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Proceedings Paper

A new technique for contact lenses measuring based on digital image processing
Author(s): Qiheng Xu; Haiyang Liao; Sumao Feng
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Paper Abstract

To ensure the functionality, safe reliability and amenity of contact lens, the center thickness tc , diameter φt and base curves r0 are three key parameters to be measured. For purpose of measuring the parameters tc , φt and r0 of contact lens in a single compact instrument with high accuracy and efficiency, a new method based on digital image processing is proposed and examined. Firstly, aim at establishing appropriate measurement environment and obtaining the measuring images properly, the instrument structure is designed and implemented according to the characteristics of contact lenses. Several main environmental factors affects the accuracy has been considered, such as measuring medium and temperature. Secondly, the procedure of the geometric features location and coordinate conversion is analyzed and demonstrated. Thanks to the Canny-Zernike edge detection, the feature points in the image can be effectively positioned at sub-pixel level without increasing the hardware costs. In order to map the feature points’ pixel coordinates to world coordinates, the homography between the measuring plane and the imaging plane is estimated based on the pinhole imaging model. Lastly, with the specific obtained feature world coordinates, the distance formula and least squares curve fitting are used to calculate the object parameters. The instrument prototype and experimental analysis show that the proposed technique has advantages in terms of accuracy, volume reduction and efficiency over existing optical-mechanical techniques.

Paper Details

Date Published: 8 October 2015
PDF: 6 pages
Proc. SPIE 9677, AOPC 2015: Optical Test, Measurement, and Equipment, 96770U (8 October 2015); doi: 10.1117/12.2199207
Show Author Affiliations
Qiheng Xu, Chongqing Univ. (China)
Haiyang Liao, Chongqing Univ. (China)
Sumao Feng, Chongqing Univ. (China)

Published in SPIE Proceedings Vol. 9677:
AOPC 2015: Optical Test, Measurement, and Equipment
Sen Han; Jonathan D. Ellis; Junpeng Guo; Yongcai Guo, Editor(s)

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