[argyllcms] Re: printer profiles - how to get max black

  • From: "Gerhard Fürnkranz" <nospam456@xxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Thu, 07 Dec 2006 15:59:20 +0100

-------- Original-Nachricht --------
Datum:  Thu, 07 Dec 2006 07:35:28 -0500
Von: Roger Breton <graxx@xxxxxxxxxxxx>
An: argyllcms@xxxxxxxxxxxxx
Betreff:  [argyllcms] Re: printer profiles - how to get max black

> > It's not shaped much like a printer gamut, which means that you're
> > not getting everything the colorants are capable of giving, and the
> > black separation has the distinctive "cone" shape that hints at
> > a poor black generation algorithm. Not much you can do about all
> > that though.
> >
> > Graeme Gill.
> Sounds like RGB profiling. Many people don't realize how RGB profiling is
> far from optimal.

At least the results still depend heavily on the printer driver behaviour, 
since an RGB profile cannot influence how the CMYK separations are generated 
from the RGB data (-> lack generation, ink limiting, etc. are still all done by 
the driver, not by the profile).

Thus it is sometimes also a problem to get optimal results with non-original 
consumables; they may need for instance different overall or per-channel ink 
limits, etc., but the driver may not offer you settings to change them (or just 
an indirect way to change them implicitly by selecting e.g. a different media 
type from the list of supported media - but that's rather a try-and-error 
procedure, and the selection of a different media type may have other undesired 
side effects).

A driver can however indeed emulate a virtual "raw" RGB device space which 
covers nearly the whole printer gamut (and which also doesn't waste too much 
unused space in the RGB cube). I remember a publication regarding this issue, 
but I don't have the URL at hand.

But if the driver is operated in some kind of sRGB mode, then you likely end up 
with a gamut which is just the intersection of the printer gamut with the sRGB 
gamut, and which has no longer the typical shape of a printer gamut. And 
profiling will have to characterize the driver's perceptual gamut mapping, in 
order that the profile can undo it (for the colorimetric intents) and apply its 
own mapping instead (for perceptual/saturation intent).


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