However obtaining the defocused images, requires delicate experimental setups, e.g.

From these images the phase shifts are numerically reconstructed, for example by sequentially solving two Poisson equations 9. One notable technique is the defocused-based phase imaging 4, 5, 6, 7, 8 based on Transport of Intensity Equation (TIE) 9, where two or more intensity images are recorded at several closely spaced planes (usually 10 μm to 100 μm apart). Many quantitative phase imaging techniques have been proposed 3. However, the conversion is not linear and the recorded image on the detector only indicates qualitative pseudo phase information, and is often substantially different from the real phase shift. annulus rings or Nomarski prisms) to convert the phase shifts into brightness changes. These methods utilize additional simple imaging modules (e.g. Two classical methods for phase imaging are phase-contrast microscopy 1 and differential interference contrast (DIC) microscopy 2. In comparison, phase imaging detects minute changes in phase when light propagates through the cell morphology, and has become the prevalent approach for fine cell strucfture distinction without employing higher radiation powers. Due to negligible absorption in the visible spectrum, most living cells exhibit low contrast under bright field microscopy, which prevents detailed examinations.

Light intensity differential equation