Monday, August 12, 2013

CNBC: Xerox machines swap numbers during scans

If someone told me about this in passing, I would assume it to be a big joke, but apparently not:

D. Kriesel, a German Ph.D. student studying computational geometry, encountered a strange problem when scanning a blueprint on a common Xerox office scanner. The numbers denoting the square footage of rooms were totally wrong, and what's more, they changed when he scanned the blueprint again.

Intrigued, Kriesel tried scanning a table of costs and figures. Numbers changed again—but not wildly, just by a little bit: 54.60 became 54.80, for instance. And it wasn't just a blurry scan or a misplaced pixel—these were fully formed, unmistakable characters.


it quickly became clear what the culprit was: an image compression algorithm called JBIG2, built into the scanner as the "normal" quality option for those who wanted to save a bit of space on their hard drive (versus "high" and "higher," which made for much bigger files).

Unlike an analog photocopier, or a digital one that simply records the black-and-white values of pixels, JBIG2 examines the whole image and finds pieces that are highly similar, replacing them with a sort of clone-stamped version that saves space. Examples of such pieces of an image might be the pattern on some wallpaper or the top of a fence—or, as it turns out, small letters and numbers that look similar, like 6s and 8s.

All I can say is "d'Oh!"

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