JP2008026672A - Automatic focusing device and imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a sense of incongruity resulting from the divergence of focus, and to shorten a focusing time even when a focal position detection accuracy by a phase difference detection system is not secured. <P>SOLUTION: An automatic focusing device includes: a first automatic focusing means to fetch the high frequency components of an image signal as a focus signal, and to adjust the focus based on the focus signal (step 409); and a second automatic focusing means to detect the focus position of the focusing member related to the object and to move the focusing member to the focus position so as to adjust the focus (step 404). In an automatic focusing mode to adjust the focus by using both the first focusing means and the second focusing means, in the case of focusing by the first automatic focusing means after the focusing operation is performed by the second automatic focusing means, a first control is performed (steps 405-406-407-409), thereafter, a second control having control responsiveness higher than that of the first control is performed (steps 406-407-408-409). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an automatic focus adjustment apparatus and an imaging apparatus that perform optimum focus adjustment control in a video camera or the like.

  2. Description of the Related Art Conventionally, a video camera automatic focus adjustment apparatus has mainly used a method (hereinafter referred to as a TV-AF method) in which automatic focus adjustment is performed by controlling a focus lens position so that a focus signal (focus evaluation value) is maximized. . In this method, while moving the focus lens, a focus signal representing the sharpness of the screen is detected from the video signal obtained by photoelectrically converting the subject image with an image sensor or the like, and the focus signal is maximized. Control the focus lens position.

  The TV-AF focus signal generally uses a high-frequency component of a video signal extracted by a band-pass filter of a certain band. When a normal subject image is photographed, the value increases as the focus is achieved as indicated by the solid line or dotted line in FIG. 2, and the point at which the level is maximum is the in-focus position.

  On the other hand, as another automatic focus adjustment method, there is an internal measurement phase difference detection method widely used in a single-lens reflex camera using a silver salt film. In the internal phase difference detection method, the light beam that has passed through the exit pupil of the photographic lens is divided into two, and the divided light beam is received by a set of focus detection sensors, and the output signal is shifted according to the amount of light received. Detect the amount. That is, by detecting the relative positional deviation amount in the beam splitting direction, the deviation amount in the focusing direction of the photographing lens is directly obtained. Therefore, once the accumulation operation is performed by the focus detection sensor, the amount and direction of the focus shift can be obtained, so that a high-speed focus adjustment operation is possible.

  Further, there is an external measurement phase difference detection method in which a distance measuring sensor is provided independently of the photographing lens even with the same phase difference detection method. In the external measurement phase difference detection method, a light beam received from an object is divided into two parts, each of the two divided light beams is received by a set of focus detection sensors, and a deviation amount of an output signal is detected according to the received light amount. . That is, the subject distance is obtained from triangulation by detecting the relative positional deviation amount in the beam splitting direction. In addition, as an automatic focus adjustment method using an external distance measuring sensor, there are a method of measuring a propagation speed using an ultrasonic sensor, a method of triangulating using an infrared sensor often used for compact cameras, and the like.

In recent years, combined with the above-mentioned auto focus adjustment method, for example, a compound type auto focus adjustment in which the lens is moved to the vicinity of the in-focus point by the internal phase difference detection method, and then the TV-AF method is shifted to adjust the focus position. A method has also been proposed (Patent Document 1).
JP 2005-1218195 A

  However, the conventional example has the following problems.

  In general, the TV-AF method can obtain in-focus with higher accuracy than other auto-focus adjustment methods, but on the other hand, the time required to obtain in-focus is compared with other auto-focus adjustment methods. Tend to be longer. Furthermore, when the subject has a low contrast or when shooting in a dark state, the in-focus position search of the TV-AF method is not always performed accurately. For this reason, if the in-focus position search is performed in the wrong direction with respect to the true in-focus position, a longer time is required until the in-focus state is obtained.

  Further, as shown in FIG. 3A, in the composite type automatic focus adjustment method, first, the focus lens is moved to a focus position by the phase difference detection method, and the focus signal (evaluation value) is more than a predetermined amount. Control is generally performed to change to the TV-AF method and stop at the in-focus position only when it is large. This is due to the fact that the TV-AF method has higher focus discrimination accuracy than other automatic focus adjustment methods. Therefore, if the focus accuracy or subject ranging accuracy due to the phase difference is not certain, the focus lens gets over the focus position that should have been obtained by the TV-AF method, and after the focus is once adjusted, there is a slight blur. appear. And when it is changed to the TV-AF system, it feels uncomfortable as it approaches the focus state again or decelerates before the focus lens reaches the in-focus position and then accelerates again to move to the in-focus position. An image with a certain focus change will be shot. FIG. 3B shows how the focus lens moves at this time.

  For such a problem, in the control method proposed in Patent Document 1, the optimum TV-AF is selected according to the comparison result between the focus signal information and the in-focus position information obtained by the phase difference sensor. Set drive parameters. This improves the accuracy of the in-focus position search by the TV-AF method, shortens the time until the in-focus is obtained, and copes with the above-described problem of focus change with an uncomfortable feeling.

  However, in the above control method, the information is not directly used for driving the focus lens, although the in-focus position is obtained by the phase difference sensor, and the information for improving the response of the TV-AF. As an indirect use. Therefore, the merit of the phase difference detection method cannot be fully utilized, and the fundamental solution for shortening the focusing time has not been reached.

(Object of the present invention)
An object of the present invention is to reduce the sense of incongruity of a focus change and shorten the focusing time at the same time even in the case where the focus position detection accuracy by a phase difference detection method or the like is not certain in a composite type auto focus adjustment device. It is an object of the present invention to provide an automatic focusing device and an imaging device that can be used.

  In order to achieve the above object, the present invention takes out a high-frequency component of a video signal obtained from an imaging means for imaging a subject as a focus signal, and performs focus adjustment by moving a focus adjustment member based on the focus signal. 1 automatic focus adjustment means, and a second automatic focus adjustment means for detecting a focus position of the focus adjustment member with respect to a subject and moving the focus adjustment member to the focus position to perform focus adjustment. In the automatic focus adjustment apparatus having an automatic focus adjustment mode for performing focus adjustment by using the first focus adjustment means and the second focus adjustment means together, the second automatic focus adjustment is performed in the automatic focus adjustment mode. When the focus is adjusted by the first automatic focus adjustment means after the focus adjustment operation by the means, the first control is performed, and then the second control with higher control response is performed. It is intended.

  Further, the present invention is an imaging apparatus including the automatic focus adjustment apparatus of the present invention.

  According to the present invention, even when the focus position detection accuracy by the phase difference detection method or the like is not certain in the composite automatic focus adjustment device, it is possible to reduce the uncomfortable feeling of focus change and simultaneously reduce the focus time. it can.

  The best mode for carrying out the present invention is as described in Examples 1 and 2 described later.

  FIG. 1 is a diagram illustrating a system configuration of an imaging apparatus that is Embodiment 1 of the present invention. In FIG. 1, 101 is a fixed first lens group, 102 is a variable power lens for zooming, 103 is a stop, 104 is a fixed second lens group, and 105 is a focal plane movement correction and focusing due to zooming. This is a focus competition lens (hereinafter referred to as a focus lens) having the above functions.

  Reference numeral 106 denotes an image sensor such as a CCD, and 107 denotes a CDS / AGC / AD converter that samples, adjusts gain, and digitizes the output of the image sensor 106. Reference numeral 108 denotes a camera signal processing circuit that processes an output signal from the CDS / AGC / AD converter 107 and generates a video signal. Reference numeral 109 denotes an output signal of the camera signal processing circuit 108 so that a photographer can monitor an image. The display device used.

  Reference numeral 110 denotes a recording device using a magnetic tape, an optical disk, a semiconductor memory, and the like. Reference numeral 111 denotes an AF gate that passes only a signal in an area used for focus detection from the output signal of the CDS / AGC / AD converter 107. A focus signal processing circuit 112 extracts a high frequency component from the signal that has passed through the AF gate 111.

  A camera / AF microcomputer 113 controls a focus lens driving source 115 (to be described later) based on the output signal of the focus signal processing circuit 112, drives the focus lens 105, and outputs an image recording command to the recording device 110. is there.

  Reference numeral 114 denotes a variable power lens driving source including an actuator for moving the variable power lens 102 and its driver.

  Reference numeral 115 denotes a focus lens driving source including an actuator for moving the focus lens 105 and its driver.

  Reference numeral 116 denotes an external key unit including a menu button operated when the photographer switches the use / non-use mode of the external distance measuring unit and a zoom switch operated when zooming, and 117 is an external distance measuring unit. The external ranging unit 117 is of the external measurement phase difference detection method, but may be an ultrasonic sensor method, an infrared sensor method, etc. as in the prior art.

  Here, an outline of the control in the composite type auto focus adjustment mode performed by the camera / AF microcomputer 113 will be described with reference to FIG.

In FIG. 4, step 401 indicates the start of processing. In step 402, it is determined whether or not the scene in which the phase difference AF is to be used, that is, whether the subject has changed due to panning or movement of the subject, and if so, the process proceeds to step 403, and if not, the process proceeds to step 406.
In step 403, the external distance measuring unit 117 performs a phase difference calculation to calculate a focus lens position corresponding to the subject distance.

  In step 404, the focus lens 105 is driven to the position calculated in step 403 at a predetermined speed.

  In step 405, a state is set in which the transition from the minute driving mode to the hill-climbing driving mode in the TV-AF control is prohibited.

  In step 406, it is determined whether or not the transition to hill-climbing driving is prohibited. If so, the process proceeds to step 407, and if not, the process proceeds to step 409.

  In step 407, it is determined whether or not a predetermined time has elapsed since the transition to the hill-climbing drive is prohibited in step 405. If so, the process proceeds to step 408, and if not, the process proceeds to step 409.

  In step 408, the state prohibiting the transition to hill-climbing driving is canceled. In step 409, TV-AF control is performed. The detailed operation here will be described with reference to FIG.

  Next, TV-AF control will be described with reference to FIG. In FIG. 5, step 501 indicates the start of processing. In step 502, the position and size of a distance measuring frame for acquiring a focus signal from the focus signal processing circuit 112 are set.

  In step 503, filter coefficients in the focus signal processing circuit 112 are set, and a plurality of band pass filters having different extraction characteristics are constructed. The extraction characteristic is the frequency characteristic of the bandpass filter, and the setting here means changing the setting value of the bandpass filter in the focus signal processing circuit 112.

  In step 504, the focus signal is acquired from the focus signal processing circuit 112. The focus signals acquired here are added at a predetermined ratio and then used for the subsequent focus adjustment control. The detailed operation here will be described later.

  In step 505, it is determined whether or not the mode is the minute drive mode. If yes, the process proceeds to step 506 and subsequent minute drive processes. If not, the process proceeds to step 513.

  In step 506, a minute driving operation is performed to drive the focus lens with a predetermined amplitude to determine whether the focus lens is in focus or in which direction the focus is present. The detailed operation here will be described with reference to FIG.

  In step 507, it is determined whether or not the focus is determined. If yes, the process proceeds to step 511. If not, the process proceeds to step 508.

  In step 508, it is determined whether or not the direction can be determined by the minute driving operation in step 506. If so, the process proceeds to step 509. If not, the process returns to step 502 to continue the minute driving mode.

  In step 509, it is determined in step 405 whether or not the transition to hill-climbing driving is prohibited. If it is not in the transition prohibition state, the process proceeds to step 510 to shift to the hill-climbing drive operation. If it is in the transition prohibition state, the process returns to step 502 to continue the minute drive mode.

  In step 511, the focus signal state at the time of in-focus is stored in the memory, and then the process proceeds to step 512 to shift to the restart determination mode.

  In step 513, it is determined whether or not the hill-climbing drive mode is selected.

  In step 514, the focus lens 105 is driven to climb up at a predetermined speed in a direction in which the focus signal increases. The detailed operation here will be described with reference to FIG.

  In step 515, it is determined whether or not the peak position of the focus signal has been found by the hill-climbing drive in step 514. If the peak position is found, the process proceeds to step 516. If not, the process returns to step 502 to continue the hill-climbing drive operation. To do.

  In step 516, the focus lens position at which the focus signal has reached its peak is set as the target position, and then the process proceeds to step 517 to shift to the stop mode.

  In step 518, it is determined whether the mode is the stop mode. If so, the process proceeds to a stop process after step 519, and if not, the process proceeds to step 521.

  In step 519, it is determined whether or not the focus lens 105 has returned to the position where the focus signal is at the peak, and if so, the process proceeds to step 520, the mode is shifted to the minute drive mode, and if not, the process returns to step 502. Continue in stop mode.

  The operations after step 521 are operations in the restart determination mode. In step 521, the focus signal held in step 511 is compared with the current focus signal to determine whether or not the level fluctuation is large. If the focus signal fluctuates greatly, the process proceeds to step 522, and the mode is shifted to the minute drive mode. If not, the process is not restarted and is stopped as it is, and the process returns to step 502.

  Next, the minute driving operation will be described with reference to FIG. In FIG. 6, step 601 indicates the start of processing. In step 602, the current value of the counter that counts the number of routine processes synchronized with the vertical synchronizing signal is determined. If 0, the process proceeds to the process in step 603 when the focus lens 105 is on the near side, and otherwise, the process proceeds to step 602. Go to 604.

  In step 603, the focus signal is held as processing when the focus lens position is on the close side. The focus signal here is based on a video signal generated from charges accumulated in the image sensor 106 when the focus lens position is on the infinite side in step 611 described later.

  In step 604, the current counter is determined. If it is 1, the process proceeds to the process of driving the focus lens 105 to the infinite side after step 605. Otherwise, the process proceeds to step 612.

  In step 605, the vibration amplitude and the center movement amplitude are calculated. These amplitudes are generally set within the depth of focus.

  In step 606, the focus signal level on the near side held in step 603 is compared with the focus signal level on the infinite side held in step 611, which will be described later. If the latter is large, the process proceeds to step 607, and if the former is large, the process proceeds to step 608. .

  In step 607, the vibration amplitude and the center movement amplitude are added to obtain the drive amplitude. In step 608, the vibration amplitude is set as the drive amplitude. In step 609, the drive amplitude obtained in step 607 or step 608 is used to drive in an infinite direction.

  In step 610, the current counter is determined. If the current counter is 2, the process proceeds to step 611 when the focus lens 105 is on the infinite side, and otherwise, the process proceeds to step 612.

  In step 611, the focus signal is held as processing when the focus lens position is on the infinity side. The focus signal here is based on the video signal generated from the charge accumulated in the image sensor 106 when the focus lens position is in the closest side in step 603.

  In step 612, the vibration amplitude and the center movement amplitude are calculated. These amplitudes are generally set within the depth of focus.

  In step 613, the focus signal level on the infinite side held in step 611 is compared with the focus signal level on the near side held in step 603. If the latter is large, the process proceeds to step 614, and if the former is large, the process proceeds to step 615.

  In step 614, the vibration amplitude and the center movement amplitude are added to obtain the drive amplitude. In step 615, the vibration amplitude is set as the drive amplitude. In step 616, the drive amplitude obtained in step 614 or 615 is used to drive in the closest direction.

  In step 617, it is determined whether or not the focal point exists in the same direction for a predetermined number of times. If so, the process proceeds to step 620, and if not, the process proceeds to step 618.

  In step 618, it is determined whether the focus lens 105 has reciprocated in the same area a predetermined number of times. If so, the process proceeds to step 619, and if not, the process proceeds to step 621. In step 619, it is determined that the in-focus determination has been made. In step 620, it is determined that the direction can be determined.

  In step 621, if the counter is 3, the counter is cleared to 0, and if it is any other value, +1 is added to the counter and the process proceeds to step 622. Step 622 indicates the end of the process.

The time course of the focus lens operation in this minute driving is shown in FIG. The upper part of the figure is a vertical synchronizing signal of the video signal, the horizontal axis of FIG. 8B represents time, and the vertical axis represents the focus lens position. Focus signal EV _A to the charge accumulated in the image pickup device 106 at the time of the label A is taken into the camera / AF microcomputer 113 at time _{T A.} Then, the focus signal EV _B to the charge accumulated in the image pickup device 106 at the time of the label B is taken into the camera / AF microcomputer 113 at time _{T B.} Comparing at time _{T C} focus signal EV _A and EV _B, to move the vibration center only if a large EV _B. Note that the movement of the focus lens 105 here is set to a movement amount that cannot be recognized on the screen on the basis of the depth of focus.

  Subsequently, the hill-climbing driving operation will be described with reference to FIG. In FIG. 7, step 701 indicates the start of processing. In step 702, it is determined whether or not the level of the focus signal has increased from the previous level. If so, the process proceeds to step 703, and if not, the process proceeds to step 704.

  In step 703, the focus lens 105 is hill-climbed at a predetermined speed in the same direction as the previous time, and the process proceeds to step 707.

  In step 704, if the focus signal has decreased beyond the peak, the process proceeds to step 706. If the focus signal has decreased due to other factors, the process proceeds to step 705.

  In step 705, the focus lens 105 is hill-climbed at a predetermined speed in the direction opposite to the previous time, and the process proceeds to step 707. In step 706, it is determined that a peak position has been found. Step 707 indicates the end of the process.

  FIG. 9 shows the movement of the focus lens 105 in the hill-climbing driving operation. In FIG. 9, when the focus lens 105 is driven as indicated by A, the focus signal is increased, so that the hill-climbing drive in the same direction is continued. Here, when the focus lens 105 is driven in the range B, the focus signal decreases beyond the peak position. At this time, the hill-climbing driving operation is terminated assuming that the in-focus point exists, and after the focus lens 105 is returned to the peak position, the operation shifts to the minute driving operation. On the other hand, when the focus signal decreases without exceeding the peak position as in C, the direction to be driven is reversed and the hill-climbing driving operation is continued.

  In this way, in the focus adjustment control by the TV-AF method, as shown in FIG. 3C, the predetermined time after the use of the phase difference AF decreases its control responsiveness, thereby restart determination → micro drive → The focus lens is moved while repeating the restart determination. Thus, the in-focus state is maintained so that the focus signal is always maximized. As a result, even when the subject ranging accuracy due to the phase difference is not certain in the composite automatic focus adjustment device, the focus change operation is reduced and the focus adjustment operation that does not give the user a sense of incongruity is provided. Time can be shortened.

  FIG. 10 is a diagram illustrating a system configuration of an imaging apparatus that is Embodiment 2 of the present invention. A description of the same components as those in the first embodiment will be omitted. In the first embodiment shown in FIG. 1, the external distance measuring unit 117 is used, but in the second embodiment, a TTL phase difference detection type focus detection device is used.

  In FIG. 10, reference numeral 1001 denotes a fixed first lens group, 1002 denotes a variable power lens for zooming, and 1003 denotes a focus competition lens (hereinafter referred to as a focus lens) having functions of focal plane movement correction and focusing accompanying zooming. It is. Reference numeral 1004 denotes a half prism that performs light division for focus detection, 1005 denotes a stop, 1006 denotes an imaging lens, and 1007 denotes an image sensor.

  Reference numeral 1008 denotes a sub-mirror, 1009 denotes an imaging lens for focus detection, 1010 denotes a phase difference detection AF sensor, and 1011 denotes an AF circuit.

  Reference numeral 1012 denotes a CDS / AGC / AD converter that samples, gain adjusts, and digitizes the output of the image sensor 1007. Reference numeral 1013 denotes a camera signal processing circuit that processes an output signal from the CDS / AGC / AD converter 1012 and generates a video signal. is there.

  A display device 1014 displays an output signal of the camera signal processing circuit 1013, and is used for a photographer to monitor an image. A recording device 1015 uses a magnetic tape, an optical disk, a semiconductor memory, or the like. Reference numeral 1016 denotes an AF gate that passes only signals in a region used for focus detection from the output signal of the CDS / AGC / AD converter 1012, and reference numeral 1017 denotes a focus signal processing circuit that extracts a high-frequency component from the signal that has passed through the AF gate 1016.

  Reference numeral 1018 denotes a camera / AF microcomputer that controls a focus lens driving source 1020 (to be described later) based on the output signal of the focus signal processing circuit 1017 and drives the focus lens 1003. At the same time, the camera / AF microcomputer 1018 outputs an image recording command to the recording device 1015 and further plays a role of detecting a deviation amount and a deviation direction from the output of the AF sensor 1010 via the AF circuit 1011.

Reference numeral 1019 denotes a variable power lens drive source including an actuator for moving the variable power lens 1002 and its driver, and 1020 denotes a focus lens drive source including an actuator for moving the focus lens 1003 and its driver.
Reference numeral 1021 denotes an external key unit including a menu button operated when the photographer switches the use / non-use mode of the phase difference AF and a zoom switch operated when performing zooming.

  During moving image shooting, the diaphragm 1005 is always operating except for a specific mode. Therefore, in the case of an imaging apparatus having such a configuration, the input light must be divided by the half prism 1004 before the diaphragm 1005.

  Also in the second embodiment, the focus adjustment control algorithm described in the first embodiment can be applied. Therefore, the flowcharts representing the features of the second embodiment are common to those in FIGS. 4, 5, 6, and 7, and the description in the drawings will be left to them.

  As described above, in the focus adjustment control by the TV-AF method, the focus lens is moved while repeating the restart determination → the minute drive → the restart determination by reducing the control responsiveness for a predetermined time after using the phase difference AF. Let Thus, the in-focus state is maintained so that the focus signal is always maximized. As a result, even when the focusing accuracy due to the phase difference is not certain in the composite automatic focusing device, the focus change time can be reduced while reducing the focus change problem and providing the user with a feeling of incongruity. Can be shortened.

1 is a diagram illustrating a system configuration of an imaging apparatus that is Embodiment 1 of the present invention. FIG. It is a figure which shows the characteristic of a focus signal. It is a figure which shows the focus lens drive example of a composite type focus adjustment system. It is a flowchart which shows the focus adjustment control of Example 1 of this invention. It is a flowchart which shows TV-AF control of Example 1 of this invention. It is a flowchart which shows the operation | movement in the micro drive mode of Example 1 of this invention. It is a flowchart which shows the operation | movement in the mountain climbing drive mode of Example 1 of this invention. It is a figure which shows the focus lens operation | movement in micro drive mode. It is a figure which shows the focus lens operation | movement in the hill-climbing drive mode. It is a figure which shows the system configuration | structure of the imaging device which is Example 2 of this invention.

Explanation of symbols

101 Fixed first lens group 102 Variable magnification lens 103 Diaphragm 104 Fixed second lens group 105 Focus lens 106 Imaging element 107 CDS / AGC / AD converter,
108 Camera Signal Processing Circuit 109 Display Device 110 Recording Device 111 AF Gate 112 Focus Signal Processing Circuit 113 Camera / AF Microcomputer 114 Variable Lens Driving Source 115 Focus Compensation Lens Driving Source 116 External Key Unit 117 External Distance Measuring Unit 1010 AF Sensor 1011 AF circuit

Claims (6)

A first automatic focus adjustment unit that takes out a high-frequency component of a video signal obtained from an imaging unit that images a subject as a focus signal, moves a focus adjustment member based on the focus signal, and performs focus adjustment;
A second automatic focus adjustment unit that detects a focus position of the focus adjustment member with respect to the subject, moves the focus adjustment member to the focus position, and performs focus adjustment;
In an automatic focus adjustment apparatus having an automatic focus adjustment mode for performing focus adjustment by using the first focus adjustment means and the second focus adjustment means together,
In the automatic focus adjustment mode, the first control is performed at the time of the focus adjustment by the first automatic focus adjustment means after the focus adjustment operation by the second automatic focus adjustment means, and then the control responsiveness is higher than that. An automatic focusing apparatus characterized by performing second control with high speed.   In the automatic focus adjustment mode, after the focus adjustment operation by the second automatic focus adjustment means, the control responsiveness of the first automatic focus adjustment means is temporarily lowered to perform the first control, and then the second control is performed. The automatic focusing apparatus according to claim 1, wherein control is performed.   3. The automatic focus adjustment apparatus according to claim 1, wherein the first control is performed for a predetermined time when shifting to the focus adjustment operation by the first automatic focus adjustment unit. 4. The first automatic focus adjustment means has a first drive mode for determining a direction in which the focus signal is maximized, and a second drive mode for determining a position in which the focus signal is maximized,
The control responsiveness of the first automatic focus adjustment unit is reduced by prohibiting the transition from the first drive mode to the second drive mode for the predetermined time. 4. The automatic focusing apparatus according to 3.   5. The in-focus position is detected by any one of an internal measurement phase difference detection method, an external measurement phase difference detection method, an ultrasonic sensor method, and an infrared sensor method. The automatic focusing device as described. An image pickup apparatus comprising the automatic focus adjustment apparatus according to claim 1.

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