JP2010107712A - Focal point control device and imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve such a problem that it is impossible to focus on any position in an image plane when photographing and to appropriately select a main subject, with respect to a multiple-point automatic focus technology. <P>SOLUTION: The device includes: a focus lens 230 that changes a focusing state of a subject image by moving forward or backward in the direction of an optical axis; a driving means 233 for driving the focus lens 230; a position detecting means 243 for detecting the position of the focus lens 230; an imaging element 110 that exposes so as to correspond to the position of the focus lens 230 and creates image data; an evaluation value-calculating means 140 for calculating an evaluation value for automatic focusing in a plurality of predetermined areas in image data based on the created image data; and a focusing state determining means 140 for determining the focusing state in the lowest priority area of a predetermined area based on the evaluation value after determining the focusing states in all positions of the high priority area where the focus lens 230 can be driven. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to focus control used in an imaging apparatus, and more particularly to contrast-based multipoint autofocus.

In an imaging apparatus such as a camera, there is a multi-point autofocus technique in which a plurality of detection frames are provided in a screen and the focus is set to any position in a shooting screen. In the conventional multi-point autofocus technology, there is a problem as to which position in the screen should be focused according to various situations at the time of shooting. As a technique corresponding to such a problem, there is a technique disclosed in Patent Document 1. In Patent Document 1, for the first group of distance measuring blocks having a defocus amount within a predetermined range with respect to the distance measuring block at the center of the screen, and the distance measuring block whose corresponding subject is closest to the first group. A technique is disclosed in which an evaluation value of each group is acquired for a second group of ranging blocks having a defocus amount within a predetermined range, and a focusing target block is selected according to the evaluation value. ing.
JP 2003-195151 A

  As described above, Patent Document 1 discloses a technique for determining which position should be focused in the multipoint autofocus technique. However, Patent Document 1 selects either the center area of the screen or the area of the subject that is closest to the camera as the focusing target block, and the area other than the center of the screen is selected. This cannot cope with a case where there are a plurality of subjects, and the main subject cannot be appropriately selected for various arrangement situations of the main subject.

  The focus control device of the present invention solves the above-mentioned problem, a focus lens that changes the focus state of a subject image by moving back and forth in the optical axis direction, and a driving unit for driving the focus lens; Position detection means for detecting the position of the focus lens, an image sensor for generating image data by exposure corresponding to the position of the focus lens, and a plurality of the image data based on the generated image data An evaluation value calculating means for calculating an evaluation value for autofocus in the predetermined area, and based on the evaluation value, a determination of an in-focus state in a low importance area of the predetermined area is performed in a high importance area. Focusing state determination means that is performed after determining the focusing state at all positions where the focus lens can be driven.

  With the above configuration, the focus control apparatus of the present invention can give importance to a plurality of focus target areas and can focus on all areas regardless of importance in the multipoint autofocus operation of the contrast method. At the same time, it is possible to avoid focusing on an area of low importance even though it can be focused on an area of high importance.

Hereinafter, an embodiment in which a focus control apparatus of the present invention is applied to a camera will be described in detail with reference to the drawings.
(Embodiment 1)
(1. Configuration)
(1-1. Overview)
FIG. 1 is a block diagram showing a configuration of a camera system 1 according to Embodiment 1 of the present invention. The camera system 1 includes a camera body 100 and an interchangeable lens 200 that can be attached to and detached from the camera body 100. The camera system 1 can perform a contrast autofocus operation based on image data generated by the CCD image sensor 110. The present invention is an invention made to perform a contrast type autofocus operation with higher accuracy.
(1-2. Configuration of camera body)
The camera body 100 includes a CCD image sensor 110, a liquid crystal monitor 120, a camera controller 140, a body mount 150, a power source 160, and a card slot 170.

  The camera controller 140 controls the entire camera system 1 such as the CCD image sensor 110 in response to an instruction from an operation member such as the release button 130. The camera controller 140 transmits a vertical synchronization signal to the timing generator 112. In parallel with this, the camera controller 140 generates an exposure synchronization signal based on the vertical synchronization signal. The camera controller 140 periodically and repeatedly transmits the generated exposure synchronization signal to the lens controller 240 via the body mount 150 and the lens mount 250. The camera controller 140 uses the DRAM 141 as a work memory during control operations and image processing operations.

  The CCD image sensor 110 captures a subject image incident through the interchangeable lens 200 and generates image data. The generated image data is digitized by the AD converter 111. The image data digitized by the AD converter 111 is subjected to various image processing by the camera controller 140. Examples of the various image processing referred to here include gamma correction processing, white balance correction processing, scratch correction processing, YC conversion processing, electronic zoom processing, and JPEG compression processing.

  The CCD image sensor 110 operates at a timing controlled by the timing generator 112. The operation of the CCD image sensor 110 includes a still image capturing operation, a through image capturing operation, and the like. Here, the through image is an image that is not recorded on the memory card 171 after image capturing. The through image is mainly a moving image, and is displayed on the liquid crystal monitor 120 in order to determine a composition for capturing a still image.

  The liquid crystal monitor 120 displays an image indicated by the display image data image-processed by the camera controller 140. The liquid crystal monitor 120 can selectively display both moving images and still images.

  The card slot 170 can be loaded with a memory card 171. The card slot 170 controls the memory card 171 based on the control from the camera controller 140. The memory card 171 can store image data generated by image processing of the camera controller 140. For example, the memory card 171 can store a JPEG image file. The memory card 171 can output image data or an image file stored therein. The image data or image file output from the memory card 171 is subjected to image processing by the camera controller 140. For example, the camera controller 140 expands the image data or image file acquired from the memory card 171 and generates display image data.

  The power supply 160 supplies power for consumption by the camera system 1. The power source 160 may be, for example, a dry battery or a rechargeable battery. Moreover, the power supplied from the outside by the power cord may be supplied to the camera system 1.

The body mount 150 can be mechanically and electrically connected to the lens mount 250 of the interchangeable lens 200. The body mount 150 can transmit and receive data to and from the interchangeable lens 200 via the lens mount 250. The body mount 150 transmits the exposure synchronization signal received from the camera controller 140 to the lens controller 240 via the lens mount 250. Also, other control signals received from the camera controller 140 are transmitted to the lens controller 240 via the lens mount 250. The body mount 150 transmits a signal received from the lens controller 240 via the lens mount 250 to the camera controller 140. The body mount 150 supplies the power received from the power supply 160 to the entire interchangeable lens 200 via the lens mount 250.
(1-3. Configuration of interchangeable lens)
The interchangeable lens 200 includes an optical system, a lens controller 240, and a lens mount 250. The optical system of the interchangeable lens 200 includes a zoom lens 210, an OIS lens 220, and a focus lens 230.

  The zoom lens 210 is a lens for changing the magnification of a subject image formed by the optical system of the interchangeable lens 200. The zoom lens 210 is composed of one or a plurality of lenses. The drive mechanism 211 includes a zoom ring or the like that can be operated by the user, transmits the operation by the user to the zoom lens 210, and moves the zoom lens 210 along the optical axis direction of the optical system. The detector 212 detects the drive amount in the drive mechanism 211. The lens controller 240 can grasp the zoom magnification in the optical system by acquiring the detection result in the detector 212.

  The OIS lens 220 is a lens for correcting blurring of a subject image formed by the optical system of the interchangeable lens 200. The OIS lens 220 moves in a direction that cancels out the blur of the camera system 1, thereby reducing the blur of the subject image on the CCD image sensor 110. The OIS lens 220 is composed of one or a plurality of lenses. The actuator 221 drives the OIS lens 220 in a plane perpendicular to the optical axis of the optical system under the control of the OIS IC 223. The actuator 221 can be realized by a magnet and a flat coil, for example. The position detection sensor 222 is a sensor that detects the position of the OIS lens 220 in a plane perpendicular to the optical axis of the optical system. The position detection sensor 222 can be realized by a magnet and a Hall element, for example. The OIS IC 223 controls the actuator 221 based on the detection result of the position detection sensor 222 and the detection result of a shake detector such as a gyro sensor. The OIS IC 223 obtains the detection result of the shake detector from the lens controller 240. Further, the OIS IC 223 transmits a signal indicating the state of the optical image blur correction process to the lens controller 240.

  The focus lens 230 is a lens for changing the focus state of the subject image formed on the CCD image sensor 110 in the optical system. The focus lens 230 is composed of one or a plurality of lenses.

  The focus motor 233 drives the focus lens 230 to advance and retract along the optical axis of the optical system based on the control of the lens controller 240. Thereby, the focus state of the subject image formed on the CCD image sensor 110 by the optical system can be changed. In the first embodiment, the focus motor 233 can be a DC motor. However, the present invention is not limited to this, and can be realized by a stepping motor, a servo motor, an ultrasonic motor, or the like.

  The first encoder 231 and the second encoder 232 are encoders that generate signals indicating the driving state of the focus lens 230. The first encoder 231 and the second encoder 232 can be realized by, for example, a rotor and a photocoupler attached to the rotation shaft of the focus motor 233. Here, the rotor is a disk body having holes opened at predetermined intervals. The photocoupler emits detection light from one surface of the rotor and receives light from the other surface. Therefore, when the rotor rotates, the ON / OFF state of the photocoupler switches between each other. The lens controller 240 has a counter 243 provided therein, and this counter 243 counts the number of ON / OFF state switching from the photocoupler. The first encoder 231 and the second encoder 232 are out of phase. Therefore, it is possible to determine the moving direction of the focus lens 230 when the state of the first encoder 231 is switched from OFF to ON. That is, the state of the second encoder 232 when the state of the first encoder 231 is switched from OFF to ON includes an ON state and an OFF state. Therefore, when the state of the first encoder 231 is switched from OFF to ON when the state of the second encoder 232 is ON, the counter 243 determines that this is normal rotation and counts it as “+1”. When the state of the encoder 232 is OFF and the state of the first encoder 231 is switched from OFF to ON, this is determined as reverse rotation and counted as “−1”. By adding this count number, the lens controller 240 can grasp the amount of movement of the focus lens 230.

The lens controller 240 controls the entire interchangeable lens 200 such as the OIS IC 223 and the focus motor 233 based on the control signal from the camera controller 140. In addition, signals are received from the detector 212, the OIS IC 223, the first encoder 231, the second encoder 232, and the like, and transmitted to the camera controller 140. The lens controller 240 performs the transmission / reception with the camera controller 140 via the lens mount 250 and the body mount 150. The lens controller 240 uses the DRAM 241 as a work memory during control. The flash memory 242 stores a program and parameters used when the lens controller 240 is controlled.
(1-4. Correspondence with Configuration of the Present Invention)
The focus motor 233 is an example of the driving means of the present invention. The configuration including the first encoder 231, the second encoder 232, and the counter 243 is an example of the position detection unit of the present invention. The CCD image sensor 110 is an example of an image sensor of the present invention. The camera controller 140 is an example of an evaluation value calculation unit of the present invention. The camera controller 140 is an example of a focus state determination unit of the present invention. The release button 130 is an example of the operation means of the present invention.
(2. Operation)
(2-1. Imaging preparation operation)
First, the operation of the camera system 1 for preparation for imaging will be described. FIG. 2 is a diagram illustrating signal transmission / reception for explaining the imaging preparation operation of the camera system 1.

  When the user turns on the power supply of the camera body 100 with the interchangeable lens 200 mounted on the camera body 100, the power supply 160 supplies power to the interchangeable lens 200 via the body mount 150 and the lens mount 250 ( S11). Next, the camera controller 140 requests authentication information of the interchangeable lens 200 from the lens controller 240 (S12). Here, the authentication information of the interchangeable lens 200 includes information regarding whether or not the interchangeable lens 200 is mounted and information regarding whether or not an accessory is mounted. The lens controller 240 responds to the lens authentication request from the camera controller 140 (S13).

  Next, the camera controller 140 requests the lens controller 240 to perform an initialization operation (S14). In response to this, the lens controller 240 performs initialization operations such as resetting the aperture and resetting the OIS lens 220. Then, the lens controller 240 returns to the camera controller 140 that the lens initialization operation has been completed (S15).

  Next, the camera controller 140 requests lens data from the lens controller 240 (S16). The lens data is stored in the flash memory 242. Therefore, the lens controller 240 reads the lens data from the flash memory 242 and sends it back to the camera controller 140 (S17). Here, the lens data is characteristic values unique to the interchangeable lens 200 such as a lens name, an F number, and a focal length.

  When the camera controller 140 grasps the lens data of the interchangeable lens 200 attached to the camera body 100, the camera controller 140 is ready for imaging. In this state, the camera controller 140 periodically requests lens state data indicating the state of the interchangeable lens 200 from the lens controller 240 (S18). The lens state data includes, for example, zoom magnification information by the zoom lens 210, position information of the focus lens 230, aperture value information, and the like. In response to this request, the lens controller 240 returns the requested lens state data to the camera controller 140 (S19).

  In this state, the camera system 1 can operate in a control mode in which an image indicated by the image data generated by the CCD image sensor 110 is displayed on the liquid crystal monitor 120 as a through image. This control mode is called live view mode. In the live view mode, the through image is displayed as a moving image on the liquid crystal monitor 120, so that the user can determine the composition for capturing a still image while viewing the liquid crystal monitor 120. The user can select whether to use the live view mode. In addition to the live view mode, another control mode that can be selected by the user is a control mode that guides the subject image from the interchangeable lens 200 to an optical viewfinder (not shown). In order to realize this control mode, a movable mirror or the like for guiding a subject image to an optical viewfinder (not shown) is required. A contrast method is suitable as a method of autofocus operation in the live view mode. This is because in the live view mode, the image data is constantly generated by the CCD image sensor 110, so that it is easy to perform a contrast-type autofocus operation using the image data.

When performing the contrast autofocus operation, the camera controller 140 requests contrast AF data from the lens controller 240 (S20). The contrast AF data is necessary for the contrast autofocus operation, and includes, for example, a focus drive speed, a focus shift amount, an image magnification, and contrast AF availability information.
(2-2. Contrast multipoint autofocus operation)
The contrast type multi-point autofocus operation in the camera system 1 ready for imaging will be described with reference to FIGS. 3 and 4. FIG. 3 is a flowchart for explaining the autofocus operation. FIG. 4 is a diagram illustrating areas in which detection is performed in the multipoint autofocus operation. In FIG. 4, a detection determination frame indicated by a solid line is an area having a high degree of importance, and is an area where focus determination is sequentially performed during detection. A non-detection determination frame indicated by a dotted line is an area of low importance and is an area where detection is performed, but focus determination is not performed during detection, and focus detection is performed after whole-area detection is performed.

  Assume that the camera controller 140 is operating in the live view mode. The camera controller 140 monitors whether or not the release button 130 is half-pressed. When the camera controller 140 detects half-pressing of the release button 130, it starts autofocus.

  The camera controller 140 starts autofocus detection from the position where the focus lens 230 is present, and determines the detection direction based on setting information such as the currently set scene mode and the image magnification at that time, Determine (S301). As a determination method, the image magnification at that time is compared with the determination image magnification set in the scene mode shown in Table 1, and when it is larger than the determination image magnification, detection is performed in the near direction and the image magnification is smaller than the determination image magnification. Performs detection in the far direction. From Table 1, in the multi-point autofocus operation, the camera controller 140 performs detection in the near direction when the image magnification at the start of autofocus is greater than 14 times, and in the far direction when the image magnification is less than 14 times.

  In this way, based on information such as the scene mode, in the current image magnification, it is determined whether the subject is likely to be close or likely to be far away, and by detecting in that direction, The time until focusing can be shortened.

  Next, the camera controller 140 instructs the lens controller 240 to start hill climbing. The lens controller 240 starts periodic transmission of the position information of the focus lens 230.

  The CCD image sensor 110 is exposed during the exposure period and transmits generated image data to the camera controller 140 via the AD converter 111. The camera controller 140 determines whether one frame has passed for the received image data (S302).

  When one frame of image data is notified, the camera controller 140 calculates evaluation values for autofocus operation (hereinafter referred to as AF evaluation values for convenience) for all of the 23 detection frames shown in FIG. 4 (S303). . Specifically, a method for obtaining an AF evaluation value by obtaining a luminance signal from image data generated by the CCD image sensor 110 and integrating high-frequency components in the screen of the luminance signal is known. The camera controller 140 stores the AF evaluation value in the DRAM 141 in association with the lens position information.

  Next, the camera controller 140 starts from the detection frame 0 shown in FIG. 4 based on the AF evaluation value stored in the DRAM 141, and for each detection frame, the position of the focus lens 230 where the AF evaluation value becomes the maximum value exists. It is determined whether to do (S304). If the detection frame to be determined is a detection frame with high importance, the camera controller 140 determines whether or not it is in focus based on the determination result in S304 (S305). If the camera controller 140 determines that the subject is in focus, it adds the AF evaluation value as a focus level (S307). The camera controller 140 executes the processes of S304 to S306 for each detection frame sequentially from the detection frame 0 to the detection frame 23. At this time, the detection frames 9 to 23 are non-detection determination frames with low importance, and the processing of S305 and S306 is not performed on these detection frames.

  Next, the camera controller 140 compares the in-focus level added in S306 with a determination threshold held in advance, and determines whether it is equal to or higher than the determination threshold (S309). If one of the detection determination frames is in focus and the total focus level of the detection determination frame exceeds the determination threshold, the camera controller 140 determines that autofocus is in focus (S312). A method in which the camera controller 140 determines which detection frame to focus on when there are a plurality of focused detection frames will be described later. In this way, focusing is performed in the detection frame with high importance, and when the total focus level is equal to or higher than the determination threshold, it is determined that the autofocus is in focus, so that autofocus is performed in the detection frame with high importance. The time until focusing can be reduced.

  If no detection determination frame is in focus, or if the focus level is smaller than the determination threshold even though the detection determination frame is in focus, the camera controller 140 It is determined that it is not in focus yet, and the process is continued.

  The camera controller 140 executes the processing from S302 to S309 while changing the position of the focus lens 230, and determines whether the processing has been completed for all the distances close to ∞ (S310). If detection has not been performed for all distances, the processing from S302 to S309 is continued. As described above, the camera controller 140 performs focus determination only for the detection detection frame with high importance, and performs detection for the non-detection determination frame with low importance but does not perform the focus determination. In this case, the focus is focused on the detection detection frame with high importance at a certain distance, but since it was focused on the non-detection determination frame with low importance before that, the focus determination of the detection determination frame with high importance is not made. A situation in which the autofocus operation ends can be avoided.

  The camera controller 140 determines whether or not all the detection frames are in focus after the entire area detection is completed (S311). If there is a focused detection frame, the camera controller 140 focuses on the detection frame (S312). A method of determining which focusing frame to focus on when there are a plurality of focused detection frames will be described with reference to the flowchart of FIG. The camera controller 140 stores information such as the position of the focus lens 230 and AF evaluation values on the DRAM 141 for a plurality of focused detection frames. The detection frame is weighted in advance by area. For example, the center frame is set to 100%, the top, bottom, left, and right are set to 60%, and the others are set to 20%. The camera controller 140 performs area-specific weighting on the focusing frame (S501). Next, the camera controller 140 calculates the distance to the subject based on the position of the focus lens 230 and performs weighting for each distance. As weighting according to distance, for example, the closest distance is set to 100%, 1 m is set to 50%, and ∞ is set to 20%. The camera controller 140 performs weighting according to distance for the focusing frame (S502). Next, the camera controller 140 performs weighting for each contrast on the focusing frame (S503). The weighting for each contrast is set to, for example, 100% at normal time and 50% at low contrast. The camera controller 140 determines the maximum weight frame as the focus frame by using the weight of the focus frame thus obtained (S504).

  On the other hand, when there is no focused detection frame, the autofocus is not focused (S313).

As described above, a detection frame that was not focused because the focus level was smaller than the determination threshold, but a focus detection was not performed before in the non-detection determination frame. The frame is also focused. In this way, by performing in-focus determination of all detection frames after whole-area detection, it is possible to focus autofocus on the focused detection frames, including non-detection determination frames with low importance. it can.
(Other embodiments)
As described above, the first embodiment has been described as the embodiment of the present invention. However, the present invention is not limited to these. Therefore, other embodiments of the present invention will be described collectively in this section.

  In the first embodiment, the detection frame shown in FIG. 4 is set as the detection frame, but the present invention is not limited to this. With respect to the number of detection frames, a larger number of detection frames may be set, or a smaller number of detection frames may be set. Further, the positional relationship between the detection frames is not limited to the positional relationship shown in FIG. 4, and may be arranged in a square shape, for example. Further, the arrangement of the detection determination frames with high importance and the non-detection determination frames with low importance is not limited to the arrangement shown in FIG. For example, only the detection frame 0, the detection frame 1, and the detection frame 2 shown in FIG. 4 may be used as detection detection frames, and the others may be non-detection determination frames. Further, in the determination of the detection determination frame and the non-detection determination frame in S305 in the flowchart of FIG. 3, the determination may be performed by setting the focus level to 0 (or a value sufficiently small with respect to the determination threshold).

  In the first embodiment of the present invention, the configuration including the zoom lens 210 and the OIS lens 220 is illustrated, but these are not essential configurations of the present invention. In other words, the present invention can be applied to a camera system equipped with a single focus lens that does not have a zoom function, and can also be applied to a camera system equipped with an interchangeable lens that does not have a camera shake correction function. It is.

  In Embodiment 1 of the present invention, a camera body that does not include a movable mirror is illustrated, but the present invention is not limited to this. For example, a movable mirror may be provided in the camera body, or a prism for separating the subject image may be provided. Moreover, the structure provided with a movable mirror not in a camera body but in an adapter may be sufficient.

  Although the first embodiment has been described using a lens-interchangeable camera system, the present invention is not limited to this and can be applied to a camera in which a camera body and a lens are integrated.

  In Embodiment 1 of the present invention, the position of the focus lens 230 is not detected directly, but is detected indirectly by detecting the rotation angle of the rotation shaft of the focus motor 233. As described above, in the present invention, the position of the focus lens 230 may be detected directly, or may be detected indirectly by detecting the position of the mechanism member interlocked with the focus lens 230. In short, it is only necessary that the position of the focus lens can be specified as a result.

  In the first embodiment of the present invention, a camera system not equipped with a phase difference detection sensor has been exemplified. However, the present invention is not limited to such examples. A phase difference detection sensor may be mounted so that a phase difference type autofocus operation and a contrast type autofocus operation can be selectively executed. In this case, the present invention is applicable when a contrast type autofocus operation is being performed.

  The present invention can be applied to an interchangeable lens camera system. Specifically, it can be applied to a digital still camera or a movie.

1 is a block diagram showing a configuration of a camera system according to Embodiment 1 of the present invention. The figure for demonstrating the imaging preparation operation | movement of the camera system which concerns on Embodiment 1 of this invention. Flowchart for explaining the multipoint autofocus operation of the camera system according to the first embodiment of the present invention. The figure which shows the area which detects in the multipoint autofocus operation | movement of the camera system which concerns on Embodiment 1 of this invention. Flowchart for determining an in-focus frame from a plurality of in-focus determination frames of the camera system according to Embodiment 1 of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Camera system 100 Camera body 110 CCD image sensor 112 Timing generator 130 Release button 140 Camera controller 200 Interchangeable lens 230 Focus lens 231 1st encoder 232 2nd encoder 233 Focus motor 240 Lens controller

Claims (5)

A focus lens that changes the focus state of the subject image by moving back and forth in the direction of the optical axis;
Driving means for driving the focus lens;
Position detecting means for detecting the position of the focus lens;
An image sensor that exposes and generates image data corresponding to the position of the focus lens;
Evaluation value calculation means for calculating an evaluation value for autofocus in a plurality of predetermined regions in the image data based on the generated image data;
Based on the evaluation value, the determination of the in-focus state in the less important area of the predetermined area is performed after determining the in-focus state in all positions where the focus lens can be driven in the higher importance area. Focusing state determination means;
A focus control device. The high importance area is an area near the center in the image data,
The focus control apparatus according to claim 1, wherein the low importance area is a peripheral area in the image data. Comprising an operating means for receiving an instruction to start focus control;
The evaluation value calculation means includes
The calculation of the evaluation value is started from the position of the focus lens at the time of start of focus control by the operation means,
Based on setting information including a shooting mode, a driving direction of the focus lens is determined, and the evaluation value is calculated.
The focus control apparatus according to claim 1 or 2. The evaluation value calculation means includes
The focus control apparatus according to claim 3, wherein a determination image magnification set for each setting information is compared with an image magnification at the time of the focus control start instruction to determine a driving direction of the focus lens. An imaging device comprising the focus control device according to any one of claims 1 to 4.

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