Just so we are transparent from the get go, we wrote this article because we used this “retro” tech in our new website for the events section, just so that we can take you with us everywhere we go. However with creativity we are sure you also can find cool ways to adapt this to your digital needs.
Before getting into the technology of 3D, let us start with the necessary information about the biology at play (we promise it will be more fun than it was in school, please don’t click away).
Try threading a needle or tying a knot with one eye, go on we will wait.
How did it go? Harder than you thought right?
Evolution has refined our perception of 3D so that we can get better information faster about the real world.
How we get to experience the sensation of depth at a physiological level is a complex subject. There are many depth cues available to the human eyes and the human brain, which, when they arise from the real world, reinforce each other to create a unambiguous mental picture of the 3D landscape before us.
When we try to trick the visual system and the human brain into a 3D illusion, all these depth cues might not be faithfully re-created and the 3D experience is affected. Therefore it is important to understand the major ones.
Stereopsis (binocular disparity)
Your eyes see it from slightly different angles, resulting in different images on the retina.
If an object is far away, the difference, or “disparity”, between the right eye and left eye images will be small. If the object is close, the disparity will be large. This allows the brain to triangulate and “feel” the distance, triggering the sensation of depth.
Stereopsis is the strongest depth cue, but it’s not the only one. As a matter of fact it is possible to experience depth with only one eye!
Close one eye and hold your index finger still in front of you. Now move your head slightly left and right, up and down. The background seems to move relatively to your finger. More precisely, your finger seems to move faster across your field of view than does the background.
This effect is called motion parallax and lets you experience depth even with one eye. It is critical in providing a realistic 3D impression when the viewer moves ever so slightly about the display.
Stereopsis without motion parallax still gives you a sense of depth, but 3D shapes are distorted. Buildings on 3D maps, for example, start to look crooked. Background objects seems to maliciously remain hidden from foreground objects. It’s rather annoying if you pay attention to it.
Motion parallax is tightly related to perspective — the fact that distant objects appear smaller than closer objects, which is a depth cue in itself.
Now even if you were sitting perfectly still (no motion parallax), with one eye closed (no stereopsis), you would still have a way to tell distant objects from close ones.
Repeat the finger experiment, hold your index finger still in front of you and make the mental effort to look at it. As the finger comes to focus, you will notice that the background becomes blurry. Now take your mind off the finger and “focus” on the background. Your finger becomes blurry as the background becomes clear. What happens is that similar to a modern camera, the eye is capable of changing its focus.
It does so by contracting the ciliary muscles resulting in a stretch of the biological lens in front of the eye.
How does the ciliary muscle know how much force must be applied? Well there is a feedback loop going on with the brain. The muscle keeps contracting and relaxing until the brain perceives the target object as maximally crisp. This takes a fraction of a second and it becomes a strenuous exercise if repeated too often.
The ciliary muscle action is triggered only for objects located at less than two meters. Beyond that distance the eye more or less relaxes and focuses at infinity.
Convergence and accommodation conflict
When your eyes focus on a point nearby, they actually rotate in their orbit . The convergence will stretch the extraocular muscles, a physical effect you can feel and actually recognize as a depth cue. You usually can “feel” your eyes converge if they focus on an object at less than 10 meters.
So when a person looks at the world with two eyes, two different sets of muscles are at play. One converges the eyes to the point of interest while the other changes the focusing power of the eye to form a crisp image on the retina. If the eyes mis-converge, the viewer will see double images; if they mis-accommodate, the viewer sees blurry images.
In the real world, convergence and accommodation always work in pair and reinforce each other. The nervous stimuli triggering both responses are actually linked.
Now that we got the biology lesson out of the way let’s focus on how we can use 3D anaglyph images in this hi-tech world.
An anaglyph image is the old-school, cheap 3D we all know and have mild nostalgic attachments to. An image has two different color layers, one for each eye, with slightly different perspectives.
When we look at them through those awesome plastic glasses (usually with red and blue lenses) that block one layer in each eye, our easily tricked brain takes the resulting separate image from each eye and mashes them together to make a 3D scene in our head.
The original. The red-blue, red-green, or magenta-cyan (or “anaglyph,” the coolest word in this story after “parallax barrier”) glasses that came to symbolize 3D split a black-and-white (and later, color) image into two complementary components.
Our easily tricked brain takes the resulting separate image from each eye and mashes them together to make a 3D scene in our head.
Troubles are mainly of the color perception variety; it’s extremely hard to balance things so that your brain takes the broken-up colors and assembles them correctly.
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