JPH03117182A - Video camera - Google Patents

Abstract

PURPOSE:To eliminate need for any mechanical part, to reduce power consumption and to improve reliability by tilting a solid-state image pickup means by a prescribed angle and comparing high frequency components of image pickup outputs of the solid-state image pickup means focused in the forward and in the backward direction of an object so as to apply focus control. CONSTITUTION:A video output signal from a CCD 3 is fed to a high pass filter HPF 17 through a gate circuit 16 to obtain an automatic focus control signal. Then a high frequency component power for each line is fed to a register 20 registered for 1H period and fed directly to a comparator circuit 21. The comparator circuit 21 compares high frequency power between adjacent lines and gives the result of comparison to a judging circuit 22. The output of the judging circuit 22 is fed to a motor 2e as a focus control signal via an output terminal 23 to move a focus lens 2a in the direction of the arrow thereby making focusing state.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a video camera having an autofocus function.

[Summary of the invention]

The present invention relates to a video camera having an autofocus function, in which imaging light is irradiated onto a solid-state imaging means such as a charge-coupled device through a focus lens, high-frequency components from the solid-state imaging means are detected, and based on this detection output, the present invention relates to a video camera having an autofocus function. In a video camera having an autofocus function that automatically changes the optical path length between the focus lens and the solid-state imaging means by driving the focus lens, the solid-state imaging means is set at a predetermined angle with respect to the optical axis of the focus lens. The focusing lens of the solid-state imaging means is tilted and has a comparing means for comparing the magnitude of high frequency components between an imaging output in a far region and an imaging output in a near region with respect to the focusing lens of the solid-state imaging means, and the driving direction of the focusing lens is determined according to the output of the comparing means. This is intended to provide a video camera that has a simple configuration, consumes little power, and can perform highly reliable autofocus control.

[Conventional technology]

Conventionally, various methods have been proposed as autofocus methods for video cameras. Autofocus methods can be broadly divided into passive methods, which use information from the light entering the imaging lens for focusing, and active methods, which emit a signal from the camera and use the signal information reflected by the subject to determine focus. Broadly classified. Among these, the active method requires a light-emitting element and a light-receiving element such as infrared rays in addition to the subject information that enters the image sensor through the imaging lens, and has many problems such as having a target value different from the imaging information.

Among the passive methods, various autofocus methods have been proposed, the representative ones being the image sensing method and the contrast method. The image sensing method uses about 24 pairs of Friar lenses and charge-coupled devices (hereinafter referred to as CCDs) - image sensors lined up in a row are installed inside a video camera, and light enters a pair of CCDs in the center depending on how the focus is adjusted. The in-focus point is determined based on whether the image is in focus or at a position away from the center, and in this case as well, an image sensor other than the subject information is required, and a similar pattern is repeated to detect the phase shift. There are problems such as inability to make judgments about certain subjects.

The contrast method (frequency separation method) uses the property that when the object image is in focus, the object image projected on the CCD has a large contrast ratio and a large frequency component to perform focusing. By shaking the focus lens or CCD etc. slightly back and forth in the direction of the optical axis of the lens, move the focus lens continuously so that the contrast ratio or frequency component at that time increases, and find the point where the contrast ratio or frequency component is the highest. This configuration is disclosed in Japanese Patent Application Laid-Open No. 55-76309, which was originally proposed by the applicant of the present invention. The principle of this autofocus will be briefly explained with reference to FIGS. 5 and 6. In Figures A, B, and C, (1) shows the subject, (2) shows the lens optical system including the zooming lens, focus lens, main lens, etc., and (3) shows the CC.
D or an imaging device such as an image pickup tube (hereinafter referred to as CC11(3)). Also, (4) shown only in Figure 5A is an autofocus motor that moves the lens optical system (2) in the direction of the optical axis of the lens optical system (2) in the direction of the arrow A-A for autofocus. Move the lens optical system (
2) and CCD (31), for example, 101
By vibrating at a wobbling frequency of about 12, the lens optical system (2) is vibrated back and forth by Δl between the positions indicated by the broken line and the solid line.

(5) is an autofocus control circuit including a high-frequency level detection circuit, which will be described later, to drive and control the autofocus motor (4).
The imaging output from the CCD (3) is supplied to the circuit (5).

Figure 5B is a schematic diagram of the optical system when the subject (1) is in focus, and Figures 5A and C are respectively focused on the subject (0).
The figure shows the state in front of the subject (+) and the state in the rear of the subject (+). Curve (6) in Figure 6 is the lens optical system (2)
This shows the relationship between the optical path length of the CCD (3) and the imaging screen, and the contrast or high frequency component of the video signal. d is the relationship between the optical path length and the contrast or high frequency component of the video signal when the subject (1) is in focus during autofocus as shown in Figure 5B. lens optical system (2) and CCD (3)
). and similarly e.

" is the distance between the lens optical system (2) and the CCD (3) when the subject (1) is focused in front and behind the subject (1) during autofocus shown in Figure 5 A and B, respectively. , and LII.The more the image output from the subject (+) of CCD (3) is in focus, the more C0D(
Contrast of the imaging surface in 3) As shown in curve (6) in Figure 6, the high frequency level detection output extracted from this output increases, and the further out of focus the C becomes.
The contrast of the imaging surface of the video output of C D (3) decreases, and the high frequency level detection output decreases.

Now, the lens optical system (2) is changed to Δ! by the wobbling signal. (Actually, C O
D (3) is vibrated with a piezoelectric element, etc.) and the focused point shown in Figure 5B, a constant DC voltage (7) with no level change is obtained as shown at point d in Figure 6. An AF circuit (5) including a high frequency level detection circuit is configured so as to be able to detect a high frequency level. Also, as shown in FIG. 5A, when focusing on the front of the subject (1), 1. . <1. When l=, a voltage is obtained from the AF open circuit 5) including the high frequency level detection circuit so that the positive part of the sine waveform (8) is depressed compared to the negative part, as shown in Figure 5C. Like when you focus behind the subject ( ).

But... and O, the AF open circuit 5) including the high frequency level detection circuit is configured to obtain a voltage with a higher level in the positive part of the sine waveform (9) than in the negative part. A focused state or a non-focused state is detected.

[Problem to be solved by the invention]

The contrast detection method in the passive method shown in the conventional configuration above uses light incident on the lens of a video camera, so there is no need to use an extra image sensor, and it has the advantage of being similar to the human eye. However, because wobbling is performed to adjust the focus and the lens optical system is shaken, the focus moves even when the focus is on. In particular, small video cameras use small batteries, so it is necessary to reduce power consumption as much as possible.Furthermore, with this contrast detection method, if the focus shifts significantly, the focus lens etc. cannot be moved in any direction. I don't know (I don't know), but it had the disadvantage of taking a long time to focus.

The present invention was made to solve the above-mentioned problems, and its purpose is to provide a video camera with a simple configuration, low power consumption, and highly reliable autofocus control. It is something.

[Failure to solve the problem]

As an example of the video camera of the present invention is shown in FIG. (3) Detects the high frequency component of - In a video camera having a focus function, the solid-state imaging means (3) is tilted at a predetermined angle θ with respect to the optical axis of the focus lens, and the solid-state imaging means (3) images an area far from the focus lens (2a). It has a comparison means (21) for comparing the output with the magnitude of the high frequency component in the imaging output of a nearby area, and determines the moving direction of the focus lens (2a) according to the output of the comparison means (21). It is something.

[Effect]

In the video camera of the present invention, solid-state imaging means (3
) is tilted at a predetermined angle θ and a focus control signal is obtained by comparing the high-frequency components of the imaging output of the solid-state imaging means (3) that are focused in front and behind the subject (1), thereby eliminating wobbling. It is possible to obtain highly reliable autofocus control that does not require a mechanical part, consumes little power, and performs autofocus control.

(Example〕 An embodiment of the present invention will be described below with reference to FIG.

In Figure 1, (1) is the subject to be imaged by the video camera, (2) is the lens optical system of the video camera, and this lens optical system (2) includes a focus lens (2a) and a zooming lens (2b). , a main lens (2c), etc. A focus lens (2a), a zooming lens (2b), etc. are moved in the direction of the arrow by a motor (2e) to perform focusing and zooming. (3) is a solid-state imaging device (hereinafter referred to as CCD) such as a CCD (charge-coupled device) or CID (charge injection device), and its photocathode has, for example, a checkered pattern of R (red) and G (green). A color filter such as r3 (blue) is arranged, and for example, a medium plate type CCD
It is said to be composed of This CCD (3) has an orthogonal surface (24
), the conical direction is tilted backward by a predetermined angle θ. This angle θ may have an extremely small value. During focusing and zooming, the lens optical system (2) and CCU
(The distance between 31 can be changed. The image of the subject (1) captured by the CCD (3) through the lens optical system (2) is converted into an electrical signal, and the video output signal of the CCD (3) is R , G, and B signals, and after performing gamma correction, white correction, etc. in a process amplifier, the matrix circuit (
11), and in the matrix circuit (11), a delay circuit (12) using four IH delay lines converts it into a luminance signal and two color difference signals using line correlation, and a low-pass filter ( 13), the respective luminance signals and two color difference signals are supplied to an encoder (14), and an NTSC video output signal is led out to an output terminal (15).

The video output signal from the COD (3) is supplied to a high pass filter (hereinafter referred to as HPF) (17) through a gate circuit (16) to obtain an autofocus control signal. This gate circuit (16) generates a wind signal (2) from a wind signal generating circuit (25) in order to focus on the subject (1) at the center of the screen imaged by the CCD (3).
In step 5a), the central rectangular portion of the imaging screen is extracted. The HPF (17) calculates the transmission ratio of the high-frequency component in the video output signal, supplies the voltage component to the squaring circuit (18), squares it, and then integrates it in the integration circuit (19) to obtain the window. The high frequency component power for each line in the line is obtained from the output end of the integrating circuit (19). A register (20) that registers the high frequency component power for each line in the IH section.
and directly to the comparison circuit (21). The comparison circuit (21) compares each line to see which has more high-frequency component power between adjacent lines, performs this operation for many lines, and uses the comparison result to determine the power of each line (22).
supply to. The determination circuit (22) determines whether the high frequency power is greater between the upper adjacent lines of the CCD (3) or between the lower adjacent lines. For example, this determination method uses a majority vote on the upper and lower lines iσ to determine whether the high frequency power is on the upper or lower side within the window of the CCD (3). The output of this judgment circuit (22) is supplied to the motor (2e) as a focus control signal via an output terminal (23), and the focus lens (2+i) is moved in the direction of the arrow to bring it into focus. The judgment result in the judgment circuit (22) is displayed on the CCD (3
) is tilted backwards, move the focus lens 2 (2a) forward and move
D (3) The lower part of the screen has a higher power of high frequency components, and when it is determined that the higher part of the screen has a higher power of high frequency components, the focus lens (2a) is moved to the rear. All you have to do is control it to bring it into focus. Therefore, the direction to be controlled can be determined.

In this example, the focus control signal was extracted using the correlation between adjacent lines, but it cannot be determined if there is no line correlation on both sides of the subject (1). It is also possible to provide a detection section that determines whether or not this is the case, and to operate the focus control circuit based on the detection output of this detection section. Furthermore, the present invention is not limited to the above-mentioned configuration, and the magnitude of high-frequency power can also be determined by, for example, continuously integrating the power difference between two lines.

FIG. 2 shows another embodiment of the present invention. In FIG. 1, high frequency power was detected in an analog manner, but in the case of FIG. Corresponding parts are given the same reference numerals and redundant explanation will be omitted. In FIG. 2, the upper side of the CCD (3) is inclined at an angle θ with respect to the orthogonal plane (24).

This configuration may be the same as that in FIG. If the video camera digitally processes the video signal obtained by the CCD (3), the digital video data will be converted into a digital HP F (
17d), but in the case of Fig. 2, the video output signal extracted in analog form is sent to the gate circuit (16).
A video signal from approximately the center of the screen is taken out via the analog-to-digital conversion circuit (26), converted into a digital signal, and a digitally configured HPF (17a) passes only high frequencies. Multiplication is then performed in the square circuit (18a). In the square circuit (18a), values to be multiplied are recorded in the memory, and the digital voltage values are multiplied, accumulated in the accumulator (19a), and the high frequency power for each line is taken out and sent to the register (20). ) and the high frequency power of the previous line resisted through
The high frequency power of the current line is compared by the comparator (21a), and the comparison output is sent to the microcomputer (22).
a) etc., determine which line contains more high frequency components, the upper line or the lower line of CCD0, and output the output data of the three lines according to the judgment result to the output terminals (2r,
” ”I’m dressed up. When the focus lens (2a) is moved forward or backward in accordance with the output data of these three sensors, it is made to stop at the in-focus position.

FIG. 3 is another embodiment showing a method of tilting the CCL of the video camera according to the present invention. In Figures 1 and 2, CCD
(3) is tilted vertically with respect to the orthogonal plane (24) perpendicular to the optical axis plane (2d) of the lens optical system, but in the case of Fig. 3, the left side with respect to the orthogonal plane (24) is at an angle o, .

This shows C CD (3a) with the right side tilted forward by an angle θ8 (3b).

With this configuration as well, a highly reliable video camera can be obtained which does not require a mechanical part such as vibrating/swiping a CCD or the like with a piezoelectric element or the like using a focus control circuit similar to that explained in FIG. 1 or 2.

Figure 4 shows a CCD that depends on tilting the CCD.
This explains a method for correcting image distortion on a musical composition.

In this example, the angle θ for tilting the CCD (3) below -L or to the left and right is an extremely small value (for example, the distance from the vertical surface (24) to the light receiving surface of the CCD (3) is about 50 μm), so the lens If the distortion is the same as the pincushion distortion or barrel distortion that occurs in the optical system, there is no need to perform distortion correction on 45, but if this tolerance is exceeded, the CCD (3)
For example, if the image of L is distorted into a trapezoid (27) shape, the exposure when forming the photoelectric conversion surface of the CCD photosensitive section should be tilted, or
Alternatively, the correction may be performed by arranging them in an inverted trapezoid (28) when designing the layout, or furthermore, the reverse correction may be performed using a lens optical system or the like.

It should be noted that the present invention is not limited to the embodiments described above (it is clear that various changes can be made without departing from the gist of the present invention).

(Effects of the Invention) According to the video camera of the present invention, CC
Since there is no need to drive D, etc., there is no need for mechanical parts, resulting in high reliability and low power consumption.

[Brief explanation of drawings]

FIG. 1 is a system diagram showing one embodiment of the video camera of the invention, FIG. 2 is a system diagram showing another embodiment of the video camera of the invention, and FIG. 4 is an explanatory diagram of distortion correction of the video camera (CCI) of the present invention; FIG. 5 is a schematic diagram of an optical system illustrating a conventional focusing method; FIG. 6 is a monomorphic curve diagram explaining the principle of the conventional O1-focus. (1) is the subject, (2) is the lens optical system, (2a) is the focus lens, (3) is the CCI), (17) is the II
P F, (18) is a square circuit, (19) is an integral circuit, (
20) is a register, (21) is a comparison circuit, and (22) is a judgment circuit. Agent Hide Matsukuma +1 JP-A-3 117182 (6) Kuyoichi

Claims (1)

[Claims] Imaging light is irradiated onto a solid-state imaging means such as a charge-coupled device through a focus lens, a high frequency component from the solid-state imaging means is detected, and the focus lens is adjusted based on the detection output. In a video camera having an autofocus function that automatically changes the optical path length between the focus lens and the solid-state imaging means by driving, the solid-state imaging means is tilted at a predetermined angle with respect to the optical axis of the focus lens. and comparing means for comparing the magnitude of high frequency components between an imaging output in a far region and an imaging output in a near region relative to the focus lens of the solid-state imaging means, and according to the output of the comparison means, the focus lens A video camera characterized in that the driving direction of the video camera is determined.