Image Decoding Transform Control for MTS and Secondary Transform
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Solution Overview
Problem
The combination of secondary transform and Multiple Transform Selection (MTS) results in insufficient performance, particularly when implicit MTS is used, leading to a loss of implicit MTS performance.
Innovation Solution
An image decoding apparatus that enables separate vertical and horizontal transforms for transform units, disabling implicit transform when secondary transform is enabled and certain conditions are not met, and deriving transform types based on TU dimensions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If secondary transform is combined with implicit MTS, then transform performance should be improved, but implicit MTS performance is lost
Solution Approach 1:
The patent applies different transform strategies to different transform units based on local characteristics. When secondary transform is enabled, implicit MTS is disabled for those specific TUs, while explicit MTS can still be applied selectively. This local differentiation resolves the contradiction by allowing secondary transform to take effect where needed without completely losing implicit MTS capabilities in other regions.
Solution Approach 2:
The patent introduces dynamic control over transform mode selection through flags and conditions. The system can dynamically switch between implicit MTS, explicit MTS, and secondary transform based on picture parameters, transform unit characteristics, and enabled features. This dynamic approach allows the system to adapt to different coding scenarios and maintain performance across varying conditions.
2Adaptability or versatility
If separate vertical and horizontal transforms are applied, then transform flexibility is improved, but processing complexity increases
Solution Approach 1:
The patent segments the transform process into independent vertical and horizontal transform stages. Each stage can be controlled separately through transform type parameters, allowing selective application of different transform types (DCT, DST, DFT) in each direction. This segmentation provides flexibility to adapt to different block characteristics while managing complexity through modular processing.
Solution Approach 2:
The patent creates a universal transform framework that can handle multiple transform types (DCT, DST, DFT) and multiple modes (implicit MTS, explicit MTS, secondary transform) through a unified interface. The same transform processing unit can perform different transform operations based on input parameters, reducing the need for separate dedicated hardware for each transform type and thereby managing complexity.
Data Source
AI summary
There is a problem in that implicit MTS performance is lost in a case that the implict MTS is combined with secondary transform. The present invention provides an image decoding apparatus that can more preferably apply transform by MTS and secondary transform. A video decoding apparatus includes: a second transformer configured to apply transform using a transform matrix to the transform coefficient to modify the transform coefficient in a case that secondary transform is enabled; a first transformer configured to apply separate transform including vertical transform and horizontal transform to the transform coefficient; and an implicit transform configuration unit configured to disable implicit transform in a case that the secondary transform is enabled, an intra subpartition mode is not used, and subblock transform is not used, and configured to derive a horizontal transform type according to a width of a target TU and derive a vertical transform type according to a height of the target TU in a case that the implicit transform is enabled. The first transformer performs transform according to the vertical transform type, and transform according to the horizontal transform type.