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    Imagick::getImageHistogram

    (PECL imagick 2, PECL imagick 3)

    Imagick::getImageHistogram — 画像のヒストグラムを取得する

    説明

    public Imagick::getImageHistogram(): array

    画像のヒストグラムを ImagickPixel オブジェクトの配列で返します。

    パラメータ

    この関数にはパラメータはありません。

    戻り値

    画像のヒストグラムを ImagickPixel オブジェクトの配列で返します。

    エラー / 例外

    エラー時に ImagickException をスローします。

    例

    例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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