Scene Adaptive Lens Shading Correction for Imaging Devices
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Solution Overview
Problem
Existing imaging devices face challenges in correcting lens shading variations across different illuminant conditions, leading to undesirable color shading errors when a gain adjustment surface calibrated for one illuminant type is applied to images captured under a different type.
Innovation Solution
The implementation of scene adaptive lens shading correction, which determines the illuminant type of a captured scene and modifies a reference gain adjustment surface with a scene adjustment surface to obtain a scene-adapted gain adjustment surface, using a second-order polynomial curve to approximate the scene adjustment surface, requiring a relatively small number of parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a gain adjustment surface calibrated for a specific illuminant type is applied to all captured images, then lens shading correction can be performed with a small number of parameters, but color shading errors occur when the image is captured under a different illuminant type
Solution Approach 1:
The patent segments the gain adjustment surface into two independent components: a reference gain adjustment surface (calibrated for a specific illuminant type) and a scene adjustment surface (specific to each illuminant type). This segmentation allows the system to store a small reference surface once and only store scene-specific adjustment surfaces for different illuminant types, reducing overall parameter storage while maintaining correction accuracy across varying lighting conditions.
Solution Approach 2:
The patent makes the gain adjustment surface dynamic by selecting or modifying it based on the detected illuminant type. Instead of using a static gain adjustment surface for all conditions, the system dynamically adapts the surface by combining the reference surface with the appropriate scene adjustment surface corresponding to the detected illuminant type, thereby maintaining correction accuracy across different lighting scenarios.
2Measurement precision
If separate gain adjustment surfaces are stored for each illuminant type, then lens shading correction accuracy is maintained across different illuminant conditions, but the number of parameters to be stored increases significantly
Solution Approach 1:
The patent extracts the common characteristics of lens shading correction into a single reference gain adjustment surface that is calibrated for a specific illuminant type. This reference surface contains the fundamental correction data that applies across all illuminant types. Only the scene-specific variations are stored as separate scene adjustment surfaces, significantly reducing the total parameter storage requirement compared to storing complete independent surfaces for each illuminant type.
Solution Approach 2:
The patent changes the parameter representation by separating the gain adjustment into a reference component and scene-specific adjustment components. This parameter transformation allows the system to store a compact reference surface once and only store incremental scene adjustment parameters for different illuminant types, rather than storing complete parameter sets for each condition, thereby reducing overall parameter complexity.
3Measurement precision
If the lens shading properties are calibrated for a specific color channel and illuminant combination, then correction accuracy is optimized for that specific combination, but the system lacks adaptability to other illuminant types
Solution Approach 1:
The patent creates a universal reference gain adjustment surface that serves all color channels and illuminant types as a base correction. This reference surface is then combined with scene-specific adjustment surfaces to achieve channel-specific and illuminant-specific correction accuracy. This multi-functional approach allows a single reference surface to serve multiple purposes while maintaining adaptability to different conditions.
Solution Approach 2:
The patent applies local quality by maintaining a single reference gain adjustment surface with uniform properties across all channels, while introducing scene-specific adjustment surfaces that provide localized corrections for specific illuminant types. This allows the system to benefit from the stability of a universal reference while adapting to local variations in different lighting conditions through the scene-specific components.
Data Source
AI summary
Methods, apparatuses, and systems for scene adaptive lens shading correction. One or more gain adjustment surfaces calibrated to a reference illuminant type is stored. At least one scene adjustment surface, which varies as a function of the illuminant type, is stored for each additional illuminant type for which lens shading correction is desired. Additionally, an imaging device with a color image sensor may define a gain adjustment surface and a scene adjustment surface for each of the color channels of the image sensor. Scene adaptive lens shading correction entails determining an illuminant type for a captured image, selecting a scene adjustment surface based on the determined illuminant type, and processing the image using a gain adjustment surface modified by the scene adjustment surface.