Regions of predominantly noise for A_V (top) and E_V−F090W = A_V − A_F090W (bottom), shown to demonstrate the distribution of these respective values when no expected signal is present. The chosen areas of noise (in red) are well outside the outer arms of VV 191b and on the back side of the background elliptical galaxy, VV 191a. The right column shows the distribution of the low-S/N pixels. Both show a near-Gaussian distribution centered at zero. It is calculated that ﹩{A}_{V}^{{\mathrm{mean}}}=-0.01﹩, ﹩{\sigma }_{{A}_{V}}=0.05﹩, ﹩{E}_{V-{{\rm{F}}}090{{\rm{W}}}}^{{\mathrm{mean}}}=-0.003﹩, and σE_V−F090W = 0.09 for these selected regions shown in red. Thus, the lower-limit threshold used in the Monte Carlo simulation, such that A_V and E_V−F090W ≤ 0.1 must equal 0.1, is a reasonable choice.