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Dear Shilesh:

Thank you very much for your reply. Very helpful, because it clarifies the procedure. What you explain is what I was thinking of, originally. But I was misguided by the descriptions in the QTR User Guide and in the Calibration Guide (from the QTR website).

In the Calibration Guide it is stated on page 4: "But it's necessary to have all the relative densities to a common value". So far so good. It is logical and in line with what you explain. But on the same page it is written: "Since the LLK will be transitioning to the LK ink in the profiles the comparison is most accurate by comparing the LLK ink to the LK ink not to the K ink." Thereafter, a calculation is made in which the relative density of LLK to LK is multiplied by the relative density of LK to K, suggesting that the result of this product would yield a more accurate relative density of LLK to K.?

1. I am not convinced that the result is more accurate, because for 3 gray inks the multiplication of fractions involves the determination of 4 data points compared to the involvement of only 2 data points for direct determination of the density ratio of LLK to K. But it may depend on the method used to measure the curves.
   
2. More importantly, the multiplication of fractions only yields the desired ratio of LLK to K if the functions L(K) for all inks would be linear, i.e. if L(K) = a + b*K with some constants a and b for all inks. But in our case the functions are exponential of the form L(K) = a + b*exp(-c*K) with a>0, b>0, c>0. For such functions the above multiplication of fractions will NOT relate the gray densities to the common K reference curve. Rather, in the example plot in my original post for HFA-PR-308 and GCVT inks the multiplication of fractions yields densities given by the abscissas of the diamonds. The densities of the gray inks (all inks are gray except for the toner) relative to the common reference ink K are given by the abscissas of the squares (confirmed by you).
   
   For an example, below I show part of my previous plot. C, LK and K denote the cartridge slots. The carts are filled as follows. C: 50%MK, LK: 100%PK, K: 100%MK. The LK cart with 100%PK prints dark gray on matte paper. From the fits (thin curves) of the data (circles) one obtains
   
   • LK to K: fraction = 0.4821 (vertical red line)
     
   • C to LK: fraction = 0.4786 (blue X)
     
   • The product of these fractions is = 0.2307 (vertical blue dotted line)
     
   • Compare this to the 'correct' value of the C to K density (vertical blue line): 0.3307.

Concerning the global ink limit, you are correct. I was thinking of using the Black Boost, because the slope of the L(K) curve for the K channel is already very small at K=100% (with global ink limit of 50%) and already L(K=100%) < 20 for the black ink.

You are correct regarding the toner. For the toner curve (open blue squares on the dashed blue line in my original plot) I have not calculated its relative density, because it requires a separate curve in the Ink Setup to neutralize the print for all gray values.

Thank you very much again!
Hendrik

Am 04.02.2025 um 04:35 schrieb shileshjani via groups.io:

• First, I am not familar with dual K inkset described by Paul Roark. But you mention that you printed at 50% limits on HPR 308, which is a coated MK paper, and as-such should yield Lmin of approximately 17.7 to 16 (Dmax ~ 1.6 to 1.7) using single MK. So you may want to look into, perhaps increase ink limit to >50% or use "Black Boost" ~70%
• Please refer to picture below on how to set the density of lighter shade of grey inks. Mind you this is only for 3 shades of grey (K, LK, and LLK) as an example. Toner inks utilize the density numbers also, but rely on "Limit" to determine how much of the toner gets used. You that either visually, or ideally with a spectro.
• Say at the calibration ink density, the solid blue line represents density of K in 5% step file. Solid orange line represnts LK ink, and solid green line is LLK ink. What you want to do is to find Lmin of LK and LLK (dashed orange and green lines respectively), and find the patch of K which prints at the same density. In the case of LK (orange vertical dash) gives you ~25%, and LLK (green vertical dash) gives you ~15%. These are the numbers you input into "Density." If I undersand your graph, it seems you are looking at these numbers from succesive lower density inks. That would not be correct. All densities should be relative to K.

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Dear all:

I am a beginner and I have a question regarding the determination of the ink densities to be used under the 'Ink Setup' tab when using multiple gray inks.?

O.k., Paul Roark calls it a 'judgement call'. With my very limited experience I fully agree. But regardless of that I would like to better understand the procedure which I found in several documents. Accordingly, the ink density to be entered under 'Ink Setup' should be the result of the product of the fractions of the respective next darker ink which would yield the same density (or Lab L) as the ink at 100%.

I measured the Lab L values from a print of the calibration image for Hahnemühle Photo Rag 308, the GCVT ink set of Paul Roark, resolution 2880-super and 50% global ink limit. The results for each ink are shown as circles in the image below.? All data can be well represented by exponentially decaying functions (lines).

If I follow the above mentioned standard procedure, the fractions are indicated by the labelled plusses and the densities to be entered under 'Ink Setup' are represented by the K values below the full diamonds (they do not lie on the K-curve, because the ink curves are not linear). Am I correct that these densities, i.e. products of fractions, should be used? I am asking, because the products of the fractions, although they certainly carry relevant information, have no obvious meaning which would help to visually understand the resulting ink curves.

Hendrik

PS: From the curves in my ink separation plot, is the global ink limit I selected (50%) adequate? The lighter inks still have a significant slope at 100%.

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A question for those of you who are more knowledgeable than I am regarding Sequoia /Print panel/ Printer Options/ Printer Settings:

What does “Finest Detail” actually do?

I usually turn it on except for impressionist or atmospheric images, since it just sounds like a good idea for detailed images.

But, I’m don’t think I can see any difference when Output Resolution is set at 1440 or 2880. ?Seeing is, of course, what it’s all about, but still I wonder whether it actually does?anything to what ends up on the paper at these resolutions.

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You also have to NOT have the AirPrint driver installed.

Roy

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