Observations and models of disc emission and silhouette. Left and centre columns show the emission at 3.2 μm (I_3.2, no astro-PAH background) and 3.29 μm (I_3.29, peak astro-PAH background), respectively. The right column shows the extincted optical depth $\tau =-\ln (T)=-\ln (I_{3.29}/(I_{3.2}+I_{3.29}^{\mathrm{ambient}}))$. The bottom row shows profile cuts along the midplane comparing observations (solid lines) and models (dashed lines). Blue lines (left) correspond to the 3.2 μm cut. Red lines (centre) are the 3.29 μm cut. Blue cuts include an offset corresponding to the astro-PAH background contribution, i.e. the expected cut if no silhouette extinction were present. Black lines (right) show $T=I_{3.29}/(I_{3.2}+I_{3.29}^{\mathrm{ambient}}$) along the midplane cut in both the model and observations.