JP2542361B2 - Automatic focus signal detection device - Google Patents

Description

The present invention relates to an automatic focusing signal detection device used in an optical device such as a camera.

(Prior Art) In a camera, the taking lens has a low-pass filter type with a frequency transfer characteristic as shown in FIG.
freq is the frequency), and when the subject image is blurred, only the low-frequency component of the spatial frequency unique to the subject passes through, and the high-frequency component also passes as the subject comes into focus. As one of the automatic focusing signal detection devices, there is one that pays attention to the frequency transfer characteristic of the imaging lens and uses the amount of high frequency components contained in the video signal from the camera. In this automatic focusing signal detection device, as shown in FIG. 14, a specific scan line of the video signal is generated by a signal from the scan line setting unit 3 at the gate 2 from the video signal obtained by imaging through the taking lens in the camera 1. A portion is selected, a high-pass filter (hereinafter referred to as HPF) 4 extracts the high-frequency component, and a peak hold circuit 5 holds the peak to detect the amount of the high-frequency component. FIG. 15 shows an example of the output voltage of the peak hold circuit 5 when the lens of the camera 1 is moved, and the output voltage of the peak hold circuit 5 becomes maximum when the lens is in focus. Since the detection of the focus signal by one scanning line portion is inaccurate, a plurality of scanning line portions are actually taken out by the gate 2.

(Problems to be Solved by the Invention) In the above-described automatic focusing signal detection device, the output voltage characteristics are shown in FIGS. 16 and 17 depending on the characteristics of the subject, the lens of the camera 1, HPF4, and the like.
It may be as shown in the figure. In the case of Fig. 16, at the point where the subject image is completely blurred, there is no output voltage and it is not known which direction the lens should be moved, the closer or infinity.
It takes time to focus. Fig. 17 shows the case where the output voltage is saturated and the case where the peak is dull. In both of these cases, the focal point is not clear and the focus is poor.

(Means for Solving the Problems) In order to solve the above problems, the present invention provides a method in which after the first set time of the rising of the horizontal synchronizing signal separated from the video signal imaged and output through the lens by the camera. Detection area setting means for generating a gate signal from the second to the second setting time, scanning line setting means for setting a scanning line to be processed in advance, and horizontal synchronizing signals separated from the video signal are counted. A scanning line detecting means for detecting a scanning line to be processed by comparing a count value with a value set by the scanning line setting means, and a plurality of high-pass filters to which the video signal is input and which have different cutoff frequencies. , A plurality of gates that take out the output signals of the plurality of high-pass filters by the gate signals from the detection area setting means, and a plurality of gates. Weighting and adding means for detecting the focus signal of the video signal by weighting and adding the video signal from the scanning line, and the output signal of the weighting and adding means by the scanning line detecting means A setting range focusing signal generating means for sample-holding and adding each time is added.

(Operation) The detection area setting means outputs the gate signal between the first set time and the second set time after the rising of the horizontal synchronizing signal separated from the video signal picked up by the camera through the lens and output. The scanning line to be processed is set in advance by the scanning line setting means. The scanning line detecting means counts the horizontal synchronizing signal separated from the video signal and compares the count value with the value set by the scanning line setting means to detect the scanning line to be processed, and the cutoff frequency is different. Video signals are input to a plurality of high-pass filters. The plurality of gates take out the output signals of the plurality of high-pass filters by the gate signals from the detection area setting means, and the weighted addition means weights and adds the video signals from the plurality of gates to add the focus signals of the video signals. To detect. Then, the setting area focusing signal creating means samples and holds the output signal of the weighting addition means for each scanning line to be processed by the output signal of the scanning line detecting means and adds the signals.

(Embodiment) FIG. 1 shows an embodiment of the present invention.

In this example, multiple HPs with different low cutoff frequencies are used.
By using F and adding appropriate weights to its output, the output voltage characteristics with a wide skirt and a sharp peak are obtained. As a result, the direction of focusing can be known even from the completely melted state, and the focusing can be performed in a short time, and the focusing can be performed accurately.

In this embodiment, the position of the camera 11 is controlled by the microcomputer 22 using the motor 31. Camera 11
Outputs a video signal by picking up an image of a subject through a lens, and this video signal always sets the same scanning line via a buffer 12 (13 to 21) and an autofocus signal generation circuit (231 to 23n, 241 to 24n, 251 ~ 25n, 26,271 ~ 27m, 28,2
Entered in 9).

First, the scanning line setting circuit will be described. The video signal from the camera 11 passes through the buffer 12 having a high input impedance, and only the sync signal component is taken out by the sync signal separation circuit 13, and the horizontal sync signal and the vertical sync signal are extracted by the horizontal sync separation circuit 14 and the vertical sync separation circuit 15. Are separated. The field detection circuit 18 determines the first from the timing of the horizontal sync signal and the vertical sync signal from the horizontal sync separation circuit 14 and the vertical sync separation circuit 15.
Either the field or the second field is detected. Here, the video signal from the camera 11 is alternately repeated for the first field and the second field. The detection area setting circuit 17 as the detection area setting means includes a horizontal sync separation circuit 14
The signal for opening the gates 241 to 24n is generated between t ₁ seconds as the _first set time and t ₂ seconds as the second set time after the rise of the horizontal synchronizing signal from the. This signal opens the gates 241 to 24n to open the peak hold circuit 25.
Only the high frequency components of the video signal are input to 1 to 25n, and those related to the sync signal are excluded. The scanning line detecting means including the horizontal synchronizing counter 16 and the digital comparator 20 detects the scanning line to be processed. That is, the value set by the scanning line setting means 22 composed of a microcomputer is latched by the latch circuit 19, the horizontal sync counter 16 counts the number of horizontal sync signals from the horizontal sync separation circuit 14, and the digital comparator 20 latches the value. The value of 19 and the value of the horizontal sync counter 16 are compared. When the value of the latch circuit 19 and the value of the horizontal synchronization counter 16 match, the control circuit 21 outputs the output of the addition coefficient unit 26 as a weighting addition means to the sample hold circuits 271 to 27m for each scanning line by the output signal of the digital comparator 20. Hold the signal.
Here, a plurality of scanning lines can be processed by setting the microcomputer 22 during one field. The control circuit 21 processes the set scanning line (output signal of the addition coefficient unit 26)
Which of the sample-hold circuits 271 to 27m is to be held is determined. Thus n ₁ .n _{2 of the} same field
... it can detect n _m video signal of the first scan line.

In FIG. 3, a indicates the output of the buffer 12, and b and c are enlarged views of a part thereof. In the figure, V is a vertical synchronizing signal and H is a horizontal synchronizing signal. The field detection circuit 18 utilizes the fact that the time t from the end of V to the output of H is different between the first field and the second field. The detection area setting circuit 17 generates a gate signal so as to take out a video signal from t ₁ seconds after t ₁ seconds to t ₂ seconds after the rise of H as in C.

Next, the autofocus signal generation circuit will be described.

A high frequency component is taken out from the video signal from the buffer 12 by a plurality of HPFs 231 to 23n, and an appropriate portion of the video signal is taken out by the gates 241 to 24n, and a peak hold circuit 25 is provided.
The peak value is detected by 1 to 25n. The output voltage characteristics of HPF231 to 23n are different.
Each output of ~ 23n is multiplied by a coefficient and added to obtain a desired output voltage characteristic. As shown in FIG. 2, the addition coefficient unit 26 is composed of coefficient units 261 to 26n that apply a coefficient to each input and an adder 260 that adds the outputs thereof. Here, the operational amplifier OP and resistors R1 to Rn, Rf are used. It is composed of.

The processing up to this point is performed for all scanning lines. Next, the output of the addition coefficient unit 26 is the sample hold circuit 27.
Adder that samples and holds for each scan line only for the scan line set by the microcomputer 22 by 1 to 27 m
The sum is taken at 28, the sum is held at the sample hold circuit 29, and converted to a digital value at the analog / digital converter 30. In this way, the sample and hold circuit 27
1 to 27 m and the adder 28 constitute setting area focusing signal generating means for sample-holding and adding the output signal of the addition coefficient unit 26 for each scanning line to be processed. Microcomputer
22 is a control circuit 2 according to the output signal of the field detection circuit 18
1. Control the analog / digital converter 30, etc., capture data from the analog / digital converter 30, and capture the camera.
Focus on 11.

By the way, HPF231-233 (n is 3) is the 4th
As shown in the figure, the low cutoff frequencies f _{1 to} f ₃ are different,
The output voltage characteristics for the same image are different as shown in FIG. The output of the HPFs 231 to 233 added with appropriate weights is as shown in FIG. 6, and the output voltage characteristic having a wide skirt and a sharp peak at the focal point is obtained.

When performing focusing, the microcomputer 22 takes in data from each analog / digital converter 30 at each camera position, compares it with the previous one, and determines the lens moving direction, etc. Move to the focal point. That is, as shown in FIGS. 7 and 8, (1) First, while measuring the output voltage (output voltage of the sample hold circuit 29) via the analog / digital converter 30, the lens of the camera 11 is arbitrarily set to the motor 31. Move in the direction of the optical axis. (2) Next, if the moved direction is the direction in which the output voltage is increased, the motor 31 is caused to continue moving the lens of the camera 11 in that direction. Conversely, if the direction in which the lens is moved is to decrease the output voltage, the motor 31 is caused to move the lens of the camera 11 in the opposite direction. (3) It is detected that the lens of the camera 11 has passed the just focus position (focus point) from the change in the output voltage from the increase to the decrease, and the focus point is stored.
(4) The motor 31 is controlled to return the lens of the camera 11 to the stored focal point and stop it. The order of focusing (1) to (4) is (1) to (8) in FIG. 7 and FIG.
Corresponds to (4).

Next, output waveforms of the buffer 12, HPFs 231-233, gates 241-243, and peak hold circuits 251-253 will be described. When an image as shown in FIG. 9 (1) is input to the camera 11, the video signal from the buffer 12 has a waveform as shown in FIG. 9 (2) for the scanning lines n _{1 to} n ₃ . This video signal is input to the gates 241 to 243 via the HPFs 231 to 233 having the characteristics shown in FIG. 4, and the output of the HPF 231 and the output of the gate 241 have a waveform as shown in FIG. 9 (3). The output of HPF231 is only the output high frequency component of buffer 12, so buffer 12
Sharp peaks appear at the rising and falling edges of the output. When the gate 241 is opened only while the gate is open as shown in FIG. 9 (2), the output of the gate 241 in which only the peak related to the video remains and the peak relating to the horizontal synchronizing signal is removed as shown in FIG. 9 (3). Obtained from The output of HPF232 and gate 242 and the output of HPF233 and gate 243 are also shown in Fig. 9 (4).
Although the waveform is as shown in (5), the low-range cutoff frequency becomes higher in the order of HPF231, 232, 233, so the output amplitude becomes smaller in the order of (3)>(4)> (5) in FIG. .
When the peak hold circuits 251-253 are set and reset at the timing shown in FIG. 9 (6), the outputs of the peak hold circuits 251-253 have the waveforms shown in FIG. 9 (7). In the figure, V ₁ , V ₂ , and V ₃ are the largest peak-to-peak voltages among the outputs of the gates 241-243. Since the output of the addition coefficient unit 26 is the output of the peak hold circuits 251-253 added at an appropriate ratio, the peak hold circuits 251-253.
The output has a waveform substantially the same as the output, and its height, that is, the voltage can be arbitrarily set by the ratio of addition.

When an image as shown in FIG. 10 (1) is input to the camera 11 and three scanning lines n _{1 to} n ₃ are selected, the buffer 12 and the gate
241, the sample hold circuits 271 to 273 (m = 3), and the output of the adder 28 have waveforms as shown in FIGS. 10 (1) to 10 (5). When the signal processing is completed for the three scanning lines l1 to l3, the output of the adder 28 is analog / digital converted by the analog / digital converter 30 at the timing of A / D conversion hold shown in FIG. 10 (5). . In this way, if the scanning lines are individually selected, if there is an output for any one of the scanning lines, that is, if any one of the scanning lines covers the subject, focusing can be performed and an appropriate interval is set. It is advisable to use a plurality of scanning lines.

In addition, it is possible to focus on an arbitrary place by setting the scanning line and the detection area (t _{1 to} t ₂ ). For example, in the case of a landscape with a person in the center, if three scanning lines and a detection area are selected as shown in FIG. 11, the person P in the center is in focus.
In addition, as shown in FIG. 12, if the scanning line and the detection area are selected, the perspective portion on the upper right of the screen is in focus.

(Effects of the Invention) As described above, according to the present invention, by adding video signals of a subject obtained from a proper number of scanning lines set in advance through weighting via a plurality of HPFs having different cutoff frequencies, Since the focus signal of the video signal is detected, an output voltage characteristic having a wide skirt and a sharp peak can be obtained.
As a result, the moving direction of the lens can be easily known, the focusing time can be shortened, and the focusing can be sharpened. Further, by changing the number of HPFs and the above weights, it is possible to make an optimal configuration for the subject, and it is possible to prevent the accuracy from being influenced by the characteristics of the subject.
Further, since the position of the scanning line can be freely set, it is possible to prevent the accuracy from being lowered due to the characteristics of the subject. In addition, the output of the HPF with the lower cutoff frequency includes the signal detected by the HPF with the higher cutoff frequency by allowing multiple HPFs to pass the frequency components above the cutoff frequency. Therefore, it is not necessary to weight the output of the HPF having a high cutoff frequency. Therefore, it is possible to deal with the focusing of a subject having various spatial frequency characteristics, and it is possible to accurately focus on a desired focus position regardless of whether the subject is minute or large. Further, by arbitrarily setting the scanning line to be processed, the focus area determined by the scanning line to be processed and the detection area can be arbitrarily set, which is suitable for an industrial microscope.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram showing an addition coefficient unit, FIG. 3 is a waveform diagram showing a buffer output waveform of the above embodiment and its expanded waveform, FIG. Is a characteristic curve diagram showing the HPF characteristic of the same embodiment, FIG. 5 is a characteristic curve diagram showing the output voltage characteristic of each HPF of the same embodiment, and FIG. 6 is a characteristic curve diagram showing the output voltage characteristic of the same embodiment, 7 and 8 are diagrams for explaining focusing in the same embodiment, FIGS. 9 and 10 are diagrams showing input image examples and signal waveforms of respective parts in the same embodiment, FIGS. 11 and 12 FIG. 13 is a diagram for explaining the present invention, FIG. 13 is a characteristic curve diagram showing a frequency transfer characteristic of a lens, FIG. 14 is a block diagram showing a conventional automatic focusing signal detection device, and FIGS. FIG. 4 is a characteristic curve diagram showing an output voltage characteristic of the device. 231 to 23n …… HPF, 26 …… Addition coefficient unit.

Claims (1)

(57) [Claims] 1. A detection for generating a gate signal between a first set time and a second set time after the rising of a horizontal synchronizing signal separated from a video signal picked up and output by a camera through a lens. Area setting means, scanning line setting means for setting a scanning line to be processed in advance, horizontal synchronizing signals separated from the video signal, and the count value is compared with the value set by the scanning line setting means. The scanning line detecting means for detecting the scanning line to be processed by, a plurality of high-pass filters with different cutoff frequencies to which the video signal is input, and output signals of the plurality of high-pass filters from the detection area setting means, respectively. Video that is obtained by weighting and adding the video signals from the multiple gates extracted by the Weighting addition means for detecting the focus signal of the signal and a setting range focus signal generating means for sample-holding and adding the output signal of the weighting addition means for each scanning line to be processed by the output signal of the scanning line detecting means. An automatic focusing signal detection device comprising: