JP2016039461A - Imaging device and control method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect a frequency of noise without a significant increase in processing time even though there is no mechanism for directly detecting a frequency of a noise source.SOLUTION: An imaging device comprises: an imaging element (102) for converting an optical image of a subject to an image signal to output the image signal; a total control part (106) for setting a drive period for scanning pixels in each scan line of the imaging element; and an image processing part (105) for detecting a frequency of noise superimposed on the output signal by a signal output from the imaging element and the drive period set by setting means. The total control part sets a first drive period for scanning some predetermined pixels of each scan line of the imaging element as the drive period when the image processing part performs detection.SELECTED DRAWING: Figure 8

Description

  The present invention relates to an imaging apparatus and a control method thereof.

  In a conventional imaging device, charges accumulated in a photodiode are converted into an electric signal by a readout circuit, and the converted electric signal is amplified and output. In this process, noise that causes a deterioration in image quality occurs in the image sensor. As a typical example, reset noise in a pixel readout circuit, noise due to variations in components constituting the readout circuit, and noise due to dark current generated in a pixel portion are known.

  In order to reduce these noises, an image sensor that reads out charges as described below is known. First, before reading out the charge from the photodiode, the subsequent circuit in the pixel excluding the photodiode and the pixel readout circuit are reset, and the noise component (N signal) generated during the reset operation is read out. Next, the charge (S signal) accumulated in the photodiode is transferred to a subsequent circuit in the pixel and read out. Then, the noise component is removed by subtracting the N signal from the read S signal (hereinafter referred to as “S-N operation”).

  However, since the sampling timing differs between the N signal and the S signal, if periodic noise is superimposed on the power supply line or ground line supplied to the image sensor during the image reading period of the image sensor, the image is striped by the SN operation. It is known that noise of the shape occurs. This is because if a difference occurs in the reference voltage when transferring the N signal and the S signal due to fluctuations in the power supply during image reading, this difference becomes an offset of the output signal of the image when the SN operation is performed. . Since reading is performed in units of one line, if the offset differs depending on the line to be read, it appears as horizontal stripe pattern noise (horizontal stripes) in the image.

  In order to correct the horizontal stripes generated in such an image, correction is performed by using the output of the horizontal optical black (HOB) area, which is a light-shielded pixel area, in addition to the non-light-shielded pixel area for outputting an image signal. How to do is known. For example, in the HOB area, an average value is calculated in the row direction to extract an offset, and a value obtained by moving and averaging the offset value for a plurality of rows in the column direction is generated as a correction value. By subtracting the correction value thus generated from the output signal of the image, the offset component can be corrected and the horizontal stripe noise can be corrected.

  As described above, the correction using the signal from the HOB area is performed by applying a certain moving average filter to the correction value so as not to be overcorrected or erroneously corrected due to the influence of random noise or micro-scratches in the HOB area. There is a need. For this reason, although correction is effective for removing low-frequency horizontal stripes, high-frequency horizontal stripes cannot be completely removed. Therefore, depending on the frequency of the noise source that generates the horizontal stripes, the above correction may not provide a sufficient effect.

  For example, if the frequency of an oscillation circuit for driving a power source supplied to an image sensor serving as a noise source fluctuates due to a change in temperature or the like, the noise frequency of the reference voltage of the image sensor also fluctuates. When the frequency of the horizontal stripes generated in the image changes to the high frequency side due to the fluctuation of the noise frequency, the horizontal stripes may remain.

  With respect to the above-described problem, in Patent Document 1, the frequency of the power supply noise is predicted from the relationship between the frequency of the power supply noise and the temperature, and the one-line readout period of the image (hereinafter referred to as “HD period”) from the predicted frequency. Has been proposed to change the frequency to be a constant multiple of the power noise frequency. Thereby, striped noise generated due to variations in power supply noise is suppressed.

JP 2010-141799 A

  However, in the prior art disclosed in Patent Document 1, magnetic noise or radio wave noise generated from an actuator or power supply circuit provided in an accessory such as an interchangeable lens is used for noise coming from a noise source outside the imaging apparatus. It was difficult to respond.

  The present invention has been made in view of the above problems, and an object thereof is to detect the frequency of noise superimposed on an image signal without significantly increasing the processing time.

  In order to achieve the above object, an image pickup apparatus according to the present invention is configured to set an image pickup device that converts an optical image of a subject into an image signal and outputs the image signal, and a driving cycle for scanning pixels of each scanning line of the image pickup device. Means for detecting the frequency of the noise superimposed on the output signal from the signal output from the image sensor and the drive cycle set by the setting means, and the detection means When performing detection, the setting unit sets a first driving cycle for scanning a predetermined part of pixels of each scanning line of the image sensor as the driving cycle.

  According to the present invention, it is possible to detect the frequency of noise superimposed on an image signal without significantly increasing the processing time.

1 is a block diagram showing a schematic configuration of an imaging apparatus according to an embodiment of the present invention. FIG. 6 illustrates a pixel region of an imaging element in an embodiment. 1 is a schematic equivalent circuit diagram of one pixel of an image sensor and a readout circuit in an embodiment. 6 is a timing chart illustrating a normal reading operation of the image sensor according to the present embodiment. The figure which shows about the offset which arises by SN operation | movement when noise mixes into a power supply line at the time of image reading. The figure which shows the relationship between the frequency of noise, HD period, and horizontal stripes. The figure which shows an example of the relationship between the read-out area | region at the time of changing the number of read-out lines of an image pick-up element, and HD period. 6 is a flowchart illustrating an operation of the imaging apparatus according to the first embodiment. The figure which shows the relationship between the frequency of noise in 1st Embodiment, HD period, and the period (number of rows) of a horizontal stripe. 9 is a flowchart showing the operation of the imaging apparatus according to the second embodiment. The figure which shows the relationship between the accessory connected to the imaging device in 2nd Embodiment, variation, and the number of read-out columns.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings.

<First Embodiment>
FIG. 1 is a block diagram showing a schematic configuration of an imaging apparatus 100 according to the first embodiment of the present invention. In FIG. 1, a well-known photographic lens (hereinafter simply referred to as “lens”) 101 is provided with a motor (not shown), and an optical image of a subject is formed on the light receiving surface of the image sensor 102 by focusing. Let me image. The image sensor 102 captures an optical image of the subject formed by the lens 101 as an image signal, and outputs it after performing noise removal processing described later.

  Here, the configuration of the image sensor 102 will be described. As shown in FIG. 2, the pixel area 200 of the image sensor 102 includes a plurality of pixels arranged two-dimensionally, and an effective pixel area 201 that is an exposed area and a horizontal optical black (a light-shielded area). HOB) area 202 (light-shielding area).

  FIG. 3 is a schematic equivalent circuit diagram of one pixel of the image sensor 102 and the readout circuit in the first embodiment. The pixel 301 includes a photodiode (PD) 302, a transfer switch 303, a floating diffusion portion (FD) 304, an amplification transistor 305, a reset switch 306, and a selection switch 307. A signal read from the pixel 301 is input to the reading circuit via the vertical output line 308. A constant current source 309 is connected to the vertical output line 308.

  The read circuit includes a clamp capacitor 310, a reset switch 311 for connecting to a reset power supply for resetting the read circuit, capacitors CTN and CTS, and switches 312 and 313 for controlling writing to the capacitors CTN and CTS. Furthermore, switches 314 and 315 for transferring signals written in the capacitors CTN and CTS to the differential amplifier 320 are included. Note that the readout circuit is shared by a plurality of pixels arranged in the same column.

  FIG. 4 is a timing chart showing a normal readout operation for one pixel in the pixel and readout circuit having the configuration shown in FIG. Here, it is assumed that a predetermined exposure time has ended and charges are accumulated in the PD 302. At time t1, the horizontal synchronization signal SYNC rises, and the control signal φSEL for the selected row (scanning line) changes from L to H. As a result, the selection switch 307 in the selected row is turned on, and a signal obtained by scanning the pixels in the selected row can be output to the vertical output line 308.

  At time t2, the reset pulse signal φRES changes from L to H, the reset switch 306 is turned on, and the potential of the FD 304 is reset. At time t3, the reset pulse signal φRES changes from H to L, the reset switch 306 is turned off, and the reset of the FD 304 is released. The potential of the FD 304 at this time is read out as a noise component (N signal) to the vertical output line 308 via the amplification transistor 305 and input to the clamp capacitor 310. At time t4, the control signal φTN1 is set to H, the switch 312 is turned on, and the clamped N signal is written into the capacitor CTN. Thereafter, at time t5, the control signal φTN1 is set to L, the switch 312 is turned off, and the writing of the N signal to the capacitor CTN is completed.

  Next, at time t6, the control signal φTS1 is set to H, the switch 313 is turned on, and a signal can be written to the capacitor CTS. Subsequently, at time t7, the transfer pulse signal φTX is set to H, and the charge (S signal) accumulated in the PD 302 is read to the FD 304. At time t8, the transfer pulse signal φTX is set to L. As a result, the FD 304 holds a signal (S + N signal) in which a noise component is superimposed on the S signal. The S + N signal held in the FD 304 is converted into a voltage by the amplification transistor 305, appears on the vertical output line 308, is clamped by the clamp capacitor 310, and is written in the capacitor CTS. At time t9, the control signal φTS1 is switched from H to L, the switch 313 is turned off, and writing to the capacitor CTS is completed. Through the operations so far, the N signal is held in the capacitor CTN and the S + N signal is held in the capacitor CTS.

  At time t10, φTS2 and φTN2 are simultaneously turned on, so that the N signal and the S + N signal held in the capacitor CTN and the capacitor CTS are simultaneously output to the differential amplifier 320, and the S signal that is the difference between them is output. (SN operation). At time t11, φTS2 and φTN2 are turned off, the control signal φSEL is changed from H to L, the selection switch 307 is turned off, and the reading of the pixels in the selected row is completed. By performing the differential operation in this manner, noise that differs for each pixel or readout circuit can be removed for each imaging operation, and noise generated in an image can be reduced.

  Returning to the description of FIG. 1, the A / D conversion unit 103 performs analog-digital conversion of the image signal output from the image sensor 102. The signal processing unit 104 performs various corrections, data compression, and the like on the image data output from the A / D conversion unit 103. Further, the signal processing unit 104 acquires a shading (offset) in the vertical direction using a signal obtained from the HOB area 202 of the image sensor 102 illustrated in FIG. Then, a moving average calculation is performed in units of a plurality of pixels in the vertical direction to calculate a correction value, and the calculated correction value is subtracted from the output signal of the pixel in the effective pixel region 201, thereby correcting horizontal stripes.

  The timing generator 113 outputs various drive timing pulses to the image sensor 102, A / D converter 103, and signal processor 104. The image processing unit 105 performs predetermined pixel interpolation processing and color conversion processing on the image signal output from the signal processing unit 104, and performs predetermined arithmetic processing using image data captured as necessary. . The image processing unit 105 also detects the horizontal stripe intensity and calculates the noise frequency. Here, the horizontal stripe strength is determined by, for example, the maximum value of the horizontal stripe amplitude. The memory unit 107 temporarily stores image data.

  The overall control unit 106 controls the entire imaging apparatus 100. The recording medium 109 includes a removable semiconductor memory for recording image data. The flash light emitting unit 111 performs AF auxiliary light projection and flash light control. The power supply unit 115 supplies a necessary voltage to each unit for a necessary period through a DC-DC converter circuit that converts a voltage supplied from a battery or the like into a desired voltage. The display unit 108 is made of, for example, a TFT type LCD. The thermometer 110 (temperature detection means) measures the ambient temperature in the shooting environment and the temperature inside the camera (such as around the image sensor).

  Next, the relationship between noise and horizontal stripes appearing in the image will be described. FIG. 5 shows an offset component generated in the SN operation when periodic noise is mixed in the reference voltage of the image sensor 102 at the time of image reading according to the first embodiment. In the image sensor 102, as described above, the timing for reading the N signal and the timing for reading the S + N signal are different (Δt), and if the reference voltage varies during reading, an offset occurs in the output signal for each row. This offset causes periodic horizontal stripes (periodic fluctuations in signal strength) in the image.

  The horizontal stripe Y when the sinusoidal noise is superimposed during such SN operation can be expressed by the following equation.

In the above equation (1), the frequency of the horizontal stripes generated in the image is the second term.

It depends on. That is, the frequency of the horizontal stripes varies depending on the noise frequency f and the one-row readout cycle (HD period) TH. Further, from the equation (2), it can be said that the frequency of the horizontal stripe of the image is equal to the case where the sine wave of the frequency f is sampled at the reciprocal f _h = 1 / TH of the HD period TH.
Note that a frequency higher than the Nyquist frequency f _h / 2 is folded by the sampling theorem.

  A specific example will be described with reference to FIG. FIG. 6 is a conceptual diagram showing the relationship between noise frequency, one-row readout cycle (HD period), and generated horizontal stripes. FIG. 6A is a diagram illustrating a case where the noise frequency is smaller than the reciprocal of twice the HD period of the image sensor. FIG. 6B is a diagram showing a case where the noise frequency is an inverse of twice the HD period.

  The image output is obtained by sampling the frequency of noise at the reciprocal frequency of the HD period. Therefore, as shown in FIG. 6A, when the noise frequency is smaller than the inverse of twice the HD period according to the sampling theorem, the noise frequency and the horizontal stripe frequency of the image correspond one-to-one. The frequency of noise can be detected from the horizontal stripe frequency. On the other hand, as shown in FIG. 6B, when the noise frequency is larger than the inverse of twice the HD period, aliasing occurs, and the noise frequency cannot be accurately detected from the horizontal stripe frequency.

  Therefore, the frequency of the horizontal stripe can be obtained by the following equation (3).

If the relationship between the noise frequency f and the HD period TH is expressed by the following equation (4) based on the sampling theorem, the horizontal stripe frequency of the image and the noise frequency f have a one-to-one correspondence.
f <1 / (2 × TH) (4)

  As described above, the relationship between the noise and the horizontal stripes appearing in the image changes depending on the relationship between the noise frequency f and the HD period TH, and when the relationship between the noise frequency f and the HD period TH satisfies Expression (4), the image It can be seen that the noise frequency f can be calculated from the frequency of the horizontal stripes appearing in FIG. In addition, when the relationship between the noise frequency f and the HD period TH does not satisfy Expression (4), it can be seen that the frequency of the horizontal stripes appearing in the image does not coincide with the noise frequency f. That is, by setting the HD period TH (first drive cycle) so that the relationship between the noise frequency and the HD period TH satisfies Expression (4), the noise frequency can be detected from the horizontal stripes appearing in the image. Is possible.

  Hereinafter, a method for detecting the noise frequency from the image output by changing the HD period TH will be described using a specific example. As an example, the size of the pixel region 200 of the image sensor 102 is 4000 rows and 6000 columns, and the HD period TH is 23.4 μsec. In this case, the maximum value of the noise frequency f detectable from the output of the image sensor 102 is about 21 kHz.

  When the HD period TH is changed by changing the number of read columns, the upper limit value of the frequency of noise that can be detected from the output of the image sensor 102 changes. For example, by setting the number of read columns to 320, the HD period TH is 1.25 μsec, and the detectable noise frequency is simultaneously changed from 21 kHz to 400 kHz.

  FIG. 7 shows an example of the relationship between the readout area and the HD period when the number of readout columns of the image sensor 102 is changed. As shown in FIG. 7B, when all the columns are read out, the HD period is long, and as shown in FIG. 6B, the noise frequency cannot be detected from the horizontal stripe period of the image output. On the other hand, FIG. 7A shows an example of the readout area and the HD period in the image sensor 102 when only a part of the columns of the image sensor 102 is read. The HD period is shortened to a time sufficient to detect the noise frequency, and the noise frequency can be detected from the horizontal stripes of the image output as shown in FIG.

  Next, noise frequency detection processing in the first embodiment of the present invention will be described with reference to the flowchart of FIG. When the noise frequency detection process is started, in S101, the image processing unit 105 determines an HD period TH for detecting the noise frequency. Here, for example, the number of read columns is set to 320 and the HD period TH = 1.25 μsec is set as the initial value. The number of read columns 320 is a value determined in advance based on the characteristics of the image sensor 102. For example, the number of read columns can be determined on the basis of the standard error value. As an example, assuming that the standard deviation of dark noise when the gain of the image sensor 102 is 16 is 16, the standard error is a value obtained by dividing the standard deviation by the positive square root of the number of samples. When the standard error is desired to be 1 or less, it is sufficient to obtain about 250 samples.

  In S102, the overall control unit 106 reads out the image sensor 102 using the HD period TH determined in S101. In step S103, the image processing unit 105 calculates a noise frequency from the horizontal stripe frequency information in the output of the image sensor 102 obtained in step S102. Specifically, the image processing unit 105 performs shading in the vertical direction on the output from the signal processing unit 104, and further performs FFT (Fast Fourier Transform) on the calculation result to calculate the noise frequency. To do.

  Next, in S104, it is determined whether the horizontal stripe strength is 10 LSB or more. If it is less than 10LSB, the process proceeds to S111 to end the noise frequency detection flow, and if it is 10LSB or more, the process proceeds to S105. In S105, the image processing unit 105 estimates the frequency of the horizontal stripes that appear in the image when shooting is performed in the HD period TH that can be used for actual image shooting, instead of the noise frequency detection HD period TH set in S101. Then, the HD period TH (second drive cycle) used for actual image shooting is determined.

  Here, FIG. 9 shows the relationship between the detected noise frequency, HD period, and horizontal stripe period (number of rows) when the result that the noise frequency is 33 kHz is obtained in S103. In the example shown in FIG. 9A, at a noise frequency of 33 kHz, the horizontal stripe period is a 4-line period at the initial value of 23.4 μsec used in actual shooting, but at 30.3 μsec, the line is 500 lines. That's it. If the horizontal stripe period (number of rows) in which the effect of horizontal stripe correction using the signal from the HOB region 202 is obtained is 15 rows, 28.4 μsec is obtained from FIG. 9B in which the periphery of 30 μsec in FIG. 9A is enlarged. It can be seen that the HD period TH should be set between 1 and 32.2 μsec.

  In S106, by changing to the HD period TH calculated in S105, it is confirmed whether or not it is within the range of a desired horizontal stripe period. Specifically, the image processing unit 105 sets the HD period TH in which the horizontal stripe period is maximum among the HD periods TH obtained from the calculation result of S103, here 30.3 μsec, and shortens the processing time. In order to do this, only some rows are read out. For example, the number of readout rows is set to 120, and an output is obtained from the image sensor 102.

  In S107, the image processing unit 105 obtains the period of the horizontal stripes of the output obtained in S107. In S <b> 108, the image processing unit 105 determines whether or not the calculation result in S <b> 107 is a cycle (15 or more rows in the above example) in which a desired correction is obtained based on the signal from the HOB area 202. As a result of the determination in S108, if the number of periodic rows is such that the desired correction is obtained, the image processing unit 105 holds the value calculated in S105 for the HD period TH, here 30.3 μsec, and is used for recording. The processing is terminated as a setting value for shooting an image.

  By acquiring an image for recording in the HD period TH set as described above, high-frequency horizontal stripes that are not subjected to horizontal stripe correction based on the signal from the HOB area 202 that appears in the image when shooting in the state before the setting are obtained. It becomes possible to change to a low frequency horizontal stripe which is effective for correction.

  On the other hand, if a result indicating that the number of rows is not more than the correctable number is obtained in S108, the horizontal stripe is not the frequency due to the assumed noise but aliasing has occurred. In this case, in order to shorten the HD period when detecting the noise frequency, the number of read columns is reduced, and in order to acquire the output, the process proceeds to S110. In S111, it is confirmed whether or not the currently set number of read columns is 80. In the first determination, since 320 columns are set in S102, the process returns to S102, and the number of read columns is changed from 320 columns to 80 columns.

  In the case of changing to 80 columns, the number of samples is 1/4 compared to 320, and the standard error is quadrupled. That is, since the standard error is 1.78 and exceeds 1, the threshold value of the horizontal stripe strength is also changed from 10LSB to 12LSB. In the first embodiment, in order to reduce errors, 320 columns are initially selected, and the number of read columns is changed only when noise having a frequency that cannot be read by setting the HD period when reading 320 columns is input. .

  The processing after S102 is as described above, and the same processing is performed by changing the number of read columns to 80 columns. By changing from 320 columns to 80 columns, the sampling period is reduced to a quarter, and the maximum value of the detectable noise frequency is quadrupled. If the output is obtained again under this condition and the confirmation result in S108 is not determined to be equal to or greater than the number of rows that can be corrected by the horizontal stripe based on the signal from the HOB area 202, the process proceeds to S110 again. Since 80 columns are set here, the number of columns cannot be reduced any more, so that it is determined that it is difficult to detect the noise frequency, and the process is terminated.

  As described above, even when the imaging apparatus does not have a mechanism for detecting the driving frequency of the noise source, the horizontal stripes are obtained from the output of the imaging device obtained by changing the number of readout columns and changing the HD period TH. It becomes possible to detect the frequency of noise. Further, by reducing the number of read columns in accordance with the characteristics of the image sensor, it is possible to detect the horizontal stripe frequency with suppressed variation of the image sensor. In addition, when confirming whether the frequency of the detected horizontal stripe can be changed to a frequency on the low frequency side where correction based on the signal from the HOB region is effective, detection is performed by setting the number of rows to be read as a part of the whole. The result confirmation time can be reduced. Further, as a result of confirmation, if the frequency cannot be changed to the low frequency side where correction is effective, the upper limit of the frequency of detectable noise can be changed by further reducing the number of read columns.

<Second Embodiment>
Next, a second embodiment of the present invention will be described. In the second embodiment, a case will be described in which an approximate value of the driving frequency of a noise source serving as a horizontal stripe generation source is available in advance. Some accessories that can be attached to and detached from the imaging apparatus 100 can detect attachment on the imaging apparatus 100 side. For example, in the case of a lens, the overall control unit 106 in the imaging apparatus 100 described in the first embodiment can communicate with the lens to acquire information about the lens.

  In the second embodiment, a case where a lens is mounted will be described. The frequency of the oscillation circuit for driving the power supply in the lens (within the accessory) varies depending on the individual. Further, even if the same individual is used, the drive frequency varies depending on the temperature change. Therefore, the frequency of horizontal stripes generated in the image also changes. Here, an example will be described in which the basic drive frequency of the mounted lens is 33 kHz, varies within a range of ± 10%, the lower limit is 29.7 kHz, and the upper limit is 36.3 kHz.

  As in the first embodiment, if the number of read columns at the time of noise frequency detection is 320 and the HD period is 1.25 μsec, the upper limit of the detectable frequency is 400 kHz. When the number of read columns is reduced, the number of samples per row is reduced, and the error becomes large. Therefore, when the upper limit of the frequency of noise to be detected is known, the error can be minimized by minimizing the amount of reduction in the number of read columns. In other words, since the upper limit of the detectable frequency is 1 / (2 × TH) where the HD period is TH, an HD period TH satisfying 1 / (2 × TH)> 36.3 kHz may be selected. I understand.

  Here, the operation in the second embodiment will be described with reference to the flowchart of FIG. Note that the configuration of the imaging apparatus according to the second embodiment has the same configuration as that described in the first embodiment, and thus description thereof is omitted here.

  When the detection of the noise frequency is started, in S201, the overall control unit 106 detects the lens 101 (accessory) attached to the imaging apparatus 100 (attachment detection means), communicates with the lens 101, and obtains lens information. . In the second embodiment, the lens information indicates the type of the lens 101, and the overall control unit 106 obtains information that the mounted lens 101 is the lens A.

  In step S <b> 202, the overall control unit 106 confirms whether information about the detected lens A is in the memory unit 107. When the overall control unit 106 determines that there is no information in S202, the process proceeds to S213, and the noise detection HD period is set to a predetermined value as in the first embodiment, regardless of the type of the lens 101. Set.

  On the other hand, if it is determined in S202 that there is information regarding the lens mounted, the overall control unit 106 determines the HD period TH in S203. For example, when the memory unit 107 has information as shown in FIG. 11, it can be seen that the lens A has a driving frequency of 33 kHz and an individual variation of 10%.

  When the number of readout columns when acquiring an image output for noise frequency detection is 320, the upper limit of the frequency of noise that can be detected is 0.4 MHz, and detection is possible by readout of 320 columns. The HD period TH when the number of read columns is 320 is 1.25 μsec. When 33 kHz varies at 10%, the maximum is 36.3 kHz and the minimum is 29.7 kHz. The HD period during which the maximum frequency can be detected satisfies 1 / (2 * TH)> 36.3 kHz. The HD period TH and TH <13.77 μsec. Since the total number of columns is 6000, and the HD period when all the columns are read out is 23.4 μsec, setting the number of read columns to 3520 columns makes the HD period TH 13.75 μsec, and the upper limit of the detectable frequency is 36.3 kHz.

  That is, by providing the memory unit 107 with information such as reading out 3520 columns for the lens A, the number of reduced columns for obtaining the output of the image sensor 102 can be minimized. Thereby, the error component can be minimized when the frequency of the horizontal stripe is detected.

  After S203 or S213, the process proceeds to S103 to detect the noise frequency from the horizontal stripe frequency. Note that the processing performed from S103 to S108 is the same as the processing performed from S103 to S108 in the flowchart of FIG. 8 in the first embodiment, and thus description thereof is omitted.

  In step S <b> 211, the image processing unit 105 determines whether the calculation result in step S <b> 108 is a cycle in which an effect can be obtained by correction based on a signal from the HOB area 202. As a result, if the image processing unit 105 determines that the correction based on the signal from the HOB area 202 is not effective, the process proceeds to S213, where the number of read columns for normal use is the same as the initial value of the first embodiment. The 320th line is set, and noise detection is performed again. If it is determined in S211 that the period is such that the correction based on the signal from the HOB area 202 is effective, the HD period TH at the time of actual shooting is held at the value obtained in S106, and the process ends. To do.

  As described above, according to the second embodiment, when the frequency information of the noise source can be acquired, it is possible to detect the frequency of the noise with as few error components as possible.

  In the second embodiment, an example in which the number of readout columns is always changed for a lens capable of detecting a rough noise frequency has been described. However, it is not always necessary to change under all conditions. For example, when the approximate frequency of noise is sufficiently low and a preset number of read-out columns for detection is sufficiently secured, a preset value may be used. That is, only when the approximate noise frequency is high and the preset number of read columns is insufficient, the number of read columns may be determined based on the acquired approximate noise frequency. In this way, even when the number of read columns is insufficient, it is possible to detect the noise frequency while suppressing deterioration in detection accuracy as much as possible. In addition, an increase in time required for detection can be reduced.

  Further, only the lens is listed as the accessory information, but it is possible to deal with other accessories by providing the accessory information in the same manner.

  101: Lens, 102: Image sensor, 106: Overall control unit, 104: Signal processing unit, 105: Image processing unit, 110: Thermometer, 113: Timing generation unit, 115: Power supply unit

Claims (11)

An image sensor that converts an optical image of a subject into an image signal and outputs the image signal;
Setting means for setting a driving cycle for scanning pixels of each scanning line of the image sensor;
Detection means for detecting the frequency of noise superimposed on the output signal from the signal output from the image sensor and the drive cycle set by the setting means;
When performing detection by the detection unit, the setting unit sets, as the driving cycle, a first driving cycle for scanning a predetermined part of pixels of each scanning line of the image sensor. An imaging apparatus characterized by the above.   When the intensity of the signal output from the image sensor periodically fluctuates in a direction perpendicular to the scanning line, the detection means includes the fluctuation frequency and the first driving period. The imaging device according to claim 1, wherein the frequency of the noise is detected based on the frequency. The imaging element has an effective pixel region composed of a plurality of pixels arranged in a two-dimensional manner for converting an optical image of a subject into an image signal and outputting the image signal, and a light shielding region composed of a plurality of light-shielded pixels, The imaging device
Correction means for correcting the image signals output from the pixels in the effective pixel region using the signals output from the pixels on the same scanning line in the light shielding region,
The frequency of the variation changes according to the frequency of noise and the driving cycle for scanning the pixels of each scanning line,
The setting means sets, based on the noise frequency detected by the detection means, a second drive cycle in which the fluctuation frequency falls within a range of a cycle that can be corrected by the correction means. The imaging apparatus according to claim 2. Determining means for determining whether the frequency of the fluctuation when scanning a part of scanning lines of the image sensor in the second driving cycle is within a frequency range that can be corrected by the correcting means. Further comprising
When the determination unit determines that the frequency is not within the frequency range that can be corrected by the correction unit, the setting unit sets a third drive cycle shorter than the first drive cycle, The imaging apparatus according to claim 3, wherein the noise frequency is detected by a detection unit.   5. The method according to claim 1, wherein when the detection is performed by the detection unit, the setting unit sets the first driving cycle based on characteristics of the imaging element. 6. Imaging device. A temperature detecting means;
The imaging apparatus according to claim 1, wherein the setting unit sets the first driving cycle according to an output of the temperature detection unit.   The setting means sets the first drive cycle such that f <1 / (2 × TH) with respect to the upper limit of the frequency f of the noise to be detected when the first drive cycle is TH. The image pickup apparatus according to claim 1, wherein the image pickup apparatus is an image pickup apparatus. A mounting detection means for detecting the mounting of an accessory detachable from the imaging device;
Recording means for recording frequency information of a noise source in the accessory;
The setting means sets the first drive cycle based on the frequency information corresponding to the accessory when the attachment detection means detects the attachment of the accessory. 8. The imaging device according to any one of items 7.   The imaging apparatus according to claim 8, wherein the frequency information includes information related to a driving frequency and variation of an oscillation circuit in the accessory.   The said setting means sets the said 1st drive period based on the said frequency information, when the frequency which the said frequency information shows is higher than the frequency of the predetermined noise, The said 1st drive period is set. The imaging device described in 1. A setting step in which a setting unit sets a first driving cycle for scanning a predetermined part of the pixels of each scanning line of the imaging device that converts an optical image of the subject into an image signal and outputs the image signal; ,
A detecting unit configured to detect a frequency of noise superimposed on the read signal from the signal read from the imaging element by scanning in the first drive period and the first drive period; And a method of controlling the imaging apparatus.

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