HD NBTV?

Forum for discussion of narrow-bandwidth mechanical television

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Re: Ideas chasps...

Postby Andrew Davie » Sun Mar 16, 2008 9:51 pm

Steve Anderson wrote:So I'm looking for a method of frame identification


Well, mmh. Doesn't the colour standard cleverly embed colour encoding digitally into the analogue B&W signal in such a way that it makes little/no difference to the visuals, but it can be separated out quite easily?

Seems to me that this is the ideal way to piggyback extra framing information. Embed it in the colour 'signal' somewhere, either time-based encoding of particular "colour values" and/or change the interpretation of the bits from the colour stream so that particular combinations can mean "new frame".

Just my 2c.

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Re: Ideas chasps...

Postby Steve Anderson » Sun Mar 16, 2008 10:36 pm

Andrew Davie wrote:Well, mmh. Doesn't the colour standard cleverly embed colour encoding digitally into the analogue B&W signal in such a way that it makes little/no difference to the visuals, but it can be separated out quite easily? A


It is very clever, and one concept that I have also considered, it's not digital, a low-level burst mixed in with the normal signal to indicate the start/end of a frame. It actually wouldn't be that difficult and to offset the visual impairment would require a simple choice of frequency which is offset from 400Hz (600Hz in my case) in the same way that the colour sub-carrier is offset by 25Hz in PAL. Editors take note.

However, to do so with the current pile of junk I have as a PC I doubt it's feasable. I'll certainly give it some neuron-time and is a very valid and perhaps even obvious solution. Anyone designed a comb-filter recently?

Thanks Andrew.

Steve A.

....now how am I going to do the colour encoding.....I took a train from Paris to Hungary in the early 80s with Dr. Horvarth, one of the developers of the SECAM colour system. Amongst the games we played to pass the time, 'Digital Racing' and the like, we brainstormed concepts which he subsequently patented. All analogue and today quaint. I don't think anyone has applied to use the patents....ho hum...
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Postby Stephen » Sun Mar 16, 2008 11:19 pm

Steve Anderson wrote:I guess it all depends on how 'authentic' one wishes to be. For the true purist it would be 30 lines with that unequal outer-edge spacing that JLB used. As far as I'm aware no-one is currently using that standard. But I'm sure I'll be proven wrong.
Actually, Mr Baird was using mirror drum cameras for broadcasting from an early date. These would have had constant line width. Also, the later Baird mirror drum projection televisors would have had constant line width as well. Therefore, I suspect that only the early scanning disc televisors had wide outer lines to achieve a somewhat stretched width picture. The distortion on the outer edges would have been minimal and probably unnoticable.
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Postby Viewmaster » Sun Mar 16, 2008 11:40 pm

Steve Anderson wrote:P.S. I'm a vegetable...oops, I mean vegetarian. Or maybe I was right in the first place.


You could arrange to have 32 beans (sync PULSES!!) spaced around the edge of your plate of salad. :lol:
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Postby Steve Anderson » Sun Mar 16, 2008 11:43 pm

Stephen wrote:Therefore, I suspect that only the early scanning disc televisors had wide outer lines to achieve a somewhat stretched width picture. The distortion on the outer edges would have been minimal and probably unnoticable.


Agreed. I'm not quite sure in what Mr. Baird was trying to achieve, I can only assume it was a factor that might have been perceived as to the lower resolution of the eye in periferal vision. Much like the compression systems used today. Please, I don't want to get on my soap-box about that...

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Postby Steve Anderson » Sun Mar 16, 2008 11:46 pm

Viewmaster wrote:You could arrange to have 32 beans (sync PULSES!!) spaced around the edge of your plate of salad. :lol:
Albert.


Very good Albert, gave me a good laugh....spun at 750 RPM one would have pulses flying eveywhere! Some might even end up in the kitchen sync.

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Postby Klaas Robers » Mon Mar 17, 2008 12:07 am

In the club-CD number 3 the extra widened lines are taken in account. I had to convert the 32 line video into 30 line Baird video. Firstly I added quite large blankings, so the active area has an aspect ratio again of 3:2. Then I interpolated the first and the last lines, so the two extra lines are spread over the wider outher lines. The advantage is that the center 26 lines needed no processing and have the same horizontal definition as in the 32 line system.

I did this because as far as I know almost everybody using the 30 line part of the CD looks onto an old and hopefully restored Baird Televisor. Only Denis Asseman makes 30 line discs of his own for the replicae of the Baird Televisor and the other contraptions that have been made in some quantities. And Denis is a purist, so of course the outer squared holes are rectangulars and placed at a wider pitch.

I don't know if Gary, in case his program is switched to 30 lines, also does this. But be assured that the mirror drum that J.L.Baird used for his camera in the studio, placed the flying spot also at a wider pitch at the beginning and the end of a frame.
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Postby Steve Anderson » Mon Mar 17, 2008 12:57 pm

Klaas Robers wrote:...for the replicae of the Baird Televisor and the other contraptions....


What a delightful use of the word 'contraption', excellent! As defined by The English Oxford Dictionary....contraption > noun, a machine or device that appears strange or unnecessarily complicated and often badly made and unsafe...

...contraption, I'll not forget that word again...

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Postby Stephen » Tue Mar 18, 2008 2:05 am

Klaas Robers wrote:But be assured that the mirror drum that J.L.Baird used for his camera in the studio, placed the flying spot also at a wider pitch at the beginning and the end of a frame.
I am still not convinced of this. Although it would have been a simple matter to adjust the mirrors of the cameras to account for wider outer lines, it would have been very difficult for the Baird mirror drum televisors. The televisors would have had to change aperture size for the outer lines as well as spacing. Otherwise there would be gaps between the outer lines. That would probably mean that they would have a complex variable aperture wheel in front of the light source synchronised to the mirror drum to change line width for the outer lines. I doubt that they had that sort of complication.

Furthermore, the photos that I have seen of Mr Baird's flat planel displays seem to have evenly spaced rows of uniformly sized bulbs in what appears to be the 3:7 aspect ratio. That is not to say that to say that the mirror drum receivers and the flat panel displays did not have some sort of compensation for wide outer lines, but I have yet to see anything in writing that would confirm this. That is why I think that the wide outer lines on the disc-type televisors were just a gimmick to display a slightly wider stretched image.
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Postby Klaas Robers » Tue Mar 18, 2008 8:11 am

Yes, I think that the Baird-viewers complained about the narrow picture size. And this was a way to make the picure somewhat wider, without making it incompatible.

I never have seen the mirrordrum pictures, but I assume that the "spot" was circular and with a gradual fall back in light intensity. Then you don't get immediately black bands in between the lines.

If you look onto a TV picture tube, then you will observe also that the focussing at the edges and especially in the corners is much worse than in the center. Ever seen this? Then you know that sharpness at the edges is of little use. Clever seen by J.L.Baird.

I always asked myself if the 3:7 aspect ratio is included the wider border lines. Then I learned that this is not the case. The aspect ratio is 3:7 for a picture with equally spaced lines, like in the center, and NO sync or blanking bar. In reality the aspect ratio becomes almost 1:2 (or 3:6).
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Postby Telehor » Tue Mar 18, 2008 7:06 pm

The dimensions of the images on a Baird Televisor disc:
Holes 1 , 2 , 3 , and 28 , 29 , 30 : 0,7 x 1 mm het others 0,7 x 0,7 mm

Denis
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A sneak preview..

Postby Steve Anderson » Sun Apr 13, 2008 12:11 am

As I mentioned in other threads I've got the 48-line CRT up and running. However in the 'poor-mans' D-A i'm using there's a small error in the vertical spacing evident in the snapshot that follows.

Give me 24 hrs and I'll iron that out.

Steve A.
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Re: A sneak preview..

Postby Stephen » Sun Apr 13, 2008 12:31 am

Steve Anderson wrote:As I mentioned in other threads I've got the 48-line CRT up and running.
This is an excellent image, Steve! It clearly shows the improvement of the 48-line format and benefit of the 4:3 aspect ratio.
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Postby DrZarkov » Sun Apr 13, 2008 2:35 am

This is indeed excellent! Are you sure you can't come next week? :wink:
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Postby Steve Anderson » Mon Apr 14, 2008 12:50 am

DrZarkov wrote:...Are you sure you can't come next week? :wink:


I wish I could, but something rather unpleasent has got in the way...it's called work!

Anyway, I've sorted out the 'poor-mans D-A' by replacing it with a more conventional constant current charged capacitor arrangement, picture attached. For some reason the camera wouldn't perform as well as last night. I'll never buy an Olympus again, and not just for this reason alone.

Also attached is a pdf of the whole shabang with circuits, waveforms, a brief description and more screen-shots.

I hope it's of use/interest.

Steve A.

P.S. I've re-done the photos so the final file size is more reasonable.

Added 20/06/08. An update to the pdf has been done that now includes the 72-line screenshots otherwise there's little change.
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