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Technical-how scanners workTechnical-image processing

6B. Technical Infrastructure: IMAGE CREATION

Key Concepts

how scanners work
scanner types
image processing




Flatbed scanners are the best-known and largest selling scanner type, and with good reason. They're versatile, easy to operate, and widely available. Their popularity for Web publishing has opened up a huge market, pushing prices for entry level units below $100. At the other end, professional units for the color graphics market now rival drum scanners in quality. All use the same basic technology, in which a light sensor (generally a CCD) and a light source, both mounted on a moving arm, sweep past the stationary document on a glass platen. Automatic document handlers (ADH) are available on some models, and can increase throughput and lessen operator fatigue for sets of uniform documents in reasonably good condition. A specialized variant of the flatbed scanner is the overhead book scanner, in which the scanner's light source, sensor array and optics are moved to an overhead arm assembly under which a bound volume can be placed face up for scanning.

Flatbed Scanner
Overhead Scanner

Sheetfeed Scanners
Sheetfeed scanners use the same basic technology as flatbeds, but maximize throughput, usually at the expense of quality. Generally designed for high-volume business environments, they typically scan in black and white or gray scale at relatively low resolutions. Documents are expected to be of uniform size and sturdy enough to endure fairly rough handling, although the transport mechanisms on some newer models reduces the stress. Using roller, belt, drum, or vacuum transport, the light sensor and light source remain stationary while the document is moved past. An important subclass of sheetfeed scanners are upright models specifically designed for oversize documents such as maps and architectural drawings.

Sheetfeed Scanner

Drum Scanners
Drum scanners produce the highest resolution, highest quality scans of any scanner type, but at a price. Besides their expense, drum scanners are slow, not suitable for brittle documents and require a high level of operator skill. Thus they are typically found in service bureaus that cater to the color pre-press market.

Drum Scanner

Microfilm Scanners
Microfilm scanners are highly specialized devices for digitizing roll film, fiche, and aperture cards. Getting good, consistent quality from a microfilm scanner can be difficult because they can be operationally complex, film quality and condition may vary, and because they offer minimal enhancement capability. Only a few companies make microfilm scanners, and the lack of competition contributes to the high cost of these devices. Specifications for some microfilm scanners are available at

Microfilm Scanner

Slide Scanners
Slide scanners are used to digitize existing slide libraries as well as photo intermediates of 3-dimensional objects and documents that are not well-suited for direct scanning, though more and more such objects will be captured directly by digital camera. The use of transparent media generally delivers an image with good dynamic range, but depending on the size of the original, the resolution may be insufficient for some needs. Throughput can be slow.


Slide Scanners

Digital Cameras
Digital cameras combine a scanner with camera optics to form a versatile tool that can produce superior quality images. Though slower and more difficult to use than flatbed scanners, digital cameras are adaptable to a wide array of documents and objects. Most fragile materials can be safely captured, though the need to provide external lighting means that light damage may be a concern. Digital camera technology continues to improve, helped along by the growing consumer market.

Digital Camera


To compare attributes of various capture devices, click on
Table: Comparison of Scanners

Computer Considerations
A computer used as a scanning workstation must avoid becoming a bottleneck in the production process. Here are some characteristics to seek in a scanning workstation:

  • Adequate RAM—512 MB recommended. More if the machine will also be used for image processing.
  • A fast CPU—minimum 1.8 Ghz Pentium IV (or compatible) or 800 Mhz G4.
  • Fast, capacious mass storage—enough space for at least temporary needs (40-60 GB), even if files are ultimately moved to other storage devices. (Methods for estimating storage needs are covered in File Management).
  • Peripheral bus—Most low- and mid-range scanners now come with USB ports, commonly available on both Wintel and Mac computers. First generation USB (v.1.0/1.1) is quite slow and not suitable for large-scale production work. USB 2.0 is (theoretically) 40 times faster but is only just becoming widely available on Wintel machines in 2002, and scanners that support it are not yet common. Scanners offering Firewire connections (about the same speed as USB 2.0) are fairly widely available and Firewire is standard on Macintoshes, though it may have to be added to some Wintel machines. High-end scanners, including both high-speed monochrome and color scanners and low-speed (but very high quality) color scanners tend to offer only SCSI connectivity. SCSI has fallen out of favor on desktop systems, but can be installed on most systems with the addition of a peripheral card.
  • High-bandwidth networking (10/100/1000 Base-T) to allow fast access to and transfer of scanned files.
  • Platform/operating system—Most scanners offering USB connectivity work equally well on Wintel and Macintosh computers, though some manufacturers do not supply software drivers for Macs (third party products can sometimes solve this problem). Some scanners are platform specific, with high-end color graphics scanners more likely to support only Macintoshes, and high-speed production scanners more likely to support only Wintel machines. Be sure to check specifications to insure the scanner you want is compatible with your existing infrastructure.

Reality Check

Which scanner(s) can be used to image a 3-dimensional object?

  Digital Camera


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Technical - how scanner workTechnical- image processing

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