Fig. 1. Speckle measuring system based on DIC method

Fig. 2. Schematic of measuring principle of DIC method

Fig. 3. Process of converting original image to GLCM

Fig. 4. Results of 4 speckle patterns after translation. (a) Error; (b) standard deviation

Fig. 5. Mean gray second derivative of 4 speckle patterns

Fig. 6. Results of speckle pattern processing. (a) Speckle patterns; (b) gray histogram

Fig. 7. Full-field displacement changes in u direction of 4 speckle patterns under different displacement quantities. (a) 0.05 pixel; (b) 0.95 pixel; (c) 1.00 pixel

Fig. 8. Effect of 4 speckle patterns with uneven illumination. (a) Image A; (b) image B; (c) image C; (d) image D

Fig. 9. Error and standard deviation of 4 speckle images with non-uniform illumination. (a) Error; (b) standard deviation

Fig. 10. Results of speckle image C under different average gray values. (a) 208.1751; (b) 140.8798; (c) 97.3179;(d) 62.6947; (e) 50.8449; (f) 23.8115; (g) 2.5869

Fig. 11. Results of 4 speckle patterns at different brightness states. (a) Error; (b) standard deviation