After taking a radiographic image of a part and processing the film, the resulting
darkness of the film will vary according to the amount of radiation that has reached
the film through the test object. As mentioned earlier, the darker areas indicate more
exposure and liter areas indicate less exposure. The processed film (or image) is usually
viewed by placing it in front of a screen providing white light illumination of uniform
intensity such that the light is transmitted through the film such that the image can be
clearly seen. The term “radiographic density” is a measure of the degree of film
darkening (darkness of the image). Technically it should be called “transmitted density”
when associated with transparent-base film since it is a measure of the light
transmitted through the film. Radiographic density is the logarithm of two
measurements: the intensity of light incident on the film ( ) and the intensity of light
transmitted through the film ( ). This ratio is the inverse of transmittance.