Level and Curve Adjustment Layers can be used to correct and color grade an image. They are closely related and extremely powerful. We will cover these in more detail when we look specifically at Color Grading. Put simply, when you use Levels and Curves, you are adjusting shadows, midtones and highlights. Levels are linear, with three control points; adjustments will affect all tones. Curves are geometric, giving you complete control on how you adjust tonality of an image; adjustments can be fine-tuned to specific regions of tone.