Recognizing Glitches
Working with three-phase scanning a bit recently, I've become very familiar with the kind of glitches that emerge. Watching Radiohead's "House of Cards" video again, I understand the glitches better now than when I first saw it:
- At :58-:59, Thom Yorke's neck separates from his head intermittently. This is due to the ambiguity of propagating a wrapped phase across shadows and depth discontinuities (from his jaw) which generally lend to a few possible interpretations of the data.
- At 1:29-1:31, someone waves their arms about a bit. If you look at the edges of their arms, you can see "barbs" coming out, something like 3d-interlacing. This is due to the nature of phase-shift scanning as a sequential structured light system rather than a continuous/fixed system. I'm a little amazed that these artifacts exist, as they were probably using a very high framerate camera.
- Throughout the video, entire scenes will jump forward and backward. This is due to the unwrapping algorithm again, and that it has to assume an absolute distance at a specific fixed point. If you get noise at that point, the entire image is shifted. I'm actually surprised this was a bug in the system they used.