It all started when images on my 24" Dell monitor started looking odd. I received files from a client that should have been a certain color, but that didn’t match a sample printed with the same color. In addition, after editing the images and sending them back to the client, it turned out that the colors he saw had changed as well. We narrowed the issue down to the color profiles that were being used on our different computers.
Color profiles are a very complex topic, and I don't plan to go into much detail here, other than to say that the different programs we were using treated the color profiles differently, either using them when editing images or not. However, this color discrepancy prompted me to look into why my monitor was showing different colors, and how to get them to coincide, as much as possible, with those my client was seeing, as well as with another Mac I use.
Basic color calibration
If you're an amateur photographer, if you like to watch videos on your Mac, or even if you're a gamer, you should consider calibrating your display. Macs use a default color profile—a group of color settings—for each connected display. But if you find that these colors look odd, or don't match the colors of real objects that you can compare to on-screen photos, you can make changes by creating your own color profile.
Open System Preferences and click the Displays icon. If you have multiple monitors, a separate window will appear on each. Click the Color tab and you'll see a number of color profiles. If you check "Show profiles for this display only," you'll see those that can be used with your monitor. (Ignore the others; if you know what they are, you'll know whether you need to use them.) If the selected profile is not ideal given the possible color response of your display, you’ll want to calibrate the monitor.
Click the "Calibrate..." button. This opens the Apple Display Calibrator Assistant, a tool that will walk you through some simple operations to help you create a color profile. You don't need any technical knowledge; you just need to move a couple of sliders on the screen and compare things you see.
Check the box for Expert Mode on the first screen, then go through the different screens and follow the instructions. Don't worry about getting everything perfect; you'll be able to go through the process again if you don't like the results. What you're doing in this process is making subtle adjustments for a number of color settings—finding out exactly how much the colors of your display are "off" from the ideal colors. When you've completed these adjustments, you'll find two screens where you may or may not want to make changes.
One of these screens is for the "white point," which is the color temperature of the white on your screen. You shouldn't change this from the default, or D65, unless you know why you want to change it. (Go ahead and try; you'll see what it does right away.)
Then there's this thing called gamma. According to this Wikipedia article "Gamma correction, gamma nonlinearity or gamma encoding . . . is a nonlinear operation used to code and decode luminance or tristimulus values in video or still image systems." Gamma settings can vary from device to device, and, until Snow Leopard was released, Macs used a target gamma of 1.8, as opposed to Windows PCs, which used a setting of 2.2. This affects the way images appear on screen; the richness of colors and the overall density and contrast are different. Also, if you're designing for the web, you'll want to see what the majority of your viewers will be seeing, so that gamma setting makes more sense. (You can see concrete examples of different gamma settings on this web page by photographer Gary Ballard. This Apple document discusses the use of different gamma settings.) For most uses, you should stick to 2.2.
When you've finished going through the Calibrator Assistant screens, name your profile, click OK, and you'll see the new look of your monitor. Does it look better? Does it solve any specific color issues you were experiencing before? (Don't forget, it may take you a while to get used to it.) If your monitor does look better, then you're fine. If not, you have two choices: calibrate it again, paying more attention to each color setting, or try calibrating it using a hardware color calibrator.
Using a hardware color calibrator
A hardware calibrator is a small device with a colorimeter—a sensor that detects colors—with a USB cable. You connect it to a USB port on your computer and hang it in front of the display. I tried two color calibrators from X-rite, the $129 hueyPro, and the $176 i1Display LT. The former is designed to remain connected to your computer, and it adjusts the brightness of the monitor as the ambient light changes; the latter has a colorimeter that examines more colors during the calibration process. What color calibrators do is examine the actual color response of your screen as their software displays test colors, then adjust the color profile to make those colors match the norms they are meant to represent. (Note that some camera stores rent out color calibrators.)
After using these devices I noticed several things. First, the resulting colors varied from one device to the other. On my MacBook Air, the hueyPro gave me profiles that were purple-tinged, while the i1Display LT resulted in natural looking colors. (The grays in Apple's System Preferences are a good barometer for variations in overall hue.)
Second, I was unable to get both my Dell monitor and my MacBook Air to match, using either of the devices. Whether or not this was a weakness of the Dell monitor is not clear. While the profile from the i1Display LT on my MacBook Air was very close to what I had done manually, this was not the case on the Dell.
Calibrating your display is a good idea for all users, and those who work with color should consider using a hardware color calibrator, especially if they need to get stable colors across monitors. However, you should bear in mind that they have limitations, and low-priced devices may not be the ideal solution.
Senior contributor Kirk McElhearn writes about more than just Macs on his blog Kirkville.