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Date:      Mon, 7 Sep 2009 05:16:02 -0600
From:      Modulok <modulok@gmail.com>
To:        "parv@pair.com" <parv@pair.com>
Cc:        freebsd-questions@freebsd.org
Subject:   Re: Is there such thing as a 'soft checksum' tool?
Message-ID:  <64c038660909070416y285e0fddv42a43a7c127d4a74@mail.gmail.com>
In-Reply-To: <20090907083112.GA2787@holstein.holy.cow>
References:  <64c038660909050933h25a91edcw56688993f5557ad2@mail.gmail.com> <44skf0c6zq.fsf@lowell-desk.lan> <20090907083112.GA2787@holstein.holy.cow>

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>> Modulok <modulok@gmail.com> writes:

>> > I'm not even sure such a tool exists, but it's worth asking:
>> >
>> > I'm looking for a pseudo-checksum tool for use with catalogging
>> > images. For example, a strict checksum algorithm, like the sha
>> > family, will produce a dramatically different checksum for two
>> > files which differ by only a single bit. I'm looking for
>> > something where two images images, which are similar, get a
>> > proportionally similar checksum. When I speak of similarities
>> > I'm referring to their image patterns. i.e two images of
>> > differing sizes, which are otherwise identical, would produce
>> > very similar checksums. So the closer the checksums are, the
>> > more similar two given images are.
>> >


>> > Does anyone know of anything like this?
>
> See if this ...
>
>   http://www.stonehenge.com/merlyn/LinuxMag/col50.html
>
>
> ... fits.
>
>
>   - parv

*laughs* It makes me feel pretty good after reading how Mr.Schwartz
went about it. Before I got any replies I started to think about how
I'd do it and began to sketch out an algorithm on the kitchen floor.
(Largest black-board in my house.) The general approach was pretty
much the same; Recursive bucketing of pixels and generating averaged
values down to a user-defined finite limit.

Thanks to all who have replied thus far!
-Modulok-



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