png transparency issue with GD

[WNO]

I am having difficulty keeping transparency on my png resizing function.  I have searched all around and tried various solutions.  However, all I keep getting is a black background.  Everything else about the function is working fine.  Any help would be appreciated.

 

Here is the code for transparency that isn't working:

			$dst_img=ImageCreateTrueColor($thumb_w,$thumb_h);
		imagealphablending($dst_img,false);
		imagesavealpha($dst_img,true);
		$transparent = imagecolorallocatealpha($dst_img, 255, 255, 255, 127);
		imagefilledrectangle($dst_img, 0, 0, $thumb_w, $thumb_h, $transparent);
		imagecopyresampled($dst_img,$src_img,0,0,0,0,$thumb_w,$thumb_h,$old_x,$old_y);

 

Here is the full function code:

		function createthumb($name,$filename,$new_w,$new_h)
	{
			$system=explode(".",$name);
		if (preg_match("/jpg|jpeg/",$system[1]))
		{
		$src_img=imagecreatefromjpeg($name);
		}
		if (preg_match("/png/",$system[1]))
		{
		$src_img=imagecreatefrompng($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,$thumb_h);
		imagealphablending($dst_img,false);
		imagesavealpha($dst_img,true);
		$transparent = imagecolorallocatealpha($dst_img, 255, 255, 255, 127);
		imagefilledrectangle($dst_img, 0, 0, $thumb_w, $thumb_h, $transparent);
		imagecopyresampled($dst_img,$src_img,0,0,0,0,$thumb_w,$thumb_h,$old_x,$old_y);

		if (preg_match("/png/",$system[1]))
		{
		imagepng($dst_img,$filename); 
		} else {
			imagejpeg($dst_img,$filename); 
		}
		imagedestroy($dst_img); 
		imagedestroy($src_img); 
	}

[mikecampbell]

imagecopyresampled() does not preserve transparency. Check this function (which unfortunately will be much slower than imagecopyresampled):

http://www.exorithm.com/algorithm/view/scale_image

[WNO]

It is working now.  My first code was correct.  My issue was in file naming (outside of this script).  My image url kept pointing to the original thumbnail with the background instead of the new one being created (which had been renamed).  Thanks for the help though...