Patent Publication Number: US-9418291-B2

Title: Information processing apparatus, information processing method, and computer-readable storage medium

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an information processing apparatus, an information processing method, and a computer program for performing 3D measurement of an object to be measured. 
     2. Description of the Related Art 
     A 3D shape measurement apparatus has been broadly used in various fields including product examination in factories in an industrial field and shape measurement of living bodies in a medical field. In particular, a non-contact measurement method is efficient in a case where a target object may be deformed or destroyed when being touched. 
     As non-contact 3D shape measurement, a method for performing triangulation on an image using image pickup means is widely used. As a more concrete example, Japanese Patent Laid-open No. 2001-356010 discloses an example in which a 3D shape measurement is performed by projecting a grid pattern on an object using a projector and capturing an image using image pickup means. More specifically, projection is performed such that a grid pattern formed by vertical lines and horizontal lines is used as a projection pattern while 2D code pattern are embedded in rectangles defined by a grid, and 2D positions on the projected pattern and 2D positions in a captured image are associated with each other. 
     Corresponding of lines which constitute the grid pattern is performed using the 2D positions on the projected pattern and the 2D positions on the captured image which correspond to each other so that 3D shape measurement is performed using triangulation employing a light-section method. However, in the Japanese Patent Laid-open No. 2001-356010 described above, grids which define the rectangles should exist in the same continuous plane for detection of the 2D patterns embedded in the rectangles. Therefore, there arises a problem in that, under a condition in which a sufficient area of a plane in vertical and horizontal directions is not obtained such as a rough region or a narrow region, the pattern is not appropriately detected resulting in an error of 3D shape measurement. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in consideration of the above situation, and has as its object to appropriately detect a pattern under a condition in which a sufficient area of a plane in vertical and horizontal directions is not obtained such as a rough region or a narrow region. According to the present invention, the foregoing object is attained by providing an information processing apparatus including reference line pattern detection means for detecting a reference line pattern from a captured image of an object to which pattern light is projected by pattern light projection means, the image being captured by image pickup means, the pattern light including line patterns having at least two directions and having at least two lines in each of the directions and including at least one reference line pattern a partial region or an entire region of which is projected on the object, and the reference line pattern serving as a reference of the line patterns, and line pattern corresponding means for establishing correspondence between line patterns projected by the pattern light projection means and line patterns captured by the image pickup means in accordance with topological positional relationship using the reference line pattern detected by the reference line pattern detection means. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  includes diagrams illustrating a system configuration according to a first embodiment. 
         FIG. 2  is a flowchart illustrating an operation according to the first embodiment. 
         FIG. 3  is a diagram illustrating a projection line pattern according to the first embodiment. 
         FIG. 4  includes diagrams illustrating an imaging line pattern, an imaging vertical line pattern, and an imaging horizontal line pattern according to the first embodiment. 
         FIG. 5  is a flowchart illustrating a method for detecting a vertical reference line pattern in step S 205 . 
         FIG. 6  is a flowchart illustrating a method for detecting a horizontal reference line pattern in step S 205 . 
         FIG. 7  is a diagram illustrating a method for establishing correspondence between an imaging vertical line pattern and an imaging horizontal line pattern which have not corresponded to each other using a reference position according to the first embodiment. 
         FIG. 8  is a diagram schematically illustrating a case where a position of an arbitrary measurement point on a measurement target line pattern is measured using a camera coordinate system setting a principle position of a camera as an origin 0. 
         FIG. 9  includes diagrams illustrating a method for defining a characteristic line pattern of a reference line pattern without using a line width. 
         FIG. 10  is a diagram illustrating a system configuration according to a second embodiment. 
         FIG. 11  is a diagram illustrating a process of changing a projection position of a reference line pattern in accordance with a change of a position of an object. 
         FIG. 12  is a diagram illustrating the positional relationship among a projector, a camera, and projection vertical line patterns. 
         FIG. 13  is a diagram illustrating an operation according to a third embodiment. 
         FIG. 14  is a diagram illustrating a projection line pattern according to the third embodiment. 
         FIG. 15  includes diagrams illustrating an imaging line pattern, imaging vertical line patterns, and imaging horizontal line patterns according to the third embodiment. 
         FIG. 16  is a flowchart illustrating a method for detecting a vertical reference line pattern in step S 1305 . 
         FIG. 17  is a diagram illustrating the relationship among a projection ID number of a projection horizontal line pattern positioned on an upper side of an arbitrary line pattern segment S nb  and a projection ID number of a projection horizontal line pattern positioned on a lower side of the arbitrary line pattern segment S nb  on a reference line pattern. 
         FIG. 18  is a diagram illustrating a method for establishing correspondence between an imaging vertical line pattern and an imaging horizontal line pattern which have not corresponded to each other using a reference position according to the third embodiment. 
         FIG. 19  is a diagram illustrating a system configuration according to a fourth embodiment. 
         FIG. 20  includes diagrams illustrating an imaging line pattern in a case where a projection line pattern is not corrected, a projection line pattern in a case where correction is performed, and an imaging line pattern in a case where correction is performed. 
         FIG. 21  is a diagram illustrating a system configuration according to a fifth embodiment. 
         FIG. 22  is a diagram illustrating a projection line pattern according to the fifth embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiments of the present invention will be described hereinafter with reference to the accompanying drawings. 
     First Embodiment 
       FIG. 1  is a diagram illustrating a system configuration according to a first embodiment. A projector  101  which is an example of pattern light projection means projects pattern light constituted by at least two vertical line patters and at least two horizontal line patterns formed on an object  102  serving as a measurement target. Note that a vertical line pattern is referred to as a “projection vertical line pattern”, a horizontal line pattern is referred to as a “projection horizontal line pattern”, and a vertical line pattern and a horizontal line pattern are collectively referred to as a “projection line pattern”. Furthermore, the projector  101  superposes a vertical reference line pattern on one of projection vertical line patterns and superposes a horizontal reference line pattern on one of projection horizontal line patterns, and simultaneously projects the vertical reference line pattern and the horizontal reference line pattern. The vertical reference line pattern and the horizontal reference line pattern are used as indices representing reference positions of the vertical line patterns and the horizontal line patterns, respectively. A camera  103  which is an example of image pickup means captures the object  102  in a state in which pattern light is projected onto the object  102 . 
     Here, an information processing apparatus  100  has a hardware configuration as illustrated in (b) of  FIG. 1 . More specifically, the information processing apparatus  100  includes a CPU  110 , a storage device  111 , and a communication device  112  which are connected to one another through a bus or the like as the hardware configuration. The CPU  110  realizes a functional configuration (software configuration) of the information processing apparatus  100  as illustrated in (a) of  FIG. 1  by executing processes in accordance with programs stored in the storage device  111 . The communication device  112  controls communication between the information processing apparatus  100  and another apparatus (such as the camera  103  or the projector  101 ) under control of the CPU  110 . 
     As illustrated in (a) of  FIG. 1 , the information processing apparatus  100  includes, as a functional configuration, a line pattern extraction unit  104 , a reference line pattern detector  105 , a line pattern corresponding unit  106 , and a 3D shape measurement unit  107 . 
     The line pattern extraction unit  104  performs a process of obtaining vertical line patterns and horizontal line patterns which are projected onto the object  102  (on the object) through image processing from an image captured by the camera  103 . The reference line pattern detector  105  detects a vertical reference line pattern and a horizontal reference line pattern included in pattern light projected onto the object  102  from imaging vertical line patterns and imaging horizontal line patterns obtained by the line pattern extraction unit  104 . The line pattern corresponding unit  106  establishes correspondence between the vertical line patterns and the horizontal line patterns which are projected by the projector  101  and the imaging vertical line patterns and the imaging horizontal line patterns with each other using the vertical reference line pattern and the horizontal reference line pattern which are obtained by the reference line pattern detector  105  as reference positions. The 3D shape measurement unit  107  calculates a depth, that is, a shape, between the camera  103  and the object  102  on which the line patterns are projected in accordance with the principle of the light-section method. 
     Note that a configuration of the information processing apparatus  100  illustrated in (a) of  FIG. 1  may be implemented by hardware. 
       FIG. 2  is a flowchart illustrating an operation according to the first embodiment. Hereinafter, the operation will be described in accordance with step numbers of the flowchart. 
     Step S 201 : The projector  101  illustrated in  FIG. 1  projects pattern light. A projection line pattern is constituted by a grid pattern including a plurality of projection vertical line patterns  301  and a plurality of projection horizontal line patterns  302  which intersect with each other as illustrated in  FIG. 3 . The projection vertical line patterns  301  have unique ID numbers 0, 1, 2, and so on assigned thereto from the top and the projection horizontal line patterns  302  have unique ID numbers 0, 1, 2, and so on assigned thereto from the left. Simultaneously, the projector  101  projects a vertical reference line pattern  303  and a horizontal reference line pattern  304  which have line widths different from the projection vertical line patterns  301  and the projection horizontal line patterns  302  in respective positions on the object  102  such that partial regions or entire regions thereof are included in a state in which the vertical reference line pattern  303  superposes on one of the projection vertical line patterns  301  and the horizontal reference line pattern  304  superposes on one of the projection horizontal line patterns  302 . The vertical reference line pattern  303  and the horizontal reference line pattern  304  similarly have projection ID numbers assigned thereto. Specifically, the projection ID number of the vertical reference line pattern  303  is 5 and the projection ID number of the horizontal reference line pattern  304  is 4 in  FIG. 3 . Note that the projector  101  projects the projection vertical line patterns  301  and the vertical reference line pattern  303  in red and projects the projection horizontal line patterns  302  and the horizontal reference line pattern  304  in blue for convenience of separation performed in later steps. 
     Step S 202 : 
     The camera  103  illustrated in  FIG. 1  captures the object  102 . The object  102  is captured in a state in which pattern light  401  is projected on the object  102  as illustrated in  FIG. 4 a   , and a captured image is transmitted to the line pattern extraction unit  104  illustrated in FIG.  1 . 
     Step S 203 : 
     The line pattern extraction unit  104  illustrated in  FIG. 1  extracts imaging vertical line patterns  402  as illustrated in  FIG. 4 b    by selecting red components of the transmitted captured image. The line pattern extraction unit  104  performs labeling on continuous regions of the extracted imaging vertical line patterns  402  so as to assign imaging ID numbers 0 to N max  which are unique to the regions. 
     Step S 204 : 
     The line pattern extraction unit  104  illustrated in  FIG. 1  extracts imaging horizontal line patterns  403  as illustrated in  FIG. 4 c    by selecting blue components of the transmitted captured image. The line pattern extraction unit  104  performs labeling on continuous regions of the extracted imaging horizontal line patterns  403  so as to assign imaging ID numbers 0 to M max  which are unique to the regions. Hereinafter, both of the imaging vertical line patterns  402  and the imaging horizontal line patterns  403  are referred to as “imaging line patterns”. 
     Step S 205 : 
     The reference line pattern detector  105  illustrated in  FIG. 1  detects a line pattern corresponding to the projected vertical reference line pattern  303  from the imaging vertical line patterns  402  and a line pattern corresponding to the projected horizontal reference line pattern  304  from the imaging horizontal line patterns  403 . 
     Here,  FIG. 5  is a flowchart illustrating a method for detecting the vertical reference line pattern  303  in step S 205 . Hereinafter, an operation in step S 205  will be described in accordance with step numbers of the flowchart. 
     Step S 501 : 
     The reference line pattern detector  105  sets an imaging horizontal line pattern maximum width W hmax  to an initial value 0. 
     Step S 502 : 
     The reference line pattern detector  105  sets an imaging ID number n of an imaging horizontal line pattern to an initial value 0. 
     Step S 503 : 
     The reference line pattern detector  105  calculates an average width W h  of an imaging vertical line pattern  402  having the imaging ID number n selected from among the extracted imaging vertical line patterns  402  illustrated in  FIG. 4 b   . The reference line pattern detector  105  can calculate an appropriate line width by calculating an average of a width of the entire line even when the object  102  has a slightly rough surface. 
     Step S 504 : 
     The reference line pattern detector  105  compares the numerical value W h  and the numerical value W hmax  with each other. When the value W hmax  is smaller than the value W h , the reference line pattern detector  105  proceeds to step S 505 , and otherwise the reference line pattern detector  105  proceeds to step S 507 . 
     Step S 505 : 
     The reference line pattern detector  105  assigns the value W h  to the value W hmax . 
     Step S 506 : 
     The reference line pattern detector  105  assigns n to N ref . 
     Step S 507 : 
     The reference line pattern detector  105  adds 1 to n. 
     Step S 508 : 
     The reference line pattern detector  105  compares n with the value N max  which is the largest imaging ID number of the imaging vertical line patterns  402 . When n is equal to or larger than the value N max , the reference line pattern detector  105  terminates the process illustrated in  FIG. 5 . Otherwise the reference line pattern detector  105  proceeds to step S 503 . 
     In the process described above, the reference line pattern detector  105  detects a value N ref  serving as an imaging ID corresponding to the vertical reference line pattern  303  illustrated in  FIG. 3  from among the imaging vertical line patterns  402  illustrated in  FIG. 4 . 
     The reference line pattern detector  105  performs a similar process on the horizontal reference line pattern  304  as illustrated in a flowchart of  FIG. 6 . By this, the reference line pattern detector  105  detects a value M ref  serving as an imaging ID corresponding to the horizontal reference line pattern  304  from among the imaging horizontal line patterns  403  (m=0 to M max ) illustrated in  FIG. 4 c   . Referring back to  FIG. 2 , the description is continued. 
     Step S 206 : 
     The line pattern corresponding unit  106  illustrated in  FIG. 1  establishes correspondence of the imaging ID numbers of the imaging vertical line patterns  402  and the imaging horizontal line patterns  403  illustrated in  FIG. 4  to the projection ID numbers of the projection vertical line patterns  301  and the projection horizontal line patterns  302  illustrated in  FIG. 3 , respectively. The imaging ID number N ref  of the vertical reference line pattern  303  and the imaging ID number M ref  of the horizontal reference line pattern  304  have been detected in step S 205 . While using the vertical reference line pattern  303  and the horizontal reference line pattern  304  as reference positions, the line pattern corresponding unit  106  establishes correspondence between the other imaging vertical line patterns  402  and the other imaging horizontal line patterns  403  in accordance with the topological positional relationship constituted by the imaging line patterns and intersections thereof. As illustrated in  FIG. 7 , the line pattern corresponding unit  106  can reach an arbitrary imaging line pattern by successively tracing the imaging line patterns adjacent to intersections of the vertical and horizontal imaging line patterns starting from the vertical reference line pattern  303  and the horizontal reference line pattern  304 . The line pattern corresponding unit  106  recognizes that a non-corresponding imaging vertical line pattern  702  is shifted by +3 in a horizontal direction relative to a reference position  701  and by −1 in a vertical direction relative to the reference position  701  when counting an amount of movement in a unit of line in the vertical and horizontal directions. 
     The line pattern corresponding unit  106  can perform the corresponding described above when it is considered that a unit of a movement for individual segment lines divided by the intersections is a phase and the relationships between phases of the projection line patterns and phases of the imaging line patterns are determined as invariants. According to the amounts of movements from the reference positions obtained as described above, the projection ID number of the vertical reference line pattern  303  (N=5 in  FIG. 7 ), and the projection ID number of the horizontal reference line pattern  304  (M=4 in  FIG. 7 ), it is determined that a projection ID number of the non-corresponding imaging vertical line pattern  702  is 8 (N=8). Furthermore, it is determined that a projection ID number of a non-corresponding imaging horizontal line pattern  703  is 3 (M=3). 
     The line pattern corresponding unit  106  applies the process described above to all the imaging vertical line patterns  402  and the imaging horizontal line patterns  403  to thereby establish correspondence between projection ID numbers and all imaging ID numbers. 
     Step S 207 : 
     The 3D shape measurement unit  107  illustrated in  FIG. 1  measures a shape of the object  102  using the imaging vertical line patterns  402  and the imaging horizontal line patterns  403  to which projection ID numbers have been assigned. 
       FIG. 8  is a diagram schematically illustrating a case where a position of an arbitrary measurement point  804  in a measurement target line pattern  803  is measured using a camera coordinate system  802  in which a principle position  801  of a camera is an origin 0 (0, 0). Assuming that the projector  101  projects a straight line pattern, the measurement target line pattern  803  is a line of intersection between a plane defined by the projected line pattern and the object  102 . 
     Here, a light section plane  805  formed by the projected line pattern is calibrated in advance using the camera coordinate system in accordance with the following expression.
 
 ax+by+cz+d= 0  Expression (1)
 
     Furthermore, the point on the measurement target line pattern  803  exists on a line  808  which is represented by an expression below using a position P (Px, Py, −f) of a projection point  807  on an image  806  captured by the camera  103  illustrated in  FIG. 1 . Here, the captured image  806  illustrated in  FIG. 8  has an actual size equal to an image projected on an image pickup element when assuming that the camera  103  illustrated in  FIG. 1  is a pinhole camera. Furthermore, it is assumed that the captured image  806  is located in a position in which a center of the image is far away from a position of an origin by −f of a focal length in a Z axis direction. 
     
       
         
           
             
               
                 
                   
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     In step S 206 , the 3D shape measurement unit  107  performs the calculation described above using all the imaging vertical line patterns  402  and the imaging horizontal line patterns  403  which correspond to the projection ID numbers as the measurement target line patterns  803  to thereby obtain an entire shape of the object. 
     In the procedure described above, a grid pattern can be projected with higher density when compared with the conventional method. Furthermore, since the detection of the reference line patterns and the corresponding using the reference positions are performed, 3D shape measurement can be performed even on a rough region which does not include a sufficient flat portion in vertical and horizontal directions and which does not accept a 2D code pattern and a narrow region. 
     Although only one vertical reference line pattern  303  and one horizontal reference line pattern  304  are included in the projection line patterns in this embodiment, when a plurality of vertical reference line patterns  303  and a plurality of horizontal reference line patterns  304  are disposed so that the number of reference positions is increased, the information processing apparatus can perform robust corresponding. When a plurality of reference line patterns are disposed, a range of a presumable depth of the object to be measured is restricted, and ranges of presumable positions of the reference line patterns in a captured image are restricted so as not to overlap with one another. By this restriction, the information processing apparatus can simultaneously detect the plurality of reference line patterns without confusion. 
     In step S 205  of  FIG. 2 , to detect the vertical reference line pattern  303  and the horizontal reference line pattern  304 , the reference line patterns are characterized by line widths. However, the reference line patterns may be characterized by other methods. 
       FIG. 9 a    illustrates a case where a reference line pattern is characterized by giving a luminance change in a line extending direction. A luminance change in two or more levels is assigned to a certain projection line pattern using the intersections as breakpoints and the reference line pattern detector  105  determines whether the luminance change occurs to thereby detect a reference line pattern  901 . 
     When a plurality of reference line patterns which are characterized by the luminance change are disposed, the reference line patterns may have luminance changes in accordance with random numerical sequences having low cross-correlativity so that the reference line pattern detector  105  can easily detect the reference line patterns. For example, coefficients of cross-correlations between the luminance changes read by the line pattern extraction unit  104  and the random numerical sequences used for the reference line patterns are calculated, and an imaging line pattern having a luminance change corresponding to the largest cross-correlation coefficient is selected so that the reference line pattern detector  105  uniquely detects a reference line pattern. As the random numerical sequence having a low cross-correlativity, the de Bruijn sequence is known, for example. When the de Bruijn sequence is used, the reference line pattern detector  105  can robustly detect a reference line pattern even in a captured image in which image noise is observed or only a portion of a reference line pattern is observed due to discontinuity of an object. 
       FIG. 9 b    illustrates a case where characterization is performed by giving a luminance change in a line cutting direction as another characterization method. A luminance change of Gaussian distribution is given on one side of a projection line pattern in the line cutting direction. After the imaging line patterns are extracted in accordance with color gamut selection, luminance changes on both sides of the lines in the cutting direction are compared with each other in all the imaging line patterns. In this way, the reference line pattern detector  105  detects a reference line pattern  902  in which luminance changes of both sides of the line are different from each other. Since the luminance is changed only on one side, luminance changes on both sides are different from each other, and therefore, even when a projection line pattern blurs in image capturing, the reference line pattern detector  105  can robustly detect a reference line pattern. 
     As still another characterization method, when a color projector is allowed to be used as the projector  101 , the characterization may be made by color. When color is used, color information is not considerably varied even in a case where the surface of the object  102  considerably tilts relative to the camera  103  when compared with the characterization using a line width. Therefore, the reference line pattern detector  105  can robustly detect a reference line pattern relative to a shape of an object. 
     Although in the foregoing embodiment, two types of projection line pattern, i.e., the projection vertical line patterns  301  and the projection horizontal line patterns  302  have been described, three directions, that is, three or more types of line pattern may be projected. When the number of directions of lines is increased, the 3D shape measurement can be more reliably performed. 
     Note that, in this embodiment, the information processing apparatus  100  is provided separately from the projector  101  and the camera  103  as described above. However, the information processing apparatus  100  may include the projector  101  and the camera  103  as components thereof so as to be used as a 3D shape measurement apparatus, for example. According to the information processing apparatus of this embodiment described above, patterns can be appropriately detected under the circumstance in which a sufficiently-large plane in the vertical and horizontal direction is not obtained such as a region having a rough surface or a narrow region. 
     Second Embodiment 
     In step S 201  of  FIG. 2 , the vertical reference line pattern  303  and the horizontal reference line pattern  304  are projected in positions overlapping with the object  102  from the first. To perform more robust measurement, an object detector  1001  may be added to an apparatus configuration as illustrated in  FIG. 10  and projection positions of reference line patterns may be appropriately changed in accordance with a change of a position of an object. 
       FIG. 11  is a diagram illustrating a process of changing projection positions of reference line patterns in accordance with a change of a position of an object. 
     A camera  103  obtains a background image  1101  in advance by projecting pattern light in a state in which only a background is provided before capturing an object  102 . Next, the camera  103  captures an object image  1102  in a state in which the object  102  is arranged. The object detector  1001  detects a difference between the background image  1101  and the object image  1102 . A region detected as a difference image  1103  obtained at this time serves as an object region. 
     The projector  101  can project reference line patterns in positions overlapping with the object by projecting a vertical reference line pattern  1104  and a horizontal reference line pattern  1105  using a position corresponding to the center of gravity of the object region as a 2D position. Since the camera  103  and the object detector  1001  perform the process described above every time a captured image is obtained, the projector  101  can update the projection positions of the reference line patterns. 
     Even when the object moves, the reference line patterns can be continued to be projected in positions overlapping with the object by performing the process described above. 
     Third Embodiment 
     As illustrated in  FIG. 12 , a camera  103  of this embodiment is installed in a position in which all projection vertical line patterns  1203  are positioned in parallel to an epipolar plane  1205  formed by three points including a projector principal point  1201 , a camera principal point  1202 , and an arbitrary point  1204  on the projection vertical line patterns  1203 . Furthermore, an angle of field of a projector  101  and an angle of field of the camera  103  are the same as each other and are controlled such that focal planes thereof are in the same position. A line pattern extraction unit  104  performs a process of obtaining vertical line patterns and horizontal line patterns projected on an object  102  using image processing from an image captured by the camera  103 . 
     A reference line pattern detector  105  detects a reference line pattern included in pattern light projected on the object  102  from among the imaging vertical line patterns obtained by the line pattern extraction unit  104 . A line pattern corresponding unit  106  establishes correspondence of projection vertical line patterns and projection horizontal line patterns which are projected by the projector  101  to imaging vertical line patterns and imaging horizontal line patterns using a vertical reference line pattern detected by the reference line pattern detector  105  as a reference position. 
     A 3D shape measurement unit  107  calculates a depth, that is, a shape, between the camera  103  and the object  102  on which the line patterns are projected in accordance with the principle of the light-section method using the imaging horizontal line patterns in which the correspondence has been established. 
       FIG. 13  is a flowchart illustrating an operation according to the third embodiment. Hereinafter, the operation will be described in accordance with step numbers of the flowchart. 
     Step S 1301 : 
     The projector  101  illustrated in  FIG. 1  projects pattern light. Projection line patterns are constituted by a grid pattern including a plurality of projection vertical line patterns  1401  and a plurality of projection horizontal line patterns  1402  which are intersect with each other as illustrated in  FIG. 14 . Hereinafter, both of the projection vertical line patterns  1401  and the projection horizontal line patterns  1402  are collectively referred to as “projection line patterns”. The projection vertical line patterns  1401  have unique ID numbers 0, 1, 2, and so on assigned thereto from the top and the projection horizontal line patterns  1402  have unique ID numbers 0, 1, 2, and so on assigned thereto from the left. Simultaneously, the projector  101  projects a reference line pattern  1403  which has line pattern segments obtained by dividing the reference line pattern  1403  by the projection horizontal line patterns and which have different widths on one of the projection vertical line patterns  1401  in an overlapping manner in a position in which a partial region or an entire region thereof is included on the object  102 . 
     A projection ID number is similarly assigned to the reference line pattern  1403  and a projection ID number of the reference line pattern  1403  in  FIG. 14  corresponds to “N=3”. Note that the projector  101  projects the projection vertical line patterns  1401  and the reference line pattern  1403  in red and projects the projection horizontal line patterns  1402  in blue for convenience of separation performed in later steps. 
     Step S 1302 : 
     The camera  103  illustrated in  FIG. 1  captures the object  102 . The object  102  is captured in a state in which pattern light  1501  is projected on the object  102  as illustrated in  FIG. 15 a   , and a captured image is transmitted to the line pattern extraction unit  104  from the camera  103 . 
     Step S 1303 : 
     The line pattern extraction unit  104  illustrated in  FIG. 1  extracts imaging vertical line patterns  1502  as illustrated in  FIG. 15 b    by selecting red components of the transmitted captured image. The line pattern extraction unit  104  performs labeling on continuous regions of the extracted imaging vertical line patterns  1502  so as to assign imaging ID numbers 0 to N max  which are unique to the regions. 
     Step S 1304 : 
     The line pattern extraction unit  104  illustrated in  FIG. 1  extracts imaging horizontal line patterns  1503  as illustrated in  FIG. 15 c    by selecting blue components of the transmitted captured image. The labeling is performed on continuous regions of the extracted imaging horizontal line patterns  1503  so that imaging ID numbers 0 to M max  which are unique to the regions are assigned. 
     Step S 1305 : 
     The reference line pattern detector  105  illustrated in  FIG. 1  detects a line pattern corresponding to the projected reference line pattern  1403  from among the imaging vertical line patterns  1502  illustrated in  FIG. 15   b.    
       FIG. 16  is a flowchart illustrating a method for detecting the reference line pattern  1403  in step S 1305 . Hereinafter, an operation in step S 1305  will be described in accordance with step numbers of the flowchart. 
     Step S 1601 : 
     The reference line pattern detector  105  sets an imaging ID number n of a target imaging horizontal line pattern to an initial value 0. 
     Step S 1602 : 
     The reference line pattern detector  105  sets a maximum cross-correlation value C max  to an initial value 0. 
     Step S 1603 : 
     The reference line pattern detector  105  selects one of the imaging vertical line patterns  1502  illustrated in  FIG. 15 b    which has the imaging ID number n and divides the imaging vertical line pattern  1502  into line pattern segments S nb  (b=0 to M max −1) in accordance with the imaging horizontal line patterns  1503 . 
     Step S 1604 : 
     The reference line pattern detector  105  calculates average width arrays W nb  (b=0 to M max −1) of the line pattern segments S nb  divided in step S 1603 . The reference line pattern detector  105  uses the average width arrays W nb  as arrays of characteristic change in steps below. 
     Step S 1605 : 
     The reference line pattern detector  105  calculates a coefficient C n  of cross-correlation between the average width arrays W nb  obtained in step S 1604  and reference length arrays W refb  (b=0 to M max −1) in accordance with the following expression. 
     
       
         
           
             
               
                 
                   
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   W   n     Expression (5)
 
   W   ref     Expression (6)
 
     Expressions (5) and (6) are arithmetic averages of all components included in a range of “b=0 to M max - 1 ” of the average width arrays W nb  and the reference length arrays W refb , respectively. Note that, as described above, the camera  103  is installed in a position in which all the projection vertical line patterns  1203  are normally parallel to the epipolar plane  1205  as illustrated in  FIG. 12 , and it is controlled that an angle of field of the projector  101  and an angle of field of the camera  103  are the same as each other and focal planes thereof are located in the same position. 
     According to the conditions described above, widths of the imaging vertical line patterns  1502  are not affected by a shape of the object  102  but normally maintain constant values. Therefore, the average width arrays W nb  are used as arrays of reference lengths of the imaging vertical line patterns  1502  and coefficients of cross-correlations between the average width arrays W nb  and the reference length arrays W refb  of the reference line patterns is calculated so that a similarity degree is obtained. In this way, a reference line pattern can be robustly detected. 
     Step S 1606 : 
     The reference line pattern detector  105  compares numerical values C n  and C max  with each other. When the value C n  is larger than the value C max , the reference line pattern detector  105  proceeds to step S 1607 . Otherwise, the reference line pattern detector  105  proceeds to step S 1609 . 
     Step S 1607 : 
     The reference line pattern detector  105  assigns the value C n  to the value C max . 
     Step S 1608 : 
     The reference line pattern detector  105  assigns n to a reference line pattern ID number N ref . 
     Step S 1609 : 
     The reference line pattern detector  105  adds 1 to n. 
     Step S 1610 : 
     The reference line pattern detector  105  compares n with the value N max  which is the largest imaging ID of the imaging vertical line patterns  402 . When n is equal to or larger than the value N max , the reference line pattern detector  105  terminates the process. Otherwise, the reference line pattern detector  105  proceeds to step S 1603 . 
     In the process described above, the reference line pattern detector  105  detects a value N ref  which is an imaging ID number corresponding to the reference line pattern  1403  from among the imaging vertical line patterns  1502 . Referring back to  FIG. 13 , the description is continued. 
     Step S 1306 : 
     The line pattern corresponding unit  106  illustrated in  FIG. 1  establishes correspondence of the imaging ID numbers of the imaging vertical line patterns  1502  and the imaging horizontal line patterns  1503  to the projection ID numbers of the projection vertical line patterns  1401  and the projection horizontal line patterns  1402 , respectively. The imaging ID number N ref  of the reference line pattern  1403  has been detected in step S 1305 . The line pattern corresponding unit  106  establishes correspondence between the imaging vertical line patterns  1502  except for the reference line pattern  1403  and the imaging horizontal line patterns  1503  in accordance with the topological positional relationship constituted by imaging line patterns and intersections thereof while using the imaging ID number N ref  as a reference position. Note that the reference line pattern  1403  in this embodiment is divided by the intersections with the imaging horizontal line patterns  1503  in a unit of line pattern segment S nb  in step S 1603 . Accordingly, the line pattern corresponding unit  106  can uniquely determine projection ID numbers of the intersecting imaging vertical line patterns. 
     For example, as illustrated in  FIG. 17 , a projection ID number of an imaging horizontal line pattern  1701  located on an upper side of an arbitrary line pattern segment S nb  is b and a projection ID number of an imaging horizontal line pattern  1702  located on a lower side of the arbitrary line pattern segment S nb  is b+1. 
     As illustrated in  FIG. 18 , the line pattern corresponding unit  106  can reach an arbitrary imaging line pattern while successively tracing the imaging line patterns adjacent to intersections of the vertical and horizontal imaging line patterns using a point  1801  on an upper side of an arbitrary line pattern segment S nb  as a reference position. The line pattern corresponding unit  106  recognizes that a non-corresponding imaging vertical line pattern  1802  is shifted by +2 in a horizontal direction relative to the point  1801  on an upper side of the line pattern segment S nb  and a non-corresponding imaging vertical line pattern  1803  is shifted by +3 in a vertical direction relative to the point  1801  when counting an amount of movement in a unit of line in the vertical and horizontal directions. 
     The line pattern corresponding unit  106  obtains a projection ID number N=5 of the non-corresponding imaging vertical line pattern  1802  from the movement amount obtained as described above and a projection ID number N=3 of the reference line pattern  1403  and the line pattern segment S nb  (b=2) illustrated in  FIG. 18 . Furthermore, the line pattern corresponding unit  106  obtains a projection ID number M=5 of the non-corresponding imaging horizontal line pattern  1803 . The line pattern corresponding unit  106  can perform the corresponding described above when the relationships between phases of the projection line patterns and phases of the imaging line patterns are determined as invariants as with the case of the first embodiment. 
     The line pattern corresponding unit  106  applies the process described above to all the imaging vertical line patterns  1502  and the imaging horizontal line patterns  1503  to thereby establish correspondence between projection ID numbers and all the imaging ID numbers. 
     Step S 1307 : 
     The 3D shape measurement unit  107  illustrated in  FIG. 1  measures a shape of the object  102  using the imaging horizontal line patterns  1503  to which the projection ID numbers illustrated in  FIG. 15  has been assigned. The 3D shape measurement unit  107  performs the process in step S 207  of the first embodiment only on the imaging horizontal line patterns  1503  in this step. The imaging vertical line patterns  1502  of this embodiment are recorded as line pattern segments which do not move in the horizontal direction. Therefore, the 3D shape measurement unit  107  does not use the imaging vertical line patterns  1502  in the 3D shape measurement. 
     According to the procedure described above, a grid pattern can be projected with higher density when compared with the conventional method. Furthermore, since the detection of the reference line pattern using a reference length which does not rely on the shape of the object and the corresponding using a reference position are performed, robust 3D shape measurement can be performed on a region which has a rough region which does not accept use of a 2D code pattern and a narrow region. 
     Fourth Embodiment 
     In the third embodiment, the angle of field of the projector  101  and the angle of field of the camera  103  are the same as each other and the focal planes are located in the same position, and therefore, the reference line pattern is detected with ease. However, it is not necessarily the case that the focal planes are arranged in the same position.  FIG. 19  is a diagram illustrating a configuration in a case where a focal plane of a projector  101  and a focal plane of a camera  103  are not parallel to each other.  FIG. 20 a    is a diagram illustrating an obtained imaging line pattern  2001 . In this condition, a projection line pattern is distorted in a trapezoid shape and a line width of a reference line pattern  2002  becomes larger toward a bottom portion, and accordingly, it is difficult to detect the reference line pattern  2002 . Therefore, a pattern light correction unit  1901  may be additionally provided so as to perform correction such that a projection line pattern  2003  is distorted in a reversed trapezoid shape as illustrated in  FIG. 20 b    at a time of projection. By this, a reference line pattern  2004  in which distortion is cancelled can be obtained as illustrated in  FIG. 20 c   , and accordingly, detection is performed with ease. 
     The pattern light correction unit  1901  may correct distortion caused by a projection optical system of the projector  101  in addition to the trapezoid distortion described above. By this, more reliable and more robust detection of a reference line pattern and a more reliable and more robust 3D shape measurement can be performed. 
     Furthermore, although only one reference line pattern is set in this embodiment, the number of reference positions may be increased by projecting a plurality of reference line patterns so that more robust corresponding is attained. 
     When a plurality of reference line patterns are disposed, reference length arrays W refb  may be assigned to the reference line patterns in accordance with a random sequence having low cross-correlativity so that detection is facilitated. As the random sequence of low cross-correlativity, the de Bruijn sequence described in the first embodiment is known. When the de Bruijn sequence is used, robust detection of a reference line pattern can be performed even on a captured image in which image noise is observed or only a portion of the reference line pattern is observed due to discontinuity of an object. 
     Fifth Embodiment 
     Although the case where the projection position of the reference line pattern is dynamically changed in accordance with the position of the object is described as an example in the second embodiment, all projection line pattern may be dynamically changed. For example, if density or line widths of all projection line patterns are changed, even when contrast of an imaging line patterns is degraded due to peripheral light, robust measurement can be continued. 
       FIG. 21  is a diagram illustrating a system configuration according to a fifth embodiment. A pattern generation unit  2101  which is an example of a pattern generation device dynamically generates projection line pattern data used for projection performed by a projector  101  (pattern data generation). The projection line pattern data generated here has at least two directions and has projection line patterns including at least two or more lines in each of the directions. Furthermore, at least the projection line patterns corresponding to one of the directions have intersections with the at least two projection line patterns corresponding to the other direction. A reference line pattern arranged in the projection line patterns is characterized by changing widths of the line pattern for individual line pattern segments defined by adjacent intersections. 
     The projection line pattern data generated in accordance with the rule described above is the same as the projection line patterns illustrated in  FIG. 14  of the third embodiment, and is used as pattern light projected by the projector  101  in step S 1301 . Hereinafter, a shape of an object can be measured by executing an operation the same as that of the third embodiment. Furthermore, in addition to the operation of the third embodiment, the projection line pattern data generated in the pattern generation unit  2101  is changed in accordance with results of the extraction of the imaging vertical line patterns  1502  and the imaging horizontal line patterns  1503  in step S 1303  and step S 1304 , respectively. When the imaging vertical line patterns  1502  and the imaging horizontal line patterns  1503  are not stably extracted, density of all the projection line patterns is made lower and line widths are made larger. When the imaging vertical line patterns  1502  and the imaging horizontal line patterns  1503  are stably extracted, density of all the projection line patterns is made higher and line widths are made smaller. As described above, by changing projection pattern data, image capturing can be performed even when contrast of the image line patterns is lowered due to peripheral light, and simultaneously, image capturing with density which is as high as possible can be performed. 
     Note that the projection vertical line patterns, the reference line pattern, and the projection horizontal line patterns are projected in red and blue so that extraction is performed by color coding without interfering with one another. However, depending on wavelengths of colors to be used, the colors may interfere with each other which causes a problem at a time of extraction. To minimize such mutual interference, projection line pattern data using a reference line pattern  2201  illustrated in  FIG. 22  may be generated. Widths of center portions of line pattern segments defined by adjacent intersections are changed and areas of intersections between a reference line pattern and projection horizontal line patterns are made smaller so that the mutual interference can be made as small as possible. Here, the term “center portions of line pattern segments” represents line pattern segments within predetermined ranges from the centers of the line pattern segments. 
     As described above, according to the embodiments described above, a pattern can be appropriately detected under a circumstance in which a sufficiently-large plane in vertical and horizontal directions is not obtained such as a region having a rough surface or a narrow region. Furthermore, according to the foregoing embodiments, references are not required to be embedded in regions surrounded by grids or the like, and therefore, fine patterns can be attained and shape measurement can be performed more precisely. That is, according to the foregoing embodiments, patterns can be projected with higher density and 3D shape measurement can be performed on a rough region or a narrow region. 
     Other Embodiments 
     Aspects of the present invention can also be realized by a computer of a system or apparatus (or devices such as a CPU or MPU) that reads out and executes a program recorded on a memory device to perform the functions of the above-described embodiments, and by a method, the steps of which are performed by a computer of a system or apparatus by, for example, reading out and executing a program recorded on a memory device to perform the functions of the above-described embodiments. For this purpose, the program is provided to the computer for example via a network or from a recording medium of various types serving as the memory device (e.g., computer-readable medium). 
     The present invention is not limited to the foregoing embodiments and various changes and modifications may be made without departing from the scope and the range of the present invention. Accordingly, claims below are attached in order to disclose the range of the present invention. 
     This application claims the benefit of Japanese Patent Application No. 2009-289614, filed Dec. 21, 2009, which is hereby incorporated by reference herein in its entirety.