Not only can an illustration or diagram put across information in a more immediate way than a textual explanation, it also serves to add visual interest to a page and break the visual monotony of continuous text, however well laid out. Yet many DTP users find it difficult to use images successfully, both in a design sense and in managing the series of steps between the original image and its printed equivalent.

This course aims to assist users to include scanned images in DTP documents, by explaining the various parameters which affect image quality, giving guidance on setting up the scanner and monitor for accurate results, and enhancing the raw material with image processing software.

Examples

Some of the examples used were scanned with a Logitech 256 hand scanner, some with a Mustek flatbed scanner, and some acquired using Photo-CD; typical of the kind of product many DTP users will employ. However, because of the variety of different scanners on the market, and the diversity of the scanning and image processing software which is supplied with them (not to mention third-party products), the information given is necessarily general. The underlying principles involved will still apply, even if the precise methods may vary according to the particular scanner that is used.

What is a Scanner?

In essence, a scanner's function is to convert an image on paper or transparency film into electronic form, so that it can be manipulated by software and then output via a desktop publishing or similar program. A light-sensitive head is passed across the item, "scanning" it line by line and measuring the light intensity (and sometimes the colour) reflected from or transmitted through the image. These readings are then stored on the computer in one of a number of different formats (explained below).

Types of Scanner

There are two main kinds of scanner: colour and monochrome. A colour scanner can handle monochrome images as well. Monochrome scanners may be simple black-and-white devices (that is, they convert any image scanned by them into areas of solid black or white), or they may be able to register 32, 64 or 256 levels of light intensity. The latter type are known generally as "greyscale" scanners. If you only wish to use simple line drawings in your documents then a black-and-white scanner will suffice; however greyscale models are only slightly more expensive and permit the scanning of photographs or other images containing a variety of tones. Colour scanners are becoming more commonly used now that prices have come down and the appropriate software and printers to produce reasonable quality results from them can be obtained at an affordable cost. Colour work does involve an extra degree of complexity which some users will not wish to undertake, especially if they are new to desktop publishing in general.

Flat-bed, Hand-held and Drum Scanners

Both colour and greyscale scanners are available in hand-held and flat-bed form. The flat-bed variety is analogous to a photocopier; the image to be scanned is placed on a glass screen and the scanning head moves across it within the unit itself. Hand-held scanners require the user to pass the whole scan unit across the image manually. Flat-bed models are more convenient to use and will handle images up to A4 (or even A3) in area, while hand scanners are usually restricted to scanning an image width of about 10cm in a single pass. Larger images can be input with a hand scanner by a process known as "stitching", in which the image is scanned in successive parallel strips which are then mated together in the scanner software, but successful results depend on both the steady hand of the operator and the capabilities of the software to ensure that the image strips line up with each other and do not vary noticeably in density. For this reason hand scanners are really only adequate for occasional use.

Some flat-bed scanners can have an adapter fitted to enable them to handle transparencies (slides) as well as reflective material. There are also dedicated scanners for transparencies only (for example,. from Nikon and Polaroid), which give very good results.

A further type commonly found in professional repro houses is the drum scanner, but the cost of these is usually prohibitive for business users, although the quality they offer is superb. If the highest quality is required, an image can be scanned for you on a drum scanner by a bureau.

Probably the most cost-effective way of inputting high-quality images, especially colour photos, is Kodak's Photo-CD.

Hand scanners (above left) are cheap but awkward to use for large drawings or scanning more than the occasional image. A flatbed scanner (above right) is more convenient and provides better quality.