An adjustment layer is a type of layer in editing programs such as Photoshop. It contains no image content, only a correction or effect, such as a change in brightness, contrast or color. It changes how the layers below it look without changing their pixels, a bit like placing a sheet of colored cellophane over a print.
This makes adjustment layers a key tool for non-destructive editing. You can change, hide or delete the adjustment at any time. Each adjustment layer comes with a mask. By painting on the mask, you can apply the effect fully, partly or not at all to different parts of the image.
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