8 bit micro font design

Continuing the discussion from Slightly Off-Topic: Why Were Color TVs Tiring?:

There’s also font design… here’s a page on 8 bit micro font design.

Sophie Wilson talks about careful design of the BBC Micro’s font to deliver 80 characters wide readable text on a TV:

However, you don’t need to do any of this if all you want is one, obviously computer, font giving you 80 characters per line. Archimedes and its predecessors - the BBC Microcomputer etc - can all manage to display a fully legible 80 characters across using 640x256 and a carefully designed character set [I know, I was that designer]. The basic technique used in the computer to provide the display is a 16MHz pixel rate - far above what one expects the TV to handle - and this does indeed cause colour aliasing if one places different coloured pixels too close together (like adjacent! - which gives an 8MHz square wave to the TV). I nullified this effect in the character set design by making all vertical lines two pixels wide - reducing the characteristic frequency to only 4MHz, easy enough for most TV sets. The font is highly legible, capable of coping with being broadcast by a TV station (the BBC, usually) and displayed on a cheap colour TV with a large triad pitch. Naturally, connecting the computer straight to a TV is better and using a monochrome TV better still.


So I learned a new vocabulary, “triad pitch”.

Here in the USA, most color TV sets simply lacked the dot pitch required for comfortably usable 80 column text. I’ve used a lot of 80 column output devices on my good old NTSC Commodore 1702 (with S-Video), and none of them resulted in very good 80 column text. (This includes C64 with 4x8 pixel fonts, 80 column 640x200 resolution cart, C128 RGBI -> Composite adapter output, and Amiga S-video 640x400 mode.)

However, the same fundamental principle of doubling pixel width applies for 40 column text. The NTSC C64 actually had an unusually narrow pixel aspect ratio - about 7:9. If you use a C64 emulator, you can see the dramatic effect this has when you switch between a PAL C64 vs NTSC C64 (PAL version has pretty much square pixels).

Anyway whatever … the point I’m getting to is that I wrote my own C64 font editor and I made a LOT of different C64 fonts. This got me intimately familiar with double-pixel width usage, and exactly how much you could get away with using single pixel width in places.

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The pixels of a PAL C64 were pretty visibly elongated vertically as well, at least on a color TV. (I guess, oval pitch masks may have contributed to this, effectively blocking some of the signal.) In effect, it was about the same, two horizontal pixels were required for a vertical line and you may have just gotten away with a sole pixel, if there was a continuous stretch of active pixels to the left. (As in “11111010”.)

Whilst not strictly in the realm of 8-bt micros, it’s worth looking at how DEC did the fonts for their vt100, etc. terminals. Not quite dot-matrix and not quite vector either, but a clever combination of bitmap and circuitry.

See: https://www.masswerk.at/nowgobang/2019/dec-crt-typography

for the detals.

And FWIW: I had a Beeb with a portable B&W TV and it displayed mode 0 (80 column) perfectly!



A rather questionable source that is… :slight_smile:

(The only thing I found out in the meantime is that the VT100/200 terminals used a normal, consumer-grade monochrome TV tube in non-interlaced mode, which should provide some idea about the vertical scan lines. Other, if I failed to make things clear, ask me anything.)


I’m surprised at how ugly and cold the VT100 character ROM dump looks to me, and how the DEC hardware magically renders it into something so attractive and warm.


Similarly with the Bedstead font: while it builds glyphs from the Mullard SAA5050 Teletext Character Generator data. it looks a bit more lumpy* as an outline font than it did on a CRT.

*: I still use it a lot, though, lumpy or not.

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I see Alan Davies has derived a re-pixelated version called Teletext50 which some might prefer:

(I remember when we got a teletext-capable VCR, that had a more conventional pixel font, which really didn’t look to me like Teletext-as-we-know-it. A bit of a shock. But it recorded the teletext lines with the TV program!)

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