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

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

On Friday 08 August 2008 12:07:58 pm Marko Milisavljevic wrote:
> Thank you for detailed response.
>
> On Fri, Aug 8, 2008 at 10:52 AM, Hal V. Engel <hv...@as...> wrote:
> > On Friday 08 August 2008 03:36:18 am Marko Milisavljevic wrote:

snip

> About targen... As far as I can tell, it doesn't think in bits - it
> outputs .ti1 file which contains floating point coordinates. Only with
> printtarg is the choice about bits made if outputting to TIFF with -t
> or -T for 8 or 16 bits respectively. 

Yes I was thinking printtarg and not targen.  These are new options for 
printtarg.  The previous version only ouput ps files and these needed to be 
converted to tiff or some other raster format and the tools to do that only 
produced 8 bit files.  I have not tried version ArgyllCMS 1.0 yet.

snip
>
> I will use ArgyllCMS first for RGB profiling to get a hang of that
> software, but I would like to eventually do CMYK profiling. How did
> you actually go about figuring out appropriate GCR settings in
> ArgyllCMS? Any advice beyond what is written here:
> http://www.argyllcms.com/doc/Scenarios.html#PP6

That is about all that is available on this subject.  Basically you want as 
much K as possible in the grays consistant with having a smooth K tone curve 
and no artifacts because of the K channel.   This is highly dependent on the 
printer.  For printers like the R2400 that have LK and LLK you will likely 
want to use more of the composit K channel for mid and light grays.  But for 
printers with only a K cart you need to transition from mostly K to mostly 
process gray farily early to avoid K channel artifacts.  

Notice how the K channel in the last example on that page is well below the 
CMY channels until about 45% density.  This is about what you need to do with 
only a K cart to avoid K artifacts like speckels in the mid and light grays.  
Where as with a printer with LK and LLK you probably want to do something in 
between the two examples above the last one.   This is sort of trial an error 
thing were you use the process outlined on that web page and some judgement 
about what might work for your printer to get it in the right ball park with 
smooth transitions and tone curves.   Then you need to do some test prints to 
make sure you don't have artifacts related to the K channel being too strong.  
If you have speckels then pull it back some if not then maybe you can push 
some more K into the grays.   

Hal