JP2002214513A - Optical system controller, optical system control method, and recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To quickly perform an autofocus, even if the main object has the bias of the color. SOLUTION: An AF control part of a digital camera is provided with a histogram generating circuit 251 which generates the histogram of the width of the edge in AF area, a noise removal part 263 which removes the noise component from the histogram, a histogram evaluation part 264 which determines the evaluation value showing the degree of the focus from the histogram, and an object color selection part 281 which selects the color component utilized for AF control. Furthermore, the AF control part is provided with a driving quantity determining part 265 which determines the driving quantity of the focus lens. In the object color selection part 281, the color component from which edge is most detected is determined as an object color from the image for every color component which constitutes the color image, and the result is inputted into the histogram evaluation part 264. In the histogram evaluation part 264, the evaluation value about the object color is obtained, and the driving quantity determining part 265 quickly positions the focus lens in the focal position, while changing the driving quantity by using the evaluation value of the object color.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an autofocus technique for acquiring an image, and can be used, for example, in a digital camera for acquiring an image as digital data.

[0002]

2. Description of the Related Art Conventionally, in an image pickup apparatus such as a digital still camera or a video camera, which acquires an image using an image pickup device of a CCD (Charge Coupled Device),
A technique called a contrast method (also called a hill-climbing method) is applied to perform autofocus. The contrast method is a method in which the contrast of an image obtained in each driving step is acquired as an evaluation value while driving a focus lens, and a lens position having the highest evaluation value is determined as a focus position.

On the other hand, as described in JP-A-5-219418, a method of extracting an edge from an image and estimating a focus position of a focus lens from a histogram of the width of the edge (hereinafter, referred to as "edge width") Method) is also proposed. Utilizing the principle that the edge width corresponding to the center of gravity of the histogram becomes a predetermined value when the optical system is in focus, the edge width method obtains a histogram of the edge width corresponding to a plurality of positions of the focus lens. In advance, the focus position of the focus lens is predicted from a plurality of histograms. The edge width method has a feature that a focus position of a focus lens can be quickly obtained.

[0004]

By the way, when the edge width method is employed in autofocusing, edge detection has conventionally been performed using a luminance component of an image. When the pixel value is composed of R, G, and B values, the luminance component of the image is mainly composed of the G value. Therefore, when the color of the image is biased to a color other than green, such as when a red flower is the main subject or when a color filter for a special effect is used, it is possible to appropriately detect edges from the image. I ca n’t,
There is a problem that the accuracy of the autofocus is reduced.

The present invention has been made in view of the above problems, and has as its main object to appropriately realize autofocus while utilizing edges even when the color of a main subject is uneven.

[0006]

According to a first aspect of the present invention, there is provided an optical system control apparatus for controlling an optical system when an image is obtained as digital data, wherein the color system comprises a color image. Calculating means for detecting an edge from an image corresponding to at least one and obtaining at least one evaluation value indicating a degree of focus from the edge; and controlling means for driving the optical system based on the at least one evaluation value; Is provided.

According to a second aspect of the present invention, in the optical system control device according to the first aspect, the calculating means obtains an evaluation value corresponding to each of a plurality of color components, The optical system is driven based on an evaluation value corresponding to a color component having the largest number of detected edges among a plurality of evaluation values.

According to a third aspect of the present invention, there is provided the optical system control device according to the first aspect, wherein the control means is configured to perform a control based on an evaluation value corresponding to a color component having the highest level among a plurality of color components. To drive the optical system.

According to a fourth aspect of the present invention, there is provided the optical system control device according to the first aspect, wherein the calculating means obtains an evaluation value corresponding to each of a plurality of color components and calculates the evaluation value from the plurality of evaluation values. A new evaluation value is obtained, and the control unit drives the optical system based on the new evaluation value.

According to a fifth aspect of the present invention, there is provided the optical system control device according to the first aspect, wherein the optical system has a focusing lens, and the arithmetic means includes a first position of the lens. Determining at least one first evaluation value corresponding to
Determining at least one second evaluation value corresponding to a second position of the lens; the control means controlling the first and second positions, the at least one first and second evaluation values, and A focus position of the lens is obtained from at least one reference evaluation value.

According to a sixth aspect of the present invention, there is provided the optical system control device according to the fifth aspect, wherein the color image is acquired by an imaging device having a G-Bayer array, and the color image is converted into R, G, and B color components. Among the corresponding reference evaluation values, the reference evaluation value corresponding to the G color component is different from the reference evaluation values corresponding to the R and B color components.

According to a seventh aspect of the present invention, in the optical system control apparatus according to the fifth or sixth aspect, the control means includes:
A focus position corresponding to each of the plurality of color components is obtained, and a new focus position is obtained from the plurality of focus positions.

According to an eighth aspect of the present invention, in the optical system control device according to the fifth or sixth aspect, the control means comprises:
A focus position corresponding to each of the plurality of color components is obtained, and the optical system is controlled based on a focus position corresponding to a closest object among the plurality of focus positions.

According to a ninth aspect of the present invention, there is provided the optical system control device according to the first aspect, wherein the calculating means obtains a first evaluation value for each of a plurality of color components, and A color component is selected based on the evaluation value, and a second evaluation value with higher accuracy than the first evaluation value is obtained for the selected color component. The optical system is controlled based on the value.

According to a tenth aspect of the present invention, there is provided an optical system control method for controlling an optical system when acquiring an image as digital data, wherein the method corresponds to at least one of color components constituting a color image. Detecting an edge from the image and obtaining at least one evaluation value indicating a degree of focus from the edge; and driving the optical system based on the at least one evaluation value.

According to an eleventh aspect of the present invention, there is provided a recording medium storing a program for causing a control device to control an optical system when acquiring an image as digital data, wherein the control device executes the program. Detecting an edge from an image corresponding to at least one of the color components constituting the color image and obtaining at least one evaluation value indicating a degree of focus from the edge; Driving the optical system based on the value.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS <1. First Embodiment><1.1 Configuration of Digital Camera> FIGS.
FIG. 1 is a diagram illustrating an example of an external configuration of a digital still camera (hereinafter, referred to as a “digital camera”) 1 that acquires a still image as digital data. FIG. 1 is a front view, FIG. 2 is a rear view, and FIG. FIG. 4 is a bottom view.

The digital camera 1 is, as shown in FIG.
It is composed of a box-shaped camera body 2 and a rectangular parallelepiped imaging unit 3.

A zoom lens 301 with a macro function, which is a photographing lens, is provided on the front side of the image pickup unit 3 and, similarly to a silver halide lens shutter camera, a light control sensor for receiving reflected light of flash light from a subject. 305 and an optical finder 31 are provided.

On the front side of the camera body 2, a grip 4 is provided at the left end, and an IRDA (Infrared Data Associate) for performing infrared communication with an external device is provided above the grip 4.
ion) interface 236, and a built-in flash 5 at the upper center, and a shutter button 8
Is provided. The shutter button 8 is a two-stage switch capable of detecting a half-pressed state and a fully-pressed state as employed in a silver halide camera.

On the other hand, as shown in FIG.
A liquid crystal display (LCD) for displaying a captured image on a monitor (corresponding to a view finder), reproducing a recorded image, etc., is provided substantially in the center of the rear side of the LCD.
y) 10 is provided. A key switch group 22 for operating the digital camera 1 is provided below the LCD 10.
1 to 226 and a power switch 227 are provided. On the left side of the power switch 227, an LED 228 that lights up when the power is on and an LED 229 that indicates that the memory card is being accessed are arranged.

Further, on the back side of the camera body 2,
A mode setting switch 14 for switching a mode between a “photographing mode” and a “reproduction mode” is provided. The shooting mode is a mode in which a photograph is taken to generate an image related to a subject, and the playback mode is a mode in which an image recorded on a memory card is read out and played back on the LCD 10.

The mode setting switch 14 is a two-contact slide switch. The slide switch is set to the lower position to operate the photographing mode, and is slid to the upper position to operate the reproduction mode.

A four-position switch 230 is provided on the right side of the rear of the camera.
The zoom magnification is changed by pressing the buttons 1 and 232, and the exposure is corrected by pressing the buttons 233 and 234.

As shown in FIG. 2, on the back surface of the imaging unit 3,
LCD button 32 for turning on / off LCD 10
1 and a macro button 322 are provided. When the LCD button 321 is pressed, on / off of the LCD display is switched. For example, when photographing is performed exclusively using the optical viewfinder 31, the LCD display is turned off for the purpose of saving power. At the time of macro shooting (close-up shooting), pressing the macro button 322 causes the imaging unit 3 to be in a state where macro shooting is possible.

As shown in FIG. 3, a terminal 235 is provided on a side surface of the camera body 2. The terminal 235 has a DC input terminal 235a and an external video monitor for displaying contents displayed on the LCD 10. And a video output terminal 235b for outputting to

As shown in FIG. 4, a battery loading chamber 18 and a card slot (card loading chamber) 17 are provided on the bottom of the camera body 2. The card slot 17 is for loading a detachable memory card 91 or the like for recording a captured image or the like. Card slot 1
7 and the battery loading chamber 18 are clamshell type lids 1.
5 makes it openable and closable. In this digital camera 1, four AA batteries are loaded into the battery loading chamber 18, and a power supply battery connected in series is used as a driving source. Also, the DC input terminal 2 shown in FIG.
By attaching an adapter to 35a, it is also possible to supply power from outside and use it.

<1.2 Internal Configuration of Digital Camera> Next, the configuration of the digital camera 1 will be described in more detail. FIG. 5 is a block diagram illustrating a configuration of the digital camera 1. FIG. 6 is a diagram schematically showing the arrangement of each component in the imaging unit 3.

As shown in FIG. 6, an image pickup circuit having a CCD 303 is provided at an appropriate position behind the zoom lens 301 in the image pickup section 3. Further, inside the imaging unit 3, a zoom motor M1 for changing the zoom ratio of the zoom lens 301 and moving the lens between the accommodation position and the imaging position, and inside the zoom lens 301 for automatically focusing. An autofocus motor (AF motor) M2 for moving the focus lens 311 and an aperture motor M3 for adjusting the aperture diameter of the aperture 302 provided in the zoom lens 301 are provided. As shown in FIG. 5, the zoom motor M1, the AF motor M2, and the aperture motor M3 are a zoom motor drive circuit 21 provided in the camera body 2.
5. AF motor drive circuit 214, aperture motor drive circuit 2
16 respectively. In addition, each drive circuit 2
14 to 216 drive the motors M1 to M3 based on control signals given from the overall control unit 211 of the camera body 2.

The CCD 303 converts the light image of the object formed by the zoom lens 301 into R (red), G (green),
The image signal is photoelectrically converted into an image signal of a B (blue) color component (a signal composed of a signal sequence of pixel signals received by each pixel) and output.

The exposure control in the image pickup unit 3 is performed by controlling the aperture 302
And the exposure amount of the CCD 303, that is, the charge accumulation time of the CCD 303 corresponding to the shutter speed is adjusted. If an appropriate aperture and shutter speed cannot be set due to a low contrast of the subject, an improper exposure due to insufficient exposure is corrected by adjusting the level of an image signal output from the CCD 303. That is, at the time of low contrast, control is performed so that the exposure level becomes an appropriate level by combining the aperture, the shutter speed, and the gain adjustment. Note that the level of the image signal is adjusted by AGC (Auto
Gain control) is performed by adjusting the gain of the circuit 313b.

The timing generator 314 generates a drive control signal for the CCD 303 based on a reference clock transmitted from the timing control circuit 202 of the camera body 2. The timing generator 314 generates clock signals such as, for example, a timing signal of integration start / end (exposure start / end) and a readout control signal (horizontal synchronization signal, vertical synchronization signal, transfer signal, etc.) of a light receiving signal of each pixel. , To the CCD 303.

The signal processing circuit 313 performs predetermined analog signal processing on an image signal (analog signal) output from the CCD 303. The signal processing circuit 313
It has a DS (correlated double sampling) circuit 313a and an AGC circuit 313b. The noise of the image signal is reduced by the CDS circuit 313a, and the level of the image signal is adjusted by adjusting the gain by the AGC circuit 313b.

The dimming circuit 304 controls the light emission amount of the built-in flash 5 in flash photography to a predetermined light emission amount set by the overall control unit 211. At the time of flash photography, the reflected light of the flash light from the subject is received by the light control sensor 305 simultaneously with the start of exposure, and when the amount of received light reaches a predetermined light emission amount, the light control circuit 304 outputs a light emission stop signal. The light emission stop signal is guided to the flash control circuit 217 via the overall control unit 211 provided in the camera body 2, and the flash control circuit 217
In response to the light emission stop signal, the light emission of the built-in flash 5 is forcibly stopped, whereby the light emission amount of the built-in flash 5 is controlled to a predetermined light emission amount.

Next, the blocks of the camera body 2 will be described.

In the camera body 2, the A / D converter 205 converts a signal of each pixel of an image into, for example, a 10-bit digital signal. A / D converter 205
Is a pixel signal (analog signal) based on an A / D conversion clock input from the timing control circuit 202.
Into a 10-bit digital signal.

The timing control circuit 202 includes a reference clock, a timing generator 314, and an A / D converter 20.
5 is generated.
The timing control circuit 202 includes a CPU (Central Processes).
sing unit).

The black level correction circuit 206 corrects the black level of the A / D converted image to a predetermined reference level. Also, a WB (white balance) circuit 207
Performs level conversion of each color component of R, G, and B of a pixel so that white balance is also adjusted after γ correction. The WB circuit 207 uses the level conversion table input from the overall control unit 211 to output R, G,
The level of each color component of B is converted. The conversion coefficient (gradient of the characteristic) of each color component in the level conversion table is set by the overall control unit 211 for each captured image.

The gamma correction circuit 208 corrects the gamma characteristics of the image. The image memory 209 stores the γ correction circuit 20
8 is a memory for storing image data output from the memory 8. The image memory 209 has a storage capacity for one frame. That is, the image memory 209 stores the CCD 30
When 3 has n rows and m columns of pixels, it has a storage capacity for data of n × m pixels, and data of each pixel is stored at a corresponding address.

The VRAM (video RAM) 210 is an LC
This is a buffer memory for images reproduced and displayed on D10.
The VRAM 210 has a storage capacity capable of storing image data corresponding to the number of pixels of the LCD 10.

In the photographing standby state in the photographing mode, L
When the LCD display is turned on by the CD button 321 (see FIG. 2), live view display is performed on the LCD 10. Specifically, A / D converters 205 to γ are applied to each image obtained from the imaging unit 3 at predetermined intervals.
After performing various kinds of signal processing in the correction circuit 208, the overall control unit 211 acquires an image stored in the image memory 209, and transfers the acquired image to the VRAM 210 so that the LC
The photographed image is displayed at D10. And LCD1
By updating the image displayed at 0 every predetermined time,
Live view display is performed. With the live view display, the photographer can visually recognize the subject from the image displayed on the LCD 10. When an image is displayed on the LCD 10, the backlight 16 is turned on under the control of the overall control unit 211.

In the reproduction mode, the image read from the memory card 91 is subjected to predetermined signal processing by the general control unit 211 and then transferred to the VRAM 210.
It is reproduced and displayed on the LCD 10.

The card interface 212 is an interface for writing and reading an image to and from the memory card 91 via the card slot 17.

The flash control circuit 217 is a circuit for controlling the light emission of the built-in flash 5.
The light emission of the built-in flash 5 is stopped on the basis of the above-mentioned light emission stop signal while the built-in flash 5 is caused to emit light based on the control signal from the CPU.

RTC (real time clock) circuit 21
Reference numeral 9 denotes a clock circuit for managing the shooting date and time.

Further, an IRDA interface 236 is connected to the overall control unit 211, and infrared communication is performed with an external device such as the computer 500 or another digital camera via the IRDA interface 236 to perform wireless transfer of images. It is possible.

The operation unit 250 includes the various switches and buttons described above, and information input and operated by the user receives information from the overall control unit 2 via the operation unit 250.
11 is transmitted.

The overall control section 211 organically controls the driving of each member in the image pickup section 3 and the camera main body section 2, and controls the overall operation of the digital camera 1.

An overall control unit 211 includes an AF (auto focus) control unit 211a for performing operation control for efficiently performing automatic focusing, and an A (automatic focus) control unit for performing automatic exposure.
E (auto exposure) calculation section 211b.

An image output from the black level correction circuit 206 is input to the AF control unit 211a, an evaluation value for use in autofocus is obtained, and each unit is controlled using the evaluation value, so that the zoom lens 301 is controlled. Is made to coincide with the image pickup surface of the CCD 303.

The image output from the black level correction circuit 206 is also input to the AE calculation section 211b, and the AE calculation section 211b calculates an appropriate value of the shutter speed and the aperture 302 based on a predetermined program. The AE calculation unit 211b calculates the shutter speed and the aperture 30 based on the contrast of the subject.
An appropriate value of 2 is calculated according to a predetermined program.

Further, in the photographing mode, when the photographing is instructed by the shutter button 8 in the photographing mode,
A thumbnail image of the image fetched into the image memory 209 and a compressed image compressed by the JPEG method based on a compression ratio set and input from a switch included in the operation unit 250 are generated, and tag information (frame number, exposure value,
Both images are stored in the memory card 91 together with information such as shutter speed, compression ratio, shooting date, flash on / off data at the time of shooting, scene information, image determination result, and the like.

When the mode setting switch 14 for switching between the photographing mode and the reproduction mode is set to the reproduction mode, for example, the image data having the largest frame number in the memory card 91 is read out, and the whole controller 211 expands the data. Then, the image is transferred to the VRAM 210, so that the image with the largest frame number, that is, the image captured last is displayed on the LCD 10.

<1.3 Outline of Operation of Digital Camera>
Next, an outline of the operation of the digital camera 1 will be described. FIG. 7 is a diagram schematically illustrating the operation of the digital camera 1.

When the operation of the digital camera 1 is set to the photographing mode by the mode setting switch 14, the camera enters a state of waiting for the shutter button 8 to be half-pressed (step S1).
1). When the shutter button 8 is half-pressed, a signal indicating that the shutter button 8 is half-pressed is input to the general control unit 211, and the general control unit 21
The AE calculation (step S12) and the AF control (step S13), which are the preparations for photographing, are executed by step 1. That is, the shutter button 8 instructs the general control unit 211 to prepare for shooting.

In the AE operation, the exposure time and the aperture value are obtained by the AE operation section 211b.
The control unit 211a sets the zoom lens 301 into a focused state. Thereafter, the state shifts to a state of waiting for the full depression of the shutter button 8 (step S14).

When the shutter button 8 is fully pressed, CC
After the signal from D303 is converted into a digital signal, it is stored in the image memory 209 as image data (step S15). Thus, an image of the subject is obtained.

After the photographing operation is completed or after the shutter button 8 is half-pressed, if the shutter button 8 is not fully pressed (step S16), the process returns to the initial stage.

<1.4 Auto Focus Control>
The configuration of the AF control unit 211a and the autofocus (AF) control in the first embodiment will be described.

FIG. 8 is a block diagram showing the configuration of the AF control section 211a shown in FIG. The AF control unit 211a includes a histogram generation circuit 251 and a contrast calculation circuit 252 to which an image is input from the black level correction circuit 206. Further, the CPU 261 and the ROM 262 in the overall control unit 211
A part of the function as a.

The histogram generation circuit 251 generates an image (hereinafter, referred to as an image) for each color component (R, G, B) constituting the color image.
This is called a “color component image”. ) Are detected, and a histogram of the edge width is generated for each color component. The contrast calculation circuit 252 obtains a contrast for each color component image. Details of these configurations will be described later.

The CPU 261 performs a part of the autofocus operation by operating in accordance with the program 262a in the ROM 262, and performs the AF motor driving circuit 2
The control signal is sent to 14. The program 262a may be stored in the ROM 262 when the digital camera 1 is manufactured, and the memory card 91 is used as a recording medium on which the program is recorded.
The program may be transferred to 62.

FIG. 9 shows the CPU 2 for auto focus.
FIG. 61 is a diagram showing the function of a block 61 together with other components in blocks. In FIG. 9, a noise removal unit 263, a histogram evaluation unit 264, a drive amount determination unit 265, a drive direction determination unit 2
The focus detection unit 267, the control signal generation unit 268, and the target color selection unit 281 correspond to functions realized by the CPU 261 performing arithmetic processing.

The noise removing section 263 removes a noise component from the histogram generated by the histogram generating circuit 251, and the histogram evaluating section 264 obtains an evaluation value indicating the degree of focus from the histogram. The drive amount determination unit 265 obtains the drive amount (number of pulses) of the AF motor M2 for changing the position of the focus lens 311. The drive direction determination unit 266 drives the AF motor M2 using the contrast from the contrast calculation circuit 252. The direction (that is, the driving (moving) direction of the focus lens 311) is determined.

The focus detection section 267 detects whether the optical system is in focus, and the control signal generation section 268 generates a control signal to the AF motor M2 and outputs the control signal to the AF motor drive circuit 214.
Give to. The target color selection unit 281 includes the black level correction circuit 2
The color component to be calculated is selected at the time of autofocusing based on the image input from 06, and the selection result is provided to the histogram evaluation unit 264 and the drive direction determination unit 266. The drive control of the lens is substantially performed by the drive amount determination unit 26.
5, executed by the drive direction determination unit 266 and the focus detection unit 267.

FIG. 10 is a diagram for explaining how the histogram generation circuit 251 detects edges for one color component image. In FIG. 10, the horizontal axis corresponds to the position of the pixel in the horizontal direction, and the upper part of the vertical axis corresponds to the pixel value (that is, density) for one color component. The lower part of the vertical axis corresponds to the detected value of the edge width.

In FIG. 10, when edges are detected from left to right, if the difference between the pixel values of adjacent pixels is equal to or smaller than the threshold value Th1, it is determined that no edge exists. On the other hand, if the difference between the pixel values exceeds the threshold Th1, it is determined that the start end of the edge exists. When the difference between the pixel values exceeding the threshold value Th1 continues from left to right, the detected edge width increases.

After the detection of the edge start end, when the difference between the pixel values becomes equal to or smaller than the threshold value Th1, it is determined that the end of the edge exists. At this time, if the difference between the pixel value of the pixel corresponding to the start end of the edge and the pixel corresponding to the end of the edge is equal to or smaller than the threshold Th2, it is determined that the edge is not an appropriate edge, and if the difference exceeds the threshold Th2. Is determined to be an appropriate edge.

By performing the above processing on the pixel array arranged in the horizontal direction in each color component image, the value of the width of the edge in the horizontal direction in each color component image is detected.

FIG. 11 is a diagram showing a specific configuration of the histogram generation circuit 251. FIGS. 12 to 14 are diagrams showing a flow of operation of the histogram generation circuit 251 for one color component. Hereinafter, generation of a histogram will be described in more detail with reference to these drawings. However, as shown in FIG. 15, it is assumed that an area (hereinafter, referred to as an “AF area”) 401 for performing autofocus is set in advance in the center of the image 400, and FIG.
, A pixel value related to one color component of the pixel at the coordinates (i, j) in the AF area 401 is expressed as D (i, j). The configuration shown in FIG.
A plurality of sets may be provided for each color component, or only one set may be provided for each color component. If only one set is provided,
Variables for processing described below are provided for each color component.

In the histogram generation circuit 251 connected to the black level correction circuit 206, the structure on the left where the first differential filter 271 is provided and the structure on the right where the second differential filter 272 is provided are symmetric as shown in FIG. When the inside of the AF area 401 of the color component image is scanned from left to right, the edge corresponding to the rising edge of the pixel value is detected by the first differential filter 271 side, and the falling edge of the pixel value is detected. The edge corresponding to the second differential filter 272
Is detected by the side configuration.

In the histogram generation circuit 251, first,
After various variables are initialized (step S101), the first
The difference (D (i + 1, j) -D (i, j)) of the pixel value between adjacent pixels is obtained by the differential filter 271, and the comparator 273 determines whether the pixel value difference exceeds the threshold value Th <b> 1. Is confirmed (step S102). Here, when the difference between the pixel values is equal to or smaller than the threshold value Th1, it is determined that no edge exists.

On the other hand, the difference (D (i, j) −D (i + 1,
j)) are also obtained, and the comparator 273 checks whether or not the difference between the pixel values exceeds the threshold value Th1 (step S).
105). When the difference between the pixel values is equal to or smaller than the threshold Th1, it is determined that no edge exists.

Thereafter, while increasing i, step S10 is performed.
2 and step S105 are repeated (FIG. 14: steps S121, S122).

In step S102, if the difference between the pixel values exceeds the threshold value Th1, it is determined that the start end of the edge (the rising edge of the pixel value) has been detected, and the first
The edge width detection value C1 (initial value 0) indicating the edge width is incremented by the edge width counter 276 on the side of the differential filter 271 and the flag CF1 indicating that the edge width is being detected is set to 1 (step). S10
3). Further, the pixel value at the start of detection is stored in the latch 274.

Thereafter, in step S102, the edge width detection value C1 is maintained until the pixel value difference becomes equal to or less than the threshold value Th1.
Increase (steps S102, S103, S121, S
122), when the difference between the pixel values is equal to or less than the threshold value Th1,
The flag CF1 is reset to 0, and the pixel value at this time is stored in the latch 275 (steps S102 and S10).
4).

When the flag CF1 is reset to 0, the pixel value difference Dd1 stored in the latches 274 and 275 is given to the comparator 277, and the pixel value difference Dd
1 is checked whether it exceeds the threshold value Th2 (FIG. 1).
3: Step S111). If the pixel value difference Dd1 exceeds the threshold value Th2, it is determined that an appropriate edge has been detected, and the edge width detection value C1 is provided from the edge width counter 276 to the histogram generation unit 278, and the edge width is determined. The frequency H [C1] of the edge that is C1 is incremented (step S112). Thus, detection of one edge having the edge width of C1 is completed.

Thereafter, the edge width detection value C1 is reset to 0 (steps S115 and S116).

When the difference between the pixel values exceeds the threshold value Th1 in step S105, it is also determined that the start end of the edge (fall of the pixel value) has been detected.
An edge width detection value C2 (initial value 0) indicating the edge width is incremented by the edge width counter 276 on the second differential filter 272 side, and a flag CF2 indicating that the edge width is being detected is set to 1. The pixel value at the start of detection is stored in the latch 274 (step S10).
5, S106).

Thereafter, in step S105, the edge width detection value C2 until the pixel value difference becomes equal to or less than the threshold value Th1.
Increase (steps S105, S106, S121, S
122), when the difference between the pixel values is equal to or less than the threshold value Th1,
The flag CF2 is reset to 0, and the pixel value at this time is stored in the latch 275 (steps S105 and S10).
7).

When the flag CF2 is reset to 0, the pixel value difference Dd2 stored in the latches 274 and 275 is given to the comparator 277, and the pixel value difference Dd
It is confirmed whether or not 2 exceeds the threshold Th2 (step S113). If the pixel value difference Dd2 exceeds the threshold value Th2, the frequency H [C2] of the edge having the edge width C2 is incremented by the histogram generation unit 278 (step S114), and one of the edges having the edge width C2 is incremented. Edge detection is completed.

Thereafter, the edge width detection value C2 is reset to 0 (steps S117, S118).

By repeating the above edge detection processing, the variable i
Becomes a value outside the AF area 401 (exactly, (i +
When 1) becomes a value outside the AF area 401), the variables other than the variable j are initialized and the variable j is incremented (FIG. 14: steps S122 to S124). Thus, edge detection is performed on the next horizontal pixel array in the AF area 401. The edge detection in the horizontal direction is repeated, and when the variable j eventually becomes a value outside the AF area 401, the edge detection ends (step S125). Through the above-described processing, the histogram generation unit 278 generates a histogram indicating the relationship between the edge width and the frequency.

Next, the contrast calculation circuit 2 shown in FIG.
52 will be described. In the digital camera 1, the contrast of the AF area 401 is used at the time of the AF control, and the contrast is obtained for each color component. As the contrast, any index value may be used as long as it is an index value indicating the degree of change of the pixel value for each color component in the AF area 401. In the digital camera 1, the value shown in Expression 1 is used. It is used as the contrast Vc for one color component. That is, as the contrast Vc, the sum of the differences between the pixel values of one color component of horizontally adjacent pixels is used.

[0085]

(Equation 1)

Where x is the AF area 40
1 is the number of pixels in the horizontal direction, and y is the number of pixels in the vertical direction (see FIG. 16). Although not shown, the contrast calculation circuit 252 has a structure in which outputs from the first differential filter 271 and the second differential filter 272 shown in FIG. 11 are accumulated. Note that a contrast detection circuit may be provided separately, or a difference between two adjacent pixels may be calculated in contrast detection instead of adjacent pixels.

FIGS. 17 to 20 show the digital camera 1.
8 is a diagram showing an overall flow of AF control (FIG. 7: step S13) in FIG. Hereinafter, the operation at the time of autofocus will be described with reference to FIGS. 17 to 20 and FIG. In the following description, the focus lens 311 driven at the time of autofocusing is appropriately abbreviated as “lens”, and the position of the focus lens 311 at which the optical system is in a focused state is referred to as “focused position”.

First, the target color selection unit 281 sets the R, G, B
An average value (hereinafter, referred to as “level”) of pixel values for each color component is obtained (steps S201 to S203). Then, the color component having the highest level is selected as the color component to be calculated (hereinafter, referred to as “target color”) (step S204). Information indicating which color component is selected is input to the histogram evaluation unit 264 and the drive direction determination unit 266.

Next, under the control of the control signal generator 268, the lens is moved from the reference position P2 by a predetermined amount (for example, 4Fδ).
(Fδ is the depth of focus to be described later)), and moves to the position P1 on the closest side (the position on the focus side of the closest object), the contrast calculation circuit 252 obtains the contrast of each color component, and the driving direction determination unit 266 Is output (step S211). Subsequently, the lens returns to the reference position P2 and the contrast is obtained (step S212). The contrast is further increased at a position P3 where the lens is moved by a predetermined amount toward infinity (a position where a subject at infinity is focused). Is obtained (step S213). Note that the driving direction determination unit 266 uses only the contrast of the target color selected by the target color selection unit 281. In the following description, reference signs Vc1, Vc2, and Vc3 are assigned to the contrasts of the target colors corresponding to the positions P1, P2, and P3, respectively.

In the driving direction determining section 266, the contrasts Vc1, Vc2, and Vc3 are set to satisfy the condition (Vc1 ≧ Vc2 ≧ Vc).
3) It is confirmed whether or not the condition is satisfied (step S214). If the condition is satisfied, the in-focus position is located closest to the current position P3, so the drive direction is determined to be the direction toward the closest position. If the driving direction is not satisfied, the driving direction is determined to be the direction toward infinity (steps S215 and S21).
6).

Next, in a state where the lens is located at the position P3, a histogram of the edge width is generated by the histogram generating circuit 251 and the noise component of the histogram is removed by the noise removing unit 263. Thereafter, the number of edges (hereinafter, referred to as “number of edges”) Ven detected from the color component image of the target color by the histogram evaluation unit 264 is obtained, and a representative value of the histogram of the target color is obtained (step S301). ). As a representative value of the histogram, in the digital camera 1, an edge width corresponding to the center of gravity of the histogram (hereinafter, referred to as “center-of-gravity edge width”).
Vew is used. Other statistical values may be used as the representative values of the histogram. For example, an edge width corresponding to the maximum frequency, a median of the edge width, or the like can be used.

FIG. 21 is a flowchart showing the details of the processing for obtaining the center-of-gravity edge width by the noise removing unit 263 and the histogram evaluating unit 264. FIGS. 22 and 23 are diagrams for explaining the operation of the noise removing unit 263. FIG.

In the noise removal by the noise removing unit 263, first, a portion having an edge width of 1 (that is, one pixel) is deleted from the histogram of the target color (step S40).
1). As shown in FIG. 22, the histogram 410 has a shape in which a portion 411 having an edge width of 1 protrudes. This is because high-frequency noise in the AF area 401 is detected as an edge having a width of 1. Therefore, by removing the portion 411 having the edge width of 1, the accuracy of the center-of-gravity edge width described later is improved.

Next, portions 412 and 413 of the histogram 410 whose frequency is equal to or less than the predetermined value Th3 are deleted (step S402). This is because a portion having a low frequency in the histogram 410 generally includes many edges other than the main subject image. In other words, a part whose frequency is higher than a predetermined value is extracted from the histogram.

Further, as shown in FIG. 23, the edge width E having the maximum frequency is detected (step S403), and within a predetermined range around the edge width E (in FIG. 23, the edge width is (E-E1)). A new histogram 414 obtained by extracting the portion (within the range of (E + E1)) is obtained (step S404). Although not shown in FIGS. 22 and 23, depending on the shape of the histogram, FIG.
The portions 412 and 413 deleted in are not always included in the portions deleted in FIG. Therefore, step S404 is further executed after step S402.

The edge width E at the center of the extraction range in step S404 may be the edge width corresponding to the center of gravity of the histogram after step S402. In order to simplify the processing, simply, a portion having an edge width equal to or less than a predetermined value,
Alternatively, a method of removing a portion having an edge width equal to or larger than a predetermined value from the histogram may be adopted. Since the width of the edge of the main subject image (that is, the edge that does not include a noise component derived from the background image) usually falls within a predetermined range, even with such simplified processing, the width of the main subject image is approximately A corresponding histogram is determined.

When the noise component is removed from the histogram, the histogram evaluation unit 264 determines that the edge width corresponding to the centroid of the extracted histogram is the centroid edge width Ve.
It is obtained as w (step S405).

Note that the edge number Ven obtained in step S301 in FIG.
The total frequency in the histogram from which noise components have been removed in step 2 may be used, or the total frequency in the histogram from which noise components have been further removed in step S404 may be used.

When the histogram evaluation unit 264 obtains the number of edges Ven and the center-of-gravity edge width Vew related to the color component image of the target color, it is checked whether the number of edges Ven is zero. It is checked whether the value is equal to or less than a predetermined value. If the value is not equal to or less than the predetermined value, it is further checked whether the center-of-gravity edge width Vew is equal to or more than 8 (steps S302, S304, S306).

When the number of edges Ven is 0, the amount of movement of the image plane due to the driving of the lens is determined by the driving amount determining unit 265 to be 16Fδ, and the lens is driven in the direction determined by the driving direction determining unit 266. (Step S30)
3). Here, F is the F number of the optical system, and δ is C
The diameter of the permissible scattering circle corresponding to the pitch (interval) between the pixels of the CD 303, and Fδ corresponds to the depth of focus. When AF control is performed using a focusing lens, the amount of movement of the image plane is equal to the amount of movement of the lens. Therefore, the amount of movement of the lens is actually determined to be 16Fδ.

When the number of edges Ven is equal to or less than a predetermined value, the lens is driven to move by 12Fδ (step S305), and when the center-of-gravity edge width Vew is 8 or more, the lens is driven to move by 8Fδ. (Step S307). The acquisition of the edge number Ven and the center-of-gravity edge width Vew and the driving of the lens correspond to the center-of-gravity edge width Vew.
It is repeated until ew becomes less than 8 (step S
301-S307).

As described above, the AF control section 211a determines the amount of lens drive using the number of edges Ven and the center-of-gravity edge width Vew. This is because these values are values that can be used as evaluation values indicating the degree of focus. The lower the degree of focus, that is, the farther the lens is away from the in-focus position, the more the lens can be driven by one drive. Is largely allowed to move.

FIG. 24 is a diagram for explaining that the edge number Ven can be used as an evaluation value for focus. In FIG. 24, the horizontal axis corresponds to the position of the lens, and the vertical axis corresponds to the total number of detected edges (that is, the number of edges Ven). In FIG. 24, the lens position is 4
In this case, the lens is located at the in-focus position. At this time, the number of edges becomes maximum. The number of edges decreases as the lens position moves away from the in-focus position. Thus, the number of edges can be used as an evaluation value indicating the degree of focus.

On the other hand, since the image becomes sharper and the width of each detected edge becomes shorter as the lens approaches the in-focus position, the center-of-gravity edge width Vew is naturally used as an evaluation value indicating the degree of focus. Can be. In this case, the higher the degree of focus, the smaller the value. If it is defined that the evaluation value increases as the degree of focus increases, the reciprocal of the center-of-gravity edge width Vew or a value obtained by subtracting the center-of-gravity edge width Vew from a predetermined value corresponds to the evaluation value.

In the case of the digital camera 1, an experiment has previously been performed to determine that 16Fδ is used when the edge number Ven is 0, and 12F when the edge number Ven is less than a predetermined value (for example, 20).
When Fδ and the center-of-gravity edge width Vew are 8 or more, it has been confirmed that the lens does not pass the in-focus position even if the lens is moved by 8Fδ. For the above reasons, the drive control of the lens in steps S301 to S307 shown in FIG. 19 is performed.

As the lens approaches the in-focus position, the center-of-gravity edge width Vew becomes less than 8 (pixels). Thereafter, the lens is driven by the hill-climbing method for the target color. That is, the contrast calculation circuit 252 obtains the contrast Vc of the target color (FIG. 20: step S311), and the drive amount determination unit 265 obtains the lens drive amount within the range of 2 to 4Fδ according to the contrast Vc, Generator 26
8 is a control signal corresponding to the driving amount, and the AF motor driving circuit 21
4 to drive the AF motor M2 (step S312).

Thereafter, the contrast Vc of the target color is acquired again, and the drive amount determination unit 265 moves the lens little by little while the focus detection unit 267 checks whether the contrast Vc has decreased (steps S312 to S312). S31
4). When the acquisition of the contrast Vc and the driving of the lens are repeated, the lens eventually passes the in-focus position, and the contrast Vc decreases (step S314). Here, by interpolating the contrast Vc corresponding to a plurality of lens positions near the current lens position, the lens position where the contrast Vc is maximum is obtained as the focus position, and the contrast Vc is calculated while oscillating the lens. The acquired and fine adjustment of the lens position is performed (Step S3)
15). With the above operation, the AF control ends.

If no edge is detected even when the lens is driven from the end on the infinity side to the end on the closest side, the AF control unit 211a determines that the subject is a low-contrast object, and A warning to the effect that control is impossible is transmitted to the user via the LCD 10. Also, when the number of edges does not exceed a predetermined value even when the lens is moved from the end at infinity to the end at the nearest side, a warning is issued via the LCD 10 or a hill-climbing method using ordinary contrast is performed. The focus position is detected. Even when the center-of-gravity edge width Vew does not become 8 or less, the method is switched to the hill-climbing method using the contrast, and the in-focus position is detected.

As described above, the digital camera 1
In, the edge is detected from the AF area 401, and the amount of one movement of the lens, that is, the driving speed of the lens is changed using the evaluation value indicating the degree of focus related to the edge of the color component image of the target color. Accordingly, even when a high-resolution still image is acquired, a focus operation with high accuracy can be quickly performed.

The digital camera 1 obtains a plurality of evaluation values corresponding to a plurality of color components, selects the color component having the highest level as a target color, and performs AF control based on only the evaluation value of the target color. . By performing the AF control after selecting the target color, appropriate AF control is realized even when the color of the main subject is biased toward a specific color component. For example, even when photographing red flowers or green trees or using a color filter for special effects such as sunsets, appropriate AF control should be performed using color components that can easily detect edges. Can be.

Generally, in order to obtain a high evaluation value from an edge, a histogram of an edge width is obtained, and it is preferable that a representative value of the histogram is used as the evaluation value. The representative value of the histogram, considering the calculation technology,
It is preferably provided as a statistical value. As the statistical value, an average value, a median, an edge width corresponding to a peak, or the like can be used. In the digital camera 1, an edge width corresponding to the center of gravity of the histogram is used as a representative value in consideration of the reliability of the evaluation value and the amount of calculation.

As a specific example of the evaluation value derived from the edge, the center-of-gravity edge width Ve based on the histogram of the edge width is used.
Not only w but also the edge number Ven can be used. In the digital camera 1, these evaluation values are compared with a predetermined value, and the driving speed of the lens is changed according to the comparison result.

Normally, the center-of-gravity edge width Vew using the histogram is more accurate as an evaluation value related to focus than the number of edges Ven. On the other hand, the edge number Ven is a value that can be obtained very easily. Therefore, the digital camera 1 uses both the low-precision evaluation value and the high-precision evaluation value to determine whether the driving speed of the lens can be increased (the amount of one movement increases) with the low-precision evaluation value. It is determined whether the driving speed of the lens can be reduced (the amount of one movement is reduced) by using a highly accurate evaluation value. Thereby, more appropriate AF control is realized.

When a plurality of types of evaluation values are properly used, when it is determined that the lens is sufficiently away from the in-focus position by using low-precision evaluation values and comparison conditions,
It is not necessary to determine a highly accurate comparison condition, which is equivalent to determining whether to use a highly accurate evaluation value using a substantially low evaluation value.

In the digital camera 1, the edge number Ven, which is an evaluation value with low accuracy, is compared with a threshold value, and the lens is largely moved according to the comparison result.
By obtaining n and repeating this operation, the lens is quickly driven until the comparison result changes. When the comparison result changes, the center-of-gravity edge width V, which is a more accurate evaluation value,
Drive using ew is performed. Thereby, evaluation and driving are performed at a plurality of levels, and high-speed AF control is realized.

On the other hand, in the digital camera 1, not only the focus evaluation value for the edge obtained by the histogram evaluation unit 264 from the color component image of the target color but also the contrast obtained by the contrast calculation circuit 252 from the color component image of the target color. By using the evaluation value of the used focus, highly accurate auto focus is realized. Specifically, the contrast Vc is used to determine the driving direction of the lens, and the final control is also performed using the contrast Vc that can increase the accuracy more than the center-of-gravity edge width.

Since the technique of obtaining the contrast at the time of autofocus is a technique already used, the digital camera 1 uses the existing technique and the technique using the edge, and furthermore, the precision of each color component. Different contrast Vc, center of gravity edge width Vew and number of edges V
By properly using en, quick and highly accurate auto-focusing is realized while considering the color deviation of the main subject. In general, when a still image is obtained, the focus lens 311 largely moves in response to an instruction for shooting preparation. Therefore, a still image is obtained by changing the driving speed of the lens while using evaluation values having different precisions. Autofocus is quickly and appropriately realized.

<2. Second Embodiment> In the first embodiment, the color component having the highest level is selected as the target color when selecting the target color. However, the selection of the target color may be performed based on other criteria. FIG. 25 illustrates the case where the target color is selected based on the number of detected edges.
It is a figure showing the flow of F control.

First, an edge is detected from each of the R, G, and B color component images (hereinafter, referred to as “R image”, “G image”, and “B image”) in the histogram generation circuit 251 (step). S221 to S224, see FIG. 9).
Then, the detected edge is output to the histogram generation circuit 25.
1 is input to the target color selection unit 281 and a color component having the largest number of detected edges is selected as a target color to be calculated (step S224). The selected target color is determined by the histogram evaluation unit 264 and the drive direction determination unit 26.
6 and thereafter, the lens is driven based on the evaluation value for the target color as in the first embodiment (FIGS. 18 to 20).

As described above, in the second embodiment, the focus lens 311 is driven based on the evaluation value corresponding to the color component having the largest number of detected edges. In addition,
As long as it is an index value indicating the color bias of the main subject, even an index value other than the level and the number of edges of the color component image can be used for selecting the target color.

<3. Third Embodiment> Next, an example of AF control in which a plurality of target colors can be selected will be described with reference to FIG. Note that, similarly to the second embodiment, the target color is selected based on the number of edges detected from the color component image.

When edges are sequentially detected from the G image, the B image, and the R image by the histogram generation circuit 251 (steps S231 to S233), the edges of each color component image are input to the target color selection unit 281. The target color selection unit 281 checks whether there are a plurality of color components whose detected edge number is equal to or more than a predetermined value (Step S23).
4) If a plurality of color components exist, a plurality of color components are selected as target colors.

The selection result is input to the histogram evaluator 264 and the drive direction determiner 266, where the settings for evaluating the histogram and determining the drive direction using a plurality of target colors are made (step S23).
5). Specifically, the histogram evaluation unit 264 calculates the average value of the number of edges and the average value of the center-of-gravity edge widths for a plurality of target colors as the number of edges Ven and the center-of-gravity edge width Vew used for driving the lens. In the driving direction determination unit 266, an average value of contrasts for a plurality of target colors is obtained as the contrast Vc used for determining the driving direction.

The number of edges Ven, the center of gravity edge width Ve
The w and the contrast Vc may not be average values but may be obtained as weighted average values proportional to the number of edges of each target color. In this case, the number of edges Ven, the center of gravity edge width Vew, and the contrast V
Affects the value of c.

If there are no plural color components having the number of edges equal to or more than the predetermined value, the target color selection unit 281 checks whether there is one color component having the number of edges equal to or more than the predetermined value (step S236). ). If there is, as in the second embodiment, a color component having a number of edges equal to or greater than a predetermined value (that is, a color component having the largest number of edges) is selected as a target color which is a color component to be calculated. (Step S23)
7).

If the number of edges detected in any of the color component images is smaller than the predetermined value, a warning is displayed on the LCD 10 (see FIG. 2) indicating that appropriate AF control cannot be performed (step S238). ), The position of the lens is controlled so that the shooting distance is about 3 m (Step S)
239).

Step S235 or step S237
When at least one color component is selected as the target color by the following, based on the number of edges Ven, the center-of-gravity edge width Vew and the contrast Vc obtained from the color component image corresponding to the at least one target color, The driving direction of the lens and the driving amount are determined in the same manner as in the embodiment (FIGS. 18 to 20).

As described above, two or more color components may be selected as target colors, and an evaluation value for each target color is obtained from edges detected from two or more color component images, and a plurality of evaluation values are obtained. The focus lens 311 may be driven based on the new evaluation value obtained. This realizes appropriate AF control even when the color of the main subject is biased toward a plurality of color components. In the third embodiment, by selecting at least one color component as the target color, appropriate AF control can be performed even when the color of the main subject is biased to a specific color (at least one color component). Has been realized.

Further, in the third embodiment, since the evaluation value and the contrast relating to edges having mutually different precisions are obtained from the color component images of at least one target color, the AF control can be performed quickly while considering the color deviation. It can be carried out.

In the third embodiment, as in the first embodiment, the target color may be selected according to the level of the color component.

<4. Fourth Embodiment> In the first to third embodiments, one drive amount (movement amount) of the focus lens is obtained by using the edge extracted from the AF area 401. It is also possible to predict the focus position using the width. Hereinafter, a basic method for predicting the in-focus position will be described, and then the AF control according to the fourth embodiment using this method will be described.

FIG. 27 is a diagram showing how the histogram of the edge width changes as the lens approaches the in-focus position. Reference numeral 431 indicates a histogram when the lens is far away from the in-focus position, and reference numeral 432 indicates a histogram when the lens is closer to the in-focus position than in the case of the histogram 431. Reference numeral 433 indicates a histogram when the lens is located at the in-focus position. Also, the code Vew
11, Vew12, and Vewf are the center-of-gravity edge widths of the histograms 431, 432, and 433, respectively.

As shown in FIG. 27, the edge width of the center of gravity decreases as the lens approaches the in-focus position. The minimum center-of-gravity edge width Vewf is determined by the MTF (Modulation Tra
nsfer Function: an index value that indicates how much the optical system can reproduce the contrast of the image with respect to the spatial frequency), shooting conditions, subject, etc.
When the criterion for judging in-focus is loose, the minimum center-of-gravity edge width Vewf when the lens is located at the in-focus position
Can be regarded as a constant value and can be obtained in advance. In the following description, the minimum center-of-gravity edge width Vewf is referred to as “reference edge width”.

FIG. 28 is a diagram showing the relationship between the lens position and the center-of-gravity edge width. The center-of-gravity edge widths corresponding to the lens positions L1 and L2 are Vew21 and Vew22, and the reference edge width corresponding to the focus position Lf. Is Vewf. FIG.
As shown in FIG. 8, generally, the lens position and the center-of-gravity edge width can be regarded as having a linear relationship. Therefore, the center-of-gravity edge width Ve corresponding to the lens positions L1 and L2
When w21 and Vew22 are obtained, the reference edge width Ve
The in-focus position Lf can be obtained by using Equation 2 using wf.

[0135]

(Equation 2)

Note that, instead of the center-of-gravity edge width, a statistical value such as an average value of the edge width, an edge width corresponding to the peak of the histogram, or a median may be used in obtaining the in-focus position.

In the method shown in FIG. 28, the in-focus position can be obtained by obtaining the center-of-gravity edge width at at least two lens positions. However, in order to further improve the accuracy, each of the lens positions L1, L2 A predetermined distance from
Positions before and after Fδ (L1 ± aFδ), (L2 ± aF
The accuracy of the center-of-gravity edge width at the lens positions L1 and L2 may be increased using the center-of-gravity edge width in δ). Specifically, the positions (L1−aFδ), L1, (L1 + aFδ)
The center of gravity edge width at Vew31, Vew32, Ve
In the case of w33, a value Vew3 obtained by applying a low-pass filter to these values is obtained as the center-of-gravity edge width of the lens position L1 by Expression 3.

[0138]

(Equation 3)

Similarly, the positions (L2-aFδ), L2,
The center of gravity edge width at (L2 + aFδ) is Vew41,
In the case of Vew42 and Vew43, the value Vew4 is obtained from Equation 4 as the center-of-gravity edge width of the lens position L2.

[0140]

(Equation 4)

Of course, the center-of-gravity edge width may be determined at three or more arbitrary lens positions, and a straight line indicating the relationship between the lens position and the center-of-gravity edge width may be determined using the least squares method.

Next, the flow of the AF control in the fourth embodiment will be described. It is assumed that the configuration and basic operation (FIG. 7) of the digital camera 1 according to the fourth embodiment are the same as those of the first embodiment.

FIGS. 29 and 30 are views showing the flow of AF control in the fourth embodiment. In the AF control, first, similarly to the third embodiment, edges are detected from the G image, the B image, and the R image by the histogram generation circuit 251 (steps S501 to S503), and the number of edges is determined by the target color selection unit 281. Are selected as target colors (step S504). If there is no color component whose edge number is equal to or greater than the predetermined value, the LCD 10
Is displayed, and the shooting distance is set to about 3 m (steps S505 to S507).

When at least one color component is selected as the target color, the driving direction determination unit 266 cites FIG. 18 referred to in the third embodiment based on the contrast of the color component image of the target color. Steps S211 to S21
The driving direction of the lens is determined in the same manner as in Step 6 (Step S508). That is, when there is one target color, the driving direction is determined using the contrasts Vc1 to Vc3 of the target colors at the three lens positions P1 to P3, and when there are a plurality of target colors, the average value of the contrast for each target color Are used as contrasts Vc1 to Vc3 to determine the driving direction.

When the driving direction is determined, the center-of-gravity edge width Vew21 is obtained from the histogram for each color component selected by the histogram evaluation section 264 (step S).
509). That is, when there is only one target color, only one centroid edge width Vew21 is obtained, and when there are multiple target colors, plural centroid edge widths Vew21 are also obtained.

Next, the lens is largely moved by a predetermined amount from the initial position (hereinafter, referred to as “position L1”) in the determined driving direction by the driving amount determining unit 265 and the control signal generating unit 268 (step S511). ), The center-of-gravity edge width Vew22 for each target color is obtained at the moved position (hereinafter, referred to as “position L2”) by the histogram generation circuit 251, the noise removal unit 263, and the drive amount determination unit 265 (step S512). . After that, the calculation based on Expression 2 is performed, and an approximate focus position is obtained for each target color (step S513). That is, the in-focus position for each target color is estimated.

Here, the reference edge width Vewf for the color G when obtaining the in-focus position is determined by a G Bayer array CCD.
In the case of, it is set smaller than that for R and B. In a G-Bayer array CCD, a G filter is provided for two pixels located diagonally out of four pixels,
The other two pixels are provided with R and B filters.
As a result, the G image contains more high frequency components than the R image and the B image, and the G image when the lens is located at the in-focus position.
Since the center-of-gravity edge width related to G is smaller than the others, the reference edge width Vewf for G is set smaller.

When the in-focus position is obtained, step S50 is performed.
If only one color component is selected as the target color in step 4, the lens quickly moves to the obtained focus position (step S516), and the lens is focused while obtaining the contrast Vc for the target color. Fine adjustment is performed so as to exactly match the position (step S517).

On the other hand, when a plurality of color components are selected as target colors, the focus position corresponding to the closest object (ie, the focus position closest to the object) among the plurality of obtained focus positions. Is selected (steps S514, S5).
15), the lens quickly moves to the determined focus position (step S516). Thereafter, fine adjustment of the lens position is performed (step S517).

As described above, in the AF control according to the fourth embodiment, the center-of-gravity edge width corresponding to at least one color component is obtained at the first position L1 and the second position L2, and these values and At least one focus position is determined from a reference edge width corresponding to at least one color component. Further, the focus lens is driven based on the obtained at least one focus position. Therefore, the lens can be quickly moved to the focus position. Further, since the lens movement using the center-of-gravity edge width and the lens movement using the contrast are used together, the lens can be accurately positioned at the in-focus position.

In the fourth embodiment, when a plurality of target colors are selected and a plurality of focus positions are obtained, the lens is moved to the closest focus position. This operation is performed for the purpose of focusing on a main subject located closer to the digital camera 1 than the background. That is, the main subject having a color bias and the background are AF
Even when the main subject is located in the area 401, the main subject can be appropriately focused by moving the lens to the closest focus position. Thereby, the problem of so-called far-field conflict is avoided.

In the fourth embodiment, another representative value of the histogram may be used as an evaluation value indicating the degree of focus instead of the center-of-gravity edge width Vew. The target color may be selected from the level of each color component instead of the number of edges.

The distance between the first position L1 and the second position L2 may be set to a fixed value in advance, but the number of edges Ven and the center of gravity edge width Vew of the target color at the position L1. It may be changed according to. That is, the distance between the position L1 and the position L2 may be set to be larger as the degree of focus indicated by these evaluation values is lower in order to appropriately estimate the focus position.

<5. Fifth Embodiment> In the fourth embodiment, after obtaining a plurality of focus positions, the lens is moved to the closest focus position. On the other hand, when various colors exist on the main subject, it may be preferable that a position other than the closest side is obtained as a final focus position.

FIG. 31 is a flowchart showing step S51 in FIG.
13 is a flowchart showing another operation of the fifth embodiment. Step S515a shown in FIG. 31 is a process of performing weighting by the ratio of the number of edges for each color component, combining a plurality of focus positions obtained for each color component, and obtaining a new focus position. By this processing, even when various colors exist on the main subject, A can be appropriately adjusted in accordance with the degree of color deviation of the main subject.
F control can be performed.

Step S515 according to the fourth embodiment
It may be possible to switch between step S515a according to the fifth embodiment and step S515a according to the state of the main subject. In this case, the user of the digital camera 1 appropriately operates the button (the operation unit 250 in FIG. 5) to execute step S515 when the main subject is biased to a specific color and wants to avoid perspective conflict. Select, otherwise step S515
Select a.

<6. Modifications> While the preferred embodiments of the present invention have been described above, the present invention is not limited to the above-discussed preferred embodiments, but allows various modifications.

For example, in the above embodiment, the imaging section 3 having an optical system and the camera body 2 for controlling the optical system can be separated, and the camera body 2 serves as a control device for the optical system. However, a digital camera having an optical system and a control system integrally may be used. Further, a configuration in which the optical system and the control device are connected using a cable may be employed. In this case, a general-purpose computer may be used as the control device.
An optical system control program is installed in advance via a recording medium such as a magnetic disk or a magneto-optical disk.

The preparation for photographing may be instructed to the AF control section 211a by a configuration other than the shutter button 8. For example,
A sensor that detects that the user has approached the eye to the viewfinder 31 or that detects that the grip unit 4 has been gripped may send a signal for instructing the AF control unit 211a to prepare for shooting. Preparation for shooting may be instructed by a signal generated by operating a button other than the shutter button 8 or a signal from a self-timer or a timer used for interval shooting. As described above, it is determined that the image is
If the control unit 211a can be instructed, various configurations can be used as the configuration for instructing the preparation for photographing.

In the digital camera 1, as shown in FIG. 8, the processing in the AF control section 211a is divided into processing by a dedicated circuit and software processing by the CPU, but all processing can be executed by the CPU. is there.
In this case, when the CPU executes the program, all of the AF control described in the above embodiment is executed. Conversely, all the processing in the AF control unit 211a can be realized by a dedicated circuit. Further, in FIG. 9, the functions of the CPU are represented using blocks, but the roles of these functional components (that is, the roles of the arithmetic processing) may be arbitrarily changed.

The edge detection (extraction) processing in the above embodiment is merely an example, and the edge may be detected by another method. Further, although the edge detection in the above embodiment is performed only in the horizontal direction, an edge may be detected in the vertical direction, or edge detection may be performed in both directions.

In the above embodiment, the contrast is used as it is as the evaluation value. However, the evaluation value may be obtained by converting the contrast. That is, in the above-described embodiment, the step of obtaining the contrast and the step of obtaining the evaluation value from the contrast in the contrast calculation circuit 252 are substantially performed as one step. However, these steps may be individually provided. The circuit may be separated every time. Using the contrast as it is as the evaluation value is just one mode of processing for obtaining the evaluation value by obtaining the contrast.

In the first embodiment, the driving direction of the lens is determined by using the contrast as the evaluation value. However, the driving direction of the lens can be determined by using the center-of-gravity edge width instead of the contrast. . In this case, the driving direction of the lens is determined without using the contrast.
Similarly, when the lens is accurately adjusted to the in-focus position, the center-of-gravity edge width can be used instead of the contrast.

Further, other evaluation values relating to edges can be used. For example, the frequency of an edge having a width of about 3 or 4 close to the reference edge width may be simply used as the evaluation value. It is also possible to use, as the evaluation value, the ratio of the frequency of the edge within the range of the predetermined edge width including the edge width to the total frequency. In this case, the higher the frequency, the higher the degree of focus.

Although the reference edge width of G is smaller than the reference edge widths of R and B in the fourth embodiment, another evaluation value (for example, a frequency of a predetermined edge width) is focused. When used as a reference evaluation value serving as a reference for calculating the position, the reference evaluation value for G is larger than the reference evaluation values for R and B. That is, when a CCD having a G Bayer array is used, an appropriate focus position is calculated based on each color component by using a reference evaluation value for G that is different from the reference evaluation values for R and B.

In the above embodiment, when determining the driving direction of the lens, the evaluation values at three lens positions are obtained. However, two evaluation values may be used. Only three evaluation values are used to increase the accuracy of the drive direction determination. 3
Even when the above evaluation values are obtained, in principle, it is determined that the direction from the lens position where the degree of focus indicated by one evaluation value is low to the lens position where the degree of focus indicated by the other evaluation values is high is adjusted. The driving direction is determined based on the principle that a focus position exists.

In the digital camera 1, AF control is performed by controlling the position of the focus lens.
The AF control was explained using the term lens position,
Even when the AF control is performed by driving a plurality of lenses, the AF control according to the above embodiment can be used. That is, the lens position in the above embodiment can be associated with the arrangement of at least one lens, and the AF control in the above embodiment can be performed at least It can be considered that the control is to set the lens group into the focused arrangement based on the evaluation value corresponding to one color component.

In the above embodiment, the result of selection by the target color selection unit 281 shown in FIG. 9 is input to the histogram evaluation unit 264 and the drive direction determination unit 266. The selection result of the target color is output by the histogram generation circuit 251. Or to the contrast calculation circuit 252. The stage at which the color component to be processed is limited may be arbitrarily determined, and a histogram and a contrast regarding only the target color may be obtained by these circuits.

In the digital camera 1, an image signal is input from the black level correction circuit 206 to the general control unit 211 in order to obtain an evaluation value for auto focus. However, the digital signal may be input to the general control unit 211 from another part. . At least one lens for imaging need not be a zoom lens.

In selecting a target color, the level of the color component image is used in the first embodiment, and the number of edges for each color component is used in the second embodiment. May be made switchable by the operation of.

In the third and fourth embodiments, a warning is displayed if the target color cannot be selected. However, if none of the color components satisfies the selection condition, the brightness is increased. Using the center-of-gravity edge width of the histogram
F control may be performed. The sum of the center-of-gravity edge widths of R, G, and B may be used as a new center-of-gravity edge width. In this case, the sum of the reference edge widths of R, G, and B is the new reference edge width. Used as

The above-described embodiment is particularly suitable for obtaining a still image because it realizes high-speed AF control by using an edge. For example, it can be applied to a video camera.

The image pickup device for acquiring an image is not limited to the CCD, but may be another type of image pickup device.

[0174]

According to the first to eleventh aspects of the present invention, the optical system can be appropriately driven at the time of auto-focusing even when the color of the main subject is deviated.

Further, according to the second and third aspects of the present invention, it is possible to appropriately drive the optical system even when the color of the main subject is biased toward a specific color component. The optical system can be appropriately driven even when the color of the main subject is biased to a plurality of color components.

According to the fifth aspect of the invention, the lens can be quickly positioned at the in-focus position. According to the sixth aspect of the invention, the in-focus position for each color component can be determined appropriately. Furthermore, according to the invention of claim 7, the lens can be appropriately positioned at the in-focus position in accordance with the degree of deviation of the color of the main subject, and the invention of claim 8 can avoid perspective conflict.

According to the ninth aspect of the present invention, by using the evaluation values of the first accuracy and the second accuracy, it is possible to drive the optical system quickly and appropriately while considering the color deviation of the main subject during autofocusing. Can be.

[Brief description of the drawings]

FIG. 1 is a front view of a digital camera.

FIG. 2 is a rear view of the digital camera.

FIG. 3 is a side view of the digital camera.

FIG. 4 is a bottom view of the digital camera.

FIG. 5 is a block diagram illustrating a configuration of a digital camera.

FIG. 6 is a diagram illustrating an internal configuration of an imaging unit.

FIG. 7 is a flowchart showing an outline of the operation of the digital camera.

FIG. 8 is a block diagram illustrating a configuration of an AF control unit.

FIG. 9 is a block diagram illustrating a functional configuration of an AF control unit.

FIG. 10 is a diagram for explaining a state of edge detection.

FIG. 11 is a block diagram illustrating a configuration of a histogram generation circuit.

FIG. 12 is a diagram showing a flow of histogram generation.

FIG. 13 is a diagram showing a flow of histogram generation.

FIG. 14 is a diagram showing a flow of generating a histogram.

FIG. 15 is a diagram showing an AF area.

FIG. 16 is a diagram showing a pixel array in an AF area.

FIG. 17 is a diagram showing a flow of AF control in the first embodiment.

FIG. 18 is a diagram showing a flow of AF control in the first embodiment.

FIG. 19 is a diagram showing a flow of AF control in the first embodiment.

FIG. 20 is a diagram showing a flow of AF control in the first embodiment.

FIG. 21 is a diagram showing a flow of calculating a center-of-gravity edge width.

FIG. 22 is a diagram illustrating a state where noise components are removed from a histogram.

FIG. 23 is a diagram illustrating a state in which a noise component is removed from a histogram.

FIG. 24 is a diagram illustrating a relationship between a lens position and the number of edges.

FIG. 25 is a diagram showing a flow of AF control in the second embodiment.

FIG. 26 is a diagram illustrating a flow of AF control according to the third embodiment.

FIG. 27 is a diagram illustrating a change in a histogram due to a change in a lens position.

FIG. 28 is a diagram illustrating a relationship between a lens position and a center-of-gravity edge width.

FIG. 29 is a diagram illustrating a flow of AF control according to the fourth embodiment.

FIG. 30 is a diagram showing a flow of AF control in a fourth embodiment.

FIG. 31 is a diagram showing a flow of AF control in a fifth embodiment.

[Explanation of symbols]

1 Digital Camera 2 Camera Body 91 Memory Card 251 Histogram Generation Circuit 252 Contrast Calculation Circuit 261 CPU 262 ROM 262a Program 264 Histogram Evaluation Unit 265 Drive Amount Determination Unit 268 Control Signal Generation Unit 301 Zoom Lens 303 CCD 311 Focus Lens S102, S103, S105, S106, S301-
S307, S311 to S314, S401 to S405,
S506, S512 to S516 Step

Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat II (Reference) H04N 9/04 G03B 3/00 A F term (Reference) 2H011 AA03 BA31 BB03 2H051 AA08 BA47 CE08 CE14 CE27 DA22 2H054 AA01 5C022 AB28 AC42 AC54 AC69 AC74 5C065 AA01 BB48 DD02 EE12 GG18

Claims (11)

[Claims] An optical system control device for controlling an optical system when acquiring an image as digital data, comprising detecting an edge from an image corresponding to at least one of color components constituting a color image, An optical system control device, comprising: arithmetic means for calculating at least one evaluation value indicating a degree of focus from the edge; and control means for driving the optical system based on the at least one evaluation value. 2. The optical system control device according to claim 1, wherein the calculating means obtains an evaluation value corresponding to each of the plurality of color components, and wherein the control means detects an evaluation value among the plurality of evaluation values. An optical system control device for driving the optical system based on an evaluation value corresponding to a color component having the largest number of edges. 3. The optical system control device according to claim 1, wherein the control unit drives the optical system based on an evaluation value corresponding to a color component having the highest level among a plurality of color components. An optical system control device comprising: 4. The optical system control device according to claim 1, wherein the calculating means obtains an evaluation value corresponding to each of the plurality of color components and obtains a new evaluation value from the plurality of evaluation values. An optical system control device, wherein the control means drives the optical system based on the new evaluation value. 5. The optical system control device according to claim 1, wherein the optical system has a focusing lens, and wherein the arithmetic unit has at least one first lens corresponding to a first position of the lens. 1 is obtained and the second value of the lens is obtained.
Determining at least one second evaluation value corresponding to the position of the first and second positions, the first and second positions, the at least one first and second evaluation values, and at least one reference evaluation An optical system control device, wherein an in-focus position of the lens is obtained from a value. 6. The optical system control device according to claim 5, wherein the color image is acquired by an imaging device having a G-Bayer array, and among the reference evaluation values corresponding to R, G, and B color components. ,
An optical system control device, wherein a reference evaluation value corresponding to a G color component is different from a reference evaluation value corresponding to R and B color components. 7. The optical system control device according to claim 5, wherein the control means obtains a focus position corresponding to each of a plurality of color components, and obtains a new focus position from the plurality of focus positions. An optical system control device for determining a focus position. 8. The optical system control device according to claim 5, wherein the control means obtains a focus position corresponding to each of the plurality of color components, and determines a closest focus position among the plurality of focus positions. An optical system control device that controls the optical system based on a focus position corresponding to a subject to be moved. 9. The optical system control device according to claim 1, wherein said calculating means is configured to perform a first operation for each of a plurality of color components.
Is determined, a color component is selected based on the plurality of first evaluation values, and a second evaluation value with higher accuracy than the first evaluation value is determined for the selected color component. The optical system control device, wherein the control means controls the optical system based on the second evaluation value. 10. An optical system control method for controlling an optical system when acquiring an image as digital data, comprising detecting an edge from an image corresponding to at least one of color components constituting a color image, An optical system control method, comprising: obtaining at least one evaluation value indicating a degree of focus from the edge; and driving the optical system based on the at least one evaluation value. 11. A recording medium recording a program for causing a control device to control an optical system when acquiring an image as digital data, wherein the control device executes the program by causing the control device to execute a color image processing. Detecting an edge from an image corresponding to at least one of the constituent color components and obtaining at least one evaluation value indicating a degree of focus from the edge; and the optical system based on the at least one evaluation value. And a step of driving the recording medium.