Ed_imageresizer::_makeGrayscale PHP Method

    private function _makeGrayscale($im)
    {
        if (imageistruecolor($im)) {
            imagetruecolortopalette($im, false, 256);
        }
        for ($c = 0; $c < imagecolorstotal($im); $c++) {
            $col = imagecolorsforindex($im, $c);
            $gray = round(0.299 * $col['red'] + 0.587 * $col['green'] + 0.114 * $col['blue']);
            imagecolorset($im, $c, $gray, $gray, $gray);
        }
        return $im;
    }