JPH0560713B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a camera equipped with an automatic tracking focus detection device, and in particular, to a camera that can quickly switch the focus detection target subject according to the photographer's intention.
The present invention also relates to a means for eliminating the possibility of unstable fluctuations occurring in the focus detection system during this switching.

(Background Art) In a camera equipped with a conventional automatic focus detection device with negligible difference, such as a video camera, the distance measurement field of view is fixed at the center of the shooting screen as shown in FIG. As shown in the figure, if the subject you want to focus on (hereinafter referred to as the focus detection target subject; in this example, a person) moves, an object at a different distance from the subject (a house in this example) will be in focus, and the focus will be changed. Since the person, which is the subject to be detected, becomes blurred, there is a drawback that the subject to be focus detected must always be placed at the center of the screen due to the screen configuration. For this reason, methods have been proposed to make the distance measurement field position variable, but these methods require the photographer to change the distance measurement field position by operating a knob, etc., and the subject may move during shooting. In case,
With these knobs, it is difficult to maintain the distance measurement field position always above the focus detection target object.

In order to eliminate the above drawbacks, the applicant first sets a movable tracking field of view, extracts the features of the object to be ranged with respect to this tracking field of view, stores the extracted features, and Detects whether or not the object is moving based on the memorized features and newly extracted features of the object to be ranged, and moves the range measurement field of view to track the object's movement according to the relative movement of the object. We have proposed an automatic tracking focus detection device (Patent Application No. 105897 of 1983, title of invention: "Automatic tracking focus detection device"), but in implementing this proposal, it is necessary to It is desirable to take measures that can stably perform the automatic tracking focus detection operation in severe cases. More specifically, when the subject being tracked moves out of the shooting screen or out of a specific area in the shooting screen, it is possible to take measures that can stably return the tracking field of view to the initial position. desirable.

(Objective) Therefore, the present invention solves the above-mentioned drawbacks of conventional cameras equipped with an automatic tracking focus detection device, and
When automatically detecting the moving position of a moving subject and moving the distance measurement field to track the movement of the subject to perform focus detection or focus adjustment,
It is an object of the present invention to provide a camera capable of quickly switching a focus detection target object to another object according to a photographer's operation during a tracking operation for a certain object.

A further object of the present invention is to provide a camera that achieves the above-mentioned object and that does not cause unstable fluctuations in focus detection operation when switching the focus detection target object to another object.

(Description based on Examples) Hereinafter, with reference to FIGS. 1 to 13, etc., the means taken in this invention to achieve the above object will be exemplified and explained. The following explanation is an overall explanation of an embodiment of the camera of the present invention, as well as a limit area setting means, a subject movement detection means, and an automatic focus in the same embodiment, regarding an example in which features of a tracked subject are extracted using color signal information. The detection means, the focus detection mark setting means, and the operations of the same embodiment are performed in this order.

(Overall explanation of the embodiment of the camera of this invention) (First
Figure 1 shows the main parts of an embodiment of the camera according to the present invention, in which 1 is a lens group for adjusting the focus in the photographic optical system, and 2 is an example of the imaging means. It shows a solid-state image sensor such as a CCD.
As is well known, the solid-state image sensor 2 is controlled by an image sensor drive circuit (not shown) to photoelectrically convert light from a subject incident on its light-receiving surface. This photoelectrically converted signal is amplified by a preamplifier (not shown), subjected to various correction processes in the signal processing circuit 3, and a color difference signal (R
-Y), (B-Y) and a luminance signal Y are created. These color difference signals and luminance signals are combined with a synchronization signal by an encoder 15 to form an output video signal, for example, an NTSC signal, which is supplied from an output terminal 16 to a device to be used, such as a video deck.

The above color difference signals (R-Y) and (B-Y), and if necessary, the luminance signal Y are input to the movement detection circuit 5 via the tracking gate circuit 4, and the same circuit detects the moving direction or movement of the subject. amount is detected. Here, since the movement between the subject and the camera is relative, the above-mentioned movement of the subject includes cases in which the camera is fixed and the subject moves, as well as cases in which the subject stops and the camera moves, or This refers to a case where both move together, and the present invention is applicable to any of the above cases.

In the tracking gate circuit 4, the gate position for the color difference signal and the like is set by the gate pulse generated by the gate pulse generation circuit 11. As a result, the position of the tracking field of view is determined for extracting the features of the subject and the features of the background, for example, in the manner shown in FIGS. 5 to 8, which will be described later. In other words,
A range of the color difference signals and the like to be input to the movement detection circuit 5 is determined, and movement of the subject is detected based on changes in this signal. This object movement detection signal is supplied to a gate movement circuit 6, which generates a signal for moving the gate position of the tracking gate circuit 4, that is, the tracking field of view position, in accordance with the movement of the object to be tracked. This signal is supplied to a gate pulse generation circuit 11, which forms a gate pulse for extracting a color difference signal at a position corresponding to the movement of the tracked object. The gate pulse generation circuit 11 is
Horizontal synchronization signal f _H generated by the synchronization signal generation circuit 10
and operates in synchronization with the vertical synchronization signal _fV . Note that the synchronizing signal generating circuit 10 is controlled by a signal obtained by frequency-dividing a clock pulse generated by a clock pulse generating circuit (not shown) that controls the timing of the entire apparatus, and furthermore, the above-mentioned image sensor driving circuit is controlled by, for example, this frequency-divided signal. The encoder 15 described above is controlled by the synchronization signal, etc., and various types of synchronization control are performed, but since these synchronization control means are well known in video signal processing systems, a detailed explanation will not be provided. Also, illustrations are omitted except for parts particularly related to the description of the features of the present invention. Further, details of the movement detection circuit 5 will be described later with reference to FIGS. 5 to 8.

On the other hand, the luminance signal Y is inputted to an automatic focus detection device 8 via a distance measurement gate circuit 7, and focus detection or focus adjustment is performed by the same device. Ranging gate circuit 7
Then, the gate position with respect to the luminance signal Y is set to the same relative position as the tracking gate by the gate pulse generated by the gate pulse generation circuit 11,
This determines the range (hereinafter referred to as distance measurement field of view) of the luminance signal Y that is input to the automatic focus detection device 8 for detecting the focus of the subject. In the embodiments of the present invention, the tracking field of view and/or distance measurement field of view can be displayed on a display device such as an electronic viewfinder if necessary, but this is not an essential means.

In FIG. 1, the tracking gate circuit 4 and the ranging gate circuit 7 are provided separately, but the same gate circuit may be provided in common, or the latter may be contacted after the former and set by the former. The distance measurement field of view may be set in a smaller area within the distance measurement field of view.
However, in any case, during the tracking operation, both fields of view must be set at the same relative position, in particular with the same center position. In the example shown in FIG. 1, the tracking field of view and the ranging field of view can each be set to arbitrary sizes. Furthermore, if the size of one or both of the fields of view is automatically adjusted by a gate size determining circuit (not shown) according to the shooting distance and the focal length of the lens, the tracking field of view or (And) A distance measurement field of view can be obtained.

In the automatic focus detection device 8 connected after the ranging gate circuit 7, automatic focus detection is performed according to known means, and its output signal is sent to the lens drive device 17.
The lens group 1 is driven by the drive motor. When the focal point is detected, the control loop described above stops operating, and the lens group 1 also stops at that position. A specific example of the automatic focus detection means will be described later with reference to FIG.

The position information obtained from the gate movement circuit 6 is supplied to the character generator 12, where a focus detection mark signal indicating the object to be focus detected is formed, and this signal is outputted from the encoder 15 as an output video signal (NTSC signal). are added by an adder circuit 13, and a video signal and a mark (for example, FM in FIG. 11) indicating a focus detection target object are displayed on a display device, such as an electronic viewfinder (EVF) 14. The details of the character generator 12 will be described later with reference to FIG. 10.

Next, the tracking field of view return means in the embodiment shown in FIG. 1 will be explained. The limit area setting circuit 18, the arithmetic circuit 19, the time setting circuit 21, the timer 22, the control circuit 24, and the related initial button 25 are activated when the subject goes outside the shooting screen or outside the limit area, which is a specific area of the shooting screen. This is an example of the main components for returning the tracking field of view to the initial position when
8 sets a limit area indicated by BA in FIG. 11, for example, under the control of the horizontal synchronizing signal _fH and vertical synchronizing signal _fV generated by the synchronizing signal generating circuit 10, according to the settings of the photographer. The limit area BA is provided for performing tracking operations only within the limit area BA, and the current position of the tracking field of view is determined in advance in the arithmetic circuit 19 according to the output signals of the limit area setting circuit 18 and the gate movement circuit 6. It is determined whether it is within the manually set limit area BA. Then, when it is determined that the position of the tracking field of view, and therefore the position of the tracked subject on the screen, has left the limit area BA, the control signal a is transmitted to the arithmetic circuit 19.
The signal is transferred to the movement detection circuit 5 and the gate movement circuit 6 to stop these operations, and
It is also transferred to the timer 22. Thereby, the timer 22 transfers the control signal b to the control circuit 24 during the period set by the time setting circuit 21. Control circuit 2
4 outputs the control signal c while receiving the control signal b, transfers it to the lens driving device 17, stops the operation of the device, and controls the focus detection system at the point when the tracking field of view leaves the limit area BA. The lens group 1 is held in a state determined by the position of the lens group 1 at . Furthermore, the control signal c is transferred to the character generator 12 and a warning circuit 20 provided as necessary, and the former stops the display operation of the focus detection mark, and the latter issues a warning that the tracking operation is stopped. .
Note that the setting time of the time setting circuit 21 can be adjusted by the photographer's operation.

When the predetermined time set by the time setting circuit 21 has elapsed, the operation of the timer 22 ends, and the control signal d is transferred from the control circuit 24 to the movement detection circuit 5 and the gate movement circuit 6 to reset these circuits.
Tracking gate circuit 4 defined by these circuits
The gate position is returned to the position corresponding to the above-mentioned initial position, thereby the tracking field of view moves to the initial position (for example, a position corresponding to the center of the photographing screen), and the movement detection circuit 5 again starts the object movement detection operation described below. ,
Further, upon termination of the control signal c, the character generator 12 and the lens driving device 17 resume their operations, the warning circuit 20 stops its operation, and the automatic tracking operation is performed again. Note that the gate position of the ranging gate circuit 7 is also returned to a position corresponding to the center of the photographing screen, following the tracking gate circuit 4.

Furthermore, in the embodiment shown in FIG. 1, it is possible to return the tracking field of view to its initial position at any time in response to an operation by the photographer. Next, an example of a specific means for this purpose will be described. That is, in addition to the signal b from the timer 22, the control circuit 24 also receives a signal e generated when the photographer operates the initial button 25, and when this signal e is input, the signal b from the timer 22 is input. Even if it is on, the control signal d is turned on and the control signal c is turned off, the tracking field of view returns to its initial position, and the lens driving device 17 and the like resume their operations. Therefore, the tracking field of view is maintained from the time the tracked subject leaves the limit area BA until the predetermined time set by the time setting circuit 21 has elapsed or until the initial button 25 is operated, whichever comes first. When the tracking field of view returns to the initial position after the return of , and related operations are performed, if there is a next object (for example, O ₂ in Fig. 11) at or near the same position, then
A tracking operation is performed for this object _O2 .

In the embodiment of the present invention, the limit area BA is a means for determining the range in which the tracking operation is performed, and does not necessarily need to be displayed on a viewfinder or the like. Further, the limit area BA is usually set within the entire surface of the photographic screen as a narrower range, or within a part of the photographic screen as a narrower range. However, if the limit area setting circuit 18 sets the entire shooting screen as the limit area by the photographer's operation, or if the entire shooting screen is fixedly set as the limit area, the tracked subject may move outside the shooting screen. It is determined that the tracking field has come out, and the above-mentioned tracking field of view is restored and related operations are performed. Furthermore, in this specification, the meaning of the term "the subject moves out of the photographic screen or out of the limit area" will be described later with reference to FIG. 4.

In the apparatus shown in FIG. 1, even when the subject is within the photographic screen or within the limit area BA, it is possible to return the tracking field of view to the initial position by operating the initial button 25.

(Limit area setting means in the embodiment of this invention)
(FIGS. 1 to 4) Next, the limit area setting means in the embodiment of the present invention will be explained with reference to FIGS. 2 to 4. In FIG. 2, 30 and 31 indicate the boundaries in the x direction of the limit area BA, and 32 and 33 indicate the boundaries in the y direction.
Boundary line 3 that determines the position in the x direction by manual operation of
0 and 31 move left and right, and lock button 41
The position is fixed by the operation. Similarly, the boundary lines 32 and 33 that define the position in the y direction are moved up and down by operating the knob 42 in FIG. 4B, and their positions are fixed by operating the lock button 43. That is, the position of the limit area BA can be variably set by operating the knobs 40 and 42, but one additional knob is provided in both the x and y directions, and the boundaries 30 and 31, as well as 32 and 33, can be set independently. , and the size of the limit area BA may also be set variably.

In order to generate signals indicating the positions of the border lines 30 to 33 in response to the operations of the above-mentioned knobs and lock buttons, the positions of the horizontal scanning lines (corresponding to 32 and 33) corresponding to these border lines and the What is necessary is to select specific positions (corresponding to 30 and 31) in each horizontal scanning line with the horizontal scanning line as the upper and lower ends. To do this, for the former, count the horizontal scanning lines in one field and select the horizontal scanning line with the number corresponding to the position of the boundary lines 32 and 33 set by the knob 42, etc., and for the latter, Generate a pulse train by multiplying the horizontal synchronization signal frequency,
Counting from the beginning of each horizontal scanning period, turn the knob 4.
It is sufficient to select the pulse number corresponding to the position of the boundary lines 30, 31 set by 0, etc. Alternatively, triangular waves synchronized with the horizontal and vertical synchronizing signals are generated, and these triangular waves are clipped at voltage levels corresponding to the positions of the boundary lines 30, 31 and 32, 33 set by the knobs 40, 42, etc., respectively. To generate a square wave, generate a pair of pulses corresponding to the leading and trailing ends of these square waves, and then take the logical sum of one square wave and the other pair of pulses ( See Japanese Unexamined Patent Publication No. 59-4384 filed by the present applicant, entitled "Video Camera".Furthermore, the same means as the character generator 12 described later may be used.

Figure 4 shows the timing relationship of the signals created as described above for one horizontal scanning period, where (a) shows a simplified video signal, and (b) shows the limit area. For details, see boundary line 3 in Figure 2.
Indicates the position where 0, 31 and the horizontal scanning line intersect,
(c) is the composite signal of the (a) signal and (b) signal, (d) is the critical region width in the x direction (defined by boundary lines 30 and 31) in Figure 2, and (e) is the composite signal of the (a) signal and (b) signal. 1 shows the gate position by the tracking gate circuit in FIG. 1, and (f) shows the time axis, respectively. In this example, the signal indicating the limit area width in (d) is at a low level in the limit area and at a high level in other parts. Further, the position of the tracking field of view is determined by the signal (e) indicating the gate position. Although FIG. 4 does not show a signal representing the limit area in the y direction of FIG. 2, this limit area is also set in the same manner as shown in FIG. The above limit area BA does not necessarily need to be displayed on the display device, but it can be displayed on the electronic viewfinder 14.
In order to display at a display position such as, the output signal of the limit area setting circuit 18 may be supplied to the character generator 12 or directly to the electronic viewfinder 14 for display.

In the arithmetic circuit 19, the gate position by the tracking gate circuit 4, that is, the tracking field of view is in the limit area BA.
In order to determine whether or not the signal exists within the range, it is determined by checking the position of the signal (e) in FIG. 4 on the time axis or the temporal relationship between the signal (d) and the signal (e). That is, in the former case, assuming that the tracked subject, in other words, the signal indicating the gate _position , moves from right to _left in _FIG . This is performed by calculating in the calculation circuit 19 whether the relationship (T ₄ −T ₃ )<T _K (here, T _K is a positive constant determined in design) is satisfied. Generally, the position within the limit area BA of the tracking field of view can be found by calculating (T ₂ −T ₁ )/(T ₄ −T ₁ ). In the latter case, if the logical sum of the signal (d) and the signal (e) is low level, it is determined that the signal is within the limit area BA, and if it is high level, it is determined that the signal is outside the limit area BA.

It is determined that the tracking field of view is outside the limit area BA, or has moved from the center of the limit area BA toward the outside of the area, and is approaching within a certain range (for example, the above-mentioned T _K ) with respect to the boundary line. Then, the arithmetic circuit 19 transfers the control signal a to the movement detection circuit 5 and the gate movement circuit 6 to stop the operation of these circuits, and then the operation of the initial button 25 by the photographer or the time setting circuit 21, the control circuit 24 outputs the control signal d.
is transferred to these circuits to return the tracking field of view to its initial position.

In this specification, when the subject moves outside the shooting screen or outside the limit area, it means that the subject moves relatively completely outside of these areas, or when the subject moves from the center of the shooting screen to near these boundaries. If (T ₂ − T ₁ ) < T _K then (T ₄ − T ₃ )
This refers to the case where the relationship ＜T _K is satisfied.

(Subject movement detection means in the embodiment of the present invention) (Figs. 1, 5 to 8) Next, the movement of the object to be tracked is detected and tracked, and the tracking gate circuit 4 of Fig. 1 A specific example of the movement detection circuit 5 for moving the gate position, that is, the tracking field of view, will be described with reference to FIGS. 5 to 8. The specific example below is an example in which the features of the tracked object are extracted as color signal information, but the features of the object can also be extracted using information such as a luminance signal, the shape of the object, temperature, or characteristic contrast in the object. This can also be done using .

To summarize the object movement detection and automatic tracking means described below, some parameter representing the characteristics of the object, in this example, the color of the object and the background, is extracted with respect to the tracking field of view set by the tracking means, and this extracted parameter is extracted. Based on the stored features and the newly extracted features of the subject, it is determined whether or not the subject has moved, and if the subject has moved, the direction or position of the subject has been detected. The direction or movement position is detected, the tracking field of view is moved to follow the movement of the subject, and the distance measurement field of view is moved in the same positional relationship as the tracking field of view is moved.

In principle, the tracking field of view has a two-dimensional extent, but for the sake of simplicity, here, as shown in Figure 5A, the tracking field of view has a one-dimensional extent extending in the horizontal direction. Suppose there is. It is also assumed that the tracking visual field is divided into three parts A, B, and C (each part is hereinafter referred to as a pixel). Note that to configure a two-dimensional tracking field of view, for example, pixel B in the same figure
Alternatively, pixels extending vertically above and below A, B, and C may be provided.

As shown in FIG. 6, the color difference signals (R-Y) and (B-Y) obtained as time-series signals from each pixel are connected to integration circuits 50a and 50b, respectively.
Sample hold (S/H) circuits 51a, 51b
Then, the A/D conversion circuits 52a and 52b perform integration, sample hold, and A/D conversion processing, and store them in the memories 53a and 53b, respectively. This stored value is applied to each pixel A, B, and C.
When plotted on (R-Y) and (B-Y) orthogonal coordinates, it is displayed as shown in FIG. 7, for example. In the figure, each point A ₀ , B ₀ and C ₀ is
It represents the signals extracted from each pixel of A, B, and C in FIG. 5A. Here, from pixel B, a signal representing only the clothes of the person who is the subject, for example, is transmitted.
It is assumed that signals are extracted from pixels A and C, in which signals representing the subject's clothing and the background are added. Furthermore, assume that the background colors on the left and right sides of the subject in the figure are different. Therefore,
Points A ₀ and C ₀ have different positions on the color difference signal coordinates.

Next, when the subject shown in Figure 5A moves to the right within the screen as shown in Figure 5B, the ratio of the subject to the background within pixels A and C changes, resulting in The obtained signal is shown in Figure 7.
They change as shown in A ₁ and C ₁ respectively. on the other hand,
Since pixel B remains within the subject as shown in FIG. 5B, the signal obtained from pixel B will hardly change if the subject's clothing is substantially monochromatic. Therefore, here, for simplicity, B ₁ =
Let B be ₀ . In this case, as shown in Figure 7, the point
C ₁ approaches point B ₀ (=B ₁ ), and point A ₁ approaches point B ₀ (=B ₁ )
As it moves away from the line, the line segments B ₁ and C ₁ become smaller than the line segments B _{0 and} C ₀ , and the line segments A ₁ and B ₁ become larger than the line segments A ₀ and B ₀ . Conversely, if the line segments B ₁ and C ₁ are larger than the line segments B ₀ and C ₀ , and the line segments A ₁ and B ₁ are smaller than the line segments A ₀ and B ₀ , the subject is shown in Figure 5B. It will be moving to the left. Assuming that the background color is the same on both the left and right sides of the subject, when the subject moves within the screen to the right in Figure 5B, the above point _A1 will be on the extension of the line segments _A0 and _B0 . The point C ₁ will occupy a position on the line segment B ₀ , C ₀ . This invention can be applied to either of the above cases.

In order to detect the movement of the tracked object using the above-mentioned phenomenon, it is sufficient to detect, for example, a change in the length of the line segments AB and BC. For this purpose, the color detection circuit in the movement detection circuit 5 is used to detect the pixels A, B,
Detect the color of the object with respect to C and store it in the memory in the movement detection circuit 5, for example, via manual mechanical input means (registration of object characteristics);
At the next time, the newly extracted signal representing the color of the subject is compared with the signal stored in the memory to detect whether or not the subject has moved, and if the subject has moved, for example, the direction of movement. The above processing is performed at 1/60th of the period of one field of the television signal.
This is done according to its average value during a period of seconds or several fields thereof. In the following, both will be explained as being processed in one field period.

FIG. 8 shows an example of a specific circuit for executing the above processing, and this circuit also shows details of the movement detection circuit 5 of FIG. 1. From the (RY) and (B-Y) signals of pixels A and B, which have passed through the tracking gate circuit 4 of FIG.
-Y) Length D _A0 of line segment A ₀ , B ₀ on coordinates

Claims (1)

[Scope of Claims] 1. In an automatic tracking device that detects the movement of a subject to be tracked and tracks the subject within a specific area within a photographic screen, the tracking field of view is set to be movable within the specific area. and automatic tracking means for extracting characteristics of the subject within the tracking field of view to detect movement of the subject and causing the subject to track the tracking field of view within the specific area; The tracking operation is stopped when the camera moves out of the area, and after a predetermined period of time, the tracking field of view is returned to the initial position. a control means for maintaining the focus control state at the time when the tracking field of view exits the specific area; and a control means for returning the tracking field of view to the initial position by an operation by a photographer, and when operated within the predetermined time; , means for releasing the holding state of the focus detection system and putting it into the operating state even before the predetermined time has elapsed. 2. The camera according to claim 1, wherein the predetermined time period is controllable.