Importing a GIF & making it transparent

Anon

Hi all

I've been trying to make a script that imports a GIF image from an external server (i have permission to do this, see below) and designates a certain colour transparent for some time now and i'm not having much luck. Can anyone help or provide a script that does this?

The images i'm using are Australian weather radar images with a rather plain brown background

http://mirror.bom.gov.au/radar/IDR503.gif

What i'd like to do is have an orographic map for the background, like this

http://www.bsch.au.com/temp/preview.jpg

The radar images are available to the public and i have permission to make these alterations

Is it possible for PHP to download a GIF image (through HTTP), designate a certain colour transparent and then display the image on the screen without saving the image to the server?

Any help i can get with this would be much appreciated

mithril

Nope, nadda, sorry. What you're looking to do is possible, but only with PNG or JPEG's..... and PHP can't convert a GIF to either of those formats. Why you ask? PHP doesn't do GIF manipulation. The reason for this lies with UniSys.

Due to a loophole in US Patent Law they were able to patent the LZW Compression Alogrythm. For a long time they didn't interfer with anyone who used this algorythm, but in the last year or so they've started charging a royalty fee to graphic software developers for the right to use LZW compression. Worse still, they can fine web developers who use GIF created with programs which haven't paid those royalties up to $5000 USD. UniSys is, unfortunately, within their legal rights to do so. At this juncture the fine folks who develop GD (the Graphics Definations module PHP uses for image manip.) dropped GIF support and moved to PNG and JPEG.

Cheers,

Geoff A. Virgo

Anon

G'day Geoff

Thanks for replying. My server actually has an old version of GD installed which has GIF support, this script ended up working fine

$id = ImageCreateFromGif("image.gif");

$trans = imagecolorexact($id, 120, 100, 90);

imagecolortransparent($id, $trans);

ImageGIF($id,"newimage.gif");

echo "done";

....have you ever struggled with something for a long time, then looked back at the very simple finished product and wondered why you had so much trouble? Being new to PHP this happens to me every other day

My only problem now is my server doesn't let me download through HTTP for the ImageCreateFromGif function - yet another brick wall. I've decided to install PHP and GD on my computer and run the scripts from here - i found an install tutorial for PHP but i'm struggling with GD - can anyone recommend a good tutorial?

mithril

Hi Benn,

There are a couple good tutorials on bar graphs and dynamic image generation in the Articles section here on PHPBuilder. It's obviously not exactly what you're trying to do, but they might give you some insight into some of the mchanics involved in using GD. However you're going to have to convert most, if not all, of the tutorials you do find into "GIF-speak" for the reasons I mentioned in my last post. If your production server also has Perl, you might want to look into using ImageMagik to convert the downloaded gif's into png's or jpeg's. While there's no need for it if your server has a GIF version of GD installed, it'd be handy to know in case you ever have to upgrade.

Cheers,

Geoff A. Virgo