Fig. 1. p type polarization light

Fig. 2. Image acquisition system for vision measurement based on polarization device

Fig. 3. Image acquisition on object surface under different polarization angles

Fig. 4. White balance processing of image and corresponding histogram features. (a) Color image; (b) histogram of color image; (c) white balanced image; (d) histogram of white balanced image

Fig. 5. Flowchart of mean-shift segmentation algorithm based on dark channel images

Fig. 6. Images acquired under different polarization angles, image with highlight components and pixel luminance distribution in two-color reflection model

Fig. 7. BP neural network model for highlight removal based on polarization information

Fig. 8. Flowchart of image highlight removal based on polarization information

Fig. 9. Effect of image highlight removal based on polarization information. (a) Image acquired under optimal polarization angle; (b) pixel luminance distribution corresponding to (a); (c) image after highlight removal; (d) pixel luminance distribution corresponding to (c)

Fig. 10. Detail comparison of SIFT feature extraction. (a) SIFT feature extraction of image under optimal polarization angle; (b) SIFT feature extraction of image under optimal polarization angle after treatment by RANSAC algorithm; (c) SIFT feature extraction of image after highlight removal; (d) SIFT feature extraction of image after highlight removal and treatment by RANSAC algorithm

Fig. 11. Detail comparison of SURF feature extraction. (a) SURF feature extraction of image under optimal polarization angle; (b) SURF feature extraction of image under optimal polarization angle after treatment by RANSAC algorithm; (c) SURF feature extraction of image after highlight removal; (d) SURF feature extraction of image after highlight removal and treatment by RANSAC algorithm

Fig. 12. Boundary contours extracted under different conditions. (a) After highlight removal; (b) under optimal polarization angle

Fig. 13. Three-dimensional space coordinates of feature points of experimental object’s contour

Table 1. Number of feature points on workpiece surface under different conditions

Table 2. Coordinates of feature points for Sobel edge detection and corresponding world coordinates

Table 3. Comparison of measurement accuracy based on image highlight removal