Black/White marks at top of screen on 'cheaper' channels

philbean

Member
At the top of the screen on a few of the 'cheaper' channels, I have a black line.. maybe 1 or 2 pixels deep with white bits. Like its supposed to be some sort of data line hidden in the picture, but its being shown.

Channels affected are Talking Pictures TV, Sony Movies, Forces TV..

The line isn't there if I just tune to the channels on my TV.. only through the Humax.

At first I thought it was just me.. but recently on twitter some people were posting screencaps from TPTV and a few had it too.


Is everyone's Humax doing this ?
Whats the technical explanation (or a name even?) ?
Why are only a few channels affected ?
Is there a fix ?


:)
 

Black Hole

May contain traces of nut
At the top of the screen on a few of the 'cheaper' channels, I have a black line.. maybe 1 or 2 pixels deep with white bits. Like its supposed to be some sort of data line hidden in the picture, but its being shown.

Channels affected are Talking Pictures TV, Sony Movies, Forces TV..

The line isn't there if I just tune to the channels on my TV.. only through the Humax.

At first I thought it was just me.. but recently on twitter some people were posting screencaps from TPTV and a few had it too.


Is everyone's Humax doing this ?
Whats the technical explanation (or a name even?) ?
Why are only a few channels affected ?
Is there a fix ?


:)
It's called overscan.

In the days of analogue TV, because the edges of the overall raster scan were somewhat undefined (combination of the transmitting end and the receiving end), it was standard to "lose" a few lines at the top and bottom of the picture and some scan width at left and right (only displaying the centre 95%-ish of the picture). The unused lines at the top eventually got used to transmit teletext data, and could be seen if the receiver's vertical scan wasn't set up correctly.

For reasons unknown to me, despite the exact dimensions of a digital image and display, the broadcasters still have guard bands all around the picture. Digital TVs have a default picture aspect ratio setting (which may be called "overscan" or "16:9" in the menus) which expand the picture to display only the centre 95%-ish (this is ludicrous IMO - this implies there is scaling going on, which destroys the fidelity of displaying a 1920x1080 HiDef image on a 1920x1080-pixel screen). If you alter the picture setting to display the picture as received ("original", "1:1", or "just scan"), you will then see the ragged edges of the broadcast picture that are not normally shown. This is particularly noticeable on something like BBC Breakfast, where the multiple different video sources from around the country don't agree where the edge of the picture should be.

If your telly isn't displaying input from HDMI the same as input from its internal tuner, that's because it has independent aspect ratio settings for the different sources. While viewing the HDMI input from the Humax, check the aspect ratio is "16:9". If it is, then the problem is simply that these minor channels have a wider guard band than normal.

What I do not expect is that the TV will show a different output from its own tuner than the Humax tuner via HDMI, unless the picture settings are different for internal tuner and HDMI input.

For more information see https://hummy.tv/forum/threads/aspect-ratio.2045/.
 
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EEPhil

Number 28
I have found this "problem" on the same channels on a 2000T and a 9150T. It is even more obvious as I'm still using an old 4:3 tv (yes, I know...). I don't remember getting the problem with a non-PVR set-top box. However, I do have a video capture device (Hauppauge) which I use to save old VCR tapes (when I get time) and this produces the same half line of dots at the top of the screen. The only way I can do anything about it is to crop the recording in an editor. Life's too short - so I just put up with the dots. I have noticed that if I step through the recording frame by frame the dots do not appear on every frame - I think it is every other frame. I suspect it is one of those things that you can do nothing about.
 

Black Hole

May contain traces of nut
I'm not sure whether there is a standard for how much overscan to use (to eliminate frame edge artefacts), but if there isn't and different set makers use different amounts, that would explain why some see it and others don't. However, the OP said that he sees it when the Humax is used as the tuner and not when the TV's internal tuner is used. This says to me that different overscan amounts are being used according to the source, hence the possibility that the aspect ratio is not set the same for both.

If you set (say) the TV's aspect ratio setting for HDMI to "just scan" (AKA 1:1), you will see the border crap (when there is any).
 

Luke

Well-Knwοn Мember
Ours don't. At least I've never seen it and SWMBO has never mentioned it. So it's probably also dependent on the TV.
Or how the TV is setup.
The default on my TV is that it is hidden. It's a 2014 Sony TV and one of the 'Screen' settings' defaults is 'Normal'. I usually have it set to 'Full Pixel' instead of 'Normal' and this displays the white dots at the top of the screen for movies4men and True Entertainment as well as the already highlighted Sony Movie Ch, Talking Pictures and Forces TV channels.
 

MikeSh

Well-Known Member
I've had a poke around and on ours there doesn't seem to be any setting for the display size beyond the various aspect ratios. It's an old (10 years) Panasonic plasma.
I've actually been watching an old (1960s, b&w) series recorded from Talking Pictures for a few weeks and it's been perfect.
 

prpr

Well-Known Member
I've actually been watching an old (1960s, b&w) series recorded from Talking Pictures for a few weeks and it's been perfect.
If you draw the curtains, you can't see people walking past outside. They doesn't mean nobody is walking past outside.
 

prpr

Well-Known Member
Doesn't mean they are either
The point is (and you seem to be ignoring) that you don't know what is happening because your display is masking it. Then you claim it's perfect, when we know it isn't (because those of us with displays that show everything see it).
Stop sticking your head in the sand.
 

Luke

Well-Knwοn Мember
I think the OP has his answer.
I too think that the OP has his 4 answers (the second question having two options), but I am still intrigued by the 2nd question's alternative question. I.e. "Whats the technical explanation?" In particular what this half line of broken white is for.
There was a discussion on what it was on DS in January but parring it down there was not a conclusion, only two speculative comments by jj20x:
the VBI data is more likely to be cue codes or something similar, not stripped out at the broadcast stage
and
Basically it isn't Sony's problem, if they are using cue signal data they won't be in a hurry to tidy up the image. I doubt that Sony will want to change their systems to make life easier for viewers using full scan for an SD channel
 

EEPhil

Number 28
It's probably AFD info., which should be blanked and isn't.
Despite my observations in post #4, you could be right. I'd noticed that the dots change position on Talking Pictures when they switch between 16:9 and 4:3 (well, their approximations to those formats) - at least they did when it was on COM7, haven't noticed since the move to ARQB.
 
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