Image color palette analysis with PHP

Ever wanted to programmatically deploy a color palette or compare two images based on their primary colors. There are many ways to achieve this, but PHP and Imagick could be handy for sure. Say we have a picture like this:

and want to extract the main colors like this:

than this is the code to follow:

 
/* The original image is the average colors */
$average = new Imagick( "test.png" );
 
/* Reduce the amount of colors to 10 */
$average->quantizeImage( 10, Imagick::COLORSPACE_RGB, 0, false, false );
 
/* Only save one pixel of each color */
$average->uniqueImageColors();
 
/* Clone the average and modulate to brighter */
$bright = $average->clone();
$bright->modulateImage ( 125, 200, 100 );
 
/* Clone the average and modulate to darker */
$dark = $average->clone();
$dark->modulateImage ( 80, 100, 100 );
 
/* Helper function to create the mini-images */
function createImages( Imagick $composite, Imagick $im )
{
    /* Get ImagickPixelIterator */
    $it = $im->getPixelIterator();
 
    /* Reset the iterator to begin */
    $it->resetIterator();
 
    /* Loop trough rows */
    while( $row = $it->getNextIteratorRow() )
    {
        /* Loop trough columns */
        foreach ( $row as $pixel )
        {      
            /* Create a new image which contains the color */
            $composite->newImage( 20, 20, $pixel );
            $composite->borderImage( new ImagickPixel( "black" ), 1, 1 );
        }
    }
}
/* This object holds the color images */
$composite = new Imagick();
 
/* Create "icons" for each palette */
createImages( $composite, $dark );
createImages( $composite, $average );
createImages( $composite, $bright );
 
/* Montage the color images into single image
   Ten images per row, three rows */
$montage = $composite->montageImage( new imagickdraw(), "10x3+0+0",
                                      "20x20+4+3>", imagick::MONTAGEMODE_UNFRAME,
                                      "0x0+3+3" );
 
/* Free some resources */
$composite->destroy();
 
/* Create an empty canvas */
$canvas = new Imagick();
$canvas->newImage( $montage->getImageWidth() + 55,
                   $montage->getImageHeight(),
                   new ImagickPixel( "white" ) );
 
/* Display the canvas as png */
$canvas->setImageFormat( "png" );
 
/* Set font size to 12 points */
$draw = new ImagickDraw();
$draw->setFontSize( 12 );
 
/* Create legends for each palette */
$canvas->annotateImage( $draw, 5, 20, 0, "Dark: " );
$canvas->annotateImage( $draw, 5, 45, 0, "Average: " );
$canvas->annotateImage( $draw, 5, 70, 0, "Bright: " );
 
/* Composite the montaged images next to texts */
$canvas->compositeImage( $montage, Imagick::COMPOSITE_OVER, 55, 0 );
 
/* Output the image */
header( "Content-Type: image/png" );
echo $canvas;

Sources:

http://valokuva.org/?p=72

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Image color palette analysis with PHP