Abstract:
A display apparatus displays a three-dimensional graphical object. The display apparatus includes a projection device for producing an autostereoscopic projection image of the object. The object is displayed for a viewer such that the viewer has an improved three-dimensional impression from the representation. The display apparatus to this end has a specularly reflective and light-transparent combiner plate, and the projection device is configured to project the projection image onto the combiner plate such that for a viewer, viewing from a predetermined viewing direction through the combiner plate, the projection image appears as a mirror image on the combiner plate.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is based on and hereby claims priority to German Application No. 10 2014 006 724.6 filed on May 8, 2014, the contents of which are hereby incorporated by reference. 
     BACKGROUND 
     The invention relates to a display apparatus for displaying a three-dimensional graphical object. This representation is based on an autostereoscopic projection image of the object. Part of the invention are also a motor vehicle in which the display apparatus is provided, and a method for displaying the three-dimensional graphical object. 
     A projection device configured as a screen for producing an autostereoscopic representation of a three-dimensional graphical object, producing a representation with a depth effect, is disclosed, for example, in DE 44 33 058 A1. Generally, an autostereoscopic representation of a three-dimensional graphical object is brought about by producing a different image of the object in each case for the right eye and the left eye of a viewer and by guiding each image only to that eye for which it is intended using a deflection device or blocking device. The two images here represent the object in each case from a slightly different viewing angle such that consequently the stereoscopic representation that is important for three-dimensional vision is produced. The above-mentioned document describes for this purpose how the deflection device can be mechanically moved in front of the screen in order to compensate for a head movement of the viewer. 
     Capturing a head movement is also described in DE 42 07 284 A1 with respect to controlling a 3D display using liquid-crystal shutter glasses for producing a stereoscopic representation. 
     EP 0 946 895 B1 describes a plurality of deflection or screening apparatuses mentioned for the autostereoscopic representation. 
     A parallax barrier of strip-shaped, opaque lamellae and a lens array and a prism array, which are both designed for location-selective deflection of the light emitted by the screen to the two eyes, are shown. 
     A lens array and an associated configuration of an LCD screen for adaptation to the lens array are disclosed in WO 2009/018381 A2. 
     SUMMARY 
     One possible object relates to displaying a three-dimensional graphical object for a viewer such that said viewer obtains a spatial impression from the representation, that is to say a 3D representation of the object. 
     The inventor proposes a display apparatus for displaying the three-dimensional graphical object has, in the manner described, a projection device for producing an autostereoscopic projection image of the object. In the projection device, a lens array or a prism array or a parallax barrier can be provided, in the known manner, for producing the autostereoscopic effect. 
     In contrast to the related art, no provision is made for the viewer to view the projection device directly, that is to say for example the screen thereof on which the 3D representation of the object is produced. Instead, the display apparatus includes a specularly reflective and light-transparent combiner plate. Such combiner plates are known for example from head-up displays. In such a display, provision is made for the viewer to view the free space behind the combiner plate through said combiner plate, which is possible owing to the light transparency of the combiner plate. The plate is oriented at an angle with respect to the viewing direction of the viewer. Specularly reflected in the plate is therefore the image of a projection device which is arranged laterally with respect to the viewing direction and which displays, for example, scales or measurement values such that they are viewable by the viewer as a mirror image on the combiner plate and appear, for the viewer, to float in the free space behind the plate. 
     In the proposed display apparatus proposed by the inventor, the projection device is designed to project the autostereoscopic projection image onto the combiner plate such that the projection image of the object appears as a mirror image on the combiner plate for a viewer looking from a predetermined viewing direction through the combiner plate. In other words, the three-dimensional graphical object appears therefore to float in the free space behind the combiner plate. Since the projection image is an autostereoscopic projection image, the 3D effect of the autostereoscopic projection image is combined with the impression of the floating image as is produced by the combiner plate. Trials have shown that on account of this subjects experience a significant improvement of the 3D impression of the representation. The reason therefor appears to be an illusion which is based on the viewer also seeing, through the combiner plate, the background located therebehind together with the representation which is floating in the space, and thereby an improved spatial perception results on account of the cognitive processing of said image impression. 
     With particular preference, at least one display device is provided in a motor vehicle. Such a motor vehicle is likewise the subject matter of the proposals. The motor vehicle having the at least one display apparatus according to one embodiment of the display apparatus is preferably configured as an automobile, in particular as a passenger car. 
     The combiner plate of the proposed display apparatus can be arranged, by way of example, in front of a hollow space, that is to say a closed space which is delimited towards one side by the combiner plate. For this purpose, a corresponding embodiment of the motor vehicle makes provision for in each case one combiner plate of the at least one display apparatus to be arranged in an instrument cluster and/or an infotainment system of the motor vehicle. This leads to the advantage that the viewer has the impression that the three-dimensional graphical object appears to float within the closed hollow space in the instrument cluster or in the infotainment system. 
     However, the combiner plate can also be arranged in the field of vision of the viewer when viewing the surrounding traffic. To this end, one embodiment of the motor vehicle makes provision for a head-up display to be provided by using a combiner plate of the at least one display apparatus. This can be used to overlay three-dimensional representations of objects in the field of vision of the viewer while the viewer views the surrounding environment of the motor vehicle. 
     The inventor also proposes a method for displaying the three-dimensional graphical object, which comes about through the operation of the display apparatus. The autostereoscopic projection image of the object is produced by the projection device, and said projection image is emitted largely or entirely toward the specularly reflective and light-transparent combiner plate. In other words, therefore, the projection device projects the projection image onto the combiner plate. The combiner plate at least partially specularly reflects the projection image, depending on the reflectance thereof or the transparency thereof, toward the viewer such that, for the viewer, the projection image appears as a mirror image on the combiner plate. 
     Further developments in conjunction with the proposed display apparatus are described below. The features of the further developments, however, also further develop both the proposed motor vehicle and the proposed method. 
     According to one embodiment, the projection device has a screen on which the autostereoscopic projection image is produced. According to this embodiment, a screen plane of the screen and a plate plane of the combiner plate enclose an angle of 35 degrees to 65 degrees, in particular 40 degrees to 50 degrees. This leads to the advantage that the screen image is perceived by the viewer on the combiner plate as a mirror image with only negligible distortions. 
     The combiner plate is preferably made of glass and/or foil. Glass has the advantage that, owing to its inherent stiffness, it will not oscillate even in the case of vibrations, as can occur for example in a motor vehicle, and therefore distortions of the projection image due to oscillations of the combiner plate are avoided. A foil has the advantage that it is particularly lightweight. In addition, the choice of the foil material can be used to adjust the light transparency or the mirror characteristic with little outlay. 
     A further improvement of the 3D effect comes about according to a particularly preferred embodiment, in which the position of the viewer is captured and said position influences the representation such that this even brings about a holographic effect, that is to say that for the viewer a spatially fixed three-dimensional object appears behind the combiner plate. To this end, a capturing device is provided which is adapted to produce positional data that indicate a position of the viewer, that is to say for example a position of the viewer&#39;s head or the viewer&#39;s eyes. A control device is adapted to control the projection device in dependence on the positional data such that the representation of the object maintains a virtual spatial position as the position of the viewer changes. In other words, therefore, the viewer can, for example, move his/her head to and fro, and, in the process, a representation of the object is moved in dependence on the current position of the head and/or the eyes such that, from the viewer&#39;s view, the object appears to remain without movement at a predetermined position behind the combiner plate. Thereby, two effects can be achieved using the control device. First, provision may be made for only an artificial parallax to be produced, as would result if the object were to be located at a specific location behind the combiner plate in front of a background. Additionally, provision may be made for the viewing angle at which the object is represented to also be configured to be dependent on the positional data, that is to say the user can move his head around the object. By way of example, it is therefore possible for a movement of the head to the right to be converted by the control device to the effect that the object is represented to have been slightly rotated, for instance as if the viewer in fact is moving his head around a plastic figure. The functional relationship between positional data and corresponding changes of the representation to achieve said holographic effect can be ascertained by simple trials or by geometric calculations. 
     For capturing the position of the viewer, according to one further development of this embodiment, at least one camera is provided which films the head of the viewer. From the image data it is possible to ascertain both the head position and advantageously the face normal, that is to say a normal vector perpendicular to the face plane, and in a particularly advantageous manner also the alignment of the eyes. 
     Even more advantageously, a relationship between the position of the viewer and the representation can be produced if the capturing device has an eye tracker. This can be used to ascertain both the position of each eye and its viewing axis and to match the representation of the object correspondingly precisely to the current position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other objects and advantages of the present invention will become more apparent and more readily appreciated from the following description of the preferred embodiments, taken in conjunction with the accompanying drawing of which: 
       The sole FIGURE (FIG.) shows a schematic sectional illustration of a potential embodiment of the proposed display apparatus. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawing, wherein like reference numerals refer to like elements throughout. 
     The exemplary embodiment explained below is a preferred exemplary embodiment. In the exemplary embodiment, however, the described components of the embodiment represent in each case individual features which are to be regarded independently from one another and which further develop the proposals in each case also independently of one another and should therefore also be considered individually or as a component part in a different combination than that shown. The described embodiment furthermore can also be supplemented by further features of the already described features. 
     The figure shows a display apparatus  10 , which can be fitted for example in a motor vehicle  12 , for example a passenger car. By way of example, the display apparatus  10  can be a component part of an instrument cluster or infotainment system of the motor vehicle  12 . The display apparatus  10  can also be a component part of a head-up display. 
     The display apparatus  10  comprises, in the example shown, a projection apparatus  14 , a refraction surface or combiner plate or in short plate  16 , a capturing device  18 , a control device  20  and a background surface  22 . The background surface  22  and the plate  16  can delimit a space  24 . In the case that the display apparatus  10  is configured as a head-up display, the display apparatus  10  does not have a background surface, but a surrounding environment of the motor vehicle  12  forms a background. 
     The figure illustrates only one eye  28  of a viewer  26  of the display apparatus  10 . The viewer  26  uses the display apparatus  10 . 
     The projection device  14  can be a lenticular 3D display or generally be a screen for autostereoscopic representation of an object  30 . In the example shown, a three-dimensional representation of a motor vehicle is intended to be displayed to the viewer  26  using the display apparatus  10  for example as the graphical object  30 . 
     On a screen surface  32  of the projection apparatus  14 , an autostereoscopic representation  34  of the object  30  is produced for a left eye from a left-hand image  36  and for a right eye of the viewer  26  from a right-hand image  38 . For the sake of clarity, the representation  34  is illustrated above the projection device  14 . The two representations  36 ,  38  are here drawn to be further apart than is actually the case in stereoscopic representation. 
     In the figure, the surface normal  40  of the screen plane  32  faces in the direction of the plate  16 . A plate plane of the plate  16  extends perpendicular to the image plane of the figure. The plate plane of the plate  16  encloses with the screen plane  32  an angle  42 , which is between 35 degrees and 65 degrees, in particular between 40 degrees and 50 degrees. The angle is preferably 42 to 45 degrees. 
     The plate  16  is see-through such that the viewer  26  can recognize the background surface  22  through the plate  16 . The representation  34  is projected from the screen plane  32  as a projection image in a projection direction  44  toward the plate  16 , and is reflected there in the direction toward the eye  28  along a display direction  46 . The reflection at the plate  16  can be brought about as a foil and/or glass pane reflection. In the opposite direction to the display direction  46 , a designated viewing direction  48  is produced, from which the viewer  26  views the plate  16  with his eye  28 . 
     To the viewer  26 , the specular reflection of the projection image  34  appears as an illusion, as if the three-dimensional object  30  appears to float in the space  24  in front of the background surface  22 . The combination of the autostereoscopic representation through the projection device  14  and the reflection at the plate  16  in front of the background surface  22  here improves the 3D effect or 3D impression as compared to a direct viewing of the screen plane  32 . 
     If the viewer  26  moves his head, the projection image  34  can be changed such that, for the viewer  26 , the object  30  appears to maintain its position within the space  24 . In other words, the movement of the head is compensated. To this end, the capturing device  18 , for example a 2D camera or 3D camera, can be used to capture the position of the viewer  26 , in particular the viewer&#39;s head position, preferably the viewer&#39;s viewing direction with the eye  28  and/or the other eye. The control device  20  couples the capturing device  18  to the projection device  14 . The control device  20  can be, by way of example, a controller or a program module in a processor device or a controller. The control device  20  controls the projection device  14  in the described manner to compensate for the head movement. By capturing the exact position of the viewer and thus influencing the representation of the object  30 , that is to say of the projection image  34 , a regular holographic effect comes about in the representation of the object  30  in the space  24 . From the view of the viewer  26 , a 3D image of the object appears to float in a spatially fixed position in the space  24 . 
     Overall, the example shows how a 3D image can be produced which appears to float, from the viewer&#39;s view, freely in the space and how a hologram as a virtual plastic body maintains its position in the space even if a head moves. In particular, a lenticular 3D display is used herefor, which produces a 3D image without glasses. By combining this 3D effect of the display with the floating image, as is produced by way of reflection at the plate  16 , the 3D impression is significantly improved. 
     The invention has been described in detail with particular reference to preferred embodiments thereof and examples, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention covered by the claims which may include the phrase “at least one of A, B and C” as an alternative expression that means one or more of A, B and C may be used, contrary to the holding in Superguide v. DIRECTV, 69 USPQ2d 1865 (Fed. Cir. 2004).