JPH06339062A - Automatic focus adjusting device - Google Patents

Abstract

(57) [Abstract] [Purpose] It is an object to provide a highly accurate automatic focus adjustment device without malfunction by optimizing selection of a distance measurement area. [Structure] Different size measurement areas can be set on the screen, and when the camera is restarted after focusing, the focus state in each of the measurement areas is determined and the measurement area is selected based on the result of the determination. To do. Also, prioritize each distance measurement area, and if the distance measurement area when the in-focus state is obtained at restart is the distance measurement area with high priority, select that distance measurement area, When the focus detection area has a low focus area, the focus area in each focus area is determined to determine the focus area. In addition, when the focus lens is driven by performing focus adjustment operation and it reaches the in-focus state, it is determined whether or not there is a distance-measurable object in the distance-measuring area with high priority. For example, automatic focus adjustment is performed using the distance measurement area with the higher priority.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focusing device.

[0002]

2. Description of the Related Art In recent years, electronic control technology for lenses has been remarkably improved along with the demand for smaller and lighter cameras. In the automatic focusing system, infrared rays or the like are projected onto the object and the object distance is recognized by the reflected light. The active AF method is shifting to a passive AF method in which focusing is performed to maximize the amount of high frequency components of a video signal.

One of the great advantages of the passive AF system is that it does not require a light projecting unit and a light receiving unit as in the active AF system and is suitable for downsizing of a camera unit.

Among the passive AF systems of this type, in the field of video cameras, the sharpness of an image is detected by extracting a high frequency component whose level changes according to the focus state from the output signal of the image sensor. However, the so-called television AF system, which drives a forensic lens so as to maximize this, has been widely used.

In this system, focus detection can be performed from the output signal of the image pickup device, a dedicated focus sensor is not required, and focus detection is performed based on the sharpness of the image.
This is because it has the advantage that it is not limited by the distance to the subject.

Then, in the AF system of the television AF system, first, only a high frequency component in the image output signal which is picked up by the image pickup element and photoelectrically converted is extracted by the bandpass filter. The amount of this high-frequency component has a maximum value when it is in focus, and its level gradually decreases as the focus shifts. This amount of high-frequency components will be referred to as the focus voltage hereinafter, and the change in the focus voltage with the movement of the focus lens is shown by characteristic curves 401 and 402 in FIG.

Considering extraction of high frequency components from a video signal, in a video camera, the type of high frequency components contained in a horizontal scanning signal is extracted by a band pass filter in view of its screen scanning method. Is common,
Therefore, the more vertical lines the screen includes, and the more distinct the vertical lines are, the larger the maximum value of the focus voltage is. As seen from FIG. 4, the image on the curve 402 has fewer lines perpendicular to the screen (for example, many diagonal lines) or the shade of the line is not clear as compared with the image on the curve 401. Then, the focus lens is driven so that the focus voltage becomes maximum, and the AF operation is executed.

By the way, in the case of such passive AF, since the focusing operation is performed based on the information of the image pickup screen, there is a problem of where to focus on the image pickup screen. For example, if the focus detection operation is always performed on the entire screen with the focus detection range on the screen,
The subject intended by the photographer is often out of focus, and other subjects are likely to be in focus.

For example, as shown in FIG. 5, when an image of a person 504 with a zebra stuffed animal as a background is to be photographed, the distribution of the focus voltage on the entire screen is shown by characteristic curves 601 as shown in FIG. It becomes like 602. Since the focal voltage 601 for the zebra is distant from the person 504, which is the main subject, the focal voltage 601 has a maximum on the relatively infinite side, and the maximum value is large because the stripe is clearly defined by the vertical line. Further, the focus voltage for the person 504 becomes maximum on the relatively close side, and the vertical line is small and unclear compared to the zebra, so the maximum value is also small.

Therefore, when the focus lens starts focusing from the infinity end, it is obvious that if the focus lens is focused on the position where the focus voltage becomes maximum, the zebra will be in focus and the person will not be in focus. Even if focusing is started from the close side, the “peaks” formed by the focus voltages overlap each other as shown in FIG.
There is a possibility that the lens may be moved to the maximum point of 601 as it is without determining the maximum portion of the focus position as the focus position.

A state in which it is not known which position to focus on with respect to a plurality of points having different distances is called a perspective conflict state. The perspective conflict state is avoided as much as possible and the subject intended by the photographer is focused. In order to adjust the distance, a method of providing a distance measuring frame, that is, a focus detection area at a specific position on the screen has been conventionally used. For example, assuming that the photographer is likely to place the subject to be photographed in the center of the screen, 503 in FIG.
As shown in, a gate frame is placed in the center of the screen, and only the video signal of the portion inside the gate frame is gated and extracted, and the signals of other portions are not used for AF.

According to this method, the subject other than the inside of the distance measuring frame 503 is out of focus, so that the phenomenon that the zebra is in focus can be eliminated. However, when the subject disappears inside the ranging frame 503, for example, when the person 504 in FIG. 5 suddenly moves out of the ranging frame and there is no subject behind the person, the focus voltage is the focus lens. Since it becomes flat at any position, the camera side cannot find the peak of the focus voltage as shown in FIGS. And, even though there is a zebra on the screen, the zebra does not focus and continues to search the lens between the closest end and the infinite end to search for the maximum value of the focus voltage.

Therefore, as the next method, another distance measuring frame 302 having a different size is provided in addition to the distance measuring frame 503 in FIG. 5, and the focus voltage of the subject inside either of the distance measuring frames 503 and 502 is used. The method of trying to measure the distance was proposed.

FIG. 8 is a flowchart of a basic process for performing AF using the distance measuring frames 503 and 502 having different sizes as described above.

FIG. 8 shows the AF operation when the subject is once in focus and is focused on a subject at another subject distance. In the figure, step 801
When the execution of the process is started in step 802, it is confirmed in step 802 whether the focus voltage is below the restart threshold value. As is clear from FIG. 7, the restart threshold value is set as a threshold value 701 with respect to the curve of the focus voltage, and the focus voltage when in the in-focus state is the restart threshold value 701. If it falls below, it is determined that the subject has clearly moved or the photographer has pointed the camera at another subject with a different subject distance, and the focus lens that has been stopped is restarted.

If it is determined in step 802 that the focus voltage is not below the restart threshold value 701, the restart operation is not performed to maintain the in-focus state, and the determination operation of step 802 is continued. If the focus voltage falls below the restart threshold, the focus is focused in step 803 with either a large range-finding frame like the range-finding frame 502 or a small range-finding frame like the range-finding frame 503. Check whether If the subject was in focus with a large frame when focusing, even if you restart the camera, it is better to focus on a subject with a large frame (for example, a composition in which nothing is in the center of the screen) as the subject. It is decided that a large frame is used in step 804 because there are many cases where it is continued, and conversely, if the small frame is focused, the small frame is restarted.

In this way, the size of the distance measuring frame is determined, AF is performed in step 806, and the AF operation is repeated until it is determined in step 807 that focusing is achieved. And step 8
If it is determined to be in focus at 07, the lens is stopped at step 808, the process returns to step 802 and waits until the restart condition is satisfied.

With the above arrangement, it is possible to determine an appropriate distance-measuring frame when the photographer continuously follows the object, and the two distance-measuring frames are used properly, so that the object is in the center. When there is a subject in the center, the subject in the center is in focus, and when there is no subject in the center, the subject outside the center is in focus. The problem of continuing to search between near ends will not occur.

[0019]

However, according to the above example, by selectively using a large distance measuring frame and a small distance measuring frame, even a subject in the near-far conflict state can be focused on the subject at the center of the screen. However, if there is no subject in the center of the screen, it becomes easier to focus on other subjects, but the size of the ranging frame is determined by the subject or ranging frame before restarting. If the AF operation is performed on a subject existing outside the center of the screen when restarting is started with a large distance measurement frame, there is a problem that the lens is stopped at the in-focus point for the subject.

In other words, by preparing a plurality of distance measurement frames, the probability of focusing on the subject at the center of the screen has increased for the near and far competing subjects, but it does not yet have the subject identifying performance that the photographer can satisfy. The problem remains.

Further, even if an object other than the center of the screen is once focused and the photographer performs an operation such as shaking the camera in order to refocus the object at the center of the screen, the range-finding frame before restart is set. Since it takes over and is restarted, there is a problem that an object other than the center of the screen is often focused again.

[0022]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and is characterized in that a first distance measuring area and the first distance measuring area are provided in a screen. Distance measuring area setting means capable of setting a plurality of distance measuring areas including a second distance measuring area having different sizes with respect to the area, and a focus adjusting operation by driving an optical element for focus adjustment from a focused state. At the time of transition, the determination means for determining the focus state in the first distance measurement area and the second distance measurement area, and the distance measurement area after the start of the focus adjustment operation are selected based on the output of the determination means. And an automatic focusing device having a selecting means.

According to the second invention of the present application, a first distance measuring area having a high priority and a second distance measuring area having a low priority with respect to the first distance measuring area are provided in the screen. A range-finding area setting unit capable of setting a plurality of range-finding areas including the range-finding area, and a measurement when the focus state is obtained when the focus adjustment optical element is driven to shift from the focus state to the focus adjustment operation. When the distance area is the first distance measurement area, the first distance measurement area is selected,
When the distance measuring area when the focused state is obtained is the second distance measuring area, the focus state in the first and second distance measuring areas is determined to determine the distance measuring area. The automatic focus adjusting device is provided with a distance measuring area selecting unit and a control unit that performs a focus adjusting operation based on the distance measuring area selected by the distance measuring area selecting unit.

According to the third invention of the present application, a first distance measuring area having a high priority and a second distance measuring area having a low priority with respect to the first distance measuring area are provided in the screen. When a focusing state is reached by driving a focusing area setting unit capable of setting a plurality of ranging areas including the focusing area and an optical element for focusing, and within the first focusing area The automatic focus adjustment device is characterized by including a control unit that determines whether or not there is a subject whose distance can be measured, and controls the drive of the optical element for focus adjustment based on the determination result.

[0025]

As a result, when the subject does not exist in the center of the screen, which is the original advantage, AF is performed on the other subjects, and the operation to avoid unnecessary hunting of the lens is maintained, At the time of start-up, re-selection processing of the distance measuring frame is added, restarting is started with an appropriate distance measuring frame, and when focusing with a large distance measuring frame, it is checked whether the subject exists in the small distance measuring frame. By providing a means for checking again and determining whether or not to perform the restart operation, it is possible to secure the subject identification performance and the AF performance that the photographer can satisfy.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A position embodiment of an automatic focusing device according to the present invention will be described in detail below.

FIG. 1 is a block diagram showing an example in which the present invention is applied to a video camera using a television AF system. In the figure, 101 is a fixed first lens group,
Reference numeral 102 denotes a second lens group (to be referred to as a variable power lens hereinafter) that performs zooming by moving in parallel to the optical axis, 103 denotes a diaphragm, 104 denotes a fixed third lens group, and 105 denotes parallel to the optical axis. Focusing is performed by moving the lens, and correction operation is performed in accordance with the movement of the lens 102 during zooming, thereby preventing movement of the focus surface during zooming. Reference numerals 106, 107, and 108 denote encoders for detecting the position or movement amount of the variable power lens 102, the diaphragm 103, and the focus lens 105, respectively.
Reference numerals 9, 110, and 111 denote actuators for driving the variable magnification lens 102, diaphragm 103, and focus lens 105, 112, 113, and 114 denote drivers for driving actuators 109, 110, and 111, and 115 denotes a CCD or the like. An image pickup surface of the image pickup device of No. 1 and an amplifier 116.

Reference numeral 117 denotes a band pass filter for passing a high frequency component in the output signal of the amplifier 116 and a high frequency component in the output signal of the amplifier 116 for a period designated by a gate control circuit 122 which will be described later. A gate circuit + bandpass filter provided with a gate circuit for setting the distance measuring frame, and 118, which is composed of a microcomputer or the like, outputs the high frequency component signal in the distance measuring frame, that is, the focus voltage output from the gate circuit + bandpass filter 117 It is input and A / D converted, and based on the value, the focus lens is driven and controlled to the in-focus point, and the gate control circuit 122 is controlled as described later to control the position and size of the ranging frame. It is a system control circuit.

Reference numeral 119 controls the driver 113 and the actuator 110 to adjust the diaphragm 103 so that the average value of the luminance signal level of the output signal of the amplifier 116 becomes constant, so that the image pickup surface 115 of the image pickup device is properly exposed. A diaphragm control circuit for controlling the horizontal sync signal HD and a vertical sync signal VD for supplying the vertical sync signal VD to the gate control circuit 122, and the gate control circuit 122 internally has a counter for the horizontal sync signal HD and the vertical sync signal VD. The system control circuit 118 is configured to set a distance measuring frame on the screen and control the gate circuit in the gate circuit + bandpass filter 117 to be opened only within the distance measuring frame. Controlled by.

In such an AF system, the image signal picked up by the image pickup device 115 and photoelectrically converted is amplified by the amplifier 116, and only the high frequency component in the output signal of the amplifier 116 is gated by the bandpass filter 117. Only the inside of the distance measuring frame set by is extracted. As described above, the amount of this high-frequency component exhibits a maximum value when the subject is in focus, and the level gradually decreases when the subject is out of focus. The relationship between the amount of high frequency components, that is, the focus voltage and the focus lens position is the same as that shown in FIG.

Also in the video camera of this embodiment, the amount of high frequency components contained in the horizontal scanning signal in the distance measuring frame is extracted by the gate circuit + bandpass filter 117, and the line vertical to the screen is The more contained, the more
The clearer the shade of the vertical line, the larger the maximum value of the focus voltage.

Next, the control algorithm of the system control circuit 118, which is a feature of the present invention, will be specifically described with reference to FIG.

FIG. 2 is a flow chart of a process characteristic of the present invention, which is executed in the system control circuit 118.

It should be noted that, in FIG. 2, the focus voltage is below the threshold 701 as shown in FIG. 7 due to the subject moving or the camera moving after the focus lens is once focused and the focus lens is stopped at the focus position. The process starts from the state of waiting until the restart condition is satisfied.

When the execution of the processing is started in step 201, it is confirmed in step 202 whether the focus voltage is lower than the restart threshold 701 as in FIG. If so, the process waits at step 202 as it is, and if it is less than that, the process proceeds to step 203.

At step 203, it is confirmed whether or not the focus detection frame is large at the time of focusing. If it is a large distance measuring frame, the process proceeds to step 204, and the threshold voltage A indicated by 302 in FIG. 3 is used to check whether the focus voltage in the large distance measuring frame is lower than the threshold value A or not. Check.

The fact that the focus voltage in the large distance measuring frame is below the threshold value A at the time of restarting can be judged to be a large blur in the entire photographing screen.
That is, it is assumed that the photographer points the camera at a completely different subject than before, suddenly a large subject appeared in front of the camera, or the subject suddenly disappeared from the front of the camera, so restart There is no need to maintain the state of the previous distance measuring frame. Therefore, in such a case, in order to focus on the subject at the center of the screen, the processing of step 205 is performed to use a small distance measuring frame.

When it is determined in step 203 that the distance measuring frame before restarting is small, the distance measuring frame at the time of focusing, that is, the small distance measuring frame is selected in step 206.

If the range-finding frame before restarting is large and it is determined in step 204 that the focus voltage exceeds the threshold value A, it means that the composition has not changed significantly from the composition taken so far. In step 206, the focus detection frame at the time of focusing, that is, a large focus detection frame is selected, and the AF operation is performed while avoiding unnecessary hunting of the focus lens.

In this way, after selecting the size of the distance measuring frame at the time of restart, the AF operation is performed in step 207, and the AF operation is continued until it is determined to be in focus in step 208. The focus lens is stopped at step 209.

Here, the AF operation is completed once, but after that, it is reconfirmed in step 210 whether or not the focusing / stopping is performed in a large distance measuring frame. As a result, focusing with a small distance measuring frame
If it has stopped, it is determined that the subject in the center of the screen is in focus, and the step 202 returns to the restart standby state.

When it is determined in step 210 that the focus is stopped / stopped in the large distance-measuring frame, the focus voltage in the small distance-measuring frame is checked again in step 211. Even if the object outside the small distance measuring frame is focused / stopped in the large distance measuring frame, if the object is present even though it is blurred within the small distance measuring frame, as shown by 603 in FIG. A finite amount of focus voltage should be detected within a small ranging frame. Therefore, in step 211, when the focus voltage in the small distance measuring frame exceeds the threshold value B (threshold value B> threshold value A) indicated by 301 in FIG. Despite the presence, it is determined that the subject outside the small range-finding frame is in focus, and steps 212, 213, 21
In step 4, the AF operation is performed again by using only the small distance measurement frame, and the focus / stop operation is performed.

If the focus voltage in the small distance measuring frame is below the threshold value B in step 211, it is determined that the in-focus point in the large distance measuring frame is appropriate, and the process returns to step 202.

The threshold value B is small. There is no subject in the range, or even if there is a subject, the peak of the focus voltage for that subject is fairly flat, and it is not possible to find a clear peak of the peak. Set to a value that can be determined to be difficult.

As described above, in addition to the conventional AF operation and range-finding frame selection processing, the re-selection of the range-finding frame at restart and the small range-finding frame at the time of focusing by using two threshold values. By reconfirming the presence or absence of the subject in the inside, even if there is a subject with a large maximum value of the focus voltage in a large ranging frame, the priority of focusing on the subject in the center of the screen is extremely increased, It is possible to secure the subject recognition ability and the AF performance that the photographer is satisfied with.

Further, when there is no subject at the center of the screen, the AF operation is performed on subjects other than the center of the screen as usual, so that the advantage of conventional AF is so-called "middle-out". It does not impair stable lens behavior for the subject.

[0047]

As described above, according to the present invention,
By confirming whether the size of the focus detection frame at the time of focusing should be maintained when restarting, and whether the subject is within the small focus detection frame in the center of the screen after focusing, If there is no image, while maintaining the advantage of improving the stability of the lens by performing the focusing operation on other subjects, it is suitable for this when the composition of the screen changes significantly. When the subject is present in the center of the screen, the priority is given to the focusing operation on the subject in the center of the screen, so that the subject identification performance that the photographer is satisfied with is improved. And it became possible to secure AF performance.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an automatic focus adjustment device according to the present invention.

FIG. 2 is a flow chart for explaining a control operation of the automatic focus adjustment device according to the present invention.

FIG. 3 is a diagram showing the relationship between the focus voltage and the focus lens position for explaining the restarting operation of the automatic focus adjustment device according to the present invention.

FIG. 4 is a diagram showing a relationship between a focus voltage and a focus lens position for explaining the operation of the automatic focus adjustment device.

FIG. 5 is a diagram for explaining a relationship among a screen, a subject, and a distance measuring frame.

FIG. 6 is a diagram showing the relationship between the focus voltage and the focus lens position related to FIG.

FIG. 7 is a diagram showing a relationship between a focus voltage and a focus lens position for explaining a restart operation of a general automatic focus adjustment device.

FIG. 8 is a flowchart for explaining a restarting operation of the conventional automatic focusing apparatus related to FIG.

Claims (4)

[Claims] 1. A range-finding region setting capable of setting a plurality of range-finding regions including a first range-finding region and a second range-finding region having a size different from that of the first range-finding region within a screen. And a determining means for determining a focus state in the first distance measuring area and the second distance measuring area when the focus adjusting optical element is driven from the focused state to shift to the focus adjusting operation. An automatic focus adjusting device, comprising: selecting means for selecting a distance measuring area after the start of the focus adjusting operation based on the output of the determining means. 2. A plurality of distance measuring areas including a first distance measuring area having a high priority and a second distance measuring area having a low priority with respect to the first distance measuring area are set in the screen. A possible distance measuring area setting means and a distance measuring area when the focused state is obtained when the focus adjusting optical element is driven from the focused state to shift to the focus adjusting operation are the first distance measuring area. If the distance measuring area is the first distance measuring area, the first distance measuring area is selected, and if the distance measuring area when the focused state is obtained is the second distance measuring area, the first distance measuring area is selected. And a range-finding region selection means for determining the focus state in the second range-finding region to determine the range-finding region, and a focus adjustment operation based on the range-finding region selected by the range-finding region selecting means. An automatic focus adjusting device, comprising: 3. A plurality of ranging areas including a first ranging area having a high priority and a second ranging area having a low priority with respect to the first ranging area are set in the screen. Focusing operation is performed by driving possible distance measuring area setting means and focus adjustment optical element,
When the in-focus state is reached, it is determined whether or not there is a distance-measurable object in the first distance-measuring area, and the drive of the focus adjustment optical element is controlled based on the determination result. An automatic focus adjusting device, comprising: 4. The control means, when a distance-measurable object exists in the first distance-measuring area, performs the focus adjustment operation based on information in the first distance-measuring area. The automatic focusing device according to claim 3, wherein the automatic focusing device is configured.