JP2010268156A - Photographing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain change of aperture stops according to the change in brightness of a subject during motion picture recording, without causing degradation in picture quality of a motion picture image. <P>SOLUTION: A photographing apparatus such as a digital single lens reflex camera is equipped with an imaging element that is controlled by an electronic shutter of a rolling method and a lens unit whose aperture stop changes stepwise. A free time ΔT after completion of integration period Te of a last pixel line 111a in each frame of a single frame cycle Tf synchronized with vertical synchronizing signal VD, is assigned with an aperture stop drive time Td for changing an aperture stop value Av. By this, degradation in picture quality of a motion picture image which is caused by fluctuation of the aperture stop value Av during exposure period (integration period Te) is prevented, to obtain appropriate change of stop value Av according to the change in brightness of subject during motion picture recording. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a photographing apparatus.

  For example, in a photographing apparatus such as a digital single-lens reflex camera, a product in which a moving image photographing function is added in addition to an original still image photographing function has appeared for the purpose of improving added value.

  In shooting such a moving image, it is necessary to keep the brightness component of the moving image signal appropriate by controlling the electronic shutter speed, the aperture, and the sensitivity of the image sensor in accordance with the change in luminance of the subject during moving image recording. .

  The electronic shutter and imaging sensitivity control are electrical controls, and can be changed instantaneously at the time of switching to the next screen (frame) in moving images. However, mechanical elements such as multiple aperture blades Since the aperture control with driving takes a relatively long time to change, it is necessary to drive the aperture during acquisition of one frame of the moving image.

In this case, during aperture control, the relationship between subject brightness, aperture value, electronic shutter speed, and sensitivity is lost, and the brightness component of the moving image is disturbed by the aperture operation, so that the image quality of the moving image is degraded.
Therefore, for example, when a captured moving image is displayed, there is a technical problem that the display image flickers and the display quality is deteriorated.

In response to such technical problems, a video camera for recording a moving image generally employs an aperture mechanism optimized for moving images, which can switch the aperture steplessly.
That is, disturbance of the luminance component is prevented by changing the aperture gradually over time and reducing the amount of luminance fluctuation per unit time.

FIG. 1 is a diagram showing aperture control when a stepless aperture is used.
A vertical synchronizing signal for controlling the image sensor is assumed to be VD. The operation of imaging one frame starts at the rise timing of the VD pulse.
The integration period is a time for accumulating the electric current output when the pixels of the image sensor receive light, and is an exposure time for imaging.

FIG. 1 shows a case where the aperture is slowly changed from F5.6 to F4 over several frames.
As shown in the diagram of FIG. 1, if the aperture is gradually changed, feedback control that controls the electronic shutter speed and sensitivity in a direction that cancels the minute change in the next frame by the minute change by the aperture results in stable operation. A moving image of the exposure amount obtained is obtained.

  However, in still image shooting, since it is important to acquire a momentary shooting scene, the aperture is required to move quickly. For this reason, the drive system for the aperture of the taking lens used for a digital single lens reflex optimized for still image shooting is generally step drive in which the aperture area of the stop is changed stepwise.

FIG. 2 is a diagram for explaining a technical problem when such a step-driven aperture is used for moving image recording.
As shown in FIG. 2, when the aperture is changed at the third VD rise from the left, the aperture opening is suddenly changed during the integration of the image sensor, and the luminance component of the image during this integration period becomes unstable. Become.

  When compensating for fluctuations in the luminance component due to aperture drive using the electronic shutter speed or sensitivity, the luminance component of the image differs depending on the ratio of the integration period during the aperture drive period, and the aperture drive speed is Varies with value. For this reason, there is a technical problem that it is difficult to predict fluctuations in luminance components due to aperture driving, and correction control is difficult.

  Furthermore, when using an image sensor, consideration should be given to the difference in the electronic shutter system as shown in FIG.

  That is, as shown in the upper side of FIG. 3, a so-called global shutter type electronic shutter that integrates all pixel lines of the image sensor at the same time has only a problem of the luminance component of the image. However, as shown in the lower side of FIG. 3, the CMOS image sensor employed in recent high-end single-lens reflex cameras is a rolling shutter type electronic device in which successive integration is performed for each pixel line in the vertical direction. It consists of a shutter.

  In such an image pickup element that performs successive integration, if a luminance component change occurs during acquisition of an image of one screen, a pixel line that receives a luminance component change and a pixel line that does not receive the luminance component are generated depending on the integration timing. There is also a technical problem that stripes of luminance components occur.

Due to these technical issues, single-lens reflex cameras for still images generally try to maintain the image quality by not changing the aperture during movie recording, but the brightness of the subject during shooting When the value changes, it is inevitable that the image quality deteriorates.
Note that a technique disclosed in Patent Document 1 is known as a technique for controlling a diaphragm during moving image shooting.

  In Patent Document 1, in a video camera that captures a moving image to be input to a moving image compression apparatus, based on the average photometric value, the iris diameter and the AGC circuit are set so that the Y value representing the luminance value is within a predetermined range. There is disclosed a configuration in which a timer and a trigger circuit for limiting an operation time within one frame are provided in a circuit system for controlling gain.

  And even if the brightness of the subject and the background is constant, the amount of compressed data is prevented from increasing due to an increase in the data difference between frames due to the change in the average luminance according to the change in the proportion of the subject in the screen. Trying to.

  That is, the iris drive control, gain control, and imaging timing are controlled in synchronism, and the imaging device starts the integration operation, and at the same time, activates and operates the iris drive circuit and the AG drive circuit, and after a predetermined time, iris control and gain Stop control.

  Thus, by controlling the iris drive time and gain control within a predetermined time within one frame, the ratio of the aperture drive period A to the integration period B can be controlled as shown in FIG. An attempt is made to reduce the increase in the amount of compressed data due to the influence of driving.

  However, the technique of Patent Document 1 is effective in a global shutter type imaging device, but in the rolling shutter type, the iris opening may vary during exposure of some pixel lines. There remains a technical problem that there is a concern that unevenness of moving images will occur.

JP-A-9-238281

  An object of the present invention is to provide a technique capable of realizing a diaphragm change according to a change in subject luminance during moving image recording without causing a deterioration in image quality of a moving image.

The present invention comprises an imaging means for converting light incident through an imaging lens having a diaphragm means whose aperture amount changes stepwise into an electrical signal;
The imaging sensitivity and electronic shutter speed of the imaging means, the aperture means are controlled, and the exposure time of the imaging means and the aperture drive time for operating the aperture means are exclusive within one frame period during moving image shooting. Control means to be assigned to
An imaging apparatus having the above is provided.

  According to the present invention, it is possible to provide a technique capable of realizing a diaphragm change according to a change in subject luminance during moving image recording without causing a deterioration in image quality of a moving image.

It is a diagram showing aperture control when a stepless aperture is used in moving image recording in a conventional camera for moving image recording. It is a diagram explaining a technical problem in the case of using a conventional step-driven aperture with a step-wise change in moving image recording. It is a conceptual diagram explaining the difference between the global shutter system and the rolling shutter system in the electronic shutter in the image sensor. It is a diagram explaining the technical subject at the time of changing a diaphragm during the exposure period of an image sensor in the prior art. It is a conceptual diagram which shows an example of a structure of the imaging device which implements the control method of the imaging device which is one embodiment of this invention. It is a flowchart which shows an example of an effect | action of the imaging device which implements the control method of the imaging device which is one embodiment of this invention. It is a program diagram which shows an example of an effect | action of the imaging device which implements the control method of the imaging device which is one embodiment of this invention. It is a conceptual diagram which shows an example of an effect | action of the imaging device which implements the control method of the imaging device which is one embodiment of this invention. It is a diagram which shows an example of an effect | action of the imaging device which enforces the control method of the imaging device which is one embodiment of this invention. It is a flowchart which shows an example of the effect | action of the automatic exposure control at the time of the video recording in the imaging device which implements the control method of the imaging device which is one embodiment of this invention. It is a program diagram which shows an example of an effect | action of the imaging device which implements the control method of the imaging device which is one embodiment of this invention. It is a timing chart which shows an example of an effect | action of the imaging device which implements the control method of the imaging device which is one embodiment of this invention. It is a timing chart which shows an example of an effect | action of the imaging device which implements the control method of the imaging device which is one embodiment of this invention. It is a flowchart which shows an example of an effect | action of the imaging device which implements the control method of the imaging device which is one embodiment of this invention.

  In the photographing apparatus of the present embodiment, as one aspect, for example, in a photographing apparatus designed so that the opening degree of the aperture mechanism of the photographing lens is changed stepwise for still image photographing, such as a digital single lens reflex camera. In addition, image quality degradation such as image flickering that occurs during aperture driving in moving image shooting is prevented.

  In other words, in this mode, when shooting a moving image in a photographing apparatus such as an interchangeable lens single-lens reflex camera having a step-by-step aperture driving mechanism optimal for still images in an optical system such as a photographing lens, it is synchronized with imaging control. Then, aperture control is performed.

  Specifically, the timing for driving the aperture and aperture control according to the aperture driving time Td corresponding to the lens characteristics so that the timing is exclusive to the integration period Te that is the imaging integration time (exposure time). Control the number of stages.

  In the program diagram during moving image shooting, when the idle time ΔT, which is the difference between the imaging integration time and the frame period, is equal to or greater than the aperture driving time of 1 STEP, the aperture control is performed with priority given to the shutter speed (Tv) value. Configure.

  In aperture control for changing the aperture to the open side, the idle time ΔT that can cover the aperture driving time Td is secured by temporarily increasing the sensitivity of the image sensor at the aperture change point.

That is, in this aspect, as an example, synchronization is performed so that exposure (imaging) and aperture driving are performed exclusively, and aperture control is performed at the timing of completion of exposure (imaging integration time) within one frame.
In this case, the idle time that covers the aperture driving time is calculated as follows for each of the global shutter method and the rolling shutter method in the image sensor.

That is, in the global shutter system that integrates all pixels of the image sensor at once,
“Aperture driving time Td (vacant time ΔT)” = “one frame period Tf” − “integration period Te”
It becomes.
In the rolling shutter system,
“Aperture driving time Td (vacant time ΔT)” = “1 frame period Tf” − “vertical synchronization time (integration start period difference Tn) × (number of pixel lines in the vertical direction N−1) + integration period Te”
It becomes.
For example, if the lens aperture 1 STEP (1/3 step) is set to 0.75 ms, the number of aperture drive possible steps is calculated by aperture drive time / (1 STEP aperture drive time).

  As a result of each of the above calculation formulas, the program line is set so that the aperture is driven at a position shorter than the shortest shutter time at which the aperture can be controlled, that is, at least brighter than the shortest shutter time at which the aperture can be driven at least 1 Step. Design the diagram.

  When aperture control is performed in a darker position than the shortest shutter speed at which aperture control is possible, the sensitivity of the image sensor is temporarily increased, and the shutter speed is increased (the exposure time is shortened). Program shift is performed to secure the idle time so that the exposure time becomes shorter (shorter exposure time) than the shortest shutter time that can be controlled, and the lens aperture control is performed within this idle time. By returning the program shift at the shutter speed to the original value, exposure is not performed in an unstable exposure state during aperture driving, and it is possible to prevent deterioration of the image quality of a moving image.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[Constitution]
FIG. 5 is a conceptual diagram showing an example of the configuration of an imaging apparatus that implements the imaging apparatus control method according to an embodiment of the present invention.
In FIG. 5, the case of a digital single-lens reflex camera is illustrated as an example of an imaging device.

  As shown in FIG. 5, this digital single-lens reflex camera (hereinafter simply referred to as “camera M (photographing device)”) includes a body unit 100 and, for example, a replaceable lens unit (that is, a lens barrel) 200. And a flash unit 181 and a recording medium 131 for recording photographed image data.

Here, the recording medium 131 is connected to the body unit 100 via the communication connector 130.
The flash unit 181 is connected to the body unit 100 via the flash communication connector 185.

  The flash unit 181 includes a light emission control circuit 182 for driving the light emitter 184 and a light emission control circuit 182 in response to commands from a body control microcomputer 101 (control means) (hereinafter abbreviated as Bμcom) described later. A microcomputer 183 for controlling the flash is provided.

  The lens unit 200 (photographing lens) is detachably attached to the body unit 100 via a lens mount (not shown) provided on the front surface of the body unit 100 and can be exchanged for the camera M. It has become.

  The lens unit 200 includes a plurality of photographing lenses 210a and photographing lenses 210b arranged in the optical axis direction, and an aperture 203 (aperture means) disposed therebetween.

  Further, the lens unit 200 includes a lens driving mechanism 204, a diaphragm driving mechanism 202, and a lens control microcomputer 201 (hereinafter referred to as “Lμcom”).

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 so that the aperture area changes stepwise.

  The Lμcom 201 controls driving of each part in the lens unit 200 such as the lens driving mechanism 204 and the diaphragm driving mechanism 202.

  The Lμcom 201 is electrically connected to a later-described Bμcom 101 provided on the body unit 100 side via a communication connector 160, and can exchange various data with the Bμcom 101, and is controlled by the Bμcom 101.

  In the case of the present embodiment, the Lμcom 201 stores an aperture drive time Td (aperture drive time) that is a time required for the aperture drive mechanism 202 to change the aperture 203 by one step (1 Av_step). It is transmitted to Bμcom 101 in the recognition processing of the lens unit 200 and the like.

  On the other hand, the body unit 100 of the camera M of the present embodiment is configured as follows.

  On the optical axis of the luminous flux from a subject (not shown) that is incident through the photographing lenses 210a and 210b and the diaphragm 203 in the lens unit 200, a subject image that has passed through the focal plane shutter unit 120 and the optical system is photoelectrically converted. An image sensor 111 (imaging means) for conversion is arranged.

The light flux that has passed through the photographing lenses 210 a and 210 b is imaged on the imaging surface of the imaging element 111. The photoelectric conversion operation of the image sensor 111 is controlled by the image sensor drive IC 110.
In other words, in the case of the present embodiment, the image sensor driving IC 110 controls the imaging sensitivity Sv (imaging sensitivity) of the image sensor 111 and the shutter speed Tv (electronic shutter speed) (exposure time) of the electronic shutter.

  Then, the imaging device 111 photoelectrically converts the subject image formed as described above by an imaging optical system such as the lens unit 200 of the camera M and converts it into an analog electric signal. The electric signal output from the image sensor 111 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.

  The body unit 100 is provided with an image processing IC 102 for performing image processing. The image processing IC 102 is recorded via an image sensor 111, an image sensor drive IC 110, an SDRAM (Synchronous Dynamic Random Access Memory) 104 provided as a storage area for image data, a liquid crystal monitor 140, and a communication connector 130. Media 131 is connected.

The image processing IC 102 and its peripheral configuration provide an electronic recording display function together with an electronic imaging function in the camera M of the present embodiment.
In the camera M of the present embodiment, a face detection engine 103 that provides face detection processing from a human image of a subject is connected to the image processing IC 102 as necessary.

  The recording medium 131 is composed of an external recording medium such as various nonvolatile semiconductor memory cards or an external hard disk drive (HDD), and can communicate data with the body unit 100 via the communication connector 130 and can be exchanged. It is attached to.

  The image processing IC 102 is connected to a body control microcomputer 101 for controlling each part in the body unit 100.

  The Bμcom 101 has functions such as a counting unit, a mode setting unit, a detection unit, a determination unit, and a calculation unit in addition to a control unit that controls the overall operation of the camera M. In the case of the present embodiment, the Bμcom 101 has a timer (not shown) that measures a shooting interval (frame period) during continuous shooting or moving image shooting.

In the case of the present embodiment, as an example, each of these units of the Bμcom 101 is realized by the Bμcom 101 executing a control program 101a (control program).
Further, Bμcom 101 stores program diagram data 101b described later and program diagram data 101c used for moving image shooting.

  The control program 101a, program diagram data 101b, and program diagram data 101c are stored in a non-volatile memory such as an electrically rewritable EEPROM provided in the Bμcom 101.

  The Bμcom 101 is connected to the communication connector 160, the shutter drive control circuit 121, and the like, and further, a liquid crystal monitor 140 for notifying the photographer of the operation state of the camera by display output, and a camera operation switch (SW). 150 and a power source (not shown) are connected.

  In the case of the present embodiment, Bμcom 101 and Lμcom 201 are electrically connected to each other through communication connector 160 by attaching lens unit 200 to body unit 100, and Bμcom 101 recognizes lens unit 200.

  The Lμcom 201 operates as a digital camera while subordinately cooperating with the Bμcom 101, thereby realizing functions illustrated in a flowchart described later.

The shutter drive control circuit 121 controls the movement of the front curtain and the rear curtain (not shown) in the shutter unit 120, and controls the opening / closing operation of the shutter unit 120 with the Bμcom 101, and when the travel of the front curtain is completed. Send and receive signals.
The liquid crystal monitor 140 visualizes and presents the operating state of the camera M to the user (photographer) by display output.

  The camera operation switch 150 is, for example, a release switch for instructing execution of a shooting operation, a mode change switch for switching a shooting mode to a continuous shooting mode or a normal shooting mode, a power switch for switching the power on / off, and the like. It is composed of a group of switches including operation buttons necessary for the operation.

  The body unit 100 is provided with a power supply circuit (not shown). The power supply circuit converts a voltage of a battery (not shown) as a power supply into a voltage required for each circuit unit of the camera M and supplies the converted voltage.

Next, an example of the operation of the camera M of the present embodiment will be described.
First, a photographing operation and a live view operation by the camera M will be described.
<Shooting operation>
First, when the image processing IC 102 is controlled by the Bμcom 101 and image data is input from the image sensor 111 and the image sensor driving IC 110 to the image processing IC 102, the image processing IC 102 stores the image data in the SDRAM 104 which is a temporary storage memory. Save to.

  The SDRAM 104 is also used as a work area for image processing by the image processing IC 102. In addition, the image processing IC 102 can perform image processing for converting the image data into JPEG data and store the image data in the recording medium 131.

  When the shutter drive control circuit 121 receives a signal for controlling the drive of the shutter from the Bμcom 101, the shutter drive control circuit 121 controls the shutter unit 120 to open / close the shutter.

  At the same time, at a predetermined timing, the Bμcom 101 outputs a light emission signal for causing the flash to emit to the flash control microcomputer 183 and the light emission control circuit 182 via the flash communication connector 185.

  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 the image data is recorded on the recording medium 131, whereby the still image shooting operation is completed.

  At the time of shooting a still image, the imaging sensitivity of the diaphragm 203, the shutter unit 120, and the image sensor 111 is controlled according to the luminance of the subject by the program diagram data 101b.

<Live view operation and movie shooting>
In the live view operation, the Bμcom 101 always opens the shutter unit 120 and operates the electronic shutter by the image sensor driving IC 110.
The light beams from the photographing lenses 210 a and 210 b are guided to the image sensor 111 and the image sensor drive IC 110.

At this time, for example, exposure is continuously performed at a rate of about 30 images per second by an electronic shutter, and image data output from the image sensor 111 and the image sensor drive IC 110 is converted into a video signal by the image processing IC 102. By giving to the liquid crystal monitor 140, the moving image of the subject can be displayed on the liquid crystal monitor 140 in real time.
At this time, moving image shooting is performed by performing predetermined image processing on the image data output from the image sensor 111 and the image sensor drive IC 110 and recording the image data on the recording medium 131.

  Such a display is known as a “live view”. In order to display the live view display of the 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, and the live view mode is displayed. Should be selected. Hereinafter, the live view may be abbreviated as “LV”.

  Further, during the LV operation, the shutter unit 120 is opened, and the light flux from the photographing lenses 210a and 210b is always guided to the image sensor 111. Therefore, a photometric process for measuring the brightness of the subject or a well-known measurement for the subject. The distance processing can be performed by the image processing IC 102 based on the image data output from the image sensor 111 and the image sensor drive IC 110.

  In the case of the present embodiment, as described above, based on the image data output from the image sensor 111 via the image sensor driving IC 110, the subject brightness metering process and the subject performed by the image processing IC 102 and the Bμcom 101 The distance measurement and automatic focusing processes for are described as “LV metering” and “LVAF”, respectively.

FIG. 6 is a flowchart showing an example of the operation of the imaging apparatus that implements the imaging apparatus control method according to the embodiment of the present invention.
The flowchart in FIG. 6 shows an example of moving image shooting in the LV operation in the camera M of the present embodiment.

<STEP310>
When the power of the body unit 100 is turned on or when the lens unit 200 is connected, if the Bμcom 101 of the body unit 100 recognizes that the lens unit 200 is connected, the process proceeds to STEP 320.

<STEP320>
The Bμcom 101 of the body unit 100 and the Lμcom 201 of the lens unit 200 communicate via the communication connector 160, and a vertical synchronization signal (VD) lens data request command of the image sensor 111 is transmitted from the body unit 100 to the lens unit 200.

  Information such as the aperture control speed, for example, the drive time required to drive the aperture 203 in one step (aperture drive time Td) is transmitted from the lens unit 200 to the body unit 100 (first step).

  A predetermined aperture driving time Td is transmitted from the body unit 100 to the lens unit 200, the lens unit 200 calculates an aperture amount that can be driven with the predetermined aperture driving time Td, and transmits the calculated aperture amount to the body unit 100. May be.

  In the case of such a lens unit 200 that cannot calculate or transmit information indicating the aperture driving speed, the Bμcom 101 of the body unit 100 is set as a larger predetermined value as the aperture driving time Td. Operate.

<STEP330>
Next, the Bμcom 101 starts the above-described live view operation. The appropriate exposure amount is maintained by controlling the diaphragm 203, the shutter speed of the electronic shutter of the image sensor 111, and the imaging sensitivity in accordance with the luminance change of the subject.

<STEP340>
Bμcom 101 determines whether the release switch button of the camera operation switch (SW) 150 is turned on. If it is ON, the process proceeds to STEP350.

<STEP350>
The Bμcom 101 starts an operation of processing the moving image obtained by the live view operation by the image processing IC 102 and recording it on the recording medium 131.

<STEP 360>
Then, during recording of this moving image, the Bμcom 101 automatically controls the imaging sensitivity at the time of the aperture of the diaphragm 203 and the electronic shutter according to the brightness of the subject by the process illustrated in the flowchart of FIG. 10 described later. Take control.

<STEP370>
Bμcom 101 checks the state of the release button after executing the automatic exposure operation. After starting the recording, the automatic exposure control operation is repeated until the release button is pressed again to continue recording the moving image.
When the release button is pressed, the process proceeds to STEP 380.

<STEP380>
The Bμcom 101 stops recording on the recording medium 131 in order to end the moving image recording, and displays that the moving image recording is stopped on the liquid crystal monitor 140.

  In the flowchart of FIG. 6 of the present embodiment, the operation of the camera M is ended after the completion of STEP 380 for the sake of simplification. However, after the recording is stopped, the process returns to the start of the live view operation of STEP 330. You may make it be in the standby state where the release button of STEP340 is on.

Next, the automatic exposure control during moving image shooting in the above-described STEP 360 in the camera M of the present embodiment will be described in more detail.
FIG. 7 is a program diagram showing an example of the operation of the imaging apparatus that implements the imaging apparatus control method according to the embodiment of the present invention.

  In the automatic exposure control by the Bμcom 101 during the live view operation, the aperture sensitivity of the aperture 203 corresponding to the subject brightness, the shutter speed of the image sensor 111, and the imaging sensitivity are obtained based on the program diagram illustrated in FIG.

  In the case of the present embodiment, the program diagram of FIG. 7 is implemented as the above-described program diagram data 101b of Bμcom 101.

  Av, Tv, Sv, and Bv in the program diagram of FIG. 7 are numerical values used in an APEX (Additive System of Photographic Exposure) calculation, and sequentially indicate an aperture value, shutter speed, imaging sensitivity, and subject luminance. .

The smaller the Av value, the larger the aperture area of the diaphragm 203, and more light enters the image sensor 111. The smaller the Tv value, the longer the exposure time and the greater the amount of light to the image sensor 111.
The exposure period in the image sensor 111 is a period in which charges generated by receiving light by a pixel are accumulated in a capacitive component existing for each pixel, and this exposure period is called an integration period.

The smaller the Sv value, the lower the imaging sensitivity Sv of the image sensor 111, and a greater amount of light is required to achieve an appropriate level. The smaller the Bv value, the darker the subject and the smaller the amount of light incident on the image sensor 111. When the relationship Av + Tv = Sv + Bv is established, the appropriate exposure amount is obtained.

  The program diagram is composed of two two-dimensional graphs as shown in FIG. 7, and the upper graph is a Bv-Sv graph showing the relationship between Bv indicating subject brightness and Sv indicating imaging sensitivity. The graph is a Tv-Av graph showing the relationship between the Av value representing the aperture amount of the lens and the Tv value representing the shutter speed.

The diagonal dotted lines straddling the upper and lower graphs indicate the same exposure value Ev value (= Av + Tv = Bv + Sv), and those on the dotted line have the same value of Av + Tv or Sv + Bv.
Description will be made with respect to points a, b, c, and d indicated by circles in FIG.

When the position of the subject brightness Bv and the imaging sensitivity Sv is the point b, the Av value and the Tv value are at appropriate levels at both the points c and d.
The same is true when the point b is replaced with the point a on the same broken line in the graph above.

  When controlling the exposure control of the camera M of the present embodiment on the thick black line (Bv vs. Sv control line L1 in the upper graph and Tv vs. Av control line L2 in the lower graph) of the program diagram of FIG. In the Bv vs. Sv control line L1, when the subject brightness is Bv = 5, it is the point b and the imaging sensitivity is indicated as 5 by the Sv value.

  As an example, in the photographing lens 210a and the photographing lens 210b used in the present embodiment, the open state is Av value = 2. In addition, the minimum value of the imaging sensitivity Sv of the image sensor 111 is 5.

  In the program diagram of FIG. 7, when the subject brightness Bv = 4 changes from Bv = 3 to the lower brightness side, the aperture 203 is controlled to be darker, that is, the control is performed to reduce the value of Av, and it is darker than Bv = 3. The Bv vs. Sv control line L1 and the Tv vs. Av control line L2 that increase the sensitivity while maintaining Av = 2 in the fully open state, that is, increase the value of the imaging sensitivity Sv are illustrated.

  Further, at high luminance, the image pickup signal is controlled not to be saturated by reducing the stop 203 (Av value is increased), and the image pickup sensitivity Sv is lowered to the lowest sensitivity, that is, the line diagram is Sv = 5.

  According to the diagrams of the Bv vs. Sv control line L1 and Tv vs. Av control line L2, the exposure value is appropriate by controlling the aperture value Av (aperture amount), shutter speed Tv, and imaging sensitivity Sv according to the subject brightness Bv. Image data can be acquired.

However, when the timing of aperture control is not taken into consideration as in the prior art, as described above, there is a technical problem that the brightness component of the image becomes unstable while moving the aperture 203 and the moving image quality deteriorates.
For example, when the subject brightness changes from Bv = 3 to Bv = 4, the aperture changes from Av = 2 to Av = 2.5, and an image change occurs.

  Therefore, in the present embodiment, the control program 101a of the Bμcom 101 executes the aperture control by assigning the aperture driving time Td to the idle time ΔT that is the non-exposure time in one frame, as illustrated in FIG. 8 below. Control to prevent deterioration of the image quality of the moving image.

  FIG. 8 is a conceptual diagram showing an example of the operation of the imaging apparatus that implements the imaging apparatus control method according to the embodiment of the present invention.

  FIG. 8 shows a plurality of (N in this case) vertical pixel lines 111a constituting the image sensor 111 when the image sensor 111 using a rolling shutter system is used as an electronic shutter in this embodiment. The example of the shift | offset | difference of integration (exposure) period (Te) of is shown.

  The rolling shutter type imaging device 111 is easily used for high-end single-lens reflex cameras, and the image is likely to be disturbed by the influence of the aperture control during moving image recording when the timing of the aperture control is not considered as in the past. It is an image pickup device.

  In the rolling shutter type image pickup device 111, the integration (exposure) timing of the plurality of pixel lines 111a differs depending on the position of the pixel line 111a in the vertical direction. For example, as shown in FIG. The integration (exposure) is sequentially performed from top to bottom depending on the scanning line (pixel line 111a).

  Depending on the conditions such as the subject brightness and the sensitivity of the image sensor 111, even if the uppermost pixel line 111a completes integration (exposure), the lower pixel line 111a is still in a state before integration (exposure) starts.

  In the example shown in FIG. 8, in the case of N scanning lines and an exposure timing difference Ts between adjacent scanning lines, the integration start period difference Tn = Ts × (N−1) = 7 ms, and the integration start period is up and down. If the exposure time corresponding to the shutter speed Tv is 8 ms according to the program diagram, that is, the integration period Te (exposure time) is 8 ms, the total pixel integration time Tt required for integration of all the imaging pixels In the example shown, (= Tn + Te) takes 15 ms.

When the frame rate is 60 fps, the period of VD (vertical synchronization signal) (one frame period Tf) is about 16 ms.
In such a case, the idle time ΔT (= Tf−Tt) excluding the total pixel integration time Tt within one cycle of VD exists for 1 ms.

When the integration period Te is shorter than 8 ms, the idle time ΔT becomes longer in the frame start direction accordingly.
In the present embodiment, this idle time ΔT is used as the aperture driving time Td necessary for controlling the aperture 203 of the lens unit 200.

FIG. 9 is a diagram showing an example of the operation of the imaging apparatus that implements the imaging apparatus control method according to the embodiment of the present invention.
FIG. 9 shows an operation example in which the control program 101a of the Bμcom 101 of the present embodiment performs aperture control in synchronization with the imaging control of the rolling shutter type imaging device 111.

  Here, it is assumed that it is necessary for the diaphragm 203 to operate in one step in less than 1 ms (that is, the diaphragm driving time Td≈1 ms). Then, the diaphragm is operated by one step in the period of the idle time ΔT of 1 ms after the completion of the total pixel integration time Tt within the VD1 cycle.

  When the electronic shutter speed is a shutter speed shorter than the exposure period of 8 ms (Tv value is 7), the aperture operation timing (aperture driving time Td) and the integration timing (integration) within one frame period Tf are thus obtained. It is possible to arrange the period Te) exclusively.

  By the way, it is necessary for the camera M to control the shutter speed of the electronic shutter in a long time slower than Tv = 7 in accordance with conditions such as the subject brightness Bv.

  Regardless of this situation, if the shutter speed of the electronic shutter of the image sensor 111 is increased unnecessarily, it is likely to be affected by flickering of the fluorescent lamp, and integration between the imaging frames is performed. Since there is an increase in the number of periods, there is a technical problem that the image is not a continuous moving image but a frame-like image and the quality of the moving image is lowered.

Therefore, in the present embodiment, the above-described technical problem is avoided and the image quality of the moving image is improved by the control according to the flowchart of FIG. 10 and the program diagram of FIG.
FIG. 10 is a flowchart showing an example of the operation of the imaging apparatus that implements the imaging apparatus control method according to the embodiment of the present invention.

FIG. 11 is a program diagram showing an example of the operation of the imaging apparatus that implements the imaging apparatus control method according to the embodiment of the present invention.
FIG. 10 shows an example of detailed operation of the automatic exposure control in STEP 360 of FIG. 6 described above by the control program 101a of Bμcom 101.

<STEP410>
Bμcom 101 acquires the value of the subject brightness Bv.

<STEP420>
The Bμcom 101 refers to the program diagram of FIG. 7 according to the acquired Bv value, and determines whether or not the aperture opening needs to be changed from the current state of the aperture 203 controlled by the previous automatic exposure control. .
And when it is necessary to change, it progresses to STEP430. On the other hand, if it is not necessary to change the aperture, the processing of this flowchart is terminated.

<STEP430>
Bμcom 101 determines whether or not there is a free time ΔT shown in FIG. 8. If there is a free time ΔT, the process proceeds to STEP 450.
On the other hand, if the idle time ΔT is insufficient, the process proceeds to STEP 440.
The determination as to whether or not there is a free time ΔT is performed as follows.

Based on the aperture specification information of the photographing lenses 210a and 210b obtained in STEP 320 in the flowchart of FIG. 6, the time required for the operation of the aperture 203 for one step (aperture driving time Td) is referred to.
If the idle time ΔT is larger than the time required for the operation of one step of the diaphragm 203, it is determined that there is an idle time ΔT.

  If the idle time ΔT is equal to or shorter than the aperture driving time Td required for the operation of the diaphragm 203 for one step, it is determined that there is no idle time ΔT.

<STEP440>
When it is determined in STEP 430 that the free time ΔT is insufficient, the Bμcom 101 performs a process of generating the free time ΔT by shortening the integration period Te while securing an appropriate exposure state as follows.

  By referring to STEP 320 in FIG. 6, the diaphragm drive time Td necessary for the operation of one step of the diaphragm 203 obtained from the lens unit 200 is referred to, and a time longer than the diaphragm drive time Td necessary for this one-step operation is described above. The free time ΔT shown in FIG.

Here, as an example, it is assumed that the aperture driving time Td for one step of the aperture 203 is less than 1 ms.
Further, in the example of FIG. 8, if the integration period Te is 8 ms or less, there is a free time ΔT of 1 ms.

  Here, a Tv value where the integration period Te is 8 ms is Tv = 7. When the Tv value is less than Tv7, the aperture driving time Td can be assigned within the range of the idle time ΔT by shifting to Tv = 7 on the program diagram of FIG.

  In order to maintain proper exposure, Av + Tv = Bv + Sv may be established. That is, assuming that Tv change amount is ΔTv and Sv change amount is ΔSv, the exposure amount can be changed to Tv7 or more with the exposure amount kept in an appropriate state as long as ΔTv = ΔSv.

  Such a shift operation is shown in the program diagram of FIG. In the case of the present embodiment, the program diagram of FIG. 11 is realized by the program diagram data 101c mounted on the Bμcom 101 as described above.

In FIG. 11, thick broken lines are the Bv vs. Sv control line L1 and Tv vs. Av control line L2 of FIG. 7, and a thick solid line is the Bv vs. Sv control line L1a and Tv vs. Av control used for the shift operation in STEP 440. This is a line L2a.
As an example, a description will be given using points e and g illustrated in FIG.

  For example, if the current state of the diaphragm 203 is set to point g, point g is Tv6 and integration period Te is 16 ms. Accordingly, the total pixel integration time Tt of all pixels for one screen is 7 + 16 = 23 ms, and the free time ΔT is 16-23 = −7 ms <1 ms, and it is determined that there is no free time ΔT.

  When it is determined that there is no free time ΔT, in order to generate the free time ΔT, Bμcom 101, for example, changes from Tv6 (point g) on the Tv vs. Av control line L2 to Tv7 (point on the Tv vs Av control line L2a). Change to h).

At the same time, Bμcom 101 shifts the point e on the Bv vs. Sv control line L1 corresponding to the point g on the Sv-Bv graph to the point f on the Bv vs. Sv control line L1a by the amount of Tv change.
With the above control, the integration period Te is the same as that in FIG. 8, and a free time ΔT = 1 ms of a length that can be assigned with the aperture driving time Td is generated.

<STEP450>
Next, Bμcom 101 calculates an aperture change amount. A difference ΔAv between the current aperture value and the subject luminance Bv value obtained in STEP 410 is obtained from the aperture value obtained from the program diagram of FIG.

<STEP460>
The Bμcom 101 calculates how many periods are distributed by the VD from the calculated ΔAv to change the aperture. In the present embodiment, one stop (Av_step) is changed for 1 VD (one frame). Therefore, the frame number Nf to be obtained is obtained by Nf = ΔAv / Av_step.

<STEP470>
The Bμcom 101 instructs the Lμcom 201 of the lens unit 200 to change the aperture 203 by one step by allocating the aperture driving time Td within the period of free time ΔT exclusive to the integration period Te in one frame period Tf (second). Step).
At the same time, the Bμcom 101 instructs the image sensor drive IC 110 of the image sensor 111 to change the Sv value or the Tv value by the same amount as Av_step every 1 VD (one frame).

FIG. 12 is a timing chart showing an example of the operation of the imaging apparatus that implements the imaging apparatus control method according to the embodiment of the present invention.
The timing chart of FIG. 12 illustrates the relationship between the aperture value Av and imaging sensitivity Sv and the timing of one frame period of VD when the aperture 203 is changed in the direction of increasing the aperture value (increasing the aperture value Av). Yes.

  When Av_step = 0.33 and the aperture is changed by 0.66 steps, Av is reduced by 0.33 steps for each VD (frame), and imaging sensitivity Sv is increased by 0.33 steps.

  Assuming that the imaging sensitivity Sv value to be changed in one frame is Sv_step, as long as Av_step = Sv_step, the relationship Av + Tv = Sv + Bv is maintained, and appropriate exposure can be maintained.

This is because, when the stop 203 is stopped, if it is attempted to maintain the appropriateness not by the imaging sensitivity Sv but by the Tv value, the integration period in FIG. 8 is extended from 8 ms, and there is no free time ΔT that can be driven by the stop.
FIG. 13 is a timing chart illustrating an example of the operation of the imaging apparatus that implements the imaging apparatus control method according to the embodiment of the present invention.

On the other hand, as shown in FIG. 13, when the stop 203 is in the opening direction, control is performed to increase the Tv value every frame (VD).
If the amount of Tv to be changed by 1 VD is ΔTv_step,
Av_step = Tv_step
As long as it is, proper exposure is maintained.

  When the diaphragm 203 is opened, the Tv value becomes shorter, so that the diaphragm driving time Td is allocated, and the idle time ΔT shown in FIG.

If the Sv value is used for control, the imaging sensitivity is lowered, and in the subsequent processing, the processing for returning the shift amount of STEP 440 causes the sensitivity to be lowered too much in STEP 470, so that the sensitivity cannot be lowered any further. I am trying not to.
In this way, it is possible to change the aperture value Av while maintaining proper exposure.

  An example of the operation of STEP 470 will be described in more detail with reference to the flowchart of FIG.

<STEP501>
First, the Bμcom 101 initializes a variable n for managing the number of frames for distributing the aperture driving time Td to 0.

<STEP502>
Next, the Bμcom 101 determines whether or not to change the aperture 203 in the direction of reducing the aperture 203 (that is, increasing the aperture value Av).
In the direction of narrowing, the process branches from STEP 503 onward, and in the direction of opening, the process branches from STEP 507 onward.

<STEP503>
In the narrowing direction, the Bμcom 101 waits for the start timing of the free time ΔT in the frame.

<STEP504>
Then, when the start timing of the idle time ΔT arrives, the Bμcom 101 increases the aperture value Av by 1 Av_step and the imaging sensitivity Sv by 1 Sv_step during the aperture drive time Td.

<STEP505>
Thereafter, the Bμcom 101 increments the variable n on the assumption that the control of the aperture 203 of the current frame is completed.

<STEP506>
Next, Bμcom 101 determines whether n has reached the number of frames Nf calculated in STEP 460 described above, and repeats the processing in STEP 503 and subsequent steps until it reaches Nf.

<STEP507>
On the other hand, when changing the aperture 203 to open (decrease the aperture value Av), the Bμcom 101 first waits for the start timing of the idle time ΔT in the current frame, as in STEP 503.

<STEP508>
In this case, when the start timing of the idle time ΔT comes, the Bμcom 101 reduces Av by 1 Av_step and increases the shutter speed Tv by 1Tv_step during the aperture driving time Td (that is, shortens the integration period Te). )

<STEP509>
Next, Bμcom 101 increments n in the same manner as in STEP 505 described above.

<STEP510>
Further, Bμcom 101 determines whether n has reached the number of frames Nf as in the above-described STEP 506, and repeats the processing from STEP 507 onward until Nf is reached.
Thereby, the aperture driving time Td can be allocated and assigned to the free time ΔT of one or a plurality of frames.

Returning to the description of the flowchart of FIG.
<STEP480>
When the aperture change of ΔAv calculated in STEP 450 is completed, the Bμcom 101 restores the Sv-Tv shift performed in STEP 440.
That is, the amount of ΔSv and ΔTv added in STEP 440 is subtracted in STEP 480.

  Thus, the automatic exposure control by the Bμcom 101 is finished, and the process proceeds to the above STEP 370 in FIG.

  This series of processing is performed by the control program 101a of the Bμcom 101, so that the technical problem of image quality degradation of the moving image caused by the overlap of the exposure of the rolling shutter type image sensor 111 described in FIG. Can be solved.

  In the present embodiment, an example in which the diaphragm 203 is operated by one step per VD (every frame) has been disclosed. However, when the operating speed of the diaphragm 203 is high or when the idle time ΔT illustrated in FIG. The control may be performed so that a plurality of aperture changing steps (aperture driving time Td) are allocated to the free time ΔT in one frame.

  Even in the case of the lens unit 200 in which the diaphragm 203 is not step-driven, the automatic exposure control of the present embodiment can be similarly applied by replacing the shortest diaphragm driving time with the one-step diaphragm driving time Td described so far.

  According to the camera M of the present embodiment, during still image shooting, high-speed aperture operation is performed by stepwise driving of the aperture 203, and during moving image recording, degradation of image quality of moving images due to aperture change is surely prevented. It becomes possible.

That is, in the camera M according to the present embodiment, it is possible to change the aperture according to the change in the subject brightness during moving image recording without causing deterioration of the image quality of the moving image.
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.

For example, the lens unit 200 can also be applied to a camera configured to be integrally fixed to the body unit 100.
Further, the present invention can also be applied to a camera in which the image sensor 111 includes a global electronic shutter.

DESCRIPTION OF SYMBOLS 100 Body unit 101 Microcomputer 101a for body control Control program 101b Program diagram data 101c Program diagram data 102 Image processing IC
103 face detection engine 104 SDRAM
110 Image sensor drive IC
111 Image sensor 111a Pixel line 120 Shutter unit 121 Shutter drive control circuit 130 Communication connector 131 Recording medium 140 Liquid crystal monitor 150 Camera operation switch (SW)
160 Communication Connector 181 Flash Unit 182 Light Emission Control Circuit 183 Flash Control Microcomputer 184 Light Emitter 185 Flash Communication Connector 200 Lens Unit 201 Lens Control Microcomputer 202 Diaphragm Drive Mechanism 203 Diaphragm 204 Lens Drive Mechanism 210a Shooting Lens 210b Shooting Lens Td Aperture driving time Te Integration period Tf 1 frame period Tn Integration start period difference Ts Exposure timing difference Tt Total pixel integration time ΔT Free time Av Aperture value Bv Subject brightness Sv Imaging sensitivity Tv Shutter speed Ev Exposure amount L1 Bv vs. Sv control line L1a Bv Sv control line L2 Tv vs Av control line L2a Tv vs Av control line M Camera

Claims (5)

Imaging means for converting light incident through an imaging lens having an aperture means whose aperture amount changes stepwise into an electrical signal;
The imaging sensitivity and electronic shutter speed of the imaging means, the aperture means are controlled, and the exposure time of the imaging means and the aperture drive time for operating the aperture means are exclusive within one frame period during moving image shooting. Control means to be assigned to
An imaging apparatus comprising: The imaging device according to claim 1,
The control means assigns the aperture driving time to an idle time that is a difference between the one frame period and the exposure time,
The imaging sensitivity and the electronic shutter speed of the imaging means are set such that the idle time is a length that can be assigned the diaphragm driving time necessary to change the opening amount of at least one stage of the diaphragm means. An imaging apparatus, wherein the exposure time is changed by controlling at least one of them. The imaging device according to claim 2,
When the control means controls at least one of the imaging sensitivity and the electronic shutter speed of the imaging means so that the idle time is a length that can be assigned the diaphragm driving time, the opening amount of the diaphragm means When controlling in the direction of reducing the aperture, control is performed to increase the imaging sensitivity, and when controlling in the direction of opening the aperture of the aperture means, control is performed to increase the electronic shutter speed. apparatus. In the imaging device according to any one of claims 1 to 3,
The imaging device is configured by a plurality of pixel columns having different start timings of the exposure time within the one frame period. In the imaging device according to any one of claims 1 to 4,
A photographing apparatus comprising a lens mount to which the photographing lens is replaceably mounted.