OPTICAL DISPLAYS

Abstract: An optical device to simulate three-dimensional display, primarily for use in advertising, comprises an assembly to be illuminated by a light box (1) provided with a diffuser screen (3). The assembly comprises a pair of photographic transparencies (5 and 6) carrying reduced - density images (5A, 6A) spaced apart by approximately 1 millimeter by means of a spacer sheet (8). The rear transparency (6) is bonded to a backing sheet (9) and a front sheet (7) protects the front transparency (6). The assembly may be illuminated by ambient light, in which case a reflector is provided behind the backing sheet and the spacer sheet is slightly opalescent.

Description: OPTICAL DISPLAYS This invention relates to optical displays of the kind intended primarily to be viewed by rear illumination. In such optical displays, which may be photographic, drawn, painted, printed and/or etched, and as opposed to those wherein an image is formed by optical projection, the image to be viewed is, for example, an enlarged trans¬ parency of a photographic print or transparency illus¬ trating the original subject. Attempts have hitherto been made to produce the effect of a stereoscopic or three- dimensional image by overlying a plurality of transparen¬ cies, each .carrying a part image of a complete object or scene to be viewed stereoscopically. However, ' techniques hitherto utilised in the preparation of such an image have been expensive and/or not fully successful in achieving a realistic three-dimensional or stereoscopic illusion. It is, accordingly, an object of the present invention to provide an improved display arrangement of relatively simple form and which gives a realistic three-dimensional impression. In accordance with the present invention a composite image is formed by superimposing two images each carrying the subject to be depicted stereoscopically, the optical density of each image being of the order of 50% and 70% of the density that would, for a given illumination, be required of a single image intended to provide an accept¬ able two-dimensional viewable image of a subject with the same pictorial content, the two said images being in vir¬ tual contact or being spaced apart by a distance of up to the order of 2 millimeters. The optimum said distance may range from virtual contact between, for example, photographic transparencies where even the images on the emulsion layers have thickness to 2 millimeters and, probably ideally, approximately 1 milli- meter, but 2 millimeters may be exceeded in exceptional cases such as in large-size hoardings. Preferably, the optical density of each image is about 50% τr> 70% of the total density of a single image intended to display the same pictorial content, or differential percentages such as 40% front and 60% back may be employed; the quoted range of 50% to 70% may be exceeded in cases of extreme differential percentages but the total should not greatly exceed or fall substantially short of a total of 100%. The invention is illustrated, by way of example, in the accompanying diagrammatic drawings in which: Figure 1 is a perspective view of an optical assembly in accordance with the invention; Figure 2 is a perspective view of a light box for use with the assembly; and, Figure 3 is a fragmentary plan view, to an exaggerated scale, of the composite optical display device. Referring to the drawings, the display device includes a light box indicated generally at 1 in Figure 2, of a general kind utilised for illuminating a transparent advertising display. Such a box incorporates, for example, an array of fluorescent lamps or tubes 2, and a diffuser screen 3 of opalescent material is provided to give a uniformly diffused illuminated background to the transparency to be viewed. The body of the box is formed with opposed slots 4 to receive the diffuser screen 3 and the display of the present invention, which display will now be described. In the display according to the present invention, the scene to be viewed may comprise two identical photographic transparencies 5 and 6, each carrying a complete scene. As can best be seen from Figure 3, the transparencies 5 and 6 are sandwiched between a clear front sheet 7, a spacer sheet 8 of transparent material which acts to maintain a given spacing between the two transparencies, and a transparent backing sheet 9. Suitably, the sheets 7, 8 and 9 are made of clear plastics or glass, and the front and rear transparencies 5 and β are bonded to the sheets 7 and 9, respectively. The transparencies are so mounted that their matt (emulsion-layer) faces 5A and βA face forwardly and their glossy faces rearwardly. Thus, the spacing between the two images which are on the emulsion layers of the photographic films, depends on the thickness of the spacer sheet 8 plus the (standard) thickness of the acetate film which carries the outer image. Experiments have shown that the spacing is critical for optimum effect and, in the present embodiment of the invention,the criti¬ cal spacing is almost exactly 1 millimeter. However, it appears that acceptable results can be achieved with a range of spacings from 0.5 to 4 millimeters, more probably 0.5 to 2 millimeters; in the present example, with colour transparencies 1.25 X 1.25 meters in size mounted on a backing sheet 9 of Perspex or suitable transparent gel, an image spacing of 1.00 millimeter has given excellent results, with a backing sheet 2 or 3 millimeters thick. The diffuser screen and the front sheet may be 2 or 3 millimeters thick, but the front sheet may be substantially thicker for use in a display device which is physically accessible to viewers. As mentioned, the illustrated trans¬ parencies 5 and 6 are colour, but at least one black-and- white transparency may be substituted. The sheet 8 is sandwiched between the other glossy and matt faces of the transparencies 5 and 6 which are held in precise register, and the assembly of the trans¬ parencies and sheets 7, 8 and 9 is inserted in the slots 4 of the light box , together with or after the di fuser screen 3. It is preferred to have a gap 10, say 25 milli¬ meters, between the backing sheet 9 and the diffuser plate, this gap possibly being provided by a peripheral spacer strip 11. Illumination of the transparencies, by the tubes 2, produces a three-dimensional or "live" effect which is ex¬ tremely attractive in, for example, illustrating a product for the purpose of advertisement. The device may be mounted, say, indoors in a theatre foyer or outdoors in a suitable The assembly (5 to 9) may be bonded to (and sold with) a diffuser plate (3), particularly for use with light boxes which do not include a diffuser plate as a standard component, and the light box may be any suitable illuminator. As stated above, it is an important feature of the present invention that not only are the two transparencies 3 and 4 maintained at a precise spacing, but also that the optical density of each transparency is significantly less than the density of a single transparency showing the equivalent pictorial content. This density Is usually judged by the (experienced) eye which may vary slightly from person to person, but can be related to the standard 400-700 gamma light ratio scale and measured by a nanometer. It has been found that, for optimum visual effect, the density of each of the transparencies should be about 50% to 70% of the density of a -corresponding single transpar¬ ency of ideal density, and this might be regarded as total¬ ling 100% to 140% of the single-transparency density. The figure of 40% can give good results with strong lighting, but should not be greatly exceeded, the lower figure of 100% may be reduced to as low as 60% if, for example, an Impression of strong contrast is required. Differential percentages of, for example, 40% in the front transparency and 60% in the rear transparency may be employed, and the specific densities may vary according to the nature and size of the display. Also, three or possibly even more superimposed transparencies may be employed, with additional spacer plate(s) 8, and in such a case the three densities could be about 30% to 40% each. Furthermore, the transparencies may be colour separated; one transparency may be printed with a blue/green Image and the other a red/yellow image. Modifications may be made without departing from the Intended scope of the invention. For example, the spacer sheet 8 may be replaced by an air gap, or the spacer sheet may be made slightly opalescent to act as a diffuser in an assembly which is to be front-illuminated as now described. OttPI Instead of utilising active rear illumination of the transparencies, the effect of rear illumination may be produced by providing a suitable reflective layer behind the transparencies; thus, ambient or artificial light incident on the front of the assembly will illuminate the superimposed transparencies, and provide a self-contained viewable unit without the need for a light source. Such an arrangement would be suitable for smaller-scale repro¬ ductions, for example, in the form of photographs or even postcards,the front sheet (7) may comprise a spray coating. To produce particularly spectacular effectsthe density of each transparency may be non-uniform; to this end also, the lighting (2) may be disposed, for example, around the periphery of the box to present a tunnel-like effect. It will be appreciated that the images may be printed on, suitably, the faces of the spacer sheet 8 or on the appropriate faces of sheets 8 and 9. Edge-illumination may also be employed, instead of rear illumination, for example into the air gap 10. The invention may also be employed with a projector, for example in projecting an advertisement onto a screen or hoarding such as in a railway station, and a similar projection may be utilised by an artist painting or drawing a large-size picture giving a three-dimensional impression. It is envisaged that a composite film composing frames according to this invention may be used in cinematography with, of course, a modified camera and possibly employing double-coated films, i.e. films with emulsion layers on both faces.

Claims: CLAIMS . An optical assembly or simulating three-dimensional display, in which a composite image is formed by superim¬ posing two images (5A, 6A) each carrying the same pictorial content, the optical density of each image being signifi¬ cantly less than the density that would, for a given illu¬ mination, be required in a single image intended to provide an acceptable two-dimensional viewable image of the subject to be displayed, the two said images being in virtual con- tact or being spaced apart by a distance (8) of up to the order of 2 millimeters. 2. An optical assembly as claimed in Claim 1 , in which said distance (8) between the two images is approximately 1 millimeter. 3. An optical assembly as claimed in Claim 1 or Claim 2, in which the optical density of each image is about 50% to 70% of the density of the single Image intended to dis¬ play the same subject. 4.. An optical assembly as claimed in Claim 3, in which differential percentages such as 40% front and 60% rear are employed. 5. An optical assembly as claimed in Claim 1 , in which more than two images carrying the same pictorial content are superimposed. 6. An optical assembly as claimed in any preceding Claim, in which the aggregate of the densities of the superimposed images is between 60% and 140% of the density of the single image intended to display the same subject. 7. An optical assembly as claimed in any preceding Claim, in which a transparent backing sheet (9) Is provided at the rearmost (6A) of the superimposed images. 8. An optical assembly as claimed in any preceding Claim, in which each superimposed image is carried on a photo¬ graphic transparency (5,6). 9. An optical assembly as claimed in Claim 8, in which said transparencies (5,6) are separated by a spacer sheet (8) or air gap of approximately 1 millimeter. 10. An optical display device comprising an optical assembly (5-9) as claimed in Claim 9 arranged to be carried by and illuminated by a light box (1) provided with a diffuser screen (3); the optical assembly comprising a pair of images (5A, 6A) separated by approximately 1 millimeter by means of a transparent spacer sheet (8) or an air gap, a backing sheet (9) behind the rear image (6A) , and a transparent sheet (7) to cover the front image (5A). 11. A device as claimed in Claim 10, in which an air gap (10) exists between said diffuser screen (3) and said back¬ ing sheet (9). 12. A device as claimed in Claim 10, in which said rear image (6A) is on a carrier such as a photographic trans¬ parency (6) bonded to said backing sheet (9). 13. An optical display device for illumination by ambient or external light, comprising an optical assembly (5-9) as claimed in Claim 9, and a rear reflector, and in which said spacer sheet (2) is adapted to act as a diffuser. 14. An optical display device comprising an optical assembly (5-9) as claimed in any of Claims 1 to 9, and a light source to project the composite image onto a screen or the like.

Inventors: SIEWIERSKI ANDRZEJ ADAM, SIEWIERSKI, ANDRZEJ, ADAM
Applicants: STEREOSCOPIC DISPLAYS LTD, STEREOSCOPIC DISPLAYS LIMITED
Application year: 1983
Main classification: G09F13
IPC codes: G09F13, G09F19