What is the primary purpose of a developer in the imaging process?

The primary purpose of a developer in the imaging process is to create a visible image. This step is crucial because, after film is exposed to light, it contains a latent image that is not yet visible. The developer's role is to chemically reduce the exposed silver halide crystals in the film emulsion, transforming them into black metallic silver. This process makes the previously latent image appear, allowing it to become an identifiable photograph.

In contrast, other options address different aspects of the imaging process but do not capture the core function of the developer. Fixing the image, for instance, refers to a later stage where the developed film is treated with a fixer to remove unexposed silver halide crystals, ensuring that the image remains stable and does not fade. Exposing the film is a separate action that occurs prior to development. Reducing fog pertains to minimizing undesirable exposure that could obscure the primary image but does not define the developer's main function. Thus, the act of transforming latent images into visible ones is central to the developer's purpose.