Bedstead

Bedstead is an outline font based on the characters produced by the Mullard SAA5050 series of Teletext Character Generators. The SAA5050 is familiar to those of a certain age as the chip that produced the MODE 7 display on the BBC Microcomputer. It generates characters from a 5 × 9 pixel matrix, smoothing diagonal lines to produce an interlaced 10 × 18 matrix for each character. Bedstead extends that algorithm to continuity, converting a 5 × 9 pixel grid into an outline with smooth diagonals.

Bedstead includes all the character designs from the SAA5050 and its various sister chips, including Cyrillic and Hebrew alphabets. It also has a large number of custom-designed glyphs, all of them of course based on the same 5 × 9 pixel grid.

[ A sample of Bedstead's characters ]

Bedstead is available in six widths. The standard version of Bedstead is based on a square pixel grid. This is good for displays with square pixels, but not entirely faithful to the SAA5050. There is a second version, Bedstead Extended, that more accurately reflects the character shapes generated by an SAA5050 driving a 576i display.

To simulate teletext double-height mode, Bedstead and Bedstead Extended each has a half-width version, Bedstead Ultra Condensed and Bedstead Extra Condensed respectively. Bedstead Condensed and Bedstead Semi Condensed provide intermediate widths.

[ Various widths of Bedstead ]

The outline version of Bedstead is generated by an ISO C program which emits a Spline Font Database file for use with FontForge, which can convert it into most reasonable font formats.

Mosaic Graphics

Bedstead includes all of the teletext mosaic graphics characters available from the SAA5050. Since these are not encoded in Unicode, Bedstead makes them available in the Private Use area between U+EE00 and U+EE7F, in the same arrangement as is used by ZVBI.

Copyright

The program that generates Bedstead and all of the newly-designed glyphs have been released into the public domain.

CC0

I believe that the original SAA5050 bitmap font is essentially in the public domain in the United Kingdom as a result of Section 55 of the Copyright, Designs and Patents Act 1988 as applied by subparagraph 14(5) of Schedule 1. I’m not a lawyer, though, so this may well be wrong.

Downloads

The code to generate Bedstead is held in Bazaar. You can get your own copy by running

bzr branch http://bjh21.me.uk/bedstead/