Adaptive Chroma Downsampling for HDR Video Quality
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Solution Overview
Problem
Conventional video coding systems face challenges in handling high-quality content like HDR and WCG, as they introduce banding and artifacts due to limited dynamic range and color format conversions, which degrade video quality upon decoding and display.
Innovation Solution
The method involves adaptive chroma downsampling, where candidate filters are evaluated for distortion and the best filter is selected based on anticipated upsampling filters, optimizing encoding and decoding processes to minimize visual distortion, and including side information for post-processing control in the bitstream.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If chroma downsampling is performed to reduce data quantity for encoding, then compression efficiency is improved, but visual distortion and banding artifacts increase
Solution Approach 1:
The patent implements adaptive chroma downsampling where the filter selection and downsampling ratio are dynamically adjusted based on local image characteristics. Different regions of the image can have different downsampling applied, with smoother regions allowing more aggressive downsampling and detailed regions preserving higher chroma resolution, thus balancing compression efficiency with visual quality
Solution Approach 2:
The patent changes the parameters of chroma downsampling by selecting from multiple candidate filters (e.g., different kernel sizes, filter types) and adjusting the downsampling ratio based on image content analysis. This allows the system to optimize the balance between data reduction and artifact prevention for different image regions and content types
2Productivity
If color space conversion is performed to improve encoding efficiency, then compression performance is improved, but color accuracy and visual quality deteriorate
Solution Approach 1:
The patent performs preliminary color space conversion and chroma downsampling before the main encoding process. By preparing the chroma components in advance with appropriate filtering and subsampling, the system optimizes the input for subsequent encoding stages, improving overall encoding efficiency while maintaining color accuracy through careful filter selection
3Device complexity
If fixed chroma downsampling is used to simplify the encoding process, then device complexity is reduced, but visual distortion increases
Solution Approach 1:
The patent segments the image into different regions based on local characteristics (e.g., smooth areas, edge areas, textured areas) and applies different chroma downsampling strategies to each segment. This allows the system to maintain relatively simple overall architecture while achieving adaptive quality optimization through region-based processing
Data Source
AI summary
A method of adaptive chroma downsampling is presented. The method comprises converting a source image to a converted image in an output color format, applying a plurality of downsample filters to the converted image and estimating a distortion for each filter chose the filter that produces the minimum distortion. The distortion estimation includes applying an upsample filter, and a pixel is output based on the chosen filter. Methods for closed loop conversions are also presented.