Linearization of Characteristic Curves in Photographic Photometry

After a survey of various definitions of the photometric characteristic curve of photographic emulsions, this paper reintroduces a long forgotten photometric parameter, the opacitance omega = opacity - 1 = 10(D) - 1 and describes its application to a characteristic function I = Aomega(n)(n approximately (1/2)), Which is linear in log-log co-ordinates over the whole range of densities of practical interest in photographic photometry. In a special case n = 1 and J = I/A = omega.