Optical: systems and elements – Projection screen
Reexamination Certificate
1999-04-08
2002-11-19
Mahoney, Christopher (Department: 2851)
Optical: systems and elements
Projection screen
C359S452000, C359S460000
Reexamination Certificate
active
06483643
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to viewing screens upon or through which images are projected, it being a general object of this invention to efficiently control and maximize light emission or “gain”, especially from large screen areas. More particularly, it is an object here to provide a variable gain viewing screen for either rear or front projection, and a screen that can be implemented without restriction to size and shape.
The basic prior art projection screen is a planar matte or flat-white surface onto which an image is projected with white light, and which requires a darkened area, room or auditorium, whereby the dark parts of the image are formed by the absence of light. And, the darker the room, the greater is the contrast. Since total darkness is difficult to obtain, particularly in theaters, the famous “silver screen” of Hollywood's heyday was devised in order to increase reflective “gain”, which increased light emission and contrast from the screen, thereby producing better black. However, as the ambient light increases in the theater, the screen image washes out.
The white or silver screen was then improved by adding minute glass beads to the reflective surface of the screen, which improved gain or light reflection efficiency by two to ten times that of a matte or flat-white screen. But unfortunately, the glass beads give the reflected image a “grainy” soft focus effect, the adhesive used to hold the beads oxidizes and yellows the screen, and the beads fall off of the screen, whereupon the gain deteriorates and the screen becomes more and more dependent upon room darkness.
An improvement over the “silver screen” is the “lenticular screen” having a vertically disposed corrugated reflective surface for the purpose of horizontally expanding the reflected “cone of light”, and silvered so as to improve image contrast when ambient light increases. The “gain” of lenticular screens is approximately two to four times that of a matte or flat-white screen. The lenticular screen produces a fairly good image even in a room with ambient light sufficient to wash out the image from a white or beaded screen, in spite of its lower gain factor which requires a higher wattage projector. However, the lenticular screen has several defects in addition to the requirement of higher projection wattage, there being visible vertical lines coextensive of the screen reducing image sharpness, and that the screen must be maintained substantially flat and cannot be overly bent and/or successfully rolled.
State of the art full color image projection recognizes that a flat white surface produces the sharpest image (definition), that a highly reflective surface efficiently returns reflected light (contrast), that a beaded effect expands the cone of reflected light (displaced observation), and that a lenticular effect expands the cone of reflected light in the horizontal plane for viewing from side to side of the theater but not so in the vertical plane (efficiency). Therefore, it is an object of the present invention to increase and control screen light emission or “gain”, to maximize focus as well as contrast for image and color definition and brightness, to provide a wide “cone effect” for horizontal as well as vertical displacement of observation, and to thereby obviate the deficiencies of prior art screens.
An object of this invention is to provide a basic high-gain viewing screen for image projection characterized by a thin film containing liquid crystal material having a light scattering function and applied as a layer on or encapsulated in a planar substrate of transparent material onto which a light image is focused and diffused therefrom in wide angled cones for front viewing rear image projection.
Another object of this invention is to provide a controllable high-gain screen for image projection characterized by a thin film containing liquid crystal material having a light scattering function in an electrically unenergized state so as to be opaque or translucent, and by a light transmitting function in an electrically energized state so as to be more or less translucent and/or transparent, and applied as a layer on or encapsulated in a planar substrate of transparent material onto which a light image is focused and diffused therethrough to emanate in wide angled cones for viewing rear image projection. In practice, “micro encapsulated” liquid crystal is employed, made as by encapsulating liquid crystal droplets within a thin polymer to form cells which are then introduced into a matrix having light scattering properties similar to Polymer Dispersal Liquid Crystal (PDLC) which is responsive to electric fields, or Encapsulated (ENCAP).
An object of this invention is to provide a basic high-gain front viewing screen for image projection and characterized by a thin film of liquid crystal material having a light scattering function and applied as a layer on or encapsulated in a planar substrate of transparent material onto which a light image is focused and refracted through a front side thereof, there being a light reflective surface contiguous to a back side of said substrate for forward reflection of the image diffused through and from the substrate in wide angled cones for front viewing of the projected image.
Another object of this invention is to provide a controllable high-gain front viewing screen for image projection and characterized by a thin film containing liquid crystal material having a light scattering function in an electrically unenergized state so as to be opaque or translucent, and by a light transmitting function in an electrically energized state so as to be more or less translucent and/or transparent, and applied as a layer on or encapsulated in a planar substrate of transparent material onto which a light image is focused and refracted through a front side thereof, there being a light reflective surface contiguous to a back side of said substrate for forward reflection of the image diffused by diffraction through and from the substrate in widened angles for front viewing. In practice, a PDLC material is employed and by means of its nematic director has light scattering properties responsive to electrical potential for controlling orientational order and diffusion by diffraction of light therethrough in widened angles for front viewing the projected image.
It is still another object of this invention to provide a high-gain Liquid Crystal Screen hereinafter referred to as an “LCS”, an image viewing screen characterized by a laminaform structure, preferably comprised of a polymer substrate including functional laminations/that implement the basic structure herein disclosed, and including the Liquid Crystal Screen (LCS) coating or lamina, transparent protective coatings or lamina, transparent electrically conductive coatings or lamina, reflective coatings or lamina, and adhesive coatings or lamina, all as may be required and as hereinafter described.
An object of this invention is to provide a unique projection screen material for use in both front and rear image projection, with high-gain image viewing, and controlled light scattering and contrast properties adjusted by film thickness, droplet size, and/or electrically to optimize viewing under ambient light conditions. In practice, the screen is a liquid crustal encapsulated in a clear substrate.
An object of this invention is to overcome the present size limitations that restrict construction of high-gain screens in theaters, by splicing and optically coupling sheet-screen segments into larger sized screens devoid of visible segment joinder, at normal viewing distances.
An object of this invention is to accomodate a plurality of image projectors electronic, video or film projectors, for projecting high resolution images on or through enlarged screens, for example large elongated theater screens. In carrying out this invention, the Liquid Crystal Screen (LCS) is segmentally zoned and each is electronically addressed to adjust light gain levels that correct the brightness factors of overlapping ima
Mahoney Christopher
Renner , Otto, Boisselle & Sklar, LLP
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