JP6700747B2 - Imaging device, control method thereof, and control program - Google Patents

Description

  The present invention relates to an imaging device such as a digital camera, a control method therefor, and a control program, and more particularly, to dimming control of a light emitting device in an imaging device including the light emitting device.

  2. Description of the Related Art In general, there is an image pickup apparatus including a light emitting device such as a strobe device, which uses a light measurement result of preliminary light emission of the light emitting device and a light measurement result of only ambient light to determine a main light emission amount at the time of shooting.

  For example, there is an imaging device that measures the reflected light of the light emitted by the preliminary light emission reflected from the subject, and further measures only the ambient light immediately before or after the preliminary light emission (see Patent Document 1). In this imaging device, reflected light and ambient light are obtained in the photometry by preliminary light emission, and the reflected light component is extracted by subtracting the photometric output obtained by only the ambient light from the photometric output to extract the reflected light component. The main light emission amount is determined according to the component.

JP, 2013-44997, A

  By the way, when the light amount of the ambient light changes with time, the light amount of the ambient light may be different between the charge accumulation timing at the time of preliminary light emission and the charge accumulation timing of only the ambient light. In this case, in Patent Document 1, the reflected light component cannot be accurately extracted, and it is difficult to accurately determine the main light emission amount. As a result, the amount of main light emission may vary from one shooting to another.

  An example in which the amount of ambient light changes with time is a flicker phenomenon caused by an artificial light source such as a fluorescent lamp. Fluorescent lamps, which are widely used as indoor light sources, have an illumination light amount that periodically fluctuates due to the influence of periodic voltage changes of a commercial power source.

  Therefore, an object of the present invention is to provide an image pickup apparatus, a control method therefor, and a control program capable of reducing the variation in the main light emission amount due to the change in ambient light.

In order to achieve the above object, an image pickup apparatus according to the present invention is an image pickup apparatus that obtains a main light emission amount that is a light emission amount at the time of shooting according to a light amount of reflected light obtained by preliminary light emission of a light emitting unit. , A charge accumulation time and a gain for the first pixel group and the second pixel group that receive the reflected light are different from those for the first pixel group and the second pixel group, and the exposure timing is controlled. And a control unit that determines the main light emission amount based on the outputs of the first pixel group and the second pixel group, the control unit having a charge storage time for the first pixel group. The charge accumulation time for the second pixel group is controlled to be a predetermined magnification, and the gain for the second pixel group is controlled to be the predetermined magnification for the first pixel group. The control is performed so that the timing of preliminary light emission of the light emitting means and the timing of exposure of the first pixel group and the second pixel group overlap .

A control method according to the present invention includes a first pixel group and a second pixel group that receive reflected light obtained by preliminarily emitting light from a light emitting unit, and the light emission amount at the time of shooting according to the light amount of the reflected light. In the method of controlling the image pickup apparatus for determining the main light emission amount, the charge accumulation time for the first pixel group is controlled to be a predetermined multiple of the charge accumulation time for the second pixel group, and Controlling the gain for the second pixel group to be the predetermined magnification of the gain for the first pixel group, the timing of preliminary light emission of the light emitting means, the first pixel group and the second pixel group. and having the steps of controlling such timing overlaps the exposure, and a Luz step to determine the main emission amount on the basis of an output of the first pixel group and the second pixel group .

A control program according to the present invention includes a first pixel group and a second pixel group that receive reflected light obtained by preliminarily emitting light from a light emitting unit, and the light emission amount at the time of photographing according to the light amount of the reflected light. Is a control program used in an image pickup apparatus for obtaining the main light emission amount, wherein a charge accumulation time for the first pixel group is set to a predetermined magnification of a charge accumulation time for the second pixel group in a computer included in the image pickup apparatus. Control so that the gain for the second pixel group is equal to the predetermined magnification of the gain for the first pixel group, the timing of preliminary light emission of the light emitting unit, and the first Luz be determined and controlling so that the timing of the exposure of the pixel group and the second pixel group overlap, the main light emission amount based on an output of the first pixel group and the second pixel group It is characterized by executing steps and.

  According to the present invention, it is possible to reduce a variation in the main light emission amount due to a change in ambient light even in a shooting environment in which ambient light changes with time.

FIG. 6 is a diagram for explaining a variation in main light emission amount due to a temporal change in the amount of ambient light. It is a figure showing the composition about an example of an imaging device by an embodiment of the invention. 3 is a flowchart for explaining a process when the camera shown in FIG. 2 shoots a flash light. FIG. 4 is a diagram for explaining driving of a photometric sensor in the light control operation shown in FIG. 3. FIG. 3 is a diagram showing an example of an array of pixel groups in an image sensor included in the photometric sensor shown in FIG. 1.

  Hereinafter, an example of the imaging device according to the embodiment of the present invention will be described with reference to the drawings.

  First, before describing the image pickup apparatus according to the embodiment of the present invention, the variation of the main light emission amount due to the temporal change of the light amount of the ambient light will be outlined.

  FIG. 1 is a diagram for explaining a variation in the main light emission amount due to a temporal change in the light amount of ambient light.

  Now, as shown in FIG. 1, it is assumed that the amount of ambient light changes in a predetermined cycle due to a flicker phenomenon or the like. At this time, in order to calculate the main light emission amount at the time of shooting, charge accumulation is performed only by ambient light and charge accumulation is performed by reflected light (including ambient light) by preliminary light emission, and only the reflected light component is extracted.

  First, the image sensor is driven (sensor drive), electric charges are stored only by ambient light (environmental light storage), and the charges are read (first read result). At this time, the amount of ambient light is almost at a peak. After that, the light emitting device (strobe) is caused to preliminarily emit light, charge is accumulated (preliminary light emission accumulation) by reflected light (including ambient light), and the charge is read (second reading result). At this time, the amount of ambient light is less than half the peak.

  As a result, even if an attempt is made to obtain the reflected light component by subtracting the first read result from the second read result, the amount of ambient light is large in the first read result, so the influence of ambient light remains. , The reflected light component cannot be obtained accurately. Further, if the timing of the ambient light accumulation and the timing of the preliminary emission accumulation are different, the influence of the ambient light is also different, and the reflected light component obtained by the extraction is different each time the main emission amount is obtained. For this reason, the main light emission amount varies for each shooting.

  Therefore, in the image pickup apparatus according to the embodiment of the present invention, variations in the main light emission amount due to such changes in ambient light are reduced as described below.

  FIG. 2 is a diagram showing the configuration of an example of the image pickup apparatus according to the embodiment of the present invention.

  The illustrated image pickup apparatus is, for example, a digital single-lens reflex camera (hereinafter simply referred to as a camera), and includes a camera body (image pickup apparatus body) 100 and a photographing lens unit (hereinafter simply referred to as a photographing lens) 200. The camera body 100 and the taking lens 200 are mechanically and electrically connected to each other.

  The camera body 100 is provided with a microcomputer (CPU: hereinafter referred to as a camera microcomputer) 101, and the camera microcomputer 101 controls the entire camera. A memory 102 such as a RAM and a ROM is connected to the camera microcomputer 101, and the memory 102 stores a control program and is used as a work area of the camera microcomputer 101.

  An image pickup device 103 such as a CCD or CMOS image sensor is arranged on the optical axis of the taking lens 200, and the image pickup device 103 is provided with an infrared cut filter, a low pass filter, and the like. Then, an optical image is formed on the image sensor 103 via the taking lens 200, and the image sensor 103 outputs an electric signal according to the optical image.

  A shutter 104 is arranged on the front side of the image sensor 103. The shutter 104 shields the image sensor 103 during non-shooting, and opens the shutter 104 during shooting to allow light to enter the image sensor 103. To do.

  A half mirror 105 is arranged in front of the shutter 104, and the half mirror 105 reflects a part of light incident through the taking lens 200 at the time of non-shooting to focus an optical image on the focusing plate 106. Image on. The half mirror 105 is retracted from the optical axis at the time of shooting.

  A display element 107 is arranged above the focusing plate 106. The display element 107 is, for example, a PN liquid crystal device, and the display element 107 displays AF distance measurement frame, image size, white balance settings, and the like.

  The optical image formed on the focusing plate 106 is guided to a photometric sensor (AE) 108 and an optical finder (not shown) via a pentaprism 109. The photometric sensor 108 includes an image sensor such as a CCD or CMOS image sensor. An image processing CPU (hereinafter referred to as ICPU) 110 drives and controls the image sensor 103 and the photometric sensor 108 under the control of the camera microcomputer 101. Further, the ICPU 110 performs light adjustment processing, subject detection processing, subject tracking, and flicker detection according to the output of the photometric sensor 108. A memory 111 such as a RAM and a ROM is connected to the ICPU 110.

  In the illustrated example, the ICPU 110 performs the above-described various processes, but the camera microcomputer 101 may directly perform the above-described processes without the ICPU 110.

  The camera body 100 is provided with a strobe device (hereinafter simply referred to as strobe) 112 which is a light emitting device. As will be described later, at the time of shooting, the ICPU 110 controls the flash 112 to emit light based on the main light emission amount.

  The taking lens 200 has a lens group such as a focus lens and a diaphragm (not shown), and a lens microcomputer (LPU) 201 drives and controls the focus lens under the control of the camera microcomputer 101 and also controls the diaphragm. . The LPU 201 also sends distance information indicating the distance between the camera and the subject to the camera microcomputer 101.

  FIG. 3 is a flow chart for explaining a process when the camera shown in FIG. 2 shoots a strobe light.

  When the power of the camera is turned on, the camera microcomputer 101 determines whether or not a photometric timer (not shown) indicating a photometric permission state is ON (step S101). The photometric timer turns on when the power of the camera is turned on, and turns off when the camera is not operated for a predetermined time. Further, when the shutter button is pressed halfway and the first shutter switch SW1 is turned on, the photometric timer is turned on.

  If the photometric timer is OFF (NO in step S101), the camera microcomputer 101 waits. On the other hand, when the photometric timer is ON (YES in step S101), the camera microcomputer 101 performs normal photometry (step S102).

  In normal photometry, ambient light is used for photometry. At this time, it is desirable that the accumulation time in the photometric sensor 108 be set to an integer multiple of the flicker cycle so that the photometric value does not vary with respect to the change in brightness due to the flicker even under a flicker light source.

  The frequency at which the brightness of the flicker light source changes (hereinafter referred to as the flicker frequency) is twice the frequency of the commercial power source, so in a region where the commercial power source frequency is 50 Hz, the flicker frequency is 100 Hz, The cycle of light and dark (flicker light emission cycle) is 10 ms. Similarly, in a region where the commercial power frequency is 60 Hz, the flicker frequency is 120 Hz, and the flicker emission period is 8.33 ms.

  In order to correspond to the above two flicker frequencies, the charge accumulation time in the photometric sensor 108 is set to about 9 ms between the flicker emission periods of 10 ms and 8.33 ms. As a result, regardless of whether the commercial power supply frequency is 50 Hz or 60 Hz, the charge is stored for about one flicker cycle. As a result, the photometric value can be stably obtained by the photometric sensor 108 even in a flicker environment. Then, the camera microcomputer 102 determines the shutter speed, aperture, ISO sensitivity, and the like for the main light emission based on the photometric value obtained by the photometric sensor 108 by the ICPU 110.

  Subsequently, the camera microcomputer 101 determines whether or not the shutter button is fully pressed and the second shutter switch SW2 is turned on (step S103). If the second shutter switch SW2 is OFF (NO in step S103), the camera microcomputer 101 returns to the process of step S101.

  On the other hand, when the second shutter switch SW2 is ON (YES in step S103), the camera microcomputer 101 performs the light control operation (light control process) by the ICPU 110 (step S104).

  FIG. 4 is a diagram for explaining the driving of the photometric sensor in the light control operation shown in FIG.

  The image sensor included in the photometric sensor 108 has a plurality of pixels grouped into a pixel group A and a pixel group B. Under the control of the camera microcomputer 101, the ICPU 110 changes the charge accumulation time (hereinafter simply referred to as accumulation time) and gain of the pixel group A and the pixel group B (that is, by changing the exposure condition), and controls the photometric sensor 108. Expose. At this time, the ICPU 110 controls the pixel groups A and B so that the charge accumulation timings are substantially the same. In the illustrated example, the accumulation time is T and the gain is twice in the pixel group A, and the accumulation time is 2T (twice the accumulation time in the pixel group A) and the gain is one in the pixel group B. That is, the ICPU 110 performs pixel reading after performing short-time accumulation for the image group A, and performs pixel reading after performing long-second accumulation for the pixel group B. At this time, the ICPU 110 pre-flashes the strobe 112.

  If there is a flicker due to a fluorescent lamp, an LED, or the like, the variation cycle of ambient light (that is, the light emission cycle) is 10 ms or 8.33 ms as described above. If the storage time is set to about 9 ms during strobe light control as in the case of normal light measurement, the reflected light from the strobe light emission may be affected by ambient light and correct light control may not be achieved. Therefore, it is desirable to set the storage time T at the time of dimming to about tens of microseconds to several hundreds of microseconds.

  When the accumulation time T is set to about several tens of microseconds to several hundreds of microseconds, even if the accumulation time of the pixel group B is twice as long as the accumulation time of the pixel group A, it is sufficiently short against the fluctuation of the ambient light. Ambient light can be regarded as almost constant.

  As described above, when the exposure conditions of the photometric sensor 108 are set and the charge accumulation timings are made to substantially coincide with each other, almost the same amount of ambient light is obtained in the pixel group A and the pixel group B, and the preliminary light emission is performed. Regarding the reflected light, the pixel group B can obtain half the light amount with respect to the pixel group A.

  Let Ea be the received light amount in the pixel group A, Eb be the received light amount in the pixel group B, Fpri be the light amount integrated value of the reflected light by preliminary light emission, and Ee(t) be the ambient light amount, and the received light amounts Ea and Eb are It is represented by the equations (1) and (2).

  Here, since the accumulation timings of the pixel group A and the pixel group B are substantially the same and the accumulation time T is sufficiently short, the relationship shown by the following expression (3) is established.

  Therefore, the relationship represented by the following expression (4) is obtained by the expressions (1) to (3).

Ea-Eb=Fpri (4)
In Expression (4), only the reflected light component is extracted by the difference between the received light amount Ea of the pixel group A (first pixel group) and the received light amount Eb of the pixel group B (second pixel group), and the ICPU 110 Determines the amount of main light emission based on the reflected light component.

  FIG. 5 is a diagram showing an example of the arrangement of pixel groups A and pixel groups B in the image sensor included in the photometric sensor shown in FIG.

  In the illustrated example, the first and second rows are the pixel group A, and the third and fourth rows are the pixel group B. Subsequently, in order to reduce power consumption and processing time in the image sensor, the fifth to eighth rows are thinned pixel groups. Then, after that, the pixel groups A and the pixel groups B are arranged every two rows, and then the thinned pixel groups of four rows are arranged. The arrangement of the pixel group A and the pixel group B, the presence/absence of the thinned pixel group, and the arrangement are not limited.

  After the main light emission amount is determined by the process of step S104, the camera microcomputer 101 causes the ICPU 110 to cause the strobe 112 to emit light at the main light emission amount and perform shooting. During the main light emission, all the pixels of the image sensor included in the photometric sensor 108 are driven under the same exposure condition.

  In the above-mentioned example, the example in which the light adjustment is performed by using one image pickup element provided in the photometric sensor 108 has been described, but the light adjustment may be performed by using two image pickup elements. Here, an example of performing light control using the image sensor 103 and the image sensor provided in the photometric sensor 108 will be described.

  Here, an example of performing light control using the image sensor 103 and the image sensor provided in the photometric sensor 108 will be described. However, two identical image sensors are provided in the camera body to perform light control. You can

  The image pickup device 103 and the photometric sensor 108 are driven by setting the charge accumulation timings substantially at the image pickup device 103 and the photometric sensor 108, and setting the accumulation time and the gain so that the ambient light has the same amount of light.

  However, the amount of light incident on the photometric sensor 108 is smaller than the amount of light incident on the image sensor 103 due to the influence of the focusing plate 106 and the display element 107. Therefore, it is desirable to adjust the reflectance of the half mirror 105 so that the same amount of light enters the image sensor 103 and the photometric sensor 108. If the same amount of light is incident on the image sensor 103 and the photometric sensor 108, the amount of main light emission can be determined by extracting the reflected light component as described above.

  On the other hand, when the light amounts incident on the image sensor 103 and the photometric sensor 108 are different, only the accumulation time is adjusted so that the light amounts of the ambient light match, and the light is adjusted.

  Now, let Es be the amount of light received by the image sensor 103, Ee be the amount of light received by the photometric sensor 108, Fpri be the integrated value of the amount of light reflected by preliminary light emission, Ee(t) be the amount of ambient light, and The difference in the number of steps of the illuminance of the photometric sensor 108 is Ed. The received light amounts Es and Ee can be expressed by the following equations (5) and (6).

Here, the accumulation time of the photometric sensor 108 is set longer by the Ed stage of the accumulation time of the image sensor 103 so that ∫E(t)dt=∫E(t)/2 ^Ed dt. As a result, the relationship shown in the following expression (7) is obtained.

In the formula (7), only the reflected light component by the preliminary light emission is extracted, and the ICPU 110 determines how many steps the light amount required for the main light emission is based on the subject reflected light amount Fpri (1-1/2 ^Ed ) by the preliminary light emission. The calculation is performed for whether they are different, and the main light emission amount is determined based on the calculation result.

  As described above, in the embodiment of the present invention, even under the environment where the ambient light changes with time, accurate dimming can be performed as a result of accurately extracting the reflected light component by the preliminary light emission, and variation in the main light emission amount can be achieved. It can be reduced.

  As is clear from the above description, in the example shown in FIG. 2, the camera microcomputer 101 and the ICPU 110 function as control means.

  Although the present invention has been described above based on the embodiments, the present invention is not limited to these embodiments, and various embodiments within the scope not departing from the gist of the present invention are also included in the present invention. ..

  For example, the functions of the above-described embodiments may be used as a control method, and the imaging apparatus may be caused to execute this control method. Further, a program having the functions of the above-described embodiments may be used as a control program, and the control program may be executed by a computer included in the imaging device. The control program is recorded in, for example, a computer-readable recording medium.

[Other Embodiments]
The present invention supplies a program that implements one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and one or more processors in a computer of the system or apparatus read and execute the program. It can also be realized by the processing. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

100 camera body 101 camera microcomputer 103 image sensor 108 photometric sensor 105 half mirror 106 focus plate 107 display element 110 ICPU
112 Strobe 200 Shooting lens

Claims (7)

An imaging device for obtaining a main light emission amount, which is a light emission amount at the time of shooting, according to a light amount of reflected light obtained by preliminarily emitting light from a light emitting means,
A first pixel group and a second pixel group that receive the reflected light;
The charge accumulation time and the gain for the first pixel group and the second pixel group are made different, the exposure timing is controlled, and based on the outputs of the first pixel group and the second pixel group, A control means for determining the amount of main light emission ,
The control unit controls the charge accumulation time for the first pixel group to be a predetermined magnification of the charge accumulation time for the second pixel group, and the gain for the second pixel group is the first gain. It is controlled so that it is the predetermined magnification of the gain for the pixel group,
An image pickup apparatus , wherein the timing of preliminary light emission of the light emitting means and the timing of exposure of the first pixel group and the exposure of the second pixel group are overlapped with each other .   The image pickup apparatus according to claim 1, further comprising a first image pickup element that has the first pixel group and the second pixel group and receives the reflected light. A first image pickup device having the first pixel group and receiving the reflected light;
A second image sensor that forms an optical image during shooting and outputs an image corresponding to the optical image,
The image pickup apparatus according to claim 1, wherein a plurality of pixels of the second image pickup element are used as the second pixel group.   4. The image pickup apparatus according to claim 1, wherein the control unit sets the charge accumulation time shorter than a cycle of fluctuation of ambient light at the time of shooting.   The control unit obtains a difference between an output of the first pixel group and an output of the second pixel group, and determines the main light emission amount based on the difference. The imaging device according to any one of 4 above. A first pixel group and a second pixel group that receive the reflected light obtained by preliminarily emitting light from the light emitting means are provided, and the main light emission amount that is the light emission amount at the time of photographing is determined according to the light amount of the reflected light. A method of controlling an imaging device, comprising:
The charge accumulation time for the first pixel group is controlled to be a predetermined magnification of the charge accumulation time for the second pixel group, and the gain for the second pixel group is set to the gain of the first pixel group. Controlling so that the predetermined magnification is obtained,
Controlling so that the timing of preliminary light emission of the light emitting means and the timing of exposure of the first pixel group and the second pixel group overlap.
And Luz step to determine the main emission amount on the basis of an output of the first pixel group and the second pixel group,
A control method comprising: A first pixel group and a second pixel group that receive the reflected light obtained by preliminarily emitting light from the light emitting means are provided, and the main light emission amount that is the light emission amount at the time of photographing is determined according to the light amount of the reflected light. A control program used in an imaging device,
In the computer included in the imaging device,
The charge accumulation time for the first pixel group is controlled to be a predetermined magnification of the charge accumulation time for the second pixel group, and the gain for the second pixel group is set to the gain for the first pixel group. Controlling so that the predetermined magnification is obtained,
Controlling so that the timing of preliminary light emission of the light emitting means and the timing of exposure of the first pixel group and the second pixel group overlap.
And Luz step to determine the main emission amount on the basis of an output of the first pixel group and the second pixel group,
A control program for executing the following.

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