DEVICE AND METHOD FOR DETERMINING IMAGING QUALITY OF AT LEAST ONE IMAGE OF AN INSPECTED ARTICLE - Patent application

Abstract

The present invention relates to a device (100) for determining the imaging quality of at least one image of an inspected item (105), the device comprising at least one projection unit (115) for outputting light (120) towards the inspected item (105) in order to project at least one luminous and / or illuminated target structure through the inspected item (105), an optical receiving unit (110) for receiving a light beam (130) of light (120) representing at least one image of the projected target structure, and a holding unit (110) arranged between the projection unit (115) and the optical receiving unit (110). and a computing unit (150) for 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 the light beam (130) transmitted or reflected by the inspected item (105) to determine an imaging quality of at least one image, the computing unit (150) being connected to the projection unit (115), the receiving unit (110), and / or the holding unit (145).

Description

[Technical Field]

[0001] The starting point of the invention is a device and a method for determining the imaging quality of at least one image representation of a specimen according to the preambles of the independent claims.The subject matter of the invention also relates to a computer program. [Background technology]

[0002] US Pat. No. 11,029,206 B2 describes an apparatus for measuring and characterizing the performance of augmented and virtual reality waveguide structures using glass substrates.

[0003] Against this background, the approach presented herein provides an improved device and an improved method for determining the imaging quality of at least one image representation of a specimen, as well as a computing unit for using the method and finally a corresponding computer program according to the main claim. Advantageous developments and improvements of the device specified in the independent claim are possible by the measures set out in the dependent claims.

[0004] The approach presented herein allows for the development of means capable of reliably identifying the properties of test objects. For example, the device can be used as a measuring device in this regard. Advantageously, this can lead to improvements in the quality of test objects and, therefore, for example, near-eye displays (NEDs), such as those that can be used in conjunction with smart glasses, augmented reality (AR), or virtual reality (VR). For example, images can be displayed in focus, which can have a positive impact on the health of the end user. Advantageously, to simultaneously obtain color measurements and improvements in systems for measuring optical parameters, it is possible to use both a colorimeter and an imaging photometer, as well as a system for measuring optical parameters. Summary of the Invention [Means for solving the problem]

[0005] An apparatus for determining the imaging quality of at least one image representation of a specimen is presented, the apparatus including at least one projection unit emitting light in a test direction to project at least one light-emitting, additionally or alternatively, illuminated target structure onto the specimen. The apparatus further includes an optical receiving unit receiving a light beam transmitted through or reflected from the specimen, the light beam representing at least one image representation of the projected target structure. In this regard, the receiving unit includes an optical system device and an optical detector. The apparatus further includes a mounting unit for holding the specimen to be inspected, the mounting unit being disposed between the projection unit and the optical receiving unit, and a computing unit for 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 the light beam transmitted through or reflected from the specimen and received using the receiving unit to determine the imaging quality of the at least one image representation of the specimen. In this regard, the computing unit is connected to the projection unit, the receiving unit, and additionally or alternatively to the mounting unit.

[0006] For example, the device may be a measuring device for an augmented reality (AR) or virtual reality (VR) system, sometimes simply referred to as AR / VR, capable of measuring a test object. For example, the test object may be in the form of a lens for a smart eyeglass or AR / VR device, sometimes referred to as a near-eye display (NED), on which or against which an image can be captured. Furthermore, the test object may also be in the form of a complete system, for example, whose imaging quality can be measured. For this purpose, it is advantageous to specify the imaging properties in advance. Thus, the test object may be in the form of an optical system to be tested, a waveguide, a combination of multiple waveguides, or alternatively, a module that may include an illumination unit and a waveguide. In this regard, the module may be capable of generating a self-illuminating target structure that may be captured by the receiving unit. Advantageously, the target structure may represent a pattern, an image, or a symbol to be imaged on the test object.

[0007] The projection unit may advantageously include a light source, such as a light-emitting diode (LED). Furthermore, the projection unit may be aligned with the specimen so that light can be transmitted through or reflected from the specimen. Advantageously, the light may be transmitted directly through the specimen or enter the specimen at an incident point and, for example, be reflected from the opposite surface of the specimen to reach an exit point on the specimen. The exit point may advantageously be aligned with the receiving unit so that the transmitted or reflected light beam can be received by the receiving unit. The receiving unit may advantageously include an optical device, which may include, for example, a lens or other optical element, and a detector. The detector may also advantageously include multiple components that can capture the light beam and information carried by the light beam in addition to or instead of the light beam. The computing unit may advantageously take the form of a control unit or controller designed to process this information. In this case, information may be transmitted and evaluated based on the light parameters, thereby enabling estimation or calculation of the imaging quality of the image representation. To be able to obtain useful results, the apparatus may include a mounting unit to which the specimen can be attached. The mounting unit may advantageously be in the form of a movable or displaceable form so that the computing unit can be used to determine the imaging quality in relation to different positions of the specimen. The mounting unit may advantageously be in the form of a multi-axis linear stage that allows for flexible positioning of the specimen in space and can be displaced accordingly, for example along the x-axis, y-axis or z-axis, either once or repeatedly.

[0008] According to one embodiment, the detector associated with the receiving unit may include multiple spectral channels and at least one image sensor. In this case, the spectral channels may be implemented, for example, using a filter unit. Advantageously, the filter unit may take the form of a filter wheel with multiple optical filters. For example, such filters may take the form of optical-quality glass or plastic panels that can be introduced, for example, by pivoting, into the beam path of the receiving unit in order to obtain a defined wavelength spectrum in the image. Alternatively, the spectral channels may be realized by multiple image sensors, each with a spectral filter. In both variants, the spectral filters may further be combined with neutral density filters to uniformly attenuate the optical intensity incident on the image sensor in order to prevent possible overexposure of the sensor. Thus, the detector may be realized, for example, as a sensor unit. It is also conceivable that the detector associated with the receiving unit is realized as a focusable camera.

[0009] Furthermore, the receiving unit may include an optical unit, which may be diffraction-limited with respect to the total captureable field angle. Advantageously, the optical unit may include at least one lens, in particular a plurality of lenses, which may be designed to be able to guide the light beam to the detector. The resolution of the optical instrument, in this case the optical device, may be diffraction-limited in relation to the field angle. For this purpose, the field angle may be, for example, characteristic of the field of view of the receiving unit, i.e., related to the capture area.

[0010] The optical device may include exchangeable components and at least one adjustable optical aperture stop, which may be designed to be able to adapt the geometry of the beam incident on the optical device, in particular the diameter of said beam. For example, in terms of its design, the optical device may be similar to a conoscope. For example, an adjustable aperture stop may be used to simulate the diameter of the iris of a human eye. Advantageously, the optical aperture stop may be physically or virtually adjustable and may, for example, take the form of an opening that can receive a light beam. By adjusting the optical aperture stop, it is advantageously possible to determine the amount of light received so that the light conditions can be corrected.

[0011] According to one embodiment, the projection unit may take the form of a focusable or non-focusable collimator, which may in particular include at least one monochromatic and additionally or alternatively polychromatically illuminated or illuminable line element. The receiving unit may therefore include an imaging telescope that captures the image generated by the collimator at infinity onto a sensor. In this case, the collimator may be designed to generate light with approximately parallel beam paths from a divergent source. As a result, the light may advantageously be steered in a specific direction. For example, monochromatism may refer to the emission of light in a very narrow wavelength range. Polychromatism may therefore refer to a mixture of different colors and thus to polychromatic light that may be spectrally broadband and include different wavelengths. Advantageously, the line element may also be called a reticle or reticle.

[0012] Furthermore, the projection unit may include at least one line element having a plurality of different target structures. Alternatively, the projection unit may include a switching mechanism for sequentially introducing different line elements having different target structures into the light beam path. In particular, the target structures may represent large-area elements, sharp edges, and additionally or alternatively lines. For example, a line element having a plurality of different target structures may be referred to as a multi-feature reticle. Thus, the target structures may be, for example, patterns including curved or straight contours or lines. Thus, the target structures may be realized, in particular, as, for example, circles, quadrilaterals, or crosses, which may be displayed on or by a specimen.

[0013] According to one embodiment, the target structures may be generated or may be generateable using self-luminous elements. Additionally or alternatively, the projection unit may include an adjustable projection aperture stop. The target structures may advantageously be realized as virtual structures. To be able to image them, the projection unit may include a projection aperture stop, which may, for example, be similar to an optical system aperture stop and take the form of an opening through which light can pass. Advantageously, the projection aperture stop may be realized physically or virtually and may additionally or alternatively be adjustable to limit the diameter of the beam emerging from the projection unit. Furthermore, the projection unit may optionally include an additional projection field stop, which is optionally adjustable to adapt the angle of view of the emerging beam.

[0014] Furthermore, the apparatus may include a first movable goniometer that may be connected to the projection unit and a second movable goniometer that may be connected to the receiving unit. The first and second goniometers may be designed to be able to move the projection unit and the receiving unit independently in at least two different directions around a single, defined rotation point. In particular, the first goniometer and, additionally or alternatively, the second goniometer may be translationally movable in at least three spatial directions relative to the test object. One or more goniometers may also be referred to as angle measuring units, for example, capable of measuring the angle between the projection unit and the receiving unit. This means that the goniometers may be connected to each other and each have a single free end connected to the projection unit and the receiving unit, respectively. As a result, the projection unit and the receiving unit may advantageously be moved in different directions so that the imaging quality of the test spectrum from different positions, and therefore from different incident radiation directions of light, may be measured and determined. Advantageously, a goniometer may be provided.

[0015] A method for determining an imaging quality of at least one image representation of a specimen using the device of the above variant is also presented, the method comprising the steps of emitting light using a projection unit such that at least one illuminated target structure and additionally or alternatively the illuminated target structure can be projected onto the specimen, and receiving using a receiving unit a light beam of light transmitted through or reflected from the specimen, the light beam representing the at least one image representation, and simultaneously evaluating using a computer unit a first light parameter representative of at least one optical light parameter and a second light parameter representative of at least one colorimetric or photometric light parameter of the light beam transmitted through or reflected from the specimen to determine the imaging quality of the at least one image representation.

[0016] For example, the imaging quality of a specimen that may be used in conjunction with smart glasses or an AR / VR system can advantageously be determined by the method. By determining the imaging quality, it is advantageously possible to ascertain or confirm the sharpness of the image representation. Within the emitting step, the light can, for example, be emitted for a duration that can advantageously be adjustable.

[0017] According to one embodiment, a further light beam of light transmitted through or reflected from the specimen may be received in the receiving step, and the further light beam may represent at least one further image representation. In the evaluating step, a further first light parameter, which may represent at least one further optical light parameter, and a further second light parameter, which may represent at least one further colorimetric or photometric light parameter, of the further light beam may be simultaneously evaluated so that a further imaging quality of the further image representation can be determined. In particular, the image representation and the further image representation may each be captured with different exposure times. In this regard, the exposure times for emitting light to the image representation may, for example, be the same or alternatively different.

[0018] The method may further comprise, after the evaluation step, combining the image representation and the further image representation to form an overall image. In the case of different exposure times in the image representations, the overall image may advantageously be generated as a high dynamic range (HDR) image, i.e. as an image with a large brightness difference. Alternatively, with different spectral settings of the light beam, the image representations may generate an overall color image using light parameters. These may be simply optionally specified for the individual images or for the overall image.

[0019] According to one embodiment, the method may further comprise, prior to the evaluating step, a step of compensating for aberrations using predetermined calibration data. The compensating step may advantageously compensate for aberrations to improve imaging quality before the optical parameters are evaluated to determine the imaging quality. The calibration data may advantageously be stored in a memory unit.

[0020] The method may be implemented, for example, in software, in hardware, or in a mixed form consisting of software and hardware, for example in a controller.

[0021] The approach presented herein also develops a computing unit designed to execute, control or implement the steps of the method variants presented herein in a corresponding device. The problem addressed by the present invention can also be solved quickly and efficiently by this variant embodiment of the invention in the form of a computing unit realized as a controller.

[0022] For this purpose, the computing unit for processing the signals or data may include at least one memory unit for storing the signals or data, at least one interface to the sensors or actuators for reading sensor signals from the sensors or outputting data or control signals to the actuators, and / or at least one communication interface for reading or outputting data embedded in a communication protocol. For example, the computing unit may be a signal processor, a microcontroller, etc., and the memory unit may be a flash memory or a magnetic memory unit. The communication interface may be designed to read or output data wirelessly and / or via a cable, and a communication interface capable of reading or outputting data via a cable may read or output these data from or to a corresponding data transfer line, for example electronically or optically.

[0023] In this case, a computing unit may be understood to mean an electrical device that processes sensor signals and outputs control and / or data signals based thereon. The computing unit may include an interface that may be designed in terms of hardware and / or software. In the case of a hardware design, the interface may be, for example, part of what is known as a system ASIC, which includes a very wide range of functions of the device. However, it is also possible for the interface to be a separate circuit, an integrated circuit of discrete component parts, or at least part of a discrete component part. In the case of a software design, the interface may be a software module, which may reside, for example, in a microcontroller in addition to other software modules.

[0024] Exemplary embodiments of the techniques proposed herein are illustrated in the drawings and explained in detail in the following description. [Brief explanation of the drawings]

[0025] [Figure 1] 1 shows a schematic diagram of an apparatus according to an exemplary embodiment; [Figure 2] 1 shows a schematic diagram of an exemplary embodiment of the device. [Figure 3] 1 shows a schematic diagram of an exemplary embodiment of a target structure of the device. [Figure 4] 1 shows a schematic diagram of an exemplary embodiment of a target structure of the device. [Figure 5] 1 shows a schematic diagram of an exemplary embodiment of a target structure of the device. [Figure 6] 1 shows a schematic diagram of an exemplary embodiment of a target structure of the device. [Figure 7] 1 shows a flowchart of an exemplary embodiment of a method for determining imaging quality of an image representation of a specimen. [Figure 8] FIG. 1 illustrates a block diagram of a computing unit according to an exemplary embodiment of an apparatus. DETAILED DESCRIPTION OF THE INVENTION

[0026] In the following description of exemplary advantageous embodiments of the present invention, the same or similar reference numerals are used for elements of similar operation shown in the various figures, and repeated descriptions of such elements are avoided.

[0027] If an exemplary embodiment includes the conjunction "and / or" between a first feature and a second feature, this should be read as meaning that the exemplary embodiment according to one embodiment has both the first feature and the second feature, and according to a further embodiment, has either only the first feature or only the second feature.

[0028] 1 shows a schematic diagram of an apparatus 100 according to an exemplary embodiment. For example, the apparatus 100 is realized as a measurement device implemented to determine the imaging quality of at least one image representation of a specimen 105. Different optical systems whose imaging quality is to be measured or determined may therefore be arranged in or on the apparatus 100. In this case, the specimen 105 takes the form of a module, for example, in the form of a waveguide, a combination of multiple waveguides, or a combination of an illumination unit and a waveguide. In this regard, the module may, for example, generate a self-luminous target structure that can be captured by the receiving unit 110 of the apparatus 100.

[0029] Accordingly, the apparatus 100 includes at least one projection unit 115 that emits light 120 in the direction of the specimen 105 in order to project at least one luminous and / or illuminated target structure onto the specimen 105. It is merely optional for the projection unit 115 to include an illumination unit, i.e., a light source 125 that generates the light 120. In this regard, the optical receiving unit 110 is also part of the apparatus 100. The receiving unit 110 is designed to receive a light beam 130 of light 120 that has been transmitted through or reflected from the specimen 105. In this case, the light beam 130 represents at least one image representation of the projected target structure. Furthermore, the receiving unit 110 includes an optical device 135 and a detector 140. For example, the detector 140 includes 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) filters) and an additional optional neutral density (ND) filter. For example, the optical device 135 is diffraction-limited with respect to the total captureable angle of view. Furthermore, the optical device 135 includes interchangeable components and at least one physically or virtually adjustable optical aperture stop 144, which is designed to adapt the diameter of the beam incident on the optical device. For example, in terms of its design, the optical device may further correspond to a conoscope.

[0030] According to this exemplary embodiment, both the projection unit 115 and the receiving unit 110 are arranged to be movable, in particular pivotable. Furthermore, in this exemplary embodiment, the projection unit 115 and the receiving unit 110 are arranged to be located on a common line, which in this case corresponds, for example, to the beam paths of the light 120 and the light beam 130. In this case, the specimen 105 is arranged between the projection unit 115 and the receiving unit 110. More precisely, the apparatus 100 includes a mounting unit 145 implemented to hold the specimen 105. In this exemplary embodiment, the mounting unit 145 also has a movable embodiment in order to move the specimen 105 in the x-, y-, and z-directions of a coordinate system. For example, the apparatus 100 according to this exemplary embodiment includes a first movable goniometer 146, also referred to as an angle measurement unit, connected to the projection unit 115 and a second movable goniometer 147 connected to the receiving unit 110. In this regard, the first goniometer 146 and the second goniometer 147 are designed to move the projection unit 115 and the receiving unit 110 independently of each other in two different directions around a defined rotation point, respectively. In particular, the first goniometer 146 and / or the second goniometer 147 are translatable or displaceable relative to the specimen 105 in at least three spatial directions.

[0031] The apparatus 100 is designed 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 a light beam 130 of light 120 transmitted through or reflected from the specimen 105 and received by the receiving unit 110, in order to determine the imaging quality of at least one image representation of the specimen 105. In this case, the computing unit 150 is connected to the projection unit 115, the receiving unit 110, and / or the mounting unit 145. According to this exemplary embodiment, the specimen 105 (in this case consisting of or including an AR module) further comprises a waveguide with a further projection unit 155, which is also connected to the computing unit 150. In this case, the projection unit 115 and the further projection unit 155 are or can be arranged offset from each other. For example, the projection unit 115 is arranged in this case such that the light 120 passes through the specimen 105 in a straight line. According to this exemplary embodiment, the further projection unit 155 is arranged, for example, in such a way that the further light 160 enters the specimen 105 at an entrance point 165, also called the entrance pupil of said specimen, and is reflected at the surface of the specimen 105 until it enters an exit point 170, also called the exit pupil of the specimen 105. The reflected further light beam 171 of the light beam 130 and / or the further light 160 is subsequently received by the receiving unit 110 and, according to this exemplary embodiment, emerges from the exit point 170. The further projection unit 155 also comprises a further light source 175 for emitting the further light 160.

[0032] In other words, a system for simultaneously measuring overall modulation transfer function (MTF), color MTF, and colorimetric or photometric parameters according to this exemplary embodiment is presented, and a method thereof is presented in Fig. 7. Thus, device 100 is realized as an all-in-one system that allows customers to measure substantially all light parameters, i.e., optical and colorimetric qualities of near-eye display (NED) systems, for example, in the AR / VR sector, using one measurement device for these systems.

[0033] Therefore, the approach generally presented in this description relates to a method and apparatus 100 for simultaneously measuring optical parameters, such as MTF and colorimetric or photometric parameters, of components and modules of an NED system. Purely by way of example, the apparatus 100 is described in connection with a receiving unit 110, including a sensor upstream of which is disposed at least one filter wheel. The filter wheel includes filters that, individually or in combination, globally and spectrally filter the incident light beam 130, e.g., with the color vision weights of the human eye. Furthermore, the receiving unit 110 is described as an optical device 135, which is mounted in front of the filter wheel and includes, as a first element on the specimen side, an optical system having a physical aperture 144, the diameter of which can be changed manually or automatically by displacement or any other type of adjustment. A fundamental characteristic of the optical device 135 is its design as diffraction-limited for the overall captureable field of view. In this case, the optical device 135 can have both a small FOV and an FOV corresponding to a conoscopic FOV.

[0034] For measuring optical parameters such as colorimetric or photometric parameters and MTF, the measurements utilize targets that are distinguished by the presence of both large-area homogeneous elements and sharp edges or lines as target structures. In addition to targets containing both features, it is also possible to use different targets, each having one feature. In this case, the targets can be generated and projected purely optionally by a self-luminous display element that is part of the specimen 105 or by a target projector that projects the target through the specimen 105. In the case of targets with only one feature, the projection can be performed sequentially, for example, in the process. For example, the optional further projection unit 155 includes a further light source 175, which 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 specimen 105 and can be realized, for example, as an LCD or LCOS element. The projection unit 115 includes a projection aperture 180, also called an exit aperture, located on the exterior side facing the specimen 105. Furthermore, the projection unit 115 comprises a homogeneously illuminated target template 182. The projection unit 115 may have a similar technical design as the further projection unit 155. The light 120, 160 is guided to the entrance pupil of the specimen 105. In this case, the projection aperture stop 180 can be realized physically or virtually.

[0035] To measure the optical and colorimetric or photometric parameters, the mentioned targets are projected by the test object 105, by way of example only, by a target projector or by projection by the test object 105 itself. The capture is performed by recording with the system as described by sequentially recording images in each case with different filtering by a filter wheel. In this case, the image recording for each filter position may include one image or multiple images, even if the exposure times are different. To measure the optical and colorimetric parameters, the recorded data is sent to the computing unit 150 and processed. For example, and not exhaustively, processing may include combining images with different exposure times to form what are known as high dynamic range images, combining images with different color weights to form a color image, and / or correcting distortions in the individual and overall images. Furthermore, processing optionally includes correcting the captured data with a calibration data set and calculating the optical and colorimetric parameters. In this case, colorimetric parameters are determined purely by way of example from large area structures, while optical parameters, such as MTF, are determined in parallel on an edge and line basis.

[0036] Furthermore, the apparatus 100 includes at least one goniometer 146, 147. More specifically, the projection unit 115 and the receiving unit 110 can each be arranged on a goniometer 146, 147, allowing independent two-axis rotation of both elements around their respective rotation points. For example, the rotation points of the respective systems can be found, for example, at the position of the specimen or of the respective apertures of the projection unit or receiving unit, but any other position is also feasible. According to this exemplary embodiment, both goniometers 146, 147 offer the option of being displaced once or repeatedly, manually or automatically, at least in the X and Y directions, and optionally also in the Z direction. In this case, the task of the goniometers 146, 147 is the independent positioning of the receiving unit 110 and the projection unit 115 relative to the specimen 105, such that at least the optical aperture diaphragm 144 of the receiving unit 110 can be adjusted at a defined measurement position and at a defined angle relative to the specimen 105. If necessary, the exit pupil of the target projector can also be aligned to correspond to the definition in terms of position and angle relative to the exit pupil. Furthermore, the test object 105 can be displaced in at least X and Y in a plane by the mounting unit 145. Depending on the receiving unit 110, measurements of the test object 105 can therefore be realised by adjusting the positioning system or by successively positioning, recording and measuring at different positions and angles. In this case, the position of the system and optionally of the target projector as required can be found, for example, either on the opposite side of the test object 105 or alternatively on the same side as the test object 105. The test object 105 can take the form of individual waveguides, individual light-guiding elements, or a combination thereof, or a module consisting of several identical or different components or an entire system.

[0037] This means that an apparatus 100 and associated methods are presented that allow performing simultaneous measurements of optical imaging parameters and colorimetric and photometric parameters of optical components or modules of a near-eye display (NED). In this regard, the term NED is understood to mean a device that is worn by a user, for example in the form of glasses, and that is capable of projecting virtual images into the user's field of vision, for example by means of augmented, mixed or augmented reality, or of generating a virtual environment, also called virtual reality.

[0038] Optical imaging parameters and light parameters are understood to mean variables that characterize the imaging quality of an optical system, such as the MTF or degree of distortion and the chief ray angle. Colorimetric and photometric light parameters are understood to mean variables that characterize the color perception of an optical system, such as the color components transmitted or the color representation in a color space. Photometric parameters are understood to mean variables that allow describing the emission characteristics or amount of light transmitted or reflected by a test object. These include, for example, the transmitted luminous flux or luminous intensity. For specific definitions of the above and / or further parameters, reference is made to standards IEC 63145 and ISO 9241.

[0039] The described technique allows for the simultaneous measurement of the above parameters and is applicable to both individual components of NEDs and pre-assembled modules, or even to complete systems.

[0040] In other words, a first exemplary embodiment of the apparatus 100 described and illustrated in detail in FIG. 1 is presented here, and its function is described in a schematic manner. According to this exemplary embodiment, the NED assembly is shown as the apparatus 100 to be tested or measured (device under test—DUT). It consists of an internal projection unit 155, which includes an illuminated LCD and, for example, a waveguide, designed to provide the image generated by the internal projection unit 155 to a user. The apparatus 100 is fixed to a mechanical mount, for example, a multi-axis linear stage, which allows the specimen 105 to be freely positioned in space. More specifically, the specimen 105 can be displaced once or repeatedly along the x-, y-, and z-axes of a coordinate system using the stage. According to the exemplary embodiment shown in FIG. 2 and described accordingly, the projection unit 115 is realized as a collimator. For example, the collimator has a fixed or variable focus setting. In general, the projection unit 115 comprises a light source 125, a line element 182, called a reticle or reticle, to which a structured target pattern is applied, and an optical system 184, e.g., a lens, having a real or virtual exit aperture 180. To ensure homogeneous illumination of the target pattern, the line elements 182 are preferably linked to different panels. If the projection unit 115 is designed as a focusable collimator, the line elements 182 can be displaced relative to the optical unit of the collimator, e.g., using a linear encoder, to simulate different target distances.

[0041] According to this exemplary embodiment, the structured target pattern advantageously includes both large-area homogeneous elements and sharp edges or lines. Both types of structures can be arranged on the line elements 182 and thus realized or achievable as what is known as a multi-feature reticle. Alternatively, a mechanical interchange mechanism can be present, whereby different line elements 182 with different structures are introduced into the beam path of the projection unit 115. Alternatively, the line structures can be used for both partial measurements. In this case, correction factors that take into account the limited surface area of ​​the light-emitting structures are used in the colorimetric and photometric evaluations. For example, if a double cross or ring is used, the optical magnification is optionally also determined and individually considered in the calculations. Examples of projected target structures are shown in Figures 3-6.

[0042] For example, the light source 125 of the projection unit 116 may be polychromatic, and suitable mechanisms may be present to allow limiting or adjusting the spectral bandwidth. For example, the light source 125 may be realized as a single polychromatic LED with appropriate spectral filtering or as a combination of multiple monochromatic beam sources. Alternatively, the projection unit may be designed such that the projection unit itself generates the virtual object structure by means of a self-luminous element, e.g., a display.

[0043] The apparatus 100 further includes an optical receiving unit 110, which is arranged on the opposite side of the projection unit 115. If the specimen 105 is to be measured in reflection, the projection unit 115 and the receiving unit 110 can be arranged on the same side. In the case of Figure 1 shown here, the measurement is shown in transmission by way of example. However, the technique works equally well for measurements in reflection.

[0044] The receiving unit 110 then includes an optical system, described as an optical system device 135, and an image sensor that can be realized as a multispectral detector 140, i.e., a detector with multiple spectral channels. Other embodiments include a filter unit or a monochromatic detector with separate channels for spectral evaluation. In other words, the spectral sensitivity of the image sensor is variable. Thus, the image sensor can spectrally weight and / or filter the incident light beam. As a result, for example, the spectral sensitivity of the sensor can be adapted to the spectral sensitivity of the human eye. In an exemplary embodiment, such a detector 140 can be realized 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 system device 135 is disposed upstream of the detector 140 and is designed to generate a diffraction-limited image representation of its entire capturable field of view (FOV). Furthermore, the optical system device 135 includes one or more interchangeable components, thereby enabling the FOV of the optical system device 135 to be adapted for different measurement specifications. For example, in the case of a maximum set FOV, the optical system design corresponds to a conoscopic design, and the first optical element is always the adjustable optical aperture stop 144, as shown in Figure 1 or 2. The adjustable optical aperture stop is preferably realized as a physical diaphragm, but alternatively as a virtual pupil.

[0045] According to the exemplary embodiment shown in FIGS. 1 and 2, both the projection unit 115 and the receiving unit 110 are further fixed to respective goniometers 146, 147, which can pivot or displace laterally independently of each other, either once or repeatedly. For example, the axes about which the projection unit and the receiving unit can pivot extend generally parallel to their respective optical axes and / or intersect centrally with their respective entrance and exit pupils. To achieve the lateral offset, each goniometer 146, 147 may be mechanically connected to a multi-axis linear stage. Pivoting and / or displacing the projection unit 115 may be required to illuminate the specimen 105 at different positions and / or different target angles or to provide target patterns at different positions or different target angles. An exemplary application is shown in FIG. 2 below.

[0046] In other words and / or in summary, this exemplary embodiment presents an apparatus 100 for measuring the imaging quality of an optical system or module of an NED system, the apparatus 100 including a projection unit 115, a mounting unit 145, also referred to as a mechanical receptacle for the optical system or module or specimen 105 to be inspected, which is translationally displaceable in three spatial directions, an optical receiving unit 110, and a computing unit 150. In this case, the apparatus 100 is capable of simultaneously determining optical parameters and colorimetric or photometric parameters of the optical system or module 105 to be inspected, the optical receiving unit 110 consisting of an optical imaging system, as described above as the optical system device 135, and an optical detector 140 having multiple spectral channels 141. For example, the optical detector 140 can be realized by a combination of an image sensor 142 and at least one filter element 143, e.g., an upstream filter wheel with a V (lambda) filter and optionally further ND filters. According to this exemplary embodiment, the optical receiving unit 110 includes an optical system 135 that is diffraction-limited with respect to the overall captureable field angle. The optical system, i.e., the optical device 135 of the receiving unit 110, optionally further includes exchangeable components and at least one physically or virtually adjustable optical aperture stop 144, thus making it possible to delimit the diameter of the incident beam, for example to simulate the dilation of the human iris. Furthermore, in terms of its design, the optical system 135 may correspond to a conoscope.

[0047] According to this exemplary embodiment, the projection unit 115 is merely optionally realized as a focusable or non-focusable collimator having a monochromatically and / or polychromatically illuminated line element 182 (reticle), and also includes a physical or virtual aperture stop, described above as the exit aperture 180. The aperture stop may optionally be adjustable to limit the diameter of the beam incident on the specimen. Furthermore, the projection unit 115 may include an adjustable field stop 181, which may be realized physically or virtually. The field stop 181 serves to adapt the field angle of the emerging beam. Such adaptation may be necessary for some specimens so that the input coupling angle is precisely adapted to the waveguide under test. Furthermore, the line element 182 optionally includes different target structures (multi-feature reticles) or is designed to use an exchange mechanism to sequentially introduce reticles with different target structures into the beam path of the projection unit 115. In this case, the target structures can be realized, for example, as both large-area elements and sharp edges or lines, which are generated as virtual structures using self-luminous elements. In other words, this means that the projection unit 115 includes at least one line element 182 having an exchange mechanism for sequentially introducing a plurality of different target structures or different line elements, e.g., reticles, having different target structures into the beam path of the light 120, in particular the target structures representing large-area elements, sharp edges, and / or, for example, curved or straight lines. In this case, the target structures are or can be generated as virtual structures using self-luminous elements. Additionally or alternatively, the projection unit 115 includes a physical or virtual projection aperture stop 180 and an optional physical or virtual projection field stop 181.

[0048] According to this exemplary embodiment, the projection unit 115 is designed to illuminate the specimen 105 in reflection or transmission. For this purpose, the projection unit 115 is arranged, for example, on a first goniometer 146, and the receiving unit 110 is arranged on a second goniometer. As a result, both units 110, 115 are pivotable in at least two directions around a respective single, defined rotation point. Each goniometer 146, 147 is therefore translatable in three spatial directions relative to the specimen 105 being tested. The goniometers are not essential for the functioning of the device. In such a case, the receiving unit is realized as a conoscope, and the projection unit has adjustable aperture and field stops to adapt the diameter and field angle of the light beam to the specimen. Overall, the test specimen takes the form of a module, for example consisting of a single waveguide, a combination of multiple waveguides, or a combination of an illumination unit and a waveguide, which is capable of generating a self-luminous target structure that can be captured by the receiving unit 110 of the device 100.

[0049] FIG. 2 shows a schematic diagram of an exemplary embodiment of the apparatus 100. The apparatus 100 shown here is similar to the apparatus 100 described in FIG. 1. According to this exemplary embodiment, the apparatus 100 shown here again includes a projection unit 115 in addition to a receiving unit 110, a computing unit 150, and a mounting unit 145 that holds the specimen 105. The specimen shown here does not include a separate, active illumination or projection element 155. According to this exemplary embodiment, light 120 enters the specimen 105 via an entrance point 165 and is reflected from the surface of the specimen 105 until it reaches an exit point 170, where the light beam 130 is transmitted to the receiving unit 110. Also according to this exemplary embodiment, the projection unit 115 is realized as a focusable or non-focusable collimator, which in particular includes at least one monochromatic and / or polychromatic illuminated or illuminable line element 182 (reticle). It is also conceivable that the (image) sensor 142 is focusable accordingly. Collimators are designed to produce light with generally parallel beam paths from a diverging source, and this collimation often serves to impart a particular direction to the light.

[0050] In other words, the imaging quality of a test object 105, e.g., a single waveguide, is measured using the apparatus 100 in the case shown in FIG. 1 . In the process, the projection unit 115 is positioned so that a target pattern is projected onto the entrance pupil 165. The target pattern may also be projected onto other regions of the NED module's waveguide. Thus, in the case of a module for AR glasses, the projection unit 115 simulates real objects from the user's surroundings. In this application, the exposure unit of the NED module also generates a self-luminous structured target pattern, merely optionally in addition to or instead of the target pattern of the projection unit 115 being captured by the receiving unit 110. In this regard, pivoting of the receiving unit 110 is necessary, for example, to record image representations of the target pattern at different angles of view. In other words, on-axis and off-axis imaging quality are determined in this way. As a result of the lateral displacement of the receiving unit 110, the optical parameters and photometric or colorimetric parameters of the measured optical system or NED module are determined at different positions within the eyebox.

[0051] The apparatus 100 further includes a computing unit 150, by means of which both the projection unit 115 and the receiving unit 110 are electronically controlled. For example, if a corresponding reticle exchange mechanism is used, the computing unit 150 is designed to control the projection unit 115 to introduce different target patterns into the beam path. In the process, large area structures are used to determine colorimetric or photometric parameters, and structures with sharp lines or edges are used to determine optical imaging parameters.

[0052] The computing unit 150 processes the images recorded by the sensor associated with the receiving unit 110 and calculates from the recorded images the desired optical and colorimetric or photometric imaging parameters of the specimen 105 being measured. For example, the computing unit 150 controls the image sensor so that it sequentially records images of the target structure projected by the specimen 105 in each available spectral channel. In this case, the sensor exposure time is also variable. In the exemplary use of a filter wheel, changing the spectral channel means changing the filter position of the filter wheel. At each filter position, for example, both a single image and multiple images are recorded and transmitted to the computing unit 150.

[0053] In this case, optical parameters or colorimetric or photometric parameters are determined, for example, for each individual one of the recorded images or for any desired combination of the individual images. For example, sequentially recorded images, each with a different exposure time, can be combined to form one or more high dynamic range (HDR) images. Alternatively, sequentially recorded images, each with a different spectral weighting, are combined to form one or more color images. When investigating a complete NED system or module, the computing unit 150 is additionally or alternatively connected to the test object 105. In such a case, the projection unit 115 and / or further projection units (not shown here) of the test object 105 are controlled so that they display a self-illuminating target structure. An example of such a self-illuminating target structure is a cross pattern or a ring, which is shown merely as an example by LCD or LED display. The computing unit 150 may also, purely optionally, contain calibration data for the measurement device, which may be read before the measurement and used to calculate and remove aberrations of the optical system units used in the projection unit 115 or the receiving unit 110, such as certain distortions, from the subsequent measurement data.

[0054] Figure 3 shows a schematic diagram of an exemplary embodiment of a target structure 300 of an apparatus such as that illustrated by way of example in Figures 1 and / or 2. For example, target structure 300 is designed as a structure used to characterize the imaging quality of a specimen.

[0055] According to this exemplary embodiment, the target structure 300 has a dark region 305 and a light region 310, which are separated from each other by a sharply defined edge. In this case, the target structure 300 takes the form of a cross. Furthermore, the target structure 300 according to this exemplary embodiment has a polygonal outline.

[0056] Figure 4 shows a schematic diagram of an exemplary embodiment of a target structure 300 of an apparatus such as that illustrated by way of example in Figures 1 and / or 2. For example, the target structure 300 is designed as a structure used to characterize the imaging quality of a specimen.

[0057] According to this exemplary embodiment, the target structure 300 has a dark region 305 and a light region 310, which are separated from each other by a sharply demarcated edge. In this case, the target structure 300 has a circular shape, in particular a ring shape, and therefore the target structure 300 according to this exemplary embodiment has a further dark region 400. Furthermore, the target structure 300 according to this exemplary embodiment has a polygonal contour.

[0058] Figure 5 shows a schematic diagram of an exemplary embodiment of a target structure 300 of an apparatus such as that illustrated by way of example in Figures 1 and / or 2. For example, the target structure 300 is designed as a structure used to characterize the imaging quality of a specimen.

[0059] According to this exemplary embodiment, the target structure 300 has a dark region 305 and a light region 310, which are separated from each other by a sharply defined edge. In this case, the target structure 300 according to this exemplary embodiment has a square shape. Furthermore, the target structure 300 according to this exemplary embodiment has a polygonal outline.

[0060] Figure 6 shows a schematic diagram of an exemplary embodiment of a target structure 300 of an apparatus such as that illustrated by way of example in Figures 1 and / or 2. For example, the target structure 300 is designed as a structure used to characterize the imaging quality of a specimen.

[0061] According to this exemplary embodiment, the target structure 300 has a dark region 305 and a light region 310, which are separated from each other by a sharply defined edge. Furthermore, the target structure 300 according to this exemplary embodiment has an additional dark region 400 and an additional light region 600. According to this exemplary embodiment, the light regions 310, 600 and the dark regions 305, 400 are in each case disposed obliquely with respect to each other such that all regions 305, 310, 400, 600 intersect at a common center 605 of the target structure 300. Furthermore, the target structure 300 according to this exemplary embodiment has a rounded contour.

[0062] 7 shows a flowchart of an exemplary embodiment of a method 700 for determining an imaging quality of an image representation of a specimen. For example, the method 700 can be performed by a computing unit of an apparatus such as those described in either of FIGS. 1 and 2. For example, the computing unit can take the form of a controller.

[0063] Thus, method 700 includes a step 705 of emitting light using a projection unit, for example for an adjustable duration, to project at least one luminous and / or illuminated target structure onto the specimen. Furthermore, method 700 includes a step 710 of receiving, using a receiving unit, a light beam of light transmitted through or reflected from the specimen, said light beam representing at least one image representation, and a step 715 of simultaneously evaluating a first light parameter and a second light parameter of the light beam transmitted through or reflected from the specimen. In this case, 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 simultaneously determine the imaging quality of the at least one image representation using a computing unit. Purely optionally, during receiving step 710, a further light beam of light transmitted through or reflected from the specimen is received, said further light beam representing at least one further image representation. This means that in this case, in order to determine a further imaging quality of the further image representation, a further first light parameter representative of at least one further optical light parameter of the further light beam and a further second light parameter representative of at least one further colorimetric light parameter of the further light beam are simultaneously evaluated in an evaluation step 715. In particular, the image representation and the further image representation were captured for this purpose with respectively different exposure times.

[0064] Further, although optional, the method 700 according to this exemplary embodiment includes a step 720 of compensating for, and thus correcting, aberrations, e.g., distortions, using specified calibration data, prior to step 725 of combining the image representation and the further image representation to form an overall image, and / or after step 715. For example, this is performed to form an overall HDR image for different exposure times or an overall color image for different spectral settings, where, for example, parameters of the individual images or the overall image are specified.

[0065] In other words, a method 700 for measuring the imaging quality of an optical system or module in an NED system is described, in which an illuminated and / or projected target structure is projected in an emission step 705, and the target structure is transmitted or reflected by the optical system or module being tested. In a reception step 710, one or more image representations of the transmitted or reflected target structure are received by a reception unit toward detectors with different spectral settings. Thus, one or more optical parameters and colorimetric or photometric parameters of the optical system or module being tested are simultaneously determined from the one or more image representations using a computing unit in an evaluation step 715. An adjustable exposure time of the detector is purely optional, in which case multiple images captured during different exposure times can be combined using a computing unit to form an overall HDR image. Furthermore, in a combination step 725, images captured with different spectral settings are combined using a computing unit to form an overall image, in which the optical parameters and colorimetric or photometric parameters can be determined purely optionally in each individual image and / or in the combined overall image.

[0066] Figure 8 shows a block diagram of a computing unit 150 according to an exemplary embodiment of an apparatus as, for example, described in Figures 1 and / or 2. The computing unit 150 is therefore designed to control and / or execute a method for determining the imaging quality of at least one image representation of a specimen, for example as described in Figure 7. The computing unit 150 therefore comprises an emission unit 800, a reading unit 805, and an evaluation unit 810. Purely optionally, the computing unit 150 further comprises a compensation unit 815 and / or a combination unit 820.

[0067] In this case, the emission unit 800 is designed to emit light using the projection unit in order to project at least one luminous and / or illuminated target structure onto the specimen. For example, the reading unit 805 is designed to read a light beam of light (meaning, for example, a first light parameter 825 and a second light parameter 830 of the light beam) transmitted through or reflected from the specimen and received by a receiving unit of the device. The evaluation unit 810 is designed to simultaneously evaluate the first light parameter 825 representing at least one optical light parameter and the second light parameter 830 representing at least one colorimetric or photometric light parameter of the light beam of light transmitted through or reflected from the specimen in order to simultaneously determine the imaging quality of at least one image representation. Purely optionally, the reading unit 805 is further designed to read a further light beam of further light (meaning, 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 beam) transmitted through or reflected from the specimen and received by a receiving unit of the device. Therefore, the evaluation unit 810 is designed to simultaneously evaluate a further first optical parameter 831 and a further second optical parameter 832 of the further light beam in order to identify a further imaging quality of the further image representation, in particular the image representation and the further image representation each being captured with a different single exposure time.

[0068] The compensation unit 815 is optionally implemented to compensate or correct for aberrations using specified calibration data 835. For example, the combination unit 820 is designed to purely combine the image representation with optionally further image representations to obtain the overall image.

[0069] In summary, with regard to the type of optical system being tested, it should be noted that a possible application of the device for which patent protection is sought is in a module for an AR / VR system. Specifically, this may relate to an individual waveguide or multiple waveguides with a dedicated projector (e.g., for AR glasses). For example, the measurement system may then include only a projection device and a receiving device. For example, both may be pivotable or displaceable. Specifically, the second projection unit is not a general component of the measurement system. The second projection unit is only present when a NED module is being measured, as illustrated in FIG. 1 . In the case of a system configured according to FIG. 1 , this is an application example that considers, from a metrology perspective, how well the waveguide transmits the image generated by the NED projector (e.g., onto AR glasses) compared to a representation of the real surroundings.

[0070] Regarding the comparison of spectral filters with neutral density filters, it should be noted that a distinction between the two types of filters should be made at the receiving unit, for example. Spectral filters ensure that the desired wavelength range can be set, especially in the case of colorimetric measurements. Examples are V (lambda) filters to match the spectral sensitivity of the human eye or Bayesian patterns (weighted distribution of RGB filters) in CCD cameras. Neutral density filters reduce the emission intensity independently of the spectrum. Both types of filters can be used in practice.

[0071] Regarding the adaptation of the field angle and beam cross section, it should be noted that, for example, the field angle of the light beam does not need to be adapted on the receiver side. Here, an optical system unit with a suitable field of view is selected, e.g., a conoscope is selected for a large field angle. However, for example, if one were to simulate the iris of a human eye, an adaptation of the beam cross section, and thus an adjustable aperture stop 144, would be useful. Adaptation of both the beam cross section and its field angle may be required on the projection side. Therefore, a field stop 181 is also proposed in FIG. 1 (the pictorial representation of the field stop is hatched). Adaptation of the beam cross section is useful to prevent undesirable effects, such as overexposure of the specimen, which can result in stray light. The field angle should be adaptable in order to obtain the desired input coupling angle into the waveguide, since in this case, all possible total internal reflection is not required.

Claims

1. An apparatus (100) for determining an imaging quality of at least one image representation of a test object (105), the apparatus comprising: at least one projection unit (115) for emitting light (120) in the direction of said test object (105) in order to project at least one luminous and / or illuminated target structure (300) onto said test object (105); an optical receiving unit (110) for receiving a light beam (130) of light (120) transmitted or reflected by the specimen (105), the light beam representing at least one image representation of the projected target structure (300), the receiving unit (110) including an optical device (135) and an optical detector (140); a mounting unit (145) for holding the specimen (105) to be tested, the mounting unit (145) being disposed between the projection unit (115) and the optical receiving unit (110); a computing unit (150) for simultaneously evaluating a first light parameter (825) representing at least one optical light parameter and a second light parameter (830) representing at least one colorimetric and / or photometric light parameter of a light beam (130) of light (120) transmitted through or reflected from the specimen and received by the receiving unit (110) in order to determine the imaging quality of the at least one image table of the specimen (105), the computing unit (150) being connected to the projection unit (115), the receiving unit (110), and / or the mounting unit (145); An apparatus (100) comprising:

2. The device (100) described in claim 1, wherein the receiving unit (140) associated with the receiving unit (110) includes a plurality of spectral channels (141) and at least one image sensor (142), and in particular the detector (140) associated with the receiving unit is realized as a focusable camera.

3. 3. The apparatus (100) of claim 1, wherein the receiving unit (110) includes an optical device (135), the optical device (135) being diffraction limited with respect to an overall captureable angle of view.

4. 4. The apparatus (100) of claim 3, wherein the optical device (135) includes replaceable components and at least one adjustable optical aperture stop (144) designed to adapt the geometric properties of the beam incident on the optical device (135).

5. The apparatus (100) according to any one of claims 1 to 4, wherein the projection unit (115) takes the form of a focusable or non-focusable collimator, in particular comprising at least one monochromatically and / or polychromatically illuminated or illuminable line element (182).

6. The apparatus (100) of claim 5, wherein the projection unit (115) comprises the at least one line element (182) having a plurality of different target structures (300), or the projection unit (115) comprises an exchange mechanism for sequentially introducing different line elements (182) having different target structures (300) into the beam path of the light (120), in particular the target structures (300) representing large area elements, sharp edges and / or lines.

7. The apparatus (100) according to any one of claims 1 to 6, wherein the target structure (300) is generated or can be generated using a self-luminous element and / or the projection unit (115) comprises a projection aperture stop (180) and / or a projection field stop (181).

8. 8. The apparatus (100) according to claim 1, comprising a first movable goniometer (146) connected to the projection unit (115) and a second movable goniometer (147) connected to the receiving unit (110), the first and second goniometers (146, 147) being designed to move the projection unit (115) and the receiving unit (110) independently of each other in at least two different directions around a respective single defined point of rotation, in particular the first goniometer (146) and / or the second goniometer (147) being translationally movable in at least three spatial directions relative to the test piece (105).

9. A method (700) for determining an imaging quality of at least one image representation of a test object (105) using an apparatus (100) according to any one of claims 1 to 8, comprising: emitting (705) light (120) using the projection unit (115) to project at least one luminous and / or illuminated target structure (300) in the direction of the test piece (105); receiving (710) using the receiving unit (110) a light beam (130) of light (120) transmitted or reflected by the specimen (105) and representing at least one image representation; simultaneously evaluating (715) a first light parameter (825) representing at least one optical light parameter and a second light parameter (830) representing at least one colorimetric or photometric light parameter of a light beam (130) of light (120) transmitted through or reflected from the specimen (105) to simultaneously determine the imaging quality of the at least one image representation using the computing unit (150); A method (700) comprising:

10. 10. The method (700) of claim 9, wherein a further light beam (171) of further light (160) transmitted through or reflected from the test specimen (105) is received in the receiving step (710), the further light beam representing at least one further image representation, and 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 beam (171) are simultaneously evaluated in the evaluation step (715) to determine a further imaging quality of the further image representation, in particular the image representation and the further image representation being captured with different single exposure times, respectively.

11. 11. The method (700) of claim 10, further comprising, after said evaluating step (715), combining (725) said image representation and said further image representation to form an overall image.

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

13. A computing unit (150) for an apparatus (100) according to any one of claims 1 to 8, said computing unit (150) being designed to control and / or execute steps (705, 710, 715, 720, 725) of the method (700) according to any one of claims 9 to 12 in corresponding units (800, 805, 810, 820).

14. A computer program adapted to perform and / or control the steps (705, 710, 715, 720, 725) of the method (700) according to any one of claims 9 to 12.

15. A machine-readable storage medium having the computer program of claim 14 stored thereon.

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