Intra Sharpening and De-ringing Filter for Video Coding
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Solution Overview
Problem
Conventional intra frame prediction mechanisms in video coding distort natural edges and cause blurring or ringing effects, particularly in blocks with low-frequency components, due to the use of quantization matrices and linear smoothing filters.
Innovation Solution
A decoder and encoder system that employs a filter unit with sharpening and/or de-ringing filters to improve prediction accuracy and image quality by selectively applying these filters based on signaling information or image properties, such as edge strength, to suppress ringing artifacts and enhance edge sharpness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If linear smoothing filters are used to reduce ringing effect, then ringing artifacts are suppressed, but natural edges are blurred
Solution Approach 1:
The patent applies different filtering operations to different regions of the image based on local characteristics. Edge regions are identified and processed differently from non-edge regions, allowing ringing suppression in smooth areas while preserving edge sharpness through selective filter application.
Solution Approach 2:
The filter type is dynamically selected based on local image properties such as gradient magnitude and variance. The system transitions between different filtering modes (smoothing vs. edge-preserving) depending on the detected characteristics of the local region, making the filtering adaptive rather than static.
2Loss of information
If quantization matrix is used to preserve low frequency components, then low frequency information is maintained, but errors increase for blocks containing natural edges
Solution Approach 1:
The patent changes the quantization parameters dynamically based on the detected edge characteristics in the block. For blocks containing natural edges, different quantization step sizes are applied compared to blocks without edges, allowing preservation of both low-frequency information and edge accuracy through parameter adaptation.
Data Source
AI summary
A decoder for decoding a block of a current frame of a video from a bitstream, the decoder comprising a reference sample selection unit configured to select reference samples of a reconstructed part of the current frame, a filter unit configured to filter the reference samples, and a block generation unit configured to generate a prediction of the block based on the filtered reference samples, wherein the filter unit comprises a sharpening filter and/or a de-ringing filter.