Results in Physics (Jan 2022)
Signal-to-noise ratio enhancement of temporal phase unwrapping using video grating projection
Abstract
Temporal phase unwrapping (TPU) has important application in fringe projection phase-shifting profilometry to measure multi-isolate objects and discontinuities surfaces. Due to the gray-scale standard of the digital projector, the gray-scale of the deformed pattern is of 256 at most. Suppose the frequency of the high-frequency patterns is enlarged for improving accuracy. In that case, it may lead to the vulnerability of intensity noise, particularly in terms of unit-frequency and low-frequency patterns. To some extent, it may challenge the reliable measurement range of the TPU method. To this end, the signal-to-noise ratio (SNR) enhancement of temporal phase unwrapping (SETPU) using video grating projection is proposed. By projecting the specially designed video grating onto the measured object instead of the traditional static grating, adequately controlling the exposure time and the gain of camera allows for the broader gray-scale patterns to be captured. The further analysis shows that the intensity modulation with the SETPU method is more than 3.7 times that with the traditional TPU method, and the SNR with the SETPU method is stronger than that with the traditional TPU method due to the broader gray-scale range so as to efficiently broaden the reliable measurement range of TPU method. The experimental results verify the validity and practicability of the proposed method.
