JPS61293076A - Autofocus circuit - Google Patents

Abstract

PURPOSE:To stability restart a focus mechanism by providing a control circuit to restart a focus drive mechanism when a change in a screen is detected by a detector circuit. CONSTITUTION:Respectively by the third through sixth comparator circuits 46-49 of the detector circuit 53, the fifth memory 37 and the sixth memory 38, the seventh memory 39 and the eighth memory 40, the ninth memory 41 and the tenth memory 41, and the eleventh memory 43 and the twelfth memory 44 are compared as to the contents. That is, the low frequency component levels of the current field and the last one at points B-E are compared. The outputs of the five comparisons are transferred to a discrimination circuit 50, where the occurrence of the change in the screen is detected by a majority system based on the variation at said five points. Only when three of the five points are of a level exceeding a threshold, an H-level signal is outputted and is transferred to the focus motor control circuit 13. The circuit 13 lets a focus motor 14 restart when the discrimination output is of H-level.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to improvements in autofocus circuits employed in video cameras.

(b) Conventional technology Conventionally, the auto-off of a video camera was taken as a single circuit.
Ij! The focus motor is controlled so that the high frequency component of the luminance signal obtained from the element is maximized. In other words, it is configured to detect temporal level changes in high-frequency components while once stopped at the focal point position, and restart autofocus operation when the amount of change exceeds a certain level (high value). has been awarded.

Furthermore, Utility Model Application No. 59-123017 subdivides the high-frequency component of the luminance signal into wide band, medium band, and narrow band, relatively compares the level changes in each band, and determines the necessity of re-driving the focus motor. Disclosed is a device configured to determine sex.

(C) Problems to be Solved by the Invention The prior art technology relies only on the high-frequency component of the luminance signal to determine whether to stop or restart the focus motor, so it can identify changes in the screen that cause restarting. It is difficult to expect high reliability from

B) Means for Solving the Problems The present invention is a focus circuit, which includes a filter that separates the low-frequency components of a video signal, and a detector that detects level changes in the low-frequency components at multiple sampling points set on the screen. and a control circuit that re-drives the focus drive mechanism based on the output of the detection circuit, and is characterized in that it detects changes in the screen in the in-focus state.

(E) Function Since the present invention is configured as described above, changes in the screen can be detected by low-frequency components that are affected by the focus state and by multiple sampling points, and based on this, the focus drive mechanism can be stabilized. It is now possible to perform a reboot.

(f) Example An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit block diagram of this embodiment.

The luminance signal in the video signal obtained from the image sensor is separated by a bypass filter (H, P, F,) + 11 into only high-frequency components, and then passed through a sampling circuit (2) to a focus area setting circuit (3). Luminance signal (2) within the focus area (FA) in Figure 3, which is preset by
Only the high frequency components of are sampled. ? The sampling output of : is sent to the detection plane M (41) and subjected to four-line width detection, and then integrated over one field in the integrating circuit (5).

The focus area setting circuit (3) receives the horizontal synchronization pulse a(), vertical synchronization pulse M, and color subcarrier (01) from the synchronization pulse generation circuit (6), and resets the horizontal synchronization pulse l: in the horizontal direction. The color subcarrier (CI) is counted as an input, and the horizontal synchronization pulse is counted in the vertical direction using the vertical synchronization pulse M as a reset input, and when both count values are within the range of the preset focus area, the sampling Each output of the synchronizing pulse generating circuit (6) also serves as a driving pulse for the image sensor.

The output of the integrating circuit (5) reaches the fixed contact (7F) of the changeover switch (7), and the movable contact piece (71) reaches the fixed contact (7F).
F), it is input to the AD conversion circuit (8) and A
The signal is converted into a D signal and is read into a read timing pulse (t 1 ) (first memory 00), which will be described later, via a read selection circuit (9). The data sent to this first mesori aα becomes the focus evaluation value at that point. 1st with
The data in the memory αl is transferred to the second memory f after one field.
forwarded to ill.

First comparison circuit f12, first memory αG and second memory ti
Compare the contents of B. That is, the current field and the evaluation value of one field before are compared. This comparison output is input to the focus motor control circuit ([31], which drives the focus motor I in the direction where the focus evaluation value becomes large, and finally detects the focused focus position where the evaluation value becomes the maximum. to stop the focus motor a4.
@ is a well-known technology as an autofocus circuit.

Next, a description will be given of the detection circuit 0 that detects the occurrence of a change in the screen when the focus motor is once in a stopped state.

The luminance signal (2) passes through a low-pass filter (L, P, F,) to separate low frequency components. The cutoff frequency of H, P, F, (11) to know the focus evaluation value is 1
Normally I QQKHz ~ 500KH2, but as shown here, p, F, (i!ilO side is 50KH
z~100KHz. This is to detect only changes in the screen without being affected by the focus state, such as being in focus or out of focus. Also, by setting the cutoff frequency low, it is possible to This makes it possible to detect changes in the screen by making level changes only at sample points.

The low frequency components obtained in this way are transmitted to the first, second, '5% fourth and fifth sample and hold circuits aυ(Iη0&a9■C
2 sent aeIJ sample hold circuit n61a?
1utts Iso is a vertical synchronizing pulse (Vl), a horizontal synchronizing pulse circle, a color subcarrier (01), and a sample hold pulse created by the sample hold pulse generation circuit +211, A% on the screen shown in Fig. 3. B1
Low frequency components at five points, 0 and D%E, are sampled and held. Note that point A and point B, and point 0 and point D are located on the same line in the horizontal direction I, and point A and point 0, and point B and point D are located on the same line in the vertical direction.

Here, the sample-and-hold pulse generating circuit C11 will be explained with reference to FIG. This sample-and-hold pulse generation circuit (2il) uses a vertical synchronization pulse M as a reset input, a horizontal synchronization pulse (Hl) as a count input, a vertical counter 021, a horizontal synchronization pulse city 1 as a reset input, and a color subcarrier (0). A horizontal counter (231) whose count input is , and a vertical counter (22
First, second, and third vertical position detection circuits C that use output as input
241e) 51 (261 and the horizontal counter c!3
The first, second, and sixth horizontal position detection circuits (2TX!; I (294) and the first vertical position detection circuit c2
41 output and the output of the first horizontal position detection circuit C3G are operated by two people, and the output of the first vertical position detection circuit 04) and the output of the second horizontal position detection circuit 2. The input of the second A N D gate) t, 111, the output of the second vertical position detection circuit (c), and the first horizontal position detection circuit 071
output and 2. The 5th AND gate (to) which serves as an input, the 4th AND gate which uses the 251 output and the 2nd horizontal position detection circuit I21C output as input, and the 6th vertical position detection circuit ■ output. The third horizontal position detection circuit (c) is composed of five AND gates, including the fifth AND gate (2) whose output is powered by two people.

The horizontal color subcarrier (010 count value) counted by the horizontal and vertical counter C231 (23) and the count value of the horizontal synchronization pulse circle in the vertical direction are output, and the first vertical position circuit is set in advance at point A and point CB. ) is set, and when the count value matches this vertical data, an output is generated.Similarly, the second
The vertical position detection circuit (c) is set with the vertical data of point O (point CD), the third vertical position detection circuit @ is set with the vertical data of point E, and the count value of the vertical counter is set. It emits an output when it matches the respective data. Also,
1st, 2nd, and 5th horizontal position detection times W6@(281r2!
For 1m2, the horizontal position data of point A (0 point), point B (point CD), and point E are input in advance, and the horizontal counter c! When it matches the count value of 3: = Output is generated.

Therefore, the first AND gate (7) outputs a hold pulse (al) at the point in time when the luminance signal at point A is obtained from the image sensor. Point, 0 point, D point,
The sample hold pulse corresponding to the ty pull point of point E (
bl(cl(dl(el) is output. By this sample hold pulse (al(bl(clldl(el), the first, second, third degree, fourth, fifth sample and hold circuits aυ1nasas■ are sampled and held, Point A, B
The level of the low-frequency component between the luminance signals at point 0, point 0, point D, and point E is detected.

This first, second, third... The 4th and 5th sample and hold circuits a61fiη616 (1112G output are the fixed contacts (7a) (7b) (7o) (7d) of the changeover switch (7)
(7) and the movable contact piece (71) to the AD conversion circuit (8).
), and further sent to the 3rd memory (to), 5th memory (b), 7th memory, 9th memory Uυ, and 11th memory by the read selection circuit (9), and After one field, each data is stored in the 4th memory (to), the 6th memory, the 8th memory (t), the 10th memory (6), and the 1st memory.
2 transferred to memory.

Here, the changeover switch (7) and the read selection circuit (9)
The operation will be explained in detail. The changeover switch (7) is controlled by a changeover pulse generation circuit I that receives the vertical synchronization pulse M.
This is done with a switching pulse from n. Sokuchi, Figure 4 (bl
The switching pulse generated as shown in Fig. 4, tel.
The movable contact piece (71) of the changeover switch (7) has fixed contacts (7F) (7a) (7b) (7c) (7d) (7e) as shown in FIG.
)(7/). Note that the fixed contact (7f) is in an open state.

Further, the control of the continuation selection circuit (9) is controlled by timing pulses (tl) (tl) (ts) rt4) from the continuation timing generation circuit (a) which slightly delays the switching pulse.
(ti) It is done by (ti).

That is, when the timing pulse (tl) is generated, the contents of the AD conversion circuit (8) are read by selecting the first memory aα, and similarly when the timing pulse (t21 memory C) is generated, the contents of the AD conversion circuit (8) are read.
11i5-G! ]) are sequentially read into θ4,
The timing pulse (t, 2) (ii) (i4) (t
s)(t4) occurs during the vertical blanking period.

Therefore, the AD conversion output of the integral output is stored in the first memory aQ, and the 3rd, 5th, 7th, 9th, and 11th memories (up to) @-A point, B point, 0 point, and The low frequency component levels at points D and E are input. 3rd memory (to) and 4th memory (to)
, that is, the comparison of the current and one field previous low frequency component levels at point A is performed in the second comparison circuit. Similarly, the fifth, fourth, fifth, and sixth comparison circuits θωθ7) (goods)
- Then, the 5th memory (sub) and the 6th memory, the 7th memory and the 8th memory (g), the 9th memory and the 10th memory □
□□, the contents of the 11th memory (goods) and the 12th memory (goods) are compared, respectively. That is, the low frequency component levels of the current field and one field spinning at points B, 0, D, and E are compared. These five comparison outputs are sent to a discrimination circuit, which detects the presence or absence of a change in the screen based on a majority vote based on level changes at five points. That is, the C:H level output is generated only when three or more of the five level changes exceed the threshold value ε. The discrimination output from the focus motor control circuit 63 is sent to the smoke control circuit (1g+), and when the discrimination output from the focus motor control circuit 63 becomes H level, the focus motor I is started to be driven again.

In this way, once the level of the high-frequency component within the focus area (FA) is at its highest, focus point position 1: is set, and while the focus motor is in a floating state while waiting for restart C:, changes in the screen are observed at five sample points. A change in the level of the 1-degree component is detected, the focus motor is restarted, and the focusing operation is restarted.

In this embodiment, the reading operation of the low frequency level at the sampling point is performed even while the focus motor is being driven, but it may be limited to only while waiting for restart.

It is also possible to perform signal processing in various circuits using software.Furthermore, the number and position of sampling points on the screen are not limited to this example, and may be set freely.
-I'' Needless to say.

The configuration and operation of the tree source side circuit have been described above, and FIG. 5 shows this as a flowchart. This flowchart will be briefly explained.

Here, Sn indicates the current focus evaluation value, 5n-1 indicates the focus evaluation value of one field song, and in function 1, the focus is set at the in-focus position so that the evaluation value of the high frequency component is maximized. Function 1 shows the mountain climbing servo that stops Tanabata. Function 2 detects changes in the screen using low-frequency components in the restart standby state after the focus has stopped overnight, and detects the need to restart the focus motor. The presence or absence of sex is determined. Furthermore, A n s B n s On s D n
s E n The low frequency level at each current sampling point is 5An-1, Bn-1, 0n-1, Dn-1, '1i
n-1 indicates the low frequency level of a 1-field song.

(G) Effects of the Invention As described above, according to the present invention, a change in the screen that causes the focus drive mechanism to be restarted once it is in a stopped state can be determined based on the brightness change signal at the east number sampling point on the screen. Since this is performed by changing the low-frequency level of , the reliability is extremely high, and as a result, stable focus control is possible, which is extremely effective.

[Brief explanation of drawings]

The drawings all relate to one embodiment of the present invention, and FIG. 1 is an overall circuit block diagram, FIG. 2 is a circuit block diagram of a sample-and-hold pulse generation circuit, FIG. 3 is a diagram showing the positions of sampling points, and FIG. The figure is a timing chart, and FIG. 5 is a flowchart.

Claims (1)

[Claims] (1) In an autofocus circuit that controls a focus drive mechanism so that the high-frequency component of the video signal obtained from the image sensor is maximized and stops the control when the in-focus position is reached, the low-frequency component of the video signal is a filter that separates the components; a detection circuit that detects a change in the level of the low-frequency component at a plurality of sampling points set on the screen to detect a change in the screen in the in-focus state; An autofocus circuit comprising: a control circuit that restarts the focus drive mechanism when the focus drive mechanism is recognized.