Question

I have a watermark script I am working on, the results are good on PNG and on JPG images however a gif image, not so good. I am using PHP and GD

Below you can see the difference in quality of the watermark.

Anyone know how to improve this?

For the gif version I am using

$image = imagecreatefromgif($source_file);
imagecopymerge($image, $watermark, $x, $y, 0, 0, $water_width, $water_height, 65);
imagegif($image, $source_file);

gif image = bad quality
gif image http://img2.pict.com/fd/46/00/1471179/0/gif.gif

jpg image = good
jpg image http://img2.pict.com/82/a1/5a/1471181/0/jpg.jpg

Answer 1

GIF images have a fixed palette that can contain a maximum of 256 colors. The issue here is probably that the image your inserting uses colors that isn’t available in the target image.

I have never tried this, but it might be worth a shot. You could try converting the gif image to a true color image first, then do the watermarking and after that converting it back to gif.

$image = imagecreatefromgif($source_file);
// create a true color image of the same size
$image2 = imagecreatetruecolor(imagesx($image), imagesy($image));
// copy the original gif image on to the true color image
imagecopy($image2, $image, 0, 0, 0, 0, imagesx($image), imagesy($image));
// copy the watermark onto the new true color image
imagecopymerge($image2, $watermark, $x, $y, 0, 0, $water_width, $water_height, 65);
// write the new image to disk
imagegif($image2, $source_file);

Try it and see if it makes a difference.

There’s also a couple of palette manipulation functions available that might help:

1. imagecolormatch()
2. imagetruecolortopalette()
3. imagepalettecopy()

I’m not sure how you would apply them, but I’m guessing that there’s a few things you could do to improve the results.