IntraBC Block Vector Restriction for Fractional-Pel Interpolation
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Solution Overview
Problem
In video coding systems, particularly in High Efficiency Video Coding (HEVC) and its extensions, the Intra Block Copy (IntraBC) mode faces challenges when dealing with fractional-pel resolution block vectors, as they often result in unavailable reference pixels for interpolation, leading to incomplete reference blocks during the prediction process.
Innovation Solution
The method restricts block vectors to ensure that neighboring pixels at integer-pel locations are available for generating fractional-pel reference pixels by modifying bitstream conformance conditions or padding unavailable pixels with neighboring available pixels, ensuring sufficient interpolation data within the reconstructed pixel area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If fractional-pel resolution block vectors are used in IntraBC mode, then prediction accuracy is improved, but reference pixel availability deteriorates
Solution Approach 1:
The patent applies preliminary action by checking the availability of neighboring pixels at integer-pel locations before allowing fractional-pel block vectors to be used. The system预先 verifies that all required neighboring pixels (at least 2L pixels where L is the interpolation filter half-length) are available within the reconstructed pixel area, ensuring that interpolation can be performed without missing reference data.
Solution Approach 2:
The patent changes the parameter constraints on block vectors based on the interpolation requirements. When fractional-pel resolution is enabled, the system modifies the valid range of block vector values to ensure they point to locations where sufficient neighboring pixels exist for interpolation. This dynamically adjusts the parameter space to maintain both high precision and reliability.
2Manufacturing precision
If block vector restrictions are imposed to ensure pixel availability, then reference block completeness is improved, but coding flexibility deteriorates
Solution Approach 1:
The patent applies dynamics by making the block vector constraints adaptive rather than fixed. The system dynamically determines the valid block vector range based on the specific picture content, reconstruction status, and interpolation filter requirements. This allows the coding flexibility to be maximized while still ensuring reference block completeness when needed.
Solution Approach 2:
The system changes the parameters of block vectors dynamically based on the coding context. When fractional-pel interpolation is required, the parameter range is adjusted to ensure completeness; when integer-pel resolution suffices, the full range of block vectors remains available, thus maintaining coding flexibility while ensuring reference block completeness when necessary.
3Measurement precision
If neighboring pixel boundaries are shifted to ensure interpolation data availability, then interpolation accuracy is improved, but search area deteriorates
Solution Approach 1:
The patent applies local quality by making the boundary shift requirement localized rather than global. Instead of shifting boundaries for the entire picture, the system only requires boundary shifts in the specific regions where fractional-pel interpolation is performed. This ensures interpolation accuracy locally while minimizing the impact on the overall search area.
Solution Approach 2:
The system applies partial action by requiring boundary shifts only to the extent necessary for successful interpolation. The patent specifies that boundaries need to be shifted by at least (L-1) pixels where L is the interpolation filter half-length, which is the minimum required to ensure sufficient neighboring pixels are available, rather than applying excessive shifts that would unnecessarily reduce the search area.
Data Source
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AI summary
A method and apparatus of video coding using IntraBC (Intra Block Copy) mode are disclosed. The system derives a block vector pointing from the current block to a reference block within a reconstructed pixel area of the current picture. If the block vector is at the fractional-pel resolution, the block vector is restricted so that neighboring pixels at integer-pel locations around fractional-pel reference pixels of the reference block for generating the fractional-pel reference pixels of the reference block using an interpolation filter are all available within the reconstructed pixel area. In another embodiment, the unavailable reference pixels for interpolation to generate fractional-pel reference pixels are padded.