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Pictures for an exhibition

Digital imagery may be more affordable than ever, but its images are only as good as the graphics tablet, scanner or camera you use. Hugh John looks at the first stage of processing in the digital darkroom. Illustrations by Michael Bennett

Silk purse, sow's ear; garbage in, garbage out. However, you express it, the simple truth is that even the most sophisticated digital imaging software can't add quality that isn't there to start with. That's why it's worth giving some serious thought to input devices - what to choose and how to use them.

The three main input devices - graphics tablets, scanners and digital cameras - lend themselves to different functions.

Graphic tablets are used in place of, or sometimes alongside, a mouse to input data. The pressure created by the pen on the tablet is translated into signals which are transferred into the computer via a USB cable. In the artroom, tablets are often used as an alternative to a mouse.

So how do you choose a tablet? The first issue is size. For home or school use the most popular sizes are 4in x 5in and 6in x 8in - anything bigger and the price doesn't escalate so much as rocket. And the bigger the tablet, the more space it takes on the desk; these measurements refer to the working area, not the whole tablet.

A pen is a pen is a pen, right? Wrong - the stylus you use is an important component. Does the pen have batteries enclosed in the body? If so, it'll be heavier and you'll have all the hassle of one more battery-operated device. Is it tethered to the tablet? If so, can it be attached to either side for left or right-handers? Does the pen have built-in buttons that can be programmed to emulate mouse functions such as double click?

Other features to look for include a transparent overlay, which enables the user to slide a photo on to the tablet and trace over it with the pen; good driver software that will customise tablet and pen use; and decent quality bundled software. At the very least expect a reduced digital imaging package to be included.

Manufacturers Wacom have always had an enviable reputation in the tablet market and the Graphire 2 model looks an excellent deal. For just under pound;100, you get a 5in x 3.65in tablet and a cordless mouse and pen. Also included is Adobe Photoshop Elements 2 and Painter Classic.

Scanners are digital workhorses, used for converting images, text, maps, graphs or paintings into information that can then be manipulated within the appropriate software. Flatbed scanners are by far the most common and these will adequately meet the needs of most schools. If you're working with transparencies, film or slides look for a scanner with a transparency hood or adaptor.

As with graphics tablets, look at the quality of the bundled software on offer. It will usually be a "lite" graphics program but you may get an OCR (Optical Character Recognition) package thrown in. This is extremely useful if you intend to scan printed pages and convert them into editable text documents.

Image resolution is the amount of information or quality contained in a scanned image and represented in dots per inch (dpi). The phrase to look for is optical resolution and the magic numbers are between 600dpi (expect to pay between pound;50-pound;100 for an Arctec, Canon or Epson model) and 1,600dpi (pound;120-plus for a Canon, Linoscan, ScanJet or Epson).

Now for the other technical stuff. Digital camera resolution is measured in megapixels (Mp). For example, a 2Mp model has a CCD (charge coupled device; think of it as the digital equivalent of film) that contains 2 million pixels. The higher the megapixel number, the better the quality of the captured image. So for all but a handful of high-end professional cameras and a few older low-resolution models the parameters for digicams are 1Mp and 5Mp. It's generally agreed a 1Mp camera is acceptable for web publishing - anything larger and the image takes too long to download from the internet. As a rough guide, 1.5-2Mp is deemed good enough for printing up to 6in x 4in and between 3-4Mp for printing up to 10in x 8in or A4 size.

However, pixel size is only one factor in the equation. Build quality, lens quality and image storage capacity should also be considered. Most cameras are fairly robust and can withstand some classroom bruising. Lens quality inevitably varies but you'll probably get better optics from conventional camera makers such as Nikon or Olympus.

Talking of lenses, if you're looking for a camera with a zoom function you'll need to know some digital-to-35mm conversion figures. A 3x zoom approximates to 35-105mm in 35mm terms, 6x is 38-230mm and 12x is 38x450mm. Incidentally, the only zoom quality worth considering is optical. Digital zoom uses electronic jiggery pokery to artificially enhance the image with a resulting loss of quality - 6x zoom is fast becoming the standard in the digital world, as is macro mode, an extremely useful function which enables you to take close-ups in fine detail.

Of other features to look for the most obvious is video. The latest digital cameras have impressive video capabilities. The new Fuji FinePix M603 can capture digital video at 640 x 480 pixels at 30 frames per second. That's good enough to view on a TV screen, claims Fuji. And sound? Voice annotations and ambient sound appended to an image can be surprisingly effective and evocative.

Digital cameras store images on removable cards which can then be transferred to the host computer or direct to a special card-reading printer. The two most important formats are CompactFlash and SmartMedia. Prices for these are similar but CompactFlash has a larger storage capacity. The Sony Mavica FD range, very popular in education, uses floppies, which are inexpensive and less likely to get lost. Watch out too for the 430RS, Pentax's first dip into digital, which packs 4 megapixels into a robust, palm-size camera.

Digicams aren't cheap, though you get a lot more for your money than you did five years ago. But as with any computer related purchase, there's never going to be a right time to buy - every package should have a "Serious risk of depreciation" heath warning stamped on the side.


Epson scanners and printers. Stand D120.

TAG Clicksmart 510 camera. Stand F50.

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