Characterization of structural changes at different cell-cycle phases using SESF. (a,b) The bright-field and (c,d) SESF images of unstained HeLa cells arrested at G1/S and G2/M phases of the cell nuclei. Scale bar: 10 μm. The color bar shows the corresponding value of spatial period in the colored images of (c) and (d). (e-f) The comparison of spatial-period profile extracted from (e) TEM images and (f) SESF images.