JP2017016064A - Focus adjustment device, focus adjustment method, and imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly accurate focus adjustment device suppressing noise of image signals and deterioration in resolution in a longitudinal direction, in a focus detection of an imaging element having a photoelectric conversion part provided with a pupil division function.SOLUTION: A focus adjustment device that performs a phase difference-based focus adjustment using focus detection signals output from an imaging element receiving a pair of light beams, having passed through pupil areas having different imaging optical systems, with a pair of photoelectric conversion parts includes ratio setting means that varies a line addition number calculated by line addition means and a frame addition number calculated by frame addition means and sets a ratio of the line addition number to the frame addition number. The ratio setting means varies the ratio on the basis of at least one of a luminance value and a contrast value.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a focus adjustment device having a focus detection function for detecting a focus state of an imaging optical system. The focus adjustment device is mounted on an imaging device as a digital still camera or a digital video camera.

  There is a phase difference detection method (hereinafter referred to as phase difference AF) as a method for detecting the focus state of the photographing lens. The light beam that has passed through the phase difference AF and the exit pupil of the photographing lens is divided into two, and the two divided beams are received by a set of focus detection sensors.

  Then, by detecting the amount of deviation of the output signal according to the amount of received light, that is, the amount of relative positional deviation in the beam splitting direction, the amount of driving of the photographing lens necessary for focusing is directly obtained. It is.

  In Patent Document 1 below, the brightness of each line of the image sensor is detected, and line addition is performed when the brightness is lower than a preset brightness.

  In Patent Document 2 below, the threshold is adjusted according to the position of the distance measuring point, and frame addition is performed until the threshold is exceeded.

JP 2010-271419 A JP 2013-37143 A

  However, in Patent Document 1, noise in the image signal used for focus detection is reduced by performing line addition based on the image signal, but the reduction in resolution in the subject vertical direction due to line addition is not considered.

  In Patent Document 2, the added luminance value is compared with the threshold value to determine the frame addition number. However, when the contrast of the subject is high, focus detection is possible even if the frame addition number is reduced. Not considered.

  Therefore, in the present invention, in focus detection in an image sensor having a photoelectric conversion unit provided with a pupil division function, a highly accurate focus detection device, imaging device, and imaging in which noise in an image signal and reduction in resolution in the vertical direction are suppressed. A system and a focus detection method are provided.

In order to solve the above problems, in the present invention, a phase difference method is used by using a focus detection signal output from an image sensor that receives a pair of light beams that have passed through different pupil regions of an imaging optical system by a pair of photoelectric conversion units. A focus adjustment device for performing focus adjustment,
Correlation for calculating a correlation amount by performing a correlation operation using a line addition unit that adds a plurality of pixels constituting the image sensor in the focus detection area in a line direction, and an addition value added by the line addition unit. An amount calculating means; a frame adding means for adding the correlation values calculated for each frame; a determining means for determining at least one of a luminance value and a contrast value of an image in the focus detection area; and the line addition. A line addition number calculated by the means and a frame addition number calculated by the frame addition means, and a ratio setting means for setting a ratio between the line addition number and the frame addition number,
The ratio setting unit varies the ratio based on at least one of the luminance value and the contrast value.

  According to the present invention, it is possible to perform focus detection using an image signal in which a reduction in resolution is suppressed and noise is suppressed with respect to a subject in a focus detection region, and a highly accurate focus detection device, imaging device, and imaging system are provided. And a focus detection method can be provided.

System configuration diagram in this embodiment Flowchart illustrating an addition ratio determination method according to the first embodiment. Explanatory drawing of the image sensor in this embodiment The figure which shows the pupil of the imaging optical system in a present Example The figure which shows the pixel line addition of the focus detection area | region in a present Example. Illustration of signal and correlation calculation in this embodiment The figure which shows the focus detection area | region in a present Example. Illustration of the optical system in this example The figure which shows the example of the to-be-photographed object inclined with respect to a focus detection area Flowchart showing a focus detection method in this embodiment Flowchart illustrating an addition ratio determination method according to the second embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In each figure, the same members are denoted by the same reference numerals, and redundant description is omitted.

  The focus adjustment apparatus of the present invention performs phase difference type focus adjustment using a focus detection signal output from an image sensor that receives a pair of light beams that have passed through different pupil regions of an imaging optical system by a pair of photoelectric conversion units. Device.

<Example 1>
(Explanation of the block diagram of FIG. 1)
First, with reference to FIG. 1, the structure of the imaging device in a present Example is demonstrated. FIG. 1 is a block diagram illustrating a configuration of the imaging apparatus 100.

  The imaging apparatus 100 is a video camera or a digital still camera that can shoot a subject and record moving image or still image data on various media such as a solid-state memory, an optical disk, and a magnetic disk, but is not limited thereto. is not.

  Each unit in the imaging apparatus 100 is connected via a bus 160. Each unit is controlled by a main CPU 151 (central processing unit).

  The imaging apparatus 100 performs imaging surface phase difference type focus adjustment using an imaging element including a plurality of photoelectric conversion elements (a first photoelectric conversion element and a second photoelectric conversion element) sharing one microlens. It is equipped with a focus adjustment device.

  Note that the focus adjustment apparatus of the present embodiment includes an imaging apparatus (imaging apparatus body) configured to be able to acquire an optical image obtained via an imaging optical system (imaging lens), and an imaging device that can be attached to and detached from the imaging apparatus body. The present invention is applied to an imaging system that includes an optical system.

  However, the present embodiment is not limited to this, and can also be applied to an imaging apparatus in which an imaging optical system is integrally provided.

  The photographing lens 101 (lens unit) includes a fixed first group lens 102, a zoom lens 111, a diaphragm 103, a fixed third group lens 121, and a focus lens 131.

  The diaphragm control unit 105 adjusts the light amount at the time of shooting by adjusting the aperture diameter of the diaphragm 103 by driving the diaphragm 103 via the diaphragm motor 104 in accordance with a command from the main CPU 151.

  The zoom control unit 113 changes the focal length by driving the zoom lens 111 via the zoom motor 112.

  The focus control unit 133 controls the focus adjustment state by driving the focus lens 131 via the focus motor 132. The focus lens 131 is a focus adjustment lens, and is simply shown as a single lens in FIG.

  A subject image formed on the image sensor 141 via these optical members (the photographing lens 101) is converted into an electric signal by the image sensor 141.

  The imaging element 141 is a photoelectric conversion element that performs photoelectric conversion of a subject image (optical image) into an electrical signal.

  In the imaging device 141, two photoelectric conversion elements (light receiving regions) are arranged in each of the light receiving elements of m pixels in the horizontal direction and n pixels in the vertical direction as described later.

  An image formed on the imaging element 141 and subjected to photoelectric conversion is arranged as an image signal (image data) by the imaging signal processing unit 142.

  The phase difference AF processing unit 135 uses image signals (signal values) output individually (independently) from two photoelectric conversion elements (first photoelectric conversion element and second photoelectric conversion element) The amount of image shift in the division direction of the image obtained by dividing the light from is detected (calculated).

  In other words, the phase difference AF processing unit 135 calculates the image shift amount by performing correlation calculation using signal values obtained independently from each of the first photoelectric conversion element and the second photoelectric conversion element. It is a quantity calculation means.

  The phase difference AF processing unit 135 is a defocus amount calculation unit that calculates a shift amount (defocus amount) in the focus direction of the photographing lens 101 based on the detected image shift amount.

  The defocus amount is calculated by multiplying the image shift amount by a coefficient (conversion coefficient).

  Each operation of the image shift amount calculation unit and the defocus amount calculation unit is performed based on a command from the main CPU 151.

  Further, at least a part of these operations may be executed by the main CPU 151 or the focus control unit 133.

  The phase difference AF processing unit 135 outputs the calculated shift amount (defocus amount) to the focus control unit 133.

  The focus control unit 133 determines a drive amount for driving the focus motor 132 based on the shift amount of the photographing lens 101 in the focus direction.

  AF control is realized by the movement control of the focus lens 131 by the focus control unit 133 and the focus motor 132.

  Image data output from the imaging signal processing unit 142 is sent to the imaging control unit 143 and temporarily stored in the RAM 154.

  The image data stored in the RAM 154 is compressed by the image compression / decompression unit 153 and then recorded on the image recording medium 157.

  In parallel with this, the image data stored in the RAM 154 is sent to the image processing unit 152. The image processing unit 152 (image processing means) processes an image signal obtained by using the addition signal of the first photoelectric conversion element and the second photoelectric conversion element.

  For example, the image processing unit 152 performs reduction / enlargement processing to an optimum size for image data.

  The image data processed to the optimum size is sent to the monitor display 150 and displayed as an image.

  Therefore, the operator can observe the captured image in real time. Note that the monitor display 150 displays the captured image for a predetermined time immediately after the image is captured, so that the operator can check the captured image.

  The operation unit 156 (operation switch) is used for an operator to give an instruction to the imaging apparatus 100. An operation instruction signal input from the operation unit 156 is sent to the main CPU 151 via the bus 160.

  The imaging control unit 143 controls the imaging element based on a command from the main CPU 151.

  Prior to this, the main CPU 151, based on an instruction from the operator input from the operation unit 156, the accumulation time of the image sensor 141, the gain setting value when performing output from the image sensor 141 to the image signal processing unit 142, Determine the aperture value of the lens unit.

  Alternatively, based on the magnitude of the pixel signal of the image data temporarily accumulated in the RAM 154, the accumulation time of the image sensor 141, the set value of the gain when performing output from the image sensor 141 to the image signal processor 142, the lens unit Determine the aperture value.

  The imaging control unit 143 receives an instruction of accumulation time and gain setting values from the main CPU, and controls the imaging element 141.

  The battery 159 is appropriately managed by the power management unit 158, and stably supplies power to the entire imaging apparatus 100. The flash memory 155 stores a control program necessary for the operation of the imaging apparatus 100.

  When the imaging apparatus 100 is activated by the operation of the operator (when the power supply is turned off from the power-off state), the control program stored in the flash memory 155 is read (loaded) into a part of the RAM 154.

  The main CPU 151 controls the operation of the imaging apparatus 100 according to a control program loaded in the RAM 154.

(Description of detection method of imaging plane phase difference method of FIGS. 3 to 5)
Next, the detection method of the imaging surface phase difference method in the present embodiment will be described. First, the configuration of the image sensor 141 will be described with reference to FIG.

  FIG. 3A is a configuration diagram (cross-sectional view) of pixels of the image sensor 141 having a pupil division function.

  The photoelectric conversion element 30 is divided into two photoelectric conversion elements 30-1 (first photoelectric conversion element) and photoelectric conversion element 30-2 (second photoelectric conversion element) per pixel, and has a pupil division function. Have.

  The microlens 31 (on-chip microlens) has a function of efficiently collecting light on the photoelectric conversion element 30, and is arranged so that the optical axis is aligned with the boundary between the photoelectric conversion elements 30-1 and 30-2.

  Further, a planarizing film 32, a color filter 33, a wiring 34, and an interlayer insulating film 35 are provided inside one pixel.

  FIG. 3B is a configuration diagram (plan view) of a part of the image sensor 141. The image sensor 141 is formed by arranging a plurality of pixels each having the configuration shown in FIG.

  In order to capture an image, R (red), G (green), and B (blue) color filters 33 are alternately arranged in each pixel, and a set of pixel blocks 40, 41, and 42 is arranged with four pixels. As a result, a so-called Bayer array is formed.

  In FIG. 3B, “1” or “2” shown below each of R, G, and B is a numerical value that represents each of the photoelectric conversion elements 30-1 and 30-2.

  FIG. 3C is an optical principle diagram of the image sensor 141, and shows a part of a cross-sectional view obtained by cutting along the line AA in FIG.

  The image sensor 141 is disposed on the planned image plane of the photographic lens 101.

  The photoelectric conversion elements 30-1 and 30-2 are configured to receive a pair of light beams that have passed through different positions (regions) of the pupil (exit pupil) of the photographing lens 101 by the action of the microlens 31. .

  The photoelectric conversion element 30-1 mainly receives a light beam that passes through the right position in FIG.

  On the other hand, the photoelectric conversion element 30-2 mainly receives a light beam that passes through the left position of the pupil of the photographing lens 101 in FIG.

  Next, the pupil of the image sensor 141 will be described with reference to FIG. FIG. 4 is a diagram illustrating the pupil 50 of the photographing lens 101 when viewed from the image sensor 141.

  51-1 is a sensitivity region (hereinafter referred to as “A image pupil”) of the photoelectric conversion element 30-1, and 51-2 is a sensitivity region of the photoelectric conversion element 30-2 (hereinafter referred to as “B image pupil”). is there. Reference numerals 52-1 and 52-2 indicate barycentric positions of the A image pupil and the B image pupil, respectively.

  When the imaging process of this embodiment is performed, an image signal can be generated by adding the outputs of two photoelectric conversion elements in which color filters of the same color are arranged in the same pixel.

  On the other hand, when performing the focus detection process of the present embodiment, the focus detection signal of one pixel is acquired by integrating the outputs from the photoelectric conversion elements corresponding to the photoelectric conversion element 30-1 in one pixel block.

  Then, it is possible to generate an A image signal by continuously acquiring this signal in the horizontal direction as in the pixel blocks 40, 41, and 42.

  Similarly, the focus detection signal of one pixel is acquired by integrating the outputs from the photoelectric conversion elements corresponding to the photoelectric conversion element 30-2 in one pixel block.

  A B image signal can be generated by continuously acquiring this signal in the horizontal direction. A pair of phase difference detection signals is generated from the A image signal and the B image signal.

  In this embodiment, as shown in FIG. 5, a pixel that has undergone pixel addition in the vertical direction in the drawing (hereinafter referred to as pixel line addition) within an appropriate range as one pixel signal of the A image signal and the B image signal. get.

  In the example of FIG. 5, an image signal used for focus detection is generated by averaging the two pixels in the Bayer array in the vertical direction (hereinafter, this case is referred to as two-line addition). The method for setting the pixel line addition number will be described later in detail.

(Explanation of correlation calculation in FIG. 6)
Next, the A image signal and the B image signal (hereinafter collectively referred to as “image signal”) will be described with reference to FIG.

  FIG. 6A is an explanatory diagram of an image signal, where the vertical axis indicates the level of the image signal and the horizontal axis indicates the pixel position. The image shift amount X of the generated pair of phase difference detection signals changes according to the imaging state (focused state, front pin state, or rear pin state) of the photographic lens 101.

  When the photographing lens 101 is in focus, the image shift amount between the two image signals is eliminated. On the other hand, in the front pin state or the rear pin state, image shift amounts in different directions occur.

  The image shift amount has a certain relationship with the distance between the position where the subject image is formed by the photographing lens 101 and the upper surface of the microlens, so-called defocus amount.

  In order to calculate the image shift amount X, correlation calculation is performed. In the correlation calculation, the correlation amount is calculated while shifting the pixels of the A image signal and the B image signal. FIG. 6B is a diagram showing a correlation amount (hereinafter referred to as a correlation amount waveform) when pixels of the image signal are shifted.

  In FIG. 6B, the horizontal axis represents the pixel shift amount, and the vertical axis represents the correlation amount between the A image signal and the B image signal at that time.

  The difference between the positions where the correlation amount is maximum is calculated as the image shift amount. When calculating the correlation amount, the two image signals are overlapped, the corresponding signals are compared with each other, and the accumulation of the smaller value is acquired.

  The accumulation of the larger value may be acquired. Moreover, you may acquire the difference of these values. Accumulation is an index indicating correlation, and when the accumulation of the smaller value is acquired, the largest value is when the correlation is high.

  When the accumulation of the larger value is acquired or when the difference is acquired, the time when this value is the smallest is the time when the correlation is high.

  The CPU 151 as the correlation amount calculation means calculates a correlation amount by performing a correlation calculation using the addition value added by the line addition means described later.

(Description of the focus detection area in FIG. 7)
Next, a focus detection area used in the focus detection method of this embodiment will be described with reference to FIG. FIG. 7 is a diagram illustrating a focus detection area. As shown in FIG. 7, a focus detection region 61 is provided at an appropriate position and at an appropriate size with respect to the imaging field angle 60.

  Each focus detection area 61 has a focus detection small area obtained by dividing the focus detection area 61 in the drawing.

  In each of the divided focus detection small areas, pixel lines for the areas are added, and a correlation calculation is performed. By performing correlation calculation for all the small areas, the correlation amount waveforms as shown in FIG.

  A correlation amount waveform in the final focus detection region 61 is obtained by adding the correlation amount waveforms corresponding to the number of divisions (hereinafter referred to as correlation amount addition). An image shift amount X that maximizes the correlation amount is calculated from the correlation amount waveform in the focus detection area 61.

  The number of divisions is the largest, which is the number of pixel lines included in the focus detection area 61, and the number of divisions, that is, how many lines are added, is switched according to the brightness of the image and other conditions. Details of this control method will be described later.

(Description of conversion from image shift amount to defocus amount in FIG. 8)
With reference to FIG. 8, the conversion from the image shift amount calculated by the correlation calculation to the defocus amount will be described.

  FIG. 8 is a diagram illustrating an optical system including the photographing lens 101 and the image sensor 141. The position p1 of the focus detection surface is on the optical axis OA at the position p0 of the planned imaging plane with respect to the subject 70.

  The relationship between the image shift amount and the defocus amount is determined according to the optical system. The defocus amount can be calculated by multiplying the image shift amount X by a predetermined coefficient K (conversion coefficient).

  The coefficient K is calculated based on the barycentric positions of the A image pupil and the B image pupil. When the position p1 of the focus detection surface moves to the position p2, the image shift amount changes according to the similarity between the triangles at the positions p0, q2, and q3 and the triangles at the positions p0, q2 ', and q3'.

  Therefore, it is possible to calculate the defocus amount at the position p2 on the focus detection surface. Based on the defocus amount, the main CPU 151 calculates the position of the focus lens 131 for obtaining a focused state with respect to the subject.

(Explanation of line addition)
Details of the pixel line addition number in this embodiment will be described. Since the image sensor in the present embodiment outputs both signals used for the focus detection unit and the image capturing unit, the image sensor is controlled based on the exposure setting value suitable for imaging. When the exposure target value with respect to the dynamic range of the pixel becomes small, the image signal used for focus detection becomes small and noise may increase.

  As a result, the variation in focus detection results also increases. Even when the operator manually sets the exposure, the image signal used for focus detection may be affected by changing the accumulation time of the image sensor or the lens aperture, and it may be difficult to detect the focus.

  Therefore, when generating one pixel of the focus detection area, it is possible to reduce noise of an image signal used for focus detection by pixel line addition.

  However, on the other hand, as shown in FIG. 9, there is a problem when the subject is tilted with respect to the focus detection area or when the contrast is low.

  In this case, if the number of pixel line additions is increased, a phenomenon such as subject collapse that reduces the resolution of the subject occurs, and as a result, the detection accuracy may decrease.

  The CPU 151 as line addition means adds a plurality of pixels constituting the image sensor in the focus detection area in the line direction (horizontal direction).

(Explanation of frame addition)
Therefore, it is conceivable to use frame addition for adding correlation amounts in time series as a method for preventing a decrease in detection accuracy due to subject crushing and a decrease in detection accuracy due to noise components.

  In this embodiment, as the frame addition, the correlation amount waveform of the focus detection area 61 shown in FIG. 7 is held, and the sum of the correlation amount waveform for a certain frame period is used as the final correlation amount.

  If the frame is added, the subject is not crushed and noise can be reduced. However, since frame addition is performed in time series, the time required until a final correlation amount result used for focus control is extended.

  In other words, low-illumination and low-brightness conditions such as when the exposure setting value is small have many noise components, and it is necessary to reduce noise using pixel line addition and frame addition, but depending on the state of the subject at that time It is important to appropriately control how much each addition method is used.

  In this embodiment, as the state of the subject, specifically, the contrast of the subject is evaluated, and the ratio of each addition method is switched according to the evaluation value.

  The contrast is calculated by calculating the square of the adjacent difference of the pixel value and calculating the accumulation for one line in the focus detection area.

  The higher the contrast, the larger this accumulated value. The calculated contrast may be the sum of absolute values of adjacent differences of pixel values.

  The CPU 151 as a frame addition unit adds the correlation values calculated for each frame.

(Description of the method for determining the ratio of line addition and frame addition in FIG. 2)
FIG. 2 is a flowchart showing a method for determining the ratio of line addition and frame addition in this embodiment. Each step in FIG. 2 is performed by the main CPU 151.

  First, in step S201, pixel values in the focus detection area 61 are read out. It is determined from the pixel value read in step S202 whether or not the luminance is low.

  As a determination method, if the average value of the pixel values for the first line is equal to or less than a predetermined value, it is determined that the luminance is low. The determination method is not limited to this, and the sampling line and the number of lines may be changed.

  Furthermore, since it is only necessary to determine whether or not the condition is that there are many noise components, the determination may be made not only based on the luminance value but also based on whether the camera is in a low illuminance condition or not.

  In step S203, if the brightness is low, the process proceeds to step S204. If the brightness is not low, the influence of the noise component is small and it is not necessary to use frame addition together.

  In step S204, the contrast value in the focus detection area 61 is calculated.

  In step S205, the number of pixel addition lines is determined from the calculated contrast value. For example, when the number of reference addition lines is 3, it is 4 if the contrast value is high, and 2 if it is low.

  In step S206, it is determined how many frames are to be added from the number of pixel addition lines determined in step S205.

  For example, if the reference frame addition number is 3 frames, the frame addition is 2 frames if the number of pixel addition lines is larger than the reference 3, and conversely, 4 frames are added if the number is smaller.

  The above is the processing for determining the addition ratio between the pixel line addition number and the frame addition number in this embodiment.

  The CPU 151 as the ratio setting means varies the line addition number calculated by the line addition means and the frame addition number calculated by the frame addition means, and sets the ratio between the line addition number and the frame addition number.

(Explanation of the flowchart showing the focus detection method of FIG. 10)
Subsequently, the focus detection method in the present embodiment will be described with reference to FIG. FIG. 10 is a flowchart showing the focus detection method. Each step in FIG. 10 is performed by the main CPU 151, the phase difference AF processing unit 135, and the focus control unit 133.

  First, in step S1001, the image sensor 141 accumulates electric charges. In step S1002, the main CPU 151 determines whether or not charge accumulation is completed.

  If the charge accumulation end time of the image sensor 141 has not been reached, the process returns to step S1001 and the image sensor 141 continues to accumulate charges.

  On the other hand, if the charge accumulation is completed in step S1002, the pixel value of the image signal in the focus detection area is read in step S1103.

  In step S1004, the main CPU 151 determines whether or not reading for a predetermined number of pixels in the focus detection area has been completed.

  If the reading for the predetermined number of pixels is not completed, the process returns to step S1003, and steps S1003 to S1004 are repeated until the reading for the predetermined number of pixels is completed.

  Subsequently, in step S1005, when the addition ratio shown in FIG. 2 is not determined, or when the addition for the determined number of frames is performed and the addition ratio is reset, the process proceeds to step S1006 and the addition ratio is determined. To do.

  If the addition ratio has already been determined, the process proceeds to step S1007.

  In step S1007, pixel line addition is performed for the first one of the focus detection small areas shown in FIG. 7 based on the set number of line additions.

  In step S1008, the main CPU 151 (the focus control unit 133 or the phase difference AF processing unit 135) performs a correlation calculation to calculate a correlation amount waveform as shown in FIG.

  In step S1009, it is determined whether or not the correlation calculation for all lines in the focus detection area has been performed. If the correlation calculation for all lines has not been completed yet, the process returns to step S1007 and the next focus detection small area is selected. From pixel line addition to correlation calculation.

  Thereafter, steps S1007 to S1009 are repeated until the correlation calculation of the all focus detection small areas included in the focus detection region 61 is completed.

  If it is determined in step S1009 that the correlation calculation has been performed for all lines, the correlation amount is added in step S1010.

  In step S1011, if the frame addition number is determined by determining the addition ratio, the process proceeds to step S1012. If not, the process proceeds to step S1014.

  In step S1012, the correlation amount calculated in step S1010 is added to the correlation amount of the previous frame addition result stored in the RAM 154, and is stored in the RAM 154 again.

  In step S1013, it is determined whether the frame addition has been performed for a predetermined period. If the frame addition has not been performed, it is necessary to continue the frame addition, and thus this flow processing ends.

  If frame addition has been performed for a predetermined period, the process proceeds to step S1014 to clear the addition ratio once determined.

  From the correlation amount calculated in step S1015, the shift amount with the highest correlation is calculated, and the image shift amount is calculated.

  Note that the calculation of the image shift amount here includes calculation of an interpolation value within one shift by performing an interpolation operation using the correlation value between the shift amount with the highest correlation and the previous and subsequent shift amounts.

  The sum of the shift amount and the interpolation value is the image shift amount X. As described above, the main CPU 151, the focus control unit 133, or the phase difference AF processing unit 135 as the image shift amount calculation unit is obtained independently from each of the first photoelectric conversion element and the second photoelectric conversion element. An image shift amount is calculated by performing correlation calculation using the obtained signal values.

  In step S1016, the main CPU 151 (focus control unit 133 or phase difference AF processing unit 135) multiplies the calculated image shift amount X by the corrected coefficient K (by the relational expression Def = K × X). ) Calculate the defocus amount.

  As described above, in this embodiment, frame addition is used under conditions such as low luminance with many noise components, and the ratio with the pixel line addition number is determined according to the state of the subject.

  Therefore, it is possible to perform focus detection using an image signal in which noise is suppressed while suppressing a reduction in resolution of the subject.

<Example 2>
Next, a method for determining the ratio of pixel line addition and frame addition in the focus detection area according to the second embodiment of the present invention will be described.

  In the first embodiment, the pixel line addition number is determined from the contrast evaluation value, and the frame addition number is determined accordingly.

  In the present embodiment, a method of setting an upper limit on the number of frame additions in consideration of whether the subject is easily affected by the movement of the subject (hereinafter referred to as subject movement condition) will be described. In the present embodiment, the same contents as those in the first embodiment are denoted by the same reference numerals and the description thereof is omitted.

  The subject movement condition in this embodiment is determined by the frame rate setting of the camera.

  When the frame rate is slow, there is an interval between frames, and it is easy to be affected by the movement of the subject.

  When the subject moves, the detection target in the small area changes as the results are added in time series, and the detection accuracy for the latest image may be reduced due to the influence of the subject that was previously captured. .

  Therefore, by providing an upper limit value for the number of frames to be added according to the frame rate, a reduction in detection accuracy due to movement of the subject is suppressed.

  In the present embodiment, the upper limit value of the number of frames added according to the frame rate, which is the subject movement condition, is 3 frames for 30 fps, 4 frames for 60 fps, 5 frames added for more frames, and 15 fps. The following is 2-frame addition.

  The subject movement condition may be determined from the zoom magnification. The higher the zoom magnification, the greater the amount of movement within the angle of view with respect to the movement of the subject. Therefore, the upper limit value is lowered when the zoom magnification is high, and conversely the upper limit value is raised when the zoom magnification is low.

(Description of the method for determining the ratio between the pixel line addition number and the frame addition number in FIG. 11)
FIG. 11 is a flowchart showing a method for determining the ratio between the pixel line addition number and the frame addition number in the focus detection area in this embodiment. Each step of FIG. 13 is performed by the main CPU 151.

  First, in step S1101, the pixel value in the focus detection area 61 is read out. It is determined from the pixel value read in step S1102 whether the luminance is low. In step S1103, if the luminance is low, the process proceeds to step S1104. If the luminance is not low, the flow processing is terminated.

  In step S1104, the contrast value in the focus detection area 61 is calculated.

  In step S1105, the pixel line addition number is determined as in the first embodiment, and in step S1106, the frame addition number is determined.

  In step S1107, a frame addition upper limit value is calculated. As described above, in the present embodiment, this upper limit value is determined from the frame rate setting.

  In step S1108, it is determined whether or not the frame addition number determined in step S1106 exceeds the frame upper limit value. When it does not exceed, this flow processing is ended, and when it exceeds, the process proceeds to step S1109.

  In step S1109, the number of frame additions is changed to the frame addition upper limit value, and this flow processing ends. This suppresses a decrease in detection accuracy due to subject movement.

  The above is the processing for determining the addition ratio between the pixel line addition number and the frame addition number in this embodiment.

  As described above, in this embodiment, frame addition is used in a condition with a lot of noise components, and the ratio of the pixel line addition number is determined in consideration of the state and movement of the subject, thereby suppressing reduction in the resolution of the subject. However, it is possible to perform focus detection using an image signal with reduced noise.

(Other embodiments)
The object of the present invention can also be achieved as follows. That is, a storage medium in which a program code of software in which a procedure for realizing the functions of the above-described embodiments is described is recorded is supplied to the system or apparatus. The computer (or CPU, MPU, etc.) of the system or apparatus reads out and executes the program code stored in the storage medium.

  In this case, the program code itself read from the storage medium realizes the novel function of the present invention, and the storage medium and program storing the program code constitute the present invention.

  Examples of the storage medium for supplying the program code include a flexible disk, a hard disk, an optical disk, and a magneto-optical disk. Further, a CD-ROM, CD-R, CD-RW, DVD-ROM, DVD-RAM, DVD-RW, DVD-R, magnetic tape, nonvolatile memory card, ROM, or the like can also be used.

  Further, by making the program code read by the computer executable, the functions of the above-described embodiments are realized. Furthermore, when the OS (operating system) running on the computer performs part or all of the actual processing based on the instruction of the program code, the functions of the above-described embodiments are realized by the processing. Is also included.

  Furthermore, the following cases are also included. First, the program code read from the storage medium is written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer. Thereafter, based on the instruction of the program code, the CPU or the like provided in the function expansion board or function expansion unit performs part or all of the actual processing.

  In addition, the present invention is not limited to devices such as digital cameras, but includes built-in or external connection of imaging devices such as mobile phones, personal computers (laptop type, desktop type, tablet type, etc.), game machines, etc. It can be applied to any device. Therefore, the “imaging device” in this specification is intended to include any electronic device having an imaging function.

Claims (9)

A focus adjustment device that performs phase difference type focus adjustment using a focus detection signal output from an image sensor that receives a pair of light beams that have passed through different pupil regions of an imaging optical system with a pair of photoelectric conversion units,
Correlation for calculating a correlation amount by performing a correlation operation using a line addition unit that adds a plurality of pixels constituting the image sensor in the focus detection area in a line direction, and an addition value added by the line addition unit. An amount calculating means; a frame adding means for adding the correlation values calculated for each frame; a determining means for determining at least one of a luminance value and a contrast value of an image in the focus detection area; and the line addition. A line addition number calculated by the means and a frame addition number calculated by the frame addition means, and a ratio setting means for setting a ratio between the line addition number and the frame addition number,
The focus adjustment apparatus, wherein the ratio setting unit varies the ratio based on at least one of the luminance value and the contrast value.   The focus adjustment apparatus according to claim 1, wherein the ratio setting unit increases the frame addition number when the luminance value is smaller than a predetermined value.   The focus adjustment apparatus according to claim 1, wherein the ratio setting unit increases the frame addition number when the contrast value is smaller than a predetermined value. A frame rate setting means for setting the frame rate;
4. The focus adjustment apparatus according to claim 1, wherein the ratio setting unit reduces the number of frame additions when the frame rate is smaller than a predetermined value. 5. Having zoom means for varying the zoom magnification;
5. The focus adjustment apparatus according to claim 1, wherein the ratio setting unit reduces the frame addition number when the zoom magnification is higher than a predetermined value. 6.   An imaging apparatus comprising: the focus adjustment apparatus according to any one of claims 1 to 5; and the imaging element. A focus adjustment method that performs phase difference focus adjustment using a focus detection signal output from an image sensor that receives a pair of light beams that have passed through different pupil regions of an imaging optical system with a pair of photoelectric conversion units,
A line addition step for adding a plurality of pixels constituting the image sensor in the focus detection area in the line direction, and a correlation for calculating a correlation amount using the addition value added in the line addition step. An amount calculating step, a frame adding step for adding the correlation values calculated for each frame, a determination step for determining at least one of a luminance value and a contrast value of an image in the focus detection area, and the line addition The line addition number calculated in the step and the frame addition number calculated in the frame addition step are varied, and a ratio setting step for setting a ratio between the line addition number and the frame addition number is provided.
The focus adjustment method, wherein the ratio setting step varies the ratio based on at least one of the luminance value and the contrast value.   A computer-executable program in which a procedure of the focus adjustment method according to claim 7 is described.   A computer-readable storage medium storing a program for causing a computer to execute each step of the focus adjustment method according to claim 7.

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