On 10 Nov 2003, John Green wrote:

Hello all, I am a software developer and I was assigned the task of
importing FITS files. Among the files that I have got are 32, 64
floating point files. I don't know how to extract the R,G,B values
from the flaoting point data.

I assume you refer to FITS images and not to other kind of FITS data
(tabular). The "I" in FITS originally meant "Image" but nowadays it
means just "Interchange" !

I don't know how is the RGB values stored in the 32, 64 floating point
data types of FITS files.

There is no such thing as "RGB values". The content of the image is some
arbitrary physical quantity (could be number of photons, flux, magnitude
[which in itself is proportional to log flux] or anything else).

The way it is usually displayed is first to apply some physical
transformation (e.g. applying low and high cut, then transforming the
values using a linear, log or other scale as some form of histogram
equalization into an array of integer values from 0 to n, say n=255).

Then apply a lookup table which makes a correspondence between the index
n and a triplet of RGB. But this purely for display. All the physics and
the capabilities of the observer are in the image content and in the
physical transformation !

There are many popular families of lookup tables. One could have a pure
grayscale ( R=G=B=n), other monochrome grayscales (e.g. R=0 G=n B-0), or
other conventional scales like a "heat" scale, a "rainbow" scale etc.
Each package has its own set of scales.

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