JPH01212981A - Automatic focussing device - Google Patents

Abstract

PURPOSE:To rapidly and smoothly control a focussing by using an optical chromatic aberration such as an image pickup lens and discriminating the direction of the deviation of the focussing based on the comparison of the integrating levels of the high frequency components of plural colors included in the light receiving picture signal of an image pickup element. CONSTITUTION:A focussing is controlled by moving the lens 1 so as to focus the light of a (d) line included in the image pickup light to the image pickup element 2. At the time of the deviation of the focussing of a front pin and a back pin, what is called, the light of a short wavelength side from the light of the (d) line and a long wavelength side, for instance, the light of the F line of 486nm in the wavelength and the light of the C line of 656nm in the wavelength are respectively focussed. Based on the separation or the synthesis of the light receiving picture element signals of respective colors included in the light receiving picture signal of the image pickup element 2, the picture signals of the three colors of the respective light colors of the (d) line, the F line, the C line are separated and extracted by a processing circuit 9 to compare the high frequency components of the (d) line, the F line, the C line, decide the front pin and the back pin and discriminate the deviation of the focussing. Thereby, the lens 1 is automatically focussing controlled rapidly and smoothly.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an autofocus device for a video camera or the like.

[Conventional technology]

Traditionally, color video cameras have been equipped with a solid-state image sensor equipped with a color separation filter, and have also been equipped with a "mountain-climbing" method.
It is equipped with an autofocus device using a control system called .

By the way, the above-mentioned "mountain-climbing method" control is performed by utilizing the characteristic that the high-frequency component of the light-receiving image signal of the image sensor increases as it approaches the in-focus point. Each time, according to the following four operations (1), (ID, GOD, (g)),
Move the imaging lens to the in-focus position.

(1) Initially move the imaging lens toward the near point or far point.

(The direction of movement from the position before movement is determined and determined based on the increase/decrease in the high frequency component of the received light image signal obtained during the initial movement of the ID.

(The imaging lens is moved in the determined movement direction from the position before the IID initial movement, and the inflection point (top) of the received light image signal during movement from increase to decrease is detected.

(1v) Memorize the position of the inflection point, and return the imaging lens to that position and stop.

On the other hand, for example, Japanese Patent Application Laid-Open No. 61-239780 (H0
4N 5/232) uses a vibration mechanism using a piezoelectric element to constantly vibrate the light-receiving surface of the image sensor in the direction of the optical axis of the imaging lens. An autofocus device is described that determines the image pickup lens and moves the imaging lens to a focusing position.

[Problem to be solved by the invention]

By the way, in the case of the conventional "mountain-climbing" autofocus device, the imaging lens is initially moved to determine the direction of defocus, and then the imaging lens is moved to the in-focus position, allowing quick and smooth focus control. There are some problems.

On the other hand, in the case of the autofocus device described in the above publication,
This eliminates the need to determine the direction of defocus, allowing for faster control than a "mountain-climbing" system, but it requires a vibration mechanism such as a piezoelectric element, which complicates the configuration. Depending on the F value, etc., there is a problem in that vibration of the image sensor appears as a flicker phenomenon, especially on the imaging screen of still images, and has an adverse effect on the imaging screen.

SUMMARY OF THE INVENTION An object of the present invention is to provide an autofocus device that performs quick and smooth focus control without providing a vibration mechanism or the like and without adversely affecting an imaging screen.

[Means to solve the problem]

Means for achieving the above object will be explained below with reference to FIG. 1, which corresponds to an embodiment.

The present invention includes a color imaging device (2) that receives imaging light from an imaging lens (1) via a color separation filter, and separates high-frequency components of multiple colors included in a received image signal of the imaging device (2). a bypass filter section (3) for extracting; a discrimination processing section (4) for comparing the integral levels of the respective high frequency components at a constant period to determine the direction of defocus and outputting a single focus control signal; The present invention provides an autofocus device characterized by comprising a lens drive section (5) that moves the lens according to a control signal.

[Effect]

Therefore, based on optical chromatic aberration, the filter section (
The level of the output signal of each color in step 3) changes according to the focal shift of the lens (1), and the processing unit (4)
The direction of defocus is quickly and accurately detected based on a comparison of the integral levels of the output signals of each color at a fixed period. By the operation of (5), lens (1)
is pulled into focus.

〔Example〕

Next, the present invention will be explained in detail with reference to FIGS. 1 to 4 showing an embodiment thereof.

In Fig. 1, (1) is an imaging lens, and (2) is a color imaging device installed at the imaging surface behind the lens (1), which is composed of a solid-state imaging device such as a CCD with a color filter. (All pixels on the light receiving surface are scanned perpendicularly to the optical axis of υ, and in each field,
One field of light-receiving image signals consisting of light-receiving pixel signals of each color is output.

(6) is an image processing circuit that converts the image signal received by the image sensor (2) into a video signal and outputs it, and (7) is a processing circuit (6
) is connected to the synchronous separation circuit, (8) is connected to the synchronous separation circuit (
7), which outputs a gate signal at the timing of the center part of the screen of each field.

(9) is a color-specific processing circuit to which the received light image signal of the image sensor (2) is input, and separates and outputs signal components of three specific colors included in the received light image signal. αQ is a gate circuit connected to the processing circuit (9), and based on the gate signal of the gate circuit (8), outputs only each output signal of the processing circuit (9) at the center of the screen of each field.

aυ, a4. α1 is a processing circuit (
Three bypass filters are inputted with each output signal of (9), and (3) is a bypass filter section consisting of a processing circuit (9), a gate circuit Oq, and a filter aυ~ side.

Q4), Q51, α→ are three detection circuits connected to filters 01) to α], α power, α mark, and θ Samurai are three integration circuits connected to detection circuits Qbro to Q6, respectively. , m, al), (c) are the three A/D conversion circuits connected to the integrating circuits αη to Q'J, respectively, and (c), (c), and (c) are the conversion circuits (a) to ( (a) Three memories connected to each; (a) is a microprocessor (hereinafter referred to as CPU) connected to the memory to (c), and outputs a focusing control signal. (4) is the detection circuit α~0
This is a discrimination processing section consisting of Q, integrating circuits aη~Q, converting circuits 4~ (goods), memories @~(c), and CPUfi.

(C) is a focus motor control circuit into which the focus control signal of the CPU is input, and (2) is a focus motor driven by the control circuit (A), which moves the lens (υ) in the optical axis direction. (5) This is a lens drive unit consisting of a control circuit (A) and a motor (A).

By the way, based on optical chromatic aberration such as the lens (υ), the position of the best image plane @ (position of the circle of least confusion) differs slightly for each wavelength of imaging light.

The optical conditions such as the imaging position where the image sensor (2) is installed are similar to those of general optical equipment, such as light of a specific wavelength,
That is, it is set based on light with a wavelength of 587 nm called d-line.

Therefore, focus control is performed by adjusting the lens (1) so that the d-line light included in the imaging light is focused on the imaging device (2)
This is done by moving the

And when there is a so-called front focus/back focus shift,
Light on the shorter wavelength side and longer wavelength side than the light of di.

For example, F-line light with a wavelength of 4861 m and C-line light with a wavelength of 6561 m are each brought into focus.

That is, let the focal positions of the lens (1) at the position of the subject, front focus, and rear focus be PO, pl, and P2, and d, which passes through the lens (1) and is focused on the image sensor (2). When the optical paths of line, F line, and C line are shown as one-dot dashed line, two-dot dashed line, and dashed line, respectively, when the front focus is on, the optical path of each line becomes as shown in Fig. 2 (a), and when the front focus is In this case, the optical path of each line becomes as shown in FIG.

Therefore, in the case of Fig. 2 (a), (b), and (C), respectively, the field & (phase) is 1;

CfLe+"J-e*昭LK 文ET','f+3 EJ
(4) + Cb), (SuX4zThl knee).

fx b, Figure 3 (a) to (C) Nioite, d, F,
C indicates the levels of the d-line, F-line, and C-line.

Therefore, by comparing the levels of the high frequency components of the three lines of light included in the image signal received by the image sensor (2), the front focus, focus, and back focus of the lens (1) can be identified, and the lens (1)
The direction of defocus can be determined.

Therefore, the processing circuit (9) separates or combines the light-receiving pixel signals of each color included in the light-receiving image signal of the image sensor (2), and calculates the three light colors of each of the D-line, F section, and C-line.
A color image signal is extracted in layers from the received light image signal.

Furthermore, the three color output signals of the processing circuit (9) are input to each of the filters α through the filter α through the gate circuit αq. , gate circuit Oq extracts only the central portion of the screen of each output signal of the processing circuit (9).

Then, the high frequency components of the signals of each color are extracted by the filters αυ~a3, and the high frequency components of each color output from the filters (n)~αυ are detected by the detection circuits Q4)~Qf.
Envelope detection is performed in each of the high-frequency components of each color, and detection signals of the respective levels of the high frequency components of each color are output from the detection circuits α to αQ to the integrating circuits Q''7' to Q.

Furthermore, each of the steep wave signals of each color is integrated by the integrating circuits αη to α1 at a constant period, that is, the period of the l field, and from the integrating circuit αη)01 to the conversion circuit ~(a),
A signal of the integral value of each field of the detection signal of each color, that is, a signal obtained by averaging errors of each color due to color deviation within the imaging region is output, and the signal of each integral value is converted into digital data.

The digital data of the converters (4) to (a) is then sent to the CPU (J) through temporary storage memory to (c).
At this time, the CPU (a) operates according to the flowchart in FIG.

That is, if the digital data of high frequency components of 62g, F line, and C line are Sd, Sf, and Sc, then each data Sd, Sf, and Sc can be expressed as 5d(Sf).
, Sc, then Sf≦Sc, Sf) It is determined that front focus/rear focus is determined by Sc, respectively, and the direction of defocus is determined.

Furthermore, according to the determination result, a focus control signal for moving the lens (1) is output to the control circuit -, and the motor (c) is driven to move the lens (1) toward the far point or near point. , When the peak or inflection point at which the magnitude relationship of the data Sf and Sc is reversed due to the movement is detected, the lens (1) is slightly moved to the position of the inflection point and the movement of the lens (1) is stopped.

Therefore, based on the determination of the direction of defocus using optical chromatic aberrations such as the lens (υ), autofocus of the lens (1) can be performed quickly and smoothly using control that eliminates the initial movement of the conventional "mountain climbing method". Control takes place.

Incidentally, the image signal received by the image sensor (2) is converted into a video signal by the processing circuit (6) and used for recording, and is also used for TTL-! ;C It is supplied to the white balance adjustment circuit and used for white balance adjustment, etc.
The imaging light of the lens (1) is utilized to the maximum extent not only for imaging but also for focus control, white balance adjustment, etc.

Therefore, the optical system and the like can be simplified, and a simple and inexpensive video camera can be provided.

In addition, in the above example, high frequency components of three colors were used, but two
It is also possible to determine the direction of defocus using color or high-frequency components of four or more colors, and in this case, the axiomatic circuit (9)
The types of colors to be separated can be set based on the wavelength used for discrimination, the characteristics of the color separation filter, etc. .

Alternatively, a high frequency component of a color difference signal generated when converting a light-receiving image signal of an image sensor into a video signal may be used.

Furthermore, it goes without saying that a bare I9 tube or the like may be used as the color image sensor.

〔Effect of the invention〕

As described above, according to the focus control device of the present invention,
Controls the focal position of the imaging lens by utilizing optical chromatic aberration of the imaging lens, etc., and determining the direction of defocus based on a comparison of the integration levels of high-frequency components of multiple colors included in the image signal received by the imaging device. As a result, the direction of defocus can be determined quickly and accurately without the need for a vibration mechanism for the image sensor, and with a simple and inexpensive configuration, it can be quickly and smoothly determined without adversely affecting the image capture screen. It is possible to perform focus control.

[Brief explanation of the drawing]

1 to 4 show one embodiment of the autofocus device of the present invention, FIG. 1 is a block diagram, and FIGS. 2(a) to 4
(C) is an explanatory diagram of the shift in focus position due to color, @3 diagram
(C) is an explanatory diagram of the high frequency components of each color in each case of the second fixation) to (C), and FIG. 4 is a flowchart for explaining the operation. (1)...imaging lens, (2)...color image sensor, (3)...bypass filter section, (4)...discrimination processing section, (5)...lens driving section.

Claims (1)

[Claims] (1) a color imaging device that receives imaging light from an imaging lens via a color separation filter; a high-pass filter section that separates and extracts high-frequency components of multiple colors included in a received image signal of the imaging device; and each of the high-frequency components. a determination processing unit that compares integral levels of constant periods of components to determine the direction of defocus and outputs a focus control signal; and a lens drive unit that moves the lens in accordance with the focus control signal. An autofocus device characterized by: