What does 18% ash mean in photometry?

The principle of photometry is simple. The reflectivity of the metering area automatically erected by the camera is 18%, and then the values of the aperture and shutter are determined by this ratio.

The gray scale of 18% is represented as the average value, and it is represented in the fifth area in the gray board. If the object in the picture is darker than this average gray value, the gray value is higher than 18%, otherwise, it is lower than 18%.

The gray scale of 18% (considered as neutral gray) is a standard, which has nothing to do with whether the object is bright or dark.

Like traditional cameras, the photometric exposure system of digital cameras has a basic principle when processing images, which is to restore all subjects according to the neutral gray brightness of 18%. Therefore, no matter what the original brightness of the object is, it should be displayed in a medium brightness tone in the end.