Digital scanners have become an important piece of computing equipment over the past few years. Many home office systems these days are sold complete with a scanner. So what are they, how are they used and what are some of the main points to remember?

What Do Scanners Do?
Scanners are first and foremost digital capturing devices that allow us to turn existing hard-copy items such as photos, negatives, slides and documents into digital format. Equipped with the right software scanners are also capable of optical character recognition (OCR). This means that books magazines and documents can be 'scanned' so as to be converted into digital documents.

The basic principle of a scanner is to analyse an image and process it in some way. Image and text capture (optical character recognition or OCR) allow you to save information to a file on your computer. You can then alter or enhance the image, print it out or display it on a your monitor.

Flatbed: Also known as desktop scanners, these are the most versatile and commonly used scanners. These are normally shallow in height and boxlike in appearance. The image or document is placed on a glass pane under a lid. Subsequently the scan head moves under the glass converting what it reads into an image.

Sheet-fed: These are similar to flatbed scanners except the document is moved and the scan head is immobile. A sheet-fed scanner looks a lot like a small portable printer. Some models have an attachment that allows the insertion of photographic film as well.

Handheld: These use the same basic technology as a flatbed scanner, but rely on the user to move them instead of a motorized belt. This type of scanner typically does not provide good image quality. However, it can be useful for quickly capturing text.

Drum: Mainly used by the publishing industry to capture incredibly detailed images. They use a technology called a photomultiplier tube (PMT). In PMT, the document to be scanned is mounted on a glass cylinder. At the centre of the cylinder is a sensor that splits light bounced from the document into three beams. Each beam is sent through a color filter into a photomultiplier tube where the light is changed into an electrical signal.

Resolution
There is an awful lot of technical information to digest when looking at the various models available. But essentially, most of the principles you need to understand in order to get the most from your scanner are generic, such as the issue of image resolution.
In simple terms, resolution refers to the amount of pixels used in an image. The higher the resolution, the more pixels, therefore the more possible detail. On most scanners, resolution can range from 72 dpi to 1200 - quite a considerable variation.

Scanned images are used for a multitude of purposes, from professional quality images that might be displayed in a glossy magazine to those baby photos you send your aunt via email. Your choices about which resolution to use when scanning images will depend on your purpose. Additionally, the higher the resolution, the larger the file size of the image, so you'll need to have thought this through before you start scanning.

In general, if you are wanting images to use in print resources or other print material, you should be aiming at a reasonably high resolution - anywhere between 300 - 600 dpi (dots per inch). In the glossier magazines, it is not unusual for the scan resolution of the image to be set at 1200 dpi.

However, if your images are going to be used exclusively on a screen (such as a computer monitor), there is no need to scan at such a high resolution. Monitors are not capable of reproducing images at the same resolution as paper based media. A mere 75 dpi will be enough to display good quality photos on your computer monitor. Higher resolutions will not result in a better picture, and will only increase the file size - not something desirable when dealing with digital files.

One important thing to bear in mind is that the quality of your final scanned image will depend on the quality of the photo or graphic being scanned. If your photo is out of focus or the light is wrong, no amount of scanning or dpi will be able to provide a better image. For these sorts of photos, you're better off finding another image to use for the scan, or manipulating the photo in a program such as Photoshop where, in some cases, these types of problems can be corrected.

Another term used when talking about scanners is bit depth, also called colour depth. This simply refers to the number of colours that the scanner is capable of reproducing. Each pixel requires 24 bits to create standard true colour and virtually all scanners on the market support this. Many of them offer bit depths of 30 or 36 bits. They still only output in 24-bit colour, but perform internal processing to select the best possible choice out of the colours available in the increased palette. There are many opinions about whether there is a noticeable difference in quality between 24-, 30- and 36-bit scanners.

Connection Methods
Scanning the document or image is only one part of the process. To use a scanned image, it needs to be transferred to your computer. There are three common connections used by scanners:

Universal Serial Bus (USB): These days this is the most common method of connecting a scanner to a computer. The USB is a type of connection (used with a range of peripheral devices) which uses a high transfer rate and allows you to "plug and play". Simple to hook up and image transfer is speedy.

Parallel Port: An older type of connection. Much slower than USB.

SCSI: The fastest connection for transferring data from the scanner to the computer. SCSI requires a special SCSI card which adds cost to your system.

What's a TWAIN?
Sometimes the TWAIN driver is mentioned in regard to scanners. This is a software driver interface that allows you to communicate with your scanner via the computer so as to adjust the orientation of your image (eg rotate it), scan portions of the image and/or a range of other functions. Check the manual that came with your scanner for specific information on how to use your twain driver.

Some important points to remember when scanning images
- Generally it is a good idea to scan images at a slightly higher resolution than required in order to get the best possible digital image. For web quality images, only 72 dpi is required. We recommend that you therefore scan your images at 75 dpi.

- You can manipulate your picture in a digital image editor (such as Photoshop) to bring it to the desired size. All scanners come with software that allows you to manipulate scanned images - it's a good idea to learn how to use the one that came with your scanner or one of the commercial products on the market.

- If you are not confident about using a digital image editor, learn to use the twain functions on your scanner to size your images to the size you want for your web page or print resource.

- Finally, it is important to know that you cannot enlarge a scanned image without loss of quality. On the other hand, you can reduce an image without any loss of quality but the detail will not be as clear. Make time to experiment with your scanner in order to learn how to get the most from your photos, documents and other images.


Resources
http://www.cnet.com
http://www.zdnet.com