JP2014204308A - Imaging apparatus and imaging method - Google Patents

Abstract

An imaging apparatus that minimizes performance degradation such as a shooting interval, has a large number of shots, and consumes relatively little power. An imaging apparatus includes a mechanical shutter, an imaging unit, and an image processing unit. The still image data is an image that is read as an image signal from the image sensor and then converted into a still image. The image processing means performs image processing on the still image data. The image processing means provides a still image lead-out VD period and a blanking period. The still image readout VD period is a period in which image data is read from the image sensor by the imaging unit when a still image is acquired. The blanking period is a period during which no image signal is output after the reading of the image signal for all pixels is completed within the still image readout VD period. The mechanical shutter opening process is completed within the blanking period. [Selection] Figure 6

Description

  The present invention relates to a digital camera, and relates to an image sensor control method and a mechanical shutter control method during still image shooting. In particular, it is suitable for a compact digital camera or the like having a small battery capacity and a limited supply power.

  In recent years, contrary to the downsizing of digital cameras, there has been a tendency to increase the size of the image pickup element and increase the diameter of the lens with a bright lens having a large open F value. Many image sensors have an APS-C size or larger, and the power consumption for driving the image sensor is larger than that of a compact digital camera, which is generally about 1 / 1.7 type.

 In addition, the number of users who desire a bright lens is increasing, and a lens that is so large that it cannot be thought of as a compact digital camera is mounted, and the ratio of the lens barrel including the lens to the volume of the camera is increasing. For this reason, other parts are inevitably wrinkled, and the size of the battery is as small as possible. On the other hand, since it is desired to increase the number of shots, the image sensor and mechanical shutter have been devised so that the number of shots can be reduced by using power saving control even with a small battery capacity (Patent Document 1).

Japanese Patent Application Laid-Open No. 2011-166397

  However, there is a problem that the ratio of the power consumption occupied by the driving power of the mechanical shutter and the image sensor is large. In addition, in order to simultaneously operate these units with a small battery, a voltage supply of a certain level or more is necessary, and it is greatly involved in determining an end voltage indicating battery exhaustion.

  Therefore, in the present invention, by devising the drive control of the image sensor, the mechanical shutter control, and the control timing of the image processing, performance degradation such as the shooting interval can be minimized, the number of shots is large, and An object of the present invention is to provide an imaging device with relatively low power consumption.

  An image pickup apparatus according to the present invention is picked up by a mechanical shutter that adjusts the exposure time of the image pickup device, an image pickup unit that performs a charge reset operation simultaneously on all pixels of the image pickup device, and read out from the image pickup device as an image signal. An image processing unit that performs image processing on the still image data that has been converted into a still image, and the image processing unit reads the image data from the image sensor with the imaging unit when acquiring the still image. A lead-out VD period and a blanking period during which no image signal is output after completion of reading of image signals for all pixels are provided in the still image lead-out VD period, and the mechanical shutter opening process is completed within the blanking period. It is characterized by making it.

  In addition, when performing multiple times of image processing on the acquired still image, the first image processing is performed while reading the still image signal during the still image reading period, and the first image processing is performed during the blanking period. It is preferable to start the second image processing. In this way, by overlapping the blanking period with the image processing time of the captured still image, it is possible to prevent a reduction in the shooting interval.

  It is preferable that the imaging unit further includes a rolling shutter mode in which a charge reset operation is performed for each pixel line of the image sensor, and the reset operation in the rolling shutter mode is started after the opening process of the mechanical shutter is completed.

  Further, within the blanking period, the mechanical shutter opening process period and the second image processing period may overlap or may be started simultaneously.

  An imaging method according to the present invention includes an imaging process in which a charge reset operation is performed simultaneously on all pixels of an imaging element, and still image data that is captured by the imaging process, read out as an image signal from the imaging element, and then converted into a still image. An image processing step for performing image processing on the image, and when the image processing step acquires a still image, the still image lead-out VD period and the still image lead-out VD period in which image data is read from the image sensor in the imaging step And a blanking period during which no image signal is output after completion of reading of the image signal for all pixels, and the opening process of the mechanical shutter is completed within the blanking period.

  In addition, when performing multiple times of image processing on the acquired still image, the first image processing is performed while reading the still image signal during the still image reading period, and the first image processing is performed during the blanking period. It is preferable to start the second image processing. In this way, by overlapping the blanking period with the image processing time of the captured still image, it is possible to prevent a decrease in the shooting interval.

  According to the present invention, it is possible to provide an imaging device in which performance degradation such as a shooting interval is minimized, the number of shots is large, and power consumption is relatively small.

It is a top view of the camera to which the embodiment of the present invention is applied. It is a front view of the camera to which the embodiment of the present invention is applied. It is a rear view of the camera to which the embodiment of the present invention is applied. It is a block diagram of a camera to which an embodiment of the present invention is applied. It is a figure showing the opening process sequence of a general mechanical shutter. It is a figure showing the opening process timing of the mechanical shutter in embodiment of this invention.

  Hereinafter, embodiments of an imaging apparatus and an imaging method according to the present invention will be described with reference to the drawings. 1 to 3 are a top view, a front view, and a rear view showing an example of a digital still camera which is an example of an imaging apparatus according to the present invention. FIG. 4 is a block diagram showing an outline of a system configuration example inside the digital still camera.

  In FIG. 1, a release switch SW1, a mode dial SW2, and a sub liquid crystal display (hereinafter referred to as LCD) 1 are disposed on the upper surface of the camera. In FIG. 2, on the front side of the camera, there are a lens barrel unit 7 including a photographing lens, an optical finder 4, a strobe light emitting unit 3, a remote control light receiving unit 6, a distance measuring unit 5, a memory card loading chamber and a battery loading chamber lid 2. Has been placed.

  In FIG. 3, on the back of the camera, a power switch 13, an LCD monitor 10, an AF LED 8, a strobe LED 9, an optical viewfinder 4, a wide angle direction zoom switch SW3, a telephoto direction zoom switch SW4, a self-timer setting and release switch SW5, A menu switch SW6, an upward movement and strobe set switch SW7, a right movement switch SW8, a display switch SW9, a downward movement and macro switch SW10, a left movement and image confirmation switch SW11, and an OK switch SW12 are arranged.

  FIG. 4 is a schematic diagram showing the configuration of internal functional blocks. The imaging device 30 includes a lens unit (mechanical shutter) 32, a CMOS sensor 36, and an analog front end AFE (imaging means) 34. The AFE 34 converts the output electrical signal (analog image data) from the CMOS sensor 36 into a sampling signal (correlated double sampling) CDS 38, an AGC (AUTO GAIN CONTROL) 40 for adjusting the gain of the sampled data, and a digital signal. An A / D converter 42 and the like are included.

  An image received by the CMOS sensor 36 via the lens unit 32 driven by the motor driver 33 is converted into a digital video signal and input to a signal processing IC (image processing means) 50. A camera interface unit 52 and an image processing unit 54 that are image processing units that convert an input signal from the imaging device 30 into a displayable format and store it in a memory; a display output control unit 56 that is a display signal output unit; The CPU 58 as color information extracting means for extracting information is all included in the signal processing IC 50.

  The signal processing IC 50 outputs a synchronization signal to the CMOS sensor 36 and captures data in accordance with the synchronization signal. Optical correction and detection of Bayer RAW data input from the CMOS interface 51 via the memory controller 53 are performed. A camera interface unit 52 that performs processing, an image processing unit 54 that interpolates input Bayer RAW data, converts the data into YUV data format, and changes the image size in accordance with the size of noise removal, edge enhancement, display, and recording, Display output control unit 56 for controlling display output, data compression unit 59 for recording in JPEG, media I / F 60 for controlling writing of image data to a memory card, overall system control, extraction of color information, etc. The CPU 58 is configured.

  The display output control unit 56 outputs a signal by adding a signal such as a synchronization signal for output to the LCD 1 built in the camera. The SDRAM 70 serves as a memory for temporarily storing image data and JPEG compressed data, a memory for holding display data, and a RAM of the CPU. The ROM 72 has a control program for controlling the camera, and the CPU 58 operates based on the program and data. The clock generation unit 74 and horizontal / vertical signal generation unit 76 control reading, and these operations will be described in detail later.

  FIG. 5 shows an example of a general shooting control sequence in the global shutter. When the release switch SW1 is pressed, AF (AUTO FOCUS) processing is performed prior to shooting. For example, the hill-climbing AF for finding the maximum contrast value while moving the focus lens is performed as the AF process. This method is described in Japanese Patent Publication No. 39-5265. This is a process of creating an AF evaluation value from the high-frequency component of the G signal (or Y signal that is a luminance value) of the video signal, calculating the focus lens position where this becomes the maximum, and moving the focus lens.

  As for the area from which the AF evaluation value is acquired, there are a multi-area AF that considers a plurality of areas and a spot area AF that considers only a part of the subject. Based on the AF evaluation value, a focus position suitable for the shooting scene is calculated, and the focus lens is moved to that point. The focus lens can be moved via a motor driver of the lens unit according to a command from the CPU. An electronic imaging device such as a digital still camera is generally equipped with an autofocus (hereinafter referred to as AF) device that automatically focuses. Note that AF processing is omitted because it is not related to the essence in the present invention.

  In the V1 period in FIG. 5, the number of electronic shutters for still image shooting, AGC 40 (see FIG. 4), and aperture are calculated. (AE (AUTO EXPOSURE) process) Parameters for driving sensors such as an electronic shutter and AGC 40 are set by a command from the CPU 58 (see FIG. 4).

  In addition to the setting for still image exposure, control is performed to change the driving mode of the CMOS sensor 36 from a draft mode such as thinning readout adopted for a through image to an all-pixel capturing mode for still image shooting. This processing needs to be performed within a specified time in synchronization with the vertical synchronization signal (VD signal) which is the start of the V2 period in FIG.

  Therefore, generally, an interrupt process is generated with a vertical synchronization signal as a trigger, and a parameter for still image shooting is set in the interrupt process. Although not shown, the parameters are set from the signal processing IC 50 for the AFE 34 (see FIG. 4). Specifically, it is implemented using a peripheral (serial communication) possessed by the signal processing IC 50. On the other hand, the horizontal / vertical synchronization signal generation unit 76 is also set with parameters for photographing a still image different from the previous parameters, and a horizontal / vertical synchronization signal for a still image is generated based on the parameters. . Then, a horizontal / vertical synchronizing signal for a still image is transmitted to the CPU 58 as a trigger, and the operation is changed to a drive for performing exposure and reading for the still image after a certain time. (V2 to V3 period in FIG. 5)

  The period V2 in FIG. 5 is an exposure period during still image shooting, and all pixels are collectively reset by the global shutter. As described above, by writing a prescribed set value via serial communication in accordance with a command from the CPU 58, the process of resetting the charge from the drive control unit of the image sensor built in the CMOS sensor 36 can be executed and realized.

  Also, control for closing the mechanical shutter is performed in synchronization with the change of the drive mode of the sensor. The mechanical shutter closing control is performed during the still image exposure in the V2 period, but is generally performed using a timer provided in the signal processing IC 50 in the signal processing IC 50 (see FIG. 4).

  That is, an exposure time is created by starting the timer with the vertical synchronization signal at the start of the V2 period in FIG. 5 as a trigger, and controlling the shutter to close when a certain period of time has elapsed. By closing the mechanical shutter before the reading operation in the V3 period (still image readout VD period) starts, exposure does not proceed within the V3 period, and an appropriate image can be read out.

  When reading of the still image in the V3 period is completed, a process of opening the mechanical shutter is executed to return to the through image. Unlike the case of closing, it is not necessary to control the exposure time, and therefore the process of opening the mechanical shutter with the completion of reading as a trigger may be performed.

  By the way, opening and closing the mechanical shutter consumes a large amount of current. This is because it is necessary to continuously apply a large voltage to the motor driver that operates the mechanical shutter for a certain period. Although the shutter itself can be opened and closed in a short time, it is necessary to continue the current for about 15 to 20 ms even after the opening and closing.

<General imaging sequence>
Referring to FIG. 5, the mechanical shutter is opened in the V4 period, but at the same time, exposure and readout processing for a through image is started. This reading process also consumes a large current in a large image sensor such as APS-C, and it is necessary to supply a considerably large current in simultaneous driving with a mechanical shutter. In particular, with a small battery of a compact digital camera, when the remaining battery capacity decreases, it becomes impossible to supply current, and the digital camera system stops.

<Imaging Sequence of the Present Invention>
Referring to FIG. 6, there is shown a control sequence of a mechanical shutter and an image sensor that avoids the above-described problem, which is an embodiment according to the present invention. The difference from the first embodiment is that a blanking period unrelated to still image reading is provided in the V3 period (still image readout VD period), and the mechanical shutter opening process is completed in this period. Thus, the peak current of the consumption current is lowered without overlapping with the imaging device driving for the through image.

  A description will be given regarding a method of adding a blanking period. First, the blanking period for reading image data from the CMOS sensor 36 includes a horizontal blanking period and a vertical blanking period. The horizontal blanking period is a blank period provided for each line of the image, and reading of the next line starts after the blank period ends. The vertical blanking period is a blank period for one screen (frame), and when the vertical blank period is completed, the next frame period is reached.

  The blank period can be added by controlling the horizontal / vertical synchronizing signal (HD, VD) period. The VD signal in the figure is generated by a horizontal / vertical synchronization signal generator 76 in the signal processing IC 50 (see FIG. 4). The horizontal / vertical synchronization signal generation unit 76 receives a clock from an external clock generation unit 74, uses the clock signal as an input source, counts the number of clocks for one horizontal period, and counts the horizontal signal (the number of repetitions). ) To generate one vertical period.

Therefore,
Horizontal period = counter value constituting one horizontal period x (1 / f)
Vertical period = horizontal number constituting one vertical period x horizontal period. f is the frequency. Note that the horizontal / vertical synchronization signal generator 76 may be inside or outside the signal processing IC 50.

  In the present embodiment, the frequency of the clock input from the external clock generator 74 is 54 Mhz, and the maximum counter value constituting one horizontal period is 65536 (16 bits) as an internal counter included in the horizontal / vertical synchronization signal generator 76. ) It is assumed that the maximum value of the horizontal book value constituting one vertical period is 8192 (13 bits). As described above, one vertical period is determined by the counter value constituting the horizontal period and the horizontal main value constituting the one vertical period.

For example, if the counter value constituting the horizontal period is 803, one horizontal period is
803 x (1/54 MHz) = 0.0000148703 ... = 0.1487 μsec
It becomes. If the number of horizontal lines including the blank period is 1122, the VD interval has a frame rate of about 59.94 fps.

  Actually, a minimum value is determined for the counter value constituting the horizontal period and the number of horizontal lines for each drive mode of the CMOS sensor 36, and the CMOS sensor 36 cannot be driven normally below this value. Conversely, if the frame rate is increased, the frame rate is lowered, but a desired frame rate can be generated. In the embodiment according to the present invention, the blanking period after image output is created by increasing the number of horizontal lines in the V3 period.

For example, the time required for the mechanical shutter opening process is 15 ms. The minimum number of one horizontal clock for driving the VD period is 1752, and the number of lines is 3360. In this case, 1752 x (1/54 MHz) x 3360
A frame rate of about 9.17 fps is possible, but to add 15 ms of mechanical shutter,
0.015 / 1752 * 1/54000000 = 463
From 3360 + 463 = 3823
And By setting in this way, a blanking period of 15 ms can be added to the V3 period.

  As described above, it is possible to lower the peak of the consumption current for driving the CMOS sensor 36 and the processing current of the mechanical shutter opening process in the V4 period, and it is possible to lower the end voltage for determining the battery end. The voltage level of the battery can be determined by reading the power supply voltage with the ADC in accordance with an instruction from the CPU 58 included in the signal processing IC 50.

  In the V3 period, since data is sequentially output from the image sensor for each horizontal line, first image processing, that is, image processing that can be handled by data for each horizontal line, such as detection, is performed. The RAW data is temporarily stored in the SDRAM 70 (see FIG. 4), and is input again from the SDRAM 70 to the signal processing IC 50. In the blanking period, the second image processing, that is, the signal processing IC 50 starts image processing for the RAW data based on the detection result and the like. The second image processing corresponds to, for example, shading correction including WB correction.

  This is because the provision of a blanking period extends the still image lead-out VD period and delays the lead-out after the completion of the still image capture, thereby delaying the timing at which the next shooting can be performed. Although the blanking period cannot be reduced from the minimum period due to the specifications of the image sensor device, it can be increased to some extent. Since image data is not output during the blanking period, power saving control of the image sensor itself is possible.

  As described above, in the embodiment according to the present invention, the image processing interval is effectively used by starting the image processing of the still image acquired in the V3 period during the blanking period added in the V3 period. Prevents from growing. Generally, the power consumed in image processing is small compared to the power for driving the mechanical shutter and the image sensor, and can be moved simultaneously with the mechanical shutter operation. That is, in the present embodiment, the mechanical shutter opening process period and the second image processing period such as shading correction can be overlapped within the blanking period, or these periods are started simultaneously. It becomes possible.

  As described above, according to the present invention, it is possible to provide an imaging apparatus in which performance degradation such as a shooting interval is minimized, the number of shots is large, and power consumption is relatively small.

32 Lens unit (mechanical shutter)
34 AFE (imaging means)
50 Signal processing IC (image processing means)

Claims (6)

A mechanical shutter for adjusting the exposure time of the image sensor;
Imaging means having a global shutter mode for performing a charge reset operation simultaneously on all pixels of the imaging device;
Image processing means for performing image processing on still image data captured by the imaging means, read out as an image signal from the image sensor and then converted into a still image,
The image processing means includes
When acquiring the still image, a still image readout VD period in which the image data is read from the image sensor by the imaging unit;
In the still image readout VD period, a blanking period in which the image signal is not output after completion of reading the image signal for all pixels is provided.
An image pickup apparatus that completes the opening process of the mechanical shutter within the blanking period. When performing multiple times of image processing on the acquired still image,
During the still image readout period, the first image processing is performed while reading out the still image signal.
The imaging apparatus according to claim 1, wherein the second image processing is started during the blanking period. The imaging means further has a rolling shutter mode for performing a charge reset operation for each pixel line of the imaging element,
The imaging apparatus according to claim 1, wherein the reset operation in the rolling shutter mode is started after the opening process of the mechanical shutter is completed.   The imaging apparatus according to claim 2, wherein the mechanical shutter opening process and the second image processing period overlap with each other or are simultaneously started within the blanking period. An imaging process for performing charge reset operation simultaneously on all pixels of the imaging device;
An image processing step of performing image processing on still image data captured by the imaging step, read out as an image signal from the image sensor, and then converted into a still image,
The image processing step includes
When acquiring the still image, a still image readout VD period in which the image data is read from the image sensor in the imaging step;
In the still image readout VD period, a blanking period in which the image signal is not output after completion of reading the image signal for all pixels is provided.
An image pickup method comprising: completing the opening process of the mechanical shutter within the blanking period. When performing multiple times of image processing on the acquired still image,
During the still image readout period, the first image processing is performed while reading out the still image signal.
The imaging method according to claim 1, wherein the second image processing is started during the blanking period.

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