Imagick::getImageHistogram

<?php
function getColorStatistics($histogramElements, $colorChannel) {
 $colorStatistics = [];
 foreach ($histogramElements as $histogramElement) {
 $color = $histogramElement->getColorValue($colorChannel);
 $color = intval($color * 255);
 $count = $histogramElement->getColorCount();
 if (array_key_exists($color, $colorStatistics)) {
 $colorStatistics[$color] += $count;
 }
 else {
 $colorStatistics[$color] = $count;
 }
 }
 ksort($colorStatistics);
 
 return $colorStatistics;
}
 
function getImageHistogram($imagePath) {
 $backgroundColor = 'black';
 $draw = new \ImagickDraw();
 $draw->setStrokeWidth(0); //make the lines be as thin as possible
 $imagick = new \Imagick();
 $imagick->newImage(500, 500, $backgroundColor);
 $imagick->setImageFormat("png");
 $imagick->drawImage($draw);
 $histogramWidth = 256;
 $histogramHeight = 100; // the height for each RGB segment
 $imagick = new \Imagick(realpath($imagePath));
 //Resize the image to be small, otherwise PHP tends to run out of memory
 //This might lead to bad results for images that are pathologically 'pixelly'
 $imagick->adaptiveResizeImage(200, 200, true);
 $histogramElements = $imagick->getImageHistogram();
 $histogram = new \Imagick();
 $histogram->newpseudoimage($histogramWidth, $histogramHeight * 3, 'xc:black');
 $histogram->setImageFormat('png');
 $getMax = function ($carry, $item) {
 if ($item > $carry) {
 return $item;
 }
 return $carry;
 };
 $colorValues = [
 'red' => getColorStatistics($histogramElements, \Imagick::COLOR_RED),
 'lime' => getColorStatistics($histogramElements, \Imagick::COLOR_GREEN),
 'blue' => getColorStatistics($histogramElements, \Imagick::COLOR_BLUE),
 ];
 $max = array_reduce($colorValues['red'] , $getMax, 0);
 $max = array_reduce($colorValues['lime'] , $getMax, $max);
 $max = array_reduce($colorValues['blue'] , $getMax, $max);
 $scale = $histogramHeight / $max;
 $count = 0;
 foreach ($colorValues as $color => $values) {
 $draw->setstrokecolor($color);
 $offset = ($count + 1) * $histogramHeight;
 foreach ($values as $index => $value) {
 $draw->line($index, $offset, $index, $offset - ($value * $scale));
 }
 $count++;
 }
 $histogram->drawImage($draw);
 
 header( "Content-Type: image/png" );
 echo $histogram;
}
?>