What is a Layer Mask?

The principle of layer masks explained

The perhaps most powerful technique within Photoshop is the use of layer masks. But maybe you wonder, what is a layer mask? Most people to whom I explain it find it difficult. It is actually quite confusing, but try to understand the explanation below, because the key to good and enjoyable working with Photoshop is understanding how it works.
Don't panic if you don't understand it the first time you read it. Read it a second time, and try to play with it in Photoshop.

If you are not sure what layers are, read my What are layers post first.

Why use Layer Masks?

With layer masks it's much easier to blend parts of layers. What I mean by this is best explained with the following example.
Look at the image below. Here I explain to myself how a camera works :-).

What is a Layer Mask? Putting me and me together is easy with a layer mask
Putting me and me together is easy with a layer mask

To make this image, I didn't have to make a difficult accurate selection. I did the following:

  • I placed the two images on top of each other and aligned them (to be explained later).
  • The top layer is the image where I'm sitting, so this is all I see at that moment.
  • In the upper layer I created a so-called Layer Mask, nothing happens yet.
  • I made this mask black (Edit> Fill...). The complete layer becomes transparent so I see the bottom image of me standing.
  • And then I painted with white and a soft brush on where I sit, until I'm completely visible.
    By using that mask in combination with a soft brush you can see that the top layer (a part of it) blends seamlessly with the bottom layer.

Do not worry if you do not immediately understand how I did it, for now it's important that you understand what the mask is for.

Take a look at the following images to help you understand the principle.

What is a Layer Mask? An example of using a layer mask
Part of the layer 0 you can see through the transparent areas of layer 1, thanks to the layer mask of layer 1
What is a Layer Mask? So black hides the content of a layer to make it transparent
So black hides the content of a layer to make it transparent, so now you can see what is a layer mask.

So what is a Layer Mask?

  • A layer mask is a grayscale image that indicates where the layer is transparent
  • With a layer mask you can hide parts of a layer
  • With a layer mask, the entire content of a layer is retained, but you only see a part of it
  • Where it is black in the mask, the layer content is transparent (invisible, you may see the contents of the underlying layer if there is one)
  • Where it is white in the mask, you see the layer content
  • Where it is gray in the mask, the layer content is 'semi-transparent'

With the knowledge you now have, try to predict what you see on your screen in the example below, where you see a part of the layer panel and at the right of the top layer's thumbnail image you see the layer mask with a black, a white and a gray part.
What do you think is the effect?

What is a Layer Mask? Two layers, the top layer with a layer mask.
Two layers, the top layer with a layer mask. What do you see on the screen? (Click to find out if you were right)

I hope your question what is a Layer Mask? is clearly answered in this post.
If you have questions or suggestions, please leave a message.

In a future post I will elaborate on different ways to use layer masks.

A final tip: pay attention to whether you are working in the layer itself or in the mask. You can see this on the white edge around the layer miniature or around the mask. See the images below.

What is a Layer Mask? Layer active.
You see the white stroke around the layer thumbnail image? Everything you do effects the content of the layer.
What is a Layer Mask? Mask active
The white stroke around the Layer Masks indicates that everything you do effects the mask

A brief summary:

What is a Layer Mask? A brief summary
What is a Layer Mask? A brief summary

Adjust your brush size

A quick and easy way to adjust your brush size

If you want to adjust your brush size in Photoshop you can do that with the slider in the options bar. But the problem is that you do not see the effect while you're adjusting.

So you'll find your self constantly moving your mouse (with the brush tool) from where you're working in your image to the option bar and vice versa.

Another way to adjust your brush size is to leave your cursor where it is and right-click in the image. A panel appears where you can adjust the size of your brush as well as the hardness.

Adjust your Brush size
Adjust Brush size and Brush Hardness

This way your cursor is still near the position where you need it.

Using Keyboard shortcuts to adjust your brush size and brush hardness

An other way to change your brush size is the use of keyboard shortcuts:

Use the bracket keys ( ']' and '[' ), so you can immediately see the effect.
[ to decrease and
] to increase

Adjust your brush size in Photoshop
Change your brush size and hardness with these keyboard shortcuts

This works for several tools, like the Quick Selection Tool, the History Brush, the Clone Stamp, the Pencil Tool and the Dodge -, Burn - and Sponge tool.

This also works in Lightroom.

To adjust the hardness use the same keys while holding down the Shift key.

So if you want to know some more about keyboard shortcuts, please read the last part of the post Keyboard shortcuts for zooming.

When you're an Apple user, check Mac keyboard shortcuts to learn some useful keyboard shortcuts.
Windows users best read Keyboard shortcuts for Windows.

Zoom in and out

Keyboard shortcuts for zooming

Working with Photoshop is much easier with these helpful keyboard shortcuts for zooming.

If I'm working with Photoshop, I find my self constantly zooming in (to work precise) and out (to have overview). I rather leave my left hand above my keyboard and leave my right hand in place (holding my Wacom pen in the right position). Therefore keyboard shortcuts for zooming are very useful.

For zooming, these are the right keyboard shortcuts:

Press Command (Apple)
or Ctrl (Windows)
and hold and press
1 to zoom in to 100% (1: 1) and
0 (zero) to see the whole picture (fit to screen)
+ To zoom in,
- To zoom out.

Keyboard shortcuts for zooming
Photoshop zoom in and out with keyboard shortcuts

And you know what? These same key combinations also work for most browsers like Safari and Internet Explorer and some other applications like Adobe Acrobat Reader. Just try it and see what happens...

Obviously, there are many ways to zoom in Photoshop, such as press and holding the Z-key and click-drag to the right (zoom in) or to the left (zoom out). Or with the Navigator (Window>Navigator) or simply with the zoom tool (Z).
More posts to follow where these ways are discussed in more detail.

A few more words about keyboard shortcuts.

A keyboard shortcut is a fast way to do 'something' without the need to move your mouse. If you're working on a picture, eg. do some local retouching, you rather don't want to move you're cursor all the way to the system menu.

Keyboard shortcuts can be only one key (B for slecting the brush tool for example) or a combination of keys, mostly two, some times three and some times even four.

If the shortcut consists of multiple keys, there are always one or more so-called modifier keys involved.

In Photoshop the modifier keys are:
Command (Cmd)
Control (Ctrl)
Option (Alt)
Shift ()

Where Apple users use the Command Key, Windows users use the Control key.

To use a keyboard shortcut, press and hold one or more modifier keys and then press and release the last key of the shortcut and finally release the modifier key(s). For example, to  use the command Save As, the shortcut is Commad-Shift-S (Control-Shift-S for Windows), press and hold both the Command key and the Shift key, then press and release the V key, then release the other keys.

When you're an Apple user, check Mac keyboard shortcuts to learn some useful keyboard shortcuts.
Windows users best read Keyboard shortcuts for Windows.

What are layers?

What are layers in Photoshop?

Many novice Photoshop users asks themselves, what are layers?
They think it's something very complex. If you're one of them, be reassured because it is very simple.  

What are layers? Layers are nothing but a stack of transparencies, that's all. See one layer as one transparent (as were used with overhead projectors in the old days).

What are layers in the old days...
Nowadays we use Keynote or PowerPoint, but there was a time we used overhead projectors for our presentations.

You can pick up a transparent, draw something on it, take another transparent, draw something on that one. Now put the second transparant on top of the first. Put the stack of transparencies on top of a white paper.
Now, when you view it from above, you see that your two drawings are combined in to one image!

Do you get it? 

Why would you use layers?

Imagine, you pick up a sketchbook and a permanent marker, and you draw a house, a tree and a dog on the same page.

A simple drawing of a house, a tree and a dog
A simple drawing of a house, a tree and a dog

Now that you have a good look at the drawing, you prefer the house in the middle and the tree to the left of the house. In the case of a sketchbook and a permanent marker, you will have to recreate the drawing.

But...

Imagine now that you draw the house on a page of your sketchbook, but you draw the tree on a transparent. And the dog on a second transparent.
You place the two transparencies on top of the drawing of the house, et voila! If you look at it from above, you see the complete drawing.
Do you want the tree on the other side of the house? Just move the transparent where the tree is on!
Just flip the 'dog transparent' 180 degrees.

So, concluding, by placing each object in an image on its own transparency (read 'its own layer'), you can adjust the objects independently. And that is why you work with layers.

What are Layers? A stack of transparencies, that's all.

So, layers in Photoshop are nothing but a stack of transparencies seen from above on the screen, that's all.

What can you do with layers?

With real transparencies the things you can do are limited, but on a computer with a program like Photoshop the possibilities are endless.

In addition to being able to change the order and position, you can also distort, enlarge or reduce the content of a layer, change color, apply an effect, duplicate, hide, group, etc. Most of these options will be covered in other posts.