JP3443820B2 - Auto focus method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an autofocus method, and more particularly to an autofocus method for adjusting focus so that a focus evaluation value becomes maximum.

[0002]

2. Description of the Related Art Conventionally, focus adjustment in a television camera or the like is an autofocus method in which a focus lens is automatically moved to adjust the focus, or a manual operation method in which a cameraman operates a focus ring or the like to directly move the focus lens. In addition, a remote operation method of moving the focus lens by a remote operation from a place remote from the main body of the television camera is performed.

In the autofocus method, for example, the sharpness of a subject image transmitted through the photographing optical system is evaluated by an electric quantity called a focus evaluation value, and the focus lens is moved so as to maximize the focus evaluation value. Are known to do. FIG. 4 is an explanatory diagram showing the state of the focus evaluation value curve near the focus. In a subject having a focus evaluation value curve as shown in the figure, when focus adjustment by the autofocus method is activated, the focus lens is set to the focus evaluation value in order to set the focus lens at the maximum point A of the focus evaluation value curve. The focus evaluation value is detected while moving in the increasing direction. Then, when the focus evaluation value starts to decrease, the maximum point A of the focus evaluation value curve is recognized, and the focus lens is moved to the maximum point A of this focus evaluation value curve and stopped.

[0004]

However, in the case of performing the focus adjustment by the conventional autofocus method, by projecting a desired subject in the autofocus area provided on the photographing screen, the focus of the subject to be focused can be improved. If there are multiple subjects with different focal lengths in this autofocus area, which of these subjects will be focused depends on the initial position of the focus lens. Sisters,
There was a problem that it was not possible to focus on the desired subject.

FIG. 5 is an explanatory diagram showing such a situation.
Three persons with different focal lengths are shown in an autofocus area 102 provided on the photographing screen 100. At this time, the state of the focus evaluation value with respect to the position of the focus lens is considered to have three maximum points as shown in FIG. The mountains A, B, and C described in FIG. 6 are formed by the persons A, B, and C who are the subjects in FIG. 5, respectively.

In FIG. 6, for example, if the focus lens is located at the point shown in FIG. 6 when the focus adjustment by the autofocus method is started, the focus lens moves in the direction in which the focus evaluation value increases, After passing the maximum point of the mountain A, the maximum point of the mountain A in the figure is detected, and the subject A is brought into focus. If the focus lens is located at the point in the figure, the subject C will be focused by the same procedure as above. Therefore, there may be a case where the desired subject cannot be focused only by the focus adjustment by the autofocus method.

In addition, when a person other than the subject to be photographed crosses the autofocus area 102 or when the contrast of the subject is low, the subject may be focused at a position different from the position of the subject. . In such a case, conventionally, the autofocus mode for performing the focus adjustment by the autofocus method is canceled once, and the remote mode for performing the focus adjustment by the remote operation or the manual mode for performing the focus adjustment by the manual operation is set, and then the focus adjustment is performed. Had to start over. Such an operation is troublesome, time-consuming, and very inconvenient.

The present invention has been made in view of the above circumstances, and when the focus is adjusted by the autofocus method,
It is an object of the present invention to provide an autofocus method that enables manual operation or remote operation and can effectively utilize the advantages of both.

[0009]

To achieve the pre-Symbol purposes SUMMARY OF THE INVENTION The invention as defined in claim 1, and converted into a video signal by the image pickup device a subject image focused by the imaging optical system including a focus lens , A focus evaluation value indicating the sharpness of the subject image is obtained from the video signal, the focus lens is moved to a lens position where the focus evaluation value is maximum, and a focus sequence for capturing the maximum focus evaluation value is executed,
In the autofocus method for executing the focusing sequence again when the maximum focus evaluation value changes after the focusing sequence ends, when a remote operation or a manual operation is performed during or after the execution of the focusing sequence, the remote operation or In addition to moving the focus lens by manual operation, the focus evaluation value after remote operation or manual operation is captured as the maximum focus evaluation value, and is made to stand by at the end of the focusing sequence to perform focus evaluation.
When the value has changed from the maximum focus evaluation value by a predetermined value or more
Is characterized in that the focusing sequence is restarted .

The invention described in claim 2 is the same as claim 1.
In the invention described in the paragraph 1,
When the predetermined switch operation is performed,
-The feature is that it is designed to restart the can
It

[0011]

[0012]

According to the present invention, when a remote operation or a manual operation is performed during focus adjustment by the autofocus method, the focusing sequence (the sequence for setting the focus lens at the maximum point of the focus evaluation value curve) is given priority. Then, the focus lens is moved by this manual operation or remote operation. Then, when the focus adjustment by the remote operation or the manual operation is completed, the focus evaluation value at the current focus lens position is taken in as the maximum focus evaluation value, and the focus lens is stopped and waits until the focus evaluation value changes. If the focus evaluation value changes, the focusing sequence is executed again, and the focus lens is moved to the position where the focus evaluation value is maximum.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the autofocus method according to the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a block diagram showing an internal configuration of an autofocus device in a television camera to which the autofocus method according to the present invention is applied.

In FIG. 1, a subject image is formed on a light receiving surface of a solid-state image pickup device (CCD) 20 by a photographing optical system 10 including a focus lens 12, a variable power lens 14, a master lens 16 and a diaphragm 18. Then, after being converted into an electric signal here, it is output to the image pickup circuit 22. The image pickup circuit 22 forms a video signal from the signal output from the CCD 20, and outputs this video signal to the external video display device 50 such as the viewfinder 48 or monitor TV. As a result, the viewfinder 48 and the external image display device 50
Displays the video being shot.

Next, focus adjustment in the television camera will be described. This television camera has an autofocus mode in which focus adjustment is automatically performed and a remote focus mode in which focus adjustment is performed by remote operation. The auto focus mode and the remote focus mode are switched by the mode switch 41. In addition to the remote focus mode, a manual focus mode in which the focus lens 12 is moved by manually operating a focus lens or the like can be provided.

First, the case where the mode switch 41 is used to switch to the autofocus mode will be described. In the auto-focus mode, the image pickup circuit 22 outputs the luminance signal to the high-pass filter (HPF) 24, and at the same time, outputs the synchronizing signal to the focus area selection gate 28, the adder 30, and the CPU 32 according to the video signal.
Output to.

The HPF 24 extracts the high frequency component contained in the luminance signal. The higher the sharpness of the image, the more the extracted high-frequency components are included. Therefore, by integrating the high-frequency components, it is possible to quantify the average sharpness of the image in the integration range. The high frequency component that has passed through the HPF 24 is converted into a digital signal by the A / D converter 26 and input to the focus area selection gate 28. The focus area selection gate 28 is a circuit that extracts only a signal corresponding to the central focus area on the imaging screen, and extracts only the information about the subject (main subject) imaged in this focus area.

The digital signal extracted by the focus area selection gate 28 is output to the adder 30, and the digital signals for one field are integrated. The integrated value is output to the 1-chip CPU 32 as a focus evaluation value indicating the sharpness of the image. The CPU 32 refers to the position of the focus lens 12 and the focus evaluation value output from the adder 30 at the position while moving the position of the focus lens 12 by the unit movement amount so that the focus evaluation value is maximized. 12 positions are being adjusted. The details will be described later.

The position of the focus lens 12 is detected by the potentiometer 40 and output to the CPU 32 via the A / D converter 38. Also, the focus lens 1
The movement of 2 is performed based on a position command signal indicating the focus lens position output from the CPU 32. That is,
The position command signal output from the CPU 32 is converted into an analog signal by the D / A converter 33 and applied to the motor drive circuit 34. The other input of the motor drive circuit 34 is from the potentiometer 40 to the focus lens 1
A signal indicating the position 2 is added, the motor drive circuit 34 takes the difference between these two input signals, and outputs a drive signal obtained by amplifying this difference signal to the focus motor 36.
When the focus motor 36 is driven, the focus lens 12 moves via a drive mechanism (not shown).

Next, the case where the mode switch 41 is used to switch to the remote focus mode will be described. In this case, the CPU 32 drives and controls the focus lens 12 based on the count value of the rotary encoder counter 46. That is, when the focus operation unit 42 is operated, a pulse signal corresponding to the operation amount (rotation amount) and the rotation direction is output from the incremental rotary encoder 44. This pulse signal is up-counted or down-counted by the rotary encoder counter 46 and digitized into a value proportional to the rotation amount. Then, the CPU 32 outputs the position command signal D / based on the count value output from the rotary encoder counter 46.
It outputs to the motor drive circuit 34 via the A converter 33 to move the focus lens 12. The count value of the rotary encoder counter 46 is reset to 0 every time the CPU 32 reads it.

Next, the procedure of focus adjustment in the autofocus mode will be described with reference to the flowchart of FIG. First, it is determined whether the auto focus mode is set (S10). If it is not in the auto focus mode, focus adjustment is performed based on remote operation.
On the other hand, in the case of the auto focus mode, step S1
In 2, it is determined whether or not a remote operation is performed. If the remote operation is not performed, the focus lens 12 is moved by the unit movement amount in the direction in which the focus evaluation value increases, and the focus evaluation value is detected (S1).
4). The direction in which the focus evaluation value increases is determined by first moving the focus lens 12 forward or backward by a unit movement amount and examining the increase or decrease in the focus evaluation value.

Next, in step S16, it is determined whether or not the maximum focus evaluation value is detected. The maximum focus evaluation value can be determined when the focus lens 12 starts to decrease as the focus lens 12 moves. Therefore, the processing from step S10 to step S16 is repeated until the focus evaluation value starts to decrease. The processing from step S10 to step S16 will be referred to as a focusing sequence.

When the maximum focus evaluation value is detected, the focus lens 12 is moved to a position where this maximum focus evaluation value is reached and stopped (S18). Here, if a remote operation is performed by the focus operating unit 42 during the focusing sequence, the process proceeds to step S20 by the determination process of step S12, and the focus lens 12 is moved according to the remote operation. Then, when the remote operation is completed, the focus lens 12 is stopped at the final movement position, and the focus evaluation value at this position of the focus lens 12 is detected (S22).

After the processing of step S18 or step S22, if there is no change in the state of the subject and no operation of the television camera is performed, the focus lens 12 is stopped. At this time, if the remote operation is performed by the focus operation unit 42, the process proceeds to step S20 by determining whether or not the remote operation is performed in step S24, and the focus lens 12 is moved based on the remote operation. Then, step S22
The focus evaluation value is detected by, and the focus lens 12 is stopped again.

In step S26, it is determined whether or not the focus evaluation value has changed, or whether or not it is in the remote focus mode. That is, when the position of the subject or the television camera changes and the position of the focus lens 12 that maximizes the focus evaluation value changes, the focusing sequence is performed again. The focus evaluation value that has been set is in any step (S22 or S2
In 6), when the focus evaluation value detected last time is changed by a predetermined amount or more, the focusing sequence is restarted.
When the current autofocus mode is changed to the remote focus mode, the autofocus mode is canceled by the process of step S10.

According to the flow chart of FIG. 2, the focus lens is normally adjusted so that the focus evaluation value is always maximized, and the object within the section on the photographing screen selected by the focus area selection gate 28 is focused. There is. That is, the focus adjustment is performed as in the conventional autofocus. However, the point that is different from the conventional one is that without providing a procedure for canceling the autofocus mode in particular,
Focusing by remote operation or manual operation can be prioritized, and the focus can be adjusted to another position.

FIG. 3 is a modification of the autofocus method in the flowchart of FIG. 2, in which steps performing the same processing as in FIG. 2 are given the same numbers. In the flowchart in FIG. 3, step S22 in the flowchart in FIG. 2 is deleted. The difference in operation is that the remote operation is performed in the autofocus mode in the focus adjustment in FIG. 2 (S12, S
24), the position of the focus lens 12 after the remote operation is stopped at the position moved by the remote operation unless the focus evaluation value changes. On the other hand, in the autofocus method in FIG. 3, when the focus lens 12 is moved according to the remote operation in step S20, the focusing sequence is started again after the remote operation is completed. That is, by deleting step S22 in FIG. 2 and not detecting the focus evaluation value, the focus evaluation value at the position of the focus lens 12 before the remote operation is compared with the focus evaluation value at the position of the focus lens 12 after the remote operation in step S26. To be done. In this case, since the focus evaluation value is changed by remote operation, the process returns to the start of the flowchart and the focus adjustment based on the focus evaluation value is started again.
Therefore, when there are a plurality of subjects with different focal lengths as shown in FIG. 5, if the target subject is out of focus, if the intended subject is focused to some extent by remote operation, it will be automatically performed after the remote operation is completed. The focus is finely adjusted based on the focus evaluation value.

If the focus adjustment is performed in the autofocus mode and the focus lens is stopped and the focus adjustment is to be restarted for some reason, the CPU 32 in FIG. 1 is indicated by a dotted line. The restarting sequence may be restarted by connecting the restarting switch 52 and pressing the restarting switch 52.

Further, in the above embodiment, the operation amount or operation speed of the remote operation or the manual operation is detected, and when the operation amount is small or the operation speed is low, the focus adjustment is performed based on the remote operation or the manual operation.
Conversely, when the operation amount is large or the operation speed is high, focus adjustment based on the focus evaluation value may be restarted.

[0030]

As described above, according to the autofocus method of the present invention, it is possible to interrupt a remote operation or a manual operation during focus adjustment by the autofocus method. When there are a plurality of subjects at different distances, it becomes easy to focus on a subject different from the subject focused by the autofocus method.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a television camera to which an autofocus method according to the present invention is applied.

FIG. 2 is a flowchart showing an embodiment of a processing procedure of an autofocus method according to the present invention.

FIG. 3 is a flow chart showing another embodiment of the processing procedure of the autofocus method according to the present invention.

FIG. 4 is a diagram showing a state of a focus evaluation value curve in the vicinity of focus.

FIG. 5 is a diagram showing an example of a state of a subject on a shooting screen.

6 is a diagram schematically showing a focus evaluation value curve formed by the subject in FIG.

[Explanation of symbols] 10 ... Shooting optical system 12 ... Focus lens 14 ... Variable magnification lens 16 ... Master lens 18 ... Aperture 20 ... CCD 22 ... Imaging circuit 24 ... HPF 28 ... Focus area selection gate 30 ... Adder 32 ... CPU 34 ... Motor drive circuit 36 ... Focus motor 42 ... Focus operation unit

Continuation of front page (56) Reference JP-A-4-37827 (JP, A) JP-A-4-207479 (JP, A) JP-A-6-67084 (JP, A) JP-A-6-121216 (JP , A) JP-A-2-124546 (JP, A) JP-A-63-113430 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G02B 7/28 G03B 13/36

Claims (2)

(57) [Claims] 1. A focus evaluation value indicating sharpness of a subject image is obtained from the video signal by converting a subject image formed by a photographing optical system including a focus lens into a video signal by an image sensor. A focus sequence is performed in which the focus lens is moved to a lens position that maximizes the maximum focus evaluation value, and when the maximum focus evaluation value changes after the focus sequence ends, the focus sequence is executed again. In the method, when a remote operation or a manual operation is performed during or after the execution of the focusing sequence, the focus lens is moved by the remote operation or the manual operation, and a focus evaluation value after the remote operation or the manual operation is finished. Captured as the maximum focus evaluation value and the focus sequence is completed To wait, focus the focus evaluation value up to the
If the point evaluation value has changed by more than a predetermined value,
An autofocus method characterized by restarting the can. 2. At the end of the focusing sequence,
When a predetermined switch operation is performed, the focusing sequence
Is restarted.
Focus method.