AN APPARATUS FORMING A BORDER FOR AN IMAGE

Abstract: An apparatus forming a border for an image comprises a first pattern (3) and a further pattern (4) superimposed on but spaced from the first pattern, the patterns comprising visually contrasting areas, overlying portions of the first pattern and the further pattern being such as to form a resultant pattern (5) appearing to lie in front of and/or behind the plane of the border. The first pattern and/or further pattern changes with time and comprises a liquid crystal panel comprising an array of addressable picture elements.

Description: ANAPPARATUSFORMINGABORDERFORANIMAGE This invention relates to an apparatus forming a border for an image, comprising a first pattern and a further pattern superimposed on but spaced from the first pattem, the pattems comprising visually contrasting areas, overlying portions of the first patte and the further pattem being such as to form a resultant pattern. When an observer views a substantially planar image (such as that formed on a television screen or a painting) the brain identifies a number of visual cues which lead to the realisation that a substantially planar image is being viewed. Such flatness cues tend to contradict depth cues, such as perspective, which may be present in the image itself. In order to make such an image appear more three dimensional, a body forming a border as described in the first paragraph may be used. Such a body is disclosed in US 3,582961. In this known border the first and further pattems are formed by dark stripes on a transparent lamina. When viewed together in transmission the pattems produce a resultant Moire interference fringe pattem. When this known border is superimposed upon the peripheral edges of a pictorial image displayed on, for example, a projection screen, the flatness cues associated with the edges of the flat screen are suppressed. An illusion of depth in the image is created from monocular depth cues (e.g. perspective and obscuration) which may be present in the flat image. Such depth cues are discussed in, for example, the paper by Harold Schlosberg in the American Joumal of Psychology, Volume 54, Number 4 October 1941 pp 601-605. There are a number of disadvantages associated with the body of US 3,582,961. For example, the pattems are one dimensional, so that motion parallax will only occur when an observer moves his or her head in a specific direction. The pattems are fixed and it is therefore difficult to alter the apparent distance between the plane of the border and the resultant pattem, other than by substitution of the original body with a different body or by physically moving one pattem. According to the invention, there is provided an apparatus forming a border for an image as defined in the first paragraph above characterised in that the first patte and/or further pattem changes with time and that the resultant pattem appears to lie in front of and/or behind the plane of the border. This provides the ability to vary the appearance and/or the position or plane of the resultant pattem without replacing or moving the whole body. Preferably, the first and/or further patte comprises a liquid crystal panel comprising an array of addressable picture elements. The presence of Moire interference fringes in liquid crystal panels used for displays is well known and is generally considered to be a disadvantage of these displays. The inventors have realised that this disadvantage with known liquid crystal panels can be used to provide an improved border which helps create apparent depth in a substantially planar image. The pattems are advantageously arranged such that the resultant pattem exhibits motion parallax in a plurality of directions. Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which; Figure 1 shows a cross-section of a first embodiment of a border according to the invention, Figure 2 shows a cross section of a second embodiment of a border, Figure 3 shows a first pattem and two further patterns according to the invention together with the respective resultant pattems, and Figure 4 shows other sets of pattems according to the invention. Figure 1 shows an apparatus forming a border (1) for an image (2). The border comprises a first patte (3) and a further pattem (4) superimposed on but spaced from the first pattem, the pattems comprise visually contrasting areas, overlying portions of the first pattem and the further pattem are such as to form a resultant pattem (5) which appears to lie in front of and/or behind the plane of the border (6). In the present example, the first pattem comprises a fixed pattem as shown in Figure 3 (a). The pattem is composed of areas of black ink (10) printed onto a transparent acetate sheet (11) such as an overhead view foil. The black ink areas are printed at a resolution of 600 dots per square inch so that some areas appear black and opaque whilst other areas appear transparent. Thus the patte comprises visually contrasting areas. In the present example the acetate sheet has a clear transparent centre portion through which the image (2) may be viewed. As an altemative the first pattem could comprise a sheet having the centre portion removed. The further pattem (4) in this first embodiment comprises a pattem formed by the light and dark electronically addressable picture elements (or pixels) of a liquid crystal display device (7). In the present example, the liquid crystal display device is arranged as a large rectangular substantially flat display which displays the image (2) in the centre portion and the further patte (4) in the outer region substantially surrounding the image (2). The liquid crystal display also comprises control means in the form of a driver circuit (8), such that the further patte may be changed with time. In order to produce a border according to the present invention, the first pattem (a fixed pattem on the transparent sheet) is placed adjacent the front face of the liquid crystal device. The further patte is then generated (by a computer program in the present example) and displayed on the liquid crystal display. The nature of the pattems are such that the two overlying pattems produce a Moire interference pattem as a resultant pattem when the further pattem is viewed through the first patte . This resultant pattem can be made to appear in a plane in front of the image or behind the image. The position of the resultant pattem depends upon the relative pitches of the two pattems and the distance between the two pattems. The patte produced on the liquid crystal display (i.e. the further patte 4 in this example) can be easily changed under software control to give another different resultant pattem without replacing either pattem physically. The resultant pattem may thus be changed as a function of time simply by changing the pattem displayed by the liquid crystal display (LCD). Animated pattems providing moving resultant pattems may thus be generated. Examples of actual pattems which can be employed are illustrated in Figure 3. In this Figure, the first pattem (which in the embodiment of Figure 1 comprised a fixed patte on a transparent sheet) is shown in Figure 3 (a). The pattem is in the form of transparent areas in a two dimensional array with a repeat distance of 11 arbitrary units. Figures 3 (b) and 3 (c) show two different further pattems generated and displayed by the LCD. The electronic pattem in Figure 3 (b) is composed of transparent features of a given shape repeated every 10 arbitrary units in a two dimensional array. The electronic pattem in Figure 3 (c) is composed of transparent features of a different shape also repeated every 10 arbitrary units in a two dimensional array. The resultant Moire interference pattem seen by an observer whilst viewing the pattems shown in Figure 3(a) and 3(b) together is shown in Figure 3(d). The resultant Moire interference pattem seen by an observer whilst viewing the patterns shown in Figure 3(a) and 3(c) together is shown in Figure 3(e). The two resultant pattems can be seen to be different in the two cases. If a third different electronically controlled pattem is produced, then a third different resultant pattem will be obtained. Many different pattems can be produced in this way. If the electronically controlled pattem is changed rapidly as a function of time a rapidly changing resultant pattem is observed. Although in the above example the further pattem comprises a liquid crystal display, many other types of display such as an electroluminescent panel or a plasma discharge display or a cathode ray tube may be used as an altemative. A second embodiment according to the invention is shown in Figure 2. This embodiment is similar to the embodiment shown in Figure 1, except for the fact that the first pattem is no longer fixed, but is formed from more and less light transmissive pixels of an LCD (21) having electronic control means (22) for addressing the pixels. In this second embodiment, the display device facing the observer must be operated in a transmissive mode so that both pattems are seen and form a resultant pattem in a different plane from that of the image or either display. This second embodiment has all the advantages of the first described above, but exhibits the ability to display a bigger range of resultant Moire interference pattems without physically changing either the first or the further pattem. By way of example, the pattems in Figure 4 show some of the combinations which become possible. Pattems 30 and 31 combine to produce the resultant patte 33, and pattems 34 and 35 combine to produce resultant patte 36. Pattem 30 has a repeat distance of 10 units, pattem 31 a repeat distance of 11 units, pattem 34 a repeat distance of 20 units and 35 a repeat distance of 21 units. It can be seen that the resultant pattems 33 and 36 are quite different. By producing a rapid sequence of such pattems it is possible to generate a resultant pattem which resembles a moving image. The resultant patte may be made to appear three dimensional by altering the relative spacing of the first and further pattems and/or changing the pattem pitches therefore changing the plane of the resultant image with time. In this way different areas of the resultant pattem may be formed at different distances above or below the plane of the first and/or further pattem. If one pattem is composed of small holes and the other is composed of an array of transparent T shaped areas, the resultant pattem is in the form of an array of larger Ts in a different plane. In this way an image of a logo can be displayed. This sort of resultant pattem is a type of integral 'photograph' of the letter T. The present invention may thus be used to produce a display of moving images in three dimensions which is of value of itself without necessarily being used as a border for a separate image as shown in the embodiments described. The resultant pattems shown in Figure 3 and Figure 4 have the advantage over conventional stripe Moire interference pattems that there is apparent motion parallax between the resultant pattem and the first or further pattems in all directions when an observer moves their point of view or when the pattern is made to change with time. For the pattems shown there is no direction in which such motion parallax can not be observed, whereas for stripe pattems motion parallel to the stripe does not produce apparent motion parallax. In order to minimise the bulk of the border and maximise convenience, it is possible to have the border edge-lit, for example by using a conventional edge lit LCD as the first and/or further pattem. An edge lit light transmissive sheet may also be provided as a modification to the first pattem of the first embodiment described above. Although a border which substantially surrounds the image has been described. a border which is only provided at strategic points on either side of the image will work in the same way and almost as effectively. In particular, a border which is only present at opposite comers of the image will give the three dimensional effect and thus provides a further embodiment of the invention herein described. Finally, the content of the accompanying abstract and the priority document (Application Number GB 9521263.5) are incorporated herein by reference.

Claims: CLAIMS 1. An apparatus forming a border for an image, comprising a first patte (3) and a further pattem (4) superimposed on but spaced from the first pattem, the pattems comprising visually contrasting areas, overlying portions of the first pattem and the further pattem being such as to form a resultant pattem (5), characterised in that the first pattem and/or further pattem changes with time and that the resultant pattem appears to lie in front of and/or behind the plane of the border. 2. An apparatus as claimed in claim 1 in which the first pattem and/or the further pattem comprises a liquid crystal panel comprising an array of addressable picture elements. 3. An apparatus as claimed in any preceding claim further comprising control means (8) being arranged to change the first pattem and/or the further pattem with time. 4. An apparatus as claimed in any preceding claim in which the resultant pattem exhibits motion parallax relative to the first or further pattem in a plurality of directions. 5. An apparatus as claimed in any preceding claim in which the first pattem and/or the further pattem is carried on a major surface of a light transmissive sheet (11). 6. An apparatus as claimed claim 5 further comprising means for inputting light through an edge of the light transmissive sheet. 7. An apparatus as claimed in any preceding claim in which the pattem nearest the observer comprises more and less transparent areas. 8. An apparatus as claimed in any preceding claim which is constructed and arranged to enclose the circumference of an image completely or incompletely. 9. An apparatus as claimed in any preceding claim including a display device. 10. An apparatus as claimed in claim 9 in which the display device displays both the image and the first pattem, the first patte being located at the perimeter of the image.

Inventors: HOLDEN JOHN, PARRY GARETH, HOLDEN, JOHN, PARRY, GARETH
Applicants: CENTRAL RESEARCH LAB LTD, HOLDEN JOHN, PARRY GARETH, CENTRAL RESEARCH LABORATORIES LIMITED, HOLDEN, JOHN, PARRY, GARETH
Application year: 1996
Main classification: G02B27
IPC codes: A47G1, B44F7, G02B27, H04N13