Luma-Based Chroma Intra Prediction for Flexible Sampling Formats
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Solution Overview
Problem
Current High Efficiency Video Coding (HEVC) systems are not flexible and inefficient for chroma intra prediction when chroma pixels do not correspond to the 4:2:0 sampling format, as they do not adaptively accommodate other chroma sampling formats, leading to ineffective use of luma-based prediction methods.
Innovation Solution
The introduction of a flexible LM-based chroma intra prediction method that supports different chroma sampling formats by using adaptive down-sampling and sub-sampling techniques based on the chroma sampling format, with the addition of a syntax element 'chroma_format_idc' to convey sampling format information, allowing for the selection of appropriate luma pixels for parameter derivation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the existing HEVC chroma intra prediction method is used, then the coding is simple, but it is not flexible and ineffective for non-4:2:0 sampling formats
Solution Approach 1:
The patent introduces dynamic adaptability by making the chroma intra prediction method flexible according to different chroma sampling formats (4:2:0, 4:2:2, 4:4:4). The system dynamically adjusts the prediction approach based on the actual sampling format, transitioning from a static fixed-method approach to a dynamic adaptive one that optimizes performance for each format.
Solution Approach 2:
The patent changes key parameters including the chroma sampling format identification (chroma_format_idc), the selection of luma pixels for parameter derivation, and the prediction calculation formulas. By adjusting these parameters according to the specific sampling format, the system achieves versatility across different formats while maintaining appropriate complexity levels for each case.
2Measurement precision
If luma-based chroma intra prediction is applied, then prediction accuracy improves, but computational complexity increases due to down-sampling and parameter derivation
Solution Approach 1:
The patent applies partial action by selectively using only the necessary luma pixels for parameter derivation based on the chroma sampling format. Instead of using all luma pixels, the method derives parameters from specific subsets (e.g., first above pixel row and second left pixel column for 4:2:0), reducing computational complexity while maintaining prediction accuracy.
Solution Approach 2:
The patent extracts only the essential luma pixels needed for chroma prediction parameter derivation, separating the necessary information from the redundant data. This extraction process reduces the computational burden by focusing only on the critical pixels that contribute to prediction accuracy.
3Manufacturing precision
If down-sampling is applied to match chroma resolution, then luma and chroma alignment is achieved, but potential aliasing occurs
Solution Approach 1:
The patent performs preliminary actions by pre-identifying and selecting the appropriate luma pixels for parameter derivation before the actual prediction process. This preliminary selection ensures proper alignment between luma and chroma samples while avoiding the harmful effects of aliasing by choosing pixels that naturally correspond to chroma sample locations.
Data Source
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AI summary
A method and apparatus for luma-based chroma intra prediction for a current chroma block are disclosed. The chroma intra predictor is derived from reconstructed luma pixels of a current luma block according to the chroma sampling format. Depending on the chroma sampling format, either sub-sampling, down-sampling or no processing is applied to the reconstructed luma pixels in horizontal or vertical direction. The information associated with the chroma sampling format can be incorporated in the sequence parameter set (SPS), the picture parameter set (PPS), the adaptation parameter set (APS) or the slice header of a video bitstream.