code: def total_sparse_pixels_from_mask(mask, unmasked_sparse_grid_pixel_centres):
      
  
      total_sparse_pixels = 0
  
      for unmasked_sparse_pixel_index in range(unmasked_sparse_grid_pixel_centres.shape[0]):
  
          y = unmasked_sparse_grid_pixel_centres[unmasked_sparse_pixel_index, 0]
          x = unmasked_sparse_grid_pixel_centres[unmasked_sparse_pixel_index, 1]
  
          if not mask[y,x]:
              total_sparse_pixels += 1
  
      return total_sparse_pixels
docs: Given the full (i.e. without removing pixels which are outside the regular-masks) pixelization grid's pixel centers
      and the regular-masks, compute the total number of pixels which are within the regular-masks and thus used by the
      pixelization grid.
  
      Parameters
      -----------
      mask : ccd.masks.Mask
          The regular-masks within which pixelization pixels must be inside
      unmasked_sparse_grid_pixel_centres : ndarray
          The centres of the unmasked pixelization grid pixels.