JP4925168B2 - Imaging method and apparatus - Google Patents

Description

  The present invention relates to an imaging method for capturing an image of a subject formed on an imaging surface through an imaging lens having a focusing lens group for changing a focus position and a zoom lens group for changing a focal length, and It relates to the device.

  2. Description of the Related Art Conventionally, an imaging apparatus that captures an image of a subject formed on an imaging surface through an imaging lens is known. Such an imaging device includes a zoom function that changes the focal length (magnification) of the imaging lens to enlarge or reduce the image of the subject that is imaged on the imaging surface, and automatically sets the focus position of the imaging lens to the position of the subject. There is known a digital still camera equipped with an autofocus function for adjusting to the camera. The focus position is the position of the subject (object point) corresponding to the image that is correctly formed on the imaging surface, and the image of the subject that is positioned at the focus position of the imaging lens is in focus on the imaging surface. The image is formed in a state.

  In the imaging apparatus as described above, if the magnification of the imaging lens by the zoom function (hereinafter also referred to as zoom magnification) is changed in a state where the subject is in focus, the focus position shifts from the subject. The deviation is corrected by the autofocus function.

  The autofocus operation is not completed instantaneously, that is, for example, the focus position detection by the contrast method for determining the focus position by determining the contrast of the image of the captured subject cannot be performed instantaneously, While the zoom function is in operation and immediately after the zoom function is finished, the subject image on the imaging surface is once blurred, and after a while after the zoom function operation is finished, the focused subject image is formed on the imaging surface. Imaged.

  As a method for correcting the shift of the focus position due to such a delay in the operation of the zoom function, a method adopted in a surveillance camera that mainly images a subject whose position is fixed is known (see Patent Document 1). . A surveillance camera adopting this method is used while being fixed to a wall surface or the like. For example, the distance to a window to be monitored is measured by the autofocus function of the surveillance camera, and the distance is stored in advance. When the zoom function of the surveillance camera is operated while monitoring the window, the focus lens group of the surveillance camera is moved so as to focus on the window using the distance to the previously stored window, and the zoom is performed. The focus position shift caused by the magnification change is corrected.

  More specifically, the monitoring camera is pointed at the window, the zoom magnification of the monitoring camera is set, and the window is focused by the autofocus function. Then, the direction of the monitoring camera, the position of the zoom lens group of the monitoring camera, and the position of the focusing lens group are stored in the monitoring camera as preset information. Thereby, the state which monitors the said window with a surveillance camera is preset.

  Here, the distance to the monitoring target window is stored in correspondence with the preset position of the focusing lens group (that is, the zoom magnification or focal length of the monitoring camera). Using this distance information, the relationship between the position of the zoom lens group and the position of the focus lens group for obtaining a state where the window is in focus is obtained in advance as a tracking curve. As a result, regardless of the position of the zoom lens group, if the position of the focus lens group is moved so as to correspond to the point on the tracking curve corresponding to the position of the zoom lens group, The focus position of the camera can be adjusted to the window.

  After setting as described above, while monitoring the area other than the window to be monitored with the monitoring camera by changing the zoom magnification or changing the focus position, the monitoring camera When instructed to return to the preset monitoring state, the surveillance camera is directed to the window, the zoom magnification is changed while the focus position is adjusted to the window using the tracking curve, and the camera automatically returns to the preset state. . At this time, the focus position is corrected using the tracking curve while the zoom magnification of the surveillance camera is changed.

The method of adjusting the focus position to the window using the distance to the subject and the tracking curve stored in advance can reduce the amount of calculation compared with the method of adjusting the focus position to the window in real time by the autofocus function. The correction of the shift of the focus position accompanying the change of the zoom magnification can be completed earlier, and the degree of blurring of the image that occurs during the change of the zoom magnification can be further reduced.
JP 2003-57526 A

  By the way, the method of correcting the focus position shift occurring during the zoom magnification change using the tracking curve is applied to a predetermined subject, for example, a window, but an arbitrary face as a subject. Even when the zoom magnification is changed, there is a demand to correct the focus position shift that occurs during the zoom magnification change using the tracking curve in the same manner as described above.

  As described above, when measuring the distance to the subject to be monitored using the autofocus function, the depth of field when the zoom magnification is set to the low magnification side (wide angle side) is the zoom magnification. Since it becomes deeper than the depth of field when is set to the high magnification side (telephoto side), the ranging accuracy on the wide angle side is lower than the ranging accuracy on the telephoto side. Therefore, when the distance to the subject is measured on the wide-angle side, an accurate tracking curve cannot be obtained, and it may be difficult to enjoy the effect of correcting the focus position shift during zoom magnification change. For example, when obtaining distance information to the subject to be monitored on the wide-angle side with a deep depth of field and low ranging accuracy, and changing the zoom magnification to the telephoto side with a shallow depth of field while monitoring the subject, Since an accurate tracking curve cannot be obtained and the focus position shift that is not noticeable on the wide angle side becomes noticeable on the telephoto side, the effect of the above correction may be hardly obtained. Note that although not as wide as the wide-angle side, the distance measurement accuracy is reduced due to the depth of field on the telephoto side. For this reason, there is also a demand for correcting a focus position shift that occurs during zoom magnification change without lowering the correction accuracy due to the influence of the depth of field.

  The present invention has been made in view of the above circumstances, and can more accurately correct a shift in the focus position that occurs when the zoom magnification is changed in a state where the focus position is set to an arbitrary face as a subject. An object is to provide an imaging method and apparatus.

  An imaging apparatus of the present invention includes an imaging lens having a focus lens group for changing a focus position and a zoom lens group for changing a focal length, and forms an image on an imaging surface through the imaging lens. In an imaging apparatus that captures an image of a subject, a standard face size storage unit that stores predetermined standard face size information, and a discrimination information storage unit that stores discrimination information for determining whether the subject is a face Detection means for detecting an image representing a face from an image captured through an imaging lens based on the discrimination information, and when the image representing a face is detected from the image, the standard face dimension information, The focal length information indicating the focal length of the imaging lens when the face is imaged, and the imaging dimension information indicating the size of the face on the imaging surface when the face is imaged are obtained. And a distance calculating means for obtaining an actual distance from the imaging lens to the face, and a position away from the imaging lens by the actual distance is always changed during the change of the focal length by the zoom lens group. And a control means for controlling the focusing lens group so as to be brought into a focus position.

  The imaging method of the present invention captures an image of a subject imaged on an imaging surface through an imaging lens having a focus lens group for changing a focus position and a zoom lens group for changing a focal length. In the imaging method, predetermined standard face dimension information and discrimination information for discriminating whether or not the face is stored are stored, and an image representing a face from an image taken through the imaging lens is stored in the discrimination information. When the image representing the face is detected from the image, the standard face dimension information, the focal length information indicating the focal length of the imaging lens when the face is imaged, and the face are imaged. Imaging dimension information indicating the size of the face on the imaging surface is obtained, an actual distance from the imaging lens to the face is obtained using the information, and the zoom lens While changing the focal length by the group, it is characterized in that for controlling the focusing lens group so allowed to the focus position of the imaging lens from the actual always the imaging lens position apart distance.

  The focus position is the position of the object point corresponding to the image that is correctly imaged on the imaging surface, and the image of the subject located at the focus position of the imaging lens is focused on the imaging surface. The

  The face size stored in the standard face size storage means can be the width of a human face or the length of a human face. As the width of the human face, an average value of the width of an adult face can be adopted. Moreover, the average value of the length of an adult's face can be employ | adopted for the length of the said person's face.

  The control means may perform the control only when the focal length of the zoom lens group is changed from the wide angle side to the telephoto side.

  An image captured when the detection unit detects a face can be a through image.

  The distance calculation means performs the calculation using focal length information and imaging dimension information obtained when the face is imaged in a state where the face is in focus, or the focal length of the imaging lens is wide angle The calculation can be performed only when set to the side. Note that the focal length is set to the wide-angle side means that the focal length of the imaging lens is an intermediate value between the maximum value and minimum value of the focal length changeable range (intermediate value = (maximum value + minimum value). Value) / 2) means that it is set to a smaller value.

  The imaging method and apparatus of the present invention stores predetermined standard face size information and discrimination information for discriminating whether or not a face is present, and represents a face from an image taken through an imaging lens. When an image is detected based on the discrimination information and an image representing a face is detected from the image, standard face dimension information, focal length information indicating a focal length of the imaging lens when the face is imaged, and Imaging dimension information indicating the size of the face on the imaging surface when the face is imaged is obtained, the actual distance from the imaging lens to the face is obtained using each information, and the focal length by the zoom lens group Since the focus lens group is controlled so that the position away from the imaging lens by the actual distance is always the focus position of the imaging lens during the change of the focus, the focus position is adjusted to an arbitrary face. Deviation of the focus position caused when changing the zoom magnification in a state can be more accurately corrected.

  In other words, in the conventional correction method, the distance to the subject is stored in advance as preset information, so that the shift of the focus position from the subject that occurs when the zoom magnification is changed is corrected using the tracking curve. In the imaging method and apparatus of the present invention, by storing the standard face size information, the distance to the subject can be stored as preset information as in the prior art, and the face to an arbitrary subject can be detected. The distance can be measured. Accordingly, the correction using the tracking curve can be applied even when the zoom magnification is changed by adjusting the focus position to an arbitrary face.

  In addition, in the conventional correction method using the autofocus function, the focus position correction accuracy may be reduced due to a decrease in distance measurement accuracy due to the influence of the depth of field. Thus, it is possible to measure the distance to the subject face without being affected by the depth of field, and it is possible to more accurately correct the shift of the focus position that occurs during the zoom magnification change.

  If the size of the face is the width of the person's face or the length of the person's face, the actual distance to the face can be determined more reliably, and the focus position can be adjusted to any face. It is possible to more accurately correct the focus position shift that occurs when the zoom magnification is changed.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. 1 and 2 show a digital still camera (hereinafter simply referred to as a digital camera) as an example of an imaging apparatus that performs an imaging method according to an embodiment of the present invention. FIG. FIG. 2 is a view showing the digital still camera as seen from the back side, FIG. 3 is a block diagram showing mainly the electrical configuration of the digital camera, and FIG. 4 is the block shown above. FIG. 5 is a flowchart showing the overall flow of processing by the digital camera, and FIG. 6 is a flowchart for detecting the face and correcting the focus during zooming. FIG. 7 is a flowchart showing the flow of face detection processing, and FIG. 7 is a diagram showing the positional relationship among the face that is the subject, the imaging lens, and the imaging surface.

  The digital camera 1 includes an imaging lens 20 having a focusing lens group 20a for changing the focus position and a zoom lens group 20b for changing the focal length, and the photoelectric conversion surface of the CCD 58 is passed through the imaging lens 20. The image of the subject imaged on the imaging surface 58a is taken.

  As shown in the block diagram of FIG. 4 and the like, the digital camera 1 is imaged through a discrimination information storage unit 81 that stores discrimination information Hj for discriminating whether or not it is a face, and an imaging lens 20. A detection unit 82 for detecting an image representing a face as a subject from the detected image based on the discrimination information Hj, and standard face dimensions for storing predetermined standard face dimension information for indicating the size of the face When the image indicating the face K as the subject is detected from the storage unit 83 and the captured image, the standard face size information and the imaging lens 20 when the face K as the subject is imaged are detected. The focal length information indicating the focal length and the imaging dimension information indicating the size of the face K as the subject on the imaging surface 58a when the face K as the subject is imaged are obtained, and the above information is used. Imaging lens 20 When the focal length is changed by the distance calculation unit 84 for obtaining the actual distance L to the face K that is the subject and the zoom lens group 20b, a position that is away from the imaging lens 20 by the actual distance L is always set. And a control unit 85 that controls the focusing lens group 20a so that the imaging lens 20 is brought into a focus position.

  The predetermined standard face dimension information for indicating the size of the face is 150 mm, which is an example of the standard dimension of the adult face width, and an example of the standard dimension of the adult face length. Information indicating a value such as 220 mm or 80 mm, which is an example of an interval between eyes of an adult face, can be employed. Here, 150 mm, which is the standard dimension of the adult face width, is stored in the standard face dimension storage unit 83 as standard face dimension information.

  The discrimination information storage unit 81, the detection unit 82, the standard face size storage unit 83, the distance calculation unit 84, the control unit 85, and the like constitute a face detection zoom focus correction unit 65.

  Hereinafter, the digital camera 1 will be described in more detail.

  As shown in FIG. 2, an operation mode switch 11 </ b> D, an imaging mode switch 11 </ b> S, a menu switching operation button 12, and a zoom lever 13 are provided on the back of the body body 10 of the digital camera 1 as an interface for a user operation. Yes. As the interface, a display cursor movement button, a display return button, a display switching button, and the like (not shown) are also provided.

  Further, a finder 17 for confirming a subject and a liquid crystal monitor 18 for displaying a captured and reproduced image are provided on the rear surface. A shutter button 19 is provided on the upper surface of the body main body 10.

  As shown in FIG. 1, an imaging lens 20, a lens cover 21 that also functions as a power switch, slides in the lateral direction, a finder window 23, a flash 24, and a self-timer lamp 25 are provided on the front surface of the body body 10. .

  The operation mode switch 11D is a slide switch for switching each operation mode of the imaging mode and the reproduction mode. When the menu switching operation button 12 is pressed or rotated, various menus for performing detailed setting of the imaging mode, detailed setting of the flash emission mode, setting of the number of recording pixels, sensitivity, and the like are displayed on the liquid crystal monitor 18. These buttons are used for selection and setting based on the menu displayed on the liquid crystal monitor 18.

  The zoom lever 13 is a lever for adjusting the focal length of the imaging lens to the telephoto side / wide angle side by moving in the vertical direction.

  The display cursor movement button is a button for moving the cursor in the menu screen displayed on the liquid crystal monitor 18 to the left and right at various settings, and the display return button is used to cancel various setting operations and return to the previous menu screen. It is a button for returning to the screen. The display switching button is a button for switching ON / OFF of display on the liquid crystal monitor 18, various guide displays, ON / OFF of character display, and the like.

  The setting contents and the like by the operation of each button and lever described above can be confirmed by the display on the liquid crystal monitor 18, the position of the lamp in the finder, the slide lever, and the like. The liquid crystal monitor 18 functions as an electronic viewfinder by displaying a later-described through image for subject confirmation at the time of imaging, and also displays a still image and a moving image after imaging and displays various setting menus. .

  The through image is an image that is captured at a predetermined time interval and displayed on the liquid crystal monitor 18 without pressing the shutter button while the imaging mode is selected. The number of pixels constituting the image captured as the through image is about 1/16 of the number of pixels constituting the main image. The main image is an image to be recorded for recording when the shutter button is fully pressed and the main image is taken, and image data indicating the main image is recorded on the external recording medium 70. Note that a through image and an image captured and acquired as a pre-image described later are not recorded.

  As shown in FIGS. 2 and 3, the digital camera 1 converts image data of a captured image into, for example, an Exif format image file, and records the image file on an external recording medium 70 that can be attached to and detached from the main body. In the image file, incidental information is stored in addition to the image data.

  This digital camera 1 includes the above-described operation mode switch 11D, imaging mode switch 11S, menu switching operation button 12, zoom lever 13, shutter button 19, switches such as a lens cover 21 that also serves as a power switch, and other displays. An operation system control unit 74 that is an interface unit for transmitting operation contents of switches such as a cursor movement button, a display return button, and a display switching button to a CPU (Central Processing Unit) 75 is provided.

  As components of the imaging lens 20, a focusing lens group 20a and a zoom lens group 20b are provided. Each of these lenses is driven by a focus lens driving unit 51 including a motor and a motor driver, and a similar zoom lens driving unit 52, and is movable in the optical axis direction. The focus lens drive unit 51 moves the focus lens group 20a based on the focus drive amount data output from the AF processing unit 62, and the zoom lens drive unit 52 uses the zoom lens 13 based on the operation amount data of the zoom lever 13. The group 20b is moved.

  The autofocus unit includes a focusing lens group 20a, a focus lens driving unit 51, an AF processing unit 62, a CPU 75, and the like.

  The diaphragm 54 is driven by a diaphragm driving unit 55 including a motor and a motor driver. The aperture drive unit 55 adjusts the aperture diameter based on aperture value data output from the AE (automatic exposure) / AWB (auto white balance) processing unit 63.

  The shutter 56 is a mechanical shutter and is driven by a shutter drive unit 57 including a motor and a motor driver. The shutter drive unit 57 controls the opening and closing of the shutter 56 according to a signal generated when the shutter button 19 is pressed and the shutter speed data output from the AE / AWB processing unit 63.

  A CCD 58, which is an image sensor, is provided behind the optical system including the focusing lens group 20a, the zoom lens group 20b, the aperture stop 54, the shutter 56, and the like. The CCD 58 has an imaging surface 58a in which a large number of light receiving elements are two-dimensionally arranged, and subject light that has passed through the optical system is imaged and photoelectrically converted on the imaging surface 58a. In front of the imaging surface 58a, a color in which a microlens array (not shown) for condensing light on each pixel on the imaging surface 58a and filters of R, G, B colors are regularly arranged. A filter array (not shown) is arranged. The CCD 58 outputs the charge accumulated for each pixel as a serial analog image signal line by line in synchronization with the vertical transfer clock and horizontal transfer clock supplied from the CCD controller 59. The time for accumulating charges in each pixel, that is, the exposure time is determined by an electronic shutter drive signal given from the CCD controller 59.

  The analog image signal output from the CCD 58 is input to the analog signal processing unit 60. The analog signal processing unit 60 includes a correlated double sampling circuit (CDS) that removes noise from the analog signal, an auto gain controller (AGC) that adjusts the gain of the analog signal, and an A / A that converts the analog signal into a digital signal. And a D converter (ADC). The image data converted into the digital signal is CCD-RAW data having R, G, and B density values for each pixel.

  The timing generator 72 generates a timing signal. This timing signal is input to the shutter drive unit 57, the CCD control unit 59, and the analog signal processing unit 60, and the operation of the shutter button 19, the opening / closing of the shutter 56, and the CCD 58 Is taken in, and the analog signal processing unit 60 is synchronized. The flash control unit 73 controls the light emission operation of the flash 24.

  The image input controller 61 writes the image data (CCD-RAW data) input from the analog signal processing unit 60 in the frame memory 68. The frame memory 68 is a working memory used when various digital image processing (signal processing) to be described later is performed on the image data. For example, an SDRAM that transfers data in synchronization with a bus clock signal having a fixed period. (Synchronous Dynamic Random Access Memory).

  The display control unit 71 is, for example, for displaying the image data stored in the frame memory 68 on the liquid crystal monitor 18 as a through image, and combines the luminance (Y) signal and the color (C) signal into one signal. Is converted to a composite signal and output to the liquid crystal monitor 18.

  The AF processing unit 62 and the AE / AWB processing unit 63 determine the imaging condition based on the pre-image. This pre-image is an image acquired for setting the shooting conditions. For example, the CPU 75 that has detected a half-press signal generated when the shutter button 19 is half-pressed performs imaging of the subject on the CCD 58. As a result, the image is based on the image data stored in the frame memory 68. Note that the number of pixels constituting the pre-image is equal to the number of pixels constituting the through image.

  The AF processing unit 62 detects a focus position where the contrast of the image is maximum based on the pre-image or the through image, and outputs focus drive amount data.

  In the present embodiment, as a normal focus position detection method, a passive method that detects the focus position using the feature that the contrast is high for a focused subject in a captured image is applied. . This point will be described in more detail later.

  The AE / AWB processing unit 63 measures the brightness of the subject based on the pre-image, determines the aperture value, the shutter speed, etc., outputs the aperture value data and the shutter speed data (AE), and at the time of imaging. Automatically adjust the white balance (AWB).

  The image processing unit 64 performs image quality correction processing such as gamma correction, sharpness correction, and contrast correction on the image data of the main image obtained by the main imaging, and converts the CCD-RAW data into Y data that is a luminance signal. And YC processing for conversion into YC data composed of Cb data as a blue color difference signal and Cr data as a red color difference signal.

  The main image is an image captured from the CCD 58 in the imaging executed when the shutter button 19 is fully pressed, and is an image based on image data stored in the frame memory via the analog signal processing unit 60 and the image input controller 61. It is. The upper limit of the number of pixels of the main image is determined by the number of pixels of the CCD 58. For example, the number of recorded pixels can be changed by setting such as fine and normal. On the other hand, the number of pixels constituting the through image or the pre-image is smaller than the number of pixels constituting the main image. For example, the number of pixels constituting the through image or the pre-image is 1/16 of the number of pixels constituting the main image. The number of pixels is about.

  The compression / decompression processing unit 67 performs compression processing on the main image data that has been corrected and converted by the image processing unit 64 in a compression format such as JPEG, and generates an image file. A tag storing incidental information based on the Exif format or the like is added to the image file. The compression / decompression processing unit 67 reads the compressed image file from the external recording medium 70 and performs decompression processing in the reproduction mode. The decompressed image data is output to the liquid crystal monitor 18.

  The media control unit 69 accesses the external recording medium 70 and controls writing and reading of the image file.

  The CPU 75 controls each part of the main body of the digital camera 1 in accordance with signals from the operation system such as the operation mode switch 11D and various processing units such as the AF processing unit 62. The data bus 76 is connected to the image input controller 61, various processing units 62 to 67, the frame memory 68, various control units 69 and 71, and the CPU 75, and exchanges digital image data and the like via the data bus 76. Information transmission and control for setting imaging conditions are performed.

  Hereinafter, a process controlled by the CPU 75 when an image is taken by the digital camera 1 having the above configuration will be described with reference to a flowchart shown in FIG. Note that the basic processing performed by the AF processing unit 62, the AE / AWB processing unit 63, and the like when this imaging is performed is as described above, and here, the processing of each unit is omitted unless necessary. The process flow controlled by the CPU 75 will be mainly described.

  First, as shown in FIG. 5, the process starts from step P1, and the process proceeds to step P2 to determine whether the operation mode is the imaging mode or the reproduction mode. Here, when it is determined that the operation mode designated by the operation mode switch 11D is the reproduction mode, reproduction processing is performed. This reproduction processing is processing for reading an image file from the external recording medium 70 and outputting the image indicated by the image file to the liquid crystal monitor 18 as described above. When this reproduction process ends, the flow of the process proceeds to Step P11 described later.

  On the other hand, when it is determined in step P2 that the operation mode is the imaging mode, the type of imaging mode is determined in the next step P3.

  Here, when the imaging mode designated by the imaging mode switch 11S is the focus correction mode during face detection zoom, a face detection process for detecting the face in step P4 and performing focus correction during zooming is executed, and the imaging mode is normal. In the case of the mode, the process of step P4 is not executed, and the mode is changed to the normal imaging mode.

  Hereinafter, with respect to the face detection process, the relationship between the size of the face that is the subject, the focal length of the imaging lens, and the size of the face imaged on the imaging surface will be described. The face detection will be described with reference to FIG. 8 and FIG. 9 showing a tracking curve based on face detection.

  The face detection process is started from step P401 in the flowchart, and the process proceeds to a detection process for detecting a face in step P402. In step P402, the through image captured through the imaging lens 20 is input to the detection unit 82 through the data bus 76, and determination information Hj for determining whether the face is a face from the determination information storage unit 81 is input to the detection unit 82. The detection unit 82 detects an image representing a face from the through image based on the discrimination information Hj. For the face detection process, a conventionally known method described in, for example, the above-described Patent Document 1 and Japanese Patent Application Laid-Open No. 2005-242640 can be applied.

  Next, the process proceeds to step P403, and when the face is detected by the detection unit 82, the process proceeds to step P404 for obtaining the size of the face that is the subject, and the face is not detected. Shifts to normal autofocus control without performing face detection in step P407.

  In Step P404, the distance from the imaging lens 20 to the face K that is the subject is obtained. In this step P404, the distance calculation unit 84 obtains a standard dimension value of the width W1 of the adult face, for example, 150 mm as standard face dimension information from the standard face dimension storage unit 83, and becomes the subject from the CPU 75. A focal length value F of the imaging lens 20 when the face K is imaged is obtained as focal length information.

  Further, the distance calculation unit 84 obtains from the image processing unit 64 imaging dimension information indicating the size of the face K on the imaging surface 58a when imaging the face K that is the subject. Here, the value of the width W2 of the face K on the imaging surface 58a, for example, 3 mm, is obtained by the image processing unit 64 based on the number of light receiving elements corresponding to the width W2 of the face K on the imaging surface 58a. This value is input to the distance calculation unit 84 as the imaging dimension information.

  The distance calculation unit 84 includes a standard dimension value 150 mm of the adult face width W1, which is the standard face dimension information, a focal length value F of the imaging lens 20, and a width K1 of the face K on the imaging surface 58a. From the value 3 mm, an actual distance L from the imaging lens 20 to the face K that is the subject is obtained.

  Then, the process proceeds to the process of Step P405 for determining whether or not the zoom lens group 20b has moved. When the CPU 75 that performs processing for driving the zoom lens driving unit 52 determines that the zoom lens group 20b has moved, the CPU 75 proceeds to Step P406 where focus control is performed by face detection zoom tracking. On the other hand, when the CPU 75 determines that the zoom lens group 20b has not moved, the CPU 75 proceeds to a return process in step P310.

  In step P406, the tracking control unit 85b of the control unit 85 zooms using the tracking curve Tk corresponding to the actual distance L obtained by the distance calculation unit 84 acquired by the tracking curve acquisition unit 85a of the control unit 85. Correct the focus position shift when changing the magnification. The tracking curve Tk acquired based on the face detection indicates the relationship between the position Pz of the zoom lens group and the position Pf of the focus lens group for bringing the face K as the subject into focus. Is shown.

  Then, the tracking control unit 85b of the control unit 85 always sets a position away from the imaging lens 20 by the actual distance L while the zoom magnification (focal length) is changed by the zoom lens group 20b. The focusing lens group 20a is controlled so as to be disguised.

  For example, when the actual distance L is 5 m, the tracking control unit 85b moves the focus lens group 20a in accordance with the movement of the zoom lens group 20b so as to satisfy the relationship indicated by the tracking curve Tk3 in FIG. Control.

  The tracking curve acquisition unit 85a obtains the tracking curve Tk corresponding to the actual distance L obtained by the distance calculation unit 84 based on the design value data and the like of the imaging lens 20 input and stored in advance. Also good.

  In addition, tracking curves Tk1, Tk2, Tk5, and Tkz corresponding to a plurality of types of actual distances assumed in advance, for example, L = 1m, 2m, 5m, and infinity are stored in the tracking curve acquisition unit 85a in the form of functions. The tracking curve acquisition unit 85a complements the tracking curves Tk1, Tk2, Tk5, Tkz stored in advance with the tracking curve Tk corresponding to the actual distance L obtained by the distance calculation unit 84. You may make it ask for it. Japanese Patent Laid-Open No. 2003-57526 and the like can be referred to for a method for complementing and obtaining the tracking curve.

  Then, when the movement of the zoom lens group 20b stops, the process proceeds to step P310 and a return process is executed.

  On the other hand, when the process shifts to the process of setting the focus position in step P407 to the initial setting position without detecting the face in the process of step P403, the focus by the normal autofocus method is executed. That is, a conventionally known autofocus process that is performed without detecting a face is executed.

  Thereafter, the process proceeds to a process of determining whether or not the zoom lens group 20b has moved in Step P408. In step P408, when the CPU 75 that performs processing for driving the zoom lens driving unit 52 determines that the zoom lens group 20b has moved, focus control based on normal zoom tracking is performed without performing face detection. Migrate to When the CPU 75 determines that the zoom lens group 20b has not moved, the CPU 75 proceeds to a return process in step P310.

  Note that JP-A-2003-57526 and the like can be referred to for conventionally known focus control by the normal zoom tracking.

  As a result of the return process in step P310, the process proceeds from the face detection process in step P4 to step P5.

  In Step P5, when it is determined that the shutter button 19 is fully pressed or half pressed, the process proceeds to Step P6 in which focusing is performed. On the other hand, if the shutter button 19 has not been pressed, that is, if the shutter button 19 has been fully pressed or half-pressed, the process proceeds to step P4 where the face detection process is performed again.

  In the focusing process in step P6, an AF processing instruction is issued to the AF processing unit 62, and the focusing process is performed.

  When the focusing process is performed, in the process of step P7, an instruction for determining the exposure is issued by the AE / AWB processing unit 63, and the exposure is determined.

  When exposure is determined, it is then determined in step P8 whether the shutter button 19 is fully pressed, half pressed, or not pressed.

  When the shutter button 19 is not pressed, that is, when both the full-press and half-press states are released, the process returns to step P4 where the face detection process is performed again.

  If it is determined that the shutter button 19 is half-pressed, the exposure adjustment process in step P7 is executed again.

  If it is determined that the shutter button 19 has been fully pressed, the process proceeds to step P9 in which the subject is imaged.

  When the main imaging in step P9 is completed, next, in step P10, an image captured by the main imaging is displayed on the liquid crystal monitor 18, and processing for recording the image on the external recording medium 70 is performed. Next, in step P11, it is determined whether or not the lens cover 21 is closed and the power is turned off. If the power is not turned off, the process returns to step P2, and a process for imaging the next subject is started. If the power is off, the process ends at step P13.

  According to the method of the present invention as described above, the focus position shift that occurs when the focal length (zoom magnification) is changed with respect to a predetermined subject has been conventionally corrected using the tracking curve. In the imaging method and apparatus of the present invention, by storing the standard face dimension information, the focus position shift that occurs when the zoom magnification is changed even when an arbitrary face is imaged is corrected using the tracking curve. can do. Furthermore, since the distance to the face is obtained based on the size of the face that is the subject, the focal length of the imaging lens, and the size of the face on the imaging surface, it is not affected by the depth of field. The distance to the face can be measured, and the focus position shift that occurs during zoom magnification change can be corrected more accurately than in the past.

  In the conventional method of obtaining the distance to the subject by the autofocus function, the distance measurement accuracy is lowered due to the influence of the depth of field, and in particular, the distance measurement accuracy on the wide angle side is lowered. Regardless of the depth of field, that is, substantially the same distance measurement accuracy can be obtained on both the wide-angle side and the telephoto side, and more accurate focus position correction is possible.

  In step P6, a focus evaluation distribution based on the focus evaluation values obtained at a plurality of different focus positions is obtained for the face area to be the subject, and the focus evaluation in the focus evaluation value distribution is obtained. The focus lens group is positioned at a position corresponding to the peak value. Hereinafter, this process will be described in detail with reference to FIG. 10 showing the focus evaluation value distribution.

  In the process of step P6, first, the focus lens driving unit 51 moves the focusing lens group 20a in the optical axis direction over the entire operating range based on the drive data output from the AF processing unit 62. In the present embodiment, this focusing operation range (search range) is, for example, a range in which an object at 60 cm on the closest side and an object at infinity on the farthest side are focused. As described above, when the focusing lens group 20 a is moved, the above-described pre-imaging is executed a plurality of times, and the captured image data is stored in the frame memory 68. This pre-imaging is performed while moving the focusing lens group 20a stepwise in one direction, and the AF processing unit 62 obtains a focus evaluation value corresponding to the contrast of the image captured at each position. For this purpose, the AF processing unit 62 performs filtering processing on the image data indicating the pre-image to obtain a high-frequency component, and sets a value obtained by integrating the absolute value of the high-frequency component as a focus evaluation value. For this purpose, the AF processing unit 62 performs filtering processing on the image data indicating the pre-image to obtain a high-frequency component, and sets a value obtained by integrating the absolute value of the high-frequency component as a focus evaluation value. As described above, the focus evaluation value continuously obtained by moving the focus position of the imaging lens 20 in one direction (moving the focus lens group 20a in one direction) is obtained from the focus lens group 20a. FIG. 10 shows a focus evaluation value distribution H indicated according to the position.

  Next, the focus position suitable for the main imaging is determined. Here, the AF processing unit 62 obtains a position Lp indicating the peak value of the focus evaluation value distribution continuously obtained while moving the focus position shown in FIG. 10 by interpolation processing or the like, and the position Lp is obtained in the main imaging. It is set as the position of the focusing lens group 20a to be set.

  In addition to determining the position Lp of the focusing lens group 20a by the above-described interpolation processing or the like, the position where the maximum value is obtained among the actually obtained focus evaluation values (position Lo in the example of FIG. 10) is peaked. For example, when two such maximum values exist, a method may be employed in which, for example, a position closer to the peak is used as the peak position.

  Further, it is not always necessary to move the focusing lens group 20a over the entire operating range. For example, if a “mountain climbing focusing operation” as disclosed in JP-A-2004-48446 is employed, the focusing lens group What is necessary is just to move 20a in the one part range in an operation | movement range. By doing so, it is possible to speed up the focusing operation.

  When the focusing process is completed as described above, the process proceeds to the exposure adjustment process in step 7 described above.

  The control unit 85 can perform the control only when the focal length of the zoom lens group 20b is changed from the wide angle side to the telephoto side.

  Further, the image captured when the detection unit 82 detects a face may be a pre-image or the like instead of a through image.

  The distance calculation unit 84 performs calculation using the focal length information and the imaging dimension information obtained when the face is imaged in a state where the face is in focus, and the focal length of the imaging lens is determined. The calculation can be performed only when the wide angle side is set.

  As described above, in the above-described embodiment, the present invention is applied to a digital still camera. However, the present invention is not limited to a digital still camera that captures and records a still image, or a video camera that captures and records a moving image, or The present invention is applicable to all imaging devices such as a surveillance camera that captures and records a moving image or a still image at a predetermined location over a long period of time.

The figure which looked at the appearance of the digital camera which is an imaging device by an embodiment of the present invention from the front side The figure which looked at the appearance of the digital camera which is an imaging device by an embodiment of the present invention from the back side Block diagram showing the electrical configuration of the digital camera The block diagram which shows in detail the structure of the focus correction | amendment part at the time of the face detection zoom in the block diagram of FIG. Flow chart showing the overall flow of imaging processing by a digital camera Flow diagram showing the flow of face detection processing that detects the face and corrects the focus during zooming The figure which shows the positional relationship of the face used as the object, the imaging lens, and the imaging surface The figure which shows the relationship between the magnitude | size of the face used as the object, the focal distance of an imaging lens, and the size of the said face imaged on the imaging surface Diagram showing tracking curve based on face detection The figure which shows the focus evaluation value which is obtained continuously while moving the focus position

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Digital camera 20 Imaging lens 20a Lens for focus 20b Lens for zoom 51 Lens drive part for focus 52 Lens drive part for zoom 58 CCD
58a Imaging surface 65 Focus correction unit during face detection zoom 75 CPU
81 Discrimination Information Storage Unit 82 Detection Unit 83 Standard Face Size Storage Unit 84 Distance Calculation Unit 85 Control Unit Hj Discrimination Information

Claims (5)

An imaging lens having an imaging lens having a focusing lens group for changing a focus position and a zoom lens group for changing a focal length, and imaging an image of a subject formed on an imaging surface through the imaging lens In the device
Standard face dimension storage means for storing predetermined standard face dimension information;
Discrimination information storage means for storing discrimination information for discriminating whether or not it is a face;
Detecting means for detecting an image representing a face from images picked up through the imaging lens based on the discrimination information;
When an image representing a face is detected from the image, the standard face size information, focal length information indicating a focal length of an imaging lens when the face is imaged, and the imaging surface when the face is imaged Distance calculation means for obtaining imaging dimension information indicating the size of the face above and obtaining an actual distance from the imaging lens to the face using the information,
While changing the focal length by the zoom lens group, said detection means and said distance calculating means by seeking the actual distance from the imaging lens to the face, always the imaging lens position apart the actual distance An image pickup apparatus comprising: control means for performing focus control by face detection zoom tracking for controlling the focus lens group so that the focus lens group is brought into a focus position.   The imaging apparatus according to claim 1, wherein the size of the face is a width of a human face.   2. The imaging apparatus according to claim 1, wherein the size of the face is the length of a human face.   4. The control unit according to claim 1, wherein the control unit performs the control only when the focal length of the zoom lens group is changed from the wide-angle side to the telephoto side. Imaging device. In an imaging method for capturing an image of a subject formed on an imaging surface through an imaging lens having a focusing lens group for changing a focus position and a zoom lens group for changing a focal length,
Predetermined standard face dimension information and discrimination information for discriminating whether or not the face is stored are stored.
A step of detecting, based on (a) the imaging lens the determination information image representing a face from within the captured image which through,
(B) When an image representing a face is detected from the image, the standard face dimension information, focal length information indicating a focal length of an imaging lens when the face is imaged, and when the face is imaged and give the imaging size information indicating the size of the face on the imaging surface, Ru obtains the actual distance from the imaging lens by using the respective information to the face step,
When (c) lens group the zoom detects that it has moved to seek the actual distance from the imaging lens to the face, the position apart the actual distance always focus position of the imaging lens A step of performing focus control by face detection zoom tracking , controlling the focusing lens group so that
(D) enabling the repetition of steps (a) to (c) during the change of the focal length by the zoom lens group ;
An imaging method characterized by comprising:

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