Layer Masks In Photoshop

Words and images by Robin Whalley - www.lenscraft.co.uk

Most users of Photoshop realise the importance of using layers in their editing process and there’s certainly no way that I could manage my own editing without them. Equally important, but often overlooked is the layer mask. As you may already know layers allow you to see the impact of an adjustment on an image without actually applying the adjustment. This provides flexibility and helps improve the quality of the final result.

Layer masks control which areas of the image the adjustment is applied to so you can target your changes. For example if you apply a black and white adjustment layer you can remove the effect from some parts of the image to leave them in colour as shown below.



In this screen shot from Photoshop you can see the image together with the “Layers” window, which can be accessed from either the Window menu or by pressing F7 on the keyboard. In the Layers window you can see the original full colour “background” image and the new “Black & White” layer over it. Attached to the “Black & White” layer is a layer mask which is half black and half white, causing part of the image to be revealed in colour. This is how layer masks can be used to target your adjustments.

Given layer masks are so important and useful in editing images, here are my top tips for using them:

Tip 1 – White reveals and black conceals whilst grey is in between

A useful little rhyme I used when I first started with layer masks as it helps you understand and remember the behaviour of the mask. When you paint on a layer mask in black it hides the effect of the layer in that area. In the white areas the effect of the layer is revealed to its full intensity. If you paint on the layer mask with grey, then the effect is partially hidden in that area. How much the effect is reduced by depends on the shade of grey. The darker the shade of grey, the more the intensity of the layer is reduced.

Tip 2 – Think in terms of targeting your adjustments

You may think this is obvious but it tends in my experience to be overlooked. It’s easy to forget the need to target adjustments and just accept a global adjustment. How can the same intensity of adjustment need to be applied equally across all areas of an image? This sort of mistake can easily lead to blocked up shadows and oversaturated shadows that just don’t look natural. It’s a rare image that can benefit from having all its adjustments applied globally.

Tip 3 – Paint your masks with a soft edge brush at a low Opacity

Nothing looks worse to me than visible adjustments on an image; they are just sloppy. You know the type I mean, where a rock has been lightened but the area around the rock has also become too light and now has a halo. Here is an example of trying to lighten trees in the image from earlier using a hard edge brush. It’s a little extreme but shows the sort of mistake that you sometimes see.

The way to avoid this is by using a soft edge brush at a low opacity and building up your mask in a number of brush strokes. You can access the brush settings in the top left of the Photoshop toolbar when you have the “brush” tool selected. Here is an example of the typical settings I will use when masking a layer.
 

Tip 4 – Fine tune your masking with a blur

Even having used a soft brush you might still find your adjustment too harsh. You could try reducing the intensity by lowering the opacity of the layer or you might try blurring the layer mask. Try applying a Gaussian blur to the layer mask, increasing the level of the blur to improve the blending. Large levels of blur can often be very effective in blending large areas of adjustment where there is continuous tone such as the sky.
 

Tip 5 - Work from global to local and from large to small

A good rule of thumb when editing images in Photoshop is to make all your global corrections first e.g. global contrast as this allows you to better assess the image. You can then identify and apply any local adjustments using new layers and layer masks.

Taking this tip a stage further, when you begin to build up a layer mask start by painting the largest areas of the mask first and then gradually reduce your brush size to attend to smaller details. You can use the [ key on your keyboard to quickly reduce the size of the brush and the ] key to increase it. Remember, you should be using a low opacity brush of around 10% in order to build up your mask which allows you to work in this way.

In this image I used a soft brush working from large areas to smaller areas to target the saturation adjustment to the wonderful light in the sky and falling on the rocks.

Tip 6 – Viewing your layer mask

From time to time it’s helpful to view your layer mask rather than the effect it is having on the final image. This might help you assess if an area is really not well enough blended or provide other important feedback. To view the actual layer mask hold down the “Alt” key and click the mask. You can then see the mask to make any adjustments. Repeat the “Alt” - click combination to return to the image.

Here is the layer mask for the above image.

Tip 7 – Use meaningful layer names

This is another obvious one to finish on but name your layers appropriately. It will help you understand at a glance what the layer is intended to achieve. It’s easy to have a file with 10 or more layers all making subtle adjustments. Naming your layer to explain their effect is a great help if you need to further adjust the file in the future e.g. lighten foreground rock or boost contrast in sky.

Persevere with a little care and layer masks might be the tool to take your photography to a new level.

Words and images by Robin Whalley - www.lenscraft.co.uk