JP2007011054A - Imaging apparatus, control method for imaging apparatus and computer program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately attain focusing by performing AF once, even when a subject moves between AF regions in the midst of AF. <P>SOLUTION: The imaging apparatus is equipped with a focus lens 2 performing focus adjustment for a subject image; a focus lens driving circuit 16 driving the focus lens 2; an imaging element 3 photoelectrically converting light to form an image via the focus lens 2; an AF evaluated value arithmetic circuit 15 calculating a contrast detection signal, based on an output signal from the imaging element 3 for a plurality of AF regions, while driving the focus lens 2; a subject movement detection part 12 detecting the movement of the subject between the AF regions from the calculated contrast detection signal; and a focusing position determining part 11 obtaining a focusing position, according to the result obtained by detecting the movement of the subject by the subject movement detection part 12. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an imaging apparatus such as an electronic still camera and a video camera, a control method for the imaging apparatus, and a computer program, and more particularly, to an apparatus having an autofocus function capable of multipoint AF.

  In a digital camera or a video camera, a method is generally used in which an output signal from an image sensor such as a CCD or CMOS is used to detect and focus a signal corresponding to the contrast of a subject.

  However, in the above method, since it is necessary to sequentially detect the contrast of the subject while the focus lens is scan-driven over a predetermined range, it takes a long time to obtain a contrast detection signal.

  In particular, when AF is performed on a moving subject, the subject changes during the AF, so it is difficult to focus accurately.

  For example, as disclosed in Patent Document 1, an AF sensor is provided separately from the imaging device, and AF is repeatedly performed on the same scene in a plurality of AF areas. There is known a method for detecting movement of a subject by observing a change in an AF result.

Japanese Patent No. 2686119

  However, in the method disclosed in Patent Document 1, since it is necessary to have an AF sensor separately from the imaging device, costs increase.

  In addition, when the same scene is repeatedly performed in a plurality of AF areas using the output signal from the image sensor and the change in the AF result is observed in the plurality of AF areas, the AF is repeated. It takes time. In addition, since it takes time for one AF itself, the reliability of the AF result when the subject moves during AF becomes low.

  The present invention has been made in view of the above points, and an object of the present invention is to enable accurate focusing with one AF even when a subject moves between AF areas during AF. .

An imaging apparatus of the present invention includes a focus lens that adjusts the focus of a subject image, a focus lens driving unit that drives the focus lens, and an imaging element that photoelectrically converts light imaged through the focus lens. An image pickup apparatus, wherein the focus lens is driven while calculating means for calculating a contrast detection signal based on an output signal from an image pickup device for a plurality of AF areas, and an AF area from the contrast detection signal calculated by the calculation means It is characterized in that it includes a subject movement detection means for detecting the movement of the subject between and a focus position determination means for obtaining a focus position in accordance with the detection result of the subject movement by the subject movement detection means.
An imaging apparatus control method according to the present invention includes a focus lens that adjusts the focus of a subject image, a focus lens driving unit that drives the focus lens, an image sensor that photoelectrically converts light imaged through the focus lens, A method for calculating a contrast detection signal based on output signals from an image sensor for a plurality of AF areas while driving the focus lens, and a subject movement detection unit The procedure for detecting subject movement between AF areas from the contrast detection signal computed by the computing means, and the focus position determining means according to the detection result of the subject movement by the subject movement detection means And a procedure for obtaining.
A computer program according to the present invention includes a focus lens that adjusts the focus of a subject image, a focus lens driving unit that drives the focus lens, and an image sensor that photoelectrically converts light imaged through the focus lens. A computer program for controlling an image pickup apparatus, wherein the focus detection lens is driven by a calculation process for calculating a contrast detection signal based on an output signal from an image pickup device while driving the focus lens, and the calculation process. Subject movement detection processing for detecting subject movement between AF areas from the detected contrast detection signal, and in-focus position determination processing for obtaining a focus position according to the detection result of subject movement by the subject movement detection processing It is characterized in that

  According to the present invention, even when there is a movement of a subject between AF areas during AF, it is possible to focus accurately with a single AF.

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.
(First embodiment)
FIG. 1 is a diagram showing a schematic configuration of a digital camera according to an embodiment to which the present invention is applied. The digital camera includes an optical system 1 and a focus lens 2 that adjusts the focus of a subject image, and photoelectrically converts light imaged by these using an imaging device 3.

  The signal photoelectrically converted by the image sensor 3 is pre-processed by a pre-processing circuit 4 having a CDS circuit for removing output noise and a non-linear amplification circuit to be performed before A / D conversion, and digitized by an A / D converter 5 After that, it is stored in the memory 7 via the memory controller 6, converted into image data by a signal processing circuit (not shown), and then recorded on the recording medium 8.

  The autofocus (AF) operation is controlled by the control unit 17. The focus lens drive circuit 16 drives the focus lens 2 for the region set by the scanning position / range setting unit 14 and, according to the contrast of the image as an AF evaluation value, based on the output signal from the image sensor 3 at each focus lens position. The signal (contrast detection signal) is calculated by the AF evaluation value calculation circuit 15. The calculation in the AF evaluation value calculation circuit 15 is performed for a plurality of AF frames (AF areas) set by the AF frame setting unit 13.

  Next, the subject movement detection unit 12 detects the movement of the subject by a method to be described later, and after the focus position determination unit 11 obtains the focus position according to the detection result, the focus lens is driven to that position. Operate.

  A focus operation is performed when the shutter switch 1 (SW1) 9 is operated, and an imaging operation and an image data recording operation are performed when the shutter switch 2 (SW2) 10 is operated.

  The calculation of the contrast detection signal (hereinafter referred to as “AF evaluation value (AF evaluation signal)”) is performed as follows. A horizontal bandpass filter is applied to each line of image data in the AF frame. Next, the bandpass output signal having the largest absolute value is selected for each line, and the selected signal is integrated in the vertical direction. A signal having a high contrast is selected in the horizontal direction, and the signal S / N is improved in the vertical direction. With the configuration as described above, it is possible to obtain a signal that has the largest value in the in-focus state and decreases in the defocus state.

  Next, a method for detecting the movement of the subject and obtaining the in-focus position using the detection result will be described in detail. Hereinafter, as shown in FIG. 2, a case where there are three AF frames (ranging frames) in the imaging screen will be described as an example.

  When the subject moves from the B frame to the C frame during AF, the AF evaluation value is as shown in FIG. In FIG. 3, the A frame shows that the contrast is low regardless of the position (subject distance), indicating that there is no subject with contrast. Further, in the B frame and the C frame, the AF evaluation value of the C frame from the B frame is abruptly changed at the position x, indicating that the subject has moved at this position. When such an AF evaluation value is obtained, it is usually difficult to obtain an accurate in-focus position for each frame.

  In this embodiment, even in such a case, an accurate in-focus position is obtained by detecting and correcting the movement of the subject between the AF frames. Hereinafter, with reference to the flowchart shown in FIG. 4, the processing operation until the in-focus position is obtained will be described. First, an AF frame to be detected is set (step S1).

Next, it is determined whether or not there is a portion where the variation of the AF evaluation value is equal to or greater than a predetermined value (step S2). For example, as shown in FIG. 5, if the AF evaluation value at the position X _i is Y _i , the absolute value Z _i = | Y _i−1 −Y _i | (1)
Z _{i + 1} > (Z _i × α) (1)
It is checked whether or not there exists a position X _{i + 1} that satisfies. Here, α is a positive value set in advance.

  The above expression (1) is an expression for determining whether or not the variation of the AF evaluation value is larger than the immediately preceding variation, and the degree of variation to be determined is changed by appropriately changing the value of α. It is possible.

If the position X _{i + 1} satisfying the above equation (1) is present in step S2, stores the position X _{i + 1} and the variation amount (step S3), and there the AF frame of the variation of the AF evaluation value Set as a frame (step S4).

On the other hand, if there is no position X _{i + 1} that satisfies the above equation (1) in step S2, this AF frame is set as a frame in which the AF evaluation value has not changed (step S7).

  Next, it is checked whether or not the above operation has been performed for all the AF frames. If the operation remains, the process proceeds to step S6, the AF frame is changed, and the above operation is repeated. For example, starting from the A frame, the operations in steps S2 to S4 and S7 are repeated for the B frame and the C frame. If all AF frames have been completed, the process proceeds to step S8.

In step S8, it is checked whether or not the frames where the AF evaluation value fluctuates are adjacent. For example, the A frame and the B frame, and the B frame and the C frame are considered to be adjacent to each other. If they are adjacent to each other, it is checked whether or not the AF frame variation positions X _{i + 1} match. If they match, the combination of the two frames is determined as a frame candidate to which the subject has moved. Note that when the gaps are provided between the AF frames, the fluctuating positions do not necessarily match. Therefore, a certain amount of width may be given, and if it can be considered that they substantially match, it may be determined as a frame candidate to which the subject has moved. .

Subsequently, the AF evaluation values are interchanged between the candidate frames to which the subject has moved, with the change position X _{i + 1} as a boundary, and the continuity is determined (step S9). For example, in the case shown in FIG. 3, when the AF evaluation values of the B frame and the C frame are switched at the position x, the result is as shown in FIG. In the example shown in FIG. 6, the connection is continuous, but the connection is not always continuous, so the continuity is detected. That is, with respect to the AF evaluation value after replacement, it is checked whether or not the variation of the AF evaluation value in the replacement portion is greater than or equal to a predetermined value by the same operation as step S2. When it is determined that there is a change, it is determined that there is no continuity as a result of the replacement of the AF evaluation value, and when it is determined that there is no change, it is determined that there is continuity.

When determining the continuity, the direction of the fluctuation of the AF evaluation value is reversed between the AF frames before and after the movement. Therefore, the sign of the fluctuation, that is, the sign of Y _i −Y _{i + 1} is reversed between the B frame and the C frame. A condition for determining that the frame has been moved may be added.

  Then, as a result of the replacement, the position where the AF evaluation value is maximized is determined for each of the AF frame determined to have continuity of the AF evaluation value and the frame where the AF evaluation value set in step S7 has not changed. Then, an optimum position is selected from them, and the in-focus position is obtained (step S10). The in-focus position may be selected, for example, by selecting the closest position from the maximum positions of a plurality of AF frames, or may be the average position of the maximum positions of each AF frame, Alternatively, the position of the maximum value among the maximum values of the AF evaluation values may be set.

  With the above operation, even when the subject moves between AF frames during AF, the movement of the subject can be detected, the AF evaluation value can be corrected, and the correct in-focus position can be obtained.

  In the above description, the movement of the subject between the AF frames is described as one place. However, even when there are a plurality of places, the same processing can be performed at each place.

  Further, the method for detecting the AF evaluation value fluctuation and the movement of the subject is not limited to those described in the present embodiment, and other methods may be used.

  In addition, when a change in AF evaluation value or movement of a subject is detected, a display that warns about this may be displayed on the display device, or the focus operation may be automatically restarted.

  In addition to the case where the subject itself moves, even if the subject moves relatively due to the movement of the camera or the angle of view, the same effect can be obtained by performing the same processing operation. It is done.

(Second Embodiment)
In the second embodiment, as in the first embodiment, the operation for obtaining the in-focus position is changed according to whether or not the subject has moved without correcting the AF evaluation value for the AF frame to which the subject has moved. By doing so, an example of improving the reliability of the in-focus position will be described.

  With reference to the flowchart shown in FIG. 7, the processing operation for obtaining the in-focus position using information on whether or not the subject has moved will be described. First, the presence / absence of movement of the subject is detected (step S11). The method for determining whether or not the subject has moved is the same as that described in the first embodiment, and details thereof are omitted.

  When there is no movement of the subject (step S12), a position where the maximum is obtained is obtained using all the acquired AF evaluation values (step S14).

  On the other hand, when the subject has moved (step S12), the AF evaluation values are divided before and after that, and the maximum position is obtained for each (step S13). For example, in the case of the B frame in FIG. 3, the AF evaluation value before the position x and the AF evaluation value after the position x are separated, and a local maximum position is obtained for each. There is no maximal position for the part before the position x, and there is a maximal position for the part after the position x. Accordingly, only the local maximum position after the position x is adopted.

  The above processing operation is performed for all AF frames (step S15), and an optimum in-focus position is obtained from the AF frames for which the maximum value has been obtained (step S16). For example, the closest one is selected and set as the in-focus position. By selecting the closest one, it is possible to avoid a void where the background is in focus and the subject in front is blurred in a scene where two people are standing apart. .

  In the above description, the AF frame in which the subject has moved is divided into the front and rear of the movement position, and the respective local maximums are obtained. However, the AF frame in which the subject has moved is not used, and there is no movement. The in-focus position may be obtained from the AF frame.

(Third embodiment)
In the third embodiment, an example in which the AF area is increased will be described. In this embodiment, as shown in FIG. 8, the AF frame (a) displayed on the display device and the actual AF frame (b) are changed and used. In other words, when viewed from the user, the auto-focus AF area operates so that there is only one point, but in actuality, AF is performed in the nine-point AF area. The purpose is to obtain an in-focus position with high accuracy using the information of the AF area.

  Specifically, the in-focus position is obtained according to the flowchart shown in FIG. First, as shown in FIG. 8B, an AF operation is performed with nine AF frames (step S17).

  Next, the movement of the subject is detected by the method for detecting the movement of the subject described in the first embodiment (step S18).

  Then, it is determined whether or not the subject has moved from the C frame to the A frame (step S19). If it is detected that the subject has moved from the C frame to the A frame, the process proceeds to step S20, which will be described in the first embodiment. The AF evaluation value is corrected by the method described above to obtain the in-focus position. On the other hand, if it is not detected that the frame has moved from the C frame to the A frame, the process proceeds to step S21 to detect the in-focus position using only the C frame.

  By configuring as described above, the user intends to perform AF at one point, so the center AF area is adjusted to the subject that he / she wants to adjust, and the direction of the camera is adjusted. Even in the case of movement, the in-focus position can be obtained using the surrounding AF results, and the reliability of the in-focus position is improved.

  In the above description, only one AF frame is displayed. However, a plurality of AF frames may be displayed as shown in FIG. 10, and more AF frames may be actually used.

  An object of the present invention is to supply a storage medium storing software program codes for realizing the functions of the above-described embodiments to a system or apparatus, and the computer (or CPU or MPU) of the system or apparatus stores the storage medium. Needless to say, this can also be achieved by reading and executing the program code stored in.

  In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the program code itself and the storage medium storing the program code constitute the present invention.

  As a storage medium for supplying the program code, for example, a flexible disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a CD-R, a magnetic tape, a nonvolatile memory card, a ROM, or the like can be used.

  Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also an OS (basic system or operating system) running on the computer based on the instruction of the program code. Needless to say, a case where the functions of the above-described embodiment are realized by performing part or all of the actual processing and the processing is included.

  Further, after the program code read from the storage medium is written to a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, the function expansion is performed based on the instruction of the program code. It goes without saying that the CPU or the like provided in the board or function expansion unit performs part or all of the actual processing, and the functions of the above-described embodiments are realized by the processing.

It is a figure which shows schematic structure of a digital camera. It is a figure which shows the example of a some AF frame. It is a figure which shows the example of AF evaluation signal in each frame when a to-be-photographed object moves. It is a flowchart for demonstrating the processing operation | movement until it calculates | requires the focus position in 1st Embodiment. It is a figure which shows the relationship between a to-be-photographed object distance and AF evaluation signal. It is a figure which shows AF evaluation signal after correction | amendment. It is a flowchart for demonstrating the processing operation | movement until it calculates | requires the focus position in 2nd Embodiment. It is a figure which shows the example of the AF frame in 3rd Embodiment. It is a flowchart for demonstrating the processing operation | movement until it calculates | requires the focus position in a 3rd Example. It is a figure which shows the other example of AF frame in 3rd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical system 2 Focus lens 3 Image pick-up element 4 Pre-processing circuit 5 A / D converter 6 Memory controller 7 Memory 8 Recording medium 9 SW1 switch 10 SW2 switch 11 Focus position determination part 12 Subject movement detection part 13 AF frame setting part 14 Scanning Position / Range Setting Unit 15 AF Evaluation Value Calculation Circuit 16 Focus Lens Drive Circuit 17 Control Unit

Claims (15)

An imaging apparatus comprising: a focus lens that performs focus adjustment of a subject image; a focus lens driving unit that drives the focus lens; and an image sensor that photoelectrically converts light imaged through the focus lens;
An arithmetic means for calculating a contrast detection signal based on an output signal from the image sensor for a plurality of AF areas while driving the focus lens;
Subject movement detection means for detecting subject movement between AF areas from the contrast detection signal calculated by the calculation means;
An imaging apparatus comprising: an in-focus position determining unit that obtains an in-focus position according to a detection result of the object movement by the object movement detecting unit.   2. The imaging according to claim 1, wherein the in-focus position determination unit corrects a contrast detection signal in an AF area where the subject moves, and obtains the in-focus position using the corrected contrast detection signal. apparatus.   The imaging apparatus according to claim 2, wherein the in-focus position determination unit performs correction by exchanging a part of the contrast detection signal between AF areas related to subject movement.   The imaging apparatus according to claim 1, wherein the in-focus position determining unit obtains an in-focus position according to whether or not the subject has moved.   The imaging apparatus according to claim 4, wherein the in-focus position determining unit obtains an in-focus position using only a contrast detection signal in an AF area where there is no subject movement.   The imaging apparatus according to claim 4, wherein the focus position determination unit divides the contrast detection signal before and after the movement of the subject in the AF area where the subject moves, and independently obtains the focus position.   The imaging apparatus according to claim 1, wherein the subject movement detection unit detects a portion where a variation amount of a contrast detection signal is large.   The imaging apparatus according to claim 7, wherein the subject movement detection unit determines whether or not a portion where the variation amount of the contrast detection signal is large matches in an adjacent AF area.   When the location where the variation amount of the contrast detection signal is large matches in an adjacent AF area, the subject movement detection means replaces the contrast detection signal of each AF area at that location and determines its continuity. The imaging apparatus according to claim 8, wherein the imaging apparatus is characterized.   10. The apparatus according to claim 1, wherein a part of the plurality of AF areas is used only when a subject movement from another AF area is detected by the subject movement detection unit. Imaging device.   The imaging apparatus according to claim 10, wherein the position or area of the AF area is not displayed on the display apparatus for the AF area used only when the movement of the subject from the other AF area is detected.   The imaging apparatus according to claim 1, wherein when an object movement is detected by the object movement detection unit, this is displayed on a display device.   The imaging apparatus according to claim 1, wherein when the subject movement is detected by the subject movement detection unit, the focus operation is re-executed. A control method for an imaging apparatus, comprising: a focus lens that adjusts the focus of a subject image; a focus lens driving unit that drives the focus lens; and an image sensor that photoelectrically converts light imaged through the focus lens. And
A calculation means for calculating a contrast detection signal based on an output signal from an image sensor for a plurality of AF areas while driving the focus lens;
A procedure in which subject movement detection means detects subject movement between AF regions from the contrast detection signal calculated by the calculation means;
A method for controlling an imaging apparatus, comprising: a focusing position determination unit that obtains a focusing position in accordance with a detection result of subject movement by the subject movement detection unit. Controlling an imaging apparatus comprising: a focus lens that adjusts the focus of a subject image; a focus lens driving unit that drives the focus lens; and an image sensor that photoelectrically converts light imaged through the focus lens A computer program,
An arithmetic process for calculating a contrast detection signal based on an output signal from the image sensor for a plurality of AF areas while driving the focus lens;
Subject movement detection processing for detecting subject movement between AF areas from the contrast detection signal computed by the computation processing;
A computer program that causes a computer to execute an in-focus position determination process for obtaining an in-focus position according to a detection result of an object movement by the object movement detection process.

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