JP2011010180A - Digital camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain the accuracy of fixed pattern noise (FPN) correction processing even when high-luminance light is made incident.SOLUTION: A digital camera comprises: an imaging device in which a plurality of pixels are disposed in a matrix shape, for picking up a subject image and outputting a first pixel signal; a change instructing means for instructing a change in operating state of signal output of the imaging device; a read means for reading a second pixel signal from a pixel included in a prescribed row, among the plurality of pixels, when the change in operating state is instructed; a calculation means which uses the second pixel signal to calculate a correction value for correcting error of the first pixel signal by pixel column; a correction means for applying correction to the first pixel signal using the correction value calculated; a determination means for determining whether the subject image meets a prescribed condition regarding lightness information each time the first pixel signal is read; and a restriction means for restricting the quantity of light made incident on the imaging device when the change in operating state is instructed by the change instructing means. In the state where the quantity of light to be made incident is restricted, the read means reads the second pixel signal.

Description

  The present invention relates to a digital camera that corrects noise included in a pixel signal from an image sensor.

  Conventionally, a camera that corrects fixed pattern noise (FPN) caused by a CMOS image sensor is known (for example, Patent Document 1). In such a camera, at the time of live view or moving image shooting mode, light enters the photodiode of the image sensor even during image reading. For this reason, when high-intensity light is incident, the charge accumulated in the photodiode leaks, the charge moves to the photodiode without passing through the transfer gate switch that transfers the charge to the photodiode, and the reset level fluctuates. There is.

JP 2007-20156 A

  As described above, if the reset level of the pixel fluctuates as a result of incidence of high-intensity light, accurate FPN correction data cannot be acquired. If such inaccurate FPN correction data is used, FPN correction processing is performed. There is a problem that the image quality deteriorates.

  According to a first aspect of the present invention, there is provided a digital camera in which a plurality of pixels are arranged in a matrix, an image sensor that captures a subject image and outputs a first pixel signal, and a change in an operation state of signal output of the image sensor. A change instruction means for instructing, a read means for reading out a second pixel signal from a pixel included in a predetermined row among a plurality of pixels when an instruction to change the operation state is given; Calculation means for calculating a correction value for correcting an error for each pixel column of the pixel signal, correction means for correcting the first pixel signal using the calculated correction value, and the first pixel signal are read out Each time the subject image satisfies a predetermined condition regarding the brightness information, and when the change instruction means instructs the change of the operation state, the determination means satisfies the predetermined condition. When judged It is provided with a limiting means for limiting the amount of incident light on the image sensor, the reading means, characterized in that reading the second pixel signal in a state where the amount of incident light is limited.

  According to the present invention, it is possible to limit the amount of light incident on the image sensor if a predetermined condition is satisfied when the change of the operation state is instructed.

The figure explaining the principal part structure of the digital camera by embodiment of this invention FIG. 1 is a block diagram illustrating a configuration of a control system of a digital camera according to an embodiment Block diagram illustrating the configuration of the image processing unit FIG. 7 illustrates a pixel configuration of an image sensor Diagram explaining FPN acquisition area The figure explaining the concept of FPN correction processing The figure explaining the timing which acquires FPN data at the time of live view mode, and the image data of each frame A block diagram for explaining a configuration of a control system of a digital camera in a modified example The figure explaining the thinning-out reading area The figure explaining the principal part structure of the digital camera in a modification.

  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. Driving of the diaphragm 20 is controlled based on a command from 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, an image sensor 14, a focus detection sensor 15, and a shutter 21 are provided.

  FIG. 2 is a block diagram of a control system of the digital camera 1 to which the interchangeable lens 2 is attached. In FIG. 2, the components shown in FIG. As shown in FIG. 2, the interchangeable lens 2 includes a photographic lens L <b> 1, a diaphragm 20, and a diaphragm driving unit 22. The aperture drive unit 22 is configured by a motor or the like that drives the aperture 20 based on a drive control signal from the digital camera 1. The digital camera 1 includes an image sensor 14, an A / D conversion circuit 16, a timing generator 17, 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 photographer. Part of the subject light passes through the semi-transmission region of the quick return mirror 10, is reflected downward by the sub mirror 10 a, and enters the focus detection sensor 15. 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 an XY address type photoelectric conversion element having a plurality of pixels 14P and a column signal processing circuit 142 arranged in a matrix. Details of the image sensor 14 will be described later. The image sensor 14 is driven in accordance with control of a control circuit 18 described later to capture a subject image input through the photographing lens L1, and outputs a pixel signal obtained by the imaging. In the present embodiment, the image sensor 14 is driven by a method of sequentially releasing the shutter for each scanning line (so-called rolling shutter method).

  For example, the imaging element 14 is configured such that imaging sensitivity (exposure sensitivity) can be changed in a predetermined step within a range equivalent to ISO 100 to ISO 1600, that is, the operation state of the signal output of the pixel signal from the imaging element 14 can be changed. ing. The imaging sensitivity is a controlled amount that changes the detection sensitivity of charges accumulated in the imaging device 14 or the amplification gain of an amplifier circuit (not shown). The operation for changing the imaging sensitivity (gain changing operation) is performed by the user using the operation unit 30 described later.

  The column signal processing circuit 142 includes an amplifier, an A / D converter, a line memory, and the like for each pixel column (pixel column), and inputs a pixel signal output from the pixel 14P. The column signal processing circuit 142 according to the present embodiment adds pixel signals adjacent in the vertical direction read from each pixel 14P of the image sensor 14 with a predetermined addition degree, and outputs the added pixel signal. In this case, the column signal processing circuit 142 is output from, for example, two pixels or three pixels adjacent in the horizontal direction or the vertical direction in accordance with an operation (adding method changing operation) of changing the addition method of the operation unit 30 by the user. The obtained pixel signals are added. In addition to the above-described operations, the column signal processing circuit 142 performs CDS (correlated double sampling) and applies a gain to the pixel signal. Note that it is not essential to incorporate the above-described addition processing function into the image sensor 14, and the above-described addition processing may be performed in a subsequent portion of the image sensor 14, for example, an image processing unit 181 described later.

  The A / D conversion circuit 16 is a circuit that performs analog processing on the pixel signal output from the image sensor 14 and then converts it to a digital pixel signal. In addition, when using the image pick-up element of the type in which this A / D conversion circuit 16 is incorporated in the image pick-up element 14, the A / D conversion circuit 16 becomes unnecessary. The timing generator 17 outputs a timing signal to the image sensor 14 and the A / D converter circuit 16 in accordance with a command from the control circuit 18 and controls the drive timing of the image sensor 14 and the A / D converter circuit 16. It is.

  The control circuit 18 has a CPU, ROM, 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. The control circuit 18 controls the timing generator 17 described above.

  The control circuit 18 includes an image processing unit 181, a compression unit 182, and an aperture control unit 184. The image processing unit 181 performs image processing such as white balance processing, gamma correction processing, color interpolation processing, contour enhancement, and vignette correction on the input digital pixel signal to generate image data. Further, the image processing unit 181 changes the imaging sensitivity by multiplying the input digital pixel signal by a gain according to a gain change operation by the user (digital gain correction). Furthermore, as shown in FIG. 3, the image processing unit 181 functionally includes a calculation unit 181a, a correction unit 181b, and a determination unit 181c. The calculation unit 181a calculates FPN data used for FPN correction using the input FPN pixel signal. The correction unit 181b performs FPN correction processing on the input normal pixel signal using the FPN correction value calculated by the calculation unit 181a.

  When the live view mode or the moving image shooting mode is set, the determination unit 181c determines whether a high-luminance subject is shot based on the output level of the normal pixel signal when generating image data for each frame. It is determined whether or not the subject image satisfies a condition regarding brightness information. Details of the calculation unit 181a, the correction unit 181b, and the determination unit 181c will be described later.

  The compression unit 182 is a circuit that performs JPEG compression processing on image data generated by image processing performed by the image processing unit 181. The temporary memory 183 is a volatile storage medium used as a buffer memory that temporarily stores data during or after image processing and image compression processing. The aperture control unit 184 outputs a drive control signal so as to reduce the aperture 20 when the determination unit 181c determines that a high-luminance subject has been shot. The output drive control signal is output to the aperture drive unit 22 of the interchangeable lens 2 via an interface (not shown). This interface is provided for performing various types of information communication between the digital camera 1 and the interchangeable lens 2.

  The memory card interface 31 is an interface to which the memory card 32 can be attached and detached. The memory card interface 31 writes image data to the memory card 32 or reads image data 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.

  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 displays the display data created by the control circuit 18 based on the image data recorded on the memory card 32 in the reproduction mode. The liquid crystal display 191 is configured to display a so-called live view image. The live view is a display mode in which the quick return mirror 10 is flipped upward before the release and an image captured by the image sensor 14 is displayed on the liquid crystal display 191 in real time, and is an imaging mode adopted in a single-lens reflex camera. is there.

  The operation unit 30 is a switch that receives a user operation. The operation unit 30 includes a power switch, a release switch, a display changeover switch for other setting menus, a setting menu determination button, a sensitivity setting switch for a gain changing operation for changing the imaging sensitivity described above, and the pixel signal adding method described above. An addition change switch for an addition method change operation for changing the value is included. The operation unit 30 can set a still image shooting mode, a moving image shooting mode, and a live view mode for displaying the above live view image as a shooting mode.

  Next, the image sensor 14 will be described in detail with reference to FIG. As shown in FIG. 4, each pixel 14P includes a pixel photodiode (PD) 141, a floating diffusion (FD) 143, a transfer gate switch (TX) 144, a reset switch (RESET) 145, a pixel amplifier (AMI) 146, and A pixel selection switch (SEL) 147 is provided. Further, the imaging device 14 includes a vertical signal line Ln for each pixel column and a vertical line selection switch 148 for each vertical signal line Ln. The vertical line selection switch 148 is a switch for selecting the pixel 14P from which the pixel signal is read out for each pixel column.

  The pixel photodiode (PD) 141 photoelectrically converts the received subject light according to its intensity. The transfer gate switch (TX) 144 is provided between the pixel photodiode (PD) 141 and the floating diffusion (FD) 143. The transfer gate switch (TX) 144 is a switch that switches on / off of electrical connection between the pixel photodiode (PD) 141 and the floating diffusion (FD) 143. When the transfer gate switch (TX) 144 is turned on in response to the timing signal from the timing generator 17, the charge photoelectrically converted by the pixel photodiode (PD) 141 is transferred to the floating diffusion (FD) 143.

  The floating diffusion (FD) 143 is provided to convert the electric charge photoelectrically converted by the pixel photodiode (PD) 141 into a voltage. The pixel selection switch (SEL) 147 is a switch that switches on / off of electrical connection between the floating diffusion (FD) 143 and the vertical signal line Ln, and is turned on / off according to a timing signal from the timing generator 17. Is switched. The reset switch (RESET) 145 is a switch for applying a voltage to the floating diffusion (FD) 143 until the reset voltage becomes the reference voltage.

  Next, pixel signal reading will be described separately for normal pixel signal reading and FPN (Fixed Pattern Noise) pixel signal reading. The normal pixel signal is a pixel signal corresponding to an image for recording acquired in the still image shooting mode or the moving image shooting mode, or a live view image displayed on the liquid crystal display 191 in the live view mode. The FPN pixel signal corrects the streak-like fixed pattern noise (FPN) generated in the vertical direction of the captured image due to the column signal processing circuit 142, that is, the fixed pattern noise (FPN) for each pixel column of the image sensor 14. This is a pixel signal acquired for the purpose.

-Normal pixel signal readout-
When the charge is read from the pixel photodiode (PD) 141, the control circuit 18 turns on the reset switch (RESET) 145 via the timing generator 17. That is, a voltage is applied to the floating diffusion (FD) 143 until the reset voltage becomes the reference voltage. Then, the control circuit 18 turns on the transfer gate switch (TX) 144 via the timing generator 17. As a result, the charge photoelectrically converted by the pixel photodiode (PD) 141 is transferred to the floating diffusion (FD) 143 and stored in the floating diffusion (FD) 143. That is, the charge (luminance level) photoelectrically converted by the pixel photodiode (PD) 141 is converted into a voltage.

  When the control circuit 18 turns on the vertical line selection switch 148 and the pixel selection switch (SEL) 147 via the timing generator 17, the voltage of the floating diffusion (FD) 143 is gained by the pixel amplifier (AMI) 146. . The gained voltage is input to the column signal processing circuit 142 via the vertical signal line Ln as a pixel signal. That is, when the vertical line selection switch 148 and the pixel selection switch (SEL) 147 are turned on, a pixel photodiode (PD) 141 that reads out a pixel signal is selected, and a signal received by the pixel 14P is photoelectrically converted to a column. This is transmitted to the signal processing circuit 142.

  The column signal processing circuit 142 outputs the pixel signal thus obtained to the A / D conversion circuit 16. The pixel signal is input to the image processing unit 181 as a normal pixel signal digitally converted by the A / D conversion circuit 16.

-Reading FPN pixel signal-
The control circuit 18 turns on the reset switch (RESET) 145 via the timing generator 17 to apply a voltage to the floating diffusion (FD) 143 until the reset voltage becomes the reference voltage. Then, the control circuit 18 turns on the vertical line selection switch 148 and the pixel selection switch (SEL) 147 via the timing generator 17. As a result, the voltage of the floating diffusion (FD) 143, that is, the reference voltage is gained by the pixel amplifier (AMI) 146. The gained reference voltage is input to the column signal processing circuit 142 through the vertical signal line Ln as a pixel signal. That is, a signal when the connection between the pixel photodiode (PD) 141 and the column signal processing circuit 142 is cut off, that is, a signal equivalent to a signal (one element of FPN) in a state where the pixel 14P is not receiving light. Is transmitted to the column signal processing circuit 142.

  The column signal processing circuit 142 includes a pixel photodiode 141 included in a predetermined row (pixel row) selected by the control circuit 18 (a transfer gate switch (TX) 144 for each pixel 14P in the selected pixel row is turned off), And the pixel signal output from the pixel selection switch (SEL) 147 is turned on. In this case, at least the pixel selection switches (SEL) 147 of the pixel photodiodes 141 included in the non-selected pixel rows are all turned off.

  The column signal processing circuit 142 holds the pixel signal obtained from the pixel 14P in the selected pixel row as an FPN pixel signal for each column. At this time, the transfer gate switch (TX) 144 and the pixel selection switch (SEL) 147 are turned on and off almost simultaneously between the selected pixels 14P. The column signal processing circuit 142 outputs the FPN pixel signal thus obtained to the A / D conversion circuit 16. The FPN pixel signal is input to the image processing unit 18 as an FPN pixel signal digitally converted by the A / D conversion circuit 16.

  The calculation unit 181a of the image processing unit 18 calculates a correction value (FPN data) by averaging the levels of the acquired FPN pixel signals for the pixel rows for each pixel column. In addition, the calculation unit 181 a stores the calculated FPN data in the temporary memory 183.

  When obtaining the FPN pixel signal, as described above, from the pixel photodiode (PD) 141 in the predetermined pixel row (selected row) (transfer gate switch (TX) 144 for each pixel 14P in the selected pixel row). In addition to the method of obtaining the pixel signal), the pixel selection switch (SEL) 147 may be turned on. For example, the transfer gate switches (TX) 144 of all the pixel rows 14P (that is, all pixels) are turned off all at once, and only the pixel selection switch (SEL) 147 of a predetermined pixel row (selected row) is turned on all at once. In this state, an FPN pixel signal may be obtained. Alternatively, the reset switch (RESET) 145 is turned on to apply a reference voltage to the floating diffusion (FD) 143, and the transfer gate switch (TX) 144 is turned on and the pixel photodiode (PD) 141 performs photoelectric conversion. You may make it perform the time required for the process which transfers an electric charge to the floating diffusion (FD) 143 in a short time.

  Next, the FPN correction processing in the image processing unit 181 will be described separately when the still image shooting mode is set, when the live view mode is set, and when the moving image shooting mode is set. To do.

-Still image shooting mode-
When the still image shooting mode is set by operating the operation unit 30 and shooting is instructed by fully pressing the release switch, the control circuit 18 acquires the FPN pixel signal in a state where the image sensor 14 is shielded by the shutter 21. . When the FPN pixel signal is acquired, the control circuit 18 exposes the image sensor 14 with the shutter 21 opened to acquire a normal pixel signal. Then, the correction unit 181b of the image processing unit 181 performs FPN correction processing on the normal pixel signal using FPN data. Details will be described below.

  The control circuit 18 instructs the timing generator 17 to acquire the FPN pixel signal from the pixel 14P included in, for example, a 1/3 region of the range of all the pixels constituting the imaging device 14. FIG. 5 shows a region (FPN data acquisition region Re) including a pixel 14P from which an FPN pixel signal is read by a hatched region. For simplicity of explanation, the number of pixels of the image sensor 14 is set to 3000 × 1500 dots. In the present embodiment, for example, 3000 pixels of pixel signals output from the pixels (3000 × 500 dots) corresponding to the central 1/3 region of the entire pixel range are read for each pixel column. That is, the control circuit 18 reads out the above-described FPN pixel signal from the 501st row to the 1000th row via the timing generator 17 to the pixels 14P included in the selected row. As a result, FPN pixel signals are read from 500 pixel photodiodes (PD) 141 for each of the first to 3000th pixel columns of the image sensor 14 and input to the column signal processing circuit 142.

  The column signal processing circuit 142 outputs the FPN pixel signals for all pixel columns, that is, 3000 columns to the image processing unit 181 via the A / D conversion circuit 16. The calculation unit 181a calculates the FPN data for each column by averaging the FPN pixel signals (500 pixels) for the 3000 pixel columns input as described above, and stores the FPN data in the temporary memory 183.

  Next, the control circuit 18 rotates the quick return mirror 10 to the position indicated by the broken line in FIG. 1 to open the shutter 21 so that the subject light that has passed through the photographing lens L1 is guided to the image sensor 14. . Further, the control circuit 18 performs the above-described normal pixel signal readout for all the pixels 14P via the timing generator 17. That is, the control circuit 18 causes the image processing unit 181 to input pixel signals output from all the pixels 14P of the image sensor 14 as normal pixel signals. The correcting unit 181b subtracts the corresponding first row of FPN data from the input first row of normal pixel signals. The correction unit 181b performs the FPN correction process by performing the above subtraction on the respective normal pixel signals for 3000 columns.

  FIG. 6 conceptually illustrates the FPN correction process. FIG. 6A shows the pixels in the horizontal direction in the normal pixel signal and the output level of each pixel, that is, the luminance. FIG. 6B shows the pixels in the horizontal direction in the FPN pixel signal and the output level of each pixel, that is, the luminance. Since the magnitude of the FPN noise is different for each pixel column, the output level is different for each pixel in the horizontal direction as shown in FIG. Since FPN noise is superimposed on the normal pixel signal for each pixel column, as shown in FIG. 6A, the output level differs depending on each pixel in the horizontal direction and is similar to the waveform in FIG. 6B. Since the output level shown in FIG. 6B is subtracted from the output level shown in FIG. 6A by the FPN correction process, each output level of the horizontal pixel after the FPN correction process is shown in FIG. As shown in FIG.

  The pixel signal subjected to the FPN correction processing is subjected to the above-described image processing by the image processing unit 181 and compression processing by the compression unit 182, and is recorded in the memory card 32 as image data.

-Live view mode-
In the live view mode, the control circuit 18 acquires the FPN pixel signal as described above before acquiring the normal pixel signal. When the FPN pixel signal is acquired, the control circuit 18 sequentially reads the normal pixel signal from the image sensor 14 at a predetermined cycle, for example, a 1/30 second cycle. Then, the correction unit 181b performs FPN correction processing on each normal pixel signal sequentially input using the FPN data stored in the temporary memory 183. Then, the image processing unit 181 generates image data using the pixel signal that has been subjected to the FPN correction process. When the user operates the operation unit 30 to perform an operation for changing the operation state of the image sensor 14 by at least one of a gain change operation and an addition method change operation (hereinafter, operation state change operation), the control circuit 18 A new FPN pixel signal is acquired, and the calculation unit 181a calculates new FPN data using the newly acquired FPN pixel signal. The correction unit 181b performs FPN correction processing on the normal pixel signals sequentially input thereafter using newly calculated FPN data.

  When the operation state changing operation is performed by the user, the output level of the normal pixel signal of the image sensor 14 is equal to or higher than a predetermined threshold (for example, the output level is set to the maximum output level that the image sensor 14 can output). In contrast, when the high brightness level is 90% or higher), that is, when a high brightness subject is photographed, the control circuit 18 performs control so that the FPN pixel signal is acquired with the aperture 20 being reduced. That is, the aperture control unit 184 outputs a drive control signal to the aperture drive unit 22 of the interchangeable lens 2 so that the aperture 20 is most contracted. Then, the calculation unit 181a calculates new FPN data using the FPN pixel signal acquired in the state where the diaphragm 20 is most narrowed down. Hereinafter, it will be described in detail with reference to the timing chart shown in FIG.

  When the live view 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. 1, opens the shutter 21, and passes through the photographing lens L1. The subject light is guided to the image sensor 14. As shown in FIG. 5, the control circuit 18 instructs the timing generator 17, and among all the pixels 14 </ b> P constituting the imaging device 14, the FPN pixel signal is read out in the same manner as in the case of reading the FPN pixel signal in the still image shooting mode described above. The FPN pixel signal is read from the pixel 14P included in the data acquisition area Re. The column signal processing circuit 142 outputs 500 FPN pixel signals (FPN) per column to the image processing unit 181 through the A / D conversion circuit 16. The calculation unit 181a averages the FPN pixel signals, calculates FPN data for each pixel column, and stores the FPN data in the temporary memory 183.

  When the FPN pixel signal is read from the pixel 14P included in the 1000th pixel row, the control circuit 18 reads the normal pixel signal to the column signal processing circuit 142 to obtain the image data of the first frame. Let The column signal processing circuit 142 outputs the read normal pixel signal to the image processing unit 181 via the A / D conversion circuit 16. The correcting unit 181b subtracts the above-described FPN data corresponding to the first column stored in the temporary memory 183 from the normal pixel signal in the first column. The correction unit 181b performs the FPN correction process by performing the above subtraction on the respective normal pixel signals for 3000 columns. The image processing unit 181 performs the above-described various image processing on the pixel signal subjected to the FPN correction process to generate image data. The control circuit 18 outputs image data to the LCD drive circuit 19 and causes the liquid crystal display 191 to display an image corresponding to the image data.

  Further, the determination unit 181c determines whether or not the output level of the signal intensity of the normal pixel signal input from all the pixels 14P is equal to or higher than a predetermined threshold (for example, the output level is the maximum that the pixel 14P of the image sensor 14 can output). Whether the luminance level is 90% or more of the luminance level). In other words, the determination unit 181c determines whether or not a high-luminance subject has been shot. When the output level is equal to or higher than the threshold value (at least the level of the signal output from the pixel 14P for obtaining the FPN pixel signal is equal to or higher than the threshold value), the determination unit 181c sets a flag (drive flag) i indicating the driving of the diaphragm 20. Is set to 1. When the output level is less than the threshold value, the determination unit 181c sets the drive flag i to 0. Note that the above-mentioned threshold is such that the charge accumulated in the pixel photodiode (PD) 141 is moved to the floating diffusion (FD) 143 without passing through the transfer gate switch (TX) 144 by being irradiated with high-luminance subject light. It is provided to prevent this from happening. This threshold value is preliminarily measured by an experiment or the like and is recorded in a memory or the like (not shown).

  After the normal pixel signals of the 1500th row (line) of the first frame are accumulated and read out, the normal pixel signals corresponding to the image data of the second frame as the next frame are accumulated and read out. For the image data after the second frame, the control circuit 18 performs the same processing as when the image data for the first frame is acquired. That is, the control circuit 18 reads the normal pixel signal from the image sensor 14. The correction unit 181b performs FPN correction processing on the normal pixel signal using the FPN data stored in the temporary memory 183, and the image processing unit 181 performs image processing to generate image data. The control circuit 18 causes the liquid crystal display 191 to display an image corresponding to the image data generated via the LCD drive circuit 19. Furthermore, the determination unit 181c determines whether or not a high-luminance subject has been shot, and sets the drive flag i to one of 0 and 1 according to the determination result.

  As shown in FIG. 7, it is assumed that when the image corresponding to the image data of the (M−1) th frame is displayed on the liquid crystal display device 191, the operation state changing operation by the user is performed. In the following description, it is assumed that a high-luminance subject is not captured in the (M−1) th frame image, that is, the drive flag i is set to 0. When the change instruction signal for instructing the change of the operation state of the image sensor 14 is input from the operation unit 30, the aperture control unit 184 checks the drive flag i. As described above, since the drive flag i is set to 0, the aperture control unit 184 does not instruct to stop the aperture 20. That is, the aperture control unit 184 does not output a drive control signal. As a result, the control circuit 18 causes the image sensor 14 to read out the FPN pixel signal in a state where the diaphragm 20 is not narrowed.

  Based on the read FPN pixel signal, the calculation unit 181 a newly generates FPN data and stores it in the temporary memory 183. When the FPN pixel signal is read from the pixel 14P included in the 1000th pixel row, the control circuit 18 causes the image sensor 14 to read a normal pixel signal corresponding to the image data of the Mth frame. Then, the correction unit 181b performs FPN correction processing on the acquired normal pixel signal using newly generated FPN data, and the image processing unit 181 generates image data of the Mth frame. The control circuit 18 outputs the image data of the Mth frame to the LCD drive circuit 19 and causes the liquid crystal display 191 to display the image.

  As shown in FIG. 7, it is assumed that when the image corresponding to the image data of the (N−1) th frame is displayed on the liquid crystal display 191, the operation state changing operation is performed by the user. In the following description, it is assumed that the image of the (N−1) th frame is a high-luminance subject, that is, the drive flag i is set to 1. When the change instruction signal for instructing the change of the operation state of the image sensor 14 is input from the operation unit 30, the aperture control unit 184 checks the drive flag i. As described above, since the drive flag i is set to 1, the aperture control unit 184 outputs a drive control signal to the aperture drive unit 22. That is, the control circuit 18 causes the FPN pixel signal to be accumulated and read out in a state where the amount of light incident on the image sensor 14 is reduced by narrowing the aperture 20 before starting the accumulation of the FPN pixel signal.

  Then, the control circuit 18 stores and reads the normal pixel signals of the 1500th row (line) of the (N−1) th frame, and then, from the image sensor 14 with the aperture 20 being squeezed, the FPN pixel. Read the signal. At this time, the image processing unit 181 performs digital gain correction for changing the imaging sensitivity on the input FPN pixel signal. That is, the image processing unit 181 multiplies the FPN image signal by a gain corresponding to the number of stages in which the aperture 20 is reduced. It is assumed that data in which the number of narrowed stages and the gain are associated with each other is recorded in advance in a memory (not shown). The calculation unit 181a newly generates FPN data based on the read FPN pixel signal and stores the FPN data in the temporary memory 183. When the FPN pixel signal is read from the pixels 14P included in the 1000th pixel row, the aperture control unit 184 returns the aperture 20 to the state before being narrowed down to acquire the FPN pixel signal. A drive control signal is output to 22. Then, the control circuit 18 causes the normal pixel signal corresponding to the image data of the Nth frame which is the next frame to be accumulated and read out.

  The image processing unit 181 performs digital gain correction for changing the imaging sensitivity on the normal pixel signal corresponding to the image data of the Nth frame. That is, the image processing unit 181 multiplies the normal pixel signal by the same gain as when the digital gain correction is performed on the FPN pixel signal. As a result, the same noise component as that added to the FPN pixel signal by digital gain correction is added to the normal pixel signal.

  The correction unit 181b performs FPN correction processing on the normal pixel signal subjected to digital gain correction using the FPN data stored in the temporary memory 183. That is, the correction unit 181b subtracts the FPN data from the normal pixel signal for each pixel column as described above. As a result, the fixed pattern noise (FPN) and the noise component superimposed on the normal pixel signal and the FPN pixel signal by the digital gain correction are canceled out by the FPN correction process. Then, the image processing unit 181 generates image data of the Nth frame. The control circuit 18 outputs the image data of the Nth frame to the LCD drive circuit 19 and causes the liquid crystal display 191 to display the image of the Nth frame. The above operation is repeated until the live view is finished.

-Movie shooting mode-
When the moving image shooting mode is set by operating the operation unit 30 and shooting is instructed by fully pressing the release switch, the control circuit 18 rotates the quick return mirror 10 to the position indicated by the broken line in FIG. Start shooting. In the moving image shooting mode as well, in the same way as in the live view mode, the control circuit 18 generates moving image data using the normal pixel signals read from all the pixels 14P constituting the image sensor 14. That is, the control circuit 18 acquires the normal pixel signal and the FPN pixel signal in the same manner as shown in the timing chart in the live view mode of FIG.

  The correction unit 181b performs FPN correction processing on the normal pixel signal using FPN data. Note that when an operation state change operation is performed while a high-luminance subject is being photographed, the control circuit 18 obtains a new FPN pixel signal with the aperture 20 closed down. It is the same as the case of. Furthermore, the point that the correction unit 181b performs the FPN correction process using the FPN data calculated by the calculation unit 181a based on the new FPN pixel signal is the same as in the live view mode. The pixel signal is subjected to the above-described image processing by the image processing unit 181 and compression processing by the compression unit 182, and is recorded in the memory card 32 as moving image data.

According to the digital camera 1 according to the embodiment described above, the following operational effects can be obtained.
(1) The image pickup device 14 has a plurality of pixels 14P arranged in a matrix, picks up a subject image and outputs a normal pixel signal, and the operation unit 30 outputs a signal output from the image pickup device 14 by the user. The change instruction signal for instructing the change of the operation state is output upon accepting the change of the operation state. When the change instruction signal is input, the control circuit 18 reads the FPN pixel signal from the pixels 14P included in a predetermined pixel row among the plurality of pixels 14P. Further, the calculation unit 181a calculates FPN data, which is a correction value for correcting an error for each pixel column of the normal pixel signal, using the FPN pixel signal, and the correction unit 181b uses the calculated FPN data. Thus, the FPN correction process is performed on the normal pixel signal. Further, each time the normal pixel signal is read, the determination unit 181c determines whether or not the subject image satisfies a predetermined condition regarding brightness information, that is, whether or not a high-luminance subject is photographed, and changes the operation state. When the determination unit 181c determines that the predetermined condition is satisfied, the aperture control unit 184 drives the aperture 20 via the aperture drive unit 22 and enters the image sensor 14. The amount of light was limited. Then, the control circuit 18 reads the FPN pixel signal in a state where the amount of incident light is limited.

  FIG. 6E shows the relationship between the horizontal pixels in the FPN pixel signal and the output level of each pixel, that is, the luminance when the FPN pixel signal is acquired when a high-luminance subject is photographed. The charges accumulated in the pixel photodiode (PD) 142 by the incidence of high-luminance subject light move to the floating diffusion (FD) 143 without passing through the transfer gate (TX) 144. Therefore, the output level of the pixel varies. FIG. 6E shows a state in which the output level of the pixels in the horizontal direction included in the range X varies as compared with the output level shown in FIG. Therefore, when the FPN correction process is performed on the normal pixel signal shown in FIG. 6D, the output level of the pixel in the horizontal direction is not smooth as shown in FIG. In other words, by performing the FPN correction process, the image quality is deteriorated.

  On the other hand, when it is determined by the determination unit 181c that a high-luminance subject has been shot, a new FPN pixel signal is acquired with the aperture 20 being reduced. That is, since the amount of light incident on the image sensor 14 is limited, the movement of the accumulated charge of the pixel photodiode (PD) 142 due to the incidence of the high-intensity subject light as described above is prevented, and the variation in the output level of the imager is suppressed. it can. Therefore, since the FPN correction process using the FPN data in which the output level fluctuates is not performed, it is possible to prevent the image quality from being deteriorated.

(2) When the reading of the FPN pixel signal is completed, the aperture control unit 184 drives the aperture 20 via the aperture drive unit 22 to end the restriction on the amount of incident light on the image sensor 14. Therefore, it is possible to prevent the live view image or moving image after acquiring the FPN pixel signal from being under-exposed and displaying an image not desired by the user on the liquid crystal display 191.

The digital camera 1 according to the embodiment described above can be modified as follows.
(1) Instead of the one that restricts the amount of light incident on the image sensor 14 by driving the diaphragm 20, for example, a neutral density (ND) filter may be used. A block diagram of the control system in this case is shown in FIG. It should be noted that the same components as those in the block diagram shown in FIG. As shown in FIG. 8, the neutral density filter 23 is disposed in front of the image sensor 14 (subject side) so that it can be driven by the drive unit 24. In the normal state, the neutral density filter 23 is stored at a position where the subject light flux is not blocked from entering the image sensor 14. In the drive state, the drive unit 24 drives the neutral density filter 23 to a position (drive position) that covers the entire surface of the image sensor 14 to limit the amount of light of the subject light flux to the image sensor 14. The drive unit 24 drives the neutral density filter 23 to the drive position in accordance with a drive control signal output from the drive control unit 185 included in the control circuit 18. Similarly to the aperture control unit 184 in the embodiment, the drive control unit 185 sends a drive control signal to the drive unit 24 when a high-luminance subject is photographed when an operation state change operation is performed by the user. Is output.

(2) When a high-luminance subject is photographed when an operation state change operation is performed by the user, the brightness of the high-luminance subject, that is, the brightness, instead of the one that drives the aperture 20 to be most squeezed The amount by which the diaphragm 20 is narrowed may be changed according to the degree. That is, the diaphragm 20 may be narrowed as the luminance of the subject increases. In this case, the determination unit 181c compares the calculated output level of the normal pixel signal of the image sensor 14 with a plurality of threshold values, for example, threshold values wth1 and wth2 (wth1> wth2). When the determination unit 181c determines that the output level of the normal pixel signal is greater than the threshold value wth1, the diaphragm control unit 184 controls the drive control signal so that the diaphragm 20 is most narrowed, as in the above-described embodiment. Is output (first state). When the determination unit 181c determines that the output level of the normal pixel signal is greater than the threshold value wth2 and equal to or less than the threshold value wth1, the aperture control unit 184 has several steps (when the aperture 20 is in the first state). For example, the drive control signal is output so as to be in an open state (second stage) (second state). When the determination unit 181c determines that the output level of the normal pixel signal is equal to or lower than the threshold value wth2, the diaphragm control unit 184 is in a state where the diaphragm 20 is opened several stages (for example, three stages) more than in the second state. A drive control signal is output so as to be (third state). Note that the above-described thresholds wth1 and wth2 are values set in advance by experiments or the like, and are recorded in a memory (not shown) or the like.

(3) The FPN pixel signal is read from the pixels 14P included in the lower end portion (for example, the 1001st row to the 1500th row) of all the pixels 14P of the image sensor 14 in consideration of the time required for narrowing down the aperture 20. It may be. That is, the control circuit 18 may change the position of the FPN data acquisition region Re to the lower end of the image sensor 14.

(4) The control circuit 18 may read the FPN pixel signal from all the pixels 14 </ b> P of the image sensor 14. In this case, the calculation unit 181a assigns a large weight in order from the pixel signal closest to the last readout row (1500th row) in the image sensor 14, and calculates FPN data by weighted average. As a result, a large weight is given to the FPN pixel signal from the pixel 14P included in the lower end portion of the image sensor 14 in which the aperture driving of the aperture 20 is completed and the amount of incident light is limited. FPN data with time taken into account can be acquired.

(5) Instead of determining whether or not a high-brightness subject is photographed using the output level of the normal pixel signal output from the pixel 14P, the determination is made based on the color information included in the normal pixel signal. It may be a thing. In this case, R (red), G (green), and B (blue) color filters are provided on the imaging surface of the imaging device 14 so as to correspond to the positions of the pixels 14P, and the imaging device 14 has an RGB color system. The normal pixel signal having the color information is output. Then, the image processing unit 181 includes, among the input normal pixel signals, normal pixel signals corresponding to a specific color component (for example, an R component signal and a G component signal, only an R component signal, only a G component signal, and only a B component signal). It is only necessary to determine whether the output level is equal to or higher than a threshold value.

(6) In the live view mode or the moving image shooting mode, instead of reading out normal pixel signals from all the pixels 14P, decimation readout for reading out normal pixel signals from the pixels 14P included in a predetermined pixel row among all the pixels 14P. You may go. FIG. 9 shows an example of a pixel row including the pixels 14P to be thinned and read. In this case, a pixel row including the pixel 14P from which the normal pixel signal is read is indicated by a hatched area. That is, the control circuit 18 selects the second row, the fifth row,..., The (3n−1) th row (n is a natural number: n ≦ 500) as the selected row, and applies to the pixels 14P included in the selected row. Thus, the normal pixel reading described above is performed. As a result, pixel signals are read from a total of 500 pixel photodiodes (PD) 141 for each pixel column of the image sensor 14 and input to the column signal processing circuit 142.

(7) In place of performing high luminance determination based on normal pixel signals output from all the pixels 14P of the image sensor 14 when performing high luminance determination for determining whether or not a high luminance subject is included. The high luminance determination may be performed using only the normal pixel signal output from the pixel 14P included in the FPN pixel signal area, that is, the FPN data acquisition area Re. In this case, the image processing unit 181 may compare the signal intensity (output level) of the normal pixel signal output from the pixel 14P included in the 501st row to the 1000th row with the above-described threshold value.

(8) The high brightness determination method is not limited to the above, and an average value, a total value, or the like may be used. For example, when the average value (average output level) of the pixels included in the FPN data acquisition area Re exceeds a certain threshold value (threshold level for an average value different from the above-described threshold level), the image processing unit 181 may determine that a high-luminance subject is included. Further, for example, when the total output value (total output level) of the pixels 14P included in the FPN data acquisition area Re exceeds a threshold (threshold level for the total value) provided separately from the above, the image processing unit 181 may determine that a high-luminance subject is included. Further, this concept may be applied not only to the FPN data acquisition region Re but also to all the pixels of the image sensor 14 (pixels in an effective imaging range that outputs an image signal of a subject image).

(9) The threshold value may be set corresponding to the temperature. In this case, the digital camera 1 includes a temperature sensor (not shown). The temperature sensor constantly measures the temperature around the image sensor 14 and outputs a temperature signal as a measurement result to the control circuit 18 via an A / D conversion circuit (not shown). Furthermore, data in which a threshold value is associated with each predetermined temperature range is recorded in advance in a memory or the like (not shown). When the operation state changing operation is performed, the control circuit 18 reads the threshold value with reference to the data based on the input temperature signal. Then, the control circuit 18 may compare the calculated output data with the read threshold value. As a result, even when the output level of the normal pixel signal varies according to the temperature change in the vicinity of the image sensor 14, it can be determined whether or not a high-luminance subject has been shot.

(10) The output level calculated based on the normal pixel signal acquired immediately before the previous FPN pixel signal acquisition may be used as the threshold value. In the case illustrated in FIG. 7, it is assumed that the operation state changing operation is performed when the image of the (N−1) th frame is displayed on the liquid crystal display 191. In this case, the image processing unit 181 uses the output level of the normal pixel signal corresponding to the image of the (M−1) th frame as the threshold immediately before the previous FPN pixel signal acquisition. Then, the image processing unit 181 may compare the output level of the normal pixel signal of the (N-1) th frame with the output level of the normal pixel signal of the (M-1) th frame.

(11) The determination of whether or not the subject image is a high-luminance subject is not limited to using a normal pixel signal. For example, in the case of a digital camera equipped with a photometric sensor, it may be determined whether the subject image is a high-luminance subject based on a photometric signal output from the photometric sensor. FIG. 10 shows a main part configuration diagram of the digital camera 1 in this case. In addition, the same code | symbol is provided to the same thing as the principal part block diagram of FIG.

  As shown in FIG. 10, the digital camera 1 includes a half mirror 31 instead of the photometric sensor 32 and the quick return mirror 10. Part of the subject light incident through the photographing lens L 1 passes through the semi-transmissive region of the half mirror 31 and is guided to the image sensor 14 through the shutter 21. Further, another part of the subject light incident through the photographing lens L 1 is reflected by the half mirror 31 and guided to the pentaprism 12.

  A part of the subject light guided to the pentaprism 12 is observed by the user through the eyepiece lens 13 and the other part is incident on the photometric sensor 32. The photometric sensor 32 is disposed at a position optically equivalent to the image sensor 14 with respect to the photographic lens L1, captures a subject image formed on the imaging surface, and detects a photoelectric according to the brightness of the subject image. The converted signal is output to the control circuit 18 as a photometric signal. Then, the control circuit 18 calculates the luminance of the subject based on the photometric signal output from the photometric sensor 32 and compares it with a preset threshold value to determine whether or not a high-luminance subject has been photographed. Good.

  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, 14P pixel, 20 aperture, 22 aperture drive unit,
30 operation unit, 142 column signal processing circuit, 18 control circuit,
181 image processing unit, 181a calculation unit, 181b correction unit, 181c determination unit,
184 Aperture control unit, 23 Attenuation filter, 24 Drive unit, 185 Drive control unit

Claims (7)

An image sensor in which a plurality of pixels are arranged in a matrix, picks up a subject image, and outputs a first pixel signal;
Change instruction means for instructing a change in the operation state of the signal output of the image sensor;
Reading means for reading a second pixel signal from pixels included in a predetermined row among the plurality of pixels when the change of the operation state is instructed;
Calculating means for calculating a correction value for correcting an error for each pixel column of the first pixel signal using the second pixel signal;
Correction means for correcting the first pixel signal using the calculated correction value;
Determining means for determining whether or not the subject image satisfies a predetermined condition regarding brightness information each time the first pixel signal is read;
A limiting unit that limits the amount of incident light on the image sensor when the determination unit determines that the predetermined condition is satisfied when the change instruction unit instructs the change of the operation state; Prepared,
The digital camera characterized in that the reading means reads the second pixel signal in a state where the amount of incident light is limited. The digital camera according to claim 1, wherein
The digital camera according to claim 1, wherein the determination unit determines that the predetermined condition is satisfied when the magnitude of the first pixel signal is equal to or greater than a predetermined threshold. The digital camera according to claim 1, wherein
The pixel signal output from the image sensor includes color information,
The determination unit determines that the predetermined condition is satisfied when the magnitude of the first pixel signal corresponding to a predetermined color component included in the color information is equal to or greater than a predetermined threshold. . The digital camera according to any one of claims 1 to 3,
The digital camera according to claim 1, wherein when the reading of the second pixel signal is completed, the limiting unit ends the limitation of the amount of incident light to the image sensor. The digital camera according to claim 1, wherein
The digital camera according to claim 1, wherein the limiting unit limits the amount of incident light to the image sensor by driving a diaphragm. The digital camera according to claim 5, wherein
When the calculation unit obtains the second pixel signal when the amount of incident light is limited using the diaphragm, the calculation unit gives weights in order from the pixel signal closest to the final readout row. A digital camera that calculates the correction value. The digital camera according to any one of claims 1 to 6,
The change in the operation state of the signal output of the image pickup device is at least one of a change in image pickup sensitivity for the image pickup device and a change in an addition method for adding and outputting the signals of the plurality of pixels included in the image pickup device. A digital camera characterized by including:

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