CDEF-Based Debanding for Compressed Image and Video
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Solution Overview
Problem
Banding artifacts, also known as contouring artifacts, remain a significant visual quality issue in modern video coding standards despite advancements, particularly noticeable in smoothly varying regions, and existing de-banding techniques are complex, costly, or reduce coding efficiency.
Innovation Solution
Repurpose the Constrained Directional Enhancement Filter (CDEF) for de-banding by using its edge-direction detection to identify banding artifacts and apply filtering orthogonal to the detected direction, combined with low-complexity methods like linear filtering and random sampling, either in-loop or post-loop, to mitigate banding while maintaining compression efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If existing de-banding techniques are applied, then banding artifacts are reduced, but device complexity and implementation cost increase significantly
Solution Approach 1:
The patent reuses the existing CDEF filter hardware and processing pipeline for debanding purposes, making the filter multi-functional. The same filter taps and directional enhancement logic are applied to both deringing and debanding tasks, eliminating the need for separate dedicated debanding hardware and reducing overall device complexity.
Solution Approach 2:
The patent leverages the output of the CDEF edge-direction detection process to identify banding regions, rather than requiring a separate detection mechanism. The filter's own operational data is reused to guide the debanding process, reducing the need for additional detection hardware or processing stages.
2Object-affected harmful factors
If complex de-banding filters are applied, then banding artifacts are reduced, but coding efficiency decreases
Solution Approach 1:
The patent applies debanding filtering selectively only to regions identified as containing banding artifacts, rather than processing the entire image uniformly. This partial application reduces the overall computational burden and maintains coding efficiency while still effectively removing banding where it occurs.
Solution Approach 2:
The patent uses the CDEF's directional detection to identify specific regions with banding artifacts and applies filtering only to those local areas. Different parts of the image receive different treatment - banded regions are filtered while other regions maintain their original quality, optimizing the balance between artifact removal and coding efficiency.
3Object-affected harmful factors
If strong filtering is applied to remove banding, then visual quality improves, but hardware complexity increases
Solution Approach 1:
The patent makes the existing CDEF filter hardware perform dual functions - both its original deringing purpose and the new debanding function. By reusing the same filter taps, processing pipeline, and control logic, the patent achieves strong debanding effect without requiring additional dedicated hardware resources.
Solution Approach 2:
The patent combines the debanding function with the existing CDEF processing stage, merging two functions (deringing and debanding) into a single unified processing pipeline. This consolidation allows strong filtering capability to be achieved while sharing hardware resources and reducing overall system complexity.
Data Source
AI summary
Low complexity, hardware-friendly techniques are proposed for video coding systems to mitigate banding artifacts while maintaining the compression efficiency. In general, the proposed techniques consist of two stages including a banding detection stage and a de-banding stage. The banding detection stage may identify the image/video regions where the banding artifact may be present based on gradient information and other information. The de-banding stage may apply corrective techniques to regions identified as likely to possess banding artifacts. In one embodiment, the de-banding adapts the filtering logic proposed by prior video coding standards for other filtering applications to mitigate banding. When implemented over the AV1 video coding standard and the AOM Video Model (AVM) reference software, the proposed technique improves subjective quality significantly at a reasonable hardware implementation cost. The methods and embodiments presented in this document can be beneficial find application in a wide variety of image/video coding standards and systems.