On this page you select the brightness levels you want to act as edge-detection breaks, and the line colour at each brightness break, plus the line thickness. The greater the difference between two brightnesses at an ‘edge’, the more opaque the resulting line will be; edges with a small amount of brightness difference will be quite translucent.

Edge detection software works in various ways, this is one of them, it is not designed offer a precise edge definition, it’s an art tool for looking at edges.