An adjustment layer applies a correction (colour, light and so on) to the whole image without modifying the original pixels.

The most useful ones

• Brightness/Contrast — balance the light.
• Hue/Saturation — boost or tone down the colours.
• Curves — fine control over tonal range.
• Black & White — convert with full control.

The key advantage

Every adjustment layer comes with its own mask: you can limit the effect to a specific area, and switch it off at any time.

Key point: always favour an adjustment layer over a direct correction. Your image stays intact and 100% editable.