ColorSync and printing -- Panther (2 of 2)
ColorSync and printing -- Panther (2 of 2)
- Subject: ColorSync and printing -- Panther (2 of 2)
- From: John Zimmerer <email@hidden>
- Date: Thu, 18 Dec 2003 18:32:20 -0800
Part 2 of 2
7) The moral of the story is ALWAYS TAG YOUR SOURCE DATA -- if you
don't, we will. Since ColorSync is always on in Mac OS X, including in
the printing system, there must always be both a source and a
destination profile. For those of you wanting to create custom ICC
profiles for printers, read on....
8) What is the source color matched to? Ahhh, stay tuned for the
caveat.... For "In Printer" (PostScript) color matching, the source
color is always matched to the active CRD by the printer. For
"Standard" color matching, there's some variation depending on the
driver. Since 10.0, Apple has asked the 3rd-party printer vendors to
have their printer drivers register one or more profiles with
ColorSync. Nearly all do. The registered profile(s) is(are) visible in
the ColorSync Utility, under Devices. Under Devices you see every
imaging device that has been connected to your Mac, the Factory Profile
that was registered by the driver, and the registered Current Profile.
By default these two (Factory and Current) will match unless/until you
change the "Current Profile". You'll notice that some printers/drivers
register actual device profiles, while some register color space
profiles (e.g., sRGB), and some report "null" meaning no profile was
registered. At print time, a PDF print spool file is created, and all
source color data is written as above into the spool file ("Save as
PDF..." simply records the print spool file to disk). The spool file is
influenced by the settings made in the Print dialog. When "Standard"
color matching is used, the printing system asks the driver to provide
the destination* color space. In theory, the driver hands the printing
system the registered* "Current Profile". This works in practice for
all PostScript devices and for CUPS-based (e.g., GIMP-Print) raster
drivers. However, Tioga-style drivers may not hand up the registered
"Current Profile", depending on the combination of settings chosen in
the Print dialog. Currently, nearly all vendor-supplied raster drivers
are the older-style "Tioga" drivers. Here's the caveat: For the most
part, if a Tioga driver offers you a PDE called something like "Color
Management" with an option called something like "ColorSync color
matching", then the Tioga driver will likely hand up the registered
Current Profile as the destination profile. This is the mode you want
to use for the best chance at having your color matched to the output
profile with no additional influence from the driver. However, if you
choose any other option (e.g., the vendor's color science), the driver
almost certainly will not hand up the expected (i.e., registered)
profile, or will almost certainly further manipulate the data AFTER it
is matched! Even when you choose whatever ColorSync option is offered
in their PDE (usually called something like "Color Management"), we
can't be sure of what a Tioga driver will do once it receives the data.
9) Controlling which profile gets used as the destination is relatively
straightforward. If you're using a CUPS-based raster driver, or are
printing to a PostScript device using "Standard" color matching, then
assign a profile using the ColorSync Utility. Click on the triangle
next to "Current Profile" and navigate to your profile of choice -- its
color space must match the mode to which you're registering the
profile. For example, I use a monochrome laser printer that has only
one mode (Gray), for which I have registered the Generic Gray
Profile.icc. You can also do this for Tioga-style drivers, but remember
the caveat above, and read the next part.
10) How do you know whether the registered "Current Profile" will be
used when printing? The Print dialog has a "Summary" PDE (also located
in the pop-up labeled "Copies & Pages"). Select the "Summary" PDE, then
scroll all the way down and you'll see something that looks like this:
...
ColorSync
Color Conversion: Standard
Profile: Generic Gray Profile
Quartz Filter: None
If this is what you see, where a profile is explicitly named, then that
profile is sure to be used by the printing system as the destination
profile when printing. But, if you see something like this:
...
ColorSync
Color Conversion: Standard
Profile: System Default
Driver may perform custom color correction: true
Quartz Filter: None
... then buyer beware, because we can't tell if the driver will use the
registered profile, or if it might tinker with the color after it's
matched.
11) When we're sure there's a registered profile and you see the
profile named in the "Summary" PDE, if you click on the "Preview"
button (bottom of the Print dialog) after setting all of your printing
options, you'll get a color-managed soft proof using the registered
"Current Profile".... Yeah, that's pretty slick. Even works for
monochrome printers and fax.
12) "What about printing a target that I want to measure, in order to
create a custom ICC profile for my printer?" As you know, ColorSync is
always on in the printing system. That doesn't mean you can't get
unmatched device data to your printer. You need to force a "null match"
-- in other words, the source color space must be the same as the
destination color space. What you need to do is tag your target file
with the same profile that you register for your printer. It doesn't
matter what the profile is, really -- you just want ColorSync to see
that source=destination. ColorSync is smart enough to realize there's
no point in matching color that is already in the destination color
space. Now, keep in mind the warning from above -- make sure the driver
will actually USE the registered "Current Profile". Panther ships with
a number of CUPS-based drivers. If nothing else, you can create a new
print queue just for profiling your printer. Select the corresponding
GIMP-Print driver for your printer; assign a "Current Profile" using
the Colorsync Utility; tag your target file with the same profile (you
can use the "Embed chosen profile" script in
/Library/Scripts/ColorSync/), and make sure to select "Standard" in the
ColorSync PDE. Then print, measure, create your profile, and assign
this new profile as the "Current Profile", as above.
Hope this helps,
JZ
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