JP6773206B2 - Imaging device - Google Patents

Description

The present invention relates to an imaging device.

A digital camera capable of taking a still image during moving image shooting is known (see Patent Document 1).

Japanese Unexamined Patent Publication No. 10-20859

With a conventional digital camera, when the brightness of the shooting screen changes, it may not be possible to obtain an image with an appropriate exposure amount.

According to the first aspect, the image pickup device includes a first pixel that photoelectrically converts light and outputs a signal, and a second pixel that photoelectrically converts light transmitted through the first pixel and outputs a signal. The image sensor is provided with a control unit that controls the exposure time of the other pixel based on a signal output from one of the first pixel and the second pixel.

According to the present invention, it is possible to reduce the time lag between the instruction to shoot a still image and the actual shooting of a still image.

It is a block diagram explaining the configuration example of a digital camera. It is a figure explaining the outline of an image sensor. It is a figure explaining the arrangement example of a pixel. It is a figure explaining the cross-sectional configuration example of an image sensor. It is a figure explaining the circuit configuration example of a pixel. It is a figure explaining the case of performing still image shooting during moving image shooting. It is a figure explaining the case of performing a long exposure photography.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating a configuration of a digital camera 1 according to an embodiment of the present invention. The digital camera 1 includes a control unit 11, an imaging unit 12, an operation unit 13, an image processing unit 14, a liquid crystal monitor 15, and a buffer memory 16. A memory card 17 is attached to the digital camera 1.

The control unit 11 includes a drive control unit 111, a long exposure control unit 112, and a display control unit 113. The control unit 11 is composed of a microprocessor and its peripheral circuits, and realizes the functions of each of these units by executing a control program stored in a ROM (not shown). The contents of the functions of each part will be described in detail later.

The image pickup unit 12 includes an image pickup element 21, an amplifier circuit 22, and an AD conversion circuit 23. The image pickup device 21 is composed of a plurality of pixels, receives a light flux from a subject via a photographing optical system (not shown), performs photoelectric conversion, and outputs an analog image signal. The amplifier circuit 22 amplifies the analog image signal output from the image sensor 21 at a predetermined amplification factor (gain) and outputs the analog image signal to the AD conversion circuit 23. The AD conversion circuit 23 AD-converts an analog image signal and outputs a digital image signal. The control unit 11 stores the digital image signal output from the image pickup unit 12 in the buffer memory 16.

The digital image signal stored in the buffer memory 16 undergoes various image processing in the image processing unit 14, is displayed on the liquid crystal monitor 15, or is stored in the memory card 17. The memory card 17 is composed of a non-volatile flash memory or the like, and is removable from the digital camera 1.

The operation unit 13 is composed of various operation buttons such as a release button, a recording button, a mode switching button, and a power button, and is operated by the user. The operation unit 13 outputs an operation signal corresponding to the operation of each of the above operation buttons to the control unit 11. The image processing unit 14 is composed of an ASIC or the like. The image processing unit 14 performs various image processing such as interpolation, compression, and white balance on the image data captured by the imaging unit 12.

<Explanation of image sensor>
FIG. 2 is a diagram showing an outline of the image pickup device 21 according to the present embodiment. Note that FIG. 2 shows a state in which the light incident side of the image sensor 21 is on the upper side. Therefore, in the following description, the direction of the image sensor 21 on the light incident side is referred to as "upward" or "up", and the direction opposite to the light incident side is referred to as "downward" or "downward". The image pickup element 21 has an upper photoelectric conversion layer 31 and a lower photoelectric conversion layer 32. The upper photoelectric conversion layer 31 and the lower photoelectric conversion layer 32 are laminated and arranged on the same optical path. The upper photoelectric conversion layer 31 is composed of an organic photoelectric film that absorbs (photoelectrically converts) light of a predetermined color component (details will be described later). Light of a color component that has not been absorbed (photoelectrically converted) by the upper photoelectric conversion layer 31 passes through the upper photoelectric conversion layer 31 and is incident on the lower photoelectric conversion layer 32, and is photoelectrically converted by the lower photoelectric conversion layer 32. The lower photoelectric conversion layer 32 performs photoelectric conversion by a photodiode. The color component photoelectrically converted by the upper photoelectric conversion layer 31 and the color component photoelectrically converted by the lower photoelectric conversion layer 32 have a complementary color relationship. The upper photoelectric conversion layer 31 and the lower photoelectric conversion layer 32 are formed on the same semiconductor substrate, and each pixel position has a one-to-one correspondence. For example, the pixels in the first row and first column of the upper photoelectric conversion layer 31 correspond to the pixels in the first row and first column of the lower photoelectric conversion layer 32.

FIG. 3A is a diagram showing the pixel arrangement of the upper photoelectric conversion layer 31. In FIG. 3A, the horizontal direction is the x-axis, the vertical direction is the y-axis, and the coordinates of the pixel P are expressed as P (x, y). In the example of the upper photoelectric conversion layer 31 shown in FIG. 3A, organic photoelectric films that photoelectrically convert Mg (magenta) and Ye (yellow) light are alternately arranged in each pixel in the odd row, and each of the even rows. Organic photoelectric films that photoelectrically convert Cy (cyan) and Mg (magenta) light are alternately arranged on the pixels. Then, the light that is not received by each pixel is transmitted. For example, the pixels P (1,1) photoelectrically convert the light of Mg and transmit the light of G (green) which is the complementary color of Mg. Similarly, the pixels P (2,1) photoelectrically convert the light of Ye to transmit the light of B (blue), which is the complementary color of Ye, and the pixels P (1,2) photoelectrically convert the light of Cy. It transmits R (red) light, which is the complementary color of Cy.

FIG. 3B is a diagram showing the pixel arrangement of the lower photoelectric conversion layer 32. The pixel positions shown in FIG. 3B are the same as those in FIG. 3A. For example, the pixels (1,1) of the lower photoelectric conversion layer 32 correspond to the pixels (1,1) of the upper photoelectric conversion layer 31. In FIG. 3B, the lower photoelectric conversion layer 32 is not provided with a color filter or the like, and the color component transmitted through the upper photoelectric conversion layer 31 (that is, the color component absorbed by the organic photoelectric film and converted to photoelectric). The light of the complementary color) is photoelectrically converted. Therefore, as shown in FIG. 3C, in the lower photoelectric conversion layer 32, the image signals of the G and B color components are displayed in the odd-numbered pixels, and the R and G color component image signals are displayed in the even-numbered pixels. can get. For example, in pixels P (1,1), an image signal of the G component of the complementary color of Mg can be obtained. Similarly, the pixel P (2, 1) obtains the image signal of the complementary color B component of Ye, and the pixel P (1, 2) obtains the image signal of the complementary color R component of Cy.

As described above, in the image pickup device 21 according to the present embodiment, the upper photoelectric conversion layer 31 composed of the organic photoelectric film acts as a color filter for the lower photoelectric conversion layer 32, and the lower photoelectric conversion layer 32 to the upper photoelectric conversion layer 32 to the upper photoelectric conversion layer 32. A complementary color image of the conversion layer 31 (an image of the Bayer array in the example of FIG. 3) is obtained. Therefore, in the image sensor 21 according to the present embodiment, a CMY image composed of three colors of Cy, Mg, and Ye can be acquired from the upper photoelectric conversion layer 31, and R, G, and B are obtained from the lower photoelectric conversion layer 32. It is possible to acquire an RGB image composed of the three colors of.

FIG. 4 is a diagram illustrating a part of a cross section of the image sensor 21. As shown in FIG. 4, in the image pickup element 21, the lower photoelectric conversion layer 32 formed on the silicon substrate and the upper photoelectric conversion layer 31 using the organic photoelectric film are laminated via the wiring layer 40. Above the upper photoelectric conversion layer 31, one microlens ML is formed for one pixel. For example, in the upper photoelectric conversion layer 31, the light receiving portion PC (1,1) formed by the organic photoelectric film constituting the photoelectric conversion portion of the pixel P (1,1) is a subject incident from the microlens ML (1,1). The light of Mg in the light is photoelectrically converted to transmit the light of G which is a complementary color. In the lower photoelectric conversion layer 32, the photodiode PD (1,1) constituting the pixel P (1,1) receives the light of G transmitted through the light receiving portion PC (1,1) of the upper photoelectric conversion layer 31. Photodiode conversion.

FIG. 5 is a diagram illustrating a circuit configuration of one pixel P (x, y) in the image sensor 21. The pixel P (x, y) has a photodiode PD, a transfer transistor Tx, a reset transistor R2, an output transistor SF2, and a selection transistor SEL2 as circuits for forming the lower photoelectric conversion layer 32. The photodiode PD accumulates an electric charge according to the amount of incident light. The transfer transistor Tx transfers the electric charge accumulated in the photodiode PD to the floating diffusion region (FD unit) on the output transistor SF2 side. The output transistor SF2 constitutes a current source PW2 and a source hollower via the selection transistor SEL2, and outputs an electric signal corresponding to the electric charge accumulated in the FD section to the vertical signal line VLINE2 as an output signal OUT2. The reset transistor R2 resets the electric charge of the FD portion to the power supply voltage Vcc.

Further, the pixel P (x, y) has a light receiving unit PC made of an organic photoelectric film, a reset transistor R1, an output transistor SF1, and a selection transistor SEL1 as a circuit for forming the upper photoelectric conversion layer 31. The light receiving unit PC using the organic photoelectric film converts non-transmitted light into an electric signal according to the amount of light, and as an output signal OUT1 via the current source PW1 via the selection transistor SEL1 and the output transistor SF1 constituting the source holower Output to VLINE1. The reset transistor R1 resets the output signal of the light receiving unit PC to the reference voltage Vref. Further, a high voltage Vpc is given for the operation of the organic photoelectric film. Each transistor is composed of MOS_FET.

Here, the operation of the circuit related to the lower photoelectric conversion layer 32 will be described. First, when the selection signal φSEL2 becomes “High”, the selection transistor SEL2 is turned on. Next, when the reset signal φR2 becomes “High”, the FD unit is reset to the power supply voltage Vcc, and the output signal OUT2 also reaches the reset level. Then, after the reset signal φR2 becomes “Low”, the transfer signal φTx becomes “High”, the charge accumulated in the photodiode PD is transferred to the FD unit, and the output signal OUT2 changes according to the amount of charge. Start and stabilize. Then, the transfer signal φTx becomes “Low”, and the signal level of the output signal OUT2 read from the pixels to the vertical signal line VLINE2 is determined. Then, the output signal OUT2 of each pixel read by the vertical signal line VLINE2 is temporarily held for each line in a horizontal output circuit (not shown), and then output from the image sensor 21. In this way, signals are read from each pixel of the lower photoelectric conversion layer 32 of the image sensor 21.

Further, the operation of the circuit related to the upper photoelectric conversion layer 31 will be described. First, when the selection signal φSEL1 becomes “High”, the selection transistor SEL1 is turned on. Next, the reset signal φR1 becomes “High”, and the output signal OUT1 also becomes the reset level. Immediately after the reset signal φR1 becomes “Low”, the charge accumulation of the light receiving unit PC by the organic photoelectric film is started, and the output signal OUT1 changes according to the amount of charge. Then, the output signal OUT1 is temporarily held for each line in a horizontal output circuit (not shown), and then output from the image sensor 21. In this way, signals are read from each pixel of the upper photoelectric conversion layer 31 of the image sensor 21.

<Video mode and still image mode>
The digital camera 1 of the present embodiment outputs a moving image mode for outputting a moving image signal and an image signal for a still image as drive modes for the upper photoelectric conversion layer 31 and the lower photoelectric conversion layer 32 of the image pickup element 21. A still image mode is provided. The moving image mode is a mode in which photoelectric conversion is performed at a set frame rate, pixels are added and thinned out so as to have a predetermined number of pixels, and drive control is performed so as to output an image signal. On the other hand, the still image mode is a mode in which photoelectric conversion is performed at a set exposure time, and for example, all pixels are read out and an image signal is output without performing pixel addition and thinning. That is, the drive is controlled so that the number of pixels of the still image is larger than that of the moving image. The moving image mode is a mode used both when generating a moving image for recording to be recorded on the memory card 17 and when generating a display image to be displayed as a through image on the liquid crystal monitor 15.

<Shooting mode for shooting still images during movie shooting>
In addition to the normal still image shooting mode and the normal moving image shooting mode, the digital camera 1 of the present embodiment is provided with a moving image still image shooting mode capable of shooting a still image during movie shooting. Has been done. In the moving image still image shooting mode, the digital camera 1 starts movie shooting when the record button is pressed, ends movie shooting when the record button is pressed again, and records the shot movie on the memory card 17. To do. When the release button is pressed during the moving image shooting, the digital camera 1 takes a still image and records the shot still image on the memory card 17.

Here, for comparison with the present embodiment, an example in which a still image is taken during moving image shooting with a conventional digital camera will be described with reference to FIG. 6A. As shown in FIG. 6A, in the conventional digital camera, when a moving image shooting is instructed by pressing the recording button, the image pickup element is driven in the moving image mode to perform the moving image shooting.

Then, when a still image shooting is instructed by pressing the release button, the conventional digital camera changes the drive mode of the image sensor from the moving mode to the still image mode and performs the still image shooting. When the still image shooting is completed, the conventional digital camera changes the drive mode of the image sensor from the still image mode to the moving image mode again, and resumes the moving image shooting.

As described above, in the conventional digital camera, when the still image is taken during the moving image shooting, the drive mode of the image sensor is changed from the moving image mode to the still image mode, so that time (mode change time) is required. Therefore, there is a time lag between the instruction to shoot the still image and the shooting of the still image. In addition, since it is not possible to shoot a moving image while shooting a still image, frames of the moving image are dropped.

Based on the above-mentioned problems of the conventional digital camera, the digital camera 1 of the present embodiment does not cause a time lag between the instruction to shoot a still image and the actual shooting of a still image and the frame dropping of a moving image. It is designed to perform shooting processing.

FIG. 6B is a diagram illustrating a drive mode in the moving image still image shooting mode in the digital camera 1 of the present embodiment. When the drive control unit 111 is instructed to shoot a moving image by pressing the recording button, the drive control unit 111 drives the upper photoelectric conversion layer 31 of the image sensor 21 in the moving image mode to shoot the moving image. The image processing unit 14 generates moving image data based on the image signal output from the upper photoelectric conversion layer 31 and records it on the memory card 17.

Then, when a still image shooting is instructed by pressing the release button, the drive control unit 111 drives the lower photoelectric conversion layer 32 in the still image mode to perform the still image shooting. The image processing unit 14 generates still image data based on the image signal output from the lower photoelectric conversion layer 32 and records it on the memory card 17.

As described above, in the moving image still image shooting mode, the digital camera 1 drives the upper photoelectric conversion layer 31 in the moving image mode when the moving image shooting is instructed, and the lower photoelectric conversion layer when the still image shooting is instructed during the moving image shooting. 32 is driven in the still image mode. Therefore, unlike the conventional digital camera, the digital camera 1 of the present embodiment does not require a mode change time from the moving image mode to the still image mode, and is stationary without causing a time lag after the still image shooting is instructed. You can take pictures.

The drive control unit 111 continues driving the upper photoelectric conversion layer 31 in the moving image mode while driving the lower photoelectric conversion layer 32 in the still image mode, and continues moving image shooting. Therefore, in the digital camera 1 of the present embodiment, it is possible to prevent frame dropping of a moving image during still image shooting.

<Long exposure shooting mode>
Further, the digital camera 1 of the present embodiment is provided with a long exposure shooting mode for shooting a still image with a long exposure time. When the digital camera 1 is switched to the long exposure shooting mode by the mode switching button, the digital camera 1 starts displaying the through image. Then, when the release button is pressed, the digital camera 1 performs long-exposure photography and records the photographed long-exposure image on the memory card 17. The exposure time in long-exposure photography is, for example, a long time of several tens of seconds to one minute or more.

Here, for comparison with the present embodiment, an example of a case where long-exposure photography is performed with a conventional digital camera will be described with reference to FIG. 7A. As shown in FIG. 7A, when the conventional digital camera is switched to the long exposure shooting mode by the mode switching button, the image sensor is driven in the moving image mode, and the through image sensor is based on the image signal captured by the image sensor. Display the image.

Then, when a still image shooting is instructed by pressing the release button, the conventional digital camera performs a predetermined exposure calculation process based on the image captured by the image sensor immediately before this, and performs a long-exposure shooting. Determines the exposure time in. Further, in the conventional digital camera, the drive mode of the image sensor is changed from the moving image mode to the still image mode, and long-exposure photography is performed with the predetermined exposure time determined above.

With such a conventional digital camera, it is not possible to display a through image during long-exposure photography, so that the user cannot confirm the shooting range (shooting angle of view). Further, in a conventional digital camera, a predetermined exposure time is determined in advance based on the brightness of the shooting screen before long-exposure shooting, so that when the brightness of the shooting screen changes during long-exposure shooting, It may not be possible to obtain an image with an appropriate exposure. For example, it is conceivable that the shooting screen suddenly becomes bright during long exposure, the image signal reaches the saturation level before the end of exposure, and the image signal is overexposed.

Based on the above-mentioned problems of the conventional digital camera, the digital camera 1 of the present embodiment can confirm the shooting range even during long-exposure shooting, and the brightness of the shooting screen changes during long-exposure shooting. Even if this is the case, the shooting process is performed so that an image with an appropriate exposure amount can be obtained.

FIG. 7B is a diagram illustrating a drive mode in the long exposure shooting mode of the digital camera 1 of the present embodiment. When the drive control unit 111 is switched to the long-exposure photography mode by the mode switching button, the drive control unit 111 drives the upper photoelectric conversion layer 31 of the image pickup element 21 in the moving image mode. The image processing unit 14 generates an image for display based on the image signal output from the upper photoelectric conversion layer 31. The display control unit 113 causes the liquid crystal monitor 15 to display the display image generated by the image processing unit 14 as a through image.

Then, when a still image shooting is instructed by pressing the release button, the drive control unit 111 drives the lower photoelectric conversion layer 32 in the still image mode to start long-exposure still image shooting. In the lower photoelectric conversion layer 32, electric charge accumulation continues until there is a trigger for the end of exposure, which will be described later.

The drive control unit 111 continues to drive the upper photoelectric conversion layer 31 in the moving image mode even during long-exposure photography. The display control unit 113 continues to display the through image based on the image signal output from the upper photoelectric conversion layer 31. As a result, the digital camera 1 allows the user to confirm the shooting range (shooting angle of view) by the through image even during long-exposure shooting.

Further, the long-exposure control unit 112 monitors the image signal output from the upper photoelectric conversion layer 31 during the long-exposure shooting, and determines the timing of the end of exposure of the lower photoelectric conversion layer 32. Specifically, when the exposure of the lower photoelectric conversion layer 32 is started, the image processing unit 14 integrates the image signals output from the upper photoelectric conversion layer 31 at a predetermined frame rate. When the long-time exposure control unit 112 reaches the level immediately before the image signal integrated by the image processing unit 14 is saturated, the exposure of the lower photoelectric conversion layer 32 is terminated as a trigger for the end of exposure. As a result, the digital camera 1 can prevent saturation of the image signal output from the lower photoelectric conversion layer 32 and obtain a long-exposure image with suppressed overexposure regardless of the change in the brightness of the shooting screen. ..

When the exposure of the lower photoelectric conversion layer 32 is completed in this way, the image processing unit 14 generates still image data based on the image signal output from the lower photoelectric conversion layer 32 and records it on the memory card 17. ..

According to the embodiment described above, the following effects can be obtained.
(1) In the digital camera 1, the drive control unit 111 drives the upper photoelectric conversion layer 31 in the moving image mode to shoot a moving image, and when the release button is pressed during the moving image shooting and the still image shooting is instructed, While the upper photoelectric conversion layer 31 is driven in the moving image mode, the lower photoelectric conversion layer 32 is driven in the still image mode to take a still image. As a result, the digital camera 1 of the present embodiment can reduce the time lag from the instruction for still image shooting to the actual still image shooting as compared with the conventional digital camera. In addition, it is possible to prevent frame dropping of a moving image during still image shooting.

(2) In the digital camera 1, the upper photoelectric conversion layer 31 is composed of an organic photoelectric film, the lower photoelectric conversion layer 32 is composed of a photodiode, the upper photoelectric conversion layer 31 is driven in the moving image mode, and the lower photoelectric conversion layer 32 is driven. Was driven in still image mode. Since the photoelectric conversion layer made of a photodiode has relatively less noise than the photoelectric conversion layer made of an organic photoelectric film, the output signal from the lower photoelectric conversion layer 32 can be used for a still image in this way. , Still image noise can be reduced. Further, since noise is less noticeable in moving images than in still images, it is preferable to use the output signal from the upper photoelectric conversion layer 31 for moving images in this way. Further, since the RGB image signal has good color reproducibility, the color reproducibility of the still image can be improved by using the RGB image signal output from the lower photoelectric conversion layer 32 for the still image.

(3) In the digital camera 1, when the lower photoelectric conversion layer 32 is exposed for a long time, the long exposure control unit 112 exposes the lower photoelectric conversion layer 32 for a long time based on the output signal from the upper photoelectric conversion layer 31. Changed to determine the end timing of. As a result, even if the brightness of the shooting screen changes during long-time exposure, a long-exposure image with an appropriate exposure amount can be obtained.

(4) In the digital camera 1, the display control unit 113 displays an image for display based on the output signal from the upper photoelectric conversion layer 31 on the liquid crystal monitor 15 as a through image during long-time exposure of the lower photoelectric conversion layer 32. I made it display. As a result, the user can confirm the shooting range even during long-exposure shooting.

(Modification example 1)
In a situation where long-exposure photography is performed, the shooting screen may be dark. In such a case, in the long-exposure photography mode described above, the through image based on the image signal from the upper photoelectric conversion layer 31 driven in the moving image mode becomes dark, which may be difficult for the user to see. Therefore, in such a case, the gain of the image signal output from the upper photoelectric conversion layer 31 may be increased to increase the output value of the image signal so that the through image based on the image signal can be easily seen. ..

(Modification 2)
Even if the digital camera 1 drives the upper photoelectric conversion layer 31 in the moving image mode in the normal still image shooting mode and displays the through image on the liquid crystal monitor 15 based on the output signal from the upper photoelectric conversion layer 31. Good. Then, when the release button is pressed, the lower photoelectric conversion layer 32 may be driven in the still image mode, and the still image data based on the output signal from the lower photoelectric conversion layer 32 may be recorded on the memory card 17.

(Modification 3)
In the above-described embodiment, the exposure of the lower photoelectric conversion layer 32 is automatically terminated in the long-exposure photography, but the present invention is not limited to this, and the exposure may be terminated according to the operation of the user's operation unit 13. However, it may end when the preset exposure time has elapsed.

(Modification example 4)
In the above-described embodiment, the upper photoelectric conversion layer 31 is driven in the moving image mode and the lower photoelectric conversion layer 32 is driven in the still image mode, but the present invention is not limited to this, and the upper photoelectric conversion layer 31 is driven in the still image mode. It may be driven and the lower photoelectric conversion layer 32 may be driven in the moving image mode.

(Modification 5)
In the above-described embodiment, an example of using the image pickup device 21 in which two photoelectric conversion layers (upper photoelectric conversion layer 31 and lower photoelectric conversion layer 32) are laminated has been described, but the present invention is not limited to two layers, but three or more layers. An image pickup element in which the photoelectric conversion layers of the above are laminated may be used.

Although various embodiments and modifications have been described above, the present invention is not limited to these contents. Other aspects conceivable within the scope of the technical idea of the present invention are also included within the scope of the present invention.

1 ... Digital camera, 11 ... Control unit, 14 ... Image processing unit, 21 ... Image sensor, 31 ... Upper photoelectric conversion layer, 32 ... Lower photoelectric conversion layer, 111 ... Drive control unit, 112 ... Long exposure control unit, 113 … Display control unit

Claims (5)

An image sensor having a first pixel that photoelectrically converts light and outputs a signal, and a second pixel that photoelectrically converts light transmitted through the first pixel and outputs a signal.
A control unit that controls the exposure time of the other pixel based on a signal output from one of the first pixel and the second pixel.
An imaging device comprising. In the imaging device according to claim 1,
The control unit controls the exposure time of the other pixel based on the signal output from one pixel while one of the first pixel and the second pixel is exposed. Imaging device. In the imaging device according to claim 1 or 2.
A generator that generates moving image data from a signal output from one of the first pixel and the second pixel, and still image data from a signal output from the other pixel.
An imaging device comprising. In the imaging device according to claim 3,
The control unit is an imaging device that controls the exposure time of pixels for generating the still image data based on the moving image data. In the imaging device according to claim 3 or 4.
The control unit is based on the moving image data while one of the first pixel and the second pixel, which is outputting a signal for generating still image data, is exposed. An imaging device that controls the exposure time of pixels that generate still image data.

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