JP2012227893A - Camera and control method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To release constrained flicker countermeasure control quickly by detecting disappearance of flicker accurately.SOLUTION: In a camera performing live view display, an imaging element is exposed by setting the integration time Tint of a shift value 502 different from a multiple of the flicker period Tf when the flicker is detected, and a predetermined flicker component is left intentionally within a range capable of correction processing so that disappearance of flicker can be detected by the presence of the flicker component. When the flicker is detected, imaging conditions for flicker countermeasure are set and deterioration of image quality due to flicker is prevented by image processing, e.g. synthesis of a plurality of continuous frames. When the flicker is not detected, the flicker countermeasure is inhibited and video display is performed by setting the quality priority imaging conditions.

Description

  The present invention relates to a camera and a camera control method.

  As a countermeasure against flicker that prevents image quality deterioration of moving images due to flicker under illumination of a flicker light source having flicker to operate with an AC commercial power supply, the electronic shutter speed (integration time) of the image sensor is commercial By setting the integral frequency of the power supply frequency or switching the shutter speed to an integral multiple of 1/100 or an integral multiple of 1/120 according to the frame rate as in Patent Document 2, the flicker cycle and the imaging element are switched. There has been proposed a technique for eliminating the influence of flicker by synchronizing the control.

Japanese Patent Publication No. 61-056915 Japanese Patent No. 3826904

The above-described prior art is effective for improving the image quality under the flicker light source, but since the data output from the imager after the countermeasure against the flicker has almost no flicker component, the flicker component is separated from the flicker light source. Even if shooting is performed under a non-flicker light source that does not have, it is impossible to detect that the flicker component has disappeared from the subject, that is, it is not necessary to take countermeasures against flicker.
If the shutter speed is limited in consideration of flicker, it is necessary to perform complicated correction processing for fine exposure adjustment with another aperture and sensitivity.
That is, if the aperture is changed frequently, the depth of field changes frequently, resulting in a moving image that does not become settled. If the sensitivity is increased, the image quality of the moving image is reduced due to increased noise.
For this reason, under a non-flicker light source, it is desirable to finely control the shutter speed by removing the restriction on the shutter speed as a countermeasure against flicker.

An object of the present invention is to provide a technique capable of accurately detecting disappearance of flicker and quickly releasing flicker countermeasure control with many restrictions.
Another object of the present invention is to provide a technique capable of maintaining an image quality in a live view in an optimum state according to the presence or absence of flicker.

According to a first aspect of the present invention, there is provided an imaging unit that acquires image data from an output of an imaging device that converts light into an electrical signal;
Luminance detection means for detecting the luminance of the subject from the output of the image sensor;
Exposure control means for controlling the integration time of the image sensor based on the brightness of the subject obtained by the brightness detection means;
Flicker detection means for detecting a flicker state in which the subject is illuminated by a flicker light source;
In a camera equipped with
When the flicker detection unit detects the flicker state, the exposure control unit adds or subtracts a predetermined second value corresponding to the first value from a first value obtained by multiplying the commercial power cycle by an integer. The camera is characterized in that the image sensor is controlled using the obtained third value as an integration time.

According to a second aspect of the present invention, there is provided a camera control method for changing an integration time of the image sensor when a flicker state in which a subject is illuminated with a flicker light source is detected from an output of the image sensor.
A first value obtained by adding or subtracting a second value corresponding to the first value from a first value that is an integral multiple of the flicker cycle at which the flicker state completely disappears is set as the integration time of the image sensor. Steps,
A second step of outputting to the display device an image signal that has been subjected to correction processing that cancels luminance fluctuations of the subject due to a flicker component remaining in the output of the image sensor in accordance with the second value;
The control method of the camera containing is provided.

According to the present invention, it is possible to provide a technique capable of accurately detecting disappearance of flicker and quickly releasing flicker countermeasure control with many restrictions.
In addition, it is possible to provide a technique capable of maintaining the image quality in the live view in an optimum state according to the presence or absence of flicker.

It is a conceptual diagram which shows an example of a structure of the camera which implements the control method of the camera which is one embodiment of this invention. It is a flowchart which shows an example of an effect | action of the camera which implements the control method of the camera which is one embodiment of this invention. It is a conceptual diagram which shows an example of the effect | action of the camera which implements the control method of the camera which is one embodiment of this invention. It is a conceptual diagram which shows the influence of the flicker in the camera using the image pick-up element of a rolling shutter system, and the effect of a continuous frame average. It is a program diagram which shows an example of the effect | action of the camera which implements the control method of the camera which is one embodiment of this invention. It is a program diagram in consideration of conventional flicker. FIG. 5 is a model diagram of a graph in which only flicker components are extracted in the time change of the brightness of an object. It is a conceptual diagram which shows the effect | action of the countermeasure against flicker which sets the integration time of an image pick-up element by the multiple of a flicker period with the reference technique of this invention. It is a conceptual diagram which shows an example of the effect | action of the camera which implements the control method of the camera which is one embodiment of this invention. It is a conceptual diagram which shows the structural example of the shutter speed table used with the camera which implements the control method of the camera which is one embodiment of this invention. It is a conceptual diagram which shows the structural example of the shutter speed table used with the camera which implements the control method of the camera which is one embodiment of this invention. It is a program diagram used with the camera which implements the control method of the camera which is one embodiment of the present invention. It is a conceptual diagram explaining the effect | action of the camera which implements the control method of the camera which is one embodiment of this invention. It is a conceptual diagram explaining the effect | action of the camera which implements the control method of the camera which is one embodiment of this invention. It is a conceptual diagram explaining the effect | action of the camera which implements the control method of the camera which is one embodiment of this invention. It is a conceptual diagram explaining the effect | action of the camera which implements the control method of the camera which is one embodiment of this invention. It is a conceptual diagram which shows an example of the live view display of the countermeasure against the flicker of the camera which implements the control method of the camera which is one embodiment of this invention. It is a conceptual diagram which shows the image of a live view display when a flicker component is strong. It is a flowchart which shows the modification of the effect | action of the camera which implements the control method of the camera which is one embodiment of this invention. It is a flowchart which shows the further another modification of the effect | action of the camera which implements the control method of the camera which is one embodiment of this invention. It is a conceptual diagram which shows the further another modification of the effect | action of the camera which implements the control method of the camera which is one embodiment of this invention.

In the present embodiment, as one aspect, in the control for changing the electronic shutter speed (integration time, exposure time) after flicker detection in the output of the image sensor of the camera, a time that is an integral multiple of the flicker cycle during which the flicker disappears completely The (first value) is set to an integration time (third value) obtained by adding / subtracting the time (second value) corresponding to the flicker component intensity or a multiple of an integer multiple. The addition / subtraction time is the minimum level at which flicker detection is possible, and is the time determined by the flicker intensity.
Then, an image signal obtained by multiplying the exposure time by an integral multiple of the flicker cycle and multiplied by the image processing gain in a direction to cancel the luminance fluctuation due to the remaining flicker component is sent to post-processing such as liquid crystal display.
By doing so, flicker components necessary for flicker detection remain in the data output from the imager, and it is possible to continue monitoring the presence or absence of flicker even during flicker countermeasure control.
When the flicker component disappears, the flicker countermeasure control by the program diagram or image processing with many restrictions is stopped.
In other words, the intensity of the flicker component of the data output from the image sensor is controlled by performing the above-described control within the range where the luminance of the subject can reach the target exposure level in the vicinity of the integration time that is a multiple of the flicker cycle. Thus, the flicker detection means can always determine whether or not flicker is detected even during flicker countermeasures, and the flicker component mitigation means can control the flicker component to be able to cope with the intensity.
As a result, when the illumination of the subject is changed from the state with flicker to the state without flicker, the camera detects flicker disappearance and can quickly cancel the flicker countermeasure control that restricts camera control and image quality.
As a result, for example, the live view quality in the live view can be maintained in an optimum state according to the presence or absence of flicker.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[Configuration of Shooting Device]
FIG. 1 is a conceptual diagram showing an example of the configuration of a camera that implements a camera control method according to an embodiment of the present invention.
FIG. 2 is a flowchart showing an example of the operation of the camera that implements the camera control method according to the embodiment of the present invention.
FIG. 3 is a conceptual diagram showing an example of the operation of the camera that implements the camera control method according to the embodiment of the present invention.
As illustrated in FIG. 1, the present embodiment shows an example in which the present invention is applied to a digital single-lens reflex camera as a camera that is a photographing apparatus.

The digital single-lens reflex camera (hereinafter simply referred to as “camera M”) of the present embodiment shown in FIG. 1 includes a body unit 100 and, for example, a replaceable lens unit (that is, a lens barrel) 200.
The body unit 100 can be loaded with a recording medium 131 for recording photographed image data. The recording medium 131 is connected to the body unit 100 via the communication connector 130.
The lens unit 200 is detachable via a lens mount (not shown) provided on the front surface of the body unit 100, and can be exchanged in the camera M.
The lens unit 200 includes a photographic lens 210 a and a photographic lens 210 b, a diaphragm 203, a lens driving mechanism 204, a diaphragm driving mechanism 202, and a lens control microcomputer (hereinafter referred to as “lens control microcomputer”) 201. It is configured.

The taking lens 210a and the taking lens 210b are driven in the optical axis direction by a DC motor (not shown) provided in the lens driving mechanism 204.
The diaphragm 203 is driven by a stepping motor (not shown) provided in the diaphragm drive mechanism 202.
The lens control microcomputer 201 drives and controls each part in the lens unit 200 such as the lens driving mechanism 204 and the aperture driving mechanism 202.
The lens control microcomputer 201 is electrically connected to a body control microcomputer 101 (described later) via a communication connector 160, and can exchange various data with the body control microcomputer 101, and is controlled by the body control microcomputer 101. Is done.
On the other hand, the body unit 100 is configured as follows.

On the optical axis of a light beam from a subject (not shown) that is incident through an optical system such as the photographing lens 210a and the photographing lens 210b in the lens unit 200 and the diaphragm 203, a focal plane shutter unit 120 and the optical system are provided. An image sensor 111 is provided for photoelectrically converting a subject image that has passed through.
The image sensor 111 is controlled in operation such as photoelectric conversion by the image sensor driving IC 110.
That is, the light flux that has passed through the photographing lens 210 a and the photographing lens 210 b is imaged on the imaging surface of the imaging element 111 via the shutter unit 120.
The image sensor 111 photoelectrically converts the subject image formed as described above and converts it into an analog electrical signal.
The electric signal is converted into a digital electric signal to be processed by the image processing IC 102 by the image sensor driving IC 110 and converted into an image signal by the image processing IC 102.

In the body unit 100, the image sensor 111, the image sensor drive IC 110, the semiconductor memory 104 provided as a storage area, the liquid crystal monitor 140, and the recording medium 131 via the communication connector 130 perform image processing. These are configured to be able to provide an electronic recording display function together with an electronic imaging function.
The semiconductor memory 104 is composed of, for example, an SDRAM (Synchronous Dynamic Random Access Memory) or the like.

  The recording medium 131 is an external recording medium such as various semiconductor memory cards or an external hard disk drive (HDD), and is attached to the body unit 100 via the communication connector 130 so as to be exchangeable.

The image processing IC 102 is connected to a body control microcomputer (hereinafter abbreviated as a body control microcomputer) 101 for controlling each part in the body unit 100.
The body control microcomputer 101 includes a control unit that controls the overall operation of the camera M, a timer (not shown) that measures a shooting interval during continuous shooting, a counting unit, a mode setting unit, a detection unit, a determination unit, a calculation unit, and the like. It has the function of
The functions of these body control microcomputers 101 are realized by a control program 103, for example. That is, when the body control microcomputer 101 executes the control program 103, the control function of the body control microcomputer 101 is realized.
In the case of the present embodiment, a flicker-related control function and a live view-related control function exemplified in a flowchart described later are realized by the control program 103.

The body control microcomputer 101 is connected to the communication connector 160 to which the lens unit 200 is connected, the shutter control drive circuit 121, and the like, and further, a liquid crystal for notifying the photographer of the operation state of the camera M by display output. A monitor 140, a camera operation switch 150 (SW), and a power source (not shown) are connected.
The body control microcomputer 101 and the lens control microcomputer 201 are electrically connected to each other via the communication connector 160 by attaching the lens unit 200 to the body unit 100.
The lens control microcomputer 201 operates in cooperation with the body control microcomputer 101 to operate as a digital camera.

The shutter control drive circuit 121 controls the movement of a front curtain and a rear curtain (not shown) in the shutter unit 120, and when a signal for controlling the opening / closing operation of the shutter and the front curtain is completed with the body control microcomputer 101. Send and receive signals.
The liquid crystal monitor 140 visualizes the operating state of the camera M and notifies the user (photographer).

In addition, the liquid crystal monitor 140 can have a touch panel or touch screen function for detecting a position touched by a finger from a change in pressing force or a change in capacitance generated on the surface of the liquid crystal screen as necessary.
In that case, when the user touches the liquid crystal monitor 140 with a finger, the position touched by the user is detected and the detected position is transmitted to the body control microcomputer 101.
Depending on the position detected by the liquid crystal monitor 140, the body control microcomputer 101 can perform control such as changing the shooting mode or displaying a menu, whereby the liquid crystal monitor 140 can be used as an operation means.
FIGS. 1 and 2 illustrate a case in which information is sent from the liquid crystal monitor 140 to the body control microcomputer 101 via the image processing IC 102.

  The camera operation switch 150 is a switch group including operation means such as an operation button necessary for the user to operate the camera M, such as a release switch for instructing execution of a photographing operation, a power switch for switching on / off the power source, and the like. Composed.

The body unit 100 is provided with a power supply circuit (not shown) that converts a voltage of a battery (not shown) provided as a power source into a voltage required by each circuit and unit of the camera M and supplies the converted voltage.
Although not particularly illustrated, the body unit 100 may be provided with a function such as a flash. In that case, a flash control microcomputer and a light emission control circuit (not shown) are connected to the body control microcomputer 101 via a flash communication connector (not shown).

Next, an example of a shooting operation and a live view operation performed by the camera M according to the present embodiment will be described.
[Shooting operation]
First, when the image processing IC 102 is controlled by the body control microcomputer 101 and image data is input to the image processing IC 102 from the imaging element 111 and the imaging element driving IC 110, the image processing IC 102 stores the image data in a temporary storage memory. Is stored in the semiconductor memory 104.
The semiconductor memory 104 is also used as a work area for the image processing IC 102 to perform image processing.
Further, the image processing IC 102 can perform image processing for converting the image data into a desired data format such as JPEG data, and can store the image data in the recording medium 131.

When the shutter control drive circuit 121 receives a signal for controlling the drive of the shutter from the body control microcomputer 101, the shutter control drive circuit 121 controls the shutter unit 120 to open and close the shutter.
At the same time, if a flash is provided, light emission for causing the flash to be emitted from the body control microcomputer 101 to the flash control microcomputer and the light emission control circuit via a flash communication connector (not shown) at a predetermined timing. Output a signal.

At this time, predetermined image processing is performed on the image data output from the image sensor 111 and the image sensor drive IC 110 and recorded in the recording medium 131, whereby the photographing operation is completed.
The light beams from the photographing lens 210 a and the photographing lens 210 b are guided to the image sensor 111.

For example, the exposure is continuously performed at a rate of about 30 sheets per second, and image data output from the image sensor 111 and the image sensor drive IC 110 at this time is converted into a video signal by the image processing IC 102 and is applied to the liquid crystal monitor 140. By providing, the moving image of the subject can be displayed on the liquid crystal monitor 140 in real time.
Such a display is called “live view” and is well known. In addition, in order to perform live view display of image data on the liquid crystal monitor 140 with the camera M of the present embodiment, the user operates the mode change switch in the camera operation switch 150 described above to change the live view mode. Just choose.
In the live view operation, since the light flux from the photographing lens 210a and the photographing lens 210b is always guided to the image sensor 111, photometry processing of the brightness of the subject and known distance measurement processing for the subject are performed. 111 and the image processing IC 102 based on image data output from the image sensor driving IC 110.
Thereafter, in this manner, subject brightness photometry processing and subject distance measurement and automatic adjustment performed by the image processing IC 102 and the body control microcomputer 101 based on the image data output from the image sensor 111 and the image sensor drive IC 110 are performed. The focus (AF) processing is referred to as “live view metering” and “live view AF”, respectively.

Next, an example of an operation related to flicker countermeasures in the camera M of the present embodiment will be described with reference to the flowchart of FIG.
The camera M according to the present embodiment performs the following series of operations illustrated in FIG. 2 when the power SW existing in the camera operation switch 150 is turned on.

(Step S101)
In step S101, the control performed when the power supply of the body unit 100 is switched from OFF to ON is performed.
Generally called initialization processing, activation of a microcomputer or IC provided in the body unit 100, initialization by power supply and communication to the lens unit 200 connected to the body unit 100, etc. I do.

(Step S102)
In step S102, preparation for starting the above-described live view operation is performed. That is, an aperture drive instruction is given to the lens unit 200 via the communication connector 160, a predetermined aperture value is set in advance, an electronic shutter integration time and sensitivity are set to the image sensor drive IC 110, and shutter control drive is performed. The circuit 121 performs control such that the shutter unit 120 is opened and the image sensor 111 receives light.

(Step S103)
In step S103, the above-described live view operation is started.
The image sensor 111 performs an integration operation at the set electronic shutter speed, and an image output result is sent to the image processing IC 102 via the image sensor drive IC 110.
At the time of step S103, the electronic shutter speed need not be a shutter speed that is conscious of the flicker light source as described above. Select an appropriate shutter speed with the highest priority on image quality.
For example, as illustrated in FIG. 3, the image processing IC 102 converts an imaging output of an image 300 a formed on the imaging element 111 into image data 300 b and displays it on the liquid crystal monitor 140. Data for calculating the luminance of the subject is transmitted to the control microcomputer 101.
The data for calculating the luminance of the subject is a numerical value that allows the microcomputer to calculate the luminance of the subject, such as data obtained by dividing the image 300a formed on the image sensor 111 into a plurality of predetermined luminance measurement regions 300 and averaging the data. This is data 301, and this numerical data is sent.

(Step S104)
In step S104, the body control microcomputer 101 performs luminance calculation.
From the numerical data 301 obtained by dividing the image data of the subject into a plurality of luminance measurement areas 300, the luminance corresponding to each divided area is calculated.
The brightness depends on the image sensor 111, the set sensitivity, the aperture value controlled by the lens unit 200, and the electronic shutter speed (the same value as the integration time of the image sensor 111). The irradiation is calculated.

(Step S105)
In step S105, it is determined whether there is flicker from the obtained luminance for each luminance measurement region 300.
Here, an example of flicker detection according to this embodiment will be described.
The frequency of the commercial power supply is 50 Hz or 60 Hz. The flicker frequency of a flicker light source of a basic fluorescent lamp that does not take countermeasures against flicker is twice the power supply frequency due to the principle of the fluorescent lamp. That is, 100 Hz or 120 Hz. When converted into periods, 1/100 [s] = 10 [ms] and 1/120 [s] = 8.33 [ms], respectively.

FIG. 4 is a conceptual diagram showing the effect of flicker in the camera M using the rolling shutter type image sensor 111 and the effect of continuous frame averaging.
In FIG. 4, a graph 401 showing the relationship between the luminance of the flicker component and the elapsed time is drawn at the top.
On the lower side of the graph 401, a scanning line 402 for each integration timing at which the rolling shutter integrates from the top to the bottom of the screen is shown. This is an example in which the upper scanning line 402 of imaging starts integration at a timing synchronized with the vertical synchronization signal VD of imaging, and integration is started with a time difference from the top to the lower scanning line 402 sequentially.

  If the luminance of the subject changes during acquisition of one frame, the imaging output obtained varies depending on the integration timing. When integration is performed at the timing when the luminance of the flicker component is the lowest, the scanning line 402 has a smaller imaging output than the other scanning lines 402, and as a result, like the image of the imaging data 403 illustrated in the lower part of FIG. A dark striped pattern 403a enters in the center.

When the flicker cycle Tf and the frame rate are not synchronized with each other, in the next frame, the scanning line 402 to be integrated at the darkest timing of luminance is different from the previous frame, and imaging data in which the position of dark stripes is changed is obtained.
The average value of the imaging output of the number of frames that is the least common multiple of the flicker cycle Tf and the image acquisition cycle (the cycle represented by the vertical synchronization signal VD in the figure) eliminates the imaging output difference between the upper and lower scanning lines 402, As a result, it is possible to obtain imaging data 404 that is hardly affected by the flicker component.

As described with reference to FIG. 3, the imaging data here can be converted into luminance data for each luminance measurement region 300, and similarly, the luminance data of the scene without flicker components can be obtained by taking the average. Is also possible.
A flicker component is obtained by taking a luminance difference between each luminance measurement region 300 and a luminance obtained by averaging the luminance of each luminance measurement region 300 obtained in one frame and the luminance measurement region 300 for each of the plurality of frames. It is possible to acquire the luminance of only the horizontal stripe-like striped pattern 403a generated in the above.
As a simple determination example, it can be determined to some extent that there is flicker if the difference between the high-intensity part and the low-intensity part of the stripe is 0.5 or more.
From the intensity of the stripe pattern 403a and the state of occurrence of the stripe, it can be determined whether or not shooting is performed under the illumination of the flicker light source.

In the case of such a determination method, in the flowchart of FIG. 2, if only the luminance of less than 3 frames has been acquired after the power is turned on, flicker determination cannot be performed, so it is determined that there is no flicker and the next processing is performed. Do.
During the processing loop from step S104 to step S115, it is possible to determine the presence / absence of flicker by the flicker detection process of step S105 with the luminance of the subject of the past three frames or more being obtained.

(Step S106)
In step S106, the process is divided according to the presence or absence of flicker detection. If the determination made in step S105 is no flicker, the process proceeds to step S107. If the determination made in step S105 is flicker, the process proceeds to step S110.

(Step S107)
In step S107, a performance-priority exposure value is calculated. That is, the aperture, shutter speed, and sensitivity are set according to the luminance.
FIG. 5 is a program diagram showing an example of the operation of the camera that implements the camera control method according to the embodiment of the present invention.
Small fluctuations in brightness are dealt with by adjusting the shutter speed, and the sensitivity is set to a sensitivity where noise is not noticeable, for example.
The aperture is controlled so as not to change.
This control is particularly effective in the configuration of an aperture mechanism that is generally employed in cameras mainly for still image shooting. This control is optimal for an optical configuration in which the depth of field changes greatly when the aperture is changed, or a configuration in which the light amount control by the lens aperture can be performed only in stages. In such a configuration, the moving image quality is better when the movement of the aperture is suppressed as much as possible.
On the other hand, the diaphragm mechanism of a video camera having a diaphragm mechanism specialized for moving images is a configuration that can use a dimming optical member called an ND filter whose depth of field does not change or can control the amount of light in a stepless manner. Even if the amount of light is controlled by the diaphragm, there is little adverse effect. Therefore, it is possible to perform fine fluctuations of the brightness with the diaphragm, and control is generally performed so that the shutter speed and sensitivity are not changed as much as possible.
In any case, however, the light amount control range of the aperture is not infinite, and it is necessary to change the shutter speed and sensitivity depending on the brightness of the subject. Here, the control that the shutter control is set according to the luminance without restriction is shown.

  If the exposure time is less than half of the total time of one frame, the moving subject is not displayed smoothly. For example, when the frame rate is 30 fps, the moving subject is smoothly displayed if the exposure time is about 16 ms, where the total time of one frame is 1/30 s = 33.33 ms. In consideration of this phenomenon, the frame rate is finely set in accordance with the luminance within the entire frame rate to half the frame rate.

FIG. 5 shows a program diagram for determining such exposure.
In the program diagram 601 in FIG. 5, an example is described in which the sensitivity is constant and only the aperture and the shutter speed are driven to simplify the description. In practice, the sensitivity is also controlled to make the aperture and shutter speed more desirable for moving image quality.
In the program diagram 601 shown in FIG. 5, the vertical axis represents an AV value indicating the aperture state (F value in parentheses), and the horizontal axis represents a TV value indicating shutter speed (seconds in parentheses).
The larger the exposure value EV (= AV + TV) is plotted in the upper right direction of the figure.
In this program diagram 601, fine control of the exposure value is performed at the shutter speed so that the area where the aperture is maintained constant at F2.8 as much as possible is increased.
In order to explain that this is “performance-priority exposure calculation”, a program diagram considering conventional flicker is shown in FIG. 6 as a comparison.

FIG. 6 is a program diagram in consideration of conventional flicker.
In the program diagram 602 of FIG. 6, the shutter speed corresponding to 50 Hz flicker is used as a shutter speed that is a multiple of the flicker cycle Tf.
When there is a restriction on the control of the TV value, the AV value is moved to follow the luminance of the subject. However, the AV value always keeps moving, and the aperture value moves greatly in the threshold for changing the shutter speed. become.
Unlike the shutter speed, there is a noticeable phenomenon that the depth of field becomes shallow when the AV value is small in an optical system with a large image circle in a camera with a large image sensor, such as a luminance follow-up delay due to a slow aperture driving speed. When the person in front is in focus, the background is repeatedly blurred or focused according to the subtle brightness of the subject due to the change in the depth of field due to the change in the AV value, and the appearance of the moving image does not settle down.
If the sensitivity (SV) compensates for the change of the AV value, the noise increases or decreases.

(Step S108)
In step S108, exposure control during live view is performed.
That is, the aperture 203 of the lens unit 200 is controlled so as to be the aperture value determined in step S107, and the image sensor 111 is controlled with the shutter speed and sensitivity determined in step S107.

(Step S109)
In step S109, live view display is performed.
That is, the imaging output obtained in step S108 is converted into image data by the image processing IC 102 and displayed on the liquid crystal monitor 140. At the same time, the image processing IC 102 stores numerical data 301 for calculating the luminance of the subject in the body control microcomputer 101. Send.

(Step S110)
In step S110, an exposure value for flicker countermeasures is calculated.
That is, the shutter speed, sensitivity, and aperture calculation processing when flicker is detected is performed. The conventional control uses a shutter speed that is a multiple of the flicker cycle Tf as shown in the program diagram of FIG. 6 described above. In the camera M of the present embodiment, the shutter speed calculation method is the same as the conventional method. Is completely different.
FIG. 7 is a model diagram of a graph in which only the flicker component is extracted in the temporal change in the brightness of the subject. The flicker component changes periodically. Further, the time for integrating the light reaching the image sensor 111 is defined as an integration time Tint. The reciprocal of this Tint is the shutter speed. The time when the integration is started is assumed to be ts.

Here, when the flicker component in the current converted by the photocurrent conversion element in the image sensor 111 is expressed by a function of the following expression (1) whose output changes at time t,
The flicker component charge amount Qflc obtained by integrating the Tint time is expressed by the following equation (2).
When a function obtained by integrating the function f (t) is represented by F (t), the above equation (2) can be represented by the following equation (3).
Here, when the integration time Tint is a multiple of the flicker cycle Tf, the relationship of the following expression (4) is established, and when the integration time Tint is set, the flicker component does not exist from the imaging output as shown in FIG. 8A. .
However, in this embodiment, the shutter speed is not set to completely remove the flicker component.
Then, a flicker component ΔQ expressed by the following equation (5) appears in the moving image.
For example, in the rolling shutter type imaging device 111 that integrates sequentially from the top to the bottom of the screen, it is represented as a striped pattern 403a as shown in FIG. 8B.
In the present embodiment, the stripe pattern 403a is controlled so that the flicker can be detected and the amount on the moving image quality is suppressed.

Since it is computationally expensive to obtain the function f (t) of the flicker component ΔQ, in this embodiment, as an example, from the data calculated in advance and the value calculated from the flicker waveform model, FIG. 9A and FIG. 9B are used. Such a shutter speed table 500 is created and used.
The shutter speed table 500 is set in the semiconductor memory 104, for example, and is accessed from the body control microcomputer 101 (control program 103).
FIG. 9A shows the shutter speed set when it is detected that the light source has 50 Hz flicker.

Conventionally, the shutter speed is set at a multiple 501 (first value) of the flicker cycle Tf shown on the left side of the shutter speed table 500 in FIG. 9A. In this embodiment, the right shift value 502 (third value) is set. ) So that the integration time is shifted short. A program diagram along the shutter speed table 500 is shown in FIG. 9C.
In the program diagram 603 of FIG. 9C, the amount of deviation (corresponding to the shift value 502) decreases as the shutter speed increases. The flicker of the flicker increases as the shutter speed increases even at the same shutter speed shift amount. This is because the impact is significant. The shifting direction is a direction in which the integration time is decreased in the case of the illustrated program diagram 603, but the same effect can be obtained in a direction in which the integration time is increased.
Similarly, a shutter speed table 500 with a light source having a commercial power frequency of 60 Hz is shown in FIG. 9B.
The idea is the same as in the case of 50 Hz in FIG. 9A described above. The basic concept regarding the setting of the shift value 502 of the shutter speed table 500 of this embodiment illustrated in FIGS. 9A and 9B will be described with reference to FIGS. 10A, 10B, and 10C.

FIG. 10A is a diagram showing that the integration value changes at the timing of integration due to a deviation from the integration time that is a multiple of the flicker cycle Tf.
A square time slot 511 below the horizontal axis indicates one cycle of flicker, and two time slots 511 including numbers “1” and “2” indicate two cycles of flicker. . The integrated value is the same regardless of the timing of these two cycles. An integral value 401a corresponding to the time indicated as “remainder” in the remainder time slot 512 (second value) obtained by dividing the integration time by the flicker cycle Tf is a portion indicated by diagonal lines of the graph 401 indicating the luminance fluctuation due to flicker. The hatched area changes depending on the integration timing. This change due to the integration timing appears as an effect of flicker.

  FIG. 10B is a diagram in which the portion of the time slot 512 described above is reduced. If the ratio of the time slot 512 is small with respect to the entire integration time, the fluctuation amount of the integration output due to the integration timing is small, and the flicker fringe becomes inconspicuous.

  FIG. 10C is a diagram illustrating an integration state in a little less time than the two flicker periods Tf. In this case, it is considered that there is a fluctuation corresponding to a decrease in the integral value 401a of the hatched portion compared to the integration for two cycles of flicker, and the hatched portion is considered to be small as in FIG. 10B. Thus, in the shift value 502, it can be considered that the flicker component ΔQ is basically reduced if the ratio of shift from the multiple of the flicker cycle Tf is reduced.

  FIG. 10D is a comparison diagram for integration times of one and two flicker periods. In the integration time of the time slot 511 corresponding to one flicker cycle, the ratio of the hatched integration value 401a to the total integration time is larger than that in the time slot 511 corresponding to two. Therefore, when the same flicker component ΔQ is left in the shift value 502, the shutter speed shift from the multiple of the flicker cycle Tf is set to be smaller as the shutter speed is shorter.

In this way, for example, in the case of an integration time of flicker period 1 time (in the case of one time slot 511), even if it is shifted from the flicker period Tf by ± 5%, for example, the image quality is not noticeable and flicker detection is 4 If it is possible to detect if approximately%, the integration time is shifted to 5%.
For example, if the amount of shift of the integration time is 10% when the integration time is twice the flicker cycle (two time slots 511), and if the flicker detection can be detected by shifting 7%, it is about 8%. A shutter speed table 500 for shifting the shutter speed is created.

In this way, when the exposure control is possible at a shutter speed longer than the flicker cycle Tf, the shutter speed that leaves the flicker component ΔQ necessary for flicker detection is used instead of the shutter speed that completely eliminates the influence of flicker. Can be controlled.
The shutter speed shift amount that is not conspicuous in terms of the moving image quality is a conspicuous shift amount including a flicker countermeasure by image processing, which will be described later in step S110.

(Step S111)
In step S111, exposure control during live view is performed.
In live view exposure control under illumination with flicker, the aperture 203 of the lens unit 200 is controlled so as to be the aperture value determined in step S110, and the image sensor 111 is controlled with the shutter speed and sensitivity determined in step S107. To do.

(Step S112)
In step S112, flicker countermeasure image processing is performed in live view display.
FIG. 11 is a conceptual diagram showing an example of the operation of a camera that implements the camera control method according to an embodiment of the present invention.
That is, in order to convert the imaging output including the flicker component ΔQ into an image in which the influence of the flicker component ΔQ is reduced and display on the liquid crystal monitor 140, the flicker cycle Tf and the image acquisition cycle (represented by the vertical synchronization signal VD) are displayed. The image processing IC 102 generates an image obtained by averaging the imaging outputs of the number of frames that is the least common multiple of the signal cycle).
For example, when live view is performed at a frame rate of 30 fps under an environment where the commercial power supply frequency is 50 Hz, FIG. 11 shows an example of the rolling shutter method, but three frames (three consecutive imaging data 403) are synthesized. Thus, the flicker component ΔQ can be reduced by generating the image (imaging data 404).
In the global shutter type imaging device 111, the same effect can be obtained by periodically synthesizing pictures with different brightness for each frame.
In such a method based on image processing, as shown in FIG. 12, when the flicker component ΔQ is strong, the synthesized image has a flicker component remaining. In addition, a method of applying a gain that is opposite to the light and dark stripes of the flicker component ΔQ is also known. If the flicker component ΔQ is bright, the dark portion is brightened by image processing, and the bright portion is darkened by image processing. If the flicker component ΔQ is strong, the gain is increased, but if the gain is increased, the noise is increased. As a result, an unnatural picture is generated.
Thus, although flicker component countermeasures by image processing are limited, in the present embodiment, the shutter speed calculated in step S110 is left with a flicker component ΔQ that can cope with flicker countermeasures by image processing in step S112. Since the shutter speed is determined, the flicker component ΔQ is appropriately removed from the picture (imaging data 404) that is constantly displayed on the final liquid crystal monitor 140.
However, if the subject is very bright and the shutter speed is not shorter than the flicker cycle Tf in the aperture and sensitivity control range, the flicker component ΔQ cannot be adjusted based on the shutter speed, and the step S112 cannot be adjusted. The flicker component can be erased only with the above measures. Therefore, it is desirable to use a lens that can increase the AV value for the diaphragm and an image sensor 111 that can set a lower sensitivity.

(Step S113)
In step S113, the operation of the release SW is determined.
If the user presses the release SW on the camera operation switch 150, the process proceeds to step S114. If not, the process proceeds to step S115.

(Step S114)
In step S114, the live view operation is temporarily stopped, and the optimum aperture value, electronic shutter speed, and sensitivity for still image shooting are calculated from the luminance value obtained in step S104 described above.
From the calculated value, the above-described “shooting operation” is performed.

(Step S115)
In step S115, the power state of the body unit 100 is determined.
If the power switch SW on the camera operation switch 150 is not turned off, the process returns to step S104 to perform the brightness calculation in order to perform the exposure operation for the next frame.
Unless the power SW is turned off, Steps S104 to S115 are repeated. During the repetition, a live view operation is performed in which successive pictures are displayed on the liquid crystal monitor 140.
If the power SW is turned off, the camera M is turned off.

The above is the operation of the camera and the camera control method of the present embodiment.
As described above, in the case of the present embodiment, the integration time Tint of the image sensor 111 is set like the shift value 502 deviated from an integral multiple of the flicker cycle Tf, and the flicker component ΔQ is intentionally set in the image sensor 111. By controlling so as to leave the flicker detection, flicker detection can be realized in step S105 even if flicker countermeasures are implemented after flicker detection.
For this reason, when the flicker component ΔQ disappears from the subject, it can be reliably determined in step S106 that the flicker has disappeared, and the process proceeds to the processing after step S107 for normal live view display that does not require any flicker countermeasures. Is possible.
Therefore, when there is flicker, the exposure control in steps S110 to S112 is performed, and when there is no flicker, the moving image quality is better, such as the control in steps S107 to S109. This is a control for switching the presence or absence of.

FIG. 13 is a flowchart showing a modified example of the operation of the camera that implements the camera control method according to the embodiment of the present invention.
The above-described step S112 in the countermeasure against flicker is not an essential process. If flicker is detected from the flicker component ΔQ having a high flicker detection capability and hardly causing a problem with the moving image quality of the live view display, As shown in the flowchart of FIG. 13, that is, flicker countermeasures by image processing in steps S111 to S112 may be omitted.
FIG. 14 is a flowchart showing still another modified example of the operation of the camera that implements the camera control method according to the embodiment of the present invention.
FIG. 15 is a conceptual diagram showing still another modified example of the operation of the camera that implements the camera control method according to the embodiment of the present invention.
The embodiments so far illustrated the correspondence when the light source is illuminated only by the flicker light source.
On the other hand, the processing of the flowchart of FIG. 14 is illustrated as an embodiment in which a mixed light source of a flicker light source and a non-flicker light source is considered.
In the flowchart of FIG. 14, steps S105, S106, and S110 in the flowchart of FIG. 2 are changed to steps S105a, S106a, and S110a, respectively.
A subject illuminated by both a light source having flicker and a light source not having flicker has different flicker intensity depending on the contribution ratio of the light source having flicker.
Therefore, in the present modification, in order to perform the minimum necessary flicker countermeasure control in consideration of such a case, the strength of the flicker component ΔQ is obtained from, for example, the brightness difference between the flicker components in step S105a, and this flicker component is obtained. The shutter speed is obtained from the intensity of ΔQ.
Hereinafter, with reference to the flowchart of FIG. 14, a modified portion from the flowchart of FIG. 2 described above will be described.

(Step S105a)
In step S105a, flicker detection is performed in consideration of a mixed light source of a flicker light source and a non-flicker light source.
If only the flicker component ΔQ is extracted by the above-described method, and the luminance fluctuation width of the flicker component ΔQ is 0.2 level or less, the flicker component ΔQ is a low level (level L1), 0.2 level or more and less than 0.5 level. In addition to the presence / absence of flicker, the flicker component ΔQ is also divided into levels such that the flicker component ΔQ is at the medium level (level L2), and the flicker component ΔQ is at the high level (level L3).

(Step S106a)
In step S106a, the level of the flicker component ΔQ is determined.
If the flicker intensity is large (level L3) or medium (level L2) among the large, medium, and small determined in step S105a, the process moves to step S110 and flicker countermeasure processing is performed. If flicker is detected and the intensity is small and the level is not noticeable on the liquid crystal monitor display (level L1), the control similar to the control without flicker is performed.

(Step S110a)
In this step S110a, an exposure calculation for flicker countermeasures when a mixed light source of a flicker light source and a non-flicker light source is considered is performed.
FIG. 15 illustrates a shutter speed table 500 showing an example of the relationship between the flicker intensity and the shift amount in an area where the commercial power supply frequency is 50 Hz.
In accordance with the flicker intensity, the shutter speed is shifted from a multiple (multiple 501) of the flicker cycle Tf to a shift value 502a (level L3) and a shift value 502b (level L2).
In this embodiment, the shutter speed table 500 in which the intensity is classified into the level L3 and the level L2 is illustrated, but the shutter speed table 500 in which the intensity is classified more may be used.
If the flicker intensity is medium (level L2), control is performed so that the flicker component ΔQ remains by exposing the shutter speed to a greater degree than when the flicker intensity is high (level L3), and the next flicker detection is stable. And do it.
In this way, flicker detection can be performed stably at any time without being affected by whether or not flicker illumination and non-flicker illumination are mixed, and flicker countermeasures can be minimized. As a result, it is possible to further minimize degradation of moving image quality in live view display or the like.

As described above, according to the embodiment of the present invention, in the camera M configured to detect flicker from the output of the image sensor 111 during live view, when calculating the shutter speed for live view control after flicker detection, By determining the shutter speed so that the flicker component ΔQ at a level where flicker can be detected remains in the imaging output, exposure control for flicker countermeasures and normal exposure control in real time against changes in the presence or absence of the flicker component of the subject Can be switched accurately.
As a result, the image quality in the live view can be maintained in an optimum state according to the presence or absence of flicker.
Needless to say, the present invention is not limited to the configuration exemplified in the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

(Appendix 1)
An image sensor and means for converting the output of the image sensor into an image;
Composition confirmation means for continuously displaying the image;
Means for acquiring subject brightness from the output of the image sensor;
An exposure control means for controlling the amount of light irradiated to the image sensor and the sensitivity of the image sensor in order to obtain a target image output level from the obtained subject luminance, and the integration time of the photoelectric conversion element in the image sensor;
Means for detecting whether the subject is illuminated by a flicker light source;
In the camera with
When the flicker is detected, the integration time is an integral multiple of 10 ms, or an integral multiple of 8.333 ms, and subject brightness that can be controlled with the integral time obtained by adding or subtracting the time corresponding to the multiple, the integration time obtained by the addition or subtraction is used. A camera characterized by control.
(Appendix 2)
An image sensor and means for converting the output of the image sensor into an image;
Composition confirmation means for continuously displaying the image;
Means for acquiring subject brightness from the output of the image sensor;
An exposure control means for controlling the amount of light irradiated to the image sensor and the sensitivity of the image sensor in order to obtain a target image output level from the obtained subject luminance, and the integration time of the photoelectric conversion element in the image sensor;
Means for detecting whether the subject is illuminated by a flicker light source;
In the camera with
When flicker is detected or when the flicker component is greater than or equal to a predetermined intensity, the integration time is set to an integral multiple of 10 ms, or an integral multiple of 8.333 ms, and the time calculated according to the flicker component intensity A camera characterized in that, with subject brightness that allows exposure control with an addition / subtraction integration time, control is performed with the addition / subtraction integration time.

100 body unit 101 body control microcomputer 102 image processing IC
103 Control Program 104 Semiconductor Memory 110 Image Sensor Drive IC
111 Image sensor 120 Shutter unit 121 Shutter control drive circuit 130 Communication connector 131 Recording medium 140 Liquid crystal monitor 150 Camera operation switch 160 Communication connector 200 Lens unit 201 Lens control microcomputer 202 Aperture drive mechanism 203 Aperture 204 Lens drive mechanism 210a Shooting lens 210b Shooting lens 300 Brightness Measurement Area 301 Numerical Data 401 Graph 401a Integration Value 402 Scan Line 403 Imaging Data 403a Stripe Pattern 404 Imaging Data 500 Shutter Speed Table 501 Multiple 502 Shift Value 502a Shift Value 502b Shift Value 511 Time Slot 512 Time Slot 603 Program Line Figure M Camera

Claims (8)

Imaging means for acquiring image data from an output of an imaging device that converts light into an electrical signal;
Luminance detection means for detecting the luminance of the subject from the output of the image sensor;
Exposure control means for controlling the integration time of the image sensor based on the brightness of the subject obtained by the brightness detection means;
Flicker detection means for detecting a flicker state in which the subject is illuminated by a flicker light source;
In a camera equipped with
When the flicker detection unit detects the flicker state, the exposure control unit adds or subtracts a predetermined second value corresponding to the first value from a first value obtained by multiplying the commercial power cycle by an integer. The camera, wherein the image sensor is controlled using the obtained third value as an integration time. The exposure control unit detects the flicker state when the flicker detection unit detects the flicker state, and the flicker state disappears when the image sensor is controlled using the third value as an integration time. If we detect that
The camera according to claim 1, wherein the control using the third value as an integration time is stopped. Display means for displaying the image data acquired by the imaging means;
When the exposure control unit controls the image sensor using the third value as an integration time, the display unit combines the plurality of pieces of image data acquired continuously by the imaging unit. The camera according to claim 1, wherein the camera is displayed.   The exposure control means includes a shutter speed table in which a relationship between the exposure time and the ratio of the flicker component in the output of the image sensor is set, and refers to the shutter speed table according to the second value. The camera according to claim 1, wherein the third value is determined. In a camera control method for changing the integration time of the image sensor when a flicker state in which a subject is illuminated by a flicker light source is detected from the output of the image sensor,
A first value obtained by adding or subtracting a second value corresponding to the first value from a first value that is an integral multiple of the flicker cycle at which the flicker state completely disappears is set as the integration time of the image sensor. Steps,
A second step of outputting to the display device an image signal that has been subjected to correction processing that cancels luminance fluctuations of the subject due to a flicker component remaining in the output of the image sensor in accordance with the second value;
A method for controlling a camera including: 6. The camera control method according to claim 5, wherein, in the second step, the correction process is suppressed when the flicker component disappears from the output of the image sensor. In the second step, when the image sensor is controlled using the third value as an integration time, an image obtained by synthesizing a plurality of image data continuously acquired from the output of the image sensor as the correction process 6. The method of controlling a camera according to claim 5, wherein data is displayed on the display device.   In the first step, a relationship between the integration time and the ratio of the flicker component in the output of the image sensor is set in a shutter speed table, and the shutter speed table is referred to according to the second value. 6. The camera control method according to claim 5, wherein the third value is determined.