Buying a Scanner

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What resolution should you get?

The resolution of a scanner refers to the maximum number of dots per inch (dpi) a scanner can capture. Resolution can range from 600x600dpi, which is fine for most day-to-day uses, to 1200x2400dpi, which is better if you plan to do sophisticated photo editing. Be careful of the term "interpolated resolution" which refers to a method of filling in the spaces between pixels, but has little to do with the actual resolution.

What do they mean by 24 bits?

"Bits" refers to the number of digital bits captured per pixel -- in other words, the number of colours that can be processed. This is known as colour depth. Be aware that while the internal colour depth may be stated as being 48 bits, many graphics applications can only handle up to 24 bits.

What kind of documents can I scan?

This can be very important when you're considering a scanner. Some low-cost scanners can only handle standard 8.5 x 11-inch paper, which could be limiting if you need to scan a legal-sized (8.5 x 14-inch) document. You also probably want to look at whether you can remove, or lift up, the cover, in order to make room for books and other bulky documents.

Can I scan transparencies or film?

If you're going to want to scan slides or negatives, you should purchase a scanner that has an adapter available. However, if you plan to regularly scan large numbers of negatives, look for a specialised film scanner -- it may be more expensive, but it will do a better job on your film.

Interface

Connecting a scanner to your computer can be done in a number of ways. Choose the one best suited to your needs. The Universal Serial Bus (USB) is very popular, offering straight-forward installation, flexible configuration and faster data transfer. Many over $1000. high-end scanners, however, connect via a SCSI port. SCSI stands for Small Computer System Interface, but everyone just says "scuzzy". This type of connection is fast but can require more work to configure and install. Macs support SCSI connection but many PC's do not.

If you want to get a SCSI scanner then you may have to open up your computer to install a SCSI controller card. Most SCSI scanners come with controller cards and SCSI cables. Even if you already have a SCSI card for another device, it may not be compatible with the scanner or the provided cables. All this bother will pay off if speed is a primary concern for you. Speed demons should also consider high-end scanners that support FireWire which is akin to USB but even faster.

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Types of Scanners

Flatbed Scanners

Flatbed scanners are constructed with a flat glass plate over the photosensitive array and a cover to go over the glass. You can place paper or objects like open books on top of the glass. Light emitted from under the glass reflects off the object being scanned and is picked up by the moving CCD array in the scan head. Flatbeds are a popular and flexible type of scanner that come in both monochrome and colour. Their only draw back is that they hog a lot of desktop space. Prices for general purpose models can start below $150, for higher image quality the range is $350 plus.

Sheetfed Scanners

Unlike a flatbed scanner, the photosensitive array in a sheetfed scanner is stationary, and the page being scanned is moved over the array. This is a good type of scanner for someone who intends to scan a lot of documents to produce editable text. If you combine a sheetfed scanner with an automatic document feeder (ADF), you don't need to feed in each sheet by hand.

Sheetfeds are available in both monochrome and colour. Although you can feed pictures or small pages into the scanner, the scanned images can get warped so flatbeds are still more flexible. Sheetfed scanners are nicely compact so they're good for limited spaces. You can pick up one of these scanners for under $150. Rapid, high volume business models can get into the thousands.

Handheld Scanners

Handheld scanners have scan heads 4-5 inches wide which makes them very portable. They plug into your parallel port so they're easy to share among people and can be a good addition to your laptop. The down side is that you will have to make several passes over a regular sized document to scan the whole thing. Usually, software is provided that will put the small scans back together, like stitching a patch-work quilt, but this is often time consuming. Moreover, unless you have the slow steady hands of a surgeon, your scans can turn out unevenly.

You can get cheap handhelds for under $150, but their declining popularity might make them hard to find. High-end wireless models with superior image quality and stitching software are available for around $750. Another kind of handheld scanner is the pen scanner. You drag a pen scanner over a line of print like a highlighter. The built-in optical recognition software turns the scan into text which can be downloaded to a computer via serial or USB port. Pen scanners can hold hundreds of text pages and cost around $200.

Portable scanners are like mini versions of sheet-fed or flatbed scanners that are compact enough to fit in a briefcase. Portable sheet-fed scanners are about the size of a three-hole punch while flatbed models are smaller than a hardcover book. These types of scanners plug into a PC Card or USB port and can scan in colour or black and white. Expect to pay about $250. Portable and handheld scanners have weaker light sources so their image quality isn't close to a full-fledged scanner.

Slide, Film, and Transparency Scanners

The typical person won't be scanning slides or transparencies, but people in the graphics or publishing industry often do. Slides, film, negatives and transparencies have to be scanned so that light transmitted through them is picked up by the photosensitive array. Most scanners have the light source and the scan head on the same side so they can't accommodate these types of images. Since slides and film are so small you need very high resolution scanners to do the job.

There are a few options if you need to scan slides. Some flatbed scanners support a transparency adapter (TPA or TPU) which costs between $150-$525. This is a backlight that you attach instead of the scanner cover. These adaptable flatbeds sometimes have a special section on the glass bed that is magnified especially for slides.

Other kinds of flatbeds come with a pull out drawer where you can place slides, but they are fairly pricey starting at about $1200. The last option is to get a dedicated slide scanner. These scanners have small scanning areas 4"x5", high resolution and high bit depth (see the criteria section) which makes them much more expensive. The cheapest start at $750 and can go as high as a few thousand.