Time-of-flight cameras measure the distances to scene points by emitting and detecting a modulated infrared light signal. The modulation frequency of the signal determines a certain maximum range within which the measured distance is unambiguous. If the actual distance to a scene point is longer than the maximum range, the measured distance suffers from phase wrapping, which makes the measured to be shorter than its actual distance by an unknown multiple of the maximum range. This paper proposes a time-of-flight camera, which is capable of restoring the actual distance by simultaneously emitting light signals of different modulation frequencies and detecting them separately in different regions of the sensor. We analyze the noise characteristic of the camera, and aquire simulated depth maps using a commercially available time-of-flight camera, reflecting the increased amount of noise due to the use of dual-frequency signals. We finally propose a phase unwrapping method for restoring the actual distances from such a dual-frequency depth map. Through experiments, we demonstrate that the proposed method is capable of extending the maximum range at least twice, with high success rates.

Date Published: 12 March 2013
PDF: 11 pages
Proc. SPIE 8650, Three-Dimensional Image Processing (3DIP) and Applications 2013, 86500H (12 March 2013); doi: 10.1117/12.2003379

Published in SPIE Proceedings Vol. 8650:
Three-Dimensional Image Processing (3DIP) and Applications 2013
Atilla M. Baskurt; Robert Sitnik, Editor(s)