JP5724208B2 - Imaging device - Google Patents

Description

  The present invention relates to an imaging apparatus capable of performing focus detection based on an output of an imaging element.

  Patent Document 1 discloses an imaging apparatus having an imaging element including an imaging pixel and a pupil division type phase difference detection type focus detection pixel. In this imaging apparatus, focus detection areas are arranged at a plurality of positions on the screen, and the user selects one of them to perform focus detection. In the conventional image pickup apparatus, the exposure control of the image pickup device has been made so that the balance of the luminance level of the image is appropriate for the entire screen. For example, when a histogram of luminance levels of all pixels is created, exposure control is performed so that the average value of the histogram falls within an appropriate luminance level range (see, for example, Patent Document 1).

JP 2007-333720 A

  However, when exposure control is performed on the entire screen as described above, depending on the luminance distribution on the screen, the luminance level of the focus detection pixels in the focus detection area falls within a range suitable for focus detection calculation processing. There is a problem that focus detection is not always possible.

The imaging device according to claim 1 is suitable for an imaging element in which a plurality of pixels are two-dimensionally arranged, a photographing optical system that forms an optical image on the imaging element, and recording of the optical image. A first exposure control means for setting an exposure amount and performing first exposure control; and focus detection for detecting a focus adjustment state of the photographing optical system with respect to the optical image based on pixel data of at least some of the plurality of pixels. Based on the image data read out from the image sensor , the second exposure control means for setting the exposure amount smaller than the appropriate exposure amount and performing the second exposure control for detecting the focus adjustment state. Display means for displaying a through image of the optical image, and the display means displays the image data read by the second exposure control at a luminance level corresponding to the appropriate exposure amount. It is characterized by that .

  According to the imaging apparatus of the present invention, focus detection is possible regardless of the luminance distribution on the screen.

It is a figure which shows the structure of the digital still camera of one embodiment. It is a figure which shows the focus detection position on the imaging | photography screen of an interchangeable lens. It is a front view which shows the detailed structure of an image pick-up element. It is a front view which shows the detailed structure of an image pick-up element. It is a circuit structure conceptual diagram of an image sensor. It is a figure which shows the cross-sectional structure of the imaging pixel and focus detection pixel of an image pick-up element. It is an operation | movement timing chart of an image pick-up element. It is an electric potential distribution diagram which shows operation of an image sensor. It is a flowchart which shows the imaging operation of the digital still camera of one embodiment. It is a brightness | luminance histogram of a pixel. It is a figure which illustrates the sight with a wide dynamic range of brightness | luminance. It is a figure which shows the processing flow which performs a focus detection calculation using the focus detection pixel data added with the past data. It is the figure which showed the effect by data addition. It is a front view which shows the detailed structure of an image pick-up element. It is a front view which shows the detailed structure of an image pick-up element.

  As an imaging apparatus according to an embodiment, an interchangeable lens digital still camera will be described as an example. FIG. 1 is a cross-sectional view showing a configuration of a digital still camera according to an embodiment. A digital camera 201 according to the present embodiment includes an interchangeable lens 202 and a camera body 203, and the interchangeable lens 202 is attached to the camera body 203 via a mount unit 204. An interchangeable lens 202 having various photographing optical systems can be attached to the camera body 203 via a mount unit 204.

  The interchangeable lens 202 includes a lens 209, a zooming lens 208, a focusing lens 210, a diaphragm 211, a lens drive control device 206, and the like. The lens drive control device 206 includes a microcomputer (not shown), a memory, a drive control circuit, and the like. The lens drive control unit 206 performs drive control for adjusting the focus of the focusing lens 210 and adjusting the aperture diameter of the aperture 211, and detecting the states of the zooming lens 208, the focusing lens 210, and the aperture 211. Further, transmission of lens information and reception of camera information (defocus amount, aperture value, etc.) are performed by communication with a body drive control device 214 described later. The aperture 211 forms an aperture having a variable aperture diameter at the center of the optical axis in order to adjust the amount of light and the amount of blur.

  The camera body 203 includes an image sensor 212, a body drive control device 214, a liquid crystal display element drive circuit 215, a liquid crystal display element 216, an eyepiece lens 217, a memory card 219, and the like. In the image sensor 212, image pickup pixels are two-dimensionally arranged (rows and columns), and focus detection pixels are incorporated in portions corresponding to focus detection positions (focus detection areas). Details of the image sensor 212 will be described later.

  The body drive control device 214 includes a microcomputer, a memory, a drive control circuit, and the like. The body drive control device 214 repeatedly performs exposure control of the image sensor 212 and readout of the pixel signal from the image sensor 212, focus detection calculation based on the pixel signal of the focus detection pixel, and focus adjustment of the interchangeable lens 202. The body drive control device 214 performs processing and recording of image signals, operation control of the digital still camera 201, and the like. Further, the body drive control device 214 communicates with the lens drive control device 206 via the electrical contact 213 to receive lens information and send camera information.

  The liquid crystal display element 216 functions as an electric view finder (EVF). The liquid crystal display element driving circuit 215 displays a through image on the liquid crystal display element 216 based on the image data read from the image sensor 212, and the photographer can observe the through image through the eyepiece 217. The memory card 219 is an image storage that stores image data captured by the image sensor 212.

  The AD conversion device 221 performs AD conversion on the pixel signal output from the image sensor 212 and sends it to the body drive control device 214. The imaging device 212 may have a configuration in which the AD conversion device 221 is incorporated.

  A subject image is formed on the image sensor 212 by the light beam that has passed through the interchangeable lens 202. This subject image is photoelectrically converted by the image sensor 212, and the pixel signals of the imaging pixels and focus detection pixels are sent to the body drive control device 214.

  The body drive control device 214 calculates the defocus amount based on the pixel signal from the focus detection pixel of the image sensor 212 and sends this defocus amount to the lens drive control device 206. In addition, the body drive control device 214 processes the pixel signal of the imaging pixel of the imaging element 212 to generate image data, stores the image data in the memory card 219, and displays the through image signal read from the imaging element 212 on the liquid crystal display. The image is sent to the element driving circuit 215 and the through image is displayed on the liquid crystal display element 216. Further, the body drive control device 214 sends aperture control information to the lens drive control device 206 to control the aperture of the aperture 211.

  The lens drive controller 206 updates the lens information according to the focusing state, zooming state, aperture setting state, aperture opening F value, and the like. Specifically, the positions of the zooming lens 208 and the focusing lens 210 and the aperture value of the aperture 211 are detected, and lens information is calculated according to these lens positions and aperture values, or a lookup prepared in advance. Lens information corresponding to the lens position and aperture value is selected from the table.

  The lens drive control device 206 calculates a lens drive amount based on the received defocus amount, and drives the focusing lens 210 to the in-focus position according to the lens drive amount. Further, the lens drive control device 206 drives the diaphragm 211 in accordance with the received diaphragm value.

  The storage device 220 stores pixel data of a plurality of focus detection areas described later over a plurality of past generations. The body drive control device 214 stores pixel data of focus detection pixels in a plurality of focus detection areas in each frame read from the image sensor 212 in the storage device 220. Further, when the focus detection calculation processing is performed using the pixel data of the focus detection pixels in each focus detection area, if the output level of the pixel data of the focus detection pixels of the latest frame is insufficient, the storage device 220 stores the data. The stored past pixel data is added. In this way, the output level of the pixel data of the focus detection pixel is recovered, and the focus detection process described later is performed in the focus detection area using the pixel data of the recovered focus detection pixel.

  FIG. 2 is a diagram showing a focus detection position (focus detection area) on the shooting screen of the interchangeable lens 202, and an image is sampled on the shooting screen when a focus detection pixel column on the image sensor 212 described later performs focus detection. An example of a region (focus detection area, focus detection position) to be performed is shown. In this example, focus detection areas 101 to 105 are arranged at the center (on the optical axis) on the rectangular shooting screen 100 and at five locations on the top, bottom, left, and right. Focus detection pixels are linearly arranged in the longitudinal direction of the focus detection area indicated by a rectangle. In the focus detection areas 101, 102, and 103, focus detection pixels are arranged in the horizontal direction, and in the focus detection areas 104 and 105, focus detection pixels are arranged in the vertical direction.

  3 and 4 are front views showing a detailed configuration of the image sensor 212. FIG. 3 shows details of the pixel array in which the vicinity of the focus detection areas 101, 102, and 103 in FIG. 2 is enlarged, and FIG. 2 shows details of the pixel array in which the vicinity of the focus detection areas 104 and 105 in FIG. Imaging pixels 310 are densely arranged on the imaging element 212 in a two-dimensional square lattice pattern. The imaging pixel 310 includes a red pixel (R), a green pixel (G), and a blue pixel (B), and is arranged according to a Bayer arrangement rule. In FIG. 4, focus detection pixels 313 and 314 for vertical focus detection having the same pixel size as the imaging pixels for vertical focus detection should be alternately arranged, and originally green pixels and blue pixels should be continuously arranged. They are continuously arranged on a straight line in the vertical direction. Similarly, in FIG. 3, focus detection pixels 315 and 316 for horizontal focus detection having the same pixel size as the imaging pixel for horizontal focus detection are alternately arranged, and originally green pixels and blue pixels are continuously arranged. It is arranged continuously on a power horizontal line.

  The shape of each microlens of the imaging pixel 310 and the focus detection pixels 313, 314, 315, and 316 is a shape obtained by cutting out from a circular microlens originally larger than the pixel size into a square shape corresponding to the pixel size.

  The imaging pixel 310 includes a rectangular microlens 10, a photoelectric conversion unit 11 whose light receiving area is limited to a square by a light shielding mask, and a color filter (not shown). The color filters include three types of red (R), green (G), and blue (B), and have spectral sensitivity characteristics corresponding to the respective colors. In the image pickup device 212, image pickup pixels 310 having respective color filters are arranged in a Bayer array.

  The focus detection pixels 313, 314, 315, and 316 are provided with white filters that transmit all visible light in order to perform focus detection for all colors. The white filter has a spectral sensitivity characteristic such that the spectral sensitivity characteristics of the green pixel, the red pixel, and the blue pixel are added, and the light wavelength region exhibiting high sensitivity is each color filter in each of the green pixel, the red pixel, and the blue pixel. Includes a light wavelength region exhibiting high sensitivity.

  As shown in FIG. 4, the focus detection pixel 313 includes a photoelectric conversion unit 13 in which a light receiving area is limited to an upper half of a square (upper half when a square is divided into two equal parts by a horizontal line) using a rectangular microlens 10 and a light shielding mask. And a white filter (not shown).

  Further, as shown in FIG. 4, the focus detection pixel 314 is a photoelectric conversion in which a light receiving area is limited to a lower half of a square (lower half when a square is divided into two equal parts by a horizontal line) by a rectangular microlens 10 and a light shielding mask. And a white filter (not shown).

  When the focus detection pixel 313 and the focus detection pixel 314 are displayed with the microlens 10 superimposed, the photoelectric conversion units 13 and 14 in which the light receiving area is limited to a half of a square by a light shielding mask are arranged in the vertical direction.

  In addition, when the remaining portion obtained by halving the square is added to the above-described half light-receiving region, a square having the same size as the light-receiving region of the imaging pixel 310 is obtained.

  As shown in FIG. 3, the focus detection pixel 315 is a photoelectric conversion unit in which a light receiving region is limited to a left half of a square (left half when a square is divided into two equal parts by a vertical line) using a rectangular microlens 10 and a light shielding mask. 15 and a white filter (not shown).

  Further, as shown in FIG. 3, the focus detection pixel 316 is a photoelectric sensor in which a light receiving area is limited to a right half of a square (right half when a square is divided into two equal parts by a vertical line) by a rectangular microlens 10 and a light shielding mask. It is comprised from the conversion part 16 and a white filter (not shown).

  When the focus detection pixel 315 and the focus detection pixel 316 are displayed with the microlens 10 superimposed, the photoelectric conversion units 15 and 16 in which the light receiving area is limited to a half of a square by a light shielding mask are arranged in the horizontal direction.

  In addition, when the remaining portion obtained by halving the square is added to the above-described half light-receiving region, a square having the same size as the light-receiving region of the imaging pixel 310 is obtained.

  In the configuration of the imaging pixel and the focus detection pixel as described above, under a general light source, the output level of the green imaging pixel and the output level of the focus detection pixel are substantially equal, and the red imaging pixel and the blue detection pixel The output level of the imaging pixel is smaller than this.

  A large number of the pair of focus detection pixels 313 and 314 described above are arranged alternately and linearly, and the output of the photoelectric conversion unit of each focus detection pixel is output to the pair of distance measurement pupils disclosed in Japanese Patent Application Laid-Open No. 2007-333720. By combining the output groups into corresponding output groups, information on the intensity distribution of the pair of images formed on the focus detection pixel array (vertical direction) by the pair of light beams respectively passing through the pair of distance measurement pupils can be obtained. By applying an image shift detection calculation process (correlation calculation process, phase difference detection process) to this information, the image shift amount of a pair of images is detected by a so-called pupil division type phase difference detection method. Furthermore, by performing a conversion operation according to the proportional relationship between the distance between the center of gravity of the pair of distance measurement pupils and the distance measurement pupil distance, the deviation between the planned image formation surface and the image formation surface at the focus detection position (vertical direction) is performed. (Defocus amount) is calculated.

  As with the focus detection pixels 313 and 314, a pair of distance measurement pupils is set for the focus detection light beams received by the focus detection pixels 315 and 316. A large number of pairs of focus detection pixels 315 and 316 are arranged alternately and in a straight line, and the output of the photoelectric conversion unit of each focus detection pixel is collected into a pair of output groups corresponding to the pair of distance measurement pupils. Information on the intensity distribution of the pair of images formed on the focus detection pixel array (horizontal direction) by the pair of light beams respectively passing through the distance pupil is obtained. Based on this information, the deviation (defocus amount) between the planned imaging plane and the imaging plane at the focus detection position (horizontal direction) is calculated.

  FIG. 5 is a conceptual diagram of a circuit configuration of the image sensor. The imaging device is configured as a CCD image sensor. The circuit configuration of the image sensor 212 will be described in a simplified manner with a layout of 8 pixels in the horizontal direction × 8 pixels in the vertical direction. FIG. 5 is drawn corresponding to the focus detection area 104 in the vertical direction of FIG. 2, and the focus detection pixels 313 and 314 are arranged in the same column in the vertical direction.

  The fourth column is a column in which the focus detection pixels 313 and 314 are arranged, and the four central focus detection pixels 313 and 314 (indicated by ◯) represent a plurality of focus detection pixels, two at the top and two at the bottom. Imaging pixels 310 (indicated by squares) represent a plurality of imaging pixels arranged above and below the focus detection pixels.

  The 1st to 3rd columns and the 5th to 8th columns are columns in which only the imaging pixels 310 (indicated by □) are arranged, and are representative of columns composed of only a plurality of left and right imaging pixels in the column in which the focus detection pixels are arranged. doing.

  In the figure, the charges generated by the imaging pixels and focus detection pixels arranged in each column are transferred to the vertical transfer CCD provided corresponding to each column, and then sequentially transferred in the direction of the horizontal transfer CCD. When the charge for one row is transferred from the vertical transfer CCD to the horizontal transfer CCD, the charge for one row is sequentially transferred in the direction of the output circuit 330. The output circuit 330 performs charge-voltage conversion and is accumulated in each pixel. A pixel signal corresponding to the charge amount is output to the outside.

  The transfer pulse generation circuit supplies drive signals necessary for the transfer operation of the vertical transfer CCD and the horizontal transfer CCD to the vertical transfer CCD and the horizontal transfer CCD. The control pulse generation circuit supplies control signals ΦU, ΦT1, ΦT2, and ΦT3 necessary for charge accumulation control of the imaging pixels and focus detection pixels and charge transfer from each pixel to the vertical transfer CCD in common to all the pixels.

  The control signal φSync output from the control pulse generation circuit is a vertical synchronization signal, and is output to the outside (body drive control device 214) for each frame.

  The input signal Tx is an input signal to the control pulse generation circuit from the outside (body drive control device 214), and is a signal for designating the charge accumulation time of the pixel. The control pulse generation circuit controls the control signals ΦU and ΦT1. The charge accumulation time is controlled (exposure control) by changing the generation timing of the signal according to this signal.

  6 is a diagram showing a cross-sectional structure of the imaging pixels and focus detection pixels of the imaging device shown in FIG. A buried photodiode (PD) composed of a P layer and an N layer is formed on a P-type semiconductor substrate, and a charge storage section composed of an N layer is formed next to the photodiode. An N layer constituting a vertical transfer CCD is further formed adjacent to the charge storage unit. An N + layer is formed adjacent to the PD and connected to the power supply voltage Vdd. A gate 602 is disposed on a channel between the charge storage unit and the PD, and a control signal ΦT1 is connected thereto. A gate 603 is disposed on the charge storage portion and connected to the control signal ΦT2. A gate 604 is disposed on a channel between the charge storage unit and the vertical transfer CCD, and a control signal ΦT3 is connected thereto. A gate 605 is disposed on the vertical transfer CCD, and a drive signal ΦVx is connected thereto. A gate 601 is disposed on a channel between the PD and the adjacent N + layer, and a control signal ΦU is connected thereto. By applying the control signals ΦU, ΦT1, ΦT2, and ΦT3 to the gates 601 to 604, the potential level under each gate is changed to control the operation of accumulating, transferring, and discarding the charges generated by the PD.

  FIG. 7 is an operation timing chart of the image sensor shown in FIG. FIG. 8 is a potential distribution diagram showing the operation of the image sensor. In a CCD image sensor, pixel reset, exposure, and signal readout are simultaneously performed by a so-called global shutter operation.

  The vertical synchronization signal φSync is generated at time t0 in synchronization with the start of the output of all pixel signals from the image sensor (output of image signals for one frame). In synchronization with the vertical synchronization signal φSync, the control pulse generation circuit generates a control signal ΦU (ON) and a control signal ΦT1 (OFF) at time t0. In response to this, when the pixel signal is output, the charge storage unit is disconnected from the PD. At this time, the image pickup device is in the potential distribution state of FIG. 8A, the charge is held in the charge storage portion formed under the gate 603, and the charge generated by the PD is discarded to the power supply voltage vdd. .

  Due to the control signal ΦT2 (OFF) and the control signal ΦT3 (ON) issued at time t1, the charges held in the charge storage unit are transferred to the vertical transfer CCD unit. At this time, the imaging device is in the potential distribution state of FIG. 8B, the potential immediately below the gate 604 is lower than the potential directly below the gate 603, and the charge directly below the gate 603 passes through the gate 604 and is transferred vertically below the gate 605. It flows into the CCD part. The electric charge transferred to the vertical transfer CCD is then output to the outside through the horizontal transfer CCD during the frame period by a drive signal. Further, the charge generated by the PD from time t1 to t2 is discarded to the power supply voltage vdd.

  With the control signal ΦT2 (ON) and the control signal ΦT3 (OFF) issued at time t2, the charge storage unit ends the charge transfer to the vertical transfer CCD. At this time, the imaging device is in the potential distribution state of FIG. 8C, and the potential immediately below the gate 604 rises to separate the charge storage unit from the vertical transfer CCD. Further, the charge generated by the PD from time t2 to t3 is discarded to the power supply voltage vdd.

  Accumulation in the charge accumulation unit of the charge generated by the PD is started by the control signal ΦU (OFF) and the control signal ΦT1 (ON) issued at time t3. At this time, the image sensor is in the potential distribution state of FIG. 8D, and the potential immediately below the gate 601 is increased to separate the PD from the power supply voltage Vdd. In addition, the potential immediately below the gate 602 becomes lower than the potential of the PD, and the charge generated by the PD passes directly under the gate 602 and is accumulated in the charge storage portion immediately below the gate 603 whose potential is lower than the potential of the gate 602. .

  By repeating the above operation for each frame, continuous image data is periodically output.

  In the above operation, the charge accumulation of the imaging pixel and the focus detection pixel is the time from the fall to the rise of the control signal φU (the time from the rise to the fall of the control signal φT1), and this time is the exposure time (charge accumulation). Period).

  As will be described later, the exposure time is determined so that the average luminance level becomes an appropriate level (for example, the median value of the luminance dynamic range) based on the luminance distribution state (luminance histogram) of the entire screen or a part thereof.

  FIG. 9 is a flowchart illustrating an imaging operation of the digital still camera 201 according to the embodiment. When the power of the camera is turned on in step S100, the body drive control device 214 starts the imaging operation after step S110. In step S100, the image sensor is set to an operation mode (for example, 60 frames are output per second) in which the image capturing operation is repeated at a constant cycle.

  In step S105, an appropriate exposure amount suitable for imaging and recording for the entire image is determined by photometry. In step S110, the charge accumulation time of the image sensor is designated so that the exposure amount is one step lower (exposure amount ½) than the appropriate exposure amount, and exposure control is performed.

  In the case of a scene having a wide luminance dynamic range, a luminance histogram of a green imaging pixel (= focus detection pixel) as shown in FIG. 10A is obtained by exposure control at an appropriate exposure level for the entire screen. For example, FIG. 11 will be described as a scene with a wide dynamic range of luminance. FIG. 11 shows a scene including a house 510, a mountain 520, a sun 530, and a sky 540. The house 510 that is backlit against the sun 530 is very dark. The mountain 520 illuminated by the sun 530 is brighter than the house 510 but darker than the sky 540. For convenience of illustration, FIG. 11 does not appear to have gradation, but the following description will be continued assuming that the actual scene has fine gradation.

  For such a scene, a high-intensity portion of the scene is included in the vicinity of the focus detection area 102 at the top of the screen and the focus detection area 105 at the right of the screen. 10 (a) becomes a C1 portion, and part of the luminance dynamic range is exceeded. Therefore, those saturated with high luminance components are clipped. That is, a part of the data of the focus detection pixel is clipped at the maximum value of the AD conversion, and the detection accuracy of the focus detection is lowered or cannot be detected. In FIG. 10A, the B1 portion located approximately at the center of the luminance histogram corresponds to the luminance histogram in the vicinity of the focus detection areas 101 and 104. In FIG. 10A, the A1 portion in the low luminance portion of the luminance histogram corresponds to the luminance histogram in the vicinity of the focus detection area 103.

  On the other hand, when exposure control is performed with the exposure amount under the exposure amount at which the entire screen has an appropriate exposure level, a luminance histogram of the green image pickup pixel (= focus detection pixel) as shown in FIG. 10B is obtained. . The luminance histogram in the vicinity of the focus detection areas 102 and 105 is the portion C2 in FIG. 10B, and the luminance dynamic range is not exceeded. Therefore, focus detection pixel data is not clipped at the maximum value of AD conversion, and accurate focus detection is possible. In FIG. 10B, the B2 portion of the luminance histogram corresponds to the luminance histogram in the vicinity of the focus detection areas 101 and 104. In FIG. 10B, the A2 portion of the luminance histogram corresponds to the luminance histogram near the focus detection area 103.

  Luminance can be detected by using the output of multi-division photometry means (not shown) or by using data of imaging pixels in the previous frame of the imaging device. First, the exposure amount is determined so that the exposure level is appropriate over the entire screen with respect to the detected luminance, and the charge accumulation time of the image sensor during imaging recording is determined based on the exposure amount with the exposure amount being uniformly under.

  In step S120, all pixel data for one frame is read. In step S130, pixel interpolation is performed on virtual imaging pixel data at each pixel position in the focus detection pixel row based on imaging pixel data around the focus detection pixel.

  For example, for a focus detection pixel that is originally arranged at a position where a green pixel should be arranged, the data of four green imaging pixels adjacent to four positions in the diagonal direction of the focus detection pixel are averaged, and the focus detection pixel is averaged. Data of the green imaging pixel at the position of the detection pixel is used. In addition, with respect to the focus detection pixel that is originally disposed at the position where the blue pixel should be disposed, the data of the two blue imaging pixels adjacent to the two positions in the left-right direction of the focus detection pixel are averaged to detect the focus detection pixel. It is assumed that the data of the blue imaging pixel at the pixel position.

  The image data corresponding to the current frame is generated by combining the imaged pixel data thus interpolated and the original imaged pixel data.

  In subsequent step S140, the luminance level of the image data corresponding to the current frame is corrected and displayed on the electronic viewfinder (live view display). The image data corresponding to the current frame is not at the proper exposure level for the entire screen because the exposure amount is below the exposure amount at which the entire screen is at the proper exposure level. Therefore, the luminance level is corrected so that an image with an appropriate exposure level is obtained for the entire screen. Specifically, for example, luminance level correction is performed so as to expand the compressed portion of the luminance histogram from FIG. 10 (a) to FIG. 10 (b). However, the luminance level correction is performed with a so-called knee characteristic so that the high luminance portion does not exceed the luminance range that can be displayed by the display means when expanding. By doing so, a high-quality display image free from white stripes can be obtained.

  In step S150, focus detection is performed based on focus detection pixel data in five focus detection areas by focus detection calculation processing, and defocus amounts in the five focus detection areas are calculated. Further, the defocus amount showing the closest distance is selected from the five calculated defocus amounts, and is set as the final defocus amount.

  When calculating the defocus amount of each focus detection area, if the data level of the focus detection pixel is insufficient, it is adjusted to the appropriate data level by adding to the past data, Focus detection calculation is performed using the focus detection pixel data at the data level. In this case, instead of the process shown in step S150, the process shown in steps S1510 to S1540 in FIG. 12 is performed. That is, in step S1510, it is determined whether the data level of the focus detection pixel in the focus detection area is insufficient. If the determination is negative, the determination is immediate. If the determination is affirmative, addition to past data is performed in step S1520, and the process proceeds to step S1530. It is determined whether or not the data level has become appropriate by adding to step S1530. If a negative determination is made, the process returns to step S1520. If the determination is affirmative, an image shift amount detection calculation is performed based on the focus detection pixel data having an appropriate data level after addition in step S1540, and a defocus amount is calculated.

  FIG. 13 is a diagram showing the effect of data addition, with the horizontal axis representing the position of the focus detection pixel and the vertical axis representing the data level of the focus detection pixel. First, the maximum value of focus detection pixel data in each focus detection area of the current frame is detected. When the maximum value does not exceed a predetermined value (for example, 1/2 of the maximum value of AD conversion), the data of the previous frame is read from the storage means and added. If the maximum value of the added data does not exceed the predetermined value, the data of the previous frame is further added. By repeating such an addition operation until the maximum value of the addition data exceeds a predetermined value, the addition data reaches a data level suitable for the focus detection calculation process.

  Since exposure control is performed with the exposure amount under the exposure amount at which the entire screen is at the appropriate exposure level, the focus detection pixel data generally tends to be at a low level. This is effective for accurate focus detection. For example, the data of the focus detection pixels in the focus detection areas 101, 103, and 104 are lower than the data of the focus detection pixels in the focus detection areas 102 and 105 with respect to the scene as shown in FIG. Even if the focus detection calculation is performed, a large error occurs or the focus cannot be detected. However, the effect of increasing the exposure amount (extending the charge accumulation time) by adding the past data is effective. As a result, high-precision focus detection can be performed.

  In step S160, it is determined whether or not the focus is in focus (the absolute value of the final defocus amount is equal to or less than a predetermined threshold value). If in focus, the process proceeds to step S180. If not in focus, the process proceeds to step S170. .

  In step S170, the defocus amount is transmitted to the lens drive controller 206, and the focusing lens 210 of the interchangeable lens 202 is driven to the in-focus position. If the reliability of the defocus amount is low or focus detection is impossible, this is transmitted to the lens drive control unit 206, and the drive control of the focusing lens 210 of the interchangeable lens 202 is not updated. Then, it returns to step S110 and repeats the operation | movement mentioned above.

  In step S180, the exposure amount is determined so that the exposure level of the entire screen is appropriate, the charge accumulation time is specified for the image sensor, and exposure control is performed. In step S190, all pixel data for one frame is read. In step S200, pixel interpolation is performed on virtual imaging pixel data at each pixel position in the focus detection pixel row based on imaging pixel data around the focus detection pixel.

  In step S210, image data corresponding to the current frame is displayed on the electronic viewfinder (live view display). In step S220, it is determined whether or not a shooting instruction has been given by an operating means (not shown). If a shooting instruction has not been given, the process returns to step S180. If a shooting instruction has been given, step S220 is executed. In S230, the image data corresponding to the current frame is stored as image data in the memory card 219, and the process returns to Step S110. In addition, when the process of returning from step S220 to step S180 is repeated a predetermined number of times, or when a predetermined time has elapsed, the process may return to step S105.

  As a general image shift detection calculation process (correlation calculation process) used in step S150 of FIG. 9, the correlation calculation process disclosed in Japanese Patent Application Laid-Open No. 2007-333720 is used. The pair of images detected by the focus detection pixels is a type that can maintain the image displacement detection accuracy with respect to the light amount balance because the distance measurement pupil may be vignetted by the aperture of the lens and the light amount balance may be lost. The correlation calculation is performed.

For a pair of data strings (A1 _{1 to} A1 _M , A2 _{1 to} A2 _M : M is the number of data) read out from the focus detection pixel string, a correlation calculation formula (1) disclosed in Japanese Patent Laid-Open No. 2007-333720 ) To calculate the correlation amount C (k).
C (k) = Σ | A1 n × A2 n + 1 + k -A2 n + k × A1 n + 1 | (1)

With the calculation method disclosed in Japanese Patent Application Laid-Open No. 2009-141791, the image shift amount shft can be calculated using the shift x that gives the minimum value C (x) of the correlation amount C (k). The image shift amount shft thus calculated is multiplied by a predetermined conversion coefficient Kd to be converted into a defocus amount def. The conversion coefficient Kd corresponds to the opening angle of the pair of light beams received by the focus detection pixel, and corresponds to a value obtained by dividing the distance measurement pupil distance d by the center of gravity distance between the pair of distance measurement pupils.
def = Kd × shft (2)

  As described above, in the present invention, when focus detection is performed, exposure control of the image sensor is performed with an exposure amount smaller than an exposure amount during normal imaging. Therefore, the probability that the data of the focus detection pixels in the focus detection area is saturated is reduced, and the focus detection calculation using the data of the focus detection pixels is not likely to be disabled or a large error is generated. Also, when displaying an image with reduced exposure, the exposure level is corrected for the entire screen even during focus detection because the exposure level is corrected for the entire screen. Images can be observed. In addition, after focusing, the exposure control is performed with the same exposure amount as that at the time of photographing, so that there is no black level gradation shortage that occurs when an image is displayed with the exposure level corrected.

  In the embodiment described above, the appropriate exposure amount for the entire image is calculated at the time of focus detection in the same manner as during imaging and recording, and the exposure amount is one step lower (exposure amount 1/2) than the appropriate exposure amount. Although focus control pixel data has been acquired by performing exposure control during such charge accumulation time of the image sensor, the present invention is not limited to this. The exposure amount at the time of focus detection may be two steps under (exposure amount ¼) or three steps under (exposure amount １ ／) from the appropriate exposure amount. In this way, even when the luminance dynamic range in the screen is wide, the probability that the focus detection data in the focus detection area that captures the high luminance portion in the image is further reduced.

  In the above-described embodiment, it has been described that the defect occurs when the data of the focus detection pixel is clipped by the dynamic range of the AD converter, but depending on the maximum charge storage capacity of the charge storage unit of the focus detection pixel. There may be a problem that data of the focus detection pixel is clipped. When performing addition processing in such a case, a predetermined value for comparing the maximum value of the data of the focus detection pixel may be determined based on the saturation data. For example, the predetermined value is ½ of the saturation data.

  In the embodiment described above, focus detection is simultaneously performed in a plurality of focus detection areas. However, the present invention is not limited to this. For example, the user manually selects a desired focus detection area, or detects a specific image pattern (for example, a human face image) from the entire image by image processing, and automatically according to the position of the specific image pattern Alternatively, the focus detection area may be selected.

  Further, the present invention is not limited to an image sensor provided with a focus detection pixel for pupil division type phase difference detection, and can also be applied to an image sensor provided with a focus detection pixel used for so-called contrast detection.

  In the above-described embodiment, the exposure control is performed by changing the charge accumulation time of the image sensor, but is not limited to this. For example, exposure control can also be performed by changing the gain of the output circuit of the image sensor or changing the aperture diameter of the stop.

---- Modified example ---
In the partial enlarged view of the image sensor 212 shown in FIGS. 3 and 4, an example is shown in which a pair of focus detection pixels 313 and 314 and a pair of focus detection pixels 315 and 316 each having one photoelectric conversion unit are provided. A pair of photoelectric conversion units may be provided in one focus detection pixel. 14 and 15 are partial enlarged views of the image sensor 212 corresponding to FIGS. 3 and 4, and the focus detection pixels 311 and 312 include a pair of photoelectric conversion units.

  The focus detection pixel 311 shown in FIG. 15 performs a function corresponding to the pair of the focus detection pixel 313 and the focus detection pixel 314 shown in FIG. 4, and the focus detection pixel 312 shown in FIG. 14 is the focus detection pixel 315 shown in FIG. And a function corresponding to a pair of focus detection pixels 316. As shown in FIGS. 14 and 15, the focus detection pixels 311 and 312 include a microlens 10, a pair of photoelectric conversion units 13 and 14, and a pair of photoelectric conversion units 15 and 16. A white filter is disposed in the focus detection pixels 311 and 312, and the spectral sensitivity characteristic is a spectral that combines the spectral sensitivity characteristic of a photodiode that performs photoelectric conversion and the spectral sensitivity characteristic of an infrared cut filter (not shown). It becomes a sensitivity characteristic. In other words, the spectral sensitivity characteristic is the sum of the spectral sensitivity characteristics of the green pixel, red pixel, and blue pixel, and the light wavelength region in which the white filter has high sensitivity is high for each color filter of the green pixel, red pixel, and blue pixel. It covers the optical wavelength region showing sensitivity.

  Although the example in which the focus detection pixel includes the white filter is shown in the image sensor in the above-described embodiment, the present invention can be applied to a case where the same color filter (for example, a green filter) as that of the image capture pixel is provided. .

  For example, only the focus detection pixels 312 shown in FIG. 14 may be two-dimensionally arranged to form an imaging device, and color filters arranged in a Bayer arrangement may be provided for the focus detection pixels arranged two-dimensionally. In such a configuration, at the time of imaging, it is possible to calculate data equivalent to the imaging pixel by adding the data of the pair of photoelectric conversion units of the focus detection pixel. In addition, when performing focus detection, correlation detection is performed between focus detection pixels of the same color, so that focus detection results for each color can be obtained, and focus detection can be performed even when contrast is not obtained only by luminance. .

  In the above-described embodiment, the present invention is applied to single shooting of a still image (recording one image frame in response to a predetermined trigger among a plurality of image frames), but the present invention is not limited to this. It is not a thing. For example, the present invention can also be applied to continuous shooting of still images (recording image frames at predetermined times out of a plurality of image frames) and moving shooting.

  In the above-described embodiment, a CCD image sensor is used as an image sensor, but a CMOS image sensor can also be used.

  In the image pickup device according to the above-described embodiment, an example in which the image pickup pixel includes a color filter with a Bayer array is shown. However, the configuration and the array of the color filter are not limited to this. For example, the present invention can be applied to an array other than the array of complementary color filters (green: G, yellow: Ye, magenta: Mg, cyan: Cy) or a Bayer array. Further, the present invention can also be applied to a monochrome image sensor that does not include a color filter.

  Note that the imaging apparatus is not limited to the digital still camera configured as described above in which the interchangeable lens is mounted on the camera body. For example, the present invention can be applied to a lens-integrated digital still camera or video camera. Furthermore, the present invention can be applied to a small camera module built in a mobile phone, a surveillance camera, a visual recognition device for a robot, an in-vehicle camera, and the like.

10 microlens, 11, 13, 14, 15, 16 photoelectric conversion unit,
100 shooting screen, 101, 102, 103, 104, 105 focus detection area,
201 digital still camera, 202 interchangeable lens, 203 camera body,
204 mount unit, 206 lens drive control device,
208 zooming lens, 209 lens, 210 focusing lens,
211 Aperture, 212 Image sensor, 213 Electrical contact,
214 body drive control device,
215 liquid crystal display element driving circuit, 216 liquid crystal display element, 217 eyepiece,
219 memory card, 220 storage device, 221 AD converter,
310 imaging pixels,
311, 312, 313, 314, 315, 316 focus detection pixel,
330 Output circuit, 601 602 603 604 605 gate

Claims (9)

An image sensor in which a plurality of pixels are two-dimensionally arranged;
A photographing optical system for forming an optical image on the image sensor;
First exposure control means for setting a proper exposure amount and performing first exposure control for recording the optical image;
Focus detection means for detecting a focus adjustment state of the photographing optical system with respect to the optical image based on pixel data of at least some of the plurality of pixels;
Second exposure control means for setting the exposure amount smaller than the appropriate exposure amount and performing second exposure control for detecting the focus adjustment state;
Display means for displaying a through image of the optical image based on image data read from the image sensor;
The image pickup apparatus , wherein the display means displays the image data read by the second exposure control at a luminance level corresponding to the appropriate exposure amount . The imaging device according to claim 1,
The brightness level of the through image of the optical image formed on the imaging element on which the second exposure control is performed by the second exposure control unit is corrected so as to be an image with an appropriate exposure level for the entire screen. further comprising a correction means,
The image pickup apparatus, wherein the display means displays the through image in which the luminance level is corrected by the correction means. The imaging device according to claim 1 or 2,
The imaging apparatus according to claim 2, wherein the second exposure control means performs exposure control by reducing an accumulation time of the imaging element to reduce exposure control or an aperture diameter. The imaging device according to claim 2 ,
The image pickup apparatus according to claim 1, wherein the correction unit performs correction having knee characteristics for high luminance data included in image data of the image for recording when the luminance level is corrected. In the imaging device according to any one of claims 1 to 4,
An imaging apparatus further comprising recording control means for controlling recording of recording image data of the optical image formed on the imaging element on which the first exposure control is performed by the first exposure control means. . In the imaging device according to any one of claims 1 to 5,
A plurality of focus detection areas for the focus detection means to detect the focus adjustment state are provided,
The focus detection unit is configured to detect each range on the image sensor corresponding to each of the plurality of focus detection areas based on pixel data of pixels within a predetermined range on the image sensor corresponding to the plurality of focus detection areas. An image pickup apparatus that detects the focus adjustment state of the photographing optical system with respect to the optical image formed on the image pickup apparatus. The imaging device according to claim 6,
Storage means for storing pixel data of pixels within the predetermined range when the second exposure control is performed by the second exposure control means;
The focus detection unit reads time-series pixel data obtained by repeatedly reading out pixel data of pixels within a specific range on the image sensor corresponding to at least one focus detection area of the plurality of focus detection areas. Detecting the focus adjustment state based on summed pixel data obtained by adding the time-series pixel data stored in the storage unit and the latest pixel data of the pixels within the specific range. An imaging device that is characterized. In the imaging device according to any one of claims 1 to 7,
In accordance with the focus adjustment state detected by the focus detection unit, the image pickup optical system further includes a focus adjustment unit that adjusts the focus of the shooting optical system so that the optical system is in focus.
The imaging apparatus, wherein after the focus adjustment by the focus adjustment unit is completed, the first exposure control unit performs the first exposure control with the appropriate exposure amount. In the imaging device according to any one of claims 1 to 8,
The plurality of pixels include a plurality of imaging pixels and a plurality of pupil division type focus detection pixels,
Each of the plurality of imaging pixels receives an imaging light beam passing through an exit pupil of the imaging optical system and outputs an imaging signal, and each of the plurality of pupil-divided focus detection pixels passes through the exit pupil. An image pickup apparatus that receives at least one of a pair of focus detection light beams and outputs a focus detection signal.

Images