JP3386491B2 - Automatic focusing method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focusing system, and more particularly to an automatic focusing system capable of performing high-speed and high-precision automatic focusing on any object. . [0002] In recent years, automatic focusing (AF) based on a video signal obtained from an imager without using a special sensor,
Automatic exposure adjustment (AE), automatic white balance (AW
Techniques for performing B) and the like by digital processing have become common. The automatic focusing method digitally integrates a high-frequency component of a video signal in a focusing target area, and uses an obtained value as an evaluation value indicating a degree of focusing.
This is a method for driving and controlling the F motor. The extraction of the high frequency component of the video signal is performed using a band pass filter. As described above, the conventional automatic focusing control is performed based on an integrated value of a high frequency component of a video signal obtained from an imager. However, in such an automatic focusing method, since a high-frequency component of a video signal in a horizontal pixel direction is extracted, a high-level high-frequency component is obtained when a subject is a vertical line, but an oblique line is obtained. Sometimes, the level of the high-frequency component decreases, and in the case of a horizontal line, no high-frequency component is obtained, so that accurate focusing control cannot be performed. For example, when the subject is the vertical line A shown in FIG. 16, the video signal obtained from the imager has a sharp fall and a rise as shown by A1 in FIG. 17A, and the signal after passing through the band-pass filter. Also becomes a high level like A2. However, when the subject is hatched as shown in FIG.
The level change of the imager output does not become steep as shown by B1 in FIG. 17B, but changes gently. Therefore, the signal level after passing through the band-pass filter decreases, and the focusing accuracy decreases. . In the case of a horizontal line subject as shown in FIG. 16C, the imager output has only a DC component.
As shown in (C), no output appears in the bump pass filter. [0004] As described above, the conventional automatic focusing method uses the following method when the subject is close to an oblique line or a horizontal line.
High-precision focusing control is not possible. For horizontal line subjects,
This problem can be solved by forming a band-pass filter for high-frequency component extraction with a vertical filter, obtaining a steep level change as shown by D1 in FIG. 16, and obtaining a high level such as D2 as the band-pass filter output. , In that case 1H
The need for the delay means not only increases the circuit configuration scale, but also causes a problem that it cannot cope with a diagonally shaded subject. In addition, although a technique for rotating the entire optical system by an optimum angle with respect to oblique or horizontal lines has been proposed (Japanese Patent Publication No. 58-708), the mechanism for rotating the optical system is complicated.
There is also a problem that the size is increased. SUMMARY OF THE INVENTION It is an object of the present invention to provide an automatic focusing system which enables high-speed and high-precision automatic focusing of any object including a horizontal line and an oblique line. In order to solve the above-mentioned problems, an automatic focusing method according to the present invention employs a focus evaluation method for information relating to a high-frequency component in a video signal corresponding to an area to be focused. An automatic focusing method used as a value, based on at least the distribution state of the photometric information related to the focusing target area, and when the form of the image in the same focusing target area is scanned in any direction, the contrast information is effectively output. An effective scanning direction recognizing means for recognizing information on whether the information can be extracted, and an image obtained by scanning at least the focusing target area in a direction effectively recognized by the effective scanning direction recognizing means. Automatic focusing means for performing a focus adjustment operation using information on a high-frequency component in the information as a focus evaluation value. According to the present invention, a scanning direction in which suitable contrast information is obtained is detected, and information relating to a high-frequency component in video information obtained by scanning in the detected direction is used as a focus evaluation value. By using this, high-speed and high-precision automatic focusing is enabled. Next, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing one embodiment of the automatic focusing system according to the present invention. In this embodiment,
A tilted image signal of a subject image is electrically rotated to an optimal angle (vertical direction), so that high-frequency component extraction can always be performed with high accuracy. For example, the original images shown in FIG. 2A are rotated by an appropriate angle to obtain images (B) to (F) at desired angles. In (B), the original image (A) is rotated to obtain an original image of the subject image having an angle surrounded by a thick frame. At this time, although the shaded portion is a portion that is not in the original image, no problem arises because the subject image exists substantially in the center. In addition, the original image portion that protrudes from the thick frame is deleted. In FIG. 1, a subject image formed on an imager 2 such as a CCD via an optical system 1 is converted into an electric signal and input to an imaging process circuit 3. The imaging process circuit 3 performs well-known signal processing on the signal from the imager 2, and outputs a video signal to a recording system via the terminal 4 a of the switch 4. The luminance Y signal from the imaging process circuit 3 is converted into a digital signal by the A / D converter 5 and written into the field memory 6. Various synchronization signals are generated from the SSG circuit 10, and the trigger circuit 9 is driven to control the operation of the imager 2, to control the operation timing of the imaging process circuit 3, and to control the write timing of the field memory 6 by the write control circuit 1.
Control via 1. Under the control of the address signal Add from the read control circuit 15, a video signal rotated by a predetermined angle as described later is read from the field memory 6 and subjected to an interpolation process using an interpolation coefficient K. The signal is converted into an analog signal by the / A converter 8 and output to the recording system via the terminal 4b of the changeover switch 4.
The microcomputer 12 sends a control signal for rotating the subject image from the imager 2 by a predetermined angle to the read control circuit 15. The Y signal converted to a digital signal by the A / D converter 5 has a low-pass component extracted by a low-pass filter 19, integrated by an integration circuit 20, and the obtained integrated value is supplied to the microcomputer 12 as AE information. Is done. The signal subjected to the interpolation processing by the interpolation processing circuit 7 is subjected to extraction of a high-frequency component by the band-pass filter 13 and the integration circuit 1
The integrated value obtained in step 4 is supplied to the microcomputer 12 as an evaluation value indicating the degree of focusing described above. Microcomputer 1
Reference numeral 2 indicates that a focusing operation is performed by driving the AF motor driver 17 based on the evaluation value through a process described later. FIG. 3 is a diagram for explaining the principle of scanning direction detection for obtaining a suitable focus evaluation value based on information on high frequency components in one embodiment of the automatic focusing method according to the present invention. . An example of a subject image (a mountain having a diagonal ridgeline against the sky) as shown in FIG. In this example, one screen is divided into 8 × 8 small blocks, and the following processing is performed for each divided block based on AE data obtained through a low-pass filter and an integration circuit.
When the image shown in (A) is scanned in the direction in which the vertical line is detected as in the related art, the output level of the bandpass filter is low because the ridgeline of the mountain is oblique, and the contrast is high as shown in (B). Therefore, an appropriate focus evaluation value cannot be obtained. In this embodiment, AE information obtained by passing a signal of each divided block through a low-pass filter is detected. As shown in FIG. 13C, the output level of the low-pass filter is high (bright) in the area corresponding to the sky, low (dark) in the area corresponding to the mountain, and the boundary area between the two areas has a brightness blurred at an intermediate value. become. Therefore, the inclination angle θ of the mountain ridge line with respect to the vertical direction as shown in (D) is obtained based on the AE information as shown in (C). A rotation process described later is performed using the tilt angle θ obtained in this manner, and as shown in FIG. 4, the original image (dotted line portion) is rotated by θ to obtain a rotated image like a solid line, and the ridge line of the mountain is set to be vertical. A suitable focus evaluation value can be obtained. The principle of address conversion for controlling the rotation of the subject image will be described with reference to FIG. FIG.
The address positional relationship when a thick line image is obtained by oblique scanning by rotating the original image indicated by the thin line by θ. In the figure, white circles indicate real pixels stored in the memory, and black circles indicate virtual pixels read from the memory. Each address position P
(00), P (10), P (20), P (01), P
(11), P (21), P (02), P (12), P
(22) Corresponding pixel data is written in the field memory 6, and using the pixel data at these address positions, the corresponding address position Q ( 10), Q (20), Q
(01), Q (11), Q (21),... Are obtained and sent to the field memory 6 as address signals Add. For example, the address position Q (1
The virtual pixel addresses 0), Q (20), Q (01), and Q (11) are obtained from the relationship shown in the drawing as follows. Q (10): x P (00) + cos θ y P (00) + sin θ Q (20): x P (00) +2 cos θ = P (10) +2 cos θ−1 y P (00) +2 sin θ = P (10 ) +2 sin θ Q (01): x P (00) −sin θ y P (00) + cos θ Q (11): x P (00) −sin θ + cos θ = P (01) −sin θ + cos θ y P (00) + cos θ + sin θ = P (01) + cos θ + sin θ−1 FIG. 6 shows an example of a circuit for generating the X address. In the XST register 151X, a pixel address to be read first, 0 in this example, is set.
XW = cos θ shown in FIG. 5 is generated from the register 152X, and XW shown in FIG.
0 = −sin θ has been generated. The output of the adder 154X is delayed by one clock (one pixel) by the delay unit 156X. The adder 154X adds cos θ from the XW register 152X and the output from the delay unit 156X.
The output of the delay unit 156X is added to the output (0 in this example) from the XST register 151X in the adder 158X. The delay unit 157X outputs the output of the adder 155X to 1
Delay by H. The adder 155X is connected to the X0 register 15
-Sin θ from 3X and the output from the delay unit 157X are added. Adder 159X adds the output of delay unit 157X and the output of adder 158X, and outputs the result as an X address signal. FIG. 7 shows an example of a circuit for generating a Y address signal similar to that of FIG. YST register 151Y
Is set to 0, and from the YW register 152Y,
Is generated, and Y0 register 153 is generated.
From Y, Y0 = cos θ shown in FIG. 5 is generated. The output of the adder 154Y is delayed by one clock (one pixel) by the delay unit 156Y. Adder 154Y adds sin θ from YW register 152Y and the output from delay unit 156Y. The output of the delay unit 156Y is YST
The output from the register 151Y (0 in this example) is added to the output by the adder 158Y. Delay unit 157Y delays the output of adder 155Y by 1H. Adder 155Y
Is cos θ from the Y0 register 153Y and the delay unit 1
The output from 57Y is added. Adder 159Y adds the output of delay unit 157Y and the output of adder 158Y, and outputs the result as a Y address signal. FIG. 8 is a diagram showing the principle of the address conversion shown in FIG. 5 and the aspect ratio (768 pixels, 2 pixels) of 3 to 4 shown in FIG.
An address conversion diagram in the case where the present invention is applied to (40 lines) and rotated by 30 degrees is shown. In this case, as shown in FIG. 9, one pixel has a size of 2.4: 1 in length and width. At this time, XST = 0 XW = 0.866 X
0 = −2.4 × 0.5 YST = 0 YW = 0.5 / 2.4 Y0 = 0.8
66, and as is apparent from the figure, the general formula representing the X address Xmn and the Y address Ymn in the number of pixels m and the number of lines n is as follows. Xmn = XST + m.XW + n.X0 Ymn = YST + m.YW + n.Y0 For example, the address (coordinate) of the 0th line (n = 0) is (XY) = (0,0), (0.866,0.208) ,
(1.732, 0.417),... In the first line (n = 1), (XY) = (− 1.2, 0.866), (−0.33)
4,1.074), (0.532, 1.28),. Here, the integer part of each address represents the address Add,
It is clear from the figure that the decimal part indicates the interpolation coefficient K. Referring to FIG. 1, the present embodiment can also cope with an electronic zoom operation when the zoom motor driver 16 is driven by the operation of the zoom switch 18.
FIG. 10 shows actual pixel addresses P (00), P (10), P (20), P (30), and P (00) indicated by white circles during the electronic zoom operation.
P (01), P (11), P (21), P (31),
The virtual pixel addresses Q (00), Q (10),
Q (20), Q (30), Q (40), Q (01), Q
(11), Q (21), Q (31), Q (41) are shown. At this time, XW and Y0 are constant values, and X0 and Y0
W is 0. The interpolation processing for extracting high-frequency components with higher accuracy using the band-pass filter in FIG. 1 is preferably, for example, a four-point weighted averaging method as shown in FIG. The address position Q to be read from the memory is
As shown in the figure, when X1 and X2 are determined, four surrounding points P (1
1) Using the weighted average of P (21), P (12), and P (22), is obtained by the following equation. Q = (1-Ky) X1 + Ky.X2 X1 = (1-Kx) P (11) + KxP (21) X2 = (1-Kx) P (12) + KxP (22) Therefore, Q = (1-Kx) ( 1−Ky) P (11) + Kx (1−Ky) P (21) + Ky (1−Kx) P (12) + Kx · Ky · P (22) (1) The operation of equation (1) is one cycle Within 4 pixel address P
(11), P (21), P (12), and P (22) can be realized by reading them simultaneously. Simultaneous reading of the four pixels can be performed using a memory configuration as shown in FIG. 10, for example. In the example shown in FIG. 12, even-numbered columns,
Even row dedicated memory (A), odd column, even row dedicated memory (B), even column, odd row dedicated memory (C) and odd column
Four independent memories of an odd-row dedicated memory (D) are provided. FIG. 13 shows an address generation circuit for reading data from a memory in order to perform an operation by the above-mentioned four-point weighted averaging circuit. An address, a column address for even-numbered memory, a row address for odd-numbered memory, and a row address for even-numbered memory are generated. Column address 0
The bit is output as a select signal HSEL, and is added to 1 to 9 bits by an adder 251. 1 to
9 bits become the column address for the odd-numbered column memory, and the adder 2
The output of 51 becomes the column address for the even-numbered column memory. Similarly, the 0 bit of the row address is output as the select signal VSEL, and is added by the adder 252 to 1 to 7 bits. Bits 1 to 7 become the row address for the odd-numbered memory, and the output of the adder 252 becomes the row address for the even-numbered memory. FIG. 14 shows an example of a circuit for performing the four-point weighted averaging operation shown in equation (1) using the read data read from the memory. In FIG. 14, selectors 253 and 254 operate on select signal HS obtained in FIG.
When EL is “H”, the “H” terminal is selected, and when “L”, the “L” terminal is selected. Similarly, the corresponding terminal of the selector 261 is selected by the select signal VSEL. The selector 253 receives the input data of the even-numbered column and the even-numbered row, and the input data of the odd-numbered column and the even-numbered row.
Even-column odd-row read data and odd-column odd-row read data are input. The two outputs from the selector 253 are respectively subjected to coefficients (1-K
x), Kx. The outputs of the multipliers 255 and 256 are added by the adder 257 and output to the two input terminals (L, H) of the selector 261. On the other hand, two outputs from the selector 254 are multiplied by coefficients (1−Kx) and Kx by multipliers 258 and 259, respectively. Multiplier 258
And 259 are added by the adder 260 and output to the other two input terminals (L, H) of the selector 261. The two outputs from the selector 261 are the above X1 and X2, and the coefficients (1-K)
x), Kx. The outputs of the multipliers 262 and 263 are added by an adder 264 to obtain interpolated data Q. In the examples of FIGS. 13 and 14, the reason why the select signal is required is that, as shown in FIG. 15, addresses of four points to be selected are generated according to four patterns # 1 to # 4. In this example, an example of pattern # 2 is shown. As described above, according to the automatic focusing method according to the present invention, high-speed and high-precision focusing control can always be performed even if the subject image is in any tilt state.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing one embodiment of an automatic focusing system according to the present invention. FIG. 2 is a diagram for explaining the principle of the automatic focusing method according to the present invention. FIG. 3 is a scanning direction detection principle diagram for obtaining a suitable focus evaluation value in the embodiment of the present invention. FIG. 4 is a diagram in which an image signal is rotated in order to obtain a suitable focus evaluation value based on the scanning direction angle obtained in FIG. FIG. 5 is an address generation principle diagram showing an image rotation principle in the embodiment of the present invention. FIG. 6 is a circuit diagram for generating an X address according to the principle diagram shown in FIG. 5; FIG. 7 is a circuit diagram for generating a Y address based on the principle diagram shown in FIG. 5; FIG. 8 is a diagram showing an address generation principle when the principle shown in FIG. 5 is applied to actual image rotation. FIG. 9 is an image configuration diagram that is the basis of the principle diagram shown in FIG. 8; FIG. 10 is a diagram illustrating a principle of an electronic zoom operation according to the embodiment of the present invention. FIG. 11 is a principle diagram of performing an interpolation process by a four-point weighted average calculation in the interpolation processing circuit 7 in the embodiment of the present invention. FIG. 12 is a memory configuration diagram used for performing the interpolation processing shown in FIG. 11; 13 is a circuit diagram showing an example of an address generation circuit for memory read used in the interpolation processing shown in FIG. FIG. 14 is a circuit diagram illustrating an example of the interpolation processing illustrated in FIG. 11; 15 is a diagram illustrating a selected 4 in the interpolation processing illustrated in FIG. 11;
It is a figure showing an example of even and odd combination of a point. FIG. 16 is a diagram illustrating vertical, horizontal, and oblique subject images. 17 is a diagram illustrating a change in a high-frequency component obtained from a band-pass filter in the conventional automatic focusing method for each subject illustrated in FIG. 16; [Description of Signs] 1 Optical system 2 Imager 3 Imaging process circuit 4 Changeover switch 5 A / D converter 6 Field memory 7 Interpolation processing circuit 8 D
/ A converter 9 Trigger circuit 10 S
SG circuit 11 Write control circuit 12 Microcomputer 13 Band pass filter 14, 20 Integrator circuit, 15 Read control circuit 16 Zoom motor driver 17 AF motor driver 18 Zoom switch 19 Low pass filter

Claims (1)

(57) [Claims] An automatic focusing method using information on a high-frequency component in a video signal corresponding to a focusing target area as a focus evaluation value, wherein at least photometry related to the focusing target area Effective scanning direction recognizing means for recognizing information relating to the direction in which the form of the image in the in-focus target area can effectively extract contrast information based on the distribution state of the information. Focusing adjustment using information relating to a high-frequency component in video information obtained by scanning at least the focusing target area in the direction recognized by the effective scanning direction recognition unit as a focus evaluation value And an automatic focusing means for performing an operation.