Building upon backglancer's and stefan's posts below, the following script will lay a 24-bit PNG watermark over any image.
To prepare a 24-bit watermark, I recommend creating a white logo or text over a transparent background in Photoshop. Save this as a 24-bit PNG via 'Save for the Web...'. Be sure to set the transparency of the logo layer in Photoshop itself. 30-40% is a good setting.
Once the assets are prepared, throw the full or relative server paths at the watermark function below:
/******************************************************************/
function watermark($sourcefile, $watermarkfile) {
#
# $sourcefile = Filename of the picture to be watermarked.
# $watermarkfile = Filename of the 24-bit PNG watermark file.
#
//Get the resource ids of the pictures
$watermarkfile_id = imagecreatefrompng($watermarkfile);
imageAlphaBlending($watermarkfile_id, false);
imageSaveAlpha($watermarkfile_id, true);
$fileType = strtolower(substr($sourcefile, strlen($sourcefile)-3));
switch($fileType) {
case('gif'):
$sourcefile_id = imagecreatefromgif($sourcefile);
break;
case('png'):
$sourcefile_id = imagecreatefrompng($sourcefile);
break;
default:
$sourcefile_id = imagecreatefromjpeg($sourcefile);
}
//Get the sizes of both pix
$sourcefile_width=imageSX($sourcefile_id);
$sourcefile_height=imageSY($sourcefile_id);
$watermarkfile_width=imageSX($watermarkfile_id);
$watermarkfile_height=imageSY($watermarkfile_id);
$dest_x = ( $sourcefile_width / 2 ) - ( $watermarkfile_width / 2 );
$dest_y = ( $sourcefile_height / 2 ) - ( $watermarkfile_height / 2 );
// if a gif, we have to upsample it to a truecolor image
if($fileType == 'gif') {
// create an empty truecolor container
$tempimage = imagecreatetruecolor($sourcefile_width,
$sourcefile_height);
// copy the 8-bit gif into the truecolor image
imagecopy($tempimage, $sourcefile_id, 0, 0, 0, 0,
$sourcefile_width, $sourcefile_height);
// copy the source_id int
$sourcefile_id = $tempimage;
}
imagecopy($sourcefile_id, $watermarkfile_id, $dest_x, $dest_y, 0, 0,
$watermarkfile_width, $watermarkfile_height);
//Create a jpeg out of the modified picture
switch($fileType) {
// remember we don't need gif any more, so we use only png or jpeg.
// See the upsaple code immediately above to see how we handle gifs
case('png'):
header("Content-type: image/png");
imagepng ($sourcefile_id);
break;
default:
header("Content-type: image/jpg");
imagejpeg ($sourcefile_id);
}
imagedestroy($sourcefile_id);
imagedestroy($watermarkfile_id);
}
