High-resolution real-time 3D absolute coordinates measurement using a fast three-step phase-shifting algorithm

High-resolution, real-time 3-D absolute coordinate measurement is highly important in many fields. This paper presents such a system that measures 3-D absolute geometric shapes and positions at 30 frames per second (fps), with an image resolution of 532 × 500. The system is based on a digital fringe projection and fast three-step phase-shifting method. It utilizes a digital-light-processing (DLP) projector to project color encoded computer generated phase-shifted fringe patterns in grayscale, a high-speed CCD camera synchronized with the projector to capture fringe images at 90 fps. Based on the three-step phase-shifting algorithm, any successive three fringe images can be used to reconstruct one 3-D shape. Therefore, the 3-D shape measurement speed is 30 fps. To obtain absolute coordinates, absolute phase is required. In this research, a tiny marker is encoded in the projected fringe pattern, and detected by software from captured fringe images accurately. Absolute coordinates can be obtained when the marker position is located and the measurement system is calibrated. To demonstrate the performance of the system, we measured human faces. The details of facial geometries and dynamic changes of facial expressions are measured clearly. We also measured a hand moving over a depth distance of approximately 700mm, again both hand shapes and positions changes are clearly captured. By using the fast three-step phase-shifting algorithm and a parallel processing technique, we successfully developed a system that acquires, reconstructs, and displays 3-D shape in real-time. Applications of such a system include manufacturing, inspection, reverse engineering, computer vision and computer graphics.