Does what it says and perfectly.
I was looking for an app to cheat and make manga backgrounds, saving drawing time. Many other apps offer the mechanized clair ligne function, but this one lets you preview the target image in real time, not simply apply the edge detect post-snap. No crashes, no issues on my iPhone 6s on 14.4.2. Its successor might have 1-4 tone shading in ziptone/screentone/halftone, with options on dots, hatching, cross hatch and noise patterns, and that would be worth more than $2.