Comments about the coincident bit counting (CBC) criterion for image registration

In a paper recently published (ibid., vol.12, p. 30-8, 1993), Chiang and Sullivan compare a new criterion for image registration called CBC (coincident bit counting) with two criteria that the authors proposed some years ago, namely SSC and DSC (stochastic and deterministic sign change criteria). The authors' nonparametric approach was demonstrated to outperform the conventional image registration criteria for robust registration in the fact that the value of their similarity measure did not take the specific pixel values into account. In light of this observation, Chiang and Sullivan have built the CBC criterion. The CBC method compares the number of coincident bits between the corresponding pixels in two different frames for a fixed amount of displacement. While the authors consider that the CBC is of interest and deserves to be studied, they feel that the comparison made by Chiang and Sullivan was not entirely accurate. Here the authors comment on this comparison and suggest possible further studies.