What is the name of the input-output curve used to express the change in density with respect to the change in radiation dose of the X-ray film?

The term that describes the input-output relationship between radiation dose and the resulting density of X-ray film is known as the Characteristic Curve. This curve, also referred to as the H&D curve (named after Hurter and Driffield), illustrates how the film's density changes as it is exposed to varying levels of radiation.

In radiography, understanding this curve is crucial because it provides insights into film sensitivity, contrast, and the exposure needed to achieve optimal imaging results. A steeper slope on the Characteristic Curve indicates greater sensitivity to changes in radiation dose, which translates to a more significant change in film density for a given change in exposure. This relationship helps radiographers in determining the appropriate amount of exposure required for high-quality images while minimizing patient dose.

The other terms mentioned, while relevant in various contexts, do not specifically denote the established relationship of density change with radiation dose in X-ray film.