JP2012252280A - Imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve detection accuracy when performing focus detection of a phase difference system using an image pickup device arranged with pixels for focus detection between pixels for imaging.SOLUTION: An imaging apparatus comprises: the image pickup device including a pixel group for imaging which images a subject image image-formed by a photographic optical system and a pixel group for focus detection which divides an exit pupil of the photographic optical system and performs the focus detection of the phase difference system using light flux from the divided regions; and an arithmetic unit which calculates a prescribed signal in which a cross talk component from an adjacent pixel in the pixel group for focus detection is corrected and performs a focus detection operation using an image signal for focus detection corrected by the prescribed signal.

Description

  The present invention relates to an image pickup apparatus that includes an image pickup device capable of picking up a moving image or a still image with a large number of two-dimensionally configured photoelectric conversion elements and performs phase difference focus detection using the image pickup device.

  In an electronic camera capable of recording a moving image or a still image, a technique for realizing focus detection by a phase difference detection method using an image recording image sensor has been proposed. In the phase difference detection method, the light beam that has passed through the exit pupil of the photographing optical system is divided into two, and the two divided light beams are received by a set of focus detection light receiving element groups. Then, by detecting the shift amount of the signal waveform of the one-to-two image output according to the received light amount, that is, the relative positional shift amount generated in the pupil division direction of the light beam, the defocus amount ( Defocus amount).

  As a configuration for realizing this phase difference detection method, there are a method using an optical system dedicated to focus detection and a light receiving sensor, and a method of performing focus detection using an image sensor for image recording. As an example of the former, there is a secondary imaging phase difference detection method employed in an AF single-lens reflex camera. This is because a pupil-dividing field lens and a secondary imaging lens are arranged on the planned imaging plane of the photographing optical system, and a one-to-two image is formed on a light receiving sensor arranged behind the lens, and a focus detection signal is generated. To get. As the latter example, a method of dividing the pupil with an on-chip microlens mounted on each pixel of the image sensor has been proposed.

  The latter method is advantageous in reducing the size and cost of the device because a mechanism dedicated to focus detection used in the secondary imaging method is unnecessary. Moreover, since imaging and focus detection can be performed simultaneously, it is particularly suitable for moving image shooting. On the other hand, this method has a problem that a pair of focus detection signals are easily distorted due to various reasons, and a focus detection error is larger than a method using a mechanism dedicated to focus detection. One cause of distortion of the focus detection signal is output interference between adjacent pixels, so-called crosstalk. Another cause is that the focus detection light beam is displaced by the exit pupil of the photographing optical system and the image is distorted. Therefore, the following techniques have been proposed in order to reduce the influence of the image distortion due to the crosstalk and luminous flux vignetting.

  For example, in Japanese Patent Application Laid-Open No. 2009-122524 (Patent Document 1), a crosstalk rate between a focus detection pixel and its surrounding pixels is measured in advance, and crosstalk correction is performed on the focus detection signal, thereby generating a focus detection signal. Corrects distortion.

  In Japanese Patent Laid-Open No. 2010-117679 (Patent Document 2), a line image distribution function representing image distortion characteristics is calculated from light reception characteristics of focus detection pixels and exit pupil information of the imaging optical system. Then, a correction filter for eliminating the image distortion is created from this line image distribution function, and the image distortion is eliminated by convolving and integrating the filter with the focus detection signal.

JP 2009-122524 A JP 2010-117679 A

  However, the above known technique has the following drawbacks. In the technique disclosed in Patent Document 1, since the image distortion due to the vignetting of the focus detection light beam is not eliminated, the degree of coincidence of the one-to-two image is lowered. As a result, a lateral shift amount detection error between the two images during the correlation calculation occurs, and a focus detection error occurs.

  In the technique disclosed in Patent Document 2, distortion due to the influence of crosstalk should also occur in the line image distribution function, but a technique for eliminating the distortion of the line image distribution function is not disclosed. Therefore, there is a concern that an error also occurs in the correction filter that eliminates distortion of the focus detection image signal, resulting in a decrease in focus detection accuracy.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to detect in the case where phase difference type focus detection is performed using an image sensor in which focus detection pixels are arranged between imaging pixels. It is to improve accuracy.

  An imaging apparatus according to the present invention divides an imaging pixel group that captures a subject image formed by a photographic optical system and an exit pupil of the photographic optical system, and uses a light beam from the divided area. An image sensor having a focus detection pixel group for performing phase difference type focus detection, a predetermined signal in which a crosstalk component from an adjacent pixel in the focus detection pixel group is corrected, and a predetermined signal are calculated. And a calculation means for performing focus detection calculation using the image signal for focus detection corrected by the signal.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to improve a detection precision in the case of performing a phase difference type focus detection using the image pick-up element by which the focus detection pixel was arrange | positioned between the image pickup pixels.

1 is a configuration diagram of an imaging apparatus according to a first embodiment of the present invention. FIG. 3 is an explanatory diagram of regions of the image sensor according to the first embodiment of the present invention. The pixel arrangement | positioning figure in the imaging region of an image pick-up element. The figure explaining the conjugate relationship of the imaging pixel and the exit pupil of the imaging optical system. The figure explaining the conjugate relation between the focus detection pixel and the exit pupil of the photographing optical system. The pixel arrangement | positioning figure in the crosstalk information acquisition area | region of an image sensor. The figure explaining the conjugate relationship of the pixel for crosstalk information acquisition, and the exit pupil of an imaging optical system. The figure which shows the crosstalk measuring method and measurement result in an image signal. The schematic block diagram of the apparatus which measures pupil intensity distribution. The figure explaining the crosstalk of a pupil intensity distribution, and its correction principle. The figure explaining pupil intensity distribution and its projection. The figure explaining the line image distribution waveform at the time of a defocus. The figure which showed the waveform before and behind performing various correction | amendment in the image signal for focus detection. FIG. 3 is a configuration diagram of a readout circuit in an image sensor. The figure explaining the image at the time of focus detection, a focus detection signal, and a defocus map. FIG. 5 is a flowchart for acquiring crosstalk of an image signal in the first embodiment. FIG. 6 is a flowchart for acquiring crosstalk of pupil intensity distribution in the first embodiment. The main control flow figure of an imaging device. FIG. 5 is a flowchart of a focus detection subroutine in the first embodiment. The block diagram of the imaging device in 2nd Embodiment. FIG. 10 is an explanatory diagram of an area of an image sensor in the second embodiment. FIG. 9 is a flowchart for acquiring crosstalk of an image signal in the second embodiment. The flowchart for acquiring the crosstalk of the pupil intensity distribution in 2nd Embodiment. The flowchart of the focus detection subroutine in 2nd Embodiment.

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

(First embodiment)
FIG. 1 is a configuration diagram of an imaging apparatus 100 according to the first embodiment of the present invention, showing an electronic camera in which a camera body having an imaging element and a photographing optical system are integrated, and a moving image and a still image are recorded. Is possible. 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 movably in the optical axis direction. Reference numeral 102 denotes an aperture, which adjusts the aperture diameter and adjusts the amount of light during shooting, and also has a function as an exposure time adjustment shutter when shooting a still image. Reference numeral 103 denotes a second lens group. The diaphragm 102 and the second lens group 103 are integrally driven in the optical axis direction, and perform a zooming function (zoom function) in conjunction with the moving operation of the first lens group 101.

  Reference numeral 105 denotes a third lens group that performs focus adjustment by movement 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 image sensor 107 is a two-dimensional single-plate color sensor in which M pixels in the horizontal direction and N pixels in the vertical direction are squarely arranged, and a primary color mosaic filter in a Bayer array is formed on-chip.

  Reference numeral 111 denotes a zoom actuator that rotates a cam cylinder (not shown) to drive the first lens group 101 to the third lens group 105 in the optical axis direction to perform a zooming operation. Reference numeral 112 denotes a diaphragm actuator that controls the aperture diameter of the diaphragm 102 to adjust the amount of photographing light, and controls the exposure time during still image photographing. A focus actuator 114 drives the third lens group 105 in the optical axis direction to adjust the focus.

  A wireless communication unit 115 includes an antenna and a signal processing circuit for communicating with a server computer through a network such as the Internet. Reference numeral 116 denotes a camera posture detection unit, which uses an electronic level for determining the shooting posture of the camera, that is, horizontal position shooting or vertical position shooting.

  Reference numeral 121 denotes a CPU, which has a calculation unit, ROM, RAM, A / D converter, D / A converter, communication interface circuit, and the like to manage various controls of the camera body. Based on a predetermined program stored in the ROM, various circuits included in the camera are driven, and a series of operations such as AF, photographing, image processing, and recording are executed.

  A communication control circuit 122 transmits a captured image from the camera to the server computer or receives an image and various information from the server computer via the communication unit 115. A posture detection circuit 123 determines the posture of the camera from the output signal of the posture detection unit 116. 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 processing such as γ conversion, color interpolation, and image compression of the image acquired by the image sensor 107.

  A focus driving circuit 126 controls the focus actuator 114 based on the focus detection result, and drives the third lens group 105 in the optical axis direction to adjust the focus. Reference numeral 128 denotes an aperture driving circuit that controls the aperture actuator 112 to drive the aperture of the aperture 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 such as an LCD, which displays information related to the shooting mode of the camera, a preview image at the time of shooting and a confirmation image after shooting, a focus state display image at the time of focus detection, camera posture information, and the like. An operation switch group 132 includes a power switch, a shooting start 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.

  Reference numeral 141 denotes an external PC that is independent from the camera, and is used as appropriate when various adjustment processes of the camera are performed, and incorporates an interface and an adjustment program for cooperating with various tools.

  FIG. 2 shows a pixel array region of the image sensor according to the first embodiment of the present invention, and is a view of the light receiving surface of the image sensor 107 viewed from the photographing optical system side. Reference numeral 107im denotes an imaging region, in which imaging pixels and focus detection pixels are two-dimensionally arranged on the XY plane. Reference numeral 107ct denotes a crosstalk information acquisition region in which pixels for obtaining crosstalk components in the focus detection signal image signal and crosstalk information in a pupil intensity distribution described later are arranged.

  FIG. 3 shows a pixel arrangement in the imaging region 107im described with reference to FIG. 2, and is manufactured using the technique disclosed in Japanese Patent Application Laid-Open No. 09-046596 by the applicant of the present application. FIG. 3 shows a state in which a range of 14 rows in the vertical direction (Y direction) and 14 columns in the horizontal direction (X direction) of the two-dimensional C-MOS area sensor is observed from the photographing optical system side.

  A first pixel group (imaging pixel group) 211 is used for imaging, and a Bayer arrangement is applied to the color filter. In other words, red (Red) and green 1 (Green) color filters are alternately provided in order from the left on the pixels in the odd-numbered rows, which are indicated by pixels 211R and 211G1, respectively. In addition, the even-numbered rows of pixels are alternately provided with green 2 (Green) and blue (Blue) color filters in order from the left, which are also indicated by pixels 211G2 and 211B. A circle provided in each pixel represents an on-chip microlens, and a rectangle disposed inside thereof represents a photoelectric conversion unit. The spectral transmittance characteristics of the green 1 and green 2 color filters are the same, but the wiring structure inside the pixels is slightly different and the arrangement of surrounding pixels is also different, so the crosstalk characteristics are also slightly different. Therefore, in this embodiment, the pixels are handled as different types of pixels.

  A second pixel group 221 is used for focus detection and is discretely arranged between the first pixel groups in accordance with a predetermined arrangement rule. In the second pixel group 221 (focus detection pixel group), two pairs 221a and 221b form a pair, and a pupil division function for phase difference detection is given by a method described later. Then, a focus detection signal is created from the outputs of the plurality of pixels 221a spaced apart in the X-axis direction and the outputs of the plurality of pixels 221b in the same region.

  Reference numeral 231 denotes a third pixel group (focus detection pixel group) which is also used for focus detection and is discretely arranged between the first pixel groups in accordance with a predetermined arrangement rule. The third pixel group 231 is also paired with two of 231c and 231d. The second pixel groups 221a and 221b perform pupil division in the X direction, while the third pixel groups 231a and 231b perform pupil division in the Y direction. The third pixel group also connects a plurality of pixel outputs spaced apart in the Y-axis direction to create a focus detection signal.

  The second and third pixel groups are arranged by replacing R and B in the first pixel group. The reason is as follows. When obtaining an image signal for recording or viewing, the main component of luminance information is acquired with G pixels. Since human image recognition characteristics are sensitive to luminance information, image quality degradation is easily recognized when G pixels are lost. On the other hand, the R or B pixel is a pixel that acquires color information (color difference information). However, since human visual characteristics are insensitive to color information, the pixel that acquires color information may have some loss. Image quality degradation is difficult to recognize. Therefore, in this embodiment, the G pixel is left as an imaging pixel, and a part of the R and B pixels is replaced with the second and third pixel groups for focus detection. For the color filters of the second and third pixel groups, a material having a high transmittance over the entire visible light band is used. This filter is called a transparent filter.

  FIG. 4 is a diagram showing a conjugate relationship of the photoelectric conversion unit with respect to the structure of the first pixel group and the exit pupil of the photographing optical system. FIG. 4A is a plan view showing a 2 × 2 portion of the first pixel group. FIG. 4B shows a cross section AA in FIG. ML is an on-chip microlens disposed on the forefront of each pixel, CFR is an R (Red) color filter, and CFG1 is a G1 (Green) color filter. PD (Photo Diode) schematically shows the photoelectric conversion unit of the C-MOS sensor described in FIG. 3, and CL (Contact Layer) forms a signal line for transmitting various signals in the C-MOS sensor. This is a wiring layer. TL schematically shows the photographing optical system.

  Here, the on-chip microlens ML and the photoelectric conversion unit PD of each pixel are configured to capture as effectively as possible the light flux that has passed through the photographing optical system TL (Taking Lens). In other words, the exit pupil EP (Exit Pupil) of the photographing optical system TL and the photoelectric conversion unit PD are designed to have a conjugate relationship with the microlens ML, and the effective area of the photoelectric conversion unit PD is as large as possible. In FIG. 4B, the incident light beam of the R pixel has been described, but the G1, G2, and B pixels have substantially the same structure. Accordingly, the exit pupil EP corresponding to each of the RGB pixels of the first pixel group has a large diameter, and the light flux (photon) from the subject is efficiently captured to improve the S / N of the image signal.

  FIG. 5 is a diagram showing the structure of the second pixel group and the pupil division function in the exit pupil of the photographing optical system. FIG. 5A is a plan view showing a 2 × 2 column portion including the second pixels 221a and 221b.

  FIG. 5B shows a cross section AA 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 imaging device, the opening width of the lowermost wiring layer CL1 is set to be narrower than the dimension of the photodiode PD, and the opening center is deviated in one direction with respect to the center line of the microlens ML. is doing. Specifically, since the opening OPHA of the pixel 221a is biased to the right side, the light beam that has passed through the left exit pupil EPHA of the imaging optical system TL is received. Similarly, since the opening OPHB of the pixel 221b is biased to the left side, the light beam that has passed through the right exit pupil EPHB of the imaging optical system TL is received. Therefore, the pixels 221a are regularly arranged in the X direction, and the subject image acquired by these pixel groups is defined as an A image. In addition, if the pixels 221b are also regularly arranged in the X direction and the subject image acquired by these pixel groups is a B image, by detecting the relative position (lateral shift amount in the X direction) of the A image and the B image, A focus shift amount (defocus amount) of the subject image can be detected.

  In the second pixel groups 221a and 221b, focus detection is possible for an object having a luminance distribution in the X direction on the shooting screen, for example, a vertical line, but focus detection is not possible for a horizontal line having a luminance distribution in the vertical direction. It is. Therefore, in the present embodiment, by using the third pixel groups 231a and 231b that perform pupil division in the Y direction, it is possible to detect a focus even on an object having a luminance distribution in the Y direction. The principle of pupil division of the third pixel group can be considered by replacing the X axis and Y axis in FIG.

  FIG. 6 is a diagram for explaining a crosstalk relationship between pixels and a pixel arrangement for obtaining crosstalk information. FIG. 6A is a diagram illustrating a crosstalk phenomenon in the vicinity of the second pixel group in the imaging region 107im of FIG. All pixels receive light waves and charge leakage from neighboring pixels, and part of the light waves and charges received by the pixels leak to the adjacent pixels. This is indicated by arrows. Since crosstalk is known to be large between pixels adjacent vertically and horizontally and relatively small between pixels adjacent to each other in the diagonal direction, in this embodiment, it is assumed that there is no crosstalk in the diagonal direction. To do.

  Here, the crosstalk that causes distortion of the focus detection signal is a component received by the second pixels 221a and 221b from surrounding pixels. That is, in the pixel 221a, leakage from two G1 pixels adjacent in the X direction and leakage from two G2 pixels adjacent in the Y direction are the main components of crosstalk. Similarly, in the pixel 221b, leakage from two G2 pixels adjacent in the X direction and leakage from two G1 pixels adjacent in the Y direction are the main components of crosstalk. That is, there are two main sources of crosstalk of focus detection pixels, G1 and G2, and the directions are four directions, positive and negative in the X direction and positive and negative in the Y direction. Therefore, it is only necessary to obtain a total of 8 types of crosstalk information of 2 types of pixels × 4 types of directions.

  FIG. 6B is an explanatory diagram of a pixel arrangement for obtaining crosstalk information. In the region of 4 vertical rows × 6 horizontal columns = 24 pixels, one each of the first pixels 211G1 and 211G2 is arranged in a normal state as illustrated. The other pixels are light-shielding pixels 211BLK in which light shielding processing is performed between the on-chip microlens and the photoelectric conversion unit. Crosstalk between these pixels is indicated by an arrow. Since the light-shielded pixels are optically shielded, the crosstalk is only a component that goes in the four directions from the two pixels 211G1 and 211G2.

  Here, the information necessary for performing the crosstalk correction on the focus detection signal is the crosstalk information in the X and Y directions of the G1 and G2 pixels as described above. These eight types of information may each refer to the output of the next pixel. First, the X direction crosstalk of the pixel G1 is obtained from the outputs of the pixels G1x + and G1x− adjacent to the left and right, and the Y direction crosstalk is obtained from the outputs of the pixels G1y + and G1y− adjacent to the top and bottom. The X direction crosstalk of the pixel G2 is obtained from the outputs of the pixels G2x + and G2x− adjacent to the left and right, and the Y direction crosstalk is obtained from the outputs of the pixels G2y + and G2y− adjacent to the top and bottom.

  FIG. 6C shows a pixel arrangement in the crosstalk information acquisition region. One row and one column of light-shielding pixels are further outside the 4 rows × 6 columns = 24 pixels shown in FIG. 6B. Is added so that the leakage into the crosstalk information acquisition pixel is limited to the leakage originating from the two pixels 211G1 and 211G2 arranged in the center. Then, this 6 rows × 8 columns = 48 pixels is set as a minimum unit, and these minimum units are arranged in eight crosstalk information acquisition regions 107ct in FIG.

  FIG. 7 is a diagram illustrating the structure of a light-shielding pixel for acquiring crosstalk information and the conjugate relationship of the photoelectric conversion unit with respect to the exit pupil of the imaging optical system. FIG. 7A is a plan view in which a 2 × 2 column portion including the pixel 211G1 of FIG. 6B and the light shielding pixel adjacent thereto is taken out.

  FIG. 7B shows a cross section AA in FIG. The conjugate relationship between the photoelectric conversion unit and the exit pupil of the photographing optical system in the left pixel 211G1 is the same as that of the pixel 211R in FIG. On the other hand, in the light shielding pixel G1x +, the opening of the uppermost wiring layer CL3 is completely shielded, and direct light incident from the microlens cannot reach the photoelectric conversion unit. That is, the output of the pixel G1x + can be regarded as a light wave and charge leakage component from the adjacent pixel 211G1.

  FIG. 8 is a diagram showing a crosstalk measurement method and measurement results for an image signal. In front of the image sensor 107, a measurement photographing optical system simply expressed by the exit pupil TL is disposed, and a uniform luminance surface ILM composed of a surface light source and a diffusion plate is disposed on the object side. In this measurement system, an appropriate exposure amount is given to the image sensor while changing the aperture value of the photographing optical system. Then, the X method and the Y direction crosstalk described in FIG. 6B are calculated for the predetermined pixel arranged in the crosstalk information acquisition region 107ct of FIG.

  FIG. 8B shows an example of the crosstalk measurement result when the aperture value of the photographing optical system is F2.8, and FIG. 8C shows an example of the crosstalk measurement result when F8. The numerical values in both figures show the signals output from the surrounding eight pixels when the output of the central imaging pixel is 1, and these numerical values correspond to the crosstalk rate. Crosstalk is caused by leakage of light waves and charges between adjacent pixels, but the incident angle characteristics of light waves incident on the pixels depend on the F value and image height of the imaging optical system, so the crosstalk rate is also F value. It varies depending on the position on the image plane. Here, the correction method based on the position will be described with reference to FIG.

  FIG. 8D shows an arrangement of the crosstalk information acquisition area 107ct shown in FIG. AFW1 and AFW2 are focus detection areas selected based on the result of subject recognition or the like. Here, the crosstalk information acquisition area 107ct is arranged outside the imaging area. On the other hand, the focus detection area is in the imaging area, and its position is different from that of the crosstalk information acquisition area. If the set of crosstalk ratios shown in FIG. Therefore, the crosstalk rate in an arbitrary focus detection region can be calculated by interpolating (interpolating) the crosstalk rates in the plurality of crosstalk information acquisition regions 107ct based on the coordinates of the focus detection region of interest. it can. FIG. 8D shows a state in which the crosstalk rate in the focus detection region of interest is calculated using the values of the three crosstalk information acquisition regions 107ct, but other interpolation methods may be used. I do not care.

  FIG. 9 is a schematic configuration diagram of an apparatus for measuring the pupil intensity distribution of each pixel arranged on the image sensor. The pupil intensity distribution refers to the direction dependency of the light receiving efficiency in the pixel, and will be described in detail later. REF is a projection plane, which is a plane defined at a position separated from the image sensor 107 in the Z direction (optical axis direction) by a predetermined dimension, and is defined as a plane substantially equivalent to the plane on which the exit pupil TL of the imaging optical system is located. Is done. LS is a light source, and is configured to freely move in the X direction and the Y direction on the projection plane REF.

  In this apparatus, a square lattice having a predetermined pitch is set on the projection plane REF, and the light source LS is driven to predetermined coordinates (X, Y) on the lattice. When the image pickup operation of the image pickup device is performed, the output obtained from each pixel of the image pickup device 107 at this time is incident on the light receiving efficiency of each pixel at a predetermined coordinate (X, Y) on the exit pupil plane of the photographing optical system. It can be regarded as direction dependency. Therefore, by driving the light source over the entire surface of the projection plane REF and processing the output signal of each pixel at each light source position, it is possible to obtain the incident direction dependency distribution of the light reception efficiency of each pixel in the exit pupil region. .

  FIG. 10 is a diagram for explaining the light receiving characteristics of each pixel shown in FIGS. FIG. 10A is a plan view in which the focus detection pixel 221a and the imaging pixel 211G1 are extracted from the four pixels illustrated in FIG. Here, as shown in FIGS. 4B and 5B, the photoelectric conversion unit PD of each pixel is projected onto the exit pupil plane of the photographing optical system by the on-chip microlens ML.

  FIG. 10B is a plan view showing a projection image of the photoelectric conversion unit of each of the two types of pixels and a projection image of the exit pupil of the photographing optical system in the projection plane shown in FIG. EP211 is a projection image of the photoelectric conversion unit of the imaging pixel 211G1, and EP221a is a projection image of the photoelectric conversion unit of the focus detection pixel 221a. TL is a projection image of the exit pupil of the photographing optical system.

  FIG. 10C is a light receiving characteristic in the section AA in FIG. 10B, the horizontal axis represents the horizontal coordinate on the projection plane, and the vertical axis represents the light receiving efficiency of the photoelectric conversion unit. 4 and 5, it has been described that the photoelectric conversion unit arranged in the pixel is in a conjugate relationship with the exit pupil of the photographing optical system by the on-chip microlens. This means that only the light beam passing through the common area of the exit pupil TL of the photographing optical system and the projection image EP of the photoelectric conversion unit on the exit pupil plane reaches the photoelectric conversion unit. Therefore, the projection image corresponds to a pixel-specific aperture stop arranged on the exit pupil plane of the photographing optical system, that is, the projection plane REF, and the vertical axis in FIG. 10C represents the transmittance distribution of each aperture stop. become. This transmittance distribution can be regarded as the light beam receiving efficiency of the photoelectric conversion unit. The distribution characteristic of the light beam receiving efficiency is referred to as “pupil intensity distribution” for convenience.

  Here, if the projection performance by the on-chip microlens is geometrically optically free of aberrations, the pupil intensity distribution is a step function having only one value of zero or one. However, since the size of each pixel is as small as about several μm, the sharpness of the image of the photoelectric conversion unit projected on the exit pupil plane is reduced due to light diffraction. Further, since the on-chip microlens is usually a spherical lens, the sharpness of the projected image is also reduced by spherical aberration. Therefore, the pupil intensity distribution of each pixel is also blurred, the shoulder of the step function is rounded, and the base is a shape with a skirt. For example, since the center of the photoelectric conversion unit of the imaging pixel 211G1 coincides with the optical axis of the microlens ML, the pupil intensity distribution EP211 is symmetric with respect to the central axis in the X direction, and the center of gravity is also located on the central axis. . In contrast, since the photoelectric conversion unit of the focus detection pixel 221a is deviated with respect to the optical axis of the microlens, the center of gravity of the pupil intensity distribution EP221a is also deviated in the positive direction of the X axis with respect to the central axis. . The shape is asymmetrical with respect to the axis passing through the center of gravity, and the skirt in the negative direction of the X axis is long. This is mainly due to distortion in the pupil intensity distribution due to crosstalk from adjacent pixels.

  FIG. 10D is a plan view in which a total of three pixels, that is, the light-shielding pixels G1x− and G1x + adjacent to the imaging pixel 211G1 shown in FIG.

  FIG. 10E is a plan view showing a projection image of the above-described three-pixel photoelectric conversion unit on the projection plane REF. EP211 is a projection image of the photoelectric conversion unit of the imaging pixel 211G1, and is the same as EP211 shown in FIG. In addition, regarding the light-shielding pixel, since the light-shielding member is disposed between the microlens and the photoelectric conversion unit, there is no projection image of the photoelectric conversion unit.

  FIG. 10F is a pupil intensity distribution in the AA cross section of FIG. 10E, and the horizontal axis and the vertical axis are the same as those in FIG. EP211 is the pupil intensity distribution of the imaging pixel 211G1, and its shape is substantially the same as the pupil intensity distribution EP211 shown in FIG. 10C, but the intensity is slightly smaller. The reason for this is that the characteristic of FIG. 10C includes crosstalk from adjacent pixels, whereas in FIG. Because there is no.

  On the other hand, CTx− is the pupil intensity distribution of the light shielding pixel G1x−. The pupil intensity distribution of the light-shielded pixels should be zero over the entire area on the X axis, but shows a certain value in the pupil intensity distribution due to leakage of light waves and charges from adjacent imaging pixels. That is, crosstalk between adjacent pixels also occurs in the pupil intensity distribution, and the pupil intensity distribution CTx− can be regarded as crosstalk that the imaging pixel 211G1 gives to pixels adjacent in the negative direction on the X axis. Similarly, CTx + is a pupil intensity distribution of the light-shielding pixel G1x +, and is crosstalk that the imaging pixel 211G1 gives to pixels adjacent in the positive direction on the X axis.

  FIG. 10G is a diagram illustrating the characteristics before and after crosstalk correction in the pupil intensity distribution of the focus detection pixels. EP221a is a pupil intensity distribution before crosstalk correction in the focus detection pixel 221a, and is a waveform EP221a shown in FIG. CTx + and CTx− are crosstalk from the imaging pixel to the focus detection pixel, and are the waveforms CTx + and CTx− shown in FIG. EP221act is a pupil intensity distribution after crosstalk correction, which is obtained by subtracting CTx + and CTx− from the waveform EP221a. By applying crosstalk correction to the pupil intensity distribution in this way, waveform distortion caused by crosstalk is reduced, and the accuracy of focus detection using the pupil intensity distribution is improved as will be described later.

  Since the pupil intensity distribution EP221a of the focus detection pixels shown in FIG. 10C varies depending on the image height, it is preferable to store a value for each of a plurality of representative positions on the photographing screen. Further, the crosstalk waveforms CTx + and CTx− shown in FIG. 10F are values acquired outside the imaging screen. Therefore, the crosstalk correction of the pupil intensity distribution shown in FIG. 10G is also performed according to the position of the focus detection pixel as shown in FIG.

  FIG. 11 is a diagram for explaining a signal processing method for obtaining correction information of the focus detection image signal from the pupil intensity distribution. FIG. 11A is a plan view of the pupil intensity distribution of the focus detection pixels projected on the projection plane REF and the exit pupil of the photographing optical system, and shows a state at the center of the photographing screen. EP221a and EP221b are contour lines showing the pupil intensity distribution on the two-dimensional plane for the focus detection pixels 221a and 221b. This value is measured by the apparatus of FIG. 9 and shows the result of crosstalk correction by the method of FIG. In FIG. 10G, the pupil intensity distribution after crosstalk correction is expressed as EP221act, but the letters “ct” are omitted in FIG. TL is an exit pupil of the photographing optical system, that is, an aperture through which a focus detection light beam can pass.

  Projecting the pupil intensity distributions EP221a and EP221b in the exit pupil TL shown in FIG. 11A onto the X axis is PRJa and PRJb in FIG. 11B. This projection is substantially equivalent to a line image distribution waveform described later, and is used to create an image correction filter for correcting a focus detection image distorted by vignetting.

  On the other hand, the projection center-of-gravity interval XG corresponds to the baseline length of the phase difference focus detection system. Since this base line length is used when the lateral shift amount of the two images for focus detection is converted into the defocus amount, the center-of-gravity interval is also calculated in the focus detection calculation described later. Further, the value obtained by integrating this projection in the X-axis direction, that is, the area of the projection waveform, is proportional to the total amount of light emitted from the reference uniform luminance light source, passing through the exit pupil of the photographing optical system, and entering the pixel. That is, since the integral value of the projection of each pixel is equivalent to the light receiving efficiency in that pixel, the integral value can be used as a coefficient for shading correction of the focus detection signal.

  FIG. 11C shows the pupil intensity distribution and the exit pupil at the peripheral positions on the imaging screen. The pupil intensity distributions EP221a and EP221b of the focus detection pixels are substantially the same as those in FIG. It is. On the other hand, the shape of the exit pupil TL of the photographing optical system changes due to vignetting, and the dimension in the X direction is small. If the distance from the image plane to the exit pupil deviates from the standard distance, the center of the opening is also decentered from the symmetry axis of the pupil intensity distribution.

  FIG. 11D shows the projection of the pupil intensity distribution in FIG. It can be seen that the shapes (width and maximum strength) of the projections PRJa and PRJb differ depending on vignetting. Accordingly, the projection center-of-gravity interval XG and the integral value of the projection used as shading correction information are also different.

  FIG. 12 explains the relationship between the projection explained in FIG. 11 and the line image distribution waveform at the time of defocusing. The subject is a thin white line drawn on a black background, and the line width is a value that can be regarded as substantially zero. The pixel of interest is a focus detection pixel 221a, and a projection image EP221a of the photoelectric conversion unit of this pixel is projected onto the exit pupil plane of the photographing optical system. This projection image EP221a corresponds to the pupil intensity distribution EP221a shown in FIG. 11A, and a light beam corresponding to this pupil intensity distribution reaches the focus detection pixels. This situation is equivalent to a gradation ND filter having a transmittance distribution having the same characteristics as the pupil intensity distribution described above being arranged on the exit pupil plane of the photographing optical system.

  The light beam emitted from the thin line subject passes through the region EP221a on the exit pupil plane of the photographing optical system and converges on the image plane. Assuming that there is no influence of aberration and diffraction in this imaging system, the subject image at the in-focus position is a line image having a width of zero, and the illuminance distribution LNa0 at the cross section obtained by cutting the line image at an arbitrary position has a width. It becomes a zero δ function. On the other hand, at the front pin position where the defocus amount is DEF, a blurred line image is projected, and the shape of the illuminance distribution LNa + at an arbitrary position is similar to the projection PRJa shown in FIG. It can be seen that the width of the illuminance distribution LNa + is proportional to the defocus amount DEF. The illuminance distribution LNa− of the blurred line image at the rear pin position can be obtained in the same manner, but the shape thereof is obtained by reversing the projection PRJa of FIG.

  That is, the line image waveform LNa + or LNa− is a transfer function that associates a thin line subject with the line image, and this transfer function is obtained from the projection PRJa of the pupil intensity distribution shown in FIG. . However, since the width of the line image waveform is proportional to the defocus amount, the defocus amount must be known in order to obtain an accurate line image. On the other hand, since the defocus amount is unknown at the time of focus detection, the line image waveform cannot be obtained at the start of focus detection, and the distortion of the focus detection image cannot be corrected. A method for avoiding this problem will be described later.

  FIG. 13 is a diagram for explaining waveforms before and after performing various corrections on the focus detection image signal. The subject here assumes that two white lines are printed on a black background, and the reflectance of these two white lines is slightly different. FIG. 13A shows the waveform of the subject image output by the imaging pixel during focusing.

  FIG. 13B shows a pair of focus detection images at the time of defocusing, AFa is an output waveform of the pixel group 221a, and AFb is an output waveform of the pixel group 221b. Due to the defocused state, the one-to-two image has a lateral shift relative to the X-axis method. If the two images have the same shape and only a lateral shift occurs, the lateral shift amount of the two images can be accurately calculated by a known correlation calculation. However, in the focus detection system used in the present embodiment, The two images are distorted mainly for the following three reasons.

  The first reason is a light amount difference due to vignetting. When the subject has uniform luminance, the amount of light incident on the focus detection pixels is the integrated value of the pupil intensity distribution of each pixel in the exit pupil TL of the photographing optical system, as shown in FIG. 11 (a) or (c). Is proportional to The position and area of the exit pupil TL change depending on the image height due to the effect of vignetting. Therefore, the amount of light incident on the focus detection pixels 221a and 221b also varies depending on the image height, and a light amount drop phenomenon called so-called shading occurs. Therefore, the output intensity of the two images has a coordinate dependency, resulting in different waveforms.

  The second reason is crosstalk in the image signal. Here, it is assumed that there is no influence of the shading, that is, no influence of vignetting, and that the one-to-two images for focus detection are completely coincident at the time of focusing. At the time of focusing, there is no lateral shift between the two images, and the signal change due to crosstalk is substantially the same for the two images, so the degree of coincidence between the two images is maintained. On the other hand, since the two images at the time of defocusing are shifted in the X-axis direction, the influence of crosstalk on the focus detection signal waveforms AFa and AFb is different. Therefore, the degree of coincidence between the two images is reduced.

  The third reason is image distortion due to vignetting. As described with reference to FIG. 12, since the transfer function that defines the relationship between the subject and the image is a δ function at the time of focusing, the focus detection image is similar to the subject, and the two images match. On the other hand, the image signal waveform at the time of defocusing has a shape obtained by convolving and integrating the line image distribution function with the waveform at the time of focusing. Since the line image distribution waveforms of the focus detection pixels 221a and 221b are different from each other, the two images at the time of defocusing have different shapes.

  The distortion of the focus detection signal due to these three causes is corrected as follows in the present embodiment.

  First, a method for correcting a light amount difference due to vignetting will be described. In FIG. 11B, it has been described that the integral value of the projection waveform is the light receiving efficiency of the pixel. Therefore, shading correction is performed by calculating the integral value of projection for each focus detection pixel used for focus detection and multiplying the reciprocal thereof by the output of the focus detection pixel (calculating a correction value). That is, a pixel with low light receiving efficiency has a small integral value of projection and a large reciprocal value thereof, so that it is possible to correct signal distortion due to a difference in light receiving efficiency.

  Crosstalk of the second image signal is obtained by extracting signals of focus detection pixels and image pickup pixels surrounding the focus detection pixels and performing signal subtraction processing based on the crosstalk rate obtained in FIG. 8B or 8C. Good.

The image distortion due to the third vignetting is
AFa ← AFa * LNb (1)
AFb ← AFb * LNa (2)
Correct with the following formula. LNa and LNb are line images shown in FIG. 12, and * represents a convolution operation. Note that the line images LNa and LNb are processed so that the area and the center of gravity position coincide with each other so as not to affect the gain and phase of the focus detection signal to be corrected. Here, the reason why the pair of focus detection signals are convolved with the other line image distribution waveforms is as follows.

  According to FIG. 12, the image signal acquired by the focus detection pixel 221a is obtained by convolving and integrating the line image LNa with an ideal image signal. Similarly, the image signal acquired by the focus detection pixel 221b is obtained by convolving and integrating the line image LNb with an ideal image signal. Therefore, when the line image LNb is convolved and integrated with the image signal AFa, the obtained signal is equivalent to the ideal image signal obtained by convolving and integrating both the line images LNa and LNb. Similarly, when the line image LNa is convolved and integrated with the image signal AFb, the obtained signal is equivalent to the ideal image signal obtained by convolving and integrating both the line images LNa and LNb. Therefore, the distortion characteristics of the one-to-two image are the same, and the two images corrected by the equations (1) and (2) have the same shape and only a lateral shift occurs.

  Here, the above-described line images LNa and LNb are obtained from the projection of FIG. 11B or 11D and the defocus amount, but since the defocus amount is unknown at the time of focus detection, the line image can be obtained. There is a problem that you can not. A method for solving this problem will be described with reference to a flowchart described later.

  By performing the above three types of correction, the two images for focus detection are restored so as to have the same shape as shown in FIG. 13C, and only the lateral shift remains. Therefore, by applying a known correlation calculation to the corrected waveform, the amount of lateral deviation between the two images can be accurately calculated, and accurate focus detection can be performed.

  FIG. 14 shows the configuration of the readout circuit in the image sensor of this embodiment. Reference numeral 151 denotes a horizontal scanning circuit, and 153 denotes a vertical scanning circuit. A horizontal scanning line 152 and a vertical scanning line 154 are wired at the boundary between the pixels, and signals are read out to the photoelectric conversion units through the scanning lines.

  Note that the image sensor of the present embodiment has the following two types of readout modes. The first readout mode is called an all-pixel readout mode and is a mode for capturing a high-definition still image. In this case, signals of all pixels are read out. The second readout mode is called a thinning readout mode, and is a mode for performing only moving image recording or preview image display. In this case, since the number of pixels required is smaller than the total number of pixels, the first pixel group reads only the pixels thinned out at a predetermined ratio in both the X direction and the Y direction. Further, the focus detection function is maintained by reading out all of the second and third pixel groups.

  FIG. 15 is a diagram illustrating a defocus map obtained from an image and a focus detection signal acquired at the time of focus detection, and a focus detection result. In FIG. 15 (a), the subject image formed on the imaging surface includes a person in the foreground in the center, a tree in the middle foreground on the left, and a mountain range in the foreground on the right. The case where the signal from the second pixel group 222 is adopted as the focus detection signal in FIG. 15 will be described.

  In FIG. 15A, 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 pair of focus detection signals AFa and AFb are obtained by the second pixel group 222 around the face area. For areas other than the face, focus detection areas are set over the entire shooting screen at a predetermined pitch. The left of FIG. 15A shows a focus detection area corresponding to a tree trunk and its signal, and the upper right shows a focus detection area corresponding to a ridgeline of a mountain and its signal. Since the pair of signals obtained in each focus detection area are laterally displaced, the lateral displacement amount u (unit converted to mm) is calculated by a known correlation calculation. Then, the defocus amount DEF (unit: mm) is calculated using the following equation (3).

θ × DEF = u (3)
In the above equation, θ is the baseline length in the phase difference focus detection system, and corresponds to the projection center-of-gravity interval XG shown in FIG. However, since the unit is radians, a value obtained by dividing the centroid distance XG (unit: mm) by the distance (unit: mm) to the projection plane REF is used.

  Thereafter, the focus lens of the photographic optical system is driven so that the defocus amount is zero for the main subject, that is, the face region located in the center in FIG.

  In the above focus adjustment process, defocus information on the entire surface of the photographing screen, so-called defocus map, can be acquired. One example is shown in FIG. This figure shows an example in which the defocus amounts are consolidated and integrated based on a predetermined resolution, and are integrated into DEF0 to DEF3 in order from the region with the smallest defocus amount.

  Note that when creating a defocus map, it is necessary to set a distance measurement area over the entire imaging area, so in order to increase the data resolution, the focus detection time becomes longer, which may reduce the responsiveness of the camera. . In that case, the resolution of the defocus map created in the camera at the time of imaging is rough, and a high-resolution defocus map may be created by an external computer after shooting.

  16 and 17 are flowcharts for acquiring the crosstalk information of the image sensor. In the manufacturing process of the camera including the image sensor, two types of crosstalk information are acquired based on the principle described with reference to FIGS. When executing this flow, the external PC 141 and the camera CPU shown in FIG. 1 cooperate to execute each step.

  FIG. 16 is a flowchart for acquiring the crosstalk rate of the image signal. The camera of the present embodiment shown in FIG. 1 acquires crosstalk information using the apparatus shown in FIG. 8 in the manufacturing process.

  In step S172, the aperture value is set, but in the first measurement, the aperture value is set to open. In step S173, the accumulation time is set based on the set aperture value and the luminance setting value of the uniform luminance surface so that the charge accumulation amount of the image sensor becomes appropriate. In step S174, imaging is performed. In step S175, the output of each pixel in the crosstalk information acquisition area is processed, and the crosstalk rate shown in FIG. 8B is calculated and stored in the in-camera CPU. In step S176, the aperture value is determined. If the measurement has not been completed for all aperture values, the process returns to step S172 to change the aperture value and repeat the same measurement. When the measurement of all the aperture values is completed, the process proceeds from step S176 to step S177, and the acquisition of the crosstalk information of the image signal is completed.

  FIG. 17 is a crosstalk measurement flow of pupil intensity distribution. As shown in FIG. 9, this measurement method does not require a photographing optical system, and therefore is performed with the measurement optical system removed. In step S182, the position of the light source LS shown in FIG. 9 is controlled. Initially, the initial position, for example, the X and Y coordinates are both driven to the maximum value in the positive driving range. In step S183, the accumulation time is set so that the charge accumulation amount of the image sensor is appropriate. In this measurement, the brightness and accumulation time of the light source may be constant over the entire measurement process. In step S184, imaging is performed. In step S185, the image signal of the pixel from which pupil intensity distribution information is to be acquired is temporarily stored. In step S186, it is determined whether measurement at all coordinates of the light source LS is completed. If the measurement is not completed, the process returns to step S182 to drive the light source LS to the next measurement coordinate and repeat the same measurement.

  When the measurement at all the set coordinates is completed, the process proceeds from step S186 to step S187, and a pupil intensity distribution at a predetermined pixel is created and stored. This is a process of organizing the data formats shown in FIGS. 10C and 10F from a plurality of sets of image information acquired in steps S182 to S186. In step S188, the acquisition of the pupil intensity distribution and its crosstalk information is completed.

  18 and 19 are flowcharts for explaining the focus adjustment and photographing process of the camera according to the present embodiment. The control flow after FIG. 18 will be described with reference to each of FIGS. 1 to 17 described above.

  FIG. 18 is a main flow of the camera. When the photographer turns on the power switch of the camera, in step S102, the CPU 121 confirms the operation of each actuator and image sensor in the camera, initializes the memory contents and the execution program, and executes the shooting preparation operation.

  In step S103, the setting of the photographing condition is accepted. Specifically, it accepts that the photographer sets the exposure adjustment mode, the focus adjustment mode, the image quality (the number of recorded pixels and the compression rate), and the like. In step S104, the zoom state, focus lens state, and aperture state of the photographing optical system are detected, and information such as the exit pupil size and exit pupil distance is read from the ROM. In step S105, the image pickup operation of the image pickup device is performed and the pixel signal is read out. In step S107, a reduced display image is created from the read pixel signal and displayed on the display 131 provided on the back of the camera. Then, the photographer looks at the preview image and performs composition determination, zoom operation, and the like.

  In step S121, a focus detection subroutine described later is executed. In step S151, it is determined whether or not the focus lens drive amount calculated in step S121 is equal to or less than a predetermined value. If the drive amount is less than or equal to the predetermined value, it is determined that focus is achieved, and the process jumps to step S153. On the other hand, if the lens driving amount is greater than or equal to the predetermined value, the focus lens is driven in step S152.

  In step S153, it is determined whether or not the photographing switch has been turned on. If not, the process jumps to step S181. If the photographing switch has been turned on, image recording is executed in step S161.

  In step S181, it is determined whether the main switch is off. If NO, that is, if the on state is maintained, the process returns to step S102, and steps S102 to S161 are repeatedly executed. If the main switch is turned off in step S181, step S182 and subsequent steps are executed.

  In step S182, the image recorded in step S161 is transmitted to the server computer via the Internet line. Then, the server computer executes processing with a large computation scale such as high-precision computation of the defocus map. In step S183, an image processed by the server computer is received. In step S184, the corrected portion processed by the server computer is added to the original image recorded in step S161, or replacement correction is performed. Then, in step S185, shooting is finished.

  FIG. 19 is a flowchart of the focus detection subroutine. When jumping from step S121 of the main flow to step S121 of this subroutine, in step S122, the subject pattern is recognized from the preview image, and the face image is discriminated and the contrast of the entire photographing screen is analyzed. In step S123, a focus detection area to be focused is determined from the recognition result in step S122. Here, the focus detection region is not limited to one location, and a plurality of locations may be selected. In step S124, a focus detection pixel signal included in the determined focus detection region is extracted to prepare a one-to-two image for correlation calculation. In step S125, the crosstalk rate of the image signal is calculated from the crosstalk information of the image signal measured and stored in the flow of FIG. 16 and the coordinates of the focus detection area. In step S126, the crosstalk correction of the focus detection signal is performed on the one-to-two image created in step S124 using the crosstalk rate calculated in step S125.

  In step S127, the exit pupil of the photographing optical system at this coordinate is calculated from the lens state detected in step S of the main flow and the coordinates of the focus detection area determined in step S123 of this flow, and FIG. Alternatively, the shape of the exit pupil TL on the projection plane REF shown in (c) is calculated. In step S128, the pupil intensity distribution in the focus detection pixel is read out, and in step S129, the crosstalk information of the pupil intensity distribution is read out. In step S130, crosstalk correction is performed on the pupil intensity distribution of the focus detection pixels from these pieces of information to calculate a pupil intensity distribution from which crosstalk has been removed. In step S131, the projection calculation of the pupil intensity distribution described in FIG. 11B is performed, and in step S132, the baseline length θ is calculated from the centroid interval of the one-to-two projection.

  In step S133, the shading correction coefficient is calculated by integrating the projection obtained in step 131. In step S134, the focus detection image signal processed in step S126 is multiplied by the shading correction coefficient calculated in step S133 to perform shading correction, thereby matching the signal intensity of the one-to-two image. In step S135, the lateral shift amount of the one-to-two image obtained in step S134 is calculated using a known correlation calculation method. In step S136, the defocus amount is calculated from the baseline length calculated in step S132 and the lateral shift amount of the two images calculated in step S135.

  In step S141, the size of the defocus amount is determined. If the defocus amount is not more than a predetermined value and can be regarded as substantially in focus, a defocus map is created for the entire shooting screen in step S142. On the other hand, if it is determined in step S141 that the image is out of focus, the process proceeds to step S143. In step S143, the line image distribution waveform LNa described in FIG. 14 is obtained from the projection calculated in step S131 and the defocus amount calculated in step S136, and this is used as an image correction filter. In FIG. 14, only the line image waveform of the focus detection pixel 221a is shown, but the line image waveform LNb of the other pixel 221b is obtained in the same manner. In step S144, the image correction filter obtained in step S143 is applied to the one-to-two image after shading correction obtained in step S134 in accordance with the above-described equations (1) and (2) to perform image correction.

  In step S145, the correlation calculation is performed again on the two corrected images, and the defocus amount is calculated in step S146. In step S147, it is determined whether or not the currently calculated defocus amount is different from the previously calculated defocus amount. When image correction is performed for the first time, the previously calculated defocus amount is the calculation without image correction calculated in step S136, and the defocus amount calculated this time is the calculation result with image correction. The focus detection signal used in the former is distorted by vignetting and has a large focus detection error. On the other hand, since the focus detection signal used in the latter is corrected for distortion due to vignetting, the focus detection error is also reduced. Therefore, the difference between the two becomes a predetermined value or more, and the process returns to step S143 to calculate the image correction filter again. As the defocus amount used at this time, the value calculated in step S146, that is, the value with reduced error can be used. Therefore, since the calculations executed in steps S144 to S146 can use two images in which distortion correction due to vignetting is corrected with higher accuracy, the focus detection error is also reduced.

  When the above steps S143 to S147 are repeatedly executed, the accuracy of image correction gradually improves, and the calculated defocus amount gradually approaches a true value. When the fluctuation of the focus detection result converges to a predetermined value or less, the process proceeds from step S147 to step S148, the last calculated defocus amount is converted into a lens drive amount, and the process returns to the main routine in step S149.

The actions and effects of the first embodiment are summarized as follows.
(1-1) When an image correction filter for correcting distortion of a focus detection signal due to vignetting is created, information that corrects crosstalk in the pupil intensity distribution is used. Correction accuracy is improved, and focus detection accuracy is improved.
(1-2) Since the crosstalk information detection pixels are arranged in a plurality of regions of the image sensor, accurate crosstalk information can be obtained and focus detection accuracy is improved.

(Second Embodiment)
In the first embodiment, a crosstalk information acquisition pixel group is arranged in an image sensor used for photographing. The second embodiment described below shows an embodiment in which crosstalk information is acquired using an image sensor dedicated for measurement, and the acquired information is provided to an image sensor for photographing.

  FIG. 20 shows a configuration of an imaging apparatus according to the second embodiment. In the measurement imaging apparatus 200, instead of the imaging element 107 included in the imaging apparatus 100 of the first embodiment shown in FIG. Image sensors 207 having different arrangements are incorporated. The CPU 121 is configured to be able to communicate with the imaging device 100 for shooting via the external PC 141. In addition, in the imaging device of the imaging apparatus 100, pixels for acquiring crosstalk information are omitted. That is, the measurement imaging apparatus 200 is used as a camera dedicated to acquiring crosstalk information, and the acquired crosstalk information is transferred to the imaging apparatus 100 via the external PC 141.

  FIG. 21 shows a pixel array region of the image sensor 207, which is a view of the light receiving surface of the image sensor 207 from the photographing optical system side, as in FIG. 2 of the first embodiment. Reference numeral 207im denotes an imaging region, and pixels for imaging and focus detection are two-dimensionally arranged on the XY plane in the same manner as 107im in FIG. And the specific part in it is replaced by the crosstalk information acquisition area 207ct. The pixel array of the crosstalk information acquisition area 207ct is the same as that in FIG. 6 of the first embodiment.

  22 and 23 are flowcharts for acquiring crosstalk information using the imaging apparatus 200. FIG. In the second embodiment, the image capturing apparatus 200 is used to acquire two types of crosstalk information based on the principle described with reference to FIGS. 8 to 10 as in the first embodiment. When this flow is executed, the acquired crosstalk information is temporarily stored in the external PC 141 shown in FIG. 20, and then transferred to the imaging device 100 for photographing.

  FIG. 22 is a flowchart for acquiring the crosstalk rate of the image signal. Information is acquired by the same method as the flowchart shown in FIG. 16 of the first embodiment. Has been added. Steps having the same contents as in FIG. 16 are denoted by the same numbers.

  In step S172, the aperture value is set, but in the first measurement, the aperture value is set to open. In step S173, the accumulation time is set based on the set aperture value and the luminance setting value of the uniform luminance surface so that the charge accumulation amount of the image sensor becomes appropriate. In step S174, imaging is performed. In step S175, the output of each pixel in the crosstalk information acquisition region is processed, and the crosstalk rate shown in FIG. 8B is calculated and stored in the in-camera CPU 121. In step S176, the aperture value is determined. If the measurement has not been completed for all aperture values, the process returns to step S172 to change the aperture value and repeat the same measurement.

  When the measurement of all the aperture values is completed, the process proceeds from step S176 to step S271, and the crosstalk information is transferred to the imaging device 100 for imaging via the external PC 141. Then, the process proceeds to step S177, and the acquisition of the crosstalk information of the image signal is completed.

  FIG. 23 shows a crosstalk measurement flow of pupil intensity distribution. Information is acquired by the same method as the flowchart shown in FIG. 17 of the first embodiment, but steps for temporarily storing and transferring data are added. . Steps having the same contents as those in FIG. 17 are denoted by the same numbers.

  Also in the measurement flow of the second embodiment, since the photographing optical system is not required as shown in FIG. 9, the measurement optical system is removed. In step S182, the position of the light source LS shown in FIG. 9 is controlled. Initially, the initial position, for example, the X and Y coordinates are both driven to the maximum value in the positive driving range. In step S183, the accumulation time is set so that the charge accumulation amount of the image sensor is appropriate. In this measurement, the brightness and accumulation time of the light source may be constant over the entire measurement process. In step S184, imaging is performed. In step S185, the image signal of the pixel from which pupil intensity distribution information is to be acquired is temporarily stored. In step S186, it is determined whether measurement at all coordinates of the light source LS is completed. If the measurement is not completed, the process returns to step S182 to drive the light source LS to the next measurement coordinate and repeat the same measurement.

  When the measurement at all the set coordinates is completed, the process proceeds from step S186 to step S187, and a pupil intensity distribution at a predetermined pixel is created and stored. This is a process of organizing the data formats shown in FIGS. 10C and 10F from a plurality of sets of image information acquired in steps S182 to S186. Subsequently, in step S281, crosstalk correction is performed on the pupil intensity distribution of the focus detection pixels to create information shown in FIG. In step S282, the crosstalk information is transferred to the imaging device 100 for photographing via the external PC 141. Then, the information is stored in the in-camera CPU 121, and the measurement of the pupil intensity distribution and the crosstalk correction are completed in step S188.

  When the two types of crosstalk information acquired in FIGS. 22 and 23 are transferred to the imaging apparatus 100 for photographing, the imaging apparatus 100 can perform focus detection using the crosstalk information. Since the main flow relating to shooting by the imaging apparatus 100 is substantially the same as that shown in FIG. 18 of the first embodiment, description thereof is omitted.

  FIG. 24 is a flowchart when focus detection is performed by the imaging apparatus 100 according to the second embodiment. The order of executing the crosstalk correction is different from the flow shown in FIG. 19 of the first embodiment, but the other steps are substantially the same, and the same steps are indicated by the same numbers. .

  When jumping from step S121 of the main flow to step S121 of this subroutine, in step S122, the subject pattern is recognized from the preview image, and the face image is discriminated and the contrast of the entire photographing screen is analyzed. In step S123, a focus detection area to be focused is determined from the recognition result in step S122. Here, the focus detection region is not limited to one location, and a plurality of locations may be selected. In step S124, a focus detection pixel signal included in the determined focus detection region is extracted to prepare a one-to-two image for correlation calculation.

  In step S127, the exit pupil of the imaging optical system at the coordinates is calculated from the lens state detected in step S104 of the main flow and the coordinates of the focus detection area determined in step S123 of the flow, and FIG. Alternatively, the shape of the exit pupil TL on the projection plane REF shown in (c) is calculated. In step S228, the crosstalk-corrected pupil intensity distribution acquired and transferred and stored in steps S281 and S282 in FIG. 23 is read. In step S131, the projection calculation of the pupil intensity distribution described in FIG. 11B is performed, and in step S132, the baseline length θ is calculated from the centroid interval of the one-to-two projection.

  In step S133, the shading correction coefficient is calculated by integrating the projection obtained in step 131. In step S134, the focus detection image signal processed in step S126 is multiplied by the shading correction coefficient calculated in step S133 to perform shading correction, thereby matching the signal intensity of the one-to-two image. In step S135, the lateral shift amount of the one-to-two image obtained in step S134 is calculated using a known correlation calculation method. In step S136, the defocus amount is calculated from the baseline length calculated in step S132 and the lateral shift amount of the two images calculated in step S135.

  In step S141, the size of the defocus amount is determined. If the defocus amount is not more than a predetermined value and can be regarded as substantially in focus, a defocus map is created for the entire shooting screen in step S142. On the other hand, if it is determined in step S141 that the image is out of focus, the process proceeds to step S241. In step S241, the crosstalk rate in the image signal acquired and transferred and stored in the flow of FIG. 22 is read, and in step S242, crosstalk correction is performed on the focus detection image signal. In step S243, the same shading correction as in step S134 is performed.

  In step S143, the line image distribution waveform LNa described in FIG. 14 is obtained from the projection calculated in step S131 and the defocus amount calculated in step S136, and this is used as an image correction filter. In FIG. 14, only the line image waveform of the focus detection pixel 221a is shown, but the line image waveform LNb of the other pixel 221b is obtained in the same manner. In step S144, the image correction filter obtained in step S143 is applied to the one-to-two image after shading correction obtained in step S134 in accordance with the above-described equations (1) and (2) to perform image correction.

  In step S145, the correlation calculation is performed again on the two corrected images, and the defocus amount is calculated in step S146. In step S147, it is determined whether or not the currently calculated defocus amount is different from the previously calculated defocus amount. When image correction is performed for the first time, the previously calculated defocus amount is the calculation without image correction calculated in step S136, and the defocus amount calculated this time is the calculation result with image correction. The focus detection signal used in the former is distorted by vignetting and has a large focus detection error. On the other hand, since the focus detection signal used in the latter is corrected for distortion due to vignetting, the focus detection error is also reduced. Therefore, since the difference between the two becomes a predetermined value or more, the process returns to step S241, and the image correction filter is calculated again in step S143. As the defocus amount used at this time, the value calculated in step S146, that is, the value with reduced error can be used. Therefore, since the calculations executed in steps S144 to S146 can use two images in which distortion correction due to vignetting is corrected with higher accuracy, the focus detection error is also reduced.

  When the above steps S241 to 147 are repeatedly executed, the accuracy of image correction gradually improves, and the calculated defocus amount gradually approaches a true value. When the fluctuation of the focus detection result converges to a predetermined value or less, the process proceeds from step S147 to step S148, the last calculated defocus amount is converted into a lens drive amount, and the process returns to the main routine in step S149.

  The focus detection subroutine of the second embodiment is different from the first embodiment in the following two points.

  The first difference is the presence or absence of crosstalk correction of the image signal during the first focus detection calculation. In the first embodiment, the crosstalk correction is performed on the image signal for focus detection used in the focus detection in steps S124 to S136, and the crosstalk correction is not performed in the second embodiment. The reason is as follows. If it is determined that the in-focus state is obtained by the first focus detection calculation, the one-to-two images coincide with each other, so that it is not necessary to perform crosstalk correction of the image signal. On the other hand, if it is determined that the in-focus state is out of focus in the first focus detection calculation, crosstalk correction is necessary, but at this time, it is executed in steps S241 and S242. That is, since the first crosstalk correction may be unnecessary, by performing this correction only when necessary, useless calculation can be omitted, and the focus detection calculation can be shortened in the second embodiment.

  The second difference is the execution timing of the crosstalk correction of the pupil intensity distribution. In the first embodiment, the focus detection subroutine of FIG. 19 is used. However, in the second embodiment, the crosstalk correction is also performed in the process of FIG. 23, that is, when the pupil intensity distribution crosstalk information is acquired. Then, the corrected pupil intensity distribution is stored in the imaging apparatus 100. Therefore, in the second embodiment, it is not necessary to carry out in the focus detection subroutine, and the focus detection time can be shortened.

According to the second embodiment described above,
(2-1) Since the information is acquired using a dedicated image sensor for detecting crosstalk information, the crosstalk information at an arbitrary position on the shooting screen can be obtained accurately, and the focus detection accuracy is improved. .
(2-2) Since the crosstalk correction of the image signal is performed only when necessary, useless calculation can be avoided, the focus detection time is shortened, and focus detection with good responsiveness is possible.
There is an effect.

  In the first and second embodiments described above, the embodiment of the consumer electronic camera capable of recording moving images and still images has been described. However, the focus detection device of the present technology includes various inspection cameras, survey cameras, The present invention may be applied to surveillance cameras, endoscope cameras, robot cameras, and the like.

Claims (5)

To divide an imaging pixel group that captures a subject image formed by a photographic optical system and an exit pupil of the photographic optical system, and perform phase difference type focus detection using a light beam from the divided area An image sensor including a focus detection pixel group;
Calculating means for calculating a predetermined signal in which a crosstalk component from an adjacent pixel in the focus detection pixel group is corrected, and performing a focus detection calculation using the image signal for focus detection corrected by the predetermined signal; ,
An imaging apparatus comprising: The calculation means further calculates a correction value for correcting distortion of the image signal due to vignetting of the photographing optical system with respect to the predetermined signal after correcting the crosstalk component. The imaging device according to claim 1.   The imaging apparatus according to claim 1, wherein the calculation unit further calculates information related to a baseline length for phase difference type focus detection based on the pixel signal after correcting the crosstalk component. .   The imaging apparatus according to claim 1, wherein the imaging element further includes a pixel group for detecting the crosstalk component.   4. The calculation unit according to claim 1, wherein the calculation unit calculates a correction value of the crosstalk component using information of a crosstalk component acquired by another imaging device for detecting the crosstalk component. The imaging device according to any one of the above.

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