Projection screen

#The present invention relates to projection screens and more particularly to projection screens having a surface which compensates for projected variations in light intensity levels which are imperceptible to the human observer but are detectable by video reproduction of an image on the screen. The invention also relates to a method for making such projection screens, as well as methods of projecting an image onto such screens.

#The projection of slide images on screens is well known. A common problem with such slide projection is that the image projected on the screens tends to be brightest at the center of the screen and dimmest on the edges.

#This phenomena is caused by the geometry and optics of conventional slide projectors in that the projector light source projects outward with a beam of light which is in the shape of a sector of a sphere. Since the screen intersects this sphere sector of light with a flat plane, the center of the screen is closer to the light source than the edges. This results in the brightest image portion at the center, with decreasing brightness radially outward therefrom. This phenomena is sometimes termed the "halo" effect.

#FIG. 1 is a schematic view depicting an arrangement for videotaping a slide projected on a projection screen constructed in accordance with preferred embodiments of the present invention;

#FIG. 2 is a schematic front view of a projection screen, depicting varying light intensity distribution patterns resulting when a slide is projected thereon by a conventional slide projector;

#FIG. 3 is a graph showing the relationship between the brightness of light distributed on the surface of a projection screen from a slide projector as a function of the distance from the center point of the projection screen, as well as corresponding light reflectance characteristics of a projection screen constructed in accordance with preferred embodiments of the present invention;

#FIG. 1 schematically depicts an arrangement for videotaping and filming of slides projected on a projection screen so that they can be shown on video TV displaying devices and the like. The slide projection screen 1 is mounted on a support 2 and is spaced a distance D from a slide projector 3 which projects slides onto the surface of the screen 1 via projector lens 4 and light source 5 in the slide projector. The slide projector 3 can be mounted on a suitable slide projector stand 6. For videotaping the slides, a video camera 7 is disposed at a position behind and aligned with the slide projector 3 so that it views the slide projection screen 1 in an ideal centrally located position. The camera 7 is preferably mounted on a camera tripod or support 8. The overall arrangement depicted in FIG. 1 is generally known. The preferred embodiments of the present invention relate to the projection screen design for the projection screen 1 so as to improve the fidelity of the videotaped and filmed images that result.

#FIG. 2 schematically depicts the front fact of the screen 1 with the distribution of light intensity over the surface of the screen, starting with maximum light intensity at the center C and diminishing light intensity as one goes radially outward along the radius R. In FIG. 2, the circles of light intensity are shown in dash lines outside of the edges of the screen. It should be understood from A. Since the light source 5 as focused and projected via the lens 4 of the slide projector 3 is an effective point source of light directed in the direction toward the projection screen 1, the light intensity is strongest at the center of the screen and decreases radially in the outward direction of the radius R to minimum values at the corners and edges of the screen 1.

#The film or video camera 7 effectively views and records the image on the screen 1, including the varying light intensity discussed above which results from the geometry of the slide projection onto the flat screen. Thus, the video images include a so called halo effect which includes this light intensity variation, thus affecting the quality of the video image when these are again viewed by human observers.