Patent Description:
<CIT> discloses that in the HEVC standard, each Coding Block (CB) greater than or equal to a minimum block size for delta QP signaling has its own quantization parameter (QP) and QP information is conveyed to the decoder side so that the decoder will use the same QP for proper decoding process. Delta QP derived by the difference between a current coding QP and a reference QP is transmitted to reduce the bit rate required for QP information. A final QP for a current CB is derived based on a signaled delta QP for the current CB and a reference QP, where the reference QP derivation is based on QP of neighboring coded quantization groups of the current CB. Two delta QPs may be signaled for the luma and chroma components respectively when the block partitioning structures for the luma and chroma components are separately determined.

<CIT> discloses, if separate luma and chroma coding trees are allowed (e.g., as may be the case for I-slices for QTBT), separate delta QP signaling may be performed. Alternatively, the delta QP for chroma (i.e., the chroma delta QP) may be derived from corresponding luma delta QP.

JVET-M010 proposes a scheme of applying delta QP for Chroma CU into YYC codec, taking into account separate tree mechanism. Delta QP is signaled only for Luma CU in case of Dual Tree and a QP value is derived for Chroma CU based on QP value of correspondent Luma CU.

Advantageous embodiments are subject to the dependent claims. In the following, each of the described methods, apparatuses, systems, examples and aspects, which does not fully correspond to the invention as defined in the appended claims, is thus not according to the invention and is, as well as the whole following description, present for illustration purposes only or to highlight specific aspects or features of the appended claims.

This disclosure describes techniques related to the quantization process and, more specifically, to determining and signaling values for determining a chroma quantization parameter (QP), using a chroma delta QP. A video decoder can be configured to determine a predicted QP value for a block based on QP values used for previously decoded blocks and without receiving any explicit syntax elements in the bitstream. The video decoder can then receive a delta QP value representing a difference between the predicted QP value and an actual QP value for the block. As the delta QP value is typically small compared to the actual QP value, the delta QP value can be signaled with relatively fewer bits compared to the actual QP value. A quantization parameter, or QP, is a variable used by the decoding process for scaling transform coefficient levels. The QP effectively represents the amount of quantization applied to the coefficient levels.

Video coding (e.g., video encoding and/or video decoding) typically involves predicting a block of video data from either an already coded block of video data in the same picture (e.g., intra prediction) or an already coded block of video data in a different picture (e.g., inter prediction). In some instances, the video encoder also calculates residual data by comparing the prediction block to the original block. Thus, the residual data represents a difference between the prediction block and the original block. To reduce the number of bits needed 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 processes may be lossy, meaning that transform and quantization processes may introduce distortion into the decoded video data.

A video decoder decodes and adds the residual data to the prediction block to produce a reconstructed video block that matches the original video block more closely than the prediction block alone. Due to the loss introduced by the transforming and quantizing of the residual data, the first reconstructed block may have distortion or artifacts. One common type of artifact or distortion is referred to as blockiness, where the boundaries of the blocks used to code the video data are visible.

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

This disclosure describes techniques related to the quantization process and, more specifically, to determining and signaling values for determining a chroma quantization parameter (QP), using a chroma delta QP. A video decoder can be configured to determine a predicted QP value for a block based on QP values used for previously decoded blocks and without receiving any explicit syntax elements in the bitstream. The video decoder can then receive a delta QP value representing a difference between the predicted QP value and an actual QP value for the block. As the delta QP value is typically small compared to the actual QP value, the delta QP value can be signaled with relatively fewer bits compared to the actual QP value.

A quantization parameter, or QP, is a variable used by the decoding process for scaling 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 chroma delta QP value for a chroma component and to determine a QP value for the chroma component based on the predicted chroma QP and the chroma delta QP value, the techniques of this disclosure may achieve the advantage of an improved rate-distortion tradeoff achieved in some coding scenarios by allowing for chroma QP values to be adjusted independent of luma QP values.

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

<FIG> is a block diagram illustrating an example video encoding and decoding system <NUM> that may perform the techniques of this disclosure. The techniques of this disclosure are generally directed to coding (encoding and/or decoding) video data. In general, video data includes any data for processing a video. Thus, video data may include raw, unencoded video, encoded video, decoded (e.g., reconstructed) video, and video metadata, such as signaling data.

As shown in <FIG>, system <NUM> includes a source device <NUM> that provides encoded video data to be decoded and displayed by a destination device <NUM>, in this example. In particular, source device <NUM> provides the video data to destination device <NUM> via a computer-readable medium <NUM>. Source device <NUM> and destination device <NUM> may comprise any of a wide range of devices, including desktop computers, notebook (i.e., laptop) computers, mobile devices, tablet computers, set-top boxes, telephone handsets such as smartphones, televisions, cameras, display devices, digital media players, video gaming consoles, video streaming device, broadcast receiver devices, or the like. In some cases, source device <NUM> and destination device <NUM> may be equipped for wireless communication, and thus may be referred to as wireless communication devices.

In the example of <FIG>, source device <NUM> includes video source <NUM>, memory <NUM>, video encoder <NUM>, and output interface <NUM>. Destination device <NUM> includes input interface <NUM>, video decoder <NUM>, memory <NUM>, and display device <NUM>. In accordance with this disclosure, video encoder <NUM> of source device <NUM> and video decoder <NUM> of destination device <NUM> may be configured to apply the techniques for chroma delta QP coding described herein. Thus, source device <NUM> represents an example of a video encoding device, while destination device <NUM> represents an example of a video decoding device. In other examples, a source device and a destination device may include other components or arrangements. For example, source device <NUM> may receive video data from an external video source, such as an external camera. Likewise, destination device <NUM> may interface with an external display device, rather than include an integrated display device.

System <NUM> as shown in <FIG> is merely one example. In general, any digital video encoding and/or decoding device may perform techniques for chroma delta QP coding described herein. Source device <NUM> and destination device <NUM> are merely examples of such coding devices in which source device <NUM> generates coded video data for transmission to destination device <NUM>. This disclosure refers to a "coding" device as a device that performs coding (encoding and/or decoding) of data. Thus, video encoder <NUM> and video decoder <NUM> represent examples of coding devices, in particular, a video encoder and a video decoder, respectively. In some examples, source device <NUM> and destination device <NUM> may operate in a substantially symmetrical manner such that each of source device <NUM> and destination device <NUM> includes video encoding and decoding components. Hence, system <NUM> may support one-way or two-way video transmission between source device <NUM> and destination device <NUM>, e.g., for video streaming, video playback, video broadcasting, or video telephony.

In general, video source <NUM> 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 video encoder <NUM>, which encodes data for the pictures. Video source <NUM> of source device <NUM> may include a video capture device, such as a video camera, a video archive containing previously captured raw video, and/or a video feed interface to receive video from a video content provider. As a further alternative, video source <NUM> 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, video encoder <NUM> encodes the captured, pre-captured, or computer-generated video data. Video encoder <NUM> may rearrange the pictures from the received order (sometimes referred to as "display order") into a coding order for coding. Video encoder <NUM> may generate a bitstream including encoded video data. Source device <NUM> may then output the encoded video data via output interface <NUM> onto computer-readable medium <NUM> for reception and/or retrieval by, e.g., input interface <NUM> of destination device <NUM>.

Memory <NUM> of source device <NUM> and memory <NUM> of destination device <NUM> represent general purpose memories. In some examples, memories <NUM>, <NUM> may store raw video data, e.g., raw video from video source <NUM> and raw, decoded video data from video decoder <NUM>. Additionally or alternatively, memories <NUM>, <NUM> may store software instructions executable by, e.g., video encoder <NUM> and video decoder <NUM>, respectively. Although memory <NUM> and memory <NUM> are shown separately from video encoder <NUM> and video decoder <NUM> in this example, it should be understood that video encoder <NUM> and video decoder <NUM> may also include internal memories for functionally similar or equivalent purposes. Furthermore, memories <NUM>, <NUM> may store encoded video data, e.g., output from video encoder <NUM> and input to video decoder <NUM>. In some examples, portions of memories <NUM>, <NUM> may be allocated as one or more video buffers, e.g., to store raw, decoded, and/or encoded video data.

Computer-readable medium <NUM> may represent any type of medium or device capable of transporting the encoded video data from source device <NUM> to destination device <NUM>. In one example, computer-readable medium <NUM> represents a communication medium to enable source device <NUM> to transmit encoded video data directly to destination device <NUM> in real-time, e.g., via a radio frequency network or computer-based network. Output interface <NUM> may modulate a transmission signal including the encoded video data, and input interface <NUM> may demodulate the received transmission signal, according to a communication standard, such as a wireless communication protocol. The communication medium may comprise any wireless or wired communication medium, such as a radio frequency (RF) spectrum or one or more physical transmission lines. The communication medium may form part of a packetbased network, such as a local area network, a wide-area network, or a global network such as the Internet. The communication medium may include routers, switches, base stations, or any other equipment that may be useful to facilitate communication from source device <NUM> to destination device <NUM>.

In some examples, source device <NUM> may output encoded data from output interface <NUM> to storage device <NUM>. Similarly, destination device <NUM> may access encoded data from storage device <NUM> via input interface <NUM>. Storage device <NUM> may include any of a variety of distributed or locally accessed data storage media such as a hard drive, Blu-ray discs, DVDs, CD-ROMs, flash memory, volatile or non-volatile memory, or any other suitable digital storage media for storing encoded video data.

In some examples, source device <NUM> may output encoded video data to file server <NUM> or another intermediate storage device that may store the encoded video data generated by source device <NUM>. Destination device <NUM> may access stored video data from file server <NUM> via streaming or download.

File server <NUM> may be any type of server device capable of storing encoded video data and transmitting that encoded video data to the destination device <NUM>. File server <NUM> may represent a web server (e.g., for a website), a server configured to provide a file transfer protocol service (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. File server <NUM> may, additionally or alternatively, implement one or more HTTP streaming protocols, such as Dynamic Adaptive Streaming over HTTP (DASH), HTTP Live Streaming (HLS), Real Time Streaming Protocol (RTSP), HTTP Dynamic Streaming, or the like.

Destination device <NUM> may access encoded video data from file server <NUM> through any standard data connection, including an Internet connection. This may include a wireless channel (e.g., a Wi-Fi connection), a wired connection (e.g., digital subscriber line (DSL), cable modem, etc.), or a combination of both that is suitable for accessing encoded video data stored on file server <NUM>. Input interface <NUM> may be configured to operate according to any one or more of the various protocols discussed above for retrieving or receiving media data from file server <NUM>, or other such protocols for retrieving media data.

Output interface <NUM> and input interface <NUM> may represent wireless transmitters/receivers, modems, wired networking components (e.g., Ethernet cards), wireless communication components that operate according to any of a variety of IEEE <NUM> standards, or other physical components. In examples where output interface <NUM> and input interface <NUM> comprise wireless components, output interface <NUM> and input interface <NUM> may be configured to transfer data, such as encoded video data, according to a cellular communication standard, such as <NUM>, <NUM>-LTE (Long-Term Evolution), LTE Advanced, <NUM>, or the like. In some examples where output interface <NUM> comprises a wireless transmitter, output interface <NUM> and input interface <NUM> may be configured to transfer data, such as encoded video data, according to other wireless standards, such as an IEEE <NUM> specification, an IEEE <NUM> specification (e.g., ZigBee™), a Bluetooth™ standard, or the like. In some examples, source device <NUM> and/or destination device <NUM> may include respective system-on-a-chip (SoC) devices. For example, source device <NUM> may include an SoC device to perform the functionality attributed to video encoder <NUM> and/or output interface <NUM>, and destination device <NUM> may include an SoC device to perform the functionality attributed to video decoder <NUM> and/or input interface <NUM>.

Input interface <NUM> of destination device <NUM> receives an encoded video bitstream from computer-readable medium <NUM> (e.g., a communication medium, storage device <NUM>, file server <NUM>, or the like). The encoded video bitstream may include signaling information defined by video encoder <NUM>, which is also used by video decoder <NUM>, such as syntax elements having values that describe characteristics and/or processing of video blocks or other coded units (e.g., slices, pictures, groups of pictures, sequences, or the like). Display device <NUM> displays decoded pictures of the decoded video data to a user. Display device <NUM> may represent any of a variety of 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.

Video encoder <NUM> and video decoder <NUM> may operate according to a video coding standard, such as ITU-T H. <NUM>, also referred to as High Efficiency Video Coding (HEVC) or extensions thereto, such as the multi-view and/or scalable video coding extensions. Alternatively, video encoder <NUM> and video decoder <NUM> may operate according to other proprietary or industry standards, such as ITU-T H. <NUM>, also referred to as Versatile Video Coding (VVC). A draft of the VVC standard is described in <NPL> (hereinafter "VVC Draft <NUM>"). Another draft of the VVC standard is described in <NPL> (hereinafter "VVC Draft <NUM>"). The techniques of this disclosure, however, are not limited to any particular coding standard.

As another example, video encoder <NUM> and video decoder <NUM> may be configured to operate according to VVC. According to VVC, a video coder (such as video encoder <NUM>) partitions a picture into a plurality of coding tree units (CTUs). Video encoder <NUM> may partition a CTU according to a tree structure, such as a quadtree-binary tree (QTBT) structure or Multi-Type Tree (MTT) structure. The QTBT structure removes the concepts of multiple partition types, such as the separation between CUs, PUs, and TUs of HEVC. A QTBT structure includes two levels: a first level partitioned according to quadtree partitioning, and a second level partitioned according to binary tree partitioning. A root node of the QTBT structure corresponds to a CTU. Leaf nodes of the binary trees correspond to coding units (CUs).

In an MTT partitioning structure, blocks may be partitioned using a quadtree (QT) partition, a binary tree (BT) partition, and one or more types of triple tree (TT) (also called ternary tree (TT)) partitions. A triple or ternary tree partition is a partition where a block is split into three sub-blocks. In some examples, a triple or ternary tree partition divides a block into three sub-blocks without dividing the original block through the center. The partitioning types in MTT (e.g., QT, BT, and TT), may be symmetrical or asymmetrical.

In some examples, a CTU includes a coding tree block (CTB) of luma samples, two corresponding CTBs of chroma samples of a picture that has three sample arrays, or a CTB of samples of a monochrome picture or a picture that is coded using three separate color planes and syntax structures used to code the samples. A CTB may be an NxN block of samples for some value of N such that the division of a component into CTBs is a partitioning. A component is an array or single sample from one of the three arrays (luma and two chroma) that compose a picture in <NUM>:<NUM>:<NUM>, <NUM>:<NUM>:<NUM>, or <NUM>:<NUM>:<NUM> color format or the array or a single sample of the array that compose a picture in monochrome format. In some examples, a coding block is an MxN block of samples for some values of M and N such that a division of a CTB into coding blocks is a partitioning.

The blocks (e.g., CTUs or CUs) may be grouped in various ways in a picture. As one example, a brick may refer to a rectangular region of CTU rows within a particular tile in a picture. A tile may be a rectangular region of CTUs within a particular tile column and a particular tile row in a picture. A tile column refers to a rectangular region of CTUs having a height equal to the height of the picture and a width specified by syntax elements (e.g., such as in a picture parameter set). A tile row refers to a rectangular region of CTUs having a height specified by syntax elements (e.g., such as in a picture parameter set) and a width equal to the width of the picture.

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

The bricks in a picture may also be arranged in a slice. A slice may be an integer number of bricks of a picture that may be exclusively contained in a single network abstraction layer (NAL) unit. In some examples, a slice includes either a number of complete tiles or only a consecutive sequence of complete bricks of one tile.

Some examples of VVC also provide an affine motion compensation mode, which may be considered an inter-prediction mode. In affine motion compensation mode, video encoder <NUM> may determine two or more motion vectors that represent nontranslational motion, such as zoom in or out, rotation, perspective motion, or other irregular motion types.

To perform intra-prediction, video encoder <NUM> may select an intra-prediction mode to generate the prediction block. Some examples of VVC provide sixty-seven intra-prediction modes, including various directional modes, as well as planar mode and DC mode. In general, video encoder <NUM> selects an intra-prediction mode that describes neighboring samples to a current block (e.g., a block of a CU) from which to predict samples of the current block. Such samples may generally be above, above and to the left, or to the left of the current block in the same picture as the current block, assuming video encoder <NUM> codes CTUs and CUs in raster scan order (left to right, top to bottom).

As noted above, following any transforms to produce transform coefficients, video encoder <NUM> may perform quantization of the transform coefficients. Quantization generally refers to a process in which transform coefficients are quantized to possibly reduce the amount of data used to represent the transform coefficients, providing further compression. By performing the quantization process, video encoder <NUM> may reduce the bit depth associated with some or all of the transform coefficients. For example, video encoder <NUM> 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 <NUM> may perform a bitwise right-shift of the value to be quantized.

Following quantization, video encoder <NUM> may scan the transform coefficients, producing a one-dimensional vector from the two-dimensional matrix including the quantized transform coefficients. The scan may be designed to place higher energy (and therefore lower frequency) transform coefficients at the front of the vector and to place lower energy (and therefore higher frequency) transform coefficients at the back of the vector. In some examples, video encoder <NUM> may utilize a predefined scan order to scan the quantized transform coefficients to produce a serialized vector, and then entropy encode the quantized transform coefficients of the vector. In other examples, video encoder <NUM> may perform an adaptive scan. After scanning the quantized transform coefficients to form the one-dimensional vector, video encoder <NUM> may entropy encode the one-dimensional vector, e.g., according to context-adaptive binary arithmetic coding (CABAC). Video encoder <NUM> may also entropy encode values for syntax elements describing metadata associated with the encoded video data for use by video decoder <NUM> in decoding the video data.

In general, video decoder <NUM> performs a reciprocal process to that performed by video encoder <NUM> to decode the encoded video data of the bitstream. For example, video decoder <NUM> may decode values for syntax elements of the bitstream using CABAC in a manner substantially similar to, albeit reciprocal to, the CABAC encoding process of video encoder <NUM>. The syntax elements may define partitioning information for partitioning of a picture into CTUs, and partitioning of each CTU according to a corresponding partition structure, such as a QTBT structure, to define CUs of the CTU. The syntax elements may further define prediction and residual information for blocks (e.g., CUs) of video data.

By determining a predicted chroma QP for a chroma component of the coding unit, signalling syntax indicating a chroma delta QP value for the chroma component of the coding unit, and determining a QP value for the chroma component of the coding unit based on the predicted chroma QP and the chroma delta QP value, video encoder <NUM> and video decoder <NUM> may enable for chroma QP values to be flexibly adjusted independent of luma QP values, in a manner that does not create an undesirable amount of additional signalling overhead.

This disclosure may generally refer to "signaling" certain information, such as syntax elements. The term "signaling" may generally refer to the communication of values for syntax elements and/or other data used to decode encoded video data. That is, video encoder <NUM> may signal values for syntax elements in the bitstream. In general, signaling refers to generating a value in the bitstream. As noted above, source device <NUM> may transport the bitstream to destination device <NUM> substantially in real time, or not in real time, such as might occur when storing syntax elements to storage device <NUM> for later retrieval by destination device <NUM>.

<FIG> are conceptual diagrams illustrating an example quadtree binary tree (QTBT) structure <NUM>, and a corresponding coding tree unit (CTU) <NUM>. The solid lines represent quadtree splitting, and dotted lines indicate binary tree splitting. In each split (i.e., non-leaf) node of the binary tree, one flag is signaled to indicate which splitting type (i.e., horizontal or vertical) is used, where <NUM> indicates horizontal splitting and <NUM> indicates vertical splitting in this example. For the quadtree splitting, there is no need to indicate the splitting type, because quadtree nodes split a block horizontally and vertically into <NUM> sub-blocks with equal size. Accordingly, video encoder <NUM> may encode, and video decoder <NUM> may decode, syntax elements (such as splitting information) for a region tree level of QTBT structure <NUM> (i.e., the solid lines) and syntax elements (such as splitting information) for a prediction tree level of QTBT structure <NUM> (i.e., the dashed lines). Video encoder <NUM> may encode, and video decoder <NUM> may decode, video data, such as prediction and transform data, for CUs represented by terminal leaf nodes of QTBT structure <NUM>. A CTU may be partitioned with either single tree partitioning or dual tree partitioning. With single tree partitioning, the chroma component of the CTU and the luma component of the CTU have the same partitioning structure. With dual tree partitioning, the chroma component of the CTU and the luma component of the CTU potentially have different partitioning structure.

In one example of the QTBT partitioning structure, the CTU size is set as 128x128 (luma samples and two corresponding 64x64 chroma samples), the MinQTSize is set as 16x16, the MaxBTSize is set as 64x64, the MinBTSize (for both width and height) is set as <NUM>, and the MaxBTDepth is set as <NUM>. The quadtree partitioning is applied to the CTU first to generate quad-tree leaf nodes. The quadtree leaf nodes may have a size from 16x16 (i.e., the MinQTSize) to 128x128 (i.e., the CTU size). If the quadtree leaf node is 128x128, the leaf quadtree node will not be further split by the binary tree, because the size exceeds the MaxBTSize (i.e., 64x64, in this example). Otherwise, the quadtree leaf node will be further partitioned by the binary tree. Therefore, the quadtree leaf node is also the root node for the binary tree and has the binary tree depth as <NUM>. When the binary tree depth reaches MaxBTDepth (<NUM>, in this example), no further splitting is permitted. A binary tree node having a width equal to MinBTSize (<NUM>, in this example) it implies that no further vertical splitting (that is, dividing of the width) is permitted for that binary tree node. Similarly, a binary tree node having a height equal to MinBTSize implies no further horizontal splitting (that is, dividing of the height) is permitted for that binary tree node. As noted above, leaf nodes of the binary tree are referred to as CUs, and are further processed according to prediction and transform without further partitioning.

Video encoder <NUM> and video decoder <NUM> may be configured to process luma delta QP values. That is, video decoder <NUM> can be configured to determine a predicted luma QP value for a block based on luma QP values used for previously decoded blocks and without receiving any explicit syntax elements in the bitstream. Video decoder <NUM> can then receive a luma delta QP value representing a difference between the predicted luma QP value and an actual luma QP value for the block.

In VVC Draft <NUM>, values for delta QP are singled in a similar way to HEVC. The syntax included in VVC Draft <NUM> is as follows:.

The syntax element cu_qp_delta_abs specifies the absolute value of the difference between the quantization parameter of the current coding unit and a predicted QP value for the coding unit. As one example, video encoder <NUM> and video decoder <NUM> may, for example, determine the predicted QP value for a current CU to be equal to the QP value used for a previously coded CU. If one or both of an above neighboring CU or a left neighboring CU are available, then video encoder <NUM> and video decoder <NUM> may use one of the QP for the above neighbor or the QP for the left neighbor as the predicted QP value. If a previously coded CU does not have a QP value, for instance if the previously coded CU was coded in a skip mode, then video encoder <NUM> and video decoder <NUM> may be configured to set the predicted QP value equal to a QP value for a last CU that utilized quantization or to a default value. In the description below, CuQpDeltaVal represents a delta QP value.

The syntax element cu_qp_delta_sign_flag specifies the sign of CuQpDeltaVal as follows:.

The syntax element cu_qp_delta_enabled_flag equal to <NUM> specifies that the cu_qp_delta_subdiv syntax element is present in the PPS and that cu_qp_delta_abs may be present in the transform unit syntax. The syntax element cu_qp_delta_enabled_flag equal to <NUM> specifies that the cu_qp_delta_subdiv syntax element is not present in the PPS and that cu_qp_delta_abs is not present in the transform unit syntax.

The syntax element cu_qp_delta_subdiv specifies the maximum cbSubdiv value of coding units that convey cu_qp_delta_abs and cu_qp_delta_sign_flag. The value range of cu_qp_delta_subdiv is specified as follows:.

When not present, the value of cu_qp_delta_subdiv is inferred to be equal to <NUM>.

CBF flags of tu_cbf_luma[ x0 ][ y0 ], tu_cbf_cb[ x0 ][ y0 ], tu_cbf_cr[ x0 ][ y0 ] being equal to <NUM> means there is a coding bin in the coding block. Otherwise, a CBF equal to <NUM> mean there is no coding bin in the coding block.

<FIG> shows an example process for determining a delta QP value for video data that supports dual tree partitioning. Video decoder <NUM> determines if a CU is partitioned in a dual tree structure (<NUM>). If the CU is not partitioned in a dual tree structure (<NUM>, NO), then video decoder <NUM> determines a single partitioning for both the luma and chroma components of the CU (<NUM>) and decodes a delta QP value (<NUM>). If the CU is partitioned in a dual tree structure (<NUM>, YES), then video decoder <NUM> determines a partitioning for a luma component of the CU (<NUM>) and separately determines a partitioning of a chroma component of the CU (<NUM>). Video decoder <NUM> also decodes a delta QP value (<NUM>).

Video encoder <NUM> and video decoder <NUM> may be configured to perform luma QP prediction. Video encoder <NUM> and video decoder <NUM> derive the predicted luma quantization parameter, qPY_PRED, as follows:.

Video encoder <NUM> and video decoder <NUM> may be configured to process a previously luma QP. Video encoder <NUM> and video decoder <NUM> can derive the previous luma quantization parameter, qPY_PREV, as follows:.

Video encoder <NUM> and video decoder <NUM> may be configured to determine a chroma QP. In VVC Draft <NUM>, a value for chroma QP is calculated based on a value for luma QP.

When treeType is equal to DUAL_TREE_CHROMA, the variable QpY is set equal to the luma quantization parameter QpY of the luma coding unit that covers the luma location ( xCb + cbWidth / <NUM>, yCb + cbHeight / <NUM> ).

The table below specifies Qpc as a function of qPi for ChromaArrayType equal to <NUM>.

Video encoder <NUM> and video decoder <NUM> may be configured to determine a chroma QP offset. The chroma QP offset may, for example, be an index value. Video encoder <NUM> and video decoder <NUM> can maintain tables that map these index values to delta QP values.

<FIG> shows an example process for decoding a chroma QP offset value for video data that supports dual tree partitioning. Video decoder <NUM> determines if a CU is partitioned in a dual tree structure (<NUM>). If the CU is not partitioned in a dual tree structure (<NUM>, NO), then video decoder <NUM> determines a single partitioning for both the luma and chroma components of the CU (<NUM>) and decodes a chroma QP offset value (<NUM>). If the CU is partitioned in a dual tree structure (<NUM>, YES), then video decoder <NUM> determines a partitioning for a luma component of the CU (<NUM>) and separately determines a partitioning of a chroma component of the CU (<NUM>). Video decoder <NUM> also decodes a chroma QP offset value (<NUM>).

Video encoder <NUM> and video decoder <NUM> may be configured to utilize quantization groups. All CUs in a quantization group typically use the same QP predictor but not necessarily the same QP. The current quantization group is a rectangluar region inside a coding tree block that shares the same qPY_PRED. The quantization group width and height are equal to the width and height of the coding tree node, of which the top-left luma sample position is assigned to the variables CuQgTopLeftX and CuQgTopLeftY.

<FIG> shows an example video coding process for determining a QP predictor, QP_pred. The techniques of <FIG> will be described with respect to video encoder <NUM> but may also be performed by video decoder <NUM>. Video encoder <NUM> determines if a CU is the first CU in a CTU line and if the above CU is available (<NUM>). If the CU is the first CU in the CTU line and the above CU is available (<NUM>, Yes), then video encoder <NUM> sets the QP predictor equal to the QP of the above CU (<NUM>). If the CU is not the first CU in the CTU line or the above CU is not available (<NUM>, No), the video encoder <NUM> determines if a QP for an above CU is available (<NUM>) and if a CU for a left CU is available (<NUM>). If a QP for an above CU is available (<NUM>, Yes), then video encoder <NUM> sets the value for a variable (QP_above) to the value of the QP for the above CU. If a QP for an above CU is not available (<NUM>, No), then video encoder <NUM> sets the value for QP_above to a previously used QP value (<NUM>). If a QP for a left CU is available (<NUM>, Yes), then video encoder <NUM> sets the value for a variable (QP_left) to the value of the QP for the left CU. If a QP for a left CU is not available (<NUM>, No), then video encoder <NUM> sets the value for QP_left to a previously used QP value (<NUM>). Video encoder <NUM> sets a value for the QP predictor to an average of the values for QP_left and QP_above, which may be expressed mathematically as QP_pred = (QP_above + QP_left + <NUM>) >> <NUM> (<NUM>).

In the example above, the previously used QP value, QP_prev, may be any previously used QP value, and need not necessarily be a QP value for a left neighboring CU or an above neighboring CU. If, for example, a left neighboring CU was coded in a skip mode without transformation or quantization, then the previously used QP value may belong to the most recently decoded CU that had a QP value even if that CU is not adjacent to the current CU.

Current techniques for determining chroma QP values include some potential problems. For example, in VVC Draft <NUM>, chroma QP values are derived as follows: <MAT> <MAT> As can be seen above, the signaling for chroma QP values is controlled at the PPS and slice level.

When a tree type for a coding unit is set to dual trees, the variable QpY is set equal to the luma QP of the luma CB that covers the luma position (xCb + cbWidth / <NUM>, yCb + cbHeight / <NUM> ). <FIG> shows an example of a chroma CU with corresponding luma CUs in a separate tree. As shown in <FIG>, one choma CB <NUM> may cover more than one luma CB (192A-192D), and these luma CBs 192A-192D may be from different QGs with different QPs. The predicted QP derived from the center position may be not a accurate prediction for the chroma CB. And pps/slice level QP offset adjustment is limited. VVC draft <NUM> provides no scheme for flexibly adjusting chroma QP values.

This disclosure describes techniques that may address some of these problems. Unless stated to the contrary, the various techniques of this disclosure may be performed either separately or in combination.

Video encoder <NUM> and video decoder <NUM> may be configured to signal chroma delta QP values for chroma QGs. In one example, video encoder <NUM> and video decoder <NUM> may be configured to signal chroma delta QP values using the same scheme used for luma delta QP singling in VVC Draft <NUM>.

Video encoder <NUM> and video decoder <NUM> may be configured to define the chroma QG based on a split depth. In one example, the chroma QG may be defined in the same way as a 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 smaller than or equal to the maximum chroma delta QP signalling depth, video encoder <NUM> and video decoder <NUM> can signal one chroma delta QP value for the CU of this leaf node, if the CU has at least one non-zero coefficient. For a CU with a depth greater than the maximum chroma delta QP signalling depth, video encoder <NUM> and video decoder <NUM> can signal one chroma delta QP value for all CUs of the split node at the maximum chroma delta QP signalling depth, if any of CUs of the child nodes of the split node have at least one non-zero coefficient.

Video encoder <NUM> and video decoder <NUM> may be configured to define the chroma QG by an area. In one example, the area may be a rectangular region specified by width and height. In one example, the area 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 in both encoder side and decoder side, or set as a value signaled from the encoder to the decoder at sequence level, picture level, slice level. For example, this value may be signaled in an SPS, PPS, or slice header.

Video encoder <NUM> and video decoder <NUM> may be configured to signal the value of chroma delta QP by signaling an absolute value and sign flag in the same way as luma delta QP. That is, video encoder <NUM> and video decoder <NUM> may signal the value of chroma delta QP using two differ a syntax element for an absolute value of the chroma delta QP value and a sign flag indicating the sign of the chroma delta QP value.

Video encoder <NUM> and video decoder <NUM> may be configured to signal the value of chroma delta QP by signaling an absolute value only without needing to signal a sign flag. That is, the values for chroma delta QP may be restricted to only values that are equal to or greater than zero, meaning the values for chroma delta QP are restricted to not include negative value.

Video encoder <NUM> and video decoder <NUM> may be configured to use the same chroma delta QP for different chroma color components can use. For example, Cb and Cr components use the same chroma delta QP.

Video encoder <NUM> and video decoder <NUM> may be configured to signal chroma delta QP for different color components separately. For example, video encoder <NUM> and video decoder <NUM> may signal a chroma delta QP for a Cb chroma component, delta QP_cb, and separately signal a chroma delta QP for a Cr component, chroma delta QP_cr.

Video encoder <NUM> and video decoder <NUM> may be configured to use signal chroma QP values using delta QP values, PPS chroma QP offsets, slice chroma QP offsets, and cu level chroma QP offsets together for chroma QP generation. For example, video decoder <NUM> may be configured to derive chroma QP values as follows: <MAT> <MAT>.

Video encoder <NUM> and video decoder <NUM> may be configured to use chroma delta QP values, PPS chroma QP offsets, and slice chroma QP offsets to generate chroma QP. For example, video decoder <NUM> may be configured to derive chroma QP values as follows: <MAT> <MAT>.

In some examples, video encoder <NUM> and video decoder <NUM> may be configured to use different combinations of chroma delta QP values, PPS chroma QP offsets, slice chroma QP offsets, and cu level chroma QP offsets to generate chroma QP.

If signaling chroma delta QP is enabled, video encoder <NUM> and video decoder <NUM> may be configured to use chroma delta QP values to determine chroma delta QP values. Otherwise, if signaling chroma delta QP is not enabled, then video encoder <NUM> and video decoder <NUM> 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 offset.

Video encoder <NUM> and video decoder <NUM> may be configured to use the QPs of neighboring chroma blocks to predict the QP of current chroma block. In one example, video encoder <NUM> and video decoder <NUM> may use the same prediction techniques used for luma QP prediction described above with respect to <FIG>. For example, if the chroma CU is the first CU in the CTU line, then video encoder <NUM> and video decoder <NUM> may use the chroma QP of an above CU as a QP predictor. If the above CU is outside the current CTU, or otherwise not available, then video encoder <NUM> and video decoder <NUM> may use a previous chroma QP that may or may not correspond to an adjacent CU, as discussed above with respect to <FIG>. Otherwise, video encoder <NUM> and video decoder <NUM> may use the average chroma QPs of the above neighbor chroma CU and left neighbor chroma CU, if the above and left neighbor CUs are inside the current CTU. If any of the neighboring CUs are unavailable, then video encoder <NUM> and video decoder <NUM> may use the previous chroma QP instead of the QP of neighbor CU.

An example technique for signaling chroma delta QP will now be described. Based on JVET-N1001 version <NUM>, the newly added parts are shown between <new text> and </end new text> and the text to be removed is marked with <remove text> and </end remove text>.

In this process, video encoder <NUM> and video decoder <NUM> may signal a chroma delta QP using a chroma delta QP absolute value and a chroma delta QP sign value for both Cb and Cr components. The QPs of Cb and Cr are defined as qPCb, and qPCr which can be derived as follows: <MAT> <MAT> <MAT>.

In this example, video encoder <NUM> and video decoder <NUM> may signal the syntax elements chroma _cu_qp_delta_enable_flag and chroma_cu_qp_delta_subdiv in a PPS for chroma. In another example, video encoder <NUM> and video decoder <NUM> can use the same flags for chroma and luma, such as, for example, cu_qp_delta_enable_flag and cu_qp_delta_subdiv for luma in VVC Draft <NUM>.

The syntax element chroma_cu_qp_delta_enabled_flag equal to <NUM> specifies that the chroma_cu_qp_delta_subdiv syntax element is present in the PPS and that chroma_cu_qp_delta_abs may be present in the transform unit syntax. The syntax element chroma _cu_qp_delta_enabled_flag equal to <NUM> specifies that the chroma_cu_qp_delta_subdiv syntax element is not present in the PPS and that the syntax element chroma_cu_qp_delta_abs is not present in the transform unit syntax.

The syntax element chroma_cu_qp_delta_subdiv specifies the maximum cbSubdiv value of coding units that convey chroma_cu_qp_delta_abs and chroma cu_qp_delta_sign_flag. The value range of chroma_cu_qp_delta_subdiv is specified as follows:.

When not present, the value of chroma_cu_qp_delta_subdiv is inferred to be equal to <NUM>.

In this example, for dual tree chroma, if the current chroma CB depth (subdiv) is equal to or smaller than a value for chroma_cu_qp_delta_subdiv, then video encoder <NUM> and video decoder <NUM> may not signal a chroma delta QP.

<FIG> is a block diagram illustrating an example video encoder <NUM> that may perform the techniques of this disclosure. <FIG> is provided for purposes of explanation and should not be considered limiting of the techniques as broadly exemplified and described in this disclosure. For purposes of explanation, this disclosure describes video encoder <NUM> in the context of video coding standards such as the HEVC video coding standard and the H. <NUM> video coding standard in development. However, the techniques of this disclosure are not limited to these video coding standards, and are applicable generally to video encoding and decoding.

In the example of <FIG>, video encoder <NUM> includes video data memory <NUM>, mode selection unit <NUM>, residual generation unit <NUM>, transform processing unit <NUM>, quantization unit <NUM>, inverse quantization unit <NUM>, inverse transform processing unit <NUM>, reconstruction unit <NUM>, filter unit <NUM>, decoded picture buffer (DPB) <NUM>, and entropy encoding unit <NUM>. Any or all of video data memory <NUM>, mode selection unit <NUM>, residual generation unit <NUM>, transform processing unit <NUM>, quantization unit <NUM>, inverse quantization unit <NUM>, inverse transform processing unit <NUM>, reconstruction unit <NUM>, filter unit <NUM>, DPB <NUM>, and entropy encoding unit <NUM> may be implemented in one or more processors or in processing circuitry. Moreover, video encoder <NUM> may include additional or alternative processors or processing circuitry to perform these and other functions.

The various units of <FIG> are illustrated to assist with understanding the operations performed by video encoder <NUM>. The units may be implemented as fixed-function circuits, programmable circuits, or a combination thereof. Fixed-function circuits refer to circuits that provide particular functionality, and are preset on the operations that can be performed. Programmable circuits refer to circuits that can be programmed to perform various tasks, and provide flexible functionality in the operations that can be performed. For instance, programmable circuits may execute software or firmware that cause the programmable circuits to operate in the manner defined by instructions of the software or firmware. Fixed-function circuits may execute software instructions (e.g., to receive parameters or output parameters), but the types of operations that the fixed-function circuits perform are generally immutable. In some examples, the one or more of the units may be distinct circuit blocks (fixed-function or programmable), and in some examples, the one or more units may be integrated circuits.

Video encoder <NUM> may include arithmetic logic units (ALUs), elementary function units (EFUs), digital circuits, analog circuits, and/or programmable cores, formed from programmable circuits. In examples where the operations of video encoder <NUM> are performed using software executed by the programmable circuits, memory <NUM> (<FIG>) may store the object code of the software that video encoder <NUM> receives and executes, or another memory within video encoder <NUM> (not shown) may store such instructions.

Mode selection unit <NUM> includes a motion estimation unit <NUM>, motion compensation unit <NUM>, and an intra-prediction unit <NUM>. Mode selection unit <NUM> may include additional functional units to perform video prediction in accordance with other prediction modes. As examples, mode selection unit <NUM> may include a palette unit, an intra-block copy unit (which may be part of motion estimation unit <NUM> and/or motion compensation unit <NUM>), an affine unit, a linear model (LM) unit, or the like.

Video encoder <NUM> may partition a picture retrieved from video data memory <NUM> into a series of CTUs, and encapsulate one or more CTUs within a slice. Mode selection unit <NUM> may partition a CTU of the picture in accordance with a tree structure, such as the QTBT structure or the quad-tree structure of HEVC described above. As described above, video encoder <NUM> may form one or more CUs from partitioning a CTU according to the tree structure. Such a CU may also be referred to generally as a "video block" or "block.

Motion estimation unit <NUM> may form one or more motion vectors (MVs) that defines the positions of the reference blocks in the reference pictures relative to the position of the current block in a current picture. Motion estimation unit <NUM> may then provide the motion vectors to motion compensation unit <NUM>. For example, for unidirectional inter-prediction, motion estimation unit <NUM> may provide a single motion vector, whereas for bi-directional inter-prediction, motion estimation unit <NUM> may provide two motion vectors. Motion compensation unit <NUM> may then generate a prediction block using the motion vectors. For example, motion compensation unit <NUM> may retrieve data of the reference block using the motion vector. As another example, if the motion vector has fractional sample precision, motion compensation unit <NUM> may interpolate values for the prediction block according to one or more interpolation filters. Moreover, for bi-directional inter-prediction, motion compensation unit <NUM> may retrieve data for two reference blocks identified by respective motion vectors and combine the retrieved data, e.g., through sample-by-sample averaging or weighted averaging.

Mode selection unit <NUM> provides the prediction block to residual generation unit <NUM>. Residual generation unit <NUM> receives a raw, unencoded version of the current block from video data memory <NUM> and the prediction block from mode selection unit <NUM>. Residual generation unit <NUM> calculates sample-by-sample differences between the current block and the prediction block. The resulting sample-by-sample differences define a residual block for the current block. In some examples, residual generation unit <NUM> may also determine differences between sample values in the residual block to generate a residual block using residual differential pulse code modulation (RDPCM). In some examples, residual generation unit <NUM> may be formed using one or more subtractor circuits that perform binary subtraction.

In examples where mode selection unit does not further partition a CU into PUs, each CU may be associated with a luma coding block and corresponding chroma coding blocks. As above, the size of a CU may refer to the size of the luma coding block of the CU. The video encoder <NUM> and video decoder <NUM> may support CU sizes of 2Nx2N, 2NxN, or Nx2N.

For other video coding techniques such as an intra-block copy mode coding, an affine-mode coding, and linear model (LM) mode coding, as few examples, mode selection unit <NUM>, via respective units associated with the coding techniques, generates a prediction block for the current block being encoded. In some examples, such as palette mode coding, mode selection unit <NUM> may not generate a prediction block, and instead generate syntax elements that indicate the manner in which to reconstruct the block based on a selected palette. In such modes, mode selection unit <NUM> may provide these syntax elements to entropy encoding unit <NUM> to be encoded.

Quantization unit <NUM> may quantize the transform coefficients in a transform coefficient block, to produce a quantized transform coefficient block. Quantization unit <NUM> may quantize transform coefficients of a transform coefficient block according to a quantization parameter (QP) value associated with the current block. Video encoder <NUM> (e.g., via mode selection unit <NUM>) may adjust the degree of quantization applied to the transform coefficient blocks associated with the current block by adjusting the QP value associated with the CU. Quantization may introduce loss of information, and thus, quantized transform coefficients may have lower precision than the original transform coefficients produced by transform processing unit <NUM>.

Filter unit <NUM> may perform one or more filter operations on reconstructed blocks. For example, filter unit <NUM> may perform deblocking operations to reduce blockiness artifacts along edges of CUs. Operations of filter unit <NUM> may be skipped, in some examples.

Video encoder <NUM> stores reconstructed blocks in DPB <NUM>. For instance, in examples where operations of filter unit <NUM> are not performed, reconstruction unit <NUM> may store reconstructed blocks to DPB <NUM>. In examples where operations of filter unit <NUM> are performed, filter unit <NUM> may store the filtered reconstructed blocks to DPB <NUM>. Motion estimation unit <NUM> and motion compensation unit <NUM> may retrieve a reference picture from DPB <NUM>, formed from the reconstructed (and potentially filtered) blocks, to inter-predict blocks of subsequently encoded pictures. In addition, intra-prediction unit <NUM> may use reconstructed blocks in DPB <NUM> of a current picture to intra-predict other blocks in the current picture.

In some examples, operations performed with respect to a luma coding block need not be repeated for the chroma coding blocks. As one example, operations to identify a motion vector (MV) and reference picture for a luma coding block need not be repeated for identifying a MV and reference picture for the chroma blocks. Rather, the MV for the luma coding block may be scaled to determine the MV for the chroma blocks, and the reference picture may be the same. As another example, the intra-prediction process may be the same for the luma coding block and the chroma coding blocks.

Video encoder <NUM> represents an example of a device configured to encode video data including a memory configured to store video data, and one or more processing units implemented in circuitry and configured to perform the chroma delta QP signaling techniques described herein. Video encoder <NUM> may, for example, generate for inclusion in a bitstream of encode video data the syntax elements chroma_cu_qp_delta_abs and chroma_cu_qp_delta_sign_flag, as described above.

<FIG> is a block diagram illustrating an example video decoder <NUM> that may perform the techniques of this disclosure. <FIG> is provided for purposes of explanation and is not limiting on the techniques as broadly exemplified and described in this disclosure. For purposes of explanation, this disclosure describes video decoder <NUM> according to the techniques of JEM, VVC, and HEVC. However, the techniques of this disclosure may be performed by video coding devices that are configured to other video coding standards.

In the example of <FIG>, video decoder <NUM> includes coded picture buffer (CPB) memory <NUM>, entropy decoding unit <NUM>, prediction processing unit <NUM>, inverse quantization unit <NUM>, inverse transform processing unit <NUM>, reconstruction unit <NUM>, filter unit <NUM>, and decoded picture buffer (DPB) <NUM>. Any or all of CPB memory <NUM>, entropy decoding unit <NUM>, prediction processing unit <NUM>, inverse quantization unit <NUM>, inverse transform processing unit <NUM>, reconstruction unit <NUM>, filter unit <NUM>, and DPB <NUM> may be implemented in one or more processors or in processing circuitry. Moreover, video decoder <NUM> may include additional or alternative processors or processing circuitry to perform these and other functions.

Prediction processing unit <NUM> includes motion compensation unit <NUM> and intra-prediction unit <NUM>. Prediction processing unit <NUM> may include addition units to perform prediction in accordance with other prediction modes. As examples, prediction processing unit <NUM> may include a palette unit, an intra-block copy unit (which may form part of motion compensation unit <NUM>), an affine unit, a linear model (LM) unit, or the like. In other examples, video decoder <NUM> may include more, fewer, or different functional components.

CPB memory <NUM> may store video data, such as an encoded video bitstream, to be decoded by the components of video decoder <NUM>. The video data stored in CPB memory <NUM> may be obtained, for example, from computer-readable medium <NUM> (<FIG>). CPB memory <NUM> may include a CPB that stores encoded video data (e.g., syntax elements) from an encoded video bitstream. Also, CPB memory <NUM> may store video data other than syntax elements of a coded picture, such as temporary data representing outputs from the various units of video decoder <NUM>. DPB <NUM> generally stores decoded pictures, which video decoder <NUM> may output and/or use as reference video data when decoding subsequent data or pictures of the encoded video bitstream. CPB memory <NUM> and DPB <NUM> may be formed by any of a variety of memory devices, such as DRAM, including SDRAM, MRAM, RRAM, or other types of memory devices. CPB memory <NUM> and DPB <NUM> may be provided by the same memory device or separate memory devices. In various examples, CPB memory <NUM> may be on-chip with other components of video decoder <NUM>, or off-chip relative to those components.

Additionally or alternatively, in some examples, video decoder <NUM> may retrieve coded video data from memory <NUM> (<FIG>). That is, memory <NUM> may store data as discussed above with CPB memory <NUM>. Likewise, memory <NUM> may store instructions to be executed by video decoder <NUM>, when some or all of the functionality of video decoder <NUM> is implemented in software to be executed by processing circuitry of video decoder <NUM>.

The various units shown in <FIG> are illustrated to assist with understanding the operations performed by video decoder <NUM>. The units may be implemented as fixed-function circuits, programmable circuits, or a combination thereof. Similar to <FIG>, fixed-function circuits refer to circuits that provide particular functionality, and are preset on the operations that can be performed. Programmable circuits refer to circuits that can be programmed to perform various tasks, and provide flexible functionality in the operations that can be performed. For instance, programmable circuits may execute software or firmware that cause the programmable circuits to operate in the manner defined by instructions of the software or firmware. Fixed-function circuits may execute software instructions (e.g., to receive parameters or output parameters), but the types of operations that the fixed-function circuits perform are generally immutable. In some examples, the one or more of the units may be distinct circuit blocks (fixed-function or programmable), and in some examples, the one or more units may be integrated circuits.

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

Filter unit <NUM> may perform one or more filter operations on reconstructed blocks. For example, filter unit <NUM> may perform deblocking operations to reduce blockiness artifacts along edges of the reconstructed blocks. Operations of filter unit <NUM> are not necessarily performed in all examples.

Video decoder <NUM> may store the reconstructed blocks in DPB <NUM>. As discussed above, DPB <NUM> may provide reference information, such as samples of a current picture for intra-prediction and previously decoded pictures for subsequent motion compensation, to prediction processing unit <NUM>. Moreover, video decoder <NUM> may output decoded pictures from DPB <NUM> for subsequent presentation on a display device, such as display device <NUM> of <FIG>.

In this manner, video decoder <NUM> represents an example of a video decoding 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. Video decoder <NUM> may, for example, decode and parse the syntax elements chroma_cu_qp_delta_abs and chroma cu_qp_delta_sign_flag, as described above.

Entropy decoding unit <NUM> may, for example, receive, in a bitstream of encoded video data, first syntax indicating a luma delta QP value for the luma component and second syntax indicating a chroma delta QP value for the chroma component. Inverse quantization unit <NUM> may, for example, determine a predicted luma quantization parameter (QP) for a luma component of a coding unit; 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 coding unit; determine a QP value for the chroma component based on the predicted chroma QP and the chroma delta QP value; dequantize a block of luma transform coefficients based on the QP value for the luma component; and dequantize a block of chroma transform coefficients based on the QP value of the chroma component. Video decoder <NUM> can decode the coding unit based on the dequantized block of luma transform coefficients and the dequantized block of chroma transform coefficients.

<FIG> is a flowchart illustrating an example method for encoding a current block. The current block may comprise a current CU. Although described with respect to video encoder <NUM> (<FIG> and <FIG>), it should be understood that other devices may be configured to perform a method similar to that of <FIG>.

In this example, video encoder <NUM> initially predicts the current block (<NUM>). For example, video encoder <NUM> may form a prediction block for the current block. Video encoder <NUM> may then calculate a residual block for the current block (<NUM>). To calculate the residual block, video encoder <NUM> may calculate a difference between the original, unencoded block and the prediction block for the current block. Video encoder <NUM> may then transform and quantize coefficients of the residual block (<NUM>). Video encoder <NUM> may, for example, signal QP values for luma components and chroma components of the video data using techniques described above. Next, video encoder <NUM> may scan the quantized transform coefficients of the residual block (<NUM>). During the scan, or following the scan, video encoder <NUM> may entropy encode the coefficients (<NUM>). For example, video encoder <NUM> may encode the coefficients using CAVLC or CABAC. Video encoder <NUM> may then output the entropy coded data of the block (<NUM>).

<FIG> is a flowchart illustrating an example method for decoding a current block of video data. The current block may comprise a current CU. Although described with respect to video decoder <NUM> (<FIG> and <FIG>), it should be understood that other devices may be configured to perform a method similar to that of <FIG>.

Video decoder <NUM> may receive entropy coded data for the current block, such as entropy coded prediction information and entropy coded data for coefficients of a residual block corresponding to the current block (<NUM>). Video decoder <NUM> may entropy decode the entropy coded data to determine prediction information for the current block and to reproduce coefficients of the residual block (<NUM>). Video decoder <NUM> may predict the current block (<NUM>), e.g., using an intra- or inter-prediction mode as indicated by the prediction information for the current block, to calculate a prediction block for the current block. Video decoder <NUM> may then inverse scan the reproduced coefficients (<NUM>), to create a block of quantized transform coefficients. Video decoder <NUM> may then inverse quantize and inverse transform the coefficients to produce a residual block (<NUM>). Video decoder <NUM> may, for example, receive syntax elements indicating QP values for luma components and chroma components of the video data using techniques described above. Video decoder <NUM> may ultimately decode the current block by combining the prediction block and the residual block (<NUM>).

In this example, video encoder <NUM> determines a QP value for a luma component of a coding unit of the video data (<NUM>). Video encoder <NUM> may quantize a block of luma transform coefficients based on the QP value for the luma component of the coding unit. To signal the QP value for the luma component of the coding unit, video encoder <NUM> determines a predicted luma QP for the luma component of the coding unit (<NUM>). Video encoder <NUM> determines a delta QP value for the luma component of the coding unit based on the QP value for the luma component and the predicted luma QP (<NUM>). Video encoder <NUM> generates, for inclusion in a bitstream of encoded video data, first syntax indicating the delta QP value for the luma component of the coding unit (<NUM>).

Video encoder <NUM> determines a QP value for a chroma component of the coding unit of the video data (<NUM>). Video encoder <NUM> may quantize a block of chroma transform coefficients based on the QP value of the chroma component of the coding unit. To signal the QP value for the chroma component of the coding unit, video encoder <NUM> determines a predicted chroma QP for the chroma component of the coding unit (<NUM>). Video encoder <NUM> determines a delta QP value for the chroma component of the coding unit based on the QP value for the chroma component and the predicted chroma QP (<NUM>).

In some examples, a CTU that includes the coding unit may be partitioned using a single tree structure, such that a luma component of the CTU and a chroma component of the CTU have a same partitioning. In other examples, a CTU that includes the coding unit may be partitioned using a dual tree structure, such that a luma component of the CTU and a chroma component of the CTU have a different partitioning. If the CTU that includes the coding unit is partitioned using a dual tree structure, video encoder <NUM> may be configured to determine a maximum chroma delta QP signaling depth for the chroma component of the CTU; determine that the coding unit and at least one other coding unit belong to a split node of the chroma component of the CTU; in response to the maximum chroma delta QP signaling depth corresponding to the split node, determine a QP value for a chroma component of the at least one other coding unit to be equal to the QP value for the chroma component of the coding unit; and quantize a block of chroma transform coefficients for the at least one other CU based on the QP value for the chroma component of the at least one other coding unit.

Video encoder <NUM> generates, for inclusion in the bitstream of the encoded video data, second syntax indicating the delta QP value for the chroma component of the coding unit (<NUM>). In some examples, video encoder <NUM> may generate, for inclusion in the bitstream of encoded video data, the second syntax indicating the chroma delta QP value for the chroma component in response to determining that signaling of chroma delta QP values is enabled for the coding unit. The second syntax may, for example, include a syntax element indicating an absolute value of the chroma delta QP value and a syntax element indicating a sign for the chroma delta QP value.

Video encoder <NUM> outputs, in the bitstream of encoded video data, the first syntax and the second syntax (<NUM>). Video encoder <NUM> may also output, in the bitstream of encoded video data, syntax indicating values for the quantized block of luma transform coefficients and the quantized block of chroma transform coefficients.

Video encoder <NUM> may also determine a second QP value for a second chroma component of the coding unit; determine a second predicted chroma QP for the second chroma component of the coding unit; based on the second QP value for the second chroma component and the second predicted chroma QP, determine a second delta QP value for the second chroma component; generating, for inclusion in the bitstream of the encoded video data, third syntax indicating the second delta QP value for the second chroma component; and output, in the bitstream of encoded video data, the third syntax.

Video decoder <NUM> determines a predicted luma QP for a luma component of a coding unit (<NUM>). Video decoder <NUM> may, for example, determine the predicted luma QP based on the QPs of neighboring CUs using any of the techniques described above.

Video decoder <NUM> receives, in the bitstream of encoded video data, first syntax indicating a luma delta QP value for the luma component (<NUM>). The first syntax may, for example, include a syntax element that indicates an absolute value of the luma delta QP value and a syntax element that indicates a sign for the luma delta QP value. Video decoder <NUM> determines a QP value for the luma component based on the predicted luma QP and the luma delta QP value (<NUM>). Video decoder <NUM> may, for example, add the luma delta QP value to a value of the predicted luma QP to determine the QP value for the luma component of the coding unit.

Video decoder <NUM> determines a predicted chroma QP for a chroma component of the coding unit (<NUM>). Video decoder <NUM> may, for example, determine the predicted chroma QP based on the QPs of neighboring CUs using any of the techniques described above. Video decoder <NUM> receives, in the bitstream of encoded video data, second syntax indicating a chroma delta QP value for the chroma component of the coding unit.

Video decoder <NUM> may, for example, receive, in the bitstream of encoded video data, the second syntax indicating the chroma delta QP value for the chroma component in response to determining that signaling of chroma delta QP values is enabled for the coding unit. The second syntax may, for example, include a syntax element that indicates an absolute value of the chroma delta QP value and a syntax element that indicates a sign for the chroma delta QP value.

In some examples, the CTU that include the coding unit may be partitioned using a single tree structure, such that a luma component of the CTU and a chroma component of the CTU have a same partitioning. In other examples, a CTU that includes the coding unit may be partitioned using a dual tree structure, such that a luma component of the CTU and a chroma component of the CTU have a different partitioning. In examples, where the luma component of the CTU and the chroma component of the CTU have a different partitioning, then to receive the second syntax indicating the chroma delta QP value for the chroma component, video decoder <NUM> may, for example, determine a maximum chroma delta QP signaling depth for the chroma component of the CTU; determine that the coding unit and at least one other coding unit belong to a split node of the chroma component of the CTU; in response to the maximum chroma delta QP signaling depth corresponding to the split node, determine a QP value for a chroma component of the at least one other coding unit based on the chroma delta QP value; and dequantize a block of chroma transform coefficients for the at least one other CU based on the QP value for the chroma component of the at least one other coding unit.

Video decoder <NUM> determines a QP value for the chroma component of the coding unit based on the predicted chroma QP and the chroma delta QP value (<NUM>). Video decoder <NUM> may, for example, add the chroma delta QP value to a value of the predicted chroma QP to determine the QP value for the chroma component of the coding unit.

Video decoder <NUM> dequantizes a block of luma transform coefficients for the coding unit based on the QP value for the luma component (<NUM>) and dequantizes a block of chroma transform coefficients for the coding unit based on the QP value of the chroma component (<NUM>). Video decoder <NUM> decodes the coding unit based on the dequantized block of luma transform coefficients and the dequantized block of chroma transform coefficients (<NUM>).

To decode the coding unit based on the dequantized block of luma transform coefficients and the dequantized block of chroma transform coefficients, video decoder <NUM> may inverse transform the dequantized block of luma transform coefficients to determine a luma residual block; inverse transform the dequantized block of chroma transform coefficients to determine a chroma residual block; determine a luma prediction block; determine a chroma prediction block; adding the luma residual block to the luma prediction block to determine a reconstructed luma block of the coding unit; and add the chroma residual block to the chroma prediction block to determine a reconstructed chroma block of the coding unit.

Video decoder <NUM> may also determine a second predicted chroma QP for a second chroma component of the coding unit; receive, in the bitstream of encoded video data, third syntax indicating a second chroma delta QP value for the second chroma component of the coding unit; determine a second QP value for the second chroma component of the coding unit based on the second predicted chroma QP and the second chroma delta QP value; dequantize a second block of chroma transform coefficients for the coding unit based on the second QP value of the second chroma component; and decode the coding unit based on the dequantized second block of chroma transform coefficients.

Combinations of the above should also be included within computer-readable media.

Instructions may be executed by one or more processors, such as one or more digital signal processors (DSPs), general purpose microprocessors, application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or other equivalent integrated or discrete logic circuitry. Accordingly, the terms "processor" and "processing circuitry," as used herein may refer to any of the foregoing structures or any other structure suitable for implementation of the techniques described herein.

Claim 1:
A method of decoding a bitstream of encoded video data, wherein a picture is partitioned into at least one coding tree unit, CTU, comprising a coding unit using a single tree structure, such that a luma component of the at least one CTU and a chroma component of the at least one CTU have a same partitioning, the method comprising:
determining (<NUM>) a predicted luma quantization parameter, QP, for the luma component of the coding unit;
receiving (<NUM>), as part of a transform unit syntax included in the bitstream, first syntax indicating a luma delta QP value for the luma component of the coding unit;
determining (<NUM>) a QP value for the luma component based on the predicted luma QP and the luma delta QP value;
determining (<NUM>) a predicted chroma QP for the chroma component of the coding unit;
receiving (<NUM>), as part of the transform unit syntax included in the bitstream, second syntax indicating a chroma delta QP value for the chroma component of the coding unit, wherein the second syntax is different from the first syntax;
determining (<NUM>) a QP value for the chroma component of the coding unit based on the predicted chroma QP and the chroma delta QP value;
dequantizing (<NUM>) a block of luma transform coefficients for the coding unit based on the QP value for the luma component;
dequantizing (<NUM>) a block of chroma transform coefficients for the coding unit based on the QP value of the chroma component; and
decoding (<NUM>) the coding unit based on the dequantized block of luma transform coefficients and the dequantized block of chroma transform coefficients.