JP3263061B2 - Focus adjustment device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention detects the sharpness of a subject image formed on an image pickup device via an image pickup optical system, and adjusts the image pickup optical system so as to increase the sharpness. And a focus adjustment device that performs focus adjustment on a subject.

[0002]

2. Description of the Related Art Recently, an electronic image of a subject is electronically captured using an image sensor, and the captured image signal is recorded and stored on a recording medium such as a floppy disk or a magnetic tape. Various electronic camera systems have been developed to reproduce images using a TV receiver or the like. In particular, the spread of home video movie systems has been remarkable, and various electronic still cameras have recently been commercialized.

In such an electronic camera system, A
As a characteristic technique of the F control (automatic focus adjustment), for example, an image sensor used for image pickup input of a subject such as a CCD is used as it is as a sensor for the AF control, and a subject image picked up by the image sensor is used. There is a technique of detecting a contrast component of a signal and adjusting the focus of an imaging optical system lens on a subject. That is, in the AF control technique, when the imaging optical system lens is in focus on the subject, the sharpness of the subject image formed on the imaging device via the imaging optical system lens increases, and particularly, Utilizing the fact that the high-frequency component is remarkably generated, a high-frequency component of an output signal (a captured image signal) of an image sensor is detected, and the sharpness of a subject image represented by the high-frequency component of the image signal is increased. The focus position of the imaging optical system lens with respect to the subject is adjusted.

FIG. 5 is a schematic diagram showing a main part of a conventional focus adjusting device of this type. Reference numeral 1 denotes an image pickup optical system lens, and 2 denotes an electronic image of a subject formed by the image pickup optical system lens 1. Image pickup device such as CCD for inputting image data
Is a pre-processing circuit that performs predetermined signal processing on a subject image signal (captured image signal) captured and input by the image sensor 2. In the preprocessing circuit 3, predetermined signal processing such as sampling processing for the subject image signal and color separation processing is executed.

[0005] A signal processing circuit (not shown) of a camera system such as a video processor inputs the image signal subjected to predetermined signal processing via the preprocessing circuit 3 and records and stores the image signal. Perform processing and the like.

The focus adjusting device is characterized in that a predetermined processing is performed through the pre-processing circuit 3 and an image signal to be supplied to a camera system is inputted to the focus adjusting device, and a high-pass filter (HPF) or Bandpass filter (BP
F) selectively extracts high-frequency components in the captured image signal through a filter circuit 4 composed of F), and uses the high-frequency components to adjust the focus of the imaging optical system lens 1 on a subject. is there. The area gate 5 performs a gating operation under the control of the system controller 6, and the filter circuit 4 is provided only for a predetermined area, for example, in the center of the screen in the image captured and input by the image sensor 2.
The high-frequency components of the image signal extracted by are extracted.

[0007] The signal extracted through the area gate 5 (high-frequency component of a predetermined area) is detected through a detector 7 and integrated through an integrator 8 over the predetermined area. Is done. Then, the integrated value of the high frequency component is digitized via the A / D converter 9,
The memory 6a of the system controller 6 serves as information for adjusting the focus of the imaging optical system lens 1 with respect to the subject, that is, information indicating the sharpness (contrast) of the subject image.
Is written to. The system controller 6 drives the focusing circuit 10 according to the control procedure shown in FIG. 7, for example, in accordance with the information indicating the sharpness written in the memory 6a, and drives the focusing mechanism of the imaging optical system lens 1 to drive the imaging optical system. Focus adjustment of the lens 1 with respect to the subject is performed.

The focus adjustment of the imaging optical system lens 1 to the subject by the system controller 6 is basically performed by a so-called hill-climbing method as shown in FIG. 6A or as shown in FIG. This is performed by a scanning method. The hill-climbing method sequentially compares the contrast information at each focusing position while driving the focusing mechanism of the imaging optical system lens 1, and sequentially shifts the focusing positions so that the contrast increases as shown in FIG. The position P, which is variable and has a peak contrast value, is determined as the focus position. On the other hand, in the scanning method, as shown in FIG. 6B, the contrast value of the entire focusing area of the imaging optical system lens 1 is checked in advance by scanning, and the focusing position at which the contrast value becomes the highest is determined as the focusing position P. And adjusts the focus of the imaging optical system lens 1 according to the information.

Regardless of the control method, the focusing of the imaging optical system lens 1 is adjusted so that the contrast of the subject image is maximized, and the focusing of the subject is adjusted.

The procedure for adjusting the focus by the hill-climbing method will be briefly described with reference to FIG. 7. First, the focusing position of the imaging optical system lens 1 is set in either direction (the longest shooting distance side or the shortest shooting distance side). Move by a predetermined amount (step a). Then, it is determined whether or not the contrast value has increased due to the movement of the lens (step b). If the increase in the contrast value is detected, the lens is moved by a predetermined amount in the same direction (step c). Then, similarly, it is determined whether or not the contrast value is increased by the movement of the lens (step d), and the movement of the lens is repeated until the increase of the contrast value is stopped. After that, when the increase in the contrast value is no longer detected, the movement of the lens is stopped (step e), the completion of focusing is displayed, and the focusing process ends (step f).

On the other hand, if no increase in the contrast value is detected in the processing in step b, the lens is moved in the opposite direction by a predetermined amount (step g). In this state, it is determined whether or not an increase in the contrast value is detected (step h). If an increase in the contrast value is detected, the imaging optical system lens 1 is combined according to the processing procedure from step c described above. Drive focus adjustment.

If the increase in the contrast value cannot be detected even when the imaging optical system lens 1 is moved in the reverse direction, the change of the lens movement direction is repeated within a predetermined number of times to increase the contrast value. Find out the direction of. If the increase in the contrast value cannot be detected (step i), the movement of the lens is stopped (step j), a message indicating that the focusing operation cannot be performed is displayed, and the focusing operation is performed. The operation is stopped (step k).

[0013]

As described above, when the focusing of the object of the image pickup optical system lens 1 is adjusted in accordance with the high frequency component of the object image obtained from the image pickup device 2, that is, the contrast information, the object illumination light is driven. The following problem occurs when light fluctuations depending on the power supply frequency are included.

That is, if the object illumination light source is a discharge lamp such as a fluorescent lamp, it is inevitable that the illumination light fluctuates in light intensity in synchronization with the power supply frequency, that is, fluctuates. For example, illumination light from a discharge lamp driven at a power supply frequency of 50 Hz is 5
There is light fluctuation at a cycle corresponding to 0 Hz or 100 Hz, and light fluctuation from a discharge lamp driven at a power supply frequency of 60 Hz has light fluctuation at a cycle corresponding to 60 Hz or 120 Hz.

On the other hand, electronic imaging of a subject image by the imaging device 2 is performed, for example, when reproduction of the captured image is performed using an NTSC TV receiver.
In the case where the image reproduction is performed in synchronization with the field frequency of 60 Hz in the C system and the image reproduction is performed using the PAL system or the SECAM system TV receiver, the imaging of the subject image is performed in synchronization with the field frequency of 50 Hz. Done.

When an electronic image of a subject image is taken in accordance with the NTSC system under illumination light conditions using a discharge lamp driven at a power frequency of 50 Hz, the cycle of illumination light fluctuation and the electronic camera Causes a flicker problem in the contrast information used for adjusting the focus of the imaging optical system lens 1 described above. Similarly, the PAL / S under the illumination light condition by a discharge lamp driven under a power frequency of 60 Hz.
The above-described flicker problem also occurs when electronic imaging of a subject image conforming to the ECAM method is performed.

For example, while the imaging optical system lens 1 is focused and driven at a constant speed, a subject is electronically imaged at the above-mentioned predetermined period, and a high-frequency component (contrast value) of the image signal is obtained. As schematically shown, a fluctuation accompanying illumination light fluctuation depending on the power supply frequency is superimposed on the contrast value. The fluctuation of the contrast value due to the fluctuation of the illumination light causes a control error of the focus adjustment using the above-described contrast value.

Therefore, conventionally, in order to deal with this kind of problem, it has been considered to change the imaging scanning frequency itself in the photoelectric conversion unit as disclosed in Japanese Patent Publication No. 26588/1990. But such a scheme
This system is very useful in a system that configures a closed system such as an imaging scan in a facsimile apparatus disclosed in this publication, but there is a problem in applying it to an electronic camera in which an imaging cycle conforming to the TV system is set.

As a countermeasure against flicker in focusing adjustment in an electronic camera, it has been proposed to make the exposure time n / 2 times the power supply cycle. However, it cannot be denied that problems such as a decrease in exposure sensitivity and jerkiness disturbance to a video signal occur. Furthermore, for example, Japanese Patent Application Laid-Open No. 57-35480 discloses a sampling cycle of an image signal used for focusing adjustment.
It has been proposed to eliminate the influence of flicker by making the flicker cycle 1 / n times. However, in this case, the period in which contrast information is obtained becomes longer, so that it is unavoidable that the speed of the focus adjustment operation is reduced.

On the other hand, Japanese Patent Application Laid-Open No. 56-106478 discloses that a level variation due to flicker is absorbed by dividing a high frequency component of an image signal by a differential value of a low frequency component of the image signal. Has been advocated. However, according to such a method, for example, when an image of a subject having a low frequency component is small, the signal input corresponding to the denominator of the above-described division becomes small, and the S / N of the contrast signal is reduced.
Is greatly deteriorated. In addition, in this case, a divider capable of operating at high speed is required, so that the system configuration becomes large-scale, causing a problem that the price is increased.

As described above, in the related art, when the focusing of a subject is adjusted using contrast information of a captured image signal obtained from an imaging device, the focus is adjusted due to fluctuation depending on the power supply frequency of the subject illumination light. If the focusing operation becomes unstable, or if countermeasures are taken against it, the operation speed will be slow, a high-cost high-speed divider will be required, and depending on the subject, S / N degradation will occur. As a result, problems such as poor controllability occurred.

The present invention has been made in view of such circumstances, and an object of the present invention is to always provide a stable and high-speed picked-up image signal irrespective of fluctuation of illumination light depending on a power supply frequency. It is an object of the present invention to provide a highly practical focus adjustment device capable of performing a focus adjustment in accordance with contrast information of an image.

It is another object of the present invention to provide a focusing adjustment device having an efficient configuration with a reduced load on an arithmetic circuit.

[0024]

A focus adjusting apparatus according to the present invention detects the sharpness of a subject image formed on an image pickup device via an image pickup optical system, and adjusts the sharpness. A focus adjustment device that adjusts the focus of the imaging optical system with respect to a subject; a first detection unit that detects a high-frequency component of a subject rubber signal captured by the image sensor; Second detection means for detecting an average signal component of the subject image signal, and first gate means for specifying a first area as a detection area of a high-frequency component of the subject image signal in the first detection means; In the second detecting means,
As the detection area of the average signal component of the subject image signal
Not the same as the first area and related to said first area;
A second gate unit for specifying a second region to be processed; and a second gate unit for detecting a high-frequency component of the first region detected by the first detection unit, the second high-frequency component being detected by the second detection unit.
Means for generating a signal indicating the sharpness for the focus adjustment by normalizing the average signal component with respect to the region of the second region, and the second region includes a portion adjacent to the first region. Is set as described above.

The focus adjusting apparatus according to the present invention is characterized in that the above-mentioned normalization is performed by digital operation.

According to the focus adjusting apparatus according to the present invention, the high-frequency component indicating the contrast information of the subject image picked up by the image sensor is converted into an average signal component of the subject image. For example, normalization is performed by division, and this normalized high-frequency component is used as contrast information for focusing adjustment.Therefore, flicker depending on the power supply frequency is included in the subject illumination light, and this causes Even if the subject image picked up has a periodic level variation, the above-described normalization can remove the level variation due to the flicker from the high frequency component of the subject image. That is, the level variation element caused by flicker included in the high-frequency component and the level variation element caused by flicker included in the average signal component are canceled out by the above-described normalization, and a subject image that is not affected by flicker is eliminated. It is possible to obtain contrast information.

Therefore, according to the present invention, it is not necessary to take measures such as changing the imaging input cycle of the subject image in accordance with the cycle of flicker as in the prior art, so that the focusing adjustment operation can be performed simply and at high speed. It is possible to make it.

Accordingly, the degree of freedom in setting an area for acquiring information is increased. For example, in general, data is generally not stored because the optimum area setting for focusing does not always match the optimum area setting for photometry. Even in the case where the data cannot be shared, it is easy to use the average signal component, which is information for normalization, as the data of the photometry circuit, and the circuit scale is reduced and the control calculation is simplified.

Further, by performing the above-mentioned normalization by digital operation, the normalization of high-frequency components can be performed by effectively utilizing the property of the A / D converter which substantially performs the division. By doing so, the load on the arithmetic circuit can be reduced, the efficiency of the circuit configuration can be increased, and the scale of the circuit configuration can be simplified.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A focus adjusting device according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic structural view of a focus adjusting device according to a first embodiment, in which the same parts as those of the conventional device shown in FIG.

The feature of the apparatus of this embodiment is that the filter circuit 4 for extracting the high-frequency component from the subject image signal obtained by the image sensor 2, the area gate 5, the detector 7, In addition to a signal processing circuit including an integrator 8, an area gate 11 for extracting a high-frequency component from the subject image signal and an average signal component thereof at the same time, and a signal processing circuit including an integrator 12 are provided. The high frequency component obtained by the integrator 8 is divided by the average signal component detected from the subject image via the integrator 11 and the integrator 12 by the divider 13.
The high frequency component normalized by the division process by 3 is digitally converted via the A / D converter 9 and written into the memory 6a of the system controller 6.

That is, the area gate 11 performs a gating operation under the control of the system controller 6, and selectively selects an image signal of a central area which is a focus adjustment target area in the subject image together with the area gate 5 described above. Has been extracted.

The difference between the area gate 11 and the area gate 5 is that the area gate 5 corresponds to a predetermined screen area in which a high-frequency component of the object image signal extracted through the filter circuit 4 is defined. On the other hand, the area gate 11 extracts the subject image signal itself corresponding to the predetermined screen area.

The subject image signal of the predetermined image area extracted through the area gate 11 is integrated by the integrator 12 over the entire image area, and the average signal component is obtained. I have. The divider 13 calculates the average signal component S of the subject image obtained by the integrator 12.
As described above, the high frequency component SB of the subject image obtained from the filter circuit 4 via the integrator 8 is divided using A, thereby normalizing the high frequency component SB.

The normalization of the high-frequency component SB by this division process will be described. The average signal component SA obtained by integrating the subject image signal over a predetermined area is represented by a coefficient K1 ( p), and a level variation element at the time of imaging in the n-th field due to the influence of flicker of the illumination light source is Fn, which is given as SA = K1 (p) · Fn (1).

The level change factor Fn due to the influence of the flicker takes a value of [1] on average, and generally, the fluctuation period depending on the power supply frequency of the subject illumination light and the fluctuation of the image pickup element 2 It is affected only by the deviation from the imaging cycle of the subject image. The level variation element Fn takes a different value, for example, periodically for each imaging field.

On the other hand, the high-frequency component SB integrated over a predetermined area of the same subject image signal generally has a coefficient K2 (p) for the high-frequency component at the time of just focus determined by a so-called picture of the subject. In this case, SB = K2 (p) .Fn.D (P, .delta.) (2) However, the function D indicates an output change due to defocus of the imaging optical system, and takes the maximum value at the just focus position of the imaging optical system. And the picture P of the subject
The function D is a function that depends on the defocus amount δ from the just focus position.
Is defined. Also, for the subject image P, when the focus is to be adjusted for a certain subject, the subject pattern is specified by this, and it can be considered that there is no change in the subject during the focusing operation period. Here, it can be considered as a certain constant determined by the subject.

As shown in the equation (2), the high frequency component SB of the subject image is generally the difference between the fluctuation cycle depending on the power supply frequency of the subject illumination light and the imaging cycle of the subject image by the image sensor 2. , And changes under the influence of a function D which largely depends on the defocus amount δ and the picture pattern P of the subject.

Incidentally, when there is no fluctuation in the subject illumination light, the high-frequency component SB of the subject image is given as SB = K2 (p) .D (P), and its value depends exclusively on the defocus amount δ. Will change. Conventionally, focusing is generally performed by utilizing the relationship between the high frequency component SB and the defocus amount δ such that the high frequency component SB is maximized.

The signal processing circuit from the filter circuit 4 to the integrator 8 obtains the high-frequency component SB of the subject image as shown in the above-mentioned equation (2). The integrator 12 provided in the above device obtains the average signal component SA of the subject image as shown in the above-mentioned equation (1). The divider 13 divides the high-frequency component SB of the subject image thus obtained by the average signal component SA, and this division has the following meaning. That is, the division process in the divider 13 is as follows.

[0042]

(Equation 1)

This means that a certain result is obtained.

As shown in the equation (3), the result of the division of the high frequency component SB by the average signal component SA obtained by the divider 13 is based on the influence of the level fluctuation factor Fn in the n-th field due to flicker. When the focusing operation period can be deemed to have no change in the subject as described above, it changes only depending on the defocus amount δ. .

That is, the coefficient K2 (p) for the high-frequency component and the coefficient K1 (p) for the average signal component at the time of just-focusing on the picture of the subject have specific values when the subject is constant, and [K2 ( p) / K
1 (p)] takes a certain value for the subject. Therefore, the above-described division result changes mainly depending only on the defocus amount δ, and indicates information obtained by normalizing the high-frequency component SB obtained from the subject image as described above.

As a result, the high frequency component [SB / SA] normalized by dividing the high frequency component SB by the average signal component SA in the divider 13 is converted into a digital signal through the A / D converter 9. The system controller 6 generates contrast information for adjusting the focus of the imaging optical system.
The memory 6a can always perform the focusing adjustment stably without being affected by the fluctuation of the subject illumination light depending on the power supply frequency.

In the embodiment shown in FIG. 1 described above, an analog integrator is used to integrate the subject image signal and each high frequency component of the subject image signal and perform a division operation between the integrated values. 8, 12 and a divider 13 were used. Therefore, in general, it is unavoidable that the hardware configuration is complicated, and there are some problems in securing the accuracy of arithmetic processing in an analog system. Therefore, it is desirable that the above-described arithmetic processing be performed digitally, and that the arithmetic processing accuracy and the like be simplified and sufficiently increased.

FIG. 2 is a schematic diagram showing a main part of a second embodiment of the focus adjusting apparatus according to the present invention based on such a viewpoint, and is basically the same as the previous embodiment. The same parts as those shown in FIG.

A feature of the apparatus of this embodiment is that a high-frequency component of a subject in a predetermined image area extracted from the filter circuit 4 through the area gate 5 and a signal extracted through the other area gate 11 are extracted. A subject image signal in a predetermined image area is digitally converted using two independent A / D converters 9a and 9b. These digitally converted signal components are stored in the memory 6a of the system controller 6, respectively, and are integrated using the arithmetic processor 6b provided in the system controller 6 to integrate the signal components and integrate them. The above-described division processing (normalization processing) is performed on the result.

According to the apparatus of the embodiment configured as described above, the subject image signal and its high-frequency component are A / D-converted in real time, and the system controller 6
Of the arithmetic processor 6b
Can be used to execute signal processing for obtaining contrast information in an all-digital manner.
As compared with the case where the analog arithmetic processing is performed as shown in the embodiment, the entry of the error element due to the variation of the analog arithmetic element is greatly reduced, and the focus adjustment is performed by obtaining the contrast information with high accuracy. Can be provided. In addition, since the hardware configuration can be greatly simplified as compared with the case where an analog signal processing circuit is constructed, practical advantages are great.

In each of the above-described embodiments, for example, the center of the screen of the subject image picked up by the image pickup device 2 is determined as the focus adjustment target range, and the area gates 5 and 1 are set.
1 and the high-frequency component SB of the subject image and the average signal component S
I asked for A. However, the area for obtaining the average signal component SA of the subject image does not necessarily need to be determined as the focus adjustment target area. For example, the average signal component SA of the subject image from the entire screen of the subject image
May be requested.

As shown in FIG. 4, when the central portion in the subject screen X is determined as the focus adjustment target area Y, the image signal of the target area Y is read from the image pickup device 2 prior to reading the image signal. , An upper region Z closely related to the target region Y (as apparent from FIG.
The average signal component SA from the image signal of the adjacent portion)
May be requested.

This can be shown as follows. That is, although the effect of removing the influence of flicker has been described using equations (1) to (3), making the extraction area of the subject image signal slightly different causes a slight difference in the picture P of the subject. Means that. Therefore, since the screen areas extracted by the area gates 5 and 11 are different,
Equations (1) and (2) described above can be considered as SA = K1 (p1) .Fn... (1) 'SB = K2 (p2) .Fn.D (P, δ)... (2)' Just do it. Here, P1 indicates a pattern in the area where the average signal component SA is determined, and P2 indicates a pattern in the area where the high frequency component SB is determined.

In this case, however, the aforementioned (3)
ceremony

[0055]

(Equation 2)

Under the above-mentioned assumption that there is no change in the subject during the focusing operation period, it is concluded that, in this case as well, there is no influence of flicker but only the defocus amount δ.

In summary, the subject image picked up by the image pickup device 2 generally includes not only the main subject to be picked up but also various other background image components. It is more preferable that the average signal component SA and the high-frequency component SB are respectively obtained from a region defined as the focus adjustment target range. However, it is also possible to determine the average signal component SA from another area related to the focus adjustment target area.

FIG. 3 is based on this viewpoint.
FIG. 11 is a diagram showing a third embodiment in which the circuit configuration is particularly simplified by utilizing the properties of the A / D converter. It is assumed that the signal extraction area is set as shown in FIG. 4 as described above.

That is, in the apparatus according to the embodiment shown in FIG. 3, the area gates 5 and 11 are independently gated and the high frequency component of the subject image for the target area Y is extracted via the area gate 5. I am trying to do it. In the other area gate 11, prior to the signal extraction timing by the area gate 5, the target area Y
Before the image signal from the image sensor 2 is read out, the image signal of the area Z from which the signal is read out is extracted, and before the image signal of the focusing target area Y is read out by the integration processing, the image signal of the subject image is read out. The average signal component SA is determined.

The average signal component SA obtained by the integrator 12 is directly given as a digitized reference signal Vref. To the A / D converter 14, and thereafter, the subject extracted via the area gate 5 The high frequency component of the image is digitally converted using the digitized reference signal Vref. Then, the digitally converted high frequency components are sequentially stored in the memory 6a of the system controller 6,
The integration is performed over the target area Y described above.

The A / D conversion is basically performed by quantizing an input analog signal using a predetermined digitized reference signal Vref. Usually, a predetermined constant digitized reference signal Vref. , The input analog signal is digitized.

Here, for the sake of comparison, the digital signal processing shown in FIG. 2 described above will be considered. An A / D converter for converting the high-frequency component of the subject image extracted through the area gate 5 will be described. 9a quantizes the high frequency component (analog value SBA) with the digitized reference signal Vref.
The digital value SBD is obtained as [SBA / Vref.]. The A / D converter 9b quantizes the subject image signal (analog value SAA) with the digitized reference signal Vref. And obtains the digital value SAD as [SAA / Vref.].

Since the average signal component SA of the subject image obtained by the integration process is represented by [= ΣSAD] and its high-frequency component SB is represented by [= ΣSBD], the normalization process is carried out.

[0064]

(Equation 3)

This means that it is performed as

On the other hand, in the third embodiment, since the average signal component SA (analog amount) is given as the digitized reference signal Vref., The A / D converter 14 shown in FIG. / SA], the output value SD is obtained. Therefore, if the integrated value S is obtained by digital operation in the system controller 6,

[0067]

(Equation 4)

This has the following meaning. As a result, A
The normalization of the high-frequency component described above can be performed using the characteristics of the / D converter, and the contrast information of the subject image can be obtained easily and efficiently.

That is, if the calculation processing of the contrast information is performed in this manner, one A / D converter 14
Can be used effectively to perform signal processing, and the amount of signal processing operation is greatly reduced. Therefore, the signal processing can be simplified and efficiently speeded up, and the signal processing load is greatly reduced. It becomes possible. Also, the signal processing accuracy can be made sufficiently high.

In this example, a region Z for obtaining the average signal component SA is set above the focusing target region Y as a region from which the subject image signal is read out before the focusing target region Y. However, signal reading from the image sensor 2 is
In a system capable of performing the operation in the reverse direction from the lower side of the screen, an area for obtaining the average signal component SA is defined below the focus target area Y as shown by a dashed line area in FIG. What should I do?

In this manner, in a general subject image, since there are many image areas that are strongly related to the focusing target area Y at the center of the screen at the bottom of the screen, the average signal component SA is located at the top of the screen. Since the uncertain factors are reduced as compared with the case where the area Z for obtaining the value is set, more accurate signal processing can be performed.

As described above, according to some embodiments of the focus adjustment apparatus according to the present invention, the present invention normalizes the high frequency component of the subject image by its average signal component,
This is used for focusing adjustment as contrast information.

According to the high-frequency components of the subject image normalized in this way, the subject illumination light is assumed to be affected by the AC power supply frequency, causing a fluctuation. The frequency (period) of the fluctuation of the illumination light Even if there is a deviation from the imaging cycle of the subject image in the imaging device 2, contrast information that is not affected by the fluctuation of the illumination light can be effectively obtained. In addition, as described in the above-described embodiment, focusing adjustment can be performed by obtaining contrast information at a high speed by a relatively simple process and by a system having a simple hardware configuration. As a result,
The present invention can be applied to various electronic cameras that electronically image a subject image using an image sensor, and has a great effect in practical use, such as being able to effectively perform focusing adjustment of the imaging optical system. .

The present invention is not limited to the above embodiment. For example, which region of the imaging screen is to be the focus adjustment target region, how large the size of the region is to be set, and the like may be determined according to the focusing specification of the electronic camera. In addition, how much frequency band of the high frequency component of the subject image signal is extracted as a signal may be determined according to the specifications. Further, in the embodiment, the contrast information is obtained by integrating the high frequency component. However, it is of course possible to obtain the contrast information by detecting a peak for the high frequency component. The subject image signal to be processed for the focus adjustment may be a color separation signal obtained through the pre-processing circuit 3, or may be the subject image signal itself read from the image sensor 2. May be. Further, it is needless to say that an imaging signal or the like subjected to γ correction may be used.
In addition, the imaging optical system lens is not limited to a single focus lens, but may be a so-called zoom lens. In short, the present invention can be implemented with various modifications without departing from the scope of the invention. it can.

[0075]

As described above, according to the present invention, a high frequency component of a subject image signal obtained from a signal component of a predetermined region in a subject image is converted into a portion adjacent to the region where the high frequency component is obtained. Is normalized by the average signal component of the subject image signal obtained from the signal component of the predetermined area including the image signal, and is used as contrast information for focus adjustment, so that there is no problem of flicker caused by fluctuation of the subject illumination light. Focus adjustment can be performed effectively.

Therefore, the degree of freedom in setting an area for acquiring information is increased. For example, in general, data is generally not stored because the optimum area setting for focusing does not always match the optimum area setting for photometry. Even in the case where the data cannot be shared, it is easy to use the average signal component, which is information for normalization, as the data of the photometry circuit, thereby reducing the circuit scale and simplifying the control calculation. The effect is obtained.

As described above, according to the present invention, a great deal of practical effects can be achieved, such as making it possible to perform focusing adjustment with high speed and high accuracy by simple processing with a simple hardware configuration. Can be done.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a focus adjustment device according to a first embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a focus adjustment device according to a second embodiment.

FIG. 3 is a schematic configuration diagram of a focus adjustment device according to a third embodiment.

FIG. 4 is a diagram illustrating a relationship between a focus adjustment target area and an average signal component detection area according to a third embodiment.

FIG. 5 is a schematic configuration diagram of a conventionally proposed focusing adjustment device.

FIG. 6 is a diagram schematically showing a form of focus adjustment according to contrast information of a subject image.

FIG. 7 is a diagram illustrating an example of a control procedure of focusing adjustment by a hill-climbing method.

FIG. 8 is a schematic signal diagram for explaining flicker of a subject image signal caused by fluctuation of subject illumination light and a problem caused by the flicker.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Imaging optical system lens 2 ... Image sensor 3 ... Preprocessing circuit 4 ... Filter circuit (high frequency component extraction means of a subject image signal) 5 ... Area gate 6 ... System controller 6a ... Memory 6b ... Arithmetic processor 7 ... Detector 8 ... Integrator 9, 9a, 9b A / D converter 10 Focusing circuit 11 Area gate 12 Integrator 13 Divider 14 A / D converter

Claims (2)

(57) [Claims] 1. A sharpness of a subject image formed on an image sensor via an imaging optical system is detected, and focus adjustment of the imaging optical system with respect to the subject is performed so that the sharpness is increased. In the focusing control device, a first detection unit that detects a high-frequency component of a subject rubber signal captured by the imaging device; and a second detection unit that detects an average signal component of a subject image signal captured by the imaging device. (2) detection means, first gate means for specifying a first area as a detection area of a high-frequency component of the subject image signal in the first detection means, and average of the subject image signal in the second detection means. signal
The component detection area is not the same as the first area, and
A second area for identifying a second area associated with the first area;
And normalizing a high-frequency component of the first area detected by the first detecting means with an average signal component of the second area detected by the second detecting means. Means for generating a signal indicating sharpness for the focus adjustment,
Wherein the second region is set so as to include a portion adjacent to the first region. 2. The focus adjusting device according to claim 1, wherein the normalization is performed by digital operation.