Fig. 1. Schematic of focus variation

Fig. 2. Ideal focusing curve

Fig. 3. An experimental image obtained using focus variation microscopy and three testing points

Fig. 4. Focus curves obtained from single point information and neighborhood information with different operators. (a) Brenner operator; (b) Roberts operator; (c) Laplace operator; (d) Tenengrad operator; (e) SMD operator; (f) gradient square; (g) Sobel operator in eight directions

Fig. 5. Focus scatter plots with different sizes of neighborhood. (a) 5; (b) 9; (c)13; (d) 17

Fig. 6. Focusing evaluation results of points with different brightness. (a) (380,280); (b) (700,390); (c) (608,218)

Fig. 7. Focusing evaluation results of three brighter points. (a) (765,115); (b) (363,1095); (c) (829,68)

Fig. 8. Schematic of wavelet fusion method

Fig. 9. Comparison of image fusion results. (a) Image fusion based on spatial regional characteristics; (b) image fusion with frequency domain wavelet; (c) color image fusion with frequency domain wavelet

Fig. 10. Experimental system

Fig. 11. Image sequence diagrams of coin surface. (a) 1st image; (b) 2nd image; (c) 30th image; (d) 31st image; (e) 80th image; (f) 81st image

Fig. 12. 3D measurement results of coin surface relief. (a) 3D point cloud; (b) 3D color reconstruction image

Fig. 13. A gauge step measurement result. (a) One of images in image sequence; (b) 3D point cloud data; (c) point cloud distribution of a section