Tuesday, April 16, 2013

Dust in the Machine

In the last year since the Digital Production Unit was added to Preservation Services we've grown and adapted to many challenges. One of our most resource-heavy projects is the Dartmouth Photo Files, a project to scan and collect the college's photographic records currently being held in Rauner Special Collections Library. So far we've scanned and uploaded nearly 8,500 photographs; merely one-tenth of the estimated total. We realized quite early that a project of this scope and type has different requirements than the smaller projects we regularly take on. This post will address the recurring issue of dust in the scanner.

While flatbed scanners like our Epson Expression 10000XL merely require the occasional spritz of glass-cleaner to maintain, our feed scanner, the Kodak PS810, is far more demanding due to its complicated internal mechanism and heavy amount of use. A piece of dust on a flatbed scanner is quite difficult to notice, and usually does not produce an unusable result (at the very worst it will catch the reflection of the scanner's lamps and discolor a few pixels). However a piece of dust inside the feed scanner will leave a quite noticeable mark on the image in the form of a colored (usually green) streak across the image. This happens when a piece of dust is trapped on the scanner lamps and the image is dragged over it, producing a line, like this:

Dealing with this dust starts at the beginning of every scanning session. Every day we use it the Kodak PS810 (as well as its surrounding area) is thoroughly cleaned. The feed rollers are wiped free of dust and the lamps are cleaned off with special polishing wipes. At the end of this process a "transport cleaning sheet" is fed through the scanner; this sheet has a sticky surface and is designed to pick up the last stray bits of dust. Afterwards the machine is ready to scan.

However, dust does not simply stay out of places that have been cleaned once, and in the Photo Files project we found that many of the photos themselves are responsible for dragging dust into the scanner's inner workings. In most cases where this occurs the dust stays on the lamp for several photos until it is dragged off, producing a sequence of photos all with the same green line across them. Needless to say, this is problematic for our finished product.

After attempting a few solutions to this problem, the best one we came up with was a spot-dusting of every photo before it goes through the scanner using a squeeze-duster like this:

While the procedure isn't perfect, it does lower instances of this problem drastically. Remaining dusty images are caught during our quality-assurance step and rescanned. Some photo scanning software claims to be able to remove this effect through digital manipulation (including Kodak's own software, which we do not use), however we chose not to adopt this in our procedures in order to maintain the integrity of the original, unaltered image. The result of such process is as claimed, removing the green dust lines, however it accomplishes by distorting the parts of the image directly above and below the dust, creating a blurred effect that is noticeable upon close inspection. While this is probably a good solution for a hobbyist, we intend to ensure the best possible condition for our scans in the long run. In this case the old saying holds true: a pinch of prevention saves a pound of cure, and by ensuring best practices at the scanning phase we can drastically reduce the need for rescans.

Written by Ryland Ianelli.

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