Calibration of Time-of-Flight Cameras

This chapter describes the metric calibration of a time-of-flight camera including the internal parameters, and lens distortion. Once the camera has been calibrated, the 2D depth image can be transformed into a range map, which encodes the distance to the scene along each optical ray. It is convenient to use established calibration methods, which are based on images of a chequerboard pattern. The low resolution of the amplitude image, however, makes it difficult to detect the board reliably. Heuristic detection methods, based on connected image components, perform very poorly on this data. An alternative, geometrically principled method is introduced here, based on the Hough transform. The Hough method is compared to the standard OpenCV board-detection routine, by application to several hundred time-of-flight images. It is shown that the new method detects significantly more calibration boards, over a greater variety of poses, without any significant loss of accuracy.