On 11/19/05, Roel Schroeven <[EMAIL PROTECTED]> wrote: > Sven Neumann wrote: > > The Lanczos implementation in CVS is buggy and unless someone shows up > > who fixes it, it will most likely end up being removed before the 2.4 > > release. > > I might take a shot at fixing that, if I can find enough time to do it. > > Is it bug 305928 you mean? On first sight that is more about the > interaction between Lanczos and the perspective tool than about Lanczos > itself.
The bug in the perspective tool is that the lanczos algorithm uses a different offset from bilinear/bicubic/adaptive supersampling. The discontinuity that can be observed in e.g. http://pippin.gimp.org/tmp/buggy.png is the threshold around the 1:1 resampling. The point where the code in the transform tool chooses between interpolation(lanczos) and decimation(adaptive supersampling). The problem with using bilinear/bicubic/lanczos for decimation is (apart from being wrong in the first place) is that you end up throwing away pixels. For bicubic a destination pixels uses information from a 4x4 source window in the original image. This is wrong. If you for instance scale to 10% of the original image size. You need to include data from at least a 10x10px window. /Øyvind K. -- «The future is already here. It's just not very evenly distributed» -- William Gibson http://pippin.gimp.org/ http://ffii.org/ _______________________________________________ Gimp-developer mailing list Gimp-developer@lists.xcf.berkeley.edu http://lists.xcf.berkeley.edu/mailman/listinfo/gimp-developer
