Time multiplexing for correcting chromatic aberration in transparent screen unit

Abstract

Various examples relate to techniques for synchronously controlling a multi-color light source and a multi-pixel display device for a picture generation unit of a transparent screen unit (e.g., a head-up display system). This allows for the reduction of chromatic aberration, for example, that occurs due to the use of holographic optical elements.

Description

[0001] priority This application claims priority to German patent application DE 10 2023 121 900.6, dated August 16, 2023, the disclosure of which is incorporated herein by cross-reference. Technical Field

[0002] Various examples of the present invention relate to techniques for synchronously controlling multicolor light sources and multipixel display devices for image generation units of transparent screen units. Background Technology

[0003] Transparent screen units are used in various applications. For example, they are used in HUD (Head-Up Display) systems in motor vehicles. HUD systems generate virtual images, allowing drivers to perceive displayed information without taking their eyes off the road. The virtual image is generated in a virtual image plane, unlike a real image displayed on a physical surface (e.g., a transparent surface). In HUD systems, this virtual image plane is located outside the vehicle. The area within which the driver can perceive the virtual image is called the eye-tracking range.

[0004] The transparent screen unit includes a picture generation unit (PGU). The PGU includes a multi-pixel display device, such as a liquid crystal display or a micromirror array. The multi-pixel display device is illuminated by a light source.

[0005] Narrowband or monochromatic light sources are typically used. This is especially true when one or more holographic optical elements (HOEs) are used in the optical imaging system of a HUD system. This is due to the wavelength-selective diffraction characteristics of HOEs. The diffraction efficiency of a HOE is a function of wavelength. HOEs are specifically manufactured for specific wavelengths.

[0006] It is a known practice to use multiple monochromatic light sources to operate multiple color channels of an optical imaging system. For example, red, green, and blue light sources can be used to illuminate corresponding color channels of a liquid crystal screen in this way. In particular, mixed-color images can be generated in this manner.

[0007] Undesirable offsets were observed between the images associated with various color channels. This is likely due to chromatic aberration in the optical imaging system of the transparent screen unit. It is known that this undesirable offset between images can be reduced or compensated for by applying pre-distortion to each color image. The pre-distortion canceled out the observed offset.

[0008] However, it has been observed that existing systems cannot fully compensate for the offsets between individual color images through pre-warping. Summary of the Invention

[0009] An improved image generation unit with multiple color channels is needed for use in transparent screen units. In particular, an image generation unit is needed to eliminate the aforementioned limitations, i.e., to better reduce or fully compensate for the offset between individual color images.

[0010] This problem is addressed by the features of the independent claims. The features of the dependent claims define the embodiments.

[0011] A method for controlling an image generation unit for a transparent screen unit is disclosed.

[0012] For example, a transparent screen unit can be, for instance, a HUD system used to reflect information into the driver's field of vision. Alternatively, a transparent screen unit can also be a holographic display that reproduces information on a transparent surface.

[0013] In this configuration, the image generation unit (PGU) comprises a multi-pixel display device and a multi-color light source. The multi-color light source is configured to emit coherent light in multiple source color channels. The multi-pixel display device is illuminated in this manner. Examples of source color channels include red-green-blue and other complementary color systems.

[0014] For example, lasers or laser diodes can be used. The use of narrowband light-emitting diodes (LEDs) is also possible.

[0015] The method includes controlling a multicolor light source to emit coherent light in time slots of a time-division multiplexing scheme. Here, in each case, each time slot is assigned to a single corresponding source color channel among multiple source color channels. For example, time slot 1 <> red; time slot 2 <> green; time slot 3 <> blue; time slot 4 <> red; and so on.

[0016] The method further includes controlling the multi-pixel display device to reproduce, in each of the time slots, the corresponding display image associated with the respective source color channel in each of the time slots under each condition. Thus, each display image is assigned to exactly one source color channel. For example, time slot 1 <> red display image; time slot 2 <> green display image; time slot 3 <> blue display image; time slot 4 <> red display image; and so on.

[0017] In this configuration, the displayed image is pre-distorted, which reduces the chromatic aberration of the optical imaging system of the transparent screen unit relative to the corresponding source color channel associated with the displayed image. For example, the optical imaging system may include one or more holographic optical elements and / or mirror and / or lens elements.

[0018] Therefore, the application of time-division multiplexing allows color differences to be corrected separately in the time domain by digitally preprocessing the corresponding displayed images. This is because color differences are typically wavelength-dependent, meaning that, for example, the direction or magnitude of the offset depends on the corresponding light from the source color channels. Regarding a reference implementation in which multiple source color channels are used simultaneously to illuminate a multi-pixel display device (in this case, the multi-pixel display device also includes multiple display color channels), higher precision color difference correction can be achieved by individually applying pre-twisting.

[0019] Various technologies are based on the understanding that in typical multi-pixel display devices, display color channels may mix. This means that pixels primarily processing light from the first source color channel are also sensitive to light from the second source color channel. Therefore, in reference implementations that pre-distort multiple source color channels and multiple display color channels in parallel instead of using time-division multiplexing, channel-specific pre-distortion mixes, which degrades the quality of color difference correction. Mixing is avoided by activating each source color channel individually. Color difference compensation can then be performed more effectively.

[0020] Specifically, translational offsets between images perceived by the user (e.g., virtual images in a HUD system) can be compensated for by shifting the displayed image in opposite directions within a multi-pixel display device. This translational offset typically arises from the use of so-called HOE stacks in the optical imaging system of a transparent screen unit. Multiple HOEs are used in this context. Light from each source color channel is assigned an appropriate HOE element. Due to the diffraction properties of holographic optics, they are highly wavelength-sensitive, and therefore it is necessary to provide a separate holographic optic element for each color channel (i.e., the source color channel). The HOEs of the (source) color channels are arranged in a stacked structure. Each HOE has a certain thickness. This produces corresponding offsets in the beam paths of light from different channels. Different multi-pixel display devices can be used. In particular, a monochrome multi-pixel display device comprising a single display color channel can be used. This single display color channel can be broadband, i.e., configured to influence (i.e., switch or appropriately deflect or modulate) the light from all source color channels in the relevant spectrum. An example will be given using a switchable (digital) micromirror array (DMD) without color filters. However, the separation of color channels in the time domain specifically allows for the output of a color image by selecting a sufficiently fast repetition rate for the time slots. For example, a time-division multiplexing scheme can have a repetition rate of not less than [missing information]. The time slot switching frequency, of which This represents the number of color channels. Typically, (For the red-green-blue channels). Therefore, color mixing is achieved in the observer's eye due to the rapid and continuous display of different color images (e.g., virtual images in a HUD system).

[0021] However, in other examples, multi-pixel display devices with multiple display color channels corresponding to the source color channels can also be used. For example, a liquid crystal screen with red-green-blue display channels can be used. For this purpose, appropriate color filters can be provided. Although the display color channels may overlap, good color difference can be achieved by sequentially activating the corresponding source color channels according to a time-division multiplexing scheme.

[0022] In various examples, phase-coherent light is used to illuminate multi-pixel display devices. Therefore, speckle noise may exist. A system (illumination system) for illuminating the pixel plane of a multi-pixel display device is disclosed, which allows for the suppression or at least reduction of speckle noise.

[0023] The system includes a laser source. For example, the laser source may include a single emitter, such as a laser diode. A multicolor laser source can also be used; for example, such a multicolor laser source may include three emitters providing red, green, and blue wavelengths of light. Aspects related to multicolor sources have already been described above. Typically, the laser source is configured to provide phase-coherent light. This can then lead to speckle noise.

[0024] The illumination system also includes a speckle noise suppression unit. As a general rule, different types of speckle noise suppression units can be used. One implementation involves using a moving diffuser, whereby the speckle pattern is "averaged out." However, other types of speckle noise suppression units exist, such as liquid crystal light modulator elements. The phase profile of the laser can be altered, particularly randomized, by the speckle noise suppression unit.

[0025] For example, the speckle noise suppression unit can take the form of a diffuser that moves within the kHz range.

[0026] The illumination system also includes an optical waveguide that guides the coherent light emitted by the light source toward the speckle noise suppression unit. Specifically, optical fiber can be used as the optical waveguide. For example, multimode fiber can be used. An output coupling lens element can be positioned at the end of the optical waveguide facing the speckle noise suppression unit.

[0027] The illumination system also includes an optical homogenizing plate. The optical homogenizing plate includes a top side, a bottom side, and (at least) one side side. Therefore, the side side is arranged on the edge between the top and bottom sides. The thickness of the optical homogenizing plate can be defined as the distance between the top and bottom sides. In a system integrated into the PGU of a HUD system, the top side can face the multi-pixel display device (the corresponding aspect related to the control of the multi-pixel display device is described above). The homogenizing plate can be made of plexiglass or glass. The homogenizing plate comprises a planar, optically transparent substrate.

[0028] The illumination system includes an input coupling structure. The input coupling structure is formed on the side of a homogenization plate, adjacent to a speckle noise suppression unit. The input coupling structure is configured to couple light input from the speckle noise suppression unit into the homogenization plate. As a separate component, the input coupling structure can be adhesively bonded to or otherwise applied to the side of the homogenization plate. However, the input coupling structure can also be formed as a surface topography variation on the side of the homogenization plate.

[0029] The illumination system further includes an output coupling structure. The output coupling structure is formed on the top side of the homogenization plate. The output coupling structure is configured to output coupled light from the homogenization plate in a manner distributed across the entire area of ​​the output coupling structure for illuminating a multi-pixel display device. This means that a specific light field, i.e., a specific intensity distribution depending on a location along the surface of the homogenization plate, can be obtained through the output coupling structure. Therefore, suitable illumination of the pixel plane of the multi-pixel display device can be achieved.

[0030] Because of the use of a homogenizing plate with an output coupling structure, a particularly compact illumination unit can be implemented, for example, especially compared to a free beam path.

[0031] The output coupling structure can be specifically implemented as a diffuser. Light is scattered by the diffuser, and thus specific emission characteristics are obtained.

[0032] As a general rule, diffusers can be implemented in various ways, such as as microstructure diffusers, holographic diffusers, volumetric diffusers, and diffusers based on surface undulations. Diffusers can be made of different materials, including plastics, glass, and optionally have coatings.

[0033] As described above, using multiple diffusers (spot noise suppression units and output coupling structures) makes it possible to obtain the desired illumination of the pixel plane.

[0034] Therefore, an additional illumination system for illuminating the pixel plane of a multi-pixel display device includes a laser source. The laser source is configured to emit light along a beam path. The illumination system also includes a speckle noise suppression unit, which is implemented as, for example, a moving diffuser. The speckle noise suppression unit is arranged in the beam path. The illumination system further includes a diffuser. The diffuser is arranged downstream of the speckle noise suppression unit in the beam path starting from the laser source and is configured to emit light with emission characteristics in the direction of the multi-pixel display device.

[0035] Therefore, a diffuser first positioned on the beam path suppresses speckle noise. Thus, a diffuser positioned on the beam path adjacent to the pixel plane of the multi-pixel display device achieves the desired emission characteristics: first illuminating the pixel plane, and then illuminating the entrance pupil of the optical imaging system positioned downstream of the multi-pixel display device on the beam path.

[0036] Optionally, another diffuser may be present, and if present, this additional diffuser is arranged between the speckle noise suppression unit and the diffuser (close to the display device), and is configured to emit light with additional emission characteristics in the direction of the diffuser arranged adjacent to the display device. This additional emission characteristic can be configured to achieve full-area illumination of the aperture of the diffuser arranged adjacent to the display device.

[0037] The illumination system described above can be part of the PGU of a HUD system. A HUD system can include one or more HOEs along the light beam path. The multi-pixel display device can be, for example, a liquid crystal display or a micromirror array.

[0038] The one or more HOEs may perform different functions. For example, it is conceivable that the one or more HOEs are part of or implement a wavefront manipulator, as described in WO 2022 / 189275 A1 (where the wavefront manipulator is referred to as a holographic element), the corresponding disclosure of which is incorporated herein by cross-reference.

[0039] A controller for controlling an image generation unit for a transparent screen unit is disclosed. The image generation unit includes a multi-pixel display device and a multi-color light source. The multi-color light source is configured to emit coherent light in multiple source color channels to illuminate the multi-pixel display device. The controller is configured to control the multi-color light source to emit coherent light in time slots of a time-division multiplexing scheme. In each case, each time step is allocated a single corresponding source color channel among the multiple source color channels. The controller is also configured to control the multi-pixel display device to reproduce, in each of these time slots, a corresponding display image associated with the corresponding source color channel. The display image has pre-distortion, which reduces the color difference of the optical imaging system of the transparent screen unit for the corresponding source color channel associated with the corresponding display image.

[0040] It also describes program code that can be executed by a processor, thereby enabling the processor to perform the methods described above.

[0041] Variations of the aforementioned technique are possible. For example, it is conceivable to activate more than a single source color channel in at least some time slots and display more than a single display image during these time slots. In this variation, in each case, the displayed image can reduce or compensate for the color difference of each of the activated source color channels. In particular, such source color channels can be activated and associated display images that are "orthogonal" to each other (i.e., for which there is no channel mixing). If the first source color has an associated display color channel whose spectrum does not overlap with the spectrum of the second display color channel assigned to the second source color channel, then there is no channel mixing between the first and second source color channels.

[0042] Without departing from the scope of protection of this invention, the features set forth above and described below may be used not only in the expressly stated applicable combinations, but also in other combinations or individually. Attached Figure Description

[0043] Figure 1 The diagram illustrates HUD systems with image generation units based on various examples.

[0044] Figure 2 This demonstrates a stacked arrangement of multiple HOEs, which are assigned to different source color channels and are Figure 1 It is part of the optical imaging system of the HUD system.

[0045] Figure 3 The diagram illustrates the lateral shift of a virtual image corresponding to multiple color channels due to color differences caused by stacked HOEs.

[0046] Figure 4 The spectrum of multiple source color channels and the spectrum of multiple display color channels are illustrated schematically.

[0047] Figure 5A The time slot sequence is schematically illustrated for a time-division multiplexing scheme for controlling a multi-color light source in a multi-pixel display device, based on various examples.

[0048] Figure 5B The time slot sequence is schematically illustrated for a time-division multiplexing scheme for controlling a multi-color light source in a multi-pixel display device, based on various examples.

[0049] Figure 6 This is a flowchart of an exemplary method.

[0050] Figure 7 This is a schematic diagram of an exemplary illumination system for illuminating a multi-pixel display device.

[0051] Figure 8yes Figure 7 Another side view of the exemplary system.

[0052] Figure 9 yes Figure 7 A three-dimensional diagram of an exemplary system.

[0053] Figure 10 The speckle noise suppression unit is illustrated schematically.

[0054] Figure 11 This is a schematic diagram of an exemplary illumination system for illuminating a multi-pixel display device.

[0055] Figure 12 yes Figure 11 A three-dimensional diagram of an exemplary system. Detailed Implementation

[0056] In the context of the following description of exemplary embodiments, the features, characteristics, and advantages of the invention described above, as well as the ways of achieving these features, characteristics, and advantages, will become clearer and more apparent, with reference to the accompanying drawings.

[0057] The present invention will now be explained in detail with reference to the accompanying drawings, based on preferred embodiments. In the drawings, identical reference numerals denote identical or similar elements. The drawings are schematic representations of various embodiments of the invention. Elements shown in the drawings are not necessarily shown to scale. Rather, the various elements shown in the drawings are presented in a manner that makes their function and general purpose readily understandable to those skilled in the art. Connections and linkages between functional units and elements shown in the drawings may also be implemented as indirect connections or linkages. Connections or linkages may be implemented in a wired or wireless manner. Functional units may be implemented as hardware, software, or a combination of hardware and software.

[0058] Figure 1 A HUD system 100 according to various examples is schematically illustrated. System 100 includes an image generation unit 115. The image generation unit 115 includes a multicolor light source 111 configured to emit red, blue, and green light. In particular, it emits coherent narrowband light. Therefore, the multicolor light source 111 is configured to emit narrowband coherent light in three source color channels 301, 302, and 303 (hereinafter referred to as color channels).

[0059] The corresponding beam paths of the three corresponding color channels 301, 302, and 303 (red-green-blue) of the HUD system 100 are shown using solid arrows, dotted arrows, and dashed arrows.

[0060] In addition, the image generation unit 115 also includes a multi-pixel display device 112. Typically, a monochrome multi-pixel display device 112 or a multi-pixel display device with multiple display color channels can be used. A liquid crystal screen with red, green, and blue display color channels would be an exemplary embodiment. An alternative would be, for example, implementing the multi-pixel display device 112 using a DMD.

[0061] The following describes in particular the technique in which the multi-pixel display device 112 has multiple display color channels. Therefore, in these examples, a monochrome multi-pixel display device 112 is not used. For example, the multi-pixel display device 112 may have three color channels, such as red-green-blue. Such a multi-pixel display device 112 is relatively common, for example, in the form of a conventional liquid crystal thin-film display (“TFT display”). Therefore, such a multi-pixel display device 112 is relatively cost-effective. In particular, multi-pixel display devices with multiple color channels are more widely available than monochrome multi-pixel display devices.

[0062] Multi-pixel display device 112 may include an array, wherein each array cell lattice contains a number of pixels corresponding to the number of display color channels. Each of these pixels is assigned to a corresponding display color channel. For example, a typical multi-pixel display device 112 may include an array, wherein each array cell lattice includes three pixels for the red-green-blue color channels. Each pixel may have a switchable liquid crystal lattice and a corresponding color filter arranged upstream or downstream therefrom. The color filters of various pixels have different filter curves. These filter curves define the spectrum of the corresponding display color channel. The filter curves of available multi-pixel display devices are typically not particularly narrow-band. In particular, the filter curves are generally wider than the curves required to efficiently reconstruct a hologram by illumination of the HOE. Therefore, in various examples, display color channels whose spectra only have a fraction of the width of the associated filter curve are used.

[0063] Optionally, an illumination system 30 configured to improve illumination of the multi-pixel display device 112 may be provided between the multi-color light source 111 and the multi-pixel display device 112.

[0064] The multicolor light source 111 and the display device 112 are controlled by a controller 119. For example, the controller 119 can be implemented as a processor with memory, wherein the processor can load program code from the memory and execute the program code. The controller 119 can be implemented as an application-specific integrated circuit or a field-programmable gate array (FPGA). Combinations of corresponding logic circuits are also conceivable.

[0065] For example, controller 119 can activate or deactivate different color channels of the multicolor light source 111. Controller 119 can display different displays on the multi-pixel display device 112, for example—in the case that the multi-pixel display device 112 is a multi-pixel display device with multiple color channels—displaying different displays on one or more color channels. Controller 119 can cut off individual color channels on the multi-pixel display device 112; in this case, control is applied to the corresponding pixels assigned to the corresponding cut-off display color channels so that no light is transmitted.

[0066] The HUD system 100 also includes an optical imaging system 113. This optical imaging system is configured to generate a virtual image representation of the displayed image of the display device 112, which is perceptible from the eye-tracking range 114. The optical imaging system 113 may include one or more lens elements and / or mirrors. In alternatives to the above-described scheme or further, the optical imaging system 113 may include, for example, one or more HOEs for beam shaping. If narrow-band and coherent light is generated specifically by the multicolor light source 111, the optical imaging system 113 and / or the image generation unit 115 may include a speckle noise suppression unit. For example, a moving diffuser can be used to reduce speckle noise. For example, the speckle noise suppression unit may be part of a system 30 for illuminating the multi-pixel display device 112.

[0067] As described above, the optical imaging system 113 may include one or more HOEs. Details in this regard are combined... Figure 2 Let's have a discussion.

[0068] Figure 2 An optical imaging system 113 is shown to include a stacked structure 150 comprising multiple HOEs 151, 152, and 153. For example, each HOE 151, 152, and 153 can be in the form of a volumetric hologram, wherein a transparent substrate is provided with a refractive index modulator. In this case, the spatial frequency of the respective refractive index modulator matches the wavelength or narrowband spectrum of the respective source color channels 301, 302, and 303, and therefore light from the respective other source color channels passes through the respective holographic optical elements unaffected. The beam paths of the color channels 301, 302, and 303 are separated due to the finite thickness of the stacked structure of the holographic optical elements 151, 152, and 153, as... Figure 2 As shown. Therefore, the virtual images 180 of color channels 301, 302, and 303 are shifted relative to each other, as... Figure 3As shown. In the reference embodiment, this lateral offset is reduced by pre-distorting the corresponding displayed images of the multi-pixel display device 112, which are assigned to the various color channels 301, 302, 303. However, in conventional multi-pixel display devices, the displayed color channels are mixed, and therefore the pre-distortion actually intended for the red source color channel 301 will also act on the green source color channel 302. This is in Figure 4 As shown in the image.

[0069] Figure 4 The corresponding spectra (dotted lines) of the multicolor light source 111 for source color channels 301, 302, and 303 are shown. These emission spectra are narrow-band, i.e., typically with a width of no more than 5 nm. This helps ensure good hologram reconstruction with reduced stray light.

[0070] Figure 4 The spectrum displaying color channels 391, 392, and 393 is also shown. From Figure 4 It is evident that, for example, the spectrum of display color channel 391 has a maximum value approximately at the location of the maximum value of the spectrum of source color channel 301 (display color channel 391 is therefore assigned to source color channel 301 because they overlap the most), but the spectrum of source color channel 302 is arranged on the slope of the spectrum of display color channel 391. Therefore, the spectrum of display color channel 391 overlaps with the spectrum of display color channel 392; similarly, the spectrum of display color channel 391 overlaps with both the spectra of source color channel 301 and source color channel 302. Figure 4 It is also evident that the spectrum of display color channel 391 does not overlap with the spectrum of source color channel 303. Therefore, source color channels 301 and 303, or display color channels 391 and 393, can be considered orthogonal to each other, as they can operate simultaneously without significant color mixing.

[0071] Because the display color channel 391 overlaps with the source color channels 301 and 302 in terms of spectrum, the pre-distortion applied to the display image of the source color channel 301 also affects the source color channel 302 to some extent. Therefore, it is impossible to completely apply the pre-distortion to the virtual image 180 (see...) Figure 3 The lateral offset between source color channels 301, 302, and 303 observed in the image is compensated for. This problem can be eliminated or at least mitigated using a time-division multiplexing scheme. This is in... Figure 5A It is displayed in the middle.

[0072] Figure 5AThe time-division multiplexing scheme 500 is shown with time slots 501-506. In this case, time slots 501 and 504 are assigned to source color channel 301; time slots 502 and 505 are assigned to source color channel 302; and time slots 503 and 506 are assigned to source color channel 303.

[0073] During time slots 501 and 504, the multicolor light source 111 is controlled to emit light only according to the source color channel 301. This means that only the source color channel 301 is activated; the other source color channels 302 and 303 are deactivated. Simultaneously, during time slots 501 and 504, the multi-pixel display device 112 is controlled to display the corresponding display image 511 associated with the source color channel 301. Then, during time slots 502 and 505, the source color channel 302 is activated; furthermore, the display image 512 with a pre-distortion suitable for the source color channel 302 is activated. During time slots 503 and 506, the source color channel 303 is activated. Furthermore, the multi-pixel display device 112 is controlled to display a display image 513, which has a pre-distortion associated with the source color channel 303. In other words, there is therefore a sequential and color-discrete multiplexing of the individual RGB color channels. For each display image associated with a single source color channel, in the corresponding time slot, a matching associated emitter associated with the same source color channel is also activated. Therefore, in each case, different color channel images are displayed sequentially on a multi-pixel display device.

[0074] When display image 511 is activated in time slot 501, the display image can be reproduced on display color channel 391. This means that the pixels of the multi-pixel display device 112 assigned to display color channel 391 are controlled based on image information from display image 511. Different variations can be envisioned by combining the remaining pixels of the multi-pixel display device 112—those pixels not assigned to display color channel 391 but assigned to display color channel 392 or display color channel 393.

[0075] In the first variant, during time slot 501, the pixels of the multi-pixel display device 112 associated with display color channels 392 and 393 are cut off. This means that such pixels no longer transmit light significantly. More generally, this therefore means that during a time slot allocated to a particular source color channel, only a single corresponding display color channel is activated, and all other display color channels are cut off. The activated display color channel reproduces the display image associated with the source color channel of the corresponding time slot.

[0076] In the second variant, more than a single display color channel is activated. For example, generally, two or more display color channels overlapping with the corresponding active source color channel are activated. In the second variant, in time slot 501, a pixel associated with at least one of display color channels 392, 393 is activated. This pixel is also controlled based on image information from the display image 511 associated with source color channel 301. In other words, this therefore means that in time slot 501, display image 511 is displayed not only on display color channel 391, but also on display color channels 392 and / or display color channel 393. More generally, this means that in the second variant, in a time slot allocated to a particular source color channel, the corresponding display color channel is activated, and at least one of the other display color channels is also activated. The activated display color channels reproduce the corresponding display image associated with the corresponding source color channel. The advantage of this second variant is that more light leaves the multi-pixel display device 112 overall, and therefore greater brightness can be achieved.

[0077] Figure 5B This demonstrates time slots 591-594 of the time-division multiplexing scheme 590. (Compared to...) Figure 5A Compared to variations of time-division multiplexing scheme 500, time-division multiplexing scheme 590 includes time slots 591, 593 allocated to more than a single source color channel. This is because, in Figure 5B In the example, time slots 591 and 593 are assigned to both source color channel 301 and source color channel 303. This takes advantage of the fact that source color channels 301 and 303 are orthogonal to each other.

[0078] In detail: It is possible to simultaneously assign time slots 591 and 593 to the two source color channels 301 and 303, because the spectrum of the display color channel 391 (which is assigned to the source color channel 301) does not overlap with the spectrum of the source color channel 303; in addition, the spectrum of the display color channel 393 (which is assigned to the source color channel 303) does not overlap with the spectrum of the source color channel 301.

[0079] Then again, the spectrum of the source color channel 302 overlaps with the spectra of all display color channels 391, 392, and 393.

[0080] therefore, Figure 5B The variant includes two types of time slots: first, time slots 591 and 593 are assigned two source color channels 301 and 303; and second, time slots 592 and 594 are assigned only a single source color channel 302 so as to achieve a mixture without color correction.

[0081] Therefore, in time slot 591, the multi-pixel display device 112 is controlled to reproduce the display image 511 on the display color channel 391 in time slot 591, and to reproduce the display image 513 on the display color channel 393 in the same time slot 591. Simultaneously, both source color channels 301 and 303 are activated. Source color channel 302 is deactivated, and display color channel 392 is cut off. Then, in subsequent time slots 592, the display color channel 392 of source color channel 302 is addressed. In subsequent time slots 592, source color channels 301 and 303 are deactivated, and display color channels 391 and 393 are cut off. Time slot 592 is allocated to source color channel 302, and the multi-pixel display device 112 is controlled to reproduce the display image 512 on the display color channel 392 in time slot 302. In this case, time slot 593 corresponds to time slot 591, and time slot 594 corresponds to time slot 592. According to... Figure 5B The advantage of this technology lies in the following fact: with Figure 5A Compared to other variants, the time interval between repeated addressing of the same source color channel or display color channel is reduced. This allows the use of multi-pixel display devices that offer lower frame rates without sacrificing the quality of color mixing perceived by the viewer.

[0082] Figure 6 This is a flowchart of an exemplary method. Figure 6 The method is implemented by computer. Figure 6 The method can be applied by the controller of the image generation unit used for the transparent screen unit. For example, Figure 6 The method can be derived from Figure 1 The controller 119 of the HUD system 100 is used.

[0083] In box 905, a check is performed to determine whether the next time slot in the time slot sequence of the time division multiplexing scheme has started or has already begun.

[0084] If this is the case, then in box 910, according to a predefined scheme (e.g., "polling," i.e., switching through all color channels one after another sequentially; see [link]),... Figure 5A To select the source color channel assigned to the corresponding time slot as the current source color channel (see...). Figure 1 Color channels 301, 302, and 303 in the image.

[0085] Then, in box 915, the currently displayed image of the active color channel is obtained, and in box 920, a specific pre-distortion of the currently displayed image is optionally calculated. The pre-distortion can also be calculated in advance. Techniques for determining the pre-distortion are known in the prior art. For example, lateral offsets caused by translational color differences can be corrected by corresponding translational shifts of pixels in the displayed image.

[0086] Then, in box 925, control the multicolor light source to activate one or more emitters of the current source color channel (see box 910).

[0087] In block 930, by means of appropriate control of the multi-pixel display device, a current image with pre-distortion is displayed on the multi-pixel display device (see blocks 915, 920). If the multi-pixel display device has multiple color channels, the current image is displayed on the display color channel associated with the current color channel, and other display color channels are either turned off or also display the current image. For multi-pixel display devices that do not have multiple color channels, the current image is displayed on a single channel.

[0088] Then, for the next time step, box 905 is executed again. By repeatedly iterating box 905 quickly enough, i.e., with sufficiently short time slots (the frequency of time slot switching), the colors of the virtual image generated by the image displayed in box 930 are mixed in the viewer's eyes.

[0089] From Figure 6 Various variations of the method are conceivable. For example, it is particularly conceivable to allocate more than a single source color channel with associated display images to a specific time slot. In particular, orthogonal source color channels can be allocated to a single common time slot. In this case, different display images, each compensated for color differences for the corresponding source color channel, can be reproduced on different display color channels.

[0090] Figure 7 A schematic illustration of a device 112 for illuminating a multi-pixel display (see...) Figure 1 The irradiation system 7030 can be implemented as follows: Figure 1 Irradiation system 30. Laser from laser source 111 (e.g., red-green-blue channel or fewer or more channels; see [link]). Figure 1 Channels 301, 302, and 303 are coupled to the speckle noise suppression unit 3—implemented here as a dynamically moving diffuser—through the optical waveguide 4. For this purpose, a lens element (e.g., a GRIN lens) can optionally be positioned at a suitable end of the optical waveguide 4. The emission characteristics of such a lens element can vary depending on the application. The lens element can provide collimation. For example, a lens element with collimation characteristics adapted to the input angle range of the speckle noise suppression unit 3 can be provided. In particular, dispersion must be considered here. In an alternative to the above scheme or further, a parabolic mirror can be used for beam spreading and collimation between the end of the optical waveguide 4 and the speckle noise suppression unit 3.

[0091] Speckle noise (also known as optical granulation or laser granulation, or simply speckle) refers to the granular interference phenomenon that can be observed when a fully coherently illuminated optically rough object surface (with inhomogeneities on the order of wavelength).

[0092] The diffuser implementing the speckle noise suppression unit 3 moves randomly in two lateral directions perpendicular to the axis of the optical waveguide, for example, randomly relative to both the optical waveguide 4 and the rest of the setup. For example, the moving frequency can be adjustable. In this way, speckle noise can be effectively suppressed.

[0093] Subsequently, light is input-coupled into the transparent substrate of the optical homogenization plate 1 (e.g., made of glass or plastic) through the input coupling structure 2 (which may also be referred to as the light redistribution structure). The input coupling structure 2 is arranged on the side 23 of the homogenization plate 1, directly adjacent to the speckle noise suppression unit 3. This allows for a compact structure; additional collimating lens elements, etc., can be omitted.

[0094] The input coupling structure 2 can be applied as a separate component to the homogenization plate 1. For example, the input coupling structure 2 can take the form of a micropillar lens array.

[0095] Typically, a micropillar lens array comprises a 1D or 2D array of micropillar lens elements (micropillar lenses) configured to refract light in different directions. For example, a 1D array can be used in which the micropillar lenses are arranged to be spaced apart from each other in a first direction and extend in a second direction perpendicular to the first direction.

[0096] The input coupling structure 2 can take the form of, for example, a film (e.g., a micropillar lens array film). However, the input coupling structure 2 can also be integrally formed with the homogenization plate 1, i.e., formed as a single component. For example, the side surface 23 can be formed with a suitable surface morphology (e.g., as an indented micropillar lens array on the side surface 23).

[0097] On the lower side 22 of the optical homogenization plate 1, the light guide substrate of the optical homogenization plate is provided with an additional transparent light redistribution structure 5, which redistributes the light field according to the desired design specifications, for example by multiple scattering and reflection 9.

[0098] The light redistribution structure 5 can be applied as a separate component to the homogenization plate 1. The light redistribution structure 5 can be implemented directly in the substrate, for example, in the form of a spherical (hemispherical) or elliptical protrusion or depression, but it can also be implemented by bonding a structural film with a refractive index-matched adhesive. Alternatively, the light redistribution structure 5 can take the form of, for example, a film (e.g., a micropillar lens array film). However, the light redistribution structure 5 can also be integrally formed with the homogenization plate 1, i.e., formed as a single component. For example, the lower side 22 can be formed with a suitable surface morphology (e.g., as a micropillar lens array in the form of indentations).

[0099] For example, the design specifications of the lateral uniformity and spatial alignment (emission characteristics of the uniform plate 1) of the light field 8 emitted by the uniform plate 1 can be set by the configuration, arrangement, size and / or quantity of this light redistribution structure (the main emission direction 205—perpendicular to the surface of the uniform plate 1—is also marked with reference numerals).

[0100] A reflector structure 6 is disposed below the light redistribution structure 5. This reflector structure, in the form of a reflective layer, is used to reduce light loss on the lower side 22 of the optical homogenization plate 1. The reflector structure 6 deflects light back towards the optical homogenization plate 1. The reflector structure 6 can be adhesively bonded to the light redistribution structure 5, for example, as a reflective film. The reflector structure 6 can also be produced, for example, as a metal vapor deposition (thin film) using aluminum.

[0101] Optionally, an output coupling structure 7 can be used on the top side 21 of the homogenization plate 1 to selectively define the angular distribution of the light field exiting the homogenization plate. The output coupling structure can take the form of a diffractor. A suitable design of the output coupling structure 7 allows for customized illumination of the pixel plane 11 of the multi-pixel display device 112. Pixel plane 11 may contain, for example, OLED pixels or micromirrors.

[0102] The output coupling structure 7 can be applied as a separate component to the homogenization plate 1. The output coupling structure 7 can take the form of, for example, a film. However, the output coupling structure 7 can also be integrally formed with the homogenization plate 1, i.e., formed as a single component. For example, the top side 21 can be formed with a suitable surface morphology.

[0103] In various examples, in particular, the optical homogenization plate 1 can be manufactured as a single integral part together with the output coupling structure 7, the input coupling structure 2, and the light redistribution structure 5. For example, such an integral part can be manufactured from a block of free plastic. For example, 3D printing or injection molding methods can be considered as manufacturing techniques.

[0104] To suppress the visibility of the diffuser features of the output coupling structure 7 to the human eye, it can be advantageous to decouple the pixel plane 11 from the output plane or the output coupling structure 7 (i.e., space it apart) (see gap 12). This depends on system requirements. Gap 12 is preferably greater than 20% of the thickness 13 of the homogenizing plate 1. The human eye adapts to the pixel plane 11. For example, if gap 12 is greater than the depth range of the eye, the diffuser features of the output coupling structure 7 are now blurred and cognitively suppressed.

[0105] Furthermore, the pixel plane 11 can be tilted or inclined relative to the homogenization plate 1.

[0106] Figure 8 It comes from Figure 7 A side view of the irradiation system 7030. From Figure 8 It is evident that the lateral extension of the input coupling structure 2 is less than the extension of the side surface 23 of the homogenization plate 1, that is, in Figure 8 The z-axis direction is along the long side of side 23. For example, in Figure 8 In the example, the input coupling structure 2 covers approximately 70% of the side surface 23. Typically, it is conceivable that the lateral extension of the input coupling structure 2 is no greater than 80%, 70%, or 50% of the side length of the side surface 23. However, in other examples, it is also conceivable that the input coupling structure 2 covers the entire side surface 23. The lateral extension of the input coupling structure 2 can be equal to the side length of the side surface 23. Furthermore, the aperture of the speckle noise suppression unit 3 is smaller than the lateral extension of the input coupling structure 2. Typically, the lateral extension of the speckle noise suppression unit 3 can, for example, not exceed 20% of the area of ​​the input coupling structure 2. Even though the speckle noise suppression unit 3 typically has a relatively limited extension relative to the side surface 23, a relatively large area of ​​input coupling to the homogenization plate 1 can be implemented using the input coupling structure 2. The extension (width on the side surface) and texture (micropillar lens texture, prism texture) of the input coupling structure 2 can be variably adapted (design freedom). For example, the input coupling structure 2 may include one or more prism structures; these act as scattering geometry for light that has already been input-coupled and internally reflected / scattered. Therefore, at the location of the input coupling structure 2, the emission characteristics of the homogenization plate 1—that is, the light distribution at the output coupling structure 7, such as uniformity—may be affected. Light is also further redistributed within the homogenization plate 1, for example, by the light redistribution structure 5. For this reason, the lateral extension of the input coupling structure 2 does not necessarily have to completely cover the entire length of the side surface 23. Figure 9 This is also clearly seen in the stereoscopic view of the 7030 irradiation system.

[0107] Figure 10 The speckle noise suppression unit 9300 is schematically shown. For example, it can be implemented... Figure 7 The speckle noise suppression unit 3. The speckle noise suppression unit 9300 includes a diffuser 9301 in the xy plane. Different types of driving devices are conceivable for moving the diffuser 9301 in the xy plane. For example, an electric drive device can be used. An electric drive device (also known as an electromagnetic drive device) uses, for example, a coil to generate an alternating magnetic field, in which a magnet then moves. The magnet is connected to the diffuser 9301. Figure 9 The image shows a corresponding actuator 9303 assembled in a fixed reference system (fastening device 9304) via a frame. The drive frequency of the electric actuator 9303 can be dynamically set over a relatively wide frequency range, thereby resonantly exciting one or more eigenmodes of, for example, a mass spring system (formed by diffuser 9301 and return spring 9302). Optimal despeckle results can be obtained under this resonant state. This type of drive can be designed as a single-axis or dual-axis system (in... Figure 10 (A dual-axis system is illustrated by way of example). Furthermore, nondeterministic movement can be initiated by one or more vibratory motors (e.g., miniature motors with eccentric flywheel mass on their shafts) connected to the carrier frame of the diffuser.

[0108] The shift frequency should not be less than 100 Hz to achieve a suitable statistical average z. However, the optimal frequency range depends on the diffuser's geometry and mass (the natural frequency of the mass-spring system). Furthermore, psychoacoustic effects should be considered in the design; that is, trade-offs may exist between different objective variables.

[0109] Figure 10 The scenario described is merely one example of a hardware implementation of a speckle noise suppression unit. Typically, the beam path of light can change over time. For this purpose, elements in the beam path (e.g., a diffuser plate, see...) can be implemented... Figure 10 Mechanical movement (e.g., vibration or rotation) of the beam path (or glass fiber). The change in the beam path over time causes the speckle to "diffuse" over time, and this reduces perceived noise. Alternatively, the phase of the incident light can also be modified, for example, by a spatial light modulator (SLM).

[0110] Figure 11 The illumination system 10500 is illustrated schematically. The illumination system 10500 provides... Figure 7 The functionality corresponding to the irradiation system 7030 in the middle. However, (with Figure 7 (Different from China) Figure 11 In this process, a free beam path of light is used to illuminate the multi-pixel plane 10506 of the multi-pixel display device 112.

[0111] Light is generated by a laser source 10501. The light propagates from the laser source 10501 towards the speckle noise suppression unit 10502. This speckle noise suppression unit can have the same characteristics as... Figure 10 It has the same design as the speckle noise suppression unit 9300 in the middle.

[0112] Light can propagate as a free beam between the laser source 10501 and the speckle noise suppression unit 10502. It is also conceivable that the light is guided by glass fibers.

[0113] The speckle noise suppression unit 10502 itself includes a movable diffuser that implements a specific emission characteristic 10507. This causes illumination of an additional diffuser 10504, which in turn provides emission characteristic 10508. Emission characteristic 10508 is configured to achieve uniform illumination of the additional diffuser 10505. Therefore, diffuser 10504 undertakes... Figure 7 The functionality of the homogenization plate 1 and the light redistribution structure 5.

[0114] Light can propagate as a free beam between the speckle noise suppression unit and the diffuser 10504, and between the diffuser 10504 and the diffuser 10505.

[0115] The diffuser 10505 has an emission characteristic 10509. This emission characteristic 10509 can be set to illuminate the entrance pupil of the optical imaging system of the HUD system as needed.

[0116] In this configuration, the pixel plane 10506 of the multi-pixel detector 112 is illuminated. The multi-pixel detector then has an emission characteristic 10510.

[0117] exist Figure 11 It is also evident that the diffuser 10505 is arranged with a certain gap between it and the pixel plane 10506. This suppresses the visibility of the diffuser features. This is helpful, especially when the optical imaging system of the HUD system greatly magnifies the pixel plane 10506 of the multi-pixel detector 112. Therefore, the virtual image of the pixel plane 10506 is perceived by the user as having considerable extension, and thus the diffuser features of the diffuser 10505—if visible—will be perceived as particularly unpleasant. Figure 12 yes Figure 11 A perspective view of a specific embodiment of system 500. Two deflecting mirrors 521 and 522 are also shown.

[0118] It goes without saying that the features of the embodiments and aspects of the present invention described above can be combined with each other. In particular, without departing from the scope of the present invention, these features can be used not only in the described combinations, but also in other combinations or individually.

[0119] For example, various aspects of HUD systems have been described above. However, other transparent screen units (e.g., holographic displays) can also benefit from the techniques described herein. Other optical imaging systems (e.g., optical imaging systems for projectors) can also benefit from the techniques described herein.

[0120] Furthermore, the above discussion primarily focuses on chromatic aberration caused by the stacking of HOEs, i.e., the translational shift of the image perceived by the user. However, compensation can also be made for other types of chromatic aberration.

Claims

1. A method for controlling an image generation unit (115) for a transparent screen unit (100), the image generation unit (115) including a multi-pixel display device (112) and a multi-color light source (111). in, The multicolor light source (111) is configured to emit coherent light in multiple source color channels (301, 302, 303) so as to illuminate the multipixel display device (112). The method includes: - Control (925) the multicolor light source (111) to emit the coherent light in time slots (501, 502, 503, 504, 505, 506) of the time-division multiplexing scheme (500), wherein, in each case, each time slot (501, 502, 503, 504, 505, 506) is respectively assigned to a single corresponding source color channel (301, 302, 303) among the plurality of source color channels (301, 302, 303), and - Control (930) the multi-pixel display device (112) so that, in each case, the corresponding display image (511, 512, 513) associated with the corresponding source color channel (301, 302, 303) is reproduced in each of these time slots (501, 502, 503, 504, 505, 506). The displayed images (511, 512, 513) have a pre-distortion that reduces the color difference of the optical imaging system (113) of the transparent screen unit (115) for the corresponding source color channels (301, 302, 303) associated with the corresponding displayed images (511, 512, 513).

2. The method as described in claim 1, in, These chromatic aberrations are caused by the layer thickness of the stacked holographic optical elements (151, 152, 153) of the optical imaging system (113). Among them, the different holographic optical elements in these stacked holographic optical elements (151, 152, 153) are associated with the different source color channels in the multiple source color channels (301, 302, 303).

3. The method as described in claim 1 or 2, in, The multi-pixel display device (112) has display color channels (391, 392, 393) assigned to each source color channel (301, 302, 303), wherein the spectra of these display color channels overlap with the spectra of the multiple source color channels (301, 302, 303).

4. The method as described in claim 3, in, The multi-pixel display device (112) is controlled in each of these time slots so that, in each case, the corresponding display image (511, 512, 513) is reproduced on the display color channels (391, 392, 393) assigned to the corresponding source color channels (301, 302, 303), and optionally on one or more additional display color channels (391, 392, 393).

5. The method as described in claim 3 or 4, in, The multi-pixel display device (112) is controlled in each of these time slots (501, 502, 503, 504, 505, 506) so that, in each case, the corresponding display image (511, 512, 513) is reproduced on the display color channel (391, 392, 393) assigned to the corresponding source color channel (301, 302, 303), and at least one other display color channel (391, 392, 393) is cut off.

6. The method as described in any of the preceding claims, in, The time-division multiplexing scheme is no less than N. The time slot switching frequency is 25 Hz, where N is the number of source color channels.

7. A method for controlling an image generation unit (115) for a transparent screen unit (100), the image generation unit (115) including a multi-pixel display device (112) and a multi-color light source (111). in, The multicolor light source (111) is configured to emit coherent light in multiple source color channels (301, 302, 303) so as to illuminate the multipixel display device (112). The method includes: - Control (925) the multicolor light source (111) so that the coherent light is emitted in time slots (591, 592, 593, 594) of the time-division multiplexing scheme (590). The first time slot (592, 594) is assigned to a single corresponding source color channel (302) among the plurality of source color channels (301, 302, 303). The second time slot (591, 593) is assigned to at least two corresponding source color channels (301, 303) among the plurality of source color channels (301, 302, 303). - Control (930) the multi-pixel display device (112) so that, in each case, one or more display images (511, 512, 513) associated with the corresponding one or more source color channels (301, 302, 303) are reproduced in each of these time slots (591, 592, 593, 594). These displayed images (511, 512, 513) have a pre-distortion that reduces the color difference of the optical imaging system (113) of the transparent screen unit (115) for the corresponding source color channels (301, 302, 303) associated with the corresponding displayed images (511, 512, 513). The multi-pixel display device (112) has associated display color channels (391, 392, 393) for each source color channel (301, 302, 303). The spectra of the source color channels allocated to these second time slots do not overlap with the spectra of the display color channels allocated to the other source color channels allocated to these second time slots.

8. A controller (119) for an image generation unit (115) of a transparent screen unit (100), the controller being configured to implement the method as described in any of the preceding claims.

9. A system (100) comprising: The controller (119) and the image generation unit (115).

10. The system (100) as claimed in claim 9, wherein, The system (100) further includes an illumination system (30, 7030, 10500) for illuminating the multi-pixel display device (112).

11. The system (100) as claimed in claim 10, wherein, The irradiation system (30, 7030, 10500) also includes a speckle noise suppression unit (3, 9300, 10502).

12. Program code that can be loaded and executed by a processor, wherein, When the program code is executed, the processor performs the method as described in any one of claims 1 to 7.

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