Overview
ISO/IEC 9637-1:1994, "Information technology - Computer graphics - Interfacing techniques for dialogues with graphical devices (CGI) - Data stream binding - Part 1: Character encoding," defines a compact character encoding for the Computer Graphics Interface (CGI). Designed to minimize data size and to work over character-oriented transmission services, this standard maps every CGI function (as specified in ISO/IEC 9636) to a compact, transportable character-stream representation suitable for storage and low-bandwidth transfer.
Note: in this context CGI = Computer Graphics Interface (not web CGI).
Key Topics
- Purpose & objectives: regular syntax for simple parsing, maximum compactness, extensibility and transportability for character-based networks.
- Overall structure: general form of the data stream and rules for entering/leaving the CGI environment.
- Function encoding: method for encoding opcodes, extension mechanisms, and soliciting functions; an annex lists CGI opcodes and escape sequences.
- Parameter encoding: formats for integers, real numbers, Virtual Device Coordinates (VDC/points), point lists, color specifiers and color lists, string parameters, enumerated and index parameters, client-specified names, input-color parameters, and data record parameters.
- Bitstream formats: 7-bit/8-bit code tables, bitstream, run-length and displacement/incremental modes for efficient coordinate and color data.
- Compatibility and conformance: conforms to ISO 2022 code-extension rules and follows ISO/IEC 646 character-set conventions.
- Auxiliary material: examples, defaults, classification and designation rules; annexes with opcode and escape-sequence listings.
Applications
- Efficient transfer of graphical commands between systems over character-oriented links (e.g., legacy terminals, narrow-band networks, serial links).
- Storage and archival of compact graphics command streams where file size matters.
- Implementations of CGI-compliant device drivers, graphics interpreters and metafile converters that must interoperate with ISO/IEC 9636 functional definitions.
- Embedded graphics systems and device controllers with constrained memory or bandwidth that benefit from compact opcode and parameter encodings.
- Tooling for graphics interchange, translation between character, binary (ISO/IEC 9637-2), and clear-text (ISO/IEC 9637-3) encodings.
Related Standards
This standard is essential reading for graphics protocol designers, implementers of device interfaces, and anyone needing a compact, standards-based character encoding for computer-graphics command streams.
Open preview (PDF)Information technology — Computer graphics — Interfacing techniques for dialogues with graphical devices (CGI) — Data stream binding — Part 1: Character encoding
