About evaluating exposure
Histograms are good tools for evaluating exposure. For example, a series of peaks in the darker side of the histogram often indicates an underexposed image that consists mainly of dark pixels.
A series of peaks in the center of the histogram often indicates a balanced exposure because a majority of the pixels are concentrated within the midtones of the histogram. They’re not too dark or too bright.
However, a series of peaks in the brighter side of the histogram often indicates an overexposed image because most of the pixels in the image are too bright.