JP2006047645A - Focus adjusting device and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable focusing including the objects outside the range finding area, while shortening the distance measuring time by measuring the distance inside the range finding area. <P>SOLUTION: This focus adjusting device makes focusing by moving the focusing lens 2, based on the image signals obtained by photographing an object. It has a controllers 11, 12 to move the focusing lens by a predetermined amount; a distance measuring range setup means 13 to set up the moving range by specifying the limits the focusing lens can move; an AF evaluation calculating circuit 14 which uses the image signals obtained by photographing at various points, by moving the focusing lens within this range and detects the focused state at each point; and a focusing position deciding section 15, which checks if there is a focusing position within the moving range by using the detected focused states, and decides the position predetermined outside the moving range as the focusing point, if there is none. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a focus adjustment apparatus and method, and more particularly, to a focus adjustment apparatus and method used in an imaging apparatus such as a video camera or a digital still camera to adjust the imaging apparatus to an appropriate in-focus state.

  Conventionally, as an automatic focus adjustment method used in video equipment such as a digital still camera and a digital video camera, for example, a video signal obtained from an image sensor such as a CCD is analyzed to create a signal for evaluating a focused state, There is a method of determining the in-focus position using the signal. Since this method does not require a sensor dedicated to autofocus, it can be realized at low cost, has no advantages of parallax, and has high accuracy. On the other hand, since it is necessary to drive the focus lens within a predetermined focus adjustment distance range, which is the movement range of the focus lens, and to sequentially generate evaluation signals, there is a disadvantage that it takes a long distance measurement time.

  As one method for shortening the distance measurement time, there is a method of narrowing a focus adjustment distance range (hereinafter referred to as a “distance distance range”) for distance measurement. For example, if the range from 50 cm to infinity is set as the distance measurement distance range during normal shooting, the distance measurement time can be shortened by setting the distance measurement distance range to 50 cm to 3 m, for example. It is possible (see, for example, Patent Document 1).

JP 05-107464 A

  However, the above-described method has a drawback that the subject cannot be focused when the subject is outside the distance measurement distance range in the distance measurement time reduction mode.

  The present invention has been made in view of the above problems, and it is possible to focus on a subject outside the distance measurement range while shortening the distance measurement time by performing distance measurement within the distance measurement range. Objective.

  In order to achieve the above object, the focus adjustment apparatus of the present invention that adjusts the focus by moving the position of the focus lens based on the image signal obtained by photographing the subject is configured to move the focus lens by a predetermined amount. Control means for controlling the focus lens, setting means for setting a movement range for specifying a part of the movable range of the focus lens, and photographing at each position where the focus lens is moved by the predetermined amount within the movement range A detection means for detecting a focus state at each position using an image signal, and determining whether or not a focus position exists within the movement range from the detected focus state, and a focus position Is determined based on the in-focus state, and when it is determined that the in-focus position does not exist, a predetermined position outside the movement range is set to the in-focus position. As decided And a focus position determining means for.

  The focus adjustment method of the present invention, which adjusts the focus by moving the position of the focus lens based on the image signal obtained by photographing the subject, sets a movement range for specifying a part of the movable range of the focus lens. A setting step for moving the focus lens by a predetermined amount within the moving range, and a detection step for detecting an in-focus state at each position using an image signal photographed at each moved position, and the detection A determination step for determining whether or not a focus position exists within the movement range from the focused state, and when it is determined that a focus position exists, the focus position is determined based on the focus state. And a focus position determination step of determining a predetermined position outside the movement range as the focus position when it is determined that the focus position does not exist.

  As described above, according to the present invention, it is possible to focus on a subject outside the distance measurement range while shortening the distance measurement time by performing distance measurement within the distance measurement distance range.

  The best mode for carrying out the present invention will be described below in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic diagram of a digital camera using a focus adjustment apparatus according to an embodiment of the present invention.

  The digital camera according to the present embodiment has an optical system 1 and a focus lens 2 and photoelectrically converts light imaged by these using an image sensor 3 and removes output noise, or a nonlinear effect performed before A / D conversion. A signal digitized through a pre-processing circuit 4 having an amplification circuit and the like and an A / D converter 5 is stored in a memory 7 through a memory controller 6, and white balance processing, γ is performed by a signal processing circuit (not shown). Processing such as conversion and compression is performed as necessary, and then recorded on the recording medium 8.

  The focus operation is performed when the focus lens driving circuit 12 drives the focus lens 2 based on the control of the control unit 11. The focus lens driving circuit 12 moves the focus lens 2 by a predetermined amount, and uses a signal corresponding to the contrast of the image (hereinafter, referred to as “focus adjustment position”) using the image signal captured at each position (hereinafter referred to as “focus adjustment position”). The AF evaluation value calculation circuit 14 calculates “AF evaluation value”.

  The AF evaluation value is calculated as follows. First, a horizontal band-pass filter is applied to each line of image data in a distance measurement frame indicating a part of an image used for distance measurement among the captured images. Next, the one having the largest absolute value of the bandpass output signal is selected for each line. Integrate the selected signal vertically. With the above configuration, a high contrast in the horizontal direction is detected, and integration in the vertical direction leads to an improvement in signal S / N. By calculating in this way, it is possible to obtain an AF evaluation value that is a signal that has the largest value in the in-focus state and decreases in the de-focused state. Therefore, a focused image can be obtained by shooting at the focus adjustment position where the maximum AF evaluation value is obtained.

  The focus lens 2 is driven within the distance measurement distance range which is the movement range of the focus lens 2 set by the distance measurement range setting unit 13 and is as described above at each focus adjustment position in the AF evaluation value calculation circuit 14. After the focus position determination unit 15 determines the focus position based on the AF evaluation value calculated in this way, the focus lens drive circuit 12 drives the focus lens 2 to that position. Note that a focus operation is performed when SW1 (9) is operated, and imaging and image recording are performed when SW2 (10) is operated.

  With reference to the flowchart of FIG. 2 and FIG. 3, the focusing operation when the distance measuring distance range is limited in the digital camera having the above configuration will be described in detail. FIG. 3 is a diagram showing the relationship between each focus adjustment position (subject distance) and the AF evaluation value calculated at each position. In this embodiment, the range of subject distances D1 to D2 is a distance measurement distance range. And

  In step S1, the focus lens 2 is driven by a predetermined amount within the distance measurement distance range (D1 to D2) set by the distance measurement range setting unit 13, and the AF evaluation value calculation circuit 14 performs AF evaluation value at each focus adjustment position. Perform the operation. FIG. 3 shows an example of the AF evaluation value when the subject is at infinity. For the purpose of explanation, the AF evaluation value is also shown for the focus adjustment position outside the distance measurement range (white point). No data is actually obtained from the AF evaluation value calculation operation in S1.

In step S2, it is determined whether or not the subject is out of the distance measuring distance range using the acquired AF evaluation value. When determining whether or not the subject is farther than the far end of the distance measuring range, the acquired AF evaluation values are E [0], E [1],... E [ n] (n is a value one smaller than the number of subject distances for which the AF evaluation value is calculated), and the maximum value of the acquired AF evaluation value is Emax.
E [0] = Emax and E [1]-E [2]> 0

Is satisfied, it is determined that the subject is at a distance farther than the distance measurement distance range. Thereby, in the example shown in FIG. 3, it turns out that it is determined that there is a subject at a distance farther than the distance measuring distance range.
In addition, when determining whether or not the subject is closer than the near end of the distance measuring distance range, among the acquired AF evaluation values, using the AF evaluation value with a short subject distance,
E [n] = Emax and E [n-1]-E [n-2]> 0

Is satisfied, it is determined that the subject is at a distance closer than the distance measurement distance range.
If it is determined in step S3 that the subject is outside the distance measurement range, the process proceeds to step S4, and if not, the process proceeds to step S5.

  In step S4, a preset focus adjustment position outside the distance measurement range is set as a focus position depending on whether the subject is farther or closer than the distance measurement range.

  On the other hand, if there is a subject within the distance measuring distance range, it is determined in step S5 whether or not focusing is possible. If focusing is possible, the process proceeds to step S6 and the subject distance having the largest AF evaluation value is determined. When the focus position is determined and focus is impossible, such as when the subject is dark, the process proceeds to step S7, and a predetermined focus adjustment position within the distance measurement distance range is set as the focus position.

  In step S8, the focus lens 2 is driven to the in-focus position set in any of steps S4, S6, or S7.

  The distance measurement range used in the present embodiment is, for example, a fixed distance measurement distance range determined in advance, or a lens that can be attached when the digital camera is an interchangeable lens type. (Specifically, according to the focal length and product type), a distance measuring distance range is stored in advance, and one of the distance measuring distance ranges stored according to the attached lens is stored. The distance measurement distance range is stored in advance according to the selected shooting mode (landscape shooting mode, portrait shooting mode, close-up shooting mode, etc.), and the distance measurement distance range stored in accordance with the set shooting mode is stored. Various methods are conceivable, such as selecting one or setting the user arbitrarily.

  In particular, the distance close to the depth of field from the infinite point is set as the far end of the distance measuring range (D1 in FIG. 3), and the object is located at the intermediate point between the infinite point and D1 (ie, the hyperfocal distance) If it is set as the in-focus position outside the distance measurement range when it is farther than the object distance, the object distance is determined when it is determined that the object is farther than the distance measurement distance range as shown in FIG. Since the subject existing in the range from D1 to infinity exists within the depth of field, the subject can be substantially focused at any distance. Therefore, it is possible to focus even when it is determined that the subject is outside the distance measurement distance range. Thus, by adjusting the distance measurement distance range and the in-focus position outside the distance measurement distance range, the distance measurement distance range is limited to D1 to D2, but the actual focus range From infinity to D2.

  As described above, according to the present embodiment, when it is determined that there is a subject outside the distance measuring distance range, the focus position is controlled outside the distance measuring distance range, and it is determined that the subject is within the distance measuring range. In this case, it is possible to perform focus control on the position of the distance measurement result, and it is possible to easily obtain a focused state for a subject outside the distance measurement distance range.

  In the above embodiment, the case where the focus adjustment device of the present invention is mounted on a digital camera has been described. However, the present invention is not limited to a digital camera. If the focus state of a captured image can be calculated, the focus adjustment is performed. Needless to say, the focus adjustment apparatus or method of the present invention can be applied to any imaging apparatus that performs the above.

<Other embodiments>
An object of the present invention is to supply a storage medium (or recording medium) in which a program code of software for realizing the functions of the above-described embodiments is recorded to a system or apparatus, and a computer (or CPU or MPU) of the system or apparatus. Needless to say, this can also be achieved by reading and executing the program code stored in the storage medium. In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiment, and the storage medium storing the program code constitutes the present invention. Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also an operating system (OS) running on the computer based on the instruction of the program code. It goes without saying that a case where the function of the above-described embodiment is realized by performing part or all of the actual processing and the processing is included. Examples of the storage medium for storing the program code include a flexible disk, hard disk, ROM, RAM, magnetic tape, nonvolatile memory card, CD-ROM, CD-R, DVD, optical disk, magneto-optical disk, MO, and the like. Can be considered. Also, a computer network such as a LAN (Local Area Network) or a WAN (Wide Area Network) can be used to supply the program code.

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

  When the present invention is applied to the above-described storage medium, the program code corresponding to the flowchart shown in FIG. 2 described above is stored in the storage medium.

1 is a block diagram illustrating a schematic configuration of a digital camera according to an embodiment of the present invention. It is a flowchart which shows the focus operation | movement in embodiment of this invention. It is a figure which shows the example of AF evaluation value when a to-be-photographed object exists in infinity in embodiment of this invention.

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
10 SW2
DESCRIPTION OF SYMBOLS 11 Control part 12 Focus lens drive circuit 13 Distance measurement range setting part 14 AF evaluation value calculation circuit 15 Focus position determination part

Claims (14)

A focus adjustment device that performs focus adjustment by moving the position of a focus lens based on an image signal obtained by photographing a subject,
Control means for controlling the focus lens to move by a predetermined amount;
Setting means for setting a moving range for specifying a part of the movable range of the focus lens;
Detecting means for detecting a focused state at each position using an image signal captured at each position where the focus lens is moved by the predetermined amount within the moving range;
From the detected focus state, it is determined whether or not a focus position exists within the movement range, and when it is determined that a focus position exists, the focus position is determined based on the focus state. And a focus position determining unit that determines a predetermined position outside the movement range as the focus position when it is determined that the focus position does not exist.   The determination means determines whether the in-focus point is on the infinite point side or the near side with respect to the movement range when the in-focus position does not exist within the movement range, and the in-focus position The focus adjustment apparatus according to claim 1, wherein the determining unit determines the predetermined position on the side determined to have the in-focus position as the in-focus position.   When the movement range does not include an overfocus position and the determination unit determines that a focus position exists on the infinite point side with respect to the movement range, the focus position determination unit determines the overfocus position as the focus position. The focus adjustment apparatus according to claim 2, wherein the focus adjustment apparatus is determined as follows.   The said setting means sets the position of the said focus lens corresponding to the distance close | similar to the distance for the depth of field from the infinite point as a far end of the said movement range, Any one of Claim 1 thru | or 3 characterized by the above-mentioned. A focus adjustment device according to claim 1.   5. The focus adjustment apparatus according to claim 1, wherein the setting unit sets the movement range according to at least one of a focal length, a type, and a shooting mode of a lens to be used.   The focus adjustment apparatus according to claim 1, wherein the setting unit sets the movement range in accordance with an instruction from a user. A focus adjustment method for performing focus adjustment by moving the position of a focus lens based on an image signal obtained by photographing a subject,
A setting step for setting a movement range for specifying a part of the movable range of the focus lens;
Within the movement range, the focus lens is moved by a predetermined amount, and using the image signal photographed at each moved position, a detection step for detecting a focused state at each position;
A determination step of determining whether or not a focus position exists within the movement range from the detected focus state;
When it is determined that the in-focus position exists, the in-focus position is determined based on the in-focus state. When it is determined that the in-focus position does not exist, a predetermined position outside the movement range is set. And a focus position determination step for determining the focus position.   In the determining step, when there is no in-focus position within the movement range, it is determined whether the in-focus position is on the infinite point side or the near side with respect to the movement range, and the in-focus position The focus adjustment method according to claim 7, wherein, in the determining step, the predetermined position on the side determined to be in focus is determined as the focus position.   If the movement range does not include an overfocus position and the determination step determines that a focus position exists on the infinite point side with respect to the movement range, the focus position determination step determines the overfocus position as the focus position. The focus adjustment method according to claim 8, wherein the focus adjustment method is determined as follows.   10. The setting step, wherein the position of the focus lens corresponding to a distance close to the distance corresponding to the depth of field from an infinite point is set as a far end of the moving range. The focus adjustment method according to any one of the above.   The focus adjustment method according to claim 7, wherein in the setting step, the moving range is set according to at least one of a focal length, a type, and a shooting mode of a lens to be used.   The focus adjustment method according to claim 7, wherein, in the setting step, the movement range is set in accordance with an instruction from a user.   A program executable by an information processing apparatus, comprising program code for realizing the focus adjustment method according to claim 7.   A storage medium readable by an information processing apparatus, wherein the program according to claim 13 is stored.

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