Method for operating multi-camera system of i.e. passenger car, involves limiting parameter values on predetermined value range by adjusting common desired value, and performing image processing algorithm using electronic computing device

The invention relates to a method for operating a multi-camera system of a motor vehicle, in which at least two cameras of the multi-camera system each provide images of a surrounding area of ​​the motor vehicle and an overall representation is generated from an image area of ​​the at least two cameras by means of an electronic computing device. When generating the overall display, the respective values ​​of at least one image parameter of the image areas are matched to one another and are set to a common target value. The invention also relates to a multi-camera system for performing such a method and to a motor vehicle with such a multi-camera system.

Camera systems for motor vehicles are already known from the prior art. As is known, a multiplicity of cameras can be used in a motor vehicle, it becoming more and more common these days to use a camera arrangement with at least two cameras for a driver assistance system of a vehicle, each of which captures a surrounding area of ​​the motor vehicle. For example, four cameras can be used, which record the entire environment around the motor vehicle. An overall representation can then be provided from the images of all cameras, namely in particular the so-called “bird-eye view”. This overall representation represents a top view of the motor vehicle and its surroundings from a bird's eye view and thus, for example, from a reference point of view directly above the motor vehicle. The provision of such an overall representation from the images of several cameras is, for example, from the document <de-docref CY="US" DNUM="2011/0156887">US 2011/0156887</de-docref> known.

When generating an overall representation from the images of a plurality of cameras, such as when generating the “bird-eye view” mentioned, the respective values ​​of at least one parameter of the images have to be matched to one another. In particular, the respective brightness values ​​of the images from different cameras should be matched to one another, as should the white balance values. Such a procedure is, for example, from the document<de-docref CY="EP" DNUM="2012271" KI="A2">EP 2 012 271 A2</de-docref> known. Here the brightness values ​​of the respective images are set to a common setpoint.

If the brightness values ​​were not adjusted to each other and each camera would set the exposure time and the amplification factor of the image sensor individually, depending on the environment depicted and therefore without regard to the other cameras, it could happen that the brightness values ​​occur under unfavorable environmental conditions the pictures are very different. In this case the brightness of the overall display would be inconsistent and would vary over the different image areas. For this very reason, it is necessary to compare the brightness values ​​of the different images when generating the overall display.

Changing the respective parameter values ​​of the different images and adapting the parameter values ​​of the images to one another represents a particular challenge in the prior art. In the document already mentioned <de-docref CY="EP" DNUM="2012271" KI="A2">EP 2 012 271 A2</de-docref> It is proposed that the parameter values ​​be compared using the electronic computing device. This means that the brightness values ​​of the respective images of different cameras are only adjusted by computer processing using image processing. However, such a procedure is associated with the disadvantage that, in the case of larger differences between the brightness values ​​of the images and thus in the case of different degrees of brightness of the surrounding areas of the motor vehicle, the computational effort in adapting the brightness values ​​is relatively large and, in addition, image information can also be lost.

It is the object of the invention to propose an improved solution compared to the prior art for the adjustment of the parameter values ​​of the respective image areas of the at least two cameras to one another.

This object is achieved according to the invention by a method, by a multi-camera system and by a motor vehicle with the features according to the respective independent patent claims. Advantageous embodiments of the invention are the subject of the dependent claims, the description and the figures.

A method according to the invention serves to operate a multi-camera system of a motor vehicle. At least two cameras each provide images of a surrounding area of ​​the motor vehicle. An overall representation or an overall image is generated from an image area of ​​the different images by means of an electronic computing device. When generating the overall display, the respective values ​​of at least one (same) image parameter of the image areas (e.g. Brightness and / or white balance) of the at least two cameras are adjusted to one another and the image parameter is set to a common setpoint in all image areas. The adjustment of the respective parameter values ​​of the image areas looks as follows: First, it is provided that by setting at least one operating parameter of the respective camera, the parameter values ​​are limited to a predetermined value range around the setpoint. The parameter values ​​of the image areas are then set to the desired value by the central computing device using an image processing algorithm.

Accordingly, a hybrid approach is proposed according to the invention: on the one hand, the respective parameter values ​​are adjusted by controlling the cameras and thus internally in the cameras at the camera level; on the other hand, the parameter values ​​are fine-tuned using the central electronic computing device, which calculates the overall display. First of all, the parameter values ​​are set on the camera side to intermediate values ​​which lie within a predetermined value range around the target value. The fine adjustment is then carried out at the level of the electronic computing device by means of an image processing algorithm. Compared to a complete adjustment of the parameter values ​​on the image processing level, the method according to the invention has the advantage that the computational effort when performing the image processing algorithm is reduced. Compared to the complete adjustment of the parameter values ​​on the camera level, the method according to the invention has the advantage that the effort of the central control of the cameras is significantly reduced and the regulation of the parameter values ​​to the desired setpoint can be carried out significantly faster. The cameras can limit the respective parameter values ​​relatively quickly to the predetermined value range around the target value, while the subsequent fine adjustment is carried out in the electronic computing device alone. The number of iterations when adapting the parameter values ​​on the camera level is thus reduced, and the computing effort in the electronic computing device is also minimal.

Optionally, the parameter values ​​can be changed in more than one step with the aim of converging to the restricted area, ie in two or three steps. For this purpose, two or more different value ranges can be defined, and the parameter values ​​can first be limited to a first larger value range and then to a second smaller value range around the target value.

The setpoint for the parameter values ​​of the image areas is preferably set during operation of the multi-camera system and thus “online”. This means that the parameter values ​​- such as the brightness values ​​of the image areas - can be set depending on the current lighting conditions in the environment. With this procedure, an overall display with a very good image quality can always be generated.

In particular, it is provided that the target value is set to a median value of the parameter values ​​of the image areas, which are recorded before the adjustment. Before the parameter values ​​are matched to one another, a median value of the current actual parameter values ​​is recorded and used as the setpoint. If, for example, a brightness is defined as the image parameter of the image areas, the brightness values ​​of the image areas are set to a brightness median value, so that overall an easily perceptible overall display with a medium brightness is generated.

According to another embodiment, the target value can be set to the parameter value of the image area of ​​one of the at least two cameras that was acquired before the adjustment. One of the cameras is thus operated as a reference camera, while the parameter values ​​of the image areas of other cameras are adjusted to the parameter value of the reference camera. This embodiment proves to be particularly advantageous if the current images of the reference camera are to be shown on a display separately from the overall display. Here, the at least one image parameter of these images can be adapted specifically for this view, and the parameter values ​​of the other cameras can be adapted to the parameter value of the reference camera.

The two above-mentioned embodiments with regard to the setting of the target value can also be combined with one another. For a predetermined time interval or in a first operating mode, the setpoint can be set to the median value of the parameter values. For a different time interval or in a second operating mode of the camera system, the setpoint can be set to the current parameter value of one of the at least two cameras. The first operating mode is activated in particular when only the overall display is shown on a display. In contrast, the second operating mode is activated in particular if, in addition to the overall display, the current images of the camera whose parameter value is used as the setpoint for the adjustment of the parameter values ​​are also displayed.

Various embodiments can be provided with regard to the at least one image parameter of the image areas: &lt;br /&gt;On the one hand, the brightness of the image areas can be defined as the image parameter. The parameter values ​​are then the brightness values ​​of the image areas, in particular the respective median values ​​of the brightness of the image areas. Y values ​​of the images in the YUV color space are preferably understood as brightness values. By adjusting the brightness values ​​of the image areas to one another - in particular by adjusting the respective median values ​​of the brightness - an overall display can be provided which has a uniform brightness and thus no brightness jumps. The overall presentation can thus be shown on a display with good quality.

The adjustment of the brightness values ​​of the image areas preferably comprises that the brightness values ​​of the image areas are initially limited to the predetermined value range around the desired value by changing the respective exposure time and / or the respective amplification factor of an image sensor of the cameras. To limit the brightness values ​​of the image areas to the predetermined value range around the target value, the respective exposure time and / or the respective gain factor are controlled as the operating parameters of the cameras, specifically at the camera level. The exposure time and the gain factor of the respective image sensor represent operating parameters of the cameras. By changing these operating parameters, the brightness of the images can be set effectively.

On the other hand, a white balance of the image areas can also be defined as an image parameter. The respective white balance values ​​of the image areas of different cameras can thus also be matched to one another, so that the same white balance values ​​are set for all image areas. The quality of the overall presentation is thus further increased.

In order to limit the white balance values ​​of the image areas to the predetermined value range around the target value, it is preferably provided that an internal white balance is carried out within the cameras by means of an internal control unit of the cameras. This internal white balance can be carried out, for example, by means of the respective image sensor (imager).

It can also be provided that in the event that one of the parameter values ​​of the image areas detected before the adjustment exceeds a predetermined limit value, the respective parameter values ​​of the image areas are not adjusted. In particular, if the brightness value of one of the image areas exceeds a predetermined limit value, this indicates very bright lighting conditions in the environment, and the adjustment of the brightness value would be associated with a relatively great effort here. In such a limit case, the adjustment of the parameter values ​​can be dispensed with.

A top view is preferably generated as the overall view, which shows a top view of the motor vehicle and its surroundings. To generate such an overall representation, the images of all cameras are processed and combined into a common image, which shows a plan view of the motor vehicle and the environment around the vehicle. The image of the motor vehicle can be pre-stored in the computing device. In order to generate such an overall representation, an image area is preferably cut out from the respective images of the cameras, which images the respective surrounding area up to a certain distance from the motor vehicle, namely for example up to a distance of 2 or 3 or 4 meters from the motor vehicle.

The invention also relates to a multi-camera system which is designed to carry out a method according to the invention. Furthermore, the invention relates to a motor vehicle with a multi-camera system according to the invention. The preferred embodiments presented with reference to the method according to the invention and their advantages apply accordingly to the system according to the invention and to the motor vehicle according to the invention.

Further features of the invention result from the claims, the figures and the description of the figures. All of the features and combinations of features mentioned above in the description and 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 respectively specified combination but also in other combinations or on their own.

The invention will now be explained in more detail using a preferred exemplary embodiment and with reference to the accompanying drawings. Show it:

<figref>1</figref> a schematic representation of a motor vehicle with a multi-camera system according to an embodiment of the invention;

<figref>2</figref> a schematic representation of a block diagram of a multi-camera system according to an embodiment of the invention;

<figref>3</figref> to <figref>6</figref> Flow diagrams of a method according to an embodiment of the invention.

An in <figref>1</figref> shown motor vehicle <b>1</b> is for example a passenger car. The car<b>1</b> has a camera system <b>2</b> with four cameras, for example <b>3</b>, <b>4</b>, <b>5</b>, <b>6</b>which on the motor vehicle <b>1</b> are distributed such that the cameras <b>3</b>, <b>4</b>, <b>5</b>, <b>6</b> overall the environment around the motor vehicle <b>1</b> capture around. It becomes the complete environment of the motor vehicle<b>1</b> and therefore captured a 360 ° image. The camera<b>3</b> is a front camera, which is in the front area of ​​the motor vehicle <b>1</b>, for example, is arranged behind the windshield. The camera<b>3</b> thus captures a surrounding area <b>7</b> in front of the motor vehicle <b>1</b>. The second camera<b>4</b> is a rear camera, which is in the rear area of ​​the motor vehicle <b>1</b> is attached, for example on a tailgate or behind the rear window or on a rear bumper. It captures a surrounding area<b>8</b> behind the motor vehicle <b>1</b>. The side cameras<b>5</b>, <b>6</b> can, for example, be integrated in the respective exterior mirrors. The third camera<b>5</b> captures the surrounding area <b>9</b> left of the motor vehicle <b>1</b>while the fourth camera <b>6</b> a surrounding area <b>10</b> on the right side of the motor vehicle <b>1</b> detected.

The number and arrangement of the cameras <b>3</b>, <b>4</b>, <b>5</b>, <b>6</b> are in <figref>1</figref> only shown by way of example and can vary depending on the embodiment.

The cameras <b>3</b>, <b>4</b>, <b>5</b>, <b>6</b> have a relatively wide opening angle, which can be, for example, in a range from 160 ° to 200 °. The cameras<b>3</b>, <b>4</b>, <b>5</b>, <b>6</b> can be so-called fisheye cameras, for example. They can be CCD cameras or CMOS cameras.

The cameras <b>3</b>, <b>4</b>, <b>5</b>, <b>6</b> are video cameras, each of which can provide a large number of individual images per second. The images are then sent to a central computing and control device<b>11</b> which transmits the images of all cameras <b>3</b>, <b>4</b>, <b>5</b>, <b>6</b> processed. The recording of the pictures by all cameras<b>3</b>, <b>4</b>, <b>5</b>, <b>6</b> is preferably synchronous.

The camera <b>3</b> thus captures the surrounding area <b>7</b> in front of the motor vehicle <b>1</b>. The camera<b>3</b> thus has a detection area or a field of view <b>12</b>, which the surrounding area <b>7</b> in front of the motor vehicle <b>1</b> covers. The second camera also points accordingly<b>4</b> a field of view<b>13</b> on what the surrounding area <b>8</b> behind the motor vehicle <b>1</b> covers. Corresponding fields of vision of the cameras<b>5</b>, <b>6</b> are in <figref>1</figref> With <b>14</b> or. <b>15</b> designated. How out<figref>1</figref> emerges, the fields of vision of the cameras <b>3</b>, <b>4</b>, <b>5</b>, <b>6</b> overlap each other in pairs and areas. And that can change the fields of vision<b>12</b> and <b>14</b> of the cameras <b>3</b>, <b>5</b>, the fields of view <b>12</b> and <b>15</b> of the cameras <b>3</b>, <b>6</b>as well as the fields of view <b>13</b> and <b>14</b> of the cameras <b>4</b>, <b>5</b> as well as the fields of view <b>13</b> and <b>15</b> of the cameras <b>4</b>, <b>6</b> overlap each other.

The computing and control device <b>11</b> receives the images from all cameras <b>3</b>, <b>4</b>, <b>5</b>, <b>6</b> and processes them. The computing and control device<b>11</b> calculated from the videos of all cameras <b>3</b>, <b>4</b>, <b>5</b>, <b>6</b> in real time an overall representation, which is a top view of the motor vehicle <b>1</b> and its surroundings <b>7</b>, <b>8</b>, <b>9</b>, <b>10</b> shows a bird’s eye view. Related to the individual images of the cameras<b>3</b>, <b>4</b>, <b>5</b>, <b>6</b> generates the computing and control device <b>11</b> from these individual images of all cameras <b>3</b>, <b>4</b>, <b>5</b>, <b>6</b> an overall picture showing such a top view of the motor vehicle <b>1</b> and shows its surroundings. Are now from the entire sequences of individual images of the cameras<b>3</b>, <b>4</b>, <b>5</b>, <b>6</b> If such total images are calculated, a temporal sequence of overall images, ie an overall video, results. This overall video is shown as an overall display in real time on a display<b>16</b> in the motor vehicle <b>1</b> shown. the display<b>16</b> represents an optical display device.

In <figref>2</figref> is a block diagram of the camera system <b>2</b> shown. As already stated, the cameras deliver<b>3</b>, <b>4</b>, <b>5</b>, <b>6</b> respective images B3, B4, B5, B6, from which an overall representation GB is generated. Although only single images B3, B4, B5, B6 are referred to below, it goes without saying that the cameras<b>3</b>, <b>4</b>, <b>5</b>, <b>6</b> each deliver an entire video and thus a temporal sequence of images.

From simultaneously captured images B3, B4, B5, B6 of the cameras <b>3</b>, <b>4</b>, <b>5</b>, <b>6</b> generates the computing and control device <b>11</b> the overall view GB, which is a plan view of the motor vehicle <b>1</b> and the area around the motor vehicle <b>1</b> shows around. For this purpose, an image area B3 ', B4', B5 ', B6' is used from each image B3, B4, B5, B6, namely that image area which represents the respective surrounding area<b>7</b>, <b>8</b>, <b>9</b>, <b>10</b> up to a predetermined distance from the motor vehicle <b>1</b> shows. These image areas B3 ', B4', B5 ', B6' of the images B3, B4, B5, B6 are then combined into an overall image or an overall representation GB and processed in such a way that the impression arises as if the overall representation GB were the respective surrounding areas<b>7</b>, <b>8</b>, <b>9</b>, <b>10</b> show from a bird's eye view. This overall representation GB is then on the display<b>16</b> displayed in real time.

When generating the overall representation GB, the respective parameter values ​​of at least one image parameter of the image areas B3 ', B4', B5 ', B6' are matched to one another. In the exemplary embodiment, the respective brightness values ​​of the image areas B3 ', B4', B5 ', B6' are matched to one another, namely the respective median values ​​of the brightness (the respective brightness median values). On the other hand, the white balance values ​​of the image areas B3 ', B4', B5 ', B6' are also matched to one another. The adjustment of the parameter values ​​of the image areas B3 ', B4', B5 ', B6' takes place in two separate stages: First, there is a first rough adjustment of the parameter values ​​by controlling the cameras <b>3</b>, <b>4</b>, <b>5</b>, <b>6</b> by means of the computing and control device <b>11</b>how this in <figref>2</figref> with control lines <b>17</b> is indicated schematically. At least one operating parameter of the cameras is used for rough adjustment of the parameter values<b>3</b>, <b>4</b>, <b>5</b>, <b>6</b> controlled, namely in the case of adaptation of the brightness values, for example the respective exposure times and / or amplification factors of the cameras <b>3</b>, <b>4</b>, <b>5</b>, <b>6</b>. If the white balance values ​​are adjusted, the internal white balance of the cameras is controlled<b>3</b>, <b>4</b>, <b>5</b>, <b>6</b>. In a second stage, the parameter values ​​of the image areas B3 ', B4', B5 ', B6' (the brightness values ​​and / or the white balance values) are computationally calculated using the computing and control device<b>11</b> fine-tuned according to a predetermined image processing algorithm and set to a target value. While the first level of adjustment is thus carried out inside the camera, the fine adjustment according to the second level takes place outside the cameras<b>3</b>, <b>4</b>, <b>5</b>, <b>6</b> and thus external to the camera solely by means of image processing of the image areas B3 ', B4', B5 ', B6'.

Although the following description relates to the adaptation of brightness values ​​of the image areas B3 ', B4', B5 ', B6', the white balance values ​​of the image areas B3 ', B4', B5 ', B6' can also be matched to one another in the same way.

In the <figref>3</figref> to <figref>6</figref> Flow diagrams of a method according to an embodiment of the invention are now shown. <figref>3</figref> shows a main loop of the method, which after activating the so-called "Topview" operating mode of the camera system <b>2</b> is repeated until this operating mode is deactivated again. The "Topview" operating mode is activated in a first step S1, whereupon the method proceeds to a second step S2. In step S2, the computing and control device receives<b>11</b> the images B3, B4, B5, B6 and cut out the image areas B3 ', B4', B5 ', B6'. In the context of step S2, further sub-steps are carried out, which are based on the flowchart in accordance with<figref>4</figref> are explained in more detail. In a step S201, the computing and control device receives<b>11</b> the image data and stores the image areas B3 ', B4', B5 ', B6'.

In a further step S202, the computing and control device calculates <b>11</b> the respective median brightness values: Ymed_A for the camera <b>3</b>, Ymed_B for the camera <b>4</b>, Ymed_C for the camera <b>5</b> and Ymed_D for the camera <b>6</b>, as well as the respective variance of the brightness values ​​of all image areas B3 ', B4', B5 ', B6': Yvar_A for the camera <b>3</b>, Yvar_B for the camera <b>4</b>, Yvar_C for the camera <b>5</b> and Yvar_D for the camera <b>6</b>. This means that for each image area B3 ', B4', B5 ', B6' the median brightness value Ymed_A, Ymed_B, Ymed_C and Ymed_D (Y median value in the YUV color space) as well as the variance of the brightness values ​​Yvar_A, Yvar_B, Yvar_C and Yvar_D ( Variance of the Y values) can be calculated.

In a further step S203, the computing and control device calculates <b>11</b> a total median value Ymed_Topview from the brightness median values ​​Ymed_A, Ymed_B, Ymed_C and Ymed_D of the image areas B3 ', B4', B5 ', B6'. This total median value Ymed_Topview is then used as a setpoint for the adjustment of the brightness median values ​​Ymed_A, Ymed_B, Ymed_C and Ymed_D of the image areas B3 ', B4', B5 ', B6'. This setpoint is saved. This is an offset-resistant indication of the average brightness of the entire top view image and is used in determining how the differences between the respective camera median values ​​Ymed_A, Ymed_B, Ymed_C and Ymed_D are addressed.

With renewed reference to <figref>3</figref> In a step S3 it is checked whether the rough adjustment of the respective brightness median values ​​Ymed_A, Ymed_B, Ymed_C and Ymed_D of the image areas B3 ', B4', B5 ', B6' is necessary or not. The computing and control device checks this<b>11</b>whether or not the current median brightness values ​​Ymed_A, Ymed_B, Ymed_C and Ymed_D of the image areas B3 ', B4', B5 ', B6' are within a predetermined value range around the setpoint Ymed_Topview. If a rough adjustment of the median brightness values ​​Ymed_A, Ymed_B, Ymed_C and Ymed_D is required, the method goes to a further step S4, in which readjustment of the operating parameters of the cameras<b>3</b>, <b>4</b>, <b>5</b>, <b>6</b> by means of the computing and control device <b>11</b> takes place, namely a readjustment of the respective exposure time and the respective gain factor. This rough adjustment of the brightness median values ​​Ymed_A, Ymed_B, Ymed_C and Ymed_D of the image areas B3 ', B4', B5 ', B6' and thus the limitation of these brightness median values ​​to the specified value range around the setpoint Ymed_Topview is therefore carried out internally in the camera under the control of the cameras<b>3</b>, <b>4</b>, <b>5</b>, <b>6</b> over the control lines <b>17</b>.

This approach is used to avoid excessive camera changes <b>3</b>, <b>4</b>, <b>5</b>, <b>6</b> and view in general. It can also be implemented as follows: If all median values ​​Ymed_A, Ymed_B, Ymed_C and Ymed_D are within a specified value range around the setpoint Ymed_Topview, i.e. within +/- TH1 around Ymed_Topview (where TH1 is set to 30, for example) or if at least one of the Median values ​​Ymed_A, Ymed_B, Ymed_C, Ymed_D lies outside a larger value range, ie outside +/- THL by Ymed_Topview (where THL is greater than TH1 and is set to 100, for example), then there is preferably no adjustment to the cameras <b>3</b>, <b>4</b>, <b>5</b>, <b>6</b> carried out. Otherwise there is an action on the cameras<b>3</b>, <b>4</b>, <b>5</b>, <b>6</b> needed.

Step S4 contains several sub-steps, which refer to <figref>6</figref> are explained in more detail: &lt;br /&gt;The embodiment according to <figref>6</figref> can be carried out in particular in the case of an ARM processor which is incorporated in the computing and control device <b>11</b> can be integrated. In a step S430, the first step is in relation to the camera<b>3</b> checks whether the median brightness value Ymed_A of the image area B3 'lies within or outside the predetermined value range TH1 around the setpoint. If a deviation is detected, the method proceeds to a further step S431, in which the required change in the exposure time and / or the amplification factor of the image sensor of the camera<b>3</b> is calculated so that the median brightness value of the image area B3 'lies within the predetermined value range TH1. In this step S431, the computing and control device intervenes<b>11</b> also on the data from a data sheet of the camera <b>3</b> to.

The registers for the exposure targets on the OV10630 image sensor are: 0xC46A, 0xC46D, 0xC464, 0xC465. Two step sizes for modifying the gain and / or the exposure targets are preferably defined: a small step size (e.g. 0x08) and a large step size (e.g. 0x10). The following scenario can be provided: If the median value Ymed_A differs from the target value Ymed_Topview by more than the specified threshold THL, no change is made. But if the difference (Ymed_A - Ymed_Topview) is greater than the threshold TH1 and less than THL, then the change in the gain factor and / or the exposure is set to the negative large step size. Analogously, if the difference (Ymed_Topview - Ymed_A) is greater than TH1, the change in the gain factor and / or the exposure is set to the positive large step size. However, if the difference (Ymed_A - Ymed_Topview) or (Ymed_Topview - Ymed_A) is greater than a smaller threshold TH2 but less than the threshold TH1, the change in the gain factor and / or the exposure is set to the negative or positive small increment. This allows adaptation to the cameras<b>3</b>, <b>4</b>, <b>5</b>, <b>6</b> be carried out step by step.

It is then checked in a step S432 whether the current change in the exposure time and / or the gain factor of the camera <b>3</b> a third change in the same direction or not. If this is not the case, the method proceeds to a further step S433, in which control signals are sent to the camera via the ARM processor mentioned<b>3</b> are emitted, which bring about the previously calculated change in the exposure time and / or the amplification factor. Here, too, is on the data sheet<b>18</b> the camera <b>3</b> accessed. This means that if it is the third step in the same direction, no changes will be made. If this is a change in the other direction or is less than a third step in a certain direction, then the change is made to the camera.

However, if it is determined in step S432 that the current change already represents a third change in the same direction, the method goes to a further step S440. Even if the camera is not activated according to step S430<b>3</b> the process proceeds to step S440. Even after step S433 has been carried out, the method continues to step S440.

Steps S440, S441, S442 and S443 correspond to steps S430, S431, S432 and S433 and relate to the second camera <b>4</b>. In step S440 it is therefore checked whether the median brightness value of the image area B4 'lies outside the predetermined value range around the target value. If this is the case, the required change in the exposure time and / or the amplification factor of the camera is carried out in accordance with step S441<b>4</b> calculated. If this change is a third change in the same direction, the adaptation is interrupted in accordance with step S442. If this is not the case, communication with the camera takes place in accordance with step S443<b>4</b> and thus the adjustment of the exposure time and / or the gain factor.

Steps S450, S451, S452, S453 also correspond to steps S430, S431, S432, S433, but relate to the camera <b>5</b>. The same applies to steps S460, S461, S462 and S463, which, however, is the fourth camera<b>6</b> affect.

With renewed reference to <figref>3</figref> after step S4 has been completed, the method proceeds to a further step S5, in which the system settles down. The system will wait n frames to decay before making another change. For example, the default value for n can be 3. The method then returns to step S2, in which new images B3, B4, B5, B6 are acquired and thus new image data are available.

It is checked again according to step S3 based on the new image data whether additional control of the cameras <b>3</b>, <b>4</b>, <b>5</b>, <b>6</b> is required or not. If this is no longer necessary and all brightness median values ​​Ymed of the image areas B3 ', B4', B5 ', B6' are within the specified value range around the target value, the method goes to a further step S6, in which it is checked whether a camera-external fine adjustment the median brightness values ​​to the setpoint is required or not. Here, the computing and control device<b>11</b> Check whether the brightness median values ​​Ymed are within a narrower and therefore smaller value range around the target value and can therefore be assumed that these median values ​​are essentially equal to the target value. If no further fine adjustment by means of image processing is required, the method returns to step S2. If the fine adjustment is necessary, it is carried out in a step S7.

This is done to determine if a post-processing step is required. In this case there is nothing on the cameras<b>3</b>, <b>4</b>, <b>5</b>, <b>6</b> processing itself is done on the video output data, and the Y values ​​are scaled accordingly. This prevents excessive modification of the cameras<b>3</b>, <b>4</b>, <b>5</b>, <b>6</b> and view in general. This can be done as follows: If all medians Ymed_A, Ymed_B, Ymed_C and Ymed_D are within a value range +/- TH3 around Ymed_Topview, whereby TH3 &lt;TH2 &lt;TH1 and for example TH3 = 5, then the post-processing of the video data is not necessary . Otherwise, post-processing is carried out.

Step S7 contains two sub-steps, which in <figref>5</figref> are shown. According to step S701, for each camera<b>3</b>, <b>4</b>, <b>5</b>, <b>6</b> First, a scaling factor is calculated by which the Y values ​​(of each pixel) and thus the brightness values ​​of the respective image area B3 ', B4', B5 ', B6' are to be multiplied or scaled. In the subsequent step S702, the Y values ​​of the pixels of the image areas B3 ', B4', B5 ', B6' are multiplied by the respective scaling factor.

However, there are two possible ways to calculate the camera alpha, and each of them can be used. According to the first, the calculation can be carried out as follows, where α_Aα_B α_C. α_D the respective alpha values ​​of the cameras <b>3</b>, <b>4</b>, <b>5</b>, <b>6</b> describe: &lt;br /&gt;for the camera <b>3</b>: α_A = basic_stepsize · | Ymed_A - Ymed_Topview |; &lt;br /&gt;for the camera <b>4</b>: α_B = basic_stepsize · | Ymed_B - Ymed_Topview |; &lt;br /&gt;for the camera <b>5</b>: α_C. = basic_stepsize · | Ymed_C - Ymed_Topview |; and&lt;br /&gt;for the camera <b>6</b>: α_D = basic_stepsize · | Ymed_D - Ymed_Topview |.

According to the second way, the calculation can be carried out as follows: α_A = α_B = α_C. = α_D = basic_stepsize.

The default value of the "basic_stepsize" parameter can be set to 0.5, but this value can also be varied. It can be any value between 0 and 1; the higher the value, the greater the scaling.

The one on the video data of the cameras <b>3</b>, <b>4</b>, <b>5</b>, <b>6</b> The scaling value to be applied is calculated as follows: <de-figure num="1"><img file="DE102012024972A1_D0001.tif" /></de-figure>

In addition, it is also possible to provide an additional scaling factor from 0 to 1, which can be determined in accordance with a brightness configuration determined by the user.

According to step S7, a fine adjustment and thus an exact adjustment of the median brightness values ​​Ymed of the image areas B3 ', B4', B5 ', B6' to the previously calculated target value takes place. In step S7, an image processing algorithm is carried out, according to which - in the present exemplary embodiment - the Y values ​​of the image areas are multiplied by a respective scaling factor. This fine adjustment takes place outside the cameras<b>3</b>, <b>4</b>, <b>5</b>, <b>6</b> by means of the computing and control device <b>11</b>.

Optionally, it can also be provided that the computing and control device in step S2 <b>11</b> checks whether at least one of the median brightness values ​​Ymed of the image areas B3 ', B4', B5 ', B6' exceeds the specified predetermined limit value THL. If such an exceeding of the limit value is detected, the adjustment of the brightness median values ​​Ymed to one another can initially be dispensed with for a predetermined time interval - for example for the duration of some images. After this period, the computing and control device<b>11</b> again calculate the respective current median brightness values ​​Ymed using the current images B3, B4, B5, B6.

QUOTES INCLUDE IN THE DESCRIPTION

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Patent literature cited

<ul list-style="bullet"><li>US 2011/0156887 <b>[0002]</b></li><li>EP 2012271 A2<b>[0003, 0005]</b></li></ul>