JP2018133685A - Imaging device, control method of the same, control program, and imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce influence of FPN corresponding to high pixelation without increasing the circuit scale and processing load.SOLUTION: The imaging device includes: a first pixel region 103 for obtaining a predetermined reference signal; a second pixel region 102 shielded from light; and a third pixel region 101 for obtaining an image signal corresponding to an optical image. When a vertical scanning circuit 104 reads out and controls the first to third pixel regions, the vertical scanning circuit reads an image signal from the third pixel region and selectively reads an output of the first pixel region and an output of the second pixel region as a read signal. A correction circuit 108 performs a predetermined offset correction on the image signal on the basis of the read signal.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image pickup device, a control method thereof, a control program, and an image pickup apparatus, and more particularly to drive control of an image pickup device such as a CMOS image sensor.

  In recent years, in an imaging device such as a digital video camera, the number of pixels that can be recorded has increased. The increase in the number of pixels is closely related to the standard of a monitor that displays an image recorded in an imaging device. For example, when the monitor standard shifts from the SD (Standard Definition) standard to the HD (High Definition) standard and a monitor with a higher resolution appears in the future, the number of pixels further increases.

  The resolution in the HD standard is mainly 1920 pixels in the horizontal direction and 1080 pixels in the vertical direction (hereinafter referred to as 1920 × 1080). On the other hand, the resolution in the next-generation monitor called the 4k2k standard is 3840 × 2160 pixels, which is four times as many pixels as the HD standard.

  The standard established in digital cinema is 4096 × 2160 pixels, which has a larger number of pixels than the 4k2k standard. Further, the 8k4k standard is considered as the next generation standard of the 4k2k standard, and the standard has a pixel number of 7680 × 4320 pixels. In a digital cinema corresponding to the 8k4k standard, the horizontal direction is considered to exceed 8k pixels.

  With such changes in monitor standards, it is required to increase the number of pixels that can be recorded even in an imaging apparatus. For example, in order to support a recording pixel in Super Hi-Vision, it is necessary to cope with a lens, an image sensor, an image processing LSI, a video output LSI, and the like corresponding to a high number of pixels.

  On the other hand, in a CMOS image sensor used as an imaging element in an imaging apparatus such as a digital camera, there is fixed pattern noise (fixed-pattern noise) in the vertical direction due to its structure. This FPN includes, for example, vertical line noise (PRNU) due to sensitivity nonuniformity, noise due to dark current nonuniformity (DSNU), and so-called point scratches due to pixel defects. For this reason, the FPN is generally corrected in real time by an image processing LSI or the like provided in the imaging apparatus.

  By the way, when correcting the FPN, OB (optical black) pixels are used. Then, the FPN in the OB pixel is detected and the FPN in the effective pixel region is corrected.

  However, when the pixel signal (that is, the video signal) is acquired from the OB pixel for FPN correction in addition to the increase in the effective pixel area, the amount of information in one frame increases, and the image processing LSI becomes large. In addition, power consumption increases.

  On the other hand, if the number of OB pixels is reduced in order to reduce the amount of information, the number of pixels for FPN correction is reduced. Therefore, the convergence time at the start-up of the imaging apparatus and switching of the column amplifiers is increased due to the influence of random noise and the like.

  In order to suppress the influence of random noise and shorten the convergence time, for example, there is one in which a random noise component is detected and the detection result is reflected in an arithmetic process for FPN correction (see Patent Document 1). Furthermore, there is a method in which OB pixels are read out a plurality of times in units of rows to secure a large area for FPN correction in one frame (see Patent Document 2).

JP 2006-25146 A JP 2013-62859 A

  However, as described in Patent Document 1, when a random noise component is detected, a detection circuit is required for this purpose, which increases the circuit scale and processing load. Furthermore, when detecting a random noise component, a large number of detection pixels are required. In particular, when the imaging apparatus is started and the column amplifier gain is switched, the top frame may be affected by FPN. is there.

  As described in Patent Document 2, when the OB pixel is read out a plurality of times in units of rows, the amount of information at the time of transferring the video signal is inevitably increased, and it may not be possible to increase the number of pixels.

  Accordingly, an object of the present invention is to provide an imaging device, a control method thereof, a control program, and an imaging apparatus capable of reducing the influence of FPN corresponding to the increase in the number of pixels without increasing the circuit scale and processing load. There is to do.

  In order to achieve the above object, an imaging device according to the present invention obtains a first pixel region for obtaining a predetermined reference signal, a shielded second pixel region, and an image signal corresponding to an optical image. An image sensor having a third pixel region, and when reading and controlling the first to third pixel regions, the image signal is read from the third pixel region and the first pixel A readout unit that selectively reads out the output of the region and the output of the second pixel region as a readout signal; and a correction unit that performs a predetermined offset correction on the image signal based on the readout signal. Features.

  According to the present invention, the influence of FPN corresponding to the increase in the number of pixels can be reduced without increasing the circuit scale and processing load.

It is a block diagram which shows the structure about an example of the image pick-up element by embodiment of this invention. It is a figure which shows an example of the pixel structure in the image pick-up element shown in FIG. It is a figure for demonstrating the correction process by the correction circuit shown in FIG. FIG. 2 is a timing diagram for explaining readout control in the image sensor shown in FIG. 1.

  Hereinafter, an example of an image sensor according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing the configuration of an example of an image sensor according to an embodiment of the present invention. The illustrated image sensor is used in, for example, an imaging apparatus such as a digital camera.

  The illustrated image sensor is, for example, a CMOS image sensor. The imaging device includes a pixel area having an effective pixel area 101, an optical black pixel area (OB pixel area) 102, and a dummy pixel area (NULL pixel area) 103. The effective pixel area 101 is an area for outputting an image signal corresponding to an optical image. The OB pixel region 102 is a light-shielded region for offset correction. The NULL pixel area 103 is an area for obtaining a predetermined reference signal.

  Unlike the effective pixel region 101 and the OB region 102, the pixel in the NULL pixel region 103 is not formed with a photodiode (PD) for photoelectric conversion and an FD (floating diffusion) for storing charges. For this reason, the NULL pixel region 103 has fewer pixel defects and random noise components than the effective pixel region 101 and the OB pixel region 102. On the other hand, in the NULL pixel region 103, since there is no dark current component due to PD, there may be a difference in offset level from the effective pixel region 101 and the OB pixel region particularly in a high temperature environment.

  The vertical scanning circuit 104 sequentially reads pixel signals from the effective pixel area 101, the OB pixel area 102, and the NULL pixel area 103 in one frame under the control of a control unit (not shown) provided in the imaging apparatus. Control. In general, readout is sequentially performed in units of rows from the upper row to the lower row in the pixel region.

  The column amplifier (AMP) 105 amplifies pixel signals read from the effective pixel region 101, the OB pixel region 102, and the NULL pixel region 103. By amplifying the pixel signal by the column amplifier 105, the level of the pixel signal against noise generated in the AD circuit 106 is improved, and the S / N is improved equivalently.

  The AD circuit 106 receives the output of the column amplifier 105 and converts the output into a digital signal. That is, the AD circuit 106 converts the pixel signals that are outputs of the effective pixel region 101, the OB pixel region 102, and the NULL pixel region into digital signals.

  The horizontal transfer circuit 107 sequentially reads out digital signals (pixel data) that are output from the AD circuit 106 under the control of a control unit provided in the imaging apparatus. The output of the horizontal transfer circuit 107 is input to the correction circuit 108.

  The correction circuit 108 performs digital signal processing. As described later, the correction circuit 108 performs offset correction such as FPN correction by digital signal processing, and performs simple gain calculation by performing shift calculation and multiplication processing.

  FIG. 2 is a diagram illustrating an example of a pixel configuration in the image sensor illustrated in FIG. 1. The illustrated pixel configuration indicates the configuration of the pixels provided in the effective pixel region 101 and the OB pixel region 102.

  The pixel 200 includes a PD (photoelectric conversion unit) 201, and the PD 201 outputs a charge corresponding to the received light. In the illustrated example, the anode of the PD 201 is grounded, and the cathode thereof is connected to the gate of the amplification MOS transistor 203 via the transfer MOS transistor 202.

  The source of the reset MOS transistor 204 for resetting the amplification MOS transistor 203 is connected to the gate of the amplification MOS transistor 203. The drain of the reset MOS transistor 204 is connected to the power supply voltage Vcc. Further, the drain of the amplification MOS transistor 203 is connected to the power supply voltage Vcc, and the source thereof is connected to the drain of the selection MOS transistor 205.

  An output (pixel signal) of the pixel 200 is output to the column amplifier 105 via the vertical signal line 206. The transfer MOS transistor 202, the reset MOS transistor 204, and the selection MOS transistor 205 are on / off controlled by the vertical scanning circuit 104. That is, the transfer MOS transistor 202 is turned on when the transfer pulse ptx sent from the vertical scanning circuit 104 is high (H) level, and the reset MOS transistor 204 is turned on when the reset pulse pres sent from the vertical scanning circuit 104 is H level. Turn on. The selection MOS transistor 205 is turned on when the selection pulse psel sent from the vertical scanning circuit 104 is at the H level.

  In the imaging device shown in FIG. 1, reading of the effective pixel region 101, the OB pixel region 102, and the NULL pixel region 103 is controlled by timing control by the vertical scanning circuit 104. In the example shown in FIG. 2, FD is not shown, and as described above, the NULL pixel region 103 is not provided with the PD 201 and the FD.

  Here, correction of fixed pattern noise (Fixed-pattern Noise: FPN) in the image sensor shown in FIG. 1 will be described.

  The image sensor shown in FIG. 1 includes a column amplifier 105 and an AD circuit 106 for each column. For this reason, streak noise may occur in the vertical direction of the image due to variations in offset between the column amplifier 105 and the AD circuit 106. In order to correct such streak noise, the above-described correction circuit 108 is used.

  FIG. 3 is a diagram for explaining correction processing by the correction circuit shown in FIG. FIG. 3A is a diagram showing a case where FPN is detected using a NULL pixel area as a correction value calculation area, and FIG. 3B is a diagram showing a case where FPN is detected using an OB pixel area as a correction value calculation area. FIG.

  Here, the FPN component is detected in the OB pixel region 102 or the NULL pixel region 103, and the correction circuit 108 performs FPN correction processing.

  As shown in FIG. 3A, when the correction value for the FPN is obtained using the NULL pixel area 103, since there are few defective pixels and random noise components in the NULL pixel area 103, the correction is performed even if the number of pixels is small. The value can be converged in a short time. On the other hand, since there is no dark current component in the NULL pixel region 103, the black level shifts with respect to the effective pixel region 101. For this reason, when the correction value is obtained using the NULL pixel region 103, the black level in the output image that is the output of the image sensor may not be appropriate.

  As shown in FIG. 3B, when the correction value is obtained using the OB pixel region 102, the defect pixel and the random noise component are larger in the OB pixel region 102 than in the NULL pixel region 103. In order to converge in a short time, a large number of pixels are required.

  Therefore, here, as described later, readout in the OB pixel region 102 and the NULL pixel region 103 is switched. That is, the OB pixel area 102 and the NULL pixel area 103 are selectively read out.

  For example, when the imaging apparatus is started up and the column amplifier gain is switched, the NULL pixel area 103 is read out in order to shorten the convergence time of the correction value for the first frame (first frame). For the second and subsequent frames, the OB pixel area 102 is read out. As a result, the variation of the offset level in the effective pixel region 101 is followed.

  FIG. 4 is a timing chart for explaining readout control in the image sensor shown in FIG. Here, in the (n + 1) th frame (n is an integer equal to or greater than 1), the relationship between the frame and the readout row when readout is switched from the NULL pixel region 103 to the OB pixel region 102 as described above will be described. .

  A NULL / OB switching signal is given to the vertical scanning circuit 104 from a control unit provided in the imaging apparatus. When the NULL / OB switching signal is at a low (L) level, the vertical scanning circuit 104 selects a NULL pixel output. On the other hand, when the NULL / OB switching signal is at the H level, the vertical scanning circuit 104 selects the OB pixel output.

  Since the NULL / OB switching signal is at the L level in the nth frame, the vertical scanning circuit 104 reads out pixels from the NULL pixel region 103 and the effective pixel region 101. The vertical scanning circuit 104 controls the selection MOS transistor 205 to select a reading row. In other words, the vertical scanning circuit 104 first reads pixels from the first row to the Nth row (N is an integer of 2 or more) in the NULL pixel region 103 by sequentially setting the NULL pixel selection signal to the H level. Subsequently, the vertical scanning circuit 104 does not read out the pixels in the OB pixel region 102, and sequentially sets the effective pixel row selection signal to the H level, so that the effective pixel region 101 is in the first to L rows (L is 2 or more). Pixels are read out to an integer.

  Assume that the NULL / OB switching signal becomes H level in the middle of the nth frame. The vertical scanning circuit 104 does not read out pixels from the NULL pixel region 103 after (n + 1) frames. The vertical scanning circuit 104 reads out pixels from the first row to the Mth row (M is an integer of 2 or more) in the OB pixel region 102 by sequentially setting the OB pixel row selection signal to the H level. Subsequently, the vertical scanning circuit 104 sequentially reads the pixels from the first row to the Lth row in the effective pixel region 101 by setting the effective pixel row selection signal to the H level sequentially.

  When such readout control is performed, for n frames, a pixel signal related to a NULL pixel and a pixel signal related to an effective pixel are output to the column amplifier 105. On the other hand, for (n + 1) frames and thereafter, the pixel signal related to the OB pixel and the pixel signal related to the effective pixel are output to the column amplifier 105.

  As a result, the correction circuit 108 can optimize the black level in the output image while converging the correction value in a short time. That is, it is possible to reduce the processing load by reducing the number of pixels used when calculating the correction value, and to reduce the influence of FPN.

  In the above-described example, readout switching of the NULL pixel region 103 and the OB pixel region 102 is performed when the imaging apparatus is activated or when the column amplifier gain is switched. On the other hand, if there is no deviation in the black level in the effective pixel region 101 and the NULL pixel region 103, it is not necessary to switch the readout region. For example, when the black level shifts due to the dark current component when the temperature rises, the temperature at which the black level fluctuates may be detected by the temperature detection sensor, and the reading area may be switched using the temperature as a threshold value. .

  By the way, the following two examples can be given as correction circuits used when correcting the FPN component.

  The first example is an integral type correction circuit (first correction circuit). The integration type correction circuit can obtain a correction value for each frame. However, if the random noise component is large, the calculation accuracy of the correction value may deteriorate.

  The second example is a cyclic correction circuit (second correction circuit). If a cyclic correction circuit is used, correction can be performed without lowering the calculation accuracy even when there is a lot of random noise as a result of taking over the correction value of the past frame. Note that when the cyclic correction circuit is used, the convergence time of the correction value becomes long.

  Therefore, here, the correction circuit is switched according to which of the NULL pixel region 103 and the OB pixel region 102 is read. For example, when the imaging apparatus is activated or when the column amplifier gain is switched, the NULL pixel area 103 is read in the first frame. Since the random noise component is small for the NULL pixel region 103, correction is performed using the first correction circuit. For the second and subsequent frames, the OB pixel area 102 is read out. Since the random noise component is large in the OB pixel region 102, correction is performed using the second correction circuit. At this time, the initial value of the correction value is set as the correction value obtained by the first correction circuit.

  By doing so, the correction value convergence time is shortened, and the correction value calculation accuracy does not decrease.

  Note that the above-described imaging element is used in an imaging apparatus such as a digital camera, for example. The imaging device includes a photographic lens, and an optical image is formed on the imaging element via the photographic lens. Then, the image sensor outputs image data corresponding to the optical image. The image data is recorded on a recording medium or the like after being subjected to predetermined image processing by the image processing unit under the control of the control unit. An image corresponding to the image data is displayed on the display unit under the control of the control unit.

  As mentioned above, although this invention was demonstrated based on embodiment, this invention is not limited to these embodiment, Various forms of the range which does not deviate from the summary of this invention are also contained in this invention. .

  For example, the function of the above embodiment may be used as a control method, and this control method may be executed by the image sensor. Further, the image sensor may be controlled by causing a computer to execute a program having the functions of the above-described embodiments as a control program. The control program is recorded on a computer-readable recording medium, for example.

[Other Embodiments]
The present invention supplies a program that realizes one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and one or more processors in the computer of the system or apparatus read and execute the program This process can be realized. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

DESCRIPTION OF SYMBOLS 101 Effective pixel area 102 Optical black (OB) pixel area 103 Dummy (NULL) pixel area 104 Vertical scanning circuit 105 Column amplifier 106 AD circuit 107 Horizontal transfer circuit 108 Correction circuit 201 Photodiode (PD)
206 Vertical signal line

Claims (10)

An imaging device having a first pixel region for obtaining a predetermined reference signal, a shielded second pixel region, and a third pixel region for obtaining an image signal corresponding to an optical image,
When reading and controlling the first to third pixel areas, the image signal is read from the third pixel area, and the output of the first pixel area and the output of the second pixel area are selectively selected. Reading means for reading out as a read signal;
Correction means for performing a predetermined offset correction on the image signal based on the readout signal;
An image pickup device comprising:   The readout means reads out the output of the first pixel area as the readout signal in the first frame, and outputs the output of the second pixel area after the second frame following the first frame. The image pickup device according to claim 1, wherein the image pickup device is read as the read signal.   The imaging device according to claim 1, wherein the first pixel region is a dummy pixel region in which the pixel does not include a photoelectric conversion unit.   4. The image sensor according to claim 1, wherein the correction unit calculates a correction value for correcting the image signal in accordance with the read signal. 5.   The reading unit switches the output of the first pixel region and the output of the second pixel region when the image sensor is activated or when the gain of an amplifier provided in the image sensor is switched. The imaging device according to claim 1.   2. The imaging according to claim 1, wherein the reading unit switches the output of the first pixel region and the output of the second pixel region with a temperature at which a black level varies depending on a dark current component as a threshold value. element.   When the output of the first pixel region is read by the reading unit, the correcting unit performs offset correction on the image signal using an integral type correction circuit, and the reading unit performs the offset correction. The image pickup device according to claim 1, wherein when the output of the second pixel region is read, an offset correction is performed on the image signal using a cyclic correction circuit. The imaging device according to any one of claims 1 to 7,
A photographic lens for forming an optical image on the image sensor;
Image processing means for performing predetermined image processing on image data output from the image sensor;
An imaging device comprising: A method of controlling an image sensor having a first pixel region for obtaining a predetermined reference signal, a shielded second pixel region, and a third pixel region for obtaining an image signal corresponding to an optical image. There,
When reading and controlling the first to third pixel areas, the image signal is read from the third pixel area, and the output of the first pixel area and the output of the second pixel area are selectively selected. A readout step for reading out as a readout signal;
A correction step for performing a predetermined offset correction on the image signal based on the readout signal;
A control method characterized by comprising: To control an image sensor having a first pixel region for obtaining a predetermined reference signal, a shielded second pixel region, and a third pixel region for obtaining an image signal corresponding to an optical image Control program
On the computer,
When reading and controlling the first to third pixel areas, the image signal is read from the third pixel area, and the output of the first pixel area and the output of the second pixel area are selectively selected. A readout step for reading out as a readout signal;
A correction step for performing a predetermined offset correction on the image signal based on the readout signal;
A control program characterized by causing

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