JP2002277730A - Method, device and program for automatic focusing control of electronic camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method, a device and a program for automatic focusing control which can perform fast, high-precision, and high-accuracy focusing operation. SOLUTION: A digital still camera is equipped with a photographic lens system 1 which forms a subject image on a CCD 31, a front-end part 3 which includes the CCD 31 and outputs image data corresponding to the subject image, an image preprocessor part 4 which processes the image data, a CPU 6 which controls the operation of respective parts, a focus lens control part 7 which drives and controls the focus lens in the photographic lens system 1 along the optical axis, and a sight line detection part 9 which detects the line of sight of a user. When the user looks in the finder, the detection part 9 detects a gaze point and determines an area including the gaze point as an AF area. The CPU 6 calculates a focusing index value according to the DCT coefficient in the AF area and controls the focus lens control part 7 according to the calculated focusing index value to move the focus lens to the focusing position.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focus control method applied to an electronic camera using an area sensor (image pickup device) such as a digital video camera and a digital still camera, and an apparatus and a program therefor.

[0002]

2. Description of the Related Art Focusing position determination methods in an automatic focus control device for a camera include an active AF method using infrared rays or ultrasonic waves, and a passive AF method such as external light passive or hill-climbing servo. 2. Description of the Related Art In an electronic camera including an area sensor such as a digital still camera, a passive AF method using an area sensor for photographing is often used. For example, Japanese Patent Application Laid-Open No. 6-181532 discloses a passive AF type focus position detecting device in an electronic camera.

The in-focus position detecting device described in the above publication stores a point spread function of an optical image pickup system or a function obtained by converting the point spread function at a focal position and lens positions before and after the focal position and stores them. Characteristic value storage means, image restoration means for restoring image data for one screen or a part thereof for each of a plurality of lens positions using the characteristic values stored in the characteristic storage means, and a lens from image restored image data A focus position estimating means for obtaining an in-focus position evaluation value for each position and estimating the in-focus position by comparing the respective evaluation values, so as to detect the in-focus position by one exposure.

[0004]

However, in the focusing control method using image restoration disclosed in the above publication, a large number of restoration filters must be prepared in order to increase the focusing accuracy. There is a problem that the capacity of the ROM for storing the data becomes large. In addition, restoration processing must be performed by the number of restoration filters.
There is also a problem that it takes time to focus on F. Furthermore, in order to determine the AF area in the photographing area, the user needs to perform an operation using a button or the like to select an area including the subject to be focused, which is complicated.

The present invention has been made in view of the above-mentioned problems of the prior art, and has as its object to provide an automatic focus control method, apparatus, and program capable of performing a high-speed, high-accuracy, and high-accuracy focusing operation. Aim.

[0006]

In order to achieve the above object, an automatic focus control method for an electronic camera according to the present invention forms an object image on an area sensor via a photographing lens and outputs the image to the output of the area sensor. In the method of determining the focusing position of the photographing lens based on the above, an arbitrary range is determined as an AF area from an image frame of the area sensor by a user operation or automatic scanning, and image data output from the determined AF area is discretely determined. The cosine transform is performed, the average value of the coefficients of the converted image data is obtained for each wave number, the wave numbers are arranged in ascending order, and the wave number having a local minimum value is searched from the average value sequence of the coefficients arranged in the wave number ascending order. The in-focus position is determined by using the obtained wave number as a focusing index value, and the focusing lens is driven to the in-focus position based on the calculated focusing index value.

An electronic camera automatic focus control device and program according to the present invention include means and steps for realizing the above method.

It is to be noted that a gaze input device for detecting the gaze of the user is provided in the electronic camera, and the area that the user gazes at is determined as the AF area based on the gaze direction output from the gaze input device. Good. Also,
An electronic camera may be provided with a voice identification device for detecting and identifying a voice, and an area designated by the user may be determined as an AF area based on a user's instruction identified by the voice identification device.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment in which an automatic focus control device according to the present invention is applied to a digital still camera will be described below in detail with reference to the accompanying drawings.

[0010]

FIG. 1 is a block diagram showing the configuration of a digital still camera according to a first embodiment. Figure 1
The digital still camera shown in FIG. 1 includes a photographing lens system 1 for forming a subject image on a CCD (area sensor) 31, an aperture stop 2 arranged behind the photographing lens system 1, and image data including the CCD 31 and corresponding to the subject image. And an image pre-processor (hereinafter referred to as “IP”) that performs various data processing of image data.
P) and a CPU interface (I /
F) 5, a CPU 6 for controlling the operation of each unit of the digital still camera, a focus lens control unit 7 for driving and controlling a focus lens included in the photographing lens system 1 in the optical axis direction, and an aperture 2
An aperture control unit 8 for controlling the aperture value (F-number) of the camera and a visual axis detection input unit 9 for detecting the visual axis of the user. The line-of-sight detection input unit 9 is arranged in a finder provided in the camera.

The front end unit 3 converts an object image formed by the photographing lens system 1 into an electric signal (analog image signal).
A signal processing unit 32 for removing noise and adjusting a gain of an electric signal output from the CCD 31; and converting an analog image signal input from the CCD 31 via the signal processing unit 32 into a digital image signal. And an A / D conversion unit 33 that converts the data to an IPP and outputs the converted data to the IPP unit 4.

The IPP unit 4 converts the digital image signal input from the front end unit 3 into RGB data.
An RGB separation unit 41 that separates each component (RGB digital image signal) into RGB components, and an RGB that adjusts the gain of each color component of the separated RGB digital signal and outputs it to the YUV conversion unit 43
A B gain adjustment unit 42, a YUV conversion unit 43 that converts an input RGB digital signal into a YUV signal (a luminance signal and a color difference signal) and outputs the YUV signal,
Discrete Cosine Transform
Digital signal processor (D)
digital signal processor (hereinafter referred to as “DSP”) core 44, an AWB evaluating unit 45 that generates an evaluation value for auto white balance (hereinafter referred to as “AWB”) from RGB digital signals, and Y of the YUV signal. (Brightness) signal from auto exposure (Auto Exposure or less,
An AE evaluator 46 that generates an evaluation value for “AE”.

The CPU 6 controls the operation of each unit of the digital still camera connected via the CPU I / F 5. Specifically, for example, the CPU 6 is a DSP.
The focus index value is calculated based on the DCT coefficient input from the core 44, and the focus lens controller 7 is controlled based on the calculated focus index value to move the focus lens to the focus position. When the hill-climbing servo method is used together, a high-frequency component integrated value is calculated based on the input DCT component,
Performs AF control by the hill-climbing servo method. Furthermore, CPU
6 also performs AWB control, AE control, and the like. Note that the DSP core 44 also serves as an image compression (JPEG format) engine.

Next, an outline of the basic AF operation of the digital still camera having the above configuration will be described with reference to FIGS. First, image data is taken in from the CCD 31 at the current focal lens position (S1: FIG. 2 in FIG. 2). The image frame is composed of 1280 × 1024 pixels. CCD
The RGB digital signals obtained from the signal processing unit 31 through the signal processing unit 32 and the A / D converter 33 are converted into IP signals for performing image signal processing.
It is input to the P section 4. In the IPP unit 4, first, Y
After being converted into a luminance signal and a color difference signal by the UV conversion unit 43, they are DCT-converted by the DSP core 44.
(S2 in FIG. 2). That is, image data is converted from a spatial component to a frequency component. However, at the time of the AF processing, only the image data of the 256 × 256 pixel AF area determined in the image frame by the user operation or the automatic operation is subjected to DCT conversion. The converted DCT component is
Output to CPU 6 via I / F5. Where CP
In U6, the high-frequency component Spc of the transformed image data is examined using the DCT transform coefficient, for example, according to equation (1) (S3 in FIG. 2). The position of the focus lens at the time of capturing an image is A, and the high-frequency component obtained at this position is Spc # A.

[0015] μ = √ (K ² + L ² ) (2) where K and L are horizontal and vertical frequencies in a two-dimensional DCT, X (K, L) is a DCT coefficient in (K, L), and μ is a wave number. is there.

In this example, 256 × 2
Although the AF area of 56 pixels is used as it is, further sub-sampling is performed to increase the speed to 128 × 12
A range of 8 pixels or 64 × 64 pixels may be used as the AF area. In addition, DCT is used as a high frequency component.
A method such as a digital filter may be used instead of the conversion coefficient.

Next, the focus lens is slightly moved (FIG. 2).
S4), and the image is captured again (S5 in FIG. 2). The position B of the focus lens after the movement is set, and the high frequency component obtained by the equation (1) is set as Spc # B (S6 and S7 in FIG. 2). By comparing the high-frequency components at the two points of the focal lens positions A and B, the direction of the focal point can be detected. That is,
Spc # B ≧ Spc # A (3) if the movement of the focus lens from A to B is closer to the focal point, but Spc # B ≦ Spc # A (4) if the movement is farther away. ). In the example of FIG. 3, the movement of the focus lens from A to B is in a direction away from the focal point, and the relationship of Expression (4) is established. Therefore, it is determined that the focusing direction is B → A (S8 in FIG. 2).

On the other hand, with respect to the image data taken in at the second focus lens position B and subjected to DCT conversion, an average value of DCT components for each wave number (hereinafter referred to as "average energy") is obtained and arranged in ascending wave number order. (S9 in FIG. 2). The wave number is defined by equation (2). The average energy at the same μ (integer) is defined by Expression (5).

E (μ) = 1 / NmΣΣ | X (K, L) | ² (5) where Nm is the number of elements having the same μ.

The upper right graph of FIG. 3 shows an example of average energies arranged in ascending wave number order. And the aligned D
A wave number having an initial local minimum (hereinafter, referred to as a “first local minimum wave number”) is searched from the average energy of the CT component, and the searched wave number is used as a defocus parameter, that is,
The focus index value is determined (S10 in FIG. 2). Based on the focus index value thus obtained, the corresponding focus lens position, that is, the focus position is specified. The CPU 6 outputs control data for instructing the focus lens control unit 7 to drive the focus lens to the in-focus position, and in response, the focus lens control unit 7 drives the focus lens to the in-focus position ( FIG.
S11).

Next, determination of an AF area in an image frame will be described. As shown in FIG. 4, the image frame has 1280 × 1024 pixels, and areas of 256 × 256 pixels are arranged in 4 rows × 5 columns so as not to overlap. In the area name described in FIG. 4, the tens place is a line number,
The first digit indicates the column number. When the user looks into the finder, the line-of-sight detection unit 9 of the digital still camera operates to detect the point of interest of the user and specify an area including the point of interest as the AF area. This is based on the viewpoint that an object that is highly likely to be watched by a user will be a subject. In FIG. 4A, the AF area 32 selected before shooting with this image frame is displayed.
FIG. 4B shows that the line of sight is detected in this image frame, and as a result, the AF area 24 is selected.

In the first embodiment, as described above, the AF area is determined based on the result of the line-of-sight detection, the focusing index value of the AF area 24 is calculated, and the focusing index value is calculated based on the focusing index value. By performing the focusing operation, it is possible to focus the photographing lens system 1 on an area where the subject is presumed to be present.

[0023]

[Second Embodiment] Next, a second embodiment will be described. The basic operation of AF processing, hardware configuration, etc.
The second embodiment is almost the same as the first embodiment, and has already been described, so that the description thereof will be omitted, and the differences will be mainly described.

FIG. 5 is a configuration diagram of a digital still camera according to the second embodiment. The difference from the first embodiment is that a voice input unit 10 is mounted instead of the visual line detection unit 9. The voice input unit 10 can also be used as the voice input unit in a digital still camera having a voice recording function and a moving image recording function. The CPU 6 has a function as a voice identification device that detects and identifies the voice input from the voice input unit 10, and a function of determining an AF area based on an instruction of the identified user. That is, the CPU 6 interprets the voice uttered by the user during the AF processing, and determines the AF area according to the content.

The determination of the AF area in the second embodiment will be described with reference to FIG. In FIG. 6, the image frame is 1280 × 1024 pixels, and an arbitrary 2
An area of 56 × 256 pixels can be used as an AF area. That is, the AF area can be moved in an arbitrary pixel unit of at least one pixel unit in the image frame, and at the time of the AF processing, only the image data in the determined area is subjected to the DCT processing, and the focusing operation is performed. .

When the user half-presses the shutter button, the audio input unit 10 of the digital still camera operates,
Detect the user's voice. The user speaks "right",
When an instruction such as “up” is issued, the digital camera moves the AF area and its display according to the instruction, and specifies the AF area. In FIG. 6A, the AF area 32 determined before photographing in this image frame is displayed on the display unit. In FIG. 6B, a voice instruction is given in this image frame, and as a result, This indicates that the AF area has been set to a predetermined subject position. When an AF area is set on a predetermined subject, the user fully presses the shutter button. At this time, the digital camera uses the determined A
The focusing index value of the F area is calculated, and the focusing operation is performed based on the focusing index value.

Although the AF area has 256 × 256 pixels in the example shown in FIG. 6, the AF area size can be changed by a user's voice instruction such as “large” or “small”. . This flexibility is achieved by preparing a CCD for the image sensor and a CCD for automatic focus control.
This is a feature that is exhibited because a method that can use the same CCD is used instead of (for example, a phase difference detection method).

The size, shape, arrangement, and the like of the image frame and the AF area are not limited to the above-described embodiment, and can be changed as appropriate.

[0029]

As described above, according to the present invention, an arbitrary AF area is determined by a user's operation or automatic scanning, and a focusing index value is calculated for the determined AF area. Since the focusing operation is performed by driving the focusing lens to the in-focus position based on the focusing index value, focusing can be performed with high accuracy, high speed, and high accuracy. In determining the AF area, the user's line of sight is detected and used,
Alternatively, when the user's voice is identified and used, it is possible to focus the photographing lens on a desired subject by a simple operation.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a digital still camera to which an automatic focus control device according to a first embodiment is applied.

FIG. 2 is a flowchart illustrating a procedure of an AF operation of the apparatus according to the first embodiment.

FIG. 3 is an explanatory diagram illustrating an example of an AF operation of the apparatus according to the first embodiment.

FIG. 4 is an explanatory diagram in an image frame showing a stage of determining a focus area of the device of the first embodiment.

FIG. 5 is a block diagram illustrating a configuration of a digital still camera to which an automatic focus control device according to a second embodiment is applied.

FIG. 6 is an explanatory diagram in an image frame showing a stage of determining a focus area of the device according to the second embodiment.

[Explanation of symbols]

 Reference Signs List 1 shooting lens system 2 aperture 3 front end unit 4 image preprocessor (IPP) unit 5 CPU I / F 6 CPU 9 line of sight detection unit 10 voice input unit

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) // H04N 101: 00 G02B 7/11 K G03B 3/00 A

Claims (9)

[Claims] 1. An automatic focus control method for an electronic camera, comprising: forming a subject image on an area sensor via a photographing lens; and determining a focus position of the photographing lens based on an output of the area sensor. Alternatively, an arbitrary range from the image frame of the area sensor is determined as an AF area by automatic scanning, discrete cosine transform is performed on image data output from the determined AF area, and an average value of the coefficients of the converted image data is determined. Determined for each wave number and arranged in ascending wave number order, search for a wave number having a local minimum value from the average value sequence of coefficients arranged in ascending wave number order, determine the focus position using the searched wave number as a focus index value, An automatic focus control method for an electronic camera, wherein a focus lens is driven to a focus position based on the calculated focus index value. 2. The electronic camera is provided with a line-of-sight input device for detecting a line of sight of a user, and based on a line-of-sight direction output from the line-of-sight input device, an area that the user is gazing at is determined as the AF area. 2. The automatic focus control method for an electronic camera according to claim 1, wherein: 3. The electronic camera is provided with a voice identification device for detecting and identifying a voice, and an area designated by the user is determined as the AF area based on a user's instruction identified by the voice identification device. 2. The automatic focus control method for an electronic camera according to claim 1, wherein: 4. An automatic focus control device for an electronic camera, which forms a subject image on an area sensor via a photographing lens and determines a focus position of the photographing lens based on an output of the area sensor. Or means for determining an arbitrary area from the image frame of the area sensor as an AF area by automatic scanning; and performing discrete cosine transform of image data output from the determined AF area, and averaging the coefficients of the converted image data. The values are obtained for each wave number, arranged in ascending wave number order, a wave number having a local minimum value is searched from the average value sequence of the coefficients arranged in ascending wave number order, and the searched wave number is determined as a focusing index value to determine a focus position. An automatic focus control device for an electronic camera, comprising: means for driving a focus lens to a focus position based on the calculated focus index value. . 5. The electronic camera is provided with a line-of-sight input device that detects a line of sight of a user, and determines an area that the user is gazing at as the AF area based on a line-of-sight direction output from the line-of-sight input device. 5. The automatic focus control device for an electronic camera according to claim 4, wherein: 6. The electronic camera is provided with a voice identification device that detects and identifies a voice, and determines an area designated by the user as the AF area based on a user's instruction identified by the voice identification device. 5. The automatic focus control device for an electronic camera according to claim 4, wherein: 7. An automatic focus control program for an electronic camera for forming a subject image on an area sensor via a photographing lens and determining a focus position of the photographing lens based on an output of the area sensor, wherein Or a step of determining an arbitrary area from the image frame of the area sensor as an AF area by automatic scanning; and performing discrete cosine transform of image data output from the determined AF area, and averaging the coefficients of the converted image data. The values are obtained for each wave number, arranged in ascending wave number order, a wave number having a local minimum value is searched from an average value sequence of coefficients arranged in ascending wave number order, and the searched wave number is determined as a focusing index value to determine a focus position. Automatic focusing control of an electronic camera, comprising: a step of driving a focusing lens to a focusing position based on the calculated focusing index value. program. 8. The electronic camera is provided with a line-of-sight input device that detects a line of sight of a user, and determines an area that the user is gazing at as the AF area based on a line-of-sight direction output from the line-of-sight input device. 8. The automatic focus control program for an electronic camera according to claim 7, wherein: 9. The electronic camera is provided with a voice identification device for detecting and identifying voice, and an area designated by the user is determined as the AF area based on a user's instruction identified by the voice identification device. 8. The automatic focus control program for an electronic camera according to claim 7, wherein: