JP2659964B2 - Automatic focusing device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an automatic focusing device using a video signal obtained from an imaging means.

[Prior Art] Conventionally, various methods have been proposed as an automatic focusing apparatus. As a method using a video signal obtained from an imaging means, a high-frequency component included in the video signal is extracted or a differential value is calculated. Then, a method of driving a lens in a direction in which these absolute amounts increase to perform automatic focus adjustment is widely used. Such a method is described in detail in NHK Technical Report Vol. 17, No. 1, No. 86, as "Automatic Focus Adjustment of Television Camera by Hill Climbing Servo System".

FIG. 4 shows a typical configuration of this "hill climbing servo system". In FIG. 1, reference numeral 1 denotes a lens, 2 denotes an image sensor that converts an image formed on a captured image by the lens 1 into an electric signal, 3 denotes a preamplifier that amplifies a video signal output from the image sensor 2, and 4 denotes a preamplifier 3. Output of NTSC
Process circuit for converting to standardized video signals such as 5
Is a band-pass filter (hereinafter referred to as BPF) for extracting only high-frequency components from the output of the preamplifier 3, 6 is a detection circuit for detecting the output of the BPF 5, and 7 drives a lens driving motor based on the output of the detection circuit 6. Is a lens drive motor for moving the lens position and adjusting the focus.

According to this configuration, the image formed on the image captured by the image sensor 2 via the lens 1 is converted into an electric signal and amplified to a predetermined level by the preamplifier 3. The high frequency component of the video signal changes according to the position of the lens, that is, the in-focus state with respect to the subject, and the high-frequency component increases as the focal point is approached. Become. FIG. 5 shows the change of the high frequency component in the video signal with respect to the lens position.
It can be seen that the point A where the high-frequency component is maximum becomes the focal point, and the higher-frequency component decreases as the distance from the focal point increases.
Therefore, the in-focus state can be obtained by driving the lens 1 in a direction in which the high-frequency component becomes the maximum and stopping the lens at the position where the maximum value is obtained.

[Problems to be solved by the invention] However, according to the automatic focusing device as described above,
When the camera shakes in the horizontal direction in a focused state, that is, a state in which the lens is stopped at the point A in FIG. 5, even if the same focused state does not change, the camera is stopped. The level of the high frequency component in the video signal is lower than in the case where the video signal is present.

The reason for this is as follows. In the image sensor 2, an image projected through the lens 1 within one field period (about 1/60 second in the NTSC system, hereinafter referred to as 1 V) is used for each picture of the image sensor 2. However, when camera shake occurs, the entire image is formed by moving the image on the imaging surface of the imaging device 2 within one field period on the imaging surface. When moving and the camera is stationary, the video components to be stored in one pixel are stored over a plurality of pixels adjacent to each other in the direction of camera shake, so a low-pass filter is applied as the video signal. This is because the same development as that described above is performed, and the high frequency component is reduced.

Therefore, the automatic focusing device determines that the in-focus state for the image cannot be obtained due to the decrease of the high-frequency component, and drives the lens driving motor 8 to perform the automatic focusing even though the image is actually in the in-focus state. The device is restarted and temporarily goes out of focus. In general, video cameras, especially home video cameras, are almost always hand-held. Therefore, it is expected that camera shake may occur frequently. As described above, measures to prevent camera focus from being out of focus are desired. Was rare.

Means for Solving the Problems The present invention has been made for the purpose of solving the above-described problems, and includes an image pickup unit and a focus state detected from an image signal output from the image pickup unit. Focus adjusting means for performing focus adjustment, and binarizing means for binarizing a predetermined signal component in an image pickup signal in each of a plurality of regions set corresponding to an image screen of the image pickup means to obtain binarized information And detecting means for comparing and calculating binarized information corresponding to each area to detect motion information of an image between two screens different in time, based on the motion information output from the detecting means. A control unit for controlling the focus adjustment unit and stopping a focus adjustment operation by the focus adjustment unit when a movement equal to or more than a predetermined value is detected by the detection unit; To determine whether the movement is the whole screen or only the subject, and according to the result, in the case of camera shake etc. where the whole screen moves, the automatic focusing operation is temporarily stopped and the The focus is prevented from deviating by following the change, and when only the subject moves in the screen, the focusing operation is continued to follow the moving subject.

[Embodiment] An embodiment of an automatic focusing apparatus according to the present invention will be described in detail below with reference to FIGS.

FIG. 1 is a block diagram of an automatic focusing apparatus according to the present invention.
The same components as those of the conventional example shown in the drawings are denoted by the same reference numerals, and description thereof will be omitted. In this embodiment, as shown in FIG. 2, the image screen is vertically divided into m equal parts and horizontal equal parts, and divided into m × n areas. Based on this, camera shake is detected.

1. In FIG. 1, reference numeral 9 denotes a clock frequency CLK which counts the horizontal address (1 to 1) of each area shown in FIG.
The counter 10 for generating n) counts the horizontal synchronizing pulse HD, and similarly the vertical address (1 to m) of each area.
And a low-pass filter 11 for removing unnecessary high-frequency components contained in the output of the preamplifier 3.
LPF), 12 compares the output of LPF 11 with reference value _Vref ,
A comparator that outputs a high level when the output of the LPF 11 is larger than the reference value _Vref , 13 is a counter that counts the clock frequency CLK only when the output of the comparator 12 is at a high level, and 14 is a reference that outputs the output of the counter 13 to the reference value A. ₁ compared to the comparator output of the counter 13 outputs a high level when it is the reference value a ₁ or more, 15 have a n bits to represent the n pieces of data corresponding to each region divided into n in the horizontal direction A shift register that shifts one bit every time the scanning on the video screen is switched between the areas and rotates n pieces of data for each one line of the video screen shown in FIG. 2 is an n-bit shift register. It is composed of l lines. Here, the reason why one n-bit register is provided will be described. Each of the n bits of each register corresponds to each of the n areas of the video screen. Each time the area on the video screen is switched, it is shifted one bit at a time. Weighted l digits are formed. Then, the number of outputs of the comparator 14 at a high level in each area is counted by 1 bit. Reference numeral 16 denotes an adder for adding 1 to a counter of 1 bit (1 digit) of the shift register 15 corresponding to the area when the output of the comparator 14 becomes high level. Therefore, every time the scanning on the video screen is switched between the areas, if the output of the comparator 14 is at a high level, 1 is added and shifted by 1 bit to obtain a bit corresponding to the next area. Thereafter, each time the area is switched in the horizontal direction, the shift is performed by one, and n areas, that is, the second
When the scanning of one line in the horizontal direction of the image screen shown in the drawing is completed, the shift register is also rotated one turn, the scanning of the next line is performed, and 1 is added if the output of the comparator 14 is at a high level for each region. . When scanning is completed up to the number of vertical lines constituting each area in this way,
Eventually, the n (l digit) counters of the shift register store the number (the number of vertical lines) of the output of the comparator 14 at the high level in each area.

17 the output of the adder 16 is compared with a reference value A _2, comparator output of the adder 16 outputs a high level when the reference value A ₂ greater than 18 based on the timing generated from the counter 9, 10 The binarized information (information binarized depending on whether the high-frequency component is equal to or greater than or equal to a predetermined value) for each area is determined by whether the output of the comparator 17 is at a high level or a low level. An mxn bit memory to be stored, 19 is a comparator for comparing the data stored in the memory 18 one field before and the data of the current field, 20 is a counter 9 for each area only when the output of the comparator 19 is at a low level. A counter 21 counts a clock generated every time, and holds the output (binary information) of the comparator 17 for one area in the horizontal direction. D flip-flop (hereinafter referred to as D-FF), 22 is D
A comparator for comparing the binarized information of the immediately preceding region obtained from the FF21 with the binarized information of the current region, and 23 is a counter for each region by the counter 9 only when the output of the comparator 22 is at a low level. Is a counter that counts the clocks generated in the clock. The degree of change based on the high frequency component between regions adjacent each of the video screen thus signals S ₁ indicating the degree of change based on the brightness level of the movie screen in the current field and the previous field from the counter 20 in the current field from the counter 23 overall signal S ₂ expressed is to be output, respectively. Reference numeral 24 denotes an A / D converter for converting the output of the detector 6 into a digital value. Reference numeral 25 denotes a lens drive based on the output of the A / D converter 24 and also based on the result of calculating the outputs of the counters 20 and 23. A control circuit 26 controls the motor 8 to comprehensively control the automatic focusing device. A D / A converter 26 converts the output of the control circuit 25 into an analog signal and supplies the analog signal to the motor 8.

The automatic focusing device according to the present invention has the above-described configuration. Next, the operation thereof will be described step by step.

The imaging surface of the imaging device 2 is divided into a grid of m × n as shown in FIG. 2, and aij (i = 1, 2,...,
m, j = 1, 2,..., n). Then, the horizontal address generation counter 9 and the vertical address generation counter 10 generate the address of each area on the screen according to the scanning on the video screen.

Here, in FIG. 2, for example, m = 32, n = 32, that is, vertical and horizontal divisions, and the clock of the counter 9 is twice the subcarrier frequency (hereinafter referred to as 2f _SC ).
Horizontal drive pulse (HD)
, Each region will include 11 clocks in the horizontal direction and 7 lines in the vertical direction in each field, as shown in FIG.

On the other hand, the comparator 12 outputs the LPF1
The signal from which unnecessary high-frequency components have been removed by 1 is compared with a reference voltage _Vref . When the output of the LPF 11 is equal to or higher than _Vref , a high level is output. The reference voltage _Vref is set to an intermediate value of the video signal, for example, a voltage corresponding to IRE50%. As a result, the output of the comparator 12 becomes a value obtained by binarizing the video signal with respect to the intermediate value.

Counter 13 the output of the comparator 12 becomes the high level, when the enable terminal EN is at high level, the enable state and counts the clock frequency 2f _SC.
The counter 13 counts the clock of 2f _SC ,
It is reset each time a horizontally divided area on the video screen shown in the figure is switched. Therefore, the counter 13
The high-frequency component of the video signal is the reference value V for each region in the horizontal direction.
_The number of clocks (= 2f _SC ) equal to or greater than _ref is output. And the output of the counter 13 is compared with the reference value A ₁ by the comparator 14, the reference value A ₁ is taken into account that the clock of 2f _SC is present 11 clock in each area, as shown in FIG. 3 For example, it is set to 6, which is the majority of the total. That is, while there are 11 clocks in the area, the number of clocks whose luminance level is higher than the reference voltage at each point is counted. Therefore, if the luminance level is equal to or higher than the reference voltage _Vref over the entire horizontal direction of the area, a maximum of 11 clocks will be counted. In this manner, the binarized information is output to the output of the comparator 14 depending on whether or not the high luminance component is equal to or more than the reference value A1 in _one horizontal line in each region. , Supplied to the adder 16 and the shift register 15
Is stored in.

The shift register 15 is composed of one n-bit shift register corresponding to the number of regions in the horizontal direction as described above.
An l-digit counter is formed for every n bits, and a clock which rises every time a horizontal area of the video screen is switched is shifted, and one bit is shifted by one bit at the same time as each area is switched. It is designed to rotate so that it goes around every time. If the output of the comparator 14 is low level, "0" is added to the adder 16, and if it is high level, it is added to the adder 16 and added to the 1-bit counter corresponding to the corresponding area to update the data of the shift register 15. Eventually, the output of the comparator 14 scans each area (7 lines) and stores how many times the output has gone high. The data in the shift register 15 is reset each time the vertical divided area is switched,
The scan immediately before the switching of the vertical divided areas, that is, the data indicating how many times the output of the comparator 14 has become high level by scanning the lines in each area in the line A shown in FIG. 3 is added. It is output from the unit 16 for each area.
In this embodiment, since the video screen is divided into 32 vertical and 32 horizontal directions and one area has 11 clocks and 7 lines, the shift register 15 has 32 bits and is equivalent to 7 lines corresponding to 7 lines. Since data needs to be supplied to the adder, the adder 16 has 3 bits and the shift register 15 has 3 columns (l
= 3) required.

Results The output (or becomes many times high in each region) are not being compared with a reference value A ₂ by the comparator 17, where, scanning the divided regions as shown in FIG. 3, This is to determine whether or not the lines exceeding the majority (high-frequency components are equal to or more than a predetermined value) are equal to or more than a reference value. Therefore, when seven scanning lines are included in one divided area, the majority 4 is set.

By the above operation, in one area shown in FIG. 3, the binary output of high and low is output in the comparator 12 depending on whether the high-frequency component is equal to or more than the reference value _Vref , and the high-level portion is in the horizontal direction. Only when the line that exceeds the majority exceeds the majority in the vertical direction, "1" is output as information in the area unit, otherwise, "0" is output, and after all, as binarized information for each area Output. Assuming that the information of each area unit is bij, bij is the average value of the brightness level of the entire screen at the position aij on the video screen of the area, for example, the average value of the brightness level in the area aij for 50% of IRE. It almost indicates whether it is large or small.

The binarized information bij for each area is sequentially stored in the memory 18 of m × n bits for one field, read out after one field or several fields, and read by the comparator 19 for each area and the information in the current field. The comparison is made, and the counter 20 is enabled in an area where the data in the memory 18 and the data of the current field are different. The counter 20 is provided with a clock that rises once in one area from the counter 9 and counts the clock only when the clock is enabled by the output of the comparator 19. Therefore the count is incremented by one each time to detect the area where data are different in the current field and the memory, the sum in the entire image screen end is output as an information S _1. Now counter 20
If the binarized information of each area one field or several fields before the output of the counter 20 is bij ', the difference from the binarized information bij of the current field is summed up by one field. ₁ is The magnitude changes according to the amount of change of the screen, that is, the amount of shake.

Incidentally, the values of S ₁ described above, even if there is no change in the entire screen, a fraction of the change, for example a subject such as a human in the screen changes even when moving. However, when only the subject on the screen moves, if the subject is in focus, the distance to the camera changes and the camera may not be in focus. It is not necessary to stop the operation of the automatic focusing device. In such a case, if the automatic focusing operation is stopped, the in-focus state is hardly obtained for a constantly moving subject, which causes an inconvenience.

In consideration of this point, in the present invention, the D-FF 21 and the comparator 22
The counter 23 eliminates the above-mentioned malfunction by using data relating to the complexity of the entire screen.

As shown in FIG. 1, D-FF21 is triggered by a clock that rises each time the horizontal divided area is switched,
The output of the comparator 17 is held for one area in the horizontal direction. Then, the output of the D-FF 21 is compared with the output of the comparator 17, and in a region where these data are different, the counter 23
Is enabled. Similar to the counter 20, a clock that rises every time the divided area is switched in the horizontal direction is supplied to the counter 23. Increment by one. S ₂ output from the counter 23 in this manner is a function that varies with respect to complexity of the entire information or screen based on the difference between the regions adjacent in the one field screen, Is defined. S ₂ is the binarized information bi of each divided block.
For j, the change with the binarized information b _i-1 , j in the left-hand region is summed over the entire screen.

The values S ₁ and S ₂ obtained as described above are subjected to the calculation of S = S ₁ / S ₂ (3) by the control circuit 25 shown in FIG. Value S representing quantity
Get.

This value S is a value obtained by normalizing the change between screens having different fields by the complexity of the screen, and can eliminate the influence of the magnitude of the change amount based on the difference in the complexity of the screen. I.e. the same blur amount, although complexity of the image of the entire screen is different when the value of S ₁ is greatly different, by'll normalized by complicated S ₂ screens, the screen is also complicated by a monotonous Even if there is, only the substantial change can be detected,
If the entire screen changes by one or more blocks in the horizontal direction, the amount of change shows one or more.

In addition, when the entire screen does not change and only a part of the subject in the screen moves, it is predicted that the change amount of the entire screen is small with respect to the complexity of the screen, and that S ₁ <S _2. 3) The value of the expression is less than 1.

Accordingly, the control circuit 25 determines whether or not the value of S in the above equation (3) is 1 or more. If the value is 1 or more, the automatic focusing operation is stopped, and if it is less than 1, the malfunction is caused by panning. Can be prevented.

In the above-described embodiment, S ₂ representing the complexity of the screen is used.
Information of the horizontally adjacent area when calculating
The comparison is performed using bij, but this is due to the fact that the video signal used to make the focus determination scans the screen horizontally in an automatic focusing device, so the one that does not use the vertical component This is because there is no need to consider the camera shake in the vertical direction, that is, so-called tilting, and the complexity in the vertical direction is considered to have little relationship.

However, according to the present invention, detection of a change in the vertical direction can be dealt with by a slight change. For example, when a component detection method corresponding to edge detection of a screen in the vertical direction and high-frequency component detection as described in JP-B-62-38083 and the like are used, it is necessary to consider the above-described tilting. Because it comes.

Therefore, in such a case, in order to perform binarization information of each region in the vertical direction, By performing arithmetic processing using S ₂ ′ as described above, it is possible to cope with a change in the vertical direction.

In the above description, whether or not to stop the operation of the automatic focusing device is determined by performing a magnitude judgment based on the value of S as 1. However, it is not particularly necessary to set it to 1. For example, the reference value can be changed in accordance with a change in the angle of view such as the zooming state of the zoom lens, and it can be changed in accordance with the number of divided areas on the screen. The design can be made as required.

[Effects of the Invention] As described above, according to the automatic focusing apparatus of the present invention,
The brightness level in each of a plurality of regions set on the video screen is represented by binarized information, and the binarized information in each region is compared between different fields to detect the motion of the screen, and the detection result is obtained. Is configured to control the automatic focusing operation based on the value normalized by the complexity of the screen, so that it is affected by the complexity of the screen, such as whether the screen state is monotonous or complicated. It is possible to accurately detect whether the change in the screen is a movement of the entire screen, such as camera shake, or a partial change in which only the main subject moves. Is stopped to prevent defocusing, and control to continue the focusing operation for the movement of the main subject can be performed. Accordingly, malfunctions due to camera shake, panning, and the like can be effectively prevented in a video camera and a video device of this type that are often hand-held.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an automatic focusing apparatus according to the present invention, FIG. 2 is a diagram showing a configuration of a video screen, and FIG. 3 is a diagram showing a configuration of a plurality of areas set on the video screen. Figure,
FIG. 4 is a block diagram showing the configuration of a typical prior art automatic focusing device, and FIG. 5 is a diagram showing the relationship between the amount of extension of a lens and the output of a detector.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hiroshi Suda 770 Shimonoge, Takatsu-ku, Kawasaki-shi, Kanagawa Prefecture Inside the Tamagawa Office of Canon Inc. (56) References JP-A-58-129878 (JP, A) JP-A-58-58 146183 (JP, A)

Claims (4)

(57) [Claims] 1. An image pickup means, a focus adjustment means for detecting a focus state from an image signal output from the image pickup means and performing a focus adjustment, and a plurality of image pickup means set corresponding to an image screen of the image pickup means A binarizing means for binarizing a predetermined signal component in an image pickup signal in each area to obtain binarized information; and comparing and computing binarized information corresponding to each area between two temporally different screens Detecting means for detecting motion information of an image, and controlling the focus adjusting means based on the motion information output from the detecting means, and when a motion equal to or more than a predetermined value is detected by the detecting means, An automatic focusing device comprising: a control unit for stopping a focus adjustment operation by the focus adjustment unit. 2. The apparatus according to claim 1, wherein said detecting means compares the binarized information of each area in a current field and a field before a predetermined period and outputs a signal based on the difference. A first detection unit; and a second detection unit that compares the binarized information of each area in the current field with an adjacent area and outputs a signal based on a difference between the two areas. Outputting a result obtained by dividing the output of the detection means, wherein the control means stops the focus adjustment operation by the focus adjustment means when the output is equal to or greater than a predetermined value. Focusing device. 3. An automatic focusing apparatus according to claim 1, wherein said predetermined signal component is a luminance signal component in a video signal output from said image pickup means. 4. The apparatus according to claim 2, wherein said detecting means outputs a result obtained by dividing an output of said first detecting means by an output of said second detecting means and normalizing the result. An automatic focusing device, characterized in that: