Film contrast refers to the ability to show what, given a change in radiation exposure?

Film contrast is a critical concept in radiographic testing, as it pertains to the film's ability to differentiate between varying levels of radiation exposure. It primarily reflects how well the film can demonstrate differences in density. When an image is exposed to radiation, the varying degrees of exposure lead to different levels of blackening on the film; this results in a visible contrast between areas of different radiation absorption.

In radiography, density refers to the darkening of the film, which occurs due to the amount of silver halide crystals that have been exposed to light during the processing. The more radiation that hits a particular area, the denser (dark) it becomes on the film. Therefore, when discussing film contrast, we focus on how well the film can delineate these density differences. High contrast means there is a clear distinction between the dark and light areas, while low contrast indicates a more gradual transition between these densities.

This understanding is essential for interpreting radiographs effectively, as certain features of the test object can only be observed with adequate contrast. Thus, film contrast is fundamentally linked to differences in density, making it the correct choice.