Patent Publication Number: US-2022237731-A1

Title: Apparatus and method for analyzing fisheye camera image

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims priority from Korean Patent Application No. 10-2021-0009699, filed on Jan. 22, 2021, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Field 
     The present invention relates to an image analysis technique, and more particularly, to a technique for analyzing a fisheye camera image that is severely distorted. 
     2. Description of Related Art 
     With artificial intelligence technology being developed, intelligent image analysis functions are being installed and utilized in actual products such as closed-circuit televisions (CCTVs) and the like. Among cameras used in CCTVs and the like, fisheye cameras that enable omnidirectional monitoring without blind spots are widely used. 
     Since images obtained by fisheye cameras are severely distorted, it is not possible to accurately recognize objects such as a person and the like using a general intelligent image analysis method. This is because an image captured by a fisheye camera is severely distorted, such as a straight line being bent into a curve or directions toward the ground and the ceiling becoming different directions in the image. Therefore, it is not easy to properly apply the general image analysis method. 
     In Korean Patent Registration No. 10-1937582 related to a safety system for walkway monitor, a system is proposed in which an image captured by a fisheye camera is segmented according to a photographing direction, distortion of the segmented images is corrected, and then objects included in the images whose distortion is corrected are identified. However, the safety system for walkway monitor may cause a problem in that an object located on a boundary between the segmented images is not recognized or is incorrectly recognized. 
     SUMMARY 
     This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
     The present invention is directed to providing an apparatus capable of analyzing a fisheye camera image, which is severely distorted, by performing pre-processing and post-processing without significantly changing a general image analyzer for analyzing camera images. 
     In one general aspect, an image analysis apparatus for analyzing a camera image is an apparatus for analyzing a fisheye camera image and includes a pre-processing unit, an image analysis unit, and a post-processing unit. 
     The pre-processing unit may segment an input fisheye camera image into segmented images with a preset size field of view and superimpose the segmented images so that some regions overlap. Further, the pre-processing unit may perform dewarping on each of the segmented images, then combine the segmented images on which the dewarping is performed using a preset combination method, and generate an analysis image 
     The image analysis unit may receive the analysis image and detect an object. 
     The post-processing unit may remove a result recognized as a duplicate from a detection result of the object of the image analysis unit. 
     The post-processing unit may determine a duplicate object on the basis of coordinates of a region of the object in the fisheye lens camera image and remove the result recognized as the duplicate from the detection result of the object or the post-processing unit may compare the images of the detected object to determine similarity of the images of the object and remove the result recognized as the duplicate. 
     The image analysis apparatus for analyzing a camera image may further include a user interface unit configured to receive a size of a field of view to be segmented and a method of combining segmented images from a user and set the size and the method. 
     Further, the user interface unit may set a region of interest (ROI) in the fisheye lens camera image according to a user&#39;s input. In this case, the pre-processing unit may segment the input image with the preset size field of view so that boundary portions of the ROI overlap. 
     Other features and aspects will be apparent from the following detailed description, the accompanying drawings, and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of an image analysis apparatus for analyzing a camera image of the present invention. 
         FIG. 2  illustrates an example of an image captured by a fisheye camera which will be analyzed by the image analysis apparatus for analyzing a camera image. 
         FIG. 3  illustrates an example of an object located on a boundary of a segmented image where an error in recognition of the object may occur. 
         FIG. 4  illustrates an example of an analysis image generated by the image analysis apparatus for analyzing a camera image of the present invention from the image of  FIG. 2 . 
         FIG. 5  is flowchart of a method of analyzing an image according to an embodiment of the present invention. 
         FIG. 6  is flowchart of a method of analyzing an image by setting a region of interest (ROI) according to another embodiment of the present invention. 
     
    
    
     Throughout the accompanying drawings and the detailed description, unless otherwise described, the same drawing reference numerals will be understood to refer to the same elements, features, and structures. The relative size and depiction of these elements may be exaggerated for clarity, illustration, and convenience. 
     DETAILED DESCRIPTION 
     The following description is provided to assist the reader in gaining a comprehensive understanding of the methods, apparatuses, and/or systems described herein. Accordingly, various changes, modifications, and equivalents of the methods, apparatuses, and/or systems described herein will be suggested to those of ordinary skill in the art. Also, descriptions of well-known functions and constructions may be omitted for increased clarity and conciseness. 
     The above-described aspects and additional aspects are embodied through embodiments described with reference to the accompanying drawings. It will be understood that components of each of the embodiments may be combined in various ways within one embodiment unless otherwise stated or there is a contradiction between them. In some cases, each block in a block diagram may represent a physical part, and in other cases, each block in the block diagram may be a logical representation of a portion of a function of one physical part or may be a logical representation of a function across a plurality of physical parts. In some cases, a block or an entity of a portion of a block may be a set of program instructions. All or some of the blocks may be implemented in hardware, software, or a combination thereof. 
       FIG. 1  is a block diagram of an image analysis apparatus for analyzing a camera image of the present invention. An image analysis apparatus  10  for analyzing a camera image according to an aspect of the present invention is an apparatus for analyzing an image captured by a fisheye camera  20  and includes a pre-processing unit  11 , an image analysis unit  13 , and a post-processing unit  15 . 
     The image analysis apparatus  10  is configured as a kind of computing device having a processor and a memory and may be used in an image surveillance system for monitoring people or objects in a specific region. The image analysis apparatus  10  for analyzing a camera image analyzes images captured by a camera installed in an indoor place or the like. In this case, since the image analysis apparatus  10  analyzes images within a visual range that the camera can acquire, the image analysis apparatus  10  uses a single camera with a relatively wide-angle lens or a plurality of cameras to recognize an object such as a person or the like. 
     The image analysis apparatus  10  may use a plurality of cameras in order to monitor a wide range, but in this case, the burden of monitoring at one time is increased, and thus the image analysis apparatus  10  may use a single camera with a wide angle of view. The fisheye camera  20  is a camera capable of photographing from a front to a side or rear thereof through a fisheye lens, which is a kind of wide-angle lens having an angle of view of 180 degrees to 360 degrees. Therefore, the image of a wide range may be analyzed using a single fisheye camera  20  instead of a plurality of cameras.  FIG. 2  illustrates an example of an image captured by a fisheye camera which will be analyzed by the image analysis apparatus  10  for analyzing a camera image. In the example illustrated in  FIG. 2 , the image captured by the fisheye camera is a 360-degree image around the camera. However, unlike general cameras, the fisheye camera provides images with different degrees of distortion according to a distance from the camera. 
     In general, the fisheye camera image may be analyzed after distortion of the image is corrected and flattened. Before the distortion of the fisheye camera image is corrected, the fisheye camera image is segmented into images with an appropriate field of view (FoV) and dewarping is performed on each of the segmented images of the fisheye camera image. However, in the process of segmenting the image, when there is an object disposed on a boundary between the segmented images, the corresponding object may not be recognized.  FIG. 3  illustrates an example of an object located on a boundary of the segmented image where an error in recognition of the object may occur. 
     In order to prevent the object disposed on the boundary between the segmented images from not being recognized or from being recognized incorrectly, the pre-processing unit  11  segments the input fisheye camera image into the images with an FoV of a preset size and superimposed the images so that some regions of the input fisheye camera image overlap. That is, the pre-processing unit  11  may form the segmented images by segmenting the fisheye camera image into the images with the FoV so that some regions overlap, and even when the object is located on the boundary of one segmented image and a portion of the object is cut off, the pre-processing unit  11  may allow the object to be completely displayed in another segmented image. 
     Further, the pre-processing unit  11  performs dewarping on each of the segmented images with the preset size FoV. In the performance of dewarping on the fisheye camera image, three-dimensional coordinates of the image are set, a distance from the center of the camera projected on these coordinates for each direction in which the image is formed is set using a function of a positive angle, and the image is decomposed so that a flattened image is derived. In this case, the projection is divided into an equidistant projection, an equisolid angle projection, a stereographic projection, and the like according to the method in which the center of the camera is projected. A dewarping algorithm of the fisheye camera is a well-known technology, and thus a detailed description thereof will be omitted. 
     Since the image analysis apparatus  10  of the present invention uses a general image analyzer with minimum changes, the image analysis apparatus  10  makes a single image and then analyzes the image instead of individually analyzing the segmented images on which the dewarping is performed. Therefore, the pre-processing unit  11  generates an analysis image by combining the images on which the dewarping is performed using a preset combination method. The analysis image is an image input to the image analyzer to recognize an object.  FIG. 4  illustrates an example of the analysis image generated by the image analysis apparatus for analyzing a camera image of the present invention from the image of  FIG. 2 . In the example of  FIG. 4 , the image captured by the fisheye camera is segmented into images with six fields of view, and after the image is segmented so that some regions overlap, the dewarping is performed on each segmented image and the segmented images are combined into a 3×2 image to generate one image. In the example of  FIG. 4 , it can be seen that some regions of each segmented image on which the dewarping is performed overlap. The 3×2 combination image is one example, and as another example, the camera image is segmented into images with eight fields of view and an analysis image may be generated as a 4×2 combination image. 
     The image analysis unit  13  receives the analysis image and detects objects included in the images. The image analysis unit  13  uses a conventional image analyzer in general use without significantly changing the image analyzer. Therefore, an image analysis algorithm used by the image analysis unit  13  may be a deep learning algorithm. As an example, the image analysis algorithm may include a FAST object search algorithm, such as You Only Look Once (YOLO), Single Shot MultiBox Detector (SSD), or the like. The image analysis unit  13  may display a range of an object generally recognized as a bounding box. 
     As illustrated in  FIG. 4 , some objects marked with bounding boxes may appear as duplicates in the segmented images and the corresponding objects may be recognized as duplicates by the image analysis unit  13 . In order to solve the problem of recognizing duplicate objects that is caused by segmenting the fisheye camera image so that some regions overlap, the post-processing unit  15  removes a result recognized as a duplicate from a detection result of the object of the image analysis unit  13 . 
     According to an aspect of the present invention, the post-processing unit  15  may determine a duplicate object on the basis of coordinates of a region of the object in the fisheye lens camera image and remove the result recognized as the duplicate from the detection result of the object. That is, the post-processing unit  15  may process the object in which large portions overlap on the coordinates of the fisheye camera image with respect to the same type of object as one object. Therefore, the coordinates of the bounding box indicating the object recognized by the image analysis unit  13  may be included as coordinates of the fisheye camera image. According to an aspect of the present invention, the coordinates of the segmented image of the bounding box may be converted into the coordinates of the fisheye camera image and whether the object is duplicated may be determined based on the converted coordinates. 
     According to an aspect of the present invention, the post-processing unit  15  may compare the images of the detected object to determine similarity of the images of the object and remove the result recognized as the duplicate. The post-processing unit  15  may determine the similarity of the images of the object using a data re-identification algorithm. 
     According to an additional aspect of the present invention, the image analysis apparatus  10  for analyzing a camera image may further include a user interface unit  17  which receives a size of an FoV to be segmented and a method of combining segmented images from a user and sets the size and method. The fisheye camera image may be segmented according to the preset size of the FoV or may be segmented according to the size of the FoV that is input by the user through the user interface unit  17 . However, even when the image is segmented according to the size of the FoV that is input by the user, the image is segmented so that some regions overlap. Further, the user may set a combination method in which an analysis image is generated by combining the segmented images, through a user interface. 
     The user may set a region of interest (ROI) in the fisheye camera image through the user interface unit  17 . In this case, the pre-processing unit  11  segments the fisheye camera image with the FoV of the set size so that boundary portions of the ROI overlap. Further, the user may set one or more ROIs. 
       FIG. 5  is flowchart of a method of analyzing an image according to an embodiment of the present invention. The method of analyzing an image according to the embodiment of the present invention in which a fisheye camera image is analyzed includes an image segmentation operation, a dewarping operation, an image combination operation, an image analysis operation, and a post-processing operation. 
     Each operation of the method of analyzing an image consists of a set of computer instructions in which at least some of its functions are performed in a kind of computing device having a processor and a memory. 
     The fisheye camera image is the distorted image as in the form of the example of  FIG. 2 . It is difficult to analyze the image without correcting and flattening the image, and in general, the image is segmented with an appropriate FoV before the dewarping is performed on the fisheye camera image, and the dewarping is performed on each of the segmented fisheye camera images. 
     Unlike the method of analyzing a fisheye camera image as illustrated in  FIG. 3 , in order to prevent a recognition error of the object disposed on the boundary between the segmented images in the image segmentation process, the image segmentation operation includes segmenting, by the image analysis apparatus  10 , the image with an FoV of a preset size and superimposing the segmented images so that some regions overlap (S 1000 ). That is, in the image segmentation operation, the image analysis apparatus  10  may form the segmented images by segmenting the image with the FoV so that some regions overlap, and even when the object is located on the boundary of one segmented image and a portion of the object is cut off, the image analysis apparatus  10  may allow the object to be completely displayed in another segmented image. 
     The dewarping operation includes performing, by the image analysis apparatus  10 , dewarping on each of the segmented images with the preset size FoV (S 1020 ). A dewarping algorithm used in this case is a well-known technique, and thus a detailed description thereof will be omitted. 
     The image combination operation includes generating, by the image analysis apparatus  10 , an analysis image by combining the images on which the dewarping is performed using a preset combination method (S 1040 ). Since the image analysis apparatus  10  of the present invention uses a general image analyzer with minimum changes, the image analysis apparatus  10  makes a single image and then analyzes the image instead of individually analyzing the segmented images on which the dewarping is performed.  FIG. 4  illustrates an example of the analysis image generated by the image analysis apparatus  10  for analyzing a camera image of the present invention from the image of  FIG. 2 , in which the image captured by the fisheye camera is segmented into images with six fields of view, and after the image is segmented so that some regions overlap, the dewarping is performed on each segmented image and the segmented images are combined into a 3×2 image to generate one image. In the method of combining the image, a size of an FoV to be segmented and a method of combining segmented images may be received from the user through a user interface and set. 
     The image analysis operation includes receiving, by the image analysis apparatus  10 , the analysis image and detecting objects included in the images (S 1060 ). A conventional image analyzer in general use is used as an image analysis function used in the image analysis operation without significantly changing the image analyzer. Therefore, an image analysis algorithm that is used by the image analysis operation may be a deep learning algorithm. As an example, the image analysis algorithm may include a FAST object search algorithm, such as YOLO, SSD, or the like. In the image analysis operation, a range of an object generally recognized as a bounding box may be displayed. 
     In order to solve the problem that some objects marked with bounding boxes appear as duplicates in the segmented image as illustrated in  FIG. 4 , the post-processing operation includes removing, by the image analysis apparatus  10 , a result recognized as a duplicate from the detection result of the object in the image analysis operation (S 1080 ). 
     According to an aspect of the present invention, the post-processing operation includes determining a duplicate object on the basis of coordinates of the region of the object in the fisheye lens camera image in the detection result of the object and removing the result recognized as the duplicate. Therefore, the coordinates of the bounding box indicating the object recognized in the image analysis operation may be included as coordinates of the fisheye camera image. According to an aspect of the present invention, the coordinates of the segmented image of the bounding box may be converted into the coordinates of the fisheye camera image and whether the object is duplicated may be determined based on the converted coordinates. 
     According to an aspect of the present invention, the post-processing operation includes comparing the images of the detected object to determine similarity of the images of the object and removing the result recognized as the duplicate. In the post-processing operation, the similarity of the images of the object may be determined using a data re-identification algorithm. 
       FIG. 6  is flowchart of a method of analyzing an image by setting an ROI according to another embodiment of the present invention. A procedure illustrated in  FIG. 6  is a procedure in which an ROI setting operation is added to the procedure illustrated in  FIG. 5 . According to another embodiment of the present invention, the method of analyzing an image includes an ROI setting operation S 2000 , an image segmentation operation S 2020 , a dewarping operation S 2040 , an image combination operation S 2060 , an image analysis operation S 2080 , and a post-processing operation S 2100 . 
     The dewarping operation, the image combination operation, the image analysis operation, and the post-processing operation are the same as those in the procedure illustrated in  FIG. 5 , and thus descriptions thereof will be omitted. 
     The ROI setting operation includes setting an ROI in the fisheye camera image according to a user&#39;s input through a user interface (S 2000 ). 
     In this case, in the image segmentation operation, the fisheye camera image is segmented with an FoV of a set size so that boundary portions of the ROI overlap (S 2020 ). Further, the user may set one or more ROIs. 
     According to the image analysis apparatus for analyzing a camera image of the present invention, a fisheye camera image that is severely distorted can be analyzed by performing pre-processing and post-processing without significantly changing a general image analyzer for analyzing camera images. 
     While the present invention has been described with reference to the embodiments and accompanying drawings, the present invention is not limited thereto. It should be understood that various modifications from the embodiments may be apparent to those skilled in the art. Appended claims are intended to include such modifications.