JPH01268366A - Auto-focus video camera - Google Patents

Abstract

PURPOSE:To suppress the variance due to interlace to accurately detect an in-focus point by obtaining a focus evaluation value from two continuous field and updating it in every field. CONSTITUTION:Outputs of high-pass filter circuits 15 and 16 are inputted to a switch circuit 17 and are alternately inputted to an integrating circuit 18, and the integral value of odd fields is updated in a first memory circuit 20 in every one frame, and that of even fields is updated in a second memory circuit 21 in every one frame. An adding circuit 22 adds integral values as contents of memory circuits 20 and 21 in every one field to output the focus evaluation value. Thus, the variance of the focus evaluation value in each field due to interlace and an influence of noise are reduced to obtain the stable evaluation value.

Description

[Detailed description of the invention] (a) Industrial application field
This invention relates to a video camera that performs automatic focus alignment.

(Taste) The conventional method of using the captured image itself from the image sensor to evaluate the focus control state in an autofocus device of a video camera essentially eliminates the presence of puff '7-! It has many excellent T points, such as being able to focus accurately even when the depth of field is shallow or for distant objects.In addition, it does not require a special sensor for autofocus and is mechanically extremely simple. Publication No. 61-105978 (
H04N5/232) discloses an example of the above-mentioned auto-failure device.

In the conventional technology, the high-frequency component level of the captured image is set at the center of the screen, A/Dfi conversion is performed within the range of the friend sampling area (71-cas area), and this converted data is sent to an integrating circuit for each field. The digital data p for one field is stored as a focus evaluation value, and compared with the evaluation value of one field old, the 7g force is driven in the direction where the focus evaluation value is maximized. The focus lens is always held at the position where the maximum evaluation value is obtained.

(c) Problems to be Solved by the Invention In the prior art described above, the autofocus operation is always controlled so that the focus evaluation value obtained from the high frequency component level of the video signal is maximized. Since the imaging signal is usually interlaced, the positions within the screen are shifted by one scanning line between the even and odd fields that make up one screen, and for this reason, even if you continue to image the entire same subject, (There is a risk that the focus evaluation value will fluctuate for each field and the position at which the maximum evaluation value is obtained will become unclear.) Section 01 - Determined means to solve the problem The present invention is configured as described above, so that the deviation in the evaluation value between the even and odd fields is removed by updating the evaluation value for each field. Even for video cameras that output images, it is possible to perform auto focus control with high precision to bring the focus to a focused point.

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

In the circuit block diagram of FIG. 1, nine pixels are connected by a lens (11), and a video signal is generated by an image pickup circuit (41) including an image pickup element, and the luminance signals therein are converted into first and second images.
Both filter circuits (151, σe are input to the filter circuit asae) are bypass filters (H, P, F) that only generate high frequency components of luminance G, but the first filter circuit (151 is the 2 filter circuit σ
Specifically, the cutoff frequency t1600KH2 of the first filter circuit Cl51 is higher than that of the second filter circuit σe.
The output of the filter circuit αS and (161 is set to 200KHz) is - Cas motor control circuit + It)
Specifically, the integrating circuit (first evaluation value detecting means) α8 is input to the switch circuit ση controlled by A
It is a disotal integrator consisting of a /D converter, an adder, and a memory circuit, and the input first and second filter circuits (151 (1G + The output of this A/D conversion is added to the value held in the memory circuit by an adder, and the value of the memory circuit is updated with the result of this addition, and reset every l field. As a result, the integrated value for one field is outputted. ◎ Integration circuit (181 output is selectively output to the first and second memory circuits by passing through the switch circuit α9t-) ◎In other words, the switching of the switch circuit a9 is done every field by the switching signal from the focus motor control a circuit in synchronization with the switch circuit ση.
The 9 integral value (PI) obtained by integrating the output of the filter circuit ff5 over 1 field is sent to the first mesori circuit ■, and the integral value (P2) obtained by integrating the output of the 2nd filter circuit σe over 1 field.
is stored in the second memory circuit CD. Therefore, in the first memory circuit (211), the integral value of the odd field is updated every frame, and in the second memory circuit (211), the integral value of the even field is updated every frame (n). 2nd evaluation value detection means) ■ is both memory circuits (
The integral value (first focus evaluation value) which is the content of 2Ian (PI
) (P2) t'', the following auto-off is added for each field and outputs the (2nd) focus evaluation value (M) t- used by one cassette operation.-1 1st memory time vlI?
■Integral value (PI) in odd field held in d!
, as shown in the second factor, at-a2, a3, etc. Similarly, the integral value (P2) in the even field stored in the second memory W&(21+) becomes bl, b2, b3. ,・
..., the focus evaluation value CM from the adder circuit)
t-11th is (al+b1), second is (1)1+6
2), the third is (a2+b2), and the fourth is (b2+a3)
), and the fifth one is (a 3 +b3).

,... ◎In other words, the focus evaluation value of the current field is the integral value of either the first or second filter circuit (151G, G output) in the current field, and the This value is obtained by adding the integral value of the output of the other filter circuit (sum of fluctuations), and the influence of noise and variations in the focus evaluation value for each field due to interlacing can be alleviated, and a stable evaluation value can be obtained.

Immediately after the autofocus operation starts, the first focus evaluation value is the maximum value! J i61 and the initial value memory (held in 71) After that, the lens is rotated in the predetermined direction t. n!2 comparator (9ν is a Bunar
The focus evaluation value after driving the focus motor and the initial value memory (compares the initial evaluation value held in 71 and outputs the magnitude) are transferred to the focus evaluation value from the focus motor control circuit (1 (I) and the second comparator (9)).
; rotates 7 in the initial direction until it outputs the output that the magnification is small, and the output that the current focus evaluation value is larger than the initial evaluation value is produced.
If so, maintain the same direction of rotation.

If it is determined that the current evaluation value is smaller than the initial evaluation value by more than a predetermined variation, vc immediately reverses the rotational direction of the motor 13+ and monitors the output of the first comparator (81).

The first ratio r+ device (8) is the maximum value memo! Jf61Vc Compare all of the maximum focus evaluation values held up to now with the current evaluation values, and if the current focus evaluation value is larger than the contents of maximum value memo month 61 (first step), set in advance. Gradually, the signal decreases below the threshold value of 1, and the comparison signal (3) of 9 (2nd
1) Output (32) n Here, the maximum value memory (61 is the first ratio device (8) If the current evaluation value is larger than the content of the maximum value memory 161 based on the output, the value is updated, and the maximum focus evaluation value up to now is always held.

α31 has a focus lens of +11? This is a motor position memory that stores the position of the supporting focus ring [instructing the position of 2+] in response to a motor rotational position signal, and similarly to the maximum value memory +61.
Ratio ffF; (The maximum evaluation value is obtained based on R+small output, and it is updated so that the Buna-kasu ring position in case t is always maintained.

7 to one customer motor control circuit 162 A1 company, second comparator 19
) is determined based on the output and force, and the focus motor (3λ) is rotated in the north direction, and the first comparator +81 output is monitored, and the focus evaluation value is compared with the maximum evaluation value than the preset threshold of Ei 1. at the same time the second mode of small is indicated) -
The blade motor 3+ is reversed □By reversing the blade 13+, the lens (11) is moved in the direction of movement, for example, from the direction approaching the image sensor to the direction away from it, or vice versa. After the reversal of Riko, which changes to the approaching direction, the contents of the motor position mesosu a3 and the current)
- is compared with the cass motor rotation position signal in the third comparator ②, and when they match, that is, the cass ring 121 returns to the position where the focus evaluation value is maximum, and at 1 o'clock, the cass motor 131 is stopped. Funer force motor control a circuit 1
111 works. At the same time, Funakasu motor control circuit r
IlFl outputs a lens stop signal (LS).

Qll is the fourth memory that holds the focus evaluation value at that time when the lens stop signal (LS) is issued after the auto-off operation by the motor control circuit a1- is completed. , the fourth lever in the second stage
The content held in the memory α1) is compared with the current focus evaluation value, and at 9 o'clock when the current focus evaluation value becomes smaller than the content held in the fourth memory (11) by a preset second threshold value or more, The object to be copied changes and is determined to be a friend, and an object change signal is output.
◎ The arithmetic circuit Q3 repeats the auto7 operation again to follow the changes in the copy. The relative ratio (R) of the integral value (Pi) (P2) at QB of the second memory circuit, that is, the integral value (P
I)/integral value (P2) is calculated. If the relationship between this relative ratio (CR) and the degree of bokeh of the subject (the amount of movement or deviation from the lens position at the time of focus) is shown in a graph, it will be a monotonically decreasing characteristic curve as shown in the fourth factor. , Figure 3 shows the relationship between the lens position and the integral value when the same two objects are being imaged. Since the first filter 〇51 has a high count-off frequency, the integral value (Pl) is determined by the lens position. On the contrary, when the frequency of the second filter 〇〇 is lower than the former, the integral value (P2) shows a gradual change with respect to the lens position, as shown in Fig. 4. The reason for this monotonically decreasing curve is that the state quantity called the relative ratio is a function value that can express the in-focus state (degree of blur) of the subject in the same way as the focus evaluation value, and is expressed as a ratio. It is a normalized state quantity of changes, but the relative ratio does not change significantly □Normally, the above-mentioned JIT is independent of the type of subject, so this relative ratio can be used as a buff meter for the degree of blur. As mentioned above, the relative ratio (R) is a quantity of 1!!4 that represents the degree of blur, so as soon as it is set in advance in the threshold holding circuit example, the threshold of 4 (specifically, 0 in the characteristic diagram of the fourth meat) is set in advance in the threshold holding circuit example.
．． The sixth comparator determines whether it is smaller or larger than 5. This determination result is input to the 7th gear motor control circuit l1l), and the rotational speed of the 1st gear motor 13+ is controlled from 7 during the focusing operation to 0, that is, the relative ratio during the focusing operation is set to 4th. If it is less than the threshold, 7 is 7-
The controller control circuit 01> instructs the control signal (NSP) to switch to normal speed mode, and
Rotates at normal speed. However, if the relative ratio is greater than the fourth threshold, the 7f-cus motor control circuit Q11 instructs the low speed mode by a control signal, and the focus motor 13+ rotates at a slower speed than the normal speed. When the relative ratio is smaller than the fourth threshold and there is an out-of-focus state of deafness, the lens Il+ moves back and forth at high speed, and the relative ratio is larger than the fourth threshold and is near the in-focus point, and the focus evaluation value for lens movement is If the change is small, the lens tl+
can move forward and backward at low speed, and the first comparator (20
0) output (S2) makes it possible to suppress the overrun 2 during reversal of the focus motor 13+ to a small value □ In this example, the fourth threshold value is set to one level, and the focus motor control speed is set to all normal settings. It is configured as a machine that can be controlled by setting it in two stages: speed mode and low speed mode, but it is extremely easy to divide each of these into several stages and develop a more fine-grained control system. In addition, instead of displacing the entire lens (1) in one step (3), it is possible to use a piezoelectric element or the like, or fix the light receiving lens and make the image sensor itself fully move forward and backward, thereby reducing the distance between the lens and the image carrying surface. ÷+
It is also possible to execute the focusing operation by roughly changing the distance, and in this case as well, it is preferable to change the displacement speed of the lens or image sensor. When used as a focus evaluation value, even if the filter is time-divisionally switched for each field, a sufficient number of samples are secured to monitor the maximum focus evaluation value, and the focus evaluation value is low. Rather than climbing a mountain using only the focus evaluation value based on Level/I/VC, which also includes low-frequency components that show gradual changes with respect to the lens position, when the differential is set to one position, it is possible to make a steep change in the lens position. By using the focus evaluation value obtained by adding the high-frequency components shown, it is possible to more accurately climb the mountain toward the apex.

By the way, in this embodiment, in order to calculate the relative ratio, two HPFs with different cut-off frequencies are used, and two consecutive fields of integral values of different filter circuit outputs are added as the focus evaluation value. However, if only one HPF is used, two consecutive fields can be updated for each field, and moreover, it can be achieved with the same filter circuit output, so a more accurate focus evaluation value can be obtained. become.

It is also possible to signal the addition results of the addition times, average them for one field, and use this average value as the focus evaluation value.In addition, the circuit operation of the first factor can be calculated by a microprocessor. It goes without saying that it can be easily processed using software. (G) Effects of the Invention As described above, according to the present invention, fluctuations due to interlacing in the focus evaluation value updated for each field are suppressed,
Able to accurately detect the focused point□

[Brief explanation of the drawing]

The drawings all relate to one embodiment of the present invention, and Fig. 1 shows a circuit block □□□, Fig. 2 shows a relation between W, 1st evaluation value and 2nd evaluation value, and Fig. 3 shows object distance and focus evaluation value. The relationship ①, the fourth item, is a diagram showing the relationship between the degree of blur and the relative ratio. 118)... Product X circuit (first evaluation value detection means), ■.
... Addition circuit (second evaluation value detection means), filN...
Funakasu motor control circuit (focus sterilization means), (
PIJ (P2)...integral value (first focus evaluation value), CM
)...Focus evaluation value (second focus evaluation value) 0

Claims (2)

[Claims] (1) a first focus evaluation value detection means for detecting a high frequency component level of a captured video signal obtained from an image sensor as a first focus evaluation value for each field; and a first focus evaluation value for two consecutive fields. is added for each field and outputted as a second focus evaluation value.
An autofocus video camera comprising: a focus evaluation value detection means; and a focus control means for controlling the relative position of the focus lens and the image sensor so that the second focus evaluation value is maximized. (2) The high frequency component level is composed of a first high frequency component level that is a particularly high frequency band, and a second high frequency component level that also includes a frequency band lower than the first high frequency component level, and 2. The autofocus video camera according to claim 1, wherein the first high-frequency component level and the second high-frequency component level are alternately changed for each field as the first focus evaluation value.