4:4:4 Video Decoding Using ACT and LMCS for Chroma Redundancy
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Solution Overview
Problem
Existing video coding technologies face challenges in efficiently encoding and decoding high-fidelity video data in 4:4:4 chroma format due to inherent redundancies, which affect compression efficiency, particularly in applications requiring sharp edge preservation.
Innovation Solution
Implementing adaptive color-space transform (ACT) with luma mapping and chroma scaling (LMCS) to decode video data by applying inverse ACT and inverse luma mapping, and optionally using block differential pulse coded modulation (BDPCM) based on syntax elements in the bitstream.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If 4:4:4 chroma format is used to preserve color information and sharp edges, then image quality is improved, but compression efficiency deteriorates due to increased data redundancy
Solution Approach 1:
The patent transforms the coding approach by changing the color space parameters from traditional YCbCr to YCgCo color space. This parameter transformation allows better exploitation of correlations among color components in 4:4:4 format, enabling improved compression efficiency while maintaining the high image quality required by the format
Solution Approach 2:
The patent applies different processing strategies to different components locally. By separately processing luma and chroma components with component-specific prediction and transform techniques, the method optimizes compression for each component type while preserving the overall image quality in 4:4:4 format
2Productivity
If adaptive color-space transform with luma mapping and chroma scaling is applied, then compression performance is improved, but device complexity increases
Solution Approach 1:
The patent performs luma mapping and chroma scaling as preliminary actions before the main transform and quantization steps. By pre-processing the chroma components based on luma values, the method reduces the complexity of subsequent processing stages while improving overall compression performance
Solution Approach 2:
The patent introduces luma mapping as an intermediary step that mediates between the luma and chroma components. This intermediary processing allows the chroma components to be scaled according to luma values, creating a more efficient representation that reduces complexity in the transform stage
Data Source
AI summary
An electronic apparatus performs a method of decoding video data, comprising: receiving, from bitstream, a first syntax element in a slice header of a slice that indicates whether luma mapping with chroma scaling (LMCS) is applied to a coding unit in the slice; receiving a second syntax element for the coding unit that indicates whether the coding unit has been coded using adaptive color-space transform (ACT); if the second syntax element has a non-zero value, decoding the coding unit by applying inverse ACT to convert luma and chroma residuals of the coding unit from a transformed color space to an original color space of the video data; and if the first syntax element has a non-zero value, decoding the coding unit by performing inverse luma mapping to the luma samples and inverse scaling to the chroma residuals of the coding unit after performing the inverse ACT.