Fig. 1. Principle diagram of displacement measurement system

Fig. 2. Simulated image of virtual moire fringe

Fig. 3. Flow chart of grayscale extreme value algorithm

Fig. 4. Simulation experiment. (a) Interference fringe; (b) gray three-dimensional model; (c) gray interpolation fitting curve; (d) bright fringe sub-pixel center line

Fig. 5. 28 fringe images with phase step of π/50

Fig. 6. Grayscale image and relative error versus phase under different algorithms. (a) Three-dimensional grayscale image; (b) grayscale extreme value method; (c) image correlation method; (d) L-K optical flow method

Fig. 7. Relative calculation time

Fig. 8. Experimental device for interference displacement measurement

Fig. 9. Experimental data graphs. (a) Step-displacement graph; (b) scatter plot of measured values; (c) residual diagram; (d) relative error-displacement needle plot