ADVICE WHEN BUYING A SCANNER

A scanner is an optical device that breaks an image into pixels and translates them into ones and zeros so the computer can interpret the image and recreate it on the screen. Before buying a scanner you need to ask yourself what you will use it for. If it’s just for posting images on a website almost any scanner will do. If you want to archive family photos you need a scanner with very high optical resolution and colour depth. These parameters are crucial for how the image is recreated.

It’s also important to check what software is included with the scanner. Some manufacturers only pack trial versions that have to be upgraded before they can be used to their full extent. Som scanners include OCR (Optical Character Recognition ) software enabling the scanner to differientiate between text and graphics so the text can be easily edited. If you will be scanning large amounts of papers it’s a nice feature that some scanners has document feeder for fast use. Some scanners can handle photographic film and OH-slides.

Scanning technology
Most scanners use CCD (Charge-Couple Device) arrays that can detect variations in light intensity and frequency. It's the quality of the CCD that determines the quality of the scanner. A new technology released to the market uses Contact Image Sensor (CIS) to scan the image. In terms of price, the CIS-based scanners are generally less expensive. However, for maximum output quality, the CCD scanner tends to provide a higher quality result.

Interface
It’s important to check that your computer supports the interface of the scanner.

USB
(Universal Serial Bus) is an external port for data transfer. With the old USB1 interface the maximum transfer rate is 10Mbit/second. The new USB2.0 standard supports speeds of up to 480Mbits/ second. USB is Plug-and-Play compatible so hardware can be installed while the computer is running.

Firewire (IEEE 1394)
Firewire (sometimes called iLink) enables transfer speeds of up to 400Mbit/s and is well suited for large amounts of data.

Colour depth
Another factor to consider is the colour depth capacity of the scanner, which allows the scanner to distinguish the range of different colours and shades in the documents to be scanned. Each point in a image is called a pixel (short for picture element), and different scanners read the pixels in varying intensities of bits. The greater the bit depth, the more colors or grayscales can be represented, and the greater the resolution. For example, a 24-bit color scanner can represent 2 to the 24th power (16.7 million) colors.

Resolution
The quality of the scan is determined by the optical resolution the scanner provides. The resolution refers to the sharpness and clarity of an image, represented in dots per inch (dpi). The more dots per inch, the higher the resolution and the clear and sharper the scan. For example, 600 dpi means that there are 600 dots across and 600 dots down, so there are 360,000 dots per square inch. Typically, scanners support resolutions of from 300 to 4000dpi or more.

Platform
Indicates which platform the scanner is compatible with.

Scan area
Indicate the surface size the scanner is capable of covering.

Scanner type
The two most popular types of scanners available on the market are: Flatbed scanners Flatbed scanners are generally considered the most versatile, as they enable you to scan a range of documents or objects regardless of their size or thickness (eg. magazines, books, maps, charts, etc)

Sheet-fed scanners These are suitable for scanning single sheets of paper, however, the materials that are scanned need to be detached from the book or magazine. These scanners look similar to a portable printer, where the item to be scanned in is fed into the scanner.

TWAIN
Scanners are generally sold with specific operating software that controls the scanning process and adjusts the scanned image. In most cases, this software, called a TWAIN driver, is easily installed on your computer and allows you to use the scanner with other applications such as texteditors or image processing programs.