Optical: systems and elements – Projection screen – Unitary sheet comprising plural reflecting areas
Reexamination Certificate
2000-08-14
2003-06-03
Mahoney, Christopher (Department: 2851)
Optical: systems and elements
Projection screen
Unitary sheet comprising plural reflecting areas
C359S457000, C359S449000
Reexamination Certificate
active
06574041
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a projection screen and a projection system and method and, more particularly, to a front projection screen and a projection method providing horizontal diffusion and vertical direction of projected light to minimize the effects of ambient light.
Audio-visual presentations are important parts of trade shows and other exhibitions. Viewers at exhibit booths are likely to stand in an arc around the front of the exhibit, some distance from a front projection screen on which images are projected. An effective presentation requires a reflected image of high intensity and good contrast. In many exhibition venues light from overhead lighting impinges on the projection screen reducing the contrast or “washing out” the projected images. Directing the light of the reflected image in a relatively narrow vertical band increases the intensity in the region of the viewers' eyes. On the other hand, the arrangement of viewers requires that light be reflected over a substantial horizontal angle.
Generally, front projection screens are either reflective, light scattering, or refractive. The surface of light scattering screens scatters the incident light in all directions rather than reflecting it at a discrete angle. Light scattering projection screens provide a wide viewing angle both horizontally and vertically but the gain of the screen is low and images are visible only under dim lighting conditions. Refractive screens are coated with tiny glass balls and light projected at an angle to the screen is returned along the path of incidence. Refractive screens are particularly useful when the projector is positioned low relative to the screen because the light is returned along the path of incidence toward a seated audience. However, glass beaded screens can be delicate and can exhibit a granular appearance because the glass beads are of sufficient size to cause disturbing refraction involving individual picture elements. Further, the luminance provided by a refractive screen decreases substantially from the center to the edges both horizontally and vertically and the homogenous nature of the glass beads does not allow a focusing difference in the horizontal and vertical planes.
Reflective screens have surfaces exhibiting behavior governed primarily by the law of reflection; that is, the angle of incidence of light equals the angle of reflection. This type of screen provides greater gain than is available with light scattering screens and, therefore, better visibility in areas of more intense ambient light. However, the viewing angle of a planar reflective screen is narrower than that of a diffusing screen so the viewer can clearly see images only within a limited arc in front of the screen. Reflective screens commonly have a surface combining reflection and limited diffusion. Light is reflected from this type of surface in a solid angle along the nominal angle of reflection.
The physical arrangement of the projector and screen can be problematic when using front projection in an exhibit. Front projectors are seldom placed normal to the screen because the projector would obstruct the field of view of the audience. A front projector is typically located above the heads of the audience and a reflective screen is used to redirect the light to the eyes of the viewers. However, mounting the projector overhead is often not practical in a trade show or exhibit booth. Positioning the projector low relative to the screen reduces obstruction to viewing the screen, but a screen that reflects the image upward to the eyes of the audience is particularly vulnerable to glare and wash out from overhead lighting.
A front projection screen comprising multiple reflective screen elements arranged in vertical columns is disclosed in Malifaud et al., U.S. Pat. No. 5,696,625. The screen elements have either a toroidal or a cylindrical reflective surface. The curvatures of the reflective surfaces of the individual screen elements can be varied to directionally focus an image. However, focusing the reflected light by altering the curvature of individual screen elements results in a complex screen assembly. Further, the screen is adapted for use in a darkened theater setting with a projector mounted above the screen.
What is desired, therefore, is a front projection screen that provides for directional focusing of an image, protection from glare and wash out by overhead lighting, and permits the projector to be positioned near the bottom of the screen out of the line of sight of viewers.
BRIEF SUMMARY OF THE INVENTION
The present invention overcomes the aforementioned drawbacks of the prior art by providing a projection screen for reflecting an image from a projector to a viewer comprising a screen defining a horizontal direction and a vertical direction and having a top and a bottom. A plurality of substantially horizontal reflective row segments are disposed on the surface, each row segment having a surface for distributing and/or diffusing light over a wide horizontal area and each row segment defining a respective angle of inclination with respect to the vertical direction, wherein the respective angle of inclination of each row segment varies from the top of the screen to the bottom of the screen. The respective angle of inclination is greater at the top of the screen than the respective angle of inclination at the bottom of the screen, so that the screen reflects light from a projector located below the center of the screen toward a viewer while directing ambient light originating from above the center of the screen away from the viewer. The respective surfaces of the horizontal row segments distribute the projected image over a large angle in the horizontal direction to make the image viewable to an audience arrayed in front of the screen. On the other hand, the varying vertical inclination of the row segments facilitates directing the image in a relatively narrow vision band in the vicinity of the viewers' eyes.
The novel screen makes possible a unique system and method of projecting an image comprising locating a projector below a sight line of a viewer of the image, projecting the image on a projection screen, and reflecting the image at an angle varying from the bottom of the screen to the top of the screen. The screen is designed to maximize the amount of light reflected from a projector located below the lines of sight of the audience, and to minimize the reflection of ambient light. In general, the sources of ambient light in a viewing area, such as at a trade show or in a conference room, are located toward the side of the screen (for example from windows) or above the screen (for example from overhead lighting). The screen directs the ambient light away from the viewer, thereby maximizing image contrast. The screen of the present invention thus provides high contrast viewing even in bright ambient lighting conditions.
The foregoing and other objectives, features and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the accompanying drawings.
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Chernoff Vilhauer McClung & Stenzel LLP
CID, Inc.
Cruz Magda
Mahoney Christopher
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