Thilo, if put my responses below a few of the questions (in italics) you raised in you first message.
There are some really interesting and powerful things that can be done with the toner inks when using the multi-shade profiles in the 8-ink printers (and even the 6-ink printers for that matter).
For every ink one can choose the following points/despriptions: "Gray ink", "Toner", "Toner 2", "Copy curve from" or "Load curve”.
My question: What is the difference between the options "Gray ink", "Toner", "Toner 2”?
You can think of “gray ink” and “toner” and “toner 2” as three separate gray partitions that can be applied separately throughout the whole grayscale. These are then all linearized to create a single consistent density increase at the final stage of the profiling/curve creation process.
The bulk of the grayscale is usually being made up from the partitioned gray inks with their higher ink limits. The toning inks and toning partitions usually have lower ink limits and run underneath the main gray partition. Although, there is no reason why you can't have two toner partitions with higher ink limits that make up the whole of the grayscale (this is a little off topic, but jut illustrates the multiple possibilities when using toning profiles).
The two different toner curves can be used together (or separately) to put different color inks into mix, or partition two or more gray inks of a different hue for toning the main gray partition. These toning curves can be partitioned from any number of inks, just like the gray curve, and they use the same method of partitioning using cross over points. They also use the same highlight, shadow, gamma, and toner_curve settings that are used to define the partitioned gray curve.
The Raw warm/neutral/selenium profiles for the K3 inks in the x800 printers were made with the intent of partitioning the C and LC and M and LM dilutions so the text file only lists the inks like this in the ink descriptor text file:
TONER_INK_1=M
TONER_VAL_1=100
TONER_INK_2=LM
TONER_VAL_2=40
This section of the ink descriptor file can be edited to add more inks to the toner partitions by increasing the N_OF_TONER_PARTS= to 3 (or more) and then adding the lines for TONER_INK_3= and TONER_VAL_3= (and add the appropriate ink and its cross over point to partition the curve properly).
Alternatively, each toner can be set to use a single ink, un-partitioned, that runs the whole length of the scale underneath the main partitioned gray inks.
Seeing this done in the qidf text file rather than the QTRgui makes it clearer as to what is going on behind the scenes, but these things can all be done in the gui too.
Is QTR handling the ink channels in a different way, depending on which option I choose?
Or are the options "Gray ink", "Toner", "Toner 2" just a convenient and/or informative way to keep record on the functions of these inks in a certain curve? (In the case of the 3880-Eboni-Variable-Tone the yellow ink is marked as "Toner", but there seems to be not difference when i make it a "Gray ink”.
These options for "Gray ink", "Toner", "Toner 2" settings are important, and are how the QTR curve creator program knows what to do with each ink and where to put it in the final set of curves.
If you mark this yellow channel as "gray ink" it would be partitioned into the gray curve using the cross over point set for that ink (this is the density setting as it is labeled in the QTRgui). If you had two inks defined as toner 1 inks they would be partitioned using the cross over/density settings for those two inks. I don't have a way to view Paul's variable tone profiles at the moment (writing this on the iPad) so I can't see if the toner uses just the yellow ink, but if it does, it would have the ink limit set somewhat low, and the "density" set to 100. Those settings would make it run the whole length of the scale with the total ink at the 100% patch being defined with the ink limit for that channel.
Hope that clears up a little of what is happening when you change those ink labels. You really have a lot of options and a lot of different ways of approaching making these custom ink mixes.
Richard Boutwell