  Image processing is an increasingly important aspect for analysis of data
from X and $\gamma$-ray astrophysics missions. In this paper, I review a method
proposed by Kebede (L. W. Kebede 1994, ApJ, 423, 878), and point out an error
in the derivation of this method. It turns out that this error is not
debilitating -- the method still ``works'' in some sense -- but as published is
rather sub-optimal, as demonstrated both on theoretical grounds and via a set
of examples.
