Camera Shading Calibration via Illuminant Transform Surfaces
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Solution Overview
Problem
Camera systems face non-uniform image response due to shading issues caused by lens and sensor misalignment, angular and spectral pixel response, and varying illumination sources, which require costly and time-consuming calibration processes, especially for small image sensor systems.
Innovation Solution
The Multiple Illuminant Transform Calibration (TransCal) method involves capturing flatfield images under multiple illuminants, calculating transform surfaces in a pre-production phase, and using these to determine shading calibration values during production with a single illuminant, allowing for accurate shading correction across various real-world illumination scenarios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple illuminants are used for module-level shading calibration to correct spectral shading variation, then shading correction accuracy for different illumination sources is improved, but production cost and calibration time increase
Solution Approach 1:
The patent performs preliminary calibration using a first illuminant to obtain initial shading correction values. Transform surfaces are pre-calculated and stored, enabling rapid conversion to other illuminants without repeating the full calibration process. This preliminary action eliminates the need for time-consuming recalibration for each illuminant scenario.
Solution Approach 2:
The patent creates transform surfaces that mathematically model the relationship between different illuminants. These transform surfaces act as copies or representations that allow conversion between illumination conditions without physically requiring multiple illuminants during production. The transform surfaces capture the spectral characteristics of different illuminants in a compressed mathematical form.
2Measurement precision
If multiple illuminants are used for module-level shading calibration to correct spectral shading variation, then shading correction accuracy for different illumination sources is improved, but production equipment complexity increases
Solution Approach 1:
The patent replaces physical multiple illuminant equipment with mathematical transform surfaces. Instead of requiring five different physical illumination sources or spectral shift filters, the system uses a single illuminant during production and applies computational transforms to simulate other illuminants. This reduces physical equipment complexity while maintaining correction accuracy.
Solution Approach 2:
The patent substitutes the mechanical/optical system of multiple physical illuminants with a computational/mathematical system. The transform surfaces perform the function of multiple illuminants through software-based spectral conversion, eliminating the need for complex optical switching mechanisms or multiple light sources in the production calibration system.
3Measurement precision
If multiple illuminants are used for module-level shading calibration to correct spectral shading variation, then shading correction accuracy for different illumination sources is improved, but the number of calibration values and storage requirements increase
Solution Approach 1:
The patent merges the calibration data for multiple illuminants into a single set of transform surfaces. Instead of storing five separate calibration value sets for five different illuminants, the system stores one calibration result and uses mathematical transforms to derive corrections for all other illuminants. This consolidation reduces the quantity of calibration values while maintaining comprehensive coverage.
Solution Approach 2:
The transform surfaces serve multiple functions: they enable conversion between any pair of illuminants, provide a universal calibration framework that works for all real-world illumination scenarios, and reduce the overall calibration data requirements. A single transform surface structure handles all illuminant combinations rather than requiring separate calibration data for each scenario.
Data Source
AI summary
The invention includes methods and apparatus for correcting shading non-uniformity in camera systems. A method includes capturing at least two sets of flatfield images from at least two sets of camera modules under first and second illuminant, respectively. Pixels for each image in the sets of flatfield images are then averaged to form first and second averaged flatfield images, respectively. The first averaged flatfield image is transformed using the second averaged flatfield image to create a transform image. The transform image is then saved in memory for calibrating the shading non-uniformity of the camera module.