Usability of Timex 512x192 screen mode on TV

[catmeows]

Hi, I wonder, can anyone share his experience with Timex 512*192 graphic mode on TV ?
Was it legible at all ?

[4thRock]

Hi,

Back in the day I used a TC2048 with a TV.
At 512x192 the pixels would blend horizontally. Any alternate pixel patterns would simply render as gray.
This is expected, because PAL encoding limited resolution to about 400 horizontal "pixels".

Using the composite output with an Amiga monitor improved things a bit.
If I remember correctly, on this monitor it was possible to disable chroma processing and recover part of the horizontal resolution. But it wasn't perfect, you still have some pixel blurring.

So no, text (using the default 8x8 font) wasn't legible.

[1024MAK]

The limitations in the video are three fold.

First the colour composite video signal is so called because it has the monochrome picture information, the colour information and the horizontal and vertical synchronisation signals all shoehorned into it. So there has to be compromises, especially as these computers were built to be inexpensive and therefore not broadcast quality. Hence the range of the signals (the frequency bandwidth) is limited. Both at the computer end and by the filtering at the TV end.

Secondly, using RF/UHF or RF/VHF further limits the quality of the signal.

Third, on a colour CRT TV, the pitch of the three colour phosphors and of the metal grid (shadow mask) that is between the glass and the electron guns limits the horizontal and vertical resolution.

For the highest resolution and the best picture, you have to use baseband video signals, for example RGB signals. Unfortunately I don’t think these are available on a connector on the Timex computers.

Mark

[4thRock]

From what I remember you'd get unfiltered luminance if you used black and white colours. So that composite out could work as luma.
But it wasn't as clear as Amiga's 640x240 with a RGB connection.

[Alcoholics Anonymous]

On my ts2068 connected to a b&w ntsc tv, I found it to be very legible. On colour, less so, and it varied with colour scheme chosen. One of the more popular word processors operated in the hi-res mode in b&w colour scheme and that seemed to work well.

Timex put a separate composite output into the machine in addition to rf for this mode specifically. On composite monitors it was clear.

[1024MAK]

Yes true monochrome composite video should be a higher quality than colour composite video. But it’s not as simple as only using black and white ‘colours’. The colour encoder circuitry must not be enabled at all or the video signal must be taken ahead of it in the signal path. This is because at the beginning of a TV line (and I’m talking PAL colour systems here, NTSC is a bit different ), a colour burst signal is added to the composite video signal. This tells a TV that the signal should be decoded as a colour video signal. If there is no colour burst signal, the TV should disable it’s colour processing circuitry and this should give a better, sharper picture, without any false colour.

Obviously a monochrome / black and white TV will ignore any colour encoding signals regardless. Monochrome CRT displays also don’t have a shadow mask and the entire screen is coated in the same phosphor coating without there being a pitch as such.

A composite monochrome video signal when used with a suitable monochrome monitor can actually give a very good high resolution image. The Atari ST demonstrates that very nicely (although in this case the refresh frequency is higher than that of a TV).

Mark