# Patent

## Title
Projector and method for projecting an image

## Abstract

A projector, having an illumination modulator having multiple illumination pixels a projection lens projecting the light being modulated in a pixel-individual manner onto an image modulator having multiple image pixels to generate the image. A controller generates illumination control data for the illumination modulator and generates image control data for the image modulator. The illumination control data has either an on-value or an off-value The illumination control data (MS) is generated such that the on-value for each illumination pixel is associated with at least one image pixel that is to represent a brightness value within the image and an off-value for all other illumination pixels, with the exception that the illumination control data for at least one of the other illumination pixels that is at a distance by not more than one predetermined pixel number, has an on-value.

## Background
PRIORITY CLAIM
The present application is a National Phase entry of PCT Application No. PCT/EP2009/004530, filed Jun. 23, 2009, which claims priority from German Patent Application Number 102008029790.9, filed Jun. 24, 2008, German Patent Application Number 102008029921.9, filed Jun. 24, 2008, U.S. Provisional Application No. 61/075,138, filed Jun. 24, 2008, and U.S. Provisional Application No. 61/075,145, 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 with multiple (e.g. each with n×m) modulator pixels which are imaged onto one another by imaging optics (in particular pixel-accurate), 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.
BACKGROUND
The black level in the generated image can be reduced by such an arrangement. However, the problem arises that an absolutely precise pixel-accurate 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 a predefined brightness in the image and which are adjacent to modulator pixels which are to represent black and therefore e.g. are not illuminated, being illuminated with less intensity than modulator pixels which are surrounded only by modulator pixels which are also to represent bright picture elements. This leads to undesired brightness fluctuations in such areas.
This effect may be wavelength-dependent due to chromatic errors in the imaging optics with the result that, when presenting multicoloured images, if colour subframes are generated in such rapid succession that the colour subframes can be detected by the user only in temporal superimposition, but not individually, the colour portions of the individual colour images fluctuate in an undesired manner, which leads to colour aberrations in the image to be projected. The same problem occurs if the colour subframes are generated simultaneously with several modulators and imaged onto the second modulator.
According to the invention a projector for projecting an image is to be provided with which these problems can be solved. Furthermore, a corresponding method for projecting an image is to be provided.
As, with the projector according to the invention, according to a first alternative precisely one image pixel is allocated to each illumination pixel on the basis of the imaging optics, and the illumination control data are generated such that they have the on-value for each illumination pixel which is allocated to an image pixel which is, according to the image data, to represent a brightness value lying above a predetermined threshold value in the image, and the off-value for all other illumination pixels, except that the illumination control data have the on-value for at least one of the other illumination pixels whose allocated image pixel is no more than a predetermined number of pixels away from an image pixel which is, according to the image data, to represent a brightness value lying above the threshold value, bright edge image pixels with which bright edge image spots adjacent to dark image spots are to be generated in the image to be projected are illuminated in the same way as bright image pixels which are surrounded exclusively by bright image pixels. Thus a very uniform illumination of the edge image pixels is also achieved, whereby the problems described at the start can be overcome.
According to a second alternative of the projector according to the invention several image pixels are allocated to each illumination pixel. As the illumination control data have the on-value for each illumination pixel which is allocated to at least one image pixel which is, according to the image data, to represent a brightness value lying above a predetermined threshold value in the image and the off-value for all other illumination pixels, except that the illumination control data have the on-value for at least one of the other illumination pixels at least one of whose allocated image pixels is no more than a predetermined number of pixels away from an image pixel which is, according to the image data, to represent a brightness value lying above the threshold value, bright edge image pixels with which bright edge image spots adjacent to dark image spots are to be generated in the image to be projected are illuminated in the same way as bright image pixels which are surrounded exclusively by bright image pixels. Thus a very uniform illumination of the edge image pixels is also achieved, whereby the problems described at the start can be overcome.
In particular the control unit can generate the illumination control data such that they have the on-value for each of the other illumination pixels whose allocated image pixel or at least one of whose allocated image pixels is no more than a predetermined number of pixels away from an image pixel which is, according to the image data, to represent a brightness value lying above the threshold value. Thus it can be ensured that all edge image pixels are illuminated in the same manner.
The predetermined number of pixels can be 0, with the result that the illumination control data have the on-value for every other illumination pixel whose allocated image pixel or at least one of whose allocated image pixels is (are) directly adjacent to an image pixel which is, according to the image data, to represent a brightness value lying above a predetermined threshold value. If the predetermined number of pixels is 0 only the black image pixels which are directly adjacent to an image pixel which is, according to the image data, to represent a brightness value lying above the predetermined threshold value are illuminated.
If not only directly adjacent black image pixels but also black image pixels further away are also to be illuminated, the number of pixels can have a corresponding higher value than 0.
Thus the predetermined number of pixels can be 1, 2, 3 or have another value. A value greater than or equal to 1 can be chosen if e.g. the imaging optics generate undesired pixel shifts. Account can thereby also be taken of the so-called spatial dithering in which, to improve the image, the control unit also switches to bright image pixels which, according to the image data, are not actually to represent a brightness lying above the predetermined threshold value.
In the projector, the illumination pixels can be switched in each case into a first state in which the light coming from the illumination pixel is imaged onto the allocated image pixel, and into a second state in which no light is imaged from the illumination pixel onto the allocated image pixel, and the image pixels can be switched in each case into a first state in which the light coming from the image pixel is used to generate the image, and into a second state in which no light from the image pixel is used to generate the image. A digital control of the two modulators is thus possible. In particular for example LCD, LCoS modulators or tilting mirror matrices can be used as modulators. The modulators can be reflective or transmissive. The projector according to the invention can contain modulators of the same or different type. In one embodiment it contains modulators of the same type, for example two tilting mirror matrices.
In the illumination control data, the on-value for the illumination pixels can be chosen by the control unit such that each illumination pixel which is allocated to an image pixel which is, according to the image data, to represent a brightness value lying above the predetermined threshold value is always switched into the first state at the times when the allocated image pixel is switched into the first state. Thus it is ensured that the desired brightness value of the image pixel can be achieved, wherein simultaneously a reduction of the black level can be achieved.
The control unit can choose the on-value for the illumination pixels in the illumination control data such that each illumination pixel which is allocated to an 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 allocated image pixel is switched into the second state. Thus an illumination matched to the switching states of the image pixels is made possible, whereby disruptive background brightness can be reduced.
Furthermore, in the illumination control data, the on-value for the other illumination pixels can be chosen such that the other illumination pixels are always switched into the first state at the times when at least one of the image pixels no more than the predetermined number of pixels away from the allocated image pixel is switched into the first state. The on-value for the other illumination pixels can in particular be chosen such that every other illumination pixel whose allocated image pixel is no more than the predetermined number of pixels away from at least one other image pixel which is to represent a brightness value which lies above the predetermined threshold value and below a maximum value is also at least sometimes switched into the second state when the at least one other image pixel is switched into the second state. Thus the illumination matched to the switching times is also carried out for the other image pixels to which the on-value is allocated. This leads to a further reduction in undesired background brightness.
In the projector, the control unit can also choose the on-value for the illumination pixels in the illumination control data such that each illumination pixel which is allocated to an image pixel which is, according to the image data, to represent a brightness value lying above the predetermined threshold value is always switched into the first state precisely only at the times when the allocated image pixel is switched into the first state. An illumination completely matched to the times of the first state is thus achieved.
In particular, the on-value for the other illumination pixels can also be chosen such that the other illumination pixels are always switched into the first state precisely only at the times when at least one of the image pixels no more than the predetermined number of pixels away from the allocated image pixel is switched into the first state.
The illumination and image control data can in each case be pulse-width modulated control data. In particular the control data for each illumination and image pixel can in each case contain a binary data value of equal bit depth, wherein the on-value for each illumination pixel which is allocated to an image pixel which is, according to the image data, to represent a brightness value lying above the predetermined threshold value in the image is chosen such that at least the same bits are set as in the binary data value of the allocated image pixel. An illumination of the image pixel matched to the bit-switching times can thus be achieved.
In particular the on-value for the illumination pixels can be chosen such that all bits are set which are set in the binary data value of the allocated image pixel and in the binary data values of all of the image pixels that are no more than the predetermined number of pixels away from the allocated image pixel.
The object is also achieved by a projector for projecting an image according to claim 27. With this projector the control unit generates the illumination control data such that they have the on-value for each illumination pixel which is allocated to at least one image pixel which is, according to the image data, to represent a brightness value lying above the predetermined threshold value in the image, and the off-value for all other illumination pixels, with the result that with these illumination control data a uniform illumination of edge image pixels is likewise also achieved as each (edge) image pixel is illuminated by the several allocated illumination pixels.
Advantageous versions of the projectors according to the invention are given in the dependent claims.
The illumination modulator and/or the image modulator can in particular have n×m pixels.
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 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.
Furthermore, a method according to claims 14 and 33 is provided. Advantageous versions of the method 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 control unit 7 of the projector 1 from FIG. 1;
FIG. 3 is a representation explaining the generation of the pattern and image data M, B;
FIG. 4 is a representation explaining the pulse-width modulated pattern control data MS for the value 255;
FIG. 5 is a representation explaining the pulse-width modulated image control data BS for the value 20;
FIGS. 6-9 are schematic representations of the incidence of light on the image modulator 5;
FIG. 10 is a schematic representation explaining the generation of the pattern and image data M, B;
FIG. 11 is a representation explaining the control data MS for the value 20;
FIG. 12 is a representation explaining the control data BS for the value 20;
FIG. 13 is a representation explaining the generation of the pattern and image data;
FIG. 14 is a representation explaining the control data MS for the value 52;
FIG. 15 is a representation explaining the control data BS for the value 20;
FIG. 16 is a representation explaining the generation of the pattern and image data M, B;
FIG. 17 is a representation explaining the control data MS for the value 23;
FIGS. 18a-18e are representations explaining the control data BS for the values 18-22;
FIG. 19 is a representation explaining the generation of the pattern and image data M, B;
FIG. 20 is a representation explaining the control data MS for the value 63;
FIG. 21 is a representation explaining the control data BS for the value 19;
FIG. 22 is a representation explaining the generation of the pattern and image data M, B;
FIGS. 23a and 23b are representations explaining the control data MS for the values 63 and 127;
FIGS. 24a and 24b are representations explaining the control data BS for the values 20 and 52;
FIG. 25 is a schematic view of a further embodiment of the projector according to the invention;
FIG. 26 is a schematic view of the projector according to the invention according to a further embodiment;
FIG. 27 is a schematic view of the first modulator 3;
FIG. 28 is a schematic view of the second modulator 5;
FIG. 29 is a schematic view of the pixel allocation of the two modulators 3, 5;
FIG. 30 is a schematic view of the control unit 7 of the projector 1 from FIG. 26;
FIG. 31 is a representation explaining the generation of the pattern and image data M, B;
FIG. 32 is a representation explaining the pulse-width modulated pattern control data MS for the value 255;
FIG. 33 is a representation explaining the pulse-width modulated image control data BS for a value 20;
FIGS. 34-37 are schematic representations of the image modulator 5;
FIG. 38 is a schematic representation explaining the generation of the pattern and image data M, B;
FIG. 39 is a representation explaining the pattern control data MS for the value 20;
FIG. 40 is a representation explaining the image control data BS for the value 20;
FIG. 41 is a representation explaining the generation of the pattern and image data M, B;
FIG. 42 is a representation explaining the pattern control data MS for the value 52;
FIG. 43 is a representation explaining the image control data BS for the value 20;
FIG. 44 is a representation explaining the generation of the pattern and image data M, B;
FIG. 45 is a representation explaining the pattern control data MS for the value 23;
FIGS. 46a-46e are representations explaining the image control data BS for the values 18-22;
FIG. 47 is a representation explaining the generation of the pattern and image data M, B;
FIG. 48 is a representation explaining the pattern control data MS for the value 63;
FIG. 49 is a representation explaining the image control data BS for the value 19;
FIG. 50 is a representation explaining the generation of the pattern and image data M, B;
FIGS. 51a and 51b are representations explaining the pattern control data MS for the values 63 and 127;
FIGS. 52a and 52b are representations explaining the image control data BS for the values 20 and 52;
FIG. 53 is a representation explaining the allocation of the pixels of the two modulators 3, 5 according to a variant;
FIG. 54 is a representation explaining the allocation of the pixels of the two modulators 3, 5 according to a further variant; and
FIG. 55 is a schematic view of a further embodiment of the projector according to the invention.



DETAILED DESCRIPTION
In the embodiment shown in FIGS. 1 and 2 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 n×m 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.
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 precisely onto one tilting mirror of the image modulator 5, with the result that precisely one tilting mirror (also called image pixel below) of the image modulator 5 is allocated to each tilting mirror (also called illumination pixel below) of the illumination modulator 3.
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 provide 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 means of 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 means of 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. 2-5. 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 (each image thus has n×m image spots) and 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 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. 1⁄3· 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 F1 and F2.
An example of the generation of the control data MS, BS from the fed-in image data BD is given below wherein, for simplification, it is assumed that the image has 7×6 image spots and the two modulators likewise each comprise a 7×6 tilting mirror. It is also 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.
In the case of the fed-in image data BD in FIG. 3, 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 n×m pattern spots M(n,m), each of which is allocated to an illumination pixel. The image data have n×m image spots B(n,m), each of which is allocated to an image pixel. 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 >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. 3, 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 255. This can also be described such that the on-value is allocated to pattern spots for the illumination pixels to each of which an image pixel is allocated which, according to the image data BD, is to represent a brightness value lying above a predetermined threshold value (here equal to 0). Thus in this step only the pattern spot M(5,3) is set to 255.
All pattern spots immediately adjacent to this pattern spot M(5,3) which has been set to 255 are then likewise set to 255. This also applies here to the eight surrounding pattern spots M(4,2), M(4,3), M(4,4), M(5,2), M(5,4), M(6,2), M(6,3) and M(6,4). Below, these eight pattern spots are also called adjacent pattern spots to the image spot B(5,3).
Setting the adjacent pattern spots to 255 corresponds to having the on-value to pattern spots for the illumination pixels whose allocated image pixels, while they are to represent the brightness value 0, are not more than a predetermined number of pixels (here equal to zero, which corresponds to the direct adjacent pixels) away from an image pixel which is to represent a brightness value greater than 0.
The pattern data according to FIG. 3 are generated with these steps.
Below, all nine pattern spots set to 255 are also called pattern spots linked to an image spot B(5,3).
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=t1) for the value 255 of the pattern spot M(5,3) are schematically represented in FIG. 4. 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. 5. A BS or MS value of 1 corresponds to a tilting mirror in the first tilting position and a BS or MS value of 0 to a tilting mirror in the second tilting position.
As FIGS. 4 and 5 show, the tilting mirror of the image modulator 5 for the image spot B(5,3) is illuminated during the entire single-image time and thus also during the bit-switching times P3 and P5 at which the tilting mirror for the image spot B(5,3) is brought into its first position. As the adjacent pattern spots M(4,2), M(4,3), M(4,4), M(5,2), M(5,4), M(6,2), M(6,3), M(6,4) are also set to 255, unavoidable imaging errors of the lens system 4 which e.g. cause the light of an illumination pixel not to be imaged precisely onto the allocated image pixel, but also partly onto adjacent image pixels are compensated. This effect is described in conjunction with the schematic representations in FIGS. 6 and 7.
FIG. 6 shows the arrangement of n×m tilting mirrors K(n,m) of the image modulator 5 as well as the illumination (hatched ellipse) of the tilting mirror K(5,3) present if only this were to be illuminated (thus if in the pattern data only the pattern spot M(5,3) were to have the value 255 and all other pattern spots the value 0). As FIG. 6 shows, the tilting mirror K(5,3) is not completely illuminated.
However, as is represented in FIG. 7, with the illumination according to the invention, not only the tilting mirror K(5,3) is illuminated, but also all bordering tilting mirrors K(4,2), K(4,3), K(4,5), K(5,2), K(5,4), K(6,2), K(6,3) and K(6,4). As a result, the tilting mirror K(5,3) which is the sole tilting mirror 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(n,m) are n=1, 2 and 7 as well as m=1 to 6 and n=3 to 6 and m=1 and 6.
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(5,3) for a different wavelength is represented schematically in FIG. 8 (illumination by only one illumination pixel) and FIG. 9 (illumination by nine illumination pixels according to FIG. 3) compared with FIGS. 6 and 7. As a comparison with FIGS. 6 and 7 shows, different-sized portions of the tilting-mirror surface of the tilting mirror K(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 adjacent pattern spots, the actual illumination on the image modulator 5 schematically corresponds to the representations of FIGS. 7 and 9. A comparison of the representations in FIGS. 7 and 9 shows that in each case approximately the same illumination intensity of the tilting mirror K(5,3) is present irrespective of the illumination wavelength. Thus the undesired colour artefacts are avoided.
As is shown in FIG. 5 the image control data BS comprise bit-switching times P3 and P5. The bit-switching time P3 corresponds to the third-lowest bit and the bit-switching time P5 to the fifth-lowest bit for the eight-bit encoding present, as 20 is to be written as 00010100 in binary numbers.
The bit-switching times P1-P8 for all eight possible bits are always the same within the single-image time and drawn schematically by dotted lines in FIG. 4. As is customary with pulse-width modulation, the bit-switching time P2 is twice the length of the bit-switching time P1, P3 is twice the length of P2 and so on, wherein the sum of all bit-switching times P1 to P8 corresponds to the T single-image time T. The shortest bit-switching time is




  
    T
    
      
        2
        q
      
      -
      1
    
  
  ,




wherein T is the single-image time and q the bit depth (here 8).

The individual bit-switching times P1-P8 can, as is shown in FIG. 4, 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. P8) 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. Therefore it is possible to set the pattern spots M(4,2), M(4,3), M(4,4), M(5,2), M(5,3), M(5,4), M(6,2), M(6,3) and M(6,4) linked to the image spot (5,3), not to the intensity value 255, but to 20, as is shown in FIG. 10.
The pulse-width modulation data MS for the intensity value 20 of the pattern data M are shown in FIG. 11. The pulse-width modulation data BS for the intensity value 20 of the image data B are shown in FIG. 12. These representations show that the linked illumination pixels (=illumination pixels which are controlled in accordance with the pattern spots linked to the image spot (5,3)) are only ever switched on (first tilting position) when the allocated image pixel (=image pixel for image spot B(5,3)) is switched on (first tilting position). When the allocated image pixel is switched off (second tilting position), the 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(4,2), M(4,3), M(4,4), M(5,2), M(5,4), M(6,2), M(6,3) and M(6,4) is strongly suppressed, as these image pixels are also illuminated only during the bit-switching times P3 and P5.
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. 13.
In this case, the pattern data M will comprise pattern spots M(n,m) which are linked to two image spots B(n,m) (thus e.g. pattern spot M(5,3) is allocated to image spot B(5,3) by the imaging optics 4 and linked to image spot B(4,3) as adjacent pattern spot on the basis of its proximity). In this case the pattern data M are generated such that the higher of the two intensity values which result from the linking to two image spots with brightness values not equal to 0 is always generated as a pattern spot value, as is schematically represented in FIG. 13. The pulse-width modulation data MS, BS for the intensity values 52 and 20 are shown in FIGS. 14 and 15.
Naturally it is also possible to set all linked pattern spots M(n,m) to 255 (not shown). This can easily be implemented in the control unit 7 and requires only a little computational outlay.
An example is shown in FIG. 16 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. 18a to 18e. The figures show that the bit-switching times P1, P2, P3 and P5 occur with these pulse-width modulation values.
Therefore the control unit 7 generates the value 23 (=10111) as a value for the linked 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. 17 with the pulse-width modulation data in FIGS. 18a-18e 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. 19) 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(4,2), M(4,3), M(4,4), M(5,2), M(5,3), M(5,4), M(6,2), M(6,3), 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. 20 and FIG. 21 respectively.
This means that the bit-switching times P6 and P4 are also set to 1, with the result that illumination lasts slightly longer than is absolutely necessary. However, in comparison with the pattern data from FIG. 3 in which the value 255 was chosen, 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. 13 with two values not equal to 0 in the image data BD is represented in FIG. 22. 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. 23a and 23b. The pulse-width modulation data of the image data values B(4,3)=52 and B(5,3)=20 are represented in FIGS. 24a and 24b. 
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.
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, only 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 in the image control data BS can thereby be taken into account.
An embodiment of the projector 1 according to the invention in which the modulators 3, 5 are designed as transmissive modulators (for example LCD modules) is shown in FIG. 25. The modulators are controlled in the same manner as was described in connection with the projector of FIG. 1.
In the embodiment shown in FIG. 26 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 several 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 K1 (also called illumination pixels below) and the second modulator 5 has 7×6 tilting mirrors K2 (also called image pixels below), as is schematically represented in FIGS. 27 and 28. Here, the tilting mirrors K1 and K2 have the same dimensions. This small number of tilting mirrors K1 and K2 is assumed to simplify the description. Naturally, the modulators 3, 5 can contain very many more tilting mirrors K1, K2. 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 K2 of the second modulator 5 in column and row direction, onto the second modulator 5, with the result that precisely four tilting mirrors K1 of the first modulator 3 are allocated to each tilting mirror K2 of the second modulator 5. If the two modulators 3, 5 have the same number of tilting mirrors K1, K2, this allocation can e.g. be achieved by not using all the tilting mirrors K2 of the second modulator 5.
As the representation of FIG. 29 shows, each tilting mirror K1 of the first modulator 3 that is allocated to a tilting mirror K2 of the second modulator 5 covers precisely one quarter of the pixel surface of the tilting mirror K2.
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 means of 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 means of 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. 30-35. 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 K2 (each image thus has 7×6 image spots) and, as is shown schematically in FIG. 30, 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 K1, K2 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. 1⁄3 · 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 F1 and F2.
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.
In the case of the fed-in image data BD in FIG. 31, 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 K1. The image data have 7×6 image spots B(n,m), each of which is allocated to an image pixel K2. 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 >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. 31, 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 255. Thus in this step the pattern spots M(5,3), M(5,4), M(6,3), M(6,4) are set to 255. The pattern data according to FIG. 31 are generated with these steps.
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=t1) for the value 255 of the pattern spot M(5,3) are schematically represented in FIG. 32. 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. 33. A BS or MS value of 1 corresponds to a tilting mirror K1, K2 in the first tilting position and a BS or MS value of 0 to a tilting mirror K1, K2 in the second tilting position.
As FIGS. 32 and 33 show, the tilting mirror of the image modulator 5 for the image spot B(5,3) is illuminated during the entire single-image time and thus also during the bit-switching times P3 and P5 at which the tilting mirror for the image spot B(5,3) is brought into its first position. As the pattern spots M(5,3), M(5,4), M(6,3), M(6,4) are set to 255 for this, unavoidable imaging errors of the lens system 4 are compensated. This effect is described in conjunction with the schematic representations in FIGS. 34 and 35.
FIG. 34 shows the arrangement of n×m (=7×6) tilting mirrors K2(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 K1 of the first modulator 3 is imaged precisely onto a tilting mirror K2 of the second modulator 5 (thus without a shift in the column and row direction). As can be seen in FIG. 34, 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. 29, is present and the four illumination pixels K1 allocated to the image pixel K2(5,3) are switched on, with the result that, as is represented in FIG. 35, the tilting mirror K2(5,3) is illuminated over all four allocated tilting mirrors K1 of the first modulator 3. As a result, the tilting mirror K2(5,3) which is the sole tilting mirror K2 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 K2(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 K2(4,2), K2(4,3), K2 (4,4), K(5,2), K(5,4), K(6,2), K(6,3) and K(6,4) immediately adjacent to the tilting mirror K2(5,3) are illuminated on the surface and only partially (FIG. 35).
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 K2(5,3) for a different wavelength is represented schematically in FIG. 36 (illumination through only one illumination pixel in the same manner as in FIG. 34) and FIG. 37 (illumination through four illumination pixels according to FIG. 35) compared with FIGS. 34 and 35. As a comparison with FIGS. 34 and 36 shows, different-sized portions of the tilting-mirror surface of the tilting mirror K2(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. 35 and 37. A comparison of the representations in FIGS. 35 and 37 shows that in each case approximately the same illumination intensity of the tilting mirror K2(5,3) is present irrespective of the illumination wavelength. Thus the undesired colour artefacts are avoided.
As is shown in FIG. 33 the image control data BS comprise bit-switching times P3 and P5. The bit-switching time P3 corresponds to the third-lowest bit and the bit-switching time P5 to the fifth-lowest bit for the eight-bit encoding present, as 20 is to be written as 00010100 in binary numbers.
The bit-switching times P1-P8 for all eight possible bits are always the same within the individual frame times and drawn schematically by dotted lines in FIG. 32. As is customary with pulse-width modulation, the bit-switching time P2 is twice the length of the bit-switching time P1, P3 is twice the length of P2 and so on, wherein the sum of all bit-switching times P1 to P8 corresponds to the single-image time T. The shortest bit-switching time is




  
    T
    
      
        2
        q
      
      -
      1
    
  
  ,




wherein T is the single-image time and q the bit depth (here 8).

The individual bit-switching times P1-P8 can, as is shown in FIG. 32, 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. P8) 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. Therefore it is possible to set the pattern spots M(5,3), M(5,4), M(6,3) and M(6,4), not to the intensity value 255 but to 20, as is shown in FIG. 38.
The pulse-width modulation data MS for the intensity value 20 of the pattern data M are shown in FIG. 39. The pulse-width modulation data BS for the intensity value 20 of the image data B are shown in FIG. 40. These representations show that the illumination pixels allocated to the image pixel K2(5,3) are only ever switched on (first tilting position) when the allocated image pixel K2(5,3) is switched on (first tilting position). When the allocated image pixel K2(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 P3 and P5.
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. 41.
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 a pattern spot value, as is schematically represented in FIG. 41. The pulse-width modulation data MS, BS for the intensity values 52 and 20 are shown in FIGS. 42 and 43.
Naturally it is also possible to set to 255 all the pattern spots allocated to the image spots with values greater than 0 (not shown). This can easily be implemented in the control unit and requires only a little computational outlay.
An example is shown in FIG. 44 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. 46a to 46e. The figures show that the bit-switching times P1, P2, P3 and P5 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. 45 with the pulse-width modulation data in FIGS. 46a-46e 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. 47) 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. 48 and FIG. 49 respectively.
This means that the bit-switching times P6 and P4 are also set to 1, with the result that illumination lasts slightly longer than is absolutely necessary. However, in comparison with the pattern data from FIG. 31 in which the value 255 was chosen, 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. 41 with two values not equal to 0 in the image data BD is represented in FIG. 50. 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. 51a and 51b. The pulse-width modulation data of the image data values B(4,3)=52 and B(5,3)=20 are represented in FIGS. 52a and 52b. 
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.
In the embodiments described thus far, the pattern data were generated such that no further image pixels are illuminated in addition to the image pixels which are to represent a brightness value greater than 0. The pattern data can, however, 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 also possible to additionally illuminate not only immediately adjacent image pixels which are to represent the brightness value 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.
The imaging optics 4 can also image the two modulators 3, 5 onto one another such that each tilting mirror K1 of the illumination modulator 3 is imaged offset by precisely half the dimension of a tilting mirror K2 of the second modulator in row direction (FIG. 53) or in column direction (FIG. 54). In this case precisely two tilting mirrors K1 of the first modulator 3 are allocated to each tilting mirror K2 of the second modulator 5.
An embodiment of the projector 1 according to the invention in which the modulators are designed as transmissive modulators (for example LCD modules) is shown in FIG. 55. The transmissive modulators are controlled in the same manner as is described in conjunction with FIGS. 26 to 55.

## Claims

1. A projector for projecting an image, comprising:
an illumination modulator struck by light with multiple illumination pixels which are arranged in columns and rows and that can be controlled independently of one another to modulate the intensity of the light pixel-by-pixel;
imaging optics, arranged downstream of the illumination modulator, which image the light modulated pixel-by-pixel onto an image modulator with multiple image pixels which are arranged in columns and rows and can be controlled independently of one another to generate the image to be projected, such that either precisely one image pixel of the image modulator is allocated to each illumination pixel of the illumination modulator or each illumination pixel is allocated to several image pixels;
a control unit, to which image data of the image to be generated are fed, and which generates pulse width modulation illumination control data from the image data for the illumination modulator and inputs the pulse width modulation illumination control data into the illumination modulator to modulate the light, and also generates pulse width modulation image control data for the image modulator and inputs the pulse width modulation image control data into the image modulator to generate an image;
wherein the pulse width modulation illumination control data for every illumination pixel has either an on-value to illuminate the allocated image pixel or the allocated image pixels of the image modulator to generate an image with the light coming from the illumination pixel, or an off-value to minimize the intensity of the light coming from the illumination pixel and imaged onto the allocated image pixel or the allocated image pixels; and wherein the pulse width modulation illumination control data are generated such that the illumination control data has the on-value for every illumination pixel which is allocated to one or at least one above threshold image pixel which is, according to the image data, to represent a brightness value lying above a predetermined brightness threshold value in the image, and has the off-value for all other illumination pixels surrounding the illumination pixels for which the control data has an on value, except that the illumination control data for at least one of the other illumination pixels whose allocated image pixel or at least one of whose allocated image pixels is not more than a predetermined number of pixels away from an image pixel which, according to the image data, is to represent a brightness value lying above the predetermined threshold value have the on-value while other illumination pixels that are more than predetermined number of pixels away from the above threshold image pixel, which according to the image data is to represent a brightness value lying above the predetermined threshold value, have the off value and wherein when the predetermined number of pixels away from the above threshold image pixel is zero, the pixels immediately adjacent to the image pixel have the on value;
wherein above threshold image pixels which are to represent a predefined brightness in the image and that are adjacent to image pixels which are to represent black are illuminated with at least equal intensity to bright adjacent image pixels that are surrounded only by bright image pixels that are to represent bright image elements whereby undesired brightness fluctuations of the image are avoided.

2. The projector according to claim 1, in which the control unit generates the pulse width modulation illumination control data such that the pulse width modulation illumination control data has the on-value for each of the other illumination pixels whose allocated image pixel or at least one of whose allocated image pixels is not more than a predetermined number of pixels away from an above threshold image pixel which, according to the image data, is to represent a brightness value lying above the predetermined threshold value.

3. The projector according to claim 1, in which the control unit generates the pulse width modulation illumination control data such that the predetermined number of pixels is zero, with a result that the pulse width modulation illumination control data has the on-value for the at least one other illumination pixel whose allocated image pixel is directly adjacent to an above threshold image pixel which is, according to the image data, to represent a brightness value lying above the predetermined threshold value, or for each of the other illumination pixels at least one of whose allocated image pixels is directly adjacent to an above threshold image pixel which is, according to the image data, to represent a brightness value lying above the predetermined threshold value.

4. The projector according to claim 1, in which
the illumination pixels can each be switched into a first state in which the light coming from the illumination pixel is imaged onto the allocated image pixel, and into a second state in which no light from the illumination pixel is imaged onto the allocated image pixel,
and the image pixels can each be switched into a first state in which the light coming from the image pixel is used to generate an image, and into a second state in which no light from the image pixel is used to generate an image.

5. The projector according to claim 4, in which, in the pulse width modulation illumination control data, the on-value for the illumination pixels is chosen such that each illumination pixel which is allocated to an above threshold image pixel which is, according to the image data, to represent a brightness value lying above the predetermined threshold value is always switched into the first state at the times when the allocated image pixel is switched into the first state or that every illumination pixel at least one of whose allocated above threshold image pixels is, according to the pulse width modulation image data, to represent a brightness value lying above the predetermined threshold value in the image, is always switched into the first state at the times when at least one of the allocated image pixels is switched into the first state.

6. The projector according to claim 5, in which, in the pulse width modulation illumination control data, the on-value for the illumination pixels is chosen such that every illumination pixel which is allocated to an above threshold 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 allocated above threshold image pixel is switched into the second state, or that every illumination pixel at least one of whose allocated above threshold image pixels 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.

7. The projector according to claim 4, in which, in the pulse width modulation illumination control data, the on-value for the illumination pixels is chosen such that every illumination pixel which is allocated to an above threshold 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 allocated above threshold image pixel is switched into the second state, or that every illumination pixel at least one of whose allocated above threshold image pixels 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.

8. The projector according to claim 4, in which, in the pulse width modulation illumination control data, the on-value for the other illumination pixels is chosen such that each of the other illumination pixels is always switched into the first state at the times when at least one of the image pixels no more than the predetermined number of pixels away from the allocated image pixel is switched into the first state or when at least one of its allocated image pixels is no more than the predetermined number of pixels away from an image pixel switched into the first state.

9. The projector according to claim 8, in which, in the pulse width modulation illumination control data, the on-value for the other illumination pixels is chosen such that each of the other illumination pixels whose allocated image pixel or at least one of whose allocated image pixels is no more than the predetermined number of pixels away from at least one other above threshold image pixel which is to represent a brightness value which lies above the predetermined threshold value and below a maximum value is at least sometimes also switched into the second state during the times when the at least one other image pixel is switched into the second state.

10. The projector according to claim 4, in which, in the pulse width modulation illumination control data, the on-value for the illumination pixels is chosen such that every illumination pixel which is allocated to an above threshold image pixel which is, according to the image data, to represent a brightness value lying above the predetermined threshold value is always switched into the first state precisely only at the times when the allocated image pixel is switched into the first state, or that every illumination pixel at least one of whose allocated above threshold image pixels is, according to the image data, to represent a brightness value lying above the predetermined threshold value in the image is always switched into the first state precisely only at the times when at least one of the allocated image pixels is switched into the first state.

11. The projector according to claim 10, in which, in the pulse width modulation illumination control data, the on-value for the other illumination pixels is chosen such that each of the other illumination pixels is always switched into the first state precisely only at the times when at least one of the image pixels no more than the predetermined number of pixels away from the allocated image pixel is switched into the first state or if at least one of its allocated image pixels is no more than the predetermined number of pixels away from an image pixel switched into the first state.

12. The projector according to claim 1, in which the pulse width modulation control data for each illumination and image pixel in each case contain a binary data value of identical bit depth, wherein the on-value for each illumination pixel which is allocated to an above threshold image pixel which is, according to the image data, to represent a brightness value lying above the predetermined threshold value in the image is chosen such that at least the same bits are set as in the binary data value of the allocated image pixel.

13. The projector according to claim 12, in which, in the illumination control data, the on-value for each of the illumination pixels is chosen such that all bits are set which are set in the binary data value of the allocated image pixel and in the binary data values of all of the image pixels that are no more than the predetermined number of pixels away from the allocated image pixel, or that all bits are set which are set in the binary data values of the allocated image pixels and in the binary data values of all of the image pixels that are no more than the predetermined number of pixels away from the allocated image pixels.

14. A method for projecting an image, comprising
directing light onto an illumination modulator with multiple illumination pixels which are arranged in columns and rows and can be controlled independently of one another in order to modulate the intensity of the light pixel-by-pixel;
imaging the light modulated pixel-by-pixel onto an image modulator with multiple image pixels which are arranged in columns and rows and which can be controlled independently of one another to generate an image to be projected such that either precisely one image pixel of the image modulator is allocated to each illumination pixel or each illumination pixel of the illumination modulator is allocated to several image pixels;
generating pulse width modulation illumination control data for the illumination modulator from image data of the image to be generated;
inputting the pulse width modulation illumination control data into the illumination modulator to modulate the light;
generating pulse width modulation image control data for the image modulator;
inputting the pulse width modulation image control data into the image modulator to generate an image;
wherein the pulse width modulation illumination control data for every illumination pixel has either an on-value to illuminate, with the light coming from this illumination pixel, the allocated image pixel or the allocated image pixels of the image modulator to generate an image, or an off-value to minimize the intensity of the light coming from this illumination pixel and imaged onto the allocated image pixel or allocated image pixels, and wherein the pulse width modulation illumination control data are generated such that the illumination control data has the on-value for every illumination pixel which is allocated to one or at least one image pixel which is, according to the pulse width modulation image data, to represent a brightness value lying above a predetermined threshold value in the image and has the off-value for all other illumination pixels surrounding the illumination pixels for which the control data has an on value, except that the pulse width modulation illumination control data for at least one of the other illumination pixels, whose allocated image pixel or at least one of whose allocated image pixels is not more than a predetermined number of pixels away from an above threshold image pixel which is, according to the image data, to represent a brightness value lying above the predetermined threshold value has the on-value while other illumination pixels that are more than predetermined number of pixels away from the image pixel, which according to the image data is to represent a brightness value lying above the predetermined threshold value, have the off value and wherein when the predetermined number of pixels away from the above threshold image pixel is zero, the pixels immediately adjacent to the image pixel have the on value;
wherein the above threshold image pixels which are to represent a predefined brightness in the image and that are adjacent to image pixels which are to represent black are illuminated with at least equal intensity to bright adjacent image pixels that are surrounded only by bright image pixels that are to represent bright image elements whereby undesired brightness fluctuations of the image are avoided.

15. The method according to claim 14, further comprising generating the pulse width modulation illumination control data such that the pulse width modulation illumination control data has the on-value for each of the other illumination pixels whose allocated image pixels or at least one of whose allocated image pixels is not more than a predetermined number of pixels away from an above threshold image pixel which is, according to the image data, to represent a brightness value lying above the predetermined threshold value.

16. The method according to claim 15, further comprising generating the pulse width modulation illumination control data such that the predetermined number of pixels is zero, with a result that the pulse width modulation illumination control data has the on-value for the at least one other illumination pixel whose allocated image pixel is directly adjacent to an above threshold image pixel which is, according to the image data, to represent a brightness value lying above the predetermined threshold value, or for each of the other illumination pixels at least one of whose allocated image pixels is directly adjacent to an above threshold image pixel which is, according to the image data, to represent a brightness value lying above the predetermined threshold value.

17. The method according to claim 14, further comprising generating the pulse width modulation illumination control data such that the predetermined number of pixels is zero, with a result that the pulse width modulation illumination control data has the on-value for the at least one other illumination pixel whose allocated image pixel is directly adjacent to an above threshold image pixel which is, according to the image data, to represent a brightness value lying above the predetermined threshold value, or for each of the other illumination pixels at least one of whose allocated image pixels is directly adjacent to an above threshold image pixel which is, according to the image data, to represent a brightness value lying above the predetermined threshold value.

18. The method according to claim 14, in which
the illumination pixels can each be switched into a first state in which the light coming from the illumination pixel is imaged onto the allocated image pixel, and into a second state in which no light from the illumination pixel is imaged onto the allocated image pixel, and
the image pixels can each be switched into a first state in which the light coming from the image pixel is used to generate an image, and into a second state in which no light from the image pixel is used to generate an image.

19. The method according to claim 18, further comprising choosing, in the pulse width modulation illumination control data, the on-value for the illumination pixels such that every illumination pixel which is allocated to an above threshold image pixel which is, according to the image data, to represent a brightness value lying above the predetermined threshold value is always switched into the first state at the times when the allocated image pixel is switched into the first state, or such that every illumination pixel at least one of whose allocated above threshold image pixels is, according to the image data, to represent a brightness value lying above the predetermined threshold value in the image is always switched into the first state at the times when at least one of the allocated image pixels is switched into the first state.

20. The method according to claim 19, further comprising choosing, in the pulse width modulation illumination control data, the on-value for the illumination pixels such that every illumination pixel which is allocated to an above threshold 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 times when the allocated above threshold image pixel is switched into the second state, or such that every illumination pixel at least one of whose allocated above threshold image pixels 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 above threshold image pixel is switched into the second state.

21. The method according to claim 19, further comprising choosing in the pulse width modulation illumination control data, the on-value for the other illumination pixels such that each of the other illumination pixels is always switched into the first state at the times when at least one of the image pixels no more than the predetermined number of pixels away from the allocated image pixel is switched into the first state, or such that each of the other illumination pixels is always switched into the first state at the times when at least one of its allocated image pixels no more than the predetermined number of pixels away from an image pixel is switched into the first state.

22. The method according to claim 21, further comprising choosing, in the pulse width modulation illumination control data, the on-value for the other illumination pixels such that each of the other illumination pixels whose allocated image pixel or at least one of whose allocated image pixels is no more than the predetermined number of pixels away from at least one other above threshold image pixel which is to represent a brightness value which lies above the predetermined threshold value and below a maximum value is at least sometimes also switched into the second state during the times when the at least one other image pixel is switched into the second state.

23. The method according to claim 18, further comprising choosing, in the pulse width modulation illumination control data, the on-value for the illumination pixels such that every illumination pixel which is allocated to an above threshold 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 times when the allocated above threshold image pixel is switched into the second state, or such that every illumination pixel at least one of whose allocated above threshold image pixels 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 above threshold image pixel is switched into the second state.

24. The method according to claim 18, further comprising choosing, in the pulse width modulation illumination control data, the on-value for the illumination pixels is chosen such that every illumination pixel which is allocated to an above threshold image pixel which is, according to the image data, to represent a brightness value lying above the predetermined threshold value is always switched into the first state precisely only at the times when the allocated above threshold image pixel is switched into the first state, or such that every illumination pixel at least one of whose allocated above threshold image pixels is, according to the image data, to represent a brightness value lying above the predetermined threshold value in the image is always switched into the first state precisely only at the times when at least one of the allocated above threshold image pixels is switched into the first state.

25. The method according to claim 24, further comprising choosing, in the pulse width modulation illumination control data, the on-value for the other illumination pixels such that each of the other illumination pixels is always switched into the first state precisely only at the times when at least one of the image pixels no more than the predetermined number of pixels away from the allocated above threshold image pixel is switched into the first state, or such that each of the other illumination pixels is always switched into the first state precisely only at the times when at least one of its allocated above threshold image pixels no more than the predetermined number of pixels away from an image pixel is switched into the first state.

26. The method according to claim 14, in which the control data for each illumination and image pixel contain a binary data value of equal bit depth, and further comprising choosing the on-value for each illumination pixel which is allocated to an above threshold image pixel or at least one image pixel which is, according to the image data, to represent a brightness value lying above the predetermined threshold value in the image such that at least the same bits are set as in the binary data value of the allocated above threshold image pixel.

27. The method according to claim 26, further comprising choosing, in the pulse width modulation illumination control data, the on-value for each of the illumination pixels such that all bits are set which are set in the binary data value of the allocated above threshold image pixel and in the binary data values of all of the image pixels that are no more than the predetermined number of pixels away from the allocated above threshold image pixel, or such that all bits are set which are set in the binary data values of the allocated image pixels and in the binary data values of all of the image pixels that are no more than the predetermined number of pixels away from the image pixels.

28. A projector for projecting an image, comprising:
an illumination modulator struck by light which has multiple illumination pixels arranged in columns and rows which can be controlled independently of one another in order to modulate the intensity of the light pixel-by-pixel;
imaging optics, arranged downstream of the illumination modulator, which image the light modulated pixel-by-pixel onto an image modulator with multiple image pixels arranged in columns and rows which can be controlled independently of one another to generate the image to be projected such that each illumination pixel is allocated to several image pixels;
a control unit, to which image data of the image to be generated is fed, and which generates from the image data pulse width modulation illumination control data for the illumination modulator and inputs the pulse width modulation illumination control data into the illumination modulator to modulate the light, and also generates pulse width modulation image control data for the image modulator and inputs the pulse width modulation image control data into the image modulator to generate an image,
wherein the pulse width modulation illumination control data for every illumination pixel has either an on-value to illuminate the allocated image pixels of the image modulator with the light coming from these illumination pixels to generate an image, or an off-value to minimize the intensity of the light coming from this illumination pixel and imaged onto the allocated image pixels, and the pulse width modulation illumination control data are generated such that the pulse width modulation illumination control data has the on-value for every illumination pixel which is allocated to at least one above threshold image pixel which is, according to the image data, to represent a brightness value lying above a predetermined threshold value in the image, and the off-value for all other illumination pixels, in which
the illumination pixels can each be switched into a first state in which the light coming from the illumination pixel is imaged onto the allocated image pixel, and into a second state in which no light is imaged onto the allocated above threshold image pixel, and
the image pixels can each be switched into a first state in which the light coming from the image pixel is used to generate an image, and into a second state in which no light from the image pixel is used to generate an image,
in which, in the pulse width modulation illumination control data, the on-value for the illumination pixels is chosen such that every illumination pixel at least one of whose allocated above threshold image pixels is, according to the image data, to represent a brightness value lying above the predetermined brightness threshold value in the image is always switched into the first state precisely only at the times when at least one of the allocated above threshold image pixels is switched into the first state and wherein when the predetermined number of pixels away from the above threshold image pixel is zero, the pixels immediately adjacent to the image pixel have the on value;
wherein the above threshold image pixels which are to represent a predefined brightness in the image and that are adjacent to image pixels which are to represent black are illuminated with at least equal intensity to bright adjacent image pixels that are surrounded only by bright image pixels that are to represent bright image elements whereby undesired brightness fluctuations of the image are avoided.

29. The projector according to claim 28, in which, in the pulse width modulation illumination control data, the on-value for the illumination pixels is chosen such that every illumination pixel at least one of whose allocated above threshold image pixels is, according to the image data, to represent a brightness value lying above the predetermined threshold value in the image is always switched into the first state at the times when at least one of the allocated above threshold image pixels is switched into the first state.

30. The projector according to claim 28, in which the control data for each illumination and image pixel each contain a binary data value of equal bit depth, wherein the on-value for each illumination pixel which is allocated to at least one above threshold image pixel which is, according to the image data, to represent a brightness value lying above the predetermined threshold value in the image is chosen such that at least the same bits are set as in the binary data values of all allocated image pixels.

31. A method for projecting an image, comprising:
directing light onto an illumination modulator which has multiple illumination pixels arranged in columns and rows which can be controlled independently of one another to modulate the intensity of the light pixel-by-pixel;
imaging the light modulated pixel-by-pixel onto an image modulator with several image pixels arranged in columns and rows which can be controlled independently of one another to generate the image to be projected such that each illumination pixel is allocated to several image pixels;
generating pulse width modulation illumination control data for the illumination modulator from image data of the image to be generated;
inputting the pulse width modulation illumination control data into the illumination modulator to modulate the light;
generating pulse width modulation image control data for the image modulator;
inputting the pulse width modulation image control data into the image modulator to generate an image;
wherein the pulse width modulation illumination control data for every illumination pixel has either an on-value to illuminate the allocated image pixels of the image modulator with the light coming from these illumination pixels to generate an image, or an off-value to minimize the intensity of the light coming from this illumination pixel and imaged onto the allocated image pixels, and are generated such that the pulse width modulation illumination control data has the on-value for every illumination pixel which is allocated to at least one above threshold image pixel which is, according to the image data, to represent a brightness value lying above a predetermined threshold value in the image, and the off-value for all other illumination pixels;
in which
the illumination pixels can each be switched into a first state in which the light coming from the illumination pixel is imaged onto the allocated image pixel, and into a second state in which no light is imaged onto the allocated image pixel; and
the image pixels can each be switched into a first state in which the light coming from the image pixel is used to generate an image, and into a second state in which no light from the image pixel is used to generate an image;
further comprising choosing, in the pulse width modulation illumination control data, the on-value for the illumination pixels such that every illumination pixel at least one of whose allocated above threshold image pixels is, according to the image data, to represent a brightness value lying above the predetermined threshold value in the image is always switched into the first state precisely only at the times when at least one of the allocated above threshold image pixels is switched into the first state and wherein when the predetermined number of pixels away from the above threshold image pixel is zero, the pixels immediately adjacent to the image pixel have the on value;
wherein the above threshold image pixels which are to represent a predefined brightness in the image and that are adjacent to image pixels which are to represent black are illuminated with at least equal intensity to bright adjacent image pixels that are surrounded only by bright image pixels that are to represent bright image elements whereby undesired brightness fluctuations of the image are avoided.

32. The method according to claim 31, further comprising choosing, in the pulse width modulation illumination control data, the on-value for the illumination pixels such that every illumination pixel at least one of whose allocated above threshold image pixels is, according to the image data, to represent a brightness value lying above the predetermined threshold value in the image is always switched into the first state at the times when at least one of the allocated image pixels is switched into the first state.

33. The method according to claim 31, in which the control data for each illumination and image pixel contain a binary data value of equal bit depth, and further comprising choosing the on-value for each illumination pixel which is allocated to at least one above threshold image pixel which is, according to the image data, to represent a brightness value lying above the predetermined threshold value in the image such that at least the same bits are set as in the binary data values of all allocated image pixels.