SDR and HDR Chroma Boost Using Luminance-Class Gain Metadata
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Solution Overview
Problem
Existing methods for enhancing chroma in SDR and HDR display signals in SL-HDRx systems lack precise control, leading to potential saturation and reconstruction errors due to uncontrolled color corrections.
Innovation Solution
A method involving analyzing chrominance components of an RGB image, applying tone mapping and joint normalization, classifying colors into classes, determining dominant luminance and chrominance gains, and encoding these as metadata for dynamic color correction based on luminance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If global color correction is applied to increase chroma in SDR and HDR signals, then chroma enhancement is achieved, but color saturation control is lost and reconstruction errors occur
Solution Approach 1:
The patent applies different color correction gains to different luminance ranges by dividing the luminance scale into multiple segments. Each segment has its own saturation gain function (SGF) parameters, allowing localized chroma enhancement without affecting other luminance regions. This resolves the contradiction by enabling precise chroma control at specific luminance levels while maintaining overall color reproduction reliability.
Solution Approach 2:
The patent dynamically adjusts color correction parameters based on the input signal's luminance characteristics. The SGF parameters are selected adaptively according to the luminance value of each pixel or region, enabling the system to optimize chroma enhancement in real-time while preventing saturation. This dynamic approach allows the system to maintain reliable color reproduction across varying luminance conditions.
2Quantity of substance
If uncontrolled color correction is applied to enhance chroma, then chroma saturation increases, but clipping and reconstruction errors occur
Solution Approach 1:
The patent performs preliminary analysis of the input signal's luminance distribution before applying color correction. Based on this analysis, appropriate SGF parameters are pre-selected to ensure that chroma enhancement remains within safe limits. This preliminary action prevents clipping and reconstruction errors by avoiding excessive chroma amplification that would cause signal fidelity degradation.
Solution Approach 2:
The patent implements a feedback mechanism where the output chroma values are monitored and used to adjust the color correction gain. If chroma values approach clipping thresholds, the gain is automatically reduced to maintain signal fidelity. This feedback control ensures that chroma intensity is enhanced without causing reconstruction errors or degrading signal quality.
Data Source
AI summary
A method comprising obtaining a current RGB image; classifying colors of pixels of the current RGB image in a plurality of classes; for each color class, determining data representative of said color class, comprising a dominant luminance value representative of a luminance at which a color in said class is predominant and determining from said data representative of said color class a value representative of a gain of chrominance representative of a margin for increasing a chrominance component in said color class; and, encoding the dominant luminance value and the value representative of the gain corresponding to each class as metadata representative of a Saturation Gain Function in a bitstream, said function defining a color correction to apply to a pixel in function of a luminance of said pixel.