In some instances, it is desirable to "print" your digital image to film. The device used for this purpose is known as a film recorder.
The concept is quite simple. A film recorder is a box (housing) that has a CRT panel at one end and a camera at the other end. The camera simply photographs the image that is produced by the CRT panel at the opposite end of the housing. The cameras used range from 35mm to 4" x 5", depending on the required output.
Some older or less expensive film recorders have quality problems. These quality problems are most noticeable at the edges of the film's frame. The two most common problems are light falloff (image fade), sharpness degradation, or distortion.
Film recorders are sold with various resolutions. The most common ones are known as 4K and 8K. This specification refers to the lines of resolution along the long axis of the film being exposed.
A 4K film recorder is capable of creating 4,096 lines of resolution (4 x 1,024) along the long axis of the film being exposed. For 35mm, this means that the image would be 2,731 lines x 4,096 lines since 35mm format has a 1:1.5 aspect ratio. The result is 2,891 lines of resolution per inch (4,096 lines divided by 1.417").
If you attach a 6x9 (medium format) film back to the same 4K film recorder, the 4,096 lines of resolution along the long axis still applies. The image would be 2,731 lines x 4,096 lines. The difference is that since the film format is larger, the lines per inch will reduce. In this case, the lines per inch drops to 1,156 lines per inch (4,096 lines divided by 3.543"). However, the lines of resolution is proportionate to the film size, therefore the reduced lines per inch of larger format film is offset by the reduction of necessary magnification and/or enlargement to utilize the film. The net result is the same amount of resolution in either case.
Since film is capable of resolving more than 1,156 lines of resolution per inch, it is beneficial to send medium and large format film more information, if possible. In order to do this, you need a higher resolution film recorder.
An 8K film recorder is capable of creating 8,192 lines of resolution (8 x 1,024) along the long axis of the film being exposed. All resulting calculations are simply double that of a 4K film recorder, therefore a 6x9 negative would now boast 2,312 lines of resolution per inch, which is more appropriate for film.
In order to attain the full available resolution of a film recorder, it is necessary to send it a file with enough information. The optimum file sizes for an 8K film recorder are calculated as follows:
For 35mm and 6x9, 8,192 (horizontal) x 5,461 (vertical) x 3 (colors - RGB) = 128MB
For 6x6, 8,192 x 8,192 x 3 = 192MB
For 4" x 5", 6,554 x 8,192 x 3 = 154MB
The above file sizes are based on the input image's aspect ratio matching the output (film's) aspect ratio. The pixel array of the input image should match the lines of resolution of the film format. For example, when making a 6x9 negative, the image that you send the film recorder should be 8,192 pixels x 5,461 pixels to get a full 8K output. If you compromise this requirement, the film recorder may not create a full 8K image since some film recorders do not interpolate the image. Therefore, if you send a 2,731 pixel x 4,096 pixel image (32MB) to an 8K film recorder, the result will be a 4K output. The image will still fill the output film's frame, but the film's image will have a lower resolution (lines per inch).
If you scan a 35mm negative with a 2,800ppi film scanner, the result is a 3,969 pixel x 2,646 pixel image, therefore if you send that image to a film recorder, a 3.9K output would result.
If you scan a 8" x 12" photograph on a flatbed scanner at 600ppi, the result is a 7,200 pixel x 4,800 pixel image, therefore if you send that image to an 8K film recorder, a 7K output would result.
It should be noted that it is not necessary to make a negative in order to print your digital files, even if RA-4 (traditional photographic process) prints are desired. Kodak's "Pegasus" printer makes RA-4 prints from digital files. Durst's "Lambda" printer also produces RA-4 prints from digital files. The cost of the equipment limits the ownership and use of these printers to commercial businesses.
There are other options, as well. Fuji's "Pictrography" line of printers produces photographic quality prints from digital files. Kodak (and others) utilizes Dye-Sublimation technology to produce photographic quality prints from digital files. These printers range from$5,000 to $20,000 which is more affordable compared to the RA-4 options. However, the cost per print is over 10X higher than RA-4 prints.
And, of course, there is simple Ink Jet technology which, when properly utilized and printed on the appropriate paper, produces near photographic results. The cost of the equipment, price per print, and diversified usage makes this a very viable option for most consumers. One of the primary concerns with ink jet prints is longevity. Ink jet prints fade quickly compared to RA-4, Pictrography, or Dye-Sublimation prints. They are also quite susceptible to smudging, smearing or similar damage.