Television – Video display – Projection device
Reexamination Certificate
1999-07-27
2002-07-02
Lee, Michael H. (Department: 2614)
Television
Video display
Projection device
C359S459000, C359S443000
Reexamination Certificate
active
06414727
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to laser projection video screen systems and methods employing a pulsed laser source and holographic projection screens.
BACKGROUND OF THE INVENTION
It has been difficult to project viewable images onto any conventional front projection screen by video projection devices powered by incandescent light sources such as CRT projectors or LCD/light valve projectors with xenon/metal halide lamps under extremely high ambient lighting conditions (outdoors in daytime, for example).
There are two problems. First, a traditional, white, front projection screen returns projected light in a random manner and is referred to as a Lambertian Scatterer with the brightness of the image appearing the same, regardless of the viewer location. This white front projection screen is typically used as a reference point, so that if a screen is able to return a projected image in a more spatially selective manner, then the screen appears brighter and is said to have “again”. The typical white front projection screen is considered to have a gain of 1; whereas, a front projection screen having more sophisticated structures that are designed to limit the returning projected image light to a specified range of horizontal and vertical direction by use of glass beads or other materials with known scattering angles is considered to have a higher gain. The gain of the screen may be a critical component to reproduce the projected image with enough contrast. When the traditional front projection screen is used in bright ambient light conditions, it will reflect back not only the projected images, but also a large portion of undesirable bright ambient light toward the direction of the viewer; therefore, high picture contrast cannot be attained.
A second problem is that the conventional video projection device is powered by an incandescent light source. Since the incandescent light source produces incoherent light rays, they have more chance of being dispersed by random scattering as they travel through the air from the projection device to the screen. The longer the projection throw distance is, the more image dispersion they suffer.
Laser video projection systems with projection screen surfaces are described in U.S. Pat. No. 4,720,747, issued Jan. 19, 1988; U.S. Pat. No. 4,851,918, issued Jul. 25, 1989; U.S. Pat. No. 5,253,073, issued Oct. 12, 1993; and U.S. Pat. No. 5,311,321, issued May 10, 1994, all hereby incorporated by reference.
It is desirable to provide an improved video projection screen, system and method to minimize image dispersion between the projector and screen and to provide screen designs which reflect back the projected image in the viewer direction.
SUMMARY OF THE INVENTION
The invention relates to a holographic projection screen and to laser video projection systems and methods employing the holographic screens.
The laser video projection system of the invention comprises a video projection device employing, for example, red (R), green (G) and blue (B) monochromatic laser light sources to form a projected full color video image, and which system includes a projection screen with a holographic pattern on the screen surface which reflects back the projected image in a selected direction, and transmits the majority of ambient light through the screen to provide a high video picture contrast on the screen.
The method comprises projecting a laser video image, typically employing R,G and B pulsed lasers to provide a full color video image onto a projection screen with a selected holographic design, in one or multiple layers on the screen surface to reflect back substantially the full color image to a viewer and to transmit the majority of ambient light through the projection screen.
A viewable projected image onto the screen is achieved by front projection format under high ambient light conditions by:
a) a video projection device powered by coherent/laser light sources (R,G,B) to minimize the image dispersion between the projector and the screen; and
b) a special front projection screen design which only reflects back the projected image to the direction of the viewers, and not to the surrounding areas where no viewer will be (highly directional design), and transmits the majority of the ambient light through the screen so that high picture contrast can be achieved.
This invention embodies two different front projection screen designs incorporating holographic patterns which can be used beneficially with video projection devices powered by laser light sources (R,G,B).
Because a full color video projection device powered by laser light sources (R,G,B) produces specific monochromatic wavelengths of red, green and blue light, it is ideal to construct reflective viewing screens with holographic patterns that will reflect back only those wavelengths of red, green and blue used in the laser video projection device.
The first design is a diffusely-reflecting holographic screen with exceptionally high gain (i.e., well defined viewing cone) which will be best suited for uses under high ambient light conditions. This screen design reflects only the specific monochromatic wavelengths of red, green and blue used in the laser video projection device, therefore, it will not be optically usable with other conventional video projection devices powered by incandescent light sources.
Because the holographic patterns constructed on the screen surface only reflect the specific monochromatic wavelengths of red, green and blue back to the viewers, all other wavelengths from the ambient light will pass through the screen. This will help to increase image contrast and thus make the image much easier to view under high ambient light conditions.
The high transmission of visible wavelengths, except for the specific monochromatic ones generated by the laser video projection device, means that the screen could offer considerable “see-through” features for blending the projected images with real background scenes behind the screen.
Holographic pattern is constructed to direct incoming specific monochromatic light from the laser video projection device into predetermined horizontal and vertical energy distribution zones, thus, this screen produces very bright images by virtue of shaping most of the projected R,G,B laser image light into very well defined, narrow viewing cones.
The method used in the recording of the holographic patterns ensures that there is maximum of diffraction at the specific monochromatic wavelengths from the laser video projection device, so that high reflection of those wavelengths towards the viewer or other direction is achieved.
Mass production of this screen is available once a printing process has been established for this type of hologram. This technique literally uses a modified optical contact printing process to bring the hologram onto thin layers of photopolymerizable plastic materials (typically less than 0.0002″ thick) supported on polycarbonate or polyester film. The holographic pattern is transferred at high speed onto the film, and the completed screen itself ends up on a roll from which the user can cut a piece to the unit size (typically 40″ wide by 80″ high). When a larger screen is required, it can be constructed by tiling smaller hologram units with nearly invisible seams. The hologram may consist of a single diffracting layer or a sandwich of two or three such layers, each optimized for separated wavelength regions.
In another embodiment a second design is a multi-layered holographic screen comprised of a diffusely-reflecting layer, as discussed above, plus an additional layer with diffracting holographic patterns which direct the reflected R,G,B laser images by the diffusely-reflecting layer into pre-determined selected “left” and “right” viewing zones.
Two video projection devices powered by R,G,B laser light sources receive stereoscopic video input signals derived from two displaced cameras. The resulting “left” and “right” images are front projected onto the multi-layer holographic screen described herein.
Alternative
Corporation for Laser Optics Research
Lee Michael H.
Ropes & Gray
LandOfFree
Video projection holographic screen, system and method does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Video projection holographic screen, system and method, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Video projection holographic screen, system and method will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2908239