Patent Publication Number: US-11388341-B2

Title: Image processing apparatus, image processing method, and storage medium

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to an image processing technique to assist image capturing by an image capturing apparatus. 
     Description of the Related Art 
     An image obtained by image capturing is conventionally displayed by a display apparatus such as a display. In the case of displaying an image obtained by image capturing, however, it is necessary to confirm distribution information of pixel values on an image capturing signal together with the image capturing signal in order to set white balance and exposure of the image capturing signal appropriately in image capturing. 
     As a technique to assist image capturing in such a case, Japanese Patent Laid-Open No. H07-38801, (PTL 1) discloses a technique to convert the distribution of luminance levels of pixel values of an image capturing signal into a histogram, superimpose the histogram on the image capturing signal, and cause a viewfinder to display the histogram. 
     However, the technique disclosed in PTL 1 only shows distribution information of pixel values corresponding to the display on the viewfinder. Accordingly, for example, in the case of clipping a part of an image capturing signal, performing a geometrical conversion of the image, and displaying the image on a display apparatus, there is a problem that a display range often does not correspond to distribution information and it is impossible to generate and provide suitable distribution information for setting white balance and exposure of the image capturing signal. 
     SUMMARY OF THE INVENTION 
     The present invention aims to provide an image capturing apparatus with distribution information on an image capturing signal suitable for a display apparatus. 
     An embodiment of an image processing apparatus of the present invention includes: an image data acquisition unit configured to acquire image data; a configuration information acquisition unit configured to acquire configuration information on a display apparatus which displays at least a part of an image indicated by the image data; a range determination unit configured to determine a range corresponding to the part of the image based on the configuration information; and a display control unit configured to cause a display unit to display the image with distribution information of pixel values corresponding to the range of the image. 
     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 diagram showing a display system; 
         FIG. 2A  is a diagram for explaining display ranges of the display system; 
         FIG. 2B  is a diagram for explaining display ranges of the display system; 
         FIG. 2C  is a diagram for explaining display ranges of the display system; 
         FIG. 3A  is a diagram showing an example of the display ranges; 
         FIG. 3B  is a diagram showing an example of the display ranges; 
         FIG. 3C  is a diagram showing an example of the display ranges; 
         FIG. 4  is a diagram showing a hardware configuration of an image processing apparatus; 
         FIG. 5  is a diagram showing a hardware configuration of an image capturing system; 
         FIG. 6  is a block diagram showing a functional configuration of the image processing apparatus; 
         FIG. 7  is a flowchart showing a procedure of processing executed by the image processing apparatus; 
         FIG. 8  is a flowchart showing a procedure of processing executed by an image clipped range determination unit; 
         FIG. 9A  is a diagram showing positions of edges of image display areas in screens; 
         FIG. 9B  is a diagram showing positions of edges of image display areas in screens; 
         FIG. 9C  is a diagram showing positions of edges of image display areas in screens; 
         FIG. 10A  is a diagram showing a three-dimensional space coordinate system; 
         FIG. 10B  is a diagram showing a three-dimensional space coordinate system; 
         FIG. 11  is a diagram showing a two-dimensional UV coordinate system; 
         FIG. 12  is a flowchart showing a procedure of processing executed by an output image generation unit; 
         FIG. 13A  is a diagram showing distribution information; 
         FIG. 13B  is a diagram showing distribution information; 
         FIG. 13C  is a diagram showing distribution information; 
         FIG. 14A  is a diagram showing an image obtained by superimposing distribution information images on an input image; 
         FIG. 14B  is a diagram showing an image obtained by superimposing distribution information images on an input image; 
         FIG. 14C  is a diagram showing an image obtained by superimposing distribution information images on an input image; 
         FIG. 15  is a flowchart showing a procedure of processing executed by the output image generation unit; 
         FIG. 16A  is a diagram showing an image obtained by superimposing distribution information images on an input image; 
         FIG. 16B  is a diagram showing an image obtained by superimposing distribution information images on an input image; 
         FIG. 16C  is a diagram showing an image obtained by superimposing distribution information images on an input image; 
         FIG. 17A  is a diagram showing an example of a curved screen; 
         FIG. 17B  is a diagram showing an example of a curved screen; 
         FIG. 17C  is a diagram showing an example of a curved screen; 
         FIG. 18A  is a diagram showing an example of a screen having a special shape; 
         FIG. 18B  is a diagram showing an example of a screen having a special shape; 
         FIG. 18C  is a diagram showing an example of a screen having a special shape; 
         FIG. 19A  is a diagram showing an image obtained by superimposing distribution information images on an input image; 
         FIG. 19B  is a diagram showing an image obtained by superimposing distribution information images on an input image; and 
         FIG. 19C  is a diagram showing an image obtained by superimposing distribution information images on an input image. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, with reference to the attached drawings, the present invention is explained in detail in accordance with preferred embodiments. Configurations shown in the following embodiments are merely exemplary and the present invention is not limited to the configurations shown schematically. 
     First, a supplementary explanation will be given of the problem to be solved by the present invention, followed by the description of the embodiments of the present invention with reference to the drawings. The embodiments described below do not limit the present invention. Not all combinations of the features described in the embodiments are essential for solving the problem to be solved by the present invention. In the description below, the same reference numerals are assigned to the same features. 
     Before the description of the embodiments, a supplementary explanation will be given of the problem to be solved by the present invention. In the case of causing a display apparatus different from an image capturing apparatus to display an image obtained by image capturing, it is necessary to clip a part of the image depending on the configuration of the display apparatus. In this case, however, if colors and exposure of a range to be clipped cannot be confirmed in framing at the time of image capturing, color tone adjustment for the entire image often interferes with image capturing settings suitable for the actually used clipped range. 
     For example, it is assumed that an image is displayed by a display system shown in  FIG. 1 . The display system of  FIG. 1  comprises three screens and three projectors. In the display system of  FIG. 1 , a left side screen  802  and a right side screen  803  are arranged at a spread angle α with respect to a center screen  801 . 
     Although not shown in  FIG. 1 , the three projectors are piled and arranged directly above a viewpoint position (viewer) to project images on the respective screens. It is assumed that the viewpoint position is apart from the center of the center screen  801  by a distance D view  in a direction orthogonal to the center screen  801 . In this manner, video is displayed using the three screens arranged to cover the greater part of the viewer&#39;s field of view, which makes it possible to provide high reality video experience as if the viewer is present there. 
       FIG. 2A  shows a captured image  901  to be displayed on the screens of the display system described above.  FIG. 2B  shows display ranges  902  to  904  to be clipped from the image in the case of displaying a part of the image on each screen of the display system described above. 
     Regarding the shapes of the display ranges, for example, in a case where the three screens of the same size are arranged side by side, all the display ranges  902  to  904  are rectangles of the same size. However, in a case where the three screens are arranged side by side, high reality video experience cannot be realized. In order to realize higher reality video experience, it is preferable to arrange the screens so as to cover a viewer&#39;s field of view as described above. That is, it is preferable to arrange the left side screen  802  and the right side screen  803  at an angle with respect to the center screen  801  like the display system shown in  FIG. 1 . 
     In the case of arranging the screens so as to cover a viewer&#39;s field of view, however, the display range  902  is rectangular, whereas the display range  903  and the display range  904  are trapezoidal as shown in  FIG. 2B . In addition, the shapes of the display ranges  902  to  904  also vary depending on a projection method of a lens used for capturing the captured image  901 .  FIG. 2B  shows the display ranges in the case of a general center projection lens. For example, in the case of using a fisheye lens of equidistant projection, display ranges  1001  to  1003  have shapes more roundish than those in the case of the center projection lens as shown in  FIG. 3B . 
     As described above, in the case of superimposing the captured image  901  shown in  FIG. 2A  on the display ranges  902  to  904  of the screens shown in  FIG. 2B  based on the premise that the display range  903  and the display range  904  are trapezoidal, the display is as shown in  FIG. 2C . 
     An image capturer captures an image while confirming an image to be captured and distribution information on the image to be captured, which are displayed on a display unit of the image capturing apparatus such as an electronic viewfinder (EVF) or a monitor, and adjusting image capturing conditions such as an angle of view, white balance, and exposure. This enables the image capturer to confirm a range of the image to be captured at that time and distribution information of pixel values on the entire image. However, in the case of displaying the captured image  901  on the screens shown in  FIG. 1 , an image capturer cannot know what ranges in the captured image  901  will be displayed on the screens. 
     Accordingly, the image capturer cannot confirm distribution information of pixel values corresponding to the clipped ranges in the captured image and may adjust, for example, the color tone of the entire image based on the distribution information of pixel values on the entire image, which often interferes with appropriate settings of white balance and exposure in the actually clipped ranges. As a result, in a case where parts of the captured image  901  are clipped and displayed on the screens, there is a problem that a captured image desired by the image capturer cannot be appropriately displayed. 
     Therefore, in the embodiments described below, an image capturer is provided with distribution information of pixel values corresponding to clipped ranges of an image obtained by image capturing at the time of image capturing. More specifically, in image capturing, clipped ranges are calculated based on the configuration of a display apparatus and the mode of display, distribution information of pixel values corresponding to the clipped ranges is generated, and the generated distribution information is superimposed on an image obtained by image capturing and displayed. 
     This enables the image capturer to know distribution information of pixel values on ranges displayable by the display apparatus in the image obtained by image capturing. In the description below, a display apparatus or display system that displays a part of a captured image after image capturing will be referred to as a first display apparatus or first display system. An apparatus that displays an image on which distribution information is superimposed in image capturing will be referred to as a second display apparatus. In a case where a display unit of an image capturing apparatus is used as the second display apparatus, the display unit will be referred to as a second display unit. 
     First Embodiment 
     Hardware Configuration of Image Processing Apparatus 
       FIG. 4  is a diagram showing a hardware configuration of an image processing apparatus  1  which generates (outputs) data for displaying generated distribution information according to a display apparatus. The image processing apparatus  1  is, for example, a computer, and comprises a CPU  101 , a RAM  102 , a ROM  103 , an HDD interface (I/F)  104 , an input I/F  106 , an output I/F  108 , and an image capturing apparatus I/F  110 . 
     The CPU  101  executes a program stored in the ROM  103  and the hard disk drive (HDD)  105  using the RAM  102  as a work memory and controls each block via a system bus  100 . The HDD I/F  104  is an interface such as a serial ATA (SATA). The HDD I/F  104  is connected to a secondary storage device such as an HDD  105  or optical disk drive. 
     The CPU  101  can read data from the HDD  105  and write data to the HDD  105  via the HDD I/F  104 . The CPU  101  can also load data stored in the HDD  105  into the RAM  102  and store the data loaded into the RAM  102  in the HDD  105 . In addition, the CPU  101  can execute the data loaded into the RAM  102  as a program. 
     The input I/F  106  is a serial bus interface such as a Universal Serial Bus (USB) or IEEE1394. The input I/F  106  is connected to an input device  107  such as a keyboard or mouse. The CPU  101  can read data from the input device  107  via the input I/F  106 . 
     The output I/F  108  is a video output interface such as a Digital Visual Interface (DVI) or a High-Definition Multimedia Interface (HDMI; registered trademark). The output I/F  108  is connected to an output device  109  such as a liquid crystal display. The output device  109  corresponds to the second display unit or second display apparatus described above. The CPU  101  transmits data to the output device  109  via the output I/F  108 , thereby performing processing such as display. 
     The image capturing apparatus I/F  110  is a serial bus interface such as a USB. The image capturing apparatus I/F  110  is connected to an image capturing apparatus  111  such as a video camera. The CPU  101  can acquire image capturing data such as frame data on a moving image from the image capturing apparatus  111  via the image capturing apparatus I/F  110 . 
     The image processing apparatus  1  does not necessarily comprise the image capturing apparatus I/F  110 . In this case, instead of the image capturing apparatus I/F  110 , the image capturing apparatus is connected to the input I/F  106 . Alternatively, an image capturing apparatus into which the image capturing apparatus  111  and the output device  109  are integrated may be connected to the image capturing apparatus I/F  110 . For example, a video camera comprising a display unit such as an EVF or monitor may be used as the image capturing apparatus  111 . In this case, the CPU  101  can perform processing such as display by transmitting data to the display unit via the image capturing apparatus I/F  110 . 
     Further, the image processing apparatus  1  may be included in the output device  109  or the image capturing apparatus  111 . For example, the image processing apparatus  1 , the output device  109 , and the image capturing apparatus  111  may be integrated into an image capturing system.  FIG. 5  shows a hardware configuration of an image capturing system  1600 . The image capturing system  1600  is, for example, a digital camera, and comprises the CPU  101 , the RAM  102 , the ROM  103 , the HDD interface (I/F)  104 , an input unit  1601 , a display unit  1602 , and an image capturing unit  1603 . 
     The input unit  1601  is an input unit such as a button. The display unit  1602  is a display unit such as an EVF or monitor. The image capturing unit  1603  is an image capturing unit including an optical system such as a lens and configured to generate an image via the optical system. The image capturing system  1600  does not necessarily comprise the input unit  1601  and the display unit  1602  separately and may comprise a touch panel display or the like into which the input unit  1601  and the display unit  1602  are integrated. The image capturing system may be a portable information terminal such as a smartphone. 
     Functional Configuration of Image Processing Apparatus 
     Next, a functional configuration of the image processing apparatus  1  will be described.  FIG. 6  is a block diagram showing a functional configuration of the image processing apparatus  1 . The CPU  101  reads a program stored in the ROM  103  or HDD  105  and executes it using the RAM  102  as a work area, thereby functioning as the functional configuration shown in  FIG. 6 . Not all the processes described below should be executed by the CPU  101 . The image processing apparatus  1  may be configured such that some or all of the processes are executed by one or more processing circuits other than the CPU  101 . 
     The image processing apparatus  1  comprises a configuration information acquisition unit  201 , an input image acquisition unit  202 , a viewpoint information acquisition unit  203 , an image capturing condition acquisition unit  204 , an image clipped range determination unit  205 , an output image generation unit  206 , and an output unit  207 . 
     The configuration information acquisition unit  201  acquires configuration information indicating a configuration of the first display system which displays an image. The configuration information on the first display system includes information about the number of screens of the first display system, the size of each screen, and the resolution of each screen, and arrangement information indicating the position and orientation of each screen. 
     The input image acquisition unit  202  is an example of an image data acquisition unit and acquires input image data indicating an input image. The input image is an image to be displayed with distribution information of pixel values corresponding to a clipped range superimposed thereon. The viewpoint information acquisition unit  203  acquires viewpoint information indicating the position of a viewpoint in the case of observing an image displayed by the first display system. The image capturing condition acquisition unit  204  acquires image capturing information indicating image capturing conditions. The image capturing information includes the sensor size of the image capturing apparatus  111 , the focal length of a lens, an angle of view, a projection method, and the resolution of an input image. 
     The image clipped range determination unit  205  determines a range to be clipped from an input image. The output image generation unit  206  generates an image with distribution information obtained by superimposing distribution information of pixel values on an input image as image data with distribution information (that is, the output image generation unit  206  is an example of an image data generation unit). In the description below, an image with distribution information and image data with distribution information will also be referred to as an output image and output image data, respectively. The output unit  207  outputs the output image data (image data with distribution information) to the output device  109 . 
     Processing Performed by Image Processing Apparatus 
     Next, the procedure of processing executed by the image processing apparatus  1  will be described with reference to the flowchart of  FIG. 7 . In the description of the flowchart, sign “S” indicates a step. 
     In S 301 , the configuration information acquisition unit  201  acquires configuration information indicating a configuration of the first display system which displays an image. The processing in S 301  is executed based on a user instruction via the input device  107 . In the present embodiment, the configuration information is acquired by selecting one of a plurality of types of configuration information prestored in the HDD  105  based on a user instruction. 
     For a supplementary explanation of the configuration information,  FIG. 1  shows the first display system of the present embodiment. As shown in  FIG. 1 , the first display system comprises the three screens and the three projectors. In the first display system, the left side screen  802  and the right side screen  803  are arranged at the spread angle α with respect to the center screen  801 . 
     Each screen has a width W mm  and a height H mm  and the three screens are equal in size. Images are projected on the screens using the respective projectors, each of which is arranged so as to display an image having a resolution of W pix ×H pix . 
     Although not shown in  FIG. 1 , the three projectors are piled and arranged directly above a viewpoint position and each project an image on the corresponding screen. The position of an image projected by each projector is adjusted by the lens shift function or keystone correction function of the projector. 
     In the case of the first display system shown in  FIG. 1 , the configuration information indicates that the number of screens is 3, the size of each screen is the width W mm  and the height H mm , and the resolution of each screen is W pix ×H pix . In the present embodiment, the resolution of each screen can be read as the resolution of a projector that projects an image on each screen. 
     In the configuration information, the screen arrangement information is represented by the position (x, y, z) of the center of a screen in a three-dimensional XYZ coordinate system and a normal vector N indicating the direction of a normal on the surface of the screen. The normal is a normal on a surface on the side of the viewpoint observing the screen. The origin of the XYZ coordinate system is the viewpoint position indicated by the viewpoint information. 
     As described above, images clipped from an input image are displayed on the respective screens arranged as shown in  FIG. 1 , whereby a viewer can be provided with video of a wider field of view than that in the case of displaying video using a single screen. In addition, since not irrelevant images on the respective screens, but one interlinked image on the plurality of screens are displayed on the respective screens, the display is close to a viewer&#39;s field of view. The screen configuration described above is only an example and the number of screens, size, arrangement and the like are not limited to those described above. 
     In S 302 , the image capturing condition acquisition unit  204  acquires image capturing information indicating image capturing conditions. The processing in S 302  is executed based on a user instruction via the input device  107 . In the present embodiment, image capturing information is acquired by selecting one of a plurality of image capturing conditions prestored in the HDD  105  for each item based on a user instruction. 
     In the image capturing information, the sensor size of the image capturing apparatus  111  is a width SW mm  and a height SH mm , the focal length of a lens is f, an angle of view is θ max , and the resolution of an input image is SW pix ×SH pix . Since the lens of the image capturing apparatus  111  of the present embodiment is a fisheye lens of equidistant projection, the projection method is equidistant projection. 
     In S 303 , the viewpoint information acquisition unit  203  acquires viewpoint information indicating the position of a viewpoint in the case of observing an image displayed by the first display system. The processing in S 303  is executed by a user instruction via the input device  107 . In the present embodiment, the viewpoint information is acquired by selecting one of viewpoint information indicating viewpoint positions prestored in the HDD  105  based on a user instruction. 
     The viewpoint information is represented by the position (0, 0, 0) of a viewpoint in the three-dimensional XYZ coordinate system described above. In the present embodiment, as shown in  FIG. 1 , the viewpoint is located in a position apart from the center of the center screen  801  by the distance D view  in the direction orthogonal to the center screen  801 . However, the position of the viewpoint is not necessarily limited to this. 
     In S 304 , the input image acquisition unit  202  acquires input image data from the image capturing apparatus  111 . More specifically, the input image acquisition unit  202  stores input image data in the RAM  102  via the image capturing apparatus I/F  110 . In the present embodiment, since the image capturing apparatus  111  is a video camera, the subsequent processing will be executed using image data corresponding to each frame of a moving image as input image data. 
     In S 305 , the image clipped range determination unit  205  determines a range to be clipped from an input image by clipping processing, that is, a range to be displayed by the first display system. The processing in this step will be described later with reference to  FIG. 8 . 
     In S 306 , the output image generation unit  206  generates distribution information of pixel values corresponding to the range to be clipped determined in S 305  and superimposes the generated distribution information on the input image data acquired in S 304 , thereby generating image data with distribution information. The processing in this step will be described later with reference to  FIG. 12 . In S 307 , the output unit  207  outputs the image data with distribution information generated in S 306  to the output device  109  via the output I/F  108 . 
     Processing of Image Clipped Range Determination Unit  205  in S 305   
       FIG. 8  is a flowchart showing a procedure of processing executed by the image clipped range determination unit in S 305 . In the processing in S 305 , in order to display images on the three screens forming the first display system shown in  FIG. 1 , clipped ranges in an input image corresponding to the respective screens are sequentially calculated. Each step of the flowchart of  FIG. 8  will be described below. 
     In S 401 , the image clipped range determination unit  205  sets a screen for which the subsequent processing from S 402  to S 407  is not executed as a processing target. In this case, the three screens shown in  FIG. 1  are sequentially set as a processing target. 
     In S 402 , the image clipped range determination unit  205  specifies positions (points) corresponding to an edge portion of an image display area on a screen at predetermined intervals based on the screen size and screen arrangement information, and calculates three-dimensional coordinates of each of the specified points P. More specifically, the output image generation unit  206  generates three-dimensional coordinates (x, y, z) of each point P as point group data. The three-dimensional coordinates used here are three-dimensional coordinates using the viewpoint position observing the screen as the origin. 
     In the present embodiment, an interval between the points P is determined based on the resolution of the screen. As described above, the size of the screen is the width W mm  and the height H mm  and the resolution of the screen is W pix ×H pix . Thus, based on the size and resolution, three-dimensional coordinates of the center point of each pixel on the screen are calculated. Out of the three-dimensional coordinates of the center points of the respective pixels, all three-dimensional coordinates of pixels corresponding to the edge portion of the image display area are generated as point group data on the processing target. 
       FIG. 9  is a diagram showing the positions of edges of image display areas on the screens.  FIG. 9A  shows the three screens in  FIG. 1  observed from the viewpoint position in front of the center screen  801 . As described above, since the entire screen is an image display area in the present embodiment, the positions of the edges in the image display areas on the screens are positions indicated by thick lines  1101  in  FIG. 9B . 
     However, the entire screen is not necessarily used as an image display area. For example, as shown by thick lines  1102  in  FIG. 9C , the edges of the image display areas may be positioned (set) inside the edges of the screens. In the case of displaying images as shown in  FIG. 9C , the output image generation unit  206  generates point group data based on the screen arrangement information and information that enables calculation of the sizes of the image display areas on the screens. 
     In S 403 , the image clipped range determination unit  205  extracts one point P (x, y, z) from the point group data and calculates an angle θ formed by a vector OP and a Z axis in the case of using the viewpoint position as the origin O with respect to the extracted point P by the following formula (1): θ 
     
       
         
           
             
               
                 
                   θ 
                   = 
                   
                     
                       cos 
                       
                         - 
                         1 
                       
                     
                     ( 
                     
                       z 
                       
                         
                           
                             x 
                             z 
                           
                           + 
                           
                             y 
                             z 
                           
                           + 
                           
                             z 
                             z 
                           
                         
                       
                     
                     ) 
                   
                 
               
               
                 
                   Formula 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ( 
                     1 
                     ) 
                   
                 
               
             
           
         
       
     
     A supplementary explanation will be given of the three-dimensional space coordinate system in the present embodiment with reference to  FIG. 10 .  FIG. 10A  is a diagram showing the three screens on the three-dimensional coordinates using the viewpoint position as the origin. In  FIG. 10 , the point P (x, y, z) indicates three-dimensional coordinates of a point on the screen to be processed.  FIG. 10B  is a diagram showing  FIG. 10A  from another angle. As described above, an angle formed by the vector OP and the Z axis is defined as θ. In addition, a foot of a perpendicular from the point P to an XP plane is defined as a point Q (x, y, 0) and an angle formed by a vector OQ and an X axis is defined as φ. 
     In S 404 , the image clipped range determination unit  205  determines a point in an input image corresponding to the point P (x, y, z) as I (u, v) and calculates an image height r at the point I on the input image by the following formula (2). In the present embodiment, since the input image is acquired at an angle of view θ max  by the fisheye lens of equidistant projection, the image height r can be represented by a ratio between 0 and θ max  as shown by the following formula: 
     
       
         
           
             
               
                 
                   r 
                   = 
                   
                     θ 
                     
                       θ 
                       max 
                     
                   
                 
               
               
                 
                   Formula 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ( 
                     2 
                     ) 
                   
                 
               
             
           
         
       
     
       FIG. 11  is a diagram showing the point I (u, v) in the input image in a two-dimensional UV coordinate system. In  FIG. 11 , normalization is performed such that the center of the input image is the origin, lower left coordinates of the image are (−1, −1), and upper right coordinates are (1, 1). An angle φ formed by a vector OI and a U axis is equal to the angle φ formed by the vector OQ and the X axis in  FIG. 10B . In the present embodiment, since the fisheye lens is used, a range actually displayed as video is an area inside an image circle  701  shown in  FIG. 11 . 
     In S 405 , the image clipped range determination unit  205  calculates coordinates (u, v) of the point I on the input image by the following formula (3) and formula (4): 
     
       
         
           
             
               
                 
                   u 
                   = 
                   
                     
                       r 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       cos 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       φ 
                     
                     = 
                     
                       
                         x 
                         
                           
                             
                               x 
                               2 
                             
                             + 
                             
                               y 
                               2 
                             
                           
                         
                       
                       ⁢ 
                       r 
                     
                   
                 
               
               
                 
                   Formula 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ( 
                     3 
                     ) 
                   
                 
               
             
             
               
                 
                   v 
                   = 
                   
                     
                       r 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       sin 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       φ 
                     
                     = 
                     
                       
                         y 
                         
                           
                             
                               x 
                               2 
                             
                             + 
                             
                               y 
                               2 
                             
                           
                         
                       
                       ⁢ 
                       r 
                     
                   
                 
               
               
                 
                   Formula 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ( 
                     4 
                     ) 
                   
                 
               
             
           
         
       
     
     In S 406 , the image clipped range determination unit  205  determines whether the processing from S 403  to S 405  described above has been executed for all the points P of the point group data corresponding to the screen to be processed. The image clipped range determination unit  205  moves the processing to S 408  in a case where the processing has been executed for all the points P and moves the processing to S 407  in a case where the processing has not been executed for all the points P. 
     In S 407 , the image clipped range determination unit  205  updates the coordinates of the point P to an unprocessed point of the point group data and moves the processing to S 403 . In S 408 , the image clipped range determination unit  205  determines whether all the screens forming the first display system have been set as a processing target. That is, in the present embodiment, it is determined whether each of the three screens, the center screen  801 , the left side screen  802 , and the right side screen  803 , has been set as a processing target. 
     The image clipped range determination unit  205  moves the processing to S 409  in a case where all the screens have been set as a processing target and returns the processing to S 401  in a case where not all the screens have been set as a processing target. In S 409 , the image clipped range determination unit  205  stores coordinate values indicating screen edge information calculated in the processing from S 401  to S 408  as clipped range information and finishes the processing shown in  FIG. 8 . The processing from S 401  to S 409  described above enables determination of a clipped range having a shape depending on the configuration of the first display system, the type of optical system of the image capturing apparatus  111 , and the like. 
     Processing of Output Image Generation Unit  206  in S 306   
       FIG. 12  is a flowchart showing a procedure of processing executed by the output image generation unit in S 306 . In S 501 , the output image generation unit  206  acquires pixel position information corresponding to the clipped range indicated by edge information on each screen calculated in S 305 . 
     In S 502 , the output image generation unit  206  generates marker image data from pixel values corresponding to the clipped range shown in the edge coordinates of the screen acquired in S 501 . The output image generation unit  206  generates marker image data having the same resolution as the input image data in the RAM  102  and initializes all the pixel values by white. In the present embodiment, the marker image data is binary data in which a pixel value can take either 0 (white) or 1 (black). In addition, the output image generation unit  206  converts pixel values corresponding to the edge coordinates from 0 to 1. 
     More specifically, since the coordinates have fractional values between −1.0 and 1.0, each of u and v is normalized by addition of 1 followed by division by 2 to take a value from 0 to 1.0. Information indicating the positions of pixels on a marker image is calculated by further multiplying u by the width SW pix  of the marker image and multiplying v by the height SH pix  of the marker image. Finally, processing of changing a pixel value to black is executed for the closest pixel out of four pixels close to (u, v). 
     In S 503 , the output image generation unit  206  acquires a range of a window in which distribution information is displayed. In the present embodiment, a rectangular window having a width W/2pix and a height H/2pix, which are ½ of the marker image, is acquired as a range of a window in which distribution information is displayed. 
     In S 504 , the output image generation unit  206  calculates a geometrical conversion parameter for converting pixel values included in the clipped range acquired in S 501  into pixel values within the range in which distribution information is displayed. In the present embodiment, first, it is assumed that upper left coordinates of the clipped range are (x1, y1), upper right coordinates are (x2, y2), lower right coordinates are (x3, y3), and lower left coordinates are (x4, y4). Next, on the assumption that upper left coordinates of the display range of the distribution information are (X1, Y1), upper right coordinates are (X2, Y2), lower right coordinates are (X3, Y3), and lower left coordinates are (X4, Y4), a matrix of projective transformation of the formula (5) is calculated: 
     
       
         
           
             
               
                 
                   
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                   Formula 
                   ⁢ 
                   
                       
                   
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                     ( 
                     5 
                     ) 
                   
                 
               
             
           
         
       
     
     In S 505 , the output image generation unit  206  acquires coordinate positions included in the clipped range. More specifically, the output image generation unit  206  acquires coordinate positions surrounded by the edge area indicating the clipped range acquired in S 501 . 
     In S 506 , the output image generation unit  206  determines whether the generated distribution information includes information about coordinate positions. The output image generation unit  206  moves the processing to S 507  in a case where it is determined that the generated distribution information includes information about coordinate positions and moves the processing to S 509  in a case where it is determined that the generated distribution information does not include information about coordinate positions. 
     In the present embodiment, a luminance histogram (frequency distribution of luminance) or a waveform signal is generated as distribution information. Alternatively, a histogram of each pixel value, a chromaticity parade, or the like may be generated as distribution information.  FIG. 13A  shows a luminance histogram and  FIG. 13B  shows a waveform signal. In the luminance histogram of  FIG. 13A , the horizontal axis represents a signal value of a pixel and the vertical axis represents the number of pixels having the pixel signal. In the waveform signal of  FIG. 13B , the horizontal axis represents a line coordinate position on the screen and the vertical axis represents a signal value of a pixel value at the position. As a supplement, a chromaticity parade is shown in  FIG. 13C . The chromaticity parade of  FIG. 13C  indicates hue by an angle and indicates chroma by a distance from the center, whereby a chromaticity distribution of a signal value can be confirmed. 
     The distribution information is selected based on a user instruction via the input device  107 . In the case of displaying distribution information, one or more types of distribution information are selected. In the present embodiment, distribution information is acquired by selecting one of a plurality of types of distribution information prestored in the HDD  105  based on a user instruction. 
     In a case where the waveform signal is selected as distribution information, that is, in a case where distribution information includes information about coordinate positions, it is necessary to appropriately inform a user of positional information. Thus, for the distribution information including information about coordinate positions, a correction of distortion of the input image (S 507 ) and a geometrical conversion to a display range (S 508 ) are executed. 
     In S 507 , since distortion occurs in the input image, the output image generation unit  206  corrects the input image based on distortion information on the lens in use. In the present embodiment, distortion information at the time of image capturing by the lens in use is prestored in the HDD  105  as a look-up table. The input image is corrected by referring to the look-up table. The look-up table describes correspondences between coordinate positions before and after the correction. 
     In S 508 , the output image generation unit  206  uses the geometrical conversion parameter calculated in S 504  to convert the coordinate positions included in the clipped range. In a case where the coordinate positions include a decimal point, the closest pixel among the close four pixels is referred to. 
     In S 509 , the output image generation unit  206  generates distribution information selected by a user from the coordinate positions converted in S 508  in a case where positional information is included in the distribution information, and generates it from signal values of pixel values of the input image corresponding to the coordinate positions in S 505  in a case where positional information is not included. 
     In S 510 , the output image generation unit  206  executes processing of superimposing the marker image and the distribution information image on the input image. A supplementary explanation will be given of the processing in S 510  with reference to  FIG. 14 . In  FIG. 14 ,  FIG. 14A  shows the input image and  FIG. 14B  shows the marker images and distribution information images.  FIG. 14C  shows an image obtained by superimposing the marker images and distribution information images in  FIG. 14B  on the input image in  FIG. 14A . That is,  FIG. 14C  shows a clipped range (a respective one of reference numerals  1201 - 1203 ) corresponding to each screen and distribution information (a corresponding one of reference numerals  1204 - 1206 ) on the image within the range. As shown in  FIG. 14C , in the present embodiment, the distribution information is associated with each screen and superimposed and displayed within the clipped range. 
     In S 511 , the output image generation unit  206  determines whether the processing from S 501  to S 510  has been completed for all the screens. In a case where the processing from S 501  to S 510  has not been completed for all the screens, the output image generation unit  206  returns the processing to S 501  to execute the processing for an unprocessed screen. In a case where the processing from S 501  to S 510  has been completed for all the screens, the output image generation unit  206  finishes the processing in S 306 . 
     As described above, according to the image processing apparatus of the present embodiment, it is possible to generate (provide) distribution information on an image capturing signal suitable for a display apparatus which displays part of video obtained by image capturing. This enables an image capturer to set exposure and white balance appropriately at the time of image capturing by referring to the provided distribution information. 
     Second Embodiment 
     In the first embodiment described above, the description has been given of the method of generating distribution information of pixel values within the clipped range, superimposing the generated distribution information on the clipped range, and displaying them. In the present embodiment, a description will be given of a method of allowing a user to select a method of superimposing distribution information on an input image from among a plurality of methods. 
     Since a hardware configuration of an image processing apparatus of the present embodiment is the same as that of the first embodiment described above, the description thereof will be omitted. Similarly, since the processing executed by the image processing apparatus is the same as that in the first embodiment described above except for the processing in S 306  (more specifically, S 510 ), the description thereof will be omitted and a description will be given of a method of adding (superimposing) the distribution information images to (on) the input image in S 510 . Further, as mentioned above, the same reference numerals are assigned to the same features as the first embodiment. 
     Operation of Output Image Generation Unit  206   
       FIG. 15  is a flowchart showing a procedure of processing executed in the output image generation unit  206 . The processing in S 510  of  FIG. 5  will be described as the processing from S 1301  to S 1311 . 
     In S 1301 , the output image generation unit  206  acquires a display mode for determining where in the input image a distribution information image is displayed. The processing in S 1301  is executed based on a user instruction via the input device  107 . In the present embodiment, the display mode is acquired by selecting one of a plurality of display modes prestored in the HDD  105  based on a user instruction (setting). 
     In the present embodiment, three display modes are stored as display modes. First, in a case where the display mode is 1, as shown in  FIG. 16A , the distribution information  1405  to  1407  is arranged outside the clipped ranges  1402  to  1404 , thereby performing display such that the composition and objects within the clipped ranges can be easily identified. 
     Next, in a case where the display mode is 2, as shown in  FIG. 16B , distribution information on the clipped ranges  1402  and  1403  is collectively arranged as shown by the reference numeral  1408  and distribution information on the clipped ranges  1402  and  1404  is collectively arranged as shown by the reference numeral  1409 . Similarly, distribution information on the clipped ranges  1402  to  1404  is collectively arranged as shown by the reference numeral  1410 . In this manner, signal values of a plurality of clipped ranges are collectively arranged. 
     In a case where the display mode is 3, as shown in  FIG. 16C , distribution information  1411  to  1413  is superimposed and arranged on the input image so as not to overlap the main objects in the input image, thereby performing display such that the objects can be easily identified. 
     In S 1302 , the output image generation unit  206  determines which display mode the display mode acquired in S 1301  is. The output image generation unit  206  moves the processing to S 1303  in a case where the display mode is 1, moves the processing to S 1305  in a case where the display mode is 2, and moves the processing to S 1309  in a case where the display mode is 3. 
     In S 1303 , the output image generation unit  206  arranges distribution information outside the clipped ranges as shown in  FIG. 16A  and outputs the distribution information superimposed on the input image to the output device  109  via the output I/F  108 . In S 1304 , the output image generation unit  206  displays the frame indicating the edge area of each distribution information in the same color as the marker indicating the edge area of the corresponding clipped range such that correspondences between the clipped ranges and distribution information on the clipped ranges can be understood. 
     In S 1305 , the output image generation unit  206  acquires a target range of calculation of distribution information as shown in  FIG. 16B . The distribution information is not necessarily generated separately for each clipped range and may be selected from among prestored target ranges based on a user instruction. Although adjacent clipped ranges and all the clipped ranges are collectively set as target ranges in  FIG. 16B , it is also possible to set left and right screens collectively as a target range, for example. 
     In S 1306 , the output image generation unit  206  regenerates distribution information based on pixel values of coordinates corresponding to the target range acquired in S 1305 . In S 1307 , the output image generation unit  206  superimposes the distribution information regenerated in S 1306  on the input image and outputs them to the output device  109  via the output I/F  108 . In S 1308 , the output image generation unit  206  determines whether the processing has been executed for all the target ranges acquired in S 1305 . The output image generation unit  206  finishes the processing shown in  FIG. 15  in a case where the processing has been executed and returns the processing to S 1305  in a case where the processing has not been executed. 
     In S 1309 , the output image generation unit  206  divides the input image into areas having the sizes of areas in which distribution information is displayed. It is assumed that the sizes of the areas of the distribution information are the same as those in the first embodiment described above. In S 1310 , the output image generation unit  206  first performs the Fourier transform for each pixel value in the areas divided in S 1309  using the following formula (6) to calculate a spatial frequency characteristic F (u, v). In the following formula, G*(x, y) represents a pixel value in the area divided in S 1309 , which is a target of the Fourier transform, and M and N represent the numbers of vertical and horizontal pixels, respectively, in the divided area. 
     
       
         
           
             
               
                 
                   
                     F 
                     ⁡ 
                     
                       ( 
                       
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                         , 
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                       ) 
                     
                   
                   = 
                   
                     
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                         N 
                       
                     
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                           0 
                         
                         
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                                       N 
                                     
                                   
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                   Formula 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ( 
                     6 
                     ) 
                   
                 
               
             
           
         
       
     
     Next, the spatial frequency characteristic calculated by the above formula (6) is compared with a predetermined threshold. In a case where the frequency is lower than the threshold, it is determined that there is no texture and the processing is moved to S 1311 . In a case where the frequency is equal to or higher than the threshold, it is determined that there is texture and the processing is returned to S 1309  to search for an area with no texture again. In S 1311 , the output image generation unit  206  arranges the distribution information on an area in which it is determined that there is no texture as a result of the processing of S 1310  and outputs the distribution information superimposed on the input image to the output device  109  via the output I/F  108 . 
     As described above, according to the image processing apparatus of the present embodiment, a user can set exposure and white balance at the time of image capturing more appropriately by selecting a method of superimposing distribution information on an input image from among a plurality of methods. 
     Modification 
     In the embodiments described above, the first display system is the three screens arranged to surround a viewer. However, the system may be a curved screen arranged to surround a viewer.  FIG. 17A  shows an example of a curved screen  1701 .  FIG. 17B  shows a display range  1703  clipped from a captured image  1702  so as to display a part of the captured image  1702  on the first display system, which is the curved screen.  FIG. 17C  shows an image obtained by superimposing a distribution information image  1704  on the input image. It is understood that the shape of the clipped range corresponds to the curved screen. 
     The first display system is not limited to the examples described above and may be a spherical screen  1801  shown in  FIG. 18A  or a curved screen  1802  having a shape partially cut off from a side surface of a cylinder shown in  FIG. 18B . Alternatively, the display system may be a spherical screen  1803  having a shape partially cut off from a sphere shown in  FIG. 18C . 
     In the embodiments described above, an image obtained by superimposing distribution information images on an input image is displayed. However, an image to be displayed may be switched according to a user instruction. For example, the display may be switched between the image alone shown in shown in  FIG. 3A , the image and frames shown in  FIG. 3C , and the image, frames, and distribution information shown in  FIG. 14C . 
     The output unit  207  in the embodiments described above outputs the generated image data with distribution information to the output device  109 . However, the output unit  207  may function as a display control unit which controls the display of an image with distribution information. 
     In the embodiments described above, the three display modes are shown as an example of a display mode. However, another display mode may be stored. For example, the distribution information  1414  on only the front clipped range  1402  may be solely arranged as shown in  FIG. 19A  without displaying a histogram of all the three screens. Alternatively, as shown in  FIG. 19B , distribution information on the clipped ranges  1402  to  1404  of the three screens may be added up and arranged as distribution information  1415 . Alternatively, as shown in  FIG. 19C , distribution information  1415  obtained by adding up the distribution information on the clipped ranges  1402  to  1404  of the three screens and distribution information  1416  on an area other than the clipped ranges  1402  to  1404  may be arranged. 
     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. 
     According to the embodiments, the image capturing apparatus can be provided with distribution information on an image capturing signal suitable for a display apparatus. 
     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 Applications No. 2019-133568, filed Jul. 19, 2019 and No. 2020-061442, filed Mar. 30, 2020 which are hereby incorporated by reference wherein in its entirety.