Grey-level coding for structured-light illumination systems

Abstract

Fringe Projection Profilometry and Phase Measuring Deflectometry Systems are well-established technologies for noncontact 3D surface measurements. A common challenge in those systems is to obtain the absolute surface information using few measurement frames. In practice both techniques often generate a series of sinusoidal fringe patterns with different frequencies and use a camera vision system to capture the (by the object) deformed patterns. The images containing the deformed patterns are then processed to obtain the 3D surface information. Sinusoidal multi-frequency techniques have been for years and are an on-going area of research, where various algorithms have been developed to measure the unwrapped phase map (at the shortest fringe period). Commonly, temporal phase shifting techniques are used to extract the phase at different frequencies. However, obtaining the phase map for every fringe period requires multiple measurement frames. In this work, the advantages of efficient grey level (GL) coding techniques are presented, where a focus is given on the reduction of frames for noncontact 3D surface measurements. A further focus is given on additional features of GL coding as e.g. the error-detecting and the error-correcting properties of those codes that make GL coding an interesting candidate for harsher measurement environments.