Attenuating Color-Cast Correction in Image Highlights
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Solution Overview
Problem
Existing digital image processing methods apply uniform color-cast corrections to all image regions, leading to unnatural color shifts in highlight areas, particularly making whites appear pastel blue, which is visually undesirable.
Innovation Solution
A method that attenuates color-cast corrections by calculating the difference between pixel colors and a selected highlight color, such as white, and applies a tailored correction based on this difference, blending the original color correction matrix with an identity matrix to maintain natural colors in highlight regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a single global transformation is applied to correct color cast in the entire image, then the midtone and shadow areas are corrected effectively, but the highlight regions develop unnatural color casts
Solution Approach 1:
The patent segments the image into different regions based on luminance levels (shadows, midtones, highlights) and applies different color correction transforms to each region. This allows the correction to be tailored to each region's characteristics, preventing the unnatural color casts that occur when a single global transform is applied to all regions.
Solution Approach 2:
The patent applies local quality by using region-specific correction matrices (M_shadow, M_midotone, M_highlight) that are optimized for each luminance region. Each region receives a correction transform that is appropriate to its local characteristics, with highlight regions receiving attenuated correction to preserve their natural appearance.
2Manufacturing precision
If uniform color correction is applied to all pixels, then the overall image color balance is improved, but white pixels become pastel blue in highlight areas
Solution Approach 1:
The patent introduces dynamic adaptation by adjusting the correction transform based on the luminance level of each pixel. The correction matrix is selected or blended based on the pixel's position in the luminance range, allowing the system to adapt its correction strength to preserve white points in highlights while still correcting color casts in other regions.
Solution Approach 2:
The patent changes the correction parameters (specifically the correction matrix) based on the luminance parameter of each pixel. By modifying which correction matrix is applied based on luminance level, the system maintains color balance accuracy in most regions while preserving the fidelity of highlight regions where whites should remain white.
3Manufacturing precision
If strong color correction is applied to eliminate color casts, then the neutral objects appear more neutral, but the highlight regions develop complementary color casts
Solution Approach 1:
The patent applies preliminary anti-action by pre-identifying highlight regions and preparing an attenuated correction transform specifically for these areas. This prevents the harmful complementary color casts from developing in the first place, rather than trying to correct them afterward. The highlight region transform is designed to minimize correction strength to preserve natural appearance.
Data Source
AI summary
A method is provided for attenuating image color-cast corrections. The method comprises: selecting a highlight color; accepting a digital image of colored pixels; calculating the difference between the color of at least one pixel and the highlight color; determining an illuminant correction for the digital image; and, attenuating the image illuminant correction for at least one pixel in response to the calculated color differences. In some aspects of the method, a highlight color with a plurality of color components is selected, for example, white. Then, calculating the difference between the color of at least one pixel and the highlight color includes calculating the difference of at least one color component of the pixel from the corresponding component in the highlight color.