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65 lines
1.6 KiB
PHP
65 lines
1.6 KiB
PHP
<?php
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/**
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* A very simple algorithm for finding the dissimilarity between images,
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* mainly useful for checking lossy compression.
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*/
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/**
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* Gets the individual components of an RGB value.
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*
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* @param int $color
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* @param int $red
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* @param int $green
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* @param int $blue
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*
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* @return void
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*/
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function get_rgb($color, &$red, &$green, &$blue)
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{
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// assumes $color is an RGB value
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$red = ($color >> 16) & 0xFF;
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$green = ($color >> 8) & 0xFF;
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$blue = $color & 0xFF;
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}
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/**
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* Calculates the euclidean distance of two RGB values.
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*
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* @param int $color1
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* @param int $color2
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*
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* @return int
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*/
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function calc_pixel_distance($color1, $color2)
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{
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get_rgb($color1, $red1, $green1, $blue1);
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get_rgb($color2, $red2, $green2, $blue2);
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return sqrt(
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pow($red1 - $red2, 2) + pow($green1 - $green2, 2) + pow($blue1 - $blue2, 2)
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);
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}
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/**
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* Calculates dissimilarity of two images.
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*
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* @param resource $image1
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* @param resource $image2
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*
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* @return int The dissimilarity. 0 means the images are identical. The higher
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* the value, the more dissimilar are the images.
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*/
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function calc_image_dissimilarity($image1, $image2)
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{
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// assumes image1 and image2 have same width and height
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$dissimilarity = 0;
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for ($i = 0, $n = imagesx($image1); $i < $n; $i++) {
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for ($j = 0, $m = imagesy($image1); $j < $m; $j++) {
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$color1 = imagecolorat($image1, $i, $j);
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$color2 = imagecolorat($image2, $i, $j);
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$dissimilarity += calc_pixel_distance($color1, $color2);
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}
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}
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return $dissimilarity;
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}
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