The Colorful Journey of Motion Picture Film
Motion Picture Film
Composition
Motion picture film is a strip of transparent material with multiple layers coating both sides. The base layer, crucial for stability, is made of chemically stable, photographically insensitive, and moisture-resistant plastic. Historically, three types of plastic have been used:
- Cellulose Nitrate: Highly flammable and discontinued by 1950.
- Cellulose Acetate: Developed as a safer replacement for cellulose nitrate. Cellulose triacetate is the most common type.
- Polyester: Stronger and more resistant, used for positive films, duplication, and specialty films.
The most important layer is the emulsion, adhered to the base by a binder. The emulsion contains silver halide crystals suspended in gelatin. These crystals are light-sensitive, and their size and sensitivity determine the film’s light requirements and graininess.
Black and White Film
Early black and white films were sensitive only to blue light. Later developments included orthochromatic film (sensitive to all colors except red) and panchromatic film (sensitive to all colors).
Color Film
Color film reproduces the full color spectrum using subtractive synthesis, combining yellow, magenta, and cyan dyes. It consists of three silver halide emulsion layers:
- Yellow Layer: Sensitive to blue light.
- Magenta Layer: Sensitive to green light.
- Cyan Layer: Sensitive to red light.
Each layer contains color couplers that form dyes corresponding to the complementary color of the light it is sensitive to. Additional layers include a binder, UV absorption layer, protective layer, and anti-halo layer.
The Negative-Positive and Reversible Color Process
When exposed to light, the film’s three emulsion layers form latent images. Chemical processing converts these latent images into visible metallic silver particles. In color negative processing, color couplers form a colored image around the exposed grains. Unexposed grains are removed, and the remaining silver grains are bleached, leaving the colored negative image.
Positive prints are made by copying the negative onto a similar multilayer film. Reversible color film uses a different process (inversion) to produce a positive image directly on the film, eliminating the need for separate positive prints.