JP2006330394A - Autofocus device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an autofocus device capable of shortening a search time of an electronic camera which performs AF processing according to a hill climbing method. <P>SOLUTION: A CPU 9 of the electronic camera decides a search movement range of a focus lens upon the AF processing for obtaining focus evaluation value hysteresis while moving the focus lens in a lens unit 1, as follows. When it holds that present position Np of focus lens ≥ hyperfocal position Op, a range from the present position Np of focus lens up to the close terminal position is set to be the search movement range. When it does not holds that present position Np of focus lens ≥ hyperfocal position Op, a range from the hyperfocal position Op up to the close terminal position is set to be the search movement range. The CPU 9 decides the hyperfocal position Op in accordance with control diaphragm value based on a focal distance of the lens unit 1 and AE calculation. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a camera autofocus technique.

  A camera focus detection method is known in which an image of a subject is picked up using an image pickup device such as a CCD, and an adjustment state of a focus position by a taking lens is detected based on an image pickup signal output from the image pickup device. A focus detection method called a hill-climbing method detects a focus position so that a focus evaluation function obtained by extracting a high-frequency component of an imaging signal takes a maximum value while driving the focus lens back and forth in the optical axis direction. Patent Document 1 discloses a technique for shortening the focus detection time in such a hill-climbing method. According to Patent Document 1, if the photographing lens is located within the focus allowable range when an instruction to start photographing is given, the camera omits driving of the photographing lens.

Japanese Patent Laid-Open No. 2004-354581

  With the camera of Patent Document 1, the shooting distance (the distance between the camera and the subject) changes after focusing once and before the start of shooting is instructed, and the shooting lens is no longer within the focus tolerance range. Therefore, it is necessary to perform a hill-climbing search in the range from the infinity position to the closest end position. In this case, the search time cannot be shortened.

An autofocus device according to the present invention is based on an image sensor that captures an image of a subject through a photographic lens and outputs an imaging signal, a hyperfocal distance of the photographic lens, and a position of the focus lens when an instruction to start focus adjustment is given. A search movement range determination means for determining the search movement range of the focus lens, a lens drive signal generation means for generating a lens drive signal for moving the focus lens in the search movement range, and imaging at a predetermined position of the focus lens. Evaluation value calculating means for calculating the integrated value of the signal, and lens position calculating means for calculating the in-focus lens position based on the integrated value by the evaluation value calculating means.
2. The auto-focus device according to claim 1, wherein the search movement range determining means is: (1) an imaging distance corresponding to a focus lens position (current position) at the time when start of focus adjustment is instructed is a hyperfocal distance; When the distance is farther, the search movement range is between the current position and the closest end position. (2) When the shooting distance corresponding to the current position is closer than the hyperfocal distance, the distance between the hyperfocus position and the closest end position is set. You may comprise so that it may become a search movement range.
3. The autofocus device according to claim 2, wherein the search movement range determining means changes the hyperfocal distance according to the photographing condition, and searches for the focus lens based on the changed hyperfocal distance and the current position of the focus lens. The movement range can also be determined.
In the autofocus device according to claim 3,
The shooting condition may include at least one of a focal length, an aperture value, a shooting scene, and subject brightness.
An auto-focus device according to the present invention captures a subject image through a photographic lens and outputs an imaging signal, and a search movement range determination unit that determines a search movement range of the focus lens according to the hyperfocal distance of the photographic lens. A lens driving signal generating unit that generates a lens driving signal for moving the focus lens in the search movement range, an evaluation value calculating unit that calculates an integrated value of the imaging signal for each predetermined position of the focus lens, and an evaluation value Lens position calculating means for calculating a focus lens position based on an integrated value obtained by the calculating means.

  In the autofocus device according to the present invention, for example, the search time when the shooting distance changes after focusing once can be shortened.

The best mode for carrying out the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram for explaining a main configuration of an autofocus (AF) electronic camera according to an embodiment of the present invention. In FIG. 1, an electronic camera includes a lens unit 1, an image sensor 2, an analog signal processing unit 3, an A / D converter 4, a digital signal processing unit 5, an EVF processing unit 6, and a D / A conversion. Device 7, EVF (electronic viewfinder) 8, CPU 9, focus motor 10, buffer memory 11, operation member 12, recording / playback signal processing circuit 13, and external storage circuit 14 is detachable Configured.

  The lens unit 1 includes a focus lens (not shown). The focus lens is a lens that adjusts the focal position so that the subject image formed by the light beam that has passed through the lens unit 1 is formed on the imaging surface of the imaging device 2. When the focus motor 10 drives a focus control mechanism (not shown), the focus lens moves back and forth in the optical axis direction. The focus motor 10 is driven by a lens drive signal output from the CPU 9.

  The image sensor 2 is configured by, for example, a two-dimensional CCD image sensor. The imaging element 2 captures a subject image on the imaging surface and outputs an imaging signal corresponding to each pixel. The image signal output from the image sensor 2 has a different signal level depending on the intensity of light incident on each pixel. Note that the image sensor 2 may be configured using a MOS sensor, a CID, or the like instead of the CCD.

  The imaging signal output from the imaging element 2 is input to the analog signal processing unit 3. The analog signal processing unit 3 includes a CDS (correlated double sampling) circuit, an AGC circuit, and the like. The CDS circuit performs noise reduction of the imaging signal, and the AGC circuit adjusts the level of the imaging signal. The imaging signal processed by the analog signal processing unit 3 is converted from an analog signal to a digital signal by the A / D converter 4.

  The digitized image signal is input to the digital signal processing unit 5. The digital signal processing unit 5 includes a gamma correction circuit, a luminance signal generation circuit, a color difference signal generation circuit, and the like, and performs predetermined digital signal processing such as gamma correction, edge enhancement, and white balance adjustment on the input image signal. . The buffer memory 11 is configured as a frame memory, and temporarily stores the data constituting the image signal input to the digital signal processing unit 5 or stores the data being processed by the digital signal processing unit 5 and the image data after processing. Store.

  The CPU 9 includes an AE calculation unit, an AF calculation unit, and the like, and performs various calculations such as automatic exposure (AE) and automatic focus detection (AF) of the electronic camera, and sequence control of camera operation. The CPU 9 comprehensively manages focus detection control and exposure control of the electronic camera according to various operation signals input from the operation member 12. The operation member 12 includes a release switch, a mode change switch, etc. (not shown).

  The EVF processing unit 6 generates a display signal corresponding to the display resolution and display magnification (electronic zoom magnification) of the EVF 8 based on the image signal input from the digital signal processing unit 5, and D / A converts the generated display signal. To the device 7. The display signal is converted from a digital signal to an analog signal by the D / A converter 7. The EVF 8 displays a reproduction image based on the analog reproduction display signal.

  The recording / playback signal processing circuit 13 records image data in a predetermined recording format output from the digital signal processing unit 5 in the external storage circuit 14. The recording / reproducing signal processing circuit 13 is further configured to read out the image data recorded in the external storage circuit 14 and output it to the digital signal processing unit 5. The external storage circuit 14 is constituted by a memory card, for example.

(AF processing)
The AF process performed by the electronic camera described above will be described. The CPU 9 performs a filtering process for extracting high frequency components from image data corresponding to a focus detection area (focus area) among the image data before digital signal processing stored in the buffer memory 11. The image data after the filtering process has a low frequency component, particularly a direct current component, removed compared to the image data before the filtering process.

  Further, the CPU 9 integrates the absolute values of the filtered image data in order to integrate the differences due to the high frequency components of the image data. This integrated value is called a focus evaluation value. The CPU 9 obtains data indicating a change in the focus evaluation value accompanying the movement of the focus lens by sequentially calculating the focus evaluation value while moving the focus lens in the optical axis direction. FIG. 2 is a diagram illustrating an example of the relationship between the position of the focus lens in the lens unit 1 and the focus evaluation value. In FIG. 2, the horizontal axis represents the position of the focus lens, and the vertical axis represents the focus evaluation value. The lens position L1 corresponding to the maximum point (left side) of the focus evaluation value is the focus position of the focus lens with respect to the background. The lens position L0 corresponding to the local maximum point (right side) of the focus evaluation value is the focus position of the focus lens with respect to the person.

  The CPU 9 performs such calculation of the focus evaluation value, for example, while moving the focus lens from the ∞ (infinity) side to the close side. The calculation rate when the CPU 9 calculates the focus evaluation value is determined by the time required for the image capturing time by the image sensor 2, the filtering process by the CPU 9, and the integrated value calculation. Therefore, the focus evaluation value actually obtained is obtained as discrete data for each calculation rate, not a continuous line as shown in FIG. The CPU 9 calculates the lens positions L1 and L0 corresponding to the maximum points of the focus evaluation value curve by performing a so-called three-point interpolation operation on the three points of discrete data including the maximum point of the focus evaluation value curve. The calculated lens positions L1 and L0 are positions at which the blur of the edges of the background image and the person image captured by the image sensor 2 is eliminated and the contrast of the image is maximized (in focus).

  In the present embodiment, the moving range when the focus lens is moved by search is determined according to the hyperfocal distance of the photographing optical system.

  The flow of AF processing performed by the CPU 9 of the AF electronic camera will be described with reference to the flowchart of FIG. The processing shown in FIG. 3 is started when, for example, a half-press operation signal (signal for instructing to start photographing) is input to the CPU 9 from a release switch (not shown). That is, the half-press operation signal also corresponds to a signal that instructs the start of focus adjustment. In step S1, the CPU 9 acquires the current position Np of the focus lens and proceeds to step S2. The current position Np of the focus lens is acquired as information indicating the lens position from a focus control mechanism (not shown), for example.

  In step S2, the CPU 9 acquires the hyperfocal position Op of the lens unit 1 and proceeds to step S3. The hyperfocal position Op is the position of the focus lens corresponding to the hyperfocal distance of the lens unit 1. The hyperfocal distance is the shortest shooting distance among shooting distances (distances from the camera to the subject) included in the depth of field in so-called pan focus shooting. In this description, the position of the focus lens on the near side that forms a sharp image on the image sensor 2 during pan-focus imaging (the image blur is smaller than the size of the permissible circle of confusion) is referred to as an overfocus position Op.

  The hyperfocal length varies depending on the focal length of the lens unit 1 and the aperture value. In the present embodiment, the data of the hyperfocal position corresponding to the focal length and the aperture is tabulated in advance and stored in a non-illustrated nonvolatile memory in the CPU 9. The CPU 9 reads out the position information (indicating the focal length) of the zoom lens (not shown) included in the lens unit 1 and the hyperfocal position data corresponding to the control aperture value determined by the AE calculation, and sets it as the overfocal position Op. .

  In step S3, the CPU 9 determines whether or not the current position Np ≧ the hyperfocal position Op is established. If Np ≧ Op is established, the CPU 9 makes an affirmative decision in step S3 and proceeds to step S4. If Np ≧ Op is not established, the CPU 9 makes a negative decision in step S3 and proceeds to step S5. When the process proceeds to step S4, the photographing distance corresponding to the current position Np of the focus lens is farther than the hyperfocal distance (within the depth of field), and when the process proceeds to step S5, the photographing corresponding to the current position Np of the focus lens is performed. This is the case when the distance is closer than the hyperfocal distance (outside the depth of field).

  In step S4, the CPU 9 sets the AF search start position St_P to the current position Np, and sets the AF search end position Stp_P to the closest end position, and proceeds to step S7. In this case, it is not necessary to move the focus lens to the AF search start position St_P.

  In step S5, the CPU 9 sets the AF search start position St_P to the hyperfocal position Op and the AF search end position Stp_P to the closest end position, and proceeds to step S6. In step S6, the CPU 9 outputs a drive signal to the focus motor 10, moves the focus lens (not shown) to the AF search start position St_P (in this case, the hyperfocal position Op), and proceeds to step S7.

  In step S7, the CPU 9 performs a hill climbing AF process as follows. FIG. 4 is a diagram showing a relationship between the elapsed time (horizontal axis) of the AF process and the focus lens position (vertical axis) when the process proceeds from step S4 to step S7 in FIG. In FIG. 4, the movement of the focus lens is stopped from timing t11 to timing t12 (section a). The stop position (current position Np) of the focus lens is the focus lens position obtained by the previous AF process.

  At timing t12 in FIG. 4, driving of the focus motor 10 is started so as to reach a predetermined lens moving speed, and the focus lens starts moving toward the closest side (search movement start). The moving time of the focus lens from the AF search start position St_P to the AF search end position Stp_P is determined by the lens moving speed. When the lens moving speed is slowed down, the number of plots of focus evaluation values increases, and when the lens moving speed is fastened, the number of plots decreases. The lens moving speed is preferably set so that the number of plots constituting one “mountain” of the focus evaluation value curve in FIG. In FIG. 4, the lens positions are shown stepwise, but they may be moved linearly.

  The CPU 9 calculates a focus evaluation value every predetermined time, and stores the calculated focus evaluation value in the internal memory as history data in association with information indicating the position of the focus lens. The CPU 9 drives the focus lens and repeats calculation and storage of the focus evaluation value until the position of the focus lens reaches the AF search end position Stp_P. As a result, while the focus lens moves from the AF search start position St_P to the AF search end position Stp_P (from timing t12 to timing t13 (section a) in FIG. 4), a plurality of focus evaluation values representing the focus evaluation value curve are obtained. can get.

  At timing t13, the drive of the focus motor 10 is stopped, and the focus lens stops at the closest end (search movement end). The CPU 9 calculates the in-focus position using the focus evaluation value history obtained by the search movement process. The in-focus position is calculated by calculating the lens position corresponding to the maximum value of the focus evaluation value history curve as shown in FIG. In the case of having a plurality of maximum values, for example, if the AF operation mode is set to the closest priority mode for the camera, the CPU 9 preferentially calculates the closest lens position (in the example of FIG. 2, the lens position L0).

  The CPU 9 outputs a lens driving signal to the focus motor 10 with the lens position L0 as the target lens position, and moves the focus lens to the target lens position at high speed. From timing t13 to timing 14 (section c) in FIG. 4 corresponds to a high-speed movement period.

  The inversion process is performed from timing t14 to timing t15 (section d). The CPU 9 once drives the focus lens from the target lens position to the infinity side by a predetermined amount and then stops, reverses the moving direction of the focus lens in the same direction as the moving direction during the search movement, and reaches the target lens position at a low speed. Move. As a result, backlash caused by play of gears and the like included in the focus control mechanism is performed, and the influence of backlash is suppressed and the stop accuracy of the focus lens with respect to the target lens position is improved.

  When the CPU 9 stops the focus lens at the focusing lens position L0 as described above, the AF process in FIG.

  FIG. 5 is a diagram showing a relationship between the elapsed time (horizontal axis) of the AF process and the focus lens position (vertical axis) when the process proceeds from step S6 to step S7 in FIG. In FIG. 5, the period from the timing t20 to the timing t22 (section K, section K) corresponds to step S6 in FIG. That is, in the interval K, the focus lens is moved from the current position Np to the hyperfocal position Op at high speed. Inversion is performed in the interval key. The focus lens is temporarily moved from the hyperfocal position Op to the infinity side by a predetermined amount and then stopped. After the direction of movement of the focus lens is reversed in the same direction as the search movement, the focus lens is moved to the hyperfocal position Op at a low speed. Moved. As described above, the accuracy of stopping the focus lens with respect to the hyperfocal position Op is improved by the backlash due to the reversal of the moving direction.

  The movement of the focus lens from timing t22 to timing t23 (section k) is the same as that in section a in FIG.

  The movement of the focus lens from the timing t23 to the timing t24 (interval) is the same as that in the interval c in FIG.

  The focus lens movement from the timing t24 to the timing t25 (section E) is the same as that in the section D in FIG.

According to the embodiment described above, the following operational effects can be obtained.
(1) An electronic camera that performs hill-climbing AF processing determines a focus lens search movement range during AF processing for obtaining a focus evaluation value history while moving the focus lens as follows. When the current position Np of the focus lens is equal to or greater than the hyperfocal position Op, the search movement range is from the current position Np to the closest end position, so the current position Np is within the shooting distance included in the depth of field. It is possible to omit a search movement farther than the shooting distance corresponding to. As a result, the time required for the AF processing can be shortened as compared with the case where the entire region from the infinity position to the close end position is set as the search movement range. In addition, since the time for moving the focus lens to the AF search start position is unnecessary, the AF processing time is further shortened.

(2) When the current position Np ≧ the hyperfocal position Op is not established, the electronic camera uses the search movement range from the hyperfocal position Op to the closest end position, so that it is farther than the shooting distance corresponding to the hyperfocal position Op. To avoid focusing on the main subject and always focus on the main subject even when the shooting distance has changed since the previous AF process (especially when the previous shooting distance is shorter than the hyperfocal distance). A search movement range is determined. Further, since the hyperfocal position Op (AF search start position) is obtained according to the focal length of the lens unit 1 and the control aperture value obtained by the AE calculation, the search movement range of the focus lens is minimized. The search movement range can be determined appropriately. As a result, the time required for the AF process can be shortened compared to the case where the entire region from the infinity position to the close end position is set as the search movement range.

(Modification)
Even when the current position Np of the focus lens is equal to or greater than the overfocus position Op, the search movement range from the overfocus position Op to the closest end position may be used. In this case, if the focus lens is moved at high speed from the current position Np to the hyperfocal position Op, the AF processing time can be further shortened. As described above, the moving range for the search movement may always be determined according to the hyperfocal distance of the photographing optical system.

  In this embodiment, the focus lens moving direction during the search movement is set to move from the infinity side to the close side, but it may be moved from the close side to the infinity side. In this case, the direction to be reversed for backlashing is also opposite to that in the above-described embodiment.

  Also, when the near end is included in the depth of field (the close end position is included in the depth of focus), the focus lens moving direction during the search movement is moved from the close side to the infinity side. Good.

  In the above description, the example in which the hyperfocal position Op is varied according to the focal length of the lens unit 1 and the control aperture value by the AE calculation has been described. However, the shooting scene mode (for example, portrait shooting) set in the electronic camera has been described. It may be configured such that the hyperfocal position Op is weighted according to the mode, landscape shooting mode, etc., or the hyperfocal position Op is weighted according to the subject brightness. By changing the hyperfocal position Op according to the shooting conditions (focal length, aperture value, shooting scene mode, brightness, etc.), the search movement range can be appropriately determined according to the shooting conditions.

  You may apply this invention not only to an electronic camera but to the focus detection apparatus of a silver salt camera and an electronic device with a camera.

  The above description is merely an example, and the interpretation of the invention is not limited to the correspondence between the components of the above-described embodiment and the components of the present invention.

It is a block diagram explaining the principal part structure of the autofocus electronic camera by one embodiment of this invention. It is a figure which shows an example of the relationship between the position of a focus lens, and a focus evaluation value. It is a flowchart explaining the flow of AF processing performed by CPU. It is a figure which shows the relationship between the elapsed time of AF process, and a focus lens position. It is a figure which shows the relationship between the elapsed time of AF process, and a focus lens position.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Lens unit 2 ... Image pick-up element 9 ... CPU
DESCRIPTION OF SYMBOLS 10 ... Focus motor 11 ... Buffer memory 12 ... Operation member

Claims (5)

An image sensor that captures a subject image through a taking lens and outputs an image signal;
A search movement range determining means for determining a search movement range of the focus lens based on a hyperfocal distance of the photographing lens and a position of the focus lens at a time when start of focus adjustment is instructed;
Lens driving signal generating means for generating a lens driving signal for moving the focus lens in the search movement range;
Evaluation value calculating means for calculating an integrated value of the imaging signal for each predetermined position of the focus lens;
An autofocus device comprising: lens position calculation means for calculating a focus lens position based on an integrated value obtained by the evaluation value calculation means. The autofocus device according to claim 1,
The search movement range determining means is (1) when the shooting distance corresponding to the position of the focus lens (current position) at the time when the start of focus adjustment is instructed is farther than the hyperfocal distance, The search movement range between the near end position and (2) when the shooting distance corresponding to the current position is closer than the hyperfocal distance, the search movement range between the hyperfocal position and the near end position. An autofocus device characterized by that. The autofocus device according to claim 2,
The search movement range determining means changes the hyperfocal distance according to a shooting condition, and determines the search movement range of the focus lens based on the changed hyperfocal distance and the current position of the focus lens. Features an autofocus device. In the autofocus device according to claim 3,
The autofocus device, wherein the photographing condition includes at least one of a focal length, an aperture value, a photographing scene, and a subject luminance. An image sensor that captures a subject image through a taking lens and outputs an image signal;
Search movement range determining means for determining a search movement range of the focus lens according to the hyperfocal distance of the photographing lens;
Lens driving signal generating means for generating a lens driving signal for moving the focus lens in the search movement range;
Evaluation value calculating means for calculating an integrated value of the imaging signal for each predetermined position of the focus lens;
An autofocus device comprising: lens position calculation means for calculating a focus lens position based on an integrated value obtained by the evaluation value calculation means.

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