Device and method for determining an imaging quality of at least one image for an inspection item

Abstract

The invention relates to a device (100) for determining an imaging quality of at least one image for an inspection item (105), the device comprising at least one projection unit (115) for outputting light (120) toward the inspection item (105) in order to project at least one luminous and / or illuminating object structure through the inspection item (105), an optical receiving unit (110) for receiving light beams (130) of the light (120), which represent at least one image of the projected object structure, a holding unit (145), which is located between the projection unit (115) and the optical receiving unit (110), and a computing unit (150) for simultaneously evaluating a first light parameter, which represents at least one optical light parameter, and a second light parameter, which represents at least one colorimetric or photometric light parameter, of light beams (130) transmitted by or reflected off the inspection item (105), in order to determine the imaging quality of the at least one image, wherein the computing unit (150) is connected to the projection unit (115), to the receiving unit (110) and / or to the holding unit (145).

Description

[0001] Device and method for determining an image quality of at least one image for a test object

[0002] State of the art

[0003] The invention relates to a device and a method for determining the image quality of at least one image for a test specimen according to the preamble of the independent claims. The present invention also relates to a computer program.

[0004] US 11029 206 B2 describes a device for measuring and characterizing the performance of augmented and virtual reality waveguide structures using glass substrates.

[0005] Against this background, the approach presented here provides an improved device and an improved method for determining the image quality of at least one image for a test specimen, a computing unit that uses this method, and finally a corresponding computer program according to the main claims. The measures listed in the dependent claims enable advantageous refinements and improvements of the device specified in the independent claim.

[0006] The approach presented here creates a way to reliably determine the properties of a test object. For example, the device can be used as a measuring device. This can advantageously improve the quality of the test object and thus, for example, of a near-eye display (NED), such as those used in conjunction with data glasses, augmented reality (AR), or virtual reality (VR). For example, images can be displayed sharply, which can have a positive impact on the health of an end user. Advantageously, both imaging colorimeters and imaging photometers as well as systems for measuring optical parameters can be used to achieve color measurement and improve the systems for measuring optical parameters simultaneously.

[0007] A device for determining the image quality of at least one image for a test object is presented. The device comprises at least one projection unit for emitting light toward the test object in order to project at least one luminous and additionally or alternatively illuminated object structure onto the test object. Furthermore, the device comprises an optical receiving unit for receiving light beams transmitted through or reflected by the test object, which represent at least one image of the projected object structure. The receiving unit comprises an optical device and an optical detector.The device also comprises a holding unit for holding the test piece to be tested, wherein the holding unit is arranged between the projection unit and the optical receiving unit, as well as a computing unit for simultaneously evaluating a first light parameter, which represents at least one optical light parameter, and a second light parameter, which represents at least one colorimetric or photometric light parameter, of light beams transmitted or reflected through or at the test piece and received using the receiving unit, in order to determine the image quality of the at least one image for the test piece. The computing unit is connected to the projection unit, the receiving unit, and additionally or alternatively to the holding unit.

[0008] The device can, for example, be a measuring device for augmented reality (AR) or virtual reality (VR) systems, which can also be referred to simply as AR / VR, by means of which the properties of the test object can be measured. The test object can, for example, be in the form of a spectacle lens for data glasses or an AR / VR device, which can also be referred to as a near-eye display (NED), and on or at which images can be projected. Furthermore, the test object can, for example, also be in the form of a complete system for which the imaging quality can be determined. For this purpose, it is advantageous to determine the imaging properties in advance. The test object can therefore be in the form of an optical system to be tested, as a waveguide, as a combination of waveguides, or alternatively as a module that can have an illumination unit and a waveguide.The module can be capable of generating a self-luminous object structure that can be detected by the receiving unit. The object structure can advantageously represent a pattern, image, or symbol to be projected onto the test object.

[0009] The projection unit can advantageously comprise a light source, for example a light-emitting diode (LED). Furthermore, the projection unit can be aligned with the test object so that the light can be transmitted through the test object or reflected by it. Advantageously, the light can either be transmitted directly through the test object or enter the test object at an entry point and, for example, be reflected by opposing surfaces of the test object until an exit point of the test object is reached. The exit point can advantageously be aligned with the receiving unit so that the transmitted or reflected light rays can be received by the receiving unit. The receiving unit can advantageously comprise the optical device, which can, for example, comprise lenses or other optical elements, and the detector.The detector can advantageously also have a plurality of components by means of which the light rays and additionally or alternatively information conveyed by them can be detected. The computing unit can advantageously be designed as a control unit or a control device designed to process this information. The information can be transported and evaluated based on the light parameters, which in turn enable a conclusion or calculation of the image quality of the image. In order to obtain a meaningful result, the device can have the mounting unit to which the test object can be attached. The mounting unit can advantageously be movable or displaceable, so that the image quality can be determined with respect to different positions of the test object using the computing unit.The holding unit can advantageously be designed as a multi-axis linear stage, which can enable free positioning of the test specimen in space and can therefore be moved, for example, once or repeatedly along an x-, y- or z-axis.

[0010] According to one embodiment, the detector of the receiving unit can have a plurality of spectral channels and at least one image sensor. The spectral channels can be implemented, for example, using a filter unit. The filter unit can advantageously be shaped as a filter wheel with a plurality of optical filters. Such filters can, for example, be shaped as a glass or plastic disc of optical quality that can be introduced, e.g., pivoted, into the beam path of the receiving unit in order to obtain a defined wavelength spectrum in the image. Alternatively, the spectral channels can be implemented via several image sensors, each with a spectral filter. In both variants, the spectral filters can additionally be combined with neutral density filters to uniformly attenuate the incident optical intensity on the image sensor with the aim of preventing possible overloading of the sensor.The detector can therefore be implemented, for example, as a sensor unit. It is also conceivable that the detector of the receiving unit is implemented as a focusable camera.

[0011] Furthermore, the receiving unit can have the optical device, which can be diffraction-limited for an entire detectable field angle. The optical device can advantageously have at least one lens, in particular a plurality of lenses, which can be designed to guide the light beams to the detector. The resolution of optical instruments, in this case the optical device, can be limited by diffraction in connection with the field angle. For this purpose, the field angle can, for example, be a parameter for a field of view of the receiving unit, i.e., related to a detection range.

[0012] The optical device can have replaceable components and at least one adjustable optical aperture stop, which can be designed to adapt the geometric properties of the beams incident on the optical device, in particular their diameter. For example, the optical device can be designed similarly to a conoscope. The adjustable aperture stop can be used, for example, to simulate the iris diameter of the human eye. The optical aperture stop can advantageously be physically or virtually adjustable and can additionally be shaped, for example, as an opening through which the light rays can be received. By adjusting the optical aperture stop, it is advantageously possible to determine how much light is received so that the lighting conditions can be correct.

[0013] According to one embodiment, the projection unit can be designed as a focusable or non-focusable collimator, which in particular can have at least one monochromatically and additionally or alternatively polychromatically illuminated or illuminable line element. The receiving unit accordingly has an imaging telescope to project the image generated by the collimator from infinity onto the sensor. A collimator can be designed to generate light with an approximately parallel beam path from a divergent source. This allows the light to be advantageously directed in a specific direction. Monochromatic can refer, for example, to light emission in a very narrow wavelength range. Polychromatic can therefore refer to multicolored light, which comprises a mixture of different colors and can thus be spectrally broadband and have different wavelengths.The line element can advantageously also be referred to as a reticle.

[0014] Furthermore, the projection unit can have at least one line element with a plurality of different object structures. Alternatively, the projection unit can have a changing mechanism for sequentially introducing different line elements with different object structures into a light beam path. In particular, the object structures can represent large-area elements, sharp edges, and additionally or alternatively lines. The line element with the plurality of different object structures can be referred to, for example, as a multi-feature reticle. The object structures can therefore be patterns that have curved or straight contours or lines, for example. The object structures can therefore be realized, for example, as a circle, square, or cross, which can be displayed, for example, on or by the test object.

[0015] According to one embodiment, the object structures can be generated or producible using a self-luminous element. Additionally or alternatively, the projection unit can have an adjustable projection aperture stop. The object structures can advantageously be implemented as virtual structures. In order to be able to image them, the projection unit can, for example, have the projection aperture stop, which, similar to the optical aperture stop, can be shaped as an opening through which the light can be emitted. The projection aperture stop can advantageously be implemented physically or virtually and, additionally or alternatively, can be adjustable to limit the diameter of the beam emerging from the projection unit. Furthermore, the projection unit can optionally have an additional projection field stop, which in turn is optionally adjustable to adapt the field angle of the emerging beams.

[0016] The device can additionally have a movable first goniometer, which can be connected to the projection unit, and a movable second goniometer, which can be connected to the receiving unit, wherein the first and the second goniometer can be designed to be able to move the projection unit and the receiving unit independently of one another around a defined point of rotation in at least two different directions. In particular, the first goniometer and additionally or alternatively the second goniometer can be movable translationally in at least three spatial directions relative to the test object. The goniometer or goniometers can also be referred to, for example, as protractors, which can, for example, measure an angle between the projection unit and the receiving unit. This means that the goniometers can be connected to one another and each connected at a free end to the projection unit or the receiving unit.The receiving unit can be connected. This allows the projection unit and the receiving unit to be advantageously moved in different directions, allowing the image quality of the test object to be measured and determined from different positions and thus from different light irradiations. Advantageously, the goniometers can be pivoted.

[0017] Furthermore, a method for determining an image quality of at least one image for a test object using a device in a previously mentioned variant is presented, wherein the method comprises a step of emitting light using the projection unit in order to be able to project at least one luminous and additionally or alternatively illuminated object structure onto the test object.The method also comprises a step of receiving light rays transmitted or reflected through or at the test object using the receiving unit, which light rays represent at least one image, and a step of simultaneously evaluating a first light parameter representing at least one optical light parameter and a second light parameter representing at least one colorimetric or photometric light parameter, of light rays transmitted or reflected through or at the test object in order to determine the image quality of the at least one image using the computing unit.

[0018] The method advantageously allows the image quality of the test object to be determined, which can be used, for example, in conjunction with data glasses or AR / VR systems. By determining the image quality, the sharpness of the images can advantageously be determined or verified. In the output step, the light can, for example, be emitted for a period of time, which can advantageously be adjustable.

[0019] According to one embodiment, in the receiving step, further light rays transmitted through or reflected by the test object can be received, which can represent at least one further image. In the evaluating step, a further first light parameter, which can represent at least one further optical light parameter, and a further second light parameter of the further light rays, which can represent at least one further colorimetric or photometric light parameter, can be evaluated simultaneously in order to be able to determine a further image quality of the further image. In particular, the image and the further image can each be captured at a different exposure time. The exposure time for emitting the light can, for example, be the same for the images or, alternatively, different.

[0020] The method may further comprise a step of combining the image and the further image into an overall image after the evaluation step. Advantageously, with a different exposure time for the images, the overall image can be generated as a high-dynamic-range (HDR) image, i.e., an image with large brightness differences. Alternatively, the images can generate an overall color image at different spectral settings of the light rays using the light parameters. These can be determined only optionally for individual images or for overall images.

[0021] According to one embodiment, the method may further comprise a step of compensating for aberrations using predetermined calibration data prior to the evaluation step. The compensating step advantageously allows aberrations to be corrected to improve the image quality before the light parameters are evaluated to determine the image quality. The calibration data may advantageously be stored on a storage unit.

[0022] This method can be implemented, for example, in software or hardware or in a mixed form of software and hardware, for example in a control unit.

[0023] The approach presented here further creates a computing unit configured to perform, control, or implement the steps of a variant of a method presented here in corresponding devices. This embodiment of the invention, in the form of a computing unit implemented as a control unit, also allows the problem underlying the invention to be solved quickly and efficiently.

[0024] For this purpose, the computing unit for processing signals or data can have at least one memory unit for storing signals or data, at least one interface to a sensor or actuator for reading sensor signals from the sensor or for outputting data or control signals to the actuator, and / or at least one communication interface for reading or outputting data embedded in a communication protocol. The computing unit can be, for example, a signal processor, a microcontroller, or the like, wherein the memory unit can be a flash memory or a magnetic storage unit.The communication interface can be designed to read in or output data wirelessly and / or wired, wherein a communication interface that can read in or output wired data can read this data, for example, electrically or optically from a corresponding data transmission line or output it to a corresponding data transmission line.

[0025] In this case, a computing unit can be understood as an electrical device that processes sensor signals and outputs control and / or data signals depending on them. The computing unit can have an interface, which can be implemented in hardware and / or software. In a hardware implementation, the interfaces can, for example, be part of a so-called system ASIC, which contains a wide variety of functions of the device. However, it is also possible for the interfaces to be separate integrated circuits or to consist at least partially of discrete components. In a software implementation, the interfaces can be software modules, which are present, for example, on a microcontroller alongside other software modules.

[0026] Examples of the approach presented here are illustrated in the drawings and explained in more detail in the following description. It shows:

[0027] Fig. 1 is a schematic representation of a device according to an embodiment;

[0028] Fig. 2 is a schematic representation of an embodiment of a device;

[0029] Fig. 3 is a schematic representation of an embodiment of an object structure for a device;

[0030] Fig. 4 is a schematic representation of an embodiment of an object structure for a device;

[0031] Fig. 5 is a schematic representation of an embodiment of an object structure for a device;

[0032] Fig. 6 is a schematic representation of an embodiment of an object structure for a device;

[0033] Fig. 7 is a flowchart of an embodiment of a method for determining an image quality of an image for a test object; and

[0034] Fig. 8 shows a block diagram of a computing unit according to an embodiment of a device. In the following description of advantageous embodiments of the present invention, the same or similar reference numerals are used for the elements shown in the various figures and having a similar effect, whereby a repeated description of these elements is omitted.

[0035] If an embodiment comprises an “and / or” link between a first feature and a second feature, this is to be read as meaning that the embodiment according to one embodiment has both the first feature and the second feature and according to another embodiment has either only the first feature or only the second feature.

[0036] Fig. 1 shows a schematic representation of a device 100 according to an exemplary embodiment. The device 100 is implemented, for example, as a measuring device designed to determine the imaging quality of at least one image for a test object 105. Accordingly, different optical systems whose imaging quality is to be measured or determined can be arranged in or on the device 100. The test object 105 is designed, for example, as a waveguide, as a combination of waveguides, or as a module designed as a combination of an illumination unit and a waveguide. The module is capable, for example, of generating a self-luminous object structure that can be detected by a receiving unit 110 of the device 100.

[0037] The device 100 accordingly has at least one projection unit 115 for emitting light 120 in the direction of the test object 105 in order to project at least one luminous and / or illuminated object structure onto the test object 105. The projection unit 115 only optionally has an illumination unit, i.e., a light source 125, which generates the light 120. The aforementioned optical receiving unit 110 is also part of the device 100. The receiving unit 110 is designed to receive light beams 130 of the light 120 transmitted through or reflected at the test object 105. The light beams 130 represent at least one image of the projected object structure. The receiving unit 110 further has an optical device 135 and a detector 140.The detector 140 has, for example, a plurality of spectral channels 141, an image sensor 142, and at least one filter unit 143, for example, a filter wheel with color filters (e.g., V(lambda) filter) as well as an additional optional neutral density (ND) filter. The optical device 135 is, for example, diffraction-limited for an entire detectable field angle. Furthermore, the optical device 135 has interchangeable components and at least one physically or virtually adjustable optical aperture diaphragm 144, which is designed to adapt the diameter of the beams incident on the optical device. Furthermore, the optical device can, for example, correspond to a conoscope in its design.

[0038] According to this exemplary embodiment, both the projection unit 115 and the receiving unit 110 are arranged to be movable and, in particular, pivotable. Furthermore, according to this exemplary embodiment, they are arranged lying on a common line, which here corresponds, for example, to a beam path of the light 120 and the light beams 130. The test object 105 is arranged between the projection unit 115 and the receiving unit 110. More precisely, the device 110 has a holding unit 145 designed to hold the test object 105. According to this exemplary embodiment, the holding unit 145 is also designed to be movable in order to move the test object 105 in the x, y, and z directions of a coordinate system.For example, the device 100 according to this exemplary embodiment has a movable first goniometer 146, also referred to as a protractor, which is connected to the projection unit 115, and a movable second goniometer 147, which is connected to the receiving unit 110. The first goniometer 146 and the second goniometer 147 are designed, for example, to move the projection unit 115 and the receiving unit 110 independently of one another around a defined rotation point in at least two different directions. In particular, the first goniometer 146 and / or the second goniometer 147 is / are translationally movable or displaceable relative to the test object 105 in at least three spatial directions.

[0039] The device 100 further comprises a computing unit 150 configured to simultaneously evaluate a first light parameter, representing at least one optical light parameter, and a second light parameter, representing at least one colorimetric or photometric light parameter, of the light beams 130 of the light 120 transmitted or reflected through or at the test object 105 and received using the receiving unit 110, in order to determine the imaging quality of the at least one image for the test object 105. The computing unit 150 is connected to the projection unit 115, the receiving unit 110, and / or to the mounting unit 145. According to this exemplary embodiment, the test object 105 (which here consists of or comprises an AR module) additionally comprises a waveguide with a further projection unit 155, which is also connected to the computing unit 150.The projection unit 115 and the further projection unit 155 are arranged or can be arranged offset from one another. The projection unit 115 is arranged, for example, such that the light 120 is transmitted linearly through the test object 105. According to this exemplary embodiment, the further projection unit 155 is arranged such that, for example, further light 160 enters the test object 105 at an entrance point 165, which is also referred to as the entrance pupil of the test object 105, and is reflected by surfaces of the test object 105 until it strikes an exit point 170, which is also referred to as the exit pupil of the test object 105. At the exit point 170, the light rays 130 and / or reflected further light rays 171 of the further light 160 exit according to this exemplary embodiment and are then received by the receiving unit 110.The further projection unit 155 also has a further light source 175 for outputting the further light 160.

[0040] In other words, according to this exemplary embodiment, a system is presented, and in Fig. 7, a method for the simultaneous measurement of a total modulation transfer function (MTF), color MTF, and colorimetric or photometric parameters. Device 100 is thus implemented as an all-in-one system that enables a customer, for example, for near-eye display (NED) systems, for example in the AR / VR sector, to measure all essential light parameters—that is, the optical and colorimetric quality of these systems—with one measuring device.

[0041] The approach generally presented in this description therefore relates to a method and a device 100 for the simultaneous measurement of optical parameters, such as MTF, and colorimetric or photometric parameters for components and modules of NED systems. For this purpose, the device 100 comprises, merely by way of example, a sensor described here in connection with the receiving unit 110, in front of which at least one filter wheel is arranged. The filter wheel comprises filters that, individually or in combination, filter the incident light rays 130 in their total quantity and spectrally, for example, with the weighting of the color perception of the human eye.Furthermore, the receiving unit 110 includes an optical system described as an optical device 135, which is mounted in front of the filter wheel and has, as the first element on one side of the test specimen, a physical aperture 144, the diameter of which can be changed manually or automatically by replacement or by some type of adjustment. A key feature of the optical device 135 is its design as diffraction-limited for an entire detectable field angle. The optical device 135 can have either a small FOV or an FOV corresponding to a conoscope.

[0042] For the measurement of colorimetric or photometric and optical parameters, such as MTF, a target is used for the measurement. This target is characterized by the fact that such an object structure contains both large-area homogeneous elements and sharp edges or lines. In addition to a target that has both of the features, various targets, each with a single feature, can also be used. The target can optionally be generated and projected using a self-luminous display element that is part of the test piece 105, or using a target projector that projects the target through the test piece 105. For targets with only one feature, the projection of these features occurs, for example, sequentially in the process. An optional additional projection unit 155, for example, has, for example, an additional light source 175 that can generate either various individual wavelengths or polychromatic light of different spectral widths.In this exemplary embodiment, the projection unit 155 is part of the test object 105 and can be implemented, for example, as an LCD or LCOS element. The projection unit 115 has a projection aperture stop 180, also referred to as an exit aperture, which is located externally on the side facing the test object 105. Furthermore, the projection unit 115 has a homogeneously illuminated target template 182. The projection unit 115 can be technically configured similarly to the further projection unit 155. The light 120, 160 is directed to an entrance pupil of the test object 105. The projection aperture stop 180 can be implemented physically or virtually.

[0043] To measure optical and colorimetric or photometric parameters, the projection of a described target through the test object 105 is carried out, for example, using the target projector or by projection using the test object 105 itself. Acquisition is performed by recording using the described system through sequential image acquisition with different filtering by the filter wheel each time. The image acquisition can contain one image per filter position or a plurality of images, even with different exposure times. To measure optical and colorimetric parameters, the recorded data is forwarded to the computing unit 150 and processed.For example, processing includes not only combining images with different exposure times to create so-called high-dynamic-range images, combining images with different color weightings to create color images, and / or correcting distortions in individual and overall images. Processing also optionally includes correcting the acquired data using calibration data sets and calculating optical and colorimetric parameters. The colorimetric parameters are determined using large-area structures as examples, while the optical parameters, such as MTF, are determined using edges and lines.

[0044] Furthermore, the device 100 has at least one goniometer 146, 147. More precisely, the projection unit 115 and the receiving unit 110 can each be arranged on a goniometer 146, 147, which enables independent biaxial rotation of both elements around respective rotation points. The rotation points of the respective systems are located, for example, at a location of respective apertures, e.g., of the test specimen or the projection or receiving unit, although any other position is also possible. According to this exemplary embodiment, both goniometers 146, 147 have the option of being moved manually or automatically, either once or repeatedly, at least in the X and Y directions, and optionally also in the Z direction.The task of the goniometers 146, 147 is the independent positioning of the receiving unit 110 and the projection unit 115 relative to the test object 105, so that at least one optical aperture diaphragm 144 of the receiving unit 110 can be adjusted to a defined measuring location and at a defined angle to the test object 105. If required, an exit pupil of the target project can also be aligned relative to the entrance pupil in accordance with the definition in terms of location and angle. Furthermore, the test object 105 can be moved at least in X and Y within a plane by means of the holding unit 145. Depending on the receiving unit 110, the measurement of a test object 105 can therefore be realized by adjusting the positioning systems or by sequential positioning, recording, and measurement at different locations and angles. The locations of the system and anyThe necessary target projector is located, for example, either on opposite sides of the test piece 105 or alternatively on the same side of the test piece 105. Test pieces 105 are formed as individual or a combination of waveguides or light-conducting elements, modules consisting of several identical or different components or complete systems.

[0045] This means that the device 100 and an associated method are presented, with which it is possible to perform a simultaneous measurement of optical imaging parameters as well as colorimetric and photometric parameters in optical components or modules of near-eye displays (NEDs). In this context, the term NED refers to devices that are worn by a user, for example, in the form of glasses, and that are capable of either projecting virtual images into the user's field of vision, for example, using augmented, mixed, or extended reality, or of generating a virtual environment, which is referred to as virtual reality.

[0046] Optical imaging or light parameters are understood to be quantities that characterize the imaging quality of an optical system, such as the MTF or the degree of distortion as well as the principal ray angle. Colorimetric and photometric light parameters are understood to be quantities that characterize color perception through an optical system, such as the transmitted color component or the color representation in a color space. Photometric parameters are understood to be quantities that allow a statement to be made about the radiation characteristics or the transmitted or reflected amount of light of the test object. These include, for example, the transmitted luminous flux or the luminous intensity. For the concrete definition of the aforementioned and / or other parameters, reference is made to the IEC 63145 and ISO 9241 series of standards.

[0047] The described approach enables simultaneous measurement of the above-mentioned parameters, which is applicable, for example, to individual components of NEDs as well as pre-assembled modules or complete systems.

[0048] In other words, a first exemplary embodiment of the device 100 is shown here, illustrated and described in more detail in Fig. 1, and its mode of operation is schematically explained. According to this exemplary embodiment, an assembly of a NED is shown as the device 100 to be tested or measured (device under test - DUT). This assembly consists of an internal projection unit 155, which comprises an illuminated LCD element and, for example, a waveguide designed to provide the image generated by the internal projection unit 155 to a viewer in a suitable manner. The device 100 is mounted in a mechanical holder, such as a multi-axis linear stage, which enables free positioning of the test object 105 in space. More precisely, the test object 105 can be moved once or repeatedly along an x-, y-, and z-axis of a coordinate system using the stage.According to the embodiment illustrated and described accordingly in Fig. 2, the projection unit 115 is implemented as a collimator. This collimator has, for example, a fixed or variable focus. The projection unit 115 generally comprises the light source 125, a line element 182 referred to as a reticle, on which a structured object pattern is applied, and an optical system 184, such as a lens, which has a real or virtual exit aperture 180. The line element 182 is preferably linked to a diffuser to ensure homogeneous illumination of the object pattern. If the projection unit 115 is designed as a focusable collimator, the line element 182 can be moved relative to the collimator's optics, for example using a linear encoder, to simulate different object distances.

[0049] According to this exemplary embodiment, the structured object pattern advantageously includes both large-area, homogeneous elements as well as sharp edges or lines. Both types of structures can be located on the line element 182, which is thus realized or can be realized as a so-called multi-feature reticle. Alternatively, a mechanical changing mechanism can be present, by means of which various line elements 182 with different structures are introduced into the beam path of the projection unit 115. Alternatively, line structures can be used for both partial measurements. In this case, a correction factor is used in the colorimetric and photometric evaluation, which takes into account the limited surface area of ​​the luminous structure. When using, for example, a double cross or a ring, the optical magnification is optionally also determined by measurement and individually taken into account in the calculation.Examples of object structures to be projected are shown in Figures 3 to 6.

[0050] For example, the light source 125 of the projection unit 115 is polychromatic, whereby a suitable mechanism may be present that allows the spectral bandwidth to be limited or adjusted. The light source 125 is implemented, for example, as a single, polychromatic LED with appropriate spectral filtering or as a combination of several monochromatic light sources. Alternatively, the projection unit can also be designed to generate a virtual object structure via a self-luminous element, such as a display.

[0051] The device 100 also includes the optical receiving unit 110, which is arranged on the opposite side of the projection unit 115. If the test object 105 is measured in reflection, the projection unit 115 and the receiving unit 110 can be arranged on the same side. Figure 1, shown here, illustrates the measurement in transmission. However, the approach works equally well for a measurement in reflection.

[0052] The receiving unit 110, in turn, comprises an optical system described as optical device 135 and an image sensor, which can be implemented as a multispectral detector 140, i.e., a detector with multiple spectral channels. Other embodiments include monochromatic detectors with filter units or separate channels for spectrometric evaluations. In other words, the spectral sensitivity of the image sensor is variable. The image sensor is thus capable of spectrally weighting and / or filtering incoming light rays. For example, this allows the spectral sensitivity of the sensor to be adapted to that of the human eye. In one embodiment, such a detector 140 can be implemented using a combination of at least one filter wheel with a V (lambda) filter and an additional ND filter.According to this exemplary embodiment, the optical device 135 is arranged in front of the detector 140 and is designed such that it generates a diffraction-limited image for its entire detectable field of view (FOV). Furthermore, the optical device 135 has one or more interchangeable components, making it possible to adapt the FOV of the optical device 135 to different measurement specifications. With a maximum FOV set, the design of the optical system corresponds, for example, to that of a conoscope, wherein the first optical element is always an adjustable optical aperture diaphragm 144, as shown in Fig. 1 or Fig. 2. This is preferably implemented as a physical diaphragm, but alternatively also as a virtual pupil.

[0053] Both the projection unit 115 and the receiving unit 110 according to the embodiment shown in Figures 1 and 2 are furthermore each attached to a goniometer 146, 147, which can be pivoted or laterally moved independently of one another, once or repeatedly. The axes about which the projection and receiving units can be pivoted run, for example, approximately parallel to the respective optical axis and / or centrally intersect the respective entrance or exit pupil. To realize a lateral offset, each goniometer 146, 147 can also be mechanically connected to a multi-axis linear stage. The pivoting and / or movement of the projection unit 115 is necessary in order to illuminate the test object 105 at different positions and / or at different object angles or to provide the object pattern at different positions or at different object angles.An example of an application is shown in Figure 2 below.

[0054] In other words and / or summarized, according to this exemplary embodiment, the device 100 for measuring the imaging quality of optical systems or modules of NED systems is presented, wherein the device 100 has the projection unit 115, a holding unit 145, also referred to as a mechanical holder for the optical system or module to be tested or the test object 105, which is translationally movable in three spatial directions, the optical receiving unit 110, and the computing unit 150. The device 100 is capable of simultaneously determining optical as well as photometric or colorimetric measurement parameters of the optical system or module 105 to be tested, wherein the optical receiving unit 110 consists of an optical imaging system, which was previously described as optical device 135, and an optical detector 140 with a plurality of spectral channels 141.The optical detector 140 can be implemented, for example, using a combination of an image sensor 142 with at least one filter element 143, for example, an upstream filter wheel with a V (lambda) filter and an optional additional ND filter. According to this exemplary embodiment, the optical receiving unit 110 has an optical system 135 that is diffraction-limited for the entire detectable field angle. The optical system, i.e., the optical device 135 of the receiving unit 100, also has optionally replaceable components and at least one physical or virtual adjustable optical aperture diaphragm 144, so that it is possible to limit the diameter of the incident beams, for example, to simulate the expansion of the human iris. The optical system 135 can furthermore correspond in its design to a conoscope.

[0055] According to this exemplary embodiment, the projection unit 115 is optionally implemented as a focusable or non-focusable collimator with a monochromatically and / or polychromatically illuminated line element 182 (reticle) and also has a physical or virtual aperture stop, previously described as exit aperture 180. The aperture stop can optionally be adjustable to limit the diameter of the beams incident on the test object. Furthermore, the projection unit 115 can contain an adjustable field stop 181, which can also be implemented physically or virtually. This serves to adjust the field angle of the exiting beams. Such an adjustment may be necessary for some test objects in order to precisely adjust the coupling angle into a waveguide under test.The line element 182 optionally further includes different object structures (multi-feature reticles) or is designed such that, using a changing mechanism, reticles with different object structures can be sequentially introduced into the beam path of the projection unit 115. The object structures can be realized, for example, as large-area elements or as sharp edges or lines, which are generated as virtual structures using a self-luminous element.In other words, this means that the projection unit 115 has at least one line element 182 with a plurality of different object structures or a changing mechanism for sequentially introducing different line elements, for example, reticules, with different object structures into a beam path of the light 120, in particular wherein the object structures represent large-area elements, sharp edges, and / or lines that are, for example, curved or straight. The object structures are generated or can be generated as virtual structures using a self-luminous element. Additionally or alternatively, the projection unit 115 has a physical or virtual projection aperture stop 180 and an optional physical or virtual projection field stop 181.

[0056] According to this exemplary embodiment, the projection unit 115 is designed to illuminate the test piece 105 in reflection or transmission. For this purpose, the projection unit 115 is arranged, for example, on the first goniometer 146 and the receiving unit 110 on the second goniometer. As a result, both units 110, 115 can each be pivoted about a defined rotation point in at least two directions. Each of the goniometers 146, 147 is therefore translationally movable in three spatial directions relative to the test piece 105 to be tested. The goniometers are not absolutely necessary for the functioning of the device. In such a case, the receiving unit would be implemented as a conoscope, and the projection unit would have an adjustable aperture and field stop to adapt the diameter and field angle of the light beams to the test piece.Overall, the test object is formed, for example, as a waveguide, a combination of waveguides or a module which consists of a combination of illumination unit and waveguide, wherein the module is capable of generating a self-luminous object structure which can be detected by the receiving unit 110 of the device 100.

[0057] Fig. 2 shows a schematic representation of an embodiment of a device 100. The device 100 shown here is similar to the device 100 described in Fig. 1. According to this embodiment, the device 100 shown here has, in addition to the receiving unit 110, the computing unit 150 and the holding unit 145 holding the test object 105, the projection unit 115. The test object shown here does not have an independent, active illumination or projection element 155. According to this embodiment, the light 120 enters the test object 105 via the entry point 165 and is reflected by the surfaces of the test object 105 until it reaches the exit point 170 and the light rays 130 are output to the receiving unit 110.According to this exemplary embodiment, the projection unit 115 is also implemented as a focusable or non-focusable collimator, which in particular has at least one monochromatically and / or polychromatically illuminated or illuminable line element 182 (reticle). It is also conceivable for the (image) sensor 142 to be correspondingly focusable. A collimator is designed to generate light with an approximately parallel beam path from a divergent source. This collimation often serves to give the light a specific direction.

[0058] In other words, in the case illustrated in Fig. 1, the imaging quality of the test object 105, for example, a single waveguide, is measured using the device 100. The projection unit 115 is positioned such that the object pattern is projected into the entrance pupil 165. The object pattern can also be projected into other areas of a waveguide of an NED module. For example, in a module for AR glasses, the projection unit 115 simulates a real object from a user's environment. In this application, the exposure unit of the NED module also optionally generates a self-luminous structured object pattern, which is captured by the receiving unit 110 in addition to or alternatively to the object pattern of the projection unit 115. Pivoting the receiving unit 110 is necessary, for example, to capture an image of the object pattern at different field angles.In other words, both axial and off-axis image quality is determined in this way. By laterally moving the receiving unit 110, the optical, photometric, or colorimetric parameters of the optical system to be measured, or of the NED module, are determined at different positions within an eyebox.

[0059] The device 100 further comprises the computing unit 150, with the aid of which both the projection unit 115 and the receiving unit 110 are electronically controlled. The computing unit 150 is designed, for example, to control the projection unit 115 in order to introduce various object patterns into the beam path if a corresponding reticle changing mechanism is used. Large-area structures are used for determining colorimetric or photometric parameters, and structures with sharp lines or edges are used for determining optical imaging parameters.

[0060] The computing unit 150 processes images recorded by the sensor of the receiving unit 110 and calculates the desired optical, colorimetric, or photometric imaging parameters of the test object 105 to be measured from the recorded images. The computing unit 150 controls the image sensor, for example, such that it records images of the object structure projected by the test object 105 in sequential order for each of the available spectral channels. Furthermore, the sensor's exposure time can be varied. In the exemplary use of a filter wheel, changing a spectral channel means changing its filter setting. For each filter setting, for example, one or more images are recorded and forwarded to the computing unit 150.

[0061] The optical, colorimetric, or photometric parameters are determined, for example, for each of the recorded images or for any combination of individual images. For example, sequentially recorded images, each with a different exposure time, can be combined to create one or more high-dynamic-range (HDR) images. Alternatively, sequentially recorded images, each with a different spectral weighting, can be combined to create one or more color images. When examining complete NED systems or modules, the computing unit 150 is additionally or alternatively connected to the test object 105. In such a case, the projection unit 115, or the additional projection unit (not shown here) of the test object 105, is controlled to display a self-luminous object structure.An example of such a self-luminous object structure would be a crosshair pattern or a ring, which are only displayed by way of example on an LCD or LED display. Furthermore, the computing unit 150 optionally has calibration data for the measuring device, which was read in prior to the measurement. This data can be used to calculate imaging errors, such as a degree of distortion, of the optics used in the projection unit 115 or receiving unit 110 from the subsequent measurement data.

[0062] Fig. 3 shows a schematic representation of an embodiment of an object structure 300 for a device, as described by way of example in at least one of Figures 1 to 2. The object structure 300 is designed, for example, as one used to determine the imaging quality of a test object.

[0063] According to this exemplary embodiment, the object structure 300 has a dark region 305 and a light region 310, which are separated from each other by sharp edges. The object structure 300 is shaped like a cross. Furthermore, according to this exemplary embodiment, the object structure 300 has a polygonal contour.

[0064] Fig. 4 shows a schematic representation of an embodiment of an object structure 300 for a device as described by way of example in at least one of Figures 1 to 2. The object structure 300 is designed, for example, as one used to determine the imaging quality of a test object.

[0065] According to this exemplary embodiment, the object structure 300 has a dark region 305 and a light region 310, which are separated from each other by sharp edges. The object structure 300 is shaped as a circle, in particular as a ring, so that the object structure 300 according to this exemplary embodiment has a further dark region 400. Furthermore, according to this exemplary embodiment, the object structure 300 has a polygonal contour.

[0066] Fig. 5 shows a schematic representation of an embodiment of an object structure 300 for a device as described by way of example in at least one of Figures 1 to 2. The object structure 300 is designed, for example, as one used to determine the imaging quality of a test object.

[0067] According to this exemplary embodiment, the object structure 300 has a dark region 305 and a light region 310, which are separated from each other by sharp edges. According to this exemplary embodiment, the object structure 300 is shaped as a square. Furthermore, according to this exemplary embodiment, the object structure 300 has a polygonal contour. Fig. 6 shows a schematic representation of an exemplary embodiment of an object structure 300 for a device, as described by way of example in at least one of Figures 1 to 2. The object structure 300 is shaped, for example, as one used to determine the imaging quality of a test specimen.

[0068] According to this exemplary embodiment, the object structure 300 has a dark region 305 and a light region 310, which are separated from each other by sharp edges. In addition, the object structure 300 according to this exemplary embodiment has the further dark region 400 and a further light region 600. According to this exemplary embodiment, the light regions 310, 600 and the dark regions 305, 400 are arranged diagonally to each other, so that all regions 305, 310, 400, 600 meet at a common center point 605 of the object structure 300. Furthermore, according to this exemplary embodiment, the object structure 300 has a round contour.

[0069] Fig. 7 shows a flowchart of an embodiment of a method 700 for determining the image quality of an image for a test object. The method 700 can be carried out, for example, by a computing unit for a device as described in one of Figures 1 to 2. The computing unit is embodied, for example, as a control unit.

[0070] The method 700 accordingly comprises a step 705 of emitting light using the projection unit, for example, for an adjustable period of time, in order to project at least one luminous and / or illuminated object structure onto the test object. Furthermore, the method 700 comprises a step 710 of receiving light rays transmitted through or reflected at the test object using the receiving unit, which represent at least one image, and a step 715 of simultaneously evaluating a first light parameter and a second light parameter of light rays transmitted through or reflected at the test object.The first light parameter represents at least one optical light parameter, and the second light parameter represents at least one colorimetric or photometric light parameter, in order to determine the image quality of the at least one image simultaneously using the computing unit. Only optionally, in step 710 of receiving, further light rays transmitted or reflected by or at the test object are received, which represent at least one further image. This means that in step 715 of evaluating, a further first light parameter, which represents at least one further optical light parameter, and a further second light parameter, which represents at least one further colorimetric light parameter, of the further light rays are simultaneously evaluated in order to determine a further image quality of the further image.In particular, the image and the further image were each captured at a different exposure time.

[0071] Additionally, but optionally, the method 700 according to this exemplary embodiment includes a step 720 of compensating and thus correcting imaging errors, such as distortion, using predetermined calibration data before the evaluation step 715 and / or a step 725 of combining the image and the further image into an overall image after the evaluation step 715. This occurs, for example, with a different exposure time for the overall HDR image, or with different spectral settings for an overall color image. In this case, parameters are determined, for example, for individual images or for overall images.

[0072] In other words, the method 700 for measuring the imaging quality of optical systems or modules of NED systems is described, wherein in step 705 of outputting, a luminous and / or illuminated object structure is projected, which is transmitted through or reflected by the optical system or module to be tested. In step 710 of receiving, one or more images of the transmitted or reflected object structure are received by the receiving unit at different spectral settings of the detector. In step 715 of evaluating, one or more optical as well as colorimetric or photometric parameters of the optical system or module to be tested are accordingly determined simultaneously from the one or more images using the computing unit.An exposure time of the detector can be set only optionally, whereby several images, each acquired at a different exposure time, can be combined into an overall HDR image using the computing unit. Furthermore, in step 725 of combining, images acquired at different spectral settings are combined into an overall image using the computing unit, whereby the optical, colorimetric, or photometric parameters can be determined only optionally for each individual image and / or for combined overall images.

[0073] Fig. 8 shows a block diagram of a computing unit 150 according to an exemplary embodiment of a device, as described, for example, in at least one of Figures 1 to 2. The computing unit 150 is accordingly designed, for example, to control and / or carry out a method for determining an image quality of at least one image for a test object, as described, for example, in Fig. 7. The computing unit 150 accordingly has an output unit 800, a read-in unit 805, and an evaluation unit 810. Only optionally does the computing unit 150 additionally have a compensation unit 815 and / or a combining unit 820.

[0074] The output unit 800 is configured to output light using the projection unit in order to project at least one luminous and / or illuminated object structure onto the test object. The reading unit 805 is configured, for example, to read in light beams received by the receiving unit of the device that were transmitted or reflected through or at the test object, i.e., for example, a first light parameter 825 and a second light parameter 830 of the light beams.The evaluation unit 810 is designed to simultaneously evaluate the first light parameter 825, which represents at least one optical light parameter, and the second light parameter 830, which represents at least one colorimetric or photometric light parameter, of light rays transmitted or reflected through or at the test object in order to simultaneously determine the image quality of the at least one image.Only optionally, the receiving unit 805 is further configured to read in further light beams of further light received by the receiving unit of the device, which were transmitted or reflected through or at the test object, i.e., for example, a further first light parameter 831 representing at least one further optical light parameter, and a further second light parameter 832 representing at least one further colorimetric or photometric light parameter, of the further light beams. Consequently, the evaluation unit 810 is configured to simultaneously evaluate the further first light parameter 831 and the further second light parameter 832 of the further light beams in order to determine a further imaging quality of the further image, in particular wherein the image and the further image were each acquired at a different exposure time.

[0075] The compensation unit 815 is further optionally configured to compensate for or correct imaging errors using predetermined calibration data 835. The combining unit 820 is configured, for example, to combine the image and a merely optional further image to obtain an overall image.

[0076] In summary, regarding the type of optical systems to be tested, it should be noted that the intended application of the patented device is modules for AR / VR systems. Specifically, these can be individual waveguides or waveguides with their own projectors (e.g., for AR glasses). The measuring system, for example, only has a projection device and a receiving device. Both can, for example, be pivotable or movable. In particular, the second projection unit is not a general component of the measuring system. It is only present when a NED module is being measured, as described, for example, in Fig. 1. In the case of the system configured according to Fig. 1, this would be an application example for measuring how well the waveguide transmits the images generated by the NED projector (e.g., with AR glasses) compared to the representation of the real environment.

[0077] When comparing spectral filters versus ND filters, it's important to note that a distinction should be made between two types of filters in the receiving unit, for example. Spectral filters ensure that a desired wavelength range can be set, especially for colorimetric measurements. Examples include V (lambda) filters for adapting to the spectral sensitivity of the human eye or Beyer patterns (weighted distribution of RGB filters) in CCD cameras. ND filters reduce light intensity regardless of the spectrum. Both types of filters can be used in practice.

[0078] Regarding the adjustment of field angles and beam cross-sections, it should be noted that on the receiving side, for example, no adjustment of the field angle of the light rays is necessary. Here, an optic with a suitable FOV is selected, e.g., a conoscope for large field angles. However, adjusting the beam cross-section is helpful, e.g., if the iris of the human eye is to be simulated, hence the adjustable aperture diaphragm 144. On the projection side, it may be necessary to adjust both the beam cross-section and its field angle. Hence the suggested field diaphragm 181 in Fig. 1 . (The field diaphragm is shown as a hatch.) Adjusting the beam cross-section is helpful to ensure that the test object is not overexposed and to prevent any disruptive effects, such as stray light, from occurring.The field angle should be adjustable to obtain a desired coupling angle into the waveguide, since not necessarily every possible total reflection is desired.

Claims

Patent claims 1. A device (100) for determining an image quality of at least one image for a test object (105), the device (100) having the following features: at least one projection unit (115) for emitting light (120) in the direction of the test object (105) in order to project at least one luminous and / or illuminated object structure (300) onto the test object (105); an optical receiving unit (110) for receiving light beams (130) of the light (120) transmitted through or reflected at the test object (105), which represent at least one image of the projected object structure (300), the receiving unit (110) having an optical device (135) and an optical detector (140); a holding unit (145) for holding the test specimen (105) to be tested, wherein the holding unit (145) is arranged between the projection unit (115) and the optical receiving unit (110);and a computing unit (150) for simultaneously evaluating a first light parameter (825), which represents at least one optical light parameter, and a second light parameter (830), which represents at least one colorimetric and / or photometric light parameter, of light beams (130) of the light (120) transmitted or reflected through or at the test object (105) and received using the receiving unit (110), in order to determine the image quality of the at least one image for the test object (105), wherein the computing unit (150) is connected to the projection unit (115), the receiving unit (110) and / or to the holding unit (145); 2. Device (100) according to claim 1, wherein the detector (140) of the receiving unit (110) has a plurality of spectral channels (141) and at least one image sensor (142), in particular wherein the detector (140) of the receiving unit is implemented as a focusable camera.

3. Device (100) according to one of the preceding claims, wherein the receiving unit (110) comprises the optical device (135) which is diffraction-limited for an entire detectable field angle.

4. Device (100) according to claim 3, wherein the optical device (135) has interchangeable components and at least one adjustable optical aperture stop (144) which is designed to adapt geometric properties of the beams incident into the optical device (135).

5. Device (100) according to one of the preceding claims, wherein the projection unit (115) is formed as a focusable or non-focusable collimator, which in particular has at least one monochromatically and / or polychromatically illuminated or illuminable line element (182).

6. Device (100) according to claim 5, wherein the projection unit (115) has the at least one line element (182) with a plurality of different object structures (300), or wherein the projection unit (115) has a changing mechanism for sequentially introducing different line elements (182) with different object structures (300) into a beam path of the light (120), in particular wherein the object structures (300) represent large-area elements, sharp edges and / or lines.

7. Device (100) according to one of the preceding claims, wherein the object structures (300) are generated or can be generated using a self-luminous element, and / or wherein the projection unit (115) has a projection aperture stop (180) and / or a projection field stop (181).

8. Device (100) according to one of the preceding claims, with a movable first goniometer (146) which is connected to the projection unit (115), and with a movable second goniometer (147) which is connected to the receiving unit (110), wherein the first and the second goniometer (146, 147) are designed to move the projection unit (115) and the receiving unit (110) independently of one another around a defined rotation point in at least two different directions, in particular wherein the first goniometer (146) and / or the second goniometer (147) is or are translationally movable relative to the test object (105) in at least three spatial directions. Method (700) for determining an image quality of at least one image for a test object (105) using a device (100) according to one of the preceding claims, wherein the method (700) comprises the following steps: Emitting (705) light (120) using the projection unit (115) to project at least one luminous and / or illuminated object structure (300) toward the test object (105); Receiving (710) light beams (130) of the light (120) transmitted or reflected through or at the test object (105) using the receiving unit (110), which represent at least one image; and Simultaneously evaluating (715) a first light parameter (825), which represents at least one optical light parameter, and a second light parameter (830), which represents at least one colorimetric or photometric light parameter, of light rays (130) of the light (120) transmitted or reflected through or at the test object (105), in order to determine the image quality of the at least one image simultaneously using the computing unit (150).Method (700) according to claim 9, wherein in the receiving step (710), further light beams (171) of further light (160) transmitted or reflected by or at the test object (105) are received, which represent at least one further image, wherein in the evaluating step (715), a further first light parameter (831), which represents at least one further optical light parameter, and a further second light parameter (832), which represents at least one further colorimetric or photometric light parameter, of the further light beams (171) are simultaneously evaluated in order to determine a further image quality of the further image, in particular wherein the image and the further image were each acquired at a different exposure time. Method (700) according to claim 10, comprising a step (725) of combining the image and the further image to form an overall image after the evaluating step (715).

12. The method (700) according to any one of claims 9 to 11, comprising a step (720) of compensating for imaging errors using predetermined calibration data (835) before the step (715) of evaluating.

13. The computing unit (150) for a device (100) according to any one of claims 1 to 8, wherein the computing unit (150) is configured to control and / or execute steps (705, 710, 715, 720, 725) of a method (700) according to any one of claims 9 to 12 in corresponding units (800, 805, 810, 820).

14. Computer program adapted to carry out the steps (705, 710, 715, 720, 725) of Method (700) according to one of claims 9 to 12 and / or to control.

15. Machine-readable storage medium on which the computer program according to claim 14 is stored.

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