WO2020146341A1 - Point cloud bitstream structure and auxiliary information differential coding - Google Patents

Abstract

A method of point cloud coding (PCC) implemented by a decoder. The method includes receiving, by a receiver of the decoder, a bitstream having atlas frames (a.k.a. access units) that each contain a point cloud, wherein at least one of the atlas frames is received out of presentation order; obtaining, by a processor of the decoder, an atlas type (a.k.a., frame type) and an atlas order count (a.k.a., frame order count) from each of the atlas frames; determining, by the processor, the presentation order of the atlas frames based on the atlas type and the atlas order count obtained from each of the atlas frames; and decoding, by the processor, the atlas frames in the presentation order.

Description

Point Cloud Bitstream Structure And Auxiliary Information Differential Coding

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This patent application claims the benefit of U.S. Provisional Patent Application No. 62/789,370, filed January 7, 2019, by Vladyslav Zakharchenko, et ah, and titled“Point Cloud Bitstream Structure and Auxiliary Information Differential Coding,” which is hereby incorporated by reference.

TECHNICAL FIELD

[0002] The present disclosure is generally related to point cloud coding, and is specifically related to the high-level syntax for point cloud coding.

BACKGROUND

[0003] The point cloud is employed in a wide variety of applications including entertainment industry, intelligent automobile navigation, geospatial inspection, three dimensional (3D) modeling of real world objects, visualization etc. Considering the non- uniform sampling geometry of the point cloud, compact representations for storage and transmission of such data is useful. Compared with the other 3D presentations, the irregular point cloud is more general and applicable for a wider range of sensors and data acquisition strategies. For example, when performing a 3D presentation in a virtual reality world or remote renderings in a tele-presence environment, the rendering of virtual figures and real time instructions are processed as dense point cloud data set.

SUMMARY

[0004] A first aspect relates to a method of point cloud coding (PCC) implemented by a decoder. The method includes receiving, by a receiver of the decoder, a bitstream having atlas frames that each contain a point cloud, wherein at least one of the atlas frames is received out of presentation order; obtaining, by a processor of the decoder, an atlas type and an atlas order count from each of the atlas frames; determining, by the processor, the presentation order of the atlas frames based on the atlas type and the atlas order count obtained from each of the atlas frames; and decoding, by the processor, the atlas frames in the presentation order.

[0005] The coding techniques disclosed herein incorporate an atlas type and an atlas order count into the bitstream. The atlas type identifies the frame as a k frame, p frame, or I frame, and the atlas order count indicates the position of a frame in a presentation order relative to the other frames. By specifying the atlas type and atlas order count, the access units (a.k.a., atlas frames) can be coded out of presentation order. Because the frames can be coded out of presentation order, coding efficiency is improved. For example, two frames that are similar to each other but are not adjacent in presentation order can nonetheless be coded consecutively to reduce the delta (i.e., change) between the frames. Because the delta is reduced, the resources (e.g., bits) needed to code the bitstream may be reduced relative to conventional coding methods.

[0006] In a first implementation form of the method according to the first aspect as such, the atlas type indicates whether an atlas frame is a key atlas frame, an intra prediction atlas frame, or an inter prediction atlas frame.

[0007] In a second implementation form of the method according to the first aspect as such or any preceding implementation form of the first aspect, the atlas type is designated pc frame type.

[0008] In a third implementation form of the method according to the first aspect as such or any preceding implementation form of the first aspect, the atlas order count indicates a position of an atlas frame in the presentation order.

[0009] In a fourth implementation form of the method according to the first aspect as such or any preceding implementation form of the first aspect, the atlas order count is designated pc frame order cnt.

[0010] In a fifth implementation form of the method according to the first aspect as such or any preceding implementation form of the first aspect, the method further comprises obtaining a reference frame identifier from at least one of the atlas frames, the reference frame identifier identifying a reference frame for an atlas frame currently being decoded.

[0011] In a sixth implementation form of the method according to the first aspect as such or any preceding implementation form of the first aspect, the reference frame identifier is designated pc_patch_reference_frame_delta_idx_minusl .

[0012] In a seventh implementation form of the method according to the first aspect as such or any preceding implementation form of the first aspect, the method further comprises resetting picture parameter set parameters to a default value and cleaning a reference frame buffer when the atlas type indicates an atlas frame is a key atlas frame.

[0013] In an eighth implementation form of the method according to the first aspect as such or any preceding implementation form of the first aspect, the reference frame identifier is able to reference any reference frame within a reference frame buffer. [0014] In a ninth implementation form of the method according to the first aspect as such or any preceding implementation form of the first aspect, the atlas type and the atlas order count are contained in an atlas frame parameter set of the bitstream.

[0015] A second aspect relates to a method of point cloud coding (PCC) implemented by an encoder. The method includes dividing, by a processor of the encoder, a three dimensional image into point clouds; assigning, by the processor, an atlas type and an atlas order count to each of the point clouds; encoding, by the processor, the point clouds into atlas frames, wherein at least one of the atlas frames is encoded out of presentation order; and storing, in a memory of the encoder, the atlas frames in a bitstream for transmission toward a decoder.

[0016] The coding techniques disclosed herein incorporate an atlas type and an atlas order count into the bitstream. The atlas type identifies the frame as a k frame, p frame, or I frame, and the atlas order count indicates the position of a frame in a presentation order relative to the other frames. By specifying the atlas type and atlas order count, the access units (a.k.a., atlas frames) can be coded out of presentation order. Because the frames can be coded out of presentation order, coding efficiency is improved. For example, two frames that are similar to each other but are not adjacent in presentation order can nonetheless be coded consecutively to reduce the delta (i.e., change) between the frames. Because the delta is reduced, the resources (e.g., bits) needed to code the bitstream may be reduced relative to conventional coding methods.

[0017] In a first implementation form of the method according to the second aspect as such, the atlas type indicates whether an atlas frame is a key atlas frame, an intra prediction atlas frame, or an inter prediction atlas frame.

[0018] In a second implementation form of the method according to the second aspect as such or any preceding implementation form of the second aspect, the atlas type is designated pc frame type.

[0019] In a third implementation form of the method according to the second aspect as such or any preceding implementation form of the second aspect, the atlas order count indicates a position of an atlas frame in the presentation order.

[0020] In a fourth implementation form of the method according to the second aspect as such or any preceding implementation form of the second aspect, the atlas order count is designated pc frame order cnt.

[0021] In a fifth implementation form of the method according to the second aspect as such or any preceding implementation form of the second aspect, the method further comprises obtaining a reference frame identifier from at least one of the atlas frames, the reference frame identifier identifying a reference frame for an atlas frame currently being decoded.

[0022] In a sixth implementation form of the method according to the second aspect as such or any preceding implementation form of the second aspect, the reference frame identifier is designated pc_patch_reference_frame_delta_idx_minusl.

[0023] In a seventh implementation form of the method according to the second aspect as such or any preceding implementation form of the second aspect, the method further comprises resetting picture parameter set parameters to a default value and cleaning a reference frame buffer when the atlas type indicates an atlas frame is a key atlas frame.

[0024] In an eighth implementation form of the method according to the second aspect as such or any preceding implementation form of the second aspect, the reference frame identifier is able to reference any reference frame within a reference frame buffer.

[0025] In a ninth implementation form of the method according to the second aspect as such or any preceding implementation form of the second aspect, the atlas type and the atlas order count are contained in an atlas frame parameter set of the bitstream.

[0026] A third aspect relates to a coding apparatus. The coding apparatus includes a receiver configured to receive a volumetric picture to encode or to receive a bitstream to decode; a transmitter coupled to the receiver, the transmitter configured to transmit the bitstream to a decoder or to transmit a decoded volumetric image to a reconstruction device configured to reconstruct the decoded volumetric picture; a memory coupled to at least one of the receiver or the transmitter, the memory configured to store instructions; and a processor coupled to the memory, the processor configured to execute the instructions stored in the memory to perform any of the methods disclosed herein.

[0027] The coding techniques disclosed herein incorporate an atlas type and an atlas order count into the bitstream. The atlas type identifies the frame as a k frame, p frame, or I frame, and the atlas order count indicates the position of a frame in a presentation order relative to the other frames. By specifying the atlas type and atlas order count, the access units (a.k.a., atlas frames) can be coded out of presentation order. Because the frames can be coded out of presentation order, coding efficiency is improved. For example, two frames that are similar to each other but are not adjacent in presentation order can nonetheless be coded consecutively to reduce the delta (i.e., change) between the frames. Because the delta is reduced, the resources (e.g., bits) needed to code the bitstream may be reduced relative to conventional coding methods. [0028] In a first implementation form of the coding apparatus according to the third aspect as such, the coding apparatus further includes a display configured to display a projected image based on the decoded volumetric picture.

[0029] A fourth aspect relates to a system. The system includes an encoder; and a decoder in communication with the encoder, wherein the encoder or the decoder includes the coding apparatus described herein.

[0030] The coding techniques disclosed herein incorporate an atlas type and an atlas order count into the bitstream. The atlas type identifies the frame as a k frame, p frame, or I frame, and the atlas order count indicates the position of a frame in a presentation order relative to the other frames. By specifying the atlas type and atlas order count, the access units (a.k.a., atlas frames) can be coded out of presentation order. Because the frames can be coded out of presentation order, coding efficiency is improved. For example, two frames that are similar to each other but are not adjacent in presentation order can nonetheless be coded consecutively to reduce the delta (i.e., change) between the frames. Because the delta is reduced, the resources (e.g., bits) needed to code the bitstream may be reduced relative to conventional coding methods.

[0031] In a first implementation form of the coding apparatus according to the fourth aspect as such, the system further includes a display configured to display a projected image based on the decoded volumetric picture.

[0032] A fifth aspect relates to means for coding. The means for coding includes receiving means configured to receive a volumetric picture to encode or to receive a bitstream to decode, reconstruct, and project; transmission means coupled to the receiving means, the transmission means configured to transmit the bitstream to a decoder or to transmit a decoded image to a display means; storage means coupled to at least one of the receiving means or the transmission means, the storage means configured to store instructions; and processing means coupled to the storage means, the processing means configured to execute the instructions stored in the storage means to perform any of the methods disclosed herein.

[0033] The coding techniques disclosed herein incorporate an atlas type and an atlas order count into the bitstream. The atlas type identifies the frame as a k frame, p frame, or I frame, and the atlas order count indicates the position of a frame in a presentation order relative to the other frames. By specifying the atlas type and atlas order count, the access units (a.k.a., atlas frames) can be coded out of presentation order. Because the frames can be coded out of presentation order, coding efficiency is improved. For example, two frames that are similar to each other but are not adjacent in presentation order can nonetheless be coded consecutively to reduce the delta (i.e., change) between the frames. Because the delta is reduced, the resources (e.g., bits) needed to code the bitstream may be reduced relative to conventional coding methods.

[0034] For the purpose of clarity, any one of the foregoing embodiments may be combined with any one or more of the other foregoing embodiments to create a new embodiment within the scope of the present disclosure.

[0035] These and other features will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] For a more complete understanding of this disclosure, reference is now made to the following brief description, taken in connection with the accompanying drawings and detailed description, wherein like reference numerals represent like parts.

[0037] FIG. 1 is a block diagram illustrating an example coding system that may utilize context modeling techniques.

[0038] FIG. 2 a block diagram illustrating an example encoder that may implement context modeling techniques.

[0039] FIG. 3 a block diagram illustrating an example decoder that may implement context modeling techniques.

[0040] FIG. 4 is a representation of a group of frames bitstream.

[0041] FIG. 5 is an embodiment of a representation of a group of frames bitstream with frames identified by frame type.

[0042] FIG. 6 is an embodiment of a representation of frames in coding order and presentation order.

[0043] FIG. 7 is an embodiment of an illustration of a buffer operation.

[0044] FIG. 8 is an embodiment of a patch side information prediction scenario containing different frame types.

[0045] FIG. 9 is an embodiment of a method of point cloud coding (PCC) implemented by a decoder.

[0046] FIG. 10 is an embodiment of a method of point cloud coding (PCC) implemented by an encoder.

[0047] FIG. 11 is a schematic diagram of a coding device.

[0048] FIG. 12 is a schematic diagram of an embodiment of a means for coding. DETAILED DESCRIPTION

[0049] It should be understood at the outset that although an illustrative implementation of one or more embodiments are provided below, the disclosed systems and/or methods may be implemented using any number of techniques, whether currently known or in existence. The disclosure should in no way be limited to the illustrative implementations, drawings, and techniques illustrated below, including the exemplary designs and implementations illustrated and described herein, but may be modified within the scope of the appended claims along with their full scope of equivalents.

[0050] Video coding standards include International Telecommunications Union Telecommunication Standardization Sector (ITU-T) H.261, International Organization for Standardization (ISO) / International Electrotechnical Commission (IEC) Moving Picture Experts Group (MPEG)-l Part 2, ITU-T H.262 or ISO/IEC MPEG-2 Part 2, ITU-T H.263, ISO/IEC MPEG-4 Part 2, Advanced Video Coding (AVC), also known as ITU-T H.264 or ISO/IEC MPEG-4 Part 10, and High Efficiency Video Coding (HEVC), also known as ITU-T H.265 or MPEG-H Part 2. AVC includes extensions such as Scalable Video Coding (SVC), Multiview Video Coding (MVC), and Multiview Video Coding plus Depth (MVC+D), and 3D AVC (3D-AVC). HEVC includes extensions such as Scalable HEVC (SHVC), Multiview HEVC (MV -HEVC), and 3D HEVC (3D-HEVC).

[0051] A point cloud is a set of data points in the 3D space. Each data point includes parameters that determine a position (e.g., X, Y, Z), a color (e.g., R, G, B or Y, U, V), and possibly other properties like transparency, reflectance, time of acquisition, etc. Typically, each data point in a cloud has the same number of attributes attached to it. Point clouds may be used in various applications such as real-time 3D immersive telepresence, content virtual reality (VR) viewing with interactive parallax, 3D free viewpoint sports replay broadcasting, geographic information systems, cultural heritage, autonomous navigation based on large-scale 3D dynamic maps, and automotive applications.

[0052] The ISO/IEC Moving Picture Experts Group (MPEG) began in 2016 the development of a new codec standard on Point Cloud Coding for lossless and lossy compressed point cloud data with substantial coding efficiency and robustness to network environments. The use of this codec standard allows point clouds to be manipulated as a form of computer data and to be stored on various storage media, transmitted and received over existing and future networks and distributed on existing and future broadcasting channels. [0053] Recently, the point cloud coding (PCC) work was classified into three categories, PCC category 1, PCC category 2, and PCC category 3, wherein two separate working drafts were being developed, one for PCC category 2 (PCC Cat2), and the other for PCC categories 1 and 3 (PCC Catl3). The latest working draft (WD) for PCC Cat2 is included in MPEG output document N17534, and the latest WD for PCC Catl3 is included in MPEG output document N17533.

[0054] The main philosophy behind the design of the PCC Cat2 codec in the PCC Cat2 WD is to leverage existing video codecs to compress the geometry and texture information of a dynamic point cloud, by compressing the point cloud data as a set of different video sequences. In particular, two video sequences, one representing the geometry information of the point cloud data and another representing the texture information, are generated and compressed by using video codecs. Additional metadata to interpret the two video sequences, i.e., an occupancy map and auxiliary patch information, is also generated and compressed separately.

[0055] Unfortunately, the existing designs of PCC have drawbacks. For example, data units pertaining to one time instance, i.e., one access unit (AU), are not contiguous in decoding order. In the PCC Cat 2 WD, the data units of texture, geometry, auxiliary information, and the occupancy map for each AU are interleaved in the units of group of frames. That is, the geometry data for all the frames in the group is together. The same is often true for texture data, and so on. In PCC Catl3 WD, the data units of geometry and the general attributes for each AU are interleaved on the level of the entire PCC bitstream (e.g., the same as in PCC Cat2 WD when there is only one group of frames that has the same length as the entire PCC bitstream). Interleaving of data units belonging to one AU inherently causes a huge end-to-end delay that is at least equal to the length of the group of frames in presentation time duration in application systems.

[0056] Another drawback relates to the bitstream format. The bitstream format allows emulation of a start code pattern like 0x0003 and therefore does not work for transmission over MPEG-2 transport stream (TS) where start code emulation prevention is needed. For PCC Cat2, currently only gro u p_o f fram e s geo m e try v i d eo pay I oad ( ) and group_of_frames_texture_video_payload( ) have start code emulation prevention in place when either HEVC or AVC is used for coding of the geometry and texture components. For PCC Cat 13, start code emulation prevention is not in place anywhere in the bitstream.

[0057] In PCC Cat2 WD, some of the codec information (e.g., which codec, profile, level, etc., of the codec) for the geometry and texture bitstreams is deeply buried in the multiple instances of the structures group_of_frames_geometry_video_payload( ) and group_of_frames_texture_video_payload( ). Furthermore, some of the information like profile and level that indicates the capabilities for decoding of the auxiliary information and occupancy map components, as well as for point cloud reconstruction, is missing.

[0058] Fligh-level syntax designs that solve one or more of the aforementioned problems associated with point cloud coding are provided. As will be more fully explained below, the present disclosure utilizes a type indicator in a data unit header (a.k.a., a PCC network access layer (NAL) header) to specify the type of content in the payload of the PCC NAL unit. In addition, the present disclosure utilizes a group of frames header NAL unit to carry the group of frames header parameters. The group of frames header NAL unit may also be used to signal the profile and level of each geometry or texture bitstream.

[0059] FIG. 1 is a block diagram illustrating an example coding system 10 that may utilize PCC video coding techniques. As shown in FIG. 1, the coding system 10 includes a source device 12 that provides encoded video data to be decoded at a later time by a destination device 14. In particular, the source device 12 may provide the video data to destination device 14 via a computer-readable medium 16. Source device 12 and destination device 14 may comprise any of a wide range of devices, including desktop computers, notebook (e.g., laptop) computers, tablet computers, set-top boxes, telephone handsets such as so-called“smart” phones, so-called “smart” pads, televisions, cameras, display devices, digital media players, video gaming consoles, video streaming device, or the like. In some cases, source device 12 and destination device 14 may be equipped for wireless communication.

[0060] Destination device 14 may receive the encoded video data to be decoded via computer-readable medium 16. Computer-readable medium 16 may comprise any type of medium or device capable of moving the encoded video data from source device 12 to destination device 14. In one example, computer-readable medium 16 may comprise a communication medium to enable source device 12 to transmit encoded video data directly to destination device 14 in real-time. The encoded video data may be modulated according to a communication standard, such as a wireless communication protocol, and transmitted to destination device 14. The communication medium may comprise any wireless or wired communication medium, such as a radio frequency (RF) spectrum or one or more physical transmission lines. The communication medium may form part of a packet-based network, such as a local area network, a wide-area network, or a global network such as the Internet. The communication medium may include routers, switches, base stations, or any other equipment that may be useful to facilitate communication from source device 12 to destination device 14. [0061] In some examples, encoded data may be output from output interface 24 to a storage device. Similarly, encoded data may be accessed from the storage device by input interface. The storage device may include any of a variety of distributed or locally accessed data storage media such as a hard drive, Blu-ray discs, digital video disks (DVD)s, Compact Disc Read- Only Memories (CD-ROMs), flash memory, volatile or non-volatile memory, or any other suitable digital storage media for storing encoded video data. In a further example, the storage device may correspond to a file server or another intermediate storage device that may store the encoded video generated by source device 12. Destination device 14 may access stored video data from the storage device via streaming or download. The file server may be any type of server capable of storing encoded video data and transmitting that encoded video data to the destination device 14. Example file servers include a web server (e.g., for a website), a file transfer protocol (FTP) server, network attached storage (NAS) devices, or a local disk drive. Destination device 14 may access the encoded video data through any standard data connection, including an Internet connection. This may include a wireless channel (e.g., a Wi Fi connection), a wired connection (e.g., digital subscriber line (DSF), cable modem, etc.), or a combination of both that is suitable for accessing encoded video data stored on a file server. The transmission of encoded video data from the storage device may be a streaming transmission, a download transmission, or a combination thereof.

[0062] The techniques of this disclosure are not necessarily limited to wireless applications or settings. The techniques may be applied to video coding in support of any of a variety of multimedia applications, such as over-the-air television broadcasts, cable television transmissions, satellite television transmissions, Internet streaming video transmissions, such as dynamic adaptive streaming over F1TTP (DASF1), digital video that is encoded onto a data storage medium, decoding of digital video stored on a data storage medium, or other applications. In some examples, coding system 10 may be configured to support one-way or two-way video transmission to support applications such as video streaming, video playback, video broadcasting, and/or video telephony.

[0063] In the example of FIG. 1, source device 12 includes a video source 18 configured to provide a volumetric image, projection device 20, video encoder 22, and output interface 24. Destination device 14 includes input interface 26, video decoder 28, reconstruction device 30, and display device 32. In accordance with this disclosure, encoder 22 of the source device 12 and/or the decoder 28 of the destination device 14 may be configured to apply the techniques for video coding. In other examples, a source device and a destination device may include other components or arrangements. For example, source device 12 may receive video data from an external video source, such as an external camera. Likewise, destination device 14 may interface with an external display device, rather than including an integrated display device.

[0064] The illustrated coding system 10 of FIG. 1 is merely one example. Techniques for video coding may be performed by any digital video encoding and/or decoding device. Although the techniques of this disclosure generally are performed by a coding device, the techniques may also be performed by an encoder/decoder, typically referred to as a“CODEC.” Moreover, the techniques of this disclosure may also be performed by a video preprocessor. The encoder and/or the decoder may be a graphics processing unit (GPU) or a similar device.

[0065] Source device 12 and destination device 14 are merely examples of such coding devices in which source device 12 generates coded video data for transmission to destination device 14. In some examples, source device 12 and destination device 14 may operate in a substantially symmetrical manner such that each of the source and destination devices 12, 14 includes video encoding and decoding components. Flence, coding system 10 may support one-way or two-way video transmission between video devices 12, 14, e.g., for video streaming, video playback, video broadcasting, or video telephony.

[0066] Video source 18 of source device 12 may include a video capture device, such as a video camera, a video archive containing previously captured video, and/or a video feed interface to receive the volumetric image or video from a video content provider. As a further alternative, video source 18 may generate the volumetric image or computer graphics-based data as the source video, or a combination of live video, archived video, and computer generated video.

[0067] In some cases, when video source 18 is a video camera, source device 12 and destination device 14 may form so-called camera phones or video phones. As mentioned above, however, the techniques described in this disclosure may be applicable to video coding in general, and may be applied to wireless and/or wired applications.

[0068] The projection device 20 is configured to project the volumetric image onto a planar surface (e.g., a bounding box) as more fully explained below. That is, the projection device 20 is configured to convert a three dimensional (3D) image to a two dimensional (2D) image or images.

[0069] In any case, the volumetric image, captured video, pre-captured video, or computer generated video may be encoded by encoder 22. The encoded video information may then be output by output interface 24 onto a computer-readable medium 16. [0070] Computer-readable medium 16 may include transient media, such as a wireless broadcast or wired network transmission, or storage media (that is, non-transitory storage media), such as a hard disk, flash drive, compact disc, digital video disc, Blu-ray disc, or other computer-readable media. In some examples, a network server (not shown) may receive encoded video data from source device 12 and provide the encoded video data to destination device 14, e.g., via network transmission. Similarly, a computing device of a medium production facility, such as a disc stamping facility, may receive encoded video data from source device 12 and produce a disc containing the encoded video data. Therefore, computer- readable medium 16 may be understood to include one or more computer-readable media of various forms, in various examples.

[0071] Input interface 26 of destination device 14 receives information from computer- readable medium 16. The information of computer-readable medium 16 may include syntax information defined by encoder 22, which is also used by decoder 28, that includes syntax elements that describe characteristics and/or processing of blocks and other coded units, e.g., group of pictures (GOPs).

[0072] The reconstruction device 30 is configured to convert the planar image or images back to the volumetric image as more fully explained below. That is, the reconstruction device 30 is configured to convert the 2D image or images back to a 3D image.

[0073] Display device 32 displays the volumetric image or decoded video data to a user, and may comprise any of a variety of display devices such as a cathode ray tube (CRT), a liquid crystal display (LCD), a plasma display, an organic light emitting diode (OLED) display, or another type of display device.

[0074] Encoder 22 and decoder 28 may operate according to a video coding standard, such as the High Efficiency Video Coding (ffEVC) standard presently under development, and may conform to the ffEVC Test Model (ffM). Alternatively, encoder 22 and decoder 28 may operate according to other proprietary or industry standards, such as the International Telecommunications Union Telecommunication Standardization Sector (ITU-T) ff.264 standard, alternatively referred to as Moving Picture Expert Group (MPEG)-4, Part 10, Advanced Video Coding (AVC), ff.265/ffEVC, or extensions of such standards. The techniques of this disclosure, however, are not limited to any particular coding standard. Other examples of video coding standards include MPEG-2 and ITU-T ff.263. Although not shown in FIG. 1, in some aspects, encoder 22 and decoder 28 may each be integrated with an audio encoder and decoder, and may include appropriate multiplexer-demultiplexer (MUX-DEMUX) units, or other hardware and software, to handle encoding of both audio and video in a common data stream or separate data streams. If applicable, MUX-DEMUX units may conform to the ITU H.223 multiplexer protocol, or other protocols such as the user datagram protocol (UDP).

[0075] Encoder 22 and decoder 28 each may be implemented as any of a variety of suitable encoder circuitry, such as one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), discrete logic, software, hardware, firmware or any combinations thereof. When the techniques are implemented partially in software, a device may store instructions for the software in a suitable, non-transitory computer-readable medium and execute the instructions in hardware using one or more processors to perform the techniques of this disclosure. Each of encoder 22 and decoder 28 may be included in one or more encoders or decoders, either of which may be integrated as part of a combined encoder/decoder (CODEC) in a respective device. A device including encoder 22 and/or decoder 28 may comprise an integrated circuit, a microprocessor, and/or a wireless communication device, such as a cellular telephone.

[0076] FIG. 2 is a block diagram illustrating an example of encoder 22 that may implement video coding techniques. Encoder 22 may perform intra- and inter-coding of video blocks within video slices. Intra-coding relies on spatial prediction to reduce or remove spatial redundancy in video within a given video frame or picture. Inter-coding relies on temporal prediction to reduce or remove temporal redundancy in video within adjacent frames or pictures of a video sequence. Intra-mode (I mode) may refer to any of several spatial based coding modes. Inter-modes, such as uni-directional (a.k.a., uni prediction) prediction (P mode) or bi prediction (a.k.a., bi prediction) (B mode), may refer to any of several temporal-based coding modes.

[0077] As shown in FIG. 2, encoder 22 receives a current video block within a video frame to be encoded. In the example of FIG. 2, encoder 22 includes mode select unit 40, reference frame memory 64, summer 50, transform processing unit 52, quantization unit 54, and entropy coding unit 56. Mode select unit 40, in turn, includes motion compensation unit 44, motion estimation unit 42, intra-prediction (a.k.a., intra prediction) unit 46, and partition unit 48. For video block reconstruction, encoder 22 also includes inverse quantization unit 58, inverse transform unit 60, and summer 62. A deblocking filter (not shown in FIG. 2) may also be included to filter block boundaries to remove blockiness artifacts from reconstructed video. If desired, the deblocking filter would typically filter the output of summer 62. Additional filters (in loop or post loop) may also be used in addition to the deblocking filter. Such filters are not shown for brevity, but if desired, may filter the output of summer 50 (as an in-loop filter). [0078] During the encoding process, encoder 22 receives a video frame or slice to be coded. The frame or slice may be divided into multiple video blocks. Motion estimation unit 42 and motion compensation unit 44 perform inter-predictive coding of the received video block relative to one or more blocks in one or more reference frames to provide temporal prediction. Intra-prediction unit 46 may alternatively perform intra-predictive coding of the received video block relative to one or more neighboring blocks in the same frame or slice as the block to be coded to provide spatial prediction. Encoder 22 may perform multiple coding passes, e.g., to select an appropriate coding mode for each block of video data.

[0079] Moreover, partition unit 48 may partition blocks of video data into sub-blocks, based on evaluation of previous partitioning schemes in previous coding passes. For example, partition unit 48 may initially partition a frame or slice into largest coding units (LCUs), and partition each of the LCUs into sub-coding units (sub-CUs) based on rate-distortion analysis (e.g., rate-distortion optimization). Mode select unit 40 may further produce a quad-tree data structure indicative of partitioning of a LCU into sub-CUs. Leaf-node CUs of the quad-tree may include one or more prediction units (PUs) and one or more transform units (TUs).

[0080] The present disclosure uses the term“block” to refer to any of a CU, PU, or TU, in the context of HEVC, or similar data structures in the context of other standards (e.g., macroblocks and sub-blocks thereof in EL264/AVC). A CU includes a coding node, PUs, and TUs associated with the coding node. A size of the CU corresponds to a size of the coding node and is square in shape. The size of the CU may range from 8x8 pixels up to the size of the treeblock with a maximum of 64x64 pixels or greater. Each CU may contain one or more PUs and one or more TUs. Syntax data associated with a CU may describe, for example, partitioning of the CU into one or more PUs. Partitioning modes may differ between whether the CU is skip or direct mode encoded, intra-prediction mode encoded, or inter-prediction (a.k.a., inter prediction) mode encoded. PUs may be partitioned to be non-square in shape. Syntax data associated with a CU may also describe, for example, partitioning of the CU into one or more TUs according to a quad-tree. A TU can be square or non-square (e.g., rectangular) in shape.

[0081] Mode select unit 40 may select one of the coding modes, intra- or inter-, e.g., based on error results, and provides the resulting intra- or inter-coded block to summer 50 to generate residual block data and to summer 62 to reconstruct the encoded block for use as a reference frame. Mode select unit 40 also provides syntax elements, such as motion vectors, intra-mode indicators, partition information, and other such syntax information, to entropy coding unit 56. [0082] Motion estimation unit 42 and motion compensation unit 44 may be highly integrated, but are illustrated separately for conceptual purposes. Motion estimation, performed by motion estimation unit 42, is the process of generating motion vectors, which estimate motion for video blocks. A motion vector, for example, may indicate the displacement of a PU of a video block within a current video frame or picture relative to a predictive block within a reference frame (or other coded unit) relative to the current block being coded within the current frame (or other coded unit). A predictive block is a block that is found to closely match the block to be coded, in terms of pixel difference, which may be determined by sum of absolute difference (SAD), sum of square difference (SSD), or other difference metrics. In some examples, encoder 22 may calculate values for sub-integer pixel positions of reference pictures stored in reference frame memory 64. For example, encoder 22 may interpolate values of one-quarter pixel positions, one-eighth pixel positions, or other fractional pixel positions of the reference picture. Therefore, motion estimation unit 42 may perform a motion search relative to the full pixel positions and fractional pixel positions and output a motion vector with fractional pixel precision.

[0083] Motion estimation unit 42 calculates a motion vector for a PU of a video block in an inter-coded slice by comparing the position of the PU to the position of a predictive block of a reference picture. The reference picture may be selected from a first reference picture list (List 0) or a second reference picture list (List 1), each of which identify one or more reference pictures stored in reference frame memory 64. Motion estimation unit 42 sends the calculated motion vector to entropy encoding unit 56 and motion compensation unit 44.

[0084] Motion compensation, performed by motion compensation unit 44, may involve fetching or generating the predictive block based on the motion vector determined by motion estimation unit 42. Again, motion estimation unit 42 and motion compensation unit 44 may be functionally integrated, in some examples. Upon receiving the motion vector for the PU of the current video block, motion compensation unit 44 may locate the predictive block to which the motion vector points in one of the reference picture lists. Summer 50 forms a residual video block by subtracting pixel values of the predictive block from the pixel values of the current video block being coded, forming pixel difference values, as discussed below. In general, motion estimation unit 42 performs motion estimation relative to luma components, and motion compensation unit 44 uses motion vectors calculated based on the luma components for both chroma components and luma components. Mode select unit 40 may also generate syntax elements associated with the video blocks and the video slice for use by decoder 28 in decoding the video blocks of the video slice. [0085] Intra-prediction unit 46 may intra-predict a current block, as an alternative to the inter-prediction performed by motion estimation unit 42 and motion compensation unit 44, as described above. In particular, intra-prediction unit 46 may determine an intra-prediction mode to use to encode a current block. In some examples, intra-prediction unit 46 may encode a current block using various intra-prediction modes, e.g., during separate encoding passes, and intra-prediction unit 46 (or mode select unit 40, in some examples) may select an appropriate intra-prediction mode to use from the tested modes.

[0086] For example, intra-prediction unit 46 may calculate rate-distortion values using a rate-distortion analysis for the various tested intra-prediction modes, and select the intra prediction mode having the best rate-distortion characteristics among the tested modes. Rate- distortion analysis generally determines an amount of distortion (or error) between an encoded block and an original, unencoded block that was encoded to produce the encoded block, as well as a bitrate (that is, a number of bits) used to produce the encoded block. Intra-prediction unit 46 may calculate ratios from the distortions and rates for the various encoded blocks to determine which intra-prediction mode exhibits the best rate-distortion value for the block.

[0087] In addition, intra-prediction unit 46 may be configured to code depth blocks of a depth map using a depth modeling mode (DMM). Mode select unit 40 may determine whether an available DMM mode produces better coding results than an intra-prediction mode and the other DMM modes, e.g., using rate-distortion optimization (RDO). Data for a texture image corresponding to a depth map may be stored in reference frame memory 64. Motion estimation unit 42 and motion compensation unit 44 may also be configured to inter-predict depth blocks of a depth map.

[0088] After selecting an intra-prediction mode for a block (e.g., a conventional intra prediction mode or one of the DMM modes), intra-prediction unit 46 may provide information indicative of the selected intra-prediction mode for the block to entropy coding unit 56. Entropy coding unit 56 may encode the information indicating the selected intra-prediction mode. Encoder 22 may include in the transmitted bitstream configuration data, which may include a plurality of intra-prediction mode index tables and a plurality of modified intra prediction mode index tables (also referred to as codeword mapping tables), definitions of encoding contexts for various blocks, and indications of a most probable intra-prediction mode, an intra-prediction mode index table, and a modified intra-prediction mode index table to use for each of the contexts. [0089] Encoder 22 forms a residual video block by subtracting the prediction data from mode select unit 40 from the original video block being coded. Summer 50 represents the component or components that perform this subtraction operation.

[0090] Transform processing unit 52 applies a transform, such as a discrete cosine transform (DCT) or a conceptually similar transform, to the residual block, producing a video block comprising residual transform coefficient values. Transform processing unit 52 may perform other transforms which are conceptually similar to DCT. Wavelet transforms, integer transforms, sub-band transforms or other types of transforms could also be used.

[0091] Transform processing unit 52 applies the transform to the residual block, producing a block of residual transform coefficients. The transform may convert the residual information from a pixel value domain to a transform domain, such as a frequency domain. Transform processing unit 52 may send the resulting transform coefficients to quantization unit 54. Quantization unit 54 quantizes the transform coefficients to further reduce bit rate. The quantization process may reduce the bit depth associated with some or all of the coefficients. The degree of quantization may be modified by adjusting a quantization parameter. In some examples, quantization unit 54 may then perform a scan of the matrix including the quantized transform coefficients. Alternatively, entropy encoding unit 56 may perform the scan.

[0092] Following quantization, entropy coding unit 56 entropy codes the quantized transform coefficients. For example, entropy coding unit 56 may perform context adaptive variable length coding (CAVFC), context adaptive binary arithmetic coding (CABAC), syntax- based context-adaptive binary arithmetic coding (SBAC), probability interval partitioning entropy (PIPE) coding or another entropy coding technique. In the case of context-based entropy coding, context may be based on neighboring blocks. Following the entropy coding by entropy coding unit 56, the encoded bitstream may be transmitted to another device (e.g., decoder 28) or archived for later transmission or retrieval.

[0093] Inverse quantization unit 58 and inverse transform unit 60 apply inverse quantization and inverse transformation, respectively, to reconstruct the residual block in the pixel domain, e.g., for later use as a reference block. Motion compensation unit 44 may calculate a reference block by adding the residual block to a predictive block of one of the frames of reference frame memory 64. Motion compensation unit 44 may also apply one or more interpolation filters to the reconstructed residual block to calculate sub-integer pixel values for use in motion estimation. Summer 62 adds the reconstructed residual block to the motion compensated prediction block produced by motion compensation unit 44 to produce a reconstructed video block for storage in reference frame memory 64. The reconstructed video block may be used by motion estimation unit 42 and motion compensation unit 44 as a reference block to inter-code a block in a subsequent video frame.

[0094] FIG. 3 is a block diagram illustrating an example of decoder 28 that may implement video coding techniques. In the example of FIG. 3, decoder 28 includes an entropy decoding unit 70, motion compensation unit 72, intra-prediction unit 74, inverse quantization unit 76, inverse transformation unit 78, reference frame memory 82, and summer 80. Decoder 28 may, in some examples, perform a decoding pass generally reciprocal to the encoding pass described with respect to encoder 22 (FIG. 2). Motion compensation unit 72 may generate prediction data based on motion vectors received from entropy decoding unit 70, while intra-prediction unit 74 may generate prediction data based on intra-prediction mode indicators received from entropy decoding unit 70.

[0095] During the decoding process, decoder 28 receives an encoded video bitstream that represents video blocks of an encoded video slice and associated syntax elements from encoder 22. Entropy decoding unit 70 of the decoder 28 entropy decodes the bitstream to generate quantized coefficients, motion vectors or intra-prediction mode indicators, and other syntax elements. Entropy decoding unit 70 forwards the motion vectors and other syntax elements to motion compensation unit 72. Decoder 28 may receive the syntax elements at the video slice level and/or the video block level.

[0096] When the video slice is coded as an intra-coded (I) slice, intra-prediction unit 74 may generate prediction data for a video block of the current video slice based on a signaled intra-prediction mode and data from previously decoded blocks of the current frame or picture. When the video frame is coded as an inter-coded (e.g., B, P, or GPB) slice, motion compensation unit 72 produces predictive blocks for a video block of the current video slice based on the motion vectors and other syntax elements received from entropy decoding unit 70. The predictive blocks may be produced from one of the reference pictures within one of the reference picture lists. Decoder 28 may construct the reference frame lists, List 0 and List 1, using default construction techniques based on reference pictures stored in reference frame memory 82.

[0097] Motion compensation unit 72 determines prediction information for a video block of the current video slice by parsing the motion vectors and other syntax elements, and uses the prediction information to produce the predictive blocks for the current video block being decoded. For example, motion compensation unit 72 uses some of the received syntax elements to determine a prediction mode (e.g., intra- or inter-prediction) used to code the video blocks of the video slice, an inter-prediction slice type (e.g., B slice, P slice, or GPB slice), construction information for one or more of the reference picture lists for the slice, motion vectors for each inter-encoded video block of the slice, inter-prediction status for each inter- coded video block of the slice, and other information to decode the video blocks in the current video slice.

[0098] Motion compensation unit 72 may also perform interpolation based on interpolation filters. Motion compensation unit 72 may use interpolation filters as used by encoder 22 during encoding of the video blocks to calculate interpolated values for sub-integer pixels of reference blocks. In this case, motion compensation unit 72 may determine the interpolation filters used by encoder 22 from the received syntax elements and use the interpolation filters to produce predictive blocks.

[0099] Data for a texture image corresponding to a depth map may be stored in reference frame memory 82. Motion compensation unit 72 may also be configured to inter-predict depth blocks of a depth map.

[00100] FIG. 4 is a representation of a group of frames bitstream 400. As shown, the group of frames bitstream 400 includes a first group of frames 402 (GOF O) and a second group of frames 404 (GOF l). For the purpose of illustration only, the first group of frames 402 and the second group of frames 404 are separated from each other by dashed lines. Although two groups of frames are depicted in FIG. 4, it should be appreciated that any number of frames may be included in the group of frames bitstream 400 in practical applications.

[00101] The first group of frames 402 and the second group of frames 404 are each formed from a collection of access units 406. The access units 406 are configured to contain frames, which contain all or a portion of a compressed image (e.g., a point cloud). The access units 406 in FIG. 4 may contain or be referred to herein as atlas frames. In an embodiment, an atlas frame is a frame that contains sufficient information to reconstruct a point cloud by mapping coded components together, where components include point geometry, point attributes, occupancy maps, patches, etc.

[00102] Each access unit 406 may contain a different type of frame. For example, an access unit 406 may contain a key frame (e.g., a k frame or a key atlas frame). In conventional coding techniques, it can be inferred that the first access unit 406 in a group of frames is a key frame. When a key frame is encountered, a picture parameter set (PPS) should be resent and a reference frame buffer should be cleared. Thus, the key frame may be referred to as an instantaneous decoder reset (IDR) frame or a clean random access (CRA) frame.

[00103] Each access unit 406 may also contain an inter frame (p frame) or an intra frame (I frame). An inter frame is a frame that refers to another frame for efficient compression. For example, only a difference or delta between the frame and its reference frame is encoded instead of the absolute values for the frames. Because the delta is encoded instead of the absolute values, coding resources are not wasted.

[00104] An intra frame is a frame that does not use any reference for prediction. When an intra frame is encountered, all of the adjusted parameters keep their values and a reference buffer is not reset.

[00105] In order to determine how many access units 406 are in the first group of frames 402 and the second group of frames 404, a group of frames header (not shown) is consulted. The group of frames header may indicate, for example, that the first group of frames 402 includes six access units 406 (e.g., numbered 0 to 5) and that the second group of frames 404 includes five access units 406 (e.g., numbered 0 to 4).

[00106] Current syntax in point cloud coding applications assumes that access units (e.g., access units 406) are presented in a consecutive decoding order in the same way that the access units have been acquired and/or will be displayed. In addition, current virtual PCC (V-PCC) software implementations are based on a group of frames concept. Each group of frames is encoded independently, and a frame index is adjusted inside each group of frames independently.

[00107] Prediction, which is referred to as delta side information coding, interceding, or predictive coding, is possible only within the same group of frames and currently a reference frame buffer may contain only a single reference frame. A reference frame may contain, for example, an auxiliary information that comprises patch side information units of a previously encoded frame. An example of a reference frame buffer is shown below.

[00108] The reference frame buffer contains atlas information for access units containing atlas frames. Once a new group of frames is encoded, all the reference picture buffers are cleaned and indexing starts from 0. Within that concept, a start point cloud frame is the first frame of the independent group of frames. [00109] In current implementations, there is no mechanism of access unit 406 type definition for metadata to distinguish between a temporal/spatial prediction method. Moreover, as shown in FIG. 4, the access units 406 are indexed in an incremental order (e.g., pcFramelndex) for the entire sequence (e.g., from 0 to pcFrameCount -1). In addition, the key frame access unit 406 definition is absent. However, the mechanism is implemented via an independent group of frames coding concept. Thus, effectively each first access unit 406 of a group of frames (e.g., group of frames 402 or 404) is a key frame access unit 406. Unfortunately, coding in this manner may not be the most efficient.

[00110] Disclosed herein are coding techniques that incorporate an atlas type and an atlas order count into the bitstream. The atlas type identifies the frame as a k frame, p frame, or I frame, and the atlas order count indicates the position of a frame in a presentation order relative to the other frames. By specifying the atlas type and atlas order count, the access units (a.k.a., atlas frames) can be coded out of presentation order. Because the frames can be coded out of presentation order, coding efficiency is improved. For example, two frames that are similar to each other but are not adjacent in presentation order can nonetheless be coded consecutively to reduce the delta (i.e., change) between the frames. Because the delta is reduced, the resources (e.g., bits) needed to code the bitstream may be reduced relative to conventional coding methods.

[00111] FIG. 5 is an embodiment of a representation of a group of frames bitstream 500 with frames identified by frame type. As shown, the group of frames bitstream 500 includes a first group of frames 502 and a second group of frames 504 each containing access units 506. Unlike the group of frames 402 and 404 in FIG. 4, the group of frames 502 and 504 in FIG. 5 are not separated from each other for the purposes of illustration. Although two groups of frames are depicted in FIG. 5, it should be appreciated that any number of frames may be included in the group of frames bitstream 500 in practical applications.

[00112] Each of the access units 506 in FIG. 5 has an atlas type. The atlas type of each access unit 506 is either K, P, or I to indicate whether the frame contained therein is a k frame, a p frame, or an I frame, respectively. In an embodiment, the atlas type is designated pc frame type.

[00113] Each of the access units 506 also has an atlas order count to indicate a position of the frame within a presentation order. The atlas order count may represent a numerical value (e.g., 0 to 5, 0 to 4) that indicates the presentation order of the corresponding access unit 506. In an embodiment, the atlas order count is designated pc frame order cnt. [00114] In FIG. 5, the first access unit 506 in the first group of frames 502 has an atlas type of K and an atlas order count of 0. The second access unit 506 in the first group of frames 502 has an atlas type of P and an atlas order count of 3. The third access unit 506 in the first group of frames 502 has an atlas type of P and an atlas order count of 1. The fourth access unit 506 in the first group of frames 502 has an atlas type of I and an atlas order count of 2. The other access units 506 are designated using a similar scheme.

[00115] In an embodiment, one or more of the access units 506 has a reference frame identifier. The reference frame identifier identifies a reference frame for an atlas frame currently being decoded. For example, an inter predicted frame in an access unit 506 having the P designation may refer to a previously decoded frame using the reference frame identifier. In an embodiment, the reference frame identifier is designated pc_patch_reference_frame_delta_idx_minus 1.

[00116] By specifying the atlas type and atlas order count of the access units 506 as shown in FIG. 5, the access units 506 can be coded out of presentation order as shown in FIG. 6. For the avoidance of doubt, the access units 506 are coded out of presentation order when at least one access unit is coded in a different order than the order used for proper display of a media sequence of point clouds.

[00117] FIG. 6 is an embodiment of a representation of frames 600 in coding order 608 and presentation order 610 (where the numbers 0-4 represent the number of each frame relative to the other frames). In FIG. 6, the coding order 608 for the frames in the access units 602 is numerically 0, 3, 4, 1, and 2. Because each of the access units 602 carries the atlas type and the atlas order count, the access units 602 can be rearranged into presentation order 610 in the correct numerical order of 0, 1, 2, 3, and 4. In an embodiment, the atlas type and the atlas order count are contained in an atlas frame parameter set of the bitstream. In an embodiment, the atlas type and the atlas order count are contained in another portion of the bitstream. For example, the information may be contained in a parameter set (e.g., a picture parameter set (PPS) or a sequence parameter set (SPS)) or a header.

[00118] If an auxiliary information delta coding flag is present in the SPS of the bitstream, the inter prediction method is used. In addition, as a current access unit (e.g., access unit 602) is encoded, the current access unit is reconstructed and placed in an auxiliary information data unit reference buffer. The reference access unit buffer may contain two parts: long term auxiliary information data unit reference list and short term auxiliary information data unit reference list. The access unit in a long term reference list may be, for example, a key frame access unit, and the access unit within a short term reference list may be a previously encoded access unit. An access unit can be present in both auxiliary information data unit reference access unit lists simultaneously.

[00119] When a key frame access unit is present, all parameters are reset to a default value (e.g., a frame index is set to 0, and all parameters shall be set to SPS/PPS that has to be signalled with a key frame access unit). The pcFramelndex can be in the range of 0 to max frame order cnt. An auxiliary information data unit (AIDU) reference list may contain several elements.

[00120] As an example, a reference frame buffer for a short term reference list and a reference frame buffer for a long term reference list are provided below. Each index contains all patches from a single frame (see FIG. 8). Patch side information includes but is not limited to uO, vO, ul, vl, dl, sizeUl, sizeVl, normalAxis, etc.

[00121] FIG. 7 is an embodiment of an illustration of a buffer operation 700. As shown, each access unit 702 may be identified relative to a frame index and a first in, first out (fifo) index. In the example of FIG. 7, the frame index progresses horizontally beneath the access units 702 from 0 to 4. The fifo index progresses vertically from 0 to 3.

[00122] In FIG. 7, the access unit 702 having a frame index number 0 and a fifo index number of 0, 1, 2, and 3 is a long term reference. The access unit 702 with the frame index number 1 and the fifo index 0, with the frame index number 2 and the fifo index 1, with the frame index number 3 and the fifo index 2, and with the frame index number 4 and the fifo index 3 is a short term reference. Thus, the short term reference access unit 702 (shown in grayscale) has a running index.

[00123] An example reference information buffer list is provided below.

[00124] In the reference information buffer list, the IDR and CRA frame types are both frame types that refresh the buffer. So, either would qualify as a key frame as described herein. Any frame that is not designated IDR or CRA is not a key frame and, hence, is either a p frame or an I frame.

[00125] FIG. 8 is an embodiment of a patch side information prediction scenario 800 for key frames, inter frames, and intra frames. As shown, the scenario 800 contains reference information 802 for a buffer. In an embodiment, the reference information 802 identifies an auxiliary reference list (AIDU RefList) and the corresponding fifo information (e.g., fifo: N-l ... N-RefListSize-1, fifo (Refresh), 0, fifo: 2, 0, and so on).

[00126] The scenario 800 also contains patch information 804 for the access units (e.g., access units 506). The patch information 804 contains, for example, a frame index (e.g., FrameIdx=N-l), a frame type (e.g., KeyFrame, I-Frame, or P-Frame), and a frame order count (e.g., FOC+N-1). The patch information 804 contains one or more patches 806 identified by a patch identifier (e.g., patch_ id 0, patch id 1, etc.).

[00127] FIG. 9 is an embodiment of a method 900 of point cloud coding (PCC) implemented by a decoder (e.g., entropy decoding unit 70). The method 900 may be performed when frames are received out of presentation order from, for example, an encoder (e.g., encoder 22).

[00128] In block 902, a bitstream having atlas frames (a.k.a., access units) each containing a point cloud are received by a receiver of the decoder. At least one of the atlas frames is received out of presentation order (e.g., presentation order 610).

[00129] In block 904, an atlas type (a.k.a., frame type) and an atlas order count (a.k.a., frame order count) are obtained from each of the atlas frames. In an embodiment, the atlas type indicates whether an atlas frame is a key atlas frame, an intra prediction atlas frame, or an inter prediction atlas frame. In an embodiment, the atlas type is designated pc frame type. In an embodiment, the atlas order count indicates a position of an atlas frame in the presentation order. In an embodiment, the atlas order count is designated pc frame order cnt.

[00130] In an embodiment, the method further comprises obtaining a reference frame identifier from at least one of the atlas frames. The reference frame identifier identifies a reference frame for an atlas frame currently being decoded. In an embodiment, the reference frame identifier is designated pc pat c li re fe re n ce_ frain e_de Ita id xjn i n us 1 .

[00131] In block 906, the presentation order of the atlas frames is determined based on the atlas type and the atlas order count obtained from each of the atlas frames. In block 908, the atlas frames are decoded in the presentation order.

[00132] In an embodiment, picture parameter set parameters are reset to a default value and a reference frame buffer is cleaned when the atlas type indicates an atlas frame is a key atlas frame. In an embodiment, the reference frame identifier is able to reference any reference frame within a reference frame buffer. In an embodiment, the atlas type and the atlas order count are contained in an atlas frame parameter set (AFPS) of the bitstream.

[00133] In an embodiment, the decoding process provides a set of independent components that should be further processed. At the processing stage, information from an atlas frame, an occupancy frame, a geometry frame, and attribute(s) frame(s) is used together to reconstruct a three dimensional (3D) volumetric picture. Thereafter, the projection of the 3D image is created on a two dimensional (2D) display based on user preference.

[00134] FIG. 10 is an embodiment of a method 1000 of point cloud coding (PCC) implemented by an encoder (e.g., entropy encoding unit 56). The method 1000 may be performed to encode frames out of presentation order. In block 1002, a three dimensional image is divided into point clouds. In block 1004, an atlas type and an atlas order count are assigned to each of the point clouds. In block 1006, the point clouds are encoded into atlas frames. At least one of the atlas frames is encoded out of presentation order (e.g., presentation order 610). In block 1008, the atlas frames are stored in a bitstream for transmission toward a decoder.

[00135] FIG. 11 is a schematic diagram of a coding device 1100 (e.g., an encoder 22, a decoder 28, etc.) according to an embodiment of the disclosure. The coding device 1100 is suitable for implementing the methods and processes disclosed herein. The coding device 1100 comprises ingress ports 1110 and receiver units (Rx) 1120 for receiving data; a processor, logic unit, or central processing unit (CPU) 1130 to process the data; transmitter units (Tx) 1140 and egress ports 1150 for transmitting the data; and a memory 1160 for storing the data. The coding device 1100 may also comprise optical-to-electrical (OE) components and electrical-to- optical (EO) components coupled to the ingress ports 1110, the receiver units 1120, the transmitter units 1140, and the egress ports 1150 for egress or ingress of optical or electrical signals.

[00136] The processor 1130 is implemented by hardware and software. The processor 1130 may be implemented as one or more CPU chips, cores (e.g., as a multi-core processor), field- programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), and digital signal processors (DSPs). The processor 1130 is in communication with the ingress ports 1110, receiver units 1120, transmitter units 1140, egress ports 1150, and memory 1160. The processor 1130 comprises a coding module 1170. The coding module 1170 implements the disclosed embodiments described above. In an embodiment, the coding module 1170 is a reconstruction module configured to project a reconstructed volumetric image. The inclusion of the coding module 1170 therefore provides a substantial improvement to the functionality of the coding device 1100 and effects a transformation of the coding device 1100 to a different state. Alternatively, the coding module 1170 is implemented as instructions stored in the memory 1160 and executed by the processor 1130.

[00137] The coding device 1100 may also include input and/or output (I/O) devices 1180 for communicating data to and from a user. The I/O devices 1180 may include output devices such as a display for displaying video data, speakers for outputting audio data, etc. The I/O devices 1180 may also include input devices, such as a keyboard, mouse, trackball, etc., and/or corresponding interfaces for interacting with such output devices.

[00138] The memory 1160 comprises one or more disks, tape drives, and solid-state drives and may be used as an over-flow data storage device, to store programs when such programs are selected for execution, and to store instructions and data that are read during program execution. The memory 1160 may be volatile and non-volatile and may be read-only memory (ROM), random-access memory (RAM), ternary content-addressable memory (TCAM), and static random-access memory (SRAM).

[00139] FIG. 12 is a schematic diagram of an embodiment of a means for coding 1200. In embodiment, the means for coding 1200 is implemented in a coding device 1202 (e.g., an encoder 22 or a decoder 28). The coding device 1202 includes receiving means 1201. The receiving means 1201 is configured to receive a picture to encode or to receive a bitstream to decode. The coding device 1202 includes transmission means 1207 coupled to the receiving means 1201. The transmission means 1207 is configured to transmit the bitstream to a decoder or to transmit a decoded image to a display means (e.g., one of the I/O devices 1180). [00140] The coding device 1202 includes a storage means 1203. The storage means 1203 is coupled to at least one of the receiving means 1201 or the transmission means 1207. The storage means 1203 is configured to store instructions. The coding device 1202 also includes processing means 1205. The processing means 1205 is coupled to the storage means 1203. The processing means 1205 is configured to execute the instructions stored in the storage means 1203 to perform the methods disclosed herein.

[00141] In an embodiment, syntax suitable for implementing the concepts disclosed herein is provided.

Syntax

[00142] Here pc frame order cnt specifies the point cloud frame order count for the current point cloud frame to support consistency for all elements frame index (Frameldx) is calculated based on total number of frames and current frame order count (FOC) value. The pc frame type specifies the frame as a key frame, I frame, or P frame. The pc_patch_reference_frame_delta_idx_minusl indicates a reference frame for the current frame (e.g., for a P frame).

[00143] In an embodiment, semantics suitable for implementing the concepts disclosed herein is provided.

[00144] Group of frames auxiliary information semantics are provided.

[00145] Point cloud frame order count (FOC): pc frame order cnt a variable that is associated with each point cloud, uniquely identifies the associated point cloud among all point clouds, and, when the associated point clound is to be output from the decoded frame buffer, indicates the position of the associated point cloud in decoded order relative to the output order positions of the other point clounds that are to be output from the decoded frame buffer.

[00146] In an embodiment, the point cloud FOC added delay to a decoded order count to align with presentation order. That is, the point could FOC can be used to implement a different order between presentation order and coding order.

[00147] Point cloud frame type pc frame type indicates that the values for all frames of the coded point clouds in the access unit are members of the set listed in Table 1 for the given value of pc frame type. The value of pc frame type shall be equal to 0, 1 or 2 in bitstreams conforming to Point Cloud Coding Specification.

Table 1. Point cloud frame type

[00148] pc frame order cnt specifies the point cloud order count for the current point cloud. The length of the pc frame order cnt syntax element may be defined by GOF size and the value of pc frame order cnt may be reset at each GOF. The value of the pc frame order cnt shall be in the range of 0 to max pc frame order cnt - 1 , inclusive. When pc frame order cnt is not present, pc frame order cnt is inferred to be equal to 0.

[00149] In an embodiment, the pc frame order count efficiently defines a size of the decoded picture buffer.

[00150] Point cloud reference index in decoded AU buffer pc_patch_reference_frame_delta_idx_minusl specifies the reference point cloud index for the current coded point cloud AU. May be different for metadata and video components of the bitstream.

[00151] poc_lookup_encoder[] specifies a list of threshold values used to define temporal consistency between frames. This table may be signaled either on sequence / key frame level, or be hardcoded into the codec itself. The decoder does not necessarily need to address this table.

[00152] RFS - reference point cloud frame set:

[00153] num negative frames specifies the number of entries in the stRfsIdx-th candidate short-term RFS that have point cloud frame order count values less than the frame order count value of the current frame. When nuh layer id of the current frame is equal to 0, the value of num negative frames shall be in the range of 0 to max dec frm buffering minusl, inclusive.

[00154] In an embodiment, the num negative frames, along with num positi ve frames, set a maximum distance for inter prediction between frames.

[00155] num positive frames specifies the number of entries in the stRfsIdx-th candidate short-term RFS that have point cloud frame order count values greater than the frame order count value of the current frame. When nuh layer id of the current frame is equal to 0, the value of num positive frames shall be in the range of 0 to max dec frm buffering minusl - num negative pics, inclusive.

[00156] delta_foc_sO_minusl[ i ] plus 1, when i is equal to 0, specifies the difference between the picture order count values of the current picture and i-th entry in the stRfsIdx-th candidate short-term RFS that has frame order count value less than that of the current frame, or, when i is greater than 0, specifies the difference between the frame order count values of the ( i - 1 )-th entry and the i-th entry in the stRfsIdx-th candidate short-term RFS that have frame order count values less than the frame order count value of the current picture. The value of delta_foc_sO_minusl[ i ] shall be in the range of 0 to 16, inclusive.

[00157] used_by_curr_frm_sO_flag[ i ] equal to 0 specifies that the i-th entry in the stRfsIdx-th candidate short-term RFS that has frame order count value less than that of the current picture is not used for reference by the current point cloud frame.

[00158] In an embodiment, used_by_curr_frm_sO_flag[ i ] is used to remove frames from the buffer once the frames are decoded because the frames are not used by any other frames for inter prediction. In an embodiment, this applies to preceding frames.

[00159] delta_foc_sl_minusl[ i ] plus 1, when i is equal to 0, specifies the difference between the frame order count values of the current frame and the i-th entry in the stRfsIdx-th candidate short-term RFS that has frame order count value greater than that of the current frame, or, when i is greater than 0, specifies the difference between the frame order count values of the i-th entry and the ( i - 1 )-th entry in the current candidate short-term RPS that have frame order count values greater than the frame order count value of the current frame. The value of delta_foc_sl_minusl[ i ] shall be in the range of 0 to 16, inclusive.

[00160] In an embodiment, delta_foc_sl_minusl[ i ] plus 1 indicates a difference in timestamps between frames to account for frames being removed from the buffer.

[00161] used by curr pic s 1 P ag[ i ] equal to 0 specifies that the i-th entry in the current candidate short-term RFS that has frame order count value greater than that of the current frame is not used for reference by the current point cloud frame.

[00162] In an embodiment, used_by_curr_pic_sl_flag[ i ] is used to remove frames from the buffer as above, but for subsequent frames. That is, it covers the SI list instead of the SO list for unidirectionaFbidirectional inter prediction.

[00163] When inter_ref_frm_set_prediction_flag is equal to 0, the variables NumNegativeFrames[ stRfsIdx ], NumPositiveFrames[ stRfsIdx ],

UsedByCurrPicS0[ stRfsIdx ][ i ], UsedByCurrPicSl[ stRfsIdx ][ i ],

DeltaFocS0[ stRfsIdx ][ i ] and DeltaFocSl[ stRfsIdx ][ i ] are derived as follows: NumNegativePics[ stRfsIdx ] = num negative pics

NumPositivePics[ stRfsIdx ] = num positive pics

UsedByCurrPicSO[ stRfsIdx ][ i ] = u sed by c u rr_p i c sO II ag[ i ]

UsedByCurrPicSl[ stRfsIdx ][ i ] = used_by_curr_pic_sl_flag[ i ]

- If i is equal to 0, the following applies:

DeltaFocS0[ stRfsIdx ][ i ] = -( delta_foc_sO_minusl[ i ] + 1 )

DeltaFocSl[ stRfsIdx ][ i ] = delta foc s 1 minus 1[ i ] +

- Otherwise, the following applies:

DeltaFocS0[ stRfsIdx ][ i ] = DeltaFocS0[ stRfsIdx ][ i— 1 ]— ( delta_foc_sO_minusl[ i ] + 1 ) DeltaFocSl[ stRfsIdx ][ i ] = DeltaFocSl[ stRfsIdx ][ i - 1 ] + ( delta_foc_sl_minusl[ i ] + 1 ) The variable NumDeltaFocs[ stRfsIdx ] is derived as follows:

NumDeltaFocs[ stRfsIdx ] = NumNegativePics[ stRfsIdx ] + NumPositivePics[ stRfsIdx ]

[00164] For encoding of the patch side information using this referencing structure, the following modifications of the syntax are made:

[00165] In order to simplify the encoding method of the patch side information elements, which can have both negative and positive values, it is suggested to encode sign and modulus separately using separate context models. In this case, there is no need to switch the entropy coding method often during the process.

[00166] In another embodiment, when the syntax in Table 1 and Table 2 is defined. It can be used to obtain the predicted information of the current point cloud frame.

[00167] Case 1: The information of the point cloud frame can be patch side information.

[00168] Patch side information includes but is not limited to u0,v0,ul,vl,dl, sizeUO, sizeVO, normalAxis, etc. The description of the patch auxiliary information is described in the below table.

Table 2 the description of the patch side information

[00169] For patch side information differential coding (or delta coding, the same meaning as differential coding):

[00170] ref idx corresponds to pc_patch_reference_frame_delta_idx_minusl

[00171] At encoder side:

[00172] 1. Obtain the reference point cloud frame of the current point cloud frame, such as

Reljref idx]. Ref is the frame buffer of all the possible reference point cloud frames, ref idx is the index of the reference point cloud frame.

[00173] 2. Obtain the patches buffer of Reljref idx], Ref[ re f idx]. patches; [00174] 3. Iterate each patch in the patches buffer of the current frame, then differential coding the patch auxiliary information like below: bestMatchedldx = patches[p]. bestMatchedldx;

Delta idx = i - bestMatchedldx;

Delta uO = patches[p].uO - Ref]ref_idx].patches[bestMatchedIdx].uO;

Delta vO = patches[p].vO - Ref]ref_idx].patches[bestMatchedIdx].vO;

Delta ul = patches[p].ul - RelJref_idx].patches[bestMatchedldx].u 1 :

Delta vl = patches[p].vl - Ref[ref_idx].patches[bestMatchedldx].vl :

Delta dl = patches[p].dl - Ref[ref_idx].patches[bestMatchedldx].d 1 :

Delta sizeUO = patches[p].sizeUO - Ref[ref_idx].patches[bestMatchedldx].sizeUO;

Delta sizeVO = patches[p].sizeVO - Ref[ref_idx].patches[bestMatchedldx].sizeVO;

[00175] At decoder side:

[00176] 1. Decode the index of the reference point cloud frame, ref idx.

[00177] 2. Obtain the reference point cloud frame of the current point cloud frame, such as

Reljref idx]. Ref is the frame buffer of all the possible reference point cloud frames, ref idx is the index of the reference point cloud frame.

[00178] 3. Obtain the patches buffer of Ref[ref_idx], Ref[ re f idx]. patches;

[00179] 4. Iterate each patch in the patches buffer of the current frame, then decoding the delta value of the patch auxiliary information, and obtain the patch auxiliary information like below:

patches[p].ref_idx = i - Delta idx ;

patches[p].u0 = Delta uO + Ref]ref_idx].patches[patches[p].ref_idx].uO;

patches[p].vO = Delta vO + Ref]ref_idx].patches[patches[p].ref_idx].vO;

patches[p].ul = Delta ul + Ref]ref_idx].patches[patches[p].ref_idx].ul;

patches[p].vl = Delta vl + Ref]ref_idx].patches[patches[p].ref_idx].vl;

patches[p].dl = Delta dl + Ref]ref_idx].patches[patches[p].ref_idx].dl;

patches[p].sizeU0 = Delta sizeUO + Ref]ref_idx].patches[patches[p].ref_idx].sizeUO; patches[p].sizeV0 = Delta sizeVO + Ref]ref_idx].patches[patches[p].ref_idx].sizeVO;

[00180] Delta_idx,delta_u0, delta vO, delta ul, delta vl, delta dl, delta sizeUO, delta sizeVO can be decoded by different methods. Such as expo Glomb Rice coding or arithmetic coding, while the decoding method should be compatible with encoding method. [00181] Case 2: The information can be the geometry or texture information of the point cloud.

[00182] Case 3: The ref idx in table2 can be used to automatically determine the threshold factor iou threshold when using Temporary consistent Packing method to find the matched patches in reference point cloud frame for each patch in current point cloud frame iou threshold is the threshould factor to check whether the maximum value of Intersect Over Union between current patch and candidate patch from reference point cloud frame. Below are some possible solutions:

[00183] 1. Compute the offset value: idx offset =|I - ref_idx|, where I is the index of the current frame, ref idx is the index of the reference point cloud frame idx offset can be used to indicate the distance between current frame and its reference frame.

[00184] 2. If idx offset is smaller than THR1, where THR1 is a user defined parameters, for example THR1 = 4, it means the the point cloud between the reference point cloud frame and current frame is very similar iou threshould can be set to a larger value: iou THR, for example, iou THR can be from 0.7 ~ 0.9.

[00185] If idx offset is larger than THR2, where THR2 is a user defined parameters, for example THR2 = 10, it means the the point cloud between the reference point cloud frame and current frame may be changed a lot. iou thre should can be set to a smaller value to find more matched patches: iou THR, for example, iou THR can be from 0.05 ~ 0.5.

[00186] idx offset can also be normalized based on max frame order cnt, like idx offset normalized = idx offset/ max frame order cnt. Then idx offset normalized should be in [0.0, 1.0]. Then:

[00187] If idx offset is smaller than THR3, where THR3 is a user defined parameters, for example THR1 = 0.4, it means the the point cloud between the reference point cloud frame and current frame is very similar iou thre should can be set to a larger value: iou THR, for example, iou THR can be from 0.7 ~ 0.9.

[00188] If idx offset is larger than THR4, where THR4 is a user defined parameters, for example THR4 = 0.6, it means the the point cloud between the reference point cloud frame and current frame may be changed a lot. iou thre should can be set to a smaller value to find more matched patches: iou THR, for example, iou THR can be from 0.05 ~ 0.5.

[00189] In a more generalized way, the iou THR can be a function of idx offset. For example, Iou THR = f(iou_THR), one possible solution is f(x) = alpha*e^A(-beta*x). Alpha and beta parameter are user defined parameters. [00190] While several embodiments have been provided in the present disclosure, it may be understood that the disclosed systems and methods might be embodied in many other specific forms without departing from the spirit or scope of the present disclosure. The present examples are to be considered as illustrative and not restrictive, and the intention is not to be limited to the details given herein. For example, the various elements or components may be combined or integrated in another system or certain features may be omitted, or not implemented.

[00191] In addition, techniques, systems, subsystems, and methods described and illustrated in the various embodiments as discrete or separate may be combined or integrated with other systems, components, techniques, or methods without departing from the scope of the present disclosure. Other examples of changes, substitutions, and alterations are ascertainable by one skilled in the art and may be made without departing from the spirit and scope disclosed herein.

Claims

CLAIMS What is claimed is:

1. A method of point cloud coding (PCC) implemented by a decoder, comprising:

receiving, by a receiver of the decoder, a bitstream having atlas frames that each contain a point cloud, wherein at least one of the atlas frames is received out of presentation order;

obtaining, by a processor of the decoder, an atlas type and an atlas order count from each of the atlas frames;

determining, by the processor, the presentation order of the atlas frames based on the atlas type and the atlas order count obtained from each of the atlas frames; and

decoding, by the processor, the atlas frames in the presentation order.

2. The method of claim 1, wherein the atlas type indicates whether an atlas frame is a key atlas frame, an intra prediction atlas frame, or an inter prediction atlas frame.

3. The method of any of claims 1 to 2, wherein the atlas type is designated pc frame type.

4. The method of any of claims 1 to 3, wherein the atlas order count indicates a position of an atlas frame in the presentation order.

5. The method of any of claims 1 to 4, wherein the atlas order count is designated pc frame order cnt.

6. The method of any of claims 1 to 5, further comprising obtaining a reference frame identifier from at least one of the atlas frames, the reference frame identifier identifying a reference frame for an atlas frame currently being decoded.

7. The method of claim 6, wherein the reference frame identifier is designated pc_patch_reference_frame_delta_idx_minus 1.

8. The method of any of claims 6 to 7, further comprising resetting picture parameter set parameters to a default value and cleaning a reference frame buffer when the atlas type indicates an atlas frame is a key atlas frame.

9. The method of any of claims 6 to 8, wherein the reference frame identifier is able to reference any reference frame within a reference frame buffer.

10. The method of any of claims 1 to 9, wherein the atlas type and the atlas order count are contained in an atlas frame parameter set of the bitstream.

11. A method of point cloud coding (PCC) implemented by an encoder, comprising: dividing, by a processor of the encoder, a three dimensional image into point clouds; assigning, by the processor, an atlas type and an atlas order count to each of the point clouds;

encoding, by the processor, the point clouds into atlas frames, wherein at least one of the atlas frames is encoded out of presentation order; and

storing, in a memory of the encoder, the atlas frames in a bitstream for transmission toward a decoder.

12. The method of claim 11, wherein the atlas type indicates whether an atlas frame is a key atlas frame, an intra prediction atlas frame, or an inter prediction atlas frame.

13. The method of any of claims 11 to 12, wherein the atlas type is designated pc frame type.

14. The method of any of claims 11 to 13, wherein the atlas order count indicates a position of an atlas frame in the presentation order.

15. The method of any of claims 11 to 14, wherein the atlas order count is designated pc frame order cnt.

16. The method of any of claims 11 to 15, further comprising obtaining a reference frame identifier from at least one of the atlas frames, the reference frame identifier identifying a reference frame for an atlas frame currently being decoded.

17. The method of claim 16, wherein the reference frame identifier is designated pc_patch_reference_frame_delta_idx_minus 1.

18. The method of any of claims 16 to 17, further comprising resetting picture parameter set parameters to a default value and cleaning a reference frame buffer when the atlas type indicates an atlas frame is a key atlas frame.

19. The method of any of claims 16 to 18, wherein the reference frame identifier is able to reference any reference frame within a reference frame buffer.

20. The method of any of claims 11 to 19, wherein the atlas type and the atlas order count are contained in an atlas frame parameter set of the bitstream.

21. A coding apparatus, comprising:

a receiver configured to receive a volumetric picture to encode or to receive a bitstream to decode;

a transmitter coupled to the receiver, the transmitter configured to transmit the bitstream to a decoder or to transmit a decoded volumetric image to a reconstruction device configured to reconstruct the decoded volumetric picture;

a memory coupled to at least one of the receiver or the transmitter, the memory configured to store instructions; and

a processor coupled to the memory, the processor configured to execute the instructions stored in the memory to perform the method in any of claims 1 to 20.

22. The coding apparatus of claim 21, further comprising a display configured to display a projected image based on the decoded volumetric picture.

23. A system, comprising:

an encoder; and

a decoder in communication with the encoder, wherein the encoder or the decoder includes the coding apparatus of any of claims 21 to 22.

24. The system of claim 23, further comprising a reconstruction module in communication with the decoder, the reconstruction module configured to project a reconstructed volumetric image.

25. A means for coding, comprising:

receiving means configured to receive a volumetric picture to encode or to receive a bitstream to decode, reconstruct, and project;

transmission means coupled to the receiving means, the transmission means configured to transmit the bitstream to a decoder or to transmit a decoded image to a display means;

storage means coupled to at least one of the receiving means or the transmission means, the storage means configured to store instructions; and

processing means coupled to the storage means, the processing means configured to execute the instructions stored in the storage means to perform the method in any of claims 1 to 20.