In 1890 Hurter and Driffield proposed the following equation for the density "D" of a photographic plate exposed for a time "t" to light of constant intensity: D = 1/a Loge (b-[b-1] e-ct) where "a", "b", and "c" are parameters.
Proceedings of the Iowa Academy of Science
©1920 Iowa Academy of Science, Inc.
Helmick, P. S.
"On Finding the Equation of the Characteristic Blackening Curve for a Photographic Plate,"
Proceedings of the Iowa Academy of Science, 27(1), 223-224.
Available at: https://scholarworks.uni.edu/pias/vol27/iss1/36