Fig. 1. Dark field detection schematic diagram

Fig. 2. Auto-focus process

Fig. 3. Sharpness evaluation function curve

Fig. 4. Calibration board

Fig. 5. Linear distorted projection model

Fig. 6. Linear distortion correction model

Fig. 7. Comparison before and after top hat transformation. (a) Grayscale map of original image; (b) grayscale map of transformation results

Fig. 8. Autofocus curve. (a) Tenengrad function curve of coarse adjustment; (b) focusing motor position curve of accurate adjustment; (c) sub-window Tenengrad function curve of accurate adjustment

Fig. 9. Image contrast before and after autofocusing. (a) Image before autofocusing; (b) image after autofocusing

Fig. 10. Binarization algorithm comparison. (a) Original image; (b) Otsu algorithm; (c) maximum entropy model; (d) mean weighted adaptive binarization algorithm; (e) Laplacian weighted adaptive binarization algorithm

Fig. 11. Results of ultra-depth microscope. (a) Microscopic image of area 1; (b) microscopic image of area 2