JP4827577B2 - Imaging apparatus and control method - Google Patents

Description

  The present invention relates to an imaging apparatus and a control method therefor, and more particularly to focus adjustment control when shooting a dark subject.

  In a conventional video camera using a solid-state imaging device typified by a CCD sensor or a CMOS sensor, various methods have been proposed for obtaining sufficient sensitivity when shooting a dark subject such as a night scene. For example, in moving image shooting, there is a method of increasing the charge accumulation time in the so-called slow shutter mode in which the charge accumulation time is increased in the solid-state imaging device and the frame or field rate is slower than normal, and in still image shooting. In addition, there has also been proposed a technique in which image signals for a plurality of frames obtained from a solid-state imaging device are sequentially accumulated and obtained to effectively obtain an image signal comparable to long-time exposure (Patent Document 1).

JP-A-5-236422

  Here, the moving image shooting process in the slow shutter mode performed in the conventional imaging apparatus will be described with reference to the timing chart of FIG.

The vertical synchronization signal is a signal that outputs a pulse at a cycle T1, and for example, an NTSC standard signal repeatedly outputs a pulse at a 1/60 second cycle. In the slow shutter mode, charges are accumulated over a plurality of vertical synchronization periods. In the example shown in FIG. 7, charges are accumulated in the image sensor during four periods from t ₃₁ to t ₃₂ (during T2). The Reference numeral 71 denotes a state in which charges are accumulated in the image sensor. Accumulated charges are read from the image sensor to t _32. From reading timing of t _32, the charge accumulation for the next moving image is started.

Further, in the t _32, the image signal read from the imaging element while being recorded, the extraction of the AF evaluation value is performed. The lens control is performed after the AF evaluation value is extracted.

As described above, in the conventional slow shutter mode, lens control is performed based on the image signal obtained by exposing the imaging device for a plurality of periods, and therefore, until the next charge accumulation is started (in the example of FIG. 7). the lens control completed by t _32), it was not possible to focus. For this reason, at each exposure time T2, the image is best focused on the middle rather than the beginning.

  Patent Document 1 does not describe AF control.

  The present invention has been made in view of the above problems, and when image signals for a plurality of frames or fields are cumulatively added to obtain one image signal for a moving image, exposure of each image signal is performed. A first object is to obtain the best focused image at the beginning of time.

Further, an image signal of a plurality of frames or fields fraction and cumulative addition, when obtaining an image signal for one sheet for video, of the total exposure time of each image signal, most often between when desired A second object is to make it possible to acquire a focused image.

In order to achieve the first object, an image pickup apparatus according to the present invention includes an image pickup device that photoelectrically converts an incident subject optical image and outputs an image signal, and the image pickup device at a preset first period. drive control means for controlling to output the image signals, and synthesizing means for synthesizing by accumulating an image signal output from the imaging device in the first period were sequentially integral multiple of the first cycle in the second period, the outputs of the disengaging made the image signal by the combining means for the recording, the second for the middle by the combining means focus detecting by Rigo made the image signal of the period And a focus adjustment unit that performs focus adjustment processing based on the image signal for focus detection between the middle of the second cycle and the end of the second cycle. And have.

Further, the control method of the present invention of the image pickup apparatus having the image pickup device that photoelectrically converts the incident subject optical image and outputs the image signal reads out the image signal from the image pickup device at a preset first cycle. When a synthesizing step of synthesizing by accumulating an image signal output from the imaging device in the first period sequentially in a second period after the integral multiple of the first cycle, synthesis at the synthesis step A first output step for outputting the image signal for recording, a second output step for outputting the image signal accumulated and synthesized in the synthesis step in the middle of the second period for focus detection, A focus adjustment step of performing a focus adjustment process based on the image signal for focus detection between the middle of the second cycle and the end of the second cycle.

Further, in order to achieve the second object, said control means in the imaging apparatus of the present invention, before SL equal second period and the period, and the image signal synthesized in the desired time is output in the third period and the different et allowed integral multiple phase of the first cycle as, you Outputs an image signal for the focus detection.

  According to the present invention, when the image signals for a plurality of frames or fields are cumulatively added to obtain one image signal for a moving image, the best focus is obtained at the beginning of the exposure time of each image signal. Images can be acquired.

Further, an image signal of a plurality of frames or fields fraction and cumulative addition, when obtaining an image signal for one sheet for video, of the total exposure time of each image signal, best if the desired time It is possible to acquire a focused image.

  The best mode for carrying out the present invention will be described below in detail with reference to the accompanying drawings.

<First Embodiment>
FIG. 1 is a block diagram showing a schematic configuration of a video camera according to the first embodiment of the present invention.

  In FIG. 1, reference numeral 101 denotes a lens unit that can be attached to and detached from a video camera constituting a part of an optical system, and includes a lens group including a single lens or a plurality of lenses. The light transmitted through the lens unit 101 enters the image sensor 102 and is converted into an electric signal. The image sensor 102 is an image sensor typified by a CCD sensor, a CMOS sensor, or the like. The image sensor 102 is exposed for a predetermined time based on a drive control signal input from the timing generator 111, and an electric signal (hereinafter, “ Called "image signal"). The timing generator 111 is controlled by a control unit 110 including a timing control circuit 108 and an image accumulation counter 109, and outputs a drive control signal in accordance with a control signal output from the timing control circuit 108. The image accumulation counter 109 is also controlled by a control signal output from the timing control circuit 108, and counts the number of photographing by synchronizing with the readout timing of the image signal of the image sensor 102 driven by the timing generator 111.

  The image synthesis circuit 103 is a circuit that synthesizes an image by accumulating the image signals converted by the image sensor 102. The synthesized image signal is recorded in the frame memory 104 via the selector 105, or Alternatively, it is output to the camera signal processing circuit 107. The selector 105 switches the output destination of the image composition circuit 103 to either the frame memory 104 or the camera signal processing circuit 107 according to the count number of the image accumulation counter 109. The camera signal processing circuit 107 performs a predetermined process on the image signal synthesized through the image synthesis circuit 103 to convert it into image data, and outputs the image data to a recording circuit or a display device (not shown). An AF evaluation value detection circuit 106 detects an AF evaluation value using an image signal recorded in the frame memory 104, and detects the AF evaluation value at a timing when the image accumulation counter 109 counts a predetermined number of times of photographing. . The AF evaluation value detection circuit 106 determines the control amount of the lens unit 101 based on the obtained AF evaluation value, and outputs it to the lens control circuit 112. The lens control circuit 112 drives the lens unit 101 based on the control amount determined by the AF evaluation value detection circuit 106 to control the subject to be focused.

  Next, shooting processing performed when shooting a dark subject with the video camera having the above configuration will be described with reference to a timing chart of FIG.

  The vertical synchronization signal is a signal that outputs a pulse at a cycle T1, and for example, an NTSC standard signal repeatedly outputs a pulse at a 1/60 second cycle.

“Charge accumulation” indicates a state in which charges are accumulated in the image sensor 102. In the first embodiment, charge accumulation and image signal reading in the image sensor 102 are performed every vertical period T1 (1/60 seconds). Therefore, the accumulated charges 11 to 14 are read from the image sensor 102 at the read timings t ₁₂ , t ₁₃ , t ₁₄ , and t ₁₅ synchronized with the vertical synchronization signal by the drive control signal input from the timing generator 111. In the first embodiment, the image signal read in the cycle T1 (hereinafter, the same reference number is also used for the image signals corresponding to the charges 11 to 14) is accumulated four times, so that the cycle T2. Assume that one piece of image data for a moving image is generated. In this case, the selector 105 selects the frame memory 104 when the count output from the image accumulation counter 109 indicates 1 to 3 times of photographing, and selects the camera signal processing circuit 107 at the fourth time. Operate.

The image signal 11 accumulated from t ₁₁ and read out from the image sensor 102 at t ₁₂ is input to the image composition circuit 103. Since this image signal 11 is the first image at the time of composition, it is accumulated. It is recorded in the frame memory 104 without performing arithmetic processing. Next, the image signal 12 accumulated from t ₁₂ and read out at t ₁₃ is input to the image synthesis circuit 103, synthesized with the image signal 11 recorded in the frame memory 104 by accumulation processing, and again stored in the frame memory. 104.

Next, the image signal 13 accumulated from t ₁₃ and read out at t ₁₄ is input to the image composition circuit 103, accumulated with the image signal 11 + 12 recorded in the frame memory 104, and again stored in the frame memory 104. To be recorded. In this way, three image signals read out in the period T2 are recorded in the frame memory 104 by the accumulation process. In this state, the image accumulation counter 109 that counts the number of times of reading from the image sensor 102 indicates the third number of times of photographing. When the image signal 13 is accumulated and recorded in the frame memory 104, the AF evaluation value detection circuit 106 is notified of the third shooting as an evaluation value extraction timing. AF evaluation value detection circuit 106 at t _14, for detecting the AF evaluation value from the image signal 11 + 12 + 13 recorded in the frame memory 104 in accordance with the evaluation value extraction timing. Further, the control amount of the lens unit 101 is obtained based on the AF evaluation value at the lens control timing, and is output to the lens control circuit 112. The lens control circuit 112 controls the lens unit 101 based on this control amount and adjusts the focus so as to focus on the subject. During the process the t ₁₄ ~t ₁₅ so far, performed or 4 piece of the image within the time the exposure of the.

Further, the image signal 14 accumulated from t ₁₄ and read out at t ₁₅ is accumulated in the image synthesis circuit 103 with the image signal 11 + 12 + 13 recorded in the frame memory 104. Here, the image accumulation counter 109 that counts the number of times of reading from the image sensor 102 indicates the fourth number of times of shooting, and outputs to the selector 105 that it is the fourth time of shooting as a composite output timing. The selector 105 switches the output destination of the image composition circuit 103 to the camera signal processing circuit 107 in accordance with the composition output timing. As a result, the combined output 16 obtained by accumulating the image signals 11 to 14 is output to the camera signal processing circuit 107 without being recorded in the frame memory 104.

  Next, the operation from the reading of the image signal from the image sensor 102 to the output to the camera signal processing circuit 107 in the video camera of the first embodiment will be described with reference to the flowchart of FIG. Note that, in this flowchart, as in the timing chart of FIG. 2, an image signal read from the image sensor 102 is accumulated four times to generate one image signal for a moving image.

  When shooting is instructed by operating a shooting button (not shown), shooting processing is started. First, in step S11, the control unit 110 resets the value of the image accumulation counter, that is, the number N of image signal readouts, to zero. Next, in step S <b> 12, the number N of image signal readouts is increased by 1, and the process proceeds to step S <b> 13 to read out image signals from the image sensor 102. In step S <b> 14, the image signal recorded in the frame memory 104 and the image signal read from the image sensor 102 are accumulated. In step S15, it is determined whether or not the read count N is four. Here, when the number of times of reading N is 4, it is determined that it is the output timing of the synthesized output subjected to accumulation processing, and the process proceeds to step S16. On the other hand, if the number of readings N is not 4, it is determined that it is not the output timing of the combined output, and the process proceeds to step S18.

  In step S18, the accumulated image signal is recorded in the frame memory 104, and in step S19, it is determined whether or not the read count N is 3. If the number of readings N is 3, it is determined that it is the AF evaluation value acquisition timing, and the process proceeds to step S20. On the other hand, if the number of times of reading N is not 3, it is determined that it is not the timing for acquiring the AF evaluation value, and the process returns to step S12.

  In step S20, an AF evaluation value is acquired from the image signal recorded in the frame memory 104. In step S21, a lens control amount is determined from the obtained AF evaluation value, and the lens control circuit 112 controls the lens unit 101. To start.

  On the other hand, when it is determined in step S15 that the number N of readings is 4, in step S16, the accumulated image signal is output to the camera signal processing circuit 107. In step S17, it is determined whether or not shooting has been completed. If it is determined that the shooting has been completed, the process ends. On the other hand, when it is determined that the photographing has not ended, the process returns to step S11.

  As described above, according to the first embodiment, since the AF control image is based on the image signals for three images, focus control is performed while the fourth image signal is being accumulated. Is possible. Thereby, in each image for moving images obtained by accumulation, it is possible to acquire an image that is best focused at the beginning of the exposure time.

  In the first embodiment, the case has been described where four image signals obtained in each vertical period are accumulated and one image is acquired. The number of sheets is not limited to four, and can be appropriately changed according to the brightness of the subject. Further, although the timing for detecting the AF evaluation value is the time when the image for three images is accumulated, this is not limited to three, but before the start of the next image to be synthesized by the accumulation processing. Any timing may be used as long as the lens control ends.

  In the above description, the case where the image signal accumulation processing is performed in the configuration of the video camera shown in FIG. 1 (that is, the subject is dark) has been described. On the other hand, when the subject is sufficiently bright, it is not necessary to perform accumulation processing, so the image accumulation counter 109 outputs an AF image synthesis timing signal and a recorded image synthesis timing signal in synchronization with each vertical period. Thereby, the selector 105 always selects the camera signal processing circuit 107, and the AF evaluation value detection circuit 106 calculates the AF evaluation value for each vertical period, and the lens unit 101 is controlled. In this case, although not shown, the AF evaluation value detection circuit 106 acquires an image signal via the image sensor 102 or the image synthesis circuit 103 without passing through the frame memory 104.

<Second Embodiment>
Next, a second embodiment of the present invention will be described.

  FIG. 4 is a block diagram showing a schematic configuration of a video camera according to the second embodiment of the present invention. In FIG. 4, the same reference numerals are given to the same components as those in FIG.

  In FIG. 4, reference numeral 101 denotes a lens unit that can be attached to and detached from a video camera constituting a part of the optical system, and includes a lens group including a single lens or a plurality of lenses. The light transmitted through the lens unit 101 enters the image sensor 102 and is converted into an electric signal. The image sensor 102 is an image sensor typified by a CCD sensor, a CMOS sensor, or the like. The image sensor 102 is exposed for a predetermined time based on a drive control signal input from the timing generator 111, and an electrical signal (image signal) corresponding to the amount of received light. Is output. The timing generator 111 is controlled by a timing control unit 405 including a timing control circuit 108 and an image synthesis timing switch 404, and outputs a drive control signal in accordance with a control signal output from the timing control circuit 108. The image composition timing switcher 404 is also controlled by a control signal output from the timing control circuit 108, and synchronizes with the number of image signal readout times of the image sensor 102 driven by the timing generator 111, thereby adjusting the image composition timing. Output.

  Image signals read from the image sensor 102 are sequentially recorded in the frame memory 104. Reference numeral 403 denotes an image composition unit including a recorded image composition circuit 401 and an AF image composition circuit 402. The image composition unit 403 reads image data recorded from the frame memory 104, and each of the recorded image composition circuit 401 and the AF image composition circuit 402 outputs image data. Perform the accumulation process. The recorded image composition circuit 401 and the AF image composition circuit 402 each output the accumulated image data in accordance with the later-described timing output from the image composition timing switcher 404.

  The AF evaluation value detection circuit 106 detects the AF evaluation value from the image data accumulated in the AF image synthesis circuit 402, and further determines the control amount of the lens unit 101 based on the obtained AF evaluation value. Output to the control circuit 112. The lens control circuit 112 drives the lens unit 101 based on the control amount determined by the AF evaluation value detection circuit 106 to control the subject to be focused.

  The camera signal processing circuit 107 performs predetermined image processing on the image data output from the recorded image combining circuit 401 at a timing based on the control signal output from the image combining timing switch 404, and converts the image data into image data. The data is output to a recording circuit (not shown) or a display device.

  Next, shooting processing performed when shooting a dark subject with the video camera having the above configuration will be described with reference to a timing chart of FIG.

  The vertical synchronization signal is a signal that outputs a pulse at a cycle T1, and for example, an NTSC standard signal repeatedly outputs a pulse at a 1/60 second cycle.

“Charge accumulation” indicates a state in which charges are accumulated in the image sensor 102. Similar to the first embodiment, in the second embodiment, charge accumulation and image signal reading are performed in the image sensor 102 every vertical period T1 (1/60 seconds). Accordingly, the stored charges 21 to ₂₆ are imaged at the read timings t ₂₁ , t ₂₂ , t ₂₃ , t ₂₄ , t ₂₅ , t ₂₆ synchronized with the vertical synchronization signal by the drive control signal input from the timing generator 111. 102. In the second embodiment, an image signal (hereinafter, the same reference number is also used for image signals corresponding to the charges 21 to 26) read out in the period T2 of the vertical synchronization signal is accumulated four times. Assume that one piece of moving image data is generated in a cycle T2.

Accumulated during T1, the image signal 21 read out from the image sensor 102 at t ₂₁ is gradually recorded sequentially in the frame memory 101. The AF image composition circuit 401 starts an accumulation process of image signals in accordance with the AF image composition timing output from the image composition timing switch 404 at t ₂₁ . Then, the image signals 22 to 25 read at the respective timings t ₂₂ , t ₂₃ , t ₂₄ and t ₂₅ are accumulated. At t ₂₅ , an AF evaluation value is detected from the image signals 22 + 23 + 24 + 25 accumulated so far, a control amount of the lens unit 101 is determined based on the detected AF evaluation value, and is output to the lens control circuit 112. The lens control circuit 112 controls the lens unit 101 based on this control amount, and adjusts the focus so that the subject is in focus. Performing processing so far between t ₂₄ ~t _25, ie, from within the time the exposure of the 4 th image in the imaging time T2.

Further, the recorded image synthesizing circuit 401 reads the image data from the frame memory 104 according to the recording image synthesizing timing signal output from the image synthesizing timing switch 404 at t _22, it starts an accumulation processing of the image data. Then, the image signals 23 to 26 read at the respective timings t ₂₃ , t ₂₄ , t ₂₅ and t ₂₆ are accumulated. At t ₂₆ , the image signal 23 + 24 + 25 + 26 accumulated so far is output to the camera signal processing circuit 107.

As can be seen from the timing chart of FIG. 5, while the image for detecting the AF evaluation value is accumulated processing time T3 of t ₂₅ from the timing t _21, the image for recording in the time T4 of t ₂₆ from t ₂₂ Obtained by accumulating.

  Next, the operation from the reading of the image signal from the image sensor 102 to the output to the camera signal processing circuit 107 in the video camera of the second embodiment will be described with reference to the flowchart of FIG. In this flowchart, as in the timing chart of FIG. 5, an image signal read from the image sensor 102 is accumulated four times to generate one image signal for a moving image.

  When shooting is instructed by operating a shooting button (not shown), shooting processing is started. First, in step S31, an image signal is read from the image sensor 102, and the image signal read in step S32 is stored in the frame memory 104. Next, in step S33, the AF image composition circuit 402 reads out image data from the frame memory 104 and performs accumulation processing. In step S34, the recorded image composition circuit 401 also reads out image signals from the frame memory 104 and performs accumulation processing. .

  In step S35, it is determined whether or not the AF evaluation value detection timing is ON. If the AF evaluation value detection timing is ON, the process proceeds to step S36 to detect the AF evaluation value from the image signal accumulated by the AF image synthesis circuit 402, and from the AF evaluation value detected in step S37. The lens control amount is determined, and the lens control circuit 112 starts controlling the lens unit 101. When the control of the lens unit 101 ends, the process proceeds to step S38.

  If the AF evaluation value detection timing is not ON in step S35, the process proceeds directly to step S38.

  In step S38, it is determined whether the recording image output timing has been turned ON. If the recording image output timing is ON, the process proceeds to step S39. On the other hand, if the recording image output timing is not ON, it is determined that it is not the timing for outputting the composite image, and the process returns to step S31 to repeat the above control.

  In step S 39, the accumulated image signal is output to the camera signal processing circuit 107. In the next step S40, it is determined whether or not shooting has been completed. If it is determined that shooting has not ended, the process returns to step S31 and the above processing is repeated. If it is determined that shooting has ended, shooting processing is performed. Exit.

  As described above, according to the second embodiment, the fourth image signal of the recording image is accumulated by shifting the image to be accumulated between the AF control image and the recording image. In-focus control can be performed during the time. Thereby, in each image for moving images obtained by accumulation, it is possible to acquire an image that is best focused at the beginning of the exposure time.

In the second embodiment, the accumulation process of the AF control image is shifted earlier than the accumulation process of the recording image for one vertical period. However, the present invention is not limited to this. It is not a thing. With respect to each moving image obtained by accumulation, it is possible to change the shift amount so as to obtain an image that is best focused on a desired time within the entire exposure time of each image .

  In the second embodiment, the case where four image signals obtained in each vertical period are accumulated to obtain one image has been described. The number of sheets is not limited to four, and can be appropriately changed according to the brightness of the subject.

  In the above description, the case where the image signal accumulation process is performed in the configuration of the video camera shown in FIG. 4 (that is, the subject is dark) has been described. On the other hand, when the subject is sufficiently bright, there is no need to perform accumulation processing. Therefore, the image composition timing switching unit 404 synchronizes the recorded image composition circuit 401 and the AF image composition in synchronization with the vertical synchronization signal for each vertical period. A control signal is output to the circuit 402. The control signal is an AF image synthesis timing signal, a recorded image synthesis timing signal, an evaluation value detection timing signal, and a recorded image output timing signal. As a result, the recorded image composition circuit 401 and the AF image composition circuit output the image signal read from the frame memory 104 to the camera signal processing circuit 107 and the AF evaluation value detection circuit 106 for each vertical period.

1 is a block diagram illustrating a schematic configuration of a video camera according to a first embodiment of the present invention. 6 is a timing chart illustrating shooting processing timing performed when shooting a dark subject with the video camera according to the first embodiment of the present invention. It is a flowchart which shows the imaging | photography process performed when image | photographing the dark to-be-photographed object of the video camera in the 1st Embodiment of this invention. It is a block diagram which shows schematic structure of the video camera in the 2nd Embodiment of this invention. It is a timing chart which shows the imaging | photography process timing performed when imaging | photography a dark subject with the video camera in the 2nd Embodiment of this invention. It is a flowchart which shows the imaging | photography process performed when image | photographing the dark to-be-photographed object of the video camera in the 2nd Embodiment of this invention. It is a timing chart which shows the imaging | photography process timing in the slow shutter mode in the conventional video camera.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Lens 102 Image pick-up element 103 Image composition circuit 104 Frame memory 105 Selector 106 AF evaluation value detection circuit 107 Camera signal processing circuit 108 Timing control circuit 109 Image accumulation counter 110 Control part 111 Timing generator 112 Lens control circuit 401 Recording image composition circuit 402 AF Image composition circuit 403 Image composition unit 404 Image composition timing switch 405 Timing control unit

Claims (4)

An image sensor that photoelectrically converts an incident subject optical image and outputs an image signal;
Drive control means for controlling the image sensor to output an image signal at a preset first period;
Synthesizing means for sequentially accumulating and synthesizing image signals output from the image sensor in the first period;
The image signal synthesized by the synthesizing unit is output for recording in a second cycle obtained by multiplying the first cycle by an integer, and the image signal synthesized by the synthesizing unit in the middle of the second cycle is output. Control means for controlling to output for focus detection;
An image pickup apparatus comprising: a focus adjustment unit that performs a focus adjustment process based on the image signal for focus detection between the middle of the second cycle and the end of the second cycle. Said control means equal the second period and the period, and, the third period of the image signal synthesized in a desired time said first et different integer multiples phase of the periodic allowed to be output in imaging apparatus according to claim 1, wherein the output to Turkey the image signal for the focus detection. The synthesizing unit includes a first image synthesizing unit and a second image synthesizing unit,
3. The imaging according to claim 2, wherein the control unit controls the first image synthesizing unit in the second cycle, and controls the second image synthesizing unit in the third cycle. apparatus. A method for controlling an image pickup apparatus having an image pickup device that photoelectrically converts an incident subject optical image and outputs an image signal,
A reading step of reading out an image signal from the image sensor at a preset first period;
A synthesis step of sequentially accumulating and synthesizing image signals output from the image sensor in the first period;
A first output step of outputting the image signal synthesized in the synthesis step for recording in a second cycle obtained by multiplying the first cycle by an integer;
A second output step of outputting the image signal synthesized in the synthesis step in the middle of the second period for focus detection;
A focus adjustment step of performing a focus adjustment process on the basis of the image signal for focus detection between the middle of the second cycle and the end of the second cycle.

Images