JP2005284156A - Camera with automatic focusing function and automatic focusing method of camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To generate a warning when a camera becomes a non-focused state during focus lock and to prevent photography at the non-focused state in accordance with transfer of the camera, etc. during the focus lock. <P>SOLUTION: After a focal lens is moved to a focused position by AF control (steps S16 to S26), whether or not the focused position continuously changes during the focus lock in which a shutter button is half-depressed is detected (steps S28 to S38). Then, when it is detected that the focused position changes during the focus lock (a step S32), the warning indicating the non-focused state is issued to a photographing person (a step S36). By this warning, the photographing person release the focus lock and makes the camera perform the AF control. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a camera with an automatic focus adjustment function and an automatic focus adjustment method for a camera, and more particularly to a technique for eliminating a macro shooting failure.

  Conventionally, there has been proposed a camera that has a normal mode for normal distance shooting and a macro mode for close-up shooting, and can prevent a shooting failure due to a setting error in these modes (Patent Document 1).

  This camera has an automatic focus adjustment function that calculates focus information according to the contrast of a subject from an image signal output from an image sensor such as a CCD, and moves the focus lens so that the focus information is maximized, When the normal mode is set, the focus information that is the maximum within the focus lens movement range corresponding to the normal mode is searched, and when the macro mode is set, the focus lens corresponding to the macro mode is moved. Searches for the maximum focus information within the range. When focus detection cannot be performed in each mode, the focus lens movement range in other modes is searched.

  As a result, appropriate shooting can be performed even when there is an error in the mode setting between the normal mode and the macro mode.

Further, a normal camera has a focus lock function that prohibits (focus lock) the movement of the focus lens after moving to the in-focus position by automatic focus adjustment when the shutter button is half-pressed. This focus lock function is usually used when the composition is changed after focusing on a certain subject, so that the focus locked subject can be focused even after the composition is changed.
JP 2000-147368 A

  By the way, the focus lock function is also used when shooting while looking at the state of the subject (composition, movement, etc.) in a state where the focus is locked so as not to miss a photo opportunity. In a situation where the photographing operation is performed while the subject is locked and the state of the subject is observed, there is a problem that if the photographer (camera) or the subject moves slightly after the focus is locked, the subject cannot be focused.

  In addition, in the case of a digital camera, there is a problem that it cannot be confirmed whether or not it is in focus from a through image displayed on a liquid crystal monitor on the back of the camera. This is because the image size of the liquid crystal monitor is smaller than the actually captured image size.

  The camera described in Patent Document 1 cannot focus on the out-of-focus problem that occurs when the photographer (camera) or the like moves after the focus is locked during macro shooting.

  The present invention has been made in view of such circumstances, and can issue a warning when the camera is out of focus during focus lock. It is an object of the present invention to provide a camera with an automatic focus adjustment function and an automatic focus adjustment method for the camera that can prevent photographing in a focused state.

  In order to achieve the above object, a camera with an automatic focus adjustment function according to claim 1 is based on an operation of an automatic focus adjustment means for automatically moving a focus lens to a focus position where a subject is in focus, and an operation of a focus lock operation member. When there is a focus lock instruction, a focus lock unit that prohibits movement of the focus lens after moving to the in-focus position, and that the in-focus position has changed while the focus lock unit prohibits movement of the focus lens. And detecting means for detecting, and warning means for giving a warning indicating that the photographer is out of focus when a change in focus position is detected by the detecting means.

  That is, whether or not the in-focus position has continuously changed even after the focus lens is moved to the in-focus position by the automatic focus adjustment means and then the focus lens movement is prohibited (focus lock) by the focus lock instruction. Is detected. When it is detected that the in-focus position has changed while the focus is locked, a warning indicating that the photographer is out of focus is issued. By this warning, the photographer can release the focus lock and again perform the focus control by the automatic focus adjustment means, thereby preventing the photographing in the out-of-focus state.

  According to a second aspect of the present invention, in the camera with an automatic focus adjustment function according to the first aspect, the automatic focus adjustment unit has a focus corresponding to the contrast of the subject from the image signal in the focus detection area output from the imaging unit. A focus information calculation means for calculating information, and a position at which the focus information calculated by the focus information calculation means is a maximum value while moving the focus lens to each lens position for which focus information is calculated by the focus information calculation means And a lens movement control means for moving the focus lens.

  That is, in the case of a camera (digital camera) having an automatic focus adjustment unit that controls the focus lens so that the contrast of the subject is maximized from the image signal output from the imaging unit, the image signal is applied to a liquid crystal monitor on the back of the camera. The in-focus state cannot be confirmed from the displayed through image, and the present invention is particularly effective in this type of camera.

  According to a third aspect of the present invention, in the camera with an automatic focus adjustment function according to the second aspect, the focus information calculation unit detects focus information from an area wider than the focus detection area while the movement of the focus lens is prohibited. It is characterized by that.

  Thereby, after the focus lock, if the subject distance does not change even if the camera or the subject moves slightly up and down, left and right, the maximum value of the focus information does not change, or the change can be minimized. It is possible to prevent unnecessary warnings from occurring.

  According to a fourth aspect of the present invention, in the camera with an automatic focus adjustment function according to the second or third aspect, the detection means includes means for sequentially acquiring focus information from the focus information calculation means while the movement of the focus lens is prohibited. Means for normalizing the acquired focus information based on the maximum value, and means for determining that the in-focus position has changed when the normalized focus information falls below a predetermined threshold. It is characterized by that.

  Since it has been determined whether or not the focus position has changed based on the standardized focus information, the focus position can be accurately changed without being affected by the contrast of the subject or shooting conditions (non-focus state). Can be detected.

  5. A camera with an automatic focusing function according to claim 1, further comprising mode setting means for setting a standard mode for standard distance shooting or a macro mode for short distance shooting. The detecting means and the warning means can be operated only when the macro mode is set by the mode setting means.

  This is because, in particular, when shooting in the macro mode, if the camera or the like slightly moves while the focus is locked, the focused state is greatly affected. On the other hand, when shooting in the standard mode, there is a shooting method in which a certain subject is focused and focus-locked, and then the composition is changed. However, in this case, it is not preferable to generate a warning.

  According to a sixth aspect of the present invention, there is provided an automatic focus adjustment method for a camera, the step of automatically moving a focus lens to a focus position where a subject is in focus, and a focus lock instruction input, after moving to the focus position. A step of prohibiting the movement of the focus lens, a step of detecting whether or not the focus position has changed while the movement of the focus lens is prohibited, and a change in the focus position while the movement of the focus lens is prohibited. And a step of giving a warning indicating that the photographer is out of focus when detected.

  According to the present invention having the above-described configuration, a warning can be generated when the in-focus state is reached while the focus is locked, and the photographer can release the focus lock and prompt the execution of automatic focus adjustment again. it can. Thereby, it is possible to prevent photographing in an out-of-focus state due to movement of the camera in focus lock or the like.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a camera with an autofocus function and a camera autofocus method according to the present invention will be described in detail below with reference to the accompanying drawings.

  FIG. 1 is a block diagram showing an embodiment of a camera with an automatic focusing function according to the present invention.

  A camera 10 with an automatic focus adjustment function shown in the figure is a digital camera. The imaging unit of the digital camera 10 includes a lens group 12 including a focus lens, an aperture 14 and an image sensor (CCD) 16, and an object image formed on the light receiving surface of the CCD 16 via the lens group 12 and the aperture 14 is Each sensor converts the signal charge into an amount corresponding to the amount of incident light. The signal charges accumulated in this way are sequentially read out as voltage signals corresponding to the signal charges. The CCD 16 has a so-called electronic shutter function that can sweep out the accumulated signal charge with a shutter gate pulse, thereby controlling the charge accumulation time (shutter speed).

  The voltage signal sequentially read from the CCD 16 is applied to an analog front end (AFE) 18. The AFE 18 includes a correlated double sampling circuit (CDS circuit), an amplifier, an A / D converter, and the like. The CDS circuit performs correlated double sampling processing on a voltage signal input based on a CDS pulse applied from the timing signal generation circuit 20. To do. The signal processed by the CDS circuit is gain-controlled by an amplifier and then applied to the A / D converter. The A / D converter converts the input signal into a digital R, G, B signal for each pixel based on the AD pulse applied from the timing signal generation circuit 20 and outputs it.

  The CCD 16 and the AFE 18 are driven in synchronism with a timing signal applied from the timing signal generation circuit 20. The focus lens and the diaphragm 14 of the lens group 12 are driven by a lens driving unit 22 and a diaphragm driving unit 24, respectively, and are subjected to focus control and aperture control.

  The R, G, B signals output from the AFE 18 are added to the main signal processing unit 26 and the AF signal processing unit 28. The R, G, and B signals applied to the main line signal processing unit 26 are temporarily stored in a memory 30 such as a DRAM, and then appropriately read out from the memory 30 to be used for white balance adjustment and gamma in the signal processing unit 26. Signal processing such as correction and YC processing is performed and stored in the memory 30 again. The YC-processed luminance signal Y and chroma signals Cr and Cb (YC signal) are output to a display unit 32 such as a liquid crystal monitor. Thereby, a through image, a captured still image, and the like can be displayed on the display unit 32.

  Further, the YC signal after photographing is compressed into a predetermined format by the compression / decompression unit 34 and then recorded on a recording medium such as a memory card by the recording device 36. Further, in the reproduction mode, the image data recorded on the memory card or the like is decompressed by the compression / decompression unit 34 and then output to the display unit 32 so that the reproduced image is displayed on the display unit 32. .

  The AF signal processing unit 28 extracts high-frequency components of the R, G, and B signals applied from the AFE 18, calculates focus information obtained by integrating the extracted high-frequency components, and uses the focus information as a central processing unit. (CPU) 38 to output.

  The CPU 38 performs overall control of each circuit based on input from the operation unit 40 (including a shutter button, a mode dial, a cross key, etc.), and an auto for driving and controlling the lens driving unit 22 and the aperture driving unit 24. Focus (AF) control, automatic exposure (AE) control, white balance (WB) correction, and the like are performed, and control for generating a warning indicating that the in-focus state is not generated from the warning generation unit 42 is performed.

  In the AF control, the focus lens is moved over a predetermined focus lens moving range, and the maximum value of the focus information input at each lens position from the AF system signal processing unit 28 at that time is obtained. This is contrast AF that moves the focus lens to a lens position where the focus lens is obtained. When the shutter button is half-pressed, the focus lens is moved to the in-focus position.

  The digital camera 10 also has mode setting means for switching between a standard mode for standard distance shooting and a macro mode for short distance shooting, and the standard mode is set during the AF control. If the macro mode is set, the focus position is searched within the focus lens movement range corresponding to the standard distance (for example, about 60 cm to infinity). The focus position is searched within the focus lens movement range corresponding to 80 cm).

  In the AE control, when the shutter button is half-pressed, R, G, and B signals are captured, and subject luminance (shooting EV value) is obtained based on an integrated value obtained by integrating these R, G, and B signals. Based on this, the aperture value and shutter speed at the time of shooting are determined. Then, when the shutter button is fully pressed, the aperture is driven so that the determined aperture value is obtained, and the charge accumulation time is controlled by the electronic shutter so that the determined shutter speed is obtained, and image data for one frame is obtained. After taking in and performing necessary signal processing, it is recorded on a recording medium.

  Next, the automatic focus adjustment method of the camera according to the present invention will be described.

  FIG. 2 is an overall flowchart including AF processing at the time of automatic focusing of the camera according to the present invention, and particularly shows a case where the macro mode is set.

  First, when the macro mode is set, the focus lens movement range corresponding to the short-distance shooting range in the macro mode is acquired (steps S10 and S12), and the AF control described below is performed within the focus lens movement range. .

  It is detected whether or not a two-stroke shutter button (a shutter button that turns on the switch S1 when pressed halfway and a switch S2 that turns on when fully pressed) is pressed halfway (the switch S1 is turned on) (step S14). When is pressed halfway, the AF system signal processing unit 28 takes in the R, G, and B signals after A / D conversion output from the AFE 18 when the subject is imaged (step S16).

  Subsequently, the AF signal processing unit 28 extracts high-frequency components of the R, G, and B signals using a high-pass filter (HPF) (step S18). FIG. 3 is a graph showing an example of the amplitude characteristic of the HPF that extracts high-frequency components of the R, G, and B signals.

  Subsequently, the high frequency components in the focus detection area 1 among the high frequency components of the R, G, and B signals that have passed through the HPF are integrated (step S20). The integrated value obtained in this way is used as focus information indicating the magnitude of the contrast of the subject in the focus detection area 1.

  The focus detection area 1 is the central four areas among the divided areas obtained by dividing one screen into 64 (= 8 × 8) as shown in FIG.

  Next, it is determined whether or not the focus lens has been moved over the focus lens movement range acquired in step S12 (whether or not the search has been completed) (step S22). If the search is not completed, the focus lens is moved by a minute amount (step S24), and the process returns to step S16. By repeating steps S16 to S24, focus information for each lens position within the focus lens movement range is acquired.

  When the search is completed, the maximum value of the focus information acquired for each lens position within the focus lens movement range is obtained, and the focus lens is moved to the lens position (focus position) where the maximum value is obtained (step S26). ).

Thereafter, the integrated value (focus information) of the focus detection areas 1 to 5 is acquired (step S28). The focus detection areas 2 to 5 are four areas around the focus detection area 1 including a part of the focus detection area 1 as shown in FIG. Subsequently, the focus information of each area 1 to 5 is normalized by dividing by the maximum value of area 1 obtained in step S28, and the maximum value H _max (= MAX {(area 1 to area 1) of the normalized focus information. 5) / area 1}) is obtained (step S30).

Next, it is determined whether or not the maximum value H _{max of the} normalized focus information is less than a predetermined threshold Th (step S32). Here, the predetermined threshold value Th is whether or not the distance between the camera and the subject has changed to such an extent that the focus lens is not in focus after the focus lens is moved to the in-focus position in step S26 (whether the in-focus state has been achieved). This is a threshold value for determining whether or not.

  Also, the reason for using the maximum value of the focus information in the area (areas 1 to 5) wider than the focus detection area 1 is that the camera does not move in the front-rear direction (the subject distance does not change). This is to prevent the maximum value obtained when the lens moves in the vertical and horizontal directions from changing with respect to the maximum value obtained during AF control. That is, when the focus information of only area 1 is used, even if the camera moves slightly only in the vertical and horizontal directions, the focus information is greatly reduced from the maximum value obtained during AF control, and the subject distance does not change. This is because it is determined to be out of focus.

  Further, the reason for normalizing the focus information of each area 1 to 5 based on the maximum value of area 1 obtained in step S28 is that the focus information is properly in-focused without being affected by the contrast of the subject and the shooting conditions. This is to determine whether or not it has become.

In step S32, when the maximum value H _max is not less than the predetermined threshold Th (that is, when the in-focus state is maintained), whether or not the shutter button is half-pressed (S1 is ON). Is discriminated (step S34). On the other hand, when the maximum value H _max is less than the predetermined threshold Th, an AF warning indicating that the in-focus state is present is generated to notify the photographer (step S36).

  This AF warning is performed by warning display in the warning generation unit 42 (FIG. 1) and the display unit 32. The warning generation unit 42 is, for example, a finder lamp (red) provided in the optical finder or in the vicinity of the optical finder, and a warning can be displayed by blinking the finder lamp. Also, the display unit 32 can display a warning by overlaying a warning message on the monitor screen. Further, a warning may be generated by voice or buzzer.

  If it is determined in step S34 that the shutter button is half-pressed, it is determined whether or not the shutter button is fully pressed (S2 is ON) (step S38). If the shutter button is not fully pressed, the process returns to step S28, and the process from step S28 to step S36 is repeated while the shutter button is half-pressed (that is, during the focus lock period).

Accordingly, when the camera or the like moves while the focus is locked and the maximum value H _max becomes less than the predetermined threshold Th, an AF warning is issued in the above-described step S36.

  On the other hand, when the half-press of the shutter button is released during the focus lock (S1 is OFF in step S34), the process returns to step S14, where it is determined whether or not the shutter button is half-pressed again.

  Therefore, when an AF warning is issued, the photographer can release the focus lock and again perform AF control in steps S16 to S26, thereby preventing photographing in an out-of-focus state. be able to. Note that when the AF warning is issued, the photographer may move the camera back and forth so that the AF warning disappears while the focus is locked.

  If it is determined in step S38 that the shutter button has been fully pressed (S2 is turned on), actual imaging is performed at the current lens position of the focus lens (step S40), and R, G, After various signal processing of the B signal, an image is recorded on the recording medium (steps S42 and S44).

  In this embodiment, the AF warning or the like when the macro mode is set has been described. However, the same AF warning or the like is also performed when the standard mode for standard distance shooting is set. Also good. In addition, although the description has been given of the automatic focus adjustment unit that performs the contrast AF using the image signal output from the CCD, the present invention is not limited thereto. For example, the subject is imaged by a pair of left and right photoelectric conversion elements (line sensors). Even those using an AF sensor that calculates the object distance from the deviation amount of the left and right sensor images obtained by the left and right line sensors, or other automatic focus adjustment means using a sensor that performs triangulation In addition, the present invention is not limited to a digital camera and can be applied to a silver salt camera.

1 is a block diagram showing an embodiment of a camera with an automatic focusing function according to the present invention. Entire flowchart including AF processing at the time of automatic focus adjustment of the camera according to the present invention Graph showing amplitude characteristics of HPF The figure which shows the division area of the whole screen used in order to demonstrate a focus detection area

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Digital camera, 12 ... Lens group, 14 ... Aperture, 16 ... Image pick-up element (CCD), 18 ... Analog front end (AFE), 22 ... Lens drive part, 24 ... Aperture drive part, 26, 28 ... Signal Processing unit 30 ... Memory 32 ... Display unit 34 ... Compression / decompression unit 36 ... Recording device 38 ... Central processing unit (CPU) 40 ... Operation unit 42 ... Warning generating unit

Claims (6)

Automatic focus adjustment means for automatically moving the focus lens to a focus position where the subject is in focus;
A focus lock means for prohibiting movement of the focus lens after moving to the in-focus position when there is a focus lock instruction by operating a focus lock operation member;
Detection means for detecting that the focus position has changed while the focus lens is prohibited from moving the focus lens;
Warning means for giving a warning indicating that the photographer is out of focus when a change in focus position is detected by the detection means;
A camera with an automatic focusing function, characterized by comprising   The automatic focus adjustment unit calculates focus information from the image signal in the focus detection area output from the imaging unit, and calculates focus information according to the contrast of the subject, and the focus information calculation unit calculates the focus information. And a lens movement control unit that moves the focus lens to each lens position and moves the focus lens to a position where the focus information calculated by the focus information calculation unit becomes a maximum value. Item 2. The camera with an automatic focusing function according to Item 1.   The camera with an automatic focus adjustment function according to claim 2, wherein the focus information calculation unit detects focus information from an area wider than the focus detection area while prohibiting movement of the focus lens.   The detection means includes means for sequentially acquiring focus information from the focus information calculation means while prohibiting movement of the focus lens; means for normalizing the acquired focus information based on the maximum value; 4. The camera with an automatic focus adjustment function according to claim 2, further comprising means for determining that the in-focus position has changed when the focus information becomes less than a predetermined threshold value.   It has mode setting means for setting a standard mode for standard distance shooting or a macro mode for short distance shooting, and the detection means and the warning means are operable only when the macro mode is set by the mode setting means. The camera with an automatic focusing function according to claim 1, wherein the camera has an automatic focusing function. Automatically moving the focus lens to the in-focus position where the subject is in focus;
A step of prohibiting movement of the focus lens after moving to the in-focus position when there is a focus lock instruction input;
Detecting whether or not the in-focus position has changed while the focus lens is prohibited from moving; and
When a change in the in-focus position is detected while movement of the focus lens is prohibited, a warning is given to the photographer indicating that the focus lens is out of focus;
A method of automatically focusing a camera, comprising:

Images