  It has often been conjectured that the effectiveness of line drawings can be
explained by the similarity of edge images to line drawings. This paper
presents several problems with explaining line drawing perception in terms of
edges, and how the recently-proposed Realism Hypothesis of Hertzmann (2020)
resolves these problems. There is nonetheless existing evidence that edges are
often the best features for predicting where people draw lines; this paper
describes how the Realism Hypothesis can explain this evidence.
