Gamma distortion is a dominant error source of phase measuring profilometry. It
makes a single frequency for the ideal sinusoidal waveform an infinite width of
spectrum. Besides, the defocus of the projector-camera system, like a spatial
low-pass filter, attenuates the amplitudes of the high-frequency harmonics. In
this paper, a generic distorted fringe model is proposed, which is expressed as
a Fourier series. The mathematical model of the harmonic coefficients is
derived. Based on the proposed model, a robust gamma calibration method is
introduced. It employs the multifrequency phase-shifting method to eliminate the
effect of defocus and preserve the influence of gamma distortion. Then, a gamma
correction method is proposed to correct the gamma distortion with the
calibrated gamma value. The proposed correction method has the advantage of high
signal-to-noise ratio. The proposed model is verified through experiments. The
results confirm that the phase error is dependent on the defocus and the pitch.
The proposed gamma calibration method is compared with the state of the art and
proves to be more robust to pitch and defocus variations. After adopting the
proposed gamma correction method, the phase precision is much enhanced with
higher quality in the measured surfaces.
© 2012 Optical Society of America
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