To refine the curve, I'd recommend using a neutralized carbon, full profile on your favorite paper. The interactions of the various elements is so non-linear that sampling and an iterative process that includes the entire workflow gets you close enough way faster than trying to decode each step.
Once you have a good neutralized profile (based on a good carbon core, hopefully) you can use the QTR sliders to blend the end points and achieve all the intermediate tones as well as lots of permutations of split toning, and that gets you straight into an area of the printing art that ABW can't reach.
Paul
Paul
On Tue, Apr 5, 2016 at 11:22 AM, andrey@... [DigitalBlackandWhiteThePrint] <DigitalBlackandWhiteThePrint@yahoogroups.com> wrote:
So I finally understood what Paul R. and Richard were talking about in their helpful posts yesterday: treat the toner as another ink channel instead of QTR's special toner type.
It turns out that in the .qidf file, as Paul's example generic-neutral file shows, you just have to specify a CURVE_Y and QTR will use the yellow channel! I hadn't changed anything else, nor specified the Y channel in anything other than the limit parameter, and as soon as I added CURVE_Y, it showed up in QTR's curveview.Using the ink as a normal ink rather than a toner gives you more flexibility to shape the curve. I don't know why, but when I put the curve into TONER_CURVE, the curve will have extra dips in it. Maybe it's wrapped around? I don't know.So for a first pass, I tried making a curve that was proportional to the b values. That is, the higher the b values, the closer the curve got to its limit value. Well that was a disaster! Lots of negative b values and blue patches. It's probably because the math is more complicated than some kind of linear relationship, and I need to do it based on the density instead. It's not a scaling thing either, ie. too much blue was added but the proportion needed was right, as I tested that with some kind of simple scaling factor.I wonder if I printed a yellow channel step wedge (which would be blue), whether I could use that to compute the amounts I'd need to add to make the greys neutral. Hmmm ....Anyway, too much thinking so I just used Paul's generic curve, and I'll be tweaking it by hand for now. Even the limit=8 toner curve is OK for now.--Andre