File Formats: (none)
Date: Wed, 1 Nov 1995 00:13:14 +0000 From: Alan Francis <[email protected]> Subject: Final version of CGM Media Type registration To CGM MIME registration people Here is the final version of the Media type registration proposal for CGM. Note that version and profile are now required parameters. Some minor changes have been made as a result of comments on the almost final version. Alan Francis 31.10.95 ============================================================= To: [email protected] Subject: Registration of new Media Type content-type/subtype Media Type name: image Media subtype name: cgm Required parameters: version=n ProfileId=profilename Optional parameters: None Encoding considerations: Recommend Base64 MIME encoding where transport not 8 bit clean Security considerations: None Published specification: ISO 8632:1992, IS 8632:1992 Amendment 1 (1994) and IS 8632:1992 Amendment 2 (1995) Person & email address to contact for further information: Alan Francis Email: [email protected] Background CGM, Computer Graphics Metafile, is the International Standard for the storage and transfer of 2D picture description information. It is specified in IS 8632:1992 Parts 1-4. It can handle vector graphics and images. It stores pictures in a way which is independent of any particular software, computer or graphics device. CGM offers the Internet community the first option for a vector-based (i.e., line-art) image type. Currently, the valid image types are JPEG, and GIF, both raster or bitmap type image files. Vector images allow for greater detail and clarity at multiple zoom levels. Also, they are usually much more compact than the equivalent bitmap. CGM is used by a number of other standards including the Office Document Architecture (ODA) standard, ATA within the commercial aviation industry, J2008 within the automotive industry and the CALS (Computer-aided Acquisition and Logistics Support) specification of the US Dept of Defence. The CGM can be used to exchange pictures between different types of applications. CAE/CAD, graphic arts, business graphics and desk top publishing packages can all use the CGM to exchange graphical information. More than 300 applications can generate and/or interpret CGM files. There are a number of public domain CGM generators and interpreters available. Parameters and Encoding The CGMs should use the binary encoding, as specified in IS 8632:1992 Part 3. Valid version numbers are those specified in ISO 8632:1992 and any amendments. (Currently Versions 1, 2 and 3 are specified in ISO 8632:1992 and version 4 is specified in IS 8632:1992 Amendment 2 (1995) which adds Application Structures which can be used to support hyper-links.) The versions are upward compatible in the sense that a valid Version 1 metafile is a valid Version 2 metafile, Version 2 is a subset of Version 3, and Version 3 is a subset of Version 4. The version number in this parameter must be the same as the version number within the CGM file itself. It is recommended that only Version 1 CGMs be used initially because most current software handles Version 1 CGMs. It is expected that in the next year or two software will be upgraded to handle version 3 and 4 CGMs. Version 2 is not expected to be widely used as a target implementation level. Profiles are used to specify limits, for example the maximum number of points in a polygon or the set of fonts which can be used. Reliable CGM interchange can only be assured with CGMs conforming to one of the principal profiles. The profile declared in this parameter must be the same as the profile declared within the CGM itself. Valid profiles are those registered with ISO as International Standardized Profiles (ISP). The Model Profile, as specified in IS 8632:1992 Amendment 1, and three others are being registered as ISPs (DISP 12071-1 Basic Scientific and Technical, DISP 12071-2 Advanced Scientific and Technical, DISP 12071-3 Basic Presentation and Visualisation (Model Profile), DISP 12071-4 Advanced Presentation and Visualisation). Acknowledgements The following people have contributed towards this registration proposal: Alan Francis (Page Description, UK) Brian DiAntonio (Electronic Book Technologies/Carberry, US) Dr Anne Mumford (Advisory Group on Computer Graphics, UK) Lofton Henderson (Henderson Software Inc, US) Steve Carson (GSC Associates, US) Contact: Alan Francis Email: [email protected] Phone: +44 1908 316921 Address: Page Description, 6 Spencer St, New Bradwell, Milton Keynes, MK13 0DW, UK.