[Openicc] GoSoC 2011: CPD and Color Management

[Graeme Gill]

Chris Murphy wrote:
> Fred Bunting, one of the RWCM co-authors, made a compelling argument against the vcgt
> tag in ICC display profiles - the idea that the profile describes the device behavior,
> not establishing device behavior. That is characterizes a device, does not calibrate
> it.

Yes, this is actually the wrong calibration information. What should be in the profile
is the device response it was created for:- ie. it should contain the calibration target
values, not the adjustment used at some instant in time to achieve calibration.
The profile calibration target information can then be used as input to calibration to
put the device in the state that the profile is applicable to, or to match
against the current calibration state (where calibration state = calibration target
values and current calibration needed to achieve these targets.)

This is a potential trap in the whole approach of adding printer settings
to a profile. If the printer settings are basic discrete operating state
(ie. DPI, screening etc.), then that's probably reasonable. If it's mechanism
used to achieve the calibration target (ie. calibration curves or parameterized
equivalent), then this is probably wrong. The distinction is whether a setting
is adjusted by the calibration process, and that this is effective in
restoring the device response such that the profile will apply accurately enough
to it again.

Graeme Gill.