Method and device for calibrating a camera using a diffractive optical element

Abstract

A method for calibrating a camera (102) using a diffractive optical element (104) comprises capturing a diffraction pattern projected onto an image sensor (112) of the camera (102) using a diffractive optical element (104) while the diffractive optical element (104) and the camera (102) are in an angular position with respect to one another, and further capturing a further diffraction pattern projected onto the image sensor (112) of the camera (102) using the diffractive optical element (104) while the diffractive optical element (104) and the camera (102) are in a further angular position with respect to one other, different from the angular position, and determining a calibration rule for calibrating the camera (102) using the diffraction patterns.

Description

[0001] Description

[0002] title

[0003] Method and device for calibrating a camera using a diffractive optical element

[0004] State of the art

[0005] The invention is based on a device or method according to the class of the independent claims. The present invention also relates to a computer program.

[0006] Cameras used in vehicles, for example, must be calibrated.

[0007] US3912395A describes a geometric camera calibration using a diffractive optical element (DOE).

[0008] Disclosure of the invention

[0009] Against this background, the approach presented here presents a method for calibrating a camera using a diffractive optical element, a device using 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.

[0010] The described approach enables the calibration of cameras with a large field of view (FOV). A method for calibrating a camera using a diffractive optical element includes the following steps:

[0011] capturing a diffraction pattern projected onto an image sensor of the camera using a diffractive optical element while the diffractive optical element and the camera are at an angular position to each other;

[0012] Further detecting a further diffraction pattern projected onto the image sensor of the camera using the diffractive optical element while the diffractive optical element and the camera are in a further angular position relative to each other that differs from the angular position; and

[0013] Determine a calibration rule for calibrating the camera using the diffraction patterns.

[0014] The camera can be an image capture device used, for example, to capture the interior or surroundings of a vehicle. Alternatively, the camera can be used in other applications, for example as a surveillance camera on a building. The camera can include the image sensor, also referred to as the camera sensor, and optics. Optical properties of essentially identical cameras can differ from one another due to manufacturing tolerances, for example. Such deviations can be detected by calibrating the camera and compensated for using the calibration rule. For example, the calibration rule can be used to ensure correct translation of pixel coordinates of an image captured by the camera into the viewing angle of the real world, and vice versa.Known procedures, such as geometric camera calibration, can be used to determine the calibration specification. The diffractive optical element can have a predetermined microstructure through which a beam incident on the diffractive optical element can be diffracted into multiple orders of diffraction, resulting in the diffraction pattern, for example, a matrix of points. Due to the optical properties of the camera, the diffraction pattern captured by the camera typically deviates from a known, ideal reference pattern associated with the microstructure of the diffractive optical element. The calibration specification can be determined by comparing the captured diffraction pattern with the known reference pattern.The different angular positions between the diffractive optical element and the camera can be selected so that the recorded diffraction patterns cover the entire area of ​​the image sensor. This allows the calibration specification to cover all pixels of the image sensor. Different angular positions can be achieved, for example, by tilting an optical axis of the camera relative to a plane of the diffractive optical element.

[0015] In the acquisition step, the diffraction pattern can be projected onto a section of the image sensor. In the further acquisition step, the additional diffraction pattern can be projected onto a further section of the image sensor that differs at least partially from the section. In this way, the entire image sensor can be gradually covered by repeated acquisitions and changing the angular position in between. Depending on the embodiment, two or more diffraction patterns can be acquired at different angular positions.

[0016] In a movement step, the camera and the diffractive optical element can be moved relative to each other to convert the angular position to the next angular position. To do this, the camera can be moved while the diffractive optical element is at rest, or vice versa. Both the camera and the diffractive optical element can also be moved. Advantageously, the movement step can be performed automatically.

[0017] In an exposure step, the diffractive optical element can be exposed to electromagnetic radiation from a side facing away from the camera. The incident radiation can be diffracted by the diffractive optical element, thereby projecting the diffraction pattern onto the image sensor. For example, the electromagnetic radiation can be provided as a laser beam.

[0018] The diffraction angle of the diffractive optical element can be smaller than the camera's field of view. Advantageously, inexpensive, high-quality diffractive optical elements with a relatively small diffraction angle relative to the field of view can be used. For example, the camera's field of view can be larger than 180°. This allows the method to be used, for example, for calibrating parking assistance cameras.

[0019] The further acquisition step can be repeated several times to acquire several additional diffraction patterns, which are projected onto the camera's image sensor using the diffractive optical element while the diffractive optical element and the camera are positioned at several additional angular positions relative to each other that differ from the angular position. Thus, diffraction patterns can be projected onto the image sensor until the entire surface of the image sensor has been covered at least once.

[0020] In the determination step, the calibration rule can be determined by comparing the diffraction patterns with a reference pattern assigned to the diffractive optical element. Information about a current angular position at which a diffraction pattern was acquired can be taken into account to assign the camera's pixel coordinates to corresponding viewing angles.

[0021] 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.

[0022] The approach presented here further provides a device designed 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 device also allows the problem underlying the invention to be solved quickly and efficiently.

[0023] For this purpose, the device can have at least one computing unit for processing signals or data, at least one memory unit for storing signals or data, at least one interface to a sensor or an 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.

[0024] In this case, a device can be understood as an electrical device that processes sensor signals and outputs control and / or data signals depending on them. The device 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 that are present, for example, on a microcontroller alongside other software modules.

[0025] Also advantageous is a computer program product or computer program with program code that can be stored on a machine-readable carrier or storage medium such as a semiconductor memory, a hard disk memory or an optical memory and is used to carry out, implement and / or control the steps of the method according to one of the embodiments described above, in particular when the program product or program is executed on a computer or a device.

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

[0027] Fig. 1 is a schematic representation of an embodiment of a device for calibrating a camera;

[0028] Fig. 2 shows a simulation of an embodiment of a diffraction pattern captured by a camera;

[0029] Fig. 3 shows a simulation of an embodiment of a diffraction pattern of a diffractive optical element with large diffraction angles;

[0030] Fig. 4 shows an output of an embodiment of an asin function;

[0031] Fig. 5 is a representation of an embodiment of a device for calibrating a camera;

[0032] Fig. 6 shows an embodiment of a diffraction pattern centered within an image;

[0033] Fig. 7 shows an embodiment of a diffraction pattern shifted within an image;

[0034] Fig. 8 shows an embodiment of a further diffraction pattern shifted within an image;

[0035] Fig. 9 shows an embodiment of a further diffraction pattern shifted within an image; Fig. 10 shows an embodiment of a further diffraction pattern shifted within an image;

[0036] Fig. 11 shows an embodiment of a further diffraction pattern shifted within an image;

[0037] Fig. 12 shows an embodiment of a further diffraction pattern shifted within an image;

[0038] Fig. 13 shows an embodiment of a further diffraction pattern shifted within an image;

[0039] Fig. 14 shows an embodiment of a difference between a bundle block calibration in front of a diffractive optical element and in front of a physical 3D target; and

[0040] Fig. 15 is a flowchart of a method according to an embodiment.

[0041] 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.

[0042] Fig. 1 shows a schematic representation of an embodiment of a device 100 for calibrating a camera 102. The device 100 comprises a diffractive optical element 104 arranged in front of the camera 102. The diffractive optical element 104 is designed to generate a projection 106 of a diffraction pattern when the diffractive optical element 104 is exposed to electromagnetic radiation 108. The projection 106 is composed of a plurality of diffracted beams. For example, the electromagnetic radiation 108 is depicted as a laser beam emitted by a laser 110. The laser 110 or another suitable radiation source is optionally part of the device 100. The electromagnetic radiation 108 impinges on a surface of the diffractive optical element 104 facing away from the camera 102.The diffraction pattern projected using the diffractive optical element 104 is captured by an image sensor 112 of the camera 102.

[0043] By way of example, in the state illustrated in Fig. 1, the image sensor 112 is aligned parallel to the diffractive optical element 104. A propagation direction of the electromagnetic radiation 108 here follows, for example, an optical axis of the camera 102. In other states, the image sensor 112 and the diffractive optical element 104 are aligned differently to one another.

[0044] According to this exemplary embodiment, the projection 106 covers only a portion of the surface of the image sensor 112. To cover the entire surface of the image sensor 112, the diffractive optical element 104 and the camera 102 are moved relative to each other. For example, the camera 102 is tilted 114 while the diffractive optical element 104 remains stationary.

[0045] As a result, diffraction patterns projected onto different areas of the image sensor 112 can be captured successively using the diffractive optical element 104 and provided as images. Any number of captured diffraction patterns can be selected, with a relative movement between the camera 102 and the diffractive optical element 104 being performed between each two capture processes, according to one embodiment.

[0046] According to one embodiment, the device 100 comprises a determination device 116 which is designed to determine a calibration rule for calibrating the camera 102 using the detected diffraction patterns.

[0047] According to one embodiment, the camera 102 is rotated in front of the diffractive optical element 104 to enlarge the covered field of view. This enables fully automatic calibration of the camera 102 with the diffractive optical element 104. For this purpose, detected markers, here the diffraction pattern in an image captured by the camera 102, are automatically compared with corresponding diffraction orders of the diffractive optical element 104. For example, corresponding steps are performed using the determination device 116.

[0048] The camera 102 can be used, for example, in vehicles for driver assistance or automated driving systems and can provide several functions, including the detection of objects in the scene using various object detection algorithms. For many of these algorithms, the world-to-camera or camera-to-world transformation must be known, which means that the optical parameters of the camera 102 should be known. These parameters include the focal length, the principal point, and optical distortion parameters, such as radial and non-radial distortion effects.

[0049] The intrinsic calibration of camera 102 and the optical distortion can be measured during the production phase of camera 102. A space- and cost-saving method for camera calibration is based on the use of the diffractive optical element (DOE) 104. An embodiment of a corresponding basic configuration of laser 110, diffractive optical element 104, and camera 102 for the geometric camera calibration of camera 102 is shown in Fig. 1.

[0050] When a monochromatic plane wave, e.g., a laser beam, strikes the diffractive optical element 104, the incident beam is diffracted into multiple orders of diffraction by the precisely manufactured microstructure of the diffractive optical element 104. The Fraunhofer diffraction pattern is visible on a screen in the far field. By using powerful optical field simulation tools, it is possible to calculate the required microstructure to generate any desired diffraction pattern.

[0051] For camera calibration, the diffractive optical element 104 is placed directly in front of the camera 102. The camera optics then function as a Fourier lens. This results in the far-field diffraction pattern being projected onto the image plane. The plane waves of each diffraction angle are projected onto the image plane as individual points, as shown in Fig. 2. The pattern on the image sensor 112 is similar to a screen arranged at infinity. Naturally, the diffraction pattern on the image plane, i.e., the image sensor 112, also referred to as the camera sensor, is altered by lens distortion. This fact is used for camera calibration.

[0052] Fig. 2 shows a simulation of an embodiment of a diffraction pattern 200 captured by a camera. For example, the diffraction pattern 200 is a pattern projectable using the diffractive optical element described with reference to Fig. 1.

[0053] Known methods can be used to perform geometric camera calibration using a diffractive optical element. Currently, DOE suppliers can achieve diffraction angles of up to + / ■ 70°. This enables the calibration of cameras with a full field of view (FFOV) of up to 140°. Cameras with an FFOV of more than 140°, e.g., parking assistance cameras that can cover 200° or more, must currently be calibrated using traditional approaches, i.e., physical 3D targets. Even if larger diffraction angles can be achieved in the future, the physical limitation of a DOE is an FFOV of 180°, which is still insufficient for the aforementioned parking assistance cameras.

[0054] In addition, the design and manufacturing effort and costs for DOEs with large diffraction angles are significantly increased compared to DOEs with comparatively small diffraction angles.

[0055] Another aspect is the distribution of the diffraction angles. Since the diffraction angle α (for normal incidence angle) follows the rule α = α sin (m ■ g / α), where m is the diffraction order, g is the grating constant of the DOE, and g is the wavelength of the laser light, the diffraction angles are not distributed equidistantly in angular space. For example, the diffraction pattern 200 shown in Fig. 2 can be used as a reference pattern for the diffractive optical element used to calibrate the camera.

[0056] Fig. 3 shows a simulation of an embodiment of a diffraction pattern 300 of a diffractive optical element with large diffraction angles recorded with a camera with a large FOV.

[0057] For a DOE designed for a wavelength of 632.8 nm, with line count = 56.4 1 / mm and 28 x 28 diffraction orders (maximum diffraction angle = 89.5°), the diffraction pattern 300 on a parking camera would look as shown in Fig. 3.

[0058] Fig. 4 shows an output of an embodiment of an asin function 450 in the parameter range [0,1].

[0059] Due to the asin function shown in Fig. 4, the angular separation between the diffraction orders increases at large diffraction orders, resulting in a very thin coverage at larger angles.

[0060] This means that even in the future, when diffraction angles may be larger than 70°, calibrating a camera with a large FOV using a DOE that only acquires a single image will not be sufficient.

[0061] Currently, DOEs with diffraction angles of up to + / - 60° or + / - 70° are used for camera calibration. Therefore, camera calibration is currently limited to cameras with an FFOV of up to 120°, with a maximum of 140°.

[0062] The approach described here creates a technique that extends the capabilities of DOE-based camera calibration to cameras with very large FOV.

[0063] Fig. 5 shows an illustration of an embodiment of a device 100 for calibrating a camera 102 using a diffractive optical element 104. The device 100 corresponds, for example, to the device schematically illustrated in Fig. 1.

[0064] To enable relative movement between the camera 102 and the diffractive optical element 104, the camera 102 is held, for example, by an alignment device 560. The alignment device 560 enables movement of the camera 102 relative to the diffractive optical element 104 in order to convert a current angular position between the camera 102 and the diffractive optical element 104 into a further angular position. According to one embodiment, an image is captured using the camera 102 in each angular position. The alignment device 560 and the camera 102 are controlled, for example, using a control device, so that the camera 102 can be moved between successive recordings.

[0065] The camera 102, which is automatically rotated in front of the diffractive optical element 104, enables a bundle-block calibration to be carried out.

[0066] The idea behind this technique is to use a bundle block approach in combination with a diffractive optical element 104 to calibrate the camera 102 with a large FOV. To do this, multiple images are acquired, with the orientation of the camera 102 relative to the diffractive optical element 104 being changed between image acquisitions. It is important that the lens of the device under test, in this case the camera 102, is always centered very close to the diffractive optical element 104 to achieve optimal image quality.

[0067] By rotating the camera 102, or alternatively the diffractive optical element 104, for example, a configuration comprising a laser beam expander and a DOE, different parts of the sensor / FOV of the camera 102 are covered with each captured image. Depending on the field of view of the camera 102 and the diffraction angles of the diffractive optical element 104, the number of images required to cover the entire field of view can vary. For example, a diffractive optical element 104 with a diffraction angle of + / - 15° is used to calibrate the camera 102 with a horizontal FOV (hFOV) of 90°.

[0068] In series production, automatic positioning of the camera 102 in various orientations is required. This can be achieved with the alignment device 560, for example, in the form of a high-precision robot arm.

[0069] The following Figures 6 to 13 show nine images used for bundle block calibration according to one embodiment.

[0070] Fig. 6 shows an embodiment of a diffraction pattern 600 centered within an image 670. The image 670 was captured, for example, using the camera shown in Fig. 5.

[0071] In this image 670, the diffraction pattern 600 is centered within the image 670. It is clearly visible that the observable diffraction orders do not cover the entire field of view of the camera.

[0072] Outside the used diffraction orders, higher orders with lower intensities are observed. Due to the low intensities in these diffraction orders, robust detection for a sufficient number of orders is not possible.

[0073] Fig. 7 shows an embodiment of a diffraction pattern 700 that is arranged shifted within an image 760.

[0074] Fig. 8 shows an embodiment of a diffraction pattern 800 that is arranged shifted within an image 860.

[0075] Fig. 9 shows an embodiment of a diffraction pattern 900 that is arranged shifted within an image 960.

[0076] Fig. 10 shows an embodiment of a diffraction pattern 1000 that is arranged shifted within an image 1060. Fig. 11 shows an embodiment of a diffraction pattern 1100 that is arranged shifted within an image 1160.

[0077] Fig. 12 shows an embodiment of a diffraction pattern 1200 that is arranged shifted within an image 1260.

[0078] Fig. 13 shows an embodiment of a diffraction pattern 1300 that is arranged shifted within an image 1360.

[0079] The diffraction patterns 600, 700, 800, 900, 1000, 1100, 1200, 1300 shown in Figures 6 to 13 do not cover the entire field of view of the camera and thus the respective entire image 670, 770, 870, 970, 1070, 1170,

[0080] 1270. 1370. By different angular positions between the camera and the diffractive optical element, where the images 670, 770, 870, 970, 1070,

[0081] 1170, 1270, 1370 were recorded, however, every area of ​​the entire field of view of the camera was covered at least once by one of the diffraction patterns 600, 700, 800, 900, 1000, 1100, 1200, 1300.

[0082] Based on the nine images 670, 770, 870, 970, shown in Figures 6 to 13,

[0083] 1070, 1170, 1270, 1370: According to one embodiment, the camera was calibrated to a maximum angle of 93° (FFOV). This is three times as large as the DOE's diffraction angles would allow when capturing a single one of images 670, 770, 870, 970, 1070, 1170, 1270, and 1370. By capturing even more images, cameras with an even larger FOV can be calibrated with the same DOE. Since rotating the camera or DOE setup and capturing an image is time-consuming, it is naturally sensible to find an optimal compromise between increasing the DOE's diffraction angles and the number of positions required to cover the entire FOV.

[0084] Fig. 14 shows an embodiment of a difference 1480 between a bundle block calibration based on the images shown in Figures 6 to 13 in front of a diffractive optical element and, in comparison, in front of a physical 3D target. The results of the aforementioned calibration are thus compared with the results of a bundle block camera calibration using a physical 3D target. The difference in the 3D->2D projection of the two obtained intrinsic parameter sets is shown in Fig. 14.

[0085] Virtual 3D coordinates are projected onto a virtual 2D sensor, using both sets of intrinsic parameters. The difference in the 2D coordinates is shown.

[0086] The difference of approximately 1.5 pixels corresponds to an angular error of 0.055°, which only occurs at the outermost edge of the image. This represents a very good agreement between the two calibration methods.

[0087] Fig. 15 shows a flow diagram of an embodiment of a method for calibrating a camera using a diffractive optical element, as already described by way of example with reference to the preceding figures.

[0088] In a step 1501, a diffraction pattern is detected using an image sensor of a camera, which is projected onto the image sensor of the camera using the diffractive optical element while the diffractive optical element and the camera are in an angular position with respect to each other.

[0089] In a step 1503, a further diffraction pattern is acquired using the camera's image sensor, which is projected onto the camera's image sensor using the diffractive optical element while the diffractive optical element and the camera are in a further angular position relative to one another that differs from the angular position in step 1501. Optionally, step 1503 is repeatedly executed in order to acquire further diffraction patterns using the camera's image sensor, which are projected onto the camera's image sensor using the diffractive optical element while the diffractive optical element and the camera are in ever-new angular positions relative to one another, each of which differs from previously applied angular positions. In a step 1505, a calibration rule for calibrating the camera is determined using the acquired diffraction patterns.For example, the diffraction patterns are compared with a reference pattern assigned to the diffractive optical element.

[0090] Between steps 1501, 1503 and possibly successively executed steps 1503, a step 1507 is optionally executed in which the camera and the diffractive optical element are moved towards each other in order to convert the respective current angular position into a new angular position.

[0091] Optionally, the method comprises a step 1509 in which the diffractive optical element is exposed to electromagnetic radiation.

[0092] Using this method, it is possible to calibrate any camera with a DOE that covers only a small portion of the camera's FOV. By rotating the camera or the DOE setup, the covered FOV can even be expanded to over 180°, exceeding the physical limitations of single-shot DOE calibrations.

[0093] Advantageously, this enables the calibration of large-FOV cameras with a DOE, even when the DOE's diffraction angles do not cover the camera's entire FOV. This is achieved by varying the camera's orientation relative to the DOE and capturing multiple images used in a bundle block calibration.

[0094] The idea behind bundle block calibration is to capture images of a 3D scene from multiple perspectives. The different arrangements of the camera and 3D scene, as well as the large number of images, allow the number of observations to be significantly increased. A separate position and orientation in space is determined for each image. However, only one set of intrinsic calibration values ​​is determined for all images combined, which may describe the 3D-->2D projection of the camera. This set of calibration values ​​must therefore be valid for all images simultaneously. This allows a high degree of decoupling of intrinsic calibration values ​​from the position and orientation of the camera in space, which means increased confidence for the determined parameters. At the same time, as previously described, the covered field of view can be enlarged if the 3D scene itself does not fill the entire camera field of view.

[0095] This technique allows cameras with a FOV of more than 180° to be calibrated using a DOE.

[0096] Even if a DOE with a diffraction angle large enough to cover the field of view of a camera is available, it might be cheaper to use a DOE with a smaller FOV and rotate the camera.

[0097] Since some important quality parameters of the DOE decrease with increasing diffraction angles, such as the uniform intensity distribution across the diffraction orders, it may be advantageous for very high-quality camera calibrations to use a high-quality DOE with smaller diffraction angles and to cover the entire FOV by rotating the camera or the DOE setup.

[0098] Compared to the currently used physical 3D targets, this method enables a significant reduction in cost and volume of the test bench for cameras with a large FOV.

[0099] Compared to the physical 3D test benches currently in use, all object information is taken from a virtual infinity distance. This results in more precise camera calibration for targets at distances > 2 m.

[0100] As mentioned above, it is possible to rotate the DOE instead of the camera. If this option is preferred, it is necessary to ensure that the angle of incidence of the laser on the DOE is not changed or permanently redefined. This means rotating the laser itself or, if an optical fiber is used, the coupling and beam-shaping optics together with the DOE. With both options, it is necessary to ensure that the lens never touches the surface of the DOE, as this would damage the microstructure of the DOE.

[0101] In general, the described approach can be used very well for calibrating cameras with a large FOV, especially cameras with FFOV > 180°.

Claims

Claims 1 . A method for calibrating a camera (102) using a diffractive optical element (104), the method comprising the following steps: detecting (1501) a diffraction pattern (600) projected onto an image sensor (112) of the camera (102) using a diffractive optical element (104) while the diffractive optical element (104) and the camera (102) are in an angular position with respect to one another; Further detecting (1503) a further diffraction pattern (700) projected onto the image sensor (112) of the camera (102) using the diffractive optical element (104) while the diffractive optical element (104) and the camera (102) are in a further angular position relative to one another that differs from the angular position; and Determining (1505) a calibration rule for calibrating the camera (102) using the diffraction patterns (600; 700).

2. Method according to claim 1, wherein in step (1501) of detecting the diffraction pattern (600) is projected onto a portion of the image sensor (112) and in step (1503) of further detecting the further diffraction pattern (700) is projected onto a further portion of the image sensor (112) which differs at least partially from the portion.

3. Method according to one of the preceding claims, comprising a step (1507) of moving the camera (102) and the diffractive optical element (104) relative to each other in order to change the angular position to the further angular position, wherein the step (1507) of moving is carried out automatically.

4. Method according to one of the preceding claims, comprising a step (1509) of subjecting the diffractive optical element (104) to electromagnetic radiation (108) from a side facing away from the camera (102).

5. Method according to one of the preceding claims, wherein a diffraction angle of the diffractive optical element (104) is smaller than a field of view of the camera (102).

6. Method according to one of the preceding claims, wherein the field of view of the camera (102) is greater than 180°.

7. Method according to one of the preceding claims, wherein the step (1503) of further detecting is carried out repeatedly in order to obtain a plurality of further diffraction patterns (800; 900; 1000; 1100; 1200; 1300) which are projected onto the image sensor (112) of the camera (102) using the diffractive optical element (104), while the diffractive optical element (104) and the camera (102) are in a plurality of further angular positions relative to one another which differ from the angular position.

8. Method according to one of the preceding claims, wherein in the determining step (1505) the calibration rule is determined by comparing the diffraction patterns (600; 700) with a reference pattern associated with the diffractive optical element (104).

9. Device (100) for calibrating a camera (102), wherein the device (100) is configured to carry out and / or control the steps of the method according to one of the preceding claims in corresponding units.

10. Computer program configured to execute and / or control the steps of the method according to one of claims 1 to 8.

Images