In this blog post, we’ll take a closer look at “the principle of polarized glasses and how we perceive 3D images.”
Introduction
We’ve all probably watched a 3D movie at least once when we were children. You probably remember the experience of wearing glasses made of red and blue cellophane and looking at the screen, seeing various objects shimmering right before your eyes. Those 3D movies, long buried in our memories, have recently regained popularity thanks to the craze surrounding the film *Avatar*, and we now watch 3D movies wearing glasses with special lenses instead of cellophane ones. What principle is hidden within these glasses that allows us to perceive 3D?
Polarization and the Principle of 3D Perception
First, let’s explore the principle behind how we perceive 3D. 3D is an abbreviation for “three-dimensional,” a term that refers to a sense of depth and spatial awareness. In our daily lives, we experience this 3D perception through both eyes. However, when we watch images on a computer or TV, we don’t perceive depth; we simply see a flat screen.
So, why do we perceive depth? The main reason is that we have two eyes. Everyone has probably had this experience as a child. While it’s a piece of cake to interlock your index fingers with both eyes open, you’ve likely noticed that doing so with only one eye open is harder than you’d expect. This experience explains exactly why we perceive depth.
When our two eyes look at an object, they don’t see exactly the same image. The left eye views the object from one angle, and the right eye views it from a slightly different angle. The brain processes these two signals generated by the eyes and interprets them as a three-dimensional image. Therefore, since images on computers or TVs are displayed on a flat surface, the signals sent to both eyes are identical, so we can only perceive them as two-dimensional.
So, is it possible for us to perceive these flat images as three-dimensional? As we saw earlier, the primary reason we perceive images as three-dimensional is due to the angular difference between our two eyes. If we could receive visual signals at different angles in each eye even when looking at a two-dimensional plane, we would be able to perceive it as three-dimensional.
Polarization and How Polarized Glasses Work
Thus, a process was needed to trick the brain into perceiving two-dimensional signals as three-dimensional, and currently, the method using polarizing filters is the most common. The glasses we wear when watching 3D movies at the theater are special glasses made with polarizing filter lenses.
Let’s first discuss what polarization is. Light has the property of oscillating in all directions within a plane perpendicular to its direction of travel. Polarization refers to the process of confining this oscillation to a single specific direction. The following example illustrates how polarization is created.
Suppose you want to insert a rubber band through a slightly open door. In this case, you’ll find that if you wiggle the rubber band up and down, it slides through easily, but if you wiggle it back and forth or side to side, it won’t go through. Similarly, while light vibrates in all directions, when it passes through a plate with vertical slits (a polarizing filter), only the light vibrating in the vertical direction passes through, while the light vibrating horizontally is blocked.
In other words, light that has passed through such a polarizing filter is polarized light.
So, how is 3D imagery created using these polarizing filters? As mentioned earlier, in order for us to perceive a flat image as 3D, a process is required to trick the brain into seeing the image as if it were caused by the angle difference between the two eyes. Therefore, if we project the image intended for the left eye—which has passed through a horizontal polarizing filter—and the image intended for the right eye—which has passed through a vertical polarizing filter—simultaneously onto a single screen, we can view them separately through special glasses equipped with polarizing filters.
In other words, if the left lens of the glasses allows only horizontally polarized light to pass through, and the right lens allows only vertically polarized light to pass through, different images reach each eye through these special glasses, enabling the brain to perceive them in three dimensions.
This is why we are able to watch 3D movies—because they utilize the scientific principle of polarization. Through the medium of polarized glasses, we can perceive three dimensions from a two-dimensional screen. However, with recent technological advancements, technologies are being developed that allow us to perceive three dimensions without the need for glasses. Therefore, it can be said that the era of watching 3D movies directly with our own two eyes is not far off.
