JPH03186075A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To execute focusing corresponding to the intension of a photographer with simple configuration by calculating a focus evaluation value while dividing an image pickup picture into plural small areas. CONSTITUTION:A signal processing circuit 6 processes a video signal from a camera circuit 5, divides the image pickup picture into the plural small areas, calculates the peak value of a high frequency component in a luminance signal for each small area and outputs the peak value to a CPU 7. The CPU 7 integrates the peak value of the high frequency component in the luminance signal for each field, compares this integrated value with the integrated value one field before and controls a focus lens 1 so that this integrated value can be made maximum based on the compared result. Thus, focusing can be executed corresponding to the intension of the photographer with the simple configuration.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to an automatic focus adjustment device for a video camera.

(Prior Art) Various autofocus (AF) systems for video cameras are known, and among them, the present invention relates to a so-called contrast detection system. This method takes advantage of the fact that the high-frequency component of the brightness signal increases as it becomes in focus, and the focus lens is driven to extract the high-frequency component of the brightness signal and maximize it. evening.

In this type of conventional method, the luminance signal of the video signal is passed through a high-pass filter, and the area (focus area) of the image capture screen from which focus information is extracted is integrated by an analog integrating circuit for each field. The integral value is used as the moving point evaluation value.

However, since the dynamic range of this integral value is quite wide, if it were attempted to be processed by an analog circuit as in the past, the circuit would become complicated and expensive.

In addition, in conventional devices, control is performed so that the high frequency component of the brightness signal in the entire focus area is maximized, so for three-dimensional objects, the control is always towards the side with a higher spatial frequency, and in actual shooting, the user The intended subject may not always be in focus. In addition, in the case of a three-dimensional subject, if the subject within the -degree screen is in focus, even if a subject at another distance comes to the center of the screen, which is the focus area, the subject with a high spatial frequency will remain in the 'pf view. If the subject is in the center of the screen, it will remain in focus, and the subject in the center of the screen will no longer be in focus.

For example, as shown in Figure 9 (a), a person's face and background
If the background has a high spatial frequency, such as a bookshelf, the focus will be on the background because it has a higher focus evaluation value.In this case,
Even if the face is in the center of the screen as shown in the same figure (b), - degrees fr
When the scenery is in focus, the face is out of focus,
The background remains in focus because the background is in focus at -1+ degrees, so its focus evaluation value is relatively high, and the gi is out of focus and blurry. This is because the focus evaluation value is low.

To further explain this point, Figure 1O shows the relationship between the focus position and focus evaluation value while manually moving the focus ring for the subject in Figure 9. There are peaks in the focus evaluation value at two locations, and the background has a high spatial frequency (Book 8)
The focus evaluation value is larger, the focus position is the 10th
If the focus is in area A in the figure, the focus lens will be driven to match the higher focus evaluation value, that is, the face, but if the focus is in area B, the evaluation focus value increases towards the background, so the background is in focus. A similar situation can be seen in Figure 11, where there is a relatively small object (flowers arranged in a vase) in the center and a detailed pattern in the background (Book II).
In this case, the flower may not be in focus, but the bookshelf behind it may be in focus.

Therefore, when a user takes a picture while flashing, if the background is in focus at first, then even if a closer object, such as a person's face, appears in the middle of the shot, the face will not be in focus immediately. , the face will come into focus only when it fills the entire focus area.

As described above, the conventional method has the disadvantage that parts not necessarily intended by the photographer are brought into focus.

(Object and structure of the invention) The present invention has been made in view of the above points, and an object of the present invention is to enable focusing as intended by the photographer with a simple structure. , divide the imaging screen into multiple small areas, find the peak value or integrated value of the high frequency component of the luminance signal for each small area, integrate these peak values or integrated values for each field, and calculate this integrated value. It was configured to control the focus lens to maximize the focus.

(Example) The present invention will be explained below based on the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of an automatic focus adjustment device according to the present invention, in which 1 is a focus adjustment lens of an imaging optical system, 2 is a zoom section of the imaging optical system, 3 is a relay lens section, 4 is an image sensor such as a CCD, and 5 is an NTSC system image fI based on the output from the image sensor 4.
The camera circuit 6 processes the video signal from the camera circuit 5, divides the imaging screen into a plurality of small areas, calculates the peak value of the high frequency component of the luminance signal for each small area, and sends it to the CPU 7. This is a signal processing circuit that outputs signals.

The CPU 7 includes an a3I means for integrating the peak value of the high frequency component of the luminance signal for each field, a comparison means for comparing this integrated value with an integrated value for the previous field, and an integrated value by the integrating means based on the result of the comparison means. It functions as a control means to control the focus lens to maximize the focus.

Further, 8 is a focus motor that drives the focus adjustment lens l, 9 is a motor drive circuit that drives the motor 20, and 10 is a zoom position sensor that detects the zoom position of the zoom section 2 and outputs zoom information to the CPU 7.

FIG. 2 is a block diagram showing the circuit configuration of the signal processing circuit 6 of FIG. 1.

A luminance signal (Y signal) is separated from the video signal output from the camera circuit 5 by a Y/C separation circuit 61, and a predetermined high frequency component is extracted via a high pass filter 62. On the other hand, the synchronization separation circuit 63 separates the vertical and
A synchronization signal is extracted. Further, the timing/area specifying circuit 64 divides the imaging screen into a plurality of small areas and sets a focus area according to a command from the microcomputer 7. A peak value detection circuit 65 detects the peak value in each small region of the high frequency luminance signal, which is roughly A/D converted by an A/D conversion circuit 66 and then output to the microcomputer 7.

The microcomputer 7 uses the data from the A/D converter circuit 66 to calculate a focus evaluation value using a method described later, and the motor drive circuit 9 focuses adjustment lens 1 is driven based on the calculation value.

As a method for calculating the focus evaluation value, there are, for example, the following methods.

(1) Weighting is applied to the area near the center (for example, by a factor of 3). Unless there is an object with a considerably high spatial frequency around 0, the area is integrated so as not to be affected.

(2) Changing the focus area depending on the zoom position. For example, as the zoom position moves toward the wide side, the focus area becomes narrower.

(3) Look at the current and previous data and integrate only the data in a small area that is in the same direction as the data change near the center.

(4) When the data near the center is small and the data around the periphery is large, it is binarized at a predetermined level and the data values around one are not used, but the binarized low level data is integrated.

Next, these methods will be explained in detail using specific examples.

First, a first embodiment using the calculation method (1) above will be described with reference to FIGS. 3 and 4.

FIG. 3 is a diagram showing focus areas, and in this embodiment, in addition to the normal focus area A, a focus area B, which is set within the focus rear A and smaller than the center of the screen, is used.

Is the entire screen the size of the horizontal period H x vertical period V?
Focus area A is 2/3HX2/3V, and focus area B is 1/3HX1/3V.

Each focus area is further divided into small areas as indicated by diagonal lines in the figure. Horizontal division is performed by the timing area designation circuit 64 using a horizontal synchronization signal as a trigger. For vertical division, for example, if n scanning lines are assigned to one small area, a counter is provided and counted up by the horizontal synchronization signal, and n
The counter may be reset by the horizontal synchronization signal of the m-th scan to separate small areas.

The focus areas Δ and B are set by the timing area designation circuit 64 by counting scanning lines and taking timing from the horizontal synchronizing signal so that the screen dimensions described above are obtained.

Now, to explain the operation using the flowchart in Fig. 4, first, after performing various initial settings (F-1), the maximum value of the luminance signal in each small area of area A is determined, and it is stored in the microcomputer γ. There are various ways to find the maximum value of the luminance signal within a small area (F-2), but for example, by scanning the peak value of the luminance signal sampled at the same timing in the horizontal direction. It is sufficient to compare line by line and leave the maximum value among the zero scanning lines in the small area in the RAM.

After the peak values of each region are thus stored in the RAM, these values are integrated to obtain a focus evaluation value a. At this time, the value within focus area B is multiplied by three and added (F-3).

That is, the signals near the center of the screen are weighted, so that even if there is a background with a high spatial frequency, as shown in FIG. 9 (b), for example, it is less affected by the background.

Now, the focus evaluation value at thus obtained is the microcomputer 7
(F-4), then it is determined whether the focus motor 8 is being driven (in other words, whether it is in the middle of a sharp blow) (F-5), and if it is not being driven, the previous focus evaluation is Value a. When it is larger or smaller than the predetermined amount ratio compared to (C2ao<at<C+ ao: C2
<1. C1 > 1) a) Drive the motor 8 by a predetermined amount in a predetermined direction (F-6). If the current evaluation value is within a predetermined value compared to the previous one, stop the motor (F-9). If the motor 8 is in 'IjA@', the current focus evaluation value a is set to the previous focus evaluation value a. Compare with (F7) *a
l or a. If it is smaller, it means that the lens 1 has been moved beyond the focus position (see Figure 1O), so the motor 8
Drive in the opposite direction (F-8) @al or hoba a.

(if the difference is within a predetermined value), the lens 1 is at the in-focus position, and the motor 8 is stopped (F-
9) If a is larger than ao, the lens l is moving toward the in-focus position, so the motor 8 is driven in the same direction (F-10).

Next, a second embodiment using the method of Section 42 (2) will be described with reference to FIGS. 5 and 6.

FIG. 5 is a diagram showing focus areas, and in this embodiment, focus rear areas D and E are set in addition to focus area C during normal operation. Focus areas are C, D,
They become smaller toward the center of the screen in the order of H. That is, C= 3/4 Hx 3/5 VD=172H
x315V E= l/4)1x l/3V, and each focus area is divided into multiple small areas as in the example in Figure 3, and the peak of the luminance signal within each of the small areas is also determined in the same way as above. It will be done.

The operation of the second embodiment is similar to the flow shown in FIG. 4 except for the focus evaluation value calculation method, that is, steps (F-2) and (F-3). The same applies to third and fourth embodiments to be described later.

The calculation method of this embodiment will be explained with reference to the flowchart in FIG. 6. After initial setting (F-1), the zoom position is first detected by the zoom position sensor 10 (5-1), and the zoom lens is moved to the telephoto side. If so, select area C (S-2
), if it is in the middle position, select area D 5-3),
If it is in the wide position, select area E (S'-4),
When an 8x zoom lens (f=8 mm to 64 mm) is used, the zoom area is divided into, for example, as follows.

Tele side f=48~640-Mitle f=24~48~Wide side f=
The peak value of each small area within the selected focus area is stored in the RAM memory of the microcomputer 7 every 8 to 24 seconds (5-S), and the values are integrated to obtain the focus evaluation value a1 (S-6). , the subsequent operations are the same as those after step (F-4) in FIG.

By doing the above, as the zoom moves toward the wide side, the focus area narrows toward the center of the screen, thereby focusing on the photographer's intended subject and reducing the influence from the surrounding background. be able to.

Next, a third embodiment using the calculation method described in item 2 (3) will be described with reference to FIG.

In this embodiment, two areas A and B shown in FIG. 3 are used as focus areas, similar to the first embodiment.

First, the peak value of each small area in the area A of the odd field is stored in the designated RAM in the microcomputer 7.T-1
), the peak values stored in the RAM corresponding to area B are integrated and S is calculated. Close and store (T-2), similarly.

The peak values of each small area in area A of the even field are stored in the designated RAM in the microcomma (T-3), and the peak values stored in the RAM corresponding to area B are integrated and stored as S2. (T-4), then S,
and S. Determine which difference is positive or negative (T-5). If negative, add only those small areas in area A where the difference between even and odd fields is negative.

Let the focus evaluation value be (T-6), while S and S.

If the difference between the even field and the odd field is positive, among the small regions in area A, the sum of those for which the difference between the even field and the odd field is positive is determined as a focus evaluation value (T-7).

As mentioned above, since the calculation is performed using only the parts that show the same change direction as the change direction of the brightness signal near the center of the screen, 1
Focusing is performed to focus on the subject in the center of the screen, and it is less likely to be affected by the background.

Next, the fourth example using the calculation method (4) above will be described in the eighth example.
This will be explained using figures. Similar to the third embodiment, this embodiment also uses two areas A and B shown in FIG. 3 as focus areas.

First, the peak value of each small area in area A is
(w-i), it is determined whether the maximum value of each small area in area B is smaller than a predetermined value α (W-2); if not, the values of all small areas in area A are If it is smaller, look at the maximum value of the area A excluding area B (A-B) and judge whether it is larger than the predetermined value β.
-4), if it is larger, mx only those smaller than the predetermined value γ among the values of the small area in area A and use it as the focus evaluation value (
W-S), if the value is not greater than a predetermined value β, the values of all small areas within area A are integrated to obtain the focus evaluation value (W-3)
.

By determining the focus evaluation value as shown in Figure 9 (B) or 11UA, it is possible to detect cases where the focus evaluation value of the background is high and the focus evaluation value of the subject to be photographed is lower than that. However, since the data from the high level background part is not used, the photographer can focus on the subject with the low focus evaluation value shown in figure a.

Examples (1) to (4) above have been shown above.

The calculation method is not limited to these, and other variations can easily be considered, and the focus evaluation value may be obtained by combining these methods, for example, the above (1) and (3), or (2).
) and (3) may be combined. Further, in each of the above embodiments, the peak value of the luminance signal after passing through the high-pass filter 62 is calculated and integrated for each small region.
However, the present invention is not limited to this, and the focus evaluation value may be determined by calculating the integral value of the luminance signal and integrating the integral value.

(Effects of the Invention) As explained above, according to the present invention, by configuring the imaging screen to be divided into a plurality of small areas to obtain the focus evaluation value, the dynamic range of each small area becomes narrow. , signal processing is easier (compared to conventional devices, the configuration is simpler and costs can be reduced). In addition, since the imaging screen is divided into multiple small areas, it is possible to weight the peak value or integral value of each small area, or select only a part of it and integrate it. You can perform focusing according to your intention.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the circuit configuration of an embodiment of the autofocus 7A device according to the present invention, FIG. 2 is a block diagram showing details of the signal processing circuit of the device shown in FIG. 1, and FIG. FIG. 4 is an explanatory diagram showing an example of the focus area, FIG. 4 is a flowchart explaining the operation of the embodiment of tsl, FIG. 5 is an explanatory diagram showing another example of the focus area, and FIGS. Flowchart explaining another embodiment, No. 9
Figures 1 through 11 are diagrams for explaining the problems of the prior art. 4... Image sensor, 6... Signal processing circuit, 7... Microcomputer, 62... High pass filter. 64-...Timing area specification circuit, 65...Peak value detection circuit

Claims (4)

[Claims] (1) A high-pass filter that extracts high frequency components from the luminance signal of the video signal obtained from the image sensor, a timing signal generation means that divides the image capture screen into a plurality of small areas, and each area divided by the timing signal generation means. peak value detection means for determining the peak value of the luminance signal after passing through the high-pass filter for each small area; integration means for integrating the peak values obtained by the peak value detection means for each field; and an integrated value of the integration means. and a control means for controlling a focus lens so that the integrated value by the integrating means is maximized based on the result of the comparing means. (2) In place of the peak value detecting means, an integrating means is used for determining the integral value of the luminance signal after passing through the high-pass filter for each of the small regions, and the integrating means integrates the integral value. Automatic focusing device as described. (3) The automatic focus adjustment device according to claim 1 or 2, wherein the peak value or integral value of each of the small regions is weighted and integrated. (4) The automatic focus adjustment device according to claim 1 or 2, wherein the integrating means integrates only a peak value or an integral value of a selected small area among the small areas.