Setting Opacity

You find opacity controls all over Photoshop. An Opacity option is available for each layer and layer group, on the options bar for many painting and retouching tools, and is an option for effects such as layer styles (Figure 13.3). The prevalence of opacity controls in Photoshop means you can combine elements and effects with many subtle degrees of transparency among them.

Figure 13.3. Opacity is an option for effects (top left), layers (top right), and tools (bottom).

Except for the Background layer, every new layer you add is transparent by defaultwhen you add a new layer, you can see right through the entire layer until you start painting on it. When you set the opacity of a layer, you change the opacity of all non-transparent areas.

Within a document, there's a hierarchy to opacity affects how layers, tools, and features interact. Being aware of this hierarchy can help you untangle mysterious interactions between features. One of the most important concepts is that a layer sets the maximum opacity for everything on it. For example, if you set a layer to 100% opacity and paint on it using a brush set to 50% opacity, you get what you expectpixels that are 50% opaque. But if you set a layer to 50% opacity and then paint on it using a brush set to 100% opacity, the painted pixels appear 50% opaque because they're limited by the opacity of their layer (Figure 13.4). Although the resulting pixels look the same in both examples, the difference is that you can raise the opacity of the layer in the second example to 100%, and then the pixels on them will become 100% opaquebecause you painted those pixels with the brush tool set to 100% opacity.

Figure 13.4. With layer opacity set to 50% (left), the brush stroke under the type appears 50% opaque (right) even though the tool itself was set to 100% opacity.

Opacity is available in layer styles, filters, and other features. For example, Opacity is an option in the Drop Shadow layer style so that you can control the transparency of a drop shadow. Like tool opacity, opacity in layer styles and other features interacts with layer opacity.

When an Opacity option is visible in the Layers palette or options bar, you can set opacity by typing number keys. Pressing 1 through 9 sets opacity to 10% through 90%, and pressing 0 (zero) sets opacity to 100%. For example, press 5 to set 50% opacity. To set a two-digit percentage, type two digits quickly; for example, type 42 to set 42% opacity. This tip is subject to the opacity hierarchy, so for example, if the Opacity option is visible both in the options bar for the brush tool and in the Layers palette, and you press 8, you set the opacity for the tool to 80%, not the layer. For the layer to pick up the shortcut, you need to select a tool, such as the rectangular marquee tool, that doesn't have an Opacity value.

If you use a pressure-sensitive graphics tablet and stylus, you can control tool opacity using stylus pressure. Just make sure the tool's Opacity Jitter is set to Pen Pressure in the Other Dynamics panel in the Brushes palette. If that sounds too complicated, just try out different brush presets; many of them are already designed to support stylus pressure.