JP2004151608A - Autofocus system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an autofocus system by which a subject is surely brought into focus even in the case of photographing the subject whose contrast in either a horizontal direction or a vertical direction is low by generating a focus evaluating value showing the distinctness (contrast) of a photographic image both in the horizontal direction and the vertical direction of the photographic image and controlling focusing of a photographic lens to attain focusing both in the horizontal direction and the vertical direction based on the focus evaluating values in both directions. <P>SOLUTION: A CPU 54 acquires focus evaluated values in the respective horizontal and vertical directions from imaging devices for detecting a focusing state 32A and 32B through a focus evaluating value generating part 58 and controls the position of a focus lens 16 by driving a focus motor 50 so that the focus evaluated values in both directions may show a state regarded as a focusing state. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an autofocus system, and more particularly to a contrast autofocus system based on a video signal.
[0002]
[Prior art]
Generally, an autofocus of a video camera or the like is based on a contrast method. This contrast method generates a focus evaluation value by integrating high frequency components of video signals within a certain range (focus area) of video signals obtained from an image sensor, and the focus evaluation value is maximum (maximum). The focus adjustment is automatically performed so that Thereby, the best focus (focusing) that maximizes the sharpness (contrast) of the image captured by the image sensor is obtained.
[0003]
Conventionally, there has been proposed a method of detecting a focus state (front focus, rear focus, focus) of a photographing lens using a plurality of image sensors arranged at positions having different optical path lengths. According to this, at the current focus position, for example, the focus evaluation value when the focus is moved back and forth can be simultaneously known from the video signals obtained from the plurality of image sensors, and from the information, the current focus state can be obtained. Can be detected. Further, it is also possible to automatically adjust the focus of the photographing lens so as to focus on the basis of the detected focus state (for example, see Patent Documents 1 to 4).
[0004]
[Patent Document 1]
Japanese Patent Application No. 2001-168246
[0005]
[Patent Document 2]
Japanese Patent Application No. 2001-168247
[0006]
[Patent Document 3]
Japanese Patent Application 2001-168248
[0007]
[Patent Document 4]
Japanese Patent Application 2001-168249
[0008]
[Problems to be solved by the invention]
By the way, usually, a video signal is scanned in a horizontal direction from the upper end to the lower end of an image of each frame, and transmitted in a time-series manner in the order of scanning the signal of each pixel. Therefore, the focus evaluation value generated by extracting and integrating the high frequency components from the video signal is a value indicating the contrast of the image in the horizontal direction. Therefore, when the contrast of the subject is high in the vertical direction but low in the horizontal direction (for example, a pattern of horizontal stripes), there is a problem that the focus cannot be normally adjusted.
[0009]
The present invention has been made in view of such circumstances, and in an autofocus of a contrast method, an autofocus system that can reliably focus on an object having high contrast only in one direction, particularly in a vertical direction. The purpose is to provide.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the invention according to claim 1 obtains a focus evaluation value indicating a sharpness of an image formed by a video signal based on a video signal obtained by an imaging unit, and calculates the focus evaluation value. In an autofocus system that controls the focus of the photographing lens based on the image signal and automatically focuses the photographing lens, extracting a high frequency component in a horizontal direction of an image formed by the video signal, Horizontal focus evaluation value generating means for generating a focus evaluation value indicating the sharpness of the image in the horizontal direction based on the component, and extracting a high frequency component in a vertical direction of the image formed by the video signal, Vertical focus evaluation value generating means for generating a focus evaluation value indicating the sharpness of an image in the vertical direction based on the frequency component of the frequency band, and the horizontal focus evaluation Horizontal focus determining means for determining whether or not focusing is performed based on the focus evaluation value generated by the generating means; and focusing or not based on the focus evaluation value generated by the vertical focus evaluation value generating means. The focus of the photographic lens is controlled such that the focus is determined by both the vertical focus determiner, the horizontal focus determiner, and the vertical focus determiner. An autofocus system comprising: a focus control unit.
[0011]
Further, the invention according to claim 2 is the invention according to claim 1, further comprising a plurality of imaging means for imaging subject light incident on the imaging lens at positions having different optical path lengths, wherein the horizontal focus evaluation value is provided. Generating means and the vertical focus evaluation value generating means generate a focus evaluation value corresponding to each imaging means based on each video signal from the plurality of imaging means; and By comparing the focus evaluation values corresponding to the respective imaging units generated by the directional focus evaluation value generation unit, it is determined whether or not the subject is in focus, and the focus for obtaining the focus when it is determined that the subject is not in focus. Is determined by comparing the focus evaluation values corresponding to the respective imaging units generated by the horizontal focus evaluation value generation unit. In addition to the determination, when it is determined that the focus is not in focus, the operation direction of focus for obtaining focus is determined, and the focus control unit is determined by the horizontal focus determination unit or the vertical focus determination unit. Controlling the focus so that both of the horizontal focus determination means and the vertical focus determination means determine the focus based on the focus operation direction for obtaining the focus. It is characterized by.
[0012]
According to the present invention, a focus evaluation value indicating the sharpness (contrast) of an image is generated in both the horizontal direction and the vertical direction of a captured image, and the focus evaluation value is calculated based on the focus evaluation values in both the horizontal direction and the vertical direction. The focus of the photographic lens is controlled so that it is in focus with respect to the subject, so even when shooting a subject with low contrast in one of the horizontal and vertical directions, it is possible to focus reliably. it can.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a preferred embodiment of an autofocus system according to the present invention will be described in detail with reference to the accompanying drawings.
[0014]
FIG. 1 is a block diagram showing a configuration of an optical system of a television camera system to which the present invention is applied. The television camera system shown in FIG. 1 includes a lens device having a photographic lens 10, a camera body 12, and the like. The camera body 12 captures an image for reproduction (for broadcast, etc.), and An image sensor (hereinafter, referred to as an image sensor for video) for outputting as a video signal or recording on a recording medium, a required circuit, and the like are mounted.
[0015]
The lens device provided with the taking lens 10 is detachably attached to the camera body 12 and mainly includes an optical system (taking lens 10) and a control system (described later). The photographing lens 10 includes a focus lens (group) 16, a zoom lens (group) 18 including a variable power system and a correction system (not shown), an iris 20, a front relay lens 22 A, and a rear relay along the optical axis O. A relay lens (relay optical system) including the lens 22B and the like are arranged.
[0016]
A half mirror 24 is disposed between the front relay lens 22A and the rear relay lens 22B of the relay optical system to split the subject light for focus state detection from the subject light for video. The half mirror 24 is installed at an angle of approximately 45 degrees with respect to the optical axis O of the photographing lens 10, and reflects, for example, 1/3 of the amount of subject light passing through the front relay lens 22 </ b> A at a right angle, Branches from the subject light for video.
[0017]
The subject light transmitted through the half mirror 24 is emitted from the rear end side of the photographing lens 10 as subject light for video, and then enters the imaging unit 14 of the camera body 12. Although the configuration of the imaging unit 14 is omitted, the subject light incident on the imaging unit 14 is separated into three colors of red light, green light, and blue light by, for example, a color separation optical system. Incident on the image pickup surface. As a result, a color image for broadcast is captured. Note that the focus plane P in the figure shows a position optically equivalent to the imaging plane of each imaging element on the optical axis O of the photographing lens 10.
[0018]
On the other hand, the subject light reflected by the half mirror 24 travels along the optical axis O ′ perpendicular to the optical axis O as subject light for focus state detection, and enters the relay lens 26. Then, the light is condensed by the relay lens 26 and enters the focus state detection unit 28.
[0019]
The focus state detection unit 28 includes two prisms 30A and 30B constituting a light splitting optical system, and a pair of image sensors 32A and 32B for focus state detection (hereinafter, referred to as focus state detection image sensors). I have.
[0020]
As described above, the subject light reflected by the half mirror 24 travels along the optical axis O ', and first enters the first prism 30A. Then, the light is equally divided into reflected light and transmitted light on the half mirror surface M of the first prism 30A. Of these, the reflected light is incident on the imaging surface of one focus state detection image sensor 32A, and the transmitted light is incident on the other focus state detection image sensor 32B. At this time, approximately 1/6 of the total subject light incident on the imaging lens 10 is incident on the imaging surfaces of the focus state detection imaging elements 32A and 32B.
[0021]
FIG. 2 is a diagram illustrating the optical axis of the subject light incident on the image pickup device of the camera body 12 and the optical axis of the subject light incident on the pair of focus state detection image pickup devices 32A and 32B on the same straight line. . As shown in the figure, the optical path length of the subject light incident on one of the focus state detection image pickup devices 32A is set shorter than the optical path length of the subject light incident on the other focus state detection image pickup device 32B. The optical path length of the subject light incident on the imaging plane (focus plane P) of the imaging element for use is set to be an intermediate length therebetween. That is, the pair of focus state detection imaging elements 32A and 32B (the imaging planes thereof) are respectively arranged at positions equidistant (d) from the imaging plane (focus plane P) of the video imaging element.
[0022]
With the pair of focus state detection image pickup devices 32A and 32B arranged as described above, the subject light incident on the imaging lens 10 is imaged at a position equidistant from the image pickup surface (focus plane P) of the image pickup device. It is supposed to be. Note that the pair of focus state detection imaging devices 32A and 32B capture images captured when the imaging surface is disposed at a position equidistant in the front-rear direction with respect to the imaging surface of the video imaging device. The relationship between the optical path lengths of the focus state detection imaging devices 32A and 32B and the video imaging device is not necessarily limited to the case shown in FIG. The focus state detection image pickup devices 32A and 32B acquire a video signal for focus state detection (autofocus control) as described later, and need not be a color image pickup apparatus. In the embodiment, it is assumed that the CCD captures a black-and-white image.
[0023]
Next, a control system related to autofocus control in the lens device will be described. FIG. 3 is a block diagram showing a configuration of a control system related to the autofocus control. The focus lens 16 is connected to a focus motor 50 as shown in FIG. 3, and when the focus motor 50 is driven, the focus lens 16 moves in the optical axis direction to change the focus. A drive voltage is applied to the focus motor 50 from a focus motor drive circuit 52, and a control signal from the CPU 54 is applied to the focus motor drive circuit 52.
[0024]
The control signal from the CPU 54 indicates, for example, a rotation speed of the focus motor 50, that is, a voltage value corresponding to the moving speed of the focus lens 16, and when the voltage value is given to the focus motor drive circuit 52, the focus motor 50 The voltage is amplified by the drive circuit 52, and the amplified voltage is applied to the focus motor 50 as a drive voltage. Thus, the rotation speed of the focus motor 50 is controlled by the CPU 54.
[0025]
Further, the current position of the focus lens 16 is detected by the focus lens position detector 56, and the detection signal is given to the CPU 54. Therefore, in the processing of the CPU 54, by controlling the rotation speed of the focus motor 50 as described above, the operating speed of the focus lens 16 can be controlled to a desired speed. By controlling the rotational speed of the focus motor 50 while reading the current position of the lens 16, the set position of the focus lens 16 can be controlled to a desired position.
[0026]
On the other hand, the autofocus control is performed based on the video signals from the focus state detection image pickup devices 32A and 32B, and the image (video image) captured by the pair of focus state detection image pickup devices 32A and 32B is used. ) Is output as a video signal for sequentially transmitting each pixel value along a plurality of scanning lines (horizontal lines) constituting one screen, and is input to the focus evaluation value generation unit 58. Although the configuration and processing of the focus evaluation value generation unit 58 will be described later, the focus evaluation value generation unit 58 converts each of the focus state detection image sensors 32A and 32B from the video signal input thereto. , 32B, the focus evaluation values indicating the level of the contrast (sharpness) of each image captured are generated, and the generated focus evaluation values are given to the CPU 54. Note that the focus evaluation value generated based on the video signal from the focus state detection imaging device 32A is referred to as the focus evaluation value of channel A (chA), and is based on the video signal from the focus state detection imaging device 32B. The generated focus evaluation value is referred to as a focus evaluation value of channel B (chB). The CPU 54 obtains the focus evaluation values of chA and chB obtained from the focus evaluation value generation unit 58 as described later in detail, and based on the obtained focus evaluation values, the focusing state of the imaging lens 10 (front focus, front focus, (In-focus, focus) is detected, and the position of the focus lens 16 is controlled so that the focus state of the photographing lens 10 is in focus.
[0027]
Next, the configuration and processing of the focus evaluation value generation unit 58 will be described with reference to the configuration diagram of FIG. Since the focus evaluation values of chA and chB are generated by similarly configured processing units, FIG. 4 shows only the configuration of the processing unit for chA, and the configuration and description of the processing unit for chB are omitted. I do. As shown in the figure, when the video signal output from the focus state detection image sensor 32A is input to the focus evaluation value generation unit 58, it is first converted into a digital signal by the A / D converter 80. It is assumed that the video signal from each focus state detecting image sensor 32A is a luminance signal indicating the luminance value of each pixel constituting the image. The video signal converted to a digital signal by the A / D converter 80 is subsequently branched into two lines a and b. Line a is a line for generating a horizontal focus evaluation value (horizontal focus evaluation value), and line b is a line for generating a vertical focus evaluation value (vertical focus evaluation value). is there. The horizontal focus evaluation value indicates the contrast in the horizontal direction of the image formed by the video signal from the focus state detection image sensor 32A, and the vertical focus evaluation value is determined by the video signal from the focus state detection image sensor 32A. 5 shows the contrast in the vertical direction of an image to be formed. As is generally known, a video signal output from the focus state detecting image sensor 32A is obtained by sequentially scanning a signal (luminance value) of a pixel sequentially scanned in a horizontal direction from an upper end to a lower end of an image in the scanning order. It is assumed that the data is transmitted in the form of transmission.
[0028]
The video signal branched to the line a is first input to a high-pass filter (HPF) 84A, and a high frequency component of the video signal is extracted by the HPF 84A. The extracted signal of the high frequency component is subsequently input to the gate circuit 86A. In the gate circuit 86A, only a signal corresponding to a pixel in a predetermined focus area (for example, a center portion of the screen) among signals of one screen (one field) of an image captured by the focus state detection imaging element 32A. Is extracted. The signal extracted by the gate circuit 86A is subsequently input to the integrating circuit 88A, and the signal for one screen is integrated by the integrating circuit 88A. Thus, the sum of the values of the high frequency components of the video signal in the focus area is obtained. The value obtained by the integrating circuit 88A in this manner is a focus evaluation value indicating the sharpness (high or low of the contrast) in the horizontal direction of the image in the focus area, and the focus evaluating value obtained by the integrating circuit 88A is channel A (ChA) is given to the CPU 54 as the horizontal focus evaluation value.
[0029]
On the other hand, the video signal branched to the line b is first input to the memory 82B. The memory 82B is, for example, a two-dimensional memory having an array of 720 in the horizontal direction and 243 in the vertical direction corresponding to pixels of an image composed of video signals for one screen (one field) as shown in FIG. The signal (luminance value) of each pixel of the video signal input to the memory 82B is sequentially stored in the memory of the corresponding pixel. Then, the signal of each pixel stored in the memory 82B is sequentially scanned in the vertical direction from the left end to the right end of the screen, for example, and is output from the memory 82B in a time series in the order of the scanning. The video signal output from the memory 82B is subsequently input to a high-pass filter (HPF) 84B, and the high-frequency component is extracted by the HPF 84B, and then input to the gate circuit 86B. Then, only the signal corresponding to the pixel in the focus area that matches the gate circuit 86A is extracted, and the signal for one screen is integrated by the integration circuit 88B. Thus, the sum of the values of the high frequency components of the video signal in the focus area is obtained. The value obtained by the integrating circuit 88B in this manner is a focus evaluation value indicating the sharpness (high or low of the contrast) in the vertical direction of the image in the focus area, and the focus evaluating value obtained by the integrating circuit 88B is the channel A This is given to the CPU 54 as the vertical focus evaluation value of (chA).
[0030]
The focus evaluation value generation unit 58 configured as described above generates the horizontal focus evaluation value and the vertical focus evaluation value of chA and chB, and these values are given to the CPU 54.
[0031]
Next, an autofocus process in the CPU 54 will be described. The CPU 54 compares the horizontal focus evaluation values obtained from chA and chB, respectively, or compares the vertical focus evaluation values obtained from chA and chB, respectively, to thereby obtain the imaging plane (focus) of the image pickup device for video. The focus state (front focus, rear focus, focus) of the photographing lens 10 with respect to the surface P) is detected.
[0032]
Here, first, the principle of detecting the focus state based on one of the horizontal focus evaluation value and the vertical focus evaluation value of chA and chB will be described with reference to FIG. In this description, a focus evaluation value in one of the horizontal focus evaluation value and the vertical focus evaluation value is simply referred to as a focus evaluation value.
[0033]
FIG. 6 is a diagram showing the state of the focus evaluation value with respect to the focus position when a certain subject is photographed, with the horizontal axis representing the position (focus position) of the focus lens 16 of the photographing lens 10 and the vertical axis representing the focus evaluation value. is there. A curve C indicated by a dotted line in the figure indicates a focus evaluation value when it is assumed that a focus evaluation value is obtained from a video signal from a video imaging device (or an imaging device arranged at a position conjugate with the video imaging device). Curves A and B shown by solid lines in the figure show focus evaluation values of chA and chB obtained from the focus state detection imaging elements 32A and 32B with respect to the focus position. Things. In the same figure, a position F3 where the focus evaluation value of the curve C is maximum (maximum) indicates a focus position.
[0034]
If the focus position of the photographing lens is set to F1 in the figure, the focus evaluation value _{V A1} of the chA becomes a value corresponding to the position F1 of the curve A, the focus evaluation value _{V B1} of chB, the position of the curve B F1 Becomes the value corresponding to. In this case, towards the focus evaluation value _{V A1} of chA is larger than the focus evaluation value _{V B1} of chB. This indicates that the focus position is set closer to the focus position (F3), that is, the front focus state.
[0035]
On the other hand, when the focus position of the photographing lens is set to F2 in the figure, the focus evaluation value V _A2 of the chA becomes a value corresponding to the position F2 of the curve A, the focus evaluation value V _B2 of chB is the curve B The value corresponds to the position F2. In this case, towards the focus evaluation value _{V A2} of chA is smaller than the focus evaluation value _{V B2} of chB. This indicates that the focus position is set on the infinity side of the focus position (F3), that is, the rear focus state.
[0036]
In contrast, when the focus position of the taking lens 10 is F3, i.e. is set to focus position, the focus evaluation value V _A3 of the chA becomes a value corresponding to the position F3 of the curve A, the focus evaluation value V of chB _B3 is a value corresponding to the position F3 of the curve B. In this case, the focus evaluation value _{V A3} and focus evaluation value _{V B3} of the chB of chA becomes equal. This indicates that the focus position is set to the focus position (F3).
[0037]
As described above, whether the current focus state of the photographing lens 10 is the front focus state, the rear focus state, or the in-focus state is detected based on the focus evaluation values of chA and chB obtained from the focus evaluation value generation unit 58. Can be.
[0038]
Therefore, by controlling the position of the focus lens 16 based on the chA and chB focus evaluation values obtained from the focus evaluation value generation unit 58, the focus lens 16 can be moved to the in-focus position. That is, when the focus evaluation values of chA and chB are determined to be the front focus, the focus lens 16 is moved toward infinity, and when the focus evaluation values are determined to be the back focus, When the focus lens 16 is moved in the close-up direction and the focus is determined to be in focus, the focus lens 16 is stopped at that position to move the focus lens 16 to the focus position. it can.
[0039]
Next, the processing procedure of the CPU 54 when the focus lens 16 is moved to the in-focus position using both the horizontal focus evaluation value and the vertical focus evaluation value of chA and chB will be described with reference to the flowchart of FIG. First, the CPU 54 acquires the horizontal focus evaluation value FH1 and the vertical focus evaluation value FV1 of chA from the focus evaluation value generation unit 58 (step S10). Further, the horizontal focus evaluation value FH2 and the vertical focus evaluation value FV2 of chB are obtained from the focus evaluation value generation unit 58 (step S12).
[0040]
Next, the CPU 54 calculates the following conditional expression:
[0041]
(Equation 1)
FH1> FH2
Holds, and the following conditional expression:
[0042]
(Equation 2)
It is determined whether or not | FH1-FH2 |> threshold holds (step S14). The threshold value of the conditional expression indicates a value determined to be in focus if | FH1−FH2 | is less than or equal to the value. The same applies to threshold values in the following determination processing. If YES is determined in this step S14, the CPU 54 moves the focus (focus lens 16) to infinity because the current focus position is closer to the in-focus position than described above with reference to FIG. (Step S16). Then, the process returns to step S10.
[0043]
If NO is determined in step S14, then the following conditional expression
[0044]
[Equation 3]
FH1 <FH2
Holds, and the following conditional expression:
[0045]
(Equation 4)
It is determined whether or not | FH1-FH2 |> threshold holds (step S18). If YES is determined in this step S14, the CPU 54 moves the focus to the closest side because the current focus position is on the infinity side from the in-focus position as described in FIG. 6 (step S20). . Then, the process returns to step S10.
[0046]
If NO is determined in step S18, that is, if it is determined that the focus state is detected in the focus state detection based on the horizontal focus evaluation value, then the following conditional expression:
[0047]
(Equation 5)
FV1> FV2
Holds, and the following conditional expression:
[0048]
(Equation 6)
It is determined whether or not | FV1-FV2 |> threshold holds (step S22). If YES is determined in this step S22, the CPU 54 moves the focus to the infinity side because the current focus position is closer to the in-focus position than the in-focus position as described with reference to FIG. 6 (step S24). . Then, the process returns to step S10.
[0049]
If NO is determined in step S22, then the following conditional expression
[0050]
(Equation 7)
FV1 <FV2
Holds, and the following conditional expression:
[0051]
(Equation 8)
It is determined whether or not | FV1-FV2 |> threshold holds (step S26). If YES is determined in this step S26, as described with reference to FIG. 6, the current focus position is on the infinity side from the in-focus position, so the CPU 54 moves the focus to the closest side (step S20). . Then, the process returns to step S10.
[0052]
If NO is determined in step S26, the focus evaluation value indicates a focused state in both the horizontal direction and the vertical direction, and therefore, the process returns to step S10 without moving the focus.
[0053]
As described above, by controlling the focus so that both the horizontal focus evaluation value and the vertical focus evaluation value indicating the contrast of the image in the horizontal direction and the vertical direction indicate the focus state, for example, only in one direction It is possible to appropriately focus on an object having a high contrast (for example, horizontal stripes and vertical stripes).
[0054]
As described above, in the processing shown in the flowchart of FIG. 7, the focus control based on the horizontal focus evaluation value and the vertical focus evaluation value is performed in order. However, as shown in the flowchart of FIG. It may be configured to determine in which direction the value difference is large and control the focus based on the focus evaluation value in the direction where the difference is large. 8, the CPU 54 first acquires the horizontal focus evaluation value FH1 and the vertical focus evaluation value FV1 of chA from the focus evaluation value generation unit 58 (step S40). Also, the horizontal focus evaluation value FH2 and the vertical focus evaluation value FV2 of chB are acquired from the focus evaluation value generation unit 58 (step S42).
[0055]
Next, the CPU 54 determines whether or not | FH1−FH2 |> | FV1−FV2 | (step S44). If YES is determined at this time, the following conditional expression:
[0056]
(Equation 9)
FH1> FH2
Holds, and the following conditional expression:
[0057]
(Equation 10)
It is determined whether or not | FH1-FH2 |> threshold holds (step S46). If YES is determined in this step S46, the CPU 54 moves the focus (the focus lens 16) to the infinity side because the current focus position is closer to the in-focus position than the in-focus position as described in FIG. (Step S48). Then, the process returns to step S40.
[0058]
If NO is determined in the step S46, then the following conditional expression:
[0059]
[Equation 11]
FH1 <FH2
Holds, and the following conditional expression:
[0060]
(Equation 12)
It is determined whether or not | FH1-FH2 |> threshold holds (step S50). If YES is determined in this step S50, the CPU 54 moves the focus to the closest distance side (step S20) because the current focus position is on the infinity side of the in-focus position as described in FIG. . Then, the process returns to step S40.
[0061]
If NO is determined in step S50, the threshold ≧ | FH1-FH2 |> | FV1-FV2 | holds, and the focus evaluation value indicates a focused state in both the horizontal direction and the vertical direction. The process returns to step S40 without moving the focus.
[0062]
If NO is determined in the step S44, then the following conditional expression:
[0063]
(Equation 13)
FV1> FV2
Holds, and the following conditional expression:
[0064]
[Equation 14]
It is determined whether or not | FV1-FV2 |> threshold holds (step S54). If YES is determined in this step S54, the CPU 54 moves the focus to infinity because the current focus position is closer to the in-focus position than the in-focus position as described in FIG. 6 (step S56). . Then, the process returns to step S40.
[0065]
If NO is determined in step S54, the following conditional expression
[0066]
[Equation 15]
FV1 <FV2
Holds, and the following conditional expression:
[0067]
(Equation 16)
It is determined whether or not | FV1−FV2 |> threshold holds (step S58). If YES is determined in this step S58, the CPU 54 moves the focus to the closest side because the current focus position is on the infinity side from the in-focus position as described in FIG. 6 (step S60). . Then, the process returns to step S40.
[0068]
If NO is determined in step S58, the threshold ≧ | FV1−FV2 |> | FH1−FH2 | holds, and the focus evaluation value indicates a focused state in both the horizontal direction and the vertical direction. The process returns to step S40 without moving the focus.
[0069]
In the above-described embodiment, a case has been described where AF control is performed by acquiring two focus evaluation values from the two focus state detection imaging elements 32A and 32B for AF. However, the present invention is not limited to this. The present invention can be applied to a case where one or three or more imaging elements are provided. That is, the present invention can be applied to the control of the autofocus employing the contrast method.
[0070]
Further, in the above-described embodiment, the case where the present invention is applied to a television camera system has been described as an example. However, the present invention is not limited to this, and can be applied to a video camera and a still camera that shoots a still image. .
[0071]
【The invention's effect】
As described above, according to the autofocus system according to the present invention, the focus evaluation value indicating the sharpness (contrast) of the image is generated in both the horizontal direction and the vertical direction of the captured image, and the focus evaluation value is generated in the horizontal direction and the vertical direction. Since the focus of the taking lens is controlled so that focusing is performed in both directions based on the focus evaluation values in both directions, the subject in which the contrast in one of the horizontal direction and the vertical direction is low is photographed. Even if there is, the focus can be surely adjusted.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an optical system of a television camera system to which the present invention has been applied.
FIG. 2 is a diagram illustrating an optical axis of subject light incident on a video imaging device and an optical axis of subject light incident on a pair of focus state detection imaging devices on the same straight line.
FIG. 3 is a block diagram illustrating a configuration of a control system related to autofocus control.
FIG. 4 is a block diagram illustrating a configuration of a focus evaluation value generation unit.
FIG. 5 is an explanatory diagram used for describing a memory in a focus evaluation value generation unit.
FIG. 6 is a diagram illustrating a state of a focus evaluation value with respect to a focus position when a certain subject is photographed, with a horizontal axis indicating a focus position of a photographing lens and a vertical axis indicating a focus evaluation value.
FIG. 7 is a flowchart illustrating an embodiment of a processing procedure of autofocus control in a CPU of the lens device.
FIG. 8 is a flowchart illustrating an embodiment of a processing procedure of autofocus control in a CPU of the lens device.
[Explanation of symbols]
Reference numeral 10: photographing lens, 12: camera body, 14: imaging unit, 16: focus lens (group), 18: zoom lens (group), 20: iris, 22A: front relay lens, 22B: rear relay lens, 24 ... Half mirror, 26 relay lens, 28 focus state detection unit, 30A first prism, 30B second prism, 32A, 32B image sensor for focus state detection, 50 focus motor, 52 focus motor drive circuit, 54, CPU, 56, focus lens position detector, 58, focus evaluation value generator, 80, A / D converter, 82B, memory, 84A, 84B, high-pass filter (HPF), 86A, 86B, gate circuit, 88A , 88B ... Integration circuit

Claims (2)

A focus evaluation value indicating the sharpness of an image formed by the video signal is obtained based on the video signal obtained by the imaging means, and the focus of the photographic lens is controlled based on the focus evaluation value to focus the photographic lens. In an auto focus system that automatically performs
Horizontal focus evaluation value generating means for extracting a high frequency component in the horizontal direction of an image formed by the video signal and generating a focus evaluation value indicating the sharpness of the image in the horizontal direction based on the high frequency component When,
Vertical focus evaluation value generating means for extracting a high frequency component in the vertical direction of an image formed by the video signal and generating a focus evaluation value indicating the sharpness of the image in the vertical direction based on the high frequency component When,
Horizontal focus determination means for determining whether or not to perform focusing based on the focus evaluation value generated by the horizontal focus evaluation value generation means;
A vertical focus determining unit that determines whether or not focusing is performed based on the focus evaluation value generated by the vertical focus evaluation value generating unit;
Focus control means for controlling the focus of the photographic lens so that both the horizontal focus determination means and the vertical focus determination means are in focus.
An auto focus system comprising: A plurality of imaging means for imaging the subject light incident on the shooting lens at different positions of the optical path length,
The horizontal focus evaluation value generation unit and the vertical focus evaluation value generation unit generate a focus evaluation value corresponding to each imaging unit based on each video signal from the plurality of imaging units,
The horizontal direction focus determination unit determines whether or not focus is achieved by comparing focus evaluation values corresponding to the respective imaging units generated by the horizontal direction focus evaluation value generation unit. If it is determined, the direction of focus operation for obtaining focus is determined,
The vertical focus determination means determines whether or not focus is achieved by comparing focus evaluation values corresponding to the respective imaging means generated by the horizontal focus evaluation value generation means. If it is determined, the direction of focus operation for obtaining focus is determined,
The focus control unit is configured to control the horizontal focus determination unit and the vertical direction based on a focus operation direction for obtaining focus determined by the horizontal focus determination unit or the vertical focus determination unit. 2. The auto-focus system according to claim 1, wherein the focus is controlled so that any of the focus determining means determines that the focus is achieved.

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