Fig. 1. Ideal focusing evaluation curve

Fig. 2. Microscope images with different clarity

Fig. 3. Fitting result of 2-peak Gaussian

Fig. 4. Experimental system

Fig. 5. Sequence diagrams of bit surface imaging. (a) 1st picture; (b) 2nd picture; (c) 17th picture; (d) 18th picture; (e) 34th picture;(f) 35th picture

Fig. 6. Three sampling locations

Fig. 7. Fitting results of operators at point A; (a) Brenner; (b) Roberts; (c) Laplace; (d) GRA

Fig. 8. Fitting results of operators at point B; (a) Brenner; (b) Roberts; (c) Laplace; (d) GRA

Fig. 9. Fitting results of operators at point C; (a) Brenner; (b) Roberts; (c) Laplace; (d) GRA

Fig. 10. GWIS operator fitting results at point C

Fig. 11. All focus image obtained by GWIS operator