This article was excerpted from: Scanners for Dummies

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Buying a scanner isn't as difficult as buying an entire computer system nor is it as simple as buying a new hard drive (which boils down to capacity, connection type, and price for everyone other than technotypes). Although a scanner falls somewhere between the two extremes, you need to ask yourself only three questions before you continue reading about the other features and luxuries you should understand.

How big can it be?

Before you start shopping, you have to decide how big is too big: Can you dedicate the desk space for a flatbed scanner, which can actually take up more room than a typical computer? Or will you stay lean and mean with a sheet-fed scanner? You need to settle on a design before you go any further.

Reasons to choose a flatbed scanner

Many people opt for a flatbed scanner. These are the reasons why they do:

• A flatbed scanner is far more versatile. With a flatbed model, you can scan materials and three-dimensional objects other than paper, such as a piece of fabric or a TV remote control (or even that new tattoo on your arm). Basically, if you've ever made copies of something on a copy machine, you can scan it with a flatbed.

• A flatbed scanner doesn't cannibalize your material. With a sheet-fed scanner, you can't scan pages from books or magazines unless you tear them out, and don't even think about scanning the surface of your arm for that tattoo. Plus, you don't have to worry about material that's too stiff (such as your driver's license) or too small (such as your driver's license). With a flatbed, material of reasonable thickness and just about any size can be scanned without fear of jamming the mechanism or losing something in the bowels of the machine.

• A flatbed scanner produces a better scan. With a flatbed scanner, the scanning head moves past the material, a process that's inherently more stable than having the material move past the scanning head (as in a sheet-fed model). This is why just about any flatbed scanner features higher resolution (and often better color depth) than a sheet-fed scanner.

The reason to choose a sheet-fed scanner

In some cases, a sheet-fed scanner is right for you. Here's one good reason: It takes up less space. A sheet-fed scanner takes up only a fraction of the area used by a flatbed scanner on your desktop. In fact, many sheet-fed models are portable enough to be used on the road with your laptop computer. Some all-in-one printer/scanner/copier/fax devices use sheet-fed scanning engines for this reason. Other models now offer a built-in flatbed scanner.

If you're interested in a specialized scanner, such as a photo scanner or negative scanner, remember that these exotic varieties are designed especially for a particular media. You can't scan anything else on them.

How many dots are enough?

The more dots per inch (dpi) you can scan, the better. How many dpi does an average person really need, though? Table 1 shows a breakdown for choosing a resolution. Remember that the "common" dpi is expressed as two numbers (horizontal x vertical). Remember also that this is optical resolution, not a resolution figure that has been enhanced or interpolated through software.

Table 1: Selecting the Right dpi

Note: You may be wondering what scavenger means in Table 1. The term refers to someone who acquires older hardware. For example, if your Uncle Milton gives you his old 600 x 600 scanner because he has just bought a new model, you're a scavenger. This concept also applies to hardware bought at a garage sale or on eBay. In Table 1, it means that you're not likely to find a new scanner on the market now with a resolution of less than 1,200 x 1,200.

Naturally, a model with a higher resolution can do everything a lower-resolution scanner can do. Also, the figures in the table are the minimum: If you find two scanners with the right features and one delivers 2,400 x 4,800 resolution for only $50 more, you may want to spend the extra money.

How much bit depth do I need?

Again, the higher the bit depth, the better the scanner. Should you spend extra cash, though, for a 42-bit or 48-bit scanner? Check out Table 2 to get some answers.

Table 2: Choosing a Bit Depth

Although 24-bit scanners technically produce more than 16 million colors, you won't find one in a store. If you're buying a new scanner these days, stick with a scanner that offers at least 36-bit color. Anything more than 36-bit is usually overkill for a typical home computer owner.

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