Fig. 1. Schematic diagram of the total focusing imaging method

Fig. 2. Schematic diagram of support vector machine

Fig. 3. Schematic diagrams of defects. (a) Aluminum test piece with pitting corrosion; (b) aluminum test piece with cracks

Fig. 4. Defect images. (a) TFM image with pitting; (b) TFM image with cracks; (c) PCI image with pitting; (d) PCI image with cracks

Fig. 5. Phase information diagrams of No.4 pitting defect in width direction. (a) Phase value; (b) phase value difference

Fig. 6. Horizontal amplitudes at different depths in images containing pitting and crack defects. (a) 400 mm (pitting); (b) 600 mm (pitting); (c) 400 mm (crack); (d) 460 mm (crack)

Fig. 7. Enhanced dataset

Fig. 8. HOG feature map. (a) Original image; (b) HOG feature map

Fig. 9. Accuracy of SVM image defect classification under different kernel functions. (a) Different dataset types; (b) before and after data enhancement