Layers are an important element of graphics programs in that they provide a capability for one to edit portions of an image without affecting the other portions. Select File>New -- in the Background Contents drop down list, you can choose White or Color which will create a Background layer which is fully opaque. If you choose Background Contents: Transparent, there will be no Background layer and the initial layer will be transparent. Transparent areas on a layer are indicated by a checkerboard pattern. You can view layers by choosing Window>Layers.
Some actions automatically create a layer - paste a selection, create type with the Horizontal or Vertical Type tool, or create a shape. To create a layer apart from these actions, display the Layers panel and click the layer which is to be immediately beneath the newly created layer. Click the New Layer button at the bottom of the panel, immediately to the left of the Trashcan. To rename the layer, double click the layer name and type the desired name. The new layer will have both Opacity and Fill percentages of 100% and a blending mode of Normal. If you want to create a layer with different properties, hold down the Alt key when you click the Add Layer button.
On the Layers panel, click on an image layer or the Background, then create a selection in the document window. Then right-click
Exercise: Use the straighten image and do a selection, first choosing one option then the other.
Click a layer, and do one of the following: right-click and choose Duplicate Layer (this will allow you to name it as you create it), or Drag the layer over the new Layer button, or Ctrl-J.
There are many things you can do to a layer that you can't to the Background but you can convert the Background to a layer which will permit these actions. To convert the Background into a layer, Right click the Background in the Layers panel and choose Layer from Background, or double click the Background on the Layers panel, or Alt double-click the Background on the Layers panel.
Click a layer, choose Layer>New>Background from Layer.
Using the Layers Panel - Select the layer or layers to be edited in the Layers panel before making an editing change. The selected layer or layers will have a blue color in the Layers panel and the layer name is shown in the title bar of the document window. Shift-click to select consecutive layers and control-click to select non-consecutive layers. Select>All selects all layers but the Background. To select all layers of a similar kind, chose Select>Similar Layers.
Using the Move Tool - Choose the Move Tool (top row, right) and then do either of the following:
Exercise: Use the Move Tool technique after you have done Layer Via Copy and Layer Via Cut and see the difference in the layers selected.
A layer that is higher than another in the layer's panel will be in front of the other layer in the document. If there are non-transparent pixels in these two layers at the same point in the image, the order of the layers will affect what is displayed in the image. To move a layer, just drag it in the layers panel to the appropriate position. To move the Background, you must first convert it to a layer (see above). You can also move a layer by selecting it and then choosing Layer>Arrange.
You can organize layers into groups -- this allows you to condense the size of the layers panel (click the arrowhead to expand or collapse a group) and do operations on a number of layers at the same time. To create a layer group:
You can drag layers in and out of groups. To delete or disband a layer group, click on the layer group and click the Delete Layer button in the Layer Panel, or right-click and select Delete Group. In either case you will be prompted to select Group Only or Group and Contents
Exercise: Use the straighten image and do selections in various parts of the image, turning them into layers by right-click and choose Layer via Cut. Then group some of the layers with an appropriate name and then disband the group.
Click on a layer in the Layers Panel and then click the Delete Layer button at the bottom right of the Layers Panel or hit Backspace or Delete.
Hiding layers can reduce distraction and hidden layers don't print. To hide or show a layer, click in the visibility column. To hide multiple layers, drag in the visibility column. To hide or show all layers and layer groups except the one you're on, right clik in the visibility column and choose Show/Hide All Other Layers
Click on the layer, layers, or the layer group whose content you want to move. Then choose the Move tool and drag in the document window to move the contents. You can use the arrow key to move one pixel at a time and Shift-arrow to move 10 pixels at a time.
Use the layers file. Click on a layer or layer group that overlaps imagery on a layer below. For example, notice that the cheese layer overlaps the left side layer. On the Layers panel, do either or both of the following: choose a blending mode at the top of the panel or change the Opacity percentage by using the slider.
To limit edits by any command or tool by locking transparent pixels. Choose a layer (not an editable type layer). Choose the Brush tool; on the Layers panel, click the Lock Transparent Pixels button then draw brush strokes on the layer. Only nontransparent pixels can be recolored.
To lock a layer or layer group, do any of the following: click the Lock Image Pixels button (you can still move the layer and change options), Lock Position button (layer content can still be edited), or Lock All button to prevent the contents of the layer from being moved or edited.
To choose thumbnail options for the Layers panel, right click a thumbnail and choose any of the following: a different thumbnail size or No Thumbnails, Clip Thumbnails to Layer Bounds (shows in the thumbnail, only the area that encompasses the opaque pixels on the layer; this may be useful if most of your layers contain silhouetted shapes) or Clip Thumbnails to Document Bounds (includes surrounding transparent pixels in the thumbnail).
The merge commands- Merge Down, Merge Layers, and Merge Visible- merge two or more selected layers onto one layer (the bottommost of the selected layers). This can reduce the file size of your document and clutter in the layers panel.
To merge layers - Do one of the following:
To merge all the visible layers, right-click one of the visible layers and choose Merge Visible
To copy and merge layers - Ctrl-click the layers you want to copy and merge then hold down the Alt key as you choose Merge Layers from the panel menu. Similarly you can copy and merge the visible layers by holding down the Alt key and selecting Merge Visible from the panel menu.
The two major reasons to flatten layers is to reduce file size and prepare it for export (only Photoshop PDF, Large Document Format, adn TIFF support layers).
To save a flattened copy of the file - Chose File>Save As and uncheck the Layers box (this will automatically check the As a Copy box), and then choose a file format. The layered version stays open, the flattened version is saved to disk.
To flatten layers - Make sure all the layers and layer groups you want to flatten are visible, right-click any layer name and choose Flatten Image.
Source: Photoshop CS4 Visual Quickstart Guide, Elaine Weinmann and Peter Lourekas, pp. 109-122. Revised: June 29, 2010
