24x80 Standard? (was: Re: HX20)

From: Hans Franke <Hans.Franke_at_mch20.sbs.de>
Date: Mon Dec 14 16:00:58 1998

>>No. I've seen 64-column text on typical mid-70s NTSC televisions, and it was
>>abysmal. The televisions had to be modified to remove their color trap
>>in order to get reasonably sharp characters.

> I remember when the Amiga was first launched, its composite output
> was purported to be able to drive 80 columns on an ordinary TV.
> Was it a matter of televisions improving in the same time period,
> or that they might've been talking about monochrome as opposed to
> color?

Jep, thats the main thing I think. And 80 columes are also
hard for B&W TV - 80 columes with 8 bits per character gives
320 lines with less than 200 ns per line. Thats more than
5 MHz - and at 5 MHz the signal would be some sinus like
wave (a 'sawtooth' with heavy rounding), and the resulting
display would be more like gray - ok, of course letters
are not strict lines of black and white, so the resulting
might display characters (together with the highly sophisticated
patern matching machine called brain). For a B&W TV signal
some 200 Lines is a _VERY_ good result, so 80 chars with
6 pixles each (240 lines) might be well readable on a good TV.

Remember, these calculations are only minimal influenced with
the quality of a TV set, but rather fixed by TV modulation
schemes. you just can't fit a 10 MHz signal within a 5 MHz
chanal. Ok, to be honest, the numbers are based on european
TV, since I just can remember them without pain - 50 (half)
pictures per second, 625 lines per (full) picture, 15625
kHz line frequency, 64 us per scan line ... (Just ask me
after beer number 10 :), but basicly the US system comes
to similar numbers when we are down to lines since the
bandwidthe (chanal) is the same.

> Certainly NTSC color has a hard time changing quickly, its
> resolution is only a hundred or so lines across, isn't it, while
> gray-scale resolution is as much four or five times that?

Jep, exactly - you have always to 'runn the colour cycle'
from one colour to the next, so you cant go from bright
yellow to blue without crossing some other colours - and
the speed to go around the cycle is the maximum frequency
of the colour signal.


Der Kopf ist auch nur ein Auswuchs wie der kleine Zeh.
Received on Mon Dec 14 1998 - 16:00:58 GMT

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