Rolling Shutter Autofocusing via Region Contrast Weighting
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Solution Overview
Problem
Rolling shutter type imaging devices in image measuring apparatuses face challenges in high-precision autofocusing due to positional errors caused by sequential imaging of light receiving elements, leading to inaccuracies when the region of maximum contrast is not at the image center.
Innovation Solution
An image measuring apparatus using a rolling shutter type imaging device, a position control system, and a computing device that divides images into regions, corrects contrast information based on imaging timing, and multiplies contrast values by weights corresponding to imaging timing to accurately determine the in-focus position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If an imaging device of the rolling shutter type is used, then the cost is reduced, but the measurement precision deteriorates due to positional errors in sequential imaging
Solution Approach 1:
The image is divided into multiple regions (e.g., first region and second region) corresponding to different imaging timings. Contrast information is calculated separately for each region, and then combined with appropriate weighting to obtain corrected overall contrast information. This segmentation approach resolves the contradiction by enabling precise measurement through region-specific contrast analysis while using the cost-effective rolling shutter device.
2Device complexity
If contrast information is calculated from the entire image, then the processing is simple, but the autofocusing precision deteriorates when the maximum contrast region is offset from the image center
Solution Approach 1:
Different regions of the image are assigned different weights based on their imaging timing and contrast characteristics. The weighting process gives appropriate emphasis to regions that contribute more accurately to the in-focus position determination. This local quality approach improves autofocusing precision by considering spatial variations in contrast reliability while maintaining reasonable processing complexity through systematic weight application.
Data Source
AI summary
An image measuring apparatus includes: an imaging device of a rolling shutter type configured to image a work; a position control system configured to output a focusing position as information representing a position in a direction of a focusing axis by controlling an in-focus position of the imaging device; and a computing device configured to calculate, from image information acquired from the imaging device, contrast information corresponding to the image information, wherein the computing device divides an acquired image into a plurality of regions and corrects the contrast information corresponding to the image information based on a position of and the contrast information corresponding to each of the regions.