# How to edit a FITS file

import pyfits
import os

# Change to directory where script is located
abspath = os.path.abspath(__file__)
dname = os.path.dirname(abspath)
os.chdir(dname)


# Method 1  - alter the original FITS file
FitsFile = pyfits.open('M33.fits',mode='update')

#image = FitsFile[0].data
#image[:,:,:] = 5.0
#FitsFile.flush()
#FitsFile.close()


# Method 2 - create a new FITS file
#FitsFile = pyfits.open('M33.fits')
#
#image = FitsFile[0].data
#header = FitsFile[0].header
#
#image[:,:,:] = 5.0
#
#pyfits.writeto('testfile.fits',image, header)


# Editing a header value - does NOT work on naxis keyword !
header= FitsFile[0].header

header['CRPIX1'] = 13

image = FitsFile[0].data

pyfits.writeto('testfile.fits',image, header)