Layers and masks used together, are possibly the most powerful capabilities of Photoshop. They offer a huge range of possibilities. To get the best out of Photoshop you will need to:
- Have a conceptual understanding of what layers and masks are. Hopefully, you will already have a firm understanding if you have worked through this course.
- Have an awareness of what you can do with layers and masks.
- Know how to use them.
What is a Layer Mask?
A layer mask is an entity which can be added to any type of layer in an image. It allows you to reveal or hide the content of any part of the layer to which it is attached. It appears as a rectangle to the right of your layer thumbnail. It can be all white, all black, a mixture of both, or a mixture of any grey tones.
In general terms, white areas of the mask will reveal content, grey areas will partially reveal content and black areas will conceal content. The following table shows what happens with different types of layer.
| Type of Layer | White | Grey | Black |
|---|---|---|---|
| Layers with visible pixels eg image and text layers | Pixel will be 100% revealed. | Pixels will be partially revealed. | Pixels will be 100% concealed. |
| Adjustment Layers | The adjustment effect will be applied fully. | The adjustment effect will be applied partially. | The adjustment effect will not be applied. |
Example 1
The original image on the left is a section of sky.
A Curves adjustment layer was added to increase the contrast of the sky. The layer mask (middle image) was split into equal thirds and filled with white, 50% grey and black.
The third image shows the result. The first third (white mask) shows the full effect of the Curves adjustment. The middle third (grey mask) shows the partial effect. The final third (black mask) shows no effect.
What can you do with Layer Masks?
Layer Masks are the main way in which we can use layers and masks together and are at the heart of Photoshop editing. They allow you to adjust very specific areas of an image without affecting the rest of the image. These areas can be large or small, simple or complex and can be used with any part of your image.
Layer masks are dynamic. At any time you can adjust the layer mask to include or exclude more content from the attached layer.
Layer masks are non-destructive. No pixels will be harmed when you use a layer mask!
How do you create a layer mask?
There are two ways to create a layer mask:
- Click the Add Layer Mask icon
at the bottom of the Layers Panel. - Add an Adjustment Layer. A layer mask will be created automatically.
What happens next is dependent on whether or not there is an active selection:
- If nothing is selected, a pure white mask is created, This means that the mask has no effect.
- If a selection is active, the layer mask will replicate that selection. White areas of the mask will reveal the corresponding areas of the image. Black areas will conceal them. With adjustment layers, white areas will be affected by the adjustment while black areas will not.
In many cases, it makes sense to create a selection before you add an image mask or an adjustment layer.
Example 2
This is the original image. The primrose petals are very clearly defined so creating a mask of these is very straightforward.
This is the mask which was created with the Magic Wand and the Lasso. It is a hard mask, and only contains pure white and pure black.
A selection of the flowers was made using the mask. A Hue/Saturation adjustment layer was added while the selection was active. A layer mask which replicates the selection made by the mask, was added automatically. The Hue of the Master channel was adjusted.
This is the result. The hue of the flowers has changed completely but the background is left untouched. The white areas of the layer mask REVEALED the effect of the Hue change while the black areas CONCEALED the effect.
The way in which layer masks work is often referred to as ‘White reveals, black conceals‘.
How do you adjust a layer mask
After you have created a layer mask, it’s possible to adjust it at any point. There are several ways to do this. In every case, ensure that the layer mask itself is selected and not the image thumbnail or the adjustment layer icon.
Using the Brush
- If you wish to reveal more of the layer, paint directly on to the image using the Brush tool with the foreground colour set to white.
- If you wish to conceal more of the layer, paint directly on to the image using the Brush tool with the foreground colour set to black.
Normally when you add a layer mask, a white mask is added. If you hold down down the ALT key and then press Add Layer Mask, a black mask is produced. Masks can also be inverted by selecting the layer mask and pressing CTRL I. This is useful if you wish to brush in a very small area.
It’s often a good idea to use the brush with opacity reduced. This allows you to build up the areas you are brushing in. It will create a more natural and seamless ‘join’ between masked and unmasked areas.
At any point, you can create a new selection and use that alongside the brush. This ensures that no paint strays into areas where you don’t want it.
Example 3
In this example, I didn’t want the orange petals to be sharp outside the centre of the flower.
I copied the layer and added a copious amount of Gaussian Blur. (Filter Menu >> Blur >> Gaussian Blur).
I added a layer mask to the Blur layer and painted the centre of the flower using a black brush set at 20% Opacity. I clicked several times in the centre to build up a result which was pure black. Fewer clicks around the centre guaranteed a smooth transition.
This blurred all of the orange petals while ensuring the centre of the flower remained sharp.
The Brush Tool
This is a very flexible tool with many options. The main ones used for adjusting layer masks are shown in the graphic below.
Select the Brush Tool from the toolbar or by clicking B. The Brush Options bar will appear at the top of your screen.
- Choose a paint colour from the toolbar – for layer masks, this will be black or white. Press D to reset the colours to the default black and white. Press X or click the Swap icon to swap between them.
- Set brush Size – you can do this by using the sliders in either of the Brush size selectors. You can also use the [ ] keys to decrease/increase the brush size. The trick is to set the biggest size which will do what you wish to do without encroaching on other areas. This will produce smoother results.
- Set Opacity – It is usually better to set this at a lower value such as 20%. This enables you to build up the effect and is much more subtle. Each time you click the brush it will apply only that percentage of ‘paint. So if you click and drag over an area it won’t result in more paint being applied. It’s usually better to click as many times as you need to so you can see the effect building.
- Set Flow – This determines the amount of paint to be be applied. Whatever percentage is set, it will keep on applying paint while the mouse button is held until 100% is reached. I usually leave this at 100% as I prefer to use opacity to control the amount of paint.
- Click the dropdown arrow next to the paintbrush icon and the Brush Panel with extra settings will appear.
- Choose a brush – a round brush is best to start with. You will find this in the General Brushes dropdown if it’s not already selected.
- Change the brush Angle and Shape to reflect the area where you are painting. More often than not, a round brush will work very well
- Set brush Hardness – A soft brush is usually better as this will give less obvious edges. I usually have this set at 0%.
- Other settings can be safely ignored at this stage.
Using Adjustments
Layer Masks can also be adjusted using a wide range of tonal adjustment tools such as Levels and Curves. These can be used to fine tune your layer mask by brightening or darkening the mask.
The Gradient Fill tool is particularly useful as this can be used to emulate graduated or radial filters.
Again, you can create a new selection to restrict these adjustments to specific areas.
Example 4
Layer Structure
Slide arrow to see Before and After versions
In this image, the sky overpowers the landscape. To tone it down, I copied the image layer and took it back into Adobe Camera RAW (Filter Menu >> ACR). I reduced both Texture and Clarity to soften the sky. Then I added a Curves layer and brightened it slightly.
I selected both of these new layers and created a Group (called Softened and Brightened). I added a layer mask to this group and applied a Gradient Fill using the Linear Gradient. This masked out all of the land which ensured that only the sky was affected by these two adjustments.