The Modern Digital Negative

A digitally produced negative can mean better, easier darkroom prints

By Dan Burkholder Back to

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Recently I was invited to address a regional photographic organization on the hows and whys of digital negatives. One participant—a film-based photographer who didn’t use Photoshop—was puzzled as to why you’d want to make another negative if you already had one from the camera in the first place. I fumbled through multiple attempts at explaining how I’d exploited digitally produced negatives for the past 16 years, using them to print on materials ranging from silver gelatin to cyanotype to platinum/palladium. I could see that I wasn’t getting through to this fellow for whom photography and computer had nothing in common. After the presentation closed, my wife Jill said I should have told this doubter, “Look, we both know you have negatives that you just haven’t been able to print well. If you’d learn how to make digital nega- tives, you’d be able to control the contrast and fix flaws in those problem negatives to make beautiful prints. Wouldn’t you like that power?” As usual, Jill’s wisdom capped the day. Sometimes the simplest answers are the best.

Reasons for making digital negatives Yes, fixing a problematic original is a good reason for making a digital negative, but there are other equally practical reasons for making negatives via your computer and an inkjet printer:

• You capture digitally so you never have a camera-original negative.

• You can only afford (or manage) a smaller camera, yet you want to make large contact prints.

• You can’t take the hassles of traveling with large sheets of film in the post- 9/11 world.

• Pushing Command/Control-P to make an inkjet print just isn’t enough of a creative expression.

• You want to composite parts from multiple images and print in the classic darkroom.

Yep, there are lots of reasons for making a digital negative.

When I started making digital negatives in 1992 (affectionately referred to as the Paleolithic era of digital imaging), the options for making negatives via the computer were very limited. Inkjet printers had yet to blossom on the scene, and film recorders were both expensive and limited in output size.

Imagesetters—large machines used by the offset-press industry—became the avenue of choice for making enlarged digital negatives. I made many such 12×18-inch imagesetter negatives for printing on hand-coated platinum/ palladium. The biggest drawback to using imagesetters was that we didn’t have them on our own desktops. If we wanted or needed to make changes to the image size, contrast, or content, we had to send another digital file to the service bureau so they could pump out another imagesetter negative. This was both time-consuming and expensive.

Jump to 2008, where our digital lives are blessed with amazingly accurate inkjet printers. Suddenly the accessibility and control of negative-making are expanded to the nth degree. Let’s explore how we can exploit these desktop wonders to make stunningly detailed and tonally accurate digital negatives. Remember, our goal is to make inkjet negatives that produce prints indistinguishable from those printed with camera original negatives. No tell- tale trace of inkjet dither pattern or other artifacts will befoul our final prints.

Though digital negatives can be (and are) used for color printing processes such as gum bichromate, the goal of this article is to describe how to make digital negatives for printing on monochromatic materials such as gelatin silver, platinum/palladium, and cyanotype.

The nature of negative densities

Our good ol’ Tri-X or Ilford Delta negatives create different densities with varying amounts of metallic silver. Silver is a very effective material for blocking both visible light (for silver-gelatin printing) and for alternative processes that are sensitive to the ultraviolet part of the spectrum. A fully exposed and developed silver-based negative can even be used as a safe solar-eclipse viewing filter. (Warning: Don’t try this with a color negative or inkjet negative; their dyes and pigments are nowhere as good at blocking harmful rays from the sun.)

Inkjet printers vary widely in the type of inks they use. Obviously, they don’t use metallic inks (not yet anyway), rely- ing on other ink formulations to create prints with a wide range of colors and densities. Not only are there the basic dye and pigment categories, the number of ink colors in different printers and the ink formulations vary widely too. These printer variables can make the here’s-how-you-do-it recipes a bit more complicated; it’s simply not possible to give a single do-it-this-way formula. Fear not, a bit of testing with your inkjet printer will put you on track for making great digital negatives.

In order to make a negative with your inkjet printer you first need a substrate that holds ink evenly. Transparency films have improved markedly since I made my first inkjet negative in 1998, and we now have several fine products with coatings capable of holding the ink loads needed for digital negatives. Two that I recommend are Inkpress Trans- parency Film and Ultra Premium OHP Transparency Film from Pictorico. Though both are fine products, I’ve found myself gravitating to the Inkpress material because of its wider selection of sheet sizes. It’s much easier to load a 17×22-inch sheet into an Epson 3800 than to cut a piece from a 66-foot roll.

Test printing time

Whether you’re working with traditional negatives or their digital cousins, the first test you make is one that determines your standard printing time. This is the exposure time needed (in seconds or minutes depending on the type of printing) to create the deepest density in your print. This step is extremely important—if you aren’t exposing your print material long enough to create the maximum black (referred to as Dmax), then the dynamic range of your prints suffers. Instead of having rich blacks, you’ll have anemic dark grays.

To determine your standard printing time, expose your print material (a sheet of Ilford Multigrade or a sheet of hand- coated platinum, for example) through a sheet of your transparency material. You should expose in classic test-strip fashion. For my platinum printing, I would make a test strip in 30-second increments, running from 30 seconds to 2.5 minutes as in Figure 2.

Examine Figure 2 carefully. Notice that I placed the smaller sheet of Inkpress Transparency Film over the platinum-sensitized watercolor paper so that there is a coated section not covered by the transparency film. Because even the thinnest and clearest of transparency films will have a certain density of their own, you need to have a reference area in your test strip that is not covered by the transparency film. In fact, if you look closely, you will see in Figure 2 that the exposed area that is covered by the transparency film is slightly lighter than the uncovered areas. This is normal for any printing process.

I’ve outlined the 120-second expo- sure step in Figure 2 because it is the first step to show maximum black. Notice that the next step (the 150-sec- ond step) is no darker than the 120-second step. Since excess exposure time only adds to the printing time with no benefit, use the shorter step. In fact, in some cases there are downsides—platinum and palladium are prone to solarize in areas of overexposure.

This example should illustrate how you conduct your own standard-exposure-time test. Your times will be different according to your printing medium, your light source, and your transparency film. Once you have established a standard printing time, all of your digital negatives will print at this time. Of course, if you change light sources, paper, chemistry, or coating methods, your standard printing time also may change. Once you’ve settled on a set of printing variables, it’s a great timesav- ing joy to have every negative print in the same amount of time. This is one of the benefits of digital negatives.

Creating negative densities

One of the qualities we need in any negative is the ability to block light. We can create these densities in two basic ways in inkjet negatives:

1. Create a physical density by applying enough ink to the substrate (transparency film).

2. Create a spectral density by creating a color that filters the light.

If I had the time and inclination to test every inkjet printer on planet Earth, I could produce a handy chart showing which method works best for any particular printer. Given that neither time nor inclination is in abundance at our house, I’m going to instead give you a simple way of determining how you can create the proper densities for your printer.

If all printing processes responded to light similarly, the job would be much easier. But different processes respond to light in various ways. Some are more sensitive to one part of the spectrum and others to another part.

Fortunately, once you know your standard printing time, your next step in finding what color negative creates the most suitable densities for your printing process is pretty easy. By printing a chart with lots of colors (using your standard printing time), you can quickly determine the color negative that creates the best density for your printing.

You can make your own color chart or download the one I created at www.DanBurkholder.com/digital- negative-items-2008/ (Figure 3). There you will find a compressed file titled spectrum.jpg.zip. Click once on this file in your browser and it will download to your hard drive, where you can decompress it.

Simply put, this chart includes different colors that get darker across the chart. Your job is to print this chart on transparency film, and then to contact-print that transparency onto your final print material of choice. You then look for the lightest area in the result- ant print. Figure 4 shows a typical printed chart.

Photographers who print on variable-contrast materials (such as Ilford Multigrade paper) may be concerned that a colorized negative will affect print contrast. Fear not, your contrast will be determined by your contrast adjustment curve (explained in a moment), not by the negative’s color.

Examine the printed color chart to determine the color that provides the greatest spectral density for your process. It probably will not be blue, but the best color could be any color from red to green. Note the coordinates in Figure 4 (much like the letters and numbers on a bingo card) that provided the best density. This shows up as the lightest area in the printed color chart, in this case at the S-14 coordinates. Looking at the color chart itself (the color image you downloaded) you see that S-14 is a deep green color. This is the color you will use to colorize your digital negative.

At this point you know how long to expose your prints (your standard printing time) and what color you need to apply to the negative. But I haven’t yet explained how to apply that color or how to adjust the image’s contrast, two final important items on the path to great digital negatives.

Adjusting contrast

Figure 5 shows one of my images with a step tablet positioned beside the image. For years I’ve encouraged students to include a step tablet like this because it serves as a terrific objective control when adjusting the negative contrast or troubleshooting problems. Every point on the curve roughly corresponds to a step in the step tablet. You can make your own step tablet or download one from the URL listed above.

One thing universally accepted in the world of digital negatives is that you must alter the image’s contrast before printing the negative. This is done because a device intended to make prints (an inkjet printer) is being used in a manner for which it wasn’t designed (making negatives). In effect, by applying a Photoshop curve, we are creating a manual profile so that our negatives have the proper density for our printing medium.

Since every negative for each printing process needs a curve adjustment in Photoshop, it makes sense to include a step tablet like that in Figure 5. This step tablet serves as a control and troubleshooting device if we need to change the image’s contrast (by modifying the curve) to create a negative that prints better.

Let’s apply this curve to the Parking Meters, New Hampshire image. The best way to do this is as an adjustment layer in Photoshop (Layer > New Adjustment Layer > Curves), as in Figure 6.

When your Curves dialog box appears, you can either move points yourself to resemble my curve in Figure 7 or you can download my curve from the URL already mentioned and load it from the Curves dialog box by clicking the Load Preset button outlined in red in Figure 7. If you’ve done this properly, you will have a new Curves adjust- ment layer in your Layers palette. Note: this curve will make your image look too light on your computer monitor.

This is normal. You’re applying the curve to prepare your image with better contrast for the negative.

Nearly every person making digital negatives learns about tweaking curves in Photoshop to make their images print perfectly. It’s beyond the scope of this article to cover the nuances of curve tweaking. The good news is that, with the help of the step tablet, you’ll know what tones (points on the curve) need to go lighter and which ones should go darker. It might take a few tests to get it right for your personal darkroom techniques.

Colorizing your negative

Now that the contrast is modified via the Curves adjustment layer, invert the image to make it a negative. Again, the best way to do this is with an adjustment layer (Layer > New Adjustment Layer > Invert). Finally, apply that green color to the inverted image. Like everything else in Photoshop there are multiple ways to apply color to the negative. For this example, I’ll do it in a way that is easily controlled; that is, it can be turned off and on as needed.

With the color-chart file open in Photoshop, use the Eyedropper tool to click on the color square at the S-14 coordinates. When you click on that color, your foreground color in Photoshop becomes that color.

Let’s apply that color to our image with another layer, this time a Solid Color layer (Layer > New Fill Layer > Solid Color). Don’t panic as your entire image turns a solid green; you’re going to fix this by changing the Blending mode for the solid color to “Color.” Figure 8 shows my Layers palette with the Solid Color layer in Color mode.

The image (Figure 9) is now ready to print as a negative. I’d suggest preparing and printing your image at 360ppi. That’s not to say other resolutions— higher or lower—won’t work; I just know that 360ppi works very well.

Summary of steps

1. Determine your standard printing time by exposing a step strip through a clear piece of transparency film. You are looking for the minimum exposure time that yields the deepest black possible.

2. Print the color chart using your standard printing time to see which color works best for your process.

3. Include a step tablet with your image in Photoshop.

4. Apply a generic curve such as the one on my server (www.DanBurkholder. com/digital-negative-items-2008).

5. Invert your image and step tablet to make a negative image.

6. Apply the color from step 2 to your image via a Layer.

7. Print this on transparency film keeping careful notes of your printer settings.

8. Expose your image and step tablet at your standard printing time and process and dry the print normally.

9. Evaluate the step tablet to check for needed tonal adjustments.

10. Adjust the curve points to improve negative contrast.

11. Repeat steps 7 and 8 as needed until your step tablet and image look perfect.

Closing comments

The first time you go through these steps, especially if you’re a bit new to Photoshop, it might be a bit overwhelming. That’s okay: Remember, you were not born with this knowledge. Soon you’ll find yourself in a digital- negative flow that feels natural and exciting. And when you pull a beautiful, tonally perfect print from the developer tray, that’s all the reward in the world you’ll ever need.


About the Author

Dan Burkholder
DBurkholder
Dan Burkholder has been teaching digital imaging workshops for 15 years at venues including The School of the Art Institute, Chicago; The Royal Photographic Society, Madrid, Spain; The International Center of Photography, New York; Mesilla Digital Imaging Workshops, Mesilla, NM and many others. Dan’s latest book, The Color of Loss (University of Texas Press, 2008), documents the flooded interiors of post-Katrina New Orleans and is the first coffee table book done entirely using HDR methods. His award-winning book, Making Digital Negatives for Contact Printing, has become a standard resource in the fineart photography community. Dan’s iPhone images can be seen at: www.iPhoneArtistry.com/.