JP2005086488A - Electronic still camera and image processing program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electronic still camera for suppressing noise in photographing by defining night view as a background. <P>SOLUTION: A CPU 18 continuously performs flash photographing and flash-off photographing in response to one time photographing start instruction. In the case of the flash photographing, the CPU 18 sets the lower most imaging sensitivity for properly exposing a person being a main subject to light. The influence of noise is suppressed as far as possible by setting the lower most imaging sensitivity. In the case of flash-off photographing, the CPU 18 sets the photographing sensitivity to be raised to be around ISO 400 so as to properly expose the night view to be the background to the light by an exposure time (e.g., 1/4 second) in which camera shake does not become a problem. The camera shake is reduced in the case of night view exposure, and also, noise to be superimposed on the person 11 being the main subject is made to be inconspicuous. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electronic still camera and a program for processing an electronic image.

  In an imaging device composed of a CCD image sensor or the like, when the number of pixels is increased within a limited device size, the light receiving area per pixel is reduced. For this reason, when the amount of light collected by each pixel is reduced, the imaging sensitivity is reduced as compared with an imaging element having a large element size. Assume a case where an electronic camera equipped with such an image sensor performs slow sync shooting with a night view as a background. If the flash device is caused to emit light during shooting, the main subject corresponding to the near view where illumination light from the flash device is likely to reach is shot with appropriate exposure. A long exposure time is required to obtain a proper exposure in a background where illumination light is difficult to reach. The exposure time needs to be longer as the sensitivity of the image sensor is lower, but a long exposure time tends to cause camera shake. When the imaging sensitivity is increased in order to shorten the exposure time, there is a problem that noise is easily superimposed on the captured image.

  Japanese Patent Application Laid-Open No. 2004-228561 describes a technique for performing shooting with the flash device and shooting without the flash device, detecting the correlation between both captured images, and correcting the captured image based on the detected correlation. .

JP 2000-102022 A

  Even if the captured image is corrected using an image shot with the flash device and an image shot without the flash device being emitted, the noise of the image before correction will not disappear.

The electronic still camera according to the present invention sets the imaging sensitivity at the time of shooting using the imaging means for imaging the subject image and the flash device for illuminating the main subject to the lowest first imaging sensitivity within a predetermined range, and the flash. Sensitivity control means for setting the imaging sensitivity at the time of shooting without using the device to the second imaging sensitivity for properly exposing the night view with a predetermined exposure time, and shooting and flashing device using the flash device in response to a single shooting instruction It is characterized by comprising imaging control means for controlling the imaging means and the sensitivity control means so as to continuously perform imaging without using the camera.
The electronic still camera may further include a distance measuring unit that detects a distance to the main subject, and a calculation unit that performs an exposure calculation using a distance measured by the distance measuring unit and a guide number of the flash device. The sensitivity control means in this case can be calculated by the calculation means, and the minimum imaging sensitivity required to make the main subject have proper exposure can be set as the first imaging sensitivity.
The electronic still camera may further include focus adjusting means for adjusting the focus of the photographing lens. In this case, the photographing control means associates the focus position at the time of photographing using the flash device with the main subject, and associates the focus position at the time of photographing without using the flash device with either the main subject or infinity. Further, the focus adjusting means can be further controlled.
The predetermined exposure time may be a camera shake limit exposure time.
The image processing program according to the present invention includes the first image data photographed using the flash device by the imaging means set to the lowest first imaging sensitivity within a predetermined range, and the exposure time of the camera shake limit. A computer that synthesizes the data of the second image captured without using the flash device by the imaging means set to the second imaging sensitivity for appropriately exposing the night view so as to add the corresponding pixel data. It is executed by an apparatus.
An electronic still camera according to the present invention includes: an imaging unit that captures a subject image; and a sensitivity control unit that sets an imaging sensitivity at the time of shooting using a flash device that illuminates a main subject to a minimum value within a predetermined range. Features.

With the electronic still camera according to the present invention, it is possible to obtain a high-quality image by suppressing noise in a captured image against a night scene.
With the image processing program according to the present invention, it is possible to obtain a high-quality image against a night scene.

The best mode for carrying out the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram of an electronic still camera according to an embodiment of the present invention. The CPU 18 that controls the electronic still camera inputs a signal output from each block to be described later, performs a predetermined calculation, and outputs a control signal to each block based on the calculation result. The image sensor 10 is configured by a CCD image sensor or the like. The image sensor 10 captures an image of subject light that has passed through a photographing lens (not shown), and outputs an image signal to the analog signal processing circuit 11. The image sensor 10 is driven at a predetermined operation timing by a drive signal from the driver 16. The driver 16 is driven by a timing signal generated by the timing generator 17.

  The analog signal processing circuit 11 performs analog processing such as gain control and noise removal on the analog imaging signal, and outputs the signal after analog processing to the A / D conversion circuit 12. The A / D conversion circuit 12 converts the analog imaging signal into a digital signal. The operation timing of the analog signal processing circuit 11 and the A / D conversion circuit 12 is controlled by the timing signal generated by the timing generator 17.

  The electronic still camera is configured so that the imaging sensitivity can be changed within a predetermined range. The imaging sensitivity refers to a sensitivity for detecting signal charges accumulated in each pixel of the image sensor 10 or a controlled amount that changes a gain of an amplifier circuit in the analog signal processing circuit 11. The imaging sensitivity is indicated by a corresponding ISO sensitivity value.

  An image processing circuit 13 composed of an ASIC or the like performs predetermined image processing on the signal after digital conversion. The image processing includes contour compensation processing, gamma correction processing, and white balance (WB) adjustment processing. The buffer memory 19 temporarily stores image data before the signal processing by the image processing circuit 13 and image data after the signal processing. The compression circuit 14 performs a compression process for compressing the image data stored in the buffer memory 19 in a format such as JPEG, and a decompression process for decompressing the data after the compression process. The image data that has been subjected to compression processing and decompression processing is also stored in the buffer memory 19.

  The display image creation circuit 20 generates display image data to be displayed on the monitor 21 using the image data temporarily stored in the buffer memory 19, and outputs the generated display image data to the display monitor 21. The display monitor 21 is composed of an LCD or the like, and displays a reproduced image based on input display image data.

  The recording medium 27 includes a flash memory that can be attached to and detached from the electronic still camera. The recording medium 27 records image data stored in the buffer memory 19.

  The half-push switch 28 outputs a half-push operation signal to the CPU 18 in conjunction with a depression operation of a release button (not shown). The release switch 29 outputs a full-press operation signal to the CPU 18 in conjunction with the release button pressing operation. The main switch 22 outputs an operation signal for switching power on / off to the CPU 18. The mode switch 30 outputs, to the CPU 18, an operation signal for switching on / off at least a shooting mode with a night scene as a background in response to an operation mode switching operation of the flash device.

  The CPU 18 is configured to communicate with the CPU on the photographing lens side via the lens communication circuit 23 when a photographing lens (not shown) is attached to the electronic still camera. Information such as the aperture value and distance ring set for the lens is transmitted to the CPU 18. Further, the CPU 18 is configured to communicate with the CPU on the flash device side via the flash device communication circuit 24 when a flash device (not shown) is attached to the electronic still camera. Information such as the guide number of the flash device is transmitted to the CPU 18. The flash device is configured to emit light with a predetermined light amount based on a control signal indicating the light emission timing and the light emission amount transmitted from the CPU 18 via the flash device communication circuit 24.

  The photometry circuit 25 detects the subject light amount, calculates the subject brightness, and outputs the calculation result to the CPU 18. The focus detection device 26 detects a focus detection state by the photographic lens and sends detection information to the CPU 18.

  When the above-described electronic still camera is turned on in the shooting mode with the night view as the background, the flash photography that causes the flash device to emit light and the flash-off photography that does not cause the flash device to emit light are continuously performed. When the shooting mode with the night view as the background is turned off, either one of flash photography in which the flash device emits light and flash-off photography in which the flash device does not emit light is taken. Whether or not the flash device is caused to emit light at the time of shooting is determined by the operation mode of the flash device set by the mode switch 30.

  The present invention is to perform shooting in a shooting mode with a night scene as a background, that is, to perform flash shooting and flash-off shooting continuously in response to a single shooting start instruction, and to provide the minimum imaging sensitivity required for each shooting. Has characteristics.

  A flow of photographing processing performed by the CPU 18 will be described with reference to a flowchart of FIG. The CPU 18 starts the processing shown in FIG. 2 when a half-press operation signal is input from the half-push switch 28 in a state where the shooting mode is set with the night view as the background. The operation mode setting of the flash device by the mode switch 30 is performed separately from the processing in FIG.

  In step S11 of FIG. 2, when the shutter button (release button) is pressed, that is, when a full-press operation signal is input from the release switch 29, the CPU 18 proceeds to step S12. In step S12, the CPU 18 performs distance measurement processing up to the person who is the main subject based on the focus detection information input from the focus detection device 26, and proceeds to step S13. The distance measurement value is used for the calculation of the lens driving amount and the exposure calculation when the focus lens is moved to the in-focus position.

  In step S13, the CPU 18 determines whether or not appropriate exposure can be given to the person at the minimum setting sensitivity. The minimum setting sensitivity is the lowest imaging sensitivity that can be set in the electronic still camera, and is equivalent to ISO 50 in this embodiment. The CPU 18 performs an exposure calculation using the guide number of the flash device and the distance measurement value, and the main subject is properly exposed at the set shutter speed (for example, 1/60 seconds) and the set aperture value. In step S13, an affirmative determination is made, and the process proceeds to step S14. In step S14, the CPU 18 sets the imaging sensitivity to the lowest value equivalent to ISO 50, and proceeds to step S17.

  On the other hand, the CPU 18 makes a negative determination in step S13 when the main subject is not properly exposed (mainly when the amount of light emitted by the flash device is insufficient), and proceeds to step S15. In step S15, the CPU 18 calculates the minimum imaging sensitivity necessary for properly exposing the main subject, and proceeds to step S16. In step S16, the CPU 18 performs setting to increase the imaging sensitivity to the value calculated in step S15, and proceeds to step S17.

  In step S17, the CPU 18 performs flash photography by causing the flash device to emit light. Specifically, the focus lens (not shown) in the photographic lens is moved to the in-focus position corresponding to the main subject, the driver 16 is instructed to start charge accumulation, and light is emitted to the flash device via the flash device communication circuit 24. When the time elapsed since the transmission of the instruction and the start of charge accumulation reaches the time corresponding to the shutter speed (in this case, 1/60 seconds), the driver 16 is instructed to end the charge accumulation. The CPU 18 further instructs the driver 16 to read out (discharge) the charge and proceeds to step S18. As a result, image data (referred to as image 1) obtained by flash photography is stored in the buffer memory 19.

  FIG. 3 is a diagram for explaining the image 1. In FIG. 3, a person 11 as a main subject is irradiated with flash light from a flash device and is properly exposed. The background street lamp 12 and the building 13 are underexposed.

  In step S18 of FIG. 2, the CPU 18 sets the imaging sensitivity to a value for night scene exposure (for example, equivalent to ISO 400), and proceeds to step S19. Imaging sensitivity values for night view exposure are stored in the CPU 18 in advance. Note that the exposure sensitivity may be calculated based on the luminance information input from the photometry circuit 25 to determine the imaging sensitivity for night scene exposure.

  In step S19, flash-off shooting is performed without causing the flash device to emit light. Specifically, the focus lens (not shown) in the photographing lens is moved to a focus position corresponding to infinity, the driver 16 is instructed to start charge accumulation, and the time elapsed since the charge accumulation was started is the shutter speed. When the time corresponding to (for example, 1/4 second) is reached, the driver 16 is instructed to end the charge accumulation. The CPU 18 further instructs the driver 16 to read out (discharge) the charge and proceeds to step S20. As a result, image data (image 2) obtained by flash-off shooting is stored in the buffer memory 19.

  FIG. 4 is a diagram for explaining the image 2. In FIG. 4, the person 11 as the main subject is underexposed because the flash light is not irradiated. The street lamp 12 in the background is appropriately exposed as a night scene. The background building 13 is also properly exposed for night scene photography.

  In step S20 of FIG. 2, the CPU 18 combines the image 1 and the image 2 and proceeds to step S21. The two images are combined by adding the corresponding pixel data between the two images.

  FIG. 5 is a diagram for explaining an image after the synthesis process. In FIG. 5, the person 11 as the main subject has been properly exposed by the pixel data of the image 1. The street lamp 12 and the building 13 in the background are each appropriately exposed as night scene shooting by the pixel data based on the image 2. The portion underexposed in common between image 1 and image 2 is underexposed even after pixel data are added.

  In step S21 of FIG. 2, the CPU 18 instructs the image data after the synthesis processing to perform predetermined image processing and compression processing, records the processed image data as a file on the recording medium 27, and performs the processing according to FIG. Exit.

According to the embodiment described above, the following operational effects can be obtained.
(1) The electronic still camera continuously performs flash photography (step S17) for causing the flash device to emit light and flash-off photography (step S19) for causing the flash device not to emit light in response to a single photography start instruction (step S11). I did it. As a result, a flash photographed image and a flash-off photographed image can be obtained without changing the light emission / non-light emission setting of the flash device and performing the release operation twice each time shooting is performed.

(2) At the time of flash photography, a minimum imaging sensitivity is set so that the person 11 as the main subject is properly exposed (steps S14, S15, and S16). In general, when the sensitivity of the image sensor 10 is set high, image quality deterioration is likely to occur due to noise. On the other hand, in this embodiment, since the minimum imaging sensitivity is set, the influence of noise can be suppressed as much as possible, and a high-quality image of the person 11 can be obtained.

(3) At the time of flash-off shooting, the imaging sensitivity is set to be equivalent to ISO400 so that the background night scene can be properly exposed with an exposure time (for example, 1/4 second) in which camera shake does not become a problem ( Step S18). The imaging sensitivity S (OFF) at the time of flash-off shooting is the imaging sensitivity S (ON) at the time of flash shooting, the exposure time limit of the camera shake limit, and the time T necessary for proper exposure of the night scene with the imaging sensitivity S (ON). And is calculated by the following equation (1).
S (OFF) = S (ON) x T / Limit (1)
For example, assuming that Limit is 1/4 second, T is 2 seconds, and S (ON) is equivalent to ISO 50, S (OFF) = 50 × 8 = 400 (ISO) equivalent is obtained. In addition to reducing camera shake during night view exposure, the person 11 as the main subject is underexposed, so noise superimposed on the person 11 is not noticeable.

(4) Since the data of the image 1 (FIG. 3) by flash photography and the data of the image 2 (FIG. 4) by flash-off photography are combined for each corresponding pixel (FIG. 5), the main subject Appropriate exposure is obtained for the person 11 and the night scenes 12 and 13 as the background. The same effects as in the case of so-called slow sync photography are obtained, but compared to conventional slow sync photography, there is less noise superimposed on the main subject and the background night scene is less likely to occur. A quality image can be obtained.

(5) During flash-off shooting (step S19), the focus lens (not shown) in the shooting lens is moved to a position corresponding to infinity, so that the background can be focused and shot.

  In the above description, after the flash photographing for causing the flash device to emit light is performed, the flash-off photographing without causing the flash device to emit light is performed. However, the photographing order may be reversed.

  The electronic still camera may be a camera with a built-in flash device or a camera using an external flash device.

  The focus adjustment position at the time of flash shooting (step S19) may be kept at the focus position corresponding to the main subject at the time of flash shooting (step S17) without moving to the focus position corresponding to infinity.

  The focus adjustment position at the time of flash-off shooting (step S19) may be selected from a focus position corresponding to infinity and a focus position corresponding to the main subject.

  The electronic still camera combines the data of the image 1 (FIG. 3) obtained by flash photography and the data of the image 2 (FIG. 4) obtained by flash-off photography, and the data of the image (FIG. 5) after the composition processing is recorded on the recording medium. 27 was recorded. Instead, the data of the image 1 (FIG. 3) and the data of the image 2 (FIG. 4) obtained by flash-off photography may be recorded on the recording medium 27, respectively. In this case, the image reproduction device (image processing device) that reproduces and displays the image based on the image data combines the data of the image 1 by flash photography and the data of the image 2 by flash-off photography (corresponding to step S20). ) And good.

  The image reproduction device (image processing device) may be configured by causing a personal computer or the like to execute the image processing program for performing the processing in step S20 and the processing in step S21.

  Although the flash shooting and the flash-off shooting are continuously performed in response to a single shooting start instruction, when the same drawing as the slow sync shooting is not required, the person 11 as the main subject is appropriately exposed. Thus, the minimum imaging sensitivity may be set and only flash photography may be performed. By setting the minimum imaging sensitivity, it is possible to suppress the influence of noise as much as possible and obtain a high-quality image of the person 11.

  Correspondence between each component in the claims and each component in the best mode for carrying out the invention will be described. The imaging means is constituted by, for example, the imaging device 10 and the analog signal processing circuit 11. The sensitivity control unit, the imaging control unit, and the calculation unit are configured by the CPU 18, for example. The distance measuring means and the focus adjusting means are constituted by, for example, the focus detection device 26 and the CPU 18. In addition, unless the characteristic function of this invention is impaired, each component is not limited to the said structure.

1 is a block diagram of an electronic still camera according to an embodiment of the present invention. It is a flowchart explaining the flow of the imaging | photography process performed by CPU. It is a figure explaining the image image | photographed by flash. It is a figure explaining the image image | photographed by flash-off. It is a figure explaining the image after a synthetic | combination process.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Image pick-up element 11 ... Analog signal processing circuit 18 ... CPU
DESCRIPTION OF SYMBOLS 19 ... Buffer memory 24 ... Flash apparatus communication circuit 25 ... Photometry circuit 26 ... Focus detection apparatus 29 ... Release switch 30 ... Mode switch

Claims (6)

Imaging means for capturing a subject image;
The imaging sensitivity at the time of shooting using the flash device that illuminates the main subject is set to the lowest first imaging sensitivity within a predetermined range, and the imaging sensitivity at the time of shooting without using the flash device is set to a night scene with a predetermined exposure time. Sensitivity control means for setting the second imaging sensitivity to make the appropriate exposure,
A shooting control unit for controlling the imaging unit and the sensitivity control unit, respectively, so as to continuously perform shooting using the flash device and shooting without using the flash device in response to a single shooting instruction; A featured electronic still camera. The electronic still camera according to claim 1.
Ranging means for detecting the distance to the main subject;
A calculation means for performing an exposure calculation using a distance measurement value obtained by the distance measurement means and a guide number of the flash device;
The electronic still camera according to claim 1, wherein the sensitivity control means calculates the first imaging sensitivity as a minimum imaging sensitivity that is calculated by the calculating means and is necessary for properly exposing the main subject. The electronic still camera according to claim 1 or 2,
It further comprises a focus adjustment means for adjusting the focus of the taking lens,
The photographing control means associates a focus position at the time of photographing using the flash device with the main subject, and associates a focus position at the time of photographing without using the flash device with either the main subject or infinity. Thus, the electronic still camera characterized by further controlling the focus adjusting means. The electronic still camera according to claim 1,
The electronic still camera according to claim 1, wherein the predetermined exposure time is an exposure time of a camera shake limit.   The first image data photographed using the flash device by the imaging means set to the lowest first imaging sensitivity within the predetermined range, and the second to make the night view appropriate exposure with the exposure time of the camera shake limit. The computer device executes a process of combining the second image data photographed without using the flash device by the imaging means set to the imaging sensitivity so as to add the corresponding pixel data. A characteristic image processing program. Imaging means for capturing a subject image;
An electronic still camera comprising: sensitivity control means for setting an imaging sensitivity at the time of photographing using a flash device for illuminating a main subject to a minimum value within a predetermined range.

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