JP2007267330A - Digital single-lens reflex camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To shorten the entire time required for photographing, by efficiently perform the function of removing fixed pattern noise in a digital single-lens reflex camera. <P>SOLUTION: The digital single-lens reflex camera comprises a movable mirror 201 capable of moving to a rising position for leading a subject luminous flux to a CCD 221, after saving the flux to the outside of a photographic optical path, and moving to the falling position for leading the subject luminous flux to a finder optical system; the CCD 221 for moving the movable mirror 201 to the rising position, and acquiring a subject image; and a liquid crystal monitor 26 for continuously displaying subject image data output from the CCD 221. The digital single-lens reflex camera predicts whether the fixed pattern noise superimposes on the subject image data during display of a through image (#43, #45). Dark image data of an imaging device is acquired (#83, #87), when subsequent still images (#59-#67) are acquired, when it is predicted that the fixed pattern is superimposed on the subject image data. Noise elimination operation of the subject image data, acquired by a still image acquisition means, is performed based on the dark image data (#89). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a digital camera having a through image display function, and more specifically, a digital single lens having a so-called through image display function (also referred to as a live view display function or an electronic viewfinder function) for displaying an image acquired by an image sensor on a display device. Reflex camera related.

In conventional compact digital cameras, the subject image was observed using an optical finder, but recently, the optical finder has been eliminated, and the output of an image sensor provided for recording subject image data is used instead. It is also used for display. That is, there are an increasing number of images having a through image display function for displaying an image acquired by an image sensor on a display device such as a liquid crystal monitor for observing a subject image.

Such a live view display function is effective, for example, during macro photography because no parallax occurs. For this reason, various examples mounted on a digital single lens reflex camera have been proposed. For example, the optical viewfinder display mode and the electronic viewfinder display mode can be selected, and when the electronic viewfinder display mode is selected, the movable mirror is retracted from the photographing optical path and the focal plane shutter is fully opened to guide the subject image to the image sensor. A digital single-lens reflex camera has been proposed in which a subject image obtained thereby is displayed on a liquid crystal monitor for observation (Patent Document 1).
JP 2002-369042 A

As described above, a digital camera having a through image display function has been proposed. However, the image sensor used here has fixed pattern noise caused by variations in output characteristics of pixels. For this reason, if the output signal of the image sensor is used as it is, fixed pattern noise is superimposed on an effective signal component, which causes deterioration of the image quality of the captured image. In particular, when the imaging operation is continued for a long time as in the case of a through image display, there is a problem that the temperature of the imaging device itself rises and the fixed pattern noise becomes extremely large.

In order to remove these fixed pattern noises, an electronic still camera having a noise reduction function has been proposed (Patent Document 2). In this noise reduction function, when an image is captured, the image sensor is first exposed with the shutter closed, and a dark image obtained thereby is recorded in a memory. Subsequently, the image sensor is exposed with the shutter opened, and the dark image stored in the memory is subtracted from the bright image signal obtained by this exposure. According to this method, since the noise component generated at the time of dark output is canceled out by the difference, it is possible to efficiently remove the defect.
JP 2006-5912 A

However, the noise reduction function of the electronic still camera disclosed in Patent Document 2 needs to perform image capturing in a light-shielded state for the same amount of time as in normal image capturing, and there is a problem that the time required for one image capturing becomes significantly longer. there were.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a digital single-lens reflex camera capable of shortening the time required for photographing as a whole by efficiently operating a noise reduction function. And

In order to achieve the above object, a digital single-lens reflex camera according to a first aspect of the present invention includes a first position for retracting out of the photographing optical path to guide the subject luminous flux to the image sensor, and the subject luminous flux in the photographing optical path to the finder optical system. Mirror means movable to the second position to be guided, imaging means for moving the mirror means to the first position and acquiring a subject image with the imaging device, and subject image output from the imaging means Through image display means for continuously displaying data on a display device, and during display of the through image by the through image display means, subject image data output from the imaging means in response to a release operation is acquired as still image data. A still image acquisition means; a prediction means for predicting that fixed pattern noise is superimposed on the subject image data output from the imaging means during the through image display; When it is predicted by the means that the fixed pattern is superimposed on the subject image data, dark image data of the image sensor is acquired at the time of subsequent acquisition of the still image, and the still image is based on the dark image data. Noise removal means for performing noise removal operation on the subject image data acquired by the acquisition means is provided.

In the digital single-lens reflex camera according to the second invention, in the first invention, the prediction means includes the fixed pattern noise in the subject image data when the through image display is continued for a predetermined time or more. Predict that they are superimposed.
Furthermore, in the digital single-lens reflex camera according to the third aspect of the present invention, the predetermined time varies depending on the ISO sensitivity.
According to a fourth aspect of the present invention, in the digital camera according to the first aspect, the noise removing unit acquires the dark image data after the subject image data is acquired by the still image acquiring unit.
Further, in the digital single-lens reflex camera according to the fifth invention, in the fourth invention, the noise removing means operates during the reset operation of the mechanism member after the subject image data is obtained by the still image obtaining means.
Furthermore, in the digital single-lens reflex camera according to the sixth invention, in the fourth invention, the noise removing means is parallel to the movement of the mirror means from the first position to the second position. The dark image data is acquired.

In order to achieve the above object, a digital camera according to a seventh aspect of the present invention receives an image of an object and photoelectrically converts it, and a through image display that continuously displays object image data output from the image sensor on a display device. A still image acquisition means for acquiring subject image data output from the imaging means as still image data in response to a release operation during the through image display by the through image display means, and the above during the through image display. When predicting that the fixed pattern noise is superimposed on the subject image data output from the imaging unit, and when the predicting unit predicts that the fixed pattern is superimposed on the subject image data, When the still image is acquired, dark image data of the image sensor is acquired, and the subject acquired by the still image acquisition unit based on the dark image data Comprising a noise removal means for removing noise operation of the data.

According to the present invention, when it is predicted by the prediction means that the fixed pattern is superimposed on the subject image data, the dark image data of the image sensor is acquired at the time of subsequent still image acquisition, and based on this dark image data Since the noise removal means for performing noise removal operation of the subject image data acquired by the still image acquisition means is provided, the time required for shooting can be shortened as a whole by operating the noise reduction function efficiently. A digital single lens reflex camera can be provided.

Hereinafter, a preferred embodiment using a digital single lens reflex camera to which the present invention is applied will be described with reference to the drawings. FIG. 1 is an external perspective view of a digital single-lens reflex camera according to an embodiment of the present invention as seen from the back.
On the upper surface of the camera body 200, a release button 21, a mode dial 22, a control dial 24, and the like are arranged. The release button 21 has a first release switch that is turned on when the photographer is half-pressed and a second release switch that is turned on when the photographer is fully pressed. When the first release switch (hereinafter referred to as 1R) is turned on, the camera performs photographing preparation operations such as focus detection, focusing of the photographing lens, and photometry of the subject brightness, and the second release switch (hereinafter referred to as 2R). When it is turned on, a photographing operation for capturing image data of a subject image is executed based on the output of a CCD (Charge Coupled Devices) 221 (see FIG. 2) as an image sensor.

The mode dial 22 is an operation member that is configured to be rotatable. By matching a picture display or symbol representing a shooting mode provided on the mode dial 22 with an index, a full-auto shooting mode (AUTO) or a program shooting mode is set. (P), aperture priority shooting mode (A), shutter shooting priority mode (S), manual shooting mode (M), portrait shooting mode, landscape shooting mode, macro shooting mode, sports shooting mode, night scene shooting mode, etc. The shooting mode can be selected. The control dial 24 is an operation member configured to be rotatable, and a desired set value, mode, or the like can be selected by rotating the control dial 24 on an information display screen or the like.

On the back of the camera body 200, a liquid crystal monitor 26, a playback button 27, a menu button 28, an up cross button 30U, a down cross button 30D, a right cross button 30R, a left cross button 30L (each of these cross buttons 30U, 30D, 30R, and 30L are collectively referred to as a cross button 30), an OK button 31, a display mode switching button 34, a white balance button 37, and an ISO sensitivity button 38 are arranged. The liquid crystal monitor 26 is a display device for reproducing and displaying a photographed subject image and displaying photographing conditions and menus. Any liquid crystal display can be used as long as it can perform these displays. The playback button 27 is an operation button for instructing the liquid crystal monitor 26 to display a subject image recorded after shooting. The subject image data stored in a later-described SDRAM 237 and recording medium 245 in a compression mode such as JPEG is expanded and displayed.

The cross button 30 is an operation member for instructing movement of the cursor in the two-dimensional direction of the X direction and the Y direction on the liquid crystal monitor 26, and displays a subject image recorded on a recording medium as will be described later. This is also used to indicate the recording medium. In addition to providing four buttons for up, down, left, and right, it is also possible to replace with a switch that can be operated in a two-dimensional direction, such as a switch that can detect the operation direction in two dimensions, such as a touch switch. is there. The OK button 31 is an operation member for confirming various items selected by the cross button 30, the control dial 24, or the like. The menu button 28 is a button for switching to a menu mode for setting various modes of the digital camera. When the menu mode is selected by operating the menu button 28, a menu screen is displayed on the liquid crystal monitor 26. The menu screen has a plurality of hierarchical structures. Various items are selected with the cross-shaped button 30, and selection is determined by operating the OK button 31.

The display mode switching button 34 is an operation button for switching between a through image display and an information display, which will be described later, and in the through image display, the subject image is observed on the liquid crystal monitor 26 based on the output of the CCD 221 for recording the subject image. The information display is a mode displayed on the liquid crystal monitor 26 in order to set display of shooting information of the camera as shown in FIG. The white balance button 37 is an operation button for setting the white balance. By operating the white balance button 37, a setting screen is displayed on the liquid crystal monitor 26, and auto, sunlight, cloudy, shade, light bulb, Each mode such as fluorescent lamps 1 to 3 and one-shot is displayed, and can be selected by rotating the control dial 24 and determined by operating the OK button 31.

The ISO sensitivity button 38 is an operation button for setting the ISO sensitivity. When the ISO sensitivity button 38 is operated, a setting screen is displayed on the liquid crystal monitor 26, and each sensitivity of auto and sensitivity 100 to 1600 is set as described above. Can be selected by rotating the control dial 24 and determined by operating the OK button 31. When the camera is left to the camera, auto is selected. When there is an intention to shoot, the photographer can arbitrarily set the sensitivity within a range of 100 to 1600. A recording medium storage lid 40 is attached to the side surface of the camera body 200 so as to be freely opened and closed. When the recording medium storage lid 40 is opened, a loading slot for the recording medium 245 is provided therein, and the recording medium 245 can be detachably loaded into the camera body 200.

Next, the overall configuration of the digital single-lens reflex camera mainly including the electric system will be described with reference to FIG. The digital single-lens reflex camera according to this embodiment includes an interchangeable lens 100 and a camera body 200. In the present embodiment, the interchangeable lens 100 and the camera body 200 are configured separately and are electrically connected by the communication contact 300, but the interchangeable lens 100 and the camera body 200 can also be configured integrally. .

Inside the interchangeable lens 100, lenses 101 and 102 for focus adjustment and focal length adjustment, and a diaphragm 103 for adjusting the aperture amount are arranged. The lens 101 and the lens 102 are driven by a lens driving mechanism 107, and the diaphragm 103 is connected to be driven by a diaphragm driving mechanism 109. The lens driving mechanism 107 and the aperture driving mechanism 109 are each connected to a lens CPU 111, and the lens CPU 111 is connected to the camera body 200 via a communication contact 300. The lens CPU 111 controls the inside of the interchangeable lens 100. The lens CPU 111 controls the lens driving mechanism 107 to perform focusing and zoom driving, and also controls the aperture driving mechanism 109 to perform aperture value control.

Within the camera body 200, there are a position inclined 45 degrees with respect to the lens optical axis in order to reflect the subject image to the observation optical system, and a position raised to guide the subject image to the image sensor (CCD 221 described later). A movable mirror 201 that can be rotated is provided. Above the movable mirror 201, a focusing screen 205 for forming a subject image is disposed, and above this focusing screen 205, a pentaprism 207 for horizontally reversing the subject image is disposed. An eyepiece lens 209 for observing a subject image is disposed on the emission side (right side in FIG. 1) of the pentaprism 207, and a photometric sensor 211 is disposed on the side of the pentaprism 207 so as not to interfere with the observation of the subject image. . The photometric sensor 211 is composed of a multi-division photometric element that divides a subject image for photometry.

Near the center of the movable mirror 201 described above is a half mirror, and on the back surface of the movable mirror 201, a sub mirror 203 for reflecting subject light transmitted through the half mirror portion to the lower part of the camera body 200 is provided. ing. The sub mirror 203 is rotatable with respect to the movable mirror 201. When the movable mirror 201 is flipped up, the sub mirror 203 is rotated to a position that covers the half mirror portion. When the movable mirror 201 is at the subject image observation position, the sub mirror 203 is illustrated. In this way, the position is perpendicular to the movable mirror 201. This movable mirror 201 is driven by a mirror drive mechanism 219. A distance measuring circuit 217 including a distance measuring sensor is disposed below the sub mirror 203. This circuit is a circuit for measuring the amount of focus deviation of the subject image formed by the lenses 101 and 102. is there.

A focal plane type shutter 213 for controlling the exposure time is disposed behind the movable mirror 201. The shutter 213 is driven and controlled by a shutter drive mechanism 215. A CCD 221 serving as an image sensor is disposed behind the shutter 213 and photoelectrically converts a subject image formed by the lenses 101 and 102 into an electric signal. In the present embodiment, a CCD is used as an image sensor. However, the present invention is not limited to this, and a CMOS (Complementary Metal Oxide) is used.
Needless to say, a two-dimensional imaging device such as Semiconductor) can be used. The CCD 221 is connected to a CCD drive circuit 223, and analog / digital conversion (AD conversion) is performed by the CCD drive circuit 223. The CCD drive circuit 223 is connected to the image processing circuit 227 via the CCD interface 225. The image processing circuit 227 performs various types of image processing such as color correction, gamma (γ) correction, and contrast correction.

The image processing circuit 227 is an ASIC (Application Specific Integrated).
Circuit-specific integrated circuit) 271 is connected to the data bus 261. In addition to the image processing circuit 227, the data bus 261 includes a sequence controller (hereinafter referred to as “body CPU”) 229, a compression circuit 231, a flash memory control circuit 233, an SDRAM control circuit 236, an input / output circuit 239, A communication circuit 241, a recording medium control circuit 243, a video signal output circuit 247, and a switch detection circuit 253 are connected.

The body CPU 229 connected to the data bus 261 controls the flow of this digital single lens reflex camera. A compression circuit 231 connected to the data bus 261 is a circuit for compressing the image data stored in the SDRAM 237 with JPEG or TIFF. Note that image compression is not limited to JPEG or TIFF, and other compression methods can be applied. A flash memory control circuit 233 connected to the data bus 261 is connected to a flash memory 235. The flash memory 235 stores a program for controlling the flow of the single-lens reflex camera. The CPU 229 controls the digital single-lens reflex camera according to the program stored in the flash memory 235. Note that the flash memory 235 is an electrically rewritable nonvolatile memory. The SDRAM 237 is connected to the data bus 261 via the SDRAM control circuit 236, and the SDRAM 237 temporarily stores the image data processed by the image processing circuit 227 or the image data compressed by the compression circuit 231. This is a buffer memory.

The input / output circuit 239 connected to the above-described photometric sensor 211, shutter drive mechanism 215, distance measuring circuit 217, and mirror drive mechanism 219 controls input / output of data with each circuit such as the body CPU 229 via the data bus 261. . The communication circuit 241 connected to the lens CPU 111 via the communication contact 300 is connected to the data bus 261, and exchanges data with the body CPU 229 and the like and communicates control commands. A recording medium control circuit 243 connected to the data bus 261 is connected to the recording medium 245 and controls recording of image data and the like on the recording medium 245. The recording medium 245 can be loaded with any rewritable recording medium such as an xD picture card (registered trademark), a compact flash (registered trademark), an SD memory card (registered trademark), or a memory stick (registered trademark). And is detachable from the camera body 200. In addition, the hard disk may be configured to be connectable via a communication contact.

The video signal output circuit 247 connected to the data bus 261 is connected to the liquid crystal monitor 26 via the liquid crystal monitor drive circuit 249. The video signal output circuit 247 is a circuit for converting the image data stored in the SDRAM 237 and the recording medium 245 into a video signal to be displayed on the liquid crystal monitor 26. The liquid crystal monitor 26 is disposed on the back surface of the camera body 200. However, the liquid crystal monitor 26 is not limited to the back surface as long as the photographer can observe the image. A switch for detecting the first and second strokes of the shutter release button, a switch for instructing a playback mode, a switch for instructing an ISO setting mode, a switch for instructing a white balance setting, and instructing the cursor movement on the screen of the liquid crystal monitor 26 Various switches 255 such as a switch for performing shooting, a switch for instructing a photographing mode, an OK switch for determining each selected mode, a switch for instructing switching of a display mode, and the like are connected to the data bus 261 via a switch detection circuit 253. ing.

Next, the outline of the display and operation mode of the camera body 200 will be described with reference to FIG.
The information display M100 is a state when the power switch of the camera body 200 is turned on, and displays basic information for photographing with the camera. The information display M100 is displayed on the liquid crystal monitor 26 as shown in FIG. A screen for displaying information such as the shooting mode, shutter speed, aperture, AF mode, flash, and the number of pixels is displayed. Shooting modes such as a program mode and a shutter speed priority mode are set by rotating the mode dial 22. Items such as sensitivity, shutter speed, aperture value, correction value, and number of pixels are selected by operating the cross key 30 on the information display screen, and numerical values are set by operating the control dial 24.

In the state of the information display M100, when the release button 21 is pressed halfway, the 1R switch is turned on, and the photographing operation AM130 is entered. When the release button 21 is released and the half-press is released, the information display M100 is displayed. Return. In this photographing operation preparation operation M130, a preparatory operation for photographing such as photometry and distance measurement is performed. Thereafter, when the release button 21 is fully pressed, a shooting operation AM 131 is performed. In this photographing operation A, a photoelectric conversion signal of the subject image is taken from the CCD 221, and image processing is performed on the recording medium 245 after image processing by the image processing circuit 227.

Further, when the display mode switching button 34 is operated in the information display mode M100, the through image display mode M300 is set. In this through image display mode, the subject image is displayed on the liquid crystal monitor 26 for observation using the output of the subject image recording CCD 221 as described above. In the through image display mode M300, no particular operation is performed when the release button 21 is half-pressed. However, when the release button 21 is fully pressed, the photographing operation B M330 is executed. In the photographing operation B, the subject image data acquired by the CCD 221 is recorded on the recording medium 245, which will be described in detail later. When the shooting operation B ends, the display returns to the through image display mode.

Next, details of the above-described through image display mode M300 will be described using the flowchart shown in FIG.
When the live view display mode is entered, the subject brightness is measured based on the output of the photometric sensor 211, and the exposure amount is calculated by calculating the shutter speed and / or the aperture value based on the subject brightness obtained here (# 1). Here, the required shutter speed and / or aperture value are determined according to the above-described shooting mode. Thereafter, preparation for obtaining a subject image is made based on the output of the CCD 221. First, the movable mirror 201 is raised (# 3), and the subject luminous flux from the lenses 101 and 102 is guided from the finder optical system to the CCD 221 side. When the raising operation of the movable mirror 201 is completed (# 5), when the raising operation is completed, the process proceeds to step # 7, where the shutter 213 is opened. When the shutter 213 is opened, a subject image is formed on the CCD 221.

Thereafter, in order to set the electronic shutter speed and sensitivity conditions for driving the CCD 221, a through-image condition setting 1 subroutine is executed using the photometry / exposure amount calculation result obtained in step # 1 (S9). . By executing this subroutine, an image with appropriate brightness (brightness) can be displayed on the liquid crystal monitor 26. Details of this subroutine will be described later with reference to FIG. When the through image condition setting 1 is completed, a predetermined time is set (# 13). This is to set the determination time in accordance with the ISO sensitivity, and as shown in FIG. 8, the determination time is shortened as the ISO sensitivity is higher. Since the through image display is now ready, display of the subject image on the liquid crystal monitor 26 is started in step # 13. The through image display operation is controlled by the image processing circuit 227 in response to the start instruction. Subsequently, the timer is started. This is for determining in step # 43, which will be described later, whether the predetermined time set in step # 11 has been reached.

Next, in step # 21, it is determined whether the release button 21 has been fully pressed, that is, whether 2R is on. If it is on, a series of operations for stopping the live view display is performed in steps # 21 to # 29 as a preparatory operation for performing the photographing operation B. First, the power supply to the CCD 221 is stopped, and the live view display on the liquid crystal monitor 26 is stopped (# 21). Subsequently, the shutter 213 is closed (# 25), the movable mirror 201 is lowered, and the subject light flux is switched from the CCD 221 side to the viewfinder optical system side (# 27, # 29). When the completion of the down movement of the movable mirror 201 is detected, the routine proceeds to the routine of the photographing operation B. Details will be described later.

Returning to step # 21, if 2R is off, the process proceeds to step # 31 to determine whether or not the display mode switching button 34 is on. If the result of determination is that the display mode switching button 34 has been operated and is on, a preparatory operation for returning to the information display mode M100 is performed. Steps # 33 to # 39 in this preparation operation are the same as steps # 23 to # 29 described above, and therefore details thereof are omitted. If it is detected in step # 39 that the movable mirror 201 is completely down, the process proceeds to step # 41, where a predetermined time flag is cleared. The predetermined time flag will be described in step # 45. In this step, if the flag is set, it is cleared, and if it is not set, it is left cleared. When the above steps are completed, the information display mode M100 is entered.

Returning to step # 31, if the result of determination is that the display mode switching button 34 is off, processing proceeds to step # 43, where it is determined whether or not a predetermined time has elapsed. This predetermined time is used to determine whether the timer started in step # 15 has reached the predetermined time set in step # 11. If the predetermined time has elapsed, a predetermined time flag is set in step # 45. This predetermined time flag is used in step # 81, which will be described later, to determine whether or not to perform dark imaging for noise removal. After setting the flag for a predetermined time, or when step # 43 is left as No, the process proceeds to step # 47 and proceeds to a subroutine for setting a through image condition 2. This through image condition setting 2 is a subroutine for the purpose of appropriately maintaining the brightness of the through image display on the liquid crystal monitor 26. Since the through image condition setting 1 in step # 9 was before the through image display, it was performed based on the output of the photometric sensor 281. However, in the through image condition setting 2, the target lightness and the screen lightness based on the previous imaging result. Then, the electronic shutter speed and sensitivity at the next imaging are determined from the difference. Here, the brightness is a value corresponding to a weighted average value of each pixel output of the CCD, for example. When the through image condition setting 2 subroutine is completed, the process returns to step # 21 to repeat the above steps.

Next, the flow of the shooting operation B will be described with reference to FIG. This routine is a case where the release button 21 is fully pressed in the through image display mode as described with reference to FIG. 3, and the routine proceeds from the above-mentioned step # 29. When this routine is entered, the same photometry / exposure amount calculation as in step # 1 is performed to determine the shutter speed and aperture value for exposure control. Subsequently, an instruction is output to the lens CPU 111 to perform the aperture operation of the aperture 103 up to the aperture value obtained in step # 51 or the manually set aperture value (# 53). Next, an instruction is given to raise the movable mirror 201 (# 55), and the completion of mirror up is awaited (# 57). When the mirror up is completed, the imaging operation by the CCD 221 is subsequently started (# 59), the shutter 213 is opened, that is, the shutter front curtain is started to travel. As a result, the subject image is incident on the CCD 221 and the CCD 221 starts photoelectric conversion of the subject image. Next, it waits for the time corresponding to the shutter speed obtained in step 51 or the manually set shutter speed to elapse (# 63), and when this set time elapses, the shutter 213 is closed, that is, the trailing curtain travels. Start. Further, the imaging operation of the CCD 221 is also stopped (# 67).

Thereafter, the photoelectric conversion signal stored in the CCD 221 is read out, converted into a digital signal, and noise is removed (# 69). In the noise removal, pixel defect information is stored in advance in the flash memory 235, which is a nonvolatile memory that can be rewritten as existing noise information for each pixel before shipment from the factory, and the noise information is read from the nonvolatile memory and digitized. Correction is performed on the photoelectric conversion signal. The image data from which noise has been removed is stored in the SDRAM 237 serving as a buffer memory (# 71). Thereafter, initialization of mechanical parts such as the diaphragm 103 and the movable mirror 201 (steps # 91 to # 95) and acquisition of dark image signals when further noise removal is necessary (steps # 81 to # 89) Do it in parallel.

First, steps for obtaining a dark image signal will be described. In step # 81, it is determined whether or not a predetermined time flag is set. As described above, it is determined in step # 43 whether the determination time shown in FIG. 8 has elapsed from the start of the live view display (# 13). If it has elapsed, the flag is set in step # 45. Since it is set, in this step, it is determined whether or not the flag is set. If the flag is set, the influence of fixed pattern noise is large, and noise removal based on the existing noise information performed in step # 69 may not be sufficient, so a dark image signal is acquired and fixed. Remove pattern noise.

The dark image signal can be acquired by imaging the CCD 221 in a dark state. Since the shutter 213 is closed in step # 65, imaging is started immediately (# 83). Since the imaging time is the same as the exposure time during bright time, it is performed over the second time set in step # 63 (# 85). When this set time elapses, imaging is stopped (# 87) and noise removal processing is performed. This noise removal processing is performed by first correcting the dark image signal with the existing noise information and subtracting the image signal obtained thereby from the bright image signal. Detailed description is omitted. Thereby, image data from which noise has been removed can be obtained, and the process proceeds to the image processing step of Step # 101. If the predetermined time flag has not been set in step # 81, the process proceeds directly to the next step # 101 without executing steps # 83 to # 89.

Next, steps for initializing the mechanism parts will be described. When the imaging is stopped, the diaphragm 103 remains in the closed state, and therefore, in step # 91, an instruction is output to the lens CPU 111 to open the diaphragm 103. Subsequently, the movable mirror 201 is lowered (# 93), and the completion of the down is waited (# 95). This completes the initialization of the camera mechanical components, and proceeds to the image processing in step # 101.

In the image processing in step # 101, various types of image processing such as color correction, gamma (γ) correction, contrast correction, and monochrome / color mode processing are performed on the image signal from which noise has been removed. When the image processing is completed, display is performed on the liquid crystal monitor 26 for a predetermined period of time based on the image data that has been picked up (# 103), and the display returns to the through image display.

As described above, in this embodiment, the determination time for performing noise removal using the dark image signal is set according to the ISO sensitivity (# 11), and when the through image display is performed beyond this determination time, (# 45, # 81), the dark image signal is acquired (# 83 to # 87), and noise is removed using this (# 89). The reason for changing the determination time according to the ISO sensitivity is that the higher the ISO sensitivity is, the higher the amplification factor of the image signal is. As a result, noise is amplified and becomes more conspicuous. In this embodiment, the determination time is changed according to the ISO sensitivity. However, the determination time is not limited to this, and the determination time may be changed according to a factor that affects the noise of the imaging signal. For example, a temperature sensor such as a temperature sensor may be provided near the CCD 221, and the determination time may be changed according to the temperature, or the determination time may be changed according to a combination of ISO sensitivity and temperature. Furthermore, it is also possible to perform the determination based on whether or not the temperature difference between the start time of the live view display and the current time has become a certain value or more.
In this embodiment, the acquisition of the dark image signal which takes time is performed in parallel while the mechanical parts such as the diaphragm and the movable mirror are initialized. There is not much new shooting time for acquisition.

Next, “through image condition setting 1” and “through image condition setting 2” will be described with reference to FIG. As described above, this subroutine is for adjusting the image brightness when displaying the subject image on the liquid crystal monitor 26. First, when the through image condition setting 1 subroutine is entered, in step S341, the electronic shutter speed TV1 and sensitivity SV1 at the time of next imaging are determined based on the output BVs of the photometric sensor 281. Since the aperture value when displaying a through image is an open aperture value, if this aperture value is AVs,
AVs + TV1 = BVs + SV1
There is a relationship
BVs-AVs = TV1-SV1
It becomes. Since the left side of this equation is a known value, TV1 and SV1 may be obtained from the value on the left side according to a program line or a table as appropriate. Thereafter, the determined electronic shutter speed TV1 and sensitivity SV1 are stored and set in the respective registers (S347). The CCD drive circuit 223 or the CCD drive circuit 283 performs drive control of the CCD 221 or 279 based on the TV1 and SV1 set and stored here, and reads out the photoelectric conversion signal.

Subsequently, in step S349 and subsequent steps, countermeasures are taken when the subject light amount that has passed through the photographing lens 101 decreases. When the amount of light received by the CCD 221 decreases, the electronic shutter speed is reduced and the sensitivity (amplification factor) is increased in order to keep the screen of the liquid crystal monitor 26 at a constant brightness. However, increasing the sensitivity increases the noise, resulting in a rough screen. Therefore, when the amount of subject light received by the CCD 221 is small, the information mode is set to a black and white mode, and when the amount of light is large, the color mode is displayed. In this case, assuming that switching between black and white and color is one threshold value, when the subject light quantity changes before and after this threshold value, the black and white and color change in small increments, making it unsightly. Therefore, a hysteresis characteristic is given to the threshold value for switching between black and white and color.

First, in step S349, it is determined whether or not the current display is in the monochrome mode. Since the color mode and the monochrome mode are set by the image processing circuit 227, the determination here is performed based on the mode set in the image processing circuit 227. If it is determined that the color mode is selected, the process proceeds to step S351 to determine whether TV1−SV1 <α, that is, whether the difference between the electronic shutter speed and the sensitivity is smaller than a predetermined value (threshold value) α. I do. Here, the predetermined value α may be appropriately set as a design value. For example, the lower limit value of the electronic shutter speed TV1 is 1/16 seconds (TV = 4), and the upper limit value of the sensitivity SV1 is ISO1600 (SV = 9). ), The predetermined value α = 4-9 = −5. If it is smaller than the predetermined value α, that is, if the subject light quantity is small and dark, the image processing circuit 227 is set to the monochrome mode (S353), and the original flow is returned to. If TV1-SV1 is greater than the predetermined value α in step S351, the subject light quantity is sufficiently bright and bright, and the process returns to the original flow without changing the color mode setting of the image processing circuit 227.

Returning to step S349, if the current mode is the monochrome mode, the process proceeds to step S355 to determine whether TV1-SV1 <α + Δα. Δα may be appropriately set as a design value, but is preferably a value larger than 0.5 and smaller than 1.5, and more preferably Δα, as a value that makes switching between black and white and color not frequent and easy to view. = 1. If TV1-SV1 is smaller than α + Δα as a result of the determination in step S355, the amount of subject light is small, so the monochrome mode is maintained and the original flow is returned to. On the other hand, when TV1-SV1 is larger than α + Δα, the monochrome mode is canceled (S355), the color mode is set in the image processing circuit 227, and the process returns to the original flow.

Next, “through image condition setting 2” will be described. When the setting 2 subroutine is entered, first, a difference ΔEV between the target image brightness (predetermined value) and the image brightness at the time of previous imaging is calculated (S343). Subsequently, the electronic shutter speed TV1 and sensitivity SV1 at the next imaging are determined so that the image brightness is constant (S345). This decision is based on the following factors:
・ Aperture value AVs
-Electronic shutter speed TV0 at the time of previous imaging
・ Sensitivity SV0 at the time of previous imaging
The difference ΔEV between the target image brightness and the previous image brightness
First, as a basic expression of the exposure condition, AVs + TV0 = BV0 + SV0
It is.

Here, BV0 is the previous luminance, but the true value is not known and is a provisional value in the above basic formula. Since the true luminance value BV0 is different from the target, ie, ΔEV,
BV0 = AVs + TV0−SV0 + ΔEV
= AV1 + TV1-SV1
Thus, TV1 and SV1 are obtained from this relational expression. Here, the difference ΔEV may be obtained from, for example, the difference between the weighted average of the output of each pixel of the image sensor and the target value. When step S345 ends, the process proceeds to step S347 described above, and after executing a predetermined step, the process returns to the original flow.

In this through image condition setting subroutine, when the subject light quantity is small, the monochrome mode is set, so that noise and roughness can be reduced in the monitor image even in the dark. In addition, since a hysteresis characteristic is provided at the time of switching between color and black and white, it is easy to see without switching between black and white and color in small increments. In this embodiment, whether to enter the monochrome mode or whether to cancel the monochrome mode is determined based on the difference between the electronic shutter speed TV1 and the sensitivity SV1, but both are based on the same data. It does not have to be. For example, whether to enter the monochrome mode may be determined by the TV-SV value, and the release may be determined based on the SV value. When entering the monochrome mode, only the TV value may be determined, and the cancellation may be based on the SV value. Also good.

In the present embodiment, the color mode and the black and white mode are switched. However, the present invention is not limited to this, and it is needless to say that the display mode may be a sepia tone instead of the black and white mode. Further, the saturation in the color mode may be changed instead of the single color mode. For example, when 8 bits are used to represent the color and the subject brightness is low, flickering of the through image display can be reduced even if the saturation is lowered, such as reducing to 4 bits to represent the color. .

In the present embodiment, the first position (up position) for retracting the object light beam to the CCD 221 as the image sensor by retracting outside the image capturing optical path and the second position (for guiding the object light beam to the finder optical system in the image capturing optical path). A movable mirror 201 that can be moved to a down position), an imaging unit that moves the movable mirror 201 to a first position and acquires a subject image by an imaging device, and subject image data output from the imaging unit. Through image display means for continuously displaying on a liquid crystal monitor 26 as a display device, and subject image data output from the imaging means in response to an operation of the release button 21 during the through image display by the through image display means. It is provided with a still image acquisition means for acquiring image data, and it is predicted that fixed pattern noise is superimposed on the subject image data output from the imaging means during through image display. However, when it is predicted that the fixed pattern is superimposed on the subject image data (steps 43 and # 45), the dark image data of the image sensor is acquired when the subsequent still image is acquired (# 59 to # 67). (# 83, # 87), noise removal operation is performed on the subject image data acquired by the still image acquisition means based on the dark image data (# 89), so that the noise reduction function is operated efficiently. This shortens the time required for shooting as a whole. In other words, the noise reduction function is operated when it is predicted that the influence of noise is large, and the time required for average photographing can be shortened. As a method for predicting that the influence of noise is large, there are various methods such as the value of the ambient temperature itself and a change in temperature in addition to the ISO sensitivity as in this embodiment.

Further, in the present embodiment, when the through image display is continued for a predetermined time or more, it is predicted that the fixed pattern noise is superimposed on the subject image data, so that it is possible to accurately predict with a simple configuration. it can. That is, if the through image display becomes longer, the temperature of the image pickup device itself gradually increases and noise increases, and the prediction accuracy is increased.
Furthermore, in the present embodiment, the predetermined time changes according to the ISO sensitivity, so that the accuracy can be further improved. That is, the higher the ISO sensitivity, the higher the amplification factor and the more noticeable noise is, so that the prediction accuracy is increased.
Further, since the noise removal is performed during the reset operation of the mechanism member after the subject image data is obtained by the still image obtaining means, the time is not newly extended for noise removal.

In this embodiment, an example in which a single-lens reflex camera is applied as a digital camera has been described. However, the present invention is not limited to a digital single-lens reflex camera, and can be applied to a digital camera such as a compact camera. Of course, the present invention can also be applied to a digital camera provided on a telephone. In any case, a digital camera or an electronic imaging device that displays an object image on a monitor for observation using the output of the recording imaging element may be used.

1 is a block diagram illustrating an overall configuration of a digital single-lens reflex camera according to an embodiment to which the present invention is applied. It is the external appearance perspective view which looked at the digital single-lens reflex camera in one Embodiment of this invention from the back. It is a block diagram which shows the display mode and operation mode in one Embodiment of this invention. It is a flowchart which shows the operation | movement of the through image display mode in one Embodiment of this invention. It is a flowchart which shows the operation | movement of the imaging operation B in one Embodiment of this invention. 6 is a flowchart of through image condition setting 1 and through image condition setting 2 in an embodiment of the present invention. An information display screen in a liquid crystal monitor in one embodiment of the present invention is shown. It is a figure which shows the relationship between ISO sensitivity and determination time in one Embodiment of this invention.

Explanation of symbols

21 Release button 22 Mode dial 24 Control dial 26 LCD monitor 27 Playback button 28 Menu button 30 Cross button 31 OK button 34 Display mode switching button 37 White balance button 38 ISO sensitivity button 40 Recording medium storage cover 100 Interchangeable lens 101 102 Lens 103 Aperture 201 Movable mirror 211 Photometric sensor 213 Shutter 219 Mirror drive mechanism 221 CCD
227 Image Processing Circuit 229 Sequence Controller (Body CPU)
243 Recording medium control circuit

Claims (7)

Mirror means movable to a first position for retracting out of the photographing optical path to guide the subject luminous flux to the image sensor and a second position for guiding the subject luminous flux to the finder optical system in the photographing optical path;
Imaging means for moving the mirror means to the first position and acquiring a subject image with the imaging element;
Through image display means for continuously displaying the subject image data output from the imaging means on the display device;
Still image acquisition means for acquiring subject image data output from the imaging means as still image data in response to a release operation during through image display by the through image display means;
Prediction means for predicting that fixed pattern noise is superimposed on subject image data output from the imaging means during the through image display;
When the prediction unit predicts that the fixed pattern is superimposed on the subject image data, dark image data of the imaging element is acquired at the time of subsequent acquisition of the still image, and the dark image data is acquired based on the dark image data. Noise removal means for performing noise removal operation of the subject image data acquired by the still image acquisition means;
A digital single-lens reflex camera characterized by comprising:   The digital single-lens reflex camera according to claim 1, wherein the prediction unit predicts that the fixed pattern noise is superimposed on the subject image data when the through image display is continued for a predetermined time or more. camera.   3. The digital single-lens reflex camera according to claim 2, wherein the predetermined time changes according to ISO sensitivity.   The digital single-lens reflex camera according to claim 1, wherein the noise removing unit acquires the dark image data after the subject image data is acquired by the still image acquiring unit.   The digital single-lens reflex camera according to claim 4, wherein the noise removing unit operates during a reset operation of the mechanism member after the subject image data is acquired by the still image acquiring unit.   5. The digital single lens reflex camera according to claim 4, wherein the noise removing unit acquires the dark image data in parallel with the mirror unit moving from the first position to the second position. camera. An image sensor that receives and photoelectrically converts a subject image;
Through image display means for continuously displaying subject image data output from the image sensor on a display device;
Still image acquisition means for acquiring subject image data output from the imaging means as still image data in response to a release operation during through image display by the through image display means;
Prediction means for predicting that fixed pattern noise is superimposed on subject image data output from the imaging means during the through image display;
When the prediction unit predicts that the fixed pattern is superimposed on the subject image data, dark image data of the imaging element is acquired at the time of subsequent acquisition of the still image, and the dark image data is acquired based on the dark image data. Noise removal means for performing noise removal operation of the subject image data acquired by the still image acquisition means;
A digital camera comprising: