JP2013024933A - Image pickup apparatus, control method thereof, and computer program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve such a problem that, when a contrast AF for AF calibration is performed under a flicker light source, the accuracy of the result of the contrast AF is deteriorated due to removal of the flicker.SOLUTION: An image pickup apparatus includes: correction means for correcting a driving amount of an optical system in focal position detection by automatic focus adjustment; instruction means for instructing a correction mode for operating the correction means; flicker detecting means for detecting flicker using an image signal output from an image pickup device; and control means that, if the flicker is detected when the correction mode is instructed by the instruction means, does not calculate a correction value of the driving amount of the optical system or changes a frame rate of the image signal to integral multiple of the period of the flicker.

Description

  The present invention relates to an imaging apparatus, and more particularly to an imaging apparatus capable of performing focus detection by a phase difference detection method and focus detection by a contrast method based on the contrast of a subject image obtained from an imaging means, a control method thereof, and a computer program.

  Conventionally, there is an autofocus (automatic focus adjustment, hereinafter referred to as AF) function for automatically controlling the focus position of a lens and focusing.

In general, in a single-lens reflex camera, in-focus position detection by a phase difference AF method is often employed. However, it is known that in this in-focus position detection, the correct in-focus position may not be detected due to the influence of phase difference AF due to secular change, the light source at the time of photographing, the color and type of the subject, and the like.
Therefore, it is conceivable to correct the in-focus position detected by the phase difference AF method according to the environment to be used.

  In order to solve the above problem, Patent Document 1 discloses an electronic camera (imaging device) that obtains correction data in a test mode and controls an AF operation in a normal mode based on the obtained correction data. . In the test mode, the relative deviation between the AF data based on the phase difference AF method from the AF sensor modules arranged at conjugate positions and the AF data of the contrast method (hereinafter referred to as TVAF) based on the output signal of the image sensor. I have data. Then, the relative deviation data of the obtained AF data is stored, and the photographing lens is driven based on the stored relative deviation data in the normal mode.

By the way, it is also known that stripes called line flicker appear on a live view (hereinafter referred to as LV) screen under a flicker light source.
The stripe appears at the same position in each frame when the frame rate of the LV and the frequency of the commercial power supply are in an integral multiple relationship (LV is 30 fps and the power supply frequency is 60 Hz). However, when the relation is not an integral multiple (LV is 30 fps, power supply frequency is 50 Hz), the position moves every frame.
It is known that the movement of the position of the line flicker becomes a disturbance of the TVAF and deteriorates the detection accuracy of the focus position.
Therefore, in TVAF under a flicker light source, control using an aperture is performed by limiting the storage time of the image sensor to the time when the flicker disappears so that the above-described line flicker does not occur (Patent Document 2).

JP 2000-292684 A JP 2009-130551 A

  However, the prior art disclosed in the above-mentioned Patent Document 1 has a problem that it requires a well-adjusted adjustment environment and there is no means for making a determination for avoiding erroneous correction.

  Also, as disclosed in Patent Document 2, when TVAF is performed in a state where the aperture is stopped under a flicker light source, the depth of field becomes deeper by the amount of the aperture, which also causes a TVAF error factor.

  Normally, the error and the TVAF error due to the line flicker allow the aperture error, and the TVAF is controlled by narrowing down so that the line flicker does not appear on the screen.

  Similarly, in TV AF in AF calibration, aperture control is performed under a flicker light source to prevent line flicker from occurring. For this reason, as a result, the change in the depth of field due to the narrowed-down amount may cause a calibration error.

  For this reason, although the AF calibration accuracy may have decreased under the flicker light source, the user always thought that the same accuracy could be maintained.

  Therefore, an object of the present invention is to provide an imaging apparatus capable of performing AF calibration with high accuracy while avoiding the possibility that the accuracy of TVAF deteriorates under a flicker light source.

  In order to achieve the above object, an imaging apparatus according to the present invention includes a correction unit that corrects a driving amount of an optical system in detection of a focus position by automatic focus adjustment, and an instruction unit that instructs a correction mode for operating the correction unit. The flicker detection means for detecting flicker using the image signal output from the image sensor and the calculation of the correction value of the driving amount of the optical system when the flicker is detected when the correction mode is instructed by the instruction means Or a control means for changing the frame rate of the image signal to an integral multiple of the flicker period.

  According to the present invention, it is possible to avoid the possibility that the accuracy of TVAF deteriorates under a flicker light source. Therefore, when AF calibration is performed, a result with good accuracy is always obtained.

Schematic sectional view of a camera which is an example of an imaging apparatus according to the present embodiment Schematic sectional view of a camera which is an example of an imaging apparatus according to the present embodiment The figure which shows the flowchart for demonstrating AF calibration concerning 1st Example of this invention. Diagram for explaining the outline of flicker detection The figure which shows the flowchart for demonstrating AF calibration concerning 2nd Example of this invention.

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

  1 and 2 show schematic cross sections of a digital single-lens reflex camera with interchangeable lenses as an example of an imaging apparatus according to an embodiment of the present invention. This camera is a camera system having a phase difference AF correction function (hereinafter referred to as calibration mode) using a contrast detection method (hereinafter referred to as TVAF).

  FIG. 1 shows a schematic cross section of the camera when the movable main mirror 20 is disposed on the optical axis of the imaging optical system 10, and FIG. 2 shows the camera when the main mirror 20 is retracted from the optical axis. A schematic cross section is shown.

  1 and 2, an imaging optical system 10 accommodated in a lens body (lens unit) 1 is composed of one or a plurality of lens groups, and a focal length or a focus position is obtained by moving all or a part thereof. Can be changed.

  The lens driving unit 11 is lens driving means for moving all or part of the lenses constituting the imaging optical system 10 in order to adjust the in-focus state.

  The lens state detection unit 12 is a detection unit that detects the focal length of the imaging optical system 10, that is, the zoom position and the focus position.

  The aperture controller 15 is an aperture controller that drives the aperture 17 to adjust the amount of light incident on the camera.

  The lens control unit 13 includes a lens storage unit 14 configured by a ROM or the like, and is a control unit that controls the lens body 1.

  The contact 16 is a contact provided in the lens body 1 and the camera body (imaging device) 2, and various information is communicated and power is supplied through the contact 16 when they are attached to each other.

  The main mirror 20 is composed of a half mirror and can be rotated according to the operating state of the camera. When the subject is observed with the viewfinder, the main mirror 20 is inserted obliquely into the photographing optical path (dotted line in the figure), and the lens body. 1 is guided to a finder optical system described later (see FIG. 1). Further, during photographing or live view, the light is retracted from the photographing optical path, and the light flux from the lens body 1 is guided to the image sensor 24 described later (see FIG. 2).

  The sub mirror 21 rotates together with the main mirror 20, and guides the light beam transmitted through the main mirror 20 to the AF sensor 22 described later when the main mirror 20 is inserted in the photographing optical path (see FIG. 1). Further, during shooting or live view, it rotates with the main mirror 20 and is retracted from the shooting optical path (see FIG. 2).

  The AF sensor 22 includes a secondary imaging lens, an area sensor composed of a plurality of CCDs or CMOSs, and the like, and can detect a focus by a phase difference method which is a known method (first detection means). .

  The shutter 23 is provided to control the incidence of the light flux from the lens body 1 to the image sensor 24, and is normally closed (see FIG. 1) and opened during shooting or live view (see FIG. 2). ).

  The image sensor 24 is composed of a CMOS image sensor and its peripheral circuits, and converts an optical image of a subject from the imaging optical system 10 into an image signal.

  The focus plate 30 is disposed on the primary imaging surface of the lens body 1, has a Fresnel lens (condenser lens) on the incident surface, and forms an optical image (finder image) of the subject on the exit surface.

  The pentaprism 31 changes the finder optical path, and corrects the subject image formed on the exit surface of the focus plate 30 to an erect image.

  The eyepiece 32 is configured to adjust the diopter according to the user's eyes when the user looks through the viewfinder.

  Here, an optical system constituted by the focus plate 30, the pentaprism 31, and the eyepiece 32 is referred to as a finder optical system.

  The AE sensor 33 is composed of a photodiode corresponding to each area in the imaging area that is divided into multiple parts for AF, and measures the luminance of the subject image formed on the exit surface of the focusing screen 30 (second). Detection means).

  The mechanical control unit 40 is a microcomputer (central processing unit; MPU) that controls the camera unit and the entire camera.

  The digital control unit 41 is a memory controller (ICU) that performs various controls of image data. The digital control unit 41 can be used as a contrast-type focus detection unit that detects the contrast of an image captured by an image sensor and determines the in-focus state using the detection result.

  The camera storage unit 42 stores settings for performing various controls, adjustment data, and the like.

  The liquid crystal monitor 43 is a display device that displays captured images and various types of shooting information.

First Embodiment Hereinafter, the AF calibration according to the first embodiment of the present invention performed in the above-described camera will be described with reference to the flowchart of FIG. In this AF calibration, processing until calculation and determination of a correction value for phase difference AF is performed. 3 (calibration mode) is realized by the mechanical control unit 40 loading and executing a control program stored in a storage unit such as the camera storage unit 42, for example.

  When AF calibration is started by user setting in step S301, flicker detection is performed according to a flicker detection method described later in step S302, and the presence / absence of flicker and the period of flicker are obtained. In the flicker detection, the digital control unit 41 determines the presence or absence of flicker from the image signal output from the image sensor 24 in accordance with a flicker detection method described later. In the present embodiment, it is not necessary to obtain the flicker frequency.

  In step S303, the process branches based on the determination in step S302. If there is flicker, the process proceeds to step S312 to generate and display an alarm for notifying the user that the adjustment value is not calculated or determined in AF calibration, and then in step S313, the live view display is displayed. In step S314, the AF calibration is terminated.

  If there is no flicker, the process proceeds to step S304 to start live view display, and then, in step S305, a screen is displayed on the liquid crystal monitor 43 for allowing the user to select whether or not the digital control means 41 performs AF calibration. Wait for user instructions.

  If the user selects execution of AF calibration, the process proceeds to step S306. If the user cancels the process, the process proceeds to step S313 to end the live view.

  In step 306, TVAF is performed under the control of the mechanical control unit 40, and the lens is moved to the in-focus position.

  In step S307, live view display is temporarily interrupted in order to perform phase difference AF.

  In step S308, under the control of the mechanical control unit 40, the AF sensor 22 performs phase difference AF at the current lens position to determine the lens defocus amount (drive amount) (third detection means). This defocus amount corresponds to the difference between the in-focus position acquired by the TVAF in step S306 and the in-focus position obtained by the phase difference AF in the current step S308.

  Next, the live view display is restarted in step S309, and an adjustment value (correction value) is calculated from the defocus amount obtained by the phase difference AF under the control of the mechanical control unit 40 in step S310.

In step S <b> 311, the digital control unit 41 performs screen display that allows the user to select whether or not the obtained correction value can be adopted as a calibration result.
When the user selects not to adopt the correction value, the mechanical control unit 40 returns the process to step S305.

  When the user decides to adopt the correction value, the process proceeds to step S313 to end the live view display, and the AF calibration is ended in step S314.

  By the calibration by the camera operation control of the present embodiment described above, it is possible to avoid the possibility that the accuracy of TVAF deteriorates under the flicker light source.

  In the present embodiment, when there is flicker, the adjustment value is not calculated by AF calibration. However, even if flicker is detected, depending on the brightness of the subject image that makes it difficult to see the flicker on the screen, it is possible to perform TVAF by controlling the accumulation time without narrowing down (opening the aperture). Therefore, in this case, there is no error (in the depth of field) due to narrowing down in the TVAF result. For this reason, even if flicker detection is performed, if the aperture is wide, AF calibration may be performed to calculate the adjustment value in the same manner as when flicker is not detected.

FIG. 4 is a diagram showing an outline of flicker detection.
The flicker detection unit will be described with reference to FIG.

  Usually, the flicker of the fluorescent lamp is generated in synchronization with the frequency of the commercial power source. Therefore, the flicker cycle is 50 Hz in eastern Japan and 60 Hz in western Japan.

As a principle of flicker detection, the frame rate of the live view is set so as to be a value shifted by a half cycle of the flicker frequency.
For example, for a power supply frequency of 50 Hz, the frame rate is 67 fps (1/15 ms), 40 fps (1/25 ms), 28 fps (1/35 ms), and 22 fps (1/45 ms).

  When a live view of an image at such a frame rate is performed under a flicker light source, the position of flicker noise (line flicker) is shifted between successive frames as shown in FIGS. 4A and 4B.

  Therefore, by taking the differentiation (difference) of the two images and taking the mapping along the time axis (vertical direction of the image), it is possible to extract the flicker noise component as shown in FIG. (Amplitude etc.) and its frequency can be known.

  In the flicker detection of the present invention, the frame rate of the live view for flicker detection is set to 22 fps so that both 50 Hz and 60 Hz flicker can be detected by one detection.

  As described above, the flicker detection needs to be live-viewed at a specific frame rate. Normally, since live view operates at a frame rate of 30 fps, it cannot be detected constantly during camera operation. Therefore, flicker detection is performed only once (without performing live view) before the start of normal live view.

Second Embodiment Next, a phase difference AF correction operation function (AF calibration) using a contrast detection method (TVAF) according to a second embodiment of the present invention will be described.

  In the first embodiment, the adjustment value is not calculated in the AF calibration when flicker is detected. In this embodiment, when flicker is detected, the frame rate of the live view is changed to an integral multiple of the flicker frequency. As a result, the flicker component is canceled in the difference processing between frames, and it is possible to avoid a decrease in the accuracy of TVAF.

  The operation of this embodiment will be described below with reference to the flowchart of FIG. 5 as an example in which the present invention is applied to the camera shown in FIGS. Therefore, description of the camera shown in FIGS. 1 and 2 is omitted here. In the flowchart of FIG. 5, the same steps as those in the flowchart of FIG. 3 are denoted by the same reference numerals, and description thereof is omitted here.

  First, when AF calibration is started by user setting in step S501, flicker detection is performed in step S302 as in the first embodiment.

  If flicker is present in step S303, the process proceeds to step S502, where the frame rate of the live view is changed to an integral multiple of the detected flicker cycle, and then live view is started in step S503. Thereafter, the same steps as in the first embodiment are executed, and the AF calibration is terminated in step S504. The live view display in S504 starts at the frame rate if the frame rate is set in S502, and starts at a frame rate of 30 fps otherwise.

  If there is no flicker in step S303, the process proceeds to step S503 to start live view display, and thereafter, steps S305 to S313 similar to those in the first embodiment are executed, and AF calibration is ended in step S504. .

  Also by the AF calibration by the camera operation control of the present embodiment described above, it is possible to avoid the possibility that the accuracy of TVAF deteriorates under a flicker light source, and it is possible to avoid a decrease in the accuracy of AF calibration.

  In each of the above-described embodiments, the example in which the present invention is applied to a single-lens reflex digital camera has been described. can do.

  3 and 5 in the above-described embodiment, the program for realizing the function of each process is read from the memory (for example, the camera storage unit 42) and executed by the CPU of the control unit. The function is realized.

  The present invention is not limited to the above-described configuration, and all or some of the functions shown in FIGS. 3 and 5 may be realized by dedicated hardware. The memory described above may be a non-volatile memory such as a magneto-optical disk device or a flash memory, a recording medium such as a CD-ROM that can only be read, or a volatile memory other than a RAM. Moreover, you may comprise from the computer-readable / writable recording medium by those combination.

  Also, a program for realizing the functions of the processes shown in FIGS. 3 and 5 is recorded on a computer-readable recording medium, and the program recorded on the recording medium is read into a computer system and executed. You may perform each process by. “Computer-readable recording medium” refers to a portable medium such as a flexible disk, a magneto-optical disk, a ROM, and a CD-ROM, and a storage device such as a hard disk built in a computer system. Furthermore, a program that holds a program for a certain period of time, such as a volatile memory (RAM) inside a computer system that becomes a server or client when the program is transmitted via a network such as the Internet or a communication line such as a telephone line Shall also be included.

  The program may be transmitted from a computer system storing the program in a storage device or the like to another computer system via a transmission medium or by a transmission wave in the transmission medium. Here, the “transmission medium” for transmitting the program refers to a medium having a function of transmitting information, such as a network (communication network) such as the Internet or a communication line (communication line) such as a telephone line.

  The program may be for realizing a part of the functions described above. Furthermore, what can implement | achieve the function mentioned above in combination with the program already recorded on the computer system, and what is called a difference file (difference program) may be sufficient.

  A program product such as a computer-readable recording medium in which the above program is recorded can also be applied as an embodiment of the present invention. The above program, recording medium, transmission medium, and program product are included in the scope of the present invention.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and includes designs and the like that do not depart from the gist of the present invention.

  Although the present invention has been described with reference to the preferred embodiments, the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope shown in the claims.

Claims (12)

An image sensor that converts an optical image of a subject obtained by an image pickup optical system including an aperture and a lens into an image signal, a first detection unit that detects an in-focus state based on a phase difference method, and an output from the image sensor In an imaging apparatus having second detection means for detecting information corresponding to the contrast of the image signal that has been made,
Third detection means for detecting a difference between the in-focus position acquired using the detection result of the first detection means and the in-focus position acquired using the detection result of the second detection means;
Correction means for obtaining a correction value of the driving amount of the lens based on the detection result of the third detection means;
Instructing means for instructing a calibration mode for operating the third detecting means;
Flicker detection means for detecting flicker using the image signal output from the image sensor;
And a control unit that does not obtain a correction value of the driving amount of the lens by the correction unit when the flicker detection unit detects flicker when the calibration mode is instructed by the instruction unit. An imaging apparatus characterized by the above.   Even if the flicker detection unit detects flicker in the calibration mode, the control unit does not obtain a correction value of the driving amount of the lens by the correction unit only when the diaphragm is stopped. The imaging apparatus according to claim 1.   3. The imaging according to claim 1, wherein the control unit generates an alarm indicating that the correction unit does not determine when the correction unit does not calculate the correction value of the driving amount of the optical system. apparatus. An image sensor that converts an optical image of a subject obtained by an image pickup optical system including an aperture and a lens into an image signal, a first detection unit that detects an in-focus state based on a phase difference method, and an output from the image sensor In the control method of the imaging apparatus having the second detection means for detecting the information corresponding to the contrast of the image signal that has been performed,
A detection step of detecting a difference between the in-focus position acquired using the detection result of the first detection means and the in-focus position acquired using the detection result of the second detection means;
A correction step for obtaining a correction value of the driving amount of the lens based on the detection result in the detection step;
An instruction step for instructing a calibration mode for performing the detection step;
A flicker detection step of detecting flicker using the image signal output from the image sensor;
A control step that does not obtain a correction value of the lens driving amount in the correction step when the flicker is detected in the flicker detection step when the calibration mode is instructed in the instruction step. A control method characterized by that. Computer
An image sensor that converts an optical image of a subject obtained by an image pickup optical system including an aperture and a lens into an image signal, a first detection unit that detects an in-focus state based on a phase difference method, and an output from the image sensor In the control method of the imaging apparatus having the second detection means for detecting the information corresponding to the contrast of the image signal that has been performed,
Third detection means for detecting a difference between the in-focus position acquired using the detection result of the first detection means and the in-focus position acquired using the detection result of the second detection means;
Correction means for obtaining a correction value of the driving amount of the lens based on a detection result of the third detection means;
Instructing means for instructing a calibration mode for operating the third detecting means;
Flicker detection means for detecting flicker using the image signal output from the image sensor;
A program that functions as a control unit that does not obtain a correction value of the driving amount of the lens by the correction unit when the flicker detection unit detects flicker when the calibration mode is instructed by the instruction unit. .   A computer-readable recording medium on which the program according to claim 5 is recorded.   The program which makes a computer function as each means of the imaging device as described in any one of Claims 1 thru | or 3. Based on an imaging device that converts an optical image of a subject obtained by an imaging optical system including an aperture and a lens into an image signal, live view display means that displays an image signal output from the imaging device, and a phase difference method In an imaging apparatus having first detection means for detecting a focused state and second detection means for detecting information corresponding to the contrast of the image signal output from the imaging element,
Third detection means for detecting a difference between the in-focus position acquired using the detection result of the first detection means and the in-focus position acquired using the detection result of the second detection means;
Correction means for obtaining a correction value of the driving amount of the lens based on the detection result of the third detection means;
Instructing means for instructing a calibration mode for operating the third detecting means;
Flicker detection means for detecting flicker and its period using the image signal output from the image sensor;
When the flicker detection unit detects flicker when the calibration mode is instructed by the instruction unit, the flicker detection unit detects the frame rate of the image signal displayed on the live view display unit. An image pickup apparatus comprising: control means for changing to an integral multiple of a flicker cycle. Based on an imaging device that converts an optical image of a subject obtained by an imaging optical system including an aperture and a lens into an image signal, live view display means that displays an image signal output from the imaging device, and a phase difference method In a control method for an imaging apparatus, comprising: first detection means for detecting an in-focus state; and second detection means for detecting information corresponding to the contrast of the image signal output from the imaging element.
A detection step of detecting a difference between the in-focus position acquired using the detection result of the first detection means and the in-focus position acquired using the detection result of the second detection means;
A correction step for obtaining a correction value of the driving amount of the lens based on the detection result in the detection step;
An instruction step for instructing a calibration mode for operating the detection step;
A flicker detection step of detecting flicker and its period using the image signal output from the image sensor;
If flicker is detected in the flicker detection step when the calibration mode is instructed in the instruction step, the flicker detection step detects the frame rate of the image signal displayed on the live view display means. And a control step for changing the flicker period to an integral multiple of the flicker cycle. Computer
Based on an imaging device that converts an optical image of a subject obtained by an imaging optical system including an aperture and a lens into an image signal, live view display means that displays an image signal output from the imaging device, and a phase difference method In a control method for an imaging apparatus, comprising: first detection means for detecting an in-focus state; and second detection means for detecting information corresponding to the contrast of the image signal output from the imaging element.
Third detection means for detecting a difference between the in-focus position acquired using the detection result of the first detection means and the in-focus position acquired using the detection result of the second detection means;
Correction means for obtaining a correction value of the driving amount of the lens based on a detection result of the third detection means;
Instruction means for instructing a calibration mode for operating the third detection means;
Flicker detection means for detecting flicker and its period using the image signal output from the image sensor;
When the flicker detection unit detects flicker when the calibration mode is instructed by the instruction unit, the flicker detection unit detects the frame rate of the image signal displayed on the live view display unit. A program that functions as a control means for changing to an integral multiple of the flicker cycle.   The computer-readable recording medium which recorded the program of Claim 10.   A program that causes a computer to function as each unit of the imaging apparatus according to claim 8.