“The camera metering system reacts to the amount of light reflected from the scene in the viewfinder and computes the camera settings needed to make a nominally correct exposure. What is adjusted depends on the mode the camera is in:”
“Metering systems can also apply some program logic to make assumptions about the content of a scene and its relative importance. Consider two landscape photos with sky at the top. In the first the sky fills the upper 2/3 of the photo and the darker foreground 1/3. In the second the sky only fills the upper 1/3 and the darker foreground 2/3. Now based solely on how the photo is framed, odds are that in the first photo which is mostly sky it is most important, but in the second which is mostly foreground.”
