Viewing the Transparency Grid

How do you indicate nothing? Specifically, how do you indicate which areas of an image are actually transparent and will appear invisible when placed in a page layout? A long time ago Adobe came up with the image of a checkerboard grid to indicate transparency. Wherever you see this transparency grid, you know you are looking at nothing.

Transparency Grid Preferences

Photoshop, Illustrator, and Acrobat all have a transparency grid, which you can use to help see the effects of transparency.

To change the appearance of the grid, in Photoshop, choose Photoshop > Preferences > Transparency & Gamut (Macintosh) or Edit > Preferences > Transparency & Gamut (Windows). This opens the dialog box where you can adjust the colors of the checker-board pattern that makes up the grid (Figure 11-16). You can also change those colors so that they are easier to see for certain images. The None setting in the Grid Size menu turns off the display.

Figure 11-16. Transparency grid controls in Photoshop.

Illustrator and Acrobat allow you to change the status of the transparency grid, but not its colors or size. In Illustrator, choose View > Show Transparency Grid. In Acrobat, choose Acrobat > Preferences > Page Display (Macintosh) or Edit > Preferences > Page Display (Windows). Check the option for Display Transparency Grid to see the transparent areas in the Acrobat file.

InDesign doesn't have a transparency grid on the document pages, but when you apply an effect or place an image that requires flattening, a checkerboard pattern appears on the spread for those pages.

What Requires Flattening?

Both Illustrator and InDesign provide a Flattener Preview that helps you determine if flattening will be necessary in a file. (This is discussed in "Previewing Flattening in Illustrator" and "Previewing Flattening in InDesign" in Chapter 16, "Preflighting and Printing.") However, rather than relying totally on the software to tell you where flattening will occur, it's a good idea if you also understand some of the principles.

Flattening: How the Magic Works

Many years ago Sandee saw Dave Thomas, the actor and magician, do a magic trick where he appeared to stick a knitting needle through his arm. The audience screamed in horror as the blood dripped from the wound. Thomas kept insisting, "It's a trick! It's just a trick!" But it didn't matter. The audience still screamed.

Transparency is similar. Uneducated users scream in horror at the thought of transparent objects mucking up their print output. But the truth is there is no actual transparency in PostScript. Every file that uses transparency has to be flattened before it can be printed. It's a trick! Transparency is a trick!

As discussed in "How the Transparency Flattener Works" in Chapter 16, "Preflighting and Printing," all the images that have some form of transparency need to be broken down into pieces called "atomic regions." These pieces can be vector shapes or raster images.

You can usually predict which transparency effects will create vector shapes and which ones will create rasters. All the "warm and fuzzy" effects such as shadows, glows, and feathers must create raster images. All transparency effects that overlap raster images will themselves create rasters. All objects that are rasters will create new raster images when effects are applied to them.

There are some situations, though, where you may not be able to anticipate if the flattened artwork will be vectors or rasters. Any time you work with gradients or gradient mesh objects, the final result may be vectors or rasters. This is where the Flattener settings are so important.

When Does Photoshop Flatten?

Many people think that it is the presence of layers in a Photoshop file that initiates the flattening process. That's not the case; it's the status of the transparency grid that triggers flattening. If the transparency grid in Photoshop is visible, then the file requires flattening when placed into InDesign (Figure 11-17). If the grid is not visible, the file may contain layers, but the flattener is not applied to the page. This status can change if you change the layer visibility in InDesign.

Figure 11-17. When the layers in the Photoshop file completely hide the transparency grid (top), flattening is not necessary when the image is placed into the InDesign file. When the transparency grid is visible in the Photoshop file (bottom), then flattening is necessary.

Illustrator and InDesign Transparency Commands

Unlike Photoshop, Illustrator and InDesign require flattening whenever you apply any transparency commands to your document. As shown in Figure 11-18, it doesn't matter if you can see the transparency grid (available in Illustrator) under the artwork or not. Any time you apply one of the effects, flattening automatically comes next.

Figure 11-18. Both these examples of a transparency effect in Illustrator require flattening when output from Illustrator or InDesign.

When to Apply Special Effects?

With drop shadows and other transparency effects in all three applications, you may wonder where you should apply transparency features. Should you apply drop shadows in Photoshop or wait and apply them in InDesign?

As a general rule, Adobe recommends adding transparency features as late in the process as possible. So with something like a drop shadow, if you place a Photoshop image into InDesign, you should apply the drop shadow to the image in InDesign.

This is because blending modes from Photoshop do not separate correctly when the Photoshop artwork is placed into Illustrator or InDesign. Similarly, blending modes applied to Illustrator artwork won't separate correctly when placed into InDesign. So a drop shadow which relies on the Multiply blend mode to create a realistic effect will not blend in with any InDesign objects below.