Hybrid image generator having an incident-light or back-light projector and an lc matrix for an hud for a vehicle

Abstract

The invention relates to a projection unit for a field of vision display device for superimposing a virtual image via reflection on a reflection pane, in particular a vehicle windscreen, arranged in the field of vision of a user, comprising: - a projector-based image generator, having a projector for generating a light beam containing the desired display content and having a projection screen illuminated by said light beam, the projector being designed to generate a real image on the projection screen and the projection screen being designed to cast the light beam resulting therefrom onto the reflection pane; and - a polarisation-filter-based contrast pixel matrix, arranged in the beam path of the light beam originating from the projection screen, the contrast pixels of which can be switched, synchronously with the generated real image, between a light-blocking state for image regions to be displayed as black and a light-transmitting state for the remaining image regions.

Description

[0001] Description

[0002] Hybrid imager with a front or rear light projector and an LC matrix for a horn for a vehicle

[0003] The invention relates to a projection unit for head-up display devices that can be used in motor vehicles or other land, air, or water vehicles and are also known as head-up displays (HUDs). They serve to generate a virtual image projected into the user's field of vision via reflection from a reflective disc, such as a windshield, rear window, or side window of the vehicle or a specially provided combiner disc arranged in the user's field of vision. The invention also relates to a corresponding operating method and to the head-up display device, as well as to a vehicle equipped therewith.

[0004] With a head-up display, for example, speed information and other useful navigation, warning and vehicle operating instructions or even entertainment content in a motor vehicle are superimposed in the form of a virtual image on the real image of the surroundings in front of the vehicle as observed by the driver and / or another passenger. Among other things, a simplified HUD design is known for generating a panoramic virtual display. In this case, an image generator is positioned directly opposite the windshield in the area near the base of the windshield without any additional projection optics such as a mirror, etc. The real image generated by the image generator is thus reflected directly off the windshield and thus reaches the viewers, such as the driver and / or front passenger. In this context, EP 2 594 987 A2, for example, proposes a HUD system for a motor vehicle with a projector-based image generator. The system comprises a standard vehicle windshield (i.e.The device comprises a non-metallic (i.e., without special coatings), an optical image projector, and an instrument panel equipped with a reflective facet surface. The projector is configured to project an image onto the reflective facet surface. This is configured to project the projector image onto a surface of the standard vehicle window oriented to reflect the image from the reflective facet surface toward an occupant. The reflective facet surface may be arranged within a plurality of troughs separated from one another by a plurality of diffusely reflecting partition walls. The plurality of troughs may be configured to shield the occupant from external reflections. The reflective facet surface may, in particular, comprise a plurality of electrically controllable facets configured as an array of electrowetting cells.

[0005] If you want to create a realistic image in a car using a projector, you immediately encounter the problem of the low contrast of such systems. The contrast is reduced by two sources of interference: firstly, unavoidable stray light from the projector itself, and secondly, ambient light. While the negative effect of ambient light can be somewhat reduced by appropriately designing the projection screen (also called a canvas or screen) by limiting its acceptance angles, this is not possible with stray light from the projector, as this inevitably falls within the acceptance angles of the screen. In other words, a contrast problem here arises in that black content in the image produced by the projector does not appear black because stray light from the projector and ambient light pass through the projection screen and into the viewer's eye.Current contrast requirements for projector-based imagers for head-up displays in vehicles reach contrast values ​​of up to 10,000:1, depending on the display type. For comparison, the contrasts currently achievable with projectors are in the range (1,000-1,500):1. Therefore, even with a perfect screen (perfect in the sense that only projector light is directed to the viewer), projectors cannot meet the contrast requirements for a HUD.

[0006] It is an object of the present invention to provide an alternative and / or improved projection unit for a field of view display device, which can be used in particular in a vehicle and can enable an improvement over known devices, for example with regard to their contrast, costs, image quality, visibility even in high ambient brightness and / or other aspects.

[0007] This object is achieved by a projection unit according to claim 1, as well as by an associated operating method, a field of view display device containing this projection unit, and a vehicle equipped therewith according to the independent claims. Further embodiments are specified in the dependent claims. All further features and effects mentioned in the claims and the following description for the projection unit also apply to the field of view display device, the operating method, and the vehicle, and vice versa.

[0008] According to a first aspect, a projection unit for a field-of-view display device is provided, which can be designed in particular for use in a vehicle. The vehicle can be a motor vehicle, but also any other land, air, or water vehicle. The field-of-view display device can be designed, for example, as a head-up display (HUD).

[0009] The projection unit is designed, during operation of the field-of-view display device, to output a bundle of light rays and project them in a suitable shape and direction onto a reflective disc arranged in the field of vision of at least one user, from which the beam is reflected back to their eyes (or their eyebox), thereby displaying a virtual image floating beyond the reflective disc. The eyebox of the field-of-view display device is, as is customary, understood to be a spatial area from which the virtual image is fully visible to the user. The reflective disc can, in particular, be designed as a partial section of a windshield or another vehicle window, or it can be a specially provided combiner disc, which can be reflective on the user side and at least partially transparent on the back.During operation of the field of view display device, it is arranged outside the projection unit, so that the projection unit can also be manufactured and sold separately from the reflection plate.

[0010] The projection unit comprises a projector-based image generator with a projector configured to generate a beam of light with the desired display content, and a projection screen illuminated by the projector. The projector is configured to generate a real image on the projection screen. The projection screen is designed to project the resulting beam of light in a predetermined shape and direction onto the reflective disc, thus presenting the user with a virtual image beyond the reflective disc as desired.

[0011] To solve the contrast problems outlined above, the projection unit also includes a polarization-filter-based contrast pixel matrix, which is arranged in the beam path of the light beam emanating from the projection screen and covers its entire beam cross-section contributing to image generation. The individual contrast pixels of this matrix can be switched independently of one another and synchronously with the actual image generated on the projection screen between a light-blocking state for those image areas that are to be displayed in black and a light-transmitting state for all remaining image areas. One idea behind this projection unit is to improve the lack of contrast in a projector-based imager by using a locally switchable, polarization-filter-based, light-absorbing module (called a contrast pixel matrix), which is mounted in front of the projection screen on the output side.Therefore, this projection unit is also suitable, among other things, for virtual image display in a transparent area of ​​the windscreen, which lies above the so-called black print area, which extends along the windscreen root and is typically printed or tinted in black or dark. Several different designs are possible for the specific layer structure of the polarization-filter-based contrast pixel matrix, of which only a few basic examples are outlined below.

[0012] According to one embodiment, the contrast pixel matrix is ​​arranged directly on the projection screen in the beam path of the light beam emanating from the projection screen. Each contrast pixel, with its linear dimensions, extends over several, ideally approximately two to three, image pixels of the real image that can be generated on the projection screen. In other words, in this embodiment, each contrast pixel, with its area, extends over several, ideally approximately five to ten, image pixels of the real image that can be generated on the projection screen. In this case, the respective contrast pixel can, for example, be switched to light transmission during operation whenever there is at least one non-black image pixel within its area.

[0013] In particular, the projection screen can be designed to reflect the light beam emanating from the projector toward the reflection plate. In other words, in this specific embodiment of the imager (also called a front-light projector), the projection screen is illuminated by the projector in reflection, and the contrast pixel matrix is ​​arranged in the beam path of the light beam reflected by the projection screen, for example, directly on the projection screen. Alternatively, the projection screen can also be illuminated by the projector in transmission. In this imager (also called a back-light projector), the contrast pixel matrix is ​​arranged in the beam path of the light beam transmitted by the projection screen, again for example directly on the projection screen.

[0014] According to one embodiment, the polarization-filter-based contrast pixel matrix comprises the following layers: a first linear polarization filter on a matrix surface facing the projection screen and / or a second linear polarization filter on a matrix surface facing away from the projection screen; and a two-dimensional polarization rotation matrix, the matrix elements of which, in cooperation with the first and / or second linear polarization filters, form the contrast pixels and, for this purpose, are each switchable between a polarization-rotating state and a non-polarization-rotating state. Each matrix element is designed, for example, to rotate a predetermined linear polarization direction of the light by a predetermined angle of, for example, up to 90° in its polarization-rotating state.The choice of the predetermined angle depends on the specific optical design of the imager and the polarization filter, as the following examples show, in order to achieve the best possible contrast effect.

[0015] In this embodiment, the double-sided polarization filter arrangement can lead to excellent contrast results even with projectors that emit unpolarized light. For projectors that emit linearly polarized light, it is expedient to align the transmission direction of a projector-side polarization filter parallel to the polarization direction of the incident projector light for the best possible energy efficiency. In the double-sided polarization filter arrangement, the first linear polarization filter and the second linear polarization filter can, for example, be configured to transmit the same polarization direction, and the matrix elements can be switched to their polarization-rotating state to rotate the polarization direction by 90° in the area of ​​black image pixels.Alternatively, the matrix elements can be switched to their polarization-rotating state to rotate the polarization direction by a predetermined angle in the region of non-black image pixels and the transmission direction of the first polarization filter and the second polarization filter can differ by exactly this angle, etc. etc.

[0016] In a specific embodiment according to this embodiment, the imager is designed as a front-light projector for generating the light beam with a predetermined linear polarization, and the projection screen is designed for polarization-maintaining reflection of this light beam. In a first variant, the contrast pixel matrix has only the first linear polarization filter, i.e., the filter facing the projection screen, whose transmission direction coincides with the polarization direction of the light beam or is rotated relative to it by the predetermined angle of the polarization rotation matrix, for example, approximately 90°.

[0017] In a modification of this variant, the contrast pixel matrix has only the second linear polarization filter, i.e., the one facing away from the projection screen. Its transmission direction coincides with the polarization direction of the light beam, and the predetermined angle of the polarization rotation matrix is ​​approximately 45°. This allows not only the stray light from the projector but also the ambient light to be specifically reduced or even completely eliminated.

[0018] Similar considerations also yield various suitable layer designs for the contrast pixel matrix for a backlight projector, such as using only a linear polarization filter facing away from the projection screen, whose transmission direction coincides with the polarization direction of the light beam or is rotated by the predetermined angle of the polarization rotation matrix, for example, approximately 90°. The polarization rotation matrix must be controlled accordingly during operation.

[0019] The polarization rotation matrix can be designed, in particular, in a conventional manner based on liquid crystals (LC), i.e., as an LC matrix. To ensure that the projection screen reflects light in a polarization-preserving manner, it can be constructed, for example, from a metallic material, in particular by a metallic coating on its surface or intermediate surface intended for image generation.

[0020] In a specific embodiment of a front-light projector, the projection screen has a mirror surface composed of a plurality of facets forming a facet grid with a sawtooth profile. Each facet has a mirror segment for directed guidance of the light beam into an eyebox predetermined for the user's eyes. Such directed eyebox illumination can significantly increase the energy efficiency of the field-of-view display device with the projector-based imager. The respective mirror segment can, in particular, be designed to be planar. Alternatively, a curved, for example, concave, design can be effective. The sawtooth profile can be created, among other things, by the mirror segments of the facets having different angles depending on their position on the facet grid or mirror array.They therefore do not always adjoin one another continuously, so that height offsets between adjacent facets can be compensated for, for example, by transition surfaces oriented almost perpendicular to their mirror segments, creating a sawtooth profile. The surfaces of the individual facets or their mirror segments can, in particular, be below a size that can be resolved with the human eye, so that the facet grid is not visible to the user in the virtual image. Their linear dimensions can, in particular, be larger than the longest wavelength of the projector light used and can, for example, be in the micrometer range. To avoid disruptive diffraction effects such as color fringes or interference, etc., the surfaces of the individual facets / mirror segments can also have varying sizes and / or shapes.

[0021] According to a further aspect, a method for operating the projection unit or field-of-view display device presented herein is provided. In this method, the projector is controlled to generate a light beam with the desired display content and a corresponding real image on the projection screen. Synchronously with the real image generated on the projection screen, the individual contrast pixels of the contrast pixel matrix are switched to their light-blocking state in the image areas to be displayed in black and to their light-transmitting state in the remaining image areas. The contrast pixels can be controlled using very simple algorithms, which, for example, essentially comprise downsampling the high-resolution projector image generated on the projection screen to the possibly lower resolution of the contrast pixel matrix and subsequent binarization (black / white).

[0022] According to a further aspect, a field of view display device is provided which can be designed in particular for use (i.e., installation) in a vehicle. In addition to the projection unit presented here, the field of view display device also comprises a control unit which is designed and configured to automatically carry out the above method. Furthermore, it comprises the above-mentioned reflection plate. In particular, the reflection plate can be arranged directly opposite the contrast pixel matrix and the projection screen located behind and / or below it, with the exception of any covers of the projection unit (for example in the form of a cover plate which allows the light beam to pass through) which have no beam-shaping, beam-deflecting, or beam-imaging optical effect on the light beam.In other words, in this specific embodiment, the field-of-view display device does not include any additional optical elements such as deflecting or concave mirrors or lenses, etc., in the beam path of the light beam between the contrast element and the reflection plate. However, any coatings of the projection screen, the contrast element, or the reflection plate with optical functionality are still possible. This embodiment allows for the implementation of a projection unit that is particularly compact in the vertical direction, which is therefore particularly well suited for large-scale virtual displays such as panoramic displays.

[0023] According to a further aspect, the aforementioned vehicle is provided. The spatial orientation terms used herein, such as "above," "below," "behind," "side," "horizontal," "vertical," etc., refer in this case to the usual vehicle-fixed Cartesian coordinate system with mutually perpendicular longitudinal, transverse, and vertical axes of the vehicle. The vehicle has, for example, at least one vehicle window, such as a windshield with an instrument panel extending beneath it, and an occupant compartment partially bounded thereby.It is equipped with the above-mentioned field of view display device, the projection unit of which can, for example, be installed directly in or below the upper surface of the instrument panel, so that the light beam from the projection unit is projected onto the windshield or a combiner disc arranged directly in the field of view of the driver and / or another passenger, which serves as the aforementioned reflection disc of the field of view display device. However, the field of view display device can also be integrated into any other suitable installation location in the vehicle, whereby other vehicle windows or combiner discs arranged at other locations in the passenger compartment can also serve as reflection discs.

[0024] In particular, the windshield can be bounded by an A-pillar of the vehicle to the left and right in the transverse direction of the vehicle, and the projection unit and its projection screen can be arranged in or below the upper side of the instrument panel in such a way that the windshield serves as a reflection screen over at least a large part of its transverse extension. This makes it possible, in particular, to create a panoramic virtual display for the driver and / or front passenger.

[0025] The above aspects of the invention and their embodiments and specific configurations are explained in more detail below with reference to examples shown in the accompanying drawings. The drawings are to be understood as purely schematic illustrations of the basic optical design principle, i.e., not to scale. They show:

[0026] Figure 1 shows a section of a vehicle with a field of view display device according to an embodiment of the invention in a vertical longitudinal section;

[0027] Figure 2 is a vertical longitudinal sectional view of a variant embodiment of a projection unit of the field of view display device of Figure 1, with a schematic representation of the beam paths of the ambient light as well as the useful and scattered light from the projector; and

[0028] Figure 3 is a vertical longitudinal sectional view of a further embodiment of the projection unit of Fig. 1 with a schematic representation of the beam paths of the ambient light and the useful and scattered light from the projector.

[0029] All of the various embodiments, alternatives, and specific design features of the projection unit, the associated operating method, the field of view display device, and the vehicle according to the above aspects of the invention mentioned above in the description and in the subsequent claims can be implemented in the examples shown in Figures 1 to 3, in particular also alternatively or in addition to the features shown therein. They will therefore not all be repeated below. The same applies accordingly to the definitions of terms and effects already given above with regard to individual features shown in Figures 1-3. Figure 1 shows a highly simplified vertical longitudinal sectional view of a section of a vehicle 1 with a field of view display device 2 according to an exemplary embodiment of the invention.The spatial orientation terms used below, such as "horizontal," "vertical," "above," "below," "below," etc., refer to the usual vehicle-fixed Cartesian coordinate system with mutually perpendicular longitudinal, transverse, and vertical directions of the vehicle 1. In this example, the vehicle 1 is a motor vehicle, which is indicated in Fig. 1 only by its windshield 3, which serves as the aforementioned reflection disc of the field of view display device 2. Below it, in an instrument panel (not separately shown), a projection unit 5 of the field of view display device 2 is arranged.

[0030] The field of view display device 2 is designed to generate a virtual image V in the field of view of at least one user, who is indicated in Fig. 1 only by a spatial area (eyebox) E in the passenger compartment of the vehicle 1 intended for their eyes. The at least one user can, for example, be a driver and / or front passenger of the vehicle 1. The field of view display device 2 can, in particular, be designed for a panoramic virtual display in that the windshield 3, with almost its entire extension in the transverse direction of the vehicle, serves as a reflection plate of the field of view display device 2. This is purely an example of a head-up display (HUD).

[0031] The projection unit 5 contains a projector-based image generator. This comprises a projector 6, which is designed to generate a light beam L with the desired display content, and a projection screen 7 (also called a screen or canvas) illuminated by the projector. The light beam L, which is also called “projector light” herein, is indicated in Fig. 1 by its edge rays, which limit the beam cross-section required for virtual image generation. In this example, the projector 6 is designed to generate a real image on the projection screen 7 in reflection and therefore illuminates it obliquely from above. The projection screen 7 is designed to project the resulting, i.e. reflected, light beam L in a predetermined shape and direction onto the front screen 3 in order to show the user the virtual image V with the desired display properties beyond the front screen 3.

[0032] Furthermore, the projection unit 5 comprises a polarization filter-based contrast pixel matrix 8, which in this example is arranged directly on the projection screen 7 and extends over the entire beam cross-section of the light beam L required for virtual image generation. As explained below using several examples with reference to Figs. 2 and 3, this allows the contrast of the real image representation on the projection screen 7 to be significantly improved.

[0033] 2 and 3 each show, in a vertical longitudinal sectional view, two different design variants of the projection unit 5 of FIG. 1 . As mentioned at the beginning, in the prior art the contrast of the real image generated on the projection screen 7 by useful light NS of the projector 6 is reduced by two stray light sources: firstly by scattered light LS from the projector 6 itself and secondly by ambient light 12 from ambient light sources 11 , such as the sun or artificial lighting in and outside the vehicle 1. FIGS. 2 and 3 show two different examples of the optical layer structure of the polarization filter-based contrast pixel matrix 8, which can be controlled to partially (indicated as thinned beam lines) or even completely (indicated as crossed beam lines) suppress the scattered light LS and the ambient light 12 in order to improve the contrast.The corresponding beam path of the useful light NS, scattered light LS and ambient light 12 is only indicated schematically.

[0034] Fig. 2 shows a polarization filter-based contrast pixel matrix 8 with only one linear polarization filter 10, positioned on the projection screen side, and a polarization rotation matrix 9 made up of switchable LC elements that can rotate the polarization direction of incident linearly polarized light by a predetermined angle of up to 90°. The transmission direction of the polarization filter 10 is selected to be either parallel or perpendicular to the polarization direction of the projector light L. By rotating the polarization axis and selectively controlling the LC elements, one can now select in which areas (LC elements 9a switched to light-blocking) the light should be absorbed in the polarization filter 10, and where (LC elements 9b switched to light-transmitting) the light can pass through the polarization filter 10.The prerequisite for the best possible contrast improvement in this design is, of course, that the projector 6 emits linearly polarized light so that useful light NS can pass through the contrast pixel matrix 8 with as little attenuation as possible.

[0035] If the LC elements are switched in accordance with the display content (transmission where image content is displayed, absorption where no image content is present), a significant contrast improvement is achieved. In effect, half an LC display (without the second polarization filter 20, see Fig. 3) is applied to the projection screen 7, the sole function of which is to absorb the stray light LS from the projector 6 in image areas without a display. The LC matrix has no color filters, but only white pixels. The pixel size of the LC matrix, or contrast pixel size, is ideally (for contrast) exactly the same size as the image pixels displayed on the projection screen 7 by the projector 6.However, since such a contrast pixel size requires extremely precise alignment of the pixel grids of the projector 6 and the LC matrix (because a deviation would result in strong moiré effects), a better option is to select the LC pixels significantly larger (x5-x15) than the pixel grid of the projector 6. In addition to reducing or completely eliminating the projector stray light LS, this embodiment also allows the unpolarized ambient light 12 and the resulting contrast deterioration to be reduced by a factor of approximately 2.

[0036] Alternatively, in Fig. 2, a single linear polarization filter 20 can be applied to the LC matrix on the projector side (not shown), i.e. as in Fig. 3, but without a polarization filter 10 on the projection screen side. In this case, the polarization filter 20 is aligned such that it transmits the polarization direction of the projector light L. In this way, an effect similar to a locally switchable circular polarizer can be achieved: With switchable LC elements that are designed to rotate the polarization direction by 45°, not only the stray light LS from the projector 6, but also the ambient light 12 can be specifically reduced or completely eliminated. Unlike in Fig. 2, this design is also suitable for backlight projection if the LC elements are designed to rotate the polarization direction by 90°.

[0037] The further variant of the polarization filter-based contrast pixel matrix 8 shown in Fig. 3 functions analogously to Fig. 2, but with the difference that here a complete LC display is used, so to speak, with linear polarization filters 10 and 20 on both sides of the LC matrix 9. This results in a significant contrast improvement, regardless of the interfering light source (projector stray light LS or ambient light 12). This embodiment has the advantage over the variant in Fig. 2 that it also works with projectors 6 that emit unpolarized light. For projectors 6 that emit linearly polarized light, the projector-side polarization filter 20 must again be aligned parallel to the polarization direction of the incident projector light L. This variant is also suitable for a front-light projector (not shown).

[0038] The contrast enhancement can be adjusted by selecting the strength of polarization filters 10 and 20. Even relatively weak polarization filters 10 and 20 provide a significant increase: for example, polarization filters 10 and 20 with 10% transmission when crossed would result in a contrast improvement by a factor of 10, which would be sufficient to meet the HUD contrast requirements mentioned above.

[0039] 1 vehicle

[0040] 2 Field of view display device

[0041] 3 Windscreen

[0042] 5 Projection unit

[0043] 6 projector

[0044] 7 Projection screen

[0045] 8 polarization filter-based contrast pixel matrix

[0046] 9 Polarization rotation matrix, especially LC matrix

[0047] 9a light-blocking matrix elements

[0048] 9b Matrix elements switched to light transmission

[0049] 10 first, i.e. projection screen-side linear polarization filter

[0050] 11 Ambient light source

[0051] 12 Ambient light

[0052] 20 second linear polarization filter facing away from the projection screen

[0053] L Light beam, also called projector light

[0054] LN useful light from the projector

[0055] LS stray light from the projector

[0056] E Eyebox

[0057] V virtual image

Claims

Claims 1. Projection unit (5) for a field of view display device (2), which is designed to display a virtual image (V) via reflection on a reflection plate arranged in the field of view of a user, in particular a vehicle window (3), comprising: a projector-based image generator with a projector (6) for generating a light beam (L) with the desired display content and a projection screen (7) illuminated by the projector, wherein the projector (6) is designed to generate a real image on the projection screen (7) and the projection screen (7) is designed to project the resulting light beam (L) in a predetermined shape and direction onto the reflection plate;and a polarization filter-based contrast pixel matrix (8) arranged in the beam path of the entire light beam (L) emanating from the projection screen (7), the individual contrast pixels of which can be switched synchronously with the real image generated on the projection screen (7) between a light-blocking state for image areas to be displayed in black and a light-transmitting state for the remaining image areas.

2. Projection unit (5) according to claim 1, wherein the contrast pixel matrix (8) is arranged directly on the projection screen (7) in the beam path of the light beam (L) emanating from the projection screen (7); and each of its contrast pixels extends with each of its linear dimensions over several, preferably about two to three, Image pixels of the real image that can be generated on the projection screen (7).

3. Projection unit (5) according to claim 1 or 2, wherein the projection screen (7) is designed to reflect the light beam (L) in the direction of the reflection disc; and the contrast pixel matrix (8) is arranged in the beam path of the entire light beam (L) reflected by the projection screen (7), in particular directly on the projection screen (7).

4. Projection unit (5) according to claim 1 or 2, wherein the projector (6) is arranged and configured to illuminate the back of the projection screen (7), and the projection screen (7) is arranged and configured to transmit the light beam (L) in the direction of the reflection plate; and the contrast pixel matrix (8) is arranged in the beam path of the entire light beam (L) transmitted by the projection screen (7), in particular directly on the projection screen (7).

5. Projection unit (5) according to one of the preceding claims, wherein the polarization filter-based contrast pixel matrix (8) comprises the following layers: a first linear polarization filter (10) on a matrix surface facing the projection screen (7) and / or a second linear polarization filter (20) on a matrix surface facing away from the projection screen (7); and a two-dimensional polarization rotation matrix (9), the matrix elements (9a, 9b) of which, in cooperation with the first and / or the second linear polarization filter (10, 20), Form contrast pixels and can be switched between a state in which the polarization is rotated by a predetermined angle and a state in which the polarization is not rotated.

6. Projection unit (5) according to claim 5 in conjunction with claim 3, wherein the projector (6) is designed to generate the light beam (L) with a predetermined linear polarization; the projection screen (7) is designed for polarization-maintaining reflection of the light beam (L); and the contrast pixel matrix (8) has only the first linear polarization filter (10), the transmission direction of which coincides with the polarization direction of the light beam (L) or is rotated by the predetermined angle of the polarization rotation matrix, preferably approximately 90°; or the contrast pixel matrix (8) has only the second linear polarization filter (20), the transmission direction of which coincides with the polarization direction of the light beam (L), and the predetermined angle of the polarization rotation matrix (9) is approximately 45°.

7. Projection unit (5) according to claim 5 or 6, wherein the polarization rotation matrix (9) is designed as an LC matrix.

8. A method for operating a projection unit (5) according to one of the preceding claims, wherein the projector (6) is controlled to generate a light beam (L) with the desired display content and a corresponding real image on the projection screen (7); and the individual contrast pixels of the contrast pixel matrix (8) are switched synchronously with the real image generated on the projection screen (7) into a light-blocking state in image areas to be displayed in black and a light-transmitting state in the remaining image areas.

9. A field of vision display device (2), in particular for use in a vehicle (1), comprising: a projection unit (5) according to one of claims 1-7; a reflection plate arranged in the beam path of the light beam (L) emitted by the projection unit (5), which reflects towards the user and is preferably at least partially transparent to the ambient light incident from behind, in particular a vehicle window (3) or a specially provided combiner plate; a control unit designed and configured to automatically carry out the method according to claim 8; wherein the reflection plate is arranged and configured in the user's field of vision in such a way that it reflects the light beam (L) to an eyebox (E) predetermined for the user's eyes, whereby the display content can be presented to the user in the form of a virtual image (V) beyond the reflection plate.

10. Vehicle (1), in particular a motor vehicle, comprising: a vehicle window, in particular a windscreen (3), and a passenger compartment partially delimited by the latter; and a field of vision display device (2) according to claim 9, the reflection disc of which is designed as part of the vehicle window or as a a combiner disc arranged in the passenger compartment.

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