About adjustment layers and fill layers

An adjustment layer applies color and tonal adjustments to your image without permanently changing pixel values. For example, rather than making a Levels or Curves adjustment directly to your image, you can create a Levels or Curves adjustment layer. The color and tonal adjustments are stored in the adjustment layer and apply to all the layers below it. You can discard your changes and restore the original image at any time.

Adjustment layer choices match the commands available in the Adjustments panel. Choosing an adjustment layer from the Layers panel displays the corresponding command settings controls in the Adjustments panel. If the Adjustments panel is closed, you can open it by double-clicking the adjustment layer thumbnail in the Layers panel.

Fill layers let you fill a layer with a solid color, a gradient, or a pattern. Unlike adjustment layers, fill layers do not affect the layers underneath them.

Adjustment layers provide the following advantages:

Nondestructive edits. You can try different settings and re‑edit the adjustment layer at any time. You can also reduce the effect of the adjustment by lowering the opacity of the adjustment layer.
Selective editing. Paint on the adjustment layer’s image mask to apply an adjustment to part of an image. Later you can control which parts of the image are adjusted by re-editing the layer mask. You can vary the adjustment by painting on the mask with different tones of gray.
Ability to apply adjustments to multiple images. Copy and paste adjustment layers between images to apply the same color and tonal adjustments.

Adjustment layers increase the image’s file size, though less than other layers. If you are working with many layers, you may want to reduce file size by merging the adjustment layers into the pixel content layers. Adjustment layers have many of the same characteristics as other layers. You can adjust their opacity and blending mode, and you can group them to apply the adjustment to specific layers. You can turn their visibility on and off to apply their effect or to preview the effect.

Original (left); adjustment layer applied to barn only (center), which brings out detail in the barn; and adjustment layer applied to entire image (right), which lightens the entire image and pixelates the clouds

An adjustment layer affects all the layers below it: you can correct multiple layers by making a single adjustment, rather than adjusting each layer separately.