# Patent

## Title
Vehicle vision system with structure and motion estimation

## Abstract

A vision system of a vehicle includes a camera disposed at the vehicle and having a field of view exterior of the vehicle. A control has an image processor that is operable, via image processing of frames of image data captured by the camera, to detect an object present in the field of view of the camera. When the vehicle is moving, the control, responsive at least in part to vehicle motion information and image processing of frames of captured image data, determines motion of the detected object relative to the moving vehicle. The control determines the relative motion of the detected object by (i) determining corresponding object points in at least two frames of captured image data, (ii) estimating object motion trajectory of the detected object responsive to the determination of corresponding object points and (iii) determining the structure of the detected object along the estimated object motion trajectory.

## Background
CROSS REFERENCE TO RELATED APPLICATION
The present application claims the filing benefits of U.S. provisional application Ser. No. 62/159,515, filed May 11, 2015, which is hereby incorporated herein by reference in its entirety.


FIELD OF THE INVENTION
The present invention relates generally to a vehicle vision system for a vehicle and, more particularly, to a vehicle vision system that utilizes one or more cameras at a vehicle.
BACKGROUND OF THE INVENTION
Use of imaging sensors in vehicle imaging systems is common and known. Examples of such known systems are described in U.S. Pat. Nos. 5,949,331; 5,670,935 and/or 5,550,677, which are hereby incorporated herein by reference in their entireties. It is known to process captured image data to detect objects in the field of view of the vehicle camera or cameras. Typically, the structure of static objects is estimated via the use of moving cameras. However, in known formulations, as soon as the object starts to move, the estimation of the structure is typically erroneous and no longer valid.
SUMMARY OF THE INVENTION
The present invention provides a collision avoidance system or vision system or imaging system for a vehicle that utilizes one or more cameras (preferably one or more CMOS cameras) to capture image data representative of images exterior of the vehicle, and provides an estimation of an object motion relative to the vehicle and camera. The movement of the camera as the vehicle moves can be determined via vehicle movement (speed, altitude, direction, roll, pitch, yaw) information and the movement of the object is determined via the mathematical model and equations of the system of the present invention.
The present invention provides for simultaneous estimation of motion and structure of a moving object using a moving camera. The method and system of the present invention incorporates the estimation of the motion and structure of the unknown object into the same paradigm. This allows for better and more reliable estimation of the object structure as well as motion. The method and system of the present invention can be incorporated into object detection and/or three dimensional (3D) reconstruction algorithms that can benefit from the enhanced estimation of object structure and motion.
These and other objects, advantages, purposes and features of the present invention will become apparent upon review of the following specification in conjunction with the drawings.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view of a vehicle with a vision system that incorporates cameras in accordance with the present invention;
FIG. 2 is a perspective view of a vehicle and pedestrians forward of the vehicle and in the field of view of the forward facing camera or cameras of the vehicle;
FIG. 3 is an image of a pedestrian in front of a vehicle as may be viewed by a driver of the vehicle; and
FIG. 4 is a schematic of a moving camera and a moving object, showing where the moving object is imaged by the moving camera.



DESCRIPTION OF THE PREFERRED EMBODIMENTS
A vehicle vision system and/or driver assist system and/or object detection system and/or alert system operates to capture images exterior of the vehicle and may process the captured image data to display images and to detect objects at or near the vehicle and in the predicted path of the vehicle, such as to assist a driver of the vehicle in maneuvering the vehicle in a rearward direction. The vision system includes an image processor or image processing system that is operable to receive image data from one or more cameras and provide an output to a display device for displaying images representative of the captured image data. Optionally, the vision system may provide a top down or bird's eye or surround view display and may provide a displayed image that is representative of the subject vehicle, and optionally with the displayed image being customized to at least partially correspond to the actual subject vehicle.
Referring now to the drawings and the illustrative embodiments depicted therein, a vehicle 10 includes an imaging system or vision system 12 that includes at least one exterior facing imaging sensor or camera, such as a rearward facing imaging sensor or camera 14a (and the system may optionally include multiple exterior facing imaging sensors or cameras, such as a forwardly facing camera 14b at the front (or at the windshield) of the vehicle, and a sidewardly/rearwardly facing camera 14c, 14d at respective sides of the vehicle), which captures images exterior of the vehicle, with the camera having a lens for focusing images at or onto an imaging array or imaging plane or imager of the camera (FIG. 1). Optionally, a forward viewing camera may be disposed at the windshield of the vehicle and view through the windshield and forward of the vehicle, such as for a machine vision system (such as for traffic sign recognition, headlamp control, pedestrian detection, collision avoidance, lane marker detection and/or the like). The vision system 12 includes a control or electronic control unit (ECU) or processor 18 that is operable to process image data captured by the camera or cameras and may detect objects or the like and/or provide displayed images at a display device 16 for viewing by the driver of the vehicle (although shown in FIG. 1 as being part of or incorporated in or at an interior rearview mirror assembly 20 of the vehicle, the control and/or the display device may be disposed elsewhere at or in the vehicle). The data transfer or signal communication from the camera to the ECU may comprise any suitable data or communication link, such as a vehicle network bus or the like of the equipped vehicle.
Surround awareness and driver assistance is a marketable feature for vision systems. Generic object detection using a fish eye camera is one such feature. Distance estimation in the scene is desired to add value to existing detection based algorithms (such as, for example, object detection (OD), blind spot detection (BSD), automatic parking spot detection or the like), and to provide a stand-alone distance estimation feature.
Distance estimation is a triangulation-based structure from motion (SfM) problem, which requires the information on corresponding feature points in consecutive images and camera parameters at each viewpoint of the moving camera. A triangulation-based method can only provide a reasonable solution to the application scenarios such as a moving vehicle with a stationary background and a stationary vehicle with moving objects.
In reality, it is often required to estimate the distance of a moving object from a moving vehicle, which leads to a challenging issue on structure and motion estimation of a moving object using a moving camera (SaMfM). Such a structure and motion estimation of a moving object using a moving camera (SaMfM) violates the principle of traditional triangulation-based solution for distance estimation. Most past developments centered around the solutions by applying different constraints to trajectories and velocities of the moving objects and simultaneous estimation of moving object and moving camera.
The present invention provides a solution for structure and motion estimation of a moving object from a known moving camera. The moving camera extrinsic parameters are retrieved from vehicle CAN messages or signals (such as velocity and trajectory information or data). The system develops solutions with respect to two different constraints on trajectories of a rigid object, which are object translation at a constant speed in a certain time period, and object translation at an arbitrary speed in a certain time period.
The present invention establishes a two-view constraint for motion ΔX and structure X of a moving object point:

xt-1TE{circumflex over (x)}t=xt-1TEPtΔX;  (1)

where correspondent feature points xt-1{circumflex over (x)}t; camera projection matrix (3×4 matrix) at t: Pt; camera motion: R, T→3×3 essential matrix: E=[T]xR

The method or system of the present invention may, in step 1, detect object features in a captured image view, and in step 2 perform feature correspondence analysis between two views or feature tracking in consecutive views, and in step 3, given a certain number of correspondent feature pairs, solve equation (1) to provide an estimate of object motion ΔX. For this, an SVD method can be used. Step 4 then calculates the structure of an object point X by using image projection equations along with the estimated ΔX.
In the case of a 3D translation




  
    
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for an object of an arbitrary translation (arbitrary speed in a particular time period), a minimum of three non-co-linear corresponding point pairs from two views are required to find a solution of ΔX using equation (1) above. For an object of constant translation (constant speed in a particular time period), only one feature object point, which is tracked in a minimum of four views, may be required to find a solution of ΔX using equation (1).

In the case of a two dimensional (2D) translation




  
    
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for an object of an arbitrary translation (arbitrary speed in a particular time period), a minimum two non-co-linear corresponding point pairs from two views are required to find a solution of ΔX using equation (1) above. For an object of constant translation (constant speed in a particular time period), only one feature object point, which is tracked in a minimum of three views, may be required to find a solution of ΔX using equation (1).

The algorithm and system and method of the present invention is operable to estimate the displacement of a rigid object in the real world from two or multiple views, given that camera information at each viewpoint and image corresponding points are available. In the case of a moving object having an arbitrary translation, a minimum of three corresponding object point pairs from two views are needed for estimation of 3D object translation, while a minimum of two corresponding point pairs are required for 2D object displacement. In case of a moving object having a constant translation, one feature point, tracked in a minimum of four views, is needed for estimation of 3D object translation, while one feature point, tracked in a minimum of three views, is required for 2D object displacement.
As shown in FIG. 4, from time instant t−1 to t, the object is moving from position X to X+ΔX, while the camera/vehicle movement is R, T. The camera projection matrix is Pt-1 and Pt. The image features xt-1 and xt are the projection of a moving object at position X onto the camera at time instant t−1 and t, and xt is the projection of a moving object at position X+ΔX onto camera at time instant t.
From epipolar geometry (a 3×3 matrix):

xt-1TExt=0  (2)

From projection geometry (a 3×4 matrix):

xt-1=Pt-1X  (3)

xt=PtX  (4)

{circumflex over (x)}t=Pt(X+ΔX)  (5)

Note that x and X are the homogeneous representations of the 2D and 3D positions of the object.

The known information or parameters include (from vehicle CAN information) the camera projection matrix (3×4 matrix) Pt-1, Pt, and camera motion (R, T→3×3 essential matrix: E=[T]xR. From feature corresponding analysis, the corresponding point pair (xt-1{circumflex over (x)}t) is also known.
The unknown parameters to be estimated (reconstruction up to a scale) include the object position X and the object translation ΔX.
The solution involves the following steps, with Step 1 (from equations (4) and (5) above) solving the equations:

{circumflex over (x)}t=Pt(X+ΔX)=xt+PtΔX  (6)

which results in: xt={circumflex over (x)}t−PtΔX  (7)

Step 2 replaces xt of equation (2) in equation (7):

xt-1TExt=xt-1E({circumflex over (x)}t−PtΔX)=0  (8)

which results in: xt-1TE{circumflex over (x)}t=xt-1TEPtΔX  (9)

Equation (9) thus provides one two-view constraint for a moving object point.

Now, In the case of the 3D translation




  
    
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for an object of an arbitrary translation (arbitrary speed in a particular time period), a minimum of three non-colinear corresponding point pairs from two views are required to find a solution of ΔX using equation (9) above. For an object of constant translation (constant speed in a particular time period), only one feature object point, which is tracked in a minimum of four views, may be required to find a solution of ΔX using equation (9).

In the case of a 2D translation




  
    
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for an object of an arbitrary translation (arbitrary speed in a particular time period), a minimum two non-colinear corresponding point pairs from two views are required to find a solution of ΔX using equation (9) above. For an object of constant translation (constant speed in a particular time period), only one feature object point, which is tracked in a minimum of three views, may be required to find a solution of ΔX using equation (9).

Thus, the coordinates (structure) X of a moving object point are calculated by using equations (3) and (4) along with the estimated ΔX.
The method and system of the present invention thus may determine the motion or path of the vehicle responsive to vehicle system inputs, such as inputs from or indicative of the vehicle steering wheel angle and/or vehicle speed and/or the like, and determines the motion and relative motion of an object in the field of view of the camera. The system may utilize aspects of the systems described in U.S. Patent Publication Nos. US-2014-0347486; US-2014-0350834; US-2015-0002670; US-2015-0291215; US-2015-0178576 and/or US-2015-0175072, which are hereby incorporated herein by reference in their entireties.
The camera or sensor may comprise any suitable camera or sensor. Optionally, the camera may comprise a “smart camera” that includes the imaging sensor array and associated circuitry and image processing circuitry and electrical connectors and the like as part of a camera module, such as by utilizing aspects of the vision systems described in International Publication Nos. WO 2013/081984 and/or WO 2013/081985, which are hereby incorporated herein by reference in their entireties.
The system includes an image processor operable to process image data captured by the camera or cameras, such as for detecting objects or other vehicles or pedestrians or the like in the field of view of one or more of the cameras. For example, the image processor may comprise an EyeQ2 or EyeQ3 image processing chip available from Mobileye Vision Technologies Ltd. of Jerusalem, Israel, and may include object detection software (such as the types described in U.S. Pat. Nos. 7,855,755; 7,720,580 and/or 7,038,577, which are hereby incorporated herein by reference in their entireties), and may analyze image data to detect vehicles and/or other objects. Responsive to such image processing, and when an object or other vehicle is detected, the system may generate an alert to the driver of the vehicle and/or may generate an overlay at the displayed image to highlight or enhance display of the detected object or vehicle, in order to enhance the driver's awareness of the detected object or vehicle or hazardous condition during a driving maneuver of the equipped vehicle.
The vehicle may include any type of sensor or sensors, such as imaging sensors or radar sensors or lidar sensors or ladar sensors or ultrasonic sensors or the like. The imaging sensor or camera may capture image data for image processing and may comprise any suitable camera or sensing device, such as, for example, a two dimensional array of a plurality of photosensor elements arranged in at least 640 columns and 480 rows (at least a 640×480 imaging array, such as a megapixel imaging array or the like), with a respective lens focusing images onto respective portions of the array. The photosensor array may comprise a plurality of photosensor elements arranged in a photosensor array having rows and columns. Preferably, the imaging array has at least 300,000 photosensor elements or pixels, more preferably at least 500,000 photosensor elements or pixels and more preferably at least 1 million photosensor elements or pixels. The imaging array may capture color image data, such as via spectral filtering at the array, such as via an RGB (red, green and blue) filter or via a red/red complement filter or such as via an RCC (red, clear, clear) filter or the like. The logic and control circuit of the imaging sensor may function in any known manner, and the image processing and algorithmic processing may comprise any suitable means for processing the images and/or image data.
For example, the vision system and/or processing and/or camera and/or circuitry may utilize aspects described in U.S. Pat. Nos. 8,694,224; 7,005,974; 5,760,962; 5,877,897; 5,796,094; 5,949,331; 6,222,447; 6,302,545; 6,396,397; 6,498,620; 6,523,964; 6,611,202; 6,201,642; 6,690,268; 6,717,610; 6,757,109; 6,802,617; 6,806,452; 6,822,563; 6,891,563; 6,946,978; 7,859,565; 5,550,677; 5,670,935; 6,636,258; 7,145,519; 7,161,616; 7,230,640; 7,248,283; 7,295,229; 7,301,466; 7,592,928; 7,881,496; 7,720,580; 7,038,577; 6,882,287; 5,929,786 and/or 5,786,772, and/or International Publication Nos. WO 2011/028686; WO 2010/099416; WO 2012/061567; WO 2012/068331; WO 2012/075250; WO 2012/103193; WO 2012/0116043; WO 2012/0145313; WO 2012/0145501; WO 2012/145818; WO 2012/145822; WO 2012/158167; WO 2012/075250; WO 2012/0116043; WO 2012/0145501; WO 2012/154919; WO 2013/019707; WO 2013/016409; WO 2013/019795; WO 2013/067083; WO 2013/070539; WO 2013/043661; WO 2013/048994; WO 2013/063014, WO 2013/081984; WO 2013/081985; WO 2013/074604; WO 2013/086249; WO 2013/103548; WO 2013/109869; WO 2013/123161; WO 2013/126715; WO 2013/043661; WO 2013/158592 and/or WO 2014/204794, which are all hereby incorporated herein by reference in their entireties. The system may communicate with other communication systems via any suitable means, such as by utilizing aspects of the systems described in International Publication Nos. WO/2010/144900; WO 2013/043661 and/or WO 2013/081985, and/or U.S. Publication No. US-2012-0062743, which are hereby incorporated herein by reference in their entireties.
Optionally, the vision system may include a display for displaying images captured by one or more of the imaging sensors for viewing by the driver of the vehicle while the driver is normally operating the vehicle. Optionally, for example, the vision system may include a video display device disposed at or in the interior rearview mirror assembly of the vehicle, such as by utilizing aspects of the video mirror display systems described in U.S. Pat. No. 6,690,268 and/or U.S. Publication No. US-2012-0162427, which are hereby incorporated herein by reference in their entireties. The video mirror display may comprise any suitable devices and systems and optionally may utilize aspects of the compass display systems described in U.S. Pat. Nos. 7,370,983; 7,329,013; 7,308,341; 7,289,037; 7,249,860; 7,004,593; 4,546,551; 5,699,044; 4,953,305; 5,576,687; 5,632,092; 5,677,851; 5,708,410; 5,737,226; 5,802,727; 5,878,370; 6,087,953; 6,173,508; 6,222,460; 6,513,252 and/or 6,642,851, and/or European patent application, published Oct. 11, 2000 under Publication No. EP 0 1043566, and/or U.S. Publication No. US-2006-0061008, which are all hereby incorporated herein by reference in their entireties. Optionally, the video mirror display screen or device may be operable to display images captured by a rearward viewing camera of the vehicle during a reversing maneuver of the vehicle (such as responsive to the vehicle gear actuator being placed in a reverse gear position or the like) to assist the driver in backing up the vehicle, and optionally may be operable to display the compass heading or directional heading character or icon when the vehicle is not undertaking a reversing maneuver, such as when the vehicle is being driven in a forward direction along a road (such as by utilizing aspects of the display system described in International Publication No. WO 2012/051500, which is hereby incorporated herein by reference in its entirety).
Optionally, the vision system (utilizing the forward facing camera and a rearward facing camera and other cameras disposed at the vehicle with exterior fields of view) may be part of or may provide a display of a top-down view or birds-eye view system of the vehicle or a surround view at the vehicle, such as by utilizing aspects of the vision systems described in International Publication Nos. WO 2010/099416; WO 2011/028686; WO 2012/075250; WO 2013/019795; WO 2012/075250; WO 2012/145822; WO 2013/081985; WO 2013/086249 and/or WO 2013/109869, and/or U.S. Publication No. US-2012-0162427, which are hereby incorporated herein by reference in their entireties.
Changes and modifications in the specifically described embodiments can be carried out without departing from the principles of the invention, which is intended to be limited only by the scope of the appended claims, as interpreted according to the principles of patent law including the doctrine of equivalents.

## Claims

1. A vision system of a vehicle, said vision system comprising:
a camera disposed at a vehicle and having a field of view exterior of the vehicle, said camera capturing frames of image data;
a control having an image processor operable to process frames of image data captured by said camera;
wherein said image processor is operable, via image processing of frames of captured image data, to detect an object present in the field of view of said camera;
wherein, when the vehicle is moving, said control, responsive at least in part to vehicle motion information and image processing of frames of captured image data, detects an object present in the field of view of said camera and determines motion of the detected object relative to the moving vehicle; and
wherein said control, responsive at least in part to vehicle motion information and image processing of frames of captured image data, determines the motion of the detected object relative to the moving vehicle by (i) determining corresponding object points in at least two frames of captured image data, (ii) estimating object motion trajectory of the detected object responsive to the determination of corresponding object points and (iii) determining the structure of the detected object along the estimated object motion trajectory.

2. The vision system of claim 1, wherein the vehicle motion information includes at least the speed of the vehicle.

3. The vision system of claim 1, wherein the vehicle motion information includes at least the direction of travel of the vehicle.

4. The vision system of claim 1, wherein said control receives the vehicle motion information via a CAN bus of the vehicle.

5. The vision system of claim 1, wherein said control, responsive at least in part to vehicle motion information and image processing of at least two frames of captured image data, determines the motion of the detected object relative to the moving vehicle.

6. The vision system of claim 1, wherein said control, responsive at least in part to vehicle motion information and image processing of at least four frames of captured image data, determines the motion of the detected object relative to the moving vehicle.

7. The vision system of claim 1, wherein said control determines the motion of the detected object relative to the moving vehicle utilizing at least two constraints on trajectories of a rigid object.

8. The vision system of claim 7, wherein the at least two constraints comprise (i) object translation at a constant speed over a certain time period and (ii) object translation at an arbitrary speed over a certain time period.

9. The vision system of claim 1, wherein the moving object points are determined via the following equation:


xt-1TE{circumflex over (x)}t=xt-1TEPtΔX; 


where xt-1 and xt are the projections of a moving object at position X onto said camera at time instants t−1 and t, {circumflex over (x)}t is the projection of a moving object at position X+ΔX onto camera at time instant t, and Pt is the camera projection matrix.

10. The vision system of claim 9, wherein said control performs a feature correspondence analysis between two frames of captured image and, given a number of correspondent feature pairs, solves the equation to provide an estimate of object motion ΔX.

11. The vision system of claim 10, wherein said control calculates the structure of an object point X by using image projection equations along with the estimated object motion ΔX.

12. A vision system of a vehicle, said vision system comprising:
a camera disposed at a vehicle and having a field of view exterior of the vehicle, said camera capturing frames of image data;
a control having an image processor operable to process frames of image data captured by said camera;
wherein said image processor is operable, via image processing of frames of captured image data, to detect an object present in the field of view of said camera;
wherein, when the vehicle is moving, said control, responsive at least in part to vehicle motion information and image processing of frames of captured image data, detects an object present in the field of view of said camera and determines motion of the detected object relative to the moving vehicle;
wherein said control receives the vehicle motion information via a CAN bus of the vehicle;
wherein the vehicle motion information includes at least the speed of the vehicle and the direction of travel of the vehicle; and
wherein said control, responsive at least in part to vehicle motion information and image processing of frames of captured image data, determines the motion of the detected object relative to the moving vehicle by (i) determining corresponding object points in at least two frames of captured image data, (ii) estimating object motion trajectory of the detected object responsive to the determination of corresponding object points and (iii) determining the structure of the detected object along the estimated object motion trajectory.

13. The vision system of claim 12, wherein said control, responsive at least in part to vehicle motion information and image processing of at least two frames of captured image data, determines the motion of the detected object relative to the moving vehicle.

14. The vision system of claim 12, wherein said control, responsive at least in part to vehicle motion information and image processing of at least four frames of captured image data, determines the motion of the detected object relative to the moving vehicle.

15. The vision system of claim 12, wherein said control determines the motion of the detected object relative to the moving vehicle utilizing at least two constraints on trajectories of a rigid object.

16. The vision system of claim 15, wherein the at least two constraints comprise (i) object translation at a constant speed over a certain time period and (ii) object translation at an arbitrary speed over a certain time period.

17. The vision system of claim 12, wherein the moving object points are determined via the following equation:


xt-1TE{circumflex over (x)}t=xt-1TEPtΔX; 


where xt-1 and xt are the projections of a moving object at position X onto said camera at time instants t−1 and t, {circumflex over (x)}t is the projection of a moving object at position X+ΔX onto camera at time instant t, and Pt is the camera projection matrix.

18. A vision system of a vehicle, said vision system comprising:
a camera disposed at a vehicle and having a field of view exterior of the vehicle, said camera capturing frames of image data;
wherein said camera is part of a multi-camera surround view vision system of the vehicle;
a display operable to display, for viewing by a driver of the vehicle, images derived from image data captured by said camera and other cameras of said multi-camera surround view vision system to assist the driver in maneuvering the vehicle;
a control having an image processor operable to process frames of image data captured by said camera;
wherein said image processor is operable, via image processing of frames of captured image data, to detect an object present in the field of view of said camera;
wherein, when the vehicle is moving, said control, responsive at least in part to vehicle motion information and image processing of frames of captured image data, detects an object present in the field of view of said camera and determines motion of the detected object relative to the moving vehicle; and
wherein said control, responsive at least in part to vehicle motion information and image processing of frames of captured image data, determines the motion of the detected object relative to the moving vehicle by (i) determining corresponding object points in at least two frames of captured image data, (ii) estimating object motion trajectory of the detected object responsive to the determination of corresponding object points and (iii) determining the structure of the detected object along the estimated object motion trajectory.

19. The vision system of claim 18, wherein the vehicle motion information includes at least the speed of the vehicle and the direction of travel of the vehicle.

20. The vision system of claim 18, wherein the moving object points are determined via the following equation:


xt-1TE{circumflex over (x)}t=xt-1TEPtΔX; 


where xt-1 and xt are the projections of a moving object at position X onto said camera at time instants t−1 and t, {circumflex over (x)}t is the projection of a moving object at position X+ΔX onto camera at time instant t, and Pt is the camera projection matrix, and wherein said control performs a feature correspondence analysis between two frames of captured image and, given a number of correspondent feature pairs, solves the equation to provide an estimate of object motion ΔX, and wherein said control calculates the structure of an object point X by using image projection equations along with the estimated object motion ΔX.