JPH06339058A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To make possible a stable AF operation without generating hunting even when the peak of a definition signal is gentle by changing an inverted threshold according to the inversion state in the driving direction of a focus lens. CONSTITUTION:A signal Fa according to definition is extracted in a BPF 11 from video signals, the signal is inputted in a system control circuit 12 and an AF operation is performed. At this time, when the signal Fa and a peak value Fa-p are compared and the difference value dFa-p becomes a prescribed value TH 1 or more in the down hill method AF operation of the signal Fa, a lens 5 is inverted by a stepping motor 18 and is moved by the positional information from a focus encoder 21 at the location of the Fa-p, and the location is defined as a focusing. When the peak of the signal Fa is gentle and the difference value of the signal Fa of the apex and the foot of the mountain is TH 1 or below, the value is changed to TH+ or -TH 2 and the apex of the mountain is determined. Thus, even for an object where a definition signal is gentle, a stable AF operaction can be performed without generating hunting.

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 a device having a two-dimensional image pickup device such as a video camera, the sharpness of the screen is detected from the video signal of the subject image, and the focusing lens position is controlled so as to maximize the sharpness of the screen for focusing. There is a known method of matching.

As the evaluation of the sharpness, generally, the strength of the high frequency component of the video signal extracted by a bandpass filter (hereinafter abbreviated as BPF) or the blur width detection strength of the video signal extracted by a differentiating circuit is used. Use the sharpness signal. When a normal subject is photographed, this is small when the subject is out of focus, increases as the subject is in focus, and reaches the maximum value when the subject is perfectly focused.

Therefore, the focus lens is controlled so that when the sharpness is small, the focus lens is moved as fast as possible in the direction of increasing, and slowly as it becomes large, the focusing lens is stopped accurately at the top of the mountain. Control. Such an autofocus (hereinafter referred to as AF) method is used as a mountain climbing method.
Abbreviated as F).

When a stepping motor is used to drive the focus lens, the focus lens position can be accurately detected. Therefore, as shown in FIG. 4A, when the sharpness signal has the maximum value. The focus lens position of the sharpness signal is stored by returning the stored maximum value to the focus lens position at the time of detection when the sharpness signal is rotated by a predetermined value TH1 below the maximum value. I try to stop at the peak of the mountain.

[0006]

However, in the automatic focusing apparatus using the video signal, the dependence of the subject is strong, and as shown in FIG. 4B, the sharpness signal is used for the subject with low contrast. In some cases, the mountain itself becomes smooth and has no undulations, and the sharpness signal may not fall below a certain value TH1. In such a case, there is a problem that the focusing point cannot be found and hunting occurs without performing the process of returning the focus lens to the focus lens position where the maximum value is obtained.

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

[0008]

The present invention has been made in order to solve the above-mentioned problems, and is characterized by an extraction means for extracting a signal corresponding to a sharpness from a video signal, Driving means for driving the focus lens, position detecting means for detecting the position of the focus lens, and driving the focus lens by controlling the driving means according to the level of the sharpness signal, The focus lens position when the level of the sharpness signal reaches the maximum value is stored, and when the sharpness signal decreases by a predetermined level from the maximum value, the driving direction of the focus lens is inverted and stored. Control means for driving the focus lens to a focus lens position, and level control means for varying the predetermined level according to the focus lens drive information. In the automatic focusing device provided.

Another feature of the present invention is the automatic focusing device, wherein the level control means is configured to lower the predetermined level when the focus lens has been inverted a predetermined number of times or more.

Another feature of the present invention is an automatic focusing device, wherein the level control means is configured to change the predetermined level based on the focus lens drive information and aperture information.

[0011]

As a result, even in the case of a special subject where the peak of the sharpness signal is gentle, hunting does not occur and stable AF operation can be performed.

Further, by controlling the predetermined level controlled by the past focus lens driving direction reversal information by the aperture information, it is possible to prevent hunting of an object whose aperture of the sharpness signal is gently narrowed.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The position embodiment of the automatic focusing device according to the present invention will be described in detail below with reference to the drawings.

<< First Embodiment >> FIG. 1 is a block diagram showing the structure of an automatic focusing apparatus according to the present invention. In the figure, 1
Is a fixed front lens that constitutes the first lens group, and 2 is the second lens
A zoom lens forming a group lens performs a zoom operation via a motor 16 and a motor drive circuit 13. Reference numeral 3 is a diaphragm, 4 is a fixed third lens group, and 5 is a focus lens for performing focus adjustment via a stepping motor 18 and a motor drive circuit 15. 6 is an image pickup device such as a CCD, 7 is a preamplifier, 8 is a video signal processing circuit for performing a predetermined signal processing on the video signal output from the preamplifier 7 to convert it into a standardized video signal and outputting it, and VO is a video This is a signal output terminal.

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

Reference numeral 10 denotes a gate circuit which gates only a video signal from the video signal from the preamplifier, which video signal corresponds to a predetermined distance measuring frame set on the image pickup surface, and 11 denotes a sharpness necessary for focus detection. Is a band pass filter (BPF) for extracting a high frequency component as an evaluation value representing

Further, the sharpness signal output from the band pass filter is supplied to a system control circuit 12 which is composed of a microcomputer which controls the entire lens system including the AF operation.

Reference numeral 19 is a zoom encoder for detecting the position of the zoom lens 2, that is, focal length information, 20 is an aperture encoder for detecting the aperture value of the aperture 3, and 21 is a focus encoder for detecting the movement position information of the focus lens 5. And each detection information is also the system control circuit 1
Entered in 2.

The system control circuit 12 performs AF control as described below based on the values of the bandpass filter 11 and each encoder, and moves the focus lens to a focal point.

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

In the figure, first, in step 201, the sharpness signal from the band pass filter 11, the aperture information from the aperture encoder 20, the focal length information from the zoom encoder, the focus lens position information from the focus encoder 21 and the like, respectively. The hill climbing AF operation is performed so that the level of the captured and sharpness signal is increased.

With respect to the focus lens position information, if the 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, this focus lens position information is expressed as an address.

At step 202, it is judged whether the sharpness signal Fa is larger than the sharpness signal peak Fa-p so far,
If it is larger, the process proceeds to step 203, where Fa and address Ad are Fa-p and peak value address Ad-p, respectively.

Then, in step 204, it is judged whether or not the focus lens is reversing the direction twice during the hill climbing AF. If it is, the predetermined value TH for reversing the focus lens is set to TH2 in step 206. If not, in step 205, TH1 is also set to the predetermined value TH.
To set. The fact that the focus lens performs direction reversal twice means that the subject is a special subject with low contrast and high brightness, and the peak shape of the sharpness signal is shown in FIG.
It is assumed that the sharpness signal Fa does not fall by the predetermined value TH1 as described above, and the predetermined value TH is switched to TH2 (<TH1).

At step 207, it is judged whether or not the difference value dFa-p between Fa-p and Fa is smaller than a predetermined value TH. If it is smaller, step 208 is given. If it is larger, step 21 is given.
Go to 1.

In step 208, it is determined whether or not the focus lens position is at the infinite end, and if it is the infinite end, the process proceeds to step 210 to reverse the driving direction of the focus lens,
Returning to step 201, the mountain climbing operation is continued.

If the focus lens position is not at the infinite end at step 208, the process proceeds to step 209 to determine whether the focus lens position is at the closest end. If it is at the very close end, the process proceeds to step 210, the direction is reversed, the process returns to step 201, and the hill climbing operation is continued. If it is not the closest end, the direction is not reversed and the process returns to step 201 to continue the hill climbing operation in the forward direction.

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

As described above, when the peak of the sharpness signal is gentle and the direction is reversed twice during climbing, the difference value of the sharpness signal at the apex and the skirt of the mountain is not TH1 minutes.
By reducing TH1 to TH2, the focal point at the top of the mountain can be found and hunting can be prevented.

<Other Embodiments> In the first embodiment, the focus lens repeats direction inversion twice or more, and the peak of the sharpness signal as shown in FIG. 4B is gentle and the contrast is low. In such a case, the predetermined value TH1 for judging the sharpness reduction level for reversing 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 depending on the depth of field, it is possible to prevent hunting of a special subject according to more shooting environments. Since 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 drive amount of the focus lens. Is large, the position sensitivity of the focus lens is small when the depth of field is deep, and the change in the sharpness signal is small even with the same drive amount of the focus lens. This is seen in the peak of sharpness signal as shown in FIG.
It means that the deeper the depth of field is, the smoother the mountain becomes and the less undulating it becomes. The second embodiment considers the characteristic change due to the depth of field.

FIG. 3 shows the value of TH2 with respect to the depth of field. The figure (a) is the depth of field level in the front lens, the smaller the value, the shallower the depth of field, and the larger the value, the deeper.

FIG. 6B shows the depth of field level in the rear focus lens as in this embodiment, which is not related to the focal length.

The figure (c) shows the value of TH2 at the depth of field level, which is shown as a ratio to TH1. Therefore, at depth of field level 1, TH2 =
TH1 x 0.7. Since the peak of the sharpness signal becomes gentler as the depth of field becomes deeper, it is possible to prevent hunting at a narrowed position by setting TH2 smaller.

[0034]

As described above, during hill climbing AF, the focus lens is inverted and stored when the sharpness signal decreases by a certain threshold value from the peak value of the sharpness signal. When the focus lens is driven to the address value when the peak value of the sharpness signal is obtained, the sharpness can be reduced by decreasing the threshold value by reversing the driving direction of the focus lens. It is possible to move the focus lens to the in-focus point reliably, smoothly and quickly without causing hunting even for a special subject having a gentle signal peak shape.

[Brief description of 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 device according to the present invention.

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

Claims (3)

[Claims] 1. Extraction means for extracting a signal corresponding to sharpness from a video signal, driving means for driving a focus lens, position detection means for detecting the position of the focus lens, and the sharpness. The driving means is controlled according to the level of the signal to drive the focus lens, and the focus lens position when the level of the sharpness signal reaches the maximum value is stored, and the sharpness signal is stored as When the predetermined level is reduced from the maximum value, the driving direction of the focus lens is reversed to control the focus lens to the stored focus lens position, and the predetermined level is changed according to the focus lens drive information. An automatic focusing device comprising: 2. Extraction means for extracting a signal corresponding to sharpness from a video signal, driving means for driving a focus lens, position detection means for detecting the position of the focus lens, and the sharpness. The driving means is controlled according to the level of the signal to drive the focus lens, and the focus lens position when the level of the sharpness signal reaches the maximum value is stored, and the sharpness signal is stored as When the predetermined level is reduced from the maximum value, the driving direction of the focus lens is inverted to drive the focus lens to the stored focus lens position, and the predetermined level is set by the focus lens drive inversion information. A level control unit that is variable and reduces the predetermined level when the focus lens has been inverted a predetermined number of times or more. Automatic focusing device, characterized in that the. 3. Extraction means for extracting a signal corresponding to sharpness from a video signal, driving means for driving a focus lens, position detection means for detecting the position of the focus lens, and the sharpness. The driving means is controlled according to the level of the signal to drive the focus lens, and the focus lens position when the level of the sharpness signal reaches the maximum value is stored, and the sharpness signal is stored as Based on the focus lens drive information and the aperture information, control means for inverting the drive direction of the focus lens when the predetermined level is reduced from the maximum value and driving the focus lens to the stored focus lens position. An automatic focusing apparatus comprising: a level control unit that changes the predetermined level.