Adaptive Loop Filtering Rounding for Video Compression
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Solution Overview
Problem
Existing video coding technologies face challenges in achieving a high compression ratio with minimal sacrifice in picture quality, particularly in adaptive loop filtering (ALF) processes.
Innovation Solution
The proposed solution involves a method for adaptive loop filtering that includes obtaining reconstructed sample values, filter coefficients from a bitstream, and calculating a sum value. This sum value is then rounded based on the vertical position of the sample within the block, using specific rounding values corresponding to right shift values during the ALF filtering process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If adaptive loop filtering is applied to improve picture quality, then compression ratio is improved, but filtering precision and consistency across different stages may be compromised
Solution Approach 1:
The patent applies parameter changes by introducing different rounding values (alfShiftY) based on the vertical position of samples within a block. Specifically, samples at certain vertical positions (e.g., near block boundaries or at specific intervals) use a rounding value of 10, while other samples use a rounding value of 7. This positional parameter variation ensures consistent filtering precision across different filtering stages while maintaining improved picture quality through adaptive loop filtering.
2Quantity of substance
If video data is compressed to reduce data size for transmission, then bandwidth utilization is improved, but picture quality may be sacrificed
Solution Approach 1:
The patent employs parameter changes in the filtering process by using position-dependent rounding values to enhance picture quality without increasing data size. The rounded sum value is calculated as (sum + alfShiftY) >> shift_amount, where alfShiftY varies based on vertical position. This allows the decoder to reconstruct higher quality images from compressed data by applying more precise filtering at critical positions, thereby improving picture quality while maintaining efficient compression.
3Productivity
If rounding is applied during ALF filtering to simplify computation, then processing speed is improved, but filtering precision may be reduced
Solution Approach 1:
The patent applies the local quality principle by using different rounding values (alfShiftY) for samples at different vertical positions within the block. Specifically, samples at certain positions (e.g., y==CtbSizeY−t−1, y==CtbSizeY−t, y==ctbHeightC−t, or y==ctbHeightC−t−1) use a rounding value of 10, while other samples use a rounding value of 7. This localized differentiation maintains filtering precision where it is most needed while preserving processing speed through efficient rounding operations.
Data Source
AI summary
A method of filtering a sample value of a picture and a video decoding apparatus are disclosed, the method comprises: obtaining a reconstructed sample value for a block of the picture; obtaining filter coefficients for adaptive loop filtering according to a bitstream; obtaining a sum value according to the filter coefficients and the reconstructed sample value for the block; rounding the sum value according to a vertical position of a sample in the block, to obtain a rounded sum value; obtaining a filter reconstructed sample value for the block according to the rounded sum value.