JP6071323B2 - Imaging device, control method thereof, and control program - Google Patents

Description

  The present invention relates to an imaging apparatus, a control method thereof, and a control program, and more particularly, to output abnormality detection of an optical black pixel unit.

  In general, a solid-state imaging device such as a CMOS imaging device used in an imaging apparatus such as a digital camera is provided with a light receiving pixel unit that outputs an electrical signal corresponding to received light. Further, a solid-state imaging device having an optical black (hereinafter referred to as OB) pixel portion shielded by a light shielding film in addition to a light receiving pixel portion is known.

  FIG. 14 is a diagram schematically illustrating a solid-state imaging device including an OB pixel unit.

  In FIG. 14, a light receiving pixel portion 1401 and an OB pixel portion 1402 are arranged adjacent to each other on the light receiving surface of the image sensor 1400 and in contact with the boundary. The image sensor 1400 includes a vertical scanning circuit 1403 for driving the light receiving pixel portion 1401 and the OB pixel portion 1402. The analog signals output from the light receiving pixel portion 1401 and the OB pixel portion 1402 are converted into digital signals by the A / D conversion portion 1404. The horizontal scanning circuit 1405 sequentially outputs the digital signal output from the A / D conversion unit 1404 to the outside of the solid-state imaging device.

  Incidentally, the light receiving pixel unit 1401 outputs an analog signal (hereinafter referred to as a video signal) according to the amount of received light. In addition to the video signal, the light receiving pixel unit 1401 corresponds to the amount of dark current generated due to the temperature of the image sensor or the like. It is also known to output an electrical signal (hereinafter referred to as a black level signal). That is, an extra black level signal is superimposed on the video signal at the output of the light receiving pixel portion 1401. As a result, in the image obtained as a result of shooting, the subject image may change to a different color from the actual subject.

  On the other hand, the black level signal is also generated in the OB pixel unit 1402, and therefore, if the output signal (black level signal) of the OB pixel unit 1402 is subtracted from the output signal of the light receiving pixel unit 1401, the temperature of the image sensor. Regardless of this, a desired video signal can be obtained.

  However, the OB pixel unit 1402 is disposed adjacent to the light receiving pixel 1401 so that the temperatures of the OB pixel unit 1402 and the light receiving pixel unit 1401 are the same. For this reason, when the high-intensity light 1406 is incident on the light receiving surface of the image sensor 1400, a part of the high-intensity light leaks to the OB pixel unit 1402, and the level of the black level signal generated in the OB pixel unit 1402 is lower than the normal level. Sometimes it gets bigger.

  As a result, the process of subtracting the above-described black level signal is affected, so-called “black sunken” may occur in the entire image or a part thereof, and the image quality may deteriorate.

  In order to prevent such “black sun”, the image sensor receives a determination signal indicating that the black level signal is normal and outputs a first drive signal to indicate that the black level signal is abnormal. Some have received a determination signal and output a second drive signal. Here, the black level signal is read from the light receiving unit from the OB pixel unit by the first drive signal, and the black level signal is not read from the OB pixel unit by the second drive signal (see Patent Document 1). ).

JP 2006-295648 A

  However, in the imaging apparatus described in Patent Document 1, the determination of the state of the black level signal is performed outside the imaging element, and the imaging apparatus must be provided with a determination circuit separately, which causes an increase in cost. End up.

  If it is determined that there is an abnormality in the black level signal, the black level signal (that is, the OB pixel signal) is not transferred from the OB pixel unit, so that it is difficult to correct the video signal read from the light receiving pixel unit. As a result, “black sun” may occur in the image.

  Accordingly, it is an object of the present invention to provide an imaging apparatus, a control method thereof, and a control program that can always reduce “black sun” without increasing costs.

In order to achieve the above object, an imaging apparatus according to the present invention is responsive to a photoelectric conversion element that converts light into electric charge, a first gate that transfers the electric charge to a floating diffusion, and a potential of the floating diffusion. A unit pixel including a second gate for outputting a signal to a signal line and a reset element for resetting the floating diffusion, wherein the plurality of unit pixels are arranged in a two-dimensional matrix; said floating diffusion before Ru reset toss, drives said second gate for at least one row but by driving the imaging device is either optical black pixels which are light receiving pixels and the light-shielding, the reset element A signal corresponding to the potential of the floating diffusion. A first driving control means for outputting to the signal line, the reset element is driven resets said floating diffusion, said charge from said photoelectric conversion element to the floating diffusion by driving the first gate Before the transfer, the second gate is driven for at least one row, and a second drive control means for outputting a signal corresponding to the potential of the floating diffusion to the signal line; the first gate; The second gate is driven, the electric charge is transferred from the photoelectric conversion element to the floating diffusion, a signal corresponding to the potential of the floating diffusion is output to the signal line, and all rows are read. a third drive control means for, in the optical black pixel The black level reference value is obtained based on the black level signal generated based on the signal output to the signal line by the second drive control means and the signal output to the signal line by the third drive control means. And a correction means for correcting the signal read from the light receiving pixel in accordance with the black level reference value, and the light receiving pixel or the optical black pixel output to the signal line by the first drive control means. And determining means for determining whether or not to use the black level signal for calculating the black level reference value in accordance with the signal.

According to the control method of the present invention, a photoelectric conversion element that converts light into electric charge, a first gate for transferring the electric charge to a floating diffusion, and a signal corresponding to the potential of the floating diffusion are output to a signal line. And a reset pixel for resetting the floating diffusion. The plurality of unit pixels are arranged in a two-dimensional matrix, and the unit pixels are light-shielded pixels and light-shielded optically. a method for controlling an imaging apparatus including the imaging element is either black pixels, the floating diffusion by driving the reset element before Ru reset Tosu, driving the second gate for at least one row In response to the potential of the floating diffusion. A first drive control step of outputting a signal to said signal line and, by driving the reset element resets said floating diffusion, said from the photoelectric conversion element to the floating diffusion by driving the first gate A second drive control step of driving the second gate for at least one row and outputting a signal corresponding to the potential of the floating diffusion to the signal line before transferring charge ; The gate and the second gate are driven to transfer the charge from the photoelectric conversion element to the floating diffusion, and a signal corresponding to the potential of the floating diffusion is output to the signal line. a third driving control step of reading, the optical Bed Black pixels based on a black level signal generated on the basis of the signal output to the signal line in the second drive control step and the signal output to the signal line in the third drive control step. A correction step of obtaining a level reference value and correcting a signal read from the light receiving pixel according to the black level reference value; and the signal line in the first drive control step in the light receiving pixel or the optical black pixel. And determining whether to use the black level signal for the calculation of the black level reference value in accordance with the signal output in step (b).

A control program according to the present invention outputs a signal corresponding to the potential of the floating diffusion to a signal line, a photoelectric conversion element that converts light into electric charge, a first gate for transferring the electric charge to the floating diffusion, and And a reset pixel for resetting the floating diffusion. The plurality of unit pixels are arranged in a two-dimensional matrix, and the unit pixels are light-shielded pixels and light-shielded optically. a control program used in an imaging apparatus including the imaging element is either black pixel, the computer in which the imaging apparatus is provided, before the floating diffusion Ru reset toss by driving the reset element, at least one The second game for one row By driving the first drive control step of outputting a signal corresponding to the potential of the floating diffusion to the signal line, to reset the floating diffusion by driving the reset element, driving the first gate Then, before transferring the charge from the photoelectric conversion element to the floating diffusion, the second gate is driven for at least one row, and a signal corresponding to the potential of the floating diffusion is output to the signal line. A second drive control step, driving the first gate and the second gate to transfer the charge from the photoelectric conversion element to the floating diffusion, and generating a signal corresponding to the potential of the floating diffusion; Output to the signal line for all rows A third driving control step of issuing seen, the optical black said at pixel second signal output to the signal line driving control step and the third signal output to the signal line driving control step of A correction step of obtaining a black level reference value based on the black level signal generated based on the reference signal and correcting a signal read from the light receiving pixel in accordance with the black level reference value; and the light receiving pixel or the optical black A determination step for determining whether or not the black level signal is used for calculating the black level reference value in accordance with the signal output to the signal line in the first drive control step in the pixel. And

  According to the present invention, it is possible to always reduce “black sun” without increasing the cost.

1 is a block diagram illustrating a configuration of an example of an imaging apparatus according to a first embodiment of the present invention. It is a figure which shows typically the structure of the image pick-up element shown in FIG. FIG. 3 is a diagram showing in detail a circuit configuration of a light receiving pixel portion and an OB pixel portion located on the upper side in the image sensor shown in FIG. 2. FIG. 4 is a timing chart for explaining a reading operation when a black sun phenomenon occurs in the image sensor shown in FIG. 3. FIG. 5 is a flowchart for explaining a read operation described in the timing chart shown in FIG. 4. FIG. 4 is a diagram showing a state where attention is paid to a pixel group in a first column in the circuit diagram of the image sensor shown in FIG. It is a figure which shows typically the electric charge which leaks from PD of the light receiving pixel part shown in FIG. 6 to FD. FIG. 4 is a timing chart for explaining a read operation for preventing occurrence of a black sun phenomenon in the image sensor shown in FIG. 3. FIG. FIG. 9 is a flowchart for explaining a read operation described in the timing chart shown in FIG. 8. FIG. FIG. 3 is a diagram schematically showing a state in which a black sun phenomenon has occurred over the entire row in the image sensor shown in FIG. 2. FIG. 3 is a diagram illustrating in detail a circuit configuration of a light receiving pixel portion and an OB pixel portion located on the left side in the image sensor shown in FIG. 2. 12 is a timing chart for explaining a read operation for preventing the occurrence of a black sun phenomenon in the image sensor shown in FIG. 11. 13 is a flowchart for explaining a read operation described in the timing chart shown in FIG. 12. It is a figure which shows typically the solid-state image sensor provided with the conventional OB pixel part.

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

[First Embodiment]
FIG. 1 is a block diagram showing the configuration of an example of an imaging apparatus according to the first embodiment of the present invention.

  The illustrated imaging device is a digital camera (hereinafter simply referred to as a camera), and the camera 100 includes a lens unit 101. A subject image (optical image) is formed on a solid-state image sensor (hereinafter simply referred to as an image sensor) 102 such as a CMOS image sensor via the lens unit 101. Although not shown, the lens unit 101 includes elements for changing the focal length, adjusting the amount of light, and blocking the incident light.

  The imaging element 102 includes a pixel unit that outputs an electrical signal (analog signal) corresponding to an optical image by photoelectric conversion, an A / D conversion unit that converts the analog signal into a digital signal, and the like. A digital signal that is an output of the image sensor 102 is supplied to the signal processing unit 103. The signal processing unit 103 performs a predetermined signal correction process on the digital signal and outputs shooting data.

  The timing generation unit (TG) 104 outputs a timing signal to the image sensor 102 and the signal processing unit 103 under the control of the overall control / calculation unit 105. The overall control / arithmetic unit 105 controls the entire imaging apparatus 100 and obtains image data by performing necessary processes and computations on shooting data according to the operation mode of the imaging apparatus 100.

  The storage unit 106 records the above-described shooting data and image data, and also stores adjustment data, signal processing data, and the like. The recording unit 107 records image data generated by the overall control / calculation unit 105. The operation unit 108 includes a button, a dial, and the like, and is a human I / F operated by a user, and gives an operation command corresponding to the user operation to the overall control / calculation unit 105.

  The display unit 109 displays an image corresponding to the image data on the screen under the control of the overall control / calculation unit 105 and displays an icon corresponding to the operation of the operation unit 108 on the screen.

  FIG. 2 is a diagram schematically showing the configuration of the image sensor 102 shown in FIG.

  The image sensor 102 has a light receiving pixel portion 201 having a plurality of pixels (light receiving pixels) and an OB pixel portion 202 having a plurality of pixels (optical black pixels). The light receiving pixel unit 201 receives an optical image via the lens unit 101 and outputs a video signal corresponding to the amount of light. The OB pixel unit 202 is used when determining the black reference of the image, and outputs a black level signal corresponding to the dark current.

  The vertical scanning circuit 203 includes a shift register, and drives the image sensor 102 by switching the voltage of the signal line for each row, as will be described later. The A / D conversion circuit (A / D conversion unit) 204 converts signals (analog signals) read from the light receiving pixel unit 201 and the OB pixel unit 202 into digital signals. Further, the A / D conversion circuit 204 performs amplification as necessary.

  Although not shown in FIG. 2, the A / D conversion circuit 204 uses a black level signal read from the OB pixel unit 202 as a predetermined reference in order to effectively use the input range when performing A / D conversion. An OB clamp circuit for setting a value is provided.

  The horizontal scanning circuit 205 includes a shift register and a storage circuit (storage circuit), temporarily stores a digital signal output from the A / D conversion circuit 204, and selects the digital signal in a predetermined order. Output.

  In the example shown in FIG. 2, the A / D conversion circuit 204 is disposed in the previous stage of the horizontal scanning circuit 205, but the A / D conversion circuit 204 is provided in the subsequent stage of the horizontal scanning circuit 205 (that is, outside the image sensor 102). It may be arranged.

  FIG. 3 is a circuit diagram showing in detail the light receiving pixel portion 201 and the OB pixel portion 202 located on the upper side in the image sensor 102 shown in FIG.

  In FIG. 3, a total of 9 pixels are shown, including 6 pixels for the light receiving pixel portion 201 and 3 pixels for the OB pixel portion 202. The configuration of each pixel is the same.

  A photodiode (PD: photoelectric conversion element) 301 receives light from the lens unit 101 and generates charges by photoelectric conversion. The transfer transistor (transfer Tr) 302 is controlled by transfer signals (transfer pulses) Tx 1 to Tx 3 from the vertical scanning circuit 203, and transfers the charges generated in the PD 301 to the floating diffusion (floating node: FD) 303. The FD 303 temporarily accumulates the charges transferred from the PD 301.

  A source follower amplifier (second gate: hereinafter referred to as SF) 304 outputs a voltage signal corresponding to the amount of electric charge (potential) accumulated in the FD 303. A reset transistor (reset Tr: reset element) 305 is controlled by reset signals (reset pulses) RST1 to RST3 from the vertical scanning circuit 203, and forcibly resets the charges of the PD 301 and the FD 303.

  The selection transistor (first gate: selection Tr) 306 is controlled by a row selection signal (row selection pulse) SEL1 to SEL3 from the vertical scanning circuit 203, and outputs a voltage signal from the SF 304 for the selected row.

  The PD 301, the transfer Tr 302, the FD 303, the SF 304, the reset Tr 305, and the selection Tr 306 form one pixel (unit pixel) 307, and these unit pixels 307 are arranged in a two-dimensional matrix.

  SFs 304 are respectively connected to vertical signal lines 308 extending in the column direction for each column, and each of these vertical signal lines 308 is connected to an A / D conversion circuit 204 having an OB clamp circuit 309 through a capacitor. ing.

  The OB pixel portion (also referred to as OB region) 202 is provided with a light shielding film (not shown), and the light passing through the lens portion 101 is blocked by the light shielding film. This prevents light from reaching the PD 301 in the unit pixel 307 of the OB pixel unit 202.

  In the example shown in FIG. 3, the case where the unit pixel 307 has four transistors of the transfer Tr 302, SF 304, reset Tr 305, and selection Tr 306 has been described, but the selection Tr 306 is omitted by controlling the reset voltage. A unit pixel having two transistors may be used. In FIG. 3, each unit pixel 307 includes one FD 303, but a plurality of unit pixels 307 may share the FD 303.

  As described above, in the image sensor 102, the OB pixel unit 202 is shielded from light by the light shielding film 310. On the other hand, in a blooming phenomenon when high-luminance light is incident and when light is incident obliquely on the surface of the image sensor 102, light enters from a slight gap between the light shielding film and the surface of the image sensor 102. The phenomenon cannot be completely prevented. That is, when light enters the OB pixel unit 202 covered with the light shielding film through a certain path and a signal corresponding to the incident light amount is generated, a so-called black sun phenomenon occurs.

  Here, in order to facilitate understanding of the image pickup apparatus according to the first embodiment of the present invention, an operation when the black sun phenomenon occurs in the image pickup element 102 shown in FIG. 3 will be described.

  FIG. 4 is a timing chart for explaining a read operation when the black sun phenomenon occurs in the image sensor 102 shown in FIG.

  Now, the mechanical shutter pulse is turned off, the light incident on the image sensor 102 is shielded by a light shielding unit (not shown) provided in the lens unit 101, and the exposure time ends. In the image sensor 102, a voltage signal (hereinafter also referred to as a pixel signal) is sequentially read from the upper row in FIG.

  First, the vertical scanning circuit 203 sets the row selection signal SEL1 to the high (H) level in the OB region of the first row shown in FIG. Subsequently, the vertical scanning circuit 203 sets the reset signal RES1 to the H level and then to the low (L) level, and reads the reset voltage signal from the falling edge at time Tn1.

  Next, when the time Tn1 elapses, the vertical scanning circuit 203 sets the transfer signal TX1 to the H level. As a result, charges generated in the PD 301 at the time Ts1 are transferred to the FD 303, and a voltage signal is output from the SF 304 for the selected row. Then, the reset voltage signal read at time Tn1 is subtracted from the voltage signal read at time Ts1, thereby correcting variations between transistors for each pixel.

  Similarly, in order to read out the second row, the vertical scanning circuit 203 sets the row selection signal SEL2 to H level, then sets the reset signal RES2 to H level, and then sets it to L level. Thus, the reset voltage signal is read at time Tn2 from the falling edge. Then, the vertical scanning circuit 203 sets the transfer signal TX2 to the H level and outputs a voltage signal from the SF 304 for the row selected at the time Ts2.

  Hereinafter, for the third row, the reset voltage signal is read at time Tn3, and the voltage signal is read at time Ts3. Then, these operations are sequentially performed up to the last line to obtain a video signal for one screen.

  FIG. 5 is a flowchart for explaining the read operation described in the timing chart shown in FIG. Here, the OB clamp circuit 309 performs the OB clamp operation on the video signal (that is, the pixel signal) read by the read operation described with reference to FIG. Further, the readout control of the image sensor 102 is executed by the overall control calculation unit 105 via the TG 104.

  When the exposure is completed (step S501), the overall control calculation unit 105 sets the OB initial value (OBave0) to the black reference value (also referred to as black level reference value: OBave) (step S502). Then, as described with reference to FIG. 4, a reading operation is performed in the image sensor 102 (step S503).

  Subsequently, the overall control calculation unit 105 determines whether or not the read pixel signal is a pixel signal from an OB pixel (step S504). Here, if the value of the pixel signal is less than a preset threshold value, the overall control calculation unit 105 determines that the pixel signal is a pixel signal from an OB pixel.

  When it is determined that the pixel signal is from the OB pixel (YES in step S504), the overall control calculation unit 105 performs OB on the pixel signal (that is, the video signal) read by the following equation (1). A black reference value (OBave) corresponding to the black level signal of the pixel unit 202 is calculated (step S505).

  Here, N1 and N2 are black level calculation coefficients, which are set to predetermined values. M is a value of a pixel signal (that is, a video signal).

  Subsequently, the overall control calculation unit 105 determines whether or not the pixel signal is a pixel signal from the last pixel (that is, the last row) (step S506). Whether or not the pixel is the final pixel is determined according to a transfer signal output from the vertical scanning circuit 203.

  If it is determined that the pixel signal is not from the final pixel (NO in step S506), overall control operation unit 105 returns to the process in step S504. On the other hand, when it is determined that the pixel signal is from the final pixel (YES in step S506), overall control calculation unit 105 ends the read operation.

  When it is determined that the pixel signal is not a pixel signal from the OB pixel (NO in step S504), the overall control calculation unit 105 sets the value M of the pixel signal to M-OBave (step S507) and proceeds to the process of step S506.

  Thus, the random noise is suppressed by obtaining the black reference value (OBave) from the pixel signals of the plurality of OB pixels in the overall control calculation unit 105. Then, by subtracting the black reference value (OBave) from the pixel signal value M, the dark current component caused by the temperature of the image sensor 102 or the like is removed, and the input range of the A / D conversion circuit 204 is further increased. Use it effectively.

  However, in the read operation shown in FIG. 5, it is not considered that factors other than the dark current component occur in the OB pixel unit 202 that calculates the OB reference value (OBave). When something other than the dark current component occurs for some reason, the video signal obtained as a result of the subtraction becomes a value lower than the desired value (black sun phenomenon). The cause of the black sun phenomenon is, for example, intrusion of light that cannot be shielded by the light shielding film.

  That is, the black sun phenomenon is caused by the output signal of the OB pixel unit 202 becoming abnormal and taking the abnormal value into the black reference value (OBave).

  In consideration of such intrusion of light into the OB pixel unit 202, here, the overall control calculation unit 105 determines whether or not the output signal of the OB pixel unit 202 is abnormal, and the output of the OB pixel unit 202. If the signal is abnormal, the output signal is not used for calculation of the black reference value (OBave).

  FIG. 6 is a diagram illustrating a state where attention is paid to the pixel group in the first column in the circuit diagram of the image sensor 102 illustrated in FIG. 3.

  Assume that high-intensity light is incident on the pixel group in the first column (shown by region 701) shown in FIG. Light leaks into the PD 301 in the first row of the OB pixel unit 202 by the high luminance light. The leaked light generates more charges than the dark current component in the PD 301 in the first row. On the other hand, the PD 301 in the first column of the light receiving pixel unit 201 generates a large amount of charge due to the directly incident high-intensity light.

  FIG. 7 is a diagram schematically showing charges leaking from the PD 301 to the FD 303 of the light receiving pixel unit 201 shown in FIG. When the charge generated in the PD 301 in the first column of the light receiving pixel unit 201 reaches the saturation level of the PD 301, the charge leaks to the adjacent FD 303 beyond the potential barrier of the transfer Tr 302.

  FIG. 8 is a timing chart for explaining a read operation for preventing the occurrence of the black sun phenomenon in the image sensor 102 shown in FIG. Here, the description will be made in comparison with the read operation described in FIG. Here, as described with reference to FIGS. 6 and 7, it is assumed that high-luminance light is incident on the pixel group (region 701) in the first column.

  As described with reference to FIG. 4, the mechanical shutter pulse is turned off, the light incident on the image sensor 102 is shielded by the light shielding unit provided in the lens unit 101, and the exposure time ends. The image sensor 102 sequentially reads out pixel signals for each row.

  First, the vertical scanning circuit 203 sets the row selection signal SEL2 shown in FIG. That is, here, the light receiving pixel portion 201 in the second row is selected. Thereby, at time Tdt, a pixel signal corresponding to the amount of charge leaked from the PD 301 into the FD 303 is read for the second row.

  As described above, since the high-intensity light is incident on the region 701, the output OUT1 of the SF 304 in the second row × first column is the outputs OUT2 and OUT3 of the SF 304 in the second row × second column and the second row × third column. The value is higher than (OUT2 / 3). If these outputs OUT1 to OUT3 are used, it is possible to detect how much light is incident near the OB region 202 before the pixel signal is transferred. In other words, whether or not the output of the OB pixel unit 202 adjacent to the light receiving pixel unit 201 is abnormal can be estimated according to the amount of charge leaked into the FD 303.

  Thereafter, pixel signals are read from the image sensor 102 in the same manner as in FIG.

  FIG. 9 is a flowchart for explaining the read operation described in the timing chart shown in FIG. In FIG. 9, the same reference numerals are assigned to the same steps as those shown in FIG. 5.

  Here, the overall control calculation unit 105 determines whether or not the output of the OB pixel unit 202 is abnormal, and excludes it from the calculation of the black reference value (OBave).

  When the exposure ends (step S501), the overall control calculation unit 105 sets the OB initial value (OBave0) as the black reference value (OBave) (step S502). Subsequently, in order to determine whether or not the output of the OB pixel unit 202 is abnormal, the overall control calculation unit 105 reads a signal corresponding to the charge amount of the FD 303 as described with reference to FIG. S901). Then, the overall control calculation unit 105 compares the signal value (level) P of the read signal (node signal) with a preset reference threshold value Pth, and determines whether the signal level is equal to or higher than the threshold value (P ≧ Pth). It is determined whether or not (step S902).

  When it is determined that P ≧ Pth (YES in step S903), the overall control calculation unit 105 determines that the high-intensity light is incident on the image sensor 102 and outputs the signal value P described above. The column address of the column is stored in an internal memory (not shown) as an abnormal column address.

  Thereafter, the overall control calculation unit 105 performs the processes of steps S503 and S504 described with reference to FIG. That is, the overall control calculation unit 105 reads the pixel signal as a read signal. If it is determined in step S504 that the pixel signal is not a pixel signal from an OB pixel (NO in step S504), the overall control calculation unit 105 performs the process of step S507 and proceeds to step S506.

  On the other hand, if it is determined that the pixel signal is from the OB pixel (YES in step S504), the overall control calculation unit 105 determines whether the address of the OB pixel is included in the abnormal column address. That is, the overall control calculation unit 105 determines whether or not the OB pixel is in the abnormal column (step S904).

  If it is determined that the OB pixel is included in the abnormal row (YES in step S904), overall control operation unit 105 proceeds to the process in step S506. When it is determined that the OB pixel is not included in the abnormal column (NO in step S904), the overall control calculation unit 105 performs the process of step S505.

  Thus, when an OB pixel is included in an abnormal column, the output signal of the OB pixel is not used for calculation of the black reference value (OBave). That is, the influence is eliminated by not using the output signal of the OB pixel that may be an abnormal value for the calculation of the black reference value (OBave).

  As described above, in the first embodiment of the present invention, it is determined whether or not the output of the OB pixel is abnormal by using the output signal of the FD 303 read before resetting. Is not used for the calculation of the black reference value (OBave), so that the influence on the black reference value can be suppressed.

  In the first embodiment, the reference threshold value Pth is set to a preset value. However, the reference threshold value Pth is lowered under a situation where high-luminance light is likely to be incident, and under a situation where the noise level is high due to high sensitivity or the like. The reference threshold Pth may be increased to increase the abnormality detection accuracy of the OB pixel output.

  Furthermore, in the first embodiment, when the output of the OB pixel is determined to be abnormal, the output is excluded from the black reference value (OBave) calculation target. However, the output of the OB pixel determined to be abnormal is determined. The output may be replaced with a predetermined value.

  In the first embodiment, the FD output of the pixel adjacent to the OB region is used for abnormality detection. However, the pixel adjacent to the OB region is not necessarily used.

  In addition, in order to increase the abnormality detection accuracy, it is desirable to use an average value of outputs from a plurality of rows as the signal value P. On the other hand, if the number of rows to be averaged increases and the photographing time is extended, the number of rows to be averaged may be changed according to the required abnormality detection accuracy.

  In the first embodiment, the output of the FD 303 before reset is used for abnormality detection. However, in order to increase the abnormality detection accuracy, the difference between the output when the FD 303 is reset and the output of the FD 303 before reset is detected by abnormality. You may make it use for. Further, the output of the light receiving pixel portion may be used as an auxiliary.

  In the first embodiment, the case where the image sensor 102 is read after the light is shielded by the light shielding unit provided in the lens unit 101 has been described. If the reading operation is performed, the black reference value can be calculated with high accuracy.

[Second Embodiment]
Next, an example of a camera according to the second embodiment of the present invention will be described. The configuration of the camera according to the second embodiment is the same as that of the camera shown in FIG.

  The effect of dark current generated at high temperatures is not always constant across the entire screen. In particular, when reading is performed row by row from the top of the screen, the amount of dark current generated at the bottom of the screen where reading is last performed is larger than that at the top of the screen, and the black level signal may increase. Are known.

  In such a case, the black level signal of the OB pixel unit 202 existing on the left or right side of the screen is used to subtract the black level signal from the output of the light receiving pixel unit for each row, thereby Can absorb the difference in dark current generated in

  FIG. 10 is a diagram schematically illustrating a state in which the black sun phenomenon has occurred over the entire row in the image sensor 102 illustrated in FIG. 2.

  Now, when the amount of dark current increases toward the bottom of the screen, when the high brightness light 1002 enters the vicinity of the boundary between the left OB pixel unit 202 and the light receiving pixel unit 201 on the light receiving surface of the image sensor 1400. A part of the high-intensity light 1002 leaks to the OB pixel unit 202. It is known that a black sun phenomenon occurs in the entire row 1001 when light leakage occurs in the left OB pixel portion 202.

  In the second embodiment, when light leaks into the OB pixel unit 202 on the left side of the screen, it is determined whether or not the output signal of the OB pixel unit 202 is abnormal. A case where the black reference value (OBave) is excluded from the calculation will be described.

  FIG. 11 is a diagram showing in detail the circuit configuration of the light receiving pixel unit 201 and the OB pixel unit 202 located on the left side in the image sensor 102 shown in FIG. In FIG. 11, the same elements as those of the circuit configuration shown in FIG.

  In FIG. 11, a total of 9 pixels are shown, including 6 pixels for the light receiving pixel portion 201 and 3 pixels for the left OB pixel portion 202. The configuration of each pixel is the same. Then, it is assumed that high-intensity light is incident on three pixels (indicated by a region 1101 in the figure) in the first row.

  FIG. 12 is a timing chart for explaining a read operation for preventing the occurrence of the black sun phenomenon in the image sensor 102 shown in FIG.

  When the mechanical shutter pulse is turned off, the light incident on the image sensor 102 is shielded by the light shielding unit provided in the lens unit 101, and the exposure time is finished, the vertical scanning circuit 203 performs FIG. The row selection signal SEL1 shown in FIG. That is, here, the pixels in the first row are selected. As a result, the pixel signal corresponding to the amount of charge leaking from the PD 301 into the FD 303 is read for the first row at time Tdt1.

  As described above, since high-intensity light is incident on the region 1101, light leaks into the PD 301 in the first row × first column, which is an OB pixel, and more charges than dark current components are generated. Further, charges leak from the PD 301 into the FD 303 in the first row × second column and the first row × third column, which are the light receiving pixels (see FIG. 7). That is, the output of the pixels in the first row is higher than the output of the pixels in the second and subsequent rows. If the output of the pixels in the first row is used, it is possible to detect how much light is incident in the vicinity of the OB area 202 before the pixel signal is transferred. In other words, whether or not the output of the adjacent OB pixel 202 is abnormal can be estimated according to the amount of charge leaked into the FD 303.

  Next, the vertical scanning circuit 203 sets the row selection signal SEL1 to the H level again after setting the row selection signal SEL1 to the L level. Subsequently, the vertical scanning circuit 203 sets the reset signal RES1 to H level and then to L level, and reads the reset voltage signal from the falling edge at time Tn1.

  When the time Tn1 elapses, the vertical scanning circuit 203 sets the transfer signal TX1 to the H level. As a result, the charge generated in the PD 301 at the time Ts1 is transferred to the FD 303, and a voltage signal is output from the SF 304 for the selected row.

  Similarly, the vertical scanning circuit 203 sets the row selection signal SEL2 to the H level, and reads out a pixel signal corresponding to the amount of charge leaking from the PD 301 to the FD 303 for the second row at time Tdt2.

  Next, the vertical scanning circuit 203 sets the row selection signal SEL2 to the H level again after setting the row selection signal SEL2 to the L level. Subsequently, the vertical scanning circuit 203 sets the reset signal RES2 to the H level and then to the L level, and reads the reset voltage signal from the falling edge at time Tn2.

  When the time Tn2 elapses, the vertical scanning circuit 203 sets the transfer signal TX2 to the H level. As a result, the charge generated in the PD 301 at the time Ts2 is transferred to the FD 303, and a voltage signal is output from the SF 304 for the selected row.

  Hereinafter, for the third row, the vertical scanning circuit 203 sets the row selection signal SEL3 to the H level, and reads out a pixel signal corresponding to the amount of charge leaked from the PD 301 to the FD 303 for the third row at time Tdt3.

  Next, the vertical scanning circuit 203 sets the row selection signal SEL3 to L level, and then sets the row selection signal SEL3 to H level again. Subsequently, the vertical scanning circuit 203 sets the reset signal RES3 to H level and then to L level, and reads the reset voltage signal from the falling edge at time Tn3.

  When the time Tn3 has elapsed, the vertical scanning circuit 203 sets the transfer signal TX3 to the H level. As a result, the charge generated in the PD 301 at the time Ts3 is transferred to the FD 303, and a voltage signal is output from the SF 304 for the selected row.

  FIG. 13 is a flowchart for explaining the read operation described in the timing chart shown in FIG. In FIG. 13, the same steps as those described in FIGS. 5 and 9 are denoted by the same reference numerals.

  Here, the overall control calculation unit 105 determines whether or not the output of the OB pixel unit 202 is abnormal, and excludes it from the calculation of the black reference value (OBave).

  When the exposure is completed (step S501), the overall control calculation unit 105 sets the OB initial value (OBave0) as the black reference value (OBave) and sets the row number N = 1 (step S1301). Subsequently, the overall control calculation unit 105 determines whether or not the output of the OB pixel unit 202 is abnormal, as described with reference to FIG. 11, in the Nth row (N is an integer equal to or greater than 1). A signal corresponding to the charge amount of the FD 303 is read (step S1302). Then, the overall control calculation unit 105 compares the read signal value P with a preset reference threshold value Pth and determines whether P ≧ Pth is satisfied (step S902).

  When it is determined that P <Pth (NO in step S902), the overall control calculation unit 105 reads pixel signals for the Nth row as described with reference to FIG. 11 (step S1303). On the other hand, when it is determined that P ≧ Pth (YES in step S903), the overall control calculation unit 105 determines that high-intensity light has entered the image sensor 102, and sets an error flag E = 1 ( Step S1304). Thereafter, the overall control calculation unit 105 proceeds to the process of step S1303.

  Subsequently, the overall control calculation unit 105 determines whether or not the pixel is an OB pixel in step S504. If it is determined that the pixel is an OB pixel (YES in step S504), the overall control calculation unit 105 checks whether or not the error flag E = 1 (step S1305).

  If the error flag E = 1 (YES in step S1305), the overall control calculation unit 105 excludes the output of the OB pixel in the row from the calculation target of the black reference value (OBave), and thus the black reference value (OBave). ) Is set with an OB initial value (OBave0) (step S1306). Then, the overall control calculation unit 105 determines whether or not the last pixel in the Nth row has been read (step S1307). When the last pixel in the Nth row is read (YES in step S1307), the overall control calculation unit 105 increments the row number (N = N + 1) and resets the error flag E (E = 0: step). S1308).

  Subsequently, the overall control calculation unit 105 determines whether reading has been performed up to the last row (step S1309). If it is determined that reading has been performed up to the last row (YES in step S1309), overall control operation unit 105 ends the reading operation. If reading has not been performed up to the last line (NO in step S1309), overall control operation unit 105 returns to the process in step S1302.

  If it is determined that the pixel is not the last pixel in the Nth row (NO in step S1307), the overall control calculation unit 105 returns to the process in step S504, and the error flag E is not 1 (NO in step S1305). The overall control calculation unit 105 performs the process of step S505 described with reference to FIG. 5, and then proceeds to the process of step S1307. If it is determined that the pixel signal is not output from the OB pixel (NO in step S504), the overall control calculation unit 105 performs the process of step S507 described in FIG. Proceed to

  As described above, in the second embodiment of the present invention, it is determined whether or not the output of the OB pixel is abnormal using the output of the FD 303 read before resetting. Since the output is not used for calculation of the black reference value (OBave), the influence on the black reference value can be suppressed.

  In the second embodiment, in order to increase the abnormality detection accuracy, it is desirable to use an average value of outputs from a plurality of columns as the signal value P. On the other hand, if the number of columns to be averaged is increased and the photographing time is extended, the number of columns to be averaged may be changed according to the required abnormality detection accuracy.

  In the second embodiment, it is determined whether or not the output of the OB pixel is abnormal in all the rows. However, the OB clamping operation is affected in the row immediately after the reading of the row located at the top of the screen. Abnormality determination may be performed only for easy lines.

  As described above, in the embodiment of the present invention, the main body control calculation unit 105 determines whether or not the output of the OB pixel is the above, and if it is abnormal, it is not used for calculating the black reference value. (In other words, since it is removed from the clamp area), the “black sun” can be effectively reduced only by adding software, and the increase in cost can also be reduced.

  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 imaging apparatus. Further, a program having the functions of the above-described embodiments may be used as a control program, and the control program may be executed by a computer included in the imaging apparatus. The control program is recorded on a computer-readable recording medium, for example.

  The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various recording media, and the computer (or CPU, MPU, etc.) of the system or apparatus reads the program. To be executed.

DESCRIPTION OF SYMBOLS 102 Image pick-up element 105 Overall control calculating part 301 Photodiode 302 Transfer transistor 303 Floating diffusion 304 Source follower amplifier 305 Reset transistor 306 Selection transistor 308 Vertical signal line 309 OB clamp circuit

Claims (9)

A photoelectric conversion element for converting light into electric charge, a first gate for transferring the electric charge to a floating diffusion, a second gate for outputting a signal corresponding to the potential of the floating diffusion to a signal line, A unit pixel including a reset element for resetting the floating diffusion, wherein the plurality of unit pixels are arranged in a two-dimensional matrix, and the unit pixel is either a light receiving pixel or a light-shielded optical black pixel An image sensor;
It said reset device by driving the floating diffusion before Ru reset Tosu, the outputs for at least one line by driving the second gate, a signal corresponding to the potential of the floating diffusion to the signal line 1 drive control means;
The second gate for at least one row before driving the reset element to reset the floating diffusion and driving the first gate to transfer the charge from the photoelectric conversion element to the floating diffusion. And a second drive control means for outputting a signal corresponding to the potential of the floating diffusion to the signal line,
Driving the first gate and the second gate, transferring the charge from the photoelectric conversion element to the floating diffusion, and outputting a signal corresponding to the potential of the floating diffusion to the signal line; A third drive control means for reading out all rows;
Based on the black level signal generated based on the signal output to the signal line by the second drive control unit and the signal output to the signal line by the third drive control unit in the optical black pixel. Correction means for obtaining a black level reference value and correcting a signal read from the light receiving pixel in accordance with the black level reference value;
Determination means for determining whether or not the black level signal is used for calculation of the black level reference value according to a signal output to the signal line by the first drive control means in the light receiving pixel or the optical black pixel. An imaging apparatus comprising:   The determination means makes the optical black pixel to which the signal is output abnormal when the level of the signal output to the signal line by the first drive control means is equal to or higher than a predetermined threshold. The imaging apparatus according to claim 1, wherein the imaging apparatus is characterized. After the signal is read in the Nth row (N is an integer of 1 or more) by the first drive control means, the third drive control means reads the signal in the Nth row. The imaging apparatus according to claim 1 or 2. The imaging apparatus according to claim 2, wherein the determination unit increases the threshold as the amount of noise of the black level signal increases. The determination unit determines whether to use the black level signal for the calculation of the black level reference value based on a signal acquired from a plurality of rows and output to the signal line by the first drive control unit. The imaging apparatus according to claim 1, wherein the imaging apparatus is characterized. The imaging apparatus according to claim 1, wherein after the light is shielded by a mechanical shutter, the first drive control unit outputs a signal corresponding to the potential of the floating diffusion to the signal line. The determination means determines the black level signal based on the difference between the signal output to the signal line by the first drive control means and the signal output to the signal line by the third drive control means. The imaging apparatus according to claim 1, wherein it is determined whether or not to use for calculation of a black level reference value. A photoelectric conversion element for converting light into electric charge, a first gate for transferring the electric charge to a floating diffusion, a second gate for outputting a signal corresponding to the potential of the floating diffusion to a signal line, A unit pixel including a reset element for resetting the floating diffusion, wherein the plurality of unit pixels are arranged in a two-dimensional matrix, and the unit pixel is either a light receiving pixel or a light-shielded optical black pixel A method for controlling an imaging apparatus including an imaging element,
It said reset device by driving the floating diffusion before Ru reset Tosu, the outputs for at least one line by driving the second gate, a signal corresponding to the potential of the floating diffusion to the signal line 1 drive control step;
The second gate for at least one row before driving the reset element to reset the floating diffusion and driving the first gate to transfer the charge from the photoelectric conversion element to the floating diffusion. And a second drive control step for outputting a signal corresponding to the potential of the floating diffusion to the signal line;
Driving the first gate and the second gate, transferring the charge from the photoelectric conversion element to the floating diffusion, and outputting a signal corresponding to the potential of the floating diffusion to the signal line; A third drive control step for reading out all rows;
Based on the black level signal generated based on the signal output to the signal line in the second drive control step and the signal output to the signal line in the third drive control step in the optical black pixel. A correction step for obtaining a black level reference value and correcting a signal read from the light receiving pixel in accordance with the black level reference value;
A determination step of determining whether the black level signal is used for calculating the black level reference value according to the signal output to the signal line in the first drive control step in the light receiving pixel or the optical black pixel. The control method characterized by having. A photoelectric conversion element for converting light into electric charge, a first gate for transferring the electric charge to a floating diffusion, a second gate for outputting a signal corresponding to the potential of the floating diffusion to a signal line, A unit pixel including a reset element for resetting the floating diffusion, wherein the plurality of unit pixels are arranged in a two-dimensional matrix, and the unit pixel is either a light receiving pixel or a light-shielded optical black pixel A control program used in an imaging apparatus including an imaging element,
In the computer provided in the imaging device,
It said reset device by driving the floating diffusion before Ru reset Tosu, the outputs for at least one line by driving the second gate, a signal corresponding to the potential of the floating diffusion to the signal line 1 drive control step;
The second gate for at least one row before driving the reset element to reset the floating diffusion and driving the first gate to transfer the charge from the photoelectric conversion element to the floating diffusion. And a second drive control step for outputting a signal corresponding to the potential of the floating diffusion to the signal line;
Driving the first gate and the second gate, transferring the charge from the photoelectric conversion element to the floating diffusion, and outputting a signal corresponding to the potential of the floating diffusion to the signal line; A third drive control step for reading out all rows;
Based on the black level signal generated based on the signal output to the signal line in the second drive control step and the signal output to the signal line in the third drive control step in the optical black pixel. A correction step for obtaining a black level reference value and correcting a signal read from the light receiving pixel in accordance with the black level reference value;
A determination step of determining whether the black level signal is used for calculating the black level reference value according to the signal output to the signal line in the first drive control step in the light receiving pixel or the optical black pixel. A control program characterized by causing

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