Adaptive Transform Selection for Video Coding
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Solution Overview
Problem
Current video coding standards, such as HEVC, rely heavily on DCT and DST-VII transforms, which may not optimally match the characteristics of Intra-predicted residual signals, leading to suboptimal energy compaction and coding performance.
Innovation Solution
Adaptive use of alternative transforms like DCT-IV and DST-IV, applied selectively based on block size, to improve energy compaction and reduce implementation complexity, with DCT-IV or DST-IV applied only to Intra-predicted residuals, and a flag used to signal the selected transform at various coding levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If DCT and DST-VII transforms are used for all block sizes, then implementation is simple and consistent, but coding performance is suboptimal for Intra-predicted residual signals
Solution Approach 1:
The patent introduces dynamic adaptability by allowing the transform type to vary based on block size and prediction mode. Specifically, DCT-IV and DST-IV are introduced as alternative transforms that can be selectively applied to Intra-predicted residuals of certain block sizes, making the transform selection dynamic rather than static. This resolves the contradiction by maintaining simple DCT/DST-VII for general cases while enabling performance-optimized alternative transforms when beneficial.
Solution Approach 2:
The patent changes the transform type parameter based on signal characteristics (Intra-prediction mode and block size). By introducing transform type as a variable parameter that can be selected from {DCT, DST-VII, DCT-IV, DST-IV} depending on the specific coding context, the system achieves both implementation simplicity (through standardized transform families) and coding performance (through adaptive selection).
2Manufacturing precision
If multiple alternative transforms are applied to all block sizes, then energy compaction improves, but implementation complexity increases
Solution Approach 1:
The patent applies the local quality principle by restricting the application of alternative transforms (DCT-IV, DST-IV) to specific local conditions: only for Intra-predicted residuals and only for certain block sizes. This localized application ensures that the complexity increase is minimal and only incurred where it provides benefit, rather than applying complex transforms universally. The transform selection becomes context-dependent, optimizing energy compaction locally without globally increasing complexity.
Solution Approach 2:
The patent employs partial action by applying alternative transforms only to a subset of transform units (those with Intra-prediction and specific block sizes) rather than all transform units. This partial application achieves energy compaction improvement where needed while avoiding the excessive complexity that would result from universal application of multiple transform types.
3Manufacturing precision
If TU splitting is enabled for optimization, then coding performance improves, but encoder complexity and computation time increase
Solution Approach 1:
The patent extracts the transform type selection from the TU splitting decision process. By making transform type selection independent of TU splitting (i.e., transform type is determined by block size and prediction mode, not by whether splitting occurs), the patent removes one layer of complexity from the encoder optimization process. This extraction allows TU splitting decisions to focus solely on rate-distortion optimization without the additional burden of simultaneous transform type selection.
Data Source
AI summary
A method and apparatus of adaptive image and video coding including an alternative transform other than the discrete cosine transform (DCT) and discrete sine transform (DST) type VII (DST-VII) are disclosed. For at least one block size belonging to the size group, a transform from multiple transforms comprising an alternative transform in addition to DCT and DST-VII is selected and applied to a current block. The alternative transform may correspond to DCT type IV (DCT-IV) or DST type IV (DST-IV).