IMAGING SYSTEMS

Abstract: A decoder screen (80) is intended for use in an imaging system in which the screen is disposed between a viewer and a composite image containing alternate portions of two images which together form a stereoscopic pair. The decoder screen (80) includes a surface on which is printed a pattern of alternating clear and opaque areas, for example, parallel stripes or a chequerboard pattern, and a plurality of lenticular elements (82). The lenticular elements may be semicircular lenses or elongate prisms. In either case, the lenticular elements are so shaped that the apparent pattern of clear and opaque areas perceived by one of the viewer's eyes is the inverse of the apparent pattern perceived by the viewer's other eye when looking at the decoder screen and a composite image positioned immediately behind it. Thus, each of the viewer's eyes perceives parts of only one of the two images forming the stereoscopic pair, resulting in an overall 3-D effect.

Description: IMAGING SYSTEMS This invention relates to an improved decoder for use in the imaging systems described in our International Patent Application No. WO90/13848 and British Patent Application No. 9015843.7 to which reference should first be made. In accordance with the invention there is provided a decoder screen for use in an imaging system in which a decoder screen is disposed between a viewer and a composite image containing alternate portions of two images which together form a stereoscopic pair, the decoder screen comprising a surface carrying a pattern of alternating clear and opaque areas and a plurality of lenticular elements which, in use, are in contact with the pattern-bearing surface and disposed between the viewer and the said surface; the lenticular elements being so shaped that the apparent pattern of clear and opaque areas perceived by one of the viewer's eyes is the inverse of the apparent pattern perceived by the viewer's other eye. The raster-lenticular hybrid decoder screen of the invention is capable of delivering two clear sharp images with the stereo differences contained between them, one to each eye. As a consequence, the raster-lenticular hybrid can produce a good 3-D effect, as each eye receives a full colour image, one of a stereo pair. Preferred forms of imaging system decoder in accordance with the invention will now be described in detail, by way of example, with reference to the drawings, in which: Figures 1(a) and 1(b) show line grid and chequerboard types of decoder screen patterns; Figure 2 illustrates a prior art system employing a decoder screen; Figure 3 illustrates the decoder screen of the invention as perceived by the right and left eyes, respectively; Figure 4 shows te images as perceived by the right and left eyes when using a decoder screen ir accordance with the invention; Figure 5 is analogous to Figure 4 but shows a screen of chequerboard pattern; Figure 6 shows schematically 'cross-over effect'; Figure 7 shows a composite image of the type used in imaging systems of the kind to which the invention relates; and ■ Figure 8 shows a raster-lenticular hybrid decoder in accordance with the invention. In an imaging system of the type in which the decoder of the invention is used, a composite image is formed for display to the viewer. The composite image includes two sets of areas which, in general, alternate, each set containing portions of one of two images separated by colour overlay, line multiplexing or a combination of the two techniques. A screen or 'decoder' is interposed between the image and the viewer, the decoder being such that, when the viewer looks at the image, each eye sees only one of the two sets of areas and, hence, the portions of only one of the two images. At the brain, the two images are combined to produce a 3-D effect, as perceived by the viewer. Two forms of decoder pattern are shown in Figures 1(a) and 1(b), the column line grid and the chequerboard. Taking for example the line grid of Figure 1(a), the decoder would be in the form of a grid of stripes of equal width, alternate stripes being clear and opaque respectively. This pattern is reflected in the form of the composite image with which the decoder would be used; the composite image for use with the line grid decoder of Figure 1(a) would comprise a similar arrangement of stripes, alternate stripes containing portions of each of the two images which combine to give the stereoscopic 3-D effect. The raster-lenticular hybrid screen or decoder of the present invention combines the action (relative to the encoded image on the screen) of a lenticular screen with that of a raster screen, that is to say, a column-line grid or chequerboard as described in our above-mentioned applications and shown in Figures 1(a) and (b). Previously, the column line grid or the chequerboard decoder 10 was positioned away from the pixel-phosphor screen 12 of the encoded image, the degree of displacement varying with the circumstances. This displacement between the plane of the decoder screen 10 and the plane of the image pixel plane 12 allowed horizontal parallax between the left and right eye, each eye looking through the clear sections 14 of the decoder screen to a different position of the encoded image, as illustrated in Figure 2. The different positions of the encoded images are due to the nature of the encoding itself, -.as specified in our abo- c-mentioned applications. Each eye sees through the clear sections 14 of the decoder screen 10 to either the left image of a stereo pair or the right image of a stereo pair, produced through pseudo stereo or through two camera-stereo recording-filming, as described in International application O90/13848. In the earlier system referred to, without displacement between the plane of the decoder screen 10 and the pixel plane 12 there is no horizontal parallax. However the raster-lenticular hybrid of the present invention employs the optical activity of its lenticular component to displace the position of the raster opponent. Consequently, the raster-lenticular hybrid decoder screen and the image plane can be in direct physical contact between the two planes with no displacement. With the RLH (Raster Lenticular Hybrid) screen, the horizontal parallax between the left and right eye is such that the optical activity of the lenticular component displaces the raster component, as shown in Figure 3. Instead of the rastei decoder screen (line grid or chequerboard) remaining in the same position, and each eye seeing through to a different position of the image plane behind it, as in Figure 2, it is the raster image which is itself displaced for each eye, uncovering for each eye a different section of the image plane directly behind it, as is illustrated by Figure 4. Figure 4 shows a monitor 40 with a RLH screen in accordance with the invention, as well as a pair of stereoscopic images 44 and 46 and the resultant composite image 48 formed from these in the image encoding system described in International application WO90/13848 referred to previously. 40(1) and 40(r) show the RLH screen as perceived by the left and right eyes respectively and 48(1) and 48(r) show the composite image portions seen by each of the two eyes. Figure 5 is analogous to Figure 4 and shows a monitor with RLH screen, this time, of chequerboard pattern. 50(1) and 50(r) show the RLH screen as perceived by the left and right eyes respectively. The RHL decoder inverts to its raster image 180° between th two eyes. As the rlH decoder and the image screen are in direct contact, there can be a perfect alignment between the encoded composite image and the RLH decoder screen. Once this alignment ha been established it will remain unchanged and then, from any position in the viewing area, the optical properties of the RLH wil take effect by virtue of the horizontal displacement between the eyes. Each eye will see an aligned left or right image view, with the opposite eye seeing the opposite view, also aligned. The different between previous line grid decoder screens an the RLH decoder screen is that, with the former, the horizontal displacement of each eye 'unlocks', through the interposition of th line grid decoder screen, one of two images encoded in the image plane, whereas with the RLH decoder screen the horizontal displacement of ecah eye 'unlocks' one of two image positions of th raster pattern and each one of the raster positions then 'unlocks' one of the two images encoded in the image plane. The improved alignment of the RLH screen, (which could be fitted to monitor or projection screen of the same variety (except the liquid crystal display) as line-grid decoder screens), means that if at the beginning of the programme the two images combined t form the composite encoded image are the words 'left' and 'right' and the viewer then positions himself to align their eyes accordingly, it will be possible, because of the high degree of alignment, to create the crossover vision effect (see Fig.6) which allows the brain to bring objects clearly out of the plane of the presentation screen. The RLH screen will enable software encoded according to the systemdescribed in the International application referred to above to create the illusion of objects eaving the screen plane, returning to the screen grid then going through and beyond into its depths. The RLH screen of the invention is designed as a standard lenticular dual image display of the type which are popularly used on badges and simple displays (see Figure 8). As shown, with the RLH screen 80, the image encoded on strips aligned behind the strip of semi-circular lenses 82, which are mostly of plastics material, is of the column-line and screen pattern, alternately, black and clear, that is, black and no-ink. For each eye the pattern switche its apparent black and clear pattern. The RLH screen may in certain circumstances consist of a series of prisms as opposed to a lenticular array. The net effect, however, must be to re-align the perceived raster position for each eye, that is, effectively to invert the raster pattern by one phase shift, by 180°. There are two gauge sizes of note in this construction. Firstly, there is the gauge of the decoder pattern which corresponds to the dimensions of the encoded image in the pixel plane shown in Figure 7. Secondly, there is the gauge of the semi-circular lenses 82 of the lenticular component of the RLH screen. This latter gauge determines the width of the strips of the decoder pattern image (see Fig. " 8). The relationship between these two gauges, i.e. their ratio will vary with the circumstances of the application of the imaging system for which the RLH is being specified. The basic principle underlying the system is believed to be that the brain does not demand stereo displacement as measured in the horizontal plane as generated by the eyes, as the only image difference acceptable for the generation of stereo 3-D images. The reason for this is that our evolution has involved several stages where our distant ancestor or precursor was predatory, fleet of foot (or rather limb) and far more acrobatic than any of use today are likely to be. As a consequence in the midst of a hective chase, a hunt for food, a chapter in survival, with boty eyes swivelling, the need for the brain to generate an accurate 3-D representation of the rapidly moving world, the precise position of branches, footholds, nooks, crannies and prey itself, was vital. Under these circumstances the eyes would be comparing simultaneous left and right i gaes that had differences between them that represented rotations, distortions and with eyes blinking asynchronously - time differentiation, as well as translations in many planes. As a consequence we have inherited neural algorithms that are capable of creating a 3-D picture from two images with differences between them other than simply a horizontal displacement and attendant perspectives transformation. The pseudo-stereo provided by the imaging system works as well as it does because of this, for the brain is invited to resolve the depth puzzle and thereby create a credible sensation of 3-D, from pictures that have differences between them that are everythin but a true horizontal displacement with attendant perspectives transformations. Pseudo-stereo invites the brain to make an intelligent guess at what the two images and their differences mean the outcome of this process is a 3-D image not historically accurate, but indistinguishable in sensation from the sensations of 3-D reality.

Claims: CLAIMS 1. A decoder screen for use in an imaging system in which a decoder screen is disposed between a viewer and a composite image containing alternate portions of two images which together form a stereoscopic pair, the decoder screen comprising a surface carrying a pattern of alternating clear and opaque areas and a plurality of lenticular elements which, in use, are in contact with the pattern-bearing surface and disposed between the viewer and the said surface; the lenticular elements being so shaped that the apparent pattern of clear and opaque areas perceived by one of the viewer's eyes is the inverse of the apparent pattern perceived by the viewer's other eye. 2. A decoder screen according to claim 1 in which the lenticular elements are a plurality of part-cylindrical lenses extending substantially parallel to one another. 3. A decoder screen according to claim 1 in which the lenticular elements are a plurality of elongate prisms extending substantially parallel to one another. 4. A decoder screen according to claim 1, 2 or 3 in which the pattern carried by the surface comprises a plurality of alternating clear and opaque stripes extending substantially parallel to the lenticular elements. 5. A decoder screen according to claim 1, 2 or 3 in which the pattern carried by the surface comprises a chequerboard pattern of alternating clear and opaque areas, one edge of each area extending substantially parallel to the lenticular elements. 6. A decoder screen according to any preceding claim in which the pattern-bearing surface is formed by the rear surfaces of the lenticular-elements which are disposed edge to edge. 7. A decoder screen substantially as hereinbefore described.

Inventors: ASHBEY JAMES AMACHI, ASHBEY, JAMES, AMACHI
Applicants: DELTA SYSTEM DESIGN LTD, DELTA SYSTEM DESIGN LIMITED
Application year: 1991
Main classification: H04N13
IPC codes: G02B27, G03B35, H04N13