Finds the edges in a picture and makes them glow, as though they were made of neon.
The edges are found the usual way, by measuring how quickly brightness changes. What is different is what happens next: instead of drawing the edge as a line, the edge strength is multiplied by the picture's own colour to make a light, and that light is added over the original.
The combination is done with a screen blend, which can only ever lighten and which approaches white smoothly rather than clipping, so bright areas near an edge glow up toward white instead of blowing out into a flat patch.
Because the glow carries the underlying colour, each edge lights up in whatever hue it runs through. shape changes the pattern of pixels the edge strength is measured across, whether a circle, diamond, square or star, which alters the character of the lines. width sets how far apart the compared pixels sit.