new_contents: 
  '''
  Dilate the existing clean mask.
  '''
  
  from astropy.io import fits
  from skimage.morphology import disk
  from scipy import ndimage as nd
  
  
  mask = fits.open("M33_14B-088_HI_mask_modified.fits", mode='update')
  pbcov = fits.getdata("M33_14B-088_pbcor.fits")
  
  pb_thresh = 0.2
  pb_mask = pbcov > pb_thresh
  
  struct = disk(100)
  
  for i in xrange(1231):
      print(i)
      mask[0].data[i, 0, :, :] = \
          nd.binary_dilation(mask[0].data[i, 0, :, :], structure=struct)
      mask[0].data[i, 0, :, :] *= pb_mask.squeeze()
  
      mask.flush()
  
  mask.close()
  
subject: Mask dilation to include missing flux near some edges