Patent Publication Number: US-11032488-B2

Title: Camera system with light shield using object contrast adjustment

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This is a continuation application and claims the benefit under 35 U.S.C. § 120 of U.S. patent application Ser. No. 15/180,271, filed Jun. 13, 2016, the entire disclosure of which is hereby incorporated herein by reference. 
    
    
     TECHNICAL FIELD OF INVENTION 
     This disclosure generally relates to a vision system, and more particularly relates to a vision system suitable for use on an automated vehicle. 
     BACKGROUND OF INVENTION 
     It is known that camera systems are severely impaired when a bright light source, such as the Sun or head-lights from an on-coming vehicle for example, is in the direct field-of-view. The light-to-dark contrast of sunlight compared to the surrounding objects may be on the order of one-hundred-ten decibels (110 dB) which typically exceeds the linear dynamic range of camera systems. The brightness of the sunlight causes the camera to reduce the exposure times to prevent saturation and consequently lowers the contrast across all image-elements resulting in a darkened image. This causes loss of critical image-data that is required for the vision functions of autonomous-vehicles, such as lane recognition, pedestrian detection, stop-light recognition, vehicle recognition and other autonomous driving object-recognition capabilities. Other vision-systems may be similarly affected such as, robot vision-systems, welding control-systems, military tracking-systems, autonomous vision-systems including space, aircraft and ground based vehicles. 
     SUMMARY OF THE INVENTION 
     Described herein is a camera system capable of significantly reducing the dynamic range of brightness of a scene in the field-of-view of the camera. 
     In accordance with one embodiment, a camera system suitable for use on an automated vehicle is provided. The camera system includes an imager used to detect an image of a field-of-view of the system. The camera system also includes a light-shield operable to block a portion of the image from being received by the imager. The camera system also includes a controller in communication with the imager and the light-shield, and the controller is configured to position the light-shield in a line-of-sight between a bright-spot and the imager. 
     Further features and advantages will appear more clearly on a reading of the following detailed description of the preferred embodiment, which is given by way of non-limiting example only and with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The present invention will now be described, by way of example with reference to the accompanying drawings, in which: 
         FIG. 1  is a prior art camera system in accordance with one embodiment; 
         FIG. 2  is a camera system that is modified with a light-shield in accordance with one embodiment; 
         FIG. 3  is a light-shield in accordance with one embodiment; 
         FIG. 4  is a graph of the light intensity reduction in accordance with one embodiment; 
         FIG. 5  is a camera system that is modified with a light-shield and an aperture-stop in accordance with one embodiment; 
         FIG. 6  is a graph of the light intensity reduction in accordance with one embodiment; 
         FIG. 7  is a camera system that is modified with a light-shield in accordance with one embodiment; and 
         FIG. 8  is a graph of the light intensity reduction in accordance with one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a non-limiting example of a camera system  10 , hereafter referred to as the camera  10 , which may be adversely affected by a bright-spot  12  in a field-of-view  14  of the camera  10 . The intensity of the light from the bright-spot  12 , illustrated by the Sun for purposes of example only, may saturate an imager  16  of the camera  10 . Both an object  18  and the bright-spot  12  are in the field-of-view  14 . A line-of-sight  20  is defined between the bright-spot  12  and a location on the imager  16  of the camera  10  where the bright-spot  12  is detected by the imager  16 . The image  22  includes an object-image  24  and a bright-spot-image  26  and other features not shown that are in the field-of-view  14  of the camera  10 , as will be recognized by one skilled in the art of optics. The adverse result of the saturated imager  16  is an object-image  24  that appears to be much darker than the object  18 . The object  18  may be a street sign, a lane marking, or a pedestrian for example, that may become undetectable by the camera  10  due to the saturation of the imager  16 . The image  22  is shown inverted on the imager  16  as the rays of light pass through a single camera-lens  28  by way of a non-limiting example only. Multiple camera-lenses  28  of varying geometries may be used in the camera  10 , as will be recognized by one skilled in the art of optics. The imager  16  may be in electrical communication with a controller  30  to process the image  22  based on the application of the camera  10  as will be recognized by one skilled in the art of vision-systems. 
       FIG. 2  illustrates an example of the camera  10  from  FIG. 1  that is modified with a light-shield  32  to reduce the intensity of light-rays  34  from the bright-spot  12  in the field-of-view  14  of the camera  10 . The addition of the light-shield  32  is expected to reduce the light-to-dark contrast of sunlight compared to the surrounding objects  18 , from levels as high as 110 dB by as much as 46 dB. Removing the brightness of the sunlight improves the image-contrast of the remaining scene. This improvement in contrast has the benefit of improved object-detection and improved object-recognition and further allows the use of less expensive vision-systems whose dynamic range is typically limited to less than 70 dB. The light-shield  32  may be located between the camera-lens  28  and the bright-spot  12 , and may be in electrical communication with the controller  30  such that the light-shield  32  may be moved to a position in the line-of-sight  20  with the bright-spot  12  and the imager  16 . The light-shield  32  may be comprised of a transparent-film  35  that supports an absorber  36  ( FIG. 3 ) sized to block a portion or all of the light-rays  34  of the bright-spot  12  from reaching the imager  16 . In the non-limiting example illustrated in  FIG. 2 , the absorber  36  may be sized to match the resultant circular diameter of the Sun on the visual horizon, based on the distance of the light-shield  32  to the camera-lens  28  and the distance to the imager  16 . The absorber  36  may be filtered to block a visible-wavelength-camera that is sensitive to wavelengths in the range of four-hundred nanometers (400 nm) to 700 nm, or it may be filtered so that it blocks the near-infrared wavelengths from 700 nm to 1000 nm for use in a night-vision-camera, or it may be filtered so that it blocks both the visible and the near-infrared wavelengths from 400 nm to 1000 nm. Other geometries of the absorber  36  are contemplated and will be recognized by one skilled in the art. The opacity of the absorber  36  may be varied across its diameter and may aid the controller  30  in tracking the bright-spot  12 . The opacity may be varied as multiple concentric circles, where the center of the absorber  36  may the darkest, with each subsequent concentric circle being less opaque. Alternatively, the opacity may be a continuous gradient. When the bright-spot  12  is not detected by the imager  16  the controller  30  may position the absorber  36  at the limits of the field-of-view  14  to minimize the amount of image-data that is obscured. The light-shield  32  may include multiple transparent-films  35  supporting the absorber  36  that may be moved independently from one another to be positioned in the line-of-sight  20  of multiple bright-spots  12 . Alternatively a liquid crystal display (LCD), or similar dynamic shape adjustment devices, may be used in place of the transparent-film  35  and absorber  36  to reduce the intensity of the light-rays  34  from the bright-spot  12 . Non-limiting examples of multiple bright-spots  12  may be headlamps from approaching vehicles, and the Sun and reflected sunlight (e.g. glint). The position of the bright-spot  12  as detected by the imager  16  may be tracked by the controller  30  across the field-of-view  14 . The controller  30  may be configured to position the light-shield  32  using ultrasonic linear motors, servo-motors, and other known devices until the intensity of the light-rays  34  from the bright-spot  12  as detected by the imager  16  are minimized. The result is a reduced maximum light level transmitted onto the imager  16  which allows for improved object-detection and improved object-recognition. 
     The location of the light-shield  32  relative to the imager  16 , and the size of the absorber  36 , affects the reduction in light intensity of the incoming light-rays  34 .  FIG. 4  is a graph  37  of a simulation of the effect of the light intensity reduction based on the diameter of the absorber  36  and its distance from the camera-lens  28  ( FIG. 2 ). At a distance of thirty millimeters (30 mm) from the camera-lens  28  the absorber  36  with a 5 mm diameter creates a thirty-six decibel (36 dB) intensity reduction of sunlight. The 30 mm distance to the camera-lens  28  is thought to be a viable placement for the absorber  36  where a windshield-mounted vision-system is used, due to the proximity of the camera-lens  28  to the windshield of the vehicle. While this simulation was performed with a particular design of the camera-lens  28 , it would be apparent to one skilled in the art of optics that the output of the simulation will vary based on the design features of the camera-lens  28 . 
       FIG. 5  illustrates another example of the camera  10  from  FIG. 1  that is modified with a light-shield  32  and an aperture-stop  38  to reduce the intensity of the light-rays  34  from the bright-spot  12  in the field-of-view  14  of the camera  10 . The light-shield  32  may be located between the camera-lens  28  and the aperture-stop  38 , and may be in electrical communication with the controller  30  such that the light-shield  32  may be moved to a position in the line-of-sight  20  with the bright-spot  12  and the imager  16 . While  FIG. 5  shows the aperture-stop  38  between the camera-lens  28  and the imager  16 , it is contemplated that the advantages of the camera  10  described herein will also be realized for configurations of cameras  10  where the aperture-stop  38  is located between lens-elements in a multi-lens assembly. That is, the interpretation of the statement that ‘an aperture-stop is located between the imager and the camera-lens’ includes examples where the aperture-stop  38  is between lens-elements in a multi-lens assembly. Additionally, the aperture-stop  38  may be placed at any location within the multi-lens assembly based on the design of the multi-lens assembly. Advantageously, the light-shield  32  is positioned at the aperture-stop  38  of the camera-lens  28  to maximize the light-blocking efficiency, as will be recognized by one skilled in the art of optics. The light-shield  32  may be comprised of a transparent-film  35  that supports an absorber  36  sized to block a portion or all of the light-rays  34  of the bright-spot  12  from reaching the imager  16 . In the non-limiting example illustrated in  FIG. 5 , the absorber  36  may be located at the aperture-stop  38  and may be sized to match the resultant circular diameter of the Sun on the visual horizon, based on the position and size of the aperture-stop  38  and the distance to the imager  16 . The absorber  36  may be filtered to block a visible-wavelength-camera that is sensitive to wavelengths in the range of 400 nm to 700 nm, or it may be filtered so that it blocks the near-infrared wavelengths from 700 nm to 1000 nm for use in a night-vision-camera, or it may be filtered so that it blocks both the visible and the near-infrared wavelengths from 400 nm to 1000 nm. Other geometries of the absorber  36  are contemplated and will be recognized by one skilled in the art. The opacity of the absorber  36  may be varied across its diameter and may aid the controller  30  in tracking the bright-spot  12 . The opacity may be varied as multiple concentric circles, where the center of the absorber  36  may be the darkest, with each subsequent concentric circle being less opaque. Alternatively, the opacity may be a continuous gradient. When the bright-spot  12  is not detected by the imager  16  the controller  30  may position the absorber  36  at the limits of the field-of-view  14  to minimize the amount of image-data that is obscured. The light-shield  32  may include multiple transparent-films  35  supporting the absorber  36  that may be moved independently from one another to be positioned in the line-of-sight  20  of multiple bright-spots  12 . Alternatively a liquid crystal display (LCD), or similar dynamic shape adjustment devices, may be used in place of the transparent-film  35  and absorber  36  to reduce the intensity of the light-rays  34  from the bright-spot  12 . Non-limiting examples of multiple bright-spots  12  may include headlamps from approaching vehicles, and the Sun and reflected sunlight (e.g. glint). The position of the bright-spot  12  as detected by the imager  16  may be tracked by the controller  30  across the field-of-view  14 . The controller  30  may be configured to position the light-shield  32  using ultrasonic linear motors, servo-motors, and other known devices until the intensity of the light-rays  34  from the bright-spot  12  as detected by the imager  16  are minimized. The result is a reduced maximum light level transmitted onto the imager  16  which allows for improved object-detection and improved object-recognition. 
       FIG. 6  is a graph  40  of a simulation for the camera  10  of  FIG. 5  and quantifies the effect of the light intensity reduction based on the diameter of the absorber  36  located at the aperture-stop  38  of the camera-lens  28 . The absorber  36  with a 0.32 mm diameter creates a 46 dB intensity reduction of sunlight. 
       FIG. 7  illustrates another example of the camera  10  from  FIG. 1  that is modified with a light-shield  32  located in close proximity to the imager  16  to reduce the intensity of the light-rays  34  from the bright-spot  12  in the field-of-view  14  of the camera  10 . The light-shield  32  may be located between the camera-lens  28  and the imager  16 , and may be in electrical communication with the controller  30  such that the light-shield  32  may be moved to a position in the line-of-sight  20  with the bright-spot  12  and the imager  16 . The light-shield  32  may be comprised of a transparent-film  35  that supports an absorber  36  sized to block a portion or all of the light-rays  34  of the bright-spot  12  from reaching the imager  16 . In the non-limiting example illustrated in  FIG. 7 , the absorber  36  may be sized to match the resultant circular diameter of the Sun on the visual horizon, based on the distance of the light-shield  32  to the camera-lens  28  and the distance to the imager  16 . The absorber  36  may be filtered to block a visible-wavelength-camera that is sensitive to wavelengths in the range of 400 nm to 700 nm, or it may be filtered so that it blocks the near-infrared wavelengths from 700 nm to 1000 nm for use in a night-vision-camera, or it may be filtered so that it blocks both the visible and the near-infrared wavelengths from 400 nm to 1000 nm. Other geometries of the absorber  36  are contemplated and will be recognized by one skilled in the art. The opacity of the absorber  36  may be varied across its diameter and may aid the controller  30  in tracking the bright-spot  12 . The opacity may be varied as multiple concentric circles, where the center of the absorber  36  may be the darkest, with each subsequent concentric circle being less opaque. Alternatively, the opacity may be a continuous gradient. When the bright-spot  12  is not detected by the imager  16  the controller  30  may position the absorber  36  at the limits of the field-of-view  14  to minimize the amount of image-data that is obscured. The light-shield  32  may include multiple transparent-films  35  supporting the absorber  36  that may be moved independently from one another to be positioned in the line-of-sight  20  of multiple bright-spots  12 . Alternatively a liquid crystal display (LCD), or similar dynamic shape adjustment devices, may be used in place of the transparent-film  35  and absorber  36  to reduce the intensity of the light-rays  34  from the bright-spot  12 . Non-limiting examples of multiple bright-spots  12  may include headlamps from approaching vehicles, and the Sun and reflected sunlight (e.g. glint). The position of the bright-spot  12  as detected by the imager  16  may be tracked by the controller  30  across the field-of-view  14 . The controller  30  may be configured to position the light-shield  32  using ultrasonic linear motors, servo-motors, and other known devices until the intensity of the light-rays  34  from the bright-spot  12  as detected by the imager  16  are minimized. The result is a reduced maximum light level transmitted onto the imager  16  which allows for improved object-detection and improved object-recognition. 
       FIG. 8  is a graph  42  of a simulation for the camera  10  of  FIG. 7  and quantifies the effect of the light intensity reduction based on the diameter of the absorber  36  located a distance of 1 mm from the imager  16 . The absorber  36  with a 0.1 mm diameter creates a 30 dB intensity reduction of sunlight. 
     Contrast improvement for image-elements that are positioned next to the absorber-blocked-image section (e.g. approximately two to five times the absorber-blocked-image area) may be achieved using histogram equalization or other image-processing techniques known in the art. The image-area around the absorber-blocked-image may be post-processed to normalize the contrast for the scene-elements that may be affected by the bright-spot-image  26  the absorber-blocked-area. This may be advantageous due to the “haloing effect” that the bright-spot-image  26  imparts around the actual bright-spot-image-area. The contrast improvement image-processing may be combined with the absorber-opacity-shape to further reduce the dynamic range of brightness in the image  22 . 
     Accordingly, a camera system  10 , and a controller  30  for the camera system  10  is provided. The use of a light-shield  32  solves the problem of a saturated imager  16  causing an object-image  24  to appear much darker than the object  18 , and allows for improved object-detection and improved object-recognition. 
     While this invention has been described in terms of the preferred embodiments thereof, it is not intended to be so limited, but rather only to the extent set forth in the claims that follow.