Alpha channels

[Murphy]

Hi,
ok, this is a bit of a newbie question, and maybe it's just my program acting up, but anyway, here it goes:

I have a couple of 24-bit textures and a couple of 8-bit black and white masks for them that I would like to use as alpha channels.

I'm using the alpha mask plug-in for Paint.NET and with that the 24-bit image is severely changed when I use one of the 8-bit images as alpha masks for it!
How can I make the 24 color bits not change at all and still add an 8-bit alpha channel based on an 8-bit image?

Basically I want to import the image into UnrealEd without the alpha checkbox checked, so it looks completely normal in the texture-browser and on surfaces, but I can still use it to give a shader alpha information by adding it as Opacity or as a Specular Mask.
The alternative would be to import the 24-bit and 8-bit images separately, like I did in NorthSea and I think Dammage, but that's not as convenient.

How would I go about this?

[Murphy]

I figured it out! If something is made completely transparent it becomes black in the color channels. The solution was to increase the brightness of the alpha mask by 1 so technically there is no pitch-black anymore. The eye probably won't notice a difference, but this preserves the color.