Project Motivation and Objectives

1. Comparison between DLP and LCOS projectors for 3-D shape measurement John Gibson1, Dr. Song Zhang2, Yajun Wang2 1Department of Computer Engineering, Bethune-Cookman University, Daytona Beach, Florida 2Department of Mechanical Engineering, Iowa State University, Ames, Iowa Project Motivation and Objectives Projector Technologies Results and Discussion Understanding the technique for 3D shape measurement Demonstrate the differences between two technologies (DLP and LCOS); show the principle of the three-step and nine-step phase-shifting algorithm; combine the technologies with the methods and compare the phase errors and conclude which one is the best combination for 3D shape measurement Figure 4: Fringe image and phase error of 0.077 rad for the LCOS using FSP without gamma calibration • Digital light processing projector (DLP) • Liquid crystal on silicon projector (LCOS) • Reflective • LED light source • Single DMD chip • Color wheel, which deliver color sequentially • Sharp images • High Resolution SVGA (800 x 600) • Used in classroom • Reflective and transmissive • LED light source • No need for color wheel, so deliver color simultaneously • Smooth images • High Resolution VGA (640 x 480) • Used in elegant home theater Figure 5: Fringe image and phase error of 0.115 rad for the DLP using FSP without gamma calibration. DLP with DBP method Results and Discussion Figure 1: A typical digital fringe projection systems DLP using FSP method • 3-step phase shifting Figure 6: Fringe image, phase error of 0.009 rad, and 3D result for the DLP using DBP method. LCOS with DBP method • Phase wrapping • I′(x, y) is the average intensity, I″(x, y) is the intensity modulation, and ϕ (x, y) is the phase to be solved for. Solving Equations (1) from (3) simultaneously, we obtain the phase Figure 2: Fringe image, phase error of 0.009 rad, and 3D result for the DLP using FSP with gamma calibration. LCOS using FSP method Figure 7: Fringe image, phase error of 0.022 rad, and 3D result for the LCOS using DBP method. Conclusions In general, an N-step phase-shifting algorithm with equal phase shifts can be given by • Remarks • The DLP projector using the FSP method with gamma calibration is better than the LCOS projector. • The LCOS projector using the FSP method without gamma calibration has a smaller phase error than the DLP projector. • Using the best defocusing level with DBP method, the DLP projector gave better results compare to the LCOS projector. • Future work • Comparing the projectors to real-time measurements. • n = 1, 2, …, N. The phase for N-step phase-shifting algorithm is given by Figure 3: Fringe image, phase error of 0.012 rad, and 3D result for the LCOS using FSP with gamma calibration.