Coefficient level escape codec

Abstract

As part of bypass decoding of a syntax element of a coefficient set in response to reaching a maximum number of conventional codec bins, the video decoder is configured to receive a prefix value for a transform coefficient; decode the prefix value using a Golomb‑Rice codec; receive a suffix value for the transform coefficient in response to a length of the prefix value being equal to a threshold; decode the suffix value using an exponential Golomb codec; and determine a level value for the transform coefficient based on the decoded prefix value and the decoded suffix value.

Description

[0001] This application claims priority to U.S. Patent Application No. 16 / 732,008, filed on December 31, 2019, which claims priority to U.S. Provisional Application No. 62 / 787,707, filed on January 2, 2019, the entire contents of each of which are incorporated herein by reference. Technical Field

[0002] The present disclosure relates to video encoding and video decoding. Background Art

[0003] Digital video capabilities may be integrated into a variety of devices, including digital televisions, digital direct broadcast systems, wireless broadcast systems, personal digital assistants (PDAs), laptop or desktop computers, tablet computers, e-book readers, digital cameras, digital recording devices, digital media players, video game devices, video game consoles, cellular or satellite radio telephones, so-called "smart phones", video teleconferencing devices, video streaming devices, etc. Digital video devices implement video codec technologies, such as those described in MPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264 / MPEG-4, Part 10, Advanced Video Codec (AVC), High Efficiency Video Codec (HEVC) standards, standards specified in ITU-T H.265 / High Efficiency Video Codec (HEVC), and extensions of such standards. By implementing such video codec technologies, video devices can more efficiently send, receive, encode, decode and / or store digital video information.

[0004] Video coding techniques include spatial (intra-picture) prediction and / or temporal (inter-picture) prediction to reduce or eliminate redundancy inherent in video sequences. For block-based video coding, a video slice (e.g., a video picture or a portion of a video picture) may be partitioned into video blocks, which may also be referred to as codec tree units (CTUs), codec units (CUs), and / or codec nodes. Video blocks in an intra-frame codec (I) slice of a picture are encoded using spatial predictions about reference samples in neighboring blocks in the same picture. Video blocks in an inter-frame codec (P or B) slice of a picture may use spatial predictions about reference samples in neighboring blocks in the same picture, or temporal predictions about reference samples in other reference pictures. Pictures may be referred to as frames, and reference pictures may be referred to as reference frames. Summary of the invention

[0005] Video coding (e.g., video encoding and / or video decoding) generally involves predicting a block of video data based on an already coded block of video data in the same picture (e.g., intra-frame prediction) or an already coded block of video data in a different picture (e.g., inter-frame prediction). In some cases, the video encoder also calculates residual data by comparing the predicted block with the original block. Therefore, the residual data represents the difference between the predicted block and the original block of video data. In order to reduce the number of bits required to signal the residual data, the video encoder transforms the residual data into transform coefficients, quantizes the transform coefficients, and signals the transformed and quantized coefficients in the encoded bitstream. The compression achieved by the transform and quantization process may be lossy, which means that the transform and quantization process may introduce distortion to the decoded video data. The present disclosure describes techniques related to transform coefficient coding, and more specifically, to a combination of Golomb-Rice and exponential Golomb coding. The techniques of the present disclosure can improve the coding efficiency of transform coefficients by reducing the number of bits required to signal the transform coefficients on average. Techniques of this disclosure may additionally limit worst-case encoding and decoding scenarios associated with signaling transform coefficients.

[0006] According to an example of the present disclosure, a method for decoding video data includes: context decoding a syntax element of a first transform coefficient set of a transform coefficient group until a maximum number of conventional codec binary bits is reached, wherein the context-decoded syntax element includes one or more importance flags, one or more parity level flags, and one or more first flags, wherein each of the one or more importance flags indicates whether an absolute level of the transform coefficient is equal to zero, each of the one or more parity level flags indicates whether the absolute level of the transform coefficient is an even number or an odd number, and each of the one or more first flags indicates whether the absolute level of the transform coefficient is greater than 2; in response to reaching the conventional codec binary number, The invention relates to a method for bypassing decoding an additional syntax element of a second coefficient set according to a context-controlled maximum number of bits, wherein the bypass decoding of the additional syntax element includes receiving a prefix value of the transform coefficient; decoding the prefix value using a Golomb-Rice codec; in response to a length of the prefix value being equal to a threshold, receiving a suffix value of the transform coefficient; decoding the suffix value using an exponential Golomb codec; determining a value of a first coefficient set of the transform unit based on the syntax element decoded by the context; and determining a value of a second coefficient set of the transform unit based on the additional syntax element, wherein determining the value of the second coefficient set of the transform unit based on the additional syntax element includes determining a level value of the transform coefficient based on the decoded prefix value and the decoded suffix value.

[0007] According to another example of the present disclosure, a device for decoding video data includes: a memory configured to store video data, and one or more processors implemented in a circuit and configured to perform the following operations: context decoding a syntax element of a first coefficient set of a transform coefficient group until a maximum number of conventional codec binary bits is reached, wherein the context-decoded syntax element includes one or more importance flags, one or more parity level flags, and one or more first flags, wherein each of the one or more importance flags indicates whether an absolute level of the transform coefficient is equal to zero, each of the one or more parity level flags indicates whether an absolute level of the transform coefficient is an even number or an odd number, and each of the one or more first flags indicates whether an absolute level of the transform coefficient is greater than 2; in response to reaching The invention relates to a method for bypassing decoding an additional syntax element of a second set of coefficients by using a conventional codec to determine the maximum number of binary bits of a conventional codec, wherein in order to bypass decoding the additional syntax element, the one or more processors are configured to: receive a prefix value of a transform coefficient; decode the prefix value using a Golomb-Rice codec; in response to a length of the prefix value being equal to a threshold, receive a suffix value of the transform coefficient; decode the suffix value using an exponential Golomb codec; determine a value of a first set of coefficients of a transform unit based on the syntax element decoded by the context; and determine a value of a second set of coefficients of the transform unit based on the additional syntax element, wherein in order to determine the value of the second set of coefficients of the transform unit based on the additional syntax element, the one or more processors are configured to: determine a level value of the transform coefficient based on the decoded prefix value and the decoded suffix value.

[0008] According to another example of the present disclosure, a computer-readable storage medium storing instructions, which, when executed by one or more processors, causes the one or more processors to context-decode syntax elements of a first transform coefficient set of a transform coefficient group until a maximum number of conventionally encoded binary bits is reached, wherein the context-decoded syntax elements include one or more importance flags, one or more parity level flags, and one or more first flags, wherein each of the one or more importance flags indicates whether an absolute level of the transform coefficient is equal to zero, each of the one or more parity level flags indicates whether an absolute level of the transform coefficient is an even number or an odd number, and each of the one or more first flags indicates whether an absolute level of the transform coefficient is greater than 2; in response to reaching to a maximum number of conventional codec binary bits, bypass decoding additional syntax elements of a second set of coefficients, wherein to bypass decoding the additional syntax elements, the instructions cause the one or more processors to receive a prefix value for the transform coefficient; decode the prefix value using a Golomb-Rice codec; in response to a length of the prefix value being equal to a threshold, receive a suffix value for the transform coefficient; decode the suffix value using an exponential Golomb codec; determine a value of a first set of coefficients of the transform unit based on the syntax elements decoded from the context; and determine a value of a second set of coefficients of the transform unit based on the additional syntax elements, wherein determining the value of the second set of coefficients of the transform unit based on the additional syntax elements includes determining a level value of the transform coefficient based on the decoded prefix value and the decoded suffix value.

[0009] According to another example of the present disclosure, a device for decoding video data includes: a component for context decoding a syntax element of a first transform coefficient set of a transform coefficient group until a maximum number of conventional codec binary bits is reached, wherein the context-decoded syntax element includes one or more importance flags, one or more parity level flags, and one or more first flags, wherein each of the one or more importance flags indicates whether an absolute level of the transform coefficient is equal to zero, each of the one or more parity level flags indicates whether the absolute level of the transform coefficient is an even number or an odd number, and each of the one or more first flags indicates whether the absolute level of the transform coefficient is greater than 2; and a component for context decoding a syntax element of a first transform coefficient set of a transform coefficient group until a maximum number of conventional codec binary bits is reached. The invention relates to a method for bypass decoding an additional syntax element of a transform unit, wherein the means for bypass decoding the additional syntax element comprises means for receiving a prefix value of a transform coefficient; means for decoding the prefix value using a Golomb-Rice codec; means for receiving a suffix value of the transform coefficient in response to a length of the prefix value being equal to a threshold; means for decoding the suffix value using an exponential Golomb codec; means for determining a value of a first set of coefficients of a transform unit based on the syntax element decoded by the context; and means for determining a value of a second set of coefficients of the transform unit based on the additional syntax element, wherein determining the value of the second set of coefficients of the transform unit based on the additional syntax element comprises determining a level value of the transform coefficient based on the decoded prefix value and the decoded suffix value.

[0010] According to another example of the present disclosure, a method for encoding video data includes: determining values ​​of coefficients of a transform coefficient group; context encoding syntax elements of a first transform coefficient set of the transform coefficient group until a maximum number of conventional codec binary bits is reached, wherein the context-coded syntax elements include one or more importance flags, one or more parity level flags, and one or more first flags, wherein each of the one or more importance flags indicates whether an absolute level of the transform coefficient is equal to zero, each of the one or more parity level flags indicates whether the absolute level of the transform coefficient is even or odd, and each of the one or more first flags indicates whether the absolute level of the transform coefficient is greater than 2; in response to reaching the maximum number of conventional codec binary bits, bypass encoding additional syntax elements of a second coefficient set of the transform coefficient group, wherein bypass encoding the additional syntax elements includes determining level values ​​of the transform coefficients of the second coefficient set; in response to the level value being greater than a threshold, encoding a prefix value of the transform coefficient using Golomb-Rice codec; and in response to the level value being greater than the threshold, encoding a suffix value using exponential Golomb codec.

[0011] According to another example of the present disclosure, a device for encoding video data includes a memory configured to store video data, and one or more processors implemented in a circuit and configured to perform the following operations: determining values ​​of coefficients of a transform coefficient group, context encoding syntax elements of a first set of coefficients of the transform coefficient group until a maximum number of conventional codec binary bits is reached, wherein the context-coded syntax elements include one or more significance flags, one or more parity level flags, and one or more first flags, wherein each of the one or more significance flags indicates whether an absolute level of the transform coefficient is equal to zero, each of the one or more parity level flags indicates whether the absolute level of the transform coefficient is even or odd, and each of the one or more first flags indicates whether the absolute level of the transform coefficient is greater than 2; in response to reaching the maximum number of conventional codec binary bits, bypass encoding additional syntax elements of a second set of coefficients of the transform coefficient group, wherein bypass encoding the additional syntax elements includes determining level values ​​of the transform coefficients of the second set of coefficients; in response to the level value being greater than a threshold, encoding a prefix value of the transform coefficient using Golomb-Rice codec; and in response to the level value being greater than the threshold, encoding a suffix value using exponential Golomb codec.

[0012] According to another example of the present disclosure, a computer-readable storage medium storing instructions, when the instructions are executed by one or more processors, causes the one or more processors to: determine the values ​​of coefficients of a transform coefficient group; context-code syntax elements of a first set of coefficients of the transform coefficient group until a maximum number of conventional codec binary bits is reached, wherein the context-coded syntax elements include one or more significance flags, one or more parity level flags, and one or more first flags, wherein each of the one or more significance flags indicates whether an absolute level of the transform coefficient is equal to zero, each of the one or more parity level flags indicates whether the absolute level of the transform coefficient is even or odd, and each of the one or more first flags indicates whether the absolute level of the transform coefficient is greater than 2; in response to reaching the maximum number of conventional codec binary bits, bypass-code additional syntax elements of a second set of coefficients of the transform coefficient group, wherein in order to bypass-code the additional syntax elements, the instructions cause the one or more processors to determine the level values ​​of the transform coefficients of the second set of coefficients; in response to the level value being greater than a threshold, encode the prefix value of the transform coefficient using Golomb-Rice codec; and in response to the level value being greater than the threshold, encode the suffix value using exponential Golomb codec.

[0013] According to another example of the present disclosure, an apparatus for encoding video data includes: a component for determining values ​​of coefficients of a transform coefficient group; a component for context encoding syntax elements of a first transform coefficient set of the transform coefficient group until a maximum number of conventional codec binary bits is reached, wherein the context-coded syntax elements include one or more significance flags, one or more parity level flags, and one or more first flags, wherein each of the one or more significance flags indicates whether an absolute level of the transform coefficient is equal to zero, each of the one or more parity level flags indicates whether the absolute level of the transform coefficient is even or odd, and each of the one or more first flags indicates whether the absolute level of the transform coefficient is greater than 2; a component for bypass encoding additional syntax elements of a second coefficient set of the transform coefficient group in response to reaching the maximum number of conventional codec binary bits, wherein the component for bypass encoding the additional syntax elements includes a component for determining level values ​​of the transform coefficients of the second coefficient set; a component for encoding prefix values ​​of the transform coefficients using Golomb-Rice codec in response to the level value being greater than a threshold; and a component for encoding suffix values ​​using exponential Golomb codec in response to the level value being greater than the threshold.

[0014] One or more examples will be described in detail in the accompanying drawings and the following description. Other features, objects, and advantages will be apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a block diagram illustrating an example video encoding and decoding system that may perform the techniques of this disclosure.

[0016] Figure 2A and Figure 2B is a conceptual diagram illustrating an example quadtree binary tree (QTBT) structure and a corresponding codec tree unit (CTU).

[0017] Figure 3 An example order of syntax elements for representing an absolute level (absLevel) in a codec group (CG) is illustrated.

[0018] Figure 4 A diagram illustrating a template for selecting a probabilistic model.

[0019] Figure 5 is a block diagram illustrating an example video encoder that may perform the techniques of this disclosure.

[0020] Figure 6 is a block diagram illustrating an example video decoder that may perform the techniques of this disclosure.

[0021] Fig. 7A and7B is a conceptual diagram illustrating a range update process in binary arithmetic coding and decoding.

[0022] Figure 8 is a conceptual diagram showing an output process in binary arithmetic coding and decoding.

[0023] Fig. 9 is a block diagram illustrating a Context-Adaptive Binary Arithmetic Coding and Decoding (CABAC) codec in a video encoder.

[0024] Fig.10 is a block diagram illustrating a CABAC codec in a video decoder.

[0025] Fig.11 is a flow chart illustrating example operation of a video encoder.

[0026] Fig.12 is a flow chart illustrating example operation of a video decoder.

[0027] Fig.13 is a flow diagram illustrating example operation of a video encoder to encode a current block of video data.

[0028] Fig.14 The video encoder is shown Fig.13 Flowchart of example operations for bypass encoding additional syntax elements for a second set of coefficients of a transform coefficient group in FIG.

[0029] Fig.15 is a flow diagram illustrating example operation of a video decoder to decode a current block of video data.

[0030] Fig.16 The video decoder is shown Fig.15 Flowchart of example operations for bypass decoding additional syntax elements for a second set of coefficients in a coefficient group. DETAILED DESCRIPTION

[0031] Video coding (e.g., video encoding and / or video decoding) typically involves predicting a block of video data based on an already coded block of video data in the same picture (e.g., intra-frame prediction) or an already coded block of video data in a different picture (e.g., inter-frame prediction). In some cases, the video encoder also calculates residual data by comparing the predicted block with the original block. Therefore, the residual data represents the difference between the predicted block and the original block of video data. In order to reduce the number of bits required to signal the residual data, the video encoder transforms and quantizes the residual data and signals the transformed and quantized residual data in the encoded bitstream. The compression achieved by the transform and quantization process may be lossy, which means that the transform and quantization process may introduce distortion to the decoded video data.

[0032] The video decoder decodes the residual data and adds it to the prediction block to produce a reconstructed video block that more closely matches the original video block than the prediction block alone could. The reconstructed block may have distortion or artifacts due to losses introduced by the transformation and quantization of the residual data. One common type of artifact or distortion is called blocking, where the boundaries of the blocks used to encode and decode the video data are visible.

[0033] To further improve the quality of the decoded video, the video decoder may perform one or more filtering operations on the reconstructed video blocks. Examples of these filtering operations include deblocking filtering, sample adaptive offset (SAO) filtering, and adaptive loop filtering (ALF). The parameters of these filtering operations may be determined by the video encoder and explicitly signaled in the encoded video bitstream, or may be implicitly determined by the video decoder without explicitly signaling these parameters in the encoded video bitstream.

[0034] As described above, the video encoder transforms the residual data to produce transform coefficients. These transform coefficients may be additionally quantized. In the present disclosure, the term "transform coefficient" or "coefficient" may refer to a quantized transform coefficient or an unquantized transform coefficient. The present disclosure describes techniques for signaling transform coefficients, such as the values ​​of quantized transform coefficients, from a video encoder to a video decoder. Such techniques include techniques related to an entropy decoding process for converting a binary representation of bits into a series of non-binary valued quantized transform coefficients. More specifically, the present disclosure describes techniques for encoding and decoding escape codes for non-contextual encoding and decoding portions representing coefficient levels, which are instead encoded and decoded as a Golomb-Rice / exponential Golomb combination. The present disclosure also describes a corresponding entropy encoding process, which is typically the inverse process of entropy decoding.

[0035] The techniques of this disclosure may be implemented in conjunction with techniques of existing video codecs, such as High Efficiency Video Codec (HEVC), or included as part of future video codecs, such as the Versatile Video Codec (VVC) standard currently under development.

[0036] Figure 1 1 is a block diagram illustrating an example video encoding and decoding system 100 that may perform the techniques of the present disclosure. The techniques of the present disclosure are generally directed to encoding and decoding (encoding and / or decoding) video data. Typically, video data includes any data used to process video. Thus, video data may include original, unencoded video, encoded video, decoded (e.g., reconstructed) video, and video metadata, such as signaling data.

[0037] like Figure 1As shown, in this example, the system 100 includes a source device 102, which provides encoded video data to be decoded and displayed by a destination device 116. Specifically, the source device 102 provides the video data to the destination device 116 via a computer-readable medium 110. The source device 102 and the destination device 116 can be any of a variety of devices, including a desktop computer, a notebook computer (i.e., a laptop computer), a tablet computer, a set-top box, a telephone handset such as a smart phone, a television, a camera, a display device, a digital media player, a video game console, a video streaming device, or the like. In some cases, the source device 102 and the destination device 116 can be equipped for wireless communication and can therefore be referred to as wireless communication devices.

[0038] exist Figure 1 In the example of, source device 102 comprises video source 104, memory 106, video encoder 200 and output interface 108. Destination device 116 comprises input interface 122, video decoder 300, memory 120 and display device 118. According to the present disclosure, the video encoder 200 of source device 102 and the video decoder 300 of destination device 116 can be configured to apply the technology for coefficient coding and decoding described in the present disclosure. Therefore, source device 102 represents an example of video encoding device, and destination device 116 represents an example of video decoding device. In other examples, source device and destination device can include other components or configurations. For example, source device 102 can receive video data from an external video source such as an external camera. Similarly, destination device 116 can be connected to an external display device without including an integrated display device.

[0039] Figure 1 The system 100 shown is only an example. In general, any digital video encoding and / or decoding device can perform the coefficient coding and decoding techniques described herein. The source device 102 and the destination device 116 are only examples of such coding and decoding devices in which the source device 102 generates coded and decoded video data for transmission to the destination device 116. The present disclosure uses a "coding" device to refer to a device that performs coding (coding and / or decoding) of data. Therefore, the video encoder 200 and the video decoder 300 represent examples of coding and decoding devices, specifically, examples of video encoders and video decoders, respectively. In some examples, the source device 102 and the destination device 116 can operate in a substantially symmetrical manner, so that each of the source device 102 and the destination device 116 includes a video coding and decoding component. Therefore, the system 100 can support one-way or two-way video transmission between the source device 102 and the destination device 116, such as for video streaming, video playback, video broadcasting, or video telephony.

[0040] Typically, video source 104 represents a source of video data (i.e., original, unencoded video data) and provides a series of sequential pictures (also referred to as "frames") of video data to video encoder 200, which encodes the data of the pictures. Video source 104 of source device 102 may include a video capture device, such as a video camera, a video archive containing previously captured original video, and / or a video feed interface receiving video from a video content provider. As another alternative, video source 104 may generate computer graphics-based data as source video, or a combination of live video, archived video, and computer-generated video. In each case, video encoder 200 encodes captured, pre-captured, or computer-generated video data. Video encoder 200 may rearrange pictures from the received order (sometimes referred to as "display order") to a codec order for encoding and decoding. Video encoder 200 may generate a bitstream comprising encoded video data. Source device 102 may then output the encoded video data onto computer-readable medium 110 via output interface 108 for receipt and / or retrieval by, for example, input interface 122 of destination device 116 .

[0041] The memory 106 of the source device 102 and the memory 120 of the destination device 116 represent general purpose memory. In some examples, the memory 106, 120 can store original video data, such as the original video from the video source 104 and the original decoded video data from the video decoder 300. Additionally or alternatively, the memory 106, 120 can store software instructions that can be executed by, for example, the video encoder 200 and the video decoder 300, respectively. Although the memory 106 and the memory 120 are shown as being separated from the video encoder 200 and the video decoder 300 in this example, it should be understood that the video encoder 200 and the video decoder 300 can also include internal memory for functionally similar or equivalent purposes. In addition, the memory 106, 120 can store encoded video data, such as encoded video data output from the video encoder 200 and input to the video decoder 300. In some examples, a portion of the memory 106, 120 can be allocated as one or more video buffers, for example, to store original, decoded and / or encoded video data.

[0042] The computer-readable medium 110 may represent any type of medium or device capable of transmitting the encoded video data from the source device 102 to the destination device 116. In one example, the computer-readable medium 110 represents a communication medium that enables the source device 102 to directly send the encoded video data to the destination device 116 in real time via, for example, a radio frequency network or a computer-based network. According to a communication standard such as a wireless communication protocol, the output interface 108 may modulate a transmission signal including the encoded video data, and the input interface 122 may demodulate the received transmission signal. The communication medium may include 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 a portion in 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 a router, a switch, a base station, or any other equipment that may help facilitate communication from the source device 102 to the destination device 116.

[0043] In some examples, source device 102 may output the encoded data from output interface 108 to storage device 112. Similarly, destination device 116 may access the encoded data from storage device 112 via input interface 122. Storage device 112 may include any of a variety of distributed or locally accessed data storage media, such as a hard drive, Blu-ray disc, DVD, CD-ROM, flash memory, volatile or non-volatile memory, or any other suitable digital storage medium for storing encoded video data.

[0044] In some examples, source device 102 may output the encoded video data to file server 114 or another intermediate storage device that may store the encoded video generated by source device 102. Destination device 116 may access the stored video data from file server 114 via streaming or downloading. File server 114 may be any type of server device capable of storing encoded video data and transmitting the encoded video data to destination device 116. File server 114 may represent a web server (e.g., for a website), a file transfer protocol (FTP) server, a content delivery network device, or a network attached storage (NAS) device. Destination device 116 may access the encoded video data from file server 114 via 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., a digital subscriber line (DSL), a cable modem, etc.), or a combination of both that are suitable for accessing the encoded video data stored on file server 114. File server 114 and input interface 122 may be configured to operate according to a streaming protocol, a downloading transmission protocol, or a combination thereof.

[0045] Output interface 108 and input interface 122 may represent wireless transmitters / receivers, modems, wired network components (e.g., Ethernet cards), wireless communication components that operate according to any of the various IEEE 802.11 standards, or other physical components. In examples where output interface 108 and input interface 122 include wireless components, output interface 108 and input interface 122 may be configured to transmit data, such as encoded video data, according to a cellular communication standard such as 4G, 4G-LTE (Long Term Evolution), Advanced LTE, 5G, etc. In some examples where output interface 108 includes a wireless transmitter, output interface 108 and input interface 122 may be configured to transmit data, such as encoded video data, according to a cellular communication standard such as IEEE 802.11 specifications, IEEE802.15 specifications (e.g., ZigBee TM ), Bluetooth TM 108, and the like. The source device 102 and / or the destination device 116 may include respective system-on-chip (SoC) devices. For example, the source device 102 may include a SoC device that performs functions belonging to the video encoder 200 and / or the output interface 108, and the destination device 116 may include a SoC device that performs functions belonging to the video decoder 300 and / or the input interface 122.

[0046] The techniques disclosed herein can be applied to video encoding and decoding to support any of a variety of multimedia applications, such as over-the-air television broadcasting, cable television transmission, satellite television transmission, Internet streaming video transmission such as Dynamic Adaptive Streaming over HTTP (DASH), digital video encoded onto data storage media, decoding of digital video stored on data storage media, or other applications.

[0047] The input interface 122 of the destination device 116 receives the encoded video bitstream from the computer-readable medium 110 (e.g., a communication medium, a storage device 112, a file server 114, etc.). The encoded video bitstream may include signaling information defined by the video encoder 200, which is also used by the video decoder 300, such as syntax elements with values ​​describing characteristics and / or processing of video blocks or other codec units (e.g., slices, pictures, groups of pictures, sequences, etc.). The display device 118 displays decoded pictures of the decoded video data to a user. The display device 118 may represent 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.

[0048] Although in Figure 12, but in some examples, the video encoder 200 and the video decoder 300 may each be integrated with an audio encoder and / or an audio decoder and may include appropriate MUX-DEMUX units or other hardware and / or software to process a multiplexed stream including both audio and video in a common data stream. If applicable, the MUX-DEMUX unit may be in accordance with the ITU H.223 multiplexer protocol or other protocols such as the User Datagram Protocol (UDP).

[0049] The video encoder 200 and the video decoder 300 can be implemented as any of a variety of suitable encoder and / or decoder circuits, 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 combination thereof. When these techniques are partially implemented in software, the device can store the instructions of the software in a suitable non-temporary computer-readable medium, and use one or more processors to run these instructions in hardware to perform the techniques of the present disclosure. Each of the video encoder 200 and the video decoder 300 can be included in one or more encoders or decoders, any of which can be integrated as part of a combined encoder / decoder (CODEC) in a corresponding device. The device including the video encoder 200 and / or the video decoder 300 can include an integrated circuit, a microprocessor, and / or a wireless communication device such as a cellular phone.

[0050] The video encoder 200 and the video decoder 300 may operate according to a video codec standard, such as ITU-T H.265 (also known as High Efficiency Video Codec (HEVC)) or its extensions such as multi-view and / or scalable video codec extensions. Alternatively, the video encoder 200 and the video decoder 300 may operate according to other proprietary or industry standards, such as the Joint Exploration Test Model (JEM) or ITU-T H.266, also known as Versatile Video Codec (VVC). The latest draft of the VVC standard is described in "Versatile Video Coding (Draft 6)" of the 15th meeting of the Joint Video Experts Group (JVET) of ITU-T SG 16WP 3 and ISO / IEC JTC 1 / SC 29 / WG 11 in Gothenburg by Bross et al. (hereinafter referred to as "VVC Draft 6") from July 3 to 12, 2019. However, the technology of the present disclosure is not limited to any particular codec standard.

[0051] Typically, the video encoder 200 and the video decoder 300 can perform block-based picture encoding and decoding. The term "block" generally refers to a structure that includes data to be processed (e.g., encoded, decoded, or otherwise used in an encoding and / or decoding process). For example, a block may include a two-dimensional matrix of samples of luminance and / or chrominance data. Typically, the video encoder 200 and the video decoder 300 can encode and decode video data represented in a YUV (e.g., Y, Cb, Cr) format. That is, the video encoder 200 and the video decoder 300 can encode and decode luminance and chrominance components instead of encoding and decoding red, green, and blue (RGB) data of the picture samples, where the chrominance components may include both red hue and blue hue chrominance components. In some examples, the video encoder 200 converts the received RGB format data into a YUV representation before encoding, and the video decoder 300 converts the YUV representation into an RGB format. Alternatively, a pre-processing and post-processing unit (not shown) may perform these conversions.

[0052] The present disclosure may generally relate to the encoding and decoding of pictures (e.g., encoding and decoding), including the process of encoding or decoding the data of a picture. Similarly, the present disclosure may relate to the encoding and decoding of blocks of a picture, including the process of encoding or decoding the data of the block, such as prediction and / or residual encoding and decoding. The encoded video bitstream generally includes a series of values ​​of syntax elements that represent codec decisions (e.g., codec modes) and partitioning of the picture into blocks. Therefore, references to a coded picture or block should generally be understood as the values ​​of the syntax elements that encode the picture or block.

[0053] HEVC defines various blocks, including codec units (CUs), prediction units (PUs), and transform units (TUs). According to HEVC, a video codec (such as the video encoder 200) partitions a codec tree unit (CTU) into multiple CUs according to a quadtree structure. That is, the video codec partitions the CTU and CU into four equal, non-overlapping squares, and each node of the quadtree has zero or four child nodes. A node without child nodes may be referred to as a "leaf node", and the CU of such a leaf node may include one or more PUs and / or one or more TUs. The video codec may further partition the PU and TU. For example, in HEVC, the residual quadtree (RQT) represents the partitioning of the TU. In HEVC, PU represents inter-frame prediction data, and TU represents residual data. The intra-predicted CU includes intra-frame prediction information, such as an intra-frame mode indication.

[0054] As another example, the video encoder 200 and the video decoder 300 may be configured to operate according to JEM or VVC. According to JEM or VVC, a video codec (such as the video encoder 200) partitions a picture into multiple codec tree units (CTUs). The video encoder 200 may partition the CTU according to a tree structure, such as a quadtree binary tree (QTBT) structure or a multi-type tree (MTT) structure. The QTBT structure removes the concept of multiple partition types, such as the separation between CU, PU, ​​and TU of HEVC. The QTBT structure includes two levels: a first level partitioned according to quadtree partitioning, and a second level partitioned according to binary tree partitioning. The root node of the QTBT structure corresponds to the CTU. The leaf nodes of the binary tree correspond to codec units (CUs).

[0055] In the MTT partitioning structure, blocks can be partitioned using quadtree (QT) partitioning, binary tree (BT) partitioning, and one or more ternary tree (TT) (also known as ternary tree (TT)) partitioning. Trinary or ternary tree partitioning is a partitioning that divides a block into three sub-blocks. In some examples, the ternary or ternary tree partitioning divides the block into three sub-blocks without dividing the original block by the center. The partitioning types in MTT (e.g., QT, BT, and TT) can be symmetric or asymmetric.

[0056] In some examples, the video encoder 200 and the video decoder 300 may use a single QTBT or MTT structure to represent each of the luma and chroma components, while in other examples, the video encoder 200 and the video decoder 300 may use two or more QTBT or MTT structures, such as one QTBT / MTT structure for the luma component and another QTBT / MTT structure for the two chroma components (or two QTBT / MTT structures for corresponding chroma components).

[0057] The video encoder 200 and the video decoder 300 may be configured to use quadtree segmentation, QTBT segmentation, MTT segmentation, or other segmentation structures in accordance with HEVC. For illustrative purposes, the description of the disclosed technology is presented for QTBT segmentation. However, it should be understood that the disclosed technology may also be applied to a video codec configured to use quadtree segmentation or other types of segmentation.

[0058] Blocks (e.g., CTUs or CUs) may be grouped in a picture in various ways. As an example, a brick may refer to a rectangular area of ​​a CTU row within a particular tile in a picture. A slice may be a rectangular area of ​​a CTU within a particular slice column and a particular slice row in a picture. A slice column refers to a rectangular area of ​​a CTU having a height equal to the height of the picture and a width specified by a syntax element (e.g., in a picture parameter set). A slice row refers to a rectangular area of ​​a CTU having a height specified by a syntax element (e.g., in a picture parameter set) and a width equal to the width of the picture.

[0059] In some examples, a slice may be partitioned into multiple bricks, each of which may include one or more CTU rows within the slice. A slice that is not partitioned into multiple bricks may also be referred to as a brick. However, a brick that is a proper subset of a slice cannot be referred to as a slice.

[0060] The tiles in a picture may also be arranged in slices. A slice may be an integer number of tiles of a picture that may be contained exclusively in a single network abstraction layer (NAL) unit. In some examples, a slice includes a continuous sequence of multiple complete slices or only complete tiles of a slice.

[0061] This disclosure may use "NxN" and "N by N" interchangeably to refer to the sample size of a block (such as a CU or other video block) in the vertical and horizontal dimensions, for example, 16×16 samples or 16 by 16 samples. Typically, a 16x16 CU will have 16 samples in the vertical direction (y=16) and 16 samples in the horizontal direction (x=16). Similarly, an NxN CU typically has N samples in the vertical direction and N samples in the horizontal direction, where N represents a non-negative integer value. The samples in a CU may be arranged in rows and columns. In addition, a CU does not necessarily need to have the same number of samples in the horizontal direction and in the vertical direction. For example, a CU may include NxM samples, where M is not necessarily equal to N.

[0062] The video encoder 200 encodes the video data of the CU representing the prediction and / or residual information and other information. The prediction information indicates how to predict the CU so as to form a prediction block for the CU. The residual information generally indicates the sample-by-sample difference between the samples of the CU and the prediction block before encoding.

[0063] In order to predict a CU, the video encoder 200 can generally form a prediction block of the CU by inter-frame prediction or intra-frame prediction. Inter-frame prediction generally refers to predicting a CU based on data of a previously coded picture, while intra-frame prediction generally refers to predicting a CU based on previously coded data of the same picture. In order to perform inter-frame prediction, the video encoder 200 can use one or more motion vectors to generate a prediction block. The video encoder 200 can generally perform a motion search to identify a reference block that closely matches the CU (e.g., in terms of the difference between the CU and the reference block). The video encoder 200 can calculate a difference metric using the sum of absolute differences (SAD), the sum of squared differences (SSD), the mean absolute difference (MAD), the mean squared difference (MSD), or other such difference calculations to determine whether the reference block closely matches the current CU. In some examples, the video encoder 200 can use unidirectional prediction or bidirectional prediction to predict the current CU.

[0064] Some examples of JEM and VVC also provide an affine motion compensation mode, which can be considered an inter-frame prediction mode. In the affine motion compensation mode, the video encoder 200 can determine two or more motion vectors representing non-translational motion, such as enlargement or reduction, rotation, perspective motion, or other irregular motion types.

[0065] To perform intra prediction, the video encoder 200 can select an intra prediction mode to generate a prediction block. Some examples of JEM and VVC provide sixty-seven intra prediction modes, including various directional modes, as well as a planar mode and a DC mode. Typically, the video encoder 200 selects an intra prediction mode that describes a neighboring sample of a current block (e.g., a block of a CU) from which the sample of the current block is predicted. Assuming that the video encoder 200 encodes and decodes CTUs and CUs in a raster scan order (from left to right, from top to bottom), such samples can typically be above, above and to the left, or to the left of the current block in the same picture as the current block.

[0066] The video encoder 200 encodes data representing the prediction mode of the current block. For example, for inter-frame prediction mode, the video encoder 200 can encode data indicating which of the various available inter-frame prediction modes is used, and motion information of the corresponding mode. For example, for unidirectional or bidirectional inter-frame prediction, the video encoder 200 can encode motion vectors using advanced motion vector prediction (AMVP) or merge mode. The video encoder 200 can use a similar mode to encode motion vectors for affine motion compensation mode.

[0067] After prediction (such as intra-frame prediction or inter-frame prediction of a block), the video encoder 200 can calculate residual data for the block. The residual data (such as a residual block) represents the sample-by-sample difference between the block and the predicted block of the block formed using the corresponding prediction mode. The video encoder 200 can apply one or more transforms to the residual block to produce transformed data in a transform domain rather than a sample domain. For example, the video encoder 200 can apply a discrete cosine transform (DCT), an integer transform, a wavelet transform, or a conceptually similar transform to the residual video data. In addition, the video encoder 200 can apply a secondary transform after the first transform, such as a mode-dependent non-separable secondary transform (MDNSST), a signal-dependent transform, a Karhunen-Loeve transform (KLT), etc. The video encoder 200 generates transform coefficients after applying one or more transforms.

[0068] As described above, after any transform produces transform coefficients, the video encoder 200 can perform quantization of the transform coefficients. Quantization generally refers to the process of quantizing the transform coefficients to minimize the amount of data used to represent the transform coefficients to provide further compression. By performing the quantization process, the video encoder 200 can reduce the bit depth associated with some or all of the transform coefficients. For example, the video encoder 200 can round down an n-bit value to an m-bit value during quantization, where n is greater than m. In some examples, to perform quantization, the video encoder 200 can perform a bitwise right shift on the value to be quantized.

[0069] After quantization, the video encoder 200 can scan the transform coefficients to generate a one-dimensional vector from a two-dimensional matrix including the quantized transform coefficients. The scan can be designed to place the transform coefficients of higher energy (and therefore lower frequency) at the front of the vector and the transform coefficients of lower energy (and therefore higher frequency) at the back of the vector. In some examples, the video encoder 200 can scan the quantized transform coefficients using a predefined scan order to generate a serialized vector, and then entropy encode the quantized transform coefficients of the vector. In other examples, the video encoder 200 can perform adaptive scanning. After scanning the quantized transform coefficients to form a one-dimensional vector, the video encoder 200 can entropy encode the one-dimensional vector, for example, according to context adaptive binary arithmetic coding (CABAC). The video encoder 200 can also entropy encode the values ​​of the syntax elements describing the metadata associated with the encoded video data for use by the video decoder 300 in decoding the video data.

[0070] To perform CABAC, the video encoder 200 may assign context within a context model to a symbol to be transmitted. The context may be about, for example, whether the neighboring values ​​of the symbol are zero values. The probability determination may be based on the context assigned to the symbol.

[0071] The video encoder 200 may also generate syntax data, such as block-based syntax data, picture-based syntax data, and sequence-based syntax data, or other syntax data, such as a sequence parameter set (SPS), a picture parameter set (PPS), or a video parameter set (VPS), to the video decoder 300, for example, in a picture header, a block header, a slice header. Likewise, the video decoder 300 may decode such syntax data to determine how to decode the corresponding video data.

[0072] In this way, the video encoder 200 can generate a bitstream including encoded video data (e.g., syntax elements describing the partitioning of a picture into blocks (e.g., CUs) and prediction and / or residual information of the blocks). Finally, the video decoder 300 can receive the bitstream and decode the encoded video data.

[0073] In general, the video decoder 300 performs a process that is inverse to the process performed by the video encoder 200 to decode the encoded video data of the bitstream. For example, the video decoder 300 may use CABAC to decode the values ​​of the syntax elements of the bitstream in a manner substantially similar to but inverse to the CABAC encoding process of the video encoder 200. The syntax elements may define partitioning of a picture into CTUs and partitioning each CTU according to a corresponding partitioning structure such as a QTBT structure to define partitioning information of CUs of the CTU. The syntax elements may further define prediction and residual information of a block (e.g., CU) of video data.

[0074] The residual information may be represented by, for example, quantized transform coefficients. The video decoder 300 may inverse quantize and inverse transform the quantized transform coefficients of the block to reproduce a residual block for the block. The video decoder 300 uses the signaled prediction mode (intra-frame or inter-frame prediction) and related prediction information (e.g., motion information for inter-frame prediction) to form a prediction block for the block. The video decoder 300 may then combine the prediction block and the residual block (on a sample-by-sample basis) to reproduce the original block. The video decoder 300 may perform additional processing, such as performing deblocking to reduce visual artifacts along the boundaries of blocks.

[0075] The present disclosure may generally refer to "signaling" certain information, such as syntax elements. The term "signaling" may generally refer to the communication of values ​​of syntax elements and / or other data used to decode encoded video data. That is, the video encoder 200 may signal the values ​​of syntax elements in a bitstream. Generally, signaling refers to generating values ​​in a bitstream. As described above, the source device 102 may transmit the bitstream to the destination device 116 in substantially real time or in non-real time (such as may occur when the syntax elements are stored to the storage device 112 for later retrieval by the destination device 116).

[0076] Figure 2A and 2B 1 is a conceptual diagram showing an example quadtree binary tree (QTBT) structure 130 and a corresponding codec tree unit (CTU) 132. Solid lines represent quadtree partitions, and dashed lines indicate binary tree partitions. In each partition (i.e., non-leaf) node of the binary tree, a flag is signaled to indicate which partition type (i.e., horizontal or vertical) is used, where in this example, 0 indicates horizontal partitioning and 1 indicates vertical partitioning. For quadtree partitioning, there is no need to indicate the partition type because the quadtree node divides the block horizontally and vertically into 4 sub-blocks of equal size. Therefore, the video encoder 200 can encode and the video decoder 300 can decode the syntax elements (such as partition information) of the regional tree level (i.e., solid line) of the QTBT structure 130 and the syntax elements (such as partition information) of the prediction tree level (i.e., dashed line) of the QTBT structure 130. The video encoder 200 can encode and the video decoder 300 can decode the video data of the CU represented by the terminal leaf node of the QTBT structure 130, such as prediction and transformation data.

[0077] generally, Figure 2B The CTU 132 may be associated with parameters defining the size of blocks corresponding to nodes at the first and second levels of the QTBT structure 130. These parameters may include a CTU size (indicating the size of the CTU 132 in samples), a minimum quadtree size (MinQTSize, indicating the minimum allowed quadtree leaf node size), a maximum binary tree size (MaxBTSize, indicating the maximum allowed binary tree root node size), a maximum binary tree depth (MaxBTDepth, indicating the maximum allowed binary tree depth), and a minimum binary tree size (MinBTSize, indicating the minimum allowed binary tree leaf node size).

[0078] The root node of the QTBT structure corresponding to the CTU may have four child nodes at the first level of the QTBT structure, each of which may be segmented according to a quadtree segmentation. That is, the nodes of the first level are leaf nodes (without child nodes) or have four child nodes. The example of the QTBT structure 130 represents such a node as including a parent node and a child node with a solid line for branching. If the node of the first level is not larger than the maximum allowed binary tree root node size (MaxBTSize), the node may be further segmented by the corresponding binary tree. The binary tree partitioning of a node may be iterated until the node generated by the partitioning reaches the minimum allowed binary tree leaf node size (MinBTSize) or the maximum allowed binary tree depth (MaxBTDepth). The example of the QTBT structure 130 represents such a node as having a dotted line for branching. The binary tree leaf node is called a codec unit (CU), which is used for prediction (e.g., intra-picture or inter-picture prediction) and transformation without any further segmentation. As described above, a CU may also be referred to as a "video block" or "block".

[0079] In one example of a QTBT partitioning structure, the CTU size is set to 128x128 (luminance sample and two corresponding 64x64 chrominance samples), MinQTSize is set to 16x16, MaxBTSize is set to 64x64, MinBTSize (both width and height) is set to 4, and MaxBTDepth is set to 4. Quadtree partitioning is first applied to the CTU to generate a quadtree leaf node. The quadtree leaf node can have a size from 16×16 (i.e., MinQTSize) to 128×128 (i.e., CTU size). If the quadtree leaf node is 128x128, the leaf quadtree node will not be further divided by the binary tree because its size exceeds MaxBTSize (i.e., 64x64 in this example). Otherwise, the quadtree leaf node will be further divided by the binary tree. Therefore, the quadtree leaf node is also the root node of the binary tree, and the binary tree depth is 0. When the binary tree depth reaches MaxBTDepth (4 in this example), no further partitioning is allowed. When the binary tree node width reaches MinBTSize (4 in this example), it means that no further horizontal partitioning is allowed. Similarly, a binary tree node with a height equal to MinBTSize means that no further vertical partitioning of the binary tree node is allowed. As described above, the leaf nodes of the binary tree are called CUs and are further processed according to prediction and transformation without further segmentation.

[0080] Trellis Coded Quantization (TCQ) is proposed in "CE7: Transform coefficient coding with reduced number of regular-coded bins (tests 7.1.3a, 7.1.3b)" by H. Schwarz, T. Nguyen, D. Marpe, T. Wiegand, M. Karczewicz, M. Coban, J. Dong, JVET document JVET-L0274, Macau, China, October 2018 (hereinafter referred to as JVET-L0274). In the technology of JVET-L0274, two scalar quantizers are switchably used for quantization / dequantization. The scalar quantizer used on the current transform / quantization coefficient is determined by the parity (least significant bit) of the quantization coefficient before the current transform / quantization coefficient in the scan order.

[0081] JVET-L0274 also proposes a transform coefficient encoding and decoding scheme combined with TCQ, by which the context selection for decoding the quantized coefficient depends on the quantizer used. Specifically, the importance flag (SIG) of the transform coefficient indicating that the transform coefficient is zero or non-zero can be encoded and decoded with one of three sets of context models, and the set selected for a particular SIG depends on the quantizer used for the associated coefficient. Therefore, when starting to decode the SIG of the current coefficient, the entropy decoder (e.g., the entropy decoder of the video decoder 300) determines the parity of the transform coefficient at the previous scan position, which determines the quantizer of the current coefficient, and therefore determines the context set of the SIG of the coefficient.

[0082] In some examples, the TU is divided into non-overlapping sub-blocks called codec groups (CGs), which are typically 4x4 samples in size. The decoding process described herein may sometimes be described with respect to a 4x4 CG, but may be extended to any other CG size. The techniques disclosed herein and therefore the description included herein primarily relate to encoding and decoding processes at the absolute level for transform coefficients in the CG. Other information associated with the CG, such as symbols, may be encoded or decoded in the manner described in JVET-L0274, but may also be encoded and decoded using alternative techniques.

[0083] The video encoder 200 and the video decoder 300 may be configured to process syntax elements in a bitstream. For example, the following syntax elements may be used to represent the absolute level value (absLevel) of a transform coefficient. Note that quantized transform coefficients typically have integer values. The absolute level is the magnitude of the transform coefficient.

[0084] sig_coeff_flag (SIG): If absLevel is 0, this flag is equal to 0; otherwise, this flag is equal to 1.

[0085] abs_level_gt1_flag: This flag is present in the bitstream if sig_coeff_flag is equal to 1. If absLevel is greater than 1, the value of abs_level_gt1_flag is equal to 1; otherwise, abs_level_gt1_flag is equal to 0.

[0086] par_level_flag: This flag is present in the bitstream if abs_level_gt1_flag is equal to 1. If absLevel is odd, the value of par_level_flag is equal to 0; if absLevel is even, the value of par_level_flag is equal to 1.

[0087] abs_level_gt3_flag: This flag is present in the bitstream if abs_level_gt1_flag is equal to 1. If absLevel is greater than 3, the value of abs_level_gt3_flag is equal to 1; otherwise, abs_level_gt3_flag is equal to 0.

[0088] abs_remainder: This syntax element is present in the bitstream if abs_level_gt3_flag is equal to 1. The abs_remainder syntax element is the residual absolute value encoded using Golomb-Rice coding at the transform coefficient level.

[0089] abs_level: This is the absolute value of the transform coefficient level encoded with Golomb-Rice code.

[0090] Hereinafter, in order to simplify the description, the syntax elements sig_coeff_flag, par_level_flag, abs_level_gt1_flag, abs_level_gt3_flag, abs_remainder, and abs_level are represented as SIG, Par, Gt1, Gt2, remLevel, absLevel, respectively.

[0091] The video encoder 200 and the video decoder 300 may be configured to set any of the above syntax elements that are not parsed from the bitstream to a default value, such as 0. Given the value of the first syntax element of the five syntax elements, the value of the absolute level of the transform coefficient may be calculated as:

[0092] absoluteLevel=SIG+Gt1+Par+(Gt2<<1)+(remLevel<<1) (1)

[0093] Alternatively, if the transform coefficients are fully coded in bypass codec mode, absoluteLevel may be coded directly as abs_level.

[0094] Figure 3 The diagram shows an example order of syntax elements representing absoluteLevels in the CG in JVET-L0274. Other orders may also be used. Figure 3 As shown, when absLevel is greater than 4, all five syntax elements mentioned above will be parsed from the bitstream.

[0095] exist Figure 3 In the example of , the video decoder 300 scans the positions in the CG in up to four passes. In the first pass 136, the video decoder 300 parses the values ​​of the SIG, Par, and Gt1 syntax elements. Only a non-zero SIG is followed by the corresponding Gt1 and Par syntax elements. That is, if the video decoder 300 determines that the SIG has a zero value, meaning that the transform coefficient level is equal to 0, the video decoder 300 does not receive an instance of the Gt1 and Par syntax elements for the coefficient. After the first pass 136, the value of the partial absoluteLevel for each position can be reconstructed, represented as absLevel1, as shown in equation (2).

[0096] absLevel1=SIG+Par+Gt1 (2)

[0097] In some embodiments, the video decoder 300 may be configured to parse up to 28 regular codec bits for 4x4 sub-blocks and up to 6 regular codec bits for 2x2 sub-blocks in the first pass 136. A limit on the number of regular codec bits may be enforced in the SIG, Gt1, and Par bit groups, meaning that each group of SIG, Gt1, and Par bits is coded as a set, and switching to bypass codec in the middle of a set is not allowed. That is, in some embodiments, each syntax element in the SIG, Gt1, and Par sets is coded as a regular codec bit (e.g., context codec) or coded in bypass mode.

[0098] If there is at least one non-zero Gtl in the first traversal 136, the video decoder 300 can be configured to scan the second traversal 138. In the second traversal 138, the video decoder 300 parses the Gt2 syntax element for the position in the CG with the non-zero Gt1 syntax element. The position in the CG is associated with the transform coefficient. The bins in the first traversal 136 and the second traversal 138 can both be conventionally coded, which means that the probability distribution of the bins is modeled by the selected context model. If there is at least one non-zero Gt2 syntax element in the second traversal 138, the video decoder 300 scans the third traversal 140. During the third traversal 140, the video decoder 300 parses the reLevel syntax element for the position with non-zero Gt2s. The remLevel syntax element is not binary, and the video decoder 300 can bypass codec the bins of the binarized version of remLevel, which means that the bins are assumed to be uniformly distributed and no context selection is required.

[0099] In the fourth pass 142, the video decoder 300 scans all remaining coefficients that were not partially represented with conventionally coded bins in the first three passes. The transform coefficient levels of the fourth pass 142 are encoded as absolute values ​​using bypass coded bins.

[0100] The video encoder 200 and the video decoder 300 may perform context modeling to entropy encode and decode some of the above-mentioned syntax elements. The context modeling used in JVET-L0274 and the modifications proposed in the present disclosure are also briefly introduced here. Context modeling, discussed in more detail below, generally refers to selecting a probability model for the binary bit being encoded or decoded, also known as a context. In JVET-L0274, the syntax elements SIG, Par, Gt1, and Gt2 are encoded and decoded using context modeling. The selection of context depends on the value of the absLevel1 syntax element in the local neighborhood, denoted as N. Positions within the template but outside the current TU can be excluded from N.

[0101] Figure 4 A diagram illustrating a template for selecting a probability model. The square marked with an "X" specifies the current scan position, and the square marked with a "Y" represents the local neighborhood used.

[0102] For the current position (see Figure 4The video decoder 300 determines the context indexes of the SIG, Par, Gt1, and Gt2 syntax elements, denoted as ctxIdxSIG, ctxIdxPar, ctxIdxGt1, and ctxIdxGt2. To determine the context indexes, the video decoder 300 may first determine three variables—numSIG, sumAbs1, and d. The variable numSIG represents the number of non-zero SIGs in N, as represented by the following equation (3):

[0103] sumSIG=∑ i∈N SIG(i) (3)

[0104] The variable sumAbs1 represents the sum of absLevel1 in N, expressed as follows:

[0105] sumAbs1=∑ i∈N absLevel1(i) (4)

[0106] The variable d represents the diagonal metric of the current position within the TU, as expressed in the following equation (5):

[0107] d=x+y, (5)

[0108] Among them, x and y represent the coordinates of the current position inside the TU.

[0109] Given sumAbs1 and d, the video decoder 300 determines the context index for decoding SIG as follows:

[0110] For brightness, ctxIdxSIG is determined by equation (6):

[0111] ctxIdxSIG=18*max(0,state-1)+min(sumAbs1,5)+(d<2?12: (d<5?6:0)) (6)

[0112] For chroma, ctxIdxSIG is determined by equation (7):

[0113] ctxIdxSIG=12*max(0,state-1)+min(sumAbs1,5)+(d<2?6:0)) (7)

[0114] In equations (6) and (7), the variable "state" represents the current state of the state machine, as defined in JVET-L0274. The state machine will be discussed in more detail below.

[0115] Given sumSIG, sumAbs1, and d, the video decoder 300 determines the context index for decoding Par as follows:

[0116] If the current scan position is equal to the position of the last non-zero coefficient, ctxIdxPar is 0.

[0117] ·otherwise,

[0118] For brightness, ctxIdxPar is determined by equation (8):

[0119] ctxIdxPar=1+min(sumAbs1-numSIG, 4)+(d==0?15: (d<3?10: (d

[0120] <10?5:0))) (8)

[0122] For chroma, ctxIdxPar is determined by (9)

[0123] ctxIdxPar=1+min(sumAbs1-numSIG, 4)+(d==0?5:0) (9)

[0124] ctxIdxGtl and ctxIdxGt2 are set to the value of ctxIdxPar.

[0125] The video encoder 200 and the video decoder 300 may be configured to perform RemLevel encoding and decoding. The video decoder 300 derives the Rice parameters (ricePar) for encoding and decoding the non-binary syntax elements remRemainder (remLevel) and absLevel as follows:

[0126] At the beginning of each sub-block, ricePar is set equal to 0;

[0127] After encoding and decoding syntax elements for remainder, Rice parameter (ricePar)

[0128] Modify as follows:

[0129] If ricePar is less than 3 and the last coded value of the remainder is greater than ((3<<ricePar)1), ricePar is increased by 1.

[0130] For the codec non-binary syntax element absLevel, representing the absolute quantization index for the full bypass codec, the following applies:

[0131] Determine the sum of the absolute values ​​in the local template, sumAbs.

[0132] The variables ricePar and posZero are determined by table lookup according to the following:

[0133] ricePar=riceParTable[min(31,sumAbs)]

[0134] posZero=posZeroTable[max(0, state-1)][min(31, sumAbs)], where the variable state represents the state of the relevant quantization (it is equal to 0 when the relevant quantization is disabled), and the tables riceParTable[] and posZeroTable[][] are given by:

[0135] riceParTable

[32] ={

[0136] 0,0,0,0,0,0,0,1,1,1,1,1,1,1,2,2,2,2,2,2,2,2,2,2,2,2,2,2,3,3,3,3

[0137] };

[0138] posZeroTable[3]

[32] ={

[0139] {0,0,0,0,0,1,2,2,2,2,2,2,4,4,4,4,4,4,4,4,4,4,4,8,8,8,8,8,8,8,8},

[0140] {1,1,l,1,2,3,4,4,4,6,6,6,8,8,8,8,8,8,12,12,12,12,12,12,12,12,16,16,16,16,16,16},

[0141] {1,1,2,2,2,3,4,4,4,6,6,6,8,8,8,8,8,12,12,12,12,12,12,16,16,16,16,16,16}

[0142] };

[0143] The intermediate variable codeValue is derived as follows:

[0144] οIf absLevel is equal to 0, codeValue is set equal to posZero;

[0145] o Otherwise, if absLevel is less than or equal to posZero, codeValue is set to absLevel-1;

[0146] o Otherwise (absLevel is greater than posZero), set codeValue equal to absLevel.

[0147] The value of codeValue is encoded or decoded using the Golomb-Rice code with the Rice parameter ricePar.

[0148] The video encoder 200 and the video decoder 300 may be configured to perform a combination of Golomb-Rice encoding and exponential Golomb encoding for residual level encoding. That is, the portion of the transform coefficient level that is not context-encoded may be represented by a combination of Golomb-Rice codes and exponential Golomb codes. The non-context-encoded portion of the transform coefficient may correspond to the value of remLevel or absLevel described above.

[0149] When it comes to coefficient codec level values, it is generally expected that non-context codec level values ​​will be relatively small. Therefore, the present disclosure proposes the use of Golomb-Rice codec, which can be an efficient codec technique for encoding small values. For those cases where the level values ​​of transform coefficients are not small, then exponential Golomb codec can be used, which can be an efficient codec technique for encoding larger values.

[0150] The switching point from Golomb-Rice to exponential Golomb codec for the values ​​of the remaining coefficients may be determined based on the following thresholds:

[0151] threshold=g_auiGoRiceRange[m_goRicePar]<<m_goRicePar

[0152] where m_goRicePar is the Rice parameter, and

[0153] g_auiGoRiceRange[MAX_GR_ORDER_RESIDUAL]={6, 5, 6, 3}

[0154] is a lookup table that determines the prefix length (i.e., length-1) of each Rice parameter. Values ​​of coefficients less than or equal to the threshold can be encoded as Golomb-Rice codes, while values ​​of coefficients greater than the threshold can be encoded using both Golomb-Rice codes and exponential Golomb codes.

[0155] The video decoder 300 may be configured to perform absoluteLevel reconstruction, which generally refers to the process of determining level values ​​based on various syntax elements. The absoluteLevel reconstruction is the same as in JVET-L0274, discussed above for syntax elements in a bitstream.

[0156] The present disclosure describes techniques for residual level encoding and decoding. According to the techniques of the present disclosure, the video encoder 200 and the video decoder 300 can be configured to use a fixed prefix length defined by RiceRange for all Rice parameters to determine the transition point between using Golomb-Rice codes and exponential Golomb codes. In one example, the threshold will be:

[0157] threshold=RiceRange<<m_goRicePar

[0158] In terms of codec performance in current VVC designs, a RiceRange value of 5 or 6 may produce good results. The techniques of the present disclosure may, for example, eliminate the need to use a lookup table without unduly sacrificing codec efficiency.

[0159] In some examples, different RiceRange may be used to encode the remLevel and absLevel portions of the transform coefficients, since remLevel represents half of the rem level, while absLevel represents the full level (a larger value).

[0160] In other examples, the video encoder 200 and the video decoder 300 may be configured to use a fixed RiceRange parameter, such as 5 or 6, for all Rice parameters except a maximum Rice parameter, which may have a smaller RiceRange parameter, such as 3.

[0161] The disclosed techniques include the proposed worst-case escape code length limit. The length of the Golomb-Rice / exponential Golomb representation of the residual level of the coefficient can exceed 32 bits. For example, for the worst case riceParam=0, the maximum value of the remLevel code is 16381, represented by 33 bits. For absLevel, 2 15 The maximum value of is represented by 35 bits. The present disclosure proposes a technique for limiting the worst-case code length to 32.

[0162] The maximum prefix code length is given by:

[0163] maximumPrefixLength=32-(RiceRange+MAX_TR_DYNAMIC_RANGE)

[0164] When this prefix length is reached, the corresponding suffix length is given by:

[0165] suffixLength=MAX_TR_DYNAMIC_RANGE-rParam

[0166] This scheme limits the worst-case escape code length for encoding and decoding the abs_remainder (remLevel) and dec_abs_level (absLevel) syntax elements to 32 bits.

[0167] The following table illustrates the proposed binarization criceParam=0.

[0168]

[0169] In the table above, the input value 5 represents the exchange point between the Golomb Rice code and the exponential Golomb code. The codeword for the input value can be viewed as the Golomb Rice code of 11111 with 0 appended, corresponding to 5+0. The next input 6 can be viewed as the Golomb Rice code of 11111 with 10x appended, corresponding to 5+1=6. The remaining inputs can be similarly viewed as the Golomb Rice code of 11111 plus the exponential Golomb value.

[0170] The following table generally shows the same encoding and decoding scheme as above, but proposes binarization criceParam=1.

[0171]

[0172] The following table generally shows the same encoding and decoding scheme as above, but proposes binarization criceParam=2.

[0173]

[0174]

[0175] The following table generally shows the same encoding and decoding scheme as above, but proposes binarization criceParam=3.

[0176]

[0177] Figure 5 is a block diagram illustrating an example video encoder 200 that may perform the techniques of this disclosure. Figure 5 For purposes of illustration, the present disclosure describes the video encoder 200 in the context of video codec standards such as the HEVC video codec standard and the developing H.266 video codec standard. However, the techniques of the present disclosure are not limited to these video codec standards and are generally applicable to video encoding and decoding.

[0178] exist Figure 5In the example, the video encoder 200 includes a video data memory 230, a mode selection unit 202, a residual generation unit 204, a transform processing unit 206, a quantization unit 208, an inverse quantization unit 210, an inverse transform processing unit 212, a reconstruction unit 214, a filter unit 216, a decoded picture buffer (DPB) 218 ​​and an entropy encoding unit 220.

[0179] Video data memory 230 may store video data to be encoded by components of video encoder 200. Video encoder 200 may receive video data from, for example, video source 104 ( Figure 1 ) receives video data stored in video data memory 230. DPB218 can act as a reference picture memory, which stores reference video data used in the prediction of subsequent video data by the video encoder 200. Video data memory 230 and DPB 218 can be formed by any of a variety of memory devices, such as dynamic random access memory (DRAM), including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM), resistive RAM (RRAM) or other types of memory devices. Video data memory 230 and DPB218 can be provided by the same storage device or a separate storage device. In various examples, video data memory 230 can be on the chip with other components of video encoder 200, as shown, or off the chip relative to these components.

[0180] In the present disclosure, references to the video data memory 230 should not be interpreted as limited to a memory inside the video encoder 200, unless otherwise explicitly described, or to a memory outside the video encoder 200, unless otherwise explicitly described. Instead, references to the video data memory 230 should be understood as references to a memory storing video data received by the video encoder 200 for encoding (e.g., video data of a current block to be encoded). Figure 1 The memory 106 may also provide temporary storage of outputs from the various units of the video encoder 200 .

[0181] Show Figure 5The various units of the video encoder 200 are provided to help understand the operations performed by the video encoder 200. These units may be implemented as fixed-function circuits, programmable circuits, or a combination thereof. A fixed-function circuit refers to a circuit that provides a specific function and pre-sets the operations that can be performed. A programmable circuit refers to a circuit that can be programmed to perform various tasks and provide flexible functions in the operations that can be performed. For example, a programmable circuit can run software or firmware so that the programmable circuit operates in a manner defined by the instructions of the software or firmware. A fixed-function circuit can run software instructions (e.g., receive parameters or output parameters), but the type of operation performed by the fixed-function circuit is generally immutable. In some examples, one or more units may be different circuit blocks (fixed function or programmable), and in some examples, one or more units may be integrated circuits.

[0182] The video encoder 200 may include an arithmetic logic unit (ALU), an elementary function unit (EFU), a digital circuit, an analog circuit, and / or a programmable core formed by a programmable circuit. In an example where software executed by a programmable circuit is used to perform the operation of the video encoder 200, the memory 106 ( Figure 1 ) may store object code for software received and executed by the video encoder 200, or another memory (not shown) within the video encoder 200 may store such instructions.

[0183] The video data memory 230 is configured to store received video data. The video encoder 200 may retrieve pictures of video data from the video data memory 230 and provide the video data to the residual generation unit 204 and the mode selection unit 202. The video data in the video data memory 230 may be original video data to be encoded.

[0184] The mode selection unit 202 includes a motion estimation unit 222, a motion compensation unit 224, and an intra prediction unit 226. The mode selection unit 202 may include additional functional units to perform video prediction according to other prediction modes. As an example, the mode selection unit 202 may include a palette unit, an intra block copy unit (which may be part of the motion estimation unit 222 and / or the motion compensation unit 224), an affine unit, a linear model (LM) unit, etc.

[0185] The mode selection unit 202 typically coordinates multiple encoding passes to test combinations of encoding parameters and the resulting rate-distortion values ​​of such combinations. The encoding parameters may include partitioning of a CTU into CUs, a prediction mode for a CU, a transform type for residual data of a CU, a quantization parameter for residual data of a CU, etc. The mode selection unit 202 may ultimately select a coding parameter combination that has a better rate-distortion value than other tested combinations.

[0186] The video encoder 200 may partition the picture retrieved from the video data memory 230 into a series of CTUs and encapsulate one or more CTUs in a slice. The mode selection unit 202 may partition the CTUs of the picture according to a tree structure (such as the QTBT structure or quadtree structure of HEVC described above). As described above, the video encoder 200 may form one or more CUs by partitioning the CTUs according to the tree structure. Such CUs may also be generally referred to as "video blocks" or "blocks".

[0187] Typically, the mode selection unit 202 also controls its components (e.g., the motion estimation unit 222, the motion compensation unit 224, and the intra prediction unit 226) to generate a prediction block for the current block (e.g., the current CU, or the overlapping portion of the PU and TU in HEVC). For inter prediction of the current block, the motion estimation unit 222 can perform a motion search to identify one or more closely matching reference blocks in one or more reference pictures (e.g., one or more previously coded pictures stored in the DPB 218). Specifically, the motion estimation unit 222 can calculate values ​​representing how similar the possible reference blocks are to the current block, such as based on the sum of absolute differences (SAD), the sum of squared differences (SSD), the mean absolute difference (MAD), the mean squared difference (MSD), etc. The motion estimation unit 222 can generally perform these calculations using the sample-by-sample difference between the current block and the reference block under consideration. The motion estimation unit 222 can identify the reference block having the lowest value resulting from these calculations, which indicates the reference block that most closely matches the current block.

[0188] The motion estimation unit 222 may form one or more motion vectors (MVs) that define the position of a reference block in a reference picture relative to the position of a current block in a current picture. The motion estimation unit 222 may then provide the motion vectors to the motion compensation unit 224. For example, for unidirectional inter prediction, the motion estimation unit 222 may provide a single motion vector, and for bidirectional inter prediction, the motion estimation unit 222 may provide two motion vectors. The motion compensation unit 224 may then use the motion vectors to generate a prediction block. For example, the motion compensation unit 224 may use the motion vectors to retrieve data for the reference block. As another example, if the motion vector has fractional sample precision, the motion compensation unit 224 may interpolate the values ​​of the prediction block according to one or more interpolation filters. In addition, for bidirectional inter prediction, the motion compensation unit 224 may retrieve data for two reference blocks identified by the corresponding motion vectors and combine the retrieved data by, for example, sample-by-sample averaging or weighted averaging.

[0189] As another example, for intra prediction, or intra prediction codec, the intra prediction unit 226 can generate a prediction block from samples adjacent to the current block. For example, for directional mode, the intra prediction unit 226 can generally mathematically combine the values ​​of adjacent samples and fill these calculated values ​​along a defined direction on the current block to generate a prediction block. As another example, for DC mode, the intra prediction unit 226 can calculate the average of adjacent samples of the current block and generate a prediction block including the generated average for each sample of the prediction block.

[0190] The mode selection unit 202 provides the prediction block to the residual generation unit 204. The residual generation unit 204 receives the original uncoded version of the current block from the video data memory 230 and receives the prediction block from the mode selection unit 202. The residual generation unit 204 calculates the sample-by-sample difference between the current block and the prediction block. The generated sample-by-sample difference defines a residual block for the current block. In some examples, the residual generation unit 204 may also determine the difference between the sample values ​​in the residual block to generate the residual block using residual differential pulse code modulation (RDPCM). In some examples, the residual generation unit 204 may be formed using one or more subtractor circuits that perform binary subtraction.

[0191] In the example where the mode selection unit 202 partitions the CU into PUs, each PU may be associated with a luma prediction unit and a corresponding chroma prediction unit. The video encoder 200 and the video decoder 300 may support PUs of various sizes. As described above, the size of the CU may refer to the size of the luma codec block of the CU, and the size of the PU may refer to the size of the luma prediction unit of the PU. Assuming that the size of a particular CU is 2Nx2N, the video encoder 200 may support PU sizes of 2Nx2N or NxN for intra-frame prediction, and symmetric PU sizes of 2Nx2N, 2NxN, Nx2N, NxN or the like for inter-frame prediction. The video encoder 200 and the video decoder 30 may also support asymmetric partitioning of PU sizes of 2NxnU, 2NxnD, nLx2N and nRx2N for inter-frame prediction.

[0192] In an example where the mode selection unit does not further split the CU into PUs, each CU may be associated with a luma codec block and a corresponding chroma codec block. As described above, the size of a CU may refer to the size of the luma codec block of the CU. The video encoder 200 and the video decoder 120 may support a CU size of 2Nx2N, 2NxN, or Nx2N.

[0193] For other video codec techniques, such as intra block copy mode codec, affine mode codec, and linear model (LM) mode codec (as a few examples), the mode selection unit 202 generates a prediction block for the current block being encoded via a corresponding unit associated with the codec technique. In some examples, such as palette mode codec, the mode selection unit 202 may not generate a prediction block, but instead generate syntax elements indicating how to reconstruct the block based on the selected palette. In this mode, the mode selection unit 202 may provide these syntax elements to the entropy coding unit 220 for encoding.

[0194] As described above, the residual generation unit 204 receives video data of a current block and a corresponding prediction block. Then, the residual generation unit 204 generates a residual block for the current block. To generate the residual block, the residual generation unit 204 calculates the sample-by-sample difference between the prediction block and the current block.

[0195] The transform processing unit 206 applies one or more transforms to the residual block to generate a block of transform coefficients (referred to herein as a "transform coefficient block"). The transform processing unit 206 can apply various transforms to the residual block to form a transform coefficient block. For example, the transform processing unit 206 can apply a discrete cosine transform (DCT), a directional transform, a Karhunen-Loeve transform (KLT), or a conceptually similar transform to the residual block. In some examples, the transform processing unit 206 can perform multiple transforms on the residual block, such as a primary transform and a secondary transform, such as a rotation transform. In some examples, the transform processing unit 206 does not apply a transform to the residual block.

[0196] The quantization unit 208 may quantize the transform coefficients in the transform coefficient block to produce a quantized transform coefficient block. The quantization unit 208 may quantize the transform coefficients of the transform coefficient block according to a quantization parameter (QP) value associated with the current block. The video encoder 200 (e.g., via the mode selection unit 202) may adjust the degree of quantization applied to the transform coefficient block associated with the current block by adjusting the QP value associated with the CU. Quantization may introduce information loss, and therefore, the quantized transform coefficients may have lower precision than the original transform coefficients produced by the transform processing unit 206.

[0197] The inverse quantization unit 210 and the inverse transform processing unit 212 may apply inverse quantization and inverse transform to the quantized transform coefficient block, respectively, to reconstruct a residual block from the transform coefficient block. The reconstruction unit 214 may generate a reconstructed block corresponding to the current block (although it may have a certain degree of distortion) based on the reconstructed residual block and the prediction block generated by the mode selection unit 202. For example, the reconstruction unit 214 may add samples of the reconstructed residual block to corresponding samples of the prediction block generated by the mode selection unit 202 to generate a reconstructed block.

[0198] Filter unit 216 may perform one or more filtering operations on the reconstructed block. For example, filter unit 216 may perform a deblocking operation to reduce blocking artifacts along the edges of the CU. In some examples, the operations of filter unit 216 may be skipped.

[0199] The video encoder 200 stores the reconstructed blocks in the DPB 218. For example, in an example where the operation of the filter unit 216 is skipped, i.e., the filtering operation is not performed, the reconstruction unit 214 may store the reconstructed blocks to the DPB 218. In an example where the operation of the filter unit 216 is performed, the filter unit 216 may store the filtered reconstructed blocks to the DPB 218. The motion estimation unit 222 and the motion compensation unit 224 may retrieve a reference picture from the DPB 218, which is formed by the reconstructed (and possibly filtered) blocks, to perform inter-frame prediction on blocks of subsequently encoded pictures. In addition, the intra-frame prediction unit 226 may use the reconstructed blocks in the DPB 218 of the current picture to perform intra-frame prediction on other blocks in the current picture.

[0200] In general, the entropy coding unit 220 may entropy code syntax elements received from other functional components of the video encoder 200. Including the syntax elements for coefficient coding and decoding described above. The entropy coding unit 220 may, for example, entropy code syntax elements for signaling transform coefficients described above. For example, the entropy coding unit 220 may entropy code the quantized transform coefficient blocks from the quantization unit 208. As another example, the entropy coding unit 220 may entropy code prediction syntax elements (e.g., motion information for inter-frame prediction or intra-frame mode information for intra-frame prediction) from the mode selection unit 202. The entropy coding unit 220 may perform one or more entropy coding operations on syntax elements as another example of video data to generate entropy-coded data. For example, entropy coding unit 220 may perform a context adaptive variable length coding (CAVLC) operation, a CABAC operation, a variable to variable (V2V) length coding operation, a syntax-based context adaptive binary arithmetic coding (SBAC) operation, a probability interval partitioning entropy (PIPE) coding operation, an exponential-Golomb coding operation, or another type of entropy coding operation on the data. In some examples, entropy coding unit 220 may operate in a bypass mode where syntax elements are not entropy encoded.

[0201] The video encoder 200 may output a bitstream including entropy-encoded syntax elements required to reconstruct a block of a slice or a picture. Specifically, the entropy encoding unit 220 may output a bitstream.

[0202] The above operations are described for blocks. This description should be understood as operations for luma codec blocks and / or chroma codec blocks. As described above, in some examples, the luma codec block and the chroma codec block are the luma and chroma components of the CU. In some examples, the luma codec block and the chroma codec block are the luma and chroma components of the PU.

[0203] In some examples, the operations performed for the luma codec block do not need to be repeated for the chroma codec block. As an example, the operations of identifying the motion vector (MV) and reference picture of the luma codec block do not need to be repeated for identifying the MV and reference picture of the chroma block. Instead, the MV of the luma codec block can be scaled to determine the MV of the chroma block, and the reference picture can be the same. As another example, the intra prediction process can be the same for the luma codec block and the chroma codec block.

[0204] Video encoder 200 represents an example of a device configured to encode video data, including a memory configured to store video data, and one or more processing units implemented in circuitry and configured to encode coefficients as described in the present disclosure.

[0205] For example, the video encoder 200 may perform a first encoding pass on a first syntax element of a transform coefficient group, wherein the first syntax element corresponds to a first set of coefficients in the transform coefficient group; perform an additional encoding pass on additional syntax elements of the transform coefficient group, wherein the additional syntax elements include at least one syntax element indicating a remaining level of a transform coefficient of the first set of coefficients; and process the at least one syntax element indicating a remaining level of the transform coefficient according to any technique in the present disclosure. For example, the first syntax element may include one or more significance flags, each of the one or more significance flags indicating whether an absolute level of the transform coefficient is equal to zero. The first syntax element may include one or more parity level flags, wherein each of the one or more parity level flags indicates whether an absolute level of the transform coefficient is even or odd. The video encoder 200 may also perform a second encoding pass on a second syntax element of the transform coefficient group before performing the additional encoding pass.

[0206] The video encoder 200 also represents an example of an apparatus configured to encode video data, the apparatus comprising a memory configured to store the video data, and one or more processing units implemented in circuitry and configured to determine values ​​of coefficients of a transform coefficient group and context encode syntax elements of a first set of coefficients of the transform coefficient group until a maximum number of conventional codec bits is reached. The context-encoded syntax elements include one or more significance flags indicating whether an absolute level of the transform coefficient is equal to zero, one or more parity level flags indicating whether an absolute level of the transform coefficient is even or odd, and one or more first flags indicating whether an absolute level of the transform coefficient is greater than 2. To context encode the syntax elements of the transform coefficient group, the video encoder 200 may be configured to perform context-adaptive binary arithmetic coding to encode the syntax elements of the transform coefficient group.

[0207] The video encoder 200 may be configured to bypass encode additional syntax elements for a second set of coefficients of the transform coefficient group in response to reaching a maximum number of conventional codec bins. To bypass encode the additional syntax elements, the video encoder 200 determines a level value for a transform coefficient of the second set of coefficients, encodes a prefix value of the transform coefficient using a Golomb-Rice codec in response to the level value being greater than a threshold, and encodes a suffix value using an exponential Golomb codec in response to the level value being greater than the threshold. For example, the video encoder 200 may determine the suffix value by subtracting the prefix value from the level value of the transform coefficient. The level value of the transform coefficient may be an absolute level value or a residual level value.

[0208] In order to bypass encode the additional syntax element, the video encoder 200 can also be configured to determine a second level value of a second coefficient of the second coefficient set, and in response to the second level value being less than a threshold, encode the prefix value of the second coefficient using Golomb-Rice codec without encoding the suffix value of the second coefficient. The threshold value can be a fixed value or a variable value for all coefficients. For example, the video encoder 200 can be configured to determine the value of the Rice parameter of the transform coefficient and determine the threshold value based on the value of the Rice parameter. For example, the threshold value can be 5 or 6, but other values ​​can also be used.

[0209] Figure 6 is a block diagram illustrating an example video decoder 300 that may perform the techniques of this disclosure. Figure 6 It is provided for the purpose of illustration and does not limit the techniques widely exemplified and described in this disclosure. For the purpose of illustration, this disclosure describes a video decoder 300 according to the technical description of JEM and HEVC. However, the techniques of this disclosure can be performed by video codec devices configured for other video codec standards.

[0210] exist Figure 6 In the example of , the video decoder 300 includes a codec picture buffer (CPB) memory 320, an entropy decoding unit 302, a prediction processing unit 304, an inverse quantization unit 306, an inverse transform processing unit 308, a reconstruction unit 310, a filter unit 312, and a decoded picture buffer (DPB) 314. The prediction processing unit 304 includes a motion compensation unit 316 and an intra prediction unit 318. The prediction processing unit 304 may include additional units to perform predictions according to other prediction modes. As an example, the prediction processing unit 304 may include a palette unit, an intra block copy unit (which may form part of the motion compensation unit 316), an affine unit, a linear model (LM) unit, etc. In other examples, the video decoder 300 may include more, fewer, or different functional components.

[0211] The CPB memory 320 may store video data, such as an encoded video bitstream, to be decoded by components of the video decoder 300. The video data stored in the CPB memory 320 may be, for example, obtained from the computer-readable medium 110 ( Figure 1 ). The CPB memory 320 may include a CPB that stores encoded video data (e.g., syntax elements) from an encoded video bitstream. In addition, the CPB memory 320 may store video data other than syntax elements of encoded pictures, such as temporary data representing outputs from various units of the video decoder 300. The DPB 314 typically stores decoded pictures, which may be output by the video decoder 300, and / or the video decoder 300 may use it as reference video data when decoding subsequent data or pictures of the encoded video bitstream. The CPB memory 320 and the DPB 314 may be formed by any of a variety of storage devices such as dynamic random access memory (DRAM), including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM), resistive RAM (RRAM), or other types of storage devices. The CPB memory 320 and the DPB 314 may be provided by the same storage device or a separate storage device. In various examples, the CPB memory 320 may be on-chip with other components of the video decoder 300, or off-chip relative to these components.

[0212] Additionally or alternatively, in some examples, video decoder 300 may retrieve the video from memory 120 ( Figure 1 ) retrieves the encoded and decoded video data. That is, the memory 120 may utilize the CPB memory 320 to store data as described above. Similarly, when some or all of the functions of the video decoder 300 are implemented in software to be executed by the processing circuitry of the video decoder 300, the memory 120 may store instructions to be executed by the video decoder 300.

[0213] Show Figure 6 Various units are illustrated in the figure to help understand the operations performed by the video decoder 300. These units can be implemented as fixed function circuits, programmable circuits, or a combination thereof. Figure 5 , fixed-function circuits refer to circuits that provide specific functions and preset the operations that can be performed. Programmable circuits refer to circuits that can be programmed to perform various tasks and provide flexible functions in the operations that can be performed. For example, a programmable circuit can run software or firmware so that the programmable circuit operates in a manner defined by the instructions of the software or firmware. Fixed-function circuits can run software instructions (e.g., receive parameters or output parameters), but the type of operations performed by the fixed-function circuits is generally immutable. In some examples, one or more units may be different circuit blocks (fixed function or programmable), and in some examples, one or more units may be integrated circuits.

[0214] The video decoder 300 may include an ALU, an EFU, a digital circuit, an analog circuit, and / or a programmable core formed by a programmable circuit. In an example where the operation of the video decoder 300 is performed by software running on a programmable circuit, an on-chip or off-chip memory may store instructions (e.g., object code) of the software received and executed by the video decoder 300.

[0215] The entropy decoding unit 302 may receive the encoded video data from the CPB and entropy decode the video data to reproduce syntax elements, including the syntax elements for coefficient encoding and decoding described above. The prediction processing unit 304, the inverse quantization unit 306, the inverse transform processing unit 308, the reconstruction unit 310, and the filter unit 312 may generate decoded video data based on the syntax elements extracted from the bitstream.

[0216] Typically, the video decoder 300 reconstructs a picture on a block-by-block basis. The video decoder 300 may perform a reconstruction operation on each block individually (where the block currently being reconstructed (ie, decoded) may be referred to as a "current block").

[0217] The entropy decoding unit 302 may entropy decode syntax elements defining quantized transform coefficients of the quantized transform coefficient block, and transform information, such as a quantization parameter (QP) and / or (one or more) transform mode indications. The entropy decoding unit 302 may, for example, entropy decode the syntax elements for signaling the transform coefficients described above. The inverse quantization unit 306 may use the QP associated with the quantized transform coefficient block to determine a degree of quantization, and similarly, determine a degree of inverse quantization to be applied by the inverse quantization unit 306. The inverse quantization unit 306 may, for example, perform a bitwise left shift operation to inverse quantize the quantized transform coefficients. The inverse quantization unit 306 may thereby form a transform coefficient block including the transform coefficients.

[0218] After the inverse quantization unit 306 forms the transform coefficient block, the inverse transform processing unit 308 may apply one or more inverse transforms to the transform coefficient block to generate a residual block associated with the current block. For example, the inverse transform processing unit 308 may apply an inverse DCT, an inverse integer transform, an inverse Karhunen-Loeve transform (KLT), an inverse rotational transform, an inverse directional transform, or another inverse transform to the transform coefficient block.

[0219] In addition, prediction processing unit 304 generates a prediction block based on the prediction information syntax element entropy decoded by entropy decoding unit 302. For example, if the prediction information syntax element indicates that the current block is inter-predicted, motion compensation unit 316 can generate the prediction block. In this case, the prediction information syntax element can indicate a reference picture in DPB 314 from which the reference block is retrieved, and a motion vector that identifies the position of the reference block in the reference picture relative to the position of the current block in the current picture. Motion compensation unit 316 can generally generate a prediction block in the same manner as described for motion compensation unit 224 ( Figure 5 ) is performed in a manner substantially similar to that described in detail above.

[0220] As another example, if the prediction information syntax element indicates that the current block is intra-predicted, the intra-prediction unit 318 can generate a prediction block according to the intra-prediction mode indicated by the prediction information syntax element. Similarly, the intra-prediction unit 318 can generally generate a prediction block in the same manner as that for the intra-prediction unit 226 ( Figure 5 The intra prediction unit 318 may retrieve data of neighboring samples of the current block from the DPB 314.

[0221] The reconstruction unit 310 may reconstruct the current block using the prediction block and the residual block. For example, the reconstruction unit 310 may add samples of the residual block to corresponding samples of the prediction block to reconstruct the current block.

[0222] The filter unit 312 may perform one or more filtering operations on the reconstructed block. For example, the filter unit 312 may perform a deblocking operation to reduce blocking artifacts along the edges of the reconstructed block. The operations of the filter unit 312 may not necessarily be performed in all examples.

[0223] The video decoder 300 may store the reconstructed blocks in the DPB 314. As described above, the DPB 314 may provide reference information to the prediction processing unit 304, such as samples of the current picture for intra prediction and previously decoded pictures for subsequent motion compensation. In addition, the video decoder 300 may output decoded pictures from the DPB for subsequent use in, for example, Figure 1 The display device 118 is displayed on the display device.

[0224] In this manner, video decoder 300 represents an example of a video decoding device that includes a memory configured to store video data, and one or more processing units implemented in circuitry and configured to decode coefficients as described in this disclosure.

[0225] For example, video decoder 300 may perform a first decoding pass for a first syntax element of a transform coefficient group, wherein the first syntax element corresponds to a first set of coefficients in the transform coefficient group; perform an additional decoding pass for additional syntax elements of the transform coefficient group, wherein the additional syntax elements include at least one syntax element indicating a remaining level of the transform coefficients of the first set of coefficients; and process the at least one syntax element indicating the remaining level of the transform coefficient according to any of the techniques in this disclosure. Video decoder 300 may determine a value of the transform coefficient based on the first syntax element and the additional syntax elements.

[0226] For example, the first syntax element may include one or more significance flags, wherein each of the one or more significance flags indicates whether the absolute level of the transform coefficient is equal to zero. For example, the first syntax element may include one or more parity level flags, wherein each of the one or more parity level flags indicates whether the absolute level of the transform coefficient is even or odd. The video decoder 300 may also perform a second decoding pass for a second syntax element of the transform coefficient group before performing an additional decoding pass.

[0227] In this manner, the video decoder 300 also represents an example of a video decoding device that includes a memory configured to store video data, and one or more processing units implemented in circuitry and configured to context-decode syntax elements of a first set of coefficients of a transform coefficient group until a maximum number of conventionally coded binary bits is reached. The context-coded syntax elements include one or more significance flags indicating whether an absolute level of the transform coefficient is equal to zero, one or more parity level flags indicating whether an absolute level of the transform coefficient is even or odd, and one or more first flags indicating whether an absolute level of the transform coefficient is greater than 2. To context-decode syntax elements of a transform coefficient group, the video decoder may be configured to perform context-adaptive binary arithmetic decoding to decode syntax elements of the transform coefficient group.

[0228] The video decoder 300 may be configured to bypass decode the additional syntax elements of the second set of coefficients in response to reaching the maximum number of conventional codec bins. To bypass decode the additional syntax elements, the video decoder 300 may be configured to receive a prefix value for the transform coefficient, decode the prefix value using a Golomb-Rice codec, receive a suffix value for the transform coefficient in response to a length of the prefix value being equal to a threshold, and decode the suffix value using an exponential Golomb codec.

[0229] The video decoder 300 may be configured to determine the value of the first set of coefficients of the transform unit based on the syntax element decoded by the context, and determine the value of the second set of coefficients of the transform unit based on the additional syntax element. To determine the value of the second set of coefficients of the transform unit based on the additional syntax element, the video decoder 300 may be configured to determine the level value of the transform coefficient based on the decoded prefix value and the decoded suffix value. To determine the level value of the transform coefficient, the video decoder 300 may be configured to add the decoded prefix value to the decoded suffix value. The level value of the transform coefficient may be an absolute level value or a residual level value.

[0230] For the second coefficient, the video decoder 300 can be configured to receive a second prefix value for the second coefficient; decode the second prefix value using the Golomb-Rice codec; and determine a level value for the second coefficient without receiving a suffix value for the second coefficient in response to a length of the second prefix value being less than a threshold.

[0231] The threshold value may be a fixed value or a variable value for all coefficients. For example, the video decoder 300 may be configured to determine the value of the Rice parameter of the transform coefficient and determine the threshold value based on the value of the Rice parameter. For example, the threshold value may be 5 or 6, but other values ​​may also be used.

[0232] The video decoder may be configured to determine a decoded transform block based on values ​​of the first coefficient set and values ​​of the second coefficient set; add the decoded transform block to the prediction block to determine a reconstructed block; perform one or more filtering operations on the reconstructed block to determine a decoded block of video data; and output a decoded picture of the video data including the decoded block of video data.

[0233] Fig. 7A and 7B An example of a CABAC process at a binary bit n is shown. Fig. 7A In example 400, at bin n, the range at bin 2 includes RangeMPS and RangeLPS, which are determined by the probability (p) of the least likely symbol (LPS) given a particular context state (σ). σ ). Example 400 illustrates the updating of the range at bin n+1 when the value of bin n is equal to the most probable symbol (MPS). In this example, the low remains unchanged, but the range value at bin n+1 is reduced to the value of RangeMPS at bin n. Figure 7BExample 402 illustrates the updating of the range at bin n+1 when the value of bin n is not equal to MPS (i.e., equal to LPS). In this example, the low is moved to the lower range value of RangeLPS at bin n. In addition, the value of the range at bin n+1 is reduced to the value of RangeLPS at bin n.

[0234] In one example of the HEVC video encoding and decoding process, the range is represented by 9 bits and the low is represented by 10 bits. There is a renormalization process to keep the range and low values ​​accurate enough. Renormalization occurs whenever the range is less than 256. Thus, after renormalization, the range is always equal to or greater than 256. Depending on the range and low values, the binary arithmetic codec (BAC) outputs "0" or "1" to the bitstream, or updates an internal variable (called BO: bits-outstanding) to reserve for future output. Figure 8 An example of a BAC output that depends on range is shown. For example, when range and low are above a certain threshold (e.g., 512), a "1" is output to the bitstream. When range and low are below a certain threshold (e.g., 512), a "0" is output to the bitstream. For example, when range and low are between certain thresholds, nothing is output to the bitstream. Instead, the BO value is incremented and the next binary bit is encoded.

[0235] In the CABAC context model of H.264 / AVC and some examples of HEVC, there are 128 states. There are 64 possible LPS probabilities (represented by the state σ), which can range from 0 to 63. Each MPS can be zero or one. Likewise, the 128 states are the 64 state probabilities multiplied by the 2 possible values ​​of the MPS (0 or 1). Thus, the states can be indexed with 7 bits.

[0236] In order to reduce the range of exported LPS σ ), the results for all cases can be precomputed and stored as approximate values ​​in a lookup table. Thus, by using a simple table lookup, the LPS range can be obtained without any multiplications. Avoiding multiplications may be important for some devices or applications, as this operation may cause noticeable latency in many hardware architectures.

[0237] Instead of multiplication, a 4-column pre-computed LPS range table can be used. The range is divided into four segments. The segment index can be derived by question (range >> 6) & 3. In practice, the segment index is derived by shifting and dropping bits from the actual range. Table 1 below illustrates the possible ranges and their corresponding indices.

[0238] Table 1 - Range Index

[0239] scope 256-319 320-383 384-447 448-511 (range>>6)&3 0 1 2 3

[0240] The LPS range table has 64 entries (one for each probability state) times 4 (one for each range index). Each entry is a Range LPS, i.e., a range times the value of the LPS probability. An example of a portion of this table is shown in Table 2 below. Table 2 describes probability states 9-12. In one proposal for HEVC, the range of probability states may be 0-63.

[0241] Table 2 - RangeLPS

[0242]

[0243] In each segment (i.e., range value), each probability state σ (state σ ) is predefined. In other words, the probability state σ The LPS range of a table is quantized into four values ​​(i.e., one value per range index). The specific LPS range used at a given point depends on which segment the range belongs to. The number of possible LPS ranges used in the table is a tradeoff between the number of table columns (i.e., the number of possible LPS range values) and the accuracy of the LPS ranges. In general, more columns result in less quantization error for the LPS range values, but more memory is required to store the table. Fewer columns increase the quantization error, but also reduce the memory required to store the table.

[0244] As mentioned above, each LPS probability state has a corresponding probability. The probability p of each state is derived as follows:

[0245] p σ =αp σ- 1

[0246] Among them, the state σ is from 0 to 63. The constant α represents the probability change between each context state. In one example, α=0.9493, or more precisely, α=(0.01875 / 0.5)1 / 63. The probability at state σ=0 is equal to 0.5 (i.e. p0= / 2). That is, at context state 0, LPS and MPS are equally likely. The probability at each consecutive state is derived by multiplying the previous state by α. Similarly, the probability of LPS occurring at context state α=1 is p0*0.9493 (0.5*0.9493=.47465). Similarly, as the index of state α increases, the probability of LPS occurring decreases.

[0247] CABAC is adaptive in that the probability state is updated to follow the signal statistics (i.e., the values ​​of previously coded bits). The update process is as follows. For a given probability state, the update depends on the state index and the value of the coded symbol identified as LPS or MPS. As a result of the update process, a new probability state is derived, which consists of a possibly modified LPS probability estimate and, if necessary, a modified MPS value.

[0248] In the case where the bin value is equal to the MPS, a given state index may be increased by 1. This applies to all states, except when the MPS occurs at state index 62, where the LPS probability is already at its minimum value (or equivalently, the maximum MPS probability is reached). In this case, the state index 62 remains fixed until the LPS is seen, or the last bin value is encoded (state 63 is used for the special case of the last bin value). When an LPS occurs, the state index changes by decreasing the state index by a certain amount, as shown in the equation below. This rule generally applies to every occurrence of the LPS, with the following exceptions. Assuming that the LPS has been encoded in the state with index σ=0, which corresponds to the case of equal probability, the state index remains fixed, but the MPS value will be toggled so that the values ​​of the LPS and MPS will be interchangeable. In all other cases, the MPS value will not change regardless of which symbol is encoded. The derivation of the transition rule for the LPS probability is based on a given LPS probability p old Its updated counterpart new The following relationship between:

[0249] If MPS occurs, p new =max(αp old ,p 62 )

[0250] If LPS appears, p new =(1-α)+αp old

[0251] Regarding the actual implementation of the probability estimation process in CABAC, it is important to note that all transition rules can be implemented by at most two tables, each with 63 entries of 6-bit unsigned integer values. In some examples, the state transition can be determined by a single table TransIdxLPS, which determines a new updated state index TransIdxLPS[σ] for a given state index σ in case LPS has been observed. MPS-driven transitions can be obtained by simply (saturated) increasing the state index by a fixed value of 1, resulting in an updated state index min(σ+1,62). Table 3 below is an example of a partial TransIdxLPS table.

[0252] Table 3 - TransIdxLPS

[0253] Possible states (σ) New state TransIdxLPS[σ] … … 9 6 10 8 11 8 12 8 … …

[0254] Above about Fig. 7A , 7B The techniques described in and 8 represent only one example implementation of CABAC. It should be understood that the techniques of the present disclosure are not limited to the described implementations of CABAC. For example, in older BAC methods (e.g., the BAC methods used in H.264 / AVC), the tables RangeLPS and TransIdxLPS are adjusted for low-resolution video (i.e., Common Intermediate Format (CIF) and Quarter CIF (QCIF) video). With HEVC and future codecs (e.g., VVC), a large amount of video content is high definition (HD), and in some cases higher than HD. Video content at or above HD resolution often has different statistical properties from the QCIF sequences used to develop H.264 / AVC 10 years ago. Similarly, the tables RangeLPS and TransIdxLPS from H.264 / AVC may cause adaptation between states in an overly fast manner. That is, the transitions between probability states, especially when LPS occurs, may be too large for smoother, higher resolution HD video content. Therefore, the probability model used according to traditional techniques may not be as accurate for HD and ultra-HD content. Furthermore, since HD video content includes a wider range of pixel values, the H.264 / AVC tables may not include enough entries to account for the more extreme values ​​that may be present in HD content.

[0255] Therefore, for HEVC and future codecs (such as VVC), the RangeLPS and TransIdxLPS tables may be modified to take into account the characteristics of this new content. Specifically, the BAC process of HEVC and future codecs may use tables that allow for a slower adaptation process and may consider more extreme cases (i.e., skewed probability). Therefore, as an example, the RangeLPS and TransIdxLPS tables may be modified to achieve these goals by including more probability states and ranges than used in BAC for H.264 / AVC or HEVC.

[0256] Fig. 94 is a block diagram of an example entropy coding unit 220 that can be configured to perform CABAC according to the techniques of this disclosure. Syntax elements 418 are input to the entropy coding unit 220. If the syntax element is already a binary valued syntax element (i.e., a syntax element with only values ​​of 0 and 1), the binarization step can be skipped. If the syntax element is a non-binary valued syntax element (e.g., a syntax element represented by multiple bits, such as a transform coefficient level), the non-binary valued syntax element is binarized by a binarizer 420. The binarizer 420 performs mapping of the non-binary valued syntax element to a sequence of binary decisions. These binary decisions are often referred to as "bins". For example, for a transform coefficient level, the value of the level can be decomposed into consecutive binary bits, each binary bit indicating whether the absolute value of the coefficient level is greater than a certain value. For example, a binary bit 0 (sometimes referred to as a significance flag) indicates whether the absolute value of the transform coefficient level is greater than 0. A binary bit 1 indicates whether the absolute value of the transform coefficient level is greater than 1, and so on. A unique mapping can be developed for each non-binary valued syntax element.

[0257] Each bin produced by the binarizer 420 is fed to the binary arithmetic coding side of the entropy coding unit 220. That is, for a predetermined set of non-binary valued syntax elements, each bin type (e.g., bin 0) is coded before the next bin type (e.g., bin 1). The coding can be performed in a normal mode or a bypass mode. In the bypass mode, the bypass codec engine 426 performs arithmetic coding using a fixed probability model, such as using Golomb-Rice or exponential Golomb coding. The bypass mode is typically used for more predictable syntax elements.

[0258] Conventional mode encoding and decoding involves performing CABAC. Conventional mode CABAC is used to encode and decode bin values, where the probability of the value of the bin is predictable given the value of the previously encoded bin. The probability that the bin is LPS is determined by the context modeler 422. The context modeler 422 outputs the bin value and the context model (e.g., probability state σ). The context model can be an initial context model for a series of bins, or can be determined based on the encoded values ​​of previously encoded bins. As described above, the context modeler can update the state based on whether the previously encoded bin is MPS or LPS.

[0259] After the context modeler 422 determines the context model and the probability state σ, the conventional codec engine 424 performs BAC on the binary bit value. According to the technology of the present disclosure, the conventional codec engine 424 uses a TransIdxLPS table 430 including more than 64 probability states σ to perform BAC. In one example, the number of probability states is 128. TransIdxLPS is used to determine which probability state is used for the next binary bit (binary bit n+1) when the current binary bit (binary bit n) is LPS. The conventional codec engine 424 can also use the RangeLPS table 128 to determine the range value of the LPS for a given specific probability state σ. However, according to the technology of the present disclosure, instead of using all possible probability states σ of the TransIdxLPS table 430, the probability state index σ is mapped to a grouped index for use in the RangeLPS table. That is, each index in the RangeLPS table 428 can represent two or more of the total number of probability states. The mapping of the probability state index σ to the group index may be linear (eg, divided by two) or non-linear (eg, a logarithmic function or a mapping table).

[0260] In other examples of the present disclosure, the difference between consecutive probability states can be made smaller by setting the parameter α to be greater than 0.9493. In one example, α=0.9689. In another example of the present disclosure, the highest probability (p0) of LPS occurrence can be set to be lower than 0.5. In one example, p0 can be equal to 0.493.

[0261] According to one or more techniques of the present disclosure, instead of using the same values ​​(e.g., window size, scaling factor (α), and probability update speed) of variables used to update probability states during binary arithmetic coding and decoding, the entropy coding unit 220 may use different values ​​of variables for different context models and / or different syntax elements. For example, the entropy coding unit 220 may determine the value of the variable used to update the probability state during binary arithmetic coding and decoding for one context model among multiple context models, and update the probability state based on the determined value.

[0262] Fig.10 is a block diagram of an example entropy decoding unit 302 that may be configured to perform CABAC according to the techniques of this disclosure. Fig.10 The entropy decoding unit 302 is Fig. 9CABAC is performed in the reverse manner of the entropy coding unit 220 described in . The codec bits from the bitstream 448 are input to the entropy decoding unit 302. The codec bits are fed to the context modeler 450 or the bypass decoding engine 452 based on whether the codec bits were entropy coded using the bypass mode or the normal mode. If the codec bits were coded in the bypass mode, the bypass decoding engine 452 may retrieve the bins of the binary valued syntax elements or non-binary syntax elements using, for example, Golomb-Rice or exponential Golomb decoding.

[0263] If the codec bits are encoded and decoded in a conventional mode, the context modeler 450 can determine the probability model of the codec bits, and the conventional decoding engine 454 can decode the codec bits to produce the bins of the non-binary valued syntax element (or the syntax element itself if it is a binary value). After the context modeler 450 determines the context model and the probability state σ, the conventional decoding engine 454 performs BAC on the bin values. According to the technology of the present disclosure, the conventional decoding engine 454 uses a TransIdxLPS table 458 including more than 64 probability states σ to perform BAC. In one example, the number of probability states is 128, but other numbers of probability states can be defined, which is consistent with the technology of the present disclosure. The TransIdxLPS table 458 is used to determine which probability state is used for the next bin (bin n+1) when the current bin (bin n) is LPS. The conventional decoding engine 454 can also use the RangeLPS table 456 to determine the range value of the LPS given a particular probability state σ. However, according to the techniques of the present disclosure, instead of using all possible probability states σ of TransIdxLPS table 458, probability state indexes σ are mapped to grouped indices for use in RangeLPS table 456. That is, each index in RangeLPS table 456 can represent two or more of the total number of probability states. The mapping of probability state indexes σ to grouped indices can be linear (e.g., divided by two) or non-linear (e.g., a logarithmic function or mapping table).

[0264] In other examples of the present disclosure, the difference between consecutive probability states can be made smaller by setting the parameter α to be greater than 0.9493. In one example, α=0.9689. In another example of the present disclosure, the highest probability (p0) of LPS occurrence can be set to be lower than 0.5. In one example, p0 can be equal to 0.493.

[0265] After the bins are decoded by the conventional decoding engine 454, the inverse binarizer 460 may perform a reverse mapping to convert the bins back to values ​​for non-binary valued syntax elements.

[0266] Fig.11 200( Figure 1 and Figure 5 ), but it should be understood that other devices may be configured to perform the same Fig.11 Similar operations.

[0267] In this example, the video encoder 200 initially predicts the current block (550). For example, the video encoder 200 may form a prediction block for the current block. The video encoder 200 may then calculate a residual block for the current block (552). To calculate the residual block, the video encoder 200 may calculate the difference between the original unencoded block and the prediction block for the current block. The video encoder 200 may then transform and quantize the coefficients of the residual block (554). Next, the video encoder 200 may scan the quantized transform coefficients of the residual block (556). During the scan, or after the scan, the video encoder 200 may entropy encode the transform coefficients (558). For example, the video encoder 200 may encode the transform coefficients using CAVLC or CABAC. The video encoder 200 may then output entropy coded data for the block (560).

[0268] Fig.12 1 is a flowchart illustrating an example operation of a video decoder to decode a current block of video data. The current block may include a current CU. Although for the video decoder 300 ( Figure 1 and Figure 6 ), but it should be understood that other devices may be configured to perform the same Fig.12 Similar operations.

[0269] The video decoder 300 may receive entropy coded data of the current block, such as entropy coded data of coefficients of a residual block corresponding to the current block and entropy coded prediction information (570). The video decoder 300 may entropy decode the entropy coded data to determine prediction information for the current block and reproduce coefficients of the residual block (572). The video decoder 300 may predict the current block (574), for example, using an intra-frame or inter-frame prediction mode indicated by the prediction information of the current block to calculate a prediction block of the current block. The video decoder 300 may then inverse scan the reproduced coefficients (576) to create a block of quantized transform coefficients. The video decoder 300 may then inverse quantize and inverse transform the transform coefficients to generate a residual block (578). The video decoder 300 may finally decode the current block (580) by combining the prediction block and the residual block.

[0270] Fig.132 is a flowchart illustrating an example operation of a video encoder to encode a current block of video data. The current block may be, for example, a transform unit or a transform block. Figure 1 and Figure 5 ), but it should be understood that other devices may be configured to perform the same Fig.13 Similar operations.

[0271] exist Fig.13 In an example of , the video encoder 200 determines values ​​of coefficients of a transform coefficient group (602), and context encodes syntax elements of a first set of coefficients of the transform coefficient group until a maximum number of conventional codec bits is reached (604). The context-encoded syntax elements include one or more significance flags indicating whether an absolute level of the transform coefficient is equal to zero, one or more parity level flags indicating whether an absolute level of the transform coefficient is even or odd, and one or more first flags indicating whether an absolute level of the transform coefficient is greater than 2. To context encode the syntax elements of the transform coefficient group, the video encoder 200 may be configured to perform context-adaptive binary arithmetic coding to encode the syntax elements of the transform coefficient group. The video encoder 200 bypass encodes additional syntax elements of a second set of coefficients of the transform coefficient group in response to reaching the maximum number of conventional codec bits (606).

[0272] Fig.14 is a flow chart illustrating example operations of a video encoder to bypass encode additional syntax elements of a second set of coefficients of a transform coefficient group. In this regard, Fig.14 Representatives can correspond to Fig.13 Example process of block 606 of FIG. Fig.14 In the example of , video encoder 200 determines a level value for a transform coefficient of a second coefficient set (608). Video encoder 200 determines whether the level value for the transform coefficient is less than a threshold value (610). If the transform coefficient is less than the threshold value (610), video encoder 200 encodes a prefix value equal to the level of the transform coefficient using Golomb-Rice codec (612). Thus, without encoding a suffix value for the transform coefficient, video encoder 200 encodes the level of the transform coefficient that is less than the threshold value.

[0273] If the transform coefficient is greater than the threshold value (610, No), the video encoder 200 encodes a prefix value equal to the threshold value using the Golomb-Rice codec (614) and encodes a suffix value using the exponential Golomb codec (616). For example, the video encoder 200 may determine the suffix value by subtracting the prefix value from the level value of the transform coefficient. The level value of the transform coefficient may be an absolute level value or a residual level value.

[0274] Fig.15 300( Figure 1 and Figure 6 ), but it should be understood that other devices may be configured to perform the same Fig.14 Similar operations.

[0275] exist Fig.15 In the example of , the video decoder 300 context-decodes syntax elements of a first set of coefficients of a transform coefficient group until a maximum number of conventionally coded binary bits is reached (620). The context-coded syntax elements include one or more significance flags indicating whether an absolute level of the transform coefficient is equal to zero, one or more parity level flags indicating whether an absolute level of the transform coefficient is even or odd, and one or more first flags indicating whether an absolute level of the transform coefficient is greater than 2. To context-decode syntax elements of a transform coefficient group, the video decoder may be configured to perform context-adaptive binary arithmetic decoding to decode syntax elements of the transform coefficient group.

[0276] The video decoder 300 bypasses decoding the additional syntax elements for the second set of coefficients in response to reaching the maximum number of conventional codec bins (622). The video decoder 300 determines values ​​for the first set of coefficients for the transform unit based on the context decoded syntax elements (624), and determines values ​​for the second set of coefficients for the transform unit based on the additional syntax elements (626). The video decoder 300 determines a decoded transform block based on the values ​​for the first set of coefficients and the values ​​for the second set of coefficients (628).

[0277] Fig.16 is a flow chart illustrating example operation of a video decoder to bypass decode additional syntax elements of a second set of coefficients of a transform coefficient group. In this regard, Fig.16 Representatives can correspond to Fig.15 Example process of block 622 of FIG. Fig.14 In the example of , the video decoder 300 receives a prefix value for a transform coefficient (630) and decodes the prefix value using the Golomb-Rice codec (632). The video decoder 300 determines whether the decoded prefix value is less than a threshold value (634). If the decoded prefix value is less than the threshold value (634, yes), the video decoder 300 determines that the transform coefficient level is equal to the decoded prefix value. In this case, the video decoder 300 determines the level value of the transform coefficient without receiving the suffix value.

[0278] If the decoded prefix value is greater than the threshold value (634, No), video decoder 300 receives the suffix value for the transform coefficient (638) and decodes the suffix value using exponential Golomb codec (640). Video decoder 300 determines the level of the transform coefficient equal to the decoded prefix value plus the decoded suffix value (642).

[0279] It should be appreciated that, according to examples, certain actions or events of any of the techniques described herein may be performed in a different order, may be added, combined, or omitted entirely (e.g., not all described actions or events are required for practice of the technique). In addition, in some examples, actions or events may be performed concurrently rather than sequentially, such as by multithreading, interrupt handling, or multiple processors.

[0280] In one or more examples, the described functions may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted through a computer-readable medium as one or more instructions or codes and executed by a hardware-based processing unit. Computer-readable media may include computer-readable storage media, which corresponds to tangible media such as data storage media, or communication media, including, for example, any media that facilitates the conversion of a computer program from one place to another according to a communication protocol. In this manner, computer-readable media may generally correspond to (1) non-temporary tangible computer-readable storage media, or (2) communication media such as signals or carrier waves. Data storage media may be any available media that can be accessed by one or more computers or one or more processors to retrieve instructions, codes, and / or data structures to implement the techniques described in the present disclosure. A computer program product may include a computer-readable medium.

[0281] As an example and not limitation, such computer-readable storage media may include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, disk storage or other magnetic storage devices, flash memory or any other device that can be used to store the required program code in the form of instructions or data structures and can be accessed by a computer. Moreover, any connection is appropriately referred to as a computer-readable medium. For example, if instructions are transmitted from a website, server or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL) or wireless technology (such as infrared, radio and microwave), the definition of the medium includes coaxial cable, fiber optic cable, twisted pair, DSL or wireless technology such as infrared, radio and microwave. However, it should be understood that computer-readable storage media and data storage media do not include connections, carriers, signals or other transient media, but are directed to non-transient tangible storage media. The disks and optical disks used herein include optical disks (CDs), laser optical disks, optical disks, digital versatile disks (DVDs), floppy disks and Blu-ray disks, wherein the disks typically reproduce data magnetically, while the optical disks reproduce data optically by lasers. The above combinations should also be included in the scope of computer-readable media.

[0282] The instructions may be run by one or more processors, such as one or more DSPs, general-purpose microprocessors, ASICs, FPGAs, or other equivalent integrated or discrete logic circuits. Therefore, the term "processor" as used herein may refer to any of the foregoing structures or any other structure suitable for implementing the techniques described herein. In addition, in some aspects, the functionality described herein may be provided within dedicated hardware and / or software modules configured for encoding and decoding, or incorporated in a combined codec. Similarly, the technology may be fully implemented in one or more circuits or logic elements.

[0283] The techniques of the present disclosure may be implemented in a variety of devices or apparatuses including wireless handsets, integrated circuits (ICs), or a set of ICs (e.g., chipsets). Various components, modules, or units are described in this disclosure to emphasize functional aspects of devices configured to perform the disclosed techniques, but do not necessarily need to be implemented by different hardware units. Rather, as described above, the various units may be combined in a codec hardware unit, or provided by a collection of interoperable hardware units including one or more processors as described above in combination with appropriate software and / or firmware.

[0284] Various examples have been described. These and other examples are within the scope of the following claims.

Claims

1. A method for decoding video data, the method comprising: Context-decoding syntax elements of a first set of transform coefficients of a transform coefficient group until a maximum number of conventionally coded bits is reached, wherein the context-decoded syntax elements include one or more significance flags, one or more parity level flags, and one or more first flags, wherein each of the one or more significance flags indicates whether an absolute level of the transform coefficient is equal to zero, each of the one or more parity level flags indicates whether an absolute level of the transform coefficient is even or odd, and each of the one or more first flags indicates whether an absolute level of the transform coefficient is greater than 1; In response to reaching the maximum number of conventionally coded bins, bypass decoding additional syntax elements of a second set of coefficients of the transform coefficient group, wherein bypass decoding the additional syntax elements comprises: A prefix value receiving a level value of a transform coefficient; determining a value of a Rice parameter for transforming the coefficient from among a plurality of Rice parameters; Decoding the prefix value using the Golomb-Rice codec; receiving a suffix value of the level value of the transform coefficient in response to a length of the prefix value being equal to a threshold, wherein the threshold is a fixed value of 6 for all the plurality of Rice parameters; and Decoding the suffix value using exponential Golomb codec; Determining values ​​of a first set of coefficients of a transform unit based on a syntax element decoded from the context; and Determining values ​​of a second set of coefficients of the transform unit based on the additional syntax element, wherein determining values ​​of the second set of coefficients of the transform unit based on the additional syntax element comprises determining level values ​​of the transform coefficients based on a decoded prefix value and a decoded suffix value.

2. The method according to claim 1, wherein: Determining the level value of the transform coefficient includes: The decoded prefix value is added to the decoded suffix value.

3. The method according to claim 1, wherein: Bypass decoding the additional syntax element further includes: receiving a second prefix value for a second coefficient; Decoding the second prefix value using a Golomb-Rice codec; In response to the length of the second prefix value being less than the threshold, a level value of the second coefficient is determined without receiving a suffix value of the second coefficient.

4. The method according to claim 1, wherein: Context decoding syntax elements of the transform coefficient groups includes performing context adaptive binary arithmetic decoding to decode syntax elements of the transform coefficient groups.

5. The method according to claim 1, wherein: The level value of the transform coefficient comprises one of an absolute level value or a residual level value.

6. The method according to claim 1, further comprising: determining a decoded transform block based on values ​​of the first set of coefficients and values ​​of the second set of coefficients; adding the decoded transform block to a prediction block to determine a reconstructed block; performing one or more filtering operations on the reconstructed block to determine a decoded block of video data; as well as A decoded picture of video data including the decoded block of video data is output.

7. The method according to claim 1, wherein: For a transform coefficient group of a 4×4 block, the maximum number of conventional codec bits is 28.

8. A device for decoding video data, the device comprising: a memory configured to store video data; and One or more processors implemented in circuitry and configured to: Context-decoding syntax elements of a first set of coefficients of a transform coefficient group until a maximum number of conventionally coded binary bits is reached, wherein the context-decoded syntax elements include one or more significance flags, one or more parity level flags, and one or more first flags, wherein each of the one or more significance flags indicates whether an absolute level of the transform coefficient is equal to zero, each of the one or more parity level flags indicates whether an absolute level of the transform coefficient is even or odd, and each of the one or more first flags indicates whether an absolute level of the transform coefficient is greater than 1; In response to reaching the maximum number of conventional codec bins, bypass decoding additional syntax elements of a second set of coefficients of the transform coefficient group, wherein to bypass decoding the additional syntax elements, the one or more processors are configured to: A prefix value receiving a level value of a transform coefficient; determining a value of a Rice parameter for transforming the coefficient from among a plurality of Rice parameters; Decoding the prefix value using the Golomb-Rice codec; receiving a suffix value of the level value of the transform coefficient in response to a length of the prefix value being equal to a threshold, wherein the threshold is a fixed value of 6 for all the plurality of Rice parameters; and Decoding the suffix value using exponential Golomb codec; Determining values ​​of a first set of coefficients of a transform unit based on syntax elements decoded from the context; and Determine values ​​of a second set of coefficients of the transform unit based on the additional syntax element, wherein in order to determine the values ​​of the second set of coefficients of the transform unit based on the additional syntax element, the one or more processors are configured to determine level values ​​of the transform coefficients based on a decoded prefix value and a decoded suffix value.

9. The device according to claim 8, wherein: To determine the level value of the transform coefficient, the one or more processors are configured to: The decoded prefix value is added to the decoded suffix value.

10. The device according to claim 8, wherein: To bypass decoding of the additional syntax element, the one or more processors are configured to: receiving a second prefix value for a second coefficient; Decoding the second prefix value using a Golomb-Rice codec; In response to the length of the second prefix value being less than the threshold, a level value of the second coefficient is determined without receiving a suffix value of the second coefficient.

11. The device according to claim 8, wherein: To context decode syntax elements of the transform coefficient groups, the one or more processors are configured to perform context adaptive binary arithmetic decoding to decode syntax elements of the transform coefficient groups.

12. The device according to claim 8, wherein: The level value of the transform coefficient comprises one of an absolute level value or a residual level value.

13. The apparatus according to claim 8, wherein: The one or more processors are configured to: determining a decoded transform block based on values ​​of the first set of coefficients and values ​​of the second set of coefficients; adding the decoded transform block to a prediction block to determine a reconstructed block; performing one or more filtering operations on the reconstructed block to determine a decoded block of video data; as well as A decoded picture of video data including the decoded block of video data is output.

14. The apparatus according to claim 8, wherein: For a transform coefficient group of a 4×4 block, the maximum number of conventional codec bits is 28.

15. A method of encoding video data, the method comprising: determining level values ​​of coefficients of a transform coefficient group; context encoding syntax elements of a first set of transform coefficients of the transform coefficient group until a maximum number of conventional codec bits is reached, wherein the context encoded syntax elements include one or more significance flags, one or more parity level flags, and one or more first flags, wherein each of the one or more significance flags indicates whether an absolute level of the transform coefficient is equal to zero, each of the one or more parity level flags indicates whether an absolute level of the transform coefficient is even or odd, and each of the one or more first flags indicates whether an absolute level of the transform coefficient is greater than 1; In response to reaching the maximum number of conventional codec bins, bypass encoding additional syntax elements of a second set of coefficients of the transform coefficient group, wherein bypass encoding the additional syntax elements comprises: determining level values ​​of transform coefficients of the second coefficient set; determining a value of a Rice parameter for transforming the coefficient from among a plurality of Rice parameters; In response to the level value of the transform coefficient being greater than a threshold, encoding a prefix value of the level value of the transform coefficient using a Golomb-Rice codec, wherein the threshold is a fixed value of 6 for all multiple Rice parameters; and In response to the level value being greater than the threshold, a suffix value of the level value of the transform coefficient is encoded using exponential Golomb codec.

16. The method according to claim 15, further comprising: The suffix value is determined by subtracting the prefix value from the level value of the transform coefficient.

17. The method according to claim 15, wherein: Bypass encoding the additional syntax element further includes: determining a second level value for a second coefficient of the second set of coefficients; In response to the second level value being less than the threshold, encoding the prefix value of the second coefficient using a Golomb-Rice codec without encoding the suffix value of the second coefficient.

18. The method according to claim 15, wherein: Context encoding the syntax elements of the transform coefficient groups includes performing context adaptive binary arithmetic coding to encode the syntax elements of the transform coefficient groups.

19. The method according to claim 15, wherein: The level value of the transform coefficient comprises one of an absolute level value or a residual level value.

20. The method according to claim 15, wherein: For a transform coefficient group of a 4×4 block, the maximum number of conventional codec bits is 28.

21. A device for encoding video data, the device comprising: a memory configured to store video data; and One or more processors implemented in circuitry and configured to: determining level values ​​of coefficients of a transform coefficient group; context encoding syntax elements of a first set of transform coefficients of the transform coefficient group until a maximum number of conventional codec bits is reached, wherein the context encoded syntax elements include one or more significance flags, one or more parity level flags, and one or more first flags, wherein each of the one or more significance flags indicates whether an absolute level of the transform coefficient is equal to zero, each of the one or more parity level flags indicates whether an absolute level of the transform coefficient is even or odd, and each of the one or more first flags indicates whether an absolute level of the transform coefficient is greater than 1; In response to reaching the maximum number of conventional codec bins, bypass encoding additional syntax elements of a second set of coefficients of the transform coefficient group, wherein bypass encoding the additional syntax elements comprises: determining level values ​​of transform coefficients of the second coefficient set; determining a value of a Rice parameter for transforming the coefficient from among a plurality of Rice parameters; In response to the level value of the transform coefficient being greater than a threshold, encoding a prefix value of the level value of the transform coefficient using a Golomb-Rice codec, wherein the threshold is a fixed value of 6 for all multiple Rice parameters; and In response to the level value of the transform coefficient being greater than the threshold, a suffix value of the level value of the transform coefficient is encoded using exponential Golomb codec.

22. The apparatus according to claim 21, wherein The one or more processors are further configured to: The suffix value is determined by subtracting the prefix value from the level value of the transform coefficient.

23. The apparatus of claim 21, wherein: To bypass encode the additional syntax element, the one or more processors are further configured to: determining a second level value for a second coefficient of the second set of coefficients; In response to the second level value being less than the threshold, encoding the prefix value of the second coefficient using a Golomb-Rice codec without encoding the suffix value of the second coefficient.

24. The apparatus of claim 21, wherein: To context encode syntax elements of the transform coefficient groups, the one or more processors are configured to perform context adaptive binary arithmetic coding to encode syntax elements of the transform coefficient groups.

25. The apparatus of claim 21, wherein: The level value of the transform coefficient comprises one of an absolute level value or a residual level value.

26. The apparatus of claim 21, wherein: For a transform coefficient group of a 4×4 block, the maximum number of conventional codec bits is 28.

27. A computer-readable storage medium storing instructions that, when executed by one or more processors, cause the one or more processors to: Context decoding is performed on syntax elements of a first set of transform coefficients of a transform coefficient group until a maximum number of conventionally coded bins is reached, wherein The context-decoded syntax element comprises one or more significance flags, one or more parity level flags, and one or more first flags, wherein each of the one or more significance flags indicates whether an absolute level of a transform coefficient is equal to zero, each of the one or more parity level flags indicates whether an absolute level of a transform coefficient is even or odd, and each of the one or more first flags indicates whether an absolute level of a transform coefficient is greater than 1; In response to reaching the maximum number of conventional codec bins, bypass decoding additional syntax elements for a second set of coefficients of the transform coefficient group, wherein to bypass decoding the additional syntax elements, the instructions cause the one or more processors to: A prefix value receiving a level value of a transform coefficient; determining a value of a Rice parameter for transforming the coefficient from among a plurality of Rice parameters; Decoding the prefix value using the Golomb-Rice codec; receiving a suffix value of the level value of the transform coefficient in response to a length of the prefix value being equal to a threshold, wherein the threshold is a fixed value of 6 for all the plurality of Rice parameters; and Decoding the suffix value using exponential Golomb codec; Determining values ​​of a first set of coefficients of a transform unit based on syntax elements decoded from the context; and Determining values ​​of a second set of coefficients of the transform unit based on the additional syntax element, wherein determining values ​​of the second set of coefficients of the transform unit based on the additional syntax element comprises determining level values ​​of the transform coefficients based on a decoded prefix value and a decoded suffix value.

28. An apparatus for decoding video data, the apparatus comprising: means for context decoding syntax elements of a first set of transform coefficients of a transform coefficient group until a maximum number of conventionally coded bins is reached, wherein the context-decoded syntax elements comprise one or more significance flags, one or more parity level flags, and one or more first flags, wherein each of the one or more significance flags indicates whether an absolute level of the transform coefficient is equal to zero, each of the one or more parity level flags indicates whether an absolute level of the transform coefficient is even or odd, and each of the one or more first flags indicates whether an absolute level of the transform coefficient is greater than 1; Means for bypass decoding additional syntax elements of a second set of coefficients of a transform coefficient group in response to reaching a maximum number of conventionally coded bins, wherein the means for bypass decoding the additional syntax elements comprises: means for receiving a prefix value for a level value of a transform coefficient; means for determining a value of a Rice parameter for transforming a coefficient from a plurality of Rice parameters; means for decoding the prefix value using a Golomb-Rice codec; means for receiving a suffix value of the level value of the transform coefficient in response to the length of the prefix value being equal to a threshold, wherein the threshold is a fixed value of 6 for all multiple Rice parameters; and means for decoding the suffix value using an exponential Golomb codec; means for determining values ​​of a first set of coefficients of a transform unit based on a syntax element decoded from a context; and means for determining values ​​of a second set of coefficients of the transform unit based on the additional syntax element, wherein determining values ​​of the second set of coefficients of the transform unit based on the additional syntax element comprises determining level values ​​of the transform coefficients based on a decoded prefix value and a decoded suffix value.

Images