What is a Histogram?

The Basics:

A histogram is a graph showing the brightness levels of pixels in the image, which can be helpful when reviewing whether a photograph is correctly exposed. The histogram is broken up into three sections; Shadows, Midtones and Highlights. There is no "perfect histogram", it depends on the type of image you are taking, but it can help you check your exposure more accurately than just viewing it on a small LCD display.
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