Photographic film. View of a roll of 35mm photographic film. When the film is exposed to light, silver halide crystals suspended in the film undergo chemical changes to form a latent image. Later the film is chemically processed to develop the latent image into a permanent image. In monochrome film there is only one layer of silver halide crystals. In colour film there are 3 separate layers of silver halide grains, which respond separately to blue, green & red light. During developing, the image recorded by each layer produces clouds of dye of the compl- imentary colour; yellow, magenta or cyan. Together the 3 layers can form any colour of the spectrum.