Fig. 1. Schematic of log-polar transformation

Fig. 2. Schematic of speckle correlation method

Fig. 3. Schematic of sub-pixel measurement

Fig. 4. (a) Speckle image; (b) speckle image after log-polar transformation

Fig. 5. Correlation coefficient of simulation experiments. (a) Cmax; (b) Cdif

Fig. 6. Results with angular displacement of 20°. (a) Traditional s'peckle method; (b) proposed method

Fig. 7. Results of simulation experiments. (a) Mean error; (b) standard deviation

Fig. 8. Experimental setup

Fig. 9. Correlation coefficient of physical experiments. (a) Cmax; (b) Cdif

Fig. 10. Results of physical experiments. (a) Mean error; (b) standard deviation