phash's Introduction

Phash

Perceptual hash implementation for PHP

This is my PHP Implementation of the AverageHash algorithm to create Perceptual Hashes

A perceptual hash is different from a typical hash as it allows you to compute a signature based on the visual features of an image rather than the actual data they contain as with a cryptographic hash. This allows you to use the Perceptual Hash for simple image matching which could prove useful in finding duplicate pictures or picture tagging.

To get a better understanding of this project see: http://www.hackerfactor.com/blog/index.php?/archives/432-Looks-Like-It.html

Sample Usage

You can use pHash methods as a class in your project and extend as you wish.

A basic implementation is as follows:

#sample implementation
$phasher = new Phash;
$phash2 = $phasher->getHash('phash2.jpg', false);
//this will echo hash in hex, then binary
echo $phasher->hashAsString($phash2, false).PHP_EOL;
echo $phasher->hashAsString($phash2).PHP_EOL;

$phash3 = $phasher->getHash('phash3.jpg', false);
//this will echo hash in hex, then binary
echo $phasher->hashAsString($phash3, false).PHP_EOL;
echo $phasher->hashAsString($phash3).PHP_EOL;

//using BIT COUNT METHOD FOR SIMILARITY
echo $phasher->getSimilarity($phash2, $phash3, 'BITS');
echo PHP_EOL;

//using HAMMING METHOD (DEFAULT) FOR SIMILARITY
echo $phasher->getSimilarity($phash2, $phash3);
echo PHP_EOL;

Notes

The bitcount algorithm for matching similarity may be siginificantly faster than hamming distance.
Calculating hamming distance between two hex based hashes may be faster but less accurate than the binary version

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