JP2006166252A - Imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging apparatus capable of providing images that are faithful to an object image, by eliminating dark noise as accurately as possible. <P>SOLUTION: When a shutter button is fully depressed at a time T=T1, when setting a long-time monitoring mode, output of pixel signals in the cycle of 1/10(sec) for each pixel is started from a time T=T2. When charge accumulation periods (exposure periods) in each cycle of each pixel are represented as "accumulation 1", "accumulation 2", ..., "accumulation 49" and "accumulation 50", dark noise derived beforehand from pixel signals obtained in the exposure terms of "accumulation 1", "accumulation 2", ..., "accumulation 49" and "accumulation 50" is subtracted from each pixel signal. Thus, the exposure time of an image, obtained at each exposure period becomes extremely shorter than in prior art, thereby very much reducing the error between the dark noise, derived in advance, and the dark noise included in each of the pixels obtained in the exposure terms. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention belongs to the technical field of an image pickup apparatus having an image pickup device such as a CCD (Charge Coupled Device), and particularly relates to a technique for removing dark noise contained in an image signal.

  Usually, an image pickup device such as a CCD (Charge Coupled Device) generates charges (dark noise, dark current) in each pixel even in the absence of light, so that the pixel signal output from the pixel is the original pixel. The pixel value shifts with respect to the pixel signal corresponding to the exposure amount, and a so-called offset (black level shift due to dark noise) occurs. In particular, when the exposure operation is performed for a relatively long time, the offset becomes large, and there is a possibility that a captured image faithful to the subject cannot be obtained.

  As a method for removing such dark noise, for example, the imaging device is caused to perform an imaging operation in a state where light from the outside is blocked, and the pixel signal of each pixel obtained by this imaging operation is regarded as dark noise, and this dark noise is detected. A method of subtracting noise from each pixel signal obtained at the time of imaging a subject is known.

  In this case, in order to obtain dark noise as close as possible to the dark noise included in the pixel signal obtained by the exposure operation at the time of subject imaging, the exposure time for derivation of the dark noise by the imaging device is set as the imaging device at the time of subject imaging. It is considered to be preferable to set the same time as the exposure time.

  On the other hand, as a technique related to noise included in such a pixel signal, in Patent Document 1 below, in order to reduce the amount of noise accumulated in each pixel of the image sensor that increases exponentially with respect to the exposure time, When the exposure time set on the camera side is long, the exposure time is divided into a plurality of times, and each time after the division is set as an exposure time (hereinafter referred to as a divided exposure time), and the image sensor is subjected to the multiple exposure operation. A technique for synthesizing images obtained by each exposure operation is disclosed.

Japanese Patent Application Laid-Open No. 2004-228561 proposes a technique for combining and displaying an image that has already been exposed on an electronic viewfinder and an image that is to be exposed at the time of multiple exposure.
JP 2003-319252 A JP-A-6-121222

  Even if the dark noise is subtracted by the noise removal method as described above, there is an error between the dark noise and the dark noise generated in the image sensor when the subject is photographed. In particular, as described above, the dark noise increases exponentially with respect to the exposure time, and the error increases as the exposure time increases. Accordingly, the longer the exposure time, the lower the noise removal accuracy.

  Further, in Patent Document 1, although noise included in a captured image is reduced, remaining noise generated in each divided exposure operation is allowed, and there is no attempt to remove this noise. Moreover, in patent document 2, there is no description regarding the removal of such dark noise.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an imaging apparatus capable of obtaining an image faithful to a subject image by removing dark noise as described above as accurately as possible.

  According to the first aspect of the present invention, an image sensor including a plurality of pixels that receive and photoelectrically convert light from a subject, and start of an exposure operation for generating a recording pixel signal to be recorded in a predetermined recording unit. And an input operation unit for instructing the image sensor, and when the input operation unit instructs the exposure start, the image sensor is caused to start an exposure operation, and the image signal is transmitted to the image sensor every predetermined time. An image pickup control unit that outputs a signal, a noise removal processing unit that removes predetermined dark noise from a pixel signal obtained at every predetermined time from the image pickup device, and a pixel from which dark noise has been removed by the noise removal processing unit An addition processing unit that sequentially adds signals and a recording unit that records pixel signals sequentially generated by the addition processing by the addition processing unit are provided.

  According to the present invention, when an exposure start instruction is given by the input operation unit, the image pickup device starts an exposure operation, and the image pickup device outputs a pixel signal every predetermined time, and the image pickup device outputs the pixel signal every predetermined time. The pixel signals obtained are sequentially added and the pixel signals sequentially generated by this addition processing are recorded, so that an image of the subject can be obtained at the exposure time desired by the photographer.

  Further, since the predetermined dark noise is removed one by one from the pixel signal obtained every predetermined time from the image sensor before the addition process, an image faithful to the subject can be obtained. That is, without using such a removal method, for example, in a state where external light is shielded, the exposure operation is performed for the exposure time for the exposure operation (main exposure operation) for generating the recording pixel signal in advance on the image sensor. The pixel signal obtained by this exposure operation is regarded as dark noise generated during the actual main exposure operation (hereinafter referred to as deemed dark noise), and this dark noise is obtained at the end of the actual main exposure operation. In the conventional configuration of subtracting from the pixel signal, the error between the assumed dark noise and the dark noise included in the pixel signal obtained by the actual main exposure operation increases as the exposure time increases.

  On the other hand, in the present invention, since the main exposure operation is divided into a plurality of exposure operations, each pixel signal (pixel signal obtained by each divided exposure operation) obtained every predetermined time from the image sensor is included. The noise is small (offset is less likely to occur), and the error between this noise and the predetermined dark noise can be reduced. As a result, an image faithful to the subject image can be obtained even with a long exposure operation.

  According to a second aspect of the present invention, in the image pickup apparatus according to the first aspect, a pixel signal output from a pixel when the image pickup device performs an exposure operation for the predetermined time while external light is blocked. Is set as the dark noise.

  According to the present invention, since the pixel signal output from the pixel is used as the dark noise when the image sensor is subjected to the exposure operation for the predetermined time in a state where the outside light is blocked, the main exposure is performed. In operation, dark noise that is as close as possible to the dark noise contained in the pixel signal obtained from the image sensor at predetermined time intervals can be derived.

  According to a third aspect of the present invention, in the image pickup apparatus according to the first or second aspect, the pixel signal sequentially generated by the addition processing by the addition processing unit is displayed on a predetermined display unit as a display image in an update manner. A display control unit is provided.

  According to the present invention, the photographer can visually recognize the exposure state (exposure state) of the image sensor during the long exposure period.

  According to a fourth aspect of the present invention, in the imaging device according to any one of the first to third aspects, an instruction to start and end an exposure operation by the imaging element for generating the recording pixel signal can be given. A mode setting unit that sets the bulb shooting mode; and an exposure time calculation unit that calculates an exposure time based on the luminance of the subject, and the noise removal processing unit is set to the bulb shooting mode by the mode setting unit. Alternatively, the dark noise removal process is performed when the exposure time calculated by the exposure time calculation unit is longer than a predetermined time.

  According to this invention, the invention according to any one of claims 1 to 3 is adopted when the bulb photographing mode is set or when the exposure time calculated by the exposure time calculation unit is longer than a predetermined time. By doing so, the effect by each invention becomes remarkable.

  According to a fifth aspect of the present invention, in the imaging apparatus according to the fourth aspect, a first input operation unit for inputting an instruction to start an exposure operation by the imaging element for generating the recording pixel signal; A second input operation unit for inputting an instruction to end the exposure operation, and after the exposure operation is started by an input of the start instruction of the exposure operation by the first input operation unit, the second input operation unit When the input operation unit inputs an instruction to end the exposure operation, the exposure operation ends, and the exposure operation performed by the second input operation unit is performed within the exposure time calculated by the exposure time calculation unit. When no termination instruction is input, the exposure operation is terminated when the exposure time calculated by the exposure time calculation unit has elapsed.

  According to the present invention, since the photographer can instruct the start and end of the exposure operation by the image sensor for generating the recording pixel signal, an image with a desired composition (the composition intended by the photographer) can be obtained. Image). Even when the second input operation unit does not input an instruction to end the exposure operation, the exposure operation is automatically ended at an appropriate time.

  The invention according to claim 6 has a third input operation unit for inputting an instruction to extend the exposure time calculated by the exposure time calculation unit in the imaging apparatus according to claim 4, The exposure operation is terminated when an instruction to end the exposure operation is input by the second input operation unit after an instruction to extend the exposure time is input by a third input operation unit. To do.

  According to the present invention, even when the exposure time is set by the imaging apparatus, the exposure time can be manually extended.

  According to the first aspect of the present invention, it is possible to obtain a beautiful and faithful image of the subject image from which dark noise is removed as accurately as possible.

  According to the second aspect of the present invention, an image that is as faithful as possible to the subject image can be obtained.

  According to the third aspect of the present invention, the user of the imaging apparatus can determine the composition while confirming the exposure state.

  According to the invention of claim 4, when the bulb photographing mode is set, or when the exposure time calculated by the exposure time calculation unit is longer than a predetermined time, any one of claims 1 to 3 The effect by the described invention becomes remarkable.

  According to the fifth and sixth aspects of the invention, the convenience of the imaging device can be improved.

  An embodiment of an imaging apparatus according to the present invention will be described. FIG. 1 is a front view of the imaging apparatus 1, and FIG. 2 is a rear view of the imaging apparatus 1.

  As shown in FIGS. 1 and 2, the imaging apparatus 1 includes a power button 2, an imaging optical system 3, an LCD (Liquid Crystal Display) 4, an optical finder 5, a built-in flash 6, and a mode setting switch 7. A quadruple switch 8, a shutter button 9, and a long-second monitoring switch 10 are provided.

  The power button 2 is for inputting an instruction to switch on and off the main power supply of the imaging apparatus 1. The imaging optical system 3 includes a zoom lens, an unillustrated mechanical shutter, and the like, and an optical image of a subject is placed on an imaging surface (light receiving surface) of an imaging element 11 (see FIG. 3) such as a CCD (Charge Coupled Device). It forms an image.

  The LCD 4 displays a live view image and an image (recorded image) recorded in an external storage unit 31 (see FIG. 3), which will be described later, and reproduces and displays an image recorded in the external storage unit 31. The live view image is an image picked up by the image pickup device 11 that is switched and displayed on the LCD 4 at a constant period (1/30 second) until the image of the subject is recorded. The state is displayed on the LCD 4 in substantially real time, and the photographer can check the state of the subject on the LCD 4. Note that an organic EL or a plasma display device may be employed instead of the LCD 4.

  The optical viewfinder 5 enables optical observation of a range where a subject is photographed. The built-in flash 6 irradiates the subject with illumination light when the amount of exposure to the image sensor 11 is insufficient.

  The mode setting switch 7 includes a “shooting mode” for shooting a subject image, a “playback mode” for playing back and displaying a shot image recorded in the external storage unit 31 on the LCD 4, and a “menu” for setting various functions. This is a switch for setting the mode switching between “mode” and “mode”. The mode setting switch 7 is composed of a three-contact slide switch that slides up and down. When the switch is set down, the image pickup apparatus 1 is set to the shooting mode. When the switch is set at the center, the playback mode is set. Is done.

  Although not described in detail, the quadruple switch 8 is a switch for performing movement of the zoom lens in the optical axis direction, exposure correction, frame advance of a recorded image to be reproduced on the LCD 4, and the like. Further, the imaging apparatus 1 of the present embodiment includes a program AE mode, an aperture priority AE mode, a shutter speed priority AE mode, and a manual mode as types of shooting modes, and a menu mode is set by the mode setting switch 7. These modes can be switched by operating the quadruple switch 8 in this state.

  The program AE mode is a mode in which a combination of an aperture value and a shutter speed is automatically set according to a preset AE (Auto Exposure) program. The aperture priority AE mode is an aperture value preset by a photographer. The shutter speed setting AE mode is a mode in which an image is taken by setting an aperture value at a shutter speed preset by the photographer, and the manual mode is a mode in which the photographer takes a picture. Is a mode in which imaging is performed with a shutter speed and an aperture value set in advance.

  The shutter button 9 is a button that is pressed in two stages, that is, a fully-pressed operation that is fully pressed and a half-pressed operation that is pressed halfway, and is mainly for instructing the timing of exposure control. In each of the shooting modes, when the shutter button 9 is not operated, an optical image of the subject is captured every 1/10 (seconds), for example, and a live view image is displayed on the LCD 4. The display switching cycle of the live view image is, for example, 1/30 seconds. In this case, the same subject image is displayed three times until the next optical image of the subject is captured. Become.

  Further, in each of the above-described shooting modes, the imaging apparatus 1 is in an imaging standby state in which the shutter speed 9 and the aperture value are set in addition to the live view image display by performing a half-press operation of the shutter button 9. When the full-press operation is set and an exposure operation is performed, an exposure operation (hereinafter referred to as a main exposure operation) by the image sensor 11 described later for generating an image of the subject to be recorded in the external storage unit 31 is started.

  When the period of the main exposure operation is significantly longer than a preset live view image display cycle (for example, 1/30 seconds), the imaging apparatus 1 of the present embodiment displays the live view image on the LCD 4 during the main exposure operation period. The mode (hereinafter referred to as “long-second monitoring mode”) displayed on the screen can be set by a long-second monitoring switch 10 described later. If any of the above-described shooting modes is set to the long-second monitoring mode, which will be described later, the optical image of the subject is captured at a predetermined cycle (for example, 1/10 (second)) during the main exposure operation. Each time an optical image is captured, the acquired images are sequentially added and recorded in the external storage unit 31 in an updated manner, and the state of the image recorded in the external storage unit 31 (the image of the subject) Is added to the LCD 4 in real time as a live view image.

  The long-second monitoring switch 10 is used to set the long-second monitoring mode when any of the above-described shooting modes is set. It is done.

  FIG. 3 is a block configuration diagram showing a system of the imaging apparatus 1. In the figure, the same members as those shown in FIGS. 1 and 2 are denoted by the same reference numerals.

  The imaging device 1 includes an imaging optical system 3, an LCD 4, an imaging device 11, a timing generator 12, a signal processing unit 13, an A / D conversion unit 14, an image memory 15, and a VRAM (Video Random Access Memory) 16. And an operation unit 17 and an overall control unit 18.

  The imaging optical system 3 corresponds to the imaging optical system 3 shown in FIG. 1 and includes a mechanical shutter as described above. The LCD 4 corresponds to the LCD 4 shown in FIG.

  The imaging device 11 includes a plurality of photoelectric conversion elements, such as photodiodes, that are two-dimensionally arranged in a matrix. For example, R (red) and G (green) having different spectral characteristics are formed on the light receiving surface of each photoelectric conversion element. ), B (blue) color filter with Bayer arrangement in which color filters of 1: 2: 1 are arranged. Hereinafter, the photoelectric conversion element in which a color filter is provided is referred to as a pixel of the image sensor 11. The imaging device 11 converts the light image of the subject formed by the imaging optical system 3 into analog electrical signals (image signals) of R (red), G (green), and B (blue) color components. Output as G and B image signals.

  Although not described in detail, the image pickup device 11 is an interline type image pickup device including a light receiving unit made of a photodiode or the like, a vertical transfer unit, a horizontal transfer unit, and the like. The charge of each pixel is determined by a progressive transfer method. Is taken out. That is, the charges accumulated in each light receiving unit are transferred to the vertical transfer unit by a vertical synchronization signal, and the charges transferred to each vertical transfer unit are sequentially transferred from the pixels close to the horizontal transfer path by the horizontal synchronization signal to the horizontal transfer path. Is taken out as a pixel signal. The timing of starting and ending the imaging operation such as reading (horizontal synchronization and vertical synchronization) of the output signal of each pixel in the imaging device 11 and the exposure operation by the imaging device 11 is controlled by a timing generator 12 described later. The

  The image pickup apparatus 1 according to the present embodiment uses a long-second monitoring switch 10 to change the method for generating a recorded image depending on whether the long-second monitoring mode is set or not.

  That is, when the long-second monitoring mode is not set, if an instruction to start the main exposure operation (start generation of a recording pixel signal) is issued by fully pressing the shutter button 9, almost all the pixels of the image sensor 11 are Then, the exposure operation is continuously performed without taking out the pixel signal. For this reason, nothing is displayed on the LCD 4 during the main exposure operation. After that, when the exposure time corresponding to the shutter speed calculated in advance elapses, the main exposure operation for almost all the pixels that have accumulated the charge is finished without taking out the pixel signal, and the pixel signal is taken out from these pixels. Then, a recorded image is generated using the extracted pixel signal.

  On the other hand, when the long-second monitoring mode is set, if an instruction to start the main exposure operation is issued by fully pressing the shutter button 9, pixel signals are extracted from almost all pixels of the image sensor 11 at predetermined time intervals. In addition, the extracted pixel signals are sequentially added (addition of pixel values of pixel signals in each pixel), and the pixel signals after the addition are stored in a second image storage unit 30 described later and sequentially after the addition. A live view image is generated using the pixel signals. Thereby, the live view image is updated and displayed on the LCD 4 at regular time intervals. Thereafter, when the exposure time corresponding to the shutter speed calculated in advance elapses, the latest added image stored in the second image storage unit 30 is recorded in the external storage unit 31 as a recorded image.

  The timing generator 12 reads out a drive control signal for the image sensor 11, for example, a timing signal for starting / ending integration (exposure start / end), and a light reception signal for each pixel based on the reference clock CLK0 transmitted from the overall control unit 18. A clock signal such as a control signal (horizontal synchronization signal, vertical synchronization signal, etc.) is generated and output to the image sensor 11.

  The signal processing unit 13 performs predetermined analog signal processing on the analog pixel signal output from the image sensor 11. The signal processing unit 13 includes a CDS (correlated double sampling) circuit and an AGC (auto gain control) circuit. The CDS circuit reduces noise of the pixel signal. The AGC circuit Level adjustment is performed.

  In the present embodiment, when the long second monitoring mode is set, dark noise derived in advance is subtracted from each pixel signal extracted from almost all pixels of the image sensor 11 at a predetermined time interval. It has become. This dark noise is a pixel signal obtained from each pixel by causing the image sensor 11 to perform an exposure operation for the predetermined time in a state where external light is blocked, and is stored in the signal processing unit 13 in advance. Yes.

  For example, assuming that pixel signals are extracted at a period of 1/10 (second) from almost all pixels of the image pickup device 11 during the main exposure period, the image pickup device 1/10 (second) is previously shielded from outside light. ) During the exposure operation, and the pixel signal obtained by this exposure operation is a dark signal included in the pixel signal (pixel signal extracted at a period of 1/10 (second)) obtained during the main exposure operation of the subject image. It is regarded as noise, and this dark noise is subtracted from the pixel signal obtained during the main exposure operation of the subject image.

  More specifically, for example, as shown in FIG. 6, when the long-second monitoring mode is set, if the shutter button 9 is fully pressed at time T = T1, each pixel is 1 / time from time T = T2. A pixel signal is output at a period of 10 (seconds). If the charge accumulation period (exposure period) in each cycle of each pixel is expressed as “accumulation 1”, “accumulation 2”,... “Accumulation 49”, “accumulation 50”, “accumulation 1”, “accumulation 2” ,..., “Accumulation 49” and “accumulation 50” are subtracted from the previously derived dark noise from the pixel signals obtained in the respective exposure periods.

  Thereby, a beautiful picked-up image can be obtained as compared with the prior art. In other words, the conventional configuration (the image sensor is allowed to perform an exposure operation for the exposure time of the main exposure operation in a state where the external light is shielded, and the pixel signal obtained by the exposure operation is obtained during the main exposure operation of the subject image. It is regarded as dark noise included in the pixel signal obtained at the end of the main exposure operation, and this dark noise is subtracted from the pixel signal obtained at the end of the main exposure operation of the subject image). Increases exponentially with respect to the exposure time, the longer the exposure time, the greater the error between this dark noise and the actual dark noise (dark noise included in the pixel signal obtained by the main exposure operation).

  On the other hand, in the present embodiment, the exposure time of the image obtained in each exposure period is very short as compared with the conventional case, so that it is included in the dark noise derived in advance and the pixels obtained in each exposure period, respectively. The error with the dark noise is very small, and the dark noise can be removed with higher accuracy than before, and as a result, a more faithful image can be obtained with the subject image.

  By the way, in the present embodiment, the exposure time is calculated in advance by the imaging apparatus 1 so that the main exposure operation can be terminated at the photographer's intention so that an image having the composition intended by the photographer can be obtained. Even so, the main exposure operation started by the full pressing operation of the shutter button 9 can be ended by the full pressing operation of the shutter button 9 again.

  The AGC circuit normally performs live by changing the gain in the amplification processing of the pixel value of the pixel signal (when the long-second monitoring mode is not set and before the main exposure operation is instructed when the long-second monitoring mode is set). Since the view image is always displayed with a constant brightness, the photographer visually recognizes the live view image displayed on the LCD 4 during the period of the main exposure operation when the long second monitoring mode is set. The gain is fixed to a constant value during the period of the main exposure operation so that the end of the main exposure operation can be instructed at the timing when a desired exposure amount is obtained. As a result, as shown in FIG. 5, the live view image displayed on the LCD 4 becomes clear as time passes, and the exposure state of the image sensor 11 can be visually recognized. The gain setting by the AGC circuit is performed by a gain setting control unit 20 described later. Note that FIG. 5 will be described in detail later.

  The A / D conversion unit 14 converts the analog R, G, and B pixel signals output from the signal processing unit 13 into digital pixel signals composed of a plurality of bits, respectively.

  The image memory 15 is a memory that temporarily stores the pixel signal output from the A / D conversion unit 14 and is used as a work area for performing processing described later by the overall control unit 18 on the image signal. is there.

  The VRAM 16 is a buffer memory for pixel signals of an image reproduced and displayed on the LCD 4, and has a pixel signal recording capacity corresponding to the number of pixels of the LCD 4.

  The operation unit 17 includes a switch for detecting a release operation of the shutter button 9, a mode setting switch 7, a quadruple switch 8, a long-second monitoring switch 10, and the like.

  The overall control unit 18 includes, for example, a microcomputer having a built-in storage unit (including first and second image storage units 29 and 30 described later) including a ROM that stores a control program and a RAM that temporarily stores data. Thus, the driving of each member described above is associated and controlled.

  Here, the significance of displaying the live view image on the LCD 4 during the main exposure operation when the long second monitoring mode is set will be described.

  When the exposure time is long when the long-second monitoring mode is set, all pixel signals obtained by the exposure operation of the image sensor 11 performed after the start of the full-pressing operation of the shutter button 9 are recorded in the external storage unit 31. When there is no pixel signal that can be used for live view image display, the state of the image recorded in the external storage unit 31 is displayed on the LCD 4 as a live view image during the main exposure operation. It is not possible.

  Further, even when the above-described configuration for displaying the live view image on the LCD 4 is provided during the main exposure operation, the configuration in which an image showing the state of the subject at each time point is displayed as a live view image is as follows. The following problems occur.

  FIG. 4 shows a live view image displayed on the LCD 4 at each time point in the 12-second period for three fireworks continuously launched for 12 seconds after the start of the main exposure operation. In FIG. 4, the state of the subject imaged 1/30 second before that is displayed as a live view image at each time point.

  In such a live view image display method, when the end of the main exposure operation is to be instructed at any timing within the 12 seconds, the fireworks locus is not displayed on the LCD 4 until the instructed timing. The person directly recognizes the state of the fireworks and determines a subject image to be imaged at a timing when the desired state such as a state where the state of the fireworks becomes the most vivid, for example.

  However, in this case, since the image displayed on the LCD 4 shows the state of the subject at each time point, what kind of image is obtained until a series of imaging operations of the imaging device 1 is completed. The image recorded in the external storage unit 31 may be significantly different from the desired image due to factors such as unknown and the fact that the optical axis of the imaging apparatus 1, that is, the photographing range is shifted by taking a posture of directly viewing the subject. is there.

  In view of the above points, in the present embodiment, the imaging apparatus 1 is provided with the long-second monitoring mode as described above, and when the long-second monitoring mode is set, the period until the exposure time calculated in advance is passed. When the exposure time of the exposure operation is significantly longer than the display period (for example, 1/30 second) of the live view image, the live view image is displayed on the LCD 4 in real time during the main exposure operation period. It is assumed that the live view image displayed during this period displays the state of the image recorded in the external storage unit 31.

  In order to realize such a configuration, as described above, when the long-second monitoring mode is set, an instruction to start a main exposure operation (start generation of a recording pixel signal) is issued by fully pressing the shutter button 9. When performed, pixel signals are extracted from almost all pixels of the image sensor 11 at a predetermined time interval (for example, 1/10 second). The extracted pixel signals are sequentially added, and the pixel signals after the addition are stored in the second image storage unit 30 and a live view image is sequentially generated using the pixel signals after the addition. Thereby, the LCD 4 can display an image displaying the state of the image recorded in the external storage unit 31 as a live view image at regular time intervals.

  For example, as shown in FIG. 5, 12 seconds after the start of the full-pressing operation of the shutter button 9, the image is superimposed as if the three fireworks launched with a time difference during the 12-second period were opened simultaneously. A live view image is generated, and the live view image is displayed on the LCD 4.

  Further, in the present embodiment, as described above, when the long-second monitoring mode is set, in order to be able to finish the main exposure operation at the photographer's intention, the operation is started by fully pressing the shutter button 9. This exposure operation can be completed by pressing the shutter button 9 fully again, and the shutter button 9 is not fully pressed again within the exposure time calculated when the shutter button 9 is pressed halfway. The exposure operation of the image sensor 11 is automatically terminated after the exposure time has elapsed. Thereby, the operativity of the imaging device 1 can be improved.

  Then, the imaging apparatus 1 is instructed to end the main exposure operation by a full-pressing operation of the shutter button 9 again by the photographer, or the latest stored in the second image storage unit 30 when the exposure time has elapsed. The added image is used as a recorded image.

  In order to realize the configuration as described above, as shown in FIG. 3, the overall control unit 18 is functionally configured to include an exposure control unit 19, a gain setting control unit 20, a first imaging control unit 21, and a first recording control unit. 22, an addition processing unit 23, an aspect correction processing unit 24, a second imaging control unit 25, an image processing unit 26, a display control unit 27, an image compression unit 28, a first image storage unit 29, and a second image storage unit 30. ing.

  The exposure control unit 19 calculates an exposure control value (exposure value corresponding to the aperture value and shutter speed) based on the luminance of the image captured during the period when the shutter button 9 is half-pressed. .

  The gain setting control unit 20 performs gain setting for amplification processing by the AGC circuit of the signal processing unit 13. As described above, the gain setting control unit 20 sets the gain of amplification processing by the AGC circuit to a constant value during the main exposure operation during the setting of the long second monitoring mode.

  Thereby, the live view image displayed on the LCD 4 becomes clear (becomes brighter) with the passage of time, and the state of the image stored in the external storage unit 31 can be visually recognized on the LCD 4. Note that the gain setting control unit 20 normally changes the gain according to the pixel value of the pixel signal (when the long-second monitoring mode is not set and before the main exposure operation is instructed when the long-second monitoring mode is set).

  The first imaging control unit 21 performs the exposure operation on substantially all pixels in the image sensor 11 during the main exposure operation when the long second monitoring mode is set, and outputs a pixel signal at a predetermined cycle from all the pixels. The clock signal output from the timing generator 12 to the image sensor 11 is controlled so as to be output. Note that the first imaging control unit 21 does not perform the pixel signal extraction operation at a predetermined cycle for all the pixels during the main exposure operation when the long second monitoring mode is not set.

  When the long-second monitoring mode is set, the first recording control unit 22 temporarily outputs first pixel signals output from almost all pixels through the A / D conversion unit 14 and the like during the main exposure operation. It is recorded in the image storage unit 29.

  The addition processing unit 23 sets the long-second monitoring mode every time an image is recorded in the first image storage unit 29 by the first recording control unit 22 after the second period after the start of the main exposure operation. An added image obtained by adding these images is generated, and the added image is recorded in the first image storage unit 29. Assuming that an image made up of pixel signals obtained in the current cycle is represented as Pn (n = 1, 2,..., K−1, k), an exposure operation with almost all pixels and pixels obtained by this exposure operation. The added image Gn when the signal reading is repeated n times is Gn = P1 + P2 +... + Pn.

  When the image is displayed on the LCD 4, the aspect correction processing unit 24 records the added image generated by the addition processing unit 23 when the long second monitoring mode is set, and is recorded in the first recording control unit 22 at other times. The image is corrected to the aspect of the LCD 4 and the aspect corrected image is recorded in the second image storage unit 30. As a result, during the main exposure operation, a live view image (an image in which all the trajectories of moving objects are displayed) can be displayed on the LCD 4 by superimposing the subject image at each time point. At the time of setting the long second monitoring mode, the image data constituting the addition image generated by the addition processing unit 23 is duplicated, and aspect correction is performed on the duplicated addition image.

  The second imaging control unit 25 is instructed to end the main exposure operation by re-operating the shutter button 9 by the photographer, or the exposure time calculated by the exposure control unit 19 has passed, whichever comes first. When it reaches, the clock signal output from the timing generator 12 to the image pickup device 11 is controlled so as to end the exposure operation of almost all pixels.

  The image processing unit 26 performs black level correction for correcting the black level to a reference black level for the added image subjected to the addition processing by the addition processing unit 23, R (red), White balance adjustment for level conversion of digital signals of G (green) and B (blue) color components, and correction of γ characteristics of digital signals of R (red), G (green), and B (blue) colors γ correction is performed.

  The display control unit 27 transfers pixel data of the image to the VRAM 16 so that the image output from the image processing unit 26 is displayed on the LCD 4. Thus, when the long second monitoring mode is not set, the period until the main exposure operation is started, and when the long second monitoring mode is set, the main exposure operation period is added to the period until the main exposure operation is started. Among them, the state of the subject (the state of the image recorded in the external storage unit 31 in the long second monitoring mode) can be displayed on the LCD 4 in real time as a live view image.

  The image compression unit 28 uses the JPEG (Joint Picture Experts Group) method such as two-dimensional DCT (Discrete Cosine Transform) conversion and Huffman coding on the pixel data of the recorded image subjected to the above-described various processes by the image processing unit 26. Predetermined compression processing is performed to generate compressed image data, and an image file in which information relating to the captured image (information such as compression rate) is added to the compressed image data is recorded in the external storage unit 31.

  The external storage unit 31 includes a memory card including a plurality of semiconductor storage elements, an MD (Mini Disk), a CD-R (Compact Disk-Recordable), a CD-RW (Compact Disk-Rewritable), an MO (Magnetic Optical Disk), and the like. The image data is recorded in time-series and recorded, and for each frame, the compressed image compressed by the JPEG method is index information about the captured image (frame number, exposure value, shutter speed). , Compression rate, shooting date, flash on / off data at the time of shooting, information such as scene information).

  Next, imaging processing of the imaging apparatus 1 when setting the long-second monitoring mode will be described with reference to a time chart shown in FIG.

  As shown in FIG. 6, when the long second monitoring mode is set, if the shutter button 9 is fully pressed at time T = T1, the first imaging control unit 21 performs a predetermined time from the time T = T1. From the time T = T2, the pixel signal is output to the pixel at a period of 1/10 second.

  At that time, as described above, the dark noise previously derived from the pixel signals obtained in the exposure periods of “accumulation 1”, “accumulation 2”,... “Accumulation 49”, “accumulation 50” is subtracted, respectively. A live view image is generated using each pixel signal after the subtraction. The display control unit 27 displays the live view image on the LCD 4, and the first recording control unit 22 clears the storage area of the first image storage unit 29, and then the pixel with a period of 1/10 second. The pixel signal read from is stored in the first image storage unit 29.

  When the acquired pixel signal is obtained in the first cycle after the start of the main exposure operation, the addition processing by the addition processing unit 23 is not executed, and the aspect correction processing unit 24 and the image are processed. The processing unit 28 performs various processes such as an aspect correction process. On the other hand, when the read pixel signal is obtained in the second and subsequent cycles, the addition processing unit 23 outputs the image output from the pixel at each time point and recorded in the first image storage unit 29. After performing the addition process of adding the addition image generated one cycle before that time, the aspect correction processing unit 24 and the image processing unit 28 perform various processes such as an aspect correction process.

  When the process such as the aspect correction process is completed, the display control unit 27 displays the image after the process on the LCD 4, and the above process is repeated until the main exposure operation is completed. As a result, a live view image on which images captured at each time point are superimposed is displayed on the LCD 4.

  In FIG. 6, since the display cycle of the live view image is 1/30 second, the pixel signal obtained in each cycle until the pixel signal is acquired from the pixel in the next cycle (1/10 second). It is shown that the image constituted by is displayed on the LCD 4 three times each. For example, the pixel signal “output 1” obtained from the pixels in the first cycle, that is, the period of “accumulation 1” after the shutter button 9 full-press operation is started, is “LCD 1” three times as “image 1”. Is displayed.

  Further, the pixel signal “output 2” obtained from the pixel in the second and subsequent cycles, for example, the period of “accumulation 2”, is added to the above-mentioned “image 1” as “image 2” constituted by this pixel signal. This added image “image 1 + 2” is displayed on the LCD 4 three times. FIG. 6 shows that the pixel signal readout operation (charge transfer to the vertical transfer path, etc.) of the pixels during the full-press operation of the shutter button 9 was periodically performed 50 times.

  Then, at time T = T3, when an end of the main exposure operation is instructed by the re-operation of the shutter button 9 by the photographer, or when the exposure time calculated by the exposure control unit 19 has elapsed, a predetermined time has elapsed from that timing. The recording exposure operation ends at time T = T4.

  Thereafter, the image processing unit 28 performs processing such as black level correction on the added image “1+... +49” stored in the second image storage unit 30, and then the image compression unit 30 performs compression processing. The compressed image is recorded in the external storage unit 31. The display control unit 27 causes the LCD 4 to display an image obtained by performing various processes such as an aspect correction process on the added image “1+... +49” generated immediately before the main exposure operation is finished.

  Note that when generating an image to be stored in the external storage unit 31, the pixel signal of “accumulation 50” is not subject to addition because the exposure time of “accumulation 50” is an appropriate exposure time (in FIG. 6, 1 / This is because there is a possibility that it is not 10 seconds).

  An imaging process at the time of setting the long second monitoring mode, which is a characteristic part of the imaging apparatus 1 of the present embodiment, will be described with reference to a flowchart shown in FIG.

  As shown in FIG. 7, when the long-second monitoring switch 10 is turned on (YES in step # 1), the exposure control unit 19 causes the shutter so that the exposure amount of the image sensor 11 becomes an appropriate value based on the luminance of the subject. The speed and aperture value are calculated (step # 2). When the calculated exposure time is equal to or longer than the predetermined value (YES in step # 3), the mode is set to the long second AE process (step # 4).

  When the shutter button 9 is fully pressed (YES in step # 5), the gain setting control unit 20 fixes the gain of amplification processing by the AGC circuit of the signal processing unit 13 to a constant value (step # 6). ). This is because the live view image displayed on the LCD 4 becomes clear as time passes and the state of the image recorded in the external storage unit 31 can be visually recognized as described above. Then, the first imaging control unit 21 captures pixel signals from almost all pixels of the imaging element 11 (step # 7).

  When pixel signals are taken in from almost all pixels of the image sensor 11 by the first imaging control unit 21, the addition processing unit 23 is generated in the previous cycle with the pixel signal from which the dark noise is subtracted by the signal processing unit 13. The pixel signals constituting the addition image are sequentially added, the aspect correction processing by the aspect correction processing unit 24 is performed on the addition image (duplicated addition image) constituted by the pixel signals after the addition processing, and this image is The image is displayed on the LCD 4 (step # 8).

  When the shutter button 9 is not fully depressed again, that is, when the end of the main exposure operation by the image sensor 11 is not instructed (NO in step # 9), the exposure time calculated in step # 2 is displayed. It is determined whether or not it has elapsed (step # 10). If the exposure time has not elapsed (NO in step # 10) as a result of the determination, the control unit 18 reads out pixel signals from substantially all pixels in the next cycle (step # 11), and step # 11. Return to the process of 8.

  On the other hand, when the exposure time has elapsed in step # 10 (YES in step # 10), the latest added image is subjected to compression processing by the image compression unit 28, and this image is recorded as a recorded image in the external storage unit 31. (Step # 12).

  In step # 9, when the full press operation of the shutter button 9 is performed again (YES in step # 9), the gain setting control unit 20 adds the added image stored in the second image storage unit 30 at that time. Is confirmed (step # 13), and the digital gain of the amplification processing by the amplifying unit (not shown) of the control unit 18 is set to a gain that eliminates the difference between the pixel value and the appropriate value. (Step # 14). As a result, the pixel value of the pixel signal after addition obtained from substantially all the pixels when the full pressing operation of the shutter button 9 is performed again is amplified with the gain set in step # 14. Then, the image compression unit 28 records the recorded image subjected to the compression process in the external storage unit 31 (step # 12).

  When the exposure time calculated in step # 2 is less than the predetermined value (NO in step # 3), a mode for performing normal automatic exposure control (exposure operation based on the calculated exposure time) is set. The exposure time is temporarily stored (step # 15). Then, while the shutter button 9 is not fully pressed (NO in step # 16), the processes of steps # 2, # 3, and # 15 are repeated, and the shutter button 9 is fully pressed. (YES in step # 16), the second imaging control unit 25 performs the exposure operation of the image sensor 11 for the exposure time calculated in step # 2 (step # 17), and outputs the pixel signal obtained by this exposure operation. Recording is performed in the external storage unit 31 (step # 18).

  After the processing of step # 12 or # 18, it is determined whether or not imaging is continued (step # 19). If imaging is continued (YES in step # 19), the process returns to step # 2. On the other hand, if imaging is not continued (NO in step # 19), imaging is terminated (step # 20).

  As described above, when the long-second monitoring mode is set, the period of the main exposure operation is configured by reading out pixel signals from almost all pixels, adding each time the pixel signals are read out, and adding the pixel signals. Since the image is displayed on the LCD 4, the image obtained by the exposure can be visually recognized during the long exposure period.

  In this embodiment, since the dark noise derived in advance is subtracted from each pixel signal extracted from almost all pixels of the image sensor 11 at a predetermined time interval, for example, external light is shielded. In this state, the image sensor was exposed for the exposure time of the main exposure operation, and the pixel signal obtained by the exposure operation was obtained at the end of the main exposure operation during the main exposure operation of the subject image. Compared to the conventional case of subtracting this dark noise from the pixel signal obtained at the end of the main exposure operation of the subject image, it is considered to be dark noise included in the pixel signal, and high-precision dark noise removal processing is performed. As a result, a captured image that is as faithful as possible to the subject image can be obtained.

  In addition, a function for ending the main exposure operation is provided by performing the full press operation of the shutter button 9 again during the main exposure operation, so that the main exposure operation can be ended at the intention of the photographer. The image of the composition (image of the composition intended by the photographer) can be obtained, and the operability of the imaging apparatus 1 can be improved.

  In addition, the following modifications [1] to [5] can be employed without being limited to the above-described embodiment.

  [1] In the above embodiment, the case where the imaging apparatus 1 is set to the long-second monitoring mode in each of the above-described imaging modes has been described. However, when the bulb imaging mode can be set, the bulb imaging mode is set. However, even when the long-second monitoring mode is set, during the period of the main exposure operation, pixel signals are read out from almost all pixels and added as described above, and an added image (replicated) obtained by the addition process is reproduced. (The added image) may be displayed as a live view image, and the latest added image obtained at the end of the main exposure operation may be recorded in the external storage unit 31 as a recorded image.

  The bulb photographing mode is a mode for performing bulb photographing in which the photographer instructs the opening / closing timing of the mechanical shutter with the shutter button 9, and recording by the image sensor 11 is performed by the electronic shutter when the shutter button 9 is fully pressed. Is a mode in which the exposure operation is ended by releasing the shutter button 9 and releasing the full press of the shutter button 9, and the exposure operation is ended for a relatively long time (for example, 10 seconds). The subject can be photographed with exposure.

  Furthermore, a function for extending the exposure time set by the exposure control unit 19 may be installed in the imaging apparatus 1. That is, if the switch is provided in any one of the four switches 8 for inputting the extension instruction, and this switch is pressed during the exposure period for recording, the exposure time set by the exposure control unit 19 is extended. When the shutter button 9 is fully pressed, the exposure operation may be terminated. Thereby, the operativity of the imaging device 1 can be further improved.

  [2] In the above embodiment, the LCD 4 is provided to display the subject image, and the live view image or the like is displayed on the LCD 4. However, the present invention is not limited to this, and an electronic viewfinder is provided instead of the optical viewfinder 5. In such a case, the live view image may be displayed on the electronic viewfinder.

  [3] In the above embodiment, the external storage unit 31 is used as a means for recording an image. However, the present invention is not limited to this, and the imaging apparatus 1 is connected to a device having a storage capacity such as a computer, a communication cable, or a communication. In a case where communication is possible via a network, an image may be recorded on a device such as the computer.

  [4] In the above embodiment, as the image sensor 11, a CCD in which primary color filters (R (red), G (green), and B (blue) color filters) are disposed on the light receiving surface of each photoelectric conversion element is employed. However, the present invention is not limited to this, and a CCD provided with complementary color filters (C (cyan), M (magenta), Y (yellow)) may be employed.

  [5] In the above-described embodiment, pixel signals are read from substantially all the pixels, addition processing is performed as described above, and an addition image (replicated addition image) obtained by the addition processing is displayed as a live view image, The latest addition image obtained at the end of the main exposure operation is recorded in the external storage unit 31 as a recorded image. However, the present invention is not limited to this, and pixels for the image sensor are used to generate a recording pixel signal. (Hereinafter referred to as a recording pixel) and a pixel for generating a live view image (live view image generating pixel), and each of the period of the main exposure operation, the recording pixel and the live view image generating pixel. A pixel signal is taken out every predetermined time and the addition process is performed, and the dark noise is removed from the pixel signal obtained from each pixel, and a recording image or a live view image is obtained. It is also possible to generate a.

  In this case, as an arrangement form of the recording pixels and the live view image generation pixels, a form in which the live view image generation pixels are arranged in a distributed manner via the recording pixels, or R (red), G (green) , B (blue) as a set of pixel groups each having a predetermined number for each color filter type, each set of pixel groups is a pixel for generating a live view image. It is assumed that each set of pixel groups is dispersedly arranged via the recording pixels.

  For example, FIG. 8A shows an example in which live view image generation pixels are dispersedly arranged via recording pixels, and a predetermined number of live view image generation pixels surrounded by dotted lines are vertically and horizontally. This is an arrangement in which the recording pixels are arranged via the recording pixels (two in FIG. 8A), and the recording pixels are arranged in a Bayer array when focusing only on the live view image generation pixels.

  FIG. 8B shows the number of R (red), G (green), and B (blue) color pixels that are predetermined for each type of color filter (one in FIG. 8B). This is an example in which each set of pixel groups is distributedly arranged via recording pixels. A pixel group composed of four live view image generation pixels surrounded by a dotted line is arranged via a predetermined number of recording pixels in the vertical and horizontal directions (four in FIG. 8B). , R (red), G (green), and B (blue) live view image generation pixels are arranged in a Bayer array at a ratio of 1: 2: 1.

It is a front view of the imaging device concerning the present invention. It is a rear view of the imaging device concerning the present invention. It is a block block diagram which shows the system of an imaging device. It is a figure which shows an example of the conventional live view image. It is a figure which shows an example of the live view image displayed in the imaging device which concerns on this invention. It is a time chart which shows the imaging process of the imaging device 1 at the time of the setting of long-seconds monitoring mode. It is a flowchart which shows the imaging process at the time of the setting of the long second monitoring mode of an imaging device. Arrangement of recording pixels and live view image generation pixels assuming that the pixels of the image sensor are divided into pixels for generating a live view image and pixels for generating a recording pixel signal It is a figure which shows the example of a form.

Explanation of symbols

1 Imaging device 4 LCD
9 Shutter Button 10 Long Second Monitoring Switch 11 Image Sensor 12 Timing Generator 18 Control Unit 19 Exposure Control Unit 20 Gain Setting Control Unit 21 First Imaging Control Unit 22 First Recording Control Unit 23 Addition Processing Unit 24 Aspect Correction Processing Unit 25 Second Imaging control unit 26 Image processing unit 27 Display control unit 28 Image compression unit 29 First image storage unit 30 Second image storage unit

Claims (6)

An image sensor including a plurality of pixels that receive light from a subject and perform photoelectric conversion;
An input operation unit for instructing the image sensor to start an exposure operation for generating a recording pixel signal to be recorded in a predetermined recording unit;
When the exposure start instruction is given by the input operation unit, the imaging control unit causes the imaging device to start an exposure operation and causes the imaging device to output a pixel signal at a predetermined time; and
A noise removal processing unit for respectively removing predetermined dark noise from the pixel signal obtained from the image sensor at each predetermined time;
An addition processing unit that sequentially adds pixel signals from which dark noise has been removed by the noise removal processing unit;
A recording unit that records pixel signals sequentially generated by the addition processing by the addition processing unit;
An imaging apparatus comprising:   2. The imaging according to claim 1, wherein a pixel signal output from a pixel is set as the dark noise when the imaging device is allowed to perform an exposure operation for the predetermined time in a state where external light is blocked. apparatus.   The imaging apparatus according to claim 1, further comprising an image display control unit configured to update and display a pixel signal sequentially generated by the addition processing by the addition processing unit on a predetermined display unit as a display image. . A mode setting unit that sets a bulb photographing mode that allows an instruction to start and end an exposure operation by the image sensor to generate the recording pixel signal;
An exposure time calculation unit that calculates the exposure time based on the luminance of the subject,
The noise removal processing unit performs dark noise removal processing when the bulb setting mode is set by the mode setting unit, or when the exposure time calculated by the exposure time calculation unit is longer than a predetermined time. The imaging apparatus according to any one of claims 1 to 3.   A first input operation unit for inputting an instruction to start an exposure operation by the image sensor for generating the recording pixel signal; and a second input operation unit for inputting an instruction to end the exposure operation; And after the exposure operation is started by the input of the exposure operation start instruction by the first input operation unit, after the exposure operation end instruction is input by the second input operation unit, When the exposure operation is finished, and the exposure operation end instruction is not input by the second input operation unit within the exposure time calculated by the exposure time calculation unit, the exposure time calculation unit calculates the exposure operation. The imaging apparatus according to claim 4, wherein the exposure operation is terminated when an exposure time has elapsed.   A third input operation unit for inputting an instruction to extend the exposure time calculated by the exposure time calculation unit, and after an instruction to extend the exposure time is input by the third input operation unit; The imaging apparatus according to claim 4, wherein when the second input operation unit inputs an instruction to end the exposure operation, the exposure operation is ended.

Images