Natural stereo images from a glasses-free, 3D display

In general, glasses-free, 3D displays have a narrow viewing zone and tend only to be effective for a single viewer sitting in a specific position. Due to the unavoidable disadvantage of the constrained viewing region, an observer must adjust his or her head to see the images within the stereoscopic viewing range.

The purpose of our research was to create a more flexible and useful glasses-free, 3D display. In general, 3D displays use parallax-barrier or lenticular screen technology, in which optical sheets are arranged in front of, or behind the display panel.^{1, 2} To solve this problem, we have proposed a variable parallax-barrier system using eye-tracking algorithms.^{3, 4} There are two ways to display stereoscopic vision using eye tracking. The first method switches the right and left images to the appropriate side, according to the x-, y-, and z-coordinates of the observer, as detected by the eye tracking. The second method switches the parallax barriers according to the observer's position.

Our system accurately tracks the observer's eye position using a depth camera, even if the person is wearing glasses.⁵ A parallax barrier, composed of four sub-barriers, is used to implement the eye-tracking system.⁶ The coordinates of the viewer, as detected by the camera, are transferred to a 3D display via serial communication. The variable barrier, which is attached to an LCD, moves electrically according to the right-eye position of the 3D images.

Figure 1. Operating principle of moving parallax barrier panel: the barrier composed of lines 1, 2, 3, and 4 operates first (left); lines 3, 4, 5, and 6 operate when the observer moves to the right (right). ITO: Indium tin oxide. FPC: flexible printed circuit. COM1, COM2: serial communication ports

The variable parallax barrier has four sub-barriers, implemented using a new cross connecter comprised of a 640-line flexible printed circuit. Cross connecters are economical to manufacture and are compatible with all panels, simply by using anisotropic conductive film. The depth camera uses the time-of-flight theory to implement eye tracking.

With a variable parallax barrier, the barrier composed of lines 1, 2, 3, and 4 operates first (see Figure 1, left). When the observer moves to the right, lines 3, 4, 5, and 6 operate (see Figure 1, right), and they work as though the parallax barrier has been transferred. Similarly, the barrier works in the opposite way if the observer moves to the left. The parallax barrier moves to the correct position after establishing the location of the observer. This system achieves more natural stereoscopic images, according to the movement of the eyes, because the variable parallax barriers use a conventional parallax barrier divided into four sub-barriers, each using common twisted nematic panels.

Using the depth camera, we were able to sample the real-time facial outline and background for each observer and let the computer locate the exact position of the eyes. This made it possible to observe natural stereoscopic images through the formation of a parallax barrier that fits the position of the eyes.

According to our computer simulations, our variable parallax-barrier system compares favorably to conventional parallax barrier systems as a method of implementing 3D stereoscopic displays. However, we are planning to conduct further research into more precise methods for assessment because the observation of stereoscopic images has a subjective aspect.

This research was supported by Ministry of Knowledge (MKE), Korea, as the project, “The development of Active Sensing-based 3D HD Depth Camera” and Research Grant of KwangWoon University in 2009.