Photoshop: Peeling Back the Layers For Easier Image Editing, Divide and Conquer Helen Bradley
Wed 9/4/02 -- Shrek says that ogres, like onions, have layers. Does that mean ogres are like Adobe Photoshop images?
Layers are a key tool in creating almost any image in Photoshop. Layers allow you to separate some parts of an image from others, so you can edit or manipulate parts in isolation. Layers can be stacked on top of one another, letting portions of layers below appear through transparent areas of layers above, and can also be used to adjust color.
This week we dig deep to uncover some ways you can use and manipulate layers with Adobe's image editor.
The background layer. The background layer is a special layer in a Photoshop image. It can't be moved -- it's always at the bottom of the pile or stacking order -- and there's only one background layer per image. You're also limited with what you can do with the background layer: you can't alter its blending mode or its opacity and it can't contain any transparent pixels.
Does this sound too limiting? All is not lost, because you can easily turn a background layer into a regular layer. To do this, double-click the background layer to open the New Layer dialog. Type a new name and click OK; the background layer disappears and is replaced with the new layer.
It's also possible to turn a regular layer into the background layer, if the image doesn't already contain a background layer -- select the layer and choose Layer/New/Background from Layer. You can also merge the visible layers in an image to create a one-layer image (the single layer is automatically the background layer) -- just choose Layer/Flatten image.
Using layers to improve an image. Layers' blending modes dictate how the pixels in the image are affected by those in layers below it. You can use the Overlay blending mode, for instance, to improve photos which have lackluster or muddy color or which are muddy; this mode has the advantage of preserving the highlights and shadows in the original image.
To use this technique, open the photo and create a duplicate layer by right-clicking and choosing Duplicate Layer. From the "Blending modes" list for this new layer, choose Overlay, then adjust the layer's Opacity downward until you get the desired result.
In and around layers. Many options are available from the Layer menu and the Layer palette, but there are a few must-have shortcuts that bypass these menus to get you to your destination more quickly.
To view one layer and hide the rest, press the Alt key while clicking on the eye icon of the desired layer (note, however, that while this makes this layer visible it doesn't make it the selected layer). To move through the currently visible layers one at a time, press Alt-] or Alt-[. To move a layer up or down in the stack, select it and press Ctrl-] or Ctrl-[.
When copying layers, you probably already know that Edit/Copy copies a selection from the current layer. You can also copy a selection from all visible layers if you choose Edit/Copy Merged. (If you're in the habit of pressing Ctrl-C for the former, try Ctrl-Shift-C for the latter.)
Finding the responsible layer. The more layers you have, the more difficult it can be to find which one contains a particular portion of the image. One solution is to name your layers carefully (to change their names, double-click each layer's name and type the new name).
Another solution is to press Ctrl while right-clicking the part of the image containing the object you're interested in -- a small, pop-up menu will show you the names of the layers containing this portion of the image. You can select a layer name from this pop-up to make that layer current, or bypass the pop-up menu by Ctrl-Alt-clicking an element to select the layer it's on.
The Move tool is also handy for working with layers. Select it from the tools list, and from the tool options choose Auto Select Layer and Show Bounding Box. Now, when you click on an object in an image, the layer it's on will be automatically selected, with a box will be drawn around it so you can see the size of the object. If the Move tool options aren't visible, choose Window/Options to display them.
Removing the halo. When you remove the background from around an object on a layer, you'll often be left with a halo or fringe of pixels around it which appear when you place the layer over a different-colored layer or background layer. You can eliminate these traces by choosing the layer containing the object and selecting Layer/Matting/Defringe. Select the number of pixels (start with 1 or 2, and increase it if the results aren't dramatic enough) and click OK.
