JPH10200904A - Automatic focusing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain sure focusing without causing malfunction by using color aberration of a lens so as to attain a high focus speed. SOLUTION: This device controls a position of an image pickup lens based on a contrast of a video signal read from an image pickup element 3 resulting from an object image by an image pickup lens 1. In this case, one color signal among a plurality of color signals included in the video signal is used with priority to move the image pickup lens 1 so that the focal position of the color signal appears before a focal plane of the image pickup lens 1 and the focusing is finished by moving the image pickup lens 1 in the same direction by a prescribed distance from the position of the image pickup lens at which the contrast of the one color signal indicates a maximum value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focusing device applicable to various optical instruments.

[0002]

2. Description of the Related Art Conventionally, a subject image is projected onto an image pickup device by an image pickup lens, and a high-frequency component (contrast value) of the subject image indicating a degree of focus is obtained from a video signal output from the image pickup device. There is a focusing method in which the position that becomes the maximum is determined as the focusing position and the imaging lens is driven to that position. This focusing method is called a “hill climbing method”. For example, an NHK technical research report (1975, 1st report)
7, Vol. 1, No. 86, pages 21-37).

[0003] A focusing operation based on the "hill climbing method" will be described with reference to Figs. FIG. 6 shows the relationship between each imaging lens position and the contrast value of the subject image when the subject is photographed. In the figure, the stop position of the imaging lens of step movement is indicated by the lens position L ₀ ~L _6, the contrast values obtained at each lens position is indicated by C ₀ -C ₆ respectively. Lens position L ₃ is a focus position.

As shown in FIG. 6, the contrast value increases from the infinity position to the in-focus position, shows a maximum value at the in-focus position, and then decreases toward the closest position, and then decreases. Is shown. The in-focus position is detected using such a contrast characteristic. Note that the infinity position of the imaging lens is ideally a lens position where the contrast value becomes 0, but in reality, the movement distance of the imaging lens is a position at which the imaging lens can move to infinity due to mechanical restrictions. Since the position is limited, the position where the imaging lens comes closest to the imaging device is treated as an infinite position.

FIG. 7 shows a flowchart of focusing control based on the "hill climbing method". The lens position is initially moved in L ₀ lenses moved closest direction (forward direction) from. First, in step S1, the contrast value C _n (FIG. 6)
C ₀₎ by entering the inputs C ₁₎ in the contrast value C _{n + 1} (FIG. 6 in step S3 from the forward driving of the motor so as to move the imaging lens by one step in step S2 in. In step S4, the magnitudes of C _n and C _{n + 1} are compared. If C _{n + 1} is larger than C _n, it is close to the in-focus position, so n is incremented in step S5, and the imaging lens is brought further closer. The motor is driven to rotate forward one step closer to the side. Then, C _n in magnitude comparison in step S4 if detected that is greater than C _{n + 1,} then the imaging lens is present in the lens position L ₄ passes through the focus position. Therefore the motor reverse rotation to at returning only one step an imaging lens to the lens position L ₀ direction at step S6, the focusing operation is completed by driving stop.

[0006] Thus, where the "hill-climbing method" in the image pickup lens has reached the lens position L _4, recognizes that it has passed the maximum contrast position L _3, focusing reversed driving the imaging Reference to a maximum contrast position The operation ends.

An automatic focusing apparatus based on the above-described "hill climbing method" and using a chromatic aberration of an imaging lens to increase the focusing speed is described in Japanese Patent Application Laid-Open No. 1-21281. I have. This automatic focusing device extracts high-frequency components of each color signal obtained from a color image sensor, determines the direction of defocus by comparing the integration levels of the high-frequency components in a fixed cycle, and determines an image based on the determination result. It drives the lens.

The focusing position slightly differs for each wavelength of the subject light based on the optical chromatic aberration of the imaging lens and the like. If an imaging lens having a predetermined chromatic aberration is used as shown in FIG. 8, the light from the point light source P forms images at points R, G, and B by red light, green light, and blue light, respectively.

When it is assumed that the lens system is designed on the basis of green light, the R, G, and B points are included in the light-receiving image signal with the imaging plane (Q1, Q2, Q3). The high frequency components of red, green and blue light are shown in FIGS. 9 (a), 9 (b) and 9 (c).
Each color ratio is as shown in FIG.

Therefore, when the result of FIG. 9 (a) is obtained, the imaging surface is at Q1, so the imaging lens is moved to the subject side, and when the result of FIG. Q
9, the imaging lens can be moved closer to the expected focal plane (Q2) by moving the imaging lens toward the imaging element.
When the result of (b) is obtained, it can be determined that the position is the in-focus position.

According to the focusing method utilizing the optical chromatic aberration of the imaging lens, the direction of defocus can be recognized without driving the imaging lens, and thus there is an advantage that the focusing speed is increased.

[0012]

However, the above-mentioned focusing system utilizing the optical chromatic aberration of the imaging lens is
There is no problem if the color components (red, green, and blue) included in the subject are evenly distributed. However, a malfunction may occur in a subject in which the color components are not uniformly distributed.

For example, in the case of a subject having many red components, the high-frequency components of red, green, and blue light contained in the light-receiving image signals on the imaging surfaces Q1, Q2, and Q3 shown in FIG.
It is expected that the color ratios shown in (b) and (c) will be obtained. As shown in FIG. 10, FIG.
When the result of (b) is obtained, the imaging lens is moved to the subject side. This is despite the focus position
Furthermore, it means that an erroneous operation of moving the imaging lens to the imaging device side has occurred.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described circumstances, and it is possible to increase the focusing speed by utilizing the chromatic aberration of a lens, and to surely focus without causing a malfunction. It is an object of the present invention to provide an automatic focusing device capable of performing the following.

[0015]

In order to achieve the above object, the present invention takes the following measures. The present invention is an automatic focusing device that forms an image of a subject on an image sensor by an imaging lens, and controls a position of the imaging lens based on a contrast value of a video signal read from the image sensor. Moving the imaging lens such that a focus position related to the one color signal appears earlier than a predetermined focal plane of the imaging lens by preferentially using one color signal from the plurality of color signals obtained; An automatic focusing device for moving the imaging lens in the same direction by a predetermined distance from a position of the imaging lens at which the contrast value of the one color signal has a maximum value, and then terminating the focusing operation.

According to the present invention, the in-focus position of one color signal is deviated from the expected focal plane of the imaging lens due to the chromatic aberration of the imaging lens, and the expected focal plane of the imaging lens is brought closer to the imaging device from a certain direction. As a result, the in-focus position related to one color signal is detected earlier than the expected focal plane of the imaging lens.
Since the distance from the lens position when the focus position of one color signal is detected to the expected focal plane of the imaging lens can be known in advance, the lens position when the focus position of one color signal is detected By moving the imaging lens in the same direction by a predetermined distance known in advance from, the expected focal plane of the imaging lens moves to the imaging plane of the imaging element to be in focus.
Therefore, the reverse rotation driving of the lens can be eliminated from the focusing operation, and the focusing speed can be increased.

[0017]

Embodiments of the present invention will be described below. FIG. 1 shows the overall configuration of the automatic focusing apparatus according to the present embodiment. Light of a subject image taken from an optical system (not shown) is guided to the imaging lens 1. The imaging lens 1 can be driven in the optical axis direction by a lens driving circuit 2 composed of a pulse-driven stepping motor, and forms a subject image having a degree of focus according to the lens position on the color imaging device 3. . The color imaging element 3 captures an image of the subject projected by the imaging lens 1 and outputs a video signal. The color image sensor 3 is driven by an image sensor driver 4
Do. The video signal output from the color image sensor 3 is input to an AMP / CDS circuit 5 that performs signal amplification, sample hold, and double correlation sampling. AMP /
The video signal subjected to the signal processing by the CDS circuit 5 is converted into an A / D signal.
The signal is input to the converter 6 and converted into a digital video signal. A
The video signal output from the / D converter 6 is input to a color separation circuit 7. The color separation circuit 7 converts the video signal into R (red), G
Each color signal of the three primary colors (green) and B (blue) is separated into a luminance signal. The R, G, and B color signals separated by the color separation circuit 7 are input to high-pass filters (hereinafter, referred to as “HPFs”) 8-1, 8-2, and 8-3 provided in correspondence with each other, and are provided with luminance. The signal is input to the HPF 8-4. Each HPF
8-1, 8-2, 8-3 and 8-4 extract the amount of high frequency component (contrast value) indicating the degree of focusing from each signal and input it to the arithmetic processing circuit 9. The arithmetic processing circuit 9 includes a CPU,
It is composed of a ROM, a RAM, and the like, and a focusing function described later is realized by the CPU executing a program stored in the ROM or the like.

The pulse generation circuit 10 generates sampling pulses for the AMP / CDS circuit 5 and the A / D converter 6 and various pulses such as a horizontal synchronization signal and a vertical synchronization signal for the color separation circuit 7.

FIG. 2 is a functional block relating to the focusing function provided in the arithmetic processing circuit 9. The R, G, B contrast values and the luminance signal contrast values input to the arithmetic processing circuit 9 are input to the color signal selection unit 11. The color signal selection unit 11 selects a contrast value of a designated color (including a luminance signal) indicated by a color selection signal set by an operator or the like.

The AF evaluation value calculation unit 12 includes a color signal selection unit 1
An AF evaluation value is calculated by integrating the contrast value selected in step (1). The vertical synchronizing signal (VD), the horizontal synchronizing signal (HD), and A constituting the input image captured by the color image sensor 3
The integration area designating signal created by using the sampling clock of the / D converter 6 is input to the AF evaluation value calculation unit 12. The position and size of the integration area can be arbitrarily set by the integration area designation signal.

The single-color focus determination section 13 determines a focus position (hereinafter, referred to as a "temporary focus position") for the designated color based on any one of the AF evaluation values of R, G, and B. A control function is provided to further move and focus the drive direction without reversing the drive direction by a defocus amount from the temporary focus position to the original focus position of the imaging lens (hereinafter, referred to as “scheduled focal plane”).

Here, the imaging lens 1 has axial chromatic aberration as shown in FIG. 3, and as shown in FIG. 4, a temporary focus position Fg based on a green component and a focus position Fy based on a luminance signal (planned focal plane). Is assumed to match. Also, the temporary focus position Fb based on the blue component is located two steps before the focus position Fy of the luminance signal from the infinity position toward the closest side,
The temporary focus position Fr based on the red component is located two steps before the focus position Fy of the luminance signal from the closest position toward the infinity side. Note that one step of lens movement corresponds to a drive amount of one step of the stepping motor of the lens drive circuit 2.

The distance (the amount of defocus) from the temporary focusing position of each color to the expected focal plane is determined in advance by the design of the imaging lens 1. In the case of the imaging lens 1 used in this embodiment, two steps are required.

When the focusing control is performed from the infinity position to the closest position by the “hill climbing method” using the AF evaluation value of the green component, the temporary focusing position Fg is obtained at a position one step after the temporary focusing position Fb. Can be recognized, and the position is a place where one step is left to the expected focal plane (Fy). Further, when the focusing control is performed from the closest position to the infinity side in the “hill climbing method” using the AF evaluation value of the red component, the temporary focusing position F is obtained at a position one step after the temporary focusing position Fr.
r can be recognized, and the position is one step left to the expected focal plane (Fy).

When the focusing control is performed from each direction by the “hill climbing method” using the AF evaluation value of each color, each temporary focusing position F
The number of steps from the position where b and Fr can be recognized to the expected focal plane (Fy) (in this example, both steps are 1 step) are stored in the defocus amount correspondence table 14, respectively.

In the example shown in FIG. 4, since the focus position Fy in the luminance signal matches the focus position Fg in the green signal, the remaining number of steps is zero for the green signal. Depending on the design of the lens, there is a case where the focus positions do not coincide with each other. In such a case, the number of remaining steps also exists for the green color.

Since the color signal currently used for focus control is determined by the color selection signal, the "remaining step number" of the color signal indicated by the color selection signal is determined by the defocus amount correspondence table 14.
And then read into the single-color in-focus determining unit 13.
Details of the focusing control by the single-color focusing determination unit 13 will be described later.

The drive control unit 15 includes a single-color focus determination unit 13
Alternatively, it is a portion that outputs an instruction of a driving direction and a driving timing to the lens driving circuit 2 based on a command value given from the luminance focusing determination unit 16.

The luminance focus judging section 16 is a section for performing the focus control of the “hill climbing method” based on the luminance signal, and outputs a command value for the focus control to the drive control section 15.
The proper use with the single color focus determination unit 13 is instructed by the operator by a color selection signal. When the luminance signal is selected by the color selection signal, the focus control is performed under the operation of the luminance focus determination unit 16.

Next, the focusing control of the embodiment configured as described above will be described. FIG. 5 is a flowchart for the focusing control by the single-color focusing determination unit 13. The flowchart in FIG. 5 shows a case where the blue signal (B) is selected as the designated color and the imaging lens is driven from the infinity position to the closest side. As an initial setting, the imaging lens 1 is moved to an infinite position farthest from the color imaging device 3.

In step T1, the "remaining step number" of the blue signal indicated by the color selection signal is fetched from the defocus amount correspondence table 14, and the focusing control is started by selecting the contrast value of the blue component.

The parameter used by the single-color focus determination unit 13 in focusing control is not the contrast value itself but the AF evaluation value. However, in comparison with the flowchart of FIG. 7, the AF evaluation value is also used in FIG. Instead, the contrast value is shown.

In step T2, the AF evaluation value (C _n ) of the blue component at the current imaging lens position (infinity position) is input from the AF evaluation value calculation unit 12 to the single color focus determination unit 13, and in step T3. The imaging lens 1 is driven forward by one step. When the blue signal is selected, the normal rotation direction is a direction in which the imaging lens 1 is moved to the closest side.

At step T4, the AF evaluation value (C _{n + 1} ) of the blue component after the one-step movement is input, and at step T5, the AF evaluation value (C _{n + 1} ) is set.
The AF evaluation value (C _n ) before the step movement is compared with the current AF evaluation value (C _{n + 1} ). If C _{n + 1} is large, it is close to the temporary focus position Fb, so n is incremented in step T6, and the imaging lens 1 is further moved in the closest direction by one step. While C _n ≦ C _{n + 1} , the process of incrementing n and moving the imaging lens 1 in the closest direction step by step is repeated, so that the imaging lens 1 passes through the temporary focusing position Fb of the blue signal. .

In step T5, the AF evaluation value (C
_n ) is larger than the current AF evaluation value (C _{n + 1} ), as shown in FIG. 4, the imaging lens 1 passes through the temporary focus position Fb and is located one step before the expected focal plane (Fy). You have moved to the point. Then, when it is detected that C _n becomes larger than C _{n + 1} , in step T7, the drive is further rotated forward by the “remaining step number” of the blue signal fetched from the defocus amount correspondence table 14 in step T1, and then stopped. Then, the focusing operation is completed.

Next, the case where the red signal is selected as the designated color will be described. In the initial setting, the imaging lens 1 is moved to the closest position closest to the color imaging element 3, and the red signal is designated by the color selection signal.

If the "number of remaining steps" of the red signal indicated by the color selection signal is taken from the defocus amount correspondence table 14 into the single color focus determination section 13, the AF evaluation value at the closest position ( C _n ) is taken, and the imaging lens 1 is driven forward by one step with the direction toward the infinity side as the normal rotation direction. Hereinafter, in the same manner as in the case of the blue signal, C _n
Is repeatedly increased until C becomes larger than C _{n + 1,} and the imaging lens 1 is moved in the infinity direction by one step. And if C _n is greater than C _{n + 1,} and ends the focusing operation by stopping after only further forward driving "number of remaining steps" of the red signal.

When it is desired to perform focusing control using a luminance signal, a luminance signal is selected by a color selection signal. When the luminance signal is selected, the contrast value of the luminance signal is set to AF.
The contrast value A, which is input to the evaluation value calculation unit 12,
The F evaluation is given to the luminance focus determination unit 16 to perform focus control of a so-called “hill climbing method”.

According to such an embodiment, when the imaging lens 1 is driven to rotate forward from the infinity position or the closest position in the facing direction, the imaging lens 1 is moved beyond the expected focal plane which is the original focusing position of the imaging lens. Focus control using the contrast value of each color component where the temporary focus position exists several steps before, find the temporary focus position by each color component, and drive forward several more steps to the expected focal plane Therefore, it is possible to eliminate the waste of inverting the imaging lens 1 and perform focusing several steps faster than focusing control using a luminance signal.

When the focus control is performed by using the luminance signal, the lens position is returned in the opposite direction after the original focusing position of the imaging lens, so that the image which was initially a blurred image is in focus. After changing to an image and then to a blurred image, it changes to an in-focus image again. On the other hand, according to the above-described embodiment, since there is no reversing operation of the lens, it stops at the focused image from the blurred image, and gives an uncomfortable feeling to the observer watching the imaging screen. The focusing operation is performed without any change.

In a low-illuminance environment, an auxiliary light source may be used. By selecting a color component close to the color light emitted from the auxiliary light source using the color selection signal, the information amount of the color signal used for focusing control is larger than that of the other color components, and the focusing accuracy can be improved. For example, if the color light emitted from the auxiliary light source is red light, the focusing accuracy can be improved by selecting the red component with the color selection signal.

The case where the imaging lens 1 having the axial chromatic aberration shown in FIG. 4 is used has been described. However, the present invention is not limited to the case shown in FIG. The number of remaining steps for focus control, the lens moving direction, and the like can be determined.

Although the embodiments have been described above, the present specification includes the following inventions. (1) In an automatic focusing device that forms a subject image on an image sensor by an image pickup lens and controls a position of the image pickup lens based on a contrast value of a video signal read from the image sensor, an image read from the image sensor. Contrast extraction means for extracting a contrast signal representing the contrast of the subject image from a plurality of color signals included in the signal, and one of the contrast signals extracted by the contrast extraction means corresponding to the moving direction of the imaging lens Calculating means for calculating an evaluation value indicating the degree of focusing in the color signal by preferentially using the contrast signal of the color signal, and an imaging lens in which the evaluation value of one color signal calculated by the calculating means is a maximum value Control means for terminating the focusing operation when the imaging lens is moved in the same direction by a predetermined distance from a position. An automatic focusing device characterized by the following.

According to the present invention, a contrast signal representing the contrast of a subject image is extracted from a plurality of color signals included in the video signal read from the image sensor, and one of the extracted contrast signals is used preferentially. An evaluation value of the contrast signal of the color signal is calculated. The imaging lens is stopped when it is further moved in the same direction by a predetermined distance from the imaging lens position where the evaluation value of this one color signal indicates the maximum value. Since the distance from the imaging lens position where the evaluation value of the color signal shows the maximum value to the expected focal plane of the imaging lens can be known in advance by designing the imaging lens, focus without moving the imaging lens in the opposite direction. Can be. (2) In an automatic focusing device that forms a subject image on an image sensor by an image pickup lens and controls the position of the image pickup lens based on a contrast value of a video signal read from the image sensor, a video read from the image sensor. Color separation means for color-separating a signal into a plurality of color signals; contrast extraction means for extracting high-frequency components from the plurality of color signals separated by the color separation means; and a plurality of color signals extracted by the contrast extraction means Color selection means for selecting a high-frequency component of one color signal to be used preferentially from the high-frequency components of the color signal; evaluation value calculation means for calculating a focus evaluation value from the high-frequency component of the color signal selected by the color selection means; The lens position at which the focus evaluation value of one color signal calculated by the evaluation value calculation means becomes maximum is determined by the imaging lens after the focus position of the one color signal appears. Moving the imaging lens in the direction in which the expected focal plane appears, and moving the imaging lens in the same direction a predetermined distance from the detected imaging lens position to end the focusing operation. An automatic focusing device comprising: a determination unit.
According to the present invention, a video signal read from an image sensor is color-separated into a plurality of color signals, and a high-frequency component of one color signal to be preferentially used is selected from high-frequency components extracted from these color signals. A focus evaluation value is calculated from the high-frequency component of the selected color signal and provided to the single-color focus determination means. When the lens position at which the focus evaluation value of one color signal is maximized is detected, the focus operation is terminated when the lens is further moved in the same direction by a predetermined distance. (3) The automatic focusing device according to the above (1) or (2), wherein one color signal close to the emission color of the auxiliary light source used at low illuminance is preferentially used. .

According to the present invention, the focusing control is performed using a color signal having a larger amount of information than other color signals, so that the focusing accuracy is improved. (4) In the automatic focusing apparatus according to the above (1) or (2), focusing control using a focusing evaluation value of one color signal from a plurality of color signals with priority and focusing of a luminance signal are performed. An automatic focusing device wherein switching between focusing control using a focus evaluation value and switching is possible. According to the present invention, it is possible to quickly switch between a focusing method using a focus evaluation value of one color signal and a focusing method using a focus evaluation value of a luminance signal.

[0046]

As described above in detail, according to the present invention, one color signal is selected from a plurality of color signals and is preferentially used for focusing control. It is possible to provide an automatic focusing apparatus which can increase the focusing speed by utilizing the apparatus and can surely perform focusing without causing a malfunction.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of an automatic focusing device according to an embodiment of the present invention.

FIG. 2 is a functional block diagram of a portion related to a focusing function of the arithmetic processing circuit in the embodiment.

FIG. 3 is a diagram illustrating axial chromatic aberration of an imaging lens.

FIG. 4 is a diagram showing a relationship between contrast characteristics of each color and luminance signal and a lens step position.

FIG. 5 is a flowchart of focusing control in the embodiment.

FIG. 6 is a diagram illustrating a relationship between a lens position of an imaging lens and a contrast value.

FIG. 7 is a flowchart showing a conventional “hill climbing method” focusing operation.

FIG. 8 is a diagram illustrating an imaging surface of each color according to chromatic aberration.

FIG. 9 is a diagram illustrating a ratio of a high-frequency component of each color of a received image signal on an imaging surface disposed at a focus position of each color component.

FIG. 10 is a diagram illustrating a ratio of a high-frequency component of each color of each light-receiving image signal in a subject in which color components are not evenly distributed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Imaging lens 2 ... Lens drive circuit 3 ... Color image sensor 4 ... Image sensor driver 5 ... AMP / CDS circuit 7 ... Color separation circuit 8-1, 8-2, 8-3, 8-4 ... HPF 9 ... Calculation Processing circuit 11: Color signal selection unit 12: AF evaluation value calculation unit 13: Single color focus determination unit 14: Defocus amount correspondence table 15: Drive control unit 16: Luminance focus determination unit

Claims (3)

[Claims] 1. An automatic focusing device that forms an image of a subject on an image sensor by an image sensor and controls a position of the image sensor based on a contrast value of a video signal read from the image sensor. Moving the imaging lens such that a focus position related to the one color signal appears earlier than a predetermined focal plane of the imaging lens by preferentially using one color signal from the plurality of color signals obtained; An automatic focusing device, wherein the focusing operation is completed after the imaging lens is moved in the same direction by a predetermined distance from the imaging lens position where the contrast value of the one color signal has a maximum value. 2. The automatic focusing apparatus according to claim 1, wherein any one of a green signal, a red signal, and a blue signal is used preferentially from a plurality of color signals included in the video signal. An automatic focusing device characterized by the following. 3. The automatic focusing apparatus according to claim 2, further comprising: a driving unit configured to move the imaging lens in a stepwise manner by pulse driving, wherein the focusing position of the red signal or the blue signal is detected. An automatic focusing apparatus, wherein a margin for a predetermined step is provided from an imaging lens position at which a focusing position can be detected to a predetermined focal plane of the imaging lens.