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    Imagick::getImageHistogram

    (PECL imagick 2, PECL imagick 3)

    Imagick::getImageHistogram — Gets the image histogram

    Descrierea

    public Imagick::getImageHistogram ( ) : array

    Returns the image histogram as an array of ImagickPixel objects.

    Valorile întoarse

    Returns the image histogram as an array of ImagickPixel objects.

    Erori/Excepții

    Emite ImagickException în caz de eroare.

    Exemple

    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;
    }

    ?>

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    User Contributed Notes 1 note

    up
    2
    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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