This is an alternative approach to obtaining darkroom photographic prints using prepress techniques and materials. Article is directed at all photography enthusiasts and visual artist. Step-by-step instructions and some technical background explanations are included. Digital workflow is explained using Adobe Creative software.
Story begins with the big box of black-and-white Kodak Polymax photo paper expired some time ago. Trashing 50 sheets of probably still good 50 × 60 cm paper would be real pity, so I came up with the idea to use Kodak paper to create own unique photo-calendar. Large B&W prints with photo, monthly calendar and credits. Limited edition handmade stuff as a gift for the clients. That’s cool, that’s great idea, but how to expose photographic paper by file?
The solution came up shortly when I picked up some transparency films for print house I cooperated with. Looking more closely at these films, I realised such transparency can be “inverted” to a negative and then contact-printed. That leads to conclusion that we can easily print any digital graphics on a traditional gelatin-silver photo paper.
In formerly most popular CtF (Computer to Film) print technology, transparency film is used to develop final print plate. Plate is coated with photosensitive material, which after controlled exposure is developed chemically. This process is basically identical to the photographic contact-printing.
High resolution of the print transparency film makes it ideal candidate to experiments with photographic techniques.
To obtain gradient and tonal reproduction in offset printing, the image have to be broken up into tiny dots arranged in a regular (or irregular) grid pattern, so-called halftone. This process is called screening:
Halftone invention comes from the nature of the offset printing technique – transfer of an ink to paper takes place only in the area where plate is wet with the ink (dot surface). This is true even for tiny points, so if we put them in a very fine mesh, eye gets the impression of a smooth tone or color transition. That’s why overall quality of the image reproduction in the offset printing does not substantially differ from conventional photographic techniques. Find out more.
CtF is now replaced with the more advanced CtP (Computer to Plate) technology, where film is eliminated from the process.
The most important step is to create print quality file which from our transparency film is produced. As the PDF (Portable Document Format) is the standard prepress exchange file type, we’re going to create one for our purposes.
1a. Create PDF file from digital image
The starting point is any digital photograph image file (JPG, TIFF, PSD, RAW, etc.). This method require input image in Grayscale mode, so first you need to convert it. If your input is color picture, I advise you to use Black & White… instead of Desaturate command.
Set desired print size with 300 dpi resolution. If the file has layers you need to flatten it (menu Layer > Flatten Image).
1. Open the file in Photoshop. My picture is actually black and white, but still in RGB. From the Image menu, select Mode > Grayscale. Image is now converted to a single-channel, grayscale mode.
2. Click the Edit menu, select Color settings… In Working spaces box, expand the CMYK menu and select Custom CMYK:
3. Enter the parameters as showed in the screenshot below:
Ink colors: Eurostandard (coated)
Dot Gain: 0 (there is no dot gain actually)
Black generation: Maximum (default: Medium)
4. Click menu Image > Mode and select CMYK.
This is the final form of our image. Go to the Channels palette to check the contents of the CMY channels – they should be empty:
5. Save your image as a Photoshop PDF by selecting High Quality Print preset. The file is ready.
1b. Create PDF from vector graphics file
If you’re familiar to Illustrator, Indesign, Corel or any other CMYK-capable software, you probably familiar with PDFs. Exporting your artwork to valid PDF is as easy as selecting High Quality Print or Press Quality preset in the Save Adobe PDF dialogue and clicking OK. There is no need to modify separation settings here if you follow these rules:
- use CMYK document color space,
- all graphics elements are set with one color (usually K),
- In the Output tab of Save Adobe PDF dialogue select: Color Conversion > No conversion and Profile Inclusion Policy > Don’t include.
You may also want to save CMYK profile and use it as a Destination in Output settings tab:
Note: using this option placed (linked) images have to be in Grayscale mode no matter it’s Illustrator or InDesign.
2. Find the service
The next step is to obtain the transparency film – our contact sheet. Locate prepress/imagesetting shop offering CtF service. You can find at least a few such places in every larger city. Using the internet you can probably find an on-line service with delivery option.
Most good imagesetters supports up to B1 (100 × 70 cm) sheet format which allows you to order negatives for virtually all sizes of available photo papers. Importantly, this will not ruin your budget – cost of the B1 sheet should not exceed 50 EUR.
Now order your film. Specify desired size and parameters.
You’ll be asked for some numbers
Standard imagesetter create raster image based on a regular grid, so-called Amplitude Modulation raster (AM). The ruling and resolution parameters specify how close the grid points are spaced in the unit of distance (usually an inch – lpi: lines per inch, dpi: dots per inch).
When receiving order, imagesetters will ask you about these parameters. Remember the ratio of raster resolution to its ruling should be 16:1, and typical values are: 2400 dpi resolution, 150 lpi ruling.
If the maximum resolution is 4000 dpi, the ruling should be 250 lpi (4000/16 = 250).
How film resolution affects the final quality of the prints? I’d venture to say that you can increase it to the maximum. In the printing process there’s strict correlation between the dot size and the quality of ink transfer to the paper (de facto print quality) and because of this, ruling rarely exceeds 175 lpi. In presented procedure we do not use any ink transfer of course. Image on the photo print is constructed by light, so you can assume mentioned restriction does not exist here and use maximal resolution. Experiment to achieve optimum results.
In the 90s of the XXth century stochastic (frequency) screening was introduced to offset printing technologies. Idea is simple – all grid dots are the same size, but varied are the distances between them (their density is modulated, in other words: frequency modulation, FM). This technology is not in widespread use. Despite giving better print quality, it imposes on the prepress and printers much higher demands for precision and quality. It’s however common in the inkjet printing devices.
For our application it may be highly desired because the random distribution of the halftone dots additionally gives the impression of negative grain emulsion.
Ask imagesetters about the possibility of preparing a film with the stochastic screening. Not every offers such service.
Imagesetter is nothing more than super-sized sophisticated laser printer. Remember you can produce such transparency by yourself using home or office printer (including inkjet printers). Just get some dedicated transparency and use it to print out your contact negative. But if you demand highest quality of the final print, forget it. Difference is incomparably better resolution and quality of CtF transparencies. Another limitation of this solution is paper size (max. A3).
3. In the darkroom
When you finally get the transparency, it’s time for a darkroom phase. You need to contact-print it. If you have some experience you can do it easily, if not, refer to google or YT. Here is recommended reading:
Brief video overview:
and more advanced tutorial:
I made the printed calendar in cooperation with my friend, Marcin Tworos whom photo was featured. After designing the layout with InDesign it was exported to PDF and sent to the service. Here’s the transparency sheet of our calendar:
As you can see, film looks like a real negative. We’ve dust off the mentioned Kodak paper box and started printing. After the first tests it turned out that results are more than satysfying. Print appeared to be quite soft and slightly dimmed, but with decent tonal scale kept:
That’s all folks. Using high resolution prepress transparency films introduces alternative way of obtaining high quality analog black and white silver gelatin prints. Please note that this procedure allows more than a image – it can be used for graphics or any type of visual expression.
I hope this tutorial inspire you to a new field of experiments, both technical and artistic. Especially, if you have bunches of an expired photographic paper untapped.
Final brain teaser:
How do you think, is it possible to manipulate print contrast using multigrade papers with this technique? Feel free to share your thoughts in comment!