Luma Value Determination for Chroma Downsampled Video Encoding
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Solution Overview
Problem
Existing video processing systems face challenges in accurately determining luma values from 4:4:4 RGB video data, particularly when converting from 4:2:0 to 4:4:4 formats, due to residual luminance interference and non-linear transfer functions like PQ-EOTF, which result in brightness and color distortion.
Innovation Solution
A method and system that determine initial coefficients for color space regions, apply these coefficients to an initial image to create a test image, assess quality, modify coefficients to improve quality, and calculate luma values for encoding chroma downsampled 4:2:0 YCbCr video data into a bitstream, using a processor and memory to execute these steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If chroma downsampled 4:2:0 YCbCr video data is used to reduce data rate and complexity, then productivity and ease of manufacture are improved, but manufacturing precision and measurement precision deteriorate due to residual luminance interference and brightness distortion
Solution Approach 1:
The patent segments the color space into multiple regions and assigns different coefficients to each region. This allows the system to handle different luminance and chroma characteristics in different parts of the color space, improving precision without increasing overall data rate. The segmentation enables region-specific optimization for luminance accuracy while maintaining the compressed 4:2:0 format.
Solution Approach 2:
The patent applies local quality by using different coefficients for different regions of the color space. Instead of using a single uniform transformation, the system adapts the YCbCr conversion coefficients based on the specific region, which improves luminance accuracy in each local area while maintaining overall compression efficiency.
2Measurement precision
If non-linear transfer functions like PQ-EOTF are used for HDR video data to achieve perceptual uniformity, then measurement precision is improved, but device complexity increases due to the highly non-linear relationship between luma and luminance
Solution Approach 1:
The patent changes the parameters of the YCbCr conversion by using different coefficients for different regions of the color space. This allows the system to adapt to the non-linear PQ-EOTF transfer function by adjusting the conversion parameters locally, maintaining perceptual uniformity while managing the complexity through region-based simplification.
Solution Approach 2:
The patent performs preliminary determination of coefficients for each color space region before actual video processing. This pre-computation of region-specific coefficients simplifies the real-time processing by having lookup tables or pre-calculated values ready, reducing the computational complexity during actual HDR video encoding while maintaining perceptual accuracy.
3Device complexity
If 4:4:4 RGB video data is converted to 4:2:0 YCbCr format to reduce complexity, then device complexity is reduced, but manufacturing precision deteriorates due to subsampling artifacts and luminance interference
Solution Approach 1:
The patent applies local quality by using different coefficients for different regions of the color space. This allows the system to maintain better color fidelity and luminance accuracy in critical regions even after chroma subsampling, while still achieving the complexity reduction benefits of 4:2:0 format.
Solution Approach 2:
The patent determines coefficients based on the characteristics of the video data in each region, which can be seen as a form of feedback mechanism. The system adapts the conversion parameters based on the actual content being processed, which helps minimize subsampling artifacts and maintain color fidelity while using the compressed 4:2:0 format.
Data Source
AI summary
A method of determining luma values from 4:4:4 RGB video data for encoding chroma downsampled 4:2:0 YCbCr video data into a bitstream. Initial coefficents are determined for a region of a colour space the region being one of a plurality of regions located in the colour space and each region having a plurality of associated coefficients. The determined initial coefficients are applied to an initial image to produce a test image, the test image being a chroma downsampled 4:2:0 YCbCr version of the initial image. A measure of quality is determined by comparing the initial image and the test image. The determined initial coefficients are modified to increase the determined measure of quality. Luma values are determined from 4:4:4 RGB video data for encoding chroma downsampled 4:2:0 YCbCr video data into a bitstream using the modified coefficients.