  We present new results from first observations of the quiet solar photosphere
performed through the Interferometric BIdimensional Spectrometer (IBIS) in
spectropolarimetric mode. IBIS allowed us to measure the four Stokes parameters
in the FeI 630.15 nm and FeI 630.25 nm lines with high spatial and spectral
resolutions for 53 minutes; the polarimetric sensitivity achieved by the
instrument is 0.003 the continuum intensity level. We focus on the correlation
which emerges between G-band bright feature brightness and magnetic filling
factor of ~ 1000 G (kG) fields derived by inverting Stokes I and V profiles.
More in detail, we present the correlation first in a pixel-by-pixel study of
an approximatively 3 arcsec wide bright feature (a small network patch) and
then we show that such a result can be extended to all the bright features
found in the dataset at any instant of the time sequence. The higher the kG
filling factor associated to a feature the higher the brightness of the feature
itself. Filling factors up to about 35 % are obtained for the brightest
features. Considering the values of the filling factors derived from the
inversion analysis of spectropolarimetric data and the brightness variation
observed in G-band data we put forward an upper limit for the smallest scale
over which magnetic flux concentrations in intergranular lanes produce a G-band
brightness enhancement (~ 0.1''). Moreover, the brightness saturation observed
for feature sizes comparable to the resolution of the observations is
compatible with large G-band bright features being clusters of sub-arcsecond
bright points. This conclusion deserves to be confirmed by forthcoming
spectropolarimetric observations at higher spatial resolution.
