Grafika\Gd\Image::getType PHP Method

    public function getType()
    {
        return $this->type;
    }

 /**
  * Dither by applying a threshold map.
  *
  * @param Image $image
  *
  * @return Image
  */
 private function ordered($image)
 {
     // Localize vars
     $width = $image->getWidth();
     $height = $image->getHeight();
     $old = $image->getCore();
     $new = imagecreatetruecolor($width, $height);
     $thresholdMap = array(array(15, 135, 45, 165), array(195, 75, 225, 105), array(60, 180, 30, 150), array(240, 120, 210, 90));
     for ($y = 0; $y < $height; $y += 1) {
         for ($x = 0; $x < $width; $x += 1) {
             $color = imagecolorat($old, $x, $y);
             $r = $color >> 16 & 0xff;
             $g = $color >> 8 & 0xff;
             $b = $color & 0xff;
             $gray = round($r * 0.3 + $g * 0.59 + $b * 0.11);
             $threshold = $thresholdMap[$x % 4][$y % 4];
             $oldPixel = ($gray + $threshold) / 2;
             if ($oldPixel <= 127) {
                 // Determine if black or white. Also has the benefit of clipping excess value
                 $newPixel = 0;
             } else {
                 $newPixel = 255;
             }
             // Current pixel
             imagesetpixel($new, $x, $y, imagecolorallocate($new, $newPixel, $newPixel, $newPixel));
         }
     }
     imagedestroy($old);
     // Free resource
     // Create new image with updated core
     return new Image($new, $image->getImageFile(), $width, $height, $image->getType());
 }