Photographic question: Why are the negative colors opposite (white is black, black is white)?

There is a chemical reaction called photochemical reaction. Simply put, it is a chemical reaction that changes after being irradiated with light.

This is the basis of the film. We extract a substance by photochemical reaction. This substance is generally made of silver halide, which is produced in the dark and sprayed on the film. Once irradiated by light, silver halide will crystallize, depending on the intensity of irradiation. There will be different degrees of crystallization.

Then, we put the irradiated film into another chemical solution, which will react with crystallized silver halide and become black silver particles and stay on the film. This process is called development (black box operation).

After development, we put the film into another chemical solution to wash away the silver halide that failed to crystallize (also in the dark)

In this way, the rest are negative, the blackened ones are irradiated, and the ones that have not been irradiated are washed away, and they are transparent.

White is strong light, so it is black, and black is weak light, so it is transparent.

Developing a photo is to repeat the above process. The difference is that silver halide is coated on the photographic paper, and the negative is used to block the light from shining on the photographic paper. In this way, black is white, and white is black, which is equivalent to coming back.

The principle of color film is the same, except that three or more kinds of silver halides are specially made, which are sensitive to different colors of light, and mixed color is color.