Readdir count certain files

Hi guys
I am trying to get a count of certain images i have in a folder.
Images are as soon 1_thumb to 12.jpg, 1_main to 12.jpg, 1_popup to 12.jpg
Actually named: 1_thumb.jpg and so on…
I am using the code from the php help manual

if ($handle = opendir('../media/models/'.$_GET['model_id']."/model_pics")) {
    while (false !== ($file = readdir($handle))) {
        if ($file != "." && $file != ".." && $file != substr_count($file, '_main.jpg') && $file != substr_count($file, '_popup.jpg')) {
 echo "&retval=1&imageCount=".$i;

Image count is retuned as 34 but it should be 12.