Bezier Patch Array Calibration for Lens Shading Correction
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Solution Overview
Problem
Conventional high-order polynomial methods for correcting lens shading effects are computationally expensive and numerically unstable, making them inefficient for hardware implementation and intuitive interpretation.
Innovation Solution
The use of Bezier surfaces, specifically Bezier patch arrays, to correct image data for lens shading and imperfections, allowing for efficient and stable image processing by determining calibration data through reciprocal values and control points.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high order polynomial is used to correct lens shading, then correction accuracy is improved, but computational complexity increases
Solution Approach 1:
The patent divides the image plane into multiple zones and uses different polynomial orders for different zones. High-order polynomials are applied only where needed (edges with severe vignetting) while lower-order or no correction is applied in the center where light distribution is more uniform. This segmentation approach maintains correction accuracy in critical areas while reducing overall computational complexity.
Solution Approach 2:
The patent applies local quality by using different correction strategies for different regions of the image. The correction parameters and polynomial orders are optimized locally for each zone rather than applying a uniform high-order polynomial across the entire image, thereby achieving accurate correction where needed while minimizing unnecessary computations in other areas.
2Measurement precision
If high order polynomial is used to correct lens shading, then correction accuracy is improved, but execution time increases
Solution Approach 1:
By segmenting the image into zones with different correction requirements, the patent reduces the total number of high-order polynomial evaluations needed. Only edge zones require complex high-order corrections, while central zones use simpler corrections, significantly reducing overall execution time while maintaining accuracy where it matters most.
Solution Approach 2:
The patent applies partial correction action by using high-order polynomials only for the portions of the image that require it (edge areas with vignetting), rather than applying full high-order correction to the entire image. This partial application of complex correction reduces computational burden and execution time while maintaining sufficient accuracy.
3Measurement precision
If high order polynomial is used to correct lens shading, then correction capability is improved, but numerical stability deteriorates
Solution Approach 1:
The patent segments the correction task by using lower-order polynomials in zones where high-order corrections are not needed, thereby avoiding the numerical instability issues that arise from evaluating high-order polynomials across the entire image. This selective application maintains correction capability where necessary while improving numerical stability overall.
Solution Approach 2:
The patent changes the polynomial order parameter dynamically based on spatial location and vignetting severity. By adjusting the polynomial order from high to low depending on the region, the system maintains correction capability in problematic areas while avoiding numerical instability in regions where simple corrections suffice.
Data Source
AI summary
A system and method for correcting image data. Embodiments of the present invention provide calibration and image correction to overcome various lens effects including lens shading and lens imperfections. In one embodiment, the correction of image data is performed via utilization of a spline surface (e.g., Bezier surface). The use of spline surfaces facilitates efficient hardware implementation. The image correction may be performed on a per channel and illumination type basis. In another embodiment, the present invention provides a method for determine a spline surface to be used for calibrating an image signal processor to be used in correcting image data.