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)

BMP (Windows Bitmaps)

This is ideal for exchanging bitmap data between Windows applications, but is not widely available outside Windows.

CGM (Computer Graphics Metafile)

The CGM is an ISO standard for capturing and transfernng picture information. "Computer Graphics Metafile" This is the first official standard for graphics files and should be a reliable solution for the storage and exchange of graphics files - but it is large and unwieldy, and different implementations are not always mutually compatible.

GIF (Graphics Interchange Format)

Bitmap format developed by Compusewe. Good for cross-platform file exchange. Widely used, file compression means smaller storage requirements.

HPGL (Hewlett Packard Graphics Language)

A line based vector format originally developed for driving HP plotters, and available on some non pen plotter devices such as laser printers. It may also be used for transferring line-based information between applications.

JPEG (Joint Photographic Experts Group)

JPEG is a standard format developed by the Joint Photographers Experts Groupw allowing transfer of files between a wide variety of platforms, using superior compression techniques.

PICT ("QuickDraw Picture Format")

This is a vector and bitmap page description language originating on the Mac. It is one of the commonest graphics standards on the Mac where it is very useful for exchanging both vector and bitmap data, but its colour support is limited, and it can only compress monochrome bitmap images. Versions of PICT are beginning to appear on PCs.

EPS (Encapsulated PostScript)

Postscript is a page descripdon language for both vector and bitmap graphics, which has become a de facto standard (see secdon 6.1 on page 28). It was originally intended for driving output devices such as pnnters, but is now widely used for storing and exchanging graphics images - for which it should be used in its "encapsulated" form EPS ("raw" PostScript can disrupt a document if it is inserted into it, rather than being sent straight to a printer). PostScript produces very portable plain text files, but these can become large and unwieldy for bitmap images. It has become a standard for desktop publishing.

PCD (PhotoCD)

This is storage format developed by Kodak for the storage of bitmap images.

PCX

Also known as PC Paintbrush, this is a Wtmap format for desktop publishing, general graphics, and video. It is particularly useful for exchanging data between PCs. It is one of the oldest, and therefore most widely established, bitmap formats for PCs, supporting colour and large images, but some implementations may not be mutually compatible.

Sun Raster Files

This are bitmap format. Widely supported by Sun utilides and applications

TIFF (Tag Image File Format)

This is a bitrnap format for exchanging data between desktop applications, and available on Macs, PCs and Unix workstations. It is widely available, flexible and well-supported, and is excellent for storage, but non-standard extensions to the basic TIFF format mean that exchanging graphics between different platforms can sometimes fail.

WMF (Windows Meta File)

WMF files are useful for storing and exchanging graphics images under the Windows operating system, producing small, well-structured, device-independent files. It supports both bitmap and vector format.

XWD (X-Windows Dump)

This is a bitmap format. It is a useful method of exchanging bitmap based graphics between most X-Windows applications.

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.

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