On Aug 8, 2010, at 6:11 PM, Angus wrote: > Hi. Forgive me if this has been brought up before, but I'm stumped. To > create anti-aliased edges of arbitrary shapes, I tried downscaling > enlarged versions of those shapes with the ANTIALIAS mode. This works > at first glance, but when zooming in, pixels with incorrect(?) > brightness can be noticed. Please try the following example code to > reproduce this problem: [...] > Zoom in far on the diagonal edge between the black and white areas of > the resulting test image. Looking from left to right or top to bottom > I expected the pixels to be increasingly dark. However, the order > seems to be: ...white -> light gray -> dark gray -> black -> *very > dark gray?!* -> black...
What you are seeing sounds like ringing artifacts from the lanczos resampling of the ANTIALIAS mode (see http://en.wikipedia.org/wiki/Lanczos_resampling ). > Is this intentional or not? If intentional, is there another way to > anti-alias edges with PIL (because I don't like these artifacts)? You could try something like this: im = im._new(im.im.stretch((15,10), Image.BILINEAR)) This will try to do an anti-aliased resizing, but use a bilinear filter instead of the default lanczos filter. This will potentially have more aliasing artifacts, but should have no ringing at all. till then, David. _______________________________________________ Image-SIG maillist - Image-SIG@python.org http://mail.python.org/mailman/listinfo/image-sig
