JP6395621B2 - Focus adjustment device, imaging device using the same, and focus adjustment method - Google Patents

Description

  The present invention relates to a focus adjustment apparatus suitable for use in an imaging apparatus such as a digital camera or a digital video camera.

  As one of autofocus (AF) methods mounted on an imaging apparatus such as a camera, there is a phase difference detection method (hereinafter referred to as phase difference AF). In the phase difference AF, the light beam that has passed through the exit pupil of the photographing lens is divided into two, and the two divided light beams are received by a set of focus detection sensors.

  Then, by detecting the shift amount of the signals output from the pair of focus detection sensors, that is, the relative positional shift amount in the beam splitting direction (hereinafter referred to as the image shift amount), A deviation amount (hereinafter referred to as a defocus amount) is obtained and the focus lens is controlled.

  Japanese Patent Application Laid-Open No. 2004-228688 discloses a configuration that eliminates the need for a dedicated focus detection sensor and provides phase difference AF at high speed by providing a phase difference detection function to an image sensor. In the configuration of Patent Literature 1, the photoelectric conversion unit of the pixel of the image sensor is divided into two parts to provide a pupil division function, and the focus detection is performed by individually processing the outputs of the two divided photoelectric conversion units. The total calculation power of the divided photoelectric conversion units is used as an image signal.

  Patent Documents 2 and 3 disclose a configuration that reduces the influence of defective pixels on focus detection in focus detection by a photoelectric conversion unit provided with a pupil division function.

  In the configuration of Patent Document 2, the position of the defective pixel of the image sensor is stored, and the output signal from the defective pixel is not used for focus detection, so that it is not affected by the focus detection result.

  In Patent Document 3, the position of the defective pixel of the image sensor is stored, and when focus detection is performed from the focus detection pixel area including the defective pixel, focus detection is performed using the defective pixel according to the shooting conditions. A configuration having a determination of whether to do is disclosed.

JP 2001-305415 A JP 2013-171257 A JP2013-003282A

  However, in the configuration of Patent Document 1, when a defective pixel is included in the focus detection region, the focus detection is performed including the output signal of the defective pixel, so that the accuracy of focus detection may be reduced. There is.

  In the configuration of Patent Document 2 or Patent Document 3, defective pixels in the image sensor are detected and stored in advance at the stage of adjustment at the factory. At the time of focus detection, it is determined whether or not the output is used for focus detection from the stored defective pixel position, thereby reducing the decrease in accuracy due to defective pixels in focus detection. The generated defective pixels are not taken into consideration.

  Therefore, the present invention provides a high-precision focus adjustment device, an imaging device, an imaging system, and a focus detection in an imaging device having a photoelectric conversion unit provided with a pupil division function, in which a decrease in focus detection accuracy due to defective pixels is suppressed. And a focus detection method.

The present invention provides an imaging device having a plurality of focus detection pixels each receiving a pair of light beams that have passed through different exit pupil regions of an imaging optical system, and a phase difference using a focus detection signal output from the imaging device. A focusing device having a focusing means for performing the focusing of the system,
Of the plurality of focus detection pixels, a signal value of a first focus detection signal of a first focus detection pixel and a signal value of a second focus detection signal of a focus detection pixel around the first focus detection pixel A defective pixel detection means for determining that the first focus detection pixel is a defective pixel when the difference value is equal to or greater than a predetermined threshold;
The threshold value when the number of focus detection pixels used for focus adjustment is larger than a predetermined value is set larger than the threshold value when the number of focus detection pixels used for focus adjustment is equal to or less than the predetermined value. And a threshold value setting means.

  ADVANTAGE OF THE INVENTION According to this invention, the fall of the precision of focus detection when a defective pixel is contained in a focus detection area can be suppressed, and a highly accurate focus adjustment apparatus can be provided.

It is a block diagram which shows the structure of the imaging device to which the focus adjustment apparatus in a present Example is applied. It is a flowchart which shows the imaging operation of the imaging device in a present Example. It is a figure for demonstrating the image pick-up element in a present Example. It is a figure for demonstrating the pupil division of the imaging lens in a present Example. It is a figure which shows typically the arrangement | sequence of the pixel of the focus detection area | region in a present Example. It is a figure which shows the focus detection area | region in a present Example. It is a figure which shows an example of the image signal in a present Example. It is a figure for demonstrating the imaging optical system in a present Example. It is a flowchart which shows the defective pixel detection and correction | amendment operation | movement in a present Example. It is a flowchart which shows the setting operation | movement of the detection threshold value of a defective pixel in a present Example. It is a flowchart which shows the focus detection operation | movement of the focus adjustment apparatus in a present Example. It is a flowchart which shows the focus control method concerning a present Example. It is a figure for demonstrating the pupil division | segmentation of the imaging lens in a state with many F values. It is a figure showing the image shift amount at the time of the maximum defocus with respect to F value. 10 is a flowchart illustrating an operation for setting a detection threshold value of a defective pixel in the second embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, the same reference number is attached | subjected about the same member in each figure, and the overlapping description is abbreviate | omitted.

<Example 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 tape, a solid-state memory, an optical disk, and a magnetic disk, but is not limited thereto. It is not something.

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

  The imaging apparatus 100 includes an imaging device including a plurality of focus detection pixels sharing one microlens, and performs phase difference type focus detection using an image signal (focus detection signal) output from the imaging device. It is equipped with a focus adjustment device.

  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 optical that can be attached to and detached from the imaging apparatus body. The present invention is applied to an imaging system composed of a 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 provided integrally with the imaging apparatus main body.

  The photographing lens 101 is configured as a lens unit including a first fixed lens group 102, a zoom lens 111, an aperture 103, a second fixed lens group 121, and a focus lens 131 as a focus adjusting unit.

  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 (focus state) by driving the focus lens 131 via the focus motor 132.

  The focus lens 131 is a focus adjustment lens, and is simply illustrated as a single lens in FIG.

  A subject image formed on the image sensor 141 by the photographing lens 101 composed of the optical member is converted into an electrical signal by the image sensor 141 having a plurality of focus detection pixels.

  The imaging element 141 includes a plurality of focus detection pixels that each receive a pair of light beams that have passed through different exit pupil regions of the imaging optical system 101.

  The imaging element 141 is a photoelectric conversion element that converts a subject image (optical image) into an electrical signal by photoelectric conversion. The image sensor 141 has a configuration in which light receiving elements each having m pixels in the horizontal direction (horizontal direction) and n pixels in the vertical direction (vertical direction) are arranged with two photoelectric conversion elements (light receiving regions) as described later. have.

  An electronic signal obtained by photoelectrically converting the subject image formed on the image sensor 141 is arranged as an image signal (image data) by the imaging signal processing unit 142.

  The imaging signal processing unit 142 includes a defective pixel detection and correction unit, which will be described later, and has a function of generating image data after detecting and correcting a defective pixel from an electrical signal obtained from the imaging element 141.

  The phase difference AF processing unit 135 captures image signals (signal values) output individually (independently) from two photoelectric conversion elements (first photoelectric conversion element and second photoelectric conversion element) as imaging signals. Obtained from the processing unit 142. Then, an image shift amount in the division direction of the image obtained by dividing the light from the subject is detected (calculated).

  An example in which one focus detection pixel includes two photoelectric conversion elements (a first photoelectric conversion element and a second photoelectric conversion element) will be described.

  Also, the phase difference AF processing unit 135 calculates the amount of defocus (defocus amount) 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).

  It should be noted that the image displacement amount calculation and defocus amount calculation operations are performed based on commands 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 (random access memory). The image data stored in the RAM 154 is compressed by the image compression / decompression unit 153 and then recorded on the 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. Thus, 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 by an operator to give an instruction to the imaging apparatus 100, and 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 determines the accumulation time of the image sensor 141 and the image signal from the image sensor 141 based on the instruction from the operation unit 156 or the magnitude of the pixel signal of the image data temporarily accumulated in the RAM 154. The gain value to be output to the processing unit 142 and the aperture value of the lens unit are determined.

  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.

  Next, with reference to FIG. 2, a photographing operation including focus control (focus adjustment) of the imaging apparatus 100 will be described. FIG. 2 is a flowchart illustrating the shooting operation of the imaging apparatus 100. Each step in FIG. 2 is performed based on a command according to the control program of the main CPU 151.

  First, in step S201, when the power of the imaging apparatus 100 is turned on, the main CPU 151 starts calculation (control). Subsequently, in step S202, flags and control variables of the imaging apparatus 100 are initialized, and in step S203, an optical member (imaging optical member) such as the focus lens 131 is moved to an initial position.

  Next, in step S204, the main CPU 151 detects whether or not a power-off operation has been performed by the operator (whether or not a power-off operation has been performed). If a power OFF operation is detected in step S204, the process proceeds to step S205.

  In step S205, the main CPU 151 moves the imaging optical member to the initial position and performs post-processing such as clearing various flags and control variables in order to turn off the power of the imaging apparatus 100. In step S206, the photographing operation (control) of the imaging apparatus 100 is terminated.

  On the other hand, if the power OFF operation is not detected in step S204, the process proceeds to step S207. In step S207, the main CPU 151 performs focus detection processing. Subsequently, in step S208, the focus control unit 133 drives the focus lens 131 according to the driving direction, speed, and position determined in step S207, and moves the focus lens 131 to a desired position.

  Subsequently, in step S209, the image sensor 141 photoelectrically converts the subject image by the main exposure to generate an imaging signal (imaging processing). The imaging signal processing unit 142 performs predetermined processing (image processing) on the imaging signal generated by photoelectric conversion and outputs an image signal.

  In step S210, the main CPU 151 detects whether or not the recording button (operation unit 156) has been pressed by the operator, and determines whether or not recording is in progress. If not, the process returns to step S204.

  On the other hand, if recording is in progress, the process proceeds to step S211. In step S <b> 211, the image signal (image data) output from the imaging signal processing unit 142 is compressed by the image compression / decompression unit 153 and recorded in the image recording medium 157. And it returns to step S204 and repeats each above-mentioned step.

  Next, the phase difference detection 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 of each pixel is divided into two photoelectric conversion elements 30-1 (first photoelectric conversion element) and photoelectric conversion element 30-2 (second photoelectric conversion element), 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.

  Each pixel is provided with a planarizing film 32, a color filter 33, a wiring 34, and an interlayer insulating film 35.

  FIG. 3B is a diagram (plan view) illustrating a part of the pixel array included in the image sensor 141. The imaging element 141 is formed by arranging a plurality of pixels 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 corresponds to 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 photographing lens 101 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 elements 30-1 in each pixel block. And it is possible to produce | generate A image signal by acquiring this signal continuously in a horizontal direction (horizontal direction) like pixel block 40,41,42.

  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 for the pixel blocks in the horizontal direction. A pair of phase difference detection signals is generated from the A and B image signals.

  In this embodiment, as shown in FIG. 5, the line luminance added in the vertical direction in the drawing is used within an appropriate range. In the example of FIG. 5, an image signal used for focus detection is generated by averaging the two pixel blocks in the Bayer array in the vertical direction. Note that the luminance addition number L1 can be arbitrarily set. The greater the number of luminance additions, the larger the focus detection area in the vertical direction with respect to the angle of view.

  Subsequently, a focus detection region used in the focus detection method of the present embodiment will be described with reference to FIG. FIG. 6 is a diagram illustrating a focus detection area. As shown in FIG. 6, a focus detection area 61 is provided at an appropriate position and at an appropriate size with respect to the imaging angle of view 60.

  The focus detection area 61 includes focus detection small areas 62 to 66 obtained by dividing the focus detection area 61 in the vertical direction in the drawing. In each of the divided focus detection small areas 62 to 66, the phase difference AF processing unit 135 generates the above-described pair of phase difference detection signals and performs focus detection.

  By performing correlation calculation for all small areas, correlation amount waveforms corresponding to the division number L2 are obtained. A correlation amount waveform in the final focus detection region 61 is acquired by adding the correlation amount waveforms corresponding to the division number L2 (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.

  It should be noted that a plurality of focus detection areas can be set on the imaging angle of view 60. In this embodiment, the method of providing two photoelectric conversion elements in all the pixels constituting the image sensor 141 and generating a phase difference detection signal from the focus detection region has been described, but the present invention is not limited to this.

  For example, the image sensor 141 having the structure (divided pixel structure) shown in FIG. 3A may be used only in the focus detection region.

  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. 7 is a diagram for explaining the image signal. 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 (focusing 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 case of the front pin state or the rear pin state, an image shift amount occurs in a different direction. The image shift amount has a fixed 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, the so-called defocus amount.

  Therefore, in order to calculate the image shift amount X, correlation calculation is performed on the two image signals. In this correlation calculation, a correlation value between two image signals is calculated while shifting pixels, and a difference between positions where the correlation value is maximized is calculated as an image shift amount.

  The correlation calculation is performed by the main CPU 151. The focus adjustment is performed by obtaining the defocus amount of the photographing lens from the image shift amount and calculating the lens driving amount so that the photographing lens is brought into focus.

  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.

  When a defective pixel is included in the focus detection area shown in FIG. 6, the accuracy of focus detection is lowered. Therefore, in the present embodiment, defective pixels are detected and corrected from the acquired image signal. With reference to the flowchart of FIG. 9, the defective pixel detection and correction operation in this embodiment will be described.

  The defective pixel detection and correction operation is performed by the main CPU 151 executing a control program and the defective pixel detection and correction unit of the imaging signal processing unit 142 performing calculations.

  In step S901, when a defective pixel detection and correction operation is started, in step S902, the imaging signal processing unit 142 obtains a pixel signal (focus detection signal) from the imaging element 141, and performs pixel detection for the defect. An average value A with the pixels before and after is calculated. In step S903, a detection threshold value for a defective pixel, which will be described later, is set.

  In step S904, the absolute value of the difference between the target pixel for defect detection and the average value A calculated in step S902 is calculated, and it is determined whether this is larger than the defective pixel detection threshold set in step S903. If it is smaller than the threshold value, it is determined that the pixel is not a defective pixel, and in step S906, the defective pixel detection and correction operation ends.

  On the other hand, if it is determined that the pixel value is larger than the threshold value, the pixel is a defective pixel. In step S905, the pixel signal of the pixel is replaced with the average value A, and then output from the imaging signal processing unit 142 to the phase difference AF detection unit 134. In step S906, the defective pixel detection and correction operation ends. .

  With the above operation, it is possible to simultaneously detect and correct defective pixels while reading an image signal. By performing a focus detection operation using image data obtained by detecting and correcting defective pixels, it is possible to reduce focus detection errors.

  The description of the average value and another form will be given below.

  The main CPU 151 as defective pixel detection means calculates the median value of the signal values of the focus detection pixels around the focus detection pixel that is the defective pixel, and the difference value between the signal value of the first focus detection pixel and the median value is predetermined. The first focus detection pixel is determined as a defective pixel when the threshold value is equal to or greater than the threshold value.

  The median means a value in the middle of the value of a plurality of signal values of the focus detection pixels around the focus detection pixel which is a defective pixel.

  For example, when there are five signal values of peripheral focus detection pixels, the third signal value is set as the median value. When calculating the average value, a calculation load is applied, but the median value has an advantage that no calculation is required.

  In other words, the main CPU 151 determines the focus when the difference value between the signal value of the focus detection signal of the focus detection pixel that is the defective pixel and the signal value of the focus detection signal of the focus detection pixel around the defective pixel is equal to or greater than a predetermined threshold value. The detected pixel is determined as a defective pixel.

  Next, details of the operation of setting the detection threshold value of the defective pixel in step S903 in FIG. 9 will be described with reference to FIG. FIG. 10 is a flowchart of the defective pixel detection threshold setting operation in this embodiment.

  In step S903, when the detection threshold is set to be small, it is possible to detect a small defect in which the output of the defective pixel has a small difference from the original output. However, the ratio of erroneous detection that is regarded as a defect may increase with respect to the output of a pixel that is not originally a defect, and the focus detection error may also increase.

  Therefore, the threshold value for detecting defective pixels is changed according to the setting of the focus detection area.

  In step S1001, when a defective pixel detection threshold setting operation is started, an initial value is set in the defective pixel detection threshold KTh in step S1002. This initial value is determined in advance according to the dynamic range of the image sensor.

  In step S1003, the luminance addition number L1 of the focus detection area is acquired, and it is determined whether the luminance addition number L1 is 4 lines or more. If it is 4 lines or more, the process proceeds to step S1004. If it is less than 4 lines, the process proceeds to step S1005. In step S1004, the defective pixel detection threshold value KTh is multiplied by L1 / 4. As the number of luminance additions increases, the detection threshold for defective pixels is increased.

  In step S1005, the correlation amount addition number L2 of the focus detection region is acquired, and it is determined whether or not the correlation amount addition number L2 is 4 lines or more. If it is 4 lines or more, the process proceeds to step S1006. If it is less than 4 lines, the process proceeds to step S1007. In step S1006, the defective pixel detection threshold value KTh is multiplied by L2 / 4. As the correlation amount addition number increases, the detection threshold value of the defective pixel is increased.

  In step S1007, the AF frame width W of the focus detection area is acquired, and it is determined whether the AF frame width W is 100 pixels or more. If it is 100 pixels or more, the process proceeds to step S1008, and if it is less than 100 pixels, the process proceeds to step S1009. In step S1008, the detection threshold value KTh of defective pixels is multiplied by W / 100.

  The detection threshold value of the defective pixel is increased as the width of the AF frame is increased. In step S1009, the defective pixel detection threshold setting operation ends.

  In other words, the main CPU 151 as the threshold setting unit uses the threshold when the number of focus detection pixels used for focus adjustment is larger than a predetermined value as the threshold when the number of focus detection pixels used for focus adjustment is equal to or less than the predetermined value. It is set larger than the threshold value.

  As described above, the larger the focus detection area is, and the larger the reference is made to the focus detection calculation, the less the influence of the defective pixel becomes. Therefore, the detection threshold is set so that the defective pixel detection becomes loose.

  Note that the condition for changing the detection threshold may refer to ISO sensitivity (a gain value output from the image sensor 141 to the image signal processing unit 142) in addition to the parameters described above.

  When the luminance addition number L1 and the correlation amount addition number L2 of the focus detection area are changed according to the ISO sensitivity, the defective pixel detection threshold value KTh is changed according to the ISO sensitivity.

  When the ISO sensitivity is low, the luminance addition number L1 and the correlation amount addition number L2 are both small, so the detection threshold value KTh for the defective pixel is set small.

  When the ISO sensitivity is high, both the luminance addition number L1 and the correlation amount addition number L2 are large, so the detection threshold value KTh for the defective pixel is set large.

  That is, the main CPU 151 serving as a threshold setting unit sets the predetermined threshold value larger as the number of pixels added in the vertical direction of the focus detection pixels in the focus detection area used for phase difference focus adjustment is larger.

  The main CPU 151 as the threshold setting means sets the predetermined threshold value larger as the correlation calculation amount using the signal value of the focus detection pixel in the focus detection area used for the phase difference type focus adjustment is larger.

  Next, with reference to FIG. 11, the phase difference AF by the focus adjustment apparatus in the present embodiment will be described. FIG. 11 is a flowchart showing the focus detection operation of the phase difference AF method by the focus adjustment apparatus in the present embodiment.

  Each step in FIG. 11 is performed by the main CPU 151 executing a control program to control each unit, and corresponds to step S207 in FIG.

  First, in step S1101, phase difference AF is started. In order to acquire the image signal used for the phase difference AF, the focus adjustment device generates an image signal (stored in the RAM 154) from the imaging signal output by the imaging device 141 imaging the subject image (step S1102). The process waits in S1103.

  The main CPU 151 and the imaging control unit 143 control the imaging device to perform charge accumulation (exposure) according to a predetermined accumulation time (step S1102). In step S1104, the pixel value of the image signal in the phase difference AF area is read. .

  In step S1105, the main CPU 151 determines whether or not reading for a predetermined number of pixels in the phase difference AF area has been completed. If the reading for the predetermined number of pixels is not completed, the process returns to step S1104, and steps S1104 to S1105 are repeated until the reading for the predetermined number of pixels is completed.

  In step S1106, the defective pixel detection and correction processing shown in FIGS. 9 and 10 is performed on the acquired image signal. In step S1107, pre-correction processing is performed on the image signal. This pre-correction process includes a filter process for removing noise and the like. In step S1108, the main CPU 151 performs a correlation operation on the image signal to calculate an image shift amount X.

  Subsequently, in step S1109, the main CPU 151 evaluates the reliability of the calculated image shift amount X. The evaluation value related to the reliability is calculated based on the contrast of the image signal, the degree of coincidence between the two image signals, and the like.

  Subsequently, in step S1110, the main CPU 151 determines whether or not a reliable image shift amount X is obtained based on the calculated reliability evaluation value.

  In this reliability determination, according to whether or not the reliability evaluation value calculated in step S1109 is larger than a predetermined threshold, it is determined that the reliability is greater than the predetermined value, and is determined to be unreliable if it is smaller than the predetermined value. To do.

  Note that this step S1110 includes determination as to whether or not the subject is not good at correlation calculation.

  If it is determined that there is reliability, in step S1111, the main CPU 151 multiplies the calculated image shift amount X by the corrected coefficient K (by the relational expression Def = K × X), and thereby the defocus amount. Def is calculated.

  In step S1113, the phase difference AF is terminated and the process returns to the main routine that called this processing. On the other hand, if it is determined in step S1111 that a reliable image shift amount could not be detected, phase difference AF is not performed in step S1112 (phase difference AF-NG). In step S1113, the phase difference AF is terminated, and the process returns to the main routine that called this processing.

  Next, with reference to FIG. 12, the focus control operation (focus adjustment operation) of the focus adjustment apparatus according to the present invention will be described. FIG. 12 is a flowchart showing the focus control operation of the focus adjusting apparatus in the present embodiment. Each step shown in FIG. 12 is performed by the main CPU 151 and the focus control unit 133, and corresponds to step S208 in FIG.

  When the focus control operation of this embodiment is started, the main CPU 151 performs a predetermined calculation according to the control program. The focus control unit 133 controls the focus motor 132 based on a command from the main CPU 151.

  First, when focus control is started in step S1201, in step S1202, the focus control unit 133 acquires the defocus amount calculated by the focus detection operation shown in FIG. In step S1203, the focus control unit 133 calculates the drive amount (lens drive amount) of the focus lens 131 based on the defocus amount.

  The calculation of the lens driving amount includes calculation of the lens driving direction and speed. Subsequently, in step S1204, the main CPU 151 (focus control unit 133) determines whether or not the absolute value of the defocus amount is equal to or less than a predetermined value.

  If the absolute value of the defocus amount is not less than or equal to the predetermined value in step S1204, the process proceeds to step S1205. In step S1205, since the position of the focus lens 131 is not considered to be the focus position (focus point), the focus lens 131 is driven according to the lens drive amount calculated in step S1203, and the process proceeds to step S1207.

  Thereafter, focus detection and focus lens driving are repeated according to the flow shown in FIG.

  On the other hand, if the absolute value of the defocus amount is equal to or smaller than the predetermined value in step S1204, the process proceeds to step S1206. At this time, since the focus lens position is considered to be in focus, lens driving is stopped in step S1206, and the process proceeds to step S1207.

  Thereafter, focus detection is performed according to the flow shown in FIG. 2, and when the defocus amount exceeds a predetermined value again, the focus lens 131 is driven.

  The operation of the imaging apparatus 100 is repeated a plurality of times until the subject is focused by repeating the flow of FIGS. 7, 10, and 11 until the power is turned off as shown in the flow of FIG. Perform focus detection.

  As described above, in this embodiment, when a defective pixel is included in the focus detection area, it is possible to simultaneously detect and correct a defective pixel while reading an image signal.

  Further, by using a value corrected for a defective pixel for focus detection, focus detection can be performed while suppressing a decrease in focus detection accuracy. Detection of defective pixels requires comparison with surrounding pixels, and a threshold value is required for that purpose, but by detecting the defective pixel detection threshold according to the setting of the focus detection area, focus detection can be performed. It is possible to perform suitable defective pixel detection.

<Example 2>
Next, an operation for setting a detection threshold value of a defective pixel according to the second embodiment of the present invention will be described. In the first embodiment, the method of setting the threshold value for detecting defective pixels according to the size of the focus detection area has been described.

  In the present embodiment, a method for setting a detection threshold value of a defective pixel in accordance with the size of a reference area when performing focus detection calculation 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.

  FIG. 13 is a diagram illustrating the pupil of the photographing lens 101 in a state where the F value is large. The pupil 53 of the photographing lens 101 with a large F value is smaller than the pupil 50 of the photographing lens 101 with a small F value. Along with this, the distance between the gravity center positions 55-1 and 55-2 of the A image pupil 54-1 and the B image pupil 54-2 becomes shorter than the distance between 52-1 and 52-2. Therefore, the predetermined coefficient K (conversion coefficient) for calculating the defocus amount from the image shift amount in the state where the F value is large is larger than that in the state where the F value is small.

  FIG. 14 shows the image shift amount when the most defocused when a photographic lens is a representative example according to the F value. The horizontal axis indicates the F value, and the vertical axis indicates the size of the reference area necessary for calculating the image shift amount in the correlation calculation. When the F value is large, the image shift between the two image signals when the photographing lens is most defocused is small. Therefore, the number of pixels required for focus detection changes.

  FIG. 15 is a flowchart of an operation for setting a detection threshold value of a defective pixel in this embodiment. Steps S1501 to S1508 are the same as steps S1001 to S1008 in FIG.

  In step S1509, the F value of the photographing lens is acquired, and it is determined whether this F value is 4 or more. If it is 4 or more, the process proceeds to step S1510. If it is less than 4, the process proceeds to step S1511. In step S1510, the defective pixel detection threshold KTh is multiplied by 4 / F. The larger the F value, the smaller the defective pixel detection threshold. In step S1511, the defective pixel detection threshold setting operation is terminated.

  In the present embodiment, as an example of changing the size of the reference area when performing the focus detection calculation, the method of changing the defective pixel detection threshold according to the F value has been described. In the system in which the focus detection is performed a plurality of times until the subject shown in the flow in FIG. 2 is focused, the present reference range can be changed according to the result of the previous focus detection.

  As described above, in this embodiment, the detection threshold value of the defective pixel is set according to the size of the reference area when performing the focus detection calculation. Therefore, when a defective pixel is included in the focus detection region, it is possible to simultaneously detect and correct the defective pixel while reading the image signal. Further, by using a value corrected for a defective pixel for focus detection, focus detection can be performed while suppressing a decrease in focus detection accuracy.

  In addition, the numerical value in a present Example is an example, and although the setting which increases / decreases the detection threshold of a defective pixel proportionally according to the brightness | luminance addition number or the correlation amount addition number was described, for example, defective pixel is adjusted by the addition / decrease of a fixed value. The detection threshold may be increased or decreased.

  Further, the initial value is arbitrary, and can be arbitrarily set according to the structure of the image sensor or the model of the image pickup apparatus to be mounted. Further, a lower limit value and an upper limit value may be added to the detection threshold value of the defective pixel.

  According to each of the embodiments described above, it is possible to provide a highly accurate focus adjustment device, an imaging device, an imaging system, and a focus detection method that suppress a decrease in accuracy of focus detection due to defective pixels.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

DESCRIPTION OF SYMBOLS 30 Photoelectric conversion element 31 Micro lens 61 Focus detection area 101 Shooting lens 103 Diaphragm 131 Focus lens 133 Focus control part 135 Phase difference AF processing part 141 Image pick-up element 142 Imaging signal processing part 143 Imaging part control part 151 CPU

Claims (11)

An image pickup device having a plurality of focus detection pixels each receiving a pair of light beams that have passed through different exit pupil regions of the image pickup optical system, and a phase difference type focus adjustment using a focus detection signal output from the image pickup device A focus adjusting device having a focus adjusting means,
Of the plurality of focus detection pixels, a signal value of a first focus detection signal of a first focus detection pixel and a signal value of a second focus detection signal of a focus detection pixel around the first focus detection pixel A defective pixel detection means for determining that the first focus detection pixel is a defective pixel when the difference value is equal to or greater than a predetermined threshold;
The threshold value when the number of focus detection pixels used for focus adjustment is larger than a predetermined value is set larger than the threshold value when the number of focus detection pixels used for focus adjustment is equal to or less than the predetermined value. And a threshold value setting means.   The defective pixel detection means calculates an average value of signal values of focus detection pixels around the first focus detection pixel, and a difference value between the signal value of the first focus detection pixel and the average value is the predetermined value. The focus adjustment apparatus according to claim 1, wherein the first focus detection pixel is determined to be a defective pixel when the threshold is equal to or greater than a threshold value.   The defective pixel detection means calculates a median value of signal values of focus detection pixels around the first focus detection pixel, and a difference value between the signal value of the first focus detection pixel and the median value is the predetermined value. The focus adjustment apparatus according to claim 1, wherein the first focus detection pixel is determined to be a defective pixel when the threshold is equal to or greater than a threshold value.   4. The threshold value setting unit sets the predetermined threshold value larger as the number of pixels in the horizontal direction of focus detection pixels in a focus detection region used for focus adjustment by the phase difference method is larger. The focus adjustment apparatus according to any one of the above.   The threshold value setting unit sets the predetermined threshold value larger as the number of vertical pixel additions of focus detection pixels in a focus detection region used for focus adjustment by the phase difference method is larger. 5. The focus adjustment device according to any one of 4.   The threshold value setting means sets the predetermined threshold value larger as a correlation calculation amount using a signal value of a focus detection pixel in a focus detection region used for focus adjustment by the phase difference method is larger. The focus adjustment apparatus according to any one of 1 to 5.   7. The focus adjustment apparatus according to claim 1, wherein the threshold setting unit increases the predetermined threshold as the aperture diameter of the imaging optical system increases.   2. The threshold value setting unit sets the predetermined threshold value larger as a gain multiplied by a signal value of a focus detection pixel in a focus detection region used for focus adjustment by the phase difference method is larger. The focus adjustment apparatus according to any one of 1 to 7. The focus adjustment is repeatedly performed until it is determined that the focus position is in-focus,
The threshold setting means sets the predetermined threshold used for the current focus adjustment to be smaller than the predetermined threshold used for the previous focus adjustment when the previous focus adjustment approaches the in-focus state. The focus adjusting apparatus according to any one of claims 1 to 8.   An imaging apparatus comprising: the focus adjustment apparatus according to any one of claims 1 to 9; and the imaging optical system. An image pickup device having a plurality of focus detection pixels each receiving a pair of light beams that have passed through different exit pupil regions of the image pickup optical system, and a phase difference type focus adjustment using a focus detection signal output from the image pickup device A focus adjustment method for a focus adjustment device, comprising:
Of the plurality of focus detection pixels, a signal value of a first focus detection signal of a first focus detection pixel and a signal value of a second focus detection signal of a focus detection pixel around the first focus detection pixel A defective pixel detection step of determining the first focus detection pixel as a defective pixel when the difference value is equal to or greater than a predetermined threshold;
The threshold value when the number of focus detection pixels used for focus adjustment is larger than a predetermined value is set larger than the threshold value when the number of focus detection pixels used for focus adjustment is equal to or less than the predetermined value. And a threshold value setting step. A focus adjustment method for a focus adjustment device.

Images