Printing & Design Tips: May 2003, Issue #22

Transparency Scanners

I recently received a question from a Quick Tips reader regarding 4" x 5" transparencies and 35mm transparencies.

Here are the rules of thumb as I understand them:

  1. The better the initial quality of a photographic image, the better the scanned and printed image will be. Each step in the process removes more image "information" (color information, detail, etc.), so start with the best possible original.
  2. Transparencies hold more detail in a wider tonal range (from darkest darks to lightest lights) with more saturated colors than does reflective art (photographic prints). This means that what you see on the press sheet more closely resembles the original image.
  3. The larger the transparency, the better. A 4" x 5" transparency will contain more detail to begin with than will a 35mm transparency. It will also need to be enlarged less than a 35mm transparency. Therefore, for a final poster-size image you would ideally want to start with a 4" x 5" image to retain the greatest tonal range, most faithful and saturated colors, and most intricate detail of surface textures in the photograph.
  4. Cameras that use 4" x 5" film are bulkier and far more expensive than 35mm cameras. Therefore, fewer people can afford them and they are less likely to be used for informal photo opportunities. Most people who want to use a 4" x 5" camera will rent it (along with special lighting equipment) for a specific (and stationary) photo shoot. Most people will not rent one to take photos of a political rally, for instance.
  5. Dedicated 35mm transparency scanners, such as the Nikon CoolScan, were all the rage when I was an art director five years ago. These scanners, while not quite the quality of drum scanners (their ultra-expensive, ultra-high-quality predecessors), were affordable and quite adequate for scanning 35mm transparencies for print publications. They also scanned film at a much higher resolution than flatbed scanners scanned prints (since the scanned 35mm transparencies needed to be dramatically enlarged).
  6. Now, special transparency adapters can be purchased for flatbed scanners (which have also improved dramatically over the last several years). In this case one could buy a single, moderately-priced scanner for scanning both reflective and transmissive art.

Enlarging Scans -- REVISTED

Issue #20 of Quick Tips was devoted to upsampling in Photoshop (or other image-editing software), I strongly urged readers not to scan a photo and then enlarge it. I wrote that when you scan a photo, the computer captures the image in a grid of squares that can be made larger or smaller by enlarging or reducing the photo, but that you have the same number of squares after you have enlarged the photo, and hence, these squares become visible and soft or fuzzy, reducing detail in the photo.

This is true. However, it only refers to the file once you have scanned it at the usual 1.5 to 2 times the line screen.

If you want to enlarge a photo without loss of detail, use the following formula to determine your correct scanning resolution:

  • multiply the print screen frequency by1.5-2.0, then multiply the result by the enlargement factor.
  • for example, if you want to enlarge an image 300 percent for a final 150 lpi screen, scan it at 675 to 900 dpi: [(150 lpi x 1.5 or 2) x 3]=a final scan of 675 to 900 dpi.

When you enlarge this 675 to 900 dpi image 300 percent, the resulting larger image will be 225 to 300 dpi: a perfectly acceptable resolution. Remember, enlarging an image reduces its resolution (from 900 to 300 dpi) just as reducing an image increases its resolution.

[Steven Waxman is a printing consultant. He teaches corporations how to save money buying printing, brokers printing services, and teaches prepress techniques. Steven has been in the printing industry for thirty-three years working as a writer, editor, print buyer, photographer, graphic designer, art director, and production manager.]