Transform Coefficient Sign Prediction for Lower VVC Bit Rate
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Solution Overview
Problem
Existing video coding standards, such as VVC, do not effectively predict and encode residual coefficient signs, leading to a significant portion of the bitstream being consumed by transmitting these signs, which hinders further bit rate gains and compression efficiency.
Innovation Solution
Implement a residual sign prediction method using gradient-based border residual sign prediction, multi-modal residual border prediction, and extended border prediction to predict residual coefficient signs across the entire TB or an expanded region, allowing for improved bit rate gains and compression efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If residual coefficient signs are transmitted as sign bits without prediction, then transmission is simple and reliable, but bit rate increases and compression efficiency decreases
Solution Approach 1:
The patent applies preliminary action by predicting residual coefficient signs before transmission. The encoder predicts signs of residual coefficients using neighboring coefficient information and gradient calculations, and the decoder performs the same prediction to reconstruct signs without transmitting them explicitly. This preliminary prediction action eliminates the need to transmit sign bits for many coefficients, reducing bit rate while maintaining reliable reconstruction.
2Quantity of substance
If residual coefficient signs are subject to prediction and coding, then bit rate gains are achieved, but prediction accuracy may be lost and computational complexity increases
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting prediction parameters based on local image characteristics. The encoder calculates gradients of neighboring coefficients and uses these gradient values to determine prediction modes and parameters. The system adapts prediction strength and methodology based on measured gradient magnitudes, optimizing prediction accuracy for different regions while maintaining computational efficiency.
3Quantity of substance
If residual coefficient signs are subject to prediction and coding, then bit rate gains are achieved, but device complexity increases
Solution Approach 1:
The patent applies local quality by performing prediction operations selectively based on local coefficient characteristics. The encoder calculates gradients and determines prediction necessity for each coefficient location, applying prediction only where beneficial. The system uses local gradient information to adapt prediction parameters, concentrating computational effort on regions where sign prediction provides the most bit rate savings rather than uniformly processing all coefficients.
Data Source
AI summary
A VVC-standard encoder and a VVC-standard decoder are provided, implementing a residual sign prediction method utilizing a sorting order of residual coefficients and an expanded region of a TB. As sign prediction accuracy is higher for larger transform coefficient levels, a VVC-standard encoder and a VVC-standard decoder sort transform coefficient signs of a TB in a one-dimensional array, based on corresponding QIdx values instead of the residual coefficient level value. The first n signs according to corresponding QIdx values, ordered from largest to smallest, are predicted using a residual sign prediction method, and the rest of the signs are signaled by EP bins. A sign prediction area is also extended, without limitation to an upper-left 4×4 region within the transform block, but to a region up to 32×32 in size; a VVC-standard encoder signals the maximum dimensions of the region to a VVC-standard decoder in syntax structures of the block.