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.|
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.
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.
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.
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.
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.