JP2018116267A - Focus detection device and method, and imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress influence for magnification aberration of an image formation optical system to give to a focus detection result, and to perform accurate focus detection in an imaging device performing automatic focus detection by means of a phase difference detection method on the basis of a signal obtained from a plurality of focus detection pixels having different spectral sensitivities to each other.SOLUTION: A focus detection device that comprises a plurality of photo-electric conversion units for each of a plurality of microlenses, that performs photo-electric conversion of injected light through an image formation optical system to output an electric signal, and that performs focus detection by means of a phase difference detection method on the basis of a signal having a plurality of colors obtained from an imaging element covered by a color filter having a plurality of colors comprises: acquisition means that acquires an addition coefficient set indicating weighting applied to the signal having the plurality of colors, according to a characteristic of chromatic aberration of magnification of the image formation optical system; generation means that generates a pair of focus detection signals by performing weighting addition of the signal having the plurality of colors using the addition coefficient set; and detection means that detects an image deviation amount between the pair of focus detection signals.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a focus detection apparatus and method, and an imaging apparatus.

  A phase difference focus detection method (phase difference AF) is known as an automatic focus detection (AF) method used in an imaging apparatus. Phase difference AF is AF that is often used in digital still cameras, and there are some in which an image sensor is used as a focus detection sensor. In Patent Document 1, in order to perform focus detection of the pupil division method, the photoelectric conversion unit of each pixel constituting the imaging device is divided into a plurality of parts, and the divided photoelectric conversion unit is a photographic lens via a microlens. Are configured to receive light beams that have passed through different regions of the pupil.

  The phase difference AF can simultaneously detect the focus detection direction and the focus detection amount based on a pair of signals obtained from focus detection pixels formed on the image sensor, and can perform focus adjustment at high speed. it can. On the other hand, since the phase difference AF performs focus detection using the phase difference of the optical image, the aberration of the optical system that forms the optical image may give an error to the focus detection result, and this error is reduced. A method for this has been proposed.

  Patent Document 2 discloses a method for correcting a focus detection error caused by a shape of a pair of optical images formed by a pair of focus detection light beams in an in-focus state being not matched due to an aberration of an optical system. Has been.

  Patent Document 3 discloses a method for correcting a focus detection error by correcting with a correction value corresponding to a combination of information relating to the state of the photographing lens, information relating to the state of the image sensor, and image height. Yes.

JP 2008-52009 A JP 2013-171251 A JP 2014-222291 A

  However, in phase difference AF, the focus detection error caused by chromatic aberration of magnification consists of a complicated mechanism involving chromatic aberration of the imaging optical system and color shading of the image sensor, and appropriate correction including manufacturing variations is performed. May be difficult.

  The present invention has been made in view of the above-described problems. In an imaging apparatus that performs automatic focus detection by a phase difference detection method based on signals obtained from a plurality of focus detection pixels having different spectral sensitivities, lateral chromatic aberration exerts an effect. It is an object to suppress focus detection error and perform highly accurate focus detection.

  To achieve the above object, a plurality of color filters that include a plurality of photoelectric conversion units for each of a plurality of microlenses, photoelectrically convert light incident through an imaging optical system, and output an electrical signal. The focus detection apparatus of the present invention that performs focus detection by a phase difference detection method based on signals of a plurality of colors obtained from an image sensor covered with an image sensor includes the plurality of colors according to the chromatic aberration of magnification of the imaging optical system. Obtaining means for obtaining an addition coefficient set indicating weighting to be applied to a color signal; and generating means for performing weighted addition of the signals of the plurality of colors using the addition coefficient set to generate a pair of focus detection signals; Detecting means for detecting an image shift amount between the pair of focus detection signals.

  According to the present invention, in an imaging apparatus that performs automatic focus detection by a phase difference detection method based on signals obtained from a plurality of focus detection pixels having different spectral sensitivities, the magnification aberration of the imaging optical system gives the focus detection result. The influence can be suppressed and high-precision focus detection can be performed.

1 is a schematic configuration diagram of an imaging apparatus according to an embodiment of the present invention. Schematic of the pixel arrangement in the embodiment. The schematic plan view and schematic sectional drawing of the pixel in embodiment. Schematic explanatory drawing of the pixel structure and pupil division in the embodiment. Schematic explanatory drawing of an image sensor and pupil division in an embodiment. FIG. 5 is a schematic relationship diagram between a defocus amount and an image shift amount of a first focus detection signal and a second focus detection signal in the embodiment. The figure which shows each color line image by the light reception signal of the 1st focus detection pixel at the time of focusing in embodiment, and the light reception signal of a 2nd focus detection pixel. 6 is a flowchart showing a flow of focus detection processing and imaging processing in the first embodiment. The figure which shows an example of the relationship between setting defocus amount and detection defocus amount at the time of changing the addition coefficient set in 3rd Embodiment.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. The embodiments have specific and specific configurations to facilitate understanding and explanation of the invention, but the present invention is not limited to such specific configurations. For example, an embodiment in which the present invention is applied to a single-lens reflex digital camera capable of exchanging lenses will be described below, but the present invention can also be applied to a digital camera and video camera in which lenses cannot be interchanged. In addition, the present invention can be implemented with any electronic device equipped with a camera, such as a mobile phone, a personal computer (laptop, tablet, desktop type, etc.), a game machine, and the like.

<First Embodiment>
[overall structure]
FIG. 1 shows a schematic configuration of a camera which is an image pickup apparatus having an image pickup device according to an embodiment of the present invention. In FIG. 1, the first lens group 101 is disposed at the tip of the imaging optical system and is held so as to be able to advance and retract in the optical axis direction. The aperture / shutter 102 adjusts the aperture diameter to adjust the amount of light at the time of shooting, and also has a function as an exposure time adjustment shutter at the time of still image shooting. The second lens group 103 moves forward and backward in the optical axis direction integrally with the diaphragm / shutter 102, and a zooming function (zoom function) can be realized in conjunction with the forward / backward movement of the first lens group 101.

  The third lens group 105 (focus lens) performs focus adjustment by advancing and retreating in the optical axis direction. The optical low-pass filter 106 is an optical element for reducing false colors and moire in the captured image. The image sensor 107 includes a two-dimensional CMOS photosensor and its peripheral circuit. The image sensor 107 is disposed on the image forming surface of the image forming optical system, photoelectrically converts light incident through the image forming optical system, and outputs an electrical signal.

  The zoom actuator 111 rotates a cam cylinder (not shown) to drive the first lens group 101 or the second lens group 103 forward and backward in the optical axis direction, and performs a zooming operation. The aperture shutter actuator 112 controls the aperture diameter of the aperture / shutter 102 to adjust the amount of photographing light, and controls the exposure time during still image photographing. The focus actuator 114 adjusts the focus by driving the third lens group 105 back and forth in the optical axis direction.

  The electronic flash 115 for illuminating the subject is preferably a flash illumination device using a xenon tube, but an illumination device including an LED that emits light continuously may be used. The AF auxiliary light emitting unit 116 projects a mask image having a predetermined opening pattern onto the object field via the projection lens, and improves the focus detection capability for a dark subject or a low-contrast subject.

  The in-camera CPU 121 manages various controls of the camera body, and includes a calculation unit, ROM, RAM, A / D converter, D / A converter, communication interface circuit, and the like. The CPU 121 drives various circuits included in the camera based on a predetermined program stored in the ROM, and executes a series of operations such as AF, photographing, image processing, and recording.

  Further, the CPU 121 stores a correction value calculation coefficient necessary for focus adjustment using the output signal of the image sensor 107. The correction value calculation coefficient includes a focus state corresponding to the position of the third lens group 105, a zoom state corresponding to the positions of the first lens group 101 and the second lens group 103, the F value of the imaging optical system, and the image sensor 107. A plurality are prepared for each set pupil distance and pixel size. When performing focus adjustment, an optimum correction value calculation coefficient is selected according to the combination of the focus adjustment state (focus state, zoom state) and aperture value of the imaging optical system, the set pupil distance of the image sensor 107, and the pixel size. The The correction value is calculated from the selected correction value calculation coefficient and the image height of the image sensor 107.

  The correction value calculation coefficient includes an addition coefficient set for weighted addition of RGB signals. In the first embodiment, this set of addition coefficients is stored so as to be selectable according to the lens ID (lens identification information) of the imaging optical system. Then, a focus detection signal is generated using the selected addition coefficient set. The addition coefficient set and the focus detection signal generation method will be described later in detail.

  In the present embodiment, the correction value calculation coefficient is described as being stored in the CPU 121, but the storage location is not limited thereto. For example, in an interchangeable lens type imaging apparatus, an interchangeable lens having an imaging optical system may have a nonvolatile memory, and a correction value calculation coefficient may be stored in the memory. In this case, for example, the correction value calculation coefficient may be transmitted to the imaging device when the interchangeable lens is attached to the imaging device or in response to a request from the imaging device.

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

  The focus drive circuit 126 controls the focus actuator 114 based on the focus detection result, and adjusts the focus by driving the third lens group 105 back and forth in the optical axis direction. The aperture shutter drive circuit 128 controls the aperture of the aperture / shutter 102 by drivingly controlling the aperture shutter actuator 112. The zoom drive circuit 129 drives the zoom actuator 111 according to the zoom operation of the photographer.

  A display 131 such as an LCD displays information related to the shooting mode of the camera, a preview image before shooting and a confirmation image after shooting, a frame of a focus detection area at the time of focus detection, a focus state display image, and the like. The operation switch group 132 includes a power switch, a release (shooting trigger) switch, a zoom operation switch, a shooting mode selection switch, and the like. The detachable flash memory 133 records captured images.

[Image sensor]
Next, an outline of the arrangement of the imaging pixels and focus detection pixels of the imaging element 107 in the present embodiment will be described with reference to FIG. FIG. 2 shows the pixel (imaging pixel) array of the two-dimensional CMOS sensor (imaging device) of this embodiment in a range of 4 columns × 4 rows and the focus detection pixel array in a range of 8 columns × 4 rows. is there.

  The pixel group 200 includes pixels of 2 rows × 2 columns covered with color filters of a plurality of colors, and a pixel 200R having a spectral sensitivity of R (red) is a pixel 200G having a spectral sensitivity of G (green) on the upper left. Are arranged in the upper right and lower left, and a pixel 200B having a spectral sensitivity of B (blue) is arranged in the lower right. Further, each pixel includes a first focus detection pixel 201 and a second focus detection pixel 202 arranged in 2 columns × 1 row.

  A large number of 4 columns × 4 rows of pixels (8 columns × 4 rows of focus detection pixels) shown in FIG. 2 are arranged on the surface to enable acquisition of a captured image (focus detection signal).

  A plan view of one pixel 200G of the image sensor 107 shown in FIG. 2 as viewed from the light receiving surface side (+ z side) of the image sensor 107 is shown in FIG. 3A, and a cross section taken along the line aa in FIG. FIG. 3B shows a cross-sectional view as seen from the −y side. As shown in FIG. 3, in the pixel 200G of the present embodiment, a microlens 305 for condensing incident light is formed on the light receiving side of each pixel, and NH division (two divisions) is performed in the x direction and NV is performed in the y direction. A divided (one-divided) photoelectric conversion unit 301 and a photoelectric conversion unit 302 are formed. The photoelectric conversion units 301 and 302 correspond to the first focus detection pixel 201 and the second focus detection pixel 202, respectively.

  The photoelectric conversion units 301 and 302 may be a pin structure photodiode in which an intrinsic layer is sandwiched between a p-type layer and an n-type layer, or an intrinsic layer may be omitted as necessary to serve as a pn junction photodiode. Also good.

  In each pixel, a color filter 306 is formed between the microlens 305 and the photoelectric conversion units 301 and 302. In the present embodiment, any of the color filter having the spectral sensitivity of R (red), the color filter having the spectral sensitivity of G (green), and the color filter having the spectral sensitivity of B (blue) is arranged. However, the spectral sensitivity characteristic of the color filter is not limited to RGB.

  Light incident on the pixel 200 </ b> G illustrated in FIG. 3 is collected by the microlens 305, dispersed by the color filter 306, and then received by the photoelectric conversion units 301 and 302. In the photoelectric conversion units 301 and 302, electrons and holes are generated in pairs according to the amount of received light and separated by a depletion layer. Then, negatively charged electrons are accumulated in an n-type layer (not shown), while holes are constant. The light is discharged outside the image sensor 107 through a p-type layer connected to a voltage source (not shown). Electrons accumulated in n-type layers (not shown) of the photoelectric conversion units 301 and 302 are transferred to a capacitance unit (FD) via a transfer gate, converted into a voltage signal, and output.

  Note that the pixels 200R and 200B illustrated in FIG. 2 also have a configuration similar to that of the pixel 200G, and output voltage signals corresponding to light separated into colors by the color filter 306 in the same manner as the pixel 200G.

  The correspondence between the pixel structure and pupil division in this embodiment shown in FIG. 3 will be described with reference to FIG. FIG. 4 is a cross-sectional view of the pixel structure of the present embodiment shown in FIG. 3A taken along the line aa from the + y side and a view showing the exit pupil plane of the imaging optical system. In FIG. 4, the x-axis and y-axis of the cross-sectional view are inverted with respect to FIG. 3 in order to correspond to the coordinate axis of the exit pupil plane.

  The first pupil partial region 501 corresponds to the photoelectric conversion unit 301 and is substantially conjugated by the microlens 305 and the light receiving surface of the photoelectric conversion unit 301 whose center of gravity is decentered in the −x direction. It represents a pupil region that can receive light. The center of gravity of the first pupil partial region 501 is eccentric to the + X side on the pupil plane.

  The second pupil partial region 502 corresponds to the photoelectric conversion unit 302, and is substantially conjugated with the light receiving surface of the photoelectric conversion unit 302 whose center of gravity is decentered in the + x direction by the microlens 305. The photoelectric conversion unit 302 Represents a pupil region capable of receiving light. The center of gravity of the second pupil partial region 502 is eccentric to the −X side on the pupil plane.

  The pupil region 500 is a pupil region that can receive light in the entire pixel 200G when all of the photoelectric conversion units 301 and 302 are combined. Reference numeral 400 denotes the aperture of the diaphragm / shutter 102.

  The imaging plane phase difference AF is affected by diffraction because pupil division is performed using the microlens 305 of the imaging element 107. While the pupil distance to the exit pupil plane is several tens of mm, the diameter of the microlens is several μm, so that the aperture value of the microlens 305 becomes several tens of thousands, resulting in diffraction blur of several tens of mm level. Therefore, the image of the light receiving surface of the photoelectric conversion units 301 and 302 does not become a clear pupil region or pupil partial region, but becomes a pupil intensity distribution (incidence angle distribution of light reception rate).

FIG. 5 is a schematic diagram illustrating a correspondence relationship between the image sensor 107 and pupil division according to the present embodiment. At the entrance pupil distance Z _s of the image sensor, the first pupil partial region 501 corresponding to the light receiving region of the photoelectric conversion unit 301 of each pixel arranged at each position on the surface of the image sensor 107 substantially matches. It is configured. Similarly, the second pupil partial region 502 corresponding to the light receiving region of the photoelectric conversion unit 302 is configured to substantially match. In other words, at the entrance pupil distance Z _s of the image sensor 107, the division position of each pixel of the image sensor 107 and the pupil division position of the first pupil partial area 501 and the second pupil partial area 502 are approximately the same. It is configured. A pair of light beams that have passed through different pupil partial regions of the imaging optical system of the first pupil partial region 501 and the second pupil partial region 502 are incident on each pixel of the image sensor 107 at different angles and are divided 2 × 1. The photoelectric conversion units 301 and 302 receive the light. In the present embodiment, an example is shown in which the pupil region is divided into two pupils in the horizontal direction, but pupil division may be performed in the vertical direction as necessary.

  In the imaging device 107 of the present embodiment, each imaging pixel includes the first focus detection pixel 201 and the second focus detection pixel 202, but the present invention is not limited to this. If necessary, an imaging pixel that receives a light beam that has passed through the pupil region 500 including the first pupil partial region 501 and the second pupil partial region 502 of the imaging optical system, and the first focus detection pixel 201 and the second focus detection pixel 201. The focus detection pixel 202 may have an individual pixel configuration. In that case, the first focus detection pixel 201 and the second focus detection pixel 202 may be partially arranged in a part of the array of imaging pixels.

  The first focus detection signal 201 is collected by collecting the light reception signals of the first focus detection pixels 201 of the respective pixels of the image sensor 107 having the above-described configuration, and the second light detection signals of the second focus detection pixels 202 of the respective pixels are collected. A focus detection signal is generated to perform focus detection. Note that each pixel in this embodiment is covered with a color filter of any one of green (G), red (R), blue (B), and green (G) as shown in FIG. Therefore, the light reception signal of the first focus detection pixel 201 and the light reception of the second focus detection pixel 202 for each pixel group 200 including four pixels of green (G), red (R), blue (B), and green (G). The signal Y calculated by adding the signals is used as the first focus detection signal and the second focus detection signal.

  Further, by adding the light reception signals of the first focus detection pixel 201 and the second focus detection pixel 202 for each pixel corresponding to each microlens 305 of the image sensor 107, an image signal (addition) having a resolution of N effective pixels is added. Signal) can be generated.

[Relationship between defocus amount and image shift amount]
Next, the relationship between the image shift amount and the defocus amount of the first focus detection signal and the second focus detection signal acquired by the image sensor 107 of the present embodiment will be described. FIG. 6 is a diagram illustrating the relationship between the defocus amounts of the first focus detection signal and the second focus detection signal and the image shift amount between the first focus detection signal and the second focus detection signal. The imaging element 107 of the present embodiment is disposed on the imaging surface 800, and the pupil region 500 of the imaging optical system is divided into two parts, a first pupil partial region 501 and a second pupil partial region 502, as in FIGS. Is done.

  The defocus amount d is negative (d <0) when the distance from the imaging position of the subject to the imaging surface 800 is a magnitude | d |, where the imaging position of the subject is closer to the subject than the imaging surface. ), The rear pin state on the opposite side of the subject from the imaging surface 800 is defined as positive (d> 0). The focus state where the imaging position of the subject is on the imaging surface 800 (focus position) is d = 0. In FIG. 6, the subject 801 shows an example in a focused state (d = 0), and the subject 802 shows an example in a front pin state (d <0). The front pin state (d <0) and the rear pin state (d> 0) are collectively referred to as a defocus state (| d |> 0).

  In the front pin state (d <0), the subject light that has passed through the first pupil partial region 501 out of the luminous flux from the subject 802 is once condensed and then spreads to the width Γ1 with the center of gravity G1 of the luminous flux as the center. The image is blurred on the imaging surface 800. The same applies to the subject light that has passed through the second pupil partial region 502, and a blurred image having a width Γ2 centered on the gravity center position G2 is formed. The blurred image is received by the first focus detection pixel 201 and the second focus detection pixel 202 constituting each pixel arranged in the image sensor 107, and the first focus detection signal and the second focus detection are obtained from the obtained light reception signal. A signal is generated. Therefore, the first focus detection signal and the second focus detection signal are recorded as subject images in which the subject 802 is blurred by the widths Γ1 and Γ2 at the gravity center positions G1 and G2 on the imaging surface 800. The blur widths Γ1 and Γ2 of the subject image generally increase in proportion as the magnitude | d | of the defocus amount d increases. Similarly, the magnitude | p | of the object image displacement amount p (= difference G1-G2 in the center of gravity of the light beam) between the first focus detection signal and the second focus detection signal is also the size of the defocus amount d. As | d | increases, it generally increases in proportion. Even in the rear pin state (d> 0), the image shift direction of the subject image between the first focus detection signal and the second focus detection signal is opposite to that in the front pin state, but the same.

  Therefore, based on the conversion coefficient K for converting the image shift amount p into the defocus amount d and the image shift amount p of the subject image between the first focus detection signal and the second focus detection signal, which are obtained in advance. The defocus amount d can be calculated.

[Focus accuracy]
The in-focus position obtained by automatic focus detection (phase difference AF) by the above-described normal phase difference detection method is a position where the defocus amount d = 0. However, due to the aberration of the imaging optical system, a detection error that does not result in the defocus amount d = 0 at the original in-focus position occurs. As a detection error suppression method, there is a method of incorporating a correction value. However, the focus detection error caused by the chromatic aberration of magnification has a complicated mechanism involving color shading of the image sensor 107, and it may be difficult to appropriately correct the focus detection error including manufacturing variations. .

  Here, a focus detection error caused by lateral chromatic aberration will be described. In the phase difference AF, the defocus amount d is detected from the image shift amount p between the first focus detection signal and the second focus detection signal. That is, the in-focus position in the phase difference AF is determined to be in focus when the centroid position G1 of the first focus detection signal and the centroid position G2 of the second focus detection signal match.

  A procedure for calculating the gravity center positions G1 and G2 of the first and second focus detection signals (signal Y) will be described with reference to FIG. FIG. 7 is a diagram illustrating an example of each color line image by the light reception signal of the first focus detection pixel 201 and the light reception signal of the second focus detection pixel 202 when the focus lens 104 is at the in-focus position. In FIG. 7, the vertical axis indicates the signal intensity, and the light reception signal of the first focus detection pixel 201 and the light reception signal of the second focus detection pixel 202 are normalized by the signal intensity of the G signal. The horizontal axis represents the pixel position where the horizontal central coordinate of the focus detection area is zero.

First, the gravity center positions of the RGB color line images on the horizontal axis in FIG. 7 are Xr, Xg, and Xb [mm], respectively. Further, the signal intensities of RGB colors on the vertical axis in FIG. 7 are Sr, Sg, and Sb. The value of the first focus detection signal is denoted by (1), and the value of the second focus detection signal is denoted by (2). The contribution ratios Pr, Pg, and Pb of each color at the time of calculating the center of gravity are Pr (1) = Sr (1) / (Sr (1) + 2Sg (1) by RGB weighting when the first and second focus detection signals are generated. ) + Sb (1))
Pg (1) = 2Sg (1) / (Sr (1) + 2Sg (1) + Sb (1))
Pb (1) = Sb (1) / (Sr (1) + 2Sg (1) + Sb (1))
Pr (2) = Sr (2) / (Sr (2) + 2Sg (2) + Sb (2))
Pg (2) = 2Sg (2) / (Sr (2) + 2Sg (2) + Sb (2))
Pb (2) = Sb (2) / (Sr (2) + 2Sg (2) + Sb (2))
It becomes. The reason why only the coefficient of Sg is 2 is that the pixel group 200 includes two pixels of green (G). Here, the center-of-gravity difference of the line images for each RGB corresponds to the chromatic aberration of magnification, and each color contribution rate corresponds to the difference in color shading between the first focus detection pixel 201 and the second focus detection pixel 202.

Here, the centroid position G1 and the centroid position G2 are obtained by the product sum of the centroid positions Xr, Xg, and Xb of the RGB color line images and the respective color contribution ratios Pr, Pg, and Pb.
G1 = ΣXi (1) Pi (1), (i = r, g, b)
G2 = ΣXi (2) Pi (2), (i = r, g, b)
ΔG = G1-G2 [mm]
It becomes. ΔG is a centroid difference between the first focus detection signal and the second focus detection signal at the focus detection focus position obtained by the phase difference AF using the first focus detection signal and the second focus detection signal.

Since the center positions of the line images of the light reception signal of the first focus detection pixel 201 and the light reception signal of the second focus detection pixel 202 in the same color are substantially equal at the focus detection focus position,
Xi (1) = Xi (2) (i = r, g, b)
Is considered.

  Therefore, when ΔG = 0, it means that the centroids of the first focus detection signal and the second focus detection signal at the focus detection focus position are equal, and therefore there is no focus detection error due to lateral chromatic aberration. On the other hand, if the chromatic aberration of magnification is large and the difference in color shading between the first focus detection pixel 201 and the second focus detection pixel 202 is large, ΔG increases, so that the focus detection error due to the chromatic aberration of magnification also increases.

  In general, there is a considerable amount of lateral chromatic aberration in the imaging optical system, and the color shading difference between the two focus detection pixels tends to increase as the distance from the central image height increases. Furthermore, since the chromatic aberration of magnification and the color shading difference are affected by manufacturing variations, it may be difficult to perform appropriate correction.

[Weighting]
Therefore, in the present embodiment, weighting (addition coefficient set) applied to a light reception signal when generating a focus detection signal from light reception signals of a plurality of focus detection pixels having different spectral sensitivities based on lens information of the imaging optical system. By changing, the focus detection error caused by the chromatic aberration of magnification is suppressed. The lens information of the imaging optical system in the present embodiment is a lens ID that constitutes the imaging optical system. Further, in the present embodiment, the plurality of focus detection pixels having different spectral sensitivities are three types and four pixels of red (R), green (G), and blue (B). Normally, the weight of the received light signal when generating the signal Y (focus detection signal) by adding the outputs of the four pixels is determined by considering that G has two pixels, R: G: B = 1: 2: 1. It is. On the other hand, the present embodiment is characterized in that the weight of the received light signal (addition coefficient set) is changed based on the lens ID.

[Flow of focus detection processing]
FIG. 8 is a flowchart showing an outline of the flow of focus detection processing in the first embodiment. Note that the operation in FIG. 8 is executed by the CPU 121 controlling each component of the camera.

  First, in S10, a lens ID of a lens constituting the imaging optical system is acquired. Next, in S <b> 11, a focus detection area for performing focus adjustment is set in the effective pixel area of the image sensor 107. In S12, a light reception signal is acquired from the first focus detection pixel 201 and the second focus detection pixel 202 in the set focus detection region.

  In S13, based on the lens ID acquired in S10, weight adjustment is performed on the received light signals composed of RGB acquired from the first focus detection pixel 201 and the second focus detection pixel 202 using the addition coefficient set. The addition coefficient set of the lens ID and the received light signal is stored in the CPU 121. For example, as shown in Table 1, the addition coefficient set when the lens ID = A is R: G: B = 1: 2: 1. An addition coefficient set in the case of ID = B is R: G: B = 0: 2: 0. When the lens ID = B, focus detection is performed using only the green (G) light reception signal.

  In S <b> 14, an addition process is performed for each pixel group 200 on the light reception signal weighted and adjusted in S <b> 13 to generate a first focus detection signal and a second focus detection signal. In order to suppress the amount of signal data, for example, addition processing may be performed for each of the three pixel groups 200 in the column direction.

  In S15, a shading correction process (optical correction process) is performed for matching the intensities of the first focus detection signal and the second focus detection signal.

  In S16, in order to improve the correlation (signal coincidence) and improve the focus detection accuracy, the first focus detection signal and the second focus detection signal are subjected to band pass filter processing having a specific pass frequency band. Examples of bandpass filters include differential filters such as {1, 4, 4, 4, 0, -4, -4, -4, -1} that perform edge extraction by cutting DC components, and high-frequency noise. There are additive filters such as {1, 2, 1} that suppress components.

  Next, in S17, a shift process for relatively shifting the first focus detection signal and the second focus detection signal after the filter process in the pupil division direction is performed, and a correlation amount representing the degree of coincidence of the signals is calculated.

  The kth first focus detection signal after the filter processing is A (k), the second focus detection signal is B (k), and the range of the number k corresponding to the focus detection area is W. When the shift amount by the shift process is s and the shift range of the shift amount s is Γ, the correlation amount COR is calculated by the equation (1).

シフト量ｓのシフト処理により、ｋ番目の第１焦点検出信号Ａ（ｋ）とｋ−ｓ番目の第２焦点検出信号Ｂ（ｋ−ｓ）を対応させて減算し、シフト減算信号を生成する。生成されたシフト減算信号の絶対値を計算し、焦点検出領域に対応する範囲Ｗ内で番号ｋの和を取り、相関量ＣＯＲ（ｓ）を算出する。必要に応じて、各行毎に算出された相関量を、各シフト量毎に、複数行に渡って加算しても良い。

By shift processing of the shift amount s, the kth first focus detection signal A (k) and the ksth second focus detection signal B (ks) are subtracted in correspondence to generate a shift subtraction signal. . The absolute value of the generated shift subtraction signal is calculated, the sum of the numbers k is calculated within the range W corresponding to the focus detection area, and the correlation amount COR (s) is calculated. If necessary, the correlation amount calculated for each row may be added over a plurality of rows for each shift amount.

  In S18, a real-value shift amount at which the correlation amount is the minimum value is calculated from the correlation amount by sub-pixel calculation, and is set as an image shift amount p. The defocus amount d is detected by multiplying the image shift amount p by the conversion coefficient K. In S19, the lens is driven based on the detected defocus amount d.

  The focus detection error caused by the chromatic aberration of magnification has a large chromatic aberration of magnification and a large difference in color shading between the first focus detection pixel and the second focus detection pixel. This is a problem that occurs when the detection signals are added together. Therefore, in the imaging optical system in which the focus detection error caused by the lateral chromatic aberration is large, the focus detection error can be suppressed by performing focus detection only with green (G) as in lens ID = B in Table 1, for example. Further, in the case of a lens having a particularly large lateral chromatic aberration of B (blue), a detection signal obtained by adding red (R) and green (G) as in lens ID = C may be used. Further, a detection signal obtained by adding red (R), green (G), and blue (B) after halving the weight of red (R) and blue (B) as in lens ID = D may be used. .

  In the first embodiment, the CPU 121 on the imaging device side stores the relationship between the lens ID and the addition coefficient set. However, the present invention is not limited to this. For example, instead of a lens ID, an ID for each group that specifies an addition coefficient set is defined, and an addition coefficient set for a lens with a group ID = A is R: G: B = 1: 2: 1, and a group ID = B The addition coefficient set of the lenses may be configured as R: G: B = 0: 2: 0. In an interchangeable lens type imaging apparatus, an interchangeable lens having an imaging optical system has a nonvolatile memory, and the above-mentioned group ID is stored in the memory. A group ID may be transmitted from the interchangeable lens side to the imaging apparatus, and weighting may be performed using an addition coefficient set corresponding to the received group ID.

  As described above, according to the first embodiment, the influence of the magnification aberration of the imaging optical system on the focus detection result can be suppressed, and highly accurate focus detection can be performed.

<Second Embodiment>
Next, a second embodiment of the present invention will be described. In the first embodiment, the lens ID of the imaging optical system or the group ID is used as lens information of the imaging optical system, and weighting is performed when signals output from a plurality of focus detection pixels having different spectral sensitivities are added. (Addition coefficient set) was changed according to lens information. On the other hand, in the second embodiment, the weighting (addition coefficient set) when adding signals of a plurality of focus detection pixels having different spectral sensitivities is changed based on the chromatic aberration magnification information as lens information of the imaging optical system. To do. In addition, since it is the same as that of 1st Embodiment except the point which changes the weighting of a detection signal, a different point is demonstrated and description about a common point, such as a structure of a camera, is abbreviate | omitted.

  Since the focus detection error caused by the chromatic aberration of magnification increases as the chromatic aberration of magnification increases, the detection error can be suppressed by reducing the weight of the light reception signal of the focus detection pixel having a large chromatic aberration of magnification. Therefore, in the second embodiment, the relationship between the chromatic aberration of magnification information and the light reception signal is stored in the CPU 121 on the imaging apparatus side. Using G as a reference color, the addition coefficient set of the received light signal is changed as shown in Table 2 according to the chromatic aberration amounts of R and G and B and G. Here, xR is a determination threshold for chromatic aberration of magnification of R and G. If the amount of chromatic aberration of magnification of R and G is less than xR (less than the threshold), the detection signal of R is used, and if xR or more (greater than the threshold) R detection signal is not used. Similarly, xB is a threshold for determining the lateral chromatic aberration of B and G. If the amount of lateral chromatic aberration of B and G is less than xB, the B detection signal is used, and if it is greater than xB, the B detection signal is not used.

  The lens-specific magnification chromatic aberration information is stored in a non-volatile memory of an interchangeable lens having an imaging optical system. Then, the chromatic aberration of magnification information is transmitted from the interchangeable lens side to the imaging device, and weighted addition is performed using an addition coefficient set corresponding to the received chromatic aberration of magnification information. Since the amount of lateral chromatic aberration varies depending on the state of the imaging optical system, for example, lateral chromatic aberration information corresponding to the zoom state or focus state may be stored in the nonvolatile memory of the interchangeable lens. In that case, magnification chromatic aberration information corresponding to the state of the imaging optical system is transmitted to the imaging apparatus, and weighting is performed using an addition coefficient set corresponding to the received magnification chromatic aberration information.

  In the second embodiment, the adjustment method for changing the addition coefficient set using the chromatic aberration of magnification information as the lens information of the imaging optical system has been described. As lens information of the imaging optical system, it is preferable to use a variable for estimating a detection error due to chromatic aberration of magnification, in order to convert the exit pupil distance and the image shift amount p to the defocus amount d in addition to the chromatic aberration of magnification. The conversion factor K can be used. In general, an imaging optical system with a short exit pupil distance is useful for estimating a detection error due to chromatic aberration of magnification because a difference in color shading between the first focus detection pixel 201 and the second focus detection pixel 202 tends to increase. is there. In addition, since an imaging optical system with a large conversion coefficient K increases detection error due to lateral chromatic aberration, an adjustment method for changing the addition coefficient set using the conversion coefficient K as information of the imaging optical system is also effective. It is. When the exit pupil distance and the conversion coefficient K are used, for example, the addition coefficient set for colors (R, B) other than the reference color is reduced with G as the reference color.

  As described above, according to the second embodiment, the influence of the magnification aberration of the imaging optical system on the focus detection result can be suppressed, and high-precision focus detection can be performed.

<Third Embodiment>
Next, a third embodiment of the present invention will be described. In an interchangeable lens type imaging apparatus, it is known to perform calibration in a state where a combination of an interchangeable lens and an imaging apparatus is determined. Therefore, in the third embodiment, in the state where the combination of the interchangeable lens and the imaging device is determined, an appropriate detection signal weight (addition coefficient set) is set at the time of calibration. In addition, since it is the same as that of 1st Embodiment except the point which changes the weighting of a detection signal, a different point is demonstrated and description about a common point, such as a structure of a camera, is abbreviate | omitted.

  Several patterns can be considered for the addition coefficient set. In the third embodiment, the patterns shown in Table 3 are used. The pixel layout of the image sensor 107 according to the third embodiment is a Bayer array composed of RGB as shown in FIG. 2, but in this embodiment, the G pixel adjacent to the R pixel is adjacent to the Gr and B pixels. G pixels to be distinguished are distinguished as Gb. The reason for distinguishing is that Gr pixels and Gb pixels are considered to have different spectral sensitivities in consideration of optical leakage from adjacent pixels.

  FIG. 9 is a diagram illustrating an example of a relationship between the set defocus amount and the detected defocus amount when each addition coefficient set is used in the third embodiment. The set defocus amount is a correct defocus amount, and the detected defocus amount was obtained by weighting and adding the detected defocus amount using any one of the addition coefficient sets of combinations 1 to 3 shown in Table 3. Defocus amount.

  When the set defocus amount is 0, when the detection defocus amount is returned as 0, it can be said that the in-focus accuracy is the highest. Therefore, from FIG. 9, the addition coefficient set with the highest focusing accuracy is combination 3, and it is optimal to perform focus detection using the addition coefficient set of combination 3 in the combination of the interchangeable lens and the imaging apparatus of the present embodiment. Become. Therefore, when focus detection is performed using the combination of the interchangeable lens and the imaging device in this case, it is preferable to store and use in the imaging device in association with the focus detection using the combination coefficient set of combination 3.

  In addition to comparing the set defocus amount and the detected defocus amount, an addition coefficient that returns the closest detection result to the focus position where the contrast is highest can be used as a method for determining an appropriate addition coefficient set. A set may be selected. In addition, the focus detection result in a single color that is considered to have the highest detection accuracy may be a correct answer, and may be compared with a case where a combination of other addition coefficient sets is used. However, since the focus detection result in a single color has a small amount of received light, there is a problem that the S / N ratio is deteriorated. In the comparison of combinations of addition coefficient sets that can obtain an equivalent result, the combination with the highest received light amount is preferable from the viewpoint of the S / N ratio.

  In addition, since the influence of the chromatic aberration of magnification on the focus detection accuracy varies depending on the state of the lens, an appropriate addition coefficient set may be set for each aperture value. In the case of a zoom lens, an appropriate addition coefficient set may be set for each zoom position. In addition, depending on the set of addition coefficients, the parameters required to calculate the focus detection result may change greatly. When the conversion coefficient K and the shading correction value described above vary depending on the addition coefficient of the focus detection signal, an appropriate value may be calculated at the time of calibration and stored in the imaging device to be used for focus detection.

  As described above, according to the third embodiment, the influence of the magnification aberration of the imaging optical system on the focus detection result can be suppressed, and high-precision focus detection can be performed.

  Further, the present invention supplies a program that realizes one or more functions of the above-described embodiment to a system or apparatus via a network or a storage medium, and one or more processors in a computer of the system or apparatus execute the program. It can also be realized by a process of reading and executing. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

  101: First lens group, 102: Shutter / shutter, 103: Second lens group, 105: Third lens group, 107: Image sensor, 121: CPU, 124: Image sensor driving circuit, 125: Image processing circuit, 126 : Focus drive circuit, 129: Zoom drive circuit

Claims (16)

Obtained from an image sensor covered with multiple color filters that have multiple photoelectric conversion units for each of the multiple microlenses, photoelectrically convert the light incident via the imaging optical system, and output an electrical signal A focus detection device that performs focus detection by a phase difference detection method based on a plurality of color signals,
Obtaining means for obtaining an addition coefficient set indicating weighting applied to the signals of the plurality of colors according to the characteristics of the chromatic aberration of magnification of the imaging optical system;
Generating means for performing weighted addition of the signals of the plurality of colors using the addition coefficient set to generate a pair of focus detection signals;
And a detecting means for detecting an image shift amount between the pair of focus detection signals.   The acquisition unit stores a plurality of addition coefficient sets in advance, and selects one of the plurality of addition coefficient sets based on information of the imaging optical system. Focus detection device.   The focus detection apparatus according to claim 2, wherein the information on the imaging optical system is lens identification information on the imaging optical system.   The acquisition means stores a plurality of addition coefficient sets in advance, and the plurality of addition coefficient sets based on information designating any of the plurality of addition coefficient sets according to the characteristics of the chromatic aberration of magnification of the imaging optical system. The focus detection apparatus according to claim 1, wherein one of the addition coefficient sets is selected.   The focus detection apparatus according to claim 1, wherein the characteristic of lateral chromatic aberration of the imaging optical system is information indicating the magnitude of lateral chromatic aberration of the imaging optical system.   The information indicating the magnitude of the chromatic aberration of magnification is the amount of chromatic aberration of magnification between the reference color and the other colors among the plurality of colors, and the amount of chromatic aberration of magnification is not less than a predetermined threshold. The focus detection apparatus according to claim 5, wherein the addition coefficient set is made smaller than when the lateral chromatic aberration is less than the threshold value.   The information indicating the magnitude of the lateral chromatic aberration is an exit pupil distance from the imaging device to the imaging optical system, and when the exit pupil distance is greater than or equal to a predetermined threshold, the exit pupil distance is The focus detection apparatus according to claim 5, wherein an addition coefficient set for a color other than a reference color among the plurality of colors is made smaller than when it is less than a threshold value.   The information indicating the magnitude of the chromatic aberration of magnification is a conversion coefficient for converting the image shift amount into a defocus amount of the imaging optical system, and the conversion coefficient is equal to or greater than a predetermined threshold. The focus detection apparatus according to claim 5, wherein an addition coefficient set for a color other than a reference color among the plurality of colors is made smaller than when the conversion coefficient is less than the threshold value.   The focus detection apparatus according to claim 1, wherein the acquisition unit acquires the addition coefficient set from the imaging optical system. The imaging optical system is detachable from an imaging device including the imaging element,
The acquisition means stores a plurality of addition coefficient sets in advance, and among image shift amounts obtained by performing weighted addition of the signals of the plurality of colors using the plurality of addition coefficient sets,
Selecting an addition coefficient set having an image deviation amount closest to a predetermined image deviation amount, and storing the combination of the imaging optical system and the imaging device in association with the selected addition coefficient set; The focus detection apparatus according to claim 1.   The acquisition unit further selects an addition coefficient set from the plurality of addition coefficient sets according to a state of the imaging optical system, and stores the addition coefficient set in association with the state of the imaging optical system. The focus detection apparatus according to claim 10. The focus detection apparatus according to any one of claims 1 to 11,
The imaging element;
An image pickup apparatus comprising: control means for controlling the imaging optical system based on the image shift amount.   The imaging apparatus according to claim 12, further comprising the imaging optical system. Obtained from an image sensor covered with multiple color filters that have multiple photoelectric conversion units for each of the multiple microlenses, photoelectrically convert the light incident via the imaging optical system, and output an electrical signal A focus detection method for performing focus detection by a phase difference detection method based on a plurality of color signals,
An obtaining step for obtaining an addition coefficient set indicating weighting to be applied to the signals of the plurality of colors according to the characteristics of the chromatic aberration of magnification of the imaging optical system;
A generating step of generating a pair of focus detection signals by performing weighted addition of the signals of the plurality of colors using the addition coefficient set;
And a detection step of detecting an image shift amount between the pair of focus detection signals.   The program for functioning a computer as each means of the focus detection apparatus of any one of Claims 1 thru | or 11.   A computer-readable storage medium storing the program according to claim 15.

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