Hi,
We talked about using QTR for digital negatives and I noticed that there are four (or maybe more) different approaches. I am trying to list them here:
Ah, a subject dear to my heart... I'll expand on this a bit.
1. QTR BW workflow with quad black inks
This is what QTR was made for. You have to use a dedicated printer with black and grey inks or one of the newer K3 printers. Third party inksets are sold by MIS or Cone and others.
Each grey ink overlaps the previous and this can be controlled in the inkdescriptor file. A no K, only grey, approach is also possible. Process related density range can be controlled by setting ink limits. Process related correction/linearization curves can be specified in the gray_curve setting or applied in photoshop. (Note: does QTR handle these curves in 16 bit? If not, it is probably better to keep using them in photoshop on 16bit files)
Yes, QTR handles the curves in a better than 8 bit fashion, although if memory serves, it's 14 bit, to allow some overhead.
Part of the "power" of the quad black approach is that it largely addresses most of the banding and dither issues some folks have been experiencing. Another part is that it allows you to run high ink levels on all the blacks and grays, and that "fills in" the gaps between dots. "negative" dots (gaps between black or dark gray dots) print as black speckles in what should be the lighter tones, and are incredibly annoying.
Another important advantage is that the carbon black inks have virtually the same density to UV as they do to visible light, just like a regular silver negative. So densitometers and sensiometric curves work. Because the density is the same to blue and green light, multi-grade papers work with their normal filtration.
And the last important advantage is that you can "read" these negatives. I've worked with all those weird "multchromic" negatives, and they just are so much work to visualize.
My own workflow uses five dilutions of black for digital negatives on one of my Epson 2200 machines. It's loaded with an inkset I call "Wiz7" (I have a tendency to name things after myself).
100% MIS "Eboni" for matte black
100% MIS PKN ("neutral" photo black, cooler than Epson's photo black)
32% PKN
10% PKN
3.2% PKN
1% PKN
MIS "glop" (a clear varnish that can be used to fill in the uninked areas of a B&W print, or applied to the whole print as an "overcoat").
For digital negatives, I print with the 5 dilutions of PKN.
For glossy prints, 5 PKN and glop
For matte prints, Eboni and 5 PKN. (Eboni for density from about 1.7 to 1.3, 100% PKN for 1.3 to 1.0, etc...)
I'm considering loading an 1800 with 8 dilutions of PKN, 100, 56, 32, 23, 10, 5.6, 3.2, and 2.3% as a dedicated negative machine. Between the smaller 1800 dot size and the extra blacks between my normal 5 "root 10" blacks, the negatives should be the best thing out there.
2. QTR BW workflow with K and LK in a printer with color inks.
As I understand Ron correctly, and after looking at his 2200 Pd and silver sample files, in his workflow only K and LK are used in combination with ink limit settings for density range control. All other inks are not used by specifying them as 'unused' or setting inklimits to zero. As an only grey approach it is not very different from the first approach but it uses only two inks.
A quite satisfactory approach, although it will result in more white speckles in light tones on the print.
3. QTR BW workflow with all (color) inks.
This workflow uses all inks with or without K an LK to print a BW negative with all inks. Default ink limit settings control negative densitity range.
Ron's earlier example files are using copy_curve to copy and set values for each color. But individual values for each ink after measuring the inkseparation print can be set in the descriptor file also.
This will work a lot better if you print a QTR calibration pattern, print that pattern onto platinum, and use it to determine the ink order based ont eh UV blocking ability of each of the colors of Epson ink. The resultant negative will look very strange, but it will work very well. As I recall, full strength magenta falls in between K and LK and "fixes" the speckles in light tones quite well.
4. QTR colorized negatives
This is a different approach and maybe combines the best of two worlds. Here the process related density range is achieved by spectral density and finetuned by ink limit settings. For each CMY color and/or two color combinations CM, CY, MY a monochrome QTR profile is made. All other inks are set to unused. CY gives a high contrast range suitable for long scale processes like salt or albumen printing. CM gives a low contrast suitable for gum printing. Contrast control and finetuning can be done by mixing two QTR-curves or by taking down inklimits (or both).
OK, this one I've honestly not seen before.
Since QTR dithers in more than 8 bits, I'd expect QTR results using just K and LK with curves built for long or short scales to exceed its performance by a wide margin.
This method would work even better with a ternary CMY calibration file of some sort to choose the right color for each process.
What approach gives the best results is difficult to say. When density range has to be very long, a spectral density negative might be the way to go.
To get the smoothest negative possible probably asks for a print with as many inks as possible. Inks that behave differently (K) than others (colors, greys) can be problematic so an 'all colors, no K' BW approach might be interesting. When using K2 K3 inksets a toner color can be mixed in for density range control.
And there's allways the printing substrate that has a big influence on the density range and smoothness of the negative. Different printers and inksets of course too.
That's an understatement.
Have fun.