Abstract
Optical metrology has experienced a fast development in recent years—cross laser-pattern has become a common cooperative measuring marker in optical metrology equipment, such as infrared imaging equipment or visual 3D measurement system. The rapid and accurate extraction of the center point and attitude of the cross-marker image is the first prerequisite to ensure the measurement speed and accuracy. In this paper, a cross laser-pattern is used as a cooperative marker, in view of the high resolution of the cross laser-pattern image in the project and the vulnerability to adverse environmental effects, such as stray light, smoke, water mist and other interference in the environment, resulting in poor contrast, low signal-to-noise ratio (SNR), uneven energy distribution. As a result, a method is proposed to detect the center point and attitude of cross laser-pattern image based on Gaussian fitting and least square fitting. Firstly, the distortion of original image is corrected in real time, the corrected image is smoothed by median filter, and the noise is suppressed while preserving the edge sharpness and detail of the image. In order to adapt to different environments, the maximum inter-class variance method of threshold automatic selection is used to determine the threshold of image segmentation to eliminate the background interference caused by different illumination intensities. To improve the real-time performance of the algorithm, the four cross laser edge pixels are obtained by line search, and then fitted by least square. With the edge lines, the transverse and portrait line of the cross-laser image are separated, then we calculate Gaussian center points of all Gaussian sections of transverse and portrait lines based on Gaussian fitting method, respectively. Based on the traditional line fitting method, the sub-pixel center of the transverse and portrait laser strip images are fitted by removing the Outlying Points, and the center coordinates and attitude information of the cross laser-pattern are calculated by using the center equation of the laser strip, realizing cross laser-pattern center and attitude accurate positioning. The results show that the method is robust, the center positioning accuracy is better than 0.6 pixels, the attitude positioning accuracy is better than ±15” under smoke and water mist environment and the processing speed is better than 0.1 s, which meets the real-time requirements of the project.
Highlights
IntroductionIn of acquired laser-pattern image data, poorcross contrast, low signal-to-noise ratio and view of the large amount of acquired cross laser-pattern image data, poor contrast, low uneven energy distribution, this method cannot meet the real-time and precision requiresignal-to-noise ratio and uneven energy distribution, this method cannot meet the real-time ments of the project
Cross laser-pattern is often used as a cooperative measuring marker in optical metrology, with a laser plane projecting on the measured surface and digital processing of the acquired images [3], such as infrared viewing equipment [4] or three-dimensional visual measurement system [5]
In of acquired laser-pattern image data, poorcross contrast, low signal-to-noise ratio and view of the large amount of acquired cross laser-pattern image data, poor contrast, low uneven energy distribution, this method cannot meet the real-time and precision requiresignal-to-noise ratio and uneven energy distribution, this method cannot meet the real-time ments of the project
Summary
In of acquired laser-pattern image data, poorcross contrast, low signal-to-noise ratio and view of the large amount of acquired cross laser-pattern image data, poor contrast, low uneven energy distribution, this method cannot meet the real-time and precision requiresignal-to-noise ratio and uneven energy distribution, this method cannot meet the real-time ments of the project. K mean clustering algorithm, the central coordinates are obtained by coordinate This method is not suitable for a wide cross laser-pattern, and cannot achieve transformation. Paper,cross crosslaser-pattern laser-pattern is used as cooperative measuring marker in shipIn this is used as cooperative measuring marker in shipboard board environment with stray smoke, water other interference, a method environment with stray light, light, smoke, water mistmist and and other interference, a method is is proposed to process the acquired digital image with poor contrast, low signal-to-noise proposed to process the acquired digital image with poor contrast, low signal-to-noise ratio (SNR) and and uneven uneven energy distribution, detect detect the center point point and and attitude attitude of of cross cross ratio (SNR).
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