Lab

Flatbed Scanners

The scanners integrated in multifunction peripherals (MFPs) can produce decent results, but if you already have a perfectly good printer or you're serious about high-quality imaging, a standalone scanner is just what you need.

We've taken a look at nine scanners designed with various purposes in mind. Two are entry-level models designed for scanning photos and simple documents. Five come with everything you need to scan negatives and slides, making them the perfect way to preserve family albums or produce your own enlargements. We've also looked at a couple of scanners designed to make it easy to copy pages from books without damaging them, which is ideal for students or teachers. Whatever you want to scan, we'll show you how to get the right imaging hardware at the right price.

The scanners here range in price from £38 to a few hundred pounds, but choosing the right scanner for your needs involves more than just financial considerations. Before you start looking, you need to work out what you want to scan.

Almost any scanner is capable of capturing basic documents, but if you want to scan photos or illustrations, image quality becomes a lot more important. If you want to scan old film or slides, a high-quality scanner with a high optical resolution is essential. If you need to scan a lot of documents or books, you'll need a fast, flexible scanner with an automatic document feed.

A satisfactory resolution

A scanner's optical resolution is measured by the number of dots per inch (dpi) the sensor can record. You can think of this as like a digital camera, where having a higher megapixel rating lets you capture more detail. Higher resolutions also result in larger images, so the higher the scanner's dpi, the bigger the enlargement you can make from an original. Remember, though, that any defects in the original document will be enlarged too, so the quality of your source material affects the maximum resolution at which you can scan.

Be careful with these resolution ratings, though. Scanners typically have two dpi ratings, such as 1,200x2,400dpi. Pay attention only to the lower figure, as this is the real resolution of the scanner's sensor; the second figure is based on how many times the moving head stops per inch - so for a 2,400dpi resolution, the head stops 2,400 times per inch. You don't capture any more detail from this, but each point on the document is scanned more than once. The combined results can improve accuracy, detail and colour.

Scanner manufacturers will often quote an interpolated dpi figure, but you can ignore this completely, as this higher figure is achieved by artificially enlarging the image. You could do the same thing in any photo-editing package simply by manually resizing the image.

For standard documents and photos, a scanner with a resolution of 1,200dpi is fine. If you want to scan negatives or slides, you need a scanner with a resolution of at least 2,400dpi, but 3,200dpi or higher is better. Typically, documents should be scanned at a minimum of 100dpi, and photos at 600dpi. Don't forget that increasing the resolution means the scanner takes longer and produces a much larger image - it's easy to get carried away and end up with a 1GB image.

It's also important to remember that a high optical resolution doesn't automatically equal excellent image quality. As with a camera, the quality of the lenses and other parts all have a big effect. We tested all the scanners here with the same film and reflective sources, and found significant differences in quality between scanners with identical quoted resolutions. Our reviews explain which scanners performed well and which were poor.

Head light

Flatbed scanners capture an image by moving a head under the glass platen. The lid holds the document flush against this glass surface, and a light source illuminates it. The light that bounces back from the document is measured by the scanner's sensor, converted to an electrical signal and stored by your PC.

This process doesn't work for transparencies and film, as they don't reflect the light. Instead, you need a scanner with a transparency adaptor, which works by turning off the light under the transparency and shining a light through it from above - similar in concept to an old-fashioned projector. Scanners that support transparencies come with special film and slide holders into which you have to clip your originals. The size of the secondary light defines how many slides you can scan at once. Our table on page 96 tells you which formats each scanner supports, if any, and how many negatives and slides it can scan at once. If you need to scan a lot of negatives, Canon's CanoScan 8800F is a good choice as it can take 12 35mm frames at once.

As film and slides are so small, they need to be scanned at very high resolutions to capture high levels of detail. This has the downside that any small imperfections, such as dust or scratches, are greatly magnified. Most scanners, such as Epson's Perfection V200 Photo, use software dust and scratch removal techniques. Canon uses its Film Automatic Retouching and Enhancement (FARE) technology in its scanners, which shines an infrared light at film to detect dust and remove it more effectively from the captured image. Our reviews tell you which technique each scanner uses.

Make sense

Each of the scanners here uses either a charge- coupled device (CCD) sensor or a contact image sensor (CIS) to record the scanned image. CCD sensors are more expensive and require more power, but they can produce higher-resolution images. They also have a wider colour range (or gamut). Film scanners tend to use CCD technology.

CIS technology is cheaper to manufacture, smaller and requires less power. Scanners that use these sensors can be powered by USB and take up a lot less room. Although the image quality is supposedly inferior to that of CCD sensors, we didn't notice much difference in our tests. Choose a CIS scanner if space is an important factor. Our table tells you which technology each scanner uses.

Easily recognised

All the scanners here have built-in control buttons for quick operation. For fine control, though, you'll need to use the scanner's interface software. This is either launched manually or, more likely, accessed directly from within your image-editing software. The interface application offers full control over the area you want to scan and the resolution, as well as advanced options such as dust removal.

Most of the image-editing applications that come free with the scanners aren't much good, although Canon's CanoScan 8800F comes with the excellent Adobe Photoshop Elements 5.0. Every scanner here comes with optical character recognition (OCR) software, which can convert a scanned document into editable text. The software supplied with HP's scanners produced the best OCR results. Our reviews tell you how accurately our test document was converted into text, while our table lists the software included with each scanner.

Unlike most printers, every scanner here comes with a USB cable, so everything you need to get scanning is included in the box.