Digital BW, The Print

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "mike_nunan"
<mike_nunan@h...> wrote:
snip...
> Sorry, I wasn't being clear. I'm talking about the toner inks as
> being effectively colour inks, albeit very unsaturated ones. I can
> see how by using the RGB or CMYK curves, you can control the ink
> proportions that are used for each grey level in the image. That's
> what I understand to be the meaning of partioning. Correct?

Partitioning, the way the term tends to be used here, and how I think
of it, has more to do with traditional quad inksets, and is expanded
from there to account for other inksets. So in it's more basic form,
it has to do with sending the appropriate part of the tonal scale in
the image to the appropriate gray ink, and making the transitions
between the inks linear. So for a normal, non-tinting quad inkset, you
are sending highlights to the light ink, mids to the middle gray ink,
dark tones to the dark gray ink, and blacks to the black ink, to put
it very simplistically. In inksets that also use toners, other issues
come into play to adjust them, but usually there are some inks to
partitioned as mentioned, and others to effect hue (they may also have
dark and light components that require partitioning).

snip...
> > The second approach allows for split toning as well depending on
> the
> > inkset. I do it all the time here with StudioPrint, the right inks,
> > and a whacked brain. The Septone system makes it easy to do, and
> I'm
> > sure others here can tell you how they do it with their inksets and
> > drivers.
> >
>
> Yes, but you can only split based upon grey level in the original
> image, true? AIUI with the other approach you can do clever stuff
> such as applying one curve set to one part of the image and a
> different curve set to another, in order to get a different split.

Yes that's true, though the newest version of ImagePrint is supposed
to have more flexibility to do what you suggest.

> > > It
> > > seems from your and Paul's comments that the Epson driver is
> still a
> > > pretty good choice though.
> >
> > Actually I believe I said it was ill suited to the task. But if
> Paul
> > or others have good curves available for the particular
> > ink/paper/printer you use you're ok.
> > Tyler
>
> You did, but you also said that you'd seen great Cone ICC prints, so
> maybe my natural optimism was running away with me a bit there! Can
> you elaborate on the shortcomings of the Epson driver?

Since it works with RGB input, everything must be done with RGB
curves. There isn't a straight through path from the file to the
specific inks, which are not three channels of R, G, and B. What the
driver does after the fact, while possibly good for standard color
printing with Epson inks and papers, may not be ideal for what we'd
like to do with these inksets, and sometimes is very difficult to
precisely predict. Not only do you have no direct control of the black
ink (you have to control it with specific RGB numbers) but some RGB
values will cause density to go down instead of up the way we are
attempting to control it. This is because at certain RGB levels the
driver is pulling out CMY to replace it with K, and this may not work
well with the inkset we are using. The way it works in general is
sometimes unpredictable, usually counter intuitive, occasionally
outright maddening as some curve change you made causes a totally
unexpected result.
It can obviously be done, but it is difficult. Even with a good
profile, which helps you predict the behavior, I wound up doing a lot
of trial and error. Way back before there was Piezography, Lyson
quads, or 1/10th the knowledge we have now, I threw in the towel and
went with a RIP, which gives direct control of each ink with no
intervention.
Every once in a while I have reason to go back and try it again
thinking I know more and have better tools now, and encounter the same
obstacles.
I believe somewhere in the files section of this list there may be a
more extensive write-up of partitioning with the Epson driver.
What Cone is doing is very interesting, but proprietory and little is
known of their method though I have a few guesses and have made
similar profiles with difficulty. I've seen the profiles and they do
indeed do all of this partitioning and preview well.
Tyler