# Is the world really 2D or 3D?

## Main Question or Discussion Point

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

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256bits
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.

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.

russ_watters
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.

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?

russ_watters
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.

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.

russ_watters
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.

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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russ_watters
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.

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. 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. 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.

thanks for all the info Russ.

russ_watters
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?

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?

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

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
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?

russ_watters
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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russ_watters
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.

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.

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.

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