The object of the invention is a pixel element for a three-dimensional screen. The pixel element of the invention comprises means for generating multiple substantially collimated, controllable light beams. These light beams are emitted in multiple directions, so that each light beam is associated to a predetermined viewing direction.
Various methods and devices have been suggested to achieve a true three-dimensional image (3D image). The underlying principle of all true 3D methods is the same. If a planexe2x80x94two-dimensionalxe2x80x94image is displayed on a surface, then every point of the surface emits or reflects light with approximately same intensity (and colour) in all directions. This is the working principle of a traditional picture, like a postcard (reflection) or a traditional TV-image (light emission). In the case when a three-dimensional image is presented, the emitted light has a different intensity (and colour) in the different directions, even if it is emitted from the same point. We may regard in this way a window pane or a hologram as a display. Hence, in order to display a three-dimensional image, there is needed a light emitting surface where the intensity (and colour) of the light emitted from a single image point (pixel) may be controlled as the function of the emission angle (exit angle), with other words, the intensity of the light emitted in the different directions may be controlled.
In order to produce true or realistic three-dimensional images, two technical problems must be solved. Firstly, a large number of light beams must be projected in the different directions in space, with the appropriate intensity/colour, which allow the viewer to see different perspectives from different viewpoints. Secondly, means must be provided to allow the feeding of the necessary data to the light sources generating the light beams. This second problem involves difficulties when video images (i.e. moving images) must be displayed, because large amounts of data (kB/s) must be forwarded into each (!) image point or pixel. Obviously, a true 3D video image providing n different viewing directions require n times the data amount of a normal video image.
There are many known technical solutions that addresses the problem of the directed light beams. The Hungarian Patent application published under No. T/63 503 discloses two methods for the presentation of three-dimensional images.
In a first version, a modulated laser beam is subjected to deflection which is controlled in time. The deflection is performed before the image pixels, according to the directions defining the viewing range. In this manner the modulated laser beam enters the image pixel deflected with an angle, the beam is parallel translated. From the image pixel the laser beam propagates with an optical deflection corresponding to the view range, or propagates further in different directions within the viewing range without further deflection. A disadvantage of this solution is that the laser beam must be focused and positioned very precisely, because the entry point of the laser beam within the image pixel defines the direction of the exiting laser beam.
In the second version, the modulated laser beam enters an image pixel in the same entry point, without deflection, and it is deflected towards the different viewing angles within the image pixel, with the help of a controllable active optical element positioned in the image pixel. The deflection of light beam with the angle-dependent intensity is performed by the active optical element. The advantage of the solution is that the positioning and focusing of the beam need not be very exact, but the active optical elements make the device extremely expensive. Also, the problem of the feeding of the data to the active pixels is not discussed.
In other known methods, in order to display true 3D images, two surfaces are used, where the first front surface is a surface with a controllable light transmission, and the second back surface is an illuminating surface comprising light sources. One point of the back surface and one point of the front surface defines unequivocally a direction. With a possible embodiment, the image is created on the back surface by controlling the intensity and/or colour of the light sources, while on the first surface only masking is performed according to the selected viewing directions, by switching the image pixels on and off. With an other possible embodiment, the light sources on the back surface are continuously on, or they are only switched on or off, while the controlling according to the image information is made on the first surface. The first surface comprising the image pixels with controllable light transmission is preferably an LCD display.
Such solutions utilising an LCD display are disclosed, among others, in the documents EP 0 316 465 and U.S. Pat. No. 5,132,839. Here, illuminated strips are used behind an LCD screen, and the light of the strips are either transmitted or blocked by the controlled image pixels of the LCD screen.
In the solution disclosed in EP 0 316 465, there is an illuminated line behind every pair of LCD-pixel columns, and the light of the line passes through either one column or the other, corresponding to the control of the LCD pixels. This arrangement allows the display of a stereoscopic image with two viewing directions, but the resolution of the LCD-display is low, because two LCD-pixels are needed for an image point. The description suggest to increase the number of LCD-pixels associated to one illuminating line, in order to increase the number of viewing directions, but this leads to a further lowering of the resolution. There is no teaching how the data must be fed to the LCD-pixels.
With another possible embodiment, it is suggested to use one illuminating line (light source) behind each LCD-pixel column. In this case every pixel is illuminated by multiple light sources, which results in several viewing directions, having independently controllable light emissions in the same image point. Such a display is described in the publication xe2x80x9cA prototype flat panel hologram-like display that produces multiple perspective views at full resolutionxe2x80x9d, by J. Eichenlaub, in: Proceedings of the SPIE Vol. 2409, pp. 102-112. Here, the number of the light sources is essentially equal to the number of the image pixels in a line. Therefore, in order to produce an image with an acceptable resolution, a large number of very small light sources are needed. These light sources are extremely expensive, due to their small size and the large quantity needed. The light sources may be manufactured by optical methods (e.g. cylindrical lens matrix, disclosed in WO 94/06249), but this requires again a very precise and costly technology, and the illumination angle is also limited. A further disadvantage of this approach is the limited intensity which may be achieved. The application of this system for moving images is clearly limited by the addressing speed of the LCD screen, and the switching speed of the light sources.
The need to provide several emitting directions from one image point is also recognised in the solution described in U.S. Pat. No. 5,521,724 (Shires). In this solution a simple electronic display is presented, which produces 3D images by binocular parallax. The effect is produced by the pixels of a traditional 2D display, which are spatially multiplexed by holographic elements. The problem of the data speed is not discussed.
There are also disclosed various forms of lenticular lens systems, which provide outgoing light beams according to different viewing directions. Such a solution used to create an autostereoscopic display is described in EP 0 786 912 A2. Again, in this document there is no teaching how the large amount of data may be fed into the subpixels of the image pixels (essentially, the pixels of an SLM, see FIG. 11.), which then produce the different images in different directions through the lenticular lenses.
In the field of laser printers, LED arrays arranged in a line are already known. These arrays contain individually adressable light sources. However, it has not been suggested to use such a LED array to produce light beams which are radiating in different directions, and thereby achieving 3D images.
Accordingly, it is an object of the present invention to provide a pixel element which simultaneously solves the optical problem of the multiple directed light beams and the problem of the data transfer to the light sources. It is a further object to provide a pixel element that is relatively easy to manufacture, replaceable, and require simple supporting systems, both in mechanical, optical, and electronic terms.
The above objectives are reached by a pixel element for a 3D screen, comprising means for generating multiple substantially collimated, controllable light beams emitted in multiple directions, so that each light beam is associated to a predetermined viewing direction. According to the invention, the pixel element comprises at least one set of substantially point source type, individually addressable light sources arranged in a line, and optical imaging means for imaging the light of each light sources in a collimated light beam and for deflecting each collimated light beam in a predetermined individual deflection direction, and further comprising means for serially addressing the light sources.
Especially, it is foreseen that the addressing means comprises a serial input shift register and/or a multiplexer for distributing the information from the input shift register to the individual light sources.
It is also suggested to use three sets of light sources radiating in the RGB colours, where each set is arranged in a line parallel with the other sets. Alternatively, one set of light sources may be arranged in multiple parallel lines. One line of light sources may be imaged by a lenticular matrix and/or an objective lens, which is associated to the line of the light sources.
In a particular embodiment, the addressing means comprises memory means for storing the input information of several operation cycles. It is also foreseen that the addressing means comprises means for evaluating the state of the light sources radiating in the neighbouring deflection directions.
The invention also includes a novel 3D display comprising pixel elements according to the invention.
Essentially, there is provided a novel light emitting pixel element, particularly for 3D screen applications. The main feature of such a pixel element is the ability to generate several independent light beams within a single unit, and without the use of expensive and bulky active optical elements. These light beams are emitted in several independent directions, so that each light beam is associated to a predetermined viewing direction. The different light beams are practically collimated, in order not to interfere with the neighbouring viewing directions. To achieve a true 3D effect, each independent light beam must be controllable on its own. The light beams are realised in the form of miniature diode lasers or LEDs, which function as substantially point source type, individually addressable light sources. The light sources are arranged in a line, which facilitates their deflection with a common optical projection system. Colour screens are created with three lines of light sources radiating in the RGB colours. The coloured lines of the light sources are positioned sufficiently close to each other, so the light beams appear to be emitted from one source.
This optical projection system includes means for imaging the light of each light sources in a collimated light beam, preferably a matrix of miniature lenses. The generated set of the parallel, collimated light beams are deflected in predetermined individual deflection directions, which corresponds to the viewing directions. This deflection is effected with a common objective lens. To keep the wiring and addressing within feasible limits, the pixel elements are provided with appropriate means for serially addressing the light sources. E.g. a serial input buffer or shift register, and/or a multiplexer could be integrated on the same chip or at least on the same ceramic plate which carries the light sources and their driver circuits.
The suggested pixel element is currently limited to provide 3D image along one axis (co-ordinate) only. To increase the viewing angle along the other axis, it is foreseen to apply a holographic plate or a cylindrical lens system as a means for establishing a divergence (diffusion) of the light beams perpendicular to the plane of deflection. To achieve a continuous image, when moving from one viewing angle to another, it is also suggested to apply some sort of diffusor to establish a divergence of the light beams in the plane of deflection. This divergence should be sufficient to cause an overlap of the edges of neighbouring light beams at least in a distance from the pixel element. The divergence or diffusion of the light beams could be done with the same holographic element, both in the perpendicular and the parallel direction.
It is fully feasible to provide the addressing logic of the pixel elements with intelligent features, like a firmware-type microprogram for evaluating the state of the light sources in neighbouring pixel elements. In this manner the whole screen of the pixel elements could act as a distributed processing unit, and e.g. certain functions of the data compression and decompression algorithms could be assigned to the microprograms in the pixels.
However, the greatest advantage of such a pixel element is the inherent simplicity of the device, which fully substitutes the functions of complicated and sensitive optical arrangements for producing a true 3D image. The pixel elements according to the present invention may be used to produce 3D screens in various sizes and resolution, using the same basic unit. The pixel element itself is relatively low-cost, if produced in large quantities. The necessary technologies to produce the different parts of the pixel element are all available and already tested in practice. The pixel element of the invention allows the realisation of a very powerful and sophisticated, and at the same time mass-produced and low-cost 3D screen.
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