These fits utilities are useful for processing 16-bit CCD images.

From the cfitsio example package --

imarith    Add, subtract, multiply, divide fits files
listhead   List a fits file header
modhead    Modify a fits file header

The utilties listhead and modhead allow reading and modifying fits headers.

The imarith utility would permit dark subtraction and flat fielding, but for
unsigned integer images it cannot handle negative pixels that may result in
dark subtraction, and it does not normalize on division.  

For routine dark subtraction and flat fielding use imdark and imflat --

imdark     Subtract a dark field from a CCD image.  
           Set negative values to zero.

imflat     Divide a CCD image by a flat field image.  
           Scale image by average of the flat field.
           
           
For spectroscopy, imrows sums the data along a columns from a start to a stop
row specified on the command line.             
           
imrows     Make a data file that is a sum of rows from an image.



           
           
           
