Image enhancement for the phase stepped interferometric process by appropriate filtering

Abstract

PSI (Phase Stepped Interferometry) is a well known technique for the measurement of surface deformation. Since in this technique phase characteristic of a linear system is computed using arctangent function, in some points the raw phase data exceeds the value 2/spl pi/. Moreover the surface roughness, phase unwrapping and extra noise imposed from the environment makes the surface look like a original surface with huge impulsive noise and simply using PSI technique does not produce accurate reconstructed surface. In this paper we propose a filtering technique that suppress the noise and enhance the image quality. We propose that the raw phase data should be prefiltered by a mean filter to eliminate Gaussian noise. Then after proper unwrapping treatment the data should be filtered with a RCM (Rank Conditioned Median) filter. This filter is effective at treating impulsive type noise and preserve step edges without blurring.