LAUSR

Existing 3-D structured light (SL) scanning methods require a high number of images (multifrequency phase shifting, MF-PS) or embed signals in the space domain (space domain modulation phase shifting, SDM-PS) to conduct phase unwrapping. These methods are either movement sensitive (for MF-PS) or low in accuracy (for SDM-PS). In this work, a new 3-D SL scanning method is proposed to use the theoretical minimum of three images only. Unlike existing methods that directly embed signals in the space domain, the assistance signals are modulated in the phase domain of PS images, inspired by the phase-shift keying (PSK) theory. Phase calculation in the proposed phase domain modulation phase shifting (PDM-PS) method is independent of embedded assistance signals. The signal to noise ratio (SNR) of phase codewords and the accuracy of phase unwrapping and 3-D reconstruction are well retained. Experimental results demonstrated that the proposed PDM-PS method using only three images was able to achieve comparable 3-D measurement accuracy as the traditional MF-PS method (three images vs. nine images, 0.03 mm vs. 0.02 mm); and both using three images, the proposed PDM-PS method outperformed the traditional SDM-PS method in terms of measurement accuracy (0.03 mm vs. 0.07 mm).