Method for operating a camera with a first operating mode and a second operating mode, camera and motor vehicle

Abstract

A method for operating a camera (2) of a motor vehicle (1), in which the camera (2) is operated in a first operating mode (12) and in the first operating mode (12) an image (13) of an area (7) of the motor vehicle (1) is recorded with the camera (2), wherein a histogram (14) of the image (13) is determined and a histogram area (26) is determined in the histogram (14), characterized in that all frequency values ​​(25) of intensity value classes (22) of the histogram (14) in the histogram area (26) are compared with a frequency limit (27) and the camera (2) is switched from the first operating mode (12) to a second operating mode (15) different from the first operating mode (12) (S2) if the compared frequency values ​​(25) in the histogram area (26) are less than the frequency limit (27).wherein in the second operating mode (15) another image (16) is taken with the camera (2) and the camera (2) is operated with an identical exposure setting (18) in the first operating mode (12) and in the second operating mode (15) wherein the method allows switching back and forth between an operating mode, in particular the first operating mode (12), for more reliable detection of oncoming motor vehicles and an operating mode, in particular the second operating mode (15), with higher image quality, in particular sharper edges and less noise.

Description

[0001] The invention relates to a method for operating a camera of a motor vehicle. The camera is operated in a first operating mode. In the first operating mode, an image of an area surrounding the motor vehicle is captured with the camera. Furthermore, a histogram of the image is determined, and a histogram range is determined within the histogram. The invention also relates to a camera configured to carry out the method and to a motor vehicle with a corresponding camera.

[0002] Methods for operating a camera in a motor vehicle are known from the prior art. For example, US 2014 / 0111637 A1 shows an image recording device for capturing an image outside a motor vehicle. The camera is operated in an exposure-dependent manner. It is generally known to determine histograms of images to create a mask for noise enhancement (see US 2015 / 0 350 513 A1).

[0003] Other known methods involve operating the camera with different exposure settings for day and night, for example. For example, the camera's exposure time is typically increased when operating at night. The light sensitivity of the camera's image sensor is also usually adjusted accordingly.

[0004] A disadvantage, however, is that the camera's exposure settings cannot be adjusted arbitrarily. The simultaneous depiction of bright and dark objects in one image is also problematic. Bright objects typically require a different exposure setting than dark objects to achieve a detailed depiction of the respective objects.

[0005] The object of the invention is to show a solution how a camera of a motor vehicle can be operated in such a way that an area surrounding the motor vehicle can be imaged with less noise and in more detail.

[0006] This object is achieved according to the invention by a method, a camera, and a motor vehicle having the features according to the respective independent claims. Advantageous embodiments of the invention are the subject of the dependent claims, the description, and the figures.

[0007] In a method according to the invention, a camera of a motor vehicle is operated. The camera is operated in a first operating mode, and in the first operating mode, an image of an area surrounding the motor vehicle is recorded with the camera. A histogram of the image is determined, and a histogram range is determined in the histogram. An essential idea of ​​the invention is that all frequency values ​​of intensity value classes of the histogram in the histogram range are compared with a frequency threshold, and that the camera switches from the first operating mode to a second operating mode that is different from the first operating mode if the compared frequency values ​​in the histogram range are smaller than the frequency threshold. In the second operating mode, another image is recorded with the camera.The camera is operated in the first operating mode and in the second operating mode with an identical exposure setting.

[0008] The method according to the invention makes it possible to operate a camera of a motor vehicle in such a way that a bright object relevant to traffic technology is imaged more clearly or in more detail, particularly in poor lighting conditions, for example at night, and a comparatively dark surrounding area is imaged more clearly or in more detail.

[0009] Each intensity value class represents a bin or column of the histogram. The intensity value class can, for example, comprise one or more intensity values ​​of the image. The height of each column of the histogram is then described by the respective frequency value.

[0010] This is possible thanks to the first and second operating modes. In the first operating mode, the camera is operated in such a way that a bright object is imaged with a finely incremented intensity value interval. Due to the finer intensity value interval, the brightness differences between the intensity values ​​for bright objects are smaller than is the case in the second operating mode. Small differences in the brightness of the bright object are therefore visible in the image. As a result, it is then possible to determine, for example, whether the bright object is the headlights of another vehicle in the surrounding area. In the second operating mode, emphasis is placed on clearly showing the surrounding area that is darker than the bright object. To do this, for example, the darker surrounding area is imaged with a finely incremented intensity value interval.Dark objects in the surrounding area can therefore be recognized more clearly and, for example, assigned to a class of obstacles for the vehicle.

[0011] The switch from the first operating mode to the second operating mode depends on the histogram of the image captured in the first operating mode. The switch occurs when all frequency values ​​in the histogram range are smaller than the frequency threshold. It can then be assumed that no bright object is present in the image. As a result, the camera switches to the second operating mode to capture the dark surrounding area more clearly, i.e., in more detail. However, it may happen that the bright object is no longer captured as clearly in the second operating mode as in the first operating mode.

[0012] The camera's exposure setting is identical during the first operating mode and the second operating mode. This allows the image and subsequent images to be captured with higher quality—i.e., with greater detail and less noise—than if the exposure setting were adjusted. For the second operating mode, the exposure setting from the first operating mode is retained. The exposure setting, in particular, specifies the camera's exposure time. However, the exposure setting can also include the light sensitivity of a camera's image sensor or the image sensor's gain setting.

[0013] In the second operating mode, the exposure time could also be increased, as less bright areas are captured. For example, the exposure time can be adjusted within a tolerance interval from the first operating mode to the second operating mode. However, with a longer exposure time, moving objects will be imaged less sharply, which would result in a lower quality of the rest of the image. If, for example, the vehicle moves with the camera, many objects—actually static in the Earth-fixed coordinate system—take on precisely the role of moving objects.

[0014] Both the first operating mode and the second operating mode are specifically intended as night operating modes, in contrast to a day operating mode of the camera which is not further described.

[0015] Preferably, the histogram range is determined within 20%, in particular 15%, of the intensity value range of the histogram with the highest intensity values, and thus the histogram range is determined within, in particular, 20%, in particular 15%, of the highest intensity values ​​of the entire intensity value range of the histogram. The histogram range is therefore preferably determined in the range of the histogram with the brightest intensity values. As a result, the histogram range can be used to determine, for example, whether there is a bright object in the image. The histogram range therefore preferably extends only within the last fifth of the intensity value range of the histogram. In particular, the histogram range also extends only within the last 15% of the intensity value range.This allows the change from the first operating mode to the second operating mode to be carried out even more reliably, since the change only occurs when bright objects falling into the last 20%, in particular the last 15%, of the intensity value range are present.

[0016] Preferably, the image in the first operating mode is recorded or generated using a first tone mapping method, in particular a local one, and the further image in the second operating mode is recorded using a second tone mapping method that is different from the first tone mapping method, in particular a local one, wherein a dynamic range of the further image is reduced less by the second tone mapping method than a dynamic range of the image recorded using the first tone mapping method. Preferably, the first tone mapping method and / or the second tone mapping method is a local tone mapping method. The tone mapping method, which is also referred to as a dynamic compression method, compresses the dynamic range of high-contrast images or HDR images (HDR - high dynamic range), i.e. digital images with a high brightness range.For example, tone mapping reduces the contrast range of a high-contrast image so that it can be displayed losslessly on output devices designed for lower dynamic ranges. Tone mapping operators used for the respective tone mapping process can be divided into the operator classes listed below. So-called global operators use a function that assigns a dynamic range compressed value to each HDR value and is applied to each pixel. In contrast, with local operators, this function is varied for each pixel depending on the local adaptation level. Frequency-based operators use a different technique in which the dynamic range of image regions is reduced depending on the spatial frequency.Finally, there are gradient-based operators that attenuate the brightness gradients of the source image for each pixel to create an LDR (low dynamic range) image. Unlike global operators, local operators can process a larger number of HDR images because they can represent a wider dynamic range without losing detail. Local operators assume that human brightness perception does not adapt to the entire image, but only to smaller regions. Overall, the wider image is thus recorded with less noise and sharper than the original.

[0017] Preferably, the image in the first operating mode is recorded using a first tone mapping method, in particular a local one, and when recording the further image in the second operating mode, the first tone mapping method, in particular any tone mapping method, is deactivated. As a result, the further image is recorded with less noise and sharper than the image, analogous to the advantageous description of the second tone mapping method.

[0018] Preferably, in the second operating mode, a plurality of adjacent image sensor elements of an image sensor of the camera are combined to form an image sensor element block of the image sensor, and the further image is recorded depending on the image sensor element block. The image sensor element block comprises, in particular, at least two image sensor elements. Pixel binning combines pixel information of the further image, in particular in the charge domain of the image sensor. In particular, the adjacent image sensor elements of the image sensor of the camera are combined. By forming image sensor element blocks, a higher light sensitivity per virtual image sensor element is achieved, wherein the signal-to-noise ratio is improved because the noise is statistically distributed. In return, however, the image resolution is also reduced in proportion to the number of combined image sensor elements, and the image becomes coarser.With pixel binning, image sensor elements are grouped together, for example, within a row and / or column. This grouping occurs by adding the brightness values, either analogically through physical charge addition and charge transport on the image sensor itself to the local line amplifier and / or digitally by adding the digitized values. Analog binning increases the camera's frame rate because fewer image sensor elements need to be read out and digitized. With an image ratio of 4:1, for example, the image sensor elements are output at half the horizontal frequency and the vertical frequency is maintained. Because the number of rows is half, capturing an image then takes only half as long. The exposure time is thus halved per virtual image sensor element, which theoretically already has four times the amount of charge.Alternatively, the adjacent image sensor elements of a line are combined in analog form, while the adjacent lines can also be combined digitally, for example. A further advantage of this method is the reduction in bandwidth during transmission to the downstream processing system, particularly when using very high-resolution sensors whose number of pixels is not required for the specific application – but where a high dynamic range is important and subsequent combining would be necessary anyway. In addition, combining can be performed not only by the chip matrix but also by a digital signal processor connected downstream of the analog-to-digital converter. Such sensors can be configured externally via a digital interface, for example, to set the desired image resolution and pre-filtering.A permanent brightness adjustment can also be performed to adjust a binning ratio to the prevailing exposure of the surrounding area.

[0019] Preferably, it is further provided that a number of image sensor elements combined to form the image sensor element block in the second operating mode is determined based on a total number of image sensor elements of the camera's image sensor and / or a resolution of a display for outputting the additional image. Based on the total number of image sensor elements and / or the resolution of the display, the number of image sensor elements in the image sensor element block is determined more accurately as needed. The number is therefore determined to be neither too low nor too excessive for the current situation. If the number is too low and the image sensor element block is therefore too small, the effect of pixel binning will be too small, whereas if the number is too high and the image sensor element block is therefore too large, the number of pixels will be unnecessarily reduced.

[0020] Preferably, it is provided that a further histogram range is determined within 20% to 80%, in particular from 30% to 70%, based on the intensity values ​​of the intensity value range of the histogram, and the change to the second operating mode is suppressed if a frequency value of an intensity value class in the further histogram range of the histogram is greater than a further frequency limit value. Based on the further histogram range arranged in the middle region of the intensity value range of the histogram, conclusions can be drawn about the temperature of the camera's image sensor. For example, the further histogram range shows at least one frequency value that is greater than the further frequency limit value when the temperature of the image sensor has reached or exceeded a certain temperature. A disadvantageous consequence of an increased temperature of the image sensor is increased noise in the image.In this case, the switch to the second operating mode is suppressed, in particular until the frequency value, in particular all frequency values ​​in the wider histogram range, is / are again less than or equal to the frequency threshold and it can therefore be assumed that the temperature is again at a level at which the image noise is acceptable for image quality. Based on the wider histogram range, the switch to the second operating mode can therefore be temperature-dependent, without the temperature of the image sensor having to be explicitly measured with a temperature sensor on the camera. In addition, the image sensor temperature can also be measured with a temperature sensor and incorporated into the decision about switching between the first operating mode and the second operating mode.

[0021] Preferably, it is provided that a further histogram of the further image is determined and a further histogram range is determined within 20% to 80%, in particular from 30% to 70%, based on the intensity values ​​of the intensity value range of the further histogram, wherein a change is made from the second operating mode to the first operating mode if a frequency value of an intensity value class in the further histogram range of the further histogram is greater than a further frequency limit value. The further histogram range is preferably also determined in the further histogram of the further image. This makes it possible to change back from the second operating mode to the first operating mode if, due to increased image sensor temperature, at least one frequency value within the further histogram range exceeds the further frequency limit value.If the image sensor temperature increases, the quality of the subsequent image would no longer be sufficient and it would preferentially switch back to the first operating mode.

[0022] In one embodiment, it can be provided that a temperature of an image sensor of the camera is determined and the switch to the second operating mode is suppressed if the temperature of the image sensor is greater than a temperature threshold. The advantage of temperature-dependent operation is also present here, as already described. In addition to determining the temperature, the switch can also be carried out depending on the evaluation of the further histogram range. Preferably, the temperature of the image sensor is determined or measured using a temperature sensor of the camera. Determining the temperature using the temperature sensor is advantageous because the temperature can then be determined precisely and thus the temperature-dependent operation of the camera in the first operating mode and in the second operating mode is more reliable. Furthermore, the ambient area is imaged with less noise thanks to the temperature-dependent operation.

[0023] Preferably, it is provided that a further histogram of the further image is determined and the histogram range in the further histogram is determined, wherein a change is made from the second operating mode back to the first operating mode if a frequency value of an intensity value class of the further histogram in the histogram range of the further histogram is greater than the frequency limit. In the event that, due to the frequency limit being exceeded by a frequency value within the histogram range of the further image, an image of a bright object is assumed in the further image, and thus the prerequisites for changing from the first operating mode to the second operating mode are no longer met, a change is preferably made from the second operating mode back to the first operating mode.This means that the surrounding area continues to be depicted with appropriate detail and clarity for the objects arranged in the surrounding area.

[0024] In particular, the change from the second operating mode back to the first operating mode is carried out depending on a hysteresis. The hysteresis is also referred to as the switching differential. This means that the change is no longer carried out depending on the fixed frequency limit. Instead, the change from the second operating mode back to the first operating mode only occurs if the frequency value is greater than the frequency limit plus a hysteresis value. The hysteresis value can, for example, be up to 10% of the frequency limit or more. In addition or alternatively, the change from the first operating mode to the second operating mode can also be carried out depending on a hysteresis. The change to the second operating mode only occurs when the frequency value is less than the frequency limit minus the hysteresis value.The hysteresis-dependent change is advantageous because it prevents high-frequency switching back and forth between the operating modes if the frequency value changes slightly within a short period of time around the frequency limit and alternately falls below it by less than, for example, 10% and exceeds it by less than, for example, 10%.

[0025] In particular, the switch to the second operating mode is also suppressed depending on the hysteresis if the frequency value of the intensity value class in the further histogram range is greater than the further frequency limit plus an additional hysteresis value. The additional hysteresis value can also be, for example, 10% of the further frequency limit.

[0026] It is preferably provided that light from motor vehicle lighting of another motor vehicle present in the surrounding area is depicted in the image and that the depicted light is unambiguously assigned to a part of a first light source of the motor vehicle lighting and unambiguously to a further part of a second light source of the motor vehicle lighting. In the first operating mode, the other motor vehicle is preferably detected by the motor vehicle lighting being detected as two spaced-apart light sources, namely the first light source and the second light source. Two light sources arranged at a certain distance from one another and appearing highly similar in terms of their shape and light color are, for example, an indication of the headlights of the other motor vehicle. It is advantageous that the other motor vehicle is thereby reliably detected in the image.Light sources depicted in the image can therefore be classified, preferably, as to whether they belong to another motor vehicle or to a non-motor vehicle object in the surrounding area. The assignment or recognition of the motor vehicle lighting as two spaced-apart light sources is performed, in particular, using a machine vision method.

[0027] In a further embodiment, it can be provided that the camera is operated with an identical gamma value in the first operating mode and in the second operating mode. The gamma value refers to a compensation factor of an imaging system adapted to the perception of the human eye. This gamma correction performed based on the gamma value is, in particular, a correction function for converting a physically proportionally increasing quantity into a quantity that grows non-linearly according to human perception. The gamma value is preferably retained unchanged in the first operating mode and the second operating mode in order to be able to provide the subsequent image with higher image quality.

[0028] Furthermore, it can be provided that when the further image is recorded in the second operating mode, black region clipping and / or a limitation of the dynamic range of the further image is deactivated. Clipping combines part of the intensity value range of the image into a single value, usually a value at the respective end of the intensity value range, for example 0 or 255, in the case of an 8-bit intensity value range. Black region clipping describes the combining of dark intensity values ​​of the intensity value range that are adjacent to the intensity value 0. As a result, a larger part of the intensity value range remains for the imaging of the remaining, brighter brightness values ​​of the surrounding area. The dynamic range or dynamic range refers in particular to the quotient of the largest and smallest brightness value that can be distinguished from noise or grain.The quotient can be specified as f-stops in the logarithm of 2. The dynamic range of a subject in the surrounding area often far exceeds the dynamic range of the camera. A high-contrast image can, for example, be captured by the camera with a single shot or created from a series of images with a low dynamic range. The individual shots are combined in such a way that the contrast of the subject is fully captured and absolute brightness values ​​are stored. To output a high-contrast image on a medium with a lower dynamic range, such as a display, a tone mapping process or dynamic compression is used.

[0029] The invention also relates to a camera for a motor vehicle, which is designed to carry out a method according to the invention.

[0030] In particular, the camera has a motor vehicle fastening element with which the camera can be attached to a motor vehicle.

[0031] The camera is preferably part of a driver assistance system of the motor vehicle, for example, a camera monitoring system (CMS), which can at least partially capture the area surrounding the motor vehicle. In the camera monitoring system (CMS), the exterior mirrors of the motor vehicle are preferably replaced by cameras. An image captured by the camera can then be used, for example, to detect traffic-relevant objects in the surrounding area, such as another motor vehicle.

[0032] Furthermore, the invention also relates to a motor vehicle with a camera according to the invention.

[0033] The preferred embodiments presented with reference to the method according to the invention and their advantages apply accordingly to the camera according to the invention and to the motor vehicle according to the invention.

[0034] Both the concrete values ​​of parameters stated in the documents and the specification of parameters and the relationship between parameters for characterising specific properties of the camera are to be regarded as being encompassed by the scope of the invention, even in the case of deviations, for example due to measurement errors, system errors, DIN tolerances, etc., so that in this context, statements regarding the equality of values ​​of said parameters are to be regarded as “essentially” the same, even in the case of a statement.

[0035] Further features of the invention emerge from the claims, the figures and the description of the figures. The features and combinations of features mentioned above in the description, as well as the features and combinations of features mentioned below in the description of the figures and / or shown alone in the figures can be used not only in the respective combination specified, but also in other combinations without departing from the scope of the invention. Thus, embodiments are to be regarded as encompassed and disclosed by the invention that are not explicitly shown and explained in the figures, but which emerge and can be produced by separate combinations of features from the explained embodiments. Embodiments and combinations of features are also to be regarded as disclosed that therefore do not have all the features of an originally formulated independent claim.Furthermore, embodiments and combinations of features are to be regarded as disclosed, in particular by the embodiments set out above, which go beyond or deviate from the combinations of features set out in the reliances of the claims.

[0036] The invention will now be explained in more detail using a preferred embodiment and with reference to the accompanying drawings.

[0037] Showing: Fig. 1 a schematic representation of an embodiment of a motor vehicle according to the invention with a camera; Fig. 2 shows a flowchart of an embodiment of a method according to the invention for operating the camera with a change from a first operating mode of the camera to a second operating mode of the camera; Fig. 3 a schematic representation of a histogram of an image taken in the first operating mode with one histogram area and another histogram area; Fig. 4 a schematic representation of the image taken in the first operating mode with motor vehicle lighting of another motor vehicle, which can be clearly assigned to a first light source of the motor vehicle lighting and clearly to a second light source of the motor vehicle lighting; Fig. 5 a schematic representation of a further image taken in the second operating mode with motor vehicle lighting of the further motor vehicle, which cannot be clearly assigned to the first light source and cannot be clearly assigned to the second light source; Fig. 6 a further schematic representation of the image taken in the first operating mode with blurred edges compared to the further image; and Fig. 7 a further schematic representation of the further image taken in the second operating mode with sharper edges compared to the image.

[0038] In the figures, identical or functionally identical elements are provided with the same reference symbols.

[0039] Fig. 1 shows an embodiment of a motor vehicle 1 with at least one camera 2. The camera 2 is arranged at a front 3 of the motor vehicle 1. However, the arrangement of the camera 2 is possible in many ways; for example, the camera 2 can also be arranged at a rear 4 of the motor vehicle 1 or a left side 5 of the motor vehicle 1 or a right side 6 of the motor vehicle 1.

[0040] According to the exemplary embodiment, the camera 2 is arranged on the motor vehicle 1 in such a way that an environmental area 7 of the motor vehicle 1 is at least partially captured.

[0041] The camera 2 has an image sensor 8 with image sensor elements 9. The image sensor 8 is preferably designed as a CCD sensor (CCD - charge-coupled device) or a CMOS sensor (CMOS - complementary metal-oxide-semiconductor). Furthermore, the camera 2 is preferably designed as a video camera that records an image sequence of individual images.

[0042] According to the exemplary embodiment, the camera 2 comprises an evaluation unit 10. The evaluation unit 10 is designed separately from the camera 2 or integrated into the camera 2. The evaluation unit 10 evaluates the image sequence and / or makes corrections, for example by applying filters, to the respective individual images.

[0043] Fig. 2 shows a flowchart 11 of a method for operating the camera 2. In a first step S1, the camera 2 is initialized for operation in low brightness conditions, in particular for nighttime operation. Nighttime operation differs from daytime operation of the camera 2, in particular, by a different exposure setting of the camera 2. The exposure setting, in particular, specifies an exposure time. Low brightness occurs in particular when the surrounding area 7 is at least partially less illuminated than is the case with normal sunlight.

[0044] According to the exemplary embodiment, the camera 2 is set into a first operating mode 12 by step S1. In the first operating mode 12, an image 13 of at least a part of the surrounding area 7 is recorded. From the, in particular the entire, image 13, a - in Fig. 3 is determined. Depending on the histogram 14 of the image 13, the camera 2 is switched to a second operating mode 15 in a step S2.

[0045] In the second operating mode 15, another image 16 is then captured. A further histogram 17 is determined from the further image 16. Depending on the further histogram 17, the system switches back from the second operating mode 15 to the first operating mode 12 in a step S3.

[0046] An exposure setting 18 of camera 2 is identical in the first operating mode 12 and in the second operating mode 15. The exposure setting 18, in particular, specifies an exposure time of camera 2. However, the exposure setting 18 can also include an aperture setting of camera 2 or a light sensitivity of image sensor 8 or a signal gain setting of image sensor 8.

[0047] In the first operating mode 12, the image 13 is recorded using a first tone mapping method 19, and in the second operating mode 15, the further image 16 is recorded using a second tone mapping method 20. In the second tone mapping method 20, a dynamic range of the further image 16 is reduced to a lesser extent than a dynamic range of the image 13 is reduced using the first tone mapping method 19.

[0048] In an alternative embodiment, no tone mapping process is performed at all in the second operating mode 15. The subsequent image 16 is thus generated without the tone mapping process. Consequently, the first tone mapping process 19 is deactivated in the second operating mode 15.

[0049] Furthermore, in the second operating mode 15, a plurality of adjacent image sensor elements 9 of the image sensor 8 are combined to form an image sensor element block of the image sensor 8 as so-called pixel binning.

[0050] According to the exemplary embodiment, the number of image sensor elements 9 combined in the second operating mode 15 is determined based on a total number of image sensor elements 9 and / or a resolution of a display 21 of the motor vehicle 1. The display 21 is coupled to the camera 2. Preferably, the additional image 16 is output on the display 21.

[0051] Fig. 3 shows the histogram 14. Intensity value classes 22 are entered on an abscissa A of the histogram 14. A respective intensity value class 22 is, for example, represented by a - also in the Fig. 4 to Fig. 7 - intensity value 23 of the image 13 is given. The respective intensity value class 22 can also comprise several intensity values ​​23. The intensity value 23 lies within an intensity value range 24 of the image 13. The intensity value range 24 extends, for example, from 0 to 255 with an 8-bit color depth. The image 13 can also have any other color depth, for example 9 bits, 10 bits, 12 bits, or 16 bits. The image 13 can also have several color channels. For the sake of clarity, only a single color channel or intensity value channel of the image 13 is assumed below. The maximum possible number of gradations or color gradations is usually specified in bits and thus designates the color depth of the image 13. These gradations represent a scale on which the actual color information is stored. The color depth is therefore the mathematical basis of the actual color information.

[0052] The respective intensity value class 22 designates a bin or column of the histogram 14. The intensity value class 22 can, for example, comprise one or more intensity values ​​23 of the image 13 and can be specified in a variety of ways. The intensity value range 24 preferably comprises all intensity values ​​23 of the image 13.

[0053] Furthermore, frequency values ​​25 are entered on an ordinate O of the histogram 14. The respective frequency values ​​25 describe how often the respective intensity value class 22 occurs in Figure 13.

[0054] A histogram range 26 is determined in the histogram 14 during the first operating mode 12. According to the exemplary embodiment, the histogram range 26 extends only over 15% of the intensity value range 24 of the histogram 14 with the highest intensity values ​​or the intensity value classes with the highest intensity values. Thus, the histogram range 26 does not extend over the entire intensity value range 24 of the histogram 14.

[0055] All frequency values ​​25 within the histogram range 26 are compared with a frequency threshold 27. If the frequency values ​​25 within the histogram range 26 are smaller than the frequency threshold 27, the system switches to the second operating mode 15.

[0056] In the second operating mode 15, the histogram range 26 is then also determined in the further histogram 17 of the further image 16. The histogram range 26 is at the same position in the histogram 14 and in the further histogram 17 and extends over the same intensity value range 24 or over the same intensity value classes 22. At least one frequency value, in particular all frequency values, of the further histogram 17 within the histogram range 26 are compared with the frequency limit value 27. If at least one frequency value of the further histogram 17 within the histogram range 26 is equal to or greater than the frequency limit value 27, the system switches back to the first operating mode 12.

[0057] The change between the operating modes 12, 15 occurs in particular depending on a hysteresis. For example, the frequency limit value 27 is supplemented or reduced in particular by a hysteresis value, whereby high-frequency oscillations between the first operating mode 12 and the second operating mode 15 are suppressed. For example, a change from the second operating mode 15 back to the first operating mode 12 only occurs if the frequency value 25 is greater than the frequency limit value 27 plus a hysteresis value. The hysteresis value is, for example, 10% of the frequency limit value 27. Additionally or alternatively, the change from the first operating mode 12 to the second operating mode 15 is also carried out depending on a hysteresis. The change to the second operating mode 15 only occurs when the frequency value 25 is less than the frequency limit value 27 minus the hysteresis value.

[0058] In addition, according to the exemplary embodiment, a further histogram range 28 of the histogram 14 is determined. In the exemplary embodiment, the further histogram range 28 extends from 30% to 70% of the intensity value range 24 of the histogram 14. At least one of the frequency values ​​25, in particular all frequency values ​​25, within the further histogram range 28 are compared with a further frequency limit value 29. If one of the frequency values ​​25 within the further histogram range 28 is greater than the further frequency limit value 29, the change from the first operating mode 12 to the second operating mode 15 is suppressed. In this case, the change is therefore not carried out even if all frequency values ​​25 within the histogram range 26 are smaller than the frequency limit value.

[0059] Furthermore, the further histogram range 28 is preferably also determined in the further histogram 17. The system then switches back from the second operating mode 15 to the first operating mode 12 if one of the frequency values ​​25 within the further histogram range 28 of the further histogram 17 is greater than the further frequency limit value 29.

[0060] In addition or as an alternative to determining the further histogram range 28, a current temperature of the image sensor 8 is determined. The temperature is determined, for example, using a temperature sensor of the camera 2. If the temperature is greater than a temperature threshold, the switch to the second operating mode 15 is suppressed or the system switches back from the second operating mode 15 to the first operating mode 12.

[0061] Fig. 4 shows image 13. Image 13 depicts a light 30 of a motor vehicle lighting 31 of another motor vehicle 32. At the time image 13 is taken, the other motor vehicle 32 is located in the surrounding area 7 of motor vehicle 1. Based on image 13, the depicted light 30 can be unambiguously assigned to a part 33 of a first light source 34 of the motor vehicle lighting 31 and unambiguously to a further part 35 of a second light source 36 of the motor vehicle lighting 31.

[0062] Fig. 5 shows the additional image 16. The additional image 16 depicts the light 30 of the motor vehicle lighting 31. Based on the additional image 16, the depicted light 30 cannot be clearly assigned to the first light source 34 or the second light source 36. The light 30 appears as if it is emitted by only a single light source. An assessment based on the depicted light sources 34, 36 as to whether the additional motor vehicle 32 is located in the additional image 16 is not as reliable as in the example shown in Figure 13.

[0063] Fig. Figure 6 shows another embodiment of image 13 recorded in the first operating mode 12. A test pattern is recorded to allow for assessing the image quality of image 13. Compared to the other image 16, edges 37 of image 13 are blurred, or the edges of the higher frequencies are more flat, and image 13 exhibits higher image noise.

[0064] Fig. 7 shows a further embodiment of the further image 16 recorded in the second operating mode 15. The test pattern from Fig. 6. Compared to image 13, edges 38 of the additional image 16 are sharper, or the edges of the higher frequencies drop more steeply, and the additional image 16 exhibits less image noise. This is made possible, among other things, by omitting the second tone mapping method 20. Now, a larger portion of the intensity value range 24 is used to image the darker areas of the surrounding area 7 than would be the case with the first tone mapping method 19 or the second tone mapping method 20. Furthermore, the temperature-dependent operation of the camera 2, in particular, leads to less noise in the respective images 13, 16.

[0065] The method makes it possible to switch back and forth between an operating mode, in particular the first operating mode 12, for more reliable detection of oncoming motor vehicles, and an operating mode, in particular the second operating mode 15, with higher image quality, in particular sharper edges and less noise. Furthermore, the heuristic method, in particular the histogram-dependent switching in steps S2 and S3, reliably determines a situation-appropriate time for the respective switch.

Claims

[1] Method for operating a camera (2) of a motor vehicle (1), in which the camera (2) is operated in a first operating mode (12) and in the first operating mode (12) an image (13) of an environmental area (7) of the motor vehicle (1) is recorded with the camera (2), wherein a histogram (14) of the image (13) is determined and a histogram range (26) is determined in the histogram (14), characterized bythat all frequency values ​​(25) of intensity value classes (22) of the histogram (14) in the histogram range (26) are compared with a frequency limit value (27) and a change is made (S2) from the first operating mode (12) to a second operating mode (15) of the camera (2) that is different from the first operating mode (12) if the compared frequency values ​​(25) in the histogram range (26) are smaller than the frequency limit value (27), wherein in the second operating mode (15) a further image (16) is recorded with the camera (2) and the camera (2) is operated in the first operating mode (12) and in the second operating mode (15) with an identical exposure setting (18), wherein the method switches between an operating mode, in particular the first operating mode (12), for more reliable detection of oncoming motor vehicles and an operating mode, in particular the second operating mode (15), with a higher image quality,especially sharper edges and less noise, allows you to switch back and forth. [2] Method according to claim 1, characterized by that the histogram range (26) is determined within 20%, in particular 15%, of the intensity value range (24) of the histogram (14) with the largest intensity values ​​(23). [3] Method according to claim 1 or 2, characterized by that the image (13) is recorded in the first operating mode (12) using a first tone mapping method (19), in particular a local one, and the further image (16) is recorded in the second operating mode (15) using a second tone mapping method (20) that is different from the first tone mapping method (19), wherein a dynamic range of the further image (16) is reduced by the second tone mapping method (20) to a lesser extent than a dynamic range of the image (13) recorded using the first tone mapping method (19). [4] Method according to claim 1 or 2, characterized bythat the image (13) is recorded in the first operating mode (12) using a first tone mapping method (19), in particular a local one, and when recording the further image (16) in the second operating mode (15), the first tone mapping method (19), in particular any tone mapping method (19, 20), is deactivated. [5] Method according to one of the preceding claims, characterized by in that in the second operating mode (15) a plurality of adjacent image sensor elements (9) of an image sensor (8) of the camera (2) are combined to form an image sensor element block of the image sensor (8) and the further image (16) is recorded depending on the image sensor element block. [6] Method according to claim 5, characterized bythat a number of image sensor elements (9) combined to form the image sensor element block in the second operating mode (15) is determined based on a total number of image sensor elements (9) of the image sensor (8) of the camera (2) and / or a resolution of a display (21) for outputting the further image (16). [7] Method according to one of the preceding claims, characterized by that a further histogram range (28) is determined within 20% to 80%, in particular from 30% to 70%, of the intensity value range (24) of the histogram (14) and the change to the second operating mode (15) is suppressed if a frequency value (25) of an intensity value class (22) in the further histogram range (28) of the histogram (14) is greater than a further frequency limit value (29). [8] Method according to claim 7, characterized bythat a further histogram (17) of the further image (16) is determined and the further histogram range (28) is determined within 20% to 80%, in particular from 30% to 70%, of the intensity value range (24) of the further histogram (17), wherein a change is made (S3) from the second operating mode (15) to the first operating mode (12) if a frequency value (25) of an intensity value class (22) in the further histogram range (28) of the further histogram (17) is greater than a further frequency limit value (29). [9] Method according to one of the preceding claims, characterized by that a temperature of an image sensor (8) of the camera (2) is determined and the change to the second operating mode (15) is suppressed if the temperature of the image sensor (8) is greater than a temperature limit value. [10] Method according to one of the preceding claims 1 to 6, characterized bythat a further histogram (17) of the further image (16) is determined and the histogram range (26) in the further histogram (17) is determined, wherein a change is made from the second operating mode (15) back to the first operating mode (12) if a frequency value (25) of an intensity value class (22) of the further histogram (17) in the histogram range (26) of the further histogram (17) is greater than the frequency limit value (27). [11] Method according to one of the preceding claims, characterized by that in the image (13) a light (30) from a motor vehicle lighting (31) of a further motor vehicle (32) present in the surrounding area (7) is depicted and the depicted light (30) is unambiguously assigned to a part (33) of a first light source (34) of the motor vehicle lighting (31) and unambiguously to a further part (35) of a second light source (36) of the motor vehicle lighting (31). [12] Method according to one of the preceding claims, characterized by that the camera (2) is operated with an identical gamma value in the first operating mode (12) and in the second operating mode (15). [13] Method according to one of the preceding claims, characterized by that when recording the further image (16) in the second operating mode (15), a black area clipping and / or a limitation of a dynamic range of the further image (16) is deactivated. [14] Camera (2) for a motor vehicle (1), which is designed to carry out a method according to one of the preceding claims. [15] Motor vehicle (1) with a camera (2) according to claim 14.

Images