QTR-Quadtone RIP

The answer is that it is very doable. And your first one is the hardest. Basically what you 
are outlining is the pretty much the right approach: You are telling the printer to use a 
specific ink percentage at a specific image percentage.

First, make sure your photoshop color settings are consistent and stay that way. I use 
gamma 2.2 for instance. Save the color settings file as 'digineg' or something. Also make 
sure you now the minimum printing time to get solid black through your inkjet substrate. 
You must be able to control the printing times and printing controls in genreral very 
accurately, or you will be attempting to linearize a moving target. I think this is where 
people can have a lot of problems with any inkjet negative method. Consistency is 
essential.

Make your basic ink profile that will deliver just about the maximum density you need for 
your proceess. I do palladium, so my basic profile produces a UV density of about 2.9.

In the linearization tab in QTRgui, or in the proper place in the .qidf file, set the basic 
linearization to the following:

"0;0 100:100" 

This last step is necessary to give you the ink mix that will be used for the rest of your 
linearization exercise. Don't know why, but you get different results if you leave it blank 
on your first pass. 


Invert the step tablet and use some text to identify it as Trial one or something similar. 
You will go crazy remembering which is which otherwise

Now print out your step tablet and then make a print in the process you have chosen.

With your reflection densitometer, measure the printed tablet. A 50% black should be a 
reflection density of about 0.48, assuming that your dmax is 1.35 and you are printing on 
a typical watercolor paper. Find the square that is closest to 0.48. It probably won't be the 
50% square. Say it is the 40% square. Now hold this up to your test strip on screen and see 
if you agree. The 0.48 number is a theoretical number from a function called the Yule 
Neilsen formula which equates dot percentage to reflection density. Like all true empirical 
formulas, there are some fudge factors in it, though, and you need to determine if it is 
giving you the right result.

This will anchor the middle of your curve. So the new linearization profile would  now 
read:

"0;0 50;40 100;100"

The middle of your curve is now anchored. Now go back and do it for your quarter tones 
at 25% and 75%. The target values should be about .21 and .83 respectively. Again, this is 
if you are printing a process with a 1.35 dmax on matte paper. And also once again, 
visually look to determine if this looks right when you compare the printed step tablet to 
the version on your screen. Say the percentage squares that do this are 35% and 65%. So 
now your linearization numbers are:

"0;0 25;35 50;40 75;65 0;100"

You can see where this is going. If you get close on this printing, it is a small mattter to 
print one more time and smooth your shadow and highlight areas by inserting more 
points. 

I have successfully linearized the 2200, 2400 and 7800 for palladium printing using this 
approach. It took about 16 pairs of input;output values to linearize the 2200 for instance. 
Patience and consistency will get you there very quickly. Good luck. I can send you a 
spreadsheet that has the Yule Neilsen formula imbedded in it if it will help.

Clay



--- In QuadtoneRIP@yahoogroups.com, "spsguru" <spsguru@...> wrote:
>
> Hi everyone
> 
> Like many I am trying to create digital negatives using QTR on a 3800.
> Well I am 22 test prints down the road and not able to get the control
> I need. I get either print highlights good and blocked up shadows or
> vise versa. Using the usual tools (gamma, shadow, highlight)only make
> it worse.
> Curves have also been unsuccessful using the method described in Ron
> Reeder's - which is a GREAT resource I have just not been successful.
> 
> so I went to try and linearize. 
> 
> I read 21 steps with an xrite 810. and entered those readings into the
> linearization line. Still no success. It ended up blocking up the
> highlights and shadows with thinning out of the midtones.
> 
> Yet I feel like if I knew how to control the values in the linearize
> line that would yield ultimate control of the ink densities.
> 
> So here are my questions - 
> 
> 1. I have so many negatives now that I can read the value I want via
> UV so I know exactly what the negative value should be for each
> printed value.
> ---Is there a way to use linearize to get a specific ink output for
> each value? In other words - I I know that I need UV of 1.5 for a 50%
> grey - can I get use a value in linear to lay down ink for 1.5 at 50%?
> 
> 2. I entered in the values as read by reflection densitometer into the
> linearize curve - but the output was no where near linear - can
> someone explain what linearize is really doing so maybe I can figure
> out what direction to tweak the values to make the curve move correctly.
> 
> thank you for any help
> Sean
>