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

[Hal V. E. <hv...@as...>]

On Thursday 07 August 2008 05:38:06 pm 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 treat my R2400 as a CMYK device why not do the same with this printer?  The 
GutenPrint driver supports it and you will have more control over the printer 
when you create the profile.  That is the profiler will be more "connected" to 
the actual device this way.  It requires a little more work to create a CMYK 
profile since you have to spend some time getting the K vhannel correctly 
setup than an RGB profile but the resulting output is better.

> 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. 

My experience with trying RAW mode is that all you end up with is a mess of 
ink on your paper.  Even patches with 30% density had too much ink for the 
paper.

I would be inclined to start out by pretending that the device had the 
standard inks to see how close or far off Uncorrected mode actually is.  You 
can always increase or decrease the density setting of any channel that is 
laying down too much or not enough ink and the cross over points between dark 
and light can also be adjusted in the GIMP plugin (which means this applies to 
CinePaint if you are using it) as well as PhotoPrint.  Although if you use 
more than one of these whatever tuning you do will have to be duplicated for 
the others.

> Also print combined inks to figure out
> total ink limit.
> - Tell Gutenprint about these limits, ideally without recompiling
> (simply change settings in driver? 

Again ink limits can be set in the GIMP print plugin and in PhotoPrint.

> modify PPDs 

Users should not modify the PPD.

> 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).

Linearization is a very hard problem.  There are no user land tools to support 
this with GutenPrint or any of the existing open source printer drivers and 
doing it by hand is difficult, error prone and time consuming.  If the 
existing curves are even close to OK (IE. farily smooth and monotonic) at this 
point the best thing to do is let the profiler handle it.  But I think you are 
best off using Uncorrected mode since this at least trys to give you an ink 
limited linearized output.  Again if the density curves of the individual 
channels are monotonic and reasonably smooth the profiler will do a good job 
for you.

>
> Any hints appreciated.
>
> Marko
>
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