JPH0370273A - Autofocus camera - Google Patents

Abstract

PURPOSE:To obtain focusing state with high accuracy in a short time by providing an interpolation means interpolating a focus evaluation value adjacent to a maximum focus evaluation value obtained by a search means and generating an interpolation focus evaluation value and a focus evaluation discrimination means. CONSTITUTION:A 2nd comparator 105 compares a maximum interpolation result so far stored in an interpolation maximum value memory 104y with a value of interpolation result outputted sequentially from a focus evaluation interpolation circuit 103 and gives an output showing that the current focus evaluation is larger than the value in the interpolation maximum value memory 104y, then the value of the interpolation maximum value memory 104y is revised and simultaneously a focus lens position at that time is stored in an interpolation position memory 104x. When the interpolation maximum value evaluation is obtained, a focus motor control circuit 107 drives a focus ring 2 from the nearest point toward an infinite point at a high speed and when the data in the interpolation position memory 104x and the position data of the current focus ring 2 are coincident, the focus motor 3 is stopped. Thus, highly accurate focusing is attained in a short time.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to an auto7 orcus camera such as an electronic still camera equipped with an autofocus function.

(b) Conventional technology The method of using the high-frequency components of the video signal itself from the imaging probe in the auto-7 orcus device of the camera for evaluating focus control is essentially parallax-free and has a depth of field. It has many advantages, such as being able to focus accurately even when the subject is shallow or far away. 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 autofocus system. Here, regarding this prior art, the fourth
The outline will be explained using FIG. 5 and FIG. FIG. 4 is an overall circuit block diagram of the conventional technology. In this figure, an image formed by a 7-orcus lens (1) is converted into a video signal by an imaging circuit (4) including an imaging device, and
It is input to the focus evaluation value generation circuit (5). The focus evaluation value generating circuit (5) is operated as HII as shown in FIG. The vertical synchronization signal (VD) and horizontal synchronization signal (HD) separated from the video signal by the synchronization separation circuit (5a) are input to the gate control circuit (5b) in order to set sampling areas as seven orcus areas. In the gate control circuit (5b), vertical synchronization signal (VD), horizontal synchronization signal (
A rectangular sampling area is set in the center of the screen based on the fixed oscillator output that drives the HD) and the image sensor, and a gate circuit (5c ).

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).

This total! (5g) specifically includes an adder that adds the A/D conversion data and the latch data of the latch circuit in the subsequent stage, and a so-called latch circuit that latches this added value and is reset for each field. is a digital integrator,
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 seven orcus areas in a time-division manner, digitally integrates this high frequency component over one field period, and uses this integrated value as the focus evaluation value for the current field. It will be output. Next, the operation of FIG. 4 will be explained with reference to the flowchart of FIG. 6. Immediately after the start of the auto 7 orcus operation, the initial heat point evaluation value is held in the maximum value memory (6) and the initial value memory (7) (S,).

After that, the 7-axis motor control circuit (10) is connected to the lens (
1) is rotated in a predetermined direction (S), and the output of the second comparator (9) is monitored. A second comparator (9>) compares the focus evaluation value after driving the seven orcus motors 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 this happens, maintain the same direction of rotation (S,).

If it is output that the current evaluation value is smaller than the initial evaluation value and the above fluctuation range, the rotation direction of the focus motor (3) is reversed (S4), and the first comparator (
8) Monitor the output of (S,).

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). There are two types of comparison signals (PI
)(P2) is output. Here, the maximum value memory (6) is
Based on the output of the first comparator (8), if the current focus evaluation value is larger than the content of the maximum value memory (6), the value is updated (S,), and the focus evaluation value up to now is always updated. The maximum value of is kept (S,).

(13) is the 7 orcus ring (1) that supports the lens (1).
This is a position memory that stores the focus ring position upon receiving the 7-occasion ring position signal indicating the position of 2), and similarly to the maximum value memory (6>), based on the output of the first comparator (8), The focus ring position is updated so as to always maintain the position when the maximum evaluation value is reached.The focus ring (2) is rotated by the focus motor (3), and the lens (1) is rotated according to this rotation. Moving forward and backward in the axial direction is a well-known technique.The 7-occas ring position signal is output by a potentiometer that detects the focus ring position, but the 7-occas ring position signal is output by a potentiometer that detects the focus ring position. It is also possible to define the amount of rotation in the periapsis and direction as positive and negative step amounts, and express it by the step amount of the focus ring or focus motor.

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, the second mode in which the second mode is smaller than the preset first threshold value (Δy) is instructed (reaches Q in FIG. 7), and at the same time the focus motor (3) is reversed (S,). After this reversal, the contents of the motor position memory (13) and the current focus ring position signal are compared for the third time! (14) is compared (SS), and the focus motor (3
) should be controlled to rotate. ), the 7-orcus motor is controlled so that the 7-orcus motor (3) is stopped (S, , ) when the focus ring (2) returns to the position (P) where the focus evaluation value is the maximum. Circuit (10) is functional. At the same time, the focus motor control circuit (10) outputs a lens stop signal (LS).

(c) Problems to be Solved by the Invention The auto 7 orcus operation in the above-mentioned prior art is capable of:
It performs one thermal operation while constantly moving the focus ring by a minute amount (every field), and it takes two seconds to move the focus lens from the close range to infinity, but the main purpose is to create m-shadows in movies. There is no problem with the video camera.

However, electronic still cameras generally capture an image of a subject as a still image in an instant, and in the conventional method described above, it takes about 2 seconds from pressing the shutter button to completing the auto 7 orcus operation. Not only is it extremely difficult to use due to the release time lag, but it is also impractical as there is a risk of missing a photo opportunity.

Therefore, the present invention provides an auto 7 orcus camera that can complete shooting, including autofocus, in an extremely short time (for example, 0.5 seconds) after the shutter button is pressed. That is.

(d) Means for Solving the Problems The present invention provides an autofocus system that performs an autofocus operation by detecting the high-frequency component level of a captured video signal obtained from an image sensor as a focus evaluation value at predetermined intervals. In order to solve the above-mentioned problem, in a camera, a search means for moving a seven-orcus lens in relatively coarse steps "C" from an infinity object distance to a close point, and obtaining a focus evaluation value for each step, and the search means an interpolation means for interpolating between a first maximum focus evaluation value obtained by and mutually adjacent focus evaluation values in the vicinity of the first maximum focus evaluation value to generate an interpolated focus evaluation value; The present invention is configured to include a focus evaluation value determining means for determining a second maximum focus evaluation value from the obtained interpolated focus evaluation value.

(E) Effect According to the above configuration, the autofocus operation is completed in an extremely short time.

(F) Embodiment Hereinafter, an embodiment of the auto 7 orcus camera of the present invention will be described with reference to FIGS. 1 to 3.

Figure 1 shows the auto 7 of an electronic still camera implementing the present invention.
FIG. 2 is a block diagram showing the parts related to the orcus, FIG. 2 is a flowchart of its operation, and FIG. 3 is a diagram for explaining the focusing operation. In addition, auto 7 orcus lens (1
) takes 2 seconds if the conventional operation is performed from the closest point to the infinity point in the focusable range of the lens. Then, since it is possible to obtain 120 fields of video signals in 2 seconds, the focus evaluation value can also be obtained by 120 steps, and therefore the focusing accuracy of the 7 orcus lens (1) is from close range to infinity within the focusing range of the lens. 1/12 far
It can be considered that it is 0.

The operation shown in FIG. 1 will be described below with reference to the operation flowchart shown in FIG. 2 and the characteristic diagram shown in FIG. 3.

First, the camera is in auto 7 orcus mode (in this case, before the autofocus operation starts) (2)
Move it to the point at infinity (S). When the auto 7 orcus operation is started, the first focus evaluation value obtained immediately after the start is stored in the 1.2.3.4 memory (100a) (1
00b) (100c) (100d) is held in the second memory (1,0Ob) of the maximum value memory (100) (S,) and then the 7 orcus motor control circuit (10
7) drives the focus motor (3) and rotates the focus ring (2) from the infinity point to the closest point at a speed 10 times that of the conventional operation, that is, 0.2 seconds (S,) . As a result, since 12 fields of video signals can be obtained in 0.2 seconds, focus evaluation values for 12 steps can also be obtained as shown in FIG.

As the focus ring (2) rotates, the first comparison 5 (102) compares the maximum focus evaluation value stored in the second memory (100b) with the current focus evaluation value. ), the current focus evaluation value is stored in the second memory (10
A signal is output when the value is larger than the content of 0b). Here, the second memory (100b) contains the first comparison! (102)
When there is an output, the value of this second memory (100b) is transferred to the first memory (100a).
00b) is updated (S,), and this second memory (1
00b) always holds the maximum value of the focus evaluation value up to now. 7 Continuing rotation of Orcasmoke (3) (S,)
In the next step, the focus evaluation value is compared again in the first comparison B (102) (S,), and when the focus evaluation value obtained in this step is smaller than the value in the second memory (100b), the focus evaluation value is compared with the first comparison B (102). (S,
).

Furthermore, the focus motor (3) continues to rotate (S).

. ) is again compared with the first comparison uOoz) (S, , ) in the next step, and when the focus evaluation value tL obtained in this step is smaller than the value in the second memory (100b),
The focus evaluation value is held in the fourth memory (100d) (S,).

(101) is the first, second, third, and fourth position memory (10
1a) (101b) (101c) (101d), where the WE2 position memory (101b) is the first comparison! as well as the second memory (100b). (102)
7 when the focus evaluation value reaches the maximum value based on the output of
This is a memory that is constantly updated to hold the lens position data.

The first position memory (101a) is a memory that is updated to always hold the focus ring position one step before the 7 Orcus ringwidth standing data when the focus evaluation value reaches the maximum value, and the third position memory (101a) 101c) is a memory that is updated to always hold the focus ring position one step after the focus ring position data when the focus evaluation value is the maximum value, and the fourth position memory (101d) is the memory that is updated to always hold the focus ring position after the focus ring position data when the focus evaluation value is the maximum value. This is a memory that is updated so as to always hold the 7th place ring position two steps after the 7th place ring position data when the value is reached.
Third and fourth position memories (101a) (101C) (10
1d) corresponds to the first, third, and fourth memories (100a) (100c) (100d) of the maximum value memory (100). These are the first to fourth position memories (LOLA) to (
The detailed function of 101d) can also be understood from (S,)(S,)(S,)(S, , ) in the 70-chart in FIG.

The above operation is performed at the infinity point of the focusing range of the lens (
00) to the closest point (, S, S),
Within 0.2 seconds after the shutter button is pressed, the maximum value among the 12 focus evaluation values and the focus evaluation values in the vicinity thereof can be held in the maximum value memory (100). In Figure 3, the maximum value memory (1 (10)
and values stored in the position memory (101), where y is the first memory (1oOa), yb is the second memory (100b), yc is the third memory (100c), and V* is the 7i44 memory. (100d) respectively, X, is the first position memory (101a), X is the second position memory (101b), and Xo is the third position memory (10+
c) and x4 correspond to the values of the fourth position memory (101d), respectively.

Next, focus ring positions of X and x6 (i.e. 7
The focus evaluation value interpolation calculation circuit (103) calculates the focus evaluation value [interpolation formula for determining the focus evaluation value] for each point when the distance between the focus lens position and the focal lens position is divided into 30 steps.
S,,). This interpolation calculation circuit (103) is, for example,
Scientific and technical calculation by C Published by JCQ Publishing Co., Ltd. PP, 1
72-PP, 205C: The described Lagrange interpolation or spline interpolation is grooved in hardware.

The interpolation results from this interpolation circuit (103) are sequentially output, but the first interpolation result to be output is from the interpolation value memory (103).
104) is held in the interpolation maximum value memory (104y).

The second comparator (105) is the interpolation maximum value memory (104y)
The value of the maximum interpolation result held so far is compared with the value of the interpolation result sequentially output from the focus evaluation value interpolation circuit (103), and the current focus evaluation value is stored in the interpolation maximum value memory (103).
When the output is larger than the value of 043.), the value of the interpolation maximum value memory (104)') is updated, and the maximum value of the interpolation results up to the present is always held in the interpolation maximum value memory (104y). At the same time, the seven-occasion lens position at that time is held in the interpolation position memory (104X).

Interpolation memo based on the output of the second comparator (105) above)
The operation of updating the contents of (104) is indicated by X in FIG.

By performing this on the 20-step interpolated focus evaluation values obtained between
It is possible to obtain the position data of the focus ring (2) when the interpolated focus evaluation value becomes the maximum [Flowchart (S, , ) in FIG. 2].

, ) (see S, , )].

In this embodiment, the interpolation value is obtained by dividing the interval from X to X1 into 20 steps, but instead of this, first the focus evaluation value y of , and if y < y, the maximum focus evaluation value is X
, and X3, therefore, the maximum focus evaluation value can be found more quickly by dividing the distance between X and X1 into 10 steps and performing the same comparison operation using lI2 comparison gain as described above. On the other hand, if y > y c, the maximum focus evaluation value always exists between X and Xb, so the maximum focus evaluation value can be obtained by dividing the interval between I can do it.

In this way, when the maximum interpolated focus evaluation value is obtained, the orcus morph control circuit (107) generates 7 orcus J (2
) is rotated at high speed from the closest point to the infinity point (S,
). Along with this, the data in the interpolation position memory (104x) and the current position data of the focus ring (2) are compared until they match (S,) CS t. ), the focus morph control circuit (107) functions to stop the 7 Orcasmoke (3) when they match (S,).

At this time, seven smoke control circuits (107)
outputs a lens stop signal (LS). Note that X is the focal point in Figure 3. , and the maximum focus evaluation value at that time is y
Show by boiling.

The above-described operation makes it possible to perform highly accurate and high-speed auto-7 orcus operation.

In the above embodiment, the 7 orcus rings were first moved to the infinity point and then moved to the closest point before starting the autofocus operation, but in contrast to this, the 7 orcus rings were first moved to the closest point. Alternatively, the object may be moved to the point at infinity after the object is moved.

In addition, it is not necessary to move the focus ring to the infinity point or the closest point before starting the autofocus operation; in other words, the first maximum focus evaluation value and its vicinity are adjusted between the infinity point and the closest point The initial position of the focus ring is not limited as long as the focus ring is moved so as to perform a search.

Furthermore, a first comparator (102), a second comparator (105),
The third comparator (106), maximum value memory (100), position memory (101), focus evaluation value (103), interpolation value memory (104), and 7-focus motor control circuit (107) are integrated into a 1-chip microcomputer. Needless to say, you can make a mistake by doing so.

(G) Effects of the Invention As described above, the autofocus camera of the present invention can obtain a highly accurate focusing state in a short time, and is particularly suitable when used as an electronic still camera.

[Brief explanation of drawings]

FIG. 1 is a block diagram of main parts showing an embodiment of an autofocus camera according to the present invention, FIG. 2 is a flowchart for explaining the autofocus operation, and FIG. 3 is a diagram showing the focusing operation according to the present invention. Characteristic diagrams for explaining. Figure 4 is a block diagram of the main parts of a conventional auto 7 orcus camera. Figure 5 is a block diagram showing details of the main parts. Figure 6 is a diagram for explaining the conventional autofocus operation. FIG. 17 is a characteristic diagram for explaining the conventional focusing operation. (1)...lens, (2)...focus ring,
(3)...7 orcus motors, (4)...imaging circuit, (5)...focus evaluation value generation circuit, (100)...
Maximum value memory, (101)...Position memory, (102
)...First comparator, (103)...Focus evaluation value correction circuit, (104)...Interpolation value memory, (105)...
・Second comparator, (106)...Third comparator, (107
)... 7-order smoke control circuit.

Claims (1)

[Claims] (1) In an autofocus camera that performs autofocus operation by detecting the high-frequency component level of the captured video signal obtained from the image sensor as a focus evaluation value at predetermined intervals, the focus lens is moved from the infinite distance of the subject. a search means for moving in relatively coarse steps over the closest point and obtaining a focus evaluation value for each step; a first maximum focus evaluation value obtained by the search means; and a first maximum focus evaluation value obtained by the search means; interpolating means for generating an interpolated focus evaluation value by interpolating between focus evaluation values that are adjacent to each other and that are adjacent to each other;
and a focus evaluation value determining means for determining a maximum focus evaluation value of the autofocus camera.