  The depolarization properties of a medium with associated Mueller matrix M
are characterized through two complementary sets of parameters, namely the
three indices of polarimetric purity (IPP), which are directly linked to the
relative weights of the spectral components of M and provide complete
information on the structure of polarimetric randomness, but are insensitive to
the specific polarimetric behaviors that originate the lack of randomness; and
the set of three components of purity (CP), constituted by the polarizance, the
diattenuation and the degree of spherical purity. The relations between these
sets of physical invariant quantities are studied by means of their
representation into a common purity figure. Furthermore, the polarimetric
properties of a general Mueller matrix are parameterized in terms of sixteen
meaningful quantities, three of them being the IPP, which together the CP
provide complete information of the amount and sources of depolarization of the
medium to which M is associated.
