A Discussion of the Factors Influencing Callier Coefficient

Abstract

The relevance of the Callier coefficient Q with regard to the various measures of performance of black-and-white films is outlined. The experimentally-determined variations with diffuse density D of Q, an analogous coefficient q defined in terms of net densities and a hybrid coefficient q' are presented. An account is given of the way in which the shape of the Q vs D curve is affected by base density and light scatter at the emulsion surface, in particular by a matting agent or reticulation. Changes in these properties can have a marked effect on the curve shape, particularly at low to moderate densities; a decrease in base density or an increase in light scatter can 'switch' the trend of the Q vs D curve from one which falls as density falls to one which rises to large values. This criticality is not observed in the cases of q or q', neither of which have been observed to fall with decreasing density. A theory is presented which adequately accounts for all the experimental observations including the criticality of the Q vs D relation.