What makes the latent image invisible in film?

The latent image in film is made invisible primarily due to the nature of the film's emulsion layer, which contains light-sensitive silver halide crystals. When film is exposed to light, these crystals undergo a chemical change that creates a latent image, meaning it is an image that is present but not yet visible until developed.

The sensitivity center plays a crucial role in this process. These are essentially the points within the silver halide crystals where the initial reaction to light occurs, leading to the formation of the latent image. However, until development processes begin, no further reactions occur to make this image visible.

In contrast, while the overcoat provides a protective layer to the film and the crystal lattice refers to the structured arrangement of the silver halide crystals, they do not directly contribute to the invisibility of the latent image in the same way that the sensitivity center does. Exposure time can affect the strength of the latent image but does not inherently relate to its invisibility. Thus, the concept of the sensitivity center is integral in understanding why the latent image remains unseen in the film until it undergoes development.