On Thu, Aug 07, 2008, [EMAIL PROTECTED] wrote: > > Anyway, attached is a serpentine Floyd-Steinberg implementation. > > The mailing list does not accept attachments, instead e-mail it directly > to this address. > > ImageMagick was originally based on a Floyd-Steinberg implementation > but in our testing we found the Hilbert curve method gave a more > visually pleasing result among a set of test images when we compared > the two methods. Our testing method was to present a set of 25 images > side by side (one the original and one dithered with either Hilbert > or Floyd-Steinberg). The Hilbert dithering was choosen a majority of > the time. Its been about 10 years, so we will revisit the issue when > we receive your patch.
I'm pretty surprised. Do you remember what quantisation method was used with these dithering tests? Here is a side-by-side comparison of the Hilbert and Floyd-Steinberg methods using "convert src.png -map pattern:gray50 dest.png" with and without my patch from yesterday: http://zoy.org/~sam/imagemagick-dithering.png So far all the tests I have done with Hilbert curve dithering were disappointing quality-wise (and believe me, I have tried very hard to improve on the idea). I *think* one of the reasons people may have preferred Hilbert dithering is the noise it adds to the image, which appears to better "spread" pixels; it can be seen with the -monochrome option: http://zoy.org/~sam/imagemagick-dithering2.png where I admit it's hard to spontaneously elect Floyd-Steinberg: the grey/black frontiers look too regular. If pixel spread is indeed an important subjective quality metric, I believe more interesting results could be achieved using random noise at the quantisation step, or by using a bigger ED kernel such as JaJuNi: x 7 5 3 5 7 5 3 / 48 1 3 5 3 1 (I can provide code for this if anyone's interested, it's easily built on top of the F-S patch) Cheers, -- Sam. _______________________________________________ Magick-developers mailing list Magick-developers@imagemagick.org http://studio.imagemagick.org/mailman/listinfo/magick-developers
