HK1237171B - Method, device, and computer-readable storage medium for encoding and decoding video data - Google Patents

Description

Method, device and computer-readable storage medium for encoding and decoding video data

This application claims the benefit of U.S. Provisional Patent Application No. 62/110,302, filed January 30, 2015, the entire contents of which are hereby incorporated by reference herein.

Technical Field

This disclosure relates to encoding and decoding content, and more particularly to encoding and decoding content according to a palette-based coding mode.

Background Art

Digital video capabilities can be incorporated into a wide range of devices, including digital televisions, digital live 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 "smartphones," video teleconferencing devices, video streaming devices, and the like. Digital video devices implement video compression techniques, such as those described in the standards defined by MPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264/MPEG-4, Part 10 Advanced Video Coding (AVC), ITU-T H.265, High Efficiency Video Coding (HEVC), and extensions of these standards. By implementing these video compression techniques, video devices can more efficiently transmit, receive, encode, decode, and/or store digital video information.

Video compression techniques perform spatial (intra-picture) prediction and/or temporal (inter-picture) prediction to reduce or remove redundancy inherent in video sequences. For block-based video coding, a video slice (i.e., a video frame or portion of a video frame) may be partitioned into video blocks. Video blocks in an intra-coded (I) slice of a picture are encoded using spatial prediction with respect to reference samples in neighboring blocks in the same picture. Video blocks in an inter-coded (P or B) slice of a picture may use spatial prediction with respect to reference samples in neighboring blocks in the same picture or temporal prediction with respect to reference samples in other reference pictures. Pictures may be referred to as frames, and reference pictures may be referred to as reference frames.

Spatial or temporal prediction produces a predictive block for the block to be coded. Residual data represents the pixel differences between the original block to be coded and the predictive block. Inter-coded blocks are encoded according to a motion vector pointing to a block of reference samples forming the predictive block, and the residual data indicates the difference between the coded block and the predictive block. Intra-coded blocks are encoded according to an intra-coding mode and the residual data. For further compression, the residual data can be transformed from the pixel domain to the transform domain, generating residual coefficients, which can then be quantized. The quantized coefficients, initially arranged in a two-dimensional array, can be scanned to generate a one-dimensional vector of coefficients, and entropy coding can be applied to achieve even more compression.

Content, such as images, can be encoded and decoded using palette mode. Generally speaking, palette mode involves using a palette to represent content. Content can be encoded so that it is represented by an index map containing values corresponding to the palette. The index map can be decoded to reconstruct the content.

Summary of the Invention

The techniques of this disclosure relate to palette-based content coding. For example, in palette-based content coding, a content coder (e.g., a content coder such as a video encoder or video decoder) may form a "palette" as a table of colors for representing video data for a particular region (e.g., a given block). Palette-based content coding may, for example, be particularly useful for coding regions of video data having a relatively small number of colors. Instead of coding the actual pixel value (or its residual), the content coder may code, for one or more of the pixels, a palette index (e.g., an index value) that relates the pixel to an entry in a palette representing the pixel's color. The techniques described in this disclosure may include various combinations of techniques for signaling palette-based coding modes, transmitting a palette, deriving a palette, deriving values for non-transmitted syntax elements, transmitting palette-based coding maps and other syntax elements, predicting palette entries, coding runs of palette indexes, entropy coding palette information, and various other palette coding techniques.

In one example, the present disclosure describes a method of decoding video data, comprising receiving a palette-mode encoded block of video data for a picture from an encoded video bitstream; receiving encoded palette mode information for the palette-mode encoded block of video data from the encoded video bitstream, wherein the encoded palette mode information includes multiple instances of a first syntax element and multiple syntax elements different from the first syntax element; decoding the multiple instances of the first syntax element using a bypass mode before decoding the multiple syntax elements different from the first syntax element using a context mode; decoding the multiple syntax elements different from the first syntax element using a context mode after decoding the multiple instances of the first syntax element using the bypass mode; and decoding the palette-mode encoded block of video data using the decoded multiple instances of the first syntax element and the decoded multiple syntax elements different from the first syntax element.

In another example, the present disclosure describes a device for decoding video data, the device comprising a memory configured to store the video data; and a video decoder in communication with the memory, the video decoder configured to: receive a palette-mode encoded video data block of a picture from an encoded video bitstream; receive encoded palette mode information for the palette-mode encoded video data block from the encoded video bitstream, wherein the encoded palette mode information includes multiple instances of a first syntax element and multiple syntax elements different from the first syntax element; decode the multiple instances of the first syntax element using a bypass mode before decoding the multiple syntax elements different from the first syntax element using a context mode; decode the multiple syntax elements different from the first syntax element using a context mode after decoding the multiple instances of the first syntax element using the bypass mode; and decode the palette-mode encoded video data block using the decoded multiple instances of the first syntax element and the decoded multiple syntax elements different from the first syntax element.

In another example, the present disclosure describes a non-transitory computer-readable storage medium having instructions stored thereon that, when executed, cause one or more processors to receive a palette-mode encoded block of video data for a picture from an encoded video bitstream; receive encoded palette mode information for the palette-mode encoded block of video data from the encoded video bitstream, wherein the encoded palette mode information includes multiple instances of a first syntax element and multiple syntax elements different from the first syntax element; decode the multiple instances of the first syntax element using a bypass mode before decoding the multiple syntax elements different from the first syntax element using a context mode; decode the multiple syntax elements different from the first syntax element using a context mode after decoding the multiple instances of the first syntax element using the bypass mode; and decode the palette-mode encoded block of video data using the decoded multiple instances of the first syntax element and the decoded multiple syntax elements different from the first syntax element.

In another example, the disclosure describes a method of encoding video data, the method comprising determining that a block of video data is to be coded in a palette mode; encoding the block of video data into an encoded bitstream using the palette mode, wherein encoding the block of video data using the palette mode comprises: generating palette mode information for the block of video data, wherein the palette mode information includes multiple instances of a first syntax element and multiple syntax elements different from the first syntax element; encoding the multiple instances of the first syntax element into the encoded bitstream using a bypass mode before encoding the multiple syntax elements different from the first syntax element into the encoded bitstream using a context mode; and encoding the multiple syntax elements different from the first syntax element into the encoded bitstream using the context mode after encoding the multiple instances of the first syntax element into the encoded bitstream using the bypass mode.

In another example, the present disclosure describes a device for encoding video data, the device comprising a memory configured to store the video data; and a video encoder in communication with the memory, the video encoder configured to: determine that a block of video data stored in the memory is to be encoded in a palette mode; encode the block of video data into an encoded bitstream using the palette mode, wherein the video encoder configured to encode the block of video data using the palette mode comprises a video encoder configured to: generate palette mode information for the block of video data, wherein the palette mode information includes multiple instances of a first syntax element and multiple syntax elements different from the first syntax element; encode the multiple instances of the first syntax element into the encoded bitstream using a bypass mode before encoding the multiple syntax elements different from the first syntax element into the encoded bitstream using a context mode; and encode the multiple syntax elements different from the first syntax element into the encoded bitstream using the context mode after encoding the multiple instances of the first syntax element into the encoded bitstream using the bypass mode.

The details of one or more embodiments of the present invention are set forth in the accompanying drawings and description below. Other features, objects, and advantages of the present invention will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

1 is a block diagram illustrating an example video coding system that may utilize the techniques described in this disclosure.

2 is a block diagram illustrating an example video encoder that may perform the techniques described in this disclosure.

3 is a block diagram illustrating an example video decoder that may perform the techniques described in this disclosure.

4 is a conceptual diagram illustrating an example of determining palette entries for palette-based video coding, consistent with the techniques of this disclosure.

5 is a conceptual diagram illustrating an example of determining an index into a palette for a block of pixels, consistent with techniques of this disclosure.

6 is a conceptual diagram illustrating an example of determining a maximum over-copy run length, assuming raster scan order, consistent with the techniques of this disclosure.

7 is a table illustrating changes in the coding order of syntax elements for palette mode.

8 is a flowchart illustrating an example process for decoding video data, consistent with techniques for palette-based video coding in this disclosure.

9 is a flowchart illustrating an example process for encoding video data, consistent with techniques for palette-based video coding in accordance with this disclosure.

DETAILED DESCRIPTION

Aspects of this disclosure are directed to techniques for content coding, such as video coding. In particular, this disclosure describes techniques for palette-based coding of content data, such as video data, and techniques for context-based adaptive binary arithmetic coding (CABAC) of palette coding information. In various examples of this disclosure, as described in greater detail below, the techniques of this disclosure may be directed to processes for predicting or coding blocks in a palette mode to improve coding efficiency and/or reduce codec complexity. For example, this disclosure describes techniques for palette index grouping, such as advanced palette index grouping.

In the CABAC process (e.g., as described in D. Marpe, H. Schwarz, and T. Wiegand, IEEE Trans. Cir. & Sys. Video Tech., "Context-Based Adaptive Binary Arithmetic Coding in the H.264/AVC Video Compression Standard," Vol. 13, July 7, 2003), there are two modes: (1) bypass mode and (2) context mode. In bypass mode, there is no context update process. Therefore, bypass mode can achieve higher data throughput than context-based mode by exploiting hardware or ISA-level parallelism. This benefit of bypass mode becomes greater as the number of bypassed bins that can be processed together increases.

In the current palette mode coding design, as described in R. Joshi and J. Xu, “High Efficiency Video Coding (HEVC) Screen Content Coding: Draft 2,” JCTVC-S1005, in screen content coding, the syntax elements palette_index_idc and palette_escape_val are CABAC bypass mode coded and interleaved with other syntax elements (e.g., palette_run_msb_id_plus1) coded in CABAC context mode. This disclosure describes techniques for grouping bypass mode coded syntax elements together. As used herein, “bypass mode coded” and “context mode coded” are interchangeable with “bypass coded” and “context coded,” respectively.

As used herein, instances of the term "content" may be changed to the term "video," and instances of the term "video" may be changed to the term "content." This is true regardless of whether the term "content" or "video" is used as an adjective, a noun, or another part of speech. For example, reference to a "content decoder" also includes reference to a "video decoder," and reference to a "video decoder" also includes reference to a "content decoder." Similarly, reference to "content" also includes reference to "video," and reference to "video" also includes reference to "content."

As used herein, "content" refers to any type of content. For example, "content" may refer to video, screen content, images, any graphical content, any displayable content, or any data corresponding thereto (e.g., video data, screen content data, image data, graphical content data, displayable content data, and the like).

As used herein, the term "video" may refer to screen content, movable content, multiple images that can be presented in sequence, or any data corresponding thereto (e.g., screen content data, movable content data, video data, image data, and the like).

As used herein, the term "image" may refer to a single image, one or more images, one or more images of a plurality of images corresponding to a video, one or more images of a plurality of images that do not correspond to a video, multiple images corresponding to a video (e.g., all images corresponding to a video or less than all images corresponding to a video), a sub-portion of a single image, multiple sub-portions of a single image, multiple sub-portions corresponding to multiple images, one or more graphics primitives, image data, graphics data, and the like.

In traditional video coding, images are assumed to be continuous-tone and spatially smooth. Based on these assumptions, various tools such as block-based transforms, filtering, and other coding tools have been developed and have demonstrated good performance for natural content video. However, in applications such as remote desktop computing, collaborative work, and wireless displays, computer-generated screen content may be the primary content to be compressed. This type of screen content often features discrete tones, sharp lines, and high-contrast object boundaries. The assumptions of continuous tone and smoothness no longer apply, and therefore traditional video coding techniques may be inefficient at compressing content (e.g., screen content).

In one example of palette-based video coding, a video encoder can encode a block of video data by determining a palette for the block (e.g., an explicitly coded palette, a predicted palette, or a combination thereof), locating entries in the palette to represent values of one or more pixels, and encoding both the palette and the block using index values that indicate entries in the palette used to represent pixel values for the block. In some examples, the video encoder can signal the palette and/or index values in the encoded bitstream. A video decoder can then obtain the palette for the block, as well as index values for individual pixels of the block, from the encoded bitstream. The video decoder can correlate the index values of the pixels with the entries of the palette to reconstruct various pixel values for the block.

For example, it may be assumed that a particular region of video data has a relatively small number of colors. A video coder (e.g., a video encoder or a video decoder) may code (e.g., encode or decode) a so-called "color palette" to represent the video data for a particular region. The color palette may be expressed as an index (e.g., a table) representing the colors or pixel values of the video data for a particular region (e.g., a given block). The video coder may code the index, which relates one or more pixel values to the appropriate value in the color palette. Each pixel may be associated with an entry in the color palette that represents the color of the pixel. For example, the color palette may include the most dominant pixel values in a given block. In some cases, the most dominant pixel values may include one or more pixel values that occur most frequently within the block. Additionally, in some cases, the video coder may apply a threshold value to determine whether a pixel value should be included as one of the most dominant pixel values in the block. According to various aspects of palette-based coding, a video coder may code an index value indicating one or more of the pixel values of a current block, rather than coding the actual pixel values or their remnants for the current block of video data. In the case of palette-based coding, the index value indicates a corresponding entry in a palette used to represent the individual pixel values of the current block. The above description is intended to provide an overview of palette-based video coding.

Palette-based coding may be particularly well-suited for coding content generated by screens or other content for which one or more traditional coding tools are inefficient. Techniques for palette-based coding of video data may be used in conjunction with one or more other coding techniques, such as techniques for inter- or intra-predictive coding. For example, as described in greater detail below, an encoder or decoder, or a combined encoder-decoder (codec), may be configured to perform inter- and intra-predictive coding, as well as palette-based coding.

In some examples, palette-based coding techniques may be configured for use with one or more video coding standards. For example, High Efficiency Video Coding (HEVC) is a new video coding standard developed by the Joint Collaboration Team on Video Coding (JCT-VC) of the ITU-T Video Coding Experts Group (VCEG) and the ISO/IEC Moving Picture Experts Group (MPEG). The finalized HEVC standard document was published by the Telecommunication Standardization Sector of the International Telecommunication Union (ITU) in April 2013 as "ITU-T H.265, Series H: Audiovisual and Multimedia Systems Infrastructure of audiovisual services—Coding of moving video—High efficiency video coding."

To provide more efficient coding of screen-generated content, the JCT-VC extended the development of the HEVC standard, referred to as the HEVC Screen Content Coding (SCC) standard. A new working draft of the HEVC SCC standard, referred to as "HEVC SCC Draft 2" or "WD2," is described in document JCTVC-S1005, "HEVC Screen Content Coding Draft 2," by R. Joshi and J. Xu (Joint Collaboration Team on Video Coding (JCT-VC) of ITU-TSG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG 11, 19th Meeting: Strasbourg, France, October 17-24, 2014).

In the context of the HEVC framework, as an example, palette-based coding techniques may be configured for use as coding unit (CU) mode. In other examples, palette-based coding techniques may be configured for use as prediction unit (PU) mode in the HEVC framework. Thus, all of the processes disclosed below described in the context of CU mode may additionally or alternatively be applied to PUs. However, these HEVC-based examples should not be considered as constraining or limiting the palette-based coding techniques described herein; thus, these techniques may be applied to work independently or as part of other existing or yet-to-be-developed systems/standards. In these cases, the unit for palette coding may be a square block, a rectangular block, or even a non-rectangular shaped region.

In some examples, a palette may be derived from one or more CUs, PUs, or any region of data (e.g., any block of data). For example, a palette may include (and may consist of): the most significant pixel values in the current CU, where for this particular example, the CU is a region of data. The size and elements of the palette are first transmitted from the video encoder to the video decoder. The size and/or elements of the palette in a neighboring CU (e.g., a coded CU above and/or to the left) may be used to directly or predictively code the size and/or elements of the palette. Thereafter, pixel values in the CU are encoded based on the palette according to a particular scan order. For each pixel position in the CU, a flag (e.g., palette_flag or escape_flag) may first be transmitted to indicate whether the pixel value is included in the palette. For those pixel values that map to entries in the palette, the palette index associated with that entry is signaled for a given pixel position in the CU. For those pixel values that do not exist in the palette, a special index may be assigned to the pixel and the actual pixel value (possibly in quantized form) may be transmitted for a given pixel position in the CU instead of sending a flag (e.g., palette_flag or escape_flag). These pixels are referred to as "escape pixels." Escape pixels may be coded using any existing entropy coding method (e.g., fixed-length coding, unary coding, etc.). In some examples, one or more techniques described herein may utilize flags such as palette_flag or escape_flag. In other examples, one or more techniques described herein may not utilize flags such as palette_flag or escape_flag.

The samples in a block of video data may be processed (e.g., scanned) using a horizontal raster scan order or other scan orders. For example, a video encoder may convert a two-dimensional block of palette indices into a one-dimensional array by scanning the palette indices using a horizontal raster scan order. Similarly, a video decoder may reconstruct a block of palette indices using a horizontal raster scan order. Thus, this disclosure may refer to previous samples as samples that precede the currently coded sample in the block in the scan order. It should be understood that scans other than horizontal raster scans (e.g., vertical raster scan orders) may also be applicable. The above examples, as well as other examples described in this disclosure, are intended to provide an overview of palette-based video coding.

FIG1 is a block diagram illustrating an example video coding system 10 that may utilize the techniques of this disclosure. As used herein, the term “video coder” generally refers to both a video encoder and a video decoder. In this disclosure, the terms “video coding” or “coding” may generally refer to either video encoding or video decoding. The video encoder 20 and video decoder 30 of the video coding system 10 represent examples of devices that may be configured to perform palette-based video coding and entropy coding (e.g., CABAC) according to various examples described in this disclosure. For example, the video encoder 20 and video decoder 30 may be configured to selectively code various blocks of video data, such as CUs or PUs in HEVC coding, using palette-based coding or non-palette-based coding. Non-palette-based coding modes may refer to various inter-predictive temporal coding modes or intra-predictive spatial coding modes, such as the various coding modes specified by the HEVC standard.

1 , video coding system 10 includes a source device 12 and a destination device 14. Source device 12 generates encoded video data. Thus, source device 12 may be referred to as a video encoding device or a video encoding apparatus. Destination device 14 may decode the encoded video data generated by source device 12. Thus, destination device 14 may be referred to as a video decoding device or a video decoding apparatus. Source device 12 and destination device 14 may be examples of video coding devices or video coding apparatuses.

Source device 12 and destination device 14 may comprise a wide range of devices, including desktop computers, mobile computing devices, notebook (e.g., laptop) computers, tablet computers, set-top boxes, handheld phones such as so-called “smart” phones, televisions, cameras, display devices, digital media players, video game consoles, in-car computers, or the like.

Destination device 14 may receive encoded video data from source device 12 via channel 16. Channel 16 may comprise one or more media or devices capable of moving the encoded video data from source device 12 to destination device 14. In one example, channel 16 may comprise one or more communication media that enable source device 12 to transmit the encoded video data directly to destination device 14 in real time. In this example, source device 12 may modulate the encoded video data according to a communication standard, such as a wireless communication protocol, and may transmit the modulated video data to destination device 14. The one or more communication media may include wireless and/or wired communication media, such as a radio frequency (RF) spectrum or one or more physical transmission lines. The one or more communication media may form part of a packet-based network, such as a local area network, a wide area network, or a global network, such as the Internet. The one or more communication media may include routers, switches, base stations, or other equipment that facilitates communication from source device 12 to destination device 14.

In another example, channel 16 may include a storage medium that stores the encoded video data generated by source device 12. In this example, destination device 14 may access the storage medium, for example, via disk access or card access. The storage medium may include a variety of locally accessible data storage media such as Blu-ray discs, DVDs, CD-ROMs, flash memory, or other suitable digital storage media for storing encoded video data.

In yet another example, channel 16 may include a file server or another intermediate storage device that stores the encoded video data generated by source device 12. In this example, destination device 14 may access the encoded video data stored at the file server or other intermediate storage device via streaming or downloading. The file server may be a type of server capable of storing and transmitting the encoded video data to destination device 14. Example file servers include a web server (e.g., for a website), a File Transfer Protocol (FTP) server, a Network Attached Storage (NAS) device, and a local disk drive.

Destination device 14 may access the encoded video data through a standard data connection, such as an Internet connection. Example types of data connections may include a wireless channel (e.g., a Wi-Fi connection), a wired connection (e.g., DSL, cable modem, etc.), or a combination of both, suitable for accessing encoded video data stored on a file server. Transmission of the encoded video data from the file server may be a streaming transmission, a download transmission, or a combination of both.

Source device 12 and destination device 14 may be configured to perform palette-based coding and entropy coding (e.g., CABAC) consistent with this disclosure. However, the techniques of this disclosure for palette-based coding or CABAC are not limited to wireless applications or settings. The techniques may be applicable, for example, to video coding supporting a variety of multimedia applications (e.g., over-the-air television broadcasts, cable television transmissions, satellite television transmissions, streaming video transmissions) over the Internet, encoding of video data stored on a data storage medium, decoding of video data stored on a data storage medium, or other applications. In some examples, video coding system 10 may be configured to support one-way or two-way video transmission to support applications such as video streaming, video playback, video broadcasting, and/or video telephony.

The video coding system 10 shown in FIG1 is merely an example, and the techniques of this disclosure may be applicable to video coding settings (e.g., video encoding or video decoding) that do not necessarily include any data communication between the encoding device and the decoding device. In other examples, data is retrieved from local memory or the like that is streamed over a network. A video encoding device may encode and store data to memory, and/or a video decoding device may retrieve and decode data from memory. In many examples, encoding and decoding are performed by devices that do not communicate with each other but only encode data to memory and/or retrieve and decode data from memory.

1 , source device 12 includes a video source 18, a video encoder 20, and an output interface 22. In some examples, output interface 22 may include a modulator/demodulator (modem) and/or a transmitter. Video source 18 may include a video capture device, such as a camera, a video archive containing previously captured video data, a video feed interface for receiving video data from a video content provider, and/or a computer graphics system for generating video data, or a combination of these sources of video data.

Video encoder 20 may encode video data from video source 18. In some examples, source device 12 transmits the encoded video data directly to destination device 14 via output interface 22. In other examples, the encoded video data may also be stored on a storage medium or a file server for later access by destination device 14 for decoding and/or playback.

1 , destination device 14 includes an input interface 28, a video decoder 30, and a display device 32. In some examples, input interface 28 includes a receiver and/or a modem. Input interface 28 may receive encoded video data via channel 16. Display device 32 may be integrated with destination device 14 or external to destination device 14. Generally, display device 32 displays the decoded video data. Display device 32 may include various display devices, such as a liquid crystal display (LCD), a plasma display, an organic light emitting diode (OLED) display, or another type of display device.

This disclosure may generally refer to video encoder 20 "signaling" or "transmitting" certain information to another device, such as video decoder 30. The terms "signaling" or "transmitting" may generally refer to the communication of syntax elements and/or other data used to decode compressed video data. This communication may occur in real time or near real time. Alternatively, this communication may occur over a span of time, for example, when syntax elements are stored in an encoded bitstream to a computer-readable storage medium at encoding time, which syntax elements may then be retrieved by a decoding device at any time after being stored on such medium. Thus, while video decoder 30 may be referred to as "receiving" certain information, the receipt of the information does not necessarily occur in real time or near real time and may be retrieved from the medium at some time after being stored.

Video encoder 20 and video decoder 30 may each be implemented as any of a variety of suitable circuits, such as one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), discrete logic, hardware, or any combination thereof. If the techniques are implemented partially in software, the device may store instructions for the software in a suitable, non-transitory computer-readable storage medium and may execute the instructions in hardware using one or more processors to perform the techniques of this disclosure. Any of the above (including hardware, software, a combination of hardware and software, etc.) may be considered to be one or more processors. Each of video encoder 20 and video decoder 30 may be included in one or more encoders or decoders, either of which may be integrated as part of a combined encoder/decoder (CODEC) in the corresponding device.

In some examples, video encoder 20 and video decoder 30 operate according to a video compression standard, such as the HEVC standard mentioned above and described in the HEVC standard. In addition to the base HEVC standard, efforts are ongoing to produce scalable video coding, multi-view video coding, and 3D coding extensions for HEVC. Additionally, palette-based coding modes (e.g., as described in this disclosure) may be provided for extending the HEVC standard. In some examples, the techniques described in this disclosure for palette-based coding may be applicable to encoders and decoders configured to operate according to other video coding standards. Thus, for purposes of example, the application of palette-based coding modes for coding of coding units (CUs) or prediction units (PUs) in an HEVC codec is described.

In HEVC and other video coding standards, a video sequence typically comprises a series of pictures. A picture may also be referred to as a "frame." A picture may include three sample arrays, denoted _SL , _SCb , and _SCr . _SL is a two-dimensional array (i.e., a block) of luma samples. _SCb is a two-dimensional array of Cb chroma samples. _SCr is a two-dimensional array of Cr chroma samples. Chroma samples may also be referred to herein as "chroma" samples. In other cases, a picture may be monochrome and may include only an array of luma samples.

To generate an encoded representation of a picture, video encoder 20 may generate a set of coding tree units (CTUs). Each CTU may be a coding tree block of luma samples, two corresponding coding tree blocks of chroma samples, and a syntax structure used to code the samples of the coding tree blocks. A coding tree block may be an N×N block of samples. A CTU may also be referred to as a “tree block” or a “largest coding unit” (LCU). A CTU of HEVC may be broadly similar to macroblocks of other standards, such as H.264/AVC. However, a CTU is not necessarily limited to a specific size and may include one or more coding units (CUs). A slice may include an integer number of CTUs ordered consecutively in a raster scan. A coded slice may include a slice header and slice data. A slice header for a slice may be a syntax structure including syntax elements that provide information about the slice. Slice data may include a coded CTU for the slice.

This disclosure may use the term "video unit," or "video block," or "block" to refer to one or more blocks of samples and syntax structures used to code the samples of the one or more blocks of samples. Example types of video units or blocks may include CTUs, CUs, PUs, transform units (TUs), macroblocks, macroblock partitions, and the like. In some cases, discussion of PUs may be interchangeable with discussion of macroblocks or macroblock partitions.

To generate a coded CTU, video encoder 20 may recursively perform quadtree partitioning on the coding treeblock of the CTU to divide the coding treeblock into coding blocks, hence the name "coding tree unit". A coding block is an N×N block of samples. A CU may be a coding block of luma samples and two corresponding coding blocks of chroma samples of a picture, the picture having a luma sample array, a Cb sample array, and a Cr sample array, and syntax structures used to code the samples of the coding blocks. Video encoder 20 may partition the coding block of a CU into one or more prediction blocks. A prediction block may be a rectangular (i.e., square or non-square) block of samples to which the same prediction applies. A prediction unit (PU) of a CU may be a prediction block of luma samples of a picture, two corresponding prediction blocks of chroma samples of a picture, and syntax structures used to predict the prediction block samples. Video encoder 20 may generate a predictive luma block, a predictive Cb block, and a predictive Cr block for the luma prediction block, Cb prediction block, and Cr prediction block for each PU of the CU.

Video encoder 20 may use intra prediction or inter prediction to generate the predictive blocks for a PU.If video encoder 20 uses intra prediction to generate the predictive blocks for a PU, video encoder 20 may generate the predictive blocks for the PU based on decoded samples of the picture associated with the PU.

If video encoder 20 uses inter prediction to generate the predictive blocks of a PU, video encoder 20 may generate the predictive blocks of the PU based on decoded samples of one or more pictures other than the picture associated with the PU. Video encoder 20 may use uni-prediction or bi-prediction to generate the predictive blocks of the PU. When video encoder 20 uses uni-prediction to generate the predictive blocks of a PU, the PU may have a single motion vector (MV). When video encoder 20 uses bi-prediction to generate the predictive blocks of a PU, the PU may have two MVs.

After video encoder 20 generates predictive blocks (e.g., predictive luma blocks, predictive Cb blocks, and predictive Cr blocks) for one or more PUs of a CU, video encoder 20 may generate a residual block for the CU. Each sample in the residual block of the CU may indicate the difference between a sample in the predictive blocks of the PUs of the CU and a corresponding sample in the coding block of the CU. For example, video encoder 20 may generate a luma residual block for the CU. Each sample in the luma residual block of the CU indicates the difference between a luma sample in one of the CU's predictive luma blocks and a corresponding sample in the CU's original luma coding block. Additionally, video encoder 20 may generate a Cb residual block for the CU. Each sample in the Cb residual block of the CU may indicate the difference between a Cb sample in one of the CU's predictive Cb blocks and a corresponding sample in the CU's original Cb coding block. Video encoder 20 may also generate a Cr residual block for the CU. Each sample in the Cr residual block of the CU may indicate the difference between a Cr sample in one of the CU's predictive Cr blocks and a corresponding sample in the CU's original Cr coding block.

Furthermore, video encoder 20 may use quadtree partitioning to decompose the residual blocks (e.g., luma residual blocks, Cb residual blocks, and Cr residual blocks) of a CU into one or more transform blocks (e.g., luma transform blocks, Cb transform blocks, and Cr transform blocks). A transform block may be a rectangular block of samples to which the same transform is applied. A transform unit (TU) of a CU may be a transform block of luma samples, two corresponding transform blocks of chroma samples, and syntax structures used to transform the transform block samples. Thus, each TU of a CU may be associated with a luma transform block, a Cb transform block, and a Cr transform block. The luma transform block associated with a TU may be a sub-block of the luma residual block of the CU. The Cb transform block may be a sub-block of the Cb residual block of the CU. The Cr transform block may be a sub-block of the Cr residual block of the CU.

Video encoder 20 may apply one or more transforms to a transform block to generate a coefficient block for a TU. A coefficient block may be a two-dimensional array of transform coefficients. The transform coefficients may be scalars. For example, video encoder 20 may apply one or more transforms to a luma transform block of a TU to generate a luma coefficient block for the TU. Video encoder 20 may apply one or more transforms to a Cb transform block of a TU to generate a Cb coefficient block for the TU. Video encoder 20 may apply one or more transforms to a Cr transform block of a TU to generate a Cr coefficient block for the TU.

After generating a coefficient block (e.g., a luma coefficient block, a Cb coefficient block, or a Cr coefficient block), video encoder 20 may quantize the coefficient block. Quantization generally refers to the process of quantizing transform coefficients to potentially reduce the amount of data used to represent the transform coefficients, thereby providing further compression. After video encoder 20 quantizes the coefficient block, video encoder 20 may entropy encode syntax elements that indicate the quantized transform coefficients. For example, video encoder 20 may perform context-adaptive binary arithmetic coding (CABAC) on the syntax elements that indicate the quantized transform coefficients.

In the case of CABAC, as an example, video encoder 20 and video decoder 30 may select a probability model (also referred to as a context model) to code symbols associated with a block of video data based on the context. For example, a context model (Ctx) may be an index or delta used to select one of a plurality of different contexts, each of which may correspond to a specific probability model. Thus, a different probability model is typically defined for each context. After encoding or decoding a bin, the probability model is further updated based on the value of the bin to reflect the latest probability assessment for the bin. For example, the probability model may be maintained as a state in a finite state machine. Each particular state may correspond to a particular probability value. The next state corresponding to the update of the probability model may depend on the value of the current bin (e.g., the currently coded bin). Thus, the selection of the probability model may be influenced by the value of the previously coded bin, as such value at least partially indicates the probability of the bin having a given value. The context coding process described above may generally be referred to as a context-adaptive coding mode.

Therefore, the video encoder 20 can use a probability model to encode the target symbol. Similarly, the video decoder 30 can use a probability model to parse the target symbol. In some cases, the video encoder 20 can use a combination of context adaptive decoding and non-context adaptive decoding to decode the syntax elements. For example, the video encoder 20 can perform context decoding on some bins by selecting a probability model or "context model" that operates on the context to decode some bins. In contrast, for other bins, the video encoder 20 can bypass decode the bin by bypassing or omitting the conventional arithmetic decoding process when decoding the bin. In these examples, the video encoder 20 can use a fixed probability model to bypass decode the bin. That is, the bypass-coded bin does not include context or probability updates.

Video encoder 20 may output a bitstream including entropy-encoded syntax elements. The bitstream may also include syntax elements that are not entropy-encoded. The bitstream may include a sequence of bits that form a representation of a coded picture and associated data. The bitstream may include a sequence of network abstraction layer (NAL) units. Each of the NAL units includes a NAL unit header and encapsulates a raw byte sequence payload (RBSP). The NAL unit header may include a syntax element indicating a NAL unit type code. The NAL unit type code specified by the NAL unit header of the NAL unit indicates the type of the NAL unit. The RBSP may be a syntax structure containing an integer number of bytes encapsulated within the NAL unit. In some cases, the RBSP includes zero bits.

Different types of NAL units may encapsulate different types of RBSPs. For example, a first type of NAL unit may encapsulate RBSPs for picture parameter sets (PPSs), a second type of NAL unit may encapsulate RBSPs for coded slices, a third type of NAL unit may encapsulate RBSPs for supplemental enhancement information (SEI), and so on. NAL units that encapsulate RBSPs for video coding data (as opposed to RBSPs for parameter sets and SEI messages) may be referred to as video coding layer (VCL) NAL units.

Video decoder 30 may receive a bitstream generated by video encoder 20. Furthermore, video decoder 30 may parse the bitstream to decode syntax elements from the bitstream. Video decoder 30 may reconstruct a picture of the video data based at least in part on the syntax elements decoded from the bitstream. The process of reconstructing the video data may be generally inverse to the process performed by video encoder 20. For example, video decoder 30 may use the MVs of the PUs to determine the predictive blocks of the inter-predicted PUs of the current CU. Similarly, video decoder 30 may generate intra-predicted blocks for the PUs of the current CU. Furthermore, video decoder 30 may inverse quantize the transform coefficient blocks associated with the TUs of the current CU. Video decoder 30 may perform an inverse transform on the transform coefficient blocks to reconstruct the transform blocks associated with the TUs of the current CU. Video decoder 30 may reconstruct the coding blocks of the current CU by adding samples of the predictive blocks of the PUs of the current CU to the corresponding residual values obtained from inverse quantization and inverse transform of the transform blocks of the TUs of the current CU. By reconstructing the coding blocks of each CU of the picture, video decoder 30 can reconstruct the picture.

In some examples, video encoder 20 and video decoder 30 may be configured to perform palette-based coding. For example, in palette-based coding, video encoder 20 and video decoder 30 may code a so-called palette as a table of colors or pixel values representing video data for a particular region (e.g., a given block), rather than performing the intra-prediction or inter-prediction coding techniques described above. In this way, the video coder may code an index value for one or more of the pixel values of the current block of video data, rather than the actual pixel values of the current block of video data or their residuals, where the index value indicates an entry in a palette used to represent the pixel values of the current block.

For example, video encoder 20 may encode a block of video data by determining a palette for the block, locating entries in the palette to represent the value of each pixel, and encoding the palette and index values for the pixels that relate the pixel values to the palette. Video decoder 30 may obtain the palette for the block and the index values for the pixels of the block from the encoded bitstream. Video decoder 30 may match the index values of individual pixels with the entries of the palette to reconstruct the pixel values of the block. If the index value associated with an individual pixel does not match any index value of the corresponding palette of the block, video decoder 30 may identify this pixel as an escaped pixel for the purposes of palette-based coding.

As described in more detail below, the basic concept of palette-based coding is that for a given block of video data to be coded, video encoder 20 may derive a palette that includes the most prominent pixel values in the current block. For example, the palette may refer to a number of pixel values that are determined or assumed to be dominant and/or representative of the current CU. Video encoder 20 may first transmit the size and elements of the palette to video decoder 30. In addition, video encoder 20 may encode the pixel values in a given block according to a particular scan order. For each pixel included in a given block, video encoder 20 may signal an index value that maps the pixel value to a corresponding entry in the palette. If a pixel value is not included in the palette (i.e., there is no palette entry that specifies a particular pixel value for the palette-coded block), the pixel is defined as an "out-of-range pixel." According to palette-based coding, video encoder 20 may encode and signal the index value reserved for out-of-range pixels. In some examples, video encoder 20 may also encode and signal the pixel values (or quantized versions thereof) of the outlier pixels included in a given block. For example, video decoder 30 may be configured to determine whether the pixel value matches or is otherwise close to a palette entry based on a distortion metric (e.g., MSE, SAD, and the like).

Upon receiving the encoded video bitstream signaled by video encoder 20, video decoder 30 may first determine a palette based on information received from video encoder 20. Video decoder 30 may then map the received index values associated with pixel positions in a given block to entries of the palette to reconstruct pixel values for the given block. In some cases, video decoder 30 may determine that a pixel of a palette-coded block is an escape pixel, for example, by determining that the pixel is palette-coded by an index value reserved for escape pixels. In the event that video decoder 30 identifies an escape pixel in a palette-coded block, video decoder 30 may receive the pixel values (or quantized versions thereof) of the escape pixels included in the given block. Video decoder 30 may reconstruct any escape pixels included in the palette-coded block by mapping individual pixel values to corresponding palette entries and reconstructing the palette-coded block using the pixel values (or quantized versions thereof).

As stated above, in the example palette coding mode, the palette may include entries numbered by an index. Each entry may represent a color component value or intensity (e.g., in a color space such as YCbCr, RGB, YUV, CMYK, or other format) that can be used as a predictor for a block or a final reconstructed block sample. As described in the standard submission JCTVC-Q0094 (Wei Pu et al., "AHG10: Suggested Software for Palette Coding based on RExt6.0," JCTVC-Q0094, Valencia, Spain, March 27, 2014 - April 4, 2014), the palette may include entries copied from a predictor palette. The predictor palette may include palette entries from blocks previously coded using the palette mode or from other reconstructed samples. For each entry in the predictor palette, a binary flag is sent to indicate whether the entry is copied to the current palette (indicated by flag = 1). This is called a binary palette prediction vector. In addition, the current palette may include (e.g., consist of) explicitly signaled new entries. The number of new entries may also be signaled.

As another example, in palette mode, the palette may include entries numbered by indices representing color component values that can be used as predictors for block samples or ultimately reconstructed block samples. Each entry in the palette may contain, for example, one luma component (e.g., a luma value), two chroma components (e.g., two chroma values), or three color components (e.g., RGB, YUV, etc.). Previously decoded palette entries may be stored in a list. For example, this list can be used to predict palette entries in the current palette mode CU. A binary prediction vector can be signaled via a bitstream to indicate which entries in the list are reused in the current palette. In some examples, run-length coding may be used to compress the binary palette predictor. For example, an order-0 exponential Golomb code (Exp-Golomb code) may be used to code the run-length value.

In this disclosure, it will be assumed that each palette entry specifies the values of all color components of a sample. However, the concepts of this disclosure are applicable to the use of independent palettes and/or independent palette entries for each color component. Also, it is assumed that the samples in a block are processed using a horizontal raster scan order. However, other scans, such as a vertical raster scan order, may also be applicable. As mentioned above, a palette may contain predicted palette entries (e.g., predicted from a palette used to code a previous block) and new entries that are specific to the current block and are explicitly signaled. The number of predicted and new palette entries may be known to the encoder and decoder and their sum may indicate the total palette size in the block.

As proposed in the example of JCTVC-Q0094 cited above, each sample in a block using palette coding may belong to one of three modes, as set forth below:

Escape mode. In this mode, sample values are not included in the palette as palette entries, and quantized sample values are explicitly signaled for all color components. This is similar to signaling a new palette entry, although for new palette entries, the color component values are not quantized.

● CopyAbove mode (also known as CopyFromTop mode). In this mode, the palette entry index of the current sample is copied from the sample located immediately above the current sample in the block of samples. In other examples, for copy-above mode, the video data block may be transposed so that the samples above the block are actually samples to the left of the block.

• Value mode (also called index mode). In this mode, the value of the palette entry index is explicitly signaled.

As described herein, a palette entry index may be referred to as a palette index or simply an index. These terms may be used interchangeably to describe the techniques of the present invention. Additionally, as described in more detail below, a palette index may have one or more associated color or intensity values. For example, a palette index may have a single associated color or intensity value associated with a single color or intensity component of a pixel (e.g., the red component of RGB data, the Y component of YUV data, or the like). In another example, a palette index may have multiple associated color or intensity values. In some cases, palette-based video coding may be applied to code monochrome video. Thus, a "color value" may generally refer to any color or non-color component used to generate a pixel value.

A run value may indicate a run of palette indices coded using the same palette coding mode. For example, with respect to the value mode, a video coder (e.g., video encoder 20 or video decoder 30) may code an index value and a run value indicating a number of consecutive subsequent samples in a scan order that have the same index value and are coded using the palette index. With respect to the CopyAbove mode, the video coder may code an indication that the index value of a current sample value is the same as the index value of an above-neighboring sample (e.g., a sample positioned above the sample is currently being coded in a block) and a run value indicating a number of consecutive subsequent samples in a scan order that also have index values copied from the above-neighboring sample. Thus, in the above examples, a run of palette index values refers to a run of palette values having the same value or a run of index values copied from an above-neighboring sample.

Thus, a run may specify, for a given pattern, the number of subsequent samples that belong to the same pattern. In some cases, signaling index values and run values may be similar to run-length coding. In an example for illustrative purposes, a string of consecutive palette index values corresponding to an index block of a block of video data may be 0, 2, 2, 2, 2, 5. Each index value corresponds to a sample in the block of video data. In this example, the video coder may code the second sample (e.g., a first palette index value of "2") using a value pattern. After coding the index value of 2, the video coder may code a run of 3, indicating that three subsequent samples also have the same palette index value of 2. In a similar manner, coding a run of four palette indices after coding the index using CopyAbove mode may indicate that a total of five palette indices are copied from the corresponding palette index values in the row above the currently coded sample position.

Using a palette, video encoder 20 and/or video decoder 30 may be configured to code a block of samples (e.g., a block of video data) into an index block, where an index block is a block that includes index values mapped to one or more palette entries and, in some examples, one or more escaped pixel values. Video encoder 20 may be configured to entropy encode the index block to compress the index block. Similarly, video decoder 30 may be configured to entropy decode the encoded index block to generate an index block, from which video decoder 30 may generate a block of samples (e.g., a block of video data encoded by encoder 20). For example, run-length-based entropy coding may be used to compress and decompress the index block. In some examples, video encoder 20 and video decoder 30 may be configured to entropy encode and decode the index block, respectively, using CABAC.

To apply CABAC coding to information (e.g., syntax elements, index blocks such as index values of index blocks, or other information), a video coder (e.g., video encoder 20 and video decoder 30) may perform binarization on the information. Binarization refers to the process of converting information into a series of one or more bits. Each series of one or more bits may be referred to as a "bin." Binarization is a lossless process and may include one or a combination of the following coding techniques: fixed-length coding, unary coding, truncated unary coding, truncated Rice coding, Golomb coding, exponential Golomb coding, Golomb-Rice coding, any form of Golomb coding, any form of Rice coding, and any form of entropy coding. For example, binarization may include representing the integer value 5 as 00000101 using an 8-bit fixed-length technique, or as 11110 using a unary coding technique.

After binarization, the video coder can identify a coding context. A coding context can identify the probability of coding a binary number with a specific value. For example, the coding context can indicate a 0.7 probability of coding a 0-valued binary and a 0.3 probability of coding a 1-valued binary. After identifying the coding context, the video coder can arithmetically code the binary based on the context, which is known as context mode coding. A binary coded using CABAC context mode coding can be referred to as a "context binary."

In addition, a video coder (e.g., video encoder 20 and video decoder 30) may use bypass CABAC coding (e.g., bypass mode coding) to code some bins instead of performing context mode coding on all bins. Bypass mode coding refers to the process of arithmetically coding a bin without using an adaptive context (e.g., coding context). That is, the bypass coding engine does not select a context and may assume that the probability of both symbols (0 and 1) is 0.5. Although bypass mode coding may not be as bandwidth efficient as context mode coding, it may be computationally less expensive to perform bypass mode coding on a bin instead of performing context mode coding on the bin. Furthermore, performing bypass mode coding may allow for higher parallelism and throughput. A bin coded using bypass mode coding may be referred to as a "bypass bin."

Video encoder 20 and video decoder 30 may be configured with a CABAC coder (e.g., a CABAC encoder and a CABAC decoder, respectively). The CABAC coder may include a context mode coding engine for performing CABAC context mode coding and a bypass mode coding engine for performing bypass mode coding. If a bin is context mode coded, the context mode coding engine is used to code the bin. The context mode coding engine may require more than two processing cycles to code a single bin. However, with proper pipeline design, the context mode coding engine may only require n+M cycles to encode n bins, where M is the overhead of the initial pipeline. M is typically greater than 0.

At the start of the CABAC coding process (i.e., each transition from bypass mode to context mode and vice versa), additional pipeline load is introduced. If a binary is coded in bypass mode, the bypass mode coding engine is used to code this binary. The bypass mode coding engine can be expected to require only one cycle to code n bits of information, where n may be greater than one. Therefore, if all bypass bins within a set of bypass bins and context bins are coded together and all context bins within the set are coded together, the total number of cycles for coding the set of bypass bins and context bins can be reduced. In particular, coding the bypass bins together before or after transitioning to context mode coding can save the additional load required to restart the context mode coding engine. For example, when encoding or decoding a block of video data using palette mode, respectively, video encoder 20 and video decoder 30 can be configured to switch between bypass mode and context mode. In another example, video encoder 20 and video decoder 30 may be configured to reduce the number of times the encoding or decoding process switches between bypass mode to context mode when encoding or decoding a block of video data using palette mode.

The techniques described in this disclosure may include techniques for signaling a palette-based video coding mode, transmitting a palette, deriving a palette, signaling a scan order, deriving a scan order, and transmitting various combinations of one or more of palette-based video coding maps and other syntax elements. For example, the techniques of this disclosure may be directed to entropy coding palette information. In some examples, the techniques of this disclosure may be particularly useful for improving coding efficiency and reducing coding inefficiencies associated with palette-based video coding. Thus, as described in more detail below, in some cases, the techniques of this disclosure may improve efficiency and improve bit rate when coding video data using a palette mode.

As described above, in the current palette mode design in screen content coding, the syntax elements of palette_index_idc and palette_escape_val are CABAC bypass coded and interleaved with other syntax elements (e.g., palette_run_msb_id_plus1) that are CABAC context coded. However, grouping bypass coded information (e.g., syntax elements) together can be beneficial, which can improve coding efficiency and/or reduce codec complexity.

For example, as defined in JCTVC-S1005, the syntax element palette_index_idc may indicate an index into an array denoted as currentPaletteEntries. The value of palette_index_idc may be in the range of 0 to (adjustedIndexMax-1), inclusive. For example, as defined in JCTVC-S1005, the syntax element palette_escape_val may specify the quantized escaped coded sample value of a component. For example, as defined in JCTVC-S1005, palette_run_msb_id_plus1 minus 1 may specify the index of the most significant bit in the binary representation of a paletteRun. For example, as defined in JCTVC-S1005, when palette_run_type_flag is equal to COPY_ABOVE_MODE, a variable paletteRun may specify the number of consecutive positions with the same palette index as a position in the row above, minus 1, or the number of consecutive positions with the same palette index, minus 1, when palette_run_type_flag is equal to COPY_INDEX_MODE. Additional details about palette_index_idc, palette_escape_val, palette_run_msb_id_plus1, currentPaletteEntries, adjustedIndexMax, and paletteRun can be found in JCTVC-S1005.

In some examples, this disclosure describes methods for grouping all syntax elements palette_index_idc before a palette index block coding portion to improve CABAC throughput. For example, video encoder 20 may be configured to encode all syntax elements palette_index_idc before a palette index block coding portion. For example, video encoder 20 may be configured to encode all syntax elements palette_index_idc before encoding syntax elements to be encoded by a context mode. Similarly, video decoder 30 may be configured to decode all syntax elements palette_index_idc before a palette index block coding portion. For example, video decoder 30 may be configured to decode all syntax elements palette_index_idc before decoding syntax elements encoded by a context mode.

As another example, video encoder 20 may be configured to bypass-mode encode all syntax elements palette_index_idc before the palette index block coding portion, such that all syntax elements palette_index_idc are encoded before syntax elements related to palette run type (e.g., CopyAbove mode or index mode) and/or run length (e.g., palette_run_msb_id_plus1) are encoded. Similarly, video decoder 30 may be configured to decode all syntax elements palette_index_idc for a block before the palette index block coding portion of the block, such that all syntax elements palette_index_idc are decoded before syntax elements related to palette run type (e.g., CopyAbove mode or index mode) and/or run length (e.g., palette_run_msb_id_plus1) are decoded.

Syntax elements regarding palette run type (e.g., CopyAbove mode or indexed mode) and/or run length (e.g., palette_run_msb_id_plus1)

As another example, example video encoder 20 may be configured to encode all syntax elements palette_index_idc before context encoding syntax elements regarding palette run type (e.g., CopyAbove mode or index mode) and/or run length (e.g., palette_run_msb_id_plus1). Similarly, video decoder 30 may be configured to decode all syntax elements palette_index_idc before context decoding syntax elements regarding palette run type (e.g., CopyAbove mode or index mode) and/or run length (e.g., palette_run_msb_id_plus1).

As another example, video encoder 20 may be configured to encode all syntax elements palette_index_idc within a palette slab coded portion before encoding syntax elements to be context-mode encoded. Similarly, video decoder 30 may be configured to decode all syntax elements palette_index_idc within a palette slab coded portion before decoding syntax elements to be context-mode encoded. As another example, video encoder 20 may be configured to encode all syntax elements palette_index_idc within a palette slab coded portion before context-encoding syntax elements regarding palette run type (e.g., CopyAbove mode or index mode) and/or run length (e.g., palette_run_msb_id_plus1). Similarly, video decoder 30 may be configured to decode all syntax elements palette_index_idc within the palette block coded portion before context decoding syntax elements regarding palette run type (eg, CopyAbove mode or index mode) and/or run length (eg, palette_run_msb_id_plus1).

In general, video encoder 20 and video decoder 30 may be configured to encode or decode palette_index_idc in bypass mode for encoding or decoding syntax elements, respectively, using context modes, without interleaving. For example, video encoder 20 and video decoder 30 may be configured to encode or decode palette_index_idc in bypass mode for encoding or decoding syntax elements, respectively, using context modes, without interleaving. As another example, video encoder 20 may be configured to bypass encode all instances of the palette_index_idc syntax element before context encoding syntax elements that require context modes. Similarly, video decoder 30 may be configured to bypass decode all instances of the palette_index_idc syntax element before context decoding syntax elements that require context modes. As another example, video encoder 20 may be configured to bypass encode all instances of the syntax element palette_index_idc before context encoding syntax elements related to palette run type (e.g., CopyAbove mode or index mode) and/or run length (e.g., palette_run_msb_id_plus1). Similarly, video decoder 30 may be configured to bypass decode all instances of the syntax element palette_index_idc before context decoding syntax elements related to palette run type (e.g., CopyAbove mode or index mode) and/or run length (e.g., palette_run_msb_id_plus1).

Video encoder 20 and video decoder 30 may also respectively encode and decode a value representing the number of occurrences of palette_index_idc. Video encoder 20 and video decoder 30 may use the value representing the number of occurrences of palette_index_idc to respectively encode or decode each of the syntax elements palette_index_idc. The techniques described in this disclosure may also eliminate redundancy of syntax elements related to palette run lengths and eliminate redundancy of palette_run_type_flag and palette_index_idc.

In some examples, this disclosure describes methods for grouping all syntax elements palette_escape_val before a palette index block coding portion of a block (e.g., a PU or CU) to improve CABAC throughput. For example, video encoder 20 may be configured to encode all syntax elements palette_escape_val before the palette index block coding portion of the block. For example, video encoder 20 may be configured to bypass-mode encode all syntax elements palette_escape_val before the palette index block coding portion so that all syntax elements palette_escape_val are encoded before encoding syntax elements for palette run type (e.g., CopyAbove mode or index mode) and/or run length (e.g., palette_run_msb_id_plus1). Similarly, video decoder 30 may be configured to decode all syntax elements palette_escape_val for a block before the palette index block coding portion of the block such that all syntax elements palette_escape_val are decoded before syntax elements for palette run type (e.g., CopyAbove mode or index mode) and/or run length (e.g., palette_run_msb_id_plus1) are decoded. As another example, video encoder 20 may be configured to encode all syntax elements palette_escape_val before encoding syntax elements to be context-mode encoded. For example, video encoder 20 may be configured to encode all syntax elements palette_escape_val before context encoding syntax elements for palette run type (e.g., CopyAbove mode or index mode) and/or run length (e.g., palette_run_msb_id_plus1). Similarly, video decoder 30 may be configured to decode all syntax elements palette_escape_val before the palette index block coded portion of a block. For example, video decoder 30 may be configured to decode all syntax elements palette_escape_val before decoding context mode encoded syntax elements in a block.

As another example, video encoder 20 may be configured to encode all syntax elements palette_escape_val within the palette plate coded portion of a block before encoding syntax elements to be context-mode encoded. Similarly, video decoder 30 may be configured to decode all syntax elements palette_escape_val within the palette plate coded portion of a block before decoding syntax elements to be context-mode encoded for the block.

In general, video encoder 20 and video decoder 30 may be configured to encode or decode the palette_escape_val of a block (e.g., a PU or CU) in bypass mode for encoding or decoding syntax elements, respectively, using a context mode for the block, without interleaving. For example, video encoder 20 and video decoder 30 may be configured to encode or decode the palette_escape_val in bypass mode for encoding or decoding syntax elements, respectively, using a context mode for palette run type (e.g., CopyAbove mode or index mode) and/or run length (e.g., palette_run_msb_id_plus1). As another example, video encoder 20 may be configured to bypass encode all instances of the palette_escape_val syntax element for the block before context encoding syntax elements that require a context mode. Similarly, video decoder 30 may be configured to bypass decode all instances of the palette_escape_val syntax element for the block (e.g., a PU or CU) before context decoding syntax elements that require a context mode for the block.

Video encoder 20 and video decoder 30 may also respectively encode and decode a value representing the number of occurrences of palette_escape_val for a block. Video encoder 20 and video decoder 30 may use the value representing the number of occurrences of palette_escape_val to respectively encode or decode each of the syntax elements palette_escape_val for the block. The techniques described in this disclosure may reduce the dynamic range of palette_index_idc for a block, which may result in improved coding efficiency.

The techniques, aspects, and/or examples described herein may be utilized in any combination or independently of one another. For example, video encoder 20 and video decoder 30 may be configured to perform any one or any suitable combination of one or more of the techniques, aspects, and/or examples described herein.

In some examples, as described above, to improve CABAC throughput, a video coder (e.g., video encoder 20) may be configured to group all occurrences of the syntax element palette_index_idc. For example, a video coder (e.g., video encoder 20) may be configured to group all occurrences of the syntax element palette_index_idc in a current block (e.g., a PU or CU) before the index-coded portion of the current block. Similarly, as described above, a video decoder (e.g., video decoder 30) may be configured to decode all occurrences of the syntax element palette_index_idc. FIG7 illustrates an example in which video encoder 20 may be configured to group all occurrences of the syntax element palette_index_idc in a current block (e.g., a CU) before the index-coded block, for example, with reference to R. Joshi and J. Xu, “High Efficiency Video Coding (HEVC) Screen Content Coding: Draft 2,” JCTVC-S1005, section 7.3.3.8. This aspect of this disclosure is referred to as Aspect 1. 7 illustrates an example of video encoder 20 that repositions an instance of the syntax element palette_index_idc to the front of an index coded block (which may also be referred to as a palette block coded portion or the front of an index coded block). By repositioning the illustrated instance of the illustrated syntax element palette_index_idc, video encoder 20 may be configured to improve CABAC throughput by coding all instances of the syntax element palette_index_idc using bypass mode and switching to a context mode to code palette information that occurs after all instances of the syntax element palette_index_idc in the index coded block are encoded in bypass mode.

According to the disclosure of JCTVC-S1005, one instance of palette_index_idc will be coded in bypass mode, followed by one instance of a syntax element for the palette run type and one instance of palette_run_msb_id_plus1 in context mode, and the process will repeat while (scanPos < nCbS * nCbS), meaning that the video encoder will switch back and forth between bypass mode coding and context mode coding because the syntax elements to be coded using bypass mode are not grouped together. This is depicted in FIG7 , where the ellipse is directly below the loop of "while (scanPos < nCbS * nCbS)" (i.e., the ellipse does not include information showing that the syntax element for the palette run type is encoded using context mode), and the block surrounding the if statement for the subsequent palette_index_idc syntax element is below the loop of "while (scanPos < nCbS * nCbS)" and the subsequent pseudo code. However, as described above, FIG7 also depicts aspect 1 of this disclosure, which is grouping (also referred to as repositioning) one or more instances of the syntax element palette_index_idc, for example, before an index coding block. By repositioning one or more syntax elements (e.g., or other palette information) to be encoded using bypass mode, a video encoder (e.g., video encoder 20) can increase the throughput of entropy coding by reducing the number of times the video encoder or video decoder must switch between bypass mode encoding and context mode encoding. Similarly, by repositioning one or more syntax elements in this manner, the throughput of a video decoder (e.g., video decoder 30) can be increased because the video decoder must switch between bypass mode decoding and context mode decoding less frequently. In some examples of the techniques described in this disclosure, all instances of the palette_index_idc syntax element are coded in bypass mode before instances of palette_run_msb_id_plus1 are coded in context mode.

In some examples, video encoder 20 may be configured to signal the number of occurrences (e.g., example) of the syntax element palette_index_idc using a syntax element called, for example, num_palette_index. For example, video encoder 20 may signal the value of num_palette_index in the bitstream, where the value represents the number of occurrences of the syntax element palette_index_idc. In some examples, video encoder 20 may be configured not to signal an index value such as palette_index_idc. In these examples, video decoder 30 may be configured to infer the index value. For example, occurrences of palette_index_idc may be counted as num_palette_index, which may be equal to the number of times a run type (e.g., COPY_INDEX_MODE) occurs in a particular block. Even when the run type (e.g., COPY_INDEX_MODE) is inferred or palette_index_idc is inferred, it is still counted in num_palette_index. As used herein, in some examples, a reference to a plurality of indices that are parsed, decoded, or held to be decoded may refer to a number of COPY_INDEX_MODEs, regardless of whether a mode or index is inferred. Video decoder 30 may be configured to determine the number of occurrences (e.g., instances) of the syntax element palette_index_idc by, for example, decoding an encoded value corresponding to the num_palette_index syntax element from a bitstream. This aspect of the disclosure is referred to as Aspect 2. Video encoder 20 and video decoder 30 may be configured to implement Aspect 1 with or without Aspect 2. In terms of syntax, according to some examples, Aspect 2 may be defined as:

indices_idc_coding(){ num_palette_index ae(v) for(i=0;i<num_palette_index;i++) palette_index_idc ae(v) }

In some examples, video encoder 20 and video decoder 30 may be configured to implement (e.g., by enabling) aspect 1 and aspect 2 only when variable indexMax is greater than 1. This aspect of this disclosure is referred to as aspect 3. Variable indexMax may specify the number of different values that the palette index has for the current coding unit. In some examples, indexMax may refer to the number of (palette size + palette_escape_val_present_flag).

In some examples, Aspect 1 and Aspect 2 may be disabled when: (a) there are no escape pixels in the current block (i.e., palette_escape_val_present_flag == 0) and the palette size is less than 2; or (b) there may be at least one escape pixel in the current block (i.e., palette_escape_val_present_flag == 1) and the palette size is equal to 0. In other examples, video encoder 20 and video decoder 30 may be configured to implement (e.g., by enabling) Aspect 1 and Aspect 2 only when variable indexMax is greater than 2. Similarly, in examples where indexMax is equal to (palette size + palette_escape_val_present_flag), Aspect 1 and Aspect 2 may be enabled (e.g., implemented) when indexMax is greater than 1. For example, if the palette size is 0 and palette_escape_val_present_flag is 1, then all pixels in the block are escape pixels; and, thus, the index is already known. As another example, if palette_escape_val_present_flag is 0 and the palette size is 1, then, again, each pixel has index 0; and, thus, it may not be necessary to signal the index.

In some examples, video encoder 20 may be configured to implement aspects 1 and 2 such that a last occurrence (e.g., instance) of the syntax element palette_run_type_flag[xC][yC] is signaled by video encoder 20 before the palette index block coding portion. This aspect of the disclosure is referred to as aspect 4. Specifically, according to some examples, a syntax table may be updated by adding a new syntax element palette_last_run_type_flag, as follows:

indices_idc_coding(){ num_palette_index ae(v) for(i=0;i<num_palette_index;i++) palette_index_idc ae(v) palette_last_run_type_flag ae(v) }

Video decoder 30 may be configured to determine the last occurrence (e.g., example) of the syntax element palette_run_type_flag[xC][yC] by, for example, decoding an encoded palette_last_run_type_flag syntax element from a bitstream. The syntax element of palette_last_run_type_flag may be bypass-mode coded or context-mode coded, for example, in CABAC. In examples where the palette_last_run_type_flag syntax element is context-mode coded, the palette_last_run_type_flag syntax element may share the same context as palette_run_type_flag[xC][yC], or the palette_last_run_type_flag syntax element may have its own context independent of the context of palette_run_type_flag[xC][yC].

In some examples, video decoder 30 may be configured to decode the syntax element palette_index_idc so that the dynamic range adjustment process is disabled for the first occurrence (e.g., instance) of the palette_index_idc syntax element. This aspect of the disclosure is referred to as aspect 5. Specifically, a process very similar to the derivation process of the adjustedIndexMax variable specified in JCTVC-S1005 section 7.4.9.6 is used. For comparison purposes, JCTVC-S1005 describes that the variable adjustedIndexMax may be derived as follows:

adjustedIndexMax=indexMax

if(scanPos>0)

adjustedIndexMax -= 1

However, according to aspect 5 of the present invention, the variable adjustedIndexMax may be derived as described below. For example, for each block, before parsing, the variable isFirstIndex is initialized to 1. In some examples, the variable adjustedIndexMax may be derived as follows:

adjustedIndexMax=indexMax

palette_index_idc

if(isFirstIndex){

adjustedIndexMax-=isFirstIndex

isFirstIndex=0

}

In some examples, before parsing and decoding a paletteRun, video decoder 30 may be configured to check one or more conditions. This aspect of the disclosure is referred to as Aspect 6. For example, as disclosed in JCTVC-S1005, when palette_run_type_flag is equal to COPY_ABOVE_MODE, the variable paletteRun may specify the number of consecutive positions having the same palette index as the position in the above row minus 1, or when palette_run_type_flag is equal to COPY_INDEX_MODE, specify the number of consecutive positions having the same palette index minus 1.

With reference to one or more conditions that video decoder 30 may be configured to check, if video decoder 30 determines that one or more of the conditions are met, video decoder 30 may be configured to bypass the parsing and decoding process for syntax elements related to the current paletteRun (i.e., palette_run_msb_id_plus1 and palette_run_refinement_bits). In this example, video decoder 30 may be configured to implicitly derive the current paletteRun as the run reaches the end of the current block (i.e., equal to maxPaletteRun). A list of one or more conditions relevant to aspect 6 includes: (i) the number of parsed/decoded palette_index_idc syntax elements is equal to num_palette_index; or, alternatively, the variable paletteIndicesLeft can be defined as equal to num_palette_index minus the number of received indices, and using that definition, this condition can be stated as paletteIndicesLeft is equal to zero; and/or (ii) the current palette run type palette_run_type_flag[xC][yC] is equal to the last palette run type palette_last_run_type_flag.

In some examples, if conditions (i) and (ii) described above for aspect 6 are not simultaneously met, video encoder 20 may be configured to encode the palette run length into the bitstream. This aspect of the disclosure is referred to as aspect 7. In other examples, if conditions (i) and (ii) described above for aspect 6 are not simultaneously met, video encoder 20 may be configured to encode the palette run length into the bitstream. According to the current draft specification JCTVC-S1005, a parameter specifying the maximum achievable run length is required as input, where the parameter is equal to maxPaletteRun = nCbS * nCbS - scanPos - 1. However, according to this disclosure, video encoder 20 may be configured to reduce the parameter specifying the maximum achievable run length to maxPaletteRun = nCbS * nCbS - scanPos - 1 - paletteIndicesLeft to improve coding efficiency. As used herein, nCbS specifies the size of the current block.

In some examples, if a block is not in palette sharing mode (i.e., palette_share_flag[x0][y0] == 0), a normative constraint may be imposed on video encoder 20 requiring it to never signal a palette with unused entries. This aspect of the disclosure is referred to as Aspect 8.

In some examples, for palette modes that do not use palette sharing, video decoder 30 may be configured to bypass decoding of the current occurrence (e.g., instance) of the syntax element palette_index_idc when one or more of the following conditions are met: condition 1, where num_palette_index is equal to indexMax, and condition 2, where paletteIndicesLeft == 1. In these examples, video decoder 30 may be configured to implicitly derive the value of the current occurrence of the syntax element palette_index_idc as an index into the palette, but already appears in the index map during the decoding process (e.g., has not appeared in the index map until this point in the decoding process). This aspect of this disclosure is referred to as Aspect 9.

Video decoder 30 may be configured to derive the currently occurring value of the syntax element palette_index_idc described above for aspect 9, because condition 1 requires that each index between 0 and (indexMax-1), inclusive, be signaled and signaled only once. Thus, after the first (indexMax-1) index value is signaled, video decoder 30 may be configured to derive the number of last index values between 0 and (indexMax-1) that have occurred during the decoding process of the current index map.

In some examples, video decoder 30 may be configured to bypass decoding of a current occurrence (e.g., instance) of the syntax element palette_run_type_flag[xC][yC] when one or both of the following conditions are met: condition 1, where paletteIndicesLeft is equal to 0, and condition 2, where the current pixel is at the last position of the block in scan order. In these examples, video decoder 30 may be configured to implicitly derive the value of the current occurrence of the syntax element palette_run_type_flag[xC][yC]. For example, when condition 1 is met, palette_run_type_flag[xC][yC] video decoder 30 may be configured to derive the value of the current occurrence of the syntax element palette_run_type_flag[xC][yC] as COPY_ABOVE_MODE. As another example, when Condition 1 is satisfied, if paletteIndicesLeft>0, then palette_run_type_flag[xC][yC] video decoder 30 may be configured to derive the currently occurring value of the syntax element palette_run_type_flag[xC][yC] as COPY_INDEX_MODE, and if paletteIndicesLeft=0, as COPY_ABOVE_MODE. This aspect of the disclosure is referred to as Aspect 10.

As described herein, video encoder 20 and video decoder 30 may be configured to determine when a condition is satisfied. For example, with respect to aspect 10, video decoder 30 may be configured to determine whether condition 1 is satisfied. Similarly, video decoder 30 may be configured to determine whether condition 2 is satisfied. In response to determining that condition 1 or condition 2 is satisfied, video decoder 30 may be configured to derive the currently occurring value of the syntax element palette_run_type_flag[xC][yC], as described above.

In some examples, video encoder 20 and video decoder 30 may be configured to encode or decode, respectively, the num_palette_index syntax element using any family of Golomb codes. For example, video encoder 20 and video decoder 30 may be configured to encode or decode, respectively, the num_palette_index syntax element using, for example, a Golombre code, an exponential Golombre code, a truncated Rice code, a unary code, or a concatenation of a Golombre code and an exponential Golombre code. This aspect of the disclosure is referred to as Aspect 11.

In other examples, video encoder 20 and video decoder 30 may be configured to encode or decode, respectively, the num_palette_index syntax element using any truncated version of any Golomb family of codes. For example, video encoder 20 and video decoder 30 may be configured to encode or decode, respectively, the num_palette_index syntax element using, for example, a truncated Golomblais code, a truncated Exponential Golomb code, a truncated Rice code, a truncated unary code, or a concatenation of a truncated Rice code and an Exponential Golomb code (e.g., the program code used to decode the coeff_abs_level_remaining syntax element). This aspect of the disclosure is referred to as Aspect 12.

In some examples, any Golomb parameter associated with Aspect 11 or Aspect 12 depends on CU size, indexMax, palette size, and/or palette_escape_val_present_flag. The dependencies may be expressed as equations or lookup tables. In some examples, video encoder 20 may be configured to signal the parameters in the lookup table or equation so that they are received by video decoder 30, for example, in an SPS/PPS/slice header. Alternatively or additionally, the parameters may be adaptively updated on a block-by-block basis. This aspect of the disclosure is referred to as Aspect 13. In some examples, the Golomb parameter cRiceParam may depend on indexMax, palette size, and/or palette_escape_val_present_flag. The Golomb parameter cRiceParam may vary from block to block.

In some examples, video encoder 20 may be configured to predictively encode num_palette_index by signaling the difference between the value of num_palette_index and a delta value, which may be expressed by a syntax element referred to as, for example, numPaletteIndexCoded. This aspect of this disclosure is referred to as aspect 14. For example, video encoder 20 may be configured to predictively encode num_palette_index by signaling the value of numPaletteIndexCoded, where numPaletteIndexCoded = num_palette_index - IndexOffsetValue. Similarly, video decoder 30 may be configured to predictively decode num_palette_index by, for example, determining the value of numPaletteIndexCoded from the bitstream. Because numPaletteIndexCoded = num_palette_index - IndexOffsetValue, video decoder 30 may be configured to determine the value of num_palette_index based on the determined value of numPaletteIndexCoded and the value of IndexOffsetValue.

In some examples, the variable IndexOffsetValue may be a constant. For example, IndexOffsetValue may be equal to a constant value of X for palette sharing mode or may be equal to a constant value of Y for non-palette sharing mode, where X and Y are integers. In some examples, X and Y may be the same (e.g., X equals Y, such as 1). In other examples, X and Y may be different (e.g., X is not equal to Y). For example, when palette sharing mode is used, IndexOffsetValue may be equal to 9, and when non-sharing mode is used, IndexOffsetValue may be equal to 33. In some examples, the variable IndexOffsetValue may depend on the syntax element palette_share_flag[x0][y0]. In other examples, the variable IndexOffsetValue may depend on the variable indexMax. For example, IndexOffsetValue may be equal to indexMax. In some examples, video encoder 20 may be configured to signal IndexOffsetValue in the SPS/PPS/slice header. Alternatively or additionally, the variable IndexOffsetValue may be adaptively updated block by block, meaning that the value corresponding to the variable IndexOffsetValue may be adaptively updated block by block.

In some examples, video encoder 20 and video decoder 30 may be configured to encode or decode, respectively, numPaletteIndexCoded, which may be coded using any Golomb code family or any truncated Golomb code family (e.g., a concatenation of a Golombrite code and an Exponential Golomb code). For example, when IndexOffsetValue is equal to 1, numPaletteIndexCoded is equal to num_palette_index-1.

In some examples, video encoder 20 and video decoder 30 may be configured to encode or decode numPaletteIndexCoded, respectively, using any family of Golomb codes. For example, video encoder 20 and video decoder 30 may be configured to encode or decode numPaletteIndexCoded, respectively, using, for example, Golombre codes, exponential Golombre codes, truncated Rice codes, unary codes, or a concatenation of Golombre codes and exponential Golombre codes.

In other examples, video encoder 20 and video decoder 30 may be configured to encode or decode numPaletteIndexCoded, respectively, using any truncated version of any family of Golomb codes. For example, video encoder 20 and video decoder 30 may be configured to encode or decode numPaletteIndexCoded, respectively, using, for example, a truncated Golomblais code, a truncated Exponential Golomb code, a truncated Rice code, a truncated unary code, or a concatenation of a truncated Rice code and an Exponential Golomb code (e.g., the code used to code the coeff_abs_level_remaining syntax element).

To code numPaletteIndexCoded, video encoder 20 may be configured to determine the sign of numPaletteIndexCoded. Video encoder 20 may be configured to signal a flag indicating whether the value of numPaletteIndexCoded is negative (e.g., whether the sign is positive or negative). This aspect of the disclosure is referred to as aspect 15. In some examples, video encoder 20 may be configured to signal the flag and then signal the value of numPaletteIndexCoded. In other examples, video encoder 20 may be configured to signal the value of numPaletteIndexCoded and then signal the flag. Video encoder 20 may be configured to encode the flag using bypass mode or context mode. If context coded, the context may depend on CU size, indexMax, palette size, and/or palette_escape_val_present_flag.

As described above, video encoder 20 may be configured to determine the sign of numPaletteIndexCoded according to some examples. If the sign of the determined numPaletteIndexCoded is negative, video encoder 20 may be configured to encode the value of (1-numPaletteIndexCoded) into the bitstream. If the sign of the determined numPaletteIndexCoded is positive, video encoder 20 may be configured to encode the value of numPaletteIndexCoded into the bitstream. Video encoder 20 may be configured to encode the value of (1-numPaletteIndexCoded) or the value of numPaletteIndexCoded using different Golomb code parameters depending on, for example, the sign of numPaletteIndexCoded, the CU size, indexMax, the palette size, and/or the palette_escape_val_present_flag.

In some examples, video encoder 20 may be configured to use a mapping operation to represent the negative portion of numPaletteIndexCoded, which may be in addition to or instead of aspect 15. This aspect of the disclosure is referred to as aspect 16. For example, a mapping interval may be introduced and defined as a variable mapInterval. Video encoder 20 may be configured to use the variable mapInterval to map negative values of numPaletteIndexCoded to equally spaced positive values equal to: mapInterval × (-numPaletteIndexCoded) - 1. The corresponding positive values of numPaletteIndexCoded may thus be shifted to accommodate the positions obtained by the mapped negative values.

For example, if mapInterval=2, and numPaletteIndexCoded is selected from {-3, -2, -1, 0, 1, 2, 3}, the mapping may be as illustrated below in Table 1. In this example, video encoder 20 may be configured to encode the value of numPaletteIndexCode using the mapped value in Table 1. For example, video encoder 20 may be configured to entropy encode the mapped value into binary form.

Table I. Codeword mapping examples

In some examples, video encoder 20 may be configured to represent the negative portion of numPaletteIndexCoded using the mapping operation described with respect to aspect 16. Video encoder 20 may also be configured to remove one or more redundancies that may arise when implementing aspect 16. This aspect of the disclosure is referred to as aspect 17. For example, the number of negative values of numPaletteIndexCoded may be in the range A = {-1, -2, ..., -IndexOffsetValue+1}. As another example, the number of negative values of numPaletteIndexCoded may be in the range A = {-1, -2, ..., -IndexOffsetValue+1, IndexOffsetValue}. In either of these examples, the mapped value need only retain the (IndexOffsetValue-1) or IndexOffsetValue position of the negative numPaletteIndexCoded value. For example, if mapInterval=2 and numPaletteIndexCoded is selected from {-3, -2, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8}, the mapping may be as illustrated in Table II below. In this example, video encoder 20 may be configured to encode the value of numPaletteIndexCode using the mapped value in Table II. For example, video encoder 20 may be configured to entropy encode the mapped value into binary form.

Table II. Codeword mapping examples

As shown in Table II above, video encoder 20 may be configured to encode mapped values corresponding to the values of numPaletteIndexCode such that negative and positive values of numPaletteIndexCode are not interleaved after a certain value. For example, in the example of Table II above, there is no interleaving of positive and negative values of numPaletteIndexCoded through the mapped values starting with the value 3 of numPaletteIndexCoded (i.e., positive values 3-8 of numPaletteIndexCoded are mapped to mapped values 6-11).

As described above, video encoder 20 may also be configured to remove one or more redundancies that may occur when implementing aspect 16. Another redundancy example different from the redundancy example described above includes that since num_palette_index is capped at the total number of pixels in the current block, numPaletteIndexCoded is also capped. Therefore, after assigning positions with all probabilities of positive codewords, negative values may be mapped to the following positions without interleaving. For example, if mapInterval=2, and numPaletteIndexCoded is selected from {-5, -4, -3, -2, -1, 0, 1, 2, 3}, then the mapping may be as illustrated in Table III below. In this example, video encoder 20 may be configured to encode the value of numPaletteIndexCode using the mapped values in Table III. For example, video encoder 20 may be configured to entropy encode the mapped values into binary form.

Table III. Codeword mapping examples

As shown in Table III above, video encoder 20 may be configured to encode mapped values corresponding to the values of numPaletteIndexCode such that negative and positive values of numPaletteIndexCode are not interleaved after a certain value. For example, in the example of Table III above, there is no interleaving of positive and negative values of numPaletteIndexCoded through the mapped values starting with a value of 4 for numPaletteIndexCoded (i.e., negative values of numPaletteIndexCoded, -4 and -5, are mapped to mapped values of 7 and 8).

In some examples, video encoder 20 may be configured to further decouple the relationship between palette indices and palette runs. This aspect of this disclosure is referred to as aspect 18. For example, rather than allowing the context of palette run coding to depend on parsed or decoded indices, video encoder 20 may be configured so that the context of palette run coding depends on the aforementioned palette run length or on palette_run_msb_id_plus1, indexMax, and/or the CU size of the aforementioned run.

In some examples, to further group bypass binaries, video encoder 20 may be configured to signal the number of escape indices and escape values in a palette block before signaling the palette run type (i.e., palette_run_type_flag[xC][yC]) as follows. This aspect of the disclosure is referred to as Aspect 19. Italicized text illustrates changes relative to the prior version of JCT-VC S1005, and bold text and "ae(v)" in the right column indicate signaling of syntax elements.

In the example above, escape_idc_coding() consists of signaling the number of escape indices and the escape value corresponding to each escape index. The number of escape indices in the palette block may not be signaled if palette_escape_val_present_flag is 0 or if indexMax is equal to 0. In the former case, the number of escape indices is inferred to be 0, and no escape value is signaled. In the latter case, when indexMax is equal to 0, the number of escape indices is inferred to be equal to the block size when palette_escape_val_present_flag is equal to 1 and an escape value is signaled, or zero when palette_escape_val_present_flag is equal to 0.

In some examples, video encoder 20 may be configured to signal the number of escape indices using the Golomb family of codes. This aspect of the disclosure is referred to as aspect 20. For example, video encoder 20 may be configured to signal the number of escape indices using, for example, Golombre codes, exponential Golombre codes, truncated Rice codes, unary codes, or a concatenation of Golombre codes and exponential Golombre codes. Truncated versions of the above codes may be used with a maximum set equal to the block size.

In some examples, a normative restriction is proposed for palette_escape_val_present_flag: when palette_escape_val_present_flag is equal to 0, there are no escaped pixels in the current block. This aspect of the disclosure is referred to as Aspect 21. When palette_escape_val_present_flag is equal to 1, there is at least one escaped pixel in the current block. Due to this restriction, in escape_idc_coding(), the number of escape indices minus 1 can be coded instead of the number of escape indices to improve coding efficiency. In that case, the maximum value of the truncated Golomb code family can therefore be adjusted to (blockSize-1).

In some examples, when the number of escape indices is signaled before coding an index tile and when all escape indices have been coded, indexMax may be decreased by 1. Furthermore, if indexMax becomes 1, index, run, and pattern coding is terminated because the indices of all remaining samples can be inferred. This aspect of the disclosure is referred to as aspect 22. As an example of aspect 22, assume that the palette size is equal to 1 and palette_escape_val_present_flag is equal to 1. Typically, the possible index values are 0 and 1, with 1 being used for escape samples. Under aspect 22, video encoder 20 may be configured to signal the number of escape values/samples. Subsequently, when the index is signaled and the last escape value/sample is encountered, both video encoder 20 and/or video decoder 30 may be configured to infer (e.g., determine) that no more escape values/samples exist. Thus, video encoder 20 and/or video decoder 30 may be configured to determine that the only index value that can be generated from the last outlying value/sample to the end of the block is 0, meaning that video encoder 20 may be configured to not signal a mode, index value, and/or run value from the last outlying value/sample to the end of the block.

In some instances, escape_idc_coding() is used in combination with indices_idc_coding(). This aspect of the invention is referred to as aspect 23. In one instance, the number of escape indices can be signaled before the number of indices is signaled. In this case, only the number of non-escape indices need be signaled with indices_idc_coding(). In one instance, the number of escape indices can be signaled after the number of indices is signaled. In this case, the maximum value of the truncated Golomb family of codes can therefore be adjusted to num_palette_index.

Video encoder 20 and/or video decoder 30 may be configured to operate in accordance with the techniques described in this disclosure. In general, video encoder 20 and/or video decoder 30 may be configured to determine that a current block is coded in palette mode, perform bypass mode coding of multiple instances of a first syntax element for use in reconstructing the current block, and, after performing bypass mode coding of the multiple instances of the first syntax element, perform context mode decoding of multiple instances of a second syntax element for use in reconstructing the current block.

FIG2 is a block diagram illustrating an example video encoder 20 that may implement the techniques of this disclosure. FIG2 is provided for purposes of explanation and should not be considered limiting of the techniques as broadly illustrated and described in this disclosure. For purposes of explanation, this disclosure describes video encoder 20 in the context of HEVC coding and, for example, the SCC extension of HEVC. However, the techniques of this disclosure may be applicable to other coding standards or methods.

Video encoder 20 represents an example of a device that may be configured to perform techniques for palette-based coding and entropy coding (eg, CABAC) in accordance with various examples described in this disclosure.

2 , video encoder 20 includes a block coding unit 100, a video data memory 101, a residual generation unit 102, a transform processing unit 104, a quantization unit 106, an inverse quantization unit 108, an inverse transform processing unit 110, a reconstruction unit 112, a filter unit 114, a decoded picture buffer 116, and an entropy encoding unit 118. Block coding unit 100 includes an inter-prediction processing unit 120 and an intra-prediction processing unit 126. Inter-prediction processing unit 120 includes a motion estimation unit and a motion compensation unit (not shown). Video encoder 20 also includes a palette-based encoding unit 122 configured to perform various aspects of the palette-based coding techniques described in this disclosure. In other examples, video encoder 20 may include more, fewer, or different functional components.

Video data memory 101 may store video data to be encoded by components of video encoder 20. The video data stored in video data memory 101 may be obtained, for example, from video source 18. Decoded picture buffer 116 may be a reference picture memory that stores reference video data for use by video encoder 20 when encoding video data, for example, in intra- or inter-coding modes. Video data memory 101 and decoded picture buffer 116 may be formed from 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 101 and decoded picture buffer 116 may be provided by the same memory device or by separate memory devices. In various examples, video data memory 101 may be on-chip with other components of video encoder 20, or off-chip relative to those components.

Video encoder 20 may receive video data. Video encoder 20 may encode each CTU in a slice of a picture of the video data. Each of the CTUs may be associated with a luma coding tree block (CTB) of equal size and a corresponding CTB for the picture. As part of encoding the CTU, block coding unit 100 may perform quadtree partitioning to divide the CTB of the CTU into progressively smaller blocks. The smaller blocks may be coding blocks of a CU. For example, block coding unit 100 may partition the CTB associated with the CTU into four equally sized sub-blocks, partition one or more of the sub-blocks into four equally sized sub-sub-blocks, and so on.

Video encoder 20 may encode a CU of a CTU to generate an encoded representation of the CU (i.e., a coded CU). As part of encoding a CU, block coding unit 100 may partition the coding blocks associated with the CU in one or more PUs of the CU. Thus, each PU may be associated with a luma prediction block and a corresponding chroma prediction block. Video encoder 20 and video decoder 30 may support PUs of various sizes. As indicated above, the size of a CU may refer to the size of the luma coding block of the CU, and the size of a PU may refer to the size of the luma prediction block of the PU. Assuming a particular CU has a size of 2N×2N, video encoder 20 and video decoder 30 may support PU sizes of 2N×2N or N×N for intra-prediction, and symmetric PU sizes of 2N×2N, 2N×N, N×2N, N×N, or the like for inter-prediction. Video encoder 20 and video decoder 30 may also support asymmetric partitioning for PU sizes of 2NxnU, 2NxnD, nLx2N, and nRx2N for inter prediction.

Inter-prediction processing unit 120 may generate predictive data for each PU of a CU by performing inter prediction on the PU. The predictive data for the PU may include the predictive block of the PU and the motion information of the PU. Inter-prediction unit 121 may perform different operations for the PUs of a CU depending on whether the PU is in an I slice, a P slice, or a B slice. In an I slice, all PUs are intra-predicted. Therefore, if the PU is in an I slice, inter-prediction unit 121 does not perform inter prediction on the PU. Therefore, for blocks encoded in I mode, the predicted block is formed using spatial prediction from previously encoded neighboring blocks within the same frame.

If the PU is in a P slice, the motion estimation unit of inter-prediction processing unit 120 may search for a reference picture in a reference picture list (e.g., "RefPicList0") for the PU's reference region for a reference picture. The PU's reference region may be a region within a reference picture that contains a sample block that most closely corresponds to the PU's sample block. The motion estimation unit of inter-prediction processing unit 120 may generate a reference index that indicates the position of the reference picture in RefPicList0 that contains the PU's reference region. In addition, the motion estimation unit may generate an MV that indicates the spatial displacement between the PU's coding block and a reference position associated with the reference region. For example, the MV may be a two-dimensional vector that provides an offset from coordinates in the current decoded picture to coordinates in a reference picture. The motion estimation unit may output the reference index and MV as the motion information for the PU. The motion compensation unit of inter-prediction processing unit 120 may generate the predictive block for the PU based on actual or interpolated samples at the reference position indicated by the PU's motion vector.

If the PU is in a B slice, the motion estimation unit may perform uni-directional prediction or bi-directional prediction for the PU. To perform uni-directional prediction for the PU, the motion estimation unit may search for a reference picture in RefPicList0 or a second reference picture list ("RefPicList1") for the reference region of the PU. The motion estimation unit may output the following as the motion information for the PU: a reference index indicating the position of the reference picture containing the reference region in RefPicList0 or RefPicList1, an MV indicating the spatial displacement between the prediction block of the PU and the reference position associated with the reference region, and one or more prediction direction indicators indicating whether the reference picture is in RefPicList0 or RefPicList1. The motion compensation unit of inter-prediction processing unit 120 may generate the predictive block of the PU based at least in part on actual or interpolated samples at the reference region indicated by the motion vector of the PU.

To perform bidirectional inter prediction for a PU, the motion estimation unit may search for a reference picture in RefPicList0 for the PU's reference region and may also search for a reference picture in RefPicList1 for another reference region of the PU. The motion estimation unit may generate a reference picture index that indicates the location of the reference picture containing the reference region in RefPicList0 and RefPicList1. In addition, the motion estimation unit may generate an MV that indicates the spatial displacement between the reference location associated with the reference region and the sample block of the PU. The motion information of the PU may include the reference index and MV for the PU. The motion compensation unit may generate the predictive block of the PU based at least in part on actual or interpolated samples at the reference region indicated by the motion vector of the PU.

According to various examples of the present disclosure, video encoder 20 may be configured to perform palette-based coding. With respect to the HEVC architecture, as an example, palette-based coding techniques may be configured for use at the CU level. In other examples, palette-based video coding techniques may be configured for use at the PU level. In other examples, palette-based coding techniques may be configured for use at the sub-prediction unit (sub-PU) level (e.g., a sub-block of a prediction unit). Thus, all disclosed processes described herein (and throughout this disclosure) in the context of the CU level may additionally or alternatively be applied to the PU level or sub-PU level. However, these HEVC-based examples should not be considered to constrain or limit the palette-based video coding techniques described herein, as these techniques may be applicable to work independently or as part of other existing or yet-to-be-developed systems/standards. In these cases, the units for palette coding may be square blocks, rectangular blocks, or even non-rectangular shaped regions.

When a palette-based encoding mode is selected, for example, for a CU or PU, palette-based encoding unit 122 may, for example, perform palette-based decoding. For example, palette-based encoding unit 122 may be configured to generate a palette having entries indicating pixel values, select pixel values in the palette to represent pixel values of at least some positions in a block of video data, and signal information associating at least some of the positions of the block of video data with entries in the palette that respectively correspond to the selected pixel values. Although various functions are described as being performed by palette-based encoding unit 122, some or all of these functions may be performed by other processing units or a combination of different processing units.

According to aspects of this disclosure, palette-based encoding unit 122 may be configured to perform any combination of the techniques for palette coding described herein.

Intra-prediction processing unit 126 may generate predictive data for a PU by performing intra prediction on the PU. The predictive data for the PU may include the predictive blocks and various syntax elements for the PU. Intra-prediction processing unit 126 may perform intra prediction on PUs in I slices, P slices, and B slices.

To perform intra prediction on a PU, intra-prediction processing unit 126 may use multiple intra-prediction modes to generate multiple sets of predictive data for the PU. Intra-prediction processing unit 126 may use samples from sample blocks of neighboring PUs to generate a predictive block for the PU. For PUs, CUs, and CTUs, assuming left-to-right and top-to-bottom coding order, the neighboring PU may be above, to the right, to the left, or to the left of the PU. Intra-prediction processing unit 126 may use various numbers of intra-prediction modes, for example, 33 directional intra-prediction modes. In some examples, the number of intra-prediction modes may depend on the size of the region associated with the PU.

Block coding unit 100 may select predictive data for PUs of a CU from the predictive data for PUs generated by inter-prediction processing unit 120 or the predictive data for PUs generated by intra-prediction processing unit 126. In some examples, block coding unit 100 selects predictive data for PUs of a CU based on rate/distortion metrics of the predictive data sets. The predictive block of the selected predictive data may be referred to herein as a selected predictive block.

Residual generation unit 102 may generate a luma residual block, a Cb residual block, and a Cr residual block for the CU based on the luma coding block, the Cb coding block, and the Cr coding block of the CU and the selected predictive luma block, the predictive Cb block, and the predictive Cr block of the PU of the CU. For example, residual generation unit 102 may generate the residual block of the CU such that each sample in the residual block has a value equal to the difference between a sample in the coding block of the CU and a corresponding sample in the corresponding selected predictive block of the PU of the CU.

Transform processing unit 104 may perform quadtree partitioning to partition the residual blocks associated with a CU into transform blocks associated with the TUs of the CU. Thus, in some examples, a TU may be associated with a luma transform block and two chroma transform blocks. The size and position of the luma transform blocks and the chroma transform blocks of the TUs of the CU may or may not be based on the size and position of the prediction blocks of the PUs of the CU. A quadtree structure referred to as a "residual quadtree" (RQT) may include a node associated with each of the regions. The TUs of a CU may correspond to leaf nodes of the RQT.

Transform processing unit 104 may generate a transform coefficient block for each TU of a CU by applying one or more transforms to the transform blocks of the TU. Transform processing unit 104 may apply various transforms to the transform blocks associated with the TU. For example, transform processing unit 104 may apply a discrete cosine transform (DCT), a directional transform, or a conceptually similar transform to the transform blocks. In some examples, transform processing unit 104 does not apply a transform to the transform blocks. In these examples, the transform blocks may be processed as transform coefficient blocks.

Quantization unit 106 may quantize the transform coefficients in a coefficient block. The quantization process may reduce the bit depth associated with some or all of the transform coefficients. For example, during quantization, an n-bit transform coefficient may be rounded down to an m-bit transform coefficient, where n is greater than m. Quantization unit 106 may quantize a coefficient block associated with a TU of a CU based on a quantization parameter (QP) value associated with the CU. Video encoder 20 may adjust the degree of quantization applied to a coefficient block associated with a CU by adjusting the QP value associated with the CU. Quantization may introduce information loss, and thus, quantized transform coefficients may have lower precision than the original transform coefficients.

Inverse quantization unit 108 and inverse transform processing unit 110 may apply inverse quantization and inverse transform, respectively, to the coefficient block to reconstruct a residual block from the coefficient block. Reconstruction unit 112 may add the reconstructed residual block to corresponding samples of one or more predictive blocks generated by block coding unit 100 to generate a reconstructed transform block associated with the TU. By reconstructing the transform blocks for each TU of a CU in this manner, video encoder 20 can reconstruct the coding blocks of the CU.

Filter unit 114 may perform one or more deblocking operations to reduce blocking artifacts in the coding blocks associated with the CU. Filter unit 114 may perform other filtering operations, including sample adaptive offset (SAO) filtering and/or adaptive loop filtering (ALF). Decoded picture buffer 116 may store the reconstructed coding blocks after filter unit 114 performs one or more deblocking operations on the reconstructed coding blocks. Inter-prediction processing unit 120 may use a reference picture containing the reconstructed coding blocks to perform inter prediction on PUs of other pictures. Additionally, intra-prediction processing unit 126 may use the reconstructed coding blocks in decoded picture buffer 116 to perform intra prediction on other PUs in the same picture as the CU.

Entropy encoding unit 118 may receive data from other functional components of video encoder 20. For example, entropy encoding unit 118 may receive coefficient blocks from quantization unit 106 and may receive syntax elements from block coding unit 100. Entropy encoding unit 118 may perform one or more entropy encoding operations on the data to generate entropy-encoded data. For example, entropy encoding unit 118 may perform a context-adaptive coding operation (e.g., a CABAC operation), a context-adaptive variable length coding (CAVLC) 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 encoding operation on the data. Video encoder 20 may output a bitstream including the entropy-encoded data generated by entropy encoding unit 118. For example, the bitstream may include data representing the RQT for the CU.

In some examples, residual coding is not performed in conjunction with palette coding. Thus, when coding using palette coding mode, video encoder 20 may not perform transform or quantization. Additionally, video encoder 20 may entropy encode data generated from the residual data using palette coding mode alone.

In accordance with one or more of the techniques of this disclosure, video encoder 20, and specifically palette-based encoding unit 122, may perform palette-based video coding of a predicted video block. As described above, the palette generated by video encoder 20 may be explicitly encoded and sent to video decoder 30, predicted from previous palette entries, predicted from previous pixel values, or a combination thereof.

According to one or more techniques of this disclosure, video encoder 20 may be configured to determine to code a current block in palette mode, bypass mode encode multiple instances of a first syntax element for use in reconstructing the current block, and, after bypass mode encoding the multiple instances of the first syntax element, context mode encode multiple instances of a second syntax element for use in reconstructing the current block, e.g., using a CABAC coding process. Video encoder 20 may be configured to bypass mode encode any two of the multiple instances of the first syntax element, e.g., using the bypass mode of the CABAC coding process, without interleaving the context mode encoding of any of the multiple instances of the second syntax element. In one example, the first syntax element includes one of a palette_index_idc syntax element or a palette_escape_val syntax element, and the second syntax element includes a palette_run_msb_id_plus1 syntax element. Video encoder 20 may be configured to bypass encode the multiple instances of the first syntax element before the index block coded portion for the current block.

Video encoder 20 may be configured to encode a third syntax element indicating a number of instances of a first syntax element, wherein bypass mode encoding the multiple instances of the first syntax element comprises bypass mode encoding the multiple instances of the first syntax element based on the third syntax element. Video encoder 20 may encode the third syntax element using a Golombrite code, an exponential Golombrite code, a truncated Rice code, a unary code, a concatenation of a Golombrite code and an exponential Golombrite code, or a truncated version of any of the foregoing codes.

FIG3 is a block diagram illustrating an example video decoder 30 that may be configured to perform the techniques of this disclosure. FIG3 is provided for purposes of explanation and does not limit the techniques as broadly illustrated and described in this disclosure. For purposes of explanation, this disclosure describes video decoder 30 in the context of HEVC coding. However, the techniques of this disclosure may be applicable to other coding standards or methods.

The details of the palette coding described above with respect to encoder 20 are not repeated here with respect to decoder 30 , but it should be understood that decoder 30 may perform a reciprocal decoding process with respect to any encoding process described herein with respect to encoder 20 .

Video decoder 30 represents an example of a device that may be configured to perform techniques for palette-based coding and entropy coding (eg, CABAC) in accordance with various examples described in this disclosure.

3 , video decoder 30 includes an entropy decoding unit 150, a video data memory 151, a block decoding unit 152, an inverse quantization unit 154, an inverse transform processing unit 156, a reconstruction unit 158, a filter unit 160, and a decoded picture buffer 162. Block decoding unit 152 includes a motion compensation unit 164 and an intra-prediction processing unit 166. Video decoder 30 also includes a palette-based decoding unit 165 that is configured to perform various aspects of the palette-based coding techniques described in this disclosure. In other examples, video decoder 30 may include more, fewer, or different functional components.

Video data memory 151 may store video data, such as an encoded video bitstream, to be decoded by components of video decoder 30. The video data stored in video data memory 151 may be obtained, for example, from computer-readable medium 16 (e.g., from a local video source (e.g., a camera)), via wired or wireless network communication of video data, or by accessing physical data storage media. Video data memory 151 may form a coded picture buffer (CPB) that stores encoded video data from the encoded video bitstream. Decoded picture buffer 162 may be a reference picture memory that stores reference video data used when decoding video data by video decoder 30 (e.g., in intra- or inter-coding modes). Video data memory 151 and decoded picture buffer 162 may be formed from 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 151 and decoded picture buffer 162 may be provided by the same memory device or separate memory devices. In various examples, video data memory 151 may be on-chip with other components of video decoder 30 , or off-chip relative to those components.

A coded picture buffer (CPB), which may be provided by video data memory 151, may receive and store encoded video data (e.g., NAL units) of a bitstream. Entropy decoding unit 150 may receive encoded video data (e.g., NAL units) from the CPB and parse the NAL units to decode syntax elements. Entropy decoding unit 150 may entropy decode the entropy-encoded syntax elements in the NAL units. Block decoding unit 152, inverse quantization unit 154, inverse transform processing unit 156, reconstruction unit 158, and filter unit 160 may generate decoded video data based on the syntax elements extracted from the bitstream.

Video decoder 30 may be configured to perform a process that is generally reciprocal to the process described herein of video encoder 20. Similarly, video encoder 20 may be configured to perform a process that is generally reciprocal to the process described herein of video decoder 30. For example, the disclosure that video decoder 30 may be configured to decode encoded syntax elements in a bitstream also necessarily discloses that video encoder 20 may be configured to encode syntax elements into the bitstream.

As another example, entropy decoding unit 150 may be configured to perform a process that is substantially reciprocal to the process of entropy encoding unit 118 described herein. According to aspects of this disclosure, entropy decoding unit 150 may be configured to entropy decode any codeword generated by entropy encoding unit 118. For example, entropy decoding unit 150 may be configured to entropy decode uniform and non-uniform k-th order truncated exponential Golomb (TEGk)-encoded values, such as binary palette prediction vectors and/or palette maps for a CU. As another example, entropy decoding unit 150 may be configured to entropy decode k-th order exponential Golomb (EGk) codewords, k-th order truncated exponential Golomb (TEGk) codewords, k-th order non-uniform truncated exponential Golomb (TEGk) codewords, or any combination thereof.

The NAL units of the bitstream may include coded slice NAL units. As part of decoding the bitstream, entropy decoding unit 150 may extract syntax elements from the coded slice NAL units and entropy decode the syntax elements. Each of the coded slices may include a slice header and slice data. The slice header may contain syntax elements for the slice. The syntax elements in the slice header may include syntax elements that identify the PPS associated with the picture containing the slice.

In addition to decoding syntax elements from the bitstream, video decoder 30 may perform a reconstruction operation on a non-partitioned CU. To perform a reconstruction operation on a non-partitioned CU, video decoder 30 may perform a reconstruction operation on each TU of the CU. By performing the reconstruction operation on each TU of the CU, video decoder 30 may reconstruct the residual blocks of the CU.

As part of performing a reconstruction operation on a TU of a CU, inverse quantization unit 154 may inverse quantize (i.e., dequantize) the coefficient blocks associated with the TU. Inverse quantization unit 154 may use the QP value associated with the CU of the TU to determine the degree of quantization and, likewise, the degree of dequantization to apply by inverse quantization unit 154. That is, the compression ratio, i.e., the ratio of the number of bits used to represent the original sequence and the compressed sequence, may be controlled by adjusting the QP value used when quantizing transform coefficients. The compression ratio may also depend on the entropy coding method applied.

After inverse quantization unit 154 inverse quantizes the coefficient block, inverse transform processing unit 156 may apply one or more inverse transforms to the coefficient block in order to generate a residual block associated with the TU. For example, inverse transform processing unit 156 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 coefficient block.

If the PU is encoded using intra prediction, intra-prediction processing unit 166 may perform intra prediction to generate predictive blocks for the PU. Intra-prediction processing unit 166 may use an intra prediction mode to generate predictive luma blocks, predictive Cb blocks, and predictive Cr blocks for the PU based on the prediction blocks of spatially neighboring PUs. Intra-prediction processing unit 166 may determine the intra prediction mode for the PU based on one or more syntax elements decoded from the bitstream.

Block decoding unit 152 may construct a first reference picture list (RefPicList0) and a second reference picture list (RefPicList1) based on syntax elements extracted from the bitstream. Furthermore, if the PU is encoded using inter prediction, entropy decoding unit 150 may extract motion information for the PU. Motion compensation unit 164 may determine one or more reference regions for the PU based on the motion information of the PU. Motion compensation unit 164 may generate a predictive luma block, a predictive Cb block, and a predictive Cr block for the PU based on sample blocks at one or more reference blocks of the PU.

Reconstruction unit 158 may use the luma transform blocks, Cb transform blocks, and Cr transform blocks associated with the TUs of the CU and the predictive luma blocks, predictive Cb blocks, and predictive Cr blocks (i.e., intra prediction data or inter prediction data) of the PUs of the CU, as appropriate, to reconstruct the luma coding blocks, Cb coding blocks, and Cr coding blocks of the CU. For example, reconstruction unit 158 may add samples of the luma transform blocks, Cb transform blocks, and Cr transform blocks to corresponding samples of the predictive luma blocks, predictive Cb blocks, and predictive Cr blocks to reconstruct the luma coding blocks, Cb coding blocks, and Cr coding blocks of the CU.

Filter unit 160 may perform a deblocking operation to reduce blocking artifacts associated with the luma, Cb, and Cr coding blocks of a CU. Video decoder 30 may store the luma, Cb, and Cr coding blocks of the CU in decoded picture buffer 162. Decoded picture buffer 162 may provide reference pictures for subsequent motion compensation, intra prediction, and presentation on a display device, such as display device 32 of FIG. 1 . For example, video decoder 30 may perform intra prediction operations or inter prediction operations on PUs of other CUs based on the luma, Cb, and Cr blocks in decoded picture buffer 162.

According to various examples of this disclosure, video decoder 30 may be configured to perform palette-based coding. When palette-based decoding mode is selected, e.g., for a CU or PU, palette-based decoding unit 165, for example, may perform palette-based decoding. For example, palette-based decoding unit 165 may be configured to generate a palette having entries indicating pixel values, receive information associating at least some pixel positions in a block of video data with entries in the palette, select pixel values in the palette based on the information, and reconstruct pixel values for the block based on the selected pixel values in the palette. Although various functions are described as being performed by palette-based decoding unit 165, some or all of these functions may be performed by other processing units or a combination of different processing units.

Palette-based decoding unit 165 may receive palette coding mode information and perform the above-described operations when the palette coding mode information indicates that the palette coding mode is applicable to the block. When the palette coding mode information indicates that the palette coding mode is not applicable to the block, or when other mode information indicates the use of a different mode, palette-based decoding unit 165 decodes the block of video data using a non-palette-based coding mode (e.g., HEVC inter-prediction coding mode or HEVC intra-prediction coding mode). The block of video data may be, for example, a CU or PU generated according to an HEVC coding process. The palette-based coding mode may include one of a plurality of different palette-based coding modes, or there may be a single palette-based coding mode.

According to aspects of this disclosure, palette-based decoding unit 165 may be configured to perform any combination of the techniques described herein for palette coding. The details of palette coding described above with respect to encoder 20 are not repeated here with respect to decoder 30, but it should be understood that decoder 30 may perform a reciprocal palette-based decoding process relative to any palette-based encoding process described herein with respect to encoder 20.

Video decoder 30 may be configured to determine that a current block is coded in palette mode, bypass mode decode multiple instances of a first syntax element for use in, for example, reconstructing the current block using a bypass mode of a CABAC coding process, and, after bypass mode decoding the multiple instances of the first syntax element, context mode decode multiple instances of a second syntax element for use in, for example, reconstructing the current block using a CABAC coding process. Video decoder 30 may bypass mode decode any two of the multiple instances of the first syntax element without interleaving the context mode decoding of any of the multiple instances of the second syntax element. In some examples, the first syntax element comprises one of a palette_index_idc syntax element or a palette_escape_val syntax element, and the second syntax element comprises a palette_run_msb_id_plus1 syntax element. Video decoder 30 may bypass decode the multiple instances of the first syntax element before the index block coded portion for the current block.

Video decoder 30 may decode a third syntax element indicating the number of instances of the first syntax element, wherein bypass mode decoding the multiple instances of the first syntax element comprises bypass mode decoding the multiple instances of the first syntax element based on the third syntax element. Video decoder 30 may decode the third syntax element using a Golombrite code, an exponential Golombrite code, a truncated Rice code, a unary code, or a concatenation of a Golombrite code and an exponential Golombrite code, or a truncated version of any of the foregoing codes.

FIG4 is a conceptual diagram illustrating an example of determining a palette for coding video data consistent with the techniques of this disclosure. The example of FIG4 includes a picture 178 having a first PAL (palette) coding unit (CU) 180 associated with a first palette 184 and a second PAL CU 188 associated with a second palette 192. As will be described in more detail below and according to the techniques of this disclosure, second palette 192 is based on first palette 184. Picture 178 also includes a block 196 coded by an intra-prediction coding mode and a block 200 coded by an inter-prediction coding mode.

For purposes of explanation, the techniques of FIG. 4 are described in the context of video encoder 20 (FIGS. 1 and 2) and video decoder 30 (FIGS. 1 and 3) and with respect to the HEVC video coding standard. However, it should be understood that the techniques of this disclosure are not limited in this manner and may be applied to other video coding processes and/or standards with other video coding processors and/or devices.

In general, a palette refers to a plurality of pixel values that are primary and/or representative for the currently coded CU (CU 188 in the example of FIG. 4 ). First palette 184 (also referred to as index 184) and second palette 192 (also referred to as index 192) are shown as including multiple palettes (also referred to as multiple indices). In some examples, according to aspects of this disclosure, a video coder (e.g., video encoder 20 or video decoder 30) may separately encode a palette (e.g., an index) for each color component of a CU. For example, video encoder 20 may encode a palette for the luma (Y) component of the CU, another palette for the chroma (U) component of the CU, and yet another palette for the chroma (V) component of the CU. In this example, entries of the Y palette may represent Y values for pixels of the CU, entries of the U palette may represent U values for pixels of the CU, and entries of the V palette may represent V values for pixels of the CU.

In other examples, video encoder 20 may encode a single palette for all color components of a CU. In this example, video encoder 20 may encode a palette with the i-th entry being a triplet of values including Yi, Ui, and Vi. In this case, the palette includes a value for each of the components of the pixel. Thus, the representation of palettes 184 and 192 as a palette set having multiple independent palettes is merely an example and is not intended to be limiting.

4 , first palette 184 includes three entries 202 through 206, each with an entry index value of 1, an entry index value of 2, and an entry index value of 3, respectively. First palette 184 correlates index values (e.g., the values shown in the left column of first palette 184) with pixel values. For example, as shown in FIG4 , one of first palettes 184 correlates index values 1, 2, and 3 with pixel values A, B, and C, respectively. As described herein, a video coder (e.g., video encoder 20 or video decoder 30) may use palette-based coding to code pixels of blocks using indices 1 through 3 (also expressed as index values 1 through 3) rather than the actual pixel values of first CU 180. That is, for each pixel position of first CU 180, video encoder 20 may encode an index value for the pixel, where the index value is associated with a pixel value in one or more of first palettes 184. Video decoder 30 may obtain index values from the bitstream and reconstruct pixel values using the index values and one or more of first palettes 184. Thus, first palette 184 is transmitted in the encoded video data bitstream by video encoder 20 for use by video decoder 30 in palette-based decoding.

In some examples, video encoder 20 and video decoder 30 may determine second palette 192 based on first palette 184. For example, video encoder 20 and/or video decoder 30 may locate one or more blocks from which a predictive palette (in this example, first palette 184) is determined. In some examples, such as the example illustrated in FIG. 4 , video encoder 20 and/or video decoder 30 may locate a previously coded CU, e.g., a left-neighboring CU (first CU 180), when determining the predictive palette for second CU 188.

4 , second palette 192 includes three entries 208 through 212, each having an entry index value of 1, an entry index value of 2, and an entry index value of 3, respectively. Second palette 192 correlates index values (e.g., the values shown in the left column of first palette 192) with pixel values. For example, as shown in FIG4 , one of second palettes 192 correlates index values 1, 2, and 3 with pixel values A, B, and D, respectively. In this example, video encoder 20 may code one or more syntax elements indicating which entries of first palette 184 are included in second palette 192. In the example of FIG4 , the one or more syntax elements are illustrated as vector 216. Vector 216 has a plurality of associated bins (or bits), where each bin indicates whether the palette predictor associated with the bin is used to predict an entry of the current palette. For example, vector 216 indicates that the first two entries (202 and 204) in first palette 184 are included in second palette 192 (value "1" in vector 216), while the third entry in first palette 184 is not included in second palette 192 (value "0" in vector 216). In the example of FIG4 , the vector is a Boolean vector.

In some examples, video encoder 20 and video decoder 30 may determine a palette predictor list (which may also be referred to as a palette predictor table) when performing palette prediction. The palette predictor list may include entries from the palette of one or more neighboring blocks that are used to predict one or more entries of the palette used to code the current block. Video encoder 20 and video decoder 30 may construct the list in the same manner. Video encoder 20 and video decoder 30 may code data (e.g., vector 216) to indicate which entries of the palette predictor list are to be included in the palette used to code the current block.

FIG5 is a conceptual diagram illustrating an example of determining an index into a color palette for a block of pixels consistent with the techniques of this disclosure. For example, FIG5 includes an index block 240 (also referred to as a map 240 or index map 240) that includes index values (e.g., index values 1, 2, and 3) that relate corresponding positions of pixels associated with the index values to entries of a color palette 244.

5 as including an index value for each pixel position, it should be understood that in other examples, not all pixel positions may be associated with an index value that relates a pixel value to an entry of palette 244. That is, as mentioned above, in some examples, if a pixel value is not included in palette 244, video encoder 20 may encode (and video decoder 30 may obtain from the encoded bitstream) an indication of the actual pixel value (or a quantized version thereof) for the position in index block 240.

In some examples, video encoder 20 and video decoder 30 may be configured to code an additional mapping that indicates which pixel positions are associated with which index values. For example, assume that the (i, j) entry in index block 240 corresponds to the (i, j) position of a CU. Video encoder 20 may encode one or more syntax elements for each entry of the index block (i.e., each pixel position) that indicate whether the entry has an associated index value. For example, video encoder 20 may encode a flag with a value of one to indicate that the pixel value at the (i, j) position in the CU is one of the values in palette 244.

In this example, video encoder 20 may also encode a palette (shown as 244 in the example of FIG. 5 ). If palette 244 includes a single entry and an associated pixel value, video encoder 20 may skip signaling the index value. Video encoder 20 may encode a flag with a zero value to indicate that the pixel value at the (i, j) position in the CU is not one of the values in palette 244. In this example, video encoder 20 may also encode an indication of the pixel value for use by video decoder 30 in reconstructing the pixel value. In some cases, the pixel value may be coded in a lossy manner.

The value of a pixel in one position of a CU may provide an indication of the values of one or more other pixels in other positions of the CU. For example, there may be a relatively high probability that adjacent pixel positions of a CU will have the same pixel value or may be mapped to the same index value (in the case of lossy coding, where more than one pixel value may be mapped to a single index value).

Thus, video encoder 20 may encode one or more syntax elements indicating a plurality of consecutive pixels or index values having the same pixel value or index value in a given scan order. As mentioned above, a string of identically valued pixels or index values may be referred to herein as a run. In an example for purposes of illustration, if two consecutive pixels or indices in a given scan order have different values, then the run is equal to zero. If two consecutive pixels or indices in a given scan order have the same value but a third pixel or index in the scan order has a different value, then the run is equal to one. For three consecutive indices or pixels having the same value, the run is two, and so on. Video decoder 30 may obtain the syntax element indicating the run from the encoded bitstream and may use the data to determine the number of consecutive positions having the same pixel or index value.

In some examples according to the techniques of this disclosure, entropy encoding unit 118 and entropy decoding unit 150 may be configured to entropy code index block 240. For example, entropy encoding unit 118 and entropy decoding unit 150 may be configured to entropy code run lengths (e.g., run length values or run length codes) and/or binary palette prediction vectors associated with the index block in palette mode.

FIG6 is a conceptual diagram illustrating an example of determining a maximum copy-over run length, assuming a raster scan order, consistent with the techniques of this disclosure. In the example of FIG6 , if none of the pixels encompassed by dashed line 280 are coded as escaped samples, the maximum possible run length is 35 (i.e., the number of unshaded pixel positions). If one or more of the pixels within dashed line 280 are coded as escaped samples, assuming the pixel marked as an escaped pixel (the pixel position with an "X") is the first escaped pixel within dashed line 280 in scan order, the maximum possible coded copy-over run length is five.

In some examples, video decoder 30 may determine the run-length mode (e.g., the palette mode in which the pixel is coded) only for pixels within dashed line 280. Thus, in the worst case, video decoder 30 makes a determination for BlockWidth-1 pixels. In some examples, video decoder 30 may be configured to enforce certain restrictions on the maximum number of pixels for which to check for run-length mode. For example, if a pixel is in the same row as the current pixel, video decoder 30 may only check pixels within dashed line 280. Video decoder 30 may infer that all other pixels within dashed line 280 are not coded as escaped samples. The example in FIG6 assumes a raster scan order. However, the techniques described are applicable to other scan orders, such as vertical, horizontal traverse, and vertical traverse.

According to an example of the present disclosure, if the current run mode is 'copy above', the context for the run length of the current pixel may depend on the index value of the index of the upper neighboring pixel relative to the current pixel. In this example, if the upper neighboring pixel relative to the current pixel is outside the current CU, the video decoder assumes that the corresponding index is equal to a predefined constant k. In some examples, k=0.

During entropy coding, an entropy encoder or decoder may arrange the bits of a symbol to be encoded or decoded into one or more binary digits. A binary digit may indicate whether the value of a symbol is equal to zero. The entropy encoder or decoder may use the binary digit to adjust the entropy coding process. In some examples, the entropy encoder or decoder may also use the binary digit to indicate whether a value is greater than a specific value, e.g., greater than zero, greater than one, etc.

In some examples, if the current mode is ‘copy above’, the first binary of the run-length codeword selects one of two candidate CABAC contexts based on whether the upper neighboring sample (e.g., pixel) relative to the current sample (e.g., pixel) is equal to 0.

As another example, if the current mode is 'previous copy', the first binary of the run-length codeword selects one of the four candidate CABAC contexts based on whether the index value is equal to 0, equal to 1, equal to 2, or greater than 2.

FIG8 is a flowchart illustrating an example process for decoding video data consistent with the techniques of this disclosure. For purposes of illustration, the process of FIG8 is generally described as being performed by video decoder 30, but a variety of other processors may also perform the process shown in FIG8. In some examples, block decoding unit 152, palette-based decoding unit 165, and/or entropy decoding unit 150 may perform one or more of the processes shown in FIG8.

In the example of FIG8 , video decoder 30 may be configured to receive a palette-mode encoded block of video data for a picture from an encoded video bitstream ( 800 ). Video decoder 30 may be configured to receive encoded palette mode information for a palette-mode encoded block of video data from an encoded video bitstream ( 802 ). In some examples, the encoded palette mode information may include multiple instances of a first syntax element and multiple syntax elements different from the first syntax element. For example, the first syntax element may include palette_index_idc or palette_escape_val , and the multiple syntax elements different from the first syntax element may include a palette_run_msb_id_plus1 syntax element. As another example, the first syntax element may be an indication of an index into an array of palette entries, or the first syntax element may specify a quantized escaped coded sample value for a color component corresponding to an escaped sample. The multiple syntax elements different from the first syntax element may include a syntax element that specifies an index to a most significant bit in a binary representation of a variable representing a run length and a syntax element that specifies a run type mode.

As another example, the plurality of syntax elements different from the first syntax element may be any and all syntax elements different from the first syntax element. As described herein with respect to some examples, the plurality of syntax elements different from the first syntax element may also be different from the second syntax element, the third syntax element, and/or the fourth syntax element. In these examples, the plurality of syntax elements different from the first syntax element, the second syntax element, the third syntax element, and/or the fourth syntax element may be any and all syntax elements different from the first syntax element, the second syntax element, the third syntax element, and/or the fourth syntax element. In some examples, the plurality of syntax elements different from the first syntax element may be any and all syntax elements that are not decoded by bypass mode and/or are not decoded by bypass mode.

Video decoder 30 may be configured to decode multiple instances of a first syntax element using a bypass mode (e.g., a bypass mode of a CABAC coding process) before decoding multiple syntax elements other than the first syntax element using a context mode (804). Video decoder 30 may be configured to decode multiple syntax elements other than the first syntax element using a context mode (e.g., a conventional CABAC mode (instead of bypass mode)) after decoding the multiple instances of the first syntax element using the bypass mode (806). In some examples, the multiple instances of the first syntax element include all instances of the first syntax element for a palette-mode encoded block of video data. In these examples, all instances of the first syntax element are decoded using the bypass mode before decoding any subsequent data (e.g., multiple syntax elements other than the first syntax element). Stated otherwise, video decoder 30 may be configured to decode multiple syntax elements other than the first syntax element using the context mode after decoding all instances of the first syntax element for a palette-mode encoded block of video data using the bypass mode.

Video decoder 30 may be configured to decode a palette-mode encoded block of video data using the decoded multiple instances of the first syntax element and the decoded multiple syntax elements different from the first syntax element 808. In some examples, the multiple instances of the first syntax element are grouped together to reduce switching between a bypass mode and a context mode when decoding the palette-mode encoded block of video data.

In some examples, the encoded palette mode information may include a second syntax element indicating the number of instances of a first syntax element (e.g., indicating how many instances of the first syntax element exist for a palette-mode encoded block of video data). Multiple syntax elements different from the first syntax element may also be different from the second syntax element. In these examples, video decoder 30 may be configured to decode the second syntax element using a bypass mode before decoding the multiple syntax elements different from the first and second syntax elements. In some examples, no instances of the second syntax element are interleaved between any two instances of the first syntax element for a palette-mode encoded block of video data. In some examples, video decoder 30 may be configured to, after decoding multiple instances of the first syntax element equal to the number indicated by the second syntax element, determine that subsequent data in the encoded video bitstream following the number of instances of the first syntax element corresponds to multiple syntax elements different from the first and second syntax elements. In some examples, video decoder 30 may be configured to decode the second syntax element using a concatenation of a truncated Rice code and an Exponential Golomb code.

In some examples, the encoded palette mode information may include a third syntax element and a fourth syntax element. In these examples, video decoder 30 may be configured to decode the third syntax element to determine that a value corresponding to the third syntax element indicates whether the palette-mode encoded video data block includes escaped pixels. Video decoder 30 may be configured to decode the fourth syntax element to determine that a value corresponding to the fourth syntax element indicates a palette size. Video decoder 30 may be configured to, after decoding multiple instances of the first and second syntax elements using the bypass mode, decode multiple syntax elements different from the first and second syntax elements using the context mode based on the determined values corresponding to the third and fourth syntax elements, respectively.

In some examples, the encoded palette mode information may include another syntax element, and video decoder 30 may be configured to decode the other syntax element to determine a value corresponding to the other syntax element, the other syntax element specifying the number of different values that the palette index has for a palette-mode encoded block of video data. Video decoder 30 may be configured to decode multiple syntax elements different from the first and second syntax elements using a context mode based on the determined value corresponding to the other syntax element after decoding multiple instances of the first and second syntax elements using the bypass mode.

In some examples, the encoded palette mode information may include another syntax element, and video decoder 30 may be configured to decode this other syntax element to determine a last instance of a syntax element whose value corresponding to this other syntax element indicates palette_run_type_flag[xC][yC] for the palette-mode encoded block of video data.

In some examples, video decoder 30 may be configured to determine that an encoded block of video data has one or more escaped samples. In these examples, video decoder 30 may be configured to decode a last escaped sample of the one or more escaped samples in the encoded block of video data. Video decoder 30 may be configured to infer index values for samples following the last escaped sample of the encoded block of video data. Video decoder 30 may be configured to decode samples following the last escaped sample of the encoded block of video data using the inferred index values for each sample following the last escaped sample.

In some examples, video decoder 30 may be configured to determine the number of palette indices received. In these examples, video decoder 30 may be configured to determine the number of palette indices remaining based on the number of palette indices received and the number of instances of the first syntax element. Video decoder 30 may be configured to determine the maximum possible run value for the encoded block of video data based on the number of palette indices received and the number of instances of the first syntax element. In some examples, video decoder 30 may be configured to determine the maximum possible run value for the encoded block of video data according to nCbS*nCbS-scanPos-1-paletteIndicesLeft, where nCbS specifies the size of the encoded block of video data, scanPos specifies the scan position, and paletteIndicesLeft specifies the number of palette indices remaining.

FIG9 is a flowchart illustrating an example process for encoding video data consistent with the techniques of this disclosure. For purposes of illustration, the process of FIG9 is generally described as being performed by video encoder 20, but a variety of other processors may also perform the process shown in FIG9. In some examples, block coding unit 100, palette-based coding unit 122, and/or entropy coding unit 118 may perform one or more of the processes shown in FIG9.

In the example of FIG9 , video encoder 20 may be configured to determine that a block of video data is to be encoded in a palette mode ( 900 ). Video encoder 20 may be configured to encode the block of video data into an encoded bitstream using the palette mode ( 902 ). In some examples, video encoder 20 may be configured to generate palette mode information for the block of video data ( 904 ). The palette mode information may include multiple instances of a first syntax element and multiple syntax elements different from the first syntax element. For example, the first syntax element may include palette_index_idc or palette_escape_val , and the multiple syntax elements different from the first syntax element may include a palette_run_msb_id_plus1 syntax element. As another example, the first syntax element may be an indication of an index into an array of palette entries, or the first syntax element may specify a quantized escaped coded sample value for a color component corresponding to an escaped sample. The plurality of syntax elements different from the first syntax element may include a syntax element that specifies an index of a most significant bit in a binary representation of a variable representing a run length and a syntax element that specifies a run type pattern.

As another example, the plurality of syntax elements different from the first syntax element may be any and all syntax elements different from the first syntax element. As described herein with respect to some examples, the plurality of syntax elements different from the first syntax element may also be different from the second syntax element, the third syntax element, and/or the fourth syntax element. In these examples, the plurality of syntax elements different from the first syntax element, the second syntax element, the third syntax element, and/or the fourth syntax element may be any and all syntax elements different from the first syntax element, the second syntax element, the third syntax element, and/or the fourth syntax element. In some examples, the plurality of syntax elements different from the first syntax element may be any and all syntax elements that are not encoded in bypass mode and/or are not encoded in bypass mode.

Video encoder 20 may be configured to encode multiple instances of a first syntax element into an encoded bitstream using a bypass mode (e.g., a bypass mode of a CABAC coding process) before encoding multiple syntax elements other than the first syntax element into an encoded bitstream using a context mode (906). Video encoder 20 may be configured to encode multiple syntax elements other than the first syntax element into an encoded bitstream using a context mode (e.g., a conventional CABAC context-based mode) after encoding the multiple instances of the first syntax element into the encoded bitstream using the bypass mode (908). In some examples, the multiple instances of the first syntax element are grouped together so that switching between the bypass mode and the context mode is reduced when encoding a palette mode encoded block of video data.

In some examples, the multiple instances of the first syntax element include all instances of the first syntax element for a block of video data. In these examples, all instances of the first syntax element are encoded using bypass mode before encoding any subsequent data (e.g., syntax elements other than the first syntax element). Stated otherwise, video encoder 20 may be configured to encode syntax elements other than the first syntax element using context mode after encoding all instances of the first syntax element for a block of video data using bypass mode.

In some examples, the palette mode information may include a second syntax element indicating the number of instances of the first syntax element (e.g., indicating the number of instances of the first syntax element present for a block of video data). The multiple syntax elements different from the first syntax element may also be different from the second syntax element. In these examples, video encoder 20 may be configured to encode the second syntax element into the encoded bitstream using a bypass mode before encoding the multiple syntax elements different from the first and second syntax elements. In some examples, video encoder 20 may be configured to encode the multiple instances of the first syntax element such that no instances of the second syntax element are interleaved between any two instances of the first syntax element for a palette-mode encoded block of video data in the encoded bitstream. In some examples, video encoder 20 may be configured to encode the second syntax element into the encoded bitstream after the encoded multiple instances of the first syntax element in the encoded bitstream. For example, video encoder 20 may be configured to first encode all instances of the first syntax element and then encode the second syntax element into the encoded bitstream. In some examples, video encoder 20 may be configured to encode the second syntax element using a concatenation of a truncated Rice code and an Exponential Golomb code.

In some examples, the palette mode information may include a third syntax element and a fourth syntax element. In these examples, video encoder 20 may be configured to encode into the encoded bitstream a value corresponding to the third syntax element, the third syntax element indicating whether the block of video data includes escaped pixels. Video encoder 20 may be configured to include into the encoded bitstream a value corresponding to the fourth syntax element indicating the palette size. In some examples, the palette mode information may include another syntax element, and video encoder 20 may be configured to encode into the encoded bitstream a value of this other syntax element corresponding to the number of different values that the palette index has for the block of video data.

In some examples, the encoded palette mode information may include another syntax element, and video encoder 20 may be configured to encode a value corresponding to this other syntax element that indicates the last instance of the syntax element of palette_run_type_flag[xC][yC] for the block of video data.

In some examples, video encoder 20 may be configured to encode a last escaping sample of one or more escaping samples in a block of video data. In these examples, video encoder 20 may be configured to infer index values applicable to samples of the block of video data that follow the last escaping sample. Video encoder 20 may be configured to encode the samples of the block of video data that follow the last escaping sample using the inferred index values for each of the samples that follow the last escaping sample.

It should be understood that all of the techniques described herein may be used alone or in combination. For example, video encoder 20 and/or one or more components thereof and video decoder 30 and/or one or more components thereof may perform the techniques described in this disclosure in any combination.

It should be appreciated that, depending on the example, certain actions or events of any of the techniques described herein may be performed in a different sequence, may be added, combined, or omitted entirely (e.g., not all described actions or events are necessary for implementation of the techniques). Furthermore, in some examples, actions or events may be performed simultaneously rather than sequentially, for example, via multithreading, interrupt handling, or multiple processors. Additionally, although certain aspects of this disclosure are described as being performed by a single module or unit for purposes of clarity, it should be understood that the techniques of this disclosure may be performed by a combination of units or modules associated with a video coder.

For purposes of illustration, certain aspects of this disclosure have been described with respect to the developing HEVC standard. However, the techniques described in this disclosure may be applicable to other video coding processes, including other standards or proprietary video coding processes that have not yet been developed.

The techniques described above may be performed by video encoder 20 (FIGS. 1 and 2) and/or video decoder 30 (FIGS. 1 and 3), both of which may generally be referred to as video coders. Likewise, video coding may refer to video encoding or video decoding, where applicable.

According to the present invention, the term "or" can be interpreted as "and/or" where the context does not indicate otherwise. In addition, although phrases such as "one or more" or "at least one" or the like may have been used with some features disclosed herein (but not others), features that do not use such language may be interpreted as implying such a meaning where the context does not indicate otherwise.

Although specific combinations of various aspects of the technology are described above, these combinations are provided only to illustrate examples of the technology described in this disclosure. Therefore, the technology of this disclosure should not be limited to these example combinations and may encompass any conceivable combination of various aspects of the technology described in this disclosure.

In one or more examples, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted via 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 that includes any media that facilitates, for example, transferring 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-transitory, 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, program codes, and/or data structures for implementing the techniques described in this disclosure. A computer program product may include computer-readable media.

By way of example, and not limitation, such computer-readable storage media may include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer. Furthermore, any connection is properly 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 technologies such as infrared, radio, and microwaves, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwaves are included in the definition of medium. However, it should be understood that computer-readable storage media and data storage media do not include connections, carrier waves, signals, or other transient media, but rather refer to non-transitory, tangible storage media. Disk and disc, as used herein, include compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk, and Blu-ray disc, where disks typically reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one or more digital signal processors (DSPs), general-purpose microprocessors, application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other equivalent integrated or discrete logic circuits. Thus, the term "processor," as used herein, may refer to any of the aforementioned structures or any other structure suitable for implementing the techniques described herein. Additionally, in some aspects, the functionality described herein may be provided within dedicated hardware and/or software modules configured for encoding and decoding, or incorporated into a combined codec. Furthermore, the techniques may be fully implemented in one or more circuits or logic elements.

The techniques of this disclosure may be implemented in a variety of devices or apparatuses, including wireless handsets, integrated circuits (ICs), or collections of ICs (e.g., chipsets). Various components, modules, or units are described herein to emphasize functional aspects of devices configured to perform the disclosed techniques, but implementation by distinct hardware units is not necessarily required. 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 conjunction with appropriate software and/or firmware.

Various examples have been described herein. Any combination of the described systems, operations, functions, or examples is contemplated. These and other examples are within the scope of the following claims.

Claims (39)

1. A method for decoding video data, the method comprising: Receive color-pattern encoded video data blocks of images from the encoded video bitstream; Encoded palette pattern information is received from the encoded video bitstream for the palette pattern encoded video data blocks, wherein the encoded palette pattern information includes multiple instances of a first syntax element and multiple syntax elements different from the first syntax element, wherein the first syntax element is an indication of an array of palette entries or specifies a quantized escape decoded sample value corresponding to a color component of an escape sample, and wherein the multiple syntax elements different from the first syntax element include a syntax element specifying an index of the most significant bit in the binary representation of a variable representing a run length and a syntax element specifying a run type pattern. The plurality of instances of the first syntax element from the encoded video bitstream are analyzed before the plurality of syntax elements that are different from the first syntax element from the encoded video bitstream are analyzed. After parsing the plurality of instances of the first syntax element from the encoded video bitstream, the plurality of syntax elements different from the first syntax element from the encoded video bitstream are parsed. The plurality of instances of the first syntax element are decoded using a context-based adaptive binary arithmetic decoding bypass mode; Decode the plurality of syntax elements different from the first syntax element using a context-based adaptive binary arithmetic decoding context mode; and The palette-mode encoded video data block is decoded using the decoded multiple instances of the first syntax element and the decoded multiple syntax elements different from the first syntax element, wherein the multiple instances of the first syntax element are grouped together such that the switching between the context-based adaptive binary arithmetic decoding bypass mode and the context-based adaptive binary arithmetic decoding context mode is reduced when decoding the palette-mode encoded video data block. 2. The method of claim 1, wherein the plurality of instances of the first syntax element comprises all instances of the first syntax element for the palette-mode encoded video data block. 3. The method of claim 1, wherein the first syntax element is palette_index_idc or palette_escape_val, and wherein the plurality of syntax elements different from the first syntax element include the palette_run_msb_id_plus1 syntax element. 4. The method of claim 1, wherein the encoded palette pattern information includes a second syntax element indicating the number of instances of the first syntax element, wherein the plurality of syntax elements different from the first syntax element are different from the second syntax element, and wherein the method further comprises: The second syntax element from the encoded video bitstream is parsed before parsing the plurality of syntax elements that are different from the first syntax element and the second syntax element from the encoded video bitstream; and The second syntax element is decoded using the context-based adaptive binary arithmetic decoding bypass mode. 5. The method of claim 4, wherein there is no interleaving of instances of the second syntax element between any two instances of the first syntax element used for the palette-mode encoded video data block. 6. The method of claim 4, further comprising: After decoding the number of instances of the first syntax element equal to the number indicated by the second syntax element, it is determined that subsequent data in the encoded video bitstream following the number of instances of the first syntax element corresponds to the plurality of syntax elements different from the first syntax element and the second syntax element. 7. The method of claim 4, wherein the encoded palette pattern information comprises a third syntax element and a fourth syntax element, wherein the method further comprises: Decode the third syntax element to determine whether the value corresponding to the third syntax element indicates whether the palette-mode encoded video data block contains an escape sample; Decode the fourth syntax element to determine the value corresponding to the fourth syntax element indicating the palette size; and The context-based adaptive binary arithmetic decoding context mode is used to decode the plurality of syntax elements that are different from the first syntax element and the second syntax element, based on the determined values corresponding to the third syntax element and the fourth syntax element, respectively. 8. The method of claim 4, wherein the encoded palette pattern information includes a third syntax element, and wherein the method further comprises: Decode the third syntax element to determine the value corresponding to the third syntax element, which specifies the number of distinct values that the palette index has for the palette-mode encoded video data block; and Based on the determined value corresponding to the third syntax element, the context-based adaptive binary arithmetic decoding context mode is used to decode the plurality of syntax elements that are different from the first syntax element and the second syntax element. 9. The method of claim 4, wherein the encoded palette pattern information includes a third syntax element, wherein the method further comprises: Decode the third syntax element to determine the last instance of the syntax element corresponding to the value of the third syntax element indicating the palette_run_type_flag[xC][yC] for the palette-mode encoded video data block. 10. The method of claim 4, further comprising: The second syntax element is decoded using a concatenation of truncated Rice code and exponential Golomb code. 11. The method of claim 1, further comprising: It is determined that the encoded video data block has one or more escaped samples; Decode the last escaped sample among the one or more escaped samples in the encoded video data block; Infer the index value of the sample following the last escaped sample applicable to the encoded video data block; and The inferred index value of each of the samples following the last escaped sample is used to decode the samples of the encoded video data block following the last escaped sample. 12. The method of claim 4, further comprising: Determine the number of received palette indices; The number of remaining palette indices is determined based on the number of received palette indices and the number of instances of the first syntax element; and Based on the number of received palette indices and the number of instances of the first syntax element, the value of the variable representing the run length is determined to be equal to the maximum possible run value for the encoded video data block. 13. The method of claim 12, wherein the maximum possible run value for the encoded video data block is equal to: nCbS*nCbS-scanPos-1-palettelndicesLeft, where nCbS specifies the size of the encoded video data block, scanPos specifies the scan position, and padettelndicesLeft specifies the number of remaining palette indices. 14. An apparatus for decoding video data, the apparatus comprising: A memory configured to store the video data; and A video decoder that communicates with the memory, the video decoder being configured to: Receive a palette-pattern-encoded block of video data containing the image from the memory; Receive encoded palette pattern information for the video data block encoded in the palette pattern, wherein the encoded palette pattern information includes multiple instances of a first syntax element and multiple syntax elements different from the first syntax element, wherein the first syntax element is an indication of an array of palette entries or specifies a quantized escape decoded sample value corresponding to a color component of an escape sample, and wherein the multiple syntax elements different from the first syntax element include a syntax element specifying an index of the most significant bit in the binary representation of a variable representing a run length and a syntax element specifying a run type pattern. The plurality of instances of the first syntax element derived from the encoded palette pattern information are analyzed before the plurality of syntax elements derived from the first syntax element derived from the encoded palette pattern information are analyzed. After parsing the plurality of instances of the first syntax element derived from the encoded palette pattern information, the plurality of syntax elements that are different from the first syntax element derived from the encoded palette pattern information are parsed. The plurality of instances of the first syntax element are decoded using a context-based adaptive binary arithmetic decoding bypass mode; Decode the plurality of syntax elements different from the first syntax element using a context-based adaptive binary arithmetic decoding context mode; and The palette-mode encoded video data block is decoded using the decoded instances of the first syntax element and the decoded syntax elements different from the first syntax element. The plurality of instances of the first syntax element are grouped together such that the switching between the context-based adaptive binary arithmetic decoding bypass mode and the context-based adaptive binary arithmetic decoding context mode is reduced when decoding the palette-mode encoded video data block. 15. The apparatus of claim 14, wherein the plurality of instances of the first syntax element comprises all instances of the first syntax element for the palette-mode encoded video data block. 16. The apparatus of claim 14, wherein the first syntax element is palette_index_idc or palette_escape_val, and wherein the plurality of syntax elements other than the first syntax element include the palette_run_msb_id_plus1 syntax element. 17. The apparatus of claim 14, wherein the encoded palette pattern information includes a second syntax element indicating the number of instances of the first syntax element, wherein the plurality of syntax elements different from the first syntax element are different from the second syntax element, and wherein the video decoder is further configured to: The second syntax element from the encoded palette pattern information is analyzed before analyzing the plurality of syntax elements that are different from the first syntax element and the second syntax element from the encoded palette pattern information; The second syntax element is decoded using the context-based adaptive binary arithmetic decoding bypass mode. 18. The apparatus of claim 17, wherein there is no interleaving of instances of the second syntax element between any two instances of the first syntax element used for the palette-mode encoded video data block. 19. The apparatus of claim 17, wherein the video decoder is further configured to determine, after decoding a number of instances of the first syntax element equal to the number indicated by the second syntax element, that subsequent data in the encoded video bitstream following the number of instances of the first syntax element corresponds to the plurality of syntax elements different from the first syntax element and the second syntax element. 20. The apparatus of claim 17, wherein the encoded palette pattern information comprises a third syntax element and a fourth syntax element, wherein the video decoder is further configured to: Decode the third syntax element to determine whether the value corresponding to the third syntax element indicates whether the palette-mode encoded video data block contains an escape sample; Decode the fourth syntax element to determine the value corresponding to the fourth syntax element indicating the palette size; and The context-based adaptive binary arithmetic decoding context mode is used to decode the plurality of syntax elements that are different from the first syntax element and the second syntax element, based on the determined values corresponding to the third syntax element and the fourth syntax element, respectively. 21. The apparatus of claim 17, wherein the encoded palette pattern information includes a third syntax element, wherein the video decoder is further configured to: Decode the third syntax element to determine the value corresponding to the third syntax element, which specifies the number of distinct values that the palette index has for the palette-mode encoded video data block; and Based on the determined value corresponding to the third syntax element, the context-based adaptive binary arithmetic decoding context mode is used to decode the plurality of syntax elements that are different from the first syntax element and the second syntax element. 22. The apparatus of claim 17, wherein the encoded palette pattern information includes a third syntax element, wherein the video decoder is further configured to: Decode the third syntax element to determine the last instance of the syntax element corresponding to the value of the third syntax element indicating the palette_run_type_flag[xC][yC] for the palette-mode encoded video data block. 23. The apparatus of claim 17, wherein the video decoder is further configured to: The second syntax element is decoded using a concatenation of truncated Rice code and exponential Golomb code. 24. The apparatus of claim 14, wherein the video decoder is further configured to: It is determined that the encoded video data block has one or more escaped samples; Decode the last escaped sample among the one or more escaped samples in the encoded video data block; Infer the index value of the sample following the last escaped sample applicable to the encoded video data block; and The inferred index value of each of the samples following the last escaped sample is used to decode the samples of the encoded video data block following the last escaped sample. 25. The apparatus of claim 17, wherein the video decoder is further configured to: Determine the number of received palette indices; The number of remaining palette indices is determined based on the number of received palette indices and the number of instances of the first syntax element; and Based on the number of received palette indices and the number of instances of the first syntax element, the value of the variable representing the run length is determined to be equal to the maximum possible run value for the encoded video data block. 26. The apparatus of claim 25, wherein the maximum possible run value for the encoded video data block is equal to: nCbS*nCbS-scanPos-1-palettelndicesLeft, where nCbS specifies the size of the encoded video data block, scanPos specifies the scan position, and padettelndicesLeft specifies the number of remaining palette indices. 27. A non-transitory computer-readable storage medium having instructions stored thereon, the instructions causing one or more processors to: Receive blocks of color-pattern-encoded video data of the image from the memory; Receive encoded palette pattern information for the video data block encoded in the palette pattern, wherein the encoded palette pattern information includes multiple instances of a first syntax element and multiple syntax elements different from the first syntax element, wherein the first syntax element is an indication of an array of palette entries or specifies a quantized escape decoded sample value corresponding to a color component of an escape sample, and wherein the multiple syntax elements different from the first syntax element include a syntax element specifying an index of the most significant bit in the binary representation of a variable representing a run length and a syntax element specifying a run type pattern. The plurality of instances of the first syntax element derived from the encoded palette pattern information are analyzed before the plurality of syntax elements derived from the first syntax element derived from the encoded palette pattern information are analyzed. After parsing the plurality of instances of the first syntax element derived from the encoded palette pattern information, the plurality of syntax elements that are different from the first syntax element derived from the encoded palette pattern information are parsed. The plurality of instances of the first syntax element are decoded using a context-based adaptive binary arithmetic decoding bypass mode; Decode the plurality of syntax elements different from the first syntax element using a context-based adaptive binary arithmetic decoding context mode; and The palette-mode encoded video data block is decoded using the decoded multiple instances of the first syntax element and the decoded multiple syntax elements different from the first syntax element, wherein the multiple instances of the first syntax element are grouped together such that the switching between the context-based adaptive binary arithmetic decoding bypass mode and the context-based adaptive binary arithmetic decoding context mode is reduced when decoding the palette-mode encoded video data block. 28. A method for encoding video data, the method comprising: The video data blocks will be decoded in palette mode; Encoding the video data blocks into a encoded bitstream using a palette pattern, wherein encoding the video data blocks using a palette pattern includes: Generate palette pattern information for the video data block, wherein the palette pattern information includes multiple instances of a first syntax element and multiple syntax elements different from the first syntax element, wherein the first syntax element is an indication of an array of palette entries or specifies a quantized escape decoded sample value corresponding to a color component of an escape sample, and wherein the multiple syntax elements different from the first syntax element include a syntax element specifying an index of the most significant bit in the binary representation of a variable representing a run length and a syntax element specifying a run type pattern. Before encoding the plurality of syntax elements different from the first syntax element into the encoded bitstream using a context-based adaptive binary arithmetic decoding bypass mode, the plurality of instances of the first syntax element are encoded into the encoded bitstream using a context-based adaptive binary arithmetic decoding context mode; and After encoding the plurality of instances of the first syntax element into the encoded bitstream using the context-based adaptive binary arithmetic decoding bypass mode, the plurality of syntax elements different from the first syntax element are encoded into the encoded bitstream using the context-based adaptive binary arithmetic decoding context mode. The plurality of instances of the first syntax element are grouped together such that the switching between the context-based adaptive binary arithmetic decoding bypass mode and the context-based adaptive binary arithmetic decoding context mode is reduced when encoding the palette-mode encoded video data block. 29. The method of claim 28, wherein the plurality of instances of the first syntax element comprises all instances of the first syntax element for the video data block. 30. The method of claim 28, wherein the first syntax element is palette_index_idc or palette_escape_val, and wherein the plurality of syntax elements different from the first syntax element include the palette_run_msb_id_plus1 syntax element. 31. The method of claim 28, wherein the palette pattern information includes a second syntax element indicating the number of instances of the first syntax element, wherein the plurality of syntax elements different from the first syntax element are different from the second syntax element, and wherein the method further comprises: The second syntax element is encoded into the encoded bitstream using the context-based adaptive binary arithmetic decoding bypass mode prior to the encoding of the plurality of syntax elements different from the first syntax element and the second syntax element. 32. The method of claim 31, wherein there is no interleaving of instances of the second syntax element between any two instances of the first syntax element used for the video data block. 33. The method of claim 31, further comprising: The second syntax element is encoded into the encoded bitstream after the encoded plurality of instances of the first syntax element in the encoded bitstream. 34. The method of claim 31, wherein the palette mode information comprises a third syntax element and a fourth syntax element, wherein the method further comprises: The value corresponding to the third syntax element, indicating whether the video data block contains an escape sample, is encoded into the encoded bitstream; and The value corresponding to the fourth syntax element indicating the palette size is encoded into the encoded bitstream. 35. The method of claim 31, wherein the palette mode information includes a third syntax element, and wherein the method further comprises: The value corresponding to the third syntax element is encoded into the encoded bitstream, the third syntax element specifying the number of distinct values that the palette index has for the video data block. 36. The method of claim 31, wherein the palette mode information includes a third syntax element, and wherein the method further comprises: The encoding corresponds to the value of the last instance of the syntax element indicating the palette_run_type_flag[xC][yC] for the video data block. 37. The method of claim 31, further comprising: The second syntax element is encoded using a concatenation of truncated Rice code and exponential Golomb code. 38. The method of claim 28, further comprising: Encode the last escaped sample among the one or more escaped samples in the video data block; Infer the index value of the sample following the last escaped sample applicable to the video data block; and The inferred index value of each of the samples following the last escaped sample is used to encode the samples of the video data block following the last escaped sample. 39. An apparatus for encoding video data, the apparatus comprising: A memory configured to store the video data; and A video encoder that communicates with the memory, the video encoder being configured to: It is determined that the video data blocks stored in the memory will be encoded in a palette mode; The video data blocks are encoded into an encoded bitstream using a palette mode, wherein the video encoder configured to encode the video data blocks using a palette mode includes a video encoder configured to perform the following: Generate palette pattern information for the video data block, wherein the palette pattern information includes multiple instances of a first syntax element and multiple syntax elements different from the first syntax element, wherein the first syntax element is an indication of an array of palette entries or specifies a quantized escape decoded sample value corresponding to a color component of an escape sample, and wherein the multiple syntax elements different from the first syntax element include a syntax element specifying an index of the most significant bit in the binary representation of a variable representing a run length and a syntax element specifying a run type pattern. Before encoding the plurality of syntax elements different from the first syntax element into the encoded bitstream using a context-based adaptive binary arithmetic decoding bypass mode, the plurality of instances of the first syntax element are encoded into the encoded bitstream using a context-based adaptive binary arithmetic decoding context mode; and After encoding the plurality of instances of the first syntax element into the encoded bitstream using the context-based adaptive binary arithmetic decoding bypass mode, the plurality of syntax elements different from the first syntax element are encoded into the encoded bitstream using the context-based adaptive binary arithmetic decoding context mode. The plurality of instances of the first syntax element are grouped together such that the switching between the context-based adaptive binary arithmetic decoding bypass mode and the context-based adaptive binary arithmetic decoding context mode is reduced when encoding the palette-mode encoded video data block.