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

Abstract

A mesh data decoding device according to embodiments may comprise: a reception unit for receiving a base mesh bitstream, a displacement vector bitstream, a texture map bitstream, and signaling information; a base mesh processing unit for reconstructing a base mesh from the base mesh bitstream; a displacement information processing unit for reconstructing displacement information from the displacement vector bitstream; a reconstruction unit for reconstructing a mesh on the basis of the base mesh and the displacement information; and a texture map processing unit for reconstructing a texture map from the texture map bitstream.

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] The technical problem according to the embodiments is to provide a device and method for efficiently performing encoding and decoding of a displacement vector.

[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 mesh data encoding method according to embodiments may include a step of encoding an original mesh, and a step of transmitting a bitstream including the encoded mesh and signaling information.

[0009] According to embodiments, the encoding step may include a base mesh processing step of encoding a base mesh generated by simplifying the original mesh to generate a base mesh bitstream, a displacement information processing step of encoding displacement information generated based on the base mesh to generate a displacement vector bitstream, a mesh restoration step of restoring a mesh based on the encoded base mesh and the encoded displacement information, and a texture map processing step of encoding a texture map generated based on the original mesh and the restored mesh to generate a texture map bitstream.

[0010] According to embodiments, the displacement information processing step may include a step of converting a coordinate system of the displacement information into a local coordinate system, a step of performing packing based on one of a first format, a second format, and a third format for at least one of a normal component, a tangential component, or a bi-tangential component included in the displacement information of the local coordinate system, and a step of encoding the packed displacement information.

[0011] According to embodiments, the packing step selectively performs packing on a bi-tangential component of the displacement information, and the signaling information may include information for identifying whether packing of the bi-tangential component has been skipped.

[0012] According to embodiments, the signaling information may include information for identifying a format applied to the displacement information.

[0013] According to embodiments, a mesh data encoding device may include an encoder that encodes an original mesh, and a transmission unit that transmits a bitstream including the encoded mesh and signaling information.

[0014] According to embodiments, the encoder may include a base mesh processing unit that generates a base mesh bitstream by encoding a base mesh generated by simplifying the original mesh, a displacement information processing unit that generates a displacement vector bitstream by encoding displacement information generated based on the base mesh, a mesh restoration unit that restores a mesh based on the encoded base mesh and the encoded displacement information, and a texture map processing unit that generates a texture map bitstream by encoding a texture map generated based on the original mesh and the restored mesh.

[0015] According to embodiments, the displacement information processing unit may include a displacement information coordinate system conversion unit that converts a coordinate system of the displacement information into a local coordinate system, a displacement information packing unit that performs packing based on one of a first format, a second format, and a third format for at least one of a normal component, a tangential component, or a bi-tangential component included in the displacement information of the local coordinate system, and a displacement information encoding unit that encodes the packed displacement information.

[0016] According to embodiments, the displacement information packing unit selectively performs packing on a bi-tangential component of the displacement information, and the signaling information may include information for identifying whether packing of the bi-tangential component has been skipped.

[0017] According to embodiments, the signaling information may include information for identifying a format applied to the displacement information.

[0018] According to embodiments, a mesh data decoding method may include a step of receiving a base mesh bitstream, a displacement vector bitstream, a texture map bitstream, and signaling information, a base mesh processing step of restoring a base mesh from the base mesh bitstream, a displacement information processing step of restoring displacement information from the displacement vector bitstream, a restoration step of restoring a mesh based on the base mesh and the displacement information, and a texture map processing step of restoring a texture map from the texture map bitstream.

[0019] According to embodiments, the displacement information processing step may include a step of decoding the displacement vector bitstream into displacement information, a step of identifying a format applied to the displacement information among a first format, a second format, and a third format, a step of depacking at least one component among a normal component, a tangential component, and a bi-tangential component included in the displacement information based on the identified format, and a step of deconstructing a local coordinate system of the depacked displacement information into an original coordinate system.

[0020] According to embodiments, the signaling information may include information for identifying a format applied to the displacement information.

[0021] According to embodiments, the signaling information further includes information for identifying whether packing of the bi-tangential component has been skipped, and the depacking step can determine a depacking method of at least one of the normal component, the tangential component, or the bi-tangential component based on the signaling information.

[0022] According to embodiments, a mesh data decoding device may include a receiving unit that receives a base mesh bitstream, a displacement vector bitstream, a texture map bitstream, and signaling information, a base mesh processing unit that restores a base mesh from the base mesh bitstream, a displacement information processing unit that restores displacement information from the displacement vector bitstream, a restoration unit that restores a mesh based on the base mesh and the displacement information, and a texture map processing unit that restores a texture map from the texture map bitstream.

[0023] According to embodiments, the displacement information processing unit may include a displacement information decoding unit that decodes the displacement vector bitstream into displacement information, a displacement information depacking unit that identifies a format applied to the displacement information among a first format, a second format, and a third format, and depacks at least one component among a normal component, a tangential component, and a bi-tangential component included in the displacement information based on the identified format, and a coordinate system deconversion unit that deconverts a local coordinate system of the depacked displacement information into an original coordinate system.

[0024] According to embodiments, a computer program stored on a computer-readable recording medium can be combined with a computer, which is hardware, to perform the above method.

[0025] According to embodiments, a computer program stored on a computer-readable recording medium can be combined with a computer, which is hardware, to perform the above method.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] The mesh data transmission method, mesh data transmission device, mesh data reception method, and mesh data reception device according to the embodiments encode and transmit only the normal component and the tangential component excluding the bi-tangential component among the normal component, the tangential component, and the bi-tangential component converted to a local coordinate system, and cause a decoder of the reception device to decode up to the bi-tangential component, thereby obtaining mesh data with an efficient bit saving effect and thus better image quality.

[0030] 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.

[0031] FIG. 1 illustrates a system for providing dynamic mesh content according to embodiments.

[0032] Figure 2 illustrates a V-MESH compression method according to embodiments.

[0033] Figure 3 illustrates pre-processing of V-MESH compression according to embodiments.

[0034] Figure 4 illustrates a mid-edge subdivision method according to embodiments.

[0035] Figure 5 illustrates a displacement generation process according to embodiments.

[0036] Figure 6 illustrates an intra-frame encoding process of V-MESH data according to embodiments.

[0037] Figure 7 illustrates an inter-frame encoding process of V-MESH data according to embodiments.

[0038] Figure 8 illustrates a lifting conversion process for displacement according to embodiments.

[0039] Figure 9 illustrates a process of packing transformation coefficients into a 2D image according to embodiments.

[0040] Figure 10 illustrates an attribute transfer process of a V-MESH compression method according to embodiments.

[0041] Figure 11 illustrates an intra-frame decoding process of V-MESH data according to embodiments.

[0042] Figure 12 shows an inter-frame decoding processor of V-MESH data.

[0043] Fig. 13 is a drawing showing an example of a transmitting device according to embodiments.

[0044] Fig. 14 is a drawing showing an example of a receiving device according to embodiments.

[0045] Fig. 15 is a drawing showing another example of a transmitting device according to embodiments.

[0046] Fig. 16 is a detailed block diagram of a displacement vector encoder according to embodiments.

[0047] Fig. 17 is a drawing showing an example of a displacement vector coefficient structure according to embodiments.

[0048] FIG. 18 is a drawing showing an example of packing displacement vector coefficients according to embodiments.

[0049] FIG. 19 is a diagram showing an example of packing displacement vector coefficient blocks by LoD according to embodiments.

[0050] FIG. 20(a) and FIG. 20(b) are diagrams showing examples of a method for packing displacement vector coefficients within a displacement vector coefficient block according to embodiments.

[0051] FIG. 21(a) and FIG. 21(b) are drawings showing an example of packing displacement vector coefficients based on the YUV 4:4:4 format according to embodiments.

[0052] FIG. 22(a) and FIG. 22(b) are diagrams showing another example of packing displacement vector coefficients based on the YUV 4:4:4 format according to embodiments.

[0053] FIG. 23(a) and FIG. 23(b) are drawings showing an example of packing displacement vector coefficients based on the YUV 4:2:0 format according to embodiments.

[0054] FIG. 24(a) and FIG. 24(b) are diagrams showing another example of packing displacement vector coefficients based on the YUV 4:2:0 format according to embodiments.

[0055] FIG. 25(a) and FIG. 25(b) are drawings showing an example of packing displacement vector coefficients based on the YUV 4:0:0 format according to embodiments.

[0056] FIG. 26(a) and FIG. 26(b) are diagrams showing another example of packing displacement vector coefficients based on the YUV 4:0:0 format according to embodiments.

[0057] Fig. 27 is a drawing showing another example of a receiving device according to embodiments.

[0058] Fig. 28 is an example of a detailed block diagram of a displacement vector decoder according to embodiments.

[0059] FIG. 29(a) and FIG. 29(b) are diagrams showing an example of reverse packing displacement vector coefficients based on the YUV 4:4:4 format according to embodiments.

[0060] FIG. 30(a) and FIG. 30(b) are diagrams showing another example of reverse packing displacement vector coefficients based on the YUV 4:4:4 format according to embodiments.

[0061] FIG. 31(a) and FIG. 31(b) are diagrams showing an example of reverse packing displacement vector coefficients based on the YUV 4:2:0 format according to embodiments.

[0062] FIG. 32(a) and FIG. 32(b) are diagrams showing another example of reverse packing displacement vector coefficients based on the YUV 4:2:0 format according to embodiments.

[0063] FIG. 33(a) and FIG. 33(b) are drawings showing an example of reverse packing displacement vector coefficients based on the YUV 4:0:0 format according to embodiments.

[0064] FIG. 34(a) and FIG. 34(b) are diagrams showing another example of reverse packing displacement vector coefficients based on the YUV 4:0:0 format according to embodiments.

[0065] FIG. 35(a) and FIG. 35(b) are diagrams showing another example of reverse packing displacement vector coefficients based on the YUV 4:0:0 format according to embodiments.

[0066] FIG. 36 is a diagram showing an example of a syntax structure of signaling information according to embodiments.

[0067] FIG. 37 is a diagram showing another example of the syntax structure of signaling information according to embodiments.

[0068] Figure 38 is a flowchart showing an example of a transmission method according to embodiments.

[0069] Figure 39 is a flowchart showing an example of a receiving method according to embodiments.

[0070] 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.

[0071] 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.

[0072] Recently, with the 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 System (GIS). 3D data can be represented as a point cloud, mesh, 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 constituting the mesh change over time, and a static mesh if they do not change.

[0073] 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.

[0074] FIG. 1 illustrates a system for providing dynamic mesh content according to embodiments.

[0075] The system of FIG. 1 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. 1 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).

[0076] The system of FIG. 1 can perform video-based dynamic mesh compression and decompression.

[0077] 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.

[0078] 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.

[0079] Currently, the MPEG standards body defines two types of dynamic mesh data: Category 1: Mesh data with texture maps as color information. Category 2: Mesh data with vertex colors as color information.

[0080] Mesh coding standards for Category 1 data are currently under development, and work on Category 2 data standards is also planned for the future. The overall process for providing mesh content services may include acquisition, encoding, transmission, decoding, rendering, and / or feedback, as shown in Figure 1.

[0081] 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.

[0082] A mesh compression system may include a transmitting device (100) and a receiving device (110) as shown in FIG. 1. 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.

[0083] 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.

[0084] 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, generally called UV coordinates or texture coordinates, associated with the mesh vertices. Meshes contain 2D attribute maps, which can be used to store high-resolution attribute information such as textures, normals, and displacement. Here, displacement can be used interchangeably with displacement, displacement information, or displacement vectors (i.e., displacement vectors).

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] The dynamic mesh video compression method described below is based on MPEG's V-Mesh method.

[0100] In this document, picture / frame can generally mean a unit representing one video of a specific time period.

[0101] 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.

[0102] 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.

[0103] As described above, the encoding process of Fig. 1 is as follows.

[0104] 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.

[0105] 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.

[0106] 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 a mapping of the surface of the mesh onto a 2D image. Mapping which part (surface or vertex) of the mesh each data of this attribute map corresponds to is based on the mapping information contained in the input mesh. Since the attribute map has data for each frame of the mesh video, it can also be expressed as an attribute map video. 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.).

[0107] 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.

[0108] In the V-Mesh compression method, the following data and information can be generated through the compression process.

[0109] 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.

[0110] Displacement: 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.

[0111] Atlas information: This is the metadata required to reconstruct a mesh using base mesh, displacement, and attribute map information. It can be created and utilized as sub-mesh units (such as patches) that make up the mesh.

[0112] Referring to FIGS. 2 to 7, a method for encoding mesh position information (or vertex position information) is described, and referring to FIGS. 6 to 10, etc., a method for encoding attribute information (attribute map) by restoring mesh position information is described.

[0113] Figure 2 illustrates a V-MESH compression method according to embodiments.

[0114] Fig. 2 illustrates the encoding process of Fig. 1, and the encoding process may include a pre-processing process and an encoding process. The mesh video encoder (102) of Fig. 1 may include a pre-processor (200) and an encoder (201) as in Fig. 2. In addition, the transmitting device of Fig. 1 may be broadly referred to as an encoder, and the mesh video encoder (102) of Fig. 1 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 in Fig. 2. The pre-processor (200) of Fig. 2 may be located in front of the encoder (201) of Fig. 2. The pre-processor (200) and the encoder (201) of Fig. 2 may be referred to as a single encoder.

[0115] 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 (or 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.

[0116] 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.

[0117] Figure 3 illustrates a pre-processing process of V-MESH compression according to embodiments.

[0118] Fig. 3 illustrates the configuration and operation of the preprocessor of Fig. 2. In Fig. 3, 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.

[0119] Fig. 3 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).

[0120] Below, each step of Fig. 3 is described.

[0121] 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.

[0122] 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.

[0123] 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.

[0124] 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.

[0125] 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 has been performed become similar to each other. In the present disclosure, the mesh on which the fitting process has been performed is referred to as a fitted subdivision mesh (or fitted subdivision mesh).

[0126] Figure 4 illustrates a mid-edge subdivision method according to embodiments.

[0127] Figure 4 illustrates the mid-edge method of the fitting subdivision surface described in Figure 3. Referring to Figure 4, an original mesh containing four vertices is subdivided to 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.

[0128] 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 displacement represents the position difference in three-dimensional space, it is also expressed as a value in the (x, y, z) space of a Cartesian coordinate system. Depending on the user input parameters, the (x, y, z) coordinate values ​​can be converted to (normal, tangential, bi-tangential) coordinate values ​​of the local coordinate system.

[0129] Fig. 5 illustrates a displacement generation process according to embodiments. The displacement generation process of Fig. 5 may be performed in a pre-processor (200) or in an encoder (201).

[0130] FIG. 5 illustrates in detail the displacement calculation method of the fitting subdivision surface (300) as described in FIG. 4.

[0131] 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 reconstructed base mesh to generate a subdivided reconstructed 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 reconstructed 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 reconstructed 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 reconstructed base mesh. For example, a positional difference value between vertices of two input meshes may be generated. The vertex positional difference value becomes a displacement.

[0132] 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.

[0133] The V-Mesh compression (reconstruction) method according to the embodiments may include intra frame encoding (Fig. 6) and inter frame encoding (Fig. 7).

[0134] 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.

[0135] Fig. 6 illustrates an intra-frame encoding process of a V-MESH compression method according to embodiments. Each component for the intra-frame encoding process of Fig. 6 corresponds to hardware, software, a processor, and / or a combination thereof.

[0136] The encoding process of FIG. 6 details the encoding of the mesh video encoder (102) of FIG. 1. That is, it shows the configuration of the mesh video encoder (102) when the encoding of FIG. 1 is an intra-frame method. The encoder of FIG. 6 may include a pre-processor (200) and / or an encoder (201). The pre-processor (200) and encoder (201) of FIG. 6 may correspond to the pre-processor (200) and encoder (201) of FIG. 3.

[0137] 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.

[0138] The quantizer (411) of the encoder (201) can quantize the base mesh and / or the fitted subdivided mesh. The static mesh encoder (412) can encode the static mesh (i.e., the quantized base mesh) and generate a bitstream (i.e., a compressed base mesh bitstream) including the encoded base mesh. The static mesh decoder (413) can decode the encoded static mesh (i.e., the encoded base mesh). The inverse quantizer (414) can inversely quantize the quantized static mesh (i.e., the base mesh) to output a reconstructed (or restored) base mesh. The displacement calculation unit (415) can generate displacements (or displacements) based on the reconstructed static mesh (i.e., the base mesh) and the fitted subdivided mesh. According to embodiments, the displacement calculation unit (415) calculates displacement, which is the position difference between each vertex of the subdivided base mesh and the fitted subdivided mesh after subdividing (or refining) the restored base mesh. In other words, the displacement is a displacement vector, which is the position difference between the vertices of the two meshes so that the fitted subdivided (or refining) mesh becomes similar to the original mesh. The forward linear lifting unit (416) can perform lifting transformation on the input displacement to generate lifting coefficients (or transform coefficients). The quantizer (417) can quantize the lifting coefficients. The image packing unit (418) can pack an image based on the quantized lifting coefficients. The video encoder (419) 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 (418), compressed through the video encoder (419), and output as a displacement bitstream (i.e., compressed displacement bitstream).

[0139] A video decoder (420) decodes a compressed displacement bitstream. An image unpacking unit (421) can perform unpacking on the decoded displacement frame to output quantized lifting coefficients. A dequantizer (422) can dequantize the quantized lifting coefficients. An inverse linear lifting unit (423) applies inverse lifting to the inverse quantized lifting coefficients to generate restored displacement. A mesh restoration unit (424) reconstructs and deforms a mesh using the restored displacement output from the inverse linear lifting unit (423) and the restored base mesh (or subdivided restored base mesh) output from the inverse quantization unit (414). The present disclosure refers to the reconstructed and deformed mesh as a restored deformed mesh.

[0140] The attribute transfer (425) 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 (426) may pad data in the attribute map based on the push-pull method. The color space conversion unit (427) 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 encoder (428) may encode the attribute map and output it as a compressed attribute bitstream.

[0141] A multiplexer (430) can generate a compressed bitstream by multiplexing a compressed base mesh bitstream, a compressed displacement bitstream, and a compressed attribute bitstream.

[0142] In Fig. 6, the displacement calculation unit (415) may be included in the pre-processor (200). In addition, at least one of the quantizer (411), the static mesh encoder (412), the static mesh decoder (413), and the inverse quantizer (414) may be included in the pre-processor (200).

[0143] As described in FIG. 6, the intra-frame encoding method includes base mesh encoding (also called static mesh encoding). That is, when performing intra-frame encoding on the current input mesh frame, the base mesh generated in the pre-processing process of the pre-processor (200) can be encoded using a static mesh compression technology in a static mesh encoder (412) after undergoing a quantization process in a quantizer (411). In the V-Mesh compression method, for example, Draco technology is applied to base mesh encoding, and vertex position information, mapping information (texture coordinates), vertex connection information, etc. of the base mesh become compression targets.

[0144] The encoder of Fig. 6 generates a bitstream by compressing the base mesh, displacement, and attributes within the frame, and the encoder of Fig. 7 generates a bitstream by compressing the motion, displacement, and attributes between the current frame and the reference frame.

[0145] Fig. 7 illustrates an inter-frame encoding process of a V-MESH compression method according to embodiments. Each component for the inter-frame encoding process of Fig. 7 corresponds to hardware, software, a processor, and / or a combination thereof.

[0146] The encoding process of Fig. 7 details the encoding of Fig. 1. That is, it shows the configuration of an encoder when the encoding of Fig. 1 is an inter-frame method. The encoder of Fig. 7 may include a 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. 3.

[0147] For a description of the components corresponding to the encoding operation of FIG. 6 among the encoding operations of FIG. 7, refer to the description of FIG. 6. That is, the operation of the quantizer (511), displacement calculation unit (515), wavelet transformer (516), quantizer (517), image packing unit (518), video encoder (519), video decoder (520), image unpacking unit (521), inverse quantizer (522), inverse wavelet transformer (523), mesh restoration unit (524), attribute transfer (525), push-pull padding (526), ​​color space conversion unit (527), video encoder (528), and multiplexer (530) of FIG. 7 is similar to that of the quantizer (411), static mesh encoder (412), static mesh decoder (413), inverse quantizer (414), displacement calculation unit (415), forward linear lifting unit (416), quantizer (417), image Since the operations described in the packing unit (418), video encoder (419), video decoder (420), image unpacking unit (421), inverse quantizer (422), inverse linear lifting unit (423), mesh restoration unit (424), attribute transfer (425), push-pull padding (426), color space conversion unit (427), video encoder (428), and multiplexer (430) are the same or similar, a detailed description thereof is omitted in FIG. 7 to avoid redundant description.

[0148] For inter-frame based encoding in FIG. 7, the motion encoder (512) can obtain a motion vector between the two base meshes based on the restored quantized reference base mesh and the quantized current base mesh, and then encode the motion vector to output a compressed motion bitstream. The motion encoder (512) can be referred to as a motion vector encoder. The base mesh restoration unit (513) can restore the base mesh based on the restored quantized reference base mesh and the encoded motion vector. The restored base mesh is dequantized in the dequantizer (514) and then output to the displacement calculation unit (515).

[0149] In Fig. 7, the displacement calculation unit (515) may be included in the pre-processor (200). In addition, at least one of the quantizer (511), the motion encoder (512), the base mesh restoration unit (513), and the inverse quantizer (514) may be included in the pre-processor (200).

[0150] As described in Fig. 7, the inter-frame encoding method may include motion field encoding (also called motion vector encoding). Inter-frame encoding may be performed when a one-to-one correspondence of vertices is established between a reference mesh and a current input mesh, and only the position information of the vertices is different. When performing inter-frame encoding, instead of compressing the base mesh, the difference between the vertices of the reference base mesh and the current base mesh, i.e., the motion field (also called motion vector), may be calculated and encoded to encode this information. The reference base mesh is the result of quantizing the already decoded base mesh data and is determined according to the reference frame index determined in the GoF generation. The motion field may also be encoded as a value. Alternatively, the predicted motion field can be calculated by averaging the motion fields of the restored 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 residual motion field value can be encoded using entropy coding.The process of encoding displacement and attribute maps, excluding the motion field encoding process of inter frame encoding, is the same as the structure of the intra frame encoding method except for the base mesh encoding.

[0151] Figure 8 illustrates a lifting conversion process for displacement according to embodiments.

[0152] Figure 9 illustrates a process of packing transformation coefficients (or lifting coefficients) according to embodiments into a 2D image.

[0153] Figures 8 and 9 illustrate the process of transforming displacement and packing transform coefficients of the encoding process of Figures 6 and 7, respectively.

[0154] The encoding method according to the embodiments includes displacement encoding.

[0155] 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 (see 415 in FIG. 6 or 515 in FIG. 7). For effective encoding, a data transform process such as wavelet transform can be applied to the displacement information (see 416 in FIG. 6 or 516 in FIG. 7).

[0156] FIG. 8 shows a process of transforming displacement information using a lifting transform in the forward linear lifting unit (416) of FIG. 6 or the wavelet transformer (516) 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 (417 or 517) and then packed into a 2D image through an image packing unit (418 or 518) as in FIG. 9. The transform coefficients are configured as one block for every 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. Transform coefficients can be packed by aligning them with Morton codes within a single block. The packed images generate displacement videos for each GoF unit, and these displacement videos can be encoded using a conventional video compression codec in a video encoder (419 or 519).

[0157] Referring to FIG. 8, the base mesh (original) may include vertices and edges for LoD0. 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 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 size of the bitstream. The prediction process means 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.

[0158] Referring to FIG. 9, a vertex has a transform coefficient (also called a lifting coefficient) generated through a lifting transformation. The transform coefficient of a vertex related to a lifting transformation can be packed into an image by an image packing unit (418 or 518) and then encoded by a video encoder (419 or 519).

[0159] Figure 10 illustrates an attribute transfer process of a V-MESH compression method according to embodiments.

[0160] According to the embodiments, FIG. 10 shows the detailed operation of the attribute transfer (425 or 525) of the encoding of FIG. 6, FIG. 7, etc.

[0161] Encoding according to embodiments includes attribute map encoding. According to embodiments, attribute map encoding may be performed in the video encoder (428) of FIG. 6 or the video encoder (528) of FIG. 7.

[0162] 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 FIGS. 6 and 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 reconstructed deformed mesh is regenerated through the attribute transfer process of attribute transfer (425 or 525).

[0163] According to embodiments, attribute transfer (425 or 525) 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 pixel location (u, v) of the new attribute map. If P(u, v) does not belong to any triangle, the pixel at that location in the new attribute map can be filled with a color value using a padding algorithm, such as the push-pull algorithm of push-pull padding (426 or 526).

[0164] The new attribute map generated through attribute transfer (425 or 525) is grouped into GoF units to form an attribute map video, which is compressed using the video codec of the video encoder (428 or 528).

[0165] 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.

[0166] The decoding process of Fig. 1 can perform the reverse process of the corresponding process of the encoding process of Fig. 1. The specific decoding process is as follows.

[0167] FIG. 11 illustrates an intra-frame decoding (or intra-decoding) process of V-Mesh technology according to embodiments.

[0168] Fig. 11 illustrates the configuration and operation of the mesh video decoder (113) of the receiving device of Fig. 1. In addition, Fig. 11 can restore mesh data by performing the reverse process of the intra-frame encoding process of Fig. 6. Each component for the intra-frame decoding process of Fig. 11 corresponds to hardware, software, and / or a combination thereof.

[0169] First, the bitstream (i.e., compressed bitstream) received and input to the demultiplexer (611) of the intra frame decoding unit (610) can be separated into a mesh substream, a displacement substream, an attribute map substream, and a substream containing patch information of the mesh, such as V-PCC / V3C. The term V-PCC (Video-based Point Cloud Compression) used in this document can be used with the same meaning as V3C (Visual Volumetric Video-based Coding), and the two terms can be used interchangeably. Therefore, the term V-PCC in this document can be interpreted as the term V3C.

[0170] According to embodiments, the mesh sub-stream may be input to a static mesh decoder (612) and decoded, the displacement sub-stream may be input to a video decoder (613) and decoded, and the attribute map sub-stream may be input to a video decoder (617) and decoded.

[0171] According to embodiments, the mesh sub-stream is decoded through a decoder (612) of a static mesh codec used in encoding, such as Google Draco, and as a result, a reconstructed quantized base mesh, for example, connection information, vertex geometry information, vertex texture coordinates, etc. of the base mesh can be reconstructed.

[0172] According to embodiments, the displacement sub-stream is decoded into displacement video through a decoder (613) of a video compression codec used in encoding, and is restored as displacement information for each vertex (i.e., Recon. displacements) through an image unpacking process of an image unpacking unit (614), an inverse quantization process of an inverse quantizer (615), and an inverse transform process of an inverse linear lifting unit (616).

[0173] According to embodiments, the base mesh restored by the static mesh decoder (612) is inverse quantized by the inverse quantizer (620) and then output to the mesh restoration unit (630). The mesh restoration unit (630) reconstructs and restores the deformed mesh (i.e., decoded mesh) through the restored displacement output from the inverse linear lifting unit (616) and the restored base mesh output from the inverse quantizer (620). That is, the inverse quantized 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.

[0174] According to embodiments, an attribute map sub-stream is decoded through a decoder (617) 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 (640) through processes such as color format conversion and color space conversion.

[0175] 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.

[0176] Referring to FIG. 11, the received compressed bitstream includes patch information, a mesh substream, a displacement substream, and an attribute map substream. A substream is interpreted as a term referring to a part of a bitstream included in a bitstream. The bitstream includes patch information (data), mesh information (data), displacement information (data), and attribute map information (data).

[0177] As described above, the decoder of FIG. 11 performs the following intra-frame decoding operations. The static mesh decoder (612) decodes the mesh sub-stream to generate a reconstructed quantized base mesh, and the inverse quantizer (620) applies the quantization parameters of the quantizer inversely to generate the reconstructed base mesh. The video decoder (613) decodes the displacement sub-stream, the image unpacking unit (614) unpacks the images of the decoded displacement video, and the inverse quantizer (615) inversely quantizes the quantized images. The inverse linear lifting unit (616) applies a lifting transform in the reverse process of the encoder to generate the reconstructed displacement. The mesh restoration unit (630) generates a reconstructed deformed mesh based on the reconstructed base mesh and the reconstructed displacement. The video decoder (617) decodes the attribute map sub-stream, and the color conversion unit (640) converts the color format and / or space of the decoded attribute map to generate a decoded attribute map.

[0178] Figure 12 illustrates the inter-frame decoding (or inter-decoding) process of V-Mesh technology.

[0179] Fig. 12 illustrates the configuration and operation of the mesh video decoder (113) of the receiving device of Fig. 1. In addition, Fig. 12 can restore mesh data by performing the reverse process of the inter-frame encoding process of Fig. 7. Each component for the inter-frame decoding process of Fig. 12 corresponds to hardware, software, and / or a combination thereof.

[0180] First, the bitstream received and input to the demultiplexer (711) of the intra frame decoding unit (710) can be separated into a motion sub-stream (also called a motion sub-stream or motion vector sub-stream), a displacement sub-stream, an attribute map sub-stream, and a sub-stream including patch information of a mesh such as V3C / V-PCC.

[0181] According to embodiments, the motion sub-stream may be input to a motion decoder (712) and decoded, the displacement sub-stream may be input to a video decoder (713) and decoded, and the attribute map sub-stream may be input to a video decoder (717) and decoded.

[0182] According to embodiments, a motion sub-stream is decoded through entropy decoding and inverse prediction processes in a motion decoder (712) and restored into motion information (or motion vector information). A base mesh restoration unit (718) combines the restored motion information with a reference base mesh that has already been restored and stored to generate a reconstructed quantized base mesh for the current frame. An inverse quantizer (720) applies inverse quantization to the restored quantized base mesh to generate a reconstructed base mesh. A video decoder (713) decodes a displacement sub-stream, an image unpacking unit (714) unpacks an image of the decoded displacement video, and an inverse quantizer (715) inversely quantizes a quantized image. The reverse linear lifting unit (716) applies a lifting transformation in the reverse process of the encoder to generate a restored displacement. The mesh restoration unit (730) generates a reconstructed deformed mesh, i.e., a final decoded mesh, based on the restored base mesh and the restored displacement.

[0183] According to embodiments, the video decoder (717) decodes the attribute map sub-stream in the same manner as intra decoding, and the color conversion unit (740) converts the color format and / or space of the decoded attribute map to generate a decoded attribute map. The decoded mesh and the decoded attribute map can be utilized by the receiver as final mesh data that can be utilized by the user.

[0184] Referring to Fig. 12, the bitstream includes motion information (also called motion vectors), displacement, and an attribute map. Since Fig. 12 performs inter-frame decoding, it further includes a process of decoding inter-frame motion information. The motion information is decoded, and a restored quantized base mesh for the motion information is generated based on the reference base mesh, thereby generating a restored base mesh. For a description of the operation of Fig. 12, which is identical to that of Fig. 11, refer to the description of Fig. 11.

[0185] Fig. 13 illustrates a mesh data transmission device according to embodiments.

[0186] FIG. 13 corresponds to the transmitting device (100) or mesh video encoder (102) of FIG. 1, the encoder (preprocessor and encoder) of FIG. 2, FIG. 6, or FIG. 7, and / or a transmitting encoding device corresponding thereto. Each component of FIG. 13 corresponds to hardware, software, a processor, and / or a combination thereof.

[0187] The operation process of a transmitter for compressing and transmitting dynamic mesh data using V-Mesh compression technology may be as shown in Fig. 13. The transmitter of Fig. 13 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.

[0188] 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.

[0189] 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.

[0190] 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).

[0191] 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).

[0192] 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).

[0193] 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 between the vertex positions of the restored base mesh 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.

[0194] 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 on the transformed displacement vector value, i.e., the transform coefficient, in a quantizer. At this time, a different quantization parameter may be applied to each axis of the transform coefficient, and the quantization parameter may be derived according to an encoder / decoder agreement. The transformed and quantized displacement vector information 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 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.

[0195] 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).

[0196] 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 a deformed mesh based on the base mesh restored by the base mesh restoration unit (815) and the displacement vector restored by the displacement vector restoration unit (819). The restored mesh (or referred to as a restored deformed mesh) has restored vertices, connection information between vertices, texture coordinates, and connection information between texture coordinates.

[0197] 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.

[0198] The generated texture map video can be encoded using a video compression codec of the texture map video encoder (822). The texture map video bitstream generated through encoding is transmitted to a multiplexer (823).

[0199] 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).

[0200] Referring to FIG. 13, a transmitting device (encoder) can encode a mesh in an intra-frame or inter-frame manner. A transmitting device according to intra-encoding can generate a base mesh, a displacement vector (or referred to as displacement), and a texture map (or referred to as attribute map). A transmitting device according to inter-encoding can generate a motion vector (or referred to as motion), a displacement vector (or referred to as displacement), and a texture map (or referred to as attribute map). The texture map obtained from the data input unit is generated and encoded based on the restored mesh. 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 position 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.

[0201] Fig. 14 illustrates a mesh data receiving device according to embodiments.

[0202] Fig. 14 corresponds to the receiving device (110) or mesh video decoder (113) of Fig. 1, the decoder of Fig. 11 or Fig. 12, and / or the receiving decoding device corresponding thereto. Each component of Fig. 14 corresponds to hardware, software, a processor, and / or a combination thereof. The receiving (decoding) operation of Fig. 14 may follow the reverse process of the corresponding process of the transmitting (encoding) operation of Fig. 13.

[0203] 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.

[0204] 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.

[0205] 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.

[0206] 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).

[0207] According to embodiments, the displacement vector video decoder (917) can decode the displacement vector bitstream as a video bitstream using a video codec.

[0208] According to embodiments, the displacement vector restoration unit (918) extracts displacement vector transform 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 transform 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 inversely transforming it into a Cartesian coordinate system may be performed.

[0209] 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.

[0210] 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.

[0211] 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).

[0212] Referring to FIG. 14, a receiving device (decoder) can decode a mesh in an intra-frame or inter-frame manner. A receiving device according to intra-decoding can receive a base mesh, a displacement vector (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.

[0213] 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 the method / device according to embodiments. The mesh data transmission and reception method / device according to embodiments may also be referred to as a 3D data transmission and reception method / device or a point cloud data transmission and reception method / device.

[0214] As described above, the V-Mesh method converts the displacement information generated during the encoding process into a video format and then compresses it using a conventional 2D video codec. Then, the compressed displacement information is restored by performing the reverse process of the 2D video codec. More specifically, the V-DMC encoder (or encoder or encoding device) calculates a displacement vector, which is the difference between the mesh restored from the base mesh and the mesh fitted in the pre-processing step, and converts the calculated displacement vector in the canonical coordinate system (i.e., in the form of x, y, z) into a displacement vector in the local coordinate system (i.e., in the form of normal, tangential, or bi-tangential), and then performs lifting transformation and quantization on the displacement vector in the local coordinate system to encode it into a displacement vector bitstream. In this case, the V-DMC decoder (or decoder or decoding device) performs the reverse process of the V-DMC encoder to restore the displacement vector. That is, rather than compressing the displacement vector information in the x, y, z form of the canonical coordinate system for efficient compression, it is converted to the normal, tangential, and bi-tangential forms of the local coordinate system, and then lifting transformation and quantization are performed, and then encoded and transmitted in the form of simple displacement vector coefficients such as 0, 1, and 2. At this time, the encoder calculates the coordinate transformation for the three components of normal, tangential, and bi-tangential, and performs a series of displacement vector encoding processes as described above for each component, which may be inefficient in terms of compression efficiency and transmission speed.

[0215] The present disclosure proposes a method for more efficient compression and transmission, in which an encoder of a transmitting device packs only the normal and tangential components of a displacement vector and skips packing the bi-tangential component to perform encoding and transmit the same as a bitstream, and a decoder of a receiving device calculates the bi-tangential component using the two normal and tangential components received and decodes it into a final displacement vector based on the calculated bi-tangential component.

[0216] That is, in the present disclosure, the encoder of the transmitting device encodes and transmits only the normal and tangential components excluding the bi-tangential component among the normal, tangential, and bi-tangential components transformed into the local coordinate system, and the decoder of the receiving device proposes a method of decoding up to the bi-tangential component using the received normal and tangential components. In addition, the present disclosure also proposes a packing method and a signaling method according to various image packing formats. In this way, compared to transmitting all of the existing normal, tangential, and bi-tangential components, by compressing and transmitting only two components, an efficient bit saving effect and thus better image quality mesh data can be obtained.

[0217] As such, the present disclosure relates to V-DMC, a method for compressing 3D dynamic mesh data based on an existing 2D video codec, and describes a device and method for encoding / decoding in units of displacement vectors in displacement vector transformation and quantization steps, and syntax and semantics information related thereto. In particular, the present disclosure describes a method for encoding and decoding by packing only two normal and tangential components among three normal, tangential, and bi-tangential components of a displacement vector, a 2D image packing method according to a displacement vector video format, whether to skip packing for the bi-tangential component of a displacement vector, and a signaling method according to an image packing format. In addition, the operation of a transmitter and a receiver to which the same is applied is described.

[0218] In the present disclosure, geometric information (or referred to as geometry or geometric data) is one of the elements that constitute a mesh, and includes vertices (or points), edges, polygons, etc. Here, a vertex defines a position in 3D space, an edge represents connection information between vertices, and a polygon forms the surface of the mesh with a combination of edges and vertices. That is, each vertex that constitutes the mesh represents a position in 3D space, and is expressed, for example, by x, y, z coordinates (i.e., canonical coordinate system). And, a polygon may be a triangle or a square. That is, geometry forms the skeleton of a 3D model, thereby defining the shape of the model and visually expressing it when rendered.

[0219] In the present disclosure, vertex, apex, and point may be used interchangeably. That is, a vertex has coordinates in 3D space, and a triangular or quadrilateral polygon can be created through connections between multiple 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 interchangeably.

[0220] In the present disclosure, displacement information can be obtained based on a refined mesh (or referred to as a sub-mesh). That is, a fitting process is performed to make the input mesh and the sub-mesh similar to each other, and the difference in the positions of each vertex of the fitted subdivision mesh and the refined restored base mesh is generated by performing refinement on the restored base mesh. The present disclosure refers to this vertex position difference value as a displacement vector. In the present disclosure, the displacement vector may be used interchangeably with the same meaning as displacement or displacement information. In addition, the displacement video may be used interchangeably with the same meaning as a displacement vector video or a displacement vector conversion coefficient video, and the displacement vector may be used interchangeably with the same meaning as a displacement vector conversion coefficient or a displacement vector coefficient.

[0221] Fig. 15 illustrates a transmitting device according to embodiments. The transmitting device of Fig. 15 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.

[0222] FIG. 15 corresponds to the transmitting device (100) or mesh video encoder (102) of FIG. 1, the encoder (preprocessor and encoder) of FIG. 2, FIG. 6, or FIG. 7, the transmitting device of FIG. 13, and / or the transmitting encoding device corresponding thereto. Each component of FIG. 15 corresponds to hardware, software, a processor, and / or a combination thereof. The execution order of each block in FIG. 15 may be changed, some blocks may be omitted, and some blocks may be newly added.

[0223] 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. 15. The transmitter of FIG. 15 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.

[0224] In Fig. 15, 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.

[0225] 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.

[0226] 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).

[0227] 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).

[0228] The final base mesh (or base mesh having a texture map) generated by the parameterization unit (11012) is input to the mesh quantization unit (11013) and quantized. According to embodiments, the mesh quantization unit (11013) may perform the 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.

[0229] 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.

[0230] 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.

[0231] 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).

[0232] According to embodiments, the quantized base mesh in the mesh quantization unit (11013) can be output to a motion vector encoder (11015) or a static mesh encoder (11016) through a switching unit (11014).

[0233] According to embodiments, the base mesh is output to a motion vector encoder (11015) through a switching unit (11014) when performing inter-encoding for the corresponding mesh frame, and is output to a static mesh encoder (11016) through a switching unit (11014) when performing intra-encoding for the corresponding mesh frame. The motion vector encoder (11015) may be referred to as a motion encoder.

[0234] 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).

[0235] As another example, when performing inter-encoding (or inter-frame encoding) on ​​the corresponding mesh frame, the motion vector encoder (11015) 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 (11015) can 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. The motion vector bitstream generated through the 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.

[0236] In FIG. 15, the base mesh decoder (11017) 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 reconstructing 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 reconstruct 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, inverse quantization can be performed on the quantized base mesh through the mesh quantization unit (11013) to reconstruct the current base mesh. As another example, the base mesh decoder (11017) can reconstruct the base mesh based on the reconstructed 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 by the motion vector decoding method and then applying (i.e., adding) the decoded motion vector to the reference reconstructed 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 reconstructed base mesh is output to the displacement vector calculation unit (11020) and the mesh dequantization unit (11024).

[0237] 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).

[0238] According to embodiments, the displacement vector coordinate system conversion unit (11021) can output the vertex displacement vector calculated in a three-dimensional Cartesian coordinate system (i.e., (x, y, z) space) (or canonical coordinate system) as is, or can convert it 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.

[0239] In the displacement vector coordinate system conversion unit (11021), whether or not the displacement vector coordinate system is converted can be determined by an encoder (i.e., transmitting device) / decoder (i.e., receiving device) agreement, or the displacement vector coordinate system conversion status flag (asps_vmc_ext_displacement_coordinate_system), which is information that can identify whether or not the displacement vector coordinate system is converted, can be signaled in signaling information (e.g., atlas sequence parameter set, ASPS) and transmitted to the receiving device. For example, if the value of the displacement vector coordinate system conversion status flag (asps_vmc_ext_displacement_coordinate_system) syntax (or field) is 0, the canonical coordinate system is used as is, and if it is 1, it can indicate that the conversion to the local coordinate system has been performed.

[0240] According to embodiments, the displacement vector of the canocial coordinate system or the displacement vector converted to the local coordinate system in the displacement vector coordinate system conversion unit (11021) is encoded into a displacement vector bitstream (or displacement vector video bitstream) in the displacement vector encoder (11022). In one embodiment, the displacement vector encoder (11022) can encode the displacement vector of the canocial coordinate system or the displacement vector converted to the local coordinate system into the displacement vector bitstream using a 2D video encoder such as H.264, HEVC, or VVC.

[0241] That is, the displacement vector encoder (11022) can perform encoding on a displacement vector or a displacement vector coefficient (or displacement vector transform coefficient). In the present disclosure, the displacement vector encoder (11022) can perform encoding through a video codec-based encoder, a zero run-length encoder, an arithmetic encoder, etc. For example, when the encoding method is video codec-based encoding, the displacement vector encoder (11022) can encode the displacement vector or the displacement vector coefficient by packing it into a frame. That is, in the displacement vector encoder (11022), the displacement vector coefficients can 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.

[0242] 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.

[0243] 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 coefficient encoded by the displacement vector encoder (11022). That is, the displacement vector restoration unit (11023) can perform displacement vector depacking (or unpacking) depending on the method of encoding the displacement vector, for example, when encoded based on a video codec. In addition, the displacement vector restoration unit (11023) can additionally perform dequantization, inverse transformation, etc. depending on whether quantization and transformation processes are performed during the displacement vector encoding process.

[0244] According to embodiments, the mesh dequantization unit (11024) can dequantize vertex coordinates or texture coordinates of the restored base mesh using the reverse process of quantization. If the quantization process is omitted in the mesh quantization unit (11013), the dequantization process is also omitted in the mesh dequantization unit (11024).

[0245] 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. According to embodiments, the mesh restored by the mesh restoration unit (11025) (or referred to as a restored mesh or a restored deformed mesh) has restored vertices, connection information between vertices, texture coordinates, and connection information between texture coordinates. The restored mesh (or restored mesh or restored deformed mesh) generated in the above mesh restoration unit (11025) is provided to the texture map generation unit (11026).

[0246] 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 texture map of the original mesh and the relationship between the original mesh and the restored mesh.

[0247] 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.

[0248] The texture map generated in the above texture map generation unit (11026) can be encoded in the texture map encoder (11027). For example, the texture map encoder (11027) can encode the texture map using a 2D video codec-based encoder, a zero run length encoder, an entropy coding-based arithmetic encoder, etc. In addition, the texture map encoder (11027) can further perform color space conversion of the texture map. Then, the texture map substream (or referred to as a texture map video bitstream) generated through the texture map encoding is transmitted to a multiplexer (not shown).

[0249] 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.

[0250] According to embodiments, a multiplexer (not shown) may multiplex an input base mesh bitstream, a displacement vector bitstream, and a texture map bitstream into a single bitstream and then transmit the multiple bitstreams to a receiving device. Alternatively, the base mesh bitstream, the displacement vector bitstream, and the texture map bitstream may be encapsulated into a file / segment and transmitted to the receiving device.

[0251] According to embodiments, the bitstream multiplexed in the multiplexer 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 a USB, SD, CD, DVD, Blu-ray, HDD, or SSD.

[0252] In this way, the V-DMC encoding device (or transmitting device) simplifies the original mesh and generates a base mesh through a mesh parameterization process. The generated base mesh is quantized, and in the case of an inter-frame, a motion vector is calculated from the previously referenced restored base mesh and encoded into a motion vector, and in the case of an intra-frame, it is transmitted as a base mesh bit stream through a static mesh encoder. In addition, the mesh data after the process of subdividing and fitting the simplified mesh from the original mesh and the mesh data restored from the previously encoded mesh are compared to calculate the displacement vector, which is the difference between each vertex. Then, in order to efficiently encode the calculated displacement vector, the displacement vector coordinate system is converted to a local coordinate system, and the displacement vector converted to the local coordinate system in the displacement vector encoder (12022) is converted and quantized into displacement vector coefficients, and then encoded into a displacement vector bit stream and transmitted.

[0253] The following describes the process of encoding the normal and tangential components among the vector normal, tangential, and bi-tangential components transformed into a local coordinate system in a displacement vector encoder (12022) by lifting and quantizing them into displacement vector coefficients, as well as the component signaling method of the displacement vector for each video image packing format. That is, the principles performed at each step are described in detail below.

[0254] Fig. 16 is a block diagram showing an example of a displacement vector encoder according to embodiments. In Fig. 16, the displacement vector encoder (11022) may include a displacement vector transformation unit (12011), a displacement vector coefficient quantization unit (12012), a displacement vector coefficient packing unit (12013), and a displacement vector image / video encoding unit (12014). Each component of Fig. 16 corresponds to hardware, software, a processor, and / or a combination thereof. The execution order of each block in Fig. 16 may be changed, some blocks may be omitted, and some blocks may be newly added. In the present disclosure, the displacement vector encoder performs displacement vector coefficient image packing for each video image format and then encodes the image-packed displacement vector coefficient using a 2D video codec.

[0255] More specifically, the displacement vector conversion unit (12011) can convert the displacement vector of the (x,y,z) or (n, t, bt) coordinate system into a displacement vector coefficient by performing linear lifting conversion, butterfly lifting conversion, wavelet conversion, etc. on the displacement vector of the (x,y,z) or (n, t, bt) coordinate system. In the (n, t, bt) coordinate system, n means normal, t means tangential, and bt means bi-tangential.

[0256] 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. 그리고, 리프팅 변환이 수행되는 경우, 예측으로 생성되는 잔차 신호를 통해 예측에 사용된 정점의 변위 벡터를 업데이트 하는 과정이 수행될 수 있다.

[0257] At this time, if packing is skipped for the bi-tangential component of the displacement vector, the displacement vector conversion unit (12011) can perform displacement vector conversion only for the normal component and tangential component excluding the bi-tangential component.

[0258] According to embodiments, the displacement vector quantization unit (12012) can perform quantization on the displacement vector value, i.e., the displacement vector or the displacement vector coefficient, converted through the displacement vector transformation unit (12011). For example, if the displacement vector transformation unit (12011) performs transformation on all of the normal component, the tangential component, and the bi-tangential component, the displacement vector quantization unit (12012) performs quantization on the displacement vector coefficients of the normal component, the tangential component, and the bi-tangential component. As another example, if the displacement vector transformation unit (12011) performs transformation on only the normal component and the tangential component, the displacement vector quantization unit (12012) performs quantization on the displacement vector coefficients of the normal component and the tangential component. In the present disclosure, the displacement vector coefficient is used interchangeably with the displacement vector transformation coefficient with the same meaning.

[0259] According to embodiments, the displacement vector quantization unit (12012) can derive a quantized value (quant) for each channel by multiplying a displacement vector coefficient (value) by a scale and adding an offset, as in the following mathematical expression 1. At this time, each channel can be x, y, z or n, t, b, respectively, according to the coordinate system of the displacement vector. In addition, when the bi-tangential component is skipped, displacement vector coefficient quantization can be performed only for the normal and tangential components. The mathematical expression 1 below is an equation for obtaining a quantized value for each channel, and the mathematical expression 2 is an equation for obtaining a scale value for each channel of the mathematical expression 1.

[0260] [Mathematical Formula 1]

[0261]

[0262] [Equation 2]

[0263]

[0264] In Equation 1, the offset is in units of sequence or frame, and a fixed value can be used for each channel. In addition, the scale of Equation 1 can be determined by the quantization parameter (QP) and the level-specific scale (level_scale), as in Equation 2.

[0265] The level_scale in mathematical expression 2 can use a value determined by frame or sequence unit for each level. In addition, can be a parameter constant value determined in the encoder. At this time, the scale can also be determined as an individual value for each channel of the displacement vector.

[0266] According to embodiments, the displacement vector coefficient packing unit (12013) can pack the quantized displacement vector coefficients into a 2D image of size WxH. That is, if the displacement vector encoder (11022) encodes the displacement vector coefficients using a video codec-based encoding method, the process of packing the displacement vector coefficients into a frame as a 2D image is performed in the displacement vector coefficient packing unit (12013). In other words, the displacement vector coefficient packing unit (12013) can pack the displacement vector coefficients into a 2D image, and the displacement vector image / video encoding unit (12014) can encode the packed 2D images using a video compression codec.

[0267] Fig. 17 is a diagram showing an example of a displacement vector coefficient structure according to embodiments. In Fig. 17, assuming that the total number of displacement vector coefficients is N, the number of displacement vector coefficients included in LoD0 is N0 (LoD0 = R0), and the number of displacement vector coefficients included in LoD1 is N1 (LoD1), the number of displacement vector coefficients of level 0 (R0) is N0, and the number of displacement vector coefficients of level 1 (R1) is N1-N0. That is, the number of displacement vector coefficients (N1) included in LoD1 is the sum of the number of displacement vector coefficients (N0) of level 0 (R0) and the number of displacement vector coefficients (N1-N0) of level 1 (R1).

[0268] According to embodiments, the displacement vector coefficient packing unit (12013) can pack N displacement vector coefficients (e.g., N quantized displacement vector coefficients) into an image of size W×H. In the present disclosure, W×H may be the size of a frame in which the displacement vector coefficients are packed as a 2D image.

[0269] That is, the lifting transformation is performed from the vertex of the LoD of the high layer, so that the displacement vector coefficients of the low LoD are stored in the front, and the displacement vector coefficients of the high LoD are stored in the back, as shown in Fig. 17. At this time, packing can be performed separately for the normal, tangential, and bi-tangential components. Alternatively, some components can be skipped without packing. For example, the bi-tangential component can be skipped without packing.

[0270] Fig. 18 is a diagram showing an example of packing displacement vector coefficients according to embodiments. That is, the displacement vector coefficients in the 1D form of Fig. 17 can be packed as a 2D image as in Fig. 18.

[0271] According to embodiments, the displacement vector coefficient packing unit (12013) can organize displacement vector coefficients (or transform coefficient levels) of a 1D vector or scalar into blocks of a size of bx*by, and pack each block according to a scanning order promised in the encoder / decoder, such as a z-scan order, a zig-zag scanning order, or a 2D Morton code order. That is, L*M displacement vector coefficient blocks can be block-packed into an image of a size of (bx*L)×(by*M) according to an order defined in the encoder / decoder. Here, L*M is the number of blocks having a size of bx*by, and bx and by can each be 16. That is, the displacement vector coefficients are organized into one block every 256 (16*16) units, and each block can be packed in a z-scan order or a zig-zag scanning order. In other words, displacement vector coefficients within one block can be packed according to the z-scan order, zig-zag scanning order, 2D Morton code order, etc. In other words, one block can be configured with the size bx*by, and can be configured with L×M blocks determined according to the number N of displacement vector coefficients. At this time, packing can be performed into a 2D image of the size W×H according to the 2D Morton code, zig-zag scanning order, etc.

[0272] If the displacement vector coefficients of all levels are packed into one frame as a 2D image, the packing can be performed sequentially in the scanning order from the displacement vector coefficient block of level 0 (R0). At this time, if the total size of the displacement vector coefficients is smaller than L*M, padding is performed so that the size is (bx*L)×(by*M), as shown in Fig. 18. That is, if the total number of displacement vector coefficients is smaller than (bx*L)×(by*M), padding can be performed to fill the displacement vector image so that the size is (bx*L)×(by*M). Fig. 18 shows an example in which padding is performed on five blocks. Here, padding means filling the corresponding block with a meaningless value (e.g., 0). As another example, if the displacement vector coefficients of multiple levels are packed into one frame as a 2D image, the packing can be performed sequentially in the scanning order from the displacement vector coefficient block of a smaller level. As another example, a 2D image can be packed by performing packing and padding in the reverse order of FIG. 18.

[0273] According to embodiments, L and M are determined according to the number (N) of displacement vector coefficients, or L (or M) is defined by a convention of the encoder / decoder, and then M (or L) can be derived according to the number (N) of displacement vector coefficients as in the following mathematical expression 3. The following mathematical expression 3 is an example of deriving M when L is defined according to the encoder / decoder convention.

[0274] [Equation 3]

[0275]

[0276] In mathematical expression 3, the round function is a function that rounds the number in parentheses to the nearest integer.

[0277] According to embodiments, the packing method of the displacement vector coefficients of the displacement vector coefficient packing unit (12013) may be determined by an agreement in the encoder / decoder, or the packing method performed in the displacement vector coefficient packing unit (12013) may be transmitted to the decoder of the receiving device.

[0278] According to embodiments, the displacement vector coefficients of all levels may be packed into one image (i.e., one frame) and encoding may be performed in the displacement vector image / video encoding unit (12014), or the displacement vector coefficients may be packed into each image (i.e., each frame) for each subdivision level (R) and encoding may be performed respectively. Alternatively, the displacement vector coefficients of a specific level may be packed into one image, and the displacement vector coefficients of multiple or more different levels may be packed into another image.

[0279] Fig. 19 is a diagram showing an example of packing displacement vector coefficient blocks by LoD according to embodiments. According to embodiments, packing of displacement vector coefficient blocks (bx×by) can be performed as in Fig. 19 according to the CTU (Coding Tree Unit) size of a 2D video encoder encoded for each LoD level. At this time, it can be performed with the median value or the last displacement vector coefficient value of the image to match the CTU size for each LoD. In Fig. 19, the CTU is used in the process of dividing a video frame into coding tree units, and is a unit used particularly when encoding by dividing a video frame into a tree structure.

[0280] As an example, FIG. 19 shows an example in which displacement vector coefficients of three levels (R0-R2) are packed into a single image. That is, this is an example in which displacement vector coefficients of R0, R1, and R2 are packed into a single frame. In this case, if the number of displacement vector coefficients of R0, R1, and R2 is smaller than the size of the frame, a padding area may exist.

[0281] When packing the displacement vector coefficients of each level into one or more frames as in Fig. 19, the displacement vector coefficients can be packed into blocks of size bx×by.

[0282] At this time, bx*by displacement vector coefficients within one displacement vector coefficient block may be packed according to a zig-zag scan order, or may be packed according to a 2D Moulton code order as shown in Fig. 20(a) and Fig. 20(b).

[0283] FIG. 20(a) and FIG. 20(b) are diagrams showing examples of a method for packing displacement vector coefficients within a displacement vector coefficient block according to embodiments.

[0284] Fig. 20(a) is an example of packing 16 displacement vector coefficients (C1-C16) in the xy Moulton code order within one displacement vector coefficient block when bx=by=4. Fig. 20(b) is an example of packing 16 displacement vector coefficients (C1-C16) in the yx Moulton code order within one displacement vector coefficient block when bx=by=4.

[0285] According to embodiments, the size of a frame into which displacement vector coefficients are packed can be obtained as (bx×L)×(by×M) by the bx and by parameters which determine the width and height of a block, respectively, and the L and M parameters which determine the number of blocks included in a row and column of the frame, respectively. The L and M parameters may be determined by a convention in the encoder / decoder, or after L (or M) is defined by a convention in the encoder / decoder, M (or L) may be derived according to the number of displacement vector coefficients (see Equation 3), or may be derived according to a level.

[0286] Meanwhile, displacement vector coefficients transformed into a local coordinate system may have normal components, tangential components, and bi-tangential components. At this time, the displacement vector coefficient packing unit (12013) can select a format such as YUV 4:4:4, YUV 4:2:0, YUV 4:0:0, etc. to perform image packing, and can configure displacement vector coefficients according to each format. In this process, packing of some components may be skipped.

[0287] In the present disclosure, the YUV 4:4:4, YUV 4:2:0, and YUV 4:0:0 formats represent formats for packing normal components, tangential components, and bi-tangential components of displacement vector coefficients into an image. In the present disclosure, sampling of displacement vector coefficients V1 (N1, T1, B1) to V4 (N4, T4, B4) can be performed differently in units of four vertices for each format.

[0288] In this disclosure, the YUV 4:4:4 format is defined as the size of the Y channel (w y *h y ), the size of the U channel (w u *h u ), size of V channel (w v *h v ) means that the YUV 4:2:0 format has the same size of the Y channel (w y *h y ) compared to the size of the U channel (w u *h u ) and the size of the V channel (w v *h v ) means that the Y channel size (w y *h y ) only exists, that is, when packing is done only in the Y channel. That is, among the Y, U, and V channels, only the Y channel exists.

[0289] For the convenience of explanation in this disclosure, the YUV 4:4:4 format will be used interchangeably with the first format, the YUV 4:2:0 format will be used interchangeably with the second format, and the YUV 4:0:0 format will be used interchangeably with the third format. In addition, for the convenience of explanation in this disclosure, the Y channel may be referred to as the first channel, the U channel as the second channel, and the V channel as the third channel. In this disclosure, the terms first, second, third, etc. may be used to describe various components, but the components should not be limited by the terms. The terms are used for the purpose of distinguishing one component from another. For example, without departing from the scope of the rights according to the concept of the present disclosure, the first component may be referred to as the second component, and similarly, the second component may also be referred to as the first component. Alternatively, the first component may be referred to as the third component.

[0290] According to embodiments, the encoder may signal image packing format information (ColourSpace_displacement_video) of a predetermined displacement vector coefficient and information for identifying whether to skip bi-tangential component packing (Bi_tangent_skip_flag) in signaling information (e.g., ASPS) and transmit it to a receiving device (or a decoder of the receiving device).

[0291] For example, the image packing format information (ColourSpace_displacement_video) of the displacement vector coefficients can indicate whether the format used for packing the displacement vector coefficients is a YUV 4:4:4 format (i.e., a first format), a YUV 4:2:0 format (i.e., a second format), or a YUV 4:0:0 format (i.e., a third format). As another example, if the value of the information (Bi_tangent_skip_flag) for identifying whether to skip bi-tangential component packing is 0, it can indicate that the bi-tangential component is not skipped, and if it is 1, it can indicate that the bi-tangential component is skipped.

[0292] FIG. 21(a) and FIG. 21(b) are diagrams showing an example of packing displacement vector coefficients based on the YUV 4:4:4 format according to embodiments. That is, FIG. 21(a) and FIG. 21(b) are examples of not skipping packing of bi-tangential components when packing displacement vector coefficients based on the YUV 4:4:4 format. In this case, the image packing format information (ColourSpace_displacement_video) indicates that the format used in packing is the YUV 4:4:4 format (ColourSpace_displacement_video = YUV444), and the value of the information (Bi_tangent_skip_flag) for identifying whether to skip bi-tangential component packing is set to 0, as an embodiment.

[0293] In this case, as in Fig. 21(a), the normal component of the displacement vector coefficient of each vertex is stored (or packed) in the Y channel, the tangential component of the displacement vector coefficient of each vertex is stored (or packed) in the U channel, and the bi-tangential component of the displacement vector coefficient of each vertex is stored (or packed) in the V channel. That is, the normal, tangential, and bi-tangential components can be stored (or packed) in order in each of the Y, U, and V channels. Fig. 21(b) is an example in which, taking displacement vector coefficients of four vertices as an example, the normal components (N1-N4), tangential components (T1-T4), and bi-tangential components (B1-B4) of the displacement vector coefficients of four vertices are packed in the Y channel, the U channel, and the V channel, respectively.

[0294] FIG. 22(a) and FIG. 22(b) are diagrams showing another example of packing displacement vector coefficients based on the YUV 4:4:4 format according to embodiments. That is, FIG. 22(a) and FIG. 22(b) are examples of skipping packing of bi-tangential components when packing displacement vector coefficients based on the YUV 4:4:4 format. In this case, the image packing format information (ColourSpace_displacement_video) indicates that the format used in packing is the YUV 4:4:4 format (ColourSpace_displacement_video = YUV444), and the value of the information for identifying whether to skip bi-tangential component packing (Bi_tangent_skip_flag) is 1, as an embodiment.

[0295] In this case, as in Fig. 22(a), the normal component of the displacement vector coefficients is stored (or packed) in the Y channel, and the tangential component of the displacement vector coefficients is stored (or packed) in the U channel. That is, the normal component is sequentially packed in the Y channel, and the tangential component is sequentially packed in the U channel, and then transmitted to the displacement vector image / video encoding unit (12014).

[0296] At this time, the bi-tangential component of the displacement vector coefficient of each vertex is skipped from packing. That is, the bi-tangential component is skipped and not packed in the V channel.

[0297] The present disclosure can fill the V channel with an intermediate value (or a fixed value) for efficient encoding / decoding. That is, in order to maintain the YUV 4:4:4 format, the V channel is filled with the intermediate value instead of the skipped bi-tangential component. FIG. 22(b) is an example in which, taking displacement vector coefficients of four vertices as an example, the normal components (N1-N4) and tangential components (T1-T4) of the displacement vector coefficients of four vertices are packed into the Y channel and the U channel, respectively, and the intermediate value (M) is packed into the V channel instead of the bi-tangential component. In one embodiment, assuming that the bitDepth of the displacement vector video image is 10 bits, the intermediate value of 1024, 512, can be packed as the M value (M=512).

[0298] FIG. 23(a) and FIG. 23(b) are diagrams showing an example of packing displacement vector coefficients based on the YUV 4:2:0 format according to embodiments. That is, FIG. 23(a) and FIG. 23(b) are examples of not skipping packing of bi-tangential components when packing displacement vector coefficients based on the YUV 4:2:0 format. In this case, the image packing format information (ColourSpace_displacement_video) indicates that the format used in packing is the YUV 4:2:0 format (ColourSpace_displacement_video = YUV420), and the value of the information (Bi_tangent_skip_flag) for identifying whether to skip bi-tangential component packing is 0, as an embodiment.

[0299] In this case, as in Fig. 23(a), the normal components of the displacement vector coefficients are stored (or packed) as they are in the Y channel. In contrast, the tangential components of the displacement vector coefficients of one vertex per four vertices are packed in the U channel, and the bi-tangential components of the displacement vector coefficients of one vertex per four vertices are packed in the V channel. That is, the normal component can be stored in the Y channel, the tangential component in the U channel, and the bi-tangential component in the V channel, respectively, in that order. At this time, the tangential component of the U channel and the bi-tangential component of the V channel can be sampled according to the encoder / decoder agreement. FIG. 23(b) is an example in which, when displacement vector coefficients of four vertices are taken as an example, the normal components (N1-N4) of the displacement vector coefficients of the four vertices are packed into the Y channel, the tangential component (T) of the displacement vector coefficient of one vertex per four vertices is packed into the U channel, and the bi-tangential component (B) of the displacement vector coefficient of one vertex per four vertices is packed into the V channel. At this time, the tangential component of the displacement vector coefficient of one vertex packed into the U channel may be the average value of the tangential components of the displacement vector coefficients of the four vertices, or may be the tangential component (i.e., representative value) of a specific displacement vector coefficient among the displacement vector coefficients of the four vertices. Similarly, the bi-tangential component of the displacement vector coefficient of one vertex packed into the V channel may be the average of the bi-tangential components of the displacement vector coefficients of four vertices, or may be the bi-tangential component (i.e., representative value) of a specific displacement vector coefficient among the displacement vector coefficients of the four vertices.

[0300] In another embodiment, the present disclosure increases the height of the Y channel by twice the packing frame image height (H) calculated by the displacement vector coefficient packing unit (12013), and stores (i.e. packs) the normal component, the tangential component, and the bi-tangential component in the Y channel component-by-component. In this case, in order to maintain the YUV 4:2:0 format, the U channel and the V channel can each be filled with an intermediate value.

[0301] FIG. 24(a) and FIG. 24(b) are diagrams showing another example of packing displacement vector coefficients based on the YUV 4:2:0 format according to embodiments. That is, FIG. 24(a) and FIG. 24(b) are examples of skipping packing of bi-tangential components when packing displacement vector coefficients based on the YUV 4:2:0 format. In this case, the image packing format information (ColourSpace_displacement_video) indicates that the format used in packing is the YUV 4:2:0 format (ColourSpace_displacement_video = YUV420), and the value of the information for identifying whether to skip bi-tangential component packing (Bi_tangent_skip_flag) is 1, as an embodiment.

[0302] In this case, as in Fig. 24(a), the height of the Y channel is increased by twice the height (H) of the packing frame image calculated by the displacement vector coefficient packing unit (12013), and then the displacement vector coefficients of the normal component and the displacement vector coefficients of the tangential component can be stored (i.e., packed) component-by-component in the Y channel. At this time, the U and V channels can be filled with intermediate values ​​for efficient encoding. Fig. 24(b) is an example in which, when the displacement vector coefficients of four vertices are taken as an example, the normal components (N1-N4) and the tangential components (T1-T4) of the displacement vector coefficients of four vertices are packed in the Y channel, and the intermediate values ​​(M) corresponding to two vertices are packed in the U channel and the V channel in order to maintain the YUV 4:2:0 format.

[0303] As another example, when the displacement vector coefficients of four vertices are taken as an example, the normal components (N1-N4) of the displacement vector coefficients of the four vertices can be packed into the Y channel, the tangential component (T) of the displacement vector coefficient of one vertex per four vertices can be packed into the U channel, and the median value can be filled into the V channel.

[0304] FIG. 25(a) and FIG. 25(b) are diagrams showing an example of packing displacement vector coefficients based on the YUV 4:0:0 format according to embodiments. That is, FIG. 25(a) and FIG. 25(b) are examples of not skipping packing of bi-tangential components when packing displacement vector coefficients based on the YUV 4:0:0 format. In this case, the image packing format information (ColourSpace_displacement_video) indicates that the format used in packing is the YUV 4:0:0 format (ColourSpace_displacement_video = YUV400), and the value of the information (Bi_tangent_skip_flag) for identifying whether to skip bi-tangential component packing is set to 0, as an embodiment.

[0305] In this case, as in Fig. 25(a), the height of the Y channel is increased by three times the packing frame image height (H) calculated by the displacement vector coefficient packing unit (12013), and then the normal components, tangential components, and bi-tangential components of the displacement vector coefficients can be stored (i.e., packed) component by component in the Y channel. Fig. 25(b) is an example in which, taking displacement vector coefficients of four vertices as an example, the normal components (N1-N4), tangential components (T1-T4), and bi-tangential components (B1-B4) of the displacement vector coefficients of four vertices are packed component by component in the Y channel.

[0306] FIG. 26(a) and FIG. 26(b) are diagrams showing another example of packing displacement vector coefficients based on the YUV 4:0:0 format according to embodiments. That is, FIG. 26(a) and FIG. 26(b) are examples of skipping packing of bi-tangential components when packing displacement vector coefficients based on the YUV 4:0:0 format. In this case, the image packing format information (ColourSpace_displacement_video) indicates that the format used in packing is the YUV 4:0:0 format (ColourSpace_displacement_video = YUV400), and the value of the information for identifying whether to skip bi-tangential component packing (Bi_tangent_skip_flag) is 1, as an embodiment.

[0307] In this case, as in Fig. 26(a), the height of the Y channel is increased by twice the packing frame image height (H) calculated by the displacement vector coefficient packing unit (12013), and then the normal components and tangential components of the displacement vector coefficients can be stored (i.e., packed) component by component in the Y channel. Fig. 26(b) is an example in which, when displacement vector coefficients of four vertices are taken as an example, the normal components (N1-N4) and tangential components (T1-T4) of the displacement vector coefficients of four vertices are packed component by component in the Y channel. That is, the bi-tangential components are skipped and therefore not packed or transmitted.

[0308] As shown in the above-described FIGS. 21 to 26, when the normal component, tangential component, and bi-tangential component (which may be skipped) of the displacement vector coefficients are packed (or stored) as a 2D image in the Y channel, U channel, and V channel according to the format, the displacement vector image / video encoding unit (12014) can perform encoding on the packed 2D image through a 2D video encoder such as H.264, HEVC, or VVC.

[0309] Fig. 27 illustrates a receiving device according to embodiments. In the present disclosure, the receiving device of Fig. 27 may be referred to as a mesh data receiving device or decoder or decoder of a receiving device or a V-Mesh decoder or a dynamic mesh decoder.

[0310] FIG. 27 corresponds to the receiving device (110) or mesh video decoder (113) of FIG. 1, the decoder of FIG. 11 or FIG. 12, the receiving device of FIG. 14, and / or the receiving decoding device corresponding thereto. Each component of FIG. 27 corresponds to hardware, software, a processor, and / or a combination thereof. The receiving (decoding) operation of FIG. 27 may follow the reverse process of the corresponding process of the transmitting (encoding) operation of FIG. 15. The execution order of each block in FIG. 27 may be changed, some blocks may be omitted, and some blocks may be newly added.

[0311] FIG. 27 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).

[0312] 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, and a texture map bitstream after file / segment decapsulation in a demultiplexer (not shown). If the current mesh has inter-screen encoding (i.e., inter-encoding) applied, the base mesh bitstream may be a motion vector bitstream.

[0313] 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).

[0314] For example, if the current mesh has inter-screen encoding (i.e., 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-screen encoding (i.e., 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.

[0315] 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.

[0316] 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.

[0317] 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.

[0318] According to embodiments, the base mesh restoration unit (15014) 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 (15014) can 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) can perform inverse quantization on the base mesh decoded (or restored) through the static mesh decoder (15012) to generate a restored base mesh (i.e., the current base mesh).

[0319] 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.

[0320] According to embodiments, the mesh refinement unit (15015) can perform refinement through methods such as mid-edge, Loop, and Catmul&Clark.

[0321] 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. In the present disclosure, the displacement vector decoder may be used interchangeably with the displacement vector transform decoder.

[0322] 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.

[0323] 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).

[0324] 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.

[0325] 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).

[0326] 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.

[0327] When the base mesh bitstream, displacement vector bitstream, and texture map bitstream encoded in 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 in the motion vector or static mesh decoder depending on whether it is inter or intra frame, and the geometry information is restored along with the decoded displacement vector information through subdivision.

[0328] In the present disclosure, a decoding method for restoring displacement vectors of normal and tangential components from a 2D image frame transmitted in various formats (e.g., YUV 4:4:4, YUV 4:2:0, YUV 4:0:0) and calculating bi-tangential components is described below in a displacement vector coefficient decoding unit. That is, the principle performed at each step is described in detail below.

[0329] Fig. 28 is a block diagram showing an example of a displacement vector decoder according to embodiments. In Fig. 28, the displacement vector decoder (15017) may include a video decoding unit (16011), a displacement vector coefficient depacking unit (16012), a displacement vector coefficient dequantization unit (16013), and a displacement vector inverse transform unit (16014). Each component in Fig. 28 corresponds to hardware, software, a processor, and / or a combination thereof. The execution order of each block in Fig. 28 may be changed, some blocks may be omitted, and some blocks may be newly added.

[0330] According to embodiments, the video decoding unit (16011) receives a displacement vector bitstream as input and performs decoding on a displacement vector coefficient image / video through a 2D video codec. Then, the restored displacement vector coefficient video restored through the video decoding unit (16011) can perform displacement vector coefficient unpacking (or unpacking) for each frame in the displacement vector coefficient unpacking unit (16012) to assign displacement vector coefficients corresponding to each vertex of the restored mesh.

[0331] In the present disclosure, the displacement vector coefficient depacking unit (16012) can perform depacking according to a scanning order defined by an encoder / decoder agreement from a restored displacement vector coefficient image corresponding to the current mesh frame or a scanning order parsed into a higher-level unit (sequence, frame, etc.). That is, the displacement vector coefficient depacking unit (16012) can perform depacking according to a scanning order defined by an encoder / decoder agreement, or can perform depacking by deriving a scanning order according to the characteristics of the displacement vector coefficient, or can receive the scanning order from an encoder of a transmitting device.

[0332] For example, as shown in Fig. 19, a displacement vector coefficient block packed according to a specific scanning order in units of bx*by, and a displacement vector coefficient packed according to a specific order (such as 2D Morton Code or Zig-zag scan) within one block can derive the displacement vector coefficient of the kth vertex according to the encoder / decoder promise or the sizes of the parsed block bx, by and L, M and the scanning order.

[0333] The following describes a method of restoring displacement vector coefficients of normal and tangential components from a 2D image frame by performing inverse packing in a displacement vector coefficient inverse packing unit (16012) when displacement vector coefficients are packed and transmitted in a 2D image frame in various formats (e.g., YUV 4:4:4, YUV 4:2:0, YUV 4:0:0) as shown in FIGS. 21 to 26, and restoring bi-tangential components based thereon.

[0334] FIG. 29(a) and FIG. 29(b) are diagrams showing an example of depacking displacement vector coefficients packed in a YUV 4:4:4 format according to embodiments. More specifically, FIG. 29(a) and FIG. 29(b) are depacking methods when the value of the image packing format information (ColourSpace_displacement_video) parsed from the received signaling information indicates that the format is YUV 4:4:4 (ColourSpace_displacement_video = YUV444) (e.g., value=3), and the value of the information (Bi_tangent_skip_flag) for identifying whether to skip bi-tangential component packing is 0. That is, as in FIG. 29(a), this is a case where the packing of the bi-tangential component is not skipped in the transmitting device (e.g., the displacement vector coefficient packing unit (12013)). And, taking the displacement vector coefficients of four vertices as an example, this is a case where the normal components (N1-N4), tangential components (T1-T4), and bi-tangential components (B1-B4) of the displacement vector coefficients of four vertices are packed into the Y channel, U channel, and V channel, respectively.

[0335] In this case, the displacement vector coefficient depacking unit (16012) can perform restoration on the normal, tangential, and bi-tangential components of the Y, U, and V channels, respectively, in the YUV 4:4:4 format, as shown in Fig. 29(b). That is, the restored displacement vector coefficients of the Y, U, and V channels can be restored as normal, tangential, and bi-tangential components, respectively, according to a specific order (displacement_scan_method) within the block. In addition, in the case of the YUV 4:4:4 format, since the transmitting device transmits all values ​​of the normal, tangential, and bi-tangential components, the data before encoding and the decoded result can be the same.

[0336] FIG. 30(a) and FIG. 30(b) are diagrams showing another example of depacking displacement vector coefficients packed in a YUV 4:4:4 format according to embodiments. More specifically, FIG. 30(a) and FIG. 30(b) are depacking methods when the value of the image packing format information (ColourSpace_displacement_video) parsed from the received signaling information indicates that the format is YUV 4:4:4 (ColourSpace_displacement_video = YUV444) (e.g., value=3), and the value of the information (Bi_tangent_skip_flag) for identifying whether to skip bi-tangential component packing is 1. That is, as in FIG. 30(a), this is a case where the packing of the bi-tangential component is skipped in the transmitting device (e.g., the displacement vector coefficient packing unit (12013)). And when the displacement vector coefficients of 4 vertices are taken as an example, the normal components (N1-N4) and tangential components (T1-T4) of the displacement vector coefficients of 4 vertices are packed into the Y channel and the U channel, respectively, and the intermediate value (M) is packed into the V channel instead of the bi-tangential components (B1-B4). That is, if the value of Bi_tangent_skip_flag is 1, the Y and U channels may be composed of displacement vector coefficients of the normal and tangential components, respectively, as in Fig. 30(a), and the V channel may be composed of the intermediate value (M). If the bitDepth of the displacement vector video image is assumed to be 10 bits, the intermediate value of 1024, 512, may be the M value of the V channel.

[0337] In this case, the displacement vector coefficient depacking unit (16012) can perform restoration on the normal, tangential, and bi-tangential components of the Y, U, and V channels, respectively, in the YUV 4:4:4 format, as shown in FIG. 30(b). That is, the displacement vector coefficients of the Y and U channels are restored as normal and tangential components, respectively, according to a specific order (displacement_scan_method) within the block, and the displacement vector coefficients with intermediate values ​​of the V channel can be restored as bi-tangential components with a value of 0. Alternatively, the bi-tangential component values ​​may not be restored and may have 0 as the initial value. In addition, since the transmitting device transmits all values ​​of the normal and tangential components, the data before encoding and the decoded results of the normal and tangential components may be the same.

[0338] FIG. 31(a) and FIG. 31(b) are diagrams showing an example of depacking displacement vector coefficients packed in a YUV 4:2:0 format according to embodiments. More specifically, FIG. 31(a) and FIG. 31(b) are depacking methods when the value of the image packing format information (ColourSpace_displacement_video) parsed from the received signaling information indicates that the format is YUV 4:2:0 (ColourSpace_displacement_video = YUV420) (e.g., value=2), and the value of the information (Bi_tangent_skip_flag) for identifying whether to skip bi-tangential component packing is 0. That is, as in FIG. 31(a), this is a case where the packing of the bi-tangential component is not skipped in the transmitting device (e.g., the displacement vector coefficient packing unit (12013)). And when taking displacement vector coefficients of four vertices as an example, the normal components (N1-N4) of the displacement vector coefficients of four vertices are packed into the Y channel, the tangential component (T) of the displacement vector coefficient of one vertex per four vertices is packed into the U channel, and the bi-tangential component (B) of the displacement vector coefficient of one vertex per four vertices is packed into the V channel.

[0339] In this case, the displacement vector coefficient depacking unit (16012) can perform restoration on the normal, tangential, and bi-tangential components of the Y, U, and V channels, respectively, in the YUV 4:2:0 format, as shown in FIG. 31(b). At this time, assuming that the tangential and bi-tangential components of the U and V channels are sampled and transmitted by the transmitting device (e.g., 1 vertex per 4 vertices is sampled), the tangential component (T'1-T'4) of the U channel and the bi-tangential component (B'1-B'4) of the V channel can be restored through a sampling method agreed upon in advance with the encoder. Alternatively, all of the normal, tangential, and bi-tangential components can be restored from the Y channel through a method agreed upon in advance with the encoder. In addition, since the transmitting device transmits all values ​​of the normal component, the data before encoding of the normal component and the decoded result can be the same. At this time, the displacement vector coefficients of the restored Y, U, and V channels can be restored according to a specific order (displacement_scan_method) within the block as normal, tangential, and bi-tangential components, respectively.

[0340] FIG. 32(a) and FIG. 32(b) are diagrams showing another example of depacking displacement vector coefficients packed in a YUV 4:2:0 format according to embodiments. More specifically, FIG. 32(a) and FIG. 32(b) are depacking methods when the value of the image packing format information (ColourSpace_displacement_video) parsed from the received signaling information indicates that the format is YUV 4:2:0 (ColourSpace_displacement_video = YUV420) (e.g., value=2), and the value of the information (Bi_tangent_skip_flag) for identifying whether to skip bi-tangential component packing is 1. That is, as in FIG. 32(a), this is a case where the packing of the bi-tangential component is skipped in the transmitting device (e.g., the displacement vector coefficient packing unit (12013)). And, when taking displacement vector coefficients of four vertices as an example, the normal components (N1-N4) and tangential components (T1-T4) of the displacement vector coefficients of four vertices are packed into the Y channel, and the median value (M) is packed into the U channel and the V channel, respectively. To this end, the transmitting device increases the height of the Y channel by twice the packing frame image height (H) and then performs packing.

[0341] In this case, the displacement vector coefficient inverse packing unit (16012) can restore the normal component from 0 to H of the Y channel and the tangential component from H+1 to 2H using the height (H) information of the previously calculated packing frame, as shown in FIG. 32(b). In addition, the displacement vector coefficients of the normal and tangential components of the Y channel can be restored according to a specific order (displacement_scan_method) within the block. At this time, the intermediate value of the U channel may not be used in the restoration process. This is because the displacement vector coefficients of the tangential component have been restored from the Y channel. In addition, the displacement vector coefficients with the intermediate value of the V channel can restore the value of 0 as the bi-tangential component. Alternatively, the bi-tangential component value may not be restored from the V channel and may have 0 as the initial value. In other words, the values ​​of the bi-tangential components may all become 0 after inverse packing. In other words, the bi-tangential component whose packing is skipped in the displacement vector coefficient packing unit (12013) of the transmitting device can be restored to 0 in the displacement vector coefficient depacking unit (16012) of the receiving device. At this time, since all values ​​of the normal component and the tangential component are transmitted through the Y channel in the transmitting device as shown in Fig. 32(a), the data before encoding of the normal component and the tangential component and the decoded result can be the same.

[0342] FIG. 33(a) and FIG. 33(b) are diagrams showing an example of depacking displacement vector coefficients packed in a YUV 4:0:0 format according to embodiments. More specifically, FIG. 33(a) and FIG. 33(b) are depacking methods when the value of the image packing format information (ColourSpace_displacement_video) parsed from the received signaling information indicates that the format is YUV 4:0:0 (ColourSpace_displacement_video = YUV400) (e.g., value=1), and the value of the information (Bi_tangent_skip_flag) for identifying whether to skip bi-tangential component packing is 0. That is, as in FIG. 33(a), this is a case where the packing of the bi-tangential component is not skipped in the transmitting device (e.g., the displacement vector coefficient packing unit (12013)). And, when taking displacement vector coefficients of four vertices as an example, only the normal components (N1-N4) of the displacement vector coefficients of the four vertices are packed component-by-component into the Y channel. At this time, the tangential components and bi-tangential components are not packed and transmitted. Therefore, the inverse packing of the tangential and bi-tangential components is not performed.

[0343] That is, the displacement vector coefficient depacking unit (16012) can perform restoration only on the normal component of the Y channel in the YUV 4:0:0 format as shown in Fig. 33(b). At this time, the restored displacement vector coefficients of the Y channel can be restored as normal components according to a specific order (displacement_scan_method) within the block. In addition, since the transmitting device transmits all values ​​of the normal components, the data before encoding the normal components and the decoded results can be identical.

[0344] FIG. 34(a) and FIG. 34(b) are diagrams showing another example of depacking displacement vector coefficients packed in a YUV 4:0:0 format according to embodiments. More specifically, FIG. 34(a) and FIG. 34(b) are depacking methods when the value of the image packing format information (ColourSpace_displacement_video) parsed from the received signaling information indicates that it is a YUV 4:0:0 format (ColourSpace_displacement_video = YUV400) (e.g., value=1), and the value of the information (Bi_tangent_skip_flag) for identifying whether to skip bi-tangential component packing is 0. That is, as in FIG. 34(a), this is a case where the packing of the bi-tangential component is not skipped in the transmitting device (e.g., the displacement vector coefficient packing unit (12013)). And, when taking displacement vector coefficients of four vertices as an example, the normal components (N1-N4), tangential components (T1-T4), and bi-tangential components (B1-B4) of the displacement vector coefficients of the four vertices are all packed component-by-component into the Y channel. To this end, the transmitting device increases the height of the Y channel by three times the packing frame image height (H) and then performs packing.

[0345] In this case, the displacement vector coefficient inverse packing unit (16012) can restore the normal component from 0 to H of the Y channel, the tangential component from H+1 to 2H, and the bi-tangential component from 2H+1 to 3H using the height (H) information of the previously calculated packing frame, as shown in FIG. 34(b). In addition, the displacement vector coefficients of the normal, tangential, and bi-tangential components of the Y channel can be restored according to a specific order (displacement_scan_method) within the block. That is, the normal, tangential, and bi-tangential components can be transmitted to the Y channel according to an agreement with the encoder, and the displacement vector coefficient inverse packing unit (16012) can restore the normal, tangential, and bi-tangential components from the Y channel, respectively.

[0346] FIG. 35(a) and FIG. 35(b) are diagrams showing another example of depacking displacement vector coefficients packed in a YUV 4:0:0 format according to embodiments. More specifically, FIG. 35(a) and FIG. 35(b) are depacking methods when the value of the image packing format information (ColourSpace_displacement_video) parsed from the received signaling information indicates that the format is YUV 4:0:0 (ColourSpace_displacement_video = YUV400) (e.g., value=1), and the value of the information (Bi_tangent_skip_flag) for identifying whether to skip bi-tangential component packing is 1. That is, as in FIG. 35(a), this is a case where the packing of the bi-tangential component is skipped in the transmitting device (e.g., the displacement vector coefficient packing unit (12013)). And, when taking displacement vector coefficients of four vertices as an example, this is a case where both normal components (N1-N4) and tangential components (T1-T4) of the displacement vector coefficients of four vertices are packed component-by-component into the Y channel. To this end, the transmitting device increases the height of the Y channel by twice the packing frame image height (H) and then performs packing.

[0347] In this case, the displacement vector coefficient inverse packing unit (16012) can restore the normal component from 0 to H of the Y channel and the tangential component from H+1 to 2H using the height (H) information of the previously calculated packing frame, as shown in FIG. 35(b). In addition, the displacement vector coefficients of the Y channel can be restored according to a specific order (displacement_scan_method) within the block. That is, the normal and tangential components can be transmitted to the Y channel according to an agreement with the encoder, and the displacement vector coefficient inverse packing unit (16012) can restore the normal component and the tangential component from the Y channel, respectively. At this time, since all values ​​of the normal component and the tangential component are transmitted through the Y channel in the transmitting device, as shown in FIG. 35(a), the data before encoding and the decoded result of the normal component and the tangential component can be the same.

[0348] Displacement vector coefficients de-packed by at least one of the de-packing methods of FIGS. 29 to 35 are provided to a displacement vector coefficient de-quantization unit (16013).

[0349] According to embodiments, the displacement vector coefficient inverse quantization unit (16013) can inverse quantize displacement vector coefficients restored by the displacement vector coefficient inverse packing unit (16012).

[0350] According to embodiments, the displacement vector inverse transform unit (16014) performs an inverse transform of the transform performed in the encoder of the transmitting device on the inverse quantized displacement vector 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 (16014), a process of updating the displacement vector of a vertex used for prediction in the encoder may be performed through a parsed residual signal.

[0351] More specifically, the displacement vector inverse transform unit (16014) performs an inverse transform of the displacement vector coefficients or inverse quantized displacement vector coefficients allocated per vertex through the displacement vector coefficient inverse packing unit (16012). Depending on the embodiment, the transform may be applied as a linear lifting transform, a butterfly lifting transform, a wavelet transform, etc. For example, if the value of asps_vmc_ext_transform_method signaled in the signaling information (ASPS) is 1, it may indicate that Linear_Lifting was used as the transform method.

[0352] If the lifting inverse 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 변위벡터 예측을 수행할 수 있다.

[0353] 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.

[0354] 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.

[0355] Additionally, when the lifting inverse transformation is performed, a process of updating the displacement vector of the vertex used for prediction in the encoder can be performed through the parsed residual signal.

[0356] More specifically, the displacement vector coefficient inverse quantization unit (16013) performs inverse quantization on displacement vector coefficients allocated per vertex or displacement vector coefficients subjected to inverse transformation through the displacement vector coefficient inverse packing unit (16012). According to embodiments, the quantization parameter (QP) for each component (Normal, Tangential, Bi-tangential) may be transmitted per sequence or frame to determine the quantization rate.

[0357] If the bi-tangential component packing skip mode is used (Bi_tangent_skip_flag=1), the displacement vector coefficient inverse quantization unit (16013) can perform inverse quantization only for the normal and tangential components and skip performing inverse quantization for the bi-tangential component.

[0358] According to embodiments, displacement vector coefficients can be quantized through different quantization parameters for each axis, and the quantization rate can be determined for each LoD level by deriving quantization parameters or scaling parameters by encoder / decoder agreement.

[0359] According to embodiments, the inversely transformed displacement vector or the inversely quantized displacement vector coefficient is provided to the displacement vector coordinate system inverse transformation unit (15020).

[0360] According to embodiments, in the displacement vector coordinate system inverse transformation unit (15020), the coordinate system transformation flag (asps_vmc_ext_displacement_coordinate_system) included in the signaling information in units of frame sequence or GOF (Group of Frames) or frame or submesh is parsed, and if the value is 1, the inverse quantized (or inversely transformed) restored displacement vector can be inversely transformed from the local coordinate system (n, t, b) to the canonical coordinate system (x, y, z).

[0361] In addition, a normal vector per vertex is calculated based on the restoration vertex position information of the restoration base mesh, and the normal value of the 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.

[0362] 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.

[0363] 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] refers to the results of normal and tangential components obtained by performing inverse transformation and inverse quantization. At this time, since the normal, tangential, and bi-tangential components are all orthogonal to each other, the displacement vector of the bi-tangential component can be calculated through the cross product of the final displacement vectors of the normal and tangential components. Alternatively, the displacement vector of the bi-tangential component can be derived and calculated using methods such as linear regression or multiple regression.

[0364] [Equation 4]

[0365]

[0366] If the displacement vector coefficients are packed in the YUV 4:0:0 format in the transmitting device, the tangential (t) and bi-tangential (b) components are not transmitted through the U and V channels, so Equation 4 for the coordinate system inversion is It can be expressed as . At this time, the coordinate system inverse transformation can be performed by multiplying the result of performing inverse quantization and inverse transformation of the n component and the calculated normal vector per vertex.

[0367] Additionally, if there are multiple results of performing inverse transformation on the same vertex coordinates, the sum of all values ​​can become the value of the final displacement vector. Depending on the embodiment, coordinate system inverse transformation can always be performed without sending a flag.

[0368] In Fig. 27, the mesh restoration unit (15016) can calculate and restore the vertex geometry information of the restoration mesh by adding a restoration displacement vector to the vertices generated through the subdivision process in the mesh subdivision unit (15015).

[0369] According to embodiments, signaling information in a transmitting device (or an encoder of the transmitting device) may be generated by a metadata processing unit (not shown, may be referred to as a metadata generator, etc.) and provided to corresponding blocks in the transmitting device and / or a receiving device (or a decoder of the receiving device), and a metadata parser (not shown) of the receiving device may parse the received signaling information and provide it to the corresponding blocks. According to embodiments, each block of the receiving device may perform each operation based on the signaling information.

[0370] FIG. 36 is a diagram showing an example of the structure of an atlas sequence parameter set (ASPS) among signaling information in a bitstream according to embodiments. In particular, FIG. 36 is a diagram showing an example of the structure of an atlas sequence parameter set extension RBSP syntax and semantics. That is, an ASPS may be extended from an atlas sequence parameter to further include parameters related to displacement vector encoding.

[0371] The displacement vector coordinate system transformation status flag (asps_vmc_ext_displacement_coordinate_system) is information that can identify whether the displacement vector coordinate system is transformed, and indicates the type of coordinate system for displacement vector encoding. For example, if the value of the displacement vector coordinate system transformation status flag (asps_vmc_ext_displacement_coordinate_system) syntax (or field) is 0, it can indicate that the transmitting device uses the canonical coordinate system as is, and if it is 1, it can indicate that the transformation to the local coordinate system has been performed. Therefore, in the displacement vector coordinate system inverse transformation unit (15020), if the value of the coordinate system transformation status flag (asps_vmc_ext_displacement_coordinate_system) is 1, the inverse quantized (or inversely transformed) restored displacement vector can be transformed from the local coordinate system (n, t, b) to the canonical coordinate system (x, y, z).

[0372] The displacement vector transformation method (asps_vmc_ext_transform_method) indicates the method for transforming the displacement vector. For example, a value of 0 indicates no transformation was performed (=None), and a value of 1 indicates that Linear_Lifting was used as the transformation method.

[0373] The displacement vector coefficient packing method (ext_packing_method) indicates the packing method for displacement vector coefficients. For example, a value of 0 indicates that displacement vector coefficients are packed in ascending order, while a value of 1 indicates that displacement vector coefficients are packed in descending order.

[0374] The displacement vector encoding method (asps_vmc_ext_displacement_method) indicates the encoding method of the displacement vector. For example, if this value is 0, it indicates None (no displacement vector encoding), 1 indicates that the displacement vector was encoded using the arithmetic coding method, and 2 indicates that the displacement vector was encoded using the video coding method.

[0375] If the displacement vector encoding method (asps_vmc_ext_displacement_method) indicates VIDEO CODING, the displacement vector packing method for each LoD (asps_vmc_ext_displacement_LoD_packing_method) and displacement vector-related packing information (asps_vmc_ext_displacement_packing_info()) may be included.

[0376] The LoD-specific displacement vector packing method (asps_vmc_ext_displacement_LoD_packing_method) indicates the LoD-specific packing method of displacement vectors. For example, a value of 0 indicates that displacement vectors are packed based on the overall level packing frame configuration, and a value of 1 indicates that displacement vectors are packed based on the level-specific packing frame configuration.

[0377] Displacement vector related packing information (asps_vmc_ext_displacement_packing_info()) may include, as shown in FIG. 37, a displacement vector scan method (displacement_scan_method), the number of unit blocks of a displacement vector video image (displacementVideoBlockSize), unit block size information (geometryVideoBlockSize), bit depth information (geometryVideoBitDepth), image packing format information (ColourSpace_displacement_video), and information for identifying whether to skip displacement vector bi-tangential component image packing (bi_tangent_skip_flag).

[0378] Fig. 37 is a diagram showing another example of the structure of an atlas sequence parameter set (ASPS) among signaling information in a bitstream according to embodiments. That is, Fig. 37 is an example of the syntax structure of displacement vector-related packing information (asps_vmc_ext_displacement_packing_info()) included in ASPS, which may be included in asps_vmc_extension( ) of Fig. 36.

[0379] In Fig. 37, the displacement vector scan method (displacement_scan_method) indicates the scan order method when packing displacement vectors. For example, if the value of displacement_scan_method is 0, it indicates that the displacement vectors are scanned using a 2D Morton Code, and if it is 1, it indicates that the displacement vectors are scanned using a zig-zag scan order.

[0380] GeometryVideoBlockSize represents the displacement vector video image block size. For example, this value can represent the number of bx*by blocks, and the default value can be 16.

[0381] GeometryVideoBitDepth indicates the bit depth of the displacement vector video image. The default value can be 10 bits. This value determines the median value when packing displacement vector coefficients.

[0382] Image packing format information (ColourSpace_displacement_video) indicates the displacement vector video packing image format. For example, if this value is 0, it indicates that displacement vector coefficients are packed based on None (no image format for displacement vector video packing), 1 indicates that the displacement vector coefficients are packed based on the yuv400 format, 2 indicates that the displacement vector coefficients are packed based on the yuv420 format, and 3 indicates that the displacement vector coefficients are packed based on the yuv444 format.

[0383] The bi-tangential component packing skip flag (Bi_tangent_skip_flag) is information for identifying whether to skip the displacement vector bi-tangential component image packing. If this value is 0, it indicates no skipping, and if it is 1, it indicates skipping.

[0384] Fig. 38 is a flowchart showing an example of a transmission method according to embodiments. The transmission method according to embodiments may include a step (21011) of encoding mesh data and a step (21012) of transmitting a bitstream including the encoded mesh data. In one embodiment, the bitstream transmitted in step (21012) includes a base mesh bitstream, a displacement vector bitstream, and a texture map bitstream.

[0385] According to embodiments, the step of encoding mesh data (21011) may include a process of encoding a base mesh, a process of encoding displacement vectors or displacement vector transform coefficients, and a process of encoding a texture map.

[0386] That is, in the process of encoding the base mesh, the original mesh to be transmitted is first simplified and mesh parameterized to generate a base mesh. The generated base mesh is quantized, and in the case of an inter-frame, the motion vector is calculated from the previously referenced restored base mesh and the motion vector is encoded. In the case of an intra-frame, it is encoded through static mesh encoding and transmitted as a base mesh bitstream.

[0387] And in the process of encoding the displacement vector (or displacement information), the displacement vector is calculated between the mesh data that has been simplified through mesh simplification, refined and fitted, and the mesh data restored from the previously encoded base mesh. In order to efficiently encode the calculated displacement vector, the displacement vector coordinate system is converted to a local coordinate system, and the displacement vector in the local coordinate system is converted and quantized into displacement vector coefficients, and then encoded into a displacement vector bitstream and transmitted.

[0388] The following describes in more detail the process of performing displacement vector coefficient image packing for each video image format during the displacement vector encoding process.

[0389] First, the displacement vectors transformed into the local coordinate system can be transformed into displacement vector coefficients by performing linear lifting transformation, butterfly lifting transformation, etc. in the displacement vector transformation unit (12011). In addition, the displacement vectors of (n, t, b) expressed in the local coordinate system can be transformed for each normal, tangential, and bi-tangential component. The displacement vector coefficients transformed in the displacement vector transformation unit (12011) can be quantized in the displacement vector quantization unit (12012), and at this time, each channel can be quantized into an individual value. If the displacement vector coefficient packing unit (12013) does not perform packing on the bi-tangential component, the lifting transformation and quantization process may not be performed on the bi-tangential component in the displacement vector conversion unit (12011) and the displacement vector quantization unit (12012), and the value of Bi_tangent_skip_flag may be signaled as 0. The present disclosure refers to bi_tangent_skip_flag as information for identifying whether to skip bi-tangential component packing. In addition, as an embodiment, bi_tangent_skip_flag is signaled and transmitted in signaling information (e.g., an atlas sequence parameter set) as in FIG. 37.

[0390] As described above, the quantized displacement vector coefficients are packed into a 2D image of size W×H in the displacement vector coefficient packing unit (12013). For example, if the displacement vector coefficients are configured as a 1D LoD ascending order as shown in FIG. 17, image packing is performed in a 2D form as shown in FIG. 18. At this time, the size Bx*by can be configured as one block, and the displacement vector video image can be configured with L*M blocks determined according to the number N of displacement vector coefficients. In addition, in order to derive L and M, the number of unit blocks (displacementVideoBlockSize), the size information of the unit block (geometryVideoBlockSize), and the bit depth information (geometryVideoBitDepth) of the displacement vector video image can be signaled in the signaling information (e.g., atlas sequence parameter set) as shown in FIG. 37. Displacement vector coefficients can be packed inside a block in a zig-zag scan order or a 2D Morton code order, and displacement vector packing order information (displacement_scan_method) can be signaled in the signaling information (e.g., atlas sequence parameter set) as in Fig. 37. At this time, padding can be performed with the median value or the last displacement vector coefficient value of the image to match the size of the basic block for each LoD or the entire 2D video image. Each displacement vector coefficient can be composed of a normal component, a tangential component, and a bi-tangential component, and some components can be skipped during the packing process. To perform 2D image packing, a format such as YUV 4:4:4, YUV 4:2:0, or YUV 4:0:0 can be selected and image packing format information (ColourSpace_displacement_video) can be signaled. For convenience of explanation, the present disclosure refers to YUV 4:4:4 as a first format, YUV 4:2:0 as a second format, and YUV 4:0:0 as a third format.

[0391] When using the YUV 4:4:4 format and not skipping the bi-tangential component packing, the normal, tangential, and bi-tangential components are packed into the Y, U, and V channels, respectively, as shown in FIGS. 21(a) and 21(b), and the ColourSpace_displacement_video (value=3) and Bi_tangent_skip_flag (value=0) information can be signaled. When using the YUV 4:4:4 format and skipping the bi-tangential component packing, the normal and tangential components are packed into the Y and U channels, respectively, and the V channel can be packed with the intermediate value, as shown in FIGS. 22(a) and 22(b), and the ColourSpace_displacement_video (value=3) and Bi_tangent_skip_flag (value=1) information can be signaled.

[0392] When using the YUV 4:2:0 format and not skipping the bi-tangent component packing, as in Fig. 23(a) and Fig. 23(b), the normal component values ​​are packed as is into the Y channel, and the values ​​of the tangential and bi-tangential components can be sampled and packed according to the agreement of the encoder / decoder. Alternatively, the tangential and bi-tangential components can also be packed together into the Y channel, and the U and V channels can be packed with intermediate values. In addition, the ColourSpace_displacement_video (value=2) and Bi_tangent_skip_flag (value=0) information can be signaled. When using the YUV 4:2:0 format and skipping the bi-tangential component packing, only the normal and tangential components are packed together in the Y channel, as shown in Fig. 24(a) and Fig. 24(b), and the U channel and V channel are packed with intermediate values, and the ColourSpace_displacement_video (value=2) and Bi_tangent_skip_flag (value=1) information can be signaled.

[0393] When using the YUV 4:0:0 format and not skipping the bi-tangential component packing, only the normal component values ​​can be packed into the Y channel as in Fig. 25(a) and Fig. 25(b), or all of the normal, tangential, and bi-tangential components can be packed into the Y channel, and the ColourSpace_displacement_video (value=1) and Bi_tangent_skip_flag (value=0) information can be signaled. When using the YUV 4:0:0 format and skipping the bi-tangential component packing, the normal and tangential components can be packed together into the Y channel, and the U and V channels can be packed with intermediate values, as in Fig. 26(a) and Fig. 26(b), and the ColourSpace_displacement_video (value=3) and Bi_tangent_skip_flag (value=1) information can be signaled.

[0394] Through the above packing method, displacement vector coefficients can be imaged for each channel to form an encoding unit in the form of a packing frame. At this time, the entire level within the mesh frame can be packed into one packing frame, or each LoD within the mesh frame can be packed into a separate packing frame. In addition, the asps_vmc_ext_displacement_LoD_packing_method syntax, which indicates the packing method for each mesh sequence, can be signaled in the signaling information (e.g., ASPS) as in FIG. 36. Then, the 2D image packed through the displacement vector coefficient packing unit (12013) is encoded through a 2D video encoder such as H.264, HEVC, or VVC in the displacement vector image / video encoding unit (12014) to generate a displacement vector bitstream.

[0395] Finally, in the process of encoding the texture map, a new texture map having color information corresponding to the texture coordinates of the restored mesh is generated through a texture map generation unit (11026), and the generated texture map is encoded through a texture map encoder (i.e., a 2D video encoder) (11027) and transmitted as a texture bitstream.

[0396] In the step (21012) of transmitting a bitstream including the above mesh data, the base mesh bitstream, displacement vector bitstream, and texture bitstream generated as described above in the step (21011) of encoding the above mesh data are generated into one bitstream through a multiplexing unit, and transmitted to a receiving device through a transmitting unit.

[0397] Fig. 39 is a flowchart showing an example of a receiving method according to embodiments. The receiving method according to embodiments may include a step (22011) of receiving a bitstream including mesh data and a step (22012) of decoding the mesh data included in the bitstream. In one embodiment, the step (22011) of receiving the bitstream including mesh data receives a bitstream including a base mesh bitstream, a displacement vector bitstream, and a texture map bitstream. In addition, the step (22011) of receiving the bitstream including mesh data also receives signaling information including an atlas sequence parameter set (ASPS). In this case, the signaling information may be received while being included in the bitstream and is also referred to as metadata.

[0398] According to embodiments, the step of decoding mesh data (22012) may include a process of decoding a base mesh bitstream, a process of decoding a displacement vector bitstream, and a process of decoding a texture map bitstream.

[0399] That is, in the step (22011) of receiving a bitstream including mesh data, the received bitstream is demultiplexed into a base mesh bitstream, a displacement vector bitstream, and a texture map bitstream through a demultiplexing unit, and then a process of decoding each of them is performed.

[0400] First, in the process of decoding the base mesh bitstream, the base mesh bitstream is decoded through a motion vector encoder (15012) for inter-frames and a static mesh decoder (15013) for intra-frames. The decoded base mesh is then passed through a base mesh restoration unit (15014) to undergo mesh refinement.

[0401] In the process of decoding the displacement vector bitstream, the displacement vector bitstream decodes the displacement vector coefficients in the reverse order of encoding, performs inverse quantization and inverse transformation, and then is inversely transformed to the coordinate system, and then the mesh geometry information is restored together with the base mesh data.

[0402] The displacement vector decoding process will be described in more detail below with reference to FIGS. 28 to 35.

[0403] That is, the video decoding unit (16011) receives a displacement vector bitstream as input and performs decoding on a displacement vector coefficient image / video through a 2D video codec. Then, depacking can be performed from a restored displacement vector coefficient image corresponding to the current mesh frame by the displacement vector coefficient depacking unit (16012). At this time, the scan order information (displacement_scan_method) at the time of displacement vector packing, the number of unit blocks of the displacement vector video image (displacementVideoBlockSize), the size information of the unit block (geometryVideoBlockSize), and the bit depth information (geometryVideoBitDepth) are parsed from the signaling information (e.g., ASPS) of FIGS. 36 and 37 to derive the block and packing frame sizes (bx, by, and L, M), and depacking can be performed on the packed displacement vector coefficients. Additionally, during the reverse packing process, the packing image format information (ColourSpace_displacement_video) and whether to skip the bi-tangential component packing (Bi_tangent_skip_flag) are parsed from signaling information (e.g., ASPS). At this time, the method for deriving the transformation coefficient may vary depending on the transmitted image packing format and the displacement vector coefficient component included.

[0404] When the parsed information is ColourSpace_displacement_video=3, Bi_tangent_skip_flag=0, the normal, tangential, and bi-tangential components can be restored from the Y, U, and V channels in sequence using the YUV 4:4:4 format as shown in Fig. 29(a) and Fig. 29(b). When ColourSpace_displacement_video=3, Bi_tangent_skip_flag=1, the normal and tangential components can be restored from the Y, U channels in the YUV 4:4:4 format as shown in Fig. 30(a) and Fig. 30(b), and the bi-tangential component can be initialized to a value of 0 or derived from the V channel.

[0405] If the parsed information is ColourSpace_displacement_video=2, Bi_tangent_skip_flag=0, the normal, tangential, and bi-tangential components can be restored from the Y, U, and V channels in order using the YUV 4:2:0 format as shown in Fig. 31(a) and Fig. 31(b). At this time, the tangential and bi-tangential components of the U and V channels may be the results sampled by the encoder / decoder agreement, and the restored values ​​or positions may also be restored in a fixed state. Alternatively, the normal, tangential, and bi-tangential components may all be packed in the Y channel, and each component may be restored from the Y channel, and the U and V channels may be composed of intermediate values. When ColourSpace_displacement_video=2 and Bi_tangent_skip_flag=1, the normal and tangential components can be restored from the Y channel in the YUV 4:2:0 format as shown in Fig. 32(a) and Fig. 32(b), and the bi-tangential component can be initialized to a value of 0 or derived from the V channel.

[0406] If the parsed information is ColourSpace_displacement_video=1, Bi_tangent_skip_flag=0, only the normal component can be restored from the Y channel using the YUV 4:0:0 format as shown in Fig. 33(a) and Fig. 33(b). Alternatively, the normal, tangential, and bi-tangential components may all be packed in the Y channel, in which case the normal, tangential, and bi-tangential components can be restored in sequence from the Y channel as shown in Fig. 34(a) and Fig. 34(b). If ColourSpace_displacement_video=1, Bi_tangent_skip_flag=1, the normal and tangential components can be restored from the Y channel in the YUV 4:0:0 format as shown in Fig. 35(a) and Fig. 35(b), and the bi-tangential component can be initialized to a value of 0 or derived from the V channel.

[0407] Inverse packing is performed by any one of the methods of FIGS. 29 to 35, and inverse quantization is performed on displacement vector coefficients allocated per vertex in the displacement vector coefficient inverse magnetization unit (16013). If the parsed information is Bi_tangent_skip_flag=1, inverse quantization can be performed only on displacement vector coefficients of normal and tangential components excluding bi-tangential components. At this time, quantization can be performed on each displacement vector coefficient through different quantization parameters for each axis, and the quantization rate can be determined for each LoD level by deriving a quantization parameter or a scaling parameter.

[0408] The displacement vector coefficients on which the above inverse quantization has been performed are inversely transformed in the displacement vector inverse transformation unit (16014) based on the transformation method parsed in the asps_vmc_ext_transform_method signaled in the signaling information, and the restored displacement vector is calculated. In addition, if the parsed information is Bi_tangent_skip_flag=1, the inverse transformation process can be performed on the inverse quantization results of the normal and tangential components excluding the bi-tangential component. Since the normal, tangential, and bi-tangential components are all orthogonal to each other, the displacement vector of the bi-tangential component can be calculated by taking the outer product of the final displacement vectors of the normal and tangential components. Alternatively, the displacement vector of the bi-tangential component can be derived using a method such as Linear Regression or Multiple Regression.

[0409] When all displacement vectors are inversely transformed through the displacement vector inverse transformation unit (16014), the displacement vector coordinate system inverse transformation unit (15020) parses the asps_vmc_ext_displacement_coordinate_system signaled in the signaling information as in FIG. 36, and if its value is 1, the restored displacement vector is inversely transformed from the local coordinate system (n, t, b) to the canonical coordinate system (x, y, z). In one embodiment, the displacement vector coordinate system inverse transformation can be performed by calculating the normal vector per vertex based on the restored vertex position information of the restored base mesh, and calculating the tangential and bi-tangential vectors orthogonal to the normal vector through the calculated normal vector per vertex.

[0410] If the value of the asps_vmc_ext_displacement_coordinate_system is 0, the calculated restoration displacement vector can become the final restored displacement vector as it is. In addition, if there are multiple results of performing inverse transformation for the same vertex coordinates, the sum of all values ​​can become the value of the final displacement vector. The mesh restoration unit (15016) can restore the final geometric information by adding the restoration displacement vector to the vertices generated through the mesh subdivision process to calculate the vertex geometry information of the restoration mesh.

[0411] And, in the process of decoding the texture map bitstream, the received texture map bitstream is decoded through a texture map decoder (15021). The decoded texture map is used to generate a final restored mesh together with the restored geometry information in the mesh wall unit (15016).

[0412] In the mesh compression technology currently applied to V-DMC, displacement vectors are transformed into a local coordinate system for compression efficiency, and then transformed into simple displacement vector coefficients through lifting transformation and quantization before compression is performed. Furthermore, in existing technologies, this process is calculated in the encoder for all normal, tangential, and bi-tangential components generated by the coordinate system transformation, and the resulting displacement vector coefficients for each component are packed into a 2D image for transmission.

[0413] The present disclosure proposes a method of packing and transmitting displacement vector coefficients of two components, normal and tangential, among three components in order to transmit data quickly with more efficient capacity, and calculating bi-tangential components after decoding the displacement vector of normal and tangential components transmitted from the decoder, as described in FIGS. 15 to 39. By doing so, the present disclosure only encodes and transmits two components of the three displacement vector components, so that a capacity saving effect of about two-thirds of the existing one can be seen in terms of the displacement vector sub-bitstream. In addition, by proposing a signaling method capable of packing and encoding / decoding according to 2D video image compression formats such as YUV 4:4:4, YUV 4:2:0, and YUV 4:0:0, as shown in FIGS. 36 and 37, efficient packing can be performed according to each video format, and is also effective in terms of real-time mesh data transmission speed due to capacity saving.

[0414] 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.

[0415] 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.

[0416] 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.

[0417] 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.

[0418] Although preferred embodiments of the embodiments have been illustrated and described, the embodiments are not limited to the specific embodiments described above, and various modifications may be made by those skilled in the art to which the invention pertains without departing from the spirit or scope of the embodiments claimed in the claims, and such modifications should not be understood individually from the technical idea or prospect of the embodiments.

[0419] 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.

[0420] 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".

[0421] 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.

[0422] 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.

[0423] 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.

[0424] 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.

[0425] As described above, the relevant contents have been described in the best form for carrying out the embodiments.

[0426] As described above, the embodiments may be applied, in whole or in part, to 3D data transmission and reception devices and systems. Those skilled in the art may variously modify or alter the embodiments within the scope of the embodiments. The embodiments may include modifications / alterations, and the modifications / alterations do not depart from the scope of the claims and their equivalents.

Claims

1. A step of receiving a base mesh bitstream, a displacement vector bitstream, a texture map bitstream, and signaling information; A base mesh processing step for restoring a base mesh from the above base mesh bitstream; A displacement information processing step for restoring displacement information from the displacement vector bitstream; A restoration step for restoring a mesh based on the base mesh and the displacement information; and A mesh data decoding method comprising a texture map processing step of restoring a texture map from the above texture map bitstream.

2. In the first paragraph, the displacement information processing step A step of decoding the displacement vector bitstream into displacement information; A step of identifying a format applied to the displacement information among the first format, the second format, and the third format, and reverse-packing at least one component among the normal component, the tangential component, or the bi-tangential component included in the displacement information based on the identified format; and A mesh data decoding method comprising a step of converting the local coordinate system of the above-described reverse-packed displacement information into the original coordinate system.

3. In paragraph 2, A mesh data decoding method wherein the signaling information includes information for identifying a format applied to the displacement information.

4. In paragraph 3, The signaling information further includes information for identifying whether packing of the bi-tangential component has been skipped, A mesh data decoding method in which the above-described reverse packing step determines a reverse packing method of at least one of the normal component, the tangential component, or the bi-tangential component based on the signaling information.

5. A receiving unit for receiving a base mesh bitstream, a displacement vector bitstream, a texture map bitstream, and signaling information; A base mesh processing unit for restoring a base mesh from the base mesh bitstream; A displacement information processing unit that restores displacement information from the displacement vector bitstream; A restoration unit that restores a mesh based on the base mesh and the displacement information; and A mesh data decoding device including a texture map processing unit for restoring a texture map from the above texture map bitstream.

6. In the fifth paragraph, the displacement information processing unit A displacement information decoding unit that decodes the displacement vector bitstream into displacement information; A displacement information depacking unit that identifies a format applied to the displacement information among the first format, the second format, and the third format, and depacks at least one component among the normal component, the tangential component, or the bi-tangential component included in the displacement information based on the identified format; and A mesh data decoding device including a coordinate system inversion unit that inversely transforms the local coordinate system of the above-described inversely packed displacement information into the original coordinate system.

7. Step of encoding the original mesh; and A mesh data encoding method comprising the step of transmitting a bitstream including the encoded mesh and signaling information.

8. In the 7th paragraph, the encoding step A base mesh processing step of generating a base mesh bitstream by encoding a base mesh generated by simplifying the original mesh; A displacement information processing step of generating a displacement vector bitstream by encoding displacement information generated based on the above base mesh; A mesh restoration step for restoring a mesh based on the encoded base mesh and the encoded displacement information; and A mesh data encoding method comprising a texture map processing step of generating a texture map bitstream by encoding a texture map generated based on the original mesh and the restored mesh.

9. In the 8th paragraph, the displacement information processing step A step of converting the coordinate system of the above displacement information into a local coordinate system; A step of performing packing based on one of the first format, the second format, or the third format for at least one of the normal component, the tangential component, or the bi-tangential component included in the displacement information of the local coordinate system; and A mesh data encoding method comprising a step of encoding the above packed displacement information.

10. In the 8th paragraph, the packing step Optionally perform packing on the bi-tangential component of the above displacement information, A mesh data encoding method wherein the signaling information includes information for identifying whether packing of the bi-tangential component has been skipped.

11. In paragraph 8, A mesh data encoding method wherein the signaling information includes information for identifying a format applied to the displacement information.

12. An encoder that encodes the original mesh; and A mesh data encoding device comprising a transmission unit for transmitting a bitstream including the encoded mesh and signaling information.

13. In the 12th paragraph, the encoder A base mesh processing unit that generates a base mesh bitstream by encoding a base mesh generated by simplifying the original mesh; A displacement information processing unit that encodes displacement information generated based on the above base mesh to generate a displacement vector bitstream; A mesh restoration unit that restores a mesh based on the encoded base mesh and the encoded displacement information; and A mesh data encoding device including a texture map processing unit that generates a texture map bitstream by encoding a texture map generated based on the original mesh and the restored mesh.

14. In the 13th paragraph, the displacement information processing unit A displacement information coordinate system conversion unit that converts the coordinate system of the above displacement information into a local coordinate system; A displacement information packing unit that performs packing based on one of the first format, the second format, and the third format for at least one of the normal component, the tangential component, or the bi-tangential component included in the displacement information of the local coordinate system; and A mesh data encoding device comprising a displacement information encoding unit that encodes the above packed displacement information.

15. In the 13th paragraph, the displacement information packing part Optionally perform packing on the bi-tangential component of the above displacement information, A mesh data encoding device wherein the signaling information includes information for identifying whether packing of the bi-tangential component has been skipped.

16. In paragraph 13, A mesh data encoding device wherein the signaling information includes information for identifying a format applied to the displacement information.

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