Transparency

Adding effects such as ghosted areas or drop shadows is an easy way to add visual interest to images. Such effects are no longer limited to Photoshop, but as you step outside Photoshop to incorporate those effects, you'll encounter some challenges. Since you can incorporate Photoshop files into Illustrator drawings and Adobe InDesign or QuarkXPress pages, it's important to realize that you're governed by the limitations of those programs. Just because Photoshop can handle an effect doesn't mean that other programs can interpret that content correctly.

For example, Illustrator and InDesign both honor transparency in placed Photoshop files, but neither program correctly handles Photoshop blending modes. Transparency and blending may sound like interchangeable terms, but they're not.

Transparency is expressed in percentage opacity. For example, a white square with 20-percent opacity allows what's underneath to show through at 80-percent strength. Opacity settings in a Photoshop file are honored by InDesign and Illustrator, which is why the dandelion in Figure 9.15 appears silhouetted when placed in an InDesign layout.

However, blending modes involve much more complicated math. For example, drop shadows created in Photoshop by selecting Layer > Layer Style > Drop Shadow are set to use the Multiply blend mode with anything they encounter in Photoshop. This results in a realistic darkening of underlying image areas, but only within Photoshop.

Unfortunately, neither Illustrator, QuarkXPress, nor InDesign can understand blending modes within a Photoshop file. So drop shadows created in Photoshop do not interact correctly with elements underneath when they're placed in Illustrator or InDesign (Figure 9.5). Instead of darkening underlying elements, Photoshop shadows knock out the shadow area.

Figure 9.5. A Photoshop shadow behaves correctly within Photoshop (left). But when the image is placed in another application, its shadow incorrectly knocks out underlying color rather than darkening it (shown on the right without the black plate).

One solution is to do what we've done for yearscombine the elements by placing them on various layers in a Photoshop file. After combining the objects, shadows, and underlying elements in Photoshop, save a layered working file for editing, and then place a flattened image in your final document. Although any changes will require you to go back two generations to the working file (and will require keeping track of both the working file and its descendant), this workflow has been used for years.

If an element requires a simple, soft-edged drop shadow, don't create the shadow in Photoshop. Instead, wait until the image is placed in Illustrator or InDesign and create it there, since both applications handle their own shadows correctly. If you're doing your final layout in QuarkXPress up through version 6.5, you can use a third-party XTension to create the shadow, such as ShadowCaster from Quark, Inc. In QuarkXPress 7.0, use the built-in Drop Shadow feature (Item > Drop Shadow).