JPH0514796A - Automatic focus detector - Google Patents

Abstract

PURPOSE:To quickly detect a focal point without erroneously measuring a distance, even when two objects, that is, a high luminance object, and a low- illuminance and low-contrast object, are present in a distance measuring frame. CONSTITUTION:High frequency components extracted from a luminance signal supplied from a camera process circuit 3, are respectively inputted to an integral circuit 7 and a peak hold circuit 8 of an AF circuit. The integrated output of the integration circuit 7 and the output of the peak hold circuit 8 are respectively converted into digital signals by A/D convertors 9 10, and supplied to a CPU 24. The CPU 24 operates a parallel processing to those outputs in order to detect a focal position, and controls a lens unit 1 so as to be positioned at a focal point.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an autofocus device such as a video camera or an electronic still camera, and more particularly to an autofocus detecting device for detecting an in-focus point by using a high frequency component of a video signal taken from an image pickup system. .

[0002]

2. Description of the Related Art A hill-climbing servo system has been proposed as an autofocus (hereinafter referred to as "AF") device using a video signal of a video camera or the like. This is a method of extracting a high-frequency component in a video signal and detecting an in-focus point based on the extracted high-frequency component, and is currently widely used in video cameras and the like. FIGS. 5 (a) and 5 (b) show the screen and the waveform when in-focus and when out of focus. At the time of focusing, the edge of the subject becomes clear, the rise of the luminance signal becomes sharp, and the HPF output becomes high level. On the other hand, when the subject is out of focus, the edge of the subject is not clearly visible and the rising edge of the luminance signal also becomes gentle, so HP
The F output also becomes low level. The detection circuit that performs signal processing after extracting the high frequency component in the video signal is roughly classified into an integral detection type and a peak detection type. Since the former integrates the signal within the set ranging frame for each screen, it draws a change curve of the focus amount based on the average of the signals. This method is a method in which the position with the highest contrast is the focal point. On the other hand, the latter is a method of detecting the peak of the signal in each screen, and thus detecting the one point with the highest contrast as the focal point.

Many of today's video cameras employ the former, that is, an integral detection type AF circuit. FIG. 6 shows an example of a focus detection device using the above integral detection type circuit. A subject image is formed on the CCD 2 by the lens unit 1. The signal photoelectrically converted by the CCD 2 is supplied to the camera process circuit 3. The camera process circuit 3 adds a synchronizing signal, a setup level, etc. to create a video signal. The video signal is sent to another circuit such as a recording circuit (not shown), and a part of the luminance signal is sent to the HPF 4 to extract a high frequency component. The high frequency component is amplified by the amplifier 5 and then sent to the integrating circuit 28. The gate circuit 6 outputs the horizontal synchronizing signal HD output from the camera process circuit 3.
Also, a gate control signal for controlling the range-finding frame range to be integrated is output based on the vertical synchronizing signal VD. The integrator circuit 28 integrates the output from the amplifier 5 based on the gate control signal from the gate circuit 6. Integration data is A /
The digital signal is converted by the D converter 26. C
The PU 11 compares the integrated data output from the A / D converter 26 in time series, and sends a control signal for driving the lens unit 1 to the motor control circuit 12 in a direction in which the output of the integration circuit 25 increases. Motor control circuit 12 is CP
The motor 13 is driven in the direction according to the instruction from U11 to move the position of the focusing lens in the lens unit 1. By continuously comparing the integrated data and continuously driving the lens, the focus adjustment lens is moved in the direction in which the integrated value of the high frequency component becomes maximum, and finally reaches the maximum value of the high frequency component, that is, the in-focus point.

[0004]

In the integral detection type AF configured as described above, there is a possibility that erroneous distance measurement may occur when subjects having different focal lengths simultaneously exist in the distance measurement frame. FIG. 8A shows an example of integral detection type characteristics when there are two subjects. This figure shows the change in the focus amount when subjects A and B exist individually within the distance measuring frame (thin solid line) and at the same time (thick solid line). There is. As is clear from Fig. 8 (a), since the integral detection type outputs the added waveforms of the individual waveforms, it is recognized that the in-focus position is at the midpoint between the two subjects. Therefore, there is a risk of incorrect distance measurement. Further, there is a drawback that sufficient output cannot be obtained when there is little contrast in the distance measurement.

FIG. 7 is a diagram showing an example of a peak detection type focus detection device. This drawing is a circuit in which the integrating circuit 28 of FIG. 6 is replaced with a peak hold circuit 27, and the focus adjusting lens is adjusted so that the peak value of the peak hold circuit 27 is reached. FIG. 8 (b) shows an example of peak detection type characteristics when there are two subjects. Since the peak detection type is output in the form of tracing the peak value of the waveform (drawn with a thick solid line), the in-focus position for each subject is recognized even if multiple subjects exist within the ranging frame. be able to. However, when a high-brightness subject is present in the distance measurement frame, the image signal is saturated and distorted, which makes it impossible to perform correct distance measurement. The present invention is based on the above consideration, and an object thereof is to quickly detect a focal position without causing an erroneous distance measurement even when a high-brightness subject, a low-illuminance low-contrast subject, two subjects, etc. are present in the ranging frame. An object of the present invention is to provide an automatic focus detection device that can be used.

[0006]

In order to achieve the above object, an automatic focus detection apparatus according to the present invention comprises a filter for extracting a high frequency component of a video signal, an integrating circuit for integrating the high frequency component extracted by the filter, A peak detection circuit that detects the peak of the high-frequency component extracted from the filter is compared with the output characteristic of the integration circuit and the output characteristic of the peak detection circuit, and focus control is performed using the output having the steepest peak. It is composed of control means. Further, a first filter for extracting a high frequency component of the video signal, a second filter having a different cutoff frequency from the first filter for extracting the high frequency component of the video signal, and a high frequency component extracted by the first filter are integrated. A first integrator circuit, a second integrator circuit that integrates the high frequency component extracted by the second filter, a peak detection circuit that detects the peak of the high frequency component extracted by the first filter, and the first and second It is composed of control means for comparing the output characteristic of the integrator circuit and the output characteristic of the peak detection circuit, and performing focus control using the output having the steepest peak.

According to the above arrangement, the peak detection and the integral detection can be simultaneously processed in parallel to quickly detect the in-focus position of any subject.

[0008]

The present invention will be described in more detail with reference to the drawings. FIG. 1 is a circuit block diagram showing an embodiment of an automatic focus detection device according to the present invention. This drawing shows only the portion directly related to the present invention, and other circuit portions are omitted. The configurations of the lens unit 1, the CCD 2, the camera process circuit 3, the HPF 4, the amplifier 5, the gate circuit 6, the motor control circuit 12 and the motor 13 are the same as the circuits denoted by the same reference numerals in FIGS. The AF circuit 14 is composed of an integrating circuit 7 and a peak hold circuit 8. The integrating circuit 7 integrates the high frequency component of the luminance signal in the distance measurement frame indicated by the gate control signal of the gate circuit 6. On the other hand, the peak hold circuit 8 simultaneously inputs the high frequency components of the luminance signal within the same distance measurement frame, detects the peak value of the level and holds it. The A / D converters 9 and 10 convert the analog outputs of the integrating circuit 7 and the peak hold circuit 8 into digital signals and send them to the CPU 24, respectively. CPU 24 is A
The characteristics input from the / D converters 9 and 10 are judged to perform the processing of detecting the in-focus point, and the drive control signal is sent to the motor control circuit 12 based on the processing.

FIG. 2 is a diagram for explaining the processing steps of the CPU 24. The processing operation is shown for a case where the subject has a high brightness, a case where the brightness is a normal brightness that is neither particularly high brightness nor low illuminance, and a case where the objects are mixed in the perspective. The characteristic diagram on the left side described in step 1 for each luminance shows the output (sig1) from the integrating circuit 7, and the characteristic diagram on the right side shows the output of the peak hold circuit 8, and the horizontal axis of each characteristic diagram is At the lens position, N represents the near side and F represents the infinity side. First, the output waveform of the integrating circuit of a high-luminance subject becomes a mountain shape, and the peak hold circuit becomes a flat waveform. In such a case, it is determined that the maximum value of the output of the integrating circuit is at the in-focus position, and a control signal is sent to the motor control circuit 12 so as to bring the lens to that position (step 2). Then, when the lens is brought to that position (step 3), the photographer confirms with the electronic viewfinder. If it is okay, the next operation will be performed. If the subject is out of focus, press the release button halfway again to start AF.
The operation will be performed.

The output waveform of the integrating circuit and the output waveform of the peak hold circuit of the normal subject are mountainous (step 1). In such a case, it is determined whether or not the maximum lens positions of the respective waveforms match (step 1 '). If they do not match, the AF operation is performed again. If they match, it is determined that the maximum value of the output of the integrating circuit is at the in-focus position, and control is performed to bring the lens to that position. Since the lens positions of the maximum values match, the maximum value of the output of the peak hold circuit 8 may be used. The following operation is the same as in the case of a high brightness subject. Next, in the case of a far-near mixed subject, the output of the integration circuit has a flat maximum value, and the output of the peak hold circuit has a waveform with two peaks. In this case, the lens is controlled so as to bring the lens to the predetermined peak value of the peak hold circuit output (step 2). The subsequent operation is the same as in the case of a high brightness subject.

FIG. 3 is a circuit block diagram showing another embodiment of the present invention. In this example, an integrating circuit for integrating a high frequency component having a high cut frequency is provided in the configuration of FIG. HPF with higher cutoff frequency than HPF4
16 is provided, the output of which is amplified by the amplifier 17, and the AF
It is supplied to the circuit 15. The AF circuit 15 is composed of a peak hold circuit 18 and integrating circuits 19 and 20. Peak hold circuit 18, integrating circuits 19 and 20
Is converted into digital signals by A / D converters 21, 22 and 23 and supplied to the CPU 25.

FIG. 4 shows the processing steps of the CPU 25. The processing operation is shown for a case where the subject has a high brightness, a case where the brightness is a normal brightness that is neither a particularly high brightness nor a low illuminance, a case where the objects are mixed in the perspective, and a case where the illuminance is low and the contrast is low. In the case of each luminance in step 1, the characteristic diagram at the left end shows the output from the peak hold circuit 18 (sig
1), the characteristic diagram on the middle side shows the output (sig
2) is the output of the integration circuit 20 (sig
3) are shown respectively. The output waveform of the peak hold circuit of the high-luminance subject becomes a flat waveform, the output waveform of the integration circuit 19 becomes a gentle peak, and the output waveform of the integration circuit 20 becomes a steep peak. In such a case, it is determined that the maximum value of the output of the integration circuit 20 is at the in-focus position, and a control signal is sent to the motor control circuit 12 to bring the lens to that position (step 2). Then, when the lens is brought to that position (step 3), the photographer confirms with the electronic viewfinder. If OK, move on to the next operation. If the subject is not in focus, the AF operation is performed by pressing the release button halfway again.

In the case of low illuminance and low contrast, the output waveform of the peak hold circuit becomes a mountain shape, the output waveform of the integrating circuit 19 becomes a mountain shape, and the output waveform of the integrating circuit 20 becomes a flat waveform (step 1). In such a case, the integration circuit 19 is controlled so as to bring the lens to the maximum value of the output waveform. The subsequent operation is the same as in the case of high brightness. In the case of normal luminance, the output waveform of the peak hold circuit has a mountain shape, the output waveform of the integrating circuit 19 has a mountain shape with saturated vertices, and the output waveform of the integrating circuit 20 has a steep mountain shape (step 1). In such a case, the integration circuit 2
It is controlled to bring the lens to the maximum value of 0 output (step 2). The subsequent operation is the same as in the case of high brightness.
Next, in the case of a perspective mixed subject, the output waveform of the peak hold circuit is a mountain with two vertices, and the integration circuits 19 and 20
The output waveform of has a flat maximum value. In this case, the lens is controlled so as to bring the lens to the predetermined peak value of the peak hold circuit output (step 2). The subsequent operation is the same as in the case of a high brightness subject.

[0014]

As described above, the automatic focus detection device according to the present invention provides the outputs of the integrating circuit for integrating the high frequency component of the luminance signal and the peak hold circuit for detecting and holding the peak value of the high frequency component of the luminance signal. Since it is configured to obtain at the same time, compare and process with a predetermined algorithm to detect the in-focus position, even if the subject has high brightness or low illumination and low contrast, the distance measuring frame Even when a plurality of subjects are mixed in, it is possible to quickly and accurately detect the in-focus position. Further, since a plurality of high-pass filters (HPFs) having different cutoff frequencies or a plurality of amplifiers having different gains are used and the detection outputs corresponding thereto are simultaneously processed in parallel, the amplifier gain is increased during the AF operation like the conventional AF control. And without switching HPF,
It enables an AF operation with better convergence. This is particularly effective for an electronic still camera that requires a quick AF operation.

[Brief description of drawings]

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

FIG. 2 is a diagram for explaining a procedure of judgment and control of the CPU of FIG.

FIG. 3 is a circuit block diagram showing another embodiment of the present invention.

FIG. 4 is a diagram illustrating a procedure of determination and control of the CPU of FIG.

FIG. 5 is a diagram for explaining a focused state and a non-focused state.

FIG. 6 is a circuit block diagram showing a conventional example of an integration detection type focus detection device.

FIG. 7 is a circuit block diagram showing a conventional example of a peak detection type focus detection device.

FIG. 8 is a diagram for explaining output characteristics of an integral detection type circuit and a peak detection type circuit.

[Explanation of symbols]

1 ... Lens unit 2 ... CCD 3 ... Camera process circuit 4, 16 ... High-pass filter 5,17 ... Amplifier 6 ... Gate circuit 7, 19, 20 ... Integrating circuit 8,18 ... Peak hold circuit 9, 10, 21, 22, 23 ... A / D converter 11, 24, 25 ... CPU 12 ... Motor control circuit 13 ... Motor 14, 15 ... AF circuit

Claims (2)

[Claims] 1. A filter for extracting a high frequency component of a video signal, an integrating circuit for integrating the high frequency component extracted by the filter, a peak detection circuit for detecting a peak of the high frequency component extracted by the filter, and the integrating circuit. And an output characteristic of the peak detection circuit are compared with each other, and the focus detection control device is configured to perform focusing control using the output having the steepest peak. 2. A first filter for extracting a high frequency component of a video signal, and a second filter having a different cutoff frequency from the first filter for extracting a high frequency component of the video signal,
A first integrator circuit that integrates the high frequency component extracted by the first filter, a second integrator circuit that integrates the high frequency component extracted by the second filter, and a peak of the high frequency component extracted by the first filter is detected. It is composed of a peak detection circuit and a control means for comparing the output characteristics of the first and second integration circuits with the output characteristics of the peak detection circuit, and performing focus control using the output having the steepest peak. An automatic focus detection device.