JPH0683388B2 - Autofocus system - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an autofocus system used in various video cameras and the like, and in particular, enables accurate focusing without being affected by noise components. It is a thing.

(Prior Art) Conventionally, attention has been paid to the fact that the voltage level of the high frequency component of a video signal obtained by shooting a subject corresponds to the definition of the reproduced image, and the voltage of this high frequency component is used as the focal voltage There is known an autofocus method in which focusing is performed by driving the focus lens so that the focus voltage becomes the maximum level, and the position of the lens is matched with the just focus position.

And, such a focusing system is known as a so-called hill climbing servo system, and this system is NHK Technical Research Report Sho. 40, Vol. 17, No. 1, Vol. 86, page 21, or Showa. It is described in detail in the technical report ED No. 675, etc., published by the Society of Television Science, published in November 1957.

Further, as such an autofocus method, there is one that detects the just focus position by successively detecting a coincidence point between the focus voltage En detected along with the movement of the focus lens and a preset reference voltage SEn. .

That is, in this autofocus method, as shown in FIG. 8, a plurality of reference voltages Sn are set in advance at a predetermined level pitch, and a reference voltage En that changes with the movement of the focus lens reaches the reference voltage Sn. Focusing is performed by determining the moving direction of the focus lens by comparing the voltage levels.

In this method, when the reference voltage SEmax of the same level is detected twice in succession, the intermediate position between the detected positions of these two times is the just focus position P. It is designed to move the focus lens.

(Problems to be Solved by the Invention) By the way, in the autofocus system as described above, when the noise component is superimposed on the focus voltage near the reference voltage as shown in FIG. 9, the focus position is not right. Regardless of this, the noise component may cause the reference voltage of the same level to be detected twice in succession.

As a result, there is a possibility that the position on which the noise component is superimposed as described above may be erroneously determined to be the just focus position, and accurate focusing cannot be realized.

(Means for Solving Problems) The present invention has been made in view of the above-mentioned actual circumstances,
An object of the present invention is to provide an autofocus method capable of performing accurate focusing even if a noise component is superimposed on the focus voltage.

In order to achieve this object, the present invention makes constant a predetermined high frequency part of a video signal obtained by photographing a subject while moving the focusing member (1) by the moving means (2) in the optical axis direction. The focus voltage (En) is taken out every time, and the focus voltage (En) and the plurality of reference voltages (SEn) preset at a predetermined level pitch in the control means (3) are detected for coincidence. It is an autofocus system in which the focusing member (1) is moved in the optical axis direction to perform focusing based on the detection result, and the control means (3) is configured in the autofocusing process to set a plurality of preset values. Each reference voltage (SEn),
The focus voltage (En) detected along with the movement of the focusing member (1) is sequentially compared, and when the comparison result is continuously increased a plurality of times, the focusing member (1) is approaching the just focus position. When it is determined that the focus voltage (En) detected is falling multiple times in succession, it is determined that the focusing member (1) is moving away from the just focus position. Focusing member (1)
The present invention provides an autofocus method characterized in that the moving direction of the lens is determined to perform focusing.

(Operation) According to the autofocus system as described above, for example, the first
As shown in the figure, even if the reference voltage SEn of the same level is detected twice consecutively by superimposing the noise component N on the focus voltage En, the focus voltage (En) immediately rises and falls, or rises and falls. Therefore, it is possible to prevent the intermediate position between the two detected positions from being erroneously determined to be the just focus position.

Further, for example, as shown in FIG. 1, the reference voltage SE of the same level
If max can be detected twice in succession and it can be determined that the focus voltage En has transitioned from rising to falling, the position from this rising to falling, that is, each position where the reference voltage SEmax is detected. The intermediate position of is the just focus position P.

As described above, according to the autofocus method of the present invention, it is possible to clearly determine whether the peak is the pseudo peak due to the noise component N or the peak of the true focus voltage En.

Consequently, according to the present invention, accurate focusing can be realized without being affected by the noise component N.

(Embodiment) A preferred embodiment of the present invention will be described in detail below with reference to FIGS. 1 to 7.

FIG. 2 is a block diagram showing a configuration of an autofocus system for realizing the autofocus system according to the present invention. This autofocus system is provided with an afocal lens 5 and a focus lens (master lens as a focusing member in this embodiment). An optical system 6 including a system lens 1 is provided.

Focusing is performed by moving the focus lens 1 in a predetermined direction (arrow A / B direction) in the optical axis direction by the pulse motor 2, and the focus lens 1 is moved at the same time when the focusing is started. The position of the focus lens 1 on the optical axis is detected by a rotary encoder provided in the pulse motor 2 and position information is obtained.
As S ₁ , a microcomputer 3 which is a control means which is an arithmetic control circuit
(Hereinafter referred to as the microcomputer 3).

Further, the image pickup light from the subject which is incident through the optical system 6 as described above is photoelectrically converted into an electric image signal S ₂ by the image pickup device 7 using a CCD (charge coupled device) or the like.

Then, the video signal S ₂ is amplified by an amplifier 8 and supplied to a camera circuit (not shown) and the like, and is also supplied to a bandpass filter (BPF) 9. The bandpass filter 9 outputs the video signal S ₂ from the video signal S _2. A predetermined high frequency component is extracted and supplied to the gain control circuit (AGC) 10.

Then, the gain control circuit 10 controls the gain of the high-frequency component according to the gain control signal S ₃ supplied from the microcomputer 3, and then supplies it to the detector (DET) 11, and the detector 11 The focus voltage En as shown in FIG. 3 corresponding to the predetermined high frequency component of the video signal S ₂ is obtained.

Here, the focus voltage En corresponds to the definition of the reproduced image reproduced from the video signal S ₂ , and the top position of the focus voltage (En) coincides with the just focus position P.

The focus voltage En is the A / D (analog-digital) converter 1
It is digitized in 2 and supplied to the microcomputer 3.

Then, in principle, the microcomputer 3 sequentially samples the focus voltage En accompanying the movement of the focus lens 1 in the optical axis direction for each field from the start of focusing.

Further, the microcomputer 3 stores a plurality of reference voltages SEn provided at a predetermined level petch as shown in FIG. 1 and a number n unique to each reference voltage SEn).

Then, the microcomputer 3 detects the focus voltage En detected as described above, after amplifying or attenuating the focus voltage En with a predetermined amplification factor, and sequentially detecting the reference voltages SEn, and when these match, the matched reference voltage SEn is obtained. Read only unique numbers.

Here, this microcomputer 3 stores the magnitude relationship between the numbers unique to each reference voltage, and when the newly read number becomes consecutively larger than the previously read number twice. That is, when the focus voltage En is rising, it is determined that the focus lens 1 has moved in the direction of the just focus position P and has not reached the just focus position P, and the focus lens 1 is left as it is. The motor drive circuit 13 sends a control signal S ₄ that keeps moving.
Supply to.

Further, the microcomputer 3 operates the focus lens 1 when the newly read number becomes twice smaller than the number read previously, that is, when the focus voltage En is lowered. It is determined that the focus lens 1 is moving away from the just focus position P, and a control signal S ₄ for changing the moving direction of the focus lens 1 is sent to the motor drive circuit 13 described above.
Supply to.

When the focusing lens 1 is initially moved at the start of focusing, the initial movement direction is maintained until the focus voltage rises or falls twice in succession.
For example, if the ascent and descent are repeated once, the movement continues as it is.

On the other hand, when the focus voltage En at the same level as each reference voltage SEn is detected, the microcomputer 3 takes in the position information S ₁ indicating the position of the focus lens 1 at this time.

In this embodiment, the focus voltage En is fetched by the microcomputer 3 as discrete information for each field.
Therefore, in this embodiment, when the detected focus voltage En first exceeds the reference voltage value SEn, it is assumed that the reference voltage SEn is reached, and the reference voltage SEn at this time and the position information S
It is designed to capture ₁ .

In the autofocus method as described above, as shown in FIG. 4, the number unique to the reference voltage SEmax taken in as the maximum reference voltage value SEmax is detected twice consecutively, and the focus voltage Enmax When A shifts from ascending to descending, the just focus position P is in the middle of these two detection positions (a) and (b).

Therefore, when the same number is read twice in succession and it is determined that the focus voltage En has changed from rising to falling, the focus lens 1 is detected twice with the same number being read. The position of the focus lens 1 can be matched with the just focus position P by moving the focus lens 1 between the positions (a) and (b).

Therefore, the microcomputer 3 supplies the motor drive circuit 13 with a control signal S ₄ for moving the focus lens 1 in the opposite direction (the direction of arrow B) by a predetermined amount M in such a case, whereby the pulse signal is generated. Focusing is performed by rotating the motor 22 in the opposite direction.

On the other hand, as shown in FIG. 5, when the number read as described above is at a lower level than the number read before it, and the focus voltage En shifts from rising to falling, The detection position C of is the just focus position P.

Therefore, in such a case, the focus lens 1
Can be made to coincide with the just focus position P by returning to the previous detection position C.

Also in this case, the microcomputer 3 is used as in the case described above.
Is supplied with a control signal S ₄ for moving the focus lens 1 in the opposite direction by a predetermined amount M to the motor drive circuit 13 for focusing.

As described above, in the autofocus system according to the present embodiment, it is determined whether the reference voltage SEn detected by the coincidence detection with the focus voltage En has risen or falled twice consecutively, and the focus lens 1 with respect to the just focus position. Since the relationship between the moving directions is determined and the just focus position is determined in consideration of the result of this determination, it is possible to prevent an erroneous determination of the just focus position due to a noise component.

In the present embodiment, the reference voltage SEn is continuously raised or lowered twice. However, the present invention may check whether the reference voltage SEn is continuously raised or lowered three times or more. The value may be set appropriately according to the magnitude of the noise component.

Further, in the above embodiment, the level pitch of each reference voltage SEn is made uniform as shown in FIG. 3, but this level pitch is set to 1 as shown in FIG. 6 according to the level of the noise component.
It may be narrowed every other book.

Then, by setting the level pitch in this way, the return amount M after passing the just focus position P once
Is the return amount M ′ when the level pitch is uniform.
Therefore, the time required for focusing can be shortened.

Further, in the autofocus system according to the above-described embodiment, after the just focus position P is once detected and the focusing is completed, the focusing is continuously or continuously for a predetermined time, thereby keeping the just focus position. Check.

As a result, for example, even when the subject changes and the focus voltage En sharply decreases, it is possible to quickly respond.

Further, when the focusing is continued after the predetermined time, the life of the apparatus becomes longer and the image becomes stable as compared with the case where the focusing is continuously continued.

Further, the focusing may be interrupted once, and the focusing may be restarted when the focus voltage drops by a predetermined level or more. In that case, the image is extremely stable unless the subject changes.

By the way, in the above-described embodiment, the level of the focus voltage En is controlled by the gain control circuit 10. However, when the gain is changed, that is, when various setting conditions of the apparatus are changed and the focusing condition is changed, as shown in FIG. As shown in the drawing, a discontinuous portion occurs, and in particular, when the discontinuous portion is not momentarily stable, the focus voltage of the discontinuous portion is detected.

Then, such a focus voltage may cause an erroneous determination of the just focus position.

Therefore, the focus voltage in the discontinuous portion after the gain is changed may be ignored. Further, such a discontinuous portion may occur when the center frequency in the filter circuit 9 or the moving speed of the lens, or the switching of the image pickup area or the zoom is performed, and in such a case, unnecessary focus voltage is similarly generated. You can ignore it.

When the discontinuous portion is far from the just focus position P, the focus lens 1 is continuously moved even at the discontinuous portion, and when the discontinuous portion is close to the just focus position P, the movement of the focus lens 1 is stopped. Inadvertent passage of the just focus position P due to this discontinuous portion can be prevented.

Whether the discontinuous portion is far or close from the just focus position P may be determined based on the magnitude of the gain in the gain control circuit 10.

Further, when the position of the focus lens 1 is far from the just focus position P (for example, when the gain in the gain control circuit 10 is large), the focus lens 1 is moved at a high speed, and when it is close, it is moved at a slow speed for focusing. The required time can be shortened, and the effect of noise components on the focus voltage En can be eliminated by moving the focus voltage En particularly quickly.

Furthermore, the moving speed of the focus lens 1 may be slowed at the start of focusing and made faster after a certain period of time elapses. In this case, the moving speed is slowed down at the time of checking the just focus position to perform an accurate check In addition, the time required for focusing can be shortened as a whole during normal focusing.

In this case, instead of time, the number of times the focus voltage is detected,
The number of fields, the moving distance, the number of pulses of the pulse motor, or the like may be used.

The setting of the fixed time or the like is carried out in one cycle of the check operation, that is, a cycle from leaving the just focus position and returning again, or one cycle within the depth of focus, that is, within the depth of focus around the just focus position. It may be determined based on the time required for the reciprocating cycle, etc.

Further, if the focus voltage greatly changes by a predetermined level or more during the check operation, it is determined that the subject has changed, and if the object is moved at a high speed simultaneously with the start of the check operation, the time required for focusing can be further shortened. .

(Effect of the invention) As is clear from the above description, the present invention can detect the correct just focus position without being affected by the noise component even when the noise component is superimposed on the focus voltage. Therefore, accurate focusing can be realized.

Further, according to the present invention, it is possible to eliminate the adverse effect caused by the discontinuous portion of the focus voltage due to the change of the focusing condition.

Further, as the focusing member according to the present invention, not only the focus lens but also the image pickup device may be moved in the optical axis direction to perform the focusing.

[Brief description of drawings]

FIG. 1 is a graph showing a focus voltage in an embodiment according to the present invention, FIG. 2 is a block diagram showing the same embodiment, FIG. 3 is a graph showing a focus voltage, and FIGS. 4 and 5 are just focus points. 6 is a graph showing the relationship between the focus voltage and the reference voltage in the vicinity of the position, FIG. 6 is a graph showing the focus voltage and the reference voltage in another embodiment of the present invention, and FIG. 7 is a graph showing the same focus voltage. FIG. 8 is a graph showing a conventional general focus voltage and a reference voltage, and FIG. 9 is a graph showing a relationship between the focus voltage on which a noise component is superimposed and the reference voltage. 1 ... Focusing member (focus lens), 3 ... Microcomputer, 7 ... Focusing member (imaging element).

Claims (3)

[Claims] 1. A focus voltage (En) for a predetermined high frequency part of a video signal obtained by photographing a subject while moving a focusing member (1) in the optical axis direction by a moving means (2). As the focus voltage (En) and a plurality of reference voltages (SEn) preset in the control means (3) at a predetermined level pitch, and the focusing is performed based on the detection result. An auto-focus method of moving a member (1) in the optical axis direction to perform focusing, wherein the control means (3) includes a plurality of preset reference voltages (SEn) in the auto-focus process.
The focus voltage (En) detected along with the movement of the focusing member (1) is sequentially compared, and when the comparison result is continuously increased a plurality of times, the focusing member (1) is approaching the just focus position. When it is determined that the focus voltage (En) detected is falling multiple times in succession, it is determined that the focusing member (1) is moving away from the just focus position. Focusing member (1)
Focusing is performed by determining the moving direction of the. 2. A focus voltage (En) for a predetermined high frequency portion of a video signal obtained by photographing a subject while moving a focusing member (1) in the optical axis direction by a moving means (2). As the focus voltage (En) and a plurality of reference voltages (SEn) preset in the control means (3) at a predetermined level pitch, and the focusing is performed based on the detection result. An auto-focus method of moving a member (1) in the optical axis direction to perform focusing, wherein the control means (3) includes a plurality of preset reference voltages (SEn) in the auto-focus process.
The focus voltage (En) detected along with the movement of the focusing member (1) is sequentially compared, and when the comparison result is continuously increased a plurality of times, the focusing member (1) is approaching the just focus position. When the detected focus voltage (En) drops multiple times in succession, it is determined that the focusing member (1) is moving away from the just focus position, and the focus voltage (En) rises. It is determined that the position shifted from the lower position to the lower right position is the just focus position, and the control signal (S4) for returning the focusing member (1) from the lower position to the upper position is supplied to the moving means (2). The auto-focus method is characterized by that. 3. A gain control means (10) gains a predetermined high frequency part of a video signal obtained by photographing a subject while moving a focusing member (1) in the optical axis direction by a moving means (2). After controlling this, the focus voltage (E
n), the focus voltage (En) and a plurality of reference voltages (SEn) preset at a predetermined level pitch in the control means (3) are detected for coincidence, and based on this detection result. It is an autofocus system that performs focusing by moving the focusing member (1) in the optical axis direction, wherein the control means (3) is configured to set a plurality of preset reference voltages (SEn) in the autofocus process. When,
The focus voltage (En) detected along with the movement of the focusing member (1) is sequentially compared, and when the comparison result is continuously increased a plurality of times, the focusing member (1) is approaching the just focus position. When the detected focus voltage (En) continuously drops for a plurality of times, it is determined that the focusing member (1) is moving away from the just focus position, and the gain control means (10) is provided. The autofocus method is characterized in that the above determination is performed by ignoring the focus voltage (En) that is detected immediately after the gain of is changed.