Drum Scanners
The original kind of scanner was a drum scanner. Drum scanners capture images using photomultiplier tubes (PMT). The image that requires scanning is mounted on a cylinder, which then rotates at high speed. Specialized optics interpret the image and send it to the array of PMTs. Today’s drum scanners use 3 PMTs, which read red, green and blue.
Drum scanners have largely fallen out of favor because they aren’t as portable and easy to use as flatbed scanners, they take a long time to scan an image, and are usually cost-prohibitive – entry-level prices can start at $15,000 for the machine alone. Drums, mounts and software can add thousands to the final price.
For those that can afford them, however, they are valued because of their ability to produce exceptionally high-resolution scans.
Flatbed Scanners
In a flatbed scanner, a bright light illuminates the image from beneath while a number of charge-coupled device (CCD) capacitors move across the image, reading (or “scanning”) the entire area. When the reflected light hits one of the CCD’s in the array, an electrical charge is created that’s directly proportional to the intensity of the reflected light. This process is repeated until the array makes its way across the entire page. The resulting sequence of electric charges is then processed and digitized.
Some flatbed scanners use of Contact Image Sensors (CIS). Whereas CCD scanners use mirrors and lenses, CIS scanners use red, green and blue LEDs to produce white light. Since mirrors and lenses are not required, flatbed CIS scanners more compact and portable. They also consume less power as a result of using LEDs instead of the xenon or cathode lights that CCD scanners use. Although CIS scanners have these advantages, images that get scanned have to be extremely close to the glass in order to remain in focus.
Film Scanners
Film scanners are used to scan sheets or strips of analog film. Most film scanners accept “negative” media, such as 35mm and 120mm photography film, and “positive” media such as mounted slide film. When scanned, the images on negative film can easily be converted into positive images by the software that either accompanies the scanner or is purchased separately.
While it’s possible to scan film using a flatbed printer, the advantage of using a dedicated film scanner is that the area to be scanned is much smaller, allowing for higher resolution scans. Film scanners also have the ability to control cropping and aspect ratio without altering the original film.
Business Card Scanners
Business card scanners function in much the same way that film scanners do. The media is fed into the scanner, and the software interprets the media. It’s that software that makes business card scanners unique.
The software – called optical character recognition (OCR) software – allows the information on business cards to be interpreted and recognized. It must be able to do more than just scan the shape of a letter. It must be able to recognize which letter it is. An “O” must not be confused with a “Q”, and so on. Secondly, the software is usually expected to format the scanned information in such a way that it can be easily and automatically entered into a number of popular software products, such as Microsoft Outlook, ACT!, and others.
Bar Code Scanners
Bar code scanners are interpretive devices only, and are rarely expected to produce some kind of output like the other scanners we’ve looked at. They use a laser to optically scan the surface of the object for a recognizable pattern, such as the product bar codes we’re all familiar with, then capture that pattern, and convert it into an input string for the computer to interpret.
For more information on how a scanner can improve your workflow, please contact us.