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See Inside September 2008

How Instant Photo Development Works

Taking apart the digital photo printer

The steady rise of digital cameras has prompted the rapid growth of a new industry: instant photographic developing. A shutterbug brings her camera’s memory stick to a store, inserts it into a kiosk, selects the photographs she wants, and moments later prints drop into a chute. The machines seem to be everywhere. “In five years the number of digital kiosks has skyrocketed to 85,000 worldwide,” says Charles S. Christ, Jr., thermal systems director at Eastman Kodak in Rochester, N.Y.

The printers use a “dry” processing technique known as thermal dye transfer (as opposed to the traditional “wet” process of bathing exposed film in liquid chemicals). As the photographic paper scrolls past a print head, tiny resistors aligned in a row each heat up to specific temperatures, transferring minute amounts of yellow, magenta or cyan dye from a ribbon onto the paper. Together the dots form color pixels.

Larger machines in full-service stores also use processes such as electrophotography but typically for two-sided jobs such as printing custom greeting cards or calendars because the resolution is not as high as that created by the thermal approach. Today’s thermal machines take about eight seconds to complete a four-by-six-inch print—down from 60 seconds in 2003—but Christ says future kiosks will be even faster.

An extreme form of dry processing is also bringing the “instant photo” back into vogue. In July, Polaroid introduced PoGo, a portable, pocket-size instant printer that makes two-by-three-inch prints from a digital camera, either over a wireless Bluetooth link or a USB cable. Start-up company Zink Imaging in Bedford, Mass., devised the process, the basic chemistry of which was invented by Stephen Telfer, now senior research fellow at the company.

In the system, colorless crystals are embedded in the photography paper. When resistors in the print head heat them to certain temperatures, they turn yellow, magenta or cyan. PoGo can produce an image in 60 seconds, run on batteries and be used anywhere: parties, vacations, company events, all of which Polaroid is targeting. The first products sold for about $150, and 30 sheets of paper were around $10. Telfer says that larger print sizes are already being prototyped. And because no ink is involved, a unit could be housed in electronic devices such as televisions to make prints of imagery on the screen.

Note: This article was originally printed with the title, "Dry Dyes".

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