for ($x = 0; $x < $this->thumbnail_width; $x++) {
                            for ($y = 0; $y < $this->thumbnail_height; $y++) {
                                $PixelColor = phpthumb_functions::GetPixelColor($this->gdimg_output, $x, $y);
                                imagesetpixel($img_alpha_mixdown_dither, $x, $y, $dither_color[$PixelColor['alpha'] * 2]);
                            }