Video Encoder Transform Selection and Signaling Optimization
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Solution Overview
Problem
Current video coding systems face challenges in improving coding efficiency and reducing complexity, particularly with the use of Enhanced Multiple Transforms (EMT) and Non-Separable Secondary Transforms (NSST), as they increase encoding complexity and bit rate due to complex signalling requirements.
Innovation Solution
The method involves selecting reduced transform sets based on block size thresholds to reduce the number of transform candidates, conditionally signalling EMT and NSST indices based on the number of non-zero coefficients, and applying size-dependent transforms to optimize transform selection for EMT and NSST processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If Enhanced Multiple Transforms (EMT) and Non-Separable Secondary Transforms (NSST) are applied to improve coding efficiency, then compression performance is improved, but encoding complexity and bit rate increase due to complex signalling requirements
Solution Approach 1:
The patent applies different transform sets and signalling mechanisms to different block sizes. Small blocks use reduced transform sets with simplified signalling, while larger blocks can utilize full EMT/NSST capabilities. This local differentiation maintains coding efficiency for various block types while reducing overall encoding complexity by avoiding unnecessary complex processing for small blocks.
Solution Approach 2:
The patent dynamically changes transform parameters (transform set selection, signalling presence) based on block size thresholds. By adjusting these parameters adaptively, the system achieves high compression performance when beneficial while reducing complexity when block characteristics don't require advanced transforms.
2Adaptability or versatility
If EMT and NSST indices are always signalled to enable flexible transform selection, then transform adaptability is improved, but bit rate increases due to additional side information
Solution Approach 1:
The patent extracts and removes unnecessary signalling information for small blocks by using reduced transform sets. Instead of always signalling full EMT/NSST indices, the system selectively omits this side information when block size makes advanced transforms unnecessary, thereby reducing bit rate while maintaining adaptability for larger blocks where full transform selection is beneficial.
Solution Approach 2:
The patent applies partial signalling action by providing full transform index signalling only when needed (for larger blocks), and using reduced or implicit signalling for smaller blocks. This partial approach avoids excessive bit rate consumption while maintaining sufficient transform adaptability for blocks that require it.
3Device complexity
If reduced transform sets are used for small blocks to reduce complexity, then encoding complexity is reduced, but coding efficiency may be compromised
Solution Approach 1:
The patent applies partial transform processing to small blocks by using reduced transform sets that provide sufficient coding efficiency for their size characteristics without the full computational overhead of complete EMT/NSST. This partial approach maintains adequate compression performance for small blocks while significantly reducing encoding complexity.
Solution Approach 2:
The patent applies different quality levels of transform processing to different block sizes. Small blocks receive simplified reduced transform sets appropriate to their characteristics, while larger blocks receive full EMT/NSST processing. This local quality differentiation ensures each block type receives appropriate processing complexity to maintain overall coding efficiency.
Data Source
AI summary
A method and apparatus for video coding incorporating enhanced multiple transform (EMT) are disclosed. According to one method, the number of candidates for EMT in the horizontal direction or vertical direction is reduced depending on the current block size. According to another method, an EMT flag, one or more EMT indices or both are signalled only if the total number of non-zero coefficients in at least a part of the 2D coefficient block is greater than a threshold, where the threshold is equal to 1 or larger. A method and apparatus for video coding using non-separable secondary transform (NSST) are disclosed. According to this method, a total number of non-zero first coefficients in a partial block of the 2D coefficient block is determined and used to determine whether to apply the NSST process.