Rotationally Asymmetric Filter for Image Sharpening
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Solution Overview
Problem
Conventional unsharp mask processing using rotationally symmetrical filters fails to effectively sharpen images deteriorated by asymmetrical point spread functions (PSF) in optical systems, leading to undershoot and insufficient correction in certain directions.
Innovation Solution
An image processing apparatus and method that employs a rotationally asymmetric filter based on the PSF of the optical system, adjusting the center of gravity position of the filter to match the target pixel, ensuring precise sharpening by using two-dimensional data with filter coefficients arranged asymmetrically relative to the target pixel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a rotationally symmetrical filter is used for unsharp mask processing, then the processing is simple and easy to implement, but it cannot correctly sharpen images deteriorated by asymmetrical PSF, leading to insufficient correction and undershoot in certain directions
Solution Approach 1:
The patent applies asymmetry by designing a rotationally asymmetrical filter that matches the asymmetrical point spread function (PSF) of the optical system. The filter coefficients are arranged asymmetrically around the target pixel, with different weight distributions in different directions, allowing the filter to correctly compensate for asymmetrical aberrations and sagittal halos that cannot be corrected by symmetrical filters.
2Manufacturing precision
If the filter coefficients are arranged rotationally asymmetrically, then the sharpening accuracy for asymmetrical PSF is improved, but the filter design and adjustment becomes more complex
Solution Approach 1:
The patent applies local quality by making the filter coefficients position-dependent, where each coefficient's value and position is specifically tailored to match the local characteristics of the PSF in different directions. The asymmetrical arrangement allows different regions of the filter to have different properties, optimizing the sharpening effect for each direction while maintaining overall accuracy.
Solution Approach 2:
The patent changes the parameters of the filter by adjusting the relative positions of the center of gravity and peak position of the filter coefficients. By independently controlling these parameters, the filter can be precisely tuned to match the PSF characteristics, achieving accurate sharpening while managing the complexity through systematic parameter adjustment.
3Adaptability or versatility
If the center of gravity position and peak position of the filter do not accord, then the filter may be easier to design for certain PSF shapes, but the sharpening effect reduces and problems occur
Solution Approach 1:
The patent systematically adjusts the parameters of the filter by independently controlling the center of gravity position and peak position. The center of gravity position is set to match the PSF's energy distribution, while the peak position is optimized for maximum sharpening effect. This parameter-based approach allows the filter to adapt to different PSF shapes while maintaining precision through controlled adjustments.
Data Source
AI summary
An image processing apparatus acquires an input image generated by image pickup via an optical system, and perform unsharp mask processing for the input image using a filter generated based on information of a PSF of the optical system. The filter is generated based on an unsharp mask used for the unsharp mask processing, and includes two-dimensional data having filter coefficients that are arranged rotationally asymmetrically with respect to a filter coefficient corresponding to a target pixel in the input image in convoluting the filter with the input image. A peak position or a center of gravity position of the unsharp mask accords with a position of the filter coefficient corresponding to the target pixel in the filter.