Re: Controlling 6 or 7 inks
Re: Controlling 6 or 7 inks
- Subject: Re: Controlling 6 or 7 inks
- From: Johan Lammens <email@hidden>
- Date: Fri, 25 Oct 2002 11:46:23 +0200
On Friday, October 25, 2002, at 07:00 AM, bruce fraser wrote:
From: bruce fraser <email@hidden>
Date: Thu Oct 24, 2002 10:12:27 PM Europe/Madrid
To: Joshua Lubbers <email@hidden>,
<email@hidden>
Subject: Re: Controlling 6 or 7 inks
Unless you're printing through one of a handful of RIPs that bypass
the printers' native screening and control the printhead directly, any
control over black generation is illusory. The stock drivers deliver
RGB input to the black box in the driver that handles both screening
and translation from RGB to CcMmYKk. (This is an OS limitation that is
theoretically removed in OS X, but nobody has made a stock driver that
passes CMYK to the printer without a conversion to RGB.)
There are two independent issues here: using the native screening
(halftoning) or not, and having control over black. The built-in PS RIP
of our DesignJet 5000ps/5500ps has a true four-channel CMYK mode that
allows full control over K (black ink) but not over the halftoning (you
always get its built-in error diffusion). It is certainly also possible
to build a RIP that uses its own halftoning but does not allow control
over K, although I don't know of any examples.
For drivers (not PS RIPs) the story is different: they only accept RGB
input to my knowledge, so control over K is by definition impossible.
This is true for Mac OS 9 (QD) and X (?) as well as for Windows (GDI).
The majority of RIPs handle these printers as RGB devices and feed
that same black box. Any RIP that uses the native screening handles
them as RGB devices, and a fair number that bypass the native
screening still handle them as RGB devices.
Not really, see above. Our internal RIP separates CMYK into CMYKcm,
i.e. it "splits" the C channel into C and c and the M channel into M
and m, but the K is straight through. Input CMYK values are only
affected by ink limiting, which is a function of the media type chosen
on the front panel, but K is typically not limited at all. Note that
you need to switch off "Black Replacement", i.e. on the Mac use "Native
without Black Replacement" mode to get full control over K.
This "contone CMYK path" as we refer to it internally is also available
to third party RIPs, and I'm pretty sure that some of them do use it
(i.e. our printmodes, halftones, ink limits, etc. with full control
over K and their job management, color management, etc.), but I can't
quote any examples.
So unless you're printing from one of these very few RIPs, you're
better off profiling the printers as RGB, because your data will go
through one fewer conversion.
If you use our internal RIP (without BR), you can and should profile in
CMYK for best results. I can't and won't comment on competitive
products, but the same general principles apply, at least in principle
;-)
Johan
-----
Johan M. Lammens, Ph.D.
Senior Color Scientist
Hewlett-Packard ICD, R&D Department
email@hidden
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