问如何在PHP中检测图像的蒙版区域？

EN

$src        = imagecreatefrompng("your-image.png");
$trans      = imageColorAllocateAlpha($src, 0, 0, 0, 127);
$transArray = imagecolorsforindex($src, $trans);

$width  = imagesx($src);
$height = imagesy($src);
for ($x = 0; $x < $width; $x++) {
   for ($y = 0; $y < $height; $y++) {
       $color  = imagecolorat($src, $x, $y);
       $colors = imagecolorsforindex($src, $color);
       if ($colors["alpha"] == $transArray["alpha"]) {
           // you have detected the first pixel of transparency
           // here you have to remember smallest $x and smallest $y
           // as well as biggest $x and biggest $y 
           // that should be your rectangle
       }
   }
 }