Color and ColorSync in Mac OS X
Color and ColorSync in Mac OS X
- Subject: Color and ColorSync in Mac OS X
- From: John Zimmerer <email@hidden>
- Date: Wed, 10 Jul 2002 05:00:15 -0700
OK, time to wade in.
1) There are Mac OS X APIs available to developers that facilitate
getting device data in and out without being color managed. So,
developers like GretagMacbeth, ColorVision, etc. have everything they
need to be able to calibrate and profile devices on Mac OS X. If you
have specific questions about how this is done, there's a separate
listserve for developer questions. You'll get the right answers there.
Specific to the printing system, if you are trying to print targets from
Preview, you can tag source data with the destination profile to force a
null match.
2) You can technically ask for and receive CMYK data from the printing
system. However, the Quartz-based PDF RIP that serves the current crop
of raster drivers from EPSON and other vendors currently only spits out
RGB data. This is just the way things have always been for raster
drivers. However, having an imaging model based on PDF certainly opens a
few doors (which I'm not at liberty to discuss).
ColorSync will match source data to whatever the driver provides. Some
drivers hand up a color space (e.g., HP hands us sRGB and they take it
from there). Some drivers hand up device profiles (e.g., EPSON when
using ColorSync color matching). Some drivers hand us nothing, in which
case we match to a rather generic profile. More info on this when we
release Jaguar. This is what happens in the EPSON drivers when you turn
off color management. This effectively mirrors the Mac OS 9 raster
printing experience.
3) When we encounter CMYK source data, what happens next completely
depends on whether the source data is tagged or untagged, and whether
we're dealing with a raster driver or PostScript device.
In the case of profiled CMYK source data going to a raster driver, we
match (i.e., convert) from the source profile to whatever profile the
raster driver hands us (see above). In the case of untagged CMYK source
data, in Mac OS X 10.1.5 and earlier, we use a one-minus rule and
effectively treat the data as RGB. Life is different in Jaguar. Can't
say any more yet.
In the case of profiled CMYK source data going to a PostScript device,
we convert the source profile to a Color Space Array and wish it luck at
the printer. Mac OS X currently does not offer on host color matching.
Only PostScript color matching is used when printing to PostScript
devices.
Unprofiled CMYK source data will be sent to us from the application
either as /DeviceCMYK or as Calibrated CMYK.
In the case of /DeviceCMYK, we have no idea which device or how it
"thought" of CMYK. We use the user-supplied Default CMYK profile from
the ColorSync preferences. Actually whenever we encounter a Device space
we use the corresponding ColorSync preference. So /DeviceRGB will be
tied to the Default RGB profile.
In the case of Calibrated CMYK data, we convert this calibrated info to
a source profile and ultimately to a CSA. Same is true of Calibrated RGB
data.
OK, that's all for now.
John Z.
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