php实现高效获取图片尺寸的方法

<?php 
/* 
* http://www.vevb.com
*/ 
 
// 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";