JP2012156805A - High-speed photographing system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To acquire a sufficient image with less overexposure and underexposure even if brightness of a subject suddenly changes.SOLUTION: A phenomenon (subject 10) being a photographing object is previously originated, and an optical sensor 3 and a light quantity change acquiring section 41 acquire a temporal change of the brightness. An appropriate exposure time/gain operating section 42 determines exposure time and a gain so that an exposure condition is within an appropriate range at every frame based on measured temporal change information of the brightness. A photographing condition time table generation section 43 generates and stores a time table showing the temporal change of the exposure time and the gain with a trigger signal as a reference. The time table is transferred to a storage section 25 of a high speed video camera 2. A photographing control section 24 controls an imaging element 21, an amplifier 22 and an image processing section 23 so that the exposure time and the gain change in accordance with the time table when the subject 10 is actually photographed. Consequently, the sufficient image in which the exposure condition is settled within the appropriate range can be obtained.

Description

  The present invention relates to a high-speed photographing system for photographing a high-speed phenomenon, and more particularly to a high-speed photographing system suitable for photographing a high-speed phenomenon accompanied by light emission and light absorption such as discharge and combustion.

  A dedicated high-speed video camera has been developed to continuously capture high-speed phenomena that are difficult to capture with normal video cameras, such as explosion, destruction, combustion, collision, discharge, or high-speed movement of objects. ing. For example, the high-speed video cameras described in Non-Patent Documents 1 and 2 are equipped with an image sensor having a special structure called a pixel peripheral recording type image sensor (IS-CCD = image storage-CCD). High-speed shooting at 1 frame per second (1Mfps) is possible.

  In general, in a video camera using a solid-state imaging device such as a CCD or a CMOS image sensor, an automatic gain adjustment (automatic adjustment) that automatically adjusts the gain of an amplifier that amplifies a signal output from the imaging device according to the brightness of the subject. Gain control: AGC), or just like a film camera, or by adjusting the aperture and shutter speed with an automatic exposure (auto exposure: AE) function that adjusts the exposure amount of each frame. Control is performed to obtain a proper exposure (see Patent Document 1). In both methods of AGC and AE, it is necessary to perform arithmetic processing based on the measurement result of the light amount, and to adjust the gain, the diaphragm, etc. according to the processing result. It can not cope with the super high-speed shooting speed of 1Mfps.

  For this reason, when shooting a phenomenon in which the temporal change of brightness is large with the high-speed video camera, overexposure is likely to occur in a frame that is too bright, and conversely, exposure is insufficient in a dark frame and the entire image tends to be black. If the exposure is adjusted to a bright frame, the image may be too dark in most frames and sufficient observation cannot be performed.

JP-A-5-103269

Kondo and five others, “Development of High-Speed Video Camera HyperVision HPV-1,” Shimadzu Review, Shimadzu Review Editorial Department, September 2005, Vol. 62, No. 1, p. 79-86 Kondo, et al., “High-speed video camera HPV-2 and high-speed shooting application”, Shimadzu review, Shimadzu review editorial department, published in March 2009, volume 65, No. 3, p. 219-227

  The present invention has been made to solve the above-described problems, and the object of the present invention is to prevent image signal saturation and underexposure even when the brightness of a subject changes greatly during high-speed shooting. Another object of the present invention is to provide a high-speed photographing system that can acquire a good moving image that can reliably observe the state of change of a subject.

The high-speed photographing system according to the present invention made to solve the above problems is
a) Image sensor, amplifier for amplifying the image signal obtained by the image sensor, A / D converter for digitizing the amplified image signal, and processing the digitized image signal to reconstruct the image An imaging means including a signal processing unit;
b) a measuring means for measuring a temporal change in the brightness of the subject in advance;
c) Based on the temporal change information of the brightness measured by the measuring means, the temporal change of the exposure time and / or the exposure condition of the reconstructed image at the time of photographing the subject is appropriate or within the appropriate range. Or a time table creating means for obtaining a time change of an analog or digital gain in a stage after the amplifier and creating and storing a time table based on the time change;
d) Shooting control means for controlling the imaging means so as to change both or one of exposure time and gain according to the time table created and stored by the time table creating means when actually shooting the subject. When,
It is characterized by having.

  Here, the subject is a phenomenon in which the reproducibility of the temporal change in brightness is high, such as a discharge phenomenon or a plasma phenomenon. Also, the subject itself does not emit light, and the brightness when viewed from the imaging means may be changed by changing the degree of absorption or reflection of the irradiated light. Is natural.

  In the high-speed imaging system according to the present invention, the measurement means uses, for example, a phenomenon that occurs when triggered by an external trigger signal as a subject, and changes the temporal change in intensity (light quantity) of light coming from the subject as the trigger signal. Measured based on the occurrence timing. Based on the temporal change of the measured light intensity, the time table creation means, for example, the exposure time for a frame with low light intensity so that the exposure condition of the reconstructed image falls within a predetermined appropriate range in each frame, for example. On the contrary, the temporal change of the exposure time is set so as to shorten the exposure time for a frame in which the light intensity is too strong. If the exposure time is shortened, signal saturation at the image sensor is unlikely to occur even if the light intensity is high, and if the exposure time is lengthened, the detection sensitivity at the image sensor can be increased even if the light intensity is weak. However, there is an upper limit on the exposure time if the frame rate of shooting is determined. Therefore, if the amount of light is insufficient even if the exposure time is maximized, the lack of exposure may be compensated by further increasing the gain.

  Note that the state in which the exposure condition of the reconstructed image is appropriate is a state in which the subject is bright enough to observe the occurrence of the subject, that is, the target phenomenon, on the reconstructed image. That is. Specifically, when the subject is bright, it is not overexposed, that is, the entire screen is whitish and the subject and its surroundings cannot be distinguished, and conversely, the subject is dark Is underexposed, that is, the entire screen is darkened and the subject and its surroundings cannot be distinguished.

  When the time change of the exposure time and the gain is obtained, the time table creation means creates and stores a time table of the exposure time and gain based on the generation timing of the trigger signal. The work and processing so far are performed before actual shooting.

  When re-occurring the phenomenon of measuring the temporal change in brightness again and actually shooting, the shooting control means generates the trigger signal generation timing according to the time table created and stored as described above. The imaging means is controlled so as to change either or both of the exposure time and the gain. Specifically, the exposure time can be controlled by controlling the opening / closing time of the electronic shutter of the image sensor. In addition, gain control can be performed in an analog manner at the stage of an amplifier or digitally performed at a stage of an A / D converter or a signal processing unit.

  In the high-speed imaging system according to the present invention, the exposure time and gain may be changed in units of a plurality of frames, but depending on the phenomenon to be observed, the brightness may change abruptly between successive frames. . Therefore, as a preferred aspect of the high-speed photographing system according to the present invention, the measuring unit measures the brightness of the subject at least once in each frame at the frame rate at the time of photographing, and the time table creating unit photographs the subject. In this case, the time table may be created by obtaining the exposure time and / or gain for each frame so that the exposure condition falls within the appropriate range. As a result, a good image can be obtained even for a subject whose brightness changes abruptly, and the observer can grasp the target phenomenon more accurately.

  Further, as one aspect of the high-speed imaging system according to the present invention, the measurement unit measures a temporal change in brightness for each pixel using the imaging element as a photodetector, and the time table creation unit includes the pixel A time table that represents a temporal change in exposure time and / or a temporal change in gain is created for each time, and the imaging control means changes both or one of the exposure time and gain for each pixel according to the time table. It is good also as a structure which controls the said imaging means. According to this configuration, even when shooting a plurality of phenomena that occur almost simultaneously, for example, a good image can be obtained so that each phenomenon can be properly captured in response to a change in brightness associated with the occurrence of each phenomenon. can do.

  According to the high-speed photographing system according to the present invention, even when the brightness of the subject changes with time, an appropriate exposure condition is set according to the change. It is possible to acquire a good image captured with certainty. This makes it possible to accurately observe extremely high speed phenomena.

The block diagram of the principal part of the high-speed imaging system which is one Example of this invention. Operation | movement explanatory drawing of the high-speed imaging system of a present Example. Operation | movement explanatory drawing of the high-speed imaging system of a present Example.

  An embodiment of a high-speed photographing system according to the present invention will be described with reference to the accompanying drawings. FIG. 1 is a configuration diagram of a main part of the high-speed photographing system of this embodiment.

  The high-speed shooting system 1 according to the present embodiment is mainly configured by a high-speed video camera 2 that performs high-speed shooting with respect to a subject 10, an optical sensor 3 such as a photodiode that detects light coming from the subject 10, and a computer. And a control device 4. The high-speed video camera 2 is a video camera described in, for example, Non-Patent Documents 1 and 2, and includes an imaging device 21, an amplifier 22, an image processing unit 23, a shooting control unit 24, a shooting condition time table storage unit 25, and the like. . The image sensor 21 is an element corresponding to ultra-high-speed shooting such as a pixel peripheral recording type image sensor in which an image signal storage unit of 100 frames or more is incorporated in the element itself. Continuous shooting at a rate of about 100 frames or more is possible.

  The control device 4 to which a detection signal from the optical sensor 3 is input includes a light quantity change acquisition unit 41, an appropriate exposure time / gain calculation unit 42, an imaging condition time table creation unit 43, and the like as characteristic function blocks. In the configuration of the present embodiment, the optical sensor 3 and the light quantity change acquisition unit 41 correspond to the measurement unit in the present invention, and the appropriate exposure time / gain calculation unit 42 and the imaging condition time table creation unit 43 correspond to the time table creation unit in the present invention. The imaging control unit 24 corresponds to the imaging control means in the present invention.

Next, the operation of the high-speed photographing system of this embodiment will be described. Here, the subject 10 is a phenomenon that is highly reproducible in the temporal change in brightness associated with a phenomenon to be photographed, such as electric discharge or plasma emission, and occurs when triggered by a trigger signal.
When photographing the subject 10 using this system, the temporal change in the brightness of the subject 10 is measured in advance, and control data is created based on the measurement result. That is, the phenomenon of the object to be photographed is triggered by the trigger signal, and the light amount change acquisition unit 41 of the control device 4 detects and records the temporal change of the light amount coming from the subject 10 at that time by the optical sensor 3. At this time, the light quantity change acquisition unit 41 samples the detection signal from the optical sensor 3 so that the light quantity value is obtained at least once in each frame in accordance with the frame rate of shooting. As a result, exposure adjustment in units of frames is possible. FIG. 2A is an example of a temporal change in the amount of light recorded.

  In the control device 4, the appropriate exposure time / gain calculation unit 42 calculates an appropriate exposure time and gain for each frame at the time of shooting based on the recorded temporal change data of the light amount. As shown in FIG. 3, the image pickup device 21 repeats an operation of accumulating photocharges for constituting an image of one frame and an operation of transferring an image signal based on the accumulated photocharges. The charge accumulation period is the exposure time. Although the frame repetition period, that is, the length of one frame period is determined by the frame rate, the exposure time can be adjusted by opening and closing an electronic shutter built in the image sensor 21. On the other hand, here, the gain is an amplification factor of the amplifier 22, but may be a gain of an A / D converter included in the image processing unit 23 or a gain in a data processing stage.

  Since the upper limit of the amount of light that causes signal saturation in the image sensor 21 is known, the appropriate exposure time / gain calculation unit 42 shortens the exposure time so that signal saturation does not occur in the image sensor 21 when the amount of light is large. On the other hand, when the amount of light is insufficient, the exposure time corresponding to the amount of light for each frame is obtained so as to make the exposure time as long as possible. The exposure time may be finely adjusted for all the light amount values, but it is sufficient if the exposure condition is within a certain appropriate range on the image reproduced after shooting. There is no need to finely adjust the exposure time. Therefore, for example, when the light amount is within a predetermined range, the exposure time is fixed to a predetermined value, and when the light amount exceeds the predetermined range, the exposure time is shortened from the predetermined value according to the amount of increase, and the light amount If the exposure time is below the predetermined range, the exposure time may be increased from the predetermined value according to the amount of decrease.

  However, the minimum value of the exposure time is not limited, but the maximum value of the exposure time is limited because one frame period is determined. Therefore, if the amount of light is insufficient even if the exposure time is maximized, the exposure is set within the appropriate range by increasing the gain. Thereby, for example, a temporal change in exposure time and gain as shown in FIG. 2B is obtained with respect to a temporal change in the amount of light of the subject 10 shown in FIG.

  The imaging condition time table creation unit 43 creates an imaging condition time table that defines the imaging conditions of each frame with reference to the trigger signal input time based on the temporal change in exposure time and the temporal change in gain as described above. create. This shooting condition time table can include various parameters related to shooting other than the exposure time and gain for each frame.

  The shooting condition time table is transferred from the control device 4 to the high-speed video camera 2 at an appropriate time before shooting, and stored in the shooting condition time table storage unit 25. It is also possible to measure the amount of light in advance for the subject 10 of various phenomena and create a shooting condition timetable and store it inside the control device 4 before actually shooting one of the subjects 10. If a shooting condition time table corresponding to the subject 10 is selected and read from the control device 4 to the high-speed video camera 2, shooting can be performed smoothly.

  When actually performing high-speed shooting, in the high-speed video camera 2, the shooting control unit 24 reads the shooting condition time table from the shooting condition time table storage unit 25, and each shooting time starts from the trigger signal input time. A shooting program is created so that the frame shooting conditions, that is, the exposure time, gain, and the like are in accordance with the shooting condition time table. In response to the input of the trigger signal, the imaging control unit 24 controls the imaging element 21, the amplifier 22, and the image processing unit 23 so as to perform imaging according to the imaging program, and executes imaging.

  Similar to the above-described measurement of the temporal change in brightness, the phenomenon of the subject to be photographed is triggered by the trigger signal, and the high-speed video camera 2 performs photographing using this as the subject 10. The exposure time and gain after the trigger signal is input change in accordance with the temporal change in the brightness of the subject 10 so that the exposure condition of the reproduced image falls within the appropriate range.

  However, the image pickup device 21 can repeatedly overwrite the image signal in the image signal storage unit having a predetermined storage capacity until an instruction to end the shooting is given from the shooting control unit 24. Therefore, if shooting is completed when an image having a predetermined number of frames corresponding to the storage capacity of the image signal storage unit is obtained from the time when the trigger signal is input, a predetermined number of frames starting from the time when the trigger signal is input. A moving image can be obtained, and if shooting is finished later than that, it is possible to obtain a moving image for a predetermined number of frames starting from a time point that is appropriately delayed rather than the time point when the trigger signal is input. it can. In any case, if the shooting condition is within the time specified in the shooting condition time table, the appropriate exposure condition can be obtained regardless of the change in the brightness of the subject 10.

  In the above embodiment, the optical sensor 3 is used to measure the change in the brightness of the subject 10, but the brightness measured in this case is the average brightness of the entire subject 10. Therefore, for example, when simultaneously shooting a plurality of objects that emit light at slightly different timings, if the exposure time of the entire image is shortened according to the amount of light from one previously emitted object, it is still It may happen that other objects that do not emit enough light are too dark to see. Therefore, in order to solve such a problem, the image to be captured is divided into a plurality of small areas, the temporal change in brightness is measured for each small area, and pixels corresponding to the small areas are measured based on the measurement result. It is preferable to determine the temporal change of the exposure time and the gain every time.

  Specifically, in the high-speed shooting system of the above embodiment, instead of using the optical sensor 30, the subject 10 is test-shot with the high-speed video camera 2 under a predetermined condition where the exposure time and gain are constant. The control device 4 obtains a temporal change in luminance for each pixel based on the image signal actually acquired by the test photographing, obtains an exposure time and a gain that make the exposure condition appropriate for each pixel, and obtains the photographing condition. Create a timetable. When actually shooting the subject 10, the shooting control unit 24 adjusts the exposure time for each pixel of the image sensor 21 and adjusts the gain of the amplifier 22 for each image signal obtained at each pixel. As a result, the exposure conditions are appropriate for each pixel, and even when a plurality of objects are photographed simultaneously as described above, it is possible to obtain a good image according to the light emission luminance of each object.

  It should be noted that the above embodiment is an example of the present invention, and it is a matter of course that modifications, changes, and additions are appropriately included in the scope of the claims of the present application within the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 ... High-speed imaging system 10 ... Subject 2 ... High-speed video camera 21 ... Imaging device 22 ... Amplifier 23 ... Image processing unit 24 ... Shooting control unit 25 ... Shooting condition timetable storage unit 3 ... Optical sensor 4 ... Control device 41 ... Light amount change acquisition unit 42 ... proper exposure time / gain calculation unit 43 ... shooting condition time table creation unit

Claims (3)

a) Image sensor, amplifier for amplifying the image signal obtained by the image sensor, A / D converter for digitizing the amplified image signal, and processing the digitized image signal to reconstruct the image An imaging means including a signal processing unit;
b) a measuring means for measuring a temporal change in the brightness of the subject in advance;
c) Based on the temporal change information of the brightness measured by the measuring means, the temporal change of the exposure time and / or the exposure condition of the reconstructed image at the time of photographing the subject is appropriate or within the appropriate range. Or a time table creating means for obtaining a time change of an analog or digital gain in a stage after the amplifier and creating and storing a time table based on the time change;
d) Shooting control means for controlling the imaging means so as to change both or one of exposure time and gain according to the time table created and stored by the time table creating means when actually shooting the subject. When,
A high-speed photographing system comprising: The high-speed imaging system according to claim 1,
The measuring means measures the brightness of the subject at least once in each frame at the frame rate at the time of shooting, and the time table creating means is configured to make the exposure condition within an appropriate range when shooting the subject. A high-speed photographing system characterized in that a time table is created by obtaining an exposure time and / or gain. The high-speed imaging system according to claim 1 or 2,
The measuring means measures a temporal change in brightness for each pixel using the imaging device as a photodetector, and the time table creating means is a temporal change in exposure time and / or a temporal change in gain for each pixel. A high-speed imaging system characterized in that a time table representing a change is created, and the imaging control unit controls the imaging unit to change either or both of an exposure time and a gain for each pixel according to the time table. .

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