[PHP]讀取JPEG圖檔dpi

讀取JPEG圖檔dpi

function get_dpi($filename){

// open the file and read first 20 bytes.
$a = fopen($filename,'r');
$string = fread($a,20);
fclose($a);

// get the value of byte 14th up to 18th
$data = bin2hex(substr($string,14,4));
$x = substr($data,0,4);
$y = substr($data,4,4);
/* $x,$y: 01 2C = 300dpi ; 00 48 = 72dpi */
return array(hexdec($x),hexdec($y));

}

程式出處: http://sandalian.com/php/get-dpi-value-of-an-image-using-php.html
JPEG結構說明: http://bytes.com/groups/php/5948-dpi-php-gd
JPEG結構&DPI說明: http://apptools.com/examples/dpi.php