JPH0323412A - Focus control circuit - Google Patents

Abstract

PURPOSE:To enable focus control without using any frequency generator by moving a focus lens, stopping the lens beyond a focusing position at constant intervals according to the comparison result of respective evaluated values and then returning the lens while wobbling it at the focusing position, and stopping the lens at the focusing position according to the comparison result of respective evaluated values. CONSTITUTION:The focus lens 2 is moved toward the focusing position to obtain the evaluated values at constant intervals and adjusted roughly according to the comparison result of the respective evaluated values so that the lens stops beyond the focusing position. After this rough adjustment, the focus lens 2 is returned to the focusing position while wobbled, an evaluated value is obtained at each external value of the wobbling period of the focus lens, and the focus control is performed by fine adjustment which stops the lens at the focusing position according to the comparison result of respective evaluated values. Consequently, the focus control is performed without providing any frequency generator nor considering the backlash quantity.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a focus control circuit using a contrast detection method used for autofocus of a video camera, for example.

[Summary of the Invention] The present invention is a focus control circuit that performs focus control by detecting spectral components in a video signal. Based on the value comparison results, the camera stops at a position beyond the in-focus position, then moves the focus lens back to the in-focus position while moving it, obtains evaluation values at regular intervals, and based on the comparison results of each evaluation value, it reaches the in-focus position. By stopping, there is no need to use the number of pulses of the frequency generator as a reference to return to the peak point in control using the so-called hill-climbing algorithm. Control becomes possible.

[Prior Art] Autofocus systems for video cameras can be classified into distance measurement systems and focus detection systems, based on the principle of the focusing system. The distance measurement method measures the distance to the subject and controls the position of the lens accordingly. The focus detection method detects the focus during imaging and controls the position of the lens to the focused position.

One of the focus detection methods is the contrast detection method. The contrast detection method performs focus control by utilizing the fact that the edges of the captured image become clearer as the lens approaches the in-focus position. The fact that the edges of the captured image become clearer corresponds to the increase in the Takagi component in the video signal. A conventional example of an O1 focus circuit using this contrast detection method is shown in FIG.

In FIG. 6, a focus lens 2 is displaced by a focus motor 1, and light from an object is emitted onto an image sensor 3 via the focus lens 2. The image sensor 3 converts the light from the subject into a video signal, and this video signal is output to a bandpass filter (BPP) 6 via a signal processing circuit 4 and an amplifier 5. Bandpass filter 6
For example, the frequency is 200 KHz ~ 2 MH
The output of the bandpass filter 6 is supplied to the detector 7. The detector 7 double-wave rectifies the input signal, and the output of the detector 7 is supplied to the A/D converter 8. The A/D converter 8 A/D converts only the signal corresponding to the focus area based on the Zanobling clock sent from the microcomputer 1O, and this digital signal is supplied to the integrating circuit 9. The integrating circuit 9 integrates the digital signal from the A/D converter 8, and the output of the integrating circuit 9 is supplied to the microcomputer 10 as a focus evaluation value. The microcomputer IO uses the mountain climbing control algorithm to control the integration circuit 9.
The purpose is to search for the position of the focus lens 2 where the output becomes maximum, and the focus lens 2 is positioned at the in-focus position as follows.

That is, the microcomputer 10 outputs a constant voltage to the focus motor 1 via the drive circuit to move the focus lens 2 toward the in-focus position at a constant speed.

During this movement, the evaluation values sequentially sent from the integrating circuit 9 are compared with the previous evaluation value, and if the evaluation value becomes larger than the previous evaluation value, the output pulses of the frequency generator 15 are counted from this point. In order to avoid erroneously determining the peak point due to fluctuations in the evaluation value due to noise, if the evaluation value from the integrating circuit 9 is larger than the previous one two or three times in a row, it is determined that the peak point has been exceeded. Focus motor 1
to stop. And a frequency generator! The focus motor 1 is reversely driven by the amount by which the count number corresponding to the amount of backlash is subtracted from the count number of the output pulses of 5, and the stop IF. By doing 74-cas lens 2
to the in-focus position.

[Problem to be Solved by the Invention 1] However, according to the above-mentioned Yokozo, since the number of pulses of the frequency generator l5 is used as a standard for returning to the peak point, the frequency generator 15 is necessary and backlash q There is a drawback that the return position of the focus motor I must be determined in consideration of the following.

Therefore, the present invention does not require a frequency generator, and
It is an object of the present invention to provide a focus control circuit capable of performing focus control without considering backlash.

[Means for Solving the Problems] A focus control circuit of the present invention for achieving the above object includes an imaging means for converting an optical signal from an object into a video signal, and a spectrum control circuit in the video signal output from the imaging means. a spectrum detection means for detecting a component; an evaluation value calculation means for obtaining an evaluation value by summing the spectrum components within the focus area detected by the spectrum detection means; In a focus control circuit, the focus control circuit has a comparison means for comparing the value with the value, and controls a focus motor based on the comparison result of the comparison means to position the focus lens at the focus position, the focus control circuit moving the focus lens toward the focus position. move, obtain evaluation values at regular intervals, and perform a rough adjustment to stop at a position beyond the in-focus position based on the comparison result of each evaluation value, and after this coarse adjustment, while moving the focus lens to the in-focus position. put it back,
An evaluation value is obtained for each extreme value of the wobbling period of the focus lens, and focus control is performed by fine adjustment to stop at the in-focus position based on a comparison result of each evaluation value.

[Operation] During rough adjustment, move the focus lens toward the in-focus position, obtain evaluation values at regular intervals, and search for the peak point of the evaluation values.
In the adjustment, the focus lens is wobbled to the in-focus position and returned, and an evaluation value is obtained for each extreme value of the wobbling cycle of the focus lens, and the focus lens is stopped at the peak point.

[Example] An embodiment of the present invention will be described below with reference to the drawings.

An embodiment of the present invention is shown in FIGS. 1 to 5, and this embodiment shows a case where the focus control circuit of the present invention is applied to a video camera.

In FIG. 1, the position of a focus lens 2 is varied by a focus motor 1, and an image of a subject is formed on an image sensor 3 via the focus lens 2. In FIG. The image sensor 3 converts light from an object into a video signal, and the output of the image sensor 3 is supplied to a signal processing circuit 4. The signal processing circuit 4 is, for example, R,
G. A luminance signal is created by adding each H signal at a predetermined ratio, and this signal is sent to a bandpass filter 6 via an amplifier 5. The bandpass filter 6, which is a spectrum detection means, is a filter that passes components having a frequency of 200 KHz to 2MHz, for example, and extracts all spectral components other than the DC component and noise component in the luminance signal.

The output of the band-pass filter 6 is supplied to a detector 7, and the detector 7 performs double-wave rectification of the output of the band-pass filter 6. The double-wave rectified output of the detector 7 is supplied to an A/D converter 8, digitized by a sampling clock, and this digital signal is output to an integrating circuit 9. This sampling clock is output from the microcomputer 10, and this sampling clock differs during coarse adjustment and fine adjustment, and only the video signal corresponding to the focus area is A/D converted. An integration circuit 9 serving as evaluation value calculation means integrates the digital signal from the A/D converter 8, and the output of the integration circuit 9 is supplied to the microcomputer 10 as a focus evaluation value.

This microcomputer IO has comparison means for comparing the evaluation value outputted by the integrating circuit 9 with the previous evaluation value.
executes the flowchart shown in FIG. Detailed control of this microcomputer 10 will be explained in the section of operation.

Further, the drive signal of the microcomputer 10 is outputted to the drive circuit l2 via the adder 11. The wobbling signal generating circuit 13 outputs a sine wave wobbling signal to the adder 11 and also supplies it to the microcomputer 10 in response to a start signal from the microcomputer 1O. Further, the output of the wobbling signal is stopped by a stop signal from the microcomputer 10.

Hereinafter, the operation of the above configuration will be explained with reference to FIG.

When shooting starts, the microcomputer 10 executes the coarse adjustment mode, and when the focus lens 2 is at the maximum position or the minimum position, or when it is at the intermediate position, the microcomputer 10 drives the microcomputer 10 at a constant voltage by comparing the evaluation values. A signal is output to drive the focus motor 1 to move the focus lens 2 toward the in-focus position. Also, microcomputer I
For example, O outputs the frequency of the color subcarrier as a sampling clock to the A/D converter 8, takes in the evaluation values (N., Nt, N. . .) sequentially sent from the integrating circuit 9, and outputs the frequency of the color subcarrier as a sampling clock to the A/D converter 8. The previous evaluation value (N...,) is compared from the evaluation value (N. (x≧1)). If the evaluation value (N8) is larger than the previous evaluation value (N.-.), the next evaluation value is taken in and the comparison is repeated in sequence.

If the evaluation value (N8) becomes smaller than the previous evaluation value (Nx-.) and this state continues several times, the focus motor 1 is stopped. The evaluation value (N.) is less than the previous evaluation value <N.
-1) When the value becomes smaller and this state continues multiple times, the in-focus position (peak value)
This means that the focus lens 2 is stopped at a position beyond the in-focus position, and the rough adjustment is completed.

Next, the microcomputer 10 executes the fine adjustment mode, and the microcomputer 10 operates in the opposite direction (direction of arrow B in FIG. 5), and
A low-speed voltage is output to drive the focus lens 2 at a minute speed compared to the above. Further, the microcomputer 10 outputs a start signal to the wobbling signal generating circuit l3, and the wobbling signal generating circuit l3 outputs a wobbling voltage. Therefore, as shown in FIG. 2, the drive circuit 12 is supplied with a composite voltage (c) that is a combination of the low-speed voltage (a) and the wobbling voltage (h), and the focus lens 2 wobbles to the in-focus position. movement). Further, based on the wobbling signal, the microcomputer 10 outputs to the A/D converter 8 sampling clocks at timings tA and tB in FIG. 2, which are the extreme values (maximum and minimum values) of the wobbling period of the focus lens 2. Then, the evaluation values nA and nB at this timing are sequentially taken in. Since the focus lens 2 wobbles, as shown in Fig. 3, A,→R→
Move in the order of A, →B, →A, →..., and at timing tA, move to A,,A. The evaluation value nA of ,... becomes the evaluation value n. of R,,11,,... at the timing ts. are respectively taken in. Then, compare the evaluation values nA and nB,
When ne becomes larger than nA, the low-speed voltage output is stopped and a stop signal is output to the wop ring signal generation circuit 13. Then, wobbling signal generation circuit 1
3 stops outputting the wobbling voltage, the focus motor I stops, and the focus lens 2 moves to the in-focus position (
peak point).

In this embodiment, the wobbling operation and the return operation were performed simultaneously to return to the peak point, but the return operation and the wobbling operation are performed alternately, and an evaluation value is taken at each extreme value of the wobbling cycle. It may be configured as follows.

[Effects of the Invention] As described above, according to the present invention, the focus lens is moved toward the in-focus position, evaluation values are obtained at regular intervals, and the comparison result of each evaluation value indicates a position beyond the in-focus position. The focus lens is then returned to the focus position while wobbling, and evaluation values are obtained at regular intervals.The focus lens is then stopped at the focus position based on the comparison results of each evaluation value, so it can be controlled using a so-called mountain climbing algorithm. Since it is not necessary to use the number of pulses of the frequency generator as a reference to return to the peak point, there is an effect that focus control becomes possible without using a frequency generator and without considering the amount of backlash.

[Brief explanation of drawings]

Figures 1 to 5 show embodiments of the present invention, Figure 1 is a block diagram of the focus control circuit, Figure 2 is a diagram of output waveforms of each part during fine adjustment, and Figure 3 is a focus lens during fine adjustment. A diagram showing the relationship between the position and the evaluation value taken in, FIG. 4 is a flowchart diagram, and FIG. 5 is a characteristic line diagram of the evaluation value.
FIG. 6 is a block diagram of a conventional focus control circuit. 2...Focus lens, 3...Imaging element (imaging means), 6...Band pass filter (spectrum detection means), 9...Integrator circuit (evaluation value calculation means), 10...
- Microcontroller (means of comparison). 1 other person

Claims (1)

[Claims] (1) An imaging means that converts an optical signal from a subject into a video signal, a spectrum detection means that detects spectral components in the video signal output by this imaging means, and a spectrum within the focus area detected by this spectrum detection means. It has an evaluation value calculation means that totals the components to obtain an evaluation value, and a comparison means that compares the evaluation value outputted by this evaluation value calculation means with the previous evaluation value, and focuses based on the comparison result of this comparison means. In a focus control circuit that controls a motor to position a focus lens at a focus position, the focus lens is moved to the focus position side, evaluation values are obtained at regular intervals, and the focus position is determined based on the comparison result of each evaluation value. After this rough adjustment, the focus lens is returned to the in-focus position while wobbling, and an evaluation value is obtained for each extreme value of the wobbling period of the focus lens, and each evaluation value is compared. A focus control circuit characterized in that focus control is performed by fine adjustment that stops at a focus position based on the result.