Imagick::getImageHistogram()

(PECL imagick 2.0.0)

Gets the image histogram

说明

Imagick::getImageHistogram(void): array

Returns the image histogram as an array of ImagickPixel objects.

返回值

Returns the image histogram as an array of ImagickPixel objects.

错误／异常

错误时抛出 ImagickException。

范例

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;
}
?>

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.