How do you use a layer mask brush in Photoshop?

Using a layer mask brush in Photoshop allows you to selectively reveal or hide parts of a layer, offering non-destructive editing control. Here's how to do it:

Steps to Use a Layer Mask Brush

1. Select the desired layer: In the Layers panel, click on the layer you want to apply the mask to.

2. Add a Layer Mask: At the bottom of the Layers panel, click the "Add Layer Mask" icon (it looks like a rectangle with a circle in the middle). This creates a white layer mask adjacent to your layer.

3. Select the Brush Tool: Activate the Brush Tool by clicking its icon in the Tools panel, or by pressing the "B" key on your keyboard.

4. Set Foreground and Background Colors: Ensure your foreground and background colors are set to black and white, respectively. You can switch between them by pressing "X."

5. Painting the Mask:

   • Painting with Black: Painting on the layer mask with black will hide the corresponding area of the layer.
   • Painting with White: Painting on the layer mask with white will reveal the corresponding area of the layer.
   • Painting with Grays: Painting with shades of gray will partially reveal the layer. Darker grays reveal less, while lighter grays reveal more.

6. Adjust Brush Settings: In the Options Bar (usually at the top of the screen), you can adjust the brush's settings to get the desired effect:

   • Size: Controls the brush diameter. Use the "[" and "]" keys for quick size adjustments.
   • Hardness: Determines the softness of the brush's edges. A lower hardness creates a feathered edge, while a higher hardness creates a sharp edge. A hardness of 0% is completely soft.
   • Opacity: Controls the transparency of the paint. Lower opacity values result in more subtle effects.
   • Flow: Controls the rate at which paint is applied.
   • Mode: Blending modes can affect how the brush strokes interact with the existing mask. Experiment with different modes for unique results.

7. Begin Painting: Carefully paint on the layer mask to hide or reveal the desired parts of the layer. Remember, this is non-destructive, so you can always undo or refine your mask.

Tips and Considerations

• Zoom in for Precision: Zooming in allows for more precise masking, especially around intricate details.

• Use Different Brush Sizes: Varying the brush size allows for both broad strokes and fine detail work.

• Soft vs. Hard Brushes: Soft brushes create smooth transitions, while hard brushes create sharp edges. Choose the appropriate brush based on the desired effect.

• Check the Mask: Alt+Click (Option+Click on Mac) on the layer mask thumbnail in the Layers panel to view the mask in black and white. This is helpful for seeing exactly what you've masked. Alt/Option-Click again to return to the normal view.

• Refine Edges: Use the "Refine Edge" feature (Select > Select and Mask) for complex selections, such as hair.

Example

Imagine you have a picture of a person standing in front of a dull background. You want to replace the background with a more exciting landscape. Here's how a layer mask brush would help:

1. Place the landscape image on a layer below the person's image.
2. Add a layer mask to the person's layer.
3. Using a black brush, carefully paint around the person to hide the dull background, revealing the landscape behind them.
4. Adjust brush size and hardness to create realistic edges, especially around hair.