Here is a simple conversion program that reads "simple" FITS image
files and outputs a corresponding "raw" data file.  The FITS image
may have 16 bit pixels.  The program rescales these to 8 bits.  The
scaling algorithum is simple.  First it finds the min and max pixel
values then computes a linear function that maps the min to zero and
the max to 255.

You can look at the code and change the scale function with not
much work.  You could try adding a log scale or use +/- 2 sigma
in place of min and max.  The simple linear scalling does not look
bad for typical TASS images.

I did this in a hurry and the program is not yet very robust.  It
does some error checking but not enough.  It is at that stange
where good input produces good output but garbage in may kill it.

To compile you will need to have the cfitsio library in /usr/local/lib
with the dot.h files in /usr/local/include.  After this is done just
type "make" to compile fits2raw.

To convert a TASS Mk III FITS file named "picture.fits to a gif do this:

fits2raw picture.fits | rawtopgm 800 896 | ppmtogif > picture.gif