Reference-Block Chroma Prediction for H.266/VVC Coding
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Solution Overview
Problem
The existing video coding standard H.266/VVC has incomplete candidate lists for non-CCLM modes, leading to poor chroma intra prediction and reduced encoding and decoding efficiency.
Innovation Solution
Enhance chroma intra prediction by determining a reference block for a current block, and when a prediction mode of a second color component of the reference block satisfies a condition, use that block to derive a reference intra prediction mode parameter for predicting the second color component.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the CCLM mode is used for chroma intra prediction, then the prediction accuracy is improved, but the device complexity increases due to the need for additional mode selection and parameter calculation
Solution Approach 1:
The patent changes the parameter representation by using a compact 2-bit flag (cclm_mode_flag) to indicate CCLM mode selection instead of maintaining separate complex mode lists. This simplifies the device complexity while preserving the ability to achieve accurate chroma prediction when CCLM is beneficial.
Solution Approach 2:
The patent extracts the CCLM mode selection logic from the complex candidate list management and handles it separately through a dedicated flag. This separates the simple binary decision (use CCLM or not) from the more complex prediction processes, reducing overall device complexity.
2Measurement precision
If more prediction modes are added to the candidate list, then the chroma intra prediction accuracy is improved, but the encoding and decoding efficiency decreases due to increased processing overhead
Solution Approach 1:
The patent applies partial action by only considering CCLM mode in specific scenarios (when cclm_mode_flag indicates so) rather than evaluating all possible prediction modes for every chroma block. This selective approach maintains prediction accuracy where needed while improving overall encoding/decoding efficiency.
Solution Approach 2:
The patent performs preliminary action by pre-determining the cclm_mode_flag based on luma prediction mode and other factors before the actual chroma prediction process. This early decision prevents unnecessary evaluation of CCLM mode in blocks where it would not be beneficial, improving efficiency.
3Device complexity
If the non-CCLM mode candidate list is used, then the device complexity is reduced, but the chroma intra prediction accuracy deteriorates due to incomplete candidate selection
Solution Approach 1:
The patent merges the CCLM mode integration into the existing prediction framework by combining it with the luma prediction mode decision process. This unified approach ensures that CCLM candidates are properly considered without requiring separate complex management, balancing device complexity and prediction accuracy.
Data Source
AI summary
Disclosed in the embodiments of the present application are an encoding method, a decoding method, a code stream, encoders, decoders, and a storage medium. The decoding method comprises: determining a reference block of the current block, wherein the reference block is a neighboring block of the current block; when a prediction mode of a second color component of the reference block meets a first condition, determining a reference intra-frame prediction mode parameter based on the reference block; and determining a predicted value of a second color component of the current block according to the reference intra-frame prediction mode parameter.