4.9 A Review of the Profile Classes
Alan Martin
We’ve now touched on the four types or classes of profiles: display, input, output, and device link. What traits do they have in common? They are:
- Specified by ICC-defined file formats
- Contain colour tables
- Have device colour values associated with device independent colour values (PCS)
- Use a measuring device (spectrophotometer) and targets for creation
- Require a specified rendering intent
- Have standard OS library locations
There are also some unique characteristics for each profile class that help define the role they play in the overall colour management process. The display class of profiles:
- Have no separate, tangible target: the device ‘is’ the target
- Can affect device behaviour
- Are mostly integrated with device calibration
The input class of profiles:
- Are unidirectional: A to B table only (device values to PCS)
- Are able to exclude any external measuring (with a supplied TDF)
- Ensure that the target’s job is tell us how the device ‘sees’ the target
Output (and device link) class of profiles:
- Use CMYK (versus RGB for display and input)
- Have black handling settings
- Have the largest and most complex colour tables
- Ensure the target’s job is to tell us how the device ‘makes’ the target
- Provides preview capability for upstream editing
We also discussed the functions of a profile in the colour equation. The two functions are source and destination. A source profile is a profile used to convert device dependent RGB or CMYK information to a device independent colour space (Lab). A destination profile is a profile used to convert information from a device independent colour space (Lab) into a device dependent colour space of an output device (RGB or CMYK). You can think of the source profile as the colour reference or the place from which our desired colour appearance comes. The destination profile describes the location where we are producing colour in the current pairing of devices. If we want a proofer to simulate the colour behaviour of a particular press, the press’s profile is the source (the desired colour behaviour) and the profile for the proofer is the destination (our colour output).
Do not confuse a profile’s class with its function; they are independent and separate characteristics. A particular output profile can assume the function of source in one colour equation and then turn around and assume the role of destination in a second. Take the example of the press above, where the press profile acted as the source. If we have multiple presses in the printing plant, and we have another press that is our master press for colour behaviour, the press profile that acted as a source for the proofer output will now function as a destination profile to align that press to the colour behaviour of the master press (the master press profile is the source profile in this pairing).
Profiles enable the two key processes of any colour managed workflow: clear communication of colour meaning and the transformation of device values to maintain colour appearance.