I have read in news groups of people searching for a teletext font so that they might reproduce their own teletext pages. These are obviously available within the software written for teletext collection by the TV card manufacturers but, unless thing have changed since I bought my Hauppage TV card, these fonts are not available to the general user. I had a great need for this myself a while ago. I had written a program, run by my teletext software, which collects teletext pages daily and assembles them into files. I wanted to be able to view these files page by page in ttx format and to skip from file to file. The supplied software couldn't handle this. Although it was straightforward to write a Visual Basic program to manage this, it was the font that gave me trouble. I eventually overcame the problem and this a description, in purely general terms, of how it may be done.
I had been brought up with the BBC microcomputer and that had the hardware to use a ttx font as its basic display. No trouble at all to produce ttx pages. Just specify the font, print the characters and there you are. I moved to a PC and found there a very different method of handling text and graphics. My ttx file viewing came to a dead stop whilst I too searched for a ttx font. Then one day, browsing around the Windows 95 CD, I came across a folder labelled 'OTHER' and inside that was a folder called 'MINITEL' and inside that were a couple of Arial type fonts. A little text file explained that these fonts were necessary if you wished emulate Minitel. This I knew was what the French used for their computer based telephone directory and that it was very similar to teletext being a mixture of text and block graphics. Worth investigating I thought.
The two fonts were one for the text and one for the graphics. Also they were intended only for black and white reproduction. The proper teletext font uses many control characters to switch background and foreground colours and to do all those clever things like double height characters, flashing characters, hiding and revealing and so on. The control character sets the mode for all following text and the mode is maintained until either a new control character, or a new line, is encountered. There is nothing of that sort in the Minitel character set; changes must be effected by the handling program. For my purposes I just wanted to be able to read the pages. This meant just text and graphics representations. The subtle bits I could manage without.
A comparison showed that all the teletext characters were available in the two fonts although their ASCII values were different. The first move was to make up a translation table. This I made a two dimensional array. The first dimension used two values, one for each of the two Minitel fonts. The second dimension was the teletext ASCII value under consideration. The array contents are the equivalent Minitel ASCII character values.
A ttx page file is a little short of 1k in size. One has to scan through the file, character by character, determining whether it is the text or graphic character set which is active. Depending on which it is, the computer's active font has to be changed to either the Minitel text or Minitel graphics. The control characters showing when the switch occurs may be seen in the Teletext Character Set. Once the correct font is in position then for each character, the equivalent Minitel ASCII value is read from the translation table. The character is then printed to the display. "Isn't that an awful lot of trouble", I hear you murmur. Well yes it is, but it is less code than you might think and what is more it works.
Click here to see a ttx page produced by this method or here to see the working part of its MS Visual Basic code subroutine (without explanation).
Having achieved this little bit of success I was tempted to go on and try to introduce colour. I can report that it is perfectly possible to reproduce the colours but it does mean much repeated scanning of the ttx file, changing foreground and background colours as well as the fonts. This results in a great deal of computation just to reproduce one page. For my general file reading purposes it resulted in a rather slow page change which was tedious. Because of this I stuck with black and white for quite a while. Recently I have returned to colour because improved processor speeds have reduced the time for page computation considerably. It is now perfectly satisfactory. I still haven't tried to introduce flashing or hidden text or a double height character set because I don't really need them, but colour does help the presentation enormously. Have a look at a coloured page produced by these Minitel fonts. Note that what should be a double height line comes out as repeated single height lines.
A.J. Donald M.Sc.,D.I.C. --- Dec. 2000 --- E-mail
The content of this article has been rather superseded by the teletext fonts becoming generally included with the latest operating systems. I am leaving it on the site however, just in case someone finds it useful.
In WindowsXP for example there is a set of fonts, found under Start/Settings/Control Panel/Fonts, with names starting WST_. These are standard teletext fonts for various languages. They still require program support in order to implement the features of teletext, e.g. double height characters, flashing characters, colour changes and so on. They do however, contain the full set of characters and graphics for page reproduction which does help somewhat.
I mentioned in the article how the old BBC microcomputer was the ideal instrument for showing teletext. Its hardware included the SAA5050 chip which gave, what was called Mode 7 operation. This was a graphics mode in which the character set used was the teletext character set. The chip gave proper hardware support for interpretation of all teletext control characters. It may be of use to anyone wishing to reproduce teletext to be aware of Richard Russell's program; BBC Basic for Windows. This language is an excellent version of the old BBC microcomputer's programming language and includes a perfect Mode 7 reproduction. Armed with this it is possible to use the teletext character set to write perfect teletext pages with the full set of features without having to write anything other than minimal software support. Almost all the control characters included in the teletext set operate under this program. It makes life very simple, well worth trying. Richard's site is www.rtrussell.co.uk, and a free download demo version is available.
Click here to see a teletext page, collected directly from the teletext card, here reproduced by BBC Basic. You have my assurance that on the original, the double height banner at the bottom of the page is flashing happily. The only problem I encountered was with the double height characters and this was the fault of the software which came with the teletext card, not of the BBC Basic. Since double height lines are repeated lines the software did not bother to collect the second line but just filled it with blanks. I had to put those second lines back in full to get the bottom half of the double height characters. The BBC Basic language is itself a neat way to write your ttx manipulating program - which I assume, is why you were interested in reproducing teletext pages in the first place. (It may also be compiled, from within the program, to give a free standing exe file).
