JP2011040799A - Imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging device capable of performing appropriate exposure control even in high-speed continuous imaging. <P>SOLUTION: The imaging device includes: an imaging means to image an image for one frame of an object before starting imaging at certain intervals to output the image as a through-image, and to image an image for one frame of the object after starting the imaging to output the image as an imaged image; a cycle detection means to detect one cycle of a luminance change when the luminance of the imaged through-image is periodically changed; an exposure value setting means to set an exposure value of each frame of the through-image corresponding to the detected one cycle; a storage means to store the set exposure value in one cycle; and an exposure control means to control the exposure value of the image imaged in a period corresponding to one cycle based on the exposure value in one cycle stored in the storage means when continuously imaging the imaged image by the imaging means when the luminance of the imaged through-image is periodically changed. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an imaging apparatus.

  In recent years, digital cameras that can perform continuous shooting at higher speed than normal continuous shooting have appeared. As exposure control during such high-speed continuous shooting, a digital camera has been proposed that controls the exposure control value calculated immediately before shooting based on the output of the light receiving element for each frame in the high-speed continuous shooting mode. (For example, refer to Patent Document 1).

JP 2000-50152 A

  In the digital camera, the output of the light receiving element is a measured value for each frame, but the exposure control value is a fixed value calculated immediately before photographing. For this reason, the exposure control value of each frame is easily affected by the luminance level of the subject immediately before shooting.

  An object of the present invention is to provide an imaging apparatus capable of performing appropriate exposure control even in high-speed continuous shooting.

  According to the first aspect of the present invention, an image of one frame of the subject before the start of shooting is captured at a constant time interval and output as a through image, and an image of one frame of the subject after the start of shooting is captured. An imaging unit that outputs the captured image as a captured image, a period detection unit that detects one cycle of a luminance change when the luminance of the through image captured by the imaging unit is periodically changed, and a detection by the cycle detection unit The exposure value setting means for setting the exposure value of each frame of the through image corresponding to the one cycle, the storage means for storing the exposure value for the one period set by the exposure value setting means, and the imaging means. When the captured image is continuously captured by the imaging unit when the brightness of the captured through image is periodically changed, the exposure value of the one cycle stored in the storage unit Based on an imaging apparatus characterized by comprising an exposure control means for controlling the exposure value of the captured image captured in a period of time corresponding to the one period, a.

  According to the present invention, it is possible to provide an imaging apparatus capable of performing appropriate exposure control even in high-speed continuous shooting.

It is a block diagram which shows the structure of the camera concerning 1st Embodiment. It is explanatory drawing which shows an example of the luminance change in a through image in 1st Embodiment. It is a flowchart which shows the process sequence in the case of imaging a picked-up image in high-speed continuous shooting mode in 1st Embodiment. It is explanatory drawing which shows the relationship between the actual luminance change in a through image, and the averaged brightness | luminance in 2nd Embodiment. It is a flowchart which shows the process sequence in the case of imaging a picked-up image in high-speed continuous shooting mode in 2nd Embodiment.

  Embodiments of an imaging apparatus according to the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the camera 1 according to the first embodiment. As shown in FIG. 1, the camera 1 of this embodiment is a digital camera including an imaging unit 10, a lens / mechanism unit 20, an operation unit 30, a recording unit 40, a memory 50, a liquid crystal monitor 60, a light emitting unit 70, and a camera CPU 80. It is configured as.

  The imaging unit 10 includes an imaging element 11 and an image processing unit 12. The image pickup device 11 is a light-electricity conversion device that converts subject light that has passed through the photographing lens 21 of the lens / mechanism unit 20 into an electric signal and outputs the electric signal. The electrical signal output from the image sensor 11 is subjected to various image processing such as noise removal, white balance adjustment, gamma correction, contour enhancement, and level adjustment in the image processing unit 12 and is output to the memory 50 as image data. .

  The imaging unit 10 captures an image of one frame of the subject before the release button of the operation unit 30 is fully pressed by the photographer (before the start of imaging) at a constant time interval (for example, 1/30 seconds). And output as a through image. The imaging unit 10 captures an image for one frame of the subject after the release button is fully pressed by the photographer (after the start of photographing), and outputs the image as a photographed image.

  The lens / mechanism unit 20 includes a photographing lens 21, a diaphragm mechanism 22, a shutter 23, and a driving unit 24. The subject light incident on the photographic lens 21 is guided to the imaging element 11 of the imaging unit 10 through an aperture mechanism 22 opened to a size of an aperture value (F value) and a shutter 23 opened at a predetermined exposure time.

  The aperture mechanism 22 adjusts the amount of subject light, and includes a plurality of aperture blades (not shown). The shutter 23 adjusts the exposure time of the subject light, and includes a shutter blade (not shown) that opens and closes at a predetermined speed during shooting. The drive unit 24 includes, for example, an actuator that drives the photographing lens 21 in the optical axis direction for focus adjustment, and an actuator that drives the aperture mechanism 22 and the shutter 23. Note that in the high-speed continuous shooting mode to be described later, an electronic shutter function for controlling the charge accumulation time in the image sensor 11 is used.

  The operation unit 30 is operated when the photographer issues various input instructions to the camera CPU 80, and includes various operation input devices such as buttons, dials, and switches (all not shown).

  Among these, a release button (not shown) can be operated in two stages, a half-press operation and a full-press operation. When the photographer turns on a power switch (not shown), an auto focus (AF) operation execution signal is transmitted to the camera CPU 80. Accordingly, the camera CPU 80 performs AF control for automatically focusing on a main subject and AE (automatic exposure) control for automatically adjusting exposure based on the output of the imaging unit 10. The image captured at this time is output as a through image to the memory 50 and displayed on the liquid crystal monitor 60 via the camera CPU 80.

  When the photographer presses the release button halfway while the through image is displayed, the focus is fixed to the subject captured at that time, and the exposure is determined. When the photographer fully presses the release button, a shooting start signal is transmitted to the camera CPU 80. Thereby, the aperture mechanism 22 and the shutter 23 are driven at a predetermined timing, and the subject light is imaged by the imaging unit 10. The image captured at this time is output to the memory 50 as a captured image and recorded in the recording unit 40 via the camera CPU 80.

  The recording unit 40 records the image data output from the image processing unit 12 on a recording medium (not shown) such as a CF card or an SD card.

  The memory 50 stores setting information input by the photographer, a program necessary for the operation and control of the camera 1, initial values and setting values necessary for executing the program, and the like, and is output from the imaging unit 10. Image data, data used when the image processing unit 12, the camera CPU 80, and the like perform arithmetic processing are stored. In the high-speed continuous shooting mode described later, the exposure value for one cycle set by the camera CPU 80 is stored.

  The liquid crystal monitor 60 displays shooting conditions such as a shutter speed and an aperture value in addition to a through image, a shot image, and a menu screen.

  The light emitting unit 70 emits illumination light for photographing to the subject under the control of the camera CPU 80 when the luminance of the subject is low.

  The camera CPU 80 is an integrated circuit that comprehensively controls each element constituting the camera 1 described above. In the camera CPU 80, as basic control of the camera 1, light measurement and distance measurement are performed based on the output of the imaging unit 10, and processing such as light emission control for determining the light emission amount of the light emitting unit 70 in addition to AE control and AF control. Is running.

  The camera CPU 80 transmits a predetermined timing signal to the imaging unit 10 and executes processing for controlling the timing of imaging and image processing. In the camera 1 of the present embodiment, a high-speed continuous shooting mode can be set in addition to the normal single shooting mode and the continuous shooting mode. In the high-speed continuous shooting mode, for example, 60 frames (frames) / second can be shot.

  Further, the camera CPU 80 has a function as a function of a period detection unit that detects one period when the luminance of the through image captured by the imaging unit 10 is periodically changed. Here, an example in which the luminance periodically changes in the through image will be described.

  FIG. 2 is an explanatory diagram illustrating an example of a luminance change in a through image. When flashing light is irradiated on a subject to be photographed at a constant cycle, the luminance periodically changes with time as shown in FIG. Since the camera CPU 80 captures an image by the imaging unit 10 at a frame rate of 1/30 seconds, for example, the periodicity of the luminance change can be detected by comparing the luminance of the image in each frame in time series. it can. In FIG. 2, the period T is detected as one cycle of luminance change.

  Further, the camera CPU 80 has a function of an exposure value setting unit that sets an appropriate exposure value for each frame in one cycle based on the detected through image of one cycle when the high-speed continuous shooting mode is set. . Here, an appropriate exposure value (hereinafter referred to as an appropriate exposure value for one cycle) is calculated for the image data of each frame of one cycle detected previously. For example, if one cycle of luminance change is 1 second, an appropriate exposure value is calculated for each of 30 frames. The appropriate exposure value for one cycle is stored in the memory 50.

  Furthermore, when the camera CPU 80 continuously captures captured images by the imaging unit 10 in the high-speed continuous shooting mode when the luminance of the through image captured by the imaging unit 10 is periodically changed, the memory 50 Is provided with a function as an exposure control means for controlling the exposure value of a photographed image captured in a period corresponding to the one cycle based on the one-cycle appropriate exposure value stored in the.

  That is, in the high-speed continuous shooting mode, it is assumed that the release button is fully pressed by the photographer when the brightness of the through image periodically changes as shown in FIG. Then, the camera CPU 80 reads out the appropriate exposure value for one cycle stored in the memory 50, and controls the exposure value of the captured image captured during the period corresponding to the one cycle based on the appropriate exposure value. Since the through image is continuously captured at a frame rate of 1/30 second, when one period of luminance change is detected, the time measurement is started from either the start point or the end point. The time point when the release button is fully pressed can be synchronized with one cycle of the luminance change.

  For example, assume that one cycle of luminance change is 1 second, and 30 frames of images are captured during that period. In this case, if the release button is fully pressed 1.5 seconds after the detection of one cycle of luminance change, the appropriate exposure value for the 15th frame of the first cycle is set to the full release button. It is set as the exposure value of the captured image that is captured immediately after. Also for the captured images taken after this, the appropriate exposure value of the corresponding frame of one cycle stored in the memory 50 is set.

  Next, in the present embodiment, a processing procedure when a captured image is captured in the high-speed continuous shooting mode will be described with reference to the flowchart of FIG. Here, it is assumed that the photographer points the camera 1 at a subject whose luminance changes periodically.

  In step S101, the camera CPU 80 controls the imaging unit 10 to capture a through image. In step S <b> 102, the camera CPU 80 detects one cycle of the luminance change for the through image captured by the imaging unit 10. In step S103, the camera CPU 80 sets an appropriate exposure value for each frame of the through image in the detected one cycle. In step S <b> 104, the camera CPU 80 stores the set appropriate exposure value for one cycle in the memory 50. In step S <b> 105, the camera CPU 80 sets an appropriate exposure value for a corresponding frame of one cycle stored in the memory 50 for a captured image captured by the imaging unit 10 after the release button is fully pressed. Take an image.

  According to the first embodiment described above, when performing high-speed continuous shooting of a subject whose luminance changes periodically, the appropriate exposure value for one cycle of luminance change before the start of shooting is set and set after the start of shooting. Since the exposure value of the captured image captured during the period corresponding to the one cycle is controlled based on the appropriate exposure value for one cycle, the exposure is set as compared with the case where the appropriate exposure value is set for each frame to be captured. Control processing can be speeded up. Further, unlike the method using the exposure value calculated immediately before shooting as a fixed value (Japanese Patent Laid-Open No. 2000-50152), it is not affected by the luminance level of the subject immediately before shooting.

  Therefore, appropriate exposure control can be performed even in high-speed continuous shooting. In particular, the exposure control shown in the present embodiment is effective when it is desired to capture an image in which the luminance change of the external light is canceled when unnecessary external light hits the subject to be photographed at a constant cycle.

  Next, a second embodiment will be described. Since the configuration of the camera 1 according to the second embodiment is the same as that of the first embodiment (FIG. 1), only differences will be described.

  The camera CPU 80 of the second embodiment has a function of an exposure value setting unit that sets an average exposure value for one cycle based on the detected through image of one cycle when the high-speed continuous shooting mode is set. . Here, an average exposure value (hereinafter referred to as an average exposure value for one cycle) is calculated for the image data of all frames of one cycle detected previously. For example, assuming that one cycle of luminance change is 1 second, an average exposure value in an image of 30 frames is calculated. The average exposure value for one cycle calculated here is stored in the memory 50. The method for calculating the average exposure value is not particularly limited.

  FIG. 4 is an explanatory diagram showing the relationship between the actual luminance change in the through image and the averaged luminance. When the flashing light is irradiated on the subject to be photographed at a constant cycle, the luminance periodically changes with time as shown in FIG. The camera CPU 80 of the present embodiment detects the periodicity of the luminance change by the same method as in the first embodiment. In FIG. 4A, the period T is detected as one cycle of luminance change. In addition, as shown in FIG. 4B, the camera CPU 80 of the present embodiment sets the average exposure value for one cycle after averaging the detected luminance change for one cycle.

  Further, the camera CPU 80 of the present embodiment performs frequency decomposition by Fourier transform on the image data, and calculates an average exposure value using only frequency components that can be recognized by humans. Specifically, among the frequency components included in the image data, the low frequency component whose luminance change frequency is less than 50 Hz is left, and the high frequency component of 50 to 60 Hz or more is removed. According to this, brightness changes that are difficult for humans to recognize, such as flickering of fluorescent lamps, do not affect the exposure of the captured image, and brightness changes that can be recognized by humans, such as blinking illumination, Will be reflected in the exposure.

  Next, in the present embodiment, a processing procedure when a captured image is captured in the high-speed continuous shooting mode will be described with reference to a flowchart of FIG. Here, it is assumed that the photographer points the camera 1 at a subject whose luminance changes periodically.

  In step S201, the camera CPU 80 controls the imaging unit 10 to capture a through image. In step S <b> 202, the camera CPU 80 detects one cycle of the luminance change for the through image captured by the imaging unit 10. In step S203, the camera CPU 80 sets an average exposure value for the image data of all the frames of the through image in the detected one cycle. At this time, as described above, the high frequency components included in the image data are removed. In step S <b> 204, the camera CPU 80 stores the set average exposure value for one cycle in the memory 50. In step S <b> 205, the camera CPU 80 sets and captures an average exposure value for one cycle stored in the memory 50 for a captured image captured by the imaging unit 10 after the release button is fully pressed.

According to 2nd Embodiment mentioned above, there exist the following effects.
(1) When high-speed continuous shooting is performed on a subject whose luminance changes periodically, an appropriate exposure value for one cycle of luminance change before the start of shooting is set, and after the start of shooting, the set average exposure value for one cycle is set. Based on this, since the exposure value of the captured image captured during the period corresponding to the one cycle is controlled, the exposure control processing is speeded up as compared with the case where an appropriate exposure value is set for each frame to be captured. be able to. Further, unlike the method using the exposure value calculated immediately before shooting as a fixed value (Japanese Patent Laid-Open No. 2000-50152), it is not affected by the luminance level of the subject immediately before shooting.

Therefore, appropriate exposure control can be performed even in high-speed continuous shooting. In particular, the exposure control shown in this embodiment is effective when it is desired to leave a change in the illumination light in the photographed image when the subject to be photographed is illuminated with illumination light that is lit up at a certain period. Become. That is, when exposure control is performed for each imaging, periodic light changes such as blinking illumination cannot be recorded in the image. However, in the exposure control of this embodiment, such light is also imaged. Therefore, it is possible to obtain an image that leaves the atmosphere at the time of shooting.
(2) Since the average exposure value is calculated using only the frequency components that can be recognized by humans among the frequency components included in the image data, the luminance change that is difficult for humans to recognize, such as flickering of fluorescent lamps. With respect to, it is possible to reflect a change in luminance that can be recognized by humans, such as blinking illumination, without affecting the exposure of the captured image.
(Deformation)

Without being limited to the embodiment described above, the present invention can be variously modified and changed as described below, and these are also within the scope of the present invention.
(1) An appropriate exposure value for each frame of the through image may be calculated, and the appropriate exposure value may be compared in time series to detect a periodic luminance change of the through image.
(2) In the second embodiment, a photographer may arbitrarily select a frequency component to be removed from frequency components included in image data.
(3) It is good also as a structure which can switch exposure control of 1st or 2nd embodiment according to a photographer's intention and a to-be-photographed object.

  Moreover, although the said embodiment and modification can be used in combination suitably, since the structure of each embodiment is clear by illustration and description, detailed description is abbreviate | omitted. Furthermore, the present invention is not limited by the embodiment described above.

  1: camera, 20: lens / mechanism unit, 30: operation unit, 40: recording unit, 50: memory, 60: liquid crystal monitor, 70: light emitting unit, 80: camera CPU

Claims (4)

An imaging unit that captures an image of one frame of a subject before the start of shooting at a constant time interval and outputs the image as a through image; and also captures an image of one frame of the subject after the start of shooting and outputs the image as a captured image; ,
A period detection unit that detects one cycle of a luminance change when the luminance of the through image captured by the imaging unit changes periodically;
Exposure value setting means for setting an exposure value of each frame of the through image corresponding to one period detected by the period detection means;
Storage means for storing the exposure value of the one cycle set by the exposure value setting means;
When the captured image is continuously captured by the imaging unit when the luminance of the through image captured by the imaging unit is periodically changed, the exposure value of the one cycle stored in the storage unit is used. Based on the exposure control means for controlling the exposure value of the captured image captured in a period corresponding to the one cycle,
An imaging apparatus comprising: The imaging apparatus according to claim 1,
The exposure value setting unit calculates an appropriate exposure value for each frame in the one cycle based on the through image of one cycle detected by the cycle detection unit, and sets the appropriate exposure value as the exposure value for the one cycle. An imaging device characterized by setting. The imaging apparatus according to claim 1,
The exposure value setting unit calculates an average exposure value for the one cycle based on the through image of one cycle detected by the cycle detection unit, and sets the average exposure value as the exposure value for the one cycle. The imaging device characterized by these. The imaging apparatus according to claim 3,
The exposure value setting unit recognizes a human body among frequency components included in the through image when calculating an average exposure value of the one cycle based on the through image of the one cycle detected by the cycle detection unit. An imaging apparatus characterized by using frequency components that can be used.

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