I've always wondered how services like Shazam work. I'm amazed that they can do this kind of perceptual hash against ANY 10 second portion of a song. How do they search against something like that when they don't know the start or end time of the segment that is being input?
How Perceptual Hashes Work
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Re: How Perceptual Hashes Work
#22This reminds me of OpenSSH's fingerprint visualization support ("VisualHostKey yes"): $ ssh A.B.C.D Host key fingerprint is b0:c9:c9:96:fb:fd:ac:a4:ff:70:8f:1b:35:f4:f9:2e +--[ECDSA 256]---+ | | | | | . . | | o * . ..| | O S o..| | . . . ..| | . o o .| | . + + +E. | | o.++*....| +-----------------+ me@A.B.C.D's password: Original article introducing this feature: http://www.undeadly.org/cgi?action=article&sid=2008061…
This is pretty much the opposite from what the article is talking about -- the article is trying to get a hash from an image in order to compare that image to another, while you're talking about synthesizing an image from an arbitrary hash...
Hence "reminds me" :)
Re: How Perceptual Hashes Work
#23Re: How Perceptual Hashes Work
#24"With pictures, high frequencies give you detail, while low frequencies show you structure."
I have a vague idea of what this means but can someone please explain it in a bit more detail?
Re: How Perceptual Hashes Work
#25I've always wondered how services like Shazam work. I'm amazed that they can do this kind of perceptual hash against ANY 10 second portion of a song. How do they search against something like that when they don't know the start or end time of the segment that is being input?
For pop/rock/rap music it probably doesn't matter. For classical, I'm not sure.
Re: How Perceptual Hashes Work
#26There's a publicly available implementation of a perceptual hashing algorithm called phash at http://phash.org. I use some of their c++ code to detect reposts on an image sharing site I run (http://lolstack.com).
Re: How Perceptual Hashes Work
#27I've always wondered how services like Shazam work. I'm amazed that they can do this kind of perceptual hash against ANY 10 second portion of a song. How do they search against something like that when they don't know the start or end time of the segment that is being input?
Yes the delta part is clever. Shazam is well described here:
www.ee.columbia.edu/~dpwe/papers/Wang03-shazam.pdf
Re: How Perceptual Hashes Work
#28I've always wondered how services like Shazam work. I'm amazed that they can do this kind of perceptual hash against ANY 10 second portion of a song. How do they search against something like that when they don't know the start or end time of the segment that is being input?
I do research in music information retrieval. See the ISMIR 2003 paper below. In short, it searches for landmarks in the spectrogram, hashes those landmarks, then compares those hashes against database hashes for temporal continuity. http://www.ee.columbia.edu/~dpwe/papers/Wang03-shazam.pdf
A seminal paper on audio fingerprinting is the one by Haitsma and Kalker. http://ismir2002.ismir.net/proceedings/02-fp04-2.pdf
Re: How Perceptual Hashes Work
#29Isn't tineye's signature algorithm based on Fourier transform?
http://www.reddit.com/r/programming/comments/bvmln/how_does_...
Re: How Perceptual Hashes Work
#30I have a feeling there is a deep connection between perceptual hashes and compressed sensing. Could someone more familiar with the latter weigh in?