JP2012220790A - Imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable precise detection of a focus by appropriately correcting a crosstalk even under a photography condition in which an imaging pixel adjacent to a focus detection pixel is saturated.SOLUTION: The imaging apparatus comprises: an imager having a first pixel group that receives a luminous flux that passes through a first pupil area of an imaging optical system that forms a subject image, and a second pixel group that receives a luminous flux that passes through a second pupil area narrower than the first pupil area; a determination part that determines whether a quantity of light accumulated in the first pixel group has reached a saturated value; and a received light quantity estimating part that estimates a quantity of received light of a pixel determined by the determination part that the pixel has been saturated. Using received light sensitivity distribution in a pupil surface of the imaging optical system of the first pixel group, a received light sensitivity distribution in a pupil surface of the imaging optical system of the second pixel group, and vignette information of the imaging optical system, the received light quantity estimating part calculates a received light quantity ratio of the first pixel group to the second pixel group. The quantity of light received by the second pixel group is multiplied by the received light quantity ratio, thereby estimating the quantity of light received by the first pixel group.

Description

  The present invention relates to an imaging apparatus capable of adjusting the focus of a photographing optical system.

  As one of methods for detecting the focus state of a photographing lens, Patent Document 1 discloses an apparatus that performs focus detection by a pupil division method using a two-dimensional sensor in which a microlens is formed in each pixel of the sensor. . In the device of Patent Document 1, the photoelectric conversion unit of each pixel constituting the sensor is divided into a plurality of parts, and the divided photoelectric conversion unit is configured to receive different areas of the pupil of the photographing lens through the microlens. Has been.

  Patent Document 2 discloses a solid-state imaging device that also serves as an image sensor in which pixels in which the relative positions of a microlens and a photoelectric conversion unit are displaced are two-dimensionally arranged. In the solid-state imaging device of Patent Document 2, when detecting the focus state of the photographic lens, the focus state of the photographic lens is detected based on an image generated by a pixel array having different relative displacement directions of the microlens and the photoelectric conversion unit. is doing. On the other hand, when a normal image is captured, an image is generated by adding pixels having different relative displacement directions between the microlens and the photoelectric conversion unit.

  Further, Patent Document 3 discloses a solid-state imaging device that performs pupil-division focus detection using a CMOS image sensor (solid-state imaging device) used in a digital still camera. The solid-state imaging device of Patent Document 3 has a configuration in which some of the many pixels constituting the solid-state imaging device have a photoelectric conversion unit divided into two in order to detect the focus state of the photographic lens. . The photoelectric conversion unit is configured to receive a predetermined region of the pupil of the photographing lens via the microlens.

  FIG. 18 is an explanatory diagram of a light reception distribution of a pixel that performs focus detection located in the center of the solid-state imaging device disclosed in Patent Document 3, and illustrates a photographic lens that can be received by each of the two photoelectric conversion units. The area on the pupil is shown. In the figure, the hatched portion in the circle indicates the exit pupil of the photographic lens, and the white area Sα and the area Sβ are areas that can be received by the photoelectric conversion unit divided into two, and the optical axis of the normal photographic lens (see FIG. It is set to be symmetric with respect to the intersection of the middle x axis and the y axis.

  In the camera, the focal state of the photographic lens is detected by performing a correlation operation between the image generated by the light beam transmitted through the region Sα on the pupil of the photographic lens and the image generated by the light beam transmitted through the region Sβ. A method of performing focus detection by performing correlation calculation of images generated from light beams transmitted through different pupil regions of the photographing lens is disclosed in Patent Document 4.

  Patent Document 4 discloses a technique for detecting a focusing state after a specific filter stored in a camera is deformed by an aperture ratio, an exit pupil position, and an image shift amount, and the deformation filter is adapted to a subject image. Has been.

JP 58-24105 (2nd page, FIG. 1) Japanese Patent No. 2959142 (2nd page, FIG. 2) Japanese Patent Laying-Open No. 2005-106994 (page 7, FIG. 3) JP-A-5-127074 (page 15, FIG. 34)

  However, in the focus detection pixel in the imaging device having the above-described configuration, the output value of the focus detection pixel is larger than the value that actually passes through the microlens of the focus detection pixel and is photoelectrically converted and output by the photoelectric conversion unit. There is a problem of becoming larger. This is due to the following two factors. One is an optical factor that a light beam entering an adjacent pixel of the focus detection pixel leaks into the photoelectric conversion unit of the focus detection pixel after passing through the color filter. The other is an electronic factor that photoelectrons generated inside the silicon substrate of an adjacent pixel are diffused and mixed into the focus detection pixels. This leakage from the adjacent pixels is called crosstalk. Regardless of the factor, the focus detection pixel output is corrected by subtracting the crosstalk correction value obtained by multiplying the adjacent pixel output value by a certain coefficient from the focus detection pixel output value. It can be reduced.

  However, in the crosstalk correction method described above, if the adjacent pixel output value of the focus detection pixel is saturated, correct correction cannot be performed. This is because the crosstalk correction value obtained by multiplying the saturated adjacent pixel output value by a certain coefficient is smaller than the actually required crosstalk correction value. As a result, there is a problem that the focus detection accuracy is lowered.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to perform appropriate crosstalk correction and perform focusing more accurately even under shooting conditions in which imaging pixels adjacent to focus detection pixels are saturated. It is to enable detection.

  An imaging apparatus according to the present invention includes a first pixel group that receives a light beam passing through a first pupil region of an imaging optical system that forms a subject image, and a second pixel that is narrower than the first pupil region. An image sensor having a second pixel group that receives a light beam passing through a pupil region, a determination unit that determines whether the amount of light accumulated in the first pixel group has reached a saturation value, and the determination unit Received light amount estimating means for estimating the received light amount of the pixel determined to be saturated by the light receiving amount estimation means, wherein the received light amount estimating means is a light receiving sensitivity distribution on a pupil plane of the imaging optical system of the first pixel group. And the light receiving sensitivity distribution on the pupil plane of the imaging optical system of the second pixel group, and the vignetting information of the imaging optical system, to the second pixel group of the first pixel group Calculate the received light amount ratio and multiply the received light amount of the second pixel group by the received light amount ratio. By, and estimates the amount of light received by the first pixel group.

  According to the present invention, it is possible to perform appropriate crosstalk correction and perform focus detection with higher accuracy even under imaging conditions in which imaging pixels adjacent to focus detection pixels are saturated.

The block diagram of the camera which concerns on one Embodiment of this invention. The schematic circuit block diagram of an image pick-up element. Sectional drawing of the pixel part of an image pick-up element. The drive timing chart of an image pick-up element. The top view and sectional drawing of the pixel for an imaging of an image pick-up element. The top view and sectional drawing of the pixel for focus detection for performing pupil division in the horizontal direction (lateral direction) of a photographic lens. The top view and sectional drawing of the pixel for focus detection for performing pupil division | segmentation to the orthogonal | vertical direction of an imaging lens. The figure which illustrates notionally the pupil division | segmentation condition of an image sensor. The figure explaining the image and focus detection area which were acquired at the time of focus detection. The schematic diagram showing the incident angle characteristic of the pixel for focus detection in the center of an image sensor. The figure explaining the vignetting of a light beam. The figure which showed the pupil area | region on the pupil surface Me. The figure which shows the pupil intensity distribution of the pixel for focus detection. The figure which showed the vignetting on the pupil surface Me of the focus detection pixel in the center of the image sensor. The figure which showed the vignetting on the pupil surface Me of the pixel of the position which has image height from the center of an image pick-up element. The focus detection flowchart. Crosstalk correction flowchart. Light reception distribution explanatory drawing of the conventional solid-state imaging device.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to FIGS.

  FIG. 1 is a diagram showing a configuration of a camera which is an embodiment of an imaging apparatus according to the present invention. Here, a digital camera in which a lens and a camera body are integrated will be described as an example. However, a single-lens reflex digital camera with interchangeable lenses may be used. In FIG. 1, reference numeral 101 denotes a first lens group disposed at the tip of a photographing optical system (imaging optical system), which is held so as to be able to advance and retract in the optical axis direction. Reference numeral 102 denotes an aperture / shutter, which adjusts the light amount at the time of shooting by adjusting the aperture diameter, and also has a function as an exposure time adjustment shutter at the time of still image shooting. Reference numeral 103 denotes a second lens group. The diaphragm shutter 102 and the second lens group 103 integrally move forward and backward in the optical axis direction, and perform a zooming function (zoom function) in conjunction with the forward and backward movement of the first lens group 101.

  Reference numeral 105 denotes a third lens group that performs focus adjustment by advancing and retreating in the optical axis direction. Reference numeral 106 denotes an optical low-pass filter, which is an optical element for reducing false colors and moire in a captured image. Reference numeral 107 denotes an image sensor composed of a C-MOS sensor and its peripheral circuits. The imaging element 107 is a two-dimensional single-plate color sensor in which a Bayer array primary color mosaic filter is formed on-chip on light receiving pixels of m pixels in the horizontal direction and n pixels in the vertical direction.

  A zoom actuator 111 rotates a cam cylinder (not shown) to drive the first lens group 111 to the third lens group 105 forward and backward in the direction of the optical axis, thereby performing a zooming operation. Reference numeral 112 denotes an aperture shutter actuator that controls the aperture diameter of the aperture / shutter 102 to adjust the amount of photographing light, and controls the exposure time during still image photographing. Reference numeral 114 denotes a focus actuator, which performs focus adjustment by driving the third lens group 105 back and forth in the optical axis direction.

  Reference numeral 115 denotes an electronic flash for illuminating an object at the time of photographing, and a flash illumination device using a xenon tube is suitable, but an illumination device including an LED that emits light continuously may be used. Reference numeral 116 denotes an AF auxiliary light device that projects an image of a mask having a predetermined aperture pattern onto a subject field via a light projection lens, thereby improving the focus detection capability for a dark subject or a low-contrast subject.

  Reference numeral 121 denotes an in-camera CPU that controls various controls of the camera body, and includes a calculation unit, ROM, RAM, A / D converter, D / A converter, communication interface circuit, and the like, and a predetermined program stored in the ROM Based on this, various circuits of the camera are driven. Then, a series of operations such as focus detection, focus adjustment, photographing, image processing, and recording are executed.

  An electronic flash control circuit 122 controls lighting of the electronic flash 115 in synchronization with the photographing operation. Reference numeral 123 denotes an auxiliary light driving circuit that controls the lighting of the AF auxiliary light device 116 in synchronization with the focus detection operation. An image sensor driving circuit 124 controls the image capturing operation of the image sensor 107 and A / D converts the acquired image signal and transmits the image signal to the CPU 121. An image processing circuit 125 performs processes such as γ conversion, color interpolation, and JPEG compression of the image acquired by the image sensor 107.

  A focus drive circuit 126 controls the focus actuator 114 based on the focus detection result, and adjusts the focus by driving the third lens group 105 back and forth in the optical axis direction. Reference numeral 128 denotes an aperture shutter drive circuit which controls the aperture shutter actuator 112 to control the aperture of the aperture / shutter 102. Reference numeral 129 denotes a zoom drive circuit that drives the zoom actuator 111 in accordance with the zoom operation of the photographer.

  Reference numeral 131 denotes a display device such as an LCD, which displays information related to the shooting mode of the camera, a preview image before shooting and a confirmation image after shooting, a focus state display image when focus is detected, and the like. An operation switch group 132 includes a power switch, a release (shooting trigger) switch, a zoom operation switch, a shooting mode selection switch, and the like. Reference numeral 133 denotes a detachable flash memory that records a photographed image.

  FIG. 2 is a diagram showing a schematic circuit configuration of the image sensor in the present embodiment, and the technique disclosed in Japanese Patent Application Laid-Open No. 09-046596 is suitable. FIG. 2 shows the range of 2 columns × 4 rows of pixels of a two-dimensional C-MOS area sensor. However, when used as an image sensor, a large number of pixels shown in FIG. Acquisition is possible. In the present embodiment, the description will be made on the assumption that the pixel pitch is 2 μm, the number of effective pixels is horizontal 3000 columns × 2000 vertical rows = 6 million pixels, and the imaging screen size is 6 mm horizontal × 4 mm vertical.

  In FIG. 2, 1 is a photoelectric conversion portion of a photoelectric conversion element comprising a MOS transistor gate and a depletion layer under the gate, 2 is a photogate, 3 is a transfer switch MOS transistor, 4 is a reset MOS transistor, and 5 is a source follower amplifier MOS. It is a transistor. Also, 6 is a horizontal selection switch MOS transistor, 7 is a source follower load MOS transistor, 8 is a dark output transfer MOS transistor, and 9 is a light output transfer MOS transistor. Further, 10 is a dark output storage capacitor CTN, 11 is a light output storage capacitor CTS, 12 is a horizontal transfer MOS transistor, 13 is a horizontal output line reset MOS transistor, 14 is a differential output amplifier, 15 is a horizontal scanning circuit, and 16 is vertical. This is a scanning circuit.

  FIG. 3 is a diagram illustrating a cross section of the pixel portion of the image sensor according to the present embodiment. In FIG. 3, 17 is a P-type well, 18 is a gate oxide film, 19 is a first-layer poly-Si, 20 is a second-layer poly-Si, and 21 is an n + floating diffusion portion (FD portion). The FD unit 21 is connected to another photoelectric conversion unit via another transfer MOS transistor. In FIG. 3, the drains of the two transfer MOS transistors 3 and the FD portion 21 are made common to improve the sensitivity by miniaturization and the capacity reduction of the FD portion 21, but the FD portion 21 may be connected by an Al wiring. .

  Next, the operation will be described with reference to the timing chart of FIG. This timing chart is for all pixels independent output.

  First, according to the timing output from the vertical scanning circuit 16, the control pulse φL is set to high to reset the vertical output line. Further, the control pulses φR0, φPG00, and φPGe0 are set high, the reset MOS transistor 4 is turned on, and the first-layer poly Si 19 of the photogate 2 is set high. At time T0, the control pulse φS0 is set high, the selection switch MOS transistor 6 is turned on, and the pixel portions of the first and second lines are selected. Next, the control pulse φR0 is set to low, the reset of the FD unit 21 is stopped, the FD unit 21 is set in a floating state, and the source and follower amplifier MOS transistor 5 is set to the through state. Thereafter, the control pulse φTN is set to high at time T1, and the dark voltage of the FD section 21 is output to the storage capacitor CTN10 by the source follower operation.

  Next, in order to perform photoelectric conversion output of the pixels on the first line, the control pulse φTX00 on the first line is set to high to turn on the transfer switch MOS transistor 3, and then the control pulse φPG00 is lowered to low at time T2. At this time, a voltage relationship is preferable in which the potential well that has spread under the photogate 2 is raised so that photogenerated carriers are completely transferred to the FD portion 21. Therefore, if complete transfer is possible, the control pulse φTX may be a fixed potential instead of a pulse.

  At time T2, charges from the photoelectric conversion unit 1 of the photodiode are transferred to the FD unit 21, so that the potential of the FD unit 21 changes according to light. At this time, since the source follower amplifier MOS transistor 5 is in a floating state, the potential of the FD portion 21 is output to the storage capacitor CTS11 with the control pulse φTs being high at time T3. At this time, the dark output and light output of the pixels in the first line are stored in the storage capacitors CTN10 and CTS11, respectively, and the horizontal output line reset MOS transistor 13 is turned on by setting the control pulse φHC at time T4 to be temporarily high. To reset. In the horizontal transfer period, the dark output and the light output of the pixel are output to the horizontal output line by the scanning timing signal of the horizontal scanning circuit 15. At this time, if the differential output VOUT is obtained by the differential amplifier 14 of the storage capacitors CTN10 and CTS11, a signal having a good S / N from which random noise and fixed pattern noise of the pixel are removed can be obtained. Further, the photoelectric charges of the pixels 30-12 and 30-22 are accumulated in the respective storage capacitors CTN10 and CTS11 simultaneously with the pixels 30-11 and 30-21. However, these signals are read out to the horizontal output line by delaying the timing pulse from the horizontal scanning circuit 15 by one pixel and output from the differential amplifier 14. In the present embodiment, a configuration in which the differential output VOUT is performed in the chip is shown, but the same effect can be obtained even if a conventional CDS (Correlated Double Sampling) circuit is used outside without including it in the chip. Is obtained.

  After outputting a bright output to the storage capacitor CTS11, the control pulse φR0 is set to high to turn on the reset MOS transistor 4 and reset the FD portion 21 to the power supply VDD. After the horizontal transfer of the first line is completed, the second line is read. In reading the second line, the control pulse φTXe0 and the control pulse φPGe0 are driven in the same manner, high pulses are supplied to the control pulses φTN and φTS, respectively, and photocharges are accumulated in the storage capacitors CTN10 and CTS11, respectively. Take the output. With the above driving, the first and second lines can be read independently. Thereafter, by scanning the vertical scanning circuit and reading out the second n + 1 and second n + 2 (n = 1, 2,...) In the same manner, all the pixels can be independently output. That is, when n = 1, first, the control pulse φS1 is set high, and then φR1 is set low. Subsequently, the control pulses φTN and φTX01 are set high, the control pulse φPG01 is set low, the control pulse φTS is set high, and the control pulse φHC is set high temporarily to read out the pixel signals of the pixels 30-31 and 30-32. Subsequently, the control pulses φTXe1, φPGe1 and other control pulses are applied in the same manner as described above, and the pixel signals of the pixels 30-41 and 30-42 are read out.

  FIG. 5 to FIG. 7 are diagrams for explaining the structures of the imaging pixel that is the first pixel group, the second pixel group, and the focus detection pixel that is the third pixel group in the present embodiment. In the present embodiment, out of 4 pixels of 2 rows × 2 columns, pixels having G (green) spectral sensitivity are arranged in 2 diagonal pixels, and R (red) and B (blue) are arranged in the other 2 pixels. A Bayer arrangement in which one pixel each having a spectral sensitivity of 1 is arranged is employed. In addition, focus detection pixels having a structure described later are distributed and arranged in a predetermined rule between the Bayer arrays.

  FIG. 5 shows a plan view and a cross-sectional view of the imaging pixel. FIG. 5A is a plan view of 2 × 2 imaging pixels located in the center of the imaging device. As is well known, in the Bayer array, G pixels are arranged diagonally, and R and B pixels are arranged in the other two pixels. The 2 rows × 2 columns structure is repeatedly arranged.

  FIG. 5B shows a cross section AA of FIG. ML is an on-chip microlens disposed on the forefront of each pixel, CFR is an R (Red) color filter, and CFG is a G (Green) color filter. PD is a schematic diagram of the photoelectric conversion unit of the C-MOS sensor described with reference to FIG. 3, and CL is a wiring layer for forming signal lines for transmitting various signals in the C-MOS sensor. TL schematically shows the photographing optical system.

  Here, the on-chip microlens ML and the photoelectric conversion unit PD of the imaging pixel are configured to capture the light beam that has passed through the photographing optical system ML as effectively as possible. In other words, the exit pupil EP of the photographing optical system TL and the photoelectric conversion unit PD are conjugated with each other by the microlens ML, and the effective area of the photoelectric conversion unit is designed to be large. Further, although the incident light beam of the R pixel has been described in FIG. 5B, the G pixel and the B (Blue) pixel have the same structure. Accordingly, the exit pupil EP corresponding to each of the RGB pixels for imaging has a large diameter, and the S / N of the image signal is improved by efficiently capturing the light flux from the subject.

  FIG. 6 shows a plan view and a cross-sectional view of focus detection pixels for performing pupil division in the x direction in the drawing of the photographing lens. FIG. 6A is a plan view of 2 × 2 pixels including focus detection pixels located at the center of the image sensor. When obtaining an imaging signal, the G pixel is a main component of luminance information. Since human image recognition characteristics are sensitive to luminance information, image quality degradation is likely to be recognized if G pixels are lost. On the other hand, the R or B pixel is a pixel that acquires color information. However, since humans are insensitive to color information, pixels that acquire color information are less likely to notice deterioration in image quality even if some loss occurs. Therefore, in the present embodiment, among the pixels of 2 rows × 2 columns, the G pixel is left as an imaging pixel, and the focus detection pixels are arranged at a ratio of pixels in positions corresponding to R and B. This is indicated by SHA and SHB in FIG.

  A cross section BB of FIG. 6A is shown in FIG. The microlens ML and the photoelectric conversion unit PD have the same structure as the imaging pixel shown in FIG. In the present embodiment, since the signal of the focus detection pixel is not used for image creation, a transparent film CFW (White) is arranged instead of the color separation color filter. Further, since pupil division is performed by the image sensor, the opening of the wiring layer CL is deviated in the x direction with respect to the center line of the microlens ML. Specifically, since the opening OPHA of the pixel SHA is deviated in the −x direction, the light beam that has passed through the exit pupil EPHA on the left side of the photographing lens TL is received. Similarly, since the opening OPHB of the pixel SHB is biased in the + x direction, the light beam that has passed through the right exit pupil EPHB of the photographic lens TL is received. Therefore, the pixels SHA are regularly arranged in the x direction, the subject image generated by these pixel groups (second pixel group) is set as an A image (second subject image), and the pixels SHB are also regularly arranged in the x direction. A subject image generated by these pixel groups (third pixel group) is defined as a B image (third subject image). Then, by detecting the relative position between the A image and the B image, the amount of defocus (defocus amount) of the subject image can be detected.

  In the pixels SHA and SHB, focus detection is possible for an object having a luminance distribution in the x direction on the photographing screen, for example, a line in the y direction, but an x direction line having a luminance distribution in the y direction. Cannot detect the focus. Therefore, in the present embodiment, a pixel that performs pupil division is also provided in the y direction of the photographic lens so that the latter can be detected in focus.

  FIG. 7 shows a plan view and a cross-sectional view of a focus detection pixel for performing pupil division in the y direction in the drawing of the photographing lens. FIG. 7A is a plan view of pixels of 2 rows × 2 columns including focus detection pixels located at the center of the image sensor. As in FIG. 6A, G pixels are left as image capture pixels, and R Focus detection pixels are arranged at a certain ratio to pixels at positions corresponding to A and B. This is indicated by SVC and SVD in FIG.

  FIG. 7B shows a cross-section C-C of FIG. 7A. The pixel of FIG. 6B has a structure in which the pupil is separated in the x direction, whereas the pixel of FIG. Only the pupil separation direction is in the y direction, and the pixel structure does not change. That is, since the opening OPVC of the pixel SVC is biased in the −y direction, the light beam that has passed through the exit pupil EPVC in the + y direction of the photographic lens TL is received. Similarly, since the opening OPVD of the pixel SVD is biased in the + y direction, the light beam that has passed through the exit pupil EPVD of the photographing lens TL in the −y direction is received. Therefore, the pixels SVC are regularly arranged in the y direction, the subject images acquired by these pixel groups are set as C images, the pixels SVD are also regularly arranged in the y direction, and the subject images acquired by these pixel groups are Let it be a D image. Then, by detecting the relative positions of the C image and the D image, it is possible to detect the focus shift amount (defocus amount) of the subject image having a luminance distribution in the y direction.

  FIG. 8 is a diagram conceptually illustrating the pupil division state of the image sensor in the present embodiment. TL is a photographing lens, 107 is an image sensor, OBJ is a subject, and IMG is a subject image. As described in the plan view and the cross-sectional view of the imaging pixel of the imaging element in FIG. 5, the imaging pixel receives the light flux that has passed through the entire exit pupil EP (first pupil region) of the imaging lens. On the other hand, the focus detection pixel includes a plan view and a cross-sectional view of the focus detection pixel for dividing the pupil in the x direction in FIG. 6, and a plan view of the focus detection pixel for performing the pupil division in the y direction in FIG. 7. As described in the cross-sectional view, it has a pupil division function. Specifically, the pixel SHA in FIG. 6 receives a light beam that has passed through the pupil on the + X direction side, that is, a light beam that has passed through the pupil EPHA (second pupil region) in FIG. Similarly, the pixels SHB, SVC, and SVD receive light beams that have passed through the pupil EPHB (third pupil region), EPVC, and EPVD, respectively. As is clear from the above description, the second pupil region is narrower than the first pupil region. The focus detection pixels are distributed over the entire area of the image sensor 107, thereby enabling focus detection in the entire image pickup area.

  FIG. 9 is a diagram illustrating an image acquired at the time of focus detection and a focus detection area. In FIG. 9, the subject image formed on the imaging surface shows a person in the center, a tree in the foreground on the left side, and a mountain range in the foreground on the right side. In the present embodiment, the focus detection pixels are arranged such that the pixel pairs SHA and SHB for detecting the x-direction deviation and the pixel pairs SVC and SVD for detecting the y-direction deviation are arranged at an equal density over the entire imaging region. Has been. In detecting the x-direction deviation, a pair of image signals obtained from the pixel pair SHA and SHB for detecting the x-direction deviation is used as an AF pixel signal for phase difference calculation. When detecting the y-direction deviation, a pair of image signals obtained from the y-direction deviation detection pixel pair SVC and SVD is used as an AF pixel signal for phase difference calculation. Therefore, it is possible to set a distance measurement area for detecting an x-direction deviation and a y-direction deviation at an arbitrary position in the imaging area.

  In FIG. 9, a human face exists in the center of the screen. Therefore, when the presence of a face is detected by a known face recognition technique, a focus detection area AFARh (x1, y1) for detecting a deviation in the x direction around the face area and a focus detection area AFARv for detecting a deviation in the y direction. (X3, y3) is set. Here, the subscript h represents the x direction, and (x1, y1) and (x3, y3) represent the coordinates of the upper left corner of the focus detection area. Then, an A image signal for phase difference detection obtained by connecting focus detection pixels SHA for detecting an x-direction shift included in each section of the focus detection area AFARh (x1, y1) over 30 sections is AFSIGh (A1). It is. Similarly, AFSIGh (B1) is a B image signal for phase difference detection obtained by connecting focus detection pixels SHB for detecting deviation in the x direction of each section over 30 sections. Then, the defocus amount (defocus amount) of the photographing lens is obtained by calculating the relative x-direction shift amount between the A image signal AFSIGh (A1) and the B image signal AFSIGh (B1) by a known correlation calculation. Can do.

  The defocus amount is similarly obtained for the focus detection area AFARv (x3, y3). Then, the two defocus amounts detected in the x-direction shift and y-direction shift focus detection regions are compared, and a highly reliable value may be adopted.

  On the other hand, the trunk of the tree on the left side of the screen is mainly composed of the y-direction component, that is, has a luminance distribution in the x-direction, so that it is determined as a subject suitable for detecting the x-direction deviation, and focus detection for detecting the x-direction deviation is performed. An area AFARh (x2, y2) is set. Further, the mountain ridge on the right side of the screen is mainly composed of x-direction components, that is, has a luminance distribution in the y-direction, so that it is determined as a subject suitable for y-direction deviation detection, and focus detection for y-direction deviation detection is performed. An area AFARv (x4, y4) is set.

  As described above, in this embodiment, since the focus detection area for detecting the x-direction shift and the y-direction shift can be set at an arbitrary position on the screen, even if the projection position of the subject and the directionality of the luminance distribution are various. , Focus detection is always possible. Since the principle is the same except that the x-direction deviation and the y-direction deviation are different from each other, the following description is for detecting the x-direction deviation, and the explanation for the y-direction deviation detection is omitted.

  10A and 10B are schematic diagrams showing the incident angle characteristics of the focus detection pixel at the center of the image sensor. FIG. 10A shows the characteristics of the pixel SHA, and FIG. 10B shows the characteristics of the pixel SHB. In FIG. 10, the x-axis and y-axis represent the incident angles of the pixel in the x-direction and y-direction, respectively. FIG. 10 shows that the received light intensity is higher as the color becomes darker. In FIG. 6, for ease of explanation, the exit pupil of the pixel SHA is shown separately as EPHA, and the exit pupil of the pixel SHB is shown separately as EPHB. However, as shown in FIG. 10, in practice, the exit pupils of the pixels SHA and SHB overlap each other in order to improve the influence of diffraction due to the openings OPHA and the openings OPHB and the SN. There is.

  FIG. 10C is a one-dimensional representation of the incident angle characteristics of the focus detection pixels. The abscissa represents the incident angle, the ordinate represents the sum of the light receiving sensitivity in the θy direction in FIG. 10, and the origin is the optical axis. As shown in FIG. 10C, in the focus detection pixel at the center of the image sensor, the incident angle characteristics of the pixel SHA and the pixel SHB are substantially symmetric with respect to the optical axis.

  FIG. 11 is a diagram for explaining vignetting of a light beam. FIG. 11A shows a light beam incident on a pixel at the center of the image sensor, and FIG. 11B shows a light beam incident on a pixel at a position having an image height from the center of the image sensor. A light beam limited by several components such as a lens holding frame of the photographing lens 101 and a diaphragm 102 is incident on the imaging element. Information on the position and size of the constituent members that limit these light fluxes is the vignetting information of the optical system of the present embodiment. The vignetting information of the optical system varies depending on the type of lens, the F value, which is a photographing condition, the zoom state, the image height, and the like. Here, in order to make the explanation easy to understand, it is assumed that there are two members that limit the light flux at any image height. In Iw1 and Iw2, a member that restricts the luminous flux is used as a window, and the luminous flux passes through the inside. Me represents the pupil plane set by the configuration of the microlens ML. With reference to FIG. 11A, vignetting of the light beam incident on the pixel at the center of the image sensor will be described. L1rc and L1lc represent the outer periphery of the light beam emitted from the window Iw1, L1rc represents the right end in FIG. 11, and L1lc represents the left end in FIG. L2rc and L2lc represent the outer periphery of the projection of the light beam emitted from the window Iw2 up to the pupil position of the microlens ML. L2rc represents the right end in FIG. 11, and L2lc represents the left end in FIG. As shown in FIG. 11A, the pupil region on the pupil plane Me of the light beam incident on the center pixel of the image sensor is indicated by a light beam having L2lc and L2rc as outer circumferences, that is, an arrow Area1.

  Next, the vignetting of the light beam incident on the pixel at the position having the image height from the center of the image sensor will be described with reference to FIG. L1rh and L1lh represent the outer periphery of the light flux emitted from the window Iw1, L1rh represents the right end in FIG. 11, and L1lh represents the left end in FIG. L2rh and L2lh represent the outer periphery of the projection of the light beam emitted from the window Iw2 up to the pupil position of the microlens ML. L2rh represents the right end in FIG. 11 and L2lh represents the left end in FIG. As shown in FIG. 11B, the pupil region on the pupil plane Me of the light beam incident on the pixel having the image height from the center of the image sensor is a light beam having L1lh and L2rh as outer circumferences, that is, an arrow Area2. Indicated by

  FIG. 12 is a diagram showing a pupil region on the pupil plane Me. FIG. 12A shows a pupil region of a pixel at the center of the image sensor, and FIG. 12B shows a pupil region of a pixel at a position having an image height from the center of the image sensor. As described with reference to FIG. 11, since the light beam limited by the same window Iw2 is incident on the pixel in the center of the image sensor, the shape of the window Iw2 is projected as it is in the pupil area Area1 as shown in FIG. . Since the window for limiting the luminous flux is circular, the shape of the pupil area Area1 is also circular. On the other hand, since the light beam limited by Iw1 and Iw2 is incident on the pixel at the image height from the center of the image sensor, the pupil area Area2 has a shape as shown in FIG.

  FIG. 13 is a diagram showing a pupil intensity distribution of focus detection pixels. This is the light reception sensitivity distribution on the pupil plane of the second pixel group and the light reception sensitivity distribution on the pupil plane of the third pixel group in this embodiment. This is equivalent to the incident angle characteristic of the focus detection pixel at the center of the image sensor shown in FIG. 10 projected onto the pupil of the microlens ML, and the vertical and horizontal axes in FIG. 13 are expanded to the coordinates on the pupil. Is. Since this pupil intensity distribution varies depending on the image height, values at several image heights are stored in the ROM in the CPU 121. The pupil intensity distribution at the intermediate image height of the stored image height is calculated by interpolation processing.

  FIG. 14 is a diagram showing vignetting on the pupil plane Me of the focus detection pixel at the center of the image sensor. FIG. 14A shows the characteristics of the pixel SHA, and FIG. 14B shows the characteristics of the pixel SHB. FIG. 14 is a view obtained by superimposing FIG. 12A and FIG. 13. A light beam transmitted through the inside of the shape indicated by Area 1 is incident on the pixel SHA and the pixel SHB with the illustrated pupil intensity distribution.

  FIG. 14C is a two-dimensional representation of the pupil intensity distribution of the incident light beam on the pupil plane Me of the focus detection pixel at the center of the image sensor. The horizontal axis represents coordinates in the x direction on the pupil plane Me, and the vertical axis represents the intensity of each coordinate. The intensity of each coordinate is obtained by adding the pupil intensity in the y direction in FIGS. 14 (a) and 14 (b). The pupil intensity distribution of the incident light beam on the pupil plane Me of the pixel SHA and the pixel SHB is indicated by EsdAc and EsdBc. As shown in FIG. 14C, the pupil intensity distributions on the pupil plane Me of the pixels SHA and SHB are symmetrical. Further, since the shape to be measured is also a bilaterally symmetric shape, the pupil intensity distribution of the incident light beam on the pupil plane Me of the pixel SHA and the pixel SHB is also bilaterally symmetric.

  FIG. 15 is a diagram showing vignetting on a pupil plane Me of a pixel at a position having an image height from the center of the image sensor. FIG. 15A shows the characteristics of the pixel SHA, and FIG. 15B shows the characteristics of the pixel SHB. FIG. 15 is a view obtained by superimposing FIG. 12B and FIG. 13. A light beam transmitted through the inside of the shape indicated by Area 2 is incident on the pixel SHA and the pixel SHB with the illustrated pupil intensity distribution.

  FIG. 15C is a two-dimensional representation of the pupil intensity distribution of the incident light beam on the pupil plane Me of the pixel having the image height from the center of the image sensor. The horizontal axis represents coordinates in the x direction on the pupil plane Me, and the vertical axis represents the intensity of each coordinate. The intensity of each coordinate is obtained by adding the pupil intensity in the y direction in FIGS. 15A and 15B in a direction orthogonal to the pupil separation direction. In FIG. 15C, the pupil intensity distribution of the incident light beam on the pupil plane Me of the pixels SHA and SHB is indicated by EsdAh and EsdbBh. The pupil intensity distribution on the pupil plane Me of the pixel SHA and the pixel SHB is symmetrical.

  Next, the flow of focus detection of this embodiment will be described using the flowchart of FIG. The operation in the flow of FIG. 16 is executed by the CPU 121 which is the saturation determination unit, the received light amount estimation unit, and the received light amount correction unit of the present embodiment.

  In step S1, lens information for knowing the vignetting state is read, and the process proceeds to step S2. Here, the lens information includes the vignetting information of the optical system in the present embodiment, in addition to the F value and zoom state which are imaging conditions. In step S2, distance measurement point information such as the distance measurement position and range set by the user is read. After completion, the process proceeds to step S3.

  In step S3, the pupil intensity distribution stored in the ROM in the CPU 121 is read for each focus detection pixel, and the line image distribution function is calculated together with the vignetting information of the optical system obtained in step S1. After completion, the process proceeds to step S4. In step S4, the center of gravity of the line image distribution function obtained in step S3 is calculated, and the baseline length is obtained. Details of the calculation method of the baseline length will be described later. When completed, the process proceeds to step S5.

  In step S5, the image signal of the focus detection pixel at the distance measurement position read in step S2 is read, and the subject A image and the subject B image are formed. At the same time, peripheral pixel signals for use in the crosstalk correction in step S6 are also read. After completion, the process proceeds to step S6.

  In step S6, crosstalk correction is performed by subtracting the estimated leakage amount from surrounding pixels from the output value of the focus detection pixel. Details of the crosstalk correction will be described later. After completion, the process proceeds to step S7. In step S7, using the vignetting information and pupil intensity distribution of the optical system obtained in step S1, the amount of vignetting of the subject image A image and the subject image B image is predicted, and the subject image A image after crosstalk correction is performed. Then, the light amount correction for adjusting the light amount ratio is performed on the subject image B image. After the light amount correction, the process proceeds to step S8.

  In step S8, the CPU 121 obtains an image shift amount by a known correlation calculation method using the subject image A image and the subject image B image after light amount correction obtained in step S7, and obtains a defocus amount. After calculating the defocus amount, the process proceeds to step S9. In step S9, it is determined whether or not the calculated defocus amount is in focus. If it is not determined that the subject is in focus, the process proceeds to step S10. If it is determined that focus is achieved, the process proceeds to step S11. In step S10, the third lens group 105 is advanced or retracted according to the calculated defocus calculation result. Then, the process returns to step S5. In step S11, a series of focus detection flows ends.

  Next, the baseline length calculation method in step S4 will be described in detail. First, a line image corresponding to the subject image A (hereinafter referred to as line image A) and a line image corresponding to the subject image B image (hereinafter referred to as line image B) are moved so as to coincide with each other. Assuming that the moved line image A and line image B are the line image A0 and the line image B0, respectively, the line image A is convolved and integrated with the line image B0, and the line image B is convolved with the line image A0. The corrected baseline length is calculated from the center of gravity interval of the corrected line image B. This is expressed as follows.

  The equation for calculating the corrected line image A is MA (x) for the corrected line image A, LA (x) for the line image A, and LB '(x) for the line image B0.

... (1)
Therefore, if the center of gravity of the corrected line image A is GA ′,

... (2)
It becomes.

  Similarly, the equation for obtaining the corrected line image B is as follows. If the corrected line image B is MB (x), the line image B is LB (x), and the line image A0 is LA ′ (x),

... (3)
Therefore, if the center of gravity of the corrected line image B is GB ′,

... (4)
It becomes.
Therefore, if the baseline length to be obtained is G ′,

... (5)
The baseline length is calculated by the above calculation.

  Next, the crosstalk correction in step S6 will be described in detail with reference to the flowchart showing the crosstalk correction operation of FIG. Note that the crosstalk correction operation in the flow of FIG. 17 is executed by the CPU 121 which is the saturation determination unit, the received light amount estimation unit, and the received light amount correction unit of this embodiment.

  In step S101, whether the output signal value SO of the imaging pixel adjacent to the focus detection pixel read out in step S5 of FIG. 16 by the CPU 121 which is the saturation determination unit of the present embodiment has reached the saturation value SOmax. Determine if. This process is performed for each of the eight adjacent pixels for one focus detection pixel. If the saturation value has been reached, the process proceeds to step S102. If the saturation value has not been reached, the process proceeds to step S105.

  In step S102, the CPU 121, which is the received light amount estimation means of the present embodiment, calculates a ratio Rsf of the received light amount of the imaging pixel that has reached the saturation value to the received light amount of the focus detection pixel adjacent thereto. For example, the amount of received light at a position having an image height from the center of the image sensor is determined by determining Area2 in FIG. 15 using the vignetting information of the optical system, and integrating each pupil intensity distribution in the Area2 area. Thus, it is possible to calculate the relative ratio of the respective received light amounts. After calculating the received light amount ratio Rsf, the process proceeds to step S103.

  In step S103, the CPU 121, which is the received light amount estimation unit of the present embodiment, saturates the saturated received light amount of the imaging pixel by multiplying the received light amount FO of the adjacent focus detection pixel by Rsf. The amount of light received SOt when there is not is estimated. After estimating the amount of received light SOt, the process proceeds to step S104.

  In step S104, the CPU 121, which is the received light amount correction means of the present invention, multiplies the received light amount SOt that is not saturated estimated in step S103 by the crosstalk correction coefficient Ecr stored in the ROM in the CPU 121. Thus, the crosstalk correction light quantity CR from each imaging pixel to the focus detection pixel is calculated. This process is performed for each of the eight adjacent pixels for one focus detection pixel. The crosstalk correction light amount CRs from each imaging pixel is summed up to calculate the crosstalk correction light amount CRs. After calculating the crosstalk correction light quantity, the process proceeds to step S106.

  In step S <b> 105, the CPU 121, which is the received light amount correction unit of the present embodiment, multiplies the output value SO of the imaging pixel adjacent to the focus detection pixel by the crosstalk correction coefficient Ecr stored in the ROM in the CPU 121. Thus, the crosstalk correction light quantity CR from each imaging pixel to the focus detection pixel is calculated. The output value SO of the imaging pixel used here is the same value as the read output value SO. This process is performed for each of the eight adjacent pixels for one focus detection pixel. The crosstalk correction light amount CRs from each imaging pixel is summed up to calculate the crosstalk correction light amount CRs. After calculating the crosstalk correction light quantity, the process proceeds to step S106.

  In step S106, the CPU 121, which is a light reception amount correction unit of the present embodiment, subtracts the crosstalk correction light amount CRs from the light reception amount FO of the focus detection pixel to perform crosstalk correction. In step S106, a series of crosstalk correction flows ends.

  According to the above configuration, even when the light output value of the adjacent pixel of the focus detection pixel reaches the saturation value, the leakage of the output from the adjacent pixel to the focus detection pixel can be corrected with higher accuracy. Is possible. In addition, since the amount of light incident on the pixel that has reached the saturation value is estimated using the vignetting information of the lens, it can be used for various lens types, various shooting conditions such as F value and zoom state, and various image heights. It becomes possible to estimate with higher accuracy. In addition, since the amount of light incident on the pixel that has reached the saturation value is estimated using the pupil intensity distribution, it is possible to estimate with higher accuracy even at various image heights. Thereby, focus detection can be performed with higher accuracy.

Claims (3)

A first pixel group that receives a light beam that passes through a first pupil region of an imaging optical system that forms a subject image, and a light beam that passes through a second pupil region narrower than the first pupil region. An image sensor having a second pixel group,
Determination means for determining whether the amount of light accumulated in the first pixel group has reached a saturation value;
A received light amount estimating means for estimating a received light amount of a pixel determined to be saturated by the determining means,
The light reception amount estimation means includes a light reception sensitivity distribution on a pupil plane of the imaging optical system of the first pixel group, a light reception sensitivity distribution on a pupil plane of the imaging optical system of the second pixel group, The received light amount ratio of the first pixel group to the second pixel group is calculated using the vignetting information of the imaging optical system, and the received light amount of the second pixel group is multiplied by the received light amount ratio. Thus, the amount of light received by the first pixel group is estimated.   A light reception amount correcting unit that corrects the light reception amount of the second pixel group adjacent to the first pixel group by using the light reception amount of the first pixel group estimated by the light reception amount estimation unit; The imaging apparatus according to claim 1.   The amount of light received by the third pixel group that receives a light beam passing through a third pupil region that is narrower than the first pupil region, and the amount of light received by the first pixel group estimated by the received light amount estimation means. And a received light amount correcting means for correcting the received light amount of the second pixel group adjacent to the first pixel group and the received light amount of the third pixel group adjacent to the first pixel group; A second subject image generated by the output of the second pixel group corrected by the received light amount correcting means, and a third object image generated by the output of the third pixel group corrected by the received light amount correcting means. The imaging apparatus according to claim 1, wherein focus detection is performed using a subject image.