Date: Tue, 08 Sep 2009 11:04:29 +0200 From: =?ISO-8859-1?Q?Micha=EBl_Gr=FCnewald?= <michaelgrunewald@yahoo.fr> To: perryh@pluto.rain.com Cc: mdc@prgmr.com, freebsd-questions@freebsd.org Subject: Re: Is there such thing as a 'soft checksum' tool? Message-ID: <4AA61E1D.6070807@yahoo.fr> In-Reply-To: <4aa6100e.tHFPjmIiNAiRpJ%2Bf%perryh@pluto.rain.com> References: <20090906012107.E2731B7DD@kev.msw.wpafb.af.mil> <4AA47981.1090103@prgmr.com> <200909071451.24123.mel.flynn%2Bfbsd.questions@mailing.thruhere.net> <4aa6100e.tHFPjmIiNAiRpJ%2Bf%perryh@pluto.rain.com>
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perryh@pluto.rain.com wrote: > Mel Flynn <mel.flynn+fbsd.questions@mailing.thruhere.net> 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
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