Optical resolution is the most commonly used specification to compare the capabilities of different scanners. It refers to how many pixels, dots, or samples per inch the scanner’s sensors can detect. Generally, the higher the resolution, the better the quality of the scanned image. Low-end scanners have a resolution of 300 ppi, while high-end scanners can detect as many as 4,000 ppi.

The 300-ppi variety will provide adequate resolution for computer-screen images, since most computer graphics cards can’t handle much more detail than this. (You can learn more about how a graphics card functions in Chapter 4.) On the other hand, if your objective is a nice copy from a laser or color printer, the results from a scanner with a 300-ppi optical resolution are likely to disappoint you. A 400 to 600 resolution will probably give you the quality you’re looking for in a printed copy.