Which video has wrong stretch ?

[Platos]

i have two videos and need help with the desicion which of them has the wrong "stretch". I will show you a screenshot of it (because it is a personal video, i cut of the head in the picture). I do deliver not more information on purpose because of a "blind test".

Which one of these pictures does show a wrong stretch? I ask you that, because i am not 100% sure. It is only about the stretch, not the picture quality.

I will not tell you (now) what i think which one the "right" one is (or if none of them are).

I would be glad if some of you could borrow me your eyes for a short time

Ps. Maybe look at it on full-size and switch with alt+tab or so. Maybe that makes it easier.

[DB83]

The 'normal' way would be to assess a circle. Slightly harder since the wheels are not full on. But if one is not true then I would have to, personally, say that the lower one is.

[Sharc]

Upper is wrong, lower is correct IMO.

[Platos]

Hmm, why the lower one? The wheel from the lower one looks wider than high. I also counted the pixels and the upper one is more circly than then lower one.

So the lower one is the "Bild53.png" right ?

The 'normal' way would be to assess a circle. Slightly harder since the wheels are not full on. But if one is not true then I would have to, personally, say that the lower one is.

What do you mean with assess a circle ? You mean to search a circle in the video? Thats what i tried with the wheel. And the upper one is more circle (when you measure the pixelcount the upper one is more circle). So on the left wheel of the bike.

[DB83]

'Assess' as in is this a perfect circle ? The lower rear wheel, in my eye, looks slightly elongated.

[Platos]

'Assess' as in is this a perfect circle ? The lower rear wheel, in my eye, looks slightly elongated.

Yeah exactly, that what i also see. the lower rear wheel looks elongated. But why should this one be the "good" one? Because you said the lower one is it.

Edit: And yes, the wheel should be perfectly in front of the camera. But it is very hard to find sth circle (and big) perfectly in front of the camera.

[DB83]

Surely you asked which has the WRONG stretch and that is how I answered = the lower one

[Platos]

Surely you asked which has the WRONG stretch and that is how I answered = the lower one

Ah ups xD

Thats true.

So then it is 2 vs 1

Sharc say the opposite. I think also the upper one is the correct.

@Sharc: Why do you mean the upper one is the wrong one? Which part did you use for comparing? Or did i also understand you wrong?

[Sharc]

The front wheel looks to be more perpendicular to the camera axis with less perspective distortion than the real wheel which is closer to the camera. Also there is a small circle just below the boy's ellbow which looks more circular in the bottom picture.
Anyway - take the one YOU think is right.
(If it is an analog PAL VHS capture with small black borders each side stretch it with 12/11 and it should be correct.)

Edit: My green reference circles on Bild53 (small wheel below the boy's arm and around pedals)

[Alwyn]

Rough pixels across the back wheel:

74: 332 high, 329 wide: 1.009

53: 418 high, 429 wide: 0.97

I therefore think that 74 is more accurate, especially given that, if the wheel was moved to be absolutely perpendicular to the camera, it would be elongated, width-wise, which would make 53 even more askew.

[johns0]

I think that it don't matter with each picture cause it's so small of a difference,best to have a minute of each in video to really see the difference if there's any.

[dellsam34]

I agree with John, Those screenshots are useless and there is no way of telling which one is right because we don't know what pixel shape is and how is it displayed during the time of taking a screenshot, Post a full frame grab from the video stream in its native resolution which you can put a black square over the head to cover it without messing with the resolution, and a brief description of the source of the video, for example analog capture will always be 720x480 4:3 for NTSC (720x576 for PAL/SECAM), DV, DVD will be the same or widescreen/anamorphic 16:9 in the same resolution, HDV is 1440x1080 16:9, none of these are square pixel by the way.

[Sharc]

I think that it don't matter with each picture cause it's so small of a difference,best to have a minute of each in video to really see the difference if there's any.

I guess the small difference we are debating are the infamous 2.3%, if this hurts someone at all.
What matters is to capture the source (VHS?) correctly in 720x576 for PAL (I think the OP is in PAL region), and stretch it according to its PAR (12/11, aka 59/54 in Vdub, for analog PAL capture). Doing a circle test on this single tilted picture is mumbo jumbo.
So yes the OP should provide a short sequence of the original unprocessed capture.

[rgr]

It will be difficult to draw a good conclusion from this picture. No shot of something square?

[Platos]

I agree with John, Those screenshots are useless and there is no way of telling which one is right because we don't know what pixel shape is and how is it displayed during the time of taking a screenshot, Post a full frame grab from the video stream in its native resolution which you can put a black square over the head to cover it without messing with the resolution, and a brief description of the source of the video, for example analog capture will always be 720x480 4:3 for NTSC (720x576 for PAL/SECAM), DV, DVD will be the same or widescreen/anamorphic 16:9 in the same resolution, HDV is 1440x1080 16:9, none of these are square pixel by the way.

That's exactly NOT what i want to do.

If it is not possible to deside which one is the non-stretched one without known a resolution, then you can't see it. That's why i dont say it, because you would just look on resolution and not really on the picture. That's why i asked here.

[Platos]

It will be difficult to draw a good conclusion from this picture. No shot of something square?

It is difficult to find sth, which you know it has to be 100% square. That's why i searched for (big) circles. But i can search again, maybe i find sth better.

I could post a video, when i find sth without people on it but with a good visible circle/square. But i did not found one. Or when i could censor a person in a video (a person which is moving around).

Edit: But a side-question: Can i somehow change the stretch from the one video to the other without reencoding (so only muxing) ? Because for having the same PAR (1/1) it needs a different resolution. I guess i can't do that without a reencode?

[dellsam34]

If it is not possible to deside which one is the non-stretched one without known a resolution, then you can't see it. That's why i dont say it, because you would just look on resolution and not really on the picture. That's why i asked here.

And I've explained to you there is no way of knowing, If you are able to tell me what's in my hand right now I'll be able to tell you which one is wrongly displayed or wrongly captured or whatever spins in your head.

Edit: But a side-question: Can i somehow change the stretch from the one video to the other without reencoding (so only muxing) ? Because for having the same PAR (1/1) it needs a different resolution. I guess i can't do that without a reencode?

Again, with no information on the contents and its origin and how it got captured, no one here can help you except good guessing.

[Platos]

i only asked for some, which can tell out of a picture, if it is stretched wrong. Nothing else. No reason to be unfriendly. If you can't tell it with that information, that's fine. But no reson for beeing unfriendly.

And for sure there is a way. You can search objects, where you know the shape (circle for example).

[Platos]

It will be difficult to draw a good conclusion from this picture. No shot of something square?

Ok, i found another scene. It is not a square, but i think it is even better: A ball. A ball should be (in 2D) always a circle, doesnt matter which perspective, isn't it?

So here is an example. Is this a better one ? The ball is not moving there on this scene, so it sits on his hand.

Edit: i have even 2 better one: some couple frames later he do lett the ball fall, so the hand is not in the way (but the ball is nearly not moving because it is only 2-3 frames after letting the ball fall):

(I think the 7 is less stretched. What do you think ?)

[dellsam34]

I'm not been unfriendly, I'm been honest. If you need help we need more info, The issue is no one can tell, You don't know what you don't know, a screen capture of 2611x1952 does not prove you're displaying the content right, Your playback software could be stretching it and you don't know, A ball may always look round in 2D but it will not look round if not displayed properly in the same proportion when it was shot originally, If this is a video tape capture there is a whole procedure on how to get non square pixels displayed properly, not by hide and seek games.

[Sharc]

Rough pixels across the back wheel:

74: 332 high, 329 wide: 1.009

53: 418 high, 429 wide: 0.97

I therefore think that 74 is more accurate, especially given that, if the wheel was moved to be absolutely perpendicular to the camera, it would be elongated, width-wise, which would make 53 even more askew.

I don't even think one can take the back wheel as a circle reference. It is distorted. Look at the fork of the wheel. Imagine what the fork would look like if the camera was pointed vertically onto the centre of the wheel - as it should for a meaningful circle test. The camera is directed from top&back onto the bike, resulting in a distorted, vertically squeezed wheel, inevitably.
Anyway, as has been said, that tilted view is useless for a test. The OP just wants to play games, as he got the info about anamorph (=non-square pixels) captures in his earlier thread and should know by now how to capture and convert to square pixels.

[lollo]

I agree with Sharc and dellsam34. There is a well established specification for analog capture about resolution, DAR, SAR and PAR. Just apply it, there is no need to play any “game”.

[DB83]

Personally, I do not think the OP is playing 'games'. Even if terms such as PAR,DAR etc were previously explained they can confuse and the OP is trying a different way to get over these hurdles.

After all, replies are given 'in good faith' since many a topic could be construed as 'playing games'.


Now the OP does not wish to present an actual, un-doctored, clip which would be the obvious way to put this 'discussion' to bed. Probably over-reacting to the privacy issue but without that it's total speculation.

[Platos]

For sure i do not play "games". I have really no time for playing games.

The point is, it is not looking right. I can not just use output-PAR, because the input-PAR is unknown. Yes, i can use as Input 12/11 or similair, but it does look not as i feel it should. That's why i asked here for others to have a look on a picture. That's why i don't ask you, which PAR or resolution i should take, because i already now that. And The output-PAR is 1/1. My Player also does not stretch it wrong.

And i can not deliver a video because of privacy. I do not censor faces for fun. And i don't know how to censor a whole video. So that's why it is a picture. And the reason because it is a screenshot and not an actual frame: It doesn't matter for my question. As i said, i know what PAR i could take. But it does not look right for me. And also for some other it does not look right. People asked for specific frames that they can have a look on the resolution and then tell me, what i have to use. As i said: That's not what my question was about. My question was only about "which one is wrongly stretched".

If you can not tell me that or not have time for that, that's ok. But i have really no time for playing games...

[Sharc]

All right. So when you feel that something does not look right, why don't you just take the one which looks right to YOU? That's all what counts at the end, and better than having sleepless nights about a possible ~2% aspect ratio error which may or may not exist.

[DB83]

I still think you are over-reacting to the 'privacy' issue. We know, as with most members on here, very little, if anything about you. Do you really think that a short sequence of 10-20 seconds of original footage will suddenly result in those that view instantly recognise who is featured ?

[zing269]

(I think the 7 is less stretched. What do you think ?)

I agree that 7 is less stretched.

[Alwyn]

I took the question to be not "which is right", but "which is more right".

The balls. I haven't made the balls the same size, but the red circle should be enough. I think 7_2's the winner.


[Attachment 79112 - Click to enlarge]

I don't even think one can take the back wheel as a circle reference.

Nobody is.

Do you really think that a short sequence of 10-20 seconds of original footage will suddenly result in those that view instantly recognise who is featured ?

I doubt it's about recognising anybody, it is probably more of a concern of the creeps of the internet using footage for their own sick purposes. I absolutely sympathise with the OP in not wanting to put up this sort of video.

[Platos]

Thanks, what Software do you use for this comparison?

So i think i will use the 7_2 Version.

And yes, i still would not upload personal videos in public.

[Alwyn]

what Software do you use for this comparison?

Just my drawing program, Xara. You should be able to overlay a circle in any of the regular drawing/illustration programs.