# Is the world really 2D or 3D?

RW2012
I am sure this question has been asked many times before. I searched for a thread on this topic and could not find one.

I am an artist. I am looking for an answer on the nature of sight. What is the best explanation for how sight occurs. Do we see a 3D world illuminated by 2D photons? Can we see 2D or is it only represented in 3D? Do we see 3D pictures in our minds, or 2D? Do we see a 3D world or actually a 2D world that we can make into 3D representations in our mind?

I'm guess we see a 3D world illuminated by 2D objects and we have 3D pictures in our minds. I would also guess that TV's project 2D images that we organize into 3D representations in our minds.

I really need to sort this out. thanks

Gold Member
I am sure that as an artist you are aware of perspective and other aspects such as shadows and angles that can be used to portray a three dimensional image on a two dimensional medium such as a canvas or paper. A good painter will also use hues and greying of colors to signify distance, and overlapping of objects, so correctly that the picture on a two dimensional medium does appear as 3D.

One eye cannot tell distance ( or 3D ) just by looking at an object. Two eyes in a figuration that humans and some other animals have, that is both eyes facing forward, will each give to the brain a slightly different scene to the brain. The brain can then use this information to interpret, with experience, as we grow older from a baby onwards, closer objects from those farther away. This is called binocular vision. One eye, by moving side to side, can send 2D images to the brain which will attempt to enterpret as 3D.

Just take a look at your ceiling where two walls meet together to from a corner. Notice that no angle is anything near 90 degrees. From experience though, your brain will interpret the two walls and ceiling as meeting at 90 degrees. You will think you see 90 degrees but you do not. If you do not believe this take a picture and measure the angles of the wall and ceiling.

RW2012
I appreciate that you tried to help, but I am looking for exact answers to the questions i posted. I would appreciate answers on these questions.

Mentor
Humans see 3d by combining the two 2d images collected by our eyes.

TV provides a 2d image that is recognized as a 2d image by our brains.

Photons are essentially non-dimensional, but that isn't really relevant to how we see.

RW2012
Humans see 3d by combining the two 2d images collected by our eyes.

how do we know they are two d images? do we think this because light is called 2d?

TV provides a 2d image that is recognized as a 2d image by our brains.

it is recognized in our brains as 2d because we call light 2d? or for another reason?

Photons are essentially non-dimensional, but that isn't really relevant to how we see.

what are the guidelines for calling something two d? that is possess no depth? if photons have h and w then why not call them 2d? what else could we call them? is there another system that could be used to organize or label material structures?

Mentor
how do we know they are two d images? do we think this because light is called 2d?
Again, no, light is not 2d. We know the images are 2d because the detectors are 2d.
it is recognized in our brains as 2d because we call light 2d? or for another reason?
No, our brains recognize that their detectors (our retinas) are 2d.
what are the guidelines for calling something two d? that is possess no depth?
Um....yeah..... something is 2d if it has two dimensions. Length and width. Our retinas have length and width, but no depth.
if photons have h and w then why not call them 2d?
Photons do not have h and w. They are essentially point particles.
what else could we call them? is there another system that could be used to organize or label material structures?
Photons are not material structures.

RW2012
retinas have no depth? i believe you mean they do not read depth, they read 2d that is interpreted into 3D?

are point particles 1d?

thanks for all this. i had to really push it so that i am fully understanding the material. i have to write an essay on planes in art, defining dimensionality is the opening part. soon i will probably have questions about planes.

Mentor
retinas have no depth? i believe you mean they do not read depth...
I mean they have two dimensions: length and width. I don't know what "read depth" is.
they read 2d that is interpreted into 3D?
They read 2d that is interpreted as 2d unless the two pictures are combined.
...are point particles 1d?
Points are 0d. Lines are 1d.

RW2012
I mean they have two dimensions: length and width. I don't know what "read depth" is. They read 2d that is interpreted as 2d unless the two pictures are combined. Points are 0d. Lines are 1d.

but when i close my eyes i still see depth. it doesn't seem like 3d is necessitated by having two eyes.

a retina is a tissue of the eye. it is a material, 3d, thing. what do you mean "they have two dimensions"?

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Mentor
but when i close my eyes i still see depth. it doesn't seem like 3d is necessitated by having two eyes.
Huh? When you close your eyes, you see nothing.
a retina is a tissue of the eye. it is a material, 3d, thing. what do you mean "they have two dimensions"?
I mean the rods and cones that detect light are arrayed in two dimensions across the surface of the retina. They are next to each other, not in front of/behind. Light does not penetrate the retina, it only hits the surface. Surfaces are 2d.

jmmccain
As a fellow artist, may I suggest the following paperback? It's inexpensive and it's very good for explaining how our eyes and brain interpret what we see (and what we think we see).

Image, Object, and Illusion: Readings from Scientific American

I used to have a copy, but I think I "loaned" it to someone else. One should be able to find a copy for less than $10. RW2012 Huh? When you close your eyes, you see nothing. I mean the rods and cones that detect light are arrayed in two dimensions across the surface of the retina. They are next to each other, not in front of/behind. Light does not penetrate the retina, it only hits the surface. Surfaces are 2d. i meant to say when i close one eye, i still perceive depth. RW2012 As a fellow artist, may I suggest the following paperback? It's inexpensive and it's very good for explaining how our eyes and brain interpret what we see (and what we think we see). Image, Object, and Illusion: Readings from Scientific American I used to have a copy, but I think I "loaned" it to someone else. One should be able to find a copy for less than$10.

thanks. i just bought a copy.

RW2012
thanks for all the info Russ.

Mentor
You're welcome...

i meant to say when i close one eye, i still perceive depth.
Perceive depth in what? What do you see that has depth when your eyes are closed?

RW2012
You're welcome...

Perceive depth in what? What do you see that has depth when your eyes are closed?

maybe i am misunderstanding you. do you see 3D when you close one eye?

Number Nine
Humans infer information about depth a number of ways, including the obscuring of far away objects by nearer ones, shadow, and the comparison of the images from both eyes. Depth perception is not destroyed when one eye is closed. Strictly speaking, both eyes report only two dimensional images; the brain constructs what we generously call a 3-dimensional representation much later in the visual stream. It would be a stretch to say that we "see in 3-dimensions".

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ModusPwnd
RW2012
you find it to be a stretch because vision is such an intricate process of 2D information processing before 3D representation occurs?

Number Nine
you find it to be a stretch because vision is such an intricate process of 2D information processing before 3D representation occurs?

I find it to be a stretch because the images we receive are two dimensional and we make inferences that allow to get a rough idea of their 3-dimensional arrangement, similar to how we infer information about depth when looking at a TV screen. We see 2-dimensional images; everything after that is the brain guessing.

ModusPwnd
RW2012
but without the 3d space and our 3d composition and the 3d realm we exist in there would not be the 2d optics that we use to create 3d. 2d is almost a subcategory of 3d in a sense. would you agree with this?

Mentor
maybe i am misunderstanding you. do you see 3D when you close one eye?
No, I misread you --- you said when you close one eye and I read "eyes". Sorry.

When you close one eye, you can, intellectually, detect signs of depth. Perspective, for example. But as an artist, you should recognize that in art, perspective is used in order to make what is 2d (a photo/painting) appear 3d, it doesn't make it actually be 3d. It is only a simulation, not real 3d. With one eye open, you can't detect a difference between a quality photo and, say, a window. With two eyes open, you can.

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Mentor
I find it to be a stretch because the images we receive are two dimensional and we make inferences that allow to get a rough idea of their 3-dimensional arrangement, similar to how we infer information about depth when looking at a TV screen. We see 2-dimensional images; everything after that is the brain guessing.
I wouldn't go that far. Stereoscopic vision doesn't provide an illusion of 3d, it provides real 3d perception. With stereoscopic vision, you can literally measure depth.
the brain constructs what we generously call a 3-dimensional representation much later in the visual stream.
While that's true, the place where it is done doesn't change the reality of what is happening: two eyes enable triangulation of distance.

RW2012
No, I misread you --- you said when you close one eye and I read "eyes". Sorry.

When you close one eye, you can, intellectually, detect signs of depth. Perspective, for example. But as an artist, you should recognize that in art, perspective is used in order to make what is 2d (a photo/painting) appear 3d, it doesn't make it actually be 3d. It is only a simulation, not real 3d. With one eye open, you can't detect a difference between a quality photo and, say, a window. With two eyes open, you can.

so without one eye being used there is degradation.
~
For the last hundred years, there has been great debate and strides taken to disavow perspective, and all forms of narrative that you find in paintings made before the advent of photography which made mimicry of the real world in the form of painting a pointless intellectual enterprise.

we can depict 3d space with paint. we then receive the painted info is as 2d in the eye. then we reformulate it back to a 3D representation in our brains. (that's quite a few steps.) in the end, we are still involved with some sort of 3D representation though not of the same type that contemporary artists are weary of. in the end, all things are at one point in this process 2d, flat, surface. yet, a canvas that is painted one color, say flat orange, is not depicting 3d space, but it is still on a 3d armature before it undergoes the process of perception which cannot edit out the perceived fact of it's material weight. in this sense, you cannot escape perspective.

RW2012
I wouldn't go that far. Stereoscopic vision doesn't provide an illusion of 3d, it provides real 3d perception. With stereoscopic vision, you can literally measure depth. While that's true, the place where it is done doesn't change the reality of what is happening: two eyes enable triangulation of distance.

so tv creates a sense of space in an illusory space, or in a pictorial space you might call it, as in the case of looking at a photograph of a forest.

akka69
Do we see a 3D world illuminated by 2D photons?

=> there is no such thing as "2D photons". We perceive a 3D world , even with one eye, in the sense that the image projected on the back of each eye is subject to 3D optical effects as: perspective (further obejcts are smaller than closer ones), blurring (depending on the distance to the focus plane, some image parts may look blurred)

Do we see 3D pictures in our minds, or 2D?
=> The eyes (not the brain!) add a "depth" signal to the color and light intensity by automatically processing parallax (same point seen from two point of vues). However the parallax processing precision decreases with distance, further objects appear to be on a "flat" background.

The eyes can add extra signals like outlines and border detection, speed detection etc.

This is part of an unconcious processing occuring in the retina (the back of your eye) and the optical nerves

Knowing the actual size of some objects like human beings, cars , buildings , boats etc. can give you a sense of their distance. That's how one eyed people can drive...
Then knowing that light comes generally from above, the brain can add a perception of depth based on shadow analysis.

The brain is responsible too for the movement perception by identifying the same image parts in consecutive images (this is used for ciname for example).

The brain image analysis can be fooled by optical illusions.

Last you must know that the eyes and optical nerves process image information in a manner where the most intense signals (like high speed movements or image part border or bright spots) are sent first to the brain, few ms before the rest.

Curious person
akka69, the information you have provided i find truly fascinating, including the last sentence on preference to intense signals. What is the source of your information for further reading?

Infinite/Zero
We see 2D and our brain make it 3D

FellowBob
We see in our eyes two 2D images of 3D things. Our brains combine these images to form a virtual 3D image in our brains.

derek10
I am stereoblind and I can still see 3D and calculate distances (probable worse than stereo capable people)

ogg

ModusPwnd
Lots of opinions here. I am firmly in the camp that we see in 2D, not 3D. Two 2D images does not make a 3D image. Furthermore, I do not think that a 2D image plus depth perception is equivelent to 3D. When we see in the x direction is an effective continum of information from left to right. That is 1D. We see an effective continum of information in the y direction from down to up, that is another dimension. To see in a third dimension we would need a continum of information in the z direction, front to back. Depth perception does not provide that. If we saw in 3D we would simultaneously see the front and backside of an object, as both the front and backside are part of that continum in the z direction. We can't do that. What we can do is take a series of 2D cross sections and then get a sense of the 3D structure. But I don't think people can even visulize 3D in their minds... what we do instead is visulalize a finite set of 2D cross sections or flay the 3D object out into a 2D image.

If 2D plus depth perception is 3D, then 1D plus depth perception is 2D? Nope, its not. A one dimensional image with information on the distance of each point does not make a two dimensional image. It makes a 1D cross section of a 2D image, and cross sections always lose a dimension.

Gold Member
Humans infer information about depth a number of ways, including the obscuring of far away objects by nearer ones, shadow, and the comparison of the images from both eyes. Depth perception is not destroyed when one eye is closed. Strictly speaking, both eyes report only two dimensional images; the brain constructs what we generously call a 3-dimensional representation much later in the visual stream. It would be a stretch to say that we "see in 3-dimensions".
I agree. People seem to think that all we perceive about the world is dominated by our binocular vision. That view is a naive as saying that the eye is 'like a camera' and leaving things at that. People with vision in only one eye and even people who have never had vision at all, can have excellent spatial perception*. We use countless clues about relative distances, sizes and even masses of objects. This is why we are relatively easily deceived by optical illusions and magicians. But those are exceptions and largely not 'natural'. A quick read through this Wiki article (despite the disclaimer at the top) should be enough to show something of what's really going on when we see a scene and retain it when we leave the room or close our eyes.
*None of us has ever seen the inside of our mouths in detail but, from the evidence that our tongue gives us, we have near perfect (3D) map of it and (mostly) can avoid chomping down on our cheeks and tongue, even during violent chewing of our favourite food.
It just ain't as simple as that!!!

Staff Emeritus
As has been hinted a few times on this thread, the OP seems to not know the difference between the human perception of 2D/3D versus the physical reality of something that is either 1D, 2D, 3D, etc...

Let's get this out of the way. If I confine an electron gas in 2D, the density of states of this electron gas looks VERY DIFFERENT than when it is in 3D. The same can be said when I compare a 1D electron gas versus 2D and 3D. Students in intro Solid State physics course are very familiar with this. This is an absolute physical property, and not a perception based on the human eyes/optics system.

Secondly, one must ask the question on why we see a 2D image from a regular photographs, but see a "3D" image from a hologram. In fact, try looking at the hologram (or go to a 3D movie) and close one eye. Do you still see the 3D effect, or at least see it as CLEARLY as when you had both eyes opened?

The problem with using what we see as a "detector", as has been stated already in this thread, is because our brain tends to "interfere" with our perception based on our experience and our evolutionary characteristics. It is why we have optical illusion, where our brain is inserting stuff into what we see even when it is not there. So the issue of 2D versus 3D observation with our eyes cannot simply be attributed to just optics or external physical properties.

As an experimentalist, I will again emphasize the fact that you must also pay attention to the device you are using to detect or measure!

Zz.

arydberg
You need to understand how a 3D camera works. It an best be understood by 2 cameras 2 1/2 inches apart. You take 2 pictures at once. The left picture is then presented to the left eye. The right picture is presented to the right eye. All the rest is the brain. With eyesight our two eyes perceive 2 slightly different pictures as they are also 2 1/2 inches apart and again the brain takes over. It is the tiny differences in these two images that give us 3D.