JPH03117277A - Automatic focus camera - Google Patents

Abstract

PURPOSE:To prevent malfunction of focusing due to effect of flicker by using a high frequency component of a luminance signal obtained from an image pickup element as 1st-3rd focus evaluation values for each field period to revise a lens relative position. CONSTITUTION:A luminance signal in a picked-up video signal from an image pickup circuit 4 is inputted to a focus evaluation generating circuit 5 and inputted to a switch circuit 20 switched sequentially for each field. The switch is thrown to a position of a fixed contact 20a in the initial state, focusing is started, the switch is thrown to a position of a fixed contact 20b in the focus evaluation for a 2nd field, and the switch is thrown to a position of a fixed contact 20c in the focus evaluation for a 3rd field. A 1st focus evaluation value fed to the contact 20a is fed to an initial value memory 7, a 2nd comparator 9 and a 1st focus position detection circuit and the focus evaluation value at the contacts 20b, 20c is fed to 2nd and 3rd focal position detection circuits 31, 41. Based on the 1st-3rd focal position data, a focal position decision circuit 51 selects the final focus position, the current lens position and the final focal position are compared and a focus motor control circuit 50 applies focusing.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to an auto-7 focus device for a camera that automatically aligns the focus based on a luminance signal in a captured video signal obtained from an image sensor.

(b) Conventional technology The method of using the high-frequency components of the video signal itself from the image sensor to evaluate focus control in the auto-7 orcus device of a camera is essentially free of variation and has a limited depth of field. It has many advantages, such as being able to focus accurately even when photographing shallow or distant objects. Furthermore, there is no need for a special sensor for Auto 7 Orcus, and the mechanism is extremely simple.

Japanese Patent Application Laid-Open No. 63-125910 (GO2B7/11)
discloses an example of the above-mentioned so-called mountain climbing auto 7 orcus system. Here, regarding this prior art, the second
The outline will be explained using the diagram and FIG. 3. FIG. 2 is an overall circuit block diagram of the conventional technology. In this figure, an image formed by a lens (1) is turned into a video signal by an image pickup circuit (4) including an image pickup element, and a focus evaluation value generation circuit ( 5). Focus evaluation value generation circuit (5
) is constructed as shown in FIG. The vertical synchronization signal (V
O), the horizontal synchronization signal (HD) is input to the gate control circuit (5b) to set the sampling area as 7 orcus areas. The gate control circuit (5b) sets a rectangular sampling area in the center of the screen based on the vertical synchronization signal (VD), the horizontal synchronization signal (HD), and the fixed oscillator output that drives the image sensor. A gate opening/closing signal is supplied to the gate circuit (5c) that allows passage of the luminance signal only within the range.

Only the luminance signals corresponding to the seven orcus areas are filtered by the gate circuit (5c) and passed through the high-pass filter (H,
P, F) (5d), only high-frequency components are separated, and the amplitude is detected in the next stage detection circuit (5e). This detection output is converted into a digital value by an A/D conversion circuit (5f) at a predetermined sampling period, and is sequentially input to an integrator (5g).

Specifically, this integrator (5g) consists of an adder that adds A/D conversion data and latch data of a subsequent latch circuit, and a latch circuit that latches this added value and is reset every l field. It is a so-called digital integrator consisting of
The sum of all A/D conversion data for one field period is output as a focus evaluation value. Therefore, the focus evaluation value generation circuit extracts the luminance signals within the 7 orcus areas in a time-division manner, digitally integrates this high-frequency component over one field period, and outputs this integrated value as the focus evaluation value for the current field. It turns out.

Immediately after starting the auto 7 orcus operation, the first focus evaluation value is held in the maximum value memory (6) and the initial value memory (7). After that, the focus motor control circuit (10) rotates the focus motor (3), which advances and retreats the lens (1) in the optical axis direction via the focus ring (2), in a predetermined direction, and performs a second comparison 5 (9). Monitor output. The second comparator (9) compares the focus evaluation value after driving the focus motor with the initial evaluation value held in the initial value memory (7) and outputs the magnitude thereof.

The focus motor control circuit (10) includes a second comparator (9).
) rotates the focus motor (3) in the initial direction until it outputs an output that is large or small, and outputs that the current focus evaluation value is larger than the initial evaluation value and larger than the preset fluctuation range. If the current evaluation value is smaller than the initial evaluation value, the rotation direction of the focus motor (3) is changed. is reversed and the output of the first comparator (8) is monitored.

The first comparator (8) compares the maximum focus evaluation value held in the maximum value memory (6) with the current focus evaluation value, and the current focus evaluation value is determined by the maximum focus evaluation value stored in the maximum value memory (6). Two types of H level comparison signals (PI) (P2) are output: one is larger than the content (first mode), and the other is reduced to more than the preset first threshold value (second mode). 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 up to now is held.

(13) is a focus ring (
This is a position memory that receives the 7-occasion ring position signal that indicates the position of 2) and stores the 7-occasion ring position as the lens position, and similarly to the maximum value memory (6), the first comparator (8) Based on the output, the lens position is updated so as to always maintain the lens position when the maximum evaluation value is reached. Here, it is a well-known technique that the seven orcus ring (2) is rotated by a focus motor (3), and the lens (1) moves forward and backward in the optical axis direction in accordance with this rotation. Note that the 7 focus ring position signal is output by the potentiometer that detects the focus ring position, but the 7 focus ring position signal is output by the potentiometer that detects the focus ring position.
is a stepping motor, and the periapsis and 0 of this motor are
It is also possible to set the amount of rotation in the point direction as positive and negative step amounts, and to express the position of the 7 orcus rings or 7 orcas smokes using these step amounts.

The focus motor control circuit (10) includes a second comparator (9).
) 7 orcus motors (
3), the output of the first comparator (8) is monitored, and in order to prevent malfunctions due to noise in the evaluation value, the current evaluation value is set to the maximum evaluation value at the output of the first comparator (8). On the other hand, when the second mode of being smaller than the preset first darkness value (Δy) is instructed (reaching Q in FIG. 4), 7 Orcasmoke (3) is reversed. After this reversal, the contents of the position memo (13) and the current focus ring position signal are compared in the third comparator (14), and when they match, that is, the lens (1) has the maximum focus evaluation value. Focus morph (3) when returning to Naruichi 1 (P)
7-axis motor control circuit (10) to stop the
works. At the same time, focus morph control circuit (10)
outputs a lens stop signal (LS) to complete the focusing operation.

(11) is a fourth memory that holds the focus evaluation value at the same time when the focusing operation by the seven-focus smoke control circuit (10) is completed and the lens stop signal (LS) is issued; The content held in this fourth memory (11) is compared with the current focus evaluation value by a fourth comparator (12) in the latter stage,
If the value becomes larger than the second threshold for restarting, it is determined that the subject has changed, and a subject change signal is output to the focus morph control circuit (10). When the 7-focus smoke control circuit (10) receives this signal, it restarts the focusing operation and follows changes in the subject.

(c) Problems to be Solved by the Invention The method of the prior art described above has extremely high followability and high focusing accuracy, but the illuminance of the subject changes at a constant frequency that is different from the frequency of one field of the video signal. If it is, the change in illuminance may cause malfunction. This situation will be explained in some detail below.

For example, in an NTSC video camera, the frequency of one field is 60H2, but such malfunctions occur when this camera is used under illumination of a discharge lamp such as a fluorescent lamp that is lit at 50Hz. Since the brightness of a discharge lamp lit at 50 Hz changes at a frequency of 100 Hz, the illuminance of the subject also changes at a frequency of 100 Hz.

Since one field of the video signal has a frequency of 60 Hz, a ripple of 20 Hz, which is the beat frequency, occurs.

That is, when a predetermined object is photographed under illumination with a constant illuminance, the average luminance level for each field is normally maintained at a constant value as shown in FIG.
Flicker occurs under the illumination of a 50 Hz discharge lamp.
As shown in Figure 5(b), (Ml)→(M
The brightness level changes as follows: 2)→(M3)→(Ml)→... By the way, similarly to the focus evaluation value average brightness level in the prior art, there is no change in the distance to the subject,
Moreover, even if the subject itself does not change, it has a characteristic that changes in proportion to the amount of light incident on the image sensor, as shown in Figure 5 (b).
) If flicker occurs, the focus evaluation value will fluctuate even though the same subject distance is maintained and the same subject is photographed. If the focusing operation is performed based on the value as in the conventional technology, the peak of the focus position may be incorrectly detected, or the maximum value of the focus evaluation value may change and the focusing operation may be performed even though there is no change in the subject. There is a habit of restarting the computer.

(d) Means for Solving the Problems The present invention provides an integrating means for integrating a high-frequency component of an imaged video signal obtained from an image sensor over one field period;
lens relative position changing means for changing the relative position of the lens with respect to the image sensor; and 3n+1, 3n+ after the start of integration.
2. Separating means for separating the integrated output of the 3nth field (n is an integer) as first to third focus evaluation values; and a relative position of the lens when each of the first to third focus evaluation values becomes maximum; The first to third points to be stored as the first to third focusing positions.
It is characterized in that it includes a position memory and maintains the relative lens position at the average position of the first to third focusing positions.

(E) Function Since the present invention is configured as described above, even if flicker occurs due to the 50 Hz discharge lamp, the influence on the focusing operation can be suppressed to a minimum.

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

FIG. 1 is an overall circuit block diagram of the apparatus of this embodiment.

In FIG. 1, the same parts as in FIG. 2 of the conventional example are given the same reference numerals, and their explanation will be omitted.

The luminance signal in the captured video signal from the imaging circuit (4) is input to the focus evaluation value generation circuit (5), and the high frequency component of the luminance signal within the 7 orcus areas at the center of the screen is calculated as in the conventional example. A digital integral value over one field period is output as a focus evaluation value for the current field.

(20) is a fixed contact (20a)-+ for each field
It is a switch circuit that has a movable contact piece (20d) that switches sequentially (20b) → (20c) → (20a) →..., and is located on the fixed contact (20a) side in the initial state, so
When the focusing operation is started, the focus evaluation value of the first field generated by the focus evaluation value generation circuit (5) is output from the fixed contact (
20a), the focus evaluation value of the second field is supplied to the fixed contact (20b), the focus evaluation value of the third field is supplied to the fixed contact (20c), and the same operation is performed thereafter. Therefore, the focus evaluation value of the 3n+1 (n is an integer) field is supplied to the fixed contact (20a) every 3 fields, the focus evaluation value of the 3n+2 field is supplied to the fixed contact (20b), and the focus evaluation value of the 3n+2 field is supplied to the fixed contact (20c). The focus evaluation values of 3n fields are supplied every 3 fields.

The focus evaluation value supplied to the fixed contact (20a) is stored as the first focus evaluation value (Fl) in the subsequent initial value memory (7), second comparison r5. C9) and first focus position detection circuit (21)
supplied to In addition, fixed contacts (20b) and (20C
) are supplied to the second and third focus position detection circuits (31) (41) as second and third focus evaluation values (F2) (F3).

The initial value memory (7) holds the first value of the first focus evaluation value, that is, the focus evaluation value immediately after the start of the focusing operation, and the second comparator (9) is held in this initial value memory (7). The initial focus evaluation value obtained after that is compared with the first focus evaluation value (Fl) obtained thereafter, and the magnitude thereof is output.

7. The smoke control circuit (50) is similar to the conventional example,
The focus morph (3) moves in a predetermined initial direction until the second comparator (9) outputs a large or small output.
If it is output that the current first focus evaluation value is larger than the initial focus evaluation value by more than a preset variation range, the current rotation direction is maintained and the variation range is If the output is smaller than , the direction of rotation of the 7 orcasmoke (3) is determined so as to reverse the direction of rotation.

After determining this rotational direction, the first to third focus position detection circuits (21), (31), and (41) detect the seven focus ring positions where the first to third focus evaluation values take the maximum value, that is, the lens position. and detect the first to third focusing position data (DI) respectively.
Output as (C2) (C3).

The first focus position detection circuit (21) has a maximum value memory (26
), Compare! (28) and a position memory (23), and as in the conventional example, the maximum value memory (26) is a comparator (2).
Based on the comparison signal (Pl) of 8), the first focus evaluation value (
The maximum value of Fl) is held, the position memory (23) stores the lens position when the maximum value held in the maximum value memory (26) is obtained, and the comparator (28) always stores the maximum value of the maximum value memory (26). ) and the first focus evaluation value (Fl), and when it is determined that the latest first focus evaluation value is larger than the maximum value data of the maximum value memory (26), a comparison signal (Pl) is emitted, and The output (F2
) is emitted. Therefore, the lens position in the position memory (23) when the H level comparison signal (F2) is issued becomes the first focus position 1 (Gl), which is the maximum value of the first focus evaluation value.
First focus position data (Dl) indicating this is output.

The second and third focus position detection circuits (31) (41) also have maximum value memories (36) (46) and comparators (38) (48).
, a position memory (33) (43), and a comparator (
38) From (48), the comparison signal (Pl) is generated every time the second and third focus evaluation values reach a maximum, and the comparison signal is generated when a drop by the first threshold value (△y) is observed from each maximum value. (
F2) is emitted. Each maximum value memory and position memory are updated every time the comparison signal (Pl) is issued, and the position memory (33) (
The lens position of 43) becomes the second and third focus positions (G2) (G3) where the second and third focus evaluation values take the maximum values,
Second and third focus position data (D2) (D3) indicating this
) is output.

The focus position determination circuit (51) determines the first to third focus positions (Gl) (based on the first to third focus position data (DI) (D2) (D3)) corresponding to each position data. G2)(
G3) serves as the final focus position (J).For example, in the example of Fig. 6, the relationship G2<G3×G1 holds, so the final focus position (J) is selected as the intermediate position within G3). The third focus position (G3) is selected.

The three comparison signals (F2) from the comparators (28), (38), and (48) are all input to an AND gate (52), and the output of this AND gate (52) is sent to a 7-occasion control circuit. (50). Then, when both comparison signals (F2) become H level, that is, the first to third focus evaluation values all range from their respective maximum values to the first threshold value (
When it is recognized that △y) is depressed, the AND game)
(52) outputs an H level output, and upon receiving this, the focus motor control circuit (50) immediately reverses the focus motor (3).

After this motor reversal, the third comparator (14) compares the current lens position and the final focus position (J), and when the two match, that is, the lens position reaches the final focus after the focus motor (3) reverses. It emits an output when it is recognized that it has returned to position (J).

Upon receiving this output, the 7-focus smoke control circuit (50) issues a lens stop signal (LS) indicating that the in-focus state has been reached, stops the focus motor (50), and completes a series of focusing operations.

FIG. 6 is a diagram showing the changes in the first to third focus evaluation values with respect to the lens position, and each curve shows the change in the first to third focus evaluation values (Fl) (F2) (F3) with respect to the lens position. The focus motor (
3) Considering the change in lens position during one field period due to driving, the first
This shows the third focus evaluation value, and the distance (L) between the two points is 7 orcasmoke (3
) corresponds to the amount of movement of the lens (1) caused by the drive of the lens (1).

In addition, in FIG. 6, the first threshold value (
It does not take into account the reversal of 7 Orcasmoke (3) due to the drop in Δy), and shows changes in focus evaluation values for the entire range from the return point to the ■ point.

To confirm changes in the subject after a series of focusing operations are completed, use the comparators (28) (38) (
48) is used to confirm changes in the subject, and the latest 1st to 3rd focus evaluation values and maximum value memory (26) (36) (46)
are constantly compared, and the comparison outputs are monitored by a seven-point smoke control circuit (50), and if any of the first to third focus evaluation values fluctuates beyond a preset second threshold If the subject moves or changes, all memories are reset, 7 Orcasmoke (3) is restarted, and the above-described focusing operation is restarted.

In the embodiment described above, the focus motor control circuit (50)
The 7 orcus motor (3) is driven and controlled based on the command, and the lens (1) moves forward and backward in the optical axis direction to change the relative position of the lens with respect to the image sensor. It is also possible to deal with this problem by fixing the image sensor and moving the image sensor forward and backward in the optical axis direction using a bimorph or a motor based on commands from the seven-focus smoke control circuit (50). In addition, in the focus position determining circuit (51), when determining the final focus position (J), the first to third
Although the intermediate position between the focus positions (Gl), (G2), and (G3) is simply selected, it is also possible to calculate the average position of the three focus positions instead.

(g) Effects of the Invention As described above, according to the present invention, it is possible to prevent malfunctions in focusing operations due to flicker even under illumination such as a 50 Hz discharge lamp.

[Brief explanation of drawings]

Fig. 1 is a circuit block diagram of an embodiment of the present invention, Fig. 6 is a diagram showing changes in focus evaluation value of this embodiment, Fig. 2 is a circuit block diagram of a conventional example, and Fig. 3 is the same main circuit. Block diagram, 4th
The figure is a diagram explaining the principle of mountain climbing auto 7 orcus, and FIG. 5 is a diagram explaining changes in brightness and bell due to flicker. (5)... Focus evaluation value generation circuit, (3)... Focus morph, (20)... Switch circuit, (23) (
33) (43)...Position memory.

Claims (1)

[Claims] (1) Integrating means for integrating the high-frequency component of the luminance signal obtained from the image sensor over one field period; Lens relative position changing means for changing the relative position of the lens with respect to the image sensor; 3n+1, 3n+2 after the start of integration; , 3n (n is an integer) field's integrated output as first to third focus evaluation values; and a lens relative position when each of the first to third focus evaluation values is maximum; It is characterized by comprising first to third position memories that are stored as first to third focus positions, and maintaining the lens relative position at a focus position obtained based on the first to third focus positions. Autofocus camera.