Choosing a Transparency Blend Space

Managing color and transparency requires different approaches in Adobe Illustrator and Adobe InDesign. While InDesign allows you to use both RGB and CMYK images and artwork in the same document, Illustrator requires you to choose a single color model (CMYK or RGB) in its documents, and you'll choose one from the very start, in the New Document dialog when setting up a new Illustrator file. For implementing transparency in Illustrator, it doesn't matter whether your document is set to CMYK or RGB; the most recent versions of Illustrator already support transparency, so the only issue you may encounter is a request from your printer to flatten transparency — and usually only if they're using a very outdated version of Illustrator and/or need a different type of file (like an .EPS). InDesign, on the other hand, will let you combine page objects and artwork with grayscale, CMYK, RGB, or LAB on the same page; it allows both CMYK and RGB profile assignments to handle the management and display of CMYK and RGB colors on the same page. Grayscale artwork and images default to using the CMYK profile (the black plate). Any new swatch you create within the document can have its own color mode, and any placed object with an embedded color profile will, by default, be managed by that color profile. A placed image or object without an embedded color profile will use the document's assigned color profile; otherwise, the document color working space will be applied. InDesign may seem more flexible color-wise, but this also means paying attention to more technicalities. Setting the Transparency Blend Space may be considered an obscure feature , and it's definitely highly technical; in fact, most InDesign users don't even know about it! Maybe you've even gotten the following error message dialog: "The document's Transparency Blend Space doesn't match the destination color space specified in the Export Adobe PDF settings. To avoid color appearance changes in the PDF, click Cancel and change either the document's transparency blend space, or the destination color space. Or click OK to continue with the current settings."

So, What Does the Transparency Blend Space Do?

You're aware that you can combine RGB and CMYK images and artwork in the same document in InDesign. Great. But as soon as you introduce ANY transparency into the document (for example, using an effect like a drop shadow, or placing an image with a transparent background), InDesign needs to convert everything in the document to EITHER RGB or CMYK. (This is why you may often see a number of colors or grayscale images suddenly change their appearance on the page when you switch the transparency blend space setting). You can test this right now (assuming you have both RGB and CMYK artwork in your document) by selecting an image or an object on your page, and then clicking the drop shadow icon in the toolbar. If you're using both RGB and CMYK elements within your document, you'll notice an immediate shift in the display on your screen when you click the toolbar icon. This effect is a result of the Transparency Blend Space kicking in. The Transparency Blend Space only affects InDesign document spreads that include transparent objects (or effects requiring some level of transparency to display). If a spread contains any such object or effect, the entire spread will display in the chosen blend space, but won't actually be converted.

Where Do I Find the Transparency Blend Space?

In Indesign, the transparency blend space setting lives at the bottom of the edit menu. You'll notice two options in the flyout submenu: Document RGB and Document CMYK. Most of the time, you'll see this set to CMYK. That's perfect IF you're going to be printing your document on a printing press (such as sending it to a commercial printer). There are two times, however, when you'll want to check and perhaps edit transparency blend space and make sure it's set to RGB.

• Are you working on an interactive document or something that will most often be read on a screen? Something like an annual report that will live on a site like Issuu.com or otherwise isn't going to print, or maybe a product information sheet that will be downloadable from your website? In this case, set the transparency blend space to Document RGB.
• Will you be printing a file, but the final printing will take place on a desktop printer (inkjet, color laser, etc) versus through a commercial printer? If so, you'll want to set your document to the Document RGB transparency blend space. This may not make sense because those machines use CMYK ink and toner cartridges, but unless it's an incredibly high end desktop printer, it's most likely designed to function like an RGB device.

What's Next in InDesign

After setting your transparency blend space (which adjusts the display and your expectations), you'll still want to avoid color issues to make sure your document prints correctly. CMYK and RGB are color models; each also requires a specific color space (Adobe RGB, sRGB, SWOP 2, etc) to be set for printing. You'll need to match the transparency blend space and document color spaces, and also match the destination color space to ensure accuracy in your final printed piece. You can check and/or change the color settings of an InDesign document in a couple of ways:

Assign Profile

This will manage the color space of the document itself, but won't change any existing color values in your InDesign document. You may notice a change in the appearance of the colors on your screen.

Convert to Profile

This both changes the color space of the document and tried to change any existing color values in your file to keep the current display of your colors. (There is still a chance this may change the appearance of colors on your screen.)

What's Next in Illustrator

You won't have the same transparency blend space settings as in InDesign, but still need to make sure that the document color space and export destination color spaces match up. There are a couple of places to check.

Color Settings

Assign Profile

Here, you can choose Working CMYK or another profile.