Posted By
TLC
on 2023-05-24
11:44:19
|  Re: Emulation video option you never knew you wanted until now!
Hey @MIK ,
I agree with you, I mean, I think... we're merely looking for clues here  .
Honestly, I can't see too much on the video. What I can notice, is a fair bit more flickering on the Commodore monitor's side. (That's maybe due to the monitor CRT's faster decay speed, but I don't want to make guesses). Can't really see the stuttering that you have mentioned earlier, that effect is probaby ruined by the resampling that happens here (camera).
I'll try to reproduce your test in the next couple of days. (My "work" room is in complete ruins these days, I'm in the process of installing a wall mounted shelf, please allow me some time to retrieve the machine plus a suitable TV.)
I might also give a try to Lotus 2, I also happen to have an A600 around (...I mean somewhere around here now).
I can test RF, composite, and RGB on the same display, but not S-Video. (I think only my 1084S has separate luma-chroma, which, of course, has no RF tuner).
Re. video standards: yes indeed. Analog video (standard analog video) was totally optimized for least required bandwith vs. resolution and picure rate. The interlace scan trick was introduced, because, it allowed for halving the frame rate (--> half the required bandwidth) without the implied CRT flickering, only making very little noticeable compromise. ("Standard" interlaced 25Hz video at a given resolution looks almost as good on CRT TV's as an 50Hz progressive equivalent would, but requires just half the bandwidth of that for aerial transmission). Composite colour processes (NTSC, PAL, SECAM, and flavours) were introduced, because they didn't want to change already existing aerial channel / transmitter / receiver setups - which practically allowed no extra bandwidth for colours. (Every and all analog composite colour systems are optimized to "fit" colour information in the more or less free remaining bandwidth between peaks of the luma signal spectrum).
The point I'm trying to make here (yet just on the theoretical level, see - let's reproduce your tests on analog stuff), that interlacing is a baseband signal property, that analog RF modulation doesn't change.
Interlaced video (on the level of the analog signal) is nothing more than a series of N-plus-a-half lines long picture fields. In Europe, N=312, so, the video consists of picture fields of 312.5 lines @ 50Hz. When displayed, the half extra line time allows the analog vertical deflector circuitry in the TV to move the beam down by half a vertical line space, before the next field starts to display. That's how finally one gets whole picture frames of true 625 lines @25Hz (that, albeit 25Hz, doesn't flicker on the CRT nearly as much as a 625 lines @25Hz progressive video normally would). Interlaced video strictly needs this N-plus-a-half-lines-long-fields property.
The TED generates uniform TV fields of integer 312 lines @50Hz*. That's how the usual (progressive, 312 lines @50Hz) picture is produced. When you transmit this signal over an RF channel (modulate it to some UHF TV channel frequency in the RF modulator, which is then demodulated in the tuner), the timing properties will not change. That is, the TV will still see a stream of uniform 312 lines long fields @50Hz.
If you want to experiment with true interlaced video (with respect to any of the available signal links i.e. anything from pure RGB to RF) as-is, the A600 should be a perfect platform for that. The HW is capable of producing a lot of video modes. If you boot up Workbench, go to screen properties, you can set and experiment with any of the available video modes there (including progressive and interlaced ones). As you'll see, interlaced modes (I'm talking about those displayable on a standard TV, not the VGA specific ones) have double the vertical resolution WRT equivalent progressive ones, with noticeable flickering added, due to the effectively halved frame rate. (...Interlacing, albeit is a good compromise for usual TV video content, isn't optimal for content with lots of pronounced edges, like WB is).
* to be precise, the TED's frame rate isn't exactly 50Hz, just close "enough".
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