|Semantics of line drawings|
We have all seen cartoons showing brick walls indicated by just a few patches of brick. Texture lines are often omitted to avoid the drawing becoming too "busy". If trying to understand Christopher Hart's drawing below, a computer would need to realise that the animal actually has fur all round its face.
"These cheek ruffles — with a large neutral space between them where they meet under the chin — are the most natural looking. The straight line of neutral space serves as good "pacing" between the ruffles. It's a place where the eye can "rest"."
From Christopher Hart, How to Draw Cartoon Baby Animals, 2000.