Adaptive Loop Filtering Across Video Unit Boundaries
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Solution Overview
Problem
Current video coding standards face challenges in efficiently handling virtual boundaries during the coding, transcoding, and decoding processes, leading to suboptimal compression efficiency and increased complexity in implementing coding and decoding tools.
Innovation Solution
The proposed solution involves methods for video processing that determine the availability of samples across virtual boundaries, using adaptive loop filtering (ALF) tools, and applying specific filtering operations based on the determination, including padding and selecting appropriate ALF sample selection methods to handle boundary conditions effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If adaptive loop filtering is applied across video unit boundaries, then filtering quality is improved, but complexity of handling boundary conditions increases
Solution Approach 1:
The patent divides the video picture into multiple video units (tiles, slices, or bricks) with defined boundaries. The ALF process is segmented to operate independently within each video unit, with boundary handling as a separate determination step. This segmentation allows the filtering to be applied systematically across boundaries without requiring complex global coordination, resolving the contradiction by structuring the processing into manageable segments.
Solution Approach 2:
The patent performs preliminary determination of sample availability across boundaries before executing the ALF filtering operation. By pre-determining whether samples from neighboring video units are accessible and preparing padding strategies in advance, the system avoids complex runtime boundary handling during filtering, thus improving filtering quality while controlling complexity through advance preparation.
2Productivity
If samples from multiple video units are accessed for filtering, then compression efficiency is improved, but implementation complexity increases
Solution Approach 1:
The patent introduces dynamic determination of sample accessibility across video unit boundaries based on configuration flags and boundary conditions. The system adaptively decides whether to access samples from neighboring video units on a per-boundary basis, allowing compression efficiency to be optimized when beneficial while avoiding complexity when not needed. This dynamic approach resolves the contradiction by making sample access flexible rather than fixed.
Solution Approach 2:
The patent applies different boundary handling strategies to different locations in the video picture based on local conditions. Each video unit boundary is evaluated independently to determine sample availability, allowing the system to access samples across boundaries in regions where it improves compression efficiency while maintaining simpler handling in regions where it would add unnecessary complexity. This localised approach optimizes the trade-off spatially.
3Stability of the object's composition
If padding is applied to unavailable samples, then filtering continuity is improved, but processing overhead increases
Solution Approach 1:
The patent applies padding to unavailable samples before the ALF filtering operation to prevent filtering discontinuities at boundaries. By pre-filling missing samples with appropriate padded values, the system ensures filtering continuity without requiring complex runtime checks during the filtering process itself. This preliminary action resolves the contradiction by addressing the continuity issue in advance with a relatively simple padding operation.
Solution Approach 2:
The patent uses padding values as temporary, disposable sample replacements that serve their purpose during the filtering operation and are then discarded. These padded samples are not permanent artifacts but transient placeholders that enable filtering continuity only when needed at boundaries, minimizing processing overhead by using simple value copying rather than complex generation or storage of permanent padding structures.
Data Source
AI summary
An example method of video processing includes determining, for a conversion between a current video unit of a video and a bitstream representation of the video, availability of one or more samples in a first neighboring region of the current block for a coding process of the conversion independently from information of a second neighboring region of the current block. The second neighboring region is adjacent to the first neighboring region, and the one or more samples are padded in case determined to be unavailable. The method includes performing the conversion based on the determining.