Abstract:
A projector having an illumination modulator to modulate the intensity of the light in a pixel-individual manner, a projection lens projecting the light being modulated in a pixel-individual manner onto an image modulator to generate the image to be projected such that each illumination pixel is associated with at least one image pixel. A controller which generates illumination control data and generates image control data for the image modulator. The illumination control data are generated such that they have an on-value for each illumination pixel that is associated with at least one image pixel intended to represent a brightness value in the image that exceeds a predetermined threshold value according to the image data, said on-value selected such that each illumination pixel being associated with at least one image pixel intended to represent a brightness value according to the image data that exceeds a predetermined threshold value and falls short of a predetermined maximum value, is also at least temporarily switched to the second state during periods when the at least one associated image pixel is switched to the second state.

Description:
PRIORITY CLAIM 
     The present application is a National Phase entry of PCT Application No. PCT/EP2009/004532, filed Jun. 23, 2009, which claims priority from German Patent Application Number 102008029786.0, filed Jun. 24, 2008, and U.S. Provisional Application No. 61/075,140, filed Jun. 24, 2008, the disclosures of which are hereby incorporated by reference herein in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a projector and a method for projecting an image. 
     In particular the invention relates to a projector for projecting an image with a first and second spatial modulator each with n×m modulator pixels which are imaged onto one another by means of imaging optics, wherein the first modulator is struck by light and the image is generated by means of the second modulator. Such a projector is known for example from U.S. Pat. No. 7,050,122 B2. 
     SUMMARY OF THE INVENTION 
     The black level in the generated image can be reduced by such an arrangement. However, the problem arises that an absolutely precise imaging is almost impossible to achieve in practice. For example, with a desired, pixel-accurate imaging, this leads to the modulator pixels of the second modulator which are to represent black and which are adjacent to modulator pixels which are to represent a certain brightness in the image being illuminated. As a result, an undesired increase in the black level occurs in the case of such modulator pixels of the second modulator. 
     According to the invention a projector for projecting an image is to be provided with which this problem can be solved. Furthermore, a corresponding method for projecting an image is to be provided. 
     The problem is solved by a projector for projecting an image as described and claimed herein. 
     As each illumination pixel which is allocated to at least one image pixel which is, according to the image data, to represent a brightness value which lies above the predetermined threshold value and below a predetermined maximum value is at least sometimes also switched into the second state during the times when the at least one allocated image pixel is switched into the second state, the background brightness can be minimized during the times when these illumination pixels are switched into the second state. 
     The predetermined threshold value is preferably chosen such that the lowest still representable brightness in the image already lies above the threshold value. Thus it is advantageously achieved that the illumination pixels can have the off-value only for image pixels which are to represent a black image spot. 
     The predetermined maximum value can be the maximum representable brightness or a lower brightness. In particular the predetermined maximum value can be half the maximum representable brightness. 
     The projector according to the invention can in particular be designed as a projector for applications in a planetarium such that the image to be projected is projected onto a curved projection surface. The curved projection surface can be part of a planetarium dome. In this design projection takes place usually in the dark, with the result that the achieved reduction in black level brings with it a clear improvement in the image. 
     The projector can furthermore be designed as a projector for front projection or as a projector for rear projection. The projection surface can be a constituent of the projector. 
     The imaging optics can be designed as 1:1 imaging optics, as enlarging or reducing imaging optics. The design as enlarging or reducing imaging optics is chosen e.g. if the two modulators are of different sizes. It is essential in particular that the desired allocation of the illumination and image pixels is realized. 
     The modulators can be designed as LCD, as LCoS modulators or as tilting mirror matrices. The modulators can furthermore be reflective or transmissive. A combination of different types of modulators is also possible. However, it is advantageous to use modulators of the same type, in particular tilting mirror matrices. 
     Furthermore, a method according to claim  7  is provided. Advantageous versions of the method according to the invention are given in the dependent method claims. 
     It is understood that the features named above and still to be explained below can be used not only in the given combinations, but also in other combinations or alone, without departing from the framework of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained in further detail below by way of example using the attached drawings which also disclose features essential to the invention. There are shown in: 
         FIG. 1  is a schematic view of the projector according to the invention; 
         FIG. 2  is a schematic view of the first modulator  3 ; 
         FIG. 3  is a schematic view of the second modulator  5 ; 
         FIG. 4  is a schematic view of the pixel allocation of the two modulators  3 ,  5 ; 
         FIG. 5  is a schematic view of the control unit  7  of the projector  1  from  FIG. 1 ; 
         FIG. 6  is a representation explaining bit-switching times of the pulse-width modulated control data MS, BS for a bit depth of 8; 
         FIG. 7  is a schematic representation explaining the generation of the pattern and image data M, B; 
         FIG. 8  is a representation explaining the pattern control data MS for the value 20; 
         FIG. 9  is a representation explaining the image control data BS for the value 20; 
         FIGS. 10-13  are schematic representations of the incidence of light on the image modulator  5 ; 
         FIG. 14  is a representation explaining the generation of the pattern and image data M, B; 
         FIG. 15  is a representation explaining the pattern control data MS for the value 52; 
         FIG. 16  is a representation explaining the image control data BS for the value 20; 
         FIG. 17  is a representation explaining the generation of the pattern and image data M, B; 
         FIG. 18  is a representation explaining the pattern control data MS for the value 23; 
         FIGS. 19   a - 19   e  are representations explaining the image control data BS for the values 18-22; 
         FIG. 20  is a representation explaining the generation of the pattern and image data M, B; 
         FIG. 21  is a representation explaining the pattern control data MS for the value 63; 
         FIG. 22  is a representation explaining the image control data BS for the value 19; 
         FIG. 23  is a representation explaining the generation of the pattern and image data M, B; 
         FIGS. 24   a  and  24   b  are representations explaining the pattern control data MS for the values 63 and 127; 
         FIGS. 25   a  and  25   b  are representations explaining the image control data BS for the values 20 and 52; 
         FIG. 26  is a representation explaining the allocation of the pixels of the two modulators  3 ,  5  according to a variant; 
         FIG. 27  is a representation explaining the allocation of the pixels of the two modulators  3 ,  5  according to a further variant, and 
         FIG. 28  is a schematic view of a further embodiment of the projector according to the invention. 
     
    
    
     DETAILED DESCRIPTION 
     In the embodiment shown in  FIG. 1  the projector  1  according to the invention for projecting an image comprises a light source  2 , an illumination modulator  3 , imaging optics  4 , an image modulator  5 , a projection lens system  6  as well as a control unit  7 . 
     The two modulators  3 ,  5  are each designed as a tilting mirror matrix having multiple tilting mirrors in columns and rows, wherein the tilting mirrors can, independently of one another, be brought into a first and into a second tilting position. 
     In the embodiment example described here the first modulator  3  has 8×7 tilting mirrors K 1  (also called illumination pixels below) and the second modulator  5  has 7×6 tilting mirrors K 2  (also called image pixels below), as is schematically represented in  FIGS. 2 and 3 . Here, the tilting mirrors K 1  and K 2  have the same dimensions. This small number of tilting mirrors K 1  and K 2  is assumed to simplify the description. Naturally, the modulators  3 ,  5  can contain very many more tilting mirrors K 1 , K 2 . In particular they can in each case contain the same number of tilting mirrors. 
     The imaging optics  4  are designed as 1:1 imaging optics with a lens  8  and a mirror  9  and image each tilting mirror of the illumination modulator  3 , offset by precisely half the dimension of a tilting mirror K 2  of the second modulator  5  in column and row direction, onto the second modulator  5 , with the result that precisely four tilting mirrors K 1  of the first modulator  3  are allocated to each tilting mirror K 2  of the second modulator  5 . If the two modulators  3 ,  5  have the same number of tilting mirrors K 1 , K 2 , this allocation can e.g. be achieved by not using all the tilting mirrors K 2  of the second modulator  5 . 
     As the representation of  FIG. 4  shows, each tilting mirror K 1  of the first modulator  3  that is allocated to a tilting mirror K 2  of the second modulator  5  covers precisely one quarter of the pixel surface of the tilting mirror K 2 . 
     The two modulators  3  and  5  are controlled by the control unit  7  based on fed-in image data BD such that the illumination modulator  3  which is struck by the light (e.g. white light) from the light source  2  is a 2-dimensionally modulated light source for the image modulator  5  with which the image to be projected is generated or modulated and then projected onto a projection surface  10  by means of the projection lens system  6 . 
     In order to produce the 2-dimensionally modulated light source, the projector  1  is designed such that only the light which is reflected by the tilting mirrors of the illumination modulator  3  which are in the first tilting position is imaged onto the allocated tilting mirrors of the image modulator  5 . The light coming from the tilting mirrors of the illumination modulator  3  which are in the second tilting position is collected by a beam trap (not shown) and is thus not imaged onto the image modulator  5 . The image is then generated or modulated by the tilting position of the image pixels (=tilting mirrors of the image modulator  5 ), as only the light coming from the image pixels in the first tilting position is projected via the projection lens system  6  onto the projection surface  10 . The light reflected from the image pixels in the second tilting position is not projected onto the projection surface  10 , but e.g. collected in a beam trap (not shown). The image to be projected which is projected by the projection lens system  6  is thus modulated or generated by the tilting positions of the image pixels. 
     In order to reduce the black level (thus the undesired residual brightness which a black image spot still displays) in the projected image, the control unit  7  generates, from the fed-in image data BD, illumination control data MS for the illumination modulator  3  and image control data BS for the image modulator  5  in the manner described below in conjunction with  FIGS. 5-9 . It is assumed in this description that with both modulators  3 ,  5  in each case, a pulse-width modulation is carried out in respect of the first and second tilting positions of the tilting mirrors to modulate the intensity of the light falling on them. 
     The image data BD are already in digital form with the suitable pixel resolution for the image modulator  5  with 7×6 tilting mirrors K 2  (each image thus has 7×6 image spots) and, as is shown schematically in  FIG. 5 , are simultaneously input in the control unit  7  into a pattern generator  11  as well as into a delay element  12 . With the help of the fed-in image data BD the pattern generator  11  generates pattern data M which are input into a first electronic control unit  13 . Based on the pattern data M, the first electronic control unit  13  generates the pulse-width modulated illumination control data MS and inputs these into the illumination modulator  3 . 
     The delay element  12  delays the fed-in image data BD such that they are input as image data B into a second electronic control unit  14  for the image modulator  4  simultaneously with the input of the pattern data M into the first electronic control unit  13 . The second electronic control unit  14  generates the pulse-width modulated image control data BS and inputs these into the image modulator  5 . 
     According to the illumination and image control data MS, BS, during the single-image time T, to generate the image the illumination and image pixels K 1 , K 2  are brought into the first and second tilting positions such that the desired image is generated and projected. The single-image time T is the time during which a single image is represented. With films this is e.g. 1/24 seconds if 24 images are represented per second. This applies to the case, described here, of the representation of monochrome images. With multicoloured images, a red, a green and a blue subframe is often generated successively for each image. The single-image time is then e.g. ⅓· 1/24 seconds. In order to generate these subframes the light source  2  successively generates e.g. red, green and blue light with which the illumination modulator  3  is illuminated. It is initially assumed for the following description that monochrome images are generated and projected. 
     The first and second electronic control units  13  and  14  can e.g. be the electronic control unit supplied by the manufacturer of the modulators  3  and  5 . In the embodiment example described here these are modulators  3 ,  5  and electronic control units  13 ,  14  from Texas Instruments. 
     Both the input of the data M, B into the two electronic control units  13 ,  14  as well as the electronic control units  13  and  14  themselves are preferably synchronized, as is indicated by the arrows F 1  and F 2 . 
     An example of the generation of the control data MS, BS from the fed-in image data BD is given below, wherein it is assumed that each image spot can be represented with a bit depth of 8 (and thus with a brightness value of 0-255), wherein 0 is to be the lowest brightness (thus black) and 255 the greatest brightness. 
     With a bit depth of 8, the eight allocated bit-switching times P 1 -P 8  (represented as dotted lines in  FIG. 6 ) result for the control data MS, BS together with the bit value 255 (represented as a continuous line in  FIG. 6 ) which corresponds to the whole single-image time T (time from t=0 to t 1 ). A BS or MS value of 1 stands for a tilting mirror K 1 , K 2  which is in the first tilting position and a BS or MS value of 0 for a tilting mirror K 1 , K 2  which is in the second tilting position. 
     As is customary with pulse-width modulation, the bit-switching time P 2  is twice the length of the bit-switching time P 1 , P 3  is twice the length of P 2  and so on, wherein the sum of all bit-switching times P 1  to P 8  corresponds to the single-image time T. The shortest bit-switching time P 1  is 
               T       2   q     -   1       ,         
wherein T is the single-image time and q the bit depth (here 8).
 
     The individual bit-switching times P 1 -P 8  can, as is shown in  FIG. 6 , each be a continuous time interval within the single-image time T. It is, however, also possible for one or other of the bit-switching times (e.g. P 8 ) to be divided into smaller time slices which are distributed over the single-image time T. Essential here is only that the bit-switching times always have the same temporal distribution relative to the single-image time T. 
     In the case of the fed-in image data BD in  FIG. 7 , all image spots BD(n,m) (n=column number, m=row number) apart from one are black image spots (value 0). The image spot BD(5,3) in the fifth column (m=5) and third row (n=3) is not black, but is to be represented with a brightness of 20. The control unit  7  generates the pattern data M from the fed-in image data BD as follows for the first electronic control unit  13  and the image data B for the second electronic control unit  14 . 
     The pattern data M have 8×7 pattern spots M(n,m), each of which is allocated to an illumination pixel K 1 . The image data have 7×6 image spots B(n,m), each of which is allocated to an image pixel K 2 . The values of the pattern spots M(n,m) and the values of the image spots B(n,m) are each given with a bit depth of 8. If the value is =0 it is also called off-value and if the value is &gt;0 it is also called on-value. 
     The image data B for the second electronic control unit  14  are not changed by the control unit  7  compared with the originally fed-in image data BD, but only issued time-delayed synchronously with the pattern data M. As is shown in  FIG. 7 , only the value of the image spot B(5,3) of the image data B is 20, while the values of the remaining image spots are 0. 
     In the pattern data M all pattern spots M(n,m) are initially set to 0. The pattern spots M(n,m) for the illumination pixels which are allocated to an image pixel which is to represent an intensity value not equal to 0 are then set to this intensity value. Thus in this step the pattern spots M(5,3), M(5,4), M(6,3), M(6,4) are set to 20. The pattern data according to  FIG. 7  are generated with these steps. 
     This choice of the intensity value of 20 for the pattern spots M(5,3), M(5,4), M(6,3) and M(6,4) is possible, as the bit-switching times P 1 -P 8  always have the same temporal distribution relative to the single-image time T and thus the tilting mirror of the image modulator  5  which is to modulate the image spot B(5,3) is illuminated whenever the tilting mirror for the image spot B(5,3) is in its first position. 
     The pulse-width control data MS of the first electronic control unit  13  for the single-image time T (time from t=0 to t=t 1 ) for the value 20 of the pattern spot M(5,3) are schematically represented in  FIG. 8 . The pulse-width modulation data BS of the second electronic control unit  14  for the image spot B(5,3) with the intensity 20 are schematically represented in  FIG. 9 . 
     As  FIGS. 8 and 9  show, the tilting mirror of the image modulator  5  for the image spot B(5,3) is illuminated only during the bit-switching times P 3  and P 5  at which the tilting mirror for the image spot B(5,3) is brought into its first position. As the four pattern spots M(5,3), M(5,4), M(6,3), M(6,4) are set to 20 for this, unavoidable imaging errors of the lens system  4  are compensated. This effect is described in conjunction with the schematic representations in  FIGS. 9 and 10 . 
       FIG. 10  shows the arrangement of n×m (=7×6) tilting mirrors K 2 ( n,m ) of the image modulator  5  as well as the illumination (hatched ellipse) of the tilting mirror K(5,3) present if only, as previously customary, the imaging optics  4  bring about a 1:1-allocation of illumination and image pixels and thus a tilting mirror K 1  of the first modulator  3  is imaged precisely onto a tilting mirror K 2  of the second modulator  5  (thus without a shift in the column and row direction). As can be seen in  FIG. 10 , the tilting mirror K(5,3) is not completely illuminated. 
     However, with the illumination according to the invention, the pixel shift in the column and row direction, as was described in conjunction with  FIG. 4 , is present and the four illumination pixels K 1  allocated to the image pixel K 2 (5,3) are switched on, with the result that, as is represented in  FIG. 11 , the tilting mirror K 2 (5,3) is illuminated over all four allocated tilting mirrors K 1  of the first modulator  3 . As a result, the tilting mirror K 2 (5,3) which is the sole tilting mirror K 2  of the image modulator  5  which is in the first position, is extremely uniformly illuminated in two dimensions. Thus the desired intensity value can be represented with a high degree of accuracy. As, furthermore, areas of the image modulator  5  in which several adjacent image pixels are to represent the brightness 0 are not illuminated because of the spatially modulated illumination via the illumination modulator  3 , the black level in these areas can also be reduced effectively. With the described example this applies to the areas in which the tilting mirrors K 2 ( n,m ) are n=1 to 3 and 7 as well as m=1 to 6 and n=4 to 6 and m=1, 5 and 6. Also, the tilting mirrors K 2 (4,2), K 2 (4,3), K 2  (4,4), K(5,2), K(5,4), K(6,2), K(6,3) and K(6,4) immediately adjacent to the tilting mirror K 2 (5,3) are illuminated on the surface and only partially ( FIG. 11 ). 
     When projecting multicoloured images the problem can arise that the actual illumination depends on the wavelength (thus of the colour subframe). The illumination (hatched ellipse(s)) of the tilting mirror K 2 (5,3) for a different wavelength is represented schematically in  FIG. 12  (illumination through only one illumination pixel in the same manner as in  FIG. 10 ) and  FIG. 13  (illumination through four illumination pixels according to  FIG. 11 ) compared with  FIGS. 10 and 11 . As a comparison with  FIGS. 10 and 12  shows, different-sized portions of the tilting-mirror surface of the tilting mirror K 2 (5,3) are illuminated, depending on the wavelength. This leads to colour artefacts when representing an image, as the subframes are then not present in the projected image as desired. 
     This can be prevented by the control means according to the invention as, because of the allocated pattern spots, the actual illumination on the image modulator  5  schematically corresponds to the representations of  FIGS. 11 and 13 . A comparison of the representations in  FIGS. 11 and 13  shows that in each case approximately the same illumination intensity of the tilting mirror K 2 (5,3) is present irrespective of the illumination wavelength. Thus the undesired colour artefacts are avoided. 
     The control of the tilting mirrors of the two modulators  3  and  5  can also be described as follows. According to the pulse-width modulation data MS and BS in  FIGS. 8 and 9 , the illumination pixels allocated to the image pixel K 2 (5,3) are only ever switched on (first tilting position) when the allocated image pixel K 2 (5,3) is switched on (first tilting position). When the allocated image pixel K 2 (5,3) is switched off (second tilting position), the allocated or linked illumination pixels are also switched off (second tilting position). Thus an illumination of the image pixels (with maximum intensity) optimally matched to the bit-switching times can be carried out. Interfering background brightness from the image pixels which are directly adjacent to the image pixel of image spot B(5,3) and are illuminated on the basis of the pattern data of the pattern spots M(5,3), M(5,4), M(6,3) and M(6,4) is strongly suppressed, as these image pixels are also illuminated only during the bit-switching times P 3  and P 5 . 
     An example in which two image spots in the image data BD have an intensity value not equal to 0, namely the intensity value 20 (image spot BD(5,3)) and 52 (image spot BD(4,3)), is shown in  FIG. 14 . 
     In this case, the pattern data M will comprise pattern spots M(n,m) which are linked to two image spots B(n,m) which comprise an intensity value greater than zero (thus e.g. pattern spot M(5,3) is allocated to image spots B(4,3) and B(5,3) by the imaging optics  4 ). The pattern data M are then generated such that the higher of the two intensity values which result from the allocation to two image spots with brightness values not equal to 0 is always generated as pattern spot value, as is schematically represented in  FIG. 14 . The pulse-width modulation data MS, BS for the intensity values 52 and 20 are shown in  FIGS. 15 and 16 . 
     An example is shown in  FIG. 17  in which, when generating the pattern data M, the so-called temporal dithering of the second electronic control unit  14  is taken into account. During the temporal dithering the electronic control unit  14  randomly generates pulse-width modulation data which represent a slightly modified intensity value. For example the second electronic control unit  14  can be designed such that it generates an intensity value in the range of from ±2 to the desired intensity value. Thus an intensity value of 18-22 can be generated in the example described here. The pulse-width modulation data BS for the values 18 to 22 are represented in  FIGS. 19   a  to  19   e . The figures show that the bit-switching times P 1 , P 2 , P 3  and P 5  occur with these pulse-width modulation values. 
     Therefore the control unit  7  generates the value 23 (=10111) as a value for the allocated pattern spots. It is thus ensured that for every possible pulse-width modulation value BS the corresponding image pixel is illuminated at all bit-switching times, such as e.g. a comparison of the pulse-width modulated illumination control data MS for the value 23 in  FIG. 18  with the pulse-width modulation data in  FIGS. 19   a - 19   e  shows. 
     This way of generating the pattern data M delivers the shortest possible illumination time in which it is ensured, for each pulse-width image control value BS possible on the basis of the temporal dithering, that the image pixel is illuminated when it is switched on. Thus the undesired background brightness of the surrounding image pixels which are switched off throughout the single-image time T is minimized. 
     In order to reduce the computational outlay for generating the pattern data, they can also be generated as follows. 
     The control unit  7  ascertains the pattern spot value by accessing with the value of the image spot a table in which a pattern data value which takes into account the temporal dithering in the described manner is filed for every possible image spot value. This pattern data value is then used in the pattern data. 
     Alternatively the temporal dithering can be taken into account as follows when generating the pattern data M. The control unit  7  ascertains the highest-value bit of the image spot B(5,3) which is set to 1 in the binary representation of the intensity value 20, and then sets all lower-value bits as well as the next-highest-value bit to 1. In the example described here ( FIG. 20 ) of 20 (=00010100) this leads to the binary number 00111111 which in base 10 corresponds to the value 63. Therefore the pattern data in the pattern spots M(5,3), M(5,4), M(6,2), M(6,3) and M(6,4) each have the value 63 and all remaining pattern spots are set to 0. The pulse-width modulated control data MS for 63 and 19 are shown as examples in  FIG. 21  and  FIG. 22  respectively. 
     This means that the bit-switching times P 6  and P 4  are also set to 1, with the result that illumination lasts slightly longer than is absolutely necessary. However, in comparison with pattern data M in the case of which e.g. the value 255 is chosen, which would be technically simple to implement, this is still clearly shorter. 
     The determining of the pattern data can be simplified as follows. The control unit ascertains the highest-value bit and then uses the value which is filed for this bit in a table. The table can e.g. be as follows: 
     
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                 Highest-value bit n 
                 Value 
               
               
                   
                   
               
             
             
               
                   
                 1 
                 00000011 
               
               
                   
                 2 
                 00000111 
               
               
                   
                 3 
                 00001111 
               
               
                   
                 4 
                 00011111 
               
               
                   
                 5 
                 00111111 
               
               
                   
                 6 
                 01111111 
               
               
                   
                 7 
                 11111111 
               
               
                   
                 8 
                 11111111 
               
               
                   
                   
               
             
          
         
       
     
     Alternatively, determination can take place in the control unit  7  such that the binary value 00010100 of the image spot B(5,3) is shifted one place to the left, resulting in 00101000, and 1 is then added on the right, whereby the value 00111111 (=63) is again obtained. 
     The example from  FIG. 14  with two values not equal to 0 in the image data BD is represented in  FIG. 23 . If the temporal dithering is also taken into account in this example, with pattern spots M(n,m) of the pattern data M which are linked to both image spots with intensity values not equal to 0 in the image data B, an OR linking of the intensity values of the image data is carried out first. 
     An OR linking of 00010100 (=20) with 00110100 (=52) is thus carried out which leads to the value 00111111. This OR-value is then the basis for one of the described variants for taking temporal dithering into account. Thus e.g. the highest-value bit which is set to 1 is ascertained, all bits to the right of this are set to 1 (already the case here) and the next-highest bit is also set to 1, resulting in the value 01111111 (=127). 
     The corresponding pulse-width modulation data of the pattern data values 63 and 127 are represented in  FIGS. 24   a  and  24   b . The pulse-width modulation data of the image data values B(4,3)=52 and B(5,3)=20 are represented in  FIGS. 25   a  and  25   b.    
     These representations show that it is ensured that the image pixels are illuminated whenever they are brought into the first tilting position. 
     The described options for generating pattern and image data can also be used in the generation and projection of multicoloured images. If the multicoloured images are generated in sequential time order by successively generating e.g. a red, a green and a blue colour subframe, one of the above-described options can be used to generate each colour subframe. It is however also possible to generate and use the same pattern data for all colour subframes of an image. The same pattern data are also used in particular when the colour subframes are generated simultaneously by means of several image modulators. 
     The imaging optics  4  can also image the two modulators  3 ,  5  onto one another such that each tilting mirror K 1  of the illumination modulator  3  is imaged offset by precisely half the dimension of a tilting mirror K 2  of the second modulator in row direction ( FIG. 26 ) or in column direction ( FIG. 27 ). In this case precisely two tilting mirrors K 1  of the first modulator  3  are allocated to each tilting mirror K 2  of the second modulator  5 . 
     Naturally it is also possible that the imaging optics  4  image the modulator  3  onto the modulator  5  such that precisely one tilting mirror of the modulator  3  is allocated to each tilting mirror of the modulator  5 . 
     In the embodiments described thus far, the pattern data were generated such that, in addition to the image pixels which are to represent a brightness value greater than 0, no further image pixels are illuminated. However, the pattern data can also be generated such that, in addition to the image pixels which are to represent a brightness value greater than 0, the image pixels which are to represent a brightness value of 0 which are arranged immediately adjacent to these are additionally illuminated. Naturally it is possible to additionally illuminate not only immediately adjacent image pixels which are to represent the brightness value of 0 but also image pixels further away. For example, of the pixels which are to have a brightness value of 0, those which are no more than one, two or e.g. three image pixels (thus a predetermined number of pixels) away from an image pixel which is to represent a brightness value not equal to 0 can be illuminated. A so-called spatial dithering of the second control electronics unit  14  in which the control electronics unit  14  randomly allocates an on-value to an off-image pixel adjacent to an on-image pixel can thereby be taken into account. 
     An embodiment of the projector  1  according to the invention in which the modulators are designed as transmissive modulators (e.g. LCD modules) is shown in  FIG. 28 .