JP2016082300A - Imaging device and signal processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging device that can clamp an imaging signal at a suitable clamp level over the whole effective pixel area even when the imaging device does not sufficiently have an OB area which is read out more early than a read-out head line of an effective pixel area within an imaging element.SOLUTION: An imaging signal output from an imaging element having an effective pixel area and an optical black area is subjected to AD conversion by an AD converter, at least an imaging signal of the optical black area out of the AD-converted imaging signal is added to the AD-converted imaging signal by an OB correction unit, and a clamp processor executes clamp processing for standardizing the black level on the AD-converted imaging signal by a clamp signal based on the imaging signal of the optical black area input from the OB correction unit so that the clamp level is quickly converged, whereby the imaging signal can be clamped at a suitable clamp level over the whole effective pixel area.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an imaging apparatus and a signal processing method.

  A conventional imaging apparatus performs an analog-digital conversion (AD conversion) process on an electrical signal (imaging signal) obtained from an image sensor, and then performs an optical black clamp process on the imaging signal in order to compensate for the black level of the signal itself. (OB clamp processing) is performed. In the OB clamp process, a difference between the image pickup signal after the AD conversion process and the image pickup signal of the optical black area (OB area) in the image pickup element is taken. The OB region is generally composed of a photodiode (photoelectric conversion element) shielded from light by a metal. Even when the black level of the imaging signal fluctuates due to dark current noise or the like by the OB clamping process, an imaging signal with a stable black level can be obtained.

  FIG. 18 shows a general clamping processing unit that performs OB clamping processing. The filter unit 1802 of the clamp processing unit 1801 selectively receives an imaging signal in the OB area from among the imaging signals input to the clamping processing unit 1801, and performs filtering on the imaging signal in the OB area to remove noise. The difference between the imaging signal input to the clamp processing unit 1801 and the reference signal (clamp signal) obtained by filtering the imaging signal in the OB region by the filter unit 1802 is obtained by the adder 1803, and the OB clamping process is performed. Done.

  The OB area in the image pickup element varies for each image pickup element such as the size of the area and the arrangement location in the image pickup element. When having an OB area that is read earlier than the reading start line of the effective pixel area in the image sensor, the clamp signal is stabilized before the imaging signal of the effective pixel area passes through the clamp processing unit, so that a stable clamp level can be obtained. OB clamping processing can be performed. However, in order to provide a large number of OB areas on the readout line earlier than the readout start line of the effective pixel area, the total number of pixels of the image sensor increases, and the photodiode in the OB area must be covered with aluminum, which increases the cost. End up. Furthermore, parasitic capacitance is generated by aluminum, and the characteristics are electrically deteriorated.

  FIG. 19 shows an example of an image sensor. The imaging element 1901 includes an invalid area 1902, an OB area 1903, and an effective pixel area 1904 that forms an optical image by a lens or the like and outputs an imaging signal. The imaging signal output from the OB region 1903 is input to the filter unit of the clamp processing unit as illustrated in FIG. The filter unit is, for example, an IIR (Infinite Impulse Response) type LPF (Low Pass Filter), and removes a high frequency component of the imaging signal in the OB region. Reference numeral 1905 denotes a clamp signal output from the filter unit, which converges according to the time corresponding to the time constant of the filter unit. FIG. 19 shows a clamp signal 1905 when an imaging signal of an OB region having a high signal level is inputted from a certain frame image due to a sudden increase in dark current. The leading line of the effective pixel region is clamped. A state of convergence at the line position 1906 before the start is shown.

  In this way, when the imaging signal of the OB region input to the filter unit of the clamp processing unit varies, in order to output a target clamp signal corresponding to the variation, a time corresponding to the time constant characteristic of the filter unit is required. Cost. Here, let us consider a case where an OB area 1907 is read out earlier than the read head line of the effective pixel area 1904 in the image sensor, like the OB area 1903 shown in FIG. The imaging signal of the OB region 1907 is input to the filter unit of the clamp processing unit prior to the effective pixel region 1904, and the clamp signal is stabilized (1906). Clamped at the part. Therefore, the imaging signal can be clamped with a clamp signal having a stable clamp level over the entire effective pixel area.

  For example, a technique described in Patent Document 1 is disclosed as a technique of OB clamping processing using an image pickup element in which an OB area that outputs a reliable optical black level cannot be secured sufficiently. For example, a technique disclosed in Patent Document 2 is disclosed regarding a technique for switching a clamp signal to an imaging signal in accordance with a changed OB level when the OB level changes rapidly.

JP 2008-67281 A JP 2009-77184 A

  In the technique described in Patent Document 1, the image circle irradiated to the image sensor is reduced, and an image sensor area that is not shielded by a metal film outside the image circle that is not irradiated with light is used for reference imaging that outputs an OB level signal. Used as an element region. As a result, a stable and sufficiently wide OB region is secured. However, it is necessary to reduce the image circle irradiated to the image sensor every time shooting is performed, and it cannot be performed under conditions where the image circle must be fixed at all times, such as when a moving image is shot. In addition, the technique described in Patent Literature 1 cannot quickly follow fluctuations in the OB level due to abrupt changes in shooting conditions such as exposure time and temperature conditions during moving image shooting.

  In the technique described in Patent Document 2, in order to cause the clamp signal to follow a rapid change in the OB level of the OB area output due to a change in the shooting mode at a high speed, a necessary clamp signal level assumed for each shooting mode is stored in advance in the memory. Hold it on a table. Then, when the shooting mode is changed, the image pickup signal is clamped with an adaptive clamp signal level. However, since the clamp signal level assumed in advance is adopted, an unexpected OB level may be output depending on a combination of photographing conditions such as exposure time and temperature conditions.

  In the technique described in Patent Document 2, the OB area does not have an OB area 1907 that is read earlier than the read head line of the effective pixel area 1904 in the image sensor as shown in FIG. 19, or the OB area is narrow. Consider the case of an image sensor. In this case, the expected clamp signal level stored in the table is different from the required clamp signal level. However, if it is not possible to secure time for the clamp signal to converge in the filter unit of the clamp processing unit, it is appropriate for the entire effective pixel region. Clamping cannot be performed. Further, with the technique described in Patent Document 2, it is generally not possible to perform OB clamp processing appropriately corresponding to OB signal characteristics that are different for each image sensor for the same reason even if the same image sensor is used.

  FIG. 20 shows an example of an image sensor that does not have an OB area that is read earlier than the read start line of the effective pixel area in the image sensor. The imaging element 2001 includes an invalid area 2002, an OB area 2003, and an effective pixel area 2004 therein. The imaging signal output from the OB region 2003 is input to the filter unit of the clamp processing unit as illustrated in FIG. 18, and the high frequency component of the imaging signal in the OB region is removed by the filter unit. Reference numeral 2005 denotes a clamp signal output from the filter unit. FIG. 20 shows a clamp signal 2005 when a dark signal is suddenly increased from a certain frame image and an imaging signal of an OB region having a high signal level is input, and the leading line of the effective pixel region is clamped. The state after convergence at the line position 2006 is shown.

  When there is no OB area that is read earlier than the reading start line of the effective pixel area in the image sensor or the OB area is narrow like the OB area 2003, the level of the clamp signal 2005 is clamped by the starting line of the effective pixel area. It converges at the timing after being done. As a result, when the imaging signal of the head line of the effective pixel area 2004 is clamped by the adder of the clamp processing unit, it is clamped at a clamp level that has not yet converged. Therefore, as shown in FIG. 21, the imaging signal in the upper part of the video may not be clamped at an appropriate clamp level, and unevenness may occur.

  An object of the present invention is to clamp an imaging signal at an appropriate clamp level over the entire effective pixel area even if the OB area is not sufficiently read out earlier than the reading start line of the effective pixel area in the image sensor. An imaging device is provided.

  An imaging apparatus according to the present invention has an effective pixel area and an optical black area, and photoelectrically converts an input optical image to output an imaging signal, and the imaging signal output from the imaging element. Conversion means for analog-to-digital conversion; correction means for adding at least the imaging signal in the optical black region of the imaging signal converted by the conversion means to the imaging signal converted by the conversion means; Clamp processing means for performing clamp processing for standardizing a black level on the image pickup signal converted by the conversion means based on the image pickup signal of the optical black area input through the correction means. It is characterized by.

  According to the present invention, the clamp level can be quickly converged, and the imaging signal can be clamped at an appropriate clamp level over the entire effective pixel region.

It is a figure which shows the structural example of the clamp process part in 1st Embodiment. It is a figure which shows the example of schematic structure of the imaging device in this embodiment. It is a figure which shows the structural example of the image pick-up element in this embodiment. It is a figure which shows the structural example of the OB correction | amendment part in 1st Embodiment. It is a flowchart which shows the example of OB correction processing in 1st Embodiment. It is a figure which shows the example of the OB correction time table in 1st Embodiment. It is a figure which shows the example of the line structure of the OB area | region input into the OB correction | amendment part. It is a figure which shows the example of the line structure of the OB area | region output from an OB correction | amendment part. It is a figure which shows the example of the imaging signal input into the clamp process part 106 in 1st Embodiment. It is a figure which shows the example of the image by which the clamp process in this embodiment was carried out. It is a flowchart which shows the example of additional line number calculation processing in 1st Embodiment. It is a figure which shows the structural example of the OB correction | amendment part in 2nd Embodiment. It is a flowchart which shows the OB correction process example in 2nd Embodiment. It is a figure which shows the example of the OB correction time table in 2nd Embodiment. It is the conceptual diagram which expanded and corrected the OB area | region in the horizontal direction. It is a flowchart which shows the OB correction process example in 3rd Embodiment. It is a figure which shows the example of the line structure of the OB area | region after correction | amendment in 3rd Embodiment. It is a figure which shows the structure of the conventional clamp process part. It is a figure which shows an example of an image pick-up element. It is a figure which shows the other example of an image pick-up element. It is a figure which shows the example of the image in which a clamp process is not appropriate.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
A first embodiment of the present invention will be described.
FIG. 2 is a block diagram illustrating a schematic configuration example of the digital imaging apparatus according to the present embodiment. The lens driving unit 211 drives the optical lens 201 for forming an optical image of the subject. The lens driving unit 211 is configured by, for example, a DC motor or the like. The aperture driver 210 controls the aperture mechanism 202 that adjusts the amount of light transmitted through the lens 201.

  The image sensor 203 is a CMOS image sensor, a CCD image sensor, or the like, and photoelectrically converts an optical image of a subject into an electrical signal. In the present embodiment, in the image sensor 203, four color filters (R, Gr, Gb, B) in a Bayer array are arranged on the photoelectric conversion element. The amplifier 204 electrically amplifies the image signal output from the image sensor 203.

  An analog-digital conversion unit (AD conversion unit) 205 converts the imaging signal from an analog signal to a digital signal. The clamp processing unit 206 performs optical black clamp processing (OB clamp processing) for fixing the black level of the imaging signal. In the clamp processing unit 206, the difference between the image pickup signal after the AD conversion process and the image pickup signal in the optical black region (OB region) in the image pickup device is taken in order to compensate for the black level of the signal itself. The OB region is composed of, for example, a photoelectric conversion element shielded from light by a metal. By the OB clamping process that standardizes the black level of the image signal, an image signal with a stable black level can be obtained even when the black level of the image signal fluctuates due to dark current noise or the like.

  The video signal processing unit 207 generates a predetermined video signal by performing signal processing such as development processing, white balance processing, and noise reduction processing. The video signal output unit 208 converts the output from the video signal processing unit 207 into a format such as a video signal, and outputs the video signal to the outside.

  The arithmetic control unit 209 is a central processing unit such as a microcomputer (microcontroller) that controls each functional unit of the imaging device based on a program or the like. For example, the arithmetic control unit 209 calculates a luminance evaluation value from the output (video signal) of the video signal processing unit 207 and transmits a drive signal to the lens driving unit 211 and the aperture driving unit 210 so as to obtain an appropriate exposure level. . The arithmetic control unit 209 transmits a control signal to the image sensor 203 so as to have a predetermined exposure time, and transmits a control signal to the amplifier 204 so as to adopt a predetermined amplification factor.

  Further, for example, the arithmetic control unit 209 transmits a control signal to the clamp processing unit 206 so that the time constant of the internal filter unit becomes a predetermined value, or transmits position information of the OB area in the image sensor 203. Or The arithmetic control unit 209 receives the video signal from the video signal processing unit 207, performs a calculation for detecting a moving object or tracking a face by taking a difference between video frames, and superimposing information on the video signal. Process.

  A timing generator (TG) 212 generates a reference clock that drives the imaging apparatus. The timing generator 212 generates a video vertical synchronization signal, a horizontal synchronization signal, and a pixel-unit drive signal (pixel clock), and supplies them to each module. The clamp processing unit 206 adopts an image pickup signal of a specific region as an image pickup signal of the OB region among the image pickup signals obtained by the image pickup device 203 based on the timing signal and information from the arithmetic control unit 209. Process.

  Next, the clamp processing unit 206 shown in FIG. 2 that performs the OB clamp processing will be described with reference to FIG. The clamp processing unit 106 receives an image signal that has undergone AD conversion processing in units of pixels for each readout line. The filter unit 102 selectively receives an imaging signal in the OB area from among the imaging signals input to the clamp processing unit 106, and performs a filtering process to remove noise on the imaging signal in the OB area. The difference between the image pickup signal input to the clamp processing unit 106 and the reference signal (clamp signal) obtained by filtering the image pickup signal in the OB region by the filter unit 102 is obtained by the adder 103, and the OB clamp processing is performed. Done.

  Here, the image sensor 203 in the present embodiment is configured by an image sensor 301 composed of a photoelectric conversion element as shown in FIG. 3, and an invalid area 302 and an OB area 303 that are not electrically guaranteed are contained therein. , And an effective pixel region 304. The effective pixel region 304 is a pixel region that forms an optical image with a lens and outputs an imaging signal. The imaging signal output from the OB region 303 is input to the filter unit 102 of the clamp processing unit 106 illustrated in FIG.

The filter unit 102 is, for example, a first-order IIR LPF. When the time constant of the filter is M, the input of the filter is X _n , and the output is Y _n , the filter characteristic is expressed by the following equation (1).
Y _n = (1 / M) × {X _n + (M−1) × Y _n−1 } (1)
Here, when the time constant M is increased, the output response characteristic with respect to the input _Xn is delayed, but when there is a pixel defect or the like in the OB region 303, the influence of the pixel defect or the like on the filter output is reduced. On the other hand, when the time constant M is reduced, the response characteristic of the output with respect to the input _Xn becomes faster and it becomes easier to follow the fluctuation of the OB level.

  However, if the time constant M is reduced, the level of the input OB signal is changed when the signal level of the imaging signal in the OB region varies greatly between frames, such as when the shooting conditions are high or exposure or gain changes greatly. The output clamp signal characteristics are delayed with respect to fluctuations. As a result, there are cases where the entire effective pixel region cannot be clamped with an appropriate clamp level, or a phenomenon such as hunting occurs in the clamped video signal. In addition, when there is a pixel defect or the like in the OB area, the filter unit 102 cannot remove the influence of the pixel defect and there is a possibility of erroneous clamping.

  The OB correction unit 101 is arranged before the digital imaging signal subjected to AD conversion processing is input to the clamp processing unit 106. In other words, the OB correction unit 101 is provided between the AD conversion unit 205 and the clamp processing unit 206 shown in FIG. The OB correction unit 101 operates in accordance with a control signal from the OB correction control unit 105 in the arithmetic control unit 104 and is synchronized with the drive timing from the timing generator 212. In the example illustrated in FIG. 1, the OB correction control unit 105 is provided in the calculation control unit 104, but may be provided separately from the calculation control unit 104.

  FIG. 4 is a diagram illustrating a configuration example of the OB correction unit 101 according to the first embodiment. The OB correction unit 101 includes a line memory 405, a line memory 406, a through line 407, an input side imaging signal changeover switch 404, and an output side imaging signal changeover switch 411. The switch 404 controls connection between an imaging signal input terminal, an input terminal 401 of the line memory 405, an input terminal 402 of the through line 407, and an input terminal 403 of the line memory 406. The switch 411 controls connection between the output terminal of the OB correction unit 101, the output terminal 408 of the line memory 405, the output terminal 409 of the through line 407, and the output terminal 410 of the line memory 406. The switches 404 and 411 are controlled to be switched by the OB correction control unit 105. The internal drive timing is driven in synchronization with the pixel clock, vertical synchronization signal, and horizontal synchronization signal supplied from the timing generator 212 shown in FIG.

  An OB correction process performed by the OB correction unit 101 and the OB correction control unit 105 will be described. FIG. 5 is a flowchart illustrating an example of the OB correction process according to the first embodiment. The OB correction control unit 105 is activated from a certain point in the activation sequence of the imaging device (S501), and control by the OB correction control unit 105 is started. The OB correction control unit 105 determines whether or not the read line of the current imaging signal that passes through the OB correction unit 101 is the head line of the OB area 303 (S502).

  If the current readout line of the imaging signal is the first line of the OB area 303, the OB correction control unit 105 calculates and determines the optimum number of additional lines to be clamped by the subsequent clamping processing unit by a method described later ( S503). Thereafter, the OB correction control unit 105 controls the switch 404 and the switch 411 in accordance with the position of the readout line of the imaging signal (S504), and the imaging signal of each line is the line memory 405, the line memory 406, or the through line 407. Pass through.

  If the result of determination in step S502 is that the current readout line of the imaging signal is not the first line of the OB area 303, the OB correction control unit 105 controls the switch 404 and the switch 411 according to the position of the current readout line. (S504). As a result, the imaging signal of each line passes through the line memory 405, the line memory 406, or the through line 407.

  FIG. 6 shows a timing table of the switch control in step S504 and the line numbers of the imaging signals stored in the line memories 405 and 406 when the additional line number calculation result in step S503 is “1”. FIG. 7 shows an example of the line configuration of the OB area 303, which is composed of a total of N lines, and the first line of the OB area 303 starts with “OB line 1”.

  As shown in FIG. 6, the line configuration of the OB area input to the OB correction unit 101 is configured by a total of N lines starting from line number 1. On the other hand, the line configuration of the OB area output from the OB correction unit 101 is a total of (N + 1) lines, and the OB area of line number 1 is added to the head. That is, the input to the OB correction unit 101 has the line configuration shown in FIG. 7, while the output from the OB correction unit 101 has the line configuration shown in FIG. As described above, the OB correction unit 101 processes and outputs the input imaging signal in units of lines.

  In this example, an example in which one line is added is shown. However, the number of additional lines differs depending on the result of calculating the number of additional lines in step S503 in FIG. 5, and one or more lines may be added. As for the memory size of the line memories 405 and 406, an area may be adaptively secured according to the result of the additional line number calculation, or the maximum additional line number x 2 lines of the additional line number calculation result is reserved in the memory area in advance. It may be.

  When the result of calculating the number of additional lines is zero, the switch 404 is connected to the input terminal 402 of the through line 407 and the switch 411 is connected to the output terminal 409 of the through line 407. It becomes a state. In other words, the image pickup signal of each line is not accumulated in the line memories 405 and 406 but passes through the OB correction unit 101. Further, when performing OB correction so that the additional line is repeated twice or more, in other words, when outputting the imaging signal of the same line a plurality of times, it is sufficient to secure a memory of the maximum number of additional lines × (the number of repetitions).

  FIG. 9 is a diagram illustrating an example of an imaging signal input to the clamp processing unit 106 after passing through the OB correction unit 101 illustrated in FIG. The OB area 904 has a configuration in which the OB area 903 added by the OB correction unit 101 is added to the OB area 303 shown in FIG. Similarly, the effective pixel area 905 has a configuration in which the effective pixel area 902 added by the OB correction unit 101 is added to the effective pixel area 304 shown in FIG. The OB area 904 is input to the filter unit 102 of the clamp processing unit 106 illustrated in FIG. 1 and used for the clamp processing.

  A clamp signal 906 is output from the filter unit 102 and converges according to a time corresponding to the time constant of the filter unit 102. FIG. 9 shows a clamp signal 906 when a dark current suddenly increases from a certain frame image and an imaging signal of an OB region having a high signal level is input, and the first line of the effective pixel region 304 is clamped. A converged state is shown at the line position 907 before being performed. In this way, when the imaging signal of the OB region input to the filter unit 102 of the clamp processing unit 106 varies, in order to output a target clamp signal corresponding to the variation, the filter unit 102 depends on the time constant characteristic. Takes time.

  In the present embodiment, like the image sensor 301 shown in FIG. 3, the OB area 303 does not have an OB area that is read earlier than the read head line of the effective pixel area 304 in the image sensor, or the OB area is narrow. In the case: First, the OB correction unit 101 adds an OB area 903 to the upper part of the OB area 303 to correct the OB area. As a result, of the corrected OB region 904, the added portion of the OB region 903 is input to the filter unit 102 of the clamp processing unit 106 before the effective pixel region 304. As a result, after the clamp signal that is the output of the filter unit 102 is stabilized (907), the image pickup signal of the read head line in the effective pixel region 304 is clamped by the clamp processing unit 106. Therefore, according to the present embodiment, the image pickup signal can be clamped with a clamp signal having a stable clamp level over the entire effective pixel region, and a good image without unevenness, for example, is obtained as shown in FIG. be able to.

Next, a method for determining the number of additional lines in step S503 in FIG. 5 will be described. FIG. 11 is a flowchart illustrating an example of the additional line number calculation process. When the additional line number calculation process is started (S1101), first, the OB correction control unit 105 normalizes the difference between the shooting parameters of the previous and subsequent frames. The black level is caused by a dark current, and the dark current increases as the temperature T, exposure time S, and gain (signal amplification factor) A of the image sensor increase. Imaging parameters E _n of a frame is expressed by the following equation (2).
E _n = T _n + S _n + A _n
Here, a detection condition for face detection and a detection condition for moving object detection that are processed by the arithmetic control unit 209 shown in FIG. 2 may be added to the left side of the expression (2).

OB correction control unit 105, using Equation (2), to obtain the difference (E _n -E _n-1) between the imaging parameter E _n-1 of the imaging parameter E _n and the previous frame of the current frame (S1102) . Next, the OB correction control unit 105 acquires the time constant M of the filter unit 102 of the clamp processing unit 106 (S1103). Then, the OB correction control unit 105 estimates the change amount Im of the dark current from the difference (E _n −E _n−1 ) between the previous and next frames of the imaging parameter derived using Expression (2). Further, the OB correction control unit 105 calculates the number of lines L required for the dark current change amount to converge from the time constant M of the filter unit 102 to determine the number of additional lines (S1104). The calculation process is terminated (S1105).

  Further, when the additional line number L determined in the additional line number calculation process in step S503 exceeds the limit of the line memory reservation amount, or the black level for inputting the clamp level with a small additional line number is desired to follow. In this case, the control may be performed as follows. For example, by reducing the time constant M only when the image signal of the additional line is being input to the filter unit 102, the clamp level can be pulled to the black level while the additional line is inputting the filter with a small number of additional lines.

(Second Embodiment)
Next, a second embodiment of the present invention will be described. The second embodiment described below is different from the first embodiment described above in the configuration and control of the OB correction unit 101, and is otherwise the same as the first embodiment, and thus the description thereof is omitted. .

  FIG. 12 is a diagram illustrating a configuration example of the OB correction unit 101 according to the second embodiment. The OB correction unit 101 includes a first-in first-out (FIFO) type line memory 1202, a through line 1203, an input side imaging signal changeover switch 1205, and an output side imaging signal changeover switch 1204. The switch 1205 controls connection between the imaging signal input terminal and the input terminal 1207 of the through line 1203 and the input terminal 1208 of the line memory 1202. The switch 1204 controls connection between the output terminal of the OB correction unit 101, the output terminal 1209 of the through line 1203, and the output terminal 1210 of the line memory 1202. The switches 1204 and 1205 are controlled to be switched by the OB correction control unit 105. Further, the driving timing inside the OB correction unit 101 is driven in synchronization with the pixel clock, vertical synchronizing signal, and horizontal synchronizing signal supplied from the timing generator 212 shown in FIG.

  An OB correction process by the OB correction unit 101 and the OB correction control unit 105 in the second embodiment will be described. FIG. 13 is a flowchart illustrating an example of the OB correction process according to the second embodiment. The OB correction control unit 105 is activated from a certain point in the imaging device activation sequence (S1301), and control by the OB correction control unit 105 is started. The OB correction control unit 105 determines whether or not the read line of the current imaging signal that passes through the OB correction unit 101 is the top line of the OB area 303 (S1302).

  When the readout line of the current imaging signal is the first line of the OB area 303, the OB correction control unit 105 is the optimum additional line for clamping by the subsequent clamp processing unit in the same manner as in the first embodiment. The number is calculated and determined (S1303). Thereafter, the OB correction control unit 105 controls the switch 1204 and the switch 1205 according to the position of the readout line of the imaging signal (S1304), and the imaging signal of each line passes through the FIFO type line memory 1202 or the through line 1203. .

  If the result of determination in step S1302 is that the current readout line of the imaging signal is not the first line of the OB area 303, the OB correction control unit 105 controls the switch 1204 and the switch 1205 in accordance with the current readout line position. (S1304). Thereby, the imaging signal of each line passes through the FIFO type line memory 1202 or the through line 1203.

  FIG. 14 shows a timing table of the line numbers of the imaging signals stored in the FIFO type line memory 1202 when the additional line number calculation result in step S1303 is “1”. As shown in FIG. 14, the line configuration of the OB area input to the OB correction unit 101 is a total of N lines starting from line number 1. On the other hand, the line configuration of the OB area output from the OB correction unit 101 is a total of (N + 1) lines, and the OB area of line number 1 is added to the head.

  In this example, one line is added. However, the number of additional lines differs depending on the result of calculating the number of additional lines in step S1303 in FIG. As for the memory size of the FIFO type line memory 1202, an area may be adaptively secured according to the result of the additional line number calculation, or the memory area may be reserved in advance for the maximum number of additional lines of the additional line number calculation result. Good. When the result of calculating the number of additional lines is zero, the switch 1205 is connected to the input terminal 1207 of the through line 1203 and the switch 1204 is connected to the output terminal 1209 of the through line 1203. Become. That is, the imaging signal of each line is not accumulated in the FIFO type line memory 1202 and passes through the OB correction unit 101.

  As described above, according to the second embodiment, similarly to the first embodiment, the imaging signal can be clamped with the clamp signal having a stable clamp level over the entire effective pixel region. Further, in the second embodiment, by adopting a FIFO type line memory as the line memory, it is only necessary to secure half the capacity of the line memory in the first embodiment.

  In the first embodiment described above, the output from the image sensor including the OB area 903, the invalid area, and the effective pixel area 901 is stored and output as it is in the line memory of the OB correction unit 101. In the second embodiment, as shown in FIG. 15, the imaging signals of the invalid area and the effective pixel area 901 are repeatedly rewritten and transmitted with the imaging signal of the OB area 903. When the imaging signal of the OB area 1503 is rewritten repeatedly as in the area 1505 shown in FIG. 15 (1504), and the OB area is enlarged and input to the clamp processing unit 106, the input area of the imaging signal to the filter unit 102 is Control is performed so that the area 1505 and the area 303 are obtained. With such control, the convergence time of the clamp signal that is the output of the filter unit 102 is based on the timing at which the read first line of the effective pixel region 304 is input to the clamp processing unit 106 by the amount of the enlarged OB region 1505. Relatively fast. Further, while the line addition region 1505 is being input to the filter unit 102, the clamp level can follow the black reference level at a higher speed by reducing the time constant of the filter unit 102.

(Third embodiment)
Next, a third embodiment of the present invention will be described. In the third embodiment, even an image sensor including a large shading characteristic can be appropriately clamped. In the following, only the differences of the third embodiment from the first and second embodiments will be described. In the following, an OB correction unit 101 similar to that of the second embodiment will be described as an example, but the OB correction unit 101 similar to that of the first embodiment can also be applied.

  The clamping process when the OB area 1907 is read earlier than the reading start line of the effective pixel area 1904 in the image sensor as the OB area as in the image sensor 1901 shown in FIG. 19 is described above. However, when the image sensor has a large shading characteristic, the shading characteristic of the end region 1907 of the OB region tends to be particularly large. When the shading characteristics of the OB area 1907 are large, the shading characteristics may affect the normal clamping process.

  Therefore, as a third embodiment, the head of the OB area 1907 is one line, and the shading characteristic is large from the first line to the (X-1) th line (X is a natural number of 2 or more), and the optical black level is high. An example in the case of an image sensor having characteristics that are not suitable as a reference region will be described. FIG. 16 is a flowchart illustrating an example of OB correction processing according to the third embodiment.

  The OB correction control unit 105 is activated from a certain point in the activation sequence of the imaging apparatus (S1601), and control by the OB correction control unit 105 is started. The OB correction control unit 105 determines whether or not the read line of the current imaging signal that passes through the OB correction unit 101 is the X-th line from the head line of the OB area 1903 (S1602).

  When the readout line of the current imaging signal is the X-th line from the first line of the OB area 1903, the OB correction control unit 105 is used for clamping by the subsequent clamp processing unit in the same manner as in the first embodiment. The optimum number of additional lines is determined by calculation (S1603). Thereafter, the OB correction control unit 105 controls the switch 1204 and the switch 1211 in accordance with the position of the readout line of the imaging signal (S1604), and the imaging signal of each line passes through the FIFO type line memory 1202 or the through line 1203. .

  If the result of determination in step S1602 is that the readout line of the current imaging signal is not the X-th line from the beginning of the OB area 303, the OB correction control unit 105 switches the switch 1204 and the switch according to the current readout line position. 1205 is controlled (S1604). Thereby, the imaging signal of each line passes through the FIFO type line memory 1202 or the through line 1203.

  When the additional line number calculation result in step S1603 is “1”, the line configuration of the OB area input to the OB correction unit 101 after the above flow is from line number 1 as in FIG. Total N lines starting. On the other hand, the line configuration of the OB area output from the OB correction unit 101 is a total (N + 1) lines, and the line number X of the OB area of the Xth line from the first line is added as shown in FIG. State.

  The imaging signal corrected by the OB correction unit 101 as described above is input to the clamp processing unit 106. Then, by issuing a command from the arithmetic control unit 104 to the filter circuit 102 so that the imaging signal of the OB region input to the filter unit 102 comes from the X-th line, the imaging signal of the OB region 1907 having high shading characteristics is not used. The OB clamping process is performed. Furthermore, when the output characteristics of the filter unit 102 converge at the line added by the OB correction unit 101, it is possible to perform an appropriate clamping process over the entire effective image area.

(Other embodiments of the present invention)
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 storage media, and a computer (or CPU, MPU, or the like) of the system or apparatus reads the program. It is a process to be executed.

  The above-described embodiments are merely examples of implementation in carrying out the present invention, and the technical scope of the present invention should not be construed as being limited thereto. That is, the present invention can be implemented in various forms without departing from the technical idea or the main features thereof.

101: OB correction unit 102: filter unit 103: adder 104: calculation control unit 105: OB correction control unit 106: clamp processing unit 203: imaging device 204: amplifier 205: AD conversion unit 206: clamp processing unit 209: calculation control Unit 212: Timing generator 301: Image sensor 302: Invalid area 303: OB area 304: Effective pixel area

Claims (8)

An imaging device having an effective pixel region and an optical black region, photoelectrically converting an input optical image and outputting an imaging signal;
Conversion means for analog-to-digital conversion of the imaging signal output from the imaging element;
Correction means for adding at least the image pickup signal of the optical black region of the image pickup signal converted by the conversion means to the image pickup signal converted by the conversion means;
Clamp processing means for performing clamp processing for standardizing a black level on the image pickup signal converted by the conversion means based on the image pickup signal of the optical black area input through the correction means. An imaging apparatus characterized by that.   The clamp processing unit outputs a difference between the image pickup signal converted by the conversion unit and a clamp signal obtained by filtering the image pickup signal of the optical black area input through the correction unit. The imaging apparatus according to claim 1.   The correction unit includes a storage unit that stores at least the image pickup signal of the optical black area among the image pickup signals converted by the conversion unit in units of lines, and the correction unit includes a line that stores the image pickup signal in the storage unit. The imaging apparatus according to claim 1, wherein the imaging signal is output to the clamp processing unit a plurality of times. An imaging device having an effective pixel region and an optical black region, photoelectrically converting an input optical image and outputting an imaging signal;
Conversion means for analog-to-digital conversion of the imaging signal output from the imaging element;
Clamp processing means for clamping the imaging signal of the effective pixel area or the optical black area after being converted by the conversion means to a black level by taking a difference from the clamping signal based on the imaging signal of the optical black area; ,
Correction means for processing the imaging signal after being converted by the conversion means in units of lines;
Correction control means for controlling the correction means,
The correction control means controls the correction means so that the image pickup signal of the effective pixel region is clamped at a black level by the clamp processing means after the image pickup signal is processed by the correction means. .   The correction means outputs an imaging signal of at least one line of the Xth line (X is a natural number) from the first line of the optical black region to the clamp processing means a plurality of times. 5. The imaging device according to any one of 4.   The imaging apparatus according to claim 5, wherein the number of lines of the imaging signal output a plurality of times is determined according to a shooting condition of the imaging apparatus.   The imaging condition includes an exposure time of the imaging device, a signal amplification factor of the imaging signal, a temperature of the imaging device, a detection condition for detecting a face from the imaging signal of the imaging device, and a moving object from the imaging signal of the imaging device The imaging apparatus according to claim 6, further comprising at least one of detection conditions for detecting an image. A conversion step of analog-digital conversion of the imaging signal output from an imaging device having an effective pixel area and an optical black area, photoelectrically converting an input optical image and outputting an imaging signal;
A correction step of adding at least the imaging signal of the optical black region of the imaging signal converted in the conversion step to the imaging signal converted in the conversion step;
A clamp processing step of performing a clamp processing for standardizing a black level on the imaging signal converted in the conversion step based on the imaging signal of the optical black region processed in the correction step. A signal processing method characterized by the above.

Images