Seek out and download George L. Smyth's "Creating the Digital Negative" (only 20 pages) which contains the information that might 'set you out in the "best direction"
Ken
All you really care about is how much UV light is blocked by the image
There may very well be, depending on which inks/pigments you are considering.Then you are saying there is no advantage of one over the other.
Here's the problem: There are three or four Photoshop-based digital negatives systems that people are using. I won't name names. All of them do a certain amount of hand-waving and end up advocating color negatives. None of them makes a really convincing case for color over grayscale. That's what I'm looking for: a convincing case. If it's true, the case shouldn't be that hard to make.
Are you talking about:
1. A "colorized" negative (created by adding a color fill layer in screen mode after inversion and flip) vs. black and white negative without such a layer
or
2. A black and white negative printed from a gray scale gamma 2.2 file vs. the same image from RGB file with R=G=B?
:Niranjan.
Yes, this is a vexing terminology problem.
When I say "grayscale" I mean either: (1) an image in Gray Gamma 2.2 or (2) an RGB image with R=G=B.
When I say "color" I mean an RGB image with R≠G≠B.
The color negatives are made by starting with a grayscale image and converting it to RGB if it is not already RGB, then adding a Photoshop adjustment that adds a color gradient (a curve, a color fill layer, a gradient map, or a LUT).
I'm not an expert by any stretch of the imagin
In that case:
The reason for using a color negative is to increase/maximize the UV opacity (if needed for a given process) since for many printers, the UV-densest ink paradoxically is not the black but some other color that is unique for a given printer/ink combo.
:Niranjan
The maximum UV opacity is determined by the printer/ink set and it's exactly the same for grayscale and color.
For example, on my printer, the maximum density I can produce with a grayscale negative is 2.10. I can't increase it to 2.15 with a color negative, because the darkest (densest) color for any color is black.
If you plot densities for red, green, blue, and grayscale negatives, all four curves start at the same density and end at the same density. But betwen the endpoints, the curves have very different shapes. So I think at least some of the arguments favoring color have to do with the intermediate shapes of the density curves. What do you think?
https://photos.app.goo.gl/JvntDurAjrZWeaTXA
Based on some recent experience with this, I found that my printer (a cheap HP) created colour negatives (i.e., visually greyscale, but printed with CMYK inks) that had a strongly non-linear curve, in which UV absorption increased too rapidly as it moved towards black. A closer analysis showed that the CMY inks weren't able to block that much UV on their own, so the printer software was probably increasing the black ink nonlinearly as the tone reached max black.
I didn't want to used a massive curve to deal with that, so I tried making coloured negs with EDN. That was a whole other rabbit hole.
For the record, and from memory, the HP ink set looked like this, from least UV blocking to most: cyan, magenta, yellow, black. Also from experience, using black ink on its own was more prone to a dithering pattern being visible in my print highlights... but it's been a while since I tried that option.
Not sure if I understand how you printed the Red, Green and Blue step wedges. Can you explain what the files would look like?
I think you have answered my question in the OP. Black ink = bad could simply be fokelore. Mark Nelson's Precision Digital Negative (PDN) system, which is one of the earliest, if not THE earliest color negative system, uses pure CMY colors that can be made without any black ink (see below). Total avoidance of black! His original tests showed he could get very high density range -- as high as 2.4 -- with these colors and Ultrachrome ink. But with my printer (an Epson SC P400), the maximum density I can achieve with PDN negatives is 1.35, which is not high enough for most processes. Anyone using PDN today would need a high-end Epson that lets you increase ink density in the print settings. Why bother? Just make grayscale negatives.I understand that the black inks in early inkjet printers was not particularly opaque in the UV used for alternative processes. Thus, folks found that using color inks gave them better density in the UV compared to using just the black inks. My feeling that this difference in opacity (between black and color inks) has diminished as newer generations of inks arrived.
Do you have a densitometer that measures UV?Thank you, Niranjan. Your example is very helpful. You may be able to help straighten out my thinking on thi subject.
If I printed your 11x11 color grid transparency on my P400 and measured all 121 cells with my X-Rite 361T, I would find that the black cell had the highest density. If I had a process requiring a density range of (say) 1.85, I would simply look at my measurements, find the color having that density, and use it to make negatives for the process. I could do this only relying only on densitometer measurements.
But the color "methods" don't rely on density measurements. They print a target using the process and ask the process to tell you which color has a density matching its exposure scale. Now in your POP example, I might get two answers: one from the densitometer (black) and one from the process (green). I just don't understand how that can be. So how do you explain the discrepancy between direct measurement of transmission density and the indirect method of printing a target and looking for a paper white cell?
Thank you, Niranjan. Your example is very helpful. You may be able to help straighten out my thinking on thi subject.
If I printed your 11x11 color grid transparency on my P400 and measured all 121 cells with my X-Rite 361T, I would find that the black cell had the highest density. If I had a process requiring a density range of (say) 1.85, I would simply look at my measurements, find the color having that density, and use it to make negatives for the process. I could do this only relying only on densitometer measurements.
But the color "methods" don't rely on density measurements. They print a target using the process and ask the process to tell you which color has a density matching its exposure scale. Now in your POP example, I might get two answers: one from the densitometer (black) and one from the process (green). I just don't understand how that can be. So how do you explain the discrepancy between direct measurement of transmission density and the indirect method of printing a target and looking for a paper white cell?
Do you have a densitometer that measures UV?
The X-Rite 361T can measure density with either UV or Ortho (white) light. My measurements were made with UV.
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