JPH07112253B2 - Autofocus video camera - Google Patents

Description

TECHNICAL FIELD The present invention relates to a video camera and an electronic still camera having an autofocus mechanism and a zoom mechanism for performing a focusing operation using an imaged video signal.

(B) Conventional technology In an autofocus device for video cameras, the method of using the evaluation of the focus control state of the image signal itself from the image sensor is essentially free from any parallelism and has a shallow depth of field. There are many advantages such as being able to accurately focus on a distant subject. Moreover, a special sensor for the autofocus is unnecessary, and the mechanism is extremely simple.

The autofocus circuit of this system basically controls the focus motor by a control method called a hill-climbing servo system as disclosed in JP-A-60-103776 (H04N5 / 232). That is, the high frequency component of the picked-up image signal is detected as an evaluation value, and this evaluation value is constantly compared with the one before one field, and the focus motor is continuously vibrated slightly so as to take the maximum value.

The maximum point is that the evaluation value changes from an increasing tendency to a decreasing tendency by driving the focus ring that supports the focus lens in one direction as seen in Japanese Utility Model No. 60-135712 (G02B7 / 11). , There are also things that return the focus ring to this point and stop it.

Furthermore, since the focus evaluation value fluctuates when the subject moves after the focus lens has stopped at the maximum point, a certain threshold value is set in advance, and the focus evaluation value fluctuates as this threshold value is exceeded. When a problem occurs, the focus motor can be restarted to enable autofocus to follow the movement of the subject.

On the other hand, a normal video camera is equipped with a zoom mechanism that moves a zoom lens that can continuously change the focal length from a telephoto to a wide angle.

In this zoom mechanism, it is generally known that the depth of field varies depending on each zoom region, that is, the position of the zoom lens, which is a variable power lens, between the telephoto and wide angles. That is, if the zoom is wide-angle, the depth of field is deep, and if the zoom is telephoto, the depth of field is shallow. Here, a deep depth of field means that the in-focus state can be easily maintained even if the subject moves slightly back and forth from the point of focus, and if the depth is shallow, it is difficult to maintain the in-focus state. Means

(C) Problems to be Solved by the Invention In a video camera having both a hill-climbing autofocus mechanism capable of detecting the movement of a subject as a change in focus evaluation value as described above and a normal zoom mechanism as described above, For a subject that is at or near the depth of field in a state where it is stopped or close to it and the level of which out-of-focus is not recognized, the change in the angle of view and the F-number (a measure of the brightness of the lens) due to zooming If the focus evaluation value changes, and this exceeds the threshold value, the focus motor restarts. If the focus operation is executed during zooming even though the focus is not recognized in this way, the zoom speed will change apparently due to the synergistic effect of the change in the angle of view due to both zooming and focusing, and the smooth zoom screen will appear. Can't get

(D) Means for Solving Problems A high-frequency component level in a central sampling area set at the center of the screen among the image pickup luminance signals obtained from the image pickup device is set as a first evaluation value, and the center of the image pickup luminance signals is The high-frequency component level in the peripheral sampling area set around the sampling area is set as the second evaluation value, and the second evaluation value is changed in accordance with the change in the second evaluation value or the first evaluation. Accordingly, the focusing operation during the zoom operation is prohibited.

(E) Operation Since the present invention is configured as described above, it is possible to prevent the change in the angle of view due to the zoom operation from affecting the focusing operation.

(F) Example Below. An embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit block diagram of an embodiment of the present invention. An image formed by the focus lens (1) becomes an image pickup signal by an image pickup circuit (4) including an image pickup element, and a luminance signal in this video signal is a gate circuit (20) (21) and a sync separation circuit (22). Entered in. The vertical and horizontal sync signals separated from the luminance signal by the sync separation circuit (22) are the central sampling area (E ₁ ) corresponding to a rectangular area in the center of the screen as shown in FIG. Input to the gate control circuit (23) to set (E ₂ ).

The gate control circuit (23) sets the central and peripheral sampling areas (E ₁ ) (E ₂ ) based on the vertical synchronizing signal, horizontal synchronizing signal, and fixed oscillator output, and sets the central sampling area (E ₁ ) area. only supplied to the gate-off signal to permit passage of the luminance signal (GC ₁₎ gate circuit (21), opens the gate to allow passage of the luminance signal area only around the sampling area (E ₂₎ (GC ₂₎ Is supplied to the gate circuit (20).

Only the luminance signal corresponding to the inside of the central sampling area by the gate circuit (21) is passed through the high-pass filter (HP
After passing through F) (24), only the high frequency component is separated and amplitude detected by the detection circuit (25) at the next stage. The detected output is integrated for each field in the integrating circuit (26), converted into a digital value in the A / D converting circuit (27), and held in the first memory (28). Therefore, in the first memory (28),
The integrated value for one field of the high frequency component in the central sampling area (E ₁ ) created by the first evaluation value generation circuit (29) composed of the gate circuit (21) and the circuits subsequent thereto is It will be held as the first evaluation value (S ₁ ).

Similarly, in response to the gate control signal (GC ₂ ), the gate circuit (2
0) allows the passage of the luminance signal only in the peripheral sampling area (E ₂ ), and will be referred to as the HPF (30) and the detection circuit (3
1), 1 field of the high frequency component of the luminance signal in the peripheral sampling area (E ₂ ) via the second evaluation value generating circuit (34) including the integrating circuit (32) and the A / D conversion circuit (33) The integrated value of minutes is held in the second memory (35) as the second evaluation value (S ₂ ). The characteristics of the respective constituent elements of the first and second evaluation value generation circuits (29) and (34) are set to be exactly the same. For example, the cutoff frequencies of HPF (24) (30) are both 500 KHz. In addition, the respective data of the first and second memories (28) and (35) are updated every one field.

The first evaluation value (S ₁ ) output from the first evaluation value generation circuit (29) is held in the first memory (28) and used as a focus evaluation value for the autofocus operation described below. To be

Immediately after the start of the autofocus operation, the first first evaluation value,
That is, the focus evaluation value is held in the maximum value memory (6) and the initial value memory (7). Thereafter, the focus motor control circuit (10) rotates the focus motor (3) in a predetermined direction and monitors the output of the second comparator (9). Second
The comparator (9) compares the focus evaluation value after driving the focus motor with the initial evaluation value stored in the initial value memory (7), and outputs the magnitude.

The focus motor control circuit (focus lens moving means) (10) is a focus motor (focus lens moving means) (3) in the first direction until the second comparator (9) outputs a large or small output. If it is output that the current focus evaluation value is larger than the initial evaluation value and is larger than the preset fluctuation range, the rotation direction is held as it is and the current evaluation value is When the output is smaller than the fluctuation range as compared with the initial evaluation value, the rotation direction of the focus motor (3) is reversed,
The outputs of the first comparator (8) are compared.

The first comparator (8) compares the current maximum focus evaluation value and the current maximum focus evaluation value held in the maximum value memory (6), and the current focus evaluation value is stored in the maximum value memory (6). Two types of comparison signals (SIG ₁ ) (SIG ₂ ) that are larger than the contents (first mode) and have decreased below the preset first threshold value (second mode) are output. Here, the maximum value memory (6) is updated based on the output of the first comparator (8) when the current focus evaluation value is larger than the content of the maximum value memory (6), and is always updated. The maximum focus evaluation value to date is held.

Reference numeral (13) is a motor position memory for storing the motor position by receiving the motor position signal indicating the position of the focus motor (3), and like the maximum value memory (6), the first comparator (8) Based on the output, the motor position when the focus evaluation value reaches the maximum value is updated so as to be always held.

The focus motor control circuit (10) includes a second comparator (9).
While rotating the focus motor (3) in the direction determined based on the output, the output of the first comparator (8) is monitored to prevent malfunction due to noise in the focus evaluation value. 8) The output indicates the second mode in which the current focus evaluation value is smaller than the preset first threshold value as compared with the maximum evaluation value, and at the same time, the focus motor (3) is reversed. . After this reverse rotation, the contents of the motor position memory (13) and the current motor position are compared by the third comparator (14), and when they match, the focus ring (2) becomes the maximum point of the focus evaluation value. The focus motor control circuit (10) functions to stop the focus motor (3) after returning. At the same time, the focus motor control circuit (10) outputs a lens stop signal (LS). The first evaluation value (S ₁ ) of the first memory (28) is input to the delay circuit (36), the subtraction circuit (37), and the restart determination circuit (38). Here, the delay circuit (36) delays the first evaluation value (S ₁ ) by one field, and the subtraction circuit (37) outputs the first evaluation value (S ₁ ) of the current field one field before the first evaluation value (S ₁ ). Evaluation value (S
S ₁₎ the absolute value is fluctuation value subtracted value _{(△ S 1) (△ S} 1
= S ₁ −SS ₁ ) is calculated. Similarly, the second evaluation value (S ₂ ) of the second memory (35) is the delay circuit (39), the subtraction circuit (40),
It is input to the restart decision circuit (38) and the second of the current field
A variation value (ΔS ₂ ) (ΔS ₂ = S ₂ ) that is the absolute value of the value obtained by subtracting the second evaluation value (SS ₂ ) one field before, which is the output of the delay circuit (39), from the evaluation value (S ₂ ). -SS ₂₎ is calculated.

(38) is the first and second memories (28) and (35) of the first and second memories (28) and (35) at the same time when the autofocus operation by the focus motor control circuit (10) ends and the lens stop signal (LS) is issued. 2 Evaluation value (S ₁ ) (S ₂ ) and subtraction circuit (37) (40)
Discriminating signal (ZS) for discriminating whether or not the fluctuation value (ΔS ₁ ) (ΔS ₂ ) which is the output of and the zoom motor (61) is driving
Based on the above, it is a restart determination circuit that detects whether or not the subject has moved and changed, and determines whether or not the focus motor (3) once in the stopped state can be restarted. Here, the zoom motor (61) is a zoom ring (62) that supports a zoom lens based on a command from a system controller (not shown).
Can be rotated via a gear to move the zoom lens forward and backward to continuously change the focal length from wide angle to telephoto.

Next, the operation of the restart determination circuit (38) will be described based on the flow chart of FIG. Central and peripheral sampling areas (E ₁ ) (E ₂ ) when the zoom motor (61) is not operating
Since the movement of the subject is monitored by the fluctuation of the evaluation value in all areas including the above, the sum of the fluctuation value of the first evaluation value (ΔS ₁ ) and the fluctuation value of the second evaluation value (ΔS ₂ ) The focus motor control circuit (10) issues a restart command (RS) by detecting whether or not the preset threshold value (L) is exceeded, and assuming that the subject has changed when the threshold value (L) is exceeded. Emit. When the focus motor control circuit (10) receives this restart command, it causes the focus motor (3) to rotate again in either direction,
Repeat the autofocus operation described above from the beginning.

Next, when it is judged that zooming is in progress by the discrimination signal (ZS), the evaluation value change due to defocusing mainly occurs in the central sampling area (E ₁ ), so the peripheral sampling area (E ₂ ). Then, it functions as a monitor for the evaluation value change due to zooming. The change in the evaluation value due to zooming is generally smaller than the change in the evaluation value due to defocusing to the extent that blur is recognized. Therefore, let a be the restart level based on the evaluation value change rate (change rate = change value / evaluation value) during normal operation not during zooming, and b be the restart level of the change rate during zooming. Set a large allowance for blurring during zooming.

Even if the subject is stationary during zooming, the first and second evaluation values (S ₁ ) (S ₂ ) change, but ΔS ₁ / S ₁ and ΔS ₂ / S ₂ are both small and comparable. Since it is the value of, the restart command (RS)
Cannot be emitted.

If the subject is out of focus during zooming, ΔS ₁ / S ₁ >> ΔS ₂ / S ₂ . Therefore, the restart condition for the autofocus operation during zooming is set as follows.

ΔS ₁ / S ₁ ≧ b, ΔS ₂ / S ₂ ≧ b In this case, the rate of change of the first and second evaluation values (S ₁ ) (S ₂ ) exceeds the restart level during zooming. As a result, the restart command (RS) is naturally issued.

ΔS ₂ / S ₂ <b, ΔS ₁ / S ₁ −ΔS ₂ / S ₂ ≧ C In this case, the fluctuation rate of the second evaluation value (S ₂ ) is below the restart level, but both The difference in the rate of change of the evaluation value exceeds the preset allowable level (C), that is, the movement of the subject always occurs in the central sampling area (E ₁ ) during zooming and in the peripheral sampling area (E ₂ ). If it does not affect, the movement of the subject cannot be monitored by the change in the evaluation value of the second evaluation value (S ₂ ), so the difference in the change rate is calculated and zooming is performed from the change in the evaluation value in the central sampling area (E ₁ ). When the value obtained by deleting the change due to is beyond the limit value (C), which is not recognized as being out of focus, the restart command (RS) is issued.

Based on the above conditions, it is determined whether or not there is a change in the evaluation value due to zooming using the second evaluation value (S ₂ ) itself. Therefore, it is determined whether or not the subject is out of focus at the center of the screen, and a restart command (RS) is issued when any of the conditions is satisfied.

In the present embodiment, the first evaluation value (S ₁ ) of the central sampling area (E ₁ ) is used as the focus evaluation value in the hill climbing autofocus operation. It goes without saying that a focus area can be provided separately.

FIG. 3 is a flow chart when the operation of the circuit block shown in FIG. 1 is processed by software.

(G) Effect of the Invention As described above, according to the present invention, in the hill-climbing autofocus operation, the change in the evaluation value due to zooming and the change in the evaluation value due to the movement of the subject can be discriminated, and the careless autofocus operation Can be controlled to obtain a smooth and easy-to-see zoom screen.

[Brief description of drawings]

The drawings are all related to one embodiment of the present invention. FIG. 1 is a circuit block diagram, FIG. 2 is an explanatory diagram of setting a sampling area, and FIG. 3 is a flow chart. (E ₁ ) …… central sampling area, (E ₂ ) …… peripheral sampling area, (S ₁ ) …… first evaluation value, (S ₂ ) ……
Second evaluation value, (29) ... First evaluation value generation circuit, (34) ...
… Second evaluation value generation circuit, (61) …… Zoom motor,
(3) ... Focus motor (focus lens moving means), (10) ... Focus motor control circuit (focus lens moving means).

Claims (1)

[Claims] 1. A first evaluation value generation means for outputting as a first evaluation value a high frequency component level in a central sampling area set at the center of the screen among the imaging brightness signals obtained from an image sensor, and the imaging brightness signal. Second evaluation value generating means for outputting a high frequency component level in a peripheral sampling area set around the central sampling area as a second evaluation value, and a zoom mechanism for performing a zoom operation between a telephoto range and a wide angle range, Focus lens moving means for performing a focusing operation for moving the focus lens to a focusing position, and according to a change in the second evaluation value or in response to a relative change in the second evaluation value with respect to the first evaluation value. An autofocus video camera comprising: a focusing operation prohibiting unit that prohibits a focusing operation during a zoom operation.