JP2004343547A - Imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging device capable of obtaining a high quality image by eliminating dark noise. <P>SOLUTION: A first storing part 351 stores image data outputted in such a manner that first photographing for exposing an object performs charge storage, a second storing part 352 stores dark noise data outputted by second photographing that performs charge storage of almost the same exposure time as that of the first photographing, a nonlinear processing part 105 applies nonlinear processing to the dark noise data and outputs the dark noise data subjected to the nonlinear processing to a subtracting part 106, and the subtracting part 106 subtracts the dark noise data subjected to the nonlinear processing by the nonlinear processing part 105 from image data. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an imaging apparatus, and more particularly to an imaging apparatus that removes dark noise generated during long-time shooting in a digital camera.
[0002]
[Prior art]
Conventionally, in a digital camera, a charge coupled device (CCD) or the like has been used as an image sensor. In general, image data captured using a CCD includes dark noise due to dark current, random noise generated on each device, and FPN (fixed pattern noise) generated fixedly in the pixels of the CCD. This is a cause of deterioration of the captured image. In particular, these noises are amplified by the influence of heat or by increasing the ISO sensitivity of PGA (Programmable Gain Amp).
[0003]
11A and 11B are diagrams for explaining dark noise included in image data. FIG. 11A is a diagram illustrating image data and dark noise captured by a CCD, and FIG. FIG. 11C is a diagram illustrating image data and dark noise amplified by the PGA, and FIG. 11C is a diagram illustrating dark noise data. Note that the image data G and the dark noise data D in FIGS. 11A, 11B, and 11C represent the current value I of each pixel output by the horizontal scanning of the CCD. 11 (a), 11 (b) and 11 (c), the vertical axis represents the current value I, and the horizontal axis represents time t.
[0004]
As shown in FIG. 11A, dark noise data D is included in image data G obtained by capturing an image of a subject. Therefore, when the image data G is displayed, dark noise data D is included in the displayed image with fine noise. Appears as. Further, as shown in FIG. 11B, when the image data G output from the CCD is amplified by PGA, the dark noise data D is also amplified together with the image data G, so that the captured image is further deteriorated. . Further, as shown in FIG. 11C, the dark noise data D includes large noise generated by heat generation of the CCD, random noise, and low-level FPN (fixed pattern noise) fixedly generated in pixels. ing.
[0005]
Such a tendency of deterioration becomes more remarkable when the shutter speed shifts to a lower speed side. In recent years, the shutter speed of digital cameras has tended to shift to lower speeds due to the miniaturization of CCDs, etc., and this trend is expected to continue in the future, and a method for preventing deterioration of a captured image due to noise. Is desired.
[0006]
Therefore, conventionally, as a method of removing dark noise, dark noise data captured in a state where light is shielded for a time equivalent to the shutter speed set when capturing an object is acquired, and dark noise data is obtained from image data obtained by capturing the object. Dark noise is removed by subtracting data (for example, see Patent Document 1).
[0007]
FIG. 12 is a diagram for explaining conventional dark noise removal. As shown in FIG. 12, conventionally, dark noise data obtained by exposing in a state where light is shielded for a time equivalent to the shutter speed is subtracted from image data obtained by exposing a subject at a predetermined shutter speed. The image data from which the dark noise has been removed is obtained by the subtraction in the unit 207.
[0008]
[Patent Document 1]
JP-A-8-37627
[0009]
[Problems to be solved by the invention]
However, as shown in FIG. 11C, the dark noise data includes random noise of each processing device when reading out from the CCD, FPN fixedly generated in pixels of the CCD, and the like. For this reason, the dark noise removal method disclosed in Patent Document 1 can remove noise such as a large scratch, but for other noises, a random noise error appears as an error in the captured image, and image deterioration is caused. There is a problem that it will increase further.
[0010]
SUMMARY An advantage of some aspects of the invention is to provide an imaging device that can obtain a high-quality image by removing dark noise.
[0011]
[Means for Solving the Problems]
An image pickup apparatus according to the present invention includes an image pickup device, a first storage unit that stores image data output from the image pickup device by accumulating charges by a first photographing that exposes a subject, and does not perform exposure. A second storage unit that stores dark noise data output from the image sensor by the second imaging in which the electric charge is stored for substantially the same exposure time as the first imaging in the state, and the second storage unit And a subtraction unit for subtracting the dark noise data nonlinearly processed by the nonlinear processing unit from the image data stored in the first storage unit. Unit.
[0012]
According to this configuration, the image data output from the image sensor due to the charge accumulation by the first photographing that exposes the subject is stored in the first storage unit, and the first photographing is performed without performing the exposure. Dark noise data output from the image sensor by the second photographing in which charge accumulation is performed for substantially the same exposure time as that described above is stored in the second storage unit. The dark noise data stored in the second storage unit is read out by the non-linear processing unit and subjected to the non-linear processing. The dark noise data subjected to the non-linear processing by the non-linear processing unit is converted from the image data stored in the first storage unit. The noise data is subtracted, and image data from which the dark noise data is subtracted is output.
[0013]
Therefore, not only can dark noise be removed, but also random noise and FPN can be removed by non-linear processing, so that a higher quality image can be obtained than by simply subtracting dark noise data from image data as in the related art. be able to.
[0014]
Further, in the above-described imaging apparatus, it is preferable that the non-linear processing unit performs non-linear processing on the dark noise data based on a non-linear parameter represented by an inverse γ-shaped characteristic curve at a luminance level.
[0015]
According to this configuration, the dark noise data is nonlinearly processed based on the nonlinear parameter represented by the inverse γ-shaped characteristic curve at the luminance level, so that the random noise at the low luminance level can be removed, and the random noise By preventing the cancellation error due to the influence, it is possible to provide an image with higher image quality than the conventional simple subtraction method.
[0016]
In the above imaging apparatus, the non-linear processing unit may select one of the plurality of non-linear parameters by calibration, and non-linearly process the dark noise data based on the selected non-linear parameter. Is preferred.
[0017]
According to this configuration, one of the plurality of non-linear parameters prepared in advance is selected by calibration, and the dark noise data is non-linearly processed based on the selected non-linear parameter. A stable noise removal process not affected by the noise can be performed.
[0018]
In the above imaging apparatus, it is preferable that the non-linear processing unit selects the nearby non-linear parameter by calibration of at least two points and performs non-linear processing on the dark noise data based on the selected non-linear parameter. .
[0019]
According to this configuration, the nearby nonlinear parameter is selected by the calibration of at least two points, and the dark noise data is subjected to the nonlinear processing based on the selected nonlinear parameter. Therefore, the accuracy in selecting the nonlinear parameter is improved. In addition, optimal noise removal processing can be performed.
[0020]
In the above-described imaging apparatus, the image capturing apparatus further includes a shutter speed detecting unit that detects a shutter speed, and a shutter speed determining unit that determines whether a shutter speed detected by the shutter speed detecting unit is equal to or higher than a predetermined value. The second storage unit stores the charge for substantially the same exposure time as the first shooting in a state where no exposure is performed when the shutter speed determination unit determines that the shutter speed is equal to or higher than a predetermined value; It is preferable to store dark noise data output from the image sensor by the second photographing for accumulation.
[0021]
According to this configuration, the imaging device further includes a shutter speed detection unit that detects a shutter speed, and a shutter speed determination unit that determines whether the shutter speed detected by the shutter speed detection unit is equal to or higher than a predetermined value. A second photographing unit that, when the shutter speed is determined by the shutter speed determining unit to be equal to or higher than a predetermined value, performs charge accumulation for substantially the same exposure time as the first photographing without performing exposure. Accordingly, dark noise data output from the image sensor is stored in the second storage unit. That is, in general, when the shutter speed is short, the influence of dark noise is relatively small. Therefore, when the shutter speed is short, the process of removing dark noise can be omitted, and the process can be simplified.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments according to the present invention will be described with reference to the drawings. In each drawing, the same components are denoted by the same reference numerals, and description thereof will be omitted.
[0023]
FIG. 1 is a top view showing an arrangement of main components included in a camera body constituting an embodiment of a digital camera according to the present invention, FIG. 2 is a right side view of the embodiment, and FIG. 3 is a rear view of the embodiment. FIG.
[0024]
As shown in FIG. 1, a digital camera 1 according to the present embodiment is a single-lens reflex camera including a camera body 2 and a lens 3 that is detachably mounted substantially at the front center of the camera body 2. In addition, as shown in FIG. 2, an electronic view finder (EVF) 4 and a pop-up type flash 5 are provided on the upper surface of the camera body 2. In the present embodiment, the digital camera 1 is described as a single-lens reflex type camera in which the lens 3 is detachably mounted on the camera body 2, but the present invention is not particularly limited to this. The lens 3 and the camera body 2 may be of a single compact camera type.
[0025]
In FIG. 1, the camera body 2 includes a mount (not shown) in which the lens 3 is mounted substantially at the center of the front, and a grip 11 for a user to grip at the left end of the front. A plurality of contacts (not shown) for making an electrical connection with the mounted lens 3 and a plurality of couplers (not shown) for making a mechanical connection are provided below the mount portion. I have.
[0026]
The electrical contact sends specific information (information such as an open F value and a focal length) relating to the lens from a lens ROM incorporated in the lens 3 to an overall control unit 90 (see FIG. 4) in the camera body 2. , For transmitting information on the position of the focus lens and the position of the zoom lens in the lens 3 to the overall control unit 90 (see FIG. 4).
[0027]
The coupler transmits a driving force of a focus lens driving motor (FM) 12 and a driving force of a zoom lens driving motor (ZM) 13 provided in the camera body 2 to each lens in the lens 3. It is.
[0028]
In FIG. 1, a battery storage room 14 and a card storage room 15 are provided inside the grip unit 11. For example, four AA batteries 16 are stored as a camera power supply in the battery storage room 14, and a memory card MC for recording image data of a captured image is detachably mounted in the card storage room 15. It is designed to be stored.
[0029]
A color image sensor 17 is provided at an appropriate position in the camera body 2 on the optical axis L of the lens 3 when the lens 3 is mounted on the mount.
[0030]
A color image sensor (hereinafter referred to as “CCD”) 17 includes R (red), G (green), and B (blue) on the surface of each CCD of an area sensor in which CCDs (Charge Coupled Devices) are two-dimensionally arranged. ) Is a so-called Bayer-type single-plate type color area sensor in which the color filters are pasted in a checkered pattern. In the present embodiment, for example, 1600 (X direction) × 1200 (Y direction) = 1920000 pieces It has a CCD (hereinafter also referred to as “pixel”).
[0031]
On the front surface of the CCD 17, a mechanical shutter S such as a focal plane shutter for mechanically moving a shutter curtain is provided. The opening and closing of the shutter S is controlled by a shutter control driver 38 (see FIG. 4). When the shutter S is opened, an exposure amount necessary for photographing is given to the CCD 17, and when the shutter S is closed, light to the CCD 17 is emitted. It is shaded. Note that the shutter speed (shutter speed) in the present embodiment indicates the time from when the shutter S changes from the open state to the closed state.
[0032]
As shown in FIGS. 2 and 3, a shutter button 18 is provided on the upper surface of the grip section 11 of the camera body 2. The shutter button 18 is configured such that an operation of “half-pressed state S1” partially depressed and an operation of “full-pressed state S2” further depressed are possible. When the shutter button 18 is half-pressed, A preparatory operation for photographing a still image of the subject (preparation operation for setting an exposure control value, adjusting focus, and the like) is performed. When the shutter button 18 is fully pressed, a photographing operation (exposing the CCD 17 and exposing the CCD 17) is performed. A series of operations of performing predetermined image processing on the obtained image signal and recording the image signal on the memory card MC) are executed.
[0033]
2 and 3, the electronic viewfinder 4 includes a finder display unit 19, an eyepiece 20, and a finder window 21. In the present embodiment, the finder display unit 19 is composed of, for example, a color liquid crystal display element having 640 (X direction) × 480 (Y direction) = 307200 pixels, and a monitor image of a subject photographed by the CCD 17, that is, a shutter button 18. This is to display an image of a subject that has been moving image-captured by the CCD 17 in a shooting standby state in which no operation has been performed. The eyepiece 20 guides the monitor image displayed on the finder display section 19 to the outside of the finder window 21. With such a configuration, the photographer can visually recognize the subject from the monitor image displayed on the finder display unit 19 by looking through the finder window 21.
[0034]
Since the monitor image is to be displayed on the viewfinder display unit 19, in the shooting standby state, the CCD 17 is operated in an operation mode different from normal still image shooting (hereinafter, referred to as "still image mode"). A monitor image having the same size as the display size of the display unit 19 is taken. That is, in the present embodiment, since the finder display section 19 has 640 × 480 pixels, in the photographing standby state, all pixels of the CCD 17 receive light, but image data is read out in X and Y directions. Is performed by thinning-out reading at an 8-pixel pitch, that is, 1/8 in both directions, thereby obtaining a monitor image having 640 × 480 pixels at high speed.
[0035]
In FIG. 3, an external display unit (liquid crystal display unit) 22 is provided substantially at the center of the rear surface of the camera body 2. In the present embodiment, the external display unit 22 is composed of, for example, a color liquid crystal display element having 400 (X direction) × 300 (Y direction) = 120,000 pixels. A menu screen for setting, etc., is displayed, and a captured image recorded on the memory card MC is reproduced and displayed in the reproduction mode.
[0036]
A power switch 23 is provided on the left side of the external display unit 22. The power switch 23 also functions as a mode setting switch for switching between a recording mode (a mode for performing a photographing function) and a reproduction mode (a mode for reproducing a recorded image on the external display unit 22). That is, the power switch 23 is composed of a three-point slide switch. When the contact is set at the center “OFF” position, the power is turned off. When the contact is set at the upper “REC” position, the power is turned on and recording is performed. When the mode is set and the contact is set to the lower “PLAY” position, the power is turned on and the reproduction mode is set.
[0037]
A quad switch 24 is provided at an upper right position of the external display unit 22. The quad switch 24 has circular operation buttons, and pressing operations in four directions, up, down, left, and right, with these operation buttons are detected as operations of the upper switch 24U, the lower switch 24D, the left switch 24L, and the right switch 24R, respectively. It has become.
[0038]
The quad switch 24 is multifunctional, and functions as an operation switch for changing an item selected on a menu screen for setting a shooting scene displayed on the external display unit 22, for example. The left switch 24L and the right switch 24R function as operation switches for changing a frame to be reproduced selected on the index screen displayed in an array. The left switch 24L and the right switch 24R function as zoom switches for changing the focal length of the zoom lens of the lens 3. Function.
[0039]
A cancel switch 25, a decision switch 26, a menu display switch 27, and a display changeover switch 28 are provided at lower right positions of the external display unit 22 as switches for performing operations related to display and display contents of the external display unit 22. I have.
[0040]
The cancel switch 25 is a switch for canceling the content selected on the menu screen. The confirmation switch 26 is a switch for confirming the content selected on the menu screen. The menu display switch 27 is used to display a menu screen on the external display unit 22 and to switch the contents of the menu screen (for example, a shooting scene setting screen and a mode setting screen related to exposure control). The menu screen switches to.
[0041]
The display changeover switch 28 is a switch for making the display on the external display unit 22 or for turning off the display. Each time the display changeover switch 28 is pressed, display and non-display of the external display unit 22 are alternately performed. Note that, in order to save power of the battery 16, the display on the external display unit 22 is not performed when the camera is started.
[0042]
An eyepiece sensor 29 for detecting an eyepiece or a non-eyepiece by a photographer is provided at a position above the external display unit 22. The eyepiece sensor 29 includes an infrared LED light emitting unit (for example, a light emitting diode) that emits an infrared LED, and a light receiving unit (for example, a photo reflector) that receives LED reflected light. The light receiving unit receives the LED reflected light when the face of the photographer approaches. The eyepiece sensor 29 recognizes the eyepiece state based on the photoelectrically converted output value, and outputs an eyepiece detection signal to the overall control unit 90 (see FIG. 4). The position at which the eyepiece sensor 29 is provided is not limited to the position above the external display unit 22, but may be any position at which the eyepiece state of the photographer can be detected. The position and the like may be appropriately changed.
[0043]
FIG. 4 is a block diagram illustrating an electrical configuration of the digital camera 1. The same components as those in FIGS. 1 to 3 are denoted by the same reference numerals. The digital camera 1 includes a lens 3, an imaging unit 30, an image memory 35, a signal processing unit 40, a light emission control unit 50, a lens control unit 60, a display unit 70, an operation unit 80, an overall control unit 90, and the like.
[0044]
The lens 3 includes a focus lens, a zoom lens, and a diaphragm for adjusting the amount of transmitted light, and stores a lens ROM (not shown) in which information specific to the lens (information such as an open F value and a focal length) is stored. Have. The lens ROM is connected to the overall control unit 90 via electrical contacts.
[0045]
The imaging unit 30 photoelectrically converts a subject light image incident through the lens 3 and outputs an image signal (electric image). The CCD 17, the timing generator 31, the analog signal processing circuit 32, the A / D conversion circuit 33, and the timing The control circuit 34 is provided.
[0046]
The CCD 17 receives a subject light image for a predetermined exposure time based on a drive control signal (accumulation start signal / accumulation end signal) input from the timing generator 31 and converts it into an image signal (charge accumulation signal). Is transmitted to the signal processing unit 40 in accordance with a read control signal (horizontal synchronization signal, vertical synchronization signal, transfer signal, etc.) input from the timing generator 31. At this time, the image signal is separated into respective color components R, G, and B and sent to the signal processing unit 40.
[0047]
In the following, for the sake of convenience of description, in order to distinguish the light receiving signal of each pixel from an image signal forming a captured image by a set of these, the light receiving signal of each pixel is converted to a pixel signal (analog value) or a pixel as necessary. Data (digital value).
[0048]
The timing generator 31 generates a drive control signal based on a control signal input from the timing control circuit 34, generates a read control signal based on a reference clock signal, and sends the read control signal to the CCD 17. The timing generator 31 generates, for example, clock signals such as integration start / end (exposure start / end) timing signals and readout control signals (horizontal synchronization signal, vertical synchronization signal, transfer signal, etc.) of the light receiving signal of each pixel. , To the CCD 17.
[0049]
The analog signal processing circuit 32 performs predetermined analog signal processing on an image signal of an analog value output from the CCD 17, and includes a CDS (correlated double sampling) circuit for reducing sampling noise of the image signal, An AGC (auto gain control) circuit for level adjustment is provided. The AGC circuit detects a level shortage of a photographed image when a proper exposure cannot be obtained with the aperture value of the diaphragm built in the lens 3 and the exposure time of the CCD 17 (for example, when photographing a very low-luminance subject). It also has a compensation function. The gain of the AGC circuit is set by the overall control unit 90. That is, the analog signal processing circuit 32 reduces the noise of the image signal by the CDS circuit, and adjusts the level of the image signal by adjusting the gain of the AGC circuit.
[0050]
The A / D conversion circuit 33 converts an image signal output from the analog signal processing circuit 32 into a digital value image signal (hereinafter, referred to as “image data”). Is converted into, for example, 12-bit pixel data. The A / D conversion circuit 33 converts each pixel signal into 12-bit image data (digital signal) based on an A / D conversion clock signal input from the timing control circuit 34.
[0051]
The exposure control in the imaging unit 30 is performed by adjusting the aperture and the exposure amount of the CCD 17, that is, the charge accumulation time of the CCD 17 corresponding to the shutter speed. If an appropriate shutter speed cannot be set when the subject brightness is low, the improper exposure due to insufficient exposure is corrected by adjusting the level of the image signal output from the CCD 17. That is, when the luminance is low, the exposure control is performed by combining the shutter speed and the gain adjustment. The level adjustment of the image signal is performed in the gain adjustment of an AGC (auto gain control) circuit in the analog signal processing circuit 32.
[0052]
The timing control circuit 34 controls a photographing operation of the CCD 17, and generates a photographing control signal based on a control signal input from the overall control unit 90. The photographing control signal includes a control signal for displaying a moving image of a subject (hereinafter, referred to as a “live view image”) on the viewfinder display section 19 of the electronic viewfinder 4 during the photographing standby in the recording mode, and a shutter button 18. A control signal for photographing a still image (hereinafter, referred to as a “recorded image”) of the subject, a reference clock signal, and a timing signal (synchronization) for signal processing of an image signal sent from the CCD 17 by the signal processing unit 40. Clock signal). This timing signal is input to the analog signal processing circuit 32 and the A / D conversion circuit 33.
[0053]
The image memory 35 is a memory for temporarily storing the A / D-converted image data and for temporarily storing the image data that has been subjected to the signal processing and output from the γ correction circuit 43. In the present embodiment, for example, It has a capacity to store image data for one frame. In this embodiment, for example, the number of pixels of the CCD 17 is 1600 × 1200 = 1920000, so that the storage capacity capable of storing one frame of image data is a capacity capable of storing 1920000 color pixel data.
[0054]
The signal processing unit 40 performs predetermined digital signal processing on the image signal sent from the CCD 17, and the signal processing of the image signal is performed for each pixel signal constituting the image signal. The signal processing unit 40 includes a black level correction circuit 41, a white balance (WB) circuit 42, and a gamma correction circuit 43. The black level correction circuit 41, the WB circuit 42, and the gamma correction circuit 43 perform digital signal processing. Configure the circuit.
[0055]
The black level correction circuit 41 corrects the black level of each A / D converted pixel data stored in the image memory 35 to a reference black level. The WB circuit 42 adjusts the white balance of the captured image. The WB circuit 42 uses the level conversion table input from the overall control unit 90 to convert the levels of the pixel data of each of the color components R, G, and B, thereby converting the captured image. Adjust the white balance. The conversion coefficient (gradient of the characteristic) of each color component in the level conversion table is set by the overall control unit 90 for each captured image.
[0056]
The γ correction circuit 43 performs gradation correction by correcting the γ characteristics of the pixel data. The gamma correction of the pixel data is performed using a predetermined gamma correction table according to the scene. In the γ correction processing, 10-bit pixel data is converted into 8-bit (256 gradation) pixel data. The reason why the pixel data before the γ correction processing is 10-bit data is to prevent the image quality from being deteriorated when the γ correction is performed with the highly nonlinear γ characteristic. The pixel data of each of the color components R, G, and B has been subjected to a predetermined level conversion in the WB circuit 42, and these pixel data are respectively γ-corrected by a γ correction table.
[0057]
The light emission control unit 50 controls light emission of the flash 5 based on a light emission control signal input from the overall control unit 90, and includes a light control circuit 51 and a light control sensor 52. The light emission control signal includes a light emission preparation instruction, light emission timing, and light emission amount.
[0058]
The dimming circuit 51 charges the main capacitor when the instruction signal of the light emission preparation is sent from the overall control unit 90 to enable the light emission, and when the light emission timing signal is sent, the main capacitor is synchronized with the timing signal. Is discharged, thereby causing the flash 5 to emit light.
[0059]
The light control sensor 52 receives the reflected light of the flash light from the subject at the same time as the exposure starts during the flash photography. When the amount of reflected light received by the light control sensor 52 reaches a predetermined light emission amount, the overall control unit 90 sends a light emission stop signal to the light control circuit 51. The dimming circuit 51 stops the discharge of the main capacitor in response to the light emission stop signal, whereby the flash 5 emits light with a required light emission amount.
[0060]
The lens control unit 60 includes a focus lens driving motor (FM) 12, a zoom lens driving motor (ZM) 13, and an aperture control driver 61.
[0061]
The aperture control driver 61 controls the aperture value of the aperture built in the lens 3, drives the aperture based on the aperture value input from the overall control unit 90, and sets the aperture to the aperture value. I have.
[0062]
The FM 12 is driven based on an AF control signal (for example, a control value such as the number of drive pulses) input from the overall control unit 90, and moves a focus lens built in the lens 3 to a focal position.
[0063]
The ZM 13 is driven based on a zoom control signal (operation information of the quad switch 24) input from the overall control unit 90, and moves the zoom lens built in the lens 3. When the operation information of the right switch 24R of the quadruple switch 24 is input from the overall control unit 90, the ZM 13 is driven in the forward direction to move the zoom lens to the wide-angle (wide) side, and the left switch 24L of the quadruple switch 24 When the operation information is input, the zoom lens is driven in the reverse direction to move the zoom lens to the telephoto side.
[0064]
In the zoom operation of the lens 3, the lens 3 continuously moves to the wide side only while the right switch 24R of the quadruple switch 24 is pressed, and the lens 3 only moves while the left switch 24L of the quadruple switch 24 is pressed. 3 continuously moves to the tele side.
[0065]
The display unit 70 includes the finder display unit (EVF in FIG. 4) 19 and the external display unit (LCD in FIG. 4) 22 and also includes VRAMs 71 and 72.
[0066]
The VRAM 71 is a buffer memory for storing a display image on the external display unit 22, and has a memory capacity capable of storing 400 × 300 color pixel data corresponding to the number of pixels of the external display unit 22. Is a buffer memory for storing a display image on the finder display unit 19, and has a memory capacity capable of storing 640 × 480 color pixel data corresponding to the number of pixels of the finder display unit 19.
[0067]
In the photographing standby state, the analog signal processing circuit 32 to the γ correction circuit 43 perform predetermined signal processing on each pixel data of an image captured by the imaging unit 30 every 1/30 (second), The data is temporarily stored in the memory 35 and transferred to the VRAM 71 and the VRAM 72 via the overall control unit 90, and displayed on the finder display unit 19 and the external display unit 22 (so-called live view display). Thereby, the photographer can visually recognize the subject image. In the reproduction mode, the image read from the memory card MC is subjected to predetermined signal processing by the overall control unit 90, and then transferred to the VRAM 71 and the VRAM 72, and displayed on the finder display unit 19 and the external display unit 22. Is done.
[0068]
The operation unit 80 is configured by the shutter button 18 (see FIG. 3) and the like, and is a two-stage switch capable of detecting a half-pressed state S1 and a fully-pressed state S2. When the shutter button 18 is set to the S1 state in the standby state during the AF (autofocus) photographing in which the focus is automatically controlled, the digital camera 1 starts the lens driving for the AF and the image memory 35 by the overall control unit 90. The lens is driven by the lens motor and stopped so that the contrast becomes the highest while evaluating the contrast of the image inside. The overall control unit 90 determines the shutter speed and the aperture value by determining the level of the image data in the image memory 35 in the S1 state, and further determines the correction value of the white balance in the WB circuit 42. In addition, during MF (manual focus) photographing in which the focus is set by the photographer, the operation unit 80 receives settings of respective control values such as a shutter speed, an aperture value, and an ISO sensitivity.
[0069]
The overall control unit 90 includes a CPU (Central Processing Unit) and the like, and includes a ROM 91, a RAM 92, and an exposure control unit 93. The ROM 91 stores a control program for controlling the operation of the CPU of the overall control unit 90. The RAM 92 temporarily stores various data in arithmetic processing and control processing. The exposure control unit 93 performs brightness determination, exposure amount setting, and ISO sensitivity setting for setting exposure control values (shutter speed, aperture value, and ISO sensitivity) during AF shooting. Note that the shutter speed, the aperture value, and the ISO sensitivity set by the exposure control unit 93 are temporarily stored in the RAM 92.
[0070]
The overall control unit 90 controls the operation of each unit of the digital camera 1 according to a control program stored in the ROM 91. When the shutter button 18 is half-pressed, a preparation operation for photographing a still image of a subject ( When the shutter button 18 is fully depressed after setting the exposure control value and performing a preparation operation such as focus adjustment, the photographing operation (exposing the CCD 17 and subjecting the image signal obtained by the exposure to predetermined image processing) is performed. A series of operations for recording on the memory card MC).
[0071]
The overall control unit 90 is connected to the memory card MC via the card I / F 36. The card I / F 36 is an interface for writing image data to the memory card MC and reading image data.
[0072]
The RTC (Real Time Clock) 37 is a clock circuit that is driven by another power source (not shown) and manages the shooting date and time.
[0073]
The shutter control driver 38 controls driving of the shutter S. The shutter control driver 38 opens and closes the shutter S based on the shutter speed input from the overall control unit 90, and controls the exposure time of the CCD 17.
[0074]
FIG. 5 is a block diagram illustrating a configuration of the imaging device 100 according to the present embodiment. The imaging device 100 according to the present embodiment includes an imaging unit 30, an image memory 35, a signal processing unit 40, and an overall control unit 90.
[0075]
The image memory 35 includes a first storage unit 351 that stores image data output from the CCD 17 by accumulating electric charges by the first photographing that exposes the subject, and performs a first photographing operation with the shutter S closed. It functions as a second storage unit 352 for storing dark noise data output from the CCD 17 by the second photographing in which the electric charge is accumulated for substantially the same exposure time as that of the second photographing.
[0076]
The overall control unit 90 includes a shutter speed (SS) detection unit 101, a shutter speed (SS) determination unit 102, a calibration processing unit 103, a nonlinear parameter selection unit 104, a nonlinear processing unit 105, a subtraction unit 106, and a temperature characteristic storage unit 107. And a non-linear parameter storage unit 108.
[0077]
The shutter speed detection unit 101 detects a shutter speed, detects a shutter speed set by a photographer using the operation unit 80 during MF shooting, and sets a shutter speed set by the exposure control unit 93 during AF shooting. Detect shutter speed.
[0078]
The shutter speed determination unit 102 determines whether or not to perform the dark noise removal processing according to the shutter speed detected by the shutter speed detection unit 101. In the present embodiment, the shutter speed determination unit 102 determines whether the shutter speed detected by the shutter speed detection unit 101 is equal to or higher than a predetermined value that is not affected by dark noise, and In the above case, the dark noise removal processing is performed. If the value is smaller than the predetermined value, the dark noise removal processing is not performed. The image data is stored in the image memory 35 and subjected to signal processing on the image data to be displayed on the display unit 70. In general, when the shutter speed is 1 second or less, the predetermined value in the present embodiment is set to 1 second because the influence of dark noise is small.
[0079]
The calibration processing unit 103 measures the output current value I of the dark noise data output from the imaging unit 30 at a predetermined measurement time t, and measures the temperature in the digital camera 1 from the measured output current value I. . A function representing the relationship between the measurement time t and the output current value I is stored in advance in the temperature characteristic storage unit 107 for each temperature, and the calibration processing unit 103 outputs the dark noise data output from the imaging unit 30. By measuring the current value I and referring to the temperature characteristic storage unit 107, the temperature associated with the measured output current value I is measured as the temperature in the digital camera 1.
[0080]
Further, in the present embodiment, the calibration processing unit 103 sets the first measurement time t ₁ Output current value I of dark noise data at ₁ And a first measurement time t ₁ Longer second measurement time t ₂ Output current value I of dark noise data at ₂ Is measured, and the measured output current values I at two points ₁ , I ₂ From the digital camera 1 is measured. The predetermined measurement time t is set to be shorter than the maximum shutter speed (sec) of the imaging device 100. For example, when the maximum shutter speed of the imaging device 100 is 30 (sec), the first measurement time t is set to the first value. Measurement time t ₁ Becomes 5 (sec), and the second measurement time t ₂ Is set to be 10 (sec). The output current value I is obtained by extracting an average value of all pixels, which is an average of output current values of all pixels, or a predetermined number of pixels, and calculating an average of the output current values of the extracted pixels.
[0081]
The nonlinear parameter selection unit 104 selects a nonlinear function (an inverse γ-shaped characteristic curve) based on the temperature inside the digital camera 1 measured by the calibration processing unit 103. The nonlinear function is stored as a nonlinear parameter in the nonlinear parameter storage unit 108 for each temperature, and the nonlinear parameter selection unit 104 selects a nonlinear parameter corresponding to the measured temperature by referring to the nonlinear parameter storage unit 108. I do. The non-linear parameter is a parameter for converting dark noise data so that dark noise at a low luminance level is substantially constant.
[0082]
The nonlinear processing unit 105 reads the dark noise data stored in the second storage unit 352, and performs nonlinear processing on the read dark noise data based on the nonlinear parameter selected by the nonlinear parameter selection unit 104. That is, the non-linear processing unit 105 converts the read dark noise data according to the non-linear parameter, and outputs the dark noise data converted according to the non-linear parameter.
[0083]
The subtraction unit 106 subtracts dark noise data nonlinearly processed by the nonlinear processing unit 105 from the image data stored in the first storage unit 351.
[0084]
The temperature characteristic storage unit 107 stores a temperature characteristic function of the output current value I with respect to the measurement time t at each temperature in order to measure the temperature inside the device.
[0085]
FIG. 6 is a diagram showing the relationship between the measurement time t for each temperature in the device and the output current value I. In FIG. 6, the vertical axis represents the output current value I, and the horizontal axis represents the measurement time (calibration time) t.
[0086]
The temperature characteristic function A in FIG. 6 shows the relationship between the measurement time t and the output current value I when the temperature T in the device is 40 ° C., and the temperature characteristic function B shows the relationship when the temperature T in the device is 30 ° C. Represents the relationship between the measurement time t and the output current value I, and the temperature characteristic function C represents the relationship between the measurement time t and the output current value I when the temperature T in the device is 20 ° C.
[0087]
The temperature characteristic storage unit 107 stores temperature characteristic functions A, B, and C of the measurement time t and the output current value I corresponding to each temperature. In the present embodiment, the temperature characteristic storage unit 107 stores the function of the measurement time t and the output current value I at intervals of 10 ° C. in the temperature range of 0 ° C. to 50 ° C. FIG. 6 shows three temperature characteristic functions A, B, and C as an example.
[0088]
For example, the calibration processing unit 103 sets the first measurement time t ₁ Output current value I at ₁ Is Ia ₁ And the second measurement time t ₂ Output current value I at ₂ Is Ia ₂ If it is, it is determined that the temperature T in the apparatus is 40 ° C. Similarly, the calibration processing unit 103 sets the first measurement time t ₁ Output current value I at ₁ Is Ib ₁ And the second measurement time t ₂ Output current value I at ₂ Is Ib ₂ If it is, it is determined that the temperature T in the apparatus is 30 ° C.
[0089]
Note that in the present embodiment, the calibration processing unit 103 sets the first measurement time t ₁ Output current value I at ₁ And a second measurement time t ₂ Output current value I at ₂ The output current value I at two points is measured, and the measured first output current value I ₁ And the second output current value I ₂ Although the temperature in the device is measured based on the above, the present invention is not particularly limited to this, the output current values I at three or more points are measured, and the output current values I at the three points are measured. The temperature inside the device may be measured. In this case, the measurement accuracy can be further improved.
[0090]
In the present embodiment, the calibration processing unit 103 determines that the output current value I to be measured does not apply to the temperature characteristic function of the output current value I and the measurement time t corresponding to each temperature stored in advance. Average interpolation is performed from a temperature characteristic function of the measured current t and the output current value I corresponding to each temperature stored in advance to estimate the temperature in the apparatus.
[0091]
FIG. 7 is a diagram for explaining a case where the measured output current value I does not apply to the temperature characteristic function of the measurement time t and the output current value I corresponding to each temperature stored in advance. In FIG. 7, the vertical axis represents the output current value I, and the horizontal axis represents the measurement time (calibration time) t.
[0092]
As shown in FIG. 7, 5 seconds (first measurement time t ₁ 1) First output current value I at the time of elapse ₁ Is Id ₁ And 10 seconds (second measurement time t ₂ 2) Second output current value I at the time of elapse ₂ Is Id ₂ In this case, the relationship between the measurement time t and the output current value I is represented by a temperature characteristic function D. Similarly, the first output current value I after the lapse of 5 seconds ₁ Is Ie ₁ And the second output current value I after 10 seconds has elapsed. ₂ Is Ie ₂ In this case, the relationship between the measurement time t and the output current value I is represented by a temperature characteristic function E. Since the temperature characteristic functions D and E do not apply to the temperature characteristic functions A, B and C stored in advance, the temperature cannot be measured from the temperature characteristic functions A, B and C. . Therefore, the calibration processing unit 103 derives the temperature characteristic functions D and E by performing average interpolation from the temperature characteristic functions A, B and C stored in advance, and derives the temperature characteristic functions D and E based on the derived temperature characteristic functions D and E. Estimate the temperature inside the device.
[0093]
Returning to FIG. 5, the non-linear parameter storage unit 108 stores non-linear parameters for each temperature.
[0094]
FIG. 8 is a diagram illustrating an example of the nonlinear parameter stored in the nonlinear parameter storage unit. In FIG. 8, the vertical axis represents output data of dark noise data, and the horizontal axis represents input data of dark noise data.
[0095]
The non-linear parameter storage unit 108 stores non-linear parameters corresponding to each temperature. That is, as shown in FIG. 8, the nonlinear parameter storage unit 108 stores, for example, a nonlinear parameter represented by a nonlinear function F corresponding to a temperature T = 20 ° C. and a nonlinear function G corresponding to a temperature T = 30 ° C. And a non-linear parameter represented by a non-linear function H corresponding to a temperature T = 40 ° C. When the calibration processing unit 103 determines that the temperature T in the apparatus is 20 ° C., the nonlinear parameter selecting unit 104 selects a nonlinear parameter represented by a nonlinear function F. That is, when the temperature T in the apparatus is 20 ° C., the nonlinear parameter represented by the nonlinear function F is selected by the nonlinear parameter selecting unit 104, and the input data of the dark noise data is converted by the nonlinear processing unit 105 into the nonlinear parameter shown in FIG. The data is converted into output data as shown by a function F and output. Similarly, when it is determined that the temperature T in the apparatus is 30 ° C., the nonlinear parameter represented by the nonlinear function G is selected by the nonlinear parameter selection unit 104, and the input data of the dark noise data is selected by the nonlinear processing unit 105. Is converted into output data as shown by the nonlinear function G in FIG. Further, when it is determined that the temperature T in the apparatus is 40 ° C., the nonlinear parameter represented by the nonlinear function H is selected by the nonlinear parameter selection unit 104, and the input data of the dark noise data is selected by the nonlinear processing unit 105. The output data is converted into output data as shown by the nonlinear function H in FIG.
[0096]
As shown in FIG. 8, the non-linear function has an inverse γ-shaped characteristic, and is set such that when the level of dark noise data input data is low, the level of converted output data is suppressed. When the level of the input data of the dark noise data is high, the level of the output data after the conversion is set to be maintained (substantially linear).
[0097]
The range in which the level of the output data after conversion is suppressed is set so as to increase as the temperature inside the device increases. That is, the rise of the output data with respect to the input data is set to be delayed as the temperature in the device rises.
[0098]
Further, in the present embodiment, when the measured temperature T does not apply to the non-linear parameters corresponding to the respective temperatures stored in advance, the average interpolation is performed from the non-linear parameters corresponding to the respective temperatures stored in advance. Even when there is no nonlinear parameter corresponding to the measured temperature, the nonlinear parameter corresponding to the temperature can be estimated. That is, when the non-linear parameter storage unit 108 stores the non-linear parameters represented by the non-linear functions F, G, and H, and the temperature measured by the calibration processing unit 103 is 35 ° C., the non-linear parameter selection unit 104 , A non-linear parameter represented by a non-linear function J is set by calculating an average interpolation of the non-linear functions G and H. The non-linear processing unit 105 converts the input data of the dark noise data into output data represented by the set non-linear function J and outputs the output data.
[0099]
Next, the operation of the dark noise removal processing by the digital camera shown in FIGS. 1 and 5 will be described. FIG. 9 is a flowchart illustrating an example of the operation of the dark noise removal processing by the digital camera illustrated in FIGS. 1 and 5. FIG. 10 is a diagram for explaining dark noise removal processing in the present embodiment. FIG. 10A is a diagram illustrating a scan line on an imaging surface, and FIG. 10B is a diagram illustrating dark noise. FIG. 10C is a diagram illustrating data, and FIG. 10C is a diagram illustrating dark noise data that has been subjected to nonlinear processing. In FIGS. 10B and 10C, the vertical axis represents the current value I, and the horizontal axis represents time t. The dark noise data in FIGS. 10B and 10C is a current read out along a scan line SL in the horizontal direction (X direction) with respect to the imaging surface 171 of the CCD 17 shown in FIG. The time-dependent change of the value I is shown.
[0100]
In step ST1, the overall control unit 90 determines whether dark noise cancellation is on or off. That is, the shutter speed determination unit 110 determines whether the shutter speed detected by the shutter speed detection unit 101 is 1 second or more. Here, if the shutter speed is 1 second or longer (YES in step ST1), the process proceeds to step ST2, and if the shutter speed is shorter than 1 second (NO in step ST1), the process proceeds to step ST9.
[0101]
In the present embodiment, dark noise cancellation is turned on / off according to the length of the shutter speed. However, the present invention is not particularly limited to this, and performs processing for removing dark noise from a captured image. It may be performed by determining whether or not the user has set in advance whether or not. In this case, a switch for turning on / off dark noise cancellation by the user is provided in the operation unit 80 in advance, and when dark noise cancellation is turned on by this switch, the process proceeds to step ST2. If the dark noise cancellation is set to off, the process proceeds to step ST9.
[0102]
In step ST2, the calibration processing unit 103 sets the first measurement time t ₁ Output current value I at ₁ And a second measurement time t ₂ Output current value I at ₂ Is measured, and a temperature characteristic function stored in the temperature characteristic storage unit 107 is selected based on the measured two output current values I, and a temperature corresponding to the selected temperature characteristic function is set to a temperature in the apparatus. And
[0103]
In step ST3, the non-linear parameter selection unit 104 selects a non-linear parameter stored in the non-linear parameter storage unit 108 based on the temperature inside the apparatus measured by the calibration processing unit 103.
[0104]
In step ST4, the overall control unit 90 determines whether or not the shutter button 18 is in the fully pressed state S2, and detects an ON signal indicating that the shutter button 18 is in the fully pressed state S2 (YES in step ST4). ), The process proceeds to step ST5, and if an ON signal indicating that the shutter button 18 is in the fully pressed state S2 is not detected (NO in step ST4), the process returns to step ST1.
[0105]
In step ST <b> 5, the overall control unit 90 controls the shutter button 18 to be fully pressed by the photographer to perform the first photographing in which the subject is exposed, and the CCD 17 is formed on the imaging surface by the lens 3. The pixel data is output to the analog signal processing circuit 32 by photoelectrically converting the subject image. The pixel data is converted into a digital signal by the analog signal processing circuit 32 and the A / D conversion circuit 33, and is stored in the first storage unit 351 of the image memory 35 as image data.
[0106]
In step ST6, the overall control unit 90 controls to perform the second photographing in which the charge is accumulated for substantially the same exposure time as the first photographing with the shutter S closed, and the CCD 17 controls the shutter S to be closed. The pixel data obtained by performing the photoelectric conversion in the obtained state is output to the analog signal processing circuit 32. The pixel data is converted into a digital signal by the analog signal processing circuit 32 and the A / D conversion circuit 33, and is stored in the second storage unit 352 of the image memory 35 as dark noise data.
[0107]
In step ST7, the non-linear processing unit 105 reads dark noise data stored in the second storage unit 352, and performs non-linear processing on the read dark noise data. That is, the nonlinear processing unit 105 converts the input dark noise data according to the nonlinear parameter selected by the nonlinear parameter selection unit 104, and outputs the converted dark noise data. Dark noise data as shown in FIG. 10B is input to the non-linear processing unit 105, and the input dark noise data is subjected to non-linear processing, thereby obtaining as shown in FIG. 10C. Dark noise data is output. As shown in FIG. 10C, the random noise and FPN other than the offset noise have been removed from the dark noise data on which the non-linear processing has been performed.
[0108]
In step ST8, the subtraction unit 106 subtracts the dark noise data nonlinearly processed by the nonlinear processing unit 105 from the image data stored in the first storage unit 351 of the image memory 35, and the dark noise data is subtracted. The image data is output to the image memory 35.
[0109]
Here, dark noise data appears more conspicuously as the shutter speed increases. Therefore, when the shutter speed is short, shooting can be performed without considering the influence of dark noise. Therefore, if it is determined in step ST1 that the shutter speed is shorter than 1 second, the process proceeds to step ST9 because it is not necessary to remove dark noise.
[0110]
In step ST9, the overall control unit 90 determines whether or not the shutter button 18 is in the fully-pressed state S2, and detects an ON signal indicating that the shutter button 18 is in the fully-pressed state S2 (YES in step ST9). ), The process proceeds to step ST10, and if an ON signal indicating that the shutter button 18 is in the fully pressed state S2 is not detected (NO in step ST9), the process returns to step ST1.
[0111]
In step ST10, the overall control unit 90 controls to perform the first photographing in which the subject is exposed by the shutter button 18 being fully pressed by the photographer, and the CCD 17 is imaged on the imaging surface by the lens 3. The pixel data is output to the analog signal processing circuit 32 by photoelectrically converting the subject image. The pixel data is converted into a digital signal by the analog signal processing circuit 32 and the A / D conversion circuit 33, and is stored in the first storage unit 351 of the image memory 35 as image data.
[0112]
In step ST11, when the dark noise data is removed (when the processing of steps ST2 to ST8 is performed), the image memory 35 stores the image data from which the dark noise data has been subtracted, and stores the dark noise data. If the image data is not removed (when the processes in steps ST9 and ST10 are performed), the image data stored in the first storage unit 351 is stored as it is.
[0113]
In step ST12, the signal processing unit 40 performs various kinds of signal processing on the image data from which the dark noise data stored in the image memory 35 has been subtracted or the image data from which the dark noise data has not been subtracted. The applied image data is output to the display unit 70. The display unit 70 displays the image data on which the signal processing has been performed.
[0114]
As described above, in the image pickup apparatus according to the present invention, the image data output from the CCD 17 due to charge accumulation by the first photographing for exposing the subject is stored in the first storage unit 351 and the shutter is closed. Then, the dark noise data output from the image sensor by the second imaging in which the electric charge is accumulated for substantially the same exposure time as the first imaging is stored in the second storage unit 352. The output current value I of the dark noise data is measured by the calibration processing unit 103, and the temperature in the apparatus is measured based on the measured output current value I. Then, the non-linear parameter selection unit 104 selects a non-linear parameter corresponding to the measured temperature in the apparatus from the non-linear parameters stored in the non-linear parameter storage unit 108 for each temperature. The non-linear processing unit 105 reads dark noise data stored in the second storage unit 352, performs non-linear processing on the read dark noise data according to the non-linear parameter selected by the non-linear parameter selection unit 104, and performs non-linear processing. The processed dark noise data is output to subtraction section 106. Then, the subtraction unit 106 subtracts the non-linearly processed dark noise data output from the non-linear processing unit 105 from the image data stored in the first storage unit 351, and subtracts the dark noise data from the image data. Is stored in the image memory 35.
[0115]
Therefore, not only can dark noise be removed, but also random noise and FPN generated at a low luminance level can be removed by non-linear processing, so that the S / N ratio of a captured image can be improved and, as in the conventional case, simply An image with higher image quality can be obtained than when dark noise data is subtracted from image data.
[0116]
Further, the nonlinear parameter storage unit 108 stores a nonlinear parameter represented by a nonlinear function having an inverse γ-shaped characteristic at the luminance level, and the nonlinear processing unit 105 generates an inverse γ-shaped characteristic curve at the luminance level. Since the dark noise data is nonlinearly processed based on the expressed nonlinear parameter, it is possible to remove random noise at a low luminance level and prevent cancellation errors due to the influence of random noise. High quality images can be provided.
[0117]
Also, one of the plurality of nonlinear functions prepared in advance in the nonlinear parameter storage unit 108 is selected by calibration, and the dark noise data is subjected to nonlinear processing based on the selected nonlinear function. A stable noise removal process that is not affected by offset noise can be performed.
[0118]
Further, by performing calibration of at least two points, a nearby nonlinear function is selected from among a plurality of nonlinear functions prepared in advance in the nonlinear parameter storage unit 108, and the dark noise data is determined based on the selected nonlinear function. Since the non-linear processing is performed, the accuracy in selecting the non-linear function increases, and optimal noise removal processing can be performed.
[0119]
If the shutter speed is determined by the shutter speed determination unit 102 to be equal to or greater than a predetermined value (1 second in the present embodiment), the charge for approximately the same exposure time as that of the first shooting is performed with the shutter closed. Dark noise data output from the CCD 17 by the second photographing for accumulation is stored in the second storage unit 352. That is, in general, when the shutter speed is short, the influence of dark noise is relatively small. Therefore, when the shutter speed is short, the process of removing dark noise can be omitted, and the process can be simplified.
[0120]
In the present embodiment, in a state where the shutter is closed, the dark noise data output from the image sensor by the second imaging in which the charge is accumulated for substantially the same exposure time as the first imaging is stored in the second storage unit 352. However, the present invention is not particularly limited to this, and a light-blocking member that blocks light between the lens 3 and the CCD 17 is provided. The dark noise data output from the image sensor by the second shooting in which the charge is accumulated for the exposure time may be stored in the second storage unit 352.
[0121]
In the present embodiment, when the shutter speed is determined by the shutter speed determining unit 110 to be equal to or more than a predetermined value (1 second in the present embodiment), the shutter is closed and substantially the same as the first shooting. The dark noise data output from the CCD 17 by the second photographing in which the charge is accumulated for the exposure time is stored in the second storage unit 352. However, the present invention is not particularly limited to this. When a shutter speed is determined by the shutter speed determining unit 110 to be equal to or higher than a predetermined value (1 second in the present embodiment), the light is shielded by the light shielding member. The dark noise data output from the CCD 17 by the second imaging in which the charge is accumulated for substantially the same exposure time as the first imaging is stored in the second storage unit 352. It may be stored.
[0122]
The specific embodiments described above mainly include inventions having the following configurations.
[0123]
(1) an image sensor;
A first storage unit that stores image data that is output from the image sensor by being charge-stored by a first shooting that exposes a subject;
A second storage unit that stores dark noise data output from the image sensor by the second shooting in which charge is stored for substantially the same exposure time as the first shooting in a state where exposure is not performed;
A non-linear processing unit that performs non-linear processing on the dark noise data stored in the second storage unit;
An imaging apparatus, comprising: a subtraction unit that subtracts the dark noise data nonlinearly processed by the nonlinear processing unit from the image data stored in the first storage unit.
[0124]
(2) The imaging apparatus according to (1), wherein the non-linear processing unit performs non-linear processing on the dark noise data based on a non-linear parameter represented by an inverse γ-shaped characteristic curve at a luminance level.
[0125]
(3) a storage unit for storing, for each temperature, a plurality of nonlinear parameters represented by an inverse γ-shaped characteristic curve at a luminance level;
The non-linear processing unit measures a temperature in the apparatus by calibration, and selects one of the plurality of non-linear parameters stored in the storage unit based on the measured temperature. The imaging device according to the above (1) or (2).
[0126]
(4) The imaging apparatus according to (3), wherein the non-linear processing unit selects the nearby non-linear parameter by performing calibration of at least two points.
[0127]
(5) The linearized processing unit non-linearly processes the dark noise data by performing average interpolation from a plurality of non-linear parameters stored in a storage unit. An imaging device according to any one of the above.
[0128]
(6) a shutter speed detection unit for detecting a shutter speed;
A shutter speed determination unit that determines whether a shutter speed detected by the shutter speed detection unit is equal to or greater than a predetermined value,
When the shutter speed is determined by the shutter speed determination unit to be equal to or higher than a predetermined value, the second storage unit stores the charge for substantially the same exposure time as the first shooting without performing exposure. The imaging apparatus according to any one of the above (1) to (5), wherein dark noise data output from the image sensor by the second photographing that performs (i) is stored.
[0129]
【The invention's effect】
According to the first aspect of the present invention, dark noise can be removed, and random noise and FPN can also be removed by non-linear processing. Therefore, dark noise data is simply subtracted from image data as in the related art. It is possible to obtain an image of higher quality than by performing.
[0130]
According to the second aspect of the present invention, dark noise data is subjected to nonlinear processing based on a nonlinear parameter represented by an inverse γ-shaped characteristic curve at a luminance level, so that random noise at a low luminance level can be removed. It is possible to provide an image with higher image quality than the conventional simple subtraction method by preventing a cancel error due to the influence of random noise.
[0131]
According to the third aspect of the present invention, one of the plurality of non-linear parameters prepared in advance is selected by calibration, and the dark noise data is subjected to non-linear processing based on the selected non-linear parameters. Therefore, stable noise removal processing not affected by offset noise can be performed.
[0132]
According to the fourth aspect of the present invention, a nearby nonlinear parameter is selected by calibration of at least two points, and the dark noise data is subjected to nonlinear processing based on the selected nonlinear parameter. In this case, the accuracy of the noise reduction is increased, and the optimum noise removal processing can be performed.
[0133]
According to the fifth aspect of the invention, in general, when the shutter speed is short, the influence of dark noise is relatively small. Therefore, when the shutter speed is short, the process of removing dark noise is omitted, and the process is simplified. Can be
[Brief description of the drawings]
FIG. 1 is a top view showing an arrangement of main members included in a camera body constituting an embodiment of a digital camera according to the present invention.
FIG. 2 is a right side view showing an arrangement of main members included in a camera main body constituting an embodiment of the digital camera according to the present invention.
FIG. 3 is a rear view illustrating an arrangement of main members included in a camera main body constituting one embodiment of the digital camera according to the present invention.
FIG. 4 is a block diagram illustrating an electrical configuration of the digital camera.
FIG. 5 is a block diagram illustrating a configuration of an imaging device according to the present embodiment.
FIG. 6 is a diagram illustrating a relationship between a measurement time t for each temperature in the apparatus and an output current value I.
FIG. 7 is a diagram for explaining a case where a measured output current value I does not apply to a temperature characteristic function of a measurement time t and an output current value I corresponding to each temperature stored in advance.
FIG. 8 is a diagram illustrating an example of nonlinear parameters stored in a nonlinear parameter storage unit.
FIG. 9 is a flowchart illustrating an example of an operation of dark noise removal processing by the digital camera illustrated in FIGS. 1 and 5;
FIG. 10 is a diagram for describing dark noise removal processing according to the present embodiment.
FIG. 11 is a diagram for describing dark noise included in image data.
FIG. 12 is a diagram for explaining conventional dark noise removal.
[Explanation of symbols]
17 CCD
30 Imaging unit
31 Timing Generator (TG)
32 analog signal processing circuit
33 A / D conversion circuit
34 Timing Control Circuit
35 image memory
40 signal processing unit
90 Overall control unit
101 Shutter speed detector
102 Shutter speed judgment unit
103 Calibration processing unit
104 Nonlinear parameter selector
105 Nonlinear processing unit
106 Subtraction unit
107 Temperature characteristic storage unit
108 Non-linear parameter storage
351 First Storage Unit
352 second storage unit

Claims (5)

An image sensor;
A first storage unit that stores image data that is output from the image sensor by being charge-stored by a first shooting that exposes a subject;
A second storage unit that stores dark noise data output from the image sensor by the second shooting in which charge is stored for substantially the same exposure time as the first shooting in a state where exposure is not performed;
A non-linear processing unit that performs non-linear processing on the dark noise data stored in the second storage unit;
An imaging apparatus, comprising: a subtraction unit that subtracts the dark noise data nonlinearly processed by the nonlinear processing unit from the image data stored in the first storage unit. The imaging apparatus according to claim 1, wherein the non-linear processing unit performs non-linear processing on the dark noise data based on a non-linear parameter represented by an inverse γ-shaped characteristic curve at a luminance level. The non-linear processing unit selects one non-linear parameter among a plurality of the non-linear parameters by calibration, and non-linearly processes the dark noise data based on the selected non-linear parameter. 2. The imaging device according to 2. The imaging apparatus according to claim 3, wherein the non-linear processing unit selects the nearby non-linear parameters by calibration of at least two points, and performs non-linear processing on the dark noise data based on the selected non-linear parameters. apparatus. A shutter speed detector for detecting a shutter speed,
A shutter speed determination unit that determines whether a shutter speed detected by the shutter speed detection unit is equal to or greater than a predetermined value,
When the shutter speed is determined by the shutter speed determination unit to be equal to or higher than a predetermined value, the second storage unit stores the charge for substantially the same exposure time as the first shooting without performing exposure. The imaging apparatus according to any one of claims 1 to 4, wherein dark noise data output from the imaging element by the second imaging that performs (i) is stored.

Images