[cl-pdf-devel] Producing a png with transparent background for use in pdf

[Mitch Berkson]

I have a png file that I edited in the GIMP to make the background 
transparent.  I used "Color to Alpha".  When I try to pdf:make-image it, 
I get the error that alpha channel is not supported.  In the cl-pdf 
mailing list archive, I see that Marc said that alpha channels are not 
supported but transparency is.

How can I modify my png to have a transparent color without using the 
alpha channel? Thank you.

Mitch Berkson