How to determine the color type of an image in php? Example tutorial

$i = imagecreatefromjpeg("image.jpg");
for ($x=0;$xfor ($y=0;$y$rgb = imagecolorat($i,$x,$y);
$r   = ($rgb >> 16) & 0xFF;
$g   = ($rgb >>  & 0xFF;
$b   = $rgb & 0xFF;
$rTotal += $r;
$gTotal += $g;
$bTotal += $b;
$total++;
}
} // bbs.it-home.org
$rAverage = round($rTotal/$total);
$gAverage = round($gTotal/$total);
$bAverage = round($bTotal/$total);