JP5784395B2 - Imaging device - Google Patents

Description

  The present invention relates to an imaging apparatus having an autofocus function.

  In recent years, many portable devices (imaging devices) with a photographing function such as a digital camera have an autofocus function. This type of imaging apparatus employs an imaging element that incorporates a focus detection pixel (hereinafter referred to as an AF pixel) in addition to an imaging pixel (normal pixel) for image configuration, and uses a pupil division phase difference method. There are some that perform autofocus. In this method, it is necessary to divide the pupil in the left-right direction, and to configure an AF pixel having an imaging unit that separately receives light beams transmitted through the left and right pupils as an imaging element. A high-speed autofocus is possible by generating an AF signal for focusing and performing focusing on an image signal by these various AF pixels (hereinafter referred to as AF calculation and correlation calculation).

  However, in order to improve the autofocus performance, it is necessary to arrange a relatively large number of AF pixels in the image sensor, and there is a drawback that the image quality of the captured image is deteriorated due to the lack of the image signal of the AF pixel portion. .

  Therefore, Patent Document 1 proposes a technique for reducing the number of AF pixels by adopting a method of estimating the pixel value of an AF pixel using a normal pixel.

    JP 2007-155929 A

However, the method of estimating the pixel value of the AF pixel proposed in Patent Document 1 is based on the photoelectric conversion of light from the same subject region, (pixel value of normal pixel) :( pixel value of AF pixel) = 2: This is a method that holds only when 1.
When the above relational expression is not satisfied, the focus accuracy based on the correlation calculation is lowered.

  Further, an on-chip lens for efficiently guiding light from the subject to the light receiving unit is employed on each pixel of the image sensor. In this on-chip lens, the top of the surface is decentered according to the position of the image sensor in order to suppress a decrease in the amount of light around the image sensor. Due to this eccentricity, even with the same type of AF pixel, the light receiving area changes according to the pixel position, and the focus accuracy based on the AF calculation using each AF pixel is lowered.

  Further, in the image sensor, vignetting may occur in the pupil of the photographing lens in the periphery of the light receiving unit. Since this vignetting changes according to the pixel position, the focus accuracy based on the AF calculation using each AF pixel is further lowered.

  In the proposal of Patent Document 1, normal pixels are used for generating an AF signal. However, since the amount of light received by the vignetting of the pupil of the photographic lens varies greatly depending on the pixel position, the proposal of Patent Document 1 has a drawback that the focus accuracy is significantly lowered due to the influence of the vignetting.

  In view of the above problems, the present invention provides an imaging apparatus capable of improving focus accuracy by correcting a signal used for correlation calculation in accordance with a ratio of pixel values of normal pixels and AF pixels. With the goal.

An image pickup apparatus according to an aspect of the present invention is an image pickup device that photoelectrically converts a subject image formed by a lens, and receives AF light that passes through a partial region obtained by dividing the exit pupil of the lens. Each of the correction information for correcting the difference in the amount of received light according to the pixel position between the AF pixel and the imaging pixel, and the imaging element including the imaging pixels for photographing and the pixels arranged in a matrix A correction memory that stores the correction information, a correction unit that reads the correction information and corrects the pixel value of the AF pixel and the pixel value of the imaging pixel, and focus detection using the pixel value corrected by the correction unit. And the correction information includes a ratio of the received light amount of the AF pixel according to the pixel position with respect to the AF pixel and a received light amount of the image pickup pixel according to the pixel position with respect to the imaging pixel. Based on ratio The correction unit corrects the pixel value of the AF pixel and the pixel value of the imaging pixel adjacent to the AF pixel by the correction information, and the focus detection unit corrects the pixel value of the imaging pixel. And the pixel value of the AF pixel corresponding to the pixel value of the virtual AF pixel that receives the light beam that passes through the region that forms a pair with the divided exit pupil region through which the light beam received by the AF pixel passes. When the focus detection is performed based on the pixel value of the AF pixel and the signal corresponding to the pixel value of the virtual AF pixel, the pixel value of the AF pixel after correction and the pixel value after correction are calculated. A signal corresponding to the pixel value of the virtual AF pixel is calculated based on the pixel value of the imaging pixel.

  According to the present invention, there is an effect that the focus accuracy can be improved by correcting the signal used for the correlation calculation according to the ratio of the pixel value of the normal pixel and the AF pixel.

1 is a block diagram showing a camera including an imaging device according to a first embodiment of the present invention. Explanatory drawing for demonstrating a pupil division | segmentation phase difference method. Sectional drawing which shows the structure of AF pixel. FIG. 4 is an explanatory diagram illustrating an example of a pixel array in the imaging unit. Explanatory drawing for demonstrating the relationship between the pixel position of AF pixel, and the light reception area | region in the position. Explanatory drawing for demonstrating the relationship between the pixel position of AF pixel, and the light reception area | region in the position. Explanatory drawing for demonstrating the relationship between the pixel position of AF pixel, and the light reception area | region in the position. Explanatory drawing for demonstrating the relationship between the pixel position of AF pixel, and the light reception area | region in the position. Explanatory drawing for demonstrating the table memorize | stored in the memory 27 for light reception amount correction | amendment. The block diagram which shows the specific structure of the body control part 24 in FIG. The flowchart for demonstrating the operation | movement of a 1st form. The block diagram which shows an example of the specific structure of the body control part employ | adopted in 2nd Embodiment. Explanatory drawing for demonstrating the information stored in the memory 17 for light reception amount correction | amendment. Explanatory drawing for demonstrating the information stored in the memory 27 for light reception amount correction | amendment. The flowchart for demonstrating operation | movement of 2nd Embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(First embodiment)
FIG. 1 is a block diagram showing a camera including an imaging apparatus according to the first embodiment of the present invention.

  In FIG. 1, the digital camera 11 includes an interchangeable lens 12 and a camera body 13, and the interchangeable lens 12 is attached to the camera body 13 by a mount portion 14.

  The interchangeable lens 12 includes a lens control unit 30, a lens driving unit 16, a diaphragm driving unit 15, a zooming lens 18, a fixed lens 19, a focusing lens 20, and a diaphragm 21. The lens control unit 30 includes peripheral components such as a microcomputer and a memory. The lens control unit 30 controls driving of the focusing lens 20 and the aperture 21, detects the state of the aperture 21, the zooming lens 18 and the focusing lens 20, and the body control unit 24. Lens information and camera information are received.

  The aperture driving unit 15 controls the aperture diameter of the aperture 21 via the lens control unit 30 based on the signal from the body control unit 24. Further, the lens driving unit 16 drives the zooming lens 18 and the focusing lens 20 via the lens control unit 30 based on the signal from the body control unit 24.

  In the present embodiment, the interchangeable lens 12 is provided with a received light amount correction memory 17. The received light amount correction memory 17 stores lens side information for correcting the received light amount of an AF pixel or the like according to the pixel position, for example, lens side correction information such as an F number, a zoom state, and a focus lens position. To do. The lens control unit 30 can read lens-side correction information stored in the received light amount correction memory 17 and transmit it to the body control unit 24.

  The camera body 13 includes an imaging unit 22, a body control unit 24, a liquid crystal display unit driving circuit 25, a liquid crystal display unit 26, a memory card 29, and the like. The imaging unit 22 includes a light receiving unit having a pixel array shown in FIG. That is, in the light receiving unit, pixels are two-dimensionally arranged, and an object image formed by the interchangeable lens 12 is imaged by being arranged on the planned image formation surface of the interchangeable lens 12. AF pixels are arranged at predetermined focus detection positions of the light receiving unit of the imaging unit 22.

  The body control unit 24 includes peripheral parts such as a microcomputer and a memory, and reads out an image signal from the imaging unit 22, corrects the image signal, and detects the focus adjustment state of the interchangeable lens 12 via the imaging unit drive circuit 28. In addition, it receives lens information from the lens control unit 30, transmits camera information (defocus amount), and controls the operation of the entire digital camera. The body control unit 24 and the lens control unit 30 communicate via the electrical contact unit 23 of the mount unit 14 to exchange various information.

  The liquid crystal display unit driving circuit 25 drives the liquid crystal display unit 26. The photographer can observe an image photographed by the liquid crystal display unit 26. The memory card 29 is removable from the camera body 13 and is a portable storage medium that stores and stores image signals.

  The subject image formed on the imaging unit 22 after passing through the interchangeable lens 12 is photoelectrically converted by the imaging unit 22, and its output is sent to the body control unit 24. The body control unit 24 stores the image data generated based on the output of the imaging unit 22 in the memory card 29 and sends an image signal to the liquid crystal display unit drive circuit 25 to cause the liquid crystal display unit 26 to display an image.

  The camera body 13 is provided with operation members (not shown) (shutter buttons, focus detection position setting members, etc.), and the body control unit 24 detects operation state signals from these operation members, and according to the detection results. The following operations (imaging operation, focus detection position setting operation, image processing operation) are controlled.

  The lens control unit 30 changes the lens information according to the focusing state, zooming state, aperture setting state, aperture opening F value, and the like. Specifically, the lens control unit 30 monitors the positions of the lens 18 and the focusing lens 20 and the aperture position of the aperture 21 and calculates lens information according to the monitor information, or a lookup table prepared in advance. Select the lens information according to the monitor information. The lens control unit 30 drives the focusing lens 20 to a focal point by a driving source such as a motor of the lens driving unit 16 based on the received lens driving amount.

  In the present embodiment, the camera body 13 is provided with a received light amount correction memory 27. The received light amount correction memory 27 stores main body side correction information for correcting the received light amount of the AF pixel or the like according to the pixel position. For example, the received light amount correction memory 27 stores a table of received light amount correction coefficients α corresponding to pixel positions as main body side correction information for each F number. The body control unit 24 corrects the pixel value of the pixel used for focus control based on the lens side correction information read from the memory 17 of the interchangeable lens 12 and the main body side correction information read from the received light amount correction memory 27. The received light amount correction coefficient α is acquired according to the pixel position. The body control unit 24 reads out pixel values such as AF pixels from the imaging unit 22, corrects the read pixel values according to the pixel position using the received light amount correction coefficient α, and then uses the corrected pixel values. Based on the pupil division phase difference method, a defocus amount in a predetermined focus detection area is calculated and output as an AF signal. The AF signal is supplied to the lens control unit 30, and the lens control unit 30 calculates a lens driving amount based on the AF signal, and controls the lens driving unit 16 based on the lens driving amount to perform focusing. ing.

  Next, information stored in the memories 17 and 27 for correcting the AF pixel value will be described with reference to FIGS. FIG. 2 is an explanatory diagram for explaining the pupil division phase difference method.

  An optical image incident on the imaging device from each point 31 of the subject via each optical path is formed on the incident surface of the imaging element 33 by the photographing lens 32. 2 is the horizontal direction, the z direction is the optical axis direction of the photographic lens 32, and the y direction (the vertical direction on the paper surface) is the vertical direction. In FIG. 2, pixels are indicated by the frames of the image sensor 33. Two image pickup units (for example, an R image pickup unit and an L image pickup unit) are configured as AF detection pixels (AF pixels), and each optical path is divided into, for example, a right direction and a left direction. The light beam (right light) transmitted through the right pupil and the light beam (left light) transmitted through the left pupil are incident on the R imaging unit and the L imaging unit, respectively. For example, by decentering the R and L imaging units with respect to the optical axis of the photographing lens 32, the right light and the left light can be incident on the R and L imaging units, respectively.

  When the subject is in focus, light from the same point of the subject enters the R and L imaging units of the same pixel. Accordingly, the image signal obtained by the plurality of R imaging units for AF detection arranged in the horizontal direction is the same as the image signal obtained by the plurality of L imaging units. When the focus is shifted, as shown in FIG. 2A, light from the same point of the subject enters the R imaging unit and the L imaging unit at positions shifted according to the focus shift amount. Accordingly, the phase of the image signal obtained by the plurality of R imaging units for AF detection arranged in the horizontal direction is different from that of the image signal obtained by the plurality of L imaging units, and the phase deviation amount corresponds to the focus deviation amount. . Autofocus can be realized by driving a lens for focus adjustment based on the phase difference between the image signals obtained by the R and L imaging units.

  In FIG. 2A, since the readout circuit is shared between the AF pixel and the normal pixel, the pixel having only the R imaging unit (hereinafter referred to as R) without forming both the R and L imaging units in the pixel. An example in which an AF pixel is configured by a pixel having only an L imaging unit (hereinafter referred to as an L pixel) is shown.

  Further, in FIG. 2B, the R pixel is omitted, only the L pixel is used as the AF pixel, and the difference between the pixel value of a plurality of normal pixels (hereinafter also referred to as N pixels) and the pixel value of the L pixel is used. An R pixel (hereinafter referred to as a virtual R pixel) is estimated, and a phase shift amount is obtained by comparing the phase of an image signal obtained by a plurality of virtual R pixels and the phase of an image signal obtained by an L imaging unit. An example is shown.

  Further, in FIG. 2C, the R pixel is omitted, and only the L pixel is used as the AF pixel, and the phase of the image signal obtained by the N pixel is compared with the phase of the image signal obtained by the L imaging unit. In this example, the amount of focus shift is obtained.

  As the N pixel used for focus detection, a method using at least one of the green pixels closest to the AF pixel is conceivable. Further, when outputting a captured image, an average value of pixel values of adjacent green pixels of the AF pixel may be used as the pixel value of the AF pixel position. Further, the pixel value at the AF pixel position may be calculated by pixel interpolation processing including pattern determination of surrounding pixels.

  By the way, when there are many horizontal lines in the captured image, it is conceivable that the images obtained by the L and R imaging units match even if the focus is shifted. In this case, for example, the exit pupil is divided into upper and lower parts, and a U imaging unit and a D imaging unit are configured to receive the light beam transmitted through the upper pupil and the light beam transmitted through the lower pupil, respectively. Good. Then, by comparing the phase of the image signal obtained by the plurality of U imaging units and the phase of the image signal obtained by the plurality of D imaging units, it is possible to detect the amount of focus shift and to focus. .

  FIG. 3 is a cross-sectional view showing the structure of such an AF pixel. FIG. 3 shows an example in which the exit pupil is divided by decentering the aperture of the pixel of the image sensor with respect to the center of the photoelectric conversion region. FIG. 3 shows the structure of one pixel of the image sensor.

  The pixel 41 has a microlens 42, a smooth layer 43 for forming a plane for forming the microlens 42, a light shielding film 44 for preventing color mixture of color pixels, and a color filter layer in order from the top. A smoothing layer 45 for flattening the surface and a photoelectric conversion region 49 are arranged. Further, in the pixel 41, the light shielding film 44 includes an opening 48 and a color filter 50 that are eccentric to the outside from the center 47 of the photoelectric conversion region 49.

  As described above, in the example illustrated in FIG. 3, the opening 48 of the pixel 41 is eccentric with respect to the center of the photoelectric conversion region 49. Since the light ray L41 is incident only on, for example, the L imaging unit in the photoelectric conversion region 49, the exit pupil is divided.

  Although FIG. 3 shows an example in which the exit pupil is divided by decentering the opening of the pixel, various methods can be adopted as a method for dividing the exit pupil. For example, the exit pupil may be divided by decentering the on-chip lens, or a method of dividing the exit pupil using a DML (digital microlens) may be employed.

  FIG. 4 is an explanatory diagram illustrating an example of a pixel array in the imaging unit 22.

  In the present embodiment, an example in which a Bayer array is adopted as the pixel array will be described. In FIG. 4, B indicates a blue pixel in which a blue filter is disposed, R indicates a red pixel in which a red filter is disposed, G indicates a green pixel in which a green filter is disposed, and a hatched portion Indicates an AF pixel. FIG. 4 shows only a partial region of the light receiving unit.

  As shown in FIG. 4, in the Bayer array, the same array is repeated in units of horizontal and vertical 2 × 2 pixels. That is, of the 2 × 2 pixels, blue and red pixels are diagonally arranged, and green pixels are arranged in the remaining two diagonal pixels. Pixels L1 to L8 indicated by hatched portions are L pixels. As described above, the AF pixels are arranged at appropriate positions in the light receiving unit.

  5 to 8 are explanatory diagrams for explaining the relationship between the pixel position of the AF pixel and the light receiving region at the position.

  5 to 8 show the position (address) of the target pixel on the light receiving unit by (x, y), and the address of the pixel passing through the optical axis of the photographing lens (hereinafter referred to as the pixel on the axis) is (0, 0). 5 to 8, an elliptical area indicates a receivable area on the pupil plane of the AF pixel (L pixel), and a broken-line circle indicates the pupil of the photographing lens when the target pixel is an on-axis pixel, that is, on the axis. A light-receivable area 51 on the pupil plane of N pixels is shown. Further, the x mark indicates the position 54 of the optical axis of the photographing lens.

  5 to 8, the pattern in the elliptical area indicating the light receiving area of the AF pixel schematically shows the intensity distribution of the incident light on the light receiving surface, and the incident intensity increases toward the center of the elliptical area. The incident intensity is lower toward the periphery of the ellipse in the minor axis direction, indicating that the incident intensity is equal on the same line. Such an intensity distribution of incident light is generated by light diffraction or the like, and is a distribution determined by an optical structure such as a stop, a focal length, and a pixel structure.

  FIG. 5 shows an example where the target pixel is an on-axis pixel. In this case, the light receivable region 51 (pupil of the photographing lens) has a circular shape centered on the optical axis position 54 of the photographing lens indicated by a cross, whereas the light receivable region 53 of the AF pixel is It is oval.

  As described above, the incident intensity of the AF pixel partially decreases, but the incident intensity of the N pixel does not change, and all light beams passing through the pupil of the photographing lens can be received. In the AF pixel on the axis, the position 54 of the optical axis of the photographing lens and the position where the on-chip lens surface apex of the AF pixel is projected onto the pupil coincide with each other.

  6 to 8 show examples of pixels in which the target pixel is shifted from a position passing through the optical axis of the photographing lens (hereinafter referred to as off-axis pixel). FIG. 6 shows an example of an off-axis pixel whose address (0, l) is shifted in the y direction. In this case, due to the effect of vignetting, the exit pupil corresponding to the position on the light receiving unit, that is, the light receivable region 52y on the off-axis N pixel pupil plane is the N-pixel pupil plane on the axis. Compared with the light receiving area 51 in FIG. 5, vignetting occurs in the y direction.

  Further, as described above, the top surface of the on-chip lens of the pixel at a position other than the position 54 of the optical axis is decentered from the central axis of the pixel for shading countermeasures. As a result, the position 54 on the optical axis of the photographing lens and the position 54y where the on-chip lens surface top of the AF pixel is projected onto the pupil do not coincide with each other, and a deviation occurs in the y direction. As a result, the light receivable area 53y of the AF pixel at the address (0, l) is shifted in the y direction from the light receivable area 53 when the AF pixel exists at the position 54 on the optical axis.

  FIG. 7 shows an example in which the target pixel is an address (k, 0) shifted in the x direction from a position passing through the optical axis of the photographing lens. In this case, vignetting occurs in the x direction in the light-receiving area 52x on the pupil plane when the target pixel is N pixels, compared to the light-receiving area 51 on the pupil plane of N pixels on the axis. Yes.

  Further, the position 54 of the optical axis of the photographing lens and the position 54x where the on-chip lens surface top of the AF pixel is projected onto the pupil do not coincide with each other, and a deviation occurs in the x direction. As a result, the light receiving area 53x of the AF pixel at the address (k, 0) is shifted in the x direction from the light receiving area 53 when the AF pixel is located at the position 54 on the optical axis.

  FIG. 8 shows an example in which the target pixel is an address (k, l) deviated in the x and y directions from the position passing through the optical axis of the photographing lens. In this case, when the target pixel is an N pixel, the light receiving area 52xy on the pupil plane is vignetted in the x and y directions compared to the light receiving area 51 on the axial N pixel pupil plane. Has occurred.

  Further, the position 54 of the optical axis of the photographing lens and the position 54xy where the on-chip lens surface top of the AF pixel is projected onto the pupil do not coincide with each other, and a deviation occurs in the x and y directions. As a result, the receivable area 53xy of the AF pixel at the address (k, l) is shifted in the x and y directions from the receivable area 53 when the AF pixel exists at the position 54 on the optical axis.

  The ellipses in FIGS. 5 to 8 show an example in which the AF pixel is an L pixel. Even if the AF pixel is not the L pixel, but the right pupil detection pixel (R pixel), the upper pupil detection pixel (U pixel), and the lower pupil detection pixel (D pixel), light can be received according to the pixel position. It is clear that the region shifts.

  For the N pixel, a light beam that has passed through the light receiving areas 51, 52y, 52x, and 52xy on the pupil plane of the N pixel is incident at a predetermined incident intensity. Therefore, for N pixels, the amount of received light corresponding to the area of the light receiving area can be obtained at each pixel position.

  On the other hand, with respect to the AF pixel, the light flux that has passed through the light-receiving area on the pupil plane of the N pixel and the light-receiving area on the pupil plane of the AF pixel is received. As described above, the incident intensity of this light beam varies depending on the position within the light receiving area. Therefore, for the AF pixel, the amount of light corresponding to the intensity distribution of the incident light is integrated in the region where the light-receiving area on the pupil plane of the N pixel and the light-receiving area on the pupil plane of the AF pixel overlap. The amount of light received can be obtained with.

  In the present embodiment, the pixel values of various pixels are corrected using the correction coefficient for each pixel position based on the change in the amount of received light according to the pixel positions of the AF pixel and the N pixel described with reference to FIGS. .

  That is, in the present embodiment, the received light amount of the L pixel and the received light amount of the N pixel at the pixel position (x, y) are IL (x, y) and IN (x, y), respectively, and the ratio of each received light amount. The received light amount correction coefficient α is determined based on the above, and the pixel value used in the pupil division phase difference method is corrected by multiplying the pixel value of the AF pixel or N pixel by the received light amount correction coefficient α.

  The exit pupil of the photographic lens also changes depending on the F number of the photographic lens. The F number also changes depending on the zoom state and the position of the focus lens. Therefore, the received light amount correction coefficient α may be changed according to the F number, the zoom state, and the position of the focus lens. The F number corresponds to the area of the exit pupil corresponding to the position on the light receiving element, and has the greatest influence on the amount of received light. Therefore, for example, the received light amount correction coefficient α may be changed for each F number.

  FIG. 9 is an explanatory diagram for explaining a table stored in the received light amount correction memory 27.

  In the present embodiment, the body control unit 24 supplies the received light amount correction coefficient α obtained by measurement to the received light amount correction memory 27 for storage. That is, a standard subject is imaged, and the amount of received light at each pixel position of the AF pixel and N pixel is obtained. According to this measurement result, the body control unit 24 obtains the received light amount correction coefficient α for each pixel position and creates a table.

  In the received light amount correction memory 27, a table of received light amount correction coefficients α corresponding to pixel positions (xy coordinates) is stored for each F number. Each table stores each received light amount correction coefficient α (x, y) corresponding to the pixel position address (x, y) of the pixel to be corrected. In the example of FIG. 9, it is shown that the received light amount correction coefficient α corresponding to the AF pixel at the n pixel positions in the x direction and the m pixel positions in the y direction is stored.

  The table value of the received light amount correction coefficient α is different for each F number. FIG. 9 shows only the received light amount correction coefficient α for one F number. Further, the received light amount correction coefficient α may be set corresponding to substantially equal pixel positions over the entire pixel area of the light receiving unit, and for each AF area set in the entire pixel area of the light receiving unit. In addition, they may be provided corresponding to pixel positions at appropriate intervals. Further, it may be set corresponding to pixel positions having different pixel intervals between the center and the periphery on the light receiving unit.

  That is, the received light amount correction coefficient α may be set corresponding to all pixel positions necessary for focus detection, or one received light amount correction coefficient α may be set for each AF area. Alternatively, the received light amount correction coefficient α may be set for each pixel necessary for focus detection in the peripheral area, and only one received light amount correction coefficient α may be set for the area in the center area.

  As the received light amount correction coefficient α, the ratio of the received light amount between the AF pixel and the N pixel can be used. For example, when an L pixel is used as the AF pixel, the pixel value of the L pixel at the address (x, y) is L (x, y), and the pixel value of the N pixel at the address (x + 1, y + 1) is N ( x + 1, y + 1), and the pixel value of the virtual R pixel at the address (x, y) is R (x, y), α (x, y) = IL (x, y) / IN (x, y). Furthermore, it is good also as R (x, y) R (x, y) = (alpha) (x, y) * N (x + 1, y + 1).

  FIG. 10 is a block diagram showing a specific configuration of the body control unit 24 in FIG.

  The imaging signal from the imaging unit drive circuit 28 is input to the imaging signal acquisition unit 62 via the signal processing unit 61. The image signal acquisition unit 62 outputs a signal based on the normal pixel among the imaging signals to the display image configuration unit 63. The display image configuration unit 63 generates a display image based on the input signal and outputs the generated image to the liquid crystal display unit drive circuit 25. The captured image is displayed on the display screen of the liquid crystal display unit 26 by the liquid crystal display unit driving circuit 25. Further, the recording image construction unit 64 is given a signal based on the normal pixel from the image signal acquisition unit 62, and interpolates the AF pixel to generate a recording image. This recorded image is supplied to and stored in the memory card 29.

  On the other hand, the image signal acquisition unit 62 outputs AF pixel and N pixel signals used for focus detection to the α calculation unit 65. When the imaging unit 22 captures a predetermined standard subject, the α calculation unit 65 determines each pixel based on the information of the received light amount and each pixel position of each AF pixel and N pixel signal used for focus detection. The received light amount correction coefficient α is calculated for each position and output to the table generating unit 66. F-number information is also input to the table generation unit 66 via a control unit 68 described later, and the table generation unit 66 generates a table of received light amount correction coefficient α shown in FIG. This table is supplied to and stored in the received light amount correction memory 27.

  At the time of actual use, the control unit 68 reads the information of the F number from the lens control unit 30 of the interchangeable lens 12 and gives it to the calculation unit / correlation calculation unit 67. The calculation unit / correlation calculation unit 67 is supplied with signals of AF pixels and N pixels used for focus detection from the image signal acquisition unit 62. The calculation unit / correlation calculation unit 67 selects a table stored in the received light amount correction memory 27 based on the F number information and corrects the received light amount according to the pixel positions of the AF pixel and the N pixel from the selected table. The coefficient α is read and the pixel value of the AF pixel or N pixel is corrected.

  The calculation unit / correlation calculation unit 67 calculates the defocus amount by performing the pupil division phase difference calculation using the corrected AF pixel value and N pixel value. The computing unit / correlation computing unit 67 outputs an AF signal based on the obtained defocus amount to the control unit 68. The controller 68 gives the AF signal to the lens controller 30.

  Next, the operation of the embodiment configured as described above will be described with reference to the flowchart of FIG. FIG. 11 shows autofocus control.

  When the image pickup apparatus 11 is turned on or the interchangeable lens is replaced, the body control unit 24 stores the received light amount correction memory 17 from the lens control unit 30 of the interchangeable lens 12 in step S11. Lens correction information is read.

  Next, the body control unit 24 determines whether or not the shooting mode is instructed. If the shooting mode is not instructed, the body control unit 24 determines whether a zoom operation has been performed (step S13). When the zoom operation is performed, the lens control unit 30 performs zoom control on the lens driving unit 16. In addition, the lens control unit 30 transmits information regarding zoom, information regarding F-number, and the like as lens-side correction information to the body control unit 24 (step S15). Thus, the body control unit 24 acquires the updated lens side correction information (Step S11).

  When the shooting mode is instructed, the body control unit 24 causes the liquid crystal display unit 26 to display a captured image (through image) in live view based on the image signal from the imaging unit 22 in step S21.

  In the next step S <b> 22, the body control unit 24 reads out the pixel values of AF pixels and N pixels used for focus detection from the imaging unit 22. The body control unit 24 reads the received light amount correction coefficient α corresponding to the pixel position of each pixel from the received light amount correction memory 27 (step S23), and sets the pixel values of the AF pixel and N pixel as the received light amount correction coefficient α. It corrects using (step S24).

  The body control unit 24 calculates the defocus amount using the corrected AF pixel and N pixel, and generates an AF signal for performing focusing (step S25). The AF signal is supplied to the lens control unit 30, and focusing is performed.

  As described above, in this embodiment, at least one of the pixel value of the N pixel and the pixel value of the AF pixel used for focus detection is corrected using the received light amount correction coefficient α corresponding to the pixel position. . Depending on the position on the light receiving unit, there is a difference in the vignetting of the exit pupil, the eccentricity of the on-chip lens, the intensity intensity distribution of the incident light of the AF pixel on the pupil plane, etc. It changes according to the position. The received light amount correction coefficient α corrects this change. By using a table that stores the received light amount correction coefficient α, the pixel values of the AF pixel and the N pixel are corrected, and high-precision focus control is performed. Can do.

  In the above embodiment, an example in which the F number and the like are variable has been described. However, when a fixed lens having a fixed F number or the like is employed, the received light amount correction memory 17 may be omitted.

  In the above-described embodiment, the example in which the received light amount correction coefficient is calculated based on the received light amount measured by imaging the standard subject and is stored in the received light amount correction memory has been described. When the amount correction coefficient α has already been obtained, the light reception amount correction coefficient α calculation unit is not necessary, and it is sufficient to provide only the light reception amount correction memory for storing the known light reception amount correction coefficient α.

(Second Embodiment)
FIG. 12 is a block diagram showing an example of a specific configuration of the body control unit employed in the second embodiment. In FIG. 12, the same components as those of FIG. 13 and 14 are explanatory diagrams for explaining information stored in the received light amount correction memories 17 and 27, respectively.

  In the first embodiment, an example has been described in which the body control unit 24 obtains the received light amount correction coefficient α using the measurement value, thereby creating a table and storing it in the received light amount correction memory 27. On the other hand, the present embodiment is different from the first embodiment in that a body control unit 71 that obtains a received light amount correction coefficient α by calculation processing is employed.

  In the present embodiment, the received light amount correction memory 17 of the interchangeable lens 12 emits the lens side correction information β (x, y) corresponding to the reference numerals 51, 52y, 52x, and 52xy in FIGS. Stores pupil information, that is, vignetting information. As shown in FIG. 13, the lens side correction information β (x, y) is provided corresponding to the pixel position for each F number. Although the example in which the lens side correction information β is provided for each F number has been described, the lens side correction information β may be provided according to the zoom state or the focus state.

  On the other hand, the received light amount correction memory 27 of the camera body 13 includes main body side correction information generated based on information on the intensity distribution of incident light of the AF pixel and information on the light receiving area of the AF pixel due to on-chip eccentricity. Stored. As shown in FIG. 14, the main body side correction information γ (x, y) is provided corresponding to the pixel position for each F number. The main body side correction information γ may also be set for each zoom state or focus state in accordance with the lens side correction information β.

  For example, the body control unit 71 selects a table of the received light amount correction memory 17 based on the F number, and reads the lens side correction information β of the selected table via the lens control unit 30. Further, the body control unit 71 selects a table of the received light amount correction memory 27 based on the F number, and reads the main body side correction information γ of the selected table.

  The body control unit 71 has an α calculation unit 72a. The α calculating unit 72a obtains the received light amount correction coefficient α by calculating the lens side correction information β and the main body side correction information γ. For example, when a correction coefficient based on asymmetry is set as the main body side correction information γ, the α calculation unit 72a multiplies the lens side correction information β corresponding to the pixel position by the correction coefficient based on the asymmetry. Thus, the received light amount correction coefficient α can be obtained.

  Note that the α calculation unit 72a, when main body side correction information γ, stores information on the intensity distribution of incident light of the AF pixel and information on the receivable area of the AF pixel due to on-chip eccentricity, these items are stored. The received light amount correction coefficient α may be obtained by integration processing using information and information related to the shape of the exit pupil.

  The body control unit 71 corrects the pixel values of the AF pixel and the N pixel at each pixel position using the received light amount correction coefficient α calculated by the α calculation unit 72a, and performs focus detection using the corrected pixel value.

  Next, the operation of the embodiment configured as described above will be described with reference to the flowchart of FIG. In FIG. 15, the same steps as those in FIG.

  The flow in FIG. 15 differs from the flow in FIG. 11 in that a main body side correction information read process in step S31 and an α calculation process in step S32 are provided instead of the α read process in step S23 in FIG.

  The body control unit 71 reads lens-side correction information in the lens information acquisition process in step S11. Further, the body control unit 71 reads the main body side correction information in step S31. In step S32, the α calculation unit 71a of the body control unit 71 calculates the received light amount correction coefficient α using the lens side correction information and the main body side correction information.

  Other operations are the same as those in the first embodiment.

  As described above, also in this embodiment, the same effect as that of the first embodiment can be obtained. In the present embodiment, the lens side correction information and the main body side correction information are stored in the received light amount correction memory provided on the lens side and the received light amount correction memory provided on the main body side, respectively. The light reception amount correction coefficient α is obtained, and there is an advantage that it is not necessary to obtain the light reception amount correction coefficient α beforehand.

  In the above embodiment, an example in which the received light amount correction coefficient α is obtained according to the pixel position has been described. However, even for an on-axis pixel, for example, the received light amount changes as the F number changes. The received light amount correction coefficient α may be set for each F number, and the pixel value of the pixel on the axis may be corrected using the table of the received light amount correction coefficient α.

  The table in this case is also stored in the received light amount correction memory on the main body side. Further, the value of the received light amount correction coefficient α can be calculated from the pixel value of the L pixel and the pixel value of the N pixel when a white uniform diffusion surface is photographed with each F number, for example. In this case, it is also possible to calculate the received light amount correction coefficient α from the lens data and the image sensor data. In addition to the F number, a received light amount correction coefficient α corresponding to the zoom state and the position of the focus lens may be set.

  In each of the above embodiments, the present invention can also be applied to the case where only AF pixels are used for focus detection. The pixel values of the AF pixels are corrected by the above-described method according to the pixel position, and high-precision focus control is performed. Can be done.

    DESCRIPTION OF SYMBOLS 10 ... Main body circuit part, 11 ... Signal processing and control part, 14 ... Imaging part, 14a ... Light receiving part, 14b ... Vertical analog addition circuit, 14c ... Horizontal digital addition circuit, 14d ... AF memory, 17 ... Recording / reproducing part, 18: Display section.

Claims (6)

An imaging element that photoelectrically converts a subject image formed by a lens, including an AF pixel that receives a light beam that passes through a partial area obtained by dividing the exit pupil of the lens, and an imaging pixel for photographing An image sensor in which pixels are arranged in a matrix;
A correction memory for storing respective correction information for correcting a difference in received light amount according to the pixel position of the AF pixel and the imaging pixel ;
A correction unit that reads out the correction information and corrects the pixel value of the AF pixel and the pixel value of the imaging pixel ;
A focus detection unit that performs focus detection using the pixel values corrected by the correction unit;
Equipped with,
The correction information is information based on the ratio of the received light amount of the AF pixel according to the pixel position regarding the AF pixel and the ratio of the received light amount of the imaging pixel according to the pixel position regarding the imaging pixel,
The correction unit corrects the pixel value of the AF pixel and the pixel value of the imaging pixel adjacent to the AF pixel by the correction information,
The focus detection unit, based on the pixel value of the imaging pixel and the pixel value of the AF pixel, passes through a region that forms a pair with the divided exit pupil region through which the light beam received by the AF pixel passes. The signal corresponding to the pixel value of the virtual AF pixel that receives light is calculated, and the correction is performed when focus detection is performed based on the pixel value of the AF pixel and the signal corresponding to the pixel value of the virtual AF pixel. An image pickup apparatus that calculates a signal corresponding to a pixel value of the virtual AF pixel based on a pixel value of the AF pixel after correction and a pixel value of the image pickup pixel after correction . The correction information related to the AF pixel is the amount of received light generated based on the shape of the exit pupil according to the pixel position, the shape of the light receiving area of the AF pixel according to the pixel position, and the incident light intensity distribution of the light receiving area. The imaging apparatus according to claim 1, wherein the information is for correcting a difference between the two. The correction information includes a ratio of a received light amount of the AF pixel according to a pixel position relating to a plurality of AF pixels according to an F number of the lens and a ratio of a received light amount of the imaging pixel according to a pixel position related to the imaging pixel. And have information based on
The imaging apparatus according to claim 1 . When the correction unit corrects the pixel value of the imaging pixel adjacent to the AF pixel based on the correction information, the correction unit calculates an average value of the pixel values of the plurality of imaging pixels having the same color filter as the AF pixel. The imaging apparatus according to claim 1, wherein a pixel value of the imaging pixel adjacent to the AF pixel is calculated based on the AF pixel . The imaging apparatus according to the exit pupil information related to the lens to claims 1 to 4, characterized by comprising a lens unit to be sent to the correction unit. The correction memory holds correction information based on the shape of the light-receiving area of the AF pixel according to the pixel position and the incident light intensity distribution of the light-receiving area,
The correction unit corrects the pixel value of the AF pixel based on exit pupil information regarding the lens acquired from the lens unit and the correction information stored in the correction memory.
The imaging apparatus according to claim 5.

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