What causes the subjective impression of graininess in processed x-ray film?

The subjective impression of graininess in processed x-ray film is primarily caused by the uneven distribution of developed grains. During the development process, the silver halide crystals in the film emulsion are reduced to metallic silver. If these grains are not distributed uniformly, or if there are variations in their sizes and densities, the resulting image can exhibit a grainy appearance. This graininess is particularly noticeable in areas of lower exposure where the concentration of developed silver is less consistent.

Other factors like film thickness, processing temperature, and the type of radiation used can influence the overall quality and sharpness of the radiographic image, but they do not directly contribute to graininess in the same way that the uneven distribution of developed grains does. Thicker films may have a different appearance, and variations in processing temperature can affect the overall contrast and detail, while the type of radiation can impact the exposure characteristics. However, it is the irregular distribution of silver grains that specifically manifests as graininess within the film.