Column densities estimated with Method A (black points) and Method B (red points) versus the true column density of Cloud I. The frames correspond to 0.3 or 3.0 times the default noise (see text). The numbers indicate the correlation coefficients r for Method A and Method B, respectively, for data with N_true > 5 × 10²¹ cm^-2. For illustration, we have included in the lower frames the corresponding results obtained with a spectral index value of β = 1.7 instead of β = 2.0.