Optical EngineeringEdge detection in a homogeneous background using the phase-shift fringe projection method
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Most existing intensity-based edge detection techniques are unable to detect edges of objects placed in a background whose intensity is same as that of the object surface, i.e., in a homogeneous background. This is mainly because under such conditions, a clear demarcation in intensity does not exist at the edge pixels. Thus, gradient- and difference-based operators such as the Sobel, Roberts and Prewitt operators are not capable of detecting the edges completely due to the absence of intensity variations at the edges. A technique for detecting the edges of multiple objects placed in a homogeneous background is proposed. In this technique sinusoidally coded stripes (fringes) are projected obliquely onto the object surfaces to form a fringe pattern image. Due to the depth of the object, intensity break points can be observed in the image and the edges can be detected by locating these points. In a simulation study, analysis carried out on the raw fringe pattern images to detect the edges, based on the proposed technique, shows that the detection error increases with the standard deviation of Gaussian noise. Analysis carried out on a phase image, obtained by applying the phaseshift method, however, shows a significant improvement in accuracy. The accuracy is also found to be almost unaffected by background noise. The results of edge detection using the proposed technique on real images are presented.