PHP GD image overlay question

[Humous]

Hi,

I'm generating a form to select various product options and would like them displayed in an image.

Eventually I'll use javascript to update the image inside a div tag as the user changes options. (I've done this part before)

Anyway I've gotten as far as merging two files togeather, basically one is a picture of an exhibition stand and the other is the same size but only has a cut out of the floor colour (I thought this would be a good test) and a white background. I did start with transparent backgrounds but the imageCopyMerge couldn't deal with it.

As you may be able to see from the code below I've currently got this working with a 30% transparency index, but what I really want is the various options I specify to overlay (100%) the base/source image.

Has anyone had any experience in doing this?

Thanks in advance,
Humous.

<?php

header("Content-type: image/png");
$floorcol = $_GET['floorcol'];

$sourcefile_id     = imagecreatefrompng("standtest.png");


switch ($floorcol)
{
    case 'red':
		$insertfile_id     = imagecreatefrompng("standtest_red.png");
        break;
    case 'blue':
        $insertfile_id     = imagecreatefrompng("standtest_blue.png");
        break;
    case 'green':
        $insertfile_id     = imagecreatefrompng("standtest_green.png");
        break;
    default:
        $insertfile_id     = imagecreatefrompng("standtest_red.png");
} 


$sourcefile_width=imageSX($sourcefile_id);
$sourcefile_height=imageSY($sourcefile_id);
$insertfile_width=imageSX($insertfile_id);
$insertfile_height=imageSY($insertfile_id); 

$transition=30;

imageCopyMerge($sourcefile_id, $insertfile_id,0,0,0,0,$insertfile_width,$insertfile_height,$transition);

imagepng($sourcefile_id);
imagedestroy($sourcefile_id);

$imageaccess=$_GET['imageaccess'];

?>