JP2009251342A - Imaging apparatus, focus control method, program and integrated circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging apparatus with an autofocus function which is good in following ability and is stable and copes with a situation in which a subject changes largely. <P>SOLUTION: In the imaging apparatus, an optical path separation part separates subject light converged by an optical system at least to a first luminous flux and a second luminous flux. An imaging part for photography converts the first luminous flux into an electrical signal and outputs it as a main line system video signal, an imaging part for autofocus converts the second luminous flux into an electrical signal and outputs it as a video signal for autofocus, and an autofocus evaluated value generation part generates a contrast evaluated value of a video. A control part achieves an AF function by automatically switching between a mode in which a focusing position is searched while changing optical path length of the second luminous flux on the basis of the contrast evaluated value, and a mode in which an optimum optical path length difference is calculated by situation and the focusing position is searched on the basis of size relation of the contrast evaluated values from a plurality of imaging parts for autofocus arranged with the calculated optical path length difference. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image pickup apparatus with an autofocus function for automatically focusing.

Conventionally, as an imaging device such as a video camera, a multi-plate type using a color separation prism (an imaging device using a plurality of imaging elements) is used. Such an imaging apparatus has a color separation prism for acquiring a luminous flux for obtaining a video signal by color-separating subject light, and further, a plurality of luminous fluxes for detecting a focus state (in-focus state). It has a branching optical path for acquisition. In such an imaging apparatus, the imaging elements that receive a plurality of light beams for detecting the focus state (light beams separated from the subject light) are arranged at positions having different optical path lengths. With this configuration, autofocus ( Hereinafter, the function is referred to as “AF”) (see, for example, Patent Document 1).
More specifically, such a conventional imaging apparatus color-separates a light beam obtained by condensing subject light with a lens into three color lights of blue light, red light, and green light. And a plurality of (at least two) optical paths for detecting the focus state. In the conventional imaging device, the imaging device for detecting the focus state is arranged at a position where the optical path length becomes shorter and a position where the optical path length becomes shorter than the optical path length of the imaging device for obtaining the color video signal. In such a conventional image pickup apparatus, each image obtained from each focus state detection image pickup element arranged at a position of a different optical path length before and after the optical path length of the image pickup element for obtaining the color video signal is used. A focus evaluation value for each focus state detection image sensor is obtained based on the high-frequency component, and a focus state is detected based on the obtained focus evaluation value for each focus state detection image sensor. Thereby, in the conventional imaging device, the in-focus position can be automatically adjusted, and a quick in-focus operation can be performed with a simple configuration without using a so-called wobbling method.

There has also been proposed an imaging apparatus with an AF function in which one of a pair of focus state detection imaging elements arranged at different optical path length positions is movable in the optical axis direction (for example, a patent) Reference 2). In such an image pickup apparatus with an AF function, it moves when the image is out of focus, that is, when the focus state (focus state) cannot be detected from each image acquired by a pair of focus state detection image sensors. The focusing operation can be continuously performed by moving one focus state detecting image pickup element configured to be on the optical axis.
JP 2002-296493 A JP 2006-215284 A

However, in the conventional imaging apparatus as described above, when the subject is largely changed, the focus state (based on the high-frequency component of each image obtained from each focus state detection image sensor disposed at a position of a different optical path length ( There is a problem that a case where the in-focus state cannot be detected occurs.
Further, in the conventional image pickup apparatus as described above, the position of the pair of focus state detection image pickup elements on the optical axis is changed by changing the position of the pair of focus state detection image pickup elements on the optical axis. Continue to focus). In this state, when the focus state is detected again based on the high-frequency component of each image acquired by the pair of focus state detection image sensors, the conventional image pickup apparatus as described above has a pair of focus states. The widths of the different optical path lengths of the detection image pickup devices (the distance between a pair of focus state detection image pickup devices arranged at different positions on the optical axis) are fixed. For this reason, in a conventional imaging device, even in the vicinity of the in-focus point due to the lens state such as the iris position (iris state) and the zoom position (zoom state) and the pattern of the subject (for example, when the subject is only a white object). There is a problem that the focus state cannot be detected and malfunction occurs.

  The present invention solves the above-described conventional problems, and in the imaging apparatus, the focus control method, the program, and the integrated circuit, the tracking capability that can cope even when the subject changes greatly (when the subject situation changes greatly). An object of the present invention is to realize a stable and stable AF function (autofocus function).

The first invention includes an optical system, an optical path separation unit, a photographing imaging unit, an autofocus imaging unit, an optical path length change unit, an autofocus evaluation value generation unit, an autofocus control mode determination unit, And an adaptive autofocus control unit.
The optical system collects light from the subject and can control the focus. The optical path separation unit separates light from the subject collected by the optical system into at least a first light flux group and two or more second light flux groups for focus detection. The photographing imaging unit converts the first light flux group into an electrical signal and outputs it as a main video signal. The autofocus imaging unit includes at least a front imaging device and a back imaging device, converts two or more second light flux groups for focus detection into electrical signals, and outputs the signals as autofocus detection video signals. To do. The optical path length changing unit changes the optical path length of the second light beam to the autofocus imaging unit by moving the autofocus imaging unit on the optical axis of the second light beam group. The autofocus evaluation value generator generates a contrast evaluation value that is a contrast evaluation value of the video signal for autofocus detection. The autofocus control mode determination unit is based on the contrast evaluation value, and changes the optical path length of the autofocus imaging unit while searching for the in-focus position, and a plurality of autofocus units arranged in different optical path lengths. The optical path length difference comparison mode for searching for an in-focus position based on the contrast evaluation value from the imaging unit is switched, and an autofocus control mode signal including information on the selected autofocus control mode is output. The adaptive autofocus control unit switches and executes the autofocus control method according to the autofocus control mode signal.
In this imaging device, based on the contrast evaluation value, the optical path length change mode for searching for the in-focus position while changing the optical path length of the autofocus imaging unit, and a plurality of autofocus imaging units arranged at different optical path lengths. The autofocus control can be performed in two autofocus control modes, that is, an optical path length difference comparison mode in which an in-focus position is searched based on the contrast evaluation value. In this imaging apparatus, the autofocus control mode can be switched accurately according to the state of the subject, so that even if the subject has changed greatly (when the subject's situation has changed significantly), it can cope with it. And a stable AF function (autofocus function) can be realized.

  2nd invention is 1st invention, Comprising: The image pick-up part for autofocus has at least the image sensor for fronts, and the image sensor for backs, and the image sensor for fronts is the auto image acquired by the image sensor for fronts The focus detection video signal is output as an AF_Front signal, and the back imaging device outputs the autofocus detection video signal acquired by the back imaging device as an AF_Back signal. The autofocus evaluation value generation unit outputs the contrast evaluation value calculated from the main line system video signal as the main line system contrast evaluation value to the autofocus control mode determination unit, and uses the contrast evaluation value calculated from the AF_Front signal as the front contrast evaluation value. Are output to the autofocus control mode determination unit, and the contrast evaluation value calculated from the AF_Back signal is output to the autofocus control mode determination unit as a back contrast evaluation value. The autofocus control mode determination unit generates an autofocus control mode signal based on the front contrast evaluation value, the back contrast evaluation value, and the main line system contrast evaluation value. The adaptive autofocus control unit generates an autofocus imaging unit position control signal and a focus position control signal based on the front contrast evaluation value, the back contrast evaluation value, and the autofocus control mode signal. The optical path length changing unit is configured to move the front imaging device and the back imaging device on the optical axis of the second light flux group based on the autofocus imaging unit position control signal. The optical system changes the focus position of the optical system based on the focus position control signal.

The third invention is the second invention, wherein the front imaging element is disposed on the optical axis at a position where the optical path length is shorter by d1 than the imaging unit for photographing, On the axis, it is arranged at a position where the optical path length is longer by d1 than the imaging unit for photographing.
In the optical path length difference comparison mode, the adaptive autofocus control unit
(1) When the front contrast evaluation value is larger than the back contrast evaluation value, auto focus control is performed so that the focus position of the optical system is moved in the infinity direction,
(2) When the back contrast evaluation value is larger than the front contrast evaluation value, auto focus control is performed so that the focus position of the optical system is moved in the close-up direction,
(3) When the back contrast evaluation value and the front contrast evaluation value are equal, auto focus control is performed by not moving the focus position of the optical system,
In the optical path length change mode,
The adaptive autofocus control unit outputs an autofocus imaging unit position control signal for sequentially changing the optical path lengths of the autofocus / front imaging device and the autofocus / back imaging device. The optical path length changing unit changes the optical path lengths of the autofocus / front imaging device and the autofocus / back imaging device based on the autofocus imaging unit position control signal. Furthermore, the adaptive autofocus control unit detects a contrast evaluation value for each optical path length, and obtains a contrast evaluation value for the total optical path length, thereby obtaining a characteristic curve indicating the relationship between the optical path length and the contrast evaluation value. In addition to the acquisition, the in-focus position of the optical system is detected, and the image pickup unit, the autofocus / front image pickup device, and the autofocus / back image pickup device set in the optical path length difference comparison mode are on the optical axis. An optimum optical path length difference d_best, which is a distance difference, is calculated from the characteristic curve, and a focus position control signal is output so that the focus position detected by the focus position of the optical system moves in the direction in which it exists. The autofocus control mode determination unit outputs an autofocus control mode signal for switching to the optical path length difference comparison mode when determining that the focus position of the optical system has approached the in-focus position.

In this imaging device, when the subject has changed greatly due to the above configuration (when the subject's situation has changed significantly), a mode for automatically searching for the in-focus position while changing the optical path length of the autofocus imaging unit The focusing operation is continued in (optical path length change mode). Further, when the focus moves to the vicinity of the in-focus position, a mode for searching for the in-focus position (optical path) based on contrast evaluation values from a plurality of autofocus imaging units arranged at different optical path lengths adapted to the current state. Return to Long Difference Comparison Mode.
As a result, in this imaging apparatus, it is possible to realize a stable AF function (auto-focus function) with good followability that can cope even when the subject changes greatly.

4th invention is 3rd invention, Comprising: In optical path length difference comparison mode, the image sensor for front and the image sensor for back are
(D1) = (optimal optical path length difference d_best)
It is arranged at a position on the optical axis.
As a result, the position of the front imaging element and the back imaging element on the optical axis in the optical path length difference comparison mode can be set to the optimum position, so that this imaging apparatus can perform autofocus control with higher accuracy. Can do.

5th invention is 4th invention, Comprising: An adaptive autofocus control part is the maximum value of contrast evaluation value from the characteristic curve which shows the relationship between the optical path length acquired in optical path length change mode, and contrast evaluation value. Cmax and the minimum value Cmin are obtained, the optical path length f0 at which the contrast evaluation value is the maximum value Cmax is obtained, and the optical path length f1 at which the contrast evaluation value is Cmid = (Cmax−Cmin) / 2 is obtained to obtain the optimum optical path. Difference in length (optimum optical path length difference d_best) = abs (f0−f1)
(Abs (x) represents the absolute value of x.)
Set to a value that satisfies.
In this imaging apparatus, the optical path length difference can be optimized by the above arithmetic expression.
As a result, accurate autofocus control is performed even when the characteristic curve indicating the relationship between the optical path length and the contrast evaluation value does not change much (for example, when a white subject is photographed). Can do.

6th invention is 4th invention, Comprising: An adaptive autofocus control part is the maximum value of contrast evaluation value from the characteristic curve which shows the relationship between the optical path length acquired in optical path length change mode, and contrast evaluation value. The optical path length f0 at which Cmax and the maximum contrast evaluation value Cmax are obtained is obtained, the optical path length f2 at which the rate of change of the contrast evaluation value with respect to the optical path length is maximized, and the optimum optical path length difference is (optimal optical path length difference d_best) = abs (F0-f2)
(Abs (x) represents the absolute value of x.)
Set to a value that satisfies.
In this imaging apparatus, the optical path length difference can be optimized by the above arithmetic expression.
As a result, accurate autofocus control is performed even when the characteristic curve indicating the relationship between the optical path length and the contrast evaluation value does not change much (for example, when a white subject is photographed). Can do.

According to a seventh aspect of the present invention, there is provided an optical system capable of condensing light from a subject and controlling focus, at least a first light flux group and two or more for focus detection from the subject collected by the optical system. An optical path separating unit that separates the first luminous flux group, an imaging imaging unit that converts the first luminous flux group into an electrical signal and outputs the signal as a main line video signal, at least a front imaging element and a back imaging A focus used in an imaging apparatus having an element, and an autofocus imaging unit that converts two or more second light flux groups for focus detection into electrical signals and outputs them as video signals for autofocus detection It is a control method. The focus control method includes an optical path length changing step, an autofocus evaluation value generating step, and an autofocus control mode determining step.
In the optical path length changing step, the optical path length of the second light flux to the autofocus imaging section is changed by moving the autofocus imaging section on the optical axis of the second light flux group. In the autofocus evaluation value generation step, a contrast evaluation value that is an evaluation value of the contrast of the video signal for autofocus detection is generated. In the autofocus control mode determination step, based on the contrast evaluation value, the optical path length change mode for searching for the in-focus position while changing the optical path length of the autofocus imaging unit, and a plurality of autofocus units arranged at different optical path lengths. The optical path length difference comparison mode for searching for an in-focus position based on the contrast evaluation value from the imaging unit is switched, and an autofocus control mode signal including information on the selected autofocus control mode is output. In the adaptive autofocus control step, the autofocus control method is switched and executed by an autofocus control mode signal.
As a result, a focus control method that achieves the same effects as the first invention can be realized.

  According to an eighth aspect of the present invention, there is provided an optical system capable of condensing light from a subject and controlling focus, at least a first light flux group and two or more for focus detection from the subject collected by the optical system. An optical path separating unit that separates the first luminous flux group, an imaging imaging unit that converts the first luminous flux group into an electrical signal and outputs the signal as a main line video signal, at least a front imaging element and a back imaging A focus used in an imaging apparatus having an element, and an autofocus imaging unit that converts two or more second light flux groups for focus detection into electrical signals and outputs them as video signals for autofocus detection A program for causing a computer to execute a control method. This program causes the computer to execute an optical path length changing step, an autofocus evaluation value generating step, an autofocus control mode determining step, and an autofocus control mode determining step.

In the optical path length changing step, the optical path length of the second light flux to the autofocus imaging section is changed by moving the autofocus imaging section on the optical axis of the second light flux group. In the autofocus evaluation value generation step, a contrast evaluation value that is an evaluation value of the contrast of the video signal for autofocus detection is generated. In the autofocus control mode determination step, based on the contrast evaluation value, the optical path length change mode for searching for the in-focus position while changing the optical path length of the autofocus imaging unit, and a plurality of autofocus units arranged at different optical path lengths. The optical path length difference comparison mode for searching for an in-focus position based on the contrast evaluation value from the imaging unit is switched, and an autofocus control mode signal including information on the selected autofocus control mode is output. In the adaptive autofocus control step, the autofocus control method is switched and executed by an autofocus control mode signal.
As a result, it is possible to realize a program having the same effects as those of the first invention.

  According to a ninth aspect of the present invention, there is provided an optical system capable of condensing light from a subject and controlling focus, at least a first light flux group and two or more for focus detection from the subject collected by the optical system. An optical path separating unit that separates the first luminous flux group, an imaging imaging unit that converts the first luminous flux group into an electrical signal and outputs the signal as a main line video signal, at least a front imaging element and a back imaging An autofocus imaging unit that converts two or more second light flux groups for focus detection into electrical signals and outputs them as an autofocus detection video signal; and an autofocus imaging unit as a second And an optical path length changing unit that changes the optical path length of the second luminous flux to the imaging unit for autofocus by moving on the optical axis of the luminous flux group. The integrated circuit includes an autofocus evaluation value generation unit, an autofocus control mode determination unit, and an adaptive autofocus control unit.

The autofocus evaluation value generator generates a contrast evaluation value that is a contrast evaluation value of the video signal for autofocus detection. The autofocus control mode determination unit is based on the contrast evaluation value, and changes the optical path length of the autofocus imaging unit while searching for the in-focus position, and a plurality of autofocus units arranged in different optical path lengths. The optical path length difference comparison mode for searching for an in-focus position based on the contrast evaluation value from the imaging unit is switched, and an autofocus control mode signal including information on the selected autofocus control mode is output. The adaptive autofocus control unit switches and executes the autofocus control method according to the autofocus control mode signal.
Thus, an integrated circuit that exhibits the same effect as that of the first invention can be realized.

  In the imaging apparatus of the present invention, when the subject changes greatly (when the situation of the subject changes greatly), the in-focus position is automatically searched while automatically changing the optical path length of the autofocus imaging unit. Continue focusing in the mode that When the focus further moves to the vicinity of the in-focus position, the mode returns to the mode for searching for the in-focus position based on contrast evaluation values from a plurality of autofocus imaging units arranged at different optical path lengths adapted to the state at that time. . As a result, the imaging apparatus of the present invention can realize a stable AF function (auto focus function) with good followability that can cope with a large change in subject.

Hereinafter, embodiments of the present invention will be described with reference to FIGS.
[First Embodiment]
<1.1: Configuration of Imaging Device>
FIG. 1 is a block diagram showing a configuration of an imaging apparatus 100 with an autofocus function according to the first embodiment of the present invention.
The imaging apparatus 100 includes an optical system 1 that collects light from a subject, an optical path separation unit 2 that separates the light collected by the optical system 1 into a light beam for obtaining an image signal and a light beam for AF detection, and a video signal. The imaging unit 3 for acquiring video signal acquisition analog video signals (Rch signal, Gch signal, and Bch signal) from the acquisition light beam, and AF control analog video signals (AF_Front signal and AF_Back signal) from the AF detection light beam ) For acquiring AF). In addition, the imaging apparatus 100 performs A / D conversion on the analog signal processing unit 5 that performs analog signal processing on the analog video signal for acquiring the video signal and the analog video signal for AF control, and the output from the analog signal processing unit 5. The AD conversion unit 6, the digital signal processing unit 7 that performs digital signal processing using the output of the AD conversion unit 6 as input, and the AF control digital video signal (AF control analog video signal output from the AD conversion unit 6). A control unit 8 that generates an AF imaging unit position control signal and a focus position control signal from a signal acquired by A / D conversion). Furthermore, the imaging apparatus 100 includes an AF optical path length changing unit 9 that changes the optical path length of the AF imaging unit 4 using an AF imaging unit position control signal.

The optical system 1 collects light from the subject and can adjust the focal length (focus position) of the light (light flux) from the subject. That is, it has a configuration capable of focus control. The optical system 1 outputs the collected light (light flux) from the subject to the optical path separation unit 2. The optical system 1 may be composed of a plurality of lenses, and is provided with a focus control lens (which may be a lens unit composed of a plurality of lenses) for performing focus control, and moves the focus control lens. Thus, focus control may be performed. Further, the optical system 1 may be configured by an interchangeable lens or the like.
The optical path separation unit 2 receives the light flux output from the optical system 1, receives the first light flux of R (red) light for photography, G (green 1) light, and B (blue) light, 2 is split into AF detection AF_Front (green 2) light and AF_Back (green 3) light. Then, the optical path separation unit 2 outputs a shooting light beam (image signal acquisition light beam) to the shooting image pickup unit 3 and outputs an AF detection light beam to the AF image pickup unit 4 which is the second shooting unit. . Here, the optical path separation unit 2 converts the photographic light flux that has passed through the optical system 1 into a plurality of photographic light fluxes (for example, three light fluxes for R, B, and G, and R light flux). , B light beam, G1 light beam, and G2 light beam). For example, an optical prism (beam splitter) as shown in FIG. 2 is preferably used as the optical path separation unit 2.

The imaging unit 3 for imaging has an imaging element such as a CMOS or a CCD. The imaging imaging unit 3 receives each imaging luminous flux (video signal acquisition luminous flux) output from the optical path separation unit 2 and converts these into electrical signals by photoelectric conversion. The converted electrical signal is output to the analog signal processing unit 5 as an analog video signal of each of the R, G, and B channels. For example, as illustrated in FIG. 2, the imaging unit 3 for imaging includes an R light imaging device (Rch imaging device) 3r, a B light imaging device (Bch imaging device) 3b, and a G light imaging device (Gch). Imaging device) 3g.
The AF imaging unit 4 includes an AF_Front channel imaging device 4a and an AF_Back channel imaging device 4b.
The AF_Front channel image sensor 4a and the AF_Back channel image sensor 4b are each composed of an image sensor such as a CMOS or a CCD, and receive the AF detection light beam output from the optical path separator 2 as an input. The analog signal of the AF_Front channel (this is called “analog AF_Front signal”) and the analog video signal of the AF_Back channel (this is called “analog AF_Back signal”) are acquired and output to the analog signal processing unit 5. To do. Further, the AF_Front channel imaging device 4a is connected to the AF_Front optical path length changing unit 9a of the AF optical path length changing unit 9, and the optical path direction can be changed by the AF_Front optical path length changing unit 9a. It can be moved to (movable parallel on the optical axis of the AF detection light beam). Similarly, the AF_Back channel imaging device 4b is connected to the AF_Back optical path length changing unit 9b of the AF optical path length changing unit 9, and the optical axis length can be changed by the AF_Back optical path length changing unit 9b. It can be moved in the direction (can be translated on the optical axis of the AF detection light beam).

The analog signal processing unit 5 receives as input analog video signals (Rch signal, Gch signal, Bch signal, analog AF_Front signal, and analog AF_Back signal) of each channel output from the imaging unit 3 for shooting and the imaging unit 4 for AF. The input analog video signal of each channel is subjected to correlated double sampling processing, gain control processing, pedestal control processing, and the like, and output to the AD conversion unit 6.
The AD conversion unit 6 converts each signal from the analog signal processing unit 5 into a digital signal. The AD conversion unit 6 outputs R and B channel digital signals (hereinafter referred to as “R signal” and “B signal”, respectively) of the converted digital signals to the digital signal processing unit 7. Also, a G channel digital signal (hereinafter referred to as “G signal”) is output to the digital signal processing unit 7 and the AF evaluation value generation unit 81 of the control unit 8. Further, a digital signal obtained by A / D converting the analog AF_Front signal and the analog AF_Back signal (hereinafter referred to as “AF_Front signal” is a signal obtained by A / D converting the analog AF_Front signal, and a signal obtained by A / D converting the analog AF_Back signal is obtained. "AF_Back signal") is output to the AF evaluation value generation unit 81 of the control unit 8.

The digital signal processing unit 7 performs normal three-plate video signal processing from the R signal, G signal, and B signal, and outputs the processed signal as a video signal for photographing. Needless to say, the digital signal processing unit 7 performs signal processing of a four-plate type, a five-plate type, or the like when the imaging apparatus 100 has a configuration of a four-plate type, a five-plate type, or the like.
The control unit 8 includes an AF evaluation value generation unit 81, an AF control mode determination unit 82, and an adaptive AF control unit 83. The control unit 8 receives the G signal, the AF_Front signal, and the AF_Back signal from the AD conversion unit 6, and generates an AF imaging unit position control signal and a focus position control signal based on these input signals. Then, the control unit 8 outputs the AF imaging unit position control signal to the AF optical path length changing unit 9 and the focus position control signal to the optical system 1.

The AF evaluation value generation unit 81 includes a calculation unit 111 and an adder 108, and receives the G signal, the AF_Front signal, the AF_Back signal, and the evaluation region signal from the AD conversion unit 6, and receives the G signal, the AF_Front signal, and the AF_Back signal. The contrast evaluation value is calculated and the calculated contrast evaluation value is output to the AF control mode determination unit 82.
FIG. 3 is a block diagram illustrating an example of the configuration of the AF evaluation value generation unit 81 of the control unit 8.
The AF evaluation value generation unit 81 includes a horizontal low-pass filter 101 (a low-pass filter for a horizontal component of a video (two-dimensional video) formed by a video signal) (hereinafter referred to as “horizontal LPF”), and a horizontal direction. High-pass filters (high-pass filters for horizontal components of video (two-dimensional video) formed by video signals for autofocus detection) (hereinafter referred to as “horizontal HPF”) 102 and 103, and high-pass filters in the vertical direction (High-pass filter for vertical component of video (two-dimensional video) formed by video signal for autofocus detection) (hereinafter referred to as “vertical HPF”) 104, accumulating units 105 to 107, and adder 108 And having.

The horizontal LPF 101 outputs frequency band components necessary for generating a contrast evaluation value for the video signal (AF detection video signal (G signal, AF_Front signal, AF_Back signal)) output from the AD converter 6. It is a horizontal low-pass filter for extraction. The horizontal LPF 101 outputs the output to the first horizontal HPF 102, the second horizontal HPF 103, and the vertical HPF 104.
Two horizontal high-pass filters 102 and 103 (hereinafter referred to as “first horizontal HPF” and “second horizontal HPF”, respectively) are high-pass filters for the horizontal component of the video signal. The first horizontal HPF 102 and the second horizontal HPF 103 pass through different frequency bands, and the first horizontal HPF 102 is a high-pass filter (for low band) that passes a lower frequency band than the second horizontal HPF 103, and the second horizontal HPF 103. Is a high-pass filter (for high band) that passes a higher frequency band than the first horizontal HPF 102. That is, the cutoff frequency of the first horizontal HPF 102 is set lower than that of the second horizontal HPF 103. The high-pass filter 104 in the vertical direction (hereinafter referred to as “vertical HPF”) is a high-pass filter for the vertical component of the video signal.

  Integration units 105 to 107 integrate the outputs of the high-pass filters 102 to 104 with respect to the video signals (AF detection video signals (G signal, AF_Front signal, AF_Back signal)) in each pixel in the AF evaluation area (described later). And output to the adder 108. An evaluation region signal is input from a drive unit (not shown) to the calculation unit 111 including the horizontal LPF 101, the first horizontal HPF 102, the second horizontal HPF 103, the vertical HPF 104, and the integration units 105 to 107. The evaluation area signal is used by the AF evaluation value generation unit 81 to select an AF evaluation area that is a target area for generating a contrast evaluation value. For example, when the AF detection video signal is a video signal that forms a central area of a screen (a two-dimensional image formed by the video signal), the evaluation area signal is a pulse signal that indicates the timing of the central part of the screen. Become. The evaluation area signal is input only to the accumulators 105 to 107, and the accumulators 105 to 107 accumulate and add the values in the AF evaluation area among the outputs of the high-pass filters 102 to 104, respectively. The data may be output to the device 108.

The adder 108 adds the outputs of the integrating units 105 to 107 and outputs the result as a contrast evaluation value. The above process is executed for each of the G signal, the AF_Front signal, and the AF_Back signal, and the adder 108 sends the contrast evaluation values for the G signal, the AF_Front signal, and the AF_Back signal to the AF control mode determination unit 82. Output.
The passbands of the horizontal LPF 101, the first horizontal HPF 102, the second horizontal HPF 103, and the vertical HPF 104 are, for example, when the video signal handled by the imaging apparatus 100 is an SDTV video signal, the horizontal LPF 101 is 0 to 2.0 MHz, It is preferable that one horizontal HPF 102 is 300 kHz or more, the second horizontal HPF 103 is 1.2 MHz or more, and the vertical HPF 104 is 20 TVs or more. When the video signal handled by the imaging apparatus 100 is an HDTV video signal, the horizontal LPF 101 is 0 to 13.2 MHz, the first horizontal HPF 102 is 2.0 MHz or higher, the second horizontal HPF 103 is 6.6 MHz or higher, and the vertical HPF 104 is It is preferable that there are 45 TV lines or more.

The AF control mode determination unit 82 receives the contrast evaluation values for the G signal, AF_Front signal, and AF_Back signal output from the AF evaluation value generation unit 81, and determines an AF control mode based on the contrast evaluation value. Specifically, the AF control mode determination unit 82 selects whether to perform the AF control in any one of the optical path length change mode and the optical path length difference comparison mode (details will be described later). Then, the AF control mode determination unit 82 outputs an AF control mode signal including information about the selected AF control mode to the adaptive AF control unit 83.
The adaptive AF control unit 83 receives the contrast evaluation value for the AF_Front signal and the AF_Back signal output from the AF evaluation value generation unit 81 and the AF control mode signal output from the AF control mode determination unit 82 as inputs. An AF imaging unit position control signal and a focus position control signal are generated. Then, the adaptive AF control unit 83 outputs the AF imaging unit position control signal to the AF optical path length changing unit 9 and the focus position control signal to the optical system 1.

<1.2: Operation of Imaging Device>
The operation of the imaging apparatus 100 configured as described above will be described below with reference to the drawings.
The light beam that has passed through the optical system 1 is input to the optical path separation unit 2 shown in FIGS. The light beam input from the optical system 1 by the optical path separating unit 2 includes R (red), G (green), and B (blue) light beams for photographing (for obtaining video signals), and AF_Front (for AF detection). Green 2) and luminous flux of AF_Back (green 3) light. The divided light fluxes are Rch imaging element 3r, Gch imaging element 3g, and Bch imaging element 3b of photographing imaging unit 3, and AF_Front channel imaging element 4a and AF_Back channel imaging element 4b of AF imaging unit 4. Are converted into electric signals.

Here, it demonstrates in detail using FIG.
FIG. 2 shows an optical path separation unit 2, a photographing imaging unit 3 (Rch imaging device 3 r, Gch imaging device 3 g, Bch imaging device 3 b), AF imaging unit 4 (AF_Front channel imaging device 4 a, AF_Back channel) It is a schematic diagram which shows an example of a more concrete structure of the image pick-up element 4b) and AF optical path length change part 9 (AF_Front optical path length change part 9a, AF_Back optical path length change part 9b). As the optical path separator 2, an optical prism (beam splitter) as shown in FIG. 2 is used.
As shown in FIG. 2, the light incident on the optical path separation unit 2 is subjected to RGB spectroscopy by the color separation prism. The G (green) light after RGB spectroscopy is further divided by a half mirror to become a light beam for AF detection. Further, the AF detection light beam is divided into two so that the split ratio is equal, and the AF_Front (green 2) light and AF_Back (green 3) light are supplied to the AF_Front channel imaging device 4a and the AF_Back channel imaging device 4b as follows. Each is incident. Then, the R (red) light, the G (green 1) light, and the B (blue) light are respectively incident on the Rch imaging device 3r, the Gch imaging device 3g, and the Bch imaging device 3b as photographing light fluxes. The The ratio of the AF detection light beam to the G light beam after RGB spectroscopy may be arbitrary (for example, 25%, 50%, etc.). Here, the ratio of the AF detection light beam is 50% of the G light beam, and the AF_Front (green 2) light and the AF_Back (green 3) light are further divided into two equal parts. Therefore, each becomes 25% of light (light flux).

The AF_Front channel imaging element 4a and the AF_Back imaging element 4b of the AF imaging unit 4 are respectively an AF_Front optical path length changing unit 9a and an AF_Back optical path length changing unit of the AF optical path length changing unit 9 that can change the optical path length. 9b.
The AF optical path length changing unit 9 is configured using, for example, a linear drive motor, a stepping motor, a piezoelectric ultrasonic linear actuator using a piezoelectric element, and a slide mechanism along the optical axis. The AF optical path length changing unit 9 has a function of sliding the AF_Front and AF_Back imaging elements in parallel on the optical axis (in the direction indicated by the bidirectional arrow D1 in FIG. 2), for example, serial communication or the like. It is controlled by.
Of the range in which the AF imaging unit 4 can be moved by the AF optical path length changing unit 9, the substantially central position is set as the reference position of the AF imaging unit 4. When the AF imaging unit 4 is at the reference position, the subject It is assumed that the optical path length from the AF to the imaging unit 4 for AF coincides with the optical path length from the subject to the imaging unit 3 for photographing. Note that the reference position does not necessarily have to be the center position.

The output (main line system video signal) of the imaging unit 3 for photographing is subjected to signal processing by the analog signal processing unit 5 and A / D conversion by the AD conversion unit 6 in the same manner as in the normal three-plate imaging system. The A / D converted signal (main line video signal) is subjected to digital signal processing by the digital signal processing unit 7 and then output as a main line, that is, a video signal for photographing.
On the other hand, the output of the AF imaging unit 4 is subjected to analog signal processing such as correlated double sampling, gain control, pedestal control and the like, as in normal signal processing, and then converted into a digital signal by the AD conversion unit 6. The result is input to the AF evaluation value generation unit 81 of the control unit 8. Specifically, an analog AF_Front signal output from the AF imaging unit 4 is A / D converted by the AD conversion unit 6, input to the AF evaluation value generation unit 81 as an AF_Front signal, and output from the AF imaging unit 4. The analog AF_Back signal is A / D converted by the AD conversion unit 6 and input to the AF evaluation value generation unit 81 as the AF_Back signal.

(1.2.1: AF control mode (optical path length change mode and optical path length difference comparison mode))
Here, the AF control mode will be described.
The imaging apparatus 100 operates by switching between two types of AF control modes.
These two types of AF control modes are an optical path length change mode and an optical path length difference comparison mode.
The optical path length change mode is a mode for searching for an in-focus position from contrast evaluation values for various optical path lengths while changing the optical path length of the AF imaging unit 4.
In the optical path length difference comparison mode, the AF_Front channel imaging device 4a and the AF_Back channel imaging device 4b of the AF imaging unit 4 are compared with the optical path length of the Gch imaging device 3g of the imaging imaging unit 3, respectively. In this mode, the in-focus position is searched based on the magnitude relationship between the contrast evaluation values of the AF_Front signal and the AF_Back signal, which are arranged at positions where the optical path length is short and long by the width d.

(1.2.2: Operation of the control unit 8)
The imaging apparatus 100 normally operates in the optical path length difference comparison mode. That is, the control unit 8 realizes the focusing operation (AF control) based on the contrast evaluation values of the AF_Front signal and the AF_Back signal. However, if the control unit 8 determines that the AF control in the optical path length difference comparison mode is not possible, such as when the subject has changed significantly, the control unit 8 switches the AF control mode to the optical path length change mode. Then, the control unit 8 sends the AF imaging unit position control signal to the AF optical path length changing unit 9 (9a) so as to move the positions of the AF_Front channel imaging device 4a and the AF_Back channel imaging device 4b on the optical axis. , 9b). The AF_Front channel imaging device 4a and the AF_Back channel imaging device 4b move on the optical axis based on the AF imaging unit position control signal.

  While the AF_Front channel imaging device 4a and the AF_Back channel imaging device 4b are moving on the optical axis, the control unit 8 detects contrast evaluation values at respective positions (positions on the optical axis), and calculates the optical path length and The in-focus position is detected based on the characteristic curve with the contrast evaluation value. At the same time, the controller 8 determines the optimum optical path length difference in the optical path length difference comparison mode (the position on the optical axis of the Gch image pickup device 3g and the light of the AF_Front channel image pickup device 4a (or AF_Back channel image pickup device 4b)). Determine the distance between the position on the axis). And the control part 8 starts the movement of a focus to the focus position detected by said operation | movement. Specifically, the control unit 8 outputs a focus position control signal to the optical system 1, and the optical system 1 moves the focus position by the focus position control signal (for example, a focus lens (not shown) included in the optical system 1). ) Is moved on the optical axis (the focus position is moved (focus control is performed)). When the control unit 8 continues to move the focus position in the vicinity of the in-focus position and again enters an area where control in the optical path length difference comparison mode is possible, the AF control mode is shifted to the optical path length difference comparison mode, The AF control operation is continued.

By performing such AF control by the control unit 8, the imaging apparatus 100 can perform AF control operation even when the subject changes greatly (when the state of the subject changes greatly), and is in focus search and for shooting. A stable AF control function with good followability can be realized without adversely affecting the video signal (main line video signal).
As shown in FIG. 3, an evaluation region signal is input to the calculation unit 111 from a drive unit (not shown), and a target image region for calculating a contrast evaluation value is set based on the evaluation region signal.
Then, the video signal (AF detection video signal (G signal, AF_Front signal, AF_Back signal)) output from the AD conversion unit 6 is input to the horizontal LPF 101. Further, the AF detection video signal output from the horizontal LPF 101 is input to the first horizontal LPF 102, the second horizontal HPF 103, and the vertical HPF, each subjected to filter processing, and the output subjected to the filter processing is integrated. Are input to the sections 105 to 107. The outputs of the integrating units 105 to 107 are added by the adder 108, and the added result is output to the AF control mode determining unit 82 as a contrast evaluation value.

Note that the above processing is executed for each of the G signal, the AF_Front signal, and the AF_Back signal, and the contrast evaluation value is calculated for each of the G signal, the AF_Front signal, and the AF_Back signal. Therefore, FIG. 3 shows only one system for convenience of explanation, but the AF evaluation value generation unit 81 may have three processing systems for the G signal, the AF_Front signal, and the AF_Back signal. Needless to say. Further, the AF evaluation value generation unit 81 may serially process the G signal, the AF_Front signal, and the AF_Back signal in one system.
The AF control mode determination unit 82 generates an AF control mode signal based on the contrast evaluation value output from the AF evaluation value generation unit 81, and the AF control mode signal is output to the adaptive AF control unit 83. Specifically, in the AF control mode determination unit 82, the AF evaluation value generation unit 81 determines the magnitude relationship between the contrast evaluation values calculated from the AF_Front signal, the AF_Back signal, and the G signal, and the AF evaluation value generation unit 81 generates the G signal. From the change in the contrast evaluation value calculated from the above, it is determined whether the imaging apparatus 100 is in focus or in which of the two AF control modes the AF control should be executed. Then, a signal indicating the determination result is generated by the AF control mode determination unit 82 and output to the adaptive AF control unit 83 as an AF control mode signal.

The adaptive AF control unit 83 performs AF control in the AF control mode determined by the AF control mode signal. Specifically, the AF evaluation value generation unit 81 generates an AF imaging unit position control signal and a focus position control signal based on the contrast evaluation values calculated from the AF_Front signal and the AF_Back signal. The AF imaging unit position control signal generated by the adaptive AF control unit 83 is output to the AF optical path length changing unit 9. Further, the focus position control signal generated by the adaptive AF control unit 83 is output to the optical system 1.
Next, the operations of the two types of AF control modes, the optical path length difference comparison mode and the optical path length change mode, will be described in more detail.
(1.2.3: Operation in optical path length difference comparison mode)
First, the operation in the optical path length difference comparison mode will be described.

FIG. 4 shows that the Gch imaging device 3g of the imaging imaging unit 3 in the optical path length difference comparison mode, the AF_Front channel imaging device 4a and the AF_Back channel imaging device 4b of the AF imaging unit 4 are on the same optical axis. FIG.
As shown in FIG. 4, the optical path length of the subject light incident on the AF_Front channel imaging device 4a is set shorter by the width d than the optical path length of the subject light incident on the Gch imaging device 3g of the imaging unit 3 for photographing. Similarly, the optical path length of the subject incident on the AF_Back channel imaging device 4b is set to be longer than the optical path length of the subject light incident on the Gch imaging device 3g by the width d. Therefore, the AF image pickup unit 4 can obtain a video signal equivalent to a case where the image pickup device of the image pickup image pickup unit 3 picks up images at equidistant positions on the optical axis.

In FIG. 5, the horizontal axis indicates the focus position, the vertical axis indicates the contrast evaluation value that is the output of the AF evaluation value generation unit 81, and the focus position and the contrast evaluation value when a certain subject is imaged by the imaging apparatus 100 are illustrated. It is the schematic diagram which showed the relationship.
Curves Front and Back shown by solid lines in the figure are curves showing contrast evaluation values obtained from the AF_Front signal and AF_Back signal, respectively, and a curve Gch shown by a broken line in the figure shows the amount of incident light for an image sensor for AF. Is a curve showing the contrast evaluation value obtained from the G signal in the case of the same.
In FIG. 5, the in-focus position is the position of F0, which is the focus position where the contrast evaluation value of the curve Gch is maximized.
For example, when the focus position of the optical system 1 is at the focus position F1 closer to the position F0, the contrast evaluation values obtained from the AF_Front signal and the AF_Back signal are the values of Cfront1 and Cback1 from the respective curves, and Cfront1 The value of is greater. Conversely, when the focus position of the optical system 1 is at the focus position F2 on the infinity side of the focus position F0, similarly, the contrast evaluation values obtained from the AF_Front signal and the AF_Back signal are the values of Cfront2 and Cback2, respectively. Therefore, the value of Cback2 is larger. In the case of F0 which is the in-focus position, Cfront0 = Cback0, which is an equal value. At this time, the contrast evaluation value of Gch (contrast evaluation value obtained from the G signal) is larger than the values of Cfront0 and Cback0.

Accordingly, AF control can be performed based on the magnitude relationship between the contrast evaluation values obtained from the AF_Front signal and the AF_Back signal.
Specifically, AF control is performed as follows.
(1) When the contrast evaluation value of the AF_Front signal is larger than the contrast evaluation value of the AF_Back signal, AF control is performed so that the focus position of the optical system 1 is moved in the infinity direction.
(2) When the contrast evaluation value of the AF_Back signal is larger than the contrast evaluation value of the AF_Front signal, AF control is performed so that the focus position of the optical system 1 is moved in the closest direction.
(3) When the contrast evaluation value of the AF_Back signal is equal to the contrast evaluation value of the AF_Front signal, AF control is performed by stopping the focus position of the optical system 1 (not moving from the current focus position).

Such AF control is AF control in the optical path length difference comparison mode.
However, the contrast evaluation values of the AF_Front signal and the AF_Back signal are also equal at the positions F3 and F4 in FIG. Therefore, when the position changes from the position F0 to the position F3 or F4 at once, that is, for example, when the subject changes greatly and becomes a so-called large-blurred state, the focus stops at the position F3 or F4 and is normal. AF control operation cannot be realized.
Therefore, in the imaging apparatus 100 according to the present embodiment, the AF control mode determination unit 82 performs imaging based on the magnitude relationship between the contrast evaluation values from the AF_Front signal, the AF_Back signal, and the G signal, the change in the contrast evaluation value from the G signal, and the like. By determining the focus state of the apparatus 100 (for example, determining whether the focus state is a large blur state) and determining that the focus state is a large blur state, the AF control mode is switched to the optical path length change mode. This solves the malfunction of large blur.

(1.2.4: Operation in optical path length change mode)
Next, the operation in the optical path length change mode will be described.
In the optical path length change mode, an evaluation value curve indicating the relationship between the optical path length and the contrast evaluation value is detected, and the optical path length is calculated based on the difference between the optical path length when the maximum contrast is achieved and the optical path length when the image sensor is at the reference position. The focus position of system 1 is detected. At the same time, the optimum value of the optical path length difference d in the optical path length difference comparison mode is calculated.
That is, the AF optical path length changing unit 9 sequentially moves the AF_Front channel imaging device 4a and the AF_Back channel imaging device 4b on the optical axis, and determines the optical path length determined from the position on the optical axis of the imaging device. A contrast evaluation value for the optical path length is acquired, and a characteristic curve indicating a relationship between the optical path length and the contrast evaluation value is acquired.

More specifically, while sequentially changing the optical path lengths of the AF_Front channel imaging device 4a and the AF_Back channel imaging device 4b over a plurality of fields, the contrast evaluation values at the respective optical path lengths are detected, and the total optical path length is detected. Get contrast evaluation value. For example, the optical path length and the contrast evaluation value are sequentially changed by sequentially changing the optical path length from the reference position toward the near side by the AF_Front imaging element 4a and sequentially changing the optical path length from the reference position to the telephoto side by the AF_Back imaging element 4b. The characteristic curve which shows the relationship with is acquired.
Thereby, the imaging apparatus 100 detects the characteristic curve between the optical path length and the contrast evaluation value in the total optical path length. Note that the method of obtaining the characteristic curve indicating the relationship between the optical path length and the contrast evaluation value is not limited to the above method, and may be another method.

FIG. 6 shows a schematic diagram of a characteristic curve between the optical path length and the contrast evaluation value.
First, the maximum contrast evaluation value optical path length f0 having the maximum contrast evaluation value is detected from the detected pair of optical path lengths and contrast evaluation values.
Next, a difference D with respect to a predetermined reference position corresponding to the optical path length of the photographing imaging unit 3 is calculated, and the focus position of the optical system 1 is calculated based on the difference value D. The AF control operation can be realized by moving the focus to the calculated focus position of the optical system 1.
At the same time, the optimum optical path length difference d in the optical path length difference comparison mode is calculated based on the characteristic curve between the optical path length and the contrast evaluation value.
The optimal optical path length difference d is calculated because the optimal optical path length difference d in the optical path length difference comparison mode differs depending on the pattern of the subject and the lens state of the imaging apparatus 100 such as the iris state and zoom state. This is because the optical path length difference d may cause problems in the AF control operation.

FIG. 7 is a schematic diagram for explaining the AF control operation in the optical path length difference comparison mode when the characteristic curve indicating the relationship between the focus position and the contrast evaluation value is gentle and the optical path length difference d is small.
The characteristic curve shown in FIG. 7 is gentler and the optical path length difference d is smaller than the characteristic curve shown in FIG. In such a case, the contrast evaluation value curve of the AF_Front signal and the contrast evaluation value curve of the AF_Back signal are close to each other, and the amount of change in the contrast evaluation value at the in-focus position F0 is small. There may be problems such as slippage.
In the imaging apparatus 100 according to the present embodiment, in the case of the characteristic curve as shown in FIG. 7, the optical path length difference d is further increased, and the curve at the in-focus position (the contrast evaluation value curve of the AF_Front signal and the contrast evaluation value curve of the AF_Back signal). ) Is increased, the influence of noise and the like is reduced, the focus position control accuracy is improved, and a stable AF control operation can be realized.

Hereinafter, a method for calculating the optimum optical path length difference d in the specific optical path length difference comparison mode of the present embodiment will be described with reference to FIG.
First, an intermediate value Cmid = (Cmax + Cmin) / 2 of the contrast evaluation value is calculated from the maximum value and the minimum value of the detected contrast evaluation value (step 1).
Next, an optical path length f1 having a contrast evaluation value of Cmid is obtained (step 2).
Finally, the difference from the maximum contrast evaluation value optical path length f0 is set as the optimum optical path length difference d (step 3).
FIG. 8 is a schematic diagram showing a similar process of calculating the optimum optical path length difference d when the characteristic curve between the optical path length and the contrast evaluation value is a gentle curve. The calculation method is the same as that in FIG.

By calculating the optimum optical path length difference d by the method of calculating the optimum optical path length difference d in the imaging apparatus 100, the optimum optical path length difference d in the case of the characteristic curve shown in FIG. 8 is compared with the case of the characteristic curve shown in FIG. Is a large value. That is, the position on the optical axis of the AF_Front channel image sensor 4a and the AF_Back channel image sensor 4b in the optical path length comparison mode can be determined by the optimum optical path length difference d thus calculated. In the imaging apparatus 100, after the positions on the optical axis of the AF_Front channel imaging device 4a and the AF_Back channel imaging device 4b are moved to the front and back positions where the optical path length difference becomes the optimum optical path length difference d (imaging imaging device). 3 (for example, the Gch imaging device 3g) is “x1”, the AF_Front channel imaging device 4a is placed on the optical axis “x1-d”, and the AF_Back channel imaging device 4b is turned on. AF control in the optical path length comparison mode is performed accurately after the movement to the position “x1 + d” on the axis), even in the case of a characteristic curve as shown in FIG. Can do.
In the present embodiment, the difference between the optical path length f1 that is the intermediate value Cmid of the contrast evaluation values and the maximum contrast evaluation value optical path length f0 is the optimum optical path length difference. However, the present invention is not limited to this, and for example, contrast The difference between the optical path length at which the gradient of the evaluation value characteristic curve becomes maximum and the maximum contrast evaluation value optical path length may be set as the optimum optical path length difference.

(1.2.5: Explanation by flowchart)
The overall operation of the control unit 8 will be described using the flowchart of FIG.
First, the AF evaluation value generation unit 81 generates and acquires contrast evaluation values from the AF_Front signal, AF_Back signal, and G signal (step S1). However, it is assumed that the G signal contrast evaluation value is generated and acquired by correcting the light amount.
Next, it is determined whether or not the imaging apparatus 100 is in an in-focus state based on the change in the contrast evaluation value of the G signal and the magnitude relationship between the contrast evaluation values of the AF_Front signal and the AF_Back signal.

In particular,
(1) When the contrast evaluation value of the G signal has not changed significantly compared to the previous value (the value acquired last time), or (2) When the contrast evaluation value of the G signal has changed significantly compared to the previous value However, if the contrast evaluation value calculated from the AF_Front signal and the contrast evaluation value calculated from the AF_Back signal are equal and the contrast evaluation value of the G signal is larger than the contrast evaluation value of the AF_Front signal or the contrast evaluation value of the AF_Back signal Judged to be in focus,
(3) Otherwise, it is determined that it is not in focus (step S2).
When it is determined that the in-focus state is not achieved, the imaging apparatus 100 determines whether AF control by the optical path length difference comparison mode is possible based on whether the contrast evaluation value of the AF_Front signal is equal to the contrast evaluation value of the AF_Back signal (step) S3). That is, if the contrast evaluation value of the AF_Front signal is equal to the contrast evaluation value of the AF_Back signal, “No” is set and the optical path length change mode control is executed (step S4). If the contrast evaluation value of the AF_Front signal is not equal to the contrast evaluation value of the AF_Back signal, “Yes” is set and AF control in the optical path length comparison mode is executed (step S9).

  In the optical path length change mode control (step S4), as described above, the focus is finally controlled to the focus position of the optical system 1 (the focus position is adjusted), and the optical path length difference d that is optimum for the current state of the imaging apparatus 100 is obtained. And the AF_Front channel imaging device 4a and the AF_Back channel imaging device 4b of the AF imaging unit 4 are arranged (moved) at positions that are front and back on the optical axis by the calculated optical path length difference d (step S5). ). Thereafter, the focus lens (not shown) of the optical system 1 is irradiated with light so that the focus position moves in the direction in which the in-focus position (the in-focus position detected in the AF control in the optical path length change mode (step S4)) exists. It is moved in the axial direction (step S6). Until the focus of the optical system 1 approaches the in-focus position detected by the AF control in the optical path length change mode (step S4) and the optical path length difference comparison mode control becomes possible, that is, the contrast evaluation value of the AF_Front signal and the AF_Backk Until the contrast evaluation value of the signal becomes different (until a value different by a predetermined threshold th or more), acquisition of the contrast evaluation value (step S7) and determination of whether the optical path length comparison mode control is possible (step S8) ) And the process of changing (moving) the focus position of the optical system 1 are repeated.

When the focus of the optical system 1 approaches the in-focus position, it is determined that the optical path length difference comparison mode control is possible (step S8), and the process proceeds to AF control in the optical path length difference comparison mode (step S9).
Here, whether or not the optical path length difference comparison mode control is possible is determined as follows, for example.
When the contrast evaluation value of the AF_Front signal is CF, the contrast evaluation value of the AF_Back signal is CB, the maximum contrast evaluation value of the AF_Front signal (or AF_Back signal) is Cmax, and the minimum value is Cmin.
abs (CF-CB) ≧ K · (Cmax−Cmin)
0.01 ≦ K ≦ 0.1
Is determined as the “time when the focus of the optical system 1 approaches the in-focus position”. Here, abs (x) indicates the absolute value of x.

In the AF control in the optical path length difference comparison mode (step S9), the AF control operation is realized by controlling the focus position of the optical system 1 based on the magnitude relationship of the contrast evaluation values of the AF imaging unit 4 as described above. . The optical path length difference d at this time is adjusted to an optimum value.
In addition, information such as iris operation detection may be added to the determination method for determining whether it is in focus (step S2).
Further, the determination of whether or not the focus is achieved (step S2) and the determination of whether or not AF control is possible in the optical path length difference comparison mode (step S3) may be performed simultaneously. In this case, control is performed as follows.
(1) When the contrast evaluation value of the G signal is greatly changed compared to the previous value, and
(2) The contrast evaluation value of the AF_Front signal is equal to the contrast evaluation value of AF_Back, and
(3) When the contrast evaluation value of the G signal is not larger than the contrast evaluation value of the AF_Front signal or the AF_Back signal,
AF control (step S4) in the optical path length change mode is executed.

In cases other than the above, AF control (step S9) in the optical path length difference comparison mode is executed.
As described above, in the imaging apparatus 100 of the present invention, at the time of AF control in the optical path length difference comparison mode, the AF control is executed based on the magnitude relationship between the contrast evaluation values of the video signal of the AF imaging unit 4, and therefore the response A good AF function can be realized. Furthermore, in the imaging apparatus 100 of the present invention, even in a large blurring state, the AF function is continued by automatically shifting to the AF control in the optical path length change mode, and then the AF control in the optical path length difference comparison mode is performed again. In this case, the AF_Front channel imaging device 4a and the AF_Back channel imaging device 4b are arranged (moved) so that the optimum optical path length difference d is obtained, so that an excellent effect that a stable AF control operation can be realized is obtained. It is done.

Further, as described above, in the imaging apparatus 100 of the present invention, both the AF control in the optical path length comparison mode and the AF control in the optical path length change mode use the AF video signal independent of the shooting video signal. Since the AF function is realized, the focus position of the optical system 1 is not changed during the search for the focus position. Therefore, in the imaging apparatus 100 of the present invention, it is possible to obtain an excellent effect that the imaging video signal output is not adversely affected.
In the present embodiment, the AF evaluation value generation unit 81 includes an arithmetic unit 111 having a horizontal LPF 101, a first horizontal HPF 102, a second horizontal HPF 103, a vertical HPF 104, accumulating units 105, 106, and 107, and an adder 108. As described above, any configuration (circuit) may be used as long as a value for evaluating the contrast of an image can be detected. For example, it may be configured by one type of horizontal HPF that can change the characteristics of the passband.

Further, the area used for AF evaluation, that is, the AF evaluation area is arbitrary in position, size, and the like.
Further, the AF evaluation area may be an area obtained by adding a plurality of places (on the image) or an area selected from the plurality of places. For example, the AF evaluation area may be determined by separately detecting the left area, the center area, and the right area of the screen and selecting the area where the subject exists. In addition, as a method for selecting a region where the subject exists, a region where the AF evaluation value is maximum may be selected, or a method for selecting by a user's switch operation, face determination, or the like may be used.
Moreover, each process of the said embodiment may be implement | achieved by hardware, and may be implement | achieved by software. Further, it may be realized by mixed processing of software and hardware.

  The specific configuration of the present invention is not limited to the above-described embodiment, and various changes and modifications can be made without departing from the scope of the invention.

Since the imaging apparatus, the focus control method, the program, and the integrated circuit according to the present invention automatically switch between the two control modes when the AF function is realized, the imaging apparatus has a large blurring state. In addition, AF control is possible, and an AF control operation with high responsiveness can be stably realized, and is useful in a video-related field such as a video camera, and the present invention can be industrially implemented. .

1 is a block diagram showing the configuration of an image pickup apparatus 100 with an autofocus function according to a first embodiment of the present invention. The schematic diagram for demonstrating the optical path separation part 2, the imaging part 3 for imaging | photography, the imaging part 4 for AF, and the optical path length change part 9 for AF by 1st Embodiment of this invention. The block diagram which shows the structure of AF evaluation value generation part 81 by 1st Embodiment of this invention. Schematic diagram for explaining the positional relationship on the optical axis between the AF imaging unit 4 and the imaging unit 3 in the optical path length difference comparison mode according to the first embodiment of the present invention. The schematic diagram which showed the relationship between the focus position at the time of imaging | photography with a certain subject by 1st Embodiment of this invention, and contrast evaluation value The schematic diagram which showed the relationship between the optical path length at the time of image | photographing a certain subject by 1st Embodiment of this invention, and contrast evaluation value Schematic diagram showing the relationship between the focus position and the contrast evaluation value for explaining the case where a malfunction occurs in the optical path length difference comparison mode FIG. 6 is a schematic diagram showing a process of calculating an optimum optical path length difference d when the characteristic curve between the optical path length and the contrast evaluation value is a gentle curve according to the first embodiment of the present invention. The flowchart explaining operation | movement of the control part 8 by 1st Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical system 2 Optical path separation part 3 Imaging imaging part 4 Analog signal processing part 5 AD conversion part 6 Signal processing part 7 AF imaging part 8 AF evaluation value generation part 9 AF control mode determination part 10 Adaptive AF control part 11 AF Optical path length changing unit 12 Control unit 101 Horizontal low-pass filter 102 First horizontal high-pass filter 103 Second horizontal high-pass filter 104 Vertical high-pass filter 105, 106, 107 Accumulating circuit 108 Adder

Claims (9)

An optical system that collects light from the subject and controls focus;
An optical path separation unit that separates the light from the subject collected by the optical system into at least a first light flux group and two or more second light flux groups for focus detection;
A photographing imaging unit that converts the first light flux group into an electrical signal and outputs the signal as a main video signal;
An autofocus imaging unit that has at least a front imaging element and a back imaging element, converts the two or more second light flux groups for focus detection into electrical signals, and outputs the electrical signals as autofocus detection video signals When,
An optical path length changing unit that changes the optical path length of the second light flux to the autofocus imaging unit by moving the autofocus imaging unit on the optical axis of the second light flux group;
An autofocus evaluation value generating unit that generates a contrast evaluation value that is an evaluation value of the contrast of the video signal for autofocus detection;
Based on the contrast evaluation value, the optical path length change mode for searching for the in-focus position while changing the optical path length of the autofocus imaging unit, and the contrast evaluation from a plurality of autofocus imaging units arranged at different optical path lengths An autofocus control mode determination unit that switches between an optical path length difference comparison mode for searching for a focus position based on the value and outputs an autofocus control mode signal including information on the selected autofocus control mode;
An adaptive autofocus control unit that switches and executes an autofocus control method according to the autofocus control mode signal;
An imaging apparatus comprising: The autofocus imaging unit includes at least a front imaging device and a back imaging device, and the front imaging device outputs an autofocus detection video signal acquired by the front imaging device as an AF_Front signal. The back image sensor outputs the autofocus detection video signal acquired by the back image sensor as an AF_Back signal,
The autofocus evaluation value generation unit outputs the contrast evaluation value calculated from the main line system video signal as a main line system contrast evaluation value to the autofocus control mode determination unit, and uses the contrast evaluation value calculated from the AF_Front signal. The front contrast evaluation value is output to the autofocus control mode determination unit, and the contrast evaluation value calculated from the AF_Back signal is output as the back contrast evaluation value to the autofocus control mode determination unit.
The autofocus control mode determination unit generates the autofocus control mode signal based on the front contrast evaluation value, the back contrast evaluation value, and the main line system contrast evaluation value,
The adaptive autofocus control unit generates an autofocus imaging unit position control signal and a focus position control signal based on the front contrast evaluation value, the back contrast evaluation value, and the autofocus control mode signal. ,
The optical path length changing unit moves the front imaging element and the back imaging element on the optical axis of the second light flux group based on the autofocus imaging unit position control signal.
The optical system changes a focus position of the optical system based on the focus position control signal;
The imaging device according to claim 1. The front imaging element is disposed on the optical axis at a position where the optical path length is shorter by d1 than the imaging imaging unit.
The back imaging device is disposed on the optical axis at a position where the optical path length is longer by d1 than the imaging imaging unit,
In the optical path length difference comparison mode,
The adaptive autofocus control unit includes:
(1) When the front contrast evaluation value is larger than the back contrast evaluation value, auto focus control is performed so as to move the focus position of the optical system in an infinite direction;
(2) When the back-contrast evaluation value is larger than the front-contrast evaluation value, autofocus control is performed so as to move the focus position of the optical system in the close-up direction,
(3) When the back contrast evaluation value and the front contrast evaluation value are equal, auto focus control is performed by not moving the focus position of the optical system,
In the optical path length change mode,
The adaptive autofocus control unit outputs the autofocus imaging unit position control signal for sequentially changing the optical path lengths of the autofocus / front imaging device and the autofocus / back imaging device,
The optical path length changing unit is configured to change the optical path length of the autofocus / front imaging device and the autofocus / back imaging device based on the autofocus imaging unit position control signal,
Further, the adaptive autofocus control unit detects the contrast evaluation value at each optical path length, and acquires the contrast evaluation value with respect to the total optical path length, whereby the relationship between the optical path length and the contrast evaluation value is obtained. A characteristic curve indicating the optical system, detecting the in-focus position of the optical system, and setting in the optical path length difference comparison mode, the photographing imaging unit, the autofocus front imaging element, and the autofocus An optimum optical path length difference d_best, which is a distance difference on the optical axis with the imaging device for the back, is calculated from the characteristic curve, and is further moved in the direction in which the in-focus position detected by the focus position of the optical system exists. The focus position control signal is output to
The auto focus control mode determination unit outputs an auto focus control mode signal for switching to the optical path length difference comparison mode when it is determined that the focus position of the optical system has approached the focus position.
The imaging device according to claim 2. In the optical path length difference comparison mode,
The front image sensor and the back image sensor are:
(The d1) = (the optimum optical path length difference d_best)
Arranged at a position on the optical axis,
The imaging device according to claim 3. The adaptive autofocus control unit includes:
The maximum value Cmax and the minimum value Cmin of the contrast evaluation value are obtained from the characteristic curve indicating the relationship between the optical path length acquired in the optical path length change mode and the contrast evaluation value, and the maximum of the contrast evaluation value is obtained. An optical path length f0 at which the value Cmax is obtained is obtained, an optical path length f1 at which the contrast evaluation value is Cmid = (Cmax−Cmin) / 2 is obtained, and the optimum optical path length difference is calculated as (the optimum optical path length difference d_best) = abs. (F0-f1)
(Abs (x) represents the absolute value of x.)
Set to a value that satisfies
The imaging device according to claim 4. The adaptive autofocus control unit includes:
From the characteristic curve showing the relationship between the optical path length acquired in the optical path length change mode and the contrast evaluation value, the maximum value Cmax of the contrast evaluation value and the optical path length f0 that becomes the maximum value Cmax of the contrast evaluation value are obtained. An optical path length f2 at which the rate of change of the contrast evaluation value with respect to the optical path length is maximized is obtained, and the optimum optical path length difference is calculated as (the optimum optical path length difference d_best) = abs (f0−f2).
(Abs (x) represents the absolute value of x.)
Set to a value that satisfies
The imaging device according to claim 4. An optical system that collects light from the subject and controls focus;
An optical path separation unit that separates the light from the subject collected by the optical system into at least a first light flux group and two or more second light flux groups for focus detection;
A photographing imaging unit that converts the first light flux group into an electrical signal and outputs the signal as a main video signal;
An autofocus imaging unit that has at least a front imaging element and a back imaging element, converts the two or more second light flux groups for focus detection into electrical signals, and outputs the electrical signals as autofocus detection video signals A focus control method used in an imaging apparatus comprising:
An optical path length changing step of changing the optical path length of the second light flux to the autofocus imaging section by moving the autofocus imaging section on the optical axis of the second light flux group;
An autofocus evaluation value generating step for generating a contrast evaluation value which is an evaluation value of the contrast of the video signal for autofocus detection;
Based on the contrast evaluation value, the optical path length change mode for searching for the in-focus position while changing the optical path length of the autofocus imaging unit, and the contrast evaluation from a plurality of autofocus imaging units arranged at different optical path lengths An autofocus control mode determination step for switching between an optical path length difference comparison mode for searching for an in-focus position based on the value and outputting an autofocus control mode signal including information on the selected autofocus control mode;
An adaptive autofocus control step for switching and executing an autofocus control method according to the autofocus control mode signal;
A focus control method comprising: An optical system that collects light from the subject and controls focus;
An optical path separation unit that separates the light from the subject collected by the optical system into at least a first light flux group and two or more second light flux groups for focus detection;
A photographing imaging unit that converts the first light flux group into an electrical signal and outputs the signal as a main video signal;
An autofocus imaging unit that has at least a front imaging element and a back imaging element, converts the two or more second light flux groups for focus detection into electrical signals, and outputs the electrical signals as autofocus detection video signals A program for causing a computer to execute a focus control method used in an imaging apparatus comprising:
On the computer,
An optical path length changing step of changing the optical path length of the second light flux to the autofocus imaging section by moving the autofocus imaging section on the optical axis of the second light flux group;
An autofocus evaluation value generating step for generating a contrast evaluation value which is an evaluation value of the contrast of the video signal for autofocus detection;
Based on the contrast evaluation value, the optical path length change mode for searching for the in-focus position while changing the optical path length of the autofocus imaging unit, and the contrast evaluation from a plurality of autofocus imaging units arranged at different optical path lengths An autofocus control mode determination step for switching between an optical path length difference comparison mode for searching for an in-focus position based on the value and outputting an autofocus control mode signal including information on the selected autofocus control mode;
An adaptive autofocus control step for switching and executing an autofocus control method according to the autofocus control mode signal;
A program that executes An optical system that collects light from the subject and controls focus;
An optical path separation unit that separates the light from the subject collected by the optical system into at least a first light flux group and two or more second light flux groups for focus detection;
A photographing imaging unit that converts the first light flux group into an electrical signal and outputs the signal as a main video signal;
An autofocus imaging unit that has at least a front imaging element and a back imaging element, converts the two or more second light flux groups for focus detection into electrical signals, and outputs the electrical signals as autofocus detection video signals When,
An optical path length changing unit that changes the optical path length of the second light flux to the autofocus imaging unit by moving the autofocus imaging unit on the optical axis of the second light flux group. An integrated circuit used in a device,
An autofocus evaluation value generating unit that generates a contrast evaluation value that is an evaluation value of the contrast of the video signal for autofocus detection;
Based on the contrast evaluation value, the optical path length change mode for searching for the in-focus position while changing the optical path length of the autofocus imaging unit, and the contrast evaluation from a plurality of autofocus imaging units arranged at different optical path lengths An autofocus control mode determination unit that switches between an optical path length difference comparison mode for searching for a focus position based on the value and outputs an autofocus control mode signal including information on the selected autofocus control mode;
An adaptive autofocus control unit that switches and executes an autofocus control method according to the autofocus control mode signal;
An integrated circuit comprising:

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