Layers are a central part of many photo editing processes, but they come in a number of different types, notably (1) a background layer, (2) image layers, (3) adjustment layers, (4) vector layers and (5) type layers.
Here’s a guide to these different layers types, how they work and when you would use them. Note that not all programs offer all these layer types. Some non-destructive applications, like Capture One and Exposure X only offer adjustment layers. Other all-purpose photo and illustration tools like Photoshop, Pixelmator and Affinity Photo will offer all of them. Layers are not strictly essential for photo-editing if you mainly work on single images, not composites or illustrations.
The sample image used for this article and its annotations was created in Photoshop.
1. Background layer
This is how images open in Photoshop and other layer-based photo editors. This ‘background’ layer is the base image you start with and other layers are added on top (you can promote this Background layer to a full layer in Photoshop if you need to change the layer order).
2. Image layers
I call them ‘image layers’ but in reality there is no specific name for them, so ‘image layers’ is a term I’ve chosen that I hope makes sense.
An image layer is used when you want to combine two or more photos. You start out by opening the first photo, which then forms the ‘background’ layer, and then when you add another photo it’s laid on top and covers the photo underneath.
To blend these two images you can adjust the opacity (transparency) of the top layer, change its ‘blend mode’ to alter the way its pixels interact with those on the layer below, or use a layer mask to selectively hide different areas of the top layer so that the one below shows through.
You can think of an image layer as being on a transparent sheet. If you reduce the opacity, you start to see more and more of what’s beneath.
Blend modes are more complex in their results. Three particularly common and useful blend modes are screen, multiply and overlay. All three show a blend of the top and bottom images but combined in a different way. Screen mode combines the top image with the bottom image with a lightening effect, multiply mode has a darkening effect and overlay mode increases the contrast.
Not all photo editors support image layers. Photoshop and Affinity Photo do, as does ON1 Photo RAW. Lightroom, Capture One and Exposure X do not. This is only an issue if your photography involves combining images – for many photographers, this is something they don’t do and don’t need.
3. Adjustment layers
Adjustment layers are different. They don’t contain images at all, simply adjustment data. They were first introduced in Photoshop as one of the first ‘non-destructive’ editing tools, but now you find them in many different programs.
If you create a Levels adjustment layer, for example, you can alter the image levels as normal, but the underlying image on the layer below is unaltered – the adjustment layer simply alters its appearance. Your changes only become permanent if you ‘flatten’ or ‘merge’ the layers or export the image.
You can add as many adjustment layers as you like, but keep in mind that they alter the appearance of all the layers below them, not just the one directly below.
What’s interesting about adjustment layers is that, as with image layers, you can change the opacity or the blend mode, or use a mask to limit their effect to specific areas. Adjustment layers are a very effective way to apply local adjustments and, unlike adjustments made directly to images, they are completely reversible.
Photoshop, Affinity Photo, Capture One and Exposure X use adjustment layers. Lightroom and DxO PhotoLab, for example, use a different system for local adjustments that achieves a similar effect.
4. Vector layers
Vectors are mathematically defined shapes and lines rather than photos and pixels. You can scale them, modify them, twist, stretch and combine them at will. Because they are defined mathematically, they don’t pixellate, regardless of how much or how many times you modify them.
Vector drawings are used for diagrams, illustrations and clip-art, but some photo editors include these vector drawing tools so that you can combine photography and illustration in the same artwork. As with other layer types, you can change the opacity and blend mode and use layer masks.
Photoshop and Affinity Photo are probably best at this kind of hybrid design work, but there’s also Pixelmator on the Mac.
5. Type layers
’Type’ is just the designer word for text, and many photo editing programs let you add text to images. These are programs that are made for designers as well as photographers, such as Photoshop, Pixelmator and Affinity Photo.
The text you add in a type layer remains editable so you can go back and modify it at any time. You can also scale it up and down without it getting pixellated because it’s made up of vector data (see the next section) rather than pixels.
Type layers, like image layers and adjustment layers, offer opacity adjustment, blend modes and masks, and with this it’s possible to blend text with your images in some very interesting and subtle ways.
Which layer types do you need?
If you only ever work on photographs rather than illustrations, you only need adjustment layers – but having said that, a number of programs don’t offer these, and have instead their own system of masks and adjustments – Lightroom and DxO PhotoLab offer very effective local masking and adjustment tools without adjustment layers.