Technology Introduction

Index Ľ

How Scanners Work

In a nutshell, a scanner is a device that analyzes the surface of an image, printed text or an object and converts it into a two-dimensional digital image. Scanners come in different shapes and sizes depending on the intended use. The most common scanner for home and offices today is the flatbed scanner. Handheld scanners were briefly popular in the early 1990s but arenít used much anymore due to the difficulty in getting high quality images. Film scanners are scanners that are used to scan positive or negative film without the need of making any prints. Drum scanners are the oldest and the most expensive of the four types of scanners and are used for high end scanning.

Flatbed Scanners

In most flatbed scanners, a bright light illuminates the image while an array of capacitors moves across the image, reading the entire area. The array used in flatbed scanners is usually a CCD (charge-coupled device) array. When light hits one of the CCD's in the array, the light photons free the electrons in the semiconducting material, in effect creating a charge that's directly proportional to the intensity of the light. This process is repeated until the array reaches the end of the image and the resulting sequence of charges is then digitized. Flatbed scanners use a one dimensional array that moves across the surface of the image instead of the two dimensional arrays that are used in digital cameras. Flatbed scanners have become increasingly popular, even in the photography industry as high end flatbed scanners are beginning to rival the image quality of drum scanners at a much lower cost. Flatbed scanners are available at a very wide price range starting at around $50 for low end units and up to $50,000 for high end units.

A newer technology that is rising in popularity in the field of flatbed scanners is the use of Contact Image Sensors (CIS). Instead of using mirrors and lenses found in a CCD scanner, CIS scanners use red, green and blue LEDs to produce white light. A single row of LED sensors are placed extremely close to the source image for scanning. Since mirrors and lenses are not used, CIS allows scanners to be more compact and portable. CIS scanners also consume less power as a result of using LEDs instead of xenon or cathode lights. One drawback to using CIS scanners is that the image has to be extremely close to the glass due to the poor field of focus. As a result, scanning the gutter of thick books can be difficult.

Sheet Feed Scanners

Sheet fed scanners are fundamentally the same as flat-bed scanners, except that instead of laying the document to be scanner flat on the imaging surface, it is fed through a roller mechanism to pass it over a fixed imaging array.  By there name, it is clear that only individual sheets of paper are fed into these scanners, so they do not offer the flexibility of flat-bed scanners, but they do offer greater performance, since sheets feed in automatically.

Sheet feeder mechanism are available for many higher-end flat-bed scanners, and they are also built into about two thirds of the All-In-One multifunction printers sold.  They are usually included in All-In-Ones to provide sheet fed fax capability.

Drum Scanners

Drum Scanners, the first type of image scanners ever invented, capture images using photomultiplier tubes (PMT). The image to be scanned is mounted on an acrylic cylinder which rotates at high speed in front of precision optics that deliver the image information to the array of PMTs. Modern drum scanners use 3 PMTs, which read red, green and blue. Even though few companies continue to produce drum scanners, they are still in demand due to their ability to produce high resolution scans. The obvious disadvantage of drum scanners is that they arenít as portable and easy to use as flatbed scanners and take a long time to scan an image. The biggest disadvantage though is price. New low end scanners start at around $16,000 while high end scanners can cost $65,000 and above. On top of that, youíll have to buy the drums that cost $1,500 to $2,500 each, drum mounting stations for $1,500 to $3,000 and high end scanning software for $1,500 to $4,000.

Film Scanners

A film scanner is a scanner that directly scans positive or negative film without the need for any intermediate printmaking. Film scanners usually accept uncut film strips and scan them using a CCD sensor. Most film scanners accept 35mm and 120 film strips and individual slides. The advantage of using a dedicated film scanner as opposed to a flatbed scanner is that the area to be scanned is much smaller, allowing for higher resolution scans. Using film scanners also has the advantage of being able to control cropping and aspect ratio without changing the original film. Dedicated film scanners will set you back around $100 for the entry level models and may go up to $1900 on the professional quality models.

Bar Code Scanners

Bar code scanners are devices used to scan encoded information usually printed on product packaging.  They fall into two different categories:  Hand Held, and Table or Surface Mounted (like at your grocery store).  In both cases they interface to your computer in the same ways that other scanners do.  These scanners are designed to use a laser to optically scan the surface of the object for a recognizable pattern, then capture that pattern, and using software, convert it into an input string to the computer.

Types of bard code systems:

  • Code 39
  • Code 128
  • UCC-128
  • UPC-A
  • UPC-E -EAN/JAN-8
  • EAN/JAN-13
  • Interleaved 2 of 5
  • Codabar
  • MSI Plessey

Business Card Scanners

Business card scanner, do what their name implies: scanning smaller single piece documents.  The also include recognition and contact information management software, to capture that actual contact information or other text contained on the card, and enter it automatically into a database. The newer business card scanners scan both color and black and white, and offer the ability to scan business cards directly into popular software products, such as: ACT!; Outlook; and Windows Contact Manager. They include accurate and efficient OCR software allowing continuous scanning and recognition of business cards. They are also  TWAIN compatible, so they can be used by any other TWAIN compatible scanning software.

Choosing Your Scanner

When choosing a scanner, you will have to carefully examine what type of scanning you want to do and how much you are willing to pay for it. To date, the best technology for ultra high resolution scans is still the drum scanner. But because of the disadvantages in price and expertise required to operate drum scanners, many individuals and even graphics and print studios have been shifting towards high end flatbed scanners.

Scanners & Windows Vista

As scanners decrease in cost, they are becoming more disposable.  As a result manufacturers are upgrading scanner drivers less and less with each new version of Windows.  With the introduction of Windows Vista, this situation became most obvious than ever.  Many scanners that were designed for Windows XP no longer work under Windows Vista, and no new driver is available.  The great irony is that almost all scanners use industry standard software interfaces and TWAIN compatibility, yet each still requires a unique driver.  Therefore, before upgrading to Windows Vista - if you love your scanner - be sure you can still use it afterwards.

Tags: Digital Scanner, OCR Software, Character Recognition, Drum Scan