Fig. 1. Four-step phase shift gray image

Fig. 2. Simulated interference fringe pattern and wrapped phase image

Fig. 3. Wrapped phase images before and after adding noises

Fig. 4. Unwrapped phase images

Fig. 5. Wrapped phase images before and after adding invalid regions

Fig. 6. Unwrapped effect images and corresponding mass maps

Fig. 7. Device for defects detection of drum roller

Fig. 8. Drum roller and its degree of modulation

Fig. 9. Mass maps of drum roller