About adjustment 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 correct multiple layers by making a single adjustment, rather than adjusting each layer separately. You can discard your changes and restore the original image at any time.
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 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 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. Likewise, you can turn their visibility on and off to apply or preview the effect.
Because adjustment layers contain adjustment data rather than pixels, they increase file size far less than standard pixel layers. If you are working with an unusually large file, however, you may want to reduce file size by merging adjustment layers into pixel layers.