Photo Overlap Transform DC Leakage Reduction
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Solution Overview
Problem
Transform coding techniques, such as those used in image and video compression, face issues with DC leakage, which lead to increased bit requirements and artifacts due to non-zero AC coefficients when quantization step sizes are small, and checker-board artifacts at low bit rates due to missing AC coefficients.
Innovation Solution
The redesign of forward and inverse transforms to eliminate or mitigate DC leakage, including removing the scaling stage from the photo overlap transform, and processing at both the encoder and decoder to estimate and compensate for DC leakage, either in the spatial or frequency domain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If transform coding is applied with small quantization step sizes, then compression fidelity is improved, but DC leakage causes non-zero AC coefficients increasing bit requirements
Solution Approach 1:
The patent extracts and removes the scaling stage from the photo overlap transform, isolating the source of DC leakage. By taking out this specific component causing the problem, the invention eliminates DC leakage without affecting other transform operations, thus preventing non-zero AC coefficients while maintaining compression fidelity.
Solution Approach 2:
The invention changes the transform parameters by removing the scaling stage entirely, altering the mathematical operations in the photo overlap transform. This parameter change eliminates DC leakage at the source, allowing small quantization step sizes to be used without generating spurious AC coefficients, thereby reducing bit requirements while maintaining high compression fidelity.
2Manufacturing precision
If quantization step sizes are reduced to minimize artifacts, then reconstruction accuracy is improved, but DC leakage still produces non-zero AC coefficients
Solution Approach 1:
The patent applies preliminary anti-action by removing the scaling stage before quantization occurs. This preventive measure eliminates DC leakage at the transform stage, so that when quantization is applied with small step sizes, no spurious AC coefficients are generated in the first place, thereby maintaining reconstruction accuracy without the harmful effect of non-zero AC coefficients.
3Productivity
If the photo overlap transform includes a scaling stage, then transform efficiency is improved, but DC leakage occurs causing compression performance degradation
Solution Approach 1:
The invention extracts and removes the scaling stage from the photo overlap transform, eliminating the source of DC leakage. This removal prevents information loss due to spurious AC coefficients while maintaining sufficient transform efficiency through the remaining transform operations, thereby improving compression performance.
4Object-generated harmful factors
If encoder and decoder processing is added to compensate for DC leakage, then artifact reduction is achieved, but system complexity increases
Solution Approach 1:
The patent applies preliminary action by removing the scaling stage at the encoder before transformation, preventing DC leakage from occurring in the first place. This eliminates the need for complex decoder-side compensation processing, reducing system complexity while still achieving artifact reduction through the preventive measure.
Data Source
AI summary
In certain embodiments, to eliminate DC leakage into surrounding AC values, scaling stage within a photo overlap transform operator is modified such that the off-diagonal elements of the associated scaling matrix have the values of 0. In certain embodiments, the on-diagonal scaling matrix are given the values (0.5, 2). In some embodiments, the scaling is performed using a combination of reversible modulo arithmetic and lifting steps. In yet other embodiments, amount of DC leakage is estimated at the encoder, and preprocessing occurs to mitigate amount of leakage, with the bitstream signaling that preprocessing has occurred. A decoder may then read the signal and use the information to mitigate DC leakage.