image resize returns black image file

[kender]

here is the function I use

function createthumb($name,$filename,$new_w,$new_h){
	$system=explode('.',$name);
	if (preg_match('jpg|jpeg',$system[3])) {
		$src_img=imagecreatefromjpeg($name);
	}
	if (preg_match('png',$system[3])) {
		$src_img=imagecreatefrompng($name);
	}

$old_x=imageSX($src_img);
$old_y=imageSY($src_img);

if ($old_x > $old_y) {
	$thumb_w=$new_w;
	$thumb_h=$old_y*($new_h/$old_x);
}
if ($old_x < $old_y) {
	$thumb_w=$old_x*($new_w/$old_y);
	$thumb_h=$new_h;
}
if ($old_x == $old_y) {
	$thumb_w=$new_w;
	$thumb_h=$new_h;
}

$dst_img=ImageCreateTrueColor($thumb_w,$thumb_h);
imagecopyresampled($dst_img,$src_img,0,0,0,0,$thumb_w,$thumb_h,$old_x,$old_y);

if (preg_match("/png/",$system[3])) {
	imagepng($dst_img,$filename); 
} else {
	imagejpeg($dst_img,$filename); 
}

imagedestroy($dst_img); 
imagedestroy($src_img); 
}

the area where I am creating the image, its after the file is uploaded (hence $FILES) - basically saying, if upload successful then make a thumbnail

	$thumbsdir = '../uploads/thumbs/tn_';
	$thumbsfile = $thumbsdir . basename($_FILES['uploadedfile']['name']);

if (move_uploaded_file($_FILES['uploadedfile']['tmp_name'], $uploadfile)) {
	createthumb($uploadfile,$thumbsfile,100,100);
}

the upload is successful, it creates a thumbnail image with the correc name, in the correct directory, but it is a total black image.

any ideas?

[kender]

changed my function

function createthumb($name,$filename,$new_w,$new_h) {
	$system=explode('.',$name);
	if (preg_match('/jpg|jpeg|JPG|JPEG/',$system[3])) {
		$src_img=imagecreatefromjpeg($name);
	}
	if (preg_match('/png|PNG/',$system[3])) {
		$src_img=imagecreatefrompng($name);
	}

$old_x=imageSX($src_img);
$old_y=imageSY($src_img);

if ($old_x > $old_y) {
	$thumb_w=$new_w;
	$thumb_h=$old_y*($new_h/$old_x);
}
if ($old_x < $old_y) {
	$thumb_w=$old_x*($new_w/$old_y);
	$thumb_h=$new_h;
}
if ($old_x == $old_y) {
	$thumb_w=$new_w;
	$thumb_h=$new_h;
}

$dst_img=ImageCreateTrueColor($thumb_w,$thumb_h);
imagecopyresampled($dst_img,$src_img,0,0,0,0,$thumb_w,$thumb_h,$old_x,$old_y);

if (preg_match('/png|PNG/',$system[3])) {
	imagepng($dst_img,$filename); 
} else {
	imagejpeg($dst_img,$filename); 
}

imagedestroy($dst_img); 
imagedestroy($src_img); 
}

it seems to only fail on .png images wth transparant backgrounds, then i get solid black