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Imagick::getImageHistogram

(PECL imagick 2, PECL imagick 3)

Imagick::getImageHistogram — Retourne l'histogramme de l'image

Description

public Imagick::getImageHistogram(): array

Retourne l'histogramme de l'image, sous forme d'un tableau d'objets ImagickPixel.

Liste de paramètres

Cette fonction ne contient aucun paramètre.

Valeurs de retour

Retourne un tableau d'objets ImagickPixel. Émet une exception ImagickException en cas d'échec.

Erreurs / Exceptions

Lance une exception ImagickException si une erreur survient.

Exemples

Exemple #1 Exemple avec 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); // en rend les lignes le plus fin possible

    $imagick = new \Imagick();
    $imagick->newImage(500, 500, $backgroundColor);
    $imagick->setImageFormat("png");
    $imagick->drawImage($draw);

    $histogramWidth = 256;
    $histogramHeight = 100; // la hauteur de chaque segment RGB

    $imagick = new \Imagick(realpath($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;
}

?>

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User Contributed Notes 1 note

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Iddles ¶

13 years ago


Scratched my head for a while trying to figure out why this only returned a list of coloured pixels, and seemingly no colour count. Well it turns out that for some reason, the ImagickPixel class has a "getColorCount" method, which seems a strange place for it but hey.

<?php
$image = new Imagick("thing.png");
$pixels=$image->getImageHistogram();
foreach($pixels as $p){
 $colors = $p->getColor();
 foreach($colors as $c){
        print( "$c\t" );
 }
 print( "\t:\t" . $p->getColorCount() . "\n" );
}
?>

This will print out something like:

252    250    252    1    :    125
194    156    182    1    :    126
109    18    79    1    :    11440
2    117    162    1    :    12761
255    255    255    1    :    40769

...where the colums are red, green, blue, alpha, followed by the number of times that colour appears in the image.

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