Editing NAPLPS (section)

== History ==
<!-- Deleted image removed: [[Image:Viewtron testing area.jpg|thumb|left|NAPLPS graphics on [[Viewtron]]]] -->

The Canadian [[Communications Research Centre]] (CRC), based in [[Ottawa]], had been working on various graphics systems since the late 1960s, much of it led by Herb Bown.<ref name="crc">{{Cite web |last=Boyko |first=Cynthia |date=August 8, 1996 |title=Telidon |url=http://www.friendsofcrc.ca/Projects/Telidon/Telidon.html |access-date=2025-03-21 |website=Friends of the CRC}}</ref> Through the 1970s they turned their attention to building out a system of "picture description instructions", which encoded graphics commands as a text stream.

Graphics were encoded as a series of instructions (graphics primitives) each represented by a single [[ASCII]] character. Graphic coordinates were encoded in multiple 6-bit strings of XY coordinate data, flagged to place them in the printable ASCII range so that they could be transmitted with conventional text transmission techniques. [[Shift Out and Shift In characters|ASCII SI/SO]] characters were used to differentiate the text from graphic portions of a transmitted "page". These instructions were decoded by separate programs to produce graphics output, on a [[plotter]] for instance. Other work produced a fully interactive version. In 1975, the CRC gave a contract to [[Norpak]] to develop an interactive graphics terminal that could decode the instructions and display them on a color display.

During this period, a number of companies were developing the first [[teletext]] systems, notably the [[BBC]]'s [[Ceefax]] system. Ceefax encoded character data into the lines in the [[vertical blanking interval]]  of normal [[television]] signals where they could not be seen on-screen, and then used a buffer and decoder in the user's television to convert these into "pages" of text on the display. The [[Independent Broadcasting Authority]] quickly introduced their own [[ORACLE (teletext)|ORACLE]] system, and the two organizations subsequently agreed to use a single standard, the "Broadcast Teletext Specification". This later became [[World System Teletext]].

At about the same time, other organizations were developing [[videotex]] systems, similar to teletext except they used modems to transmit their data instead of television signals. This was potentially slower and used up a telephone line, but had the major advantage of allowing the user to transmit data back to the sender.  The UK's [[General Post Office]] developed a system using the Ceefax/ORACLE standard, launching it as [[Prestel]], while France prepared the first steps for its ultimately very successful [[Minitel]] system, using a rival display standard called [[Antiope (teletext)|Antiope]].

By 1977, the Norpak system was running, and from this work the CRC decided to create their own teletext/videotext system. Unlike the systems being rolled out in Europe, the CRC decided from the start that the system should be able to run on any combination of communications links. For instance, it could use the vertical blanking interval to send data to the user, and a modem to return selections to the servers. It could be used in a one-way or two-way system.<ref name=crc/>

In teletext mode, character codes were sent to users' televisions by encoding them as dot patterns in the vertical blanking interval of the video signal. Various technical "tweaks" and details of the [[NTSC]] signals used by North American televisions allowed the downstream videotex channel to increase to 600 bit/s, about twice that used in the European systems. In videotext mode, [[Bell 202]] modems were typical, offering a 1,200 bit/s download rate. A set top box attached to the TV decoded these signals back into text and graphics pages, which the user could select among. 

The system was publicly launched as '''Telidon''' on August 15, 1978. Compared to the European standards, the CRC system was faster, bi-directional, and offered real graphics as opposed to simple [[character graphic]]s. The downside of the system was that it required much more advanced decoders, typically featuring [[Zilog Z80]] or [[Motorola 6809]] processors with RGB and/or RF output. The [[Innovation, Science and Economic Development Canada]] (then Department of Communications) launched a four-year plan to fund public roll-outs of the technology in an effort to spur the development of a commercial Telidon system.<ref name=crc/>

[[AT&T Corporation]] was so impressed by Telidon that they decided to join the project.{{citation needed|date=August 2021}} They added a number of useful extensions, notably the ability to define original graphics commands (''macro'') and character sets (''DRCS''). They also tabled algorithms for proportionally spaced text, which greatly improved the quality of the displayed pages. A joint [[Canadian Standards Association|CSA]]/[[American National Standards Institute|ANSI]] working group (X3L2.1) revised the specifications, which were submitted for standardization. In 1983, they became CSA T500 and ANSI X3.110, or NAPLPS.<ref>{{Cite book |last=Dixon |first=Douglas F. |title=Proceedings of the 10th annual conference on Computer graphics and interactive techniques - SIGGRAPH '83 |chapter=A Core Graphics Environment for Teletext Simulations |year=1983 |pages=175–181 |doi=10.1145/800059.801148 |isbn=0897911091 |s2cid=2774740 |chapter-url=https://dl.acm.org/doi/pdf/10.1145/800059.801148}}</ref> The data encoding system was also standardized as the [[NABTS]] (North American Broadcast Teletext Specification) protocol.

Business models for Telidon services were poorly developed. Unlike the UK, where teletext was supported by one of only two large companies whose whole revenue model was based on a read-only medium (television), in [[North America]] Telidon was being offered by companies who worked on a subscriber basis.