Which of the following describes the action of the developer in an automatic film processor?

The action of the developer in an automatic film processor is best described as changing the exposed silver halide crystals into black, metallic silver. This is a crucial step in the developing process, as the developer reacts chemically with the exposed crystals that have been influenced by the x-ray exposure during the imaging process.

When film is exposed to radiation, certain areas of the silver halide crystals become altered. The developer solution contains reducing agents that facilitate the conversion of these exposed areas into visible metallic silver, creating the dark areas on the developed film. The areas that were not exposed to radiation remain unchanged and will be removed in subsequent processing steps.

This process is essential for producing a recognizable and usable radiographic image, as it directly correlates to the contrast and detail visible in the final output. Other options in the question do not accurately describe the primary role of the developer, as they pertain to different functions in the overall processing system. Enhancing color contrast, exposing unexposed crystals, or removing non-exposed areas are not directly tied to the specific action of the developer in the film development process.