Digital BW, The Print

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Joost Horsten" 
<j.h.j.h@...> wrote:
>
> Thanks Greg,
> 
> I love your trick to determine the maximum ink load. Makes absolute 
> sense. Your statement on the combined ink loads confirms what I 
> expected. I ran some further simulations in Excel. If you really want 
> too keep the ink load to ~80% of the max, it will be a though job to 
> get 4-5 jets firing simultanuously. Perhaps lower it to 3. This seems 
> to counteract some info I read on Cone's website that the even the 
> lightest inks contribute to the very dark gray levels. 
> 
> Joost

The lightest inks can contribute to the darks areas, but why? WHy spray 
all that solvent down when you can more effectively use a darker tone 
to fill in between dots. Truthfully, with the RIPs I have used, I see 
no need to ever have more than 2 inks going at a single time. Maybe 
this is different with QTR, I never really got very far into it.

Now, that said, if you want to use 3 heads firing at once, here is what 
I would suggest. There is a point is each dilution where you get full 
coverage, but not full density. Determine you maximum density, which is 
the point were the paper can take no more ink, or more ink does not 
give you more density. We will refer to this as the full amount, or 
100% (not the real 100% from the heads but 100% for the paper). Now 
start with the lightest shade and work backwards (this is opposite from 
the Epson way). Find the point where you reach complete coverage 
(probably about half way to the cut off), and then you start to mix in 
the next darker shade. You can slowly decrease the the amount of the 
lightest ink, and decrease it until you get to the complete coverage of 
the second shade. Now mix in the third shade following the same 
pattern. All of this needs to be determined by density, not strixctly 
by percentage. If you graph the density vs percentage sprayed on the 
paper it will help you to figure this out. ANd if you graph the 
percentage of ink on paper for the total of the two inks, you will get 
some truly odd looking graphs.

How I arrived at the values was from the linarizing step in the RIP 
which gives you the percentage of ink vs the measured density. Yes it 
is a little obscure, but it sure did work for me. And I do realize that 
describing it in words is a little difficult to translate between what 
I say and what is really happening.

And to make all this harder, the linearity of the full black is your 
guide post. You need to mix the inks so that they end up doing the same 
that the linearized full black is doing, otherwise you end up with a 
non-linear output. Often the RIP software will handle this for you 
automatically, but sometimes not.