Comparison between a DLP and LCOS projector for 3-D shape measurement

1. Comparison between a DLP and LCOS projector for 3-D shape measurement John Gibson Dr. Song Zhang, Yajun Wang, Laura Ekstrand 3D Machine Vision Laboratory

2. Structured light system

3. Phase-shifting algorithm 3-step phase shifting Phase wrapping Subtracting Equations (1) from (3) simultaneously, we obtain the phase

4. DLP The digital light processing (DLP) projector uses tiny mirrors to reflect light . White light passes through a color wheel then to the DMD chip. The color wheel which can produce 16.7 million colors.

5. LCOS LCOS or Liquid Crystal over Silicon projectors are a hybrid of LCD and DLP. The projectors use three LCOS chips, one each to modulate light in the red, green, and blue channels. The LCOS projects light simultaneously. no spinning color wheel

6. Differences between the projectors DLP LCOS Reflective and transmissive 3 chips (red,blue,and green channels Resolution (1365 x 1024) Pixel are smooth so smooth images • Reflective • Single-chip • Resolution (1280 x 720) • Pixel are sharp so sharp images

7. Differences between the fringe methods Defocusing Binary Patterns(DBP) Focusing Sinusoidal patterns(FSP) The phase error is larger if no gamma calibration is adopted The camera and projector must be precisely synchronized • There is no need to calibrate the nonlinear gamma • Easy to generate sinusoidal fringe patterns • No need for precisely synchronizing the projector with the camera.

8. DLP DBP FSP w/ gamma calibration Phase standard error 0.0470 rad Phase standard error 0.2407 rad

9. LCOS results DBP FSP w/ gamma calibration Phase standard error 0.0314 rad Phase standard error 0.0769 rad

10. Future Work Phase wrapping and unwrapping objects. Sculpture reconstruction and comparison Get better images Data analysis

11. Questions?