Digital Negatives

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Curving Cyanotype

Posted by on 26 Nov 2007 | Tagged as: Digital Negatives

I made a few cyanotype test prints to define a correction curve to be used with image files. The curve was created with the Hinkel & Reeder method, printing grayscale negatives using all inks of an Epson R1800.

The ink density produced by the printer seems to be high enough for the traditional cyanotype, which I was using. But it would not be adequate if I were to try it with the new cyanotype or, say, salt print.

There are, however, methods to increase ink densities – one of them is to use QuadTone RIP which will allow you to bypass the Epson printer driver limitations and create custom profiles which control the printerÂ’s ink settings. More on this on the Digital Negatives website.

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Two samples of test prints from Epson R1800 grayscale negatives. After creating the correction curves they turned out to be nearly identical for Somerset (left) and Canson papers.

I will do some testing with the new cyanotype too – there is yet another method for colorized negatives to be tried. More on that later.

Colorized Negatives

Posted by on 03 Nov 2007 | Tagged as: Digital Negatives

It looks like printing grayscale negatives using an inkjet printer’s all inks works well, when the tone range of the intended photographic printing process is quite short, so that we need relatively low contrast negative. We aim for a negative with enough density to print “paper white” with standard exposure (the shortest exposure to produce Dmax, the maximum black) for the printing process in use. Not all inkjet printers can lay down enough density to produce decent negatives for some long tonal range processes (salted paper, new cyanotype, palladium…). In that case it may be possible to make colorized negatives, trying to find an ink color which acts as a color filter, blocking UV-light more than gray-tone negatives can do. With printing the negative with this particular color we can use its UV blocking density to produce paper white in our photographic printing process. For more on the subject see the sidebar link RNP Array.

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This image (The HSL Array) can be downloaded from the RNP Array website and printed with an inkjet printer on transparency. We have used this image for determining our “blocking colors”, according to the instructions by Michael Koch-Schulte at the RNP Array site.

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This print from the HSL Array output, made with an Epson R1800, then contact printed on Kodak Polycontrast paper, is one of our first exercises with colorized negatives. We have chosen R0-G12-B51 for the optimum blocking color here.

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Another print on the same paper, printed with the same settings as the one above. The inkjet transparency was made with an Epson Pro3800. This time R242-G20-B0 was chosen for the blocking color, because it makes a nice and smooth grayscale (and we wanted to try something that is far from neutral gray).

We can notice that two given printers can build somewhat different shades of colors from the same image file, when used without any color management. Anyway, choosing any of the acceptable blocking colors should do the job equally well.

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These are our colorized step wedge files, ready to be printed on transparency. Two different printers – two different colors: The R1800 (left) and the Pro3800 (right). Although their colors are very different, they should print about the same grayscale gradation on b&w photographic paper.

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The contact print from the colorized negatives with the standard exposure. We chose to continue experimenting with the 3800 negative (right), because of slightly better highlight tone separation (and because we wanted to see how the red negative will manage the process).

The print highlights look quite good, but the shadows are dark and blocked. We need a correction curve in Photoshop to fix this. Measuring the test print’s density values and calculating the shape of the correction curve by hand can be laborious, but fortunately there is a computer software to do all this: ChartThrob by Kevin Bjorke is a javascript for Photoshop, it can automatically both create a step wedge to print on transparency and evaluate the print made from the transparency, and even build the correction curve needed.

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The next print with the curve applied. Looks much better now, here we are getting basically a nice full tone range.

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Only printing “real world” photographs will finally tell us about the usability of the chosen blocking color and correction curve for the chosen photographic printing process. This is how a red, corrected Epson 3800 negative looks.

Test Prints
A few test prints on Kodak Polycontrast II RC, made with the Epson 3800 red negatives and correction curves built by ChartThrob (you can click pictures larger):

Our first print with colorized negatives. Looks ok, except for some posterization in the deepest shadows (which is evident in the negative too), and when compared to the image on the computer screen, we wanted the lower midtones slightly darker. So, after this print the curve was tweaked a little.

Again the print is acceptable but not perfect. A little more shadow darkening was made to the curve after this print.

We’re satisfied, the colorizing / curve correction tool is working for us! This print is very close to what we see on the computer monitor.

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The starting curve (left) calculated by ChartThrob, and the adjusted curve after test printing.

About Correction Curves

Posted by on 14 Oct 2007 | Tagged as: Digital Negatives

Correction curves for hand sensitized contact printing processes normally look like inverted S-shapes in Photoshop, meaning they tend to flatten image contrast. As an exercise we tried to build a correction curve for standard RC silver paper (Kodak Polymax RC II). In the final print the tone range is clearly better with the correction curve, but we need to print also some “real world” pictures later to see if we need some further adjustments.

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An example of how the correction looks after plotting the curve for Polymax II RC paper, using the Epson R1800 to print the negative. The test image looks very flat after correction, but the curve definitely improves tone separation in the contact print.

We also tried to build correction curves for MACO Black Magic liquid silver emulsion, but resulting from roughness of the paper, it was hard to measure the test print accurately with a scanner. And a different story is the trouble with coating any paper evenly with the emulsion, thereÂ’s a lot to learn about that. WeÂ’ll be returning to this topic laterÂ…

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Two quick tests with MACO liquid emulsion. They are slightly overexposed, but you can see that the emulsion is quite contrasty (although it’s VC (variable contrast), and we used the lowest grade (#0) filtration). The left test was exposed on a single coated, and the right one on a double coated paper. The paper (Arches Aquarelle) was too textured for this test – it is hard to find even areas of tones for density readings.

Tests with Digital Negatives

Posted by on 12 Oct 2007 | Tagged as: Digital Negatives

When making digital negatives we have ended up using two different methods. Quite straightforward and simple way with inkjet printers is to let the printer render the grayscale image using all inks. These transparencies are easy to read and evaluate, and corrections to the tone scale can be done with effortless and straightforward thinking. This method usually seems to suit art students well – they want quick results and donÂ’t care to make the matter too scientific. 😉

The easiest way to make a digital negative is to print the image file, converted to grayscale and inverted to negative, onto suitable transparency material. It is also the fastest way, but the final result will not necessarily be very good, because the tone range of the original image will distort somewhat when the neg is contact printed, depending on the contact printing process used, and you will need a method for correcting the tone scale. Usually you can make corrections using a correction curve attached to the image file in Adobe Photoshop. Actually the correction curve should be built for every combination of printing process, printing paper, developer, and other variables occurring in the printing process.

We have started building correction curves in Photoshop in a simple way: by printing a digital negative with known gray tones on transparency, printing the negative with some standardized contact printing method (common silver print, cyanotype), measuring the print’s tone range distortion with a scanner or densitometer, building a correction curve to remove the distortion, and finally printing a new, corrected negative. We are printing with the Epson R1800 and Pro 3800, the transparency material is Agfa CopyJet film.

The purpose is to remove guesswork from exposing hand sensitized materials, so that with using proper correction curves we could easily produce “perfect prints” without too many tests.

This entire method is described very well in Digital Negatives, a book by Ron Reeder and Brad Hinkel. In fact we have used the step tablet image downloaded from the authorsÂ’ website in making our own correction curves.

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We will post here some pictures of our curves and tests later.

Inkjet Printers

Posted by on 06 Jun 2007 | Tagged as: Digital Negatives

Many printmakers say that high quality digital transparencies for exposing light-sensitive materials can be made with consumer inkjet printers. Since alternative processes are mainly contact printing techniques, a film (negative or positive, depending on the process) of the final print size is needed. Here the digital method of making enlarged films will be a great advantage. In addition to making the film to desired size, with digital techniques we can adjust the tone range to match exactly each of our printing processes.

There are many great sources on making digital negatives with inkjet printers; so far we have read texts of Dan Burkholder, Ron Reeder & Brad Hinkel, and Mark Nelson, and also good web sources like the Digital Negatives forum on Hybrid Photo, or The RNP-Array System, among others.

There will be two Epson inkjet printers at our service: Stylus Photo R1800 (print size A3+) and Stylus Pro 3800 (A2). Both of them should be fine for printing transparencies. In fact these printers are made for printing photo quality full color images on special papers (and they are good at that), but we want them to print monochrome on transparency… I guess there will be a lot of adjustments to do.

We started with printing a 21-step grayscale wedge from Photoshop on Agfa CopyJet transparency material, using all inks and no color management in the printer driver. We tried to find media settings to reproduce the gradually increasing gray densities as smoothly as possible, with all the steps readable. Succeeding in that would be a good starting point for building our own correction curves.