Declining costs and increasing quality and size of flat-panel LCD monitors have made it possible for many digital sign shops to rely on monitor previews, or “soft proofing,” to check color before final output. Today you can get a 24-inch flat panel monitor for as little as $200. These monitors do not take up much depth on the desktop and are light enough to carry in one hand. Furthermore, their large size, color stability, and flicker-free illumination make LCD displays great for soft-proofing. However, with LCD monitors, it is not enough to achieve an accurate soft-proofing, you still need to calibrate the display and pair its color profile with an accurate printer profile.

When choosing a display, you can opt for a low-cost unit from your local electronics store or a high-end display from a prepress dealer. But what’s the difference between the two? And, how do you calibrate both of them?

Monitor Calibration
To calibrate your monitor, you’ll need a low-cost monitor colorimeter. If you have a reflective color measurement instrument for print profiling, it may also be able to read emitted color from monitors. The declining cost of color measurement instruments has enabled many users to afford accurate monitor calibration. In fact, many users have become obsessed in getting the most accurate monitor previews. To the soft-proofing “connoisseur,” accurate monitor calibration is a multi-step process, similar to a gourmet meal.

The old-time color separators agreed on three criteria for image quality, which will help you sort out the monitor calibration process. They wanted (1) good contrast and detail (technically known as tone reproduction), (2) freedom from color casts (gray balance), and (3) accurate hues and realistic color saturation (color correction).

Calibration software enables you to set the monitor’s tone reproduction (gamma) and gray balance (white point). And, the color profile captures the monitor’s “color correction,” or ability to render accurate hues and saturation levels. The trick is, if you can set these values “closer to home” using the monitor’s hardware controls, your profile will be more accurate and longer-lasting.

How to Calibrate a Monitor
Monitor calibration uses a four-step process known as the “4 Cs” of color management (Figure 1 , above).

Step 1: Consistency. In monitor profiling, the first step is to achieve consistency on the monitor by optimizing the hardware settings (if available) for contrast, brightness and color temperature. Optimized settings provide the best image reproduction on-screen.

Most monitor calibration programs help you set the monitor’s hardware or software controls to values close to your calibration aimpoints. This step is known as optimization or, to fit within the “4 Cs,” consistency.

Let’s say you want to calibrate your monitor to a certain color balance, but your monitor has hardware controls that allow settings of 5,000, 6,500, and 9,300 K. Which one should you pick? The best choice is 6,500 K because the calibration curve won’t need to correct the display as much as it would if you set it to start at 9,300 K. A further explanation concerning color balance will be discussed in Step 2.

Without monitor optimization, calibration cannot fix all color discrepancies. For example, if you have a 10-year old CRT monitor and phosphor fading has made it so dim that it is hard to see anything, a monitor calibration program can’t calibrate it because there is not enough brightness and contrast. On the other hand, a monitor calibration program won’t be able to calibrate a monitor with a faulty circuit in the video card that is producing a bright, high contrast display. You must have your monitor aligned as close as possible to your intended calibration levels for successful calibration (Figure 2).

Don’t confuse the optimization of monitor controls with calibration. As long as the monitor falls within a reasonable contrast and color balance range, your color management program should be able to calibrate it. For example, if you want to calibrate to 6,500 K and your monitor’s preset is 6,700 K, it should be close enough to calibrate.

Self-optimizing displays are a recent trend in graphics monitors. Models such as those from LaCie and Eizo (Figure 3) can automatically set the optimum contrast, brightness and color temperature using an emissive colorimeter.

Step 2: Calibration. Calibration means achieving a known standard of performance. For monitors, the standards are contrast (gamma) and color balance (white point).

Gamma is measured on a scale of 1.00–2.40; the higher number representing darker contrast. Macintosh‘s established gamma is 1.80, while Microsoft uses 2.20. Since either setting can be used on either platform, most color management equipment manufacturers recommend a gamma value of 2.20.

White point is measured on a scale of 5,000–9,300 Kelvin (K). Lower values are redder, and higher values are more blue. When the white point is set to “Native,” the program uses the monitor’s current white point without changing it. (Figure 4).
Graphic artists who plan to print on offset presses typically prefer to use 5,000 K, which is the ISO standard for the graphic arts. However, since viewing standards were written for fluorescent light bulbs and monitors are generally dimmer, many users find that 5,000 K is too warm and prefer to use higher settings like 5,500 K or 6,500 K.

Monitor calibration creates a curve that gives the monitor a specified value. The calibration curves are saved to the computer’s video card.
On Windows, the calibration curves are downloaded to the video card upon startup. If you switch profiles, the display won’t change because the new calibration curves won’t be loaded until you restart the computer. Macintoshes dynamically load calibration curves each time a monitor profile is selected, so when you select a new profile, the display’s contrast and color balance will change right away.

Step 3: Characterization. After optimizing and calibrating, the monitor calibration program will create an ICC profile. Characterization, or setting it as the standard profile, is the third step in the “4 Cs.”

To help keep track of your profiles, it is recommended that you create a monitor profile naming convention. Including the monitor name, calibration values, and creation date will help you locate specific profiles based on the type of monitor, the specific values, or the date it was created. For example, if you calibrate a Sony monitor to 6,500 K and gamma 2.20 on Sept. 2, 2008, you could name it “Sony_D65G220_090208.icc.”

Step 4: Conversion. The final “C” in the calibration process is converting the file from the standard working space, such as Adobe RGB or sRGB, to your monitor’s profile. This final step will confirm “what you see is what’s in the file” (WYSIWIF). Be sure to convert images captured on a scanner or digital camera to a standard working space profile, such as Adobe RGB, instead of to the monitor profile. Graphics applications that are ICC compliant, such as Adobe and Quark, will automatically convert to the display profile. (Figure 5).

A calibrated display does not necessarily ensure that prints will match the screen. Color management can convert documents from their standard working spaces to the monitor profile for display, or to the printer profile for output. Either device will match the original to the best of its ability. To view soft-proofs on-screen, the program that is being used must have a soft-proof function that links the printer profile to the monitor profile. An example is Photoshop’s View > Proof Setup command, which enables you to specify the printer profile to be used for the on-screen previewing.

How to Check a Monitor Profile
After you have completed each of the steps in the “4 C’s” of color management—consistency, characterization, calibration and conversion—you should verify that the profile you created is accurate.

Evaluating color. The best way to do this is by comparing a test photo displayed on the monitor with a printed sample of the photo. Ideally, the print should be viewed next to the monitor in a 5,000 K viewing booth, and printed with a printer profile that you know is accurate. It should also represent the type of work that you print, such as portraits with fleshtones, products with memory colors such as reds, greens and blues that people “know” how they should look, gray scales, highlights, and shadows (Figure 6a).

Evaluating shadow reproduction. To check your monitor’s ability to render shadow detail, create the following documents in Photoshop:

1. A square with three gray levels: RGB = 0 0 0, 8 8 8, and 12 12 12 (Figure 6b above). Check that your monitor can resolve all three gray levels.

2. A blend from black to white (Figure 6c above). Make an empty document, 6 in. wide x 1 in. high, 72 ppi. With the ‘Gradient Tool’, make a blend from black (RGB 0 0 0) to white (256 256 256). Check that shadows and highlights can be resolved.

To check that your monitor profile is working, view these test images with the profile turned on and off. To turn off the monitor profile, select View > Proof Setup > Monitor RGB. This shows the image with the calibration, but not the profile. To view with both the calibration and the profile, uncheck Proof Colors.

Advanced Features
Several advanced monitor calibration features are available on various monitor-calibration programs. These advanced features could be valuable if you use multiple monitors in the same studio, or if you regularly compare screen previews to printed samples.

Ambient Light Measurement. To ensure you are viewing the print in the same light as the monitor, use a colorimeter or spectrophotometer with an ambient light head to check the lighting of the surround. Ideally prints should be viewed in 5,000 K standard viewing conditions for comparison to monitor previews.

Luminance adjustment. If you want all of the monitors in your studio to display the same brightness, you may find the ability to set monitor luminance valuable in candelas per square meter (cd/m2).
An image viewed simultaneously on three profiled monitors should match to the best of the monitors’ capabilities. However, the monitors’ brightness levels and background may look different.

Profiling Dual Displays. If you use more than one monitor on the same computer, you may want to profile both displays. Monitor calibration values are stored in the video card, so if your video card only supports the calibration of one monitor, you can only calibrate one of the displays.
There are a few options for overcoming this. You can calibrate one color-critical monitor and use the uncalibrated monitor for tool palettes, use a separate video card for each monitor, or use a video card that supports calibration of multiple displays.
Today’s Macintosh computers support multiple monitor calibration. PC video cards that support multiple monitor calibration are available from Matrox (www.matrox.com) and ATI (www.ati.com).
To use network monitor calibration, you must first pick one display as the “standard.” Save the calibration values, then use values as a standard for the other monitors. This ensures closer matching on multiple machines.

High- vs. Low-End Displays
What are the advantages of buying a high-end display that costs several thousand dollars, versus one from the electronics store that costs a few hundred dollars? To compare displays, we have profiled a $200 Samsung and a $600 24-inch Acer displays from the electronics store, an $800 Apple Cinema display, and a $3,500 high-end EIZO display. To round out the data, we also included a MacBook.

As you can see in a gamut graph (Figure 7), the three of the large displays all had about the same-size color gamut, while the laptop’s gamut was much smaller. The two low-end and one high-end monitor displays all had contrast, brightness, and color temperature controls that could be used to optimize prior to calibration. The high-end display interfaced directly with the color measurement instrument to optimize itself prior to calibration.

The value of a high-end display is consistency, which is important in using multiple displays. Jason Lisi, assistant professor in Ryerson’s School of Graphic Communications Management, said, “If you buy two or more high-end displays, they are more likely to agree with each other. Also, if you buy one high-end display today and another one next month, the two displays purchased at different times are more likely to match.”

Joey Sanchez, marketing specialist with Eizo Nanao Technologies, Inc., which makes high-end displays, said, “Eizo displays provide a hardware-based color calibration that controls the monitor’s color look-up table and does not rely on the graphics card for calibration. Further, each monitor is individually factory-adjusted to the optimal gamma curve measurement using highly sophisticated equipment so there is consistency between different monitors. Also, the ColorEdge CG301W has a unique feature, the Digital Uniformity Equalizer, which compensates for inconsistencies across the screen. With this feature, the monitor constantly reads color on the back end to ensure consistent corner-to-corner color. All of these added processes are controlled by EIZO’s own patented chip circuitry and are expensive processes to put in place, thus making the monitor more expensive. We have always felt that the added benefits outweigh the price tag and save the user money over time with less necessity for re-working images to get accurate color matching.”

When cost is a concern, a low-end display can be considered, but may not be as accurate as a high-end display over time or from point-to-point on the screen. Despite the fact that one of the low-end displays has a slightly lower gamut than other high-end displays, these monitors might be acceptable as long as their color gamut is larger than that of the output device.

Conclusion
Taking the time to calibrate your monitor so that what you see on the display matches what you will see when you print can save you a considerable amount of time and money.