[Openicc] Printing targets: App or driver ? Profiling RGB or CMYK

[Chris Murphy]

We are talking primarily about Gutenprint inkjet printer drivers, correct?

If so, I could better understand how the driver presently functions with respect to internal transforms. 

Some inkjet printers are CMYK, most have more than four colorants. But most of those consumer printers with more than four colorants don't provide access to individual channels, i.e. DeviceN not possible. Michael Sweet has pointed out a while ago that this is trending all the more toward sRGB only input. So we have variable input color modes and spaces for inkjet printers.

1. If a printer has an sRGB path, I think that needs to be made directly available to the user, unmodified, so they can have platform parity.

2. Not clear to me is the exact nature of alternative paths to these printers, when available. Are they unspecified RGB? CMYK? Or DeviceN? I know on the Pro Epson printers there is DeviceN.

3. If DeviceN is available, how is this utilized by Gutenprint? Is there first a CMYK to DeviceN LUT? And then there is a separate RGB to CMYK LUT? Is RGB is reached via concatenation of RGB-CMYK-DeviceN LUTs? Or is it a separately developed RGB-DeviceN LUT? What what is the basis for the RGB space? sRGB or other?

Chris Murphy


On May 17, 2011, at 9:38 AM, Jan-Peter Homann wrote:

> Hello Edmund and all,
> I support, that profiling for Gutenprint should start based on the avilable RGB Gutenprint setups.
> May questions are about possibilities to allow an easier CMYK based profiling for Gutenprint in future (no need to prioritize).
> 
> The main idea behind:
> Gutenprint must handle total inklimit and blackgeneration if it can be driven with RGB-data.
> If we have working Gutenprint settings, we may could use the information to configure the Argyll profiler for CMYK based profiling and may be also the Argyll target generation (may be necessary for media ink combinations with very low total ink limit), .
> In this case, we need special targets, which contain only patches under the ink-limit.
> 
> But as i said, this needs no priorization and is more interesting to color geeks, which e.g. want to compare the results for RGB and CMYK based profiling for the same media settings.
> 
> Best regards
> Jan-Peter
> 
> Am 17.05.11 16:21, schrieb edmund ronald:
>> I don't understand anymore where this is going. Yes Gutenprint can be profiled in CMYK. There are no technical issues, I have done it, any color consultant can do it. No, this cannot be done easily with tools available to hobbyists, and with the current Linux software driving GP, and the quality one gets with the built-in RGB==>CMYK  I don't think there is an immediate need to prioritize this route.
>> 
>> Edmund
>> 
>> 
>> On Tue, May 17, 2011 at 2:59 PM, Robert Krawitz <rlk at alum.mit.edu> wrote:
>> On Tue, 17 May 2011 10:03:26 +0200, Jan-Peter Homann wrote:
>> > Hi Alastair,
>> > You made a good point. For a smooth step forward, with current available tools and settings (Argyll / Gutenprint), you correct, that profiling in RGB based on a good Gutenprint RGB->CMYK Setting is easier for crowd profiling, which is quite important for the next months.
>> >
>> > Question to Robert Krawitz:
>> > There are a lot of testet Gutenprint settings available, which include the Gutenprint specific RGB->CMYK conversion.
>> > - Is it possible to create a Gutenprint "CMYK-only" setting by just deactivating the RGB->CMYK conversion ?
>> 
>> "Deactivate the RGB->CMYK conversion"?  I don't understand.  If one
>> were to do that, they would get RGB output (or perhaps CMY, depending
>> upon how it's defined; Gutenprint does offer CMY output).
>> 
>> Based on the rest of this, are you really asking "is it possible to
>> determine the internal settings Gutenprint is actually using"?
>> 
>> > - Is it possible to to read easily following parameters from the deactivated RGB->CMYK conversion:
>> >      - Black generation settings ?
>> >      - Total ink limit ?
>> 
>> No, not at present.  I can see API changes that would make it
>> possible.
>> 
>> > For stepping into CMYK profiling, this could lead to following workflow
>> > - read the Gutenprint settings black geneartion and ink-limit for an tested setting
>> > - deactivate the Gutenprint RGB-CMYK conversion
>> > - Print the testchart
>> > - generate profile with similar settings for black generation and ink-limit
>> >
>> > Question to Graeme Gill:
>> > Some Ink / Media Combinations need heavy total ink limits. Is it possible with Argyll to create CMYK-testcharts which are alraedyoptimize for an ink limit and black generation ?
>> 
> 
> 
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