At the most simplistic level, layers are nothing more than layers, or planes, of information. Each layer contains specific information and has a specific purpose. For instance, a simple image might have the following layer structure:
As can be seen, each layer has a different purpose.
Layers are managed in the Layers palette. Anytime a new image is created in Photoshop, a Layers palette is created for that image. Anytime an existing image is opened in Photoshop, the Layers palette is available for that image. If the Layers palette is not open, it can be accessed by choosing Windows/Layers. Figure 1 shows an image that was edited with layers. Figure 2 shows the Layers palette for this image.
This image has fourteen layers, each optimized for a specific effect (in Photoshop CS2, the number of layers that can be added is limited only by the computer that is being used to edit the image).
Each layer covers the layers below it. What can be seen depends on the type of area that is being viewed in a layer. Each layer can have up to three types of areas (the area type is determined by masks and Blend Modes):
When an image is viewed, it is viewed from the top layer down. So, in areas where the top layer is opaque, the viewer will see only the top layer. The effects of the lower layers will not be seen. In areas where the top layer is transparent or semitransparent, the viewer will see the effects of the next to the top layer. In areas where both the top two layers are transparent or semitransparent, the viewer will see the effects of the next layer down. This continues down to the bottom layer.
The first question that should be asked about layers is, "Why should we even bother with layers?" After all, the image editing could simply be done on the original image layer. Then, the image would have only one layer. While this might sound much simpler than using multiple layers, utilizing layers provides six major benefits.
In short, the use of layers opens up vast capabilities in the area of image editing.
There is one downside to layers; each layer increases the file size. Therefore, unnecessary layers should be avoided (e.g., delete layers if it is determined that they are no longer needed.
There are many types of layers. Each has its own uses, advantages, and limitations. The first step in mastering layers is to understand the various types of layers.
Anytime a new image is opened in Photoshop, the image is created as a Background layer. Figure 3 shows a new image that was just opened but has not yet been edited. Figure 4 shows that the image has been opened as a Background layer in the Layers Palette.
Adjustment layers allow tonal or color edits to be made to an image. In Photoshop CS2, there are twelve adjustment layers: Levels, Curves, Color Balance, Brightness/Contrast, Hue/Saturation, Selective Color, Channel Mixer, Gradient Map, Photo Filter, Invert, Threshold, and Posterize (it is beyond the scope of this article to go into each of these adjustment layers).
Adjustment layers can be added to an image by choosing Layer/New Adjustment Layers. The appropriate adjustment layer can then be chosen from the menu. Another option is to click on the Create new fill or adjustment layer button on the Layers palette (see Figure 5).
Once an adjustment layer has been added, tonal or color edits can be made with that layer.
An Image layer is any layer that contains image data. An image layer can be created in a number of ways (e.g., image data pasted from another layer or an image layer dragged over from another image).
Figures 8 -- 10 show how an image layer can be used. Figure 8 shows the original image seen earlier. To improve the quality of the image, it was decided to lighten up the detail in the ocean; so, a lighter copy of the image was converted from the raw file (see Figure 9). This layer was then dragged over to the original image. Figure 10 shows the Layers palette with the new, image layer (the lighter copy of the image). Further work with masks and blending modes will allow the ocean to be lightened a bit by utilizing the added image layer.
An Empty layer is a layer that is just that -- empty. It has no image data, and it contains no tonal or color edits. It may seem a little bit odd to add Empty layers to an image. After all, Empty layers do not change the image in any way. However, an Empty layer provides a layer where further editing can be done.
An Empty layer can be added to an image by choosing Layer/New/Layer or by clicking on the Create a new layer button on the Layers palette (see Figure 11). Figure 12 shows the Layers palette with an Empty layer added.
A Neutral Layer is a layer that is filled with neutral gray. Like an Empty layer, A Neutral layer, initially, has no image data and contains no tonal or color edits. However, again like an Empty layer, a Neutral layer provides a layer where further editing can be done.
One of the easiest ways to create a Neutral layer is to choose Layer/New/Layer. The New Layer Dialog Box will appear (see Figure 15). In the dialog box, the Use Previous Layer to Create Clipping Mask option should be unchecked. The color should be set to None and the Opacity to 100%. When the dialog box first appears, the Mode will be set to Normal. With this setting, the Fill with Overlay-neutral color option will be grayed out and can not be selected. In order to create a neutral layer, one of the other Modes that will activate this option, such as Overlay, will need to be selected. Then, the Fill with Overlay-neutral color option is checked. Clicking OK will create the new layer, which will now be found in the Layers palette (see Figure 16).
A Fill layer is a layer that is filled with a solid color, a gradient, or a pattern. These layers are often used for creating special effects.
A fill layer can be added to an image by choosing Layer/New Fill Layer or by clicking on the Create a new fill or adjustment layer button on the Layers palette (see Figure 19). A menu will allow a Solid Color, Gradient, or Pattern layer to be chosen. A couple of dialog boxes will provide several more options. These options vary depending on which type of layer is chosen and the desired effect that is being created (the proper selection of these options for various effects is beyond the scope of this article). Figures 20 -- 22 show examples of the three types of Fill layers.
A Duplicate layer is simply a layer that has been created by duplicating another layer.
A Duplicate layer is created by selecting the layer that is to be duplicated and choosing Layer/Duplicate Layer and completing the Duplicate Layer dialog box or by simply dragging the layer down to the Create a new layer button at the bottom of the Layers palette (see Figure 23). Figure 24 shows the Layers palette with the Background layer duplicated. This duplicated layer can now be used for image editing without altering the original image data in the Background layer.
A Text layer is a layer that contains text and a Line layer is a layer that contains a line or arrow.
A Text layer is created by selecting one of the Type tools from the Tools palette (see Figure 25) and clicking on the image. The text can then be typed. The formatting and placement of the text can be edited as desired.
A Line layer is created by selecting the Line tool from the Tools palette (see Figure 28) and drawing the line on the image. The formatting and placement of the line can be edited as desired.
Figure 28, which is used to illustrate the Line tool, is a good example of an image with a line added. In this case, the image was a graphic that needed a line for illustrative purposes. Figure 29 shows the associated Layers palette (since this image is a graphic created in Photoshop, rather than an image that is opened in Photoshop, there is no Background layer).