JP2011232371A - Imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a focus detection which does not depend on a luminance distribution on an image plane.SOLUTION: When a focus detection is performed with an exposure suitable for recording, a focus detection accuracy may degrade because of an output saturation (A) of focus detection pixel data. An image deviation amount detection operation is performed based on the focus detection pixel data read out by performing an exposure control of an image sensor with the exposure suitable for a selected focal point detection area, and a defocus amount is calculated. The output saturation of the focus detection pixel data is avoided by means of the exposure suitable for the focal point detection area (B), and the focus detection accuracy does not degrade.

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 apparatus according to claim 1, 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 a photographing optical system for the optical image on the imaging element. A focus detection area for detecting the focus adjustment state, an exposure control means for performing a first exposure control of the image sensor so that a region near the focus detection area is exposed with a first exposure amount, and a first exposure control. And focus detection means for detecting the focus adjustment state based on the pixel data of the focus detection area.

  According to the imaging apparatus of the present invention, focus detection can be performed regardless of the luminance distribution on the screen, and an image with an appropriate luminance level can be displayed.

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-section of the image pick-up 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 restrict | limits the appropriate exposure control for the focus detection area vicinity selected as object. It is a figure which shows the focus detection area selection processing flow by a specific image pattern detection. It is a figure which shows the processing flow which selects one focus detection area according to the obtained several focus detection result. 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. The 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. The body drive control device 214 communicates with the lens drive control device 206 through the electrical contact 213 to receive lens information and transmit 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 a recording medium as 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 operation member 220 is a member that is manually operated by the user in order to select one focus detection area from a plurality of focus detection areas described later. The body drive control device 214 performs focus detection processing in the focus detection area selected via the operation member 220.

  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.

  The focus detection areas 101, 102, 103, 104, and 105 shown in FIG. 2 are defined on the photographing screen 100. However, the corresponding portions where the focus detection pixels on the image sensor are arranged are also referred to as focus detection areas. I will call it. 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 cut out from a circular microlens that is 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. is 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, the position of the focus detection area is selected. In the present embodiment, the position of the focus detection area is selected by the user via the operation member 220. In step S110, photometry is performed to measure the brightness of the optical image in the vicinity of the focus detection area including the focus detection area. Photometry is performed based on the pixel output of the image sensor 212, and an appropriate exposure amount suitable for focus detection is determined for the vicinity of the focus detection area based on the photometry output. An appropriate exposure amount suitable for imaging and recording for the entire image may be determined by photometry, or may be determined in step S180 described later. Photometry may be performed with a separate photometric sensor. In step S115, the charge accumulation time is specified for the image sensor so that the exposure amount in the vicinity of the focus detection area is appropriate, and exposure control is performed.

  In the case of a scene with 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 with an appropriate exposure amount 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.

  When the focus detection area 102 at the top of the screen is selected for such a scene, since the high brightness portion of the scene is in the vicinity of the focus detection area 102, the brightness histogram near the focus detection area 102 is shown in FIG. A portion of (a) becomes part of the luminance dynamic range. 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.

  On the other hand, when exposure control is performed so that the exposure amount in the vicinity of the selected focus detection area 102 is appropriate, a luminance histogram of a green imaging pixel (= focus detection pixel) as shown in FIG. 10B is obtained. The luminance histogram in the vicinity of the focus detection area 102 is a portion B 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. 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. In accordance with the brightness detected in the vicinity of the selected focus detection area, an exposure amount (charge accumulation time of the image sensor) is determined such that the exposure amount in the vicinity of the selected focus detection area is appropriate.

  It should be noted that not the selected focus detection area itself but the exposure amount so that the exposure amount in the vicinity of the focus detection area is appropriate is usually determined because the main subject is located in the vicinity of the focus detection area. This is because there may be a case where it does not fall within the focus detection area. In addition to the case where the main subject region includes the entire range of the focus detection area and the vicinity thereof, the main subject region may include a part of the range of the focus detection area and the vicinity thereof.

  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 has an appropriate exposure amount in the vicinity of the selected focus detection area, but is not an appropriate exposure amount for the entire screen. Therefore, photometry is performed on the entire screen, and the luminance level is corrected so that an image with an appropriate exposure amount is obtained on 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 the selected focus detection area, and a defocus amount is calculated. In step S160, it is determined whether or not the focus is satisfied (the absolute value of the calculated 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. move on.

  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 recorded 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.

  Next, as a general image shift detection calculation process (correlation calculation process) used in step S150 of FIG. 9, a 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 ) 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, exposure control is performed so that the exposure amount is appropriate in the vicinity of the selected focus detection area. Therefore, the focus detection pixel data (luminance) is not saturated, and the focus detection calculation using the focus detection pixel data is not disabled or causes a large error. In addition, when displaying an image with an appropriate exposure amount in the vicinity of the selected focus detection area, the entire screen is corrected so that the exposure amount is appropriate for the entire screen. In contrast, an image with an appropriate exposure amount can be observed. In addition, after focusing, the exposure control is performed so that the exposure amount is appropriate for the entire screen in the same manner as when shooting, so that it may occur when the image is displayed with the exposure amount corrected. Insufficient black level gradation does not occur.

  When displaying an image with an appropriate exposure amount in the vicinity of the selected focus detection area, if the image is displayed as it is without correction, the luminance level is appropriate in the vicinity of the selected focus detection area. This makes it easier to use in some situations. It is also possible to select whether or not to correct the brightness level when displaying an image.

  In the above-described embodiment, it has been described that a problem occurs when the data of the focus detection pixel is clipped by the dynamic range of the AD converter. However, there may be a problem that data of the focus detection pixel is clipped according to the maximum charge storage capacity of the charge storage unit of the focus detection pixel.

  In the embodiment described above, the exposure control is performed so that the exposure amount is appropriate in the vicinity of the selected focus detection area. The peak of the luminance histogram in the vicinity of the selected focus detection area is shown in FIG. Alternatively, although it has been described that the charge accumulation time of the image sensor is controlled so that the average value is approximately in the center of the luminance dynamic range (AD conversion range), the present invention is not limited to this. For example, the effect of the present invention can be obtained if about 80% of the luminance histogram in the vicinity of the selected focus detection area falls within the luminance dynamic range (AD conversion range).

  In the embodiment described above, the exposure control is performed so that the exposure amount is appropriate in the vicinity of the selected focus detection area. However, the region for which the exposure control is performed is limited to the focus detection pixels in the selected focus detection area. The exposure control may be performed so that the data of the focus detection pixel is at an appropriate level. For example, if exposure control is performed so that the maximum value of the focus detection pixel data in the selected focus detection area is about 80% of the maximum value of AD conversion, all the data (luminance of the focus detection pixels used for the focus detection calculation) ) Can be guaranteed to be below the saturation level.

  In the above-described embodiment, the case where the luminance in the vicinity of the selected focus detection area is higher than the average luminance of the entire screen has been described. However, even when the brightness in the vicinity of the selected focus detection area is lower than the average brightness of the entire screen, the same effect can be obtained by performing exposure control so that the exposure amount is appropriate in the vicinity of the selected focus detection area. Is obtained.

  If the vicinity of the focus detection area selected when performing exposure control on the entire focus detection screen is low brightness, the focus detection pixel becomes insufficient and the focus detection becomes impossible or a large focus detection error occurs. Will occur. However, accurate focus detection can be performed reliably by performing exposure control (exposure amount increase) so that the exposure amount is appropriate in the vicinity of the selected focus detection area.

  However, when exposure control is performed to increase the brightness level (elongate the charge accumulation time) in this way, the middle to high brightness portions in the image may exceed the brightness dynamic range. Even if the brightness correction is performed when displaying the image, there is a possibility that a white portion will occur. Therefore, the body drive control device 214 prohibits exposure control that increases the brightness level (increases the exposure amount = lengthens the charge accumulation time) or changes the brightness level by the exposure control. You may make it restrict | limit.

  FIG. 12 is a diagram showing a processing flow for restricting proper exposure control for the vicinity of the selected focus detection area. It is executed by the body drive control device 214. If the determination process shown in step S1010 of FIG. 12 is positive, the process shown in step S1020 of FIG. 12 is performed instead of the process shown in step S115 of FIG. That is, in step S1010, it is determined whether or not the vicinity of the selected focus detection area has low luminance with respect to the entire screen. If the determination is affirmative, in step S1020, exposure control is performed so as to limit the degree of change in the luminance level according to the exposure control, and the process proceeds to step S120 in FIG. In the case of negative determination, as described above, in step S115, exposure control of the image sensor is performed so that the exposure amount in the vicinity of the selected focus detection area is appropriate, and the process proceeds to step S120.

  In the embodiment described above, the focus detection area is manually selected by the user. However, the present invention is not limited to this. For example, a specific image pattern (for example, a human face image) may be detected from the entire image by image processing, and the focus detection area may be automatically selected according to the position of the specific image pattern.

  FIG. 13 is a diagram showing a focus detection area selection processing flow based on specific image pattern detection. It is executed by the body drive control device 214. Instead of the process shown in step S105 in FIG. 9, the processes shown in steps S1110 and S1120 in FIG. 13 are performed. That is, in step S1110, a specific image pattern is detected from the entire image by image processing. In step S1120, a focus detection area is selected according to the position of the specific image pattern. For example, the focus detection area at the position closest to the position of the specific image pattern is selected.

  Alternatively, focus detection may be performed simultaneously in a plurality of focus detection areas in the first step when the power is turned on, and one focus detection area may be automatically selected according to the obtained plurality of focus detection results. For example, it is possible to select a focus detection area that gives the closest result among a plurality of focus detection results.

  FIG. 14 is a diagram illustrating a processing flow for selecting one focus detection area in accordance with the obtained plurality of focus detection results. It is executed by the body drive control device 214. Instead of the process shown in step S105 in FIG. 9, the processes shown in steps S1210 and S1220 in FIG. 14 are performed. That is, in step S1210, focus detection is simultaneously performed in a plurality of focus detection areas. In step S1220, one focus detection area such as the closest focus detection area is selected according to a plurality of focus detection results obtained simultaneously.

  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 embodiment described above, the exposure control is performed so that the exposure amount is appropriate in the vicinity of one selected focus detection area, but the present invention is not limited to this.

  For example, in FIG. 2, two or more focus detection areas are selected, and exposure control is performed so that the exposure amount of an area capturing the most bright image portion in the vicinity of the two or more selected focus detection areas is appropriate. May be performed. Alternatively, the focus detection area is not selected, focus detection is always performed in five focus detection areas, and the exposure amount of the area capturing the highest brightness image portion in the vicinity of all focus detection areas is appropriate. Exposure control may be performed so that

  For example, the charge accumulation time of the image sensor is set so that the maximum value of data of all focus detection pixels in five focus detection areas is within the AD conversion range. Further, in the focus detection area where the output level of the data of the focus detection pixel is lowered, the data of the focus detection pixel in the latest past plural frames is stored. Then, focus detection may be performed after increasing the output level of the focus detection pixel data by adding the focus detection pixel data in the past frame and the focus detection pixel data in the current frame.

  Note that when focus detection results are obtained in a plurality of focus detection areas, the body drive control device 214 outputs a final focus detection result based on a predetermined determination criterion (for example, closest distance).

  In the embodiment described above, the exposure control is performed so that the exposure amount is appropriate in the vicinity of the focus detection area selected from the plurality of focus detection areas, but the present invention is not limited to this. Absent. Even when only one focus detection area is provided (for example, only the central focus detection area 101 in FIG. 2 is provided), when performing focus detection, the exposure amount is appropriate in the vicinity of one focus detection area. The effects of the present invention can be obtained by performing exposure control.

  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. FIGS. 15 and 16 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. 16 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. 15 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. 15 and 16, 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 exhibits 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. 15 may be two-dimensionally arranged to form an imaging device, and color filters arranged in a Bayer arrangement may be provided for the two-dimensionally arranged focus detection pixels. 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 operation member, 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 (13)

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;
A focus detection area provided on a part of the imaging device for detecting a focus adjustment state of the photographing optical system with respect to the optical image;
Exposure control means for performing first exposure control of the image sensor so that a region near the focus detection area is exposed with a first exposure amount;
An imaging apparatus comprising: focus detection means for performing the first exposure control and detecting the focus adjustment state based on pixel data of the focus detection area. The imaging device according to claim 1,
Further comprising photometric means for measuring the brightness of the optical image in the vicinity region and outputting a photometric output;
The imaging apparatus according to claim 1, wherein the first exposure amount is determined based on the photometric output of the photometric means. The imaging device according to claim 2,
The imaging apparatus according to claim 1, wherein the first exposure amount is determined so that a maximum pixel value included in pixel data within the predetermined range is equal to or less than a predetermined value based on the photometric output. The imaging device according to any one of claims 1 to 3,
Display means for displaying an image for recording preparation of the optical image based on pixel data of the plurality of pixels;
A correction unit that corrects a luminance level of the recording preparation image of the optical image formed on the imaging element on which the first exposure control is performed by the exposure control unit;
The image pickup apparatus, wherein the display unit displays the recording preparation image whose luminance level is corrected by the correction unit. The imaging apparatus according to claim 4,
The image pickup apparatus according to claim 1, wherein the correction unit performs correction having knee characteristics for high luminance data included in the image data of the recording preparation image when the luminance level is corrected. In the imaging device according to any one of claims 1 to 5,
A selection means for selecting a specific focus detection area from a plurality of focus detection areas including the focus detection area;
The exposure control unit performs the first exposure control of the imaging element so that a region near the specific focus detection area selected by the selection unit is exposed with the first exposure amount, and
The imaging apparatus, wherein the focus detection unit detects the focus adjustment state based on pixel data of the specific focus detection area. The imaging device according to claim 6,
An imaging apparatus, further comprising: a designation unit for a user to designate the specific focus detection area selected by the selection unit through a manual operation. The imaging device according to claim 6,
The image pickup apparatus, wherein the selection unit selects the specific focus detection area based on a focus detection result in the plurality of focus detection areas. The imaging device according to claim 6,
A specific image detecting means for detecting a specific image having a specific characteristic included in the recording preparation image;
The imaging device according to claim 1, wherein the selection unit selects the specific focus detection area based on the specific image detected by the specific image detection unit. The imaging device according to any one of claims 1 to 9,
Each of the plurality of pixels includes a charge storage photoelectric conversion element, and the exposure control unit controls a charge storage time of the charge storage photoelectric conversion element. In the imaging device according to any one of claims 1 to 10,
When the first exposure amount is larger than a second exposure amount applied to display the recording preparation image by the display unit, the exposure control unit uses an exposure amount different from the first exposure amount to capture the image sensor. An imaging apparatus, further comprising a changing unit that changes the first exposure control so as to perform the exposure control. In the imaging device according to any one of claims 1 to 11,
Focus adjusting means for performing focus adjustment of the photographing optical system so that the photographing optical system is in focus with respect to the optical image in accordance with the focus adjusting state detected by the focus detecting means;
Recording means for recording the output of the image sensor on a recording medium in response to a photographing instruction;
The exposure control means performs second exposure control of the image sensor with a third exposure amount after the focus adjustment by the focus adjustment means is completed,
The image pickup apparatus, wherein the recording unit records an output of the image pickup element exposed with the third exposure amount. In the imaging device according to any one of claims 1 to 12,
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