Adaptive Sharpening Filter for Video Prediction Blocks
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Solution Overview
Problem
Existing video coding techniques suffer from blurred edges and reduced high-frequency details in upsampling, leading to poor quality and artifacts in predictive coding, especially in inter layer prediction for scalable video codecs.
Innovation Solution
A video coder and decoder employing an adaptive sharpening filter that applies spatial adaptive sharpening to prediction blocks based on edge strength estimation, using context-adaptive binary arithmetic coding (CABAC) to selectively apply or bypass the filter, thereby improving prediction efficiency and reducing artifacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If upsampling filter is used for inter layer prediction, then base layer frame can be upsampled to match enhancement layer resolution, but edges become blurred and high frequency details are lost
Solution Approach 1:
The patent applies a sharpening filter with adjustable strength parameter to the upsampled prediction block. The filter modifies the frequency characteristics of the prediction block by adding high-frequency components, thereby restoring edge sharpness and detail information that were lost during upsampling. The sharpening strength can be adapted based on block characteristics to optimize the balance between edge enhancement and artifact suppression.
2Productivity
If short-tap upsampling filter is used, then filtering is computationally efficient, but high frequencies are suppressed and interpolated frame becomes additionally blurred
Solution Approach 1:
The patent introduces a sharpening filter as an intermediary processing step that operates on the output of the upsampling filter. This intermediate sharpening operation compensates for the high-frequency suppression caused by the upsampling filter, effectively decoupling the computational efficiency requirement from the edge sharpness requirement. The sharpening filter acts as a corrective mediator that restores quality without requiring a change in the upsampling filter design.
3Manufacturing precision
If long-tap upsampling filter is used, then high frequencies are preserved, but ringing artifacts are generated near sharp edges
Solution Approach 1:
The patent applies sharpening selectively based on local block characteristics such as edge strength and variance. By analyzing the properties of different regions within the prediction block, the filter applies appropriate sharpening strength only where needed, rather than uniformly across the entire block. This local adaptation prevents excessive sharpening in smooth regions that would generate artifacts, while still enhancing edges in regions that require it.
4Manufacturing precision
If adaptive sharpening filter is applied to all prediction blocks, then prediction quality improves, but signaling overhead increases
Solution Approach 1:
The patent applies adaptive sharpening selectively to only those prediction blocks that benefit from it, rather than uniformly to all blocks. By evaluating block characteristics such as variance and edge content, the method determines which blocks require sharpening enhancement. This partial application approach maintains prediction quality for blocks that need it while avoiding unnecessary processing and signaling overhead for blocks that would not benefit from sharpening.
Data Source
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AI summary
The present invention relates to a video coder (400, 600) for predictive coding, into an encoded video bit stream, of an original block of an original frame based on a prediction block obtained from a reference frame, comprising a buffer (401, 601) configured to store the original block, a buffer (408, 608) configured to store the prediction block, and an adaptive sharpening filter (409, 609) configured to apply a spatial adaptive sharpening filtering to the prediction block.