In-vehicle imaging device

Abstract

To provide an on-vehicle imaging device capable of ensuring the uniformity of brightness of captured images.SOLUTION: An on-vehicle imaging device includes a front camera 2 and a processing unit. The front camera 2 is installed inside a vehicle cabin of a vehicle and takes an image of the outside of the vehicle through a windshield 5 of the vehicle. The processing unit performs correction processing of the captured image taken by the front camera 2. The windshield 5 is positioned so that it approaches the front end of the vehicle as it goes from an upper side of the vehicle to a lower side. The windshield 5 is inclined with respect to an optical axis 2a, in the XZ plane including the optical axis 2a of the front camera 2. The processing unit 16 corrects the brightness of the captured image by multiplying the luminance of pixels in an upper region of the captured image by a first correction value and by multiplying the luminance of pixels in a lower region of the captured image by a second correction value that is larger than the first correction value.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to an in-vehicle imaging device. [Background technology]

[0002] International Publication No. WO 2016 / 132923 is a known technical document relating to an in-vehicle imaging device that captures an image of the outside of a vehicle through the vehicle's window glass. International Publication No. WO 2016 / 132923 discloses a technology for preventing double images from appearing in a captured image by blocking the progression of a secondary light beam emitted from the same location as the primary light beam when the window glass is tilted. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2016 / 132923 Summary of the Invention [Problem to be solved by the invention]

[0004] When the window glass is tilted as in the above-mentioned prior art, the light transmittance of the window glass depends on the angle of incidence of the incident light, which may result in a decrease in the uniformity of the brightness of the captured image.

[0005] An object of the present disclosure is to provide an in-vehicle imaging device that can suppress a decrease in the uniformity of the luminance of a captured image. [Means for solving the problem]

[0006] The in-vehicle imaging device of the present disclosure includes a camera that is provided in a vehicle interior and captures an image of the outside of the vehicle through a window glass that constitutes an exterior surface of the vehicle, and a processing unit that executes correction processing of the captured image captured by the camera, The camera does not have a polarizing filter that separates light for each polarization direction, so the captured image is not a polarized image.The window glass is positioned so that it approaches the outer edge of the vehicle as it moves from the top to the bottom, and is inclined with respect to the optical axis of the camera in a vertical cross section including the optical axis.The processing unit corrects the brightness of the captured image by multiplying the brightness of pixels in the upper region of the captured image by a first correction value and multiplying the brightness of pixels in the lower region of the captured image that does not overlap with the upper region by a second correction value that is greater than the first correction value.

[0007] The in-vehicle imaging device of the present disclosure includes: the camera further comprises a relative angle acquisition unit that acquires the relative angle between the window glass and the camera each time the camera is started up, a view angle acquisition unit that acquires the view angle each time the camera is started up, a storage unit that stores information on the light transmittance characteristics of the window glass, and a correction map creation unit that creates a correction map including a plurality of correction values ​​that gradually increase from the top to the bottom of the captured image based on the information on the relative angle acquired by the relative angle acquisition unit, the information on the view angle of the camera acquired by the view angle acquisition unit, and the information on the light transmittance characteristics of the window glass stored in the storage unit, The processing unit may correct the luminance of the captured image by multiplying the luminance of a pixel by the correction map according to the position of the pixel in the captured image. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to provide an in-vehicle imaging device that can suppress a decrease in the uniformity of the luminance of a captured image. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a block diagram showing an in-vehicle imaging device according to an embodiment; [Figure 2] FIG. 2 is a side view of the windshield and forward-facing camera. [Figure 3] FIG. 2 is a schematic diagram of an image captured by a front camera. [Figure 4] 1 is a graph showing light transmittance characteristics of a windshield. [Figure 5] 5A and 5B are schematic diagrams of captured images before and after correction processing. [Figure 6] 10 is a flowchart showing a correction process for a captured image. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0011] As shown in FIG. 1, the vehicle-mounted imaging device 1 includes a front camera 2, an angle sensor 3, a display 4, and an ECU (Electronic Control Unit) .

[0012] The front camera 2 is provided inside the vehicle's cabin. The front camera 2 captures an image in front of the vehicle. The front camera 2 transmits information about the captured image to the ECU 10. The angle sensor 3 detects the tilt angle of the front camera 2 relative to the horizontal direction. The angle sensor 3 transmits information about the tilt angle of the front camera 2 to the ECU 10. The display 4 is provided, for example, on the instrument panel of the vehicle. The display 4 displays a screen according to a signal from the ECU 10.

[0013] The ECU 10 is an electronic control unit having a central processing unit (CPU) and a storage unit such as a read-only memory (ROM) or a random access memory (RAM). The ECU 10 realizes various functions by, for example, executing programs stored in the storage unit by the CPU.

[0014] As shown in FIG. 2, the windshield (window glass) 5 forms the outer surface of the vehicle and is disposed so as to approach the outer periphery of the vehicle from the top to the bottom. Specifically, the windshield 5 is a plate-shaped glass that is inclined so as to approach the front end of the vehicle from the top to the bottom in the Z-axis direction (vertical direction). The upper end of the windshield 5 is located closer to the rear end of the vehicle than the lower end of the windshield 5. The front camera 2 captures an image of the outside of the vehicle through the windshield 5 of the vehicle. The optical axis 2a of the front camera 2 extends along the X-axis direction (the front-to-rear direction of the vehicle).

[0015] The optical axis 2a of the front camera 2 is inclined with respect to the windshield 5 in a vertical cross section (XZ plane) including the optical axis 2a. In the XZ plane, the relative angle α between the optical axis 2a of the front camera 2 and the windshield 5 is, for example, an acute angle. The relative angle α is the angle between the portion of the optical axis 2a that extends from the intersection of the optical axis 2a and the windshield 5 toward the interior of the vehicle, and the portion of the windshield 5 that is above the optical axis 2a.

[0016] Incident light L enters the front camera 2 within the range of the angle of view β of the front camera 2. The range of angles that the incident light L that enters the front camera 2 makes with the optical axis 2a of the front camera 2 is greater than or equal to -β / 2 and less than or equal to +β / 2. As described above, since the relative angle α between the optical axis 2a of the front camera 2 and the windshield 5 is an acute angle, the angle that the incident light L makes with the normal N of the windshield 5 (hereinafter referred to as the "incident angle") gradually increases from the top to the bottom in the Z-axis direction. The minimum incident angle γ1 of the incident light L in the XZ plane and the maximum incident angle γ2 of the incident light L in the XZ plane are each determined by the relative angle α and the angle of view β.

[0017] As shown in FIG. 3, the captured image 20 captured by the front camera 2 includes multiple regions lined up in the Z-axis direction (height direction of the captured image 20). The captured image 20 includes an upper region 21 and a lower region 22 located below the upper region 21. The upper region 21 and the lower region 22 each extend to both ends of the captured image 20 in the Y-axis direction (width direction of the captured image 20). The upper region 21 and the lower region 22 are any two regions of the captured image 20 that are lined up in the Z-axis direction. The upper region 21 and the lower region 22 may be adjacent to each other or may be separated from each other. The upper region 21 and the lower region 22 do not overlap.

[0018] The upper region 21 is a region corresponding to the incident light L1 (see FIG. 2). That is, the image of the incident light L1 is displayed in the upper region 21. The lower region 22 is a region corresponding to the incident light L2 (see FIG. 2). That is, the image of the incident light L2 is displayed in the lower region 22. The incident light L2 is incident on the windshield 5 and the front camera 2 from below the incident light L1 in the XZ plane. The incident angle of the incident light L2 is larger than the incident angle of the incident light L1.

[0019] As shown in Fig. 4, the windshield 5 has a light transmittance characteristic T. The light transmittance characteristic T indicates the correlation between the angle of incidence of incident light L (horizontal axis) and the light transmittance of the windshield 5 (vertical axis). The light transmittance decreases as the angle of incidence of the incident light L increases within the range between the minimum incident angle γ1 and the maximum incident angle γ2.

[0020] As described above, because the angle of incidence of incident light L2 is larger than the angle of incidence of incident light L1, the light transmittance of incident light L2 through the windshield 5 is smaller than the light transmittance of incident light L1 through the windshield 5. Therefore, the luminance reduction rate of the lower region 22 of the captured image 20 corresponding to incident light L2 tends to be larger than the luminance reduction rate of the upper region 21 of the captured image 20 corresponding to incident light L1. The luminance reduction rate is the difference between the luminance when incident light enters the camera not through the window glass and the luminance when incident light enters the camera through the window glass, divided by the luminance when incident light enters the camera not through the window glass.

[0021] The ECU 10 executes a correction process for the captured image 20. Specifically, as shown in Fig. 1, the ECU 10 includes, as functional components, a relative angle acquisition unit 11, a field of view acquisition unit 12, a light transmittance characteristic acquisition unit 13, a correction map creation unit 14, a storage unit 15, and a processing unit 16.

[0022] The relative angle acquisition unit 11 acquires information on the relative angle α between the optical axis 2a of the front camera 2 and the windshield 5. The relative angle acquisition unit 11 acquires information on the relative angle α based on information on the inclination angle of the windshield 5 stored in advance in the storage unit 15 and information on the inclination angle of the front camera 2 transmitted from the angle sensor 3. The relative angle acquisition unit 11 acquires information on the relative angle α each time the front camera 2 is activated.

[0023] The angle of view acquisition unit 12 acquires information on the angle of view β of the front camera 2 based on the imaging conditions (focal length, etc.) of the front camera 2. The angle of view acquisition unit 12 acquires information on the angle of view β every time the front camera 2 is started. The light transmittance characteristic acquisition unit 13 acquires information on the light transmittance characteristic T of the windshield 5 that is stored in advance in the storage unit 15.

[0024] The correction map creation unit 14 creates a correction map based on information on the relative angle α, information on the angle of view β of the front camera 2, and information on the light transmittance characteristic T. The correction map is a map used to correct the brightness of the captured image 20. The correction map includes a plurality of correction values ​​corresponding to each region of the captured image 20. The correction map indicates the correlation between the angle of incidence of the incident light L corresponding to each region of the captured image 20 and the correction value.

[0025] The correction map shows a trend opposite to that of the light transmittance characteristic T. The correction values ​​of the correction map increase as the angle of incidence of the incident light L increases. In other words, the correction values ​​of the correction map gradually increase from the top to the bottom of the captured image 20 in the Z-axis direction. Each correction value is, for example, a positive number. The correction value is, for example, the reciprocal of the luminance reduction rate of the area of ​​the captured image 20 corresponding to the correction value.

[0026] The correction map includes a first correction value corresponding to an upper region 21 of the captured image 20 and a second correction value corresponding to a lower region 22 of the captured image 20. The second correction value is larger than the first correction value. The first correction value is, for example, the reciprocal of the luminance reduction rate of the region of the captured image 20 corresponding to the incident light L1. The second correction value is, for example, the reciprocal of the luminance reduction rate of the region of the captured image 20 corresponding to the incident light L2. The correction map creation unit 14 creates a correction map each time the front camera 2 is activated.

[0027] The storage unit 15 stores the correction map created by the correction map creation unit 14. The storage unit 15 also stores information on the inclination angle of the windshield 5, information on the light transmittance characteristic T of the windshield 5, and the like.

[0028] The processing unit 16 corrects the luminance of the captured image 20 by executing a correction process on the captured image 20. Specifically, the processing unit 16 multiplies the luminance of pixels in the upper region 21 of the captured image 20 by a first correction value, and multiplies the luminance of pixels in the lower region 22 of the captured image 20 by a second correction value. Because the second correction value is greater than the first correction value, the difference in luminance of the lower region 22 before and after correction is greater than the difference in luminance of the upper region 21 before and after correction.

[0029] The processing unit 16 multiplies the luminance of a pixel in the captured image 20 by a correction map including a first correction value and a second correction value according to the position of the pixel in the captured image 20. Specifically, the processing unit 16 multiplies the luminance of a pixel in the captured image 20 by the correction map so that a larger correction value corresponds to a pixel located further downward in the captured image 20. The processing unit 16 corrects the luminance of multiple regions in the captured image 20 in a single process. The processing unit 16 multiplies the luminance of a pixel in the captured image 20 by the correction map created each time the front camera 2 is activated each time the front camera 2 is activated.

[0030] As shown in (a) of FIG. 5, the light transmittance of incident light L2 through the windshield 5 is lower than the light transmittance of incident light L1 through the windshield 5, so the luminance reduction rate in the lower region 22 of the captured image 20 tends to be higher than the luminance reduction rate in the upper region 21 of the captured image 20. As an example, the lower region 22 tends to be darker than the upper region 21. When such a captured image 20 is multiplied by the correction map described above, the difference between the luminance reduction rate in the upper region 21 and the luminance reduction rate in the lower region 22 becomes smaller, as shown in (b) of FIG. 5. In other words, the luminance unevenness in the captured image 20 caused by differences in the transmittance of the incident light L is reduced.

[0031] Next, the processing of the ECU 10 will be described. As shown in Fig. 6, in step S1, the ECU 10 acquires the relative angle α between the windshield 5 and the front camera 2. In step S2, the ECU 10 acquires the angle of view β of the front camera 2. In step S3, the ECU 10 acquires the light transmittance characteristic T of the windshield 5. In step S4, the ECU 10 creates a correction map based on the relative angle α, the angle of view β, and the light transmittance characteristic T. In step S5, the ECU 10 corrects the brightness of the captured image 20 by multiplying the correction map by the brightness of the pixels of the captured image 20.

[0032] As described above, in the in-vehicle image capture device 1, the windshield 5 is disposed so as to approach the front end of the vehicle as it moves from the top to the bottom. The windshield 5 is inclined with respect to the optical axis 2a of the forward-facing camera 2 in the XZ plane including the optical axis 2a. In such a case, the optical transmittance of the incident light L2 corresponding to the lower region 22 of the captured image 20 through the windshield 5 is lower than the optical transmittance of the incident light L1 corresponding to the upper region 21 of the captured image 20 through the windshield 5. Therefore, the luminance reduction rate of the lower region 22 tends to be greater than that of the upper region 21. The processing unit 16 corrects the luminance of the captured image 20 by multiplying the luminance of the pixels in the upper region 21 by a first correction value and by multiplying the luminance of the pixels in the lower region 22 by a second correction value greater than the first correction value. This reduces the difference between the luminance reduction rate of the upper region 21 and the luminance reduction rate of the lower region 22. Therefore, the in-vehicle image capture device 1 can suppress deterioration in the uniformity of the luminance of the captured image 20. If the decrease in the uniformity of the brightness of the captured image 20 is suppressed, it is possible to prevent the same object from being recognized as separate objects due to the decrease in uniformity of the brightness, or to prevent a decrease in the detection accuracy based on the brightness threshold.

[0033] In the in-vehicle image capture device 1, the processing unit 16 corrects the luminance of the captured image 20 by multiplying the luminance of a pixel in the captured image 20 by a correction map including a plurality of correction values ​​that gradually increase from the top to the bottom of the captured image 20, depending on the position of the pixel in the captured image 20. According to this configuration, by performing a single correction process on one captured image 20, it is possible to efficiently suppress a decrease in the uniformity of the luminance of the captured image 20.

[0034] In the in-vehicle image capture device 1, the processing unit 16 multiplies the luminance of the pixels of the captured image 20 by the correction map created each time the front camera 2 is activated. With this configuration, even if the tilt angle of the front camera 2 with respect to the windshield 5 changes, accurate correction processing can be performed using an accurate correction map based on the accurate tilt angle of the front camera 2.

[0035] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments. The present disclosure can be implemented in various forms including the above-described embodiments and various modifications and improvements based on the knowledge of those skilled in the art.

[0036] Although the correction values ​​of the correction map are, for example, the reciprocals of the luminance reduction rate of the region of the captured image 20 corresponding to the correction values, the correction values ​​may be the reciprocals of the light transmittance of the incident light L corresponding to the correction values. The first correction value may be the reciprocal of the light transmittance of the incident light L1. The second correction value may be the reciprocal of the light transmittance of the incident light L2.

[0037] The processing unit 16 does not need to create a correction map. The processing unit 16 may use a correction map that is calculated based on the design values ​​of the vehicle (such as the tilt angle of the windshield 5) and stored in advance. In this case, the ECU 10 does not need to include the relative angle acquisition unit 11, the angle of view acquisition unit 12, the light transmittance characteristic acquisition unit 13, and the correction map creation unit 14. The processing unit 16 only needs to be able to execute the correction process for the captured image 20. Furthermore, the in-vehicle image capture device 1 does not need to include the angle sensor 3 or the display 4.

[0038] The processing unit 16 does not need to use a correction map when correcting the luminance of the captured image 20. Specifically, the storage unit 15 stores several correction values ​​corresponding to several incident light beams L. The processing unit 16 calculates correction data indicating the correlation between the incident angle and the correction value based on each incident angle and each correction value. The processing unit 16 corrects the luminance of the captured image 20 by multiplying the correction data by the luminance of the captured image 20. In such a case, the amount of data stored in the storage unit 15 can be reduced.

[0039] Although the windshield 5 is shown as an example of window glass, the window glass may be a rear window or a side window. Although the front camera 2 is shown as an example of a camera, the camera may capture an image of the outside of the vehicle through a rear window or a side window. The vehicle equipped with the in-vehicle imaging device 1 may be an autonomous vehicle. [Explanation of symbols]

[0040] 1...in-vehicle imaging device, 2...front camera, 2a...optical axis, 5...windshield, 16...processing unit, 20...captured image, 21...upper region, 22...lower region

Claims

1. a camera provided in a vehicle interior for capturing an image of the outside of the vehicle through a window glass that constitutes an exterior surface of the vehicle; a processing unit that executes a correction process for the captured image captured by the camera, The camera does not have a polarizing filter that separates light into different polarization directions, The captured image is not a polarized image, the window glass is disposed so as to approach an outer periphery of the vehicle from an upper side to a lower side of the vehicle, and is inclined with respect to the optical axis of the camera in a vertical cross section including the optical axis of the camera, the processing unit corrects the brightness of the captured image by multiplying the brightness of pixels in an upper region of the captured image by a first correction value, and by multiplying the brightness of pixels in a lower region of the captured image that does not overlap with the upper region by a second correction value that is greater than the first correction value.

2. A relative angle acquisition unit that acquires a relative angle between the window glass and the camera each time the camera is started; a field of view acquisition unit that acquires a field of view each time the camera is started; a storage unit that stores information about the light transmittance characteristics of the window glass; a correction map creation unit that creates a correction map including a plurality of correction values ​​that gradually increase from the top to the bottom of the captured image, based on information about the relative angle acquired by the relative angle acquisition unit, information about the angle of view of the camera acquired by the angle of view acquisition unit, and information about the light transmittance characteristics of the window glass stored in the storage unit; and Further provided with The vehicle-mounted image capture device according to claim 1 , wherein the processing unit corrects the luminance of the captured image by multiplying the luminance of the pixel by the correction map according to the position of the pixel in the captured image.

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