|The relative darkness of an image in a
finished film is called simply density.
Photographic density for film is determined by measuring the
incident to transmitted light ratio and expressing the value as a
Density (D) = Log (Intensity of Incident Light /
Intensity of Transmitted Light)
For example if 100 is the intesity of the viewing bow and 10 is
the value transmitted through a film the film density = Log (100/10)