JPH04280172A - Automatic focus adjusting device - Google Patents

Abstract

PURPOSE:To attain stable automatic focus detection under any condition with immunity to the effect of external disturbance such as hand blur. CONSTITUTION:This device is provided with a modulation means 6 changing periodically the image forming state at a light receiving face of an image pickup means 2, a detection means detecting a signal in response to the focusing from the image pickup section outputted from the image pickup means 2, an extract means 10 extracting a reply signal of the modulation means 6 by the detection means, a selection means 19 selecting the detection means or the extract means and driving a focus adjustment means 1 based on the selected signal, and a communication which allows the extract means to be selected for a prescribed time and selects the detection means when the selection means 19 selecting the extract means is switched to select the detection means.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focus adjustment device suitable for use in video cameras and the like.

[Background technology] In recent years, automatic focus detection devices (hereinafter referred to as AF) have become essential for imaging devices such as video cameras. An automatic focus detection method that extracts and evaluates a signal according to sharpness and performs a focus detection operation of an optical system is attracting attention.

There are various types of AF systems of this type, but first, the basic circuit configuration of an AF device to which the present invention can be applied will be explained with reference to FIG. The subject image is
An image is formed by a focusing lens 1, an image is formed on an imaging surface of an image sensor 2 such as a CCD, and the image is photoelectrically converted into a video signal. The image sensor 2 is periodically vibrated in the optical axis direction by an image sensor drive circuit 6 driven at the timing of a reference clock generated by a timing generation circuit 5.
The imaging state is slightly changed (wobbling). The video signal photoelectrically converted by the image sensor 2 is amplified by the preamplifier 3, and subjected to predetermined processing such as γ correction, blanking processing, and addition of a periodic signal in the process circuit 4, and is converted into a standard video signal. At the same time, the bandpass filter 7
is input. A bandpass filter 7 extracts a high frequency component that is converted according to the focus state of the video signal, that is, sharpness, and then a gate 8 extracts a signal corresponding to a focus detection area set at a predetermined position on the screen. The peak detection circuit 9 rectifies and holds the peak, and outputs a signal S0. and synchronous detection circuit 10
By performing synchronous detection at the timing of the reference clock generated by the timing generation circuit 5, a signal S1 representing a focused state in response to minute wobbling in the optical axis direction of the image sensor 2 is obtained. In addition, the output S0 of the peak detection circuit 9 is delayed by 1V (V is the vertical synchronization period) in the 1V delay circuit 11, and compared with S0 in the comparator circuit 12 to determine whether the peak detection circuit 9 is currently climbing or descending. A signal S1 is obtained.

Furthermore, the signal S0 is also input to a mode determination comparator 13, and when the value of the signal S0 is larger than the threshold value VH, the switch 14 is switched to the signal S1 side, and the signal S1 in response to wobbling is applied to the motor. By applying power to the driver 15, driving the motor 16, and moving the focusing lens 1, automatic focusing operation in a closed loop mode is performed. On the other hand, when the signal S0 is smaller than VH, the switch 14
is switched to the mountain climbing signal S2 side, and the motor driver 1
5 performs autofocus operation in mountain climbing mode without using wobbling.

Next, the automatic focus adjustment operation will be further explained using FIG. 6. FIG. 6A shows the output level S0 of the peak detection circuit 9 with respect to the position of the focusing lens 1 when in focus/out of focus. When the focusing lens position is closer than the in-focus point, a response signal AN to the wobbling of the image sensor is detected. Furthermore, when the focusing lens position is located on the far side than the in-focus point, a response signal AF to wobbling of the image sensor is detected. At the time of focus, a response signal AM is detected. Since the phase is opposite when the lens is on the near side and on the far side, front focus and rear focus information can be obtained. When these signals are synchronously detected using the reference timing of the output of the timing generation circuit 5, the signal S1 shown in FIG. 6(b) is obtained.
becomes. In other words, since the AN at short distance is in the same phase as the reference timing, the synchronous detection output S1 is a positive signal, and the AF at long distance is in reverse phase with the reference timing, so the synchronous detection output S1 is a negative signal. is output. Further, when in focus, the signal S1 becomes approximately 0 level. Therefore, by inputting this signal S1 to the motor drive circuit 15, the motor 16 can be driven. Below is a description of the motor driver inputs in closed loop mode. However, the signal S1 has a drawback, and when it becomes very blurred, it becomes as shown in Fig. 6(a).
Since S0 becomes smaller and the output of S1 in FIG. 6(b) also becomes smaller, the motor speed becomes slower. therefore,
When S0 is less than or equal to VH, S1 is not used, as shown in FIG. 6(c).
A comparison was made with S0 of 1 V ago as shown in FIG. A comparison signal S2 is used. This signal S2 is a comparator output, so it has a constant value and has only a sign, which should drive the lens. The following is mountain climbing mode. The motor drive circuit 15 changes the absolute level of signals S1 and S2 when a positive signal is input to drive the motor from a short distance to a long distance direction, and when a negative signal is input to a motor drive circuit from a long distance to a short distance direction. To,
Drive at the compared speed and move the focusing lens. Therefore, when a focusing lens has a large blur, it moves rapidly toward the in-focus point at a speed of S2, and when it approaches the in-focus point, it converges to the in-focus point at a speed of S1, where S1 becomes zero, so that automatic focusing is performed. Adjustment actions are performed.

[0006]

[Problem to be Solved by the Invention] However, in the above conventional example, switching between the closed loop mode using the modulation signal response and the mountain climbing mode not using the modulation signal response is performed only by the level of the bandpass filter output. Therefore, due to camera shake, etc., the bandpass filter output S0 may be temporarily changed.
When the focus drops, the camera should be close to focus and remain in closed-loop mode, but instead enters mountain-climbing mode, instead moving away from the focus, resulting in blur. There were drawbacks.

[0007]

[Means for Solving the Problems] The present invention has been made for the purpose of eliminating the above-mentioned problems, and is characterized by periodically changing the imaging state on the light receiving surface of the imaging means. a detection means for detecting a signal according to the degree of focus from among the imaging signals output from the imaging means; an extraction means for extracting a response signal of the modulation means by the detection means; selection means for selecting one of the detection means and the extraction means and driving the focus adjustment means based on the selected signal; and a state for the selection means to select the detection means from a state for selecting the extraction means. and a control means for switching to the detection means after maintaining a state in which the extraction means is selected for a predetermined period of time when switching to the detection means.

[0008]

[Operation] This allows the drive control of the focus adjustment motor to optimally use the response signal of the modulation means without being affected by temporary camera shake or disturbances such as noise. Good automatic focus detection operation can be achieved under these conditions.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of an automatic focus adjustment device according to the present invention will be described in detail with reference to the respective figures.

FIG. 1 is a block diagram showing the configuration of an embodiment of an automatic focus detection device according to the present invention. Note that the structures indicated by reference numerals 1 to 12 and 14 to 16 have the same structure and operate in the same manner as those shown in FIG.

The imaging signal output from the preamplifier 3 is input to the bandpass filter 7 and at the same time, it is also input to the edge width detection circuit 17. The edge width detection circuit generates an electrical signal (edge width signal) proportional to the width of the edge part of the subject image (large when it is blurred, and smallest when it is in focus).
Output. This edge width signal is input to the synchronous detection circuit 10, and at the same time as a signal E6 representing a focused state in response to minute wobbling in the optical axis direction of the image sensor 2 is obtained, it is input to the mode determination circuit 18. In the mode determination circuit, based on the input object edge width signal,
In the switch 19 that generates the switching signal for the switch 19,
An automatic focus detection operation is performed by selecting one of the signals E6 and S1 and applying it to the motor driver.

The edge width signal is used here simply because the high frequency components extracted by a bandpass filter etc. vary greatly depending on the contrast and brightness, but this edge width signal is normalized to the brightness level. Since it is a signal, it is less affected by brightness, contrast, etc.
This is a signal that changes depending only on the degree of focus, and is used to reliably discriminate between the vicinity of the in-focus point and the state of large blur.

Next, the operation of the edge width detection circuit 17 will be explained using FIGS. 2 and 3. FIG. 3 shows the internal configuration of the edge width detection circuit 17. A signal E0 input to the edge width detection circuit 17 is differentiated by a differentiation circuit 21 and outputs a differential signal E1. This differential signal E1 is converted to an absolute value by an absolute value circuit 22, and a gate circuit 23 extracts only the signal corresponding to the focus detection area on the screen. This signal is
It is integrated by an integrator 24 over a certain specific width, and becomes the denominator input to a divider 25. Also, the output signal of the gate 23 is the divider 2
This becomes the numerator input of 5. Then, the output of the divider 25 is peak held in a peak hold circuit 26 in order to obtain the maximum value, thereby obtaining the edge width. That is, for each integration period of the integrator 24, a peak value obtained by dividing the peak value of that period by the integrator output is held. FIG. 3 is a diagram showing signals E0 to E4 for in-focus edges and out-of-focus edges having different contrasts. (b-1)
-(f-1) are in-focus edges, and (b-2) to (f-2) are out-of-focus edges. As can be seen from this figure, the final output E4 represents the width of the edge (that is, the degree of focus) without depending on the contrast.

Next, using FIG. 4, the mode determination circuit 18
The operation of the device will be explained mainly.

[0015] When the flow starts in the same figure, first, in step 1, it is determined whether or not the object is in focus.
If it is in focus, the process proceeds to step 7, where the focusing lens is held in a stopped state, and then, in step 8, a restart determination is made.

[0016] If the focus is not in step 1,
Proceeding to step 2, the mode determination circuit 18 first compares the input edge width signal E5 with a predetermined threshold value VE, and if E5 is greater than VE, the switch 19 selects signal E6. Output the signal (step
3) It is determined that the focal point is relatively close, the closed loop mode using the wobbling response is set, the focusing lens is driven in step 4, and the process returns to the focus determination process in step 1. As a result, it is possible to perform a focus adjustment operation with high precision near the in-focus point.

Further, in step 2, if E5 becomes less than or equal to VE, the process moves to step 5, and E5 becomes lower than VE.
It is determined whether a predetermined period of time has elapsed since the temperature became less than or equal to E. Until a certain period of time has elapsed, st
After moving to step 3 and outputting a signal for selecting signal E6 with the switch 19, the focusing lens is driven in step 4.

Therefore, during this period, the focusing lens is driven using the wobbling response signal E6.

In step 5, after a certain period of time has elapsed, the process proceeds to step 6, in which a signal is output for switching the switch 19 to select the difference signal S2 of the peak value of the level of the high frequency component output from the comparator circuit 12. ,
Proceed to step 4 and drive the focusing lens. Therefore, the focusing lens is controlled for hill climbing by a focus detection operation that does not use a wobbling response.

With these operations, even if the edge signal E5 of the subject temporarily decreases due to camera shake, etc., the automatic focus adjustment operation is stable without immediately shifting from the closed-loop mode to the mountain-climbing mode for searching. can be done.

[0021]

Effects of the Invention As explained above, the image sensor is modulated at a predetermined timing, a signal corresponding to the degree of focus is extracted from the image signal, and near the focus, based on the modulation response signal,
When a large blur is detected, the automatic focus detection device that drives the focusing lens based on the focus degree signal performs a closed loop hold for a certain period of time when it determines that the blur is large from near focus, thereby eliminating disturbances such as camera shake. This has the effect of making it possible to perform stable automatic focus detection operations under all conditions without being affected.

[Brief explanation of the drawing]

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

FIG. 2 is a configuration diagram of an edge width detection circuit in the present invention.

FIG. 3 is a diagram for explaining the operation of the edge width detection circuit in the present invention.

FIG. 4 is a flowchart for explaining mode switching in the present invention.

FIG. 5 is a configuration diagram of an automatic focusing device that is a premise for applying the present invention.

FIG. 6 is a diagram for explaining the operation of the device shown in FIG.

Claims (1)

[Claims] 1. Modulating means for periodically changing the imaging state on the light receiving surface of the imaging means; detection means for detecting a signal according to the degree of focus from among the imaging signals output from the imaging means; extraction means for extracting the response signal of the modulation means by the detection means; selection means for selecting either the detection means or the extraction means and driving the focus adjustment means based on the selected signal; When switching the selection means from a state in which the extraction means is selected to a state in which the detection means is selected, the control means maintains the state in which the extraction means is selected for a predetermined period of time and then switches to the detection means. An automatic focus adjustment device comprising: