  In this paper the bright-field defocusing microscopy (DM) technique is
presented. DM is able to obtain quantitative information of each plane/surface
of pure phase objects, as live unlabeled cells, and its application to red
blood cells (RBCs) is demonstrated. Based on contrast, simple methods to obtain
thickness profile and three dimensional (3D) total reconstruction of RBCs are
proposed and the actual height profiles of upper and lower surface-membranes
(lipid bilayer$/$cytoskeleton) of discocyte and stomatocyte red cells are
presented as examples. In addition, using the mean square contrast fluctuation
and modeling the RBC membranes fluctuations spectra as dependent of a bending
modulus $(\kappa_c)$, a surface tension $(\sigma)$ and a confining potential
$(\gamma)$ term, slowly varying quantities along the cell radius, a genetic
algorithm (GA) is used and the radial height fluctuations of each
surface-membrane are accessed, separately. The radial behaviors of $\kappa_c$,
$\sigma$ and $\gamma$ are also obtained, allowing the discussion of physical
aspects of the RBC membrane.
