JP2008113276A - Imaging apparatus, noise eliminating method, and noise elimination control program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging apparatus capable of eliminating not only a dark current noise component (static noise) but also a device noise component (dynamic noise) from the electric charge signal of an imaging element with a simple configuration and control, and to provide a noise eliminating method and noise elimination control program. <P>SOLUTION: A CPU 12 sends a control signal to a light reception control part 9, makes a liquid crystal shutter 2 perform an on/off operation at a predetermined timing cycle, and makes a CCD 3 transfer the output signal of the CCD 3 to image field buffers in different areas respectively at timing when a liquid crystal shutter 2 changes from ON to OFF and at time when the liquid crystal shutter 2 changes from OFF to ON. Next, the value of data in an OFF section of the liquid crystal shutter 2 is subtracted from the value of an ON section data of the liquid crystal shutter 2 and stored as frame data in an image frame buffer 7. An SN ratio caused by the noise portion of the OFF section is calculated, and the value is used for timing adjustment of ON/OFF of the liquid crystal shutter 2 at the next timing. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a noise removal technique related to an imaging apparatus that captures a subject image with an imaging element.

  In an electronic camera that captures a subject image using an image sensor such as a digital camera, the dark current portion of the image sensor is also captured as data. Therefore, when capturing a dark portion, the dark current charge is less than the charge obtained from the image capture. There is a problem that the size cannot be ignored.

  Conventionally, as a technique for solving this problem, image information from an image sensor is stored in an image information memory, and a dark current noise component read out from the image sensor when the light is shielded for the same time is stored in the dark current noise memory. Noise reduction to reduce the dark current noise component of the solid-state imaging device from the image information by subtracting the dark current noise component stored in the dark current noise memory from the image information stored in the image information memory There exists a technique (for example, patent document 1).

Further, the output image data of the image sensor is temporarily stored in the memory, the exposure condition for shooting is determined, the first image data corresponding to the output signal read from the image sensor after shooting, and the light shielding state After the data of the same pixel are temporally matched based on the second image data corresponding to the dark output signal (dark current noise component) read from the image sensor, There is an electronic imaging device that generates final image data by performing computation on the first and second image data (subtracting the second image data from the first image data) (see, for example, Patent Document 2).
JP-A-4-40763 JP-A-8-51571

  However, in the technique described in Patent Document 1, since the dark current is subtracted from the photographed image in the light-shielded state for the same amount as the photographing time, the fixed pattern noise of the image sensor is suppressed, but the random noise increases. There was a problem of doing.

  In the technique described in Patent Document 2, after determining the exposure condition for shooting, the captured image data stored in the memory and the dark current component data are temporally matched and then the dark current between them is captured. Therefore, noise (static noise) due to dark current can be removed for each pixel, but dynamic noise (for example, device noise such as 50 Hz noise) could not be reduced. .

  The present invention has been made to solve the above problems, and removes not only the dark current noise component (static noise) but also the device noise component (dynamic noise) from the charge signal of the image sensor with a simple configuration and control. An object of the present invention is to provide an imaging device, a noise removal method, and a noise removal control program.

  In order to solve the above-described problem, an imaging apparatus according to a first aspect of the present invention includes an imaging unit that converts an optical image into image information including an electrical signal, and an optical image incident on the imaging unit is periodically blocked or passed. An image for storing a field image signal converted by the imaging unit from the optical image incident in the first section in which the optical image is periodically incident on the imaging unit by the control of the blocking control unit. Storage means; and noise component storage means for storing field noise components including dark current noise components generated from the imaging means in a second section in which an incident optical image is periodically blocked by the control of the cutoff control means; The subtraction means for subtracting the field noise component stored in the noise component storage means from the field image signal stored in the image storage means, and the subtraction means. Frame data storage means for sequentially storing the difference as frame data, and the SN ratio is obtained from the ratio of the signal intensity of the field image signal and the signal intensity of the field noise component, and the optical image is blocked or passed by the light shielding means. And a light-shielding timing adjusting means for adjusting.

According to a second aspect of the present invention, in the imaging apparatus according to the first aspect of the present invention, the light-shielding timing adjusting means is first when α << Β and when a positive number α ≦ SN ratio ≦ Β. Based on the timing adjustment means which is always the first section when the SN ratio> Β, and the section change information adjusted by the timing adjustment means. A light shielding timing changing means for providing light shielding timing changing information to the light shielding control means;
It is provided with.

  According to a third aspect of the present invention, in the imaging apparatus according to the second aspect of the present invention, the light shielding control means controls the optical image controlled when the light shielding timing change information is acquired from the light shielding timing changing means. The periodic blocking or passing operation of the optical image incident on the imaging unit is controlled based on the change information of the light shielding timing acquired after the periodic blocking or passing operation is completed.

  According to a fourth aspect of the present invention, in the imaging apparatus according to any one of the first to third aspects, the subtracting means is stored in the noise component storage means from the field image signal stored in the image storage means. When subtracting the field noise component, if the lengths of the first section and the second section are different, the field image signal and the field noise component indicate the lengths of the first section and the second section. The subtraction is performed after adjusting the field image signal or the field noise component so as to obtain the acquired data when they are equal.

  According to a fifth aspect of the present invention, in the noise removal method according to the fifth aspect of the present invention, in an imaging apparatus including an imaging unit that converts an optical image into image information including an electrical signal, the optical image incident on the imaging unit is periodically blocked or passed And first storing the field image signal converted by the imaging unit from the optical image incident in the first section in which the optical image is incident on the imaging unit in the first step, and temporarily storing the field image signal in the first buffer. A second step of temporarily storing, in the second buffer, field noise components including dark current noise components generated from the imaging means in a second section in which the optical image incident in step 1 is periodically blocked; The third step of subtracting the field noise component stored in the second buffer from the field image signal stored in the first buffer, and the difference obtained in the third step is used as frame data. Then, the SN ratio is acquired from the ratio of the signal intensity of the field image signal and the field noise component in the fourth step of sequentially storing in the third buffer, and the timing of blocking or passing the optical image of the light shielding means is obtained. And a fifth step of adjusting.

  According to a sixth aspect of the present invention, there is provided a noise removal control program for periodically interrupting or passing an optical image incident on an image pickup means through a computer having an image pickup means for converting an optical image into image information composed of an electrical signal. An image storage for storing, in a memory, a field image signal converted by the imaging unit from the optical image incident in the first section in which the optical image is periodically incident on the imaging unit under the control of the blocking control unit. A noise component storage means for storing a field noise component including a dark current noise component generated from the imaging means in a second section in which the incident optical image is periodically blocked by the control of the block control means; The field noise signal stored in the memory by the noise component storage means from the field image signal stored in the memory by the means. Subtracting means for subtracting, frame data storage means for sequentially storing the difference obtained by the subtracting means as frame data in the memory, and obtaining the SN ratio from the ratio of the signal intensity of the field image signal and the signal intensity of the field noise component to block the light It functions as a light shielding timing adjusting means for adjusting the optical image blocking or passing timing of the means.

  According to the present invention, since a simple digital bandpass filter (simple BPS) for noise removal at the time of shooting can be configured, this filter effect enables not only the dark current noise component (static noise) of the image sensor but also the device. Noise components (dynamic noise) can be removed. Further, since the light shielding timing (cycle, duty ratio) can be changed by the SN ratio due to noise at the time of light shielding, the accuracy of the simple BPF described above can be improved.

  FIG. 1 is a block diagram showing an embodiment of main components of the imaging apparatus of the present invention. In the following embodiments, the digital camera 100 will be described as an example. However, the present invention is not limited to the digital camera, and can be applied to an image pickup apparatus including an image pickup unit using an image pickup device such as a CCD.

  In FIG. 1, reference numeral 1 denotes an optical system including a plurality of lens groups including a zoom lens and a focus lens. The optical system 1 forms an object light image on the light receiving surface of the CCD 3.

  Reference numeral 2 denotes a liquid crystal shutter, and the liquid crystal shutter 2 functions as a light shielding switch that performs a switch operation for blocking (blocking) or passing light from the optical system 1 at a predetermined period based on the control of the light receiving control unit 8 during photographing. To do. In the embodiment, the liquid crystal shutter is used as the light shielding switch. However, the liquid crystal shutter is not limited to the liquid crystal shutter, and a member that operates as the light shielding switch at a predetermined cycle can be used instead of the liquid crystal shutter 2.

  The CCD 3 is typically an imaging element (solid-state imaging device) that captures an image of several tens of frames per second. The CCD 3 is driven by a drive signal sent from the light reception control unit 9 and the amount of accumulated charge changes according to the amount of light. A two-dimensional optical image (optical signal) of a subject received on its own light receiving surface via the optical system 1 using an element is converted into an electric charge and output as an electric signal (analog signal).

  The output signal of the CCD 3 is correlated double sampling and gain adjustment by the CDS circuit 4 and converted to a digital signal by the A / D conversion circuit 5. The imaging element is not limited to a CCD, and a solid-state imaging device such as a CMOS (Complementary Metal Oxide Semiconductor) can be used.

  Reference numeral 4 denotes a CDS circuit. The CDS circuit 4 performs correlated double sampling and gain adjustment on the image signal (analog signal) output from the CCD 3 and outputs the result to the A / D converter 5. Reference numeral 5 denotes an A / D converter. The A / D converter 5 converts the image signal (analog signal) subjected to correlation double sampling and gain adjustment by the CDS circuit 6 into a digital signal to convert the image field buffer 6 and the focus. Output to the filter unit 10.

  Reference numeral 6 denotes an image field buffer. Although not shown, the image field buffer 6 includes a first image field buffer for temporarily storing field data (including dark current and device noise) obtained by converting the image signal from the optical system 1 by the CCD 3, and the optical system. A second image field buffer for temporarily storing field data (including device noise) obtained by converting electric charges (dark current) output from the CCD 3 while the image signal from 1 is shielded by the liquid crystal shutter 2; ing.

  Reference numeral 7 denotes an image frame buffer. The image frame buffer 7 accumulates (stores) the addition result of frame data output by field image calculation (FIG. 2 (step S9); see FIG. 4) described later.

  Reference numeral 8 denotes a signal processing unit. The signal processing unit 8 performs color process processing including image interpolation processing and γ correction processing on the digital signal (image data) output from the image frame buffer 7 to generate YUV data (digital value luminance signal Y and color difference signal Cb). Cr), data for one frame is sequentially DMA-transferred to a built-in memory (not shown) and stored in an image data storage area secured in the built-in memory. The output YUV data output from the signal processing unit 8 is sent to the liquid crystal display controller 13, where it is converted into a video signal and then displayed on the liquid crystal display screen 14.

  Reference numeral 9 denotes a light reception control unit, and the light reception control unit 9 performs ON / OFF control of the liquid crystal shutter 2 at a predetermined timing cycle (for example, 60 Hz) under the control of the CPU 12. The light receiving control unit 9 generates a drive signal for the CCD 3 under the control of the CPU 12 and drives the CCD 3. Reference numeral 10 denotes a focus filter unit.

  Reference numeral 11 denotes a lens control unit. The lens control unit 11 controls the operation of a drive mechanism such as a drive motor of the optical system 1 based on control data from the CPU 12 to perform exposure control based on shutter speed and aperture adjustment by AE (auto iris), zoom control, AF ( Perform autofocus control by autofocus. A known technique can be used for operation control of the optical system 1 in exposure control, zoom control, automatic focusing control, and the like by the lens control unit 11.

  Reference numeral 13 denotes a liquid crystal display controller. The liquid crystal display controller 13 converts the YUV data output from the signal processing unit 8 into a video signal and displays it on the liquid crystal display screen 14. Reference numeral 14 denotes a liquid crystal display screen.

  Reference numeral 15 denotes a shutter button. The shutter button 8 performs a release operation at the time of shooting. For example, the shutter button 8 has a stroke of two steps. In the still image shooting mode, the first step (half-pressed state) automatically and auto-focus (AF). A focus instruction signal for performing exposure (AE) is generated, and a shooting instruction signal for performing a shooting process in the second stage operation (fully pressed state) is generated. Each generated instruction signal is immediately sent to the CPU 12.

  Further, when the shutter button 15 is operated when the high sensitivity mode is set in the photographing mode, the noise removal control start instruction signal of the present invention is generated. The generated noise removal control start instruction signal is immediately sent to the CPU 12.

  Reference numeral 16 denotes a mode button. By operating the mode button 16, the user can set the photographing mode to a high sensitivity mode for executing the noise removal control of the present invention.

  Reference numeral 12 denotes a CPU. Each block described above is controlled by the CPU (or MPU) 12, and the program and data required for the CPU 12 to control each block are a program memory (FIG. 1) that is a rewritable nonvolatile memory such as an EEPROM or a flash memory. (Not shown). The CPU 12 functions as the noise removal control means of the present invention in response to the program and the noise removal control start instruction signal generated when the shutter button 5 is operated when the high sensitivity mode is set in the shooting mode.

  FIG. 2 is a flowchart showing a photographing operation control sequence by the CPU 12 of the digital camera 100 according to the present invention, and is for explaining a program for causing the digital camera 100 to realize the noise removal control function during photographing according to the present invention. is there. In FIG. 2, steps S6 to S13 correspond to the operation of the noise removal control program of the present invention.

  The processing shown below is basically explained by an example in which the CPU 12 executes in accordance with a program stored in advance in a program memory (not shown), but it is not necessary to store all functions in the program memory. A part or all of them may be realized by receiving via a network, for example. Hereinafter, a description will be given with reference to FIGS. In the following description, it is assumed that the lengths of the ON section and the OFF section in the initial state are equal.

  In FIG. 2, in the shooting mode, the user can set the shooting mode to the high sensitivity mode by operating the mode button 16. The CPU 12 checks whether or not the high sensitivity mode has been set by the mode button 16 (step S1), and when the signal indicating that the high sensitivity mode has been set by the operation of the mode button 16 is detected, the high sensitivity mode setting flag is turned ON (step S1). Step S2).

  The CPU 12 turns on the liquid crystal shutter 2 to form a subject light image on the light receiving surface of the CCD 3 via the optical system 2, and then executes the shooting preparation process. When the shooting preparation process is completed, the process proceeds to step S4 (step S4). S3). The shooting preparation processing here is the initial setting for shooting, the execution of AE processing at the focal length corresponding to the zoom value at that time, the through image display based on the subject image from the optical system 1, for example, the shutter button 15 A known technique can be used for the control operation for the shooting preparation process, such as an autofocus process based on an autofocus instruction by a half-press operation.

  When the shooting preparation process in step S3 is completed, the user can give a shooting instruction by fully pressing the shutter button 15 at a desired timing. The CPU 12 checks whether or not the shutter button 15 has been fully pressed. If the shutter button 15 has been fully pressed, the process proceeds to step S5 (step S4).

  When the shutter button 15 is fully pressed in step S4, the CPU 12 checks whether the high sensitivity mode is set (that is, whether the high sensitivity mode setting flag is ON), and the high sensitivity mode is set. If YES in step S6, the flow advances to step S6. If the high sensitivity mode is not set, shooting processing with normal sensitivity is performed (step S5).

  If the light reception controller 9 receives an ON / OFF timing setting change instruction signal from the CPU 12, the process proceeds to step S7, and if not received, the process proceeds to step S8 (step S6).

  The light reception controller 9 checks whether or not the ON / OFF operation controlled when the change instruction is received is completed, and when the ON / OFF operation is completed, the liquid crystal shutter 2 is turned ON / OFF at the changed timing cycle. The process proceeds to step S9. If the ON / OFF operation controlled when the change instruction is received is not completed, the control waits until the ON / OFF operation is completed (step S7).

  The CPU 12 sends a control signal to the light receiving control unit 9 to turn on / off the liquid crystal shutter 2 at a predetermined timing cycle (for example, 60 Hz) (step S8).

  The CPU 12 controls the light receiving control unit 9 to cause the CCD 3 to transfer the output signal to the image field buffer in different areas at the timing when the liquid crystal shutter 2 is turned from ON to OFF and from the OFF to ON. (Step S9). That is, in this step, at the timing when the liquid crystal shutter 2 is turned from ON to OFF, the field data obtained by converting the image signal from the optical system 1 by the CCD 3 is transferred to the first image field buffer to be temporarily stored, and the liquid crystal shutter At the timing when 2 is turned from OFF to ON, field data obtained by converting charges (dark current) output from the CCD 3 while the image signal from the optical system 1 is shielded by the liquid crystal shutter 2 is transferred to the second image field buffer. And temporarily memorize it.

  Next, the CPU 12 determines the ON section data of the liquid crystal shutter 2 (referred to as data transferred from the CCD 3 at the timing when the liquid crystal shutter 2 is turned from ON to OFF) from the OFF section data of the liquid crystal shutter 2 (from the liquid crystal shutter 2 is turned off). The value is deducted and stored in the image frame buffer 7 as differential OFF frame data (see FIG. 3). When subtracting, if the lengths of the ON section and the OFF section are different, subtraction is performed after weighting by multiplying or dividing the data so that the ON section and the OFF section have the same length. (Step S10).

  Next, the CPU 12 calculates the S / N ratio for the noise in the OFF section from the ON section data and the OFF section data output from the CCD 3 when the liquid crystal shutter 2 is turned ON / OFF, and based on this value, at the next timing. This is used for adjusting the ON / OFF timing (cycle, duty ratio) of the liquid crystal shutter 2. Specifically, the S / N ratio is obtained from the ratio of the signal intensity of the entire screen obtained from the ON section and the noise intensity obtained from the OFF section, and when the S / N ratio is relatively high, it is an integer multiple (twice or more) of the ON section. The ON / OFF timing of the liquid crystal shutter 2 is set at the same time, and when the signal-to-noise ratio is sufficiently high and the device noise level is negligible with respect to the image pickup signal level, it is always turned on to increase the exposure time. . Also, this ON / OFF timing change instruction is immediately given to the light reception control unit 9, and after the ON / OFF operation controlled when the change instruction is issued, the ON / OFF timing is changed. On / off control of the liquid crystal shutter 2 is performed at the OFF timing (see FIG. 4) (step S11).

  Next, the CPU 12 sequentially adds the field data output by the field operation (subtraction) in step S11 and saves (stores) it in the frame image buffer 7 as frame image data (step S12).

  Next, the CPU 12 checks whether or not the number of acquired fields stored in the frame image buffer 7 (that is, the number of times frame data is stored) has reached the number corresponding to the shutter time, and all the field numbers have not been acquired. In this case, the process returns to step S9 to perform the field data acquisition operation again. When all the field numbers have been acquired, the process proceeds to step S14 (step S13). Here, when the number of frame data corresponding to the shutter time is stored in the image frame buffer, one frame of image data is stored.

  The CPU 12 subjects the image data stored in the frame image buffer 7 to image compression processing by the JPEG circuit 26, records an image file composed of the compressed data in a storage memory (not shown), and completes imaging for one frame. (Step S14).

  With the above configuration, not only the dark current noise component (static noise) but also the device noise component (dynamic noise) is removed from the charge signal of the imaging device with a simple configuration and control, and the SN ratio at the time of imaging is further improved. be able to.

  Specifically, a simple digital bandpass filter that subtracts noise components that are not synchronized with the light shielding period (60 Hz in the embodiment, but not limited to this) by periodically turning on and off a liquid crystal shutter as a light shielding switch. (Digital BPF) is configured. This filter effect can reduce not only static noise such as intrinsic noise of the image sensor but also dynamic noise (for example, device noise such as 50 Hz power supply noise). As described above, the SN ratio at the time of imaging can be further improved as compared with the case where only static noise such as the intrinsic noise of the imaging element is reduced. In addition, the frequency characteristic graph of the simplified BPF described above is shown in FIG.

  Further, as shown in step S11 of the flowchart of FIG. 2, the SN ratio due to noise in the OFF section is calculated based on the ON section data and the OFF section data of the liquid crystal shutter 2, and the next timing is calculated based on the calculated value. Since the accuracy of the simple BPF described above can be improved by changing the ON / OFF timing (cycle, duty ratio) of the liquid crystal shutter 2, the SN ratio at the time of imaging can be further improved. Can do. A detailed flowchart of step S11 in FIG. 2 is shown in FIG.

  In step S7 in FIG. 2, the light reception controller 9 checks whether or not the ON / OFF operation controlled when the change instruction is received is completed, and after the ON / OFF operation is completed, the liquid crystal shutter 2 Is turned ON / OFF at the changed timing cycle, so that the ON / OFF timing of the liquid crystal shutter 2 is not changed until image data for one frame is stored in the image frame buffer 7. Therefore, image distortion that occurs when the ON / OFF timing of the liquid crystal shutter 2 is changed in the middle does not occur.

  Further, when subtracting noise components that are not synchronized with the light shielding period in step S10 in FIG. 2, an ON section in which an optical image incident from the optical system 1 is periodically incident on the CCD 3 and an optical image incident from the optical system 1 are obtained. If the length of the OFF section that is periodically interrupted is different, the data is multiplied or divided so that the ON section and the OFF section have the same length, and then the subtraction is performed. Therefore, even if the ON / OFF timing (cycle, duty ratio) of the liquid crystal shutter 2 is changed, it is possible to accurately obtain the SN ratio due to noise in the OFF section.

  FIG. 3 is an explanatory diagram of a simplified BPF configured according to the present invention. FIG. 3A shows the optical system 1, the liquid crystal shutter 2, the CCD 3, and the simplified BPF 24 of the digital camera 100. The simple BPF 24 is a digital bandpass filter including an A / D converter 5, an image field buffer 6, a light reception control unit 9, and a CPU 12. In FIG. 3A, reference numeral 21 denotes a light beam from the subject, and reference numeral 22 denotes incident light incident on the light receiving surface of the CCD 3 from the optical system 1. Incident light 22 is periodically shielded by the liquid crystal shutter 2 as shown in FIG.

  Reference numeral 23 denotes an analog signal composed of ON section data (image signal and noise component) or OFF section data (noise component) composed of an electrical signal converted by the CCD 3. The noise component includes CCD 3 noise (dark current) and device noise. These data are converted into digital signals between the CCD 3 and the image field buffer 6, ON section data is temporarily stored in the first area of the image field buffer 6, and OFF section data is stored in the second area of the image field buffer 6. Is temporarily stored.

  Reference numeral 25 denotes image frame data. The frame data is difference data obtained by removing noise components from the image field data by the simple BPF 24 as shown in FIG. 3D, and the difference data is sequentially stored (stored) in the image frame buffer 7 as image frame data. And stored in the image frame buffer 7. When the image frame data for one frame is stored in the image frame buffer 7, it is output to the signal processing unit 8 (see FIGS. 1 and 2 (step S12)).

  FIG. 3B is a diagram showing the CCD transfer timing by the ON / OFF operation of the liquid crystal shutter 2, and the vertical axis shows the light intensity and the horizontal axis shows the time (t1, t2,...). In FIG. 3B, t1 to t2, t3 to t4,... Are periods in which the liquid crystal shutter 2 is OFF. During this period, the light 21 from the optical system 1 is blocked and only CCD noise is output from the CCD 3. . In FIG. 3 (b), t0 to t1, t2 to t3, t5,... Are periods in which the liquid crystal shutter 2 is ON, during which the light 22 from the optical system 1 is incident on the light receiving surface of the CCD 3, The CCD 3 outputs image signal + CCD 3 noise.

  FIG. 3C is a diagram showing a time-dependent transition of ON section data (image signal and noise component) and OFF section data (noise component). The vertical axis represents input data to the image field buffer 6, and the horizontal axis represents Black points on the time (t1, t2,...) And the graph indicate interval data. The section data k1, k2, k3,... Acquired at times t1, t3, t5,... Are ON section data consisting of image signal + CCD3 noise + device noise, and acquired at times t2, t4,. The section data g1, g2,... Are OFF section data composed of CCD3 noise + device noise, and the ON section data k1, k2, k3,..., And OFF section data g1, g2,. It has a noise component consisting of equipment noise.

  FIG. 3D is a diagram showing adjacent difference data (frame data) acquired by the simplified BPF 24, where the vertical axis indicates the value of the adjacent differential data, the horizontal axis indicates time (t2, t4,...), And on the graph. The black points q1 and q2 indicate adjacent difference data. The adjacent difference data is the ON section data (for example, the ON section data k1, k2, k3,... Shown in FIG. 3C) and the adjacent OFF section data (for example, the OFF section data g1 shown in FIG. 3C). It is obtained by subtracting g2,. The acquired adjacent difference data is sequentially stored in the image frame buffer 7 as frame data.

  FIG. 4 is a flowchart showing the detailed operation of step S11 of FIG. 2, and specifically, is a flowchart showing the timing change operation of the liquid crystal shutter ON / OFF by the calculation of the SN ratio by the noise component in the OFF section. .

  In step S10 in FIG. 2, after the liquid crystal shutter 2 is turned ON / OFF, the value of the ON section data output from the CCD 3 and the difference OFF frame data between the OFF section data are stored in the image frame buffer 7, and then the CPU 12 obtains from the ON section. The SN ratio is obtained from the ratio of the signal intensity of the entire screen to be obtained and the noise intensity obtained from the OFF section (step S11-1), and SN is compared with a predetermined value α and Β. The process proceeds to step S12. If α ≦ SN ratio ≦ Β, the process proceeds to step S11-3, and if SN ratio <Ｓ, the process proceeds to step S11-4 (step S11-2). Here, α is a relatively high value, and Β is a value that is sufficiently high (alpha << Β) that device noise is negligible with respect to the imaging signal level, and is set at the time of design.

  In the case of α ≦ SN ratio ≦ Β, the CPU 12 sets the ON interval to an integer multiple (2 times or more) of the OFF interval according to the SN ratio (that is, changes the duty ratio according to the SN ratio). The liquid crystal shutter 2 is turned ON / OFF, and the process proceeds to step S11-5 (step S11-3).

  When the S / N ratio> Β, the CPU 12 always sets the ON / OFF timing of the liquid crystal shutter 2 to ON so as to increase the exposure time, and proceeds to step S11-5 (step S11-4). That is, when the SN ratio is sufficiently high and the device noise level is negligible with respect to the image signal level, the ON / OFF timing of the liquid crystal shutter 2 can be always set to ON to increase the exposure time.

  The CPU 12 sends an ON / OFF timing setting change instruction signal including the ON / OFF timing value of the liquid crystal shutter 2 set in step S11-3 or S11-4 to the light reception control unit 9, and proceeds to step S12 in FIG. Step S11-5).

(Modification)
In the above-described embodiment, the liquid crystal shutter 2 is configured to shield light. However, the liquid crystal shutter 2 may be configured to shield light using a mirror or a prism. Further, the imaging device such as a CCD may have a dual configuration, and a mirror or a prism may be used so that light from the optical system 1 is alternately incident on each of the two imaging devices.

  As mentioned above, although several Example of this invention was described, it cannot be overemphasized that this invention is not limited to said each Example, A various deformation | transformation implementation is possible.

It is a block diagram which shows one Example of the main components of the imaging device of this invention. It is a flowchart which shows the imaging | photography operation | movement control sequence by CPU of the digital camera based on this invention. It is explanatory drawing of the simple BPF comprised by this invention. It is a flowchart which shows the detailed operation | movement of step S11 of FIG. It is a graph which shows the frequency characteristic of the simple BPF comprised by this invention.

Explanation of symbols

1 Optical system 2 Liquid crystal shutter 3 CCD
6 Image field buffer 7 Image frame buffer 8 Signal processing unit 9 Light reception control unit 11 Lens control unit 12 CPU
15 Shutter button 16 Mode button 24 Simple BPF
100 digital camera

Claims (6)

Imaging means for converting an optical image into image information composed of electrical signals;
A light shielding control means for periodically blocking or passing an optical image incident on the imaging means;
An image storage means for storing a field image signal converted by the imaging means from an optical image incident in a first section in which an optical image is periodically incident on the imaging means under the control of the blocking control means;
A noise component storage means for storing a field noise component including a dark current noise component generated from the imaging means in a second section in which the incident optical image is periodically blocked by the control of the cutoff control means;
Subtracting means for subtracting the field noise component stored in the noise component storage means from the field image signal stored in the image storage means;
Frame data storage means for sequentially storing the difference obtained by the subtraction means as frame data;
A light-shielding timing adjusting unit that obtains an SN ratio from a ratio of the signal intensity of the field image signal and the signal intensity of a field noise component, and adjusts the timing of blocking or passing the optical image of the light-shielding unit;
An imaging apparatus comprising: The light-shielding timing adjusting means sets the length of the first section to an integral multiple of 2 or more of the second section when α ≦ Β is set to a positive number α << Β, A timing adjusting means that is always the first section when the SN ratio> Β,
A light shielding timing changing means for providing light shielding timing change information to the light shielding control means on the basis of the section change information adjusted by the timing adjusting means;
The imaging apparatus according to claim 1, further comprising:   The light shielding control means is based on the change information of the light shielding timing acquired after completion of the periodic shielding or passing operation of the optical image controlled when the light shielding timing change information is obtained from the light shielding timing changing means. The imaging apparatus according to claim 2, wherein a periodic blocking or passing operation of the optical image incident on the imaging unit is controlled.   When the subtracting unit subtracts the field noise component stored in the noise component storage unit from the field image signal stored in the image storage unit, the lengths of the first section and the second section are different. In this case, the field image signal or the field noise component is adjusted so that the field image signal and the field noise component become data acquired when the lengths of the first interval and the second interval are equal. The imaging apparatus according to claim 1, wherein subtraction is performed after the first time. In an imaging apparatus provided with imaging means for converting an optical image into image information consisting of electrical signals,
A first step of periodically blocking or passing an optical image incident on the imaging means;
The field image signal converted by the imaging unit from the optical image incident in the first section in which the optical image is periodically incident on the imaging unit in the first step is temporarily stored in the first buffer, and the first buffer A second step of temporarily storing a field noise component including a dark current noise component generated from the imaging means in a second buffer in a second section in which an optical image incident in step 1 is periodically blocked;
A third step of subtracting the field noise component stored in the second buffer from the field image signal stored in the first buffer;
A fourth step of sequentially storing the difference acquired in the third step as frame data in a third buffer;
A fifth step of obtaining an S / N ratio from a ratio of a signal intensity of the field image signal and a signal intensity of a field noise component, and adjusting a timing of blocking or passing the optical image of the light shielding unit;
A noise removal method comprising: A computer having an imaging means for converting an optical image into image information composed of electrical signals,
A light shielding control means for periodically blocking or passing an optical image incident on the imaging means;
Image storage means for storing, in a memory, a field image signal converted by the imaging means from an optical image incident in a first section in which an optical image is periodically incident on the imaging means under the control of the blocking control means;
Noise component storage means for storing, in a memory, field noise components including dark current noise components generated from the imaging means in a second section in which the incident optical image is periodically blocked by the control of the cutoff control means;
Subtracting means for subtracting the field noise component stored in the memory by the noise component storing means from the field image signal stored in the memory by the image storing means;
Frame data storage means for sequentially storing the difference obtained by the subtracting means as frame data in a memory;
A light shielding timing adjusting means for obtaining an SN ratio from the ratio of the signal intensity of the field image signal and the signal intensity of the field noise component, and adjusting the timing of blocking or passing the optical image of the light shielding means;
Noise removal control program to function as.

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