Hands on: Using layers in Photoshop

If you’ve never bothered with layers you’re missing out on one of image editing’s big features. From colour correction and retouching to making montages and adding type effects, layers will help you make more of your digital images.

Layers allow you to stack elements on top of one another and move them around, revealing detail underneath.

Every budget application has layers and many offer a high level of sophistication and control with a variety of blend modes, opacity control, the ability to group and merge layers and add drop shadows and other style attributes.

What follows is an introduction to how layers work and what you can do with them, along with some Hands On tips for getting the most from them. Though I’ll be using Photoshop to provide the examples, as usual, much of what I cover applies to other image-editing programs.

Lock and load
At the top of Photoshop’s Layers palette are four small buttons, which are easily ignored but have the power to make life much easier for you. I’ve often spent time building complex selections or creating fiddly layer masks before realising that I could achieve what I wanted simply by clicking one of these lock buttons.

The first locks transparency, so you can paint away with the Brush, Clone Stamp or any other tool and only non-transparent pixels will be affected. All the transparent pixels in your layer stay transparent. If you like, it stops you accidentally going over the edges.

The second button does the reverse, allowing you to paint or otherwise alter only the transparent pixels and locking everything else. The next button locks the layer’s position and the final one locks everything ­ click this when you’ve done everything you want to a layer, to be sure you won’t mess it up inadvertently at some stage.

Blend modes
Layer Blend modes determine how pixels in the selected layer interact with those directly below. In Normal mode, pixels in the top-most layer obscure those on underlying layers.

Photoshop blend modes include Darken, Lighten, Multiply, Screen, Overlay, Soft light and Difference. They can be useful for special effects ­ particularly with type on images.

Adjustment layers
Adjustment layers allow you to make global image adjustments without permanently altering the pixel data in the image. Levels, Curves, Hue/Saturation, Colour Balance and other adjustments are destructive edits ­ when you apply them, some image information is permanently lost ­ so you don’t want to use them too often. To use an obvious example, if you remove all the colour from a photo using Hue/Saturation, there’s no getting it back later ­ unless you use an Adjustment layer.

Let’s say you apply a Levels adjustment layer to increase the contrast of a flat image. You make some other adjustments, then unsharp mask the layer, and at this point you notice that some of the shadow and highlight detail has disappeared. Double-clicking on the Adjustment layer thumbnail brings up the Levels dialogue box with your original adjustment settings ready to edit.

Using Adjustment layers has other advantages over a straight adjustment. As with conventional layers you can reduce the layer opacity, which in this case tones down the degree of adjustment.

You can also add a layer mask to an Adjustment layer to restrict the adjustment to certain parts of the image. An adjustment layer affects only the layers beneath it, so by careful layer ordering and grouping you can restrict adjustments to specific layers and leave other parts of the image untouched.