Imagick::getImageHistogram

(PECL imagick 2, PECL imagick 3)

Imagick::getImageHistogramGets the image histogram

Description

public Imagick::getImageHistogram(): array

Returns the image histogram as an array of ImagickPixel objects.

Parameters

This function has no parameters.

Return Values

Returns the image histogram as an array of ImagickPixel objects.

Errors/Exceptions

Throws ImagickException on error.

Examples

Example #1 Generates 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;
}

?>