An image can be flattened by merging all of the layers. When an image is flattened, all of the layers are merged into the Background layer. This reduces the file size. To flatten an image, Layer/Flatten Image is chosen.
Figure 1 shows a Layers palette with multiple layers. Figure 2 shows the Layers palette after the image was flattened.
When layers are linked, they can be moved and rotated together. First, the layers to be linked are selected. Then, the Link Layers icon at the bottom of the Layers palette is clicked (see Figure 3).
Once layers have been linked, a link symbol will appear on each linked layer (see Figure 4).
A clipping mask allows for two or more images to be combined in such a way that the base (bottom) layer masks the effects of the layers above (which belong to the clipping mask). The pixels in the clipping mask layers only show through the areas that are opaque in the base layer. Clipping masks can be created by clicking between two layers while holding down the Alt key or by selecting a layer above the base layer and choosing Layer/Create Clipping Mask.
Figures 5 -- 8 illustrate the use of a clipping mask. Figure 5 shows a Layers Palette without a clipping mask, and Figure 6 shows the image from that Layers palette. Figure 7 shows the same Layers palette except Layer 6 now is part of a clipping mask. Figure 8 shows what the image looks like with the clipping mask. The important thing to understand in these figures is that in Figure 8, the green color in Layer 6 is only able to show through where Layer 5 is opaque.
Clipping masks are also great for when there are two or more layers that all need to affect the same area of an image. Instead of putting the same mask on all of the layers. One mask can be put on the base layer. This mask will also apply to the layers in the clipping mask. That way, if the mask needs to be changed, only one mask needs to be edited.
Figure 9 shows a clipping mask. The Mountain layer is the base layer. The Curves: Blue layer was added to reduce a blue cast on the mountains in the distance. Because the Curves: Blue layer is part of the clipping mask, it will only affect the part of the image where the mask on the base layer (the Mountain layer) is transparent.
Layer groups allow layers to be grouped together. Layers can be grouped by selecting the layers and choosing Layer/Group Layers or by clicking on the Create a new group icon at the bottom of the Layers palette (see Figure 10). Once the layer group has been created, the selected layers are placed into the new group. Layers can be added to the group by dragging them into the group. New layers can also be created in the group by following same procedures as covered previously.
Figure 11 to 13 show the results of creating a layer group. Figure 11 shows a Layers palette with two layers selected for grouping. Figure 12 shows the new layer group. By clicking on the triangle on the group layer, the group is expanded to show the individual layers within the group (see Figure 13).
A layer group behaves as if it were a single layer. For instance, the group can be moved or a mask can be put on the group. The Blend mode that is assigned to the group is Pass Through. With the Pass Through Blend mode, you get the same effect as would occur if the layers had not been grouped. If the Blend mode is changed to some other mode, the group will act as if the layers in the group were merged and the new blend mode placed on the merged layer.
Layer Masks Layer masks can be used to restrict a layer's effects/content to specific parts of an image. To add a mask to a layer, select the layer and choose Layer/Layer Mask. A menu with four options will appear:
Once the appropriate option is selected, a mask will be added to the layer. Figures 14 and 15 show a Layers palette before and after adding a mask to a layer.
The impact of a layer's Opacity depends on the layer's type:
Blend Modes are an extremely powerful part of layers. The Blend modes alter how layers interact. The Blend mode for a layer is set by choosing the mode from the Blend mode pop-up in the upper left side of the Layers palette (see Figure 18). The topic of Blend Modes is far too extensive to cover in this article (interested readers can read my series on Blend Modes).
Layer Styles offer a wide array of effects that can be applied to images. After selecting a layer, layer styles can be applied by choosing Layer/Layer Style or by clicking the Add a layer style icon at the bottom of the Layers palette (see Figure 19). A menu with a large selection of layer styles will appear. It would be impractical to cover all of the possible layer styles in this article, so one will be selected as an example (Bevel and Emboss).
The Blend If tool determines how the tonal regions of a layer and the underlying layer blend together. The Blend If tool is accessed by choosing Layer/Layer Style/Blending Options. The Layer Style dialog box appears as shown in Figure 23. The Blend If controls are found in the Advanced Blending section of the dialog box.
The details of using the Blend If tool are beyond the scope of this article. However, the specifics of this tool can be found in my Blend If article.
This series has shown the various aspects of layers and how they are accessed. An upcoming article will show how layers were used to produce a fine art print.