Many types of scientific images and data are complex and are easier to interpret when observed in three dimensions. This is especially true for information presented visually in the form of multiparameter graphs and tables, as well as for images of physical events, such as turbulent flows. Furthermore, the appearance of depth in stereoscopic displays adds greatly to the understanding and analysis of scientific imagery, especially of physical events. This is, of course, true for other images as well — wherever rendition of depth is important — for example, in mechanical engineering, architecture, medicine, and other fields of endeavor.

Dimension Technologies Inc. (DTI) has developed and patented a unique method for generating three-dimensional images by use of stereo pairs. Much of this work has been done under contracts from NASA and other federal agencies. The project described here was successfully carried out in close cooperation with NASA Ames Research Center under a Small Business Innovation Research (SBIR) contract. The results of this work have been commercialized, and an innovative autosteroscopic display, the Virtual Window™, was introduced.

Unlike other stereoscopic displays, this unit generates vivid, full-color three-dimensional images that can be viewed without the need to wear special eyeglasses. This feature makes the use of the autosteroscopic displays very convenient and is particularly important in commercial applications.

The principle of autostereoscopic image presentation is frequently used in three-dimensional postcards and large advertising displays that are intended to enable the observer to perceive depth by looking at a two-dimensional picture. A stereo pair (i.e., a pair of images corresponding, respectively, to the views through the left and right eyes) are interlaced in alternate columns in a two-dimensional image. A special optical device, called the "lenticular lens," is placed in front of the interlaced image or, in the case of a postcard, bonded directly to the front surface. The lenticular lens is an array of very narrow vertical cylindrical lenslets spaced to correspond to the columns of the interlaced stereo pair. In this manner, the appropriate images of the stereo pair are directed to the proper eyes thus generating a three-dimensional image.

As illustrated in (a) and (b) of the figure, DTI has applied the same principle to its autostereoscopic displays, which contain liquid-crystal displays (LCDs) that are viewed by observers. To generate three-dimensional images, the LCD presents left and right halves of a stereo pair on alternate columns of pixels at a rate of 60 frames per second. The left image appears on the odd columns and the right image appears on the even columns. If the LCD in use has 1,024 columns and 768 rows of pixels, each complete stereoscopic image consists of 512 columns and 768 rows.

Both halves of a stereo pair are displayed simultaneously and directed to the corresponding eyes. This is accomplished with a special illumination plate located behind the LCD and employing a lenticular lens of the type mentioned above. Using light from compact, intense light sources, the illumination plate optically generates a lattice of very thin, very bright, uniformly spaced vertical light lines. The lines are precisely spaced with respect to pixel columns of the LCD, and, because of the parallax inherent in binocular vision, the left eye sees all of these lines through the odd columns of the LCD, while the right eye sees them through the even columns, thus enabling the observer to perceive the image in three dimensions. This arrangement, exclusive to DTI, is called "parallax illumination."

Some of the Principles behind these autostereoscopic displays involve (a) LCD and the illumination plate, (b) geometric relationship between the light line and the LCD pixel, and (c) the viewing zones in front of the display where the observer perceives three-dimensional images.

There is a fixed relation between (1) the distance between the LCD and the illumination plate and (2) the distance between the observer's face and the LCD screen (the viewing distance) that in part determines the dimensions and positions of the "viewing zones," which are depicted in (c) of the figure. These viewing zones are the regions in front of the display where the observer can perceive three-dimensional images.