WO2004051364A2

WO2004051364A2 - A projection screen for front projection

Info

Publication number: WO2004051364A2
Application number: PCT/ZA2003/000164
Authority: WO
Inventors: Patrick Normand Argall
Original assignee: Patrick Normand Argall
Priority date: 2002-11-05
Filing date: 2003-11-05
Publication date: 2004-06-17
Also published as: AU2003302535A1; WO2004051364A3

Abstract

A front projection screen, which produces a realistic color temperature correct image with depth of field; whilst masking the pixilation produced by the projector; to produce a smooth realistic high quality image. In a preferred form of the invention, the projection screen for front projection which forms the subject of this invention comprises a rigid substrate on which is provided a reflective, mirrored surface (12). Adjacent to this surface is a transparent layer (13); alternatively a laminated or cast transparent layer is applied to the reflective surface. Adjacent to this surface is a translucent layer (14), alternatively a laminated translucent film is applied to the transparent surface, and other layers may clearly be added to the composition of the screen and or elements embodied within the various layers to correct the colour or image or affect its optical properties or to facilitate manufacture.

Description

TITLE OF THE INVENTION

A Projection Screen for front projection

FIELD OF THE INVENTION

This invention relates to a projection screen, onto which an image is projected from the same side as that from which it is viewed.

BACKGROUND TO THE INVENTION

Problems which exist with front projection screens in general are that the projected image is very poor, lifeless, dull and not colour correct; this becomes incredibly apparent when compared to a TV monitor, especially under high ambient light conditions. When you add gain (increasing the reflective properties of the screen i.e. reflecting more light; a brighter image) the effective field of view of the screen material is reduced (the viewing area in which the full brightness of the screen may be enjoyed) LCD (Liquid Crystal Display) projection devices use pixels (small rectangles into which the picture is broken down to control the light which when combined produce the full image) the gap between them, results in a black grid being projected onto the screen, which breaks the image.

The following specific problems need to also be addressed.

1 ) Lustre and Realism (lifelikeness): The image has no lustre or depth as would be experienced in reality, but appears lifeless and flat.

2) Colour: The colours are shades of grey and differentiating between blood samples for example is impossible as they all appear to be the same shade of red.

3) Contrast: This also requires special attention in all but a totally dark theatre.

4) Hot spotting: Where the image is brighter in a spot in the centre this becomes progressively worse as the gain (reflective properties) increases.

4) Surface uniformity: Ripples, Creases and the like have to be prevented (the screen material is not flat or of uniform curvature, but creased or wrinkled).

5) Brightness: There is also the problem of utilising all of the limited light emitted by the projector. OBJECT OF THE INVENTION

These shortcomings led me to investigate and develop a new method of producing an image and retro reflecting (reflecting the light back at the audience) the light in a controlled fashion, whilst masking the LCD projected grid (Liquid Crystal Display, forms a black grid in the screen, where no light is projected between the pixels).

In the process a wide field of view, a smooth image with high gain was achieved. Thus, combining the properties of both existing screen types; namely lambertian (a diffuse material whogs brightness appears uniform from any viewing angle) and high gain screens (screen material which focuses the reflected light back at the source), with the advantage of smoothing the image by hiding the LCD grid.

The following specific problems were addressed.

1 ) Lustre and Realism (lifelikeness): The image has a natural metallic lustre and depth as would be experienced in reality.

2) Colour: The colours are temperature correct; it is now possible to differentiate between shades if grey and shades of colours.

3) Contrast: vastly improved even in high ambient light (the level of light present in the projection/viewing environment).

4) Hot spotting: (the reduced brightness / reflected lights drop off as the angle of incidence decreases towards the outer edges) this is not noticeable.

4) Surface uniformity: The screen material is flat or of uniform curvature, thus Ripples, Creases and the like have been prevented.

5) Brightness: The entire screen surface is utilised to convert all of the limited light emitted by the projector in to a uniform, bright and lifelike image. SUMMARY OF THE INVENTION

According to the invention there is provided a projection screen for front projection with a focal error (the screen produces an image slightly out of focus to reduce the resolution in order to mask the pixilation and produce a smooth realistic image) comprising:

A layer of translucent material;

A layer of transparent material;

A reflective surface;

The layer of transparent material may be between the layer of translucent material and the reflective surface

There is however the possibility of introducing a protective and or anti glare coating on the opposite side of the layer of translucent material to the transparent layer

Typically the reflective surface is metallic, the transparent layer is glass and the translucent layer is a urethane.

Alternatively the reflective surface may be achieved by a metallised film, reflective paint, metal plated, reduced metal oxide or vapour deposited on to the surface, the transparent layer may be provided by applying a transparent film, such as urethane or acrylic to the reflective surface, the translucent layer may be provided by applying a translucent layer, such as film to the reflective surface or matting a film of silicon oxide, chemically or by abrading the surface.

Preferably, the front projection screen comprises a flexible substrate in the case of a roll up screen or a rigid substrate in the case of a rigid screen, onto which the reflective surface is applied and the transparent layer is provided on the opposite side of the reflective surface to the substrate, the translucent layer is provided on the opposite side of the transparent layer to the reflective surface. Various embodiments of the invention are described in detail in the following passages of the specification which refer to the accompanying drawing. The drawing however is merely illustrative of how the invention might be put into effect, so that the specific form and arrangement of the features shown is not to be understood as limiting on the invention.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING

The accompanying drawing is a diagrammatic cross-sectional view through a flat front projection screen according to the invention.

DETAILED DESCRIPTION OF AN EMBODIMENT

Referring to the accompanying drawing, the projection screen for front projection which forms the subject of this invention comprises a rigid substrate on which is provided a reflective, mirrored surface 12.

Adjacent to this surface is a transparent layer 13; alternatively a laminated or cast transparent layer is applied to the reflective surface.

Adjacent to this surface is a translucent layer 14, alternatively a laminated translucent film is applied to the transparent surface, and other layers may clearly be added to the composition of the screen and or elements embodied within the various layers to correct the colour or image or affect its optical properties or to facilitate manufacture.

The translucent surface is achieved by spraying a uniform layer of urethane developed for this purpose on to the transparent surface. Alternatively, the translucency may be achieved by roughening, or abrading the surface of a transparent layer or by laminating or electrostatically applying a translucent film to the surface of the transparent layer.

It may be of varying thickness and varying degrees of translucency and may have properties to enhance or reduce various colour spectra within the visible spectrum of light. The reflective, mirrored surface may be provided with silvering, as in a common mirror, or a metallised plastic film. As with the translucent and transparent layer this surface may include various properties to either enhance or reduce various colour spectra within the visible spectrum of light.

The accompanying drawing depicts an embodiment of the invention in which the projection screen is flat. It will nevertheless be appreciated that the screen may be curved in one or more planes

One method of manufacturing a projection screen according to the invention is to produce a rigid glass reinforced plastic substrate of determined two plane curvature and texture, to mirror the concave surface. Thereafter a transparent urethane of controlled thickness is spray applied to the mirrored surface Thereafter a translucent urethane is spray applied to the transparent surface.

Claims

A Front Projection Screen, whish produces a superior realistic color temperature correct image with depth of field; whilst masking the pixilation produced by the projector. A projection screen according to claim 1 where the transparent layergs (13) presence and thickness controls the focus to mask the pixilation.

A projection screen according to claim 1 where the transparent layout may be solid, hollow, rigid or flexible. A projection screen according to claim 1 in a rollup or rigid form.

A projection screen according to claim 1 which produces a cathode ray tube (TV) quality image in high or low ambient light. A projection screen according to claim 1 in which the intended gain can be controlled during manufacture. A projection screen according to claim 1 where the image has a natural metallic lustre and depth (lifelikeness) as would be experienced in reality. A projection screen according to claim 1 where the contrast is sufficiently high such that it is possible to differentiate between shades of grey and shades of colours. A projection screen according to claim 1 where hot spotting (the reduced brightness / reflected lights drop off as the angle of incidence decreases towards the outer edges) is not detectable.

A projection screen according to claim 1 where the screen material is flat or of uniform curvature thus preventing ripples, creases and the like. A projection screen according to claim 1 where the entire screen surface is utilised to convert all of the light emitted by the projector in to a uniform, bright and lifelike image.