JP6501512B2 - Focus control apparatus, focus control method and focus control program - Google Patents

Description

  The present invention relates to focus control in optical devices such as imaging devices such as digital still cameras and digital video cameras and interchangeable lenses, and more particularly to focus control using imaging surface phase difference AF and contrast AF in combination.

  In the imaging plane phase difference AF, on an image pickup element for picking up an object image formed by an optical system, a pair of object images having a shift amount according to the focus state of an imaging system including the optical system and the image pickup element Let it form. Then, the defocus amount of the imaging system is obtained from the shift amount (phase difference) of the pair of image signals obtained by photoelectrically converting the pair of subject images by the image sensor, and the drive amount calculated from the defocus amount By moving the focusing element by only the focus state of the imaging system can be obtained.

  On the other hand, in contrast AF, high frequency components are extracted from the output of the image pickup element obtained by photoelectrically converting an object image, and a contrast evaluation value indicating the contrast state of the object image is acquired. Then, the focusing element is moved to the focusing position where the contrast evaluation value becomes maximum (peak) to obtain the focusing state.

  In Patent Document 1, based on the focus detection result obtained by phase difference AF, the focus lens is moved to the vicinity of the position where the in-focus state can be obtained, and after that, the contrast AF is performed to achieve high speed and high accuracy. An imaging device capable of obtaining a focused state is disclosed. Further, in the imaging device of Patent Document 1, when the reliability of the focus detection result obtained by the phase difference AF is high, the focus lens is moved based on the focus detection result until the focus state is approached, and then the contrast is obtained. Perform AF. Thereby, the in-focus state can be obtained at a higher speed.

JP, 2010-256824, A

  However, even if contrast AF is performed after phase difference AF is performed as disclosed in Patent Document 1, in the situation where the subject is illuminated by a fluorescent lamp, the effect of the flicker generated by the fluorescent lamp is sufficient. There is a possibility that the in-focus state may be erroneously determined although the in-focus state is not achieved. As a result, the in-focus state can not be obtained at high speed and with high accuracy.

The present invention, when used in combination the phase difference AF and contrast AF, providing a focus control equipment which is adapted focus state is obtained at high speed and with high accuracy by reducing the influence of flicker.

A focus control apparatus according to one aspect of the present invention controls driving of a movable focus element in an imaging system that photoelectrically converts an object image formed by an optical system by an imaging device. The focus control apparatus includes a first focus detection means for performing phase difference focus detection calculating the phase difference or La Defense focus of a pair of image signals generated using the output of the image sensor, the driving of the focus element Accordingly, the second focus detection unit that generates a contrast evaluation value corresponding to the contrast of the subject image using the output of the imaging device, the luminance change detection unit that detects a periodic luminance change of the object, and the defocus amount It has a phase difference focus control which controls the drive of a focus element based on it, and a control means which performs contrast focus control which controls drive of a focus element using contrast evaluation value. Then, the control means performs contrast focus control when a predetermined condition regarding at least one of the focus state of the optical system, the reliability of phase difference focus detection, and the defocus amount is satisfied when the above-mentioned change in luminance is detected. When the above conditions are not satisfied, phase difference focus control is performed.

A focus control method as another aspect of the present invention is a method of controlling driving of a movable focus element in an imaging system that photoelectrically converts an object image formed by an optical system by an imaging device. The focus control method includes the steps of performing phase difference focus detection calculating the phase difference or La Defense focus of a pair of image signals generated using the output of the image pickup device, with the driving of the focus element, the imaging element The step of generating a contrast evaluation value corresponding to the contrast of the subject image using the output, the step of detecting the periodic luminance change of the subject, and the phase difference focus control of controlling the drive of the focusing element based on the defocus amount. And a control step of performing contrast focus control to control driving of the focus element using the contrast evaluation value. Then, in the control step, when the change in the brightness is detected, the contrast focus control is performed when a predetermined condition regarding at least one of the focus state of the optical system, the reliability of phase difference focus detection and the defocus amount is satisfied. When the above conditions are not satisfied, phase difference focus control is performed.

A focus control program according to another aspect of the present invention causes a computer of an optical device to control driving of a movable focus element in an imaging system that photoelectrically converts an object image formed by an optical system by an imaging device. It is a computer program. The focus control program causes the computer to perform the phase difference focus detection calculating the phase difference or La Defense focus of a pair of image signals generated using the output of the image pickup device, with the drive of the focus element, imaging The phase difference focus control and contrast which generate the contrast evaluation value corresponding to the contrast of the subject image using the output of the element, detect the periodic luminance change of the subject, and control the drive of the focusing element based on the defocus amount. A control process is performed to perform contrast focus control to control the drive of the focus element using the evaluation value. Then, when the above-mentioned change in brightness is detected, in the control processing, when the computer satisfies a predetermined condition regarding at least one of the focus state of the optical system, the reliability of phase difference focus detection and the defocus amount, Focus control is performed, and when the condition is not satisfied, phase difference focus control is performed.

According to the present invention, it is possible to avoid that contrast focus control is not performed accurately due to the influence of periodical luminance change of an object, so even if such luminance change occurs, focusing can be performed quickly and accurately. You can get the status.

3 is a flowchart illustrating AF processing in Embodiment 1 of the present invention. FIG. 1 is a block diagram showing the configuration of an imaging device according to a first embodiment. FIG. 6 is a diagram for explaining a flicker detection method in the first embodiment. The figure explaining contrast AF. It is a figure explaining setting of the step width of lens drive amount. 6 is a flowchart illustrating AF processing in Embodiment 2 of the present invention. 10 is a flowchart for explaining calculation processing of the degree of focusing in the second embodiment. FIG. 8 is a diagram for explaining a peak determination threshold at the time of flicker detection in the second embodiment. FIG. 8 is a diagram for explaining the reliability threshold value of phase difference focus detection in the second embodiment.

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

  In the first embodiment, a single-lens reflex digital camera in which an interchangeable lens can be attached and detached is described as an imaging device. FIG. 2 shows the configuration of the single-lens reflex digital camera of this embodiment. The camera has an interchangeable lens unit 100 and a camera body (optical apparatus) 120. The interchangeable lens unit 100 is detachably connected to the camera body 120 via a mount M shown by a dotted line in the figure.

  The interchangeable lens unit 100 includes an imaging optical system including a first lens group 101, a diaphragm shutter 102, a second lens group 103, and a focus lens group (hereinafter simply referred to as a focus lens) 104 in order from the object side, and lens control described later Have a system. The imaging optical system forms a subject image on light from a subject (not shown).

  The first lens group 101 is movably held in the optical axis direction OA of the imaging optical system. The diaphragm / shutter 102 adjusts the amount of light by changing the diameter of the aperture, and functions as a shutter when capturing a still image. The aperture-shutter 102 and the second lens group 103 move integrally in the optical axis direction OA, and perform magnification change with the moving first lens group 101. A focusing lens 104 as a focusing element moves in the optical axis direction OA to perform focusing.

  The lens control system includes a zoom actuator 111, an aperture shutter actuator 112, a focus actuator 113, a zoom drive circuit 114, an aperture shutter drive circuit 115, a focus drive circuit 116, a lens MPU 117, and a lens memory 118. The zoom actuator 111 moves the first lens group 101 and the second lens group 103 in the optical axis direction OA during zooming. The zoom actuator 111 has a zoom position detection unit (not shown) that detects the current position (zoom position) of the first and second lens groups 101 and 103. The aperture shutter actuator 112 opens and closes the aperture shutter 102. The focus actuator 113 moves the focus lens 104 in the optical axis direction OA. The focus actuator 113 has a focus position detection unit (not shown) that detects the current position (focus position) of the focus lens 104.

  The zoom drive circuit 114 drives the zoom actuator 111 according to the zoom operation of the user. The shutter drive circuit 115 drives the aperture shutter actuator 112. The focus drive circuit 116 drives the focus actuator 113.

  The lens MPU 117 can communicate with a camera MPU 125 described later through a communication terminal provided on the mount M. The lens MPU 117 controls the zoom drive circuit 114, the shutter drive circuit 115, and the focus drive circuit 116 in accordance with an instruction from the camera MPU 125. The lens MPU 117 detects the current zoom position and focus position and notifies the camera MPU 125 of the detected zoom position and focus position. The lens memory 118 stores optical information necessary for auto focus (AF), and the lens MPU 117 transmits the optical information to the camera MPU 125 in response to a request from the camera MPU 125.

  The camera body 120 includes an optical low pass filter 121, an imaging device 122, and a camera control system described later. The optical low pass filter 121 reduces false color and moiré of a captured image. The imaging element 122 is constituted by a C-MOS sensor and its peripheral circuit, and has a plurality of pixels consisting of m pixels (horizontal direction) × n pixels (vertical direction). The imaging element 122 is configured to be able to output independently from each pixel.

  The imaging element 122 also includes a plurality of pixels that output a phase difference focus detection signal used to perform focus detection calculation according to the phase difference detection method. The phase difference focus detection signal is a signal generated by photoelectric conversion of a pair of optical images (object images) whose shift amount changes according to the focus state of the imaging system including the imaging optical system and the imaging device 122. is there. The phase difference focus detection signal is used to generate a pair of image signals corresponding to the pair of optical images.

  As the imaging element 122, it is possible to use one having a plurality of pairs of phase difference focus detection pixels for photoelectrically converting light fluxes which have passed through different regions of the exit pupil of the imaging optical system, in addition to the plurality of imaging pixels. it can. A pair of image signals can be generated using outputs from a plurality of (or part of) pairs of phase difference focus detection pixels. In addition, as the imaging element 122, each of all the pixels has a micro lens and a pair of photoelectric conversion portions, and a pair of optical images formed of two light beams divided by the micro lenses is photoelectrically converted It is also possible to use one that can generate a pair of image signals. In the imaging device having this configuration, a pixel signal for imaging can be extracted by combining the outputs of the pair of photoelectric conversion units of each pixel.

  The camera control system includes an imaging element drive circuit 123, an image processing circuit 124, a camera MPU 125, a display 126, an operation switch group 127, and a memory 128. Furthermore, the camera control system includes an imaging plane phase difference focus detection unit (first focus detection unit) 129 and a contrast focus detection unit (second focus detection unit) 130.

  The imaging device driving circuit 123 causes the imaging device 122 to perform a photoelectric conversion operation and a pixel signal reading operation, A / D converts the read pixel signal, and outputs it to the image processing circuit 124 and the camera MPU 125. The image processing circuit 124 performs image processing such as γ conversion and color interpolation on the digital pixel signal to generate an image signal, and further performs processing such as compression on the image signal.

  The camera MPU 125 includes an imaging element driving circuit 123, an image processing circuit 124, a display 126, an operation SW 127, a memory 128, an imaging surface phase difference focus detection unit (hereinafter referred to as a phase difference focus detection unit) 129, and a contrast focus detection unit 130. Control. Also, the camera MPU 125 transmits a command or request to the lens MPU 117, and receives optical information of the interchangeable lens unit 100 from the lens MPU 117.

  The camera MPU 125 performs AF processing as focus control processing while controlling the phase difference focus detection unit 129 and the contrast focus detection unit 130. Further, in the imaging surface phase difference AF performed while controlling the phase difference focus detection unit 129, the camera MPU 125 has the reliability of the detection result by the phase difference focus detection unit 129 due to the influence of vignetting when the image height of the focus detection position is high. Because it decreases, it also processes to correct it. Furthermore, the camera MPU 125 performs imaging processing while controlling the imaging element driving circuit 123 and the image processing circuit 124. The camera MPU 125 incorporates a ROM 125a storing a computer program for controlling various operations of the camera body 120, a RAM 125b storing variables used for various calculations, and an EEPROM 125c storing parameters used for various controls.

  The display 126 is configured by an LCD or the like, and displays information regarding an imaging mode, a preview image generated before recording for recording, a recording image generated by recording for recording, and a focusing state at the time of focus detection.

  The operation switch group 127 includes a power switch, a release (imaging trigger) switch, a zoom operation switch, an imaging mode selection switch, and the like. A memory 128 is a flash memory that can be attached to and detached from the camera body 120, and records an image for recording.

  The phase difference focus detection unit 129 performs focus detection (phase difference focus detection) by the phase difference method. Specifically, the phase difference focus detection unit 129 performs a correlation operation on a pair of image signals generated using the output from the image pickup device 122 to obtain a phase difference that is a shift amount of the pair of image signals. Calculate Then, the defocus amount corresponding to the focus state of the imaging system (in the present embodiment, the imaging optical system) is calculated from the phase difference. The driving amount of the focus lens 104 (phase difference focusing driving amount: hereinafter, also simply referred to as focusing driving amount) which brings the imaging system into focus can be obtained from the defocus amount. The in-focus state of the imaging system includes not only the state in which the defocus amount is zero but also the state in which the defocus amount is close to zero. That is, it means that the focus state of the imaging system is within a predetermined range (focusing range) that can be regarded as the in-focus state.

  On the other hand, the contrast focus detection unit 130 performs focus detection (contrast focus detection) by a contrast detection method also referred to as a TVAF method. Specifically, the contrast focus detection unit 130 uses the high frequency component etc. of the image signal generated by the image processing circuit 124 using the output of the imaging device 122 to handle the contrast of the image signal (that is, the object image). To generate a contrast evaluation value (TVAF evaluation value). The contrast evaluation value is generated each time the focus lens 104 is driven by a predetermined drive amount (hereinafter, referred to as an AF pitch amount). The position of the focus lens 104 at which the contrast evaluation value is maximum (peak) is the in-focus position where the imaging system is in focus (hereinafter referred to as the contrast in-focus position). Although details will be described later, the AF pitch amount is set to a first pitch amount (a first predetermined amount) in a state where the focus lens 104 is away from the contrast in-focus position. And if it is located in the vicinity of the contrast focusing position, it is changed to a second pitch amount (second predetermined amount) smaller than the first pitch amount.

  As described above, the camera body 120 of this embodiment can perform both imaging plane phase difference AF (phase difference focus control) and contrast AF (contrast focus control), and these can be used alone or in combination. Use this to bring the imaging system into focus.

  Next, AF processing performed by the camera MPU 125 will be described with reference to FIG. FIG. 1 is a flowchart showing the contents of the AF process. The camera MPU 125, which is a computer, executes this process according to a focus control program, which is a computer program. The camera MPU 125 also functions as a luminance change detection unit and a control unit. In FIG. 1, "S" is an abbreviation of step.

  The camera MPU 125, which has started the AF process in step 100, exposes the image sensor 122 in step 101. As a result, it is possible to obtain an output signal from the imaging element 122 for acquiring a pair of image signals used for imaging surface phase difference AF and a contrast evaluation value used for contrast AF.

  Next, in step 102, the camera MPU 125 causes the contrast focus detection unit 130 to perform contrast focus detection. That is, the contrast focus detection unit 130 generates a contrast evaluation value while driving (moving) the focus lens 104 via the lens MPU.

  Subsequently, in step 103, the camera MPU 125 causes the phase difference focus detection unit 129 to perform phase difference focus detection. That is, the phase difference focus detection unit 129 generates a pair of image signals, and performs a correlation operation on the pair of image signals to calculate their phase difference, and further, based on the phase difference, the defocus amount (hereinafter , Detect defocus amount).

  Next, in step 104, the camera MPU 125 calculates the reliability of phase difference focus detection by the phase difference focus detection unit 129. In other words, the reliability of the defocus amount obtained by the phase difference focus detection is calculated. The reliability is determined based on not only the degree of coincidence of the pair of image signals used for phase difference focus detection but also the contrast of the pair of image signals. The reason for considering the contrast of a pair of image signals is that a pair of image signals obtained from a subject with high contrast can calculate the coincidence more accurately than a pair of image signals obtained from a subject with low contrast, As a result, their phase differences can also be calculated with high accuracy.

Specifically, the reliability is obtained as follows.
First, the coincidence between the pair of image signals is obtained as follows. The correlation operation shown in equation (1) is performed on a pair of image signals (a1 to an, b1 to bn: n is the number of data) read out from the phase difference focus detection pixel, and the correlation amount Corr (l) Calculate

In equation (1), l represents the image shift amount, and the number of data when the image is shifted is limited to n−1. Further, the image shift amount l is an integer, and is a relative shift amount in units of data intervals of the data string. When the correlation between the pair of data is the highest, the correlation amount Corr (l) is minimized. Furthermore, using the correlation amount Corr (m) (the shift amount m which becomes the minimum) and the correlation amount calculated in the shift amount close to m, the local minimum value Corr (for the continuous correlation amount by the three-point interpolation method) d) Find the shift amount d that gives. The coincidence degree FLVL of the pair of image signals is set to a value Corr (d) at the highest degree of correlation with the correlation amount Corr (l) calculated by the equation (1).

  When the defocus amount is large, the asymmetry of the A image and the B image becomes large, so the FLVL becomes large and the reliability deteriorates. Generally, FLVL for the defocus amount is calculated lower as the lens position is closer to the in-focus position, and the reliability tends to be high.

Next, the contrast PB of the pair of image signals is determined as follows. Let amax be a maximum value of a1 to an, amin be a minimum value of a1 to an, bmax be a maximum value of b1 to bn, and bmin be a minimum value of b1 to bn. in this case,
PBa = amax-amin (2)
PBb = bmax-bmin (3)
It becomes. The contrast PB of the pair of image signals is set to the smaller value of PBa and PBb calculated by the equations (2) and (3).

  The reliability is calculated by normalizing the coincidence degree FLVL of the pair of image signals and the contrast PB of the pair of image signals, and the higher the FLVL and PB, the higher the reliability.

  Next, in step 105, the camera MPU 125 determines the presence or absence of flicker. The flicker referred to herein is a periodic change in luminance of the subject due to a periodic change in luminance of a light source such as a fluorescent lamp that illuminates the subject. The method of flicker determination will be described with reference to FIG. 3 showing temporal change in luminance of an image signal obtained by imaging an object under a fluorescent lamp. In FIG. 3, the frequency of the power source for lighting the fluorescent lamp is 50 Hz, and a periodic luminance change is shown as a flicker waveform when the occurrence frequency of the flicker of the fluorescent lamp is 100 Hz (flicker cycle = about 10 ms). . The camera MPU 125 is a partial image signal of the contrast evaluation range (and its vicinity) which is a focus detection target area in the contrast AF among the image signals of the entire photographed screen generated by the image processing circuit 124 as the luminance for flicker determination. Measure using Hatched circles shown on the flicker waveform in FIG. 3 indicate measurement points of luminance when the operation cycle of the image sensor 122 corresponding to the frame rate of the image signal is 60 fps (exposure cycle = about 16.7 ms). ing.

  The camera MPU 125 performs flicker determination, for example, as follows. First, the camera MPU 125 sets a time sufficiently longer than the exposure cycle of the image sensor 122 as the flicker measurement range, and measures the luminance (hereinafter referred to as measurement luminance) in the partial image signal described above for each exposure cycle. Then, the camera MPU 125 detects the minimum value T11 and the maximum value T12 of the measured luminance in the flicker measurement range, and if the difference between the minimum value T11 and the maximum value T12 is larger than a predetermined flicker determination threshold (predetermined luminance difference), flicker occurs. It determines that it exists. In order to improve the accuracy of the flicker determination, the flicker determination may be repeatedly performed in a plurality of flicker measurement ranges, and it may be finally determined that the flicker is present when the determination of the presence of the flicker is performed a predetermined number of times or more.

  The process of flicker determination in step 105 is not performed every time in the next and subsequent routines started by returning from step 115 to step 101 described later, but every predetermined number of routines (that is, every predetermined period) To do). Within one predetermined period, the result of the flicker determination made in the first routine of that period is held.

  Further, the processes of steps 101 to 105 do not necessarily need to be performed after the start of the AF process, and may be performed before the start of the AF process. In addition, a method of determining (detecting) the presence or absence of flicker is a method other than the method shown in FIG. 3, for example, a method using the output of a light receiving element that directly receives reflected light from an object without using an image signal. It is also good.

  In step 106, the camera MPU 125 determines whether the reliability of phase difference focus detection calculated in step 104 is higher than the focusable threshold (first reliability). If the in-focus threshold is a reliability higher than this, at least the in-focus state described above can be obtained by driving the focusing lens 104 by the in-focus driving amount calculated based on the defocus amount obtained by phase difference focus detection. It is the degree of confidence that the in-range focus state can be obtained. If the degree of reliability is higher than the focusable threshold value, the process proceeds to step 107.

  In step 107, the camera MPU 125 calculates the drive amount (phase difference focus drive amount) of the focus lens 104 corresponding to the defocus amount calculated in step 103. Then, in step 108, the camera MPU 125 drives the focus lens 104 by the calculated phase difference focusing drive amount.

  Thereafter, in step 109, the camera MPU 125 exposes the image sensor 122, obtains the phase difference between the pair of image signals again, and obtains the detected defocus amount from the phase difference. Then, in this step, it is determined whether or not the detected defocus amount falls within the in-focus range, that is, whether or not the in-focus state is obtained. If the in-focus state is obtained, the camera MPU 125 ends the AF processing. If the in-focus state is not obtained, the camera MPU 125 returns to step 107.

  Here, although the case of confirming whether the in-focus state has been obtained in step 109 after driving the focus lens 104 in step 108 has been described, the confirmation is not necessarily required. For example, when the in-focus drive amount calculated in step 107 is smaller than a predetermined value, it is possible to consider that the error in the detected defocus amount and the in-focus drive amount is small and to omit confirmation of the in-focus state.

  On the other hand, when it is determined in step 106 that the reliability of phase difference focus detection is lower than the in-focus threshold, the camera MPU 125 determines in step 110 whether or not it is determined in step 105 that flicker is present.

  If it is not determined that there is flicker (if it is determined that there is no flicker), the camera MPU 125 proceeds to step 111 and determines whether or not the peak of the contrast evaluation value has been detected. FIG. 4A shows the relationship between the position (horizontal axis) of the focus lens 104 and the contrast evaluation value (vertical axis) in contrast AF when no flicker occurs. Every time the focus lens 104 is driven from the contrast AF start position T1 by the AF pitch amount, a contrast evaluation value is acquired. The hatched circles indicate the position of the focus lens 104 at which the contrast evaluation value is acquired until the peak of the contrast evaluation value is detected (hereinafter referred to as the contrast evaluation value acquisition position). As shown in FIG. 4A, in the camera MPU 125, the change in the contrast evaluation value accompanying the driving of the focus lens 104 switches from an increase to a decrease, and a decrease equal to or more than a predetermined decrease amount, a peak determination threshold, occurs. judge.

  If a peak is detected in step 111, the camera MPU 125 calculates the drive amount of the focus lens 104 for driving the focus lens 104 to the contrast in-focus position where the peak is detected in step 112. Then, the camera MPU 125 performs control to drive the focus lens 104 to the contrast in-focus position through the lens MPU 117 in step 113, and ends the contrast AF and further the AF processing.

  On the other hand, when a peak is not detected in step 111, the camera MPU 125 proceeds to step 114 and calculates the drive amount of the focus lens 104 by a drive amount calculation method described later. Then, the camera MPU 125 performs control to drive the focus lens 104 by the drive amount calculated in step 114 through the lens MPU 117 in step 115, and then returns to step 101.

  If it is determined in step 110 that there is flicker, the camera MPU 125 does not determine whether or not the peak of the contrast evaluation value is detected (step 111), and focuses on the driving amount calculation method described later in step 114. The driving amount of the lens 104 is calculated. Then, the camera MPU 125 performs control to drive the focus lens 104 by the drive amount calculated in step 114 through the lens MPU 117 in step 115, and then returns to step 101.

  Here, the reason why the determination as to whether or not the peak of the contrast evaluation value is detected when it is determined that there is flicker will be described. FIG. 4B shows the relationship between the position (horizontal axis) of the focus lens 104 and the contrast evaluation value (vertical axis) in the contrast AF when flicker is generated. Every time the focus lens 104 is driven from the contrast AF start position T1 by the AF pitch amount, a contrast evaluation value is acquired. The hatched circles indicate the contrast evaluation value acquisition positions shown in FIG. 4A.

  In general, the contrast evaluation value increases as the contrast, which is the contrast between the subject and the subject, increases. Also, the higher the luminance of the subject, the higher the contrast, and the higher the contrast evaluation value. Therefore, the amount of change in the contrast evaluation value with respect to the amount of driving (pitch amount) of the focus lens 104 differs according to the contrast and the luminance of the subject.

  Since the brightness of the image signal periodically changes when flicker occurs, the contrast evaluation value obtained as the focus lens 104 is driven includes the original evaluation value component corresponding to the focus state of the imaging system. Not only the change but also the periodically changing component due to the flicker is included. In such a case, as shown in FIG. 4B, at the position T6 before the true contrast in-focus position T4, the decrease amount of the contrast evaluation value which has turned from an increase to a decrease becomes equal to or higher than the peak determination threshold. Is falsely determined to have been detected. As a result, a false contrast in-focus position T5 different from the true contrast in-focus position T4 is detected as the contrast in-focus position. That is, even if the focus lens 104 is driven to the false contrast in-focus position T5, the in-focus state of the imaging system can not be obtained.

  In this embodiment, in order to avoid the contrast AF based on the detection of such a false contrast in-focus position, the peak detection of the contrast evaluation value is not performed in the state where the flicker occurs. That is, the imaging plane phase difference AF based on the detected defocus amount obtained by the phase difference focus detection in step 103 is performed without performing the contrast AF. In the imaging plane phase difference AF, the detected defocus amount is obtained by one exposure of the imaging element 122, and therefore, it is difficult to be affected by the flicker.

  Next, a method of calculating (setting) the drive amount of the focus lens 104 at step 114 will be described. Although the focus lens 104 is not driven by the contrast AF in the state where the flicker occurs, in this step, the first pitch amount or the second pitch amount as the drive amount of the focus lens 104 described above is set.

  FIG. 5 shows the relationship between the first and second pitch amounts and the contrast evaluation value. The horizontal axis indicates the position of the focus lens 104, and the vertical axis indicates the contrast evaluation value. In FIG. 5, a graph connecting white circles shows an example of a change in contrast evaluation value with respect to the driving amount of the focus lens 104 when the subject has high contrast and high luminance. The graph connecting the black circles shows an example of the change in the contrast evaluation value with respect to the drive amount of the focus lens 104 when the object has low contrast and low luminance. White circles and black circles indicate the position of the focus lens 104 for obtaining the contrast evaluation value.

  When the subject has high contrast and high luminance, the change in the contrast evaluation value with respect to the drive amount of the focus lens 104 is large, so the AF pitch amount of the focus lens 104 is set to a second pitch amount R2 smaller than the first pitch amount R1. Set For example, it is assumed that R2 = 1/2 × R1. Thereby, the position where the contrast evaluation value peaks can be detected with high precision.

  On the other hand, when the subject has low contrast and low luminance, the change in contrast evaluation value with respect to the driving amount of the focus lens 104 is small. Therefore, if the AF pitch amount of the focus lens 104 is set to the narrow second pitch amount R2, a clear change in the contrast evaluation value can not be detected. In general, the contrast evaluation value includes noise due to signal noise and change in the condition of the subject, in addition to the contrast component corresponding to the contrast of the subject. For this reason, when the contrast evaluation value itself is low or the change in the contrast evaluation value for each drive of the focus lens 104 is small, the contrast evaluation value may change due to the influence of the noise, which does not correspond to the subject's contrast. As a result, the focus lens 104 may be driven in a direction different from the true contrast in-focus position. Therefore, when the subject has low contrast and low luminance, the AF pitch amount of the focus lens 104 is set as the first pitch amount R1 to make it easy to detect a change in the correct contrast evaluation value.

  Further, in the present embodiment, the camera MPU 125 determines whether the subject has high contrast (and high luminance), as in the case of the luminance measured for the above-described flicker determination. ) Using the partial image signal in the vicinity). Specifically, the sum of the output differences of adjacent pixels in the partial image range in which the partial image signal is acquired is calculated as the contrast of the subject. Then, it is determined whether or not the subject is high contrast depending on whether the contrast of the subject is equal to or more than a predetermined threshold value, and the AF pitch amount is set to the second pitch amount and the first pitch amount.

  More simply, it may be determined whether the subject is in high contrast or not based on whether or not the maximum signal value of the partial image signal in the contrast evaluation range (and its vicinity) is equal to or more than a predetermined threshold. Furthermore, when a plurality of image signals (captured images) are obtained in advance by multiple times of imaging with different positions of the focus lens 104, the sum of squares of the output difference between adjacent pixels in each image signal is a predetermined value. Whether or not the subject is in high contrast may be determined based on whether it is equal to or greater than a threshold.

  Thus, in step 114, the camera MPU 125 sets the drive amount of the focus lens 104 to the first pitch amount or the second pitch amount.

  According to the present embodiment, the erroneous detection of the in-focus state (peak of the contrast ratio evaluation value) by the contrast AF is performed by performing only the imaging surface phase difference AF without performing the contrast AF in the state where the flicker is generated. You can prevent. As a result, it is possible to reduce the influence of flicker and obtain an in-focus state at high speed and with high accuracy.

  Next, a second embodiment of the present invention will be described. In the first embodiment, the contrast AF is not performed when the flicker occurs. On the other hand, in the present embodiment, even when flicker occurs, predetermined conditions (a state near the in-focus state described later, a low reliability of phase difference focus detection, or a small detection defocus amount) When the above condition is satisfied, contrast AF is performed.

  The configurations of the camera body and the interchangeable lens unit in the present embodiment are the same as in Embodiment 1, and the components common to those in Embodiment 1 are assigned the same reference numerals as in Embodiment 1. The AF processing performed by the camera MPU 125 will be described. FIG. 6 is a flowchart showing the contents of the AF process. The camera MPU 125, which is a computer, executes this process according to a focus control program, which is a computer program. The camera MPU 125 also functions as a flicker detection unit, a reliability acquisition unit, and a control unit. In FIG. 6, "S" is an abbreviation of step.

  The processes of steps 201 to 210 are the same as the processes of steps 101 to 110 in the first embodiment (FIG. 1), and thus the description thereof will be omitted.

  The camera MPU 125 determines in the camera step 210 whether or not it is determined in step 205 that there is flicker. If it is not determined that there is flicker (if it is determined that there is no flicker), the camera MPU 125 proceeds to step 211 and determines whether the peak of the contrast evaluation value is detected as in step 111 of the first embodiment. judge.

  On the other hand, if it is determined in step 210 that there is flicker, the camera MPU 125 proceeds to step 214 and uses the contrast evaluation value to determine that the current focus state is near the in-focus state (hereinafter referred to as in-focus state). It is determined whether or not The camera MPU 125 determines whether or not it is in the near in-focus state using the degree of focusing (hereinafter referred to as PL) calculated by the processing shown in the flowchart of FIG. 7.

  In FIG. 7, in step S501, the camera MPU 125 obtains the difference between the maximum value and the minimum value of luminance in the partial image signal in the contrast evaluation region (hereinafter referred to as MMP). By using this MMP, it is possible to estimate to some extent the contrast of the subject within the contrast evaluation range even if it is not in focus.

In step S502, the camera MPU 125 acquires a contrast evaluation value (hereinafter also referred to as EVA). EVA becomes larger as it gets closer to the in-focus state. Then, in step 503, the camera MPU 125 calculates PL according to the following equation using MMP and EVA.
PL (%) = (EVA / MMP) x 100
PL indicates the ratio (%) of the current contrast evaluation value to the contrast of the subject. Therefore, the degree of blurring of the subject image, that is, the degree of focusing of the imaging system with respect to the subject can be obtained according to the size of PL. Then, when the degree of focusing is equal to or higher than a predetermined threshold, the camera MPU 125 determines that the state is in the near in-focus state.

  As a method different from this, an increase amount of the contrast evaluation value with respect to a predetermined drive amount (AF pitch amount) of the focus lens 104 within a predetermined time is calculated as an evaluation value increase rate (change rate). If it is equal to or higher than a predetermined threshold value, it may be determined as a near in-focus state.

  The camera MPU 125 that has determined in step 214 to be in the near in-focus state proceeds to step 211, and determines whether or not the peak of the contrast evaluation value is detected. In general, the change in the contrast evaluation value becomes larger as the focus state is approached, so that erroneous detection of the peak hardly occurs even if the contrast evaluation value changes due to the influence of the luminance change due to the flicker. For this reason, in the present embodiment, when it is determined to be in the near in-focus state, peak detection is performed. If a peak is detected in step 211, the camera MPU 125 proceeds to step 212 and step 213. The processes of step 212 and step 213 are the same as the processes of step 112 and step 113 of the first embodiment, and thus the description thereof is omitted.

  On the other hand, the camera MPU 125 that has determined in step 214 not to be in the near in-focus state proceeds to step 215. In step 215, the camera MPU 125 determines whether the reliability of phase difference focus detection obtained in step 204 is higher than the defocus usable threshold (second reliability) as the predetermined reliability. If the defocus enable threshold value is higher than this, it is permitted to use the detected defocus amount by phase difference focus detection as an aid, assuming that the final focus state is obtained by the contrast AF. It is the degree of reliability that can be done. This defocus usable threshold is lower in reliability than the focusable threshold described in step 106 of the first embodiment (in this embodiment, used in step 206).

  If it is determined in step 215 that the reliability is lower than the defocus available threshold value, the camera MPU 125 proceeds to step 211 and determines whether a peak of the contrast evaluation value is detected. This is because, when the reliability of phase difference focus detection is low, it can not be determined whether or not it is close to the in-focus state, and therefore peak detection of the contrast evaluation value is performed to avoid as much as possible non-focusability. .

  If the reliability is higher than the defocus usable threshold value in step 215, the camera MPU 125 proceeds to step 216 and the detected defocus amount obtained in step 203 is equal to or larger than the predetermined defocus amount (or larger than the predetermined defocus amount). It is determined whether or not. If the detected defocus amount is smaller than the predetermined defocus amount, the camera MPU 125 proceeds to step 211 and determines whether the peak of the contrast evaluation value is detected. This is because it can be determined that the state in which the detected defocus amount is small is close to the in-focus state, and therefore there is no problem in performing peak detection.

  If it is determined in step 216 that the detected defocus amount is equal to or greater than the predetermined defocus amount, the camera MPU 125 proceeds to step 217 without determining whether or not the peak of the contrast evaluation value is detected in step 211.

  At step 217, the camera MPU 125 calculates the phase difference focusing drive amount of the focus lens 104 corresponding to the detected defocus amount obtained at step 203. Then, the camera MPU 125 calculates a drive amount smaller by a predetermined drive amount than the phase difference focusing drive amount. The predetermined drive amount is set so that the focus lens 104 is positioned sufficiently in front of the peak of the contrast evaluation value while driving the focus lens 104 in contrast focus detection to be performed in the subsequent and subsequent routines. Ru. The camera MPU 125 may change the predetermined drive amount so as to increase as the defocus amount increases.

  Then, in the next step 218, the camera MPU 125 controls the focus lens 104 to be driven by the drive amount calculated in step 217. Thereafter, the camera MPU 125 returns to step 101.

  In the present embodiment, the peak detection (step 211) of the contrast evaluation value is performed by satisfying a predetermined condition even in the state where flicker is occurring, but at this time, the peak judgment threshold is used as flicker. It is desirable to make it larger than when not doing it. This makes it possible to avoid erroneous peak detection even if the contrast evaluation value fluctuates due to the influence of flicker. This will be described with reference to FIG.

  FIG. 8 shows the relationship between the position (horizontal axis) of the focus lens 104 and the contrast evaluation value (vertical axis) in contrast AF in the case where flicker is occurring, as compared with FIG. 4B. The peak determination threshold is increased. Every time the focus lens 104 is driven from the contrast AF start position T1 by the AF pitch amount, a contrast evaluation value is acquired. The hatched circles indicate the positions for obtaining the contrast evaluation value.

  In FIG. 8 as well as FIG. 4 (b), the contrast evaluation value which has been increasing up to that point is turned to decrease at a position T6 before the true contrast in-focus position T4, but the amount of decrease is a peak It is smaller than the judgment threshold. Therefore, the drive of the focus lens 104 is continued, and a decrease in the contrast evaluation value above the peak determination threshold occurs at the position T7 beyond the true contrast in-focus position T4, so that the peak of the contrast evaluation value is detected. . This makes it possible to avoid false peak detection due to the influence of flicker.

  In addition, when flicker occurs, the threshold value regarding the reliability of phase difference focus detection may be changed from the case where flicker does not occur. This will be described with reference to FIG. FIG. 9A shows a focusable threshold value and a defocus available threshold value, which are thresholds relating to the reliability of phase difference focus detection when no flicker occurs. FIG. 9B shows the focusable threshold value and the defocus available threshold value in the case where the flicker occurs. If flicker is occurring, there is a high possibility that the correct AF state can not be obtained by the contrast AF. Therefore, as shown in FIG. 9 (b), the focusable threshold and the defocus available threshold are set lower than in the case where the flicker shown in FIG. 9 (a) is not generated, respectively. The phase difference AF can be facilitated.

  According to this embodiment, contrast AF is performed only when predetermined conditions regarding the focus state, the reliability of phase difference focus detection, and the defocus amount at the time of occurrence of flicker are satisfied, and in the other cases. Performs an imaging plane phase difference AF. By not performing the contrast AF when not in the in-focus state, it is possible to prevent erroneous detection of the in-focus state (peak of the contrast evaluation value) due to the influence of flicker. In addition, when the reliability of the phase difference focus detection is lower than the defocus available threshold value, performing the contrast AF can prevent the focusing failure. Furthermore, when the defocus amount is smaller than the predetermined defocus amount, the in-focus state can be obtained at high speed by permitting the contrast AF. As described above, it is possible to perform AF processing in which accuracy and speed are compatible.

  In the above embodiment, the periodic luminance change of the subject caused by the flicker of the light source illuminating the subject is detected. However, the periodic luminance change occurs in the subject due to any other cause. The AF processing described in the above embodiment may be applied to

  In the above embodiment, the focus adjustment is performed by driving the focus lens 104 as the focus element in the optical axis direction. However, the imaging element 122 is driven (moved) as the focus element in the optical axis direction. You may adjust the focus with

In the above embodiment, the case where the camera MPU 125 provided in the lens exchange type camera body (optical apparatus having an imaging device) 120 performs phase difference and contrast AF has been described. However, the interchangeable lens unit 100 as an optical apparatus having an optical system is provided with first and second focus detection means for performing phase difference and contrast AF, luminance change detection means, reliability acquisition means, and control means. It is also good. Further, the first and second focus detection means, the luminance change detection means, the reliability acquisition means, and the control means may be provided in a lens-integrated camera (optical apparatus having an optical system and an imaging device).
(Other embodiments)
The present invention supplies a program that implements one or more functions of the above-described embodiments to a system or apparatus via a network or storage medium, and one or more processors in a computer of the system or apparatus read and execute the program. Can also be realized. It can also be implemented by a circuit (eg, an ASIC) that implements one or more functions.

  The embodiments described above are only representative examples, and various modifications and changes can be made to the embodiments when the present invention is implemented.

100 imaging optical system 122 imaging device 125 camera MPU
129 Imaging plane phase difference focus detection unit 130 Contrast focus detection unit

Claims (10)

A focus control device that controls driving of a movable focus element in an imaging system that photoelectrically converts an object image formed by an optical system by an imaging device, comprising:
A first focus detection means for performing phase difference focus detection calculating the phase difference or La Defense focus of a pair of image signals generated using the output of the image sensor,
A second focus detection unit configured to generate a contrast evaluation value corresponding to the contrast of the subject image using the output of the imaging device as the focusing device is driven;
Luminance change detection means for detecting a periodic luminance change of an object;
Control means for performing phase difference focus control for controlling the drive of the focus element based on the defocus amount and contrast focus control for controlling the drive of the focus element using the contrast evaluation value;
When the change in luminance is detected, the control means
Focus state before Symbol optical system, the performs the contrast focus control when a predetermined condition is satisfied for at least one of the reliability and the defocus amount of the phase difference focus detection, the position when not satisfied the conditions A focus control apparatus characterized by performing phase difference focus control. Wherein the predetermined condition is focal condition focus control device according to claim 1, characterized in that it is in a predetermined focus near state. Said control means, before whether the Kigoase near state, a ratio or the focus element of the difference between the contrast evaluation value of the maximum value and the minimum value of the image signal generated from the output of the image sensor The focus control device according to claim 2, wherein the determination is made using a change rate of the contrast evaluation value accompanying driving.   The focus control device according to claim 1, wherein the predetermined condition is that the reliability is lower than a predetermined reliability.   5. The focus control apparatus according to claim 4, wherein the control unit makes the predetermined reliability lower than that in the case where the change in luminance is not detected when the change in luminance is detected. The focus control device according to claim 1, wherein the predetermined condition is that the defocus amount is smaller than a predetermined defocus amount. The control means
The peak of the contrast evaluation value is detected by the change of the contrast evaluation value from the increase to the decrease with the driving of the focusing element and the amount of the decrease being larger than the predetermined decrease amount;
In the contrast focus control performed when the predetermined condition is satisfied, when the change in luminance is detected, the predetermined amount of decrease is made larger than when the change in luminance is not detected. The focus control device according to any one of 6.   The focus control apparatus according to any one of claims 1 to 7, wherein the luminance change detection unit detects the luminance change from an image signal generated using an output from the imaging device. A focus control method for controlling driving of a movable focus element in an imaging system that photoelectrically converts an object image formed by an optical system by an imaging device, comprising:
And performing phase difference focus detection calculating the phase difference or La Defense focus of a pair of image signals were generated using the output of the image sensor,
Generating a contrast evaluation value corresponding to the contrast of the subject image using the output of the imaging device as the focusing device is driven;
Detecting a periodic luminance change of the subject;
It has a phase difference focus control for controlling the drive of the focus element based on the defocus amount, and a control step for performing the contrast focus control for controlling the drive of the focus element using the contrast evaluation value,
In the control step, when the change in luminance is detected,
Focus state before Symbol optical system, the performs the contrast focus control when a predetermined condition is satisfied for at least one of the reliability and the defocus amount of the phase difference focus detection, the position when not satisfied the conditions A focus control method characterized by performing phase difference focus control. A focus control program as a computer program that causes a computer of an optical apparatus to control driving of a movable focus element in an imaging system that photoelectrically converts an object image formed by the optical system by an imaging device,
On the computer
To perform the phase difference focus detection calculating the phase difference or La Defense focus of a pair of image signals generated using the output of the image sensor,
With the drive of the focusing element, the output of the imaging element is used to generate a contrast evaluation value corresponding to the contrast of the subject image,
Detect periodic changes in luminance of the subject,
A control process is performed to perform phase difference focus control for controlling the drive of the focus element based on the defocus amount and contrast focus control for controlling the drive of the focus element using the contrast evaluation value.
When the change in luminance is detected, the control processing includes:
Focus state before Symbol optical system, to perform the contrast focus control when a predetermined condition is satisfied for at least one of the reliability and the defocus amount of the phase difference focus detection, the when not satisfied the conditions A focus control program characterized by performing phase difference focus control.