JP6244824B2 - Imaging apparatus and imaging method - Google Patents

Description

  The present invention relates to an imaging apparatus applicable to a digital camera or the like, and more particularly to a pixel signal readout process from an imaging element.

  In digital cameras and the like, the light of the subject captured by the photographic lens is imaged on the image sensor to generate and record image data, and the photometric image sensor that detects the brightness of the subject, the image sensor for focus adjustment, etc. In addition to the image sensor for photographing, various image sensors are provided depending on the application.

  For example, in the case of a single-lens reflex digital camera, a photometric sensor is arranged near the optical viewfinder, and light passing through the photographing lens is guided to the optical viewfinder by a movable mirror and imaged on the photometric sensor. The pixel signal read from the photometric sensor is input to the image signal processing unit, and thereby the brightness of the subject is detected.

  When a recording operation is performed on the release button, the movable mirror is raised, and the light of the subject is formed on the rear image sensor. When the exposure is completed, the movable mirror is lowered and the pixel signal is read from the image sensor. The read pixel signal is input to the image signal processing unit, thereby generating image data.

  In such a camera based on TTL photometry, when continuous shooting is performed, in order to detect the brightness of the subject again by the photometric sensor, the movable mirror is driven (up) again to perform photometric processing, and the movable mirror is driven again. (Down). Therefore, in continuous shooting, a series of operations including imaging by an image sensor, driving of a movable mirror, and imaging by a photometric sensor are repeated (see, for example, Patent Document 1).

JP2013-88759A

  When the number of pixels of the imaging element for photographing increases, the time until the pixel signal is read from the imaging element becomes longer. On the other hand, depending on the shooting situation such as continuous shooting, it is necessary to quickly follow the subject luminance change caused by the movement of the subject, and so on before the pixel signal reading from one image sensor is completed. A situation arises in which exposure of two image sensors must be started.

  However, when pixel signals output from two image sensors are captured by one image signal processing unit, usually only pixel signals from one image sensor can be captured and cannot be input simultaneously. Therefore, until the reading of one pixel signal is completed, it is necessary to wait for reading of the pixel signal in the other image sensor.

  This may lead to a situation in which proper exposure cannot be realized in an image sensor in a pixel signal readout standby state. For example, in an image sensor for photometry, exposure time exposure adjustment is performed in order to appropriately detect the luminance level of a subject ranging from a low luminance level to a high luminance level. However, when the pixel signal is read out in accordance with the completion of reading of the pixel signal of the imaging element for photographing and recording, the exposure time must be continued until the reading is completed, and appropriate exposure adjustment cannot be performed.

  Therefore, in an imaging apparatus that selectively transmits pixel signals output from two imaging elements to an image processing unit, it is necessary to be able to arbitrarily set the exposure time and pixel signal output timing of the imaging element.

  The imaging device of the present invention includes a first imaging element, a second imaging element, a first pixel signal read from the first imaging element, and a second pixel signal read from the second imaging element. An image signal processing unit that selectively reads one and executes image signal processing, and a control unit that controls exposure of the first and second imaging elements and pixel signal reading. Note that the first pixel signal is a pixel signal corresponding to one frame / field read from the first image sensor or a part of the pixel signal, and the second pixel signal is read from the first image sensor. It represents a pixel signal corresponding to one frame / field or a part of the pixel signal.

  Then, the controller starts exposure of the second image sensor and then starts exposure of the first image sensor before the completion of reading the second pixel signal. When a predetermined exposure period has elapsed, accumulation is performed. The charge is moved to the charge holding portion of the first image sensor, and held there after the movement. Then, in response to the completion of the reading of the second pixel signal, the control unit makes it possible to read the first pixel signal from the first image sensor and read the first pixel signal.

  The control unit is capable of generating a pulse signal having a cycle shorter than the second pixel signal readout period after the exposure of the first image sensor and enabling the first pixel signal readout, Reading of the first pixel signal is started by the first pulse signal generated after the completion of reading of the second pixel signal.

  For example, the first image sensor is a charge transfer type image sensor, and the accumulated charge is temporarily held in the vertical transfer unit of the first image sensor.

  The control unit switches the exposure operation, the movement and holding operation of the accumulated charge, and the first pixel signal readout operation in the first image sensor by an operation switching pulse signal sent to the first image sensor through one signal line. It is possible to make it. For example, the operation switching pulse signal is a vertical synchronization signal.

  The control unit outputs the vertical synchronization signal at a cycle shorter than the cycle of the vertical synchronization signal before the end of exposure of the second image sensor between the end of exposure of the second image sensor and the completion of reading of the second pixel signal. Can be generated.

  For example, the control unit controls the first and second imaging elements so that the pixel signal readout of the second imaging element is prioritized over the pixel signal readout of the first imaging element.

  The imaging apparatus can be applied to a camera including a photographic optical system. For example, exposure control for the second imaging element is performed based on a first pixel signal read from the first imaging element.

  In the case of continuous shooting by the camera, the control unit performs a first operation after the second pixel signal is read out from the start of exposure of the second image sensor when a recording operation is performed on the release button in the continuous shooting mode setting state. It is possible to repeatedly execute the operation up to reading of the pixel signal.

  For example, like a single-lens reflex camera, an optical finder that forms an image of light from a subject that has passed through the photographing optical system on a first image sensor is provided, and light from the subject that has passed through the photographing optical system is A movable mirror that leads to either one of the two image sensors is provided. Alternatively, a photometric optical system that forms an image of light from a subject not passing through the photographing optical system on the first image sensor, such as a compact camera, is provided.

  An imaging method according to another aspect of the present invention selectively reads either a first pixel signal read from a first image sensor or a second pixel signal read from a second image sensor, and outputs an image signal. An imaging method for executing processing and controlling exposure and pixel signal readout of the first and second imaging elements, after starting exposure of the second imaging element and before completion of readout of the second pixel signal When the exposure of the first image sensor is started and a predetermined exposure period elapses, the accumulated charge is moved to and held in the charge holdable portion of the first image sensor, and the second pixel signal is read out. Upon completion, the first pixel signal can be read from the first image sensor.

  According to the present invention, when pixel signals are alternately read from two image sensors, appropriate exposure such as setting an appropriate exposure time for each image sensor can be performed.

It is a block diagram of the digital camera which is this embodiment. It is a schematic block diagram between an image sensor, AE sensor, and a signal processing apparatus. It is the figure which showed the partial circuit structure of the AE sensor. It is the flowchart which showed a series of recording operation processes. 5 is a timing chart of exposure and pixel signal readout processing for an AE sensor and an image sensor.

  Below, the digital camera which is this embodiment is demonstrated with reference to drawings.

  FIG. 1 is a block diagram of a digital camera according to the present embodiment.

  The digital camera 10 is a single-lens reflex camera in which the photographing lens 20 can be detachably attached to the main body 15, and the photographing mode, the reproduction mode, and the like can be set by operating a mode dial / button (not shown). As the shooting mode, a normal shooting mode for recording one image and a continuous shooting mode for performing continuous shooting operations can be set.

  In the normal photographing mode, the reflected light from the subject passes through the aperture 22 and the photographing lens 20, and a part thereof is guided toward the optical viewfinder 12 by the quick return mirror 24. Part of the reflected light passes through the quick return mirror 24 and is guided to the AF sensor 32 by the half mirror 26.

  When the light incident on the optical viewfinder 12 is imaged, the user can confirm the subject image through the eyepiece 17. The light of the subject is also imaged on the light receiving surface of the AE sensor (first image sensor) 34 disposed near the optical finder 12.

  The signal processing device 40 configured by a DSP or the like outputs control signals to the shutter 27, the image sensor driving unit 28, the AE sensor driving unit 29, the LCD 48, a timing generator (not shown), and the like, and is detected by the button switch 45. Based on the input operation or the like, the entire camera operation control such as the recording operation of the captured image, the reproduction display, and the focusing operation is performed. A camera operation control program is stored in the nonvolatile memory 44.

  When the release button 19 is pressed halfway, a focusing operation and an exposure calculation process are executed. In the focusing operation, the taking lens 20 is driven by an AF driver (not shown) based on the phase difference detected by the AF sensor 32. The exposure control unit 50 provided in the signal processing device 40 detects the brightness of the subject based on the luminance signal sent from the AE sensor 34 via the AFE (Analog Front End). Then, exposure calculation processing such as shutter speed and aperture value calculation is executed. Here, the AE sensor 34 is constituted by a CCD of a charge transfer type solid-state imaging device.

  Further, when the release button 19 is fully pressed, a series of recording operation processing is executed. That is, the quick return mirror (movable mirror) 24 and the half mirror 26 are retracted from the optical path connecting the photographing lens 20 and the image sensor 30, and the diaphragm 22 and the shutter 27 are driven based on the set exposure values. . By such exposure control, a subject image is formed on the light receiving surface of the image sensor (second image sensor) 30, and a charge (pixel signal) corresponding to the subject image is generated.

  The image sensor 30 on which a subject image for photographing / recording is formed is a CMOS sensor of an XY address type image sensor, and is configured with a high number of pixels (for example, 10 million pixels or more). . A color filter (not shown here) is arranged on the light receiving surface of the image sensor 30. A series of pixel signals generated in the image sensor 30 is sent to the signal processing device 40 by the image sensor driving unit 28.

  The signal processing device 40 performs image signal processing such as white balance adjustment and color conversion processing on the pixel signal for one frame output from the image sensor 30 in the image signal processing unit 41 to generate image data. . The generated still image data is temporarily stored in the internal memory 42 and then recorded in an external memory 46 such as a memory card in a compressed / uncompressed state.

  The exposure control unit 50 outputs control signals to the image sensor driving unit 28 and the AE sensor driving unit 29, respectively, and can adjust the output timing of the driving signals for the image sensor 30 and the AE sensor 34. Thereby, the exposure operation of the image sensor 30 and the AE sensor 34, the pixel signal readout operation, and the like are controlled.

  The exposure control unit 50 can adjust the exposure value by performing exposure control so that the exposure amount of the AE sensor 34 becomes an exposure amount appropriate for the brightness of the subject. When the pixel signal output from the AE sensor 34 is sent to the image signal processing unit 41, the brightness (luminance value) of the subject image is detected. Based on the detected brightness, the exposure time by the electronic shutter function is adjusted.

  FIG. 2 is a schematic block diagram between the image sensor 30, the AE sensor 34, and the signal processing device 40. FIG. 3 is a diagram showing a partial circuit configuration of the AE sensor 34.

  The AFE 39 includes a communication unit 37, a timing generator 38, and a signal conversion unit 36. The signal conversion unit 36 includes a CDS circuit, an AGC circuit, and an A / D conversion circuit (all not shown). The communication unit 37 can communicate with the signal processing device 40.

  In the signal processing device 40, a pixel signal for one frame read from the AE sensor 34 (hereinafter referred to as a first pixel signal if necessary) and a pixel signal for one frame read from the image sensor 30 (hereinafter referred to as necessary). (Hereinafter referred to as a second pixel signal) is processed in the image signal processing unit 41.

  Since the first pixel signal and the second pixel signal cannot be simultaneously captured due to circuit characteristics or the like, here, the first pixel signal and the second pixel signal are alternately read. Yes. Specifically, the AE sensor 34, the image sensor 30, and the AFE 39 are controlled so that the second pixel signal output from the image sensor 30 is preferentially read.

  As described above, the AE sensor 34 is composed of a CCD, and a plurality of photodiodes (pixels) PD are arranged in a matrix along the vertical direction / column direction and horizontal direction / row direction. In FIG. 3, 24 pixels PD having 6 rows and 4 columns are shown.

  In addition, a vertical transfer unit VT is provided along the column direction next to the photodiode, and the charge generated in each photodiode PD due to photoelectric conversion is transferred to the vertical transfer unit VT after a predetermined exposure period elapses. Moved. The accumulated charges shifted to the vertical transfer unit VT are transferred to the horizontal transfer unit HT and output from the horizontal transfer unit HT via the amplifier AP.

  The second pixel signal is read from the AE sensor 34 by performing such exposure (charge accumulation), charge transfer, charge transfer, and charge output. The sequence operations of charge transfer, charge transfer, and charge output can be switched by a vertical synchronization signal (VD) output from the timing generator 38, respectively. Specifically, the sequence operation can be switched in synchronization with the falling pulse of the vertical synchronization signal. The vertical synchronization signal is sent to the AE sensor 34 by one signal line.

  When the reading of the second pixel signal to the image sensor 30 is completed, data indicating the end of reading is transmitted from the signal processing device 40 to the communication unit 37. When the data is received by the communication unit 37, the sequence operations of charge transfer to the AE sensor 34 and first pixel signal readout are sequentially executed.

  In the present embodiment, when the recording operation is performed in the continuous shooting mode, as described later, the charge transfer and the charge transfer are not continuously performed at a time, and the accumulated charge is temporarily held in the vertical transfer unit VT. Store. Although the vertical transfer unit VT is not originally a circuit for storing accumulated charges, it can be temporarily held.

  FIG. 4 is a flowchart showing a series of recording operation processing. FIG. 5 is a timing chart of exposure and pixel signal readout processing for the AE sensor 34 and the image sensor 30. The exposure and pixel signal readout processing for the image sensor 30 and the AE sensor 34 during continuous shooting will be described with reference to FIGS.

  When the release button 19 is pressed halfway, the brightness of the subject image is detected along with the AF operation process (S101 to S103). Then, exposure values for the image sensor 30 such as a shutter speed and an aperture value are determined (S104).

  When the release button 19 is fully pressed, a series of recording operation processes such as exposure control such as opening / closing of the shutter and image data generation are executed. First, the first recording operation is performed based on the exposure value for the image sensor 30 set when the release is half-pressed. When the shutter 27 is opened for a predetermined time, charges are accumulated in the image sensor 30, and when the exposure time ends, the second pixel signal is read to the image signal processing unit 41 (S105 to S107). Further, after the exposure is completed, the quick return mirror 24 moves to the original position.

  Then, exposure of the AE sensor 34 is started during the reading of the second pixel signal (S108). As shown in FIG. 5, the readout period RT for reading out all the second pixel signals from the image sensor 30 is very long (for example, 100 ms or more) because of high pixels. If the brightness of the subject changes due to movement of the subject, changes in illumination, etc. during continuous shooting, it is not possible to quickly adjust the exposure following that. Therefore, the exposure of the AE sensor 34 is started before the second pixel signal reading is started.

  Then, when a predetermined exposure period E elapses from the start of exposure, the exposure of the AE sensor 34 ends, and the charge accumulated in the AE sensor 34 is shifted to the vertical transfer unit VT by the sequence operation of the accumulated charge shift (S109). ). Then, by the charge holding sequence operation, the charge is not transferred from the vertical transfer unit VT to the horizontal transfer unit HT as it is, but the charge is held in the vertical transfer unit VT (S109).

  Further, in step S109, the vertical synchronization signal CLK having the period T0 is output as a sequence operation switching pulse signal in accordance with the end of the exposure of the AE sensor 34. The period T0 is sufficiently shorter than the readout period RT (for example, 2 ms). As described above, the sequence operation switching from charge holding to charge transfer can be performed by the vertical synchronization signal CLK.

  In step S110, it is determined whether or not the second pixel signal readout from the image sensor 30 has been completed. When it is determined that the second pixel signal reading is completed, after the next vertical synchronization signal is received, data notifying the end of reading is sent to the communication unit 37 of the AFE 39 shown in FIG. As a result, the first pixel signal readout from the AE sensor 34 can be started in synchronization with the fall of the vertical synchronization signal immediately after that, and the first pixel signal is read out (S111).

  Then, the quick return mirror 24 is raised, and the second recording operation is started (see FIG. 5). The first pixel signal readout period ST is much shorter than the second pixel signal readout period RT due to the relatively small number of pixels. Therefore, the transition to the second recording operation proceeds rapidly. While the release button 19 is fully pressed, the same recording operation is repeated (S112).

  As described above, according to this embodiment, the AE sensor 34 and the image sensor 30 are provided, and one frame of pixel signals (first pixel signal) read from the AE sensor 34 and one frame of data read from the image sensor 30 are included. In the single-lens reflex camera configured to selectively read one of the pixel signals (second pixel signal) in the signal processing device 40, before continuous readout of the pixel signal from the image sensor 30 during continuous shooting. Exposure to the AE sensor is started. When the exposure period E of the AE sensor 34 ends, a sequence operation is performed in which the accumulated charge is moved to the vertical transfer unit VT and the accumulated charge is temporarily held in the vertical transfer unit VT.

  The vertical transfer unit is not a circuit part that originally holds charges, but can hold charges by delaying the transfer timing. When the second pixel signal readout period RT elapses and the second pixel signal readout is completed, the first pixel signal can be read from the AE sensor 34, and the first operation is performed by the sequence operation of charge transfer and pixel signal readout. One pixel signal is taken into the signal processing device 40.

  The exposure of the AE sensor 34 is started before all the recording pixel signals read out from the image sensor 30 are read out, so that the photometric processing at the time of continuous shooting and the exposure and recording operations for the image sensor overlap in time series. It becomes possible to make it. This shortens the time interval for continuous shooting, and can quickly capture the change in luminance of the subject and perform shooting with an appropriate exposure for each recording operation.

  In addition, by providing three sequence operations of accumulated charge shift, accumulated charge retention, and pixel signal readout (output), a period for retaining the accumulated charge can be arbitrarily set. For this reason, the exposure period E of the AE sensor 34 is not affected by the second pixel signal readout period RT, and the exposure amount for the AE sensor 34 can be appropriately maintained. Can be detected with high accuracy.

  Further, by outputting the vertical synchronization signal CLK having a very short cycle before the completion of the reading of the second pixel signal, the first pixel signal reading process can be performed without providing a time interval immediately after the completion of the reading of the second pixel signal. Be started. The charge held in the vertical transfer unit of the AE sensor 34 deteriorates due to a dark current component generated with the passage of time. However, by outputting the vertical synchronization signal CLK, the charge holding period is shortened, Deterioration can be suppressed.

  In addition, by performing sequence operation switching based on a vertical synchronization signal sent via one signal line, exposure, transfer, holding, and readout processing can be appropriately performed without complicated signal reception and transmission. Can do.

  In this embodiment, the AE sensor 34 is a CCD and the image sensor 30 is a CMOS sensor. However, the AE sensor 34 is an XY address type image pickup device such as a CMOS sensor, and the image sensor 30 is a charge transfer type such as a CCD. You may comprise as an image pick-up element. In the case where the two image sensors are constituted by CCDs, an input switching unit to the AFE is provided or a dedicated AFE is provided. In any case, the accumulated charge may be moved and shifted from the light receiving portion and held in a device such as a circuit or a memory that can be temporarily held.

  The detection of the completion of the second pixel signal readout, the switching operation from the charge holding sequence to the pixel signal readout sequence in the AE sensor, and the control thereof are not limited to the above-described configuration. The sequence operation may be switched by a dedicated pulse signal other than the vertical synchronization signal. Further, the pulse signal may be output during the entire period from the end of exposure of the image sensor to the completion of pixel signal reading, or may be output partially from the middle.

  Even in a shooting situation other than the continuous shooting mode, the above-described readout switching control of the first pixel signal and the second pixel signal may be performed. Further, the present invention can be applied to a digital camera (compact camera, mirrorless camera, etc.) provided with a dedicated AE sensor other than a single-lens reflex camera.

  Furthermore, the present invention is not limited to pixel signal readout control between the image sensor and the photometric sensor, and is a camera or other imaging device in which exposure and pixel signal readout operations are performed in time series between two imaging devices. An overlapping imaging device may be configured to hold the above-described charge.

10 Digital Camera 12 Optical Finder 20 Shooting Lens 24 Quick Return Mirror (movable mirror)
28 Image sensor drive unit 29 AE sensor drive unit 30 Image sensor (second image sensor)
34 AE sensor (first image sensor)
40 signal processor 50 exposure control unit

Claims (12)

A first image sensor;
A second imaging device;
An image signal processing unit that selectively reads either the first pixel signal read from the first image sensor or the second pixel signal read from the second image sensor, and executes image signal processing; ,
A controller that controls exposure and pixel signal readout of the first and second image sensors,
After the controller starts exposure of the second image sensor, the controller starts exposure of the first image sensor before reading of the second pixel signal, and when a predetermined exposure period has elapsed, Moving the accumulated charge to the charge retaining portion of the first image sensor and holding it;
The image pickup apparatus, wherein the control unit enables reading out the first pixel signal from the first image pickup device in response to completion of reading out the second pixel signal. The controller generates a pulse signal that is shorter than the second pixel signal readout period after the exposure of the first image sensor and enables the first pixel signal readout,
The imaging apparatus according to claim 1, wherein reading of the first pixel signal is started by a pulse signal generated first after completion of reading of the second pixel signal. The first image sensor is a charge transfer type image sensor;
The image pickup apparatus according to claim 1, wherein the accumulated charge is temporarily held in a vertical transfer unit of the first image pickup element.   An operation switching pulse sent from the control unit to the first image sensor through one signal line for an exposure operation, a movement and holding operation of accumulated charges, and a first pixel signal readout operation in the first image sensor. The imaging apparatus according to claim 3, wherein the imaging apparatus is switched by a signal.   The imaging apparatus according to claim 4, wherein the operation switching pulse signal is a vertical synchronization signal. Wherein the control unit is, during a period from the exposure end of said first imaging element to the second pixel signal reading completion, at the period shorter than the period of the vertical synchronizing signal before the end of exposure the first image sensor, vertical The imaging apparatus according to claim 5, wherein a synchronization signal is generated.   The control unit controls the first and second image sensors so that pixel signal readout of the second image sensor has priority over pixel signal readout of the first image sensor. The imaging device according to claim 1. A camera comprising a photographing optical system and the imaging device according to any one of claims 1 to 7,
An exposure control for the second image sensor is performed based on a first pixel signal read from the first image sensor.   When the controller performs a recording operation on the release button in the continuous shooting mode setting state, from the start of exposure of the second image sensor to the reading of the first pixel signal after the completion of the second pixel signal reading. The camera according to claim 8, wherein the operation is repeatedly executed. An optical viewfinder that forms an image of light from a subject passing through the photographing optical system on the first image sensor;
10. The movable mirror according to claim 8, further comprising: a movable mirror that guides light from a subject that has passed through the photographing optical system to one of the optical finder and the second image sensor. 10. camera.   10. The camera according to claim 8, further comprising a photometric optical system that forms an image of light from a subject that does not pass through the photographing optical system on the first image sensor. 11. Selectively reading either the first pixel signal read from the first image sensor or the second pixel signal read from the second image sensor, and performing image signal processing;
An imaging method for controlling exposure and pixel signal readout of the first and second imaging elements,
After the exposure of the second image sensor is started, the exposure of the first image sensor is started before the reading of the second pixel signal is completed. Move to and hold the charge-holding portion of one image sensor,
An imaging method comprising: reading out a first pixel signal from the first imaging element in response to completion of reading out a second pixel signal.

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