where T is the set period of the system of interference fringes. So, the interference-contrast image (interferogram) visualizes phase silhouette of the micro-object in the form of the deviated lines; and the phase shifts can be measured just by a "ruler". This makes it possible to calculate optical thickness of the micro-object in every point. The method allows measuring thickness of the micro-object if its refractive index is known or to measure its refractive index if the thickness is known. If the micro-object has a homogeneous refractive index distribution, it is possible to reconstruct its physical 3D shape under digital processing the images.
