JP2004096328A - Electronic camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electronic camera capable of reducing a CCD (charged coupled device) noise in the case of a long time photographing. <P>SOLUTION: A temperature sensor 442 senses the temperature within a prescribed area including a CCD 214, and when the temperature sensed by the temperature sensor 442 is a prescribed temperature or higher, a backlight 441 is turned off and a liquid crystal display device 3 is turned off. Thus, the generated heat of the backlight 441 and the generated heat of a battery supplying power to the backlight 441 can be suppressed. As a result, the temperature of the CCD 214 is reduced to decrease the CCD noise. As a noise reduction method, there are methods of decreasing the aperture to reduce the shutter time and of decreasing a gain of the CCD 214 or the like in addition to turning off of the backlight 441, and the combination of the methods may be applicable. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electronic camera that captures a subject image using an image sensor.
[0002]
[Prior art]
In general, a CCD (Charged Coupled Device) is used as an image sensor of an electronic camera. The CCD is one of photoelectric conversion devices that converts the intensity of light of an irradiated optical image into an electric signal corresponding to the intensity. The image signal output from the CCD is converted into a digital signal, subjected to image processing, and recorded on a recording medium (for example, a memory card) provided in the camera.
[0003]
[Problems to be solved by the invention]
By the way, in night scene photography, astronomical photography, or the like with low subject brightness, long long-time shooting with a shutter time is performed so that a sufficient exposure amount can be obtained. However, there is a problem that CCD noise is accumulated in such long-time shooting, and image quality deterioration due to the noise becomes conspicuous. CCD noise includes, for example, noise due to dark current. This noise is caused by generation of hole-electron pairs due to thermal excitation, and has a strong temperature dependence. Many electronic cameras are equipped with a liquid crystal monitor for displaying images, and when the temperature inside the camera rises due to heat generation of a backlight or a battery, the influence of noise becomes remarkable.
[0004]
An object of the present invention is to provide an electronic camera that can reduce CCD noise during long-time shooting.
[0005]
[Means for Solving the Problems]
A description will be given with reference to FIG. 1 showing an embodiment of the invention.
(1) An electronic camera according to the first aspect of the present invention is configured to reduce noise of an image sensor 214 that captures a subject image and outputs an image signal, and that reduces noise of the image sensor 214 when a shutter time is equal to or longer than a predetermined time. A control circuit 439 for controlling at least one of the camera components 453, 454, 3 is provided to achieve the above object.
(2) According to a second aspect of the present invention, in the electronic camera according to the first aspect, the camera component is a display monitor 3 that displays a captured image, and detects a temperature in a predetermined area including the image sensor 214. A temperature sensor 442 is provided, and the display monitor 3 is turned off when the temperature detected by the temperature sensor 442 is equal to or higher than a predetermined temperature.
(3) Explaining in association with FIG. 7, the third aspect is the electronic camera according to the second aspect, wherein the predetermined temperature T0 is changed according to the shutter time t.
(4) In the electronic camera according to the first aspect, the temperature sensor 442 for detecting a temperature in a predetermined area including the imaging element 214, the setting unit 439 for setting an exposure amount, and the temperature sensor When the temperature detected at 442 is equal to or higher than a predetermined temperature, an exposure control means 439 for reducing the aperture value and shortening the shutter time without changing the exposure amount set by the setting means 439 is provided. is there.
(5) The electronic camera according to claim 1, further comprising a temperature sensor 442 for detecting a temperature in a predetermined area including the imaging element 214, wherein the temperature detected by the temperature sensor 442 is a predetermined temperature. At this time, the gain of the image sensor 214 is reduced and the aperture is increased.
[0006]
In the meantime, in the section of the means for solving the problems described above, the drawings of the embodiments of the present invention are used to make the present invention easy to understand, but this does not limit the present invention to the embodiments of the present invention. Absent.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described below with reference to FIGS. 1A and 1B are views showing an embodiment of an electronic camera according to the present invention, wherein FIG. 1A is a plan view of the electronic camera as viewed from above, and FIG. 1B is a rear view of the camera as viewed from behind. As shown in FIG. 1A, on a top surface of the electronic camera 1, a main switch 4 for turning on / off a power, a release button 5, and a command dial 6 for switching between a recording mode and a reproduction mode are provided. And a display panel 7 for displaying camera information. Here, the recording mode is a mode in which a subject image can be photographed and its image data can be recorded, and the reproduction mode is a mode in which the recorded image data is read out and the liquid crystal display 3 (FIG. b)) is a mode for reproducing and displaying.
[0008]
As shown in FIG. 1B, in addition to a liquid crystal display 3 for displaying an image, a finder eyepiece window 8, a zoom switching button 9 for performing a zoom operation on the photographing optical system 2, and various operations on the rear of the camera. Buttons are provided. When the zoom switch button 9 is pressed on the W side, the photographing optical system 2 is driven toward the wide angle side, and when the T side is pressed, the photographing optical system 2 is driven toward the telephoto side. In the recording mode, a subject image picked up by a CCD 214 described later is sequentially displayed on the liquid crystal display 3, and in the reproduction mode, a thumbnail display of images stored in a recording medium 424 described later and a reproduction display of individual images are performed. Is performed by
[0009]
Reference numeral 10 denotes a menu button for displaying a setting menu on the liquid crystal display 3. When performing various settings, a setting menu is displayed, and items to be set are selected by the selection buttons 11a to 11d. For example, the electronic camera 1 is provided with a plurality of shooting modes capable of performing optimum shooting according to the shooting scene. When a shooting mode menu is displayed on the liquid crystal display 3, the shooting modes such as a night view mode, a portrait mode, and a landscape mode are displayed. The type is displayed. The exposure mode is set in the same manner. Reference numeral 12 denotes a monitor on / off button for turning on / off the display of the liquid crystal display 3. Reference numeral 13 denotes a flash mode button for performing settings relating to the flash device, for example, settings such as forced light emission and light emission inhibition.
[0010]
FIG. 2 is a circuit block diagram of the electronic camera shown in FIG. 1. When the main switch 4 is turned on, the power of the electronic camera 1 is turned on, and the control program stored in the ROM 443 is started by the CPU 439. When the recording mode is set by the command dial 6, the electronic camera 1 can take a picture. On the other hand, when the reproduction mode is set, an image based on the image data recorded on the memory card 424 is reproduced and displayed on the display LCD 447. Can be. In the recording mode, an image based on the image pickup signal from the CCD 214 is displayed on the liquid crystal display 3 in FIG. Reference numeral 441 denotes a backlight for illuminating the LCD. The liquid crystal display 3 in FIG. 1 includes an LCD 447 and a backlight 441.
[0011]
The photographing optical system 2 has a plurality of lenses 201 to 204, and a shutter plate 208 and a stop 215 are provided between the lenses 203 and 204. The subject light that has entered the photographing optical system 2 passes through the lenses 201 to 204, the shutter plate 208, and the aperture plate 215 and forms an image on the imaging surface of the CCD 214. The aperture plate 215 and the shutter plate 208 are formed in a disk shape, and are driven by step motors 408 and 415 provided at the center of rotation of the disk. The diaphragm plate 215 is provided with a plurality of diaphragm openings having different opening areas. The diaphragm plate 215 is rotated by a step motor 415, and one arbitrary diaphragm opening is disposed on the optical axis.
[0012]
The shutter plate 208 is provided with a complete light blocking portion for blocking all the light beams passing through the lens 203 and an opening for passing all the light beams. During exposure, the opening of the shutter plate 208 is set on the optical path. At the end of the exposure, the complete light shielding portion is set on the optical path. Reference numeral 453 denotes an aperture drive circuit for controlling the drive of the step motor 415, and reference numeral 454 denotes a shutter drive circuit for controlling the drive of the step motor 408. At the time of photographing, first, the electric charge accumulated in the CCD 214 is discharged, and a predetermined opening of the aperture plate 215 is set on the optical path. When the CCD 214 is exposed for a predetermined time, charges are accumulated again. The time from the discharge of the charges until the light path is shielded by the complete light blocking portion of the shutter plate 208 corresponds to the exposure time.
[0013]
The focus adjustment operation of the photographing optical system 2 is performed by the lens drive circuit 430. The focus adjustment operation by the lens drive circuit 430 is normally performed by a command from the CPU 439, but the focus adjustment operation can also be performed by an operation signal output when the distance ring 462 is manually operated.
[0014]
When a subject image is formed on the imaging surface of the CCD 214, signal charges corresponding to the intensity of light of the subject image are accumulated. The CCD 214 is supplied with a horizontal drive signal from a digital signal processor (hereinafter referred to as DSP) 433 and a vertical drive signal from a CCD drive circuit 434 controlled by the DSP 433. That is, the timing of the CCD 214 is controlled by the DSP 433 and the CCD drive circuit 434, and a signal from the CCD 214 is input to the image processing unit 431.
[0015]
The image processing unit 431 has a noise removal circuit, a DC reproduction circuit, and the like. The image processing unit 431 performs analog processing such as noise removal and gain control on an image signal output from the CCD 214, and then performs an analog / digital conversion circuit (hereinafter, referred to as an analog / digital conversion circuit). , A / D conversion circuit) 432. The A / D conversion circuit 432 converts the image signal output from the image processing unit 431 into a digital signal, and outputs the converted image data to the DSP 433 described above.
[0016]
The DSP 433 performs image processing such as contour compensation, gamma correction, and white balance adjustment on the image data output from the A / D conversion circuit 432. Also, the DSP 433 controls the data bus connected to the buffer memory 436 and the memory card 424 to temporarily store the image data subjected to various image processing in the buffer memory 436, and then to transfer the image data from the buffer memory 436. The data is read, data is compressed in a predetermined compression format (for example, JPEG system), and is recorded on the memory card 424.
[0017]
The DSP 433 stores the image data captured by the CCD 214 and subjected to the above-described image processing and the image data read and expanded from the memory card 424 in the frame memory 435, and converts the image based on the image data into an electronic image. The image is displayed on a display LCD 447 provided in the camera 1. Further, the DSP 433 also manages data input / output timing in recording the above-described image data on the memory card 424 and recording the decompressed photographed image data on the buffer memory 436.
[0018]
A buffer memory 436 in which image data based on the output of the CCD 214 is temporarily stored is used to reduce a difference in input / output speed of image data with respect to the memory card 424 and a difference in processing speed between the CPU 439 and the DSP 433. You. The timer 445 has a built-in clock circuit, outputs time data corresponding to the current time to the CPU 439, and is used as a timer for monitor on / off control described later. This time data is recorded on the memory card 424 together with the image data described above.
[0019]
The colorimetric element 417 detects the color temperature of the main subject and its surroundings, and outputs data of the detected color temperature to the colorimetric circuit 452. The colorimetric circuit 452 performs predetermined processing on the analog signal output from the colorimetric element 417 to convert the analog signal into a digital value, and outputs the converted digital signal to the CPU 439. The interface 448 is provided so as to connect a predetermined external device (not shown) and transmit and receive data between the CPU 439 and the connected external device. Reference numeral 440 denotes a display circuit that controls the display panel 7 on which setting contents in the photographing operation are displayed. Reference numeral 442 denotes a temperature sensor for detecting the temperature of the CCD or its surroundings, for example, a thermistor.
[0020]
《Recording mode》
Next, the operation in the recording mode will be described. When shooting with an electronic camera, the command dial 6 is set to the recording mode and the main switch 4 is turned on, or the command dial 6 is set to the recording mode after the main switch 4 is turned on. The image signal output from the CCD 214 is subjected to analog processing such as noise removal and gain control by an image processing unit 431, and then converted to a digital signal by an A / D conversion circuit 432. The digitally converted signal is guided to the above-described DSP 433, where image pre-processing such as contour compensation and gamma correction is performed and temporarily stored in the buffer memory 436.
[0021]
Thereafter, image data is exchanged between the CPU 439 and the buffer memory 436 to obtain a white balance adjustment value from the image data, and the DSP 433 performs white balance adjustment based on the adjustment value. The image data after the white balance adjustment is stored in the buffer memory 436 again. The image data stored in the buffer memory 436 is processed by the DSP 433 into image data to be displayed on the display LCD 447. The processed image data is written into the frame memory 435 and displayed on the display LCD 447 as a photographed monitor image called a through image. This through image is sequentially updated at predetermined intervals based on subject light incident on the imaging optical system 2 by repeating the above operation.
[0022]
When a half-press switch (not shown) is turned on by half-pressing the release button 5, the focus adjustment state of the photographing optical system 2 is detected based on the contrast of the image data, and an in-focus subject image is formed on the CCD 214. A focus adjustment operation by the lens drive circuit 430 is performed so that an image is formed. When the release button 5 is half-pressed, the CPU 439 detects the brightness of the subject from the image data, and performs an exposure calculation based on the detected brightness.
[0023]
When the release button 5 is fully pressed after the release button 5 is half-pressed, a full-press switch (not shown) is turned on. As a result, after the signal charges accumulated in the CCD 214 are once discharged, the shutter plate 208 and the diaphragm plate 215 are driven based on the result of the exposure calculation, and the CCD 214 performs imaging. At the time of this photographing, the flash device 446 may emit light depending on the result of the exposure calculation and the setting by the flash mode button 13 (FIG. 1).
[0024]
The image signal output from the CCD 214 by this imaging is subjected to the series of processes described above and stored in the buffer memory 436. The image data stored in the buffer memory 436 is processed by the DSP 433 into image data to be displayed on the display LCD 447, and then written into the frame memory 435, and a captured image called a freeze image is displayed on the display LCD 447. The image data that has been subjected to such image preprocessing is further subjected to data compression by the DSP 433, is given a predetermined data name by the CPU 439, and is provided with time information from the timer 445 and a recording medium such as a flash memory (PC card). , Compact flash (registered trademark) card, etc. 424.
[0025]
《CCD noise reduction method for long-time shooting》
Next, a method of reducing CCD noise during long-time shooting will be described. It is known that this noise greatly increases as the temperature of the CCD 214 increases. In the present embodiment, the noise is reduced when the temperature inside the camera detected by the temperature sensor 442 becomes higher than a predetermined temperature T0, for example, 50 ° C. or more. Function works.
[0026]
FIG. 3 is a flowchart showing the procedure of the noise reduction process. When the recording mode is set by the command dial 6, the process starts. In step S1, it is determined whether or not the mode is the recording mode. If the determination is YES, the process proceeds to step S2. If the mode is switched to the reproduction mode and the determination is NO, the process in FIG. 3 ends. In step S2, it is determined whether or not the shooting mode is set to the night scene mode. If the determination is YES, the process proceeds to step S13. If the determination is NO, the process proceeds to step S3.
[0027]
When the process proceeds from step S2 to step S13, the aperture value is reduced and the shutter speed is reduced while maintaining the exposure value with respect to the aperture value and the shutter speed set as the night scene mode. When the process in step S13 ends, the process proceeds to step S7.
[0028]
On the other hand, when the process proceeds from step S2 to step S3, in step S3, the brightness of the subject is calculated based on the image signal output from the CCD 214, and the optimum exposure value is calculated based on the brightness. In step S4, an aperture value and a shutter speed are calculated based on the optimum exposure value calculated in step S3. For example, when the exposure mode is the program AE mode, the aperture value and the shutter speed are determined based on the program diagram L1 as shown in FIG. In the example shown in FIG. 4, the aperture value fa1 and the shutter speed ts1 at the intersection P1 of the straight line L2 and L1 representing EV value = E0 are set.
[0029]
In step S5, it is determined whether or not the shutter speed ts1 is equal to or longer than a predetermined time t0. If the determination is YES, the process proceeds to step S6, and if the determination is NO, the process proceeds to step S14. Here, the time t0 is a reference time for determining whether or not the shooting is the long-time shooting, and is set, for example, as t0 = 1 (sec). If it is determined in step S5 that long-time shooting is to be performed and the process proceeds to step S6, a program diagram used to determine an aperture value and a shutter speed is applied to normal time shooting from long-time setting L1 shown in FIG. Change the setting to L3. On the other hand, when the process proceeds from step S5 to step S14, after the setting of the program diagram is reset to L1 in step S14, the backlight 441 is turned on in step S15, and the process proceeds to step S9.
[0030]
As shown in FIG. 4, the straight line L2 of the EV value E0 and the program diagram L3 intersect at P2, and in this case, the aperture value fa2 and the shutter speed ts2 are set. Comparing this with the case of the program diagram L1, the aperture value is set smaller than fa2> fa1, and the shutter speed is set shorter such as ts1> ts2. As a result, when photographing is performed using L3, the charge accumulation time of the CCD 214 is shortened, and noise is reduced. The program diagrams L1 and L3 are stored in the ROM 443 in advance.
[0031]
In step S7, it is determined whether or not the temperature T detected by the temperature sensor 442 is equal to or higher than a predetermined temperature T0. If the determination is YES, the process proceeds to step S8, where the backlight 441 of the display LCD 447 is turned off, and the determination is NO. Then, the process proceeds to step S15 to turn on the backlight 441. Here, the temperature T0 is a temperature at which noise of the CCD 214 is noticeable, and is set in advance such as, for example, T0 = 50 ° C. and stored in the ROM 443. That is, when the temperature inside the camera detected by the temperature sensor 442 rises and becomes T0 or more, the backlight 441 is turned off, so that the heat generation of the backlight 441 is eliminated and the battery (supplying power to the backlight 441 ( Power consumption (not shown) is reduced, and battery heat generation is also reduced. As a result, an increase in the temperature inside the camera is prevented, and an increase in noise can be prevented.
[0032]
Steps S9 to S12 show the procedure of the photographing process. In step S9, it is determined whether or not the release button 5 is half-pressed. When YES is determined in step S9, the process proceeds to step S10, and when NO is determined, the process returns to step S2. In step S10, a photographing preparation operation such as a focus adjustment operation of the photographing optical system 2 and a setting of an aperture value and a shutter speed based on the optimum exposure value is performed. The setting of the aperture value and the shutter speed here is the setting in step S13 in the case of the night view mode, and in the case of the program AE, the program diagram L3 in step S6 or the program diagram L1 in step S14 is used. Is set.
[0033]
Next, in step S11, it is determined whether or not the release button 5 has been fully pressed. If the determination is YES, the process proceeds to step S12, and if the determination is NO, the process returns to step S9. When the process proceeds from step S11 to step S13, the process returns to step S2 after performing the photographing operation in step S13.
[0034]
In the processing shown in the flowchart of FIG. 3, as a first step of the noise reduction measure, when the shutter time is longer than a predetermined time t0, the aperture is opened and the shutter speed is reduced, and the charge of the CCD 214 is reduced. Noise is reduced by shortening the accumulation time. When the internal temperature of the camera becomes higher than the predetermined temperature and the noise increase due to the temperature rise cannot be suppressed only by the measures in the first stage, the backlight 441 is turned off in the second stage, and the heat of the backlight 441 is generated. Further, the heat generation of the battery is suppressed to prevent an increase in noise.
[0035]
As a countermeasure for the first stage described above, besides reducing the shutter speed, the gain of the CCD 214, that is, the sensitivity may be reduced to lower the noise level. In addition, steps S3 to S6, steps S13, and S14 in FIG. 3 may be omitted, that is, the first step of reducing the shutter speed may be omitted, and only the backlight turning off in the second step may be performed.
[0036]
Furthermore, the backlight 441 may be always turned off in the night view mode, and the backlight 441 may be turned on for a predetermined time when a monitor-on operation, a zoom operation, or a half-press operation is performed. FIG. 5 and FIG. 6 are flowcharts showing an example of such a processing operation. Note that in the flowcharts shown in FIGS. 5 and 6, steps that perform the same processing as the steps in FIG. 3 are denoted by the same reference numerals, and the following description will focus on those parts that differ from FIG.
[0037]
In the flowchart of FIG. 5, when it is determined in step S2 that the mode is the night scene mode and the process proceeds to step S13, the process proceeds to step S20 when the process of step S13 is completed. In step S20, it is determined whether an operation such as monitor on or zooming has been performed. If YES is determined, the process proceeds to step S21, where the backlight 441 is turned off and the timer 445 is started. On the other hand, if NO is determined in the step S20, the process skips the step S21 and proceeds to the step S9 in FIG.
[0038]
If it is determined in step S9 that the release button 5 has been half-pressed, the process proceeds to step S22, in which the backlight 441 is turned on, and a shooting preparation operation is performed in step S10. On the other hand, if it is determined in step S9 that the button has not been half-pressed, the process proceeds to step S23. In step S23, it is determined whether the time of timer 445 has expired. If YES is determined in the step S23, the process proceeds to the step S24 to turn off the backlight 441, and returns to the step S2 in FIG. 5. If NO is determined, the step S24 is skipped and returns to the step S2.
[0039]
In the above-described embodiment, the temperature T0 is a constant temperature. However, as shown in FIG. 7, the temperature T0 may be changed according to the photographing time. With this control, the monitor-off control is performed before the temperature in the camera rises extremely, so that the temperature rise of the CCD 214 is suppressed and the noise reduction effect can be improved. Further, a temperature detecting sensor may be provided in the driving portion of the photographing optical 2 in some cases. However, instead of providing the temperature sensor 442, the temperature sensor of the driving portion may also be used. Further, instead of detecting the temperature in the camera with the temperature sensor 442, a table indicating the relationship between the backlight lighting time and the camera temperature may be stored in the ROM 443, and the temperature may be obtained from the backlight lighting time. .
[0040]
In the correspondence between the embodiment described above and the elements described in the claims, the CCD 214 is an image sensor, the aperture driving circuit 453, the shutter driving circuit 454 and the liquid crystal display 3 are camera components, and the CPU 439 is a control circuit and setting means. And exposure control means.
[0041]
【The invention's effect】
As described above, according to the present invention, when the shutter time is equal to or longer than the predetermined time, the aperture value, the shutter time, and the display monitor are controlled so that the noise of the image sensor is reduced, and the long time is used. Noise can be reduced even in shooting.
According to the second aspect of the present invention, the display monitor is turned off when the temperature detected by the temperature sensor is equal to or higher than the predetermined temperature, and the temperature of the image sensor is suppressed from rising, thereby reducing noise. At this time, the temperature rise suppression effect can be improved by changing the predetermined temperature according to the shutter time as in the third aspect of the invention.
Further, when the detected temperature is equal to or higher than the predetermined temperature, noise is reduced by shortening the shutter time in the invention of claim 4, and noise is reduced by lowering the gain of the image sensor in the invention of claim 5. Can be
[Brief description of the drawings]
FIG. 1 is a view showing an embodiment of an electronic camera according to the present invention, wherein (a) is a plan view of the electronic camera and (b) is a rear view.
FIG. 2 is a circuit block diagram of the electronic camera shown in FIG.
FIG. 3 is a flowchart illustrating a procedure of a noise reduction process.
FIG. 4 is a diagram showing a program diagram.
FIG. 5 is a flowchart illustrating another example of the noise reduction processing.
FIG. 6 is a flowchart showing a series of processes following the process shown in FIG.
FIG. 7 is a diagram illustrating a relationship between a shooting time and a temperature T0.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 electronic camera 2 shooting optical system 3 liquid crystal display 4 main switch 5 release button 6 command dial 9 zoom switch button 10 menu button 12 monitor on / off button 208 shutter plate 214 CCD
215 aperture plate 439 CPU
441 LCD backlight 442 Temperature sensor 447 Display LCD

Claims (5)

An image sensor that captures a subject image and outputs an image signal;
An electronic camera, comprising: a control circuit for controlling at least one of camera components so as to reduce noise of the image sensor when a shutter time is equal to or longer than a predetermined time. The electronic camera according to claim 1,
The camera component is a display monitor that displays a captured image, and includes a temperature sensor that detects a temperature in a predetermined area including the image sensor, when the temperature detected by the temperature sensor is equal to or higher than a predetermined temperature. An electronic camera, wherein the display monitor is turned off. The electronic camera according to claim 2,
An electronic camera, wherein the predetermined temperature is changed according to the shutter time. The electronic camera according to claim 1,
A temperature sensor for detecting a temperature in a predetermined area including the image sensor,
Setting means for setting an exposure amount;
When the temperature detected by the temperature sensor is equal to or higher than a predetermined temperature, an exposure control unit that reduces an aperture value and shortens a shutter time without changing an exposure amount set by the setting unit. Electronic camera featuring. The electronic camera according to claim 1,
A temperature sensor for detecting a temperature in a predetermined region including the image sensor, wherein when the temperature detected by the temperature sensor is equal to or higher than a predetermined temperature, the gain of the image sensor is reduced and the aperture is increased. Electronic camera.

Images