Help me understanding the QuadToneRIP digital negative workflow

[RogerHyam]

Please can you help me check I've understood the QuadToneRIP workflow for alternative processes. I've been reading and watching YouTube but it is all screen shots and people wiggling sliders and I need an overview!


Firstly this is how I see a normal inkjet workflow. An ICC profile is used to specify how the image appears on the monitor and another is used to specify how the printer should render the image.

We replace the regular printer driver with QuadToneRIP which is configured using a .quad file like this.

(The image is actually inverted before sending to QuadToneRIP but you get the idea). We can optionally produce an ICC from the .quad in order to soft proof what the print will look like on the monitor.

We need to develop a .quad file for our specific process (all the materials and skills involved). We do this using QuadToneProfiler by printing and scanning targets till we have a .quad file that produces a linear step wedge. This should then print any image the same.

Is my world view correct or am I fundamentally misunderstanding something?

 

[koraks]

Your understanding is correct. There are a few possible variations in practical implementation here and there, but they don't change much about the basic concept, which as far as I can tell you've understood correctly.

One notable variation is the choice between linearization using QTR, or linearization using an adjustment curve in a photo editor (Photoshop, GIMP) etc. In either case QTR can be used for output to the printer. For instance, if you use a separate curve adjustment (not done in QTR) but still output to QTR, there will still be a QTR profile that defines the printer behavior in terms of ink channels, density per channel etc.

We can optionally produce an ICC from the .quad in order to soft proof what the print will look like on the monitor.

I've personally never done this or experience the need for it for monochrome alt. processes. Color would be a different story, in my personal opinion.

If you do linearizations in QTR, note that there's a major difference in workflow between Mac- and PC-based systems. Both offer the possibility to turn density measurements into an adjustment curve, but the workflow is very different.

 

[RogerHyam]

One notable variation is the choice between linearization using QTR, or linearization using an adjustment curve in a photo editor (Photoshop, GIMP) etc. In either case QTR can be used for output to the printer. For instance, if you use a separate curve adjustment (not done in QTR) but still output to QTR, there will still be a QTR profile that defines the printer behavior in terms of ink channels, density per channel etc.

This is the bit I am not totally sure about. Why use QuadToneRip at all if you aren't developing your own .quad profiles?

Answering my own question: I presume it is to do with the maximum blocking power of the ink. If the .quad allows you to add MORE ink than a profile for another paper then you could never get true whites (or blacks in a positive process) when using an ICC profile for a generic paper.

Doubting my own answer: It is unlikely that an ICC for a matte paper would clip the amount of ink needed to print max black on a transparency paper and, indeed, the demos I've seen seem to show that a maximum blocking ink value is a way down the scale of what could be applied by the printer.

Or do you create corrections in Photoshop and then use those to create .quod files?

Is it feasible to develop you own way of optimising an intermediate image and get similar results to using QTR etc?

 

[koraks]

I presume it is to do with the maximum blocking power of the ink. If the .quad allows you to add MORE ink than a profile for another paper then you could never get true whites (or blacks in a positive process) when using an ICC profile for a generic paper.

That's part of it, yes. Related to this is the ink configuration; e.g. for an alt. process negative you'd typically use only a few channels (or perhaps even only one), and that's what QTR allows you to do. This brings me to something else: you mention ICC and QTR profiles as if they're similar, but really, they aren't! An ICC profile is basically a color translation table or algorithm that translates between two color spaces. A QTR (.quad/.qidf) 'profile' is a translation between color data and amounts of ink to be deposited from different channels. They may seem somewhat similar from a distance, but they're entirely different animals. Note also that an ICC 'profile' for an inkjet printer is really not a deterministic profile, but rather a descriptive characterization of the printer's response to given color data. This can then be taken into account by the application software to determine an adjustment based on the printer's real-world behavior. This is fundamentally different from a QTR ink description, which really controls the actual printer behavior.

a maximum blocking ink value is a way down the scale of what could be applied by the printer.

It depends on the media and if you're talking about alt. printing processes, the process involved and even such intricacies as wavelength distribution of the light source.
Note btw that the relationship between optical blocking power/density and ink load is not as straightforward as it may seem. You might be led to believe that the blocking power of e.g. a matte black ink is sufficient to 'get the job done' and therefore there's never a reason to 'max out' the ink deposit of that channel. However, in reality, what you often do with alt. process negatives for continuous tone application is combine a couple of channels to get smooth tonality (actual resolution per channel is only a fraction of the nominal resolution of the printer). Combining several inks with varying blocking powers means that you'll easily end up deposting a lot more ink per surface area on the OHP film than the film can bear. In short, the maximum ink deposit the printer can give is in practice not the limitation you run into. It's the film's ability to take this ink without causing problems with puddling, uneven drying etc.

Or do you create corrections in Photoshop and then use those to create .quod files?

No, correction curves as used in e.g. Photoshop are distinct from QTR ink definitions. They can (and do) stack up on top of each other. Basically, the QTR ink definitions determine the printer's behavior, any additional adjustment curve can compensate for the specific response of the alt. process on the digital negative. What makes it a little confusing is that you can integrate this correction curve into the QTR ink definition.

Is it feasible to develop you own way of optimising an intermediate image and get similar results to using QTR etc?

Yes and no. In terms of linearization & adjustment curves, yes. This is what Easy Digital Negatives and similar workflows do. But what sets QTR apart is that it effectively takes the place of the printer driver and directly controls how much ink from each nozzle is being output (sort of; close enough for our understanding). So to accomplish something similar to what you can do with QTR, you'd have to do linearization in e.g. Photoshop and control the printer's behavior with the Epson printer driver. The good news is that the Epson driver offers fairly good (and in practice, sufficient) control over which channels are used (using the advanced B&W mode and its color toning function) and total ink density (through the media/paper profile, which can be manually adjusted).

 

[RogerHyam]

Easy Digital Negatives

Ha yes I saw EDN a while ago but had totally forgotten about it. So many ways to skin a cat!

 

[Alan9940]

IMO, trying to build profiles with the necessary linearization for alt process printing is a bit of a pain. It can certainly be done...just depends on how much time and effort you intend to put into it.

It's not clear to me if your using Richard Boutwell's QuadToneProfiler-DN software, though you have posted the icon for it in your original post. I would highly recommend Richard's software and if you'd like some clear A -> Z instruction on working with it, check out the series of videos Bill Schwab (North Light Photographic) did on YouTube. FWIW, I played around with the EDN techniques, but wasn't as satisfied as I am with the negative procduced by QCDN.