JP2013255005A - Electronic camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electronic camera capable of suppressing the occurrence of flicker.SOLUTION: An image sensor 16 repeatedly outputs images representing scenes captured on an imaging surface. A driver 18 exposes the imaging surface every 1/30 seconds that corresponds to a frame rate. A CPU 26 executes correction processing to advance an exposure period every 1/30 seconds on the basis of deviation between "1/100 seconds" and "1/30 seconds" that correspond to a period during which brightness of a light source of scenes captured by the imaging surface changes.

Description

  The present invention relates to an electronic camera, and more particularly to an electronic camera that reads an image signal photoelectrically converted by an image sensor.

  An example of this type of camera is disclosed in Patent Document 1. According to this background art, in a solid-state imaging device that controls an electronic shutter at a shutter speed equal to a cycle corresponding to a frequency that is an integral multiple of a light emission cycle, the drive timing condition setting unit includes a total of light emission cycles. The total exposure amount including each exposure period divided into a plurality of exposure periods or the last one light emission period in one frame is controlled. The drive timing generation unit generates an output timing of the drive control signal based on the drive timing condition set by the drive timing condition setting unit. The drive signal generation unit generates a drive control signal for driving and controlling the CCD solid-state imaging device based on the output timing of the drive control signal from the drive timing generation unit.

JP 2010-258722 A

  However, in the background art, the exposure amount is adjusted by increasing / decreasing the number of charges read out during the exposure period, and the exposure time is limited to an integral multiple of the blinking cycle of the light source. Therefore, when the exposure time is shortened, flicker may occur due to the difference between the exposure time and the blinking cycle of the light source.

  Therefore, a main object of the present invention is to provide an electronic camera capable of suppressing flicker.

  An electronic camera according to the present invention (10: reference numeral corresponding to the embodiment; the same applies hereinafter) includes imaging means (16, 62, 64) for repeatedly outputting an image representing a scene captured on the imaging plane, and the imaging plane with a frame rate. Exposure means (58, 60) for exposure at a predetermined cycle equivalent to the above, and a correction process for advancing the exposure timing of the exposure unit based on a deviation between a predetermined cycle and the cycle at which the brightness of the scene light source captured on the imaging surface changes Is provided with control means (S5 to S11) for executing the above in a predetermined cycle.

  Preferably, the correction processing is performed for each period corresponding to the remainder obtained by dividing the predetermined period by a period corresponding to one half of the reciprocal of the frequency of the commercial power source employed in the area to which the scene captured on the imaging surface belongs. This corresponds to a process for advancing the exposure time of the means.

  More preferably, there is further provided initialization means (S13 to S15) for periodically initializing the timing correction amount by the correction processing.

  More preferably, the initialization means initializes the timing correction amount every time the period corresponding to the timing correction amount matches an integer multiple of the reciprocal of the frequency of the commercial power supply.

  Preferably, the detection means (46) for detecting the frequency of the commercial power source employed in the area to which the scene captured on the imaging surface belongs, and the control means when the frequency of the commercial power source detected by the detection means deviates from the predetermined condition Limiting means (S1) for limiting processing is further provided.

  An exposure control program according to the present invention includes an imaging means (16, 62, 64) for repeatedly outputting an image representing a scene captured on an imaging surface, and an exposure means (58 for exposing the imaging surface at a predetermined cycle corresponding to a frame rate). , 60) is corrected by the processor (26) of the electronic camera (10) to advance the exposure time of the exposure means based on the difference between the predetermined period and the period when the luminance of the light source of the scene captured on the imaging surface changes. This is an exposure control program for executing control steps (S5 to S11) for executing the above in a predetermined cycle.

  The exposure control method according to the present invention includes an imaging means (16, 62, 64) for repeatedly outputting an image representing a scene captured on the imaging surface, and an exposure means (58 for exposing the imaging surface at a predetermined cycle corresponding to a frame rate. , 60), an exposure control method executed by the electronic camera (10), wherein the exposure time of the exposure means is based on a deviation between a predetermined period and a period at which the luminance of the scene light source captured on the imaging surface changes Control steps (S5 to S11) for executing a correction process for speeding up the process at predetermined intervals.

  According to the present invention, the exposure time and the blinking cycle of the fluorescent lamp coincide with each other by advancing the exposure time based on the difference between the cycle in which the luminance of the light source changes and the cycle corresponding to the frame rate. Thereby, the occurrence of flicker can be suppressed.

  The above object, other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments with reference to the drawings.

It is a block diagram which shows the basic composition of one Example of this invention. It is a block diagram which shows the structure of one Example of this invention. FIG. 3 is an illustrative view showing one example of a configuration of a timing generator applied to the embodiment in FIG. 2; It is an illustration figure which shows an example of the use environment of FIG. 2 Example. It is an illustration figure which shows an example of operation | movement of the image sensor applied to the FIG. 2 Example. It is an illustration figure which shows another example of the use environment of the FIG. 2 Example. It is an illustration figure which shows another example of operation | movement of the image sensor applied to the FIG. 2 Example. It is a flowchart which shows a part of operation | movement of CPU applied to the FIG. 2 Example. It is an illustration figure which shows an example of operation | movement of the image sensor applied to the other Example of this invention.

Embodiments of the present invention will be described below with reference to the drawings.
[Basic configuration]

  Referring to FIG. 1, the electronic camera of this embodiment is basically configured as follows. The imaging unit 1 repeatedly outputs an image representing a scene captured on the imaging surface. The exposure unit 2 exposes the imaging surface at a predetermined cycle corresponding to the frame rate. The control unit 3 executes a correction process for advancing the exposure time of the exposure unit at a predetermined cycle based on a deviation between a predetermined cycle and the cycle at which the luminance of the light source of the scene captured on the imaging surface changes.

The exposure time and the blinking cycle of the fluorescent lamp coincide with each other by advancing the exposure time based on the difference between the cycle of changing the luminance of the light source and the cycle corresponding to the frame rate. Thereby, the occurrence of flicker can be suppressed.
[Example]

  Referring to FIG. 2, the digital camera 10 of this embodiment includes a focus lens 12. The optical image that has passed through the focus lens 12 is irradiated onto the imaging surface of the image sensor 16. The clock generation circuit 24 outputs a reference clock for driving the entire system, and the timing generator 22 generates a vertical synchronization signal Vsync and a horizontal synchronization signal Hsync based on the reference clock. The driver 18 drives the image sensor 18 based on the vertical synchronization signal Vsync and the horizontal synchronization signal Hsync created by the timing generator 22.

  Specifically, the driver 18 has a charge sweep pulse that defines the exposure timing of the imaging surface, a charge readout pulse that reads out the charge generated by photoelectric conversion from the imaging surface, and a transfer pulse that transfers the readout charge ( A vertical transfer pulse and a horizontal transfer pulse) are applied to the image sensor 16. As a result, a raw image signal based on the charges read from the imaging surface is repeatedly output from the image sensor 16 in a raster scanning manner.

  The signal processing circuit 20 performs processing such as white balance adjustment, color separation, and YUV conversion on the raw image signal output from the image sensor 16, and YUV format image data generated thereby is sent to the SDRAM 32 through the memory control circuit 30. Write. The LCD driver 36 repeatedly reads out the image data stored in the SDRAM 32 through the memory control circuit 30 and drives the LCD monitor 38 based on the read image data. As a result, a real-time moving image (through image) representing the scene captured on the imaging surface is displayed on the LCD monitor 38.

  Of the image data generated by the signal processing circuit 20, Y data is also provided to the CPU 26. The CPU 26 calculates an appropriate exposure time by performing AE processing on the given Y data in order to appropriately adjust the brightness of the image. The calculated exposure time is set in the decoder 58 described later.

  The timing generator 22 and the driver 18 are configured as shown in FIG. The reference clock output from the clock generation circuit 20 is given to the CLK terminal of the H counter 50. The output of the comparator 52 is also supplied to the RST terminal of the H counter 50. The count value of the H counter 50 is incremented in response to the rising edge of the reference clock, and is reset in response to the rising edge of the output of the comparator 52.

  The comparator 52 compares the count value of the H counter 50 with a threshold value REF_H corresponding to the number of horizontal pixels on the imaging surface, and sets the output to the L level when the count value is less than the threshold value REF_H, while the count value is equal to or greater than the threshold value REF_H. In this case, the output is set to H level. Therefore, the output of the comparator 52 temporarily rises at a period corresponding to the number of horizontal pixels on the imaging surface. Such an output corresponds to the horizontal synchronization signal Hsync.

  The output of the comparator 52 is given to the CLK terminal of the V counter 54. The output of the comparator 56 is also supplied to the RST terminal of the V counter 54. The count value of the V counter 54 is incremented in response to the rising edge of the output of the comparator 52, and is reset in response to the rising edge of the output of the comparator 56.

  The comparator 56 compares the count value of the V counter 54 with a threshold value REF_V corresponding to the number of vertical pixels on the imaging surface, and sets the output to the L level when the count value is less than the threshold value REF_V, while the count value is equal to or greater than the threshold value REF_V. In this case, the output is set to H level. Accordingly, the output of the comparator 56 temporarily rises at a period corresponding to the number of vertical pixels on the imaging surface. Such an output corresponds to the vertical synchronization signal Vsync. The vertical synchronization signal Vsync is output every 1/30 seconds.

  The decoder 58 creates a charge sweeping pulse based on the count values given from the H counter 50 and V counter 54, the exposure time set by the CPU 26, and the timing correction amount GP registered in the register RGST66. Further, the decoder 60 creates a charge read pulse based on the count values given from the H counter 50 and the V counter 54 and the timing correction amount GP registered in the register RGST 66.

  The charge sweeping pulse is repeatedly output during the period from the start to the end of each frame, and the charge sweeping pulse is used at the exposure start time (= the time that goes back from the end by the period obtained by adding the timing correction amount GP to the exposure time). Output is interrupted. In addition, the charge readout pulse is output at the exposure end time (= a time that goes back by the time corresponding to the time correction amount GP from the end of each frame). As a result, the charge generated on the imaging surface during the period from the exposure start time to the exposure end time is read out to the charge transfer path.

  The decoder 62 creates a vertical transfer pulse based on the given count value, and the decoder 64 creates a horizontal transfer pulse based on the given count value. The charges read out to the charge transfer path are transferred by the vertical transfer pulse and the horizontal transfer pulse and output from the image sensor 16.

  When the exposure end time is adjusted to the end of each frame, when the digital camera 10 is used under a fluorescent lamp FL driven by a commercial power supply of 50 Hz (see FIG. 4), the exposure time of the image sensor 16 and the fluorescent lamp Flicker is caused by the difference between the FL flicker cycle.

  In order to suppress the occurrence of such flicker, the timing correction amount GP is adjusted as follows. That is, the fluorescent lamp FL blinks with a period of 1/100 second, which is a period corresponding to one half of the reciprocal of the power supply frequency of 50 Hertz. The remainder obtained by dividing the generation period 1/30 second of the vertical synchronization signal Vsync by the blinking period 1/100 second of the fluorescent lamp FL is “1/300 second”.

The CPU 26 updates the variable k between “0” and “2” in response to the vertical synchronization signal Vsync, and sets “k / 300 seconds” as the timing correction amount GP. As a result, focusing on three consecutive frames, the end of the exposure time in the first frame is aligned with the end of the first frame,
The end of the exposure time in the second frame is advanced by “1/300 second” from the end of the second frame, and the end of the exposure time in the third frame is advanced by “2/300 second” from the end of the third frame. . When the exposure time is “T”, the exposure process is executed as shown in FIG.

  Note that the range in which “k” changes is limited to “0 ≦ k ≦ 2”. If “k = 3”, k / 300 seconds and the blinking cycle 1/100 seconds of the fluorescent lamp FL are one. This is because the exposure amount matches that when “k = 0”.

  Referring to FIG. 6, when the digital camera 10 is used outdoors, it is not necessary to change the above-described exposure timing control. Referring to FIG. 7, when sunlight is used as a light source, the light source does not blink, and flicker does not occur regardless of the timing of exposure.

  When the shutter button 28sh provided in the key input device 28 is depressed, a still image capturing process and a recording process are executed. One frame of image data obtained by exposure immediately after the shutter button 28 sh is pressed is taken into the SDRAM 32 by the still picture taking process. The captured image data of one frame is read from the SDRAM 32 by the I / F 40 activated in association with the recording process, and is recorded on the recording medium 42 in a file format.

  The CPU 26 executes a plurality of tasks in parallel including the exposure timing control task shown in FIG. Note that control programs corresponding to these tasks are stored in the flash memory 44.

  Referring to FIG. 8, in step S <b> 1, the current position is detected with reference to GPS device 46, and it is determined whether the frequency of the commercial power source at the detected current position is 50 Hz. If the determination result is NO, the timing correction amount GP (= 0 second) is set in the register 66 in step S3, and then the process returns to step S1. On the other hand, if a determination result is YES, it will progress to Step S5.

  In step S5, "0" is set to the variable k, and in step S7, it is repeatedly determined whether or not the vertical synchronization signal Vsync has been generated. When the determination result is updated from NO to YES, the timing correction amount GP (= 1/300 seconds × k) is set in the register 66 shown in FIG. 3 in step S9.

  In step S11, the variable k is incremented, and in step S13, it is determined whether or not the value of the variable k exceeds “2”. If the determination result is NO, the process returns to step S7, whereas if the determination result is YES, the variable k is set to “0” in step S15, and then the process returns to step S7.

  As can be seen from the above description, the image sensor 16 repeatedly outputs an image representing a scene captured on the imaging surface. The driver 18 exposes the imaging surface every 1/30 seconds corresponding to the frame rate. The CPU 26 performs a correction process for advancing the exposure time on the basis of a difference between “1/100 seconds” and “1/30 seconds” corresponding to a cycle in which the luminance of the light source of the scene captured on the imaging surface changes. It is executed every second (S5 to S11).

  The exposure time and the blinking cycle of the fluorescent lamp coincide with each other by advancing the exposure time based on the difference between the cycle in which the luminance of the light source changes and the cycle corresponding to the frame rate. Thereby, the occurrence of flicker can be suppressed.

  In this embodiment, the frame rate of the image sensor 16 is 30 fps, but an image sensor that is driven at a frame rate corresponding to an integer multiple of 30 fps or a fraction of an integer may be used.

  For example, when an image sensor driven at a frame rate of 60 fps is used, the exposure end time may be advanced by “k / 150” seconds from the generation of the vertical synchronization signal Vsync. In this case, since 3/150 seconds is an integral multiple of the blinking cycle 1/100 seconds of the fluorescent lamp FL, “k” may be an integer that periodically changes in the range of “0 ≦ k ≦ 2”.

  In this embodiment, the timing correction amount GP is fixed to “0 seconds” in an area where the frequency of the commercial power supply is 60 Hz (see steps S1 to S3 in FIG. 8). However, as long as the condition that the exposure timing is advanced by a period corresponding to an integral multiple of the remainder obtained by dividing the period corresponding to the frame rate by the period corresponding to one half of the reciprocal of the frequency of the commercial power supply is satisfied, There is no need to change the process according to the frequency of the commercial power supply, and the timing correction amount GP may be adjusted by a common process.

  That is, when an image sensor driven at a frame rate of 30 fps is used in a region where the frequency of the commercial power supply is 60 Hz, the above-mentioned remainder becomes zero and the timing correction amount GP is fixed to “0 second” as a result. . Thus, the exposure process is executed in the manner shown in FIG. 9 with respect to the blinking cycle of the light source.

  Furthermore, in this embodiment, the imaging surface is exposed at a cycle (= 1/30 second) corresponding to the frame rate, but the exposure cycle may be an integer multiple of the frame rate. For example, the charge transfer process may be output every 1/30 seconds, while the exposure process may be executed every 1/15 seconds. In this case, black images and subject images are output alternately.

  In this embodiment, the digital still camera has been described. However, the present invention can also be applied to a digital video camera, a tablet computer, a mobile phone terminal, a smartphone, or the like.

DESCRIPTION OF SYMBOLS 10 ... Digital camera 16 ... Image sensor 18 ... Driver 20 ... Signal processing circuit 22 ... Timing generator 24 ... Clock generation circuit 26 ... CPU

Claims (7)

Imaging means for repeatedly outputting an image representing a scene captured on the imaging surface;
An exposure unit that exposes the imaging surface at a predetermined cycle corresponding to a frame rate, and an exposure time of the exposure unit based on a deviation between a cycle in which luminance of a light source of a scene captured on the imaging surface changes and the predetermined cycle An electronic camera comprising control means for executing correction processing for speeding up the image at the predetermined cycle.   The correction process is performed for each period corresponding to the remainder obtained by dividing the predetermined period by a period corresponding to one half of the reciprocal of the frequency of the commercial power source employed in the area to which the scene captured on the imaging surface belongs. 2. The electronic camera according to claim 1, which corresponds to a process for advancing the exposure time of the exposure means.   The electronic camera according to claim 2, further comprising initialization means for periodically initializing a timing correction amount by the correction process.   The electronic camera according to claim 3, wherein the initialization unit initializes the timing correction amount every time a period corresponding to the timing correction amount matches an integer multiple of a reciprocal of the frequency of the commercial power source. Detection means for detecting the frequency of the commercial power source employed in the area to which the scene captured on the imaging surface belongs, and the processing of the control means is limited when the frequency of the commercial power source detected by the detection means deviates from a predetermined condition The electronic camera according to any one of claims 1 to 4, further comprising a restricting unit. In a processor of an electronic camera including an imaging unit that repeatedly outputs an image representing a scene captured on an imaging surface, and an exposure unit that exposes the imaging surface at a predetermined period corresponding to a frame rate,
A control step for executing a correction process for advancing the exposure timing of the exposure means at the predetermined period based on a shift between a period at which the luminance of the light source of the scene captured on the imaging surface changes and the predetermined period; , Exposure control program. An exposure control method executed by an electronic camera including an imaging unit that repeatedly outputs an image representing a scene captured on an imaging plane, and an exposure unit that exposes the imaging plane at a predetermined period corresponding to a frame rate,
Exposure control comprising: a control step of executing a correction process for advancing the exposure timing of the exposure means at the predetermined period based on a deviation between a period at which the luminance of the light source of the scene captured on the imaging surface changes and the predetermined period Method.

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