CMOS Image Sensor Color Shading Correction via Matrix Lookup
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Solution Overview
Problem
CMOS image sensors experience color shading distortion, particularly around image edges, due to optical and electrical cross-talk between pixels, leading to non-uniform color representation across the image.
Innovation Solution
A method and device for color shading correction using local color matching, where each pixel's RGB value is treated as a one-by-three matrix multiplied by a three-by-three matrix generated during factory calibration, with interpolation used to determine matrices for each pixel location, enabling effective color matching and correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a high-quality lens and sensor are used to achieve uniform color across the image, then color shading is reduced, but the cost of the imaging system increases significantly
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing correction matrices in a lookup table during the manufacturing process. These matrices are computed in advance to compensate for color shading artifacts, allowing the system to use lower-quality, cheaper optical components while achieving uniform color output through pre-computed corrections applied during image capture.
Solution Approach 2:
The patent changes parameters by applying position-dependent correction matrices to pixel values based on their location in the image sensor array. The correction matrices modify the RGB values of pixels according to their spatial coordinates, effectively compensating for optical imperfections and achieving uniform color across the entire image without requiring high-quality lenses.
2Manufacturing precision
If complex color correction processing is applied to each pixel to correct color shading, then color accuracy is improved, but processing time and computational complexity increase
Solution Approach 1:
The patent pre-computes correction matrices for all possible pixel positions and stores them in a lookup table during manufacturing. This preliminary action eliminates the need for complex real-time calculations during image processing, as the system simply retrieves pre-computed matrices based on pixel coordinates, significantly reducing processing time while maintaining color accuracy.
Solution Approach 2:
The patent uses a lookup table that contains copies of pre-computed correction matrices for different regions of the image sensor. Instead of performing complex calculations for each pixel, the system copies and applies the appropriate pre-computed matrix from the lookup table based on the pixel's position, greatly simplifying the processing operation and reducing computational time.
Data Source
AI summary
A device for color shading correction is provided. Local color matching is performed as follows. For each pixel of the image that is being color matched, the RGB value is treated as a one-by-three matrix, which is multiplied by a three-by-three matrix that is generated during factory calibration. The matrix product is a one-by-three matrix that is used as the RGB value for the pixel in the color matched image.