JP2020145624A - Imaging apparatus and control method therefor, program, and storage medium - Google Patents

Abstract

To provide an imaging apparatus allowing for prevention of a decrease in focusing accuracy due to flicker and deterioration of a display image on a display unit.SOLUTION: The imaging apparatus comprises an imaging device of which the drive frequency can be changed for each area in a screen, designation means which designates a plurality of areas for dividing the screen of the imaging device, setting means which sets the drive frequency for the plurality of areas, detection means which detects an area in which exposure unevenness occurs due to the influence of flicker from among the plurality of areas when the plurality of areas are driven at a drive frequency set by the setting means, changing means which changes the drive frequency of the area where the exposure unevenness is detected in such a manner that the exposure unevenness is reduced when exposure unevenness is detected by the detection means, and display means which displays images of the plurality of areas obtained by driving at a drive frequency changed so that the exposure unevenness is reduced.SELECTED DRAWING: Figure 2

Description

The present invention relates to a technique for improving the focus detection accuracy and the appearance of the display unit in an imaging device such as a digital camera.

Conventionally, in an imaging device such as a digital camera, a focal position is adjusted by using an autofocus function and displayed on a display unit before taking a still image (or moving image) of a subject. This makes it possible to confirm the state of the still image (or moving image) to be captured in advance.

In such processing, it is desirable to process the moving image displayed on the display unit in the live view operation or the like at a relatively low frame rate (for example, 30 fps) in order to reduce the processing load. On the other hand, when performing autofocus processing, it is desirable to perform processing at a high frame rate (for example, 240 fps) in order to improve responsiveness and focus detection accuracy.

Therefore, in general, a method is used in which a moving image before shooting is displayed on a display unit at a low frame rate, and when a user instructs a focusing operation, the image is switched to a high frame rate. However, in this case, when switching the frame rate, unnecessary time may occur and the operability may deteriorate.

As a method of shortening such unnecessary time, in Patent Document 1, by simultaneously reading an image from an image sensor at a plurality of types of frame rates, from a shooting instruction by a user operation to the start of still image shooting. Techniques for improving operability are disclosed.

Further, when the above processing is performed under an artificial light source such as a fluorescent lamp, a horizontal stripe-like brightness change (line flicker) occurs in the screen at a high frame rate, and the focus detection result for each line fluctuates. As a result, the focusing accuracy of autofocus may be adversely affected. In addition, line flicker may occur in the moving image displayed on the display unit, which may deteriorate the appearance.

As a method for preventing the deterioration of focusing accuracy and the appearance of the display unit due to such flicker, Patent Document 2 divides the use for focus detection and display for each pixel line, and images at a plurality of frame rates. Is disclosed, and a technique for performing independent processing for each application is disclosed. As a result, the focusing accuracy is improved and the deterioration of the appearance of the display unit is suppressed.

Japanese Patent No. 5862126 Japanese Unexamined Patent Publication No. 2015-108778

However, in the technique disclosed in Patent Document 1 above, as already described, when reading signals at a plurality of frame rates at the same time under a flicker light source, line flicker may occur in processing at a high frame rate. There is. Therefore, the difference in the frame rate may cause a difference in the focus detection result of autofocus and the captured moving image.

Further, in the technique disclosed in Patent Document 2, since the use is divided for each pixel line, the number of pixels of the image used for display is reduced, and the resolution is lowered as compared with the case of displaying using all the pixels. ..

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an imaging device capable of preventing a decrease in focusing accuracy due to flicker and deterioration of a display image on a display unit. ..

The image pickup apparatus according to the present invention is driven with respect to an image pickup element capable of changing the drive frequency for each region in the screen, a designation means for designating a plurality of regions for dividing the screen of the image pickup element, and the plurality of regions. A setting means for setting a frequency and a region in which exposure unevenness due to the influence of flicker is generated among the plurality of regions when the plurality of regions are driven by the drive frequency set by the setting means is detected. The detection means, the changing means for changing the drive frequency of the region where the exposure unevenness is detected when the exposure unevenness is detected by the detection means, and the changing means for reducing the exposure unevenness. It is characterized by comprising a display means for displaying an image of the plurality of regions obtained by driving at a changed driving frequency.

According to the present invention, it is possible to provide an image pickup apparatus capable of preventing a decrease in focusing accuracy due to flicker and deterioration of a display image on a display unit.

The block diagram which shows the structure of the digital camera which is 1st Embodiment of the image pickup apparatus of this invention. The flowchart which shows the flow of the whole operation of the digital camera of 1st Embodiment. The figure which shows the region setting method which changes the drive frequency of the image pickup element in 1st Embodiment. The figure which shows the flicker generated in the region which changed the drive frequency in 1st Embodiment, and the flicker period. The flowchart which shows the operation flow of the digital camera of 2nd Embodiment. The figure which shows the region setting method which changes the drive frequency of the image sensor in 2nd Embodiment.

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. The following embodiments do not limit the invention according to the claims. Although a plurality of features are described in the embodiment, not all of the plurality of features are essential to the invention, and the plurality of features may be arbitrarily combined. Further, in the attached drawings, the same or similar configurations are designated by the same reference numbers, and duplicate description is omitted.

(First Embodiment)
FIG. 1 is a block diagram showing a configuration of a digital camera according to a first embodiment of the imaging device of the present invention.

In FIG. 1, the digital camera 100 of the present embodiment is configured such that a photographing lens 102 is interchangeably attached to a camera body 101.

The photographing lens 102 includes a zoom lens 103, a focus lens 104, an aperture 105, and a lens control circuit 106 that controls their drive. The camera body 101 and the photographing lens 102 are electrically connected by the mount contact portion 107, and the lens control unit 106 can receive information from the camera body 101 via the mount contact portion 107.

The camera body 101 incorporates a system control circuit 108, and the system control circuit 108 controls each part of the camera. The power supply 109 is composed of a primary battery such as an alkaline battery, a secondary battery such as a NiCd battery, a NiMH battery, and a Li ion battery, an AC adapter, and the like, and supplies electric power to each part of the camera via a system control circuit 108.

The operation SW (operation switch) 110 is composed of various switch groups, and includes, for example, a main power switch, a release switch, a playback switch, a zoom switch, a cross key, a SET switch, and the like (not shown). The main power switch is a switch for activating the camera body 101 and supplying power. The release switch is composed of a two-stage switch, and in the first stroke (SW1), an instruction signal for starting a shooting preparation operation such as AE processing and AF processing performed prior to the shooting operation is generated. Then, in the second stroke (SW2), an instruction signal for starting the actual shooting operation is generated. The playback switch starts the playback operation, and the zoom switch moves the zoom lens 103 of the photographing lens 102 to perform zooming. The cross key is used for the user to input the selection operation, and the SET switch is used for inputting each determination operation.

The shutter 111 is arranged between the photographing lens 102 and the image pickup element 112, and is driven by the shutter control circuit 113 so as to control the exposure time of the light incident from the photographing lens 102.

The image sensor 112 converts the light incident from the photographing lens 102 into an electric signal and outputs an analog image signal. The signal output from the image sensor 112 is subjected to various image processing by the image pickup circuit 114. In the A / D conversion circuit 115, the analog image signal processed by the image pickup circuit 114 is converted into a digital image signal. The drive frequency of the image sensor 112 can be changed for each divided region in the screen, and the drive frequency for each divided region is controlled by the system control circuit 108.

The memory 116 is a memory such as a buffer memory that temporarily stores a digital image signal output from the A / D conversion circuit 115. The D / A conversion circuit 117 reads the image signal stored in the memory 116 and converts it into an analog signal, and also converts it into an image signal in a form suitable for reproduction display. The display unit 118 is composed of a liquid crystal display (LCD) or the like, and displays an image signal converted by the D / A conversion circuit 117. The compression / decompression circuit 119 reads the image signal temporarily stored in the memory 116, performs compression processing and coding processing, and converts the image data into image data in a form suitable for storage in the storage memory 120. The storage memory 120 stores image data processed by the compression / decompression circuit 119. Further, the compression / decompression circuit 119 reads the image data stored in the storage memory 120, performs decompression processing and decoding processing, and converts the image data into an image data having an optimum form for reproduction display.

As the storage memory 120, various forms of storage means can be applied. For example, it may be a semiconductor memory such as a flash memory having a card shape or a stick shape that can be attached to and detached from the device, or a magnetic storage medium such as a hard disk or a flexible disk.
The AE processing circuit (automatic exposure processing circuit) 121 performs automatic exposure (AE) processing using the image signal output from the A / D conversion circuit 115. The exposure change at this time is controlled by the system control circuit 108. Further, the AF processing circuit 122 performs autofocus (AF) processing using the image signal output from the A / D conversion circuit 115.

The timing generator (hereinafter, TG) 123 generates a predetermined timing signal. The sensor driver 124 drives the image sensor 112 based on the timing signal from the TG 123.
The EEPROM 125 is an electrically rewritable read-only memory in which programs for performing various controls and data used for performing various operations are stored in advance. The RAM 130 is used to expand the program stored in the EEPROM 125 so that the system control circuit 108 can execute it. It is also used as a work area of the system control circuit 108.

The flicker detection circuit 126 receives the output image signal from the A / D conversion circuit 115, detects the presence or absence of flicker from the brightness fluctuation in the screen, and calculates the generation cycle of the detected flicker.

Next, FIG. 2 is a flowchart showing the overall operation flow of the digital camera 100 of the present embodiment.

In S201, power is supplied to each part of the camera when the user turns on the main power switch included in the operation SW110.

In S202, the system control circuit 108 instructs the shutter control circuit 113 to shift the shutter 111 to the open state, and guides the light through the image pickup lens 102 to the image sensor 112. In S203, the system control circuit 108 starts the exposure of the image sensor 112.

In S204, the system control circuit 108 performs display control. Specifically, the light incident from the photographing lens 102 is photoelectrically converted by the image sensor 112, and the converted electrical signal is subjected to various image processing by the image pickup circuit 114 to generate an image signal. After that, the analog image signal is converted into a digital image signal by the A / D conversion circuit 115, and is temporarily stored in the memory 116. The stored digital image signal is converted into an analog image signal again by the D / A conversion circuit 117 and displayed on the display unit 118.

Since S203 and S204 are processes before the region division for changing the drive frequency of the image sensor 112, which will be described later, is performed, the entire angle of view is driven at a low frequency (for example, 30 fps or the like).

In S205, the system control circuit 108 determines whether or not the first stroke of the release switch included in the operation SW110 has been operated (whether or not SW1 has been turned on). If SW1 is turned on, the process proceeds to S206, and if it is not turned on, the process proceeds as it is.

In S206, the system control circuit 108 determines the presence / absence of a region to be controlled by changing the drive frequency of the image sensor 112, which will be described later, and the position and range of the region. If there is no region for changing the drive frequency, the process proceeds to S207, and if there is a region for changing the drive frequency, the position and range of the region are set and the process proceeds to S214.

Here, the setting of the region for changing the drive frequency will be described with reference to FIG. FIG. 3 is a diagram showing an example of region setting for changing the drive frequency of the image sensor 112. In FIG. 3, a display unit 118, a focus detection area 127 currently selected by the user, an area 128 for changing the drive frequency, and a cross key and a set button of the operation SW110 are shown.

The region 128 for changing the drive frequency of the image sensor 112 may be automatically set around the focus detection region 127 as shown in FIG. 3A, or may be set by the user as shown in FIG. 3B. You may specify the position by operating the cross key. Further, as shown in FIG. 3C, the display unit 118 may be provided with a touch panel function, and the area may be designated by a user's touch operation. The method of setting the region is not limited to these examples, and various modifications and changes are possible.

S207 to S213 are normal shooting sequences that do not change the drive frequency of the image sensor 112.

In S207, the system control circuit 108 performs a photometric operation using the AE processing circuit 121, and in S208, each exposure parameter (for example, sensitivity, aperture value) related to the brightness is changed and displayed so as to obtain an appropriate exposure. Update the display of part 118.

In S209, the system control circuit 108 performs an autofocus operation using the AF processing circuit 122, and when it is determined that the system is in focus, the process proceeds to S210.

In S210, the system control circuit 108 determines whether or not the second stroke of the release switch included in the operation SW110 has been operated (whether or not the SW2 has been turned on). If SW2 is ON, the process proceeds to S211. If SW2 is not ON, the process proceeds to S211.

In S211 the system control circuit 108 causes the image sensor 112 to take a still image and shifts the shutter 111 to the closed state.

In S212, the system control circuit 108 reads out the electric charge accumulated in the image sensor 112, and processes the digital image signal via the image pickup circuit 114, the A / D conversion circuit 115, the memory 116, and the compression / decompression circuit 119. It is stored in the storage memory 120.

In S213, the system control circuit 108 causes the display unit 118 to display the image stored in the storage memory 120 for a predetermined time, and returns to S202.

S214 to S222 are cases where the imaging region of the image sensor 112 is divided into a plurality of regions and control is performed to change the drive frequency of at least one region, and the image sensor 112 is not affected by the flicker light source (for example, outdoors). ) Case shooting sequence.

In S214, the system control circuit 108 changes the drive frequency of at least one region used for the autofocus operation to the high frequency side in the region divided by S206. Here, as an example, when the drive frequency of the region for autofocus operation is 1/120 second (read rate is 120 fps) and the drive frequency of the other region is 1/130 second (read rate is 30 fps). explain. When the change of the drive frequency is completed, the process proceeds to S215.

In S215, the system control circuit 108 performs a photometric operation using the AE processing circuit 121, and proceeds to S216.

In S216, the system control circuit 108 uses the flicker detection circuit 126 to show the presence or absence of flicker in the region where the drive frequency is changed in the output from the A / D conversion circuit 115 (presence or absence of exposure unevenness due to flicker). To judge. Specifically, as shown in FIG. 4, the presence or absence of flicker is determined based on the presence or absence of brightness fluctuation in the region after the drive frequency is changed. If there is no flicker, the process proceeds to S217. If flicker has occurred, the flicker generation cycle t is calculated and the process proceeds to S223.

In S217, in the system control circuit 108, the region where the drive frequency is changed is properly exposed (equivalent to other regions) based on the information of the drive frequency changed in S214 and the luminance information obtained by the photometric operation of S215. Each exposure parameter (exposure condition) such as sensitivity related to brightness and aperture value is changed so as to be (exposure). Then, the display of the display unit 118 is updated. As an example, in S214, the drive frequency of the region for autofocus operation is 1/120 second (read rate is 120 fps), and the drive frequency of the other region is 1/130 second (read rate is 30 fps). Therefore, the area for the autofocus operation has a lower two-step exposure than the other areas. Therefore, the sensitivity of the region where the drive frequency for the autofocus operation is changed is changed to the high sensitivity side by two steps. When the change of the exposure parameter is completed, the process proceeds to S218.

In S218, the system control circuit 108 performs an autofocus operation using the AF processing circuit 122, and when it is determined that the system is in focus, the process proceeds to S219.

In S219, the system control circuit 108 determines whether or not the second stroke of the release switch included in the operation SW110 has been operated (whether or not the SW2 has been turned on). If SW2 is ON, the process proceeds to S220, and if SW2 is not ON, the process proceeds as it is.

In S220, the system control circuit 108 causes the image sensor 112 to take a still image and shifts the shutter 111 to the closed state.

In S221, the system control circuit 108 reads out the electric charge accumulated in the image sensor 112, and processes the digital image signal via the image pickup circuit 114, the A / D conversion circuit 115, the memory 116, and the compression / decompression circuit 119. It is stored in the storage memory 120.

In S222, the system control circuit 108 causes the display unit 118 to display the image stored in the storage memory 120 for a predetermined time, and returns to S202.

S223 to S230 are cases where the imaging region of the image sensor 112 is divided into a plurality of regions and control is performed to change the drive frequency of at least one region, and is affected by a flicker light source (for example, fluorescence). This is the shooting sequence when (under the light).

In S223, the drive frequency changed in S214 is changed again to a drive frequency that is not affected by the flicker (a frequency at which the cycle of the drive frequency is an integral multiple of the cycle of the flicker). As an example, when the flicker period is 50 Hz, the drive frequency of the region for autofocus operation is 1/50 second (read rate is 50 fps), and the drive frequency of the other region is 1/30 second (read rate is 30 fps). ). When the re-change of the drive frequency is completed, the process proceeds to S224.

In S224, the system control circuit 108 performs a photometric operation using the AE processing circuit 121, and proceeds to S225.

In S225, in the system control circuit 108, the region where the drive frequency is changed is properly exposed (equivalent to other regions) based on the information of the drive frequency re-changed in S223 and the luminance information obtained by the photometric operation of S224. Each exposure parameter (exposure condition) such as sensitivity related to brightness and aperture value is changed (exposure control) so as to be (exposure). Then, the display of the display unit 118 is updated. As an example, in S223, the drive frequency of the region for autofocus operation is set to 1/50 second (read rate is 50 fps), and the drive frequency of the other region is set to 1/30 second (read rate is 30 fps). Therefore, the area for autofocus operation has about two-thirds less exposure than the other areas. Therefore, the sensitivity of the region where the drive frequency for the autofocus operation is changed is changed to the high sensitivity side (increase side) by 2/3 steps (sensitivity adjustment). When the change of the exposure parameter is completed, the process proceeds to S226.

In S226, the system control circuit 108 performs an autofocus operation using the AF processing circuit 122, and when it is determined that the system is in focus, the process proceeds to S227.

In S227, the system control circuit 108 determines whether or not the second stroke of the release switch included in the operation SW110 has been operated (whether or not the SW2 has been turned on). If SW2 is ON, the process proceeds to S228, and if SW2 is not ON, the process proceeds as it is.

In S228, the system control circuit 108 causes the image sensor 112 to take a still image, and shifts the shutter 111 to the closed state.

In S229, the system control circuit 108 reads out the electric charge accumulated in the image pickup device 112, and processes the digital image signal via the image pickup circuit 114, the A / D conversion circuit 115, the memory 116, and the compression / decompression circuit 119. It is stored in the storage memory 120.

In S230, the system control circuit 108 causes the display unit 118 to display the image stored in the storage memory 120 for a predetermined time, and returns to S202.

As described above, in the present embodiment, even when the drive frequency of a part of the image sensor is increased for the autofocus operation, if flicker is detected, the drive frequency is further changed. As a result, even when a part of the image sensor is processed at a high frame rate for autofocus operation, it is possible to prevent deterioration of focusing accuracy due to flicker and deterioration of the display image on the display unit. Become.

In the above description, an example of dividing the screen of the image sensor into two regions has been described, but the present invention is not limited to the two regions, and the screen is divided into three or more regions. It may be divided and the drive frequency may be changed for each region. In that case, it is determined whether or not exposure unevenness due to flicker has occurred in each of the plurality of regions, and if so, the drive frequency in that region is further changed.

(Second Embodiment)
Next, a second embodiment of the present invention will be described. The second embodiment is different from the above-described first embodiment in that it has means for changing the display setting (display setting means) and the display of the divided area can be changed when flicker is detected. Since the block configuration of the digital camera is the same as that of the first embodiment shown in FIG. 1, the description thereof will be omitted.

FIG. 5 is a flowchart showing the operation of the digital camera of the second embodiment. In FIG. 5, the same step numbers are assigned to the steps having the same processing contents as the steps described in FIG. 2, and the description thereof will be omitted as appropriate.

First, when flicker is detected in S216, the process proceeds to S501.

In S501, the system control circuit 108 determines whether or not to display the region in which the drive frequency has been changed on the display unit 118. As an example, it will be described with reference to FIG.

FIG. 6A shows a case where the drive frequency change region is set in a horizontal line shape, and FIG. 6B shows a case where the drive frequency change region is set in a vertical line shape. When a plurality of small drive frequency change areas are provided as shown in FIG. 6, if the sensitivity is changed and displayed on the display unit, the appearance will be deteriorated due to noise. In such a case, the display unit is not displayed. Better.

Therefore, in S501, the system control circuit 108 determines whether or not to display on the display unit 118 depending on whether or not the area of at least one drive frequency-changed region is equal to or less than the threshold value. If it is determined that the display is not displayed, the process proceeds to S502, an autofocus operation is performed, and the process proceeds to S227. If it is determined that the display is to be displayed, the process proceeds to S224. The threshold value for determining the area is stored in EEPROM 125. Since S224 to S230 are the same as those described in FIG. 2, the description thereof will be omitted.

As described above, in the present embodiment, even when the flicker is detected, if the region where the drive frequency is changed is small, it is determined whether or not to display based on the size of the region. This makes it possible to prevent a decrease in focusing accuracy due to flicker and deterioration of the display image on the display unit.

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

The invention is not limited to the above embodiments, and various modifications and modifications can be made without departing from the spirit and scope of the invention. Therefore, a claim is attached to make the scope of the invention public.

108: System control circuit, 112: Image sensor, 118: Display unit, 121: AE processing circuit, 122: AF processing circuit, 126: Flicker detection circuit

Claims (13)

An image sensor that can change the drive frequency for each area on the screen,
Designating means for designating a plurality of areas for dividing the screen of the image sensor, and
A setting means for setting the drive frequency for the plurality of regions, and
When the plurality of regions are driven at the drive frequency set by the setting means, the detection means for detecting the region in which the exposure unevenness due to the influence of the flicker occurs among the plurality of regions.
When exposure unevenness is detected by the detection means, a changing means for changing the drive frequency of the region where the exposure unevenness is detected so as to reduce the exposure unevenness, and
A display means for displaying images of the plurality of regions obtained by driving at a drive frequency changed so as to reduce the exposure unevenness, and
An imaging device characterized by comprising. The imaging device according to claim 1, wherein the changing means changes the driving frequency of the region where exposure unevenness is detected so that the period of the driving frequency is an integral multiple of the period of the flicker. The imaging according to claim 1 or 2, further comprising an exposure control means for controlling the exposure condition of the region whose drive frequency has been changed by the changing means so as to be equivalent to the exposure condition of the other region. apparatus. The third aspect of the present invention, wherein the exposure control means controls the sensitivity of each region so that the exposure condition of the region where the drive frequency is changed becomes equivalent to the exposure condition of the other region. Imaging device. The imaging device according to any one of claims 1 to 4, wherein the designated means automatically divides the screen into a region including a focus detection region and another region. The imaging device according to claim 5, wherein the setting means sets the drive frequency of the region including the focus detection region higher than the drive frequency of the other region. The imaging device according to claim 6, further comprising a sensitivity adjusting means for increasing the sensitivity of a region including the focus detection region by an amount corresponding to an increased amount of the drive frequency. The imaging device according to any one of claims 1 to 4, wherein the designated means divides the screen into a plurality of areas by a user operation. The imaging device according to any one of claims 1 to 8, wherein the display means simultaneously displays images of the plurality of regions. The imaging device according to any one of claims 1 to 8, further comprising a display setting means for setting whether or not to display an image of the plurality of regions on the display means. It is a method of controlling an image pickup device provided with an image pickup element capable of changing the drive frequency for each area in the screen.
A designation step of designating a plurality of areas for dividing the screen of the image sensor, and
The setting process for setting the drive frequency for the plurality of regions and
When the plurality of regions are driven at the drive frequencies set in the setting step, a detection step of detecting a region in which exposure unevenness is generated due to the influence of flicker among the plurality of regions is used.
When exposure unevenness is detected in the detection step, a changing step of changing the drive frequency of the region where the exposure unevenness is detected so as to reduce the exposure unevenness, and
A display step of displaying images of the plurality of regions obtained by driving at a drive frequency changed so as to reduce the exposure unevenness, and
A method for controlling an imaging device, which comprises. A program for causing a computer to execute each step of the control method according to claim 11. A computer-readable storage medium that stores a program for causing a computer to execute each step of the control method according to claim 11.