From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 30736 invoked by alias); 15 Aug 2011 16:00:31 -0000 Received: (qmail 30606 invoked by uid 22791); 15 Aug 2011 16:00:09 -0000 X-Spam-Check-By: sourceware.org Received: from aquarius.hirmke.de (HELO calimero.vinschen.de) (217.91.18.234) by sourceware.org (qpsmtpd/0.83/v0.83-20-g38e4449) with ESMTP; Mon, 15 Aug 2011 15:59:56 +0000 Received: by calimero.vinschen.de (Postfix, from userid 500) id D3EE72CCC1E; Mon, 15 Aug 2011 17:59:53 +0200 (CEST) Date: Mon, 15 Aug 2011 16:00:00 -0000 From: Corinna Vinschen To: cygwin-apps@cygwin.com Subject: Re: 256x256 px icons Message-ID: <20110815155953.GB29857@calimero.vinschen.de> Reply-To: cygwin-apps@cygwin.com Mail-Followup-To: cygwin-apps@cygwin.com References: <4E4245B4.3020107@etr-usa.com> <20110810100725.GA6563@calimero.vinschen.de> <20110810102335.GD6563@calimero.vinschen.de> <4E428F62.4090001@etr-usa.com> <20110811103856.GC24478@calimero.vinschen.de> <4E44444A.2080700@etr-usa.com> <20110812065957.GH16226@calimero.vinschen.de> <20110812091232.GA7658@calimero.vinschen.de> <4E492E3B.8060607@etr-usa.com> <4E493EF1.9070408@cwilson.fastmail.fm> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <4E493EF1.9070408@cwilson.fastmail.fm> User-Agent: Mutt/1.5.21 (2010-09-15) Mailing-List: contact cygwin-apps-help@cygwin.com; run by ezmlm Precedence: bulk Sender: cygwin-apps-owner@cygwin.com List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Mail-Followup-To: cygwin-apps@cygwin.com X-SW-Source: 2011-08/txt/msg00180.txt.bz2 On Aug 15 11:44, Charles Wilson wrote: > On 8/15/2011 10:33 AM, Warren Young wrote: > > The hard edges in the original art are causing stair-stepping when doing > > a direct downsample, though. (Look at the pointy bits.) By blurring > > the high-res version and then downsampling by a non-integral amount, you > > can get a much smoother result. > > This is only the case if the "downsample" operation used by GIMP, when > d/s by an integral amount, is to simply pick every Nth pixel. That's > very fast -- but is not the correct operation (I'd posit a GIMP bug, in > fact). > > Sampling theory says a downsample SHOULD be preceded, automatically, by > a low-pass filter (blurring) operation of a specific type and, er, > "radius" for lack of a better word. (IOW, GIMP /should/ be doing this > blur FOR you, automatically). There's lots of theory behind this, to > select the proper kind of filter (gaussian is not correct -- but is > probably a good enough approximation) and its 'radius' (which should > scale with the downsampling factor). > > Since GIMP is apparently not doing that, then yes -- you need to apply a > blurring filter yourself, before using GIMP's braindead 'pick every Nth > pixel' version of "downsampling". Are you talking about recent gimp versions? In my gimp I have the choice of four different interpolation algorithms, "None", "Linear", "Cubic", and "Sinc (Lanczos3)", whatever each of them means. I guess I just don't want to know in such great detail... Corinna -- Corinna Vinschen Please, send mails regarding Cygwin to Cygwin Project Co-Leader cygwin AT cygwin DOT com Red Hat