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;
         }

     }
 }