In GIMP, use Filters-> Colors->Color To Alpha.  Choose black as the
color.  Then save it in a format that respects the alpha, like PNG.

-sjbrown

On Tue, 2003-09-09 at 04:44, Erlend Strømsvik wrote:
>  Hi
>  
>  Just started trying out Pygame and my first project is coming along
>  nicely: A Tank Wars game. (Got to start somewhere ;)
>  
>  To be able to create some nice explosions I thought I would use some
>  images and 'throw' them around. For the images I already have some .bmp
>  files which I took from another game. 
>  Here is the problem though. These .bmp files are all with a black
>  background, and all have their edges etc. antialiased against black. The
>  game where the images are used the images black background turns fully
>  transparent, then less dark pixels get some transparency and only bright
>  pixels are none transparent.
>  How this is done has me a bit puzzled. The .bmp images are 24 bit no
>  alpha channel.
>  
>  Could I just add together the RGB layers and create an alpha channel
>  from those? Is that viable solution? Or how would -you- do it? :)
>  I could always just use some transparent .gifs but the effects wouldn't
>  be so nice then, with transparency only being limited to one color.
>  
>  I'm also a bit unsure about how to use images with alpha channel or how
>  to add an alpha channel to a image.
>  
>  >From searching the in Internet I guess the term for this is 'alpha
>  blending'? :)
>  
>  
>  Anyway, I really like pygame. I've been using BlitzBasic earlier, but
>  with pygame you much of the same functionality but with a much better
>  programming language.
>  
>  Also, I see now need for future support for older versions of python.
>  
>  
>  
>  -
>  Erlend Stromsvik
-- 
+-------------------------------------------------------------+
| Shandy Brown                               Digital Thinkery |
| shandy@[...].net             http://www.digitalthinkery.com |
+-------------------------------------------------------------+