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Scanning and Resolution

Compiled and written for my clients, students, and my own work. Provided here for your convenience. If you take information from these sheets to use elsewhere, please provide the appropriate credits along with the information.

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Digital Photography procedural overview and expectations for the new client

Resolution technical information and samples on the effects of resolution on scans and prints. This three page article covers color changes, line weights, and suggestions for antique photos.
Short cuts to specific resolution issues:

  Effect on Color- includes samples * References - recommended books and assumptions
  Effect on Detail- includes samples * Determination - what resolution to use
  Effect on Line & Type Sizes- includes samples * Film & Print Detail - the differences *
  Effect on Image Size- includes samples * Output Options- samples at different resolutions *

* hardware and software i.e. your monitor, videocard, operating system, etc. - will affect the appearance of the samples provided. An effort has been made to compensate , as much as possible, for these differences.

Scanning and Restoring

Choosing a scanner can be a daunting task. The information available makes little sense to the average person. And in some cases is purposefully designed to confuse the novice buyer. Some manufacturers list dots per inch, some pixels per inch, some list numbers that match none of these systems. How do you decide which one to choose? Its easier now that most printers are also scanners leading people to just buy a printer and hope for the best on the scanner. If you have slides or negatives, you are going to need to buy a dedicated scanner.

There are several determining factors that can be compared if you know what to look for. Consider a scanner the way you would a camera. A cheap lens will distort the image no matter how much range it has. The camera body can be made of cardboard if the optics are first class, but if the moving parts don't align properly the exposure cannot be controlled. The best camera in the world will not make up for bad film, careless developing, or an inexperienced operator.

The first factor to consider in a scanner is the resolving power. Most are given in two numbers: 300/600, 600/1200, 1200/2400. The first number use to be the actual resolving power of the optics and the second is the resolving power with software "interpolation." Now it is common to see the horizontal and vertical scan rates instead. More confusion designed at making it hard for you to compare equipment accurately. (They want you to believe the ads not the specs)

Interpolation means that the software is using a complicated algorithm to increase the image - in other words, it's making up information that isn't there based on what is. Really good, i.e. expensive, software can fool the average person into thinking it created something out of very little. In truth, only an experienced retoucher can do this kind of thing successfully - mostly because they have the advantage of a human brain to make complicated, rational decisions about how it should look. Inexpensive software makes assumptions based on some programmer's idea of what you want to do without ever having seen YOUR image.

This sample is of the same 35mm print scanned at 600 pixels/inch on two different scanners; a new 300/600 ppi $150 Umax (on the right), and a 1200/2400 ppi $2000 Agfa (on the left). If you have a 32bit display you will see the Agfa picked up detail only hinted at by the Umax. If your display is 8 or 16 bit you probably can't tell much difference. Look at the shirt pattern detail

Which brings up the second practical matter: what do you want to do with it? If you are scanning family photos to add to your website or print out using laser or inkjet printers, then the Umax is a pretty good choice. At $150 its almost too good to be true! However, if you are archiving photos for posterity or restoring with the intention of producing new negatives and photographic prints the Agfa or something similar is a necessity.

Image editing software is the next consideration. The color balance of this photo had shifted very far to the red side

Restoring it to something close to the original is a complicated task, but with the right software and an experienced operator, the illusion of miracles can be performed...

[Brutes watching over David, Larry, Gina, and David 1975 ]

Additional information can be found at the Library of Congress Home Page, Library of Congress: Frequently Asked Questions on Preservation

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