Convert 2MASS ALTAS images into MJy/sr (and subtract background)

convert_2mass.py

# Convert 2MASS ATLAS images into MJy/sr, and subtract background value
# estimated by 2MASS pipeline.
#
# Example:
#
# >>> atlas_to_MJysr('glimpse_k_test.fits', 'glimpse_k_cal.fits')
#

import pyfits
import pywcs
import numpy as np


zeromag = {'j': 1594., 'h': 1024., 'k': 666.7}


def arcperpix(wcs):
    return degperpix(wcs) * 3600.


def degperpix(wcs):
    try:
        pscale = np.sqrt(wcs.wcs.cd[0, 0] ** 2 + wcs.wcs.cd[1, 0] ** 2)
    except AttributeError:
        pscale = np.abs(wcs.wcs.cdelt[0])
    return pscale


def atlas_to_MJysr(input_file, output_file):

    # Read in ATLAS image
    hdu = pyfits.open(input_file)[0]

    # Extract required values from header
    magzp = hdu.header['MAGZP']
    filter = hdu.header['FILTER']
    skyval = hdu.header['SKYVAL']

    # Convert to Jy
    image = zeromag[filter] * (hdu.data - skyval) * 10. ** (-0.4 * magzp)

    # Convert to MJy
    image /= 1.e6

    # Find pixel area
    wcs = pywcs.WCS(hdu.header)
    pixel_scale = arcperpix(wcs)
    pixel_area = (pixel_scale / 206265.) ** 2.

    # Convert to MJy/sr
    image /= pixel_area

    # Write out file in MJy/sr
    pyfits.writeto(output_file, image, hdu.header, clobber=True)

Please I want to understand something about your work. First of all, which software did you use ? is it CASA or directly terminal and this steps or from this steps can I calculate bulge's magnitude or this steps just for all galaxy?