Chroma Prediction Direction Derivation for Low-Complexity VVC Decoding
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Solution Overview
Problem
The existing chroma intra prediction modes in Versatile Video Coding (VVC) suffer from high complexity and prediction inaccuracy due to high sequence dependence and reliance on neighboring blocks, with fixed modes like HOR, VER, and 66 being rarely selected, and the use of Direct Mode (DM) failing to account for multiple collocated luma blocks.
Innovation Solution
A method for determining a prediction direction by acquiring a Direct Mode (DM) and deriving an index number based on an offset N and index number M to enhance the DM derived mode, reducing complexity and improving prediction accuracy by incorporating DM derived modes into the candidate list.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Multiple Direct Mode Signaling (MDMS) with 17 candidates is used for chroma intra prediction, then prediction accuracy may be improved, but decoding complexity increases significantly
Solution Approach 1:
The patent extracts only the most relevant prediction modes from the full candidate list. Instead of evaluating all 17 MDMS candidates, it selectively uses DM derived modes (DM+N and DM-N) along with a limited set of other modes, reducing the candidate list size while maintaining prediction accuracy for chroma blocks.
Solution Approach 2:
The patent segments the prediction mode selection process by creating different candidate lists for different block types. For chroma blocks, it uses a specialized candidate list focused on DM derived modes, while other block types can use different mode selections, allowing optimized processing for each case.
2Device complexity
If fixed modes (HOR, VER, 66) are used as default candidates for angular DM, then decoding complexity is reduced, but prediction accuracy deteriorates due to high sequence dependence
Solution Approach 1:
The patent replaces static fixed modes with dynamic DM derived modes that adapt to the actual DM value. Instead of always using HOR (18), VER (50), or 66, the system calculates DM+N and DM-N based on the actual DM, creating a dynamic candidate list that adapts to each block's characteristics while maintaining low complexity through the simple offset calculation.
3Device complexity
If only local texture feature of chroma block is used in DM, then decoding complexity is low, but prediction accuracy is insufficient when chroma block corresponds to multiple collocated luma blocks
Solution Approach 1:
The patent makes the DM derived modes universally applicable to chroma blocks regardless of the number of collocated luma blocks. The DM+N and DM-N modes work for both single-luma-block and multi-luma-block scenarios, eliminating the need for separate handling while maintaining prediction accuracy through the adaptive offset approach.
Data Source
AI summary
Provided are a method for determining a prediction direction, a decoder and a computer storage medium. The method is implemented by a decoder. The method includes that: a Direct Mode (DM) in a chroma intra prediction mode of a block to be decoded is acquired (S101); and an index number of a prediction direction in a DM derived mode is determined based on an offset N and an index number M of a prediction direction in the DM to determine the DM derived mode (S102).