JP3380627B2 - Auto focus device - 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 device mounted on a video camera or the like.

[0002]

2. Description of the Related Art As a control system of an autofocus device mounted on a video camera or the like, there is a so-called hill-climbing servo system which uses a video signal as focus information. First, an outline of this method will be described with reference to FIG.

FIG. 4 is a block diagram showing the structure of an autofocus device. 1 is an image pickup lens system, 2 is a focus lens which is a part of the image pickup lens system 1, and 3 is a CCD (charge coupled device) which is an image pickup device. Reference numeral 4 is a camera process circuit, 5 is a video signal processing circuit, 6 is a gate circuit, 7 is a high-pass filter (hereinafter referred to as HPF), 8 is an integrating circuit, 9 is focus motor drive control means, and 10 is focus motor drive means. , 11 is a focus motor, 12 is a lens position detecting means, and 13 is a lens position memory.

The subject image formed by the image pickup lens system 1 is converted into an electric signal by the CCD 3. This electric signal becomes a video signal by the camera process circuit 4,
Further, the video signal processing circuit 5 separates and outputs the luminance signal. Of this luminance signal, only the signal within the focus area passes through the gate circuit 6, and the high-frequency component is extracted by the HPF 7 in the next stage. A focus evaluation value is obtained by integrating the high frequency component of the luminance signal by the integrating circuit 8 for each field. The focus evaluation value is an integral value of the high frequency components of the luminance signal in the focus area thus set in advance, and is obtained in one field cycle. The focus evaluation value (hereinafter, referred to as an evaluation value) increases as the focus lens 2 approaches the in-focus position, and reaches the maximum value at the in-focus position. If the focus lens 2 is driven in the same direction after passing the in-focus position, the evaluation value decreases.

The focus motor drive control means 9 judges whether the evaluation value increases or decreases due to the movement of the focus motor 11,
The position where this evaluation value is maximum is determined, and the focus lens 2 is controlled to move and stop at this position. The focus motor 11 is driven by the focus motor driving means 10 based on such a servo system.

Next, the conventional focus motor drive control means 9 will be described in more detail. The evaluation value acquired at the current position of the focus lens 2 (hereinafter referred to as the lens position) and the evaluation value acquired at the position of the focus lens 2 immediately before are stored in a memory (not shown), and these values are stored. The focus motor drive control means 9 determines the drive direction of the focus motor 11, the on / off of the drive, and the timing thereof, and controls the drive of the focus motor via the focus motor drive means 10 at the in-focus position. . The stop operation at the in-focus position is performed by the focus motor 11 when the evaluation value decreases from the maximum value to a predetermined threshold value or more.
Can be achieved by reversing the above and returning the focus lens 2 to the position where the evaluation is maximized.

Further, conventionally, as in the technique described in Japanese Examined Patent Publication No. 6-42718, the first evaluation value detecting means showing a sharp change in the evaluation value and the second evaluation value showing a gentle change with respect to the lens position. It has two evaluation value detection means, monitors the evaluation values obtained from these two evaluation value detection means, and when the evaluation value from the first evaluation value detection means is below a preset reference level, The focus evaluation value is obtained by performing the focusing operation by the evaluation value from the second evaluation value detecting means, and by performing the focusing operation by using the evaluation value from the first evaluation value detecting means when it is higher than the reference level. A means has been proposed for realizing a highly accurate focusing operation regardless of whether the curve is steep or gentle.

[0008]

FIG. 5 is a graph showing a focus evaluation value curve. When the evaluation value is plotted with the position of the focus lens 2 as the horizontal axis as shown in FIG. 5, the object, the object situation and the evaluation value are plotted. The characteristics of the mechanism that obtains
For example, it can be seen that the shape of the curve changes variously depending on the optical characteristics of the lens and the characteristics of the HPF.

Accordingly, the thus determined the threshold uniquely, e.g., Oh clear contrast when (typically subject to draw a sharp curve as curve A in FIG.
The same threshold value Δk can be applied when a gentle curve like the curve a in the figure is drawn (when the contrast of the subject is not clear in general).
On the other hand, the movement amount of the focus lens takes different values of ΔL1 and ΔL2 (ΔL2> ΔL1).
Therefore, when attempting to focus on a subject having a curve a, the amount of overrun from the focus position until the decrease is detected becomes unsightly, and the image is unsightly. There was a problem that the time would be long.

Further, in the focus evaluation detecting means described in Japanese Patent Publication No. 6-42718, two focus detecting means are prepared according to the evaluation value detecting means, but optimization of this overrun is considered. However, the above problems still remain.

The present invention solves these problems, reduces the overrun amount of the focus lens, reduces the unsightlyness due to the overrun amount of the image pickup screen, and shortens the time to focus. An object of the present invention is to provide an automatic focusing device.

[0012]

In order to achieve the above-mentioned object, an autofocus device of the present invention comprises a focus evaluation value detecting means for detecting a high frequency component level of a luminance signal obtained from an image pickup element, and the detected value. A focus motor that moves the focus lens based on the above, a motor position memory that stores the motor position of the focus motor when the detected value reaches the maximum value, and a predetermined value after the detected value once reaches the maximum value. When the value exceeds the threshold value and decreases from the maximum value, an increase / decrease of the detection value is preset in an autofocus device including a focus motor driving unit that reverses and stops the focus motor at the motor position where the maximum value is detected. First comparing means for detecting with a threshold value, difference means for calculating a difference value between detection values in the vicinity of the in-focus position, and the difference value Second comparing means for comparing a predetermined threshold value to detect the magnitude and one of a plurality of threshold values are selected according to the comparison result of the second comparing means, and a decrease from the maximum value is determined. Threshold value setting means for setting a threshold value for setting, a third comparing means for detecting that the detected value exceeds the threshold value and decreasing from the maximum value, and outputting as a decrease detection signal, 1 If the increase in the detected value is detected by the comparison means, or if the decrease is detected and the decrease is detected again after the focus motor is reversely driven, the third comparison means decreases. When the detection signal is output, it is determined that the focus lens has passed the in-focus position based on the decrease detection signal, and the focus lens is driven to the in-focus position where the maximum detection value is detected. Fo Characterized in that a focus position passage determination means for controlling the Kasumota drive means.

Further, the averaging means for averaging a plurality of difference results obtained from the difference means to obtain an average value, and the average value as one of the threshold values for judging the decrease of the detected value from the maximum value. And a threshold setting means for setting.

Further, the third comparing means has a decreasing number counting means for counting the number of decrease detections detected by the third comparing means, and when the decreasing number counting means detects the decreasing times twice consecutively, the third comparing means It is characterized in that a decrease detection signal indicating that a decrease in the detected value from the maximum value is detected is output to the focus position passage judging means.

[0015]

According to the above construction, the threshold value can be set according to the degree of change of the evaluation value, and the overrun amount of the in-focus position can be made constant regardless of the subject.

[0016]

Embodiments of the present invention will now be described in detail with reference to the drawings. The embodiment described below is an improvement of the focus motor drive control means 9 constituting the control system shown in FIG. Therefore, means having the same functions as those of the control system shown in FIG. 4 are designated by the same reference numerals, and detailed description thereof is omitted.

FIG. 1 is a block diagram showing the control system of the first embodiment of the present invention, in which reference numerals 20 and 21 store the evaluation values obtained by the integrating circuit 8 (see FIG. 4) which is the focus evaluation value detecting means. memory, the maximum value memory 22 for storing the maximum value among the evaluation values stored in the memories 20 and 21, threshold memory for storing a threshold value of the predetermined value 23, 24 is a memory 20, 21, 22 , 23 for comparing the values of 23,
25 is a difference means for obtaining the difference between the values of the memory 20 and the memory 21, 26 and 27 are memories for storing the difference value obtained by the difference means 25, 28 is a threshold memory for storing a threshold value of a predetermined value, 29 is a second comparing means for comparing the values of the memories 26, 27 and 28, 30 and 31 are threshold value memories storing a threshold value of a predetermined value, and 32 is a second comparing means 29.
Threshold value setting means for setting an optimum threshold value from among the threshold value memories 30 and 31, and 33 compares the values of the memory 20, the maximum value memory 22 and the threshold value setting means 32. Third comparing means, 34 is first and third comparing means 2
The focus position passage determining means for determining the passage of the focus position on the basis of the signals from 4, 33 is shown.

Next, the operation will be described with reference to FIGS.

The respective evaluation values when the position of the focus motor 11 moves from the position of k-1 to the position of _k are I _k-1 and I _k .

The position information of the focus lens 2 detected by the lens position detecting means 12 composed of a potentiometer or the like is stored in the lens position memory 13, and the integrating circuit 8 is provided.
The evaluation values obtained by are stored in the memory 20 and the memory 21, respectively. Actually, the evaluation value I _k-1 stored in the memory 20 is transferred to the memory 21, and the current evaluation value I _k is stored in the memory 20.

Here, the evaluation value I is calculated by the first comparing means 24.
_{When k−1} and the evaluation value I _k are compared in magnitude, and the evaluation value I _k is larger than the evaluation value I _k−1 and exceeds the threshold value stored in the threshold value memory 23, Evaluation value I _k
Is stored in the maximum value memory 22 as the maximum value. After that,
When the evaluation values stored in the memories 20 and 21 are compared with each other and the value of the memory 20 is judged to be larger than the value of the memory 21 by the first comparing means 24, the next memory 20
And the contents of the maximum value memory 22 are compared. As a result, the content of the maximum value memory 22 is updated to the content of the memory 20 only when the content of the memory 20 is larger than the content of the maximum value memory 22 by a predetermined value. The maximum value
The initial value of the memory 22 is 0.

As shown in FIG. 5, the evaluation value increases as it approaches the in-focus position. Therefore, when the evaluation value I _k is larger than the evaluation value I _k-1 , the focus motor 1 moves in the forward direction.
Drive 1 Then, when it is determined that the focus position passage determination unit 34, which will be described in detail later, has passed the position where the evaluation value is the maximum, the focus position passage determination unit 34 is the position where the evaluation position is the maximum, that is, Focus motor to focus position
Focusing operation is performed by controlling the focus motor driving means 10 so that 11 is reversed and stopped.

Next, the focus position passage determining means 34 will be described.

In the vicinity of the in-focus position, the evaluation value increases as it approaches the in-focus position, so the contents of the memory 20 are larger than the contents of the memory 21 until the in-focus position is reached. However, the content of the maximum value memory 22 is not always updated every time depending on how the threshold value is taken. Therefore, first, the difference means 25 subtracts the contents of the memory 21 from the contents of the memory 20. That is, I _k −I _k−1 (hereinafter referred to as ΔI _k ) is calculated. Since this calculation is performed for three values including the current evaluation value I _k, that is, I _k-1 , I _k-2 , the memories 26 and 27 have ΔI _k and ΔI _k-1 (=
The value I _k-1 −I _k-2 ) is stored.

Next, the second comparing means 29 causes the memories 26, 27
And the threshold value I ₀ preset in the threshold memory 28 are compared. As a result of the comparison, two values ΔI _k and Δ
When both I _{k- 1} are larger than the threshold value I ₀ , the threshold value setting means 32 reads the threshold value S1 stored in the threshold value memory 30, and the threshold value S1 is compared with the third comparison value. The means 33 sets it as a threshold value when comparing the contents of the memory 20 and the contents of the maximum value memory 22.
Then, as a result of the comparison by the third comparing means 33, if the content of the memory 20 is smaller than the content of the maximum value memory 22 by more than the threshold value S1, the third comparing means 33 causes the decrease detection signal to that effect. (For convenience, referred to as a K signal) is a focus position passage determination unit.
Send to 34.

Here, the focus motor driving means 10 is
While the in-focus position passage determining unit 34 has not determined that the in-focus position has passed, as a result of the comparison between the contents of the memory 20 and the memory 21 by the first comparing unit 24, the contents of the memory 20 are compared with the contents of the memory 21. If it is decreasing, the focus motor 11 is reversed, and if it is increasing, the focus motor 11 is driven in the same direction. Further, the in-focus position passage determining means 34 is either in the case where the first comparing means 24 detects that the content of the memory 20 is larger or smaller than the content of the memory 21 and drives the focus motor 11 in the reverse direction. After that, when the K signal is sent from the third comparing means 33, it is determined that the focus lens 2 has passed the in-focus position, and as described above, the focus lens 2 is stopped at the in-focus position. The focus motor driving means 10 is controlled.

When either of the two values ΔI _k and ΔI _k-1 is smaller than or equal to I ₀ , the threshold value S2 stored in the threshold value memory 31 is read out, and the threshold value S2 is read from the maximum value. When it decreases beyond S2, the focus position passage determination is performed, and the focus motor 11 (see FIG. 2) is controlled to be driven to the focus position as described above.

As described above, when different focus evaluation value curves have different focus evaluation curves as shown in FIGS. 5A and 5B, the threshold can be switched to an appropriate value and set. The overrun amount of the focus position can be made constant regardless of the subject.

FIG. 2 is a block diagram showing a control system according to the second embodiment of the present invention. In this second embodiment, averaging is performed instead of the threshold memory 31 in the first embodiment shown in FIG. Means 35 are provided, and this averaging means 35 is provided in the memory 26.
And the value of the memory 27, that is, ΔI _k and ΔI _k-1 are averaged, and this value is used as the threshold value S2.

That is, when the values in the memories 26 and 27 both exceed I _0, and when either one is smaller than or equal to I ₀ , the average of ΔI _k and ΔI _k-1 is the averaging means.
Calculated as 35, and using this value as the threshold S2,
As in the case of the embodiment, the maximum value is determined by the in-focus point passage determination means 34.

FIG. 3 is a block diagram showing the control system of the third embodiment of the present invention. This third embodiment is the first embodiment shown in FIG.
The reduction number counting means 36 is connected to the third comparing means 33 in the embodiment.

Also in the third embodiment, the processing when the values of the memory 26 and the memory 27 both exceed I ₀ is the same as that of the first embodiment, and one of them is smaller than or equal to I _0. As a result of the comparison by the third comparing means 33 in the case, when the decrease in the content of the memory 20 is detected from the content of the maximum value memory 22 beyond the threshold value set by the threshold value setting means 32, The number-of-decrease counting means 36 counts the number of times, and when the number-of-decrease counting means 36 is counted twice in succession, the third comparing means 33 sends out the K signal as in the first embodiment.

[0033]

As described above, according to the autofocus device of the present invention configured as described above, even if a subject having a low contrast is photographed, the focus signal is not passed. Optimal threshold value for judgment
Since the amount of overrun of the focus lens from the in-focus position can be set to a small value, it is possible to reduce the unpleasantness of the captured image due to overrun and to shorten the time to focus.

[Brief description of drawings]

FIG. 1 is a block diagram showing a control system of a first embodiment of the present invention.

FIG. 2 is a block diagram showing a control system of a second embodiment of the present invention.

FIG. 3 is a block diagram showing a control system of a third embodiment of the present invention.

FIG. 4 is a block diagram showing a configuration of an autofocus device.

FIG. 5 is a graph showing a focus evaluation value curve.

[Explanation of symbols]

1 ... Imaging lens system, 2 ... Focus lens, 3 ... C
CD, 4 ... Camera process circuit (HPF), 5 ... Video signal processing circuit, 6 ... Gate circuit, 7 ... High pass filter, 8 ... Integration circuit, 9 ... Focus motor drive control means, 10 ... Focus motor drive means, 11 ... Focus motor, 12 ... Lens position detecting means, 13 ... Lens position memory, 20, 21, 26, 27 ... Memory, 22 ... Maximum value memory, 23, 28, 30, 31 ... Threshold memory, 24 ... First comparison Means, 25 ... Difference means, 29 ... Second comparing means 32 ...
Threshold setting means, 33 ... Third comparing means, 34 ... Focus position passage judging means, 35 ... Averaging means, 36 ... Decrease number counting means.

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H04N 5/222-5/257 G02B 7/28 G02B 7/36 G03B 13/36

Claims (3)

(57) [Claims] 1. A focus evaluation value detecting means for detecting a high frequency component level of a luminance signal obtained from an image pickup device, a focus motor for moving a focus lens based on this detection value, and this detection value becomes a maximum value. And a motor position memory that stores the motor position of the focus motor when the detected value reaches the maximum value and then exceeds the predetermined threshold value and decreases from the maximum value. In an autofocus device including a focus motor driving unit that reverses and stops the focus motor at a position, a first comparing unit that detects an increase / decrease in a detected value with a preset threshold value, and a detected value near the in-focus position Difference means for calculating the difference value of the second comparison means, second comparison means for comparing the difference value with a predetermined threshold value to detect the magnitude, and the second comparison means. Threshold setting means for selecting one of a plurality of threshold values according to the result of the step comparison and setting the threshold value as a threshold value for determining a decrease from the maximum value; When the increase in the detected value is detected by the third comparing means which detects that the value exceeds the maximum value and outputs as a decrease detection signal and the first comparing means, or when the decrease is detected, the focus motor is reversed. After any of the cases where the decrease is detected again after driving, and the third
When the comparison unit outputs the decrease detection signal, it is determined that the focus lens has passed the in-focus position based on the decrease detection signal, and the focus lens is moved to the in-focus position where the maximum detection value is detected. An autofocus device comprising: a focus position passage determining unit that controls a focus motor driving unit so as to be driven. 2. An averaging means for averaging a plurality of difference results obtained from the difference means to obtain an average value, and the average value as one of the threshold values for judging the decrease of the detected value from the maximum value. The autofocus device according to claim 1, further comprising a threshold value setting unit that sets the threshold value. 3. A reduction number counting means for counting the number of reduction detections detected by the third comparison means, wherein the reduction number counting means detects the number of reductions twice in succession.
2. The autofocus device according to claim 1, wherein the comparing means outputs a decrease detection signal indicating that the decrease in the detected value from the maximum value is detected, to the focus position passage judging means.