QTR-Quadtone RIP

Hi all,

In view of the confusion we had lately on this forum on the different
QTR workflows, I decided to do a small experiment, comparing two
workflows.

Workflow 1
1) editing the image. I used both AdobeRGB and Gray Lab as workspaces,
without differences, and (at least to my understanding) the editing
workspace is of NO relevance here. Any workspace will do

2) softproofing the image with the gray-matte-paper icc profile
(setting: "preserve numbers"=OFF, "rendering intent"="relative
colorimatric", "blank point compensation"=ON, "simulate black ink"=ON)

3) flatten, convert to 8-bit grayscale

4) convert profile to "gray-lab" and save as tif

5) print the image with QTRGUI

Workflow 2
1) editing:  same as workflow 1

2) NO softproofing

3) flatten, convert to 8-bit grayscale, smae as workflow 1

4) convert profile to "gray-matte-paper" and save as tif

5) print the image with QTRGUI, same as workflow 1


The hypothesis for this experiment was that these workflows, although
different, are actually equivalent.

  It's hard to get the hard physical, quantitative evidence from the
results.  It would involve direct comparison of screen luminances with
print luminances and  I do have a spectrometer but I have currently no
idea how to directly compare emissive and reflective values.

Nevertheless a qualitative comparison DOES support the hypothesis. In WF
1, the softproofing lightens  the image, with respect to the original
image. So if ones edits with Softproofing "on", the actual image is a
bit darker. In WF2, the conversion of the image the gray-matte-paper,
darkens the image. This is NOT visible on the screen, since photoshop
compensates for this, but it can be checked with the eye-dropper: the
LAB values drop (or the K-values increase which is the same) after
conversion.

So in BOTH cases  a darker image is sent to the printer than the one
displayed on the screen.  My explanation is as follows:  the dynamic
range/contrast of paper is lower than that of a screen. Paper can
typically display L-values between 15 and 95.  So, especially in the
blacks there is quite some descrepancy between paper black and image
black.  Both WF1 and WF2 are ways to compensate for this. WF1 uses the
gray-matte-profile to compensate the screen-paper difference on the
screen, while WF2 compensates it in the printer.

WF2 is the workflow as advocated by Roy, WF1 is the one I (and some
others) use. But now my (preliminary, since based on incomplete
evidence) conclusion is that they lead to the same result. I personally
always could live better with the theoretical foundation of  WF1, but
now I think I understand that it's just a matter of taste.

Open for any comment and critique. For the ones more knowledgeable than
I: please check if I used the right settings for softproofing.

Joost









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