Digital negative (transparency)
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The digital negative is a new technology which allows photographers to use digital files to create negatives on transparency film. These negatives can be used to contact print, or in some cases if the negative is made large enough (about 4x5") they can be enlarged. It is different from the Digital negative (DNG) file format, although this format may be used to create the digital images.
Creation of digital negatives
Before creating a digital negative it is important to know the process to which it will be applied. Since contemporary inks and printers cannot cover a gamut as wide as traditional silver negatives and it is imperative that each process have its own tonal curve to apply to a photograph so that the photographer can take full advantage of its gamut. Also, different processes react to colors in different ways; sometimes photographers print out a monochromatic negative in a specific color to get a specific contrast range. For example, some use purple inks and low contrast curves for the small gamut of cyanotype printing, while the platinum/palladium process necessitates a high contrast curve that works best with green ink. Before the color cast is added, however, it is important to remember to invert the image to ensure that the negative prints a positive if contact printing (some also flip their image horizontally since the final print will be a mirror image of the negative), or sometimes it may be left as a positive (in the case of a positive image on a dry or wet plate).
The photographer has a number of options to create a digital negative. Usually, the process involves a lot of testing and reprinting. Chemical procedures must be standardized to allow for repeatable results. First, a tonal scale is printed out on the transparency film and this is used to create a print using whatever process is being tested. Next, the print is scanned and the resulting tones are examined either by the photographer or by a program and a new contrast curve is generated to compensate for whatever inadequacies that may exist in the first negative. The photographer may also decide here to use a different ink color. The new negative is printed and again is tested. This process may continue for as long as the photographer deems necessary. The final negative should create a final print that has both blacks and whites, and a smooth tonal range between.
Digital negatives can be enlarged and printed using the standard analog gelatin silver process. However, since printers cannot spray small enough drops of ink to ensure detail in the smaller traditional sizes such as 35 mm, a larger format such as 4x5" is normally used.
Often however, they are used with one of the alternative processes such as Inkodye or cyanotype. In these cases digital negatives are most commonly printed full-size to create contact prints. The negative is sandwiched printer ink-to-emulsion in a contact printing frame then exposed under a UV light source. They can also be used to create positives (where the initial digital file is not inverted) to make positives on emulsions such as collodion processes.
Advantages and disadvantages
Digital negatives offer many advantages. Photographers can enjoy the ease of shooting with a digital camera and editing digitally while still working with alternative or traditional photographic processes. Small, analog negatives can be scanned and enlarged digitally to create new negatives instead of using the traditional enlarging film that must be processed in a darkroom. Another advantage to digital negatives is their reproducibility: if a photographer ruins their negative with chemicals they can simply make another without having to reshoot the original negative.
Generally, digital negatives are made from an inkjet printer using black ink only, adjusted to the proper density to suit the process. This can be achieved simply with curves or other adjustments in Photoshop, for example, or using special printer drivers (or Raster Image Processors) such as QuadToneRip. A comprehensive beginner's guide to creating digital negatives using black ink for various processes is the book Digital Negatives by Brad Hinkel and Ron Reeder.
If the photographer has an advanced understanding, they may use different colors in areas of an image to create contrast differences selectively when printing their negatives, similar to using colored filters on black and white film. It is, in effect, using a red filter only on the sky, and perhaps a green filter on just the grass, all at once (for example: the red filter would darken the sky and the green filter would lighten the grass). Mark Nelson's digital negative process covers this extensively.
Disadvantages to using digital negatives exist mostly because of printer limitations. As mentioned above, very small negatives tend to be blurry and grainy due to large ink droplets. Also, some inks can create banding not evident in the negative but obvious in the final print. Epson K3 Ultrachrome inks have shown to work very well in the creation of digital negatives.
Some types of transparency film work better than others: it is important to ensure that the film does not have any agents in it that block UV since this will allow only a very small amount of necessary UV to expose the print. Some films do not respond well to inks and even after drying will smudge and smear.