JP2005037519A - Automatic focusing system and method for camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an automatic focusing system and method for a camera, whereby images which are adequate enough for practical use can be recorded even when a subject is, in particular, dark or low in contrast as a result of the emission of AF auxiliary light to the subject. <P>SOLUTION: The automatic focusing system for the camera is used for contrast AF. When a subject has a low luminance, a low contrast, etc., an evaluation value based upon an image signal outputted from a CCD 52 may not be obtained even after an AF auxiliary light is flashed. In this case, an AF auxiliary light diffusion area is created on the subject upon the emission of the AF auxiliary light to the subject. Therefore, the size of the diffusion area is evaluated, and a distance from the camera to the subject is found from the evaluated size. Next, a photographic lens 12 is moved to a moved position corresponding to the thus found distance. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an automatic focusing apparatus and method for a camera, and more particularly to an automatic focusing apparatus for a camera that automatically adjusts the lens position of a focus lens (hereinafter referred to as “contrast AF”) so that the contrast of a subject is maximized. And a method.
[0002]
[Prior art]
Contrast AF, which is the mainstream in digital cameras, etc., takes an image while moving a focus lens that affects focus adjustment in the photographic optical system, extracts high-frequency components from the output image signal, and evaluates for focusing A value is calculated, and the focus lens is moved to a position where the evaluation value is maximized (where the contrast is maximized) to focus.
[0003]
However, in contrast AF, when the contrast of the subject is low (when the subject itself is originally low like a wall or when the subject is dark and the contrast is low), the focus lens is moved over the focus adjustment range. There is a problem in that the focus evaluation value obtained becomes small as a whole, and the lens position of the focus lens that maximizes the evaluation value cannot be obtained accurately.
[0004]
Therefore, the automatic focus adjustment apparatus described in Patent Document 1 below irradiates the subject with auxiliary light (hereinafter referred to as “AF auxiliary light”) so that the subject can obtain contrast when the subject is dark. In particular, the light amount of the AF auxiliary light is controlled so as to obtain an appropriate amount of light according to the subject brightness, thereby saving power.
[0005]
However, when the subject is particularly dark or the contrast is low, the subject may not be grasped even when the AF auxiliary light is irradiated, and the focus may not be determined.
[0006]
In the following Patent Document 2, when the subject is not grasped even when the AF auxiliary light is irradiated, it is first determined that the defocus is large, the focus position is searched within the movable range of the lens, and the focus position is obtained as a result of the search. If is not detected, it is determined that the subject is far away. In this case, even if the subject is near, there is a possibility that an image whose focus is adjusted at the distance to the subject that is determined to be far without being detected is recorded.
[0007]
[Patent Document 1]
JP 2000-121924 A
[Patent Document 2]
JP-A-6-94988
[Problems to be solved by the invention]
In consideration of the above circumstances, the present invention is an automatic focus adjustment of a camera capable of recording an image that can withstand practical use even when the subject is irradiated with AF auxiliary light, even when the subject is particularly dark or the contrast is low. An object is to provide an apparatus and method.
[0010]
[Means for Solving the Problems]
The present invention moves an imaging lens over a focus adjustment range, obtains an evaluation value corresponding to a contrast component of a subject based on an image signal output from an imaging unit each time the imaging lens moves by a predetermined amount, and the imaging lens An automatic focus adjustment device for a camera that obtains a movement position at which an evaluation value reaches a peak based on the movement position and the evaluation value obtained for each movement position, and moves the photographing lens to the obtained movement position,
AF auxiliary light emitting means for emitting AF auxiliary light;
Diffusion region evaluation means for evaluating the size of the AF auxiliary light diffusion region in the subject irradiated with the emitted AF auxiliary light;
A distance calculating means for obtaining a distance from the evaluated AF auxiliary light diffusion region to the subject;
Photographing lens moving means for moving the photographing lens to a movement position corresponding to the calculated distance;
The camera's automatic focusing device.
[0011]
According to the present invention, in contrast AF, the photographing lens is moved over the focus adjustment range, and an evaluation value corresponding to the contrast component of the subject is collected every time the photographing lens moves by a predetermined amount. In such a case, the evaluation value is obtained based on the image signal output from the imaging unit by emitting AF auxiliary light. When the AF auxiliary light is irradiated on the subject, an AF auxiliary light diffusion region is formed on the subject. The size of this diffusion region varies depending on the distance between the camera and the subject. If the distance between the camera and the subject is short, the diffusion region is small, and if the distance between the camera and the subject is long, the diffusion region is large. The size of the diffusion region is evaluated, and the distance from the camera to the subject is obtained from the evaluated size. The photographing lens is moved to a moving position corresponding to the obtained distance.
[0012]
In the case where the photographing lens is a zoom lens, the distance calculating means obtains the distance to the subject from the zoom magnification and the evaluated size of the AF auxiliary light diffusion region.
[0013]
The AF auxiliary light emitting means is also used as a light emitting means for emitting photographing auxiliary light at the time of flash photography, and the light emitting means is constituted by any one of a light emitting diode, an organic electroluminescence, and a plasma light emitting element. Can be configured.
[0014]
Further, the AF auxiliary light emitting means can control the current applied to the light emitting element or the number of elements that selectively emit light, thereby reducing the light amount of the AF auxiliary light from the light amount of the photographing auxiliary light.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of an automatic focusing apparatus for a camera according to the present invention will be described in detail with reference to the accompanying drawings.
[0016]
FIG. 1 is an external view of a digital camera to which the present invention is applied. A photographing lens 12, a finder window 14, a strobe light emitting unit 16, and a light control sensor 17 are provided on the front surface of the digital camera 10, and a shutter button 18 and a power switch 20 are provided on the upper surface of the camera. A card slot 26 for mounting a memory card 24 is provided on the side of the camera opposite to the grip portion 22.
[0017]
A zoom lens is applied to the photographing lens 12, and a CCD image sensor (not shown in FIG. 1, described as reference numeral 52 in FIG. 3) is disposed behind the photographing lens 12. The shutter button 18 is configured in a two-stage system, and the contrast AF (AF) and automatic exposure control (AE) are activated in a “half-pressed” state in which the shutter button 18 is lightly pressed and stopped to lock AF and AE. Shooting is performed in a state of “full press” where the press is further pushed.
[0018]
The power switch 20 is also used as a mode switch, and is an “OFF position” where the power is turned off, a “shooting ON position” where the power is turned on in the still image shooting mode, and a “reproduction ON position” where the power is turned on in the playback mode. 3 positions can be switched. In place of the power switch (hereinafter referred to as a power combined mode switch) 20 as in this example, a power switch only for power ON / OFF and mode switching means such as a mode dial for switching between a still image shooting mode and a playback mode are provided. It may be provided.
[0019]
FIG. 2 is an external view of the back side of the digital camera 10. On the back of the digital camera 10, a viewfinder 28, a liquid crystal monitor 30, a zoom switch 32, a multifunction cross button 34, an AE lock button 36, a menu key 38, an execution key 40, and a cancel key 42 are provided. The liquid crystal monitor 30 is a display unit that can be used as an electronic viewfinder for checking the angle of view at the time of shooting, and can display a preview image of the shot image, a reproduced image read from the memory card 24, an AF auxiliary light diffusion region, and the like. Further, menu selection using the cross button 34 and setting of various items in each menu are also performed using the display screen of the liquid crystal monitor 30.
[0020]
The zoom switch 32 is composed of a lever switch that can be operated in the vertical direction. The zoom switch 32 is zoomed in the telephoto (TELE) direction by operating the switch in the upward direction, and in the wide angle (WIDE) direction by operating in the downward direction. Move the zoom. The cross button 34 can input instructions in the corresponding four directions (up, down, left, right) by pressing one of the top, bottom, left, and right edges. It is used as an operation button for instructing selection and change of setting contents, and as a means for instructing electronic zoom magnification adjustment and playback frame return / return.
[0021]
The menu key 38 is used when transitioning from the normal screen to the menu screen in each mode. The execution key 40 is used for confirming the selection contents and instructing execution (confirmation) of processing. The cancel key 42 is used when canceling (cancelling) an item selected from the menu or returning to the previous operation state.
[0022]
The photographer operates the zoom switch 32 to determine the angle of view while confirming the real-time image (through image) displayed on the finder 28 or the liquid crystal monitor 30, and depresses the shutter button 18 to perform photographing.
[0023]
FIG. 3 is a block diagram showing the internal configuration of the digital camera 10. The photographing lens 12 includes a four-group inner focus zoom lens including a fixed lens 44, a variable power lens 46A, a correction lens 46B, and a focus lens 48.
[0024]
The zoom lens 46A and the correction lens 46B move along the optical axis while the positional relationship between them is regulated by a cam mechanism (not shown) to change the focal length. For convenience of explanation, the variable power optical system including the variable power lens 46A and the correction lens 46B is referred to as a “zoom lens 46”.
[0025]
The light that has passed through the photographing lens 12 is incident on a CCD image sensor (hereinafter referred to as CCD) 52 after the amount of light is adjusted by the diaphragm 50. Photosensors are arranged in a plane on the light receiving surface of the CCD 52, and a subject image formed on the light receiving surface of the CCD 52 via the photographing lens 12 has an amount of signal charge corresponding to the amount of incident light by each photosensor. Is converted to The CCD 52 has a so-called electronic shutter function that controls the charge accumulation time (shutter speed) of each photosensor according to the timing of the shutter gate pulse.
[0026]
The signal charge accumulated in each photosensor is sequentially read out as a voltage signal (image signal) corresponding to the signal charge based on a pulse given from the CCD driver 54. The image signal output from the CCD 52 is sent to the analog processing unit 56. The analog processing unit 56 includes signal processing circuits such as a sampling hold circuit, a color separation circuit, and a gain adjustment circuit. The analog processing unit 56 performs correlated double sampling (CDS) processing and R, G, B color signals. Color separation processing is performed, and signal level adjustment (pre-white balance processing) of each color signal is performed.
[0027]
The signal output from the analog processing unit 56 is converted into a digital signal by the A / D converter 58 and then stored in the memory 60. The timing generator (TG) 62 gives timing signals to the CCD driver 54, the analog processing unit 56, and the A / D converter 58 in accordance with instructions from the CPU 64, and the circuits are synchronized by this timing signal. .
[0028]
The data stored in the memory 60 is sent to the signal processing unit 68 via the bus 66. The signal processing unit 68 is an image processing unit composed of a digital signal processor (DSP) including a luminance / color difference signal generation circuit, a gamma correction circuit, a sharpness correction circuit, a contrast correction circuit, a white balance correction circuit, and the like. The image signal is processed according to the command.
[0029]
The image data input to the signal processing unit 68 is converted into a luminance signal (Y signal) and a color difference signal (Cr, Cb signal) and is subjected to predetermined processing such as gamma correction and then stored in the memory 60. Is done. When the captured image is displayed and output, the image data is read from the memory 60 and transferred to the display memory 70. The data stored in the display memory 70 is converted into a predetermined display signal (for example, an NTSC color composite video signal), and then the liquid crystal monitor (LCD) 30 via the D / A converter 72. Is output. Thus, the image content of the image data is displayed on the screen of the liquid crystal monitor 30.
[0030]
The image data in the memory 60 is periodically rewritten by the image signal output from the CCD 52, and the video signal generated from the image data is supplied to the liquid crystal monitor 30, whereby the image input via the CCD 52 is real-time. Is displayed on the liquid crystal monitor 30. The photographer can confirm the shooting angle of view with an image (through image) displayed on the liquid crystal monitor 30 or the optical viewfinder 28.
[0031]
When the photographer operates the zoom switch 32, the instruction signal is input to the CPU 64, and the CPU 64 controls the zoom drive unit 74 based on the signal from the zoom switch 32 to move the zoom lens 46 in the tele (TELE) direction or wide ( WIDE) direction. The zoom driving unit 74 includes a motor (not shown), and the zoom lens 46 is driven by the driving force of the motor. The position (zoom position) of the zoom lens 46 is detected by a zoom position sensor 76, and a detection signal from the sensor 76 is input to the CPU 64.
[0032]
Similarly, the focus driving unit 78 includes a motor (not shown), and the focus lens 48 moves back and forth along the optical axis by the driving force of the motor. The position (focus position) of the focus lens 48 is detected by a focus position sensor 80, and a detection signal from the sensor 80 is input to the CPU 64.
[0033]
When the still image shooting mode is set by the power mode switch 20 and the shutter button 18 is pressed, a shooting start instruction (release ON) signal is issued. The CPU 64 detects the release ON signal and executes a recording imaging operation. That is, the CPU 64 controls the focus drive unit 78 based on the result of evaluation value calculation described later to move the focus lens 48 to the in-focus position, and controls the aperture diameter of the diaphragm 50 and the electronic shutter of the CCD 52. Perform exposure control. Further, the CPU 64 sends a command to the strobe control circuit 82 as necessary to control the light emission of the slot light emitting unit 16. Details of the strobe light emitting unit 16 and the strobe control circuit 82 will be described later.
[0034]
In this way, in response to the pressing operation of the shutter button 18, the capturing of the image data for recording is started. When the mode for compressing and recording image data is selected, the CPU 64 sends a command to the compression / decompression circuit 84. The compression / decompression circuit 84 compresses the image data taken into the memory 60 in accordance with JPEG or another predetermined format.
[0035]
The compressed image data is recorded on the memory card 24 via the card interface 86. When the mode for recording non-compressed image data (non-compression mode) is selected, the compression processing by the compression / decompression circuit 84 is omitted, and the image data is recorded on the memory card 24 without being compressed.
[0036]
When the playback mode is set by the power mode switch 20, the image file is read from the memory card 24. The read image data is decompressed by the compression / decompression circuit 84 as necessary, and is output to the liquid crystal monitor 30 via the display memory 70.
[0037]
The CPU 64 is a control unit that performs overall control of each circuit of the camera system. The CPU 64 controls the operation of the corresponding circuit based on input signals received from the power mode switch 20, shutter button 18, zoom switch 32, and other operation units, and controls the strobe, display control on the liquid crystal monitor 30, and autofocus. (AF) control, automatic exposure (AE) control, and the like are performed.
[0038]
The ROM 59 stores programs and data values for performing various controls.
[0039]
Here, the autofocus control will be described. The image signal converted into a digital signal by the A / D converter 58 is input to the evaluation value calculation unit 88. The evaluation value calculation unit 88 includes a high frequency component extraction circuit 90 and an integration circuit 92. The evaluation value calculation unit 88 samples the G component data in the input image signal and performs high frequency in an AF detection target area (hereinafter referred to as a focus area). The component is extracted and its absolute value is taken, and a value (equivalent to an evaluation value) obtained by integrating the absolute value data in the focus area is provided to the CPU 64.
[0040]
During the AF operation, the CPU 64 moves the focus lens 48 in the focus adjustment area from the nearest to infinity (or from infinity to the nearest) direction as shown in FIG. Then, the contrast of the central portion of the image is detected, and an evaluation value (indicated by a black circle) is calculated for each search point as shown in FIG. Then, by combining the evaluation values calculated at each point, the lens position where the evaluation value is maximum is determined as the in-focus position, and the focus driving unit 78 is moved so as to move the focus lens 48 to the obtained in-focus position. Control. If the evaluation value cannot be calculated because the contrast in the center of the image is not clear or dark, the size of the irradiation area on the subject by AF auxiliary light irradiation, which will be described later, is evaluated and it is considered to be closest to the in-focus position The focus driving unit 78 is controlled to move the focus lens 48 to the position.
[0041]
Next, the strobe light emitting unit 16 will be described.
[0042]
The strobe light emitting unit 16 has a strobe light source unit 100 as shown in FIG. 5A is a cross-sectional view of the strobe light source unit 100, and FIG. 5B is a front view of the strobe light source unit 100.
[0043]
The strobe light source unit 100 includes a reflector 102, LED groups 104 (R, G, and B LEDs 104R, 104G, and 104B), and a diffusion plate 106. A large number of R, G, and B LEDs 104R, 104G, and 104B are arranged in an array as shown in FIG. Further, the diffusion plate 106 diffuses light having high directivity emitted from the LED group 104 so as to be uniform. Note that the number of LEDs 104R, 104G, and 104B does not have to be the same. For example, it is preferable that the LEDs 104R, 104G, and 104B are arranged in such a ratio that white light is emitted when the LEDs 104R, 104G, and 104B are fully lit.
[0044]
FIG. 6 is a block diagram of a strobe device including the strobe light emitting unit 16, the strobe control circuit 82, and the like.
[0045]
In addition to the light control sensor 17 for light control and the LED group 104, the strobe device includes a voltage up-converter 112 supplied with power from a battery 110, a large-capacitance capacitor 114, an operational amplifier, as shown in FIG. 116, 118, 120, a controller 122, a dimming circuit 124, and a temperature sensor 126 are provided.
[0046]
The controller 122 performs overall control of the strobe device, controls the voltage up-converter 112, boosts the voltage of the battery 110 (for example, 6V) to about 10V, and charges the capacitor 114 with the boosted voltage. The capacitor 114 is charged for a long time of about 2 to 5 seconds, for example, and can continuously supply current to the LED group 104 for 1/60 seconds (about 16 milliseconds) or longer.
[0047]
The electrical energy stored in the capacitor 114 is supplied to the R, G, and B LEDs 104R, 104G, and 104B via the operational amplifiers 116, 118, and 120. The controller 122 controls the operational amplifiers 116, 118, and 120. , R, G, and B LEDs 104R, 104G, and 104B are controlled in light emission time and light emission amount.
[0048]
The controller 122 takes in various signals from the CPU 64 shown in FIG. 3 such as charging start, a light emission signal synchronized with the shutter button 18, a light emission amount, and a signal indicating the light emission timing. Since the light amount of the LED varies depending on the ambient temperature, a temperature sensor 126 for detecting the ambient temperature of the LED group 104 is provided, and the controller 122 detects the ambient temperature of the LED group 104 detected by the temperature sensor 126. Based on this, current control to the LED group 104 is performed so that a required light emission amount can be obtained regardless of the ambient temperature.
[0049]
Next, operations of the CPU 64 and the controller 122 when flash light (hereinafter referred to as “shooting auxiliary light”) is emitted from the flash light emitting unit 16 during flash photography will be described.
[0050]
First, for example, the CPU 64 outputs a charge start signal to the controller 122 when the camera power is turned on. When this charge start signal is input, the controller 122 outputs a signal instructing charging to the voltage up-converter 112 and the capacitor 114 When charging is started and charging of the capacitor 114 is completed, the charging operation by the voltage up-converter 112 is stopped, and the CPU 64 is notified of the completion of charging.
[0051]
Thereafter, when the shutter button is half-pressed, the controller 122 takes in information for determining the flash emission amount such as a guide number from the CPU 64. Thereafter, when the shutter button is fully pressed and the shutter is opened, the CPU 64 outputs a light emission signal synchronized with the shutter opening to the controller 122, and the controller 122 performs control indicating predetermined R, G, and B light emission levels by this light emission signal. The signals are output to the positive inputs of operational amplifiers 116, 118, and 120, respectively. Signals corresponding to the current values flowing through the LEDs 104R, 104G, and 104B are added to the negative inputs of the operational amplifiers 116, 118, and 120. The operational amplifiers 116, 118, and 120 have predetermined R, G, and B light emission levels. Control is performed so that a corresponding constant current flows through each of the LEDs 104R, 104G, and 104B.
[0052]
Thereby, the LED group 104 emits photographing auxiliary light having a required light amount.
[0053]
When photographing auxiliary light is emitted from the LED group 104, the light control circuit 124 detects the light emission amount via the light control sensor 17. When the detected light emission amount matches the reference value for adjusting the light emission amount, a light emission stop signal is output to the controller 122 in order to stop the light emission. When the light emission stop signal is input from the dimming circuit 124, the controller 122 outputs a control signal for stopping the light emission of the LED group 104 to the operational amplifiers 116, 118, and 120. Thereby, the electric current which flows into LED group 104 is interrupted | blocked, and light emission of LED group 104 stops.
[0054]
Next, operations of the CPU 64 and the controller 122 when the strobe device is used as AF auxiliary light emitting means will be described.
[0055]
First, when the shutter button 18 is half-pressed, the CPU 64 performs AE control and AF control, and locks AF and AE while the shutter button 18 is half-pressed.
[0056]
Here, in the AE control, R, G, and B signals are taken, subject luminance (shooting EV value) is obtained based on an integrated value obtained by integrating these R, G, and B signals, and shooting is performed based on the taken EV value. Determine the aperture value and shutter speed. The aperture 50 is controlled so that the determined aperture value is obtained when the shutter button 18 is fully pressed, and the charge accumulation time is controlled by the electronic shutter so that the determined shutter speed is achieved.
[0057]
Further, in the AF control, the focus lens 48 is moved to the in-focus position by the contrast AF described with reference to FIG. 4, but the CPU 64 detects that the brightness of the subject (shooting EV value) is equal to or less than a predetermined value. To emit AF auxiliary light.
[0058]
Hereinafter, the emission timing of the AF auxiliary light, the measurement of the area of the light in the subject irradiated with the AF auxiliary light, the timing of driving the motor in the focus driving unit 78, and the like will be described with reference to FIGS.
[0059]
First, as shown in FIG. 7A, when the shutter button is half-pressed, AE processing is performed as described above (FIG. 7D), and the brightness of the subject is measured (step of FIG. 10). 202).
[0060]
Next, it is determined whether or not the brightness of the subject is equal to or greater than a predetermined value (step 204 in FIG. 10). Here, the CPU 64 refers to the result of the AE process described above to determine whether the state of the captured image signal including the desired subject is dark. The criterion for determining whether or not the image is dark at this time is a criterion such as luminance information indicating whether or not the AF auxiliary light needs to be emitted when performing AF processing, and is set in advance based on, for example, experimentally acquired data or the like It is what has been. This reference value is stored in advance in the ROM 59, and the CPU 64 refers to the reference value read from the ROM 59 when executing the processing of step 204, and compares this with the AE processing result.
[0061]
If the brightness of the subject is greater than or equal to the predetermined value in step 204, the normal contrast AF operation can be performed without emitting the AF auxiliary light, so the normal contrast AF operation is performed (FIG. 10). Step 218).
[0062]
If the subject brightness is less than or equal to a predetermined value in step 204, AF auxiliary light is emitted for a predetermined light emission period (FIG. 7E, step 206 in FIG. 10). The light emission period of the AF auxiliary light is within a light reception period in which the CCD 52 receives subject light in order to obtain an image signal.
[0063]
Note that the amount of AF auxiliary light may be smaller than the emission amount of the photographing auxiliary light as long as an evaluation value necessary for the contrast AF and AF auxiliary light diffusion region size evaluation is obtained (FIG. 7C). The exposure due to the irradiation of the AF auxiliary light may not be the exposure determined in the above AE, but may be the aperture value and the exposure time during AF. The amount of light emitted from the strobe light emitting unit 16 is controlled by controlling the current applied to the LED group 104 or the number of elements that selectively emit light.
[0064]
Subsequently, an image signal for obtaining an evaluation value is fetched from the focus area of the CCD 52 (FIG. 7F), and it is determined whether or not the evaluation value can be obtained from the image signal (step 208 in FIG. 10). Acquisition of an evaluation value depends on whether a value greater than a predetermined value can be acquired, that is, whether a high-frequency component greater than a predetermined value can be acquired. When obtaining the evaluation value, as shown in FIG. 4B, the focus motor is driven to move the focus lens by a predetermined amount (move to the next search point) (FIG. 7G).
[0065]
While the focus lens is moving, AF auxiliary light is emitted substantially, and an image signal is captured from the CCD 52. As shown in FIG. 4B, an image signal is captured from the CCD 52 for each search point while the focus lens is moved in the focus adjustment region from close to infinity (or from infinity to close).
[0066]
When the evaluation value based on the image signal at each search point is calculated, the calculated evaluation values are combined to calculate the lens position where the evaluation value is maximized. When the maximum evaluation value cannot be obtained or when an evaluation value equal to or greater than a predetermined value cannot be obtained, it is determined that focusing is impossible (step 208), and the measurement of the size of the irradiation area of the subject with the AF auxiliary light is started (step 208). 210).
[0067]
When measuring the size of the irradiation area, an image signal when the focus lens is set to the center position in the focus adjustment area is used among the image signals captured when the focus lens is moved in the focus adjustment area. An image in which the subject is irradiated with AF auxiliary light from the captured image signal is displayed on the LCD 30. The LCD 30 has a luminance resolution of 32 × 32 (or 16 × 16), and the LCD 30 is divided into regions (32 × 32 or 16 × 16) corresponding to the luminance resolution. An image in which the subject is irradiated with the auxiliary light is displayed on the LCD 30, and the number of areas occupied by the bright area (AF auxiliary light diffusion area) is measured.
[0068]
As a result of the measurement, the distance between the camera 10 and the subject is obtained from the number of evaluated areas by referring to the distance table (step 212). The distance table is stored in the CPU 64 or the ROM 59. FIG. 8 is a diagram illustrating an example in which a diffusion region of AF auxiliary light emitted from the camera 10 and emitted to the subject is displayed on the LCD 30. A photographed image on the LCD 30 when the subject is located 1 m away from the camera 10, a photographed image on the LCD 30 when the subject is located 2 m away from the camera 10, and the subject is located 3 m away from the camera 10. A photographed image on the LCD 30 in this case is shown as an example. The farther the subject is, the more diffusive directional AF auxiliary light that is emitted is diffused, so that the irradiated image on the LCD 30 has a larger area. The distance table is a correlation table between the number of irradiated areas and the distance from the camera 10 to the subject. By preparing this correlation table in advance, the approximate distance can be known if the number of irradiation areas is known. It has become. In the distance table, in addition to distances of 1 m, 2 m, and 3 m determined from the number of irradiation areas, 0.5 m, 1.5 m, 2.5 m, 3.5 m, and the like can be prepared.
[0069]
In the case of a camera equipped with a zoom lens, the area size when the auxiliary light is irradiated in the screen differs depending on the zoom magnification, so a table that shows the distance from the zoom value and the irradiation area as shown in FIG. 9 is prepared. Has been. For example, in the case of the zoom value a and the area size A, the distance E is estimated. This table is also stored in the CPU 64 or the ROM 59.
[0070]
If the distance from the camera 10 to the subject is estimated, the distance is estimated as the in-focus position, the focus lens is moved to the in-focus position, and the AF operation is terminated (step 214).
[0071]
Thereafter, when the shutter button is fully pressed (FIG. 7B), photographing auxiliary light having a required light emission amount is emitted as described above (FIGS. 7C and 7E). When the photographing auxiliary light is emitted in this way, an image signal indicating the subject photographed by the photographing auxiliary light is taken from the CCD (FIG. 7F, step 220 in FIG. 10).
[0072]
In step 208, an evaluation value based on the image signal at each search point is calculated, and when the lens position that maximizes the evaluation value is calculated by combining the calculated evaluation values, it is determined that focusing is possible. Then, a contrast AF operation using normal auxiliary light is performed (step 216 in FIG. 10). When the in-focus positions are obtained in steps 218 and 216, the focus lens is moved to the in-focus positions, and the AF operation is terminated (step 214).
[0073]
According to the present embodiment, when the subject is irradiated with AF auxiliary light, the AF operation is performed by estimating the distance from the camera to the subject even when the subject is particularly dark or the contrast is low. Images can be recorded.
[0074]
As the strobe light emitting means, instead of the R, G, B LEDs 104R, 104G, 104B, an organic electroluminescence panel (organic EL panel), a plasma light emitting element panel in which plasma light emitting elements are arranged in an array, light emission An LED having a milky white color or a xenon tube can be applied.
[0075]
【The invention's effect】
According to the present invention, it is possible to obtain a captured image having a practical level of focus even for a low-brightness, low-contrast subject.
[Brief description of the drawings]
FIG. 1 is an external view of a digital camera to which the present invention is applied.
FIG. 2 is an external view of the back side of the digital camera.
FIG. 3 is a block diagram showing an internal configuration of the digital camera.
4A is a diagram illustrating a state in which an evaluation value is calculated for each search point, and FIG. 4B is a diagram illustrating a plurality of AF detection points while the focus lens is moved in the focus adjustment region from the closest to infinity direction. The figure which showed the state which detects the contrast of the image center part.
FIG. 5 is a diagram showing a structure of a strobe light source provided in a strobe light emitting unit.
FIG. 6 is a block diagram of a strobe device including a strobe light emitting unit and a strobe control circuit.
FIG. 7 is a timing chart used to explain the emission timing of AF auxiliary light, the timing of motor drive in the focus drive section, and the like.
FIG. 8 is a diagram illustrating an example in which a diffusion region of AF auxiliary light emitted from a camera and irradiated on a subject is displayed on an LCD.
FIG. 9 is a table showing a distance from a zoom value and an irradiation area.
FIG. 10 is a flowchart showing a flow from luminance measurement to AF auxiliary light emission, light area measurement in an object irradiated with AF auxiliary light, photographing, and the like.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Digital camera, 12 ... Shooting lens, 16 ... Strobe light emission part, 17 ... Light control sensor, 18 ... Shutter button, 48 ... Focus lens, 52 ... CCD, 78 ... Focus drive part, 80 ... Focus position sensor, 82 ... Strobe control circuit, 88 ... evaluation value calculation unit, 90 ... high frequency component extraction circuit, 92 ... integration circuit, 100 ... strobe light source unit, 102 ... reflective umbrella, 104 ... LED group, 104R ... R LED, 104G ... G LED 104B ... B LED 106 ... Diffusion plate

Claims (7)

The photographic lens is moved over the focus adjustment range, and an evaluation value corresponding to the contrast component of the subject is obtained based on the image signal output from the imaging means every time the photographic lens moves by a predetermined amount, and the moving position of the photographic lens An automatic focus adjustment device for a camera that obtains a movement position where an evaluation value reaches a peak based on the evaluation value obtained for each movement position, and moves a photographing lens to the obtained movement position,
AF auxiliary light emitting means for emitting AF auxiliary light;
Diffusion region evaluation means for evaluating the size of the AF auxiliary light diffusion region in the subject irradiated with the emitted AF auxiliary light;
A distance calculating means for obtaining a distance from the evaluated AF auxiliary light diffusion region to the subject;
Photographing lens moving means for moving the photographing lens to a movement position corresponding to the calculated distance;
The camera's autofocus device. 2. The automatic focus adjustment apparatus for a camera according to claim 1, wherein when the photographing lens is a zoom lens, the distance calculation means obtains a distance to a subject from a zoom magnification and the size of the evaluated AF auxiliary light diffusion region. The AF auxiliary light emitting means is shared with a light emitting means for emitting photographing auxiliary light at the time of flash photography, and the light emitting means is constituted by any one of a light emitting diode, an organic electroluminescence, and a plasma light emitting element. 3. The automatic focusing apparatus for a camera according to claim 1, wherein the automatic focusing apparatus is a camera. The AF auxiliary light emitting means controls the current applied to the light emitting element or the number of selectively emitting elements to reduce the light amount of the AF auxiliary light from the light amount of the photographing auxiliary light. The automatic focusing apparatus for a camera according to claim 3. The photographic lens is moved over the focus adjustment range, and an evaluation value corresponding to the contrast component of the subject is obtained based on the image signal output from the imaging means every time the photographic lens moves by a predetermined amount, and the moving position of the photographic lens Based on the evaluation value obtained for each movement position, a movement position at which the evaluation value reaches a peak is obtained, and an automatic focus adjustment method of the camera for moving the photographing lens to the obtained movement position,
Emitting AF auxiliary light;
Evaluating the size of the AF auxiliary light diffusion region in the subject irradiated with the emitted AF auxiliary light; and
Obtaining a distance from the size of the evaluated AF auxiliary light diffusion region to the subject;
Moving the taking lens to a moving position corresponding to the obtained distance;
An automatic focusing method for a camera. 6. The automatic focusing method of a camera according to claim 5, wherein when the photographing lens is a zoom lens, the distance to the subject is calculated from a zoom magnification and the evaluated size of the AF auxiliary light diffusion region. An automatic focusing device for a camera,
AF auxiliary light emitting means for emitting AF auxiliary light;
Diffusion region evaluation means for evaluating the size of the AF auxiliary light diffusion region in the subject irradiated with the emitted AF auxiliary light;
A distance calculating means for obtaining a distance from the evaluated AF auxiliary light diffusion region to the subject;
Photographing lens moving means for moving the photographing lens to a movement position corresponding to the calculated distance;
The camera's autofocus device.

Images