Lens Shading Correction Using B-Spline Zone Partitioning
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Solution Overview
Problem
Conventional lens shading correction methods, such as the symmetric method and two-direction multiplication method, fail to accurately correct for asymmetrical and non-uniform shading effects in image sensors, particularly in packaged sensors with imperfect optical alignment and components, leading to undesirable intensity variations in images.
Innovation Solution
A multi-zone technique using two-dimensional B-spline curve fitting is employed to partition the image sensor into multiple zones, with piecewise continuous quadratic polynomial correction curves in each zone, allowing for accurate shading correction of both center and edge regions, and adapting to different lighting conditions by storing shading corrections for various illuminants.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the symmetric method is used to correct lens shading, then the correction process is simple and fast, but the correction accuracy deteriorates for packaged image sensors with imperfect optical alignment
Solution Approach 1:
The patent divides the image sensor into multiple zones (e.g., center zone and corner zones) and applies different correction functions to each zone. This segmentation allows the correction system to handle the complexity of asymmetric shading in packaged sensors while maintaining computational efficiency through zone-specific rather than pixel-by-pixel processing.
Solution Approach 2:
The patent applies different correction characteristics to different regions of the image sensor. The center zone uses one correction approach while corner zones use another, allowing each region to be optimized for its specific shading characteristics rather than applying a uniform correction across the entire sensor.
2Adaptability or versatility
If the two-direction multiplication method is used to correct lens shading, then the correction can be applied in both x and y directions, but the correction accuracy deteriorates in corner regions
Solution Approach 1:
The patent segments the image sensor into distinct zones including corner regions, allowing separate correction functions to be applied to corner zones rather than using a single global correction function. This enables optimized correction for corner-specific shading patterns.
Solution Approach 2:
The patent implements zone-specific correction functions where corner zones receive customized correction parameters different from the center zone, allowing each region to be corrected according to its local shading characteristics rather than applying uniform correction across the entire sensor.
3Device complexity
If a single quadratic polynomial is used to correct lens shading, then the correction function is simple and computationally efficient, but the correction accuracy deteriorates across the entire image
Solution Approach 1:
The patent divides the image sensor into multiple zones and applies different correction functions to each zone. This segmentation allows the use of simpler polynomial functions within each zone while achieving better overall correction accuracy through the combination of zone-specific corrections.
Solution Approach 2:
The patent applies different correction characteristics to different regions of the image sensor. The center zone uses one correction approach while corner zones use another, allowing each region to be optimized for its specific shading characteristics rather than applying a uniform correction across the entire sensor.
Data Source
AI summary
An image sensing system provides for accurate lens shading correction even when there is significant lens shading asymmetry and non-uniformity. A two-dimensional B-spline technique is used to determine lens shading correction surfaces. The number of zones is selected to achieve accurate correction of center, edge, and corner regions of an image. Separate lens shading correction surfaces are calculated for a set of standard illuminants to permit lens shading correction to be adapted based on the illuminant used to capture the image.