New 3D technology for comfortable smart phone viewing

Scientists have developed a new display with three-dimensional visual effects, which will enable viewers to watch a 3 D movie on their smartphone without getting a headache or feeling nauseous.
The device is based on a "super multi-view technique" which works to reduce viewer discomfort, and also greatly decreases the required number of microdisplays, which makes a compact design possible.
"There are many causes for 3D-viewing discomfort, but the most substantial one is the vergence-accomodation conflict," said Lilin Liu from Sun Yan-Sen University in China.
Vergence-accommodation conflict is a mismatch between the point at which the eyes converge on an image and the distance to which they focus when viewing 3D images, researchers said.

Human eyes are separated by about six centimetres, which means that when we look at an object, the two eyes see slightly different images.
Our brain directs both eyes to the same object and the distance at which the eyes' sight lines cross is technically called "vergence distance."

Meanwhile, our brain adjusts the focus of the lens within each eye to make the image sharp and clear on the retina. The distance to which the eye is focused is called "the accommodative distance."
Failure to converge leads to double images, while mis-accommodation results in blurry images.
In natural viewing, human's vergence and accommodation responses are correlated with each other and adjust simultaneously. In other words, vergence and accommodation distance are almost always the same - that is why we can always see an object clearly and comfortably.

Conventional 3D displays try to mimic the natural viewing by creating images with varying binocular difference, which simulates vergence changes in the natural 3D landscape.
But the accommodative distance remains unchanged at the display distance, resulting in the so-called vergence-accommodation conflict that causes viewer discomfort.
"Conventional 3D displays usually deliver some views of the displayed spatial spot to a single eye pupil. That is why accommodative distance remains fixed on the display screen and cannot adjust simultaneously as vergence distance does, causing vergence-accommodation conflict," said Liu.
Researchers' solution is to project numerous 2D perspective views to viewpoints with intervals smaller than the pupil diametre of the eye. This means the device can deliver at least two different views to a single eye pupil.

The prototype system consists of 11 elementary projecting units. Each projecting unit is constructed by an organic light-emitting diode micro-display, a rectangular projecting lens, two vertical baffles and a group of gating apertures (liquid crystal panel) attached to the projecting lens.
To test viewers' reactions to the prototype system, eight subjects were asked to observe a displayed 3D image of an apple in the lab environment and no headache or discomfort was reported.
The findings were published in the journal Optics Express.