Abstract
Fringe projection profilometry (FPP) using a digital video projector is widely used for three-dimensional shape measurement. However, the gamma nonlinearity, system vibration, and noise cause the captured fringe patterns to be nonsinusoidal waveforms and have a grayscale deflection from their true value. This leads to an additional phase measurement error for a general phase-shifting algorithm. Based on the theoretical analysis, we propose a method to eliminate the phase error considering two factors. In this method, four-step phase-shifting is done four times with an initial phase offset of 22.5 deg and the average of these four phase maps precisely results in the real phase. As a result, phase error caused by gamma nonlinearity can be effectively suppressed. In addition, every image in phase shifting is replaced by the average of 20 fringe images continuously captured at the same state to avoid the phase error caused by system vibration and noise. Experimental results show that this method is effective in eliminating the phase error in practical phase-shifting FPP. In general, more than 90% of the phase error can be reduced.
Highlights
Fringe projection profilometry (FPP) using a digital video projector is one of the most common and effective techniques in fast three-dimesnional (3-D) shape measurement for its low cost, high reliability, high accuracy, and fast speed
The phase error elimination method proposed in this paper can effectively remove the periodical phase error due to gamma nonlinearity, system vibration, and noise and obtain a more accurate result with a better visual effect
We analyze the influence of system vibration and noise and gamma nonlinearity on phase error
Summary
Fringe projection profilometry (FPP) using a digital video projector is one of the most common and effective techniques in fast three-dimesnional (3-D) shape measurement for its low cost, high reliability, high accuracy, and fast speed It has been widely used in many fields, including biomedical applications,[1] human body shape measurement,[2] reverse engineering,[3] and quality control.[4] For phase-shifting methods, a series of sinusoidal fringe patterns generated by the computer are projected on to the object and captured by the camera. Huang et al proposed a double three-step phase-shifting algorithm and the error level has been reduced to less than half.[7] Pan et al presented an iterative method and simplified phase error to one order.[8] Guo et al have proposed a gamma-correction technique on the basis of statistical analysis of the fringe images.
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