JPS62203485A - Focal point detector - Google Patents

Abstract

PURPOSE:To improve a focussing accuracy by predicting the position of the focal point of a focussing lens and moving the focussing lens according to the predicted position of the focal point. CONSTITUTION:There are provided an arithmetic means consisting of a microcomputer or the like, a control unit 10 as a detection means, and a motor driving circuit 11 for driving the motor of a photographing lens 1 constituting an image pickup means. The control unit 10 operates the prediction quantity of the focal point and the moving quantity of the focussing lens in accordance with a control procedure from the focussing quantity (quantity indicating a focussing state) f(x) supplied from an integrating circuit 8 as a signal processing means and the focussing lens position calculated based on the motor driving output pulse P of the motor driving circuit 11 and outputs a control signal for driving the motor to the motor driving circuit 11. The motor driving circuit 11 moves the focussing lens of the photographing lens 1 to the focal point direction according to the control signal of the control unit 10.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a focus detection device used in an imaging device such as a video camera, and more particularly to a focus detection device that performs focus adjustment using a video signal.

(Prior Art) Conventional focus detection devices can be broadly classified into active type and passive type. Among these, the active type is
There are some ultrasonic type cameras, but in recent years there are infrared type cameras that emit infrared light from the camera side to form a spot image on the subject, and then focus by detecting the reflected light with a light receiving element. It is commonly used because it has relatively high distance measurement accuracy. However, this infrared method requires a mechanical interlocking mechanism to move the light-receiving element etc. according to the subject distance, which inevitably results in a complicated structure and requires complicated adjustments, which is a disadvantage in that work efficiency is poor. was there.

On the other hand, regarding passive types, there are those that use a video signal from the imaging system and those that do not. Among these, methods that do not use video signals include the Honeywell method that uses so-called shift detection and blur detection, and the Canon 5ST (Solid
5tate triangulation) system, etc., but these also require unnecessary optical parts in the photographing system and require advanced adjustment techniques.

On the other hand, a focus detection device using a video signal has the advantage of not requiring unnecessary optical components in the imaging system.

A conventional focus detection device using a video signal will be explained with reference to FIG. As shown in this figure, an image formed by a photographing lens 1 constituting an imaging means is converted into an electrical signal by an image sensor 2 serving as an imaging means, and this signal is amplified by a preamplifier 3. The signal amplified by the preamplifier 3 passes through a process circuit 4 and is input as a video signal to a monitor or video tape recorder (not shown). At the same time, the signal amplified by the preamplifier 3 is limited to only high frequency components by a bandpass filter (hereinafter referred to as OFF) 5, and furthermore, a predetermined screen range to be focused when displayed on a monitor etc.
For example, after the distance measurement field of view is limited through a gate circuit 6 that extracts only a signal corresponding to a substantially central range of a photographed image, the signal is converted by a detection circuit 7 and an integration circuit 8 into a quantity indicating the focus state. These components 3, 5, 6, 7 and 8 constitute a signal processing means. There is a relationship between the amount indicating the focus state (hereinafter referred to as the focus amount) and the defocus fi (focal shift amount) of the photographing lens 1 as shown in FIG. 4, and according to this relationship, the motor drive circuit 9
drives the focusing lens in the photographing lens 1 via a motor to a position where the amount indicating the focus state is maximum.

Next, the operation of the motor drive circuit 9 shown in FIG. 3 will be explained with reference to FIG. The current focus at the start of distance measurement
Assume that the state is at position A in the figure. Further, the focus position when the focusing lens in the I-most shadow lens 1 is moved very slightly by a predetermined pitch is designated as B in the figure.

The motor drive circuit 9 uses the focal amount f(A) at the position A and the focal amount f (Fi”) at the position B obtained from the integrating circuit 8.
If f CB) > f (A), then rotate the motor in the same rotational direction as when moving from position A to position B, and if f (8° < f (A), then rotate the motor in the same direction as when moving from position A to position B. The direction of rotation is reversed, thereby moving the focusing lens in the photographing lens 1 in the direction of the in-focus point Xo.

[Problem that the invention seeks to solve]

However, in the conventional focus detection device using the video signal as described above, the in-focus point cannot be determined until the object has passed the in-focus point once, which has the disadvantage that the photographed screen becomes unnatural.

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to eliminate the above-mentioned drawbacks of a focus detection device using a video signal and to provide a focus detection device that does not cause unnaturalness to a photographic screen of a monitor or the like.

[Means for solving problems]

In order to achieve such an object, the present invention includes a signal processing means that outputs a signal related to the degree of focus from a video signal obtained from the image pickup means, and a signal processing means that outputs a signal related to the degree of focus from a video signal obtained from the image pickup means, and a method that combines an image into the image pickup means when the output of the signal processing means is processed. A detection means detects the absolute address X of the focusing lens to be imaged, and at least two sets of data of the output value f (Z) obtained from the signal processing means and the absolute address X obtained from the detection means are used to determine the in-focus point of the focusing lens. It is characterized by comprising a calculation means for calculating the predicted position X.

(Function) In the present invention, the signal processing means outputs a signal related to the degree of focus from the video signal obtained from the imaging means. At the same time, a detection means such as an encoder detects the absolute address (movement position) X of the focusing lens that forms an image on the above-mentioned imaging means.

Furthermore, the output value fc obtained from the above-mentioned signal processing means,
, and the absolute address X obtained from the detection means, at least two pieces (XL, f(x+)), (L,,
f tiz)), the expected in-focus position x of the focusing lens is calculated by a calculation means such as a computer unit.
Calculate O.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows the configuration of a focus detection device according to an embodiment of the present invention. In this figure, reference numeral 10 is a control unit as a calculation means and detection means comprising a storage device, a microcomputer having a calculation function, etc., and 11 is a motor drive circuit for driving the motor of the photographing lens 1 constituting the imaging means. The control unit 10 uses the focus amount (amount indicating the focus state) ft1) supplied from the integrating circuit 8 as a signal processing means and the focusing lens position calculated based on the motor drive output pulse P of the motor drive circuit 11. In accordance with the control procedure shown in FIG. 2, the predicted in-focus point amount and the focusing lens movement amount are calculated, and a control signal for driving the motor is output to the motor drive circuit 11.

The motor drive circuit 11 rotates a motor (not shown) in the forward or reverse direction in response to a control signal from the control unit 10, thereby moving the focusing lens of the photographic lens 1 toward the in-focus point. The rest of the configuration is similar to the conventional autofocus device shown in FIG. 3 described above, so detailed explanation thereof will be omitted.

The control unit 10 receives and receives the output (focal point i) f, x indicating the focus state of the integrating circuit 8, and at the same time captures the absolute address X of the focusing lens in the photographic lens 1 using the output pulse P of the motor drive circuit 11. , the address (hereinafter referred to as
〕〕X is called an orcasing lens) in the internal memory (
(not shown).

The above-mentioned quantity f(cm) indicating the focus state can be approximated by a Gaussian distribution with respect to the focusing lens position A coefficient indicating the maximum value of , b is also a coefficient.

Therefore, each quantity (X+, ft) represents the respective focus states at three points at different focusing lens positions.

If (Xp, b), (X3, f3), then the following formula (
2) The in-focus lens position X is determined.

X = ") A flowchart that realizes the algorithms of the above equations (1) and (2) is shown in FIG. 2.Next, referring to the flowchart of FIG. 2, the control unit 10 of FIG.
The control operation will be explained. It is assumed that 5t-5ll indicates the step number of the control procedure and is preliminarily stored in the internal program memory of the control unit 10.

First, input the focusing lens position x1 and focal length f (: cm) into the internal memory at the start of operation of the automatic focusing device (Sl). Move it in the specified direction (Sl), and adjust the lens position x in the same way as Sl.
input the focal amount f, xyu, into the internal memory (S3
). Next, compare the magnitudes of f(F5. and f(xY) (S4), and if f(F), < f(XY), move the focusing lens further by Smm in the same direction (S5)
, f(work 1)〉f(eyu, then 2Sm in the opposite direction from before)
Move the focusing lens by n+ (S6), 5
Input ×3 and f (X3' at the IrlIJ position into the internal memory (S7).

Next, the above-mentioned focusing point calculation formula (2) is applied to 51. The three sets of values obtained in S3 and S7 (X+, ft), (X
q, fz) and (X3.f, y) to find the expected focused point Xσ (S8). Next, it is determined by the following equation (3) how much the current position x of the focusing lens within the photographic lens deviates from the expected in-focus point x0 (
S9).

1X3-Xol>ε...(3) However, C
is a value of a predetermined minute dead zone width.

If it is determined in S9 that the deviation amount l
.

On the other hand, if it is determined in S9 that the deviation amount l
m)) Replace the value of (XL, fouJ) with the value of (XL, fouJ),
After setting the value of (x3.fcxlN to (X:1.f,,,)) value dR* jh ; and set this position X to x3 (Sll). Returning to S7 again, measure f(X)), find the expected focal point Xo as before, and calculate 1X1-X
This process is repeated until ol<ε.

”: =XJ + Slgn (X, -X3) ・S
-, (4) Furthermore, if the maximum value a of the Gaussian distribution is calculated using the above formula (1) at the same time as the prediction of the upper A focal point, the G of the amplifier in the detection circuit 7 in FIG.
It becomes possible to always use a1n (gain) in advance within a range in which the amplifier is not saturated, and distance measurement accuracy can be improved. Furthermore, depending on the difference between the current position of the focusing lens, the expected focal point
By making the IIIJ amount X variable in several steps, it is possible to further improve the distance measurement accuracy near the in-focus point.

In the above-mentioned embodiment, the output of the integrating circuit is used to obtain a signal corresponding to the degree of focus, but it is also possible to obtain the signal corresponding to the degree of focus.

Furthermore, in this embodiment, the predicted in-focus position of the focusing lens is predicted by calculation using Gaussian distribution using three sets of data, but the present invention is not limited to this, and for example, experimental values prepared in advance may be used. It is also possible to obtain the predicted position of the focused point from two sets of data using the distribution curve set as the basis.

〔Effect of the invention〕

As described above, according to the present invention, the position of the in-focus point of the focusing lens is predicted and the focusing lens is moved according to the predicted position of the in-focus point, thereby improving focusing accuracy. It is possible to obtain the effect of making it possible to make the photographing screen such as the monitor screen easier to see.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the circuit configuration of an embodiment of the present invention; FIG. 2 is a flowchart showing the control operation of the embodiment of FIG. 1; FIG. 3 is a block diagram showing the circuit configuration of a conventional device; Figure 4 shows the position X of the focusing lens and the focal amount f(,
, is a characteristic diagram showing the relationship between . 1... Photographing lens (with built-in focusing lens), 2... Image pickup element, 3... Preamplifier, 5... Bandpass filter, 6... Gate circuit, 7... Detection circuit, 8. ...Integrator circuit, 10...Control unit, 11...Motor drive circuit. Shoboichi C1→1nヱKeiroku 1'l1m, 170-4
Ya-F Figure 2

Claims (1)

[Scope of Claims] 1) a) signal processing means for outputting a signal related to the degree of focus from a video signal obtained from the imaging means; and b) the imaging means when the output of the signal processing means is processed. c) detecting means for detecting an absolute address x of a focusing lens that forms an image on the image; 1. A focus detection device comprising: calculation means for calculating an expected in-focus position X_o of a focusing lens.