When you take a digital photograph and print it on a sign, banner, or some other type of print, you might expect the color to match from the original scene to the print. This is a difficult expectation, though, when the devices you’re working with don’t “see” in color. Digital cameras actually record black-and-white or more accurately red-and-black, green-and-black, and blue-and-black. Printers “see” in cyan-, magenta-, yellow-, and black-and-white.
No wonder they don’t match!

The science of color management came into being in the early 1990s and was slow to be adopted by commercial printers whose primary output process was lithography. When inkjet printing started to boom, with its myriad printers, inks, and media, the large-format industry quickly realized its potential for matching color from input to output.

Common problems that can be solved with color management include:

• The color looks different on the print than it did on the monitor.
• The color in product or copy photos doesn’t match the original.
• The color you see on the monitor doesn’t match the file.
• The color of a proof doesn’t match the press sheet or printer.

The first step in color managing files is to know what the color actually looks like in the file. This requires the file to be in a known standard working space, and that the monitor be calibrated and profiled.

STANDARD WORKING SPACE
Standard working spaces are standardized ICC profiles like sRGB, Adobe RGB, or SWOP CMYK that are distributed with software. They are a place to store color data until you know what you want to do with it—e.g., view, archive, or print it. Standard working spaces were introduced in Photoshop 5, at which time the majority of users had no idea what they were. Reason: Photoshop 4 used Apple RGB without users’ general knowledge.
Standard working spaces have different sized color gamuts and thus affect the appearance of color. So two people can view a file and see the same color, the standard working space profile can be embedded into the file at the time it is saved (Figure 1, at right). When the file is opened, the profile is automatically read by ICC-compliant software, which includes most of today’s applications.

MONITOR CALIBRATION AND PROFILING
The second thing you need to accurately view a file is a calibrated monitor. This requires an instrument capable of reading light emitted by the monitor, and an application to run it.
Monitor profile. In the profiling process, the software displays a series of color patches on-screen that are read by the instrument and used to create a monitor profile. If the monitor profile is set as the standard system profile, applications will read this profile upon startup and use it to display accurate color.
Monitor calibration. Prior to profiling, you should calibrate your monitor to set its appearance to known standards. Standards include gamma, a numerical measure of contrast, and white point, a measure of color balance (warm or cool; see Figure 2, at right). Most monitor calibration utilities allow you to pick a gamma of 1.00–2.20. Higher values indicate greater contrast. When the Macintosh computer was first introduced, Apple chose a gamma of 1.80 as its standard, as they felt it gave the closest appearance to ink on paper. Microsoft chose 2.20 as its standard for Windows. Either value can be set on either platform.

Color temperature values range from 5000–9300 K. Higher values indicate a cooler (bluer) appearance, while lower values indicate a warmer (more reddish) look. Most CRT monitors have a native color temperature of 9300 K, which is quite bluish. This is suitable for viewing text and spreadsheets, but not color. Many graphic arts users choose 5000 K (corresponding to noon daylight) after noting that the ISO standard viewing conditions for graphic arts specify this color temperature for viewing color. However, 5000 K often makes the monitor look dingy and yellow. The reason is that the RGB channels must be balanced to produce neutral white. Blue is the strongest channel and must be reduced considerably in intensity to achieve 5000 K. A more neutral-looking appearance can be achieved by setting 6500 K, which is nearly the same as 5000 K and corresponds to noon sky light.

A more recent trend in color temperature settings has been to use the monitor’s “native” white point (see the color temperature pop-up at right). This is especially useful with LCD displays, which are very stable and typically optimized for graphic arts use. “Native” is the color temperature that the monitor turns out to be after calibrating its contrast (gamma).

Once you have calibrated and profiled your screen, the color management application will ask you to save the profile. A good naming convention for the profile enables you to identify the monitor, settings for white point and gamma, and date the profile was made. For example, “ACD_G220D65_081507.icc” indicates an Apple Cinema Display calibrated to a gamma of 2.20 and a color temperature of 6500 K (D65) on August 15, 2007.

Monitor optimization. Monitor calibration works by creating a set of correction curves that are stored in the ICC profile and loaded into the computer’s video card when you start the computer. These curves adjust lightness, darkness, and color balance to the gamma and color temperature values you selected for calibration.
Some monitors have hardware controls to set contrast and brightness. Contrast, usually indicated with a half-moon icon, actually sets the monitor’s white point. Brightness, indicated with a sun icon, sets the monitor’s black point. Some calibration programs have proprietary algorithms to measure these white and black points and help you to determine optimum settings prior to calibration. While such optimization isn’t essential, it does help maximize the monitor’s color gamut and helps the calibration to last longer.

During the optimization process, the application will ask you to set the contrast to maximum, measure it, and then set it to a value that the program calculates. Then it will ask you to set brightness to the minimum, measure it, and set a calculated brightness value. Some monitors also have hardware controls for color temperature. If these are set in advance, close to the color temperature you want, it will make the calibration more stable and longer-lasting.

Some monitors (e.g., Eizo, LaCie) have an automatic optimization procedure. When a compatible monitor calibration instrument is connected, the monitor will automatically measure contrast, brightness, and color temperature, then set the optimum values.

Other monitors (e.g., Apple) are already optimized for graphic arts use and lack controls for contrast and color temperature. In this case, simply proceed with calibration without first optimizing the display.

PROCEDURE
In this example, assume you have taken a digital photo in JPEG mode and have set your camera to export it in Adobe RGB standard working space (left).

Or, you may have set the camera to take Adobe Camera Raw images that you have opened in a Camera Raw processing software such as Photoshop with the Camera Raw plug-in and assigned a standard working space profile (right). The photo is in a known color space, the first requirement for accurate viewing. Now, to display it accurately, you will optimize, calibrate, and profile your monitor.

1. Optimize the screen.
a. Set white point (contrast), if available, using monitor hardware controls.
b. Set the black point (brightness).
c. Set the color temperature to 6500 K.

2. Run the calibration.
a. Set gamma (1.00–2.20, 2.20 recommended)
b. Set white point (5000, 6500, or native)
c. Run the calibration. The program will:

• display a series of color patches on-screen that are read by the colorimeter/spectrophotometer
• create a calibration file that is downloaded to the video card

3. Create and save an ICC profile.
Concurrent with the calibration procedure, the color management program will take measurements that are used to make an ICC profile that is used to correct color for accurate on-screen viewing. Save the profile using a standard naming convention, e.g., “Monitor_Gamma_WhitePoint_Date.icc.” Verify that the profile has been set as the standard system profile (right).

ADVANCED MONITOR PROFILING
Does it really work?
After creating your monitor profile, you’ll probably want to check it. The best way to do this is to compare the on-screen preview with a color print that you know is accurate. Making a color print requires either that your printer understands standard working spaces or that you have an accurate printer profile for the media used.
Gamma 1.80 or 2.20? Of the two commonly used monitor contrast settings, which one should you use? A 2.20 gamma will make the screen icons and desktop background look darker with more contrast. But, this will have no effect on an image displayed with an ICC compliant application, because the profile will compensate for whatever gamma you have set—as long as the monitor can display the full contrast range of the image. To check contrast, create an image of dark squares with RGB values of 0 0 0 (black), 8 8 8, and 12 12 12 (dark gray).
Display the image using your monitor calibration and profile. If you can distinguish all three squares, your monitor can render shadows with the contrast you’ve set. Also, create a B&W gradient of RGB values from 255 255 255 (white) to 0 0 0 (black). If you see a smooth transition, the contrast setting is able to render highlights and shadows.

I want them all to match! If you’re using multiple displays to get more screen “real estate,” you probably want both screens to match. Or perhaps you have multiple workstations in your shop and you want them all to match. Theoretically, if you calibrate side-by-side screens to different gammas and white points, their backgrounds will look different, but any images displayed with an ICC-compliant application should look the same. Reason: the ICC profile compensates for the gamma and white point settings. To get the closest match on two screens, of course, you should calibrate both to the same gamma and white point. Even then, they may look different due to different luminance levels. Luminance is controlled by the screen’s black point setting (brightness, the sunshine icon). Monitor calibration programs have luminance adjustments that are measured in candelas per meter squared (cd/m2). The purpose of these adjustments is to help make two screens look as close as possible by setting them to the same luminance value.

What went wrong: the calibration or the profile? Sometimes things go wrong in monitor profiling and the screen looks “whacked out”, posterized, color-casted, or for some other reason incorrect. The problem may be with the calibration (gamma, white point, luminance) or with the ICC profile. To turn off the profile and view an image with the calibration settings only, open the image in Photoshop and select View > Proof Setup > Monitor RGB.

If the image still looks incorrect, the problem is with the calibration and not the profile. This may be due to a software conflict, incompatibility of the video card and calibration software (check for firmware updates), or a faulty calibration instrument.

In conclusion, a calibrated and profiled monitor gives you a true “window” to accurate color, as long as your file has an embedded standard working space. On my faculty Web site (www.ryerson.ca/~r3adams/signbusiness) I have placed several white papers on color management. One describes standard working spaces, while another details the monitor calibration process.

(Click here to read Part 2 of this article series.)

(Click here to read Part 3 of this article series.)