The Stereoscopic 3D Map
Before we talk about head mounted displays, it’s important to understand how 3D monitors work. Here is a top view diagram of how your eyes interact with a virtual 3D video game environment with an S-3D display:
Circles “L” and “R” are your left and right eyes.
The “S” line is the virtual screen glass. Professionals call this “Zero Parallax”, but we will call it the “Neutral Point” because everything behind this position appears in the distance, and everything in front of it is an out of screen effect and will appear to pop out at you! Lots of fun! This is a virtual line and is not representative of your monitor’s physical screen location.
To make this easier to follow, symbol “D” refers to “distance”, and “P” refers to “pop-out”.
Let’s see how everything relates!
First, the boxes all represent the same object, but from different 3D perspectives. Remember that when you are wearing 3D glasses, your left and right eyes each see a unique 2D image, and your brain combines the two to create the 3D experience. This diagram is showing what things look like without the 3D glasses on so you can follow the relationships.
Box “N” is your object at the “Neutral Point” or “Zero Parallax”. If you were looking at this with your naked eye without 3D glasses, it would be a single box because there is absolutely no separation to create a 3D effect. If this was the only thing on the screen, it would appear to be 100% flat.
Box D(L) and Box D(R) is the same box with a space in the middle. This space is called “separation”, and the 3D distance is determined by the amount of separation between D(L) and D(R). If you were wearing 3D glasses, your brain would take these two images, consider the separation between them, and create a deep 3D experience for you.
Notice how D(L) and D(R) are aligned with your left and right eye? For the depth sensation to work, it is important that the image matches the eye that is seeing it. For example, if you open just your left eye, you will see D(L), and if you open just your right eye, you will see D(R).
It is important that the separation does not go beyond the actual space between your eyes or you will experience something called “divergence”, or encourage your eyes to point uncomfortably apart from each other. Also, the space shown in this diagram is exaggerated in two respects. First, the separation is usually no more than an inch to two inches apart for distant objects. Second, when the images have the same separation as the distance between your eyes, it is as though you are looking into infinity which is unlikely to happen in your video game experience.
P(R) and P(L) is also the same box, but if you were wearing 3D glasses, it would appear to be popping out at you! How is this feat accomplished? If you look at boxes P(R) and P(L), their perspectives are crossed from D(L) and D(R) – everything is opposite! If you opened just your right eye, you will see P(R), and if you open just your left eye, you will see P(L). In both cases, these are opposite perspectives of where your eyes are accustomed to seeing things.
Separation impacts this pop-out effect too, and the space between P(R) and P(L) tends to be less than D(L) and D(R) because the pop-out will be distracting and unattractive if overused.
When you are using your stereoscopic 3D solution, you will have the flexibility to choose where line S or “Zero Parallax” is so you can have the 3D experience that is right for you.