JPH06165017A - Automatic focus detector - Google Patents

Abstract

PURPOSE:To provide operation characteristics, which are not affected by noise in an image pickup signal and are made stable and speedy while eliminating malfunction such as hunting, by delaying the image pickup signal for the integer multiple of a horizontal scanning term and controlling the focus state of an optical system based on an output adding the signal at a prescribed ratio. CONSTITUTION:An output image signal outputted from an imaging device 2 is converted to a digital signal S1 by an A/D converter 12 and outputted. On the other hand, delay signals S2 and S3 delaying the digital signal S1 for terms 1H and 2H with 1H delay lines 13 and 14 are generated. The signals S1, S2 and S3 are multiplied with a prescribed coefficient by coefficient circuits 18, 29 and 20 and turned to the integer multiple or the reciprocal of the integer multiple and afterwards, they are supplied to an adder 21 and added. Then, an image pickup signal S4 is generated as a base to be used for automatic focus detection. Thus, the noise is removed by turning the video signal output to a delayed output of the interger multiple of a horizontal synchronizing signal and adding them at a certain ratio, and automatic focus detection is performed by using this video signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focus detection device suitable for use in a video camera or the like.

[0002]

2. Description of the Related Art Conventionally, as an automatic focus detection device used in video equipment such as a video camera, a high-frequency component representing a focus state, that is, a sharpness of a subject image is detected from a video signal output from an image pickup device such as a CCD. However, there is known a so-called "mountain climbing" focus control method in which the photographic lens is driven so as to maximize the high-frequency component for focusing.

Such an automatic focus detection method does not require a special optical member for focus detection, as compared with a so-called active automatic focus detection apparatus which irradiates infrared rays and detects the reflected light. The advantage is that even a distant subject can be accurately focused regardless of the distance to the subject. This type of automatic focus detection method is shown in FIG.
Will be explained.

In the figure, reference numeral 1 is a focus lens that moves in the direction of the optical axis to perform focus adjustment, and reference numeral 2 is an image pickup signal obtained by photoelectrically converting a subject image formed on the image pickup surface by the focus lens. An image pickup device such as a CCD that outputs a signal, 3 is a dual correlation sampling circuit (CDS circuit) that samples and holds a discrete image signal output from the image pickup device 2 and converts it into a continuous image pickup signal, 4 is a CDS circuit 3 The AGC circuit 5 for automatically controlling the gain so as to keep the image pickup signal output from the AGC circuit at a predetermined level is a standard television standard which is standardized by subjecting the image pickup signal output from the AGC circuit 4 to predetermined signal processing. A camera process circuit for converting the signal into a signal and outputting the signal, a bandpass filter (6) for extracting a high-frequency component that changes according to the focus state from the image pickup signal output from the AGC circuit (6). A lower BPF), 7 is a gate circuit for extracting and extracting only a signal corresponding to a range set as a focus detection area within the imaging screen for the high frequency component extracted by the bandpass filter 5. , 8 are peak hold circuits for performing peak hold at intervals synchronized with the vertical synchronizing signal of the high frequency component signal passing through the gate circuit 7 and corresponding to the high frequency component signal, that is, an integral multiple of the field period. Hereinafter, the peak value of the high frequency component output from the peak hold circuit will be referred to as a focus signal.

Reference numeral 9 indicates the driving direction of the focus lens driving motor in which the focus signal voltage level increases from the peak value output from the peak hold circuit 8, that is, the change in the focus signal voltage level, and from the focus signal voltage level. A control circuit 10 composed of a microcomputer for calculating the driving speed of the focus lens driving motor according to the degree of focus is a motor driver for controlling the focus lens driving motor 11 based on the output of the control circuit 9. is there.

That is, the control circuit 9 determines the driving direction of the focus lens drive motor in which the focus voltage increases from the change in the focus voltage, and when it is determined from the focus voltage level that the focus lens is out of focus. The focus lens driving motor is driven at a high speed, and when it is determined that the focus lens is close to the focal point and is in the small blur state, the focus lens driving motor is set at a low speed. By these operations, so-called "mountain climbing" control which has been conventionally known is performed.

[0007]

However, according to the above-described automatic focus adjusting device, first, noise generated in the image pickup device and the circuit subsequent thereto or noise mixed from the outside is superimposed on the image pickup signal. , The focus evaluation value varies due to the influence, and the focus adjustment accuracy deteriorates.
There is a problem that the automatic focusing operation becomes unstable due to a malfunction such as hunting.

Secondly, since the conventional device uses the peak evaluation of one point on the screen as the focus evaluation value,
There is a problem in that the focus evaluation value may temporarily change due to external noise or camera shake, and inconvenience such as hunting is likely to occur.

Further, from near the focus to the state of large blur,
In order to detect the focus condition in a wide range,
Prepare a plurality of filters with different bands in the above BPF,
These must be switched according to the focus state, and there is a problem that the configuration and control become complicated.

Therefore, an object of the present invention is to solve the above-mentioned problems, and to realize stable and quick operation characteristics with no malfunction such as hunting without being affected by noise in an image pickup signal with a simple structure. An object is to provide an automatic focus detection device.

[0011]

In order to solve the above-mentioned first problem, according to the automatic focus detection device of the present invention, an object image formed by an optical system is photoelectrically converted to obtain an image pickup signal. An image pickup means for outputting the image pickup means, a delay means for delaying the image pickup signal outputted by the image pickup means by an integral multiple of a horizontal scanning period, an image pickup signal outputted by the image pickup means, and a delayed image pickup signal outputted by the delay means. Are added at a predetermined ratio, filter means for extracting a predetermined frequency component from the output signal of the adding means, and control means for controlling the focus state of the optical system based on the output of the filter means. Prepare

In order to solve the above-mentioned first problem, according to the present invention, an image pickup means for photoelectrically converting a subject image formed by an optical system to output an image pickup signal, and the image pickup signal. Filter means for extracting a predetermined frequency component from the inside, peak hold means for holding a peak value on a horizontal line in the screen of the signal output from the filter means, and the above-mentioned on a plurality of horizontal lines in the screen An adding unit that adds the output of the peak hold unit within the vertical scanning period and a control unit that controls the focus state based on the output of the adding unit are provided.

[0013]

As a result, even if the focus evaluation value fluctuates due to external noise or the focus evaluation value temporarily changes due to camera shake or the like, stable and smooth focus adjustment operation is realized without being affected by them. In addition, the configuration and control can be simplified.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following is a detailed description of the preferred embodiments of the present invention applied to a video camera, with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of a first embodiment of an automatic focus detection device according to the present invention. In the figure, the same components as those in the block diagram shown in FIG.

In the figure, 22 is an image pickup element 2 and a CDS.
It is a reference clock oscillator that supplies a driving clock C1 to each of the circuit 3 and the A / D converter 12. Image sensor 2
The output image signal output from the reference clock oscillator 2
2 is read out in synchronism with the cycle of the reference clock C1 output from the reference clock 2, sample-held by the CDS circuit 3, and amplified by the AGC circuit 4 with an optimum gain.
The / D converter 12 converts the analog signal into a digital signal S1 at a rate synchronized with the reference clock C1 and outputs the digital signal S1. The 1H delay lines 6 and 7 delay the digital signal S1 by one horizontal synchronization period. A delayed signal S2 delayed by 1H period and a delayed signal S3 delayed by 2H period are generated from S1.

These delay lines are 1H delay lines forming a color separation circuit for separating the image pickup signal output from the image pickup device into a luminance signal and a color signal, and the luminance signal and the color signal are obtained by using three-line correlation. Is separated and may be provided in the camera process circuit 15.

These signals S1, S2, S3 are respectively supplied to the camera process circuit 13, and a well-known matrix circuit generates a luminance signal and a chrominance signal, and is subjected to gamma correction, blanking processing and the like. After that, it is output as a luminance signal and a color signal, respectively corrected by the D / A converters 14 and 15 into analog signals, and supplied to the next stage. In this case, it goes without saying that if the processing in the circuit of the next stage is performed on the digital signal, the digital signal is output as it is without D / A conversion.

The output signals S1, S2 and S3 of the A / D converter 12, the delay line 13 and the delay line 14 are multiplied by a predetermined coefficient in coefficient circuits 18, 19 and 20, respectively, and multiplied by an integer or an integer. After being incremented by 1, it is supplied to the adder 21 to be added, and an image pickup signal S4 which is a source used for automatic focus detection is generated.

The image signal S4 for focus detection is supplied to the digital low-pass filter 26 and the differential filter 33 to extract a predetermined high-frequency component representing the sharpness which changes according to the focus state, and outputs it as a high-frequency component signal S5. To be done.

The digital low-pass filter 26 is a transversal filter composed of flip-flops 27, 28, coefficient units 29, 30, 31, and an adder 32, and the flip-flops 27, 28 are clock signals C1 output from the reference clock oscillator 22. Is driven by the clock C4, which is selected by the switch 25, of the frequency dividing clock C2 or C3 whose frequency is divided by the frequency divider A23 or frequency divider B24 having different frequency division ratios. It is becoming like this.

Then, the flip-flops 27 and 28 delay the image pickup signal S4 by one clock to obtain signals S41 and S4.
Generate a clock delayed signal S42,
4, S41 and S42 are multiplied by predetermined coefficients in coefficient units 29, 30 and 31, respectively, and multiplied by an integer or an integer, and then added by an adder 32 and output. As a result, the signal S of the low frequency component in the image pickup signal S4 (here, it means a signal having a frequency equal to or lower than the cutoff frequency of the digital low-pass filter of the image pickup signal, and does not mean low frequency)
Only 43 is extracted and supplied to the differential filter 33 in the next stage.

The differential filter 33 is a low frequency component signal S43 of the signal S4 output from the adder 32 in the low pass filter 26 by a flip flop 34 driven by a clock C4 as in the digital low pass filter 26. To generate a signal S44 delayed by 1 clock and extract the high frequency component in the signal 43 by taking the difference from the original signal S43 in the adder 35, and operate as a high-pass filter. .

That is, by driving the digital low-pass filter 26 and the differential filter 33 by the common clock C4, a band-pass filter characteristic is realized, and its pass characteristic depends on the clock C4, and by varying this clock. Controlled (passband changes).

The reference clock C1 is input to the frequency divider A23 and the frequency divider B24, and frequency-divided into different frequencies to generate clock signals C2 and C3. The clock signals C2 and C3 are switched and controlled by a control microcomputer 41 which will be described later.
5 and is supplied to the digital low pass filter 26 and the differential filter 33, respectively, and the pass band thereof is controlled.

In this embodiment, it is assumed that the frequency division ratio of the frequency divider 23 is smaller than that of the frequency divider 24 and the frequency of the clock after frequency division has a relationship of C2> C3.

The high-frequency component signal S5 that has passed through the differential filter 33 is supplied to the absolute value circuit 36 and its absolute value is taken, and the gate circuit 37 sets the distance measuring frame, that is, the focus, set in the image pickup screen (not shown). Only the signal of the portion corresponding to the detection area is passed and supplied to the H peak hold circuit 38.

The H peak hold circuit 38 holds the peak value of the high frequency component signal S5 in one horizontal period and outputs it as the peak value of one horizontal period, that is, the focus signal S6. The focus signal S6 is added to the output of the register 40 by the adder 39 to form a signal S7, which is supplied to the control microcomputer 41 for controlling the entire system and at the same time input to the register 40.

The register 40 has a horizontal blanking period (H-BL
NK) holds the new input, that is, the output signal of the adder 39, and is reset in the vertical blanking period (V-BLNK).

As a result, a value obtained by adding the peak value S6 as the focus signal held by the H peak hold circuit 38 for each horizontal line is accumulated in the register 40,
By taking this added value into the control microcomputer 41 immediately before the end of the vertical period, a signal S7 representing the sum of the peak values of each horizontal line added during one vertical period is generated as the focus state evaluation signal, It will be taken into the control microcomputer 41.

Based on the focus evaluation signal S7, the control microcomputer 41 calculates information on the driving direction and the driving speed of the focus lens 1 so that the signal S7 becomes large, and sends it to the motor driver 10. The focus lens driving motor 11 is supplied to drive the focus lens driving motor 11. As a result, the focus lens 1 is moved to the focal point in the optical axis direction, and the automatic focus detection operation by so-called hill climbing control is performed.

Next, the characteristics of the bandpass filter composed of the digital lowpass filter 26 and the differential filter 33 will be described with reference to FIG.

FIG. 2 is a diagram showing changes in the evaluation signal S7 when the focus lens 1 is moved from the closest end to the infinite end.

By the switch 25, the filters 26 and 33 are
The frequency divider 23 with the higher frequency in the clock C4 that drives the
That is, when the division clock C2 is selected,
The band pass filter including the digital low pass filter 26 and the difference filter 33 has a higher pass band,
The high-pass filter characteristics exhibiting steep characteristics in the vicinity of the in-focus point having a high spatial frequency as shown in FIG.

Further, the frequency divider 24, that is, the frequency division clock C3.
Is selected and the frequency of the clock C4 supplied to the digital low-pass filter 26 and the differential filter 33 is set low, the low-frequency component is extracted as compared with the band-pass filter pass band of the clock C2. As shown by B in the figure, a steep characteristic is not obtained in the vicinity of the in-focus point, but the focal signal can be detected even if the in-focus point is separated.

That is, when the focus voltage level is high and it is determined that the focus voltage is near the in-focus point, the characteristic of A in FIG. 2 is selected to stop the focus lens at the in-focus point with high accuracy. Shows the characteristic shown in FIG. 9B so that the slope of the characteristic curve can be detected even in a large blur state away from the focal point, and the driving direction of the focus lens can be determined. When approaching, it is sufficient to switch to a filter having a sharp characteristic of characteristic A.

Therefore, the control micro-computer 41 switches the switch 25 to the frequency divider 23 to select the clock signal C2 having a high frequency, and the band pass filter consisting of the digital low-pass filter 26 and the differential filter 33. 2 is switched to the high-frequency extraction characteristic shown in FIG. 2A, the output level of the H peak hold circuit 38 is high and the change with respect to the movement of the focus lens is large. The waste lens 1 is driven and stopped.

When the output level of the H peak hold circuit 38 is low and the change with respect to the movement of the focus lens 1 is small, and focus detection cannot be performed as it is, the switch 25 is switched to the frequency divider 24 and the low frequency clock is used. By selecting the signal C3 and switching the pass characteristic of the band pass filter composed of the low pass filter 26 and the difference filter 33 to the low frequency band extraction characteristic shown in FIG. 2B,
The slope of the characteristic curve can be detected, the focus lens drive direction is determined, and hill climbing control is performed. The focus level of the focus lens is close to the focus level, and the output level of the H peak hold circuit 38 rises. When the change of the focus signal with respect to the movement becomes large, the focus extraction can be switched to the high-frequency extraction characteristic shown in FIG. 2A, and the focus lens 1 can be stopped at the in-focus point with high accuracy and reliability.

By switching the filter characteristics in accordance with the focus signal level in this way, the slope of the characteristic curve can be always detected at the maximum, and high-speed and highly accurate focus adjustment operation can be performed without malfunction. it can.

Further, conventionally, in the vicinity of focus and in the state of large blur, it is necessary to provide bandpass filters by the number of characteristics required for focus detection, and it is necessary to switch between them according to the situation. Therefore, the number of filters increases and hardware is increased. According to the present invention, the switching operation according to the focus state of the bandpass filter characteristic including the lowpass filter 26 and the differential filter 33 is driven by the filter according to the present invention. Since the clock frequency can be realized by a simple structure in which the control microcomputer 41 is used, the structure and control can be simplified.

Further, when it is desired to change the filter characteristics due to the difference in resolution when image pickup elements having different characteristics are used, conventionally, the constants of the constituent elements of the filter must be changed, and the hardware is made common. However, according to the present invention, the filter characteristics can be matched by appropriately selecting the drive clock of the digital filter, and the image pickup device of any drive cycle can be used by using common hardware. Therefore, the optimum automatic focus detection operation can be performed.

Further, since the driving clock of the digital filter for focus detection described above is configured to be supplied by dividing the driving clock for driving the image pickup element by an integral multiple, the clock for driving the filter is generated. The device can be omitted, the circuit can be simplified, and noise from the focus detection digital filter can be prevented from entering the video signal processing system.

According to the above-described embodiment, the case where the delay circuit for extracting the signals of a plurality of horizontal lines for obtaining the vertical correlation is shared with the delay line of the color separation circuit has been described, but the present invention is not limited to this. Instead, it can be shared with, for example, the 1H delay line used in the vertical aperture correction circuit. FIG. 3 shows an example thereof.

In FIG. 3, the same components as those in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted. Further, for simplification of the drawing, the color separation circuit is provided in the camera process circuit 42 and is not shown.

In the figure, 43 is a vertical aperture correction circuit, which is a 1H delay line 44, 45 and adders 46, 48, 4.
9. The coefficient unit 47 is used to emphasize the contour portion of the luminance signal waveform, but since its operation is well known in the art, detailed description thereof will be omitted, and only the waveform of each part will be omitted. It will be shown in FIG. The waveforms a to f in FIG. 4 are the waveforms of the signal lines a to f in FIG.

The signal a before being delayed outputted from the camera process circuit 42 and the 1H delay lines 44 and 45 constituting the vertical aperture correction circuit are respectively set to 1
The signals b and c delayed by H and 2H are respectively calculated by the coefficient unit 1
It is added by the adder 21 via 8, 19, 20 and is supplied to the band pass filter as described in the first embodiment.

After that, the same operation as that of the first embodiment described above is performed, and it is possible to realize a stable and malfunction-free focus detection operation based on the data having vertical correlation.

[0048]

As described above, according to the present invention,
The video signal output is a delay output that is an integral multiple of the horizontal sync signal,
Noise is removed by adding at a certain ratio, and automatic focus detection is performed using the video signal from which this noise has been removed, so that a stable automatic focus detection operation can be performed quickly on any subject without erroneous operations such as hunting. Can be realized.

Also, external noise can be removed by adding the peak value at each horizontal line in the vertical direction without using the peak value at one point on the screen as the focus evaluation value, and also in low illuminance and low contrast. Since the detection sensitivity can be increased, there is an effect that a stable automatic focus detection operation can be performed quickly on any subject without hunting.

Further, as compared with the method of integrating the entire video signal in the focus detection area, there is an effect that the absolute value of the evaluation value does not change extremely depending on the subject.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment in which an automatic focus detection device according to the present invention is applied to a video camera.

FIG. 2 is a diagram showing a bandpass filter characteristic in the automatic focus detection device of the present invention.

FIG. 3 is a block diagram showing another embodiment of the automatic focus detection device according to the present invention.

FIG. 4 is a waveform diagram showing the operation of the aperture correction circuit in the embodiment of FIG.

FIG. 5 is a block diagram showing an example of a conventional automatic focus detection device.

Claims (6)

[Claims] 1. An image pickup means for photoelectrically converting a subject image formed by an optical system to output an image pickup signal, and a delay means for delaying the image pickup signal outputted by the image pickup means by an integral multiple of a horizontal scanning period. An adding unit for adding the image pickup signal output from the image pickup unit and the delayed image pickup signal output from the delay unit at a predetermined ratio; and a filter for extracting a predetermined frequency component from the output signal of the adding unit. An automatic focus detection device comprising: a means for controlling a focus state of an optical system based on an output of the filter means. 2. The automatic focus according to claim 1, wherein the delay means is also used as a delay line of a color separation means for separating an image pickup signal output from the image pickup means into a luminance signal and a color signal. Detection device. 3. The automatic focus detection device according to claim 1, wherein the delay unit is also used as a delay line of an aperture correction unit that corrects a contour of an image pickup signal output from the image pickup unit. 4. An image pickup means for photoelectrically converting a subject image formed by an optical system to output an image pickup signal, a filter means for extracting a predetermined frequency component from the image pickup signal, and the filter means. Peak hold means for holding the peak value of the output signal on a horizontal line in the screen, and adder means for adding the outputs of the peak hold means on a plurality of horizontal lines in the screen within a vertical scanning period. An automatic focus detection device comprising: a control unit that controls a focus state based on an output of the addition unit. 5. An image pickup means for photoelectrically converting a subject image formed by an optical system to output an image pickup signal, and an A / D converter for converting the image pickup signal outputted by the image pickup means into a digital signal. A digital filter for extracting a predetermined frequency component from the digital signal output from the A / D converter image pickup means, a changing means for changing the frequency of the driving clock of the digital filter, and an output based on the output of the digital filter. An automatic focus detection device comprising: a driving unit that drives a focus lens to a focal point. 6. An image pickup means for photoelectrically converting a subject image to output an image pickup signal, a driving means for supplying a driving clock to the image pickup means, and an image pickup signal output from the image pickup means according to a focus state. An image pickup apparatus comprising: a digital filter for extracting a changing predetermined frequency component; and a frequency dividing unit for generating a drive clock of the digital filter by dividing a drive clock of the drive unit.