Patent Publication Number: US-7715644-B2

Title: Image calibration method, image calibration processing device, and image calibration processing terminal

Description:
TECHNICAL FIELD 
   The present invention relates to an image calibration method of performing a camera calibration on an image photographed by a general camera to correct distortions due to the lens in the image photographed by the camera, and in particular to an image calibration method which does not impose precise calibration calculations on the side of a camera user. 
   The present invention also relates to an image calibration processing device capable of performing such precise calibration calculations as to allow, for example, stereo viewing. The present invention further relates to an image calibration processing terminal capable of transmitting an image photographed by a camera or photographing information on the camera to an image calibration processing device, and displaying a corrected subject image on which a calibration calculation has been performed. 
   BACKGROUND ART 
   Conventionally, when a plurality of single photographs are photographed and a panorama photograph is formed therefrom, it is necessary to correct the photographs to be combined so as to remove image distortions. Also, when an image photographed two-dimensionally is used to measure dimensions of an object, it is necessary to correct the photographed image so as to remove image distortions. 
   When a three-dimensional shape of a measuring object is measured based on two images photographed, measurement points on the measuring object are found based on the principle of a stereo method. In order to perform a three-dimensional measurement, a calibration of a camera, namely interior localizations (amount of lens distortions, focal length, and principal point position) of the camera, needs to be performed beforehand. Since the three-dimensional shape of the measuring object is found using the parallax between the images photographed by the camera, the distortions due to the camera lens used in the photographing need to be corrected very precisely. 
   [Patent Document 1] 
   JP-A-Hei09-329418 (Paragraphs 0006 and 0020, and FIG. 4 and FIG. 5) 
   [Patent Document 2] 
   JP-A-Hei11-351865 (Paragraphs 0002 and 0004, and FIG. 1 and FIG. 3) 
   DISCLOSURE OF THE INVENTION 
   Problem to be Solved by the Invention 
   However, performing a calibration of a camera as described above requires three-dimensional targets distributed over a wide range and measured accurately, an analysis software program, know-how for photographing, and the like. Therefore, the calibration work would be too complicated work for construction site or archaeological excavation site workers, clothing store clerks, or the like, for example. A calibration object suitable for calibration of a camera was disclosed by the present applicant in Patent Document 1 mentioned above. Even when such a calibration object is used, a software program for calibration needs to be purchased and the know-how on the photographing object, photographing method, and analysis is required. Therefore, formation of a panorama photograph by combining a plurality of single photographs, measurement of dimensions of an object using an image photographed two-dimensionally, or three-dimensional measurement based on the principle of a stereo method would evoke a great resistance to construction site or archaeological excavation site workers, clothing store clerks, or the like who are unskilled in those works. 
   The present invention has been made in view of the foregoing problems, and has a first object of providing an image calibration method that allows acquisition of a corrected subject image in which distortions due to the camera lens are corrected, even for those unskilled in three-dimensional measurement based on the principle of a stereo method, precise two-dimensional measurement, and precise image formation, such as construction site or archaeological excavation site workers, clothing store clerks, or the like. 
   A second object of the present invention is to provide an image calibration processing device that allows acquisition of a corrected subject image in which distortions due to the camera lens are corrected to such a degree as to allow three-dimensional measurement, precise two-dimensional measurement, and precise image formation in a concise manner. A third object of the present invention is to provide an image calibration processing terminal that allows access to an image calibration processing device and acquisition of a corrected subject image in which distortions due to the camera lens are corrected in a concise manner. 
   Means for Solving the Problem 
   In order to achieve the first object, an image calibration method according to the present invention comprises, as shown for example in  FIG. 1  and  FIG. 2 , the steps of: receiving, at an image calibration processing device  10 , a calibration request from a user terminal  20  (S 10 ); receiving, at the image calibration processing device  10 , a calibration object image photographed in accordance with an instruction for calibration photographing (S 16 ); performing a calibration process using the received calibration object image (S 26 ); receiving, at the image calibration processing device  10 , a subject image transmitted from the user terminal  20  and photographed by a camera  2  used to photograph the calibration object image (S 30 ); performing a calibration on the subject image in accordance with results of the calibration process to form a corrected subject image (S 32 ); and returning the formed corrected subject image from the image calibration processing device  10  to the user terminal  20 . 
   According to an image calibration method including steps as described above, the image calibration processing device  10  receives a calibration object image photographed by the camera  2  as an object of calibration, performs a calibration process on the calibration object image received, and calculates the results of the calibration process necessary for correction of the lens distortions or the like. Then, the image calibration processing device  10  receives a subject image photographed by the camera  2 , performs a calibration on the subject image in accordance with the results of the calibration process, and forms a corrected subject image. The corrected subject image is returned from the image calibration processing device  10  to the user terminal  20 . In this manner, the user terminal  20  needs only to transmit a calibration object image photographed by the camera  2 , and then a subject image photographed by the camera  2 , to the image calibration processing device  10  in accordance with an instruction for calibration photographing. Meanwhile, the image calibration processing device  10  bears the burden of complicated calculation processing for a corrected subject image, thereby reducing the calculation load for the user terminal  20 . Since the user terminal  20  is used at a work site or a travel destination, a light calculation load will reduce the power consumption and stabilize the workability of the user terminal  20 . 
   Preferably, in the image calibration method as described above, as shown for example in  FIG. 18  and  FIG. 19 , the calibration object image and the subject image are a common image in which a calibration object  4  and a subject  6  are photographed at a time, and the method further comprises the step of performing a three-dimensional measurement on the subject using the corrected subject image. Then, a three-dimensional image measurement on the subject can be performed. Thus, the image calibration processing device  10  can provide a three-dimensional image measurement to users who require it, as an additional service to the calibration process. 
   In order to achieve the first object, an image calibration method according to the present invention comprises, as shown for example in  FIG. 14  and  FIG. 15 , the steps of: receiving, at an image calibration processing device  30 , a calibration request from a user terminal  40  (S 100 ); receiving, at the image calibration processing device  30 , a calibration object image photographed in accordance with an instruction for calibration photographing (S 106 ); performing a calibration process using the received calibration object image (S 116 ); and transmitting results of the calibration process calculated in the calibration process from the image calibration processing device  30 . And, the user terminal  40  performs a calibration on a subject image photographed by a camera used to photograph the calibration object image (S 120 ), using the results of the calibration process transmitted from the image calibration processing device  30 , to form a corrected subject image (S 122 ). 
   According to an image calibration method including steps as described above, the image calibration processing device  30  receives a calibration object image photographed by the camera  2  as an object of calibration, performs a calibration process on the calibration object image received, and calculates the results of the calibration process necessary for correction of the lens distortions or the like. The calculated results are returned to the user terminal  40 . Meanwhile, the user terminal  40  performs a calibration on a subject image photographed by the camera  2  using the results of the calibration process transmitted from the image calibration processing device  30 , and forms a corrected subject image. Then, the user terminal  40  can obtain a corrected subject image from the subject image photographed by the camera  2 , using the results of the calibration process obtained from the image calibration processing device  30 . At this time, since the user terminal  40  bears the burden of calculation processing for a corrected subject image, a corrected subject image can be reliably obtained even in cases where a communication line between the user terminal  40  and the image calibration processing device  30  has a narrow bandwidth or is not stable. 
   Preferably, in the image calibration method as described above, as shown for example in  FIG. 20  and  FIG. 21 , the calibration object image and the subject image are a common image in which a calibration object  4  and a subject  6  are photographed at a time, and the user terminal  40  is configured further to perform a three-dimensional measurement on the subject using the corrected subject image (S 234 ). 
   Preferably, in the image calibration method as described above, the method further includes the step of transmitting the instruction for calibration photographing from the image calibration processing device ( 10 ,  30 ) to the user terminal ( 20 ,  40 ) (S 12 , S 102 ). There may be cases where an instruction for calibration photographing is not carried to a site or a travel destination by mistake. In such cases, an instruction can be downloaded to the user terminal ( 20 ,  40 ) by making an access to the image calibration processing device ( 10 ,  30 ). Preferably, the instruction includes an image showing a photographing state. Such an image will facilitate understanding of photographing work for a calibration object image, for an operator who photographs a calibration object image by the camera  2  as an object of calibration. 
   Preferably, the image calibration method as described above includes the step of: receiving at the image calibration processing device ( 10 ,  30 ) at least a focal length in the photographing and a model of the camera, or a focal length in the photographing and a size of an imaging device used in the photographing, together with the calibration object image transmitted from the user terminal ( 20 ,  40 ) (S 16 , S 106 ). The focal length in the photographing and the model of camera, or the focal length in the photographing and the size of an imaging device used in the photographing, are useful information for calibration processing. 
   Preferably, the image calibration method as described above includes the step of: reading, at the image calibration processing device ( 10 ,  30 ), data necessary for the calibration process from photographing information affixed to the calibration object image transmitted from the user terminal ( 20 ,  40 ) (S 16 , S 106 ). The read data is used for the calibration process. 
   Preferably, in the image calibration method as described above, the results of the calibration process includes at least one of a principal point position, distortion data, and a focal length of a lens used in the photographing, of the camera involved in the photographing of the calibration object image. Then, parameters necessary for calculation processing for a corrected subject image can be obtained. 
   Preferably, the image calibration method as described above includes the step of: accumulating the calculated results of the calibration process in a calibration database ( 19 ,  39 ) when the image calibration processing device ( 10 ,  30 ) performs the calibration process using the received calibration object image. The results of the calibration process accumulated may be utilized, for example, in CRM (Customer Relation Management) or the like. 
   In order to achieve the first object, an image calibration method according to the present invention is, as shown for example in  FIG. 12  and  FIG. 13 , used with an image calibration processing device  10  including a calibration database  19  in which results of a calibration process are accumulated according to a model of a camera. That is, the method comprises the steps of: receiving, at the image calibration processing device  10 , a calibration request from a user terminal  20 , together with a model of a camera  2  used to photograph the subject image (S 10 , S 11   b ); retrieving, from the calibration database  19 , results of the calibration process corresponding to the received model of the camera; performing a calibration on the calibration object image using the retrieved results of the calibration process to form a corrected subject image (S 32 ); and returning the formed corrected subject image from the image calibration processing device  10  to the user terminal  20 . 
   According to an image calibration method including steps as described above, the results of the calibration process are accumulated beforehand in the calibration database  19  according to the model of the camera  2  as an object of calibration. Since the image calibration processing device  10  receives a calibration request from the user terminal  20 , together with the model of the camera  2  used to photograph the subject image, results of the calibration process accumulated in the calibration database  19  and corresponding to the model of the camera  2  can be read. In cases where the model of the camera  2  and the results of the calibration process correspond to each other within a certain tolerable range, the results of the calibration process accumulated in the calibration database  19  and corresponding to the model of the camera  2  can be used and the calibration object image photographed in accordance with an instruction for calibration photographing does not need to be used. Thus, the user terminal  20  does not need to transmit the calibration object image photographed by the camera  2  to the image calibration processing device  10 , and the image calibration processing device  10  does not need to calculate the results of the calibration process necessary for correction of the lens distortions or the like, thereby allowing the work to go smoothly. 
   In order to achieve the first object, an image calibration method according to the present invention is, as shown for example in  FIG. 16  and  FIG. 17 , used with an image calibration processing device  30  including a calibration database  39  in which results of a calibration process are accumulated according to a model of a camera. That is, the method comprises the steps of: receiving, at the image calibration processing device  30 , a calibration request from a user terminal  40 , together with a model of a camera  2  used to photograph a subject image (S 100 , S 101   b ); retrieving, from the calibration database  39 , results of the calibration process corresponding to the received model of the camera (S 101   c ); and transmitting the retrieved results of the calibration process from the image calibration processing device  30  (S 118 ). And, the user terminal  40  performs a calibration on the subject image using the results of the calibration process transmitted from the image calibration processing device  30 , to form a corrected subject image (S 122 ). 
   According to an image calibration method including steps as described above, the results of the calibration process are accumulated beforehand in the calibration database  39  according to the model of the camera  2  as an object of calibration. Thus, in cases where the model of the camera  2  and the results of the calibration process correspond to each other within a certain tolerable range, the results of the calibration process accumulated in the calibration database  39  and corresponding to the model of the camera  2  can be used and the calibration object image photographed in accordance with an instruction for calibration photographing does not need to be used. Also, the user terminal  40  can obtain a corrected subject image from the subject image photographed by the camera  2 , using the results of the calibration process obtained from the image calibration processing device  30 . At this time, since the user terminal  40  bears the burden of calculation processing for a corrected subject image, a corrected subject image can be reliably obtained even in cases where a communication line between the user terminal  40  and the image calibration processing device  30  has a narrow bandwidth or is not stable. 
   In the image calibration method above, preferably the calculated results of the calibration process are accumulated in the calibration database ( 19 ,  39 ), together with the model of camera, when a calibration process is performed using the calibration object image received from the user terminal ( 20 ,  40 ). 
   In order to achieve the first object, an image calibration method according to the present invention comprises, as shown for example in  FIG. 1  and  FIG. 2 , the steps of: transmitting a calibration request to an image calibration processing device  10  from a user terminal  20  (S 10 ); transmitting a calibration object image photographed by a predetermined camera  2  in accordance with an instruction for calibration photographing from the user terminal  20  to the image calibration processing device  10  (S 16 ); transmitting a subject image photographed by the camera  2  used to photograph the calibration object image to the image calibration processing device  10  (S 30 ); and receiving, at the user terminal, a corrected subject image transmitted from the image calibration processing device  10  and formed by performing a calibration on the subject image in accordance with results of a calibration process obtained using the transmitted calibration object image (S 34 ). 
   In order to achieve the first object, an image calibration method according to the present invention, as shown for example in  FIG. 14  and  FIG. 15 , comprises the steps of: transmitting a calibration request to an image calibration processing device  30  from a user terminal  40  (S 100 ); transmitting a calibration object image photographed by a predetermined camera  2  in accordance with an instruction for calibration photographing from the user terminal  40  to the image calibration processing device  30  (S 106 ); receiving at the user terminal  40  results of a calibration process calculated by the image calibration processing device  30  (S 118 ); and performing a calibration on a subject image photographed by the camera  2  used to photograph the calibration object image using the received results of the calibration process, to form a corrected subject image (S 122 ). 
   In order to achieve the second object, an image calibration processing device  10  according to the present invention, comprises, as shown for example in  FIG. 1 , a receiving section for user terminal  11  for receiving a use request for image calibration transmitted from a user terminal  20 , a calibration object image photographed in accordance with an instruction for calibration photographing, and a subject image photographed by a camera used to photograph the calibration object image; a calibration processing section  14  for performing a calibration process using the calibration object image received by the receiving section for user terminal  11 ; a corrected subject image forming section  15  for performing a calibration on the subject image in accordance with results of the calibration process to form a corrected subject image; and a transmission section for user terminal  16  for returning the corrected subject image formed by the corrected subject image forming section  15  to the user terminal  20 . 
   Preferably, the image calibration processing device  10  according to the present invention further comprises: a display section  16   a  for displaying the corrected subject image formed by the corrected subject image forming section  15 . Preferably, in the image calibration processing device  10 , as shown for example in  FIG. 18 , the calibration object image and the subject image are a common image in which a calibration object and a subject are photographed at a time, and the device comprises a three-dimensional measurement section  15   a  for performing a three-dimensional measurement on the subject using the corrected subject image. 
   In order to achieve the second object, an image calibration processing device  30  according to the present invention comprises, as shown for example in  FIG. 14 , a receiving section for user terminal  31  for receiving a use request for image calibration transmitted from a user terminal  40  and a calibration object image photographed in accordance with an instruction for calibration photographing; a calibration processing section for performing a predetermined calibration process on the calibration object image received by the receiving section for user terminal  31 ; and a transmission section for user terminal  36  for returning results of the calibration process calculated by the calibration processing section  34  to the user terminal  40 . And, the user terminal  40  performs a calibration on a subject image photographed by a camera used to photograph the calibration object image using the results of the calibration process transmitted from the transmission section for user terminal  36 , to form a corrected subject image. 
   Preferably, in the image calibration processing device  30  according to the present invention, as shown for example in  FIG. 20 , the calibration object image and the subject image are a common image in which a calibration object  4  and a subject  6  are photographed at a time, and the user terminal  40  is configured to further include a three-dimensional measurement section  47  performing a three-dimensional measurement on the subject using the corrected subject image. 
   Preferably, the image calibration processing device ( 10 ,  30 ) according to the present invention further comprises: an instruction retrieving section ( 13 ,  33 ) for retrieving the instruction suitable for the use request for image calibration received by the receiving section for user terminal ( 11 ,  31 ), and the transmission section for user terminal ( 16 ,  36 ) is configured to return the instruction retrieved by the instruction retrieving section ( 13 ,  33 ) to the user terminal ( 20 ,  40 ). Preferably, the instruction described above further includes an image showing a photographing state. Such an image will facilitate understanding for a person in charge of photographing a calibration object image and a subject image. 
   Preferably, in the image calibration processing device ( 1 . 0 ,  30 ) according to the present invention, the receiving section for user terminal ( 11 ,  31 ) is configured to receive at least a focal length in the photographing and a model of the camera, or a focal length in the photographing and a size of an imaging device used in the photographing, together with the calibration object image or the subject image transmitted from the user terminal ( 20 ,  40 ). The focal length in the photographing and the model of the camera, or the focal length in the photographing and the size of an imaging device used in the photographing, are useful information for calibration processing. 
   Preferably, the image calibration processing device ( 10 ,  30 ) according to the present invention includes an information reading section ( 14   b ,  34   b ) for reading data necessary for the calibration process from photographing information affixed to the calibration object image transmitted from the user terminal ( 20 ,  40 ). The data read by the information reading section is used for the calibration process by the calibration processing section ( 14 ,  34 ). Preferably, in the image calibration processing device ( 10 ,  30 ) according to the present invention, the calibration processing section ( 14 ,  34 ) is configured to calculate results of the calibration process including at least one of a principal point position, distortion data, and a focal length of a lens used in the photographing, of the camera involved in the photographing of the subject image. 
   In order to achieve the second object, an image calibration processing device  10  according to the present invention comprises, as shown for example in  FIG. 12 , a receiving section for user terminal  11  for receiving a calibration request and a subject image from a user terminal  20 , together with a model of a camera  2  used to photograph the subject image; a calibration database  19  in which results of a calibration process are accumulated according to a model of a camera  2 ; a calibration process results retrieving section  14   a  for retrieving, from the calibration database  19 , results of the calibration process corresponding to the received model of the camera; a corrected subject image forming section  15  for performing a calibration on the subject image transmitted from the user terminal  20  using the retrieved results of the calibration process, to form a corrected subject image; and a transmission section for user terminal  16  for returning the formed corrected subject image to the user terminal  20 . 
   In order to achieve the second object, an image calibration processing device  30  comprises, as shown for example in  FIG. 16 , a receiving section for user terminal  31  for receiving a calibration request from a user terminal  40 , together with a model of a camera  2  used to photograph a subject image; a calibration database  39  in which results of a calibration process are accumulated according to a model of a camera; a calibration process results retrieving section  34   a  for retrieving, from the calibration database  39 , results of the calibration process corresponding to the received model of the camera; and a transmission section for user terminal  36  for transmitting the retrieved results of the calibration process to the user terminal  40 . And, the user terminal  40  is configured to perform a calibration on the subject image using the results of the calibration process transmitted from the transmission section for user terminal  36 , to form a corrected subject image. 
   In order to achieve the third object, an image calibration processing terminal  20  comprises, as shown for example in  FIG. 1 , a transmission section for processing device  21  for transmitting a use request for image calibration, a calibration object image photographed in accordance with an instruction for calibration photographing, and a subject image photographed by a camera  2  used to photograph the calibration object image, to an image calibration processing device  10 ; a receiving section for processing device  24  for receiving a corrected subject image transmitted from the image calibration processing device  10  and formed by performing a calibration on the subject image; and a display section  25  for displaying the corrected subject image received by the receiving section for processing device  24 . 
   In order to achieve the third object, an image calibration processing terminal comprises, as shown for example in  FIG. 14 , a transmission section for processing device  41  for transmitting a use request for image calibration, and a calibration object image photographed in accordance with an instruction for calibration photographing, to an image calibration processing device  30 ; a receiving section for processing device  44  for receiving results of a calibration process transmitted from the image calibration processing device  30 ; and a corrected subject image forming section  46  for performing a calibration on a subject image photographed by a camera  2  used to photograph the calibration object image using the results of the calibration process received by the receiving section for processing device  44 , to form a corrected subject image. 
   EFFECT OF THE INVENTION 
   According to an image calibration method of the present invention, an image calibration processing device, located away from a user terminal, performs a calibration process on a camera, by performing the steps of receiving a calibration object image photographed in accordance with an instruction for calibration photographing with an image calibration processing device, and performing a calibration process using the calibration object image received. Since a calibration is performed on a subject image photographed by the camera used to photograph the calibration object image in accordance with the results of the calibration process, to form a corrected subject image, a corrected subject image in which influences of the lens aberrations of the camera are compensated can be easily obtained. 
   Also, an image calibration method of the present invention includes the steps of transmitting information on the model of a camera used to photograph a subject image from a user terminal to an image calibration processing device having a calibration database in which the results of a calibration process are stored according to the model of camera, and retrieving results of the calibration process corresponding to the model of the camera received from the calibration database. Therefore, if the results of the calibration process retrieved can be applied to a subject image from the camera, a user of the camera can easily obtain a corrected subject image without the need to photograph a calibration object image in accordance with an instruction for calibration photographing. 
   The basic Japanese Patent Application No. 2002-272858 filed on Sep. 19, 2002 is hereby incorporated in its entirety by reference into the present application. 
   The present invention will become more fully understood from the detailed description given hereinbelow. The other applicable fields will become apparent with reference to the detailed description given hereinbelow. However, the detailed description and the specific embodiment are illustrated of desired embodiments of the present invention and are described only for the purpose of explanation. Various changes and modifications will be apparent to those ordinary skilled in the art on the basis of the detailed description. 
   The applicant has no intention to give to public any disclosed embodiments. Among the disclosed changes and modifications, those which may not fall within the scope of the present claims constitute, therefore, a part of the present invention in the sense of doctrine of equivalents. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a general block diagram illustrating the structure of a first embodiment of the present invention. 
       FIG. 2  is a flowchart for illustrating a method of the first embodiment of the present invention. 
       FIG. 3  is a plan view showing an example of a two-dimensional chart. 
       FIG. 4  is a view illustrating an example of the results of a calibration process. 
       FIG. 5  is a view illustrating an example of the results of the calibration process performed on a zoom lens. 
       FIG. 6  is a flowchart showing the details of instructions used to photograph a calibration object image. 
       FIG. 7  illustrates an example of an item entry sheet. 
       FIG. 8  is a perspective view illustrating an arrangement of a camera when measuring the lens aberrations at various focal lengths of the camera. 
       FIG. 9  illustrates a procedure for photographing the two-dimensional chart by means of the camera, where (A 1 ), (A 2 ), (A 3 ), and (A 4 ) show an image from the camera, and (B 1 ), (B 2 ), (B 3 ), and (B 4 ) show positional relation between the two-dimensional chart and the camera  2  corresponding to the image from the camera. 
       FIG. 10  is a diagram showing camera intervals when measuring the lens aberrations at a focal length equivalent to a standard lens or a telephoto lens. 
       FIG. 11  is a flowchart illustrating an example of a procedure for photographing a calibration object image in accordance with the instructions. 
       FIG. 12  is a general block diagram illustrating the structure of a second embodiment of the present invention. 
       FIG. 13  is a flowchart for illustrating a method of the second embodiment of the present invention. 
       FIG. 14  is a general block diagram illustrating the structure of a third embodiment of the present invention. 
       FIG. 15  is a flowchart for illustrating a method of the third embodiment of the present invention. 
       FIG. 16  is a general block diagram illustrating the structure of a fourth embodiment of the present invention. 
       FIG. 17  is a flowchart for illustrating a method of the fourth embodiment of the present invention. 
       FIG. 18  is a general block diagram illustrating the structure of a fifth embodiment of the present invention. 
       FIG. 19  is a flowchart for illustrating a method of the fifth embodiment of the present invention. 
       FIG. 20  is a general block diagram illustrating the structure of a sixth embodiment of the present invention. 
       FIG. 21  is a flowchart for illustrating a method of the sixth embodiment of the present invention. 
   

   BEST MODE FOR CARRYING OUT THE INVENTION 
   First Embodiment 
   The present invention is described below with reference to the drawings.  FIG. 1  is a general block diagram illustrating the structure of a first embodiment of the present invention. As shown in the figure, an image calibration processing system of the present invention includes a camera  2 , a calibration object  4 , a subject  6 , a communication line  8 , an image calibration processing device  10 , and a plurality of user terminals  20 . The camera  2  is an optical instrument with relatively large lens aberrations such as, for example, a general-purpose single-lens reflex camera or digital camera, compared to cameras for high-precision measurement purposes. The calibration object  4  is a chart used to perform a calibration to compensate the lens aberrations, and may be a three-dimensional chart or a two-dimensional chart. A three-dimensional chart has reference points, of which respective two-dimensional positions and heights have been precisely found. A two-dimensional chart will be described in detail later. The subject  6  is an object to be photographed by the camera  2 , and may be a subject for a panoramic photograph (for example a landscape) or a subject for two-dimensional or three-dimensional measurement (for example a work piece, a geographical feature, or the like). The communication line  8  may be a public line or a dedicated line, either wired or wireless, which allows data communication. 
   The image calibration processing device  10  includes a receiving section for user terminal  11 , a user authentication section  12 , an instruction retrieving section  13 , a calibration processing section  14 , an information reading section  14   b , a corrected subject image forming section  15 , a transmission section for user terminal  16 , a display section  16   a , a user database  17 , an instruction database  18 , and a calibration database  19 . An instrument with a high calculation capacity such as, for example, a server or a workstation may be used as the image calibration processing device  10 . 
   The receiving section for user terminal  11  receives, via the communication line  8 , a use request for image calibration, a calibration object image photographed in accordance with an instruction for calibration photographing, and a subject image of the subject  6  photographed by the camera  2  transmitted from a user terminal  20 . The calibration object image and the subject image are basically images in which the calibration object  4  or the subject  6 , respectively, is individually photographed by the common camera  2 . The use request for image calibration may conveniently include photographing condition information useful for calibration processing, such as a model or focal length of the camera, and/or the like. The photographing condition information may be transmitted as independent data, or included as supplementary information in the calibration object image or the subject image. For example, a basic format adopted for digital cameras called “Exif” includes, at the beginning of the format, photographing condition information such as a photographing instrument, date, aperture, shutter speed, and the like used in the photographing. 
   The user authentication section  12  is used by an operator of the image calibration processing device  10  to certify a user of the user terminal  20  as having a proper title for use. The user authentication section  12  uses, for example, an address and name of the user, a number of a telephone line utilized as the communication line  8 , an authentication key distributed by the image calibration processing device  10 , and/or the like. The user database  17  has registered therein users of the user terminals  20  with a proper title for use. The user database  17  stores a registration date, a valid period of membership registration, and a number of times of use in cases where a membership system is adopted, or an accounting status in cases where a pay system is adopted. When the user authentication section  12  has certified a user of the user terminal  20  as having a proper title for use, the use request for image calibration received by the receiving section for user terminal  11  can then be dealt with. 
   The instruction retrieving section  13  retrieves, from the instruction database  18 , an instruction for calibration photographing suitable for the use request for image calibration received by the receiving section for user terminal  11 . When an instruction for calibration photographing is already available to the user of the user terminal  20 , the instruction retrieving section  13  may not retrieve one. The instruction database  18  stores instructions for calibration photographing according to the model of the camera  2  and/or the type of the calibration object  4 . The models of the camera  2  may include, for example, a zoom lens, a wide-angle lens, a telephoto lens, a panoramic lens, a standard lens, and/or the like. The types of the calibration object  4  may include, for example, a two-dimensional chart, a three-dimensional chart, and/or the like. 
   The calibration processing section  14  performs a calibration process using the calibration object image received by the receiving section for user terminal  11 . The calibration process is performed to find various parameters used to compensate the camera aberrations, and will be described in detail later. The information reading section  14   b  reads data necessary for the calibration process from the photographing information affixed to the calibration object image transmitted from the user terminal  20 . The information reading section  14   b  reads, for example, the photographing information included in the basic format for digital cameras “Exif.” The calibration database  19  has accumulated therein results of the calibration process according to the model or the lens focal length of the camera  2 . 
   The corrected subject image forming section  15  performs a calibration on the subject image received by the receiving section for user terminal  11  in accordance with the calibration process, to form a corrected subject image. The transmission section for user terminal  16  transmits, via the communication line  8 , the instruction retrieved by the instruction retrieving section  13  and the corrected subject image formed by the corrected subject image forming section  15  to the user terminal  20 . The display section  16   a  may be a CRT or liquid crystal display screen. The display section  16   a  displays the corrected subject image formed by the corrected subject image forming section  15 , the results of the calibration process by the calibration processing section  14 , the calibration object image and the subject image received by the receiving section for user terminal  11 , and/or the like. 
   The image calibration processing terminal  20  of the present invention includes a transmission section for processing device  21 , a key entry section  22 , a receiving section for processing device  24 , and a display section  25 . A personal computer, a personal digital assistant, or a mobile phone terminal with a built-in camera, for example, may be used as the image calibration processing terminal  20 . The transmission section for processing device  21  and the receiving section for processing device  24  may be provided with a modem for connection to the communication line  8 . The transmission section for processing device  21  transmits, via the communication line  8 , a use request for image calibration, a calibration object image photographed in accordance with an instruction for calibration photographing, and a subject image photographed by the camera  2  used to photograph the calibration object image, to the image calibration processing device  10 . The use request for image calibration may be transmitted together with authentication information indicating that the user has a proper title for use, and/or the photographing condition information. 
   The key entry section  22  is used when the user inputs alphanumeric, kana, and other operating commands, and may be formed with, for example, a keyboard, a touch panel utilizing the display section  25 , a push button, and/or the like. The receiving section for processing device  24  receives the corrected subject image formed by performing a calibration on the subject image and transmitted from the image calibration processing device  10 . The receiving section for processing device  24  also receives, via the communication line  8 , an instruction for calibration photographing, when necessary. The display section  25  displays the instruction for calibration photographing and the corrected subject image received by the receiving section for processing device  24 . The display section  25  may display a calibration object image or a subject image. 
   The operation of an apparatus constituted as described above will be described.  FIG. 2  is a flowchart for illustrating a method of the first embodiment of the present invention. A user terminal  20  transmits a calibration request (service request) for the camera  2  to the image calibration processing device  10  via the communication line  8  (S 10 ). In response to the calibration request, the image calibration processing device  10  authenticates whether or not a user of the user terminal  20  has a proper title for use. When the user of the user terminal  20  is certified as having a proper title for use as a result of authentication, the image calibration processing device  10  returns an instruction for calibration photographing according to the model of the camera  2  to the user terminal  20  (S 12 ). The instruction for calibration photographing may be accompanied by, for example, a two-dimensional chart as the calibration object  4 . In cases where the user terminal  20  has a three-dimensional chart as the calibration object  4 , the three-dimensional chart may be used, instead of the two-dimensional chart transmitted, as the calibration object  4 . 
   On the user terminal  20  side, the calibration object  4  is photographed by the camera  2  in accordance with the instruction for calibration photographing (S 14 ). The calibration object image photographed is transmitted from the user terminal  20  to the image calibration processing device  10  via the communication line  8 , together with the photographing data (S 16 ). The image calibration processing device  10  makes a determination on the photographing quality of the calibration object image transmitted, for example, as to whether or not the image is unsuitable for the calibration process because the image is out of focus or the calibration object  4  image is too small (S 18 ). If the calibration object image is determined to be unsuitable, rephotographing of the calibration object  4  by the camera  2  is requested (S 20 ). At this time, it should be advantageous to give a comment suggesting to what should be paid attention in order to obtain a calibration object image suitable for the calibration process. In response to the request for rephotographing, the user photographs the calibration object  4  by the camera  2  (S 22 ), while paying attention to what is suggested in the comment. The calibration object image photographed is transmitted from the user terminal  20  to the image calibration processing device  10  via the communication line  8 , together with the photographing data (S 24 ), and a determination is made on the photographing quality of the calibration object image in S 18 . 
   If the photographing quality of the calibration object image is suitable, the calibration processing section  14  performs a calibration process using the calibration object image received (S 26 ). The results of the calibration process are accumulated in the calibration database  19 , together with the model of the camera. On the user terminal  20  side, the subject  6  is photographed by the camera  2  used to photograph the calibration object image (S 28 ). The user terminal  20  transmits the subject image to the image calibration processing device  10  via the communication line  8  (S 30 ). The image calibration processing device  10  performs a calibration on the subject image received, in accordance with the results of the calibration process obtained in S 26 , to form a corrected subject image (S 32 ). The corrected subject image formed is returned from the image calibration processing device  10  to the user terminal  20  (S 34 ). 
   The image calibration processing device  10  may make a determination on the photographing quality of the subject image transmitted at this time. For example, a determination may be made as to whether or not the image is unsuitable for the correction process because the image is out of focus or the subject  6  image is too small. If the subject image is determined to be unsuitable, rephotographing of the subject  6  by the camera  2  is requested. In cases of a pay service, a process necessary for accounting is performed as use information is accumulated in the user database  17 . 
   The two-dimensional chart as the calibration object  4  is described. Here, the two-dimensional chart is exemplified by a sheet of paper or plastic on which predetermined marks are printed. However, the two-dimensional chart can be a flat screen on which an image with predetermined marks are arranged.  FIG. 3  is a plan view showing an example of the two-dimensional chart. The two-dimensional chart is shaped as a flat sheet. Viewable first marks and second marks constituted of a plurality of dots are printed on the front side of the two-dimensional chart. The first marks are used in the calibration process, and also used to determine the photographing angle at which the camera  2  photographs the two-dimensional chart. The first marks are provided at least three locations on the two-dimensional chart, and preferably provided respectively in the four quadrants equally dividing the two-dimensional chart. The second marks, which may also be referred to as targets, are used to designate the position of the image data on the two-dimensional chart photographed by the camera  2 . Preferably, the second marks are distributed with a uniform density all over the two-dimensional chart. The second marks are provided preferably at 30 locations or more, and more preferably at about 100-200 locations, on the two-dimensional chart. 
   In this example, the two-dimensional chart has a total of five first marks arranged thereon, which have a diamond external shape and a mark at its center used commonly as the second mark. The first marks  1   a ,  1   b ,  1   c , and  1   d  are respectively provided in the four quadrants dividing the two-dimensional chart. The first mark  1   a  is located in the upper left quadrant,  1   b  in the upper right quadrant,  1   c  in the lower left quadrant, and  1   d  in the lower right quadrant. The first mark  1   e  is provided at the origin common to all the quadrants. For example, the first marks  1   a ,  1   b ,  1   c , and  1   d  are positioned at an equal distance d from the first mark  1   e . Here, an assumption is made that the two-dimensional chart is rectangular, the vertical interval between the first mark  1   a ,  1   b  and the first mark  1   e  is h, and the horizontal interval between the first mark  1   c ,  1   d  and the first mark  1   e  is l. On this assumption, the distance d between the first mark  1   a ,  1   b ,  1   c ,  1   d  and the first mark  1   e  satisfies the following relation:
 
 d =( h   2   +l   2 ) 1/2   (1)
 
   The first marks and the second marks should beforehand be printed so as to conform to desired dimensions, or subjected to a measurement of dimensions. The positions of the first marks and the second marks may conveniently be stored in the calibration database  19  beforehand, to allow them to be printed on a sheet so as to conform to the stored coordinates. 
     FIG. 4  is a view illustrating an example of the results of the calibration process. The display section  16   a  may display, for example, a focal length, a principal point position, and distortion parameters as calibration elements. As for the distortion indicating the lens aberrations, a curve before correction  142 , a curve after correction  144 , and an ideally corrected curve  146  may be displayed in graphical form for easy understanding. 
     FIG. 5  shows an example of the results of the calibration process performed on a zoom lens, where (A) shows a coefficient k1, (B) a coefficient k2, (C) an x-axis deviation coefficient x0 for an x-axis deviation between the camera principal point and the image center in an image coordinate system x, and (D) a y-axis deviation coefficient y0 for a y-axis deviation between the camera principal point and the image center in an image coordinate system y. Here, the focal length of the zoom camera  2  is assumed to be adjustable from 7.2 mm to 50.8 mm. With the number of measurement points for focal length data being six, 7.2 mm and 52.2 mm are respectively used as the most wide-angle and most telephoto measurement points, and 8.7 mm, 11.6 mm, 24.8 mm, and 39.0 mm are selected as intermediate measurement points uniformly distanced in terms of optics. The coefficients k1 and k2 will be used in the equation (4) for a bundle adjusting method with self-calibration described later, and take maximum values on the most wide-angle side and smaller values on the most telephoto side. 
     FIG. 6  is a flowchart showing the outline of the instructions used to photograph a calibration object image, illustrating the details at the calibration request (service request) stage. The image calibration processing device  10  transmits an item entry sheet to the user terminal  20  (S 50 ). The item entry sheet includes items necessary for the calibration process, such as whether a two-dimensional chart or an existing three-dimensional chart is used as a photographing target as the calibration object  4 . 
   The user terminal  20  prints or displays the item entry sheet transmitted (S 52 ), to allow entry or addition of the necessary items such as the camera  2 , calibration object  4 , subject  6 , and photographing conditions. Upon request from the user terminal  20 , a two-dimensional chart as the calibration object  4  is transmitted (S 54 ). The user terminal  20  prints or displays the two-dimensional chart as the calibration  4  transmitted (S 56 ). The user terminal  20  returns the item entry sheet after entering or adding the photographing conditions and/or the like to the image calibration processing device  10 , to signal the completion of preparation for photographing (S 58 ). At this time, on the user terminal  20  side, the printed two-dimensional chart should be affixed on a wall, or the display section  25  of the user terminal  20  should be placed in an appropriate position to display the two-dimensional chart transmitted. Depending on the camera angle as a photographing condition or the desired correction precision, the two-dimensional chart transmitted in S 56  may not be satisfactory in terms of precision. In such a case, only a two-dimensional chart precisely printed or a three-dimensional chart precisely fabricated could attain the precision required for the corrected subject image, and therefore another two-dimensional chart or three-dimensional chart necessary has to be waited for to be mailed or transmitted. 
   The image calibration processing device  10  transmits an instruction for calibration photographing corresponding to the model of the camera  2  to the user terminal  20  (S 60 ). The instruction may be transmitted as a batch file, or transmitted sequentially in real time as the photographing progresses like “streaming”. On the user terminal  20  side an image of the calibration object  4  is photographed by the camera  2 , in accordance with the instruction for calibration photographing (S 62 ). When the photographing of the calibration object has been completed, the user terminal  20  transmits a photographing completion signal to the image calibration processing device  10  (S 64 ). The image calibration processing device  10  prepares for the reception of the calibration object image, and then transmits an image transmission request signal to the user terminal  20  (S 66 ). 
     FIG. 7  illustrates an example of the item entry sheet, showing a sheet screen to be transmitted online. The item entry sheet screen is provided with a default camera parameters configuration screen, a correction model configuration screen, and an other camera parameters confirmation screen. The default camera parameters configuration screen is provided with entry sections for a focal length default value, and an imaging device sizes and image resolutions. 
   A description is made of a procedure for photographing the two-dimensional chart by means of the camera  2 , as an instruction for calibration photographing.  FIG. 8  is a perspective view illustrating an arrangement of a camera when measuring the lens aberrations at various focal lengths of the camera. Performing a calibration may be possible when two or more images of the two-dimensional chart photographed from different directions are available. In cases where a two-dimensional chart printed on a sheet is used, preferably the two-dimensional chart is photographed from three or more directions. In this manner, even for wide-angle lenses with a short focal length, measurement values for the respective calibration elements, in particular for the focal length, can be stable and reliable. 
     FIG. 8  shows a procedure where the photographing is performed from five directions, namely the very front (I), the upper left (II), the upper right (III), the lower left (IV), and the lower right (V). With the depth precision at the actual photographing site set at about 1 cm, the photographing incident angle between the optical axis of the camera  2  and the two-dimensional chart is preferably in the range of 10 degrees-30 degrees, and more preferably in the range of 12 degrees-20 degrees, considering the in-focus distance associated with the focal depth of the lens being limited. Typically, the photographing incident angle between the optical axis of the camera  2  and the two-dimensional chart may conveniently be 15 degrees. The various focal lengths typically refer to focal lengths equivalent to a standard lens, a wide-angle lens, and a telephoto lens used for a single-lens reflex camera. 
   With reference to  FIG. 9 , a description is made of a procedure for photographing the two-dimensional chart by means of the camera. In  FIG. 9 , (A 1 ), (A 2 ), (A 3 ), and (A 4 ) show an image from the camera, and (B 1 ), (B 2 ), (B 3 ), and (B 4 ) show positional relation between the two-dimensional chart and the camera  2  corresponding to the image from the camera. The numbers (I)-(V) correspond to the camera positions shown in  FIG. 8 . 
   (I): The two-dimensional chart is photographed from the very front such that all the first marks and the second marks on the two-dimensional chart are distributed all over but still included in the resulting image ( FIG. 9  (A 1 ) and (B 1 )). By allowing the first marks and the second marks to be distributed all over the photographed image to corners thereof, distortion correction can be securely performed to peripheral portions of the lens. The photographing distance H varies depending on the focal length of the camera.
 
(II): Then, in cases where the focal length of the zoom camera is equivalent to a telephoto lens or a standard lens, the camera is moved to a position about one third of the photographing distance H away from the very front camera position. That is, the camera position is changed such that the first mark  1   a  in the upper left quadrant, for example, comes to the photographing center ( FIG. 9  (A 2 ) and (B 2 )). However, in cases where the focal length of the zoom camera is equivalent to a wide-angle lens and the photographing distance H is about 1 m or less, the camera  2  can simply be moved such that the target first mark comes to the very front of the camera  2 . While keeping the camera  2  in the same position, the camera  2  is directed such that the central first mark  1   e  comes to the center of the resulting image ( FIG. 9  (A 3 ) and (B 3 )). The camera  2  is then moved closer to the two-dimensional chart such that the first marks and the second marks are distributed all over the image photographed by the camera  2  ( FIG. 9  (A 4 ) and (B 4 )).
 
(III): The camera position is changed such that the first mark  1   b  in the upper right quadrant comes to the photographing center. While keeping the camera in the same position, the camera is directed such that the central first mark  1   e  comes to the center of the resulting image, to perform photographing with the first marks and the second marks distributed all over the resulting image.
 
(IV): The camera position is changed such that the first mark  1   c  in the lower left quadrant comes to the photographing center. While keeping the camera in the same position, the camera is directed such that the central first mark  1   e  comes to the center of the resulting image, to perform photographing with the first marks and the second marks distributed all over the resulting image.
 
(V): The camera position is changed such that the first mark  1   d  in the lower right quadrant comes to the photographing center. While keeping the camera in the same position, the camera is directed such that the central first mark  1   e  comes to the center of the resulting image, to perform photographing with the first marks and the second marks distributed all over the resulting image.
 
   By following the procedure as described above, the angle of the camera  2  can be secured as the difference between necessary photographing angles and therefore the focal length can be securely measured. 
   The distance H between the camera  2  and the two-dimensional chart can be determined from the focal length f of the zoom camera. For example, in cases where the focal distance of the zoom camera is equivalent to a 35 mm standard lens, the photographing distance H is about 90 cm. Since the interval d between the first marks provided on the two-dimensional chart is, for example, 20 cm, an angle of about 10 degrees can be secured as the photographing angle, when the photographing direction is tilted from the very front (I) to the upper left (II) or the like. 
   An upper limit of the tilt angle of the photographing direction is determined according to the focal depth or the like. In other words, when the tilt angle of the photographing direction is large, the distances between the camera  2  and the respective first marks differ greatly, resulting in blurred images of the first marks in the resulting image. Therefore, the upper limit of the tilt angle of the photographing direction is set, for example, to 30 degrees. The actual photographing procedure is as described above in (I)-(V). Photographing such that the first marks and the second marks are distributed all over the camera screen naturally satisfies the conditions above, and hence satisfies the conditions of the photographing distance and position. 
     FIG. 10  is a diagram showing camera intervals when measuring the lens aberrations at a focal length equivalent to a standard lens or a telephoto lens. In cases where the focal length is equivalent to a standard lens or a telephoto lens, the narrow field angle of the photographing lens does not allow a large difference in the photographing angle. Therefore, an angle of 10 degrees cannot be secured as the photographing angle, when the photographing direction is tilted from the very front (I) to the upper left (II) or the like. In other words, this is because the interval d between the first marks is only about 20 cm while the photographing distance H between the camera  2  and the two-dimensional chart is 1 m or more, in cases of a long focal length. To deal with this, using the very front camera position as the center, the left camera positions (II) and (IV) and the right camera positions (III) and (V) can be determined. At this time, the camera is positioned about one third of the photographing distance H away from the very front (I) position to the left or the right, to allow photographing from the upper left (II) and the lower left (IV), and the upper right (III) and the lower right (V) as described above. The optical axis of the camera may conform to the direction of a line normal to the two-dimensional chart, or may be directed toward the two-dimensional chart. 
   In the instruction for calibration photographing described above, five photographing positions, namely the very front (I), the upper left (II), the upper right (III), the lower left (IV), and the lower right (V), are used. However, the number of photographing positions may be two, namely left and right, at minimum, or may be three or more. In cases of the two, left and right, directions, the two-dimensional chart is photographed such that an angle of about 10 degrees can be secured as the photographing angle. 
   Instructions for calibration photographing are described using a flowchart.  FIG. 11  is a flowchart illustrating an example of a procedure for photographing a calibration object image in accordance with the instructions. The figure shows a case where the image calibration processing device  10  and the user terminal  20  transmit and receive the instructions in an interactive manner to photograph a calibration object image. However, the photographing procedures may all be transmitted to a client side at a time in a batch manner, to allow the client to perform photographing while referring to the instructions as appropriate on a computer. Here, a description will be made of a case where the two-dimensional chart is photographed from five directions, namely the very front (I), the upper left (II), the upper right (III), the lower left (IV), and the lower right (V), as shown in  FIG. 8 . 
   With respect to the very front (I) direction, a photographing method  1  is transmitted from the image calibration processing device  10  to the user terminal  20  (S 70 ). The photographing method  1  allows photographing in a state shown, for example, in  FIG. 9  (A 1 ) and (B 1 ). Preferably, the user terminal  20  displays a simple message indicating the photographing procedure, saying, for example, “Set the camera  2  so that the central first mark  1   e  comes to the center and the entire two-dimensional chart fills the screen, and then photograph.” The user terminal  20  may also display the diagrams of  FIG. 9  (A 1 ) and (B 1 ), simultaneously with the message or sequentially upon request from the client. To display the first mark  1   e  as a photographing target on the display section  25 , a switching operation is made to display a photographing target image, to allow photographing. Since photographing will be performed with the two-dimensional chart filling much of the screen, the photographing distance H can naturally be determined according to the field angle of the camera  2 . 
   The first mark  1   e  on the two-dimensional chart is photographed using the camera  2  (S 72 ). At this time, an operator photographs the calibration object  4  while checking if an image similar to that displayed according to the instruction is seen through a finder (monitor). The image calibration processing device  10  is notified of the completion of photographing the first mark  1   e  (S 74 ). If the instructions have been downloaded in a batch manner beforehand, a sequential communication at the completion of photographing the first mark  1   e  is not necessary. If the camera is connected to a computer or if the transmission of a photographed image is not a trouble, the photographed image may be transmitted in S 74 . Immediate transmission of a calibration object image that has just been photographed will facilitate evaluation of the calibration object image and rephotographing of the calibration object in case of a low photographing quality. 
   Photographing procedures for the four points on the two-dimensional chart in the respective quadrants, namely the first marks  1   a ,  1   b ,  1   c , and  1   d , are sequentially displayed, to allow photographing of such points while checking, as follows. To photograph the first mark  1   a , a procedure  1  of a photographing method  2  is transmitted (S 76 ). For example,  FIG. 9  (A 2 ) and (B 2 ), and a message are transmitted, which says, “Now, let&#39;s move on to photographing the first mark  1   a . First of all, move the camera so that the center of the camera comes to the position of the first mark  1   a , while keeping the photographing distance. The moving distance should be about one third of the photographing distance.” In response, the user changes the photographing arrangement of the calibration object  4  and the camera  2  to an arrangement as shown in  FIG. 9  (B 2 ), and checks if an image seen through the finder is similar to that according to the message (S 78 ). A completion signal of the procedure  1  is transmitted from the user terminal  20  to the image calibration processing device  10  (S 80 ). 
   A procedure  2  is transmitted from the image calibration processing device  10  (S 82 ). As for  FIG. 9  (A 3 ) and (B 3 ), a message is transmitted, which says, “Then, direct the camera so that the first mark  1   e  in the center position comes to the center, while keeping the camera in the same photographing position.” In response, the user changes the photographing arrangement of the calibration object  4  and the camera  2  to an arrangement as shown in  FIG. 9  (B 3 ), and checks if an image seen through the finder is similar to that according to the message (S 84 ). A procedure  2  completion signal is transmitted from the user terminal  20  to the image calibration processing device  10  (S 86 ). 
   A procedure  3  is transmitted from the image calibration processing device  10  (S 88 ). As for  FIG. 9  (A 4 ) and (B 4 ), a message is transmitted, which says, “Finally, move the camera forward so that the targets are filled in the entire screen, while keeping the first mark  1   e  at the center. And press the shutter button.” In response, the user changes the photographing arrangement of the calibration object  4  and the camera  2  to an arrangement as shown in  FIG. 9  (B 4 ), and checks if an image seen through the finder is similar to that according to the message (S 90 ). A photographing completion signal for the first mark  1   e  is transmitted from the user terminal  20  to the image calibration processing device  10  (S 92 ). The resulting image may be transmitted in S 92 , in which case the image can be evaluated to allow retransmitting of a photographing method. In such a case, procedures similar to those in S 18 , S 20 , S 22 , and S 24  of  FIG. 2  are taken. 
   The other three first marks  1   b ,  1   c , and  1   d  on the two-dimensional chart are respectively subjected to procedures  1 - 3  of photographing methods  3 - 5 , which are similar to the procedures  1 - 3  of the photographing method  2  for the first mark  1   a , in procedures similar to those in S 76 -S 92  of  FIG. 11 . 
   Second Embodiment 
     FIG. 12  is a general block diagram illustrating the structure of a second embodiment of the present invention. In  FIG. 12 , components having the same functions as those in  FIG. 1  described above are given the same reference numerals and symbols, and descriptions of such components will not be repeated. The image calibration processing device  10  includes a calibration process results retrieving section  14   a , in addition to the calibration processing section  14  and the calibration database  19 . The calibration process results retrieving section  14   a  retrieves, from the calibration database  19 , results of the calibration process corresponding to the model of the camera received, utilizing the results of the calibration process accumulated in the calibration database  19  according to the camera model data. In cases where normal values are required in terms of precision for the corrected subject image, the results of the calibration process accumulated in the calibration database  19  can be utilized to substitute for the calibration process performed by the calibration processing section  14  on the specific camera  2 . 
   The operation of an apparatus constituted as described above will be described.  FIG. 13  is a flowchart for illustrating a method of the second embodiment of the present invention. A user terminal  20  transmits a calibration request (service request) for the camera  2  to the image calibration processing device  10  via the communication line  8  (S 10 ). When the user of the user terminal  20  is certified as having a proper title for use as a result of authentication, the image calibration processing device  10  requests model data on the camera  2  (S 11   a ). The user terminal  20  side acquires the model data on the camera  2 , by allowing entry using the key entry section  22 , using an identification function for the camera  2  provided in the user terminal  20 , or the like, to transmit the acquired model data to the image calibration processing device  10  via the communication line  8  (S 11   b ). The calibration process results retrieving section  14   a  searches the results of the calibration process stored in the calibration database  19 , to retrieve the corresponding model data on the camera (S 11   c ). 
   If the calibration process results retrieving section  14   a  has been able to retrieve the corresponding model data on the camera, the process proceeds to S 28 . At this time, it may be advantageous to consider variations in the results of the calibration process for the model data on the camera retrieved from the calibration database  19 . For example, in cases where a high precision is required in the corrected subject image, the process may be configured to proceed to S 28  only when the obtained results of the calibration process satisfy the required precision. The descriptions of S 28 -S 34  have already been made in relation to  FIG. 2 , and therefore are not repeated here. 
   On the other hand, if the calibration process results retrieving section  14   a  has been unable to retrieve the corresponding model data on the camera in S 11   d , the process proceeds to S 12 , where a calibration object image is photographed using the camera  2  to acquire results of the calibration process suitable for the specific camera  2 . The descriptions of S 12 -S 26  have already been made in relation to  FIG. 2 , and therefore are not repeated here. 
   According to the second embodiment of the present invention, the results of the calibration process are accumulated in the calibration database  19 , and results of the calibration process corresponding to the model data on the camera are retrieved and transmitted to the user terminal, upon request from the user. Thus, the second embodiment of the present invention provides a significantly convenient method that allows the user to acquire intended results of the calibration process, even without the need to photograph a calibration object image. In the image calibration processing device  10 , by accumulating results of the calibration process in the calibration database  19 , the model data on cameras to be supported can be enhanced due to the cumulative effect, thereby improving the efficiency. 
   Third Embodiment 
     FIG. 14  is a general block diagram illustrating the structure of a third embodiment of the present invention. The third embodiment is different, compared with the first embodiment, in that the corrected subject image forming section is provided on the user terminal  40  side. In other words, the image calibration processing device  30  is configured that the results of the calibration process calculated by the calibration processing section  34  are transmitted from the transmission section for user terminal  36  to the user terminal  40 . The user terminal  40  is provided with a corrected subject image forming section  46  for processing a subject image into a corrected subject image. For descriptions of components of the third embodiment shown in  FIG. 14 , the descriptions of those of the first embodiment shown in  FIG. 1  with the same names should be referred to, as long as the natures of the two counterparts will not contradict, and the detailed description will not be repeated. 
   As shown in the figure, the image calibration processing device  30  includes a receiving section for user terminal  31 , a user authentication section  32 , an instruction retrieving section  33 , a calibration processing section  34 , an information reading section  34   b , a transmission section for user terminal  36 , a display section  36   a , a user database  37 , an instruction database  38 , and a calibration database  39 . The image calibration processing terminal  40  includes a transmission section for processing device  41 , a key entry section  42 , a receiving section for processing device  44 , a display section  45 , and a corrected subject image forming section  46 . 
   The operation of an apparatus constituted as described above will be described.  FIG. 15  is a flowchart for illustrating a method of the third embodiment of the present invention. A user terminal  40  transmits a calibration request (service request) for the camera  2  to the image calibration processing device  30  via the communication line  8  (S 100 ). In response to the calibration request, the image calibration processing device  30  authenticates whether or not a user of the user terminal  40  has a proper title for use. When the user of the user terminal  40  is certified as having a proper title for use as a result of authentication, the image calibration processing device  30  returns an instruction for calibration photographing according to the model of the camera  2  to the user terminal  40  (S 102 ). 
   On the user terminal  40  side the calibration object  4  is photographed by the camera  2 , in accordance with the instruction for calibration photographing (S 104 ). The calibration object image photographed is transmitted from the user terminal  40  to the image calibration processing device  30  via the communication line  8 , together with the photographing data (S 106 ). The image calibration processing device  30  makes a determination on the photographing quality of the calibration object image transmitted, for example, as to whether or not the image is unsuitable for the calibration process because the image is out of focus or the calibration object  4  image is too small (S 108 ). If the calibration object image is determined to be unsuitable, rephotographing of the calibration object  4  by the camera  2  is requested (S 110 ). In response to the request for rephotographing, the user photographs the calibration object  4  by the camera  2  (S 112 ), while paying attention to what is suggested in the comment. The calibration object image photographed is transmitted from the user terminal  40  to the image calibration processing device  30  via the communication line  8 , together with the photographing data (S 114 ), and a determination is made on the photographing quality of the calibration object image in S 108 . 
   If the photographing quality of the calibration object image is suitable, the calibration processing section  14  performs a calibration process using the calibration object image received (S 116 ). The results of the calibration process are accumulated in the calibration database  19 , together with the model of the camera. The model of the camera is acquired, for example, by reading the photographing state information attached to the calibration object image in the information reading section  14   b . The image calibration processing device  30  returns the results of the calibration process obtained in S 116  to the user terminal  40  (S 118 ). 
   On the user terminal  40  side the subject  6  is photographed by the camera  2  used to photograph the calibration object image (S 120 ). The user terminal  40  performs a calibration on the subject image in accordance with the results of the calibration process receiving the subject image, to form a corrected subject image (S 122 ). The corrected subject image formed may be, for example, displayed on the display section  45 , printed on a paper medium, or accumulated in an electromagnetic storage medium. 
   Fourth Embodiment 
     FIG. 16  is a general block diagram illustrating the structure of a fourth embodiment of the present invention. In  FIG. 16 , components having the same functions as those in  FIG. 1 ,  FIG. 12 , and  FIG. 14  described above are given the same reference numerals and symbols, and descriptions of such components will not be repeated. The image calibration processing device  30  includes a calibration process results retrieving section  34   a , in addition to the calibration processing section  34  and the calibration database  39 . The corrected subject image forming section  46  is provided on the user terminal  40  side, and not in the image calibration processing device  30 . The calibration process results retrieving section  34   a  retrieves, from the calibration database  39 , results of the calibration process corresponding to the model of camera received, utilizing the results of the calibration process accumulated in the calibration database  39  according to the camera model data. 
   The operation of an apparatus constituted as described above will be described.  FIG. 17  is a flowchart for illustrating a method of the fourth embodiment of the present invention. A user terminal  40  transmits a calibration request (service request) for the camera  2  to the image calibration processing device  30  via the communication line  8  (S 100 ). When a user of the user terminal  40  is certified as having a proper title for use as a result of authentication, the image calibration processing device  30  requests model data on the camera  2  (S 101   a ). The user terminal  40  side acquires the model data on the camera  2 , by allowing entry using the key entry section  22 , using an identification function for the camera  2  provided in the user terminal  40 , or the like, to transmit the acquired model data to the image calibration processing device  30  via the communication line  8  (S 101   b ). The calibration process results retrieving section  34   a  searches the results of the calibration process stored in the calibration database  39 , to retrieve the corresponding model data on the camera (S 101   c ). 
   If the calibration process results retrieving section  34   a  has been able to retrieve the corresponding model data on the camera, the process proceeds to S 118 . The descriptions of S 118 -S 122  have already been made in relation to  FIG. 15 , and therefore are not repeated here. 
   On the other hand, if the calibration process results retrieving section  34   a  has been unable to retrieve the corresponding model data on the camera in S 101   d , the process proceeds to S 112 , where a calibration object image is photographed using the camera  2  to acquire results of the calibration process suitable for the specific camera  2 . The descriptions of S 112 -S 116  have already been made in relation to  FIG. 15 , and therefore are not repeated here. 
   Fifth Embodiment 
     FIG. 18  is a general block diagram illustrating the structure of a fifth embodiment of the present invention. In  FIG. 18 , components having the same functions as those in  FIG. 1  described above are given the same reference numerals and symbols, and descriptions of such components will not be repeated. In this embodiment, the camera  2  photographs the calibration object  4  and the subject  6  as one image, and the user terminal  20  deals with a resulting stereo image photographed from at least two, namely left and right, photographing directions. The image calibration processing device  10  is provided with a three-dimensional measurement section  15   a  between the corrected subject image forming section  15  and the transmission section for user terminal  16 . 
   The three-dimensional measurement section  15   a  includes a stereo image generating section  151  and an image measurement section  152 . The stereo image generating section  151  has a function of generating a rectified image by performing an orientation (relative orientation and absolute orientation) and a rectification on the stereo image photographed by the camera  2 . Typically, the stereo image generating section  151  comprises a computer-executable software program. Here, the rectified image refers to a pair of images photographed in stereo from the right and left photographing directions and subjected to a rectification and an adjustment so as to be viewed stereoscopically. The image measurement section  152  performs a so-called absolute orientation on the stereo image generated by the stereo image generating section  151 , to calculate ground coordinates of each pixel. The details of this processing are disclosed, for example, in JP-A-Hei 11-351865. The use of the image measurement section  152  allows accurate measurement of a three-dimensional shape such as projections and depressions on the measuring object  30  surface. 
   The operation of an apparatus constituted as described above will be described.  FIG. 19  is a flowchart for illustrating a method of the fifth embodiment of the present invention. A user terminal  20  transmits a calibration request (service request) for the camera  2  to the image calibration processing device  10  via the communication line  8  (S 200 ). The calibration request includes a request for a three-dimensional image measurement on the subject  6  using a stereo image. In response, the image calibration processing device  10  authenticates whether or not a user of the user terminal  20  has a proper title for use. When the user of the user terminal  20  is certified as having a proper title for use as a result of authentication, the image calibration processing device  10  returns an instruction for calibration photographing according to the model of the camera  2  to the user terminal  20  (S 202 ). The instruction for calibration photographing includes important notices in a three-dimensional image measurement on the subject  6  using a stereo image. 
   On the user terminal  20  side the calibration object  4  and the subject  6  is photographed in stereo at a time so as to be included in one image, by the camera  2 , in accordance with the instruction for calibration photographing (S 204 ). This photographing in stereo yields a pair of images photographed in stereo from the right and left photographing directions using the camera  2 . The calibration object/subject image photographed in stereo is transmitted from the user terminal  20  to the image calibration processing device  10  via the communication line  8 , together with the photographing data (S 206 ). 
   The image calibration processing device  10  makes a determination on the photographing quality of the calibration object/subject image transmitted, for example, as to whether or not the image is unsuitable for the calibration process because the image is out of focus or the calibration object  4  image is too small (S 208 ). If the calibration object/subject image is determined to be unsuitable, rephotographing of the calibration object  4  and the subject  6  by the camera  2  is requested (S 210 ). At this time, it should be advantageous to give a comment suggesting to what should be paid attention in order to obtain a calibration object/subject image suitable for the calibration process. In response to the request for rephotographing, the user photographs the calibration object  4  and the subject  6  by the camera  2  (S 212 ), while paying attention to what is suggested in the comment. The calibration object/subject image photographed is transmitted from the user terminal  20  to the image calibration processing device  10  via the communication line  8 , together with the photographing data (S 214 ), and a determination is made on the photographing quality of the calibration object/subject image in S 208 . 
   If the photographing quality of the calibration object/subject image is suitable, the calibration processing section  14  performs a calibration process using the calibration object  4  image included in the calibration object/subject image received (S 216 ). The results of the calibration process are accumulated in the calibration database  19 , together with the model of the camera. On the user terminal  20  side a corrected subject image is generated from the calibration object/subject image (S 218 ), and is transmitted to the user terminal  20  via the communication line  8  (S 220 ). In addition, in the image calibration processing device  10 , the three-dimensional measurement section  15   a  performs a three-dimensional measurement on the corrected subject image. The three-dimensional measurement results obtained are returned from the image calibration processing device  10  to the user terminal  20  (S 224 ). At this time, the corrected subject image may be converted into an ortho image and then returned from the image calibration processing device  10  to the user terminal  20 . The foregoing description is directed to a case where a three-dimensional measurement is performed by a stereo method using two images. However, various methods may alternatively be adopted, such as a single-photograph orientation method using a single image in which the calibration object  4  and the subject  6  are photographed, or a bundle adjusting method with self-calibration using a plurality of images. 
   Sixth Embodiment 
     FIG. 20  is a general block diagram illustrating the structure of a sixth embodiment of the present invention. In  FIG. 20 , components having the same functions as those in  FIG. 18  described above are given the same reference numerals and symbols, and descriptions of such components will not be repeated. In this embodiment, the three-dimensional measurement section is provided on the user terminal  40  side, and not in the image calibration processing section  30 . The three-dimensional measurement section  47  includes a stereo image generating section  471  and an image measurement section  472 . For descriptions of the stereo image generating section  471  and the image measurement section  472 , the descriptions of the stereo image generating section  151  and the image measurement section  152  should be referred to. 
   The operation of an apparatus constituted as described above will be described.  FIG. 21  is a flowchart for illustrating a method of the sixth embodiment of the present invention. Descriptions of S 200 -S 216  of  FIG. 21  are the same as those of S 200 -S 216  of  FIG. 19 , and therefore will not be repeated. The results of the calibration process in S 216  are accumulated in the calibration database  19 , together with the model of the camera, and transmitted to the user terminal  40  (S 230 ). The user terminal  40  uses the results of the calibration process transmitted, to generate a corrected subject image from the calibration object/subject image (S 232 ). In addition, in the user terminal  40 , the three-dimensional measurement section  47  performs a three-dimensional measurement on the corrected subject image (S 234 ). At this time, the corrected subject image may be converted into an ortho image. The corrected subject image may be, for example, displayed on the display section  45  of the user terminal  40 , displayed on a television set for stereo display, or the like. 
   The bundle adjusting method with self-calibration used in the first through sixth embodiments is described. The calibration processing performed by the calibration processing section  14 ,  34  uses a “bundle adjusting method with self-calibration” used in the field of photogrammetry for example. The term “bundle adjusting” refers to a method of adjusting the position and the tilt of the camera (exterior orientation elements) and the coordinate positions of the second marks at the same time, by establishing observation equations for every ray bundle of each image based on a collinearity condition that a ray bundle connecting a subject, a lens, and a CCD surface must be collinear, and applying a least squares method. The term “with self-calibration” indicates that the calibration elements, namely interior localizations of the camera (lens aberrations, principal point, and focal length) can also be found with the method. The basic equations of the collinear condition for the bundle adjusting method with self-calibration (hereinafter referred to as “bundle adjusting method” for simplicity) are represented by (Equation 2) and (Equation 3) as follows: 
   
     
       
         
           
             
               
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   Here, the elements a 11 -a 33  are elements of a rotation matrix at a camera tilt (ω, φ, κ). The symbols ω, φ, κ represent the tilts of the camera at the time of photographing with respect to the three axes X, Y, Z constituting the object coordinate system, and are called exterior orientation elements. (X, Y, Z) represents coordinates of an object such as a reference mark in the object coordinate system, and (X 0 , Y 0 , Z 0 ) represents coordinates of a projection center point Oc. (See the specification of Japanese Patent Application No. 2002-195058, paragraphs [0052], [0056], and [0068].) The bundle adjusting method is used to perform a least squares approximation using (Equation 2) and (Equation 3) with a plurality of images to find various solutions. The bundle adjusting method allows calculating the exterior orientation elements of the camera at respective photographing positions at the same time. In other words, the method allows calculation of the calibration elements of the camera. 
   As an example of a correction model for the interior localizations (lens aberrations), radial lens distortions can be represented by (Equation 4) as follows: 
   
     
       
         
           
             
               
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   The correction model is not limited to this example, but may be selected as suitable for the lens used. Such calculations can be made with a successive approximation method, if six or more reference points are available in the ground coordinate system and the image coordinate system. 
   Calculation of lens aberrations using a two-dimensional chart shown in  FIG. 3  as the calibration object  4  is already disclosed in the specification of Japanese Patent Application No. 2002-195058 proposed by the present applicant, or the like. The specifics of the calculation of lens aberration using a two-dimensional chart are hardly related to the subject of the present invention, and therefore the specification is incorporated herein by reference in order to avoid redundancy. As an alternative to the two-dimensional chart as shown in  FIG. 3 , other types of two-dimensional chart or three-dimensional chart may be used as the calibration object  4 . The calibration processing can be performed using the obtained equations for calculating lens aberrations corresponding to the respective charts.