title: Cropping very large fits files using specified boundaries
body: <p>I have a large fits file (over 30,000 x 30,000) pixels. <a href="http://iraf.noao.edu/" rel="nofollow">IRAF</a> cannot handle this size of image. How can one crop a file of this size while retaining correct header information, as IRAF does when using its standard cropping mode?</p>