Observational data and theoretical calculations show that significant
small-scale substructures are present in dark molecular clouds. These
inhomogeneities can provide precious hints on the physical conditions inside
the clouds, but can also severely bias extinction measurements. We present
NICEST, a novel method to account and correct for inhomogeneities in molecular
cloud extinction studies. The method, tested against numerical simulations,
removes almost completely the biases introduced by sub-pixel structures and by
the contamination of foreground stars. We applied NICEST to 2MASS data of the
Pipe molecular complex. The map thereby obtained shows significantly higher (up
to 0.41 mag in A_K) extinction peaks than the standard NICER (Lombardi et al.
2001) map. This first application confirms that substructures in nearby
molecular clouds, if not accounted for, can significantly bias extinction
measurements in regions with A_K > 1 mag; the effect, moreover, is expected to
increase in more distant molecular cloud, because of the poorer physical
resolution achievable.Comment: 13 pages, A&A in pres
