Fig. 1. Flow chart of proposed method

Fig. 2. Pretreatment process. (a) Original image; (b) mask region; (c) region of interest

Fig. 3. Window scanning trace

Fig. 4. Structure of CrackCNN

Fig. 5. Loss and accuracy of CrackCNN

Fig. 6. Beamlets at different scales. (a) Scale is 0; (b) scale is 1; (c) scale is 2; (d) scale is 3

Fig. 7. Comparison of different threshold methods

Fig. 8. Detection results of three methods