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Illumination & Displays

Polarizer slit enables full-screen high-resolution dual-view display

The parallax barriers normally used to send different images to different viewers can cut image resolution in half, but a new technique gets around this problem.
23 May 2006, SPIE Newsroom. DOI: 10.1117/2.1200603.0185

With Sharp Corporation, we have developed a liquid crystal display (LCD) that can simultaneously show different images to the right and left view zones.1,2 The display allows visual content to be tailored to each user: for example, one user can view the display as a computer screen while another user watches a video.

This kind of two-way display needs an image separator—such as a parallax barrier—that must meet demanding requirements such as being thin, flat, and placed the appropriate distance from the image screen. However, as is shown in Figure 1, such a barrier cuts the resolution in half: pixels seen in the images for the right and left users are, respectively, only those in the columns marked R and L through the slit aperture. The purpose of our research was to solve this problem.

Figure 1. In a conventional dual-view display, half the pixels are seen by one viewer and half by the other, thus cutting the image resolution in half.

Our solution involves the projection of two polarized images in orthogonal directions: e.g., ±45° for linear polarization. LCD projectors already contain polarizers as part of their structure: see Figure 2. Using a piece of half-wave plate (whose function is shown in Figure 6) on each projector allows polarization angles to be adjusted so that the two projected images have vertical and horizontal orientation.

Figure 2. Liquid crystal displays use polarizers as the first and last stages of amplitude modulation: in the example shown, light will only emerge where the liquid crystal has rotated its polarization from the initially-set vertical state.

Figure 3 shows our polarization-based dual-view display. This system is composed of two projectors, a polarizer slit barrier (striped polarizer), a striped half-wave plate, and a diffusion screen. The two projectors project their different polarized images for each user onto the diffusion screen. In Figure 3(a) and (b), the left and right images are shown projected onto the odd and even (and even and odd) columns respectively. A half-wave plate is attached to the even columns on the diffusion screen, rotating the polarization of the incoming light.

Figure 3. All pixels in both images can be routed to the appropriate viewers using the new display.

Each observer views separate images by looking through a slit aperture that is a vertical polarizer. The polarization direction of the left images is rotated by the half wave plate, and the striped left and right images are oriented horizontally. Consequently, if light goes through the horizontal polarizer, then the vertically-oriented polarizer will block it: otherwise it will go through. Likewise for the opposite polarizer pair. So, depending on the initial polarization of the light (which depends on which image it comes from) and it's path (which polarizers it goes through), the combined images can be split out again for the for the different viewers.

Figure 4 shows how each of the observers perceives both horizontally- and vertically-polarized images elements from the dual-view system. The display is therefore twice the resolution of a conventional parallax-barrier device. In addition, it does not have the main disadvantage of images with divided unidirectional resolution: the observers can see full-area images without black stripes (see Figure 4).

Figure 4. Full-screen high-resolution images can be viewed using polarizer slits.

This display system can also provide different images to another user sitting across a table as shown in Figure 5. When the first user sits down opposite the second, each must view a different version of the image so as not to see it upside down. The display image consists of both text areas and regions of graphics (figures or pictures). The graphics can be seen as identical on both sides of the table, so that image features can be pointed at, but the text is automatically rotated inside the text area boxes according to the viewer's position (see Figure 6). Each user can therefore read all notes associated with the figure.

Figure 5. The desktop dual-view display combines and then separates two full-resolution images for two different viewers.

Figure 6. By providing an upside-down view of the text for viewers on opposite sides of the table, both can see and point to an identically-oriented image while having all notes readable.

The described desktop dual-view display uses polarizer slits to enable two observers to view full-screen high-resolution images. Thus, the system overcomes one of the major problem of conventional parallax barriers: split resolution.

Kunio Sakamoto
Interdisciplinary Faculty of Science and Engineering, Shimane University
Matsue, Shimane
Kunio Sakamoto is an associate professor at the Department of Mathematics and Computer Science of Shimane University. He is working on the spatial imaging, 3D display systems, and interaction systems.