PHP GD水印脚本产生空白水印

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!