AGOCG logo
Graphics Multimedia VR Visualisation Contents
Training Reports Workshops Briefings Index

Next Back
Next: Selecting An Output Device.

Using Graphics Files and Images

When preparing a document there are a number of sources from which images may be obtained. You may produce them yourself using a Drawing or Charting package or you may obtain them 'already drawn' as Clipart. In either case the image will probably be stored at some point in a file.

If you produce them yourself you need only select a suitable exchange format which is common to the export/import facilities of the packages concerned. Alternatively it may be possible to bypass the file stage completely by the use of the 'Cut and Paste' facilities.

If you use Clipart, it usually supplied in the native image format used by that particular package. Often a package will also support other than it's own native format, so a wide variety of clipart may be available to you.

Popular file formats

There are a large number of different formats for storing graphics information in files. This list below only enumerates some of the more popular ones that are supported by the leading software packages. For more information you are recommended to consult either Graphics File Formats by Davis C. Kay and John R. Levine (Windorest/McGraw-Hill, 1992) or Encyclopedia of Graphics File Formats by (O'Reilly & Associates, 1994)

Graphics Metafiles

A Graphics Metafile is a file which contains a description of a picture (or set of pictures) expressed in some well-defined, formal manner. Graphics metafiles help to provide device independence by allowing pictures to be printed on a variety of devices; metafiles also facilitate picture portability by enabling the image(s) to be transferred to wherever they are required.

The ISO standard metafile is the 'Computer Graphics Metafile' (CGM). There are also proprietary standards such as the Microsoft Windows MetaFile (WMF) and the Macintosh PICT file - these are particularly useful for transferring images between applications in the same operating system, although it is often possible to use, say a PICT, file in a Windows environment. CGM, where supported, allow transfers of information between all systems.

Apart from the above three graphics metafiles, there are numerous other graphics file formats in use, particularly on microcomputer software. These other graphics file formats tend to be used both for the compression of picture data and for the interchange of picture information between software packages, What usually happens is that the package exports the picture in a particular format which is then imported in that format by another package. The list of file formats available is extensive: the commonest are summarised in chapter 5. Additionally the matrix in Appendix 2 shows which files are interchangeable between chosen packages via the import/export mechanism.

Clip ART

The term 'clip-art' applies generally to any collection of computer-based images or symbols which can be readily incorporated within a user's picture. Most popular presentation graphics packages now include clip-art libraries covering a wide range of subjects. The idea is that the user's picture can be enhanced by the judicious use of particular images. For example, a chart which shows motor car production in the UK may be improved by including an image of a motor car. A clip-art library will typically contain a set of images of everyday objects such as space rockets, telephones, washing machines, houses, furniture, airplanes, books, thermometers, ... indeed just about most things imaginable. Exactly how clip-art images are included within a user picture varies from package to package, but it is usually a straightforward process, and - again depending on the package - it is usually possible to expand, shrink or rotate the clip-art symbol so that it can be integrated within the picture to suit the user's requirements.

Note! Users should take care that they do not inadvertently infringe copyright restrictions by including images within their pictures, such as for example company trademarks or logos, which may require copyright permission.

Next Back
Next: Selecting An Output Device.

Graphics     Multimedia      Virtual Environments      Visualisation      Contents