Using LED Illumination in Fringe Projection Profilometry with a Sinusoidal Phase Grating

Abstract

Fringe projection profilometry is a well-established method in optical metrology for capture of 3D objects [1]. The information is retrieved from the phase of the deformed fringe pattern formed by imaging the object onto a CCD camera after projection of a structured light pattern onto its surface. A variety of phase retrieval algorithms requires projection of sinusoidal fringes. Thin diffraction sinusoidal gratings under coherent illumination are a suitable choice for generation of good quality fringes focused in a large measurement volume [2]. The main drawback of coherent projection is the speckle noise. The lateral spacing of fringes produced by coherently illuminated sinusoidal grating does not depend on the wavelength. Thus, a light source with a wider spectrum can be used for reduction of the speckle noise in the fringe patterns recorded by the CCD camera provided the spatial coherence of the source is kept intact [3]. The aim of the present report is to prove speckle reduction in fringes projected with a sinusoidal phase grating (SPG) by using low coherent point light source with emphasis on LED illumination.