Edges
Zero crossing
Zero crossings of the Laplacian — the edge as a boundary, not a slope.
Controls
- blur
- Which size of edge counts as an edge. Without blur the second derivative finds zeroes everywhere and draws a cobweb
- kernel
- Four looks along the sides only, eight also along the diagonals — the difference shows on slanted borders
- threshold
- How steep a change in brightness has to be to count as an edge. High up the scale only the hardest borders survive
- thickness
- A number from 1 to 4 pixels, 1 by default.
- directional
- Colours every edge by the direction it runs instead of using one ink: a map of angles rather than a drawing
- contrast
- A number from -1 to 1, 0 by default.
- invert
- On or off, off by default.
- ink
- A colour, #ffffff by default.
- paper
- A colour, #000000 by default.