What is the contrast in photography?

Contrast refers to the ability of a lens to express darkness. An image must have two contrasts, bright and dark. High contrast means that the separation of light and shade is obvious, and there may not be too many layers in the middle. Low contrast means that the light and shade are not obvious enough or bright enough, but there are many layers, which may make people feel dull. For color or black and white images, the definition of contrast is the same.