Object detection enhancement of reflection-based imaging unit

Imaging system and method, the system including a main detection unit, an auxiliary detection unit, an image processor, and a controller. The main detection unit includes a light source that emits light pulses and a gated image sensor that receives reflections of the light pulses reflected from a selected depth of field in the environment and converts the reflections into a reflection-based image. The auxiliary detection unit includes a thermal sensor that detects infrared radiation emitted from the environment and generates an emission-based image. The image processor processes and detects at least one region of interest in the acquired reflection-based image and/or acquired emission-based image. The controller adaptively controls at least one detection characteristic of a detection unit based on information obtained from the other detection unit. The image processor detects at least one object of interest in the acquired reflection-based image and/or acquired emission-based image.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Phase application filed under 35 U.S.C. § 371 of PCT International Application No. PCT/IL2015/051173 with an International Filing Date of Dec. 3, 2015, which claims priority to Israel Patent Application No. 236114, filed on Dec. 7, 2014, the entire contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to active and passive imaging systems in general, and to imaging systems for object detection in a vehicular environment, in particular.

BACKGROUND OF THE INVENTION

Night vision imaging systems produce visible images of an environment having minimal ambient light, which would otherwise not be visible to the human eye. Such systems are used by military and law enforcement units, as well as various civilian applications. One such application is improving the visibility of a vehicle driver during night, rain, fog, or other poor visibility driving conditions. The generated image of the area surrounding the vehicle may be processed to provide various driver assistance and safety features, such as: forward collision warning (FCW), lane departure warning (LDW), traffic sign recognition (TSR), and the detection of pedestrians, obstacles, oncoming vehicles, or other objects of interest along the driving route. The image may also be displayed to the driver, for example projected on a head-up display (HUD) on the vehicle windshield. A vehicle night vision system may also be used to enable autonomous driving at low light levels or poor visibility conditions.

An imaging system may operate using “active imaging” or “passive imaging”. An active imaging system involves actively illuminating the environment and accumulating reflections of the illumination light, whereas a passive imaging system merely collects existing ambient light or emitted/reflected radiation without additional illumination. For example, a passive imaging system may utilize a thermal or infrared camera, which senses differences in infrared radiation emitted by objects in the surrounding area and generates an “emission-based image” according to the sensed radiation differences. A passive imaging system may also collect light emitted or reflected from sources present in the environment, such as: vehicle high beams, streetlights, traffic lights, and the like. An active imaging system requires a light source to illuminate the environment and an imaging sensor to accumulate the reflected light, producing a “reflection-based image”. Active imaging allows for a visible image to be generated even when there is little or no ambient light present in the environment. The light source may be, for example, an LED, a filtered light bulb, or a laser diode, and may transmit light in the form of continuous wave (CW) or in a series of pulses. The image sensor may be semiconductor based, such as charge-coupled devices (CCD), or active-pixel sensors (APS) produced using the complementary metal-oxide-semiconductor (CMOS) or the N-type metal-oxide-semiconductor (NMOS) processes.

The technique of synchronizing the illumination pulses with the camera activation in active imaging systems in order to image a particular depth of field (DOF) is known as “gated imaging”. After the illumination pulse is transmitted, the camera remains in an off state (i.e., does not accumulate any reflected photons), while the pulse reaches the target area and light is reflected back toward the camera. When the reflected light is due to arrive at the camera, the camera is activated to open (i.e., to accumulate reflected photons). After the pulse is received, the camera is turned back off, while awaiting the transmission and reflection of the subsequent illumination pulse. The camera remains off for the duration of time required for the pulse to travel toward the target area and be reflected back, and is subsequently activated only for the duration required to receive the reflected light from the desired DOF. In this manner, the camera receives only reflections from the desired range, and avoids reflections from unwanted objects, such as particles in the atmosphere which may cause backscattering and reduce the contrast of the target area in the generated image. Gated imaging may also be employed to reduce the potential for oversaturation and blooming effects in the sensor, by collecting fewer pulses from shorter distances, thereby lowering the overall exposure level of the camera to near-field scenery and avoiding high intensity reflections from very close objects. Similarly, the light intensity or the shape of the illumination pulse may be controlled as a function of the distance to the target object, ensuring that the intensity of the received reflected pulse is at a level that would not lead to overexposure of the image sensor.

Vehicle-mounted imaging systems that operate solely using a reflection-based image (active illumination imaging) may sometimes produce unclear and indecipherable image content, such as insufficient contrast between potential objects of interest and the background, or insufficiently lit objects (due to the reflected signal intensity being too low). As a result, it may be difficult to ascertain with a high degree of confidence the presence of relevant objects in the environment (such as a pedestrian or a vehicle along the road), and to accurately identify whether they pose a potential hazard. A reflection-based image typically has a high resolution (e.g., at least VGA), where each pixel output is at least 8 to 10 bits if not more. Accordingly, a considerable amount of data must be processed in a reflection-based image in order to allow for object detection. The increased time and processing required to accurately determine potential hazards and relevant objects in the vehicle path based on such reflection-based images also necessitates a longer decision making period for the vehicle operator, which may increase the likelihood of a traffic accident. Finally, a single camera (or sensor) may be restricted to a particular spectral range, which may limit the object detection capabilities.

Conversely, vehicle-mounted imaging systems that operate solely using passive emission-based imaging provide very limited information, and are only capable of detecting objects in the environment that radiate above a sufficient level (or that are above at least a certain temperature) and that radiate in the selected wavelength range (e.g., infrared). Accordingly, such passive emission-based imaging systems typically fail to provide a comprehensive image of the entire environment, and can only provide the vehicle operator with limited information relating to relevant objects and potential hazards in the vicinity of the vehicle. Moreover, it is often difficult for an average person to properly understand and interpret a displayed emission-based image (such as a thermal image). Even for individuals that have experience and familiarity with these types of images, it usually still takes some time to process and register the connection between the contents of the thermal image and the real-world environment that is represented. Thus, the increased processing time to identify potential hazards in the thermal image also increases the decision making time of the vehicle operator, which ultimately raises the likelihood of a vehicle accident.

U.S. Pat. No. 7,786,898 to Stein et al., entitled: “Fusion of far infrared and visible images in enhanced obstacle detection in automotive applications”, describes a vehicle warning system and method that determines a danger of collision between the vehicle and an object in the vehicle environment. The system includes a visible (VIS) light camera, a far infrared (FIR) camera, and a processor. The VIS camera is mounted in the vehicle cabin and acquires, consecutively and in real-time, multiple VIS image frames of a first field of view (e.g., in the direction of travel of the vehicle). The FIR camera is mounted in front of the vehicle engine and acquires, consecutively and in real-time, multiple FIR image frames of a second field of view (e.g., in the direction of travel of the vehicle). The processor detects an object in at least one of the VIS image frames, and locates the detected object in at least one of the FIR image frames. The processor determines a distance between the vehicle and the object responsive to the location of the detected object in both the VIS and FIR image frames, and determines if there is a danger of collision between the vehicle and the object at least partially responsive to the determined distance.

U.S. Patent Application No. 2006/0006331 to Adameitz et al., entitled: “Method for representing a front field of vision from a motor vehicle”, describes a device and method that generates a representation of the field of vision in front of a vehicle, based on three detectors: a near-infrared (NIR) camera system, a far-infrared (FIR) camera system, and a sensor system (e.g., radar sensors and/or ultrasonic sensors and/or ultraviolet sensors). The information generated by each detector undergoes optimization, such as noise filtering, edge filtering, and contrast improvement, and is forwarded to a display after determining whether to superimpose the NIR data with the FIR data. If superimposition is carried out, the image areas of the two cameras are adapted to one another, and if appropriate also restricted. The optimized data of each detector also undergoes feature extraction to assist object detection. If an object which presents danger is recognized, a visual or audible warning is issued.

U.S. Pat. No. 8,525,728 to Lundmark et al., entitled: “Method of detecting object in the vicinity of a vehicle”, discloses a method and system for detecting objects in the vicinity of a driven vehicle. The vehicle is equipped with a forward-facing camera and side-facing cameras. A processor analyzes the camera signals to detect objects by employing one or more detection criteria. The detection is regulated by detection parameters that define the sensitivity with which objects appearing in the camera images are detected. The detected objects are classified into different categories, following which an indication may be provided to the driver and one or more vehicle safety systems may be activated as necessary. A counter maintains a count of the number of objects detected in an image, and passes the information to a parameter adjuster. The parameter adjuster adjusts the detection parameters in accordance with the number of objects detected in previous frames relative to an optimum number of detections, such that the processing capability of the processor is utilized as completely as possible, in order to maximize the possibility of detecting the most relevant objects and enhance vehicle safety.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, there is thus provided an imaging system, which includes a main detection unit, an auxiliary detection unit, an image processor, and a controller. The main detection unit includes a light source and a gated image sensor. The light source is configured to emit light pulses toward an environment to be imaged, and the image sensor is configured to receive reflections of the light pulses reflected from a selected depth of field (DOF) in the environment and to convert the reflections into a reflection-based image. The auxiliary detection unit includes at least one thermal sensor, configured to detect infrared radiation emitted from the environment and to generate an emission-based image. The image processor is configured to process and to detect at least one region of interest (ROI) in an acquired reflection-based image and/or an acquired emission-based image. The controller is configured to adaptively control at least one detection characteristic of the main detection unit and/or the auxiliary detection unit, based on information obtained from the other one of the main detection unit or the auxiliary detection unit. The image processor is further configured to detect at least one object of interest in a reflection-based image and/or an emission-based image.

In accordance with another aspect of the present invention, there is thus provided an imaging method. The method includes the procedure of acquiring reflection-based images of an environment with a main detection unit, by emitting light pulses toward the environment using at least one light source, and receiving the reflections of the pulses reflected from a selected DOF in the environment and converting the reflections into a reflection-based image using at least one gated image sensor. The method further includes the procedure of acquiring emission-based images of the environment with an auxiliary detection unit, by detecting infrared radiation emitted from the environment and generating an emission-based image using a thermal sensor. The method further includes the procedure of processing and detecting at least one ROI in at least one acquired reflection-based image and at least one acquired emission-based image. The method further includes the procedure of adaptively controlling at least one detection characteristic of the main detection unit and/or the auxiliary detection unit, based on information obtained from the other one of the main detection unit or the auxiliary detection unit. The method further includes the procedure of detecting at least one object of interest in the reflection-based image and/or the emission-based image.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention overcomes the disadvantages of the prior art by providing an imaging system and method that enhances the object detection capabilities of a reflection-based imaging (e.g., active illumination) detection unit, using an auxiliary detector based on emission-based (e.g., passive) imaging. The imaging system adaptively sets or adjusts a detection characteristic relating to the reflection-based detection unit, such as by selectively modifying at least one imaging parameter or detection threshold, based on information obtained from the emission-based imaging detection unit. The imaging system may further adaptively set or adjust a detection characteristic relating to the emission-based detection unit, based on information obtained from the reflection-based imaging detection unit. A reflection-based image and emission-based image may be combined to form a merged image, which may be processed and/or displayed. Following an initial processing of the images acquired by both detection units, and controlling detection characteristics of each detection unit as applicable, the imaging system detects objects of interest in the environment, and provides an indication thereof. The imaging system may be mounted on a vehicle, allowing for enhanced detection and identification of objects of interest in the vicinity of a moving vehicle, to provide various driving assistance features, such as alerts of potential road hazards. The imaging system may operate in variable ambient lighting conditions (e.g., daytime or nighttime) and varying environmental conditions (e.g., different weather and climates).

Reference is now made toFIG. 1, which is a schematic illustration of an imaging system, generally referenced100, for object detection, constructed and operative in accordance with an embodiment of the present invention. System100includes a main detection unit130and an auxiliary detection unit140. Main detection unit130includes at least one light source102and at least one camera104. Auxiliary detection unit140includes a thermal sensor107. System100also includes a controller106, an image processor108, a display110, a database122, and a data communication channel119. Image processor108is coupled with controller106, with display110, and with database122. Controller106is further coupled with light source102, with camera104, and with thermal sensor107. Image processor108may optionally be directly coupled to camera104and/or to thermal sensor107(as shown inFIG. 2).

Main detection unit130generally operates using active imaging, in which an image of the scene is generated from accumulated light reflections (by sensor105) after the transmission of light (by light source102) to illuminate the scene. It is noted however that sensor105may also accumulate ambient or emitted light (such as vehicle headlights), i.e., without illumination from light source102. For example, an image sensor105embodied by a CMOS image sensor (CIS) may operate in a passive imaging mode by using a “global shutter” function for a “5T” CIS configuration. Main detection unit130is configured with a gated imaging capability, such that the activation of camera104is synchronized with the illumination pulses (116) in order to image a particular depth of field (DOF). For example, camera104is activated to accumulate photons when the reflected pulses (118) from a specific distance are due to arrive at camera104, and is deactivated or prevented from accumulated photons during other time periods. Main detection unit130may also operate in a non-gated imaging mode.

Light source102emits a series of light pulses, such as light pulse116, toward an area to be imaged by system100. Light source102may alternatively emit continuous wave (CW) radiation. The emitted light may be any suitable wavelength, such as in the near infrared (NIR) (e.g., between approximately 780-870 nm) or short wave infrared (SWIR) spectral range, or in the visible spectral range. For example, light source102may include a subunit that emits light in the visible spectrum (e.g., a smaller projector), such that once an object of interest is detected, the visible light projector is activated to illuminate the object for the vehicle driver (thereby alerting the driver to a potential hazard). Light source102may be embodied by a laser diode, such as an edge-emitting semiconductor laser or a vertical-cavity surface-emitting laser (VCSEL), or by a non-laser light source, such as a light-emitting diode (LED) or a gas discharge lamp. The particular characteristics of the emitted light may be selected in accordance with the imaged area and the environmental conditions. For example, the pulse width, the duty cycle, the pulse rise/fall time, the intensity (peak power), the polarization and/or the shape of the illumination pulse116may be controlled as a function of the distance to an object to be imaged (i.e., the desired DOF).

Camera104receives reflected light, such as reflected light pulse118, reflected from objects illuminated by emitted light pulses116. Camera104includes at least one image sensor105that accumulates reflected light pulses118and generates an image of the scene. Image sensor105may be, for example, a CCD sensor or a CMOS sensor, such as an active pixel sensor (APS) array. Image sensor105may also be a hybrid sensor (e.g., an indium gallium arsenide (InGaAs) based photodetector or a mercury cadmium telluride (MCT) based photodetector), with or without gain. Camera104may also include an image intensification device (e.g., an image intensifier) coupled with the sensor array105. Image sensor105operates in a substantially similar spectral range as light source102(e.g., in the visible, NIR, and/or SWIR wavelengths). Image sensor105is configured to acquire at least one image frame, such as a sequence of consecutive image frames representing a video image, which may be converted into an electronic signal for subsequent processing and/or transmission. The image generated by image sensor105is referred to herein as a “reflection-based image” or a “main image”, interchangeably, which encompasses any optical or digital signal representation of a scene acquired at any spectral region, and encompasses both a single image frame and a sequence of image frames (i.e., a “video image”).

Camera104further includes optics (not shown), configured to direct reflected light pulses118to image sensor105, such as: lenses, mirrors, fiber optics, waveguides, and the like. Camera104further includes optional filters114, configured to filter out incoming light118according to particular filtering criteria. Filters114may be integrated with image sensor105and/or disposed in the adjacent optics. For example, filters114may include at least one bandpass filter, which passes through only wavelengths in the spectral range emitted by light source102(e.g., NIR light), while blocking light at other wavelengths. Such a bandpass filter may thus reduce incoming light from high-intensity light sources in the imaged scene, such as those that reflect/emit visible light (e.g., the headlights of oncoming vehicles). Filters114may also include a spectral filter, such as to direct selected wavelengths to different pixels of image sensor105. Filters114may further include a polarization filter, such as in conjunction with a light source102that emits polarized light, where the polarization filter is configured to block incoming light having a particular polarization from reaching image sensor105. Generally, objects reflect light without preserving the polarization of the incident light, but certain highly reflective objects, such as retroreflective traffic signs, do preserve the incident light polarization. Thus, a polarization filter may be configured to pass through received pulses118with a substantially perpendicular polarization to that of the emitted pulses116, thereby reducing intense reflections from highly reflective objects, and mitigating potential saturation or blooming effects in the reflection-based image. Main detection unit130may adjust the degree by which the polarization is altered, such as by applying a partial rotation of the polarization (e.g., between 0-90° rotation) to reduce reflections from objects further away in the environment. Main detection unit130may adjust the emitted light polarization by roll adjustment of light source102. Filters114may be implemented on the pixel array of image sensor105(i.e., such that different sensor array pixels are configured to only accumulate light pulses having different wavelength/spectral/polarization properties).

Main detection unit130may optionally include multiple cameras104and/or image sensors105, such that different cameras/sensors are configured to collect reflections of different emitted pulses116. For example, 3D information (i.e., a stereoscopic image) can be extracted using a triangulation and/or pulsing/gating scheme.

Auxiliary detection unit140operates using passive imaging, whereby thermal sensor107detects the thermal (e.g., infrared) radiation128emitted from the imaged environment, and then converts the detected radiation into thermal data (electronic signals or electrical charges) which can be stored, transmitted, or used to generate a thermal image, also referred to herein as an “auxiliary image” or “emission-based image”. The terms “thermal image”, “auxiliary image”, and “emission-based image” encompasses both a single image frame and a sequence of image frames or a “video image”, and more generally encompasses any signal data or information obtainable by thermal sensor107, regardless of the amount of emitted infrared radiation actually detected within a given image (e.g., even if none of the pixels in the thermal image includes any “readable” image data). Thermal sensor107may be a relatively inexpensive sensor, characterized by: low resolution, small and basic optics (e.g., a single lens), a small processor (e.g., sufficient for low resolution), and basic electro-mechanical components. For example, the resolution of an image acquired by thermal sensor107may be approximately 10% of the resolution of an image acquired by image sensor105. Thermal sensor107can be a forward looking infrared (FLIR) camera. Thermal sensor107may operate in the short wave infrared (SWIR) spectrum (e.g., between approximately 1.5-2.2 μm); medium wave infrared (MWIR) spectrum (e.g., between approximately 3-5 μm); or far infrared (FIR) spectrum (e.g., between approximately 8-14 μm). Thermal sensor107may be, for example, composed of: indium gallium arsenide (InGaAs), indium antimonide (InSb), vanadium oxide (VOx), galium arsenide (GaAs), a quantum-well infrared photodetector (QWIP), and/or materials such as zinc sulfide (ZnS). Auxiliary detection unit140may optionally include filters (not shown), such as spectral filters to enable the detection of different heat signatures (e.g., to distinguish an animal from a vehicle).

Controller106dynamically and adaptively controls the operation of main detection unit130and auxiliary detection unit140. For example, controller106synchronizes the emission of laser pulses116by light source102with the exposure of camera104for implementing active gated imaging. Controller106also sets the various parameters of the transmitted light pulses116, such as the pulse start time, the pulse duration (i.e., pulse width), the number of pulses per frame, and the pulse shape and pattern. Controller106may also adjusts the frame rate or other parameters relating to the image frames captured by camera104and thermal sensor107. For example, controller106may establish the illumination level for each acquired frame and for each portion or “slice” (i.e., DOF) of a frame, such as by controlling the number of transmitted light pulses116and collected reflections118for each frame slice, controlling the number of frame slices within each frame, controlling the exposure duration of camera104as well as the timing of the exposure with respect to the transmitted light pulse116. Controller106may also control the gain of image sensor105(or thermal sensor107), such as using an automatic gain control (AGC) mechanism. Controller106may also control the exposure of image sensor105(or thermal sensor107), such as using an automatic exposure control (AEC) mechanism. In general, controller106may dynamically adjust any parameter as necessary during the course of operation of imaging system100. Controller106may be integrated in a single unit together with camera104, with thermal sensor107, and/or with image processor108.

Image processor108receives the reflection-based image captured by camera104and the thermal image acquired by thermal sensor107, and performs relevant processing and analysis of the images. Image processor108may merge or combine information from the reflection-based image and the thermal image to generate a fused image, as will be discussed further hereinbelow. Image processor108may also analyze the acquired images (and/or a fused image) to detect and/or identify at least one object of interest in the environment, as will be discussed further hereinbelow. For example, image processor108may be configured to help provide various driver assistance features in a vehicle-mounted imaging system.

Display110displays the images generated by imaging system100, such as a main image from main detection unit130, an auxiliary image from auxiliary detection unit140, and/or a fused image that combines at least a portion of a main image with at least a portion of an auxiliary image. The displayed image may be combined with the ambient scenery, allowing a user to view both the display image and the ambient scene simultaneously, while maintaining external situational awareness. For example, display110may be a head-up display (HUD), such as a HUD integrated in a vehicle windshield of a vehicle-mounted imaging system. When an object of interest in the environment is detected, display110may present a view of the detected object being illuminated by a visible light subunit of light source102.

Database122stores relevant information, which may be used for assisting the detection and identification of objects in the acquired images, such as thermal signature data associated with different objects in different environmental conditions.

Data communication channel119allows for sending and receiving images, alerts or other data to internal system components or to an external location. Data communication channel119may include or be coupled with an existing system communications platform, such as in accordance with the CAN bus and/or on-board diagnostics (OBD) protocols in a vehicle. For example, imaging system100may receive information relating to the current vehicle status, such as: velocity; acceleration; orientation; and the like, through the vehicle communication bus. Imaging system100may also receive information from external sources over communication channel119, such as location coordinates from a global positioning system (GPS), and/or traffic information or safety warnings from other vehicles or highway infrastructure, using a vehicular communication system such as vehicle-to-vehicle (V2V) or vehicle-to-infrastructure (V2I).

Imaging system100may optionally include and/or be associated with additional components not shown inFIG. 1, for enabling the implementation of the disclosed subject matter. For example, system100may include a power supply (not shown) for providing power to the various components, which may be integrated with, or receive power from, the main power source in the vehicle. System100may further include an additional memory or storage unit (not shown) for temporary storage of image frames, thermal image data, or other data. System100may also include an operator interface (not shown) for allowing an operator of system100to control various parameters or settings associated with the components of system100. System100may also include a vehicle interface (not shown) for allowing another system in the vehicle to control various parameters or settings of system100.

The components and devices of imaging system100may be based in hardware, software, or combinations thereof. It is appreciated that the functionality associated with each of the devices or components of system100may be distributed among multiple devices or components, which may reside at a single location or at multiple locations. For example, the functionality associated with controller106or image processor108may be distributed between multiple controllers or processing units.

According to an embodiment of the present invention, imaging system100is mounted onto a vehicle. The term “vehicle” as used herein should be broadly interpreted to refer to any type of transportation device, including but not limited to: an automobile, a motorcycle, a truck, a bus, an aircraft, a boat, a ship, and the like. It is appreciated that the imaging system of the present invention may alternatively be mounted (at least partially) on a non-vehicular platform, such as a stationary, portable or moveable platform, e.g., a pole, fence or wall of a secured perimeter or surveillance zone.

Reference is now made toFIG. 2, which is a schematic illustration of a top view of the imaging system (100) ofFIG. 1mounted in a vehicle, referenced120, constructed and operative in accordance with an embodiment of the present invention. Display110is mounted in front of a user, such as the driver of vehicle120, and may be a heads-up display (HUD) which projects images on the vehicle dashboard or windshield. Imaging system100may be installed in vehicle120in a “forward looking configuration”, in which light source102, camera104, and thermal sensor107face toward the front side of vehicle120(as depicted inFIG. 2). Alternatively, imaging system100may be installed in a “rear looking configuration” in vehicle120, where the components face the rear side of vehicle120. Further alternatively, the components may be installed in a “surrounding configuration”, in which multiple cameras104and/or thermal sensors107collectively provide substantially 360° coverage around vehicle120. Light source102may be integrated in the vehicle headlights103(in a forward looking configuration) or taillights (in a rear looking configuration). Alternatively, light source102can be a standalone unit, such as a fog lamp or other illuminator mounted at the front grille (as depicted inFIG. 2), or in the bumper or a side mirror of vehicle120. Light source102may be embodied as multiple elements (e.g., within two separate vehicle headlights103). Thermal sensor107may be integrated with light source102, and may also be integrated into an existing light source of vehicle (such as vehicle headlights103), or may be installed as a standalone unit. Camera104and thermal sensor107may be mounted on an external surface of vehicle120, such as on the front (exterior) side of the vehicle, in order to avoid degradation (transmission loss) of the reflected or emitted signals (e.g., incoming reflection pulses118and/or thermal radiation signal128) due to the windshield or window. Alternatively, camera104and/or thermal sensor107may be installed on an interior vehicle surface, such as the inside of the vehicle windshield (configured to be penetrated by the incoming reflected pulses118and thermal radiation128), such as behind the rear-view mirror. If thermal sensor107is installed on an external surface, then auxiliary detection unit140may optionally include a cleaning mechanism, such as a wiper and/or a cleansing spray.

The field of view (FOV) of camera104(depicted by the dotted lines154) overlaps with and is substantially similar to the field of illumination (FOI) of light source102(depicted by the dashed lines152). In the configuration ofFIG. 2, the FOV of camera104is encompassed within the FOV of thermal sensor107(depicted by the dotted lines157). More generally, the FOV of camera104at least partially overlaps with the FOV of thermal sensor107. For example, camera104has a narrow FOV and high resolution, and is operative for capturing light reflected from objects illuminated by light source102, while thermal sensor107has a wide FOV and low resolution, and is operative for capturing emitted thermal radiation in a FOV157that encompasses the FOV154of camera104. Alternatively, camera104may have a wider FOV than thermal sensor107, or camera104and thermal sensor107may have substantially similar FOVs.

Controller106and database122are disposed in or mounted on vehicle120, and may be integrated with other system elements (such as camera104or image processor108), or with other vehicle control units (not shown). All the elements of system100are configured and mounted such that they do not interfere with the functioning of other existing vehicle components and produce minimal interference to the driver of vehicle120.

System100images the environment in the vicinity of vehicle120, by generating at least one main image using main detection unit130, and generating at least one auxiliary image using auxiliary image unit140. In particular, light source102emits a series of light pulses to illuminate the environment in the vicinity of vehicle120, and camera104collects the light reflected from the illuminated environment and generates a main (reflection-based) image. Concurrently, thermal sensor107collects thermal data from the environment in the vicinity of vehicle120and generates an auxiliary (emission-based) image. Image processor108processes the main image and the auxiliary image to detect regions of interest (ROIs) in the environment. Controller106adaptively controls at least one detection characteristic relating to main detection unit130and/or auxiliary detection unit140(as elaborated upon further hereinbelow), based on the ROIs determined in the main image and auxiliary image. Subsequently, image processor108detects at least one object of interest in the main image and/or the auxiliary image. An “object of interest” (or a “region of interest”) may be any size, shape or pattern corresponding to one or more physical points in a real-world environment. For example, the object of interest may represent a unified physical object or entity located in the environment, or may represent a general environmental feature or collection of features (and not necessarily a unified physical object). The object of interest may be dynamic, such that at least one characteristic of the object changes over time. For example, the object of interest may be in motion, such that its position relative to vehicle120is continuously changing while being imaged. Processor108may designate at least one object of interest in the environment for further investigation, or to be brought to the attention of a driver or passenger of vehicle120. For example, processor108detects relevant objects located along the current route of vehicle120, some of which may pose a potential danger to a driver or passenger of vehicle120.

Upon detection of an object of interest, system100may perform one or more appropriate actions. For example, system100may generate an alert or notification relating to the detected object of interest, such as a visual or audio indication of the object of interest, such as by presenting augmented reality (AR) content on display110(e.g., symbols/graphics/text/imagery relating to the driving environment). The alert or notification relating to a detected object of interest may be integrated with a driving assistance module in vehicle120configured to provide a driving assistance feature, such as: forward collision warning (FCW), lane departure warning (LDW), traffic sign recognition (TSR), high beam control, detection and/or identification of objects (such as vehicles, pedestrians or animals), and any combination thereof.

Imaging system100adaptively sets or adjusts at least one detection characteristic of main detection unit130and/or auxiliary detection unit140, following processing of obtained main images and auxiliary images, such as to enhance object detection capabilities. In general, a detection characteristic relating to one detection channel (main or auxiliary) may be selected or modified, based on the information obtained in the other detection channel. Controller106may establish or modify the operating parameters of main detection unit130, such as by applying selected imaging parameters of light source102and/or camera104when acquiring subsequent reflection-based images. For example, controller106may direct main detection unit130to acquire additional images in a selected ROI identified in an auxiliary image detected by thermal sensor107, such as by limiting the FOV154of camera104and/or the FOI152of light source102, and/or by further restricting the imaged DOF. For example, processor108may detect a potential object candidate in the auxiliary image (i.e., a “coarse” or “partial” object detection), such as by identifying a general ROI characterized by larger (or smaller) thermal radiation (i.e., a higher/lower temperature region) than other regions in the thermal image, which is considered insufficient for accurate detection of an object. Controller106may then direct main detection unit130to focus on the ROI identified in the auxiliary image, which may represent a potential object. Main detection unit130may also be configured to track the ROI or potential object, using object tracking techniques known in the art. Controller106may adaptively adjust at least one imaging parameter of main detection unit130, including but not limited to: a gating parameter; a pulse width; a pulse intensity; a pulse shape; a gating cycle duration; a delay time of a gating cycle; the frame rate of image sensor105; a DOF to be imaged; a maximum range to be imaged; the FOI of light source102; the FOV of image sensor105or camera104; the sensitivity of image sensor105; and any combination thereof. Conversely, controller106may adaptively set or adjust at least one imaging parameter of auxiliary detection unit140, including but not limited to: the direction (alignment), the FOV, and/or the sensor gain of thermal sensor107, such as to focus on a selected ROI detected in a main image. The FOV of thermal sensor107can be modified by binning pixels in the FPA or by moving lens elements.

A further detection characteristic that may be adaptively controlled is an object detection threshold in at least one of the detection channels. For example, a detection threshold in main detection unit130may be lowered in at least a main image region corresponding to an ROI detected in an auxiliary image. Conversely, a detection threshold in auxiliary detection unit140may be lowered in at least an auxiliary image region corresponding to an ROI detected in a main image. The detection threshold adjustment may be implemented by adjusting at least one of the following: a candidate detection module; a control points classification module; a nearest neighbor classification module; a clustering module; a tracker module; a motion detection module; a final detection module; and/or the object classifications stored in database122. The candidate detection module is an initial screening process for all pixels in an image, which determines whether a pixel is located in the center of a bright vertical object. By adjusting a candidate detection threshold, the more complex processes of the object detection algorithm may be applied on a smaller percentage of the image pixels. The control points classification module is an initial shape-based classification process intended to determine whether the image pixels of an object candidate (identified in a candidate threshold process) are located at the center of an object (e.g., a pedestrian), using the pixel values within the detection window. The nearest neighbor classification module is a second shape-based classification process intended to further eliminate false positive detections (i.e., false alarms) that were incorrectly detected as objects in the control points classification. This module is a classification process trained off-line and based on histograms of oriented gradients, using a K-nearest neighbor (KNN) algorithm. The clustering module establishes a boundary for each object in the image, by clustering close points from the same resolution and from different resolutions into a single point per object and then determining a suitable bounding region. The tracker module is intended to ensure that only a single detection is provided for each object, to enable temporal filtering of objects, and to track an object even in image frames the object was not detected in. In order to track the object through the image frames in which the object appears, the tracker module associates between detections of the same object in different image frames. The motion detection module allows for further reducing false positives by using temporal data of the object. For example, a pedestrian is (typically) a non-rigid moving object, as opposed to other objects in the environment that are stationary (e.g., traffic signs, vehicles, lampposts). Accordingly, a pedestrian may be detected by examining a series of consecutive image frames and searching for objects with internal movement. The final decision module integrates the various temporal and spatial data relating to the object, in order to detect and identify the object (e.g., determining whether the object represents a pedestrian).

Controller106may also adaptively set the number of processed image frames of a main image and/or an auxiliary image, before finalizing the detection of an object of interest. For example, following the detection of an ROI in an acquired thermal image, image processor108may be directed to further process and analyze the corresponding image regions in at least a minimum number of subsequent reflection-based images (e.g., at least the next three reflection-based images) in order to verify the presence of an object within the ROI. In general, each detection unit130,140may be selectively controlled in accordance with information obtained in the respective image of the other detection unit130,140. It is noted that such information is not limited to the detection of an ROI in one of the images. For example, image processor108may determine that a particular environmental area was not fully or clearly imaged in the reflection-based image (e.g., due to obstructions or interference in the propagation path of the emitted/reflected pulses, or alternatively, due to pixel saturation of image sensor105resulting from high-intensity reflective/transmitting sources in the environment). Controller106may then direct auxiliary detection unit140to focus on the particular environmental area(s) for which insufficient image content was obtained by main detection unit130. For another example, the imaged environment may result in lower quality or unusable thermal images acquired by thermal sensor107, such as due to smog, rain or fog in the atmosphere, or oversaturation, in which case processor108may be directed to exclude at least a minimum number of subsequent emission-based images (e.g., excluding all thermal image frames acquired while the environmental conditions were not conducive).

System100may optionally generate a merged image by combining a reflection-based image obtained by main detection unit130with an emission-based image obtained by auxiliary detection unit140. In particular, image processor108may combine at least a portion of an emission-based image obtained by thermal sensor107with at least a portion of a reflection-based image captured by image sensor105, using suitable image fusion techniques. Image processor108may also add further supplementary content onto the combined image, such as symbols/graphics/text/imagery relating to the driving environment. Display110may then display the merged image to the user (e.g., a driver or passenger of vehicle120).

Reference is now made toFIG. 3, which is a first exemplary set of images acquired by the imaging system (100) ofFIG. 1, operative in accordance with an embodiment of the present invention. Main detection unit130acquires a main (reflection-based) image170, while auxiliary detection unit140acquires an auxiliary (emission-based) image180, e.g., following Non-Uniformity Correction (NUC) and AGC threshold control. Image processor108receives main image170from main detection unit130, and attempts to identify objects of interest in main image170. Processor108detects and identifies an object in image region172, and further detects a region of interest (representing a potential object candidate) in image region174. Whereas the object in image region172is easy to detect and identify (as a vehicle), image region174appears unclear and indefinite and is obscured by other elements in the environment. For example, an unclear image region of a reflection-based image may depict a general outline or crude shape, or may be characterized with minimal contrast between the potential object and the background, or the potential object may be obscured by other image features. As a result, processor108cannot ascertain the presence and/or type of object in image region174with a high degree of confidence (i.e., with a high “probability of detection (POD)”). Image processor108further receives emission-based image180from auxiliary detection unit140. Processor108identifies regions of interest (ROIs)182,184in emission-based image180, which are characterized by substantially larger thermal radiation (higher temperatures) than other regions in emission-based image180. Processor108proceeds to enhance reflection-based image170using details from emission-based image180. In particular, processor108may generate merged image190, by combining the thermal information of ROIs182,184in auxiliary image180with the respective image regions172,174of main image170, using suitable image fusion techniques. In addition to (or instead of) generating a merged image, controller106may direct main detection unit130to obtain further reflection-based images focused particularly at the respective DOF associated with ROIs182,184. More generally, processor108may analyze each detection channel (130,140) to obtain potential object candidates (ROIs), and then controller106may adjust imaging parameters of main detection unit and/or auxiliary unit140, which then collect additional reflection-based images and/or additional emission-based images, as necessary, in order to reduce the number of potential candidates. This process may be repeated in an iterative manner, by continuously obtaining feedback from the images (170,180) and adjusting imaging parameters of each detection channel (130,140) accordingly. Subsequently, processor108can analyze merged image190, and/or the additionally acquired reflection-based/emission-based images (that may also be used to generate additional merged images), to accurately detect the presence of objects that may not have been detectable in the original images170,180. Processor108may further categorize and identify the detected objects, using information from database122if applicable. For example, image processor108may compare thermal data (i.e., “thermal signatures”) obtained in emission-based image180with predefined information stored in database122associating different objects with their expected thermal signatures. In the example ofFIG. 3, image region194is identified as a pedestrian and image region192is identified as a vehicle. System100may then indicate the detected objects to user, such as by presenting merged image190on display110together with text or symbols indicating information or characteristics associated with each detected object (e.g., type of object; distance from vehicle120; level of potential danger; and the like). System100may also provide warnings relating to the detected objects, as necessary, such as in conjunction with relevant driving assistance modules.

Reference is now made toFIG. 4, which is a second exemplary set of images acquired by the imaging system (100) ofFIG. 1, operative in accordance with an embodiment of the present invention. Image processor108receives a reflection-based image200acquired by main detection unit130, and an emission-based image210acquired by auxiliary detection unit140(after Non-Uniformity Correction (NUC) and AGC threshold control), and attempts to detect object candidates or ROIs in each image200,210. Processor108identifies an ROI202in reflection-based image200, where ROI202appears unclear and difficult to accurately identify. Processor108identifies an ROI212in emission-based image210(corresponding to ROI202of reflection-based image200). Processor108may generate merged image220, by combining image data (thermal information) of ROI212in emission-based image210, with the corresponding ROI202of reflection-based image200, using suitable image fusion techniques. Controller106may also direct main detection unit130and/or auxiliary detection unit140to collect additional reflection-based images and/or emission-based images, after adjusting imaging parameters of at least one of the detection channels130,140according to image information obtained from the initially acquired images200,210(e.g., based on analysis of ROIs202,212). Processor108then detects objects of interest in merged image220(and/or using additionally reflection-based/emission-based images), and may further categorize and identify the detected objects. In the example ofFIG. 3, image region222(corresponding to ROIs202,212) is identified as a pedestrian.

In some cases, it may be possible to obtain sufficient information from the original images acquired by one of the detection channels130,140and to identify objects of interest directly in the acquired images. Reference is now made toFIG. 5, which is a third exemplary set of images acquired by the imaging system (100) ofFIG. 1, operative in accordance with an embodiment of the present invention. Main detection unit130acquires a reflection-based image230(e.g., with light-source102non-operational), and auxiliary detection unit140acquires an emission-based image240. Image processor108identifies object candidates (ROIs)232,234,236in reflection-based image230, and identifies object candidates (ROIs)244,246,248in emission-based image240, where ROIs244and246correspond to ROIs234and236, respectively. It is noted that processor108does not identify an ROI in emission-based image240corresponding to ROI232of reflection-based image, due to the low contrast in this spectrum associated with ROI232. Nevertheless, image regions232,234,236appear sufficiently clear in reflection-based image230such that processor132can identify all of the respective objects (including object232), as representing: a pedestrian (232) and vehicles (234,236), respectively. By analyzing both images230,240, image processor108may obtain further relevant information, such as determining that ROI248of emission-based image240represents the sky, as evident from reflection-based image230(where images230,240were collected during daytime and bright ambient light conditions).

Referring back toFIG. 1, main detection unit130may operate in a gated imaging mode in order to image a selected DOF (or multiple selected DOFs), which may help reduce image clutter and facilitate image processing. For example, main detection unit130may implement gated imaging in order to avoid receiving intense reflections from highly reflective objects (e.g., retroreflective traffic signs, retroreflective vehicle rear bumper) that are known to be located at a particular DOF relative to vehicle120, which can lead to saturation or blooming effects in the active image. Gated imaging may also be employed to minimize reflections from atmospheric particles in the immediate vicinity, which may cause backscattering and reduce the contrast of the target area in the generated reflection-based image. Controller106may control and synchronize the operation of light source102and camera104to accumulate a different number of reflected pulses for different scenery ranges or “slices” (e.g., accumulating fewer reflected pulses from shorter distances, and a greater number of reflected pulses from farther distances). For example, controller106may adjust the pulse intensity, the pulse width, the pulse shape, the duty cycle, the pulse rise/fall time, and/or the number of pulses emitted by light source102, as well as the timing and duration of camera104activation (exposure time), to selectively accumulate different reflections from different DOFs. For example, main detection unit130may generate a short-range reflection-based image by emitting/accumulating a small number of pulses; an intermediate-range active image by emitting/accumulating a moderate number of pulses; and a long-range active image by emitting/accumulating a high number of pulses. Thus, consecutive image frames may differ in illumination level, which allows for focusing on a selected DOF in the reflection-based images, such as following a “partial detection” of a potential object candidate in an earlier image.

According to an embodiment of the present invention, image processor108may perform character recognition of objects in the imaged scene with text or numerical data, such as traffic signs, for example by using optical character recognition (OCR) techniques known in the art. Image processor108may also analyze textual or numerical content to provide supplemental driving assistance features, such as to identify potential driving hazards or for navigation purposes. For example, system100may notify the driver of vehicle120if he/she is turning onto the correct road, by analyzing the content of traffic or street signs in the vicinity of vehicle120, optionally in conjunction with available maps and the real-time location of vehicle120. System100may determine the optimal illumination level for imaging, in order for the visibility of characters on the sign to be as high as possible, and adjust imaging parameters accordingly. For example, controller106may adjust the operating parameters of light source102and/or camera104such as to acquire the lowest illumination image that will accurately enable pattern and text recognition (e.g., in order to conserve power and to minimize saturation effects). Following a general determination of the type of traffic or street sign (or other high-intensity source), such as based on the shape and/or image information associated with the sign (e.g., text/numerical data), image processor108may also add color information to the traffic signs on an acquired or generated (fused) image. Such color information may also be obtained from spectral filters114implanted on image sensor105of camera104. Active-gated imaging may also be applied for removing unwanted markings in the image frames, such as road tar marks or concrete grooves.

It is noted that camera104and thermal sensor107may be characterized with different imaging parameters or characteristics, such as at least one of: FOV, resolution, pixel dimensions, sensitivity, and the like. Main detection unit130and auxiliary detection unit140may use at least some of the same optics and/or detection channel. Such a configuration may reduce the overall power consumption of system100.

Imaging system100may optionally include additional detection/measurement units or imaging sources (not shown), in addition to detection units130,140, including but not limited to: a radar detector; a lidar detector; stereoscopic cameras; and the like. The additional detection sources may be remotely located from at least some components of system100, and may forward measurement data to system100via an external (e.g., wireless) communication link. The information obtained from the additional sources may be used to enhance the object detection capabilities, such as in determining how or whether to adaptively control detection characteristic of detection units130,140. For example, system100may obtain distance information relative to potential objects in the environment, and controller106may then adjust at least one gating parameter of main detection unit130accordingly. The distance information may be obtained from an external measurement unit (e.g., a laser rangefinder), or alternatively may be determined based on information from main detection unit130(e.g., based on the relative timing between emitted pulses116from light source102and detected pulses118by image sensor105). Processor108may also utilize distance information for object detection and identification purposes. For example, image processor108may determine an expected thermal signature from a particular object located at a certain distance (DOF), and then compare the thermal signature in the obtained emission-based image at that distance with information stored in database122to identify the object. Image processor108may also take into account how the thermal signature changes as a function of distance (e.g., the thermal signature of a person will be expected to change in a certain way as the person approaches or recedes). For another example, system100may obtain information relating to the environmental conditions in the imaged environment, such as for example: lighting conditions (e.g., sunny or overcast); weather or climate conditions (e.g., rain, fog, or snow); time of day (e.g., day or night); month of year or season; and the like. The obtained environmental conditions may be utilized for enhancing a main image, auxiliary image, and/or merged image (e.g., adjusting the brightness level in the image); for controlling the operation of detection units130,140(e.g., adjusting at least one imaging parameter of light source102, camera104, and/or thermal sensor107); and/or for enhancing object detection and identification (e.g., selectively modifying an object detection threshold). In particular, the thermal signature from an object may be substantially influenced by the environmental conditions, and so image processor108may take the environmental conditions into account when attempting to identify a potential object in a reflection-based image and/or an emission-based image (and/or a merged image). For yet another example, image processor108may use a digital map or other location data source to assist and enhance the interpretation of detected objects, such as to navigate a driver of vehicle120based on character recognition of street signs in the images in conjunction with map analysis. In general, a detection characteristic of main detection unit130and/or auxiliary detection unit140may be modified as a function of real-time parameters including but not limited to: the speed of vehicle120; the location of vehicle120(e.g., urban road, inter-city road, etc); the weather conditions; the type of object(s) desired to detect; and the type of object(s) actually detected.

It is appreciated that detection units130,140may be configured to operate during both day and night, and in variable weather and climate conditions (e.g., clear and sunny, or overcast, rain, fog, snow, hail, etc), allowing for effective imaging and object identification by system100in varying environmental conditions. It is further appreciated that the use of auxiliary detection unit140may serve to enhance the object detection capabilities of main detection unit130. In particular, by supplementing the information of the main detection channel obtained in one spectral range (e.g., NIR-SWIR) with information in other spectral ranges (e.g., MWIR-FIR) of the auxiliary detection channel, a higher probability of detection (POD) may be achieved, as well as a lower false detection rate. Furthermore, the use of a relatively small and low resolution thermal sensor107in auxiliary detection unit140(e.g., approximately 10% of the resolution of image sensor105) may provide various benefits, including: ease of installation and integration, and the ability to use small (low cost) optics and small (low cost) electronics. A low resolution thermal sensor107may also result in reduced power consumption for image processing. In particular, a reflection-based image (such as images170,200,230) is typically characterized by relatively high resolution (e.g., at least VGA), which requires a substantial amount of data processing (e.g. at least 8-10 bits or more) to enable object detection. Therefore, since image processor108initially attempts to identify potential object candidates in the emission-based image, and may limit the subsequent analysis in the reflection-based image to only the relevant regions identified from the emission-based image, the overall processing power of imaging system100may be reduced considerably.

According to another embodiment of the present invention, a plurality of imaging systems, similar to system100ofFIG. 1, can operate together in a common environment. The timing of parameters relating to an image frame of at least one of the imaging systems can be determined in accordance with a random hopping scheme.

Reference is now made toFIG. 6, which is a block diagram of an imaging method for object detection, operative in accordance with an embodiment of the present invention. In procedure252, a reflection-based image of an environment is acquired using a main detection unit. Referring toFIGS. 1 and 3, light source102emits light pulses116toward an environment to be imaged, such as along a road being traveled by vehicle120. Camera104accumulates reflections118reflected from objects illuminated by the emitted light pulses116, and generate a reflection-based image170from the accumulated reflections118. Main detection unit130may operate in a gated imaging mode, to image a selected DOF in the environment.

In procedure254, an emission-based image of the environment is acquired using an auxiliary detection unit. Referring toFIGS. 1 and 3, thermal sensor107of auxiliary detection unit140detects thermal radiation128emitted from objects in the imaged environment and generates an emission-based image180.

In procedure256, supplementary information of the environment is obtained. Referring toFIG. 1, system100receives information relating to the imaged environment, by means of a supplemental detection unit or data source (not shown). For example, system100may obtain the lighting or weather conditions in the vicinity of vehicle120(e.g., via an ambient sensor or humidity sensor). System100may also obtain the location and driving route of vehicle120(e.g., via a GPS and/or digital map), or real-time parameters of vehicle120, such as velocity and acceleration (e.g., via the vehicle communication bus). A further example is a radar or lidar detector or laser rangefinder, which may provide the relative distances to potential objects in the environment.

In procedure258, the acquired reflection-based image and the acquired emission-based image are processed and regions of interest are detected. Referring toFIGS. 1 and 3, image processor108analyzes reflection-based image170acquired by main detection unit130and detects ROIs172and174, where ROI172is identified as a vehicle, whereas ROI174appears unclear and obscured and cannot be accurately identified. Image processor108further analyzes emission-based image180acquired by auxiliary detection unit140and detects ROIs182and184, corresponding to ROIs172and174of image170.

In procedure260, a detection characteristic of the main detection unit and/or the auxiliary detection unit is adaptively controlled, based on information obtained from the emission-based image and/or the reflection-based image. Referring toFIGS. 1 and 3, controller106sets or adjusts at least one detection characteristic relating to main detection unit130and/or auxiliary detection unit140, based on the processing of reflection-based image170and emission-based image180. For example, controller106may modify at least one operating parameter of main detection unit130, such as a gating/imaging parameter of light source102and/or image sensor105. Alternatively or additionally, controller106may modify at least one operating parameter of auxiliary detection unit140, such as by adjusting an imaging parameter of thermal sensor107(e.g., direction, FOV, gain). For example, controller106may direct main detection unit130to obtain further reflection-based images in a particular DOF following a partial detection of a potential object (e.g., ROI184in auxiliary image180), such as by altering the FOV of camera104or FOI of light source102, and/or by adjusting at least one gating parameter of light source102and/or camera104(e.g., pulse width, pulse intensity, cycle duration, and the like). Controller106may also direct main detection unit130to track a ROI identified in an auxiliary image. Further alternatively, controller106may adjust an object detection threshold relating to main detection unit130and/or auxiliary detection unit140. For example, controller106may lower a detection threshold in a reflection-based image, in accordance with an ROI detected in an emission-based image. Image processor108may restrict processing of a reflection-based image to certain pixels or image regions in accordance with information obtained from an initial processing of an emission-based image (e.g., after identifying ROI184as a potential object candidate in emission-based image180, processor108focuses further analysis to the corresponding image region174of reflection-based image170). The decision process may be based upon: motion detection, object tracking, classification, etc. This may be performed after each image frame, or intermittently after a certain number of frames. Image processor108may also be directed to process at least a minimum number of reflection-based images and/or emission-based images, before establishing a detected object of interest. Image processor108may further be directed to exclude a certain number of reflection-based images and/or emission-based images, such as if environmental conditions preclude full, clear or useful imaging by a respective detection unit130,140. In general, controller106may (iteratively) adjust imaging parameters or other detection characteristics of main detection unit130and/or of auxiliary unit140when collecting additional reflection-based images and/or emission-based images, based on analysis of previously acquired reflection-based images and/or emission-based images, in a manner that reduces the potential object candidates in the additional images, thereby improving the detection and identification of objects of interest. A detection characteristic of main detection unit130and/or auxiliary detection unit140may also be controlled in accordance with the obtained supplementary information of the environment (procedure256). For example, controller106may direct main detection unit130to image a selected range slice (DOF), based on the measured distance to a potential object provided by a radar detector.

In procedure262, a merged image is generated by image fusion of the reflection-based image and the emission-based image. Referring toFIGS. 1 and 3, image processor108generates merged image190, by image fusion of reflection-based image170and emission-based image180, such as by combining thermal information of ROIs182,184in emission-based image180with the respective image regions172,174of reflection-based image170.

In procedure264, the merged image is displayed. Referring toFIGS. 1 and 3, display110displays merged image190, such as to a driver or passenger of vehicle120. Display110may also present supplementary content, such as text or symbols indicating characteristics associated with detected objects in the displayed image.

In procedure266, at least one object of interest is in the reflection-based image, the emission-based image, and/or the merged image. Referring toFIGS. 1 and 3, image processor108processes and analyzes merged image190(and/or additional reflection-based images and emission-based images acquired after images170,180) and detects objects of interest in the imaged environment, including objects that may not have been detectable in initially acquired images170,180. For example, processor108identifies image region194in image190as a pedestrian, corresponding to previously detected ROI184of emission-based image180and ROI174of reflection-based image170. Processor108may classify or identify detected objects using information from database122, such as based on thermal signature data. Processor108may also update new object classifications in database122.

In procedure268, an indication of a detected object is provided. Referring toFIGS. 1 and 3, system100provides an alert or notification relating to a detected object of interest, such as a visual, tactile or audio indication of a potential road hazard to an operator of vehicle120, such as by highlighting pedestrian194on image190on display110, or by illuminating the object directly in the environment with a visible light subunit of light source102. System100may also provide warnings or notifications relating to the detected objects in conjunction with a driving assistance module. Different types of indications may be provided for different detected objects, in accordance with detection metrics or other relevant criteria. For example, display110may present different objects with different visual characteristics, based on their respective confidence level or reliability (i.e., the validity or veracity of the object detection and/or object classification), such as by using a first color to represent a “highly reliable” object detection while using a second color to represent a “less reliable” object detection.

The method ofFIG. 6is generally implemented in an iterative manner, such that at least some of the procedures are performed repeatedly or continuously, in order to keep imaging the surrounding environment for at least a selected duration. Accordingly, imaging system100may use information learned from previous imaging sessions in order to enhance future performance, for example, by selecting optimal imaging parameters for different environmental conditions and/or by adjusting imaging parameters (or other detection characteristics) of detection units130,140in an optimal manner, based on previous results. System100may implement artificial intelligence techniques, such as machine learning and pattern recognition, in order to learn relevant information from previous imaging sessions.

While certain embodiments of the disclosed subject matter have been described, so as to enable one of skill in the art to practice the present invention, the preceding description is intended to be exemplary only. It should not be used to limit the scope of the disclosed subject matter, which should be determined by reference to the following claims.