<?php
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/*---------------------------------------------------------------*/
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/*
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Titre : Egalisation des couleurs d'une image
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URL : https://phpsources.net/code_s.php?id=971
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Date édition : 15 Fév 2019
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*/
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/*---------------------------------------------------------------*/
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function image_equalize($img){
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$NUM_PIXELS = imagesx($img) * imagesy($img);
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/**
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* Get a repartition table of R, V, B channel components. Get also the min and max value of each components.
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* @return array['r'=>[0..255 => nb of occurence], 'v'=>[0..255 => nb of occurence], 'b'=>[0..255 => nb of occurence],
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* 'r_min'=>minimum R value, 'r_max'=>maximum R value, 'v_min'=>minimum V value, 'v_max'=>maximum V value, 'b_min'=>minimum B value,'b_max'=>maximum B value ]
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* @warning time consumming function.
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*/
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function image_getcolorstable($img)
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{
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$width = imagesx($img);
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$height = imagesy($img);
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$lut_r = array_fill(0, 255, 0);
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$lut_v = array_fill(0, 255, 0);
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$lut_b = array_fill(0, 255, 0);
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$r_min = $v_min = $b_min = 9999;
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$r_max = $v_max = $b_max = 0;
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for($x = 0; $x < $width; $x++)
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{
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for($y = 0; $y < $height; $y++)
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{
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$c = imagecolorat($img, $x, $y);
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$r = ($c & 0xFF0000 ) >> 16;
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$v = ($c & 0x00FF00 ) >> 8;
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$b = ($c & 0x0000FF );
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$lut_r[$r] = @$lut_r[$r] + 1;
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$lut_v[$v] = @$lut_v[$v] + 1;
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$lut_b[$b] = @$lut_b[$b] + 1;
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if ($r > $r_max)
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$r_max = $r;
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if ($r < $r_min)
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$r_min = $r;
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if ($v > $v_max)
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$v_max = $v;
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if ($v < $v_min)
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$v_min = $v;
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if ($b > $b_max)
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$b_max = $b;
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if ($b < $b_min)
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$b_min = $b;
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}
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}
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return array('r'=>$lut_r, 'v'=>$lut_v, 'b'=>$lut_b,
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'r_min'=>$r_min, 'r_max'=>$r_max,
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'v_min'=>$v_min, 'v_max'=>$v_max,
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'b_min'=>$b_min, 'b_max'=>$b_max);
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}
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/**
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* Equalize a channel components.
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* @param lut : Look Up Table of channel occurence
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* @param min : minimum channel component value (usually 0)
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* @param max : minimum channel component value (usually 255)
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* @param $num_pixels : number of pixels (whidth x height) of the image
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* @return a new equalized look up table
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*/
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function lut_equalizechannel($lut, $min, $max, $num_pixels)
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{
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$c = count($lut);
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$new_lut = array_fill(0, $c, 0);
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$sum = 0;
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for($i = 0; $i < $c; $i++)
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{
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$sum += $lut[$i];
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$result = $sum * $max / $num_pixels;
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$new_lut[$i] = (int)$result;
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}
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return $new_lut;
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}
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$lut = image_getcolorstable($img);
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$MAX_SAMPLE = $lut['r_max'];
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$lut_r = lut_equalizechannel($lut['r'], 0, $MAX_SAMPLE, $NUM_PIXELS);
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$lut_v = lut_equalizechannel($lut['v'], 0, $MAX_SAMPLE, $NUM_PIXELS);
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$lut_b = lut_equalizechannel($lut['b'], 0, $MAX_SAMPLE, $NUM_PIXELS);
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$width = imagesx($img);
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$height = imagesy($img);
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for ($x = 0; $x < $width; $x++)
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{
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for ($y = 0; $y < $height; $y++)
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{
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$c = imagecolorat($img, $x, $y);
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$r = ($c & 0xFF0000 ) >> 16;
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$v = ($c & 0x00FF00 ) >> 8;
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$b = ($c & 0x0000FF );
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$new_r = $lut_r[$r];
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$new_v = $lut_v[$v];
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$new_b = $lut_b[$b];
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imagesetpixel($img, $x, $y, ($new_r << 16) | ($new_v << 8) |
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$new_b);
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}
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}
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}
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?>
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