Three-color Ronchi pattern for surface profilometry

Abstract

In Fourier transform profilometry (FTP), the measurement accuracy is greatly influenced by the phase errors induced by some inherent complications like the non-linear response of the optical system and filtering method for the fundamental frequency. In this paper, a new form of color pattern in the form of Ronchi fringes was proposed for enhanced surface measurement in FTP. The Ronchi pattern is structured with color channels red, green and blue that are spatially separated from one another and has a pulse width of 1/3 of its period. Since the proposed color Ronchi pattern has three color channels, three individual surface profiles of a distorted canvas were reconstructed from a single-shot image. A smoother surface profile was obtained by averaging the three reconstructed surfaces which provides lesser phase error. Moreover, compared to conventional sinusoidal patterns that has range of intensities (gray-value), the Ronchi pattern is single-valued which offers fast and simple fringe calibration. Reconstructions show that the proposed pattern can be effectively used for surface profilometry and effectively enhances the measurement for FTP method.