Generally speaking, the original films are all dx-coded and can be pasted directly, instead of the original films, or subcontracted films, as well as so-called educational practice films. Either there is no DX code, or the DX code is different from the ISO sensitivity of the actually installed film, so the film with DX code must be attached.

Film, also called negative film, is an imaging device. At present, the widely used film is coated with silver halide on the basis of polyacrylate film, and it is very soft and easy to use when rolled into a whole roll. When the light shines on the silver halide, the silver halide is transformed into black silver, which is fixed on the film base after the development process and becomes a black and white negative that we often see. Color negative is coated with three layers of silver halide to show three primary colors. In addition to negative films, there are positive films, negative films, one-time imaging films and so on.