“…The joint histograms of I 1 •w and I 2 within their region of overlap are constructed by binning the corresponding intensity pairs (I 1 (w(x)), I 2 (x)), and the marginal histograms are obtained by integrating over rows and columns, respectively. Substituting (12) into (11) and rearranging following [4,9], yields the first variation of Φ M I :…”