Fig. 1. Schematic of overall hardware device in detection system

Fig. 2. Overall flow chart of defect detection of workpieces

Fig. 3. Schematic of progressive image denoising algorithm based on BM3D

Fig. 4. Schematic of image preprocessing algorithm of highly reflective workpiece

Fig. 5. Variation of edge pixels of image. (a) Original image; (b) edge pixels of local gray image; (c) 3D image

Fig. 6. Subpixel edge extraction based on Zernike moment. (a) Original edge position; (b) edge position after rotation; (c) generated template image

Fig. 7. Pixel contour lines of edge positioning error

Fig. 8. Experimental results. (a) Original images; (b) algorithm in Ref. [21]; (c) algorithm in Ref. [22]; (d) proposed algorithm

Fig. 9. Comparative experimental results under different illumination. (a) Workpiece images under different illumination; (b) results of algorithm in Ref. [21]; (c) results of algorithm in Ref. [22]; (d) results of proposed algorithm