[argyllcms] Re: hplip printer driver and color management
- From: Kai-Uwe Behrmann <ku.b@xxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Thu, 28 Aug 2008 07:26:32 +0200 (CEST)
Am 27.08.08, 23:50 +0200 schrieb Gerhard Fuernkranz:
> Hal V. Engel wrote:
> >
> > However color management support in GhostScript has it's issues. When
> > displaying the "Is your system v4 ready" pdf* from the color.org web
> > site it does not display any of the content that has an ICC profile.
> > But when I open this pdf in cinepaint the v2 profiles in the pdf are
> > working but not the v4 parts of the pdf. Cinepaint uses ghostscript to
> > handle the PDF file. So it appears that there is some CM capabilities
> > in GhostScript for PDF files if it is invoked the correct way. In
> > addition, I had a quick look at the docs for GhostScript and I
> > couldn't even find a switch to use to specify an output ICC profile
> > but I may have missed something.
> >
>
> My understanding is that ghostscript basically does support full
> PostScript and PDF color management as defined by the PLRM and PDF spec.
> The output color space for the generated raster data needs however to be
> defined by a PostScript CRD and not an ICC profile [also in case of PDF
> input]. Defining the output color space alternatively by an ICC profile
> seems to be a project on their TODO list. I would not be surprised if
> ICC V4 profiles embedded in PDFs don't work, since GS uses Argyll's
> icclib, and icclib does not support V4 yet.
>
> In order to prepare GS as a fully color managed RIP you certainly need
> to supply a PostScript prolog first, which sets up things like
>
> * your desired halftoning (if halftoning is done by gs, i.e. if the
> raster output is not con-tone)
> * the desired transfer functions (may be included in the halftone
> dictionary)
> * a CRD describing the output color space and rendering intent
> * UseCIEColor, if desired
> * your desired CSAs for remapping Device{RGB,CMYK,Gray} to CIE-based
> color spaces, in order to tell GS that it should for instance
> interpret DeviceRGB or DeviceCMYK colors non-color managed PS and
> PDF documents as say sRGB or ISOCoated
> * etc.
>
> I'm just not sure, whether I'm already fully convinced by the accuracy
> of ghostscript's color transformations. It has significantly improved
> from GS 7.x to GS 8.x, and I certainly haven't tested the most recent GS
> versions yet, but when I did some test some time ago, a direct ICC-based
> conversion [e.g. RGB image to printer CMYK] with cctiff or tifficc IMO
> still gave superior results with more accurate colors and less banding
> artifacts.
This is still the case for the later gs versions. As long as the target
colour space defined in the CRD is not that far off to Ghostscripts target
then it appears to work. Otherwise, e.g. photo printers, the quality
suffers visually on the monitor.
One can easily deploy this inside CinePaint by using the PDF loader
plug-in. It's CVS versions deploys Ghostscripts CRD path with the default
Cmyk editing profile as target.
The Cmyk editing profile is to be set through Oyranos.
Cmyk import is preselected.
The command line sequence used in CinePaint's PDF loader can be read here
on ColourWiki:
https://www.oyranos.org/wiki/index.php?title=Ghostscript
Feedback is of course welcome.
kind regards
Kai-Uwe Behrmann
--
developing for colour management
www.behrmann.name + www.oyranos.org
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