2D becomes 3D when looked at by one eye

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  • #26
sophiecentaur
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I don't know what the precise definition of "3D vision" is, assuming there is an agreement about that. But in this context, where the authors of the paper I was citing actually use the phrase "seeing in 3-D", I thought it was clear enough what I meant.

I love to nitpick too. But I recognize it as a vice.
My problem is that there is an implication that, viewing with one eye should somehow prevent you from or detract from getting 3D information of a scene. It is a serious over simplification of the process. That video demonstrates to me that binocular vision is not necessarily a help in 'seeing' a 3D scene. The title of the thread implies that this is a big surprise but why should it be?

In that video (which is on a screen, say 60cm away from you) your binocular vision is telling you that the objects you are seeing are in a single plane (which they are, actually). When you look with one eye, you lose that information about the distance from the screen (your head is stationary so no parallax help) and start to use the other, in this case very strong, clues about the scene. If you were actually viewing that scene directly in place of the camera, you would be getting lots of information about depth from the non stereoscopic information. Stereoscopic vision could be telling you that there is some depth to the scene ( that not everything is just 60cm away, as on a TV screen) but it's all the other clues that go together to form the internal model of the scene. Can you really argue that this paragraph is a 'nitpick'?

EDIT: PS @DaveC426913 if you read what I wrote and look at the video again, you could, perhaps convince yourself about the effect. It might be that one of your eyes is very dominant and that you do not get strong stereo information. My Daughter in Law grew up with strabismus and, even though it has been largely corrected, never learned to use stereo vision effectively (so she tells me). She can choose to look at an object with one eye or the other, at will but can't actually get the 'natural' stereo effect that most people do. Perhaps if you look at the edge of the screen. the plane of the picture may get into your brain better and you might see a 'flatter' scene' I see the effect very clearly and it confirms my idea about the reason for it.
 
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  • #27
DaveC426913
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EDIT: PS @DaveC426913 if you read what I wrote and look at the video again, you could, perhaps convince yourself about the effect. It might be that one of your eyes is very dominant
This is actually quite true. While both my eyes are equally adept at seeing (I don't have any kind of partial vision loss), I have always habitually read with one eye firmly closed, so I look like a pirate missing his patch. My right eye is very dominant over my left.

TMI: I attribute it more to a difficulty keeping them both pointed at the same spot. When fatigued, it is very difficult to keep my eyes from going "de-crossed" (wall-eyed). And they rotate. If I stop trying, the image from one eye might easily rotate 20 degrees from the other eye.

Still, I'm at a loss to understand what you're describing. Except for this habit, my vision is perfectly fine.

What I do experience very strongly - though it is unrelated to this topic - is a very strong tendency to see colours as 3-D layers. Red recedes several millimetres, while blue advances several millimetres. It is inadvertent. I cannot not see this. There's a name for this effect.

Our post boxes just fuhREAK me out!

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  • #28
Tom.G
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Now that you mention it, I too noticed the 3D effect in the mailbox image. I suspected it had something to do with brightness, so investigated.
Converting to Grey scale reduced but did not eliminate the effect. Also the Red has a wider dynamic range of brightness, 0 - 100%. Whereas the Green ranges 0- 74% and Blue ranges 0- 80%.

Maybe we're just built that way with individual sensitivities to the effect.
 
  • #29
sophiecentaur
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Still, I'm at a loss to understand what you're describing.
Thanks for that reply Dave; it sort of confirms my thesis. It also shows that binocular vision is far from essential for most human lifestyles. I'm not surprised that you haven't actually been able to see 'the effect' because you have not been using binocular vision, which would be needed for you to identify the planar layout of a TV screen at the level that your brain would need. You have missed out very little with your vision if the only time it's been needed has been to produce an optical illusion!

Vision, along with hearing, sense of colour, taste and touch, is a very 'private' thing. No one can be sure of how another person is perceiving the World. It's only when we use sophisticated tests on many individuals or when we try to reproduce the senses in machines that we can approach anything like an understanding of these things.
This is why I get so cross when people (even on the well-informed and deep-thinking PF) try to dismiss our perception with over simplified models.

PS to @Tom.G too. The red post box effect also make me unwell. I suggest that it could be because of the Chromatic Aberration of our optical system which our processing mostly manages to compensate for. Also, the acuity of red and blue vision is lower than the luminance, which is sensitive to the mid range of frequencies. The post box pattern could be one of those things that Evolution never prepared us for but it wouldn't surprise me to find that the effect is used by brightly coloured birds and insects, to make them harder to catch by (binocularly advantaged) predators. Evolution is responsible for everything.
 
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My problem is that there is an implication that, viewing with one eye should somehow prevent you from or detract from getting 3D information of a scene....

...The title of the thread implies that this is a big surprise but why should it be?
Because that's the common reaction. People are surprised.

When you're looking a real scene and you close one eye there is usually a sense of things flattening out, a loss of 3D perception. But the opposite happens with a photograph. It surprises people.
 
  • #31
sophiecentaur
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When you're looking a real scene and you close one eye there is usually a sense of things flattening out, a loss of 3D perception.
There are very few instances of having to keep still when looking at a scene and binocular only comes into its own when your head is stationary (hunting lions and other cats). Parrots do a lot of head bobbing but they have side mounted eyes. Even owls do a lot of head tilting and they have seriously binocular vision. It's obviously a very complicated business with a huge range of strategies to make the best of vision.
I think the 'one eye' effect could be more a matter of seeing what you have 'learned ' to see. The binocular effect, imo, seems to operate only close up. The breathtaking 3D of some landscapes and garden scenes is, I'm sure, well beyond the scope of our binocular vision. And there is little reason why it should be particularly useful. I am sure that the redundancy of doubling up on the senses is a much better reason than the spatial awareness advantage. Losing one eye out of two is a bit inconvenient but losing one of one is disaster - unless one wants to turn nocturnal.
 
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The binocular effect, imo, seems to operate only close up. The breathtaking 3D of some landscapes and garden scenes is, I'm sure, well beyond the scope of our binocular vision. And there is little reason why it should be particularly useful. I am sure that the redundancy of doubling up on the senses is a much better reason than the spatial awareness advantage.
Evolving two eyes has the obvious value of redundancy that you point out. But we evolved stereoscopic vision as well.

There's no debate that binocular vision provides depth clues only out to a moderate distance. But the vast majority of the time there are objects quite near to us. Even breathtaking landscapes typically include a foreground. With one eye closed that part of the view diminishes in 3D quality. That the opposite occurs when looking at a 2D projection of the same image is what results in surprise... and is the whole point of this thread.
 
  • #33
Tom.G
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Slightly off-subject curiousity.

There's no debate that binocular vision provides depth clues only out to a moderate distance.
Agreed...mostly. There just isn't enough resolution and distance between the eyes for disparate images of distant objects. There is, however, visual processing in the Brain to consider.

Several years ago, my wife had bilateral cataracts dense enough that the whole world was 18% Beige. She had put off having them removed until I had to lead her around. When the first one was corrected she of course had no depth perception. When the second was removed there was still no depth perception, apparently she had 'forgotten' how to extract depth from the two images. A few days later we were driving home at night on the Freeway, and had a side view of a vehicle bridge a few miles away. The bridge was festooned with a whole bunch of LED decorative clearance lights. She exclaimed, rather surprised, that she suddenly could discern distance again! Doing 70mph with an oblique view of that bridge seemed enough to remind her Brain of what was needed.

Cheers,
Tom
 
  • #34
sophiecentaur
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When the first one was corrected she of course had no depth perception.
great to hear that the surgery was a success. A very heartwarming experience for you both but I do wonder about what experimental evidence such a striking experience can provide.
I could agree that she had impaired depth perception. If one eye equals no depth perception then you would surely expect that one eyed people wouldn't be allowed to drive cars. Your post confirms my opinion that the models people have of spatial perception is way over simplified. I suggest that her lightbulb moment (sorry about the pun) when you were driving past the bridge was because her reactivated binocular vision allowed her to have an improved appreciation of the 3D layout of the scene.
There are many instances in which binocular vision cannot help at all with depth perception - take the example of distant hills and nearby trees (particularly when you are moving past). Parallax can always be used for depth perception, even for objects laying around on the desk in from of me but, at that distance, two eyes help a lot. From what you have been implying, a one eyed person couldn't even reach for a pint of beer without risking knocking it over. That's clearly not the case.

A lovely story: My four year old granddaughter was walking down our lane with me in the late afternoon on a sunny day. We could see the Sun through the hedge on our right. "Grandad; the Sun is following us!". Now, what would be as suitable explanation for her? I just said how smart she was to have noticed it and that it happens all the time. One day, we'll do the full parallax thing, I guess.

Binocular vs 'focussing' as a judge of distance and how much we really rely on binocular vision: When I look over the ploughed field behind our house, I can appreciate and evaluate the distance of the nearby furrows but the distances of the parts of the huge and trees on the side hedge, is not at all obvious - despite the hedge running diagonally. I would say that angular size would be the dominant clue. However, when I use my astronomical telescope (120mm aperture), the focussing easily distinguishes between the far hedge distance and the hills, several miles away, behind the hedge. The angle subtended is very similar in both cases but I would say that 'focussing' is a far more critical measure of distance. The perception of the 3D layout of the land is there, with one or with two eyes. To resolve distances in excess of a km or so, a binocular rangefinder with a baseline of almost 1m is needed. Our eye separation is about 60mm.
 
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This apple video uses parallax(relative motion of foreground vs background) along with relative size to deliver a partial (In the opening, when we do not expect) depth experience.
 
  • #36
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This apple video uses parallax(relative motion of foreground vs background) along with relative size of apples to deliver a partial (In the opening only, when we do least expect) depth experience.
 
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  • #37
sophiecentaur
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This apple video uses parallax(relative motion of foreground vs background) along with relative size of apples to deliver a partial (In the opening only, when we do least expect) depth experience.
It strikes me as pretty impressive that our brain does its very best with the information it gets. We never evolved a specific skill to watch scenes (and get sense out of them) when they are presented on a flat screen or picture. That is a totally different way for the world to be presented to us but we are (nearly) all happy with films and TV (and even time mobile phone screens. Our binocular vision is SHOUTING at us that it's not real but we just get on with it and enjoy the view. Amazing. I reckon that implies that our brains all have the Plan B - only one eye available - capability, just in case.
 

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