I know the basics, that by measuring how much x-ray signal reaches each 'pixel' on the receiver we can measure how much has been absorbed. But this gives only a single channel of information, e.g a greyscale image. However I'm sure I've seen images where there are opaque white parts (bones) and opaque black parts (metal)... this seems to imply color and opaqueness are two separate channels and I cannot see how that works.
Can anyone go beyond the basics to describe the real way a fluoro scan ends up as a picture I can look at? Better references than wikipedia would also be welcome.