ABSTRACT
In the early 1960s, the National Bureau of Standards aided the photographic and printing industries by conducting research on precise measurement of optical transmission and reflection density, providing physical standards to calibrate instruments, and writing national and international documentary standards on optical density measurement. Optical density is a logarithmic measure of the darkness of a photograph or printed image. The combination of light source and optics directing light to a specimen was called an "illuminator" or "irradiator" and the optical system collecting and evaluating the light reflected or transmitted in a specified direction was called a "receiver." To measure optical modulation, the geometrical and spectral conditions of measurement must simulate the geometrical and spectral conditions for the use of the modulation. Photographic wedges are widely used in photographic science. The wedge may be straight, the density varying linearly with length, or it may be circular, the density varying linearly with rotational angle.
