On Wed, Nov 24, 2010 at 4:25 PM, Bill Skaggs <weskaggs@xxxxxxxxx> wrote: > Maybe it would help to have a general explanation of the principle behind > the filter. > > The basic idea of the Unsharp Mask is to enhance the difference between the > original image > and a blurred version of it. The algorithm first blurs the image, then > calculates the difference > between the original image and the blurred version, and then alters the > original image by > moving each pixel farther away from its blurred value. > > The convolution is simply a way of blurring the image. There are countless > ways of > doing a blur -- the filter is using a rather crude approximation of a > Gaussian blur, which > is the most commonly used blurring algorithm. In GEGL unsharp mask is implemented at a higher level of abstraction than low-level filters and reuses gaussian blur directly, thus speed improvements to gaussian blur in GEGL will also benefit unsharp mask directly. See http://git.gnome.org/browse/gegl/tree/operations/common/unsharp-mask.c this version of unsharp mask can already be used in GIMP through the GEGL-tool, it would probably be good if the unsharp-mask in GIMP was properly replaced with the GEGL one. /Øyvind Kolås _______________________________________________ Gimp-developer mailing list Gimp-developer@xxxxxxxxxxxxxxxxxxxxxx https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-developer
