Histogram equalization and specification in interferometry

Equalization of histogram is used to process photographic digitized images composed mostly of pixels that are either very dark or very bright components. Equalization provides equal distribution of the number of pixels over the intensity range, which results in increased contrast and highlighted details. We apply here the histogram equalization to maximize the discernible number of fringes in a speckle pattern interferometry image, maximize the contrast of fringes and correct uneven exposure. When fitting the interferogram to a sinusoidal fringe pattern for phase determination, the closeness to the sinusoidal shape is important. Histogram processing allows ideal or near-ideal sinusoidal fringes to be obtained from non-sinusoidal patterns.