Frequently asked questions
This section list questions frequently asked about color management
5.1. What's the difference between calibration and characterization?
Many people are initially confused about the difference between calibration and characterization. Calibration is the process of modifying the color behavior of a device. This is typically done using two mechanisms:
- Changing controls or internal settings that it has.
- Applying curves to its color channels.
The idea of calibration is to put a device is a defined state with regard to its color response. Often this is used as a day to day means of maintaining reproducible behavior. Typically calibration will be stored in device or systems specific file formats that record the device settings or per-channel calibration curves.
Characterization (or profiling) is recording the way a device reproduces or responds to color. Typically the result is stored in a device ICC profile. Such a profile does not in itself modify color in any way. It allows a system such as a CMM (Color Management Module) or a color aware application to modify color when combined with another device profile. Only by knowing the characteristics of two devices, can a way of transferring color from one device representation to another be achieved.
Note that a characterization (profile) will only be valid for a device if it is in the same state of calibration as it was when it was characterized.
In the case of display profiles there is some additional confusion because often the calibration information is stored in the profile for convenience. By convention it is stored in a tag called the vcgt tag. Although it is stored in the profile, none of the normal ICC based tools or applications are aware of it, or do anything with it. Similarly, typical display calibration tools and applications will not be aware of, or do anything with the ICC characterization (profile) information.
5.2. Missing information for whole-screen color correction
Unfortunately, many vendor-supplied ICC profiles do not include the information required for whole-screen color correction. These profiles can still be useful for applications that can do color compensation, but you will not see all the colors of your screen change.
In order to create a display profile, which includes both calibration and characterisation data, you will need to use a special color measuring instruments callled a colorimeter or a spectrometer.
5.3. Which color measuring instruments are supported?
GNOME Color Manager relies on ArgyllCMS to support color instruments. Thus the following display measuring instruments are supported:
- Gretag-Macbeth Eye-One Pro (spectrometer)
- Gretag-Macbeth Eye-One Monitor (spectrometer)
- Gretag-Macbeth Eye-One Display 1, 2 or LT (colorimeter)
- X-Rite ColorMunki Design or Photo (spectrometer)
- X-Rite ColorMunki Create (colorimeter)
- Pantone Huey (colorimeter)
- MonacoOPTIX (colorimeter)
- ColorVision Spyder 2 and 3 (colorimeter)
- Colorimètre HCFR (colorimeter)
5.4. Which target types are supported?
GNOME Color Manager supports the following types of targets:
- CMP DigitalTarget
- ColorChecker 24
- ColorChecker DC
- ColorChecker SG
- i1 RGB Scan 14
- LaserSoft DC Pro
- QPcard 201
- IT8.7/2
5.5. Where do I purchase targets from?
You can purchase targets from well-known vendors like KODAK, X-Rite and LaserSoft in various online shops. Alternatively you can buy targets from Wolf Faust at a very fair price.