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Aspects of aspect ratio

Black Hole said:
Can somebody else confirm the files download and play correctly/incorrectly?
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They work OK for me.

I have a nice Test Card W which I generated from an image. Forgot to add sound, so the Humax whines (about the audio format!).
 
I have a recording of the test cards from the old BBCHD somewhere.. must dig them out.
 
af123 said:
I have a recording of the test cards from the old BBCHD somewhere.. must dig them out.
Click to expand...
Yes, I've got the ones from the last day of HD. The HD test card wasn't a completely pukka version as transmitted though.
 
Amazing! I never knew about that trick. However, for me the test card came up as 4:3, and the Humax had to be set to Auto to fill 16:9.

If you press blue while the test card is up, you get a list of credits.

I can't find a way back to live TV! (OK, got it now: escape by pressing Guide and selecting a new channel)
 
My Humax is set to 16:9 with Pillarbox, 1080p passed through an AV Receiver to a Samsung 1080p TV with the input set to 1:1 (i.e. no overscan).

I've not observed the effect that selectortone reported, so this is complete speculation based on us having ruled out a problem in the display equipment (TV/ Humax)... But is it possible (and you'd need a _very_ good eye) that it's pincushion/barrel distortion in the camera lens being used? This might tie in with the report that the effect varies between channels and even programmes.

But as I say, I've not observed this myself (and I have a reasonably critical eye for these things) so it's pure speculation. Just a thought.
 
I did suggest something of the sort in post 12. The OP hasn't reported back on the result of my linearity test cards.
 
Black Hole said:
I did suggest something of the sort in post 12. The OP hasn't reported back on the result of my linearity test cards.
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I haven't tried the test card because it's irrelevant to my original observation - that the picture is occasionally distorted when BBC News 24 transmits in slightly less than 16:9 and the Humax Display Format is set to 'Auto'.

I know what I'm seeing - I trained as a TV engineer after I left school so I know my way around a test card and I do understand terms like 'pincushion'.

I was just curious to see if anyone else had noticed this phenomenon. It isn't a big deal; as I said, setting Display Format to letterbox cures the problem.
 
My in-laws have a panasonic tv & I'm sure it mentions in the manual about it stretching the image to fill the screen but not equally, the edge is stretched more than the middle.

Next time we visit them I will ask to see the manual & take a copy of it.


Sent from my GT-I9300
 
ian_j said:
My in-laws have a panasonic tv & I'm sure it mentions in the manual about it stretching the image to fill the screen but not equally, the edge is stretched more than the middle.

Next time we visit them I will ask to see the manual & take a copy of it.


Sent from my GT-I9300
Click to expand...

I'm aware of 'stretch 4:3' which is a technique used to fill a 16:9 screen when displaying a 4:3 image by progressively stretching the image at the edges (and is very apparent and looks dreadful).

That's not what I'm observing - occasionally BBC News 24 broadcasts what appears to be a 16:9 picture but there are narrow black bars on each side, maybe 20 or 30 pixels or so (except for the scrolling banner which reaches to the full horizontal extent). Like this - NOT the Hummy (so no pinching), recorded on Virgin Tivo, but it shows the 'slightly less than 16:9' picture I'm talking about (apologies for crappy cellphone pics):

aspect1.jpg


aspect2.jpg


The 'slightly-less-than-16:9' picture with black bars can be seen quite clearly.

When viewing this on the Hummy with Display Format set to 'auto' there is a slight pinching in the very centre of the screen, which makes the newscaster's head appear slightly squashed vertically.

Note: overscan is switched OFF on the Panasonic TV.
 
selectortone said:
That's not what I'm observing - occasionally BBC News 24 broadcasts what appears to be a 16:9 picture but there are narrow black bars on each side, maybe 20 or 30 pixels or so (except for the scrolling banner which reaches to the full horizontal extent).
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Have you tried reporting this to the BBC? It would be interesting to understand why they sometimes broadcast in this mode.
 
I reported the reduced width of the picture on this forum previously. Broadcasters expect TVs to be set for overscan. http://hummy.tv/forum/threads/adjusting-telly-picture-size-tv-settings.3455/#post-41758

selectortone said:
I haven't tried the test card because it's irrelevant to my original observation - that the picture is occasionally distorted when BBC News 24 transmits in slightly less than 16:9 and the Humax Display Format is set to 'Auto'.
Click to expand...
I may be mistaken, but I understood your original query to implicate the Humax in producing this non-linearity of which you speak. The test cards I generated provide suitable material for judging non-linearity (traditional broadcast test cards do not), my Humax/TV combination shows no non-linearity when displaying them, so if yours does it seems conclusive to me that the problem is with the TV. If your Humax/TV combination shows no non-linearity, all that is left is the broadcast source, which obviously the Humax can do nothing about.

Therefore, I submit, they are indeed relevant (and not exactly difficult to "just try it").
 
Overscan doesn't give the best quality picture, especially at HD resolutions. In the days of scan coils and CRTs overscan was necessary because analogue TVs needed to be individually set up. Modern flat panel displays and HDMI make 1:1 pixel mapping possible and it provides the best possible quality. (Suspect I may be preaching to the choir here....)

As regards the test card, I am 100% certain that I will see no distortion. As I keep saying, it only happens when BBC broadcast at slightly less than 16:9. When viewed from the Humax, with Display Format set to 'auto' the picture exhibits subtle distortion. The same picture from a Virgin Tivo box doesn't.
 
OK, I'll reserve judgement until I see for myself. At least you have described the circumstances somewhat better than previously. Again it should be possible to devise a test card.

I agree about overscan and best HiDef resolution, and have posted about it previously. However, many or even most TVs do not offer the facility to turn off overscan on tuner input. I do not understand why there is a need to have a guard area in a digital broadcast system, but they do.
 
I am still not with it. I have set my Qumi to no overscan, the HD-FOX driving it to Auto, and I have Breakfast content showing the usual variability in picture width (with the title bars extending to the full 1920 pixels on HiDef). From what I gather from selectortone's posts, I should be seeing the horizontal width being stretched in Auto to fill the display frame (with some non-linearity in the stretch), but I do not. The width variability remains.

In fact, I have also noticed vertical variability according to source material (less frequent than horizontal, and despite the 'FOX setting to Auto and there being no title bars to define the full height).

In my opinion, this is (at best) "unproven", and presuming the Humax is not attempting to fill the display frame dynamically I see no opportunity for it to introduce linearity issues. When I get a few minutes I will knock up a couple of test cards with non-standard pixel sizes.
 
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