The Layers Concept
Layers in Photoshop act like separate layers of acetate sheets over an image, each sheet holding its own image. Images on each layer will block any images that sit directly below. The combination of all sheets in a register is used to make the final image (figure 1).

Photoshop layers work in a similar manner, allowing the user to make changes to individual layers of an image file without affecting information on other layers.

When you open a photograph for the first time in Photoshop, the image shows as a single layer, called Background. New, separate layers can be created for any additions or changes to the image. Other images can also be added to the image as new layers. Layer modifications can be made to individual layers or to groups of layers in many ways.

Special features, like adjustment layers, layer masks, and layer styles, are also available for making sophisticated effects within an image.

The Layers Palette
The Layers palette is where all layers can be created, organized and grouped. You can create, name, link, and group all image layers. You can hide, show, or even change layer opacities. Text layers can be added and modified. There are also various layer commands and options available in the Layers palette menu.

This section will cover the features, functions, and layout of the Layers palette. Figure 2 shows the structure and components available in the palette.

The palette can be closed or minimized by clicking one of the buttons at the top, left of the palette (figure 3). Clicking one of these buttons will apply to all palettes docked together.

The palette can be reopened from the Window tab in the Photoshop main menu or by keyboard function key F7.

Figures 4 - 13 show the components of the Layers palette.

Every file opened in Photoshop will initially have a layer named Background. This layer will be the actual image from the camera or scanner. If a new file is created within Photoshop, the layer will be all white by default, or transparent, or the current background color from the Tool palette (figure 4).

This Background layer is always locked, meaning it cannot be repositioned or placed above other layers. Layer masks are not available the Background layer, but brushes and filters can be applied. It cannot be trashed unless first converted to an editable layer.

The Background layer can be converted to an unlocked, fully editable layer with the Layer Properties command. Converted Background layers are only supported as Photoshop .psd files.

New layers are created with the Create a new layer command button at the bottom of the palette. This looks like a sheet of paper with a corner turned up (figure 5).

You can also use the Layer tab > New Layer command in the Photoshop main menu or by pressing Shift-⌘-N (Shift-Ctrl-N).

Clicking the icon will create a new layer named Layer 1. This layer will be 100% transparent, meaning that there is no pixel information yet on the layer. The checkerboard pattern of the layer thumbnail indicates layer transparency (figure 6).

You can copy a layer by dragging the layer over the Create a new layer icon. You can also use the Layer tab > Duplicate Layer command in the Photoshop main menu or by pressing ⌘-J (Ctrl-J).

The light blue color of the layer indicates that it is the active layer. Any tools, commands, or filters are applied only to active layers.

The background layer is always locked in position and is indicated as such with the lock symbol to the right of the layer name.

Other layers may be locked with the Lock menu icons near the top, left of the Layers palette. You have the option to lock transparent pixels, lock image pixels, lock position, or lock all.

Figure 7 shows the Lock All command applied to Layer 1. A layer with the dark-color lock icon is in the Lock All state.

A layer can be locked to protect transparent pixels, or image pixels, or to lock in position (figure 8). Any of these three locked states is represented with the light-color lock icon next to the layer name.

At the bottom of the Layers palette is a robust set of layer tool buttons (figure 9).
These buttons are for:

• Linking layers
• Adding layer styles (such as drop shadows)
• Creating a layer mask
• Creating an adjustment layer
• Creating a layer group (set)
• Creating a new layer
• Discarding a layer (trash)
• Resizing the layer palette window

Layer visibility can be turned on/off with the eye icon to the left of each layer thumbnail. To turn off layer visibility, click on the eye. The eye will disappear (figure 10). Click again in the empty square to turn layer visibility back on again.

You can also use the Layer tab > Hide Layers/Show Layers command in the Photoshop main menu.

Non-visible layers cannot be modified with filters or paint tools, however they can be repositioned.

Blending modes can be assigned to individual layers (figure 11). These are the same blending modes that are available for Photoshop paint tools. The default setting is Normal.

These layer-blending modes can be used with great results. We encourage Photoshop users to explore the possibilities of using these modes. For most situations, however, this should be set to Normal.

Layer opacity (visibility) can be set with percentage values with fully opaque layers are set at 100% opacity. There are two methods for setting layer opacity in the layers palette.

The Opacity and Fill layer percentages can be set anywhere from 0% (invisible) to 100% (fully visible). These can be set by typing a value in the text field or using the value slider accessible with the arrow on the right of the field.

These two options are very similar. Opacity changes will proportionally affect any layer effects applied. Fill changes will not change any layer effects. Figure 12 shows this on an image with a Drop Shadow layer effect applied.

The Opacity setting can also be set in 10% increments with a keystroke when the Move tool is selected. Simply press a number, such as 3 for 30% or 8 for 80%. Settings can also be set from the main menu tab Layer > Layer Style > Blending Options.

Layer options are accessible by clicking on the encircled arrowhead at the top, to the right of the palette. You can duplicate, delete, merge, group, or flatten layers from this pop-up window.

Figure 13 shows available options in dark gray. Unavailable options for that layer are grayed out. On a mouse rollover, the option will highlight in a blue bar. Here we have selected Layer Properties.

Now that you are familiar with the basic components of the Layers palette, let's look closer at the available functions and features of layers.

The Layer Properties dialog box is used to rename a layer. Here we named a layer "My Layer One" (figure 14).

You can also specify a color to tag the layer. Here we selected orange to tag a layer. The area around the visibility icon (eye) is now orange (figure 15).

You can also rename a layer without opening the Layer Properties dialog box. Just double-click on the current layer name, type in a new name, then click away from the name or press "Enter".

Working with Multiple Layers
The Layers Palette allows you to organize and coordinate several layers to build your image file. When working with multiple layers, you can change the hierarchy of layers, link layers together, group layers as sets, and so on.

Layer order is very important for setting up an image file.

Figure 16 shows a group of three shapes of different colors. The order of layers from the top is:

1. Green triangle
2. Red square
3. Blue circle

Layers can be moved up or down in the palette (figure 17). Just click-drag a layer to the desired position.

Layers can also be arranged from the main menu under Layers > Arrange or with keystrokes (figure 18).

You can temporarily select multiple layers to move, merge together, reposition in the palette, or group together.

Select one layer, then ⌘-click (Ctrl-click) all other layers you want to select. Or, if all layers to be selected are positioned together, you can select the upper-most layer, then Shift-click on the lower-most layer. Those two and all layers in between will be selected (figure 19).

Layers can be linked together to hold these layers as a selectable group, while you continue working on your file.

To link layers together, select the layers as shown above. Then click on the link icon at the bottom, left of the Layers palette. These layers can now be selected as a group whenever you want (figure 20).

On Photoshop versions prior to CS2, the link button is next to the visibility button (eye) on each layer. To link layers, select one of the layers, then click on the link icon of each layer to be linked.

Selected layers can also be resized as one.

To resize multiple layers, select the layers to be resized. Then choose from the main menu Edit > Free Transform, or use keystroke ⌘-T (Ctrl-T). An outline of a box will appear around the perimeter of all the selected layers (figure 21).

Click and drag from a corner of the box outline until the desired resize is made, then press Enter.

This image shows all three layers enlarged from the one single Transform command (figure 22).

Clipping groups can be set to allow the bottom-most layer of the group to act as a mask.

The higher layers in a group (more than 2 layers can comprise a clipping group) will appear only where pixels exist on the lowest layer of the group.

In figure 23, the red square and the blue circle have been joined as a clipping group. The green triangle is not part of the group. Notice how the red square appears only where there is an image on the blue circle layer.

Making a clipping group is a great way to make dramatic text in an image.

Here we show how to build a clipping group for text. Figure 24 shows an image layer of bamboo positioned over a text layer.

The text layer is moved to sit directly beneath the image layer (figure 25).

You can make a Clipping Group by pointing the cursor over the line dividing the two layers, then Opt-clicking (Alt-click) on the line. The thumbnail of the higher layer will shift to the right and will display an arrow pointing down to the lower layer. This indicates that the two layers are joined in a clipping group. To cancel the group, repeat the same keystroke command.

Figure 26 shows the text now has the image of the bamboo.

Adjustment Layers
Several types of Adjustment Layers are available to apply to the image file, some layers, or just an individual layer. Adjustment layers can be altered like any image layer, including applying filter effects and masking of the layer.

The adjustment layers available are:

• Solid Color
• Gradient
• Pattern
• Levels
• Curves
• Color Balance
• Brightness/Contrast
• Hue/Saturation
• Selective Color
• Channel Mixer
• Gradient Map
• Photo Filter
• Invert
• Threshold
• Posterize

We will demonstrate the power of using adjustment layers with this image of two yellow calla lilies (figure 27). We will change the color of the calla lilies by using the Hue/Saturation adjustment layer.

Adjustment layers are accessed from the bottom of the layer palette by clicking the black and white circle. The submenu of choices will appear.

We chose the Hue/Saturation option (figure 28).

The Hue/Saturation dialog box appears (figure 29). We chose to alter the color by dragging the Hue slider to the left until we found a rich red color (figure 30). Pressing OK will apply the changes.

Our calla lilies are now red (figure 31).

Had we instead used the option of changing the Hue from the main menu (Image > Adjustments > Hue/Saturation), our change would be permanent. Using an Adjustment Layer leaves us with the option of modifying or deleting our mask.

Notice that the adjustment layer thumbnail is all white. This means that none of the layer is being masked.

We used the Brush tool with the black foreground color to paint a mask for this layer. The flower behind the main flower was painted over (on the adjustment layer) to create a mask, essentially blocking any layer information from the affecting layers below (figure 32). We now have a red calla lily and a yellow calla lily.

Using varying tones of gray and black and white will alter the adjustment layer accordingly. All types of adjustment layers can be edited this way.

An adjustment layer can be treated as any other layer. It can be joined in a clipping group to affect only the layer directly below or it can be positioned to affect all layers below. It can be masked with paint tools and can be modified with filters. Layer opacity can be changed and blending modes applied.

Layer Groups
Layer Groups (previously called Layer Sets) can be created to better manage a Photoshop file. This is especially helpful for files with many layers.

A new layer group is represented by a "folder" icon in the Layer palette. This folder, or group, can contain any number of layers. This Layer Group can be masked or have attributes applied as one layer. Opacity can be set and several blending options are available.

Figure 33 shows a Photoshop file with several groups. One group, named PhotoGear, is visible in our photo (notice the eye icon is active for this folder and its layers). The layers of the group show in the Layers palette because the arrow points down indicating an open group.

Groups not being used can be closed by clicking on the groups arrow. This helps to keep complex files organized and easy to work with.

Blending Modes
Several layer-blending modes are available to determine how pixels of a layer will blend with underlying pixels on other layers. Special effects can be made with creative use of blending modes. Often times, the opacity of a layer and the blending mode set will determine the look of the effect.

Figure 34 is a chart showing many of the blending modes working on two image layers.

Layer Effects and Styles
Many fully adjustable effects, such as glows, drop shadows, overlays, and embossing, can be applied to individual layers. Effects will update with any layer modifications.

The layer style is the sum of all the active effects for the layer. In the layer palette, an "F" will appear on the layer when there is an active style. Layer styles can be saved as a custom style and will be accessible in the layer style preset area.

Figure 35 shows the Layer Style dialog box accessible from the main menu (Layer > Layer Style) or by double-clicking on the layer thumbnail. Style options are available on the left side. On choosing a style option, the center of the dialog box will show the adjustable parameters for that effect. Multiple effects can be set within the dialog box to set the layer style.

Layer Masks
A Layer Mask allows a layer to be blocked to varying degrees. Areas of a mask can be used to block visibility of different areas of the same layer. Note: A Background layer cannot have a layer mask.

When a layer mask is created for a layer without an active selection, the mask will be completely white, resulting in the whole layer being visible as though the mask did not exist. When a selection is active, a newly created mask will show the layer area that was selected while blocking the non-selected areas. Partially selected areas will appear to the degree of selection.

Figures 36 and 37 show an image layer with an active selection before and after a layer mask is created.

Paint tools can be used to paint white, black, or shades of gray to the mask. Filters can also be applied to a mask.

To view a mask, Opt-click (Alt-click) on the mask thumbnail. Use this keystroke again to return to normal view.

To hide a mask, Shift-click on the mask thumbnail. A red "X" will appear on the thumbnail. Use this keystroke again to return to normal view.

To move the image or the mask independently of each other, click on the link icon that sits in between. The link icon will disappear. Either the image or the mask can then be moved without moving the other. Click again on the invisible link icon to re-link.

Copy Layers
There are a few methods for copying a layer in Photoshop:

• With the layer selected, click ⌘-J (Ctrl-J). The copy layer will sit directly above the original layer. One layer at a time can be created this way.
  Selected areas of a layer can be copied using the same keystroke command.
• Another method is to select the layer, or multiple layers, then drag over the layer (page) icon at the bottom of the Layer palette.
• Yet another method is to use the main menu. Select Layer > Duplicate Layer(s).

Importing/Exporting Layers
You can use the Move tool to copy whole layers or a selection of a layer from one file to another open file. You can simply drag the layer between images.

You can also use the Copy, Copy Merged, Cut, and Paste commands to copy and move selections. These commands are found in the main menu. However, dragging layers with the Move tool will save memory because the clipboard is not used as it is with these commands.

In the main menu under the Edit command:

• Copy will copy the selected area on the active layer.
• Copy Merged will copy of all the visible layers in the selected area into one merged layer.
• Paste will paste a cut or copied selection into another part of the image or into another image as a new layer.

Discarding Layers
Each layer adds to the file size of your image. Therefore, it is good practice to delete unused layers in order to save file space.

Single and multiple layers can be discarded by selecting the layers, then

• Dragging the selected layers to the trash icon at the bottom of the Layers palette
• Clicking on the trash icon
• Selecting Layer > Delete > Layers in the main menu
  
• Clicking the Layers palette option arrow and selecting Delete Layers

Layer Options
Layer options are accessible by clicking on the encircled arrowhead at the top, right of the palette. Most of the options available here are also accessible from the Layer tab in the main menu. You can duplicate, delete, merge, group, or flatten layers from this pop-up window. Managing layers is easily done with this Layers palette options drop-down menu.

To Wrap Up...
Layers allow for very robust image development. The use and management of layers takes some practice, but the results make the effort well worthwhile.

Remember that layers are editable and changes can be applied that are not necessarily permanent. This lends a great advantage to those who want to experiment with images and explore the variety of results that can be reached.