JP3109812B2 - Imaging device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an automatic focusing device suitable for use in an imaging device such as a video camera and an electronic still camera.

(Prior art) Conventionally, in an imaging device such as a video camera, the CCD
There is known a method of detecting the definition of an image based on a high-frequency component of a video signal output from an image pickup means, and controlling the position of a focusing lens so as to maximize the degree, thereby achieving focusing.

Further, in a camera that converts an optical image into an electric signal by such an imaging unit, a method is proposed in which a part of an imaging screen is set as a focus detection area, and this is followed by movement of a subject to automatically adjust the focus state. (For example,
60-249477).

According to this conventional apparatus, the moving position of the subject is known by detecting a characteristic point of the subject in the focus detection area and detecting a change in the feature point, and the focus detection area is centered on the moving position. This is to reset to a small area.

(Problems to be Solved by the Invention) However, in such a conventional apparatus, the subject is tracked at the same response speed by the focus detection area having the same size in each field regardless of the photographing situation. For example, when the depth of field is deep, in the tracking for extracting the peak of the high frequency component of such an image, it becomes difficult to distinguish the main subject from its surroundings, that is, the background (so-called far-field conflict), and focus detection is performed. There is a problem that the region moves unstable regardless of the subject.

(Means for Solving the Problems) Accordingly, the present invention solves the conventional problems and makes the movement of the focus detection area natural even when the depth of field is deep, and follows the target object image. The purpose of the present invention is to provide an automatic focusing device capable of causing a detection area set on an imaging screen to move in accordance with the movement of a subject image. So,
Position detecting means for detecting a position of a subject on the imaging screen, area setting means for controlling a set position of the detection area based on an output of the position detecting means, and a moving direction of the detection area based on depth of field information And control means for controlling the control of the imaging device.

Another feature of the present application is an imaging apparatus capable of moving a detection area set on an imaging screen by following the movement of a subject image, wherein the position detection unit detects a subject position on the imaging screen; An area setting unit that controls a set position of the detection area based on an output of the position detection unit; and a control unit that controls a moving direction, a movement response speed, and a size of the detection area based on depth of field information. In the imaging device.

(Operation) This makes it possible to always optimally control the size of the focus detection area, the movement response speed, and the movement direction irrespective of the shooting conditions, and to ensure that the subject always exists in the focus detection area. A possible, stable and reliable subject tracking and focusing operation can be performed.

(Embodiment) One embodiment of the automatic focusing apparatus according to the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a block diagram showing a case where the automatic focusing apparatus of the present invention is applied to a video camera or the like.

In FIG. 1, reference numeral 1 denotes a photographing lens system, which includes a focusing lens 1A for performing focus adjustment and a zoom lens 1B for performing a zoom operation. The driving of the focusing lens 1A is controlled via a focusing motor drive circuit 9 and a focusing motor 10. The zoom lens 1B includes a zoom motor drive circuit 11 and a zoom motor.
The drive is controlled via 12. Reference numeral 2 denotes a stop (iris) for controlling the amount of incident light, which is driven and controlled via an iris drive circuit 7 and an ig meter 8 for driving the stop. Reference numeral 3 denotes an image sensor such as a CCD for photoelectrically converting a subject image formed on an image pickup surface by the focusing lens 1 into an image pickup signal, and 4 denotes an image pickup signal output from the image pickup device 3 at a predetermined level. The preamplifier 5 performs predetermined processing such as gamma correction, blanking processing, and addition of a synchronization signal on the video signal output from the preamplifier 4 to convert the video signal into a standardized standard television signal. This is the process circuit to output. The television signal output from the process circuit 5 is supplied to a monitor 23 such as a video recorder (not shown) or an electronic viewfinder.

Reference numeral 6 denotes a video signal output from the preamplifier 4, and an ig meter 8 via an iris drive circuit 7 for controlling the aperture of the diaphragm 2 so that the level of the video signal is kept at a predetermined level. It is an iris control circuit that performs automatic control.

Reference numeral 13 denotes a full-range filter set so that the magnitude of the contrast of the subject can be determined from the video signal output from the preamplifier 4, and reference numeral 14 denotes a filter necessary for performing focus detection from the video signal output from the preamplifier 4. A band-pass filter that extracts high-frequency components. 15 is a detection circuit that detects the blur width of the subject image from the video signal (the width of the edge of the subject image), and uses the property that the blur width of the subject decreases as the focus state approaches. To perform focus detection. The focus detection method itself by the blur width detection circuit has been known, for example, in Japanese Patent Application Laid-Open No. 62-103616, and a detailed description thereof will be omitted.

16 is a subject discrimination filter 13, a band pass filter 14,
A gate circuit that gates the output of the blur width detection circuit 15 and passes only a signal corresponding to a designated area on the imaging screen, according to a gate pulse supplied by a logic control device 18 described later. Only a signal corresponding to a designated area in the signal is passed, thereby setting a pass area for extracting a high-frequency component at an arbitrary position in the imaging screen, that is, a focus detection area for performing focus detection. (FIG. 4 shows a focus detection area set on the imaging screen, and the state of each figure will be described later).

Reference numeral 17 denotes a peak position detection circuit for detecting the horizontal and vertical positions in the imaged screen where the peak value of the high-frequency component is obtained from the video signal corresponding to the focus detection area extracted by the gate circuit 16. is there. This peak position detection circuit detects which peak position detected in one field period is located in a block obtained by dividing the focus detection area into a predetermined number of blocks in the horizontal and vertical directions, and determines the horizontal and vertical coordinates thereof. Is output.

Reference numeral 19 denotes a focus encoder that detects the movement position of the focusing lens 1A, reference numeral 20 denotes a zoom encoder that detects focal length information that is changed by the zoom lens 1B,
Reference numeral 21 denotes an iris encoder that detects the opening amount of the diaphragm 2. These pieces of detection information are supplied to the logic control unit 18.

Reference numeral 18 denotes a logic control unit that controls and controls the entire system.
For example, it is constituted by a microcomputer, and includes an input / output port (not shown), an A / D converter, a read only memory (ROM), and a random access memory (RAM). This logic control circuit is a peak position detection circuit
The peak value of the high-frequency component in one field period based on the output of the bandpass filter 14 output from 17 and the coordinates of the peak position, subject contrast information based on the output of the subject discrimination filter 13, and the output of the blur width detection circuit 15 The blur width information and the detection information from each encoder are taken in and calculated according to a predetermined algorithm.From these chronological changes, the position, size, moving direction, The setting of the movement response speed, that is, the tracking of the subject, is performed, and the movement direction and the movement speed of the focusing lens at which the in-focus point is obtained are calculated.

That is, the movement of the subject is detected for each field on the basis of the peak value of the high-frequency component in one field period based on the output of the bandpass filter 14 and the coordinates of the peak position, and the changed peak position, that is, the subject position is centered. A gate pulse is supplied to the gate circuit 16 in order to set a focus detection area at a position to be controlled to open and close the gate circuit 16 so that only the video signal corresponding to the portion of the video signal corresponding to the focus detection area is passed.

The logic control unit 18 performs focus detection on the subject based on the video signal corresponding to the set focus detection area, and performs focus adjustment. That is, the blur width information supplied from the blur width detection circuit 15 and the peak value information of the high-frequency component supplied from the band-pass filter 14 are taken in, and the blur width in one field period is minimized, and the peak value of the high-frequency component is maximized. In order to drive the focusing lens 1A to the position, a control signal such as a rotation direction, a rotation speed, and a rotation / stop of the focusing motor 10 is supplied to the focus drive circuit 9 to control the control signal. In accordance with the degree of focus and the depth of field calculated from the aperture value and the focal length detected by the aperture encoder 21 and the zoom encoder 20,
The size of the focus detection area, the movement range, and the movement response speed are controlled.

In this way, it is possible to continue focusing while automatically tracking a moving subject.

Here, in the present invention, the blur width detection circuit 15 is used for focus detection.
The bokeh width signal output from the above and the peak value of the high frequency component output from the bandpass filter 14 are used.
For the following reasons.

In other words, the blur width becomes smaller as the distance to the focal point becomes smaller and becomes the minimum at the focal point, and has a feature that high focus detection accuracy can be obtained because it is hardly affected by the contrast of the subject, but the dynamic range is narrow, If the focal point is largely out of focus, sufficient detection accuracy cannot be obtained.

On the other hand, the high-frequency component has a wide dynamic range and can obtain an output corresponding to the degree of focus even if the focus is greatly deviated. Focusing accuracy cannot be obtained.

Therefore, by combining these, it is possible to realize a focus detection method that has a wide dynamic range and high detection accuracy near the focal point.

The logic control unit 18 always captures the contrast in the focus detection area in the imaging screen based on the output of the subject determination filter 13 and constantly detects the contrast, thereby determining the presence or absence of the subject on the imaging surface. .

In other words, when the subject image goes out of the imaging plane, or when the contrast between the subject and the background is hardly obtained in a large blur state, it is difficult to discriminate the subject itself, and it is impossible to accurately track the subject, resulting in malfunction. The focus adjustment cannot be performed accurately.

In the present invention, in consideration of this point, the presence or absence of a subject is determined based on the contrast in the imaging surface, and when the subject does not exist, the movement of the focus detection area, that is, the subject tracking operation is stopped, and the unnaturalness of the focus detection area is determined. Erroneous movements, malfunctions caused by erroneously detecting objects other than the subject, and the like are prevented.

In the present invention, in performing the above-described automatic tracking of the subject, the depth of field is detected, and the size, the moving direction, and the response speed of the focus detection area are controlled so that the optimal subject tracking operation can be performed. Configuration.

The gate pulse output from the logic control unit 18 is subjected to predetermined signal processing not only through the gate circuit 16 but also through the display circuit 22 and then superimposed on the television signal output from the process circuit 5, The focus detection area is supplied to the monitor 23, and is configured to be able to superimpose the focus detection area in the monitor screen.The display of the focus detection area is lit or blinked according to the focus adjustment state. It can be carried out.

Next, the control operation of the focus detection area by the automatic focusing device of the present invention will be described step by step with reference to the flowchart shown in FIG. Note that the subject automatic tracking operation according to the present invention operates in an AF (automatic focus adjustment) mode, and is in a non-operating state in a manual focus adjustment mode, and does not display a focus detection area on a monitor screen. .

Also, in the present invention, an AF mode involving a subject tracking operation,
The normal AF mode without the subject tracking operation is facilitated, and the operating mode is identified by the display on the monitor.

In FIG. 2, when the subject tracking control flow is started, the system is initialized in step S1, the focus detection area is set to a predetermined initial position in the approximate center of the imaging screen, and the size is increased. And

Then, in step S2, it is determined whether the automatic subject tracking mode is on.

If the tracking mode is off in step S2, the process proceeds to step S26, in which a setting for lighting and displaying on the monitor screen while fixing the focus detection area at the initial position substantially at the center of the imaging screen is performed, The AF operation shown in steps S27 to S33 is performed. The algorithm of this AF operation is the same as the AF operation shown in steps S5 to S12 in the subject tracking operation described later, and the description thereof will be described later.

After the end of the flow of the AF operation, the process proceeds to step S34, the focus detection area is lit on the monitor screen in accordance with the setting of step S26, and the process returns to step S2. That is, the normal AF mode without the subject tracking operation is displayed by lighting the focus detection area.

If the tracking mode was set in step S2,
Proceeding to step S3, it is determined whether the tracking operation has been started or the standby state before the start of the tracking operation. If the tracking operation is in the standby mode, the process proceeds to step S35, and the focusing effect area is set in step S35.
After the setting for blinking the focus detection area on the monitor screen to indicate the tracking standby state with the initial position set in step 1, the AF operation is performed in steps S27 to S33. After that, the process proceeds to step S34, where the focus detection area is blinked on the monitor screen in accordance with the setting of step S26, and the process returns to step S2. That is, the standby mode of the subject tracking operation is displayed by blinking the focus detection area on the monitor screen.

If the tracking is started in step S3, the process proceeds to step S4 to indicate that the automatic detection mode is an automatic subject tracking mode in which the focus detection area is kept in focus while automatically tracking the movement of the subject within the imaging screen. Make settings for blinking display on the monitor screen. In the display of the subject tracking mode, for example, the blinking cycle is made different to distinguish it from the tracking standby mode.

When the automatic subject tracking operation is started, the aperture value detected by the aperture encoder 21 in step S5 is fetched into the logic control unit 18 for each field, and the A / D conversion circuit in the logic control unit 18 outputs, for example, one byte. After being converted to digital information, it is read into the memory. In step S6, the digital signal of the focal length information detected by the zoom encoder 20 is taken into the logic control unit 18, and is read into the memory for each field.

In step S7, the depth of field is calculated based on the aperture value and the focal length taken in steps S5 and S6. The calculation of the depth of field is performed in advance in the logic control unit 18.
The determination is made using the depth of field determination table shown in FIG. 3 written in the ROM. In the example of the information table shown in FIG. 3, the information of the aperture value F and the focal length f indicates the area DP1,
The depth of field is determined in three stages DP2 and DP3. In the figure, the depth of field increases in the order of DP1, DP2, and DP3.

In step S8, 1 is obtained from the output of the peak position detection circuit 17.
Information on the horizontal and vertical positions of the peak position of the high-frequency component of the luminance signal in the field period in the imaging screen in units of blocks is read by the logic control unit 18.

In step S9, the blur width information in the field output from the blur width detection circuit 15 is subjected to A / D conversion in the logic control unit 18 in step S10. In step S10, the peak value information in the field output from the bandpass filter 14 is converted. Read into memory. In step S11, focus is detected from the depth of field information, blur width information, and high frequency component peak value information obtained in steps S7 to S10, and the driving speed according to the driving direction and the degree of focus of the focusing lens 1A is determined. Is calculated and determined. At this time, the speed of the focusing lens is corrected in consideration of the depth of field obtained from the aperture value and the focal length. When determining the depth of field and the speed, as described above, the logic control unit 16
The calculation time is determined by referring to the information table shown in FIG. 3 stored in advance in the ROM or the speed setting information table for determining the speed based on the focus degree and the depth of field (not shown). The program can be shortened and the program can be simplified.

In step S12, the focusing lens drive information (control signals for the focusing motor drive speed, drive direction, drive / stop, etc.) determined in step S11 is supplied to the focus motor drive circuit 9, and the focusing motor 10 is driven to drive the focusing lens. Drive 1A to focus.

In step S13, the analog contrast information in the field output from the subject discriminating filter 13 is A / D converted and read into a predetermined memory area in the logic control unit 18, and a predetermined operation is performed in step S14 to obtain the contrast of the subject. Is determined. Specifically, the contrast of the subject is determined by comparing the information of the luminance signal level output from the subject determination filter 13 with a predetermined threshold, and highly accurate automatic tracking based on the change in the peak value of the high frequency component is possible. , Or whether the object tracking is impossible with low luminance.

If it is determined in step S14 that the subject has a sufficiently high contrast in the focus detection area and the subject can be tracked with high accuracy, the process proceeds to step S15 and thereafter, and the focus detection area is determined. (Also serves as subject tracking area)
The size, the moving direction, and the response speed are calculated based on the depth of field information obtained in step S7.

That is, in step S15, the depth of field determined in step S7 is determined, and the depth of field is the deepest.
If it is DP3, the process proceeds to step S16, where the size of the focus detection area is set to the maximum and fixed at the center of the imaging screen.
The position and size of the focus detection area may be the same as the initial setting area set in step S1, or may be set separately.

If the depth of field is medium DP2, the process proceeds to step S17, where the size of the focus detection area and the response speed are medium, and the moving direction is only the horizontal direction.

If the depth of field is DP1, which is the shallowest, the process proceeds to step S18, where the size of the focus detection area is minimized, the response speed is maximized, and the moving direction is set in both the horizontal and vertical directions. I do.

Here, based on the depth of field, the size of the focus detection area,
The reason for variably controlling the response speed and the moving direction will be described in detail with reference to FIG.

When the depth of field is the shallowest in DP1 as shown in step S18, the size of the focus detection area is set to the minimum as shown in FIG. The area is set to 30% vertically and 30% horizontally with respect to the screen. Then, the moving direction can be moved vertically, horizontally, and diagonally.

Also, when the depth of field is DP2 and at an intermediate level, as shown in step S17, the size of the focus detection area is 40% vertical to the entire screen, as shown in FIG. 4 (b). , The horizontal direction is set only in the horizontal direction, and the response speed is also set to the intermediate value.

Also, as shown in step S16, when the depth of field is the deepest in DP3, as shown in FIG. 4 (c), the size of the focus detection area is It is set to a maximum of 60% horizontally. At this time, the focus detection area is fixed and does not move.

In general, when the depth of field is shallow, the degree of focus changes greatly between in-focus and out-of-focus conditions in the imaging screen, making it easy to focus on the main subject, and discriminating between the main subject and the background. , The high-frequency component from the main subject can be accurately detected, and a change in the high-frequency component due to the shift of the focal point or the movement of the subject can also be accurately detected. Therefore, the size of the focus detection area is set to a minimum value in order to accurately capture the main subject and accurately track the main subject. In addition, when the depth of field is shallow, the focal length is long, and the proportion of the subject in the imaging screen is often large, and even a slight movement appears largely in the imaging screen, so that the response speed of the focus detection area is also high. Is set to

In addition, when the depth of field is deep, it is easy to focus at many points on the imaging screen irrespective of the main subject. Operation becomes difficult. In other words, in such a state where the depth of field is deep and focus is easily achieved, the need for a tracking operation for focusing is reduced. In particular, when the zoom lens is zoomed to the wide side to increase the depth of field, the angle of view is widened, the movement of the subject is generally slow, and the moving direction is reduced, especially in the vertical direction. come. Therefore, the size of the focus detection area is increased to set a large focus detection area in order to avoid malfunction due to perspective conflict, and the focus detection area is fixed at the center of the imaging screen.

Also, as shown in step S17 above, when the depth of field is at an intermediate level, the depth of field is an intermediate state between a case where the depth of field is deep and a case where it is shallow, so the size of the focus detection area is , The response speed is set to an intermediate value, and the direction of movement of the focus detection area is limited only to the horizontal direction where movement is particularly large.

In this way, unnecessary tracking operation is eliminated by finely controlling the size, moving direction, and response speed of the focus detection area according to the depth of field, and smoother tracking can be realized.

Here, returning to the flowchart of FIG. 2 again, the description will be continued. After the setting conditions of the focus detection area according to the photographing situation are determined in the above-described steps S16, S17, and S18,
Proceeding to step S19, in step S8, based on the horizontal and vertical coordinates of the peak point detection position of the high frequency component in the current field output from the peak position detection circuit 17 and stored in a predetermined memory area in the logic control unit 18, In consideration of the response speed and moving direction information of the focus detection area obtained in steps S16 to S18, the automatic position in the next field of the focus detection area centering on the peak position is calculated.

At this time, the set position of the focus detection area is not determined only by comparison with the information in the previous field, but by averaging the information in the past predetermined number of fields,
It is possible to perform stable position setting without the influence of noise or the like (for example, Japanese Patent Application No. 1-2139 filed earlier by the present applicant).
The setting direction of the focus detection area disclosed in No. 21 can be applied).

In step S20, it is monitored in which direction the coordinate value of the focus detection area in the screen of the next field obtained in the previous step has changed with respect to the coordinate value of the current screen, and If it is other than the direction, it is set not to move in that direction.

In step S21, the size of the focus detection area is set based on the size of the focus detection area obtained in steps S16 to S18.

Step S22 is based on the information on the position and size of the focus detection area set by the above flow, and the gate circuit 16
To control the position of extracting the image signal within the image screen, that is, the setting position of the focus detection area. As a result, the position and size of the focus detection area on the imaging screen are actually updated.

This gate pulse is also supplied to the display circuit 22 at the same time, and is controlled by the control signal from the logic control unit 18 at the same time. In step S23, the display of the focus detection area corresponding to the mode, that is, step S4 is performed. Is converted into a blinking signal indicating that the mode is the subject tracking mode set in step, and is superimposed on the screen of the monitor.

At the stage where the above flow is executed, one subject tracking operation is completed, and the process returns to step S2.

In this way, a moving subject can be automatically tracked by detecting the movement of the peak detection position.

In the above step S14, if the subject luminance information obtained by the subject discrimination filter 13 is calculated by the subject discriminating filter 13, it is determined that the subject is low in luminance and high-precision tracking is impossible. The subject is not located in the detection area or is in an extremely large blur state, making it difficult to identify the subject.Even if tracking the subject continues, not only malfunction occurs, but also the movement of the focus detection area becomes unstable and Since the focusing operation itself becomes difficult, the process proceeds to step S24 to forcibly set the position of the focus detection area to the reset position, and stops the tracking operation. In this reset operation, the initial position coordinates and the size of the initial state at the substantially central portion of the imaging screen set in step S1 are set, and the process proceeds to step S25. A gate pulse corresponding to the reset position is sent to the gate circuit 16. This is done by outputting.

After performing the reset operation of the focus detection area when the tracking of the subject is not possible, the process proceeds to step S35, the mode shifts to the subject tracking standby mode, and the display according to the mode is performed even when the monitor is in the plane as described above. Perform

This prevents a malfunction of the focus detection area when tracking is impossible, and makes the movement natural.

By repeatedly performing the above control flow in the field cycle, a moving object can be automatically tracked while continuing to focus.

According to the above-described embodiment, when the depth of field is at an intermediate level, the focus detection area is moved only in the horizontal direction. However, the moving range of the focus detection area is not limited to this. In consideration of the fact that the weight for the movement is reduced, for example, as shown in FIGS. 5 (a) to 5 (c),
It may be movable horizontally and upward. The correspondence between the figures is the same as in FIGS. 4 (a) to 4 (c).

In the above-described embodiment, the depth of field is controlled in three stages. However, the number of stages does not need to be limited. For example, the depth of field can be controlled in five stages or two stages. However, when changing the number of steps, the size of the focus detection area,
Needless to say, the moving range and the response speed need to be optimized according to each of the divided depths of field.

(Effects of the Invention) As described above, according to the imaging apparatus of the present invention, the size, moving direction, and response speed of the focus detection area in the imaging screen are appropriately switched and controlled according to the depth of field. Therefore, regardless of the depth of field, the main subject can always be captured in the focus detection area, and stable and accurate subject tracking without malfunction such as perspective conflict can be performed. Can be kept in focus.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an automatic focusing apparatus according to the present invention, FIG. 2 is a flowchart for explaining a control operation of the image capturing apparatus according to the present invention, and FIG. FIG. 4 is a diagram showing a depth calculation table, FIG. 4 is a diagram showing a positional relationship of a focus detection area in the imaging device of the present invention in the imaging plane, and FIG. FIG. 9 is a diagram for explaining another embodiment of the control in.

Claims (3)

(57) [Claims] 1. An imaging apparatus capable of moving a detection area set on an imaging screen by following a movement of a subject image, wherein: a position detection means for detecting a subject position on the imaging screen; An image pickup apparatus comprising: an area setting unit that controls a setting position of the detection area based on the output of the control unit; and a control unit that controls a moving direction of the detection area based on depth of field information. 2. The apparatus according to claim 1, wherein said control means changes a moving direction of said detection area in said imaging screen from up, down, left, right, or oblique according to a depth of field. An imaging apparatus characterized in that it is configured to select an optimal combination in accordance with a situation. 3. An imaging apparatus capable of moving a detection area set on an imaging screen by following a movement of a subject image, wherein: a position detection means for detecting a subject position on the imaging screen; An image pickup apparatus comprising: an area setting unit configured to control a setting position of the detection area based on an output of the control unit; and a control unit configured to control a moving direction, a movement response speed, and a size of the detection area based on depth of field information.