Using the Brush Tool to Paint a Mask

Refine mask using the brush tool

How To Use The Brush Tool to Paint a Mask

The Brush Tool is one of the most commonly used tools in Photoshop. It can be used for all manner of things, from simply painting or adding depth. We are going to show you how it is used to build a layer mask. Using a hard or soft edge and finding out the difference between opacity and flow. Follow our tutorial for beginners to learn how you can build your very own masks quickly and easily, using the brush tool in photoshop.

Using the Brush Tool to Paint a Mask


The Difference Between Opacity and Flow

Opacity is the level of transparency of your brush. A solid brush has an opacity of 100%, . Whereas, a brush with 1% Opacity will barely be seen at all. When you left-click and hold to paint with a brush that has a low opacity level such as 20%. It doesn’t matter how often you paint over the same area, that area won’t get any darker. Only when you release the mouse button and then click it again, does it then darken by another 20%. Essentially, the way opacity works if by stacking levels of opacity ontop of each other. The downside to this is sometimes you can get banding where the opacity layers haven’t blended well. 

Flow works differently, All you need to do is hold down the left mouse button once. If you set the brush Flow to 20%, hold down left-click and begin to paint. Every time you paint over the same area it gets darker. There is no need to click multiple times. Because flow works continuously, you can afford to reduce it dramatically go give a smoother blend. Using a setting as low as 5% will work excellently and always produce a soft graduated fade.


How To Manually Brush In A Layer Mask

Starting with two images stacked, I have the base image on the bottom and a darker image on top. The top layer has a Black Mask applied so that we can see any of the darker layer. Using the Paint Brush tool we will paint in the darker sky, keeping the brightness and colours of the foreground.

1. Select the Black Mask. 

Black Mask

2. Select the Brush Tool by clicking on the icon or by pressing the B key on your keyboard.

Brush Tool

3. Make sure you have a white foreground colour.

white foreground

4. Click on the small down arrow to adjust your brush.

change brush

5. Here you can change the size and hardness of the brush.

For this tutorial, we are going to give the brush a hard edge by making the hardness 100%. 

brush hardness

6. Now with the Brush tool selected with 100% hardness begin to paint over the sky.

paint with hard brush

7. Once you have finished painting hold down the Alt key on a PC, or Opt key on a Mac. Then left-click on the Black mask to reveal the mask you have painted. 

reveal mask

  Notice the solid line which will result in a very harsh blend. To undo the mask you have painted with paint over it again with a black foreground or press Crtl+Alt+Z on a PC, or Cmd+Opt+Z on a Mac.

8. This time we will paint in the mask with a soft edge. Move the Brush Hardness to 0%.

soft edge brush

9. Paint in your mask just like you did previously. This time make sure there is plenty of overlap with your brush strokes.

0% brush hardness

10. Hold down the Alt or Opt key and left-click on the layer mask to show the mask again.


  Notice this time the bottom of the mask has a nice feathered edge giving a smoother blend than before. To undo the mask you have painted with paint over it again with a black foreground or press Crtl+Alt+Z on a PC, or Cmd+Opt+Z on a Mac.

11. Now with the hardness still set to Zero. Lower the Opacity.

brush opacity

12. Now paint the mask with your lowered opacity brush. To reveal more of the layer release your left mouse button and then re-apply it an carry on painting. 

You can blend very gradually with this method but sometimes you can get banding. To reduce banding keep the opacity level low, the lower the better. 

brush opacity masking
The entire blend from top to bottom is smoother after several clicks and painting over areas more than others. The whiter areas show where has been painted over the most. Undo this for the last time in this tutorial by painting over with a black brush or by pressing Crtl+Alt+Z on a PC, or Cmd+Opt+Z on a Mac.

13. Lower the Brush Flow and begin to paint in your mask. Remember with Flow, every time you paint over the same area with your left mouse button pressed the brush application will become stronger.

brush flow

14. The final blend with a lower Flow is a much softer and smoother graduated fade.

brush flow mask


By using the brush tool to paint a mask, we have been able to blend our two layers softly. Resulting in a darker sky faded into a brighter foreground. 

Brush Tool to Paint a Mask


Additional Resources

If you liked this tutorial on how to adjust levels in photoshop, you might also like What Level Adjustments Do And How They Affect Your Image.


Online Resources

Here is a wealth of knowledge on Refining a Layer Mask with the Brush Tool.

Another popular site for beginners to learn How to Use Layer Mask Gradient and Brush Tools in Photoshop CS6 is on dummies.com

I found another quick example on youtube on how to use the brush tool to build a layer mask in photoshop.

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