Focus detection device and image sensor

Abstract

The present invention provides a focus detection device that can repeatedly detect the focus state of an optical system at appropriate timings. [Solution] A focus detection device comprising: an image sensor having multiple regions in which multiple pixel groups are arranged, each receiving light from a subject that has passed through an optical system and outputting a signal based on the received light; and a detection unit that detects the focus state of an image of the subject formed by the optical system based on the signal output from a number of pixel groups that is fewer than the number of pixel groups arranged in one of the regions, selected based on the contrast of the signals output from the pixel groups.

Description

[Technical Field]

[0001] The present invention relates to a focus detection device and an image sensor. [Background technology]

[0002] Conventionally, a technique has been known in which a focus detection device equipped with multiple light-receiving sensors calculates the amount of defocus for each of the multiple light-receiving sensors, and then selects one of the calculated defocus amounts to perform focus detection based on the selected defocus amount (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2003-215437 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, with conventional technology, the amount of defocus is calculated for all of the multiple light-receiving sensors, which takes time to calculate the amount of defocus. As a result, it was sometimes not possible to repeatedly detect the focus state of the optical system at the appropriate timing.

[0005] The problem that this invention aims to solve is to provide a focus detection device and an image sensor that can repeatedly detect the focus state of an optical system at an appropriate timing. [Means for solving the problem]

[0006] The present invention solves the above problems by the following means.

[0007] [1] A focus detection apparatus according to the present invention is an image sensor in which a plurality of focus detection areas are arranged, comprising: an image sensor having a plurality of pixels arranged in a first pixel row and a second pixel row within one focus detection area, the pixels receiving light that has passed through an optical system and outputting signals based on the received light; and a control unit that, based on contrast information of signals output from the plurality of pixels arranged in the first pixel row in the focus detection area and contrast information of signals output from the plurality of pixels arranged in the second pixel row in the focus detection area, specifies either one of the plurality of pixels arranged in the first pixel row and the plurality of pixels arranged in the second pixel row as the plurality of pixels to be used for calculating a defocus amount, and calculates the defocus amount using signals output from the specified plurality of pixels. [2] In the invention relating to the focus detection apparatus described above, the image sensor has a plurality of pixels arranged in a plurality of pixel rows including the first pixel row and the second pixel row, the pixels receiving light that has passed through an optical system and outputting signals based on the received light, and the control unit may specify said one as the plurality of pixels to be used for calculating a defocus amount based on contrast information of signals output from the plurality of pixels arranged in the plurality of pixel rows in the focus detection area. [3] In the invention relating to the focus detection apparatus described above, the control unit may specify, among the plurality of pixels arranged in the first pixel row and the plurality of pixels arranged in the second pixel row, one having higher contrast or one containing more high-frequency components as the plurality of pixels to be used for calculating a defocus amount. [4] In the invention relating to the focus detection apparatus described above, the control unit may specify said one as the plurality of pixels to be used for calculating a defocus amount based on high-frequency components of signals output from the plurality of pixels arranged in the first pixel row in the focus detection area and signals output from the plurality of pixels arranged in the second pixel row in the focus detection area. [5] In the invention relating to the focus detection device described above, the control unit may identify the plurality of pixels to be used for calculating the amount of defocus based on the different frequency components of the signals output from the plurality of pixels arranged in the first pixel row in the focus detection area and the plurality of pixels arranged in the second pixel row in the focus detection area. [6] In the invention relating to the focus detection device described above, the plurality of pixels may include pixels that receive light that has passed through the first pupil of the optical system and pixels that receive light that has passed through the second pupil of the optical system. [7] In the invention relating to the focus detection device described above, the control unit may detect the contrast information of the signals output from the plurality of pixels arranged in the first pixel row in the focus detection area selected via the operation unit and the contrast information of the signals output from the plurality of pixels arranged in the second pixel row in the focus detection area, and based on the detected contrast information, identify either the plurality of pixels arranged in the first pixel row or the plurality of pixels arranged in the second pixel row as a plurality of pixels to be used for calculating the amount of defocus. [8] In the invention relating to the focus detection device described above, the control unit performs face recognition processing on image data output from the image sensor, detects the contrast information of the signals output from the plurality of pixels arranged in the first pixel row in the focus detection area selected based on the result of the face recognition processing, and detects the contrast information of the signals output from the plurality of pixels arranged in the second pixel row in the focus detection area, and based on the detected contrast information, identifies either the plurality of pixels arranged in the first pixel row or the plurality of pixels arranged in the second pixel row as a plurality of pixels to be used for calculating the amount of defocus. [9] An image pickup device according to the present invention is an image pickup device in which a plurality of focus detection areas are arranged, the image pickup device comprising: a plurality of pixels arranged in a first pixel row and a second pixel row within one focus detection area, configured to receive light that has passed through an optical system and output signals based on the received light; and a calculation unit that, based on contrast information of signals output from the plurality of pixels arranged in the first pixel row in the focus detection area and contrast information of signals output from the plurality of pixels arranged in the second pixel row in the focus detection area, identifies either one of the plurality of pixels arranged in the first pixel row and the plurality of pixels arranged in the second pixel row as the plurality of pixels to be used for calculating a defocus amount, and transmits information of the identified plurality of pixels. Effects of the Invention

[0008] According to the present invention, detection of the focus state of an optical system can be repeatedly performed at appropriate timing. Brief Description of the Drawings

[0009] [Figure 1] FIG. 1 is a block diagram showing a camera according to the present embodiment. [Figure 2] FIG. 2 is a front view showing an image pickup surface of the image pickup device shown in FIG. 1. [Figure 3] FIG. 3 is a front view schematically showing an arrangement of image pickup pixels 221 and focus detection pixels 222a, 222b, obtained by enlarging portion III in FIG. 2. [Figure 4] FIG. 4(A) is an enlarged front view showing one of the image pickup pixels 221, FIG. 4(B) is an enlarged front view showing one of first focus detection pixels 222a, FIG. 4(C) is an enlarged front view showing one of second focus detection pixels 222b, FIG. 4(D) is an enlarged cross-sectional view showing one of the image pickup pixels 221, FIG. 4(E) is an enlarged cross-sectional view showing one of the first focus detection pixels 222a, and FIG. 4(F) is an enlarged cross-sectional view showing one of the second focus detection pixels 222b. [Figure 5] FIG. 5 is a cross-sectional view taken along line V-V in FIG. 3. [Figure 6]Figure 6 is a flowchart showing the operation of the camera according to the first embodiment. [Figure 7] Figure 7 is a diagram illustrating an example of the operation of camera 1 according to this embodiment. [Figure 8] Figure 8 is a diagram illustrating an example of how a conventional camera operates. [Figure 9] Figure 9 is a schematic diagram showing the arrangement of the first focus detection pixel 222a and the second focus detection pixel 222b according to this embodiment. [Figure 10] Figure 10(A) is a graph showing the relationship between the correlation amount and the shift amount in this embodiment, and Figure 10(B) is a graph showing the relationship between the correlation amount and the shift amount in the prior art. [Figure 11] Figure 11 is a flowchart showing the operation of the camera according to the second embodiment. [Figure 12] Figure 12 is a schematic front view showing the arrangement of focus detection pixels 222a and 222b according to another embodiment. [Figure 13] Figure 13 is a schematic front view showing the arrangement of focus detection pixels 222a and 222b according to another embodiment. [Figure 14] Figure 14 is a schematic front view showing the arrangement of focus detection pixels 222a and 222b according to yet another embodiment. [Modes for carrying out the invention]

[0010] Embodiments of the present invention will be described below with reference to the drawings.

[0011] 《First Embodiment》 Figure 1 is a diagram showing the main components of a digital camera 1 according to an embodiment of the present invention. The digital camera 1 of this embodiment (hereinafter simply referred to as camera 1) consists of a camera body 2 and a lens barrel 3, and the camera body 2 and lens barrel 3 are detachably connected by a mount portion 4.

[0012] The lens barrel 3 is a detachable interchangeable lens for the camera body 2. As shown in Figure 1, the lens barrel 3 contains an imaging optical system including lenses 31, 32, 33 and an aperture 34.

[0013] Lens 32 is a focusing lens, and by moving it in the direction of the optical axis L1, the focus state of the imaging optical system can be adjusted. The focusing lens 32 is mounted so as to be movable along the optical axis L1 of the lens barrel 3, and its position is detected by the encoder 35 and adjusted by the focusing lens drive motor 36.

[0014] The aperture 34 is configured to have an adjustable aperture diameter around the optical axis L1 in order to limit the amount of light in the light beam that passes through the above-mentioned imaging optical system to the image sensor 22 and to adjust the amount of blur. The aperture diameter of the aperture 34 is adjusted, for example, by sending an appropriate aperture diameter calculated in automatic exposure mode from the camera control unit 21 via the lens control unit 37. Alternatively, the set aperture diameter can be input from the camera control unit 21 to the lens control unit 37 by manual operation using the operation unit 28 provided on the camera body 2. The aperture diameter of the aperture 34 is detected by an aperture sensor (not shown), and the current aperture diameter is recognized by the lens control unit 37.

[0015] The lens control unit 37 controls the entire lens barrel 3, including driving the focus lens 32 and adjusting the aperture diameter with the diaphragm 34, based on commands from the camera control unit 21.

[0016] Meanwhile, the camera body 2 has an image sensor 22 that receives the light beam from the above-mentioned imaging optical system, which is located at the planned focal plane of the imaging optical system, and a shutter 23 is provided in front of it. The image sensor 22 is composed of a device such as a CCD or CMOS, and converts the received light signal into an electrical signal and sends it to the camera control unit 21. The captured image information sent to the camera control unit 21 is sequentially sent to the liquid crystal drive circuit 25 and displayed in the electronic viewfinder (EVF) 26 of the observation optical system. Furthermore, when the release button (not shown) provided on the operation unit 28 is fully pressed, the captured image information is recorded in the memory 24, which is a recording medium. The memory 24 can be either a removable card-type memory or an internal memory. Details of the structure of the image sensor 22 will be described later.

[0017] The camera body 2 is equipped with an observation optical system for observing the image captured by the image sensor 22. The observation optical system in this embodiment includes an electronic viewfinder (EVF) 26 made of a liquid crystal display element, a liquid crystal drive circuit 25 that drives the EVF, and an eyepiece 27. The liquid crystal drive circuit 25 reads the captured image information captured by the image sensor 22 and sent to the camera control unit 21, and drives the electronic viewfinder 26 based on this information. This allows the user to observe the currently captured image through the eyepiece 27. Alternatively, instead of, or in addition to, the above observation optical system using the optical axis L2, a liquid crystal display can be provided on the back of the camera body 2 or elsewhere, and the captured image can be displayed on this liquid crystal display.

[0018] The camera body 2 is equipped with a camera control unit 21. The camera control unit 21 receives various lens information and transmits information such as the amount of defocus and aperture diameter to the lens control unit 37. In addition, as described above, the camera control unit 21 reads pixel output from the image sensor 22 and generates image information by performing predetermined information processing on the read pixel output as needed, and outputs the generated image information to the liquid crystal drive circuit 25 and memory 24 of the electronic viewfinder 26. Furthermore, the camera control unit 21 is in charge of controlling the entire camera 1, including correcting the image information from the image sensor 22 and detecting the focus adjustment state and aperture adjustment state of the lens barrel 3.

[0019] In addition to the above, the camera control unit 21 also detects the focus state of the imaging optical system using a phase detection method and a contrast detection method, based on the pixel data read from the image sensor 22. The specific method for detecting the focus state will be described later.

[0020] The control unit 28 is an input switch for the photographer to set various operating modes of the camera 1, such as the shutter release button, and allows switching between autofocus mode and manual focus mode. The various modes set by this control unit 28 are sent to the camera control unit 21, which controls the operation of the entire camera 1. The shutter release button also includes a first switch SW1 that turns ON when the button is half-pressed and a second switch SW2 that turns ON when the button is fully pressed.

[0021] Next, the image sensor 22 according to this embodiment will be described.

[0022] Figure 2 is a front view showing the imaging surface of the image sensor 22, and Figure 3 is an enlarged front view of part III in Figure 2, schematically showing the arrangement of the imaging pixels 221 and focus detection pixels 222a and 222b.

[0023] As shown in Figure 3, the image sensor 22 of this embodiment has a plurality of imaging pixels 221 arranged two-dimensionally on the plane of the imaging surface, with green pixels G having a color filter that transmits the green wavelength region, red pixels R having a color filter that transmits the red wavelength region, and blue pixels B having a color filter that transmits the blue wavelength region arranged in a so-called Bayer arrangement. That is, in four adjacent pixel groups 223 (dense square grid arrangement), two green pixels are arranged on one diagonal, and one red pixel and one blue pixel are arranged on the other diagonal. The image sensor 22 is constructed by repeatedly arranging these Bayer-arranged pixel groups 223 as units in a two-dimensional manner on the imaging surface of the image sensor 22. In this embodiment, these four pixel groups 223 constitute one pixel.

[0024] Furthermore, the arrangement of the unit pixel group 223 can be other than the dense square grid shown in the diagram, for example, a dense hexagonal grid. Also, the configuration and arrangement of the color filter are not limited to this, and a complementary color filter (green: G, yellow: Ye, magenta: Mg, cyan: Cy) can also be used.

[0025] Figure 4(A) is a magnified front view showing one of the imaging pixels 221, and Figure 4(D) is a cross-sectional view. One imaging pixel 221 consists of a microlens 2211, a photoelectric conversion unit 2212, and a color filter (not shown). As shown in the cross-sectional view of Figure 4(D), the photoelectric conversion unit 2212 is fabricated on the surface of the semiconductor circuit board 2213 of the image sensor 22, and the microlens 2211 is formed on its surface. The photoelectric conversion unit 2212 is shaped to receive the imaging light beam passing through the exit pupil (for example, F1.0) of the imaging optical system 31 via the microlens 2211, and receives the imaging light beam.

[0026] Furthermore, as shown in Figure 2, at a total of nine locations on the imaging surface of the image sensor 22, including the center, positions symmetrical to the left and right from the center, and positions symmetrical to the top and bottom, focus detection pixel arrays 22a to 22i are provided, where focus detection pixels 222a and 222b are arranged in place of the aforementioned imaging pixels 221. As shown in Figure 3, each focus detection pixel array is composed of four focus detection pixel arrays L1 to L4, and each focus detection pixel array L1 to L4 is composed of multiple first focus detection pixels 222a and second focus detection pixels 222b arranged adjacent to each other alternately in a horizontal row. Also, as shown in Figure 3, in this embodiment, in focus detection pixel arrays L1, L3 and focus detection pixel arrays L2, L4, the focus detection pixels 222a and focus detection pixels 222b are arranged in opposite directions in the X-axis direction. Furthermore, in this embodiment, as shown in Figure 3, the first focus detection pixels 222a and the second focus detection pixels 222b are densely arranged without any gaps between the green pixels G and blue pixels B of the Bayer-arranged imaging pixels 221.

[0027] Note that the positions of the focus detection pixel arrays 22a to 22i shown in Figure 2 are not limited to those shown, and can be any one, two to eight, or more than ten locations. Furthermore, during actual focus detection, the photographer can manually operate the control unit 28 to select a desired focus detection pixel array from among the multiple focus detection pixel arrays 22a to 22i to use as the focus detection area AFP for adjusting the focus.

[0028] Figure 4(B) is a magnified front view of one of the first focus detection pixels 222a, and Figure 4(E) is a cross-sectional view of the first focus detection pixel 222a. Figure 4(C) is a magnified front view of one of the second focus detection pixels 222b, and Figure 4(F) is a cross-sectional view of the second focus detection pixel 222b. As shown in Figure 4(B), the first focus detection pixel 222a is composed of a microlens 2221a and a rectangular photoelectric conversion unit 2222a. As shown in the cross-sectional view in Figure 4(E), the photoelectric conversion unit 2222a is fabricated on the surface of the semiconductor circuit board 2213 of the image sensor 22, and the microlens 2221a is formed on that surface. Furthermore, as shown in Figure 4(C), the second focus detection pixel 222b is composed of a microlens 2221b and a photoelectric conversion unit 2222b. As shown in the cross-sectional view in Figure 4(F), the photoelectric conversion unit 2222b is fabricated on the surface of the semiconductor circuit board 2213 of the image sensor 22, and the microlens 2221b is formed on its surface. These focus detection pixels 222a and 222b are arranged in a horizontal row, adjacent to each other and alternating, as shown in Figure 3, thereby constituting each focus detection pixel row L1 to L4.

[0029] The photoelectric conversion units 2222a and 2222b of the first and second focus detection pixels 222a and 2222b are shaped to receive a light beam passing through a predetermined region (for example, F2.8) of the exit pupil of the imaging optical system using microlenses 2221a and 2221b. Furthermore, the first and second focus detection pixels 222a and 222b are not provided with color filters, and their spectral characteristics are a combination of the spectral characteristics of the photodiode that performs photoelectric conversion and the spectral characteristics of an infrared cut filter (not shown). However, they can also be configured to include one of the same color filters as the imaging pixel 221, for example, a green filter.

[0030] Furthermore, although the photoelectric conversion units 2222a and 2222b of the first focus detection pixel 222a and second focus detection pixel 222b shown in Figures 4(B) and 4(C) are rectangular in shape, the shape of the photoelectric conversion units 2222a and 2222b is not limited to this, and other shapes such as semicircular, elliptical, or polygonal shapes can also be used.

[0031] Next, we will explain a so-called phase-difference detection method, which detects the focus state of the imaging optical system based on the pixel output of the focus detection pixels 222a and 222b described above.

[0032] Figure 5 is a cross-sectional view along the VV line in Figure 3, showing that the focus detection pixels 222a-1, 222b-1, 222a-2, and 222b-2, which are located near the optical axis L1 and adjacent to each other, receive the light beams AB1-1, AB2-1, AB1-2, and AB2-2, respectively, emitted from the rangefinder pupils 351 and 352 of the exit pupil 350. In Figure 5, only the focus detection pixels 222a and 222b located near the optical axis L1 are shown as examples, but other focus detection pixels besides those shown in Figure 5 are similarly configured to receive the light beams emitted from the pair of rangefinder pupils 351 and 352.

[0033] Here, the exit pupil 350 is the image set at a distance D in front of the microlenses 2221a and 2221b of the focus detection pixels 222a and 222b, which are positioned at the planned focal plane of the imaging optical system. Distance D is a value uniquely determined according to the curvature and refractive index of the microlens, the distance between the microlens and the photoelectric conversion unit, and this distance D is called the distance measuring pupil distance. Furthermore, distance measuring pupils 351 and 352 refer to the images of the photoelectric conversion units 2222a and 2222b projected by the microlenses 2221a and 2221b of the focus detection pixels 222a and 222b, respectively.

[0034] In Figure 5, the orientation of the focus detection pixels 222a-1, 222b-1, 222a-2, and 222b-2 coincides with the orientation of the pair of distance measuring pupils 351 and 352.

[0035] Furthermore, as shown in Figure 5, the microlenses 2221a-1, 2221b-1, 2221a-2, and 2221b-2 of the focus detection pixels 222a-1, 222b-1, 222a-2, and 2221b-2 are positioned near the planned focal plane of the imaging optical system. The shapes of each photoelectric conversion unit 2222a-1, 2222b-1, 2222a-2, and 2221b-2, which are positioned behind each microlens 2221a-1, 2221b-1, 2221a-2, and 2221b-2, are projected onto the exit pupil 350, which is located at a distance D from each microlens 2221a-1, 2221b-1, 2221a-2, and 2221b-2, and the projected shapes form the distance measuring pupils 351 and 352.

[0036] In other words, the relative positional relationship between the microlens and the photoelectric conversion unit at each focal detection pixel is determined so that the projection shapes of the photoelectric conversion units (distancing pupils 351, 352) of each focal detection pixel coincide on the exit pupil 350 at the distance D, and the projection direction of the photoelectric conversion unit at each focal detection pixel is determined accordingly.

[0037] As shown in Figure 5, the photoelectric conversion unit 2222a-1 of the first focus detection pixel 222a-1 outputs a signal corresponding to the intensity of the image formed on the microlens 2221a-1 by the light beam AB1-1 that passes through the distance measuring pupil 351 and is directed toward the microlens 2221a-1. Similarly, the photoelectric conversion unit 2222a-2 of the first focus detection pixel 222a-2 outputs a signal corresponding to the intensity of the image formed on the microlens 2221a-2 by the light beam AB1-2 that passes through the distance measuring pupil 351 and is directed toward the microlens 2221a-2.

[0038] Furthermore, the photoelectric conversion unit 2222b-1 of the second focus detection pixel 222b-1 outputs a signal corresponding to the intensity of the image formed on the microlens 2221b-1 by the light beam AB2-1 that passes through the distance measuring pupil 352 and is directed toward the microlens 2221b-1. Similarly, the photoelectric conversion unit 2222b-2 of the second focus detection pixel 222b-2 outputs a signal corresponding to the intensity of the image formed on the microlens 2221b-2 by the light beam AB2-2 that passes through the distance measuring pupil 352 and is directed toward the microlens 2221b-2.

[0039] Then, by combining the outputs of the photoelectric conversion units 2222a and 2222b of the focus detection pixels 222a and 222b into output groups corresponding to the distance measuring pupil 351 and the distance measuring pupil 352, respectively, data is obtained regarding the intensity distribution of a pair of images formed on the focus detection pixel array by the focus detection light beam passing through the distance measuring pupil 351 and the distance measuring pupil 352, respectively.

[0040] The camera control unit 21 then performs a correlation calculation shown in equation (1) below, while relatively shifting in one dimension the data sequence relating to the intensity distribution of the pair of images, that is, the data sequence based on the first focus detection pixel 222a and the data sequence based on the second focus detection pixel 222b among the focus detection pixel sequences. C(k) = Σ|I A(n+k) -I B(n) | …(1) In equation (1) above, the Σ operation represents an accumulation operation (sum operation) with respect to n, and I A(n+k) , I B(n) This is limited to the range in which the data exists. Also, the image shift amount k is an integer and is the shift amount in units of the pixel interval between each focus detection pixel 222a, 222b. Note that in the calculation result of equation (1) above, the correlation amount C(k) becomes minimal (the smaller the value, the higher the correlation) at a shift amount where the correlation between the pair of image data is high.

[0041] Then, according to equation (1) above, the correlation amount C(k) is calculated, and based on the shift amount x at which the minimum value of the correlation amount C(x) is obtained, the defocus amount df is calculated according to equation (2) below. In equation (2) above, k is the conversion coefficient (k-factor) for converting the shift amount x at which the minimum value of the correlation amount C(x) is obtained into the defocus amount. df = x·k …(2)

[0042] Furthermore, in this embodiment, the camera control unit 21 detects contrast information from the outputs of a plurality of focus detection pixel sequences L1 to L4, and determines a specific focus detection pixel sequence to be used for calculating the amount of defocus based on the detected contrast information.

[0043] Specifically, the camera control unit 21 acquires the output of each focus detection pixel sequence L1 to L4 from the image sensor 22, and filters the acquired output of focus detection pixel sequences L1 to L4 with a high-frequency transmission filter to extract high-frequency components from the output of focus detection pixel sequences L1 to L4. The camera control unit 21 then compares the high-frequency components of each focus detection pixel sequence L1 to L4, and based on the comparison result, determines the focus detection pixel sequence corresponding to the subject with the highest contrast among the multiple focus detection pixel sequences L1 to L4 as the specific focus detection pixel sequence. Alternatively, the camera control unit 21 may be configured to determine the focus detection pixel sequence containing the most high-frequency components in its output among the multiple focus detection pixel sequences L1 to L4 based on the above comparison result as the specific focus detection pixel sequence.

[0044] In this embodiment, the camera control unit 21 has been shown as an example of a configuration in which it obtains the output of a plurality of focus detection pixel sequences L1 to L4 from the image sensor 22 and determines a specific focus detection pixel sequence from among the plurality of focus detection pixel sequences L1 to L4. However, the configuration is not limited to this, and for example, the image sensor 22 may have a calculation unit that detects contrast information for each point detection pixel sequence L1 to L4 based on the output of each focus detection pixel sequence L1 to L4, determines a specific focus detection pixel sequence from among the plurality of focus detection pixel sequences L1 to L4 based on the detected contrast information, and transmits the information of the determined specific focus detection pixel sequence to the camera control unit 21.

[0045] The camera control unit 21 then calculates the amount of defocus based on the output of the determined specific focus detection pixel sequence. In this embodiment, since the amount of defocus is calculated based only on the output of the focus detection pixel sequence determined as the specific focus output pixel sequence among the multiple focus detection pixel sequences L1 to L4, the time required for calculating the amount of defocus can be reduced.

[0046] In other words, conventionally, when there were multiple focus detection pixel sequences, the defocus amount was calculated for all focus detection pixel sequences, and the defocus amount to be used to drive the focus lens 32 was selected from among the multiple calculated defocus amounts. Therefore, conventionally, not only was the calculation of defocus amounts other than the selected defocus amount was wasted, but there was also the problem that the calculation time for the defocus amount was long because the defocus amount was calculated for all of the multiple focus detection pixel sequences L1 to L4. In contrast, in this embodiment, the defocus amount is calculated based only on the output of the focus detection pixel sequence determined as the specific focus output pixel sequence, so the time required to calculate the defocus amount can be shortened, and as a result, the time required for focus detection can be shortened.

[0047] In this embodiment, multiple focus detection area AFPs are set within the shooting screen of the imaging optical system, corresponding to the focus detection pixel arrays 22a to 22i of the image sensor 22, and the photographer can set the focus detection area AFP to be used for focus adjustment via the operation unit 28. For example, if the photographer selects the focus detection area AFP corresponding to the focus detection pixel array 22a as the focus detection area AFP to be used for focus adjustment, the camera control unit 21 calculates the amount of defocus based on the output of the focus detection pixel arrays L1 to L4 included in the focus detection pixel array 22a. Furthermore, the method of setting the focus detection area AFP is not limited to the method selected by the photographer; for example, the camera control unit 21 may perform face recognition processing based on image data output from the image sensor 22, and set the focus detection area AFP corresponding to the subject's face as the focus detection area AFP to be used for focus adjustment. Alternatively, the system may be configured to acquire the output of focus detection pixel sequences L1 to L4 for all focus detection area AFPs set within the shooting screen, and then set the focus detection area AFP to be used for focus adjustment based on the acquired output of focus detection pixel sequences L1 to L4.

[0048] Furthermore, in this embodiment, the camera control unit 21 performs focus detection using a contrast detection method in addition to the phase difference detection method described above. Specifically, the camera control unit 21 reads out the output of the imaging pixels 221 of the image sensor 22 and calculates a focus evaluation value based on the read-out pixel output. This focus evaluation value can be obtained, for example, by extracting the high-frequency components of the image output from the imaging pixels 221 of the image sensor 22 using a high-frequency transmission filter and integrating them. Alternatively, it can be obtained by extracting high-frequency components using two high-frequency transmission filters with different cutoff frequencies and integrating them.

[0049] The camera control unit 21 then sends a control signal to the lens control unit 37 to drive the focus lens 32 at a predetermined sampling interval (distance), obtains a focus evaluation value at each position, and determines the position of the focus lens 32 where the focus evaluation value is maximum as the focus position. This focus position can be determined, for example, by performing calculations such as interpolation using the focus evaluation values ​​when the focus evaluation value is calculated while driving the focus lens 32, and the focus evaluation value rises twice and then falls twice.

[0050] Next, an example of the operation of camera 1 in this embodiment will be explained in accordance with the flowchart shown in Figure 6.

[0051] First, in step S101, the image sensor 22 acquires output data for the imaging pixel 221, as well as for each of the first focus detection pixels 222a and second focus detection pixels 222b that constitute the multiple focus detection pixel sequences L1 to L4.

[0052] In step S102, the camera control unit 21 selects a focus detection area AFP to be used for focus adjustment. For example, if the photographer sets a focus detection area AFP to be used for focus adjustment via the operation unit 28, the camera control unit 21 can select the focus detection area AFP set by the photographer as the focus detection area AFP to be used for focus adjustment. Alternatively, the camera control unit 21 may be configured to perform face recognition processing on the image data output from the image sensor 22 and select the focus detection area AFP corresponding to the subject's face as the focus detection area AFP to be used for focus adjustment. Or, the camera control unit 21 may be configured to select a focus detection area AFP to be used for focus adjustment by analyzing the output of the focus detection pixel sequences L1 to L4 of all focus detection area AFPs set in the shooting screen.

[0053] In step S103, the camera control unit 21 detects contrast information for each focus detection pixel sequence L1 to L4 based on the output of each focus detection pixel sequence L1 to L4. Specifically, the camera control unit 21 filters the outputs of multiple focus detection pixel sequences L1 to L4 corresponding to the focus detection area AFP selected in step S102 using a high-frequency transmission filter to extract high-frequency components from the pixel outputs of focus detection pixel sequences L1 to L4. Then, for each focus detection pixel sequence L1 to L4, the camera control unit 21 detects information including the amount and intensity of the extracted high-frequency components as contrast information.

[0054] In step S104, the camera control unit 21 determines the specific focus detection pixel sequence. Specifically, based on the contrast information for each focus detection pixel sequence L1 to L4 detected in step S103, the camera control unit 21 determines the focus detection pixel sequence that corresponds to the subject with the highest contrast, or the focus detection pixel sequence that contains the most high-frequency components in its pixel output, as the specific focus detection pixel sequence.

[0055] Then, in step S105, the camera control unit 21 calculates the amount of defocus based on the output of the specific focus detection pixel sequence determined in step S104. Then, in step S106, the amount of drive for the focus lens 32 is calculated and the focus lens 32 is driven based on the amount of defocus calculated in step S105.

[0056] As described above, focus detection is performed in the optical system according to the first embodiment.

[0057] Next, an example of the operation of the camera 1 according to this embodiment will be described based on Figure 7. Figure 7 is a diagram illustrating an example of the operation of the camera 1 according to this embodiment. In Figure 7, the horizontal axis represents time, and it shows the scene at time t5 when the shutter release button is half-pressed. For example, in the example shown in Figure 7, at time t1, the focus detection pixels 222a and 222b of the image sensor 22 start accumulating charge according to the incident light. In this embodiment, the focus detection pixels 222a and 222b are, for example, CMOS image sensors, and in parallel with the accumulation of charge, the transfer of a pixel signal corresponding to the amount of charge accumulated since time t1 is started. At time t3, the transfer of the pixel signal that started at time t2 is completed, and contrast information is detected and a specific focus detection pixel sequence is determined (steps S103, S104). At time t4, the calculation of the defocus amount is started based on the output of the determined specific focus detection pixel sequence (step S105). This allows the lens drive amount to be calculated, and after the calculation of the lens drive amount, at time t6, a lens drive instruction is sent to the lens barrel 3, and the focus lens 32 is driven. In the example shown in Figure 7, the shutter release button is half-pressed at time t5, before the lens drive instruction is given, so the focus lens 32 is driven based on the lens drive instruction at time t6.

[0058] Furthermore, in this embodiment, even after the shutter release button is half-pressed, the amount of defocus is repeatedly calculated according to the frame rate of the image sensor 22, and the focus lens 32 is repeatedly instructed to drive based on the calculated amount of defocus. For example, in the example shown in Figure 7, at time t2, charge accumulation for the second frame begins, and as a result, at time t7, the amount of defocus for the second frame is calculated, and at time t8, the focus lens 32 is instructed to drive based on the output results of the focus detection pixel sequences L1 to L4 for the second frame. Similarly, for the third frame and beyond, the calculation of the amount of defocus and the driving of the focus lens 32 based on the amount of defocus are repeated for each frame based on the output of the focus detection pixel sequences L1 to L4.

[0059] As described above, in this embodiment, the calculation of the defocus amount and the driving of the focus lens 32 based on the defocus amount are repeated for each frame according to the frame rate of the image sensor 22. In order to calculate the defocus amount and instruct the driving of the focus lens 32 for each frame, it is necessary to perform the calculation of the defocus amount and the instruction to drive the focus lens 32 within the time of one frame. In this embodiment, however, by determining one specific focus detection pixel sequence based on contrast information and calculating the defocus amount only for the output of this specific focus detection pixel sequence, the time required to calculate the defocus amount can be shortened, as shown in Figure 7. Therefore, the defocus amount can be calculated within the time of one frame, and the focus lens 32 can be driven based on the calculated defocus amount.

[0060] On the other hand, Figure 8 is a diagram illustrating an example of operation of a conventional camera, and, like Figure 7, the horizontal axis shows time. In the example shown in Figure 8, the calculation of the defocus amount, which takes a relatively long time, is performed for all focus detection pixel sequences L1 to L4, so the calculation time for the defocus amount is longer compared to the embodiment shown in Figure 7. As a result, in the example shown in Figure 8, the time required from the calculation of the defocus amount to the lens drive instruction becomes longer than the time of one frame of the frame rate, and there were cases where it was not possible to give a lens drive instruction for each frame. Specifically, in the example shown in Figure 8, it is not possible to perform the calculation of the defocus amount to the lens drive instruction within the time of one frame, so the time lag T2 from charge accumulation to the drive instruction of the focus lens 32 is twice as large as the time lag T1 of the embodiment shown in Figure 7.

[0061] As a result, in the example shown in Figure 8, the focus lens 32 is instructed to be driven at time 12 based on the focal state of the optical system at time t11. This can lead to the focus lens 32 being driven far beyond the focus position or the subject tracking performance being reduced. In contrast, in this embodiment, as shown in Figure 7, the focus lens 32 can be instructed to be driven at time t10, with minimal time lag, based on the focal state of the optical system at time t9. Therefore, compared to the conventional example shown in Figure 8, the focus lens 32 can be driven appropriately to the focus position.

[0062] As described above, in the first embodiment, contrast information is detected for each focus detection pixel sequence L1 to L4 based on the output of each focus detection pixel sequence L1 to L4 within the focus detection area AFP. Then, based on the detected contrast information, the focus detection pixel sequence to be used for focus detection is determined. That is, among the multiple focus detection pixel sequences L1 to L4, the focus detection pixel sequence corresponding to the subject with the highest contrast, or the focus detection pixel sequence whose pixel output contains the most high-frequency components, is determined as a specific focus detection pixel sequence, and the amount of defocus is determined only for this specific focus detection pixel sequence. This makes it possible to detect the focus state of the optical system for the subject with the highest contrast or the subject with the most high-frequency components, and it is possible to reduce the time required to calculate the amount of defocus compared to the conventional method of calculating the amount of defocus for all of the multiple focus detection pixel sequences L1 to L4, and to repeatedly detect the focus state at an appropriate timing.

[0063] Furthermore, in the first embodiment, since the defocus amount is calculated based on the output of one of the multiple focus detection pixel sequences L1 to L4, the following effects can be achieved compared to the case where the outputs of multiple focus detection pixel sequences L1 to L4 are added or averaged. That is, if the subject has contrast in the diagonal direction of the imaging pixel 221, adding or averaging the outputs of multiple focus detection pixel sequences L1 to L4 may actually reduce the contrast, making it impossible to properly detect the subject. In contrast, in this embodiment, since the defocus amount is calculated based on the output of one specific focus detection pixel sequence, even in such cases, a decrease in contrast can be prevented, and the subject can be properly detected.

[0064] 《Second Embodiment》 Next, a second embodiment of the present invention will be described. In the second embodiment, the camera 1 shown in Figure 1 has the same configuration as the first embodiment described above, except that it operates as described below.

[0065] In the second embodiment, the camera control unit 21 includes a plurality of filters that transmit frequency components of different frequency bands, extracts frequency components of multiple different frequency bands from the output of each focus detection pixel sequence L1 to L4, and detects multiple contrast information for each focus detection pixel sequence L1 to L4 based on the extracted frequency components. For example, if the camera control unit 21 includes three filters that extract frequency components of three different frequency bands, the camera control unit 21 can detect three pieces of contrast information from the output of one focus detection pixel sequence. The frequency bands of the frequency components extracted in the second embodiment are not particularly limited and can be any frequency band from low frequency to high frequency.

[0066] The camera control unit 21 then detects one or more focus detection pixel sequences L1 to L4 from among the multiple focus detection pixel sequences L1 to L4, based on the multiple contrast information, to be used for focus detection, as a specific focus detection pixel sequence. For example, the camera control unit 21 can detect one or more focus detection pixel sequences from among the multiple focus detection pixel sequences L1 to L4, where the magnitude of the contrast of the corresponding subject is greater than or equal to a predetermined value, as a specific focus detection pixel sequence. Alternatively, the camera control unit 21 can detect one or more focus detection pixel sequences where the amount of high-frequency components included in the output is greater than or equal to a predetermined value, as a specific focus detection pixel sequence.

[0067] Furthermore, when the camera control unit 21 determines a specific focus detection pixel sequence, it determines the sequence such that the number of specific focus detection pixel sequences is less than the number of focus detection pixel sequences L1 to L4 corresponding to the focus detection area AFP. For example, in this embodiment, since there are four focus detection pixel sequences L1 to L4 in the focus detection area AFP, the camera control unit 21 determines the sequence such that the number of specific focus detection pixel sequences is at least three or less.

[0068] When the camera control unit 21 determines a plurality of focus detection pixel rows as the specific focus detection pixel rows, it adds or averages the outputs of the plurality of specific focus detection pixel rows, and calculates the defocus amount based on the added or averaged outputs of the plurality of specific focus detection pixel rows. Here, FIG. 9 is a diagram schematically showing only the first focus detection pixels 222a and the second focus detection pixels 222b constituting the four focus detection pixel rows L1 to L4, with the imaging pixels 221 removed from the imaging surface of the image sensor 22 shown in FIG. 3. For example, when adding the outputs of a plurality of specific focus detection pixel rows, the camera control unit 21 adds the pixel A1 of the first focus detection pixel row L1 shown in FIG. 9 L1 output and the pixel A1 of the second focus detection pixel row L2 that receives the focus detection light flux passing through the same ranging pupil as this output L2 output and the pixel A1 of the third focus detection pixel row L3 L3 output and the pixel A1 of the fourth focus detection pixel row L4 L3 output to obtain a pixel addition output I A1 . Similarly, the pixel B1 of the first focus detection pixel row L1 L1 output and the pixel B1 of the second focus detection pixel row L2 that receives the focus detection light flux passing through the same ranging pupil as this output L2 output and the pixel B1 of the third focus detection pixel row L3 L3 output and the pixel B1 of the fourth focus detection pixel row L4 L4 output are added to obtain a pixel addition output I B1 . Hereinafter, similarly, I is obtained from the outputs of A2 L1 , A2 L2 , A2 L3 and A2 L4 , I A2 is obtained from the outputs of B2 L1 , B2 L2 , B2 L3 and B2 L4 , I B2 is obtained from the outputs of A3 L1 , A3 L2 , A3 L3 and A3 L4 , I A3 is obtained from the outputs of B3 L1 , B3 L2 , B3 L3 and B3 L4 , I B3 is obtained.

[0069] Then, the camera control unit 21 uses the obtained pixel summation output to generate a data sequence based on the first focus detection pixel 222a, i.e., the first image data sequence I A1 ,I A2 ,I A3 ,...,I An And, a data sequence based on the second focus detection pixel 222b, i.e., the second image data sequence I B1 ,I B2 ,I B3 ,...,I Bn The correlation operation shown in equation (1) above is performed while relatively shifting the two elements in a one-dimensional manner.

[0070] Here, as shown in Figure 3, in the focus detection pixel sequences L1 to L4, the first focus detection pixel 222a and the second focus detection pixel 222b are positioned 0.5 pixels apart from each other. Conventionally, only one of the first focus detection pixel sequence L1 and the second focus detection pixel sequence L2 of this embodiment is used as the focus detection pixel sequence, so the first focus detection pixel 222a and the second focus detection pixel 222b are positioned 0.5 pixels apart from each other, and the first image data sequence I obtained using these focus detection pixels A1 ,I A2 ,I A3 ,...,I An And, the second image data sequence I B1 ,I B2 ,I B3 ,...,I Bn This meant that the data was shifted by 0.5 pixels from each other. Therefore, when correlation calculation was performed, the minimum value of the correlation amount C(k) also ended up being shifted by 0.5 pixels, as shown in Figure 10(B). In such cases, it was necessary to use interpolation or other methods to calculate the shift amount and defocus amount at which the correlation amount C(k) shows a minimum value, which sometimes resulted in a decrease in focus detection accuracy. This problem tended to be particularly pronounced when the contrast level of the output detected by the focus detection pixel was low.

[0071] In contrast, in this embodiment, the first focus detection pixel 222a and the second focus detection pixel 222b are positioned at a distance of 0.5 pixels in the X-axis direction from the focus detection pixel sequences L1 and L3 and L2 and L4. Therefore, when using the pixel sum output obtained by adding the pixel outputs, as shown in Figure 10(A), the shift amount that gives the smallest value of the correlation amount C(k) in the in-focus state (a state where the amount of defocus is zero) can be accurately determined, thereby appropriately improving the focus detection accuracy.

[0072] Next, the operation of camera 1 according to the second embodiment will be described with reference to Figure 11. Figure 11 is a flowchart showing an example of the operation of camera 1 according to the second embodiment.

[0073] In step S201, similar to step S101 of the first embodiment, the image sensor 22 acquires output data for the imaging pixel 221 and each of the first focus detection pixels 222a and second focus detection pixels 222b that constitute the plurality of focus detection pixel sequences L1 to L4. Also, in step S202, similar to step S102 of the first embodiment, the camera control unit 21 selects the focus detection area AFP to be used for focus adjustment.

[0074] Then, in step S203, the camera control unit 21 detects contrast information. In the second embodiment, the camera control unit 21 extracts multiple frequency components from each output of each focus detection pixel sequence L1 to L4 by filtering the output of each focus detection pixel sequence L1 to L4 using a plurality of filters that extract frequency components of different frequency bands. The camera control unit 21 then detects information including the amount and intensity of the extracted frequency components as contrast information.

[0075] In step S204, the camera control unit 21 determines a specific focus detection pixel sequence based on the multiple contrast information detected in step S203. Specifically, based on the contrast information detected in step S203, the camera control unit 21 determines one or more focus detection pixel sequences from among the multiple focus detection pixel sequences L1 to L4 in which the contrast of the corresponding subject is equal to or greater than a predetermined value, as the specific focus detection pixel sequence. Alternatively, based on the multiple contrast information detected in step S203, the camera control unit 21 determines one or more focus detection pixel sequences from among the multiple focus detection pixel sequences L1 to L4 in which the amount of high-frequency components included in the output is equal to or greater than a predetermined value, as the specific focus detection pixel sequence.

[0076] Then, in step S205, the camera control unit 21 calculates the amount of defocus used to drive the focus lens 32 based on the one or more specific focus detection pixel sequences determined in step S204. For example, if the camera control unit 21 determines multiple focus detection pixel sequences as specific focus detection pixel sequences, it can calculate an output of 1 by adding or averaging the outputs of the multiple specific focus detection pixel sequences, and then calculate the amount of defocus used to drive the focus lens 32 based on this output.

[0077] In step S206, similar to step S106 of the first embodiment, the amount of drive for the focus lens 32 is calculated and the focus lens 32 is driven based on the amount of defocus calculated in step S205.

[0078] As described above, focus detection is performed in the optical system according to the second embodiment.

[0079] Thus, in the second embodiment, for each focus detection pixel sequence L1 to L4, frequency components of different frequency bands are extracted based on the output of the focus detection pixel sequence L1 to L4, and multiple contrast information is detected based on the extracted multiple frequency components. Then, based on the multiple contrast information, one or more specific focus detection pixel sequences are determined from among the focus detection pixel sequences L1 to L4, and the amount of defocus is determined based on the pixel output of the determined specific focus detection pixel sequence. In this way, in the second embodiment, instead of calculating the amount of defocus for all focus detection pixel sequences L1 to L4, the calculation time for the amount of defocus is shortened by calculating the amount of defocus for a number of specific focus detection pixel sequences that is fewer than the number of focus detection pixel sequences L1 to L4, and as a result, it becomes possible to repeatedly detect the focus state at an appropriate timing.

[0080] Although embodiments of the present invention have been described above, these embodiments are provided to facilitate understanding of the present invention and are not intended to limit it. Therefore, each element disclosed in the above embodiments is intended to include all design modifications and equivalents that fall within the technical scope of the present invention.

[0081] For example, in the embodiment described above, a configuration is shown in which four focus detection pixel rows L1 to L4 are provided in one focus detection area AFP. However, the number of focus detection pixel rows is not limited to this, and the number of focus detection pixel rows in one focus detection area may be two or three, or five or more.

[0082] Furthermore, in the above-described embodiment, an example was given in which the image sensor 22 is equipped with focus detection pixel sequences L1 to L4, and the amount of defocus is calculated based on the output of the focus detection pixel sequences L1 to L4. However, the system is not limited to this configuration. For example, a phase-difference AF detection module may be provided separately from the image sensor 22, and the amount of defocus may be calculated based on the light received signal received by this phase-difference AF detection module. Specifically, the phase-difference AF detection module may have a plurality of pairs of line sensors that receive light beams passing through the optical system, detect contrast information for each line sensor, and determine a pair of line sensors to be used for focus detection from among the plurality of line sensors based on the detected contrast information. When determining a pair of line sensors to be used for focus detection, the calculation unit provided in the phase-difference detection module may determine the pair of line sensors to be used for focus detection, or the camera control unit 21 may determine the pair of line sensors to be used for focus detection by acquiring the output of each pair of line sensors.

[0083] Thus, the "light-receiving sensor" of the present invention may be a focus detection pixel array L1 to L4, or the pair of line sensors described above. Furthermore, the "focus detection device" of the present invention may be an image sensor 22 or a camera 1 equipped therewith, or a phase-detection AF detection module or a camera 1 equipped therewith.

[0084] Furthermore, in the embodiment described above, the first focus detection pixel 222a and the second focus detection pixel 222b are arranged in opposite directions in the X-axis direction in the focus detection pixel arrays L1, L3 and L2, L4. However, the configuration is not limited to this, and for example, as shown in Figure 12, the focus detection pixels 222a and 222b constituting the focus detection pixel arrays L1a to L4a may be arranged to be in the same position in the X-axis direction.

[0085] Furthermore, as shown in the focus detection pixel arrays L1b and L2b in Figure 13, each focus detection pixel 222a and 222b may be configured to include a pair of photoelectric conversion units 2222a and 2222b. Specifically, as shown in Figure 13, in each focus detection pixel 222a and 222b, a pair of photoelectric conversion units 2222a and 2222b are arranged in the X-axis direction, and the light beam emitted from the distance measuring pupil 351 is received by one of the pair of photoelectric conversion units 2222a and 2222b, while the light beam emitted from the distance measuring pupil 352 is received by the other photoelectric conversion unit. As a result, each focus detection pixel array L1b and L2b can output a pair of image data arrays. In Figure 13, the photoelectric conversion unit that receives the light beam emitted from the rangefinder pupil 351 is shown in gray, and the photoelectric conversion unit that receives the light beam emitted from the rangefinder pupil 352 is shown in white.

[0086] Furthermore, the arrangement of the first focus detection pixels 222a and the second focus detection pixels 222b that constitute each focus detection pixel sequence only needs to be such that they are arranged alternately on the same sequence. For example, as shown in the focus detection pixel sequences L1c to L4c in Figure 14, the sequence may include a normal imaging pixel 221.

[0087] In addition to the embodiments described above, if the contrast (or brightness) of the subject is greater than or equal to a predetermined value, as shown in the first embodiment, the focus detection pixel sequence L1 to L4 corresponding to the subject with the greatest contrast, or the focus detection pixel sequence whose output contains the most high-frequency components, is determined as the specific focus detection pixel sequence. On the other hand, if the contrast (or brightness) of the subject is less than a predetermined value, as shown in the second embodiment, one or more focus detection pixel sequences L1 to L4 whose corresponding subject's contrast is greater than or equal to a predetermined value, or one or more focus detection pixel sequences whose output contains a greater than or equal to a predetermined value, are determined as the specific focus detection pixel sequences. [Explanation of Symbols]

[0088] 1… Digital camera 2…Camera body 21...Camera control unit 22…Image sensor 221…Image pixels L1~L4...Focus detection pixel sequence 222a, 222b… Focus detection pixels 3…Lens barrel 32... Focus lens 36…Focus lens drive motor 37…Lens control unit

Claims

[Claim 1] An image sensor having multiple focus detection areas, wherein the image sensor has multiple pixels arranged in a first pixel row and a second pixel row within one focus detection area, which receive light that has passed through the optical system and output a signal based on the received light, A control unit that, based on the contrast information of the signals output from a plurality of pixels arranged in the first pixel row in the focus detection area and the contrast information of the signals output from a plurality of pixels arranged in the second pixel row in the focus detection area, identifies either the plurality of pixels arranged in the first pixel row or the plurality of pixels arranged in the second pixel row as a plurality of pixels to be used for calculating the defocus amount, and calculates the defocus amount using the signals output from the identified plurality of pixels, A focus detection device equipped with the following features.

Images