4. How does the celluloid film work? The film is sensitive to light. The light strikes the film, changes the chemistry of the film itself, and that's then saved. It's called a latent image.
5. How does the latent image work? A latent image on photographic film is an invisible image produced by the exposure of the film to light. When the film is developed, the area that was exposed darkens and forms a visible image. It's an image that's there, but not seen yet.