Graphics professionals used to be the only ones who needed to worry about the colour accuracy of their monitors. These pros make their living working with images in one form or another. Making sure the colours they see on their monitors are the same colours seen in a project's final form can mean the difference between keeping clients and losing them to other graphics pros.
Display Calibration For Everyone
Nowadays, just about everyone works with images, although not all of our livings depend on them. We keep a library of photos on our Macs; we print images using colour printers; and we use digital cameras that can make capturing images as simple as point and click.
But what happens when that bright red flower you remember seeing in your camera's viewfinder looks a bit muddy on your Mac's display, and downright orange when it comes out of your inkjet printer? The problem is that the devices in the chain - your camera, display, and printer - aren't working in the same colour space. They haven't been calibrated to ensure that a colour remains the same throughout an entire process, no matter which device is displaying or producing the image.
Getting photos on your Mac to match the colours of the original images starts with calibrating your display. The best calibration systems use hardware-based colorimeters, devices that attach to a display and measure the way it behaves in response to various images. Colorimeter-based systems then tweak a graphics card's LUTs (lookup tables) to produce the correct colours.
Hardware-based calibration systems can be very accurate, but most of the time, they're a bit on the pricey side for casual use. But that doesn't mean you have to suffer from bad colours. With a little bit of help from software-based calibration systems, you can ensure your monitor is at least in the right ballpark, so that under careful scrutiny, the images you see on your display are a pretty close match to the original versions.
ICC Colour Profiles
Most displays come with ICC (International Colour Consortium) profiles. The calibration files, usually referred to as colour profiles, tell your Mac's graphics system how to accurately display images. Your Mac is more than happy to use these colour profiles, and in fact comes pre-loaded with dozens of profiles for popular displays and other devices.
When you buy a new monitor, it will probably come with a colour profile you can install on your Mac. "So," you may be wondering, "if my Mac already has and recognizes colour profiles, why do I need to calibrate my display?"
The answer is that colour profiles are just a starting point. They may be accurate the first day you turn on your new monitor, but from that day forward, your monitor begins to age. With age, the white point, luminance response curve, and gamma curve all begin to change. Calibrating your monitor can return it to like-new viewing conditions.
Let's get started with the software-based calibration process, using software that comes free with a Mac.
We're going to use the Mac's built-in Display Calibrator Assistant to run through the calibration process, which is relatively simple. The Assistant will display various images and ask you to make adjustments until each image matches the description. For instance, you may see two grey patterns and be asked to adjust brightness until the two images appear to be of equal brightness.
Before You Start the Display Calibration Process
Before you begin calibrating your display you should take the time to ensure you have your monitor set up in a good working environment. Some obvious things to watch out for include keeping reflections and glare from impinging on the display. Be sure you sit at a 90-degree-angle to the plane of the monitor, and aren't looking at the display from an off-angle. Likewise, the display shouldn't be too high or too low; you shouldn't have to tilt your head for an overall view of the display.
Make your workspace comfortable. Remember, there's no need to work in the dark. A well-lit room is fine, as long as you protect the display from glare and bright reflections.
Start the Display Calibrator Assistant
The Display Calibrator is part of Apple's ColourSync utilities. You can find it by digging through system libraries, but the easiest way to launch the Display Calibrator is to use the Display preference pane.
- Click the 'System Preferences' icon in the Dock, or select 'System Preferences' from the Apple menu.
- Click the 'Displays' icon in the 'Hardware' section of the System Preferences window.
- Click the 'Colour' tab.
Starting With a Colour Profile
If you already have a colour profile in use for your monitor, it will be listed and highlighted under 'Display profile.' If you have no specific profile for your current display, then a generic profile has probably been assigned.
If you only have a generic profile, it may be a good idea to take a look at your monitor manufacturer's web site, to see if there are ICC profiles you can download. Calibrating your display is easier when starting from a specific profile than a generic one. But don't worry; if a generic profile is your only option, the Display Calibrator Assistant can still create a decent profile to use. It just may take a bit more fiddling with the calibrator controls.
Make sure a profile you wish to start with is highlighted.
- Click the 'Calibrate…' button.
- The Display Calibrator Assistant will start.
- Place a check mark in the 'Expert Mode' box.
- Click the 'Continue' button.
The Display Calibrator Assistant starts by helping you set the display's contrast and brightness. (This step applies to external monitors only; it does not apply to iMacs or notebooks.) You will need to access your monitor's built-in controls, which vary from manufacturer to manufacturer. There may be an onscreen display system that lets you make brightness and contrast adjustments, or there may be dedicated control surfaces on the monitor for these adjustments. Check the monitor's manual for guidance, if needed.
Display Calibrator Assistant: Display Adjustment
The Display Calibrator Assistant starts by asking you to turn your display's contrast adjustment to the highest setting. For LCD displays, this may not be a good idea, because doing so will increase the brightness of the backlight, consume more power, and age the backlight more quickly. I've found that it's not necessary to crank contrast up to achieve an accurate calibration. You may also find your LCD display has no, or very limited, contrast adjustments.
Next, the Display Calibrator will display a grey image that consists of an oval in the center of a square. Adjust the display's brightness until the oval is just barely discernable from the square.
Click 'Continue' when done.
The Display Calibrator Assistant will determine the display's native luminance response curve. This is the first step in a five-step process; all five steps are similar. You are shown a square object made up of black and grey bars, with a solid grey Apple logo in the center.
There are two controls. On the left is a slider that adjusts relative brightness; on the right is a joystick that allows you to adjust the tint of the Apple logo.
- Start by adjusting the brightness slider until the Apple logo matches the background square in apparent brightness. You should just barely be able to see the logo.
- Next, use the tint control to get the Apple logo and the grey background to be the same color or as close as possible.
- You may need to readjust the brightness slider as you adjust the tint.
- Click 'Continue' when you're finished with the first step.
The same pattern and adjustment controls will be displayed four more times. While the process appears to be the same, you're actually adjusting the luminance response at different points of the curve.
Repeat the adjustments you performed for the first step above for each of the four remaining luminance response curve calibrations.
Click the 'Continue' button after you finish each of the steps.
Target gamma defines an encoding system used to compensate for the non-linear nature of how we perceive brightness, as well as the non-linear nature of displays. Gamma is probably better thought of as controlling the contrast of a display; what we call contrast is actually the white level. Going one step further, what we commonly call brightness is the control of the dark level. Because the terminology can get very confusing, we will stick with the conventional approach and call this gamma.
Macs historically used a gamma of 1.8. This matched the standards used in print processes, which was one reason the Mac did very well in the printing industry in its early days; it made the interchange of data from the Mac to pre-press much easier and more reliable. Today most Mac users target output other than professional print services. As a result, Apple changed the preferred gamma curve to 2.2, which is the same gamma used by browsers to display images. It's also the native format of PCs and most graphics applications, such as Photoshop.
You can choose any gamma setting you wish, from 1.0 to 2.6. You can also choose to use your display's native gamma. For anyone with a newish display, using the native gamma setting is probably a good idea. For the most part, modern displays have a native gamma setting around 2.2, though it will vary slightly.
The main reason not to use the native gamma setting is if you have an older display, say a year or more old. Display components can age over time, shifting the target gamma away from the original setting. Manually setting the target gamma will let you nudge the gamma back into the desired area.
One last point: When you manually select a gamma, the graphics card's LUTs are used to make the adjustments. If the necessary correction is excessive, it can lead to banding and other display artifacts. So, don't try to use manual gamma settings to push a display too far beyond its native gamma.
Click 'Continue' after you make your selection.
You can use the Display Calibrator Assistant to set the target white point, which is a set of color values that define the color white. The white point is measured in degrees Kelvin, and is a reference to the temperature of an ideal black-body radiator that emits the white hue when heated to a specific temperature.
For most displays, this tends to be 6500K (also known as D65); another common point is 5000K (also known as D50). You can choose any white point you wish, from 4500K to 9500K. The lower the value, the warmer or more yellow the white point appears; the higher the value, the colder or more blue it seems.
You also have the option of using your display's native white point by placing a check mark in the 'Use native white point' box. I recommend this option when using the visual calibration method.
One thing to note: Your display's white point will drift over time as components of your display age. Even so, the native white point will usually give you the best color appearance, as the drift is usually not enough to be noticeable by eye. If you use a colorimeter, the drift will be easily detectable and you can set the white point accordingly.
Click the 'Continue' button.
The last steps of the Display Calibrator Assistant are deciding whether the color profile you created should be available to just your user account or all users, and giving the color profile file a name.
This option may not be present if you're not logged in with an administrator account.
- If you want to share the colour profile, put a check mark in the 'Allow other users to use this calibration' box. This will let every account on your Mac use the calibrated display profile.
- Click 'Continue.'
Name the Calibrated Color Profile
The Display Calibrator Assistant will suggest a name for the new profile by appending the word 'Calibrated' to the existing profile name. You can of course change this to suit your needs. I recommend giving the calibrated display profile a unique name, so you don't overwrite the original display profile.
- Use the suggested name or enter a new one.
- Click 'Continue.'
The Display Calibrator Assistant will display a summary of the profile, showing the options you selected and the response curve discovered during the calibration process.
Click 'Done' to exit the calibrator.