PHP编程：php实现高效获取图片尺寸的方法

<?php
/*
*
*/
?
// Retrieve JPEG width and height without downloading/reading entire image.
function getjpegsize($img_loc) {
??? $handle = fopen($img_loc,"rb") or die("Invalid file stream.");
??? $new_block = NULL;
??? if(!feof($handle)) {
??????? $new_block = fread($handle,32);
??????? $i = 0;
??????? if($new_block[$i]=="xFF" && $new_block[$i+1]=="xD8" && $new_block[$i+2]=="xFF" && $new_block[$i+3]=="xE0") {
??????????? $i += 4;
??????????? if($new_block[$i+2]=="x4A" && $new_block[$i+3]=="x46" && $new_block[$i+4]=="x49" && $new_block[$i+5]=="x46" && $new_block[$i+6]=="x00") {
????????????????
// Read block size and skip ahead to begin cycling through blocks in search of SOF marker
?
??????????????? $block_size = unpack("H*",$new_block[$i] . $new_block[$i+1]);
??????????????? $block_size = hexdec($block_size[1]);
??????????????? while(!feof($handle)) {
??????????????????? $i += $block_size;
??????????????????? $new_block .= fread($handle,$block_size);
??????????????????? if($new_block[$i]=="xFF") {
????????????????????????
// New block detected,check for SOF marker
?
??????????????????????? $sof_marker = array("xC0","xC1","xC2","xC3","xC5","xC6","xC7","xC8","xC9","xCA","xCB","xCD","xCE","xCF");
??????????????????????? if(in_array($new_block[$i+1],$sof_marker)) {
????????????????????????????
// SOF marker detected. Width and height information is contained in bytes 4-7 after this byte.
?
??????????????????????????? $size_data = $new_block[$i+2] . $new_block[$i+3] . $new_block[$i+4] . $new_block[$i+5] . $new_block[$i+6] . $new_block[$i+7] . $new_block[$i+8];
??????????????????????????? $unpacked = unpack("H*",$size_data);
??????????????????????????? $unpacked = $unpacked[1];
??????????????????????????? $height = hexdec($unpacked[6] . $unpacked[7] . $unpacked[8] . $unpacked[9]);
??????????????????????????? $width = hexdec($unpacked[10] . $unpacked[11] . $unpacked[12] . $unpacked[13]);
??????????????????????????? return array($width,$height);
??????????????????????? } else {
????????????????????????????
// Skip block marker and read block size
?
??????????????????????????? $i += 2;
??????????????????????????? $block_size = unpack("H*",$new_block[$i] . $new_block[$i+1]);
??????????????????????????? $block_size = hexdec($block_size[1]);
??????????????????????? }
??????????????????? } else {
??????????????????????? return FALSE;
??????????????????? }
??????????????? }
??????????? }
??????? }
??? }
??? return FALSE;
}
?>

$url='http://www.xxxx.com/images/1331189004_28093400.jpg';
$image_content = file_get_contents($url);
$image = imagecreatefromstring($image_content);
$width = imagesx($image);
$height = imagesy($image);
echo $width.'*'.$height."nr";