Figure 1: Standard working spaces are places to store color data while you edit it and until you know what you want to do with it, such as display or print it. Standard working spaces have different color gamuts. Experts recommend picking one with a size closest to that of your final output.

Tech Talk

The first three articles in our “Digital Basics” series discussed computer software, vector graphics, and bitmapped graphics. Vector graphics include logos, diagrams, and other artwork defined by points, lines, and curves that can be scaled upon output. Bitmapped graphics (see Part 3 of this series) are scans and digital camera photos that capture the real world using a mosaic of microscopic “picture elements,” or pixels.

So, after you have created or captured all of these vector and bitmapped graphics, how do you get the color to match? The first thing you’ll probably want to do is view them on-screen. But how do you know that the color you see on-screen matches the original file? Then, how do you know that the print you produce will match the file? Digital capture, editing, and output involves a variety of plug-and-play devices that don’t “know about” each other, or their color reproduction capabilities. It’s no wonder that the color may not match from one step to the next. Enter, color management!

THE DEVICE PROBLEM
If you capture an imagine on a digital camera, store it on a computer, view it on a monitor and print it, you might think that all of these devices ought to match in color. The fact is, they all use different primary colors to depict a wide range (gamut) of original colors. For example, a digital camera uses red, green, and blue (RGB) filters to separate colors. A computer stores color files in a mathematically-defined RGB color space. And a monitor displays them using RGB phosphors. Most printers use the opposite colors (cyan, magenta, yellow, and black—CMYK) to represent print colors. It’s practically impossible to synchronize all of these colorants. Hence ICC color profiles were created to enable the closest possible color matching.

HERE COMES THE ICC!
During the desktop publishing revolution of the 1990s digital imaging equipment vendors developed ways of profiling their devices to obtain a better color match. The problem was that each vendor had a different file format that only worked with their software or equipment.

The International Color Consortium (ICC)—founded Adobe, Agfa, Apple, Kodak, Taligent, Microsoft, Sun, and Silicon Graphics—was formed in order to develop platform-independent standards for color profiles. Membership in the ICC (www.color.org), which now includes over 70 member companies, is open to all who work in color management. ICC color profiles are the standard currently used in color management systems.

HOW PROFILES WORK
In color management parlance, each device—whether scanner, camera, monitor, or printer—has a unique set of colorants and reproduces device-dependent color. This means that the color you see depends upon the device with which it’s captured, displayed, or printed.

ICC profiles assume that color will be viewed by humans, whose color vision is the greatest common denominator. Profiles relate the device-dependent color of a scanner, camera, monitor, or printer to the model of human vision known as the profile connection space which is encoded in L*A*B*. A profile is a computer file that can range from 4 K to 4 MB or larger. Profiles can be embedded into images or used as standalone files.

Because the ICC specifies a standard profile format, profiles are neither vendor- nor platform-specific. The same profile can be used by various software programs such as Adobe Photoshop, Adobe Illustrator, or QuarkXPress. It can also be used on different operating systems, including Macintosh, Windows, and UNIX.

PUTTING PROFILES TO WORK
When considering workflow, keep in mind that the goals of using color management in digital workflow are to have:

• accurate, consistent color from original scene, photographic print, or transparency to final output (printed or displayed);
• accurate monitor previews of the original file, final output, or proof; and
• proofs that simulate press sheets or production printers.

These workflow objectives are facilitated by four types of ICC profiles:

• Source Profile—This profile describes the color space in which the image was created or currently exists—generally a scanner or camera profile. It could also be a standard working space profile. Ideally all images with a scanner or camera profile should be converted to a standard working space, and the standard working space profile should be embedded into files, so users can identify it down the line. If you or your customer does not know what standard working space was used, you won’t be able to get matching color.
• Standard Working Space Profile—A standard working space is a place to store data until you know what you want to do with it (display, proof, print, or archive it). Adobe Photoshop and other applications support several standard RGB working spaces, including (from largest to smallest) Adobe RGB, ColorMatch RGB, and sRGB. Most content creators today use the largest, Adobe RGB. Users with CMYK workflows can use one of Adobe’s standard CMYK working spaces, such as U.S. Sheetfed Coated or U.S. Web Coated. Of these, Sheetfed Coated has the larger gamut, but the Specifications for Web Offset Publications (SWOP) is more common. SWOP was the first color specification developed.
• Destination Profile—This profile describes the device or process to which the file will be output. The destination could be a color monitor (for display), an inkjet printer (for proofing), or a production printer (for final output).
• Simulation Profile—Used for soft- or hard proofing, this profile is an ordinary device profile that describes the device or process that the image should look like when proofed. When proofed on a small inkjet printer, for example, the simulation profile would be that of the production printer.

WHERE TO START?
To get more specific, let’s assume that you never heard of color management before, but, like many users, you would like to have faith that the color will match throughout your system.

Standard Working Space. The first decision you’ll need to make is what standard working space to use. The standard working space was first introduced in Photoshop 5 in 1998 and has since been extended to other programs, including Illustrator, InDesign, Quark, and Corel. The standard working space is a place to store color data while you’re editing it and until you know what you want to do with it, such as display it or print it. The two most common spaces are sRGB (“standard” RGB) and Adobe RGB, but there are others.
Experts recommend choosing a standard working space whose color gamut is closest to your final output (see Figure 1). Of the two most common spaces, sRGB has the smallest color gamut. Its goal is not to “leave anyone out” by holding colors that are too bright and saturated for home computer displays. If you use sRGB for a large-gamut inkjet printer, you may not be taking advantage of the printer’s color gamut by getting as saturated output as it can print. Adobe RGB is a larger space that’s more suitable for large-gamut inkjet printers and for printing by sheet-fed lithography. Its disadvantage is that home computer users—especially those with older displays—may not be able to see all the colors. So Adobe RGB may not be the most suitable space for Web work.

Figure 2: Most advanced digital cameras, such as this Pentax K100D, offer a choice of standard working spaces into which they will output color. For the most accurate captures, such as for fine-art or catalog photography, users who have a color management system can make custom camera profiles.

Getting the Color into the Standard Space. There are several ways to get captured and created colors into your choice of the standard working space. Most of today’s more advanced digital cameras offer a selection of standard working spaces—including sRGB and Adobe RGB—into which they will output color (see Figure 2). So you should set the camera to the space you want to use and be aware of its setting. If you have a color management system you can also profile your camera to get the most accurate color match to the original scene or objects.

Photos with no standard working space can have one applied in Photoshop using the Edit > Assign Profile command. This assigns the standard working space you select to the image and will not change the image’s color.

Embedding the Profile. When an image is saved, the standard working space profile can be embedded into the image (see Figure 3). When someone else opens the file, their computer will know which space it’s in and the image will display accurately on their screen.

Figure 3: For the most accurate color, the standard working space profile should be embedded into the image, as shown in Photoshop’s Save as dialog box. This ensures that color will display accurately when the file is opened on another computer.

WHAT’S NEXT?
To get accurate monitor display and printed color, you’ll need to profile your monitor and printer. This may involve researching “canned” or pre-made profiles available from your equipment or media vendor, or investing in a color management system, with a color measuring instrument and software to make your own profiles. As this series continues, we will describe the steps and logic involved in profiling your camera, monitor, printer, and proofer.