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The Mysterious Overscan Line
Posted: Wed 22 Sep, 2010 23.09
by Chie
Watching TV with the overscan area visible, I sometimes notice a thin black line in the top-left corner of some recorded programmes.
The line appeared on an episode of Coach Trip I was watching on 4oD this evening, meaning that for the first time I can show you an example of what I mean:
Can someone please tell me what causes the mysterious black line?
Re: The Mysterious Overscan Line
Posted: Wed 22 Sep, 2010 23.17
by Bail
Timecode, generally, depending on how much overscanning you do/don't get you'll see this and white seemingly random flashing dots, basically timecode in barcode format that various broadcast vtrs can use.
Re: The Mysterious Overscan Line
Posted: Wed 22 Sep, 2010 23.57
by Ebeneezer Scrooge
Line 23 is the first active video line (ie the first line that isn't timecode or subtitles/data). PAL defines only the second half of this line as active video, so the first half was utilised as wide screen signalling as it is an easy way to describe the picture format in a way that will guarantee that that information will always travel with the picture.
More often than not, this WSS data is stripped in transmission today as it is deemed ugly. Previous to that, it was there, but most TVs hid it in the overscan area.
Re: The Mysterious Overscan Line
Posted: Thu 23 Sep, 2010 01.32
by Chie
Ah, I see. Thank you.
Yes, the flashing white dots and dashes make an appearance every now and then too. It's nice to finally know they actually have a purpose and what that is.
Re: The Mysterious Overscan Line
Posted: Thu 23 Sep, 2010 02.02
by Inspector Sands
Ebeneezer Scrooge wrote:Line 23 is the first active video line (ie the first line that isn't timecode or subtitles/data). PAL defines only the second half of this line as active video, so the first half was utilised as wide screen signalling as it is an easy way to describe the picture format in a way that will guarantee that that information will always travel with the picture.
More often than not, this WSS data is stripped in transmission today as it is deemed ugly. Previous to that, it was there, but most TVs hid it in the overscan area.
There is a WSS signal one that you see occasionally on the opposite side of the picture (top right) this is added by some cameras, particually DVCAM, and was fairly common to see about 5-10 years ago. It's fairly easy to turn off in the camera if you plough through the menus and I think it must now get blanked in the transmission stream