JP3131971B2 - Auto focus device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an autofocus device suitable for use in, for example, a video camera.

[Summary of the Invention]

The present invention relates to an autofocus apparatus, and by performing control by averaging a plurality of fields of a predetermined evaluation value for each field, it is possible to always perform a good operation without being affected by flicker or the like of illumination. Things.

[Conventional technology]

For example, in an autofocus device used for a video camera, it has been considered to measure and evaluate a captured video signal to control a lens system.

That is, for example, in FIG. 4, (1) is a lens system, and image light from a subject (not shown) is imaged on the CCD image pickup device (2) via the lens system (1).
Then, a signal read from the CCD element (2) is supplied to a signal processing circuit (3), where a desired video signal is formed and output to an output terminal (4).

At the same time, a luminance signal component of the video signal from the processing circuit (3) is supplied to a band-pass filter (BPF) (5) to extract a high component of the luminance signal.
The data is converted into digital data by the converter (6) and supplied to the integrating circuit (7). And in this integrating circuit (7),
For example, as shown in FIG. 5, only data included in a predetermined range substantially at the center of the screen formed by the video signal is integrated and extracted for each field.

The integrated value (evaluation value) is supplied to an evaluation microcomputer (μ-con) (8). Here, in the computer (8), the supplied evaluation value is supplied to the comparing means (81) and also to the memory (82), as shown by the functional block in the figure, and the evaluation value is supplied from the memory (82) to the last time. The supplied evaluation value is supplied to the comparing means (81).
As a result, a signal of "1" is taken from the comparing means (81) when the current evaluation value is smaller than the previous evaluation value, and a signal of "0" is taken out otherwise, and the signal from the comparing means (81) is output from the computer (81). 8).

And the output signal from this computer (8) is D / A
The signal is supplied to the drive circuit (10) of the focus motor (11) through the converter (9). When the signal from the computer (8) is "0", the current rotation is continued and when the signal becomes "1". Is controlled so that the rotation is reversed.

As a result, the motor (11) is controlled so that the evaluation value from the integrating circuit (7) is maximized. Here, the evaluation value from the integrating circuit (7) is set to the signal level of the high frequency component of the luminance signal. The corresponding signal level of the high-frequency component increases when the lens system (1) is properly focused.

[Problems to be solved by the invention]

However, in the above-described device, this device is, for example, 50 Hz
When used under fluorescent light, which is powered by commercial power,
Flicker having a period of three fields occurs in the video signal.
That is, the fluorescent lamp is normally blinking at twice the frequency (100 Hz) of the power supply, and between this and the video camera's field frequency (60 Hz), the greatest common divisor (20 Hz = 3 field periods) is applied to the video signal. Flicker occurs.

When such flicker is superimposed on the video signal, the signal level that should originally change as shown by the broken line in FIG. 6 becomes as shown by the solid line due to the flicker, and as described above, the image level in each field unit is changed. In a device that performs control using a signal, a correct operation cannot be performed.

This application is made in view of such a point, and aims at providing an apparatus which has a simple structure and is not affected by flicker or the like.

[Means for solving the problem]

The present invention is an autofocus apparatus used for a video camera for sequentially obtaining a captured video signal for each field, wherein the captured video signal is provided for each field in a predetermined range within the field. Integrating means (circuit (7)) for integrating the signal level and storage means (memory (8) for sequentially storing the evaluation values obtained by this integration.
4)), and when the flicker cycle of the captured video signal is an n-field cycle, the latest evaluation value for each field and the stored evaluation values for the past n-1 fields are summed. Means (circuit (83)) for calculating the average value divided by the above-mentioned n, and comparison means (circuit (81)) for comparing this average value with the previous average value (memory (82)) for each of the fields. And a control means (drive circuit (10), motor (11)) for controlling the lens (1) system for photographing so that the average value becomes maximum. is there.

[Action]

According to this, since the control is performed using the average value of the evaluation values of a plurality of fields, the influence of the flicker of the video signal is removed by the averaging. A favorable operation can be performed without being affected by the above.

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the drawings, portions corresponding to those of the above-described conventional technology will be denoted by the same reference numerals, and detailed description thereof will be omitted.

In FIG. 1, the configuration of the lens system (1) to the integrating circuit (7) is the same as that of the conventional device. On the other hand, the functional blocks of the microcomputer (μ-con) (8) are changed as shown.

That is, the evaluation value supplied from the integrating circuit (7) for each field is supplied to the averaging means (83) and to the memory (84). The evaluation values for the past predetermined fields stored in the memory (84) are supplied to the averaging means (83), and the average values of these evaluation values are supplied to the comparison means (81) and the memory (82). You.

The output signal from this computer (8) is D / A
It is supplied to the drive circuit (10) of the focus motor (11) through the converter (9). The function block comparison means (81), the memory (82) and the D / A converter (9) to the motor (1)
The configuration of 1) is the same as the conventional device.

FIG. 2 shows a flowchart of a program of the microcomputer (8) for realizing the above-mentioned functional blocks. That is, FIG. 7A shows a main routine. When the operation is started, an interrupt by the vertical synchronizing signal is awaited in step [1]. Then, when an interrupt by the vertical synchronization signal occurs, a subroutine shown in FIG.

In this subroutine, in step [11], the evaluation value from the integrating circuit (7) is fetched, and in the next step [12], the evaluation value for the past (n-1) fields from the memory (84) is stored. The evaluation value captured this time is added and divided by n to obtain an average value. Then, in step [13], the previous average value from the memory (82) is compared with the current average value. If (previous average)> (current average) is YES, the rotation of the motor (11) is performed in step [14]. Is inverted, and the current evaluation value is stored in the memory (8
Written in 4) and returned to the main routine. Note that the writing to the memory (84) in step [15] is performed so that the past evaluation values are sequentially shifted by this writing, and the oldest one is saved.

Thus, according to the above-described autofocus device, the control is performed using the average value of the evaluation values of a plurality of fields. Therefore, the influence of the flicker of the video signal is removed by the averaging, and the flicker occurs in the video signal. In such a case, it is possible to perform a good operation without being affected by the influence.

That is, in the above-described apparatus, when the evaluation value including the flicker as shown in FIG. 3A is supplied from the integrating circuit (7), for example, three fields of the supplied value are averaged, so that the average is obtained. The values are as shown in FIG. B, and the influence of flicker is removed.

Therefore, by using this apparatus, extremely stable and good autofocus can be performed.

The number of fields (n) for performing the above-mentioned averaging is suitably three fields in the case of the above-described fluorescent lamp illumination.

On the other hand, for example, when a CCD image pickup device is used and a signal level difference occurs between odd and even fields, flicker of a two-field cycle occurs. Averaging is required.

Furthermore, averaging of these least common multiples of 6 fields is required to remove flicker from both this and the fluorescent lamp described above.

In addition, there are flickers due to circuit noise and the like, and elimination of these requires averaging for as long a period as possible. On the other hand, if the averaging period is lengthened, the responsiveness of the device deteriorates. Considering this, averaging of up to about 6 fields is considered appropriate.

〔The invention's effect〕

According to the present invention, the control is performed using the average value of the evaluation values of a plurality of fields. Therefore, the influence of the flicker of the video signal is removed by the averaging. It is possible to perform a good operation without being affected by the above.

[Brief description of the drawings]

FIG. 1 is a block diagram of an example of an autofocusing device according to the present invention, FIG. 2 is a flowchart of its operation, FIG. 3 is a waveform diagram for explaining the same, FIG. FIG. 5 is a diagram for the explanation, and FIG. 6 is a waveform diagram. (1) is a lens system, (2) is a CCD image sensor, (3) is a signal processing circuit, (4) is an output terminal, (5) is a bandpass filter, (6) is an A / D converter, (7) ) Is an integrating circuit,
(8) is a microcomputer, (9) is a D / A converter,
(10) drive circuit, (11) focus motor, (81)
Is a comparison means, (82) and (84) are memories, and (83) is an averaging means.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 5/232 G02B 7/28 G03B 13/36 H04N 5/235

Claims (1)

(57) [Claims] 1. An auto-focusing device for use in a video camera for sequentially obtaining a captured video signal for each field, wherein the captured video signal is provided for each field in a predetermined range within the field. Integration means for integrating the signal levels of the above, storage means for sequentially storing the evaluation values obtained by the integration, and the latest flicker cycle for each field when the flicker cycle of the photographed video signal is an n-field cycle. Calculating means for summing the evaluation value and the stored evaluation values for the past n-1 fields to obtain an average value divided by n; and comparing the average value with the previous average value for each of the fields An auto-focusing device, comprising: comparing means for controlling the lens system for photographing such that the average value is maximized.