Digital filtering methods used in eliminating diffraction halo of speckle interferograms

摘要

Homomorphic filtering and digital processing methods to eliminate diffraction halo in speckle interferograms are proposed in this paper. According to the principle of speckle interferometry, speckle pattern can be regarded as the one which is composed of two multiplying parts: diffraction halo and fringe. The light intensity change of speckle diffraction halo is much slower than that of fringes in the direction perpendicular to fringes, not only does the diffraction halo cause the decrease of the speckle fringe's contrast, but also the deviation of the fringe's extremum positions. Because all of the useful information is contained in fringes, the two multiplying parts can be divided into two additive parts to make digital filtering in frequency domain by homomorphic processing method in order to compress the diffraction halo and enhance the fringe's contrast. Digital methods to eliminate diffraction halo effect are realized by using the simulation of the light intensity distribution of diffraction halo. These methods can effectively eliminate or reduce the diffraction halo background in speckle patterns.