Digital BW, The Print

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, John 
Labovitz <johnl@j...> wrote:
> On 12/25/02 10:22 AM, "Charles Bandes <byronbulb@y...>"
> <byronbulb@y...> wrote:
> 
> > 6 inks - I am taking wild guesses at the %% here, please 
assume they
> > are incorrect. You get Black (100%) Neutral Grey (75%) 
Blue-grey (35%)
> > Pale Blue-grey (12%), Warm-grey (35%), pale warm-grey 
(12%)
> > 
> > It seems to me that what happens is basically that the printer 
has two
> > complete quadtone sets - a warm and cool set, and that it 
mixes equal
> > parts of cool and warm to make neutral for the neutral set
> 
> Huh.  That's totally different than I was assuming, which is 
okay.
> 
> So do you VM-using folks choose one of warm/cool/neutral?  
Or does it work
> well enough to be able to mix a slightly-cool versus a 
really-cool?
> 
> -- 
> John Labovitz
> johnl@j...
> www.johnlabovitz.com

I've been using the VM inks for a while so maybe I can shed
some light on the basic idea and how they are used.

I think its easiest to understand the 4 ink printers first.  The
original VM inks are a black, a warm dark gray , a warm
light gray, and a blue toner  -- these are in the K,C,M,Y ink
positions respectively.  The basic concept is to use the
3 grays (includes black) in a partitioned set to get the whole
spectrum of grays.    The steps of gray are quite warm,  and
this would be the "warm curves".    Then to make cooler
steps small amounts of the blue toner are added in to
neutralize the warm tone.  In concept its simple but there are
a couple of complications that make the curves difficult to
design.  First is that adding blue toner also adds density so
more toner also requires reduced gray to conpensate.
Second, the real difficulty is that control of the black ink is totally
by GCR (gray color replacement).  The driver has a builtin
algorithm to replace high density C,M,Y combinations with
black ink.  Its basically a trial and error effort to see how each
printer's driver does this.

There is now another VM ink set called VM-Sepia.  Its a 
similar idea but the gray inks are neutral (or slightly cold)
grays and the toner color is sepia.  This reverses which
curves give which result.  No-toner is a cold tone print
whereas lots-of-toner gives a warm sepia print.  

I think for the most part people just pick one curve for a
print rather than trying to blend a combination.   The GCR
for each curve is likely not compatible.

---------

The 6 ink printers are based on the same concept as the
4 ink printers.   The epson drivers all have a builtin idea
of 2 pairs of inks i.e. C and light c, and M and light m.   They
are automatically assumed to have a fixed density difference
and the driver will automatically transition from the light
one to the dark one.   For the 4 ink printers Y is used for
the toner, but this would result in 5 grays and 1 toner.  So for
the 6 ink printers it was decided to use  M and m for the
toner and KCcY for 4 grays.   This makes the curves look very
different but its just a color difference -- still the same concept.
The 6 ink printer curves are created in the same way but
with so many builtin transitions (Cc, Mm, and GCR) there
can be some very steep looking curves.
 
----------

The main beauty of using gimp-print (when the full 6 color
control works) will be avoiding the builtin transitions and
controlling them best for multi-gray inks instead of the
control that was designed for colors.

Roy Harrington
www.harrington.com