A layer mask controls which parts of a layer are visible without deleting any pixels: white areas show the layer, black areas hide it, and shades of gray give partial transparency. Because the original image data stays intact, you can change your mind at any time, which is the core of non-destructive editing.
The Basic Idea
Every mask is a grayscale image attached to a layer. Brushing with black on the mask hides that part of the layer, and brushing with white brings it back. Gray sits in between. Nothing is erased, so a mistake is fixed by brushing the opposite color.
Add and Brush a Mask
- Select the layer you want to control in the Layers panel.
- Click the Add Layer Mask button at the bottom of the panel. A white thumbnail appears beside the layer, and everything is still visible.
- Choose the Brush tool and press D to reset the colors to black and white.
- Press X to swap the colors, so black is the foreground color for hiding.
- Set a soft brush with a flow or opacity around 20 to 40 percent as a baseline, and build the effect up in several passes.
- Brush over the area you want to hide. Press X to switch to white and brush back anything you removed too far.
Useful Masking Habits
- Hold Alt (Windows) or Option (Mac) and click the mask thumbnail to see the mask alone, which makes rough spots easy to find.
- Use the Properties panel to adjust Feather and Density when edges look harsh.
- Press the backslash key to show the mask as a colored overlay while brushing.
- Use Invert in the Properties panel, or press Ctrl+I, to flip a mask from white to black and back.
- Hold Shift and click a mask thumbnail to switch it off temporarily and compare.
Masks on Adjustment Layers
Adjustment layers, such as Curves, Hue and Saturation, or Levels, come with a mask already attached. This is where masks shine for photographers. You can brighten a face, darken a sky, or tone down one stray color, and each change remains editable. Selections made with the Quick Selection tool or Select Subject can be turned into a mask by clicking the Add Layer Mask button while the selection is active.
Common Mistakes
| Mistake | Better habit |
|---|---|
| Brushing on the layer, not the mask | Click the mask thumbnail so it shows a highlighted border |
| Hard brush edges | Use a soft brush and lower the opacity |
| Using the Eraser tool | Brush black on a mask instead |
| Forgetting to name layers | Rename layers so a long file stays readable |
FAQ
What is the difference between a layer mask and the Eraser tool?
The Eraser removes pixels permanently, while a mask only hides them. With a mask you can restore any area later.
Can I reuse a mask on another layer?
Yes. Hold Alt or Option and drag the mask thumbnail to another layer to copy it. Dragging without the key moves the mask.
The Short Version
Use white to reveal, black to hide, and gray for partial effects. Brush on the mask with a soft, low-opacity brush, view the mask alone to catch mistakes, and keep adjustments on separate layers so every edit stays reversible.
