Range unfolding for Time-of-Flight depth cameras

Time-of-Flight depth cameras provide a direct way to acquire range images, using the phase delay of the incoming reflected signal with respect to the emitted signal. These cameras, however, have a challenging problem called range folding, which occurs due to the modular error in phase delay-ranges are modulo the maximum range. To our best knowledge, we exploit the first approach to estimate the number of mods at each pixel from only a single range image. The estimation is recasted into an optimization problem in the Markov random field framework, where the number of mods is considered as a label. The actual range is then recovered using the optimal number of mods at each pixel, so-named range unfolding. As demonstrated in the experiments with various range images of real scenes, the proposed method accurately determines the number of mods. In result, the maximum range is practically extended at least twice of that specified by the modulation frequency.