JP2008252683A - Image sensing apparatus and control method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make cyclic noise hardly stand out in a photographed image without complicating a configuration. <P>SOLUTION: In an image sensing apparatus including an image sensing unit (14) that performs image sensing by converting incoming light into electrical signals, a horizontal cycle for driving the image sensing unit is set to a first cycle (S307), a first image sensing signal is obtained by performing image sensing in the first cycle while exposing the image sensing unit (S309), the horizontal cycle for driving the image sensing unit is set to a second cycle different from the first cycle (S313), a second image sensing signal is obtained by performing image sensing in the second cycle while shielding the image sensing unit from light (S315), and the first image sensing signal is processed by the second image sensing signal (S316). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an imaging apparatus and a control method thereof, and more particularly to an imaging apparatus that captures a subject image using a solid-state imaging device such as a CCD and a control method thereof.

  In recent years, an image pickup apparatus such as a digital camera that records and reproduces an image picked up by a solid-state image pickup device such as a CCD using a memory card having a solid-state memory element as a recording medium has been actively developed and widely spread. Further, in such an imaging apparatus, there is a demand for improvement in resolution and operation speed related to still image and moving image shooting. Therefore, the drive signal frequency for driving the solid-state imaging device constituting the digital camera or the like, and the drive frequency for the analog signal processing circuit, the A / D converter, and the subsequent digital signal processing circuit are rapidly increasing. Yes.

  Recently, in addition to the improvement of image quality such as high image quality and high definition, there has been a further demand for ease of shooting with few failures in various shooting scenes. Therefore, for example, in order to follow a fast-moving subject such as a sports scene or to prevent camera shake in indoor shooting under low illumination, the shutter speed is increasing. Furthermore, in order to enable shooting at places where strobe shooting is prohibited, such as museums and aquariums, it is required to further increase the sensitivity of the image sensor.

  An example of a conventional digital camera will be described below.

  FIG. 8 is a block diagram illustrating a schematic configuration of an imaging unit inside a general digital camera.

  In FIG. 8, reference numeral 501 denotes an image sensor such as a CCD (hereinafter referred to as “CCD”). Reference numeral 502 denotes an image pickup circuit that processes the output signal of the CCD 501, and reference numeral 503 denotes an A / D converter for converting the processed analog image pickup signal into a digital signal. In addition, the frame indicated by 500 indicates an analog signal processing area. Reference numeral 504 denotes a digital signal processing unit that performs various kinds of signal processing for storing the digitally converted image pickup signal in a storage medium or displaying it on a liquid crystal monitor. 505 is an oscillation circuit (OSC1), 506 is a timing generator (TG), 507 is a synchronization signal generator (SSG), and 508 is an oscillation circuit (OSC2). A system control unit 509 includes a CPU for controlling the operation of the entire digital camera.

  The oscillation circuit (505) supplies an operation clock for the timing generator 506, and the oscillation circuit (508) supplies an operation clock for the system control unit 509. The timing generator 506 supplies an operation clock (TGCLK) to the synchronization signal generator 507, and the synchronization signal generator 507 counts a predetermined number of the operation clocks to generate a horizontal synchronization signal (HD) and a vertical synchronization signal (VD). Is supplied to the timing generator 506. The timing generator 506 supplies various drive signals to the CCD 501 in synchronization with the horizontal synchronization signal (HD) and the vertical synchronization signal (VD) supplied from the synchronization signal generator 507. The sampling clock signal is supplied to the imaging circuit 502, the A / D converter 503, and the digital signal processing unit 504, respectively. The system control unit 509 controls the operation of the digital signal processing unit 504 as well as the presence / absence of generation of the horizontal synchronization signal (HD) and the vertical synchronization signal (VD) and the period setting for the synchronization signal generator 507. ing.

  FIG. 9 is a schematic diagram showing a configuration example of the CCD 501 shown in FIG. In FIG. 9, 1 is a photoelectric conversion element, and 2 is a vertical transfer CCD (VCCD). In addition, among the photoelectric conversion elements 1, the photoelectric conversion elements 1 indicated by shading in the leftmost column are light-shielded photoelectric conversion elements (light-shielding portions), and other photoelectric conversion elements 1 are light-shielded. It is a photoelectric conversion element in an effective pixel region that is not. Each photoelectric conversion element 1 and each VCCD 2 form a pair, and an image pickup region is formed by arranging a plurality of pairs in two dimensions, and an image is picked up by converting a light beam from a subject into an electric charge. . Reference numeral 4 denotes a horizontal transfer CCD (HCCD) for transferring charges sequentially transferred from the VCCD 2 in the horizontal direction.

  The charges generated in the photoelectric conversion element 1 are transferred to the VCCD 2 and then sequentially transferred to the HCCD 4 in the vertical direction in units of one horizontal row. Thereafter, the voltage is transferred in the horizontal direction by the HCCD 4, converted from a charge to a voltage by the charge / voltage conversion amplifier 5, and output.

  Note that the VCCD 2 and the HCCD 4 constituting the CCD 501, the photoelectric conversion element 1 in the effective pixel region, and the photoelectric conversion element 1 in the light shielding portion are all configured by a larger number than that shown in FIG. 9. For example, in FIG. 9, the photoelectric conversion elements of the light shielding unit are represented by one column at the left end, but actually are configured by a plurality of columns.

  FIG. 10 is a block diagram showing a more detailed circuit configuration inside the imaging circuit 502.

  In FIG. 10, the imaging circuit 502 includes a correlated double sampling (CDS) circuit 600, an amplifier 601, and a clamp circuit 602.

  Normally, a CDS circuit for removing a reset noise component generated during charge transfer in the CCD is provided at the subsequent stage of the CCD sensor. The output of the CCD 501 is composed of a feed-through period that is a reference for the signal level for each pixel in one horizontal transfer cycle and a video signal period in which a video signal is output in proportion to the exposure amount. The CDS circuit 600 obtains a difference between the signal level of the feedthrough period and the signal level of the video signal period in the output signal from the CCD 501, and thereby eliminates a correlation noise component of one pixel period from the video signal. It is. The amplifier 601 amplifies the imaging signal output via the CDS circuit 600 to a predetermined signal level in accordance with the input range of the subsequent A / D converter 503 by the amplifier 601 and supplies the amplified signal to the clamp circuit 602. The clamp circuit 602 adjusts the DC voltage level so that the charges output from the pixels in the light shielding portion of the CCD 501 have a predetermined black reference value. Note that a period in which charges are output from the pixels in the light shielding portion is referred to as an optical black (OB) period.

  FIG. 11 is a timing chart showing main signals for driving the digital camera shown in FIGS.

  Here, the operating clock frequency of OSC1 (505) is 33.75 MHz, and the operating clock frequency of the timing generator 506 is 27 MHz.

  The operating frequency for each pixel output from the CCD 501 is determined by the CCD drive signal generated by the timing generator 506, and is generated from 33.75 MHz which is the same as the frequency of the operating clock of the OSC1 (505). That is, one pixel period of the CCD output signal at this time is 29.6 ns (= 1 / 33.75 MHz), and this includes the above-described feedthrough period and video signal period.

  Further, the timing generator 506 performs CCD driving of an S / H pulse (SH1) for sample-holding the signal level during the feedthrough period and an S / H pulse (SH2) for sample-holding the signal level during the video signal period for each pixel. Generate to synchronize with the signal.

JP 2001-285726 A

  Increasing the drive frequency of the imaging signal in the imaging apparatus can be a major factor that degrades the S / N ratio of the imaging signal. In particular, an unnecessary clock signal is likely to leak into an analog imaging signal inside a digital imaging device that is driven by a plurality of operation clock signals and includes a mixture of analog signals and digital signals. The leaked unnecessary clock signal is superimposed on the generated image at an equal pitch as interference clock noise. Since the pitches are equal, there is a problem that even if the level is lower than the thermal noise random noise of the CCD sensor or the circuit, it is easily noticeable in terms of visual feeling.

  Such a deterioration in the S / N ratio of the image pickup signal has a problem that the sensitivity condition of the image pickup apparatus is set higher, and the image signal is more likely to be manifested when the image signal amplification degree of the image pickup circuit is larger.

  For example, in the configuration shown in FIG. 8, the S / H pulse (SH1, SH2) and the sampling clock (ADCLK) of the A / D converter 503 are also increased in accordance with the speeding up of the system operation and the driving frequency of the imaging signal. It is becoming. For this reason, it is becoming increasingly difficult to avoid these clock noise components (system clock components) leaking into the imaging signal in the analog signal processing area 500 by timing adjustment.

  Here, a case where the output of the CCD 501 is sampled by the S / H pulse (SH1, SH2) having the pixel clock of 33.75 MHz and the sampling clock (ADCLK) of the A / D converter 503 will be described. When the above-described system clock component (27 MHz) leaks into the imaging signal of the analog signal processing region 500, the image data after sampling has a difference frequency component of 6.75 MHz (= 33.75-27 MHz). As a result, periodic noise remains. This is a 1/5 frequency of 33.75 MHz of the drive pulse of the CCD 501, that is, an equal pitch noise with a period of 5 pixels. The equal pitch noise due to the interference of this pulse depends on the pitch size, but the features are easier to catch compared to the thermal noise random noise of CCD sensors and imaging circuits. .

  In the case of a CCD sensor, a rough breakdown of one horizontal (1H) period is as shown in FIG. That is, a blanking period in which the transfer drive pulses H1 and H2 for the HCCD 4 are stopped, and a period of pixel readout being driven (OB period + effective pixel period).

  The appearance of the equal pitch noise superimposed on the imaging signal in a one-dimensional manner changes depending on the number of pixel clocks constituting one horizontal period for a two-dimensional image developed in the horizontal and vertical directions by a CCD area sensor or the like.

  In the case of equal pitch noise with a 5-pixel period, as shown in FIGS. 13A to 13E, the noise patterns to be formed are five patterns according to a remainder system of 5 depending on the number of pixel clocks constituting one horizontal period. There are variations. As can be seen from FIG. 13, there is no change in the noise pitch in the horizontal direction, but since the angle of the noise pattern changes on the developed two-dimensional image, it has been confirmed that the degree of conspicuousness changes somewhat.

  Incidentally, dark noise correction is generally performed when imaging is performed using a solid-state imaging device such as a CCD. In dark noise correction, the actual captured image data read after charge accumulation with the image sensor exposed and the dark image data read after charge accumulation similar to the main image capture without exposing the image sensor The arithmetic processing is performed using. With dark noise correction, it is possible to shoot a high-quality image by correcting captured image data with respect to image quality degradation such as dark current noise generated in the image sensor and pixel defects due to minute scratches inherent to the image sensor.

  In particular, since dark current noise increases with the charge accumulation time and the temperature rise of the image sensor, a large image quality improvement effect can be obtained when performing exposure at long seconds or exposure at high temperatures.

  In the imaging apparatus that performs such dark noise correction processing, as shown above, an example of a noise pattern in which the equal pitch noise of the 5-pixel period superimposed on the imaging signal is developed on the image after the dark noise correction processing is shown in FIG. Show.

  The noise pattern example of FIG. 14 shows dark noise correction processing (in this case, subtraction processing) when one horizontal period is composed of 5N + 1 pixel clocks as shown in FIG. ) Is shown.

  As shown in FIG. 14, there are five types of images (a) to (e) in the image after the dark noise correction processing due to the phase difference of the noise pattern between the captured image data and the dark image data. Noise pattern is generated.

  In FIG. 14, an approximate distribution state is created by setting the level of periodic noise before dark noise correction processing to 2 at the central pixel and 1 at adjacent pixels, and dark noise correction processing is performed based on the noise pattern phase difference from the dark image. The situation where the noise level later changed is shown schematically.

  With respect to five noise patterns, how the noise stands out is classified into three cases. That is,

(1) Case inconspicuous compared to the actual captured image (phase difference 1, (a) and (c) in FIG. 5).
(2) A case that is significantly conspicuous compared to the actual captured image (phase difference 2, (d) and (e) in FIG. 5).
(3) A case in which the image is not conspicuous at all compared with the captured image (phase difference 0, FIG. 5B).
If the phase relationship can be managed accurately so that the periodic noise pixels of the main photographed image and the dark image are successfully canceled, it is conceivable to finally generate an image without periodic noise.

  However, in many cases, the OSC1 (505) operation clock (33.75 MHz) and the OSC2 (508) operation clock (27 MHz) in FIG. In the case of free run, the phase of the noise pattern of the actual captured image and the dark image moves depending on the accuracy of each oscillation circuit and temperature drift, and it is difficult to always manage the phase relationship with high accuracy.

  The operating clock (33.75 MHz) of OSC1 (505) can be generated from the operating clock (27 MHz) of OSC2 (508) using a method such as a phase-locked loop (PLL) circuit. In this case, since the noise pattern and phase relationship between the frame fields can be determined with high accuracy, the noise pattern after dark correction processing can be managed. However, in that case, the operating clock (27 MHz) of the OSC2 (508) must be routed through the PLL circuit to the timing generator 506 in the vicinity of the analog signal processing region 500 that is vulnerable to noise. Therefore, the risk that the system operation clock (27 MHz) leaks excessively into the analog imaging signal increases.

  Patent Document 1 discloses a technique for reducing unnecessary beat noise that occurs when frequency spreading means is applied to analog signal processing of an imaging apparatus. According to this technique, it is suggested that beat noise in response to the frequency spreading period is superimposed on the imaging signal by the frequency spreading means. Then, the beat noise is reduced by resetting the phase of the frequency diffusion unit at random timing in the horizontal transfer blank period of the image sensor.

  However, as shown in FIG. 8, in a digital camera that does not have a frequency spreading unit, noise with unnecessary periodicity that occurs outside the frequency spreading unit cannot be reduced by the method of Patent Document 1.

  The present invention has been made in view of the above problems, and an object of the present invention is to make periodic noise in captured images less noticeable without complicating the configuration.

  In order to achieve the above object, an imaging apparatus of the present invention includes an imaging unit that performs imaging by converting incident light into an electrical signal, and a first imaging signal that performs an imaging operation in a state where the imaging unit is exposed. Control means for controlling the first imaging operation for obtaining the second imaging operation for obtaining the second imaging signal by performing the imaging operation in a state where the imaging means is shielded from light, and the first imaging signal for the second imaging operation. Signal processing means for processing with a second imaging signal, and the control means varies a horizontal period for driving the imaging means between the first imaging operation and the second imaging operation.

  Further, in the control method of the present invention of the image pickup apparatus having the image pickup means for picking up an image by converting incident light into an electric signal, a first setting step of setting a horizontal period for driving the image pickup means to a first period. A first imaging step for obtaining a first imaging signal by performing an imaging operation in the first cycle in a state in which the imaging unit is exposed, and a horizontal cycle for driving the imaging unit. A second setting step of setting a second cycle different from the cycle, and a second imaging step of obtaining a second imaging signal by performing an imaging operation in the second cycle with the imaging means shielded from light And a signal processing step of processing the first imaging signal with the second imaging signal.

  According to the present invention, periodic noise in captured images can be made inconspicuous without complicating the configuration.

  The best mode for carrying out the present invention will be described below in detail with reference to the accompanying drawings.

  FIG. 1 is a block diagram illustrating a configuration of an imaging apparatus having an image processing function according to an embodiment of the present invention. In the present embodiment, a digital camera will be described as an example of the imaging device. As other imaging devices, there are digital video cameras, camera-equipped mobile terminals (including camera-equipped mobile phones), scanners, etc., as long as they can convert an optical image of an object and output an electrical image signal. The present invention can be applied.

  As shown in FIG. 1, the imaging apparatus according to the present embodiment mainly includes a camera body 100 and an interchangeable lens type lens unit 300.

  In the lens unit 300, 310 is an imaging lens composed of a plurality of lenses, 312 is a diaphragm, and 306 is a lens mount that mechanically couples the lens unit 300 to the camera body 100. The lens mount 306 includes various functions for electrically connecting the lens unit 300 to the camera body 100. Reference numeral 320 denotes an interface for connecting the lens unit 300 to the camera body 100 in the lens mount 306, and 322 denotes a connector for electrically connecting the lens unit 300 to the camera body 100.

  The connector 322 transmits a control signal, a status signal, a data signal, and the like between the camera body 100 and the lens unit 300, and also has a function of supplying or supplying a current of various voltages. The connector 322 may be configured to transmit not only electrical communication but also optical communication, voice communication, and the like.

  Reference numeral 340 denotes an aperture control unit that controls the aperture 312 in cooperation with a shutter control unit 40 that controls a shutter 12 of the camera body 100 described later based on photometric information from the photometry control unit 46. Reference numeral 342 denotes a focus control unit that controls focusing of the imaging lens 310, and 344 denotes a zoom control unit that controls zooming of the imaging lens 310.

  A lens system control circuit 350 controls the entire lens unit 300. The lens system control circuit 350 includes a memory for storing operation constants, variables, programs, and the like. Further, a non-volatile memory that holds identification information such as a number unique to the lens unit 300, management information, function information such as an open aperture value, a minimum aperture value, and a focal length, and current and past setting values is also provided.

  Next, the configuration of the camera body 100 will be described.

  Reference numeral 106 denotes a lens mount that mechanically couples the camera body 100 and the lens unit 300, and reference numerals 130 and 132 denote mirrors, which guide light beams incident on the imaging lens 310 to the optical viewfinder 104 by a single-lens reflex system. The mirror 130 may be either a quick return mirror or a half mirror. Reference numeral 12 denotes a shutter having a diaphragm function, and reference numeral 14 denotes an image sensor that converts incident light into an electrical signal. In this embodiment, the image sensor 14 has the same configuration as the CCD 501 described above with reference to FIG. To do. The light beam incident on the imaging lens 310 is guided by the single-lens reflex system through the aperture 312 that is a light amount limiting unit, the lens mounts 306 and 106, the mirror 130, and the shutter 12, and forms an optical image on the imaging element 14.

  Reference numeral 16 denotes an A / D converter that converts an analog signal output from the image sensor 14 into a digital signal. The image sensor 14 and the A / D converter 16 are areas for processing analog signals. A timing generation circuit 18 supplies a clock signal and a control signal to the image sensor 14, the A / D converter 16, and the D / A converter 26, respectively, and is controlled by the memory control circuit 22 and the system control circuit 50.

  An image processing circuit 20 performs predetermined pixel interpolation processing and color conversion processing on the data from the A / D converter 16 or the data from the memory control circuit 22. Further, the image processing circuit 20 performs a predetermined calculation process using the image data output from the A / D converter 16. Then, based on the obtained calculation result, the system control circuit 50 controls the shutter control unit 40 and the focus adjustment unit 42, TTL (through the lens) type autofocus (AF) processing, automatic exposure ( AE) processing and flash light control (EF) processing are performed. Further, the image processing circuit 20 performs predetermined arithmetic processing using the image data output from the A / D converter 16, and also performs TTL auto white balance (AWB) processing based on the obtained arithmetic result. ing.

  In the example shown in FIG. 1 in the present embodiment, the focus adjustment unit 42 and the photometry control unit 46 are provided exclusively. Therefore, the AF adjustment process, the AE process, and the EF process are performed using the focus adjustment unit 42 and the photometry control unit 46, and the AF process, the AE process, and the EF process using the image processing circuit 20 are not performed. It does not matter. Further, AF processing, AE processing, and EF processing are performed using the focus adjustment unit 42 and the photometry control unit 46, and further, AF processing, AE processing, and EF processing are performed using the image processing circuit 20. It is good also as a structure.

  A memory control circuit 22 controls the A / D converter 16, the timing generation circuit 18, the image processing circuit 20, the image display memory 24, the D / A converter 26, the memory 30, and the compression / decompression circuit 32. Image data output from the A / D converter 16 is written into the image display memory 24 or the memory 30 via the image processing circuit 20, the memory control circuit 22, or only through the memory control circuit 22.

  Reference numeral 24 denotes an image display memory, 26 denotes a D / A converter, and 28 denotes an image display unit made up of a TFT type LCD or the like. Display image data written in the image display memory 24 is stored in the D / A converter 26. Via the image display unit 28. An electronic viewfinder (EVF) function can be realized by sequentially displaying captured image data using the image display unit 28. Further, the image display unit 28 can arbitrarily turn on / off the display according to an instruction from the system control circuit 50, and when the display is turned off, the power consumption of the camera body 100 can be significantly reduced. it can.

  Reference numeral 30 denotes a memory for storing captured still images and moving images, and has a storage capacity sufficient to store a predetermined number of still images and a moving image for a predetermined time. This makes it possible to write a large amount of images to the memory 30 at high speed even in continuous shooting or panoramic shooting in which a plurality of still images are continuously shot. The memory 30 can also be used as a work area for the system control circuit 50.

  A compression / decompression circuit 32 compresses / decompresses image data using a known compression method such as adaptive discrete cosine transform (ADCT). The compression / decompression circuit 32 reads an image stored in the memory 30, performs a compression process or an expansion process, and writes the processed data to the memory 30 again.

  Reference numeral 40 denotes a shutter control unit that controls the shutter 12 in cooperation with an aperture control unit 340 that controls the aperture 312 based on photometry information from the photometry control unit 46. A focus adjusting unit 42 performs AF (autofocus) processing. A light beam incident on the imaging lens 310 in the lens unit 300 is incident as a single-lens reflex system through a diaphragm 312, lens mounts 306 and 106, a mirror 130, and a focus adjustment submirror (not shown), thereby forming an optical image. The in-focus state of the imaged image is measured.

  A photometry control unit 46 performs AE (automatic exposure) processing. A light beam incident on the imaging lens 310 in the lens unit 300 is incident on the single lens reflex system through the diaphragm 312, the lens mounts 306 and 106, the mirror 130, and the photometric sub mirror (not shown), thereby forming an optical image. Measure the exposed state of the captured image. A flash 48 has an AF auxiliary light projecting function and a flash light control function. The photometry control unit 46 also has an EF processing function in cooperation with the flash 48.

  As described above, exposure control and AF control may be performed based on the calculation result calculated by the image processing circuit 20 using the image data from the A / D converter 16. In this case, the system control circuit 50 can perform exposure control and AF control using the video TTL system for the shutter control unit 40, the aperture control unit 340, and the focus control unit 342.

  Further, the AF control may be performed using the measurement result by the focus adjustment unit 42 and the calculation result obtained by calculating the image data from the A / D converter 16 by the image processing circuit 20. Furthermore, exposure control may be performed using the measurement result obtained by the photometry control unit 46 and the calculation result obtained by calculating the image data from the A / D converter 16 by the image processing circuit 20.

  Reference numeral 50 denotes a system control circuit that controls the entire camera body 100, and incorporates a known CPU. A memory 52 stores constants, variables, programs, and the like for operating the system control circuit 50.

  Reference numeral 54 denotes a notification unit for notifying the outside of an operation state, a message, and the like using characters, images, sounds, and the like in accordance with execution of a program in the system control circuit 50. As the notification unit 54, for example, a display unit that performs visual display using an LCD, an LED, or the like, or a sound generation element that performs voice notification, etc., is used, and the notification unit 54 is configured by a combination of one or more of these. In particular, in the case of the display unit, it is installed at one or a plurality of locations near the operation unit 70 of the camera body 100 that are easy to see. In addition, the notification unit 54 has a part of its function installed in the optical viewfinder 104.

  Among the display contents of the notification unit 54, the following are displayed on the LCD or the like. First, there are displays relating to shooting modes such as single-shot / continuous-shot shooting display, self-timer display, and the like. In addition, there are displays relating to recording such as compression rate display, recording pixel number display, recording number display, and remaining image number display. In addition, there are displays relating to shooting conditions such as shutter speed display, aperture value display, exposure correction display, flash display, and red-eye reduction display. In addition, there are a macro shooting display, a buzzer setting display, a clock battery remaining amount display, a battery remaining amount display, an error display, an information display by a multi-digit number, and an attachment / detachment state display of the recording media 200 and 210. Furthermore, the attachment / detachment state display of the lens unit 300, the communication I / F operation display, the date / time display, the display indicating the connection state with the external computer, and the like are also performed.

  Further, among the display contents of the notification unit 54, examples of what is displayed in the optical finder 104 include the following. In-focus display, photographing preparation completion display, camera shake warning display, flash charge display, flash charge completion display, shutter speed display, aperture value display, exposure correction display, recording medium writing operation display, and the like.

  Further, among the display contents of the notification unit 54, examples of what is displayed by an LED or the like include the following. In-focus display, shooting preparation completion display, camera shake warning display, flash charge display, flash charge completion display, recording medium writing operation display, macro shooting setting notification display, secondary battery charge display, and the like.

  Further, among the display contents of the notification unit 54, what is displayed on the lamp or the like includes, for example, a self-timer notification lamp. This self-timer notification lamp may be shared with AF auxiliary light.

  Reference numeral 56 denotes an electrically erasable / recordable non-volatile memory in which programs and the like to be described later are stored. For example, an EEPROM or the like is used. The nonvolatile memory 56 stores various parameters, set values such as ISO sensitivity, and the like.

  Reference numerals 60, 62, 64, 66, and 70 are operation means for inputting various operation instructions of the system control circuit 50, and include one or a plurality of switches, dials, touch panels, pointing by line-of-sight detection, voice recognition devices, and the like. Composed of a combination.

  Here, a specific description of these operating means will be given.

  Reference numeral 60 denotes a mode dial switch, which is a mode changeover switch for distinguishing between starting of the still image shooting mode and the moving image shooting mode.

  Reference numeral 62 denotes a shutter switch SW1, which is turned on while a shutter button (not shown) is being operated (for example, half-pressed), and instructs to start operations such as AF processing, AE processing, AWB processing, and EF processing.

  A shutter switch SW2 64 is turned on when a shutter button (not shown) is completed (for example, fully pressed), and instructs the start of a series of processes including exposure processing, development processing, and recording processing. First, in the exposure process, the signal read from the image sensor 14 is written into the memory 30 via the A / D converter 16 and the memory control circuit 22, and further the calculation in the image processing circuit 20 and the memory control circuit 22 is performed. Development processing using is performed. Further, in the recording process, the image data is read from the memory 30, compressed by a compression / decompression circuit, and written to the recording medium 200 or 210.

  Reference numeral 66 denotes a playback switch, which instructs to start a playback operation for reading an image shot in the shooting mode state from the memory 30 or the recording medium 200 or 210 and displaying it on the image display unit 28.

  An operation unit 70 includes various buttons and a touch panel. For example, the menu button, set button, macro button, multi-screen playback pagination button, flash setting button, single shooting / continuous shooting / self-timer switching button, menu movement + (plus) button, menu movement-(minus) button Including. Furthermore, playback switch shooting image quality selection button that can set each function mode such as playback image move + (plus) button, playback image move-(minus) button, playback mode, multi-screen playback / erase mode, PC connection mode, etc. including. It also includes an exposure compensation button, a date / time setting button, and the like. The functions of the plus button and the minus button can be selected more easily with numerical values and functions by providing a rotary dial switch. Also included is an ISO sensitivity setting button that can set the ISO sensitivity by changing the gain setting in the image sensor 14 or the image processing circuit 20.

  In addition, a selection / switch button that sets selection and switching of various functions when performing shooting and playback in panorama mode, etc., and determination and execution of various functions when performing shooting and playback in panorama mode and the like There is a decision / execution button. In addition, there is an image display ON / OFF switch for setting ON / OFF of the image display unit 28, and a quick review ON / OFF switch for setting a quick review function for automatically reproducing image data taken immediately after shooting. Further, there is a compression mode switch that is a switch for selecting a compression rate of JPEG compression, or for selecting a CCD RAW mode in which a signal from an image sensor is directly digitized and recorded on a recording medium. In addition, there is an AF mode setting switch that can set a one-shot AF mode and a servo AF mode. In the one-shot AF mode, an autofocus operation is started when the shutter switch SW1 (62) is pressed, and once focused, the focused state is maintained. In the servo AF mode, the autofocus operation is continued while the shutter switch SW1 (62) is being pressed.

  Reference numeral 72 denotes a power switch, which can switch and set the power-on and power-off modes of the camera body 100. Also, the power on and power off settings of various accessory devices such as the lens unit 300, the external flash, and the recording media 200 and 210 connected to the camera body 100 can be switched.

  A power control unit 80 includes a battery detection circuit, a DC-DC converter, a switch circuit that switches a block to be energized, and the like. The power supply control unit 80 detects the presence / absence of a battery, the type of battery, and the remaining battery level, controls the DC-DC converter based on the detection result and an instruction from the system control circuit 50, and requires a necessary voltage. It is supplied to each part including the recording medium for a period.

  Reference numerals 82 and 84 denote connectors, 86 denotes a primary battery such as an alkaline battery or lithium battery, a secondary battery such as a NiCd battery, NiMH battery, Li-ion battery, or Li polymer battery, an AC adapter, or the like.

  Reference numerals 90 and 94 denote interfaces with recording media such as memory cards and hard disks, and reference numerals 92 and 96 denote connectors for connecting to recording media such as memory cards and hard disks. A recording medium attachment / detachment detection circuit 98 detects whether or not the recording medium 200 or 210 is attached to the connectors 92 and / or 96.

  Although the present embodiment has been described as having two systems of interfaces and connectors for attaching the recording medium, the interface and connectors for attaching the recording medium may have a single or a plurality of systems. . Moreover, it is good also as a structure provided with combining the interface and connector of a different standard.

  As the interface and the connector, it is possible to configure using interfaces that comply with various storage medium standards. For example, a PCMCIA (Personal Computer Memory Card International Association) card, a CF (Compact Flash (registered trademark)) card, an SD card, or the like. When the interfaces 90 and 94 and the connectors 92 and 96 are configured using a standard conforming to a PCMCIA card, a CF (registered trademark) card, or the like, various communication cards can be connected. Communication cards include LAN cards, modem cards, USB (Universal Serial Bus) cards, and IEEE (Institute of Electrical and Electronic Engineers) 1394 cards. In addition, there are P1284 card, SCSI (Small Computer System Interface) card, PHS, and the like. By connecting these various communication cards, image data and management information attached to the image data can be transferred to and from other computers and peripheral devices such as a printer.

  Reference numeral 104 denotes an optical viewfinder, which guides a light beam incident on the imaging lens 310 through an aperture 312, lens mounts 306 and 106, and mirrors 130 and 132 by a single-lens reflex method, and forms an optical image for display. it can. Thereby, it is possible to perform imaging using only the optical viewfinder without using the electronic viewfinder function of the image display unit 28. In addition, in the optical viewfinder 104, some functions of the notification unit 54, for example, in-focus state, camera shake warning, flash charging, shutter speed, aperture value, exposure correction, and the like are displayed.

  A communication unit 110 has various communication functions such as RS232C, USB, IEEE1394, P1284, SCSI, modem, LAN, and wireless communication. Reference numeral 112 denotes a connector for connecting the camera body 100 to another device by the communication unit 110 or an antenna in the case of wireless communication.

  Reference numeral 120 denotes an interface for connecting the camera body 100 to the lens unit 300 in the lens mount 106.

  A connector 122 electrically connects the camera body 100 to the lens unit 300. Whether or not the lens unit 300 is attached to the lens mount 106 and / or the connector 122 is detected by a lens attachment / detachment detection unit (not shown). The connector 122 transmits a control signal, a status signal, a data signal, and the like between the camera body 100 and the lens unit 300, and has a function of supplying currents of various voltages. Further, the connector 122 may be configured to transmit not only electrical communication but also optical communication, voice communication, and the like.

  Reference numerals 200 and 210 denote recording media such as a memory card and a hard disk. The recording media 200 and 210 include recording units 202 and 212 configured by a semiconductor memory, a magnetic disk, and the like, interfaces 204 and 214 with the camera main body 100, and connectors 206 and 216 for connecting with the camera main body 100, respectively. Yes.

  As the recording media 200 and 210, a PCMCIA card, a memory card such as a compact flash (registered trademark), a hard disk, or the like can be used. Of course, it may be constituted by a micro DAT, a magneto-optical disk, an optical disk such as CD-R or CD-WR, a phase change optical disk such as DVD, or the like.

  FIG. 2 is a flowchart showing a basic routine related to photographing in the imaging apparatus.

  Upon power-on such as battery replacement, the system control circuit 50 initializes flags, control variables, and the like, and performs predetermined initial settings necessary for each part of the camera body 100 (step S101).

  Next, the system control circuit 50 determines the set position of the power switch 72 (step S102). If the power switch 72 is set to power OFF, the system control circuit 50 changes the display of each display unit to the end state, and sets necessary parameters, setting values, and setting modes including flags, control variables, and the like in a nonvolatile manner. Recorded in the memory 56. Further, the system control circuit 50 performs a predetermined end process such as shutting off unnecessary power of each part of the imaging apparatus including the image display unit 28 by the power control unit 80 (step S103), and then ends the routine.

  If the power switch 72 is set to ON in step S102, the process proceeds to step S104. In step S <b> 104, the system control circuit 50 determines whether or not the remaining capacity of the power source 86 configured by a battery or the like or the operation status has a problem in the operation of the imaging apparatus by the power source control unit 80. If there is a problem (NO in step S104), a predetermined warning is displayed by an image or sound using the notification unit 54 (step S105), and the process returns to step S102.

  On the other hand, if there is no problem with the power supply 86 (YES in step S104), the process proceeds to step S106. In step S106, the system control circuit 50 determines whether or not the recording medium 200 or 210 is attached by the recording medium attachment / detachment detection circuit 98, and acquires management information of image data recorded on the recording medium 200 or 210. Further, it is determined whether or not the operation state of the recording medium 200 or 210 has a problem in the operation of the imaging apparatus, particularly the recording / reproducing operation of the image data with respect to the recording medium 200 or 210. If there is a problem (NO in step S106), a predetermined warning is displayed by image or sound using the notification unit 54 (step S105), and the process returns to step S102.

  On the other hand, if there is no problem with the recording medium 200 or 210 (YES in step S106), the process proceeds to step S107 and electronic finder display is started.

  In the electronic finder display, the system control circuit 50 controls the timing generation circuit 18 with the shutter 12 opened, and reads out the charge of the image sensor 14 at a predetermined cycle by a method such as line thinning or line addition. Thus, by reading out the charge of the image sensor 14 by a method such as line thinning or line addition, the number of pixels is reduced to the number of lines suitable for electronic viewfinder display, and at the rate required for a moving image for viewfinder display. Then, the data read out sequentially from the image sensor 14 through the A / D converter 16 and the memory control circuit 22 and sequentially written into the image display memory 24 is transferred through the memory control circuit 22 and the D / A converter 26. Images are sequentially displayed by the image display unit 28. In this way, electronic viewfinder display is realized.

  Next, in step S108, the state of the shutter switch SW1 (62) is determined. If it is not pressed, the process returns to step S102. If the shutter switch SW1 (62) is pressed, the system control circuit 50 detects the state of the mode dial 60 (step S109). If the still image shooting mode is set, the moving image mode flag is reset (step S111). If the moving image shooting mode is set, the moving image mode flag is set (step S110). Then, the process proceeds to AF / AE / AWB processing (step S112).

  In step S112, first, AF processing is performed to focus the imaging lens 310 on the subject. At this time, the system control circuit 50 causes the light beam incident on the imaging lens 310 to enter the focus adjustment unit 42 via the stop 312, the lens mounts 306 and 106, the mirror 130, and a distance measuring sub mirror (not shown), A focusing state of an image formed as an optical image is determined. Then, AF control for detecting the in-focus state is performed using the focus adjustment unit 42 while driving the imaging lens 310 using the focus control unit 342 until it is determined to be in focus. When it is determined that the focus is achieved, the system control circuit 50 determines the focused distance point from the plurality of measured distance points on the shooting screen, and the focused data and / or setting parameters together with the determined distance point data. Is stored in the internal memory of the system control circuit 50 or the memory 52.

  Next, AE processing is performed. Here, first, the system control circuit 50 causes the light beam incident on the lens 310 to enter the photometry control unit 46 via the stop 312 and the photometry lens (not shown), and the exposure state of the image formed as an optical image. Measure. Then, photometry processing is performed using the photometry control unit 46 until the exposure is determined to be appropriate.

  When it is determined that the exposure is appropriate, the system control circuit 50 stores photometric data and / or setting parameters in the internal memory or the memory 52 of the system control circuit 50. Then, a sensitivity value (Dv value), an aperture value (Av value), and a shutter speed (Tv value) are determined according to the detected exposure result. As a result of photometry, if necessary, the flash flag is set and the flash is set. Then, the system control circuit 50 determines the charge accumulation time of the image sensor 14 according to the shutter speed (Tv value) determined here. Further, the system control circuit 50 determines the input dynamic range of the A / D converter 16 according to the sensitivity value (Dv value) determined here.

  Further, the system control circuit 50 performs predetermined arithmetic processing using the image data captured by the image processing circuit 20 after the AF processing and the AE processing. Then, based on the obtained calculation result, WB setting parameters for WB (white balance) processing are stored in the internal memory of the system control circuit 50 or the memory 52, and the AF / AE / AWB processing (step S112) is completed. To do.

  Various signals are exchanged between the system control circuit 50 and the aperture control unit 340 or the focus control unit 342 through the interface 120, the connectors 122 and 322, the interface 320, and the lens system control circuit 350.

  After the AF / AE / AWB process (step S112) is completed, the state of the shutter switch SW2 (64) is confirmed. If pressed (ON in step S113), the moving image mode flag is confirmed (step S114), and if reset, the process proceeds to still image shooting processing (step S116), and if set, moving image shooting processing (step S117). Proceed to

  On the other hand, if the shutter switch SW2 (64) is not pressed (OFF in step S113), the current processing is repeated until the shutter switch SW1 (62) is released (while ON in step S115). When the shutter switch SW1 (62) is released (OFF in step S115), the process returns to step S102.

  When the still image shooting process (step S116) and the moving image shooting process (step S117) are completed, the process returns to step S102. The still image shooting process in step S116 will be described in detail with reference to the flowchart in FIG. 3 and the timing chart in FIG. Note that the operation shooting process in step S117 may be performed by well-known moving image shooting, and is not directly related to the present invention, and thus detailed description thereof is omitted here.

<First Embodiment>
The basic configuration of the analog imaging signal region including the imaging device 14 and the A / D converter 16 and the timing generation circuit 18 in FIG. 1 is the same as the configuration of the imaging unit described in the background art with reference to FIG. It has. The function similar to that of the synchronization signal generation circuit (SSG) 507 in FIG. The function similar to OSC1 (505) is built in the timing generation circuit 18, and the function similar to OSC2 (508) is built in the system control circuit 50. Further, the digital signal processing unit 504 in FIG. 8 is not shown as a single configuration in FIG. 1, but is divided into the image processing circuit 20, the memory control circuit 22, the image display memory 24, etc., and shown in a more detailed configuration. ing.

  FIG. 3 is a flowchart showing details of the still image shooting process in step S116 of FIG. 2, and FIG. 4 is a timing chart of the imaging operation in the still image shooting process.

  In the still image shooting process of FIG. 3, various signals are exchanged between the system control circuit 50 and the aperture control unit 340 or the focus control unit 342 via the interface 120, the connectors 122 and 322, the interface 320, and the lens system control circuit 350. Done.

  First, in step S301, the system control circuit 50 controls the aperture 312 by the aperture controller 340 in accordance with exposure conditions such as aperture value (Av value) and shutter speed (Tv value) and photometric data stored in the internal memory or the memory 52. Drives to a predetermined aperture value. Then, the timing generation circuit 18 sets the CCD drive mode (step S302) and the electronic shutter (step S303), and starts exposure of the image sensor 14 (step S304).

  The system control circuit 50 waits for the exposure of the image sensor 14 to end according to the photometric data, closes the shutter 12 via the shutter controller 40 (step S305), and ends the exposure of the image sensor 14 (step S306). Then, the system control circuit 50 performs setting (first setting) for reading out the imaging signal from the imaging element 14 to the timing generation circuit 18 (step S307). The system control circuit 50 sets the period of the vertical and horizontal synchronization signals to be supplied to the timing generation circuit 18 from the built-in synchronization signal generation unit and starts supply (step S308). The imaging signal is read from the imaging device 14 in synchronization with the vertical and horizontal synchronization signals supplied from the timing generation circuit 18 (step S309). Here, the charge signal is read out from the image sensor 14, and the memory is sent via the A / D converter 16, the image processing circuit 20, the memory control circuit 22, or directly from the A / D converter 16 via the memory control circuit 22. Still image data is written in 30 predetermined areas. Note that the above-described shooting for exposing the image sensor 14 and recording the obtained image data is referred to as “main shooting”, and the obtained image and image data are referred to as “main shooting image” and “main shooting”, respectively. It is called “image data”. The captured image data corresponds to the first imaging signal in the claims, and the processing from step S303 to step S309 described above corresponds to the first imaging operation in the claims.

  Next, the system control circuit 50 sets the electronic shutter again (step S310), and starts exposure (CCD accumulation) of the image sensor 14 with the shutter 12 kept closed (step S311). Then, after the same predetermined accumulation time as that at the time of actual photographing, the exposure is finished (step S312). Note that photographing with the shutter 12 closed is hereinafter referred to as “dark image photographing”. The system control circuit 50 performs setting (second setting) for reading out the imaging signal in the dark image shooting from the imaging device 14 to the timing generation circuit 18 (step S313). The system control circuit 50 newly sets the period of the vertical and horizontal synchronization signals supplied to the timing generation circuit 18 from the built-in synchronization signal generation unit and starts supply (step S314). The timing generation circuit 18 reads out the charge signal from the image sensor 14 in synchronization with the supplied vertical and horizontal synchronization signals (step S314). Here, the charge signal is read out from the image sensor 14, and the memory is sent via the A / D converter 16, the image processing circuit 20, the memory control circuit 22, or directly from the A / D converter 16 via the memory control circuit 22. Image data is written in 30 predetermined areas. Note that images and data obtained by dark image shooting are referred to as “dark images” and “dark image data”, respectively. The dark image data corresponds to the second imaging signal in the claims, and the above-described processing from step S310 to step S315 corresponds to the second imaging operation in the claims.

  Next, in the still image recording process (step S316), first, the system control circuit 50 performs a process of subtracting the dark image data from the actual captured image data written in the predetermined area of the memory 30. Then, after dark correction processing is performed to cancel out dark current noise and the like of the image sensor 14, writing is performed in a predetermined area of the memory 30. Then, a part of the still image data after the dark correction processing is read out via the memory control circuit 22, AWB integration calculation processing and OB integration calculation processing necessary for performing the development processing are performed, and the calculation result is sent to the system control circuit. 50 internal memory or memory 52.

  The system control circuit 50 uses the memory control circuit 22 and, if necessary, the image processing circuit 20 to read out still image data after dark correction processing written in a predetermined area of the memory 30. Then, using the calculation results stored in the internal memory of the system control circuit 50 or the memory 52, various development processes including AWB processing, gamma conversion processing, and color conversion processing are performed.

  Thereafter, the system control circuit 50 reads the still image data after dark correction processing written in a predetermined area of the memory 30, and the compression / decompression circuit 32 performs image compression processing according to the set mode. Then, image data that has been shot and finished a series of processing is written into the empty image portion of the image storage buffer area of the memory 30. The system control circuit 50 reads the image data stored in the image storage buffer area of the memory 30 along with the execution of a series of photographing. Then, the data is written into the recording medium 200 or 210 such as a memory card or a compact flash (registered trademark) card via the interface 90 or 94 and the connector 92 or 96.

  The recording process described above is executed on the image data every time new data is written in the empty image portion of the image storage buffer area of the memory 30 after photographing and completing a series of processes. In order to notify the user that the writing operation is being performed while the image data is being written to the recording medium 200 or 210, the notification unit 54 displays a recording medium writing operation display such as blinking an LED. . Further, an image obtained by resizing the main image that has been subjected to the dark correction processing and recorded on the recording medium 200 or 210 to an image size suitable for the image display unit 28 is separately generated and stored in the image display memory 24. This is displayed on the image display unit 28 for a predetermined captured image display time.

  When the series of processing is finished, the still image shooting processing (step S116) is finished, and the flow returns to the basic operation flow of FIG.

  FIG. 4 is a timing chart for explaining the timing of the imaging operation in the still image shooting process (step S116).

  In FIG. 4, VD is a vertical synchronization signal, HD is a horizontal synchronization signal, and φV is a V transfer pulse for reading out the pixel charge of the photoelectric conversion element 1 (FIG. 9) of the image sensor 14 to the VCCD 2.

  The shutter 12 which is a mechanical shutter controls the exposure by mechanically opening and closing, and the electronic shutter controls the exposure by applying a pulse to the substrate potential of the CCD sensor and extracting (resetting) the pixel charge toward the substrate. The exposure time is the time from when the pixel charge reset by the electronic shutter is completed until the mechanical shutter is closed. The time from when the pixel charge reset by the electronic shutter is completed until the pixel charge of the photoelectric conversion element 1 is read out to the VCCD 2 is the CCD accumulation time.

  FIG. 5 is a timing explanatory diagram for explaining that the horizontal period is changed by adjusting the length of the horizontal blanking period between the main photographing and the dark image photographing. FIG. 5A is a timing chart showing the length of the horizontal blanking period in each horizontal (1H) period (first period) at the time of actual shooting, and FIG. 5B is a timing chart showing each horizontal period (at the time of dark image shooting). It is a timing chart which shows the length of the horizontal blanking period in the (second cycle).

  In the case of a CCD, the number of pixel clocks constituting one horizontal period of the imaging signal is determined by the blanking period in which the transfer drive pulses (H1, H2) of the HCCD 4 are stopped and the pixel readout period (OB period) being driven. + Effective pixel period).

  In the first embodiment, as shown in FIG. 5, by changing the length of the horizontal blanking period, which is a period other than the effective pixel period, between the main photographing and the dark photographing, Different horizontal cycles without affecting them.

  As shown in FIG. 5A, the number of pixel clocks in the blanking period at the time of actual photographing is “BLK0”. On the other hand, at the time of dark image shooting, the number of pixel clocks in the blanking period is changed to “BLK0 + n” by adding n clocks to BLK0 as shown in FIG. The period of the horizontal line at the time of dark image photography can be lengthened.

  As a specific operation, the following setting is performed in the TG setting process (steps S307 and S313) in the above-described still image shooting process (step S116) shown in FIG. That is, at the time of actual photographing, in step S307, the horizontal blanking active period is set to BLK0 from the system control circuit 50 to the timing generation circuit 18 (first setting). At the time of dark image shooting, in step S313, the system control circuit 50 sets the horizontal blanking active period corresponding to (BLK0 + n) to the timing generation circuit 18 (second setting).

  The timing generation circuit 18 receives the information of the horizontal blanking active period set from the system control circuit 50, and sets the horizontal blanking period while PBLK is LOW. The timing generation circuit 18 starts the supply of all horizontal timing signals to the analog signal processing area including the image sensor 14 and the A / D converter 16 at the end of each horizontal blanking period. Have For example, in the case of the clamp pulse (CLPOB), as can be seen from FIGS. 5A and 5B, the clamp pulse is linked to the expansion of PBLK (horizontal blanking period) with reference to the beginning of each horizontal period. The timing at which (CLPOB) is output changes. The clamp pulse is a pulse indicating the OB pixel period in order to adjust the DC voltage level so that the level of the OB pixel becomes the black reference value of the imaging signal.

  Next, in the still image shooting process (step S116), by changing the horizontal period using the blanking period between the main shooting and the dark image capturing operation, A change in appearance when noise is mixed will be described.

  In the background art, the equal pitch noise superimposed one-dimensionally on the imaging signal is seen by the number of pixel clocks constituting one horizontal period for a two-dimensional image developed in a horizontal direction and a vertical direction by a CCD area sensor or the like. I have already explained that this is changing. As described with reference to FIG. 13, for example, in the case of equi-pitch noise with a 5-pixel cycle, a noise pattern is formed in five variations according to a remainder system of 5, depending on the number of pixel clocks constituting one horizontal period. The In each pattern, the noise pitch in the horizontal direction does not change, but the degree of conspicuousness changes because the angle of the noise pattern changes on the developed two-dimensional image.

  In the first embodiment, the fact that the angle of the noise pattern described above changes according to the remainder system of the noise pitch is used. In other words, the noise pattern on the developed two-dimensional image is changed by changing the horizontal period between the main shooting and the dark image shooting with respect to the periodic equal pitch noise superimposed on the main shooting image and the dark image. Control the angle. In addition, as described above, this method changes the horizontal period by adjusting the length of the horizontal blanking period, and therefore has no effect on the original image contributing to display.

  FIG. 6 shows an example of a noise pattern with a 5-pixel cycle superimposed on the actual captured image and the dark image.

  FIG. 6A shows a noise pattern when N is a positive integer and the horizontal period at the time of actual photographing is (5N + 3). FIG. 6B shows a noise pattern when the blanking period is increased by one pixel clock at the time of dark image shooting and the horizontal period is set to (5N + 4). FIG. 6C shows a dark correction obtained by subtracting the dark image having the noise pattern shown in FIG. 6B from the actual captured image having the noise pattern shown in FIG. 6A. It is a figure which shows an example of the noise pattern in the still image after a process.

  As can be seen from FIG. 6, by changing the horizontal blanking period by one pixel clock, the angle of the noise pattern varies greatly between the actual captured image and the dark image. For this reason, on the still image after the dark correction processing, the periodic features of the noise pattern originally possessed by the actual photographed image are canceled out, and the noise pattern becomes inconspicuous.

  Note that if the relationship between the pixel clock frequency and the system clock frequency that causes equal pitch noise is free-running, the phase relationship cannot be managed, so phase shifts easily due to frequency deviation or temperature drift. Occurs. However, the noise pattern is completely changed between frames as the horizontal period changes with respect to the phase change due to these frequency deviations and temperature drifts, so the noise pattern between the actual captured image and the dark image is correlated. The features are not emphasized.

  As described above, according to the first embodiment, the horizontal period is changed by changing the length of the horizontal blanking period between the main photographing and the dark image photographing. As a result, the original image contributing to the display is not affected at all, and the periodicity of the periodic noise can be destroyed to make the noise inconspicuous.

<Second Embodiment>
Next, a second embodiment of the present invention will be described.

  In the first embodiment described above, a method of adjusting the horizontal blanking period by adjusting the length of the horizontal blanking period between the main shooting and the dark image shooting without affecting the pixel reading period is used. did. In the case of this method, in conjunction with the timing change at the end of the horizontal blanking period, all the horizontal timing signals supplied to the CCD elements, analog signal processing circuits, and A / D converters in the image sensor 14 are displayed. It is necessary to change the drive start timing. Therefore, although the function is given to the timing generation circuit 18, the case where the timing generation circuit 18 does not have such a function is also assumed.

  If the timing generation circuit 18 can change the timing in a programmable manner with respect to all related horizontal timing signals, it is not impossible to change the timing simultaneously during vertical blanking immediately before the start of dark image capturing. . However, the task of the system control circuit 50 becomes heavy accordingly. In addition, if there is a timing signal that cannot be changed at a fixed timing, or if there is a timing signal that does not immediately change even if the change is set, it is impossible to change the horizontal period in the vertical blanking period between frames using this method. Is possible.

  With respect to such a timing generation circuit 18, in the second embodiment, the horizontal period is changed by another method between the main photographing and the dark image photographing.

  In the case of a CCD imaging device, one horizontal period includes a blanking period in which driving pulses (H1, H2) for transfer of HCCD 4 (FIG. 9) are stopped and a pixel readout period in which driving is performed (OB period + effective pixel period) It has already been explained that it is roughly divided into In the second embodiment, the horizontal blanking period is not changed as it is, and the horizontal cycle is changed by adding an empty transfer period of the HCCD 4 to the end of the pixel readout period (OB period + effective pixel period). To do. Thereby, the lengths of periods other than the effective pixel period can be varied.

  In the idle transfer, after all the charges accumulated in the photoelectric conversion element 1 in the effective pixel area are read out through the HCCD 4, the drive pulses (H1, H2) for transfer are continuously sent to the HCCD 4. In this case, it indicates an idle reading state in which a signal with no accumulated charge is output.

  FIG. 7 is a timing explanatory diagram for explaining that the horizontal period is changed by adjusting the length of the empty transfer period of the HCCD 4 between the main photographing and the dark image photographing. FIG. 7A is a timing chart showing the length of the empty transfer period in each horizontal period (first period) during the imaging operation during the main photographing, and FIG. 7B is each horizontal during the imaging operation for dark. It is a timing chart which shows the length of the idle transfer period in a period (2nd period).

  As shown in FIG. 7A, the number of pixel clocks in the empty transfer period provided at the end of the effective pixel period of the image pickup signal at the time of actual photographing is (H0). In this case, as shown in FIG. 7B, the number of pixel clocks in the empty transfer period at the time of the next dark image shooting is changed to (H0 + n) by adding n clocks.

  As a specific operation, the following setting is performed in the TG setting process (steps S307 and S313) in the above-described still image shooting process (step S116). That is, at the time of actual shooting, in step S307, the system control circuit 50 sets the timing generation circuit 18 so that the horizontal transfer drive pulses (H1, H2) corresponding to the horizontal synchronization signal HD are maintained until the next HD input. I do. Then, at the next HD input, a setting is made to reset the drive start timings of all horizontal timing signals supplied to the CCD elements, analog signal processing circuits, and A / D converters in the image sensor 14.

  This eliminates the need to change the timing of the clamp pulse (CLPOB) indicating the OB pixel period as shown in the first embodiment for each frame.

  Further, the empty transfer period is a period adjustment after the effective pixel period of the HCCD 4 is completed, and is not performed during the effective pixel period. Therefore, there is a concern that the transfer charge remaining in the HCCD 4 may adversely affect the next charge signal reading. Nor. Therefore, the original image contributing to the display is not affected at all.

  As described above, according to the second embodiment, empty transfer is performed after the effective pixel period, and the horizontal period is changed by changing the empty transfer period between the main shooting and the dark image shooting. As a result, the original image contributing to the display is not affected at all, and the periodicity of the periodic noise can be destroyed to make the noise inconspicuous.

It is a block diagram which shows the structure of the imaging device in embodiment of this invention. It is a flowchart which shows the basic operation | movement of the imaging device in embodiment of this invention. It is a flowchart which shows the still image shooting process in the 1st Embodiment of this invention. 3 is a timing chart illustrating still image readout timing in the first embodiment of the present invention. It is a timing chart for demonstrating the change of the horizontal period in the 1st Embodiment of this invention. It is explanatory drawing which shows the noise pattern in the 1st Embodiment of this invention. It is a timing chart for demonstrating the change of the horizontal period in the 2nd Embodiment of this invention. It is a block diagram which shows schematic structure of the imaging | photography part inside the conventional digital camera. It is a figure which shows schematic structure of an image pick-up element. It is a block diagram which shows the detailed structure of the imaging circuit 502 shown in FIG. It is a timing chart which shows the operation | movement in the conventional digital camera. It is a timing chart for demonstrating the structure of the conventional 1 horizontal period. It is a figure which shows the example of a noise pattern. It is a figure which shows the example of the noise pattern after a dark correction process.

Explanation of symbols

12: Shutter, 14: Image sensor, 16: A / D converter, 18: Timing generation circuit, 20: Image processing circuit, 22: Memory control circuit, 24: Image display memory, 26: D / A converter, 28 : Image display unit, 30: Memory, 32: Compression / decompression circuit, 40: Shutter control unit, 42: Focus adjustment unit, 46: Photometry control unit, 48: Flash, 50: System control circuit, 52: Memory, 54: Notification unit, 56: nonvolatile memory, 60: mode dial, 62: shutter switch SW1, 64: shutter switch SW2, 66: playback switch, 70: operation unit, 74: real-time clock, 80: power control unit, 82, 84 : Connector, 86: Power supply, 90, 94: I / F, 92, 96: Connector, 98: Recording medium attachment / detachment detection unit, 100: Imaging device, 110: I F, 112: Connector, 200: Recording medium, 210: PC, 202, 212: Recording unit, 204, 214: I / F, 206, 216: Connector, 300: Lens unit, 310: Imaging lens, 312: Aperture, 306: Lens mount, 320: I / F, 322: Connector, 340: Aperture control unit, 342: Focus control unit, 344: Zoom control unit, 350: Lens system control circuit

Claims (10)

Imaging means for imaging by converting incident light into an electrical signal;
A first imaging operation for obtaining a first imaging signal by performing an imaging operation with the imaging means exposed, and a second imaging signal for obtaining a second imaging signal by performing an imaging operation with the imaging means shielded from light. Control means for controlling the imaging operation;
Signal processing means for processing the first imaging signal by the second imaging signal;
The image pickup apparatus characterized in that the control means varies a horizontal cycle for driving the image pickup means between the first image pickup operation and the second image pickup operation.   The control means makes the horizontal period different between the first imaging operation and the second imaging operation by making the length of the period other than the effective pixel period in each horizontal period of the horizontal period different. The imaging apparatus according to claim 1, wherein the imaging apparatus is characterized.   3. The control unit according to claim 2, wherein the horizontal period is different between the first imaging operation and the second imaging operation by changing a blanking period in each horizontal period of the horizontal period. The imaging device described in 1.   3. The control unit according to claim 2, wherein the horizontal period is different between the first imaging operation and the second imaging operation by changing an empty transfer period in each horizontal period of the horizontal period. The imaging device described in 1.   5. The imaging apparatus according to claim 1, wherein the signal processing unit subtracts the second imaging signal from the first imaging signal. 6. A method for controlling an imaging apparatus having imaging means for imaging by converting incident light into an electrical signal,
A first setting step of setting a horizontal period for driving the imaging means to a first period;
A first imaging step of obtaining a first imaging signal by performing an imaging operation in the first cycle in a state where the imaging means is exposed;
A second setting step of setting a horizontal period for driving the imaging means to a second period different from the first period;
A second imaging step of obtaining a second imaging signal by performing an imaging operation in the second period with the imaging means shielded from light;
And a signal processing step of processing the first imaging signal with the second imaging signal.   The control according to claim 6, wherein the first period and the second period are made different by making the lengths of periods other than the effective pixel period in each horizontal period of the horizontal period different. Method.   The control method according to claim 7, wherein the first period and the second period are made different by making a blanking period in each horizontal period of the horizontal period different.   The control method according to claim 7, wherein the first cycle and the second cycle are made different by making the idle transfer period in each horizontal period of the horizontal cycle different.   The control method according to claim 6, wherein in the signal processing step, the second imaging signal is subtracted from the first imaging signal.

Images