JP2016029756A - Imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging device capable of appropriately correcting a residual image phenomenon caused by an electric charge gradually mixed in a signal charge in driving for reading signals of a still image.SOLUTION: An imaging device comprises: an image pickup element in which pixels each including a photoelectric conversion part are arranged like a matrix; light-shielding means for optically shielding the image pickup element; control means for controlling the activation of the image pickup element, reading out a first pixel signal accumulated by the photoelectric conversion part in a state of being exposed to light, and further reading out an optically shielded pixel signal accumulated by the photoelectric conversion part in a state of being optically shielded; and residual image correcting means for calculating a residual image amount based on a time from the start of accumulation of the optically shielded pixel signal until the readout of the first pixel signal, a time from the start of accumulation of the first pixel signal until the readout of the first pixel signal, and a time from the start of accumulation of the first pixel signal until the readout of the optically shielded pixel signal for each pixel, and subtracting the residual image amount from the first pixel signal for each pixel.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an imaging apparatus, and more particularly to correction of an image signal.

  In recent years, an image sensor used for a digital camera or the like can obtain a smooth moving image by continuously reading an image signal at a predetermined frame rate in a live view (hereinafter referred to as LV) display function or a moving image shooting function.

  Rolling electronic shutter drive is often used for reading image signals in LV display and moving image shooting. Rolling electronic shutter drive is a method of reading signals from a photodiode (hereinafter referred to as PD), which is a photoelectric conversion unit for each pixel, by sequentially scanning pixels arranged in a matrix on the image sensor in units of one or several rows. It is. Further, in the rolling electronic shutter, similarly to the readout scanning, the signal charge of the PD is reset by sequentially scanning in units of one row or several rows, so that the signal readout time from the reset of each PD is all rows. Any storage time that is equal and uniform within the screen can be controlled.

  By the way, in Patent Document 1, a part of the signal charge accumulated in the pixels of the image sensor remains, and an afterimage due to the residual charge is generated at the time of imaging in the next frame period, and the imaging image quality is improved. It describes the problem of deteriorating.

JP 2013-98825 A

  The generation mechanism of this problem is described in Patent Document 1 as follows. The intrinsic semiconductor layer constituting the imaging device has a large number of defect orders. Immediately after the end of the signal charge readout period, charges are trapped at these defect levels. However, when a certain amount of time elapses from the reading period, the charge trapped in the defect level is released from the intrinsic semiconductor layer to the outside of the photoelectric conversion element. As a result, a part of the signal charge remains in the pixel (residual charge is generated).

  Thus, for example, when a still image is shot from the state of LV display (or moving image shooting) of the digital camera, the signal charge generated during the LV display and trapped in the defect level is being driven to read out the still image. In addition, there is a problem that an afterimage occurs in a still image when it is released over time.

  Therefore, in view of such a problem, an object of the present invention is to provide an imaging apparatus that appropriately corrects an afterimage phenomenon caused by charges that are gradually mixed with signal charges during read driving of a still image signal.

  The configuration of the imaging apparatus according to the present invention includes: an imaging element in which a plurality of pixels each including a photoelectric conversion unit are arranged in a matrix; a light shielding unit that can shield the imaging element; and driving and controlling the imaging element. Control means for reading out the first pixel signal accumulated in the photoelectric conversion unit in the exposure state, and further reading out the light-shielded pixel signal accumulated in the light-shielding state in the photoelectric conversion unit, the light-shielded pixel signal for each pixel, and The afterimage amount is calculated based on the time from the start of accumulation of the first pixel signal to the readout of the first pixel signal and the time from the start of accumulation of the first pixel signal to the readout of the light-shielded pixel signal. And an afterimage correction unit that subtracts the afterimage amount for each pixel from the first pixel signal.

  According to the present invention, it is possible to provide an imaging apparatus that appropriately corrects an afterimage phenomenon caused by a charge that is gradually mixed with a signal charge during driving for reading a still image signal.

It is a system block diagram which shows the structure of the imaging device based on the Example of this invention. It is a schematic diagram which shows the structure of the image pick-up element based on the Example of this invention. It is a schematic diagram which shows the circuit concerning the structure of pixel, and reading based on the Example of this invention. It is a figure which shows the relationship between a vertical scanning and time, and the relationship between a signal amount and time when performing a still image photography from the LV display state according to Embodiment 1 of the present invention. It is a figure which shows the control flow of an imaging device and the processing flow of an image signal based on the Example of this invention. It is a figure which shows the relationship between a vertical scanning and time, and the relationship between a signal amount and time when performing still image photography from the LV display state according to Embodiment 2 of the present invention. It is a figure which shows the relationship between a vertical scanning and time, and the relationship between a signal amount and time when performing a still image photography from the LV display state according to Embodiment 3 of the present invention.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[Example 1]
FIG. 1 is a system block diagram illustrating a configuration of an imaging apparatus according to an embodiment of the present invention. In FIG. 1, reference numeral 101 denotes an optical system including a focus lens, a zoom lens, and a diaphragm. Reference numeral 102 denotes an image sensor that receives an optical image formed by the optical system 101. Reference numeral 103 denotes an optical system drive unit that controls the focus lens position of the optical system 101 by a control signal in accordance with optical system drive information output from an AF control unit (not shown). Reference numeral 104 denotes an analog front end (hereinafter referred to as AFE). The AFE 104 includes an AD converter, and performs reference black level adjustment, analog / digital conversion processing, and the like.

  However, if the image sensor 102 includes an AD converter, the AFE 104 does not necessarily include the AD converter. A digital front end (hereinafter referred to as DFE) 105 receives the digital output of each pixel and performs digital processing such as pixel rearrangement. A digital signal processing unit 106 performs image processing such as color conversion, white balance correction, and gamma correction, resolution conversion processing, image compression processing, and the like on the image signal obtained from the DFE 105, and performs display unit 108 and recording. The processed image signal is output to the medium 109. A storage unit 107 is used as a working memory for the digital signal processing unit 106 or as a buffer memory for continuous shooting or the like.

  In the present invention, the storage unit 107 is used as an image memory for temporarily storing a still image signal and a correction black image signal. Reference numeral 108 denotes a display unit that displays a preview of a continuous image received from the digital signal processing unit 106 during LV display and a still image after shooting. Reference numeral 109 denotes a recording medium. In this embodiment, image data that has been subjected to afterimage correction is recorded.

  FIG. 2 is a schematic diagram illustrating a configuration of the image sensor 102 according to the embodiment of the present invention. As shown in FIG. 2, the image sensor 102 according to the present invention includes a pixel unit 201, a vertical scanning unit 202, a reading unit 203, a horizontal scanning unit 204, and a vertical signal line 206. In the pixel unit 201, a plurality of pixels 205 that receive an optical image formed by the optical system 101 are arranged in a matrix. For the sake of explanation, only 6 rows in the vertical direction and 8 columns in the horizontal direction are shown.

  The vertical scanning unit 202 sequentially selects the rows of the pixel unit 201 in the vertical direction, and samples the signal of each pixel 205 to the reading unit 203. The reading unit 203 includes a gain amplifier for each column, an AD converter, and the like, and samples the signal of the row selected by the vertical scanning unit 202. The horizontal scanning unit 204 outputs the signal of each pixel 205 sampled by the reading unit 203 to a circuit such as the subsequent AFE 104 by sequentially selecting in the horizontal direction. The vertical signal line 206 is configured to output the signal of each pixel 205 to the reading unit 203.

  FIG. 3 is a schematic diagram illustrating a configuration of the pixel 205 and a circuit related to readout according to the embodiment of the present invention. For the sake of explanation, only one pixel 205 and its signal output path are shown. In FIG. 3, reference numeral 301 denotes a PD. The PD 301 functions as a photoelectric conversion unit that generates and accumulates signal charges according to the amount of received light. Reference numeral 302 denotes a transfer switch, and 303 denotes a floating diffusion (hereinafter referred to as FD). The transfer switch 302 is driven by the signal pulse PTX and transfers the electric charge accumulated in the PD 301 to the FD 303. The FD 303 functions as a charge holding unit that holds charges transferred from the PD 301. The FD 303 also functions as a charge-potential conversion unit that converts the held charge into a potential signal.

  Reference numeral 304 denotes a reset switch. The reset switch 304 is driven by a signal pulse PRES and has a configuration capable of discharging the electric charge held in the FD 303. Reference numeral 305 denotes a signal output unit, and reference numeral 307 denotes a constant current source. The signal output unit 305 outputs a signal based on the potential of the FD 303 as a pixel signal of the pixel 205. The signal output unit 305 constitutes a source follower circuit together with the constant current source 307. Reference numeral 306 denotes a selection switch. The selection switch 306 is driven by the signal pulse PSEL and connects the signal output unit 305 and the vertical signal line 206. The signal of the signal output unit 305 output to the vertical signal line 206 is sampled for each vertical signal line 206 by the reading unit 203 and then output to a circuit such as the subsequent AFE 104.

  4 shows the relationship between vertical scanning and time (FIG. 4 (a)) and the relationship between signal amount and time (FIG. 4 (b), ( It is a figure which shows c) and (d)). However, the time on the horizontal axis of FIGS. 4A, 4B, 4C, and 4D is illustrated so as to match.

  FIG. 4B is a diagram showing a signal amount due to charges generated by photoelectric conversion in the PD 301 in particular. Here, in the following description, a signal component due to charges generated by photoelectric conversion in the PD 301 is referred to as an optical signal. FIG. 4C is a diagram showing the signal amount due to the charge that is gradually mixed with the signal charge of the PD 301 to generate an afterimage. Here, in the following description, a signal component due to charge that is gradually mixed with the optical signal charge of the PD 301 to generate an afterimage is referred to as an afterimage signal and is distinguished from an optical signal. FIG. 4D is a diagram showing the pixel signal amount read from the pixel 205 to the reading unit 203, and is the sum of the optical signal amount and the afterimage signal amount.

  In FIG. 4A, 401 indicates reset scanning in the vertical direction. Reference numeral 402 denotes an image signal readout scan for LV display. Therefore, the interval between the reset scan 401 and the LV display image reading 402 represents the accumulation time for each row of the PD 301. Reference numeral 403 denotes electronic front curtain shutter scanning for still image shooting. The electronic front curtain shutter scan 403 electronically controls the start timing of signal charge accumulation by sequentially releasing the reset state of each row of the PD 301.

  Reference numeral 404 denotes rear curtain scanning by a mechanical shutter (not shown). The mechanical shutter is disposed between the image sensor 102 and the optical system 101 and controls the exposure / light-shielding state of the image sensor 102. Since the mechanical shutter has a property that the traveling speed changes with time as illustrated in 404 of FIG. 4A, the electronic front curtain shutter 403 is arranged line by line in accordance with the traveling curve of the rear curtain mechanical shutter 404. It is controlled to release the reset state. Therefore, the electronic front curtain shutter 403 and the rear curtain mechanical shutter 404 control a still image exposure period 407 having the same accumulation time within the surface of the pixel unit 201.

  Reference numeral 405 denotes scanning for reading a still image signal. In the still image signal readout 405, the signal charges accumulated in the PD 301 after being shielded by the rear curtain mechanical shutter 404 are sequentially read out row by row. At this time, the signal read by the still image signal reading 405 is a signal in an uncorrected state with respect to the afterimage phenomenon which is the subject of the present invention. As described above, a still image signal may include an afterimage signal by gradually mixing charges trapped in a semiconductor defect or the like, but in the present invention, it is based on a correction black image signal to be described later. Afterimage signal amount is calculated, and correction subtraction processing is performed.

  Here, when the charge of the PD 301 is transferred to the FD 303 in the still image signal reading 405, the charge accumulated in the PD 301 is once lost. The charge transferred from the PD 301 and held in the FD 303 is sampled as a signal for each pixel by the reading unit 203 and then discharged to the power supply SVDD through the reset switch 304.

  Reference numeral 406 denotes a correction black image signal readout scan. In the correction black image signal image reading scan 406, after the still image signal reading scan 405, a signal in a light-shielded state is read in order to gradually reach the PD 301 and acquire the accumulated afterimage signal amount. According to the present invention, a corrected image signal can be obtained by calculating an afterimage signal amount based on a signal obtained by reading out a correction black image and subtracting and correcting the afterimage signal from the still image signal. The light shielding state by the rear curtain mechanical shutter 404 is maintained until the scanning of the correction black image reading 406 is completed.

  FIG. 4B is a diagram showing an example of the relationship between the amount of optical signal and time when attention is paid to one pixel in the n-th row shown in FIG. When the n-th row of the pixel unit 201 is scanned by the electronic front curtain shutter 403 at time T0, accumulation of optical signal charges in the exposure period 407 is started. The optical signal amount L (t) of the pixel in the n-th row is shown to increase depending on the accumulation time in the period from time T0 to T1.

  When the pixel in the nth row is shielded by the rear curtain mechanical shutter 404 at time T1, the increase in the amount of optical signal stops, but the optical signal charge generated by time T1 is accumulated in the PD 301 until time T2. It has been done. Therefore, L (T1) = L (T2). The optical signal charge of the PD 301 is transferred to the FD 303 and disappears when it is read by the still image signal reading scan 405 at time T2. Note that the pixel signal read according to the optical signal amount L (T2) = L (T1) not including the afterimage signal at time T2 corresponds to the image signal in which the afterimage component signal which is the object of the present invention is corrected. Yes.

  FIG. 4C is a diagram illustrating an example of a relationship between an afterimage signal amount and time when attention is paid to one pixel in the n-th row illustrated in FIG.

  When the reset state for each row of the PD 301 is released by the electronic front curtain shutter 403 at time T0, charges trapped in the defect level of the semiconductor layer of the image sensor during LV display gradually flow out to the PD 301. It starts to accumulate.

Here, the afterimage signal amount N (t) increases depending on the function of the time t shown in the following Expression 1.
N (t) = N0 × [1-exp {− (t−T0) / τ}] Equation 1
(However, in the following description, T0 = 0. Therefore, N (T0) = 0)
In Equation 1, τ is a time constant, and N0 is the total amount of charges trapped in a defect or the like in the semiconductor of one pixel. Unlike the optical signal amount L (t), the afterimage signal amount N (t) continues to increase according to Equation 1 even when the pixel 205 in the nth row is shielded by the rear curtain mechanical shutter 404 at time T1. Then, the afterimage signal charge in the PD 301 is transferred to the FD 303 when it is read out by the still image signal reading scan 405 at time T2, but is temporarily lost, but is discharged from the defect level during the period from time T0 to time T2. The trapped electric charges are further springed out after time T2.

  After the time T2, the afterimage signal charge accumulated in the PD 301 is transferred to the FD 303 and temporarily disappears when it is read out as a correction black image signal in the correction black image signal readout scanning 406 at time T3. At time T3, the trapped charges that are not released from the defect level and are trapped further spring out after time T3.

  FIG. 4D is a diagram illustrating the amount of pixel signal read from the pixel 205 to the reading unit 203, and is the sum of the amount of optical signal and the amount of afterimage signal. The afterimage signal amount N (t) starts to be mixed with the optical signal amount L (t) from time T0 and increases with time. When the rear curtain mechanical shutter blocks light at time T1, the increase in the optical signal amount stops at L (T1), but the afterimage signal amount continues to increase according to Equation 1.

  When the pixel signal S (T2) in the n-th row is read as a still image signal at time T2, S (T2) is the sum of the optical signal amount L (T2) and the afterimage signal amount N (T2). . When the still image signal S (T2) is read at time T2, all the charges accumulated in the PD 301 are once transferred via the transfer switch 302. However, as described above, there is an afterimage signal charge that reaches the PD 301 over a longer time after the time T2.

  At time T3, the pixel signal S (T3) in the nth row is read out by the correction black image reading scan 406. The pixel signal S (T3) read out as the black image signal for correction at time T3 is a pixel signal read out in a light-shielded state by the rear curtain mechanical shutter 404, and therefore includes charges generated by photoelectric conversion at the pixel. Absent. Therefore, the correction black image signal S (T3) can be regarded as being equal to the afterimage charge amount N (T3) associated with the charge generated after the still image signal readout 405 and from the time T2 to the time T3.

  In the present invention, an afterimage signal amount N (T2) mixed in the still image signal S (T2) is calculated using the signal S (T3) obtained by reading the correction black image, and the exposure period 407 An optical signal amount (that is, equivalent to the corrected image signal amount) L (T2) due to the photoelectrically converted charge is obtained.

The optical signal amount L (T2) is expressed by Equation 2.
L (T2) = S (T2) −N (T2) Equation 2
As described above, since the correction black image signal S (T3) can be regarded as being equal to the afterimage charge amount N (T3), Expression 3 is obtained.

S (T3) = N (T3) Equation 3
Here, Equations 4 and 5 are obtained from Equation 1 using N (T2) and N (T3).
N (T2) = N0 × {1-exp (−T2 / τ)} Expression 4
N (T2) + N (T3) = N0 × {1-exp (−T3 / τ)} Expression 5
From Equation 3, Equation 4, and Equation 5, N0 can be calculated according to Equation 6.
N0 = S (T3) / {exp (−T2 / τ) −exp (−T3 / τ)} Expression 6
Next, from Equations 4 and 6, N (T2) can be calculated according to Equation 7.

N (T2) = S (T3) × {1-exp (−T2 / τ)}
/ {Exp (-T2 / τ) -exp (-T3 / τ)} Equation 7
Then, the corrected still image signal L (T2) is calculated by Expression 8 from Expression 2 and Expression 7.
L (T2) = S (T2) −S (T3) × {1-exp (−T2 / τ)}
/ {Exp (-T2 / τ) -exp (-T3 / τ)} Equation 8
As described above, the afterimage signal amount is obtained by using the afterimage signal amount, amount S (T3) = N (T3) and the still image signal amount S (T2) obtained by reading out the correction black image according to Expression 7. N (T2) can be calculated. Then, according to Expression 8, an optical signal amount L (T2) corresponding to the signal amount of the corrected image excluding the afterimage signal component can be obtained. In the above description, the description has been made by paying attention to the pixel 205 in the n-th row in FIG. 4, but actual times of T0, T1, T2, and T3 are set to drive the imaging device and the imaging element 102. Since the fixed value is taken for each pixel 205 in accordance with the parameters, the optical signal amount L (T2) can be calculated for all the pixels 205 according to Equation 8.

  Further, when the correction black image signal is read out, the gain of the gain amplifier of the reading unit 203 may be read out higher than when the still image signal is read out. By driving in this way, even when the afterimage signal charge amount is small, the correction black image signal corresponding to the afterimage signal charge amount can be amplified and read out by the gain amplifier, so that the accuracy of calculating the afterimage amount is improved. Can be expected. However, in this case, it is necessary to calculate the corrected image signal after converting the correction black image signal S (T3) according to the ratio between the amplification factor of the still image signal and the correction black pixel image signal. is there.

  FIG. 5 is a diagram showing a control flow and an image signal processing flow of the imaging apparatus of the present invention. First, a mechanical shutter (not shown) is opened (step 501), and a drive setting signal is given to the image sensor 102 (step 502) to activate the LV display function (step 503).

  In step 503, exposure control is performed continuously until the release switch is pressed in step 504, and the LV display image is also updated in order to control the exposure amount prior to shooting. As described above, after the exposure is confirmed, when the release switch is pressed, still image shooting is started.

  Thereafter, as described with reference to FIG. 4A, the readout scanning 402 of the LV display image is completed, and the pixel reset state is sequentially released for each row by the electronic front curtain shutter scanning 403 (step 505). Thus, the exposure (step 506) is performed for still image shooting, and signal charges (photo signal charges) corresponding to the amount of light incident on each pixel are accumulated in the PD 301. When the set accumulation time has elapsed, the image sensor 102 is shielded from light by the second curtain mechanical shutter scanning 404 (step 507), and the exposure period 407 ends. Thereafter, the signal read from each pixel and AD-converted by the AFE 104 (step 508) is temporarily stored in the storage unit 107 as a still image signal (step 509).

  Next, the output signal of each pixel is read as a black image signal for correction while maintaining the state of being shielded from light by the rear curtain mechanical shutter 404, and AD converted by the AFE 104 (step 510). Temporarily stored (step 511).

  Next, signal processing for obtaining a corrected image in which the afterimage signal component is corrected is performed based on the still image signal stored in the storage unit 107 in step 509 and step 511 and the correction black image signal. .

  First, the digital signal processing unit 106 gives a pixel count initial value m = 0 (step 512). Next, an afterimage corrected image signal of one target pixel is calculated according to the above-described equation 9 (step 513). Next, the pixel count m is incremented (step 514), and the same calculation is performed until all the number of pixels M of the image sensor is reached (step 515).

  Finally, in step 516, the calculated afterimage corrected image signals of all the pixels are recorded on the recording medium 109, and a series of photographing operations is completed.

  As described above, according to the present embodiment, after the still image signal is read out, the correction black image signal is read out in a light-shielded state. Then, by using the still image signal and the correction black image signal, the signal amount excluding the signal component due to the afterimage charge included in the still image signal is calculated as the corrected image signal, so that the afterimage correction is appropriately performed. Can be obtained. For example, according to the imaging apparatus of the present embodiment, it is possible to reduce image quality degradation due to an afterimage phenomenon in still image shooting from the LV display state.

[Example 2]
Next, a second embodiment of the present invention will be described. The second embodiment is characterized in that the reading scan time is shortened by reading out the correction black image in the row direction, and the processing time for obtaining the afterimage corrected image signal from the start of still image shooting is reduced. .

  6 shows the relationship between vertical scanning and time (FIG. 6 (a)) and the relationship between signal amount and time (FIG. 6 (b), ( It is a figure which shows c) and (d)). However, the time on the horizontal axis of FIGS. 6A, 6B, 6C, and 6D is illustrated so as to match. FIG. 6B shows the amount of optical signal. FIG. 6C shows the amount of afterimage signal. FIG. 6D is a diagram showing the amount of pixel signal read from the pixel 205 to the reading unit 203, and is the sum of the amount of optical signal and the amount of afterimage signal.

  In FIG. 6, the same portions as those in FIG. 4 of the first embodiment are denoted by the same reference numerals, and the description thereof is omitted. In FIG. 6A, reference numeral 601 denotes vertical thinning scanning of the correction black image. In the first embodiment, all the rows are scanned in the same manner as the still image in order to obtain the correction black image. However, in the second embodiment, the time required to read out the image by reading out this as a vertical thinning scan. Is shortened. In the vertical thinning scanning, for example, the number of rows to be read can be reduced at a rate of one row in three rows or one row in five rows.

  In the second embodiment, since the signal is not necessarily read out from the pixel of the correction black image signal having the same address as the pixel from which the still image signal is read out, it is read out from the address closest to the address of the still image signal. The afterimage-corrected image signal may be calculated using the correction black image signal as in the first embodiment.

  Also in the second embodiment, after the still image signal is read out, the correction black image signal is read out subsequently. Then, by using the still image signal and the black image signal for correction to calculate the signal amount excluding the afterimage signal amount included in the still image signal as a corrected image signal, a good image that has been appropriately afterimage-corrected Can be obtained.

[Example 3]
Next, a third embodiment of the present invention will be described. In the third embodiment, the correction black image is thinned out in the row direction to shorten the readout scanning time, and the correction black image signal is read out twice at different times, thereby shortening the readout scanning time and making the afterimage signal more accurate. It is characterized by obtaining a corrected image signal that is well corrected.

  FIG. 7 shows the relationship between vertical scanning and time (FIG. 7 (a)) and the relationship between signal amount and time (FIG. 7 (b), ( It is a figure which shows c) and (d)). However, the time on the horizontal axis of FIGS. 7A, 7B, 7C, and 7D is illustrated so as to match. FIG. 7B shows the amount of optical signal. FIG. 7C shows the amount of afterimage signal. FIG. 7D is a diagram showing the pixel signal amount read from the pixel 205 to the reading unit 203, and is the sum of the optical signal amount and the afterimage signal amount.

  In FIG. 7, the same portions as those in FIG. 4 of the first embodiment are denoted by the same symbols, and the description thereof is omitted. In FIG. 7A, reference numeral 701 denotes the first scan for reading the correction black image. Reference numeral 702 denotes the second scan of the correction black image readout. The correction black image reading is illustrated as an example of reading by vertical thinning scanning as in the second embodiment.

  In Example 3, an afterimage charge amount N (T2) included in the still image signal S (T2) is calculated using the signals S (T3) and S (T4) obtained by reading the correction black image. An optical signal amount (that is, corresponding to the corrected image signal amount) L (T2) due to the electric charge photoelectrically converted in the exposure period 407 is obtained.

  First, similarly to the first embodiment, the third embodiment also uses the signal S (T3) read by the correction black image reading scan 701 and the times T0, T2, and T3, and N (T2) according to Expression 7. Can be calculated.

  Further, in the third embodiment, the signal S (T4) read out by the correction black image reading scan 702 has the relationship of the following Expression 9.

S (T4) = N (T4) Equation 9
Here, Expressions 10 and 11 are obtained from Expression 1 using N (T2), N (T3), and N (T4).

N (T2) + N (T3) = N0 × {1-exp (−T3 / τ)} Expression 10
N (T2) + N (T3) + N (T4) = N0 × {1-exp (−T4 / τ)}
... Formula 11
From Formula 9, Formula 10, and Formula 11, N0 can be calculated according to Formula 12.

N0 = S (T4) / {exp (−T3 / τ) −exp (−T4 / τ)} Expression 12
Next, from Equation 4 and Equation 12, N (T2) can be calculated according to Equation 13.

N (T2) = S (T4) × {1-exp (−T3 / τ)}
/ {Exp (−T3 / τ) −exp (−T4 / τ)} Expression 13
As described above, in the third embodiment, N (T2) can be calculated by two methods according to Expression 7 and Expression 13 using the signals S (T3) and S (T4) of the two correction black images. Finally, the optical signal amount L (T2) corresponding to the afterimage-corrected image signal can be calculated according to Equation 2 using, for example, a value obtained by averaging the two calculated N (T2).

  Since the afterimage signal charge increases according to the exponential function curve as shown in Equation 1, other noise (such as a random noise component) included in the correction black image signal causes a large error in the calculation accuracy of the afterimage corrected signal. Can give. Accordingly, the calculation accuracy of the afterimage-corrected signal can be increased by increasing the number of times the correction black image is read and suppressing the influence of other noises. In the third embodiment, the corrected black image signal is read twice at different times, thereby obtaining a corrected image signal in which the afterimage component is corrected with higher accuracy than in the first embodiment.

  However, in this embodiment, the signal readout is performed twice as the correction black image. However, in order to further increase the calculation accuracy, the readout may be performed three times or more.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

  In the above description, the configuration in which the image sensor 102 is a CMOS image sensor has been described as an example. However, the present invention is not limited to this and can be applied to a configuration that is a CCD image sensor.

  In the above description, an example of obtaining a corrected image in which an afterimage component is corrected when taking a still image with electronic front curtain scanning from LV has been described. However, a high-luminance subject that causes an afterimage phenomenon is described. If there is no, there is no need to execute the afterimage component correction process.

  For example, according to the signal output level of the last frame in the LV before the still image shooting process, the presence / absence of a high-luminance subject is confirmed, and the correction process of the present invention is executed only when a light source exceeding a certain luminance is detected. You may make it do. Further, for example, the imaging apparatus includes a light source detection unit (not shown in FIG. 1), and the correction process of the present invention is executed only when the light source detection unit detects a light source exceeding a certain luminance. Also good.

  In the above description, the control method when taking a still image with electronic front curtain scanning from LV is described as an example, but the present invention is not limited to this. For example, the present invention can also be applied to still image shooting from LV with a mechanical shutter front curtain. Further, for example, the present invention can be applied even during continuous shooting of still images.

DESCRIPTION OF SYMBOLS 101 Optical system, 102 Image sensor, 103 Optical system drive part, 104 AFE,
105 DFE, 106 Digital signal processing unit, 107 Storage unit, 108 Display unit,
109 recording medium, 201 pixel unit, 202 vertical scanning means, 203 reading unit,
204 horizontal scanning means, 205 pixels, 206 vertical signal lines, 301 PD,
302 Transfer switch, 303 FD, 304 Reset switch,
305 signal output unit, 306 selection switch, 307 constant current source

Claims (6)

An image sensor in which a plurality of pixels each including a photoelectric conversion unit are arranged in a matrix;
A light shielding means capable of shielding the image sensor;
Control means for driving and controlling the image sensor to read out the first pixel signal accumulated in the photoelectric conversion unit in an exposure state, and further to read out the light-shielded pixel signal accumulated in the light-shielding state in the photoelectric conversion unit;
For each pixel, the time from the start of accumulation of the light-shielded pixel signal and the first pixel signal to the readout of the first pixel signal, and the readout of the light-shielded pixel signal from the start of accumulation of the first pixel signal An afterimage correction unit that calculates an afterimage amount based on the time until and subtracts the afterimage amount for each pixel from the first pixel signal;
An imaging apparatus comprising: An image sensor in which a plurality of pixels each including a photoelectric conversion unit are arranged in a matrix;
A light shielding means capable of shielding the image sensor;
Control means for driving and controlling the imaging device to read out the first pixel signal accumulated in the photoelectric conversion unit in the exposure state, and further reading out a plurality of frames of the light-shielded pixel signal accumulated in the light-shielding state in the photoelectric conversion unit; ,
For each pixel, a plurality of frames of the light-shielded pixel signal, a time from the start of accumulation of the first pixel signal to the reading of the first pixel signal, and a plurality of frames from the start of accumulation of the first pixel signal. An afterimage correction unit that calculates an afterimage amount based on the time until the light-shielded pixel signal is read, and subtracts the afterimage amount for each pixel from the first pixel signal;
An imaging apparatus comprising:   The imaging apparatus according to claim 1, wherein the afterimage correction unit calculates the afterimage amount using a predetermined formula that approximates the increase curve of the remaining amount. The image sensor is
A gain amplifier for amplifying the first pixel signal and the light-shielded pixel signal; and an amplification factor of the gain amplifier is greater when reading the light-shielded pixel signal than when reading the first pixel signal. The imaging apparatus according to any one of claims 1 to 3, wherein the imaging apparatus is characterized.   The imaging device further includes a detection unit that detects a high-luminance subject, and the control unit does not read out the light-shielded pixel signal when the high-luminance subject is not detected by the detection unit. The imaging device according to claim 4. The detection unit detects a high-luminance subject when at least some of the pixels exceed a certain signal level in a frame before reading out the first pixel signal. 5. The imaging device according to 5.