In many fields of science, technology and entertainment, images, image sequences or films are currently being displayed on two-dimensional surfaces, for example the display screens of computer monitors or of television sets. Spatial depth can be simulated in the case of such two-dimensional displays only by perspective displays.
There is thus a need in many fields to display spatial objects as true three-dimensional images that can, for example, also be viewed from different directions and therefore possess a substantially higher information content than the purely two-dimensional display. True three-dimensional images therefore offer not only a more realistic visual impression in films or video games, but can be used advantageously, in particular, even in science and technology. Mention may be made by example of the three-dimensional display of complex protein structures or the three-dimensional display of organs or entire body areas that are calculated from data obtained by NMR tomography or computer tomography. Mention may be made as a further example of the three-dimensional display of radar images that, by contrast with the customary two-dimensional display, is attended by a decisive improvement in safety, since height information is to be seen in a directly visual fashion and need no longer be coded by numerical codes in the two-dimensional display.
In the meantime, numerous methods and apparatuses have become known that are intended to convey the impression of a three-dimensional image to the viewer. In accordance with a widespread method, an attempt is made to use technical aids to simulate the three-dimensional impression of the surroundings caused by human binocular vision. In this case, two images that correspond to sightlines slightly offset from one another and, for example, had been taken by stereophotography or generated by computer, are projected onto a screen. Suitable aids such as polarization or color filter spectacles ensure that the viewer sees only one of the two images with each eye. The three-dimensional effect thus simulated does not convey any additional information for the viewer that goes beyond the spatial depth. Thus, for example, the viewer is not able to view the scene being displayed from a new viewing angle by changing his position.
Moreover, many users find the necessity of wearing special spectacles irksome.
Raster image walls, in the case of which, at a specific distance, the viewer respectively sees with one eye only the image strips belonging to the left- or right-hand image, manage without such an aid. Here, as well, the viewer is incapable of changing position.
U.S. Pat. No. 6,005,608 describes a three-dimensional display apparatus that enables the display of true three-dimensional images that can be perceived by the viewer without special aids such as polarization or color filter spectacles. In this case, the two-dimensional image of a picture tube is projected onto a screen moving perpendicular to the image plane of the picture tube. The dimensions of the two-dimensional image source correspond here to the length and width of the volume displayed, while the movement amplitude of the screen perpendicular to this plane corresponds to the depth of the volume displayed. The contours, produced at each instant by the picture tube, of the three-dimensional image to be displayed are synchronized with the instantaneous spatial position of the screen. However, such an imaging system has a very low aperture, since the projection of the picture tube onto the screen is performed via a shadow mask and can therefore be operated only given a low level of ambient light.
A similar principle forms the basis of the 3-D display screen system marketed by the American company of Actuality Systems and described, for example, in the International patent application WO 02/21851, in the case of which a light beam is projected onto a rotating screen via a scanner optics. The 3-D display screen of the Actuality Systems company is very heavy and expensive because of the complicated mechanism. In addition, the image resulting from the deflection of a single light beam in order to produce images has a very low light level and can be viewed only in darkened rooms.
An apparatus for three-dimensional display of images is described in Japanese patent application JP 56-113116 A. In accordance with this document, two-dimensional individual images are projected onto a screen via an imaging device moving periodically to and fro together with the screen. However, it is possible with this known apparatus to build up the three-dimensional image only with four individual images that are projected onto the screen by four separate projectors, the respectively active projector being controlled via switches that are actuated depending on the instantaneous position of the imaging lens. Since the depth information is restricted to only four different two-dimensional individual images, the quality of the spatial display is not satisfactory. A change in the two-dimensional image information, or even the three-dimensional display of moving scenes is impossible with this apparatus. Moreover, the imaging of a two-dimensional individual image onto a screen with the aid of a projector leads to substantial restrictions with regard to the viewing angle under which the image on the screen can still be perceived in adequate brightness. In any event, taking account of the performance of conventional projectors it may be assumed that observing the image requires the room to be extensively darkened.
Again, an apparatus for producing three-dimensional images is described in Japanese patent application JP 57-062020 A. In accordance with this document, images are produced by moving an array composed of light-emitting diodes (LED array) back and forward. In the case of the apparatus described, the entire array must be moved together with the circuit electronics for controlling the array such that high forces act on the array itself, on the drive and on the mechanical guide. Japanese patent application JP 07-33546 A describes a further apparatus for producing three-dimensional images. In the case of the apparatus described there, the images are produced by three linear LED arrays that are arranged offset from one another, the offsetting of the three linear arrays defining the maximum possible image depth. Three flat images are produced in each case from the three depth staggered image lines by moving a mirror. In the case of this apparatus, as well, the viewer has available only a very restricted number of depth information items, and so it is not possible to talk of a true production of three-dimensional images.
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