On Thu, Jan 20, 2005 at 08:48:59PM +0100, Joerg Rossdeutscher wrote:
> Am Donnerstag, den 20.01.2005, 09:32 +1030 schrieb David Purton:
> > On Wed, Jan 19, 2005 at 08:45:33PM +0100, Joerg Rossdeutscher wrote:
>
> > > Am Mittwoch, den 19.01.2005, 16:21 +0100 schrieb Piotr Kopszak:
> > > > I would be interested in any of your ideas concerning the question in
> > > > the subject or simply(?) in receiving a command line parameters
> > > > necessary to obtain RGB jpeg from CMYK EPS Photoshop 8.0 files in
> > > > appropriate colours. I'm using GNU Ghostscript 7.07 that comes with
> > > > Debian.
> > >
> > > 1. Install ImageMagick.
> > > 2. "convert my.eps my.jpg"
> >
> > This wont give you the right colours. You need something that
> > understands colour management.
>
> 1. ImageMagick uses colormanagement (liblcms)
Ah - does it? I didn't realise this. You still need to get some
profiles from somewhere, even if you only care enough to use generic
CMYK and RGB profiles.
But I see you can at least do a:
convert -profile cmyk.icc -profile rgb.icc cmyk.tif rgb.tif
It does not seem possible to create onscreen proofs, though - just
conversions.
It does not however work starting from an eps - see below for why.
>
> 2. there is nothing like "right" colors when changing colorspace
> between RGB and CMYK. Except for pure white the color is always
> wrong.
>
You are of course, right, but the whole point of colour management is
to try and get it as least wrong as possible given what you know about
the colour capabilities of the intended output device. And even pure
white is usually wrong, since your paper is not white.
Doing a straight "convert my.eps my.jpg" will give the "most" wrong
answer though since no colour management is used at all.
> > You will need Little CMS (excellent colour management library) and some
> > colour profiles. Google for adobe icc profiles to get some standard ones
> > from adobe.
>
> And exactly that one is used by ImageMagick.
>
> > Although, you with some stuffing around, you might be able to use
> > gs7.07, I *highly* recommend you use gs8.50, unfortunately not available
> > yet as a deb, so you will need to grab source.
> >
> > gs8.50 has a tiff32nc device that will give you a CMYK tiff from your
> > eps, e.g:
> >
> > gs -sDEVICE=tiff32nc -sOutputFile=cmyk_image.tif cmyk.eps
>
> ImageMagick just delegates postscript to ghostscript. If you use IM, you
> use GS. Just easier.
ImageMagick appears to use the pnmraw device from gs which is an RGB
format, so the actual conversion to RGB is done using gs. If you attempt
to specify an import cmyk profile to convert, you will get an lcms error.
You could also try:
$ GS_OPTIONS=-dUseCIEColor convert my.eps my.jpg
But, IMHO it does not give as good results as using profiles.
Boy, colour management is a pain :( So much to learn and understand and
it still seems like black magic if you end up with anything like a good
preview on screen. *sigh*
cheers
dc
--
David Purton
dcpurton@chariot.net.au
For the eyes of the LORD range throughout the earth to
strengthen those whose hearts are fully committed to him.
2 Chronicles 16:9a
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