About adjustment layers

Adjustment layers let you experiment with color and make tonal adjustments to an image without permanently modifying the pixels in the image. The color and tonal changes reside within the adjustment layer, which acts as a veil through which the underlying layers appear. By default, an adjustment layer affects all the layers below it. This means that you can correct multiple layers by making a single adjustment, rather than making the adjustment to each layer separately. To limit the adjustment to a portion of the image, you can select an area in your image before adding the adjustment layer. If you want the adjustment layer to only affect a single layer, you can group them together. (See Creating grouped layers.)


Original image, and image with levels adjustment applied