Abstract:
Generating images to be projected at different projection distances with a multi-aperture projection display, statically or without any conversion, neither mechanically nor at the imager, is enabled by designing the single images of the multi-aperture projection display in a suitable manner, namely by combining provisional single images for the projection channels of the multi-aperture projection display, which are intended for each of the at least two images to be projected, projection channel by projection channel, to the actual or final single images.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of copending International Application No. PCT/EP2014/059581, filed May 9, 2014, which claims priority from German Application No. 10 2013 208 625.3, filed May 10, 2013, which are each incorporated herein in its entirety by this reference thereto. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to multi-aperture projection displays and single image generation for the same. 
         [0003]    So far, no satisfying technical solution exists for mapping different patterns onto different geometries or projection distances. Some solutions enable these mapping characteristics by changing the object structures, such as in the form of a digital imager, or by mechanical manipulation of the mapping optics according to the mapping equation, such as by changing the focal length or back focal length. However, such solutions are expensive. 
         [0004]    A specific case of the just described mapping characteristics is maintaining a fixed light pattern across a defined distance range. This characteristic is equivalent to the depth of focus in optics. 
         [0005]    The screen-side depth of focus (DoF) of a projector results, according to geometric considerations, from projection distance L, pupil expansion D and the acceptable blur angle β according to  FIG. 13  by the following relation (W. J. Smith, Modern Optical Engineering (McGraw-Hill, 2007)). 
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         [0006]    Thus, increasing the depth of focus for a given distance L and an accepted blur angle β according to (1) and (2) is only possible by reducing the pupil size D. This is accompanied by brightness loss of the projection, since the transmitted light flux is proportional to the accepted solid angle of each object point in the plane and is thus also reduced when reducing the pupil area D 2  (W. J. Smith, Modern Optical Engineering (McGraw-Hill, 2007)). 
         [0007]    An alternative approach for obtaining a great projector depth of focus is the usage of laser-illuminated MEMS mirrors using a scanning image buildup. Due to the small mirror area, the same do inherently have a great depth of focus, however, for a good image impression, the same necessitate both coherent light sources and fast, movable mechanical members (MEMS mirrors), which limits their robustness and potential fields of application. Further, the projection image generated in this manner can be adversely influenced by coherent effects, such as speckle, as long as no further technical measures for minimizing the same are taken. 
         [0008]      FIG. 14  shows a multi-aperture arrangement of micro-projectors, i.e., an array projector described, for example, in DE 102009024894 A1. The multi-aperture approach used therein allows decoupling the system installation length of the projection system from the obtainable light flux, allowing compact and, at the same time, bright projection systems. Previous publications concerning this optics approach describe a regular two-dimensional arrangement of micro-projectors, each consisting of a field lens  902 , an object structure/slide  903  and projection optics  904 . The overall arrangement is backlit by an extended or planar light source  901 . The projected overall image results from the focused superposition of all single images at a precise projection distance L. This is performed by a well-defined arrangement of the individual slides  903  with regard to the corresponding project lenses  904  according to equation (3). 
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         [0009]    Here, p means the center aperture distance between the individual projection lenses  904  and p+Δp means the center distance between the object structures or single images  903 . For the common sizes, reference is made to  FIG. 15 , which shows that s is the image distance, i.e., the distance between single image  903  and respective projection optics  904  and F is the focal length of the projection optics  904 . 
         [0010]    Due to the small apertures of each individual projection lens  904 , the depth of focus of the individual projectors is very large (cf. equation (2)). Here, the hyperfocal distance of the individual projections is typically significantly below the distance L. 
         [0011]    The set distance where the overall image results by superposition of all single images is essentially determined by the focal length/back focal length of the individual projectors  904  and the center distance difference Δp of the object structures  903  with respect to the corresponding projection lens array of lenses  904  (cf. Marcel Sieler, Peter Schreiber, Peter Dannberg, Andreas Brauer, and Andreas Tünnermann, “Ultraslim fixed pattern projectors with inherent homogenization of illumination,” Appl. Opt. 51, 64-74 (2012)). 
         [0012]    Thus, in equation 3, F corresponds to the focal length and p to the distance or center distance of the projector lenses  904  to one another and Δp to the center distance difference between the slides  902  and the lenses  904 , wherein s describes the back focal length resulting according to the paraxial mapping equation by combining L and F. From equation 3, it results that the depth of focus of the overall image  905  projected by superposing the individual micro-projectors, by neglecting geometric aberrations, corresponds to the one of a classical single channel project having a pupil size corresponding to the lateral expansion D of the micro-projector array (cf. Marcel Sieler, Peter Schreiber, Peter Dannberg, Andreas Brauer, and Andreas Tunnermann, “Ultraslim fixed pattern projectors with inherent homogenization of illumination,” Appl. Opt. 51, 64-74 (2012)). 
         [0013]      FIG. 16  shows, for example, the blur behavior of a conventional single channel projector as shown exemplarily in  FIG. 13 , namely at reference number  906 , and a single projector lens and an array projector according to  FIG. 14  and  FIG. 15  at  908 . All systems are focused onto a set distance of 533 mm. The blur behavior of an individual projection channel and an array projector correspond to one another insofar that they are commonly represented by the curve  908 . This means that the blur behavior of a single channel projector and a conventional array projector of the same pupil size correspond to one another by neglecting further aberrations and vignetting effects by dead zones. 
         [0014]    It would be desirable to have a system enabling the display of different images on different projection distances or geometries in a more objective manner. 
       SUMMARY 
       [0015]    According to an embodiment, a single image generator for a multi-aperture projection display with a plurality of projection channels may have: an input that is implemented to receive image data representing at least two images to be projected at different projection distances; a single image calculator that is implemented to calculate a provisional single image for each of the at least two images to be projected per projection channel of the multi-aperture projection display; and a combiner that is implemented to combine, for each projection channel, the provisional single images of the respective projection channel calculated for the at least two images to be projected to a final single image for the respective projection channel. 
         [0016]    Another embodiment may have a multi-aperture projection display including an inventive single image generator. 
         [0017]    Another embodiment may have a multi-aperture projection display including a plurality of laterally adjacent projection channels including one single image generator each for generating a respective single image and optics for mapping the respective single image which lies in an object plane of the optics into a projection direction of the multi-aperture projection display, wherein the single images of the projection channels are implemented such that the mappings of the single images of the projection channels are superposed at at least two different projection distances to one respective projected image each, wherein the single images are darkened more with respect to a positive superposition at locations where the non-zero-valued portions of the projected images reside when back-projected via the optics of the projection channels into the object plane of the optics of the projection channels reside at least partly, but no superposition of all of them, than at locations where the non-zero-valued portions of the projected images are all superposed with one another when back-projected via the optics of the projection channels into the object plane of the optics of the projection channels. 
         [0018]    According to another embodiment, a method for single image generation for a multi-aperture projection display including a plurality of projection channels may have the steps of: receiving image data representing at least two images to be projected at different projection distances; calculating a provisional single image for each of the at least two images to be projected per projection channel; and combining, for each projection channel, the provisional single images of the respective projection channel calculated for the at least two images to be projected, to a final single image for the respective projection channel. 
         [0019]    Another embodiment may have a production method with an inventive method for single image generation and a production of an array of optical masks such that the same correspond to the final single images generated according to  FIG. 16 . 
         [0020]    Another embodiment may have a computer program having a program code for performing the inventive method when the program runs on a computer. 
         [0021]    The core idea of the present invention is the finding that it is possible to generate images to be projected with a multi-aperture projection display at different projection distances, statically or without any adjustment, neither mechanical nor at the imager, when the single images of the multi-aperture projection display are designed in the suitable manner, namely by combining provisional single images for the projection channels of the multi-aperture projection displays, intended for each of the at least two images to be projected, projection channel by projection channel into the actual or final single images. 
         [0022]    According to embodiments, this is performed such that, for each projection channel, the final single image is—at locations where portions of the provisional single images of the respective projection channel intended for the images to be projected, which are valued unequal to zero, such as transmissive or luminous locations, reside at least partly, i.e. where the non-zero-valued portion of at least one image to be projected, but not all of them are superposed—darkened more with respect to a positive superposition of the provisional single images of the respective projection channel than at locations where the non-zero-valued portions of the provisional single images of the respective projection channel calculated for the images to be projected all are superposed. For the combination, for example, a logic operation is used between the provisional single images intended for the images to be projected, such as a logical AND- or OR-operation. 
         [0023]    Thus, according to an embodiment, for single image generation for a multi-aperture projection display having a plurality of projection channels, image data are used that represent at least two images to be projected at different projection distances, and for each of the at least two images to be projected, a provisional single image is calculated per projection channel of the multi-aperture projection display, wherein a combiner is implemented to combine, for each projection channel, the provisional single images of the respective projection channel calculated for the at least two images to be projected to a final single image for the respective projection channel. 
         [0024]    However, embodiments also provide a multi-aperture projection display, wherein the single images of the projection channels are implemented such that the mappings of the single images of the projection channels are superposed to one projected image each at at least two different projection distances, wherein the single images are darkened more with respect to a positive superposition at locations where the non-zero-valued portions of the projected images reside when back-projected via the optics of the projection channels into the object plane of the optics of the projection channels at least partly, but no superposition of all of them, than at locations where the non-zero-valued portions of the projected images all are superposed with one another when back-projected via the optics of the projection channel into the object plane of the optics of the projection channels. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    Embodiments of the present invention will be detailed subsequently referring to the appended drawings, in which: 
           [0026]      FIG. 1  shows a schematic three-dimensional view of a multi-aperture projection display according to an embodiment with real projection; 
           [0027]      FIG. 2  shows a top view of the multi-aperture projection display of  FIG. 1  for illustrating relative positions of optics and single images of the individual channels according to an exemplary example; 
           [0028]      FIG. 3  shows schematically a back projection of two images to be projected into the object plane of the optics of the channels and an AND-operation of the transmissive areas of the mask data or provisional single images, wherein object structures lying at the outside in the images to be projected are allocated to a shorter projection distance; 
           [0029]      FIG. 4   a  shows a top view of the object structure resulting from the AND-operation of  FIG. 3  illustrating the final single images; 
           [0030]      FIG. 4   b  shows the projected portion of channel  12 ′ of  FIG. 4   a  at the projected image as resulting at the shorter project distance with the final single images, according to  FIG. 4   a;    
           [0031]      FIG. 4   c  shows the projected portion of channel  12 ″ of  FIG. 4   a  at the projected image as resulting at the shorter project distance with the final single images, according to  FIG. 4   a;    
           [0032]      FIG. 4   d  shows the projected portion of channel  12 ′ of  FIG. 4   a  at the projected image as resulting at the longer project distance with the final single images, according to  FIG. 4   a;    
           [0033]      FIG. 4   e  shows the projected portion of channel  12 ″ of  FIG. 4   a  at the projected image as resulting at the longer project distance with the final single images, according to  FIG. 4   a;    
           [0034]      FIG. 5  shows schematically an array of projector lenses arranged in a square as well as a notation for indexing the channels used in the description; 
           [0035]      FIG. 6  shows a three-dimensional view of an exemplary positional relationship between the multi-aperture projection display of  FIG. 1  and exemplarily projected images resulting in an extension of the depth of focus (EDoF), wherein, in particular, the set light distributions in both set distances are illustrated here exemplarily in the form of a rectangle that is enlarged according to the mapping scale; 
           [0036]      FIG. 7  shows a schematic view illustrating how a final single image having the area pattern intersection  results by object structures in the projector channel ( 2 ,  4 ) of  FIG. 5  in the shape of pattern L 1 ( 1 ) and pattern L 2 ( 2 ) by an intersection examination; 
           [0037]      FIG. 8  shows a comparison of the mapping characteristics of a bright-dark edge by a conventional projector and an array projector with EDoF at different projection distances; 
           [0038]      FIG. 9  shows schematically the edge expansion behavior of a conventional projector and an array projector with EDoF; 
           [0039]      FIG. 10  shows schematically a block diagram of an single image generator according to an embodiment; 
           [0040]      FIG. 11  shows a schematic spatial view of a multi-aperture projection display in the form of a single mirror system for mirroring virtual projection images according to an embodiment; 
           [0041]      FIG. 12  shows a sectional view of a multi-aperture projection display for close eye application and fading-in of virtual image projections into an eye according to an embodiment; 
           [0042]      FIG. 13  shows schematically a single aperture projector and a schematic diagram for illustrating its depth of focus; 
           [0043]      FIG. 14  shows schematically a three-dimensional view of an array projector with regularly arranged projection channels, exemplarily an arrangement of 7×7 individual projectors tightly packed in a square with planar backlighting; 
           [0044]      FIG. 15  shows a schematic cross-section of the arrangement of  FIG. 14  for illustrating a 2D layout for determining the distance at which a focused image results by superposing the projection channels; and 
           [0045]      FIG. 16  shows the blur behavior of a conventional single channel projector, a single projection channel and an array projector without depth of focus extension. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0046]    Before specific embodiments of the present application will be described below, first of all an attempt is made to describe the basic idea underlying the embodiments described below. The embodiments described below are, for example, suitable for enabling mapping of several light patterns onto different geometries or set distances. A specific case thereof is maintaining a unique light pattern according to mapping scale across an enlarged distance range. This can be referred to as extending the depth of focus. For illustrating the principles underlying the embodiments described below, this specific case will be discussed first. 
         [0047]    Mapping characteristics of an array projector or a multi-aperture projection display are the basis. Due to the two-dimensional arrangement of micro projectors or projection optics typically having an aperture D singie &lt;1 mm, a comparatively large depth of focus results for the individual projector, i.e. an individual projection channel, compared to a single channel projector having an overall aperture equivalent to the array. For typical projection distances of more than 300 mm, hyperfocal mapping of each projection channel exists, i.e., no real far distance L F  of the depth of focus range exists. 
         [0048]    Starting point of the subsequent embodiments is the generation of specific object structures or single images within the object plane of the projection optics whose image-side superposition resulting from the optical mappings of all projection optics constructively contribute to the overall image in the desired depth of focus range. A multichannel projection display according to  FIG. 4B  is considered as specific example. The projection display is exemplarily set to a screen distance of 400 mm. Set in that way, each projection channel has a depth of focus range extending from, for example, 200 mm to infinity. As described above, the whole array has, analogous to a single aperture projector having entrance pupils size D (cf.  FIG. 15 ), an expansion of the whole optics array, merely a depth of focus extending from 350 . . . 450 mm. It is the object to make better use of the depth of focus of the individual channels and still maintain the brightness of a multichannel projection display. The following embodiments use the following approach: when an image to be projected is viewed within the intended depth of focus range and tracing back for each projection distance within the depth of focus range to which object structure the same corresponds in the object plane of the projection channel, it can be seen that there are areas in the object planes of the projection channels that contribute to the image to be projected at any distance within the intended depth of focus range. The following embodiments utilize this fact by manipulating each channel-specific contribution to the overall image such that the image information for the image to be projected is maintained for all desired distances within the depth of focus range. For this, as will be explained below, locations in the object planes of the projection channels where the object structures of the back projection of the image to be projected exist only partly at the varying distances within the depth of focus range, i.e., not all of them overlap, are darkened or even removed, i.e. for example the shadow mask is shaded there, such that, as the following statements will show, the depth of focus range can actually be significantly increased. However, this tough procedure corresponding to an AND-operation could also be modified. 
         [0049]    As the following embodiments will show, the images to be projected at the different distances are not limited to images to be projected that are self-similar or that can be converted into one another according to the optical projection. Rather, any image content can be obtained at the different projection distances. First, based on  FIGS. 1 to 2 , the train of thought or the construction instruction for the single image content of the individual object structures, that are channel dependent, will be described based on the specific case of the extended depth of focus. 
         [0050]    First, the description is made based on the projection of a bright object, here a letter “F” onto two perpendicular screen planes. An extension to any number of (intermediate) distances is obvious and will also be described mathematically below. 
         [0051]    Thus, the image content of the individual object structures or single images is channel-dependent. The construction instruction of the same will be described in more detail, first, based on the specific case of the extended depth of focus, but then, the description and the indication that different image contents can be generated at different projection distances will follow. 
         [0052]    First of all,  FIG. 1  shows the structure of a multi-aperture projection display according to an embodiment. The multi-aperture projection display includes a plurality of laterally adjacent projection channels  12 , i.e., a projection channel array. Each projection channel has a single image generator  14  for generating a respective single image and optics  16  for mapping the respective single image residing in an object plane  42  of the optics  16  into a projection direction  18  of the multi-aperture projection display  10 . The single image generators  14  are, for example, shadow masks that can be backlit. The same can be formed, for example, of parts of a common shadow mask. The single image generators  14 , however, can also be self-luminous elements, such as OLEDs having illuminating areas corresponding to the respective single image of the respective channel  12 . The single image generators could also be displays, for example, that are able to display varying image content, wherein in this case a control  20  would exist for adjusting the image content of the single image generators to the respective single images, as will be described in more detail below. For backlighting, if present, a planar light source  22  as shown exemplarily in Fig. could be used, or one light source per channel  12 . The planar light source  22  is, for example, an OLED, an LED array or the same. The planar light source  22  could be implemented to emit an already pre-collimated backlighting light. In the projection direction  18 , planar light source  22 , image generator  14  and optics  16  are connected in series, such that the backlighting passes through transmissive portions of the single images of the single image generator  14  and the bright portions of the single images are mapped by the optics  16  into the projection direction  18 , where the same are superposed in a suitable manner so as to result in an image to be projected, as will also be described in more detail below. For obtaining Köhler backlighting, optionally, one collimator  24  can be provided per projection channel  12 ; in this way, the light flux through the channels  12  and, hence, the light yield can be increased. 
         [0053]      FIG. 2  shows a top view of the array of channels  12  with array of optics  16 , whose apertures  26  are shown here exemplarily as squares and whose entrance pupil positions  28  are exemplarily indicated by stars. As can be seen in  FIG. 2 , the optics can be arranged regularly in an array of rows and columns, but any other arrangement is also possible. Additionally, the entrance pupils  28  can be arranged centrally to the respective apertures  26  but variation options exist here as well.  FIG. 2  also shows the array of single images  30  of the single image generators. The same also form a lateral arrangement. In particular, the single images  30  are positioned in a lateral arrangement which is geometrically similar to the lateral arrangement of the entrance pupils  28 . In the case of  FIG. 1 , the same results from a centric extension around a center  32  of the array of entrance pupils  28  from the arrangement of entrance pupils  28 . Optionally, a translatory offset relative to the array of entrance pupils  28  can be added. Here, the center of the single image arrays and the center of the entrance pupil array coincide. The optical axis  34  of the multi-aperture projection displays  10 , as indicated in  FIG. 1 , passes through the just stated centers. Deviations from the geometric similarity would also be possible, for example, for performing adaptations to curved screen geometries. This is not the case in  FIG. 2 . 
         [0054]    Before continuing with the further description, some general statements will be made. In  FIG. 1  it has been exemplarily assumed that the single image generators are shadow masks  14 , such as chrome masks having dark portions or blocking portions and bright portions or transmissive portions. However, it is also possible to use a reflectivity of masks instead of backlighting. In other words, the single image generators  14  could also be reflective masks having bright or reflective portions and dark or non-reflective portions. The front lighting could be realized by a light conductor plate which is arranged between optics array and single image generator array, is illuminated from the side and transmits reflective light to the optics  16  at the reflective portions of the masks  14  on its side facing the single image generators  14 . In the case of self-luminous single image generators, in a similar manner, also bright or self-luminous portions exist and dark or non-luminous portions and, in the following, the bright portions are sometimes called non-zero-valued portions and the dark portions zero-valued portions. OLEDs would be an option for forming fixed single images and displays or imagers, such as LCDs or the same, examples for adjustable single image generators that can change their respective image content. As mentioned, the single image generators  14  can also represent different parts of an individual single image array generator, such as an array of portions of a mask, an array of portions of an imager. 
         [0055]    The distance of the projection optics  16  to the single images or single image generators  14  or the distance between the array of optics  16  and the array of single images  13  or the array of single image generators  14  indicated exemplarily by d in  FIG. 1 , corresponds approximately to the focal length F of the individual projection optics  16 . Thus, with relation to each individual channel  12 , the single images  26  are mapped along the optical axis  36  specific for the respective channel  12  with a very large depth of focus reaching to infinity. In the case that all single images  30  are equal to one another, a focused image would result at a projection distance L 1  which depends, and described above, on the center distance difference Δp between single images  30  and entrance pupils  28 . 
         [0056]    As will be defined in more detail below, according to embodiments of  FIG. 1 , the single images  26  are not equal to one another but, rather, the same are designed in a suitable manner such that the mappings of the single images  30  of the projection channels  12  are superposed at at least two different projection distances L 1  and L 2  to respectively one projected image  38  or  40 , wherein the single images are darkened more with respect to a positive superposition at locations where non-zero-valued portions of the projected images at least partly reside when back-projected via the optics  16  of the projection channels  12  into the object plane  42 , where the single images  30  lie, but no superposition of all of them, than at locations where the non-zero-valued portions of the projected images  38  and  40  are all superposed with one another when back-projected via the optics  16  into the object plane  42 . In the following, this will be explained in more detail but, for the time being: if a screen is held in front of the projection display  10 , such that the screen is arranged behind the projection display  10  in mapping direction  18 , it can be seen that the image projected onto this screen has a maximum focus at the distances L 1  and L 2  from the projection display  10 . The single images  30  are specifically designed for these distances, as will be described in more detail below. These are set distances. These images have bright portions  44  and dark portions  46 . In the case of  FIG. 1 , this is exemplarily the depth of focus extension case and, hence, the case where the projected images  38  and  40  are those that can be converted into one another by centric extension or projection onto the point  32 , i.e., the intersection between optical axis  34  and entrance pupil plane but, in the following, it will be described that this is merely an example. If the back projection of these projected images  38  and  40  is considered separately, each of these projected images  38  or  40  will generate bright portions and dark portions, i.e., non-zero-valued and zero-valued portions in the object plane  42 , where the single images lie. 
         [0057]    The non-zero-valued portions of the back projection of the different images  38  and  40  overlap only to a certain extent. At locations where at least one non-zero-valued portion of one of the images  38  and  40  lies due to back projection, but these non-zero-valued portions do not completely overlap, i.e., not from all images  38  and  40 , i.e., at locations onto which a bright portion  44  of only one of the images  38  or  40  is back-projected, the single images  30  of the single image generators  14  are now darkened, namely darkened compared to the comparative case where the back projections were combined additively or by an OR-operation for obtaining positive superposition. 
         [0058]    The above described matter will be illustrated in more detail based on the specific example as illustrated in  FIG. 1 , namely based on the projection of a bright object, here a letter “F” onto two perpendicular planes at the distances L 1  and L 2 , in the following sometimes called “screen planes” for simplicity reasons. And extension to any number of (intermediate) distances by other images is obvious. First, the set distances L 1 :L 2 =1:2, are considered, where the desired superposition figures are to occur. According to equation (3), a unique slide array or an array of provisional single images results for both set distances. Due to the logic AND-operation (intersection) of the transmissive areas of both slide arrays, merely those area elements are maintained which provide a constructive contribution to the overall image at both projection distances.  FIG. 3  shows exemplarily a top view of the result of a back projection of the two projected images  38  and  40  shown in  FIG. 1  at the distances L 1  and L 2  onto the object plane  42 , wherein circles in  FIG. 3  exemplarily indicate the position of the optics apertures  26 . Here, the same are exemplarily illustrated as lying adjacent to one another in a hexagonal arrangement which is tightly packed. Above this,  FIG. 3  exemplarily assumes a lower single image center distance compared to the aperture center distance, wherein such embodiments will be described below. The basic idea of  FIG. 3 , however, also applies to the embodiment of  FIG. 1 , namely that the back projection of the bright portions  44  of the closer image  38  having the distance L 1  results in the non-zero-valued or bright portion  48  in the object plane  42  in the individual channels, wherein those portions  48  are illustrated in  FIG. 3  in a shaded manner from the right top to the left bottom, while the bright portions  44  of the projected image  40  at the greater distance L 2  results in non-zero-valued or bright portions  50  in the object plane  42  in the channels  12 , which are illustrated in a shaded manner in  FIG. 3  from the left top to the right bottom. Due to the greater distance L 2 , the images  50  resulting from the back projection of the image  40  have a lower center distance to one another than the images  48  resulting from the back projection of the image  38  at the lower distance L 1 . For this reason, the intersection or overlap where the bright areas  48  and  50  overlap differs from channel to channel. As can be seen in  FIG. 3 , the overlap has a smaller area the further the respective channel is apart from the optical axis  34  of the multi-aperture projection display. The intersection areas where both non-zero-valued portions  48  and  50  in the respective channels overlap are illustrated in  FIG. 3  by the dark areas  52 . 
         [0059]    According to an embodiment, each single image  30  is selected such that the areas  48  and  50  beyond the intersection areas  52  are darkened. Thus, in the mask embodiment, the masks are not transmissive there. The same are merely transmissive in the overlapping area  52 . This is again described in  FIG. 4   a  which shows, like  FIG. 3 , a top view of the object plane  42 , i.e., a top view of the resulting single images  30 , whose non-zero-valued portions, e.g., transmissive portions correspond to the intersection areas  52  of  FIG. 3 . 
         [0060]      FIG. 4   b  shows exemplarily the contribution or the bright area  53  resulting by an exemplarily taken channel  12 ′ at the distance L 1 , in relation to the bright portion  44  as it results by superposition of the single images or the bright portions  52  of all channels in the image  38  at this distance L 1 . In the attempt of explaining why the area  44  at the distance L 1  in the image  38  still forms a “fine” “F”,  FIG. 4   c  shows the contribution resulting from the transmissive area of the single image  30  of any other arbitrary channel  12 ″, wherein this area is again indicated by  53  in its relative position in the overall area  44 . Obviously, the same covers other parts of the area  44  than the channel  12 ′ at the distance L 1 .  FIGS. 4   d  and  4   e  show the contribution  53  for the exemplarily selected channels  12 ′ and  12 ″ according to their contributions  53  to the bright area  44  of the projected image  40  in the distance L 2 ,  FIG. 4   d  for the channel  12 ′ and  FIG. 4   e  for the channel  12 ″. Again they cover different parts of the image or the bright area  54  of the image  40 . Again, other channels cover other zones of the areas  44  in the images  38  and  40  which results exactly in the desired areas  44 . 
         [0061]    In other words, according to the just described embodiments, for obtaining the mask array of  FIG. 4   a,  first, it is checked for all elements of the overall object structure, i.e., for the transmissive areas of the mask array of masks  14  whether the same provide a transmissive portion for all patterns belonging to the projection distances L 1  and L 2 , i.e., whether the same lie within the overlap area  53 . If this check is positive, the same will be maintained, otherwise the same will be removed from the resulting object structure or the masks, i.e., such locations are darkened or made non-transmissive. Mathematically, this corresponds to an element or location selective AND-operation, i.e., the intersection  52  of all object structures  48 ,  50 , each allocated to a projection distance. Thus,  FIG. 4A  shows the resulting mask structure according to the just described intersection check. 
         [0062]    In other words, according to the above embodiment, a unique stamp or transmissive structure is generated in each channel, which provides at both or several set distances or even in a continuous projection depth area such a contribution to the overall overlap that the contours of the respective set images or the set image are maintained at the respective set distances. 
         [0063]    A consistent description of both the image projection variable according to distance and the extended depth of focus will follow. 
         [0064]    The object structure plane is considered and the coordinate origin is placed at its center. Pattern L     k   (i, j) ∪ R 2  describes, for the lenslet or channel  12  (i,j), wherein, as illustrated in  FIG. 5  (i,j) indicates exemplarily the lateral position measured from the positon relative to the optical axis  38  measured in units p, the pattern to be mapped for the distance or the geometry L k  ∈          . For the array projector of [2] |         |=1, i.e., there is only one geometry onto which mapping is to be performed in a focused manner. The present invention allows the generation of a focused image for two or more geometries          ={L 1 , . . . , L n }. This can be the same pattern (depth of focus extension) or also different patterns for different distances. 
         [0065]    A desired image image Lk  is given for a specific projection distance L k  (here, simplified: perpendicular screen). Generalization to freeform screen geometries is possible according to [3]. According to the mapping rules (equation (3)), the following slide or object structure Pattern Lk (i,j) results for an array (image  13 ) arranged in a square on the object side for the individual channel (i,j): 
         [0000]    
       
         
           
             
               
                 Pattern 
                 
                   L 
                   k 
                 
               
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                 ( 
                 
                   i 
                   , 
                   j 
                 
                 ) 
               
             
             = 
             
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               } 
             
           
         
       
     
       Here,  
       [0066]    
       
         
           
             
               M 
               k 
             
             = 
             
               
                 L 
                 k 
               
               s 
             
           
         
       
     
         [0000]    os the mapping scale for the k-th projection distance p x =p y =p of the distance of the lenses of this array and 
         [0000]    
       
         
           
             
               Δ 
                
               
                   
               
                
               
                 p 
                  
                 
                   ( 
                   
                     L 
                     k 
                   
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                  
                 
                     
                 
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                       ( 
                       
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                         M 
                         k 
                       
                     
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                     p 
                   
                 
               
             
           
         
       
     
         [0000]    is the projection distance dependent center distance difference. Now, by Pattern intersection (ij) those area(s) are described that result in the channel (i,j) by the following AND operation: 
         [0000]      Pattern Intersection ( i,j ):=∩ L     k     ∈           Pattern L     k   ( i,j ) and          ={ L   1   , . . . , L   n }.
 
         [0067]    The overall transmission of such a projection system is proportional to the sum of the transmissive areas of the individual slides. Here, for the illuminated area content of a channel A pattern (i,j) the following applies: 
         [0000]        A   Pattern ( i,j ):=∫∫ I   Pattern     Intersection     (i,j) ( x,y ) dx dy  
 
         [0068]    Here, I is the indicator function (or also characteristic function) and is defined as follows: 
         [0000]    
       
         
           
             
               
                 I 
                 M 
               
                
               
                 ( 
                 
                   x 
                   , 
                   y 
                 
                 ) 
               
             
             = 
             
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                       1 
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                         if 
                          
                         
                             
                         
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                       ∈ 
                       M 
                     
                   
                 
                 
                   
                     
                       0 
                       , 
                     
                   
                   
                     else 
                   
                 
               
             
           
         
       
     
         [0069]    The transmissive overall area of all projection channels 
         [0000]        A   overall =Σ i,j   A   Pattern ( i,j ).
 
         [0000]    is significant for the overall transmission of a projector arrangement generated according to this method. 
         [0070]    As example 1, a centered rectangle is described which is, in the screen plane, (L 1 =400 mm the measure width×height=B 1 ×H 1 =5 mm×20 mm and in L 2 =800 mm according to the screen distance ratios L 2 :L 1 =2:1) B 2 ×H 2 =2·(B 1 ×H 1 )=10 mm×40 mm ( FIG. 6 ). 
         [0000]    
       
         
           
             
               
                 Pattern 
                 
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                   1 
                 
               
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               } 
             
           
         
       
       
         
           
             
               
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                   L 
                   2 
                 
               
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                   y 
                   ≤ 
                   
                     
                       
                         + 
                         
                           1 
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                        
                       
                         
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                           2 
                         
                         
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                           2 
                         
                       
                     
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                       · 
                       
                         ( 
                         
                           
                             Δ 
                              
                             
                                 
                             
                              
                             
                               
                                 p 
                                 y 
                               
                                
                               
                                 ( 
                                 
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                                   2 
                                 
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                         ) 
                       
                     
                   
                 
               
               } 
             
           
         
       
     
         [0071]    For (i,j)=(2,4),          ={400 mm, 800 mm} and p=0.8 mm (with array structure of  FIG. 5 ) for the following rectangle, object structures analogous to  FIG. 7  result: 
         [0000]      Pattern Intersection (2,4)={( x, y )∈           2 : 3.2035 mm×3.2205 mm and 1.558 mm≦y≦1.654 mm}
 
         [0072]    This describes the transmissive area (cf.  FIG. 7 ) for the lenslet (2,4). For the transmissive area of this exemplarily selected projector lenslet, the following results: 
         [0000]        A   pattern (2,4):=∫∫ I   Pattern     Intersecion     (2,4) ( x, y ) dx dy =1.632·10 −3  mm 2 .
 
         [0073]    If the transmissive area of the entire array projector is compared to the extended depth of focus with the one of a conventional one according to [2], a relative light loss of 26% results. 
         [0000]    
       
         
           
             
               
                 
                   ∑ 
                   
                     i 
                     , 
                     
                       j 
                       = 
                       
                         - 
                         5 
                       
                     
                   
                   5 
                 
                  
                 
                     
                 
                  
                 
                   
                     A 
                     Pattern 
                   
                    
                   
                     ( 
                     
                       i 
                       , 
                       j 
                     
                     ) 
                   
                 
               
               
                 121 
                 · 
                 
                   
                     A 
                     Pattern 
                   
                    
                   
                     ( 
                     
                       0 
                       , 
                       0 
                     
                     ) 
                   
                 
               
             
             ≈ 
             
               74 
                
               % 
             
           
         
       
     
         [0074]    The depth dependent mapping characteristics of an array projector with manipulated object structures according to the invention depends heavily on the light patterns to be projected and differs fundamentally from the ones of a conventional single channel projection system. 
         [0075]    Exemplarily, a greatly simplified example will show below in as much the mapping of a simple bright-dark edge behaves for the different optical systems to subsequently be able to compare two equivalent systems. 
         [0076]    In the following, it is examined based on a bright-dark edge how the optical mapping of an array projector differs from the one of a conventional single channel projector or array projector with single set distance. Here, a differentiation is to be made in:
       a) the projection distance of the individual channels L foc , given by the back focal lengths of the projection optics (in the example 533 mm) and   b) the set distances at which a focused image is to be generated by the above described arrangement or method (in the example: 400 mm and 800 mm).       
 
         [0079]      FIG. 8  shows the result of an analytical simulation of the mapping of a bright-dark edge for a conventional projector (curve  60 ) and an array projector with extended depth of focus (EDoF). In particular,  FIG. 8  shows a comparison of the mapping characteristics of a bright-dark edge by a conventional projector (curve  60 ) and an array projector with EDoF (curve  62 ) at 400 mm, 533 mm and 800 mm. The abscissa in the diagram corresponds to the lateral coordinate in the image space. An area having an expansion of 10 mm is illustrated. The single channel projector has a lateral expansion of 8.8×8.8 mm (square aperture), while the array of 11×11 individual projector lenslets consists of a single expansion of 0.8×0.8 mm. The back focal length of each projector lenslet is set to 533 mm according to mapping equation. The set distances of the array projector with EDoF are at 400 mm and 800 mm. 
         [0080]    From the analysis, it can be seen that the suggested arrangement can improve the visibility of image edges across a wide projection distance range. In the images, it becomes clear that in contrary to the classic single channel projector both an asymmetric blur behavior when mapping at non-set distances as well as a shift of the edge center K center  occurs. 
         [0081]    The same can be defined as follows: 
         [0000]    
       
         
           
             
               
                 Kcenter 
                 EDoF 
               
                
               
                 ( 
                 L 
                 ) 
               
             
             = 
             
               arg 
                
               
                   
               
                
               
                 
                   min 
                   x 
                 
                  
                 
                    
                   
                     
                       
                         Intensity 
                          
                         
                           ( 
                           
                             L 
                             , 
                             x 
                           
                           ) 
                         
                       
                       - 
                       0 
                     
                     , 
                     5 
                   
                    
                 
               
             
           
         
       
     
         [0082]    This results in the (relative) intensity of the superposition of all channels by considering the washout occurring due to defocusing. 
         [0083]    Due to the asymmetric edge expansion behavior in the image space it is necessitated to differentiate the following cases: The margin of the edge expanding into illuminated areas, is referred to by K bright . Analogously, K dark  characterizes the margin of the edge into dark image areas: 
         [0000]    
       
         
           
             
               
                 Kdark 
                 eDoF 
               
                
               
                 ( 
                 L 
                 ) 
               
             
             = 
             
               max 
                
               
                 ( 
                 
                   
                     ar 
                      
                     g 
                   
                    
                   
                       
                   
                    
                   
                     
                       min 
                       x 
                     
                      
                     
                       ( 
                       
                         Intensity 
                          
                         
                           ( 
                           
                             L 
                             , 
                             x 
                           
                           ) 
                         
                       
                       ) 
                     
                   
                 
                 ) 
               
             
           
         
       
       
         
           
             
               
                 Kbright 
                 eDoF 
               
                
               
                 ( 
                 L 
                 ) 
               
             
             = 
             
               min 
                
               
                 ( 
                 
                   arg 
                    
                   
                       
                   
                    
                   
                     
                       min 
                       x 
                     
                      
                     
                       ( 
                       
                         Intensity 
                          
                         
                           ( 
                           
                             L 
                             , 
                             x 
                           
                           ) 
                         
                       
                       ) 
                     
                   
                 
                 ) 
               
             
           
         
       
     
         [0084]    These equations apply for the exemplarily selected bright-dark distribution (left-dark, right-bright). The inverse case results analogously. For the selected projection distances, here exemplarily 400 mm, 533, 800 mm,  FIG. 9  shows at the top the area of the dark edge area  66  and the bright edge area  68 . At the bottom, the blur behavior of a conventional projector is illustrated with dotted lines and an array projector with EDoF (areas). Both systems have an identical overall aperture of 8.8×8.8 mm 2 . Both the asymmetric edge washout (curves  70 ,  72 ) and the edge shift (curve  74 ) are clearly visible. 
         [0085]    The illustrated shift of the edge positions can be counteracted by adapting the light patterns at the set distances. 
         [0086]    The effect is as follows: A conventional single channel projector is defined by the following parameters: aperture: D=8.8 mm (square), focal length: L foc =533 mm, and in the following it will be examined how much its pupil would have to be reduced in order to have the same blur behavior with respect to the suggested arrangement at a distance of 400 mm and 800 mm. The evaluation of equation (3) shows that the pupil of the single channel projector would have to be limited to 1.46 mm, which corresponds to a reduction of the light flux to approximately 3%. By using the arrangement suggested herein for extension of depth of focus (EDoF), this value is opposed by a light flux of approximately 74% (example: bright rectangle, see above). Here, it should be noted that this transmission loss of the suggested system heavily depends on the image to be projected or the selected set distances. For typical image contents and projection distances, values of &gt;60% are to be expected. 
         [0087]    With reference to the above statements,  FIG. 10  shows an embodiment for a single image generator for a multi-aperture projection display having a plurality of projection channels. Generally, the single image generator is indicated by reference number  80 . The single image generator  80  of  FIG. 10  includes an image data input  82  for receiving image data  84  representing at least two images to be projected at different projection distances, such as the images  38  and  40  at the distances L 1  and L 2 . Further, the single image generator  80  includes a single image calculator  86  that is implemented to calculate, for each of the at least two images to be projected, a provisional single image per projection channel  12  of the multi-aperture projection display such as, for example, exactly those images  48  and  50 . A combiner  88  of the single image generator  80  combines, for each projection channel, the provisional single images of the respective projection channel calculated for the at least two images to be projected to a final single image for the respective projection channel, such as exactly those final single images as illustrated in  FIG. 4   a.  As mentioned, extensions to more images to be projected etc., is also possible. 
         [0088]    Basically,  FIG. 10  also represents the steps of a respective single image generation method, namely receiving image data at  82 , calculating provisional single images at  86  and combining the same at  88 . The following detailed function description is thus also understood as a description of the respective method. 
         [0089]    Before the image generation according to  FIG. 10  will also be described in more detail, it should be noted that the image generation according to  FIG. 10  can be performed offline or online. This means the following. Single image generation, for example in the embodiment of  FIG. 1 , could be performed within the control  20 . Then, it would be possible to feed in image data  84  indicating the desired images  38  and  40 , and the single image generation then controls the single image generators  14  of  FIG. 1  accordingly, such that the same indicate the finally calculated single images. However, the single image generator or the single image generation method of  FIG. 10 , can also be a pure design tool or part of a production method for producing the single image generators  14 , such as the masks, in the case that the single image generators  14  are formed of masks. The latter alternatives are summed up in a dotted box  90  in  FIG. 10 , which is indicated by “single image generation”. Thus, the same can be a mask generator or mask generation. As an alternative, the result of combining  88  could also be outputting data, for example in stored form, on a suitable data carrier, which represents the arrangement of single images  30  as it results from the combination. 
         [0090]    A simple case as described above is that the image data  84  represent the at least two images  38  and  40  to be projected in a binary manner, i.e., exclusively comprising merely bright areas  44  and dark areas  46 . In this case, the single image calculation in the calculator  86  calculates, for example, for each of the images  38  or  40  to be projected, the array of provisional single images  30  such that, for each image  38  or  40  to be projected, the respective array of provisional single images or the provisional single images themselves represent a back projection via the array of optics  14  into the object plane  42 . The result would be binary provisional single images, as indicated exemplarily in  FIG. 3  at  48  or  50 . This means the calculation would be performed by using optical parameters of the multi-aperture projection display  10 , such as optical mapping parameters, such as the projection distances L 1 , L 2 , the aperture center distances p, the object distance d and possibly optionally further parameters. However, the calculation can also be more complex. In particular, the same does not have to be unique. For example, it would be possible to perform the calculation for projection planes that are not perpendicular to the optical axis  34  or even curved, for which reference is made exemplarily to [3]. Image portions can be distributed differently to the channels, such as for increasing the focus. 
         [0091]    Then, the combiner  88  performs the combination of the binary provisional single images or the arrangement of binary valued provisional single images, such as by the above mentioned logic operation, namely an AND-operation in the case that the logic 1 corresponds to the bright portions and a logic OR-operation in the case that the logic 1 corresponds to the dark portions. The result would thus be a final binary single image per channel or an arrangement of such final single images with dark or bright portions which can represent, for example, transmissive, reflective or self-luminous portions, as described above. In the case of transmissive masks, respective chrome masks would be produced as has also been described above. Otherwise, a pixelated imager is controlled in a suitable manner for indicating the bright or dark areas. 
         [0092]    Another option is that the images to be projected  38  or  40  are not represented in a binary manner by the image data  84 . Thus, the same can have a higher value, they can, for example, be trivalent. In this case, the single image calculator  86  distributes, for example, the differently valued portions of the images  38  and  40  to a different amount of channels  12  in its calculation, such that per image to be projected  38 , the calculated provisional single images are binary, but, when the same are superposed, result in the multi-valued image to be projected  38  at the respective projection distance. The combination in the combiner  88  then functions again exactly as in the case of purely binary images to be projected  38  or  40 . 
         [0093]    It should be noted that it is an advantage of embodiments of the present invention that a maximum of a difference amount between the at least two different projection distances L k , i.e., max({∀i, j≦number of projection distances 
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         [0000]    can be greater than the commonly obtainable depth of focus of the projection display for, for example. the average projection distance L of all projection distances L k , i.e., greater than 
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         [0000]    wherein D is, overall, a pupil expansion of the optics of the projection channels, 
         [0094]    L an average value of the different projection distances and β=0.005. Thus, this is particularly interesting for the case that the images to be projected are indicated by the image data  84  such that the same actually result from one another due to centric extension at the intersection of optical axis  34  and entrance pupil plane, which has been described above as depth of focus extension. Here, for example, the image data  84  can be already designed such that they exist in a format according to which, in the image data  84  of the different projection distances, only one image is contained, from which the at least two images to be projected result by the central extension in dependence on the respective projection distance. 
         [0095]    Merely for the sake of completeness,  FIGS. 11 and 12  also show that, according to other embodiments, a multi-aperture projection display having the advantages as described above might also be implemented as head-up-display for fading-in the images  38  and  40  as virtual images in the sight of a person via a suitable fading-in area, such as a window  92  of a vehicle or as near-eye display for fading in the images  38  or  40  as virtual images into the sight of the eye  94  of the viewer, such as in the form of electronic glasses. In the case of  FIG. 11 , the single image generators  14  are, for example, portions of a common mask or portions of a common display. 
         [0096]    Contrary to  FIG. 1 , merely the entrance pupil center distance is greater than the single image center distance in the case of  FIG. 11 , wherein the expansion of the display, i.e., the area covered all-in-all by the projection optics aperture is determined by the expansion D (cf.  FIG. 15 ) of the solid angle area where the display can indicate the images  38  or  40  to the user. In the case of  FIG. 11 , the individual channels  12  serve to cover the eye motion box of the person in the sight of whom fading-in is performed. In the case of  FIG. 12 , exemplarily, reflectively operating single image generators  14  are provided, such as reflective masks. Illumination is performed via a beam splitter  94  between the optics  16  and the single image generators  14 . A light source  22  is formed by a divergent light source  96  and a collimator  98 , which introduce collimated light laterally into the beam splitter  94 , such that the reflective single image generators  14  are illuminated and reflect, at the positions defined by the single images, light by the beam splitter and the optics  16  into the eye  94 , where the mappings of the single images are superposed in the retina for forming the virtual images  38  or  40 . 
         [0097]    The following remarks are made with regard to the above embodiments for eliminating the impression that the embodiments as described above cannot be extended or amended.
       1) The above embodiments are particularly suited for projecting binary light patterns, but can also be extended to gray-level images by:
           Superposing different binary images having a defined number   Superposing suitable gray value slides having a defined number   
           2) Generating colored image contents can be performed analogously to point 1). Possibly, the light pattern is to be separated into its primary color portions before performing the mathematical operations.   3) According to the De Morgan law          (a ∪b)=         a ∩         b), the described operation can also be applied to the absorbing parts of the object structures resulting respectively for all set distances. Instead of an AND-operation, a logic OR-operation results.       
 
         [0103]    In the above embodiments, compared to a projection system of conventional technology as described in the introductory part of the description, there is the inherent option of projecting an alternating light pattern across the projection distance without further mechanical means. As a specific case maintaining a light pattern across a defined distance range will result. If the optical analogon to this is considered (depth of focus extension), compared to classical systems, a drastic gain of system transmission and, hence, efficiency increase will result. The above embodiments provide these advantages or the mapping characteristic of generating different patterns on different geometries or projection distances without the necessity of a separate control or control circuit. 
         [0104]    Thus, above embodiments allow optical imaging of a plurality of high-contrast light patterns at different projection distances or screen geometries. A specific case, which is also covered by the described examples, is the maintenance of a fixed light pattern across varying project distances or geometries. While no technical solution is known when generating alternating image content, the significant technical advantage of increasing the depth of focus is a drastic increase of the effective system transmission. For generating the described mapping characteristics, no mechanical changes of lenses or pupils are necessitated. Merely the object structures are manipulated, in which the exact technical design has been described above. The restriction to the manipulation of image content allows the realization of simple, compact and robust protection systems. 
         [0105]    Possible fields of application of the above embodiments for distance-dependent representation of different image contents and for extending the depth of focus are, for example, 3D measurement technology as well as structured illumination and information display. 
         [0106]    While some aspects have been described in the context of an apparatus, it is obvious that these aspects also represent a description of the respective method, such that a block or device from an apparatus can also be seen as a respective method step or as a feature of a method step. Analogously, aspects described in the context of a method step or as a method step also represent a description of a corresponding block or detail or feature of a corresponding apparatus. Some or all of the method steps may be executed by (or using) a hardware apparatus, like for example, a microprocessor, a programmable computer or an electronic circuit. In some embodiments, some or several of the most important method steps may be executed by such an apparatus. 
         [0107]    Depending on certain implementation requirements, embodiments of the invention can be implemented in hardware or in software. The implementation can be performed using a digital storage medium, for example a floppy disk, a DVD, a Blu-Ray, a CD, a ROM, a PROM, an EPROM, an EEPROM or a FLASH memory, a hard drive or other magnetic or optical memory having electronically readable control signals stored thereon, which can cooperate or cooperate with a programmable computer system such that the respective method is performed. Therefore, the digital storage medium may be computer readable. 
         [0108]    Some embodiments according to the invention comprise a data carrier having electronically readable control signals, which are capable of cooperating with a programmable computer system, such that one of the methods described herein is performed. 
         [0109]    Generally, embodiments of the present invention can be implemented as a computer program product with a program code, the program code being operative for performing one of the methods when the computer program product runs on a computer. The program code may for example be stored on a machine readable carrier. 
         [0110]    Other embodiments comprise the computer program for performing one of the methods described herein, wherein the computer program is stored on a machine readable carrier. 
         [0111]    In other words, an embodiment of the inventive method is, therefore, a computer program having a program code for performing one of the methods described herein, when the computer program runs on a computer. 
         [0112]    A further embodiment of the inventive methods is, therefore, a data carrier (or a digital storage medium, or a computer-readable medium) comprising, recorded thereon, the computer program for performing one of the methods described herein. 
         [0113]    A further embodiment of the inventive method is, therefore, a data stream or a sequence of signals representing the computer program for performing one of the methods described herein. The data stream or the sequence of signals may for example be configured to be transferred via a data communication connection, for example via the Internet. 
         [0114]    A further embodiment comprises a processing means, for example a computer, or a programmable logic device, configured to or adapted to perform one of the methods described herein. 
         [0115]    A further embodiment comprises a computer having installed thereon the computer program for performing one of the methods described herein. 
         [0116]    A further embodiment according to the invention comprises an apparatus or a system configured to transfer a computer program for performing one of the methods described herein to a receiver. The transmission can be electronical or optical. The receiver may, for example, be a computer, a mobile device, a memory device or the like. The apparatus or system may, for example, comprise a file server for transferring the computer program to the receiver. 
         [0117]    In some embodiments, a programmable logic device (for example a field programmable gate array) may be used to perform some or all of the functionalities of the methods described herein. In some embodiments, a field programmable gate array may cooperate with a microprocessor in order to perform one of the methods described herein. Generally, in some embodiments, the methods are performed by any hardware apparatus. The same can be a universally usable hardware, such as a computer processor (CPU) or hardware specific for the method, such as an ASIC. 
         [0118]    While this invention has been described in terms of several advantageous embodiments, there are alterations, permutations, and equivalents which fall within the scope of this invention. It should also be noted that there are many alternative ways of implementing the methods and compositions of the present invention. It is therefore intended that the following appended claims be interpreted as including all such alterations, permutations, and equivalents as fall within the true spirit and scope of the present invention. 
       LITERATURE  
       [0119]    [1] W. J. Smith, Modern Optical Engineering (McGraw-Hill, 2007). 
         [0120]    [2] DE102009024894A1 
         [0121]    [3] DE102011076083A1 
         [0122]    [4] Marcel Sieler, Peter Schreiber, Peter Dannberg, Andreas Brauer, and Andreas Tünnermann, “Ultraslim fixed pattern projectors with inherent homogenization of illumination,” Appl. Opt. 51, 64-74 (2012).