Interference problem of multiple Kinects (1)

Why interference?

"Multiple Kinects tend to interfere with one another. A Kinect measures the depth of a point by projecting a pattern of infrared dots into the scene and detecting how far they appear shifted due to parallax. This is great when there is only one Kinect but if you have more than one there is no way of separating out their dots. What this means is that one Kinect could project an infrared dot that another Kinect "sees" as its own and hence incorrectly estimates the distance."

Solutions:

Time division multiplexing approach

Schroder et al. [1] implemented a time decision multiplexing approach, where IR emitter on each Kinect is blocked in turn so that the IR pattern don't interfere. However, the frame rate of depth images are reduces with the number of Kinects.

Shake n Sense (moving Kinect)

By adding a motor with an offset-weight vibration to one of the Kinects, the IR signals from IR camera are "modulated. The IR camera of the Kinect will move in harmony, which means that depth sensing works as normal, though a little blurs are introduced. Butler et al. [2] proved that even minor almost imperceptible motion of the sensor in this way causes blurring of structured light patterns from other units which serves to eliminate most of the cross-talk.

Hole filling algorithm

Instead of preventing the interference, Maimone and Fuchs [3] used a hole filling algorithm to fill missing depth caused by the interference and median filtering to reduce the noise. Their system can present real-time merging of the data from multiple Kinect and keep frame rate at 30 fps.

Reference:

Schroder, Y. and Scholz, A. and Berger, K. and Ruhl, K. and Guthe, S. and Magnor, M. Multiple kinect studies, Computer Graphics 2011.
Butler, D.A. and Izadi, S. and Hilliges, O. and Molyneaux, D. and Hodges, S. and Kim, D., Shake'n'sense: reducing interference for overlapping structured light depth cameras, Proceedings of the 2012 ACM annual conference on Human Factors in Computing Systems.
Maimone, A. and Fuchs, H. Encumbrance-free telepresence system with real-time 3d capture and display using commodity depth cameras, Mixed and Augmented Reality (ISMAR), 2011 10th IEEE International Symposium