Colormanagement Primer Part 4: Calibrating
Calibration is the act of changing the behaviour of a device to best match the desired colors. Some devices such as monitors and printers can be calibrated, some such as scanners and cameras cannot. Only devices whose behaviour can be changed can be calibrated.
However, as long as a device is stable, it can be profiled. That is: we can produce a color profile and use it to fit the device in our color managed system. Stable means that the device produces the same colors in the afternoon as it did in the morning. Which is true for most monitors and inkjet printers, but not necessarily true for many a laser printer.
How can we profile and calibrate?
Calibrating a monitor is done with a calibration utility that can either be hardware or software. A hardware calibration utility is more accurate but also more expensive than software calibration. Hardware calibration is recommended for professionals such as people in the graphics industry, designers, photographers, etc. The rest of the world may be happy with a free software calibrator such as the Apple calibration utility which is built into every Mac, or with Calibrize for Windows. A software calibration utility depends on the human eye to measure the monitor. The result may not be expert grade, but it will surely enhance the performance of your monitor and will bring you at least in the right color ballpark. Most utilities calibrate and profile in one go.
Printers are profiled through measuring a printed target and then generating a color profile. Unfortunately, the process of profiling a printer is often rather laborious and requires an expensive measuring device. It involves measuring up to hundreds of printed color patches. However, most low-end printers ship with 'canned' color profiles. These profiles are provided by the manufacturer of the printer. They generally do an acceptable job, as long as you stick to the ink and paper of the same manufacturer.
Most scanners cannot be calibrated. But profiling a scanner is quite easy, as long as you have the right (generally expensive) software. It involves scanning a target and running the resulting image file through profiling software. It will produce a color profile in a few seconds.
A digital camera could be regarded as a small scanner with a lens fitted in front of it. Like a scanner, a camera cannot be calibrated. A camera can be profiled, but its use is limited. The difference between a camera and a scanner is that a scanner has its own light source which always has the same angle to the scanned target. This makes the colors of a scanner predictable. After all, color involves a colored surface as well as light. If the light changes, colors will change too and all bets are off with regard to color consistency. This means there's no way you can profile a camera to have consistent colors in all circumstances. However, a camera profile is useful because at least it will provide you with predictable camera behaviour. A camera profile takes out some of the guesswork out of the process, but not all.
A camera profile could perhaps be compared to film, back in the olden days of analogue photography. You would use a film best suited for the task at hand. For exterior you would use another film than for interior, with dim light another film than with bright light, etc. The same goes for camera profiles. You could perhaps make a profile for each different task. Making a profile is actually quite simple, once you have the right gear. So there nothing holding you back from making several profiles instead of one.
Traveling into Color Space
Now what? (suggestions for a follow-up)
Calibrize's Color Management Primer is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 Netherlands License.