, a specific number of segmentations, i.e., a specific LoD, may be obtained from signaling information or input from a user, or may be determined by various factors such as network environment, receiver performance, display characteristics, etc.

[0588] The step of decoding an attribute in the above bitstream (S32013) restores the attribute data by decoding the attribute sub-bitstream based on a video codec.

[0589] The base mesh, displacement data, and attribute data decoded in steps S32011-S32013 can be rendered after undergoing post-processing such as mesh restoration and reconstruction.

[0590] At this time, the rendered mesh data corresponds to a specific LoD (i.e., target LoD). Here, the target LoD may be the entire LoD or a part of the entire LoD.

[0591] The decoding method of the present disclosure can be performed by a decoding device (decoder). The decoding device includes a memory and at least one processor connected to the memory, and the at least one processor can be configured to decode a basemesh within a bitstream, decode a displacement within the bitstream, and decode an attribute within the bitstream.

[0592] As described above, when the displacement vector encoding / decoding method of the transmitting device of the present disclosure is based on a video codec, the encoder of the transmitting device of the present disclosure compresses the quantized displacement vector transform coefficients by packing them into one frame for each LoD level. In the present disclosure, the decoder of the receiving device can extract and decode a portion of the displacement vector bitstream corresponding to an area in which displacement vector transform coefficients up to a specific LoD level are packed among the displacement vector bitstreams. In addition, by extracting and decoding a portion of the bitstream for each LoD level from the displacement vector bitstream through the present disclosure, the scalability of the geometry (i.e., displacement) information of the dynamic mesh can be supported.

[0593] In addition, the present disclosure can perform decoding and restoration by extracting only a portion of a mesh bitstream of LoD (or resolution) suitable for the decoder environment. The present disclosure can decode and restore a mesh of a resolution (or LoD) suitable for the decoder environment by taking into account various environments of a receiver where decoding and restoration are performed (e.g., network conditions, display characteristics, receiver performance, etc.), thereby allowing for the extraction and decoding of only a portion of a bitstream corresponding to a low-resolution mesh (or a low LoD level). This may require less memory than a high-resolution mesh, and mesh decoding and restoration may be performed only up to a low LoD level, thereby enabling the use of low-resolution mesh content with a smaller amount of computation than a high-resolution mesh.

[0594] That is, in the present disclosure, when performing decoding in sub-mesh units, the function of performing decoding at various mesh resolutions based on the LoD level can be supported by decoding the mesh up to a specific LoD level.

[0595] Each of the parts, modules, or units described above may be software, processors, or hardware parts that execute sequential execution processes stored in memory (or storage units). Each of the steps described in the embodiments described above may be performed by processors, software, or hardware parts. Each of the modules / blocks / units described in the embodiments described above may operate as a processor, software, or hardware. In addition, the methods presented in the embodiments may be implemented as code. This code may be written on a processor-readable storage medium and thus may be read by a processor provided by an apparatus.

[0596] Furthermore, throughout the specification, when a part is said to "include" a component, this does not exclude other components, unless otherwise specifically stated, but rather implies the inclusion of other components. Furthermore, terms such as "part" described in the specification mean a unit that processes at least one function or operation, which may be implemented using hardware, software, or a combination of hardware and software.

[0597] For convenience of explanation, this specification has been described separately in each drawing. However, it is also possible to design new embodiments by combining the embodiments described in each drawing. Furthermore, designing a computer-readable recording medium containing a program for executing the previously described embodiments, as required by those skilled in the art, is also within the scope of the embodiments.

[0598] The devices and methods according to the embodiments are not limited to the configurations and methods of the embodiments described above, but the embodiments may be configured by selectively combining all or part of each embodiment so that various modifications can be made.

[0599] Although preferred embodiments of the embodiments have been illustrated and described, the embodiments are not limited to the specific embodiments described above, and various modifications may be made by those skilled in the art to which the present disclosure pertains without departing from the spirit or scope of the embodiments claimed in the claims, and such modifications should not be understood individually from the technical idea or prospect of the embodiments.

[0600] The various components of the devices of the embodiments may be implemented by hardware, software, firmware, or a combination thereof. The various components of the embodiments may be implemented by a single chip, for example, a single hardware circuit. The components according to the embodiments may be implemented by separate chips. At least one of the components of the devices of the embodiments may be configured with one or more processors capable of executing one or more programs, and the one or more programs may perform, or include instructions for performing, one or more of the operations / methods according to the embodiments. The executable instructions for performing the methods / operations of the devices of the embodiments may be stored in non-transitory CRMs or other computer program products configured to be executed by one or more processors, or may be stored in temporary CRMs or other computer program products configured to be executed by one or more processors. In addition, the memory according to the embodiments may be used as a concept including not only volatile memory (e.g., RAM, etc.), but also non-volatile memory, flash memory, PROM, etc. Additionally, it may include implementations in the form of carrier waves, such as transmissions via the Internet. Furthermore, processor-readable recording media may be distributed across network-connected computer systems, allowing processor-readable code to be stored and executed in a distributed manner.

[0601] 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".

[0602] Various elements of the embodiments may be implemented by hardware, software, firmware, or a combination thereof. Various elements of the embodiments may be implemented on a single chip, such as a hardware circuit. In some embodiments, the embodiments may optionally be implemented on separate chips. In some embodiments, at least one of the elements of the embodiments may be implemented within one or more processors that include instructions for performing operations according to the embodiments.

[0603] Additionally, the operations according to the embodiments described in this document may be performed by a transceiver device including one or more memories and / or one or more processors according to the embodiments. One or more memories may store programs for processing / controlling the operations according to the embodiments, and one or more processors may control various operations described in this document. One or more processors may be referred to as a controller, etc. The operations according to the embodiments may be performed by firmware, software, and / or a combination thereof, and the firmware, software, and / or a combination thereof may be stored in a processor or a memory.

[0604] Terms such as "first" and "second" may be used to describe various components of the embodiments. However, the various components according to the embodiments should not be interpreted in a limited manner 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 necessarily mean the same user input signals unless the context clearly indicates otherwise.

[0605] The terminology used to describe the embodiments is for the purpose of describing particular embodiments and is not intended to be limiting of the embodiments. As used in the description of the embodiments and in the claims, the singular is intended to include the plural unless the context clearly dictates otherwise. The expressions “and / or” are used to mean all possible combinations of the terms. The expression “comprises” or “includes” describes the presence of features, numbers, steps, elements, and / or components, but does not mean that additional features, numbers, steps, elements, and / or components are not included. Conditional expressions such as “if” or “when” used to describe the embodiments are not intended to be limited to only optional cases. When a specific condition is satisfied, a related action is performed in response to a specific condition, or a related definition is intended to be interpreted.

[0606] As described above, the relevant contents have been described in the best form for carrying out the embodiments.

[0607] As described above, the embodiments may be applied, in whole or in part, to mesh data transmission and reception devices and systems. Those skilled in the art will appreciate that various modifications and variations may be made to the embodiments within the scope of the embodiments. The embodiments may include modifications and variations, and such modifications and variations do not depart from the scope of the claims and their equivalents.

Claims

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

2. In the first paragraph, the step of decoding the base mesh A decoding method comprising a step of performing subdivision on the base mesh a number of times corresponding to a specific LoD (Level of Detail) level.

3. In the second paragraph, the step of decoding the displacement data A step of decoding displacement data included in the bitstream based on a video codec up to a specific LoD level according to the number of subdivisions, A step of depacking the decoded displacement data up to the above specific LoD level, A step of dequantizing the displacement data depacked up to the above specific LoD level, and A decoding method comprising a step of inversely transforming displacement data dequantized up to the above specific LoD level.

4. In paragraph 3, A decoding method further comprising a step of checking whether decoding function support is possible up to the above specific LoD level.

5. In paragraph 4, A decoding method for determining whether decoding function support is possible up to the above-mentioned specific LoD level based on information indicating whether decoding is possible up to the specific LoD level included in the signaling information.

6. In paragraph 5, The above signaling information is a decoding method that is an atlas sequence parameter set.

7. In paragraph 4, A decoding method in which whether or not decoding function support is possible up to the specific LoD level is derived based on whether or not scalability function support is possible when texture map and displacement data are packed into one frame and encoded into video and received.

8. In paragraph 4, When the above displacement data is received encoded based on a video codec, whether or not the decoding function can be supported up to the specific LoD level is a decoding method derived by packing the LoD-based displacement data by LoD level and whether or not it is possible to extract it by LoD level.

9. Memory; and At least one processor connected to the memory; At least one processor of the above: Decode the basemesh within the bitstream; Decoding displacement data within the bitstream; and configured to decode attribute data within the above bitstream; Decoding device.

10. In the 9th paragraph, the at least one processor, A decoding device including a subdivision unit that performs subdivision on the base mesh a number of times corresponding to a specific LoD (Level of Detail) level.

11. In the 10th paragraph, the at least one processor, A displacement decoding unit that decodes displacement data included in the bitstream up to a specific LoD level based on a video codec according to the number of subdivisions mentioned above; A depacking unit that depacks displacement data decoded up to the above-mentioned specific LoD level, A dequantization unit that dequantizes displacement data depacked up to the above-mentioned specific LoD level, and A decoding device further comprising an inverse transform unit for inversely transforming displacement data dequantized up to the above-mentioned specific LoD level.

12. Step of encoding the base mesh of mesh data; A step of encoding displacement data of the above mesh data; and A step of encoding attribute data of the above mesh data; comprising; 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; Encode displacement data of the above mesh data; and Encoding attribute data 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 12.

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

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