Mass Media & Technology

Teletext data as .vtc files

How to view them? (June 2016)

This site closed in March 2021 and is now a read-only archive
NG
noggin Founding member
dosxuk posted:
Might dig out the RISC PC from under the stairs, it can do proper mode 7 graphics, so could be used as a source of the character bitmaps.

No direct data transfer though as it only has a floppy drive and I don't own any discs or other drives...


The RISC PC (and Archimedes) had a horrible Mode 7 typeface compared to the nice character rounding that the SAA5050 did in the BBC Micro.
NG
noggin Founding member
davidhorman posted:
This page seems to cover most of the control codes.

I'm trying to find an accurate bitmap of the BBC B's teletext characters, but I'm having trouble. All the emulators either use a non-authentic font, or draw anti-aliased characters Sad


http://www-uxsup.csx.cam.ac.uk/~bjh21/BBCdata/SAA5050.pdf That's the "Mode 7 chip" used in a BBC, and includes a basic bitmap for each character. It also includes the control codes which may be of use.

The Mode 7 bitmap characters were based on a 5 x 9 matrix. HOWEVER - the bitmap wasn't displayed directly - the SAA5050 was cleverer than that. It did some nice on-the-fly character rounding to smooth out the jaggies (which was also interlace aware). From memory it used to add a quarter pixel where it detected a diagonal - though I may be wrong. (**EDIT - and the data sheet confirms it **)

If you look on the internet you can find both at least two Mode 7 style OTF/TTF fonts - one of which is pretty close (and goes blocky when at large type sizes)
DA
davidhorman
noggin posted:

The Mode 7 bitmap characters were based on a 5 x 9 matrix. HOWEVER - the bitmap wasn't displayed directly - the SAA5050 was cleverer than that. It did some nice on-the-fly character rounding to smooth out the jaggies (which was also interlace aware). From memory it used to add a quarter pixel where it detected a diagonal - though I may be wrong. (**EDIT - and the data sheet confirms it **)


That explains a lot!
DA
davidhorman
PNGs: http://horman.net/tvforum/pngs.zip

And a Datablast!


I took a few liberties with the font and the graphics blocks and took a few shortcuts, but it should be fairly accurate.
EL
elmarko
Outstanding work! Nice treasure trove there
DA
davidhorman
I got the impression that BillyH has a lot more files than just the one uploaded. BillyH?
NG
noggin Founding member
davidhorman posted:
PNGs: http://horman.net/tvforum/pngs.zip

And a Datablast!


I took a few liberties with the font and the graphics blocks and took a few shortcuts, but it should be fairly accurate.


Very impressed David. Top work!
LL
Larry the Loafer
davidhorman posted:
No need! I've managed to get bitmaps out of a BBC emulator. Thanks though!

In the meantime, here's the hidden teletext message I discovered in a 1980s episode of Doctor Who (the text is my translation of the graphics blocks above):

http://horman.net/images/twindilemma.jpg


Throw in an anti-Top Gear message and that summarises Dalek's short-lived lifespan on TV Forum.
Rory and London Lite gave kudos

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