Ben's answer was exactly what I was looking for. Thanks!
For the sake of the archives I'll slightly modify his answer for
other new users like myself to follow in the future:
>> I have two images, A and B, which are black and white, from a
>> proprietary program but saved as TIFFs. They open as RGB in the GIMP
>> 2.2 on my Mac, with the image visible in all three channels.
>> I want to create a final image, C, consisting of image A in the red
>> channel and image B in the blue channel, and no image in the green
> 1) Open the images representing each channel.
> 2) Convert these images to grayscale mode (as any given single
> could be represented as a grayscale image.) (Image --> Mode -->
> 3) If necessary, open a third image/layer as a blank one, since you
> wanted nothing in the green channel. (A new blank image such as
> this must be
> black and also in greyscale mode) To do this: File --> New, then
> OK. Then Edit --> Fill with FG Color (which should be black).
> Finally make it greyscale as in #2.
> 4) Perform the "compose" function found in Filters --> Colors -->
> Compose and
> choose the layers for the appropriate channels.
The compose dialog is straightforward and easy to use, and generates
a new file with the desired result.
Thanks again, Ben. This is very useful to scientists who have single
channel images from microscopes.
This way those images are false colored and merged in one step.
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