Re: Panther, sRGB, web browsers
Re: Panther, sRGB, web browsers
- Subject: Re: Panther, sRGB, web browsers
- From: Chris Murphy <email@hidden>
- Date: Mon, 15 Dec 2003 09:43:23 -0700
On Dec 15, 2003, at 5:55 AM, Uli Zappe wrote:
Somehow I seem to misunderstand what you say here.
For test purposes, I have created an RGB test profile (with Display
Calibrator Assistant) that's "way off", so that you can easily see
when this profile is used. Now, when I switch to this profile (to be
my display profile) in the Displays System Preferences, *every*
content of my display changes color, be it from TextEdit, Preview,
whatever - even movies in DVDPlayer.
So obviously, this setting influences the displaying colors of every
app that's running, just as it should. And as far as I can see, that's
*all* a display profile should do - correct the display on this one
specific monitor I use. So where do we misunderstand?
Aha. Yes this is confusing. You are seeing the effect of calibration,
not the profile itself. Displays are calibrated through the adjustment
of a set of tables in the video card. The intent of it is to set white
point and gray balance primarily. And the Display Calibrator assumes
that you are following its instructions, and have ended up with a well
behaved monitor. So when it builds the profile, it includes the
calibration information for the video card, and then builds the
characterization of the monitor (now well behaved) to the profile as
well.
So technically we have a shotgun wedding between calibration and
characterization when it comes to display profiles. The
characterization portion is what's involved in defining the actual
primaries, tone response, white point, etc. of your display, and is the
only portion used by ColorSync. The display manager (if it's still
called that on OS X), grabs only the calibration data when you log in,
and applies that to the video card. This affects things system wide,
and is not a ColorSync induced conversion, but rather data being passed
through, effectively, a set of curves in the video card.
Yes, the LaserJet 5500 (at least my configuration) is a network
PostScript printer. However, it seems to accept only RGB ColorSync
profiles:
The Factory Profile, according to ColorSync Utility > Devices, is
/Library/Printers/hp/Profiles/sRGB_A.icc
an HP supplied file that comes with Panther.
On its web site, HP also offers a specific CYMK ColorSync Profile for
the 5500, but Color Sync Utility wouldn't let me choose that as
Current Profile instead of the Factory Profile (it seems it only
accepts RGB profiles for the 5500!?!).
If I choose another RGB profile instead of the Factory Profile,
nothing happens. If this file isn't consulted, not used by the RIP or
whatever, I wonder why Apple/HP installed a ColorSync Factory Profile
in the first place.
I don't have an answer, and can only speculate wildly. Maybe HP is
under the impression ColorSync (like it would have on OS 9) will
convert everything to this profile before data is sent to the printer.
If they were thinking this, they'd want everything converted to the
same RGB source the printer's internal color management assumes which
is almost certainly sRGB. And then uses an internal CRD as the
destination. Either way something isn't quite right. I'd need to see a
bunch of different PostScript files generated by the system with
different settings, and then also print a bunch of tests to the printer
in order to figure it all out though.
That's the problem with depending on PostScript color management.
Each RIP does things differently, and I see PostScript color
management as a totally unreliable way of doing color management.
But as a consequence, that means that each app has to offer its own
color management settings for printing, correct? And that also means
that printing from apps that don't offer such a setting is guaranteed
to fail color-wise, right? Which would mean that even to print a
simple letter with the correct colors of e.g. a company logo on it
requires a layout application?
No, the way the system currently works is that non-color managed
applications get to use OS/driver level color management. It works on a
series of assumptions. The first is that document data is monitor RGB
(which it gets from the Displays panel), so that's the source profile.
In certain instances it's Generic RGB. The second is the default
profile selected by the manufacturer for the device/media you are
printing to. For non-PostScript devices, ColorSync converts before it
gets printed. For PostScript devices, it just builds CSA's (PostScript
source profiles) from either the display profile or Generic RGB
profile, leaving everything unconverted, and expects the printer to
know what to go do with itself (convert everything in its RIP).
If this is really the way it is, frankly, coming to all this from the
outside, I'm shocked by the archaic state of affairs in the year 2003.
I thought color management is difficult because of the physics
involved and the software and hardware technologies necessary.
Instead, much of it seems to come down to a simple lack of
standardization and cooperation between apps, drivers and the OS. :-/
Pretty much. And I can't say it's that different on Windows because it
too works on a series of assumptions for non-color managed apps (sRGB
is assumed), but really that whole system pretty much isn't even using
ICM by default. It relies on print drivers assuming sRGB and then using
proprietary color management to do the conversion. (But that's even how
it works on Mac OS by default too with the vast majority of printer
drivers.)
At least if the GUI becomes a bit clearer. From what it says right
now, I just couldn't figure out which of the two settings I should use
if I wanted to apply system-wide color correction via the profile I
choose for the 5500 in the ColorSync Utility:
Color Conversion > Standard (the GUI says it uses the configured
ColorSync profile which is what I want...)
or:
Color Conversion > In Printer (the GUI says this setting creates
colors for PostScript printers which also seems to apply in my
case...)
Part of my confusion is, of course, that there seem to be too many
things at once that don't work so in the end I got paranoid about
*where* the problems is...
Welcome to the color management club!
Chris Murphy
Color Remedies (TM)
www.colorremedies.com/realworldcolor
---------------------------------------------------------
Co-author "Real World Color Management"
Published by PeachPit Press (ISBN 0-201-77340-6)
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| References: | |
| | >Re: Panther, sRGB, web browsers (From: Roger Breton <email@hidden>) |
| | >Re: Panther, sRGB, web browsers (From: Uli Zappe <email@hidden>) |
| | >Re: Panther, sRGB, web browsers (From: Chris Murphy <email@hidden>) |
| | >Re: Panther, sRGB, web browsers (From: Uli Zappe <email@hidden>) |
| | >Re: Panther, sRGB, web browsers (From: Chris Murphy <email@hidden>) |
| | >Re: Panther, sRGB, web browsers (From: Uli Zappe <email@hidden>) |