A DISPLAY DEVICE

Abstract: A display device having a display area for displaying a substantially planar image of an object, the display device further comprising a substantially transparent sheet or LCD overlying the display area and carrying an array of less transparent areas which co-operate with a first pattern generated in the plane of the image by the display device, thereby producing a resultant Moiré interference background pattern which appears to lie in a different plane to that of the image. This arrangement can provide an enhanced 3D effect in a compact and easily fabricated device without the use of additional electrical power.

Description: A DISPLAY DEVICE This invention relates to a display device having a display area for displaying a substantially planar image of an object, and particularly, though not exclusively, to visual display units and advertising displays. Many display devices have been described in recent years including (inter alia) Uquid crystal displays, cathode ray tubes and plasma discharge displays. When an observer views a substantially planar image on such a device 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. Specially designed systems to display images in three dimensions or suspended in space have been proposed but have the disadvantages of high cost and restricted viewing angles. In order to make a two dimensional image appear more three dimensional, a border such as that disclosed in US 3,582961 may be used. In this known border first and further patterns are formed by dark stripes on a transparent lamina. When viewed together in transmission the patterns produce a resultant Moire interference fringe pattern which appears to lie in a different plane to that of the border. When this known border is combined with a pictorial image displayed on, for example, a television screen, the flatness cues associated with 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 Journal of Psychology, Volume 54, Number 4 October 1941 pp 601-605. A further known border for an image which works in a similar way is disclosed in WO 9527228. According to the present invention, there is provided a display device having a display area for displaying a substantially planar object or an image of an object, characterised in that the display device includes means for generating a resultant pattern appearing in the display area, the resultant pattern lying in a different plane to that of the display area. The resultant pattern thus appears to lie in a different plane to that of the image or object displayed upon the display area thus helping to create a three dimensional effect.. The resultant pattern is preferably a Moire interference pattern. The means for generating the resultant pattern preferably comprises a substantially transparent sheet having an array of less transparent areas, the sheet overlying the display area in use. Very preferably, the array of less transparent areas co-operates with a first pattern being displayed in the display area to produce the resultant pattern. The presence of Moire interference fringes in liquid crystal panels used for displays is well known, but 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 display which can help to create apparent depth in a substantially planar image. The resultant pattern is advantageously used as a background pattern for an image of an object, the background pattern appearing to lie in a plane behind the plane of the image. The object may appear stationary or be made to change it's location or orientation or shape with time. 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 display device according to the invention, Figure 2 shows a cross section of a second embodiment of a display device, and Figure 3 shows a first pattern and a further pattern according to the invention together with the respective resultant pattern. Figure 1 shows a display device comprising a liquid crystal display panel (1) having a display area (2) for displaying a substantially planar image, and means for generating a pattern (2 and 3) which appears to lie in a different plane (4) to that of the image. In the present example the means comprises the display area itself together with a fixed pattern carried by a substantially transparent sheet (3) as shown for example in Figure 3 (a). The pattern 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. The acetate sheet in this example is arranged to overlie the whole of the display area of the liquid crystal panel, providing a layer which masks small areas of the whole display area in a two dimensional array of relatively less light transmissive (or opaque) spots or dots. To the naked eye, the acetate sheet appears in isolation like a neutral density filter, as the more and less transparent areas are not resolved by the eye unless the sheet is examined closely. In operation, the array of less transparent areas (10) co-operates with a first pattern (5) being displayed in the display area to produce the resultant pattern. The first pattern (5) in this first embodiment comprises a pattern formed by the light and dark electronically addressable picture elements (or pixels) of a liquid crystal display device ( 1 ). In the present example, the liquid crystal display device is arranged as a large rectangular substantially flat display which displays an image of an object (6) in the display area (2) and the first pattern in the outer region substantially surrounding or encircling the image (6). It should be noted that if the image of he object has internal areas which would let an observer see through the object - for example the hole in the middle of a doughnut - this part of the display area should also display the first pattern. The liquid crystal display also comprises control means in the form of a driver circuit (8), such that the pattern and/or the image of an object may be changed with time. In the present example the LCD and driver circuitry is provided by a notebook computer which may be readily obtained from one of several companies such as IBM or Compaq or Apple. In order to produce a resultant pattern according to the present invention, the transparent sheet having an array of less transparent areas is placed adjacent the front face of the liquid crystal device. The first pattern is then generated (by a computer program in the present example) and displayed on the liquid crystal display. The nature of the patterns are such that the pattern and the array co-operate to produce a Moire interference pattern as a resultant pattern when the first pattern is viewed through the substantially light transmissive sheet having an array of less transparent areas. This resultant pattern can be made to appear in a plane in front of the image or behind the image. The position of the resultant pattern depends upon the relative pitches of the pattern and the array and the distance between the patterns and the array. The pattern produced on the liquid crystal display (i.e. the first pattern in this example) can be easily changed under software control to give another different resultant pattern without replacing the substantially light transmissive sheet physically. The resultant pattern may thus be changed as a function of time simply by changing the pattern displayed by the liquid crystal display (LCD). Animated patterns providing moving resultant patterns may thus be generated. Examples of actual patterns which can be employed are illustrated in Figure 3. In this Figure, the fixed pattern comprising an array of less light transmissive areas on a transparent sheet is shown in Figure 3 (a). The fixed pattern is in the form of less transparent areas or opaque areas having a diameter of 10 arbitrary units, in a two dimensional array with a repeat distance of 21 arbitrary units. The arbitrary units in the present example are l/600th inch (or (25.4)/600th mm). Figures 3 (b) shows a different further pattern generated and displayed by the LCD. The electronic pattern in Figure 3 (b) is composed of white features of a given shape repeated every 3 arbitrary units in a two dimensional array on a black background. In the present embodiment the white features are 1 pixel in size with two pixels therebetween giving a pitch of 3 pixels. The display area displays 640 pixels by 480 pixels in a display area 179 mm by 130 mm respectively. The resultant Moire interference pattern seen by an observer whilst viewing the patterns shown in Figure 3(a) and 3(b) together is shown in Figure 3(c). If a second different electronically controlled pattern is produced, then a different resultant pattern will be obtained. Many different patterns can be produced in this way. If the electronically controlled pattern is changed rapidly as a function of time a rapidly changing resultant pattern is observed. Although in the above example the further pattern 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. Although the image of the object displayed in the display area is covered by the fixed pattern in addition to the background pattern, it is only this latter background pattern which has the matching areas to produce the Moire interference pattern. Thus it is only the background which seems to be projected behind the plane of the image (i.e. the plane of the display area). Consequently, the image of the object appears to float in space in front of a distant background. The light transmissive sheet carrying the 'fixed' pattern is light and discrete enough that it is not noticed in normal use and does not effect the visibility of the image. As an alternative, in the case of still images, the fixed pattern may be made to cover the background areas only. The three dimensional effect is best if the further pattern displayed by the display area extends right up to the edge of the image being displayed. This however requires a good deal of computing power to achieve for a moving image in real time. As an altemative, it reduces the computing effort required considerably if the white pixels are made to extend over the whole display area including the area of the image of the object. At first sight this seems to be undesirable. One might think that as the Moire pattern would appear on top of the object, the object would seem to appear in the same plane as the background. This expected disadvantage does not however occur when using this alternative approach. Instead, the object still appears to lie in the plane of the display area but appears to be more or less translucent depending upon the contrast between the image of the object and the further pattern. As an altemative to the above arrangement, the acetate sheet carrying the first pattern may be placed behind the liquid crystal display, so that the position of the first and further patterns are reversed. The liquid crystal display would then have to be operated in transmissive mode. In this example, the essential requirement for the first pattern is that it comprises visually contrasting regions. Therefore the more and less light transmissive areas of the acetate sheet may be replaced by an array of light sources or light scattering centres or red and blue alternate areas. The areas may be backlit or edge lit or even front lit. The liquid crystal display in front of the arrangement providing the image and the further pattern must comprise more and less light transmissive areas in this example, unlike in the previous example in which reflective mode devices could be used equally well. An advantage of the present example is that because what is in effect a neutral density filter is no longer placed in front of the image it can be brighter. One advantage of the above embodiments over prior art display devices is that the resultant pattern is viewable over a very wide angle. Another advantage is that there are no bulky additional items which are difficult to position relative to the display device and/or consume additional power. The 3D effects which they produce are improved because the brain of an observer receives fewer flatness cues. If an acetate sheet is used in need not be flat. Curved or otherwise non planar first patterns may be employed. A further 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 'fixed' pattern is no longer fixed, but is formed from more and less light transmissive pixels of a second 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 patterns are seen and form a resultant pattern 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 different resultant Moire interference patterns without physically changing the array. By producing a rapid sequence of different resultant patterns it is possible to generate a resultant pattern which appears to move with time. As in the case of the first embodiment above, the fixed pattern may be made to cover the background areas only so that the areas in front of the image are substantially transparent. As an alternative, the LCD closest to the observer may be made to be the one displaying the image ofthe object and the further pattern, as described previously for one of the examples using an acetate sheet behind the LCD. In all the embodiments, the resultant pattern may be made to appear three dimensional by altering the relative spacing of the first and further patterns and/or changing the pattern pitches therefore changing the plane of the resultant background pattern with time. In this way different areas of the resultant background pattern may be formed at different distances above or below the plane of the image. This effect may also be achieved - in both the first embodiment and this further embodiment - by changing the spacing between the first pattern and the further pattern. Another 6 alternative is to alter the relative orientation of the two patterns. If one pattern is composed of small 'holes' and the other is composed of an array of white or transparent shaped areas, the resultant pattern is in the form of an array of larger 'T's in a different plane. In this way an image of a logo can be displayed. This sort of resultant pattern 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 background for a separate image as shown in the embodiments described. The resultant pattern shown in Figure 3 (c) has the advantage over conventional stripe Moire interference patterns that there is apparent motion parallax between the resultant pattern and the image in all directions when an observer moves their point of view or when the pattern is made to change (and/or move) with time. For the patterns 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. Although in the above embodiments the patterns have been monochrome, differently coloured areas may be used to achieve coloured backgrounds if desired. Although the above embodiments have described a display area which displays an image, the display area may display an image of an object or an object itself, such as for example the metal hands of a watch. Finally, the content of the accompanying abstract and priority documents are incoφorated herein by reference.

Claims: CLAIMS 1. A display device ( 1 ) having a display area (2) for displaying a substantially planar object or an image of an object, characterised in that the display device includes means (2, 3) for generating a resultant pattern (4) appearing in the display area, the resultant pattern lying in a different plane to that of the display area (2). 2. A display device as claimed in claim 1 in which the resultant pattern (4) comprises a Moire interference pattern. 3. A display device as claimed in claim any preceding claim in which the means for generating the resultant pattern comprises an array of relatively more (11) and relatively less ( 10) transparent areas overlying the display area (2) in use. 4. A display device as claimed in claim 1 or claim 2 in which the means for generating the resultant pattern comprises a substantially transparent sheet ( 11) having an array of less transparent areas (10), the sheet overlying the display area in use. 5. A display device as claimed in claim 3 in which the means for generating the resultant pattern comprises a liquid crystal device (21). 6. A display device as claimed in claim 3 or claim 4 or claim 5 in which the array of less transparent areas co-operates with a first pattern being displayed in the display area to produce the resultant pattern. 7. A display device as claimed in any preceding claim in which the resultant pattern is a background for an image being displayed in the display area. 8. A display device as claimed in claim 1 or claim 2 in which the means for generating a resultant pattern comprises a liquid crystal device having more and less light transmissive areas overlying an array of visually contrasting areas.

Inventors: MARMAROPOLOUS GEORGE, MARMAROPOLOUS, GEORGE
Applicants: CENTRAL RESEARCH LAB LTD, MARMAROPOLOUS GEORGE, CENTRAL RESEARCH LABORATORIES LIMITED, MARMAROPOLOUS, GEORGE
Application year: 1996
Main classification: G02B27
IPC codes: G02B27