JPH05316401A - Automatic focus detector - Google Patents

Abstract

PURPOSE:To avoid the effect of a fluctuation component of a focus signal caused by noise or flicker onto the detection by implementing the discrimination of increase/decrease in a focal point signal and the discrimination of focusing through the comparison of a threshold level including the fluctuation component of focus signal with the mean data of focus signal. CONSTITUTION:An image pickup element (CCD) 14 receives a light 13 of an object made incident through a zoom lens 11 and a focus lens 12, a camera process circuit 15 processes the light as a video signal and the processed signal is generated and outputted as a luminance signal and a chrominance signal. An AF window circuit 16 extracts only a luminance signal in an area required for the focus automatic control and the result is inputted to a BPF 17 passing only a signal band required for the focus automatic control. A microcomputer 20 gives an integration clear signal CR to an integration device 19 at the start of one field and receives integration data FD at the end of one field. Furthermore, the microcomputer 20 outputs a lens drive signal AS for each field. A focal point signal (focal point voltage) is obtained through the repetition of the operation of the microcomputer 20.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus automatic detection device for use in optical equipment such as video cameras and electronic still cameras.

[0002]

2. Description of the Related Art In video cameras and electronic still cameras,
A focus matching means for detecting a high-frequency component relating to contrast as a focus signal from the video signal output from the image pickup device and moving the focus lens so as to maximize the focus signal is provided.

Such a focus matching means operates according to a graph showing the relationship between the focus signal and the position of the focus lens shown in FIG. 3, that is, a so-called hill climbing curve (focal voltage curve). Is becoming

Assuming that the focus lens is moved from the infinity position to the closest position, at time tn-1, the lens position CCn-1, focus signal Sn-1, and at time tn-1.
Then, since the lens position is CCn and the focus signal is Sn, the difference data ΔSn of the focus signal is ΔSn = Sn−Sn−1 (1).

If the difference data ΔSn is greater than a certain threshold value A, it is determined to be increased, and if it is less than a certain threshold value -B, it is determined to be decreased. When shifting to the determination, it is determined that the maximum value of the focus signal has been passed. Increase determination ΔSn = Sn-Sn-1> A (2) Decrease determination ΔSn = Sn-Sn-1 <-B (3)

According to this decrease determination, the focus lens is moved back to the lens position Co at which the focus signal is maximized and focused.

The difference data ΔSn is the maximum value Smax and the minimum value Smin of the focus signal Sn detected up to the present time.
The increase / decrease may be determined using. ΔSn = Sn−Smin> A (4) ΔSn = Sn−Smax <−B (5)

On the other hand, since the focus voltage curve shown in FIG. 3 changes according to the voltage level of the focus signal, the above thresholds A and B are changed according to the voltage level of the focus signal to improve the accuracy. An increase / decrease determination means for increasing the increase has already been proposed.

Further, in order to remove the influence of noise and flicker component of the subject from the focus signal, means for judging increase or decrease by using data obtained by averaging the focus component Sn has been developed.

[0010]

The above-mentioned focus matching means operates effectively when the focus voltage curve as shown in FIG. 3 draws an ideal mountain, but in reality, noise and flicker of an object are observed. -It is difficult to improve the accuracy of focus adjustment due to the influence of.

For this reason, a focus voltage curve for obtaining the average data of the focus signal is often used. (Fig. 4
However, in the case of such a configuration, it is necessary to increase the threshold values A and B to determine the maximum value.

However, if the thresholds A and B are set to be large,
Since the sensitivity of the increase / decrease determination is made dull, there is a problem that the determination of the maximum value is delayed when the focus voltage curve is an ideal curve or a curve close to this.

Further, when the contrast of the subject is low, the level of the focus signal also becomes small, so that it becomes impossible to judge the maximum value, and there is a problem that the focusing sensitivity is lowered.

[0014]

In order to achieve the above object, according to the present invention, the high frequency component of the video signal obtained from the image pickup means for receiving the incident light of the photographing lens is detected a plurality of times to detect the average defocus of the focus signal. -Sequentially detecting the data, comparing the average data with a predetermined threshold value to determine whether the focus signal is increasing or decreasing, and moving the focus lens included in the photographing lens,
In the automatic focus detection device for focusing by moving the focus lens back so that the focus signal becomes maximum based on the decrease determination immediately after the focus signal has passed the maximum value,
At the initial stage of detecting the focus signal, the first means for obtaining the signal fluctuation component from the maximum value and the minimum value of this signal is compared with the threshold value including the signal fluctuation component by the first means and the average data, and the focus is compared. Second means for determining increase or decrease of the signal, third means for obtaining a signal fluctuation component from the maximum value and the minimum value of the focus signal when the focus signal has passed the maximum value, and -Comparing the average data of the focus signal when the cus lens is moved back and the maximum value average data of the focus signal obtained by the second means, and this comparison value is the third value.
According to another aspect of the present invention, there is provided a focus automatic detection device including a fourth means for determining focus when the focus is within a threshold including the signal fluctuation component.

[0015]

In the initial stage of detecting the focus signal, the noise and flicker components contained in the focus signal are detected by the first means. That is, the maximum value and the minimum value are selected from the focus signals detected several times, and the signal fluctuation component is obtained. This signal fluctuation component is used as one element in the threshold value for the subsequent increase / decrease determination.

In the second means, the average data of the focus signal is compared with the threshold value to judge whether the focus signal increases or decreases. That is, the threshold value including the signal fluctuation component obtained by the first means is compared with the average data of the focus signal, and the increase determination and the decrease determination are performed.

Immediately after the maximum value of the focus signal has passed,
While the cas lens is stopped, the signal fluctuation component is obtained from the focus signal detected at this point by the third means. This signal fluctuation component is used for the focus determination performed by the fourth means.

The focus lens is moved so that the focus signal becomes maximum by the decrease determination by the second means after the maximum value of the focus signal has passed. The fourth means compares the average data of the focus signal when the focus lens is moved in this way with the maximum value data of the focus signal obtained by the second means, and When the comparison value is within the threshold including the signal fluctuation component by the third means, the focus determination is made.

[0019]

An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an example of a circuit implemented as an automatic focus detection device for an electronic still camera.

In the figure, reference numerals 11 and 12 denote zoom lenses and focus lenses included in the photographing lens, and a subject light 13 incident through these lenses 11 and 12 is received by a CCD 14, which is an image pickup device, to form an image. Output a signal.

The video signal output from the CCD 14 is processed by the camera process circuit 15 to generate a luminance signal and a color signal, which are then output. Note that FIG. 1 shows only the luminance signal (Y) necessary for the focus automatic control.

This luminance signal (Y) is input to the AF window circuit 16, and after extracting only the luminance signal in the area required for automatic focus control, a bandpass filter that passes only the signal band required for automatic focus control. (B, P, F) 1
Input to 7.

The luminance signal (Y) output from the band pass filter 17 is input to the arithmetic unit (ALU) of the microcomputer 20 through the absolute value circuit 18 and the integrator 19.

The integrator 19 integrates the luminance signal (Y) for one field, and then clears the integrated data by the integration clear signal CR sent from the microcomputer 20.

The microcomputer 20 judges the start of one field from the input vertical synchronizing signal (VD) and horizontal synchronizing signal (HD), and tells the integrator 19 at the start of one field. The integration clear signal CR is sent and the integration data FD is loaded into the arithmetic unit (ALU) at the end of one field.

A focus signal (focus voltage) is obtained by repeating this operation of the microcomputer 20. Then, the microcomputer 20 outputs a lens drive signal As to drive the focus lens 12 for each field. The driving speed of the focus lens 12 is changed according to the position of the zoom lens 11 and the subject brightness.

The operation of the above-described automatic focus detection device is performed according to PHASE shown in Table 1 below. The operation will be described below with reference to the flowchart shown in FIG.

[0028]

[Table 1]

When a moving image is handled like a video camera, the initial position of the focus lens at PHASE "0" is an arbitrary position, but in a case where a still image is handled like an electronic still camera, this focus is set. -Move the waste lens 12 to the ∞ position or the closest position.

In this PHASE "0", the focus voltage is detected No times with the focus lens 12 stopped, and the fluctuation range δSo is calculated from the maximum value and the minimum value of the focus voltage detected No times, and δSo = Somax-Somin> Ao (6) The flicker is determined from the equation. Then, the averaged data So of the detected focus voltage is obtained and stored as the initial data in the RAM of the microcomputer 20. (Step ST100)

When the above equation (6) is satisfied, P
Go to HASE “1”. For the focus voltage after PHASE “1”, averaged data of Ni times (i indicates each PHASE) is used. The averaging is performed by the focus lens 1
Not only when the focus lens 12 is stopped but also when the focus lens 12 is being driven, the moving average is used to obtain the signal average data by the following equation (7). Sin = (Sn + Sn-1 + ... + Sn-ni) / Ni (7) Note that Sn is the current focus voltage.

In the front-back determination in PHASE "1", a value obtained by adding the fluctuation range δSo to the normal thresholds A ₁ and B ₁ is used as the determination threshold for increase / decrease. (Step ST10
(0, ST200) In practice, taking into account the averaging data, by adding a value obtained by multiplying the fluctuation range δSo by the coefficient C ₁ , the increase in the influence of the fluctuation component of the focus voltage
Decrease determination control can be performed. Also, C ₁ In view of the number of times of averaging, it is preferable to C ₁ = ₁ / N.

If the front-back determination is expressed by a mathematical expression, it becomes as follows. Difference data ΔS ₁ n = S ₁ n−S ₁ , n−1 (8) Increase determination ΔS ₁ n> A ₁ + C ₁ · δSo ···· .. (9) Decrease judgment ΔS ₁ n <− (B ₁ + C ₁ · δSo) (10) The difference data ΔS ₁ n is calculated from the maximum value and the minimum value of the focus voltage. When obtaining, ΔS ₁ n = S ₁ n−So (11) (Steps ST400 to ST700)

According to the above-mentioned increase / decrease judgment, PHA
Move to SE "2". In this operation stage, the focus lens 12 is driven to move in the direction of increasing the focus voltage according to the increase determination.

In this PHASE "2", the focus lens 12 is moved and driven until the focus voltage shifts to decrease while increasing and decreasing according to the following expressions (12) to (14). The maximum value S ₂ max of the voltage and the moving position CCmax of the focus lens 12 at which the focus voltage shows the maximum are described in the memory of the microcomputer 20. (Steps ST400, ST500, ST80
0)

Difference data ΔS ₂ n = S ₂ n−S ₂ , n−1 (12) Increase determination ΔS ₂ n> A ₂ + C ₂ · δSo (13) Decrease determination ΔS ₂ n <B ₂ + C ₂ · δSo (14) In addition, the difference data is the maximum value S ₂ max and the minimum value S _{2 of the} focus voltage. When it is calculated from min, ΔS ₂ n = S ₂ n−S ₂ min (15) ΔS ₂ n = S ₂ n−S ₂ max (16)

When the decrease determination is entered, PHASE
Move to “3”. At this stage, the focus lens 12 is stopped and the fluctuation range of the focus voltage is obtained by the following equation (17). (Step ST900) δS ₃ = S ₃ max-S ₃ min (17)

Next, the process moves to PHASE "4" and the focus lens 12 is moved to CCma obtained by PHASE "2".
Move back to the x position. (Step ST1000)

Subsequently, the flow shifts to PHASE "5" to make a focus determination according to the following equations (18) and (19). In this operation step, the maximum value S ₂ max of the focus voltage obtained by PHASE “2” is compared with the current focus voltage, and this difference data S ₅ n is the fluctuation range δS _{3 of the} focus voltage.
When it is within a threshold including (Step S
T1100)

Difference data ΔS ₅ n = Sn−S ₂ max (18) Focus determination − (B ₅ + C ₅ · δS ₃ ) <ΔS ₅ n <A ₅ + C ₅ · δS ₃ ·· (19) in this way, focus determination step, for comparison with the threshold value, including the fluctuation range delta] S ₃ focus voltage, it is possible to perform in-focus determination is not affected by variation component of focusing voltage.

[0041]

As described above, according to the present invention, the increase / decrease determination of the focus signal and the in-focus determination are made in comparison with the threshold value including the fluctuation component of the focus signal. The influence of the fluctuation of the focus signal that occurs is small, and the threshold values A and B can be set to a small value. As a result, the sensitivity of the increase / decrease determination and the focus determination does not decrease, and even a subject with low contrast can be accurately It becomes an automatic focus detection device that can focus.

[Brief description of drawings]

FIG. 1 is a block diagram showing a circuit example in which the present invention is implemented as an automatic focus detection device for an electronic still camera.

FIG. 2 is a flowchart for explaining the operation of the above focus automatic detection device.

FIG. 3 is a diagram showing a focus voltage curve conventionally used for automatic focus detection.

FIG. 4 is a diagram showing a focus voltage curve obtained by averaging focus signals.

[Explanation of symbols]

 11 zoom lens 12 focus lens 13 subject light 14 CCD 15 camera process circuit 16 AF window circuit 17 bandpass filter 18 absolute value circuit 19 integrator 20 micro computer

Claims (1)

[Claims] 1. An average data of a focus signal is sequentially detected by detecting a high frequency component of a video signal obtained from an image pickup means for receiving incident light of a photographing lens a plurality of times, and the average data and a predetermined threshold value. The focus lens included in the photographing lens is moved to determine whether the focus signal becomes maximum based on the decrease determination immediately after the focus signal has reached the maximum value. -In a focus automatic detection device for returning a cus lens to move the focus to focus, first means for obtaining a signal fluctuation component from the maximum value and the minimum value of this signal at the initial stage of detection of the focus signal, and the first means Second means for comparing the threshold value including the signal fluctuation component by the means with the average data to judge increase / decrease of the focus signal, and the maximum value and the minimum value of the focus signal at the time when the maximum value of the focus signal has passed. Calculate the signal fluctuation component from The third means for adjusting the focus signal, the average data of the focus signal when the focus lens is moved back based on the decrease determination, and the maximum value average data of the focus signal obtained by the second means are compared. The focus automatic detection device further comprises: a fourth means for making a focus determination when the comparison value is within a threshold including the signal fluctuation component by the third means.