How to Use Layer Masks

There are some things I have been doing for so long that it’s easy to forget there was a time I didn’t know about them. Layers Masks are one of those things. They have become so routine in my workflow that I could never go back to not using them. In this post I’ll explain what they are and how they are beneficial to your editing workflow.

While the following editing steps are specific to Adobe Photoshop, the same concepts can be applied to most editing programs.

What are Layer Masks?

Simply put, a layer mask is an extra layer in your working file that hides and/or shows the details of the layer beneath it. There are a couple of benefits of using Layer Masks. The first benefit is that you can apply effects to a part of the image, as opposed to the entire image. The second and most important benefit, is that when you use a Layer Mask, the original pixels are left untouched. In other words, using a Layer Mask is a non destructive editing technique. This is helpful if you want to test different editing techniques on an image, or if there is a chance you will re-visit your editing at a later date.

The layer mask on the top layer (orange) allows the bottom layer (blue) to be seen

How to use a Layer Mask?

The first thing you need to do is create the layer mask. With both your images combined into one document, select the top layer and go to Layer->Layer Mask->Reveal All. You will want to check off Use Previous Layer to Create Clipping Mask as this will allow your mask to work with layer immediate below, as opposed to affecting every single layer beneath it.

By using the paintbrush tool, you can selectively paint which areas you want to mask. Areas in the layer mask that you paint in black will be opaque while areas in white will be transparent. Transparent areas of the mask will allow the layer below to show through while opaque areas of the mask will not be shown. Gray areas will be treated as transparent. The amount of transparency will depend on the relative lightness or darkness of the gray values.

Now, with the Layer Mask selected, grab the paint brush tool and make sure the foreground colour is set to black. In the main work area, carefully paint the areas which you wish to use. Don’t forget you can always switch back and forth between black and white in order to adjust your layer mask.

Some common reasons why I might use a Layer Mask include:

  • If I want to seamlessly combine elements from multiple photographs
  • If I want to sharpen the image, but do not want the sharpening to affect the out of focus areas (see example below)
  • If I want to manually create an HDR image by combining multiple layers and masking out the areas I don’t want to use

The layer mask allows the top layer, which is sharpened, to only affect the reflective sphere and not the out of focus leaves on the ground

Using Adjustment Layers

To be honest, I rarely use Layer Masks on their own. These days I only use Layer Masks in conjunction with Adjustment Layers.

An adjustment layer is when you apply an effect to your image on a separate layer. Again, the advantage is that the changes are non destructive and you can use layer masks to select which areas of the image you want to apply the effect.

By creating multiple Adjustment Layers, you can quickly and easily test out different edits.

Some common reasons why I might use a mask on an adjustment layer include:

  • If I want to blur the background but keep the foreground subject in focus
  • If I am applying an Adjustment Layer such as Brightness/Contrast, Hue/Saturation or Curves, but don’t want it to affect the entire image
  • If I want to selectively saturate/desaturate the image (see example below)

An example of a Black & White Adjustment Layer with a Mask

Conclusion

In my opinion, using the eraser tool to combine layers is very amateurish and not nearly as precise as using layer masks. It’s also permanent which means if you want to re-edit a photograph, you’ll have to start from scratch.

The overlying message of this post is that by having more control over your editing process, you significantly increase the chances of improving the quality of your images. If you are interested in taking your editing to the next level, I highly suggest you take the time to learn more about Layer Masks and Adjustment Layers.

 

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