JP4320767B2 - Automatic focusing apparatus and method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an automatic focus adjustment apparatus and method, and more particularly to a technique for detecting a high-frequency component of an image based on an output signal from an image sensor and performing autofocus (AF) control using the detection result. .
[0002]
[Prior art]
A video camera that picks up an image of a subject and outputs the video signal is picked up while moving the focus lens that affects focus adjustment in the photographic optical system, and extracts high-frequency components from the output video signal for focusing. The evaluation value of is calculated. If the evaluation value increases as a result of the movement of the focus lens, it continues to drive in the same direction. Conversely, if the evaluation value decreases as the lens moves, it is driven in the opposite direction to search for the peak of the evaluation value. The so-called “mountain climbing servo system” is employed.
[0003]
Also, in the digital still camera, a “contrast AF method” is employed in which the focus lens is driven from close to the infinite distance of the subject, and the focus lens is driven and focused at the point where the evaluation value is maximized. . As for detecting the in-focus state from the evaluation value acquisition result, it is determined whether the contrast is low from the maximum value and the minimum value of the imaging signal (JP-A-6-125493), or the evaluation value is continuous. Thus, there has been proposed a method (Japanese Patent Laid-Open No. 2000-152065) that detects a decrease and determines a focus position (peak position).
[0004]
[Problems to be solved by the invention]
However, in the conventionally proposed method, when there are a plurality of subjects having different distances in the focus area, a plurality of evaluation value peaks may occur, and only from the decreasing tendency around the evaluation value peak, There is a problem that an accurate in-focus position cannot be determined.
[0005]
The present invention has been made in view of such circumstances, and it is an object of the present invention to provide an automatic focus adjustment apparatus and method capable of high-speed and accurate focusing even when a plurality of subjects having different distances exist. .
[0006]
[Means for Solving the Problems]
  In order to achieve the above object, the present invention provides an automatic focusing apparatus that adjusts the focal position of a lens that forms an image of a subject on the imaging unit based on an image signal output from the imaging unit. A lens moving means for moving the lens within the focus adjustment region; and a contrast component of the subject is extracted from an image signal output from the imaging means, and an evaluation value corresponding to the contrast component is obtained for each moving position of the lens. An evaluation value calculating means for calculating each lens, a control means for controlling the lens moving means to move the lens to each position for obtaining the evaluation value, and a predetermined amount w or more from an end point of the focus adjustment region Evaluation value change detection means for detecting a change in the evaluation value at a distant lens position, evaluation values at each position obtained by the evaluation value calculation means, and the evaluation value change detection means Determination means for determining the in-focus state based on a detection result, and in automatic focus adjustment in still image shooting, the control means moves the lens from one end point of the focus adjustment area, and After detecting that there is a peak from the increase / decrease in the evaluation value acquired along with the movement, the lens is moved to further acquire the evaluation value, and is separated from the position of the lens where the peak is detected by a certain amount d. When the evaluation value at the lens position is equal to or less than a predetermined threshold, the interruption of the movement of the lens is determined, and when the evaluation value at the lens position exceeds a predetermined threshold, the continuation of the movement of the lens is determined, When the movement of the lens is continued, if the remaining detection amount to the other end point of the focus adjustment area is equal to or greater than the predetermined amount w, it is determined to continue the evaluation value acquisition process, and the remaining detection There wherein less than a predetermined amount w, when the increase of the evaluation value in the lens position distant a predetermined amount w from the end point of the focusing area is not detected in the movement of the lensInterruptionAnd when the increasing tendency of the evaluation value is detected, the movement of the lensContinuedAnd when the plurality of evaluation value peaks are detected, the determination unit determines that the lens position where the maximum value of the evaluation value is detected is an in-focus position, and the lens moving unit determines the in-focus state. The lens is moved to a position.
[0007]
  That is, an evaluation value is acquired at each position while moving a lens (focus lens) for performing focus adjustment within the focus adjustment range. The AF speed can be increased by evaluating the suitability of the peak determination based on the evaluation value at the lens position that is a certain amount or more away from the peak position after the peak of the evaluation value is detected. Accurate focusing is possible even when there are multiple subjects with different sizes, and so-called “out of focus” can be prevented..
[0008]
  That is,The determination means compares an evaluation value at a position away from the lens position where the peak is obtained by a predetermined amount d with a predetermined threshold value, and when the evaluation value is equal to or less than the threshold value, It is determined that the in-focus state can be obtained at the lens position where the peak of the evaluation value is obtained or at a position in the vicinity thereofbe able to.
[0009]
  If the evaluation value at the lens position that is a fixed amount away from the position where the evaluation value is maximum (peak position) is larger than the threshold, it can be determined that there are multiple subjects, and the evaluation value acquisition operation (AF search) is continued. By doing so, accurate focus adjustment becomes possible. If the evaluation value at the lens position that is a certain amount away from the peak position is equal to or less than the threshold value, it can be determined that there is no subject ahead, and the AF search is interrupted at that time to speed up the AF process. be able to.Further, if the evaluation value at a position away from the end point of the focus adjustment range by a predetermined amount w does not tend to increase, it is determined that there is no subject ahead, and the lens is brought into the in-focus position (the maximum evaluation value is obtained). By moving the lens to (lens position), a focused state can be obtained without moving the lens to the end point, and the speed of automatic focus adjustment can be increased.
[0010]
According to another aspect of the present invention, the control means includes a first search operation in which the interval between the lens positions for obtaining the evaluation value in the focus adjustment region is relatively large, and during the first search control. And a second search operation for obtaining the evaluation value at a small interval, and the determination means performs the determination at the time of the first search operation.
[0011]
That is, first, a first search operation (rough search) with a large search point interval (search step) is performed, and the vicinity of the resulting peak is searched in detail by a second search operation (detailed search) with a small search step. By doing so, an accurate in-focus position is obtained. When such a control method is adopted, an unnecessary search range can be omitted and the AF process can be speeded up by performing the focus determination by the determination means in the first search operation with a large search step. .
[0012]
  Also, ContractClaim1Includes the described autofocus deviceElectronic camera is also preferable.
[0015]
  In order to provide an automatic focus adjustment method that achieves the above object, the present invention provides an automatic focus adjustment that adjusts a focus position of a lens that forms an image of a subject on the image pickup means based on an image signal output from the image pickup means. In the method, the method includes a lens moving step of moving the lens within a focus adjustment region, extracting a contrast component of the subject from an image signal output from the imaging unit, and obtaining an evaluation value corresponding to the contrast component. An evaluation value calculating step for calculating for each moving position of the lens; a control step for controlling the lens moving means to move the lens to each position for acquiring the evaluation value; and An evaluation value change detecting step for detecting a change in the evaluation value at a lens position separated by a predetermined amount w or more from the end point; an evaluation value at each position obtained by the evaluation value calculating means; A determination step of determining an in-focus state based on a detection result of the evaluation value change detection means, and in the automatic focus adjustment in still image shooting, the control step starts from one end point of the focus adjustment region. The position of the lens where the peak is detected after moving the lens to further obtain the evaluation value after it is detected that there is a peak from the increase / decrease in the evaluation value acquired along with the movement of the lens. If the evaluation value at a lens position that is a predetermined amount d away from the lens is less than or equal to a predetermined threshold value, interruption of the movement of the lens is determined, and if the evaluation value at the lens position exceeds a predetermined threshold value, When it is determined to continue the movement and the movement of the lens is continued, the evaluation value acquisition process is continued if the remaining detection amount to the other end point of the focus adjustment area is equal to or greater than the predetermined amount w. Constant, and the less than the rest of the detected amount is the predetermined amount w, of the movement of the lens when the increase of the evaluation value in the lens position distant a predetermined amount w from the end point of the focusing area is not detectedInterruptionAnd when the increasing tendency of the evaluation value is detected, the movement of the lensContinuedAnd when the plurality of evaluation value peaks are detected, the determination step determines that the lens position where the maximum value of the evaluation value is detected is an in-focus position, and places the lens at the in-focus position. It is characterized by being moved.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Preferred embodiments of an automatic focusing apparatus and method according to the present invention will be described below with reference to the accompanying drawings.
[0017]
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, and a strobe light emitting unit 16 are provided on the front surface of the digital camera 10, and a shutter button 18 and a power switch 20 are disposed 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.
[0018]
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 automatic focus (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 the state of “full press”, which is further pressed from “half press”.
[0019]
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. May be provided.
[0020]
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 means 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, 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.
[0021]
The zoom switch 32 is composed of a lever switch that can be operated in the up / down direction. By operating the switch in the upward direction, the zoom switch 32 is zoomed in the telephoto (TELE) direction, and operated in the downward direction in the wide angle (WIDE) 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.
[0022]
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.
[0023]
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.
[0024]
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.
[0025]
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”.
[0026]
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.
[0027]
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.
[0028]
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. .
[0029]
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.
[0030]
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.
[0031]
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.
[0032]
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 ( Move in the (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.
[0033]
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.
[0034]
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.
[0035]
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.
[0036]
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.
[0037]
In the digital camera 10 of this example, for example, smart media (Solid-State Floppy Disk Card) is applied as means for storing image data. The form of the recording medium is not limited to this, and it may be a PC card, a compact flash, a magnetic disk, an optical disk, a magneto-optical disk, a memory stick, etc., and read / write according to an electronic, magnetic, optical, or a combination thereof. Various possible media can be used. A signal processing means and an interface corresponding to the medium to be used are applied. A configuration in which a plurality of media can be mounted regardless of different types or the same type of recording media may be adopted. The means for storing the image file is not limited to the removable medium that can be attached to and detached from the camera body, but may be a recording medium (internal memory) built in the digital camera 10.
[0038]
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.
[0039]
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 performs display control and autofocus (AF) on the liquid crystal monitor 30. Control and automatic exposure (AE) control are performed.
[0040]
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 describes an AF detection target area (denoted by reference numeral 94 in FIG. The high-frequency component in the area) is extracted and its absolute value is obtained, and the value (equivalent to the evaluation value) obtained by integrating the absolute value data in the focus area 94 is provided to the CPU 64.
[0041]
The target area for AF detection does not have to be the entire image area, and a partial area at the center of the image is set as the focus area 94 as shown in FIG. During the AF operation, the CPU 64 detects the contrast of the central portion of the image at a plurality of AF detection points (search points) while moving the focus lens 48 from infinity to close (or close to infinity) within the focus adjustment region. The evaluation value is calculated. 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.
[0042]
As the focal length of the photographic lens 12 becomes longer and the aperture diameter of the stop 50 becomes larger, the depth of field becomes shallower, and the amount of lens driving from infinity to the closest distance increases. FIG. 5 shows the relationship between the focal length of the photographic lens 12 and the focus adjustment region 300. The figure shows an example of the photographing lens 12 whose focal length can be changed stepwise from 7 mm to 21 mm. As the focal length of the photographing lens 12 becomes longer, the focus adjustment region 300 by the focus lens 48 becomes wider. For example, when the focal length is 7 mm, the movable range of the focus lens 48 from infinity to the nearest distance is 8.17 μm, and the focus adjustment region 300 when the focal length is 21 mm is 735 μm.
[0043]
The CPU 64 determines the AF step width 302 indicating the width of the lens position (search point) for calculating the evaluation value and the number of step steps (number of detection points) in accordance with the focus adjustment region 300 that varies in accordance with the focal length of the photographing lens 12. Set.
[0044]
As for the number of focus steps, the focus adjustment region 300 at each focal length may be equally divided by the AF step width 302, or the short-distance (closest limit) side AF step width 302 is shorter than the infinity side, The number of search points on the side may be increased to increase the focus accuracy.
[0045]
As shown in FIG. 5, as the focal length of the photographic lens 12 becomes longer, the focus adjustment area 300 becomes wider, and it becomes difficult to determine where the subject is in that area. Therefore, in the present embodiment, as shown in FIG. 6, the initial position and search direction of the AF search are changed according to the relationship between the current focus position and the focus adjustment area 300. That is, as shown in FIG. 6A, when the current position is on the far side from the intermediate position M of the focus adjustment region 300, first, focus driving is performed at infinity, and AF is performed from infinity toward the nearest. The search is executed and the evaluation value is acquired at each point. In the example of FIG. 9A, the evaluation value gradually increases with the focus movement by the AF search operation toward the closest direction (NEAR direction). Eventually, the evaluation value starts to decrease beyond the peak of the evaluation value, and the AF search is interrupted when a predetermined condition is satisfied. Then, the focus lens 48 is moved to a focus position (focus position) corresponding to the detected peak position to obtain a focus state.
[0046]
Conversely, as shown in FIG. 6B, when the current focus position is closer to the intermediate position M than the intermediate position M, first, the focus is driven to the closest side, and AF from the closest limit toward infinity is performed. Perform a search to obtain an evaluation value at each point. According to FIG. 5B, the evaluation value gradually increases with the focus movement by the search operation toward the infinity direction (FAR direction), and when the evaluation value starts to decrease beyond the peak and satisfies a predetermined condition. AF search is interrupted. Then, the focus lens is moved to a focus position (focus position) corresponding to the detected peak position to obtain an in-focus state.
[0047]
As described above, since the AF search direction is automatically selected according to the current focus position, the average time for driving the focus lens 48 to the search start position (initial position) can be shortened. In addition, when the shutter button 18 is half-pressed continuously, the subject distance hardly changes during this time, and the AF search time at the time of repetition becomes high.
[0048]
FIG. 7 shows a flowchart of AF control. When AF processing is started by half-pressing the shutter button 18, the CPU 64 first sets the focus area 94 (step S110). For example, the shooting screen is divided into 64 blocks of 8 × 8 with the same area, and a predetermined plurality of blocks in the center portion are set as the focus area 94 for evaluation value calculation.
[0049]
Next, the state of the “peak present flag” is cleared, and the peak present flag = OFF is set as an initial setting (step S112). Thereafter, the current value of the focal length of the photographic lens 12, that is, information on the current zoom position (ZOOMPOS) is acquired (step S114). After step S114, the process proceeds to step S116, and calculation processing for determining the initial position of the AF search is performed. The contents of the focus lens initial position calculation process will be described later with reference to FIG.
[0050]
In accordance with the result of the focus lens initial position calculation process in step S116 of FIG. 7, the focus lens 48 is moved to the initial position (step S118).
[0051]
In the subsequent step S120, an evaluation value at the current focus stage (search point) is calculated, and the obtained evaluation value is input to the CPU 64. The CPU 64 stores the evaluation value at the search point in a memory (not shown).
[0052]
Next, the process proceeds to step S122, and a process for determining whether or not to interrupt the AF search operation is performed. The contents of the interruption determination process will be described later with reference to FIG. Based on the result of the interruption determination process in step S122 of FIG. 7, the CPU 64 determines whether the AF search operation is continued / interrupted (step S124). In the case of “Continue”, the process proceeds to step S126, and it is determined whether or not the focus lens 48 has reached the final position of the search point.
[0053]
If NO is determined in step S126, the process proceeds to step S128, the focus lens 48 is moved from the current focus stage by one search step (AF step width 302), and the process returns to step S120. Thus, the evaluation value is calculated from the frame image data that is moved to the next search point and has a different focus position. The processing in steps S120 to S128 is repeated for each point in the focus adjustment area 300, and the evaluation value of each point is sequentially acquired.
[0054]
If the focus lens 48 has reached the final position in step S126, or if a determination of “interruption” is obtained in step S124, the process proceeds to step S130. In step S130, the position (focus position) at which the maximum evaluation value is obtained is obtained from the result of the evaluation value obtained at each point, and the focus lens 48 is moved to the focus position. The focus lens 48 is held at the in-focus position until the half-pressed state of the shutter button 18 is released. At the same time, the operation of the evaluation value calculation unit 88 is stopped, and the photographing / recording permission state is set (step S132). Thus, the automatic focus adjustment process ends.
[0055]
When the photographing and recording permission state is obtained, the operation state of the shutter button 18 is confirmed by the CPU 64, and the subject is imaged by the current zoom position and the focused focus position in response to the full depression of the shutter button 18. Image data that has undergone predetermined signal processing is recorded in the memory card 24 together with the attached information.
[0056]
FIG. 8 is a flowchart showing the procedure of the initial position calculation process. After step S114 described in FIG. 7, the process proceeds to a subroutine of FIG. 8 as step S116. In this initial position calculation process, first, information on the current focus position (P) is acquired (step S210). Next, after acquiring information on the near side position (N) and the infinity side position (I) that define the focus adjustment region 300 (step S212), an intermediate position M in the focus search range is expressed by the following equation (1):
[0057]
[Expression 1]
M = (I + N) / 2 (1)
(Step S214).
[0058]
Then, it is determined whether the current focus position (P) is on the infinity side or the near side with respect to the intermediate position M (step S216). If the current position is on the infinity side, the process proceeds to step S218. In step S218, the focus initial position that is the AF search start position is determined to be “infinity”, and the far lens driving direction during AF search is determined to be the direction from infinity toward the near side.
[0059]
On the other hand, in step S216, when the current position is on the near side, the process proceeds to step S220. In step S220, the focus initial position, which is the AF search start position, is determined to be “close”, and the far lens driving direction at the time of AF search is determined to be a direction from close to infinity. In FIG. 8, whether or not “P <M” is determined in step S216. If the current position matches the intermediate position M, the process proceeds to step S220, but the current position is the intermediate position. When the value coincides with M, the focus initial position may be set to the infinity side.
[0060]
When the focus initial position and the search direction are determined in step S218 or step S220, this subroutine is terminated and the process returns to the flowchart of FIG.
[0061]
Instead of the initial position calculation process described with reference to FIG. 8, a mode in which the initial focus position and the search direction are determined according to the current zoom position is also possible. In a camera equipped with a zoom function, when considering the shooting distance, the subject is often at a far distance on the telephoto side, and is often on the close side on the wide side. From this point of view, it is possible to perform a high-speed focus search by changing the focus search direction according to the focal length.
[0062]
FIG. 9 shows an example of the focus search direction at each zoom position. According to the figure, the photographing lens 12 can be stopped at eleven zoom positions from the wide end to the tele end, and a focus search direction is defined for each zoom position. When the current zoom position is in the range from the wide zoom position “0” to “4”, the initial focus position is set to the nearest (NEAR), and the search operation is performed from the nearest (NEAR) to infinity (FAR). I do. When the current zoom position is in the range of “5” to “10” on the tele side, the initial focus position is set to infinity (FAR), and the search operation is performed from infinity (FAR) to the nearest (NEAR). I do.
[0063]
A table as shown in FIG. 9 is stored in the non-volatile memory, and the search direction is determined with reference to the table at the start of the AF search. That is, the process proceeds to the subroutine shown in FIG. 10 as step S116 in FIG. 7. In step S310, the initial focus position and search direction are determined with reference to the table in FIG. It is also possible to return to the flowchart.
[0064]
Next, still another aspect of the initial position calculation process will be described.
[0065]
In FIG. 6 described above, it is determined whether the current focus position is on the infinity side or the close side with reference to the intermediate position M of the focus range. However, the reference position (switch It is also possible to change the position) according to the zoom position. For example, as shown in FIG. 11, the switching position M ′ is defined as a position of m% of the entire focus adjustment region starting from infinity, and this switching position coefficient m (%) is determined according to the zoom position. Prepare as a table in advance. Then, the switching position M ′ is determined with reference to the table from the current zoom position.
[0066]
As shown in FIG. 5A, when the current position is on the infinity side with respect to the switching position M ′, first, the focus is driven to infinity, and AF search is performed from infinity to the closest position. Get evaluation value with points.
[0067]
On the other hand, as shown in FIG. 11B, when the current focus position is closer to the switching position M ′, first, the focus drive is performed first, and the AF search is performed from the nearest distance to infinity. Run to get an evaluation value at each point.
[0068]
For example, on the wide side of the zoom, the intermediate position M (m = 50%) of the focus adjustment area is set as the switching position M ′, and the switching position M ′ is shifted to the closest side as the zoom moves to the telephoto side. By doing so, the probability that the initial focus position is on the infinity side increases as the zoom is on the tele side. Since it is considered that the subject is often at a long distance when shooting on the tele side, it is highly possible that the peak of the evaluation value can be detected early by starting the AF search from the infinity side. Combined with the AF search interruption process, the average AF process time can be further shortened.
[0069]
FIG. 12 is a flowchart of a calculation process for determining the initial focus position by changing the switching position M ′. Instead of the flowchart described in FIG. 8, the initial position calculation process shown in FIG. 12 can be applied. According to the figure, first, information on the current focus position (P) is acquired (step S410). Next, after acquiring information on the near side position (N) and the infinity side position (I) (step S412), the switching position M ′ is expressed by the following equation (2):
[0070]
[Expression 2]
M ′ = (IN) × m (2)
(Step S414). Here, m represents a switching position coefficient (%).
[0071]
Then, it is determined whether the current focus position (P) is on the infinity side or the near side with respect to the switching position M ′ (step S416). If the current position is on the infinity side, the process proceeds to step S418. In step S418, the initial focus position as the AF search start position is determined to be “infinity”, and the lens driving direction during the AF search is determined to be a direction from infinity toward the closest side.
[0072]
On the other hand, if it is determined in step S416 that the current position is on the near side, the process proceeds to step S420. In step S420, the focus initial position, which is the AF search start position, is determined to be “close”, and the lens driving direction during AF search is determined as a direction from close to infinity. When the focus initial position and the search direction are determined in step S418 or step S420, this subroutine is terminated and the process returns to the flowchart of FIG.
[0073]
As a modification of the form described in FIG. 12, a table as shown in FIG. 13 may be used. According to the figure, at the wide end of the zoom, regardless of the current focus position, it is set to always drive to the NEAR side during AF search and to perform the search operation from the near (NEAR) to infinity (FAR) direction. ing. Thereby, the AF search is always started from the NEAR side near the wide end.
[0074]
Further, in the zoom middle region, when the current focus position is on the infinity side from the switching position M ′ defined by the switching position coefficient (m), the FAR side is closer to the switching position M ′. The AF search is started from the NEAR side, and the AF search is always started from the FAR side near the tele end. As described above, by adopting a method of determining the AF search direction in consideration of the current zoom position and focus position in total, finer control becomes possible.
[0075]
Next, the contents of control when the AF search operation is interrupted will be described. FIG. 14 shows an example in which an evaluation value is acquired by AF search. When there is only one main subject in the focus area 94, only one evaluation value peak appears as shown in FIG. In this case, the focus lens 48 may be moved here with the lens position (P) where the peak is detected as the in-focus position. On the other hand, as shown in FIG. 15, when there are a plurality of subjects in the focus area 94, it is not possible to focus on both subjects, and focus is performed on one of the subjects. There is a need.
[0076]
FIG. 16 shows an example of an evaluation value acquisition result when there are a plurality of subjects in the focus area 94. As shown in the figure, when there are a plurality of subjects in the focus area 94, there are a plurality of peaks in the evaluation value curve. When detecting one mountain and ending the AF search, only one mountain can be detected, and a plurality of mountains cannot be detected. For example, in FIG. 16, when the AF search operation is started from the infinity side and the AF search operation is terminated when the peak at the infinity side is detected, another peak on the near side can be detected. Therefore, it is impossible to focus on the closest main subject.
[0077]
As another method, it is possible to focus on the first mountain by always starting the AF search operation from the closest side, but in the case of a high-power zoom lens, a situation where a subject at a long distance is photographed Therefore, it can be said that it is preferable to start the search from the infinity side in consideration of high speed AF processing.
[0078]
Therefore, in the present embodiment, the following measures are taken in order to realize an efficient AF search operation. That is, comparing FIG. 14 with FIG. 16, in the graph of FIG. 14, after the peak of the evaluation value was detected by the AF search operation from infinity to the closest distance, the evaluation value was further acquired by moving the lens in the same direction. In this case, when the focus lens 48 moves away from the peak position P by a certain distance d, the evaluation value decreases to near zero level. On the other hand, when there are a plurality of subjects as shown in FIG. 16, the first peak is detected. Since then, the evaluation value has started to increase again without falling to near zero level.
[0079]
Focusing on this fact, if the evaluation value at a position that is a fixed distance d away from the lens position where the peak of the evaluation value is detected is equal to or smaller than a predetermined threshold T, it is determined that there is no subject ahead, and AF When the search is finished, the focus lens 48 is driven to the detected first peak position.
[0080]
On the other hand, if the evaluation value at a position that is a certain distance d away from the lens position where the peak of the evaluation value is detected is a value larger than the predetermined threshold T, another subject may exist beyond that. And the AF search operation in the same direction is continued. The distance d from the peak position P is preferably set to about 10 to 20 times the allowable circle of confusion. When a plurality of peaks are detected by the AF search operation, the closest peak position is determined as the focus position.
[0081]
By the way, when the subject is dark, noise of the imaging signal is generated, and as shown in FIG. 17, there may be a situation where the evaluation value does not become the threshold value T or less even if there is only one peak. However, as can be seen from a comparison between FIG. 17 and FIG. 16, when another subject is present on the closest side (FIG. 16), there is a tendency for the evaluation value to increase from a position somewhat before the closest distance. On the other hand, if the evaluation value does not decrease due to noise or the like (FIG. 17), the evaluation value does not turn to an increasing trend even if it is a certain distance w or more before the closest distance.
[0082]
  Therefore, from the nearestPredetermined amountJudging whether the evaluation value is in an increasing direction at a distance greater than wInTherefore, it is possible to determine whether another subject exists on the close side. From the nearestPredetermined amountIf the evaluation value beyond w is not in the increasing direction, it is determined that there is no subject on the close side, and the AF search operation is terminated, and focus driving is performed at the lens position where the peak is detected. In addition,Predetermined amountIt is preferable to set w to about 5 to 10 times the allowable circle of confusion. Although the close side has been described with reference to FIG. 17, the AF search operation in the FAR direction is similarly performed from infinity.Predetermined amountIf the evaluation value does not tend to increase at a position separated by w, it can be determined that the subject exists on the infinity side.
[0083]
FIG. 18 is a flowchart of the interruption determination process. As a step S122 after the step S120 described with reference to FIG. When the interruption determination process starts, first, it is determined whether or not a peak whose evaluation value turns from increasing to decreasing is detected (step S510). This determination is made based on the state of a “peak present flag” described later.
[0084]
If no peak is detected in step S510 (NO determination), the process proceeds to step S512 to determine whether or not the evaluation value has decreased. If NO is obtained in step S512, it is determined to continue the evaluation value acquisition process (step S518), the present subroutine is terminated, and the process returns to the flowchart of FIG.
[0085]
If it is detected in step S512 that the evaluation value has decreased, the process branches to step S514. In step S514, it is determined whether or not the evaluation value before decreasing tends to increase. If YES is obtained in step S514, the “peak present flag” is set to ON and the data of the variable P indicating the focus position (peak position) where the peak is detected is updated (step S516). After step S516 or when NO determination is obtained in step S514, the process proceeds to step S518, and the continuation of the evaluation value acquisition process is determined.
[0086]
When the “peak flag” is set to ON, a YES determination is made in step S510. In this case, the process proceeds to step S520, and it is determined whether or not the search direction is the NEAR direction. When the search direction is the NEAR direction (when YES is determined), it is determined whether or not the current focus position (search point) is on the near side beyond a predetermined distance (d) from the peak position P ( Step S522). If the current position is within a predetermined distance d from the peak position P (NO determination), the process proceeds to step S528, and it is determined whether the number of remaining detection points in the search direction is smaller than a predetermined value (w). I do. The predetermined value w is a value corresponding to the distance w described in FIG.
[0087]
In step S528, when the number of remaining detection points is equal to or greater than the predetermined value w (NO determination), it is determined to continue the evaluation value acquisition process (step S532), and the process returns to the flowchart of FIG. On the other hand, when a YES determination is obtained in step S528, the process proceeds to step S530 to determine whether or not the evaluation value has increased.
[0088]
If an increase in the evaluation value is detected in step S530 (during YES determination), the process proceeds to step S532 to decide to continue the evaluation value acquisition process (step S532), but if the evaluation value has not increased in step S530 ( When the determination is NO, the process proceeds to step S536, where the interruption of the evaluation value acquisition process is determined, and the process returns to the main routine of FIG.
[0089]
Further, when the current focus position is on the near side beyond the predetermined distance d from the peak position P in step S522 (when YES is determined), the process branches to step S524. In step S524, it is determined whether or not the evaluation value at the current focus position is smaller than a predetermined threshold T.
[0090]
If the evaluation value is equal to or greater than the threshold T in step S524 (NO determination), the process proceeds to step S528 in consideration of the possibility that the subject is present closer to the current position. On the other hand, if the evaluation value is smaller than the threshold value T in step S524 (when YES is determined), it is determined that no subject is present closer to the current position, and interruption of the evaluation value acquisition process is determined ( Step S536).
[0091]
If NO in step S520, that is, if the search direction is the FAR direction, the process proceeds to step S526. In step S526, it is determined whether or not the evaluation value has continuously decreased a predetermined number of times. A reference value serving as a criterion for determining the number of consecutive reductions is appropriately set in consideration of the depth of field.
[0092]
When NO determination is obtained in step S526, the process proceeds to step S528, and interruption or continuation is determined in steps S528 to S536 described above. On the other hand, if YES is obtained in step S526, the process proceeds to step S538, the interruption of the evaluation value acquisition process is determined, and the process returns to the flowchart of FIG.
[0093]
By following the interruption determination process shown in FIG. 18, the peak of the evaluation value corresponding to the subject can be detected accurately and quickly in both the NEAR direction and the FAR direction, and the AF process can be speeded up. realizable.
[0094]
Next, an example of control that can achieve a further increase in AF processing speed will be described. As described above with reference to FIG. 5, as the focal length of the photographic lens 12 increases, the focus feed amount (number of pulses) in the focus adjustment region 300 (from infinity to the nearest) increases and the AF time increases. Therefore, the “rough search” is first performed to obtain the evaluation value in the AF search step in which the focus feed amount is increased, and when the approximate focus position is detected by the rough search, the search step in which the focus feed amount is further reduced in the vicinity region. It is preferable to perform a “detailed search” for obtaining an evaluation value.
[0095]
FIG. 19 shows a conceptual diagram of rough search and detailed search. In the figure, it is assumed that the focus feed amount from infinity to the nearest is 240 pulses, the number of focus feed pulses during rough search is set to 20 pulses, and the number of focus feed pulses during detailed search is set to 2 pulses.
[0096]
According to the figure, first, a rough search is started in the NEAR direction from infinity. In the rough search, the search point is changed every 20 pulses, the evaluation value is calculated at each point, and the interruption determination process as described in FIG. 18 is performed.
[0097]
When a peak is detected in the rough search and, for example, the interruption of the evaluation value acquisition process is determined at the position of 100 pulses, the focus is moved to the initial position (Pds) of the detailed search, and the detailed search is started in this direction from here. . In the detailed search, the search point is changed every two pulses, the evaluation value is calculated at each point, and after the peak is detected, if the evaluation value decreases continuously a predetermined number of times, the interruption of the evaluation value acquisition process is determined, and the peak position ( The focus lens 48 is driven to the in-focus position.
[0098]
FIG. 20 shows a flowchart of AF control combining rough search and detailed search. In the figure, steps S610 to S628 including the rough search portion are the same processing as steps S110 to S128 of the flowchart described in FIG. Further, the interruption determination (1) process in step S622 of FIG. 20 is applied with the interruption determination process flowchart described in FIG.
[0099]
When it is determined in step S624 in FIG. 20 that “interruption” is obtained, or when the final position of the focus stage is reached in step S626, the process proceeds to step S640. In step S640, an operation for obtaining the range of the detailed search is performed based on the result of the rough search. Then, according to the obtained detailed search range, a process for driving the focus lens 48 to the detailed search start position (detail search initial position) is performed (step S642).
[0100]
Next, an initial value “0” is set in the register n of the CPU 64 (step S644), and the process proceeds to step S646. In step S646, an evaluation value at the current focus position (search point) is calculated, and the obtained evaluation value is input to the CPU 64. The CPU 64 stores the evaluation value at the search point in a memory (not shown).
[0101]
Next, the process proceeds to step S648, and a process for determining whether or not to interrupt the AF search is performed. The contents of the “interruption determination (2) process” will be described later with reference to FIG. The CPU 64 determines whether the AF search is interrupted or continued based on the result of the interruption determination (2) process (step S648) (step S650). When the determination “continuation” is obtained in step S650, the process proceeds to step S652, and it is determined whether or not the final position of the search point has been reached.
[0102]
If NO is determined in step S625, the process proceeds to step S654, the focus lens 48 is moved by one AF search step (2 pulses) from the current focus position, and the process returns to step S646. Thus, the evaluation value is calculated from the frame image data that is moved to the next search point and has a different focus position. The processing in steps S646 to S654 is repeated for each point in the detailed search range, and the evaluation value of each search point is acquired.
[0103]
If the focus lens 48 has reached the final position of the search point in step S652, or if “interruption” is determined in step S650, the process proceeds to step S660. In step S660, the position where the evaluation value is maximized is obtained from the result of the evaluation value obtained at each point, and the focus lens 48 is moved to that position (in-focus position). Thus, the photographing / recording permission state is set (step S662), and the automatic focus adjustment process is ended.
[0104]
FIG. 21 shows a flowchart of the interruption determination (2) process shown in step S648 of FIG. In this interruption determination (2) process, first, a table value “C_TABLE” corresponding to the current focal length [ZOOMPOS] is set in the register C (step S710). This is a process of setting an interruption determination value C, which is a determination criterion for determining that the AF search is interrupted when the evaluation values calculated at each focus stage (search point) continuously decrease. .
[0105]
The interruption determination value C is set to the same numerical value as the focus step number (“4” in the example of FIG. 5) or a value close thereto on the short focus side (wide side), and is set so as not to perform the interruption process substantially. ing. Further, the interruption determination value C increases as it approaches the long focus side (tele side), and is set to an integer value of about 50% to 30% of the number of focus stages.
[0106]
Next, the process proceeds to step S712, where it is determined whether or not the acquired evaluation value has decreased. When the evaluation value has not decreased (NO determination), it is determined to continue the AF search (step S722), the process exits from this subroutine, and returns to the flowchart of FIG.
[0107]
When it is determined in step S712 that the evaluation value is decreasing (YES determination), 1 is added to the value of the register n (step S714), and the value of the register n is set to the value of the register C in the subsequent step S716. It is determined whether the value is exceeded. If the value of the register n is equal to or smaller than the value of the register C (NO determination), the process proceeds to step S722 to decide to continue the AF search, and the process returns to the flowchart of FIG. Thereby, the AF search is continued until the evaluation value continuously decreases C times.
[0108]
If YES is obtained in step S716, that is, if it is detected that the evaluation value has continuously decreased C times, the process proceeds to step S718. In step S718, it is determined whether or not the difference between the maximum value (AFmax) and the minimum value (AFmin) of the evaluation values calculated by the detailed search is greater than a predetermined value K. If the difference between the evaluation values is larger than the predetermined value K (YES determination), it indicates that there is a predetermined contrast, so that the AF search is interrupted (step S720). If the difference between the evaluation values is equal to or smaller than the predetermined value K (NO determination), the process proceeds to step S722, and the continuation of the AF search is determined.
[0109]
When the determination of “interrupt” or “continue” is made in step S720 or step S722, this subroutine is terminated, and the process proceeds to step S650 in the flowchart of FIG. The processing contents thereafter are as described in FIG.
[0110]
In the above embodiment, the example in which the photographing magnification is changed by the optical zoom has been described. However, the present invention is also applied to a camera that performs a zoom operation using an electronic zoom function instead of or in combination with the optical zoom. Can do.
[0111]
<Appendix>
According to the said embodiment, invention (1)-(7) of the structure shown below can be obtained. These inventions (1) to (7) can be combined with the invention of each claim described in “Scope of claims”.
[0112]
Invention (1): In an automatic focus adjustment device that adjusts a focal position of a lens that forms an image of a subject on the image pickup means based on an image signal output from the image pickup means, the device moves the lens to a focus adjustment region. A lens moving means for moving the lens, a lens position detecting means for detecting the position of the lens, a contrast component of the subject is extracted from an image signal output from the imaging means, and an evaluation value corresponding to the contrast component is obtained. Evaluation value calculation means for calculating each movement position of the lens, direction determination means for determining a lens movement direction during a focus adjustment operation based on a current lens position detected by the lens position detection means, and the direction determination The lens movement for obtaining the evaluation value is controlled according to the determination of the means, and the lens is moved to a position where the evaluation value reaches a peak. Automatic focusing apparatus characterized by comprising control means for controlling the lens moving means so as to obtain an in-focus state, the Te.
[0113]
Invention (2): The direction determining means sets a switching position that divides the focus adjustment area into two areas, a short distance area and a long distance area, and determines the positional relationship between the current lens position and the switching position. In comparison, when the current lens position is in the short distance region, the evaluation value acquisition start position is set as the closest side, and the lens movement direction when acquiring the evaluation value is changed from the closest direction toward the infinity. On the other hand, when the current lens position is in the long distance region, the acquisition start position of the evaluation value is set to the infinity side, and the lens moving direction when acquiring the evaluation value is changed from infinity to the closest direction. The automatic focusing apparatus according to the invention (1), wherein the automatic focusing apparatus is determined.
[0114]
Invention (3): In an automatic focus adjustment device that adjusts the focal position of a lens that forms an image of a subject on the image pickup means based on an image signal output from the image pickup means, the device includes:
Lens moving means for moving the lens within a focus adjustment region;
Zoom means for changing the shooting magnification;
Zoom position detecting means for detecting a zoom position by the zoom means;
An evaluation value calculating means for extracting a contrast component of the subject from an image signal output from the imaging means and calculating an evaluation value corresponding to the contrast component for each moving position of the lens;
Direction determining means for determining a lens moving direction during a focus adjustment operation based on a current zoom position detected by the zoom position detecting means;
According to the determination of the direction determining means, the lens movement for obtaining the evaluation value is controlled, and the lens moving means is controlled so as to obtain an in-focus state by moving the lens to a position where the evaluation value reaches a peak. Control means to
An automatic focusing apparatus characterized by comprising:
[0115]
Invention (4): In the automatic focusing apparatus according to invention (3), when the current zoom position is on the wide side, the direction determination means sets the evaluation value acquisition start position as the closest side, and sets the evaluation value When the current zoom position is on the tele side, the acquisition start position of the evaluation value is set to the infinity side, and the evaluation value is set to the infinity side. An automatic focus adjustment device, wherein the lens movement direction at the time of acquisition is determined to be a direction from infinity to the closest distance.
[0116]
Invention (5): In the automatic focus adjustment apparatus according to invention (3), the apparatus has lens position detection means for detecting the position of the lens, and the direction determination means is obtained from the lens position detection means. An automatic focus adjustment apparatus, wherein the lens moving direction is determined based on a lens position to be obtained and a zoom position obtained from the zoom position detection means.
[0117]
Invention (6): In an automatic focus adjustment method for adjusting a focal position of a lens for forming an image of a subject on the image pickup means based on an image signal output from the image pickup means, the method comprises:
A lens moving step of moving the lens within a focus adjustment region;
A lens position detecting step for detecting the position of the lens;
An evaluation value calculating step of extracting a contrast component of the subject from an image signal output from the imaging means, and calculating an evaluation value corresponding to the contrast component for each movement position of the lens;
A direction determining step for determining a lens moving direction during a focus adjustment operation based on a current lens position detected by the lens position detecting unit;
An evaluation value acquisition control step for controlling lens movement for acquiring the evaluation value according to the determination in the direction determination step;
Based on the evaluation value obtained in the evaluation value acquisition control step, a control step for controlling the lens moving means so as to obtain a focused state by moving the lens to a position where the evaluation value reaches a peak;
An automatic focusing method characterized by comprising:
[0118]
Invention (7): In an automatic focus adjustment method for adjusting a focal position of a lens for forming an image of a subject on the image pickup means based on an image signal output from the image pickup means, the method comprises:
A lens moving step of moving the lens within a focus adjustment region;
A zoom position detecting step for detecting a zoom position by a zoom means for changing a photographing magnification;
An evaluation value calculating step of extracting a contrast component of the subject from an image signal output from the imaging means, and calculating an evaluation value corresponding to the contrast component for each movement position of the lens;
A direction determining step for determining a lens moving direction during a focus adjustment operation based on a current zoom position detected by the zoom position detecting unit;
An evaluation value acquisition control step of controlling lens movement for acquiring the evaluation value according to the determination of the direction determination means;
Based on the evaluation value obtained in the evaluation value acquisition control step, a control step of controlling the lens moving means so as to obtain a focused state by moving the lens to a position where the evaluation value reaches a peak;
An automatic focusing method characterized by comprising:
[0119]
【The invention's effect】
As described above, according to the present invention, after a peak of an evaluation value is detected, whether or not the peak determination is appropriate is determined based on an evaluation value at a lens position that is a predetermined amount or more away from the peak position. As a result, it is possible to increase the speed of the AF process and to accurately focus even when there are a plurality of subjects having different distances.
[Brief description of the drawings]
FIG. 1 is a front external view of a digital camera according to an embodiment of the present invention.
2 is an external view of the back side of the digital camera shown in FIG.
FIG. 3 is a block diagram showing the internal configuration of the digital camera of this example.
FIG. 4 is a diagram showing an example of a focus area set at the center of the screen
FIG. 5 is a diagram illustrating a change in an AF search step width according to a zoom position and a focus position.
FIG. 6 is a conceptual diagram illustrating an example of control for changing an AF search start position and a search direction according to a focus position at the start of AF.
FIG. 7 is a flowchart showing a control procedure for automatic focusing in the present example.
FIG. 8 is a flowchart showing the contents of the focus lens initial position calculation process shown in FIG. 7;
FIG. 9 is a table showing an example of a table for designating an AF search direction according to a zoom position.
FIG. 10 is a flowchart of initial position calculation processing using the table of FIG.
FIG. 11 is a conceptual diagram illustrating another control example in which the AF search start position and the search direction are changed according to the focus position at the start of AF.
12 is a flowchart of initial position calculation processing for carrying out the control example shown in FIG. 11;
FIG. 13 is a table showing an example of a table for designating an AF search direction according to a zoom position and a focus position.
FIG. 14 is a graph showing an example of evaluation values that change as the focus lens moves.
FIG. 15 is a diagram illustrating a state in which a plurality of subjects exist within a focus area.
FIG. 16 is a graph showing an example of evaluation values that change as the focus lens moves when there are a plurality of subjects.
FIG. 17 is a graph illustrating a phenomenon in which the evaluation value does not decrease due to the influence of noise or the like.
FIG. 18 is a flowchart showing the contents of the interruption determination process shown in FIG.
FIG. 19 is a conceptual diagram of an automatic focus adjustment operation combining a rough search and a detailed search.
FIG. 20 is a flowchart showing a control procedure of automatic focus adjustment combining rough search and detailed search.
FIG. 21 is a flowchart showing the contents of the interruption determination (2) processing shown in FIG. 20;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Digital camera, 12 ... Shooting lens, 46 ... Zoom lens (zoom means), 48 ... Focus lens, 52 ... CCD (imaging means), 64 ... CPU (control means, judgment means, evaluation value change detection means), 78 ... Focus drive part (lens moving means), 88 ... Evaluation value calculation part (Evaluation value calculation means)

Claims (2)

In an automatic focusing apparatus that adjusts the focal position of a lens that forms an image of a subject on the imaging unit based on an image signal output from the imaging unit, the apparatus includes:
Lens moving means for moving the lens within a focus adjustment region;
An evaluation value calculating means for extracting a contrast component of the subject from an image signal output from the imaging means and calculating an evaluation value corresponding to the contrast component for each moving position of the lens;
Control means for controlling the lens moving means to move the lens to each position for obtaining the evaluation value;
Evaluation value change detection means for detecting a change in the evaluation value at a lens position separated by a predetermined amount w or more from an end point of the focus adjustment region;
A determination unit that determines an in-focus state based on the evaluation value at each position obtained by the evaluation value calculation unit and the detection result of the evaluation value change detection unit;
With
In automatic focus adjustment in still image shooting, the control means moves the lens from one end point of the focus adjustment area, and after detecting that there is a peak from the increase / decrease of the evaluation value acquired along with the movement of the lens Further, the lens is moved in order to obtain an evaluation value, and the lens is moved when the evaluation value at a lens position separated by a certain amount d from the position of the lens where the peak is detected is equal to or less than a predetermined threshold value. Is determined, and if the evaluation value at the lens position exceeds a predetermined threshold value, the continuation of the movement of the lens is determined. When the movement of the lens is continued, the other end point of the focus adjustment region is determined. If the remaining detection amount up to the predetermined amount w is greater than or equal to the predetermined amount w, the continuation of the evaluation value acquisition process is determined, the remaining detection amount is less than the predetermined amount w, and predetermined from the end point of the focus adjustment region When the increase of the evaluation value in the lens position away w is not detected, it determines the interruption of the movement of the lens, when the increase of the evaluation value is detected to determine the continuation of the movement of the lens,
When a plurality of peaks of the evaluation value are detected, the determination unit determines that the lens position where the maximum value of the evaluation value is detected is an in-focus position, and the lens moving unit sets the lens at the in-focus position. An automatic focusing device characterized by moving the lens. In an automatic focus adjustment method for adjusting a focus position of a lens that forms an image of a subject on the image pickup means based on an image signal output from the image pickup means, the method includes:
A lens moving step of moving the lens within a focus adjustment region;
An evaluation value calculating step of extracting a contrast component of the subject from an image signal output from the imaging means, and calculating an evaluation value corresponding to the contrast component for each movement position of the lens;
A control step for controlling the lens moving means to move the lens to each position for obtaining the evaluation value;
An evaluation value change detection step of detecting a change in the evaluation value at a lens position separated by a predetermined amount w or more from an end point of the focus adjustment region;
A determination step of determining an in-focus state based on the evaluation value at each position obtained by the evaluation value calculation unit and the detection result of the evaluation value change detection unit;
Including
In automatic focus adjustment in still image shooting, the control step moves the lens from one end point of the focus adjustment area, and after detecting that there is a peak from the increase / decrease in the evaluation value acquired along with the movement of the lens Further, the lens is moved in order to obtain an evaluation value, and the lens is moved when the evaluation value at a lens position separated by a certain amount d from the position of the lens where the peak is detected is equal to or less than a predetermined threshold value. Is determined, and if the evaluation value at the lens position exceeds a predetermined threshold value, the continuation of the movement of the lens is determined. When the movement of the lens is continued, the other end point of the focus adjustment region is determined. If the remaining detection amount up to the predetermined amount w is greater than or equal to the predetermined amount w, the continuation of the evaluation value acquisition process is determined, the remaining detection amount is less than the predetermined amount w, and predetermined from the end point of the focus adjustment region When the increase of the evaluation value in the lens position away w is not detected, it determines the interruption of the movement of the lens, when the increase of the evaluation value is detected to determine the continuation of the movement of the lens,
In the determination step, when a plurality of peaks of the evaluation value are detected, the lens position where the maximum value of the evaluation value is detected is determined as an in-focus position, and the lens is moved to the in-focus position. A feature of automatic focus adjustment.

Images