Effect of the nonlinearity of the CCD in Fourier transform profilometry on spectrum overlapping and measurement accuracy

Abstract

In Fourier transform profilometry (FTP), we must restrain spectrum overlapping caused by the nonlinearity of the charge coupled device (CCD) and increase the measurement accuracy of the object shape. Firstly, the causes of producing higher-order spectrum components and inducing spectrum overlapping are analysed theoretically, and a simple physical explanation and analytical deduction are given. Secondly, aiming to suppress spectrum overlapping and improve measurement accuracy, the influence of spatial carrier frequency of projection grating on them is analysed. A method of increasing the spatial carrier frequency of projection grating to restrain or reduce the spectrum overlapping significantly is proposed. We then analyze the mechanism of how the spectrum overlapping is reduced. Finally, the simulation results and experimental measurements verify the correction of the proposed theory and method.

Method for reducing phase errors due to CCD nonlinearity

“…A schematic of the experimental equipment is shown in Fig. 2 [5]. For the practical experiments, we chose d = 400 mm, L o = 900 mm, and T 0 = 24 mm.…”

“…It is also widely used in such fields as machine vision, solid modeling, automated industrial testing equipment, and medical diagnostics [1][2][3][4][5][6][7][8][9][10][11]. Phase measurement is generally performed using the phase-shifting method [1][2][3] and the Fourier transform method [4,5].…”

“…Their method is based on the finding that nonsinusoidal waveforms depend on a projector's gamma nonlinearity only [11]. Although these proposed nonlinearity correction methods can improve phase accuracy to a certain degree, further improvement for applications requiring very high accuracy can be achieved by reducing the charge coupled device (CCD) nonlinearity effect, which has not yet been adequately studied [5,12]. Therefore, in this paper, we present a method for reducing the CCD nonlinearity induced phase error.…”

Nonlinear effect of the structured light profilometry in the phase-shifting method and error correction

“…But, two major error sources exist in experiment. One is the harmonic spectrums overlapping, [7,17] and the other is the complex spectrum of irregular deformed fringes. Therefore, in experiment, undesired harmonics cannot be completely eliminated and phase error exists.…”

“…One is the gamma phenomenon in off-the-shelf digital projectors, [5,6] and the other is the nonlinearity of digital cameras. [7,8] The problem seriously reduces the accuracy of the SL 3D system. [9,10] In this paper, a theoretical model of the SL 3D system nonlinearity is analyzed, and a nonlinear correction method based on the Fourier spectrum analysis is proposed.…”