Contour

Contour

Contour filters convert filled raster areas of the image to one-pixel outlines. The 4-coupling filter creates 4-coupling contour; the 8-coupling filter creates 8-coupling contour. In the 4-coupling filter the contiguous areas can only be coupled with their sides; the 8-coupling filter analyses corner contiguity, so such images look thinner.
The figure shows the result of Contour filtration.

To convert raster objects to outlines

Select part(s) of the raster or image(s) and click the 4-coupling or 8-coupling from Contour submenu of Filters menu or press the button on Filters toolbar.