Inverse Transform Filter for Extended Depth of Field
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Solution Overview
Problem
Conventional image capturing apparatuses using inverse transform filters derived from a single focus position are limited in correcting blur across a wider range of depth of field, as they fail to maintain normal correction at positions with different spot shapes, restricting the extension of the depth of field to only a specific range.
Innovation Solution
An image capturing apparatus with an optical system providing aberration and an inverse transform unit that performs processing using an inverse transform filter, which includes frequency characteristics from multiple defocus positions, ensuring that the output image includes both higher and lower frequency characteristics compared to an ideal image, thereby extending the depth of field.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If an inverse transform filter is derived based on the MTF in one focus position, then the blur correction is effective at that focus position, but the correction fails at positions with different spot shapes, limiting the depth of field extension
Solution Approach 1:
The patent divides the depth of field range into multiple focus positions and derives a separate inverse transform filter for each position. This segmentation allows each filter to be optimized for its specific focus position, maintaining high correction precision across the entire depth of field range rather than using a single filter that compromises all positions.
Solution Approach 2:
The patent creates a set of inverse transform filters that collectively cover multiple focus positions, making the system universally applicable across the entire depth of field range. Each filter in the set serves a specific focus position, and together they provide comprehensive blur correction for all positions within the extended depth of field.
2Measurement precision
If the inverse transform filter is optimized for one focus position, then the MTF value is maximized at that position, but the spot shape variation at other positions causes correction failure
Solution Approach 1:
The patent applies local quality by deriving inverse transform filters with characteristics specifically matched to each focus position's spot shape. Each filter has local optimization for its target position's MTF and spot shape characteristics, rather than using a uniform filter design that cannot adapt to position-specific variations.
Solution Approach 2:
The patent changes the parameters of the inverse transform filter according to the focus position. By adjusting filter parameters to match the MTF and spot shape characteristics at each position, the system maintains both high MTF values and spot shape consistency across the depth of field range.
Data Source
AI summary
An image capturing apparatus includes: an optical system that provides an aberration to incident light; an image capturing unit that transforms the light passing through the optical system into pixels to capture an image; and an inverse transform unit that performs inverse transform processing on the image captured by the image capturing unit in a predetermined range on an optical axis of the optical system using an inverse transform filter that causes frequency characteristics of pixels in an output image in two or more of defocus positions within the predetermined range to include at least one frequency characteristic with a larger value and at least one frequency characteristic with a smaller value with respect to frequency characteristic of pixels in an ideal image of a subject.