A Structured Light Range Imaging System Using a Moving Correlation Code

We describe a system which produces a dense accurate range image using 8 consecutive frames of camera data in conjunction with a special projector. A prototype has been built and tested, and yields a typical range error of about 0.2 mm at 2 meters range with a baseline just over one meter. The camera is directed at a scene, along with a stripe projector consisting of a thin light source (xenon tube and slit) on the axis of a turntable, and a binary mask conforming to a cylinder coaxial with this. The mask has alternate opaque and transparent stripes parallel to the axis. It forms a sequence in which each subsequence of given length n (8 here) is different. No lens is used in the projector, deliberately smoothing the resulting illumination in a shadowing process. In operation, the turntable rotates, and images are taken at uniform angular intervals for several consecutive frames. In the consecutive frames, a given pixel records samples of the brightness of a fixed surface point. The vector consisting of those samples, when normalized, is unique to the place in the sequence from which it came, thus enabling the computation, via a fast indexing process, of the 3D position of the surface point. The code is similar to a DeBruijn sequence, but modified to reduce range error. Several types of calibration and error compensation were used to produce an accurate range image.