Chroma Delta Quantization Parameter in Video Coding

Abstract

A video decoder may be configured to: determine a predicted luma quantization parameter (QP) for a luma component of a decoding unit; receive, in a bitstream of encoded video data, a first syntax indicating a luma delta QP value for the luma component; determine a QP value for the luma component based on the predicted luma QP and the luma delta QP value; determine a predicted chroma QP for a chroma component of the decoding unit; receive, in the bitstream of encoded video data, a second syntax indicating a chroma delta QP value for the chroma component of the decoding unit; and determine a QP value for the chroma component of the decoding unit based on the predicted chroma QP and the chroma delta QP value.

Description

[0001] This application claims the benefit of priority of U.S. Patent Application No. 16 / 912,232, filed Jun. 25, 2020, which claims the benefit of priority of U.S. Provisional Application No. 62 / 868,771, filed Jun. 28, 2019, the entire contents of each of the above applications being incorporated herein by reference. Technical Field

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

[0003] Digital video capabilities can be incorporated into a wide range of devices, including digital televisions, digital live 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 wireless telephones, so-called "smart phones", video teleconferencing devices, video streaming devices, etc. Digital video devices implement video decoding 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 such standards). By implementing such video decoding techniques, video devices can more efficiently transmit, receive, encode, decode, and / or store digital video information.

[0004] Video decoding techniques include spatial (intra-picture) prediction and / or temporal (inter-picture) prediction to reduce or remove redundancy inherent in a video sequence. For block-based video decoding, a video slice (e.g., a video picture or a portion of a video picture) can be divided into video blocks, which may also be referred to as coding tree units (CTUs), coding units (CUs), and / or coding nodes. Video blocks in an intra-coded (I) slice of a picture are encoded using spatial prediction with respect to reference samples in adjacent blocks in the same picture. Video blocks in an inter-coded (P or B) slice of a picture can be encoded using spatial prediction with respect to reference samples in adjacent blocks in the same picture or temporal prediction with respect to reference samples in other reference pictures. A picture may be referred to as a frame, and a reference picture may be referred to as a reference frame. Summary of the Invention

[0005] The present disclosure describes techniques related to the quantization process, and more specifically, the present disclosure describes techniques related to using a chrominance delta quantization parameter (QP) to determine and signal a value for determining a chrominance QP. A video decoder may be configured to determine a predicted QP value for a block based on the QP value for a previously decoded block and without receiving any explicit syntax elements in the bitstream. The video decoder may then receive a delta QP value representing the difference between the predicted QP value for the block and the actual QP value. Since the delta QP value is typically smaller than the actual QP value, relatively fewer bits may be used to signal the delta QP value compared to the actual QP value. The quantization parameter or QP is a variable used by the decoding process to scale the transform coefficient levels. The QP effectively represents the amount of quantization applied to the coefficient levels.

[0006] According to one example, a method of decoding a bitstream of encoded video data includes: determining a predicted luminance quantization parameter (QP) for a luminance component of a coding unit; receiving, in the bitstream of the encoded video data, a first syntax indicating a luminance delta QP value for the luminance component; determining a QP value for the luminance component based on the predicted luminance QP and the luminance delta QP value; determining a predicted chrominance QP for a chrominance component of the coding unit; receiving, in the bitstream of the encoded video data, a second syntax indicating a chrominance delta QP value for the chrominance component of the coding unit; determining a QP value for the chrominance component of the coding unit based on the predicted chrominance QP and the chrominance delta QP value; dequantizing a luminance transform coefficient block for the coding unit based on the QP value for the luminance component; dequantizing a chrominance transform coefficient block for the coding unit based on the QP value for the chrominance component; and decoding the coding unit based on the dequantized luminance transform coefficient block and the dequantized chrominance transform coefficient block.

[0007] According to another example, a method for encoding video data includes: determining a quantization parameter (QP) value for a luminance component of a decoding unit for the video data; determining a predicted luminance QP for the luminance component of the decoding unit; determining an incremental QP value for the luminance component of the decoding unit based on the QP value for the luminance component and the predicted luminance QP; generating a first syntax indicating the incremental QP value for the luminance component of the decoding unit to be included in a bitstream of encoded video data; determining a QP value for a chrominance component of the decoding unit for the video data; determining a predicted chrominance QP for the chrominance component of the decoding unit; determining an incremental QP value for the chrominance component of the decoding unit based on the QP value for the chrominance component and the predicted chrominance QP; generating a second syntax indicating the incremental QP value for the chrominance component of the decoding unit to be included in the bitstream of the encoded video data; and outputting the first syntax and the second syntax in the bitstream of the encoded video data.

[0008] According to another example, a device for decoding video data includes: a memory configured to store video data; and one or more processors implemented in circuitry and configured to: determine a predicted luminance quantization parameter (QP) for a luminance component of a decoding unit; receive, in a bitstream of encoded video data, a first syntax indicating a luminance incremental QP value for the luminance component; determine a QP value for the luminance component based on the predicted luminance QP and the luminance incremental QP value; determine a predicted chrominance QP for a chrominance component of the decoding unit; receive, in the bitstream of the encoded video data, a second syntax indicating a chrominance incremental QP value for the chrominance component of the decoding unit; determine a QP value for the chrominance component of the decoding unit based on the predicted chrominance QP and the chrominance incremental QP value; dequantize a luminance transform coefficient block for the decoding unit based on the QP value for the luminance component; dequantize a chrominance transform coefficient block for the decoding unit based on the QP value for the chrominance component; and decode the decoding unit based on the dequantized luminance transform coefficient block and the dequantized chrominance transform coefficient block.

[0009] According to another example, an apparatus for encoding video data includes: a memory configured to store video data; and one or more processors implemented in circuitry and configured to: determine a quantization parameter (QP) value for a luminance component of a decoding unit for the video data; determine a predicted luminance QP for the luminance component of the decoding unit; determine an incremental QP value for the luminance component of the decoding unit based on the QP value for the luminance component and the predicted luminance QP; generate a first syntax indicating the incremental QP value for the luminance component of the decoding unit to be included in a bitstream of the encoded video data; determine a QP value for a chrominance component of the decoding unit for the video data; determine a predicted chrominance QP for the chrominance component of the decoding unit; determine an incremental QP value for the chrominance component of the decoding unit based on the QP value for the chrominance component and the predicted chrominance QP; generate a second syntax indicating the incremental QP value for the chrominance component of the decoding unit to be included in the bitstream of the encoded video data; and output the first syntax and the second syntax in the bitstream of the encoded video data.

[0010] According to another example, a device for decoding a bitstream of encoded video data includes: a unit for determining a predicted luminance quantization parameter (QP) for a luminance component of a decoding unit; a unit for receiving, in a bitstream of encoded video data, a first syntax indicating a luminance incremental QP value for the luminance component; a unit for determining a QP value for the luminance component based on the predicted luminance QP and the luminance incremental QP value; a unit for determining a predicted chrominance QP for a chrominance component of the decoding unit; a unit for receiving, in the bitstream of encoded video data, a second syntax indicating a chrominance incremental QP value for the chrominance component of the decoding unit; a unit for determining a QP value for the chrominance component of the decoding unit based on the predicted chrominance QP and the chrominance incremental QP value; a unit for dequantizing a luminance transform coefficient block for the decoding unit based on the QP value for the luminance component; a unit for dequantizing a chrominance transform coefficient block for the decoding unit based on the QP value for the chrominance component; and a unit for decoding the decoding unit based on the dequantized luminance transform coefficient block and the dequantized chrominance transform coefficient block.

[0011] According to another example, a computer-readable storage medium stores instructions that, when executed by one or more processors, cause the one or more processors to perform the following operations: determine a predicted luminance quantization parameter (QP) for a luminance component of a decoding unit; receive, in a bitstream of encoded video data, a first syntax indicating a luminance delta QP value for the luminance component; determine a QP value for the luminance component based on the predicted luminance QP and the luminance delta QP value; determine a predicted chrominance QP for a chrominance component of the decoding unit; receive, in the bitstream of the encoded video data, a second syntax indicating a chrominance delta QP value for the chrominance component of the decoding unit; determine a QP value for the chrominance component of the decoding unit based on the predicted chrominance QP and the chrominance delta QP value; dequantize a luminance transform coefficient block for the decoding unit based on the QP value for the luminance component; dequantize a chrominance transform coefficient block for the decoding unit based on the QP value for the chrominance component; and decode the decoding unit based on the dequantized luminance transform coefficient block and the dequantized chrominance transform coefficient block.

[0012] According to another example, an apparatus for encoding video data includes: a unit for determining a quantization parameter (QP) value for a luminance component of a decoding unit of the video data; a unit for determining a predicted luminance QP for the luminance component of the decoding unit; a unit for determining a delta QP value for the luminance component of the decoding unit based on the QP value for the luminance component and the predicted luminance QP; a unit for generating a first syntax indicating the delta QP value for the luminance component of the decoding unit to be included in a bitstream of encoded video data; a unit for determining a QP value for a chrominance component of the decoding unit of the video data; a unit for determining a predicted chrominance QP for the chrominance component of the decoding unit; a unit for determining a delta QP value for the chrominance component of the decoding unit based on the QP value for the chrominance component and the predicted chrominance QP; a unit for generating a second syntax indicating the delta QP value for the chrominance component of the decoding unit to be included in the bitstream of the encoded video data; and a unit for outputting the first syntax and the second syntax in the bitstream of the encoded video data.

[0013] A computer-readable storage medium storing instructions that, when executed by one or more processors, cause the one or more processors to perform the following operations: determining a quantization parameter (QP) value for a luminance component of a decoding unit for the video data; determining a predicted luminance QP for the luminance component of the decoding unit; determining an incremental QP value for the luminance component of the decoding unit based on the QP value for the luminance component and the predicted luminance QP; generating a first syntax indicating the incremental QP value for the luminance component of the decoding unit to be included in a bitstream of the encoded video data; determining a QP value for a chrominance component of the decoding unit for the video data; determining a predicted chrominance QP for the chrominance component of the decoding unit; determining an incremental QP value for the chrominance component of the decoding unit based on the QP value for the chrominance component and the predicted chrominance QP; generating a second syntax indicating the incremental QP value for the chrominance component of the decoding unit to be included in the bitstream of the encoded video data; and outputting the first syntax and the second syntax in the bitstream of the encoded video data.

[0014] Details of one or more examples are set forth in the accompanying drawings and the following description. Other features, objects, and advantages will be apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0017] Figure 3 illustrates an example process for determining an incremental QP value for video data that supports dual-tree partitioning.

[0018] Figure 4 illustrates an example process for decoding a chrominance QP offset value for video data that supports dual-tree partitioning.

[0019] Figure 5 illustrates an example video coding process.

[0020] Figure 6 illustrates an example of a chrominance CU having a corresponding luminance CU in a separate tree.

[0021] Figure 7 is a block diagram illustrating an example video encoder that may execute the techniques of the present disclosure.

[0022] Figure 8 is a block diagram showing an example video decoder that can execute the technology of the present disclosure.

[0023] Figure 9 is a flowchart showing an example video encoding process.

[0024] Figure 10 is a flowchart showing an example video decoding process.

[0025] Figure 11 is a flowchart showing an example video encoding process.

[0026] Figure 12 is a flowchart showing an example video decoding process. Detailed Description

[0027] Video coding (e.g., video encoding and / or video decoding) generally involves predicting a video data block (e.g., intra prediction) based on already-coded video data blocks in the same picture or predicting a video data block based on already-coded video data blocks in different pictures (e.g., inter prediction). In some cases, a video encoder also calculates residual data by comparing a predicted block with an original block. Thus, the residual data represents the difference between the predicted block and the original block. To reduce the number of bits required to signal the residual data, the video encoder transforms and quantizes the residual data and signals the transformed and quantized residual data in the encoded bitstream. The compression achieved by the transform and quantization process may be lossy, meaning that the transform and quantization process may introduce distortion into the decoded video data.

[0028] A video decoder decodes the residual data and adds it to the predicted block to produce a reconstructed video block that more closely matches the original video block than the individual predicted block. Due to the loss introduced by the transform and quantization of the residual data, the first reconstructed block may have distortion or artifacts. A common type of artifact or distortion is referred to as blocking, where the boundaries of the blocks used to encode the video data are visible.

[0029] To further improve the quality of the decoded video, a video decoder may perform one or more filtering operations on the reconstructed video block. Examples of these filtering operations include deblocking filtering, sample adaptive offset (SAO) filtering, and adaptive loop filtering (ALF). The parameters for these filtering operations may be determined by the video encoder and signaled explicitly in the encoded video bitstream, or may be determined implicitly by the video decoder without the need to explicitly signal the parameters in the encoded video bitstream.

[0030] The present disclosure describes techniques related to quantization processes, and more particularly, the present disclosure describes techniques related to using a chrominance delta quantization parameter (QP) to determine and signal values for determining a chrominance QP value. A video decoder may be configured to determine a predicted QP value for a block based on QP values for previously decoded blocks and without receiving any explicit syntax elements in a bitstream. The video decoder may then receive a delta QP value representing a difference between the predicted QP value for the block and an actual QP value. Since the delta QP value is typically smaller than the actual QP value, relatively fewer bits may be used to signal the delta QP value compared to the actual QP value.

[0031] A quantization parameter or QP is a variable used by a decoding process to scale transform coefficient levels. The QP effectively represents the amount of quantization applied to the coefficient levels. By configuring a video decoder to receive in a bitstream of encoded video data syntax indicating a chrominance delta QP value for a chrominance component and to determine a QP value for the chrominance component based on a predicted chrominance QP and the chrominance delta QP value, the techniques of the present disclosure can achieve the advantage of an improved rate-distortion tradeoff achieved in some decoding scenarios by allowing the chrominance QP value to be adjusted independently of the luma QP value.

[0032] The techniques described may be used in conjunction with any existing video codec (such as High Efficiency Video Coding (HEVC), Versatile Video Coding (VVC)), or as an efficient coding tool in any future video coding standard. The techniques of the present disclosure will be described with respect to HEVC, JEM, and VVC, but the techniques described herein are not limited to any particular standard.

[0033] Figure 1 FIG. 100 is a block diagram illustrating an example video encoding and decoding system 100 that may perform the techniques of the present disclosure. Generally, the techniques of the present disclosure relate to encoding (encoding and / or decoding) video data. Typically, video data includes any data for processing video. Thus, video data may include raw unencoded video, encoded video, decoded (e.g., reconstructed) video, and video metadata (e.g., signaling data).

[0034] As Figure 1As shown, in this example, system 100 includes a source device 102 that provides encoded video data to be decoded and displayed by a destination device 116. Specifically, the source device 102 provides the video data to the destination device 116 via a computer-readable medium 110. The source device 102 and the destination device 116 can include any of a variety of devices, including desktop computers, notebook computers (i.e., laptop computers), mobile devices, tablet computers, set-top boxes, telephone handsets such as smart phones, televisions, cameras, display devices, digital media players, video game consoles, video streaming devices, broadcast receiver devices, and the like. In some cases, the source device 102 and the destination device 116 can be equipped for wireless communication and can thus be referred to as wireless communication devices.

[0035] In Figure 1 the example of, the source device 102 includes a video source 104, a memory 106, a video encoder 200, and an output interface 108. The destination device 116 includes an input interface 122, a video decoder 300, a memory 120, and a display device 118. According to the present disclosure, the video encoder 200 of the source device 102 and the video decoder 300 of the destination device 116 can be configured to apply the techniques for chrominance delta QP decoding described herein. Thus, the source device 102 represents an example of a video encoding device, while the destination device 116 represents an example of a video decoding device. In other examples, the source device and the destination device can include other components or arrangements. For example, the source device 102 can receive video data from an external video source such as an external camera. Similarly, the destination device 116 can interface with an external display device rather than include an integrated display device.

[0036] As Figure 1The illustrated system 100 is merely an example. In general, any digital video encoding and / or decoding device may perform the techniques for chrominance delta QP decoding described herein. The source device 102 and the destination device 116 are merely examples of such decoding devices, where the source device 102 generates encoded video data for transmission to the destination device 116. This disclosure refers to a "decoding" device as a device that performs decoding (e.g., encoding and / or decoding) of data. Thus, the video encoder 200 and the video decoder 300 represent examples of decoding devices (specifically, a video encoder and a video decoder), respectively. In some examples, the source device 102 and the destination device 116 may operate in a substantially symmetric manner such that each of the source device 102 and the destination device 116 includes video encoding and decoding components. Thus, the system 100 may support one-way or two-way video transmission between the source device 102 and the destination device 116, e.g., for video streaming, video playback, video broadcast, or video telephony.

[0037] In general, the video source 104 represents a source of video data (i.e., raw, unencoded video data) and provides a sequential series of pictures (also referred to as "frames") of the video data to the video encoder 200, which encodes the data for the pictures. The video source 104 of the source device 102 may include a video capture device, such as a camera, a video archival unit containing previously captured raw video, and / or a video feed interface for receiving video from a video content provider. As another alternative, the video source 104 may generate computer graphics-based data as the source video, or a combination of live video, archived video, and computer-generated video. In each case, the video encoder 200 encodes the captured, pre-captured, or computer-generated video data. The video encoder 200 may reorder the pictures from the received order (sometimes referred to as the "display order") to a decoding order for decoding. The video encoder 200 may generate a bitstream including the encoded video data. Then, the source device 102 may output the encoded video data to a computer-readable medium 110 via the output interface 108 for reception and / or retrieval by, e.g., the input interface 122 of the destination device 116.

[0038] The memories 106 of the source device 102 and 120 of the destination device 116 represent general memories. In some examples, the memories 106, 120 may store raw video data, e.g., raw video from the video source 104 and raw decoded video data from the video decoder 300. Additionally or alternatively, the memories 106, 120 may store software instructions that may be executed by, for example, the video encoder 200 and the video decoder 300, respectively. Although the memories 106 and 120 are shown as separate from the video encoder 200 and the video decoder 300 in this example, it should be understood that the video encoder 200 and the video decoder 300 may also include internal memories for functionally similar or equivalent purposes. Further, the memories 106, 120 may store, for example, encoded video data output from the video encoder 200 and input to the video decoder 300. In some examples, portions of the memories 106, 120 may be allocated as one or more video buffers, e.g., to store raw decoded and / or encoded video data.

[0039] The computer-readable medium 110 may represent any type of medium or device capable of conveying the encoded video data from the source device 102 to the destination device 116. In one example, the computer-readable medium 110 represents a communication medium that enables the source device 102 to directly send the encoded video data to the destination device 116 in real time, e.g., via a radio frequency network or a computer-based network. The output interface 108 may modulate the transmission signal including the encoded video data according to a communication standard such as a wireless communication protocol, and the input interface 122 may demodulate the received transmission signal according to a communication standard such as a wireless communication protocol. The communication medium may include any wireless or wired communication medium, e.g., the radio frequency (RF) spectrum or one or more physical transmission lines. The communication medium may form part of a packet-based network such as a local area network, a wide area network, or a global network such as the Internet. The communication medium may include routers, switches, base stations, or any other devices that may be useful for facilitating communication from the source device 102 to the destination device 116.

[0040] In some examples, the source device 102 may output the encoded data from the output interface 108 to the storage device 112. Similarly, the destination device 116 may access the encoded data from the storage device 112 via the input interface 122. The storage device 112 may include any of a variety of distributed or locally accessible data storage media, such as a hard disk drive, a Blu-ray disc, a DVD, a CD-ROM, flash memory, volatile or non-volatile memory, or any other suitable digital storage media for storing the encoded video data.

[0041] In some examples, the source device 102 may output the encoded video data to a file server 114 or to another intermediate storage device that may store the encoded video data generated by the source device 102. The destination device 116 may access the stored video data from the file server 114 via streaming or downloading.

[0042] The file server 114 may be any type of server device capable of storing the encoded video data and sending the encoded video data to the destination device 116. The file server 114 may represent a web server (e.g., for a website), a server configured to provide file transfer protocol services (such as File Transfer Protocol (FTP) or File Delivery over Unidirectional Transport (FLUTE) protocol), a content delivery network (CDN) device, a Hypertext Transfer Protocol (HTTP) server, a Multimedia Broadcast Multicast Service (MBMS) or Enhanced MBMS (eMBMS) server, and / or a Network Attached Storage (NAS) device. The file server 114 may additionally or alternatively implement one or more HTTP streaming protocols, such as HTTP-based Dynamic Adaptive Streaming over HTTP (DASH), HTTP Live Streaming (HLS), Real-Time Streaming Protocol (RTSP), HTTP Dynamic Streaming, etc.

[0043] The destination device 116 may access the encoded video data from the file server 114 via any standard data connection, including an Internet connection. This may include a wireless channel (e.g., Wi-Fi connection), a wired connection (e.g., Digital Subscriber Line (DSL), cable modem, etc.), or a combination of both, suitable for accessing the encoded video data stored on the file server 114. The input interface 122 may be configured to operate in accordance with any one or more of the various protocols discussed above for retrieving or receiving media data from the file server 114 or other such protocols for retrieving media data.

[0044] The output interface 108 and the input interface 122 can represent a wireless transmitter / receiver, a modem, a wired networking component (e.g., an Ethernet card), a wireless communication component operating according to any of various IEEE 802.11 standards, or other physical components. In examples where the output interface 108 and the input interface 122 include wireless components, the output interface 108 and the input interface 122 can be configured to transmit data (such as encoded video data) according to cellular communication standards (such as 4G, 4G-LTE (Long Term Evolution), enhanced LTE, 5G, etc.). In some examples where the output interface 108 includes a wireless transmitter, the output interface 108 and the input interface 122 can be configured to transmit data (such as encoded video data) according to other wireless standards (such as IEEE 802.11 specifications, IEEE 802.15 specifications (e.g., ZigBee TM ), Bluetooth TM standards, etc.). In some examples, the source device 102 and / or the destination device 116 can include corresponding system-on-a-chip (SoC) devices. For example, the source device 102 can include an SoC device for performing the functions assigned to the video encoder 200 and / or the output interface 108, and the destination device 116 can include an SoC device for performing the functions assigned to the video decoder 300 and / or the input interface 122.

[0045] The techniques of the present disclosure can be applied to video coding to support any of various multimedia applications, such as over-the-air television broadcasting, cable television transmission, satellite television transmission, Internet streaming video transmission (such as HTTP-based Dynamic Adaptive Streaming over HTTP (DASH)), digital video encoded onto a data storage medium, decoding of digital video stored on a data storage medium, or other applications.

[0046] The input interface 122 of the destination device 116 receives an encoded video bitstream from a computer-readable medium 110 (e.g., a communication medium, a storage device 112, a file server 114, etc.). The encoded video bitstream can include signaling information such as the following syntax elements defined by the video encoder 200 (which are also used by the video decoder 300): The syntax elements have values that describe the characteristics and / or processing of video blocks or other coding units (e.g., slices, pictures, groups of pictures, sequences, etc.). The display device 118 displays the decoded pictures of the decoded video data to the user. The display device 118 can represent any of 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.

[0047] Although in Figure 1Although not shown in the figure, in some examples, the video encoder 200 and the video decoder 300 may each be integrated with an audio encoder and / or an audio decoder, and may include appropriate MUX-DEMUX units or other hardware and / or software to process a multiplexed stream that includes both audio and video in a common data stream. If applicable, the MUX-DEMUX unit may follow the ITU H.223 multiplexer protocol or other protocols (such as the User Datagram Protocol (UDP)).

[0048] The video encoder 200 and the video decoder 300 may each be implemented as any of a variety of suitable encoder and / or decoder circuits, such as one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), discrete logic, software, hardware, firmware, or any combination thereof. When the technology is implemented partially in software, the device may store instructions for the software in a suitable non-transitory computer-readable medium and use one or more processors to execute the instructions in hardware to perform the techniques of the present disclosure. Each of the video encoder 200 and the video decoder 300 may be included in one or more encoders or decoders, and any of the encoders or decoders may be integrated as part of a combined encoder / decoder (CODEC) in a corresponding device. Devices including the video encoder 200 and / or the video decoder 300 may include integrated circuits, microprocessors, and / or wireless communication devices (such as cellular phones).

[0049] Video encoder 200 and video decoder 300 may operate according to a video coding standard, such as ITU-T H.265 (also known as the High Efficiency Video Coding (HEVC) standard) or an extension thereof (such as multi-view and / or scalable video coding extensions). Alternatively, video encoder 200 and video decoder 300 may operate according to other proprietary or industry standards, such as ITU-T H.266, also known as Versatile Video Coding (VVC). Drafts of the VVC standard are described in the following documents: Bross et al., "Versatile Video Coding (Draft 5)", Joint Video Team (JVT) of ITU-T SG 16 WP 3 and ISO / IEC JTC1 / SC 29 / WG 11, 14th meeting: Geneva, Switzerland, March 19 - 27, 2019, JVET-N1001-v9 (hereinafter referred to as "VVC Draft 5"). Another draft of the VVC standard is described in the following document: Bross et al., "Versatile Video Coding (Draft 9)", Joint Video Team (JVT) of ITU-T SG 16 WP 3 and ISO / IEC JTC 1 / SC29 / WG 11, 18th meeting: by teleconference, April 15 - 24, 2020, JVET-R2001-v11 (hereinafter referred to as "VVC Draft 9"). However, the techniques of the present disclosure are not limited to any particular coding standard.

[0050] Generally, video encoder 200 and video decoder 300 may perform block-based coding of pictures. The term "block" generally refers to a structure that includes data to be processed (e.g., to be encoded, decoded, or otherwise used during the encoding and / or decoding process). For example, a block may include a two-dimensional matrix of samples of luminance and / or chrominance data. Generally, video encoder 200 and video decoder 300 may code video data represented in YUV (e.g., Y, Cb, Cr) format. That is, instead of coding the red, green, and blue (RGB) data of the samples for a picture, video encoder 200 and video decoder 300 may code the luminance and chrominance components, where the chrominance components may include both the red hue and blue hue chrominance components. In some examples, video encoder 200 converts the received RGB-formatted data to a YUV representation before encoding, and video decoder 300 converts the YUV representation to RGB format. Alternatively, preprocessing and postprocessing units (not shown) may perform these conversions.

[0051] Generally speaking, the present disclosure may relate to the decoding (e.g., encoding and decoding) of pictures, including the process of encoding or decoding the data of pictures. Similarly, the present disclosure may relate to the decoding of blocks of pictures, including the process of encoding or decoding the data for blocks (e.g., prediction and / or residual decoding). An encoded video bitstream typically includes a series of values for representing decoding decisions (e.g., decoding modes) and syntax elements that partition a picture into blocks. Thus, a reference to decoding a picture or block should generally be understood as decoding the values of the syntax elements that form the picture or block.

[0052] HEVC defines various blocks, including coding units (CUs), prediction units (PUs), and transform units (TUs). According to HEVC, a video decoder (such as video encoder 200) partitions a coding tree unit (CTU) into CUs according to a quadtree structure. That is, the video decoder divides the CTU and CU into four equal, non-overlapping squares, and each node of the quadtree has zero or four children. A node without children may be referred to as a "leaf node", and the CU of such a leaf node may include one or more PUs and / or one or more TUs. The video decoder may further partition the PUs and TUs. For example, in HEVC, a residual quadtree (RQT) represents the partitioning of TUs. In HEVC, a PU represents inter-predicted data, while a TU represents residual data. An intra-predicted CU includes intra-prediction information, such as an intra-mode indication.

[0053] As another example, video encoder 200 and video decoder 300 may be configured to operate according to VVC. According to VVC, a video decoder (such as video encoder 200) divides a picture into a plurality of coding tree units (CTUs). Video encoder 200 may divide the CTU according to a tree structure (such as a quadtree-binary tree (QTBT) structure or a multi-type tree (MTT) structure). The QTBT structure eliminates the concept of multiple partitioning types, such as the separation between CUs, PUs, and TUs in HEVC. The QTBT structure includes two levels: a first level that is divided according to quadtree partitioning, and a second level that is divided according to binary tree partitioning. The root node of the QTBT structure corresponds to the CTU. The leaf nodes of the binary tree correspond to coding units (CUs).

[0054] In an MTT partitioning structure, a quadtree (QT) partition, a binary tree (BT) partition, and one or more types of ternary trees (TTs) (also referred to as trinary trees (TTs)) can be used to partition blocks. A ternary tree or trinary tree partition is a partition in which a block is divided into three sub-blocks. In some examples, a ternary tree or trinary tree partition divides a block into three sub-blocks without dividing the original block through the center. The types of partitions in MTT (e.g., QT, BT, and TT) can be symmetric or asymmetric.

[0055] In some examples, video encoder 200 and video decoder 300 can use a single QTBT or MTT structure to represent each of the luminance component and the chrominance components, while in other examples, video encoder 200 and video decoder 300 can use two or more QTBT or MTT structures, such as one QTBT / MTT structure for the luminance component and another QTBT / MTT structure for the two chrominance components (or two QTBT / MTT structures for the respective chrominance components).

[0056] Video encoder 200 and video decoder 300 can be configured to use quadtree partitioning, QTBT partitioning, MTT partitioning, or other partitioning structures per HEVC. For purposes of explanation, a description of the techniques of the present disclosure is given with respect to QTBT partitioning. However, it should be understood that the techniques of the present disclosure can also be applied to video decoders configured to use quadtree partitioning or also use other types of partitioning.

[0057] In some examples, a CTU includes a coding tree block (CTB) of the luminance samples of a picture, two corresponding CTBs of the chrominance samples (the picture having three sample arrays), or a CTB of the samples of a monochrome picture or a picture coded using three separate color planes, and a syntax structure for coding the samples. A CTB can be an NxN sample block for some value of N such that dividing the component into CTBs is a partition. The component can be one array or a single sample from among the three arrays (luminance and two chrominance) that make up a picture in a 4:2:0, 4:2:2, or 4:4:4 color format, or an array or a single sample of an array that makes up a picture in a monochrome format. In some examples, a coding block is an MxN sample block for some values of M and N such that dividing the CTB into coding blocks is a partition.

[0058] Blocks (e.g., CTUs or CUs) can be grouped in a picture in various ways. As an example, a brick can refer to a rectangular region of CTU rows within a particular tile in the picture. A tile can be a rectangular region of CTUs within a particular tile column and a particular tile row in the picture. A tile column refers to a rectangular region of CTUs that has a height equal to the height of the picture and a width specified by a syntax element (e.g., such as in a picture parameter set). A tile row refers to a rectangular region of CTUs that has a height specified by a syntax element (e.g., such as in a picture parameter set) and a width equal to the width of the picture.

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

[0060] Bricks in a picture can also be arranged in slices. A slice can be an integral number of bricks of the picture that can be uniquely contained within a single network abstraction layer (NAL) unit. In some examples, a slice includes a plurality of complete tiles or a contiguous sequence of complete bricks that include only one tile.

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

[0062] Video encoder 200 encodes video data for the representation prediction and / or residual information of a CU and other information. The prediction information indicates how the CU will be predicted to form a prediction block for the CU. The residual information generally represents the sample-by-sample difference between the samples of the CU before encoding and the prediction block.

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

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

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

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

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

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

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

[0070] To perform CABAC, the video encoder 200 may assign contexts within a context model to symbols to be sent. The context may relate to, for example, whether the adjacent values of the symbol are zero values. Probability determination may be based on the context assigned to the symbol.

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

[0072] In this way, the video encoder 200 may generate a bitstream that includes encoded video data, for example, syntax elements that describe the segmentation of a picture into blocks (e.g., CUs) and prediction and / or residual information for the blocks. Ultimately, the video decoder 300 may receive the bitstream and decode the encoded video data.

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

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

[0075] By determining a predicted chrominance QP for a chrominance component of a decoding unit, signaling syntax that indicates a chrominance delta QP value for the chrominance component of the decoding unit, and determining a QP value for the chrominance component of the decoding unit based on the predicted chrominance QP and the chrominance delta QP value, video encoder 200 and video decoder 300 can enable flexible adjustment of the chrominance QP value independent of the luma QP value in a manner that does not incur an undesired amount of additional signaling overhead.

[0076] Generally, the present disclosure may relate to "signaling" certain information, such as syntax elements. The term "signaling" generally may refer to the conveyance of values for syntax elements and / or other data used to decode the encoded video data. That is, video encoder 200 may signal the value for a syntax element in the bitstream. Generally, signaling refers to generating a value in the bitstream. As described above, source device 102 may transmit the bitstream to destination device 116 substantially in real time or not in real time, such as may occur when storing the syntax elements to storage device 112 for later retrieval by destination device 116.

[0077] Figure 2A and Figure 2B is a conceptual diagram showing an example quadtree binary tree (QTBT) structure 130 and corresponding coding tree unit (CTU) 132. Solid lines represent quadtree splits, while dashed lines indicate binary tree splits. In each split (i.e., non-leaf) node of the binary tree, a flag is signaled to indicate which split type (i.e., horizontal or vertical) is used, where, in this example, 0 indicates a horizontal split and 1 indicates a vertical split. For quadtree splits, since a quadtree node splits a block horizontally and vertically into 4 sub-blocks of equal size, there is no need to indicate the split type. Thus, video encoder 200 may encode, and video decoder 300 may decode, syntax elements (such as split information) for the region tree level (i.e., solid lines) of QTBT structure 130, and syntax elements (such as split information) for the prediction tree level (i.e., dashed lines) of QTBT structure 130. Video encoder 200 may encode video data (such as prediction and transform data) for a CU represented by a terminal leaf node of QTBT structure 130, and video decoder 300 may decode the video data. The CTU may be split using single-tree splitting or dual-tree splitting. With single-tree splitting, the chrominance component of the CTU and the luma component of the CTU have the same split structure. With dual-tree splitting, the chrominance component of the CTU and the luma component of the CTU potentially have different split structures.

[0078] Generally, Figure 2BThe CTU 132 can be associated with parameters that define the size of blocks corresponding to nodes at the first and second levels of the QTBT structure 130. These parameters can include the CTU size (representing the size of the CTU 132 in the sample), the minimum quadtree size (MinQTSize, which represents the minimum allowable quadtree leaf node size), the maximum binary tree size (MaxBTSize, which represents the maximum allowable binary tree root node size), the maximum binary tree depth (MaxBTDepth, which represents the maximum allowable binary tree depth), and the minimum binary tree size (MinBTSize, which represents the minimum allowable binary tree leaf node size).

[0079] The root node of the QTBT structure corresponding to the CTU can have four child nodes at the first level of the QTBT structure, and each child node can be split according to quadtree splitting. That is, the nodes at the first level are leaf nodes (without child nodes) or have four child nodes. An example of the QTBT structure 130 represents such a node as including a parent node and child nodes with solid lines for the branches. If the nodes at the first level are not larger than the maximum allowable binary tree root node size (MaxBTSize), these nodes can be further split by the corresponding binary tree. The binary tree splitting of a node can be iterated until the nodes resulting from the splitting reach the minimum allowable binary tree leaf node size (MinBTSize) or the maximum allowable binary tree depth (MaxBTDepth). An example of the QTBT structure 130 represents such a node as having dashed lines for the branches. The binary tree leaf nodes are referred to as coding units (CUs), which are used for prediction (e.g., intra-picture or inter-picture prediction) and transformation without any further splitting. As discussed above, the CU can also be referred to as a "video block" or a "block".

[0080] In an example of the QTBT partitioning structure, the CTU size is set to 128x128 (luma samples and two corresponding 64x64 chroma samples), MinQTSize is set to 16x16, MaxBTSize is set to 64x64, MinBTSize (for both width and height) is set to 4, and MaxBTDepth is set to 4. First, quadtree partitioning is applied to the CTU to generate quadtree leaf nodes. The quadtree leaf nodes can have sizes ranging from 16x16 (i.e., MinQTSize) to 128x128 (i.e., CTU size). If the quadtree leaf node is 128x128, since this size exceeds MaxBTSize (i.e., 64x64 in this example), the leaf quadtree node will not be further split by the binary tree. Otherwise, the quadtree leaf node will be further split by the binary tree. Thus, the quadtree leaf node is also the root node for the binary tree and has a binary tree depth of 0. When the binary tree depth reaches MaxBTDepth (4 in this example), further splitting is not allowed. A binary tree node with a width equal to MinBTSize (4 in this example) means that no further vertical splitting (i.e., division of the width) is allowed for this binary tree node. Similarly, a binary tree node with a height equal to MinBTSize means that no further horizontal splitting (i.e., division of the height) is allowed for this binary tree node. As described above, the leaf nodes of the binary tree are called CUs and are further processed according to prediction and transformation without further splitting.

[0081] Video encoder 200 and video decoder 300 can be configured to handle luma delta QP values. That is, video decoder 300 can be configured to determine a predicted QP value for a block based on the luma QP value for a previously decoded block and without receiving any explicit syntax elements in the bitstream. Then, video decoder 300 can receive a luma delta QP value representing the difference between the predicted luma QP value and the actual luma QP value for the block.

[0082] In VVC draft 5, the delta QP value is signaled in a similar way to HEVC. The syntax included in VVC draft 5 is as follows:

[0083]

[0084]

[0085] The syntax element cu_qp_delta_abs specifies the absolute value of the difference between the quantization parameter of the current coding unit and the predicted QP value used for the coding unit. As an example, the video encoder 200 and the video decoder 300 may determine, for example, that the predicted QP value for the current CU is equal to the QP value of the previously coded CU. If one or both of the upper neighboring CU or the left neighboring CU are available, the video encoder 200 and the video decoder 300 may use one of the QP of the upper neighbor or the QP of the left neighbor as the predicted QP value. If the previously coded CU does not have a QP value, for example, if the previously coded CU was coded in skip mode, the video encoder 200 and the video decoder 300 may be configured to set the predicted QP value to be equal to the QP value of the last CU coded with quantization or a default value. In the following description, CuQpDeltaVal represents the delta QP value.

[0086] The syntax element cu_qp_delta_sign_flag specifies the sign of CuQpDeltaVal as follows: – If cu_qp_delta_sign_flag is equal to 0, the corresponding CuQpDeltaVal has a positive value. – Otherwise (cu_qp_delta_sign_flag is equal to 1), the corresponding CuQpDeltaVal has a negative value. When cu_qp_delta_sign_flag is not present, the value of cu_qp_delta_sign_flag is inferred to be equal to 0.

[0087] When cu_qp_delta_abs is present, the variables IsCuQpDeltaCoded and CuQpDeltaVal are derived as follows:

[0088] IsCuQpDeltaCoded = 1 (7-130)

[0089] CuQpDeltaVal = cu_qp_delta_abs * (1 - 2 * cu_qp_delta_sign_flag) (7-131) The value of CuQpDeltaVal shall be in the range of -(32 + QpBdOffsetY / 2) to +(31 + QpBdOffsetY / 2) (inclusive).

[0090] The syntax element cu_qp_delta_enabled_flag being equal to 1 specifies that the syntax element cu_qp_delta_subdiv is present in the PPS, and cu_qp_delta_abs may be present in the transform unit syntax. The syntax element cu_qp_delta_enabled_flag being equal to 0 specifies that the syntax element cu_qp_delta_subdiv is not present in the PPS, and cu_qp_delta_abs is not present in the transform unit syntax.

[0091] The syntax element cu_qp_delta_subdiv specifies the maximum cbSubdiv value of the decoding unit that conveys cu_qp_delta_abs and cu_qp_delta_sign_flag. The value range of cu_qp_delta_subdiv is specified as follows:

[0092] – If slice_type is equal to I, the value of cu_qp_delta_subdiv shall be in the range from 0 to 2*(log2_ctu_size_minus2 - log2_min_qt_size_intra_slice_minus2 + MaxMttDepthY) (inclusive).

[0093] – Otherwise (slice_type is not equal to I), the value of cu_qp_delta_subdiv shall be in the range from 0 to 2*(log2_ctu_size_minus2 - log2_min_qt_size_inter_slice_minus2 + MaxMttDepthY) (inclusive).

[0094] When not present, the value of cu_qp_delta_subdiv is inferred to be equal to 0.

[0095] The CBF flags of tu_CBF_luma[x0][y0], tu_CBF_cb[x0][y0], and tu_CBF_cr[x0][y0] being equal to 1 means that there are bins in the decoded block. Otherwise, CBF being equal to 0 means that there are no bins in the decoded block.

[0096] Figure 3Illustrated is an example process for determining an incremental QP value for video data that supports dual-tree splitting. The video decoder 300 determines whether the CU is split in a dual-tree structure (140). If the CU is not split in a dual-tree structure (140, no), the video decoder 300 determines a single split for both the luminance and chrominance components of the CU (142), and decodes the incremental QP value (142). If the CU is split in a dual-tree structure (140, yes), the video decoder 300 determines the split of the luminance component of the CU (146), and separately determines the split of the chrominance component of the CU (148). The video decoder 300 also decodes the incremental QP value (150).

[0097] The video encoder 200 and the video decoder 300 may be configured to perform luminance QP prediction. The video encoder 200 and the video decoder 300 derive the predicted luminance quantization parameter qP as follows Y_PRED :

[0098] – If all of the following conditions are true, then qP Y_PRED is set to be equal to the luminance quantization parameter Qp of the decoding unit that contains the luminance decoding block covering (xQg, yQg - 1) Y :

[0099] – availableB is equal to TRUE.

[0100] – The current quantization group is the first quantization group in the CTB row within the tile

[0101] – Otherwise, qP is derived as follows Y_PRED :

[0102] qP Y_PRED =(qP Y_A +qP Y_B +1)>>1

[0103] The video encoder 200 and the video decoder 300 may be configured to process the previous luminance QP. The video encoder 200 and the video decoder 300 may derive the previous luminance quantization parameter qP as follows Y_PREV :

[0104] – If one or more of the following conditions are true, then qP Y_PREV is set to be equal to SliceQp Y :

[0105] – The current quantization group is the first quantization group in the slice.

[0106] – The current quantization group is the first quantization group in the tile.

[0107] – Otherwise, qP Y_PREVis set to be equal to the luma quantization parameter qP of the last luma coding unit in the previous quantization group in the decoding order Y_PREV .

[0108] Video encoder 200 and video decoder 300 may be configured to determine the chroma QP. In VVC draft 5, the value of the chroma QP is calculated based on the value of the luma QP.

[0109] When treeType is equal to DUAL_TREE_CHROMA, the variable QpY is set to be equal to the luma quantization parameter QpY of the luma coding unit covering the luma position (xCb + cbWidth / 2, yCb + cbHeight / 2).

[0110] – Derive the variables qPCb, qPCr, and qPCbCr as follows:

[0111] qPiCb = Clip3(-QpBdOffsetC, 69, QpY + pps_cb_qp_offset + slice_cb_qp_offset)

[0112] qPiCr = Clip3(-QpBdOffsetC, 69, QpY + pps_cr_qp_offset + slice_cr_qp_offset)

[0113] qPiCbCr = Clip3(-QpBdOffsetC, 69, QpY + pps_joint_cbcr_qp_offset + slice_joint_cbcr_qp_offset)

[0114] – If ChromaArrayType is equal to 1, set the variables qPCb, qPCr, and qPCbCr to be equal to the values of QpC specified in the following table based on the index qPi being equal to qPiCb, qPiCr, and qPiCbCr, respectively.

[0115] – Otherwise, set the variables qPCb, qPCr, and qPCbCr to be equal to Min(qPi, 63) based on the index qPi being equal to qPiCb, qPiCr, and qPiCbCr, respectively.

[0116] – Derive the chroma quantization parameters for the Cb and Cr components (Qp′Cb and Qp′Cr) and the joint Cb - Cr coding

[0117] Qp′CbCr as follows:

[0118] Qp′Cb = qPCb + QpBdOffsetC

[0119] Qp′Cr = qPCr + QpBdOffsetC

[0120] Qp′CbCr = qPCbCr + QpBdOffsetC

[0121] The following table specifies Qp as a qPi function for ChromaArrayType equal to 1 C specified

[0122] qPi <30 30 31 32 33 34 35 36 37 38 39 40 41 42 43 >43 <![CDATA[Qp C > = qPi 29 30 31 32 33 33 34 34 35 35 36 36 37 37 = qPi - 6

[0123] Video encoder 200 and video decoder 300 may be configured to determine a chroma QP offset. The chroma QP offset may be, for example, an index value. Video encoder 200 and video decoder 300 may maintain a table that maps these index values to delta QP values.

[0124] Figure 4 An example process for decoding chroma QP offset values for video data that supports binary tree partitioning is shown. Video decoder 300 determines whether the CU is partitioned in a binary tree structure (152). If the CU is not partitioned in a binary tree structure (152, no), then video decoder 300 determines a single partition of the luminance and chroma components of the CU (154) and decodes the chroma QP offset value (156). If the CU is partitioned in a binary tree structure (152, yes), then video decoder 300 determines the partition for the luminance component of the CU (158) and separately determines the partition for the chroma component of the CU (160). Video decoder 300 also decodes the chroma QP offset value (162).

[0125] Video encoder 200 and video decoder 300 may be configured to utilize quantization groups. All CUs within a quantization group typically use the same QP predictor, but not necessarily the same QP. The current quantization group is a rectangular region within a decoding tree block that shares the same qP Y_PRED The quantization group width and height are equal to the width and height of the decoding tree node, where the top - left luminance sample position is assigned to variables CuQgTopLeftX and CuQgTopLeftY.

[0126] Figure 5 An example video decoding process for determining the QP predictor QP_pred is shown. The techniques described will be Figure 5 described with respect to video encoder 200, but may also be performed by video decoder 300 Figure 5technique. The video encoder 200 determines whether the CU is the first CU in the CTU row and whether the upper CU is available (170). If the CU is the first CU in the CTU row and the upper CU is available (170, yes), the video encoder 200 sets the QP predictor to be equal to the QP of the upper CU (172). If the CU is not the first CU in the CTU row or the upper CU is not available (170, no), the video encoder 200 determines whether the QP of the upper CU is available (174) and whether the CU of the left CU is available (176). If the QP of the upper CU is available (174, yes), the video encoder 200 sets the value of the variable (QP_above) to the value of the QP for the upper CU. If the QP for the upper CU is not available (174, no), the video encoder 200 sets the value of QP_above to the previously used QP value (178). If the QP of the left CU is available (176, yes), the video encoder 200 sets the value of the variable (QP_left) to the value of the QP for the left CU. If the QP for the left CU is not available (176, no), the video encoder 200 sets the value of QP_left to the previously used QP value (180). The video encoder 200 sets the value for the QP predictor to the average of the values of QP_left and QP_above, which can be mathematically expressed as QP_pred = (QP_above + QP_left + 1) >> 1 (182).

[0127] In the above example, the previously used QP value QP_prev can be any previously used QP value and does not need to be the QP value for the left adjacent CU or the upper adjacent CU. For example, if the left adjacent CU is decoded in the skip mode without transformation or quantization, the previously used QP value may belong to the most recently decoded CU with a QP value, even if the CU is not adjacent to the current CU.

[0128] Current techniques for determining the chroma QP value include some potential problems. For example, in VVC draft 5, the chroma QP value is derived as follows:

[0129] qPi Cb = Clip3(-QpBdOffset C , 69, Qp Y + pps_cb_qp_offset + slice_cb_qp_offse)

[0130] qPi Cr = Clip3(-QpBdOffset C , 69, Qp Y(+pps_cr_qp_offset + slice_cr_qp_offset)

[0131] As can be seen above, the signaling for the chroma QP value is controlled at the PPS and slice levels.

[0132] When the tree type for the decoding unit is set to a dual tree, the variable Qp Y is set to be equal to the luma QP of the luma CB covering the luma position (xCb + cbWidth / 2, yCb + cbHeight / 2). Figure 6 An example of a chroma CU having a corresponding luma CU in a separate tree is shown. As Figure 6 shown, one chroma CB 190 can cover more than one luma CB (192A - 192D), and these luma CBs 192A - 192D can come from different QGs with different QPs. The predicted QP derived from the central position may not be an accurate prediction for the chroma CB. And the pps / slice level QP offset adjustment is limited. VVC Draft 5 does not provide a scheme for flexibly adjusting the chroma QP value.

[0133] This disclosure describes techniques that can address some of these problems. Unless otherwise specified, the various techniques of this disclosure can be performed individually or in combination.

[0134] Video encoder 200 and video decoder 300 can be configured to signal a chroma delta QP value for a chroma QG. In one example, video encoder 200 and video decoder 300 can be configured to signal the chroma delta QP value using the same scheme as that for luma delta QP signaling in VVC Draft 5.

[0135] Video encoder 200 and video decoder 300 can be configured to define a chroma QG based on the split depth. In one example, the chroma QG can be defined in the same way as the luma QG but based on the depth of the chroma split. For example, chroma_cu_qp_delta_subdiv can represent the maximum chroma delta QP signaling depth for chroma. For a leaf node with a depth less than or equal to the maximum chroma delta QP signaling depth, if the CU has at least one non - zero coefficient, video encoder 200 and video decoder 300 can signal a chroma delta QP value for the CU of that leaf node. For a CU with a depth greater than the maximum chroma delta QP signaling depth, if any CU of the child nodes of the split node has at least one non - zero coefficient, video encoder 200 and video decoder 300 can signal a chroma delta QP value for all CUs of the split node at the maximum chroma delta QP signaling depth.

[0136] The video encoder 200 and the video decoder 300 may be configured to define the chroma QG by regions. In one example, the region may be a rectangular region specified by width and height. In one example, the region may be specified by the number of pixels in the QG. In this example, the width / height of the region or the specified number of pixels may be predefined on the encoder side and the decoder side, or set to a value signaled from the encoder to the decoder at the sequence level, picture level, or slice level. For example, this value may be signaled in the SPS, PPS, or slice header.

[0137] The video encoder 200 and the video decoder 300 may be configured to signal the value of the chroma delta QP by signaling the absolute value and the sign flag in the same way as the luminance delta QP. That is, the video encoder 200 and the video decoder 300 may use two different syntax elements for the absolute value of the chroma delta QP value and the sign flag indicating the sign of the chroma delta QP value to signal the chroma delta QP value.

[0138] The video encoder 200 and the video decoder 300 may be configured to signal the value of the chroma delta QP by signaling only the absolute value without signaling the sign flag. That is, the value of the chroma delta QP may be limited to values equal to or greater than zero, which means that the value of the chroma delta QP is restricted to not include negative values.

[0139] The video encoder 200 and the video decoder 300 may be configured to use the same chroma delta QP that different chroma color components can use. For example, the Cb and Cr components use the same chroma delta QP.

[0140] The video encoder 200 and the video decoder 300 may be configured to signal the chroma delta QP for different color components separately. For example, the video encoder 200 and the video decoder 300 may signal the chroma delta QP (delta QP_Cb) for the Cb chroma component and signal the chroma delta QP (chroma delta QP_Cr) for the Cr component separately.

[0141] The video encoder 200 and the video decoder 300 may be configured to use the signaled chroma QP value, together with the delta QP value, PPS chroma QP offset, slice chroma QP offset, and CU-level chroma QP offset for chroma QP generation. For example, the video decoder 300 may be configured to derive the chroma QP value as follows:

[0142] qPi Cb= Clip3(minmum, maximum, predQP + pps_cb_qp_offset + slice_cb_qp_offset + cu_chroma_qp_offset + ChromaCuQpDeltaVal)

[0143] qPiCr = Clip3(minmum, maximum, predQp + pps_cr_qp_offset + slice_cr_qp_offset + cu_chroma_qp_offset + ChromaCuQpDeltaVal)

[0144] Video encoder 200 and video decoder 300 may be configured to generate chroma QP using chroma delta QP values, PPS chroma QP offsets, and slice chroma QP offsets. For example, video decoder 300 may be configured to derive chroma QP values as follows:

[0145] qPiCb = Clip3(minmum, maximum, predQP + pps_cb_qp_offset + slice_cb_qp_offset + ChromaCuQpDeltaVal)

[0146] qPiCr = Clip3(minmum, maximum, predQp + pps_cr_qp_offset + slice_cr_qp_offset + ChromaCuQpDeltaVal)

[0147] In some examples, video encoder 200 and video decoder 300 may be configured to generate chroma QP using different combinations of chroma delta QP values, PPS chroma QP offsets, slice chroma QP offsets, and CU-level chroma QP offsets.

[0148] If signaling of chroma delta QP is enabled, video encoder 200 and video decoder 300 may be configured to use chroma delta QP values to determine chroma delta QP values. Otherwise, if signaling of chroma delta QP is not enabled, video encoder 200 and video decoder 300 may be configured to use SPS-level chroma QP offsets, PPS-level chroma QP offsets, slice-level chroma QP offsets, and / or CU-level chroma QP offsets.

[0149] Video encoder 200 and video decoder 300 may be configured to predict the QP of a current chroma block using the QPs of adjacent chroma blocks. In one example, video encoder 200 and video decoder 300 may use the above regarding Figure 5The same prediction techniques described for luminance QP prediction. For example, if the chrominance CU is the first CU in a CTU row, the video encoder 200 and the video decoder 300 may use the chrominance QP of the upper CU as the QP predictor. If the upper CU is outside the current CTU or otherwise unavailable, the video encoder 200 and the video decoder 300 may use the previous chrominance QP, which may or may not correspond to an adjacent CU, as described above with respect to Figure 5 discussed. Otherwise, if the upper and left neighbor CUs are within the current CTU, the video encoder 200 and the video decoder 300 may use the average chrominance QP of the upper neighbor chrominance CU and the left neighbor chrominance CU. If any adjacent CU is unavailable, the video encoder 200 and the video decoder 300 may use the previous chrominance QP instead of the QP of the neighbor CU.

[0150] Example techniques for signaling chrominance delta QP will now be described. Based on JVET-N1001 version 8, the newly added portion is shown between <new text> and < / end new text>, and the text to be removed is utilized <removetext>and < / end remove text> markers.

[0151]

[0152]

[0153] In this process, the video encoder 200 and the video decoder 300 can signal the chroma delta QP using both the absolute value of the chroma delta QP and the chroma delta QP sign value for both the Cb and Cr components. The QP for Cb and Cr is defined as qP Cb and qP Cr , and can be derived as follows:

[0154] ChromaCuQpDeltaVal = chroma_cu_qp_delta_abs * (1 - 2 * chroma_cu_qp_delta_sign_flag)

[0155] qPiCb = Clip3(-QpBdOffsetC, 69, QpY + pps_cb_qp_offset + slice_cb_qp_offset + cu_chroma_qp_offset + ChromaCuQpDeltaVal)

[0156] qPiCr = Clip3(-QpBdOffsetC, 69, QpY + pps_cr_qp_offset + slice_cr_qp_offset + cu_chroma_qp_offset + ChromaCuQpDeltaVal)

[0157] In this example, the video encoder 200 and the video decoder 300 can signal the syntax elements chroma_cu_qp_delta_enable_flag and chroma_cu_qp_delta_subdiv in the PPS for chroma. In another example, the video encoder 200 and the video decoder 300 can use the same flags for chroma and luma, such as cu_qp_delta_enable_flag and cu_qp_delta_subdiv for luma in VVC draft 5.

[0158] The syntax element chroma_cu_qp_delta_enabled_flag being equal to 1 specifies that the chroma_cu_qp_delta_subdiv syntax element is present in the PPS, and that the chroma_cu_qp_delta_abs may be present in the transform unit syntax. The syntax element chroma_cu_qp_delta_enabled_flag being equal to 0 specifies that the chroma_cu_qp_delta_subdiv syntax element is present in the PPS, and that the chroma_cu_qp_delta_abs syntax element is not present in the transform unit syntax.

[0159] The syntax element chroma_cu_qp_delta_subdiv specifies the maximum cbSubdiv value of the decoding unit that conveys chroma__qp_delta_abs and chroma_cu_qp_delta_sign_flag. The value range of cu_qp_delta_subdiv is specified as follows:

[0160] – If slice_type is equal to I, the value of cu_qp_delta_subdiv shall be in the range from 0 to 2*(log2_ctu_size_minus2-log2_min_qt_size_intra_slice_minus2+MaxMttDepthY), inclusive.

[0161] When not present, the value of cu_qp_delta_subdiv is inferred to be equal to 0.

[0162] In this example, for dual-tree chrominance, if the current chrominance CB depth (subdiv) is equal to or less than the value of chroma_cu_qp_delta_subdiv, the video encoder 200 and the video decoder 300 may not signal the chrominance delta QP.

[0163]

[0164] Figure 7 is a block diagram illustrating an example video encoder 200 that may perform the techniques of the present disclosure. Figure 7 is provided for purposes of explanation and should not be considered limiting of the techniques generally illustrated and described in the present disclosure. For purposes of explanation, the present disclosure describes the video encoder 200 in the context of video coding standards such as the HEVC video coding standard and the H.266 video coding standard under development. However, the techniques of the present disclosure are not limited to these video coding standards and are generally applicable to video encoding and decoding.

[0165] In Figure 7 this example, the video encoder 200 includes a video data memory 230, a mode selection unit 202, a residual generation unit 204, a transform processing unit 206, a quantization unit 208, an inverse quantization unit 210, an inverse transform processing unit 212, a reconstruction unit 214, a filter unit 216, a decoded picture buffer (DPB) 218, and an entropy encoding unit 220. Any one or all of the video data memory 230, the mode selection unit 202, the residual generation unit 204, the transform processing unit 206, the quantization unit 208, the inverse quantization unit 210, the inverse transform processing unit 212, the reconstruction unit 214, the filter unit 216, the DPB 218, and the entropy encoding unit 220 may be implemented in one or more processors or in processing circuitry. Additionally, the video encoder 200 may include additional or alternative processors or processing circuitry to perform these and other functions.

[0166] The video data memory 230 may store video data to be encoded by components of the video encoder 200. The video encoder 200 may receive the video data stored in the video data memory 230 from, for example, a video source 104 ( Figure 1 ). The DPB 218 may act as a reference picture memory that stores reference video data for use in predicting subsequent video data by the video encoder 200. The video data memory 230 and the DPB 218 may be formed of any one of various 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. The video data memory 230 and the DPB 218 may be provided by the same memory device or by separate memory devices. In various examples, the video data memory 230 may be on-chip (as shown) with other components of the video encoder 200, or off-chip relative to those components.

[0167] In this disclosure, a reference to the video data memory 230 should not be construed as limited to a memory internal to the video encoder 200 (unless so specifically described), or limited to a memory external to the video encoder 200 (unless so specifically described). Rather, a reference to the video data memory 230 should be understood as a reference memory that stores video data received by the video encoder 200 for encoding (e.g., video data for a current block to be encoded). Figure 1 The memory 106 of

[0168] also may provide temporary storage of outputs from the various units of the video encoder 200. Figure 7 The various units are provided to assist in understanding the operations performed by video encoder 200. These units can be implemented as fixed-function circuitry, programmable circuitry, or a combination thereof. Fixed-function circuitry refers to circuitry that provides a specific function and is pre-set with respect to the operations that can be performed. Programmable circuitry refers to circuitry that can be programmed to perform various tasks and provides flexible functionality with respect to the operations that can be performed. For example, programmable circuitry can execute software or firmware that causes the programmable circuitry to operate in a manner defined by the instructions of the software or firmware. Fixed-function circuitry can execute software instructions (e.g., to receive parameters or output parameters), but the types of operations performed by fixed-function circuitry are generally immutable. In some examples, one or more of these units can be different circuit blocks (fixed-function or programmable), and in some examples, one or more of the units can be an integrated circuit.

[0169] Video encoder 200 can include an arithmetic logic unit (ALU), a basic function unit (EFU), digital circuitry, analog circuitry, and / or a programmable core formed from programmable circuitry. In examples where software executed by programmable circuitry is used to perform the operations of video encoder 200, memory 106( Figure 1 ) can store the object code of the software received and executed by video encoder 200, or another memory (not shown) within video encoder 200 can store such instructions.

[0170] Video data memory 230 is configured to store the received video data. Video encoder 200 can retrieve pictures of the video data from video data memory 230 and provide the video data to residual generation unit 204 and mode selection unit 202. The video data in video data memory 230 can be the original video data to be encoded.

[0171] Mode selection unit 202 includes a motion estimation unit 222, a motion compensation unit 224, and an intra prediction unit 226. Mode selection unit 202 can include additional functional units that perform video prediction according to other prediction modes. As an example, mode selection unit 202 can include a palette unit, a block copy unit (which can be part of motion estimation unit 222 and / or motion compensation unit 224), an affine unit, a linear model (LM) unit, etc.

[0172] The mode selection unit 202 generally coordinates multiple encoding passes to test combinations of encoding parameters and the rate-distortion values obtained for such combinations. The encoding parameters can include splitting a CTU into CUs, prediction modes for the CUs, transform types for the residual data of the CUs, quantization parameters for the residual data of the CUs, etc. The mode selection unit 202 can ultimately select a combination of encoding parameters that has a better rate-distortion value than other tested combinations.

[0173] The video encoder 200 can split a picture retrieved from the video data memory 230 into a series of CTUs and encapsulate one or more CTUs within a slice. The mode selection unit 202 can split the CTUs of the picture according to a tree structure (such as the QTBT structure or quadtree structure of HEVC described above). As described above, the video encoder 200 can form one or more CUs by splitting the CTUs according to a tree structure. Such CUs can generally also be referred to as "video blocks" or "blocks".

[0174] Generally, the mode selection unit 202 also controls its components (e.g., the motion estimation unit 222, the motion compensation unit 224, and the intra prediction unit 226) to generate a prediction block for the current block (e.g., the current CU, or the overlapping portion of the PUs and TUs in HEVC). To perform inter prediction on the current block, the motion estimation unit 222 can perform a motion search to identify one or more closely matching reference blocks in one or more reference pictures (e.g., one or more previously decoded pictures stored in the DPB 218). Specifically, the motion estimation unit 222 can calculate a value representing how closely a potential reference block will match the current block, for example, according to the sum of absolute differences (SAD), the sum of squared differences (SSD), the mean absolute difference (MAD), the mean squared difference (MSD), etc. The motion estimation unit 222 can generally use the per-sample differences between the current block and the considered reference blocks to perform these calculations. The motion estimation unit 222 can identify the reference block with the lowest value obtained from these calculations, which indicates the reference block that most closely matches the current block.

[0175] The motion estimation unit 222 may form one or more motion vectors (MVs) that define the position of a reference block in a reference picture relative to the position of a current block in the current picture. Then, the motion estimation unit 222 may provide the motion vectors to the motion compensation unit 224. For example, for uni-directional inter prediction, the motion estimation unit 222 may provide a single motion vector, and for bi-directional inter prediction, the motion estimation unit 222 may provide two motion vectors. Then, the motion compensation unit 224 may use the motion vectors to generate a prediction block. For example, the motion compensation unit 224 may use the motion vectors to retrieve data of the reference block. As another example, if the motion vectors have fractional sample precision, the motion compensation unit 224 may interpolate values for the prediction block according to one or more interpolation filters. Further, for bi-directional inter prediction, the motion compensation unit 224 may retrieve data for two reference blocks identified by the respective motion vectors and combine the retrieved data, for example, by sample-by-sample averaging or weighted averaging.

[0176] As another example, for intra prediction or intra prediction coding, the intra prediction unit 226 may generate a prediction block according to samples adjacent to the current block. For example, for a directional mode, the intra prediction unit 226 may generally mathematically combine values of adjacent samples and fill the calculated values in a defined direction across the current block to produce a prediction block. As another example, for the DC mode, the intra prediction unit 226 may calculate an average value of adjacent samples of the current block and generate a prediction block to include the obtained average value for each sample of the prediction block.

[0177] The mode selection unit 202 provides the prediction block to the residual generation unit 204. The residual generation unit 204 receives an original, unencoded version of the current block from the video data memory 230 and receives the prediction block from the mode selection unit 202. The residual generation unit 204 calculates the sample-by-sample difference between the current block and the prediction block. The resulting sample-by-sample difference defines a residual block for the current block. In some examples, the residual generation unit 204 may determine differences between sample values in the residual block to generate the residual block using residual differential pulse code modulation (RDPCM). In some examples, one or more subtractor circuits that perform binary subtraction may be used to form the residual generation unit 204.

[0178] In an example where the mode selection unit 202 divides a CU into PUs, each PU may be associated with a luminance prediction unit and a corresponding chrominance prediction unit. The video encoder 200 and the video decoder 300 may support PUs of various sizes. As noted above, the size of a CU may refer to the size of the luminance coding block of the CU, and the size of a PU may refer to the size of the luminance prediction unit of the PU. Assuming that the size of a particular CU is 2Nx2N, the video encoder 200 may support PU sizes of 2Nx2N or NxN for intra prediction, and 2Nx2N, 2NxN, Nx2N, NxN, or similar symmetric PU sizes for inter prediction. The video encoder 200 and the video decoder 300 may also support asymmetric partitioning for PU sizes of 2NxnU, 2NxnD, nLx2N, and nRx2N for inter prediction.

[0179] In an example where the mode selection unit does not further divide a CU into PUs, each CU may be associated with a luminance coding block and a corresponding chrominance coding block. As described above, the size of a CU may refer to the size of the luminance coding block of the CU. The video encoder 200 and the video decoder 300 may support CU sizes of 2Nx2N, 2NxN, or Nx2N.

[0180] For other video coding techniques (by way of example, such as intra-block copy mode coding, affine mode coding, and linear model (LM) mode coding), the mode selection unit 202 generates a prediction block for the current block being encoded via a corresponding unit associated with the coding technique. In some examples (such as palette mode coding), the mode selection unit 202 may not generate a prediction block, but instead generates a syntax element indicating the manner in which the block is to be reconstructed based on the selected palette. In such a mode, the mode selection unit 202 may provide these syntax elements to the entropy coding unit 220 for coding.

[0181] As described above, the residual generation unit 204 receives video data for the current block and the corresponding prediction block. Then, the residual generation unit 204 generates a residual block for the current block. To generate the residual block, the residual generation unit 204 calculates the sample-by-sample difference between the prediction block and the current block.

[0182] The transform processing unit 206 applies one or more transforms to the residual block to generate a block of transform coefficients (referred to herein as a "transform coefficient block"). The transform processing unit 206 may apply various transforms to the residual block to form a transform coefficient block. For example, the transform processing unit 206 may apply a discrete cosine transform (DCT), a directional transform, a Karhunen-Loeve transform (KLT), or a conceptually similar transform to the residual block. In some examples, the transform processing unit 206 may perform multiple transforms on the residual block, such as a primary transform and a secondary transform (such as a rotation transform). In some examples, the transform processing unit 206 does not apply a transform to the residual block.

[0183] The quantization unit 208 may quantize the transform coefficients in the transform coefficient block to produce a quantized transform coefficient block. The quantization unit 208 may quantize the transform coefficients of the transform coefficient block according to the quantization parameter (QP) value associated with the current block. The video encoder 200 (e.g., via the mode selection unit 202) may adjust the degree of quantization applied to the transform coefficient block associated with the current block by adjusting the QP value associated with the CU. Quantization may cause information loss, and thus, the quantized transform coefficients may have lower precision compared to the original transform coefficients generated by the transform processing unit 206.

[0184] The inverse quantization unit 210 and the inverse transform processing unit 212 may apply inverse quantization and inverse transform to the quantized transform coefficient block, respectively, to reconstruct the residual block from the transform coefficient block. The reconstruction unit 214 may generate a reconstructed block corresponding to the current block (although potentially with some degree of distortion) based on the reconstructed residual block and the prediction block generated by the mode selection unit 202. For example, the reconstruction unit 214 may add the samples of the reconstructed residual block to the corresponding samples from the prediction block generated by the mode selection unit 202 to produce the reconstructed block.

[0185] The filter unit 216 may perform one or more filter operations on the reconstructed block. For example, the filter unit 216 may perform a deblocking operation to reduce block effect artifacts along the edges of the CU. In some examples, the operation of the filter unit 216 may be skipped.

[0186] Video encoder 200 stores the reconstructed blocks in DPB 218. For example, in an example where the operations of filter unit 216 are not performed, reconstruction unit 214 may store the reconstructed blocks into DPB 218. In an example where the operations of filter unit 216 are performed, filter unit 216 may store the filtered reconstructed blocks into DPB 218. Motion estimation unit 222 and motion compensation unit 224 may retrieve reference pictures formed by the reconstructed (and potentially filtered) blocks from DPB 218 to perform inter prediction on blocks of subsequently encoded pictures. Additionally, intra prediction unit 226 may use the reconstructed blocks of the current picture in DPB 218 to perform intra prediction on other blocks in the current picture.

[0187] Generally, entropy coding unit 220 may perform entropy coding on syntax elements received from other functional components of video encoder 200. For example, entropy coding unit 220 may perform entropy coding on the quantized transform coefficient blocks from quantization unit 208. As another example, entropy coding unit 220 may perform entropy coding on prediction syntax elements (e.g., motion information for inter prediction or intra mode information for intra prediction) from mode selection unit 202. Entropy coding unit 220 may perform one or more entropy coding operations on syntax elements as another example of video data to generate entropy-coded data. For example, entropy coding unit 220 may perform context-adaptive variable-length coding (CAVLC) operations, CABAC operations, variable-variable (V2V) length coding operations, syntax-based context-adaptive binary arithmetic coding (SBAC) operations, probability interval partitioning entropy (PIPE) coding operations, exponential Golomb coding operations, or another type of entropy coding operation on the data. In some examples, entropy coding unit 220 may operate in a bypass mode where the syntax elements are not entropy coded.

[0188] Video encoder 200 may output a bitstream that includes the entropy-coded syntax elements required to reconstruct the blocks of a slice or picture. Specifically, entropy coding unit 220 may output the bitstream.

[0189] The above operations have been described with respect to blocks. Such a description should be understood as applying to the operations of luminance decoding blocks and / or chrominance decoding blocks. As described above, in some examples, the luminance decoding block and the chrominance decoding block are the luminance component and the chrominance component of a CU. In some examples, the luminance decoding block and the chrominance decoding block are the luminance component and the chrominance component of a PU.

[0190] In some examples, operations performed on the luma coding blocks need not be repeated for the chroma coding blocks. As an example, operations for identifying the motion vectors (MVs) and reference pictures for the luma coding blocks need not be repeated to identify the MVs and reference pictures for the chroma blocks. Rather, the MVs for the luma coding blocks can be scaled to determine the MVs for the chroma blocks, and the reference pictures can be the same. As another example, the intra prediction process can be the same for the luma coding blocks and the chroma coding blocks.

[0191] Video encoder 200 represents an example of a device configured to encode video data, the device including: a memory configured to store video data; and one or more processing units implemented in circuitry and configured to perform the chroma delta QP signaling techniques described herein. For example, video encoder 200 can generate the syntax elements chroma_cu_qp_delta_abs and chroma_cu_qp_delta_sign_flag to include in the bitstream of the encoded video data, as described above.

[0192] Figure 8 is a block diagram illustrating an example video decoder 300 that can perform the techniques of the present disclosure. Figure 8 is provided for explanatory purposes and does not limit the techniques generally illustrated and described in the present disclosure. For explanatory purposes, the present disclosure describes video decoder 300 in terms of the techniques of JEM, VVC, and HEVC. However, the techniques of the present disclosure can be performed by video coding devices configured for other video coding standards.

[0193] In Figure 8 example, video decoder 300 includes a coded picture buffer (CPB) memory 320, an entropy decoding unit 302, a prediction processing unit 304, an inverse quantization unit 306, an inverse transform processing unit 308, a reconstruction unit 310, a filter unit 312, and a decoded picture buffer (DPB) 134. Any one or all of the CPB memory 320, entropy decoding unit 302, prediction processing unit 304, inverse quantization unit 306, inverse transform processing unit 308, reconstruction unit 310, filter unit 312, and DPB 134 can be implemented in one or more processors or in processing circuitry. Additionally, video decoder 300 can include additional or alternative processors or processing circuitry to perform these and other functions.

[0194] The prediction processing unit 304 includes a motion compensation unit 316 and an intra prediction unit 318. The prediction processing unit 304 may include an addition unit that performs prediction according to other prediction modes. As an example, the prediction processing unit 304 may include a palette unit, a block copy unit (which may form part of the motion compensation unit 316), an affine unit, a linear model (LM) unit, etc. In other examples, the video decoder 300 may include more, fewer, or different functional components.

[0195] The CPB memory 320 may store video data to be decoded by components of the video decoder 300, such as an encoded video bitstream. For example, the video data stored in the CPB memory 320 may be obtained from a computer-readable medium 110( Figure 1 ). The CPB memory 320 may include a CPB that stores encoded video data (e.g., syntax elements) from the encoded video bitstream. In addition, the CPB memory 320 may store video data other than the syntax elements of the decoded pictures, such as temporary data representing the output of the respective units from the video decoder 300. The DPB 314 generally stores decoded pictures. The video decoder 300 may output decoded pictures and / or use the decoded pictures as reference video data when decoding subsequent data or pictures of the encoded video bitstream. The CPB memory 320 and the DPB 314 may be formed of any of a variety of memory devices, such as DRAM, including SDRAM, MRAM, RRAM, or other types of memory devices. The CPB memory 320 and the DPB 314 may be provided by the same memory device or separate memory devices. In various examples, the CPB memory 320 may be on-chip or off-chip relative to the other components of the video decoder 300.

[0196] Additionally or alternatively, in some examples, the video decoder 300 may retrieve decoded video data from the memory 120( Figure 1 ). That is, the memory 120 may utilize the CPB memory 320 to store data as discussed above. Similarly, when some or all of the functions of the video decoder 300 are implemented with software to be executed by the processing circuitry of the video decoder 300, the memory 120 may store instructions to be executed by the video decoder 300.

[0197] is shown Figure 8 The various units shown in Figure 7 , A fixed - function circuit refers to a circuit that provides a specific function and is pre - set with respect to the operations that can be performed. A programmable circuit refers to a circuit that can be programmed to perform various tasks and provides flexible functionality in terms of the operations that can be performed. For example, a programmable circuit can execute software or firmware, and the software or firmware causes the programmable circuit to operate in a manner defined by the instructions of the software or firmware. A fixed - function circuit can execute software instructions (e.g., to receive parameters or output parameters), but the type of operations performed by the fixed - function circuit is generally immutable. In some examples, one or more of these units can be different circuit blocks (fixed - function or programmable), and in some examples, one or more units can be an integrated circuit.

[0198] The video decoder 300 can include an ALU, an EFU, digital circuits, analog circuits, and / or programmable cores formed by programmable circuits. In an example where the operations of the video decoder 300 are performed by software executed on the programmable circuit, on - chip or off - chip memory can store the instructions (e.g., object code) of the software that the video decoder 300 receives and executes.

[0199] The entropy decoding unit 302 can receive the encoded video data from the CPB and perform entropy decoding on the video data to reproduce the syntax elements. The prediction processing unit 304, the inverse quantization unit 306, the inverse transform processing unit 308, the reconstruction unit 310, and the filter unit 312 can generate the decoded video data based on the syntax elements extracted from the bitstream.

[0200] Generally, the video decoder 300 reconstructs pictures block - by - block. The video decoder 300 can perform the reconstruction operation on each block individually (where the block that is currently being reconstructed (i.e., decoded) can be referred to as the "current block").

[0201] The entropy decoding unit 302 can perform entropy decoding on the syntax elements that define the quantized transform coefficient blocks of the quantized transform coefficients and transform information such as the quantization parameter (QP) and / or the transform mode indication. The inverse quantization unit 306 can use the QP associated with the quantized transform coefficient block to determine the quantization level, and similarly, determine the inverse quantization level to be applied by the inverse quantization unit 306. The inverse quantization unit 306 can, for example, perform a bit - shift - left operation to inverse - quantize the quantized transform coefficients. The inverse quantization unit 306 can thus form a transform coefficient block including the transform coefficients.

[0202] After the inverse quantization unit 306 forms the transform coefficient block, the inverse transform processing unit 308 can apply one or more inverse transforms to the transform coefficient block to generate a residual block associated with the current block. For example, the inverse transform processing unit 308 can apply an inverse DCT, an inverse integer transform, an inverse Karhunen-Loeve transform (KLT), an inverse rotation transform, an inverse direction transform, or another inverse transform to the transform coefficient block.

[0203] In addition, the prediction processing unit 304 generates a prediction block according to the prediction information syntax element entropy decoded by the entropy decoding unit 302. For example, if the prediction information syntax element indicates that the current block is inter-frame predicted, the motion compensation unit 316 can generate a prediction block. In this case, the prediction information syntax element can indicate the reference picture in the DPB 314 from which the reference block is to be retrieved, and the motion vector that identifies the position of the reference block in the reference picture relative to the position of the current block in the current picture. The motion compensation unit 316 can generally perform the inter-frame prediction process in a manner substantially similar to the manner described with respect to the motion compensation unit 224 ( Figure 7 ).

[0204] As another example, if the prediction information syntax element indicates that the current block is intra-frame predicted, the intra-frame prediction unit 318 can generate a prediction block according to the intra-frame prediction mode indicated by the prediction information syntax element. Again, the intra-frame prediction unit 318 can generally perform the intra-frame prediction process in a manner substantially similar to the manner described with respect to the intra-frame prediction unit 226 ( Figure 7 ). The intra-frame prediction unit 318 can retrieve the data of the neighboring samples of the current block from the DPB 314.

[0205] The reconstruction unit 310 can use the prediction block and the residual block to reconstruct the current block. For example, the reconstruction unit 310 can add the samples of the residual block to the corresponding samples of the prediction block to reconstruct the current block.

[0206] The filter unit 312 can perform one or more filter operations on the reconstructed block. For example, the filter unit 312 can perform a deblocking operation to reduce the block effect artifacts along the edges of the reconstructed block. The operation of the filter unit 312 is not necessarily performed in all examples.

[0207] The video decoder 300 can store the reconstructed block in the DPB 314. As discussed above, the DPB 314 can provide reference information (such as the current picture for intra-frame prediction and the samples of the previously decoded pictures for subsequent motion compensation) to the prediction processing unit 304. In addition, the video decoder 300 can output the decoded picture from the DPB 314 for subsequent presentation on a display device such as Figure 1 the display device 118.

[0208] In this manner, video decoder 300 represents an example of a video decoding device that includes: a memory configured to store video data; and one or more processing units implemented in circuitry and configured to perform the chroma delta QP signaling techniques described herein. For example, video decoder 300 may decode and parse the syntax elements chroma_cu_qp_delta_abs and chroma_cu_qp_delta_sign_flag as described above.

[0209] For example, entropy decoding unit 302 may receive in the bitstream of the encoded video data a first syntax indicating a luminance delta QP value for a luminance component and a second syntax indicating a chroma delta QP value for a chroma component. For example, inverse quantization unit 306 may determine a predicted luminance quantization parameter (QP) for the luminance component of the decoding unit; determine the QP value for the luminance component based on the predicted luminance QP and the luminance delta QP value; determine a predicted chroma QP for the chroma component of the decoding unit; determine the QP value for the chroma component based on the predicted chroma QP and the chroma delta QP value; dequantize the luminance transform coefficient block based on the QP value for the luminance component; and dequantize the chroma transform coefficient block based on the QP value for the chroma component. Video decoder 300 may decode the decoding unit based on the dequantized luminance transform coefficient block and the dequantized chroma transform coefficient block.

[0210] Figure 9 is a flowchart showing an example method for encoding a current block. The current block may include a current CU. Although described with respect to video encoder 200 ( Figure 1 and Figure 7 ), it should be understood that other devices may be configured to perform methods similar to those of Figure 9 .

[0211] In this example, video encoder 200 initially predicts the current block (350). For example, video encoder 200 may form a prediction block for the current block. Then, video encoder 200 may calculate a residual block (532) for the current block. To calculate the residual block, video encoder 200 may calculate the difference between the original unencoded block and the prediction block for the current block. Then, video encoder 200 may transform and quantize the coefficients of the residual block (354). For example, video encoder 200 may use the techniques described above to signal QP values for the luminance and chrominance components of the video data. Next, video encoder 200 may scan the quantized transform coefficients of the residual block (356). During or after the scan, video encoder 200 may entropy code the coefficients (358). For example, video encoder 200 may use CAVLC or CABAC to encode the coefficients. Then, video encoder 200 may output the entropy-coded data of the block (360).

[0212] Figure 10 is a flowchart illustrating an example method for decoding a current block of video data. The current block may include a current CU. Although described with respect to video decoder 300 ( Figure 1 and Figure 8 ), it should be understood that other devices may be configured to perform methods similar to the Figure 10 method.

[0213] Video decoder 300 may receive the entropy-coded data for the current block (such as the entropy-coded prediction information and the entropy-coded data of the coefficients for the residual block corresponding to the current block) (370). Video decoder 300 may entropy decode the entropy-coded data to determine the prediction information for the current block and reproduce the coefficients of the residual block (372). Video decoder 300 may predict the current block (374), for example, using an intra or inter prediction mode indicated by the prediction information of the current block to calculate a prediction block for the current block. Then, video decoder 300 may inverse scan the reproduced coefficients (376) to create a block of quantized transform coefficients. Then, video decoder 300 may inverse quantize and inverse transform the coefficients to produce a residual block (378). For example, video decoder 300 may use the techniques described above to receive a syntax element indicating QP values for the luminance and chrominance components of the video data. Finally, video decoder 300 may decode the current block by combining the prediction block and the residual block (380).

[0214] Figure 11 is a flowchart illustrating an example method for encoding a current block. The current block may include a current CU. Although described with respect to video encoder 200 ( Figure 1 and Figure 7 ) has been described, but it should be understood that other devices may be configured to perform methods similar to those of Figure 11 .

[0215] In this example, video encoder 200 determines a QP value (400) for the luminance component of the decoding unit for the video data. Video encoder 200 may quantize the luminance transform coefficient block based on the QP value for the luminance component of the decoding unit. To signal the QP value for the luminance component of the decoding unit, video encoder 200 determines a predicted luminance QP (402) for the luminance component of the decoding unit. Video encoder 200 determines an incremental QP value (404) for the luminance component of the decoding unit based on the QP value for the luminance component and the predicted luminance QP. Video encoder 200 generates a first syntax indicating the incremental QP value for the luminance component of the decoding unit to be included in the bitstream of the encoded video data (406).

[0216] Video encoder 200 determines a QP value (408) for the chrominance component of the decoding unit for the video data. Video encoder 200 may quantize the chrominance transform coefficient block based on the QP value for the chrominance component of the decoding unit. To signal the QP value for the chrominance component of the decoding unit, video encoder 200 determines a predicted chrominance QP (410) for the chrominance component of the decoding unit. Video encoder 200 determines an incremental QP value (412) for the chrominance component of the decoding unit based on the QP value for the chrominance component and the predicted chrominance QP.

[0217] In some examples, a single-tree structure may be used to partition a CTU including a decoding unit such that the luminance component of the CTU and the chrominance component of the CTU have the same partition. In other examples, a dual-tree structure may be used to partition a CTU including a decoding unit such that the luminance component of the CTU and the chrominance component of the CTU have different partitions. If the CTU including the decoding unit is partitioned using a dual-tree structure, video encoder 200 may be configured to determine a maximum chrominance incremental QP signaling depth for the chrominance component of the CTU; determine a split node of the chrominance component of the decoding unit and at least one other decoding unit belonging to the CTU; in response to the maximum chrominance incremental QP signaling depth corresponding to the split node, determine that the QP value for the chrominance component of at least one other decoding unit is equal to the QP value for the chrominance component of the decoding unit; and quantize the chrominance transform coefficient block for at least one other CU based on the QP value for the chrominance component of at least one other decoding unit.

[0218] Video encoder 200 generates a second syntax indicating the delta QP value for the chrominance component of the decoding unit to be included in the bitstream of the encoded video data (414). In some examples, in response to determining that signaling of the chrominance delta QP value is enabled for the decoding unit, video encoder 200 may generate a second syntax indicating the chrominance delta QP value for the chrominance component to be included in the bitstream of the encoded video data. For example, the second syntax may include a syntax element indicating the absolute value of the chrominance delta QP value and a syntax element indicating the sign of the chrominance delta QP value.

[0219] Video encoder 200 outputs the first syntax and the second syntax in the bitstream of the encoded video data (416). Video encoder 200 may also output in the bitstream of the encoded video data a syntax indicating the values of the quantized luminance transform coefficient block and the quantized chrominance transform coefficient block.

[0220] Video encoder 200 may also determine a second QP value for the second chrominance component of the decoding unit; determine a second predicted chrominance QP for the second chrominance component of the decoding unit; determine a second delta QP value for the second chrominance component based on the second QP value and the second predicted chrominance QP for the second chrominance component; generate a third syntax indicating the second delta QP value for the second chrominance component to be included in the bitstream of the encoded video data; and output the third syntax in the bitstream of the encoded video data.

[0221] Figure 12 is a flowchart showing an example method for decoding a current block of video data. The current block may include a current CU. Although described with respect to video decoder 300 ( Figure 1 and Figure 8 ), it should be understood that other devices may be configured to perform methods similar to those of Figure 10 .

[0222] Video decoder 300 determines a predicted luminance QP for the luminance component of the decoding unit (420). For example, video decoder 300 may use any of the above techniques to determine the predicted luminance QP based on the QPs of neighboring CUs.

[0223] Video decoder 300 receives in the bitstream of the encoded video data a first syntax indicating the predicted luminance QP value for the luminance component (422). The first syntax may include, for example, a syntax element indicating the absolute value of the luminance delta QP value and a syntax element indicating the sign of the luminance delta QP value. Video decoder 300 determines the QP value for the luminance component based on the predicted luminance QP and the luminance delta QP value (424). For example, video decoder 300 may add the luminance delta QP value to the value of the predicted luminance QP to determine the QP value of the luminance component of the decoding unit.

[0224] Video decoder 300 determines a predicted chrominance QP (426) for the chrominance component of the decoding unit. For example, video decoder 300 may use any of the above techniques to determine the predicted chrominance QP based on the QP of adjacent CUs. Video decoder 300 receives a second syntax (428) in the bitstream of the encoded video data that indicates a chrominance delta QP value for the chrominance component of the decoding unit. For example, in response to determining that signaling of the chrominance delta QP value is enabled for the decoding unit, video decoder 300 may receive, in the bitstream of the encoded video data, a second syntax that indicates the chrominance delta QP value for the chrominance component. For example, the second syntax may include a syntax element that indicates the absolute value of the chrominance delta QP value and a syntax element that indicates the sign of the chrominance delta QP value.

[0225] In some examples, a single-tree structure may be used to partition a CTU including a decoding unit such that the luma component of the CTU and the chrominance component of the CTU have the same partition. In other examples, a dual-tree structure may be used to partition a CTU including a decoding unit such that the luma component of the CTU and the chrominance component of the CTU have different partitions. In an example, in the case where the luma component of the CTU and the chrominance component of the CTU have different partitions, in order to receive the second syntax that indicates the chrominance delta QP value for the chrominance component, for example, video decoder 300 may determine a maximum chrominance delta QP signaling depth for the chrominance component of the CTU; determine that the decoding unit and at least one other decoding unit belong to a split node of the chrominance component of the CTU; in response to the maximum chrominance delta QP signaling depth corresponding to the split node, determine a QP value for the chrominance component of the at least one other decoding unit based on the chrominance delta QP value; and dequantize the chrominance transform coefficient block for the at least one other CU based on the QP value for the chrominance component of the at least one other decoding unit.

[0226] Video decoder 300 determines a QP value for the chrominance component of the decoding unit based on the predicted chrominance QP and the chrominance delta QP value (430). For example, video decoder 300 may add the chrominance delta QP value to the value of the predicted chrominance QP to determine the QP value for the chrominance component of the decoding unit.

[0227] Video decoder 300 dequantizes the luma transform coefficient block for the decoding unit based on the QP value for the luma component (432), and dequantizes the chrominance transform coefficient block for the decoding unit based on the QP value for the chrominance component (434). Video decoder 300 decodes the decoding unit based on the dequantized transform coefficient block and the dequantized chrominance transform coefficient block (436).

[0228] To decode a decoding unit based on a dequantized transform coefficient block and a dequantized chrominance transform coefficient block, video decoder 300 may perform an inverse transform on the dequantized luminance transform coefficient block to determine a luminance residual block; perform an inverse transform on the dequantized chrominance transform coefficient block to determine a chrominance residual block; determine a luminance prediction block; determine a chrominance prediction block; add the luminance residual block to the luminance prediction block to determine a reconstructed luminance block of the decoding unit; and add the chrominance residual block to the chrominance prediction block to determine a reconstructed chrominance block of the decoding unit.

[0229] Video decoder 300 may also determine a second predicted chrominance QP for a second chrominance component of the decoding unit; receive, in a bitstream of the encoded video data, a third syntax indicating a second chrominance delta QP value for the second chrominance component of the decoding unit; determine a second QP value for the second chrominance component of the decoding unit based on the second predicted chrominance QP and the second chrominance delta QP value; dequantize the second chrominance transform coefficient block for the decoding unit based on the second QP value of the second chrominance component; and decode the decoding unit based on the dequantized second chrominance transform coefficient block.

[0230] It should be appreciated that, according to examples, certain actions or events of any of the techniques described herein may be performed in a different order, may be added, combined, or entirely omitted (e.g., not all described actions or events are necessary for implementing the techniques). Additionally, in certain examples, actions or events may be performed, for example, concurrently rather than sequentially via multithreading, interrupt processing, or multiple processors.

[0231] In one or more examples, the described functionality may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functionality may be stored on or transmitted via a computer-readable medium as one or more instructions or code and executed by a hardware-based processing unit. The computer-readable medium may include a computer-readable storage medium corresponding to a tangible medium such as a data storage medium or a communication medium including any medium that facilitates transfer of a computer program from one place to another, e.g., according to a communication protocol. In this manner, the computer-readable medium generally may correspond to (1) a non-transitory tangible computer-readable storage medium, or (2) a communication medium such as a signal or carrier wave. The data storage medium may be any available medium that can be accessed by one or more computers or one or more processors to obtain instructions, code, and / or data structures for implementing the techniques described in this disclosure. A computer program product may include a computer-readable medium.

[0232] By way of example and not limitation, such a computer-readable storage medium can include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, flash memory, or any other medium that can be used to store the desired program code in the form of instructions or data structures and that can be accessed by a computer. Additionally, any connection is properly termed a computer-readable medium. For example, if instructions are transmitted using coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies (such as infrared, radio, and microwave) are included in the definition of the 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 instead are directed to non-transitory, tangible storage media. As used herein, disk and optical disks include compact disk (CD), laser disk, optical disk, digital versatile disk (DVD), floppy disk, and Blu-ray disk, where disks typically reproduce data magnetically, while optical disks utilize lasers to optically reproduce data. Combinations of the above should also be included within the scope of computer-readable media.

[0233] The instructions can be executed by one or more processors, such as one or more digital signal processors (DSPs), general microprocessors, application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or other equivalent integrated or discrete logic circuitry. Thus, as used herein, the terms "processor" and "processing circuitry" can refer to any one of the foregoing structures or any other structure suitable for implementing the techniques described herein. Additionally, in some aspects, the functions described herein can be provided within dedicated hardware and / or software modules configured for encoding and decoding, or incorporated into a combined codec. Further, the techniques can be implemented entirely within one or more circuits or logic elements.

[0234] The techniques of the present disclosure can be implemented in a variety of devices or apparatuses, including wireless handsets, integrated circuits (ICs) or a group of ICs (e.g., a chipset). In the present disclosure, various components, modules, or units are described to emphasize functional aspects of devices configured to perform the disclosed techniques, but need not necessarily be implemented by different hardware units. Rather, as described above, the various units can 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.

[0235] Various examples have been described. These and other examples are within the scope of the appended claims.< / removetext>

Claims

1. A method for decoding a bitstream of encoded video data, the method comprising: Determining a predicted luminance quantization parameter (QP) for a luminance component of a decoding unit; Receiving a first syntax that is part of a transform unit syntax included in the bitstream of the encoded video data, the first syntax indicating a luminance delta QP value for the luminance component of the decoding unit; Determining a QP value for the luminance component based on the predicted luminance QP and the luminance delta QP value; Determining a predicted chrominance QP for a chrominance component of the decoding unit, wherein the chrominance component of the decoding unit and the luminance component of the decoding unit are partitioned using a single tree structure; Receiving a second syntax that is part of the transform unit syntax included in the bitstream of the encoded video data, the second syntax indicating a chrominance delta QP value for the chrominance component of the decoding unit, wherein the second syntax is different from the first syntax; Determining a QP value for the chrominance component of the decoding unit based on the predicted chrominance QP and the indicated chrominance delta QP value; Dequantizing a luminance transform coefficient block for the decoding unit based on the QP value for the luminance component; Dequantizing a chrominance transform coefficient block for the decoding unit based on the QP value for the chrominance component; and Decoding the decoding unit based on the dequantized luminance transform coefficient block and the dequantized chrominance transform coefficient block.

2. The method according to claim 1, wherein The first syntax includes a syntax element indicating an absolute value of the luminance delta QP value and a syntax element indicating a sign for the luminance delta QP value.

3. The method according to claim 1, further comprising: Determining a second predicted chrominance QP for a second chrominance component of the decoding unit; Receiving, in the bitstream of the encoded video data, a third syntax indicating a second chrominance delta QP value for the second chrominance component of the decoding unit; Determining a second QP value for the second chrominance component of the decoding unit based on the second predicted chrominance QP and the second chrominance delta QP value; Dequantizing a second chrominance transform coefficient block for the decoding unit based on the second QP value for the second chrominance component; And Decoding the decoding unit based on the dequantized second chrominance transform coefficient block.

4. The method according to claim 1, further comprising: In response to determining that signaling of a chrominance delta QP value is enabled for the decoding unit, receiving, in the bitstream of the encoded video data, the second syntax indicating the chrominance delta QP value for the chrominance component.

5. The method according to claim 1, wherein The predicted chrominance QP for the chrominance component of the decoding unit is determined based on the determined QP value for the corresponding luminance component of the decoding unit.

6. The method according to claim 1, wherein, The first syntax includes the syntax elements cu_qp_delta_abs and cu_qp_delta_sign_flag.

7. The method according to claim 1, further comprising: Receive a chrominance delta QP enable flag that indicates whether the chrominance delta QP value is included in the transform unit, and in response to the chrominance delta QP enable flag indicating that the chrominance delta QP value is included in the transform unit, receive the second syntax indicating the chrominance delta QP value for the chrominance component of the decoding unit.

8. The method according to claim 7, wherein, The chrominance delta QP enable flag is received in a picture parameter set syntax structure.

9. The method according to claim 1, wherein Decoding the decoding unit based on the dequantized luminance transform coefficient block and the dequantized chrominance transform coefficient block further includes: Performing an inverse transform on the dequantized luminance transform coefficient block to determine a luminance residual block; Performing an inverse transform on the dequantized chrominance transform coefficient block to determine a chrominance residual block; Determining a luminance prediction block; Determining a chrominance prediction block; Adding the luminance residual block to the luminance prediction block to determine the reconstructed luminance block of the decoding unit; and Adding the chrominance residual block to the chrominance prediction block to determine the reconstructed chrominance block of the decoding unit.

10. The method according to claim 1, wherein, The second syntax is received using a syntax element for the absolute value of the chrominance delta QP.

11. A method for encoding video data, the method comprising: Determining a quantization parameter (QP) value for a luminance component of a decoding unit for the video data; Determining a predicted luminance QP for the luminance component of the decoding unit; Based on the QP value for the luminance component and the predicted luminance QP, determining a delta QP value for the luminance component of the decoding unit; Generating a first syntax to be included in a bitstream of the encoded video data as part of a transform unit syntax, the first syntax indicating the delta QP value for the luminance component of the decoding unit; Determining a QP value for a chrominance component of the decoding unit for the video data, wherein the chrominance component of the decoding unit and the luminance component of the decoding unit are partitioned using a single tree structure; Determining a predicted chrominance QP for the chrominance component of the decoding unit; Based on the QP value for the chrominance component and the predicted chrominance QP, determining a delta QP value for the chrominance component of the decoding unit; Generating a second syntax to be included in the bitstream of the encoded video data as part of the transform unit syntax, the second syntax indicating the delta QP value for the chrominance component of the decoding unit, the second syntax being different from the first syntax; and Outputting the first syntax and the second syntax in the bitstream of the encoded video data.

12. The method according to claim 11, further comprising: Quantizing a luminance transform coefficient block based on the QP value for the luminance component of the decoding unit; Quantizing a chrominance transform coefficient block based on the QP value for the chrominance component of the decoding unit; And Outputting syntax in the bitstream of the encoded video data that indicates values for the quantized luminance transform coefficient block and the quantized chrominance transform coefficient block.

13. The method according to claim 11, wherein, The first syntax includes a syntax element indicating an absolute value of an incremental QP value of the luminance component and a syntax element indicating a sign of the incremental QP value for the luminance component.

14. The method according to claim 11, further comprising: determining a second QP value for a second chrominance component of the decoding unit; determining a second predicted chrominance QP for the second chrominance component of the decoding unit; determining a second incremental QP value for the second chrominance component based on the second QP value and the second predicted chrominance QP for the second chrominance component; generating a third syntax indicating the second incremental QP value for the second chrominance component to be included in the bitstream of the encoded video data; and outputting the third syntax in the bitstream of the encoded video data.

15. The method according to claim 11, further comprising: generating, in response to determining that signaling of a chrominance incremental QP value is enabled for the decoding unit, the second syntax indicating the chrominance incremental QP value for the chrominance component to be included in the bitstream of the encoded video data.

16. The method according to claim 11, wherein, The predicted chrominance QP for the chrominance component of the decoding unit is determined based on the determined QP value of the corresponding luminance component of the decoding unit.

17. The method according to claim 11, wherein, The first syntax includes the syntax elements cu_qp_delta_abs and cu_qp_delta_sign_flag.

18. The method according to claim 11, further comprising: generating a chrominance incremental QP enable flag to be included in the bitstream of the encoded video data, wherein the chrominance incremental QP enable flag is set to a value indicating that the chrominance incremental QP value is included in the transform unit.

19. The method according to claim 18, wherein, The chrominance incremental QP enable flag is included in a picture parameter set syntax structure.

20. An apparatus for decoding video data, the apparatus comprising: a memory configured to store video data; one or more processors implemented in circuitry and configured to: determine a predicted luminance quantization parameter (QP) for a luminance component of a decoding unit; receive a first syntax as part of a transform unit syntax included in a bitstream of encoded video data, the first syntax indicating a luminance incremental QP value for the luminance component of the decoding unit; determine a QP value for the luminance component based on the predicted luminance QP and the luminance incremental QP value; determine a predicted chrominance QP for a chrominance component of the decoding unit, wherein the chrominance component of the decoding unit and the luminance component of the decoding unit are partitioned using a single tree structure; receive a second syntax as part of the transform unit syntax included in the bitstream of the encoded video data, the second syntax indicating a chrominance incremental QP value for the chrominance component of the decoding unit, wherein the second syntax is different from the first syntax; determine a QP value for the chrominance component of the decoding unit based on the predicted chrominance QP and the indicated chrominance incremental QP value; Dequantize the luminance transform coefficient block for the decoding unit based on the QP value for the luminance component; Dequantize the chrominance transform coefficient block for the decoding unit based on the QP value for the chrominance component; and Decode the decoding unit based on the dequantized luminance transform coefficient block and the dequantized chrominance transform coefficient block.

21. The apparatus according to claim 20, wherein, The first syntax includes a syntax element indicating the absolute value of the luminance delta QP value and a syntax element indicating the sign of the luminance delta QP value.

22. The device according to claim 20, wherein The one or more processors are further configured to: Determine a second predicted chrominance QP for a second chrominance component of the decoding unit; Receive, in a bitstream of the encoded video data, a third syntax indicating a second chrominance delta QP value for the second chrominance component of the decoding unit; Determine a second QP value for the second chrominance component of the decoding unit based on the second predicted chrominance QP and the second chrominance delta QP value; Dequantize the second chrominance transform coefficient block for the decoding unit based on the second QP value for the second chrominance component; And Decode the decoding unit based on the dequantized second chrominance transform coefficient block.

23. The device according to claim 20, wherein, The one or more processors are further configured to: In response to determining that signaling of the chrominance delta QP value is enabled for the decoding unit, receive, in a bitstream of the encoded video data, the second syntax indicating the chrominance delta QP value for the chrominance component.

24. The device according to claim 20, wherein The predicted chrominance QP for the chrominance component of the decoding unit is determined based on the determined QP value for the corresponding luminance component of the decoding unit.

25. The device according to claim 20, wherein The first syntax includes the syntax elements cu_qp_delta_abs and cu_qp_delta_sign_flag.

26. The device according to claim 20, wherein, The one or more processors are further configured to: Receive a chrominance delta QP enable flag indicating whether the chrominance delta QP value is included in the transform unit, wherein the reception of the second syntax indicating the chrominance delta QP value for the chrominance component of the decoding unit is in response to the chrominance delta QP enable flag indicating that the chrominance delta QP value is included in the transform unit.

27. The apparatus according to claim 26, wherein The chrominance delta QP enable flag is received in a picture parameter set syntax structure.

28. The apparatus according to claim 20, wherein To decode the decoding unit based on the dequantized luminance transform coefficient block and the dequantized chrominance transform coefficient block, the one or more processors are further configured to: Perform an inverse transform on the dequantized luminance transform coefficient block to determine a luminance residual block; Perform an inverse transform on the dequantized chrominance transform coefficient block to determine a chrominance residual block; Determine a luminance prediction block; Determine a chrominance prediction block; Add the luminance residual block to the luminance prediction block to determine a reconstructed luminance block of the decoding unit; And Add the chrominance residual block to the chrominance prediction block to determine a reconstructed chrominance block of the decoding unit.

29. The device according to claim 20, wherein The second syntax is received using a syntax element for the chrominance delta QP absolute value.

30. The device according to claim 20, wherein The device includes a wireless communication device, and the wireless communication device includes a display configured to display decoded video data blocks.

31. The device according to claim 30, wherein, The wireless communication device includes a cellular phone, and the cellular phone includes a receiver configured to demodulate a signal including an encoded representation of the video data according to a wireless communication standard.

32. A device for encoding video data, the device comprising: a memory configured to store video data; one or more processors implemented in circuitry and configured to: determine a quantization parameter (QP) value for a luminance component of a decoding unit for the video data; determine a predicted luminance QP for the luminance component of the decoding unit; based on the QP value for the luminance component and the predicted luminance QP, determine an incremental QP value for the luminance component of the decoding unit; generate a first syntax to be included in a bitstream of the encoded video data as part of a transform unit syntax, the first syntax indicating the incremental QP value for the luminance component of the decoding unit; determine a QP value for a chrominance component of the decoding unit for the video data, wherein the chrominance component of the decoding unit and the luminance component of the decoding unit are partitioned using a single tree structure; determine a predicted chrominance QP for the chrominance component of the decoding unit; based on the QP value for the chrominance component and the predicted chrominance QP, determine an incremental QP value for the chrominance component of the decoding unit; generate a second syntax to be included in the bitstream of the encoded video data as part of the transform unit syntax, the second syntax indicating the incremental QP value for the chrominance component of the decoding unit, the second syntax being different from the first syntax; and output the first syntax and the second syntax in the bitstream of the encoded video data.

33. The apparatus according to claim 32, wherein, The one or more processors are further configured to: quantize a luminance transform coefficient block based on the QP value for the luminance component of the decoding unit; quantize a chrominance transform coefficient block based on the QP value for the chrominance component of the decoding unit; and output a syntax in the bitstream of the encoded video data, the syntax indicating values for the quantized luminance transform coefficient block and the quantized chrominance transform coefficient block.

34. The apparatus according to claim 32, wherein, The first syntax includes a syntax element indicating an absolute value of the incremental QP value for the luminance component and a syntax element indicating a sign of the incremental QP value for the luminance component.

35. The apparatus according to claim 32, wherein, The one or more processors are further configured to: determine a second QP value for a second chrominance component of the decoding unit; determine a second predicted chrominance QP for the second chrominance component of the decoding unit; based on the second QP value for the second chrominance component and the second predicted chrominance QP, determine a second incremental QP value for the second chrominance component; generate a third syntax indicating the second incremental QP value for the second chrominance component to be included in the bitstream of the encoded video data; and Output the third syntax in the bitstream of the encoded video data.

36. The apparatus according to claim 32, wherein, The one or more processors are further configured to: In response to determining that signaling of the chrominance delta QP value is enabled for the decoding unit, generate the second syntax indicating the chrominance delta QP value for the chrominance component to be included in the bitstream of the encoded video data.

37. The apparatus according to claim 32, wherein, The predicted chrominance QP for the chrominance component of the decoding unit is determined based on the determined QP value of the corresponding luma component for the decoding unit.

38. The apparatus according to claim 32, wherein, The first syntax includes the syntax elements cu_qp_delta_abs and cu_qp_delta_sign_flag.

39. The device according to claim 32, wherein, The one or more processors are further configured to: Generate a chrominance delta QP enable flag to be included in the bitstream of the encoded video data, the chrominance delta QP enable flag being set to a value indicating that the chrominance delta QP value is included in the transform unit.

40. The apparatus according to claim 39, wherein, The chrominance delta QP enable flag is included in the picture parameter set syntax structure.

41. The apparatus according to claim 32, further comprising: A camera configured to capture the video data.

42. An apparatus for decoding a bitstream of encoded video data, the apparatus comprising: A unit for determining a predicted luma quantization parameter (QP) for a luma component of a decoding unit; A unit for receiving a first syntax as part of a transform unit syntax included in the bitstream of the encoded video data, the first syntax indicating a luma delta QP value for the luma component of the decoding unit; A unit for determining a QP value for the luma component based on the predicted luma QP and the luma delta QP value; A unit for determining a predicted chrominance QP for a chrominance component of the decoding unit, wherein the chrominance component of the decoding unit and the luma component of the decoding unit are partitioned using a single tree structure; A unit for receiving a second syntax as part of the transform unit syntax included in the bitstream of the encoded video data, the second syntax indicating a chrominance delta QP value for the chrominance component of the decoding unit, wherein the second syntax is different from the first syntax; A unit for determining a QP value for the chrominance component of the decoding unit based on the predicted chrominance QP and the indicated chrominance delta QP value; A unit for dequantizing a luma transform coefficient block for the decoding unit based on the QP value for the luma component; A unit for dequantizing a chrominance transform coefficient block for the decoding unit based on the QP value for the chrominance component; and A unit for decoding the decoding unit based on the dequantized luma transform coefficient block and the dequantized chrominance transform coefficient block.

43. A computer-readable storage medium storing instructions that, when executed by one or more processors, cause the one or more processors to perform the following operations: Determine a predicted luma quantization parameter (QP) for a luma component of a decoding unit; Receive a first syntax that is part of a transform unit syntax included in a bitstream of encoded video data, the first syntax indicating a luminance delta QP value for a luminance component of the decoding unit; Determine a QP value for the luminance component based on the predicted luminance QP and the luminance delta QP value; Determine a predicted chrominance QP for a chrominance component of the decoding unit, wherein the chrominance component of the decoding unit and the luminance component of the decoding unit are partitioned using a single-tree structure; Receive a second syntax that is part of the transform unit syntax included in the bitstream of the encoded video data, the second syntax indicating a chrominance delta QP value for the chrominance component of the decoding unit, wherein the second syntax is different from the first syntax; Determine a QP value for the chrominance component of the decoding unit based on the predicted chrominance QP and the indicated chrominance delta QP value; Dequantize a luminance transform coefficient block for the decoding unit based on the QP value for the luminance component; Dequantize a chrominance transform coefficient block for the decoding unit based on the QP value for the chrominance component; and Decode the decoding unit based on the dequantized luminance transform coefficient block and the dequantized chrominance transform coefficient block.

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