If you have ever wondered how a printed page is transformed into a
computer file that we can read with synthetic speech, the article below
explains it all.  This is a little more comprehensive than the scattered
descriptions provided by sighted assistants through the years.

kelly

from The New York Times

      March 11, 1999

      HOW IT WORKS

Scanners: Softening Up Hard Copies

      By DAVID KUSHNER

     Since the paperless office has turned out to be a fantasy, there
     have to be ways to get all those words and pictures on pieces of
     paper into a computer. Thus, the scanner.

     Technically, a scanner and a digital camera do the same thing. Each
     takes an image and translates it into digital information that a
     computer can store. Each uses a number of lenses and an
     analog-to-digital conversion chip to convert an image into binary
     bits. The difference is that scanners are made specifically for
     processing images of documents, not images of people or vistas.

     Back in the mid- and late 1980's, when scanners first came to
     market, they were predominantly the domain of graphic artists and
     designers. As computer design became part of everyday business,
     artists needed a way to store and manipulate things like
     photographs and newspaper and magazine clippings.

     The first scanners mimicked the style and shape of a standard
     photocopying machine. A large "flatbed" surface supports the
     document that is being reproduced. But the machine produces a
     digital image instead of a paper copy. Scanners can also be used
     with optical character recognition software, which reads the image
     of a page of text after it has been captured by a scanner, then
     translates the image into the computer code that a word processor
     can read (details are in the Q&A, this page). Without such
     software, a page of text is stored in the same way a drawing or
     photograph is stored, as an image, not text.

     The technology used is generally the same from scanner to scanner.
     A light source shines upon the selected document, and the image is
     reflected through a series of mirrors. Then it passes through a
     lens, which reduces the image and focuses it onto an array of
     charge-coupled devices. A C.C.D., a semiconductor chip that is
     sensitive to even tiny amounts of light, measures light intensity
     and converts it into voltage.

     This C.C.D. array is part of a circuit board that contains other
     electronics as well. Through the use of color filters, the
     information the array stores about the image includes the intensity
     of each of three colors: red, green and blue. The colors and shapes
     are translated into different patterns of voltages by the C.C.D.
     array. Through other chips, the voltage levels, which are analog
     signals, are given digital values. In the end, that allows the
     computer attached to the scanner (or the scanner itself, depending
     on the system) to recreate the image.

     Scanners to satisfy all types of consumers are now available from
     companies like Hewlett-Packard, Visioneer and Epson. Today's
     flatbed scanners are about half the size and weight of the original
     models, but they are still the largest and most cumbersome
     scanners. They remain the most popular because they provide a
     clean, efficient way to handle a large volume of documents, like
     newspaper articles and fragile family photographs.

     Sheet-fed scanners are smaller and more compact because the
     document is fed through a narrow slot in the middle of the device.
     They are less versatile than flatbeds because a large object may
     not fit through the slot and a small one might get crumpled. The
     image quality tends to suffer, but frequent travelers find that it
     is enough to get the job done.

     For people who want more of a hands-on experience, handheld
     scanners are the most portable of all. They are most often used to
     scan small objects, like business cards or newspaper headlines; the
     photosensitive strips tend to be only a few inches wide.

     Companies like Canon and Hewlett-Packard have been introducing more
     comprehensive, all-in-one scanning systems, which combine a
     scanner, a fax machine, a printer and a copier into one device.
     Because only one slot is included in the product, however, the
     scanner is limited to a sheet-fed design. With all these new
     scanners on the market, prices are dropping accordingly. Ten years
     ago, a scanner might cost nearly $1,500; today, some can be had for
     as little as $100. In addition, more consumer software like
     greeting card programs, photo-manipulation packages and Web-page
     creation tools takes advantage of digital imaging.

     Greg Pershall, public relations manager for Hewlett-Packard
     Scanjets, said that nearly 60 percent of the company's scanners
     were purchased for home use. The most popular use for a scanner is
     storing and transferring photographs, he said. It seems that the
     family album is increasingly ending up online. Of course, there
     will always be those who find other uses for the devices. Earlier
     this year in the Williamsburg section of Brooklyn, a theater group
     performed "Abacusparts," a play in which an actress used a handheld
     scanner to digitize herself onto a screen. The resulting image,
     needless to say, was grotesque. Perfection in digital imaging,
     alas, is not always the point.

     How It Works is published on Thursdays in the Circuits section.

********************


It's Done With Light and Mirrors

     Of course, scanning also requires software, computer hardware, a
     lens, a lamp and a drive belt, at least in the case of a flatbed
     scanner. Flatbeds are an odd mix of the mechanical and the digital;
     the whole internal assembly must be moved while the document stays
     in one place. The colors and shapes of the image are turned into
     zeroes and ones. Then the computer linked to the scanner can
     reconstitute the image.


     1. First, a photograph or other image is placed face down on the
     glass plate of a flatbed scanner, and the lid is closed.
     2. When the scanner is started, a lamp is turned on and its
     brightness is adjusted. Software on the computer attached to the
     scanner is also activated.

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     3. A drive belt pulls the scanner carriage under the object to be
     scanned. The carriage contains a light source, lens and
     charge-coupled devices, or C.C.D.s, which translate light
     intensities into analog voltage levels.


                                  [INLINE]



                                  [INLINE]

     4. The voltage from the C.C.D. array is sent through another chip,
     which amplifies it.
     5. The analog-to-digital converter changes the voltage into
     corresponding digital signals.

                                  [INLINE]

     6. Data are generated faster than they can be processed by the
     computer, so they are funneled through a buffer, which pauses
     intermittently as the computer software processes the information.
     7. In the scanner or the attached computer, depending on the
     system, the data for colors and shapes are assembled into a final
     image.

     8. The image appears in a viewing window on the monitor, where a
     user can manipulate it with special software.

           Illustration by Gorka Sampedro for The New York Times

      Source: Robert G. Gann; Hewlett-Packard Company; Greeley, Colo.

   Copyright 1999 The New York Times Company


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