Narrow-Bandwidth Television Association

[Lowtone]

Hello,

It says that in the original 30 lines system, 3 lines on each side are wider than the others. Can someone explain me why?

thanks.

[gary]

To give the illusion of more lines (width) without increasing bandwidth. The eye is less sensitive to resolution at the periphery of vision.

[Klaas Robers]

In the beginning Baird had a picture with an aspect ratio of 7:3. This was very narrow and tall. To improve that he decided to make the first 3 lines and the last 3 lines 1.5 times as wide. The standard wasn't changed. Then the picture is 2:1, which was better.

The resolution at the edges became less due to the wider lines, but that is acceptable because in most cases there is nothing interesting at the edges. The camera man is seeing for that. This is comparable to CRT behaviour. A picture tube is never focussen over the total area. The corners and the edges are really unsharp, but nobody sees it. Try to see the line structure at these places. It is completely gone.

In club CD number 3 the 30-lines part takes this in account. In fact the first 4 lines and the last 4 lines of the 32 line video are spread over the first 3 lines and the last 3 lines of the 30 line video. This is done in software of course. Then a firm blanking brings the active part of the picture to a netto aspect ratio of 3:2. So the 30-line viewer sees the same picture as the 32-line viewer.

CD 1 is 32 lines only and in CD 2 this is done in a less sophisticated way.

[Lowtone]

I see. Thanks for the answer. Clever idea, but it still looks weird

[Klaas Robers]

Clever ideas most of the time look weird, until you have learnt the backgrounds behind them. Then you smash yourself: "Why haven't I invented this myself!"

[Lowtone]

Hehe, sometimes i got ideas and... i found it already exists