Palette Predictor Update for Screen Content Coding
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Solution Overview
Problem
Current palette coding techniques in HEVC are limited to coding units and do not efficiently utilize sub-blocks or prediction units, leading to suboptimal coding efficiency for screen content materials.
Innovation Solution
The method involves applying palette coding to sub-blocks or prediction units within a coding unit, allowing each sub-block to use its own palette table and enabling more flexible partition modes, such as NxN, 2NxM, and asymmetric partitions, while skipping quantization matrices when residuals are not transformed into the frequency domain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If palette coding is applied to the entire coding unit, then coding efficiency is improved, but prediction accuracy is insufficient due to lack of local adaptation
Solution Approach 1:
The patent divides the coding unit into multiple sub-blocks, with each sub-block having its own palette table and prediction parameters. This segmentation allows local adaptation to different color distributions within the coding unit, improving prediction accuracy while maintaining overall coding efficiency through parallel processing of sub-blocks.
Solution Approach 2:
The patent applies different palette tables and prediction modes to different sub-blocks based on their local color characteristics. Each sub-block can use its own optimized palette, allowing the coding system to adapt to local variations in screen content while maintaining high coding efficiency across the entire coding unit.
2Measurement precision
If each sub-block uses its own palette table, then prediction accuracy is improved, but device complexity increases
Solution Approach 1:
The patent merges palette tables from multiple sub-blocks to form a combined palette for the entire coding unit. This reduces the total number of unique colors that need to be encoded in the bitstream, simplifying palette management while still allowing each sub-block to use its own optimized palette for prediction, thus balancing prediction accuracy with reduced complexity.
3Reliability
If quantization matrices are always applied, then coding completeness is maintained, but bitstream size increases unnecessarily for non-transformed residuals
Solution Approach 1:
The patent applies quantization matrices only when residual transformation is performed, and skips quantization when residuals are not transformed. This partial application of quantization avoids unnecessary processing steps and reduces bitstream size while maintaining coding completeness for cases where transformation is beneficial, effectively removing excessive actions that do not contribute to coding performance.
Data Source
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AI summary
A method of palette coding to apply the palette coding to sub-blocks of a coding unit and to allow each sub-block to use an individual palette table is disclosed. If the current coding block is not partitioned, the palette coding is applied to the current coding block using a first palette. If the current coding block is partitioned into multiple sub-blocks, the palette coding is applied to each sub-block using an individual second palette. Each sub-block may correspond to one prediction unit (PU). In another embodiment of the present invention, a method is disclosed that skips update of palette predictor such as last coded palette table, last coded palette size and palette predictor size associated with the current coding block if the current palette size is smaller than or equal to palette update size.