LaserWriter color management ABC
LaserWriter color management ABC
- Subject: LaserWriter color management ABC
- From: Henrik Holmegaard <email@hidden>
- Date: Sun, 7 Jan 2001 10:04:09 +0100
Chris Murphy <email@hidden>
PostScript Color Matching is used when you are printing from an
application that generates its own PostScript. Examples are PhotoShop,
QuarkXPress, Illustrator, InDesign - etc. This means you need to know
which apps make their own PostScript before you can effectively use this
option. The result is this option includes a Color Rendering Dictionary
(CRD) into the print stream generated by the application, and tells the
RIP to convert images based on CSA's (source profiles) and CRD's
(destination profiles).
None of the LaserWriter driver controls apply when printing from an
application that generates its own PostScript.
The PostScript Color Matching option is two options and not one:
a. Select 'Printer Default' and a rendering intent, and the driver
writes a CSA for the monitor profile plus the PostScript 3
'findcolorrendering' (: fCRD) command into the PS job. The RIP is
supposed to preselect a group of CRDs based on automatic recognition
of its media state. Not all four CRDs may in fact be implemented in
the RIP, so the RIP programmer will within the scope of his :fCRD
procedure also define a 'nearest equivalent'.
b. Select a printer profile and a rendering intent, and the driver
writes a CSA for the monitor profile plus a CRD for the LUT in the
ICC profile. However, while you may choose this option with 'pass
through' applications like QXP and AI, the RIP is not obliged to use
the CRD.
c. Select Color / Grayscale and the pixels are the same as in (a) and
(b) because (c) assumes the host has already done the conversion and
(a) and (b) just write source and destination color space
specifications which the RIP will implement using CIEBased procedures.
d. Select ColorSync Color Matching and the pixels are different than
(a) and (b) and (c) because the QuickDraw - ColorSync - LaserWriter
driver combination takes the system profile as source (unless the
application intelligently hands off using a color space conversion
profile or RGB printer profile to make multiple workstations convert
into the same CMYK numbers the way say Linocolor does), makes you
select a destination ICC profile and intent, and finally pixel
converts on the Mac rather than in the RIP.
The reality is that Apple folks say the color conversions were about
30% faster on Macs compared to in the Color LaserWriter controller.
The general argument for in-RIP used to be that the RIP has the most
horsepower.
This is because it can be safely assumed that the monitor
profile is source, and the destination profile is the printer you're
using. The monitor profile is assumed automatically (as the System
Profile or Display Profile depending on which version of ColorSync you're
using).
Not quite, see above. To access the QuickDraw printing pipeline from
within Linocolor, deselect the checkbox 'Direct PostScript Output' (I
posted a note about this a while back).
Also, John Gnaegy posted a note some time back explaining how the
QuickDraw PictureViewer hands off RGB. It'll use an embedded profile
if there is one, and the system profile if it is forced into an
assumed source strategy by untagged, color blind RGB pixels.
QuarkXPress won't even generate CSA's
This isn4t a deficiency on Quark's part.
Adobe Illustrator never generated CSAs and CRDs. I checked with
Shankar Iyer for AI6 and again recently.
Meaning that PostScript Color Management was never a reality, and
that vector data were always handed off without a CIE reference,
either to the PS CMS (CIEXYZ) or the ICC CMS (CIELab / CIEXYZ).
Hope this helps -:).
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Henrik Holmegaard, TechWrite
Stationay +45 3880 0721 - +45 3881 0721
Mobile +45 2178 3959
Toelloesevej 69, 2700 Broenshoej, Denmark
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