Hi solar, On Fri, Aug 1, 2008 at 6:58 AM, <solar@xxxxxxxxxxx> wrote: > On Wed, 30 Jul 2008 15:53:36 +0200, David Gowers <00ai99@xxxxxxxxx> wrote: > >> I've finished checking, and am just sending off the results and >> webpage to Sven now. >> David > > Thanks for all the hard work on this. A very interesting comparison. > (Perhaps too many engraving type images tho'). > > My main interest was in lanczos results since I spent some time on this > (initially intending to use it as a pixelisation filter rather than > interpolation method). > > > > One of the most interesting differences between cubic (csplines) and > lanczos3 is shown here: > http://svenfoo.org/scaletest/33-9.html > > the cubic scaling shows some exagerated contrasts especially on the top of > the head. Almost like it has some party glitter sprinkled on it. In this > example the linear may even, atypically, be preferable to cubic. > > This artifact is probably a good example of the tendancy of csplines to > overshoot near sharp changes. The orange part of the throat is also softer > and more natural than the cubic which show fairly obvious pixelisation > there. > > Aside that, many of the samples show little discernable difference though > the predominance of etched images , which are basically binary in tone, > would not demonstate the overshoot phenomenon. > > Maybe a couple of tests with block style graphics would be a useful > addition. Simple graphics with areas of uniform colour. I included a pixel art (image #8) for this purpose. I agree it's not simple -- it only has areas of uniform color. the original is found here: http://www.pixeljoint.com/pixelart/5647.htm#; each of the two sprites have about 22 colors each; the borders are flat and comprise an additional 2 colors. The picture was by me, and I felt that lanczos performed outstandingly for downscaling -- and in general, all scaling methods did a better job of preserving the salient features of the image than the old code. Pixel art ('block graphics'?) is a pathological case for most scaling algorithyms, and no algorithym old or new performed very well on upscaling image #8. David _______________________________________________ Gimp-developer mailing list Gimp-developer@xxxxxxxxxxxxxxxxxxxxxx https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-developer
