JP2000155257A - Method and device for autofocusing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an autofocusing device capable of preventing focusing from being disabled and adequately deciding focusing by appropriately selecting a focusing area. SOLUTION: An evaluation value obtaining circuit 42 calculates evaluation values for focusing for plurality set focusing areas #0, #1, #2, #3, and #4 and stores them in a memory 43 based on the data of an image picked up by an imaging device (CCD) 18 at an image pickup part 12. The adequate focusing are is selected from the AF evaluation values at a control part 40, and a lens for focusing is moved to a lens position in accordance with the maximum value of the AF evaluation value calculated at the selected area and controlled to be a focusing condition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focus adjusting device and method for adjusting a focal position formed by an image pickup lens, based on image information obtained by an image pickup device such as a CCD solid-state image pickup device. The present invention relates to an automatic focusing device and method for adjusting a focal position of an imaging lens to obtain a desired in-focus state.

[0002]

2. Description of the Related Art In a video camera which captures an object scene and outputs an image signal of the image, the image is taken while moving a focus lens of an image pickup lens, and a high-frequency component is extracted from the output image signal to focus. The evaluation value is calculated, and if the evaluation value increases as a result of the movement of the focus lens, the movement in the same direction is continued, and if the evaluation value decreases, the lens is moved in the opposite direction. A so-called hill-climbing servo system in which the focus lens is driven to a position where the value is maximum is adopted.

On the other hand, in a digital still camera intended to capture a still image, it is necessary to instantaneously adjust the focus according to the shutter release, so that the above-described hill-climbing method cannot be simply adopted. For example, for example, a high-frequency component is extracted from a video signal captured while moving the focus lens, a high-frequency component in a predetermined focusing area is integrated, and the integration result is used as an evaluation value for focus adjustment, and the maximum focus lens is obtained. An autofocus method (CCDAF method) that recognizes a position as in-focus has been put to practical use. The video signal when a high-contrast subject is imaged contains many high-frequency components, and the evaluation value between the focused state and the focused state greatly differs. can do.
However, when a low-contrast subject is imaged, it is often impossible to determine that the subject is in focus because there is almost no difference between the evaluation values calculated at each lens position.
It is also a disadvantage of the F method.

In order to solve this problem, when it can be determined that the subject has low contrast, a method of extracting a high-frequency component by expanding a pass band of a signal frequency for extracting a high-frequency component to a lower frequency side, or extracting a high-frequency component It is conceivable that the image area to be integrated is made wider than usual and focus detection is performed using the obtained evaluation value.

[0005]

However, the former method has no effect when the contrast of the subject is scarce, and there is a problem that focusing becomes impossible.
In the latter case, there are many cases where optical images having different object distances are mixed in the detection area, so that there has been a problem that the object distance side different from the photographer's intention is erroneously determined to be in focus. .

Therefore, it is conceivable to divide the imaging area from which the object scene image is obtained into a plurality of blocks and to select a desired area by using the divided predetermined blocks as evaluation value calculation areas. However, when capturing various pictures,
There is a problem that it is difficult for the user to quickly and accurately select a desired area, and that an appropriate evaluation value is not always obtained when performing focus control on the selected area itself.

The present invention solves such disadvantages of the prior art, and when adjusting the focal position of an image pickup lens based on an image signal picked up by an image pickup element, a situation in which focusing becomes impossible occurs. It is an object of the present invention to provide an automatic focus adjustment device and a method capable of performing appropriate focus determination by automatically selecting an appropriate evaluation value detection area.

[0008]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides an image pickup device that forms an image of an object field on an image pickup device based on an image signal picked up and output by the image pickup device. In an automatic focus adjustment device for adjusting a focal position of a lens, the device includes a moving unit for moving a lens for performing focus adjustment within a focus adjustment area, and a focus adjustment unit at a central portion of a screen formed by an image signal. A first focus area for obtaining an AF evaluation value for performing AF is set, a plurality of other focus areas for obtaining an AF evaluation value are set around the first focus area, and an image of the set focus area is set. An evaluation value calculating means for extracting a contrast component of the signal and calculating an AF evaluation value corresponding to the contrast component for each focus area; Selecting means for selecting a focus area based on the AF evaluation value to obtain an AF evaluation value, and determining a focusing position of the lens on the basis of the AF evaluation value in the focus area selected by the selecting means. And control means for controlling the lens to move to the in-focus position.

According to another aspect of the present invention, a focus position of an image pickup lens for forming an image of a field on an image pickup means based on an image signal picked up and output by the image pickup means. In the automatic focus adjustment method for adjusting the focus, the method includes moving a lens for performing focus adjustment within a focus adjustment area, and performing focus adjustment on a center portion of a screen formed by an image signal. First to get AF evaluation value
Is set, a plurality of other focus areas for obtaining an AF evaluation value are set around the first focus area, and a contrast component of an image signal of the set focus area is extracted. An evaluation value calculating step of calculating a corresponding AF evaluation value for each focus area, and a selecting step of selecting a focus area to obtain an AF evaluation value for adjusting focus among the plurality of focus areas based on the AF evaluation value, A control step of determining a focus position of the lens based on the AF evaluation value in the focus area selected in the selection step, and controlling the moving means to move the lens to the focus position. I do.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of a digital camera to which the present invention is applied will be described in detail with reference to the accompanying drawings. Referring to FIG. 1, there is shown a digital camera 10 having an automatic focusing function. The camera 10 includes an imaging lens 14, an aperture 16, and an imaging device provided in an imaging unit 12.
(CCD) A still camera having a moving image mode that continuously captures an object scene by using 18 and displays the captured image in the moving image mode on a liquid crystal monitor device provided in the display unit 20 at the time of shooting. . When the switch S1 is turned on in the first stroke in which the release button 22 is pressed, the imaging lens 14 is driven to perform focus adjustment, the captured image is in focus, and the second stroke in which the release button 22 is pressed. When the switch S2 is turned on, the single-frame shooting process and the captured image recording process in the still image mode are performed. Imaging unit
The still image signal of one frame imaged at 12 is processed by a signal processing circuit
The data is input to the recording processing unit 32 through the A / D conversion circuit 26, the buffer memory 28, and the compression processing circuit 30, and the encoded data is recorded on a memory card 34 that is removably mounted on the camera 10 body. Imaging lens 14 arranged in imaging section 12
Is advantageously applied to a zoom lens having a variator lens system for continuously changing a focal length, and has a focus lens system for adjusting a focal position. In addition,
The imaging lens 12 may adjust the focal position by extending the whole or a part of the lens. The focal length and the focal position of the imaging lens 14 are adjusted by rotation of a motor or the like, and a drive signal for driving the motor is supplied from a drive circuit 36.

A stop 16 for adjusting the amount of incident light is arranged at an afocal portion of the imaging lens 14, and the amount of the stop is adjusted by a drive signal supplied from a drive circuit 36. An image sensor (CCD) 18 is arranged on the focal plane behind the stop 16, and the image sensor 18 includes, for example, R, G, B primary color filters and microlenses for improving light collection efficiency are arranged on the image plane. The configuration including a photodiode that converts an optical image formed on an imaging surface into electric charges and a charge-coupled device (CCD) that transfers electric charges in the vertical and horizontal scanning directions allows image pickup pixels to be read out by an output amplifier. Output as an electric signal. The image sensor 18 in the present embodiment transfers pixels that are photoelectrically converted by photodiodes constituting about 1.3 to 1.5 million pixels in accordance with a drive signal supplied from the CCD drive circuit 38, and has a predetermined image size. An image signal representing the captured image is output. FIG. 2 conceptually shows screen formation based on the image signal. Among the output signals of the captured image in the still image mode, the screen 200 based on the effective pixels includes, for example, 1280 pixels in the horizontal scanning direction (H), Scan direction (V)
1024 pixels. When the image sensor 18 is driven in the moving image mode, an image signal representing a screen formed of, for example, 640 × 512 pixels is decimated to approximately pixels in the horizontal and vertical directions, respectively. It may be output for each frame.

When the power of the camera 10 is turned on and the monitor display function is enabled, the image of each frame is generated until the second stroke of the release button 22 occurs prior to the actual photographing recording. The signal is read from the image sensor 18, and the read image signal is supplied to the display unit 20. In this case, in the first stroke in which the release button 22 is pressed and the switch S1 is connected to the ground G, the focal position of the imaging lens 14 is adjusted based on the image signals of a plurality of frames. Further, in the second stroke in which the release button 22 is pressed and the switch S2 is connected to the ground G, an image signal of one frame is read out from the image sensor 18, and the signal processing and the compression encoding processing for the still image are performed. Thereafter, the encoded data is recorded on the memory card 34.

The output of the image pickup device 18 constitutes the output of the image pickup section 12 and is connected to a signal processing circuit 24. Signal processing circuit 24
Performs a process of correcting and adjusting a signal level relating to brightness, color, gradation, and the like for an input image signal. Further, the signal processing circuit 24 operates in the still image mode.
It has a function of interpolating each pixel of the RGB image signal and forming a YC format image signal composed of luminance and color components. The output of the signal processing circuit 24 is analog / digital
The A / D conversion circuit 26 is connected to an (A / D) conversion circuit 26, which converts the image signal into digital image data of, for example, 8 to 10 bits and outputs the digital image data.

One of the outputs of the A / D conversion circuit 26 is connected to a display unit 20 having a liquid crystal panel for displaying input image data in a color image, and the other is connected to a buffer memory 28. The buffer memory 28 is a line buffer that temporarily stores and outputs image data. In the present embodiment, in the moving image mode, the image data is output at the output timing required by the evaluation value calculation circuit 42. In the still image mode, the buffer memory 28 outputs YC image data at a timing required by the compression processing circuit 30.

The compression processing circuit 30 is an encoding circuit for compressing and encoding image data input in the still image mode in a predetermined format corresponding to the recording medium 34 loaded in the recording processing unit 32. The compression processing circuit 30 in the present embodiment performs two-dimensional DCT processing on image data for each block of 8 × 8 pixels, and performs Huffman coding on the processed transform coefficients.
The image data is encoded at a compression ratio set by the control unit 40 by a compression encoding process such as the JPEG method. The output of the compression processing circuit 30 is connected to the recording processing unit 32,
Has a recording / reading function of writing encoded image data and its accompanying information to the memory card 34 and reading information recorded on the memory card 34.

The evaluation value acquisition circuit 42 is a circuit for calculating an evaluation value for controlling the focus position of the imaging lens 14. Specifically, the evaluation value acquisition circuit 42 is output from the imaging element 18 when the focus lens of the imaging lens 14 moves so as to focus from infinity to the closest position when the first stroke of the release button 22 occurs. The G component data is sampled from the color image signal, and high frequency components in each of a plurality of focus areas designated by the control unit 40 are extracted to obtain a contrast component of the subject image. This contrast information is 1280x1024 shown in FIG.
The imaging screen formed of pixels is divided into 64 blocks 202
Are autofocus (AF) evaluation values calculated based on G component image data corresponding to the AF area, with a portion in four blocks as one focus area (hereinafter, referred to as an AF area). A plurality of AF areas are set at a plurality of positions under the control of the control unit 40. In this embodiment, the AF areas are arranged as shown in FIG. Specifically, on the screen 200, AF areas # 0, # 1, # 2, # 3, and # 4, each of which uses four of the blocks 202, are set, and the AF area # 0 uses four blocks at the center of the screen. The image is arranged in a 320x256 image size. The AF area # 0 is an area in which the reliability of the AF evaluation value is evaluated in the order of the highest priority during the focus adjustment. AF areas # 1 and # 2 are AF areas respectively
AF areas # 3 and # 4 are similarly arranged on the left and right of area # 0. These multi-divided AF areas are configured to have the same shape and image size, and simple comparison of AF evaluation values and photometric values calculated based on the image signal in each AF area between these AF areas can do. The evaluation value acquisition circuit 42
The AF evaluation value in the AF area is calculated every time the focus lens is moved at a predetermined interval. The evaluation value acquisition circuit 42
It has a memory 43 for storing the calculated AF evaluation value of each AF area. The evaluation value acquisition circuit 42 scans the lens so that it focuses from infinity to the closest direction and stores the AF evaluation value of each AF area at each evaluation value calculation position.
The AF evaluation value of each area stored in the area is read and output to the control unit 40.

The evaluation value acquisition circuit 42 has a photometric function of measuring the luminance level of the object scene image in each AF area based on the input image data.
Notify 40. The control unit 40 determines an exposure value EV at the time of imaging based on the notified photometric value, controls a shutter speed and an aperture value in the imaging unit 12 according to the determined exposure value EV, and further controls the signal processing circuit 24. The gain of the signal amplification is controlled. The evaluation value acquisition circuit 42 measures the luminance level of each area immediately before acquiring the evaluation value, and determines the photometric value (EV _af [0] to EV
_It has a function of storing _af [4]) in the memory 43 and a function of storing the actual exposure value EV at the time of obtaining the evaluation value in the memory 43.

A control unit 40 for controlling each unit includes a release button 22
This is a processing system that detects the operation state of the camera 10 and controls each unit of the camera 10 to display a captured image on a monitor and to record the captured image on the memory card 34. The control unit according to the present embodiment is configured by a microcomputer system including a CPU, a ROM, a RAM, an I / O circuit, and controls each unit according to a program stored in the ROM. It has a function of calculating these values based on the AF evaluation value and the photometric value.

First, the control unit 40 detects the states of the switches S1 and S2 which are turned on / off by the release button 22 via an I / O circuit. Exposure control and focus adjustment processing are started to capture an image. The photometry process is performed for each of the values calculated by the evaluation calculation circuit 42.
Metering values for AF areas # 0, # 1, # 2, # 3, and # 4 (EV _af [0], EV _af [1], EV
_{Based on af} [2], EV _af [3], EV _af [4]), an exposure value EV that defines an aperture value for the aperture 16 and an electronic shutter speed value in the image sensor 18 is determined. The control unit 40 sets the exposure value EV
Are output to the driving circuit 36 and the CCD driving circuit 28, respectively. The drive circuit 36 adjusts the aperture of the diaphragm 16 in response to the control signal. The CCD drive circuit 38 drives the image sensor 18 in response to a control signal output from the control unit 40, and
The exposure accumulation time of light incident on the photodiode via 14 is adjusted.

When the photometric processing is completed, the control unit 40 supplies a control signal for causing the focus lens to perform an AF search for moving the focus lens from infinity to the closest direction in the focus area to the drive circuit 36, and provides an evaluation value acquisition circuit. A lens position for obtaining a focused state is determined based on the AF evaluation value obtained in 42, and a control signal for moving the focus lens to the focused position is supplied to the drive circuit 36.

More specifically, the control unit 40 determines lens positions for calculating an evaluation value in accordance with the movement width of the lens that changes in accordance with the focal length of the imaging lens 14, and performs AF evaluation at each lens position. The value is calculated by the evaluation value acquisition circuit 42. In response to the control signal supplied from the control unit 40, the drive circuit 36 moves the focus lens so that the focus position of the imaging lens 14 on the field moves in a certain direction from the infinity position to the closest position. To perform the AF search. In the present embodiment, the AF search for obtaining the evaluation value is performed by moving the focus lens so that the focus is adjusted from the infinity position to the close position. However, the present invention is not limited to this. The movement of the lens may be started so as to focus from the closest position to the position at infinity. The control unit 40 finally moves the focus lens to the position where the focus lens has the maximum value based on the evaluation values created at the positions of the plurality of focus stages corresponding to the focal length.

The control unit 40 calculates the maximum value (AFmax [0] to AFmax [4]) and the minimum value from the AF evaluation values of the AF areas # 0 to # 4 stored in the memory 43 by the evaluation value acquiring circuit 42. (AFmin [0]-AF
min [4]) is detected for each AF area, and the AF level reliability (AF _lb 0 to AF _lb 4) representing the reliability of the AF evaluation value is calculated for each AF area as shown in the following equation (1). It is calculated from the difference between the maximum value and the minimum value every time. In the following equation, the area code value of each AF area is shown in "[]".

[0023]

[Formula 1] AF _lb [] = Kl * (AFmax []-AFmin []) (1) where Kl is a correction multiplier.

The control unit 40 also calculates the exposure value EV at the time of calculating the AF evaluation value and the photometric values (EV _af [0] to EV _af [4]) of each AF area obtained before the calculation of the AF evaluation value. Based on this, the exposure level (exposure) reliability (AF _exp [0] to AF _exp [4]) of each AF area is calculated for each AF area as shown in the following equation (2).

[0025]

(2) AF _exp [] = (C− (| EV−EV _af [] |)) * Kc (2) where C is a calculated multiplier and Kc is a correction multiplier.

The control unit 40 controls the calculated AF level reliability (AF
_lb 0 to AF _lb 4) and exposure level reliability (AF _exp [0] to AF _exp [4])
Is added for each area and the AF evaluation value reliability of each area
Calculating the _{(AF Trust [0] ~AF Trust} [4]).

[0027]

## _EQU3 ## That is, AF _Trust [] = AF _exp [] + AF _lb [] (3)

In this way, the control unit 40 determines the area of the AF area where the difference between the photometric value EV _af and the exposure value EV is small as the exposure level.
Recognizing that it is an area with high reliability of AF _exp ,
An area having a large difference between the maximum value and the minimum value of the evaluation value is recognized as an area having a high AF-level reliability AF _Trust . The control unit 40 adds these values, considers both values, determines the reliability of the AF evaluation value in each AF area, and determines the priority of each area.

That is, the control unit 40 controls the area other than the central AF area # 0.
AF evaluation value reliability the _{(AF Trust [1] ~AF Trust} [4]), and ranked in the order that the value is large, the variable register No1~No4 for storing the rank variable for the AF evaluation value reliability, decreasing order The area code value (# 1 to # 4) corresponding to the AF area is stored.
As a result, area codes in the order of reliability of each area except the AF area # 0 are stored in the variable registers No1 to No4. That is, the variable area register No. 1 stores the AF area code value having the maximum reliability, the variable area register No. 2 stores the AF area code value having the second highest reliability,
No. 3 stores the AF area code value with the third highest reliability, and the variable register No. 4 stores the AF area code value with the fourth highest reliability.

The control unit 40 evaluates the reliability of the AF evaluation value of the central AF area # 0 and the contrast state, that is, the reliability of the AF level. The same evaluation is performed for AF areas # 1 to # 4 in the order of. Then, when the control unit 40 determines an AF area of a focusable level, the AF area obtained in the AF area is determined.
The AF evaluation value is read from the memory 43, the lens position corresponding to the maximum value is determined as the focal point, and the lens is moved to that position.

When the focus lens is moved to a position satisfying the in-focus state, the control unit 40 permits photographing,
When the ON state of S2 is detected, the mode shifts to the still image mode and the shooting and recording process is performed. The control unit 40 generates processing parameters for performing signal processing in the signal processing circuit 24, and performs signal processing for a still image according to the parameters. Control unit 40
Controls, for example, contour enhancement processing, color balance correction, and gamma correction processing.

The control unit 40 sets the compression rate of the compression encoding process in the compression processing circuit 30. The control unit 40 has a function of compressing and encoding image data at a compression ratio specified by an operator according to the storage capacity of the memory card 34, for example. When storing the encoded image data in the memory card 34, the control unit 40 supplies the additional information of the image to the recording processing unit 32, and stores the shooting date and the date in an area corresponding to the recording format of the memory card 34. Photographing information such as time and exposure, compression ratio and compression format information, and print information for designating printing when a recorded image is printed are recorded.

The autofocus operation of the camera 10 having the above configuration will be described with reference to FIGS.
The release button 22 is pressed, and the image sensor 18 is driven by the first stroke. In step 500 shown in FIG. 5, the focus lens is controlled to a position where the focus is focused on the infinity position of the initial position, and the image sensor 18 is driven. The image of the object image formed by the image pickup lens 14 is photoelectrically converted from the image pickup element 18, and the image pickup signal is input to the signal processing circuit. The imaging signal output from the imaging element 18 is converted into a digital image signal by the A / D conversion circuit 26, input to the display unit 20, and input to the evaluation value acquisition circuit 42 via the buffer memory 28.

In step 502, the evaluation value acquisition circuit 42 measures the luminance of the object scene based on the signal level of the image data. In step 504, each of the focus areas # 0 to # 4
Corresponding photometric value _{EV af [0] ~EV af [} 4] are calculated, the photometric value of each area calculated is stored in the memory 43. When the respective photometric values are stored, the process proceeds to step 506, and based on the stored respective photometric values, the exposure value EV for imaging the object scene is determined by the control unit 40, and the shutter speed and the aperture value are controlled. Is supplied to the imaging unit 12, and the exposure is adjusted according to the control signal.

Next, at step 508, the AF of each area is performed based on the image data input to the evaluation value acquisition circuit 42.
An evaluation value is calculated. In this case, for example, a plurality of AF evaluation values for each of the areas # 0, # 1, # 2, # 3, and # 4 as shown in FIG. 4 are calculated at the respective evaluation value calculation positions accompanying the movement of the lens. The calculated AF evaluation values are stored in the memory 43.

The AF evaluation value calculated at the closest position is stored in the memory.
When stored in 43, the process proceeds to step 510, where each AF area # 0
Exposure level reliability AF _exp [0] to AF _exp [4] of # 4 to # 4 are calculated according to the above equation (2). Further, in step 512, the difference between the maximum value and the minimum value of the AF evaluation value is multiplied by a predetermined correction multiplier Kl in accordance with the above equation (1), and the AF of each AF area is calculated.
The level reliability AF _lb is calculated. Exposure level reliability and AF
When the level reliability is obtained, the process proceeds to step 514, and the reliability is added for each area according to the equation (3), and the evaluation value reliability AF _Trust [0] to AF for each area is added.
_Trust [4] is calculated. In step 516, step 51
AF evaluation value reliability calculated in 4 AF _Trust [1] to AF
_Trust [4] is ranked and the variable register No.
AF evaluation value reliability except AF area # 0 is higher in order of 1 to No4
Area code values in the AF area order are stored.

Next, in step 518, the AF area determination processing and the focus determination processing are performed. As shown in FIG. 6, the following processing is performed in step 518. Steps
At 600, first, the evaluation value reliability AF _Trust [0] is compared with a predetermined value A for evaluating the reliability, and the reliability AF
Step if the value of _Trust [0] exceeds the predetermined value A
Proceed to 602, and if not, proceed to step 606. In step 602, the area code value "0" indicating the area # 0 is stored in the buffer S storing the AF selection area.
Next, proceeding to step 604, the AF level reliability AF _lb [0] of the area # 0 corresponding to the value stored in the buffer S is set to AF
It is determined whether or not the value exceeds a predetermined value B for evaluating the level evaluation value. If not, the process proceeds to step 606. If the AF level reliability AF _lb [0] exceeds the predetermined value B, the flow proceeds to step 632.

In step 606 following step 600 and step 604, the first priority AF area excluding the central area
For [No1], the same processing and determination as the processing in steps 600 to 604 are performed, and the evaluation value reliability AF _{Trust of} this area exceeds the above-mentioned predetermined value A, and the AF level reliability becomes the aforementioned level. If it exceeds the predetermined value B, the process proceeds to step 632. If it does not exceed the predetermined value B, the determination process for the next priority AF area No. 2 is performed.
Steps 606 to 610 are performed.

Thereafter, similarly, in steps 612 to 628, the reliability of the area of the next rank is determined, and the reliability of the AF evaluation value and the reliability of the AF level of the area of the next rank are determined by the predetermined value A and the predetermined level, respectively. From the step satisfying the comparison judgment using the value B, the process proceeds to step 632. On the other hand, if the comparison judgment is not satisfied, the reliability evaluation of the next AF area priority is performed.

As described above, even if the evaluation value reliability AF _Trust [4] in the fourth rank area does not exceed the predetermined value A or exceeds the predetermined value A (step 624), the area # If the AF level evaluation value of 4 does not exceed the predetermined value B (step 628), the process proceeds to step 630,
A value indicating an error is stored in the buffer S, and it is determined that satisfactory focusing cannot be obtained in each AF area. Further, in each of the above steps 604, 610, 616, 622, 628, if the AF level reliability exceeds the predetermined value B and the process proceeds to step 632, the AF area [S] corresponding to the value stored in the buffer S is adopted, and The maximum value of the evaluation value calculated by
Recognized by 40. When the maximum value is recognized, the control unit 40 determines the lens position at which the maximum value is obtained, and determines that the position is the optimum focus position.

When the in-focus position is determined, the process proceeds to step 520 shown in FIG. 5, in which the lens is moved to the determined in-focus position and held there. When the lens is driven to the in-focus position, the control unit 40 enters a state indicating permission for shooting, and when the ON state of the switch S2 of the release button 22 is detected here, each unit starts shooting and recording processing in the still image mode. . As a result, the release lock is possible, the object scene is imaged in a state where the focus is adjusted according to the maximum evaluation value obtained in the AF area of the maximum reliability, and image data representing the imaged image is encoded. To the memory card 34.

As described above, the reliability of the AF evaluation value is evaluated for each AF area based on the exposure level reliability and the AF level reliability calculated for each AF area, and the center of the screen is displayed. The AF area to be located is given the highest priority, and the remaining AF areas are ranked according to the degree of contrast in the area, and are used for focus control based on the evaluation value reliability and the AF level reliability. It is possible to determine an area in which an appropriate evaluation value has been calculated, and determine a focus position based on the evaluation value obtained therefrom.

In this case, the screen is divided into a plurality of blocks, and the divided blocks or a plurality of the blocks are used as an AF area for calculating an evaluation value. One of them is arranged in the center of the screen, and the other AF areas are used. Since it is located at the top, bottom, left and right, the center part is emphasized, and even if an appropriate evaluation value cannot be obtained from the center area, the evaluation value from the surrounding AF area with higher ranking is used. Focus control can be performed.

If it is determined that a sufficient focusing result cannot be obtained in the AF area in the center of the screen, an appropriate AF area is selected from the AF areas arranged adjacent to the central AF area. Using the AF evaluation value calculated corresponding to the selected AF area, it is possible to satisfactorily perform focus adjustment on the object scene. In addition, since the AF area is arranged in the vertical and horizontal cross direction adjacent to the center AF area, good AF can be performed regardless of the camera's vertical or horizontal position.
The area can be determined and used, which is well suited to general shooting conditions and shooting methods. Since the AF areas located around these areas are evaluated according to their order of reliability, these four AF areas include:
There is no fixed priority, and the AF evaluation value of the AF area according to the contrast and brightness of the subject image in the AF area is adopted.

The AF arranged at the center of the screen as described above
The reliability of the evaluation value is determined with priority given to the area. If the evaluation value is not good, the area having the highest reliability among the remaining areas is evaluated, and according to the evaluation result,
An appropriate AF area can be selected by evaluating the next AF area. In this case, since the AF area is not simply expanded, erroneous determination of an evaluation value based on a desired subject image is reduced.

In the exposure determination, an exposure value may be determined according to the result of photometry based on image data of the entire AF area or the central AF area and the entire screen. Also,
Focusing on the photometry value in the AF area finally selected,
Re-set the exposure value with emphasis on this metering value,
Still image shooting may be performed with the reset exposure.

Further, in addition to the automatic mode in which the optimum area is automatically selected as in the above-described embodiment, an input means such as a cross key is used so that the operator can arbitrarily select the AF area. It is also possible to focus on various subjects by using an area selection function that can be freely selected.

In the above embodiment, each AF area has the same size. However, except for extreme cases, AF areas having different sizes may be set. In this case, it is preferable to obtain a weighted and normalized evaluation value according to the area size.
Similarly, one AF area set by a plurality of blocks may have different shapes. This AF
The shape of the area may be set so as to be changeable according to the shooting conditions, the purpose, and the state of the subject. For example, an area arranged in the horizontal direction or the vertical direction for four blocks may be set as one AF area. In this case, the AF area is also preferably arranged adjacent to the central AF area. In addition, each AF
The case where the area is configured so that the small blocks divided into 64 are not overlapped has been described. However, the present invention is not limited to this.
An AF area in which some small blocks constituting another AF area of about a block overlap may be set.

[0049]

As described above, according to the present invention, when the lens for focusing is moved to obtain the AF evaluation value and the focus is determined, the optimum area among the plurality of focus areas can be adopted. it can. In this case, the reliability of the AF evaluation value in the focus area is determined, and the AF with high reliability is determined.
It is possible to determine whether focusing is possible or not in the area in which the evaluation value was obtained, and the AF acquired in the appropriate focus area
Automatic focus adjustment can be performed based on the evaluation value.
In addition, one focus area is set in the center of the screen, and a plurality of areas are set in the vertical and horizontal directions adjacent to the focus area. Possible and
Focus determination can be performed without difficulty for various pictures to be taken. Further, the process of selecting an appropriate area from a plurality of set focus areas can be performed by a simple comparison calculation process, and the processing load is small and a quick area determination process is possible. Therefore, when adjusting the focal position of the imaging lens, it is possible to reduce the occurrence of a situation in which focusing cannot be performed.In addition, an appropriate AF evaluation value detection area can be automatically selected, and appropriate focusing can be performed. A determination can be made.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a digital camera to which the present invention is applied.

FIG. 2 is a diagram conceptually showing an imaging screen.

FIG. 3 is a diagram illustrating a force area set on an imaging screen.

FIG. 4 is a diagram showing a change in an evaluation value for each focus area.

FIG. 5 is a flowchart illustrating an operation of automatic focus adjustment in the embodiment.

FIG. 6 is a flowchart showing an operation of an area determination process and a focus determination in the flowchart shown in FIG. 5;

[Explanation of symbols]

 10 Digital camera 12 Imaging unit 14 Imaging lens 18 Image sensor (CCD) 40 Control unit (CPU) 42 Evaluation value acquisition circuit

Claims (14)

[Claims] 1. An automatic focusing apparatus for adjusting a focal position of an imaging lens for forming an image of an object scene on an image pickup means based on an image signal picked up and outputted by an image pickup means. Moving means for moving a lens for performing focus adjustment within a focus adjustment area; and a first focus area for obtaining an AF evaluation value for performing focus adjustment at a central portion of a screen formed by the image signal. Is set, a plurality of other focus areas for obtaining the AF evaluation value are set around the first focus area, and a contrast component of an image signal of the set focus area is extracted. Evaluation value calculating means for calculating an AF evaluation value corresponding to each of the focus areas; and a focus for obtaining an AF evaluation value for adjusting focus among the plurality of focus areas. Selection means for selecting on the basis of the rear on the AF evaluation value, the focus area selected by said selecting means
Based on the AF evaluation value, determine the focus position of the lens,
Control means for controlling said moving means to move said lens to said in-focus position. 2. The automatic focus adjustment device according to claim 1, wherein the control unit includes, as upper and lower left and right sides of the first focus area, as the other focus areas, respectively.
Setting second, third, fourth, and fifth focus areas; the evaluation value calculating means calculates the AF evaluation value for each of the first to fifth focus areas; An automatic focus adjustment device, wherein the in-focus position is determined based on AF evaluation values calculated in first to fifth focus areas selected by a selection unit. 3. The automatic focusing apparatus according to claim 1, wherein the apparatus includes a photometer that measures the luminance of the object field in the focus area based on an image signal in the set focus area. The selecting means includes a light metering result obtained by the light metering means and the AF
An automatic focus adjustment device, wherein a focus area for obtaining an AF evaluation value for adjusting the focus is selected based on the evaluation value. 4. The automatic focusing apparatus according to claim 1, wherein the control unit gives priority to the first focus area and sets the first focus area based on an AF evaluation value calculated in the first focus area. Determining the reliability of the AF evaluation value of the focus area, and determining the in-focus position according to the AF evaluation value obtained in the focus area according to the determination result that the reliability is determined to be high. Automatic focus adjustment device. 5. The automatic focusing device according to claim 4, wherein said control means controls the first focus area.
When it is determined that the reliability of the AF evaluation value is low, the order of reliability of the AF evaluation values calculated in the other focus areas is determined, and the focus areas in the order of high reliability according to the determination result are determined. An automatic focus adjustment device for determining the reliability of the AF evaluation value of (i) and determining the in-focus position based on the AF evaluation value of the focus area according to the determination result. 6. The automatic focus adjustment device according to claim 5, wherein the control unit determines a first reliability value indicating a reliability of the AF evaluation value and a reliability according to an exposure level in the focus area. A second reliability value is calculated for each of the focus areas, and the first reliability value and the second reliability value are calculated.
The reliability order of the focus area is determined based on the total value obtained by adding the reliability values of the focus areas, and it is determined whether or not to adopt the AF evaluation value of the focus area in the reliability order based on the total value. An automatic focus adjustment device for determining the in-focus position based on an AF evaluation value of a focus area determined to be adopted. 7. The automatic focusing apparatus according to claim 6, wherein the control unit further determines the reliability of the focus area based on the second reliability value, and determines the reliability of the focus area based on the determination result. An automatic focus adjustment device, which determines whether to adopt a focus area. 8. An automatic focus adjustment method for adjusting a focal position of an image pickup lens for forming an image of a field on an image pickup means based on an image signal picked up and output by the image pickup means. Moving a lens for performing focus adjustment within a focus adjustment area; and a first focus area for obtaining an AF evaluation value for performing focus adjustment at a central portion of a screen formed by the image signal. Is set, a plurality of other focus areas for obtaining the AF evaluation value are set around the first focus area, and a contrast component of an image signal of the set focus area is extracted. An evaluation value calculating step of calculating an AF evaluation value corresponding to each of the focus areas; and a focus obtaining an AF evaluation value for adjusting a focus among the plurality of focus areas. A selection step of selecting based on the rear on the AF evaluation value, the focus area selected by said selecting step
Based on the AF evaluation value, determine the focus position of the lens,
Controlling the moving means to move the lens to the in-focus position. 9. The automatic focus adjustment method according to claim 8, wherein the control step includes setting the other focus areas on the upper, lower, left, and right sides of the first focus area.
Setting second, third, fourth and fifth focus areas; the evaluation value calculating step calculates the AF evaluation value for each of the first to fifth focus areas; An automatic focus adjustment method, wherein the in-focus position is determined based on an AF evaluation value calculated in first to fifth focus areas selected in the step. 10. The automatic focus adjustment method according to claim 8, wherein the method includes a photometric step of photometrically measuring the brightness of a field in the focus area based on the image signal in the set focus area. The automatic focus adjustment method, wherein the selecting step selects a focus area for obtaining an AF evaluation value for the focus adjustment based on the photometry result and the AF evaluation value. 11. The automatic focus adjustment method according to claim 8, wherein the control step gives priority to the first focus area based on an AF evaluation value calculated in the first focus area. Determining the reliability of the AF evaluation value of the focus area, and determining the in-focus position according to the AF evaluation value obtained in the focus area according to the determination result that the reliability is determined to be high. Automatic focus adjustment method. 12. The automatic focus adjustment method according to claim 11, wherein, when the control step determines that the reliability of the AF evaluation value of the first focus area is low, calculation is performed in the other focus area. The reliability of the AF evaluation value of each focus area is determined in the order of the focus area having the highest reliability according to the determination result, and the AF of the focus area according to the determination result is determined. An automatic focus adjustment method, wherein the in-focus position is determined based on an evaluation value. 13. The automatic focus adjustment method according to claim 12, wherein said control step includes: a first reliability value indicating a reliability of an AF evaluation value; and a reliability according to an exposure level in said focus area. A second reliability value is calculated for each of the focus areas, and the order of reliability of the focus area is determined based on a total value obtained by adding the first reliability value and the second reliability value. Determining whether to adopt the AF evaluation value of the focus area in the order of the reliability based on the total value, and determining the in-focus position based on the AF evaluation value of the focus area determined to be adopted. An automatic focusing method characterized by the following. 14. The automatic focusing method according to claim 13, wherein the control step further determines the reliability of the focus area based on the second reliability value, and determines the reliability of the focus area based on the determination result. An automatic focus adjustment method, comprising determining whether to adopt a focus area.