||"Eagle albumin solutions were prepared at tonicities of 300, 217, 157, and 131 milliosmoles (mOsm)...Optically, the RBC [red blood cell] is a phase object it alters the phase of the electromagnetic wave but not its amplitude. The wave can be represented by a complex function (equation 1:)(UI(X,Y)~e^[if(X,Y)]. X,Y are spatial coordinates in the plane of the cell as viewed in the microscope f(X,Y) is the phase alteration of the incident wave due to the cell. According to (1) the energy of the wave which is the product of U, and its complex conjugate U*I, E~UIU*I, is practically independent of the cell phase change. Hence if [researchers] are only able to detect the energy of the electromagnetic radiation, the cell would appear almost transparent. To measure the phase shift f(X,Y) and determine the geometry of the RBC, researchers use an interference microscope, analyze the image according to the principles of holography, and compensate for the effects of diffraction by a mathematical program, the details of which are given by Evans (1970a,b). The method may be called microscopic holography. Holography is a form of interferometry that combines a reference wave with an object-scattered wave in order to preserve the object phase information. In the Mach- Zehnder type of interference microscope (Fig. 3) the object wave is imaged onto a hologram (Fig. 2)." Researchers used Fourier transform and inverse Fourier transform. See article for more details.