Coded Modulation Phase Unwrapping for Time-of-Flight Cameras

In recent years, application fields such as secure face recognition or autonomous driving increased the demand on efficient depth sensing systems. Robustness and power consumption are directly related to the number of measurements. Time-of-Flight (ToF) sensors are well suited to these applications. The measurement principle is based on measuring the phase and consequently the delay of emitted and reflected light. Problems arise by this measurement principle as the depth is without ambiguity due to phase wrapping. The depth of the scene is wrapped in the distance of the first 2 pi phase shift. In this paper, we aim to solve this problem by proposing a new Time-of-Flight phase unwrapping approach. We unwrap the traditional continuous wave ToF measurement with coded modulation. Images captured with coded modulation show a pixel response only within selected distance limits. With coded modulation we are able to separate the continuous wave range in different regions. These regions can then be unwrapped, by simple comparison of values. As our evaluation shows, our method is able to reduce the number of measurements from traditionally eight to only six. Furthermore, our approach improves the robustness as objects out of range are filtered.