  In this study we investigate the optical photometric properties of early-type
galaxies in the Virgo cluster core region, by analysing their location on the
colour magnitude relation (CMR) and the structural scaling relations down to
faint magnitudes, and by constructing the luminosity function to compare it
with theoretical expectations. We visually select potential cluster members
based on morphology and angular size, excluding spiral galaxies. A photometric
analysis has been carried out for 295 galaxies, using surface brightness
profile shape and colour as further criteria to identify probable background
contaminants. 216 galaxies are considered to be certain or probable Virgo
cluster members. Our study reveals 77 galaxies not catalogued in the VCC (with
13 of them already found in previous studies) that are very likely Virgo
cluster members because they follow the Virgo CMR and exhibit low Sersic
indices. Those galaxies reach -8.7 mag in V band. The CMR shows a clear change
in slope from dEs to dSphs, while the scatter of the CMR in the dSph regime
does not increase significantly. Our sample might, however, be somewhat biased
towards redder colours. The scaling relations given by the dEs appear to be
continued by the dSphs indicating a similar origin. The observed change in the
CMR slope may mark the point at which gas loss prevented significant metal
enrichment. The almost constant scatter around the CMR possibly indicates a
short formation period, resulting in similar stellar populations. The
luminosity function shows a Schechter function's faint end slope of
-1.50\pm0.17, implying a lack of galaxies related to the expected number of
low-mass dark matter haloes from theoretical models. Our findings could be
explained by suppressed star formation in low-mass dark matter halos or by
tidal disruption of dwarfs in the dense core region of the cluster.
