JP2721471B2 - Automatic focusing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focusing device using a video signal.

[0002]

2. Description of the Related Art In an apparatus having a two-dimensional image pickup device such as a video camera, the sharpness of a screen is detected from a video signal of a subject image, and the position of a focusing lens is controlled so that the sharpness is maximized. Is known.

In general, the sharpness is evaluated by measuring the intensity of a high-frequency component of a video signal extracted by a band-pass filter (hereinafter abbreviated as BPF) or the blur width detection intensity of a video signal extracted by a differentiating circuit or the like. Use the sharpness signal. This is because when a normal subject is photographed, it is small when the subject is out of focus, increases when the subject is in focus, and reaches a maximum value when the subject is completely focused.

Accordingly, the focus lens is controlled such that, when the sharpness is small, the focusing lens is moved as quickly as possible in the direction in which the sharpness is increased, and slowly as the sharpness is increased, so that the focusing lens is accurately stopped at the top of the mountain. Control. Such an auto focus (hereinafter referred to as AF) method is referred to as a hill climbing auto focus (hereinafter referred to as hill climbing A).
F).

When a stepping motor is used to drive the focus lens, the position of the focus lens can be accurately detected. Therefore, when the sharpness signal has the maximum value as shown in FIG. When the sharpness signal is shifted below the maximum value by a predetermined value TH1 and the stored maximum value is returned to the focus lens position at the time of detection, the focus lens is moved to the sharpness signal. I try to stop at the peak of the mountain.

[0006]

However, in an automatic focusing apparatus using a video signal, there is a strong dependence on the subject, and as shown in FIG. May be smooth and uneven, and the sharpness signal may not fall below a certain value TH1. In such a case, there has been a problem that the focusing point cannot be found without performing the process of returning the focus lens to the focus lens position where the maximum value is obtained, and hunting occurs.

If the predetermined value TH1 is set to a sufficiently small value in order to prevent this, in the case of a normal subject image, it immediately exceeds the predetermined value TH1 due to noise or the like, and the operation becomes extremely unstable.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and is characterized by extracting means for extracting a focus signal corresponding to sharpness from a video signal. Driving means for driving the focus lens, position detection means for detecting the position of the focus lens, and driving the focus lens by controlling the drive means in accordance with the level of the focus signal, and driving the focus lens. The focus lens position when the signal level reaches the maximum value is stored, and the drive direction of the focus lens is reversed when the focus signal is lower than the maximum value by a predetermined level to the stored focus lens position. Control means for driving the focus lens;
When the drive state of the focus lens is detected, and the drive direction of the focus lens is inverted a predetermined number of times,
Level control means for changing the predetermined level in a decreasing direction.

Another feature of the present invention is that the level control means is controlled based on depth of field information, and the predetermined level is reduced when the depth of field becomes deep. In the focus device.

Another feature of the present invention is that the level control means controls the number of reversals of the driving direction of the focus lens and depth of field information, and controls the number of reversals of the driving direction of the focus lens. Is smaller than a predetermined number of times, or when the depth of field becomes deeper, the above-mentioned predetermined level is reduced.

[0011]

As a result, a stable AF operation can be performed without hunting even in the case of a special subject in which the peak of the focus signal is gentle.

Also, by controlling the predetermined level controlled by the past focus lens driving direction reversal information based on the aperture information, the focus signal has a gentle peak and a large depth of field when the aperture is narrowed. Even in the situation, hunting to the subject image can be prevented.

[0013]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of an automatic focusing apparatus according to the present invention.

FIG. 1 is a block diagram showing the configuration of an automatic focusing apparatus according to the present invention. In the figure, 1
Denotes a fixed front lens constituting the first group lens, and 2 denotes the second lens.
The zoom operation is performed via the motor 16 and the motor drive circuit 13 by the zoom lens constituting the group lens. Reference numeral 3 denotes an aperture, 4 denotes a fixed third group lens, and 5 denotes a focus lens, which performs focus adjustment via a stepping motor 18 and a motor drive circuit 15. Reference numeral 6 denotes an image pickup device such as a CCD, 7 denotes a preamplifier, 8 denotes a video signal processing circuit which performs predetermined signal processing on a video signal output from the preamplifier 7 to convert it into a standardized video signal, and outputs VO. Signal output terminal.

Reference numeral 9 denotes an aperture control circuit for controlling the drive circuit 14 and the ig meter 17 to automatically control the aperture 3 so that the level of the video signal is kept at a predetermined level.

Reference numeral 10 denotes a gate circuit which gates only a video signal corresponding to a predetermined distance measuring frame set in the imaging plane from video signals from the preamplifier, and 11 denotes a sharpness required for performing focus detection. Is a band-pass filter (BPF) for extracting a high-frequency component as an evaluation value representing.

The sharpness signal output from the bandpass filter is supplied to a system control circuit 12 comprising a microcomputer for controlling the entire lens system including the AF operation.

Reference numeral 19 denotes a zoom encoder for detecting the position of the zoom lens 2, ie, focal length information; 20, an aperture encoder for detecting the aperture value of the aperture 3; 21, a focus encoder for detecting the movement position information of the focus lens 5. And the respective detection information is also stored in the system control circuit 1.
2 is input.

The system control circuit 12 performs the following AF control based on the values of the bandpass filter 11 and the encoders, and moves the focus lens to the focal point.

FIG. 2 shows a flowchart of the processing performed in the system control circuit 12, which is a feature of the present invention.

Referring to FIG. 1, first, in step 201, a sharpness signal is transmitted from the bandpass filter 11, aperture information is transmitted from the aperture encoder 20, focal length information is transmitted from the zoom encoder, and focus lens position information is transmitted from the focus encoder 21. The hill-climbing AF operation is performed so that the level of the capture and sharpness signal increases.

Here, regarding the focus lens position information, if a stepping motor is used, the focus lens position can be determined by counting the number of driving pulses, so that accurate and accurate information can be obtained. Here, the focus lens position information is expressed as an address.

At step 202, it is determined whether or not the sharpness signal Fa is larger than the previous sharpness signal peak Fa-p.
If it is larger, the process proceeds to step 203, where Fa and the address Ad at that time are Fa-p and peak value address Ad-p, respectively.

Subsequently, in step 204, it is determined whether or not the focus lens has reversed the direction twice during the hill-climbing AF, and if so, in step 206, a predetermined value TH for focusing lens reversal is set to TH2. If not, at step 205, the predetermined value TH is set to TH1.
Set. The fact that the focus lens performs direction reversal twice means that the subject is a special subject with low contrast or high luminance, and the shape of the peak of the sharpness signal is as shown in FIG.
It is assumed that the sharpness signal Fa does not decrease by the predetermined value TH1 and the predetermined value TH is switched to TH2 (<TH1).

In step 207, it is determined whether or not the difference value dFa-p between Fa-p and Fa is smaller than a predetermined value TH.
Proceed to 1.

At step 208, it is determined whether or not the focus lens position is at the infinite end. If the focus lens position is at the infinite end, the process proceeds to step 210 to reverse the drive direction of the focus lens.
Returning to step 201, the hill climbing operation is continued.

If the focus lens position is not at the infinite end in step 208, the flow advances to step 209 to determine whether or not the focus lens position is at the closest end. If it is at the near end, the process proceeds to step 210, reverses the direction, returns to step 201, and continues the hill climbing operation. If it is not the closest end, the flow returns to step 201 without reversing the direction, and the hill climbing operation is continued in the forward direction.

If the difference dFa-p between Fa-p and Fa is equal to or larger than the predetermined value TH in step 207, the process proceeds to step 211 to drive the focus lens to the position of Ad-p. And that position is focused.

As described above, when the peak of the sharpness signal is gentle and the direction inversion is performed twice while climbing the mountain, the difference value of the sharpness signal between the peak and the foot of the mountain is not TH1.
By reducing TH1 to TH2, it is possible to find the focal point at the top of the mountain, and prevent hunting.

<< Other Embodiments >> In the first embodiment, the focus lens repeats the direction inversion twice or more, and the peak of the sharpness signal as shown in FIG. In such a case, the predetermined value TH1 for judging the level of decrease in sharpness for inverting the focus lens after passing the peak value of the peak of the sharpness signal is switched to a smaller value TH2. By changing TH2 according to the depth of field, hunting of a special subject can be prevented in accordance with more photographing environments. Because the position sensitivity of the focus lens changes depending on the depth of field, when the depth of field is shallow, the position sensitivity of the focus lens is large and the sharpness signal changes even with the same amount of driving the focus lens. Is large, and when the depth of field is deep, the position sensitivity of the focus lens decreases, and the change in the sharpness signal decreases even with the same amount of driving the focus lens. This can be seen from the peak of the sharpness signal shown in FIG.
The deeper the depth of field, the smoother the mountain and the smaller the undulation. The second embodiment takes into account the characteristic change due to the depth of field.

FIG. 3 shows the value of TH2 with respect to the depth of field. FIG. 7A shows the depth of field level of the front lens. The smaller the value, the shallower the depth of field, and the larger the value, the deeper the depth of field.

FIG. 6B shows the depth of field of the rear focus lens as in the present embodiment, irrespective of the focal length.

FIG. 3C shows the value of TH2 at the depth of field level, which is shown as a ratio to TH1. Therefore, at the depth of field level 1, TH2 =
TH1 × 0.7. As the depth of field becomes deeper, the peak of the sharpness signal becomes gentler. Therefore, by setting TH2 smaller, it is possible to prevent hunting at a narrowed position.

[0034]

As described above, during the hill-climbing AF, when the focus signal is lowered by a predetermined level from the peak value of the focus signal, the focusing lens is inverted and the stored focus signal is inverted. In an automatic focusing device that performs an operation of driving a focusing lens to an address value when a peak value is obtained, the predetermined level can be reduced according to the number of inversions of the driving direction of the focus lens and according to the depth of field. The convergence of the focus lens can be surely, smoothly, and quickly made to the focal point without causing hunting even for a special subject in which the peak shape of the focus signal is gentle.

[Brief description of the drawings]

FIG. 1 is a block diagram of an automatic focusing device according to the present invention.

FIG. 2 is a flowchart for explaining the operation of the automatic focusing device according to the present invention.

FIG. 3 is a diagram for explaining a second embodiment of the automatic focusing apparatus according to the present invention.

FIG. 4 is a diagram illustrating a relationship between a focus lens position and a change in a sharpness signal for explaining the operation of the automatic focusing apparatus according to the present invention.

Claims (3)

(57) [Claims] An extracting unit for extracting a focus signal corresponding to sharpness from a video signal; a driving unit for driving a focus lens; a position detecting unit for detecting a position of the focus lens; The focus lens is driven by controlling the driving means in accordance with the level of the focus lens, and the focus lens position when the level of the focus signal reaches the maximum value is stored. Control means for reversing the drive direction of the focus lens when lowered to drive the focus lens to the stored focus lens position; detecting the drive state of the focus lens and reversing the drive direction of the focus lens Is performed a predetermined number of times,
An automatic focusing device, comprising: a level control unit that changes the predetermined level in a decreasing direction. 2. An extractor for extracting a focus signal corresponding to sharpness from a video signal, a driving unit for driving a focus lens, a position detection unit for detecting a position of the focus lens, and the focus signal. The focus lens is driven by controlling the driving means in accordance with the level of the focus lens, and the focus lens position when the level of the focus signal reaches the maximum value is stored. Control means for inverting the drive direction of the focus lens when lowered to drive the focus lens to the stored focus lens position; controlling the predetermined level according to the depth of field; And a level control means for changing the predetermined level in a direction to decrease when the depth becomes deeper. . 3. An extracting means for extracting a focus signal corresponding to sharpness from a video signal, a driving means for driving a focus lens, a position detecting means for detecting a position of the focus lens, and the focus signal. The focus lens is driven by controlling the driving means in accordance with the level of the focus lens, and the focus lens position when the level of the focus signal reaches the maximum value is stored. Control means for inverting the drive direction of the focus lens when lowered to drive the focus lens to the stored focus lens position; and adjusting the predetermined level according to the drive state of the focus lens and the depth of field. Control, and when the drive direction of the focus lens is reversed a predetermined number of times, or when the depth of field becomes deeper. Automatic focusing apparatus characterized by comprising a, a level control means for changing the direction to decrease said predetermined level when the.