Abstract:
A full color stereoscopic display having polarizers for color multiplexing and effecting three-dimensional full color viewing from a single direct view display. Color polarization of color images provides the basis for discriminating the different perspectives of three-dimensional images. Polarization may be linear or circular. The viewer may perceive three-dimensional images with merely the aid of polarized glasses.

Description:
BACKGROUND OF THE INVENTION 
     The present invention pertains to stereoscopic direct view color displays. More particularly, the invention pertains to color multiplexed stereoscopic direct view displays. 
     Numerous methods have been proposed for providing stereoscopic information with color display devices. One such method is disclosed in U.S. Pat. No. 4,995,718 which discloses a color multiplexing technique for projection displays. U.S. Pat. No. 4,995,718, by K. Jachimowicz et al., issued Feb. 26, 1991, is hereby incorporated by reference. Color channels are selectively polarized in Jachimowicz et al., prior to combination of the color channels via standard projection methods. 
     SUMMARY OF THE INVENTION 
     The present invention is a stereoscopic method that achieves channel separation of the various views by switchable colored filters, preferably involving colored polarizers. This enables channel separation to be done with nearly any kind of color display, including direct view devices such as shadow mask cathode-ray tubes, flat panel liquid crystal displays, and electroluminescent panels. The present invention also applies to unmodified color projection displays, since polarizing means need not be added to the image sources prior to combining the image sources, as referred to in the above noted patent. Present invention is an improvement over that disclosed in the related-art patent. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 shows the basic layout of a full-color stereoscopic display system. 
     FIG. 2 reveals the display system having two color polarizers. 
     FIG. 3 illustrates the display system having separate components for each perspective of the displayed image. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 reveals the basic layout of stereoscopic system 10. Image source 11, such as a cathode ray tube or liquid crystal display, provides a full color image. Image switches 12, 13 and 14 control the data from two separate data channels representing two perspectives, left and right, of the displayed image. Red image data for left and right perspectives is conveyed to switch 12. Green image data of left and right perspectives is presented to switch 13. Blue image data of left and right perspectives is presented to switch 14. Switches 12, 13 and 14 may select left or right perspectives of the respective image data. For instance, switch 12 and switch 14 at one moment receive data for the left perspective of the red and blue images, respectively. At the same time, switch 13 receives data from the right perspective of green image data. Switches 12, 13 and 14 synchronously switch perspectives, in accord with stereo switch 22. When switches 12 and 14 are receiving data of the right perspective from the red and blue images, switch 13 is receiving data of the left perspective of the green image. The data from the red, green and blue images are simultaneously presented to a display 11. Display 11 present one perspective of the blue and red images and the other perspective of the green image. Colored polarizers 15, 16 and 17 polarize each color bin of the green, red and blue images, respectively. The color bins, respectively, are green, red and blue. As noted, red and blue, i.e., magenta, data are from one stereoscopic channel and the green data is from the other. The image switches 12, 13 and 14, are toggled at the display&#39;s frame or field rate, depending upon such parameters as response time and interlace factor, if any. Colored polarizers 15, 16 and 17 are magenta, cyan and yellow for polarizing the green, red and blue color bands, respectively. The polarization axis of the magenta polarizer is orthogonal to the cyan and yellow polarizers. Polarizers 15, 16 and 17 may be circular instead of linear. In the circular case, the magenta polarizer has a direction different from that of the cyan and yellow polarizers (e.g., right circular versus left circular). The image from display 11 after passing through polarizers 15, 16 and 17, passes through a polarization rotator such as a variable retarder 18. Retarder 18 periodically rotates the polarization of each color band, red, green and blue, between two orthogonal polarization states, or changes the direction of the circular polarization. Retarder 18 may be a TEKTRONIX pi cell, a ferroelectric liquid crystal, a twisted nematic liquid crystal cell, an electro-optic ceramic (e.g., PLZT), or any other device or assembly which produces a effective differential retardation of one-half wave. In the case of linear polarizing, the axis of retarder 18 is normally situated at 45 degrees relative to the polarization axes of polarizers 15, 16 and 17. Neutral analyzer polarizers 19 and 20 select which color beams are to be seen by each of the viewer&#39;s eyes. Thus, the left and right eyes see the left and right perspectives of the image. Each of the perspectives alternate between the magenta (i.e., red and blue) and green images, bands or components. Retarder 18 is electronically switched in synchronism by stereo switch 22, with switches 12, 13 and 14 to provide the alternation of the green magenta images for the corresponding perspectives to each eye. The perception of flicker by the viewer is minimized without any increase in system bandwidth. This minimization holds particularly for non-saturated colors as, for instance, the luminance of the green and magenta components are comparable. The degree of flicker reduction is dependent upon the displayed data, display luminance, field and frame rate, ambient lighting, and other parameters. The present invention has only one (optical) source of images. Despite having only a sole source, the original spatial resolution of the display or screen as a non-interlaced device is preserved. Further, the screen is not split. Thus, in the case of a 60 hertz display, a 60 hertz time sequential presentation of images is possible. 
     Each of the polarizers 15, 16 and 17, ideally removes only a single polarization of its respective color band, thereby allowing all of the other light of the other color bands to pass unaffected. For example, magenta polarizer 15 removes half of the green light but does not affect the red or blue light. Likewise, cyan polarizer removes half of the red light but does not affect the green or blue light, and yellow polarizer 17 removes half of the blue light but does not affect the red or green light. Polarizers 15, 16 and 17 may be absorption mode polarizers. An example is a polarizer having a dichroic dye oriented by a stretched polymer or other means. Alternatively, cholesteric liquid crystal or cross-linked polymers may be used as polarizers 15, 16 and 17. The latter polarizers function as circular polarizers, wherein polarizer 15 may have a circular polarization direction opposite of that of polarizers 16 and 17. Polarizers 15, 16 and 17 may instead be thin film polarizers, prism polarizers or other types of polarizers. 
     Neutral analyzer polarizers 19 and 20, which are polarization optics, may be goggles or eyeglasses, similar to other kinds of available stereoscopic goggles or eye glasses. Analyzer polarizers 19 and 20 typically are separate from display 11, but as an option all elements can be separate from display 11. If polarizers 19 and 20 are preferred to be circular polarizers, and polarizers 15, 16 and 17 are linear polarizers, then a quarter wave retarder 21 may be inserted between polarizers 19 and 20, and pi cell 18. 
     To minimize cross talk between the left and right channels, color notch filters may be added to system 10 to minimize the overlap in the magenta and green signal output spectra. Residual cross talk between the left and right channels can be reduced further by electronic comparison of the two-channel data by taking into consideration the spectral overlap, switching speed, phosphor decay, non-ideal retarder or polarizer performance and other effects of concern, and applying appropriate compensation. Typically, complete compensation is possible in the mid tones; however, some ghosting may be detectable in areas of the image having very high contrast. 
     Alternate configurations of the invention exist. For instance, the polarized output of a flat panel liquid crystal display 11 may go directly into a pi cell 18. Then the image could be viewed through crossed magenta polarizer 15 and a green polarizer 23 which could be a combination of cyan and yellow polarizers 16 and 17, as illustrated in FIG. 2, with polarized displays such as liquid crystal displays. The green colored polarizer polarizes the red and blue light, and thus appears green. The colored polarizer pair for the left eye would pass the orthogonal polarizations states from those for the right eye. A configuration having only polarizers 15 and 23 for each eye piece would be evident. 
     There may be alternate arrangements, configurations, types and orders of the polarizers, waveplate and retarder. For example, the entire polarizer assembly may be in a self-contained goggle form. Also, there may be alternate color schemes. The color polarizers may be switchable, mechanically or electronically. There may be mechanical or electronic color filter wheels or other kinds of color filters. There may be switched polarizers such as dichroic liquid crystal devices (LCD&#39;s). There may be polarized displays such as LCD&#39;s or certain projection displays. All the elements of display system 10, between the observer and the display, may be incorporated in the observer&#39;s eyeglasses or goggles, for unpolarized displays, as illustrated in FIG. 3. Elements 15 and 23 for one eye are rotated 90 degrees relative to elements 15 and 23 for the other eye. 
     Tests using dichroic (i.e., absorbing) polarizers, a pi cell and a shadow mask color cathode-ray tube monitor, show a moderate amount of stereo separation between the left and right image channels. Improvements may be made with spectral matching polarizer purity (e.g., using cholesteric polarizers) and electronic compensation. 
     This invention provides color multiplexing that is compatible with unmodified direct view and projection displays, including consumer cathode ray tubes and computer monitors. The quality of the resulting stereoscopic images depends upon the display parameters and the degree of implementation of improvement techniques.