How to watermark GIF image with 24-bit PNG with transparency in PHP?

Question

Hi!

I am creating a script that can put a 24-bit transparent PNG image as a water mark on JPG/GIF/PNG images.

So, far i had success with JPEG and PNG.

But how can i achieve same with gif files? for GIF files, watermark do appear, but without transparency.

Please help.

Thanks, Anjan

Answer 1

GIF images use indexed color palettes. In order to combine another image (your watermark) with the GIF image, whatever image library you're using (I'm guessing gd) is probably converting the PNG to an indexed-color format which is stripping out the alpha channel when it does so.

You probably need to find a way to convince it to convert the GIF image to a non-indexed color format first, then combine it with the watermark, and then write it back to an indexed-color GIF again.