In-Loop Filtering for Virtual Boundaries in VR360 Video
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Solution Overview
Problem
In-loop filtering processes for 360-degree virtual reality (VR360) pictures often produce undesirable results due to discontinuous edges, as they rely on pixels from the opposite side of the boundary, leading to noticeable artefacts.
Innovation Solution
Disabling or using a smaller-size loop filter when the filtering process crosses a virtual boundary, ensuring that the filtering process does not use pixels from the opposite side of discontinuous edges, thereby preventing artefacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If in-loop filtering is applied to reconstructed pictures in VR360 video coding, then coding artefacts are reduced, but discontinuous edges cause noticeable artefacts and degraded image quality
Solution Approach 1:
The patent applies different filtering strategies to different regions of the picture: standard in-loop filtering is applied to regular blocks, while virtual boundary blocks are identified and excluded from filtering or use reduced filter sizes. This local differentiation prevents artefacts at discontinuous edges while maintaining filtering benefits in continuous regions.
Solution Approach 2:
The patent segments the picture into regular blocks and virtual boundary blocks based on projection format characteristics. By identifying blocks that contain or are adjacent to virtual boundaries (discontinuous edges), the filtering process is selectively applied only to appropriate segments, avoiding the harmful effect of filtering across discontinuous edges.
2Reliability
If standard in-loop filtering is applied across the entire picture, then coding artefacts are reduced, but computational overhead increases due to unnecessary filtering at virtual boundaries
Solution Approach 1:
Instead of applying filtering to the entire picture, the patent applies filtering only to non-virtual-boundary blocks. This partial action approach avoids the excessive computation of filtering at virtual boundaries where it provides no benefit and may produce artefacts, thereby improving computational efficiency while maintaining adequate artefact reduction in relevant regions.
Data Source
AI summary
Method and apparatus of coding pictures containing one or more virtual boundaries, such as 360-degree virtual reality (VR360) video are disclosed. According to this method, a reconstructed filtered unit associated with a loop filter for a current reconstructed pixel is received. The loop filtering process associated with the loop filter is applied to the current reconstructed pixel to generate a filtered reconstructed pixel, where if the loop filtering process for the current reconstructed pixel is across a virtual boundary of the picture, the loop filtering process is disabled when fixed-size loop filtering is used or a smaller-size loop filter is selected when adaptive-size loop filtering is used for the current reconstructed pixel, where the filtered reconstructed pixel is the same as the current reconstructed pixel when the loop filtering process is disabled. The filtered reconstructed pixel is the same as the current reconstructed pixel.