Auto Levels analyzes the histogram data and uses that information to modify the individual R (red), G (green), and B (blue) channels. In many cases, Auto will correct or markedly improve color balance and exposure issues.
In this example, we’ll use a photograph of a young Cheetah. The original has a mild green colorcast and is slightly underexposed.
Click the Auto button in the Levels section to automatically adjust color.
Move the midtones slider to refine the adjustment to taste. Moving the slider to the left will add more light, and moving it to the left will subtract light.