Calibration vs. Profiling
Colour management systems rely on system-wide calibration as an essential first step in bringing consistency to the color reproduction process. Individual devices cannot be reliably profiled or characterized until they are calibrated. Although these terms are often used interchangeably, they are actually separate processes.
Calibration is the process of modifying the behavior of a device to compensate for factors affecting its response to known stimulus. Calibration is accomplished by sending colour signals to the device and using the measured results to modify its response. In the case of a monitor, when a display is properly calibrated, the gamma, white point, black point, and colour balance are adjusted and corrected to known standards.
An ICC profile is a snapshot of a device’s behavior at a single point in time. Because device performance fluctuates over time, periodic calibration is required in preparation of profiling. Device characterization is the process of creating a mathematical model—or profile— that describes how a device processes colour. Characterization is accomplished by sending known values to the device and measuring its response. The results are then compared, correlated, and used to construct the mathematical model—or profile—which describes the device’s use of colour.
The ICC Colour Management Workflow
The most important issue with regards to colour management undoubtedly will be the need for accuracy of what is shown on their screen. Photographers, DTP'ers and graphic designers all require the need for accurate soft proofing.
Before you can enjoy a colour management workflow in which you can depend on colours looking on-screen as they will be printed, you need a properly calibrated and characterized monitor. Without a monitor that is properly calibrated and profiled, you will not be able to use soft proofing. If you just want to address all the colours your printer is capable of, you can skip this step —but be warned that you will NOT be able to see the effects of your profile on-screen without a profiled monitor.
Monitor Calibration and Profiling: preparations
Monitor profiles are created by using a measurement device to measure a series of colour patches that are sent to the display by the profiling software. The collected data is analyzed and used, along with other monitor attributes (gamma and white point), to calibrate and profile your monitor. Most CRT monitors will enable proper calibration, most LCD monitors will not. Some noteable exceptions are EIZO's high-end range of monitors and Quato monitors.
With most profiling software for monitors, you can choose to create a profile using a full "calibrate before profiling procedure". Unless you are confident the current calibration is good, a calibration is always a good idea to perform before the actual characterization. Note that with some monitors, GretagMacbeth's Eye-One Display 2 will perform a calibration for you automatically.
Because computer monitors fluctuate over time—on CRTs phosphors age and gamma settings shift—periodic calibration is required to ensure the best profile possible. Most profiling applications will allow you to perform a periodical checkup of the profile and the monitor drift. This enables you to only re-calibrate when it is absolutely necessary. Once a monitor is profiled, there are a few points to keep in mind:
Monitor profiles are not interchangeable; they are monitor specific. You cannot use a profile created for one monitor with a different monitor.
Profiles of CRT monitors are based on phosphor measurements and certain information you supply about your monitor—white point, gamma, brightness, and contrast settings. If you adjust a monitor's brightness, contrast, and color controls after it has been profiled, the profile will no longer be accurate. The same applies to LCDs: as soon as the monitor has been profiled, it is best to stay away from the hardware controls.
The appearance of a displayed image is strongly influenced by the ambient lighting in the room. Any increase in ambient light decreases the effective monitor gamut. Profiles should be used under the same lighting conditions that were used when the profile was created. Ideally, your monitor should be in a room with just enough light to create a comfortable viewing environment, and preferably with 5000K light temperature. Avoid using bright lights or intensely colored objects near your workstation. These variables can change your perception of colour.
Before you begin profiling your CRT monitor, do the following:
- Turn on your monitor, and allow it to stabilize by letting it warm up for at least one hour prior to calibrating your display. This will increase the accuracy of color readings.
- Become familiar with your monitor's brightness, contrast, white point, and RGB color controls. Set the monitor bit depth to maximum resolution.
- Set your desktop pattern to a light gray or as close to neutral as possible.
- Connect your colorimeter or spectrophotometer, and be sure the proper drivers are installed.
- Set your room lighting to the level you typically use when evaluating images. Avoid bright lights; they may affect the profiling process. If you are creating a profile to use when evaluating images for press, turn the room lighting off with the exception of your viewing booth. In this manner, you replicate the conditions used to evaluate proofs.
- Clean the surface of your display following the manufacturers recommended procedures. Dust and fingerprints can foul readings. DO NOT use household glass cleaners. They can damage the display surface.
- If applicable, clean the suction cup(s) on the colorimeter using a damp lint-free cloth. Dust on a cup can cause the colorimeter to loose suction during the measurement process.
- Do not use other calibration or gamma correction software, or functionality may be impaired. Remove any other monitor calibration or gamma correction software from your system. If you are using a Windows version of Adobe Photoshop, uninstall the Adobe Gamma Loader. Do not remove the Adobe Gamma Control Panel.
- For the profiling itself, follow the instructions of your profiling package. With LCD monitors, the warming phase is less of an issue, although LVD displays should be allowed to warm up prior to measuring as well. With LCD displays, there is an additional precaution you should be aware of: do not use the suction cups attached to your measuring device as these will damage the surface of the monitor at removal time. All colorimeters currently on the market, have alternatives for the suction cups used on CRT monitors.
- Consult your device's manual if necessary.
About White Point
The white point setting used by your monitor determines the colour of your monitor's white. This displayed white can range from warm (yellow-red) to cool (blue) white. A colour temperature of 5000 K appears yellowish, and a colour temperature of 9300 K appears bluish.
When selecting a white point, your objective is to choose the setting that is closest in color temperature to the white point of the lighting in your room or viewing environment. If you are a graphic or industrial designer and view images and proofs using a viewing booth, choose the white point that matches the temperature of the lights used in the viewing booth. Standard viewing booths use 5000 K to 6500 K illuminants. Once you've determined the white point of your viewing environment, you can set the monitor's white point to match. (Note that not all monitors have a white point adjustment.) Photographers should create a profile for every illuminant their work will be displayed with. This means they should be able to select from monitor profiles for their studio environment, for the exhibition environment, museum, etc., in order for them to judge colour adjustments accurately for every purpose.
A white point of 5000 K or 6500 K is typically used in most settings and for general designing usage. There are varying intensities of simulated daylight.
| Light Source | Degrees K |
| Match Flame | 1700 |
| Candle Flame | 1850 |
| 40-Watt Incandescent Tungsten Lamp | 2650 |
| 75-Watt Incandescent Tungsten Lamp | 2820 |
| 100-Watt Incandescent Tungsten Lamp | 2865 |
| 200-Watt Incandescent Tungsten Lamp | 2960 |
| 500-Watt Incandescent Tungsten Lamp | 2980 |
| 1000-Watt Incandescent Tungsten Lamp | 2990 |
| 3200-Degree Kelvin Tungsten Lamp | 3200 |
| “C.P.”(Color Photography) Studio Tungsten Lamp | 3350 |
| Photo Flood or Reflector Flood Lamp | 3400 |
| Daylight Blue Photo Flood Lamp | 4800 |
| White Flame Carbon Arc Lamp | 5000 |
| Xenon Arc Lamp | 6420 |
| Daylight | 6500 |
| Sunlight: Sunrise or Sunset | 2000 |
| Sunlight: One Hour After Sunrise | 3500 |
| Sunlight: Early Morning | 4300 |
| Sunlight: Late Afternoon | 4300 |
| Average Summer Sunlight at Noon (Washington DC) | 5400 |
| Direct Mid-summer Sunlight | 5800 |
| Overcast Sky | 6000 |
| Average Summer Sunlight (plus blue skylight) | 6500 |
| Light Summer Shade | 7100 |
| Average Summer Shade | 8000 |
| Summer Skylight (will vary from) | 9500 to 30000 |