rgb转灰度 RGB To Gray php Adobe RGB (1998) [gamma=2.20]

<?php
/**
 * Date: 2016/10/24
 * Time: 0:52
 */
// Gray = (R^2.2 * 0.2973 + G^2.2 * 0.6274 + B^2.2 * 0.0753)^(1/2.2)
$size = getimagesize('png.png');
$res = imagecreatefrompng('png.png');
for ($i = 0; $i < $size[1]; ++$i) {
    for ($j = 0; $j < $size[0]; ++$j) {
        $rgb = imagecolorat($res, $j, $i);
        // var_dump($rgb);
        $rgbarray = imagecolorsforindex($res, $rgb);
        print_r($rgbarray);
        $wr = $rgbarray['red'];
        $wg = $rgbarray['green'];
        $wb = $rgbarray['blue'];
        $gray = ($wr ^ 2.2 * 0.2973 + $wg ^ 2.2 * 0.6274 + $wb ^ 2.2 * 0.0753) ^ (1 / 2.2);
        echo $gray, '<br>';

        //???
        if ($rgbarray['red'] < 125 || $rgbarray['green'] < 125 ||
            $rgbarray['blue'] < 125
        ) {
            $data[$i][$j] = 1;
        } else {
            $data[$i][$j] = 0;
        }

    }
}