In last month’s column I revealed a few essential layer techniques for polishing an image. Included were basic processes used to position layer content in the picture plane. I also demonstrated blending modes and adjustment layers used for spiking color and enhancing contrast.
Layers are the key to Photoshop’s overall workflow, a powerful feature that allows many processes to be performed on isolated elements. They keep the working procedure flexible and dynamic and offer creative tools that enhance image quality and effectiveness.
In this installment, I will discuss the best ways to manage layered files. These techniques simultaneously select, manage and affect multiple layers. We’ll also take a closer look at layer masks as a way to conceal layer content. Finally, I’ll show how to best consolidate information on images to produce the most efficient file sizes without compromising the flexibility of layers.

MULTIPLE LAYERS
Some techniques can be simultaneously applied to two or more selected layers. When multiple layers are selected, their contents can be transformed (scale, rotate, distort, etc.) as in Figure 1. They can also be simultaneously repositioned in the stack, merged, their contents aligned, locked and grouped. To highlight two or more layers in the Layers palette, shift click each layer to select a range of contiguous layers, or Cmnd/Cntrl click to select noncontiguous layers.

When two layers are highlighted at the same time, they can’t be painted on, and users can’t apply image adjustments, or control opacity. These operations can be performed with other techniques including:

Adjustment Layers: (Image > Adjustments >etc.) Used to modify color and contrast.
Blending Modes: Used to affect the relationship between the pixels on two consecutive layers.
Clipping Masks: To use the transparency of one layer to hide portions of a layer immediately below it in the stack.
Align Layers: (Layer > Align Layers) for aligning the content of two or more layers.
Auto-Align Layers: to automatically align layers based on similar content in different layers, such as corners and edges (see Figure 2).
Layer Groups: for organizing, controlling opacity, positioning two or more contiguous layers in the stack, and for transforming or moving layer content.

GROUPING LAYERS
A Photoshop document can support an unlimited number of layers. However, a document with dozens of layers can be a real bear to handle. It helps to organize layers into groups to better manage them. To create a group, first, select multiple layers in the stack, then choose New Group from the Layers palette Options menu. Groups can be repositioned in the stack by dragging them. Layers can be added or eliminated from the group by drgging them onto the layer stack.
A layer group is indicated in the Layers palette by a folder icon, as in Figure 3. Click on the arrow to the left of the icon to expand the folder to see its contents.
To simultaneously affect all the layers in the group, click on the folder to highlight it, then apply the operation. The group can be revealed or concealed by clicking the eye icon, and the layers can be moved or transformed simultaneously. The opacity of the group can be controlled with the opacity slider, and blending modes can be applied to the entire layers group to effect the layer below.

COLOR CHANNELS
To change the color characteristics of a highlighted layer group, choose Group Properties, from the Layers palette Option menu, or the Layers menu. In the dialog box, click the Red, Green or Blue color checkboxes to determine what color information will be visible. The boxes display the individual or combined color channel information of all of the layers in the group. Some rather interesting effects can be produced, especially if applying a blending mode to the group, as in Figure 4.

LAYER MASKS
Masks are really powerful. The Opacity slider on the Layers palette is a global adjustment – it controls the transparency of all the pixels on the layer. Reducing the opacity gives the ability to see through the layer content to the layers below. Layer masks control the opacity of the specific region of a layer. Layer masks reside in the Layers palette next to the thumbnail of the layer. To create a layer mask, choose Layer> Layer Mask>Reveal All. Click on the layer mask to target it. A double border indicates that it is ready for editing. Paint on the image with 100 percent black to conceal areas on the layer and display the content of the layer beneath it. Paint with gray to create transparency and with white to erase any black or gray that’s been painted.

REVEAL SELECTION
If a selection is active, choose Layer> Layer Mask>Reveal Selection, to fill the contents of the selection outline on the layer mask with white. Areas outside the selection outline will fill with black. The contents of the selection are visible in the image window, and the pixels that are not selected are not visible, as in Figure 5.

CONSOLIDATING LAYERS
Quite a few layers may accumulate during the editing process. With each new layer, the file size increases, depending on the amount of information the layer contains. To work more efficiently, periodically merge layers. Merging layers combines the content of two or more layers into one layer. It’s best to merge non touching elements, or content that will not change, into one layer.
There are several ways to merge layers, all of which can be selected from the Layers menu or the Layers palette Options menu.

Merge Visible merges the content of all visible layers into one layer. First, click off the eye icon on the layers that shouldn’t be merged, then choose Merge Visible.
Merge Layers merges all highlighted layers into one layer. The layer retains the name of the topmost highlighted layer.
Merge Down merges the content of the targeted layer and the layer immediately below it into one layer. The layer retains the name of the highlighted layer.

Here is a neat trick to merge the content of selected layers into a single new layer: press Opt/Alt and choose one of the merge options from the Layers menu or Layers palette Options menu. This gives the advantage of preserving the original layers and produces a layer with the combined elements, as in Figure 6.
A more radical option for consolidating an image is to flatten it. Flattening discards all layers and combines all layer content into a single background. Before flattening an image, make a duplicate version and save the original in PSD or TIFF format- both support layers. Flatten the duplicate, because once the image has been flattened, saved and closed, it cannot be unflattened. Be sure all layers are visible (Photoshop will discard layers that are not visible!) and choose Flatten Image from either the Layers menu or the Layers palette Options menu.

In Photoshop, Layers rule! So many operations are associated with Layers that it’s essential to learn to use them. Layers can make life in the virtual fast-lane a lot easier, and enable the production of images that really have impact.
These two articles have merely scratched the surface of Layers. In future Digital Eye articles, I will occasionally focus on layer operations and reveal how to get the most out of these powerful techniques.

(Click here to read Part 1 of this article series.)