Flexible Transform Tree Structure for Video Coding Efficiency
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Solution Overview
Problem
Existing video coding technologies face challenges with non-square transform blocks, particularly in HEVC, where the use of non-square predictive blocks can reduce compression performance due to changes in total energy and increased normalization factors, and division operations are required for certain calculations, which are complex and time-consuming.
Innovation Solution
The introduction of a flexible transform tree structure that allows nodes to have two child nodes, enabling sub-sampling of reference samples to ensure a power of 2 number of reference samples, allowing for right shift operations instead of division, and the use of non-square quadtree structures to improve coding performance by aligning transform blocks with predictive blocks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If non-square predictive blocks are used, then coding flexibility is improved, but compression performance deteriorates due to changes in total energy and increased normalization factors
Solution Approach 1:
The patent implements dynamic block shape selection where the transform block shape (square or non-square) is adaptively chosen based on the prediction mode and content characteristics. The system can switch between different block configurations (e.g., 2N×2N, 2N×N, N×2N) to optimize for both flexibility and compression efficiency, rather than being constrained to fixed square blocks.
Solution Approach 2:
The patent modifies the transform block dimensions as a variable parameter that can be adjusted according to the prediction unit partitioning. By changing the block shape parameters to match the predictive block dimensions, the system maintains energy compactness while achieving the flexibility needed for different coding scenarios.
2Measurement precision
If division operations are used for calculations, then precision is improved, but computational complexity increases and processing time is consumed
Solution Approach 1:
The patent replaces complex division operations with simpler multiplication and bit-shifting operations in the normalization process. By using pre-computed normalization factors and integer-based arithmetic, the system achieves the required precision while significantly reducing computational complexity and avoiding floating-point operations.
Solution Approach 2:
The patent pre-computes normalization factors and stores them for later use. This preliminary action allows the system to avoid performing complex division operations during real-time encoding/decoding, instead using simple table lookups and bit-shifting operations that maintain precision while reducing computational burden.
3Ease of manufacture
If transform blocks are misaligned with predictive blocks, then processing simplicity is improved, but coding efficiency deteriorates
Solution Approach 1:
The patent introduces asymmetric block configurations where transform blocks can have different dimensions than the standard square CTU structure. By allowing non-square transform blocks (e.g., 2N×N or N×2N) that align with the predictive block shapes, the system achieves both processing simplicity and coding efficiency, eliminating the misalignment problem between transform and prediction boundaries.
Solution Approach 2:
The patent segments the transform processing into multiple independent transform units that can be applied to different regions with different block shapes. This segmentation allows each transform block to be optimally aligned with its corresponding predictive block, improving coding efficiency while maintaining processing simplicity through modular, independent transformation operations.
Data Source
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AI summary
A video coder determines a coding unit (CU) is partitioned into transform units (TUs) of the CU based on a tree structure. As part of determining the CU is partitioned into the TUs of the CU based on the tree structure, the video coder determines that a node in the tree structure has exactly two child nodes in the tree structure. A root node of the tree structure corresponds to a coding block of the CU, each respective non-root node of the tree structure corresponds to a respective block that is a partition of a block that corresponds to a parent node of the respective non-root node, and leaf nodes of the tree structure correspond to the TUs of the CU.