Patent Publication Number: US-2022219607-A1

Title: Driver assistance method and apparatus

Description:
TECHNICAL FIELD 
     The present disclosure relates to a driver assistance method and apparatus. Aspects of the invention relate to a driver assistance system, a vehicle, a method of assisting a vehicle driver, computer software and a computer readable medium. 
     BACKGROUND 
     It is known to provide an imaging device, such as a camera, on a trailer or similar towed vehicle. The image captured by the imaging device may be output to a display provided in a towing vehicle (connected to the trailer) to help a driver view objects which are obscured from view by the trailer. However, it may prove difficult for the driver to judge precisely the location of any such objects in the displayed image. 
     It is an aim of the present invention to address one or more of the disadvantages associated with the prior art. 
     SUMMARY OF THE INVENTION 
     Aspects and embodiments of the invention provide a driver assistance system, a vehicle, a method of assisting a vehicle driver, computer software and a computer readable medium as claimed in the appended claims. 
     According to an aspect of the present invention there is provided a driver assistance system for a towing vehicle coupled to a towed vehicle, the driver assistance system comprising a controller, the driver assistance system being configured to:
         receive first image data from a towed vehicle imaging device disposed on the towed vehicle, the first image data comprising a first scene behind the towed vehicle;   process the first image data to identify object image data representative of one or more objects of interest in the first scene;   determine an object distance from a reference point to the or each object of interest identified in the first scene; and   output a signal indicative of the object distance. The object distance may be output for display, for example to improve driver awareness of the presence and/or location of the one or more objects of interest. The objects of interest may, for example, comprise another vehicle or a stationary obstacle.       

     The reference point is a virtual reference point and may defined in relation to the towing vehicle or the towed vehicle. The reference point could, for example, correspond to a longitudinal position of a driver in towing vehicle. Alternatively, the reference point could correspond to a location of a display device for displaying the first image data. 
     The object distance may be determined by analysing the first image data. 
     The towed vehicle imaging device may be orientated in a rearward-facing direction. The towed vehicle imaging device may be a stereo camera. The object distance may be determined using a technique such as disparity mapping. The towed vehicle imaging device may be a mono camera. The object distance may be determined using a technique such as structure from motion analysis. The object distance may be determined by comparing first and second images captured at respective first and second times. The size of the object of interest may be calculated with reference to the distance travelled in the time interval between capturing the first and second images. Alternatively, or in addition, may determine perceived size of a known object of interest in the image scene, for example using pattern matching techniques to classify the identified object of interest as a particular vehicle type. The system may, for example, differentiate between cars, motorbikes, lorries (trucks), vans etc. 
     The driver assistance system may be configured selectively to display the first image data. The object distance may selectively be overlaid on the first image data. 
     The driver assistance system may be configured to compare the object distance to a threshold distance. A proximity notification may be generated when the comparison identifies the object distance as being less than or equal to the threshold distance. 
     The driver assistance system may, for example, perform a trailer blind spot monitoring function. The notification may comprise displaying the first image data on the display screen with the object distance displayed as an overlay. The object distance may be displayed coincident with or adjacent to the object of interest within the displayed image. 
     The driver assistance system may be configured to control one or more vehicle systems, for example to control dynamic operation of the vehicle. For example, a vehicle braking system may be activated when the towing vehicle is reversing in dependence on the proximity notification. 
     The driver assistance system may be configured to receive second image data from a towing vehicle imaging device disposed on the towing vehicle. The towing vehicle imaging device may be orientated in a rearward-facing direction. 
     The driver assistance system may be configured selectively to display the second image data. The object distance may be selectively overlaid on the second image data. The object distance may be overlaid onto the second image data at a position corresponding to a determined position of the object of interest (even if the object of interest is partially or completely obscured by the towed vehicle. 
     The driver assistance system may be configured to combine a part of the first image data and a part of the second image data to generate composite image data. The composite image data represents a composite image combining at least a portion of the first image data and the second image data. The composite image data may be selectively output to a display. The driver assistance system may be configured selectively to overlay the object distance on the composite image data. The object distance may be displayed coincident with or adjacent to the object of interest within the composite image. 
     According to a further aspect of the present invention there is provided a vehicle comprising a driver assistance system as described herein. 
     According to a still further aspect of the present invention there is provided a method of assisting a driver of a towing vehicle coupled to a towed vehicle, the method comprising:
         receiving first image data from a towed vehicle imaging device disposed on the towed vehicle, the first image data comprising a first scene behind the towed vehicle;   identifying one or more objects of interest in the first scene;   determining an object distance from a reference point to the or each object of interest identified in the first scene; and   outputting the determined object distance.       

     The method may comprise analysing the first image data to determine the object distance. 
     The towed vehicle imaging device may comprise a mono camera or a stereo camera. 
     The method may comprise selectively displaying the first image data. The method may comprise overlaying the object distance on the first image data. 
     The method may comprise comparing the object distance to a threshold distance. A proximity notification may be generated when the comparison identifies the object distance as being less than or equal to the threshold distance. 
     The method may comprise activating a braking system when the towing vehicle is reversing in dependence on the proximity notification. 
     The method may comprise receiving second image data from a towing vehicle imaging device disposed on the towing vehicle. The method may comprise selectively displaying the second image data. The object distance may be overlaid on the second image data. 
     The method may comprise combining a part of the first image data and a part of the second image data to generate composite image data. The composite image data may be selectively displayed. The method may comprise selectively overlaying the object distance on the composite image data. 
     According to a further aspect of the present invention there is provided a computer software that, when executed, is arranged to perform the method(s) described herein. 
     According to a further aspect of the present invention there is provided a non-transitory, computer-readable storage medium storing instructions thereon that, when executed by one or more electronic processors, causes the one or more electronic processors to carry out the method(s) described herein. 
     Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
         FIG. 1  shows a schematic representation of a driver assistance system according to an embodiment of the present invention provided in a towing vehicle and a towed vehicle; 
         FIG. 2  shows a schematic representation of the towing vehicle incorporating a controller for implementing the driver assistance system shown in  FIG. 1 ; 
         FIG. 3A  shows a towed vehicle image captured by a camera disposed in the towed vehicle; 
         FIG. 3B  shows a towing vehicle image captured by a camera disposed in the towing vehicle; 
         FIG. 4  shows a schematic representation of the controller of the driver assistance system; 
         FIG. 5  shows an image captured by the towed vehicle imaging device augmented with an object distance; 
         FIG. 6A  shows an example of a towed vehicle image captured by the first imaging device disposed at the rear of the towed vehicle; 
         FIG. 6B  shows a first modified version of the towed vehicle image shown in  FIG. 6A  augmented to highlight objects of interest within the field of view of the first imaging device; 
         FIG. 6C  shows a second modified version of the towed vehicle image shown in  FIG. 6A  augmented to highlight objects of interest within the field of view of the first imaging device; and 
         FIG. 7  shows a flow diagram representing operation of the driver assistance system. 
     
    
    
     DETAILED DESCRIPTION 
     A driver assistance system  1  in accordance with an embodiment of the present invention will now be described with reference to the accompanying figures. The driver assistance system  1  is configured to determine an object distance (or range) D-n between a reference point R 1  and one or more objects of interest O-n. 
     The driver assistance system  1  is suitable for use in a towing vehicle V 2  which is coupled to a towed vehicle V 1 . In the present embodiment, the towing vehicle V 2  and the towed vehicle V 1  are connected to each other by an articulated coupling. A schematic representation of the driver assistance system  1  provided in the towing vehicle V 2  and the towed vehicle V 1  is illustrated in  FIG. 1 . The towing vehicle V 2  in the present embodiment is an automobile. Other types of towing vehicle V 2  are contemplated, such as a utility vehicle, a sports utility vehicle, a tractor, a truck etc. The towed vehicle V 1  in the present embodiment is a trailer. The towed vehicle V 1  has a first longitudinal axis XVI; and the towing vehicle V 2  has a second longitudinal axis XV 2 . A schematic representation of the towing vehicle V 2  is shown in  FIG. 2 . 
     The reference point R 1  is a virtual point (or origin) defined in a fixed location on the towing vehicle V 2 . In the arrangement illustrated in  FIG. 1 , the reference point R 1  is defined at a longitudinal position coincident with a seating location of a driver of the towing vehicle V 2  (for example aligned with a hip point of the driver). The object distance D-n in this arrangement represents a distance between the driver and the object of interest O-n. By defining the reference point R 1  in relation to the position of the driver, the driver may more readily visualise the relative position of the or each object of interest O-n. In a variant, the reference point R 1  could be defined in a fixed location on the towed vehicle V 1 , for example at a rearmost position on a centreline of the towed vehicle V 1 . 
     A first imaging device C 1  is disposed on the towed vehicle V 1  and oriented in a rear-facing direction. The first imaging device C 1  is mounted centrally at the rear of the towed vehicle V 1 , for example above a rear license plate (not shown). Other mounting locations for the first imaging device C 1  are contemplated. The first imaging device C 1  comprises a towed vehicle camera C 1 . The towed vehicle camera C 1  has an optical axis substantially parallel to the first longitudinal axis XV 1 . The towed vehicle camera C 1  has a first field of view FOV 1  which encompasses a region to the rear of the towed vehicle V 1 . In use, the towed vehicle camera C 1  generates first image data DIMG 1  corresponding to a towed vehicle image IMG 1 . The towed vehicle image IMG 1  comprises a rear-facing scene from the towed vehicle V 1  captured by the towed vehicle camera C 1 . The towed vehicle image IMG 1  may, for example, include an image of a section of road behind the towed vehicle V 1 . The towed vehicle image IMG 1  may include one or more objects of interest O-n. The objects of interest O-n may, for example, comprise one or more other vehicles travelling behind the towed vehicle V 1  and/or offset laterally from the towed vehicle V 1 . The towed vehicle camera C 1  outputs a first signal SIN 1  comprising said first image data DIMG 1  corresponding to the towed vehicle image IMG 1 . A towed vehicle image IMG 1  is shown in  FIG. 3A  by way of example. 
     A second imaging device C 2  is disposed on the towing vehicle V 2  and oriented in a rear-facing direction. The second imaging device C 2  is mounted centrally at the rear of the towing vehicle V 2 , for example above a rear license plate (not shown). Other mounting locations for the second imaging device C 2  are contemplated. The second imaging device C 2  comprises a towing vehicle camera C 2 . The towing vehicle camera C 2  has an optical axis substantially parallel to the second longitudinal axis XV 2 . The towing vehicle camera C 2  has a second field of view FOV 2  which encompasses a region to the rear of the towing vehicle V 2 . In use, the towing vehicle camera C 2  generates second image data DIMG 2  corresponding to a towing vehicle image IMG 2 . The towing vehicle image IMG 2  comprises a rear-facing scene from the towing vehicle V 2  captured by the towing vehicle camera C 2 . The towing vehicle image IMG 2  may, for example, include at least a portion of a front of the towed vehicle V 1  as well as some of the environment around the towed vehicle V 1 , for example to the sides and/or above and/or below the towed vehicle V 1 . The towing vehicle camera C 2  outputs a second signal SIN 2  comprising said second image data DIMG 2  corresponding to the towing vehicle image IMG 2 . A towing vehicle image IMG 2  is shown in  FIG. 3B  by way of example. As shown in  FIG. 3B , the towed vehicle V 2  is visible in the towing vehicle image IMG 2  and partially obscures the field of view. 
     The towed vehicle camera C 1  and the towing vehicle camera C 2  are digital video cameras. The towed vehicle camera C 1  is operable to capture a plurality of first image frames IMG 1 -F(n) per second. The towing vehicle camera C 2  is operable to capture a plurality of second image frames IMG 2 -F(n) per second. The towed vehicle camera C 1  and the towing vehicle camera C 2  each have a wide-angle lens with an angle of view of approximately 180°. The angle of view of the towed vehicle camera C 1  and the towing vehicle camera C 2  could be narrower. The towed vehicle camera C 1  and/or the towing vehicle camera C 2  may be a mono camera or a stereo camera. The towed vehicle camera C 1  can function as a reversing camera to provide a parking aid when the towed vehicle V 1  is coupled to the towing vehicle V 2 . The towing vehicle camera C 2  can selectively function as a reversing camera to provide a parking aid when the towed vehicle V 1  is not coupled to the towing vehicle V 2 . The towed vehicle camera C 1  and the towing vehicle camera C 2  are arranged at approximately the same vertical height above ground level. In alternate arrangements, the towing vehicle camera C 2  and the towed vehicle camera C 1  may be offset from each other in a vertical direction and/or a transverse direction. A correction may be applied to allow for any vertical offset between the towed vehicle camera C 1  and the towing vehicle camera C 2 . Alternatively, or in addition, a correction may be applied to correct for an angular offset between the towed vehicle camera C 1  and the towing vehicle camera C 2 . 
     The driver assistance system  1  comprises one or more controller  10 . The controller  10  is in communication with the towed vehicle camera C 1 . The driver assistance system  1  is configured to receive the first image data DIMG 1  from the towed vehicle camera C 1  disposed on the towed vehicle V 1 . The first imaging device C 1  is orientated in a rearward-facing direction such that the first image data DIMG 1  represents a scene behind the towed vehicle V 1 . The controller  10  processes the first image data DIMG 1  to identify object image data DO-n representative of one or more objects of interest O-n in the first scene. The controller  10  determines the object distance D-n between the reference point R 1  to the or each object of interest O-n identified in the first scene. As described herein, an object distance signal SOUT 1  is output by the controller  10  to indicate the object distance D-n. 
     In the present embodiment, the controller  10  is disposed in the towing vehicle V 2 . In a variant, the controller  10  could be provided in the towed vehicle V 1 , or the processing could be performed by separate controllers  10  provided on the towed vehicle V 1  and the towing vehicle V 2 . It is to be understood that the or each controller  10  can comprise a control unit or computational device having one or more electronic processors (e.g., a microprocessor, a microcontroller, an application specific integrated circuit (ASIC), etc.), and may comprise a single control unit or computational device, or alternatively different functions of the or each controller  10  may be embodied in, or hosted in, different control units or computational devices. As used herein, the term “controller,” “control unit,” or “computational device” will be understood to include a single controller, control unit, or computational device, and a plurality of controllers, control units, or computational devices collectively operating to provide the required control functionality. A set of instructions could be provided which, when executed, cause the controller  10  to implement the control techniques described herein (including some or all of the functionality required for the method described herein). The set of instructions could be embedded in said one or more electronic processors of the controller  10 ; or alternatively, the set of instructions could be provided as software to be executed in the controller  10 . A first controller or control unit may be implemented in software run on one or more processors. One or more other controllers or control units may be implemented in software run on one or more processors, optionally the same one or more processors as the first controller or control unit. Other arrangements are also useful. 
     As illustrated in  FIG. 4 , the or each controller  10  comprises at least one electronic processor  12  having one or more electrical input(s)  14  for receiving one or more input signals from the towed vehicle camera C 1  and the towing vehicle camera C 2 ; and one or more electrical output(s)  16  for outputting the output signal S 1 . The or each controller  10  further comprises at least one memory device  18  electrically coupled to the at least one electronic processor  12  and having instructions  20  stored therein. The at least one electronic processor  12  is configured to access the at least one memory device  18  and execute the instructions  20  thereon so as to perform the method(s) described herein. 
     The, or each, electronic processor  12  may comprise any suitable electronic processor (e.g., a microprocessor, a microcontroller, an ASIC, etc.) that is configured to execute electronic instructions. The, or each, electronic memory device  18  may comprise any suitable memory device and may store a variety of data, information, threshold value(s), lookup tables or other data structures, and/or instructions therein or thereon. In an embodiment, the memory device  18  has information and instructions for software, firmware, programs, algorithms, scripts, applications, etc. stored therein or thereon that may govern all or part of the methodology described herein. The processor, or each, electronic processor  12  may access the memory device  18  and execute and/or use that or those instructions and information to carry out or perform some or all of the functionality and methodology describe herein. 
     The at least one memory device  18  may comprise a computer-readable storage medium (e.g. a non-transitory or non-transient storage medium) that may comprise any mechanism for storing information in a form readable by a machine or electronic processors/computational devices, including, without limitation: a magnetic storage medium (e.g. floppy diskette); optical storage medium (e.g. CD-ROM); magneto optical storage medium; read only memory (ROM); random access memory (RAM); erasable programmable memory (e.g. EPROM ad EEPROM); flash memory; or electrical or other types of medium for storing such information/instructions. 
     The first signal SIN 1  comprising the first image data DIMG 1  is input to the controller  10  via the one or more input(s)  14 . The connection between the controller  10  and the towed vehicle camera Cl could be a wired connection (for example comprising an electrical connection between the towed vehicle V 1  and the towing vehicle V 2 ). In the present embodiment, however, a wireless connection is established between the controller  10  and the towed vehicle camera C 1 . The towed vehicle camera C 1  is connected to a transmitter  22  configured to transmit the first image data DIMG 1  as a radio frequency (RF) signal to a receiver  24  provided in the towing vehicle V 2 . The receiver  24  is connected to the one or more input(s)  14  of the controller  10 . The second signal SIN 2  comprising the second image data DIMG 2  is input to the controller  10  via the one or more input(s)  14 . The connection between the controller  10  and the towing vehicle camera C 2  is a wired connection. For example, the towing vehicle camera C 2  may be connected to the controller  10  over a vehicle communication network  26 , such as a CAN bus. In use, the first image data DIMG 1  and the second image data DIMG 2  is input to the controller  10 . The towing vehicle V 2  comprises a display screen  28  on which the towed vehicle image IMG 1  and the towing vehicle image IMG 2  (received from the towed vehicle camera C 1  and the towing vehicle camera C 2  respectively) can be selectively displayed. 
     The controller  10  is configured to process the first and second image data DIMG 1 , DIMG 2 . In particular, the controller  10  implements an image processing module to analyse the first and second image data DIMG 1 , DIMG 2 . The controller  10  processes the first image data DIMG 1  to identify one or more objects of interest O-n in the image captured by the towed vehicle camera C 1 . An image processing algorithm may determine an optical flow of image elements in the first image data DIMG 1 . An optical flow vector may be generated for each image element to represent a direction and magnitude of the movement of the image elements, for example between a plurality of temporally offset image frames. By analysing the optical flow vectors, the controller  10  may identify the or each object of interest O-n. The controller  10  may, for example, use the optical flow vectors to differentiate between image elements corresponding to background features (which tend to be transient within the first image data DIMG 1  when the towed vehicle V 1  is moving); and image elements corresponding to one or more other vehicles (which have a greater persistency within the image data DIMG 1  if they are travelling in the same direction as the towed vehicle V 1 ). The image elements identified as corresponding to another vehicle is classified as an object of interest O-n. Other image processing algorithms include edge detection and pattern matching. One or more of these image processing algorithms may be used to identify the objects of interest O-n in the first image data DIMG 1 . Other image processing algorithms may usefully be employed. 
     The controller  10  determines the object distance D-n from the reference point R 1  to the or each object of interest O-n identified in the first image data DIMG 1 . In embodiments in which the towed vehicle camera C 1  comprises a stereo camera having spatially separated first and second cameras, the object distance D-n may be determined by comparing the images captured by the first and second cameras, for example by performing disparity mapping. In embodiments in which the towed vehicle camera Cl comprises a mono camera, the object distance D-n may be determined using analysis techniques such as structure from motion. 
     The controller  10  may be configured to identify (or classify) the object of interest O-n as being a particular object type. The controller  10  may, for example, identify the object of interest O-n as being a particular type of vehicle, such as a cyclist, a motorbike, an automobile, a van, a bus, a tram, or a truck. The object of interest O-n may be identified in dependence on a determined similarity with one or more predefined models. The predefined models may represent a plurality of different types of objects, for example the aforementioned different vehicle types. The object of interest O-n may be identified in dependence on the determined similarity. The object distance D-n may be determined in dependence on a perceived size of the identified object type. The controller  10  can identify the object of interest O-n as being a particular object or vehicle type and then determine the object distance D-n in dependence on a size of the object of interest O-n in the first image IMG 1 . 
     The towing vehicle V 1  comprises a display  30  on which the towed vehicle image IMG 1  and the towing vehicle image IMG 2  can be selectively displayed. The controller  10  is configured to output the object distance signal SOUT 1 . The controller  10  may optionally also be configured to output the identification (or classification) of the object of interest O-n. The object type may be overlaid onto the image displayed on the display  30 . 
     The object distance signal SOUT 1  may be used to augment the towed vehicle image IMG 1  and/or the towing vehicle image IMG 2  with the object distance D-n. As illustrated in  FIG. 5 , the object distance D-n may be overlaid onto the towed vehicle image IMG 1  and/or the towing vehicle image IMG 2 . The object distance D-n may be positioned on the towed vehicle image IMG 1  and/or the towing vehicle image IMG 2  at a location coincident with or adjacent to the object of interest O-n within that image. The controller  10  could be configured to generate augmented towed vehicle data AD-n and/or augmented towing vehicle data AD 2  comprising the object distance signal SOUT 1 . 
     The controller  10  may be configured to modify the towed vehicle image IMG 1  and/or the towing vehicle image I MG 2  to highlight the object of interest O-n. As illustrated in  FIG. 5 , an object identifier  32  may be displayed over at least a portion of the object of interest O-n within the towed vehicle image IMG 1  and/or the towing vehicle image IMG 2 . The object identifier  32  may comprise an outline of the object of interest O-n, for example. The outline of the object of interest O-n could, for example, be determined using the image processing techniques described herein to determine the external visible boundary (or edge) of the towed vehicle V 1 . In the illustrated arrangement, the object identifier  32  comprises a semi-transparent overlay. The object identifier  32  may be coloured. The controller  10  may alter the colour of the object identifier  32  in dependence on the determined object distance D-n. For example, the colour of the object identifier  32  may be modified to provide a visual indication that the object of interest O-n is within a predefined distance threshold. The colour of object identifier  32  may be modified as follows: coloured green if the object distance D-n is greater than a first distance threshold; coloured amber (orange) if the object distance D-n is less than the first distance threshold and greater than a second distance threshold; and coloured red if the object distance D-n is less than the second distance threshold. At least in certain embodiments, the object identifier  32  may provide an alert to the driver, for example to indicate that the object of interest O-n is in close proximity to the towing vehicle V 1 . Alternatively, or in addition, the colour of the object identifier  32  may be modified in dependence on a rate of change of the object distance D-n. Other alerts, such as an audible alert or a haptic alert, may be generated in dependence on the determined object distance D-n. 
     A further example of the operation of the driver assistance system  1  to augment the towed vehicle image IMG 1  will now be described with reference to  FIGS. 6A, 6B and 6C . In this example, the combined towed vehicle V 1  and the towing vehicle V 2  are reversing and a plurality of objects of interest O-n are identified in the towed vehicle image IMG 1 . As shown in  FIG. 6A , the objects of interest O-n in this example are in the form of traffic cones. The controller  10  processes the first image data DIMG 1  and identifies the objects of interest O-n. The controller  10  also determines the object distance D-n for the or each object of interest O-n. The object distance D-n may be determined in relation to a reference point R 1  disposed at a rear of the towed vehicle V 1 . The reference point may comprise a coordinate, an axis or a plane form which the object distance D-n may be determined. The object distance D-n may be determined in a single direction (for example along the longitudinal axis); or in a plurality of directions (for example along the longitudinal axis and the transverse axis). 
     The controller  10  augments the towed vehicle image IMG 1  with at least one object identifier  32  comprising a rectangular frame. In the example shown in  FIG. 6B , a first object identifier  32  is displayed over the plurality of objects of interest  0 - 1  on the left-hand side of the towed vehicle image IMG 1 ; and a second object identifier  32  is displayed over the single object of interest  0 - 2  on the right-hand side of the towed vehicle image IMG 1 . The colour of each object identifier  32  may be modified in dependence on the determined distance from the reference point R 1 . For example if the object distance D-n is less than a predefined first distance threshold, the object identifier may be displayed in a first colour (for example orange); and if the object distance D-n is less than a predefined second distance threshold (which is smaller than the first distance threshold), the object identifier may be displayed in a second colour (for example red). The controller  10  may be configured to differentiate between the objects of interest O-n in the left and right groups. A separate object distance D-n may be calculated for each object of interest O-n. As shown in  FIG. 6C , a separate object identifier  32  may be displayed for each object of interest O-n. The object identifiers  32  may be colour coded in dependence on the determined object distance D-n for the associated objects of interest. In the example shown in  FIG. 6C , the object identifier  32  associated with the object of interest O- 1  furthest from the reference point R 1  (i.e. having the largest object distance D-n) is displayed in a first colour (orange in the original image IMG 1 ); and the remaining object identifiers  32  are displayed in a second colour (red in the original image IMG 1 ). 
     Alternatively, or in addition, the controller  10  may be configured to identify an edge or outer profile of each object of interest. The controller  10  may generate an object identifier  32  in dependence on the edge or outer profile. For example, the object identifier  32  may correspond to at least a portion of an identified outline of each object of interest O-n. The object identifier  32  could be colour-coded in dependence on the determined object distance D-n, for example by displaying an overlay over the object of interest O-n. 
     The operation of the driver assistance system  1  will now be described with reference to a flow diagram  100  shown in  FIG. 7 . The controller  10  receives the towed vehicle image IMG 1  and the towing vehicle image IMG 2  from the towed vehicle camera C 1  and the towing vehicle camera C 2  respectively (BLOCK  110 ). The controller  10  processes the towed vehicle image IMG 1  (and optionally also the towing vehicle image IMG 2 ) to identify one or more objects of interest O-n (BLOCK  120 ). The controller  10  determines an object distance D-n from the predefined reference point R 1  to the or each object of interest O-n (BLOCK  130 ). The controller  10  outputs the object distance signal SOUT 1  (BLOCK  140 ). The object distance D-n is overlaid onto the towed vehicle image IMG 1  or the towing vehicle image IMG 2  to generated augmented towed vehicle data AD-n and/or augmented towing vehicle data AD 2  (BLOCK  150 ). The augmented towed vehicle data AD-n and/or augmented towing vehicle data AD 2  is output to the display  30  for display (BLOCK  160 ). 
     The display of the object distance D-n facilitates determination of the relative position of the other vehicles and the like in relation to the towing vehicle V 2 . When the towed vehicle V 1  and the towing vehicle V 2  are connected, at least a portion of the towing vehicle image IMG 2  may be obscured by the presence of the towed vehicle V 1 . The object distance D-n may be overlaid onto the towing vehicle image IMG 1  to improve driver awareness of the presence and/or location of other vehicles. 
     The driver assistance system  1  may be configured to control one or more vehicle systems VS-n to control dynamic operation of the towing vehicle V 2 . For example, during a reversing manoeuvre, the driver assistance system  1  may be configured to actuate a vehicle braking system VS- 1  if the determined object distance D-n decreases to less than a predefined distance threshold. The predefined distance threshold may be defined, for example, in dependence on a combined length of the towed vehicle V 1  and the towing vehicle V 2 . 
     Example controllers  10  have been described comprising at least one electronic processor  12  configured to execute electronic instructions stored within at least one memory device  18 , which when executed causes the electronic processor(s)  12  to carry out the method as herein described. However, it is contemplated that the present invention is not limited to being implemented by way of programmable processing devices, and that at least some of, and in some embodiments all of, the functionality and or method steps of the present invention may equally be implemented by way of non-programmable hardware, such as by way of non-programmable ASIC, Boolean logic circuitry, etc. 
     The controller  10  may be configured to combine at least a portion of the first image data DIMG 1  with at least a portion of the second image data DIMG 2  to generate composite image data. The controller  10  may, for example, analyse the towing vehicle image IMG 2  to identify a periphery of the towed vehicle V 1  representing an external visible boundary (or edge) of the towed vehicle V 1  from the view point of the towing vehicle camera C 2 . The controller  10  may, for example, identify the periphery by calculating optical flow vectors of pixels between two or more frames of the towing vehicle image IMG 2 . The region of the towing vehicle image IMG 2  enclosed by the periphery represents the towed vehicle V 1  within the towing vehicle image IMG 2 . 
     At least a portion of the towed vehicle image IMG 1  may be selectively inserted into a region of the towing vehicle image IMG 2  disposed inside the identified periphery P 1 . The resulting composite image data DIMG 3  may be output to the display  30 . The composite image data DIMG 3  may represent a composite image IMG 3  comprising at least a portion of each of the towed vehicle image IMG 1  and the towing vehicle image IMG 2 . The object distance D-n may be displayed in the composite image. For example, the object distance D-n may be overlaid on the composite image, for example coincident with or adjacent to the corresponding object of interest in the composite image. 
     It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application. 
     The controller  10  has been described with particular reference to the identification of other vehicles, for example when the towed vehicle V 1  and the towing vehicle V 2  are moving. Objects of interest O-n other than vehicles are also contemplated. The object of interest O-n could, for example, comprise one or more of the following: a kerb, a traffic cone, a parking bollard, a ramp, a wall and an obstacle. The object of interest O-n could be a visual marking or indicator, for example indicating a boundary of a parking space or a road marking. Alternatively, or in addition, the object of interest could be a person. The controller  10  could be configured to identify one or more pedestrians. The controller  10  may be configured to generate a skeletal model of the or each person by identifying body landmarks. 
     Other techniques may be used to determine the object distance D-n. One or more proximity sensors provided on the towed vehicle V 1  and/or the towing vehicle V 2  may be used to determine the object distance D-n. The one or more proximity sensors may comprise one or more of the following: an ultrasonic sensor, a LIDAR sensor and a RADAR sensor. 
     The controller  10  optionally determines a heading (or bearing) of the object of interest O-n relative to the towed vehicle V 1 . The heading may optionally be output for display, for example as an overlay on the towed vehicle image IMG 1  and/or the towing vehicle image IMG 2 . 
     Aspects of the invention are laid out in the following numbered clauses. 
     1. A driver assistance system for a towing vehicle coupled to a towed vehicle, the driver assistance system comprising a controller, the driver assistance system being configured to:
         receive first image data from a towed vehicle imaging device disposed on the towed vehicle, the first image data comprising a first scene behind the towed vehicle;   process the first image data to identify object image data representative of one or more objects of interest in the first scene;   determine an object distance from a reference point to the or each object of interest identified in the first scene; and   output a signal indicative of the object distance.       

     2. A driver assistance system according to clause 1, wherein the object distance is determined by analysing the first image data. 
     3. A driver assistance system according to clause 2, wherein the towed vehicle imaging device comprises a mono camera or a stereo camera. 
     4. A driver assistance system according to any one of the preceding clauses, wherein the driver assistance system is configured selectively to display the first image data; and selectively to overlay the object distance on the first image data. 
     5. A driver assistance system according to any one of the preceding clauses, wherein the driver assistance system is configured to:
         compare the object distance to a threshold distance; and   generate a proximity notification when the comparison identifies the object distance as being less than or equal to the threshold distance.       

     6. A driver assistance system according to clause 5, wherein the driver assistance system is configured to activate a braking system when the towing vehicle is reversing in dependence on the proximity notification. 
     7. A driver assistance system according to any one of the preceding clauses, wherein the driver assistance system is configured to:
         receive second image data from a towing vehicle imaging device disposed on the towing vehicle.       

     8. A driver assistance system according to clause 7, wherein the driver assistance system is configured selectively to display the second image data; and selectively to overlay the object distance on the second image data. 
     9. A driver assistance system according to clause 7 or clause 8, wherein the driver assistance system is configured to:
         combine a part of the first image data and a part of the second image data to generate composite image data; and   selectively to display the composite image data.       

     10. A driver assistance system according to clause 9, wherein the driver assistance system is configured selectively to overlay the object distance on the composite image data. 
     11. A vehicle comprising a driver assistance system according to any one of the preceding clauses. 
     12. A method of assisting a driver of a towing vehicle coupled to a towed vehicle, the method comprising:
         receiving first image data from a towed vehicle imaging device disposed on the towed vehicle, the first image data comprising a first scene behind the towed vehicle;   identifying one or more objects of interest in the first scene;   determining an object distance from a reference point to the or each object of interest identified in the first scene; and   outputting the determined object distance.       

     13. A method according to clause 12 comprising analysing the first image data to determine the object distance. 
     14. A method according to clause 13, wherein the towed vehicle imaging device comprises a mono camera or a stereo camera. 
     15. A method according to any one of clauses 12, 13 or 14 comprising selectively displaying the first image data; and selectively overlaying the object distance on the first image data. 
     16. A method according to any one of clauses 12 to 16 comprising:
         comparing the object distance to a threshold distance; and   generating a proximity notification when the comparison identifies the object distance as being less than or equal to the threshold distance.       

     17. A method according to clause 16 comprising activating a braking system when the towing vehicle is reversing in dependence on the proximity notification. 
     18. A method according to any one of clauses 12 to 17 comprising:
         receiving second image data from a towing vehicle imaging device disposed on the towing vehicle.       

     19. A method according to clause 18 comprising selectively displaying the second image data; and selectively overlaying the object distance on the second image data. 
     20. A method according to any one of clauses 12 to 19, wherein the method comprises:
         combining a part of the first image data and a part of the second image data to generate composite image data; and   selectively displaying the composite image data.       

     21 A method according to clause 20, wherein the method comprises selectively overlaying the object distance on the composite image data. 
     22. Computer software that, when executed, is arranged to perform a method according to any one of clauses 12 to 21. 
     23. A non-transitory, computer-readable storage medium storing instructions thereon that, when executed by one or more electronic processors, causes the one or more electronic processors to carry out the method of any one of clauses 12 to 22.