Adaptive Chroma Loop Filtering With Limited Filter Signaling
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Solution Overview
Problem
Existing adaptive loop filters (ALF) in video coding, such as linear and non-linear extensions, lack flexibility and efficiency in managing memory usage and filtering quality, particularly in versatile video coding (VVC) standards.
Innovation Solution
Implementing a method to control adaptive loop filters by signaling alternative chroma filters with a limited maximum number, using truncated unary binarization, and sharing filter coefficients through adaptation parameter sets to manage memory and improve filtering quality versus coding efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple alternative chroma filters are provided in the adaptive loop filter, then filtering quality is improved, but memory requirements and device complexity increase
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the number of alternative chroma filters based on picture characteristics such as chroma_qp_offset_cb and chroma_qp_offset_cr. When chroma quantization parameters indicate high quality requirements, more alternative filters are made available; when lower quality is acceptable, fewer filters are used. This resolves the contradiction by making the filtering quality adaptive rather than static, matching the quality level to the actual needs of each picture region.
Solution Approach 2:
The patent implements dynamics by making the set of alternative chroma filters changeable based on picture conditions. The number and type of alternative filters are not fixed but are dynamically selected based on chroma_qp_offset values and other picture characteristics. This allows the system to optimize between filtering quality and memory usage in real-time, rather than being constrained by a static configuration.
2Measurement precision
If multiple alternative chroma filters are signaled in the bitstream, then filtering quality is improved, but coding efficiency decreases due to increased bitstream overhead
Solution Approach 1:
The patent uses parameter changes to control the signaling of alternative chroma filters based on chroma_qp_offset_cb and chroma_qp_offset_cr values. When these parameters indicate that high chroma quality is required, alternative filters are signaled and used; when lower quality is acceptable, the overhead of signaling multiple filters is avoided. This resolves the contradiction by making filter signaling conditional rather than universal.
3Measurement precision
If the adaptive loop filter uses more filters, then filtering quality is improved, but the complexity of filter management and selection increases
Solution Approach 1:
The patent simplifies filter management by using chroma_qp_offset parameters as the primary basis for selecting alternative chroma filters. Instead of complex multi-factor decision algorithms, the system primarily responds to changes in chroma_qp_offset_cb and chroma_qp_offset_cr values. This parameter-driven approach reduces the complexity of filter selection logic while still achieving adaptive filtering quality.
Data Source
AI summary
A method of controlling an Adaptive Loop Filter comprises obtaining for a slice containing one or more coding tree blocks, data indicating a number of available alternative chroma filters, obtaining for a coding tree block in the slice, an alternative filter index identifying one of the available alternative chroma filters, and selecting the alternative chroma filter identified by the index to filter chroma image data in the coding tree block.