Science and Visualization

Stereo Viewing for Scientific Visualization

Adel Hanna

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The two eyes on a human head see slightly different views of the world due to their different locations on the head. Because of this difference, corresponding areas of the retinas do not always receive exactly the same visual image. Through the ages, people have wondered why we do not see a double image of the visual world.

Wheatstone's stereoscope: the viewer places his or her nose where the mirrors L and R join, and the eyes see images at L1 and L2.

In 280 AD, Euclid showed that two eyes see more of a sphere than either eye individually. But it was Sir Charles Wheatstone who demonstrated in 1838 that the mind fuses the two retina images to produce stereopsis, 3-D depth perception, by presenting slightly different images to the two eyes with a device he called a stereoscope. A stereoscope display is an optical system that functions by presenting the mind with the same kind of left and right views one sees in the visual world. In 1939, View-Master stereoscopes became available and gained wide use. If you close one eye while looking into a View-Master viewer, the image looks flat; with both eyes open, you see an image with stereoscopic depth.

A View-Master stereoscope.

Stereo viewing in scientific visualization enhances the comprehension and understandability of the information conveyed in three-dimensional data; it harnesses the power of the human perception vision as a means of gaining understanding and insight into the data. By presenting three-dimensional data in stereo mode, it is possible to create strong depth impressions from pictures by sending to each eye separately the projective drawing that the eye would see if an actual object in depth were presented. Among the areas which are using stereo are medical science (radiology), molecular modeling for chemistry and biology, computational fluid dynamics, cartography, archaeological reconstruction, and oceanography.

To view stereoscopic images on a computer screen, each eye must see only its appropriate image. The most common way to do this is to alternately draw each image on the screen and to use special eyewear that alternately blocks the vision of each eye synchronously with the display of the images. The ACF Scientific Visualization Laboratory {http://www.nyu.edu/pages/scivis/} Replacement URL: http://www.nyu.edu/its/scivis/, has made available CrystalEyes from StereoGraphics Corporation {www.stereographics.com} Replacement URL: http://www.reald-corporate.com/). CrystalEyes consists of a pair of synchronizing goggles that are driven by an infrared emitter box connected to a special port on the workstations. A stereo synchronization signal is sent from the graphics display system to the emitter box, which sends an infrared signal to the stereo goggles. This signal tells the goggles when the image for the left or right eye is being displayed, so that the stereo goggles can synchronize the opacity of the lens for each eye with the display. The left image on the screen is shown while the right lens of the goggles is made opaque. The opposite behavior occurs respectively with the right image and left lens.

In a binocular system, each eye sees a view with a slightly different perspective.

The display is redrawn at a high rate, so the user perceives the left and right images simultaneously. Common rate is 120 fields per second, depending on the stereo display method used. In full-screen stereo viewing, the screen is divided into left and right pixel lines. When the monitor is put in stereo mode, half of the screen's vertical resolution and the full horizontal resolution is used for each view, that is, 1280 lines wide by 492 lines high.

An alternative technique for viewing stereoscopic images is to use the VREX 3-D LCD projector display technology from VRex, Inc. (www.vrex.com). The VRex system, which is also available at the Scientific Visualization Laboratory, uses spatially multiplexed imaging. Spatial frame buffers in the 3-D LCD panel essentially keep both left and right images on the display simultaneously for optical multiplexing by Pol (encoding left and right views using orthogonal polarization) and optical de-multiplexing by passive, polarized glasses. This technique can be more cost effective because the glasses run cheaper than CrystalEyes for applications in which many people view one display, such as a presentation to a large group.

How CrystalEyes works: An emitter sitting on top of the monitor broadcasts an infared signal to the goggles. The eyewear uses this signal to synchronize its shutters to the video field rate.

Now scientists are beginning to recognize that stereoscopic visualization of scientific data greatly facilitates their efforts to gain support for research and to help them get needed funding. Presenting their work in 3-D stereo in a way that clearly conveys the meaning of the data not only helps explain the researcher's idea, but also casts a glow of both credibility and capability.

For access to the Stereoscopic Displays at ACF, or for more information on using these resources, contact the author at {adel.hanna@nyu.edu}.