Patent Publication Number: US-10771769-B2

Title: Distance measuring apparatus, distance measuring method, and imaging apparatus

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a distance measuring apparatus, a distance measuring method, and an imaging apparatus. 
     Description of the Related Art 
     Recently, there has been proposed a technique for acquiring distance information from an image obtained by capturing. For example, there has been proposed a technique for acquiring a plurality of images having different view points, calculating a parallax amount on the basis of a correlation among the acquired plurality of images, and measuring a distance on the basis of the calculated parallax amount (Japanese Patent No. 5192096). There has been proposed a technique for projecting a patterned light on an object having a poor texture to thereby improve measurement accuracy of a correlation, thereby improving measurement accuracy of a distance (S. B. Kang, J. A. Webb, C. L. Zitnick, and T. Kanade, “A Multibaseline Stereo System with Active Illumination and Real-time Image Acquisition”, Proceedings of IEEE International Conference on Computer Vision, (1995) p. 88 to 93, Japanese Patent Application Laid-Open No. 2008-232776). 
     SUMMARY OF THE INVENTION 
     However, in the conventional techniques, a distance cannot always be satisfactorily measured. 
     An object of the present invention is to provide a distance measuring apparatus, a distance measuring method, and an imaging apparatus that can satisfactorily measure a distance. 
     According to an aspect of an embodiment, there is provided a distance measuring apparatus including: an imaging unit capable of acquiring a plurality of images having view points different from one another; and a controlling unit configured to perform control to acquire the plurality of images with the imaging unit in a state in which a patterned light is projected on any region using a projecting unit disposed in a position optically conjugate to the imaging unit and measure a distance on the basis of the plurality of images acquired by the imaging unit. 
     According to the present invention it is possible to provide a distance measuring apparatus, a distance measuring method, and an imaging apparatus that can satisfactorily measure a distance. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating an imaging apparatus according to a first embodiment. 
         FIGS. 2A, 2B, 2C, 2D and 2E  are diagrams illustrating examples of projecting units. 
         FIG. 3  is a diagram illustrating an example in which a parallax occurs between the projecting unit and an imaging unit. 
         FIG. 4  is a flowchart illustrating the operation of the imaging apparatus according to the first embodiment. 
         FIGS. 5A, 5B and 5C  are diagrams illustrating examples of segmentation. 
         FIG. 6  is a flowchart illustrating a method of detecting a position of a main object. 
         FIGS. 7A, 7B and 7C  are diagrams illustrating examples of grouping. 
         FIGS. 8A and 8B  are diagrams illustrating a characteristic value map. 
         FIG. 9  is a diagram illustrating examples of block matching. 
         FIG. 10  is a diagram illustrating a relation between the distance to an object and a parallax. 
         FIG. 11  is a block diagram illustrating an imaging apparatus according to a second embodiment. 
         FIGS. 12A, 12B, 12C, 12D and 12E  are diagrams illustrating an imaging unit. 
         FIG. 13  is a flowchart illustrating the operation of the imaging apparatus according to the second embodiment. 
         FIG. 14  is a flowchart illustrating the operation of an imaging apparatus according to a modification 1 of the second embodiment. 
         FIG. 15  is a block diagram illustrating an imaging apparatus according to a modification 2 of the second embodiment. 
         FIG. 16  is a block diagram illustrating an imaging apparatus according to a third embodiment. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Preferred embodiments of the present invention will now be described in detail in accordance with the accompanying drawings. 
     Embodiments of the present invention are described in detail below with reference to the drawings. Note that the present invention is not limited to the embodiments described below. The embodiments described below may be combined as appropriate. 
     First Embodiment 
     A distance measuring apparatus, a distance measuring method, and an imaging apparatus according to a first embodiment are described with reference to the drawings.  FIG. 1  is a block diagram illustrating the imaging apparatus according to the first embodiment. 
     As illustrated in  FIG. 1 , an imaging apparatus  100  according to this embodiment includes a distance measuring apparatus (a ranging finding apparatus)  107 . The distance measuring apparatus  107  according to this embodiment includes imaging units  101   a  and  101   b  that can acquire a plurality of images having view points different from one another, a projecting unit  102   a  that can project a patterned light, a processing unit  103 , a controlling unit  104 , an optical element  106   a , and a memory  108 . 
     The imaging unit (a first imaging unit)  101   a  includes an imaging element (an image sensor)  109   a  in which a not-illustrated plurality of pixels is disposed in a matrix shape on a not-illustrated imaging surface. The imaging unit  101   a  includes an imaging optical system (a lens unit)  110   a . The imaging optical system  110   a  may be non-detachable or may be detachable from the imaging unit  101   a . The imaging unit  101   a  captures an object  105  to thereby acquire a first image (first image data). 
     The imaging unit (a second imaging unit)  101   b  includes an imaging element (an image sensor)  109   b  in which a not-illustrated plurality of pixels is disposed in a matrix shape on a not-illustrated imaging surface. The imaging unit  101   b  includes an imaging optical system  110   b . The imaging optical system  110   b  may be non-detachable or may be detachable from the imaging unit  101   b . The imaging unit  101   b  captures the object  105  to thereby acquire a second image (second image data). 
     The imaging unit  101   a  and the imaging unit  101   b  are disposed in positions different from each other. Therefore, a parallax occurs between a first image and a second image acquired by the imaging unit  101   a  and the imaging unit  101   b . An image in which a mutual parallax occurs is called parallax image as well. The parallax image is formed by the first image and the second image. Note that, when an imaging unit in general is described, reference numeral  101  is used. When individual specific imaging units are described, reference signs  101   a  and  101   b  are used. An image (image data) acquired by the imaging unit  101  may be, for example, a color image or may be a luminance image (a grey scale image). The color image includes, for example, color information of RGB. The luminance image includes brightness information (luminance information) and does not include color information. The imaging unit  101   a  and the imaging unit  101   b  can be considered as configuring the imaging unit in conjunction with each other. The imaging unit configured by the imaging unit  101   a  and the imaging unit  101   b  can be considered as including a plurality of the imaging elements  109   a  and  109   b  disposed in positions different from each other. The image, that is, the image data acquired by the imaging unit  101  is input to the processing unit  103 . 
     The processing unit (an arithmetic unit)  103  stores, in the memory  108 , the first image input from the imaging unit  101   a  and the second image input from the imaging unit  101   b . The memory  108  can be configured by, for example, a DRAM (Dynamic Random Access Memory) or a flash memory. The processing unit  103  can perform an arithmetic operation for calculating a correlation between the first image and the second image, that is, a correlation operation. The processing unit  103  can calculate the distance (a distance value) to the object  105  on the basis of a correlation value acquired by the correlation operation. The processing unit  103  can generate a distance image, which is an image showing a two-dimensional distribution of a distance value, on the basis of the distance value calculated in this way. The processing unit  103  can generate, on the basis of the image acquired by the imaging unit  101  and the distance image generated as described above, projection control information (region illumination information) for projecting a patterned light on any region (range or place). The projection control information is information indicating, for example, whether the patterned light is projected on the region, what kind of a pattern the patterned light is, illuminance (brightness) of the patterned light, and a color (a wavelength) of the patterned light. The processing unit  103  can be configured by, for example, a CPU (Central Processing Unit) or a DSP (Digital Signal Processor). 
     The projecting unit  102   a  can project a patterned light on any region in a projectable range. The projecting unit  102   a  is disposed in a position optically conjugate to the imaging unit  101 . Specifically, the projecting unit  102   a  is disposed in a position optically conjugate to the imaging unit  101   a . That is, an exit pupil of the projecting unit  102   a  is disposed in a position optically conjugate to an entrance pupil of the imaging unit  101   a  via the optical element  106   a  such as a prism or a half mirror. At least a part of a field of view of the imaging unit  101  and at least a part of the projectable range of the projecting unit  102   a  overlap each other. The projectable range of the projecting unit  102   a  desirably coincides with the field of view of the imaging unit  101  or includes the field of view of the imaging unit  101 . 
     The controlling unit  104  controls the entire imaging apparatus  100 . The controlling unit  104  controls the projecting unit  102   a  on the basis of projection control information to thereby project a patterned light on any region as appropriate within the projectable range of the projecting unit  102   a . The projecting unit  102   a  can also project a patterned light of a single color or can also project a color patterned light. That is, the projecting unit  102   a  can project, as appropriate, a plurality of patterned lights having colors different from one another on any region. The controlling unit  104  can be configured by, for example, a CPU. The processing unit  103  and the controlling unit  104  can be considered as configuring a controlling unit in conjunction with each other. The controlling unit  104  can control, for each of regions, a pattern, illuminance, or a wavelength of the patterned light projected using the projecting unit  102   a . The controlling unit  104  can determine, on the basis of an image acquired by the imaging unit  101 , a region on which the patterned light is projected. The controlling unit  104  can determine, on the basis of space frequencies of textures of respective regions in the image acquired by the imaging unit  101 , the region on which the patterned light is projected. The controlling unit  104  can determine, on the basis of possibility of measurement of a distance based on a plurality of images acquired by the imaging unit  101 , the region on which the patterned light is projected. The controlling unit  104  can perform control to project another patterned light having a pattern, illuminance, or a wavelength different from the pattern, the illuminance, or the wavelength of the patterned light on a first region where a distance cannot be measured on the basis of the plurality of images acquired by the imaging unit  101  in a state in which the patterned light is projected. The controlling unit  104  can perform control to measure a distance on the basis of a plurality of images acquired by the imaging unit in a state in which the other patterned light is projected. When the luminance of the first region at the time when the patterned light is projected is smaller than a first threshold, the controlling unit  104  can perform control to project another patterned light having illuminance higher than the illuminance of the patterned light on the first region. The controlling unit  104  can perform control to measure a distance on the basis of a plurality of images acquired by the imaging unit  101  in a state in which the other patterned light is projected. When the luminance of the first region at the time when the patterned light is projected is smaller than the first threshold, the controlling unit  104  can project another patterned light having a wavelength different from the wavelength of the patterned light on the first region. The controlling unit  104  can perform control to measure a distance on the basis of a plurality of images acquired by the imaging unit  101  in a state in which the other patterned light is projected. The controlling unit  104  can perform control to project a patterned light on a region where a repeated pattern is present. 
       FIGS. 2A to 2E  are diagrams illustrating examples of projecting units.  FIGS. 2A and 2B  illustrate an example of a transmission-type projecting unit. As illustrated in  FIG. 2A , the projecting unit  102   a  includes a light source  201 , a transmission-type light modulator  202 , and a projection lens  203 . Light is emitted from the light source  201 . As the light source  201 , for example, a semiconductor light emitting element that emits white light is used. As such a semiconductor light emitting element, for example, a light emitting diode (LED) or an organic light emitting diode (OLED) is used. As such a semiconductor light emitting element, a laser diode (LD) may be used. 
     The light modulator (a light modulating element)  202  modulates the light emitted from the light source  201 . As the light modulator  202 , for example, a transmission-type electrooptical panel is used. As the transmission-type electrooptical panel, for example, a transmission-type liquid crystal panel is used.  FIG. 2B  is a diagram illustrating an example of pixels included in the light modulator  202 . As illustrated in  FIG. 2B , the light modulator  202  includes a plurality of unit pixels (pixels)  204 . The plurality of unit pixels  204  is arrayed two-dimensionally, that is, in a matrix shape. The respective unit pixels  204  include pixels R corresponding to red (R), pixels G corresponding to green (G) and pixels B corresponding to blue (B). The pixels R include red color filters. The pixels G include green color filters. The pixels B include blue color filters. Lights passing through the respective pixels R, G and B are respectively colored by the color filters. The light modulator  202  performs control on the respective pixels R, G and B on the basis of the projection control information to thereby modulate, that is, spatially modulate the light emitted from the light source  201 . The projection control information includes information indicating the luminance of the R, G and B pixels included in the respective unit pixels  204 . 
     Note that a light condensing optical system widely used in a general-purpose projector may be provided between the light source  201  and the light modulator  202 . 
     As the projection lens  203 , for example, a convex lens is used. The projection lens  203  expands the light modulated by the light modulator  202  and projects a patterned light on a predetermined surface configuring an object. For example, such a patterned light can be projected on a floor surface configuring the object. Such a patterned light can be projected on an object such as a piece of furniture disposed on the floor surface. 
     The projecting unit  102   a  can project the patterned light on, for example, any region within a projectable range T illustrated in  FIG. 2A . A range of a projectable range T may be equal to a range of a floor surface F, may be wider than the range of the floor surface F, or may be narrower than the range of the floor surface F. As illustrated in  FIG. 2A , for example, projection regions T 1  to T 4  and a non-projection region Tb are located within the projectable range T. The projection regions T 1  to T 4  are regions on which the patterned light is projected. The non-projection region Tb is a region on which the patterned light is not projected in the projectable range T. The projecting unit  102   a  performs the projection of the patterned light by controlling the light modulator  202  on the basis of the projection control information. As described above, the projection control information is information indicating whether the patterned light is projected on the region, what kind of a pattern the patterned light is, illuminance of the patterned light, and a color of the patterned light. Therefore, the projecting unit  102   a  can perform the projection of the patterned light such that the patterned light is projected on a certain region in the projectable range and the patterned light is not projected on a certain region in the projectable range. The projecting unit  102   a  can set a type of a pattern for each of regions, can set brightness of the patterned light for each of the regions, and can set a color of the patterned light for each of the regions. 
       FIG. 2C  illustrates an example of a reflection-type projecting unit. As illustrated in  FIG. 2C , the projecting unit  102   a  includes the light source  201 , a reflection-type light modulator  205 , and the projection lens  203 . As the reflection-type light modulator  205 , for example, a DMD (Digital Micromirror Device) can be used.  FIG. 2D  is a diagram illustrating an example of micromirrors included in the light modulator  205 . As illustrated in  FIG. 2D , the light modulator  205  includes a plurality of movable micromirrors  206 . The plurality of micromirrors  206  is disposed in a matrix shape. The light modulator  205  performs control on the respective micromirrors  206  on the basis of the projection control information to thereby modulate, that is, spatially modulate light emitted from the light source  201 . The projecting unit  102   a  includes a not-illustrated light-source controlling unit (a light source driver) that controls the light source  201  and a not-illustrated DMD controlling unit (a DMD driver) that controls inclination (rotation) of the respective plurality of micromirrors  206  included in the light modulator  205 . The projecting unit  102   a  controls the inclination of the respective micromirrors  206  as appropriate with the DMD controlling unit while adjusting a color (a wavelength) of a patterned light and illuminance (a light amount or brightness) of the patterned light as appropriate with the light-source controlling unit. Consequently, the projecting unit  102   a  can control projection of the patterned light on the projection regions T 1  to T 4  and non-projection of the patterned light on the non-projection region Tb. 
       FIG. 2E  illustrates an example of a projecting unit including a self-light emitting panel. As illustrated in  FIG. 2E , the projecting unit  102   a  includes a self-light emitting panel  207  on which self-light emitting elements are disposed in a matrix shape and the projection lens  203 . As the self-light emitting panel  207 , for example, an organic EL panel on which organic light emitting diodes are disposed in a matrix shape or an LED panel on which light emitting diodes are disposed in a matrix shape can be used. 
     Note that the projecting unit  102   a  is not limited to these projecting units. For example, a plurality of shutters (not illustrated in  FIGS. 2A to 2E ) may be disposed in front of the light source  201  to respectively correspond to the projection regions T 1  to T 4 . The patterned light may be projected on the projection regions T 1  to T 4  as appropriate by opening and closing the shutters as appropriate. In  FIGS. 2C and 2D , an example is described in which the DMD is used as the reflection-type light modulator  205 . However, the reflection-type light modulator  205  is not limited to the DMD. For example, a LCOS (Liquid crystal on silicon), which is a reflection-type liquid crystal panel, may be used as the light modulator  205 . A Galvano scanner obtained by combining a laser light source and a Galvano mirror may be used in the projecting unit  102   a.    
     In this way, the projecting unit  102   a  can perform the projection of the patterned light such that the patterned light is projected on a certain region in the projectable range and the patterned light is not projected on a certain region in the projectable range. The projecting unit  102   a  can set a type of a pattern for each of regions, can also set brightness of the patterned light for each of the regions, and can also set a color of the patterned light for each of the regions. 
     As described above, the projecting unit  102   a  is disposed in the position optically conjugate to the imaging unit  101   a . That is, the exit pupil of the projecting unit  102   a  is disposed in a position optically conjugate to the entrance pupil of the imaging unit  101   a  via the optical element  106   a  such as a prism or a half mirror. The projecting unit  102   a  is disposed in the position optically conjugate to the imaging unit  101   a  because of a reason described below. When the exit pupil of the projecting unit  102   a  is not disposed in the position optically conjugate to the entrance pupil of the imaging unit  101 , a parallax occurs between the projecting unit  102   a  and the imaging unit  101 .  FIG. 3  is a diagram illustrating an example in which a parallax occurs between the projecting unit  102   a  and the imaging unit  101 . When it is attempted to project a patterned light on a part of attention  304  of the object  105  on the basis of an image  301  obtained by the imaging unit  101 , a problem described below occurs if a parallax is present between the projecting unit  102   a  and the imaging unit  101 . That is, in such a case, if a positional relation between the projecting unit  102   a  and the imaging unit  101  and a distance value z from the imaging unit  101  to the part of attention  304  cannot be specified, it cannot be specified where on an epipolar line viewed from the projecting unit  102   a  the part of attention  304  is present. Therefore, in such a case, it is difficult to project the patterned light on the part of attention  304  from the projecting unit  102   a . Because of such a reason, in this embodiment, the projecting unit  102   a  is disposed in the position optically conjugate to the imaging unit  101   a.    
       FIG. 4  is a flowchart illustrating the operation of the imaging apparatus according to this embodiment. 
     First, in step S 401 , the controlling unit  104  acquires an image by performing imaging using the imaging unit  101  in a state in which a patterned light is not projected. 
     In step S 402 , the processing unit  103  generates projection control information, for example, as described below using the image acquired in step S 401 . That is, the processing unit  103  performs, on the image acquired in step S 401 , area division, that is, segmentation with, for example, graph cut in which a super pixel is used.  FIGS. 5A to 5C  are diagrams illustrating an example of the segmentation.  FIG. 5A  illustrates an example of an input image, that is, the image acquired in step S 401 . As illustrated in  FIG. 5A , an image  501  includes objects  502  and  503 . The processing unit  103  performs grouping on such an image  501  as described below. That is, when a difference between an evaluation value of a certain group and an evaluation value of a certain element is equal to or smaller than a preset threshold, the processing unit  103  combines the element with the group. On the other hand, when the difference between the evaluation value of the group and the evaluation value of the element exceeds the threshold, the processing unit  103  does not combine the element with the group. Such an element may be, for example, a pixel or may be a block. Such an evaluation value can be determined on the basis of a coordinate, a luminance value, and color information. The luminance value and the color information are obtained by converting, for example, data of YCrCb. By performing the grouping with such a method, groups  504 ,  505  and  506  illustrated in  FIGS. 5B and 5C , that is, segments are generated. Note that such a grouping method is described in, for example, “New Edition Image Analysis Handbook”, Mikio Takagi and Haruhisa Shimoda, University of Tokyo Press, 2004. Such a grouping method is called region growth method.  FIG. 5C  illustrates a state in which the segmentation is performed. In this way, the segmentation is performed on the image  501  acquired in step S 401 . Thereafter, the processing unit  103  performs, through a Wavelet analysis or a frequency analysis, a texture analysis on the segments obtained by the segmentation, that is, a region of interest. The processing unit  103  generates projection control information on the basis of a result of the texture analysis. As described above, the projection control information is information for controlling, for example, whether the patterned light is projected on the region, what kind of a pattern the patterned light is, illuminance (brightness) of the patterned light, and a color (a wavelength) of the patterned light. The processing unit  103  generates, for example, projection control information for projecting the patterned light on a region having a poor texture and not projecting the patterned light on a region having a rich texture. For example, when the patterned light is projected on the region although a sufficiently fine texture is present in the region, the resolution of a correlation value is likely to decrease to the contrary. Therefore, for example, projection control information for not projecting the patterned light on a region where a sufficiently fine texture is present is generated. When the patterned light is irradiated on a region where a repeated pattern is present, projection control information for erasing the repeated pattern with a repeated pattern of a complementary color of the repeated pattern and projecting light of a desired pattern may be generated. A material and a reflectance of an object may be estimated according to a color and a texture to adjust a color and illuminance of the patterned light as appropriate. For example, since a black region highly likely has a low reflectance, a patterned light having large illuminance may be projected. A type of a pattern may be set as appropriate on the basis of the breadth of a region on which the pattern light is projected. The type of the pattern may be set as appropriate on the basis of a tilt of a surface of the region on which the patterned light is projected. The tilt of the surface can be estimated, for example, on the basis of a change gradient of a gradation. Examples of the type of the pattern include a bar-like pattern, a checker pattern, and a circular pattern. For example, when light of the circular pattern is projected on a surface, the normal of which greatly tilts with respect to the optical axis of the imaging unit  101 , accuracy of a calculated distance value decreases. However, robust association can be formed. 
     Note that a generation method for projection control information is not limited to the methods described above. For example, projection control information for projecting a patterned light on a region where a main object is located and not projecting the patterned light on a region other than the region where the main object is located. Such projection control information can be generated, for example, on the basis of a position of the main object detected as described below 
       FIG. 6  is a flowchart illustrating a method of detecting a position of the main object. In step S 601 , the processing unit  103  performs grouping, that is, grouping processing as described below on the image acquired in step S 401 .  FIGS. 7A to 7C  are diagrams illustrating an example of the grouping.  FIG. 7A  illustrates an image  701  acquired in step S 401 . The image  701  is a color image or a luminance image.  FIG. 7B  is a diagram illustrating raster scan. Arrows conceptually indicate the raster scan. As indicated by the arrows in  FIG. 7B , the scan is started from the upper left of the image  701  and performed until the scan reaches the lower right. The grouping processing may be performed in units of a pixel or may be performed in units of a block, which is a set of local pixels. An example is described in which the grouping is performed in units of a block. However, the grouping can be performed in units of a pixel in the same manner as the grouping in units of a block. The processing unit  103  performs determination described below among a certain block G(x, y), a block G(x, y−1) located on the upper side of the block G(x, y), and a block G(x−1, y) located on the left side of the block G(x, y). That is, the processing unit  103  determines whether these blocks are included in the same group. By sequentially performing such determination, the processing unit  103  can resultantly determine whether adjacent blocks are included in the same group. In this case, no block is present on the upper side of a block located on the upper edge of the image  701 , that is, a block of y=0. Therefore, such determination processing is not performed on the block. No block is present on the left side of a block located on the left edge of the image  701 , that is, a block of x=0. Therefore, such determination processing is not performed on the block. The processing unit  103  records a result of the determination in the memory  108 . For example, a number  1  is affixed to, for example, a block corresponding to a group detected first. For example, a number  2  is affixed to, for example, a block corresponding to a group detected second. For example, a number  3  is affixed to, for example, a block corresponding to a group detected third. Processing for affixing numbers to blocks is called labeling.  FIG. 7C  is a diagram illustrating a state in which the labeling is performed. As illustrated in  FIG. 7C , a number  1  is affixed to a block corresponding to an object  702 , a number  2  is affixed to a block corresponding to an object  703 , and a number  3  is affixed to a block corresponding to an object  704 . When a difference between an evaluation value of a certain block and an evaluation value of a block adjacent to the block is equal to or smaller than a preset threshold, the processing unit  103  determines that these blocks belong to the same group. On the other hand, when a difference between an evaluation value of a certain block and an evaluation value of a block adjacent to the block exceeds the threshold, the processing unit  103  determines that these blocks do not belong to the same group. Such evaluation values can be determined on the basis of gradation, specifically, a luminance value and color information. Such evaluation value can also be determined on the basis of a distance value, which is the distance to an object. 
     In step S 602 , the processing unit  103  calculates a characteristic value, which is a value indicating a characteristic of each group located in the image, in other words, each group located in a capturing space. Such a characteristic value is used to determine a main object region in step S 603  described below. Examples of such a characteristic value include a main object degree. For example, the processing unit  103  calculates a main object degree, which is a characteristic value, with respect to an object corresponding to each group. The main object degree is comprehensively calculated on the basis of a distance J to the object corresponding to the group, width C of the group in the image, height H of the group in the image, and a distance P from the center of the image to the center of gravity position of the group. For example, a main object degree S can be calculated on the basis of Expression (1) described below.
 
 S =( a 1× C+a 2× H )/ P+a 3× J   (1)
 
     Note that, in Expression (1), a 1 , a 2  and a 3  are weighting constants. For example, the distance J to the object may be, for example, an average distance to parts of the object or may be a representative value of the distance to the object. The distance J to the object can be calculated, for example, on the basis of a correlation between the first image acquired by the imaging unit  101   a  and the second image acquired by the imaging unit  101   b . When the distance J to the object is the average distance to the parts of the object, for example, distances to the parts of the object are calculated for each of blocks. 
       FIGS. 8A and 8B  are diagrams illustrating a characteristic value map.  FIG. 8A  is a characteristic value map  801  corresponding to the image  701  illustrated in  FIG. 7A . In  FIG. 8A , a characteristic value is higher as luminance is higher. That is, a white portion in  FIG. 8A  has a highest characteristic value. A black portion in  FIG. 8A  has a lowest characteristic value. Numerical values illustrated in  FIG. 8A  indicate descending order of characteristic values. The characteristic value is higher as the numerical value illustrated in  FIG. 8A  is smaller. As illustrated in  FIG. 8A , the object  703  that occupies a large area in the image  701  and is close to the center in the image  701  and located in a place close to the imaging apparatus  100  has a high characteristic value. On the other hand, the object  702  that occupies a small area in the image  701  and is located in the peripheral part in the image  701  and located in a place far from the imaging apparatus  100  has a low characteristic value. 
     In step S 603 , the processing unit  103  selects a main object region, for example, as described below. For example, the processing unit  103  determines a group having a high main object degree as a group corresponding to a main object and sets, as a main object region, a region corresponding to a block belonging to the group determined as the group corresponding to the main object. As described above, in  FIG. 8A , a characteristic value is higher as a numerical value is smaller. Therefore, an object having a highest characteristic value is an object located in a place to which a numerical value 1 is affixed in  FIG. 8A . The region to which 2 is affixed in  FIG. 7A  corresponds to a region having a highest characteristic value. Therefore, a region labeled as  2  in  FIG. 7C  is determined as a main object region. 
     In step S 604 , the processing unit  103  determines whether a region characteristic value of the main object region determined in step S 603  is equal to or larger than a threshold. When the characteristic value is equal to or larger than the threshold (YES in step S 604 ), that is, when a main object is present in the image, the processing unit  103  issues a flag indicating that the main object is present and shifts to step S 605 . On the other hand, when the characteristic value is smaller than the threshold (NO in step S 604 ), that is, a main object is absent in the image, the processing unit  103  issues a flag indicating that a main object is absent and ends the processing illustrated in  FIG. 6 . 
     In step S 605 , the processing unit  103  determines a position of the main object. The position of the main object is determined, for example, on the basis of a coordinate of a pixel corresponding to the main object. 
     In this way, main object information indicating whether a main object is included in the image and the position of the main object is acquired. 
     The processing unit  103  generates, on the basis of the main object information obtained in this way, projection control information for projecting a patterned light on only the main object region.  FIG. 8B  is a diagram illustrating an example of the projection control information. A region to which 1 is affixed in  FIG. 8B  indicates a region on which a patterned light is projected. The region to which 1 is affixed in  FIG. 8B  corresponds to the region to which 2 is affixed in  FIG. 7C , that is, a region corresponding to the object  703 . As the patterned light, for example, a bar-like pattern, which is a most orthodox pattern, is used. 
     In this way, the projection control information for projecting the patterned light on the region where the main object is located and not projecting the patterned light on the region other than the region where the main object is located may be generated. 
     In step S 403 , the controlling unit  104  performs imaging using the imaging unit  101   a  and the imaging unit  101   b  in a state in which the patterned light is projected using the projecting unit  102   a  on the basis of the projection control information generated in step S 402 . Consequently, a first image and a second image in a state in which the patterned light is irradiated on a desired region are acquired. 
     In step S 404 , the processing unit  103  performs, on the basis of a correlation between the first image and the second image acquired in step S 403 , distance measurement for calculating distances to parts in the image. The processing unit  103  generates a distance image (a distance map) indicating a two-dimensional distribution of a distance value on the basis of a result of the distance measurement. A correlation value is calculated on the basis of the first image and the second image captured in the state in which the patterned light is irradiated on the desired region. A distance value is calculated on the basis of the correlation value. Therefore, a satisfactory distance image can be obtained. 
     Note that the distance image obtained in this way can be used for, for example, processing described below. For example, it is possible to perform processing for focusing on any part, that is, auto-focus processing on the basis of the distance value indicated by the distance image. By performing, as appropriate, on the image acquired by the imaging unit  101   a , processing based on a two-dimensional distribution of the distance value indicated by the distance image, it is possible to perform any blur addition processing. It is also possible to perform refocus processing on the basis of the two-dimensional distribution of the distance value indicated by the distance image. 
     A correlation between the first image and the second image can be calculated, for example, as described below.  FIG. 9  is a diagram illustrating an example of block matching. The block matching is a method of detecting corresponding points according to a correlation. A first image  901  located on the left side of  FIG. 9  is a standard image. A second image  902  located on the right side of  FIG. 9  is a reference image. The first image  901  is, for example, an image acquired by the imaging unit  101   a . The second image  902  is, for example, an image acquired by the imaging unit  101   b . A motion vector between the first image  901 , which is the standard image, and the second image  902 , which is the reference image, corresponds to a parallax. The processing unit  103  sets, as a template  903 , a partial region having a predetermined size centering on a point (a point of attention)  904  in the first image  901 . The processing unit  103  sets any search range  907  in the second image  902  and sequentially moves, in the search range  907 , a partial region  906  having a predetermined size centering on a point (a point of attention or a corresponding point)  905 . The processing unit  103  searches for a position where the template  903  and the partial region  906  coincide most while sequentially moving the partial region  906 . Note that the first image  901  and the second image  902  may be color images, may be luminance images, or may be a modulated image such as a differential image. The processing unit  103  calculates a similarity degree between the template  903  and the partial region  906  as described below. That is, the processing unit  103  calculates the similarity degree with a correlation operation such as a SSD (Sum of Square Difference), a SAD (Sum of Absolute Difference), or a normalized cross-correlation. A similarity degree R(x, y, x′, y′) in the normalized cross-correlation is calculated by Expressions (2) and (3) described below. 
     
       
         
           
             
               
                 
                   
                       
                   
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     Note that (x, y) indicates the position of the center of the template  903  in a standard image I, that is, the first image  901 . That is, (x, y) indicates the position of the point (the point of attention)  904 . (x′, y′) indicates the position of the center of the partial region  906  in the second image  902 . That is, (x′, y′) indicates the position of the point (the corresponding point)  905 . I (x, y) (i, j) indicates an image corresponding to the template  903 . I′ x′,Y′) (i, j) indicates an image corresponding to the partial region  906 . 
     The processing unit  103  regards the point  905  having a highest similarity degree as a point (a corresponding point) corresponding to the point  904  as a result of generally calculating the similarity degree between the template  903  and the partial region  906  while sequentially moving the partial region  906  in the search range  907 . Examples of such a similarity degree include a correlation score. The processing unit  103  calculates a motion vector on the basis of the point  904  and the point (the corresponding point)  905  corresponding to the point  904 . If there is no occlusion, basically, motion vectors are calculated by the number of points  904  set in the first image  901 . The motion vector is represented by a vector starting from the position of the point  904  in the first image  901  and ending in the position of the point  905  in the second image  902 . Such a vector is represented by Expression (4) described below.
 
( x,y,x′,y ′) i   ,i= 1, . . . , m ( m :the number of motion vectors)  (4)
 
     Note that polynomial fitting may be carried out on the correlation score acquired by sequentially moving the partial region  906  within the search range  907 . A peak position of the similarity degree may be more highly accurately calculated. The point  905  corresponding to the point  904  may be calculated at sub-pixel accuracy by performing processing for increasing pixels of the first image  901  and the second image  902 . 
     The processing unit  103  acquires a dense corresponding point image by calculating, in the second image, points (pixels) corresponding to all points (pixels) in the first image. A positional deviation amount d=(x′−x) between the point  904  in the first image  901  and the point  905  in the second image  902  is called parallax. 
       FIG. 10  is a diagram illustrating a relation between the distance to the object and the parallax. When the parallax is represented as d and the distance from the imaging unit  101  to the object is represented as z, Expression (5) described below holds. 
     
       
         
           
             
               
                 
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     Note that B represents a base line length, specifically, the distance between the imaging unit  101   a  and the imaging unit  101   b , λ represents a pixel size, and f represents a focal length of the imaging unit  101 . The processing unit  103  generates a distance image indicating a two-dimensional distribution of a distance value z on the basis of Expression (5). 
     In this way, according to this embodiment, the projection control information is generated on the basis of the image acquired by the imaging unit  101   a  disposed in the position optically conjugate to the projecting unit  102   a . The projection of the patterned light is performed by the projecting unit  102   a  on the basis of the projection control information. Therefore, according to this embodiment, it is possible to provide a distance measuring apparatus and an imaging apparatus including the distance measuring apparatus that can project a patterned light on a desired region and satisfactorily measure a distance. 
     Second Embodiment 
     A distance measuring apparatus, a distance measuring method, and an imaging apparatus according to a second embodiment are described with reference to the drawings.  FIG. 11  is a block diagram illustrating an imaging apparatus  1100  according to this embodiment. The same components as the components of the imaging apparatus according to the first embodiment illustrated in  FIGS. 1 to 10  are denoted by the same reference numerals and signs. Description of the components is omitted or simplified. 
     As illustrated in  FIG. 11 , the imaging apparatus  1100  according to this embodiment includes a distance measuring apparatus  1102 . The distance measuring apparatus  1102  includes one imaging unit  1101 , three projecting units  102   a  to  102   c , the processing unit  103 , the controlling unit  104 , optical elements  106   a  and  106   b , and the memory  108 . 
       FIG. 12A  is a diagram illustrating the imaging unit  1101 . As illustrated in  FIG. 12A , an imaging element  1202  is included in a body (main body)  1216  of the imaging unit  1101 . An imaging optical system (a lens or a lens unit)  1207  including a lens  1201  is included in the main body  1216  of the imaging unit  1101 . The imaging optical system  1207  is an imaging optical system, that is, a pupil division optical system configured to divide an exit pupil  1205  into a first pupil region  1206   a  and a second pupil region  1206   b  different from each other. The imaging optical system  1207  may be detachably from the main body  1216  of the imaging unit  1101  or may be non-detachable from the main body  1216 . The imaging unit  1101  can acquire a plurality of optical images, that is, a first optical image and a second optical image formed by a first light beam  1214   a  and a second light beam  1214   b  respectively passing through the first pupil region  1206   a  and the second pupil region  1206   b  of the imaging optical system  1207 . The first optical image is called A image as well and the second optical image is called B image as well. The processing unit (the arithmetic unit)  103  calculates a parallax amount, which is a relative positional deviation amount between the A image and the B image acquired by the imaging unit  1101 , and converts the parallax amount into a defocus amount using a conversion coefficient based on the base line length to thereby calculate a distance to an object. In other words, the processing unit  103  converts the parallax amount into a distance value on the basis of the base line length and a geometrical relation. For example, an interval on the exit pupil  1205  between the center of gravity of the first light beam  1214   a  passing through the first pupil region  1206   a  and the center of gravity of the second light beam  1214   b  passing through the second pupil region  1206   b  corresponds to the base line length. In this way, a distance from the imaging unit  1101  to the object is calculated. 
     On an imaging surface (a pixel array region)  1215  of the imaging element  1202 , a large number of unit pixels  1207 R,  1207 G and  1207 B are disposed in a matrix shape.  FIG. 12B  is a diagram illustrating a layout of the unit pixels  1207 R,  1207 G and  1207 B disposed on the imaging surface  1215  of the imaging element  1202 . As illustrated in  FIG. 12B , the unit pixels (rang finding pixels)  1207 R,  1207 G and  1207 B are arrayed on an xy plane. Such an array is called Bayer array. Note that an example is described in which the array of the unit pixels  1207 R,  1207 G and  1207 B is the Bayer array. However, the array of the unit pixels  1207 R,  1207 G and  1207 B is not limited to the Bayer array and can be set as appropriate. Note that, when a unit pixel in general is described, reference numeral  1207  is used. When specific unit pixels are described, reference numerals  1207 R,  1207 G and  1207 B are used.  FIG. 12C  is a sectional view of the respective unit pixels. As illustrated in  FIG. 12C , photoelectric conversion sections  1208 Ra,  1208 Rb,  1208 Ga,  1208 Gb,  1208 Ba and  1208 Bb are formed on semiconductor substrates  1209 . Note that, when a photoelectric conversion section in general is described, reference numeral  1208  is used. When specific photoelectric conversion elements are described, reference signs  1208 Ra,  1208 Rb,  1208 Ga,  1208 Gb,  1208 Ba and  1208 Bb are used. As the semiconductor substrates  1209 , for example, silicon substrates are used. The photoelectric conversion section  1208  is formed by, for example, an ion injection method. The unit pixel  1207 R of red (R) includes a divided pixel  1207 Ra including the photoelectric conversion section  1208 Ra and a divided pixel  1207 Rb including the photoelectric conversion section  1208 Rb. The unit pixel  1207 G of green (G) includes a divided pixel  1207 Ga including the photoelectric conversion section  1208 Ga and a divided pixel  1207 Gb including the photoelectric conversion section  1208 Gb. The unit pixel  1207 B of blue (B) includes a divided pixel  1207 Ba including the photoelectric conversion section  1208 Ba and a divided pixel  1207 Bb including the photoelectric conversion section  1208 Bb. The divided pixels  1207 Ra,  1207 Ga and  1207 Ba are pixels for acquiring the A image. The divided pixels  1207 Rb,  1207 Gb and  1207 Bb are divided pixels for acquiring the B image. 
     Interlayer insulating films  1211  are formed on the semiconductor substrates  1209  on which photoelectric conversion sections  1208  are formed. Not-illustrated wires are formed on the interlayer insulating films  1211 . Waveguides  1210  are embedded in the interlayer insulating films  1211 . The waveguides  1210  are respectively formed with respect to the unit pixels  1207 R,  1207 G and  1207 B. The color filters  1212 R,  1212 G, and  1212 B are respectively formed on the interlayer insulating films  1211  in which the waveguides  1210  are embedded. The color filter  1212 R is formed in the unit pixel  1207 R of R, the color filter  1212 G is formed in the unit pixel  1207 G of G, and the color filter  1212 B is formed in the unit pixel  1207 B of B. The color filter  1212 R has a spectral characteristic corresponding to a wavelength band of red. Consequently, light in the wavelength band of red reaches the photoelectric conversion sections  1208 Ra and  1208 Rb. The color filter  1212 G has a spectral characteristic corresponding to a wavelength band of green. Consequently, light in the wavelength band of green reaches the photoelectric conversion sections  1208 Ga and  1208 Gb. The color filter  1212 B has a spectral characteristic corresponding to a wavelength band of blue. Consequently, light in the wavelength band of blue reaches the photoelectric conversion sections  1208 Ba and  1208 Bb. Microlenses  1213  are respectively formed on the interlayer insulating films  1211  on which the color filters  1212 R,  1212 G and  1212 B are formed. The microlenses  1213  are respectively formed with respect to the unit pixels  1207 R,  1207 G and  1207 B. 
     The first light beam  1214   a  having passed through the first pupil region  1206   a  in the exit pupil  1205  reaches the divided pixels  1207 Ra,  1207 Ga and  1207 Ba. The second light beam  1214   b  having passed through the second pupil region  1206   b  in the exit pupil  1205  reaches the divided pixels  1207 Rb,  1207 Gb and  1207 Bb. The first signal forming the first image, that is, the A image is configured by a set of signals acquired by the large number of divided pixels  1207 Ra,  1207 Ga and  1207 Ba. The second signal forming the second image, that is, the B image is configured by a set of signals acquired by the divided pixels  1207 Rb,  1207 Gb and  1207 Bb. The divided pixels  1207 Ra,  1207 Ga and  1207 Ba are pixels for obtaining the A image. Therefore, the divided pixels  1207 Ra,  1207 Ga and  1207 Ba are called A pixels as well. The divided pixels  1207 Rb,  1207 Gb and  1207 Bb are pixels for obtaining the B image. Therefore, the divided pixels  1207 Rb,  1207 Gb and  1207 Bb are called B pixels as well. The A image and the B image acquired in this way are transmitted to the processing unit  103 . Range finding operation processing is performed in the processing unit  103 . 
     The processing unit  103  calculates a defocus amount, which is distance information, on the basis of a deviation amount between the A image and the B image, that is, an image deviation amount. An optical image of the object  105  is focused on the imaging element  1202  via the imaging optical system  1207 .  FIG. 12A  illustrates a state in which the first light beam  1214   a  and the second light beam  1214   b  having passed through the exit pupil  1205  are respectively focused on an image forming surface  1203  and defocused optical images reach the imaging surface  1215  of the imaging element  1202 . Note that the defocus means a state in which the image forming surface  1203  and the imaging surface  1215  do not coincide and the image forming surface  1203  deviates in the direction of an optical axis  1204  with respect to the imaging surface  1215 . A defocus amount is the distance between the imaging surface  1215  and the image forming surface  1203  in the direction of the optical axis  1204 . The processing unit  103  calculates a distance to the object  105  on the basis of the defocus amount. A relation indicated by Expression (6) below holds between an image deviation amount r indicating a relative positional deviation between the A image and the B image and a defocus amount ΔL. 
     
       
         
           
             
               
                 
                   
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                       - 
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     Note that W represents a base line length and L represents the distance between the imaging surface  1215  and the exit pupil  1205  in the direction of the optical axis  1204 . The base line length W is equivalent to an interval on the exit pupil  1205  between the center of gravity of the first light beam  1214   a  passing through the first pupil region  1206   a  and the center of gravity of the second light beam  1214   b  passing the second pupil region  1206   b.    
     Expression (6) can be simplified like Expression (7) below using a conversion coefficient K.
 
Δ L≅K·r   (7)
 
     Note that a calculation method for the defocus amount is not limited to the method described above. Other publicly-known methods may be used as appropriate. 
     The projecting unit (a first projecting unit)  102   a  is disposed in a position optically conjugate to the imaging unit  1101 . That is, the exit pupil of the projecting unit  102   a  is disposed in a position optically conjugate to an entrance pupil of the imaging unit  1101  via the optical element  106   a  such as a prism or a half mirror. The projecting unit (a second projecting unit)  102   b  is disposed in a position optically conjugate to the imaging unit  1101 . That is, the exit pupil of the projecting unit  102   b  is disposed in a position optically conjugate to the entrance pupil of the imaging unit  1101  via the optical element  106   b  such as a prism or a half mirror. In this way, in this embodiment, the two projecting units  102   a  and  102   b  are disposed in the positions optically conjugate to the imaging unit  1101 . At least a part of a field of view of the imaging unit  1101  and at least a part of the projectable ranges of the projecting units  102   a  and  102   b  overlap each other. The projectable ranges of the projecting units  102   a  and  102   b  desirably coincide with the field of view of the imaging unit  1101  or include the field of view of the imaging unit  1101 . 
     Like the projecting unit  102   a  described above in the first embodiment, the projecting unit  102   a  can project a patterned light on a desired region within the projectable range. The projecting unit  102   a  can also project a single color patterned light and can also project a color patterned light. 
     The projecting unit (the second projecting unit)  102   b  can project a patterned light different from the patterned light projected by the projecting unit  102   a . For example, the projecting unit  102   b  can project a patterned light having a wavelength different from the wavelength (the color) of the patterned light projected by the projecting unit  102   a . For example, a patterned light of visible light may be projected by the projecting unit  102   a  and a patterned light in a near infrared region may be projected by the projecting unit  102   b . The projecting unit  102   b  can project a patterned light having illuminance different from the illuminance of the patterned light projected by the projecting unit  102   a . For example, a patterned light having extremely high illuminance with respect to the patterned light projected by the projecting unit  102   a  may be projected by the projecting unit  102   b . The controlling unit  104  can perform control to calculate a distance on the basis of a plurality of images acquired by the imaging unit  1101  in a state in which a patterned light is projected using another projecting unit  102   b  disposed in the position optically conjugate to the imaging unit  1101 . The patterned light projected by the projecting unit  102   a  and the patterned light projected by the other projecting unit  102   b  are different from each other in the wavelength or the illuminance. 
     The projecting unit (a third projecting unit)  102   c  is disposed in a position not optically conjugate to the imaging unit  1101  and the projecting units  102   a  and  102   b . When the luminance of a second region where a distance cannot be measured on the basis of a plurality of images acquired by the imaging unit  1101  in a state in which a patterned light is projected is equal to or larger than a second threshold, the controlling unit  104  can perform control as described below. That is, the controlling unit  104  can project a patterned light on the second region using the other projecting unit  102   c  disposed in a position different from the position of the projecting unit  102   a . The controlling unit  104  can perform control to measure a distance on the basis of a plurality of images acquired by the imaging unit  1101  in a state in which a patterned light is projected on the second region using the other projecting unit  102   c.    
       FIG. 13  is a flowchart illustrating the operation of the imaging apparatus according to this embodiment. 
     In step S 1301 , the controlling unit  104  acquires an image using the imaging unit  1101  in a state in which a patterned light is not projected. 
     In step S 1302 , the processing unit  103  calculates a distance to the object  105  using a first image and a second image, that is, a parallax image acquired by the imaging unit  1101 . A distance can be satisfactorily calculated concerning a portion where a texture is present in the object  105 . On the other hand, a distance cannot be satisfactorily calculated concerning a portion where a texture is absent and a portion where a repeated texture is present in the object  105 . The processing unit  103  performs an analysis of the texture of the object  105  to thereby generate first projection control information (first region illumination information) for irradiating a suitable patterned light on a region where a distance cannot be satisfactorily calculated. 
     In step S 1303 , the controlling unit  104  performs imaging using the imaging unit  1101  in a state in which a patterned light is projected using the projecting unit (the first projecting unit)  102   a  on the basis of the first projection control information generated in step S 1302 . 
     In step S 1304 , the processing unit  103  performs, on the basis of a correlation between the first image and the second image acquired in step S 1303 , distance measurement for calculating distances to parts in the images. The processing unit  103  also performs the distance measurement for a region where a distance is already successfully satisfactorily calculated in step S 1302 . Since the distance is calculated on the basis of the parallax image acquired in the state in which the patterned light is irradiated, a distance can be satisfactorily calculated in a region wider than the region where the distance is successfully satisfactorily calculated in step S 1302 . The processing unit  103  generates a distance image indicating a two-dimensional distribution of a distance value on the basis of a distance value acquired in this way. However, even if the distance is measured on the basis of the parallax image acquired in the state in which the patterned light is projected based on the first projection control information, a region where a distance cannot be satisfactorily calculated is sometimes present. For example, in a region having a low reflectance in the object, sufficient reflected light cannot be obtained even if the patterned light is projected. Therefore, a distance sometimes cannot be satisfactorily calculated in the region. When a difference between a color of the region and a color of the patterned light is insufficient, a sufficient texture is not given to the region even if the patterned light is projected. A distance sometimes cannot be satisfactorily calculated. When light mirror-reflected in the region reaches the imaging unit  1101 , a pixel value (luminance) is saturated. Therefore, a distance cannot be satisfactorily calculated. Therefore, in this embodiment, processing described below is performed. 
     In step S 1305 , the processing unit  103  determines whether a pixel value of the region where a distance cannot be satisfactorily calculated is smaller than a preset first threshold. When the pixel value of the region is smaller than the first threshold, it is conceivable that the reflectance of the region is extremely low or a difference between a color of the patterned light projected using the projecting unit  102   a  in step S 1303  and a color of the region is insufficient. Therefore, in this case (YES in step S 1305 ), the processing unit  103  shifts to step S 1306 . On the other hand, when the pixel value of the region is equal to or larger than the first threshold (NO in step S 1305 ), the processing unit  103  shifts to step S 1309 . 
     In step S 1306 , the processing unit  103  generates second projection control information. For example, second projection control information for projecting a patterned light having large illuminance (a large light amount) on the region with the projecting unit (the second projecting unit)  102   b  is formed. The processing unit  103  may form second projection control information for projecting, on the region, a patterned light having a color sufficiently different from the color of the patterned light projected using the projecting unit  102   a  in step S 1303 . If such a patterned light is projected on the region, it is possible to add a sufficient texture to the region. 
     In step S 1307 , the controlling unit  104  performs capturing using the imaging unit  1101  in a state in which a patterned light is projected using the projecting unit (the second projecting unit)  102   b  on the basis of the second projection control information generated in step S 1306 . 
     In step S 1308 , the processing unit  103  performs, on the basis of the correlation between the first image and the second image acquired in step S 1307 , distance measurement for calculating distances to the parts in the images. The processing unit  103  may perform the distance measurement again or may not perform the distance measurement again for a region where a distance is already successfully satisfactorily calculated. Since the distance is calculated on the basis of the parallax image acquired in the state in which the patterned light is irradiated using the projecting unit  102   b  on the basis of the second projection control information, a distance sometimes can be satisfactorily calculated in a region where a distance is not successfully satisfactorily calculated in step S 1304 . For example, when the reflectance of the region is low or when a difference between a color of the patterned light projected using the projecting unit  102   a  in step S 1303  and a color of the region is insufficient, a distance to the region can be satisfactorily calculated in step S 1308 . The processing unit  103  updates the distance image generated in step S 1304  using a distance value successfully satisfactorily acquired anew. In this way, a more satisfactory distance image is obtained. 
     In step S 1309 , the processing unit  103  determines whether a pixel value of the region where a distance cannot be satisfactorily calculated is equal to or larger than a preset second threshold. Note that the second threshold is equal to or larger than the first threshold. When the pixel value of the region is equal to or larger than the second threshold, it is conceivable that light mirror-reflected in the region reaches the imaging unit  1101 . Therefore, in this case (YES in step S 1309 ), the processing unit  103  shifts to step S 1310 . On the other hand, when the pixel value of the region is smaller than the second threshold (NO in step S 1309 ), the processing unit  103  ends the processing illustrated in  FIG. 13 . 
     In step S 1310 , the processing unit  103  generates third projection control information. The processing unit  103  generates third projection control information for projecting a patterned light with the projecting unit (the third projecting unit)  102   c  not optically conjugate to the imaging unit  1101 . If the patterned light is projected by the projecting unit  102   c  not optically conjugate to the imaging unit  1101 , that is, the projecting unit  102   c  not optically conjugate to the projecting unit  102   a , it is possible to prevent the light mirror-reflected in the region from reaching the imaging unit  1101 . 
     In step S 1311 , the controlling unit  104  performs capturing using the imaging unit  1101  in a state in which a patterned light is projected using the projecting unit (the third projecting unit)  102   c  on the basis of the third projection control information generated in step S 1310 . 
     In step S 1312 , the processing unit  103  performs, on the basis of a correlation between a first image and a second image acquired in step S 1311 , distance measurement for calculating distances to parts in the images. The processing unit  103  may perform the distance measurement again or may not perform the distance measurement again for a region where a distance is already successfully satisfactorily calculated. The distance is calculated on the basis of a parallax image acquired in a state in which a patterned light is projected using the projecting unit  102   c  on the basis of the third projection control information. Therefore, a distance sometimes can be satisfactorily calculated in a region where a distance is not successfully satisfactorily calculated in step S 1304  or step S 1308 . For example, when the patterned light projected using the projecting units  102   a  and  102   b  is mirror-reflected in the region and reaches the imaging unit  1101 , a distance to the region can be satisfactorily calculated in step S 1312 . The processing  103  updates the already generated distance image using a distance value successfully satisfactorily acquired anew. In this way, a more satisfactory distance image is obtained. 
     According to this embodiment, a distance value is calculated on the basis of the parallax image acquired in the state in which the patterned light projected using the projecting units  102   b  and  102   c  is projected on the basis of the second or third projection control information different from the first projection control information. Therefore, it is possible to satisfactorily calculate a distance value for a region where a distance value cannot be satisfactorily acquired on the basis of the parallax image acquired in the state in which the patterned light projected using the projecting unit  102   a  is projected on the basis of the first projection control information. Therefore, according to this embodiment, it is possible to provide a distance measuring apparatus and an imaging apparatus including the distance measuring apparatus that can more satisfactorily measure a distance. 
     (Modification 1) 
     A distance measuring apparatus, a distance measuring method, and an imaging apparatus according to a modification 1 of this embodiment are described with reference to  FIG. 14 .  FIG. 14  is a flowchart illustrating the operation of the imaging apparatus according to this modification. The configuration of the imaging apparatus according to this modification is the same as the configuration of the imaging apparatus described above with reference to  FIGS. 11 to 12E . In step S 1401 , the controlling unit  104  performs imaging using the imaging unit  1101  in a state in which a patterned light is projected on the entire region of the projectable range of the projecting unit (the first projecting unit)  102   a . Steps S 1402  to S 1410  are the same as steps S 1304  to S 1312  described above with reference to  FIG. 13 . Therefore, description of the steps is omitted. A distance may be measured in this way under an environment in which it is difficult to measure a distance without projecting a patterned light. 
     (Modification 2) 
     A distance measuring apparatus, a distance measuring method, and an imaging apparatus according to a modification 2 of this embodiment are described with reference to  FIG. 15 .  FIG. 15  is a block diagram illustrating the imaging apparatus according to this modification. As illustrated in  FIG. 15 , an imaging apparatus  1500  according to this modification includes a distance measuring apparatus  1503 . The distance measuring apparatus  1503  includes two imaging units  1101  and  1501 , the three projecting units  102   a  to  102   c , the processing unit  103 , the controlling unit  104 , the optical elements  106   a  and  106   b , and the memory  108 . 
     The imaging unit  1501  is disposed in a position optically conjugate to the imaging unit  1101 . That is, an entrance pupil of the imaging unit  1501  is disposed in a position optically conjugate to the entrance pupil of the imaging unit  1101  via an optical element  1502  such as a prism or a half mirror. The imaging unit  1501  includes an imaging element  1504 . The imaging unit  1501  includes an imaging optical system (a lens or a lens unit)  1505 . Like the imaging optical system  1207 , the imaging optical system  1505  is an imaging optical system configured to be divided into a first pupil region and a second pupil region, exit pupils of which are different from each other, that is, a pupil division optical system. The imaging optical system  1505  may be detachable or may be non-detachable from a main body of the imaging unit  1501 . Like the imaging unit  1101 , the imaging unit  1501  includes the imaging element  1504 . Like the imaging element  1202 , the imaging element  1504  can acquire a plurality of optical images, that is, a first optical image and a second optical image formed by a first light beam and a second light beam respectively passing through the first pupil region and the second pupil region of the imaging optical system  1505 . Capturing sensitivity of the imaging unit  1501  is different from capturing sensitivity of the imaging unit  1101 . The capturing sensitivity of the imaging unit  1101  is set, for example, relatively low. On the other hand, the capturing sensitivity of the imaging unit  1501  is set, for example, relatively high. Since the capturing sensitivity of the imaging unit  1101  is set relatively low, if a distance is measured on the basis of a parallax image acquired by the imaging unit  1101 , it is possible to satisfactorily measure the distance even when the luminance of an object is relatively high. On the other hand, since the capturing sensitivity of the imaging unit  1501  is set relatively high, if a distance is measured on the basis of the parallax image acquired by the imaging unit  1101 , it is possible to satisfactorily measure the distance even when the luminance of the object is relatively low. If a distance image is generated using results of these measurements as appropriate, it is possible to obtain a satisfactory distance image. 
     Note that an example is described in which the capturing sensitivity of the imaging unit  1101  and the capturing sensitivity of the imaging unit  1501  are differentiated. However, the present invention is not limited to this. For example, a capturing wavelength region of the imaging unit  1101  and a capturing wavelength region of the imaging unit  1501  may be differentiated. The capturing wavelength region of the imaging unit  1101  is, for example, a visible light region. The capturing wavelength region of the imaging unit  1501  is, for example, a near infrared region. The processing unit  103  performs distance measurement using a parallax image acquired by the imaging unit  1101 . The processing unit  103  performs distance measurement using a parallax image acquired by the imaging unit  1501 . If a distance image is generated using results of the distance measurements as appropriate, it is possible to obtain a satisfactory distance image. 
     Third Embodiment 
     A distance measuring apparatus, a distance measuring method, and an imaging apparatus according to a third embodiment are described with reference to  FIG. 16 .  FIG. 16  is a block diagram illustrating the imaging apparatus according to this embodiment. The same components as the components of the imaging apparatus according to the first or second embodiment illustrated in  FIGS. 1 to 15  are denoted by the same reference numerals and signs. Description of the components is omitted or simplified. 
     As illustrated in  FIG. 16 , an imaging apparatus  1600  according to this embodiment includes a distance measuring apparatus  1601 . The distance measuring apparatus  1601  includes three imaging units  101   a  to  101   c , three projecting units  102   a ,  102   c  and  102   d , the processing unit  103 , the controlling unit  104 , the optical elements  106  and  106   b , and the memory  108 . The configuration of the imaging unit  101   c  is the same as the configuration of the imaging units  101   a  and  101   b  described with reference to  FIG. 1 . The imaging units  101   a  to  101   c  are disposed in positions different from one another. The imaging units  101   a  to  101   c  perform capturing from view points different from one another. According to this embodiment, images are acquired using the three imaging units  101   a  to  101   c  disposed in positions different from one another. Therefore, three images, among which a parallax occurs, are obtained. Capturing performed using three imaging units is called trinocular stereo view as well. The imaging unit (the third imaging unit)  101   c  includes an imaging element (an image sensor)  109   c  in which a not-illustrated plurality of pixels is disposed in a matrix shape on a not-illustrated imaging surface. The imaging unit  101   c  includes an imaging optical system (a lens unit)  110   c . The imaging optical system  110   c  may be detachable or may be non-detachable from the imaging unit  101   c . The imaging unit  101   c  captures the object  105  to thereby acquire a first image (third image data). 
     The projecting unit  102   a  is disposed in a position optically conjugate to the imaging unit  101   a . That is, the exit pupil of the projecting unit  102   a  is disposed in a position optically conjugate to the entrance pupil of the imaging unit  101   a  via the optical element  106   a  such as a prism or a half mirror. The projecting unit  102   d  is disposed in a position optically conjugate to the imaging unit  101   b . That is, an exit pupil of the projecting unit  102   d  is disposed in a position optically conjugate to an entrance pupil of the imaging unit  101   b  via an optical element  106   c  such as a prism or a half mirror. 
     In a state in which a patterned light is projected on a desired region using the projecting unit  102   a , the controlling unit  104  performs imaging using the imaging units  101   a  to  101   c  and acquires a first parallax image formed by three images, among which a parallax occurs. 
     In a state in which a patterned light is projected on a desired region using the projecting unit  102   c , the controlling unit  104  performs imaging using the imaging units  101   a  to  101   c  and acquires a second parallax image formed by three images, among which a parallax occurs. 
     When the first parallax image is acquired, a patterned light optimum for acquiring the first parallax image is projected from the projecting unit  102   a . When the second parallax image is acquired, a patterned light optimum for acquiring the second parallax image is projected from the projecting unit  102   d . The patterned light projected by the projecting unit  102   a  when the first parallax image is acquired and the patterned light projected by the projecting unit  102   d  when the second parallax image is acquired are different from each other. 
     The processing unit  103  measures a distance with, for example, a multi-baseline stereo method on the basis of the first parallax image. The processing unit  103  measures a distance with, for example, the multi-baseline stereo method on the basis of the second parallax image. The processing unit  103  generates a distance image using results of the measurements as appropriate. According to this embodiment, since a distance is measured using the three images, among which a parallax occurs, it is possible to more highly accurately measure the distance. 
     Modified Embodiment 
     The present invention is described above with reference to the exemplary embodiments of the present invention. However, the present invention is not limited to these specific embodiments. Various forms in a range not departing from the spirit of the present invention are included in the present invention. 
     For example, in the first embodiment, the imaging unit  101   a , the imaging unit  101   b , the optical element  106   a , the projecting unit  102   a , the processing unit  103 , and the controlling unit  104  may be included in a not-illustrated body of the imaging apparatus  100 . 
     In the second embodiment, the example is described in which the processing unit  103  and the controlling unit  104  are disposed separately from the imaging unit  1101 . However, the present invention is not limited to this. For example, the processing unit  103 , the controlling unit  104 , the optical elements  106   a  and  106   b , and the projecting units  102   a  to  102   c  may be included in the body  1216  of the imaging unit  1101 . 
     In the third embodiment, the imaging units  101   a  to  101   c , the optical elements  106   a  and  106   c , the projecting units  102   a ,  102   c  and  102   d , the processing unit  103 , and the controlling unit  104  may be included in a not-illustrated body of the imaging apparatus  1600 . 
     In the embodiments, the example is described in which the processing units (the arithmetic unit)  103  and the controlling unit  104  are separately provided. However, the present invention is not limited to this. The processing unit  103  and the controlling unit  104  may be integrated. The processing unit  103  can be grasped as a part of the controlling unit. The controlling unit  104  and the processing unit  103  may be configured by a system LSI. 
     A method of detecting presence or absence of an object, a position of the object, and a region of the object is not limited to the embodiments. For example, a position of an object and a region of the object may be detected on the basis of a change in luminance and a change in a color in an image (see Japanese Patent Application Laid-Open No. H11-190816). Presence or absence of an object, a position of the object, and a region of the object may be detected on the basis of distance information (see Japanese Patent Application Laid-Open No. 2007-96437). Presence or absence of an object, a position of the object, and a region of the object may be detected on the basis of a change in a luminance gradient (see Japanese Patent Application Laid-Open No. 2000-207564). A position of an object and a region of the object may be detected using K-means clustering (“Comparison of Segmentation Approaches” by Beth Horn, et. al., Decision Analyst Inc., (2009)). 
     In the embodiments, a feature value calculating method such as an SIFT (Scale-Invariant Feature Transform) may be supplementally performed. The region of the object may be further precisely calculated supplementally using information obtained by the feature value calculating method. For example, an SIFT feature value may be further aggregated into a BoF (Bug Of Features). The region of the object may be precisely calculated using the BoF. A multidimensional feature value such as the BoF may be used for determination of presence of absence of a main object and determination of the main object likeness (“Objects in context” by A. Rabinovich, et. al., 2007 IEEE 11th International Conference on Computer Vision, (2007)). A manufacturer or a user of the imaging apparatus may cause a discriminator such as a neural network, deep learning, or an n-ary tree to learn, beforehand, a multidimensional feature value extracted from an image of an object of a main object candidate. A search may be executed on the multidimensional feature value extracted from the image to calculate likelihood of the main object likeness. Consequently, it is possible to flexibly recognize, as the main object, any object that the manufacturer or the user considers as the main object. The region of the object may be detected supplementally using a technique such as Graph Cut. A change in region information in a time direction may be used for improvement of detection accuracy of a boundary. 
     In the third embodiment, the example is described in which the three imaging units are provided. However, four or more imaging units may be provided. 
     Other Embodiments 
     Embodiment(s) of the present invention can also be realized by a computer of a system or apparatus that reads out and executes computer executable instructions (e.g., one or more programs) recorded on a storage medium (which may also be referred to more fully as a ‘non-transitory computer-readable storage medium’) to perform the functions of one or more of the above-described embodiment(s) and/or that includes one or more circuits (e.g., application specific integrated circuit (ASIC)) for performing the functions of one or more of the above-described embodiment(s), and by a method performed by the computer of the system or apparatus by, for example, reading out and executing the computer executable instructions from the storage medium to perform the functions of one or more of the above-described embodiment(s) and/or controlling the one or more circuits to perform the functions of one or more of the above-described embodiment(s). The computer may comprise one or more processors (e.g., central processing unit (CPU), micro processing unit (MPU)) and may include a network of separate computers or separate processors to read out and execute the computer executable instructions. The computer executable instructions may be provided to the computer, for example, from a network or the storage medium. The storage medium may include, for example, one or more of a hard disk, a random-access memory (RAM), a read only memory (ROM), a storage of distributed computing systems, an optical disk (such as a compact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™), a flash memory device, a memory card, and the like. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2017-090624, filed Apr. 28, 2017, which is hereby incorporated by reference herein in its entirety.