Colored slightly off-axis method for self-occluding shading in projection profilometry

We present a phase demodulation technique for fringe analysis in fringe projection profilometry, based on digital moiré and the co-phase technique. The approach involves the use of stereo illumination and the simultaneous projection and acquisition of two π-shifted sinusoidal patterns from each projector. By taking advantage of color multiplexing, we code the sinusoidal patterns in the red and blue channels of the color images, so we need to project and acquire one image for each digital light projector. The phase demodulation involves three steps: first, digitally generating the moiré pattern for each colored fringe pattern using the synchronous detection method; second, computing the analytic signals for the two moiré patterns via a third-order low-pass Butterworth filter in the frequency domain; and third, calculating the final phase by merging the two analytic signals with the co-phasing technique.