# US 2024/0205404 A1 · Chroma quantization in video coding

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- Number: US 2024/0205404 A1
- Document ID: US20240205404A1
- Status: Published application
- Kind: A1
- Application number: 18/596,008
- Filed: 2024-03-05
- Published: 2024-06-20
- Earliest claimed: 2013-09-09
- Assignees: Apple Inc.
- Applicants: Apple Inc.
- Inventors: Alexandros Tourapis; Guy Cote
- Web page: https://patentgrep.com/patent/US20240205404A1

## CPC

- H04N 19/124: Quantisation
- H04N 19/126: Details of normalisation or weighting functions, e.g. normalisation matrices or variable uniform quantisers
- H04N 19/13: Adaptive entropy coding, e.g. adaptive variable length coding [AVLC] or context adaptive binary arithmetic coding [CABAC]
- H04N 19/136: Incoming video signal characteristics or properties
- H04N 19/15: by monitoring actual compressed data size at the memory before deciding storage at the transmission buffer
- H04N 19/157: Assigned coding mode, i.e. the coding mode being predefined or preselected to be further used for selection of another element or parameter
- H04N 19/159: Prediction type, e.g. intra-frame, inter-frame or bidirectional frame prediction
- H04N 19/174: the region being a slice, e.g. a line of blocks or a group of blocks
- H04N 19/186: the unit being a colour or a chrominance component
- H04N 19/30: using hierarchical techniques, e.g. scalability (H04N19/63 takes precedence)
- H04N 19/463: by compressing encoding parameters before transmission
- H04N 19/51: Motion estimation or motion compensation
- H04N 19/61: in combination with predictive coding
- H04N 19/70: characterised by syntax aspects related to video coding, e.g. related to compression standards
- H04N 19/86: involving reduction of coding artifacts, e.g. of blockiness
- H04N 19/172: the region being a picture, frame or field
- H04N 19/176: the region being a block, e.g. a macroblock
- H04N 19/96: Tree coding, e.g. quad-tree coding
- H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION

## Abstract

A method of signaling additional chroma QP offset values that are specific to quantization groups is provided, in which each quantization group explicitly specifies its own set of chroma QP offset values. Alternatively, a table of possible sets of chroma QP offset values is specified in the header area of the picture, and each quantization group uses an index to select an entry from the table for determining its own set of chroma QP offset values. The quantization group specific chroma QP offset values are then used to determine the chroma QP values for blocks within the quantization group in addition to chroma QP offset values already specified for higher levels of the video coding hierarchy.

## Claims

### Claim 1

(canceled)

### Claim 2

A apparatus comprising:
one or more processing units; and
memory storing instructions that, when executed, are configured to cause the one or more processing units to perform operations comprising:
receiving, in a bitstream, an encoded group of video pictures, including an encoded first video picture with a hierarchical coding structure having at least a first coding level, a second coding level and a third coding level, the encoded first video picture comprising two or more sets of chroma quantization parameter (QP) offset values at the first coding level and the second coding level, each set of chroma QP offset values providing information about chroma QPs of video units encompassed by one level of the hierarchical coding structure, the encoded first video picture further comprising one or more chroma quantization groups (QGs) at the third coding level;
for a particular chroma QG of the one or more chroma QGs at the third coding level, identifying an additional set of chroma QP offsets, the identifying comprising:
determining, based on information included in the first coding level or the second coding level, a parameter specifying the maximum length of a binary string in the bitstream, and
identifying the additional set of chroma QP offsets using the parameter; and
decoding the encoded first video picture by computing chroma QP values corresponding to the one or more chroma QGs of the encoded first video picture, the decoding comprising, for the particular chroma QG:
selecting the identified additional set of chroma QP offsets, and
computing the chroma QP values corresponding to the particular chroma QG using the selected set of the chroma QP offsets.

### Claim 3 (depends on 2)

The apparatus of claim 2, wherein computing the chroma QP values further comprises combining the chroma QP offsets in the selected set with one or more luma QP values corresponding to the particular chroma QG.

### Claim 4 (depends on 3)

The apparatus of claim 3, wherein at least the particular chroma QG is associated with a plurality of luma QP values, and wherein computing the chroma QP values for the particular chroma QG comprises computing a plurality of different chroma QP values corresponding to the plurality of luma QP values.

### Claim 5 (depends on 3)

The apparatus of claim 3, wherein at least the particular chroma QG is associated with a single luma QP value, and wherein computing the chroma QP values for the particular chroma QG comprises computing a single chroma QP value corresponding to the single luma QP value.

### Claim 6 (depends on 2)

The apparatus of claim 2, wherein receiving in the bitstream the encoded first video picture comprising two or more sets of chroma QP offsets at the first coding level and the second coding level comprises receiving, in the bitstream, first chroma QP offsets corresponding to the first coding level of the encoded first video picture and second chroma QP offsets corresponding to the second coding level of the encoded first video picture, the operations further comprising:
receiving, in the bitstream, third chroma QP offsets corresponding to the third coding level of the encoded first video picture.

### Claim 7 (depends on 6)

The apparatus of claim 6, wherein the first and second coding levels are higher in a hierarchy of coding levels in the hierarchical coding structure compared to the third coding level, and
wherein computing the chroma QP values corresponding to the particular chroma QG comprises using the first chroma QP offsets.

### Claim 8 (depends on 7)

The apparatus of claim 7, wherein computing the chroma QP values corresponding to the one or more chroma QGs of the encoded first video picture comprises computing chroma QP values for the one or more chroma QGs associated with the third coding level of the encoded first video picture using the first chroma QP offsets.

### Claim 9 (depends on 7)

The apparatus of claim 7, wherein the first coding level corresponds to a picture level, the second coding level corresponds to a slice level, and the third coding level corresponds to one of a coding tree unit level, a coding unit level, or a transform unit level, and
wherein computing the chroma QP values corresponding to the particular chroma QG comprises using chroma QP offsets specified in a picture parameter set (PPS) of the encoded first video picture.

### Claim 10 (depends on 2)

The apparatus of claim 2, the operations further comprising:
receiving, in the bitstream, one or more indices corresponding to the one or more chroma QGs of the encoded first video picture; and
selecting, for at least a first chroma QG of the one or more chroma QGs, a chroma QP offset value from the set of chroma QP offset values using an index corresponding to the first chroma QG.

### Claim 11 (depends on 2)

The apparatus of claim 2, wherein the parameter specifying the maximum length of a binary string in the bitstream comprises the cMax parameter used in a binarization process.

### Claim 12 (depends on 11)

The apparatus of claim 11, wherein the encoded first video picture is encoded using Context Adaptive Binary Arithmetic (CABAC) coding.