Re: [Gimp-print-devel] Strategy for profiling Epson R280 with Ultrachrome K3 inks

[Marko M. <mar...@gm...>]

Many thanks for the response. I copied over K3 settings minus gray
inks, and the results are very promising - printing "uncorrected"
looks almost passable without a profile, while it looked pretty bad
with original settings. I can use this as a starting point for icm
profiling. I do have some followup questions if I may:

Q: In media/<model>.xml files, PrintMethod parameters are different
between R280/Claria and R2400/K3, even for same paper types and
resolutions.

Should my hybrid file have PrintMethod parameters from R280/Claria or R2400/K3?

Q: Paper definitions have "SubchannelCutoff" parameter. What is this
called in the GUI? Googling it returns nothing.

Q: Ink definition file says:

...
  <shade count="1">1.000000</shade>
  <shade count="2">1.000000 0.350000</shade>
  <shade count="2">1.000000 0.200000</shade>
...

Does this mean that 35% M is same density as 100% LM, and thus that
default setting for "Light Magenta Value" in GUI is 0.35?

Marko


On Thu, Aug 7, 2008 at 6:13 PM, Robert Krawitz <rl...@al...> wrote:
> Marko Milisavljevic wrote:
>>
>> Hello list,
>>
>> I have an Epson R280 printer loaded with MIS K4 inks (3rd party
>> substitute for Ultrachrome K3 inks), without LK and LLK, of course. I
>> am trying to figure out the best way to profile it. I will probably
>> use ArgyllCMS for profile generation.
>>
>> If these inks were standard on this printer, I would treat it is RGB
>> printer and print patches using "Uncorrected" mode, but that is not
>> the case. I am thus looking for advice on general approach, so I don't
>> go barking up too many wrong trees. I imagine I need to do this:
>> - Print a gradient for each of the 6 inks using "Raw" option to figure
>> out ink limits for individual channels and where is the crossover
>> between photo and regular inks. Also print combined inks to figure out
>> total ink limit.
>> - Tell Gutenprint about these limits, ideally without recompiling
>> (simply change settings in driver? modify PPDs or
>> /usr/share/gutenprint/5.2/xml/escp2/media/something.xml maybe)
>> - Linearize - not exactly sure how. I see Gutenprint has some HSL
>> curves in media/something.xml - I assume this is the famed
>> "linearization"? I don't see how to linearize individual inks or
>> combinations of inks (M+LM) other then some gamma settings.
>> Alternatively, print unlinearized with "Density" option and let the
>> profiling software sort it out (I'm working in 16-bit).
>
> So this printer is essentially a CcMmYK printer, correct?
>
> One option you might start with -- you'll need the latest CVS to do this --
> would be to copy the appropriate data file from escp2/inks and change
> escp2/model/model_81.xml to point to the new file, and change the
> appropirate escp2/media file (probably start by copying the file for one of
> the K3 printers).  Assuming that the K4 ink really does match the K3 ink,
> you'll get (basically) the same results as a real K3 printer, other than the
> light black inks.  The good news is that you won't need to recompile
> anything to make this work!
>
> After you do this, you'll need to regenerate the PPD file.  You should be
> able to do this with cups-genppdupdate.
>
> The HSL curves are not linearization curves; they're color correction curves
> for people not doing their own color management.  You'll be using
> Uncorrected, Density, or Raw color correction, so they won't come into play.
>  The parameters you're interested in are:
>
>        + The Value parameters (such as Light Cyan Value) specify the
>          relative darkness of the light vs. dark inks.
>
>        + The Cutoff parameters now specify the point at which the
>          darker ink is first used, relative to the value of the light
>          ink.
>
>        + The Scale parameters now specify the amount of light ink
>          used (essentially the density of the light ink).  This is
>          the same as the parameters previously called Cutoff.
>
> Does this help you get started?
>
> --
> Robert Krawitz                                     <rl...@al...>
>
> Tall Clubs International  --  http://www.tall.org/ or 1-888-IM-TALL-2
> Member of the League for Programming Freedom -- mail lp...@uu...
> Project lead for Gutenprint   --    http://gimp-print.sourceforge.net
>
> "Linux doesn't dictate how I work, I dictate how Linux works."
> --Eric Crampton
>