QTR-Quadtone RIP

--- In QuadtoneRIP@yahoogroups.com, "Randy Rancier" <randy_rancier2004@...> wrote:
>
> I've created my curves and have linearized them.  Comparing the densitometer readings to 
> the ideal density readings aren't too bad for the most part; although I would like to tweak 
> them just a bit more.  My highlights are consistantly a little too dark as are the shadows; I'd 
> like to get a little more separation in the shadows.
> 
> Can you use the "GRAY_HIGHLIGHT=" and the "GRAY_SHADOW=" entry to adjust these areas 
> and get more separation after Linearization?  I haven't had time yet to experiment with these 
> controls; but from the documentation I've read I thought these controls were for those that 
> choose not to linearize.  I don't want to lose any of my dmax, but just get a little more 
> separation leading up to the dmax. 

As a note the follwing, except the very last, should be done before linearization.  Also getting your file as close to 
linear as possible will always give you a better linearization

GRAY_SHADOW and GRAY_HIGHLIGHT will shift the curves to the right (increase) or left (decrease) with the tops of 
the curves staying the same but the beginning, end and some mid-points changing.  These you must simply play 
with.  You can change the values in the curve txt file, install it and then observe the results in the quad file with 
QTR-CurveView.  These adjustments are pretty fine but fairly global if you are trying to influence only one area.  

Increase/decrease in ink limits will usually accomplish the most, with the ink limit values also being global across 
the area covered by that ink.  Because of the interaction between multiple inks the results may not always be linear.

There are two more techniques that use Photoshop ACV curves that can help here.  One method is to apply a GRAY 
CURVE.  This can be done by adding the command line GRAY_CURVE=   at the bottom of the gray section if it is not 
already in your template.  The curve can be defined after the = and can be defined in two ways:

="0;0 100;100"""  would define an ACV curve as it would run from lower left to upper right in Photoshop curves in 
Pigment mode.  That curve would have no effect, much like opening a new curve box in Photoshop.  You can then 
define with points a curve of any shape PS will allow (you still have the PS spline to deal with)  With a pigment curve 
any part of the curve dipping below the original line will lighten that area and any area above will darken that area 
much like a simple 'S" contrast curve in Pigment% mode.

You can also draw the curve in Photoshop, save it, then Paste it into that location.  For example:

GRAY_CURVE=/Users/RPB/Desktop/1800-ACVs/ILFGFSLK GC-1.acv

Points QTR to the curve named ILFGFSLK GC-1.acv located on my machine at that address.  You can drag an alias 
from the ACVs location and drop it into place in the txt file as long as the ACV file remains resident in that location.  
One caveat is that the ACV curve must be made in grayscale and then saved.  Easiest way is to open in PS a New file 
in Grayscale/16bit mode then go to Layers/New Adjustment Layer/Curves/OK and then change the mode to Pigment 
Ink%.  Create your curve, save it then drag and drop an alias into your text file at the correct location.

I find the above method works very well for fine tuning glossy profiles and is used by Ron Reeder to fine tune 
Digital Negative files.  For Matte profiles, especially with Eboni as the MK I find that a PS curve added to the image 
just before printing works better for opening up the last bit of shadows.  You can start with a 0,0 100,100 curve 
then lock down the curve above 90% with multiple points then shape the curve to lighten the dark end.

What follows is an observation with QTR, Eboni and R1800s  (It also applies to the Epson Driver so is not really a 
QTR issue per se).  And that is the mk inks even when applied only at the very end (100%) will still lay down ink 
down as far as 95% and beyond and definitely further than the sharpest curve can control.

I tested this by creating a curve that used only Eboni with the sharpest upward curve I could create at the 100% 
point.  Installing the curve  creates the quad file.  You can then copy the quad file and open it by changing the quad 
suffix to txt.  What you see is the output that is actually sent to the printer.  I then modify the Eboni curve by 
replacing all the values with zeros except for the last value.  (In theory that should only be the last half of the input 
to the 100% point of a file.)  Then by printing a 90-100 (in 1 point increments) step wedge with the curve you can 
see a great deal of ink also gets laid onto the patches below the 100 patch.  The Epson driver behaves the same and 
it seams to be a limitation with Eboni/MK and r1800s.  I have profiled an 1800 to use the UT3D inkset and the 
glossy inks do not have this problem and as mentioned above very, very good shadow separation was achieved with 
the GRAY_CURVE.  I'd be interested in hearing if any other printers behave the same with Eboni.  I have a r220 
mothballed and don't feel like putting ink in it just for the curiosity aspect but I do remember it behaving much the 
same