Palette Coding for Non-444 Video Formats
Solution Overview
Problem
Existing palette coding techniques are designed for 4:4:4 color formats and do not efficiently handle non-444 color formats, where chroma samples have reduced spatial resolution, leading to suboptimal coding performance.
Innovation Solution
The method involves converting non-444 video data to 4:4:4 format, using multiple palette tables for luma and chroma components, and signaling palette prediction and sharing flags separately for each component, allowing for improved palette coding in 4:2:0 and 4:2:2 formats by padding chroma samples to match luma resolution and using distinct palette tables for each component.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single palette table is used for all color components in non-444 format, then device complexity is reduced, but coding efficiency deteriorates due to mismatched chroma resolution
Solution Approach 1:
The patent divides the single palette table into separate component-specific palette tables: one for luma (Y) component and another for chroma (CbCr) components. This segmentation allows each palette to be optimized for its specific color component's resolution characteristics, with the luma palette matching full resolution and chroma palette matching subsampled resolution in non-444 formats.
Solution Approach 2:
The patent applies different palette structures to different spatial locations and color components. Specifically, the luma component uses a full-resolution palette while the chroma component uses a subsampled-resolution palette appropriate to its sampling rate (4:2:0 or 4:2:2). This local quality adaptation resolves the contradiction by optimizing each component's representation according to its specific requirements.
2Quantity of substance
If chroma samples are subsampled in non-444 format, then bit rate is reduced, but measurement precision of color information deteriorates
Solution Approach 1:
The patent creates a virtual full-resolution chroma palette by copying and interpolating subsampled chroma samples to match luma resolution during palette derivation. This copying process allows the encoder to work with a full-resolution palette structure while the actual chroma data remains subsampled, thus maintaining bit rate efficiency while improving the precision of color representation in the palette.
Data Source
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AI summary
A method of video coding using palette coding mode for color video in a non-444 color format is disclosed. The non-444 video data can be converted to the 444 format so that the palette designed for the 444 format can be used for the non-444 video data. For the 4:2:0 color format, each chroma sample collocated with corresponding quad luma samples is padded with three chroma samples to form converted quad chroma samples. For the 4:2:0 color format, if a current pixel does not belong to the color palette, one or more escape values are signaled for the current pixel and the escape value associated with the chroma sample of the current pixel for each color component is not signaled for three of the quad chroma sample locations collocated with corresponding quad luma samples.