A fast, robust and precise method for measuring scratches on optical surfaces

CHEN Shaojie; LI Bailin; ZHAO Wenchuan; XIONG Ying; LIU Jiajia

doi:10.7510/jgjs.issn.1001-3806.2016.03.016

In order to improve location and width measurement precision of optical surface scratches, a sub-pixel edge detection algorithm based on discrete orthogonal polynomial surface fitting was proposed. Sub-pixel edge detection was realized by fitting the edge points and their neighborhood into surfaces instead of by curve fitting only in the gradient direction of the edge points. By using the acceleration strategy of the region of interest and the method of fast solving surface equation parameters based on discrete orthogonal polynomial, the processing time was greatly reduced. In terms of width calculation, the Euclidean distance of each section was calculated after the scratch was divided into a series of small segments adaptively and then the maximum width was the width of scratch. The experimental results show that the proposed method has high accuracy and strong robustness. Mean error of width is less than 5.2% and standard deviation of width is less than 0.3 of the same scratches measured under different visual windows by this algorithm. In terms of processing time to solve the surface model parameter, the processing time of acceleration strategy is 7.35% of the least square method and is greatly reduced. This method can meet the requirements of fast and high precision measurement in engineering application.

A fast, robust and precise method for measuring scratches on optical surfaces

Corresponding author: LI Bailin, blli62@263.net;

1. College of Mechanical Engineering, Southwest Jiaotong University, Chengdu 610031, China;

2. The Institute of Optics and Electronics, Chinese Academy of Sciences, Chengdu 610209, China

Received Date: 2015-03-11

Accepted Date: 2015-04-11

Available Online: 2016-05-25

Abstract: In order to improve location and width measurement precision of optical surface scratches, a sub-pixel edge detection algorithm based on discrete orthogonal polynomial surface fitting was proposed. Sub-pixel edge detection was realized by fitting the edge points and their neighborhood into surfaces instead of by curve fitting only in the gradient direction of the edge points. By using the acceleration strategy of the region of interest and the method of fast solving surface equation parameters based on discrete orthogonal polynomial, the processing time was greatly reduced. In terms of width calculation, the Euclidean distance of each section was calculated after the scratch was divided into a series of small segments adaptively and then the maximum width was the width of scratch. The experimental results show that the proposed method has high accuracy and strong robustness. Mean error of width is less than 5.2% and standard deviation of width is less than 0.3 of the same scratches measured under different visual windows by this algorithm. In terms of processing time to solve the surface model parameter, the processing time of acceleration strategy is 7.35% of the least square method and is greatly reduced. This method can meet the requirements of fast and high precision measurement in engineering application.

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Reference (17)

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A fast, robust and precise method for measuring scratches on optical surfaces

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