Source: https://patents.google.com/patent/JP4970516B2/en
Timestamp: 2020-02-25 10:41:31
Document Index: 360356639

Matched Legal Cases: ['art 161', 'art 121', 'art 131', 'art 110', 'art 121', 'art 131', 'art 141', 'art 151', 'art 161']

JP4970516B2 - Surrounding confirmation support device - Google Patents
Surrounding confirmation support device Download PDF
JP4970516B2
JP4970516B2 JP2009226373A JP2009226373A JP4970516B2 JP 4970516 B2 JP4970516 B2 JP 4970516B2 JP 2009226373 A JP2009226373 A JP 2009226373A JP 2009226373 A JP2009226373 A JP 2009226373A JP 4970516 B2 JP4970516 B2 JP 4970516B2
JP2009226373A
JP2011077772A5 (en
JP2011077772A (en
2011-04-14 Publication of JP2011077772A publication Critical patent/JP2011077772A/en
2011-08-11 Publication of JP2011077772A5 publication Critical patent/JP2011077772A5/ja
2012-07-11 Publication of JP4970516B2 publication Critical patent/JP4970516B2/en
The present invention relates to a surrounding confirmation support device that displays a vehicle surrounding image captured by an in-vehicle camera and assists a passenger to check the surroundings of the vehicle.
When parking the vehicle in the parking lot, it recognizes the white line drawn on the road surface and the space without other vehicles, automatically recognizes the parking space that can be parked, and senses the surrounding situation before parking A method for supporting the operation is known.
For example, a steering state detection means for detecting the steering state of the vehicle, a parking area detection means for detecting a parking area by image recognition based on an image from a camera, and a predicted travel path of the vehicle based on information from the steering state detection means. There has been proposed a parking assistance device that includes a predicted traveling locus calculation means to be calculated, and a notification means that provides information to assist the parking to the driver based on the predicted traveling locus and parking section information (see, for example, Patent Document 1). .
In recent years, for the purpose of easily grasping the relative position between the vehicle and the parking section during the parking operation, images from a plurality of in-vehicle cameras are synthesized, and an overhead image equivalent to that obtained by directly imaging the vehicle is obtained. The technology to create is proposed.
However, when creating a single bird's-eye view image by combining multiple images captured by multiple in-vehicle cameras, the brightness and contrast cannot be adjusted properly between the cameras or in the images of each in-vehicle camera. There is a problem that the object cannot be observed with good visibility. For example, even if an in-vehicle camera captures a clean and easy-to-view image, another in-vehicle camera often faces the sun, and another in-vehicle camera is in the shadow of an adjacent vehicle. . And since the orientation of each in-vehicle camera cannot be controlled and is often fixed, the state of the subject for each camera changes from moment to moment due to changes in the road up and down, traveling direction, weather, etc. The brightness and color balance of the captured image of the camera changes from moment to moment.
For example, Patent Documents 2 and 3 are known as techniques for combining images captured by a plurality of cameras. Japanese Patent Application Laid-Open No. 2004-228561 discloses a technique for performing gradation correction using an average luminance value of overlapping areas of images captured by a plurality of in-vehicle cameras as a reference value. In the technique disclosed in Patent Document 2, images with different exposure amounts are photographed while a vehicle is moving, and a plurality of photographed images are combined after overhead conversion so that the dynamic range is wide and the visibility is high. Is intended to generate.
Further, Patent Document 3 discloses a technique for extracting partial images with appropriate exposure amounts from images captured by a plurality of cameras and synthesizing the images. The technique disclosed in Patent Document 3 generates a composite image by extracting images with appropriate exposure amounts from a plurality of images obtained by photographing the same region using a plurality of imaging devices having different exposure amounts. The purpose is to generate easy-to-view composite video.
JP 11-339194 A Japanese Patent No. 3297040 JP 2004-96488 A
However, when a plurality of images are adjusted using the luminance value of the overlapping portion based on the technology disclosed in Patent Document 2, the user wants to visually confirm parking lot lines and surrounding people in the images in each camera. When the contrast of a part is lowered or when halation due to intense light occurs, the brightness in a dark region is further lowered due to the influence. In particular, when a bird's-eye view video is provided for the purpose of monitoring the surroundings during the parking operation, it is a big problem that the visibility is lowered and the surrounding persons cannot be seen.
Further, according to the technique disclosed in Patent Document 3, when an appropriate partial image is extracted from the overlapped image and synthesized, it becomes discontinuous at the boundary portion of the synthesis, so that the visibility is also lowered.
The present invention has been made in view of the above problems, and an object of the present invention is to provide a surrounding confirmation support device that assists an occupant to easily confirm the surroundings of a vehicle based on an image captured by an in-vehicle camera. Is to provide.
A surroundings confirmation support device of the present invention that solves the above-described problem is a surroundings confirmation support device that displays an image of the surroundings of a vehicle and assists a passenger to check the surroundings of the vehicle. An image capturing unit that captures an image with an exposure amount, an image recognition unit that recognizes a predetermined recognition target by performing image processing on a plurality of images captured by the image capturing unit and having different exposure amounts, and recognition by the image recognition unit An image composition unit that generates a composite image from an image based on the result, and a display unit that displays the composite image synthesized by the image composition unit.
ADVANTAGE OF THE INVENTION According to this invention, the visibility of the object which a driver should pay attention in parking operation | movement, such as a parking frame line and a pedestrian around a self-vehicle, can be improved in the outdoor environment where an illumination fluctuation is large.
The system block diagram of the circumference | surroundings confirmation assistance apparatus concerning this Embodiment. The figure which shows the example of arrangement | positioning of the imaging part mounted in a vehicle. The figure which shows the structure with a single imaging part. The figure which shows a structure when a control signal cannot be given to a shutter speed control part. The figure which shows a structure in the case of having a some image memory | storage part. The figure which shows the flow of the whole process. The figure which showed how a person is reflected in a bird's-eye view image. The figure explaining the content of the parking assistance method. The figure which shows overhead view conversion. The figure which shows the surrounding condition of the own vehicle at the time of parking assistance. The figure which shows the example of an image obtained from a camera. The figure which shows the example of an image obtained from a camera. The figure which shows that the appearance of a parking frame changes with exposure amounts. The figure which shows the image of different exposure amount, and its weight map. The figure which shows the recognition result of a parking frame. The figure which shows the system which changes shutter speed. The figure which shows the system which changes a different shutter speed. The figure which shows the production | generation method of the weight map in 1st Embodiment. The block diagram which uses the brightness correction parameter of image recognition instead of physical shutter control. The figure which shows the recognition result of a parking frame. The figure which shows the image of different exposure time, and its weight map.
Next, the surrounding confirmation support apparatus according to the first embodiment will be described with reference to the drawings.
For example, an object that is noticed by a driver who is an occupant in a parking operation varies depending on the scene and purpose. In the present embodiment, a parking frame drawn on the ground will be described as an example. In addition to parking frames, objects such as pedestrians and other vehicles that move around the vehicle, three-dimensional structures such as walls, pillars, wheel stops, and stopped vehicles, dangerous objects such as falling objects and side grooves, There are various things.
The driver pays attention to the parking frame that forms the outer periphery of the parking space in order to ensure that the vehicle travels within the parking space that is the parking destination and finely adjusts the position and orientation (for example, FIG. See FIG. The parking frame 20 is usually composed of a white line or a yellow line as a road marking drawn on the ground such as asphalt or concrete road surface. For example, as shown in FIG. 10, the parking frame 20 is formed by a front line 21, left and right side lines 22, and a rear line 23. The
In an environment with strong lighting, a parking frame 20 is drawn with a bright yellow line on a white concrete road surface, and considering an environment where there is black oil stains in the vicinity, images shot in such an environment are usually Although the contrast of the entire image itself is high, the contrast between the road surface and the frame line that are likely to be overexposed is low and the visibility is poor.
In this case, it is possible to increase the contrast between the road surface and the frame line by reducing the aperture diameter of the camera and shortening the exposure time (decreasing the exposure amount), but the image becomes dark at other portions. . As described above, when trying to improve the image quality using the conventional technology, there is a problem that the visibility of a necessary target cannot always be improved.
In the surrounding confirmation support device according to the present embodiment, a parking frame recognition process is performed on each of a plurality of images acquired so that the exposure amounts are different from each other. Therefore, it is preferentially used for image composition.
<Description of the configuration of the surrounding confirmation support device (basic part)>
FIG. 1 is a diagram illustrating the configuration of the surrounding confirmation support apparatus according to the present embodiment.
The surrounding confirmation support device 1 stores a plurality of imaging units 101 to 104, shutter speed control units 111 to 114 for controlling exposure of the imaging units 101 to 104, and images captured by the imaging units 101 to 104. Image storage unit 121, image recognition unit 131 that performs object recognition processing from images stored in image storage unit 121, images stored in image storage unit 121, and image recognition obtained from image recognition unit 131 An image composition unit 141 that composes images based on the result of the above, and a display unit 151 that displays a composite image obtained from the image composition unit 141.
The image capturing units 101 to 104 capture a predetermined range around the host vehicle and input the image to the image storage unit 121, and are configured by a camera having a CCD and a lens, for example. Each of the imaging units 101 to 104 captures images with different exposure amounts.
FIG. 2 is a diagram illustrating an arrangement example of the imaging units mounted on the vehicle. As shown in FIG. 2, the imaging unit 101 is arranged on the left side of the vehicle 10 to form a left side camera that images the left side of the vehicle 10, and the imaging unit 102 is arranged on the right side of the vehicle 10. Thus, a right side camera that images the right side of the vehicle 10 is configured.
The imaging unit 103 is arranged at the rear of the vehicle 10 to form a rear camera that images the rear of the vehicle 10, and the imaging unit 104 is arranged at the front of the vehicle 10 and images the front of the vehicle 10. The front camera is configured.
For example, when the vehicle 10 is parked in a parking space as shown in FIG. 10, the imaging units 101 to 104 are attached to the vehicle 10 so as to capture a range of about 5 meters around the host vehicle. Therefore, for example, images as shown in FIGS. 11 and 12 are obtained by the imaging units 101 and 102. Further, the vehicle 10 is mounted with a light for illuminating the periphery of the vehicle as a lighting built in a door mirror (none of which is shown). The distance of 5 meters described above is an example, and may be changed depending on the size of the host vehicle and the operating environment. For example, when the present invention is used for the purpose of improving the visibility of surrounding persons in a construction machine such as a large hydraulic excavator, it is suitable to capture a wider range.
The image storage unit 121 stores each image obtained from the imaging units 101 to 104, the time when the image was obtained, and the exposure time as a set. In addition, the latest image captured by each of the imaging units 101 to 104 is provided to the image recognition unit 131. Furthermore, any stored image including images stored in the past is provided in response to a request from the image composition unit 141. As a storage form of the image storage unit 121, for example, a memory such as a RAM, a communication interface, a control microcomputer, or a computer program instead of an independent module may be used.
The image recognizing unit 131 executes image recognition processing for recognizing the parking frame 20 with respect to an image at a certain time and a certain exposure amount obtained from the imaging units 101 to 104. Among the imaging units 101 to 104, when the result of parking frame recognition for images with different exposure amounts obtained from the same imaging unit is different, which exposure amount is based on the accuracy of the parking frame 20 recognized by the image recognition process. Whether the image area is suitable for recognition, that is, whether the visibility is high. The accuracy represents the accuracy of recognition of the recognition object by the image recognition unit 131.
The image synthesizing unit 141 synthesizes a plurality of images having different exposure amounts based on the visibility (accuracy) of the image area calculated by the image recognizing unit 131. First, with respect to a plurality of images having different exposure amounts respectively obtained by the imaging units 101 to 104, the images are synthesized for each of the imaging units 101 to 104, and one synthesized image for each of the imaging units 101 to 104. Is generated. Next, by synthesizing and synthesizing four highly visible composite images created for each of the imaging units 101 to 104, a highly visible vehicle surrounding composite image (see, for example, FIG. 20) is generated. .
Note that visibility is not always high when all regions of one image obtained from a certain imaging unit have a single exposure amount. Figure 13 is a diagram showing an example of an image captured on the left side of the vehicle, the image I1 captured by exposure E1, shows an image I2 captured with an exposure amount E2.
For example, the image I1 picked up with the exposure amount E1 has high visibility in the left area of the image and low visibility in the right area of the image. Further, the image I2 captured with the exposure amount E2 has high visibility in the right side area of the image and low visibility in the left side area of the image.
In such a case, the image combining unit 141 generates an image I3 that is a combined image obtained by combining the left region of the image I1 and the right region of the image I2. Therefore, the visibility of the parking frame 20 that is the recognition target in the composite image I3 can be increased.
Then, the image composition unit 141 concatenates and composes the composite images created for each of the image pickup units 101 to 104, and generates a vehicle surrounding composite image that is an overhead view image equivalent to the image of the vehicle 10 taken from directly above. Generate.
The display unit 151 is a device for presenting the vehicle surroundings composite image generated by the image composition unit 141 to a driver who is a user. For example, it is possible to present video information to a user such as a driver, such as a car navigation monitor, a monitor built in a rearview mirror, or a projector device that can project onto a windshield. In this configuration, first, images of a plurality of exposure amounts are synthesized in the areas of the imaging units 101 to 104, and then the synthesized images of the imaging units 101 to 104 are connected and synthesized, whereby the imaging units 101 to 104 are combined. There is an effect that it can be optimized so as to improve the visibility.
Moreover, in addition to the above-mentioned structure, you may have the vehicle information provision part 161 and the exposure amount information holding | maintenance part as an expansion part. The vehicle information providing unit 161 and the exposure amount information holding unit are used to improve the processing of the image recognition unit 131 and the image composition unit 141.
In the vehicle information providing unit 161, the vehicle position, the wheel speed, the rudder angle, the wheel angle, and the information on sensors mounted on the vehicle 10 such as the vehicle position measurement system are used to determine the relative vehicle position in each captured image. It is calculated and added to information when the image storage unit 121 stores the image.
When multiple images with different exposure amounts are captured by the same imaging unit, the imaging timing of each image is different, so if the subject vehicle or surrounding objects are moving, the imaging object moves in the image and Image composition cannot be performed.
For this reason, the apparent amount of movement between the images can be calculated based on the relative own vehicle position, and the image composition unit 141 can align a plurality of images. In addition, when the brake lamp lighting information by the side brake is obtained, it is clear that the host vehicle is stopped, and it is understood that it is not necessary to align a plurality of images. The information can be added to the information when the image is stored in the unit 121 and used for the composition processing in the image composition unit 141.
In addition, when headlamp lighting information and wiper operation information are obtained, the external illumination state is dark and the captured image is likely to be blurred, and clear feature points when combining multiple images Therefore, it can be used for the composition processing in the image composition unit 141 by adding it to the information when the image storage unit 121 stores the image.
The exposure amount information holding unit stores exposure amount information in images captured by the imaging units 101 to 104. The image recognition unit 131 is optimally determined by determining how to change the exposure amount in the future depending on the exposure amount of each of the imaging units 101 to 104 stored in time series and whether or not the image recognition unit 131 can recognize. A combination of exposure amounts can be determined, and the shutter speeds can be controlled by the shutter speed control units 111 to 114 to specify the exposure amounts of the imaging units 101 to 104. The exposure amount information holding unit may be provided in the image storage unit 121.
<Processing flow (basic part)>
Next, in the present embodiment, a processing flow corresponding to the above-described apparatus configuration will be described.
First, the imaging units 101 to 104 capture images around the vehicle at a plurality of different exposures at different timings according to the designation of the shutter speed control units 111 to 114. The obtained image and imaging parameters are stored in the image storage unit 121.
The parameters at the time of imaging include a shutter speed and an imaging time at the time of imaging, and vehicle information. The vehicle information is received between a plurality of devices of the vehicle 10 by a network inside the vehicle such as vehicle speed, wheel speed, rudder angle, wheel angle, own vehicle position by the own vehicle position measurement system, headlamp lighting information, and wiper operation information. This is information that is passed, and includes information that is transmitted to and received from the host vehicle through inter-vehicle communication and road-to-vehicle communication.
Next, the image memorize | stored in the image memory | storage part 121 is sent to the image recognition part 131, and a parking frame recognition process is performed. This parking frame recognition process is composed of two stages: recognition of a line segment forming the parking frame 20 and determination of whether or not a combination of line segments is appropriate as the parking frame 20. For example, line segment recognition is performed by applying vertical and horizontal Sobel filters to an image, binarizing with an appropriate threshold value, and extracting edge points in the image, and the coordinates of the extracted edge points. By applying the Hough transform to the group, it is possible to extract a group of edge points arranged in a straight line.
In addition, for example, when recognizing the parking frame 20 for an ordinary passenger car, the determination as to whether or not the parking frame 20 is appropriate is an interval of 2 m to 4 m (parallel parking frame) corresponding to the vehicle width, or the vehicle length. When it can be detected that two substantially parallel parking frame lines 22 and 22 are drawn on the road surface at a considerable interval of 4 to 6 m (vertical parking frames), What is necessary is just to confirm as the parking frame 20 which can stop 10.
This parking frame recognition is performed for images with a plurality of different exposure amounts, but for an image for which shutter speed control is inappropriate for the environment around the vehicle, the edge points in the image are extracted. Not.
For example, when the shutter speed is slow and the exposure is performed for a long time in a bright illumination environment, the image is whitened and there is no difference in luminance value between adjacent pixels. A point is not extracted and the parking frame 20 is not recognized.
If there is an image area that is not recognized in a certain video image, it means that there is no parking frame 20 in the area or the image quality is not recognizable because the exposure adjustment is inappropriate.
In addition, the image recognition unit 131 calculates the accuracy of parking frame recognition on the basis of how clearly the edge points can be detected and how accurate the linearity is when the Hough transform is performed.
Although a specific calculation example will be described later, an indicator is set so that the higher the accuracy, the clearer the parking frame recognition is. As described above, an area where an object can be clearly recognized by image recognition can be considered highly visible to humans. As described above, the image recognition unit 131 obtains as output the position where the parking frame 20 that can be detected from an image of a certain exposure exists and the accuracy of the detected parking frame 20.
In addition, the image recognition unit 131 sends a signal to the shutter speed control units 111 to 114 so as to capture an image with one different exposure among a plurality of preset shutter speeds. When the vehicle information providing unit 161 is present, the headlamp lighting signal and the wiper operating status are checked, and when the surrounding environment is dark, the shutter speed is slower so that a bright image can be obtained. Signals are sent to the units 111 to 114.
If the vehicle speed information from the vehicle information providing unit 161 is high, the image may be blurred. Therefore, the shutter speed is increased so that a sharp image without blurring can be obtained. A signal is sent to the control units 111 to 114.
The image composition unit 141 synthesizes images with different exposure amounts based on the image area where the parking frame 20 recognized by the image recognition unit 131 is present and the recognition accuracy, that is, the visibility. In this synthesis, first, a weight map is created that indicates how much weight each area of each image is used between images that have been aligned in consideration of the amount of movement between the images.
Next, in accordance with this weight map, a luminance value and color information (hue and saturation) of each pixel of the plurality of images are mixed to create a composite image. At this time, since color information is often lost in an image with poor visibility, only luminance value information may be subject to mixing, and the value of an image with high saturation may be used as the color information.
FIG. 18 is a diagram illustrating an example of a weight map. The weight maps M1 and M2 indicate how easy each part of the images I1 and I2 is to be recognized. The white portions in the figure are highly visible and black compared to other exposed images. The portion is a grayscale image indicating that the visibility is low. The output image I3 is obtained by taking the product sum of the weight maps M1 and M2 and the images I1 and I2.
For example, consider an image I1 imaged with a small amount of exposure and an image I2 imaged with a large amount of exposure, taken at the same time by the same imaging unit. In each of the images I1 and I2, three parking frame lines are shown. In the image I1, only the parking frame lines L1 and L2 on the left side of the image, and in the image I2 the parking frame line L2 on the right side of the image. , Only L3 is detected.
According to the detected area of the parking frame line, the image composition map C1 is generated according to the detection accuracy and the distance from the detection area. A method of calculating the detection accuracy will be described later. In the image composition map C1, a region A1 is a region that uses 100% of the image I1, a region A2 is a region that uses 51 to 99% of the image I1, and the rest is a region that uses the image I2, and a region A3 is the image I1 and the image I2. 50% of each area, area A4 uses 51 to 99% of the image I2 and the rest uses the image I1, and area A5 uses 100% of the image I2. It is defined so that the rate at which is used changes continuously. In accordance with the image composition map C1, the input images I1 and I2 are weighted and added and synthesized to generate an output image I3.
Distortion correction is performed on the four composite images obtained from the respective imaging devices, and the overhead view conversion is performed by connecting and synthesizing in consideration of the relative relationship between the imaging units 101 to 104. A composite image around the vehicle is generated. As shown in FIG. 9, the overhead view conversion assumes that all points in the image are on the road surface G based on the video obtained by the imaging units 101 to 104, and from the virtual camera viewpoint 105. It is a kind of image conversion method that converts as if looking down. Since the method for generating the vehicle surroundings composite image is a known technique, it is not particularly described here.
The shutter speed control units 111 to 114 control the imaging units 101 to 104 so as to adjust the shutter speed in accordance with the signal from the image recognition unit 131 and send a signal for imaging. The image composition unit 141 composes an image according to the weight of the mask image from the mask image at each exposure obtained from the image recognition unit 131 and the camera image at the corresponding exposure obtained from the image storage unit 121. To the display unit 151.
In addition, when the vehicle is moving, if the vehicle is moving, the position shifts and the combined image becomes blurred or double-copyed. To do. The own vehicle movement amount can be obtained by calculating an optical flow from an image in addition to a wheel speed sensor, a vehicle speed sensor, a positioning sensor, and the like. The display unit 151 is, for example, a projection display unit for a liquid crystal monitor or window glass, and displays an image obtained from the image composition unit 141. FIG. 6 is a flowchart showing the above-described processing flow.
<Details of parking frame accuracy calculation method>
The accuracy of the parking frame can be defined as the sum of the accuracy Rimg of the image quality information and the accuracy Rstr of the structure information to be recognized.
The accuracy Rimg of the image quality information can be defined from the contrast and sharpness of the image area near the parking frame line. For example, in the case of a parking frame line, if the parking frame line has a width W and a length L, the parking frame line includes a road surface having the same width as the frame line on both sides. Can be defined as a region having a width of 3 W and a length of L centered on the central axis.
The contrast of the image area can be defined as the ratio between the minimum luminance value Ymin and the maximum luminance value Ymax included in the area, that is, Ymax / Ymin. This is an index that indicates how much the parking frame line that is the target of attention and the road surface can be recognized, and takes a small value when the image visibility is poor. Sharpness is the reciprocal of the distance between extreme values when a straight line perpendicular to the boundary between the frame region and the road surface is considered and the second derivative of the luminance value is taken on this straight line. In the case of an image with blurred boundaries and poor visibility, this value is small.
Further, the accuracy Rstr of the structural information to be recognized can be defined as an evaluation index for the apparent shape obtained from the image, such as the linearity and parallelism of the frame line, and the distortion with respect to the right angle. The distortion with respect to the linearity of the frame line can be defined as the sum of squares of the distances from the approximate line to each edge point by calculating the approximate line by the Hough transform or the like for the coordinates of the edge point group described above.
For example, when a parking frame is composed of two line segments, if the angle formed by the approximate straight line of each line segment is θ (0 ≦ θ ≦ 90 [deg]), the distortion with respect to the parallelism of the frame line is expressed as cos θ. Can be defined. In addition, the distortion with respect to the right angle of the frame line is, for example, when a parking frame is composed of two line segments, assuming a line connecting the end points on the parking frame entrance side of each frame line, If the angle formed by the approximate straight line of the frame line is θ (0 ≦ θ ≦ 90 [deg]), it can be defined as cos θ. In addition, when the parking frame is comprised by four line segments, it can define similarly as the cosine of the angle which the approximate straight line of each frame line makes. Both of these values become smaller when the distortion is large.
As described above, the accuracy Rimg of the image quality information and the accuracy Rstr of the structural information to be recognized take a small value when the distortion is large and the visibility is low, and conversely take a large value when the distortion is small and the visibility is good. .
<Details of synthesis method>
Details of the image composition method will be described with reference to FIG. Consider performing parking frame recognition on four images 701 to 704 captured at different times by the same imaging unit. However, the image 701 is an image captured at time T1 and an exposure amount E1, and the image 702 is an image captured at time T2 and an exposure amount E2 different from the image capture time of the image 701. An image 703 is an image captured at time T3 and exposure amount E3 different from the images 701 and 702, and an image 704 is an image captured at time T4 and exposure amount E4 different from the images 701 to 703.
The image recognition unit 131 performs parking frame line recognition processing on each of the images 701 to 704, and sends the recognition result area and the parking frame accuracy to the image composition unit 141. For example, in FIG. 15, two parking frames P11 and P12 are recognized in the image 701, and one parking frame P21 is recognized in the image 702, and the accuracy of parking frame recognition at that time is R11, R12, and R21 (R11 <R21). ).
When the host vehicle is stationary, P11 and P21 are in substantially the same position in the image, so it is clear that they are the same parking frame. However, since the accuracy R21 of the parking frame P21 is large, in this image area It can be seen that the visibility of the image 702 is high.
If the weight maps for the images 701 and 702 are 711 and 712, respectively, the weight of the area corresponding to the parking frame P11 in 711 is R11 / (R11 + R21), and the weight of the area corresponding to the parking frame P21 in 712 is R21 /. It can be defined as (R11 + R21). That is, in this region, the exposure amount E1 and the exposure amount E2 were both appropriate, but the image with better visibility was the image 702.
On the other hand, since the parking frame corresponding to the parking frame P12 of the image 701 is not recognized in the image 702, it can be understood that only the exposure amount E1 is appropriate in this region and the exposure amount E2 is inappropriate. For this reason, the weight of the area corresponding to the parking frame P12 in the weight map 711 is 1, and the weight of the area corresponding to the parking frame P12 in the weight map 712 is 0.
The weight of the area where the parking frame is not recognized from either of the images 701 and 702 can be determined by propagating the weight according to the distance from the area where the weight is determined. That is, in FIG. 15, since the weight of the point P in the image 701 is L1 from the area of the parking frame P11 and L2 from the area of the parking frame P12, the ratio of the distance from the determined weight. The weight can be changed in accordance with {R11 / (R11 + R21)} × {L2 / (L1 + L2)} + {R21 / (R11 + R21)} × {L1 / (L1 + L2)}. The propagation of the weight may be proportional to the square of the distance or may be converted by an appropriate monotone function such as a sigmoid function.
Further, the image recognition unit 131 may have a function of stabilizing the synthesized image brightness with respect to time series.
Without this function, parking frame recognition is unstable, and when detecting / non-detecting is repeated for each frame, changing the weight map each time, the brightness of the output image may change drastically, making it difficult to see is there. In order to cope with such a problem, in order to stabilize the brightness of the composite image, a weight map may be held for each exposure amount so that the weight does not change abruptly.
That is, the weight maps of the exposure amounts E1 and E2 at time t−1 are W (t−1, E1) and W (t−1, E2), respectively, and the exposure amount E1 at time t calculated as described above, If the respective weights of E2 are W (t, E1) and W (t, E2), the weight map at time t used for image composition is W ′ (t, E1) = α × W (t, E1 ) + (1−α) × W (t−1, E1), W ′ (t, E2) = α × W (t, E2) + (1−α) × W (t−1, E2) Thus, a sudden change in the weight map can be avoided. Here, α represents the degree of reflecting the weight calculated from the new image, and is an appropriate coefficient determined experimentally. Alternatively, W ′ may be stabilized using a Kalman filter.
If the vehicle is moving, the apparent vehicle movement is calculated from the image, and the image is affine transformed such as rotating or translating to align it, and the vehicle is stationary. The same can be considered. This apparent amount of movement can be calculated by calculating the motion of the image by, for example, feature point tracking using an optical flow method or SIFT (Scale Invariant Feature Transform).
Next, a vehicle peripheral image with high visibility is generated by connecting and synthesizing four images with high visibility created for each imaging unit.
In the present embodiment, the case where the surrounding confirmation support apparatus 1 has a plurality of imaging units 101 to 104 has been described as an example, but there is no problem even if the number of cameras changes. That is, for example, even with the configuration of two cameras on the left side and the rear, or the configuration of one camera only on the rear, it can be easily analogized that an image with high visibility can be provided by means as described above. FIG. 3 is a diagram showing a configuration in the case of one camera.
<Processing of vehicle information providing unit>
The role of the vehicle information providing unit 161 is to provide information for acquiring a moving amount of the own vehicle and the surrounding environment from the sensor information and performing more appropriate image composition.
In order to calculate the amount of movement of the host vehicle, information such as vehicle speed, wheel speed, rudder angle, and wheel angle is acquired from a sensor mounted on the vehicle 10. Since the calculation method of the own vehicle movement amount from these sensor information is the same as the general dead reckoning method or autonomous navigation, description here is abbreviate | omitted.
Further, when an absolute vehicle position with respect to the earth can be obtained by the vehicle position measurement system, the movement amount of the vehicle can be calculated by taking the difference of the time series information. By storing the movement amount of the own vehicle in the image storage unit 121, an effect of improving the alignment accuracy between images can be expected.
When the brake lamp lighting information by the side brake is obtained to recognize the surrounding environment, the movement amount of the own vehicle is stored as 0 in the image storage unit 121, and it is clarified that the position between the images does not change. Thus, the effect of increasing the certainty of the identification process of the recognition target can be expected.
Further, when the headlamp lighting information and the wiper operation information are obtained, the image storage unit 121 stores that the external illumination state is dark due to night or rainy weather. The image recognition unit 131 is binarized so that edges can be extracted from a blurred image because it is highly possible that a captured image is blurred and it is difficult to generate clear feature points when combining multiple images. The effect of improving the recognition performance can be expected by changing parameters such as a threshold. Moreover, since the local area of the road surface ahead of the host vehicle is illuminated by the headlamp and the parking frame line is erroneously recognized, the effect of improving the recognition performance can be achieved by causing the image recognition unit 131 to perform processing that ignores the edge of the area. Can be expected.
<Processing of exposure amount information holding unit>
The role of the exposure amount information holding unit is to store the exposure amount in the image captured by each of the past image capturing units 101 to 104, plan what exposure amount each image capturing unit should capture in the future, The exposure amount is designated to the shutter speed control units 111 to 114.
When an image of each exposure amount is captured, it is possible to determine which one of a plurality of current shutter controls is appropriate by storing how the recognition result in each image is obtained. For example, consider a camera in which two shutter speeds, a certain shutter speed S1 and a shutter speed S2 longer than that, are alternately repeated.
As in section a in FIG. 16, some recognition result is obtained at both shutter speeds S1 and S2, but when a more appropriate recognition result is obtained in the case of S1, the shorter shutter time is appropriate. Therefore, by using an appropriate change coefficient ΔS, S1 ′ = S1−ΔS, S2 ′ = S2−ΔS, and both of the shutter times are adjusted to be shorter.
The recognition target can be detected for an image with a high dynamic range by adjusting so that the average value of the optimum shutter speed is sandwiched between the shutter speeds S1 and S2. If a recognition result is obtained at the shutter speed S1, but no recognition result is obtained at the shutter speed S2, for example, assuming that ΔS = S2−S1, the recognition result is obtained as shown in FIG. While taking images at a shutter speed, a video with a shorter shutter speed and a video with a longer shutter speed can be alternately photographed to search for a suitable shutter speed, and the effect of stabilizing the search for the shutter speed is achieved. is there. In addition, when no recognition result is obtained at both shutter speeds S1 and S2, there is a possibility that the setting of the shutter speed is greatly deviated and there is a possibility that there is no recognition target in the image. In such a case, the shutter speed may be reset to a standard shutter speed.
Although the description has been made with the configuration in which the shutter speed is physically changed so far, for example, a configuration may be used in which a gamma conversion coefficient, binarization, and a threshold value for edge detection are changed. That is, the processing may be executed while sequentially changing the threshold value when it is assumed that an image with a large exposure amount is input and the coefficient and threshold value of gamma conversion when an image with a small exposure amount is input. For example, as shown in FIG. 19, a brightness correction parameter holding unit 510 may be provided to hold a plurality of parameters for correcting the exposure amount of an image in the image recognition of the image recognition unit 131.
FIG. 4 is a block diagram showing a modification of FIG. The surrounding confirmation support apparatus 1 shown in FIG. 4 has a configuration in which control to the shutter speed control 110 cannot be performed. Differences from FIG. 3 will be mainly described. Unlike the configuration of FIG. 3, the shutter speed control 110 does not receive a signal from the image recognition unit 131, and thus sends a plurality of shutter speeds defined in advance to the imaging unit 100 and also to the image recognition unit 131.
FIG. 5 is a block diagram showing another modification of FIG. The surrounding confirmation support apparatus 1 illustrated in FIG. 5 has a configuration including two imaging units 100, shutter speed control units 110, and image storage units 121. Differences from FIG. 3 will be mainly described. When two imaging units 100 are capturing the same object, the image recognition unit 131 outputs a control signal having a different shutter speed to each shutter speed control unit 110, so that a plurality of images with different exposures can be displayed at the same time. Obtainable. In addition, since the plurality of image capturing units 100 cannot be placed in the same space, the same effect can be obtained by using a plurality of image capturing units 100 at the same location by using image viewpoint conversion such as overhead view conversion. . Thus, the present invention can be applied to the configuration of a single imaging unit and the configuration of a plurality of imaging units.
Next, a second embodiment will be described below with reference to FIGS. The same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.
What is characteristic in the present embodiment is that a composite image around the vehicle is first generated by connecting and synthesizing images captured by a plurality of imaging units, and then a plurality of composite images around the vehicle with different exposure amounts. Image recognition is performed, and images with a plurality of exposure amounts are synthesized according to the recognition result.
This will be described with reference to FIG. First, each of the imaging units 101 to 104 captures a plurality of images having different exposure amounts, performs distortion correction on the plurality of images, and combines and combines them in consideration of the relative relationship of the imaging units 101 to 104. For example, an image 701 is generated by concatenating and combining four images with a small exposure amount captured at a high shutter speed, and four images with a large exposure amount captured at a low shutter speed are combined. Thus, an image 702 is generated.
The images 701 and 702 are images in which the exposure amounts between the imaging units 101 to 104 are substantially matched. The point that parking frame recognition is performed on the images 701 and 702 and images with different exposures are generated in accordance with the result is the same as the image synthesizing method in each camera video described above.
As shown in FIG. 21, an output image 715 can be obtained by defining weight maps 711 to 714 for images around the connected vehicle and adding the weighted input images 701 to 704. .
As described above, in this configuration, first, an image captured by each of the imaging units 101 to 104 is connected and synthesized to generate a surrounding image of the own vehicle. After that, a plurality of vehicle surroundings composite images with different exposure amounts are synthesized. Therefore, there is an effect that the appearance of the images connected as a whole can be optimized to be in a smooth natural state without falling into local optimization.
In the present embodiment, a case will be described in which the target of attention is a moving body (pedestrian) that moves around the own vehicle.
Now, the parking operation that repeats forward and backward and makes a sharp turn with a large steering angle has many blind spots around the host vehicle and the inner ring difference when turning is large, so it is easy to induce an accident and the wall around the entire circumference. And pay attention to pedestrians. In order to perform such a parking operation safely, an object that the driver should pay particular attention to is a pedestrian who moves around the vehicle (hereinafter referred to as a moving body).
In general, the contrast between the moving object and the road surface is lower than the contrast between the white line of the parking frame and the road surface, and the driver is careful when combining images based on the contrast of a certain area range as in the conventional technology. There is a problem that an image with a poor contrast of an object to be generated is generated. If the target object is stationary, this problem can be solved by the above-described first embodiment, but cannot be applied as it is when the target is moving.
In the present embodiment, recognition processing is performed on each image acquired at a plurality of exposure amounts, the moving body is tracked, and the moving position is predicted even if the recognition is not successful. By appropriately adjusting the brightness and contrast of the predicted position, an image with high visibility can be generated. Since the camera arrangement and the device configuration itself are the same as those in the first embodiment, description thereof is omitted here.
The flow of processing in the present embodiment will be described with a focus on differences from the first example. First, the imaging units 101 to 104 take images of a vehicle periphery at a plurality of different exposures at different timings according to the designation of the shutter speed control units 111 to 114, and store the obtained images and parameters at the time of imaging. Sent to the unit 121 and stored therein.
Next, the image stored in the image storage unit 121 is sent to the image recognition unit 131, and a mobile object recognition process is attempted. In this moving body recognition, when the host vehicle is stationary, a background difference method is used, and binarization is performed with an appropriate threshold value, whereby a changed area can be extracted as a moving body area. When the vehicle is moving, the motion vector of the image is detected using the optical flow method, and the road surface region and the moving body region are separated by segmenting the motion vector based on the direction and size. Can be obtained.
This moving object recognition is performed on images with a plurality of different exposure amounts, but for images where shutter speed control is inappropriate for the environment around the vehicle, the brightness value is saturated on the bright side or dark side. Therefore, no difference or motion vector is extracted. If there is an image area that is not recognized in an image of a certain exposure, it means that the area does not have a moving object or the image quality is not recognizable due to inappropriate exposure adjustment.
Further, the image recognition unit 131 calculates the accuracy of moving object recognition based on the contrast inside the moving object region, the extracted moving object shape, and the like. From the image recognizing unit 131, the position where the moving body that can be detected from the image of a certain exposure exists and the accuracy of the detected moving body are obtained as output.
The image synthesis unit 141 synthesizes images with different exposure amounts on the basis of the image area where the moving body recognized by the image recognition unit 131 exists and the recognition accuracy, that is, the visibility. The shutter speed control unit 111 controls the imaging units 101 to 104 so as to adjust the shutter speed in accordance with the signal from the image recognition unit 131 and sends a signal for imaging. The image composition unit 141 composes an image based on the result from the image recognition unit 131, sends the image to the display unit 151, and displays the composite image.
<Details of accuracy calculation method for moving object recognition>
The accuracy of moving body recognition can be defined as the sum of the accuracy Rimg of image quality information and the accuracy Rstr of shape information to be recognized.
The accuracy Rimg of the image quality information can be defined from the contrast inside and near the moving object region and the complexity of the texture. The contrast inside and near the moving body region is, for example, a region in which the moving body region is expanded by about 10%, and the ratio between the minimum luminance value Ymin and the maximum luminance value Ymax included in this region, that is, Ymax / Ymin Can be defined. The complexity of the texture means the energy, entropy, correlation, local uniformity, moment, etc. inside the moving object region are calculated from the simultaneous normal matrix, and the average, variance, and histogram symmetry of the luminance values of the pixels in the moving object region (Strain) and sharpness of the histogram are used to define the value to be larger if it is more complicated. Since these are general image processing techniques, a detailed description is omitted here.
The accuracy Rstr of the shape information of the recognition target can be defined from the recognized human shape. For example, as shown in FIG. 7, a person 32 standing with his / her foot closed behind the vehicle 10 (see FIG. 7 (a)) is observed as a fan-shaped shape 35 on the overhead image 38 based on the foot position. (See FIG. 7B).
In particular, the foot position is on the ground plane and can be converted from the size on the image to the size in real space. What is necessary is just to define so that such a shape and size may become high if it corresponds with the model of the size of a general person.
For example, the size of a foot is the size of the foot in the real space when the conversion parameter between the image and the real space is β [cm / pixel] and the size of the foot is observed as w [pixel] on the image. Assuming that f [cm] is f = β × w, typically 25 cm, and generally in the range of 20 ≦ f ≦ 30, the accuracy Rfoot = of the shape information regarding the foot size When 5- | β × w−25 | and | β × w−25 |> 5, Rfoot = 0.
Thus, the accuracy Rimg of the image quality information and the accuracy Rstr of the structure information to be recognized take a large value when the visibility is good. In this way, the accuracy of moving object recognition can be defined and calculated.
DESCRIPTION OF SYMBOLS 1 Surrounding confirmation assistance apparatus 10 Vehicle 20 Parking frame 100-104 Imaging part 110-114 Shutter speed control part 121 Image storage part 131 Image recognition part 141 Image composition part 151 Display part 161 Vehicle information provision part
A surrounding confirmation support device that displays an image of the surroundings of a vehicle and assists a passenger to check the surroundings of the vehicle,
An imaging unit for imaging a predetermined range around the vehicle with different exposure amounts;
An image recognition unit that performs image processing on a plurality of images captured by the imaging unit and having different exposure amounts, and recognizes a preset recognition target;
An image composition unit that generates a composite image from the image based on a recognition result of the image recognition unit;
And a display unit for displaying a synthesized image synthesized by the image synthesizing unit.
The image composition unit compares regions of recognition results in a plurality of images in which the recognition object is recognized by the image recognition unit, and extracts an image region of the recognition object from each of the plurality of images. The surrounding confirmation support apparatus according to claim 1, wherein a composite image is generated based on the extracted image region.
The image composition unit creates a weight map that defines a ratio of each image area used when performing the image composition according to the accuracy of the recognition object and the distance from the detection area of the recognition object, The surrounding confirmation support apparatus according to claim 2, wherein the composite image is generated according to the weight map.
The surrounding confirmation support apparatus according to claim 3, wherein the image composition unit generates the composite image by mixing luminance values of pixels of the plurality of images according to the weight map.
A vehicle information providing unit that calculates a relative vehicle position in an image captured by the imaging unit based on predetermined vehicle information;
The surroundings according to any one of claims 1 to 4, wherein the image composition unit generates the composite image using information on the vehicle position calculated by the vehicle information providing unit. Confirmation support device.
The vehicle information includes at least one of vehicle speed, wheel speed, rudder angle, wheel angle, brake lamp lighting information, headlamp lighting information, wiper operation information, and own vehicle position information by the own vehicle position measurement system. The surrounding confirmation support apparatus according to claim 5, wherein:
The surrounding confirmation support apparatus according to claim 1, further comprising a shutter speed control unit configured to control a shutter speed of the imaging unit based on a recognition result of the image recognition unit.
An exposure amount information holding unit for storing information on an exposure amount of an image captured by the imaging unit;
The shutter speed control unit controls the shutter speed of the imaging unit based on the exposure amount information stored in the exposure amount information holding unit and the recognition result of the image recognition unit. Item 8. A surrounding confirmation support apparatus according to Item 7.
The surrounding confirmation support apparatus according to any one of claims 1 to 8, wherein a plurality of the imaging units are provided, and a plurality of images having different exposure amounts are obtained in each imaging unit.
The surrounding confirmation support apparatus according to any one of claims 1 to 8, wherein a plurality of images having different exposure amounts are obtained by imaging a plurality of times with the same imaging unit.
The object tracking unit according to claim 1, further comprising: a target tracking unit that tracks a moving object based on a recognition result by the image recognition unit and predicts a moving position of the moving object even when the recognition by the image recognition unit is not successful. The surrounding confirmation assistance apparatus as described in any one of Claims 1-10.
The surrounding confirmation support apparatus according to claim 11, wherein the target tracking unit predicts movement of the moving body by tracking each moving body recognized by the image recognition unit in time series.
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