[Image-SIG] Saving gifs with transparency

[Will Stephenson]

On Monday 16 February 2004 15:00, Will Stephenson wrote:
> On Monday 16 February 2004 12:34, Will Stephenson wrote:
> > Even if I just load the gif and save it again without drawing on it,
> > transparency is lost.  I'm checking the result using Gimp and KDE image
> > viewers as I see XV doesn't support transparency.
>
> The plot thickens.  I had a look at GifImagePlugin, and noticed there was
> an option to use an external module to save the gif and a check to see if
> there is a key 'transparency' in the im.encoderinfo dictionary, so I added
> some debug prints to see what was going on there.

More GifImagePlugin internals:
I discovered that the contents of im.encoderinfo determine whether or not the 
transparency chunk/block/header gets written, and this dictionary is 
initialised with the 'options' argument to Image.save.  

Back in my script, I got PIL to write transparent gifs by passing the contents 
of im.info back in via 'options':

im.save( outfile, 'GIF',                    
transparency=im.info['transparency'] )

So does anyone know why I'm having to jump through these hoops just to 
preserve the image's existing transparency?  PIL is a good library - I've 
managed to pick enough up to achieve my needs with it in half a day - so I 
hope I'm just getting something monumentally wrong.

regards

Will 

-- 
Will Stephenson
IRC: Bille