JPH04280176A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To reduce a time when the state is in a largely out of focus discriminating it to be in a largely by out of focus state when a mount climb mode is entered without use of a modulation signal and the mode is stayed for a prescribed time so as to quicken the drive speed of a focusing lens. CONSTITUTION:The device is provided with a modulation means 6 varying periodically an image forming state at a light receiving face of an image pickup means 2, a detection means detecting a signal in response to the degree of focusing from an image pickup signal outputted from the image pickup means 2, an extract means 10 extracting a reply signal of the modulation means 6 by the detection means, an output means 20 outputting a prescribed speed signal, a selection means 19 selecting either the detection means or the output means 20 and drive means 15, 16 driving the focusing means 1 to the focal point based on the signal selected by the selection means 19.

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.

0002

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

There are various types of AF systems of this type, and first, a circuit configuration showing an example of an AF system to which the present invention can be applied will be described with reference to FIG. A subject image is formed by a focusing lens 1, and is formed on an imaging surface of an image sensor 2 such as a CCD, and photoelectrically converted into a video signal. The image sensor 2 includes a ticing generation circuit 5
The imaging device driving circuit 6 driven by the timing of the reference clock generated by the imaging device drive circuit 6 periodically vibrates in the optical axis direction, causing slight changes (wobbling) in the imaging state. The video signal photoelectrically converted by the image sensor 2 is amplified by the preamplifier 3, and subjected to γ correction, blanking processing, and
The signal is subjected to predetermined processing such as addition of a synchronization signal and converted into a modernized standard video signal, and is simultaneously input to the bandpass filter 7. A bandpass filter 7 extracts high frequency components that vary depending on the focus state, that is, sharpness, in the video signal, and then a gate 8 extracts only signals corresponding to the focus detection area set at a predetermined position on the screen. is passed through, rectified by the peak detection circuit 9, held at its peak, and outputted as a signal S0. Then, the synchronous detection circuit 10 performs synchronous detection using the timing of the reference clock generated from the timing generation circuit 5, so that the image sensor 2
A signal S1 representing a focused state in response to minute wobbling in the optical axis direction 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 output is currently climbing or descending the mountain. A signal S1 is obtained.

Furthermore, the signal S0 is transmitted to a mode determination comparator 1.
3, 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 driver 15, driving the motor 16, and driving the focusing lens 1. By moving it, automatic focus operation in closed loop mode is performed. On the other hand, when the signal S0 is smaller than VH, the switch 14 is switched to the hill-climbing signal S2 side, and the signal is applied to the motor driver 15, thereby performing autofocus operation in the mountain-climbing mode without using wobbling.

Next, the automatic focus adjustment operation will be further explained using FIG. 6. FIG. 6(a) shows the peak detection circuit 9 for the position of the focusing lens 1 when in focus/out of focus.
represents the output level S0 of. When the focusing lens position is closer to the in-focus point,
A response signal AN to wobbling of the image sensor is detected. Further, 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 ticing output from the ticing generation circuit 5, a signal S1 is obtained as shown in FIG. 6(b). In other words, since the AN at short distance is in phase with the reference timing, the synchronous detection output S1 is a positive signal, and the AF at long distance
is in opposite phase to the reference timing, so a negative signal is output as the synchronous detection output S1. 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. The above is an explanation of the motor driver in closed loop mode.However, the signal S1 has a drawback and if it becomes very blurred, S0 in Fig. 6(a) becomes small and the output of S1 in Fig. 6(b) also becomes small, so the motor driver The speed will be slower. Therefore, when S0 is less than VH, S1
Instead, a comparison signal S2 is used, which is compared with S0 1V before, as shown in FIG. 6(c). This signal S2 is a comparator output, so it is a signal having a constant value and only the sign that should drive the lens. The above is mountain climbing mode. The motor drive circuit 15 moves the motor from a short distance to a long distance when a positive signal is input, and from a long distance to a short distance when a negative signal is input, in proportion to the absolute level of the signals S1 and S2. Drive with speed and move the focusing lens. Therefore, when there is a large blur, the focusing lens 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, and automatic focus adjustment is performed. will be carried out.

[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. When the band-pass filter output S0 temporarily drops due to camera shake, etc., the camera accidentally enters mountain-climbing mode, even though it should remain close to focus and remain in closed-loop mode, instead of moving away from focus. There was a problem in that the object moved away from the object, causing blurring, and it took a long time to return to the focused point.

[0007]

[Means for Solving the Problems] The present invention has been made for the purpose of solving the above-mentioned problems, and is characterized by periodically changing the imaging state on the light receiving surface of the imaging means. a modulation 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, and a constant speed signal. an output means for outputting, a selection means for selecting one of the extraction means, the detection means, and the output means; and a drive for driving the focus adjustment means to the in-focus point based on the signal selected by the selection means. There is an automatic focusing device equipped with means.

[0008]

[Operation] According to the present invention, if the mountain climbing mode that does not use a modulation signal is entered and the mode remains in that mode for a certain period of time,
It is possible to shorten the period of large blur by assuming that the object is in a large blur state and increasing the driving speed of the focusing lens.

[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. It should be noted that the structures indicated by reference numerals 1 to 12 and 14 to 16 are the same structures as those shown in FIG.

The image pickup signal output from the preamplifier 3 is input to the band pass filter 7 and at the same time to the edge width detection circuit 17. The edge width detection circuit outputs an electric signal (edge width signal) proportional to the width of the edge portion of the subject image (large when it is blurred, and smallest when it is in focus). This edge width signal is input to the synchronous detection circuit 10 to obtain a signal E6 representing the in-focus state in response to minute wobbling in the optical axis direction of the image sensor 2, and simultaneously input to the mode determination circuit 18. A speed control circuit 20 outputs a high-speed search drive signal at a constant level to the motor driver 15 via a switch 19 to drive the motor at a constant speed when a large blur is detected. The mode determination circuit 18 generates a switching signal for the switch 19 based on the input object edge width signal. switch 19
is switched and controlled by the output of the mode determination circuit 18, and selects one of the signals E6, S2, and S10 and applies it to the motor driver, thereby operating to perform an automatic focus adjustment operation.

The edge width signal is used here simply because the high frequency components extracted by a band pass filter etc.
Although it changes greatly depending on the contrast and brightness, this edge width signal is a signal normalized to the brightness level, so it is less affected by brightness, contrast, etc., and changes only depending on the degree of focus. This is because the purpose is to use this signal to reliably determine whether the state is close to the in-focus point or the state is largely blurred.

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 a partial signal corresponding to the focus detection area on the screen. This signal is integrated by an integrator 24 over a certain width, and becomes the denominator input to a divider 25. Furthermore, the output signal of the gate 23 is transmitted to the divider 25.
becomes the molecular input. The output of the divider 25 is held at its peak 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. Figure 3 shows E for in-focus and out-of-focus edges with different contrasts.
It is a figure showing each signal of 0-E4. (b-1)～(
f-1) is an in-focus edge, and (b-2) to (f-2) are out-of-focus edges. As you can see from this figure, the final output E
4 represents the width of the edge (that is, the degree of focus) without depending on the contrast.

Next, using FIG. 4, the operation of the apparatus centering on the mode determination circuit 18 will be explained.

[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 8, where the focusing lens is held in a stopped state, and then, in step 9, 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 VE, and if E5 is greater than VE, the switch 19 selects the signal E6. Output (step
3) Set the closed loop mode using the wobbling response, drive the focusing lens in step 4, and return to the focus determination process in step 1.

In step 2, if E5 is less than or equal to VE, the process proceeds to step 5, where it is determined whether a predetermined period of time has elapsed. Until a certain period of time has elapsed, proceed to step 7, output a signal for selecting signal S2 with switch 19, and then proceed to step 7.
4 to drive the focusing lens. Therefore, during this period, the focusing lens is driven according to the difference in the level of the high frequency component output from the comparator circuit 22 without using a signal related to the wobbling response.

In step 5, after a certain period of time has elapsed, the process proceeds to step 6, where a signal is applied to switch the switch 19 so as to select the high-speed drive signal S10 for large blur search, which indicates a constant speed and is output from the speed control circuit 20. is output, and the process proceeds to step 4 to drive the focusing lens. Therefore, the focusing lens is driven at a constant speed for high-speed search, which is preset by the speed control circuit 20.

With this operation, even if the edge signal E5 of the object temporarily decreases due to camera shake or the like and the mode shifts from the closed loop to the mountain climbing mode, the focusing lens is not immediately driven with the constant signal S10 for large blur search. Since the driving speed signal S2 for large blur search is used for a certain period of time, the inconvenience that the signal representing the degree of focus is small and the shape of the characteristic curve is flat, resulting in large blur, is eliminated. Even if the image is blurred, the drive speed S10 for high-speed search is selected after a certain period of time, so there are advantages such as less time during which the image is largely blurred and a better operational feel.

[0020]

[Effects of the Invention] As explained above, the image sensor is modulated with a predetermined timing, a signal corresponding to the degree of focus is extracted from the image signal, and near the focus, when a large blur is detected, based on the response signal of the modulation, The automatic focus detection device that drives the focusing range based on the focus degree signal determines that there is a large blur from the vicinity of the focus, and if this continues, it drives at a speed for mountain climbing control for a certain period of time, and then By driving at a faster speed after that time, it is possible to shorten the time during which the image is completely out of focus, and to obtain good AF performance.

[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 focus adjustment 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. 5;

Claims (2)

[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 a response signal of the modulation means by a means; output means for outputting a constant speed signal; selection means for selecting one of the extraction means, the detection means, and the output means; and the selection means An automatic focus adjustment device comprising: a drive means for driving the focus adjustment means to a focused point based on a signal selected in the above. 2. A first focus detection means that performs focus detection based on a first signal component that changes according to the degree of focus from among the modulated imaging signals output from the imaging means; a second focus detection means that changes in accordance with the degree of focus and performs focus detection based on a second signal component having a different dynamic range from that of the first focus detection means; a focus adjustment means; a first mode in which the focus adjustment means is driven based on the output of the focus detection means; a second mode in which the focus adjustment means is driven based on the output of the second focus detection means; and a predetermined signal. and a control means for controlling the selection means in accordance with the output of the second focus detection means. Features an automatic focus adjustment device.