Merging 2 bitmap objects

Hello,

here is what i am trying to do…

I have 2 diferent bitmap objects.
one with a picture… and enother with gradiant filll with transparant from 0 to 256.

idea is to merge 2 bitmaps and produse a fog efect on an image.
I tried to play with diferent color channels, but fail with my task.

of course i could run my picture bitmap pixel by pixel and change its chanels acordingly to make them darker. but I gues this metod will be too slow.
(I gues…)

here is little example what I am trying to do…
http://flashmx.puslapiai.lt/BITMAPTEST022.swf [FLASH 8]

I have a MC with transparant gradient put over my bitmap.

eny ideas?

maybe some thoughts ho to make this effent in bitmap level?

Deril