Image Signal Processing Color Shading Correction
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Solution Overview
Problem
Digital cameras embedded in electronic devices face challenges in effectively correcting color shading issues, which occur when light is received at an angle, leading to noticeable color shifts near the edges of images.
Innovation Solution
A method and apparatus for image signal processing that includes generating modified image representations using color shading adjustments, such as gain mapping and polynomial mapping, to correct color shading across various light spectrums, including halogen, fluorescent, and daylight, by calculating and comparing frequency distributions of red to green channel ratios in pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If color shading correction is applied to digital camera images, then color accuracy is improved, but image processing complexity increases
Solution Approach 1:
The patent applies preliminary color shading correction by generating a correction map based on sensor position and light angle calculations before the actual image processing. This pre-computed correction data is then applied to pixels during image rendering, separating the complex calculation phase from the application phase to reduce overall processing complexity while maintaining color accuracy.
Solution Approach 2:
The patent implements local quality correction by applying different correction factors to different regions of the image based on pixel position and light angle. Each pixel or pixel group receives customized correction parameters calculated according to its specific location and the angle of incident light, allowing precise color correction without uniformly processing the entire image.
2Adaptability or versatility
If multiple light spectrum corrections are implemented, then adaptability to different lighting conditions is improved, but processing time increases
Solution Approach 1:
The patent uses parameter changes by pre-calculating correction parameters for multiple light spectrums (halogen, fluorescent, daylight, etc.) and storing them as lookup tables. During image processing, the appropriate spectrum parameters are selected based on detected lighting conditions, avoiding the need to perform complex calculations for each spectrum in real-time and significantly reducing processing time while maintaining adaptability.
3Measurement precision
If gain mapping and polynomial mapping are used for color shading correction, then color accuracy is improved, but computational requirements increase
Solution Approach 1:
The patent implements a dynamic approach by selecting between gain mapping and polynomial mapping based on the severity of color shading and processing requirements. For mild color shading, simpler gain mapping is used to reduce computational load. For severe color shading or when higher precision is required, polynomial mapping is applied. This dynamic selection optimizes the balance between color accuracy and computational requirements.
Data Source
Figure 1a~1b
Figure 2
Figure 3a~4b
AI summary
In one embodiment of the present invention, a method comprises generating at least one modified image representation of a subject image representation using at least one color shading adjustment (10), calculating at least one frequency of color ratio values for each of the at least one modified image representation (20), and determining one of said at least one modified image representation and the subject image based at least in part on the at least one frequency (25). The method can correct for light source dependent color shading or vignetting artifacts in digital images.