Optimal window selection for obtaining an extended-depth-of-focus image from white light interference microscopy images

White Light Scanning Interferential Microscopy (WLSI) is a widely used technique for determining the 3D topography of surfaces with nanometer resolution. However, despite obtaining the topography with adequate resolution, the precise information of the object's reflectance is lost due to a degrading of the microscopy images with interference fringes. These fringes make it challenging to obtain an extended focus image (EFI) to inspect details of the entire surface, as is done in standard microscopy. The typical procedure to estimate the reflected intensity of the object is to perform an averaging of the depth interference intensity signal. However, for many samples of the intensity signal, the effect of blurring becomes noticeable. Alternatively, in the case of few samples, remnant artifacts of the interference fringe patterns remain. In this work, we determine an adequate axial range that represents an optimal window for averaging and estimating the intensity of an EFI. A series of WLSI interference images were simulated, and EFI images were calculated by averaging over axial lengths normalized relative to the depth of field. Each EFI was compared with the reference image using the signal-to-noise ratio (SNR) and the universal quality index (UQI) metrics with the highest values obtained of 44.332 and 0.9997, respectively, for an axial range of 0.28DOF.