From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 24681 invoked by alias); 15 Aug 2011 15:45:09 -0000 Received: (qmail 24664 invoked by uid 22791); 15 Aug 2011 15:45:08 -0000 X-SWARE-Spam-Status: No, hits=-2.0 required=5.0 tests=AWL,BAYES_00,DKIM_SIGNED,DKIM_VALID,RCVD_IN_DNSWL_LOW X-Spam-Check-By: sourceware.org Received: from out4.smtp.messagingengine.com (HELO out4.smtp.messagingengine.com) (66.111.4.28) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Mon, 15 Aug 2011 15:44:51 +0000 Received: from compute3.internal (compute3.nyi.mail.srv.osa [10.202.2.43]) by gateway1.messagingengine.com (Postfix) with ESMTP id D267621F96 for ; Mon, 15 Aug 2011 11:44:50 -0400 (EDT) Received: from frontend1.messagingengine.com ([10.202.2.160]) by compute3.internal (MEProxy); Mon, 15 Aug 2011 11:44:50 -0400 Received: from [158.147.67.90] (158-147-67-90.harris.com [158.147.67.90]) by mail.messagingengine.com (Postfix) with ESMTPSA id 8A4A141DABA; Mon, 15 Aug 2011 11:44:50 -0400 (EDT) Message-ID: <4E493EF1.9070408@cwilson.fastmail.fm> Date: Mon, 15 Aug 2011 15:45:00 -0000 From: Charles Wilson Reply-To: Charles Wilson User-Agent: Mozilla/5.0 (Windows NT 5.2; WOW64; rv:5.0) Gecko/20110624 Thunderbird/5.0 MIME-Version: 1.0 To: Mailing List: CygWin-Apps Subject: Re: 256x256 px icons References: <20110808204351.GP11601@calimero.vinschen.de> <4E4062F8.5020508@etr-usa.com> <20110809072534.GS11601@calimero.vinschen.de> <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> In-Reply-To: <4E492E3B.8060607@etr-usa.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit 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/msg00178.txt.bz2 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". -- Chuck