Glasses-free 3-D uses content-adaptive parallax barriers

May 5, 2011
HR3D Display

The HR3D display uses a dual-LCD display and determines the optimal set of front and rear LCD images by using Non-negative Matrix Factorization (NMF), thereby increasing resolution and brightness in the perceived images of the 3D content compared to parallax barriers (credit: MIT Media Lab, Camera Culture Group)

A fundamentally new approach to glasses-free 3-D, called HR3D, could double the battery life of devices like Nintendo’s 3DS portable gaming system without compromising screen brightness or resolution, researchers from MIT’s Media Lab have shown.

The 3DS relies on a century-old technology known as a parallax barrier. Like most 3-D technologies, this one requires two versions of the same image, one tailored to the left eye and one to the right. The two images are sliced into vertical segments and interleaved on a single surface.

By itself, the composite image looks like an incoherent jumble. But if you place a screen with vertical slits in it — the parallax barrier — just in front of the image and stand the right distance away, a 3-D image pops out.

The 3DS screen consists of two parallel liquid-crystal displays (LCDs) a small distance apart. When the device is operating in 3-D mode, the front display serves as the parallax barrier, depicting a series of opaque vertical stripes. Since the stripes block half the light coming from the screen, the device’s backlight has to be twice as bright, which drains the battery twice as quickly.

The MIT researchers decided to rethink glasses-free 3-D from the ground up. In the real world, as a viewer moves around an object, his or her perspective on it changes constantly. A convincing simulation of 3-D visual experience might require a display that offers a dozen different perspectives as the viewer moves from right to left, the researchers said.

But with parallax-barrier 3-D, each new perspective further restricts light emission. Adding multiple perspectives in the vertical direction as well as the horizontal would require a parallax barrier with horizontal as well as vertical bands. For a display with enough different views, the parallax barrier ends up looking like an opaque sheet with pinholes poked in it.

Like the 3DS, the MIT researchers’ HR3D system uses two layers of liquid-crystal displays. But instead of displaying vertical bands, as the 3DS does, or pinholes, as a multiperspective parallax-barrier system would, the top LCD displays a pattern customized to the image beneath it. They developed a parallax barrier that consists of thousands of tiny slits, whose orientations follow the contours of the objects in the image.

While the HR3D is very computationally intensive, the researchers say that it can be refined so that it would require far less computation and, using a specially designed chipset, would consume much less power than a general-purpose processor performing the same computations.

Their research was presented in a paper at last year’s SIGGRAPH Asia graphics conference.