Intra Prediction Mode Derivation for Lower-Bit Video Coding
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Solution Overview
Problem
Existing video coding standards like VVC face challenges in efficiently signaling intra prediction modes, particularly when they are not in the Most Probable Modes (MPM) list, leading to increased data requirements and reduced coding efficiency.
Innovation Solution
Implement Decoder Side Intra Mode Derivation (DIMD) and Template-based Intra Mode Derivation (TIMD) to derive and signal intra prediction modes, partition modes into groups, and include derived modes in the MPM list, reducing the number of candidates for remaining modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If intra prediction modes are signaled directly without derivation, then the signaling process is simple, but the number of bits required increases and coding efficiency decreases
Solution Approach 1:
The decoder derives intra prediction modes autonomously using template matching and gradient calculations on previously decoded samples, eliminating the need for encoder-side mode selection and signaling. This self-service approach reduces bit rate while maintaining prediction accuracy.
Solution Approach 2:
The system performs preliminary template matching and gradient calculations on reconstructed samples before actual prediction, pre-computing candidate modes that are then used to reduce the search space and minimize signaling requirements.
2Measurement precision
If all intra angular prediction modes are considered as candidates, then prediction accuracy is maximized, but the number of modes to be signaled increases data requirements
Solution Approach 1:
The 65 intra angular prediction modes are segmented into multiple groups based on gradient directions and template matching results. Only the most probable groups are signaled, reducing data requirements while maintaining prediction accuracy through selective mode consideration.
Solution Approach 2:
The system changes the parameter representation by deriving modes from gradient calculations and template matching rather than directly signaling mode indices. This transformation reduces the number of bits required to represent prediction modes while preserving accuracy.
3Productivity
If MPM list is used for intra prediction modes, then signaling efficiency is improved, but modes not in the MPM list still require additional data
Solution Approach 1:
The decoder derives remaining modes that are not in the MPM list using template matching and gradient calculations, eliminating the need to signal these modes explicitly. This self-service mechanism further reduces bit rate while maintaining comprehensive mode coverage.
Solution Approach 2:
Template matching and gradient calculations serve as intermediaries between the MPM list and remaining modes, providing a bridge that allows the decoder to derive accurate prediction modes without requiring additional signaling for non-MPM modes.
Data Source
AI summary
Methods and apparatus for video coding. When a current intra angular prediction mode for the current block is not in the MPM list, a mode syntax related to a current intra prediction mode for the current block is signalled or parsed depending on first information derived according to DIMD or TIMD. A final intra predictor is generated based on second information comprising the first information and the mode syntax. The current block is encoded or decoded using a final mode derived based on information comprising the syntax.