PHP GD watermark script produces blank watermark

Question

I'm trying to add a watermark to images right after uploading them to my website, but it seems the watermark keeps coming out as a black object with no details. I believe the script is working a little bit because if it wasn't, I probably wouldn't see any kind of watermark or the script would fail.

This is my script so far:

$watermark = imagecreatefrompng('preview-watermark.png');  
$watermark_width = imagesx($watermark);  
$watermark_height = imagesy($watermark);        
$image = imagecreatetruecolor($watermark_width, $watermark_height);  
$image = imagecreatefromjpeg($portfolio_preview_dir.'/'.$file);  
$size = getimagesize($portfolio_preview_dir.'/'.$file);  
$dest_x = $size[0] - $watermark_width - 5;  
$dest_y = $size[1] - $watermark_height - 5;  
imagecopymerge($image, $watermark, $dest_x, $dest_y, 0, 0, $watermark_width, $watermark_height, 100);  
imagejpeg($image, $portfolio_preview_dir.'/'.$file);  
imagedestroy($image); 
imagedestroy($watermark);

This is what it's producing. The shape of the watermark is correct, as the watermark is 325x37 pixels:

I have tried playing with the watermark image itself. My first attempt was to save the photoshop watermark (with transparent bg) using 'save for web' and selected 'PNG-24'. This didn't work, so I then saved it as a normal PNG (without 'save for web') and it still fails.

I'm not sure whether it's the script or the image! Can somebody please share some knowledge with me and help fix this issue?

Answer 1

$watermark = imagecreatefrompng('preview-watermark.png');
imagealphablending($watermark , false);
imagesavealpha($watermark , true);
$watermark_width = imagesx($watermark);  
$watermark_height = imagesy($watermark);        
$image = imagecreatetruecolor($watermark_width, $watermark_height);  
$image = imagecreatefromjpeg($portfolio_preview_dir.'/'.$file);  
$size = getimagesize($portfolio_preview_dir.'/'.$file);  
$dest_x = $size[0] - $watermark_width - 5;  
$dest_y = $size[1] - $watermark_height - 5;  
imagecopy($image, $watermark, $dest_x, $dest_y, 0, 0, $watermark_width, $watermark_height);  
imagejpeg($image, $portfolio_preview_dir.'/'.$file);  
imagedestroy($image); 
imagedestroy($watermark);

There are things:

1. imagecopymerge does not allow transparency for PNG-24

(Source: https://drupal.org/node/80369)

1. imagesavealpha + imagealphablending allow to save transparency

(Source: http://php.net/manual/en/function.imagesavealpha.php)

I hope it fixes your problem.

Also you output a JPEG, why? Stay with PNG and your image will support transparent watermarks, right now it does not!

Answer 2

There are many solution on SO and php.net as well. This is one (without creating new image itself)

// Load the stamp and the photo to apply the watermark to
$stamp = imagecreatefrompng('stamp.png');
$im = imagecreatefromjpeg('photo.jpeg');

// Set the margins for the stamp and get the height/width of the stamp image
$marge_right = 10;
$marge_bottom = 10;
$sx = imagesx($stamp);
$sy = imagesy($stamp);

// Copy the stamp image onto our photo using the margin offsets and the photo 
// width to calculate positioning of the stamp. 
imagecopy($im, $stamp, imagesx($im) - $sx - $marge_right, imagesy($im) - $sy - $marge_bottom, 0, 0, imagesx($stamp), imagesy($stamp));

// Output and free memory
header('Content-type: image/png');
imagepng($im);
imagedestroy($im);

edit

Watermark should be saved with alpha channek (transparency). Photoshop since CS2 (save for web) should do the thing, also GIMP works great.