From owner-freebsd-questions@FreeBSD.ORG Tue Sep 8 09:34:32 2009 Return-Path: Delivered-To: freebsd-questions@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id E79ED1065676 for ; Tue, 8 Sep 2009 09:34:32 +0000 (UTC) (envelope-from michaelgrunewald@yahoo.fr) Received: from mx2.mpim-bonn.mpg.de (mx2.mpim-bonn.mpg.de [195.37.209.170]) by mx1.freebsd.org (Postfix) with ESMTP id 793348FC2A for ; Tue, 8 Sep 2009 09:34:31 +0000 (UTC) X-IronPort-AV: E=McAfee;i="5300,2777,5734"; a="290377" X-IronPort-AV: E=Sophos;i="4.44,351,1249250400"; d="scan'208";a="290377" Received: from mailout.mpim-bonn.mpg.de (HELO ismene.mpim-bonn.mpg.de) ([192.168.42.38]) by mx2.mpim-bonn.mpg.de with ESMTP; 08 Sep 2009 11:04:33 +0200 Received: from [192.68.254.7] (aeria.mpim-bonn.mpg.de [192.68.254.7]) by ismene.mpim-bonn.mpg.de (8.13.8/8.13.8) with ESMTP id n8894UcA020140; Tue, 8 Sep 2009 11:04:31 +0200 (CEST) Message-ID: <4AA61E1D.6070807@yahoo.fr> Date: Tue, 08 Sep 2009 11:04:29 +0200 From: =?ISO-8859-1?Q?Micha=EBl_Gr=FCnewald?= User-Agent: Thunderbird 2.0.0.21 (X11/20090311) MIME-Version: 1.0 To: perryh@pluto.rain.com References: <20090906012107.E2731B7DD@kev.msw.wpafb.af.mil> <4AA47981.1090103@prgmr.com> <200909071451.24123.mel.flynn+fbsd.questions@mailing.thruhere.net> <4aa6100e.tHFPjmIiNAiRpJ+f%perryh@pluto.rain.com> In-Reply-To: <4aa6100e.tHFPjmIiNAiRpJ+f%perryh@pluto.rain.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 8bit Cc: mdc@prgmr.com, freebsd-questions@freebsd.org Subject: Re: Is there such thing as a 'soft checksum' tool? X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 08 Sep 2009 09:34:33 -0000 perryh@pluto.rain.com wrote: > Mel Flynn wrote: > > However, thinking about this inquiry and JPEG in the same sentence > has given me an idea that might help the OP: JPEG is a "lossy" > compression, with the degree of loss related to the chosen image > quality, so two "similar" images might become identical -- or at > least more similar -- if compressed to a sufficiently low quality > using the JPEG algorithm. This seems to be an excellent idea. A similar approach can (successfully) be used to let a computer recognize songs through a micrOphone: the incoming signal is transformmed to MP3 at a rather low quality, which provides a sort of fingerprint of the input. The quality factors shall be adujsted adequately for this application: there is a tradeoff between stability (noise insensitivity) and separation to find. The case of images is much more complicated if one wishes to recognize the same image at two different scales. -- Cheers, Michaël