Creating alpha-transparency mask from flat image?

Is it possible to create an alpha-transparency mask from a flat raster image?

For example, I have a bitmap which was alpha-blended onto a solid color (fuschia) background. I want to be able to re-create the original aplha-blended without the background. I think this can be done if the program can someway consider the background color as 100% opague and subtract from the other colors depending on their relation to the background color. Is this possible?

Here's the flattened image I'm trying to restore to it's alpha-blended original:

http://wwww.ejstembler.com/images/8ball.bmp

Edward J. Stembler wrote:

Is it possible to create an alpha-transparency mask from a flat raster image?

For example, I have a bitmap which was alpha-blended onto a solid color (fuschia) background. I want to be able to re-create the original aplha-blended without the background. I think this can be done if the program can someway consider the background color as 100% opague and subtract from the other colors depending on their relation to the background color. Is this possible?

Here's the flattened image I'm trying to restore to it's alpha-blended original:

http://wwww.ejstembler.com/images/8ball.bmp

Double-click on Background to make it a layer. Background does not support transparency.

--
Comic book sketches and artwork:
http://www.sover.net/~hannigan/edjh.html