It Takes Two
Color management is easier to understand if you can keep one simple rule in mind: A single profile simply describes color data; it always takes two profiles to change the numbers in a document. It's almost always a good idea to embed a profile in your documents, especially if you routinely send files to other folks or you hold onto them for any period of time (remember that as your monitor ages, its colors change). When you embed a profile in a document, you're attaching a description of what actual colors are represented by the numbers in the file, but you aren't changing the numbers themselves. When you ask the CMS to match the color on a device, you need to specify two profiles, one representing where the color came from, the other where the color is going.

Without a profile embedded, a color is simply a bunch of numbers open to very different interpretations, as we saw in Figure 1. When we embed profiles, the CMS can tell that the scanner's RGB 247, 260, 91, the monitor's RGB 250, 175, 100, and the printer's RGB 244, 192, 148 all represent the same pale orange with LAB values of 79, 19, 46.

Fully color-managed applications such as Adobe Photoshop and Illustrator add an extra wrinkle. They encourage the use of "abstract" RGB spaces that aren't based on any particular device, and they take the monitor out of the loop by doing an on-the-fly transform of the data that gets sent to the video card, so that the color displays correctly on each individual's monitor. But the underlying process is still the same: The application looks at the source profile (the application's working space) and determines the actual colors represented by the RGB values. Then it looks at the destination profile (the monitor) and determines what RGB values are needed to display those actual colors, and it changes them accordingly.

This approach can cause problems when you go from a color-managed application such as Photoshop to a non-color-managed app like Adobe GoLive, because while Photoshop translates the document's RGB values into monitor RGB, GoLive doesn't; it simply sends the numbers in the document to the screen, so the image looks different in the two applications. But you can use color management to solve this problem, too. Before you transfer your image from Photoshop to GoLive, convert it from your working-space RGB to monitor RGB. Then when you open the image in GoLive, it will look the same as it did in Photoshop.

There are many more ramifications to color management, such as the issue of rendering intents, but if you keep the simple rule in mind -- you need one profile to describe the color, you need two profiles to match the color across two devices -- then you'll find that color management makes sense, and saves a great deal of time and hassle.

Read more by Bruce Fraser.