Replace a color with transparency?

[bnuttin]

I am a total newbie to image manipulation, so please be patient

I have an image with a black background and an image in various shades of grey. I would like to, i guess, "invert it" in such a way that black becomes white, and the various shades of gray become transparent. Basically I want to have the following:

Black -> White with 100% opacity - totally white

Grey with 10% black -> White with 90% opacity - white with a bit of transparency

Grey with 70% black -> White with 30% opacity - white with a lot of transparency

White -> White with 0% opacity - completely transparent

How can I achieve this?

Thanks!

[Ego Eram Reputo]

Sounds like a job for the Grim Color Reaper plugin.

The plugin will remove the color you specify, allowing you to add in another color.

An alternative for the plugin would be the Magic Wand tool , however this may leave the edges a little ragged if your image has quite soft edges. Then some anti-aliasing (there is a plugin) would be required.

For best results, recolor a separate layer below the first image (that you removed the background from).