JP2913530B2 - Automatic focus control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focus control device, and more particularly to an automatic focus control device suitable for use in video equipment such as a video camera and an electronic still camera.

[0002]

2. Description of the Related Art In recent years, the progress of video equipment such as video cameras has been remarkable, and auto focus control, auto iris control, zoom function, etc. have been standardized, and operability has been improved and multi-functionalization has been achieved in all parts. It is planned.

When looking at an auto-focus adjusting device, the sharpness of a screen is detected from a video signal obtained by subjecting a subject image to photoelectric conversion by an image sensor or the like, and a focus lens position is set so that the sharpness is maximized. A system in which focus adjustment is performed by control is becoming mainstream.

Generally, the evaluation of the sharpness is made by a plurality of band-pass filters (BPs) having different band limits.
F) is performed using the intensity of the high frequency component of each video signal extracted in F). This is because, when a normal subject image is captured, the level of the high-frequency component increases as the focus becomes higher, and the point at which the level becomes the maximum is the focus position.

Therefore, in the control of the focus lens, when the sharpness is low, the focus lens is driven at a speed as high as possible in the direction in which the sharpness is increased, the speed is reduced as the sharpness is increased, and the focus lens is stopped accurately at a point where the sharpness is high. Such a control method is generally referred to as a hill-climbing autofocus method.

In this type of autofocus, the point at which the signal of the band-limited high-frequency component (focal voltage) becomes maximum is determined to be in focus on the subject, and the drive of the focus motor is stopped. When the focus voltage further changes from that state, it is determined that the subject has changed, and the focus motor is restarted to detect a new focus point of the subject.

[0007]

However, in the above conventional example, it is determined that the subject has changed due to a change in the focus voltage. Therefore, even if the subject actually changes, it is assumed that the focus voltage has substantially the same value. In some cases, the focus motor is determined to be in focus without restart determination, and the focus motor is kept stopped.

For example, even if the subject changes from being in focus to a low-contrast object on the near side to a distant high-luminance subject, the focus voltage in the blurred state is substantially the same as the focus voltage for the low-contrast object. , The focus determination may be maintained. In such a case, there is a disadvantage that a distant subject remains blurred because the focus lens is stopped.

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to always be able to optimally focus on a subject to be photographed.

[0010]

According to the present invention, there is provided an automatic focus control apparatus for controlling an amount of incident light from an object, an aperture value detecting means for detecting an aperture value of the aperture means, and an image of the object. Focus control means for detecting a focus state from an image pickup signal and performing focus adjustment based on a signal corresponding to the detected focus state, and is controlled by the focus control means to drive a focus lens to perform focus adjustment. Focus driving means for performing, a focus determination means for stopping the focus driving means when the focus lens is moved, and a focus driving means for re-driving the focus driving means when the subject changes. Starting determination means for performing restart determination by the restart determination means using the aperture value information detected by the aperture value detecting means. It is characterized in that the the like.

Another feature of the automatic focus control device of the present invention is that a focus adjusting means for performing focus adjustment based on a signal corresponding to a focus state detected from an image pickup signal of an object, A position detection unit that detects an adjustment position of the focus adjustment unit; and a center position among a plurality of focus positions having the same focus state is determined based on a signal corresponding to the focus state and an output of the position detection unit. Computing means for performing the operation.

[0012]

[0013]

Since the present invention has the above technical means, not only the change of the focus voltage but also the change of the focus voltage when making the restart judgment after stopping the focus motor due to the in-focus state.
Since the aperture value information is also used, it is possible to improve the accuracy of detecting a change in the subject and to set an optimum focus on the subject to be photographed. Further, according to another feature of the present invention, since the center position among a plurality of focus positions in the same focus state is obtained and set as the focal point, even when the peak of the peak of the focus voltage is flat, the peak center position can be obtained. The lens can be stopped at any time, and the inconvenience of the lens being moved carelessly can be eliminated.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention applied to a video camera will be described below in detail. FIG.
FIG. 1 is a block diagram showing a case in which the present invention is applied to a video camera. 1 is provided with a focus lens 1A for performing focus adjustment with a photographing lens, a zoom lens 1B for performing a zoom operation, and a lens 1C for imaging.

Reference numeral 2 denotes an aperture, 3 denotes an image sensor for photoelectrically converting a subject image formed on an image pickup surface into an electric image signal, and 4 samples and holds an image signal output from the image sensor 3. Further, it is a sample and hold circuit (S / H circuit) for amplifying the level, and outputs a video signal.

Reference numeral 5 denotes a process circuit for performing predetermined processing such as gamma correction, color separation and blanking processing on the video signal output from the sample hold circuit 4, and outputs a luminance signal Y and a chroma signal C. The chroma signal C output from the process circuit 5 is corrected by a color signal correction circuit 21 for white balance and color balance at a color signal correction circuit 21.
Output as -Y, BY.

The luminance signal Y output from the process circuit 5 and the color difference signals RY and BY output from the color signal correction circuit 21 are converted into an encoder circuit (ENC circuit) 24.
And is output as a standard television signal.
Then, it is supplied to a monitor EVF such as a video recorder (not shown) or an electronic viewfinder.

Reference numeral 6 denotes an iris control circuit which controls the iris drive circuit 7 based on the video signal supplied from the sample-and-hold circuit 4 and stops the iris so that the level of the video signal becomes a predetermined level. The ig meter 8 is automatically controlled so as to control the opening amount of the ig 2.

Reference numerals 13 and 14 denote band-pass filters (BPF) having different band limits for extracting high-frequency components necessary for performing focus detection from the video signal output from the sample hold circuit 4. First bandpass filter 13 (BPF1) and second bandpass filter 1
4 (BPF2) is output from the gate circuit 15
And a gate signal of a focus gate frame, and the peak value is held and detected by a peak detection circuit 16 and input to a logic control circuit 17. This signal is called a focus voltage, and the focus is adjusted by this focus voltage.

Reference numeral 18 denotes a focus encoder for detecting the moving position of the focus lens 1A, 19 a zoom encoder for detecting the focal length of the zoom lens 1B, 20
Is an iris encoder for detecting the opening amount of the diaphragm 2. The detected values of these encoders are supplied to a logic control circuit 17 that performs system control.

The logic control circuit 17 detects the focus of the subject and adjusts the focus based on the video signal corresponding to the set focus detection area. That is, the peak value information of the high frequency component supplied from each of the band-pass filters 13 and 14 is fetched, and the focus driving circuit 9 is driven by the focus driving circuit 9 to drive the focus lens 1A to the position where the peak value of the high frequency component is maximum. A control signal such as a rotation direction, a rotation speed, and a rotation / stop is supplied to control this.

Next, the operation of the automatic focus control device of this embodiment will be described. First, the chroma signal C generated by the process circuit 5 is input to the gate circuit 22 via the color signal correction circuit 21. Here, the gate pulse signal generated by the gate pulse generation circuit 23 is gated by a gate frame signal smaller than the focus gate frame, and the gated color difference signals RY and BY are integrated by the integration circuit 25 and then subjected to logical control. Input to the circuit 17. Then, it is taken in here as color information and used for judging hue.

Next, the focus control operation of this embodiment will be described.
The description will be made step by step with reference to the flowchart shown in FIG. When the operation starts in step P1, the focus mode is set to auto focus (AF) in step P2.
Is determined.

If it is determined in step P2 that autofocus is to be performed, the focus motor is driven in step P3.
Next, in Step P4, the focus motor is rotated in the normal direction for an arbitrary period. Then, the focus voltage at that time is detected, it is determined whether the subject is in front focus or back focus, and the focus motor is rotated in the direction in which the subject is focused.

In the next step P5, a hill-climbing judgment is made so that the focal voltage becomes maximum. Next, the process proceeds to Step P6, where it is detected that the focal voltage is at the top of the mountain,
Make a focus decision. Then, when the focus is determined in Step P6, the focus motor 10 is stopped in Step P7.

Next, the program proceeds to a step P8, in which it is monitored whether or not the focus voltage at that time has changed instead. When it changes, it is determined that the subject has changed. In this case, after the process proceeds to step P10 to determine the restart, the process returns to step P3, and the focus motor is driven again.

If there is no change in step P8, the process proceeds to step P9 to monitor whether there is a change in hue. If there is a change in hue, step P10
After the restart determination is made in Step P3, the process returns to Step P3, and the focus motor is driven again. If there is no change in hue in Step P9, the process returns to Step P7, and the focus motor 10 is kept stopped.

As described above, the automatic focus control device according to the present embodiment determines the restart in the auto focus not only based on the conventional change in the focus voltage but also on the change in the hue. Detection can be performed reliably, and the drawback of being blurred can be eliminated.

Next, a second embodiment of the present invention will be described with reference to the flowchart of FIG. As is apparent from FIG. 3, only the operation of step P9 is different between the control of this embodiment and the control of the first embodiment shown in FIG.

That is, in the second embodiment shown in FIG.
In step P9, the presence or absence of a hue change is detected, and a restart is determined based on the presence or absence of a hue change.
On the other hand, in the second embodiment, whether or not the aperture value has changed is detected in step P9.

If there is no change in the aperture value in step P9, the process returns to step P7 to stop the focus motor. Here, the aperture value is input from the aperture encoder circuit 20 to the logic control circuit 17, and
The aperture value information is always obtained continuously.

As described above, the restart determination in the auto focus is also performed on the basis of the aperture value information, whereby the change of the subject can be reliably detected.
The disadvantage that the photographed image remains blurred can be eliminated.

Next, a third embodiment of the present invention will be described with reference to FIGS. Since the focus control is performed automatically as described above, in order to stop the focus voltage at the highest point as shown in FIGS. 6A and 6B, the focus voltage is increased while moving the lens. When that happens, update that value and lens position. If the temperature continues to decrease, the lens is inverted with the highest point so far as the focal point, and returned to the focal point.

However, when focusing is performed in this way, when the peak of the peak of the focal voltage is flat, the lens always stops at the end of the peak as shown in FIG. 6B. Will be. Therefore, as shown in FIG. 7A, when the subject subsequently moves opposite to the top, the focus voltage immediately drops, and the automatic focus adjustment must be performed again. For this reason, there has been a problem that the lens is inadvertently moved and calm is lost.

In order to solve such inconvenience, in this embodiment, an automatic focus control device is configured as shown in FIG. That is, in FIG. 4, reference numeral 101 denotes a fixed first lens group, 102 denotes a second lens group (zoom lens) that performs zooming, 103 denotes an aperture, and 104 denotes a fixed third lens group.
A lens group 105 is a fourth lens group (focus lens or compensator lens) having both a function of correcting the movement of a focal image due to zooming and a function of focusing.

Reference numeral 106 denotes an image pickup surface of the image pickup device.
Next, 107, 108 and 109 are the zoom lens 10
2. An actuator for moving the aperture 103 and the focus lens 105, respectively. And 11
Drivers 0, 111, and 112 are actuators 107, 108, and 10 based on signals provided from a system control circuit 119 that controls the entire system.
9 is to be driven.

Numerals 113, 114 and 115 denote position encoders for detecting mechanical positions of the zoom lens 102, the aperture 103 and the focus lens 105 and converting them into electric signals. 114 is an iris encoder, and 115 is a focus encoder. Reference numeral 116 denotes an amplifier that amplifies the output of the image sensor 106 to a predetermined level, and 117 denotes a bandpass filter that extracts a wide-range component used for focus detection from the output signal of the image sensor 116.

Reference numeral 118 denotes an iris adjuster for controlling the state of an aperture using the output signal level of the image sensor 116; 119, the overall control of the entire system;
4. Based on the output signals of the focus encoder 115 and the band-pass filter 117, the actuators 107, 1
09 is a system control circuit that controls a microcomputer 09.

In the camera system configured as shown in FIG. 4, in general, automatic focus adjustment (AF) is performed by moving the focus lens 105 so that the output signal level of the bandpass filter 117 becomes maximum.

In this embodiment, in order to stop at the center point among the highest points of the focus voltage, the focus voltage and the lens position are acquired while moving the lens in step P1 of FIG. Compare with the peak values up to. As a result of the comparison in Step P2, if the focus voltage is equal to or higher than the peak value, the process proceeds to Step P3, and it is determined whether or not the focus voltage is equal to the peak value or is in a range that can be regarded as equal.

If the peak value is the same or a range that can be regarded as the same, the process proceeds to step P4, and the value obtained by subtracting the past lens position from the current lens position is added to the counter. This causes the counter to indicate the length of the peak. Then, in step P5, the peak value and the lens position are updated.

On the other hand, if the focus voltage is less than the past peak value in step P2, the process proceeds to step P6, and it is determined whether or not the voltage has continued for a predetermined time. If the result of this determination is not continued, the process returns to step P1. If it is continued, the process proceeds to Step P7.

In Step P7, the lens is reversed and the lens is moved to the peak lens position. further,
Advance the lens by one half of the counter. Thereafter, it is determined whether or not the focal point has been reached in Step P8. As a result of this determination, if the focal point has been reached, the process ends, and if not, the process returns to step P7.
Shown).

In the case of the third embodiment, since the automatic focus control is performed in this manner, the lens can always be stopped at the center position of the peak even if the peak of the peak of the focus voltage is flat. Thus, even if the subject moves in the opposite direction from the top after focusing, the focus voltage immediately drops, and automatic focus adjustment is not performed again. Therefore, it is possible to prevent the lens from moving carelessly.

[0045]

As described above, according to the present invention,
Focus determination is performed at the time of autofocus, and when performing a restart determination after stopping the focus motor due to the in-focus state, not only the change in the focus voltage but also the aperture value information is used. Therefore, it is possible to reliably detect a change in the subject, eliminate the drawback that the image remains blurred, and focus on the subject to be photographed optimally.

According to another feature of the present invention, the center of the plurality of focus positions in the same focus state is determined and focused, so that the peak of the peak of the focus voltage is flat. Even in this case, the lens can always be stopped at the center of the peak. This eliminates the inconvenience of having to perform automatic focus adjustment again because the focus voltage immediately drops when the subject moves to the opposite side from the top after focusing, and the lens may move carelessly. Can be prevented.

[0047]

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an imaging device showing a first embodiment of an automatic focus control device of the present invention.

FIG. 2 is a flowchart illustrating an operation of the automatic focus control device according to the first embodiment.

FIG. 3 is a flowchart illustrating an operation of the automatic focus control device according to the second embodiment.

FIG. 4 is a configuration diagram of an image pickup apparatus showing a third embodiment of the automatic focus control device of the present invention.

FIG. 5 is a flowchart showing the operation of the automatic focus control device according to the third embodiment.

FIG. 6 is a diagram illustrating a relationship between a lens position and a focal voltage.

FIG. 7 is a diagram illustrating a relationship between a lens position and a focal voltage.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photographing lens 2 aperture 3 image sensor 4 sample hold circuit 5 process circuit 6 iris control circuit 7 iris drive circuit 9 focus drive circuit 10 focus motor 11 zoom drive circuit 12 zoom motor 13 bandpass filter 14 bandpass filter 15 gate circuit 16 peak Value detection circuit 17 Logic control circuit 18 Focus encoder 19 Zoom encoder 20 Aperture encoder 21 Color signal correction circuit 22 Gate circuit 23 Gate pulse generation circuit

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04N 5/232 G02B 7/28 G02B 7/36

Claims (2)

(57) [Claims] A diaphragm means for controlling an amount of incident light from a subject; a diaphragm value detecting means for detecting a diaphragm value of the diaphragm means; and detecting the focus state from an image signal obtained by photographing the subject. A focus control unit that performs focus adjustment based on a signal corresponding to the focus state that has been set; a focus drive unit that is controlled by the focus control unit and drives a focus lens to perform focus adjustment; and the focus lens moves. A focus determining means for stopping the focus driving means when the subject is in focus; and a restart determining means for re-driving the focus driving means when the subject changes, the aperture value detecting means Automatic restart control, wherein the restart determination is performed by the restart determining means using the aperture value information detected by the automatic focus control. apparatus. 2. A focus adjustment means for performing focus adjustment based on a signal corresponding to a focus state detected from an imaging signal obtained by imaging an object; a position detection means for detecting an adjustment position of the focus adjustment means; An automatic focus control device comprising: a calculation unit that determines a center position among a plurality of focus positions having the same focus state based on a signal corresponding to a focus state and an output of the position detection unit. .