[Algorithms] Alpha Channel

[Pai-Hung C. <pa...@ac...>]

Hi,

I want to use billboard in my program but cannot find a good way to create
32-bit bitmap with alpha channel of appropriate values.  Basically I want to
create a bitmap of tree with leaves in various green colors (with alpha =
255) and all non-green colors transparent (alpha = 0) so that I can use it
as the texture for my billboarded trees.  It would be nice if I can specify
a non-green color C and make the alpha of all the pixels of color C in the
bitmap to 0.  Is there any program capable of doing that with 32-bit bitmap
with alpha channel?  This may be off-topic and you could send your advise to
me off-line.

Thanks in advance,

Pai-Hung Chen