QTR-Quadtone RIP

Hello all,

I'm hoping some of the ubertechs on the list can help me out.  I have  
been working with QTR off and on for a couple months and thought I  
had a pretty good grasp on the process. However, I recently purchased  
a densitometer to create more accurate linearizations. This has  
resulted in some serious confusion for me. I had mentioned a couple  
weeks ago that I was going to post some of the curves I had  
generated, but have decided not to at least for now as I discovered I  
am entirely unsure of their accuracy. I've read everything I could  
get my hands on re: QTR including searches through past messages and  
have still not found the answers I'm looking for.

Before working with the densitometer, I was using my scanner and  
eyeballing the final curves. This was resulting in quite excellent  
screen to print matching (with a few discrepancies, depending on the  
image) without any need for a custom dot gain profile or any of the  
other methods used for screen/print matching. In other words, I was  
able to print an image straight through QTR and get essentially what  
was on my screen.

Now however, using the densitometer readings, aside from getting a  
smooth ramp, after linearizing and achieving near ideal densities (at  
least as far as what is listed in the available documentation) the  
images print quite dark when printed directly and require a PS  
adjustment layer to print properly. It seems to me that the curve  
needs to be lighter, but if I make it lighter then the densities will  
no longer match the ideal values.

 From what I understand of the average color management workflow,  
there are essentially two steps in the process of managing a device,  
ie: calibration and profiling/characterization. Calibration is the  
process of modifying the devices behavior (linearizing the inks,  
aligning the printhead(s) etc.)  in order to bring it to a standard  
state and profiling is the process of recording its behavior after  
calibration, and creation of the profile with its LUTs for future  
conversions so that the color that is printed, is approximately what  
we see on our screens. If working with color inks, the profile is  
clearly necessary as the linearization of the inks does not  
necessarily result in the exact expected colors when the inks are mixed.

So, in the case of BW, I assumed that since we're working  
monochromatically, there wouldn't really be any need for profiling,  
as the linearization should result in the desired values. To be a  
little more specific, since the process of linearization is setting  
up the curves so that the printer produces specific densities when  
receiving cmyk values in a single ramp (as opposed to mixing multiple  
ramps for color mixing), the process of profiling the printer's  
output would only be redundant as the only purpose would be to  
profile the output of values since there isn't any color to consider  
(aside from the issue of being able to soft proof with the correct  
tonality).

Since a color management system is meant to translate values as  
accurately as possible from one device to another via the PCS, I  
figured that what appeared to be 50% grey on my monitor would  
correlate to the corresponding ideal density for the 50% patch on the  
test print. But, this has not been the case each time I have redone  
the process.

So in specific, I'm hoping someone could clarify the following,

1. If an ink/paper combination is properly linearized, should the  
output be reasonably close to what's on the screen if the display has  
been properly profiled? Or is it also necessary to profile the BW  
output or use one of the other screen/print matching processes to get  
this type of match?

2. What exactly would be the purpose of profiling BW output, aside  
from being able to soft proof for tonal variations?

3. Since QTR will either take an image converted to 2.2 gamma and  
print it without altering the values or in the case of images not  
saved in 2.2 gamma, will convert to 2.2 gamma prior to printing, ie:  
change the numbers to correlate to the previous color space,  what  
would be the purpose of using one color space over another since what  
is seen on screen and subsequently encoded in the 2.2 gamma space, is  
what is printed?

4. Are the ideal densities meant to correspond to our visual response  
to changes in value? I thought this was the case but now I'm not sure.

5. Although the curves are not profiles are they meant to be used as  
such, or are they more like the Epson driver settings that just  
control the ink limits etc. and should be used in conjunction with  
destination profiles?

6. Am I just way off base, regarding my understanding of this  
process, or am I headed in the right direction?

By the way, I'm working on a mac with OS X, the beta version of QTR,  
using an X-Rite DTP-32 (have calibrated it at least once a week), and  
using a 1280 with a modified version of the UT2 inkset that replaces  
the sepia ink in the yellow position for the light, cool grey FSN-Y.  
I'm also using a 2200 with UC inks, an R200 with some experimental  
inks and a 7600 with the UT7 inkset, so I really want to know how to  
do this stuff right.

Thanks in advance for any help or information.

Eric
www.ericashworth.net