php实现高效获取图片尺寸的方法

// 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;
}
?>