Fourier analysis of RGB fringe-projection profilometry and robust phase-demodulation methods against crosstalk distortion

Abstract

Abstract:In this paper we apply the frequency transfer function (FTF) formalism to analyze the red, green and blue (RGB) phase-shifting fringeprojection profilometry technique. The phase-shifted fringe patterns in RGB fringe projection are typically corrupted by crosstalk because the sensitivity curves of most projection-recording systems overlap. Crosstalk distortion needs to be compensated in order to obtain high quality measurements. We study phase-demodulation methods for null/mild, moderate, and severe levels of RGB crosstalk. For null/mild crosstalk, we can estimate the searched phase-map using Bruning's 3-step phase-shifting algorithm (PSA). For moderate crosstalk, the RGB recorded data is usually preprocessed before feeding it into Bruning's PSA; alternatively, in this paper we propose a computationally more efficient approach, which combines crosstalk compensation and phase-demodulation into a single process. For severe RGB crosstalk, we expect non-sinusoidal fringes' profiles (distorting harmonics) and significant uncertainties on the crosstalk calibration (which produces pseudo-detuning error). Analyzing these distorting phenomena, we conclude that squeezing interferometry is the most robust demodulation method for RGB fringe-projection techniques. We support our conclusions with numerical simulations and experimental results.Centro de Investigaciones en Optica, 2016-05-13.

3D Measurement of Human Chest and Abdomen Surface Based on 3D Fourier Transform and Time Phase Unwrapping

“…According to Equation (14), N 0 is obtained from q r , q g , and q b , then the absolute phase can be obtained by the following equation:…”

“…For compound color stripe image sequences, color coupling correction and color separation should be made based on the correction matrix of each pixel, and the three RGB primary color fringe image sequences of different periods can be separated. Because the color coupling phenomenon exists at the coincident intersection of the three color channel spectral response curves in the 3CCD industrial camera [14], the color calibration based on hardware equipment should be completed before the measurement. That is to say, the projector projects four patterns of full red, full green, full blue, and full black to the chest and abdomen surface, and the four images will be captured by the camera.…”

Color profilometry techniques: A review

“…Phase-shifting techniques have been frequently used in 3D imaging, because of their accuracy and speed, although, as it was mentioned before, some limitations are observed. In recent years the merging of color information has been increasingly used in an attempt to develop either a single-shot or multi-shot phaseshifting, able to encode supplementary surface data on an image or images to reduce the ambiguity presented in traditional grey-level phase-shifting on discontinuous surfaces [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29].…”

“…According to the topography of the tested area, the pattern will be distorted allowing to retrieve the phase of the object, and by extracting the color planes from the acquired image, three phase-shifted sinusoidal patterns are achieved. Then the traditional phase-shifting methods to retrieve the wrapped and unwrapped phases can be applied [15][16][17][18][19][20][21][22][23][24]. Fig.…”

“…This technique is able to retrieve the 3D reconstruction through a single image for irregular surfaces, eliminating the background noise often presented in Fourier analysis. Padilla et al [22] also use a single color phase-shifted pattern with Fourier transform analysis. Three sinusoidal fringes are encoded onto a single color pattern that is then projected onto a surface, and a single color image is taken.…”