JPH02217075A - Automatic focusing circuit - Google Patents

Abstract

PURPOSE:To reduce the influence of a background and to attain stable focus control by using an evaluation value obtained by weighting 1st and 2nd evaluation values and adding both values to control the position of a lens. CONSTITUTION:The levels of an intermediate and high frequency components in a brightness signal in a comparatively small focus area A1 formed on the approximate center of a screen 21 are detected and the intermediate and high frequency levels of a brightness signal in a focus area A2 included in a range larger than the area A1 are detected, the integrated value VAL1 of the intermediate and high frequency component levels of the brightness signal in the area A1 is multiplexed by a proper weighting factor (k), the multiplexed value is added to the integrated value VAL2 of the intermediate and high frequency level of the brightness signal in the area A2, and an evaluation value VAL is formed from the added output. The position of the lens is controlled by ascending. Consequently, a background screen is not focused, the effect of the background can be reduced and stable focus control can be attained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an autofocus circuit used for focus control of a video camera.

[Summary of the invention]

This invention provides an autofocus circuit used for focus control of a video camera, in which a first
A second focus area is set in a wider range than the first focus area, and a second focus area is set in a wider range than the first focus area.
A first evaluation value is obtained from the mid-high range components of the video signal within the focus area, a second evaluation value is obtained from the mid-high range components of the video signal within the second focus area, and the first evaluation value and The background glare is reduced by adding the second evaluation value with appropriate weighting and controlling the position of the lens using the evaluation value obtained by the addition.

[Conventional technology]

At the focused point, taking advantage of the fact that the frequency components in the video signal excluding the DC level are maximized, the middle and high frequency components in the video signal within a predetermined focus area are integrated to obtain an evaluation value, and this evaluation value is An autofocus circuit has been proposed that controls the position of the lens to the maximum position to obtain the in-focus position.

In such an autofocus circuit, in order to obtain the focus position where the evaluation value is maximum, successive evaluation values are compared while moving the lens in one direction, and the evaluation value data obtained continuously is So-called hill-climbing control is performed in which a lens position that changes from an increase to a decrease is detected and a lens position where the evaluation value is maximized is searched for.

This mountain climbing control will be explained. Assume now that the relationship between the lens position and the evaluation value has a characteristic as shown in FIG. In FIG. 6, the horizontal axis indicates the lens position, and the vertical axis indicates the evaluation value obtained by integrating middle and high frequency components in the video signal within a predetermined focus area.

In FIG. 6, it is assumed that the lens is moved in one direction, for example, in the direction of arrow P. At this time, the lens position! The evaluation value D1 indicated by 7 and the lens position that follows it! ! ,a. The evaluation value D7.1 indicated by 1 is compared.

Until the lens passes through the lens position lf where the evaluation value is maximum,
Successive evaluation values increase. That is, the evaluation value D
n + 1 is greater than the evaluation value. Lens position is lens position! , the evaluation value starts to decrease. That is, the evaluation value D7.1 becomes smaller than the evaluation value D11.

Therefore, by performing control such as moving the lens in one direction and determining whether or not the successive evaluation values DA and D7.1 turn from increasing to decreasing, the evaluation value can be maximized. Lens position I! , f can be determined to have passed.

However, with this type of conventional autofocus circuit,
If there is another object at a different distance in addition to the subject within the focus area, there is a problem that the subject will not be in focus, but the other object at a different distance will be in focus. Such a phenomenon is called background scratching.

In other words, as shown in FIG.
Assume that a screen in which a subject 101 and a background object 102 are present in the IO is being imaged.

When the subject 101 and the background object 102 are in the focus area AIO in this way, as shown in FIG. A peak occurs at the position f flll, and the lens position I focuses on the subject 102!
, a peak occurs at f12.

In mountain climbing control, the lens is moved in one direction and the successive evaluation values obtained at this time are compared, and the lens position where the continuously obtained evaluation value data changes from increasing to decreasing is detected and the evaluation value is calculated. The lens position where the maximum is the maximum is searched.

Therefore, the initial position of the lens is at position L in FIG.
If it is on the left side (closer distance side) than l+1, the lens position N j that focuses on the subject 101 is N j! The position of the lens can be controlled at tlr. However, if the initial position of the lens is to the right (■ side) of position LIO in FIG.
Lens position 1 to focus on! The position of the lens is controlled toward rIt.

Therefore, in order to improve such background glare, it is conceivable to set the focus area small. If the focus area is set small, only the subject will be within the focus area and no background objects will be present. Therefore, background blur can be reduced.

However, if the focus area is set small, the evaluation value will fluctuate greatly and the lens will become more unstable. Therefore, a problem arises in that stable focus control cannot be performed.

[Problem to be solved by the invention]

In this way, conventional autofocus integrates the mid-high frequency components of the video signal within the focus area to obtain an evaluation value, and uses hill climbing control to detect the position where this evaluation value is maximum to obtain the in-focus position. The circuit has a problem in that so-called background grazing occurs in which a background object is brought into focus.

Furthermore, if the focus area is made smaller in order to be strong against background scratches, a problem arises in that stable focus control cannot be performed.

Therefore, an object of the present invention is to provide an autofocus circuit that can reduce background glare and perform stable focus control.

[Means to solve the problem]

This invention provides a first focus area A approximately in the center of the screen.
1, a second focus area A2 is set in a wider range than the first focus area A1, and a first evaluation value VAL 1 is obtained from the mid-high frequency components of the video signal in the first focus area A1. , second focus area A
The second evaluation value VAL is calculated from the middle and high frequency components of the video signal in 2.
2, the first evaluation value VALI and the second evaluation value VAL2
The autofocus circuit controls the position of the lens using the evaluation value VAL obtained by weighting and adding the first evaluation value and the second evaluation value VAL2. be.

[Effect]

The level of medium and high frequency components in the luminance signal within a relatively small focus area Al located approximately in the center of the screen 21 is detected, and the level of medium and high frequency components in the luminance signal within a focus area A2 which is larger than the focus area A1 is detected. is detected, and the integral value VALI of the level of the middle and high frequency components in the luminance signal in the focus area Al is multiplied by an appropriate weighting coefficient k, and the integral value VAL 1 multiplied by this coefficient k and the luminance signal in the focus area A2 are calculated. The integrated value VAL2 of the middle and high range level is added, and the evaluation value VAL is calculated from this addition output.
is formed. Using this evaluation value VAL, the position of the lens is controlled by mountain climbing control.

〔Example〕

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

FIG. 1 shows an embodiment of the present invention.

In FIG. 1, a subject image is captured by a lens 1, and the subject image through the lens 1 is formed on a CCD image sensor 2. The imaging output of the CCD imaging device 2 is supplied to a video signal processing circuit 3.

The position of the lens l is controlled by a lens drive motor 4. A drive signal is supplied to the lens drive motor 4 from the motor driver 3 .

A video signal processing circuit 3 forms a luminance signal and a chroma signal from the imaging output of the CCD image sensor 1. A luminance signal Y formed by the video signal processing circuit 3 is supplied to a bandpass filter.

Further, the video signal processing circuit 3 outputs horizontal and vertical synchronizing signals 5YNC. This synchronization signal 5YNC is supplied to the focus area control circuit 6. The focus area control circuit 6 generates focus area setting signals SAI and SA2 for setting two focus areas A1 and A2, respectively, as shown in FIG.

As shown in FIG. 2, the focus area A2 is
1, and its size is, for example, 1/4 of the entire screen. The size of this focus area A2 is
This is approximately the same as the focus area of a conventional focus control circuit. Focus area A1 is this focus area A
2, and its size is, for example, 1/4 of the focus area A2.

In FIG. 1, the bandpass filter 7 has a characteristic that allows middle and high frequency components of the luminance signal to pass through. The bandpass filter extracts middle and high frequency components from the luminance signal Y output from the video signal processing circuit 5. The middle and high frequency components in the luminance signal extracted by the bandpass filter 7 are supplied to the detection circuit 8. A detection circuit 8 detects the levels of middle and high frequency components in the extracted luminance signal.

The output of the detection circuit 8 is supplied to an A/D converter 9.

The A/D converter 9 digitizes the detection level of middle and high frequency components in the luminance signal. The output of the A/D converter 9 is supplied to the integrating circuit 10A, and the integrating circuit 10
B is supplied.

A focus area setting signal SAI corresponding to the focus area A1 is supplied from the focus area control circuit 6 to the integrating circuit 10A. The integrating circuit 10A digitally integrates middle and high frequency components in the luminance signal within the focus area A2. This integral value VALI is the coefficient multiplier circuit 11
is supplied to

A focus area setting signal SA2 corresponding to the focus area A2 is supplied from the focus area control circuit 6 to the integrating circuit 10B. The integrating circuit 10B digitally integrates middle and high frequency components in the luminance signal within the focus area A2. This integral value VAL2 is supplied to the adder circuit 12.

The integral value VAL 1 from the integrating circuit 10A is supplied to the coefficient multiplier circuit 11, and the integral value VAL 1 from the integrating circuit 10A is supplied to the coefficient multiplier circuit 11.
The integral value VALI is multiplied by a predetermined coefficient k. The output of the coefficient multiplication circuit 11 is supplied to the addition circuit 12.

The adder circuit 12 calculates the integral value VALI from the integrating circuit 10A.
The integral value k·VALI multiplied by the weighting coefficient k and the integral value VAL2 from the integrating circuit 10B are added. The output of this adder circuit 12 is supplied to the system controller 13 as an evaluation value VAL. That is, an evaluation value VAL of VAL=k·VAL l +VAL 2 is obtained from the output of the adder circuit 12, and this evaluation value VAL is supplied to the system controller 13.

From the system controller 13, the lens drive motor 2
A control signal for controlling the motor is output, and this control signal is supplied to the motor driver 5.

The lens drive motor 4 is rotated based on this control signal, and the position of the lens l is controlled.

The system controller 13 performs mountain climbing control based on the evaluation value VAL from the addition circuit 12. That is, while the lens 1 is moved in one direction, a lens position where the continuous evaluation value VAL changes from increasing to decreasing is detected. Thereby, the position of the lens 1 is controlled to the in-focus position.

As described above, in one embodiment of the present invention, the level of the mid-high frequency component in the luminance signal within the relatively small focus area Al located approximately in the center of the screen 21 is detected, and the level of the mid-high frequency component in the luminance signal is detected within a range larger than the focus area A1. The mid-high range level in the brightness signal in the focus area A2 is detected, and the integrated value VAL1 of the level of the mid-high range component in the brightness signal in the focus area A1 is multiplied by an appropriate weighting coefficient k. The integral value k・VALI and the integral value VAL2 of the mid-high level in the luminance signal within the focus area A2
The evaluation value VAL is formed from the output of this addition. Therefore, focus control that is strong against background glare can be performed.

For example, now, as shown in Figure 3, focus area A
Assume that an image is taken of a screen in which there is a background object 31 in addition to the subject 31.

When capturing an image of such a screen, the level of the middle and high frequency components in the luminance signal in the focus area A2 is determined by the integral value V.
AL2 is the lens position where the subject 31 is in focus, as shown by curve F2 in FIG. A peak occurs at f1, and a peak occurs at lens position lf2 where the background object 32 is focused. - On the other hand, at this time, the integral value VAL 1 of the mid-high range level in the luminance signal within the focus area Al is:
As shown by the curve F1 in FIG. 4, a peak occurs only at the lens position lf1 where the subject 31 is in focus.

Focus area A shown by curve F1 in FIG.
Integral value VAL of the mid-high range level in the luminance signal within l
is multiplied by a weighting coefficient k (for example, = 2) and added to this by the integral value VAL2 of the middle and high frequency level in the brightness signal Y in the focus area A2 shown by the curve F2 in FIG. Evaluation value VA of characteristics as shown by F
L is required. This characteristic, as shown by curve F in FIG. 5, shows that the lens position j! The lens position where a peak occurs only at fl and is focused on the background object 32! f
2, no peak occurred. In addition, with this characteristic, the evaluation value does not change abruptly with respect to changes in the lens position. Therefore, regardless of the initial position of the lens 1, the lens 1 can always be brought into focus on the subject 31, and stable focus control can be performed.

〔Effect of the invention〕

According to this invention, the level of mid-high frequency components in a luminance signal within a relatively small focus area Al located approximately in the center of the screen 21 is detected, and
The mid-high frequency range level in the luminance signal in the focus area A2, which is in a larger range, is detected, and the integrated value VALI of the level of the mid-high frequency component in the luminance signal in the focus area Al is multiplied by an appropriate weighting coefficient k, and this coefficient is calculated. The integral value VALI multiplied by k is added to the integral value VAL2 of the mid-to-high range level in the luminance signal within the focus area A2, and an evaluation value VAL is formed from this addition output. The control controls the position of the lens.

If such an evaluation value is used, the background screen will not be in focus, and background blur can be reduced.

Furthermore, compared to the case where the focus area is made smaller, there is less fluctuation in the evaluation value, and stable focus control can be performed.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an embodiment of this invention, Fig. 2 is a route map used to explain the focus area in an embodiment of this invention, and Fig. 3 is a route diagram used to explain an embodiment of this invention. , FIG. 4, and FIG. 5 are graphs used to explain one embodiment of the present invention. Figure 6 is a graph used to explain mountain climbing control, Figure 7 is a route diagram used to explain a conventional autofocus circuit, and Figure 8 is a graph used to explain mountain climbing control.
The figure is a graph used to explain a conventional autofocus circuit. Explanation of main symbols in the drawings 1: Lens, 2: CCD image sensor, 3: Video signal processing circuit, 6: Focus area control circuit. 7: Bandpass filter, IOA, IOB: Integrating circuit,
11: Coefficient multiplication circuit, 12: Addition circuit. 13 Niji system controller. Agent Patent Attorney Tadashi Sugiura Chitaku Figure 6 Figure 1

Claims (1)

[Claims] A first focus area is set at approximately the center of the screen, a second focus area is set in a wider range than the first focus area, and a video signal within the first focus area is set. A first evaluation value is obtained from the level of the mid-high frequency component, a second evaluation value is obtained from the level of the mid-high frequency component in the video signal within the second focus area, and the first evaluation value and the first evaluation value are obtained from the level of the mid-high frequency component in the video signal within the second focus area. The first evaluation value and the second evaluation value are weighted and added, and the position of the lens is controlled using the evaluation value obtained by weighting and adding the first evaluation value and the second evaluation value. autofocus circuit.