METHOD FOR ADAPTING A BRIGHTNESS OF A HIGH-CONTRAST IMAGE AND CAMERA SYSTEM

Abstract

The invention relates to a method for adapting a brightness (28) of a high-contrast image (20, 22) of an environmental region (9) of a motor vehicle (1) including the following steps of: a) capturing a first image with a first camera parameter of a camera system (2) of the motor vehicle (1) and a second image with a second camera parameter of the camera system (2) by means of the camera system (2), b) generating a first high-contrast image (20) of the environmental region (9) with the first image and the second image, c) determining a high-contrast brightness value (23) of the first high-contrast image (20), d) comparing the high-contrast brightness value (23) to a predetermined high-contrast target brightness value, e) adapting the first high-contrast image (20) depending on the comparison according to step d), f) determining a first brightness value of the first image and/or a second brightness value of the second image, g) comparing the first brightness value to a first target brightness value (26) and/or the second brightness value to a second target brightness value (27), h) adapting the first camera parameter and/or the second camera parameter depending on the comparison according to step g), i) capturing a third image of the environmental region (9) with the adapted first camera parameter and a fourth image of the environmental region (9) with the adapted second camera parameter by means of the camera system (2), j) generating a second high-contrast image (22) of the environmental region (9) with the third image and the fourth image, k) providing the second high-contrast image (22) as a high-contrast image (20, 22) adapted in brightness for representing the environmental region (9) of the motor vehicle (1).

Claims

1. A method for adapting a brightness of a high-contrast image of an environmental region of a motor vehicle comprising: a) capturing a first image with a first camera parameter by a first camera of a camera system of the motor vehicle and a second image with a second camera parameter by a second camera of the camera system; b) generating a first high-contrast image of the environmental region with the first image and the second image; c) determining a high-contrast brightness value of the first high-contrast image; d) comparing the high-contrast brightness value to a predetermined high-contrast target brightness value; e) adapting the first high-contrast image depending on the comparison according to step d); f) determining a first brightness value of the first image and/or a second brightness value of the second image; g) comparing the first brightness value to a first target brightness value and/or the second brightness value to a second target brightness value; h) adapting the first camera parameter and/or the second camera parameter depending on the comparison according to step g; i) capturing a third image of the environmental region with the adapted first camera parameter and a fourth image of the environmental region with the adapted second camera parameter by means of the camera system; j) generating a second high-contrast image of the environmental region with the third image and the fourth image; and k) providing the second high-contrast image as a high-contrast image adapted in brightness for representing the environmental region of the motor vehicle.

2. The method according to claim 1, wherein the first camera parameter and/or the second camera parameter are characterized by an exposure time parameter of the camera system and/or a light sensitivity parameter of the camera system.

3. The method according to claim 1, wherein a further high-contrast brightness value is determined from the second high-contrast image, and the second high-contrast image is adapted depending on a comparison to the further high-contrast brightness value and the high-contrast target brightness value according to step e).

4. The method according to claim 1, wherein in that the adaptation according to step e) is characterized by shifting the histogram of the first high-contrast image.

5. The method according to claim 1, wherein the adaptation according to step e) is restricted by a lower brightness variation limit value and/or an upper brightness variation limit value.

6. The method according to claim 5, wherein the first camera parameter and/or the second camera parameter are adapted in step h) only if the first high-contrast image is not completely adapted to the high-contrast target brightness value due to the lower brightness variation limit value and/or the upper brightness variation limit value.

7. The method according to claim 1, wherein at the same time with the second high-contrast image, at least one further second high-contrast image is generated according to steps a) to j), and an overall high-contrast image, a plan view high-contrast image of the environmental region, is generated from the two second high-contrast images.

8. The method according to claim 7, wherein the brightness of the second high-contrast image provided with step k) and the at least one further second high-contrast image is further adapted until a predetermined target homogeneity value of the brightness of the second high-contrast image and the further second high-contrast image is achieved.

9. The method according to claim 8, wherein the high-contrast target brightness value is determined depending on the target homogeneity value.

10. The method according to claim 1, wherein the first high-contrast image and the second high-contrast image are generated as a component of an image sequence.

11. method according to claim 1, wherein the first brightness value and/or the second brightness value and/or the high-contrast brightness value are determined depending on a weighting function.

12. The method according to claim 1, wherein in capturing at least one of the first image, and/or the second image, the third image and the fourth image, an aperture of the camera system is additionally adapted depending on the lighting conditions in the environmental region.

13. A camera system for a motor vehicle including at least one camera and at least one evaluation unit, which is adapted to perform a method according to claim 1.

14. The camera system according to claim 13, wherein the first and the second camera of the camera system are formed as an HDR camera.

15. A motor vehicle with a camera system according to claim 13.

Description

[0046] Below, embodiments of the invention are explained in more detail based on schematic drawings.

[0047] There show:

[0048] FIG. 1 in schematic plan view an embodiment of a motor vehicle according to the invention with a camera system;

[0049] FIG. 2 a schematic illustration of a known plan view high-contrast image of the environmental region with heterogeneous high-contrast images;

[0050] FIG. 3 a schematic illustration of an embodiment of a plan view high-contrast image of the environmental region adapted in brightness generated according to the invention with substantially homogenous high-contrast images;

[0051] FIG. 4 a sketchy illustration of the adaptation of the brightness of the high-contrast image according to FIG. 3 of the environmental region with a high-contrast target brightness value, a first target brightness value and a second target brightness value; and

[0052] FIG. 5 a flow diagram for adapting a brightness of a high-contrast image of an environmental region of the motor vehicle.

[0053] In the figures, identical or functionally identical elements are provided with the same reference characters.

[0054] In FIG. 1, a plan view of a motor vehicle 1 with a camera system 2 or a camera device according to an embodiment of the invention is schematically illustrated. The camera system 2 can be encompassed by a driver assistance system or a driver assistance device of the motor vehicle 1. In the embodiment, the camera system 2 includes a first camera 3, a second camera 4, a third camera 5 and a fourth camera 6. According to the embodiment, the first camera 3 is disposed on a front 7 of the motor vehicle 1, and the third camera 5 is disposed on a rear 8 of the motor vehicle 1. The second camera 4 and the fourth camera 6 are each laterally disposed on the motor vehicle 1. However, the arrangement of the cameras 3, 4, 5, 6 is variously possible, however, preferably such that an environmental region 9 around the motor vehicle 1 can be captured.

[0055] The first camera 3 captures a first partial area 10 of the environmental region 9, the second camera 4 captures a second partial area 11 of the environmental region 9, the third camera 5 captures a third partial area 12 of the environmental region 9 and the fourth camera 6 captures a fourth partial area 13 of the environmental region 9. The partial areas 10, 11, 12, 13 overlap in overlap areas 14, which are respectively disposed where partial areas 10, 11, 12, 13 directly adjoin each other. The overlap areas 14 can for example be divided by overlap area separating lines 15. Based on the overlap area separating lines 15, it can for example be determined, which of the partial areas 10, 11, 12, 13 is to be displayed in the motor vehicle 1.

[0056] The camera system 2 further includes at least one evaluation unit 16 and a display unit 17. The evaluation unit 16 is disposed centrally in the motor vehicle 1 according to the embodiment. However, the arrangement of the evaluation unit 16 is variously possible, for example, the evaluation unit 16 can be integrated in the camera 3, 4, 5, 6 or be formed as a separate unit. Multiple evaluation units 16 can for example also be provided. The display unit 17 is for example a screen. The screen can for example be formed as an LCD screen. According to the embodiment, the display unit 17 is disposed on a center console 18 of the motor vehicle 1. However, the arrangement of the display unit 17 is variously possible in the motor vehicle 1, however preferably such that a user, in particular the driver of the motor vehicle 1, has an unobstructed view to the display unit 17.

[0057] According to the embodiment, the partial areas 10, 11, 12, 13 are output on the display unit 17 for example via the evaluation unit 16.

[0058] FIG. 2 shows a known plan view high-contrast image 19 as it is provided in the prior art. The known plan view high-contrast image 19 is generated from four first high-contrast images 20. The first high-contrast images 20 are assembled to the known plan view high-contrast image 19. The boundary between the assembled first high-contrast images 20 is marked by the overlap area separating lines 15. By the known plan view high-contrast image 19, the environmental region 9 of the motor vehicle 1 can be presented on the display unit 17. This can for example be helpful in a parking procedure for a user of a motor vehicle. However, the known plan view high-contrast image 19 is disadvantageous in that the brightness of the first high-contrast images 20 is different. Thereby, a severe gradient or a severe brightness decrease or brightness increase unpleasant to the human eye arises thereby in particular at the overlap area separating lines 15. The consequence is that the known plan view high-contrast image 19 seems non-homogenous or heterogeneous to the human eye.

[0059] FIG. 3 shows a plan view high-contrast image 21 adapted according to an embodiment of the invention. The plan view high-contrast image 21 is generated from four second high-contrast images 22—according to the embodiment. The second high-contrast images 22 are further adapted with respect to their brightness than it is the case in the first high-contrast images 20. FIG. 3 thus shows the plan view high-contrast image 21, which is more homogenous with respect to the brightness or the brightness distribution than the known plan view high-contrast image 19. In particular, the plan view high-contrast image 21 is in particular homogenous or free of brightness gradients in the area of the overlap area separating lines 15. In the plan view high-contrast image 21, thus, severe brightness variations in the area of the overlap area separating lines 15 unpleasant to the human eye in particular do not arise. The brightness of the second high-contrast images 22 is preferably determined based on a target homogeneity value of the brightness of the second high-contrast images 22.

[0060] FIG. 4 shows a scheme according to an embodiment according to the invention with a high-contrast brightness value 23, which is determined from the first high-contrast image 20. The determination of the high-contrast brightness value 23 can for example be effected with an arithmetic mean or a weighting function. The high-contrast brightness value 23 can also be determined only in certain areas in the first high-contrast image 20. The high-contrast brightness value 23 is in particular a scalar. A brightness 28 of the first high-contrast image 20 is adapted within a lower brightness variation limit value 24 and an upper brightness variation limit value 25. The adaptation is for example effected based on the histogram of the first high-contrast image 20. Thus, the brightness 28 of the high-contrast image 20, 22 can be adapted. The brightness 28 can be adapted by the first target brightness value and/or the second target brightness value and the consequent adaptation of the first camera parameter and/or the second camera parameter via the boundaries of the lower brightness variation limit value 24 and/or the upper brightness variation limit value 25. The brightness 28 is preferably adapted via a luminance channel of the high-contrast image 20, 22. The luminance channel can for example be described by the Y channel in a YUV color model. However, the first image and/or the second image and/or the third image and/or the fourth image and/or the first high-contrast image 20 and/or the second high-contrast image 22 can for example also be present in another color model such as an RGB color model.

[0061] FIG. 5 shows an exemplary flow diagram of the invention for adapting the brightness 28 of the first high-contrast image 20. In a step S1, based on the target homogeneity value of the brightness 28 of the second high-contrast images 22, it is determined if the first high-contrast image 20 is adapted with respect to the brightness 28. If the brightness 28 of the first high-contrast image 20 matches with respect to the target homogeneity value, thus, the first high-contrast image 20 is displayed or output on the display unit 17 as the second high-contrast image 22 in the plan view high-contrast image 21 with a step S2. If the target homogeneity value is not yet satisfied by the first high-contrast image 20, thus, the first high-contrast image 20 is adapted depending on a high-contrast target brightness value in a step S3. To this, a high-contrast brightness value is determined from the first high-contrast image 20, which is compared to the high-contrast target brightness value or a YUV log target value. Depending on the comparison, the first high-contrast image 20 is adapted with respect to the brightness 28. The first high-contrast image 20 is preferably in a YUV color model, and preferably the luminance channel, thus the Y channel, of the first high-contrast image 20 is adapted. However, the adaptation in step S3 is restricted by the lower brightness variation limit value 24 and the upper brightness variation limit value 25 in the amount of the brightness adaptation. This means that the brightness 28 of the first high-contrast image 20 can only be adapted within the limits of the lower brightness variation limit value 24 and the upper brightness variation limit value 25. In a step S4, it is determined if the adaptation of the first high-contrast image 20 within the lower brightness variation limit value 24 and the upper brightness variation limit value 25 was sufficient to satisfy the criterion of the target homogeneity value. If the criterion of the target homogeneity value can be satisfied by the adaptation in step S3, thus, a step S6 follows, in which the high-contrast brightness value 23 in context of step S1 is compared to the target homogeneity value to homogenously integrate the first high-contrast image 20 in the plan view high-contrast image 21 as the second high-contrast image 22. If the adaptation of the first high-contrast image 20 in step S3 does not satisfy the target homogeneity value, thus, subsequent to step S4, a further adaptation of the brightness 28 of the first high-contrast image 20 is performed. Thus, in a step S5, a first camera parameter and a second camera parameter are adapted. The first high-contrast image 20 is generated with a first image and a second image. The first image is captured with the first camera parameters and the second image is captured with the second camera parameters. If it is now determined in step S4 that the first high-contrast image 20 cannot be further adapted with respect to the brightness 28 due to the lower brightness variation limit value 24 and/or the upper brightness variation limit value 25, thus, the first camera parameter and/or the second camera parameter are accordingly adapted in the temporally subsequent capturing process. Thus, for the second high-contrast image 22, which is provided after the first high-contrast image 20 in time, a third image and a fourth image are captured to generate the second high-contrast image 22. For the third image and the fourth image, the adapted first camera parameter and the adapted second camera parameter are used. By adapting the first camera parameter and/or the second camera parameter, thus, the second high-contrast image 22 can satisfy the high-contrast target brightness value 23 in step S2 in a next passage of the flow diagram of FIG. 5, or otherwise the adaptation in step S3 can be allowed without the adaptation being restricted by the lower brightness variation limit value 24 and/or the upper brightness variation limit value 25.

[0062] The first high-contrast image 20 and/or the second high-contrast image 22 are preferably characterized by 20 bits with respect to their bit depth.

[0063] The cameras 3, 4, 5, 6 can be CMOS (complementary metal-oxide-semiconductor) cameras or else CCD (charge-coupled device) cameras or else special HDR cameras. The cameras 3, 4, 5, 6 are in particular video cameras, which continuously provide an image sequence. The special HDR camera can simultaneously provide the first image and the second image or the third image and the fourth image. With the camera 3, 4, 5, 6 as a conventional LDR camera, the third image and the fourth image or the first image and the second image are in particular consecutively captured.

[0064] The first camera parameter and the second camera parameter are in particular characterized by an exposure time parameter of the camera 3, 4, 5, 6 and/or a light sensitivity parameter of the camera 3, 4, 5, 6. Thus, it can thereby be responded to the lighting conditions in the environmental region 9 for the third image and the fourth image due to the experience from the first image and the second image. The first camera parameter and/or the second camera parameter are therefore correspondingly adapted to the lighting conditions of the environmental region 9. The first image and the second image and the third image and the fourth image are provided within a fraction of a second, whereby a variation of the lighting conditions in the environmental region 9 occurs only to a limited extent and the effects thereof can therefore be tolerated.

[0065] Preferably, before displaying the plan view high-contrast image 21 on the display unit 17, a tone mapping method is performed to reduce the plan view high-contrast image 21 with respect to its bit depth, in particular to 8 bits for each color channel of the plan view high-contrast image 21.