DESCRIPTION OF THE DISCLOSURE

The present disclosure relates to a method and device for calibration and/or testing of an optical assembly such as a camera device or a lens device.

Many vehicle environment detection systems comprise one or more sensors such as for example radar sensor, LIDAR sensors, camera devices and ultrasonic sensors. These are used for collecting data used for safety arrangements as well as for driver assistance systems.

Camera devices are used to collect object data from the environment and to form an image from these object data. For this purpose, the camera device comprises a lens device and an image sensor/recording device onto which the image is projected by means of the lens device.

Due to lens design, distortion may occur during image formation, visible in the formed image as either pincushion or barrel distortion. When testing or calibrating a camera device or a lens only device, object data are collected from a plurality of target objects which are distributed, and, in the case of for example spatial frequency response (SFR) calculations, usually comprise slanted edges as described in IS012233. A certain slant angle interval is required in order to be able to use the collected object data for each target object. However, as a result of the previously mentioned distortion, the slant angles of the target objects may be changed when the corresponding images are formed. These angles may be outside an acceptable interval for test image evaluation, which may adversely affect the quality of such a measurement .

It is therefore desirable to provide an enhanced test, calibration and/or quality assessment method and corresponding device where distortion is managed or controlled in such a way that this negative effect is reduced or eliminated.

The object of the present disclosure is to provide such a test, calibration and/or quality assessment method and corresponding device.

This object is obtained by means of a target object arrangement for testing and/or calibrating an optical assembly that at least comprises a lens device. The target object arrangement comprises at least one target object adapted to be positioned at a plurality of positions with regard to a center for a horizontal axis and a vertical axis, where each target object has at least one defined straight edge. Said target object is arranged at each one of said plurality of positions such that, for each position, at least one straight edge coincides with an extension that extends from the center and presents a predetermined slant angle to the horizontal axis or the vertical axis such that the slant angle is the same for all positions.

In this way, a geometry is provided where the slant angle is preserved during the transformation from object to image space via the lens assembly. This means that the distortion is managed or controlled in such a way that its negative effects are reduced or eliminated

According to some aspects, each target object comprises two perpendicular straight edges. In this way, two straight edged can be used for test, calibration and/or quality assessment.

According to some aspects, there is a first extension that presents the slant angle to the horizontal axis and a second extension that presents the slant angle to the vertical axis.

According to some aspects, the images of said target object are arranged symmetrically along the extensions.

According to some aspects, the slant angle is defined in the interval 7 ° ±4 ° .

This corresponds to some standards.

According to some aspects, the horizontal axis and the vertical axis correspond to a horizontal image axis and a vertical image axis formed relative a sensor pixel grid on the image sensor.

According to some aspects, the optical assembly is constituted by a camera device with a lens device and an image sensor.

In this way, the lens device can independently be subject to test, calibration and/or quality assessment.

The present disclosure also relates to a corresponding method that is associated with the above advantages.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will now be described more in detail with reference to the appended drawings, where: Figure 1 shows a schematical cut-open side view of a camera device in a calibration/test setup;

Figure 2 shows a schematical front view of a typical target object arrangement according to prior art;

Figure 3 shows a schematical front view of a target object featuring slanted edges, with its corresponding image to the right;

Figure 4 shows a schematical front view of a target obj ect arrangement according to the present disclosure

Figure 5 shows a schematical front view of an image of a target object arrangement according to the present disclosure ;

Figure 6 shows a schematical perspective side view of the

target object arrangement and a lens device;

Figure 7 shows a flowchart for a method according to the present disclosure; and

Figure 8 shows a schematical side view of a lens device in a calibration/test setup.

DETAILED DESCRIPTION

Figure 1 schematically shows a schematic cut-open side view of a camera device 1 that comprises a lens device 2, an image sensor 3 or any other light sensitive device on which the image is formed for further processing, and a control/memory unit 20. The image sensor 3 comprises a schematically indicated sensor pixel grid 40. The camera device 1 can point into any direction in space. Without loss of generality, in the following a local coordinate system relative to the sensor pixel grid 40 is used to describe the test geometry. The vertical and horizontal directions are defined to lie within the sensor surface and are parallel to either cardinal direction of the sensor pixel grid 40.

During camera device calibration, testing or quality assessment, a spatial frequency response (SFR) is calculated. The corresponding measurement on a lens device produces a so- called modulation transfer function (MTF) . The naming convention is to a certain degree arbitrary and the evaluation of a test image for either the lens device 3 or the camera device 1 is fundamentally the same, except that for lens device testing, the contribution from the image sensor 3 is removed from the results. In the following and without loss of generality, MTF is used to describe both cases.

To calculate the MTF, the lens creates images of test objects, or target objects, with a lower angular resolution than the geometrical image of an ideal lens, which perfectly matches the target object.

Pin-cushion and barrel distortion are two example of common distortions. For sampling reasons, the image of the test target objects should feature slanted edges relative to the sensor pixel grid 40 of the image sensor 3 as described in e.g. IS012233 : 2017.

Figure 2 shows an example of a prior art target object arrangement forming a test device 21 with a plurality of target objects 22, 23, 24, 25, 26, 27, 28, 29, 30 which all have a slant angle a as illustrated for a first straight edge 31 and a second straight edge 32 at a target object 200 in Figure 3. The first straight edge 31 presents the slant angle a to a horizontal axis 33 and the second straight edge 32 presents the slant angle a to a vertical axis 34. The target objects 22, 23, 24, 25, 26, 27, 28, 29, 30 are arranged at several imaging field points, adapted for probing imaging system quality at this particular position/direction.

When the objects are transformed to an image on the image sensor 3 by the lens device 2, as illustrated for a target object image 200' in Figure 3 where the imaging is indicated with an arrow A, both slant angles a are usually altered.

In Figure 3, horizontal distortion is acting on non-horizontal and non-vertical target edges, and the vertical and horizontal slant angles alter differently. Distortion affects slant angles in image space. In the general case, where slant angles are neither parallel nor orthogonal to the acting distortion, both angles will be changed.

In more detail, the target object image 200' has a first straight image edge 31' that presents a first image slant angle f to a horizontal image axis 33' , and a second straight image edge 32' presents a second image slant angle d to a vertical image axis 34' . The slant angle a for the object 25 is inserted for reasons of comparison. As stated above, according to some aspects, the first image slant angle f and the second image slant angle d may in general have mutually different values.

As illustrated in Figure 4, there is a device 19 for testing and/or calibrating a camera device 1 according to the above, the camera device 1 being subjected to the limitations discussed above. The device 19 constitutes a target object arrangement and comprises six target objects 7, 8, 9, 10; 11,

12 positioned at a plurality of positions with respect to a center 4 on the intersection of a horizontal axis 5 and a vertical axis 6. Each target object 7, 8, 9, 10; 11, 12 has a first straight edge 13, 15 and a second straight edge 14, 16.

According to the present disclosure, the target objects 7, 8,

9, 10; 11, 12 are arranged at each one of said plurality of positions such that, for each position, at least one straight edge 13, 14; 15, 16 coincides with an extension 17, 18 that extends from the center 4 at a predetermined slant angle a to the horizontal axis 5 or the vertical axis 6 or is orthogonal to it. In this manner, the slant angle a is the same for all positions, and each straight edge 13, 14; 15, 16 has an inclination of the slant angle a with respect to the horizontal axis 5 or the vertical axis 6. The geometry effectively describes a purely sagittal and meridional MTF measurement for each position in object space, which effectively circumvents the problem of slant angle change during image formation.

According to some aspects, as shown in Figure 4, there is a first extension 17 that presents the slant angle a to the horizontal axis 5 and a second extension 18 that presents the slant angle a to the vertical axis 6. sagittal According to some aspects, four target objects 7, 8, 9, 10 are arranged symmetrically on the first extension 17 with respect to the center 4, and two other target objects 7, 8, 9, 10 are arranged symmetrically on the first extension 17 with respect to the center 4.

With reference to Figure 5, the target object arrangement 19 is shown transformed to image space and projected on the image sensor 3 with its sensor pixel grid 40. The sensor pixel grid 40 is only schematically indicated in Figure 5. Corresponding target object images 7', 8', 9', 10'; 11', 12' are shown, where the center 4 in Figure 4 here corresponds to a distortion center 4', where furthermore there is a corresponding horizontal image axis 5' and vertical image axis 6' formed relative the sensor pixel grid 40 on the image sensor 3. There is further a corresponding first image extension 17' that presents the slant angle a to the horizontal image axis 5' and a second image extension 18' that presents the slant angle a to the vertical image axis 6' . The slant angle a is preserved during the transformation from object to image space at the image sensor 3 via the lens assembly 2.

The target object images 7', 8', 9', 10'; 11', 12' are arranged along the image extensions 17', 18' and have corresponding meridional straight image edges 14', 15' and corresponding orthogonal, i.e. sagittal, straight image edges 13', 16', where the straight image edge 13', 14'; 15', 16' coincide with the corresponding extension 17', 18'. Therefore, each straight image edge 13', 14'; 15', 16' has an inclination of the slant angle a with respect to the horizontal image axis 5' or the vertical axis 6' , and the inclination of the straight image edges 13', 14'; 15', 16' is preserved during the transformation from object to image space on the image sensor 3 via the lens assembly 2.

Although the target object images 7', 8', 9', 10'; 11', 12' are subjected to distortion compared to the corresponding target objects 7, 8, 9, 10; 11, 12 as indicated in Figure 5, the distortion takes place radially relative to the distortion center 4' and thus also along the image extensions 17', 18', and by the inventive arrangement of the target objects 7, 8,

9, 10; 11, 12, the slant angle a is preserved for the straight image edge 13', 14'; 15', 16' of the target object images 7',

8', 9', 10'; 11', 12'. This underlying principle is true and applies for any measurement on a meridional edge, i.e. sagittal MTF measurement. It is true to first order for any meridional MTF measurement using a sagittal edge.

According to some aspects, the present disclosure relies on the geometry used for the target objects 7, 8, 9, 10; 11, 12 at the target object arrangement 19.

For sampling reasons, according to some aspects, the slant angle a is frequently chosen as a shallow angle about 7°. In general and for application of this concept, a may have any suitable value for performing calibration and/or testing. According to some aspects, the slant angle a is defined in the interval 7 ° ±4 ° .

Figure 6 illustrates an example of viewing angles in relation to a part of the target object arrangement 19 with a test target object 8. A sightline 35 connects the test target object 8 to the image sensor through an entrance pupil determined by the lens device 2. According to some aspect, this defines a field angle p relative to an optical axis z. The slant angle a is also indicated.

With reference to Figure 7, the present disclosure relates to a method for testing and/or calibrating an optical assembly, where the optical assembly at least comprises a lens device 2, 2a. The method comprises capturing S101 images of at least one target object 7, 8, 9, 10; 11, 12 at a plurality of positions with regard to a center 4 for a horizontal axis 5 and a vertical axis 6 using an image sensor 3. Each target object 7, 8, 9, 10; 11, 12 has at least one defined straight edge 13,

14; 15, 16. The method further comprises arranging S102 said target object 7, 8, 9, 10; 11, 12 at each one of said plurality of positions such that, for each position, at least one straight edge 13, 14; 15, 16 coincides with an extension 17, 18 that extends from the center 4 and presents a predetermined slant angle a to the horizontal axis 5 or the vertical axis 6 such that the slant angle a is the same for all positions.

According to some aspects, each target object 7, 8, 9, 10; 11, 12 comprises two perpendicular straight edges 13, 14; 15, 16.

According to some aspects, there is a first extension 17 that presents the slant angle a to the horizontal axis 5 and a second extension 18 that presents the slant angle a to the vertical axis 6.

According to some aspects, the method comprises arranging S1021 the images of said target object symmetrically along the extensions 17, 18.

According to some aspects, the horizontal axis 5 and the vertical axis 6 correspond to a horizontal image axis 5' and a vertical image axis 6' formed relative a sensor pixel grid 40 on the image sensor 3.

According to some aspects, the optical assembly is constituted by a camera device 1 with a lens device 2 and an image sensor

3.

The present disclosure is not limited to the examples above, but may vary freely within the scope of the appended claims. For example, the target object arrangement 19 can comprise all the targets objects 7, 8, 9, 10; 11, 12 which are distributed on a surface. Alternatively, the target object arrangement 19 can comprise one or more targets objects, but less than all the target objects of the target object arrangement 19, where said one or more targets objects can be moved to the desired positions such that the positions of all the targets objects 7, 8, 9, 10; 11, 12 are occupied by a target object over time.

As described above, the target object arrangement 19 can be used for testing and/or calibrating a complete camera device 1. Alternatively, as shown in Figure 8, the target object arrangement 19 can be used for testing and/or calibrating a lens device 2a only. In the latter case, a separate image sensor 3a is used for capturing images from the lens device

2a. The lens device 2a and the separate image sensor 3a are attached to a test fixture (not shown) in a previously well- known manner.

The number of target objects can be of any suitable number, and the target objects can be distributed along the extension in any suitable manner that need not be symmetrical.

The lens device may be an individual lens or a lens assembly/obj ective lens that can comprise a complex lens system with lens objectives.

The image sensor 3 is to be regarded as constituted by any kind of light sensitive device on which one or more images are formed for further processing, and can be comprised in an image plate.

The particular shape and pattern of a target object may vary, but common to all are straight lines at an angle relative to the cardinal directions of the image sensor that are then used to determine image sharpness. Any target object design with a straight line can be used. The camera device 1 can according to some aspects be a vehicle camera device that is comprised in a vehicle environment detection system.

Generally, the present disclosure also relates to a target object arrangement 19 for testing and/or calibrating an optical assembly that at least comprises a lens device 2, 2a. The target object arrangement 19 comprises at least one target object 7, 8, 9, 10; 11, 12 adapted to be positioned at a plurality of positions with regard to a center 4 for a horizontal axis 5 and a vertical axis 6, where each target object 7, 8, 9, 10; 11, 12 has at least one defined straight edge 13, 14; 15, 16. Said target object 7, 8, 9, 10; 11, 12 is arranged at each one of said plurality of positions such that, for each position, at least one straight edge 13, 14; 15, 16 coincides with an extension 17, 18 that extends from the center 4 and presents a predetermined slant angle a to the horizontal axis 5 or the vertical axis 6 such that the slant angle a is the same for all positions.

According to some aspects, each target object 7, 8, 9, 10; 11, 12 comprises two perpendicular straight edges 13, 14; 15, 16.

According to some aspects, there is a first extension 17 that presents the slant angle a to the horizontal axis 5 and a second extension 18 that presents the slant angle a to the vertical axis 6.

According to some aspects, the images of said target object are arranged symmetrically along the extensions 17, 18.

According to some aspects, the slant angle a is defined in the interval 7 ° ±4 ° . According to some aspects, the horizontal axis 5 and the vertical axis 6 correspond to a horizontal image axis 5' and a vertical image axis 6' formed relative a sensor pixel grid 40 on the image sensor 3.

According to some aspects, the optical assembly is constituted by a camera device 1 with a lens device 2 and an image sensor

3.