What is defined as the difference in density between the light and dark areas on the processed film?

The concept being described is contrast, which refers to the difference in density between the lighter and darker areas of a processed radiographic film. Contrast is crucial in radiography because it enables clear differentiation between various structures and materials within the image, enhancing visibility and diagnostic accuracy. A high contrast indicates a significant difference in density, making dark areas darker and light areas lighter, which is essential for identifying potential anomalies or details in the radiograph.

The other terms mentioned have different meanings in the context of radiography. Brightness typically refers to the overall luminance of the image as displayed on a monitor, whereas density represents the degree of blackening or opacity of the film itself without comparing light and dark areas. Illumination refers to the level of light that illuminates the film while being viewed but does not pertain directly to the relationship between light and dark areas in terms of density differences. Thus, the correct term that captures the difference in density between light and dark areas in a film is contrast.