Photoshop's Advanced Layer-Blending Options
Once you start using Photoshop layers, it's usually not long until you discover the Blend Modes at the top of the layers palette. These control how the pixels on the active layer blend with the pixels of any underlying layers.
Seventeen blend modes are available for the layers palette, with names such as Multiply, Overlay, Screen, Darken, Difference, and Exclusion (see Figure 1). The effects that they produce may seem strange and random at first, but each one is governed by a specific mathematical algorithm that compares the color values of the active layer with the values of the layer below, runs a calculation, and then displays the results. If you're burning to know exactly what's going on here, check out Chapter 31 in Photoshop 6 Artistry, by Barry Haynes, Wendy Crumpler, and myself (New Riders, 2001), or dig into Photoshop's online Help section (you'll find the blend modes described under Painting, Setting Options for Painting and Editing Tools, Selecting a Blending Mode).
Figure 1 The blending modes available in the Layers palette.
The basic blend modes are very easy to find, and even if you don't know precisely why they affect the image in a certain way, you can at least see what's going on. For this article, I'm going to delve a bit further into the more obscure advanced layer-blending controls that are tucked away in the Layer Style dialog box (see Figure 2). This is definitely one of those areas in Photoshop that qualifies for the "road less traveled" status. Many people rarely venture into these settingsor, if they do, they're not really sure what's going on. If you've ever found yourself at this particular Photoshop crossroads and wondered just what these were for, read a little farther and I'll do my best to demystify these controls.
Figure 2 The advanced blending controls in Photoshop's Layer Style dialog box.
If you want to follow along with the same image that I'm using as an example, I've provided the layered file for you to download for Windows or Macintosh. It may seem like an odd combination of elements, but I've found that if you want to really figure out how something works in Photoshop, it helps to have certain things present in your file. Areas that are filled with black, 50% gray, and white (0, 128, and 255 on the tonal scale) are usually very helpful, as is a spectrum gradient that enables you to see how colors are interacting. This makes it much easier to see what's happening with layer blending, rather than relying strictly on a photographic image. Some of the blending effects are pretty surreal; if you were trying to figure them out using only a photographic layer, you could become very confused!
This setting can be confusing, especially if you are trying to use it on a layer that does not have any layer effect applied to it. Basically, the Fill Opacity setting separates the layer opacity from the layer effect opacity.
The following steps help demonstrate how the Fill Opacity affects the image:
If you are working with the downloaded file, make the car layer active. Notice that it has a drop shadow and a bevel layer effect. Double-click this layer to open the Layer Style dialog box.
In the left column, make sure that you have highlighted Blending OptionsDefault. You can use two separate opacity controls in this panel. The top one, under the General Blending section, is the same as the opacity control at the top of the layers palette. The blend modes that you see here are also the same as those found in the layers palette.
Lower the first opacity to 30%. This controls the Master Opacity for the layer and modifies the opacity for the shadow and bevel layer effects as well. Return this to 100% and now lower the Fill Opacity to 30%. Notice that the layer interior (the "fill") becomes more transparent, but the bevel and the shadow are not affected. (See Figure 3.)
Figure 3 The General Blending Opacity setting affects the layer and its layer effect, whereas the Advanced Blending Fill Opacity affects only the layer transparency, leaving the bevel effect alone.
When you're finished experimenting, return both opacity settings to 100% and exit the dialog box.