  We studied the radiative properties of small magnetic elements (active region
faculae and the network) during the rising phase of solar cycle 23 from 1996 to
2001, determining their contrasts as a function of heliocentric angle,
magnetogram signal, and the solar cycle phase. We combined near-simultaneous
full disk images of the line-of-sight magnetic field and photospheric continuum
intensity provided by the MDI instrument on board the SOHO spacecraft. Sorting
the magnetogram signal into different ranges allowed us to distinguish between
the contrast of different magnetic structures. We find that the contrast
center-to-limb variation (CLV) of these small magnetic elements is independent
of time with a 10% precision, when measured during the rising phase of solar
cycle 23. A 2-dimensional empirical expression for the contrast of photospheric
features as a function of both the position on the disk and the averaged
magnetic field strength was determined, showing its validity through the
studied time period. A study of the relationship between magnetogram signal and
the peak contrasts shows that the intrinsic contrast (maximum contrast per unit
of magnetic flux) of network flux tubes is higher than that of active region
faculae during the solar cycle.
