RNP-Array Digital Negatives

I settled on the RNP-Array as a name for my alt hybrid negative method. More info and a website to follow...promise!
Part one is choosing a blocking colour for your process.
Print one or all of the attached arrays at your standard print time -- if you want a fill colour right away. If you want to use the densest colour your printer can create, extend your print time until a particular hue reveals itself as a super blocker (and don't assume it's the black square, it might not be).
The advantage to using this method is that the increased colour palette may open up the use of printers and inks for making alt-process negatives which would not normally be possible with other methods. I make no promises. But it works for me.

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Enjoy.

~m

g'day mk

could you plz explain this concept a little more

why three arrays?

if i was to print them, i assume you mean as a neg for an alternative process or silver gelatin, what would i be looking for in the resulting positive?

why would i need to find and use the densest colour, traditional film negs do not have entirely opaque areas?

why colour arrays and not just greyscale?

what substrate should i print the arrays onto?

Works for me, too. mkochsch sent me the red/green array when I got stuck working with Dan Burkholder's method. The discovery point was that inks and pigments absorb UV light differently. Dan's color was for the Epson 2200, IIRC, which gave different results when I used it with the Epson R2400. Finding the right blocking color from the red/green array gave me good results.

Don't you also need to know the weakest blocker so that you can use it to smooth out the printer dot pattern?

Best,
Helen

Ray Heath said:

g'day mk

could you plz explain this concept a little more

why three arrays?

if i was to print them, i assume you mean as a neg for an alternative process or silver gelatin, what would i be looking for in the resulting positive?

why would i need to find and use the densest colour, traditional film negs do not have entirely opaque areas?

why colour arrays and not just greyscale?

what substrate should i print the arrays onto?

Click to expand...

I wanted to cover more colour combinations in the RGB model. Remembering that RGB is additive and that you will eventually be printing using a subtractive colour model (CMY-K) means R needs two dots (Magenta-Yellow), G also needs two dots (Yellow-Cyan) and Blue (Cyan-Magenta). Where these channels combinations overlap you start to get oranges, turquoise and purple colours as well.

You print them as they are do not invert them, although that might be interesting, you will probably get the least saturated colours in the RGB model, the colours that tend toward clear white. When you print the arrays out you may start to see that some colours block UV light (or visible for that matter) better than others. Some squares will print paper white, some very dark and some will be somewhere in between. Paths may emerge, where a column starts dark and then turns white. These are paths of interest.

Why find the densest colour? Good question. And it's debatable for sure. My original hypothesis was that if colour was indeed responsible for blocking UV (i.e. spectral density) why not utilise that fact to minimise ink usage. Find that colour (the superblocker) and just desaturate it until you achieve the correct density for your process. Also, when inkjet printers start "pouring on the ink" to create density that creates other problems -- like banding. But initially the idea was "economy" of ink.

Why colours and not greyscale? Another good question, again debatable. Some of which I just covered in the last paragraph. One thing I wanted was to know that all the inkjets were firing and that my printer's maximum DPI resolution was being utilized. For example, if you use Epson's "Black Only" option you essentially lower the printer's resolution because black dithering isn't going to be the same as the dithering produced when all the heads are firing to produce the tone. However, when the ink combinations overlap you also get colours moving toward the CMY black colour. At some point the printer may also introduce actual black ink too. So, in short, better resolution and possibly less ink drained from the printer. n.b. I routinely use "grey" to make digital negatives but it's the grey created by combining CcMcY and maybe a little K ink.

Print the arrays onto Pictorico OHP for alt processes, or Pictorico High Gloss White Film for Black and White. Although other substrates may also work.

~m

Joe Lipka said:

Works for me, too. mkochsch sent me the red/green array when I got stuck working with Dan Burkholder's method. The discovery point was that inks and pigments absorb UV light differently. Dan's color was for the Epson 2200, IIRC, which gave different results when I used it with the Epson R2400. Finding the right blocking color from the red/green array gave me good results.

Click to expand...

...and the beautiful print pt/pd print you sent me (in thanks) hangs near the main entrance of my home and always receives glowing comments. Thanks again Joe!

~m

Helen Bach said:

Don't you also need to know the weakest blocker so that you can use it to smooth out the printer dot pattern?

Best,
Helen

Click to expand...

There are two methods here and people need to understand that. The first method is similar to other systems where you find a negative fill colour that effectively sets the density (PDN). These arrays just give you more possibilities.

The second method, if it applies to your situation and needs, selects the hue that blocks the most UV light. On my printer, with my inks for example, it happened to be [RGB 176,176,0]. On some printers this colour might not work they may need to use something closer to black ink. When I found this colour I created a second stepwedge (in black & white) and then filled it (using a new layer set to "screen" mode) with this colour, printed to my process to find a less saturated version of that colour which set the density for my process. (Hint use the HSB option in the info palette to examine the example stepwedges, pay attention to the "Saturation" numbers). That colour becomes my negative fill colour. For example, a colour like RGB [204,204,90] (aka Hue:60, Saturation:56 Brightness:80) may be the correct density for cyanotype on my workflow. Doing things this way is an extra step, the trade off for possibly not having to change ink carts as often. Also all your negatives will be the same colour, which could be good or bad.

Normal Stepwedge:
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Stepwedge after colour is applied:
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Part of the reason for me releasing this information is to get more feedback for people who want an alternative method for making digital negatives or who think they can't because they can't achieve the required density with their current hardware or workflow. Also, I've been e-mailing it out to a lot of people in the last month and I'm tired of doing that so I'm just going to post the information here....if that's ok with everybody.
~m

mkochsch said:

Part of the reason for me releasing this information is to get more feedback for people who want an alternative method for making digital negatives or who think they can't because they can't achieve the required density with their current hardware or workflow. Also, I've been e-mailing it out to a lot of people in the last month and I'm tired of doing that so I'm just going to post the information here....if that's ok with everybody.
~m

Click to expand...

I appreciate the fact that you made these arrays possible, and made use of them this past evening in selecting a color that would match the exposure scale of the Ilford papers I tested. for the Epson 1400. That part was very smooth, especially since I use a transmission densitometer and all that was necessary to chose a good match was to read the density of squares on the array and determine which one produced the desired density. I chose a process ES of 1.6 and there were a number of matching squares on all three arrays.


However, I was quite surprised at how different some of the squares of eaqual density printed, both on the OHP substrate, when you visually compared them with a loupe, and when printing. One square right next to another would be perfectly smooth and visually show little grain, while the one next to it, with almost equal reading, would show severe dithering and grain. I don't know why this, whether a problem of the printer driver or the mechanism that Photoshop uses to send data to the printer, but it surprised me a lot. However, resolving why this happens would be important. Of course, maybe this is a printer specifc issue?

Bottom line is that in order to find out what square of same density actually printed the best (smoothest, least grain) involved a series of trial and error testing. I believe tht in the end I got to where I needed to go, but for printers that have sufficient density for the PDN combinations it is very easy to tell which color will print smoother. Course, using the PDN colors was not an option with the 1400 at all for alternative printing since the UV blocking of the Claria inks is very low.

Sandy

Michael,

I think this is a great addition to the inkjet negative mix. I agree with you that it is the most comprehensive approach to color determination I have yet seen. I am in the middle of a calibration exercise with a new Epson 7800, and its inks are very different than the 2200, so these grids may come in very handy.

A question:Have you ever loaded up a printer profile for the pictorico and done a soft proof with this grids? I did that a while ago with the ternary diagram approach, and I was surprised to find out that some of the colors were out of gamut for the printer I was using at the time. It may be a moot point, since it won't print what it can't print, but it is interesting to see that some RGB combinations cannot be printed...

One approach I am also fiddling around with right now is using the Imageprint RIP (that I bought for color printing, mostly) with this printer for making diginegs. Their profile library is incredibly accurate and they have a profile for Pictorico glossy white film. The reason this interests me is that their RIP has their own rasterization/dithering algorithm that I think may be an improvement over the Epson driver, and it also has the benefit of being a true 16bit RIP, at least according to their marketing blurb. As you can imagine, the ability to keep your file in 16 bits all the way through the printing stage ought to have some advantages, at least in theory, over the Epson driver's conversion of 16 bit data to 8 bit data for output to the printer. I can't say right now if there actually is any advantage, but I aim to find out. I am going to print your grids tonight with the Imageprint RIP and see what I get.

As an aside, the other advantage that the Imageprint RIP offers to those of us using roll media is that you can tile many images in the same print job and really optimize the media usage with no additional hassle. It is also about 3X faster than the Epson driver....

Clay

clay said:

Michael,

I think this is a great addition to the inkjet negative mix. I agree with you that it is the most comprehensive approach to color determination I have yet seen. I am in the middle of a calibration exercise with a new Epson 7800, and its inks are very different than the 2200, so these grids may come in very handy.

A question:Have you ever loaded up a printer profile for the pictorico and done a soft proof with this grids? I did that a while ago with the ternary diagram approach, and I was surprised to find out that some of the colors were out of gamut for the printer I was using at the time. It may be a moot point, since it won't print what it can't print, but it is interesting to see that some RGB combinations cannot be printed...
Clay

Click to expand...

Thanks everybody. No Clay I haven't created a printer profile for the arrays. I don't currently possess a calibration system that can accurately generate a profile. Somewhat moot, perhaps. Photoshop may show many of these colours as being out of gamut in the CMYK space but it still prints something. I'm finding that knowing actual density is nice but it is becoming less relevant since all the calibration is being confined within the program. Stouffer wedges are still pretty handy for keeping me on track though (i.e. detecting flaws in chemistry like fogging, poor clearing etc.)

The point that I was trying to make was that it may be better (smoother) to use a different combination of inks for the low densities than that used for the high densities.

Best,
Helen

Helen Bach said:

The point that I was trying to make was that it may be better (smoother) to use a different combination of inks for the low densities than that used for the high densities.

Best,
Helen

Click to expand...

Sure. Sandy has pointed out that on his printer some squares are very banded and rough, some are smooth. If you're suggesting mixing different colours for different densities I'm not sure how one would go about setting up the negative (colour filling) for that purpose. I've thought about that but I don't know how to implement it yet.

~m

This is mad-scientist territory, but what about mapping the image to a gradient that goes between the weakest UV blocker and the strongest UV blocker? In theory, that would give you the most ink in all the parts of your negative.

I am very encouraged with the look of the negatives using the imageprint RIP. They looks smoother under a 10x loupe than the Epson driver negatives. I am going to do some printing tests this weekend to see if this turns out to be the case. If this works, it means that one adjustment curve can be used for any printer that Imageprint supports, since they profile all of their printers to behave the same way. I'll report in.

mkochsch said:

Sure. Sandy has pointed out that on his printer some squares are very banded and rough, some are smooth. If you're suggesting mixing different colours for different densities I'm not sure how one would go about setting up the negative (colour filling) for that purpose. I've thought about that but I don't know how to implement it yet.

~m

Click to expand...

If I only had Photoshop I'd do it using the duotone curves. As I have IJC/OPM I can do it with that. Both IJC/OPM and QTR give you full control over what inks are used for what greyscale value.

Best,
Helen

OK, I give.... what is IJC/OPM?

Kerik said:

OK, I give.... what is IJC/OPM?

Click to expand...

Hi Kerik,

Thaks for asking.

Very relieved to see that I am not the only other totally ignorant person following this thread!!

Sandy

Kerik said:

OK, I give.... what is IJC/OPM?

Click to expand...

It's a RIP- raster image processor - a fancy pants inkjet printer driver that provides very high levels of control for the printer for making inkjet prints or digital negatives. In this case IJC sends 16 bit data to the printer instead of 8 bit amongst other tweaks the user can make in a high level user interface.

From the web site:

Supports Most Epson Printers.
Use with Epson UltraChrome Inks or Popular Quadtone Inksets.
Achieve "Dotless" Highlights with Quadtone Inks.
DEEP Blacks and Ultra-smooth gradations.
Make NEUTRAL Prints without "rainbows" in the gradations.
Create Sepia or Cool toned Prints and the unique Blend Feature to vary hue between warm and cool IJC/OPM Profiles.

http://www.bowhaus.com/index.php4

Don Bryant

Thanks, Don. I know what a RIP is, I just wasn't familiar with IJC/OPM. Any thoughts from users how IJC/OPM compares to Quadtone RIP?

While I haven't seen the output from IJC/OPM rip, I have had a chance to compare the output between Imageprint RIP, Quadtone RIP and the Epson driver on the 7800. They all have slightly different dither patterns and the dots just look different when you stick on loupe on the paper. I'm guessing that IJC/OPM will have yet another slight variation in the way it makes the printer lay down its inkload.

Any comments, Helen??

Kerik said:

Thanks, Don. I know what a RIP is, I just wasn't familiar with IJC/OPM. Any thoughts from users how IJC/OPM compares to Quadtone RIP?

Click to expand...

An interesting idea....

clay said:

This is mad-scientist territory, but what about mapping the image to a gradient that goes between the weakest UV blocker and the strongest UV blocker? In theory, that would give you the most ink in all the parts of your negative.

I am very encouraged with the look of the negatives using the imageprint RIP. They looks smoother under a 10x loupe than the Epson driver negatives. I am going to do some printing tests this weekend to see if this turns out to be the case. If this works, it means that one adjustment curve can be used for any printer that Imageprint supports, since they profile all of their printers to behave the same way. I'll report in.

Click to expand...

Very Interesting. This also goes back I think to what Helen proposed in her response. I was playing around with some old VDB yesterday and had a sort of happy accident. The VDB is getting old and I was over-exposing by about a stop and a half. BUT LOOK!. In the Array on the right (Red-Blue) I have a white square and a damn near black square on the same array! right on the 300 degree axis of the HSB palette!. The only variable that changes is the Brightness. I'm going to try to make some chartthrob curves and see how straight it is...just looking at it make me think it's pretty linear...

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clay said:

This is mad-scientist territory,

Click to expand...

I am not mad! Don't call me mad!

Maybe a bit angry, or possibly a trifle peeved. Or maybe irked. Yes, irked, that's it...

I'm an irked scientist!

clay said:

but what about mapping the image to a gradient that goes between the weakest UV blocker and the strongest UV blocker? In theory, that would give you the most ink in all the parts of your negative.

Click to expand...

That will work, if your printing process is in the control of a RIP. For example, to set this up with QTR, print their standard cal chart in color, print that chart onto the paper of interest (PT, PD, cyanotype, etc) and measure the densities of the print. Then subtract all the densities from DMAX, because the QTR calibration process won't work with print density that decreases as ink density increases.

clay said:

I am very encouraged with the look of the negatives using the imageprint RIP. They looks smoother under a 10x loupe than the Epson driver negatives. I am going to do some printing tests this weekend to see if this turns out to be the case. If this works, it means that one adjustment curve can be used for any printer that Imageprint supports, since they profile all of their printers to behave the same way. I'll report in.

Click to expand...

They don't profile anything to "behave the same way" in the UV, or in the transparency mode. That's the big drawback with making digital negatives with colored inks to begin with, you never know when Epson is going to make a little change in the UV absorbtion of the cyan ink, or in the visible blue blocking ability of the yellow ink. (those are both real examples from about 18 months ago).

Best thing in the world for digital negatives is still lots of dilutions of neutral carbon black.

Helen Bach said:

The point that I was trying to make was that it may be better (smoother) to use a different combination of inks for the low densities than that used for the high densities.

Click to expand...

You're quite right. One approach I used a couple of years ago was to print a thousand square chart, all possible combinations of red, green, and blue at 10 values.

0, 28, 57, 85, 113, 142, 170, 198, 227, 255

This was printed on transparency material at 9x7 with 1/4 inch squares, contact printed, scanned on a 4800 dpi flatbed, and dumped into a matlab program that spend the next few days chewing on a 1.4 gigapixel image computing the mean, variance, and standard deviation (use to judge the "smoothness" of each square) and then give me a list of the smoothest colors for 15 target density neighborhoods.

After that, computing the curves was a snap.

And, the next time Epson changes the UV blocking characteristics of the green without changing the other colors, you can flush the whole thing down the toilet.

clay said:

While I haven't seen the output from IJC/OPM rip, I have had a chance to compare the output between Imageprint RIP, Quadtone RIP and the Epson driver on the 7800. They all have slightly different dither patterns and the dots just look different when you stick on loupe on the paper. I'm guessing that IJC/OPM will have yet another slight variation in the way it makes the printer lay down its inkload.

Click to expand...

Quadtone RIP and BowHaus Inkjet Control / OpenPrintMaker should be very similar, as both use versions of the Gimp Print engine. I don't know what version IJC/OPM uses, but QTR uses version 4.3.5, a development "fork" of the 4.2 platform that was a precursor to 5.0.

wiz said:

You're quite right. One approach I used a couple of years ago was to print a thousand square chart, all possible combinations of red, green, and blue at 10 values.

0, 28, 57, 85, 113, 142, 170, 198, 227, 255

This was printed on transparency material at 9x7 with 1/4 inch squares, contact printed, scanned on a 4800 dpi flatbed, and dumped into a matlab program that spend the next few days chewing on a 1.4 gigapixel image computing the mean, variance, and standard deviation (use to judge the "smoothness" of each square) and then give me a list of the smoothest colors for 15 target density neighborhoods.

After that, computing the curves was a snap.

And, the next time Epson changes the UV blocking characteristics of the green without changing the other colors, you can flush the whole thing down the toilet.

Click to expand...

An excellent and bold analysis attempt to be sure! You're way ahead of the curve...to pardon a pun. I have a pile of questions.

What did you learn from printing out those 1000s of squares? Was there an advantage in doing this? Did you end up with using a single hue as fill? How did you apply the colour to the negative after matlab processing revealed the smoothest colours? Was the curve even necessary? Did any of the study involve analysing the final print outs, did you use a UV densitometer? Was the smoothness in visible light often different than that under UV light? Can you post some excerpts or some abstracts? Thx.
~m

mkochsch said:

An excellent and bold analysis attempt to be sure!

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Glad you enjoyed it.

mkochsch said:

You're way ahead of the curve...to pardon a pun. I have a pile of questions.

What did you learn from printing out those 1000s of squares?

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I learned that the different visible light and UV absorbtion of the different colors of ink makes negatives act very strangely. You may find one color that prints the smoothest light grays, but is much grainier than another color in the dark grays.

mkochsch said:

Was there an advantage in doing this?

Click to expand...

Yes. I was able to find the color that produced the smoothest print at each desired density.

mkochsch said:

Did you end up with using a single hue as fill?

Click to expand...

No, I had a complex "zigzag" of hues through density space. Light colors were black, as density increased it went green, then cyan, then red (if memory serves)

mkochsch said:

How did you apply the colour to the negative after matlab processing revealed the smoothest colours?

Click to expand...

I output three comma separated value lists of curves, then import those into PhotoShop through a utility that converts .csv to .acv files (I think it's called curvalicious).

mkochsch said:

Was the curve even necessary?

Click to expand...

Very much so. Three curves, red, green, and blue, instead of just one.

mkochsch said:

Did any of the study involve analysing the final print outs, did you use a UV densitometer?

Click to expand...

Yes, and no. The equivalent density was computed by measuring print density where the print also contained a Stoufer wedge, and interpolating density values to the curve for the Stoufer.

mkochsch said:

Was the smoothness in visible light often different than that under UV light?

Click to expand...

Yes. The colors required for a negative varied dramatically depending on whether printing a UV or visible light process.

mkochsch said:

Can you post some excerpts or some abstracts?

Click to expand...

Not at this time. It's a long abandoned project.

mkochsch said:

Thx.
~m

Click to expand...

You're welcome