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© 1998 by Michael Cervantes. All Rights Reserved.
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When I became a freelancer my budget did not let me buy a Mac system, then the standard in the graphic arts industry. Since then, a question travels in my brain and in yours. Why is Mac the standard? After several years of workarounds, dealing with service bureaus (being an inferior PC user according to Mac gospel), and praying to get WYSIWYG printing pieces, I found the secret answer: Gamma 1.8!
The gamma is the value of the exponent of the power function that more closely models the luminance-pixel relationship of the monitor. Almost every monitor has a power function of 2.5. We would think that if we have a formula, then we could create a table with all possible input values and store it as a Look Up Table. This LUT will translate pixel values to our monitor correctly and precisely. Wrong! Gamma correction depends on different factors: the gamma of input devices (scanner, digital cameras, etc.), viewing condition (the room lighting conditions and any object reflecting color in our monitor including our clothes), and printing conditions (weather, paper, ink, press etc.)
When a point is printed, the printed color absorbs more external color than necessary. To correct this, a transfer function similar to gamma is created. Usually this exponent is 1.7. PCs do not have built-in hardware gamma correction, the output signal is 2.5. Mac systems do have built-in hardware gamma correction of 1/1.4 that translates output signal to 1.8. Photoshop does software gamma correction--by default its gamma is set to 1.8--and when applied to 1/2.5 hardware correction output signal match input signal value. That is mainly why Photoshop and the Mac have gained the standard position in the industry.
PC systems, due to clone development freedom, grew faster than Mac. Now we have PCs equal or better than Macs. In our field the main key is a video card with capability for gamma correction, strong 2D, and a 32 bit True Color palette. When gamma correction of 1.8 is set in our graphics card, 1.8 output signal will match input signal. Macs, now we are equal! The first step to calibrate your system correctly is a video card with the characteristics mentioned above. Matrox Millenium II with 8MB or higher, or Number Nine Revolution video cards will help accomplish this step.
Editor's Note: More information on recommended video cards can be found on our Dream PC page.
Images corrected at night will display differently the next morning. Why? Color is defined from the human eye's capabilities. We perceive colors from reflection of lights and the way our brain processes information captured by our eyes. Different lighting conditions will make us perceive colors differently. This is why we see an image that we correct tonight with different colors in the morning.
Having our work space with stable ambience light is very important, preferable low. Our room's wall color affects the way we perceive color in our monitor. If you are serious about your job, your workspace walls, and curtains or shades should be neutral gray, and your Microsoft Windows desktop appearance scheme as well. Now that we have everything in place, let us go into Corel's Color Management System.
Corel's Color Management System is Kodak Color Sync 2, used by Adobe applications, Windows 98, and Mac OS. Corel Color Manager 7 and Corel Color Profile Wizard 8 are the same systems with little differences in the way dialog settings display. I'll be using version 8 for this article, but those running version 7 can easily compare and apply this method.
Figure 1 |
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Run Corel Color Wizard 8 to get the dialog box shown in Figure 1. In Device, select Monitor. In Profile, select Generic Profile, and then click the Tune button.
Figure 2 |
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In the next dialog, Figure 2, you will be asked to specify your monitor manufacturer, model, and any annotation you want to add. Click Next.
If you have a profile for your monitor select copy another monitor characteristic and point to your factory monitor profile. If you do not have any, leave this option blank and click Next.
Since most users do not have a device to calibrate other than their eyes, please do not check this option. Click Next. By the way, there is not an electronic or optical device on the market that compares with our eyes. They are the best calibrators you can find.
Figure 3 |
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In the dialog box shown in Figure 3, select Monitor White Point of 5000 Kelvin. In Gamma section, check identical RGB value, and type 1.8. Now check Red and open your video card application dialog where gamma controls reside. Move this window so that you can see the Corel wizard's red color swatches. The Matrox Millenium II controls are shown in Figure 4 below. Click and hold Red handle and move it until you see that the red color swatches match each other. You have to move away from your monitor to a distance so that you cannot discern the line dithering in the left swatch and/or squint your eyelids until dithering disappears. Repeat this process for Green and Blue selecting them in the Corel Wizard and moving the sliders for your video card. When all three colors are set, click OK. If your video card has numerical gamma controls, set it to gamma 1.8, and do not match swatch color.
Figure 4 |
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From personal experience and information collected from other Corelians, scanner software does a much better job than scanner profiles. I do not recommend using scanner profiles as it usually adds a blue cast to images. Test to see if selecting gamma 1.8 transfer in your scanner software gives a better result than no gamma transfer. If you obtain better results with your scanner profile, then use it.
Place Corel CD#1 in CD drive. In the Corel Color Profile Wizard's main dialog select Device Composite Printer. For Profile, select Get Profile from disk. Point to the /color folder on your CD. Select the eight profiles named Generic US Negative Proofing. These profiles are SWOP (Specifications for Web Offset Printing). SWOP dictates the total ink value in any area. They have different GCR and Total Ink coverage. Light Gray Component Replacement is recommended in most cases since it controls how much of the black in the shadows will be replaced by CMY. This prevents overinking of cyan, magenta, or yellow that will affect the basic hue. When major parts of the image are light and neutral, GCR helps guard against the possibility of color variation on press. Total ink selection depends on press conditions, and the quality of paper. Lesser-quality paper requires less total ink. I highly recommend Professional Photoshop 5: The Classic Guide to Color Correction by Dan Margulis and Makeready: A Prepress Resource by Dan Margulis to increase your knowledge about this topic. Margulis uses Photoshop as a model, but his techniques apply to any professional graphic or image editing application. These books should be nearby all the time as you will be consulting them more than you might think.
Select the same profiles for Separations Printer. Using the same profile in composite and separations may help to match proofing with final press print. I have used these profiles with great results on a Canon 610 inkjet, Xerox DocuColor, Indigo E-Print 100, and to output film from different imagesetters. The film negatives have been used to print to different quality paper, and presses, including full color newspaper ads. Newspaper is the lower quality paper, and the most difficult printing conditions.
Now that Corel Color Manager is set, we need to evaluate our monitor, and fine tune our calibration.
The brightness setting of our monitor affects gamma. This is why it is very important to set it properly. Timo Autiokari developed excellent graphic images to set it properly. Figure 5 is a gamma space 1.8 image optimized to set your monitor gamma, brightness, and contrast properly. Before we start, our monitor should be running for 30 minutes or more. Timo's 1.8 gamma image should be displayed in your browser. Browsers do not have color management systems, which is why it is the proper place to display this image for correct monitor calibration. You can also open it in CorelDRAW or Corel PHOTO-PAINT with Corel's Color Management disabled. If you are running in Windows 98 and you've set the Windows 98 Color Manager System, you'll need to disable it.
Figure 5 |
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Set the Contrast knob of the monitor to maximum. Increase the Brightness knob of the monitor so that the cheeseboard in the 0.4% strip is visible then decrease the Brightness knob until the 0.4% cheeseboard just fades away (at reading distance). Then evaluate the levels 0, 1 and 2 in the Black-Point swatch. The step from level 0 to level 1 should appear similar in amount to the step from level 1 to level 2. In cases where the step from level 0 to level 1 is larger than the step from level 1 to level 2 then decrease the Brightness knob until the steps appear to be equal.
Evaluate the gamma swatches. If they do not show good overall matches then open your video card gamma settings and readjust gamma sliders. Gamma swatches must be viewed at such distance that the dithering is fully averaged by the eye. This is about 2 to 3 meters (Editor's Note: that's 6 to 9 feet for those of us using Imperial measurements) away.
For those with video cards that do not support gamma control, follow the above proceedings using the image in Figure 6 optimized for gamma 2.5.
Figure 6 |
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Open Corel's Color Profile Wizard and follow these steps until you reach the dialog where the gamma swatches reside as shown in Figure 7. Check to see if they match each other when viewed at a distance. If everything is fine, close the Color Profile Wizard and open Corel PHOTO-PAINT.
Figure 7 |
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In Photo-Paint, activate Color Manager. Select any RGB image and convert to CMYK. When conversion is done, we should not notice the conversion. Images should display the same in RGB and CMYK. Now we have a friendly monitor that is more trustworthy than before. We may actually start thinking that Corel's Color Manager really works.
Color Managers are not 100% reliable, they may do well, but under certain conditions they do not. Several colors that display well on your monitor cannot be reproduced in print. They are out of gamut. Do not trust Color Managers, learn to read CMYK. Corel PHOTO-PAINT has a very good Info dialog (Ctrl+F1) and you should use it constantly. Read your shadows, highlights, and neutral colors after a CMYK image is done. Adjust them using curves. Shadows should be C80 M70 Y70 K70. Highlight C5M2Y2K0. By reading CMYK and adjusting them, you can get good prints all of the time. Study the Dan Margulis books seriously and you will become a professional color manager.
Read more articles by Michael Cervantes along with a short bio.
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