[Openicc] New options on the mainline

[Kai-Uwe Behrmann]

Thanks for switching to a new thread subject. To be honest, I was not 
convinced with complete capitalisation in the subject line for the sake 
of repeating ideas.

Am 19.01.08, 19:31 -0500 schrieb Robert Krawitz:
>    Date: Sun, 20 Jan 2008 01:19:04 +0100
>    From: Gerhard Fuernkranz <nospam456 at gmx.de>

>    I'm wondering, whether user-supplied channel-splitting/calibration
>    curves, i.e. Cyan input => Dark Cyan and Cyan input => Light Cyan,
>    wouldn't provide more flexibility for the user to establish an
>    arbitrary blending between the dark and light inks? I guess that
>    such curves would also make 2) 3) and 4) obsolete?
> 
> Yes, although it would be more complicated to implement.  If it turns
> out to be really necessary, we can look at it then.  Of course,
> someone else might want to go ahead and implement it :-)

IMO linearisation, like the above ones, can be easily created as a 
linearisation Device Link (DL) ICC profile with just the according curves 
and of course with no n-channel table corrections. A belonging curve 
editor could then simply implement a pair wise curve editing for light / 
dark inks. Some additional sliders int the UI to set start/end points or a 
gamma to start with would be of help. The values resulting from the 
slider must only be mirrored for the ligth/dark channels respectively.

Of course it would help to support measured input as well. This would 
allow for manual corrections of measured linearisations. G7 could then be 
consulted as of Jan-Peter's suggestion.

This can completely happen outside of Gutenprint. To link a linearisation 
DL profile into the final conversion is not at all a problem other than 
selecting the DL and assigning it in the last position of the colour 
conversion profile chain of a multi profile transform.

This is the workflow I intended for CinePaint, but dropped due to too many 
other tasks at this application and no interesst (testers/discussion 
among CinePaint users) at time.
I write this in the hope other developers have interesst and more time 
and use than I to go with such a concept.
Possibly this is a nice feature for LProf or a separate application 
with the advantage of minimal impact to existing applications. 

>    > * Color Correction should be set to one of the following:
>    >
>    >   + Raw if you want to adjust all the settings manually.  In Raw color
>    >     correction mode, there will be no automatic correction of any
>    >     kind, including density adjustment.  If you're not careful, you
>    >     may find yourself using an excessive amount of ink with this
>    >     setting.  You will need to adjust the Density control or the
>    >     controls for the densities of the individual colors.  You may want
>    >     to use this to establish custom densities and ink limits to
>    >     achieve maximum gamut.
>    >   + Density if you want to use Gutenprint's choice of density, but
>    >     otherwise have no automatic color correction applied.  This choice
>    >     of setting should be safe (at least in RGB mode; in CMYK mode it's
>    >     possible for too much ink to be applied).  This is useful if
>    >     you're satisfied with Gutenprint's default ink limits, but want to
>    >     adjust the linearization yourself.
> 
>    Do "raw" and "density" mode honor user-supplied linearization
>    curves? Or in other words, which mode do I need to select, if I
>    want _Gutenprint_ to apply _my own_ linearization (and possibly
>    channel-splitting) curves, which I supply as parameters? (my
>    understanding is that this is basically the most desired mode of
>    operation, at least for CMYK printers, and for CcMmYKk printers
>    which are not operated in a multicolor mode, but which emulate CMYK
>    by channel splitting).
> 
> Yes, they do honor user-supplied linearizations.  They just don't
> apply the defaults.

Is the switch of for the defaults something to decide in PPD's as well?
 
>    > Comments please.
> 
>    And how to deal with multicolor printers? Do I understand
>    correctly, that there is currently no print mode available, which
>    accepts "DeviceN" input (i.e. one input channel for each ink)?
> 
> Yes there is, actually -- see src/testpattern to see how to use it.
> If someone wants to do N-channel linearization and RGB->DeviceN or
> CMYK->DeviceN, it will work just fine with Gutenprint (if they have a
> way of talking to the driver).

I remember at least one person who did n-colour printing with Gutenprint's 
tools. It should be searchable in the gutenprint / gimp-print email 
archives.

kind regards
Kai-Uwe Behrmann
--
developing for colour management 
www.behrmann.name + www.oyranos.org