Scanners may produce digital output, but they’re largely analog devices. Component quality and engineering precision will have as big an impact on the quality of results as the electronics and software. To get the best from it, you need to get to know your scanner. We explain the different types, their strengths, weaknesses and ways in which you can squeeze out that last ounce of quality.

Your needs
Do you want to scan reflective originals (documents and prints) or transparencies (slides and negatives)? The plain fact is that a single scanner can’t do both – not properly, anyway.

Flatbed scanners are very good at reflective originals, and even low-cost models offer higher resolution than the level of detail you’re likely to find in any original you want to scan. Many models can also scan slides and negatives using transparency adaptors which are either optional extras or supplied with the scanner. So why buy a dedicated film scanner? It’s a question of design and engineering. Technically, flatbed scanners can deliver resolutions as high as 2400dpi or 3200dpi, which is film scanner territory. In practice, however, cruder engineering and design restricts their defining power. A 3200dpi flatbed produces files as big as a 3200dpi film scanner, but the detail will be significantly softer, and that even applies to Epson’s brand new Perfection, probably the best flatbed currently on the market.

Don’t rule flatbeds out yet, though. A medium-format film scanner will cost you £2500+, while large-format photographers are restricted to professional drum-scanning bureaus. But flatbeds like the Perfection 3200 will also scan medium format and large-format film up to 5x4ins. With these larger film sizes, the quality compromises will be far less important because the enlargement factor when you make prints will be a lot lower.

What are you scanning?
If you’re scanning reflective originals, the first thing your scanner will need to know is whether it’s dealing with a photographic print, a magazine page or a newspaper cutting. Manual colour settings will be self-evident – full-colour, greyscale and mono (1-bit), typically. Unfortunately, many simpler scanners in a misguided attempt at user-friendliness, disguise these options as document ‘types’, like ‘colour photo’, ‘document’, ‘text’ and so on. You may need to examine the manual to discover exactly what sort of file it’s going to output and what colour/mono mode it’s going to use when it does so.

There’s another possible stumbling block. If you’re scanning magazine pages, you’ll almost certainly need to apply ‘descreening’ to counter the moiré effects you tend to get at certain scanning resolutions (100-300dpi), where the printed dot pattern interferes with the scanner’s ‘dots’ (pixels). Most scanners offer an optional descreening filter which combats any interference effects and disguises the printed dot pattern to produce a more smooth-toned scan. The complicating factor is that some scanners offer a descreening function visibly, as a checkbox or menu option, while others – again, in a misguided attempt at user-friendliness – wrap it up instead in a ‘magazine’ option on the list of items you might be wanting to scan. If your scanner doesn’t appear to offer a descreening option, this is where you’re most likely to find it.

A question of scale
Make sure that you get the scanning resolution and scale right. It should be simple but isn’t. The decision for documents is pretty straightforward – you’re unlikely to want to change the scale, so you just pick an appropriate resolution. A 2400dpi scanner is a nice luxury, but even at a modest 150dpi the text in most documents is going to be perfectly legible.

Scanning photos isn’t so straightforward. Quite often you’ll want to print a scanned photo larger than the original – or smaller. This is where you can easily get in a tangle over resolution and scaling. Different scanner drivers handle these two settings in different ways, so it’s difficult to generalise over strategies.

Try scanning photos at 600dpi by all means, but you’re likely to find that a 300dpi scan at 100 per cent scaling (no enlargement or reduction) extracts as much definition from a print as it possesses. Should you need to print it larger, resize it in Photoshop or let your printer scale it. Either will do just as good a job as scanning at a higher resolution in the first place. If the detail’s not there, don’t bother chasing it.

Levels and curves
Do you adjust levels and curves while scanning, or later in Photoshop? It’s an important question, since all scanning software offers image adjustment options. There are two schools of thought here. One is that Photoshop is far more sophisticated and effective than any bundled TWAIN software and that it, or any mid-range image-editor will do a better job than your scanner. It’s a tempting proposition, but it’s not quite as simple as that. On a practical level, it may prove a lot quicker to adjust brightness, contrast and colour at the scanning stage rather than opening up the file later to do it in Photoshop.

There are arguments on a theoretical level, too. Firstly, scanners operate at a higher bit-depth than their final output files. All but high-end models produce 24-bit images (8 bits per channel). This is fine for scans which need little subsequent modification, but if you apply heavy tonal manipulation later, this can cause a degree of tonal separation, which results in colour banding or digital noise. Scanner manufacturers are seldom very clear about this particular aspect, but if you give them the benefit of the doubt and assume that tonal and colour adjustments are applied before the 8-bit conversion, you should end up with a higher quality result by adjusting these parameters at the scanning stage.

Secondly, it may well be that the scanning software is carefully attuned to the scanner’s particular characteristics. The CanoScan FS2710 film scanner, for example, tends to need some curve adjustment in shadow areas to improve shadow detail rendition. Do this in Photoshop and you exaggerate the shadow noise which is characteristic of this particular scanner. Apply the same curve adjustment in the scanner software, though, and the noise is controlled far better.

Saturation
Now’s the time for saturation and sharpening adjustments. Untreated scans can look distinctly lifeless, though this tends to be more of an issue with cheaper scanners. Applying brightness, contrast, levels or curves can often restore colour too, so make sure you carry out these adjustments before increasing saturation.

You may be loath to apply any sharpening at this point, on the assumption that a 2400dpi scanner (say) ought to be able to produce a razor-sharp 300dpi scan. It doesn’t quite work like that, and any scanner you’ll ever use will almost certainly need sharpening, either at the scanning stage or later on. Get used to it.

In principle, the scanner’s makers should know exactly how much and what sort of sharpening the scanner needs, so the built-in sharpen filter should be all the sharpening you require. In practice, higher-resolution files need different treatment to low-res ones, and you may find you need to apply some Unsharp Mask adjustments in Photoshop instead of, or as well as those applied by the scanning software. Scan previews are a hopeless guide to sharpening strength, since you’re seeing the effect applied to a low-res screen image, not the high-res output file. You can only judge the results properly by examining final scan files.

The specs
It’s worth spending some time examining your scanner’s documentation to make sure you understand what it can do, and how to make it do it. With experimentation you can learn your scanners strengths and weaknesses along with methods to exploit the former and get round the latter. Getting to know your scanner is one thing, getting to make sense of scanner specifications is quite another. See the box on scanner specs to find out what they’re supposed to mean, what they really mean, and how they can help you make an informed choice when you’re shopping for your next scanner.

Flatbed versus films
Flatbeds are engineered to scan large areas and their optics and drive mechanisms aren’t ideally suited to the minute proportions of 35mm negatives and slides. Flatbeds simply can’t match the definition of film scanners. Flatbeds have fixed-focus optics – your originals need to lie on precisely the right plane to be in perfect focus. Better film scanners include hardware-based dust reduction systems which can eliminate tedious retouching with no visible quality loss. Few flatbeds offer this as yet.

Film scanners generally scan slides and transparencies a lot faster than flatbeds with transparency adaptors. Film scanners offer higher dynamic range and cope better with high-contrast originals that flatbeds would render with dense black shadows. Most film scanners offer adjustable ‘exposure’ options, which change the speed of scanning and enable the CCD to accumulate more image data from extra-dense or light originals.

What those specifications mean
Optical resolution: The only figure that counts. Remember that reflective originals seldom need scanning beyond 300dpi, but that higher-resolution scanners produce crisper results at any resolution. For flatbeds with film adaptors, 2400dpi is the bare minimum.

Interpolated resolution: Marketing nonsense. At their maximum optical res, scanners are already up against their detail-recording limits. Interpolation just adds more ‘empty’ pixels and produces colossal files with no additional detail.

Bit-depth: In theory, the higher the bit-depth, the subtler and smoother the colour rendition. In practice, it’s a calculated figure that makes no allowances for the scanner’s engineering, CCD quality or signal-to-noise ratio.

Dynamic range: The higher the dynamic range, the better the scanner will cope with extreme contrast and density. In practice, the figure is often calculated from the bit-depth, and makes no allowances for signal-to-noise ratios which can render much shadow unusable in cheaper scanners.

Scan speeds: Sometimes quoted by makers as an indication of how fast you might be able to scan a text document, for example. Like maximum printer speeds, they’re quoted under ideal circumstances and make no allowance for descreening filters or sharpening options.

Interface options: FireWire and USB 2.0 are both many times faster than USB 1.1, and are worth having – though arguably not worth paying a great deal extra for. The increased speed of more expensive scanners comes from their components and design as much as from faster interfaces. The final data transfer isn’t the only bottleneck.

16/48-bit output: 16-bit files are useful for heavy tonal modifications with minimum image ‘damage’, but only a limited number of image-editors can handle 16-bit files. Of those that do, you’ll find they’re limited to certain editing functions only. With the right scanner and initial adjustments, 16-bit output is far from essential.