65 lines
1.9 KiB
PHP
65 lines
1.9 KiB
PHP
<?php
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namespace Image\PerceptualHash\Algorithm;
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use LengthException;
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use Image\PerceptualHash\Algorithm;
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class DifferenceHash implements Algorithm
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{
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const SIZE = 8;
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/**
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* {@inheritDoc}
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*/
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public function bin($resource)
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{
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$width = static::SIZE + 1;
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$heigth = static::SIZE;
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// Resize the image.
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$resized = imagecreatetruecolor($width, $heigth);
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imagecopyresampled($resized, $resource, 0, 0, 0, 0,
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$width, $heigth, imagesx($resource), imagesy($resource));
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$bin = '';
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$one = 1;
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for ($y = 0; $y < $heigth; $y++) {
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// Get the pixel value for the leftmost pixel.
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$rgb = imagecolorsforindex($resized, imagecolorat($resized, 0, $y));
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$left = floor(($rgb['red'] + $rgb['green'] + $rgb['blue']) / 3);
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for ($x = 1; $x < $width; $x++) {
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// Get the pixel value for each pixel starting from position 1.
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$rgb = imagecolorsforindex($resized, imagecolorat($resized, $x, $y));
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$right = floor(($rgb['red'] + $rgb['green'] + $rgb['blue']) / 3);
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// Each hash bit is set based on whether the left pixel is brighter than the right pixel.
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// http://www.hackerfactor.com/blog/index.php?/archives/529-Kind-of-Like-That.html
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$bin .= $left > $right ? 1 : 0;
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$left = $right;
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$one = $one << 1;
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}
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}
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imagedestroy($resized);
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return (string) $bin;
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}
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/**
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* {@inheritDoc}
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*/
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public function hex($bin)
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{
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if (strlen($bin) !== self::SIZE * self::SIZE) {
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throw new LengthException('Binary length must be ' . self::SIZE * self::SIZE);
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}
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$hex = '';
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foreach (str_split($bin, 4) as $bin) {
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$hex .= dechex(bindec($bin));
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}
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return (string) $hex;
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}
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}
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