Fig. 1. Femtosecond laser processing platform and ablated spot image. (a) Processing platform; (b) strip ablation trace; (c) plasma spot image

Fig. 2. Enhancement effect comparison. (a) Original image; (b) grayscale image; (c) PCA enhancement image; (d) histogram equalization

Fig. 3. Grayscale pseudo-color enhancement effects obtained by different filtering methods

Fig. 4. Core ablation zone segmentation. (a) Segmentation result; (b) mask

Fig. 5. Pseudo-color maps of plasma spot along different processing directions. (a) Downward; (b) upward; (c) steering

Fig. 6. Flow chart for judging machining direction

Fig. 7. Examples of flow chart for judging machining direction. (a) Steps for judging downward processing; (b) steps for judging upward processing; (c) steps for judging steering processing

Fig. 8. Luminance characteristics based on Niblack segmentation mask. (a) Pseudo color; (b) segmentation; (c) segmentation effect; (d) mask

Fig. 9. Brightness characteristic and direction label of sample A. (a) Total brightness; (b) average brightness; (c) direction label

Fig. 10. Brightness characteristic and laser power label of sample B. (a) Total brightness; (b) average brightness; (c) power