Lens Shading Correction Using Singular Value Decomposition
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Solution Overview
Problem
CMOS image sensors face challenges in optimizing individual pixels due to lens shading effects, such as vignetting and light diffraction, which affect image quality, especially with reduced pixel sizes and increased image quality demands.
Innovation Solution
A lens shading correction system that includes pre-processing, singular value decomposition, reconstruction weight approximation, and polynomial fitting to determine and apply shading correction coefficients, using a block diagram and flow charts to generate and store coefficients for polynomial-fitted correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If lens shading correction is applied to improve image quality, then image quality is improved, but device complexity increases due to multiple processing steps
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing correction coefficients for different illuminant conditions before actual image capture. The system characterizes the imaging device under multiple illuminants in advance, performs singular value decomposition to determine correction coefficients, and stores these coefficients for rapid application during image processing, eliminating the need for complex real-time calculations
Solution Approach 2:
The patent utilizes parameter changes by varying illuminant conditions (different light sources and spectra) during the characterization process to capture how the imaging device responds to different lighting scenarios. This allows the system to adapt correction parameters dynamically based on the actual illuminant present, improving correction accuracy without requiring complex real-time analysis
2Measurement precision
If multiple illuminant characterization is performed to improve correction accuracy, then correction accuracy is improved, but loss of time increases due to extended calibration process
Solution Approach 1:
The patent performs preliminary characterization under multiple illuminant conditions during the manufacturing or setup phase, storing the results as correction coefficients. This preliminary action ensures high correction accuracy is achieved without requiring time-consuming multi-illuminant calibration at the point of use, as all necessary data is pre-computed and stored for rapid retrieval
Solution Approach 2:
The patent creates simplified copies or representations of the complex multi-illuminant characterization data in the form of correction coefficients stored in memory. Instead of storing full spectral data or requiring repeated measurements, the system uses compact coefficient representations that can be quickly applied during image processing while maintaining high correction accuracy
Data Source
AI summary
Methods and systems for determining shading correction coefficients of an imaging device. An inversion surface is determined based on an image captured by the imaging device. The inversion surface is approximated using the captured image and eigenvectors associated with singular values of the inversion surface, to form multiple reconstruction weights. A polynomial fit is applied to: i) the multiple reconstruction weights to determine a first set of polynomial coefficients and ii) the eigenvectors to determine a second set of polynomial coefficients. The first and second sets of polynomial coefficients are used to form the shading correction coefficients.