Asymmetric Unsharp Mask for Aberration Correction
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Solution Overview
Problem
Conventional unsharp mask processing struggles to effectively correct intricately shaped aberrations and sharpen images due to its reliance on rotationally symmetric filters, which fail to address asymmetric aberrations and sagittal halos, and requires storing extensive data for various image-pickup conditions, making it memory-intensive.
Innovation Solution
The use of a rotationally asymmetric unsharp mask based on the point spread function (PSF) of the optical system for image sharpening, which allows for more accurate correction by matching the unsharp mask to the PSF, reducing the need for extensive data storage by approximating the PSF with a function and its coefficients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a rotationally symmetric filter is used for unsharp mask processing, then the processing is simple and computationally efficient, but it cannot sufficiently correct intricately shaped aberrations such as asymmetric aberration and sagittal halo
Solution Approach 1:
The patent applies an asymmetric unsharp mask filter whose shape corresponds to the asymmetric point spread function (PSF) of the optical system. This asymmetric filter design enables sufficient correction of intricately shaped aberrations including asymmetric aberration and sagittal halo, which cannot be corrected by rotationally symmetric filters. The filter coefficients are determined based on the PSF characteristics, allowing the filter to match the specific aberration pattern of the optical system.
2Manufacturing precision
If asymmetric correction is applied in azimuth directions with large aberration, then the aberration correction is improved, but undershoot occurs in azimuth directions with small aberration
Solution Approach 1:
The patent applies different filter coefficients to different azimuth directions based on the local aberration characteristics. The unsharp mask filter is designed with coefficients that vary according to the PSF distribution in different directions, allowing strong correction in directions with large aberration while providing appropriate suppression in directions with small aberration to prevent undershoot. This directional adaptivity resolves the contradiction between correction strength and undershoot prevention.
3Manufacturing precision
If conventional unsharp mask processing is used, then the processing method is simple, but it requires storing extensive data for various image-pickup conditions making it memory-intensive
Solution Approach 1:
The patent extracts the essential characteristics of the PSF and represents them using a reduced set of parameters or a parametric model. Instead of storing complete PSF data for all possible image-pickup conditions, the system uses a compact representation that captures the key features needed for unsharp mask filtering. This parameter-based approach significantly reduces memory requirements while maintaining sharpening accuracy across different imaging conditions.
4Manufacturing precision
If a one-dimensional filter is used as in Japanese Patent Laid-open No. 2010-81263, then asymmetry in the image height direction is addressed, but asymmetries in other directions cannot be improved
Solution Approach 1:
The patent transitions from one-dimensional filtering to two-dimensional unsharp mask filtering that operates in both image height and image width directions. The 2D filter coefficients are determined based on the PSF distribution across the entire image plane, enabling correction of asymmetric aberrations in all directions including sagittal halo and other direction-dependent aberrations. This multi-dimensional approach provides comprehensive coverage of asymmetric aberration patterns.
Data Source
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Figure 4A~5B
AI summary
An image processor includes a correction signal generator (202) configured to generate a correction signal by calculating a difference between an image and an image obtained by applying an unsharp mask generated based on a PSF corresponding to an image-pickup conditions of an image-pickup optical system to the image, and a correction signal applier (203) configured to sharpen the image by multiplying the correction signal generated by the generator by a constant and by adding a multiplied correction signal to the image.