Buying a scanner is not difficult. But a few simple guidelines should help you to avoid getting a disappointing unit and achieve results from your machine.

Image quality: Scanners can put more pixels (individual cells that make up a digital picture) into an image than the most expensive digital camera.

A 1,200 ppi (pixels per inch) scanner makes up the image with 1,200 individual pixels in every square inch, a 2,400ppi scanner twice as many. The more pixels per inch, the better the resolution (or clarity) of the image. A 2,400 ppi scanner will create a more detailed image but, sadly, it is usually more expensive.

It is possible to buy a scanner offering a higher resolution because it uses software "interpolation" to achieve its results.

Interpolation is a method of increasing the pixel count by adding new pixels of an appropriate colour. The software looks at the original pixel colours and then "guesses" what colours should be used to make up the numbers.

If you require extreme colour accuracy, avoid a scanner that relies on interpolation.

For most purposes, however, it is regarded as acceptable.

Some scanners offer the facility to scan photographic film and slides. In the main, these work very well and can be an alternative to taking your film to the processors for printing.

It is possible to print photographs at home with a colour inkjet printer.

A scanner is often advertised as being 16-bit colour or 24-bit colour or even 42-bit colour. Bit depth is an indication of the number of "levels" or colours a scanner can see. A scanner with a higher bit depth will be able to reproduce images containing a larger number of colours.

If you intend to scan photographs, you probably do not need a scanner with more than 1,200 ppi capacity. Text requires a much more detailed scan quality because it is composed of pixels that have to be in a finite order to be read.

Photographic data is a lot more flexible than text and is sometimes deliberately scrambled (dithered) to give a regular toned appearance to a finished image.