[Openicc] New options on the mainline

[Hal V. Engel]

On Sunday 20 January 2008 10:58:15 Robert Krawitz wrote:
>    Date: Sun, 20 Jan 2008 19:30:00 +0100 (CET)
>    From: Kai-Uwe Behrmann <ku.b at gmx.de>
>
>    About exporting the current calibrations: from the previous post
>    I'd guess most parts are already somehow available through a
>    interface. How much work would it be to make a small tool to export
>    the Uncorrected curves to something readable? I could help on
>    transforming say integer or double arrays to the above mentioned DL
>    profiles inside such a tool. With the tool, I'd guess, the
>    Uncorrected mode is not that much desired to keep stable across
>    releases. Uncorrected still remains as a good starting calibration.
>    The created DL profiles would not at all know about device
>    states. So this part remains open. I would later connect this as
>    well, i.e. make the DL knowing about the Gutenprint options.
>
> Right now there's no straightforward way to extract those curves --
> they're not generated until very late in the initialization process,
> and the GCR curves are computed in a different module from the other
> color curves.  But it would be worthwhile to figure out how to do
> this.
>
> The format I would dump them out in would be either the Gutenprint XML
> curve format, or as a dump of the internal lookup table structure
> (probably just the curves), which itself would contain a collection of
> curves.  But I'm open to other suggestions.

Robert,

When I looked at trying to linearize my printer a few weeks back what I wanted 
was to start with the existing curves and to be able to apply a correction to 
that curve.  The problem of course was the UI does not make that curve 
available and there was no way to get this without resorting to making API 
calls to the GutenPrint driver and even then it was not clear from the API 
docs that these calls are really what I wanted.

I think that what is really needed is an API that allows for applying a 
correction curve to the existing base curves.  I believe that this is how 
most RIPs operate but I really don't have any experience with them.  Once 
there was such an API exposing it in a UI so that users could hand enter a 
set of correction values would be a good starting place.  For example the 
QuadTone RIP Eye-One-ReadMe document shows a set of examples based on taking 
a set of measurements of a 21 step gray ramp (this is a B&W RIP) and then 
loading this into an application called QTR-Linearize-Data that analysis 
those measurements and gives a result something like:

LINEARIZE="96.55 92.14 86.45 81.02 75.65 70.55 64.85 59.60 54.62 50.06 45.73 
41.99 37.63 33.91 30.95 27.75 25.01 21.80 19.84 18.43 16.95"

The user then takes this data and drops it into the QuadTone UI and tells it 
to use these measurements to correct the printers output.  The data above is 
nothing more than the L* values from the measurements.  We already have the 
tools to make similar sets of measurements and to create similar data sets.  
Of course the real issue is what would the GutenPrint API do with these 
measurements to make the linearization corrections?   

Anyway I thought that I would through this out there to see if this sort of 
thing was possible.  I suspect that long term what it does should be based on 
some standard that tries to establish an ideal set of curves for each 
channel.  This might be based on something like G7.

Hal