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I remember that when researching and learning about vanishing points and vantage points of art pieces, that by closing one eye and viewing a painting from an exact point in space, it would give this effect of looking through a window (correct perspective and an enhanced sense of depth).

I then noticed that whenever I looked at a video or picture, with one eye closed, gave this similar effect of enhanced depth. I’m sure this has something to do with eliminating stereoscopic vision and perhaps with the fact that a camera only has one pupil. Nevertheless, I would really appreciate if someone could explain why this is? And if so, why don’t we view movies like this all the time?

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  • $\begingroup$ Conjecture but paintings are inherently 2D in the first place, so using stereoscopic vision might introduce extraneous information not intended to the experience. $\endgroup$
    – DKNguyen
    Jan 23 at 21:30
  • $\begingroup$ Interesting, that does sound like a intuitively simple and plausible explanation $\endgroup$
    – vannira
    Jan 23 at 22:12

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Depth perception is a fusion concept. We don't acquire any depth information directly from the senses (other than touch), but it can be inferred by comparing the results from each sense. The brain actually uses many sources of information. Stereographic information, trying to pair features from one eye against features in another eye, is one source of information. Depth of field is another. And, as you and artists have noticed, shapes can be used to convey depth even when painted on a flat surface. We can even use our ears to sense depth. If we notice that a person is speaking, the shape of the reverberations and the near/far field effects of the sound can be used to assign a depth to that person.

As you noticed, closing one eye removes one source of information that is telling you that a scene is flat on a wall. That can encourage the brain to emphasize the other sources of depth, such as apparent vanishing points.

As for why we don't watch movies with one eye, that's more of a psychology question than a physics question. I can venture a guess that the goal of a movie is to be immersive, not merely to have a sense of depth. Closing one eye might help with depth but would make it feel less immersive.

It's also worth noting that there's plenty of other hints suggesting to the brain that the scene is flat. In particular, it's presented on a wall, and we all know what a wall is like. As a counter example, people do set up non-motion flight simulators, where the construct a fake cockpit, but it remains stationary -- there's no hydraulics moving it up and down. The screens on the outside of the plane "windows" are flat, and not 3d. However, in that situation, you have many hints telling you that a scene is "real." People who make such flight simulations often hear that pilots can't believe how real it feels, even though there's no actual motion. And said pilots certainly keep both eyes open while using the simulator.

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  • $\begingroup$ Thank you for the great reply $\endgroup$
    – vannira
    Jan 25 at 11:24
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Looking at a screen showing a 3d scene presents a dilemma for the brain: Its clear by all physical evidence, that the picture is flat, while the interpretation with respect to perspective, sharpness, light and color gradients and movements suggest a 3d scene.

Closing one eye removes the possibility to detect the fixed 2d distance by a check of the constancy of the focus angle between the two axis of each eye, that is hardwired with the cilary muscles adapting the focal length. Interpretation is switched to 3d normal, one eyed, thats normal for distances over some 20 m, where stereoscopic effects become negligible and both eyes deliver the same picture.

I remember, that learning to look movies the first years after a living free of 2d-picture for the first years as a child, yielded headache. Reconstruction of 3d from 2d is a training field.

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  • $\begingroup$ Your answer could be improved with additional supporting information. Please edit to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers in the help center. $\endgroup$
    – Community Bot
    Jan 24 at 1:00
  • $\begingroup$ Interesting, thank you $\endgroup$
    – vannira
    Jan 25 at 11:24

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