Abstract:
A device for the production of holographic reconstructions having light modulators is disclosed. The device comprises at least one pixelated light modulator illuminated by at least one light source, and a focusing optical element field arrangement which images the light sources in an image plane after the light modulator. For the reconstruction, only one order of diffraction of the Fourier spectrum of the hologram should be used. The light modulator is provided with an assigned filter-aperture field arrangement which is located in the area of the image plane of the light source images and which has a plurality of aperture openings. Said aperture openings are designed in such a way that they each allow the passage of a prespecified area of the overall dimensions either smaller or the same as a diffraction order of the diffraction spectrum following Fourier transformation and produced from the holographic coding of the light modulator.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority of PCT/EP2008/054584, filed on Apr. 16, 2008, which claims priority to German Application No. 10 2007 019277.2, filed Apr. 18, 2007, the entire contents of which are hereby incorporated in total by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a device for generating holographic reconstructions with light modulators, comprising:
         At least one pixelated light modulator, which is illuminated by at least one light source,   A focussing optical element array, where each optical element is assigned to a group of encodable pixels of the light modulator, and where the optical elements image the light sources into an image plane downstream the light modulator so as to form light source images, and   A control unit, which is connected to the light modulator, and which computes with the help of programming means the holographic code for the pixelated encoding surface of the light modulator.       

     The term ‘pixelated light modulator’ shall not necessarily be understood in the context of this invention as a modulator which comprises an arrangement of discretely controllable elements. It can also be a modulator with a continuous encoding surface, which is formally divided into discrete elements by the information to be displayed. 
     Further, the term ‘optical elements’ shall not necessarily be understood to be or to comprise conventional glass lenses, but it can be construed in a wider sense to be or to comprise refractive or diffractive optical elements which fulfill the same function. 
     A device for generating holographic reconstructions of representations, in particular three-dimensional scenes, is described in document WO 2006/119920 A1. 
     If information for example of a computer-generated hologram is stored on the pixelated light modulator, and if the light modulator is illuminated with sufficiently coherent light, a reconstruction of a three-dimensional scene will be generated in a reconstruction space. However, undesired periodic continuations also occur in the form of higher diffraction orders, because of the discrete representation of the hologram in the light modulator. Depending on the hologram encoding method employed, undesired regions can also occur within a diffraction order, which must therefore be filtered. 
     A conventional method for eliminating disturbing diffraction orders is to use a filter unit, e.g. a 4f arrangement, which can filter such diffraction orders. The filter unit can be dimensioned such that it only lets pass regions which are smaller than or identical to one diffraction order. 
     Such a method is applied for example in document DE 10 2005 023 743 A1. This document describes a holographic projection device and a method for generating holographic reconstructions of scenes using one-dimensionally and two-dimensionally encodable light modulators, said device comprising a light source, a focussing optical system, the corresponding light modulator, a projection system, and a filtering aperture, which is arranged between the light modulator and the projection system, and which lies in the image plane of the light source image. 
     The focussing optical system represents for the light modulator an optical illumination system, and for the light source an optical imaging system which images the light source into the image plane of the optical illumination system, where the Fourier transform of the light modulator is simultaneously generated in the image plane of the light source. 
     The projection device comprises a control unit which does not only encode the light modulator dynamically, but which also tracks the visibility region and thus the holographic reconstruction to a changing observer position. To achieve this, a position detection system is provided, which is connected to the control unit. The code on the light modulator is modified such that the reconstruction of the three-dimensional scene appears in a horizontal, vertical and/or axial position horizontally and/or vertically displaced and/or turned by an angle, according to the actual observer position. 
     In a dimensioned modification of the size relations of the above-described projection device in the form of a large, observer-friendly direct-view device, e.g. with a display with a diagonal of 20 inches, which is the size of a typical desktop monitor, a filtering process is performed on the light modulator, where a single light source is provided for the coherent illumination of the entire light modulator in conjunction with a filter unit. The direct-view device with the 20-inches display can comprise the light source, a focussing optical system, the corresponding light modulator, a projection system, and a filtering aperture, which is arranged between the light modulator and the projection system, and which lies in the image plane of the light source image. The filtering aperture comprises an opening which only lets pass the desired one diffraction order of the Fourier transform of the light modulator. The projection system images the aperture into another plane, which represents the observer plane at the same time. The observer in the observer plane can see the holographic reconstruction in a visibility region which corresponds to one diffraction order of the Fourier spectrum. 
     The corresponding filter unit requires in addition to the filtering aperture at least two lenses of which at least one is about as large as the light modulator that represents the display. This means for example in the case of the holographically encoded 20-inches display panel that one lens must have a diameter of at least 40 centimeters. 
     Because lenses typically only exhibit an adequate image quality at a ratio of focal length and aperture of much larger than one, and because the filtering takes place at the position of the light source image, here in the focal plane of the first lens, a filter unit first wide lens, filtering aperture, second wide lens—which has a depth of substantially larger than 40 centimeters in front of the light modulator panel is required in this example. In the direct-view device with a light modulator panel as a screen, if a large display is used (e.g. with a diagonal of 20 inches), it is rather complicated to provide a wide lens which has about the size of the screen, where, in addition, the filter unit has a very large depth, as described. 
     One problem is that the design of a holographic direct-view device with the described dimensions of the optical components is very voluminous and heavy, which is undesired. 
     A further problem is that, in display holography, because of the pixel dimensions of commercially available light modulators, only very small useable diffraction angles are provided, which, in turn, cause a small observer window. 
     According to a method of display holography described in document U.S. Pat. No. 3,633,989, HPO (horizontal-parallax-only) holograms are used, where a hologram encoding is only performed in one dimension. Values for the one-dimensional hologram are computed independently of each other and are typically written to individual rows of a light modulator. In order to increase the diffraction angle, hologram values, which are typically encoded in multiple pixels arranged side by side, can in this case be encoded in pixels which are arranged below one another in multiple rows. 
     When using one-dimensional holographic codes within the light modulator, it will only be possible for a one-dimensional holographic reconstruction to take place. The light wave diffracted by the one-dimensional HPO hologram of the light modulator accordingly extends in the horizontal direction in the visibility region. 
     SUMMARY OF THE INVENTION 
     It is therefore the object of the present invention to provide a device for generating holographic reconstructions with light modulators, said device being designed such that an expensive arrangement at least of the optical system can be avoided on the one hand and that the diffraction angle which is used for the visibility region can be increased, on the other hand. The dimensions of the device in the axial direction shall be kept as small as possible. 
     The object is solved with the help of the features of claim  1 . 
     The device for generating holographic reconstructions with light modulators comprises:
         At least one pixelated light modulator, which is illuminated by at least one light source,   A focussing optical element array, where each optical element is assigned to a group of encodable pixels of the light modulator, and where the optical elements image the light sources into an image plane downstream the light modulator so as to form light source images, and   A control unit, which is connected to the light modulator, and which computes with the help of programming means the holographic code for the pixelated encoding surface of the light modulator,
 
where according to the characterising clause of claim  1 
 
the light modulator is assigned with a filtering aperture array which has a multitude of apertures, and which is situated near the image plane of the light source images, and whose apertures in the filtering aperture array are formed such that they let pass a defined region of the diffraction spectrum which has been generated by holographic encoding of the light modulator, said defined region having a size that is smaller than or identical to one diffraction order of the Fourier transform.
       

     A light source with an optical beam widening system can be arranged in front of the light modulator for illuminating the light modulator. 
     A dynamic shutter modulator can be provided between the optical beam widening system and the focussing optical element array. 
     As an alternative for illuminating the light modulator, a light source array with a multitude of light sources can be disposed in front of the light modulator. 
     The device can comprise a light source array, a first optical element array as an optical beam widening system, and a second optical element array with multiple spherical optical elements, e.g. in the form of spherical lenses, as a screen for the observer. 
     A power supply unit is assigned to the light source or the first light source array. 
     The control unit for encoding the light modulator is a part of a control system, which also comprises a unit for controlling the light source array, and/or a unit for controlling the filtering aperture array, and a position detection unit for detecting the actual observer position. 
     The position detection unit can be connected to the two units; at least by signal. 
     The two units can optionally be connected to a displacing device which displaces in their respective planes the light sources of the light source array, and/or the filtering apertures of the filtering aperture array, which represent the movable components, in response to signals from the position detection unit. However, the first and the second optical element array can also be of a displaceable design. 
     Both the light source array and the filtering aperture array can be designed either as static components, or as dynamic optical components which are adjusted by the control system. 
     The pixelated encoding surface of the light modulator can for example have pixels of a square design. 
     The first optical element array represents for the light modulator an optical illumination system, and for the light source array an optical imaging system which images the light source array into the focal plane which is given as the Fourier plane of the light modulator, where the images of the light source array coincide with the Fourier transform of the pixels of the respective subsection of the light modulator through which the light shines, and where the filtering aperture array which lets pass the given diffraction order is disposed near the focal plane. 
     The filtering aperture array can exhibit a grid of apertures which only let pass the given diffraction order of the Fourier transform, or only parts thereof. 
     The projecting second optical element array with the particularly two-dimensional spherical lenses images the apertures of the filtering aperture array into a second plane, which serves as the observer plane at the same time. Optical elements and filtering apertures are mutually arranged such that the images of all apertures overlap in the observer plane, thus forming an observer window. 
     The first optical element array can be a two-dimensional arrangement of spherical lenses which are disposed downstream the point light sources of the light source array. 
     A single spherical lens of the first optical element array and a single spherical lens of the second optical element array can have a size which typically ranges between about three and ten millimeters. 
     The size of the apertures of the filtering aperture array depends on the pixel pitch p of the light modulator and on the focal length of the lenses of the first optical element array. 
     The filtering aperture array can be a shutter modulator whose controllable openings have the dimensions of one or multiple pixels of the shutter modulator. 
     The programming means for encoding the pixels of the light modulator in the control unit can be adapted to the design of the device according to the present invention. 
     If HPO holograms are used, the hologram values can be encoded in multiple horizontally or vertically adjacently arranged pixels of one or multiple rows of the light modulator. 
     In the control system, in particular in the control unit, it is possible to carry out a holographic encoding in only one dimension, where the values written to a group of rows or columns of the light modulator are related to each other. 
     The first optical element array can then be a lenticular array with cylindrical lenses, which is illuminated by line light sources and which is assigned with a filtering aperture array with slotted apertures. 
     A sufficiently coherent illumination of the light modulator must then only be achieved in the area of the group of a few rows. 
     In order to track the visibility region to the observer, a dynamic shutter modulator for displacing the position of the apertures can be used as a filtering aperture array. 
     The light source array can comprise an arrangement of adjacent light sources which can be turned on individually one after another, where said arrangement illuminates a certain vertical section in a certain interval of time, which can be controlled by the control system. 
     In order to enlarge the visibility region used by the observer, particularly in the vertical direction, diverging lenses can be used, where the entirety of diverging lenses can also have the form of a diverging lens array, which is disposed directly downstream the filtering aperture array. 
     Optionally, depending on the design and encoding method used for the light modulator, one-dimensional, slotted filtering aperture arrays or two-dimensional filtering aperture arrays with round apertures can be employed. 
     The filtering aperture array can be designed statically in the form of an aperture mask. 
     In order to track the visibility region or to periodically scan a certain viewing range, a dynamic filtering aperture array can be provided which is realised with the help of the controllable displacing devices of the control system. 
     The filtering aperture array can be a fast switching amplitude-modulating light modulator where the variation of the transmittance of individual pixels causes a filtering effect, where the activated pixels, which then serve as apertures, roughly correspond to the size of the opening of the apertures of the static filtering aperture array. 
     The light source array can, in agreement with the dynamic filtering aperture array, be a fast switching amplitude-modulating light modulator, which is entirely illuminated by a light source, and where the variation of the transmittance of individual pixels causes light beams to be let pass, where the pixels, which then serve as openings for beam passage, have about the size of the diameter of the light sources of the static light source array. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be described in more detail below with the help of a number of embodiments and drawings, wherein: 
         FIG. 1  shows schematically the side view or top view of a device for generating holographic reconstructions according to the present invention; 
         FIG. 2  shows a detail of the encoding surface of a two-dimensionally encodable, pixelated light modulator with square pixels; 
         FIG. 3  shows schematically the side view of a variant of the device for generating holographic reconstructions according to the present invention, where 
         FIG. 3   a  shows the arrangement of device components which are essential to the invention, and 
         FIG. 3   b  shows a detail of the encoding surface of a one-dimensionally encodable, pixelated light modulator; 
         FIG. 4  shows schematically the side view of a device for generating holographic reconstructions according to the present invention with an adjustable filtering aperture array and an adjustable light source array according to  FIG. 1  and  FIG. 3   a;    
         FIG. 5  shows schematically the side view of a device for generating holographic reconstructions according to the present invention according to  FIG. 3   a  with a dispersing lens array; 
         FIG. 6  shows schematically a part of a 4f arrangement of the device according to this invention; 
         FIG. 7  shows the phases of the two pixels of the macro pixel at the phase unit circle according to  FIG. 6 ; 
         FIG. 8  shows two amplitude-phase position diagrams for a macro pixel which comprises two pixels according to  FIGS. 6 and 7 , where 
         FIG. 8   a  shows the dependence of the amplitude on the position before the filtering, and 
         FIG. 8   b  shows the amplitude in dependence on the position after filtering by a lenticular array. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows schematically a device  1  for the holographic reconstruction of a three-dimensional scene  9  according to the present invention with a light modulator  2 , said device having a housing  3  which comprises at least:
         A light source array  4  with multiple light sources  41 ,   At least one pixelated light modulator  2 , which is disposed downstream the light source array  4 ,   A focussing lens array  5 , where each lens  51  is assigned to a group of encodable pixels  21  of the light modulator  2 , and where the lenses  51  image the individual light sources  41  of the light source array  4  into an image plane  6  downstream the light modulator  2  so as to form light source images  42 , and   A control unit  7 , which is connected to the light modulator  2 , and which computes with the help of programming means the holographic code for the pixelated encoding surface  22  of the light modulator  2 .       

     According to the present invention, the light modulator  2  is assigned with a filtering aperture array  8  which has a multitude of apertures  81 , and which is situated near the image plane  6  of the light source images  42 , and whose apertures  81  in the filtering aperture array  8  are formed such that they let pass one specific diffraction order or parts thereof of the diffraction spectrum which has been generated by holographic encoding of the light modulator. 
     The inventive device  1  according to  FIG. 1  can further comprise a light source  11  with an optical beam widening system  12  and a second lens array  13  with multiple spherical lenses  131  as a screen for the observer  14 , instead of a light source array  4 . A power supply unit  15  is assigned to the light source  11  or, independent of the light source  11 , to the first light source array  4 . The control unit  7  for encoding the light modulator  2  can be a part of a control system  16  which, according to  FIG. 1 , can further comprise a unit  17  for controlling the light source array  4  and a unit  18  for controlling the filtering aperture array  8  and a position detection unit  19  for detecting the position of the observer  14 . The position detection unit  19  is connected to the two units  17  and  18 , at least by signal. The two units  17  and  18  are connected to a displacing device  20  which displaces the movable components in their respective planes, e.g. the light sources  41  of the light source array  4 , and/or the filtering apertures  81  of the filtering aperture array  8 , or the lenses  51  of the lens array  5 , in response to signals from the position detection unit  19 . 
       FIG. 1  thus shows a filtering process on a holographically encoded light modulator  2 , which forms a part of the device  1  according to the present invention, and in which the light source array  4  is used in conjunction with the first lens array  5 , the filtering aperture array  8  and the second lens array  13 . 
       FIG. 2  shows schematically the pixelated encoding surface  22  of the light modulator  2 , where the pixels  21 , which are here of a square design, are disposed in the xy plane of the xyz coordinate system  10  which is shown in  FIG. 1 . Here, p denotes the distance between the centres of two adjacent pixels  21 , and the coordinate z denotes the axial direction in which the optical components which belong to the device  1  are disposed. 
     Referring to  FIG. 1 , the first optical element array  5  represents for the light modulator  2  an optical illumination system, and for the light source array  4  an optical imaging system which images the light source array  4  into the focal plane  6  which is given as the Fourier plane of the light modulator, where the images of the light source array  4  coincide with the Fourier transform of the pixels of the respective subsection of the light modulator  2  through which the light shines, and where the filtering aperture array  8  which lets pass the given diffraction order is disposed near the focal plane. The filtering aperture array  8  exhibits a grid of apertures  81  which only let pass the given diffraction order of the Fourier transform or parts thereof. The projecting second lens array  13  with the two-dimensionally arranged spherical lenses  131  images the apertures  81  into a second plane  61 , which serves as the observer plane at the same time, where the images of the individual apertures  81  overlap in a visibility region. The holographic reconstruction  9  of the three-dimensional scene can be seen by an observer  14  in the observer plane  61 , in the visibility region which corresponds to one diffraction order of the Fourier spectrum. 
     The first optical element array  5  can be a two-dimensional arrangement of spherical lenses  51  which are disposed downstream the point light sources  41  of the light source array  4 , where a two-dimensional filtering aperture array  8  of apertures  81  and a second optical element array  13  are provided as well.  FIG. 1  shows a sectional view of the device  1  through the rows or columns of the arrays  4 ,  5 ,  6 ,  13 . 
     A single lens  51  of the first optical element array  5  and a single lens  131  of the second optical element array  13  can for example have a size which typically ranges between three and ten millimeters. 
     The total depth of the device  1  in the z direction only increases moderately due to the filtering with the arrays  4 ,  5 ,  6 ,  13 , and is much smaller than the dimensions of the arrangement involving wide lenses which are described in the prior art section. 
     The filtering aperture array  8  here is a two-dimensional grid with small openings, namely the apertures  81 . The size of the apertures  81  depends on the pixel pitch p of the light modulator  2 , as shown in  FIG. 2 , and on the focal length of the lenses  51  of the first optical element array  5 , which determine the extent of a diffraction order in the Fourier plane. A given value can be in the range of between 0.1 mm and 0.2 mm. 
     The filtering aperture array  8  can alternatively be a shutter modulator with controllable openings which have the dimensions of one or multiple pixels of the shutter modulator. 
     The programming means for the holographic encoding of the pixels  21  of the light modulator  2  in the control unit  7  can be adapted to the design of the device  1 . 
       FIGS. 3 ,  3   a  shows schematically the device  1  for generating holographic reconstructions  91  according to the present invention, in a reduced form compared to  FIG. 1 , comprising a light source array  43 , a first optical element array  5 , a light modulator  23 , and a filtering aperture array  8  which is disposed downstream the light modulator  23  and which lies in the image plane  6  of the light source images  42 . 
     In order to reduce the required hologram computing time, HPO (horizontal parallax only) holograms are used in prior art display holography, where the hologram is only encoded in one dimension, e.g. in the y direction, as shown in  FIGS. 3 ,  3   b . Amplitude and phase values which are computed independently of each other are typically written to individual rows of the light modulator  23 . When using one-dimensional holographic encoding  24 ,  25 ,  26 ,  27  within the light modulator  23 , it will only be possible for a one-dimensional holographic reconstruction to take place. The light wave which is for example diffracted by the one-dimensional HPO hologram of the light modulator  23  accordingly only extends in the horizontal direction in the visibility region in the plane  61 . 
     Here, the first optical element array  5  and/or the second optical element array  13 , as shown in  FIG. 1 , can be lenticular arrays with cylindrical lenses which are illuminated by line light sources  41  and which are assigned to a filtering aperture array  8  with slotted apertures  82 . For HPO holograms,  FIG. 1  shows a top view of the device  1 . However, it is generally also possible to use VPO (vertical parallax only) holograms, where everything is turned by 90 degrees. 
     In order to enlarge the diffraction angle and thus the useable visibility region in the plane  61 , it can be possible in the case of an HPO hologram for example to use a combination of multiple rows of a hologram, instead of multiple columns, in order to encode a complex hologram value. 
     One possibility for the computation in the control unit  7  is here for example a representation of a complex number by multiple phase values, where the one-dimensional arrangement of complex hologram values is computed in the horizontal direction, i.e. in the y direction, while the phase values which form a complex number are arranged in pixels one above another in the vertical direction. To achieve this, a coherent illumination is only required for a group  28  of a few rows  24 ,  25 ,  26 ,  27 . If a group  28  of rows  24 ,  25 ,  26 ,  27  of a light modulator  23  is coherently illuminated, this will cause in the vertical direction, i.e. in the x direction an undesired retardation of optical path among the individual rows, where said retardation is angle-specific, and leads to a deviation of the expected reconstruction. 
       FIG. 3   a  shows that, if multiple rows  24 ,  25 ,  26 ,  27  are coherently illuminated, the hologram computation will only be carried out with horizontal parallax, and the filtering process will be carried out with the help of a filtering aperture array  8  with slotted apertures  82 ; each one for a group  28  of coherently illuminated rows  24 ,  25 ,  26 ,  27 . This makes it possible to encode hologram values which were hitherto encoded in horizontally adjacently arranged pixels, in pixels which are arranged vertically below one another. 
     While filtering units of a 4f-arrangement type according to  FIG. 1  require an arrangement of at least two optical element arrays  5  and  13  disposed one behind another of which the first optical element array  5  realizes a Fourier transformation and the second optical element array  13  realizes a back-transformation, a back-transformation to the image plane  6 , as shown in  FIGS. 3 ,  4 ,  5 , is not necessary in this embodiment of the device, where few light modulator rows  24 ,  25 ,  26 ,  27  are coherently added. 
     The complex amplitude and phase values on the light modulator  23 , as shown in  FIGS. 3   a ,  4 ,  5 , are computed in the control unit  7  just by way of a one-dimensional Fourier transformation in the horizontal direction. 
     In the vertical direction, the desired signal itself, as a coherent addition of multiple light modulator rows  24 ,  25 ,  26 ,  27 , is transmitted (or undesired portions thereof are filtered out) in the image plane  6 , and not its Fourier transform. However, an observer  14  must also be able to move vertically within the visibility region in the plane  61 , so that he can watch the original reconstruction  91 , or the accordingly displaced reconstruction  92 , from multiple vertical positions, as shown in  FIG. 4 . To achieve this, light must propagate from the image plane  6  to the corresponding vertical position. 
       FIG. 5  shows a diverging lens array  53 , which is disposed downstream the image plane  6 , and which widens the angle under which the light propagates in the vertical direction. 
     However, a preferred alternative for adjusting the visibility region in the plane  61  to the observer  14  can be a dynamic shutter for displacing the position of the apertures  81  or  82  in the filtering aperture array  8 . This can be achieved in conjunction either with a modification of the values represented on the light modulator  2 ,  23 —for example by adding a certain phase offset for an entire row when employing a phase encoding method—or with a movable light source array  4 . This has the advantage that a light modulator  2  with comparatively slow switching speed can be used as well. 
     Referring for example to  FIG. 4 , the latter can also be a light source array  4  where adjacently arranged light sources  41  are switched on one after another controlled by the unit  17  for controlling the light source array  43 . A certain vertical section, which is given with the direction sign L, can thus be scanned in a certain interval. 
       FIG. 4  also shows a possible displacement, with the direction sign F, of the apertures  82  of the filtering aperture array  8  in the image plane  6 , where the filtering aperture array  8  can also be a dynamic light modulator. 
       FIG. 5  illustrates the above-mentioned possibility to use additional diverging lenses  52  for enlarging the usable visibility region in the plane  61  for the observer  14 , where the entirety of the parallel-oriented diverging lenses  52  has the form of a diverging lens array  53 , which can be disposed directly downstream the filtering aperture array  8 . 
     In conjunction with a light source array  4 , the device  1  according to the present invention allows undesired diffraction orders to be filtered out for each single section of a hologram, which is illuminated with sufficient coherence by a light source  41 . This particularly allows small, compact filter units to be used, which can also be disposed in front of a large holographic screen  13 . Optionally, depending on the design and encoding method used for the light modulator  2 ,  23 , one-dimensional directed —preferably slotted —filtering aperture arrays  8 , or two-dimensional filtering aperture arrays  8  —preferably with round apertures —can be used. 
     The filtering aperture array  8  can be static, in the form of an aperture mask. 
     A further embodiment of the device  1 , which allows a certain visibility region in the plane  61  for the observer  14  to be tracked or to be scanned periodically, is the dynamic design of the filtering aperture array  8  through the controllable displacing devices  20  of the control system  16 . 
     The filtering aperture array  8  can then for example be a fast switching amplitude-modulating light modulator where the variation of the transmittance of individual pixels or pixel groups effects a filtering. The pixels or pixel groups, which can then serve as apertures  81 , then have about the size of the opening of the apertures  81 . Because the individual filter units of the filtering aperture array  8  are illuminated by light sources which are incoherent in relation to each other, no new diffraction structure will be created by the filtering aperture array  8 . 
     The light source array  4  can, in agreement with the filtering aperture array  8 , be a fast switching amplitude-modulating light modulator, where the variation of the transmittance of individual pixels or pixel groups causes light to be let pass, where the pixels or pixel groups, which then serve as openings for light passage, have about the size of the diameter of the light sources  41  of the static light source array. 
     A preferred application of the filtering aperture array described above is to filter out an angle-dependent phase shift among pixels, which is not desired but cannot be avoided when encoding complex hologram values in multiple adjacent phase pixels. This undesired phase shift, which occurs in addition to a programmed, desired phase shift, is caused by the fact that the pixels which represent one hologram value are arranged side by side and not one behind another. This will now be explained with the example of an embodiment where the optical element arrays  5  and  13  and the filtering aperture array  8  are understood to form a 4f filtering arrangement, and where one complex hologram value is encoded with the help of mere phase values in two adjacent pixels. 
       FIG. 6  shows a longitudinal section of a part of a 4f arrangement  31  with a light modulator  2 , a first focussing optical element array  5 , which is disposed downstream in this embodiment, and a second focussing optical element array  13 , which is disposed downstream, after which the filtered pixel information of the light modulator  2  is provided as an exit  30 , where the filtering aperture array  8  with the apertures  81  is disposed between the two optical element arrays  5  and  13 . 
     The first optical element array  5  comprises focussing lenses as optical elements  51 , and the second optical element array  13  also comprises focussing lenses as optical elements  131 , where the two optical element arrays can be designed in the form of lenticular arrays. 
     Two pixels  291 ,  292  each form a group or macro pixel  29  for the two-phase encoding of the complex hologram value, where the macro pixel  29  has the same size as the lenses  51 . The size of the lenses  51  is exemplarily given as 60 μm in  FIG. 6 , the apertures  81  have a size of 10 μm, and the distances between the light modulator  2  and the filtering aperture array  8 , and between the exit  30  and the filtering aperture array  8  are 1 mm each. The dimensions are specified in particular in order to provide a comparison to the dimensions of the prior art direct-view device. 
       FIG. 7  shows the encoding of a complex hologram value by two mere phase values in the phase unit circle  293  with the axes Im (imaginary part) and Re (real part), where the phase  2911  of the pixel  291  and the phase  2921  of the pixel  292  of the light modulator  2  are added according to a parallelogram  295  so as to form a resultant complex value  294  of the macro pixel  29 , where said resultant value exhibits the desired amplitude value different from 1 and the desired phase value. This is illustrated in  FIG. 8  with a numerical example. 
       FIG. 8   a  shows a two-phase representation of a complex value of 0.3 exp 1.1i of an ideal complex-valued macro pixel  32 , where the amplitude is represented by the value ‘0.3’ and the phase by the value ‘1.1rad’. According to  FIG. 7 , the complex value is created from the two encoded phase values 1 exp 2.17i of the pixel  291  and 1 exp −0.17i of the pixel  292 . The amplitudes of the two phase pixels are identical and have the value ‘1’, the pixel phase  2911  of the pixel  291  is ‘2.17rad’, and the pixel phase  2921  of the pixel  292  is ‘−0.17rad’. 
     In addition to the shown phase values of the two single pixels, a further, illumination-angle-dependent phase shift would occur between the two pixels if they were illuminated at an oblique angle, because the pixels are disposed side by side. This additional phase shift would falsify the desired complex value, but it is filtered out by the 4f filtering for each pixel group, so that the macro pixel  32  indeed exhibits the desired phase and amplitude value at the exit of the 4f system. 
       FIG. 8   b  shows a comparison before and after the filtering in the image plane  6  between practical filtering in the 4f arrangement  31  and calculated filtering, where the values before filtering the encoding of the pixels  291 ,  292  in the light modulator  2 , and the values after filtering at the exit  30  immediately downstream the optical element array  13 , which can be a lenticular arrangement, are represented by the straight line as regards amplitude and phases, said straight line being drawn almost parallel to the position coordinate. The minor deviations in  FIG. 8   b  as regards both the resultant amplitude distribution and the resultant phase distribution between the filtered macro pixel  29  and the ideal complex-valued macro pixel  32  can be widely neglected, and there is great agreement between the function of the device  1  according to this invention and the calculations of the complex values with programming means used. 
     LIST OF REFERENCE NUMERALS 
     
         
           1  Device 
           2  First light modulator 
           21  Pixel 
           22  Encoding surface 
           23  Second light modulator 
           24  First line 
           25  Second line 
           26  Third line 
           27  Fourth line 
           28  Group 
           29  Macro pixel 
           291  First pixel 
           2911  Pixel phase 
           292  Second pixel 
           2921  Pixel phase 
           293  Unit circle 
           294  Resultant phase 
           295  Phase parallelogram 
           3  Casing 
           4  First light source array 
           41  Light sources 
           42  Light source images 
           43  Second light source array 
           5  First optical element array 
           51  Lenses 
           52  Diverging lenses 
           53  Diverging lens array 
           6  Image plane 
           61  Plane of the visibility region 
           7  Control unit 
           8  Filtering aperture array 
           81  First apertures 
           82  Second apertures 
           9  Reconstruction 
           91  Reconstruction 
           92  Displaced reconstruction 
           93  Enlarged reconstruction 
           10  xyz coordinate system 
           11  Light source 
           12  Optical beam widening system 
           13  Second optical element array 
           131  Lenses 
           14  Observer 
           15  Power supply unit 
           16  Control system 
           17  Unit for controlling the light source array 
           18  Unit for controlling the filtering aperture array 
           19  Position detection system 
           20  Displacing devices 
           30  Exit 
           2  Part of a 4f arrangement 
           32  Ideal complex-valued macro pixel 
         Im Imaginary part 
         Re Real part