JPH0946571A - Image pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image pickup device capable of operating stable focus adjustment without malfunction even when a focus evaluation fetch range is reduced in response to image magnification processing in an electronic zooming. SOLUTION: The video camera is provided with a gate circuit setting plural fetch ranges F1-F3 in an image pickup pattern, an AF evaluation value processing circuit 115 extracting a high frequency component in a video signal at each fetch range as a focus evaluation value, a focus adjustment function moving a focus lens so as to maximize the focus evaluation value for the focus adjustment, an image magnification function consisting of a field memory 116 and an interpolation circuit 117, and a camera AF microcomputer 118 having a function for revising a fetch range to be used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an autofocus device used for various video cameras and the like.

[0002]

2. Description of the Related Art In recent years, the progress of video equipment such as video cameras has been remarkable,
Auto iris control, high-magnification zoom function, and electronic zoom function that electronically magnifies images by image processing are standard equipment, improving operability and increasing multifunctionality in all parts. .

[0003] By the way, looking at the autofocus device,
A method in which the sharpness of the screen is detected from the video signal obtained by photoelectrically converting the subject image with an image sensor, etc., and the focus lens position is controlled to maximize it, and focus adjustment is performed. Is becoming mainstream.

As the evaluation of the sharpness, generally, the level (focus voltage) of the high frequency component of the video signal extracted by the band pass filter of a certain band is used.

This is because when a normal subject image is taken,
As shown in FIG. 2, the level of the high-frequency component (focus voltage) increases as the focus is achieved, and the point at which the level becomes maximum is the in-focus position.

The range for capturing the focus voltage is usually set near the center of the finder screen. This is empirically determined because the photographer often places the subject he or she normally wants to photograph in the center of the viewfinder screen.

FIG. 3 shows a focus evaluation value fetch range for a normal image pickup screen. As described above, the focus evaluation value acquisition range is usually set near the center of the image pickup screen. Here, 301 is an imaging screen, 302 is a focus evaluation value acquisition range, for example, three areas F
1, F2, F3, and the focus evaluation values of each area are f1, f2, and f3.

Usually, AF control is performed so that the focus evaluation value f2 in the central capture area F2 is maximized.

When there is no suitable subject image in the central capture area F2 and the focus evaluation value f2 is low and focusing cannot be performed, three focus evaluation value acquisition areas F2 are obtained.
Average of focus evaluation values in 1, F2, F3 (f1 + f2 + f
3) / 3 is used to perform AF control.

Next, considering an electronic zoom for electronically enlarging an image, enlarging an image by the electronic zoom is a process of reading out a part of the original image within one screen and enlarging it. Therefore, the imaging range after the electronic zoom processing is greatly reduced to the original image of one screen.

Therefore, when the enlargement process is performed by the electronic zoom, if the focus evaluation value acquisition range before the enlargement is used as it is, the focus evaluation value acquisition range includes information outside the imaging range after the electronic zoom. There is a risk that a subject outside the imaging range is in focus and an erroneous operation such as blurring of the image within the imaging range occurs.

Therefore, when the image is magnified by the electronic zoom, the applicant of the present invention reduces the focus evaluation value acquisition range in accordance with the enlargement ratio, and the focus evaluation value acquisition range is set after the electronic zoom. An image pickup apparatus has been previously proposed that prevents malfunction of AF by not including information outside the image pickup range.

FIG. 4 shows a focus voltage fetch range with respect to an image pickup screen which is magnified twice by electronic zoom. Here, 301 is the imaging range before expansion,
Reference numeral 401 is an enlarged imaging range, and 402 is a focus evaluation value acquisition range. As a result, it is possible to prevent an erroneous operation in which the image is out of focus even during the electronic zoom.

[0014]

However, the above example has the following drawbacks. That is, when the capture range is reduced during electronic zooming as shown in FIG. 4, for example, when the image is magnified twice by electronic zooming, the fluctuation of the image pickup screen is smaller than normal for a constant movement of the subject. Doubled.

Therefore, since the fluctuation of the focus evaluation value due to the change of the subject also becomes large, if the focus lens is moved by the increase or decrease of the focus evaluation value, there is a risk of causing an erroneous operation in which the focus lens moves in the wrong direction and appears fluffy. is there.

Therefore, an object of the present invention is to provide an image pickup apparatus capable of performing stable focus adjustment operation without malfunction even when the focus evaluation value acquisition range is reduced in accordance with image enlargement processing by electronic zoom operation. To do.

[0017]

In order to solve the above-mentioned problems, according to the invention described in claim 1 of the present application, a plurality of capturing ranges for capturing a video signal at a plurality of positions within a photographing screen are set. A capturing range setting means, an extracting means for extracting a predetermined high frequency component as a focus evaluation value from a video signal corresponding to an arbitrary capturing range among the plurality of capturing ranges, and a focus adjusting member in the optical axis direction. Moving means for moving, focus adjusting means for moving the focus adjusting member so as to maximize the focus evaluation value for focus adjustment, image enlarging means for electrically enlarging an image in the photographing screen, The size of the capture range is changed according to the enlargement ratio of the enlargement unit, and the control unit for changing the capture range to be used is provided.

According to a second aspect of the present invention, in the first aspect, the control means is configured to enlarge the capture range by the image enlarging means as the enlargement ratio increases. It is configured to reduce so that it fits within the angle of view.

According to a third aspect of the present invention, in the first aspect, when the image enlarging means is in a non-operating state, the control means controls the central capture range of the plurality of capture ranges. The focus adjusting means is controlled based on the focus evaluation value corresponding to the inside, and when the image enlarging means is in the operating state, the focus adjusting means is based on the average value of the focus evaluation values in each of the plurality of capturing ranges. Are configured to control.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an example of an image pickup apparatus according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing an example of the configuration when the present invention is applied to a video camera.

In the figure, 101 is a fixed first lens group, 102 is a zoom lens for zooming, 103 is a diaphragm, and 1 is a diaphragm.
Reference numeral 04 denotes a fixed second lens group, and reference numeral 105 denotes a focus compensating lens (hereinafter referred to as a focus lens) as a focus adjusting member having both the function of correcting the movement of the focal plane due to zooming and the function of focusing.

Reference numeral 106 denotes an image pickup device such as CCD, 107
Is an AGC amplifier that amplifies the image pickup signal output from the image pickup element 106 and controls it so as to be constant at a predetermined level.

Reference numeral 108 denotes a camera signal processing circuit, which is an AG
With respect to the image pickup signal output from the C amplifier, a luminance signal,
A camera signal processing circuit that performs predetermined signal processing such as generation of color difference signals, gamma conversion, blanking processing, etc. to convert to a standardized video signal, and 109 is a camera signal processing circuit 10.
8 is a storage device such as a VTR for recording the video signal output from the device 8.

Reference numeral 120 is a camera signal processing circuit 108.
It is an electronic viewfinder (EVF) as a monitor for displaying the video signal output from the device.

Reference numerals 110 and 112 respectively denote a variable power lens 10.
2. Actuators such as step motors for moving the focus lens 105, and 111 and 113 are drivers for driving the actuators 110 and 112 by signals from a camera AF microcomputer 118, which will be described later. These actuators constitute the moving means of the present invention.

Reference numeral 114 denotes a gate circuit which passes only a signal corresponding to an image pickup signal output from the AGC amplifier 107 and which corresponds to a capture range used for focus detection in a photographing screen, and controls the opening / closing timing of the gate circuit 114. By doing so, it is possible to extract an imaging signal corresponding to an arbitrary capture range within the shooting screen. The opening / closing timing of the gate circuit 14, that is, the focus evaluation value fetching range within the image pickup screen is controlled by the camera AF microcomputer 118 described later.

Further, 115 extracts a high-frequency component that changes according to the focus state as a focus evaluation value from the image pickup signal corresponding to the focus evaluation value fetching range in the photographing screen extracted by the gate circuit 114. It is an AF evaluation value processing circuit. The output of the AF evaluation value processing circuit 115 is supplied to a camera AF microcomputer 118 described later.

The gate circuit 114 and the AF evaluation value processing circuit 115 constitute the extraction means of the present invention.

Reference numeral 116 denotes a video signal composed of a luminance signal and a color signal generated by the camera signal processing circuit 108.
A field memory 117 which stores fields and whose reading and writing are controlled by a camera AF microcomputer 118 described later is designated by a field memory 116 by a signal from the camera AF microcomputer 118 described later.
It is an interpolation circuit that interpolates the video signal read from
The field memory 116 and the interpolation circuit 117 constitute the image enlarging means of the present invention for realizing the image enlarging process, that is, the electronic zoom function.

Reference numeral 118 denotes a camera AF microcomputer that controls the AF system and the electronic zoom function in addition to controlling the entire system, and controls the driver 113 based on the output signal of the AF evaluation value processing circuit 115. By driving the actuator 112, the focus lens 105 is moved in the optical axis direction to perform the AF operation.

The focus lens can be positioned at the in-focus point by adjusting the focus lens so that the level of the focus evaluation value output from the AF evaluation value processing circuit 115 becomes maximum. This function corresponds to the focus adjusting means in the present invention.

The driver 111 is controlled according to the operation state of the zoom switch 119, and the actuator 110
To drive the variable power lens 102 to perform an optical zoom operation. Then, when the variable power lens 102 is driven to the tele side and the variable power lens 102 reaches the optical tele end and becomes inoperable further, it shifts to the electronic zoom operation and electronic image enlargement processing is performed. Is executed.

Regarding the electronic zoom function, the read-out range of the image signal for one field stored in the field memory 116 is reduced to be smaller than the size of one screen (as the enlargement ratio of the electronic zoom increases, The read-out range becomes smaller) and the read-out rate when reading the image within the read-out range is changed, so that the reduced read-out range can be enlarged and displayed in the size of the actual monitor screen. As a result, a specific portion is substantially enlarged and displayed from the image for one screen. Camera AF microcomputer 118
Controls the read range and read rate of the image from the field memory 116 according to the enlargement ratio of the electronic zoom, that is, the magnification.

Further, the interpolation circuit 117 causes a loss of information between pixels and between scanning lines caused by enlarging the image read from the field memory 116 to the size of an actual monitor screen, for example, on both sides thereof. By performing an interpolation process of replacing with an average value of information of pixels and scanning lines, deterioration of image quality due to enlargement processing is prevented.

Further, an electronic zoom mode is provided which enables execution of electronic zoom processing regardless of the optical zoom, and the field switch 116 is operated by inputting the zoom switch 119.
Alternatively, the interpolation circuit 117 may be controlled to enlarge or reduce the image pickup screen.

As will be described later, the camera AF microcomputer 118 controls the gate circuit 114 to change the capture range of the focus evaluation value to optimize it when performing the electronic zoom operation. I do.

The video camera, which is one of the embodiments of the present invention, has the above-mentioned configuration. Next, the feature of the present invention is to focus on the electronic zoom operation performed in the camera AF microcomputer 118. The control of the acquisition range of the evaluation value signal will be described with reference to the flowchart shown in FIG. The control means in the present invention is realized by the function of the camera AF microcomputer that performs this processing.

The flowchart of FIG. 5 shows a case where the electronic zoom function is operated by operating the zoom switch 119 in the electronic zoom operation area.

In the flowchart of FIG. 5, when the process is started, the operation state of the zoom switch 119 is read in step 501, and the zoom switch 119 is read in step 502.
It is determined whether or not the tele side is pressed. If not, the process proceeds to step 503, and if it is pressed,
The process moves to step 505.

In step 503, it is determined whether or not the wide side of the zoom switch is pressed, and if it is pressed, step
Move to processing of 504, and if not pressed, step 50
The processing shifts to 6.

At step 504, since the zoom operation is performed on the wide side, the enlargement ratio is reduced. At step 505, since the zoom operation is performed on the tele side, the enlargement ratio is increased, and the process proceeds to step 506.

In step 506, the enlargement ratio set by the zoom switch 119 is sent to the field memory 116 and the interpolation circuit 117, and as described above, the read range corresponding to the enlargement ratio is set in the field memory 116 and the enlargement is performed. The electronic zoom operation is executed by instructing the interpolation circuit 117 of the information lacking portion corresponding to the magnification and interpolating the enlarged image.

In step 507, the gate area control information of the gate circuit 114 for setting the focus evaluation value fetching range to the optimum value is calculated according to the magnification of the electronic zoom determined in the processing up to now, and it is determined in step 508. The gate area control information is sent to the gate circuit 114 to set the focus evaluation value fetch area.

That is, as the enlargement ratio of the electronic zoom increases, the read range in the original screen is reduced, so the capture range of the focus evaluation value is also reduced in accordance with the reduction of the read range, and the capture range is the read range. It is controlled so as not to include outside information.

Further, the camera AF microcomputer 118 controls so that the ratio of the focus evaluation value fetch range to the image pickup range is always constant regardless of whether the image pickup range is expanded by the electronic zoom or not. The electronic zoom is turned on / off.
F, the focus evaluation value always corresponding to the imaging range does not cause a sudden change in the focus adjustment state or a malfunction such as focusing on a subject different from the imaging range, even when the magnification of the electronic zoom changes. The focus adjustment state based on the capture range can be stably executed, and stable imaging operation can be performed.

With the above processing, reliable focus adjustment can be realized without focusing outside the screen even during electronic zooming.

In step 509, a focus evaluation value (high frequency component in the video signal) corresponding to the focus evaluation value acquisition range set in step 508 is acquired from the AF evaluation value processing circuit 115, and in step 510, the focus evaluation value is maximum. Then, the driver 113 and the actuator 112 are controlled to drive the focus lens 105 to a focal point.

By repeating the above operation, the AF evaluation value is captured while optimizing the setting of the focus evaluation value capture range according to the electronic zoom magnification, and the focus is displayed outside the screen even during the electronic zoom. It is possible to realize a reliable focus adjustment without causing a mismatch, and to always perform stable AF control with high accuracy and without malfunction, regardless of the magnification of the electronic zoom and its change.

The essential points of the present invention will be described below. The st
FIG. 6 shows a flowchart explaining the ep 509 in detail. In step 601, it is determined whether or not the electronic zoom is being performed. If the electronic zoom is not being performed, the process proceeds to step 602, and if the electronic zoom is being performed, the process proceeds to step 603. In step 602, the value f1 in the central capture range is used as the evaluation value. step
In 603, the average value (f1 + f2 + f3) / 3 of the three capture ranges is used as the evaluation value. step
At 604, it is determined whether the evaluation value determined at step 602 or step 603 is smaller than the previous value,
If it is increasing, go to step 606, while if it is decreasing,
After reversing the drive direction of the focus lens in step 605
Go to step 606. In step 606, the focus lens is driven by a predetermined amount. Then the processing is exited.

That is, when the image is enlarged by the electronic zoom operation, the focus evaluation value acquisition range is reduced so that it is within the enlarged angle of view, and the information outside the picked-up image screen is focused and picked up. It is possible to prevent erroneous operations such as blurring of the image on the screen, and increase the change in the focus evaluation value due to the reduction of the capture range by changing the capture range to be used from a plurality of capture ranges ( In the present embodiment, F1, F2, and F3 are used as average values of all focus evaluation values to average partial changes, and the correction is performed, so that the operation is stable without malfunction and the focus is fluffy. It is possible to realize reliable focus adjustment without any problems.

[0052]

As described above, according to the invention described in claim 1 of the present application, the size of the focus evaluation value fetching range and the fetching range to be used are changed according to the enlargement ratio of the image. Therefore, even during the electronic zoom, it is possible to realize a reliable focus adjustment without focusing out of the screen, and prevent a malfunction due to a change in the focus evaluation value due to a change in the size of the capturing range. Therefore, it is possible to always perform stable AF operation with high accuracy and without malfunction.

According to the second aspect of the present invention, as the enlargement ratio increases, the capture range is reduced so as to be within the angle of view after enlargement by the image enlarging means. Even during the electronic zoom, it is possible to achieve reliable focus adjustment without focusing outside the screen, and to prevent malfunctions due to changes in the focus evaluation value due to changes in the size of the capture range. Therefore, it is possible to always perform a stable AF operation with high accuracy and without malfunction.

According to the invention of claim 3 in the present application, when the image enlarging means is in the non-operating state, the focus adjustment is performed based on the focus evaluation value corresponding to the central capture range of the plurality of capture ranges. When the image enlarging means is in the operating state, the focus adjusting means is controlled based on the average value of the focus evaluation values in each of the plurality of capture ranges. It is possible to prevent a malfunction due to a change in the focus evaluation value when the size of is changed, and it is possible to always perform a stable AF operation with high accuracy and without malfunction.

As described above, by changing the range in which the focus voltage used during the electronic zoom is taken in, the focus is prevented from becoming fluffy, and reliable focus adjustment can be realized.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a focus lens position and a focus evaluation value.

FIG. 3 is a diagram showing a focus evaluation value acquisition range for a normal screen.

FIG. 4 is a diagram showing a focus evaluation value acquisition range for a screen enlarged by electronic zoom.

FIG. 5 is a flowchart showing a control operation of the camera AF microcomputer according to the embodiment of the present invention.

FIG. 6 is a flowchart for explaining the AF control shown in the flowchart of FIG. 5 in the embodiment of the present invention.

[Explanation of symbols]

 102 variable magnification lens 105 focus lens 106 image sensor 108 camera signal processing circuit 114 gate circuit 115 AF evaluation value processing circuit 116 field memory 117 interpolation circuit 118 camera AF microcomputer 119 zoom switch 120 electronic viewfinder

Claims (3)

[Claims] 1. A capture range setting means for setting a plurality of capture ranges for capturing a video signal at a plurality of positions within a shooting screen, and a video signal corresponding to an arbitrary capture range of the plurality of capture ranges. Extraction means for extracting a predetermined high frequency component from the inside as a focus evaluation value, moving means for moving the focus adjustment member in the optical axis direction, and focus adjustment by moving the focus adjustment member so as to maximize the focus evaluation value. Focus adjusting means for performing, an image enlarging means for electrically enlarging the image in the photographing screen, and changing the size of the capture range according to the magnification rate by the magnifying means, the capture range to be used An image pickup apparatus comprising: a control unit that changes the image pickup apparatus. 2. The control unit according to claim 1, wherein the control unit reduces the capture range so as to be within the angle of view after being enlarged by the image enlarging unit as the enlargement ratio increases. An image pickup apparatus comprising: 3. The focus control unit according to claim 1, wherein when the image enlarging unit is in a non-operating state, the control unit determines the focus based on a focus evaluation value corresponding to a center capture range of the plurality of capture ranges. The adjusting means is controlled, and when the image enlarging means is in an operating state, the focus adjusting means is controlled based on an average value of focus evaluation values in each of the plurality of capturing ranges. Image pickup device.