Adaptive High Dynamic Range for Time-of-Flight Cameras

The limited dynamic range of conventional digital cameras is a well-known problem. A common solution is to apply high-dynamic-range (HDR) techniques over several images acquired using different exposure times. Time-of-flight (ToF) cameras using a photonic mixer device (PMD) are not an exception, since the dynamic range of its dual pixels is also limited. Furthermore, in this case, the saturation of the pixel channels leads to wrong depth measurements. An appropriate solution is the suppression of background illumination (SBI) system designed by the PMD. This system actually extends the dynamic range of the camera by hardware, but it also introduces noise when activated. In this paper, we present an adaptive HDR (AHDR) solution to the problem for the ToF case that overcomes the limited dynamic range of the system, allowing sensing along a theoretically infinite dynamic range with the only limitations of the power of the illumination system and the decay of the SNR with higher distances or lower illumination intensities. Our method is able to detect and segment relevant scene regions responsible for unexpected saturation, i.e., close foreground objects, from the rest of the scene and adjust the exposure times of the acquired images considering them. The results show a reduction in detail losses and a higher SNR in the AHDR raw images, with respect to single acquisitions. This results in a dramatic depth error reduction and effective axial resolution improvement in critical areas, while keeping a high frame rate. In addition, the SBI-related noise is eliminated.