  The near infrared extinction powerlaw index ($\beta$) and its uncertainty is
derived from three different techniques based on star counts, colour excess and
a combination of them. We have applied these methods to 2MASS data to determine
maps of $\beta$ and near infrared extinction of the small cloud IC 1396 W. The
combination of star counts and colour excess results in the most reliable
method to determine $\beta$. It is found that the use of the correct
$\beta$-map to transform colour excess values into extinction is fundamental
for column density profile analysis of clouds. We describe how artificial
photometric data, based on the model of stellar population synthesis of the
Galaxy (Robin et al. 2003), can be used to estimate uncertainties and derive
systematic effects of the extinction methods presented here. We find that all
colour excess based extinction determination methods are subject to small but
systematic offsets, which do not affect the star counting technique. These
offsets occur since stars seen through a cloud do not represent the same
population as stars in an extinction free control field.
