JP2019220888A - Imaging apparatus - Google Patents

Abstract

To provide an imaging apparatus having a small difference in exposure of a still image obtained by exposure control by a mechanical shutter and exposure control by a rolling shutter.SOLUTION: By adjusting a timing of at least one of a reset release scan and a readout scan of an image sensor when capturing a still image on the basis of operation accuracy of a mechanical shutter, a control is performed so that exposure amounts of one entire frame substantially coincide with each other between a mode for controlling exposure time using the mechanical shutter and a mode for controlling the exposure time by a reset release scan and a readout scan of the image sensor without using the mechanical shutter.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an imaging device.

  2. Description of the Related Art An imaging device such as a digital camera includes a CMOS (Complementary Metal Oxide Semiconductor) image sensor. In a CMOS image sensor, an image can be taken while controlling the exposure time by using a line exposure sequential reading method (a so-called rolling electronic shutter).

  In addition, the speed of reading image signals from the CMOS image sensor is increased, the rolling shutter distortion, which has been a problem in the past, is suppressed, and high-quality still image shooting is enabled. Further, in still image shooting using a rolling electronic shutter, since there is no driving sound caused by the mechanical shutter as compared with still image shooting using a conventional mechanical shutter, there is an advantage that the user can shoot with a quiet sound.

JP 2012-42785 A

  In recent years, a still image can be shot with a shutter at a high speed of 1/8000 sec. When controlling exposure using a mechanical shutter, in such high-speed shutter shooting, the exposure amount may deviate from an ideal value due to a response delay of the mechanical shutter, a change in running resistance, and the like. As a countermeasure, it has been proposed to correct the shutter speed of a mechanical shutter according to the temperature at the time of factory adjustment or actual shooting (see Patent Document 1).

  However, even if the speed of the mechanical shutter is corrected, it is very difficult to completely match the operation of the mechanical shutter with the ideal value. Therefore, due to the response delay of the mechanical shutter and the like, a difference in the exposure amount may be visually recognized between the case where the exposure control is performed using the mechanical shutter and the case where the exposure control is performed using the electronic shutter of the image sensor. Was.

  SUMMARY OF THE INVENTION It is an object of the present invention to reduce a difference in exposure amount between still images captured in a mode in which exposure control is performed using a mechanical shutter and a mode in which exposure control is performed using an electronic shutter.

  In order to solve the above problems, an image pickup apparatus according to the present invention includes an image pickup device having a plurality of pixels arranged in a matrix, a mechanical shutter for exposing and shielding the image pickup device, and an image pickup device using the mechanical shutter. One of a first exposure control mode for controlling the exposure time of the element and a second exposure control mode for controlling the exposure time of the imaging element by reset release scanning and readout scanning of the imaging element without using the mechanical shutter. And control means for controlling to capture a still image in the second exposure control mode, based on the operation accuracy of the mechanical shutter. The first exposure control mode and the second exposure control mode are adjusted by adjusting at least one of the timing of the reset release scan and the readout scan of the image sensor. Wherein the exposure amount of the entire frame in the exposure control mode is controlled to substantially coincide.

  ADVANTAGE OF THE INVENTION According to this invention, the exposure amount difference by the exposure control using a mechanical shutter and the exposure control using only the electronic shutter of the image sensor can be reduced, and a good still image can be generated.

FIG. 1 is a block diagram illustrating an example of a configuration of an imaging device according to an embodiment. 5 is a flowchart illustrating a driving method of the imaging device according to the embodiment. 6 is a timing chart illustrating exposure control during still image shooting.

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

  FIG. 1 shows an example of a configuration of an imaging device 100 to which the present invention can be applied.

  In FIG. 1, an imaging lens 101 forms an optical image of a subject on an imaging surface of an imaging element 106 based on an instruction from a lens control unit 102. The aperture 103 adjusts a light beam that passes based on an instruction from the exposure control unit 105.

  The mechanical shutter 104 includes a mechanical front curtain and a mechanical rear curtain, and is disposed immediately before the image sensor 106 with respect to the incident direction of the optical image. Opening / closing control is performed by an exposure control unit 105 to control exposure of an optical image to the image sensor 106.

  The imaging element 106 is, for example, a CMOS image sensor, and converts an optical image formed on a pixel array on an imaging surface by the imaging lens 101 into an image signal, which is amplified by a predetermined gain and A / D converted. , As a digital image signal to the downstream DSP 107.

  The image sensor 106 includes a plurality of pixels arranged in a matrix, a reset scan in which a plurality of pixels are scanned so as to be sequentially reset in units of predetermined rows, and a method of sequentially reading signals from the plurality of pixels in units of the predetermined rows. It is possible to perform a read-out scan to make the scan.

  The DSP 107 is controlled by the CPU 108 and receives a digital image signal output from the image sensor 106. Further, various correction processing, development processing, compression processing, and the like are performed on the digital image signal using various data stored in the ROM 109 while using the RAM 110 as a work area.

  The DSP 107 performs a process of writing image data to the recording medium 112 and a process of displaying various data on the display unit 111. The CPU 108 controls the image sensor 106, the exposure control unit 105, the lens driving unit 102, and the DSP 107.

  The display unit 111 displays the captured image data processed by the DSP 107. Further, a menu screen for allowing the user to perform various shooting settings such as the aperture 103 and the ISO sensitivity is also displayed.

  The recording medium 112 is composed of a semiconductor memory or the like, and is detachably connected. The still image and moving image data for recording processed by the DSP 107 are recorded on the recording medium 112.

  The user selects a shooting mode with the mode dial 116, presses the first switch 114 to instruct AF (automatic focus control), and further presses the second switch 115 to instruct a shooting operation.

  Hereinafter, with reference to FIGS. 2 and 3, a shooting sequence and a method of adjusting an exposure period during still image shooting according to the present embodiment will be described. FIG. 2 is a flowchart in a case where still image shooting is performed under the control of the CPU 108.

  In S201, it is determined whether or not the first switch 114 has been pressed by the user. If it is determined that the first switch 114 has been pressed, autofocus control is performed.

  In S202, a lens focus position according to the focus control is determined.

  In S203, the shutter speed is set according to the shooting mode set by the user.

  In S204, it is determined whether the second switch 115 has been pressed by the user. If it is determined that the second switch 115 has been pressed, the process proceeds to S205.

  In step S <b> 205, it is determined whether the first exposure control mode for performing exposure control of the image sensor 106 using the mechanical shutter 104 has been set by the user. If the first exposure control mode has been set by the user, the process proceeds to S206.

  Here, the exposure control by the mechanical shutter 104 will be described in detail with reference to FIG. FIG. 3A illustrates a first exposure control mode using a mechanical front curtain and a mechanical rear curtain of the mechanical shutter 104.

  In step S206, the CPU 108 controls the driving of the image sensor 106 so that all pixels are collectively reset before the start of traveling of the mechanical front curtain. At this timing, the imaging surface is in a light-shielded state.

  In S207, the CPU 108 outputs a mechanical front curtain running start signal SH_1M to the exposure control unit 105 at the timing of starting exposure, and the mechanical shutter 104 starts running the mechanical front curtain. At this time, the mechanical front curtain travels as shown by the traveling curve 1, and exposure of the imaging surface of the imaging element 106 is started.

  After the exposure time according to the shutter speed set in S203 has elapsed, in S208, the CPU 108 outputs a mechanical rear curtain running start signal SH_2M to the exposure control unit 105 at the timing of the end of exposure, and the mechanical shutter 104 Start driving the second curtain.

  At this time, if the mechanical rear curtain travels as indicated by the traveling curve 2, ideal exposure control can be performed. However, due to a change in the running resistance of the shutter curtain due to, for example, temperature, it is assumed that the mechanical rear curtain actually travels like the traveling curve 3. In this case, an exposure time difference Δ occurs with respect to the ideal exposure time T corresponding to the set shutter speed, and the actual exposure time becomes T + Δ.

  In step S209, in a state where the rear curtain of the mechanical shutter 104 travels and the image sensor 106 is shielded from light, the CPU 108 controls the image sensor 106 to perform read-out scanning, and stops in the first exposure control mode using the mechanical shutter 104. The image shooting ends.

  If it is determined in step S205 that the first exposure control mode using the mechanical shutter 104 has not been set by the user, the process proceeds to step S210.

  In S210, it is determined whether or not the user has set a third exposure control mode in which the electronic shutter of the image sensor 106 and the mechanical shutter 104 are used to control the exposure of the image sensor 106. If the third exposure control mode has been set by the user, the process proceeds to S211.

  Next, a third exposure control mode using both the electronic shutter of the image sensor 106 and the mechanical shutter 104 will be described in detail with reference to FIG. FIG. 3B illustrates a third exposure control mode using an electronic front curtain shutter that uses both the electronic shutter of the image sensor 106 and the mechanical shutter 104.

  In S211, the CPU 108 controls the driving of the image sensor 106 so as to reset all the pixels at once.

  In step S212, the CPU 108 outputs the electronic front curtain travel start signal SH_1E to the image sensor 106 at the timing of starting the exposure, and starts reset release of the pixel unit of the image sensor 106 in a predetermined row unit. That is, electronic front curtain scanning is started. At this time, the electronic front curtain scanning is performed at the timing indicated by the running curve 4, and exposure (charge accumulation) of the imaging surface of the imaging element 106 is started. Here, it is assumed that the reset release scanning timing of the image sensor 106 is set so that the traveling curve 4 of the electronic front curtain scanning becomes equal to the traveling curve 2 of the mechanical rear curtain.

  After the exposure time according to the shutter speed set in S203 has elapsed, in S208, the CPU 108 outputs a mechanical rear curtain travel start signal SH_2M to the exposure control unit 105 at the timing of the exposure flow rate, and the mechanical shutter 104 Start driving the second curtain.

  As described above, if the mechanical rear curtain travels as indicated by the traveling curve 2, ideal exposure control can be performed. However, actually, it is assumed that the mechanical rear curtain travels like the traveling curve 3. In this case, an exposure time difference Δ occurs with respect to the ideal exposure time T corresponding to the set shutter speed, and the actual exposure time becomes T + Δ.

  In step S209, the CPU 108 controls the image sensor 106 to perform read scanning in a state where the rear curtain of the mechanical shutter 104 travels and the image sensor 106 is shielded from light. Then, the still image shooting in the third exposure control mode using both the electronic shutter of the image sensor 106 and the mechanical shutter 104 ends.

  If it is determined in S204 that the second switch 115 has been pressed by the user, and if it is determined in S210 that the third exposure control mode has not been set by the user, the process proceeds to S213.

  In S213, it is determined whether or not the user has set the second exposure control mode using only the electronic shutter of the image sensor 106. If the second exposure control mode has been set by the user, the process proceeds to S214.

  Next, a second exposure control mode using only the electronic shutter of the image sensor 106 will be described in detail with reference to FIG. FIG. 3C illustrates a second exposure control mode based on the rolling electronic shutter driving of the image sensor 106.

  In step S214, the CPU 108 performs reset scanning on the pixel unit of the image sensor 106 in predetermined row units, and starts reset release scanning in predetermined row units at the timing of exposure start. That is, the reset of the pixel portion of the image sensor 106 is sequentially performed in a predetermined row unit at the timing indicated by the traveling line 5.

  The timing to start the reset release scanning of the image sensor 106 is set earlier than the frame synchronization signal VD by the exposure time corresponding to the shutter speed set in S203.

  After the elapse of the exposure time according to the shutter speed set in S203, in S209, the reading scan of the image sensor 106 as indicated by the traveling line 6 is started at the timing of the frame synchronization signal VD, and the pixel portion of the image sensor 106 Control is performed so that signals are read out in predetermined row units. Then, the exposure ends, and the still image shooting in the second exposure control mode ends.

  Here, in the present embodiment, the exposure control in the first exposure control mode and the third exposure control mode using the mechanical shutter 104 and the exposure control in the second exposure control mode using the rolling electronic shutter of the image sensor 106. Control is performed to reduce the difference between the exposure amounts.

  That is, taking into account the exposure time difference Δ caused by the operation accuracy of the mechanical shutter (based on the operation accuracy of the mechanical shutter), the exposure time (charge accumulation time) in the second exposure control mode using the rolling electronic shutter becomes T + Δ. Control. It is to be noted that the timing of both the reset release scanning and the readout scanning of the image sensor may be adjusted, but at least one of the timings may be adjusted.

  Here, in the rolling electronic shutter drive, the exposure time (charge accumulation time) can be set in units of the horizontal synchronization signal HD. That is, the exposure time T + Δ is set in terms of the horizontal synchronization signal HD. For example, in the example shown in FIG. 3C, the exposure time T + Δ is a time corresponding to five pulses of the horizontal synchronization signal HD.

  If one pulse period of the horizontal synchronization signal HD is sufficiently short with respect to the exposure time difference Δ, the exposure time can be controlled with high accuracy.

  As described above, by setting the exposure time of the rolling electronic shutter drive in consideration of the exposure time difference Δ that may be caused due to the operation accuracy of the mechanical shutter, shooting was performed at the same shutter speed between the three exposure control modes. In this case, the difference in exposure amount can be reduced.

  That is, the exposure amounts of the entire one frame in each exposure control mode can be made substantially equal, and a good still image can be obtained.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to these embodiments, and various modifications and changes can be made within the scope of the gist.

104 Mechanical shutter 105 Exposure control unit 106 Image sensor 108 CPU
116 mode dial

Claims (6)

An image sensor having a plurality of pixels arranged in a matrix,
A mechanical shutter for exposing and shielding the image sensor,
A first exposure control mode for controlling the exposure time of the image sensor using the mechanical shutter, and a second exposure control mode for controlling the exposure time of the image sensor by reset release scanning and readout scanning of the image sensor without using the mechanical shutter. Control means for controlling to shoot a still image in any one of the exposure control modes,
The control unit adjusts at least one timing of reset release scanning and readout scanning of the image sensor when capturing a still image in the second exposure control mode based on the operation accuracy of the mechanical shutter. An image pickup apparatus, wherein control is performed such that the exposure amount of one entire frame in the first exposure control mode and the second exposure control mode substantially coincides with each other. The image sensor includes a reset release scan that scans the plurality of pixels so as to sequentially release reset in a predetermined row unit and a read scan that scans so that signals from the plurality of pixels are sequentially read out in the predetermined row unit. Configured
The mechanical shutter has a front curtain that travels to expose the image sensor and a rear curtain that travels to shield the image sensor from light,
In the first exposure control mode, the exposure of the image sensor is started by running the front curtain of the mechanical shutter, and control is performed so that the exposure of the image sensor is completed by running the rear curtain of the mechanical shutter.
In the second exposure control mode, the exposure of the image sensor is started by the reset scan of the predetermined row unit by the image sensor, and the exposure of the image sensor is terminated by the read scan of the predetermined row unit. The imaging device according to claim 1, wherein the control is performed. The control unit further controls to perform still image shooting in a third exposure control mode that controls exposure of the image sensor using both the image sensor and the mechanical shutter,
The first exposure control is performed by adjusting at least one of the reset release scan and the readout scan of the image sensor when capturing a still image in the second exposure control mode based on the operation accuracy of the mechanical shutter. 2. The imaging apparatus according to claim 1, wherein the control is performed such that exposure amounts of the entirety of one frame in the mode, the second exposure control mode, and the third exposure control mode substantially match. The image sensor includes a reset release scan that scans the plurality of pixels so as to sequentially release reset in a predetermined row unit and a read scan that scans so that signals from the plurality of pixels are sequentially read out in the predetermined row unit. Configured
The mechanical shutter has a front curtain that travels to expose the image sensor and a rear curtain that travels to shield the image sensor from light,
In the first exposure control mode, the exposure of the image sensor is started by running the front curtain of the mechanical shutter, and control is performed so that the exposure of the image sensor is completed by running the rear curtain of the mechanical shutter.
In the second exposure control mode, the exposure of the image sensor is started by the reset release scan of the predetermined row unit by the image sensor, and the exposure of the image sensor is ended by the read scan of the predetermined row unit. Control,
In the third exposure control mode, the exposure of the image sensor is started by the reset release scanning of the predetermined row unit by the image sensor, and the rear curtain of the mechanical shutter is driven to end the exposure of the image sensor. Control,
The first exposure control mode and the second exposure control are performed by setting the exposure start and exposure end timings when performing a still image shooting in the second exposure control mode based on the operation accuracy of the mechanical shutter. The imaging apparatus according to claim 2, wherein the control is performed such that an exposure time in the third exposure control mode substantially coincides with an exposure time in the third exposure control mode. The image pickup device is capable of electronic front curtain scanning to adjust the timing of the reset release scanning of the plurality of pixels in a predetermined row unit to the movement of the front curtain of the mechanical shutter,
In the third exposure control mode, the control unit starts the exposure of the image sensor by the electronic front curtain scanning, and controls the end of the exposure of the image sensor by moving the rear curtain of the mechanical shutter. The imaging apparatus according to claim 3, wherein the imaging is performed.   The imaging apparatus according to any one of claims 1 to 5, wherein the control unit drives the imaging element in a rolling electronic shutter mode in the second exposure control mode.

Images