Thank you so much Rob, but actually I am already able to read and
display FITS files of 8,16,32 bits per pixel I just fail to do so for
those of -32, -64 bits per pixel.

32 bits per pixel means that a 32 bit integer represents each pixel
-32 bits per pixel means that a 32 bit float represents each pixel
-64 bits per pixel means that a 64 bit float represents each pixel

My exact problem in reading -32,-64 bits per pixel files is in reading
the image colors.

I don't face any problem reading 32 bits per pixel files for example
because it is a standard color depth, any developer involved in
imaging knows exactly how to deal with it ( just read the 4 bytes,
extract the 3 bytes related to color: R,G,B and feed them into the
bitmap )

But a -32 bit (32 bit floating point) color depth is something I have
never heard of. Simply I don't know how to extract the 3 color bytes
(R,G,B) from the floating point data.

To cut it short: I have just one specific problem: how to extract
R,G,B data from the -32 bits per pixel FITS images.