Resize GIF with transparent background

I have a series of gifs that have transparent backgrounds that I want to create thumbnails of when they are uploaded. When I try to resize them, the background becomes black. Can someone tell me how to preserve the transparency of the image? Here is my code:

$img = $_SERVER['DOCUMENT_ROOT'] . "/images/test.gif";
$thumb = $_SERVER['DOCUMENT_ROOT'] . "/images/tn/test.gif";
#------------------------------------------------------------------------------------------#
$source = imagecreatefromgif($img);
imagecopyresized($thumb, $source, 0, 0, 0, 0, $newWidth, $newHeight, $width, $height);
imagegif($thumb,$thumbnail);
chmod($thumbnail, 0644);
return str_replace($_SERVER['DOCUMENT_ROOT'],"",$thumbnail);
LVL 1
rbichonAsked:
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Steve BinkCommented:
I've read quite a bit about palette vs truecolor images.  I'm left with the impression that most of the palette-based functions do not carry over transparency.  Here's a comment I found in the PHP manual that may be of some use:

http://www.php.net/manual/en/function.imagecopy.php#48355

I've also notice this function being used a bit in the context of dealing with transparency:

http://www.php.net/manual/en/function.imagecreatetruecolor.php
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rdivilbissCommented:
The manual states you must tell imagegif the color of the transparancy using imagecolortransparent() http://us3.php.net/manual/en/function.imagecolortransparent.php.

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Steve BinkCommented:
The imagecolortransparent() function maps a single color as transparent on an existing image.  That's fine for what it does, but he's getting his transparency lost when he creates the copy.  The notes below the function explanation detail what he needs:

----------------------------------------------
    Note:  Transparency is copied only with imagecopymerge() and true color images, not with imagecopy() or pallete images.

    Note: The transparent color is a property of the image, transparency is not a property of the color. Once you have set a color to be the transparent color, any regions of the image in that color that were drawn previously will be transparent.
----------------------------------------------

So, worst case scenario, use imagecreatetruecolor() to create a new, 100% transparent image, then merge it with the GIF you are opening.  The resulting picture should retain the transparency.
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rbichonAuthor Commented:
The transparency became too much. The thumbnail is on a white background anyway so I decided to merge the image with a white one. Here is my code:

$img = $_SERVER['DOCUMENT_ROOT'] . "/images/test.gif";
$thumbnail = $_SERVER['DOCUMENT_ROOT'] . "/images/thumbs/test.gif";
$new = imagecreatetruecolor($newWidth, $newHeight);
$source = imagecreatefromgif($img);
$white = imagecolorallocate($new, 255, 255, 255);
imagefill($new,0,0,$white);
imagecopyresized($new, $source, 0, 0, 0, 0, $newWidth, $newHeight, $width, $height);
imagegif($new,$thumbnail);
chmod($thumbnail, 0644);
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