In a white light interferometry, the light beam from the light source is split into two: one to the reference surface and the other to the measurement surface, then these light beams are reflected and interfere with each other. An interference pattern occurs when the optical path difference (OPD) between these two light beams is small. The interference pattern is known as interfero- gram, and is recorded by area-based photo-sensitive sensor such as charge-coupled device (CCD) camera. Correlogram is the function of intensity response of each pixel against the OPD, and its envelope function is known as fringe contrast function.