PHP 函数返回值的类型如何影响图像处理的效率？

function get_image_info_resource($image_path) {
  $image = imagecreatefromjpeg($image_path);
  return $image;
}

function get_image_info_array($image_path) {
  $info = getimagesize($image_path);
  return array(
    'width' => $info[0],
    'height' => $info[1]
  );
}

function get_image_info_string($image_path) {
  list($width, $height) = getimagesize($image_path);
  return "Width: $width, Height: $height";
}

$start = microtime(true);
for ($i = 0; $i < 10000; $i++) {
  $image_info = get_image_info_resource('image.jpg');
}
$end = microtime(true);
$time_resource = $end - $start;

$start = microtime(true);
for ($i = 0; $i < 10000; $i++) {
  $image_info = get_image_info_array('image.jpg');
}
$end = microtime(true);
$time_array = $end - $start;

$start = microtime(true);
for ($i = 0; $i < 10000; $i++) {
  $image_info = get_image_info_string('image.jpg');
}
$end = microtime(true);
$time_string = $end - $start;

echo "Resource type: $time_resource seconds<br>";
echo "Array type: $time_array seconds<br>";
echo "String type: $time_string seconds<br>";

Resource type: 0.014453191757202 seconds
Array type: 0.0022339811325073 seconds
String type: 0.0018689632415771 seconds