Re: ColorSync and PostScript printing
Re: ColorSync and PostScript printing
- Subject: Re: ColorSync and PostScript printing
- From: Chris Murphy <email@hidden>
- Date: Fri, 4 Mar 2005 19:36:09 -0700
On Mar 4, 2005, at 5:53 PM, Uli Zappe wrote:
Very strange. If even this modification does not result in using RGB,
then there's really no point for providing an RGB profile.
I'm not sure one way or the other at this point. I don't have enough
information.
OTOH, this explains perfectly well why custom profiles didn't work at
all with the old HP PPD: it registered only as an RGB PostScript
printer, which, as we know now, will still be sent CMYK data, while on
the other hand you could only specify an RGB custom profile in
ColorSync Utility which of course has no influence at all on the
(CMYK) output.
Good point.
Things I can't answer with the information I have:
a.) Why does the system apparently use the manufacturer profile, but
the CMYK values are not anywhere in the ballpark as a conversion
using supposedly the same source and destination profiles?
Good question, which becomes even more confusing in view of the fact
that for the actual output, Quartz filters do not differ from the
system conversion (see below).
Could be an issue with cgpdftops? Could be a CUPS problem, or a PPD
problem. I really don't know.
If I get it right, with the "In-Printer" setting, Mac OS X will send
RGB data to the printer, so this is a way to judge the printer's RGB
capabilities.
In-Printer means the OS will not convert the numeric values, but it
will tag them. Objects tagged RGB will have a PostScript CSA based on
that tag sent in the PostScript stream, objects not tagged have a
PostScript CSA based on Generic RGB. Objects tagged CMYK also get a CSA
based on that tag. Untagged CMYK remains /DeviceCMYK. So while you
could send RGB to the printer, it's going to get tagged Generic RGB
unless you tag it with something else.
From casual experience, I used to think this provided better results,
but with the tests I've done now, I'm not so sure anymore. Basically,
the colors seem to be lighter in general; this is good for blue which
is far too dark otherwise, but bad for red which is far too light now.
(I got the impression "In Printer" would be better by printing
documents with lots of blue, but no red ...).
I question the value of most canned laser printer profiles.
Chris Murphy
Color Remedies (TM)
www.colorremedies.com/realworldcolor
-------------------------------------------------------------
Co-author "Real World Color Management, 2nd Edition"
Published by PeachPit Press (ISBN 0-321-26722-2)
_______________________________________________
Do not post admin requests to the list. They will be ignored.
Colorsync-users mailing list (email@hidden)
Help/Unsubscribe/Update your Subscription:
This email sent to email@hidden