Patent Publication Number: US-10789767-B2

Title: Reducing computational complexity in three-dimensional modeling based on two-dimensional images

Description:
This application is a continuation of U.S. patent application Ser. No. 15/703,393, filed on Sep. 13, 2017, which is a continuation of PCT Application No. PCT/CN2016/075837 filed on Mar. 8, 2016, which claims priority to Chinese Patent Application No. 201510117117.2, filed on Mar. 17, 2015, the entire contents of each which are hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     This disclosure relates to computer-implemented three-dimensional (3D) modeling using two-dimensional (2D) image data. 
     BACKGROUND 
     In some computer-implemented imaging-related applications (for example, computer vision, image enhancement, and object recognition), 2D image data can be used for 3D modeling. For example, information associated with a 2D image, such as light streams, shadows, and texture, can be used to determine a depth of an object, which is an essential characteristic in constructing a 3D model. In some cases, methods that use 2D data, such as light streams, shadows, and texture to calculate depth values for 3D modeling, can have high calculation complexity. In practice, a trade-off exists between accuracy of depth determination and method processing speed. On the one hand, processors with limited processing power, such as those associated with mobile devices, can have difficulty performing real-time 3D modeling using such methods. On the other hand, the accuracy of 3D modeling can be compromised if the data quantity is intentionally reduced to accommodate for processors with limited processing power. 
     SUMMARY 
     The present disclosure describes three-dimensional (3D) modeling technology based on two-dimensional (2D) images. 
     In an implementation, a first image of an object oriented in a first direction and a second image of the object oriented in a second direction are obtained, a plurality of feature points of the object in the first image and a plurality of matching feature points of the object in the second image that correspond to the plurality of feature points of the object in the first image are determined. Similarity values between the plurality of feature points and the corresponding plurality of matching feature points, depth values of the plurality of feature points, and weighted depth values based on the similarity values and depth values are calculated. The 3D modeling of the object is then performed based on the weighted depth values. 
     The previously described implementation is implementable using a computer-implemented method; a non-transitory, computer-readable medium storing computer-readable instructions to perform the computer-implemented method; and a computer-implemented system comprising a computer memory interoperably coupled with a hardware processor configured to perform the computer-implemented method/the instructions stored on the non-transitory, computer-readable medium. 
     The subject matter described in this specification can be implemented in particular implementations, so as to reduce computational complexity for calculating depth in 3D modeling based on 2D images while maintaining computational accuracy. Other advantages will be apparent to those of ordinary skill in the art. 
     The details of one or more implementations of the subject matter of this specification are set forth in the Detailed Description, the claims, and the accompanying drawings. Other features, aspects, and advantages of the subject matter will become apparent from the Detailed Description, the claims, and the accompanying drawings. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a flowchart illustrating an example method of three-dimensional (3D) modeling, according to an implementation of the present disclosure. 
         FIG. 2  is a flowchart illustrating an example method of acquiring feature points of an image, according to an implementation of the present disclosure. 
         FIG. 3  is a flowchart illustrating an example method of determining matching feature points of a second image that correspond to feature points of a first image, according to an implementation of the present disclosure. 
         FIG. 4  is a flowchart illustrating an example method of calculating similarities between feature points from two two-dimensional (2D) images, according to an implementation of the present disclosure. 
         FIG. 5  is a schematic diagram illustrating a general representational example of a real world human face rotating clockwise of an elevation angle α from Y axis to Z axis on a YZ plane, according to an implementation of the present disclosure. 
         FIG. 6  is a schematic diagram illustrating a general representational example of a real world human face rotating counter-clockwise of a deflection angle β from X axis to Z axis on an XZ plane, according to an implementation of the present disclosure. 
         FIG. 7  is a schematic diagram illustrating a general representational example of a real world human face rotating counter-clockwise of a rotation angle γ from X axis to Y axis on an XY plane, according to an implementation of the present disclosure. 
         FIG. 8  is a schematic diagram illustrating an example of initial feature points obtained on a first image, according to an implementation of the present disclosure. 
         FIGS. 9A and 9B  are schematic diagrams illustrating an example of filtering initial feature points using a first grid, according to an implementation of the present disclosure. 
         FIG. 10  is a schematic diagram illustrating an example of searching a second image for a matching feature point A′ that corresponds to a feature point A on a first image, according to an implementation of the present disclosure. 
         FIG. 11  is a flowchart illustrating another example method of 3D modeling, according to an implementation of the present disclosure. 
         FIG. 12  is a schematic diagram illustrating examples of a front face image, a front face elevated image, a front face left-turned image, and a front face right-turned image of a human face captured by a mobile device, according to an implementation of the present disclosure. 
         FIG. 13  is a schematic diagram illustrating example modules of a 3D modeling device, according to an implementation of the present disclosure. 
         FIG. 14  is a block diagram illustrating an example computer system used to provide computational functionalities associated with described algorithms, methods, functions, processes, flows, and procedures as described in the instant disclosure, according to an implementation of the present disclosure. 
     
    
    
     Like reference numbers and designations in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     The following detailed description describes three-dimensional (3D) modeling of an object based on two-dimensional (2D) images, and is presented to enable any person skilled in the art to make and use the disclosed subject matter in the context of one or more particular implementations. Various modifications, alterations, and permutations of the disclosed implementations can be made and will be readily apparent to those or ordinary skill in the art, and the general principles defined can be applied to other implementations and applications, without departing from scope of the disclosure. In some instances, details unnecessary to obtain an understanding of the described subject matter can be omitted so as to not obscure one or more described implementations with unnecessary detail and inasmuch as such details are within the skill of one of ordinary skill in the art. The present disclosure is not intended to be limited to the described or illustrated implementations, but to be accorded the widest scope consistent with the described principles and features. 
     In some computer-implemented imaging-related applications (for example, computer vision, image enhancement, and object recognition), 2D image data can be used for 3D modeling. For example, information associated with a 2D image, such as light streams, shadows, and texture, can be used to determine a depth of an object, which is an essential characteristic in constructing a 3D model. In some cases, methods that use 2D data, such as light streams, shadows, and texture to calculate depth values for 3D modeling, can have high calculation complexity. In practice, a trade-off exists between accuracy of depth determination and method processing speed. On the one hand, processors with limited processing power, such as those associated with mobile devices, can have difficulty performing real-time 3D modeling using such methods. On the other hand, the accuracy of 3D modeling can be compromised if the data quantity is intentionally reduced to accommodate for processors with limited processing power. The described concepts can be used to reduce computational complexity for 3D modeling while preserving 3D modeling accuracy, particularly for computing devices with limiting processing power. 
     For example, in some implementations and at a high-level, an example 3D modeling process starts by taking at least two 2D images of an object with respect to two directions. The process then acquires feature points on one of the images, and determines corresponding matching feature points of the object in another direction on another image. The feature points and corresponding matching feature points are used to calculate depths of the feature points. The calculated depth values are then weighted by similarity values evaluated between the feature points and the matching feature points. The process then performs 3D modeling of the object based on the weighted depth values of the feature points. Variations of this example 3D process consistent with this disclosure are considered to be within the scope of this disclosure. 
       FIG. 1  is a flowchart illustrating an example method  100  of 3D modeling, according to an implementation of the present disclosure. For clarity of presentation, the description that follows generally describes method  100  in the context of the other figures in this description. However, it will be understood that method  100  can be performed, for example, by any suitable system, environment, software, and hardware, or a combination of systems, environments, software, and hardware, as appropriate. In some cases, various steps of method  100  can be run in parallel, in combination, in loops, or in any order. 
     At  110 , the example method  100  captures a first image of an object with respect to a first direction and a second image of the object with respect to a second direction. The object can be any real-world 3D object, such as a human face. The second direction can be different from the first direction by its elevation angle, deflection angle, rotation angle, or any combination thereof. For example, the first image and the second image can be captured from different angles of the object, or they can be captured from the same position but by varying the angle(s) of the object. In some cases, the first image and the second image can be color images that have red, green, and blue (RGB) color channels. In some cases, the pixel resolution of both images are at least 392×440. In some cases, the first image and the second image can be greyscale images that have one color channel. 
     In some implementations, the difference between the first direction and the second direction in terms of angles is illustrated as in  FIGS. 5-7 . Referring to  FIGS. 5-7 ,  FIGS. 5-7  illustrate an example general representation of a front view of a real world human face ( 510 ,  610 , and  710 , respectively) referenced in coordinate systems. The front view of the human face  510 ,  610 ,  710  can be considered as the first image. The X axis can be defined as a horizontal axis with respect to the front view of the human face, the Y axis can be defined as a vertical axis with respect to the front view of the human face, and the Z axis can be defined as and understood to be perpendicular to the X axis and the Y axis and corresponding to a depth measurement of the human face. 
       FIG. 5  is a schematic diagram illustrating a general representational example  500  of a real world human face rotating clockwise with an elevation angle α  540  from Y axis to Z axis on a YZ plane, according to an implementation of the present disclosure.  FIG. 6  is a schematic diagram illustrating a general representational example  600  of a real world human face rotating counter-clockwise of a deflection angle β  640  from X axis to Z axis on an XZ plane, according to an implementation of the present disclosure.  FIG. 7  is a schematic diagram illustrating a general representational example  700  of a real world human face rotating counter-clockwise of a rotation angle γ  740  from X axis to Y axis on an XY plane, according to an implementation of the present disclosure. The α, β, and γ angles ( 540 ,  640 , and  740 , respectively) represent differences between the first direction and second direction of the human face. Returning to  FIG. 1 , from  110 , method  100  proceeds  120 . 
     At  120 , one or more feature points on the first image are acquired. In some cases, the acquisition of the feature points can be based on edge detection to acquire points from the first image that have significant variations in brightness compared to their surroundings. The use of edge detection processing can reduce an amount of data processed, while preserving structural attributes of the image, such as discontinuities in depth or surface direction, and changes in material property or illumination. One or more implementations of this step is further illustrated in the following description of  FIG. 2 . In some other cases, corner detection can be used instead of edge detection for feature point acquisition. From  120 , method  100  proceeds to  130 . 
     At  130 , matching feature points of the second image that correspond to the feature points acquired from the first image are determined. Referring to  FIGS. 9A and 10 ,  FIG. 9A  is a schematic diagram  900 A illustrating an example of filtering initial feature points using a first grid. Assuming that a feature point A  920  at the tip of the nose as shown on  FIG. 9A  is acquired from the first image, then the objective of  130  is to search for a matching feature point A′ that corresponds to the tip of the nose on the second image. This process can be repeated to determine a plurality of feature points on the second image that matches the feature points acquired on the first image. One or more implementations of this step is further illustrated in the following description of  FIG. 3 . Returning to  FIG. 1 , from  130 , method  100  proceeds to  140 . 
     At  140 , similarities are calculated between the feature points acquired from the first image and the matching feature points on the second image, and depth values of the feature points are calculated. One or more implementations of this step is further illustrated in the description of  FIG. 4 . Returning to  FIG. 1 , from  140 , method  100  proceeds to  150 . 
     At  150 , weighted depth values are calculated based on the depth values and values associated with the similarities between the feature points acquired from the first image and the matching feature points on the second image. In some cases, the weighted depth value can be expressed as, weighted depth value=depth value Z×(sum of average color difference of all feature points except the feature point subject to weighted depth value calculation/sum of the average color value difference of all the feature points). From  150 , method  100  proceeds to  160 . 
     At  160 , the 3D modeling of the object is performed based on the weighted depth values. In some cases, the 3D modeling can be performed based on a triangular grid, where feature points are selected from the vertices of the triangular grid. In alternative implementations, a polygonal grid/polygonal-type modeling or other types of grids/modeling can be used without departing from the scope of the present disclosure. After  160 , method  100  ends. 
       FIG. 2  is a flowchart illustrating an example method  200  of acquiring feature points of an image, according to an implementation of the present disclosure. For clarity of presentation, the description that follows generally describes method  200  in the context of the other figures in this description. However, it will be understood that method  200  can be performed, for example, by any suitable system, environment, software, and hardware, or a combination of systems, environments, software, and hardware, as appropriate. In some cases, various steps of method  200  can be run in parallel, in combination, in loops, or in any order. 
     At  210 , one or more initial feature points are acquired on the image. For example, referring to  FIG. 8 ,  FIG. 8  is a schematic diagram  800  of a human face illustrating an example of initial feature points obtained on a first image  810 . In the illustration of  FIG. 8 , the initial feature points (for example, feature point  820 ) are, in some implementation, based on edge detection processing and indicated by cross marks. The initial feature points can represent prominent features of a human face, including eyes, eyebrows, nose, mouth, cheeks, chin, forehead, or other features. Returning to  FIG. 2 , from  210 , method  200  proceeds to  220 . 
     At  220 , the first image is matched with a first grid. For example, referring again to  FIG. 9A , a first grid  910  with a square shaped grid cell is matched to an image of a human face (for example, the first image  810  of  FIG. 8 ). It is to be understood that grid cells with other shapes, such as triangular, hexagonal, or other shapes can also be used in alternative implementations. The initial feature points of the first image can fall into different grid cells of the first grid  910 . In some cases, the match between the first image and the first grid can be performed by a processor, such as a built-in processor of a cell phone, without any help from a user. Returning to  FIG. 2 , from  220 , method  200  proceeds to  230 . 
     At  230 , initial feature points are filtered to a smaller amount of feature points. Referring again to  FIG. 9A , the number of initial feature points in different grid cells cannot be uniformly distributed. Some grid cells can include more feature points than others. In some cases, certain grid cells can contain a large number of initial feature points that calculating depth for every initial feature point can be burdensome or unnecessary, especially for mobile devices with limited processing power. Strategically filtering the initial feature points to a smaller amount of feature points can still preserve the features of the human feature while reducing the computational complexity. 
     In some cases, the filtering of the initial feature points can reduce the number of initial feature points to a same amount of feature points in each feature point-containing grid cell. For example, referring to  FIG. 9B ,  FIG. 9B  is a schematic diagram  900 B illustrating an example of filtering initial feature points using the first grid  910  of  FIG. 9A . The process of filtering the initial feature points can be described as follows. First, for each feature point-containing grid cell, determine the distances between the initial feature points and the center of the cell. Second, select the initial feature point closest to the center of the grid cell as the filtered feature point  940 . Third, for the grid cells that do not contain any initial feature point, mark the center of those cells as their filtered feature points  930  (shown as hollow circles in  FIG. 9B ). 
     In some cases, average coordinate values of the initial feature points of each grid cell can be calculated. The filtered feature points can be set as points determined by the calculated average of the coordinate values. 
     In some other implementations, instead of reducing the number of initial feature points to the same amount of feature points, the difference in numbers of feature points in different feature point-containing grid cells can be maintained under a pre-determined threshold after filtering. For example, after filtering, the maximum number of feature points contained in a grid cell can be no larger than two of the minimum number of feature points contained in a grid cell. Returning to  FIG. 2 , after  230 , method  200  ends. 
       FIG. 3  is a flowchart illustrating an example method  300  of determining matching feature points of a second image that correspond to feature points of a first image, according to an implementation of the present disclosure. For clarity of presentation, the description that follows generally describes method  300  in the context of the other figures in this description. However, it will be understood that method  300  can be performed, for example, by any suitable system, environment, software, and hardware, or a combination of systems, environments, software, and hardware, as appropriate. In some cases, various steps of method  300  can be run in parallel, in combination, in loops, or in any order. 
     At  310 , the example method  300  determines pre-matching feature points on the second image that correspond to the feature points of the first image based on direction information of the object in the first image and the second image. The directional information associated with the first image and the second image can be determined by a variety of methods. For example, in some implementations, a mobile device with a built-in camera can be used to capture the first image and the second image of an object. The directional information associated with the first image and the second image can be determined based on motion data sensed by mobile device sensors, such as a gyroscope, accelerometer, digital compass, GPS, magnetometer, light detector, cellular/WIFI/Bluetooth, or other sensors. 
     In some cases, the directional information associated with the first image and the second image can be determined based on a posture measurement algorithm. For example, referring again to  FIGS. 5-7 , assume that a first image of a human head oriented at a first direction and a second image of the human head oriented at a second direction are captured. Let C ( 515 ,  615 , and  715 , respectively) represent the rotation center of the human head and r ( 525 ,  625 , and  725 , respectively) represent the distance between the center of two eyes and the rotation center, coordinate values C X , C Y , and C Z , of the rotation center C  515 ,  615 , and  715  can be estimated based on knowledge of human anatomy. Similarly, (U X , U Y ) are the coordinates of U that represent the center point of the two eyes on the first image ( 530 ,  630 , and  730 , respectively) and (V X , V Y ) are the coordinate of V that that represent the center point of the two eyes on the second image ( 535 ,  635 , and  735 , respectively). 
     The depth E Z  of the center of the two eyes when the human head is front facing can be estimated. The elevation angle α  540 , deflection angle β  640 , and rotation angle γ  740  can then be calculated as: 
               α   =         sin     -   1       ⁡     (         V   Y     -     C   Y       r     )       -       sin     -   1       ⁡     (         U   Y     -     C   Y       r     )           ,     
     ⁢         where   ⁢           ⁢   r     =           (       U   γ     -     C   γ       )     2     +       (       E   Z     -     C   Z       )     2           ;                   β   =         sin     -   1       ⁡     (         V   X     -     C   X       r     )       -       sin     -   1       ⁡     (         U   X     -     C   X       r     )           ,     
     ⁢         where   ⁢           ⁢   r     =           (       U   X     -     C   X       )     2     +       (       E   Z     -     C   Z       )     2           ;   and                 γ   =         sin     -   1       ⁡     (       V   Y       -     V   X         )       -         sin     -   1       ⁡     (       U   Y       -     U   X         )       .             
From  310 , method  300  proceeds to  320 .
 
     At  320 , the example method  300  matches the second image with a pre-determined second grid. For example, referring to  FIG. 10 ,  FIG. 10  is a schematic diagram  1000  illustrating an example of searching a second image  1010  for a matching feature point A′  1020  that corresponds to the feature point A  920  on a first image  910 . Squares in the schematic diagram  1000  are used as the shape of the grid cells of the second grid in this particular implementation. The area of the cells of the second grid can be smaller than the area of the cells of the first grid. This means that the second grid would include more cells than the first grid for the same overall grid area. The additional cell can be used to increase the accuracy of the matching feature point&#39;s calculation. From  320 , method  300  proceeds to  330 . 
     At  330 , the example method  300  sets the center points of grid cells of the second grid that contain pre-matching feature points as the matching feature points. After  330 , method  300  stops. 
       FIG. 4  is a flowchart illustrating an example method  400  of calculating similarities between feature points from two 2D images and matching the feature points, according to an implementation of the present disclosure. For clarity of presentation, the description that follows generally describes method  400  in the context of the other figures in this description. However, it will be understood that method  400  can be performed, for example, by any suitable system, environment, software, and hardware, or a combination of systems, environments, software, and hardware, as appropriate. In some cases, various steps of method  400  can be run in parallel, in combination, in loops, or in any order. 
     At  410 , the example method  400  acquires color values of all pixels in the grid cells of the first grid that contain at least one feature point. In some cases, the color values can be the particular R, G, and B color channel values associated with the pixels. From  410 , method  400  proceeds to  420 . 
     At  420 , the example method  400  acquires color values of all pixels in the grid cells of the second grid that contain at least one feature point. From  420 , method  400  proceeds to  430 . 
     At  430 , the example method  400  calculates average color value difference between the pixels in a grid cell of the first grid that contains at least one feature point and the pixels in a grid cell of the second grid that contains at least one matching feature point. The average color value difference can indicate the similarities between the at least one feature point of the grid cell of the first grid and the at least one feature point of the grid cell of the second grid. In some implementations, the calculation of the average color value difference S can be expressed as: 
               S   =     λ   ⁢       ∑   i             ⁢       ∑   j             ⁢         R   ⁡     (       F   ij     ,     S   ij       )       +     G   ⁡     (       F   ij     ,     S   ij       )       +     B   ⁡     (       F   ij     ,     S   ij       )           3   ⁢        F                    ,         
where i and j are coordinate values of a pixel within its corresponding grid cell of the first grid, is a feature point with pixel coordinates (i, j), S ij  is a matching feature point with pixel coordinates (i, j), R(F ij , S ij ) is an absolute value of the difference between points F ij  and S ij  on the R channel, G(F ij , S ij ) is an absolute value of the difference between points and S ij  on the G channel, B(F ij , S ij ) is an absolute value of the difference between points and S ij  on the B channel, ∥F∥ is the area of the grid cells of the first grid (that is, the number of pixels contained within the grid cell of the first grid), and λ is a constant, which can be calculated, in some implementations, as:
 
               λ   =     (     1   +              sp   ·   x     -     fp   ·   x              max   ⁢           ⁢   X       +              sp   ·   y     -     fp   ·   y              max   ⁢           ⁢   Y         )       ,         
where max X and max Y are the farthest distance values (unit in pixels) away from the corresponding feature points within one grid cell of the first grid; and fp.x and fp.y are coordinate values of the feature points, and sp.x and sp.y are coordinate values of the matching feature points.
 
     The similarity between the feature points and the matching feature points can be determined based on the calculated average color value difference of the corresponding grid cell pixels. The greater the difference, the lower the similarity between the feature points and matching feature points. 
     In some cases, the feature points can be filtered based on a similarity between the feature points and the matching feature points. For example, a feature point eliminating threshold can be determined based on the similarity between a plurality of feature points and a corresponding plurality of matching feature points, such as the similarity S calculated based on the previously shown equation. Individual feature point and its matching feature point can be filtered out if the similarity between them is less than the feature point eliminating threshold. When the similarity between a feature point and its matching feature point is less than the eliminating threshold, it can be inferred that the matching feature point is not be the corresponding point on the second image to the feature point on the first image. Accordingly, it can be determined that the matching of the feature point has failed and the failed feature points are not to be included in subsequent 3D modeling calculation. 
     Referring again to  FIGS. 5-7 , in some implementations, the depth of a feature point can be obtained by combining depths of matching feature points at an elevation angle Z α , a deflection angle Z β , and a rotation angle Z γ  (for example, elevation angle α  540 , deflection angle β  640 , and rotation angle γ  740  in  FIGS. 5-7 ). Using the depths of the matching feature points at different angles can improve the accuracy of the depth calculation. In some implementations, the depth of a feature point at the elevation angle can be calculated as: 
                 Z   α     =       C   Z     -         (       V   Y     -     C   Y       )     -       (       U   Y     -     C   Y       )     ⁢   cos   ⁢           ⁢   α         sin   ⁢           ⁢   α           ,         
the depth of a feature point at the deflection angle can be calculated as:
 
                 Z   β     =       C   Z     -         (       V   X     -     C   X       )     -       (       U   X     -     C   X       )     ⁢   cos   ⁢           ⁢   β         sin   ⁢           ⁢   β           ,         
and
 
the depth of a feature point at a rotation angle can be calculated as:
 
 Z   γ   =U   Y  cos γ− U   X  sin γ.
 
where (U X , U Y ) are the coordinates of the feature point on the first image and (V X , V Y ) are the coordinates of the matching feature point on the second image. In some implementations, the depth of the feature point, Z, can then be calculated based on Z α , Z β  and Z γ , that can be expressed as:
 
     
       
         
           
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     The depth value Z can be used to calculate a weighted depth value as discussed in the description of  150  of  FIG. 1 . The weighted depth value can be used to perform 3D modeling of the object. After  430 , method  400  stops. 
       FIG. 11  is a flowchart illustrating another example method  1100  of 3D modeling, according to an implementation of the present disclosure. For clarity of presentation, the description that follows generally describes method  1100  in the context of the other figures in this description. However, it will be understood that method  1100  can be performed, for example, by any suitable system, environment, software, and hardware, or a combination of systems, environments, software, and hardware, as appropriate. In some cases, various steps of method  1100  can be run in parallel, in combination, in loops, or in any order. 
     At  1110 , the example method  1100  captures images of an object in a plurality of directions. From  1110 , method  1100  proceeds to  1120 . 
     At  1120 , the example method  1100  acquires a plurality of feature points on a first of the plurality of images. From  1120 , method  1100  proceeds to  1130 . 
     At  1130 , the example method  1100  determines matching feature points on the other images that correspond to the plurality of feature points on the first image. From  1130 , method  1100  proceeds to  1140 . 
     At  1140 , the example method  1100  calculates similarities between the plurality of feature points on the first image and the corresponding matching feature points on the other images, and calculates depth of the matching feature points. From  1140 , method  1100  proceeds to  1150 . 
     At  1150 , the example method  1100  calculates depths of the plurality of feature points according to direction information about the plurality of images and the depths of the matching feature points. From  1150 , method  1100  proceeds to  1160 . 
     At  1160 , the example method  1100  performs weighted calculation on the depths of the plurality of feature points according to the similarities between the plurality of feature points and the corresponding matching feature points. From  1160 , method  1100  proceeds to  1170 . 
     At  1170 , the example method performs 3D modeling on the object based on the weighted depths of the plurality of feature points. After  1170 , method  1100  stops. 
       FIG. 12  is a schematic diagram illustrating examples  1200  of a front face image  1210 , a front face elevated image  1240 , a front face left-inclined image  1220 , and a front face right-inclined image  1230  of a human face captured by a mobile device, according to an implementation of the present disclosure. The first direction of the object in the front face image  1210  can be considered the reference direction. The three directions of the object in the second, third, and fourth images ( 1240 ,  1220 , and  1230 , respectively) can be different in elevation, deflection, or rotation angles from the reference direction when captured. Matching feature points that correspond to the feature points acquired on the front face image  1210  can be substantially identified on the front face elevated image  1240 , the front face left-inclined image  1220 , or the front face right-inclined image  1230 . As such, the depth calculation can take advantage of the depths at different angles as previously discussed to improve accuracy. 
     In the illustrated examples  1200 , four images with four directions of the object are used for 3D modeling. It is to be understood that in other implementations, a different number of images can be used depending on the processing power of the 3D modeling device and accuracy requirement. 
       FIG. 13  is a schematic diagram illustrating example modules  1300  of a 3D modeling device, according to an implementation of the present disclosure. The example modules  1300  can include an image capturing module  1310 , a feature point detection module  1320 , a calculation module  1325 , a matching module  1330 , a calculation module  1340 , a filtering module  1350 , and a model generation module  1360 . 
     In some cases, the image capture module  1310  can capture at least a first image of an object in a first direction and a second image of the object in a second direction. The feature point detection module  1320  can acquire initial feature points on the first image, match the first image with a pre-set first grid, and filtering the initial feature points such that the number of initial feature points is the same in each grid cell of the first grid, as discussed in the description of  230  of  FIG. 2 . In some cases, the 3D modeling can be performed based on a triangular grid, where feature points are selected from the vertices of the triangular grid. In alternative implementations, a polygonal grid/polygonal modeling or other grid/modeling shape can be used without departing from the scope of the present disclosure. 
     In some cases, the feature detection module  1320  can include a calculation unit  1325 . The calculation unit  1325  can calculate distances from the initial feature points to center points of their respective grid cells of the first grid. The feature detection module  1320  can also determine the closest initial feature point to the center of the corresponding grid cell as the feature point. The feature detection module  1320  can further determine the center of the grid cell as a feature point if the cell does not contain any initial feature points as discussed in the description of  230  of  FIG. 2 . 
     The matching module  1330  can determine matching feature points on the second image that correspond to the feature points on the first image. The matching module  1330  can determine, according to direction information of the first image and the second image, pre-matching feature points on the second image that correspond to the feature points on the first image, match the second image with a pre-set second grid, and determine the center points of grid cells of the second grid where the pre-matching feature points are located as the corresponding matching feature points, as discussed in the description of  FIG. 3 . 
     The calculation module  1340  can calculate similarities between the feature points and the corresponding matching feature points, calculate depths of the plurality of feature points, and perform a weighted calculation of the depths of the feature points based on the similarities between the feature points and the corresponding matching feature points. The calculation module  1340  can acquire color values of all pixels in the grid cells of the first grid that contain at least one feature point, color values of all pixels in the grid cells of the second grid that contain at least one feature point, and calculate average color value difference between the pixels in a grid cell of the first grid that contains at least one feature point and the pixels in a grid cell of the second grid that contains at least one matching feature point. The similarities between the feature points and the matching feature points can be determined based on the calculated average color value difference of the corresponding grid cell pixels, as discussed in the description of  FIG. 4 . 
     The calculation module  1340  can also calculate weighted depth values based on the depth values and values associated with the similarities between the feature points acquired from the first image and the matching feature points on the second image. In some cases, the weighted depth value can be expressed as: weighted depth value=depth value Z×(sum of the average color value errors of all the feature points except the feature points to be subjected to the weighted calculation/sum of the average color value errors of all the feature points), as discussed in the description of  150  of  FIG. 1 . 
     In some cases, the area of the cells of the second grid can be smaller than the area of the cells of the first grid. This means that the second grid would include more cells than the first grid for the same overall grid area. The additional cell can be used to increase the accuracy of the matching feature point&#39;s calculation. 
     The filtering module  1350  can filter the feature points based on the similarities between the feature points and the corresponding matching feature points prior to performing the weighted calculation of the depths of the feature points. In some cases, the filtering module  1350  can determine a feature point eliminating threshold based on the similarities between the feature points and the corresponding matching feature points. Individual feature point and its matching feature point can be filtered out if the similarity between them is less than the feature point eliminating threshold, as discussed in the description of  430  of  FIG. 4 . 
     The model generation module  1360  can perform 3D modeling on the object based on the depths of the feature points after being subjected to the weighted calculation. 
     In some cases, the image capture module  1310  can capture a plurality of images of an object in more than two directions. For example, as discussed in the description of  FIG. 12 , the image capture module  1310  can capture four images of a human face, including a front face image, a front face elevated image, a front face left-turned image, and a front face right-turned image of a human face captured by a mobile device. The first direction of the object in the first image can be considered the reference direction. The three directions of the object in the second, third, and fourth images can be different in elevation, deflection, or rotation angles from the reference direction when captured. 
     The feature detection module  1320  can acquire a plurality of feature points on one of the plurality of images. The matching module  1330  can determine matching feature points on the remaining images that correspond to the plurality of feature points. The calculation module  1340  can calculate the similarities between the plurality of feature points on the first image and the corresponding matching feature points on the other images, and calculates depth of the matching feature points, the depths of the plurality of feature points according to direction information about the plurality of images and the depths of the matching feature points, and perform weighted calculation on the depths of the plurality of feature points according to the similarities between the plurality of feature points and the corresponding matching feature points. The model generating module  1360  can perform 3D modeling on the object based on the weighted depths of the plurality of feature points. 
       FIG. 14  is a block diagram of an example computer system  1400  used to provide computational functionalities associated with described algorithms, methods, functions, processes, flows, and procedures, as described in the instant disclosure, according to an implementation of the present disclosure. The illustrated computer  1402  is intended to encompass any computing device such as a server, desktop computer, laptop/notebook computer, wireless data port, smart phone, personal data assistant (PDA), tablet computing device, one or more processors within these devices, or any other suitable processing device, including physical or virtual instances (or both) of the computing device. Additionally, the computer  1402  can comprise a computer that includes an input device, such as a keypad, keyboard, touch screen, or other device that can accept user information, and an output device that conveys information associated with the operation of the computer  1402 , including digital data, visual, or audio information (or a combination of information), or a graphical-type user interface (UI) (or GUI). 
     The computer  1402  can serve in a role as a client, network component, a server, a database or other persistency, or any other component (or a combination of roles) of a computer system for performing the subject matter described in the instant disclosure. The illustrated computer  1402  is communicably coupled with a network  1430 . In some implementations, one or more components of the computer  1402  can be configured to operate within environments, including cloud-computing-based, local, global, or other environment (or a combination of environments). 
     At a high level, the computer  1402  is an electronic computing device operable to receive, transmit, process, store, or manage data and information associated with the described subject matter. According to some implementations, the computer  1402  can also include or be communicably coupled with an application server, e-mail server, web server, caching server, streaming data server, or other server (or a combination of servers). 
     The computer  1402  can receive requests over network  1430  from a client application (for example, executing on another computer  1402 ) and respond to the received requests by processing the received requests using an appropriate software application(s). In addition, requests can also be sent to the computer  1402  from internal users (for example, from a command console or by other appropriate access method), external or third-parties, other automated applications, as well as any other appropriate entities, individuals, systems, or computers. 
     Each of the components of the computer  1402  can communicate using a system bus  1403 . In some implementations, any or all of the components of the computer  1402 , hardware or software (or a combination of both hardware and software), can interface with each other or the interface  1404  (or a combination of both), over the system bus  1403  using an application programming interface (API)  1412  or a service layer  1413  (or a combination of the API  1412  and service layer  1413 ). The API  1412  can include specifications for routines, data structures, and object classes. The API  1412  can be either computer-language independent or dependent and refer to a complete interface, a single function, or even a set of APIs. The service layer  1413  provides software services to the computer  1402  or other components (whether or not illustrated) that are communicably coupled to the computer  1402 . The functionality of the computer  1402  can be accessible for all service consumers using this service layer. Software services, such as those provided by the service layer  1413 , provide reusable, defined functionalities through a defined interface. For example, the interface can be software written in JAVA, C++, or other suitable language providing data in extensible markup language (XML) format or other suitable format. While illustrated as an integrated component of the computer  1402 , alternative implementations can illustrate the API  1412  or the service layer  1413  as stand-alone components in relation to other components of the computer  1402  or other components (whether or not illustrated) that are communicably coupled to the computer  1402 . Moreover, any or all parts of the API  1412  or the service layer  1413  can be implemented as child or sub-modules of another software module, enterprise application, or hardware module without departing from the scope of this disclosure. 
     The computer  1402  includes an interface  1404 . Although illustrated as a single interface  1404  in  FIG. 14 , two or more interfaces  1404  can be used according to particular needs, desires, or particular implementations of the computer  1402 . The interface  1404  is used by the computer  1402  for communicating with other systems that are connected to the network  1430  (whether illustrated or not) in a distributed environment. Generally, the interface  1404  comprises logic encoded in software or hardware (or a combination of software and hardware) and is operable to communicate with the network  1430 . More specifically, the interface  1404  can comprise software supporting one or more communication protocols associated with communications such that the network  1430  or interface&#39;s hardware is operable to communicate physical signals within and outside of the illustrated computer  1402 . 
     The computer  1402  includes a processor  1405 . Although illustrated as a single processor  1405  in  FIG. 14 , two or more processors can be used according to particular needs, desires, or particular implementations of the computer  1402 . Generally, the processor  1405  executes instructions and manipulates data to perform the operations of the computer  1402  and any algorithms, methods, functions, processes, flows, and procedures as described in the instant disclosure. 
     The computer  1402  also includes a database  1406  that can hold data for the computer  1402  or other components (or a combination of both) that can be connected to the network  1430  (whether illustrated or not). For example, database  1406  can be an in-memory, conventional, or other type of database storing data consistent with this disclosure. In some implementations, database  1406  can be a combination of two or more different database types (for example, a hybrid in-memory and conventional database) according to particular needs, desires, or particular implementations of the computer  1402  and the described functionality. Although illustrated as a single database  1406  in  FIG. 14 , two or more databases (of the same or combination of types) can be used according to particular needs, desires, or particular implementations of the computer  1402  and the described functionality. While database  1406  is illustrated as an integral component of the computer  1402 , in alternative implementations, database  1406  can be external to the computer  1402 . 
     The computer  1402  also includes a memory  1407  that can hold data for the computer  1402  or other components (or a combination of both) that can be connected to the network  1430  (whether illustrated or not). Memory  1407  can store any data consistent with this disclosure. In some implementations, memory  1407  can be a combination of two or more different types of memory (for example, a combination of semiconductor and magnetic storage) according to particular needs, desires, or particular implementations of the computer  1402  and the described functionality. Although illustrated as a single memory  1407  in  FIG. 14 , two or more memories  1407  (of the same or combination of types) can be used according to particular needs, desires, or particular implementations of the computer  1402  and the described functionality. While memory  1407  is illustrated as an integral component of the computer  1402 , in alternative implementations, memory  1407  can be external to the computer  1402 . 
     The application  1408  is an algorithmic software engine providing functionality according to particular needs, desires, or particular implementations of the computer  1402 , particularly with respect to functionality described in this disclosure. For example, application  1408  can serve as one or more components, modules, or applications. Further, although illustrated as a single application  1408 , the application  1408  can be implemented as multiple applications  1408  on the computer  1402 . In addition, although illustrated as integral to the computer  1402 , in alternative implementations, the application  1408  can be external to the computer  1402 . 
     The computer  1402  can also include a power supply  1414 . The power supply  1414  can include a rechargeable or non-rechargeable battery that can be configured to be either user- or non-user-replaceable. In some implementations, the power supply  1414  can include power-conversion or management circuits (including recharging, standby, or other power management functionality). In some implementations, the power-supply  1414  can include a power plug to allow the computer  1402  to be plugged into a wall socket or other power source to, for example, power the computer  1402  or recharge a rechargeable battery. 
     There can be any number of computers  1402  associated with, or external to, a computer system containing computer  1402 , each computer  1402  communicating over network  1430 . Further, the term “client,” “user,” and other appropriate terminology can be used interchangeably, as appropriate, without departing from the scope of this disclosure. Moreover, this disclosure contemplates that many users can use one computer  1402 , or that one user can use multiple computers  1402 . 
     Described implementations of the subject matter can include one or more features, alone or in combination. 
     For example, in a first implementation, a computer-implemented method, comprises, obtaining a first image of an object oriented in a first direction and a second image of the object oriented in a second direction; determining a plurality of feature points of the object in the first image; determining a plurality of matching feature points of the object in the second image that correspond to the plurality of feature points of the object in the first image; calculating similarity values between the plurality of feature points and the corresponding plurality of matching feature points; calculating depth values of the plurality of feature points; calculating weighted depth values based on the similarity values and depth values; and performing 3D modeling of the object based on the weighted depth values. 
     The foregoing and other described implementations can each, optionally, include one or more of the following features: 
     A first feature, combinable with any of the following features, comprises determining a plurality of initial feature points of the object in the first image; and matching the first image with a first grid that includes a plurality of grid cells, wherein determining a plurality of feature points of the object in the first image further comprises filtering the plurality of initial feature points until the number of feature points is the same in each grid cell, and wherein each grid cell includes at least one initial feature point. 
     A second feature, combinable with any of the previous or following features, wherein determining a plurality of feature points of the object in the first image further comprises, calculating distances from the plurality of initial feature points to center points of the grid cells the plurality of initial feature points are located; and determining, for each grid cell that includes at least one initial feature point, an initial feature point that is closest to the center of the grid cell as the feature point. 
     A third feature, combinable with any of the previous or following features, wherein determining a plurality of feature points of the object in the first image further comprising determining a center point of a grid cell as a feature point of the grid cell if the grid cell does not include an initial feature point. 
     A fourth feature, combinable with any of the previous or following features, comprises, determining, a plurality of pre-matching feature points in the second image that correspond to the plurality of feature points based on direction information of the object in the first image and the object in the second image; and matching the second image with a second grid; and wherein determining a plurality of matching feature points of the object in the second image further comprises determining center points of grid cells of the second grid that include at least one pre-matching feature point as the plurality of matching feature points in the second image. 
     A fifth feature, combinable with any of the previous or following features, wherein determining the similarity values between the plurality of feature points and the corresponding plurality of matching feature points further comprises, determining color values of all pixels within the grid cells of the first grid that include at least one feature point; determining color values of all pixels within the grid cells of the second grid that include at least one matching feature point; calculating average color value differences between all the pixels within the grid cells of the first grid that include at least one feature point and all the pixels within the grid cells of the second grid that include at least one matching feature point; and determining the similarity values of the plurality of feature points and the corresponding plurality of matching feature points based on the average color value differences. 
     A sixth feature, combinable with any of the previous or following features, wherein a weighted depth value of a feature point is calculated as: weighted depth value=depth value×(sum of the average color value differences of the plurality of feature points except the feature point subject to the weighted depth value calculation/sum of the average color value differences of the plurality of feature points). 
     A seventh feature, combinable with any of the previous or following features, wherein the area of the grid cells of the second grid are smaller than the area of the grid cells of the first grid. 
     An eighth feature, combinable with any of the previous or following features, comprises filtering the plurality of feature points based on the similarity values before calculating the weighted depth values. 
     A ninth feature, combinable with any of the previous or following features, wherein filtering the plurality of feature points further comprises, determining a feature point eliminating threshold based on the similarity values; and eliminating a feature point when its corresponding similarity value is less than the feature point eliminating threshold. 
     A tenth feature, combinable with any of the previous or following features, wherein the grid cells of the first grid have triangular shape. 
     In a second implementation, a non-transitory, computer-readable medium storing one or more instructions executable by a computer system to perform operations comprises, obtaining a first image of an object oriented in a first direction and a second image of the object oriented in a second direction; determining a plurality of feature points of the object in the first image; determining a plurality of matching feature points of the object in the second image that correspond to the plurality of feature points of the object in the first image; calculating similarity values between the plurality of feature points and the corresponding plurality of matching feature points; calculating depth values of the plurality of feature points; calculating weighted depth values based on the similarity values and depth values; and performing 3D modeling of the object based on the weighted depth values. 
     The foregoing and other described implementations can each, optionally, include one or more of the following features: 
     A first feature, combinable with any of the following features, comprises determining a plurality of initial feature points of the object in the first image; and matching the first image with a first grid that includes a plurality of grid cells, wherein determining a plurality of feature points of the object in the first image further comprises filtering the plurality of initial feature points until the number of feature points is the same in each grid cell, and wherein each grid cell includes at least one initial feature point. 
     A second feature, combinable with any of the previous or following features, wherein determining a plurality of feature points of the object in the first image further comprises, calculating distances from the plurality of initial feature points to center points of the grid cells the plurality of initial feature points are located; and determining, for each grid cell that includes at least one initial feature point, an initial feature point that is closest to the center of the grid cell as the feature point. 
     A third feature, combinable with any of the previous or following features, wherein determining a plurality of feature points of the object in the first image further comprising determining a center point of a grid cell as a feature point of the grid cell if the grid cell does not include an initial feature point. 
     A fourth feature, combinable with any of the previous or following features, comprises, determining, a plurality of pre-matching feature points in the second image that correspond to the plurality of feature points based on direction information of the object in the first image and the object in the second image; and matching the second image with a second grid; and wherein determining a plurality of matching feature points of the object in the second image further comprises determining center points of grid cells of the second grid that include at least one pre-matching feature point as the plurality of matching feature points in the second image. 
     In a third implementation, a computer-implemented system, comprises one or more computers; and one or more computer memory devices interoperably coupled with the one or more computers and having tangible, non-transitory, machine-readable media storing instructions that, when executed by the one or more computers, perform operations comprises obtaining a first image of an object oriented in a first direction and a second image of the object oriented in a second direction; determining a plurality of feature points of the object in the first image; determining a plurality of matching feature points of the object in the second image that correspond to the plurality of feature points of the object in the first image; calculating similarity values between the plurality of feature points and the corresponding plurality of matching feature points; calculating depth values of the plurality of feature points; calculating weighted depth values based on the similarity values and depth values; and performing 3D modeling of the object based on the weighted depth values. 
     The foregoing and other described implementations can each, optionally, include one or more of the following features: 
     A first feature, combinable with any of the following features, comprises determining a plurality of initial feature points of the object in the first image; and matching the first image with a first grid that includes a plurality of grid cells, wherein determining a plurality of feature points of the object in the first image further comprises filtering the plurality of initial feature points until the number of feature points is the same in each grid cell, and wherein each grid cell includes at least one initial feature point. 
     A second feature, combinable with any of the previous or following features, wherein determining a plurality of feature points of the object in the first image further comprises, calculating distances from the plurality of initial feature points to center points of the grid cells the plurality of initial feature points are located; and determining, for each grid cell that includes at least one initial feature point, an initial feature point that is closest to the center of the grid cell as the feature point. 
     A third feature, combinable with any of the previous or following features, wherein determining a plurality of feature points of the object in the first image further comprising determining a center point of a grid cell as a feature point of the grid cell if the grid cell does not include an initial feature point. 
     A fourth feature, combinable with any of the previous or following features, comprises, determining, a plurality of pre-matching feature points in the second image that correspond to the plurality of feature points based on direction information of the object in the first image and the object in the second image; and matching the second image with a second grid; and wherein determining a plurality of matching feature points of the object in the second image further comprises determining center points of grid cells of the second grid that include at least one pre-matching feature point as the plurality of matching feature points in the second image. 
     A fifth feature, combinable with any of the previous or following features, wherein determining the similarity values between the plurality of feature points and the corresponding plurality of matching feature points further comprises, determining color values of all pixels within the grid cells of the first grid that include at least one feature point; determining color values of all pixels within the grid cells of the second grid that include at least one matching feature point; calculating average color value differences between all the pixels within the grid cells of the first grid that include at least one feature point and all the pixels within the grid cells of the second grid that include at least one matching feature point; and determining the similarity values of the plurality of feature points and the corresponding plurality of matching feature points based on the average color value differences. 
     Implementations of the subject matter and the functional operations described in this specification can be implemented in digital electronic circuitry, in tangibly embodied computer software or firmware, in computer hardware, including the structures disclosed in this specification and their structural equivalents, or in combinations of one or more of them. Software implementations of the described subject matter can be implemented as one or more computer programs, that is, one or more modules of computer program instructions encoded on a tangible, non-transitory, computer-readable computer-storage medium for execution by, or to control the operation of, data processing apparatus. Alternatively, or additionally, the program instructions can be encoded in/on an artificially generated propagated signal, for example, a machine-generated electrical, optical, or electromagnetic signal that is generated to encode information for transmission to suitable receiver apparatus for execution by a data processing apparatus. The computer-storage medium can be a machine-readable storage device, a machine-readable storage substrate, a random or serial access memory device, or a combination of computer-storage mediums. Configuring one or more computers means that the one or more computers have installed hardware, firmware, or software (or combinations of hardware, firmware, and software) so that when the software is executed by the one or more computers, particular computing operations are performed. 
     The term “real-time,” “real time,” “realtime,” “real (fast) time (RFT),” “near(ly) real-time (NRT),” “quasi real-time,” or similar terms (as understood by one of ordinary skill in the art), means that an action and a response are temporally proximate such that an individual perceives the action and the response occurring substantially simultaneously. For example, the time difference for a response to display (or for an initiation of a display) of data following the individual&#39;s action to access the data can be less than 1 ms, less than 1 sec., or less than 5 secs. While the requested data need not be displayed (or initiated for display) instantaneously, it is displayed (or initiated for display) without any intentional delay, taking into account processing limitations of a described computing system and time required to, for example, gather, accurately measure, analyze, process, store, or transmit the data. 
     The terms “data processing apparatus,” “computer,” or “electronic computer device” (or equivalent as understood by one of ordinary skill in the art) refer to data processing hardware and encompass all kinds of apparatus, devices, and machines for processing data, including by way of example, a programmable processor, a computer, or multiple processors or computers. The apparatus can also be, or further include special purpose logic circuitry, for example, a central processing unit (CPU), an FPGA (field programmable gate array), or an ASIC (application-specific integrated circuit). In some implementations, the data processing apparatus or special purpose logic circuitry (or a combination of the data processing apparatus or special purpose logic circuitry) can be hardware- or software-based (or a combination of both hardware- and software-based). The apparatus can optionally include code that creates an execution environment for computer programs, for example, code that constitutes processor firmware, a protocol stack, a database management system, an operating system, or a combination of execution environments. The present disclosure contemplates the use of data processing apparatuses with or without conventional operating systems, for example LINUX, UNIX, WINDOWS, MAC OS, ANDROID, IOS, or any other suitable conventional operating system. 
     A computer program, which can also be referred to or described as a program, software, a software application, a module, a software module, a script, or code can be written in any form of programming language, including compiled or interpreted languages, or declarative or procedural languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program can, but need not, correspond to a file in a file system. A program can be stored in a portion of a file that holds other programs or data, for example, one or more scripts stored in a markup language document, in a single file dedicated to the program in question, or in multiple coordinated files, for example, files that store one or more modules, sub-programs, or portions of code. A computer program can be deployed to be executed on one computer or on multiple computers that are located at one site or distributed across multiple sites and interconnected by a communication network. 
     While portions of the programs illustrated in the various figures are shown as individual modules that implement the various features and functionality through various objects, methods, or other processes, the programs can instead include a number of sub-modules, third-party services, components, libraries, and such, as appropriate. Conversely, the features and functionality of various components can be combined into single components, as appropriate. Thresholds used to make computational determinations can be statically, dynamically, or both statically and dynamically determined. 
     The methods, processes, or logic flows described in this specification can be performed by one or more programmable computers executing one or more computer programs to perform functions by operating on input data and generating output. The methods, processes, or logic flows can also be performed by, and apparatus can also be implemented as, special purpose logic circuitry, for example, a CPU, an FPGA, or an ASIC. 
     Computers suitable for the execution of a computer program can be based on general or special purpose microprocessors, both, or any other kind of CPU. Generally, a CPU will receive instructions and data from and write to a memory. The essential elements of a computer are a CPU, for performing or executing instructions, and one or more memory devices for storing instructions and data. Generally, a computer will also include, or be operatively coupled to, receive data from or transfer data to, or both, one or more mass storage devices for storing data, for example, magnetic, magneto-optical disks, or optical disks. However, a computer need not have such devices. Moreover, a computer can be embedded in another device, for example, a mobile telephone, a personal digital assistant (PDA), a mobile audio or video player, a game console, a global positioning system (GPS) receiver, or a portable storage device, for example, a universal serial bus (USB) flash drive, to name just a few. 
     Computer-readable media (transitory or non-transitory, as appropriate) suitable for storing computer program instructions and data includes all forms of permanent/non-permanent or volatile/non-volatile memory, media and memory devices, including by way of example semiconductor memory devices, for example, random access memory (RAM), read-only memory (ROM), phase change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), and flash memory devices; magnetic devices, for example, tape, cartridges, cassettes, internal/removable disks; magneto-optical disks; and optical memory devices, for example, digital video disc (DVD), CD-ROM, DVD+/−R, DVD-RAM, DVD-ROM, HD-DVD, and BLURAY, and other optical memory technologies. The memory can store various objects or data, including caches, classes, frameworks, applications, modules, backup data, jobs, web pages, web page templates, data structures, database tables, repositories storing dynamic information, and any other appropriate information including any parameters, variables, algorithms, instructions, rules, constraints, or references thereto. Additionally, the memory can include any other appropriate data, such as logs, policies, security or access data, reporting files, as well as others. The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry. 
     To provide for interaction with a user, implementations of the subject matter described in this specification can be implemented on a computer having a display device, for example, a CRT (cathode ray tube), LCD (liquid crystal display), LED (Light Emitting Diode), or plasma monitor, for displaying information to the user and a keyboard and a pointing device, for example, a mouse, trackball, or trackpad by which the user can provide input to the computer. Input can also be provided to the computer using a touchscreen, such as a tablet computer surface with pressure sensitivity, a multi-touch screen using capacitive or electric sensing, or other type of touchscreen. Other kinds of devices can be used to provide for interaction with a user as well; for example, feedback provided to the user can be any form of sensory feedback, for example, visual feedback, auditory feedback, or tactile feedback; and input from the user can be received in any form, including acoustic, speech, or tactile input. In addition, a computer can interact with a user by sending documents to and receiving documents from a device that is used by the user; for example, by sending web pages to a web browser on a user&#39;s client device in response to requests received from the web browser. 
     The term “graphical user interface,” or “GUI,” can be used in the singular or the plural to describe one or more graphical user interfaces and each of the displays of a particular graphical user interface. Therefore, a GUI can represent any graphical user interface, including but not limited to, a web browser, a touch screen, or a command line interface (CLI) that processes information and efficiently presents the information results to the user. In general, a GUI can include a plurality of user interface (UI) elements, some or all associated with a web browser, such as interactive fields, pull-down lists, and buttons. These and other UI elements can be related to or represent the functions of the web browser. 
     Implementations of the subject matter described in this specification can be implemented in a computing system that includes a back-end component, for example, as a data server, or that includes a middleware component, for example, an application server, or that includes a front-end component, for example, a client computer having a graphical user interface or a Web browser through which a user can interact with an implementation of the subject matter described in this specification, or any combination of one or more such back-end, middleware, or front-end components. The components of the system can be interconnected by any form or medium of wireline or wireless digital data communication (or a combination of data communication), for example, a communication network. Examples of communication networks include a local area network (LAN), a radio access network (RAN), a metropolitan area network (MAN), a wide area network (WAN), Worldwide Interoperability for Microwave Access (WIMAX), a wireless local area network (WLAN) using, for example, 802.11 a/b/g/n or 802.20 (or a combination of 802.11x and 802.20 or other protocols consistent with this disclosure), all or a portion of the Internet, or any other communication system or systems at one or more locations (or a combination of communication networks). The network can communicate with, for example, Internet Protocol (IP) packets, Frame Relay frames, Asynchronous Transfer Mode (ATM) cells, voice, video, data, or other suitable information (or a combination of communication types) between network addresses. 
     The computing system can include clients and servers. A client and server are generally remote from each other and typically interact through a communication network. The relationship of client and server arises by virtue of computer programs running on the respective computers and having a client-server relationship to each other. 
     While this specification contains many specific implementation details, these should not be construed as limitations on the scope of any invention or on the scope of what can be claimed, but rather as descriptions of features that can be specific to particular implementations of particular inventions. Certain features that are described in this specification in the context of separate implementations can also be implemented, in combination, in a single implementation. Conversely, various features that are described in the context of a single implementation can also be implemented in multiple implementations, separately, or in any suitable sub-combination. Moreover, although previously described features can be described as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can, in some cases, be excised from the combination, and the claimed combination can be directed to a sub-combination or variation of a sub-combination. 
     Particular implementations of the subject matter have been described. Other implementations, alterations, and permutations of the described implementations are within the scope of the following claims as will be apparent to those skilled in the art. While operations are depicted in the drawings or claims in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed (some operations can be considered optional), to achieve desirable results. In certain circumstances, multitasking or parallel processing (or a combination of multitasking and parallel processing) can be advantageous and performed as deemed appropriate. 
     Moreover, the separation or integration of various system modules and components in the previously described implementations should not be understood as requiring such separation or integration in all implementations, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products. 
     Accordingly, the previously described example implementations do not define or constrain this disclosure. Other changes, substitutions, and alterations are also possible without departing from the spirit and scope of this disclosure. 
     Furthermore, any claimed implementation is considered to be applicable to at least a computer-implemented method; a non-transitory, computer-readable medium storing computer-readable instructions to perform the computer-implemented method; and a computer system comprising a computer memory interoperably coupled with a hardware processor configured to perform the computer-implemented method or the instructions stored on the non-transitory, computer-readable medium.