CfL Bias Derivation for More Accurate Chroma Prediction
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Solution Overview
Problem
Existing video coding technologies face challenges in efficiently determining chroma samples from luma samples in cross-component intra prediction, leading to suboptimal compression ratios and video quality, particularly in applications with varying distortion tolerance.
Innovation Solution
Applying a bias term in cross-component intra prediction modes, such as CCLM and CCCM, to determine chroma samples based on luma samples using a filter with weighing factors and a nonlinear term, with the bias term being adaptively derived for each coding block.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If cross-component intra prediction is used to determine chroma samples from luma samples, then compression ratio is improved, but video quality deteriorates due to suboptimal prediction accuracy
Solution Approach 1:
The patent applies a bias term to the cross-component intra prediction formula, changing the parameters of the prediction model. This bias term is derived from the difference between luma and chroma sample values in the reference area, allowing the prediction to be adjusted to better match the actual chroma values, thereby improving prediction accuracy while maintaining compression efficiency
Solution Approach 2:
The patent uses feedback by deriving the bias term from the actual difference between luma and chroma samples in the reference area. This feedback mechanism allows the prediction model to learn from the actual data and adjust accordingly, improving the accuracy of chroma sample prediction without significantly increasing complexity
2Manufacturing precision
If a bias term is adaptively derived for each coding block, then prediction accuracy is improved, but device complexity increases
Solution Approach 1:
The bias term is derived automatically from the reference area samples using a standardized formula. The encoder and decoder both perform the same self-service calculation independently, without requiring complex communication or coordination, thus improving accuracy while keeping the complexity manageable and symmetric
Solution Approach 2:
The bias term is derived in advance during the encoding process and can be stored or transmitted efficiently. This preliminary action allows the decoder to use the pre-computed bias term without performing complex real-time calculations, reducing decoding complexity while maintaining prediction accuracy
Data Source
AI summary
The various implementations described herein include methods and systems for coding video. In one aspect, a video bitstream includes distinct coding blocks of a current image frame and signals a cross-component intra prediction mode. A method includes for each distinct coding block, identifying a chroma component, a luma sample co-located with the chroma component, and neighboring luma samples of the luma sample. The method includes deriving a respective bias value based on a set of luma samples within a reference area of the respective coding block, which includes one or more coding blocks that are adjacent to, and decoded prior to, the respective coding block in the current image frame. The method further includes combining the luma sample, the neighboring luma samples, and the respective bias value to generate the chroma component and reconstructing the distinct coding blocks including the chroma component of each distinct coding block.