Adaptive Filtering for Image Sensor Focus Detection Accuracy
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Solution Overview
Problem
Conventional focus detection techniques using pupil division methods face challenges in defocus direction detection accuracy due to insufficient pupil division performance and significant vignetting effects, especially when the f-number is small, leading to enhanced distortion and difficulty in detecting the defocus direction.
Innovation Solution
The proposed image capturing apparatus employs a filtering unit that selectively applies summation filtering when the f-number is small and combines summation and differential filtering when the f-number is larger than a threshold, to improve defocus direction detection accuracy without enhancing distortion caused by asymmetry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If differential filtering is applied to improve defocus detection accuracy, then defocus detection accuracy is improved, but distortion is enhanced when f-number is small
Solution Approach 1:
The patent changes the filtering parameter (type of filter) based on the f-number parameter. When f-number is small, summation filtering is used instead of differential filtering, avoiding distortion enhancement while maintaining acceptable defocus detection accuracy.
Solution Approach 2:
The patent dynamically selects the filtering method based on the f-number condition. The system transitions from differential filtering to summation filtering when f-number is small, making the filtering process adaptive to different imaging conditions.
2Speed
If pupil division method is used for focus detection, then high-speed focus adjustment is enabled, but defocus direction detection accuracy deteriorates when pupil division performance is insufficient
Solution Approach 1:
The patent changes the filtering approach based on the f-number parameter, which indirectly addresses the pupil division performance issue. By using summation filtering when f-number is small, the system maintains defocus direction detection accuracy even when pupil division performance is insufficient.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances defocus direction detection performance by accurately determining the focus position even under conditions of insufficient pupil division and significant vignetting, improving the precision of focus detection.
Implementation Method 1
an image sensor that generates image signals in response to light from an object
Data Source
AI summary
An image capturing apparatus performs focus detection based on a pair of image signals obtained from an image sensor including pixels each having a pair of photoelectric conversion units capable of outputting the pair of image signals obtained by independently receiving a pair of light beams that have passed through different exit pupil regions of an imaging optical system. In the focus detection, an f-number of the imaging optical system is acquired, the pair of image signals undergo filtering using a first filter formed from an summation filter when the f-number is less than a predetermined threshold, or using a second filter formed from the summation filter and a differential filter when the f-number is not less than the threshold, and focus detection is performed by a phase difference method based on the pair of filtered image signals.