Phase and colour calculation in colour fringe projection

Abstract

In this paper, we present a novel method to simultaneously extract the phase (and hence XYZ shape) and colour, red, green and blue (RGB) information from composite RGB fringe patterns captured by a colour fringe projection system. Three sinusoidal fringe patterns with different fringe numbers determined by an optimized three-frequency selection method are encoded in the red, green and blue channels forming composite RGB colour fringe patterns. Due to mismatch and overlap of the spectra from commercially available colour CCD cameras and data projectors, coupling effects between the colour channels are unavoidable. However, the magnitude of the coupling effects can be determined. Using a commercial off-the-shelf three-chip colour CCD camera and digital light processing (DLP) projector without modification, a software-based optimization method was developed to simultaneously calculate the phase and colour information based on a mathematical model including the coupling effects. The performance of the algorithm has been determined using simulated and experimental data. The results show that a high phase resolution and reliable modulation values can be obtained even with large coupling effects between the colour channels. Using the optimized three-frequency selection method, absolute unwrapped phase values are determined, and hence the proposed method can measure objects with discontinuities or large slope changes.