JP2014075644A - Imaging element and driving method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent deterioration of dynamic resolution and a drop of an S/N ratio, which occur when a driving method of an imaging element is changed from a regular shutter mode to a draft slow shutter mode.SOLUTION: In a driving method of an imaging element where a plurality of pixels are two-dimensionally arranged, the imaging element can be driven with first driving (t1 to t2) for controlling accumulation and reading of charge signals of the plurality of pixels at a previously determined period, second driving (t3 and thereafter) for controlling the accumulation and reading of the charge signals of the plurality of pixels divided into a plurality of regions at the plurality of periods of the period by shifting one period for each region, and third driving (t2 to t4) for sequentially controlling the accumulation and reading of the charge signals of the plurality of pixels divided into the plurality of regions at the period for each region. When the first driving is changed to the second driving, the third driving is performed for at least a period shorter than the plurality of periods by one period. The number of regions is equal to that of the plurality of periods.

Description

  The present invention relates to an image pickup element in an image pickup apparatus and a driving method thereof.

  Conventionally, in an imaging apparatus such as a video camera, the shutter mode for controlling the exposure time includes a normal shutter mode for controlling the exposure time with a time of one field or less and a slow shutter for controlling the exposure time with a time of one field or more. There is a mode. In the normal shutter mode, the update timing of one field is every 1/60 seconds in the NTSC system and every 1/50 seconds in the PAL system. However, in the slow shutter mode, exposure for one field period or more is performed, and accordingly, the update timing is also delayed. For example, when the shutter speed is one field period or more and two field periods or less, the update timing is every 1/30 seconds in the NTSC system and every 1/25 seconds in the PAL system. For this reason, when shooting in the slow shutter mode, an image with an unnatural motion with a reduced dynamic resolution is generated as compared with the normal shutter mode.

  In order to improve this, the odd line and the even line are exposed at different timings, and the draft can be updated at the same timing as the normal shutter mode while ensuring an exposure time of one field period or more. There is a slow shutter mode. In the draft slow shutter mode, the odd-numbered lines start accumulating in the first field and read out the electric charges accumulated in the second field. Then, accumulation is started again in the third field, and electric charges are read out in the fourth field. In the even-numbered line, accumulation is started in the second field, and the charge accumulated in the third field is read out. Then, accumulation is started again in the fourth field, and electric charges are read out in the fifth field. In this way, it is possible to secure an exposure time of 1 field or more and 2 fields or less, and even-numbered lines and odd-numbered lines can be read alternately every field. The draft slow shutter mode is an effective technique because it does not involve deterioration in vertical resolution, particularly in an imaging apparatus that outputs video in an interlaced manner.

  However, the draft slow shutter mode has the following problems. That is, the field image can be updated every time as described above, but when shifting from the normal shutter mode to the draft slow shutter mode, one field at the time of switching cannot secure a sufficient exposure time, The video cannot be updated.

  FIG. 6 shows an example of a case where the video cannot be updated. FIG. 6 is a diagram showing the accumulation timing when switching from the 1/60 second normal shutter mode to the 1/30 second draft slow shutter mode.

  In FIG. 6, accumulation starts at time t1, readout starts at time t2, and an image is output at time t3. In the next cycle, as in the previous cycle, accumulation starts at time t2, readout starts at time t3, and an image is output at time t4. To be precise, the reading of charges starts slightly earlier than the next accumulation start time, and the next accumulation is started by sequentially ending the reset performed after the reading.

  When entering the draft slow shutter mode at time t3, accumulation of odd lines starts at time t3, reading starts at time t5, and an image of odd lines is output at time t6. For even lines, accumulation starts at time t4, readout starts at time t6, and an image of odd lines is output at time t7. As described above, data is not output in a cycle starting from time t5 when the normal shutter mode is shifted to the draft slow shutter mode, and thus discontinuity occurs in the video.

  Several methods have been proposed to avoid this problem. For example, in a field where a sufficient exposure time cannot be secured, there is a method of using an image obtained in the immediately preceding field as it is. In this method, it is only necessary to store the immediately preceding video, and no complicated processing is required. As another technique, there is a technique disclosed in Patent Document 1. In this method, when an ideal accumulation time is not obtained in one field at the time of switching, gain correction is performed on data obtained by the ratio of the actual accumulation time and the ideal accumulation time. It is. In this way, it is possible to update each field image while maintaining a sufficient exposure time even when shifting from the normal shutter mode to the draft slow shutter mode.

JP 2007-228433 A

  However, the above conventional example has the following problems. First, when sufficient exposure time is not obtained in the switching field, if the video obtained in the previous field is used as it is, the same video is output continuously for 2 fields, so the video seems to stop for a moment. It seemed to be. In the method of Patent Document 1, when gain correction is performed, not only a signal component to be corrected but also a noise component is amplified at the same time, so that S / N is higher than a video obtained by performing normal accumulation. The ratio gets worse.

  The present invention has been made in view of the above problems, and prevents degradation of dynamic resolution and S / N ratio that occur when the driving method of the image sensor is switched from the normal shutter mode to the draft slow shutter mode. With the goal.

  In order to achieve the above object, the driving method of the present invention for an image pickup device in which a plurality of pixels are arranged two-dimensionally performs a charge signal accumulation and readout control of the plurality of pixels at a predetermined cycle. A second driving for performing charge signal accumulation and readout control of the plurality of pixels divided into a plurality of regions in a plurality of cycles of the cycle while shifting each cycle by one cycle; and the cycle Thus, the image sensor can be driven by a third drive that sequentially performs charge signal accumulation and readout control of the plurality of pixels divided into the plurality of regions for each region. When changing from driving to the second driving, it has a switching step of performing the third driving for a period that is at least one cycle shorter than the plurality of cycles, and the number of the plurality of regions is the number of the plurality of cycles. Is equal to

  According to the present invention, it is possible to prevent deterioration in dynamic resolution and a decrease in S / N ratio that occur when the driving method of the image sensor is switched from the normal shutter mode to the draft slow shutter mode.

1 is a block diagram of an imaging apparatus according to an embodiment of the present invention. The figure which shows the color filter array of the image pick-up element in one Embodiment of this invention. FIG. 3 is a diagram illustrating drive timing of the image sensor according to the first embodiment. The figure showing the drive timing of the image sensor in a 2nd embodiment. The figure showing the drive timing of the image sensor in a 3rd embodiment. The figure showing the drive timing of the image sensor in a prior art.

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

  FIG. 1 is a block diagram showing a configuration of a video camera (imaging device) according to an embodiment of the present invention. The type of the imaging apparatus of the present invention is not limited as long as it is a camera having a draft slow shutter mode.

  In FIG. 1, a lens (photographing optical system) 101 forms an optical image of a subject and moves in the optical axis direction during zooming and a zoom lens that moves in the optical axis direction during zooming. Including a focus lens. In addition, the lens 101 includes an aperture and an ND filter that control the amount of incident light.

  The image sensor 102 is configured by a CCD, a CMOS sensor, or the like that includes a plurality of two-dimensionally arranged pixels that photoelectrically convert an optical image formed by the lens 101 into a charge signal. The video signal processing unit 103 converts the charge signal generated by the image sensor 102 into a video signal having a predetermined format. The video signal processing unit 103 can process a progressive signal at the input, and uses a signal input to image processing such as calculation of a position vector for image stabilization and an NR filter. On the other hand, the video signal processing unit 103 converts the input signal into an interlaced signal and outputs it. For this reason, even when the readout of the image sensor 102 is switched from the all-line readout to the draft slow shutter, the signal output from the video signal processing unit 103 is always an interlaced signal before and after the switching. For this reason, the vertical resolution does not drop in the output.

  The overall control calculation unit 104 controls the entire video camera. The timing control unit 105 controls the operation timing of the image sensor 102 and the video signal processing unit 103. The timing control unit 105 receives a signal from the overall control calculation unit 104, transmits the drive timing to the image sensor 102, and transmits the video signal synchronization timing to the video signal processing unit 103. The lens control unit 106 controls the lens 101. The overall control calculation unit 104 calculates an appropriate exposure amount from the output signal of the video signal processing unit 103, the aperture and ND filter inside the lens 101, the shutter speed of the image sensor 102, and the video signal processing unit 103. Controls the gain value applied with. The shutter speed here is the exposure time of the electronic shutter, and the overall control calculation unit 104 sends the charge accumulation start timing and the charge read start timing to the image sensor 102 via the timing control unit 105. Control.

  The memory unit 107 temporarily stores the calculation result of the overall control calculation unit 104 and the output signal of the video signal processing unit 103. The recording medium 109 is a DVD, a hard disk, a nonvolatile memory, or the like. The recording medium control I / F unit 108 controls data input / output with the recording medium 109. The external I / F unit 110 can output the captured video to an external monitor or recorder, and can input the video from another video camera or playback device. Alternatively, it is possible to connect to a computer via the external I / F unit 110 and acquire necessary information via the computer and the Internet.

  FIG. 2 is a diagram showing a color filter array in the image sensor 102 of FIG. Here, a Bayer array is used as an example of the pixel array. R (red) is arranged as the first pixel, green (G) is arranged as the second pixel, green (G) is arranged as the third pixel, and (B) is arranged as the fourth pixel. In the present embodiment, as shown in FIG. 2, the number of vertical lines (number of rows) and the number of horizontal columns are determined by taking the first pixel to the fourth pixel as a set.

<First Embodiment>
In the first embodiment, when the shutter speed is changed from 1/60 seconds (one cycle of a predetermined cycle) to 1/30 seconds (two cycles), the all-line readout mode is changed to the draft slow shutter mode. An example of switching the sensor driving method is described below.

  FIG. 3 is a conceptual diagram showing the drive timing of the image sensor 102 in the first embodiment. In FIG. 3, from time t1 to time t2, an all-line readout mode with shutter speed 1/60 seconds (first driving), and from time t2 to time t4, a draft slow shutter mode with shutter speed 1/60 seconds (third). ) To drive the image sensor 102. After time t3, the image sensor 102 is driven in a draft slow shutter mode (second drive) with a shutter speed of 1/30 seconds (multiple cycles).

  Accumulation of all lines is started at time t1, and reading of all lines is started at time t2. To be precise, the reading of charges starts slightly earlier than the next accumulation start time, and the next accumulation is started by sequentially ending the reset performed after the reading. The same applies to the following charge readout and reset timings.

  Further, at time t2, accumulation is started only for odd lines (first region), and reading of the odd lines is started at time t3. Next, at time t3, accumulation of odd lines (first area) and even lines (second area) is started, and only even lines are read at time t4, and odd lines are read at time t5. Do.

  At time t4, only the even lines are accumulated, and at time t6, the even lines are read. After time t5, assuming that n is a natural number, accumulation of odd lines starts at time t (2n-1) and starts reading at time t (2n + 1). For even lines, accumulation starts at time t (2n), and reading is performed at time t (2n + 2).

  As the video output signal, the charge accumulated from time t1 to t2 in the all-line readout mode is output at time t3. In addition, the odd-numbered line charges accumulated from time t2 to t3 in the draft slow shutter mode with a shutter speed of 1/60 seconds are output at time t4, and the even-line charges accumulated from time t3 to t4 are time t5. Is output. Further, the odd-numbered line charges accumulated from time t3 to t5 in the draft slow shutter mode with a shutter speed of 1/30 seconds are output at time t6, and the even-line charges accumulated from time t4 to t6 are time t7. Is output.

  According to the first embodiment, by performing the drive control as described above, the data from the image sensor is not interrupted when the mode is switched, and the continuity of the video can be maintained.

<Second Embodiment>
In the second embodiment, a description will be given of a case where only even-numbered lines during one cycle at the time of switching are driving control in the draft slow shutter mode with a shutter speed of 1/60 seconds in the switching of the reading mode.

  FIG. 4 is a conceptual diagram showing the drive timing of the image sensor 102 in the second embodiment. In FIG. 4, the control from time t1 to time t2 and after time t3 is the same as that in the first embodiment, and thus the description thereof is omitted. In the second embodiment, unlike the first embodiment, at time t2, accumulation of odd lines (first region) is started and accumulation of even lines (second region) is also started. At time t3, the odd lines are read and the even lines are read. In this way, in the first embodiment, the data output at time t4 is data for only odd lines, whereas in the second embodiment, data for all lines is output at time t4. Therefore, data for all lines is displayed until immediately before switching. That is, until just before switching, it is possible to more accurately perform processing such as image stabilization and image quality correction using data of all lines.

<Third Embodiment>
In the third embodiment, a description will be given of a case where only odd lines in one cycle at the time of switching are driving control in the draft slow shutter mode with a shutter speed of 1/60 seconds in the switching of the reading mode.

  FIG. 5 is a conceptual diagram showing the accumulation timing of the sensor in the third embodiment. Regarding the accumulation timing in FIG. 5, the processing from time t <b> 1 to time t <b> 2 and after time t <b> 4 is the same as that in the first embodiment, and thus description thereof is omitted. At time t2, accumulation of odd lines is started and accumulation of even lines is also started. At time t3, only odd lines are read out. Further, accumulation of only odd lines (first region) is started at time t3, and reading of only even lines is performed at time t4. In this way, in the first embodiment, the data output at time t5 (the data read at time t4) was for the shutter speed 1/60 second, whereas the third embodiment In the embodiment, data at a shutter speed of 1/30 seconds can be output at time t5. That is, the shutter speed can be changed one cycle earlier, and the response to the change in luminance of the subject is completed quickly.

  In the first to third embodiments described above, the example of switching from the shutter speed 1/60 seconds to the shutter speed 1/30 seconds has been described, but the shutter speed is not limited to this value. The present invention can be applied to switching from an arbitrary shutter speed of one cycle or less to an arbitrary shutter speed of one cycle or more. For example, if you switch from 1/60 second shutter speed to 1/60 second draft mode and switch to 1/59 second draft mode, stable switching with little change in brightness is possible. is there. Also, if the shutter mode is 1/120 seconds, the draft mode with shutter speed 1/60 seconds is sandwiched in one cycle, and the mode is switched to the draft mode with shutter speed 1/30 seconds. Switching is possible.

  Further, in the above-described example, one cycle at the time of switching is set to 1/60 seconds of shutter speed, but may be set to any value as long as it is 1/60 seconds or less. In addition, the draft mode of 1/60 second or less at the time of switching is not limited to one cycle, and may be continued for a plurality of cycles.

  In the above embodiment, the case where the shutter speed after switching is one cycle or more and less than two cycles has been described. However, the present invention is not limited to this, and can be applied to a case where the shutter speed is two cycles or more. It is. For example, in the case of two cycles or more and less than three cycles, the image sensor 102 is read every two lines in each cycle, and at the time of switching, a draft having a shutter speed of one cycle for at least two cycles shorter than three cycles Read in mode.

  Although the present invention has been described in detail based on preferred embodiments thereof, the present invention is not limited to these specific embodiments, and various forms within the scope of the present invention are also included in the present invention. included. A part of the above-described embodiments may be appropriately combined.

Claims (10)

A method for driving an image sensor in which a plurality of pixels are two-dimensionally arranged,
A first drive for performing charge signal accumulation and readout control of the plurality of pixels at a predetermined cycle;
A second drive for performing charge signal accumulation and readout control of the plurality of pixels divided into a plurality of regions in a plurality of cycles while shifting each cycle by one cycle;
In the cycle, the image sensor can be driven by a third drive that sequentially performs charge signal accumulation and readout control of the plurality of pixels divided into the plurality of regions for each region,
When the control unit changes from the first drive to the second drive, the control unit includes a switching step of performing the third drive for a period shorter by at least one cycle than the plurality of cycles,
The number of the plurality of regions is equal to the number of the plurality of periods.   2. The image sensor driving method according to claim 1, wherein the number of the plurality of periods is a number of periods necessary for accumulating charges in the plurality of pixels for a predetermined time. The plurality of cycles are two cycles, and the plurality of pixels are divided into a first region and a second region, and the switching step includes a first drive that drives the first region by the third drive. Steps,
And a second step of driving the second region by the third drive and driving the first region by the second drive after the first step. The method for driving an image sensor according to claim 1. The plurality of cycles are two cycles, and the plurality of pixels are divided into a first region and a second region,
3. The imaging device according to claim 1, wherein, in the switching step, the first area is driven by the second drive, and the second area is driven by the third drive. 4. Driving method. The plurality of cycles are two cycles, and the plurality of pixels are divided into a first region and a second region,
3. The imaging device according to claim 1, wherein in the switching step, the first region is driven by the third drive, and the second region is driven by the second drive. 4. Driving method. A plurality of pixels arranged two-dimensionally;
A first drive that performs charge signal accumulation and readout control of the plurality of pixels at a predetermined period, and accumulation of charge signals of the plurality of pixels divided into a plurality of regions at the plurality of periods. And the second drive, which is performed while shifting the readout control by one period for each region, and the charge signal accumulation and readout control of the plurality of pixels divided into the plurality of regions in the cycle are sequentially performed for each region. Driving means for driving the plurality of pixels by performing third driving;
Control means for controlling to perform the third drive for at least one period shorter than the plurality of periods when changing from the first drive to the second drive;
The number of the plurality of regions is equal to the number of the plurality of periods.   The imaging device according to claim 6, wherein the number of the plurality of periods is a number of periods necessary for accumulating charges in the plurality of pixels for a predetermined time. The plurality of cycles are two cycles, and the plurality of pixels are divided into a first region and a second region,
When the control unit changes from the first drive to the second drive, the control unit drives the first region by the third drive, and then drives the second region by the third drive. The image pickup device according to claim 6, wherein the imaging device is driven and the first region is driven by the second drive. The plurality of cycles are two cycles, and the plurality of pixels are divided into a first region and a second region,
The control means drives the first region by the second drive and changes the second region by the third drive when changing from the first drive to the second drive. The image pickup device according to claim 6, wherein the image pickup device is driven. The plurality of cycles are two cycles, and the plurality of pixels are divided into a first region and a second region,
The control means drives the first region by the third drive and changes the second region by the second drive when changing from the first drive to the second drive. The image pickup device according to claim 6, wherein the image pickup device is driven.

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