Replaces colors an image with those defined by replacement. The colors are replaced with the closest possible color. This method is available if Imagick has been compiled against ImageMagick version 6.4.5 or newer.
function remapImage($image_path, $dither_type)
{
    $imagick = new \Imagick(realpath($image_path));
    $palette = new \Imagick(realpath("images/NetscapeWebSafeColours.gif"));
    $imagick->remapImage($palette, $dither_type);
    header("Content-Type: image/png");
    echo $imagick->getImageBlob();
}