Hue-Plane Preserving Color Correction Using Weighted Constrained Matrices
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Solution Overview
Problem
Existing color correction methods for digital cameras lack effective hue-plane preservation, leading to inaccuracies in color channel value transformations and instability, especially with saturated colors and varying illuminants.
Innovation Solution
The method employs Hue Plane Preserving Color Correction (HPPCC) using weighted constrained 3x3 matrices, where each matrix is calculated as a normalized weighted sum of pre-calculated training matrices based on hue-angle specific weighting functions, ensuring differentiability and local influence for improved accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional color correction methods are used, then the color transformation process is simple, but hue-plane preservation is lost leading to color inaccuracies
Solution Approach 1:
The color correction method segments the color space into multiple hue-planes, each characterized by a specific hue angle. Instead of applying a single global transformation matrix to all colors, the method divides the correction process into multiple hue-specific segments. Each hue-plane is corrected using its own optimized 3x3 matrix, allowing precise preservation of hue relationships while maintaining manageable computational complexity through localized corrections.
Solution Approach 2:
The invention applies local quality by using hue-angle dependent weighting functions that adapt the transformation matrix locally to each color's specific hue. The weighting function w(φ) = 1/(1 + k·|φ - φ₀|) provides stronger local influence for colors closer to the reference hue angle φ₀, ensuring that each local region in color space receives optimized correction parameters tailored to its specific hue characteristics, thereby improving overall color accuracy.
2Measurement precision
If hue-angle dependent weighting functions are used, then local influence and accuracy are improved, but computational complexity increases
Solution Approach 1:
The method performs preliminary action by pre-calculating the hue angle φ for each color channel combination before the actual color transformation. The hue angle is computed once as φ = atan2(G - B, R - G) and then reused in the weighting function for all subsequent matrix operations. This preliminary calculation avoids redundant computations and enables efficient application of the hue-angle dependent weighting during the color correction process.
Solution Approach 2:
The invention utilizes parameter changes by dynamically adjusting the transformation matrix parameters based on the hue angle φ. The weighting function modifies the matrix elements M_ij according to the hue-specific parameter w(φ), transforming the fixed global matrix into a variable local matrix. This parameter adaptation allows the system to achieve high transformation accuracy by tailoring matrix parameters to each color's hue characteristics while maintaining computational efficiency through the structured parameterization approach.
Data Source
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AI summary
Color correction methods relate device dependent sensor responses (RGB) to device independent color values (XYZ). The present invention discloses a new approach to Hue Plane Preserving Color Correction (HPPCC) using weighted constrained 3 x 3 matrices. Accordingly, the methods of the present invention employ hue angle specific weighted matrixing. Given a device RGB from which a device hue angle is derived, a corresponding transformation matrix is found as the normalized weighted sum of all pre-calculated constrained white point and training color preserving matrices. Each weight is calculated as a power function of the minimum difference between the device and the training color hue angle. The weighting function provides local influence to the matrices that are in close hue angle proximity to the device color. The power of the function can be further optimized for global accuracy. The methods of the present invention are termed HPPCC-WCM for Hue Plane Preserving Color Correction Weighted Constrained Methods. Experiments performed using different input spectra demonstrate that the claimed methods consistently improve the stability and accuracy of state-of-the-art methods for color correction.