JP5644232B2 - Imaging device - Google Patents

Description

  The present invention relates to an imaging apparatus.

  Conventionally, during continuous shooting using the rolling shutter method, based on a frame image shot at a shutter speed of 1/100 sec and a frame image shot at a shutter speed of 1/120 sec, these two There is known a camera that detects the occurrence of flicker by comparing the luminance of common areas of frame images (for example, Patent Document 1).

JP 2007-329658 A

  However, since it is necessary to capture two flicker detection images during continuous shooting, there is a problem in that the frame rate decreases.

The imaging device according to claim 1, wherein a plurality of pixels are arranged in a matrix, an imaging device that captures an image of a subject using a rolling shutter method and outputs an image signal, and an image of the subject using the imaging device. When continuously capturing images, a plurality of pixels constituting a plurality of first pixel rows out of a plurality of pixels arranged in a matrix are exposed at a first exposure time at predetermined time intervals. together to output one screen image signal, among the plurality of pixels arranged in a matrix, a plurality of pixels constituting the plurality of different second pixel row and the first pixel row is different from the first exposure time second an imaging element control means for outputting a second Ima signal exposed with second exposure time, a generation unit for generating a difference image data corresponding to the difference between the first image signal and the second image signal, generated difference Based on the image data, the periodicity of the light illuminating the subject And a detection means for detecting the presence of flicker occurring in the captured image by the amount change detection means, the difference image data to the averaging process in the row direction, the averaging process data from the Fourier transform processed data A feature is that high-frequency components of a predetermined frequency or higher are excluded, and the presence or absence of flicker occurring in the captured image is detected from data obtained by performing inverse Fourier transform on the data after the exclusion .
An image pickup apparatus according to claim 10, wherein a plurality of pixels are arranged in a matrix, an image pickup device that picks up an image of a subject by a rolling shutter method and outputs an image signal, and an image of the subject using the image pickup device. When continuously capturing images, a plurality of pixels constituting a plurality of first pixel rows out of a plurality of pixels arranged in a matrix are exposed at a first exposure time at predetermined time intervals. While outputting one image signal, a plurality of pixels constituting a plurality of second pixel rows different from the first pixel row among a plurality of pixels arranged in a matrix form are different from the first exposure time. Image sensor control means for outputting a second image signal after exposure for an exposure time, generation means for generating difference image data corresponding to the difference between the first image signal and the second image signal, and generated difference image data Based on the periodicity of light illuminating the subject And detecting means for detecting the presence or absence of flicker occurring in the photographed image due to a change in the amount of light. When the first time is set and the image data obtained by continuous imaging is not recorded on the recording medium, a second time longer than the first time is set as a predetermined time interval, and the detecting means sets The presence or absence of flicker occurring in the captured image is detected at a time interval of the first time or the second time.

  According to the present invention, the first image signal output by exposing the first pixel row of the plurality of pixels at the first exposure time and the second image row output by exposing the second pixel row at the second exposure time. The presence or absence of flicker is detected based on the difference image data corresponding to the difference from the second image signal. As a result, flicker can be detected while suppressing a decrease in the frame rate when continuously capturing images.

The figure explaining the principal part structure of the digital camera by embodiment of this invention 1 is a block diagram illustrating a configuration of a control system of a digital camera of an embodiment FIG. 6 is a diagram for explaining an example of arrangement of a first pixel row group and a second pixel row group in an image sensor. The figure explaining various image data generated by subtraction processing typically The figure explaining the relationship between the frequency and amplitude intensity in detection image data Flow chart explaining operation of digital camera The figure explaining the example of arrangement of the 1st pixel row group and the 2nd pixel row group on an image sensor in a modification.

  The digital camera of this embodiment is intended to prevent coloring (flicker) that occurs in a photographed image under illumination light from a fluorescent lamp. The fluorescent lamp in this case refers to a lamp whose lighting is controlled using a commercial frequency AC power supply (non-inverter system). That is, it is a fluorescent lamp that repeatedly blinks at twice the commercial frequency (for example, 100 Hz when the commercial frequency is 50 Hz and 120 Hz when the commercial frequency is 60 Hz).

  A camera according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a main configuration of the digital camera 1. An interchangeable lens 2 including a photographing lens L1 and a diaphragm 20 is detachably mounted on the body of the digital camera 1. On the body side of the digital camera 1, a quick return mirror 10, a focusing screen 11, a pentaprism 12, an eyepiece lens 13, and an image sensor 14 are provided.

  FIG. 2 is a block diagram schematically showing the control system of the digital camera 1. In FIG. 2, the components shown in FIG. The control system of the digital camera 1 includes an image sensor 14, a buffer memory 16, a control circuit 18, an LCD drive circuit 19, a liquid crystal display 191, an operation unit 30, and a memory card interface 31.

  Referring to FIG. 1, the subject light that has passed through the interchangeable lens 2 and entered the digital camera 1 is guided upward by a quick return mirror 10 positioned as shown by a solid line in FIG. 1 before the shutter release. An image is formed on the focusing screen 11. The subject image formed on the focusing screen 11 is guided to the eyepiece 13 by the pentaprism 12. As a result, the subject image is observed by the user. Part of the subject light passes through the semi-transmissive region of the quick return mirror 10, is reflected downward by the sub mirror 10a, and enters a focus detection sensor (not shown). After the release, the quick return mirror 10 is rotated to the position indicated by the broken line in FIG. 1, the subject light is guided to the imaging device 14, and the subject image is formed on the imaging surface.

The control system will be described in detail with reference to FIG.
The imaging element 14 is configured by a CMOS sensor including an XY address type photoelectric conversion element (imaging pixel) having a plurality of pixels arranged in a matrix. The image sensor 14 is driven in accordance with the control of the control circuit 18 to be described later, images a subject image input through the imaging lens L1, and outputs an image signal obtained by the imaging. Further, the image sensor 14 is driven by a method (so-called rolling shutter method) in which a shutter is sequentially released for each scanning line every predetermined horizontal scanning period.

  The image signal output from the image sensor 14 is subjected to analog processing (gain control or the like) by an AFE circuit (not shown) or the like, and is converted into a digital image signal by an A / D conversion circuit (not shown). The image signal converted into the digital signal is input to the buffer memory 16. The buffer memory 16 is configured by a volatile memory that temporarily stores the pixel signal output from the image sensor 14.

  The control circuit 18 includes a CPU, a ROM, a RAM, and the like (not shown), and is an arithmetic circuit that controls each component of the digital camera 1 and executes various data processing based on a control program. The control program is stored in a nonvolatile memory (not shown) in the control circuit 18.

  The control circuit 18 functionally includes an image processing unit 181, an image recording unit 182, a drive control unit 183, a subtraction processing unit 184, a detection unit 185, and an exposure time control unit 186. The image processing unit 181 performs various image processing on the input image signal on the digital image signal to generate image data. Further, the image processing unit 181 generates display image data to be displayed on the liquid crystal display 191 based on the image data recorded on the memory card 32. The image recording unit 182 performs compression processing on the image data generated by the image processing unit 181 by a predetermined method such as JPEG, and records it in the memory card 32 in a format such as EXIF.

  The drive control unit 183 controls the drive timing of the image sensor 14 via a timing generator or the like (not shown). The drive control unit 183 controls the drive of the image sensor 14 at predetermined time intervals when a moving image shooting mode or a live view mode, which will be described later, is set, and an image signal (hereinafter referred to as “flicker detection process”). , A detection image signal). The subtraction processing unit 184 uses the output detection image signal to generate flicker detection image data (hereinafter, detection image data). The detection unit 185 uses the generated detection image data to determine the presence / absence of flicker, in other words, whether photographing under illumination light from a fluorescent lamp is being performed. When flicker is detected by the detection unit 185, the exposure time control unit 186 changes the exposure time so that the captured image is not affected by the flicker. The details of the drive control unit 183, the subtraction processing unit 184, the detection unit 185, and the exposure time control unit 186 will be described later.

  The LCD drive circuit 19 is a circuit that drives the liquid crystal display 191 based on a command from the control circuit 18. The liquid crystal display 191 is a liquid crystal display panel having an aspect ratio of, for example, vertical 3: horizontal 4. The liquid crystal display 191 has an image corresponding to the display image data created by the control circuit 18 based on the image data recorded on the memory card 32 together with a live view display that displays an image captured by the image sensor 14 in real time. Is displayed. The liquid crystal display 191 displays a menu screen for various settings of the digital camera 1 based on the operation of the operation unit 30.

  The operation unit 30 includes various switches provided corresponding to various operation members operated by the user, and outputs an operation signal corresponding to the operation of the operation member to the control circuit 18. The operation member is, for example, a release button, a menu button for displaying the above menu screen, a cross key operated when selecting and operating various settings, and a setting selected by the cross key. A determination button, a mode switching button for switching the operation of the digital camera 1 between the shooting mode and the playback mode, and the like are included. Further, the operation unit 30 can set a still image shooting mode, a moving image shooting mode, a live view mode, and the like as the imaging mode.

  The memory card interface 31 is an interface to which the memory card 32 can be attached and detached. The memory card interface 31 is an interface circuit that writes an image file to the memory card 32 and reads an image file recorded on the memory card 32 based on the control of the control circuit 18. The memory card 32 is a semiconductor memory card such as a compact flash (registered trademark) or an SD card.

Hereinafter, a flicker detection process when the moving image shooting mode is set according to the operation of the operation unit 30 by the user, that is, when the acquired image data is recorded on the memory card 32 will be described.
When the live view mode or the moving image shooting mode is set by operating the operation unit 30, the control circuit 18 rotates the quick return mirror 10 to the position indicated by the broken line in FIG. It is guided to the image sensor 14. Further, the control circuit 18 causes the image sensor 14 to output an image signal for each pixel row every horizontal scanning period tH. At this time, the control circuit 18 sets the readout cycle (frame rate) of the image signal to 1/30 [s], for example.

  When shooting in the moving image shooting mode is started, the drive control unit 183 instructs the image sensor 14 to output a detection image signal at a predetermined time interval (for example, 0.5 second interval). At this time, the drive control unit 183 sets the exposure time of the imaging pixels constituting the pixel rows included in the first pixel row group, that is, the shutter speed to 1/100 second. In addition, the shutter speed of the imaging pixels constituting the pixel rows included in the second pixel row group is set to 1/120 seconds. Then, the drive control unit 183 drives the imaging pixels included in the first pixel row group and the imaging pixels included in the second pixel row group for each pixel row by a rolling shutter method, and outputs an image signal for each pixel row. Output. That is, at the time of acquiring one frame of image data, the drive control unit 183 exposes a part of the image sensor 14 at a shutter speed of 1/100 second, and the other area of the image sensor 14 has a shutter speed of 1/120. Expose in seconds. In the following description, the image signal output from the imaging pixel included in the first pixel row group is the first detection image signal, and the image signal output from the imaging pixel included in the second pixel row group is the second detection. This is called an image signal for use. A flicker detection process is performed based on the first and second image signals.

  FIG. 3 shows an arrangement relationship between the first pixel row group and the second pixel row group in the image sensor 14. In the following description, the horizontal direction of the image sensor 14 is the pixel row direction, and the vertical direction is the pixel column direction. As shown in FIG. 3, the first pixel row L (1), the third pixel row L (3),..., The (2n−1) th pixel row L (2n−1). The imaging pixels included in the first pixel row group LG1. In addition, the imaging pixels included in the second pixel row L (2), the fourth pixel row L (4),..., The second nth pixel row L (2n) are the second pixel row group. LG2 is configured. That is, the pixel rows constituting the first pixel row group LG1 and the pixel rows constituting the second pixel row group LG2 are alternately arranged in the pixel column direction. In addition, the image sensor 14 has pixel columns of the first column to the m-th column. In FIG. 3, the pixel rows included in the second pixel row group LG2 are indicated by hatching.

  The subtraction processing unit 184 generates detection image data using the first detection image signal and the second detection image signal output from the image sensor 14. When generating detection image data, first, the subtraction processing unit 184 generates image data (hereinafter referred to as first image data) using the first detection image signal. Further, the subtraction processing unit 184 generates image data (hereinafter referred to as second image data) using the second detection image signal. Then, the subtraction processing unit 184 takes the difference between the first image data and the second image data, and generates detection image data. The detection image data generated as described above includes a contour portion of a subject and a flicker component when photographing is performed under illumination light from a fluorescent lamp.

  With reference to the schematic diagram shown in FIG. 4, the contour portion of the subject and the flicker component included in the detection image data will be described. In FIG. 4, the subject S photographed during the flicker detection process and the first pixel row group LG1 and the second pixel row group LG2 included in the image sensor 14 are shown superimposed on the same screen. FIG. 4A shows the relationship between the subject imaged when performing the flicker detection process, the first image row group LG1, and the second pixel row group LG2. In FIG. 4A as well, a region corresponding to the second pixel row group LG2 is indicated by hatching. FIG. 4B shows the first image data when the subject S shown in FIG. FIG. 4C shows second image data when the subject S in FIG. 4A is photographed.

  It is assumed that the fluorescent lamp is controlled to be lit at a commercial frequency of 50 Hz, that is, photographing is performed under illumination light that repeatedly blinks at 100 Hz. In this case, the flicker component is superimposed on the first detection image signal from the first pixel row group exposed at the shutter speed of 1/100 second. As a result, the first image data includes a flicker component. The subtraction processing unit 184 calculates the difference between the first image data in FIG. 4B and the second image data in FIG. 4C to generate detection image data. In this case, the subtraction processing unit 184 includes first image data corresponding to the pixel row L (1) of the first pixel row group LG1, and a second image corresponding to the pixel row L (2) of the second pixel row group LG2. Calculate the difference with the data. Similarly, the subtraction processing unit 184 calculates a difference between the first image data corresponding to the pixel row L (3) and the second image data corresponding to the pixel row L (4), and the pixel row L A difference is calculated between the first image data corresponding to (2n−1) and the second image data corresponding to the pixel row L (2n). In other words, the subtraction processing unit 184 calculates a difference between image data corresponding to two pixel rows adjacent in the pixel column direction among pixel rows belonging to different pixel row groups, and generates detection image data. .

  The first image data and the second image data correspond to images obtained by photographing the same subject. Therefore, the detection image data, which is the difference data between the first image data and the second image data, ideally has an output value of 0 if no flicker occurs. However, as described above, the fluorescent lamp is photographed under illumination light whose lighting is controlled at a commercial frequency of 50 Hz, and the flicker component is superimposed on the first detection image signal. Accordingly, when flicker occurs, an output value corresponding to the flicker component is obtained by calculating the difference between the first image data and the second image data.

  Furthermore, since the subtraction processing unit 184 calculates a difference between image data corresponding to pixel rows adjacent in the pixel column direction, it does not calculate a difference between image data corresponding to the same portion of the subject S. Absent. Therefore, for example, in a portion where the output value of the image data corresponding to the contour of the subject S is large, the output value also remains in the detection image data generated by the subtraction processing unit 184. Therefore, the detection image data includes the flicker component and the contour portion of the subject S as output values.

  FIG. 4D schematically shows detection image data having the above-described features. In FIG. 4D, the flicker component is included in the image data included in the area shown with dots, that is, in the area corresponding to the first pixel row group LG1. Since the pixel rows of the first pixel row group LG1 and the pixel rows of the second pixel row group LG2 are alternately arranged in the pixel column direction, image data including flicker components is generated at intervals of one row. Furthermore, in FIG.4 (d), the outline part of the to-be-photographed object S is shown with a broken line.

  The detection unit 185 detects the presence or absence of flicker using detection image data having characteristics as shown in FIG. First, the detection unit 185 calculates an average of the output values of the image data for each pixel row of the detection image data. That is, the detection unit 185 calculates an average of output values of image data from the first pixel column to the m-th pixel column in the first row. Similarly, the detection unit 185 calculates the average of the output values of the image data from the first pixel column to the m-th pixel column for each of the second to second nth rows.

  FIG. 4 (e) shows a plot of the above-described addition average result by the detection unit 185. The pixel data on which the flicker component is superimposed, that is, the value obtained by averaging the output values of the image data corresponding to the first pixel row group LG1 (pixel row L (2n-1)) is a pixel on which the flicker component is not superimposed. The value is larger than the value obtained by averaging the output values of the image data corresponding to the row, that is, the second pixel row group LG2 (pixel row L (2n)). Therefore, in FIG. 4E, peaks appear as peaks P (1) to P (2n-1). In addition, a peak reflecting the contour portion of the subject S appears in the value obtained by averaging the output values of the image data corresponding to the second pixel row group LG2 (pixel row L (2n)). Based on the plot result, the detection unit 185 detects that flicker is generated when the amplitude intensity corresponding to the frequency (50 Hz or 60 Hz) corresponding to the predetermined flicker component exceeds a predetermined threshold. . That is, the detection unit 185 detects whether or not the flicker component included in the output values of the peaks P (1) to P (2n−1) is greater than or equal to a predetermined threshold value.

  In order to detect the presence or absence of flicker, the detection unit 185 performs Fourier transform on a value obtained by adding and averaging output values for each pixel row, and calculates an amplitude intensity for each frequency. FIG. 5 shows a result of Fourier transform of a value obtained by averaging the output values for each pixel row shown in FIG. As described above, since the fluorescent lamp is photographed under illumination light whose lighting is controlled at a commercial frequency of 50 Hz, a high peak Pf appears in the amplitude intensity near the frequency of 50 Hz.

  Furthermore, as shown in FIG. 5, a peak Ps appears in the amplitude intensity even in the vicinity of the frequency corresponding to the contour portion of the subject S (for example, 70 Hz or more). However, since this high frequency component is irrelevant when detecting the presence or absence of flicker, the detection unit 185 removes the high-frequency component, for example, the one corresponding to 70 Hz or more from the obtained amplitude intensity, Generate post-removal data. Then, the detection unit 185 determines whether or not the amplitude intensity value corresponding to the frequencies 50 Hz and 60 Hz among the amplitude intensity from which the high frequency component has been removed is equal to or greater than a predetermined threshold Th.

  The detection unit 185 determines that 50 Hz flicker occurs in the captured image when the amplitude intensity corresponding to the frequency of 50 Hz is equal to or greater than the predetermined threshold Th. The detection unit 185 determines that 60 Hz flicker occurs in the captured image when the amplitude intensity corresponding to the frequency of 60 Hz is equal to or greater than the predetermined threshold Th. In the case shown in FIG. 5, the detection unit 185 determines that 50 Hz flicker occurs in the captured image.

  In the above description, it is assumed that the fluorescent lamp is photographed under illumination light whose lighting is controlled at a commercial frequency of 50 Hz. However, when the image is taken under illumination light that repeatedly blinks at a commercial frequency of 60 Hz, that is, 120 Hz, flicker components are included in the second detection image signal output from the pixel rows included in the second pixel row group LG2. Superimpose. For this reason, when the detection unit 185 calculates an average of the output values of the detection image data for each pixel row and performs Fourier transform, a high peak Pf appears in the amplitude intensity near the frequency of 60 Hz.

  When the detection unit 185 detects the frequency of flicker that occurs in the captured image, the exposure time control unit 186 sets an exposure time, that is, a shutter speed, to be used in the subsequent moving image shooting mode. At this time, the exposure time control unit 186 sets the shutter speed to a predetermined multiple of 1/100 seconds when flicker with a frequency of 50 Hz is detected, and when flicker with a frequency of 60 Hz is detected, The shutter speed is set to a predetermined multiple of 1/120 second. Then, the exposure time control unit 186 drives the image sensor 14 at the set shutter speed.

  When the live view mode is set according to the operation of the operation unit 30 by the user, that is, when the acquired image data is not recorded in the memory card 32, the drive control unit 183 has a longer time interval than in the moving image shooting mode. The image sensor 14 is instructed to output a detection image signal (for example, at intervals of 1 second). The processing of the subtraction processing unit 184, the detection unit 185, and the exposure time control unit 186 using the detection image signal is the same as that in the moving image shooting mode.

  The operation of the digital camera 1 according to the present embodiment will be described with reference to the flowchart shown in FIG. The processing in FIG. 6 is performed by executing a program in the control circuit 18. This program is stored in a memory (not shown), and is activated and executed when a release button included in the operation unit 30 is operated to input a signal instructing to start photographing.

  In step S101, it is determined whether or not a predetermined time interval has been reached (0.5 second interval in the moving image shooting mode and 1 second interval in the live view mode). If the predetermined time interval is reached, an affirmative determination is made in step S101 and the process proceeds to step S102. If the predetermined time interval is not reached, a negative determination is made in step S101 and the determination process is repeated.

  In step S102, the image sensor 14 is instructed to output a detection image signal, and the process proceeds to step S103. In step S103, the first image data is generated using the first detection image signal output from the image sensor 14, the second image data is generated using the second detection image signal, and the process proceeds to step S104. In step S104, the difference between the first image data and the second image data is calculated to generate detection image data, and the process proceeds to step S105.

  In step S105, the output values of the detection image data are averaged for each pixel row, subjected to Fourier transform, and the process proceeds to step S106. In step S106, the amplitude intensity corresponding to the high frequency component of 70 Hz or more is removed from the amplitude intensity for each frequency that has been subjected to Fourier transform, and the process proceeds to step S107. In step S107, it is determined whether the amplitude intensity corresponding to the frequency 50 Hz or the frequency 60 Hz is equal to or greater than a predetermined threshold Th. If the amplitude intensity corresponding to the frequency 50 Hz or the frequency 60 Hz is equal to or greater than the predetermined threshold Th, an affirmative determination is made in step S107 and the process proceeds to step S108. In step S108, it is determined that flicker has occurred, the frequency is detected, and the process proceeds to step S109. In step S109, the shutter speed is changed according to the detected flicker frequency, and the process proceeds to step S111.

  When the amplitude intensity corresponding to the frequency 50 Hz and the frequency 60 Hz is less than the predetermined threshold Th in step S107, a negative determination is made and the process proceeds to step S110. In step S110, it is determined that no flicker has occurred, and the process proceeds to step S111. In step S111, it is determined whether or not shooting has been completed. When an operation signal for instructing the end of shooting is input from the operation unit 30 in response to the user operating the release button, an affirmative determination is made in step S111 and the process ends. If an operation signal for instructing the end of shooting is not input from the operation unit 30, a negative determination is made in step S111 and the process returns to step S101.

According to the digital camera 1 according to the embodiment described above, the following operational effects can be obtained.
(1) A plurality of image pickup pixels are arranged in a matrix on the image pickup device 14, and the image pickup device 14 picks up an image of a subject by a rolling shutter system and outputs an image signal. The drive control unit 183 is configured to capture a plurality of images arranged in a matrix at predetermined time intervals (for example, 1 second or 0.5 seconds) when continuously capturing images of the subject using the image sensor 14. Among the pixels, a plurality of imaging pixels included in the first pixel row group LG1 are exposed at a shutter speed of 1/100 seconds to output a first detection image signal. Furthermore, the drive control unit 183 selects a plurality of imaging pixels constituting a plurality of second pixel row groups LG2 different from the first pixel row group LG1 from among a plurality of imaging pixels arranged in a matrix at a shutter speed of 1. The exposure is performed at / 120 seconds to output a second detection image signal. The subtraction processing unit 184 generates detection image data corresponding to the difference between the first image data generated using the first detection image signal and the second image data generated using the second detection image signal. . The detection unit 185 detects the presence or absence of flicker that occurs in the captured image due to a periodic change in the amount of light that irradiates the subject, based on the generated detection image data. Accordingly, flicker can be detected while suppressing a decrease in the frame rate during continuous shooting, so that it is possible to suppress the occurrence of problems such as unnatural movement of the shot subject.

(2) The detection unit 185 performs addition averaging processing on the detection image data in the pixel row direction, and detects the presence or absence of flicker occurring in the captured image based on data obtained by performing Fourier transform processing on the data subjected to the addition averaging processing. I did it. Therefore, since the Fourier transform process is performed on the one-dimensional value added in the pixel row direction, the processing time can be shortened compared to the case where the Fourier transform process is performed two-dimensionally on the detection image data. Can do.

(3) The detection unit 185 excludes high-frequency components of a predetermined frequency or higher, for example, 70 Hz or higher, from the Fourier-transformed data, and the presence / absence of flicker generated in the captured image from the data obtained by performing the inverse Fourier transform on the data after the exclusion It was made to detect. In other words, the detection unit 185 generates high-frequency components included in the detection image data and generates post-removal image data, and detects the presence or absence of flicker from the post-removal image data. Therefore, the processing time required for flicker detection can be shortened.

(4) The drive control unit 183 sets, for example, 0.5 seconds as a predetermined time interval when recording image data acquired by continuous imaging on the memory card 32, and acquired by continuous shooting. When image data is not recorded in the memory card 32, for example, 1 second is set as the predetermined time interval. Therefore, when continuously capturing images to be recorded, flicker detection processing can be performed with high frequency. Furthermore, when the acquired image is not recorded, the frequency of flicker detection processing is reduced, so that the processing load can be reduced.

(5) The detecting unit 185 detects the presence of flicker when the signal intensity of the component corresponding to the flicker frequency included in the detection image data exceeds a predetermined threshold Th. Therefore, since the presence / absence of flicker is detected using the signal intensity of the frequency component that is likely to be affected by flicker, the processing load can be reduced.

(6) The drive control unit 183 is configured such that the plurality of pixel rows of the first pixel row group LG1 and the plurality of pixel rows of the second pixel row group LG2 are alternately arranged in the pixel column direction. Therefore, when generating the detection image data, the influence of the contour component of the subject S can be suppressed and the flicker detection process can be performed at high speed.

(7) The exposure time control unit 186 changes the exposure time during continuous imaging when the flicker is detected by the detection unit 185, and changes the exposure time during continuous imaging when flicker is not detected. Change of exposure time is prohibited. Then, when the flicker component is detected, the exposure time control unit 186 changes the shutter speed to a shutter speed obtained by multiplying either one of the shutter speed 1/100 seconds and 1/120 seconds, that is, the exposure time. did. Therefore, when flicker is detected, the influence of the flicker on the photographed image can be suppressed and deterioration of the image quality can be prevented.

The digital camera 1 of the embodiment described above can be modified as follows.
(1) The detection unit 185 adds and averages the output values of the detection image data for each pixel row, and after performing Fourier transform, replaces the amplitude intensity corresponding to the high frequency component from the amplitude intensity for each frequency. Alternatively, high frequency components may be removed by performing Fourier transform on the detection image data. In this case, the detection unit 185 performs inverse Fourier transform after performing a Fourier transform on the detected image data as shown in FIG. As a result, an output value obtained by adding and averaging the output values for each pixel row shown in FIG. 4E and removing the output corresponding to the contour portion of the subject S is obtained. The detection unit 185 further performs a Fourier transform on this value, thereby obtaining the correspondence between the frequency and amplitude intensity shown in FIG. 5 from which the high frequency component has been removed.

(2) The detection image signal may not be output from the imaging pixels in the entire area of the imaging element 14. For example, the drive control unit 183 may output the detection image signal from the imaging pixels arranged in the upper third region of the imaging element 14 or the area near the center of the imaging element 14. Even in this case, it is assumed that the pixel rows included in the first pixel row group LG1 and the pixel rows included in the second pixel row group LG2 are alternately arranged in the pixel column direction.

(3) When the image sensor 14 is instructed to output the detection image signal from the drive control unit 183, the image sensor 14 detects the difference after calculating the difference between the first detection image signal and the second detection image signal. It may be output as an image signal. In this case, the subtraction processing unit 184 can obtain the detection image data by converting the input detection image signal into an analog signal without generating the first image data and the second image data.

  Further, when the image sensor 14 outputs the detection image signal subjected to the above difference calculation, the pixel row included in the first pixel row group LG1 and the pixel row included in the second pixel row group LG2 are output. The arrangement is not limited to the arrangement shown in FIG. FIG. 7 shows an example of the arrangement of the first pixel row group LG1 and the second pixel row group LG2 on the image sensor 14 in this case. In FIG. 7, the drive control unit 183 sets the imaging pixels included in the pixel rows L (1), L (4), L (5),... To the first pixel row group LG1, and the shutter speed 1 / Exposure is performed in 100 seconds. Then, the drive control unit 183 sets the imaging pixels included in the pixel rows L (2), L (3), L (6),... To the second pixel row group LG2, and the shutter speed is 1/120 seconds. To expose.

  The image sensor 14 calculates the difference between the first detection image signal output from the pixel row L (1) and the second detection image signal from the pixel row L (2). Similarly, the image sensor 14 calculates a difference between the pixel rows L (3) and L (4), and calculates a difference between the pixel rows L (5) and L (6). Then, the image sensor 14 outputs each difference result to the control circuit 18 as a detection image signal.

  In addition, the present invention is not limited to the above-described embodiment as long as the characteristics of the present invention are not impaired, and other forms conceivable within the scope of the technical idea of the present invention are also within the scope of the present invention. included. The embodiments and modifications used in the description may be configured by appropriately combining them.

14 ... Image sensor, 18 ... Control circuit,
183 ... Drive control unit, 184 ... Subtraction processing unit,
185 ... detection unit, 186 ... exposure time control unit

Claims (10)

An image sensor in which a plurality of pixels are arranged in a matrix and which captures an image of a subject using a rolling shutter method and outputs an image signal;
When continuously capturing images of the subject using the image sensor, a plurality of first pixel rows among the plurality of pixels arranged in the matrix are configured at predetermined time intervals. a plurality of pixels with to output the first Ima signal by exposing the first exposure time, of the plurality of pixels arranged in the matrix, a plurality of second pixels that is different from the first pixel row an imaging element control means for outputting a second Ima signal by exposing a different second exposure time and a plurality of pixels the first exposure time constituting a row,
Generating means for generating difference image data corresponding to a difference between the first image signal and the second image signal;
Detecting means for detecting the presence or absence of flicker occurring in a photographed image due to a periodic light amount change of light irradiating the subject based on the generated difference image data ;
The detection means performs an averaging process on the difference image data in a row direction, excludes a high frequency component having a predetermined frequency or more from data obtained by performing a Fourier transform process on the data subjected to the averaging process, and performs an inverse Fourier transform on the data after the exclusion. An imaging apparatus, wherein the presence or absence of the flicker occurring in the photographed image is detected from the converted data . The imaging device according to claim 1 ,
The image sensor control means sets a first time as the predetermined time interval when recording the image data acquired by the continuous imaging on a recording medium, and the image acquired by the continuous imaging. An image pickup apparatus, wherein when the data is not recorded on the recording medium, a second time longer than the first time is set as the predetermined time interval. In the imaging device according to claim 1 or 2 ,
The imaging apparatus detects the presence of flicker when a signal intensity of a component corresponding to the flicker frequency included in the difference image data exceeds a predetermined value. The imaging device according to claim 3 .
The image pickup device control means sets the first exposure time and the second exposure time corresponding to the frequency of the flicker. In the imaging device according to any one of claims 1 to 4 ,
The generating means generates first image data using the first image signal, generates second image data using the second image signal, and subtracts the first image data and the second image data. And generating the difference image data. In the imaging device according to any one of claims 1 to 5 ,
The imaging element control unit sets the plurality of first pixel rows and the plurality of second pixel rows so that the first pixel rows and the second pixel rows are alternately arranged in a pixel column direction. An imaging apparatus characterized by that. In the imaging device according to any one of claims 1 to 6 ,
When the flicker is detected by the detection means, the exposure time during the continuous imaging is changed, and when the flicker is not detected, the change of the exposure time during the continuous imaging is prohibited. An imaging apparatus comprising: an exposure time changing means for performing. The imaging apparatus according to claim 7 ,
The exposure apparatus according to claim 1, wherein when the flicker is detected, the exposure time changing means changes the exposure time to a value obtained by multiplying one of the first exposure time and the second exposure time by a predetermined value. In the imaging device according to any one of claims 1 to 8 ,
In the continuous imaging, the image signal continuously acquired by the image sensor is displayed on a display device without being recorded on a recording medium, or the continuously acquired image signal is recorded on the recording medium. An image pickup apparatus including a moving image recording operation for recording. An image sensor in which a plurality of pixels are arranged in a matrix and which captures an image of a subject using a rolling shutter method and outputs an image signal;
When continuously capturing images of the subject using the image sensor, a plurality of first pixel rows among the plurality of pixels arranged in the matrix are configured at predetermined time intervals. A plurality of pixels are exposed at a first exposure time to output a first image signal, and a plurality of second pixel rows different from the first pixel row among the plurality of pixels arranged in a matrix form An image sensor control unit that outputs a second image signal by exposing a plurality of pixels constituting the second exposure time different from the first exposure time;
Generating means for generating difference image data corresponding to a difference between the first image signal and the second image signal;
Detecting means for detecting the presence or absence of flicker occurring in a photographed image due to a periodic light amount change of light irradiating the subject based on the generated difference image data;
The image sensor control means sets a first time as the predetermined time interval when recording the image data acquired by the continuous imaging on a recording medium, and the image acquired by the continuous imaging. When data is not recorded on the recording medium, a second time longer than the first time is set as the predetermined time interval,
The image pickup apparatus, wherein the detection means detects the presence or absence of flicker occurring in a shot image at the set time interval of the first time or the second time.

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