Patent Publication Number: US-10311317-B2

Title: Teacher data generation method

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a technology of generating teacher data for image recognition. 
     Description of the Related Art 
     There has been proposed a method for recognizing two-dimensional rotated character by configuring a discriminator with a learning sample generated by performing three-dimensional rotation processing on a computer in advance (for example, refer to Non-Patent Literature 1: [Three-Dimensional Rotation Immutable Character Recognition] by Ryo Narita et al. ([Image Recognition⋅Understanding Symposium (MIRU2011)] July 2011) Information Processing Society of Japan Electronic Library (https://ipsj.ixsq.nii.ac.jp/ej/index.php?action=pages_main&amp;active_action=repository_action_common_download&amp;item_id=77644&amp;item_no=1&amp;attribute_id=1&amp;file_no=1&amp; page_id=13&amp;block_id=8). There has been also proposed a method for extracting an image of the same object by using SIFT (Scale-Invariant Feature Transform) which recognizes the object by using a luminance gradient of the image. More specifically, this is a method of matching the same object between an original image and an image which has been generated by three-dimensionally rotating the original image and projecting it on a two-dimensional plane (for example, refer to Non-Patent Literature 2: [Matching 3-D Transformed Images Using Scale-Invariant Feature Transform] by Okao (Kochi University of Technology, Thesis for Bachelor Degree (Mar. 1, 2013) (http://www.kochitech.ac.jp/library/ron/2012/2012info/ 1130317.pdf)). 
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     However, in order to extract an object from an image, in a case of generating teacher data for image recognition based on image data of the object captured from a large number of different viewpoints (for example, 7000 or more), it is concerned that the man-hour and the cost required for generating the teacher data would considerably increase. 
     Therefore, the object of the present invention is to provide a method for generating teacher data for image recognition while reducing the number of images used as the basis. 
     Means for Solving the Problem 
     The present invention is a method for generating teacher data for image recognition of an object, comprising: a step of obtaining a plurality of captured images by imaging the object by imaging device arranged at each of a plurality of first designated positions; a step of extracting a basic image region from each of the plurality of captured images; and a step of generating the teacher data as a result of coordinate transformation of the basic image region from one image coordinate system to each coordinate system of the plurality of captured images by the imaging device on an assumption that the imaging device is arranged at each of a plurality of second designated positions which are different from the plurality of first designated positions. 
     Effect of the Invention 
     According to the method of the present invention, it is able to generate sufficient number of teacher data necessary for image recognition while reducing the number of images used as the basis. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an explanatory diagram showing a producing method of teacher data as an embodiment of the present invention. 
         FIG. 2  is an explanatory diagram illustrating an imaging position of an imaging device C. 
         FIG. 3A  and  FIG. 3B  are explanatory diagrams in which  FIG. 3A  illustrates a method of changing a camera position, and  FIG. 3B  illustrates internal parameter setting of the camera. 
         FIG. 4A  and  FIG. 4B  are explanatory diagrams in which  FIG. 4A  illustrates images of an object actually captured from a plurality of different positions, and  FIG. 4B  illustrates estimation images of the object on an assumption that the object is captured from the plurality of different positions. 
         FIG. 5  is an explanatory diagram illustrating an evaluation result of a deviation between the actual captured images and the estimation images. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A method for generating teacher data for image recognition as an embodiment of the present invention will be described. 
     First, a first index i which expresses the number of captured images used as the basis is set to “1” ( FIG. 1 /STEP 11 ). The position P of an imaging device C is adjusted to a first designated position P i  ( FIG. 1 /STEP 12 ). The posture of the imaging device C is adjusted so that the optical axis thereof is directed to one point of an actual space polar coordinate system. 
     For example, as shown in  FIG. 2 , on a hemisphere face of a radius R, having the origin of the three-dimensional polar coordinate system as the center and having a pole above the center, in addition to the pole P 1 , four points P 2  to P 5  which are arranged at equal intervals in the longitude direction at a latitude expressed as θ i =θ(20°≤θ≤70°), are defined as the first designated positions. In this case, the first designated position P i  is expressed by coordinate values of the three-dimensional polar coordinate system (r i  sin θ i  cos φ i , r i  sin θ i  sin φ i , r i  cos θ i ). The position and the posture of the imaging device C is adjusted manually by the operator, and then fixed by an appropriate tool such as the platform or the like, or may be automatically adjusted by a driving device such as a robot arm. 
     Next, the Object is captured by the imaging device C at position P to obtain the captured image ( FIG. 1 /STEP 13 ). 
     A basic image region S i  is extracted from the captured image ( FIG. 1 /STEP 14 ). For example, a person (an operator) manipulates through an input interface while visually recognizing the captured image displayed through an output interface to extract a region recognized as being a substantially flat surface as the basic image region S i . The extraction of the basic image region S i  is performed only for a few numbers of arbitrary captured images. The distance r between the optical center of the imaging device and the basic image region S i  is measured by an appropriate range sensor. 
     It is determined whether or not the first index i is a first specified number N 1  or more ( FIG. 1 /STEP 15 ). The first specified number N 1  is, for example, set to “5”. If it is determined that the first index i is less than the first specified number N 1  ( FIG. 1 /STEP 15  . . . NO), the first index i is increased by “1” ( FIG. 1 /STEP 16 ). And then, the processes after the adjustment of the position and the posture of the imaging device C are repeated ( FIG. 1 /STEP 12  to STEP 15 ). Each of a plurality of imaging devices C can be arranged at each of the plurality of designated positions, and used. 
     If it is determined that the first index i is equal to or more than the first specified number N 1  ( FIG. 1 /STEP 15  . . . YES), a second index j expressing the number of generated estimation images, is set to “1” ( FIG. 1 /STEP 21 ). The position P of a virtual imaging device C is adjusted to a second designated position P j  which is different from the first designated position P i  ( FIG. 1 /STEP 22 ). For example, the second designated position P j  is also defined on a hemisphere face similar to the first designated position P i  (refer to  FIG. 2 ). 
     More specifically, in addition to the optical center P=e (three-dimensional vector) of the imaging device C as shown in  FIG. 3A , by using unit vector 1=(c−e)/|c−e| expressing the azimuth of the center of the image (basic image region S i ) with the optical center P of the image device C as the reference, unit vector u′=s×1 and unit vector s=1×u expressing the upper direction of the imaging device C after the optical center of the imaging device C is moved, the coordinate transformation matrix M 1  which changes the optical center position P of the imaging device C is defined by expression (1). 
     
       
         
           
             
               
                 
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     In addition to the lower limit value d n  and the upper limit value d f  of the depth of field of the imaging device C as shown in  FIG. 3B , by using the angle of view θ y  in the vertical direction, the aspect ratio a of the angle of view θ x  in the horizontal direction with respect to the angle of view θ y  in the vertical direction, and f=1/tan (θ y /2), the transformation matrix M 2  based on internal parameter of the imaging device C is defined by expression (2). 
     
       
         
           
             
               
                 
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     As a result of coordinate transformation of the basic image region S i  according to expression (3), S i ^ is generated as one of the teacher data ( FIG. 1 /STEP 23 ). 
     [Expression 3]
 
S i ^=M 2 M 1 S i   (3)
 
     It is determined whether or not the second index j is a second specified number N 2  or more ( FIG. 1 /STEP 24 ). The second specified number N 2  is set to a sufficient number necessary as the teacher data for image recognition, for example “7000”. If it is determined that the second index j is less than the second specified number N 2  ( FIG. 1 /STEP 24  . . . NO), the second index j is increased by “1” ( FIG. 1 /STEP 25 ). And then, the processes after the adjustment of the position and the posture of the imaging device C are repeated ( FIG. 1 /STEP 22  to STEP 24 ). Then, if the second index j is determined to be equal to or more than the second specified number N 2  ( FIG. 1 /STEP 24  . . . YES), the series of processing terminates. In addition to the basic image region obtained as above, the estimation image group as calculated above is accumulated in the database as the teacher data. 
     After that, the basic image region is extracted from the captured image obtained under an arbitrary environment, and the extraction result is collated with or used for pattern matching with the teacher data accumulated in the database, thereby recognizing that an object related to the teacher data exists in the actual space corresponding to the basic image region. 
     EXAMPLE 
     In a three-dimensional coordinate system having a surface center of an object having a substantially rectangular flat plate shape as the origin and its surface being a part of the x-y plane, the object was imaged by intermittently changing the latitude (or the elevation angle in the three-dimensional polar coordinate system) of the position of the imaging device C on the hemisphere face having a pole on the z axis, while keeping the longitude constant.  FIG. 4A  shows the actual captured images in such case in order from the left.  FIG. 4B  shows the estimation images according to the above method in the case it is assumed that the same object is imaged by changing the position of the imaging device C similarly from the left. 
       FIG. 5  shows by plotting the relation between an elevation angle θ expressing an actual (or virtual) position of the imaging device C and an angle in the image coordinate system of one corner angle of the substantially rectangular flat plate shaped object in each of the actual captured image and the estimation image. It is assumed to generate the estimation image in the range of 20°≤θ≤160°. As shown in  FIG. 5 , although there is a tendency that the deviation of the corner angles gradually becomes larger as θ becomes larger (as the position of the imaging device C comes closer to the x-y plane), the maximum relative deviation is 1.9%. Therefore, it is verified that the recognition accuracy of the object is improved by using the estimation image group as the teacher data. 
     EXPLANATION OF THE REFERENCE SIGNS 
     
         
         C . . . imaging device, P 1  to P 5  . . . first designated positions, S i  . . . basic image region