[Openicc] ALL YOU NEED IS A PROFILE, THE MYTH. (WAS CC Profiles In X Specification and dispwin)

[Gerhard Fuernkranz]

Robert Krawitz wrote:
> Yes, but we need to handle these cases. The simple channel splitting
> model for light channels has some limitations; I suspect, for example,
> that the hue and saturation doesn't perfectly match.

Does it really matter if hue/saturation don't match, as long as they are
smoothly blended? But I agree that a simple channel splitting may likely
result in a smaller gamut than the optimal utilization of all inks.
Nevertheless I guess that it is still frequently done in this way,
because it is simple. Possibly even by commercial RIPs.

> Then there's the whole issue of ink limiting.

Per channel ink limiting can be done by the per-channel linearization
curves, and the total ink limit will be established by the ICC profile.

> For black ink, sometimes the light inks
> have a significant hue and the darkest black is neutral.

Does this matter? The profile will eventually correct this if necessary.
It is just an important prerequisite for the profiling success that the
device is well linearized, and the characteristics of the linearized
device should be as smooth as possible.

> You also missed the drop size issue.

I see the drop size issue rather as an issue of the halftoning process.

> The way we do CMYKRB (it extends to additional inks) is to convert to
> HSL, and pick the right combination of color inks from the hue (we
> don't use the auxiliary inks in gray/black generation).  It's not all
> that scientific; it kindasorta works, but I'd like to do better.

Possibly multicolor profiles could be used here, in conjunction with
simple 1D linearization curves for each ink channel. I just don't have
experience how well multicolor profiles actually work. I think for
instance ProfileMaker supports the creation of such profiles. Argyll
currently does not support multicolor ICC profiles, it does support a
multicolor model called "mpp", though. But again, I have no experience
with this model yet either.

CcMmYKk devices could possibly be treated as multicolor devices too
(instead of channel splitting) in order to utilize their full gamut.

> Well, OK, but the question of handling the different physical printer
> setups is very important for modern printers...

But each printer setup will need different tables/profiles as long as a
non-parametric device characterization is used. I do not see a
reasonable solution to overcome this. Otherwise one would need not ICC
profiles, but rather a mathematical model which predicts the colors
based on the physical printing process, and then things are getting very
complicated, and possibly still not as accurate as desired...

Regards,
Gerhard