Phase Contrast Microscopy - Biomedical Optical Phase Microscopy and Nanoscopy - page 14

fluorescence because the background is bright, whereas it is dark in fluorescence and so the
ratio of intensities is much larger. But the enhanced edge contrast provided by phase is
adequate for identification of the edge of cells thus providing a very useful tool. The second
advantage of phase contrast is the enhanced edge definition is provided symmetrically
around the cell. With DIC (see Chapter 2), enhanced edge contrast is also provided but the
shadow effect means it is bright on one side of the cell and dark on the other. Our visual
system has no problem understanding this arrangement but an image analysis process
looking only at differences in intensity needs to be smarter than one analyzing a
symmetrical pattern. Figure 1.9 shows the ability of easy identification of a cell by phase

(A) (B) (C)

Figure 1.9
Threshold-based cell identification in (A) brightfield, (B) phase contrast, and (C) DIC.