Digital BW, The Print

On Sunday, December 21, 2003, at 06:58  PM, Steve Kale wrote:

> Today was my first attempt to delve a litle deeper into QTR and to try 
> to create a
> curve.  I want to be able to do this so that at a minimum I don't have 
> to bother Roy,
> Carl or others if I decide to try a different paper.  However, as a 
> result I have a bunch
> of questions on which I would appreciate some help.
>
> To put a toe in the water I did the following:  I duplicated the 
> EEM_2200-cool Ink
> Descriptor File provided with the download.  I changed the name to 
> EEM_2200-test,
> deleted the LINEARIZE line at the bottom (leaving all other variables 
> the same), created
> and installed this curve and used it to print the 21-step wedge (100% 
> this curve).  I
> then followed the helpful directions to use Eye-One Measure Tool to 
> measure the strip
> and calculate the densities.  I then compared these to the LINEARIZE 
> figures in the
> EEM_2200-cool file.  I expected to get very similar numbers but did 
> not.  Fromm 55 to
> 100 I got quite different figures.  My results were:
>
> LINEARIZE="0.029 0.079 0.142 0.215 0.294 0.374 0.463 0.547 0.635 0.717 
> 0.802 0.
> 878 0.957 1.040 1.116 1.208 1.287 1.366 1.432 1.514 1.607 "
>
> Is this sort of variance to be expected (from printer to printer) or 
> have I done
> something wrong?
There could be printer differences, Eye-One (or other instrument) 
differences, or differences in drying time before measurement.  This 
why it is a good idea to do your own linearization.
>
> I think I almost understand the basic components of the Ink Descriptor 
> Files but am
> not sure how many of their values have been determined.  For example 
> looking at the
> EEM_2200-cool and warm files, why are the ink limits set at the values 
> they are?  Is
> this just trial and error or is there some method here?
Some trial and error but also determined in the calibration steps 
outlined in the instructions.
>   More specifically:
>
> 1) At what point does Boost kick in and why not allow it to go to 100 
> at the very high
> end?  (Why set it to 90 for EEM and 95 for PFA? What would it be for 
> HPR?)
Roy can answer more specifically, but I think it kicks in for just the 
last few percent of the curve.  Actual value by trial and error, but 90 
or 95 is the usual value used.
> 2) K is limited to the default limit which is 75.  Why?
Measured as described in step 1 of the calibration procedure.
> 3) Why is LK limited to 56 (cool)/ 60 (warm)?
You answered this question in #4 below.
> 4) I assume the limits for LC and LM need to be the same to balance 
> against
> metamerism and that LC and LM are used to cool the Epson K and LK (and 
> I guess it
> follows that one might lower the LK limit a little in the cool file).
The idea was to adjust LC and LM, relative to LK,  to produce a very 
cool curve that could be used for blending with the warm curve to 
produce the desired tone.
>     Is a cool curve is
> one that takes the warm and at 50:50 is neutral?
It could be adjusted to do so, but perfect neutrality at 50% would be 
fortuitous.
>
> 5) If so, how does one measure neutral?
You could use the LAB or XYZ values from the Eye-One to evaluate 
neutrality.
>
> 6) Was the cool file created by steadily increasing the limit on LC 
> and LM until this was
> achieved?
I wasn't shooting for neutral with the cool curve - just a very cool 
curve that could be subsequently blended with warm to get the desired 
tone.
> 7) Is Gray_Val of LK set to 35 because the Epson Light Black is 35% 
> black?
No.  This was determined by measurement as described in step 2 of the 
calibration procedure.
> 8) Why is Unused_Ink_3 not set to Y?
Because Y is used by the UC-NEUTRALIZER function when sepia is desired 
and Y must be set to 0 otherwise.
> 9) When is Calibration set to Yes?  The documentation says that it is 
> used for the two
> calibration steps but it is not mentioned again.

I think you may have overlooked the calibration read-me file that 
describes the two step calibration procedure.
>
> Also I took a peek at the sepia file and thought I would see 
> UC_SEPIA=YES....

No longer required, this function is now included in the UC_NEUTRALIZER 
- see #8.
>
> Sorry for the long list but I thought it would make it easier to 
> answer.  Is there a good
> general reading source that would help me with this stuff or does one 
> have to be a
> real technician?
>
> Thanks in advance
>
> Steve
>