One of Photoshop's most powerful features is the use of layers. Each layer in a Photoshop document is a separate image which can be edited apart from any other layer. A layer can be envisioned as an image on a sheet of clear material. Together, all the layers form a stack of images:
1. Layers are managed with the Layers palette (below left). The Layers palette displays a small thumbnail view of each layer to help identify it. The appearance of a Photoshop document is a view of the layer stack from the top down (below right).
Though, it's not enough to create a layer. You should know how to use html layers properly!
2. You can turn layer visibility on and off and completely change the appearance of an image without permanently affecting a single pixel. The eye icon to the left of each layer controls its visibility. A layer is made visible or hidden by clicking its eye icon (below left). The result is the same Photoshop document shown previously with the exception that one of its layers has been hidden revealing the white background underneath.
3. Opt/Alt-clicking a layer's eye icon will make it visible and will hide all others (below left). In the example below, the layer named "paint" becomes the only visible layer (below right). Note that the layer named "photo" is still highlighted. The highlighted layer in the Layers palette indicates that it is the active (or selected) layer. This means that all editing in the document window will be applied to the active layer.
4. Click a layer to activate it (circled below left). Now all editing in the document window will be applied to the "paint" layer.
Note: that there is no change in the appearance of the document window (below right). Look to the Layers palette to see which layer is active, not to the document window.
5. You can quickly select all opaque areas in a layer by Cmd/Ctrl-clicking the layer in the Layers palette. When you hold down the Cmd/Ctrl key, the mouse pointer turns into a hand with a square selection marquee (below left). The result will be that all the pixels in the layer will be selected. You will see a row of "marching ants" around the selected pixels in the layer (below right).
6. To delete a layer, click it and drag it to the Trash button in the Layers palette (below left). The result is shown below right.
7. To create a new layer, click the New Layer button in the Layers palette (below left). The new layer will appear just above the active layer (below right).
8. To duplicate a layer, drag it to the New Layer button. In the example below, a new layer will be created named "photo copy".
9. To change the layer stacking order, click a layer and move it up or down in the Layers palette.
10. You can adjust a layer's opacity by dragging the Opacity slider (below left). Alternately, you can simply enter a value for the opacity. In the example below, the shadow layer is made to appear more transparent by setting its opacity to 75% (below right).
Layer Blending Modes
Each layer has a blending mode. A blending mode is the way layer pixels blend with the layers beneath it. The default blending mode is "Normal", but there are several to choose from. Below are just a few examples of using different blending modes on the shadow layer:
11a. Normal
11b. Dissolve
11c. Overlay
Linking Layers
12. Layers can be linked so they can be repositioned as a unit. Click the column to the left of the layer (to the right of the layer's eye icon) to link it to the active layer (below left). In the example below, the "paint", "palette" and "shadow" layers have been linked together. When using the Move Tool and any of these layers is selected, all will move as a unit (below right).
Layers Palette Menu
The Layers palette has a menu which can be accessed by clicking the small triangle on the right side of the palette. There are several commands which are available in this menu. For example, in our sample image, we can combine the "paint" an "palette" layers with "Merge Down".
13a. Click the paint layer to select it.
13b. Click the small triangle on the right side of the Layers palette to access the Layers Palette Menu. Then choose "Merge Down".
13c. The paint layer will be combined with the palette layer. The name of the layer underneath will be retained and the name of the layer on top will be discarded. In this case, the remaining name is "palette".
Renaming a Layer
14a. To rename a layer, double-click it in the Layers palette.
14b. Enter the new name in the dialog and click "OK" when done.
14c. The new name will appear in the Layers palette.
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