JP4928191B2 - Automatic focusing device and imaging device - Google Patents

Description

  The present invention relates to an automatic focus adjustment device and an imaging device used for a video camera or the like.

  In recent years, an automatic focus adjustment device of a video camera detects a focus signal (focus evaluation value) representing the sharpness of a screen from a video signal obtained by photoelectrically converting a subject image with an image sensor or the like, and the focus signal is A method of adjusting the focus by controlling the position of the focus lens so as to be maximized is the mainstream.

  The focus signal generally uses a high-frequency component of a video signal extracted by a bandpass filter. When a normal subject image is photographed, as shown in FIG. 2, the value increases as the focus is achieved, and the point where the level is maximum is the in-focus position. As a characteristic of the focus signal, when the center frequency of the bandpass filter is increased with respect to the band of the video signal, the shape of the mountain becomes steep as shown by the dotted line in FIG. It is known that the mountain shape becomes gentle as shown by the solid line.

  The frequency characteristics of the band-pass filter that extracts the focus signal clearly determine the peak of the focus signal because the focus signal can be sufficiently reduced by moving the focus lens within the focal depth before and after focusing. Is possible. Even when the focus lens is at a position far from the focal point, a clear focus signal difference can be obtained by moving the focus lens by the depth of focus so that the in-focus direction can be determined.

  The automatic focusing apparatus using the video signal as described above has the following problems.

  As shown in FIG. 3, it is assumed that there is a main subject A to be focused inside the first distance measuring frame at the center of the shooting screen. In this case, if a subject B different from the main subject A exists in the second distance measurement frame located around the first distance measurement frame, the extracted focus signal is affected by the subject B.

  Here, there is no problem if the main subject A and the subject B are equidistant, but if the distances are different, the subject B, not the main subject A, is in focus, contrary to the intention of the photographer. There is. Further, in such a situation, it is easily affected by camera shake or the like, and subject B enters or exits the second distance measuring frame, thereby causing fluctuations in the focus signal and making the autofocus operation unstable.

For such a problem, in Patent Document 1, when the focus position of the focus lens is different between the first distance measurement frame and the second distance measurement frame, the focus position is determined from the focus signal of the first distance measurement frame. Thus, the background is not focused.
JP 2004-309722 A

  However, since the above-mentioned conventional apparatus basically gives priority to the center, it is difficult for the photographer to change the composition flexibly. In addition, when the main subject is out of the first distance measurement frame and momentarily falls out, the background is mistakenly focused, so that the fundamental solution to this problem has not been reached.

(Object of invention)
An object of the present invention is to provide an automatic focus adjustment device and an imaging device capable of suppressing the influence of a subject different from a main subject on a focus signal and performing stable autofocus control.

In order to achieve the above object, the automatic focus adjustment apparatus of the present invention is the automatic focus adjustment apparatus that performs focus adjustment based on a focus signal corresponding to the contrast of an image extracted from the output signal of the imaging means. Setting means for setting a first autofocus area and a second autofocus area corresponding to a frame around the first autofocus area in the screen of the means, and the imaging means corresponding to the autofocus area A plurality of band-pass filters having different frequency characteristics for extracting a focus signal from the output signal of the output signal, and when the focus signal is extracted from the second autofocus area, the first autofocus area is selected. to without selecting a bandpass filter having a high frequency of frequency characteristic, a band pass with a frequency characteristic of the low frequency Select filter, the first auto-focus area and the second auto-focus corresponding to the region extracting means for adding to extract focus signal from the output signal of the imaging means passing through the selected band-pass filter It is characterized by having.

  In order to achieve the above object, the present invention is an imaging apparatus including the automatic focus adjustment apparatus of the present invention.

  According to the present invention, it is possible to provide an automatic focus adjustment device or an imaging device capable of suppressing the influence of a subject different from a main subject on a focus signal and performing stable autofocus control.

  The best mode for carrying out the present invention is as shown in Example 1 and Example 2 below.

  FIG. 1 is a block diagram illustrating a circuit configuration of the imaging apparatus according to the first embodiment 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, and 104 is a fixed second lens group. Reference numeral 105 denotes a focus lens (hereinafter referred to as a “focus lens”) that has both a focal plane movement correction and a focusing function associated with zooming.

  Reference numeral 106 denotes an image sensor such as a CCD, and 107 denotes a converter that samples, adjusts gain, and digitizes the output of the image sensor 106. Reference numeral 108 denotes a memory that cuts out only a signal in an area used in camera signal processing, which will be described later, in the high level direction from the output of the converter 107, and synchronizes the clock timing. A camera signal processing circuit 109 processes an output signal from the memory 108 to generate a video signal. A recording device 110 uses a magnetic tape, an optical disk, a semiconductor memory, or the like.

  Reference numeral 111 denotes a drive pulse generator for driving the image sensor 106, 112 denotes an actuator for moving the focus lens 105, and 113 denotes a driver for driving the actuator 112 by a signal from an AF microcomputer 114 described later. Reference numeral 114 denotes an AF microcomputer that drives the focus lens 105 by controlling the driver 113 based on a focus signal (focus evaluation value) output from a focus signal processing circuit 115 described later. A focus signal processing circuit 115 extracts a high frequency component used for focus detection from the output signal of the memory 108.

Next, autofocus control performed by the AF microcomputer 114 will be described with reference to the flowchart of FIG .

  The process starts from step S401. First, in step S402, the position and size of a distance measurement frame (autofocus area) for acquiring a focus signal from the focus signal processing circuit 115 are set. Specifically, the first distance measurement frame and the second distance measurement frame in FIG. 3 are set. In the next step S403, filter coefficients in the focus signal processing circuit 115 are set, and a plurality of band pass filters having different extraction characteristics are constructed. The extraction characteristic is a frequency characteristic of the band pass filter (BPF), and the setting here means changing a set value of the band pass filter in the focus signal processing circuit 115. For example, in the case of an FIR type digital filter as shown in FIG. 5, this is equivalent to changing the coefficients h0 to h4. Here, the FIR type digital filter is taken as an example, but the configuration of the band pass filter is not particularly limited. Specifically, a high-frequency and low-frequency bandpass filter is constructed for the video signal of the first distance measurement frame, and a low-frequency bandpass filter is constructed for the video signal of the second distance measurement frame. To do. The reason will be described later.

  In the next step S404, the focus signal is acquired from the focus signal processing circuit 115. The focus signals acquired here are added at a predetermined ratio and then used for subsequent autofocus control. The detailed operation here will be described later. In the next step S405, it is determined whether or not the mode is the micro drive mode. If so, the process proceeds to the micro drive process after step S406, and if not, the process proceeds to step S412.

  If it is determined that the mode is the minute drive mode, the process proceeds to step S406. Here, a minute drive operation is performed, and the focus lens 105 is driven within the depth of focus to determine whether the focus is in focus or in which direction the focus is present. To do. The detailed operation will be described later with reference to FIG. In the next step S407, it is determined whether or not the focus can be determined. If the focus can be determined, the process proceeds to step S410 described later. On the other hand, if the focus cannot be determined, the process proceeds to step S408, and it is determined whether the direction can be determined by the minute driving operation in step S406. As a result, if the direction can be determined, the process proceeds to step S409, shifts to the hill-climbing drive mode, and then returns to step S402. If the direction cannot be determined, the process immediately returns to step S402 to continue the minute drive mode.

  If it is determined in step S407 that the in-focus state has been determined and the process proceeds to step S410, the focus signal state at the time of in-focus state is stored in the memory 108 here. And it progresses to step S411 and transfers to restart determination mode. Thereafter, the process returns to step S402.

  If it is determined in step S405 that the mode is not the minute drive mode, the flow advances to step S412 to determine whether the mode is the hill climbing drive mode. As a result, if the hill-climbing drive mode is set, the process proceeds to the hill-climbing drive process after step S413, and if not, the process proceeds to step S417.

  If it is determined that the current mode is the hill-climbing drive mode and the process proceeds to step S413, the focus lens 105 is hill-climbed at a predetermined speed in the direction in which the focus signal increases. The detailed operation here will be described later with reference to FIG. In the next step S414, it is determined whether or not the peak position of the focus signal has been found by the hill-climbing drive in step S413. As a result, if the peak position is found, the process proceeds to step S415. If the peak position is not found, the process immediately returns to step S402, and the hill-climbing drive mode is continued.

  If the peak position is found and the process proceeds to step S415, the focus lens position at which the focus signal is peaked is set as the target position. Then, in the next step S416, the process shifts to the stop mode. Thereafter, the process returns to step S402.

  If it is determined in step S412 that the mode is not the hill-climbing drive mode and the process proceeds to step S417, it is determined here whether the mode is the stop mode. As a result, if it is the stop mode, the process proceeds to a stop process after step S418, and if it is not the stop mode, the process proceeds to step S420.

  If it is determined that the mode is the stop mode and the process proceeds to step S418, it is determined here whether or not the focus lens 105 has returned to the position where the focus signal peaked. As a result, if it is determined that the peak position has been returned, the process proceeds to step S419, the mode is changed to the minute drive mode, and thereafter, the process returns to step S402. On the other hand, if it is determined that the focus lens 105 has not returned to the focus signal peak position, the process immediately returns to step S402 to continue the stop mode.

  If it is determined in step S417 that the mode is not the stop mode and the process proceeds to step S420, the focus signal held in step S410 is compared with the current focus signal to determine whether the level fluctuation is large. As a result, if the focus signal has fluctuated greatly, the process proceeds to step S421, proceeds to the minute drive mode, and thereafter returns to step S402. The operations after step S420 are operations in the restart determination mode. On the other hand, if the focus signal does not fluctuate significantly, the process immediately returns to step S402.

  Next, the acquisition of the focus signal from the focus signal processing circuit 115 will be described by taking the scene of FIG. 3 as a problem to be solved as an example.

  In FIG. 3, although the main subject A to be focused exists in the first distance measuring frame in the center of the shooting screen, the main subject is located in the second distance measuring frame located around the first distance measuring frame. There is a subject B different from A. Therefore, the subject B has been affected by the extracted focus signal. FIG. 8 shows the state of the focus signal at this time, and the result of performing a conventional calculation for use in autofocus control is as shown in FIG. That is, when the current focus position is within the range b due to the influence of the subject B on the focus signal, the main subject A cannot be found, and the subject B matches the subject B against the photographer's intention. It will be burnt.

  In general, the sharp focus signal obtained from the high-frequency bandpass filter is large for determining the focus of the subject, and the relatively flat focus signal obtained from the low-frequency bandpass filter is large for determining the direction when there is a large blur. To contribute.

  Accordingly, when the high frequency component is not used in the second distance measurement frame in which there is a high possibility that the subject B other than the main subject A exists, the result of adding the focus signals in FIG. 8 at a predetermined ratio when only the low frequency component is used. Is as shown in FIG. When autofocus control is performed using this calculation result, it is possible to move to the position of the main subject A regardless of the current focus position.

  The above processing is nothing but selecting a focus signal having a main extraction characteristic to be used for autofocus control according to the state of the distance measurement frame, that is, the position and size of the distance measurement frame on the shooting screen. As a result, the influence of the subject B, which is present in the second distance measurement frame, different from the main subject A on the focus signal is suppressed, and stable autofocus control is performed on the main subject A intended by the photographer. it can. The focus signal in FIG. 10 is acquired in step S404 in FIG.

  Next, the minute driving operation executed in step S406 of FIG. 4 will be described according to the flowchart of FIG.

  The process is started from step S601. First, in step S602, the current value of the counter that counts the number of routine processes synchronized with the vertical synchronization signal is determined. If 0, the focus lens 105 in step S603 is on the near side. Proceed to the process, otherwise proceed to step S604.

  If it is determined that the current counter is 0 and the process proceeds to step S603, the focus signal is held here as processing when the focus lens position is on the close 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 on the infinite side in step S611 described later.

  If it is determined that the current counter is not 0, the process proceeds to step S604. Here, the current counter is determined again. If it is 1, the process proceeds to the process of driving the focus lens to the infinite side after step S605. Proceed to step S610.

  If the current counter is 1 and the process proceeds to step S605, the vibration amplitude and the center movement amplitude are calculated here. These amplitudes are generally set within the depth of focus. In the next step S606, the focus signal level on the near side held in step S603 is compared with the focus signal level on the infinite side held in step S611 described later. As a result, if the latter is larger, the process proceeds to step S607, and the drive amplitude is obtained by adding the vibration amplitude and the center movement amplitude. If the former is large, the process proceeds to step S608, and the vibration amplitude is set as the drive amplitude.

  Thereafter, the process proceeds to step S609, and driving is performed in an infinite direction using the drive amplitude obtained in step S607 or step S608. Then, the process proceeds to Step S617 described later.

  If it is determined in step S604 that the current counter is not 1, the process proceeds to step S610. Here, the current counter is determined again. If it is 2, the process proceeds to step S611 when the focus lens is on the infinite side. If so, the process proceeds to step S612.

  If it is determined that the current counter is 2 and the process proceeds to step S611, the focus signal is held here as processing when the focus lens position is on the infinite 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 on the close side in step S603.

  If the current counter is not 2 in step S610 and the process proceeds to step S612, the vibration amplitude and the center movement amplitude are calculated here. These amplitudes are generally set within the depth of focus. In the next step S613, the infinite focus signal level held in step S611 is compared with the close focus signal level held in step S603. As a result, if the latter is larger, the process proceeds to step S614, where the vibration amplitude and the center movement amplitude are added to obtain the drive amplitude. If the former is large, the process proceeds to step S615, and the vibration amplitude is set as the drive amplitude.

  Thereafter, the process proceeds to step S616, and driving is performed in the closest direction using the drive amplitude obtained in step S614 or step S615. Then, the process proceeds to step S617.

  In step S617, it is determined whether a focal point exists in the same direction continuously for a predetermined number of times. If so, the process proceeds to step S620, where it is determined that the direction has been determined, and the process proceeds to step S621. Otherwise, the process proceeds to step S618.

  If it is determined that the in-focus point does not exist in the same direction for a predetermined number of times, the process proceeds to step S618, where it is determined whether the focus lens 105 has reciprocated in the same area a predetermined number of times. As a result, when reciprocating within the same area a predetermined number of times, the process proceeds to step S619, where it is determined that the in-focus determination has been made, and the process proceeds to step S621. On the other hand, if the predetermined area has not been reciprocated in the same area, the process immediately proceeds to step S621.

In step S621, if the counter is 3, the counter is reset to 0, and if it is any other value, the counter is added, and the process returns to the main routine of FIG. 4 in step S622.
Step S622 indicates the end of the process.

  FIGS. 11A and 11B show the time course of the focus lens operation in the minute driving described above. FIG. 11A shows a vertical synchronizing signal of the video signal, where the horizontal axis indicates time and the vertical axis indicates the focus lens position.

The focus signal EV _A for the charge accumulated in the image sensor 106 at the time of label A is taken into the AF microcomputer 114 at time T _A. Further, the focus signal EV _B for the electric charge accumulated in the image sensor 106 at the time of label B is taken into the AF microcomputer 114 at time T _B. At time _{T C,} comparing the focus signal EV _A and EV _B, to move the vibration center only if a large EV _B. Here, the movement of the focus lens 105 is set to a movement amount that cannot be recognized on the screen on the basis of the depth of focus.

  Next, the hill-climbing driving operation executed in step S413 in FIG. 4 will be described according to the flowchart in FIG.

  The process starts from step S701. First, in step S702, it is determined whether the level of the focus signal has increased from the previous one. As a result, if it has increased, the process proceeds to step S703, the focus lens 105 is hill-climbed and driven in the same direction as the previous time at a predetermined speed, and in the next step S707, the process returns to the main routine of FIG.

  If the level of the focus signal has not increased from the previous level, the process proceeds to step S704, where it is determined whether the focus signal has decreased beyond the peak. As a result, if the focus signal has decreased beyond the peak, the process proceeds to step S706, where it is determined that the peak position has been found, and in the next step S707, the process returns to the main routine of FIG. On the other hand, if it is decreased due to other factors, the process proceeds to step S705, the focus lens 105 is hill-climbed at a predetermined speed in the direction opposite to the previous time, and the process returns to the main routine of FIG. 4 in the next step S707.

  FIG. 12 shows the movement of the focus lens 105 during the hill-climbing driving operation. In FIG. 12, when the focus lens 105 is driven as in the range 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 the range C, the driving direction is reversed and the hill-climbing driving operation is continued.

  In this way, the AF microcomputer 114 performs control so that the focus signal is always maximized by moving the focus lens 105 while repeating the restart determination → micro drive → mountain climbing drive → stop → micro drive → restart determination. , Maintain the in-focus state.

  FIG. 13 is a block diagram illustrating a circuit configuration of an imaging apparatus according to Embodiment 2 of the present invention. In FIG. 13, reference numeral 1301 denotes a fixed first lens group, 1302 denotes a variable power lens for zooming, 1303 denotes a stop, and 1304 denotes a fixed second lens group. Reference numeral 1305 denotes a focus lens (hereinafter referred to as a “focus lens”) having both a focal plane movement correction and a focusing function associated with zooming.

  Reference numeral 1306 denotes an image sensor such as a CCD, and 1307 denotes a converter that samples, gain adjusts, and digitizes the output of the image sensor 1306. Reference numeral 1308 denotes a memory that cuts out only a signal in a region used in camera signal processing, which will be described later, in the high level direction from the output of the converter 1307 and matches the clock timing. A camera signal processing circuit 1309 generates an image signal by processing an output signal from the memory 1308. A recording device 1310 uses a magnetic tape, an optical disk, a semiconductor memory, or the like.

  Reference numeral 1311 denotes a drive pulse generator for driving the image sensor 1306, 1312 an actuator for moving the focus lens 1305, and 1313 a driver for driving the actuator 1312 by a signal from an AF microcomputer 1314 described later. Reference numeral 1314 denotes an AF microcomputer that controls the driver 1313 based on an output signal of a focus signal processing circuit 1315 described later to drive the focus lens 1305. Reference numeral 1315 denotes a focus signal processing circuit that extracts a high frequency component used for focus detection from the output signal of the memory 1308. Reference numeral 1316 denotes a changeover switch, which can be switched between a high-resolution format (HD) and a conventional resolution format (SD).

  When the recording method is a high resolution format (HD), a more sensitive in-focus determination is required. Therefore, a sharp focus signal is used by setting the center frequency of the bandpass filter in the focus signal processing circuit 1315 high. It is common. On the other hand, when the recording format is a conventional resolution format (SD), it is not necessary to use a steep focus signal as in the former case for the focus determination.

  Therefore, in the second embodiment, a focus signal acquisition method of a main extraction characteristic to be used for autofocus control is determined based on the recording format determined by the changeover switch 1316. That is, selection of the focus signal extraction characteristic according to the state of the distance measurement frame, which is a feature of the first embodiment, is permitted when the recording format is high resolution, and is prohibited otherwise.

  As a result, problems such as the scene of FIG. 3 in the high-resolution format can also suppress the influence of the subject B, which is present in the second distance measurement frame, on the focus signal, which is different from the main subject A, and can perform stable autofocus control. It can be carried out.

It is a figure which shows the system configuration | structure of the imaging device which concerns on Example 1 of this invention. It is a figure which shows the characteristic of a focus signal. It is a figure which shows the example of the scene where a focus signal is influenced by subjects other than the main subject. It is a flowchart which shows the autofocus control in Example 1 of this invention. It is a block diagram which shows the FIR type digital filter which concerns on Example 1 of this invention. 5 is a flowchart showing an operation in the minute drive mode of FIG. 4. It is a flowchart which shows the operation | movement at the time of the hill-climbing drive mode of FIG. It is a figure which shows the focus signal state of each ranging frame in the scene of FIG. It is a figure which shows the focus signal calculation result by a conventional method. It is a figure which shows the focus signal calculation result by Example 1 of this invention. It is a figure which shows the focus lens operation | movement of a micro drive in Example 1 of this invention. It is a figure which shows the focus lens operation | movement of the mountain climbing drive in Example 1 of this invention. It is a figure which shows the system configuration | structure of the imaging device which concerns on Example 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 1st group lens 102 Variable magnification lens 105 Focus lens 106 Imaging element 108 Memory 109 Camera signal processing circuit 110 Recording apparatus 114 AF microcomputer 115 Focus signal processing circuit 1301 1st group lens 1302 Variable magnification lens 1305 Focus lens 1306 Imaging element 1308 Memory 1309 Camera signal processing circuit 1310 Recording device 1314 AF microcomputer 1315 Focus signal processing circuit

Claims (5)

In an automatic focus adjustment device that performs focus adjustment based on a focus signal corresponding to a contrast of an image extracted from an output signal of an imaging means,
And setting means for setting a first autofocus area, and the second auto focusing area corresponding to the frame around the said first autofocus area on the screen of the imaging means,
A plurality of band pass filters having different frequency characteristics for extracting a focus signal from an output signal of the imaging means corresponding to the autofocus region;
When extracting a focus signal from the second autofocus area, a band having a low frequency frequency characteristic is selected without selecting a bandpass filter having a high frequency characteristic selected in the first autofocus area. select-pass filter, and adding the extracted focus signal from an output signal of said first auto focusing area and the imaging means corresponding to the second autofocus area to pass through the band pass filter the selected extracted And an automatic focusing device. The extraction means does not select a bandpass filter having a frequency characteristic for extracting a high-frequency component in an autofocus region where there is a high possibility that another subject other than the main subject exists, and has a frequency characteristic for extracting a low-frequency component. The automatic focusing apparatus according to claim 1 , wherein a band-pass filter is selected. 3. The automatic focus adjustment apparatus according to claim 1, wherein the operation of the extraction unit is permitted or prohibited in accordance with a selection to any one of two or more different recording formats. The storage format, the automatic focusing device according to any one of claims 1 to 3, characterized in that the format defining the resolution. Imaging apparatus characterized by comprising an automatic focusing device according to any one of claims 1 to 4.

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