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The Computer Graphics Metafile (CGM) is the International Standard for storage and exchange of 2D graphical data. Although initially a vector format, it has been extended in 2 upwardly compatible extensions to include raster capabilities and provides a very useful format for combined raster and vector images.
A metafile is a collection of elements. These elements may be the geometric components of the picture, such as polyline or polygon. They may be details of the appearance of these components, such as line colour. They may be information to the interpreter about how to interpret a particular metafile or a particular picture. The CGM standard specifies which elements are allowed to occur in which positions in a metafile.
CGM also has profile rules and a Model Profile to attempt to solve the problem of flavours of standards. 4 Internationally Standardised Profiles (ISPs) have been developed for CGM. CGM has been accepted as a MIME data type.
CGM became an international standard in 1987 - IS 8632: 1987 and was also adopted as a national standard in many countries, such as the UK (by BSI) and the USA (by ANSI).
Following a number of published ammendments to give it increased functionality, such as font naming, external symbol libraries, compound clipping paths, curve primitives and colour calibration support, a revised standard was published in 1992 - IS 8632: 1992.
CGM was one of the standards chosen by the US Department of Defence for their major CALS open documentation initiative.
CGM is also being discussed by W3C as a standard for graphics on the WWW. Where vector diagrams are being sent across the netwerk, the use of CGM would result in lower file size, faster transfer and editable files when compared with raster formats such as GIF.
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