Patent Publication Number: US-10776945-B2

Title: Dimension measurement device, dimension measurement system, and dimension measurement method

Description:
This application is a National Stage Entry of PCT/JP2016/003389 filed on Jul. 19, 2016, which claims priority from Japanese Patent Application 2015-145623 filed on Jul. 23, 2015, the contents of all of which are incorporated herein by reference, in their entirety. 
     TECHNICAL FIELD 
     The present invention relates to a dimension measurement device, a dimension measurement system, and a dimension measurement method for measuring dimensions of an object. 
     BACKGROUND ART 
     A following method is proposed as a method for measuring an object using an image captured by a camera. Specifically, a measurer disposes or projects a marker (reference scale) having a pattern indicating a length reference in dimension on a measurement surface (a surface of a measuring object, or an extension plane of a measuring object), and captures an image of the reference scale and an object that is a measuring object by an imaging device, such as a camera, in such a manner that the reference scale and the object both fall within the image. Then, a measurement device calculates a ratio between the reference scale and the measuring object from data on the above-mentioned image, and calculates and outputs dimensions (a length, an area, a circumferential length, and the like) of the measuring object. 
     PTL 1 describes a method for accurately measuring dimensions by converting an image which is obliquely captured and indicates a rectangular marker with known dimensions on a measurement surface, into a front image. 
     PTL 2 describes a method for measuring dimensions of a rectangular parallelepiped by using a marker with known dimensions on a measurement surface. 
     PTL 3 describes a technique for measuring, by using a marker including a combination of a lenticular lens and a black and white pattern, a relative relationship (a position, an angle, and the like) between the marker and an observed object obtained by observing the marker, from a grayscale pattern of the marker. 
     CITATION LIST 
     Patent Literature 
     [PTL 1] Japanese Unexamined Patent Application Publication No. 2014-025748 
     [PTL 2] Japanese Unexamined Patent Application Publication No. 2003-303222 
     [PTL 3] Japanese Unexamined Patent Application Publication No. 2012-145559 
     [PTL 4] Japanese Translation of PCT International Application Publication No. 2008-539437 
     [PTL 5] Japanese Unexamined Patent Application Publication No. 2002-286420 
     SUMMARY OF INVENTION 
     Technical Problem 
     In PTL 1, an image obliquely captured can be converted into a front image. However, when the rectangular marker (reference scale) is neither disposed nor projected on a measurement surface (for example, deviates from the measurement surface), accuracy of measuring dimensions deteriorates. 
     PTL 2 describes a method for measuring dimensions of a rectangular parallelepiped by using a marker with known dimensions on a measurement surface. However, it is difficult to maintain dimension measurement accuracy when a reference scale is neither disposed nor projected on the measurement surface. 
     PTL 3 is a technique in which a marker including a combination of a lenticular lens and a black and white pattern is used to measure a relative relationship (a position, an angle, and the like) between the marker and an observed object obtained by observing the marker. However, PTL 3 is not a technique for accurately measuring dimensions of a measuring object. 
     In the case of measuring dimensions by the methods described in PTL 1 and PTL 2 described above, it is necessary to dispose or project a reference scale on a measurement surface. However, a case where it is difficult to dispose or project a reference scale on a measurement surface, and a case where the reference scale is inclined with respect to the measurement surface due to a change over time in a dimension measurement system are not assumed. There is a demand for a technique to measure dimensions without deteriorating measurement accuracy in the above-mentioned cases. 
     The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a dimension measurement device, a dimension measurement system, and a dimension measurement method which are capable of maintaining measurement accuracy even when a reference scale is neither disposed nor projected on a measurement surface. 
     Solution to Problem 
     A dimension measurement device comprising: 
     reference scale extraction means that extracts an image obtained by forming an image of a length reference from captured image data including a reference scale, based on a relationship between a pattern function and an image formation color function indicating the length reference whose image is formed on an imaging device, the pattern function indicating the length reference displayed on a lens depending on a change of a predetermined angle formed between an optical axis of the imaging device and the reference scale, the reference scale including a film having a pattern for displaying the length reference and the lens in contact with the film; 
     measuring object extraction means that extracts an image of a measuring object from captured image data including the reference scale; 
     and dimension calculation means that calculates dimensions of the measuring object, based on dimensions of an image obtained by forming an image of the length reference and an image of the measuring object. 
     A dimension measurement method comprising: 
     extracting an image obtained by forming an image of a length reference from captured image data including a reference scale, based on a relationship between a pattern function and an image formation color function indicating the length reference whose image is formed on an imaging device, the pattern function indicating the length reference displayed on a lens depending on a change of a predetermined angle formed between an optical axis of the imaging device and the reference scale, the reference scale including a film having a pattern for displaying the length reference and the lens in contact with the film; 
     extracting an image of a measuring object from captured image data including the reference scale; and 
     calculating dimensions of the measuring object, based on dimensions of an image obtained by forming an image of the length reference and an image of the measuring object. 
     Advantageous Effects of Invention 
     According to a dimension measurement device of the present invention, an advantageous effect that measurement accuracy can be maintained even when a reference scale is neither disposed nor projected on a measurement surface can be obtained. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram illustrating an example of a configuration of a reference scale according to a first example embodiment of the present invention; 
         FIG. 2  is an enlarged sectional view illustrating a part of the reference scale according to the first example embodiment of the present invention; 
         FIG. 3  is a diagram for illustrating the principle of the reference scale according to the first example embodiment of the present invention; 
         FIG. 4  is a diagram illustrating an example of a dimension measurement system using the reference scale according to the first example embodiment of the present invention; 
         FIG. 5  is a functional block diagram illustrating an example of a functional configuration of each of a dimension measurement device and a storage device in the dimension measurement system according to the first example embodiment of the present invention; 
         FIG. 6  is a diagram illustrating an example of a processing flow in the dimension measurement device according to the first example embodiment of the present invention; 
         FIG. 7  is a diagram illustrating an example of a configuration of a reference scale according to a second example embodiment according to the present invention; 
         FIG. 8  is a diagram illustrating an example of a configuration of a reference scale according to a third example embodiment according to the present invention; 
         FIG. 9  is a diagram illustrating an example of a configuration of a reference scale according to a fourth example embodiment according to the present invention; 
         FIG. 10  is a diagram illustrating an example of a configuration of a reference scale according to a fifth example embodiment of the present invention; and 
         FIG. 11  is a diagram illustrating an example of a configuration of a dimension measurement device according to a sixth example embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Exemplary Embodiment 
     A first example embodiment of the present invention will be described in detail with reference to the drawings. 
     The first example embodiment is directed to a dimension measurement system  100  ( FIG. 4 ). Hereinafter, a reference scale  3000  is mainly described with reference to  FIGS. 1 to 3  and then the entire dimension measurement system  100  is described with reference to  FIG. 4  to  FIG. 6 . The reference scale  3000  and the dimension measurement system  100  according to the present invention are not limited to the configurations and processing illustrated in  FIGS. 1 to 6 . 
       FIG. 1  is a diagram illustrating an example of a configuration of a reference scale  3000  according to the first example embodiment. 
     As illustrated in  FIG. 1 , the reference scale  3000  according to this example embodiment includes a film  2000  and a lenticular lens  1000  which is attached onto an upper surface of the film  2000 . 
     The film  2000  is a thin-film member having a surface on which a pattern of a predetermined black pattern is formed by printing or the like on a white film member, or a thin-film member having a surface on which a pattern of a predetermined white pattern is formed by printing or the like on a black film member. The film  2000  may be formed by a combination of white and black films, or by forming a pattern by polarization using a combination of polarizing plates having different polarization directions. The pattern of the film  2000  may be displayed on a liquid crystal monitor. The configuration of the film  2000  and the method for forming the pattern of the film  2000  are not limited to those illustrated in  FIG. 1 . 
     The film  2000  may be disposed at a focal length of the lenticular lens  1000  from an optical center thereof. However, in actual use, the location where the film  2000  is disposed may deviate from the focal length within an allowable range of measurement errors. Referring to  FIG. 1 , the lenticular lens  1000  is used as an example of the lens of the reference scale  3000 . However, the lens used for the reference scale  3000  according to this example embodiment is not limited to this lens. 
     The principle that variations in the pattern on the film  2000  indicating a length reference observed from a viewpoint of an imaging device  5000  (see  FIG. 3 ) is reduced even when the reference scale  3000  according to this example embodiment is disposed with an inclination with respect to a measurement surface  200  (see  FIG. 3 ), or the angle formed between the reference scale  3000  and the measurement surface  200  changes due to a change over time will be described. 
       FIG. 2  is an enlarged sectional view illustrating a part of the reference scale  3000  according to the first example embodiment of the present invention. 
     Referring first to  FIG. 2  and focusing on one flat-convex cylindrical lens  1000 A of the lenticular lens  1000 , a positional relationship between a sight line angle and an enlarged pattern displayed on the lens will be described in detail. 
     The lenticular lens  1000  has a structure in which a large number of flat-convex cylindrical lenses  1000 A are arranged in one direction.  FIG. 2  is a sectional view illustrating a surface orthogonal to a generatrix direction in one flat-convex cylindrical lens (hereinafter, also referred to simply as a lens)  1000 A of the lenticular lens  1000 . A generatrix refers to an axis that is parallel to a Y-axis in  FIG. 1  in a direction in which image formation ability of the flat-convex cylindrical lens  1000 A is not present. 
     It is assumed that a lens pitch is represented by P L  and a focal length is represented by f. As described above, the film  2000  (specifically, the pattern of the film  2000 ) may be disposed at a position of the focal length f of the lens from the optical center thereof. Accordingly, in the following discussion, it is assumed that the lenticular lens  1000  having the focal length f is used and the reference scale  3000  has a configuration in which the film  2000  is disposed immediately below the lenticular lens  1000 . An X-axis is set in a direction orthogonal to the generatrix direction on a bottom surface of the lenticular lens  1000 , and a coordinate system is determined in such a manner that an intersection between an optical axis  400  and the bottom surface of the lenticular lens  1000  is set as an origin O. When an angle (sight line angle) formed between an observation sight line (an optical axis  300  of the imaging device  5000  illustrated in  FIG. 3 ) and the optical axis  400  is represented by θ, the following formula is established at a position x on the X-axis of the film  2000  that is enlarged and displayed on the lens.
 
[Formula 1]
 
 x=−f ·tan θ  (1)
 
     As illustrated on the left side of  FIG. 2 , a state where the sight line angle is the same as the optical axis  400  of the lenticular lens  1000  and is vertical to the reference scale  3000  corresponds to θ=0 (deg), and thus the pattern of the film  2000  at a position of x=−f·tan θ=0 is enlarged and displayed on the lens  1000 A. 
     As illustrated on the right side of  FIG. 2 , when an angle θ is set in such a manner that the sight line angle is not 0 (deg), the pattern located at the position of x=−f·tan θ is enlarged and displayed on the lens  1000 A. 
     Next, a behavior of the reference scale  3000  when a plurality of lenses constituting the lenticular lens  1000  are considered will be described with reference to  FIG. 3 .  FIG. 3  is a diagram for illustrating the principle of the reference scale  3000  according to the first example embodiment of the present invention. 
     Referring to  FIG. 3 , the reference scale  3000  is installed with an inclination of the angle θ with respect to the measurement surface  200 , and is observed by the imaging device  5000  from a position apart from a distance L from the measurement surface  200 . It is assumed that the optical axis  300  of the imaging device  5000  is vertical to the measurement surface  200 . Description is made here by using a camera as the imaging device  5000 , but the camera is merely an example and not limited, and the reference scale may be observed with human eyes. In the imaging device  5000 , a distance A between an image formation lens  5100  and a sensor surface  5200  is adjusted so that the imaging device  5000  comes into focus on a plane of the distance L. Specifically, when the focal length of the image formation lens  5100  is represented by F, the following formula 
                   [     Formula   ⁢           ⁢   2     ]                               1   A     +     1   L       =     1   F             (   2   )               
is satisfied for the lens of the imaging device  5000 .
 
     In  FIG. 3 , a U-axis is an axis in a direction along the sensor surface  5200 . An origin in the coordinate system is an intersection between the optical axis  300  and the measurement surface  200 . The total number of lenses of the lenticular lens  1000  of the reference scale  3000  according to this example embodiment is represented by N L , and the lenses are assigned numbers of 0 to (N L −1) in order from the lens  1000 A which is located at one end of the lenticular lens  1000 , (0th lens  1000  ( 0 ) to (N L −1)th lens  1000 (N L −1)). The X-axis is set on the bottom surface of the lenticular lens  1000 , and the coordinate system in which the center position of the reference scale  3000  is set as an origin is determined. 
     A position (coordinates) x k  on the X-axis of the k-th lens  1000 (K) is expressed by the following formula using a lens pitch P L . 
     
       
         
           
             
               
                 
                   [ 
                   
                     Formula 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     3 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     x 
                     k 
                   
                   = 
                   
                     
                       ( 
                       
                         k 
                         - 
                         
                           
                             
                               N 
                               L 
                             
                             - 
                             1 
                           
                           2 
                         
                       
                       ) 
                     
                     · 
                     
                       P 
                       L 
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
     As discussed above, the lenticular lens  1000  has a function of enlarging and displaying different positions on the X-axis of the pattern of the film  2000  below the lenticular lens  1000  according to the angle of the observation sight line. When the formula (1) is used, it is obvious that when the sight line angle is θ, the pattern located at a position x k −f·tan θ on the X-axis is enlarged and displayed on the k-th lens  1000 (K). The color of the pattern located at this position is represented by C(x k −f·tan θ). C(x k −f·tan θ) is also referred to as a pattern function C. 
     Next, in the imaging device  5000 , at which position on the sensor surface  5200  the image of the pattern of the film  2000  that is enlarged and displayed on the lenticular lens  1000  is formed will be described continuously with reference to  FIG. 3 . The angle θ formed between the optical axis  300  of the imaging device  5000  and the optical axis  400  of the lenticular lens  1000  corresponds to the sight line angle θ that is discussed above with reference to  FIG. 2 . The optical center position x k  of the k-th lens  1000 (K) is focused at a position u k  on the U-axis given by the following formula in consideration of the sight line angle θ. 
     
       
         
           
             
               
                 
                   [ 
                   
                     Formula 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     4 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     u 
                     k 
                   
                   = 
                   
                     
                       F 
                       
                         L 
                         - 
                         F 
                       
                     
                     ⁢ 
                     
                       x 
                       k 
                     
                     ⁢ 
                     cos 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     θ 
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
     Formula (4) is approximated assuming that a value x k ·cos θ, which is generated when the reference scale  3000  is inclined with the angle θ, is sufficiently smaller than the distance L between the imaging device  5000  and the measurement surface  200  (L&gt;&gt;x k ·cos θ). A color of an image formed at this position on the sensor surface  5200  is represented by H(u k ). The image formed on the sensor surface  5200  is subjected to, for example, spectroscopic processing or analog-to-digital conversion processing using a camera by the dimension measurement system  100  described below, and is then subjected to image processing such as demosaicing or noise removal and converted into a final observation value. If the sensor surface  5200  is a human eye, the sensor corresponds to a retina. An image formed on the retina becomes an electric signal by optic cells and the electric signal is subjected to processing in a visual cortex and is then converted into an observation value that is perceived by a human. The observation value that is subjected to the conversion and located at the position “u” on the sensor surface  5200  is represented by I(u). An observation value function can be considered assuming that, for example, the observation value represented by I(u) is “1” when the color of an image formed at the position “u” on the sensor surface  5200  is white, and is “0” when the color of the image is black. The observation value function having two values as described above is illustrated by way of example. The observation value may be a scalar value such as a luminance value, or a vector value such as a RGB (Red Green Blue) color value, or an HSV (Hue Saturation Value) color value. In addition, the observation value may be an optical physical quantity such as a light wavelength, a phase, polarization characteristics, a radiant intensity, or a modulation amount, or a psychophysical quantity such as a definition or glossiness, and thus the observation value is not limited. 
     It is assumed herein that a given observation value function Ω(u) is predetermined and an image formation color function H(u) corresponding to the observation value function can be also calculated in advance. The image of the pattern that is enlarged and displayed on the k-th lens  1000 (K) of the reference scale  3000  is formed at the position u k  on the U-axis represented by Formula (4). Even when the reference scale  3000  is disposed with an inclination with reference to the measurement surface  200 , or the positional relationship between the reference scale  3000  and the measurement surface  200  is changed due to a change over time, in order to reduce variations in the pattern indicating the length reference observed from the viewpoint of the imaging device  5000 , i.e., the actual observation value I(u), the pattern of the film  2000  may be determined in such a manner that the color of pattern (pattern function C) that is enlarged and displayed on the lenticular lens  1000  of the reference scale  3000  and an image formation color function H(u k ) satisfy the following relational expression.
 
[Formula 5]
 
 C ( x   k   −f  tan θ)= H ( u   k ))  (5)
 
     The position where the lenticular lens  1000  forms an image of the pattern on the sensor surface  5200  is discrete (see Formula (6)).
 
[Formula 6]
 
 u={u   0   ,u   1   , . . . ,u   N     L-1   }  (6)
 
     Accordingly, the lenticular lens  1000  having the lens pitch P L  of a sufficiently small value may be selected so that the actual observation value I(u) has a sufficient resolution with respect to the given observation value function Ω(u). 
     A method for designing the pattern function C in such a manner that variations in the pattern indicating the length reference observed from the viewpoint of the imaging device  5000  is reduced even when the reference scale  3000  is disposed with an inclination with respect to the measurement surface  200 , or the angle formed between the reference scale  3000  and the measurement surface  200  is changed due to a change over time will be described below. 
     It is assumed that the pattern indicating the length reference is a white belt-like pattern having a width of 10 cm on a black background. It is also assumed that a camera is used as the imaging device  5000 . It is assumed that the focal length of the image formation lens  5100  in the imaging device  5000  is F=75 mm and the distance between the imaging device  5000  and the measurement surface  200  is L=3 m. 
     An image sensor of the imaging device  5000  has black and white 256 tones and a pixel size of a 2.5 μm square lattice shape. Parameters described herein are examples for explanation and are not limited to these values. 
     Under the conditions described above, the white belt-like pattern having a width of 10 cm corresponds to the following formula. 
     
       
         
           
             
               
                 
                   [ 
                   
                     Formula 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     7 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     
                       F 
                       
                         L 
                         - 
                         F 
                       
                     
                     × 
                     10 
                     × 
                     
                       10 
                       
                         - 
                         2 
                       
                     
                     × 
                     
                       1 
                       
                         2.5 
                         × 
                         
                           10 
                           
                             - 
                             6 
                           
                         
                       
                     
                   
                   ≈ 
                   
                     1000 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       ( 
                       pixels 
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   7 
                   ) 
                 
               
             
           
         
       
     
     The size of the formed image on the sensor surface  5200  is 2.5 mm. It is assumed that the observation value function Ω(u) has a predetermined threshold for a pixel value of captured image data, and the function is “1” for the threshold or more and is “0” for other values. According to this function, the given observation value function Ω(u) is defined as follows. 
     
       
         
           
             
               
                 
                   [ 
                   
                     Formula 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     8 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     Ω 
                     ⁡ 
                     
                       ( 
                       u 
                       ) 
                     
                   
                   = 
                   
                     { 
                     
                       
                         
                           1 
                         
                         
                           
                             
                               - 
                               1.25 
                             
                             &lt; 
                             u 
                             ≤ 
                             1.25 
                           
                         
                       
                       
                         
                           0 
                         
                         
                           otherwise 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   8 
                   ) 
                 
               
             
           
         
       
     
     Each of −1.25 and 1.25 are expressed in units of mm and represents a length from a right boundary to a left boundary when u=0 is the central position because, as described above, the size of the image obtained by forming an image of the white belt-like pattern is 2.5 mm. 
     The corresponding image formation color function H(u) is expressed by the following formula. 
     
       
         
           
             
               
                 
                   [ 
                   
                     Formula 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     9 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     H 
                     ⁡ 
                     
                       ( 
                       u 
                       ) 
                     
                   
                   = 
                   
                     { 
                     
                       
                         
                           white 
                         
                         
                           
                             
                               - 
                               1.25 
                             
                             &lt; 
                             u 
                             ≤ 
                             1.25 
                           
                         
                       
                       
                         
                           black 
                         
                         
                           otherwise 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   9 
                   ) 
                 
               
             
           
         
       
     
     When Formula (5) is used, the pattern function C(x k −f·tan θ) is obtained as follows. 
     
       
         
           
             
               
                 
                   [ 
                   
                     Formula 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     10 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     C 
                     ⁡ 
                     
                       ( 
                       
                         
                           x 
                           k 
                         
                         - 
                         
                           f 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           tan 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           θ 
                         
                       
                       ) 
                     
                   
                   = 
                   
                     { 
                     
                       
                         
                           white 
                         
                         
                           
                             
                               - 
                               1.25 
                             
                             &lt; 
                             
                               u 
                               k 
                             
                             ≤ 
                             1.25 
                           
                         
                       
                       
                         
                           black 
                         
                         
                           otherwise 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   10 
                   ) 
                 
               
             
           
         
       
     
     Thus, the pattern function is defined by the position x k −f·tan θ on the pattern enlarged and displayed by the lens  1000 (K), and the value of the image formation color function H(u k ) at the position u k  where the image is formed on the sensor surface  5200  of the lens  1000 (K). 
     As described above, the reference scale  3000  according to this example embodiment is characterized by including a film having the pattern determined by the pattern function C, and the lenticular lens  1000  disposed on the film. The pattern function of the pattern is a function of one variable defined in the direction orthogonal to the generatrix direction of the lenticular lens  1000 . The pattern formed at the position enlarged and displayed by the lens  1000 (K) is a given image formation pattern defined at the image formation position of the lens  1000 (K) in the imaging device  5000 . Accordingly, the pattern of the film  2000  is a one-dimensional pattern. It is considered that the pattern indicating the length reference to be observed is, for example, a striped one-dimensional pattern. 
     With this configuration, when the angle between the reference scale  3000  and the measurement surface  200  is changed about the axis in the generatrix direction of the lenticular lens  1000 , the reference scale  3000  enlarges and displays different positions of the pattern of the film  2000  disposed below the lenticular lens  1000  by the function of the lenticular lens  1000 . Thus, variations in the pattern indicating the length reference to be observed in the imaging device  5000 , i.e., the observation value I(u), are suppressed. 
     As described above, according to the reference scale  3000 , even when the angle between the reference scale  3000  and the measurement surface  200  is changed about the axis in the generatrix direction of the lenticular lens  1000 , variations in the pattern indicating the length reference to be observed in the imaging device  5000 . Consequently, an advantageous effect that dimension measurement accuracy can be continuously maintained even when the reference scale  3000  is disposed with an inclination with respect to the measurement surface  200 , or the angle between the reference scale  3000  and the measurement surface  200  is changed about the axis in the generatrix direction of the lenticular lens  1000  due to a change over time can be obtained. 
       FIG. 4  is a diagram illustrating an example of the dimension measurement system  100  using the reference scale  3000  according to the first example embodiment. 
     As illustrated in  FIG. 4 , a dimension measurement system  100  is a system for measuring dimensions of a measuring object  4000 . As illustrated in  FIG. 4 , the dimension measurement system  100  includes a reference scale  3000 , the measuring object  4000 , an imaging device  5000 , a dimension measurement device  6000 , a storage device  7000 , and a display device  8000 . As illustrated in  FIG. 4 , an optical axis  300  of the imaging device  5000  is installed vertically to a measurement surface  200 . The measurement surface  200  indicates a surface or section on which measurement of the measuring object  4000  is performed, or an extension plane thereof. The reference scale  3000  may be installed in such a manner that a bottom surface of the reference scale  3000  is disposed on the measurement surface  200 . However, the position of the reference scale may deviate in the direction of the optical axis  300  of the imaging device  5000  within the allowable range of measurement errors in actual use. 
     The devices are connected to each other by using, for example, a LAN (Local Area Network) cable or the like. This example embodiment is not limited to this, but instead the devices may be connected to each other wirelessly. 
     The imaging device  5000  is a device that captures images of the reference scale  3000  and the measuring object  4000 . The imaging device  5000  is implemented by, for example, a general digital camera, web camera, or the like which is capable of outputting image data having a number of pixels enough to observe an image region including the measuring object  4000  and the reference scale  3000 . The imaging device  5000  is implemented by, for example, a web camera including a CCD (Charge Coupled Device) image sensor or a CMOS (Complementary Metal-Oxide-Semiconductor) image sensor having 1920×1080 pixels to be output, or the like, but the present invention is not limited to this.  FIG. 4  illustrates a configuration in which images of the reference scale  3000  and the measuring object  4000  are simultaneously captured, but the present invention is not limited to this configuration. Images of the reference scale  3000  and the measuring object  4000  may be captured at different timings. The imaging device  5000  transmits image data (captured image data) indicating the captured images of the reference scale  3000  and the measuring object  4000  to the dimension measurement device  6000 . 
     The dimension measurement device  6000  receives the captured image data from the imaging device  5000 . The dimension measurement device  6000  measures dimensions of the measuring object  4000  by using the received captured image data. A specific functional configuration of the dimension measurement device  6000  will be described with reference to  FIG. 5  by changing the drawing. 
     The storage device  7000  is a device in which the dimensions of the reference scale  3000  are stored in advance. 
     The dimensions of the reference scale  3000  indicate actual dimension values (in units of, for example, cm) of the pattern indicating the length reference to be observed. For example, the pattern defined by the pattern function as illustrated above stores information indicating that “a white belt-like region has a length of 10 cm”. 
     The display device  8000  is a means that displays processing results of the dimension measurement device  6000 , or image data captured by the imaging device  5000 . 
     Referring next to  FIG. 5 , the functional configuration of the dimension measurement device  6000  according to this example embodiment will be described.  FIG. 5  is a functional block diagram illustrating an example of each functional configuration of the dimension measurement device  6000  and the storage device  7000  in a dimension measurement system  100  according to this example embodiment.  FIG. 5  also illustrates the imaging device  5000  and the display device  8000 . 
     As illustrated in  FIG. 5 , the dimension measurement device  6000  includes a reference scale extraction unit  6100 , a measuring object extraction unit  6200 , and a dimension calculation unit  6300 . 
     The reference scale extraction unit  6100  receives captured image data from the imaging device  5000 . 
     The reference scale extraction unit  6100  extracts an image region (also referred to as an observed pattern) of the pattern of the film  2000  indicating the length reference displayed on the lenticular lens  1000  of the reference scale  3000  from the captured image represented by the received captured image data. Specifically, the reference scale extraction unit  6100  distinguishes the above-mentioned captured image from the observed pattern and other regions by using color information, and extracts the region distinguished as the above-mentioned observed pattern from the captured image data. As the observed pattern of the reference scale  3000 , an example in which a white belt-like pattern is formed on a black background and two values are taken is illustrated in the design of the above-mentioned pattern function. Accordingly, the reference scale extraction unit  6100  may extract the above-mentioned observed pattern by using the features of the colors and the pattern for the extraction processing described above. Alternatively, the observed pattern may be extracted by a manual operation using image analysis software. The observed pattern extraction processing performed by the reference scale extraction unit  6100  uses a general method, and thus the description thereof is omitted in this example embodiment. 
     The measuring object extraction unit  6200  receives captured image data from the imaging device  5000 . The measuring object extraction unit  6200  extracts the image region of the measuring object  4000  from the captured image represented by the received captured image data. Specifically, the measuring object extraction unit  6200  distinguishes the above-mentioned captured image from the measuring object  4000  and other regions by using color information, and extracts the region distinguished as the above-mentioned measuring object  4000  from the captured image data. Alternatively, the image region of the measuring object  4000  may be extracted by a manual operation using the image analysis software. The processing for extracting the measuring object  4000  performed by the measuring object extraction unit  6200  is not particularly limited and a general method is used. Accordingly, the description thereof is omitted in this example embodiment. 
     The dimension calculation unit  6300  receives the image regions of the observed pattern generated by the reference scale extraction unit  6100  and the measuring object  4000  generated by the measuring object extraction unit  6200  from the reference scale extraction unit  6100  and the measuring object extraction unit  6200 , respectively. In general, for example, when the imaging device  5000  is a camera, pixels are used as the units of image data representing the image regions of the observed pattern and the measuring object  4000 . The dimensions of the observed pattern are represented by S P  (pixels), and the dimensions of the measuring object  4000  are represented by W P  (pixels). The actual dimension values of the measuring object  4000  are represented by W R  (cm). The units of the actual dimension values are cm. However, this is merely an example and the units of the actual dimension values are not limited. The dimension calculation unit  6300  is intended to calculate the actual dimension values W R  of the measuring object  4000 . Accordingly, the dimension calculation unit  6300  refers to the dimensions of the reference scale  3000  stored in the storage device  7000  (reference scale dimension storage unit  7100 ). The dimensions of the reference scale  3000  are actual dimension values S R  (cm) of the pattern indicating the length reference to be observed. The actual dimension values W R  of the measuring object  4000  can be calculated by the following formula. 
     
       
         
           
             
               
                 
                   [ 
                   
                     Formula 
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                     11 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     W 
                     R 
                   
                   = 
                   
                     
                       
                         S 
                         R 
                       
                       
                         S 
                         P 
                       
                     
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                       W 
                       P 
                     
                   
                 
               
               
                 
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     The dimension calculation unit  6300  supplies the calculated actual dimension value W R  of the measuring object  4000  to the display device  8000 . 
     In this case, the reference scale extraction unit  6100 , the measuring object extraction unit  6200 , and the dimension calculation unit  6300  are composed of, for example, hardware circuits such as logic circuits. 
     The storage device  7000  (reference scale dimension storage unit  7100 ) is composed of, for example, a storage device such as a disk device or a semiconductor memory. 
     The display device  8000  is composed of, for example, a display. 
     Referring next to  FIG. 6 , an operation of the dimension measurement system  100  according to this example embodiment in the dimension measurement device  6000  will be described.  FIG. 6  is a diagram illustrating an example of a processing flow in the dimension measurement device  6000 . 
     As illustrated in  FIG. 6 , the reference scale extraction unit  6100  extracts, from the captured image data transmitted from the imaging device  5000 , the observed pattern (the image region of the pattern indicating the length reference displayed on the lenticular lens  1000  of the reference scale  3000 ) (step S 10 ). 
     Next, the measuring object extraction unit  6200  extracts the image region of the measuring object  4000  from the captured image data transmitted from the imaging device  5000  (step S 20 ). 
     Next, the dimension calculation unit  6300  calculates the actual dimension values of the measuring object  4000  from the actual dimension values S R  of the observed pattern of the reference scale stored in the storage device  7000 , the observed pattern extracted in step S 10 , and the image region of the measuring object  4000  extracted in step S 20  (step S 30 ). 
     This processing allows the dimension measurement device  6000  to measure the dimensions of the measuring object  4000  as actual dimension values. 
     As described above, according to the dimension measurement system  100  of this example embodiment, an advantageous effect that the measurement accuracy can be maintained even when the reference scale  3000  is neither disposed nor projected on the measurement surface is obtained. 
     This is because the dimension measurement system  100  includes the following configuration. First, the dimension measurement system  100  includes the reference scale  3000  including both the film  2000  having the pattern for displaying the length reference and the lenticular lens  1000  in contact with the film  2000 . Second, the reference scale extraction unit  6100  of the dimension measurement device  6000  utilizes the relationship between the pattern function indicating the length reference displayed on the lens according to a change of a predetermined angle formed between the reference scale and the optical axis  300  of the imaging device  5000 , and the image formation color function indicating the length reference whose image is formed on the imaging device. Specifically, the reference scale extraction unit  6100  extracts the image of the length reference formed on the imaging device from the captured image data including the reference scale  3000 , based on the relationship. 
     Second Exemplary Embodiment 
     Next, a second example embodiment of the present invention will be described in detail with reference to the drawings. 
       FIG. 7  is a diagram illustrating an example of a configuration of a reference scale  3100  according to the second example embodiment. 
     It is assumed that the reference scale  3100  operates in the dimension measurement system  100  like in the first example embodiment. 
     As illustrated in  FIG. 7 , the reference scale  3100  according to this example embodiment includes a film  2100  on which a pattern is formed, and a lens  1100  which is attached onto an upper surface of the film  2100 . The film  2100  may be disposed at the position of the focal length of the lens  1100  from the optical center thereof. However, the location where the film  2100  is disposed may deviate from the focal length within the allowable range of measurement errors in actual use. While  FIG. 7  illustrates that a lens array is used as an example of the lens  1100 , the lens  1100  used for the reference scale  3100  according to this example embodiment is not limited to this. 
     Differences between the reference scale  3000  illustrated in  FIG. 1  and the reference scale  3100  in  FIG. 7  will be described. The pattern function of the film  2000  of the reference scale  3000  illustrated in  FIG. 1  is a function of one variable defined in the direction orthogonal to the generatrix direction of the lenticular lens. However, the pattern function of the film  2100  of the reference scale  3100  illustrated in  FIG. 7  is a two-variable function defined on a plane containing the X-axis and the Y-axis. The pattern function is a given image formation color function in which the pattern at the position enlarged and displayed by the lens  1100  is defined at the image formation position in the imaging device  5000  of the lens  1100 . Accordingly, the pattern of the film  2100  is a two-dimensional pattern. The pattern indicating the length reference to be observed can be, for example, a checker board-like two-dimensional pattern. 
     As described above, according to the reference scale  3100  of this example embodiment, variations in the pattern on the film  2100  indicating the length reference to be observed in the imaging device  5000  is suppressed even when the reference scale  3000  is disposed with an inclination with respect to the measurement surface  200 , or the angle formed between the reference scale  3100  and the measurement surface  200  is changed due to a change over time. In the reference scale  3000  illustrated in  FIG. 1 , the advantageous effect that variations in the pattern indicating the length reference to be observed in the imaging device  5000  are suppressed is obtained only for a change in the angle about one axis only in the generatrix direction of the lens, while in the reference scale  3100  according to this example embodiment, this advantageous effect can be obtained even for both changes in angles about the X-axis and the Y-axis. 
     This is because the lens  1100  has a shape with which an advantageous effect similar to that of the lenticular lens can be obtained on a section on the X-axis as well as on a section of the Y-axis, and can obtain an advantageous effect similar to that of the first example embodiment. 
     According to the reference scale  3100  of this example embodiment, an advantageous effect that the measurement accuracy can be maintained even when the reference scale  3100  is neither disposed nor projected on the measurement surface, can be obtained even for both changes in angles about the X-axis and the Y-axis. 
     This is because the pattern function of the film  2100  of the reference scale  3100  is a two-variable function defined on a plane containing the X-axis and the Y-axis. Also, it is because the lens  1100  has a shape with which an advantageous effect similar to that of the lenticular lens can be obtained on a section on the X-axis as well as on a section of the Y-axis. 
     Third Exemplary Embodiment 
     Next, a third example embodiment of the present invention will be described in detail with reference to the drawings. 
       FIG. 8  is a diagram illustrating an example of the configuration of a reference scale  3200  according to the third example embodiment. 
     It is assumed that the reference scale  3200  operates in the dimension measurement system  100  like in the first example embodiment. 
     As illustrated in  FIG. 8 , the reference scale  3200  according to this example embodiment includes a film  2200  on which a pattern is formed, and a lens  1200  which is attached onto an upper surface of the film  2200 . The film  2200  may be disposed at the position of the focal length of the lens  1200  from the optical center thereof. However, the location where the film  2200  is disposed may deviate from the focal length within an allowable range of measurement errors in actual use. 
     Differences between the reference scale  3000  illustrated in  FIG. 1  and the reference scale  3200  in  FIG. 8  will be described below. In other words, each of the lens  1200  and the film  2200  of the reference scale  3200  illustrated in  FIG. 8  is a curved surface (including a flat surface) having any shape. On the other hand, the pattern function of the film  2200  is a two-variable function defined on the curved surface (including a flat surface). 
     As described above, according to the reference scale  3200  of this example embodiment, an advantageous effect similar to that of the reference scale  3000  illustrated in  FIG. 1  can be obtained, and another advantageous effect that the reference scale can be installed on a curved surface having any shape and the degree of freedom of installation is higher can be obtained. 
     This is because each of the lens  1200  and the film  2200  of the reference scale  3200  is a curved surface (including a flat surface) having any shape. On the other hand, this is because the pattern function of the film  2200  is a two-variable function defined on a curved surface (including a flat surface). 
     Fourth Exemplary Embodiment 
     Next, a fourth example embodiment of the present invention will be described in detail with reference to the drawings. 
       FIG. 9  is a diagram illustrating an example of a configuration of a reference scale  3300  according to the fourth example embodiment. 
     It is assumed that the reference scale  3300  operates in the dimension measurement system  100  like in the first example embodiment. 
     As illustrated in  FIG. 9 , the reference scale  3300  according to this example embodiment includes a film  2300  on which a pattern is formed, and a lens  1300  which is attached onto an upper surface of the film  2300 . The film  2300  may be disposed at the position of the focal length of the lens from the optical center thereof. However, the location where the film  2300  is disposed may deviate from the focal length within the allowable range of measurement errors in actual use. 
     Differences between the reference scale  3200  illustrated in  FIG. 8  and the reference scale  3300  in  FIG. 9  will be described below. In other words, each of the lens  1300  and the film  2300  of the reference scale  3300  illustrated in  FIG. 9  is a curved surface having any shape and is made of a deformable material. On the other hand, the pattern function of the film  2300  is a two-variable function defined on the curved surface (including a flat surface). 
     As described above, according to the reference scale  3300  of this example embodiment, an advantageous effect similar to that of the reference scale  3200  illustrated in  FIG. 8  can be obtained, and another advantageous effect that the reference scale can also be installed on a curved surface that is deformable and the degree of freedom of installation is higher can be obtained. Also, even when the reference scale  3300  according to this example embodiment is installed on a flat surface or a curved surface having a known shape, for example, the reference scale can be carried in a compact folded state, and thus there is also an advantageous effect that the transportation of the reference scale can be simplified. 
     This is because each of the lens  1300  and the film  2300  of the reference scale  3300  is a curved surface having any shape and is made of a deformable material. 
     Fifth Exemplary Embodiment 
     Next, a fifth example embodiment of the present invention will be described in detail with reference to the drawings. 
       FIG. 10  is a diagram illustrating an example of a configuration of a reference scale  3400  according to the fifth example embodiment. 
     It is assumed that the reference scale  3400  operates in the dimension measurement system  100  like in the first example embodiment. 
     As illustrated in  FIG. 10 , the reference scale  3400  according to this example embodiment includes a film  2400  on which the pattern similar to that illustrated in  FIG. 1  is formed, a film  2410  (hereinafter referred to as the film  2410  so as to distinguish the film  2410  from the film  2400  on which a pattern for displaying the length reference is formed) on which a region only for a pattern is formed, and a lens  1400  which is attached onto an upper surface of each of the film  2400  and the film  2410 . The film  2400  and the film  2410  may be disposed at the position of the focal length of the lens  1400  from the optical center thereof. However, the location where the film  2400  and the film  2410  are disposed may deviate from the focal length within the allowable range of measurement errors in actual use. While a lenticular lens is used as an example of the lens  1400  in  FIG. 10 , the lens  1400  used for the reference scale  3400  according to this example embodiment is not limited to this. 
     The reference scale  3400  in  FIG. 10  differs from the reference scale  3000  illustrated in  FIG. 1  in that the film  2410  is added in the reference scale  3400 . For example, a QR (Quick Response) code (registered mark) or an AR (Augmented Reality) marker can be disposed on the film  2410 . The QR code can be used as an identification ID by using, for example, the image analysis software. The AR marker can be used to estimate a posture (position, angle) of the plane on which the AR marker is disposed with respect to the imaging device  5000  by using, for example, the image analysis software. 
     As described above, according to the reference scale  3400  of this example embodiment, an advantageous effect similar to that of the reference scale  3000  illustrated in  FIG. 1  can be obtained, and another advantageous effect that additional information can be buried in the reference scale  3400  by using the film  2410  can be obtained. As one example, when a QR code is disposed on the film  2410 , an advantageous effect that a plurality of different reference scales  3400  can be identified by using, for example, the image analysis software can be obtained. As another example, when an AR marker is disposed on the film  2410 , the AR marker can be used to estimate a posture (position, angle) of the reference scale  3400  with respect to the imaging device  5000  by using, for example, the image analysis software. 
     This is because the film  2410  is added in the reference scale  3400 , and, for example, a QR code or an AR marker can be disposed on the film  2410 . 
     Sixth Exemplary Embodiment 
     Next, a sixth example embodiment of the present invention will be described in detail with reference to the drawings. 
       FIG. 11  is a diagram illustrating an example of a configuration of a dimension measurement device  9000  according to the sixth example embodiment. As illustrated in  FIG. 11 , the dimension measurement device  9000  according to this example embodiment includes a reference scale extraction unit  9100 , a measuring object extraction unit  9200 , and a dimension calculation unit  9300 . 
     The reference scale extraction unit  9100  utilizes a reference scale which includes a film having a pattern for displaying a length reference, and a lens in contact with the film. The reference scale extraction unit  9100  utilizes the relationship between the pattern function indicating the length reference displayed on the lens according to a change of a predetermined angle formed between the reference scale and the optical axis of the imaging device, and the image formation color function indicating the length reference whose image is formed on the imaging device. Specifically, the reference scale extraction unit  9100  extracts, based on the relationship, an image obtained by forming an image of the length reference from captured image data including the reference scale. 
     The measuring object extraction unit  9200  extracts the image of the measuring object from the captured image data including the reference scale. 
     The dimension calculation unit  9300  calculates dimensions of the measuring object based on dimensions of the image obtained by forming an image of the length reference and the image of the measuring object. 
     As described above, the dimension measurement device  9000  according to this example embodiment provides an advantageous effect that the measurement accuracy can be maintained even when the reference scale is neither disposed nor projected on the measurement surface. 
     This is because the reference scale extraction unit  9100  extracts the image obtained by forming the image of the length reference from the captured image data including the reference scale based on the relationship between the pattern function indicating the length reference displayed on the lens of the reference scale and the image formation color function indicating the length reference whose image is formed on the imaging device. 
     While example embodiments of the present invention have been described above with reference to the drawings, the present invention is not limited to the example embodiments described above. The configuration and details of the present invention can be modified in various ways that can be understood by those skilled in the art within the scope of the present invention. 
     EXAMPLES 
     In this example, the reference scale and the dimension measurement system according to the first example embodiment were used. Next, experimental results obtained after comparing measurement errors between this example and the reference scale of the related art are described below. 
     As the reference scale of the related art, a flat plate including a white belt-like region having a width of 10 cm and a height of 5 cm was created at a central portion of a black board having a width of 20 cm and a height of 5 cm. This is referred to as a first reference scale. 
     As the reference scale  3000  according to the first example embodiment, a reference scale including the lenticular lens (lens pitch P L =2.4 mm, focal length f=2.3 mm, thickness t=2.3 mm)  1000  having a width of 20 cm and a height of 5 cm, and a film  2000  having a pattern below the lenticular lens was created. The pattern function C was designed in such a manner that a white belt-like pattern having a width of 10 cm is observed on a black background. The pattern is attached immediately below the lenticular lens by printing with a resolution of 265 dpi (dots per inch). This reference scale is referred to as a second reference scale. 
     As the imaging device  5000  used for observation, a camera having a configuration in which a high-resolution lens having a focal length of 75 mm is attached to FL3-U3-32S2M-CS (3,200,000 pixels, pixel size: 2.5 μm, in a square lattice shape) manufactured by PointGray Inc. was used. The distance from the optical center of the camera to the 0th lens of the reference scale was set to 3 m. Focusing was adjusted so as to be focused on the distance plane. 
     As an evaluation method, the first and second reference scales were observed by changing the first and second reference scales to sight line angles of 0 to 27 (deg), and the pixel width of the white belt-like region was measured. Further, the degree of variation in the width of the white belt-like region when the reference scales were observed at the sight line angle θ was calculated with respect to the width of the white belt-like region when the reference scales were observed at a sight line angle of 0 (deg). 
     As a result, the width of the white belt-like region when the first reference scale was observed at the sight line angle of 0 (deg) was 1000 (pixels). Next, when the reference scales were observed by changing the sight line angle to 0 to 27 (deg), the width of of the white belt-like region varied most when the reference scales were observed at a sight line angle of 27 (deg), and the width of the white belt-like region was 891 (pixels). When dimensions are measured by using the reference scale having 1000 (pixels)=10 cm as the first reference scale, 12% of measurement errors occur at the sight line angle of 27 (deg). 
     On the other hand, the width of the white belt-like region when the second reference scale was observed at the sight line angle of 0 (deg) was 1006 (pixels). Next, when the reference scales were observed by changing the sight line angle to 0 to 27 (deg), the width of the white belt-like region varied most and the width was 1023 (pixels). When dimensions are measured by using the reference scale having 1006 (pixels)=10 cm as the second reference scale, 1.7% at maximum of measurement errors occur within an angle range of sight line angles of 0 to 27 (deg). 
     The above experimental results confirm that an advantageous effect that dimensions can be measured with higher accuracy in the second reference scale than in the first reference scale can be obtained, even when the angle formed between the measurement surface and the reference scale deviates. 
     The present invention has been described above by using the above-described example embodiments as exemplary examples. However, the present invention is not limited to the example embodiments described above. In other words, the present invention can be applied to various modes that can be understood by those skilled in the art within the scope of the present invention. 
     This application is based upon and claims the benefit of priority from Japanese patent application No. 2015-145623, filed on Jul. 23, 2015, the disclosure of which is incorporated herein in its entirety by reference. 
     REFERENCE SIGNS LIST 
     
         
           100  Dimension measurement system 
           200  Measurement surface 
           300  Optical axis 
           400  Optical axis 
           1000  Lenticular lens 
           1000 A Flat-convex cylindrical lens 
           1000 ( 0 ) 0th lens 
           1000 (K) k-th lens 
           1000 (N L −1) (N L −1)th lens 
           1100  Lens 
           1200  Lens 
           1300  Lens 
           1400  Lens 
           2000  Film 
           2100  Film 
           2200  Film 
           2300  Film 
           2400  Film 
           2410  Film 
           3000  Reference scale 
           3100  Reference scale 
           3200  Reference scale 
           3300  Reference scale 
           3400  Reference scale 
           4000  Measuring object 
           5000  Imaging device 
           5100  Image formation lens 
           5200  Sensor surface 
           6000  Dimension measurement device 
           6100  Reference scale extraction unit 
           6200  Measuring object extraction unit 
           6300  Dimension calculation unit 
           7000  Storage device 
           7100  Reference scale dimension storage unit 
           8000  Display device 
           9000  Dimension measurement device 
           9100  Reference scale extraction unit 
           9200  Measuring object extraction unit 
           9300  Dimension calculation unit