Join Jan Kabili for an in-depth discussion in this video What is a layer?, part of Photoshop CS4: Layers in Depth.
If you ask me to name the single most important feature in Photoshop, I would have to say it's layers, and I'd wager that most Photoshop users would agree with me. In this chapter, I'll cover why layers are so important. But first, what is a layer? At the simple level, a layer is a virtual transparent platform that holds some content. That content could be text, it could be a photo, it could be graphics. In a file that has more than one layer, these virtual platforms each holding separate pieces of content are stacked, one on top of the other.
An important property of these layers is that they are transparent by nature. So you may have heard the metaphor that a layer is like a flat pane of glass that has some opaque areas that are covered by content and some other areas that remain completely or partially transparent, and where a layer is transparent you can see down through it to the content of the layers below. To help you visualize all this I have opened two files here. On the right is a layered Photoshop composition and on the left is an illustration that shows the layers in the same file in perspective.
In this illustration on the left the areas that are transparent on each layer are represented by these pale white pixels. Say for example, if you look at the third layer down you can see that it contains this image of candies at the top of the layer but that the rest of the layer is transparent. So you can see down through it to the image of the sleeping boy on the layer below. And that layer, the bottom-most layer happens to be completely filled with pixels so that there are no transparent areas. This illustration is just a fictional representation of what's happening in the layers in the actual image on the right.
When you look at the real image on the right, the perspective shifts a little so that it's if you were standing at the top of layer stack and looking down through the transparent areas of each layer. So here in the image just like in the illustration you can see through the transparent pixels on the candyies layer to the sleeping boy on the layer below. Another way to visualize the layers in an image is to take a look at the Layers panel. In the default arrangement of panels here in Photoshop CS4, the Layers panel is down at the bottom. And the panels above are taking up so much space that you can't see all of the layers in this file. To create more room for the Layers panel I'm going to close these panel groups above. To do that I'll go to the top panel group and I'm going to click on this small icon on the right side of the panel group. That opens the panel menu and I'll choose Close Tab Group from there.
I'm going to do the same with this Adjustments and Masks panel group, clicking on its panel icon and choosing Close Tab Group. I'll also close the Paths panel and the Channels panel that are grouped here with the Layers panel. I'll click on the tab for the Channels panel, I'll go to its panel menu on the right and I'll choose Close and I'll do the same for the Paths panel, clicking on its tab, going to its Paths panel and choosing Close. I've done this because I'm going to be focusing on the Layers panel throughout this course. So I think it's a good idea to save this panel configuration so that it's easy to get back to it any time. To do that I'm going to go up to the Workspace menu here on the application on a Mac or on the menu bar on a PC.
And I'll click there I'll choose Save Workspace, and in the Save Workspace window I'll name the workspace Layers. I'll make sure that Panel Locations is checked and I'll click Save. Later, if you happened to switch to another workspace, as I'll do now here going back to the Essentials workspace, it will be quick and easy to switch back to the Layers workspace by going back to the Workspace menu and choosing Layers. Now that you can see the Layers panel better notice that it contains four bars, each of which represents one of the layers in this image. By the way, if your Layers panel doesn't show these particular four layers, be sure to click on the tab of the image on the right to make that the active image.
To see what's on a particular layer in this file, you can make only that layer visible. So for example, to see what's on the boy layer I'm going to move my mouse over the eye icon to left of the boy layer, I'm going to hold down the Option key on a Mac or the Alt key on a PC and I'm going to click on that eye icon, and that makes all the other layers temporarily invisible. You can see that the photograph on this layer covers the entire layer. To bring back the other layers, I'll hold the Option key on a Mac, the Alt key on a PC again and click on that same eye icon. And I'm going to be using that technique throughout this course. To see what's on the candies layer, the same way I'll Option or Alt-click on the eye icon on the candies layer and you can see that there is some content appear at the top of the layer and that the rest of the layer is transparent or semi-transparent. The gray-and-white checkerboard here represents transparency throughout Photoshop.
I'll Option or Alt-click again on the candies eye icon to bring back the rest of the layers. To give you a better sense of the transparent nature of a layer I'd suggest that you go ahead and make a new layer with me. To create a new transparent layer I'm going to go down to the bottom of the Layers panel and I'm going to click this icon, the one with the turned-up edge. When I click that icon a new layer appears here in the layers stack. And if I hold the Option of Alt key and click on the eye icon to the left of this new layer, you can see that it is completely transparent. There is nothing on it now. I'll Option or Alt-click again on the eye icon to the left of that new layer and I'm going to go ahead and add some simple content to this layer.
I'll make a brush stroke underneath the words 'dreamy treats' so that it's easier to read that text. The first step is to make sure that the new layer, Layer 1, is highlighted in blue in the Layers panel; if it isn't you want to click on that bar and that selects that layer. Next, I'm going to select a color to paint with. I'll go over to the toolbox and I'll select the Eyedropper tool here. Then I'll move into the image on the right and I'll hover over a color like this pink and I'll click to sample that color and that color now appears down here in the foreground color box in the toolbox.
Now I'm going to select the Brush tool to paint with here in the toolbox. I'll move over the image and I can see by the circular icon the size of my current brush. It's a little smaller than I would like. To make it bigger I'm going to hold down the Ctrl key and the Option key on a Mac, on a PC that's hold down the Alt key as you right-click, and then I'll drag to the right to make the brush bigger and as I do, I can see a representation of the size of the brush here in this red overlay. Now I'm just going to click-and-drag with the mouse to paint with pink, and the important point is that that paint is now located on the new layer 1. So if I Option or Alt-click on the eye icon to the left of Layer 1 you'll see that it contains not only transparent pixels but also the paint that I just added to the layer. And I'll Option or Alt- click again on the eye icon on Layer 1 to bring back the other layers.
The content of this new layer like the content of all the layers in this file is independent of the rest of the image, and that independence is what makes layers such a key feature in Photoshop. As you'll see, as you work through the movies to follow.
- Creating, selecting, and organizing layers
- Controlling layer visibility, opacity, and stacking order
- Working with type and shape layers
- Practical uses for layer blend modes
- Adding dimension with layer effects and layer styles
- Using clipping layers to shape content
- Merging and saving layers
- Introducing 3D layers, video layers, and Smart Object layers