how to fuse two images of different intensity?

I am trying to overlay one image (foreground, false color image containing information about signal to noise ratio, intensity range 0-20) on top of another one (background, grayscale image, intensity range 0.8-1.2). The foreground image should be transparent (transparency about 80%). Could you help me on that?

Answer 1

[Image Analyst]

Just do a weighted average, or check this out:

http://blogs.mathworks.com/steve/2009/02/18/image-overlay-using-transparency/