JP2010193074A - Device and method for adjusting focus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device and method for adjusting focus capable of rapidly bring an object to be focused into focus by suppressing degradation of detection performance of a main object in a low-illuminance condition. <P>SOLUTION: The device for adjusting focus includes a focus lens, a photoelectric conversion means, an extraction means, and a control means. The photoelectric conversion means converts an object image imaged by the focus lens to an electric signal. The extraction means extracts a signal component of a specific frequency band from an output signal of the photoelectric conversion means. The control means executes a first operation for identifying an object region to be focused by executing an AF scan operation before imaging preparation, and executes a second operation different from the first operation by executing the AF scan operation to execute a focusing operation in the imaging preparation. When the brightness of the object is smaller than a first threshold value before the imaging preparation, a third operation different from the first operation is executed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to a focus adjustment device, a focus adjustment method, and the like applied to an imaging device such as an electronic still camera having a focus adjustment function.

Conventionally, when performing autofocus (also referred to as AF) in an electronic still camera or a video camera, the lens position where the high frequency component of the luminance signal obtained from an image sensor using a CCD (charge coupled device) is maximized A method of setting the in-focus position is used. As one of these methods, the following scan method is known. That is, an evaluation value (also referred to as a focus evaluation value) based on the high frequency component of the luminance signal obtained from the image sensor while driving the lens over the entire moving range is stored each time. Among these, the lens position corresponding to the maximum value is set as the focus position.

As another method, a hill-climbing method (so-called Continuous AF, also referred to as continuous AF) is known in which the lens is moved in the direction in which the focus evaluation value increases and the position where the focus evaluation value is maximized. Yes.

In addition, a method for reducing the AF operation time by limiting the AF moving range by the scanning method performed after the shooting preparation instruction by performing continuous AF before the shooting preparation instruction and maintaining the in-focus state until now. (See Patent Document 1).

Japanese Patent No. 4106485

In the continuous AF, when an attempt is made to move the lens in the direction in which the focus evaluation value increases, the subject to be focused cannot be focused unless the region to be focused in the screen is known. In Patent Document 1, in the continuous AF, the focusing operation is made faster by combining the scan methods. However, since the user does not determine the subject to be focused (also referred to as the main subject) on the screen that the user wants to focus on, the subject to be focused cannot be focused depending on the shooting scene. This can happen.

On the other hand, when the subject is dark and the level of the video signal is low, using the video signal as it is, in addition to lack of brightness, it is difficult to obtain the original signal component of the focus evaluation value due to the influence of noise of the image sensor Become.

In view of the above problems, as technical features of the present invention, photoelectric conversion means for converting a subject image formed using a focus lens into an electrical signal, and a specific frequency band in a focus detection region from an output signal of the photoelectric conversion means A focus adjustment method in an imaging apparatus, comprising: an extraction means for extracting the signal component of the image sensor; a control means for controlling the operation of the entire apparatus; and a detection means for detecting the brightness of the focus detection area. First operation of moving the focus lens and specifying an object region to be focused by performing an AF scan operation for acquiring the output signal of the extraction means in the set focus detection region in association with the position of the focus lens And a second operation different from the first operation by performing the AF scan operation and performing a focusing operation during shooting preparation. A second step to be performed, and a third operation that performs a third operation different from the first operation when the brightness obtained by the detection means before the preparation for photographing is less than a first threshold value. And a process.

According to the present invention, it is possible to suppress a decrease in detection performance of a main subject in a low illuminance state and quickly focus on a subject to be focused. That is, for example, when determining a subject area to be focused in a screen in a low-light environment and focusing before preparing for shooting, the detection performance of the main subject area is reduced due to the S / N reduction of the focus evaluation value. To improve. In this way, it is possible to quickly focus on the subject to be focused upon when preparing for shooting.

1 is a block diagram illustrating a configuration of an imaging apparatus that is an embodiment of the present invention. It is a flowchart showing operation | movement of the focus adjustment apparatus which is an Example of this invention. It is a flowchart explaining the subroutine of stability determination in FIG. 3 is a flowchart for explaining a face detection AF scan subroutine in FIG. 2; It is a flowchart explaining the subroutine of the scene change determination in FIG.4, FIG.11, FIG.14 and FIG. 16 is a flowchart for explaining a focus determination subroutine in FIGS. 4, 12, and 15. It is a figure explaining the method of the focus determination in FIG. 3 is a flowchart for explaining a sub-routine for subject area specifying AF scanning in FIG. 2. It is a figure explaining the example of AF frame setting in FIG. It is a flowchart explaining the subroutine of the last reference determination in FIG. 10 is a flowchart for explaining a subroutine of a previous reference AF scan in FIG. 8. 12 is a flowchart for explaining a main subject area determination subroutine in FIG. 11; FIG. 13 is a diagram for explaining main subject region determination in FIG. 12. FIG. 9 is a flowchart for describing a zone AF scan subroutine in FIG. 8. FIG. FIG. 15 is a flowchart illustrating a subroutine for zone update determination in FIG. 14. FIG. It is a figure explaining the example of the zone update determination in FIG. It is a flowchart explaining the subroutine of uniform surface determination in FIG. It is a flowchart explaining the subroutine of a uniform surface determination in FIG. It is a figure explaining the method of the uniform surface determination in FIG. FIG. 9 is a flowchart for explaining a focus driving subroutine in FIG. 8. FIG. 3 is a flowchart for explaining a subroutine of continuous AF in FIG. 2. 3 is a flowchart illustrating a subroutine for determining scene instability in FIG. 2. FIG. 3 is a flowchart for explaining a subroutine of photographing processing in FIG. 2. FIG. FIG. 24 is a flowchart for explaining a main exposure AF subroutine in FIG. 23. FIG. FIG. 25 is a flowchart for explaining a main exposure AF scan subroutine in FIG. 24. FIG. It is a flowchart explaining the subroutine of this exposure process in FIG. 3 is a flowchart for explaining a subroutine of subject area specifying AF frame setting processing in FIG. 2 according to the first embodiment. FIG. 28 is a diagram for describing subject area specifying AF frame setting processing in FIG. 27; 6 is a flowchart for explaining a subroutine of subject area specifying AF frame setting processing in FIG. 2 according to the second embodiment. FIG. 30 is a diagram for explaining subject area specifying AF frame setting processing in FIG. 29;

Embodiments of the present invention will be described.
The following points are important in the apparatus and method of the present invention. If the brightness of the obtained subject is less than the first threshold before shooting preparation, a third operation different from the first operation for specifying the subject region to be focused by performing the AF scan operation is performed. Is to implement.

Based on the above concept, the basic embodiment of the apparatus and method of the present invention has the following configuration. The focus adjustment apparatus includes a focus lens for performing focus adjustment and its driving means, a photoelectric conversion means, an extraction means, a control means, and a subject luminance detection means. The photoelectric conversion means is an image sensor such as a CCD or a CMOS that converts an object image formed using a focus lens into an electric signal. The extraction unit extracts a signal component (typically a high frequency component) in a specific frequency band related to the luminance of the subject from the output signal of the photoelectric conversion unit. The subject luminance detecting means detects the brightness of the focus detection area. The control means controls the operation of the entire apparatus.

The control means may control the driving means to move the focus lens and perform an AF scan operation for acquiring the output signal of the extraction means in the focus detection region set by the photoelectric conversion means in association with the position of the focus lens. it can. Further, the control means can control the focus lens via the driving means based on the acquired output of the extracting means to perform the focusing operation. In addition, the control unit can perform a first operation for specifying a subject area to be focused by performing an AF scan operation before preparation for photographing. In addition, the control unit can perform a second operation different from the first operation by performing the AF scan operation and performing the focusing operation at the time of shooting preparation. Further, the control unit performs a third operation different from the first operation when the brightness obtained by the subject luminance detection unit is less than the first threshold before the preparation for photographing.

The focus adjustment method is a focus adjustment method in the image pickup apparatus having the above-described means, and includes the following first to third steps. In the first step, an AF scan operation is performed to acquire the output signal of the extraction unit in the focus detection area set by the setting unit or the like in association with the position of the focus lens, before moving to the preparation for photographing. Then, a first operation for specifying a subject area to be focused is performed. In the second step, at the time of shooting preparation, the AF scan operation is performed to perform the focusing operation, and a second operation different from the first operation is performed. In the third step, a third operation different from the first operation is performed when the brightness obtained by the subject luminance detection means is less than the first threshold before the preparation for photographing.

In the basic embodiment, more specific embodiments as described below are possible.
The third operation is an operation for specifying a subject area to be focused by performing the AF scan operation in which the operation mode of the photoelectric conversion unit and the frequency band in the extraction unit are set different from the first operation. It can be. The third operation may be an operation for specifying a subject region to be focused by performing the AF scan operation in which the size of the focus detection region is set to be different from that of the first operation. . The third operation may be an operation for specifying a subject region to be focused by performing the AF scan operation in which the number of the focus detection regions is set differently from the first operation.

In addition, the control means can perform a focus fixing operation that operates to fix the focus to a specific subject distance. In this case, the third operation is a subject to be focused by performing the AF scan operation when the brightness obtained by the subject luminance detecting means is equal to or higher than a second threshold that is darker than the first threshold. The operation is to specify the area. Then, when the brightness obtained by the subject brightness detection means is less than the second threshold, the operation is performed by the focus fixing operation.

The control means can perform the following continuous AF operation. In the continuous AF operation, when the focus lens is moved next from the output signal of the extraction means extracted before moving the focus lens by a predetermined amount and the output signal of the extraction means extracted after the movement. Determine the direction of movement. Then, the focus lens is moved in the movement direction, and this movement operation is repeated to move the focus lens to the peak position of the output signal of the extraction means. In this case, the third operation is a subject to be focused by performing the AF scan operation when the brightness obtained by the subject luminance detecting means is equal to or higher than a second threshold that is darker than the first threshold. The operation is to specify the area. When the brightness obtained by the subject brightness detecting means is less than the second threshold, the operation is performed by the continuous AF operation.

The control means can perform the focus fixing operation and can perform the continuous AF operation. In this case, the third operation is a subject to be focused by performing the AF scan operation when the brightness obtained by the subject luminance detecting means is equal to or higher than a second threshold that is darker than the first threshold. The operation is to specify the area. When the brightness obtained by the subject brightness detection means is less than the second threshold and greater than or equal to the third threshold that is darker than the second threshold, the operation is performed by the continuous AF operation. When the brightness obtained by the subject brightness detecting means is less than the third threshold value, the operation is performed by the focus fixing operation.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram illustrating a configuration of an electronic camera that is an imaging apparatus including a focus adjustment apparatus to which an embodiment of the present invention is applied.

In FIG. 1, reference numeral 101 denotes a photographing lens including a zoom mechanism. Reference numeral 102 denotes an aperture and a shutter which are light quantity control means for controlling the incident light quantity. Reference numeral 103 denotes an AE (Automatic Exposure) processing unit including driving means for the light quantity control means. Reference numeral 104 denotes a focus lens for focusing on an image sensor described later. Reference numeral 105 denotes an AF processing unit including a driving unit for the focus lens 104. Reference numeral 106 denotes a strobe. Reference numeral 107 denotes an EF (flash dimming) processing unit.

Reference numeral 108 denotes an image sensor as light receiving means or photoelectric conversion means for converting reflected light from the subject into an electrical signal. Reference numeral 109 denotes an A / D converter including a CDS (correlated double sampling processing) circuit that removes output noise of the image sensor 108 and a non-linear amplification circuit that performs processing before A / D conversion. An image processing unit 110 includes a luminance calculation unit that calculates the luminance of the subject from the output signal of the photoelectric conversion unit and an extraction unit that extracts a signal component in a specific frequency band from the output of the luminance calculation unit. Reference numeral 111 denotes a WB (white balance) processing unit. Reference numeral 112 denotes a format conversion unit.

Reference numeral 113 denotes a high-speed built-in memory (for example, a random access memory or the like, also referred to as DRAM). An image recording unit 114 includes a recording medium such as a memory card and its interface. Reference numeral 115 denotes a system control unit (also referred to as a CPU) that controls the system such as a photographing sequence as a control unit that controls the operation of the entire apparatus. 116 is an image display memory (also referred to as VRAM).
It is. Reference numeral 117 denotes an operation display unit that displays a shooting screen and a focus detection area at the time of shooting, in addition to image display, display for assisting operations, and display of camera status. Reference numeral 118 denotes an operation unit for operating the camera from the outside. Reference numeral 119 denotes a shooting mode switch for performing settings such as switching the face detection mode to ON or OFF.

Reference numeral 120 denotes a main switch for turning on the system. Reference numeral 121 denotes a shooting standby switch (also referred to as SW1) which is a focus position determination instruction means for performing shooting standby operations such as AF and AE.
It is. By operating SW1 (121), a focus position for photographing of the focus lens 104 is determined. The procedure for this determination will be described later. Reference numeral 122 denotes a photographing switch (also referred to as SW2) that performs photographing after the operation of SW1.

A face detection module 123 performs face detection using the image signal processed by the image processing unit 110 and sends one or more pieces of detected face information (position / size / reliability) to the CPU 115. Since the face detection method is not the main point of the present invention, detailed description thereof is omitted.

A moving object detection unit 124 detects whether or not the subject and background in the screen are moving and sends moving object information to the system control unit 115. Specifically, among the image signals processed by the image processing unit 110, two images arranged in time series are compared, and subject / background moving body information (motion amount, position, range) is obtained from the difference information. Is detected. An angular velocity sensor unit 125 detects the angular velocity of the camera itself and sends camera motion information to the CPU 115. Using this angular velocity sensor unit, it is also possible to detect whether the camera is held in a vertical position or a horizontal position.

The DRAM 113 is used as a high-speed buffer as temporary image storage means, or a working memory for image compression / decompression. The operation unit 118 includes, for example, the following. There are a menu switch for performing various settings such as a shooting function of the image pickup apparatus and a setting at the time of image reproduction, a zoom lever for instructing a zoom operation of the shooting lens, an operation mode switching switch between a shooting mode and a playback mode, and the like.

Next, the operation of the electronic camera according to the present embodiment will be described with reference to the flowchart of FIG. First, in S201, the CPU 115 determines the state (ON / OFF) of SW1 instructing to prepare for shooting. If the state is ON (on), the process proceeds to S212, and if it is OFF (off), the process proceeds to S202. move on. In S202, a scene stability determination is performed according to a procedure described later (see FIG. 3). In S203, it is checked whether or not the shooting scene is determined to be stable in S202. If it is determined that the photographing scene is stable, the process proceeds to S204, and if it is not determined that it is stable, the process returns to S201. Here, the state in which the photographing scene is stable means that the state of the subject to be photographed and the camera is stably maintained and is suitable for photographing.

In S204, it is checked whether or not a face is detected by the face detection module 123. If a face is detected, the process proceeds to S207, and if no face is detected, the process proceeds to S205. In S207, a face detection AF scan is performed according to a procedure described later (see FIG. 4), and the process proceeds to S209.

In S205, AF frame setting for subject area specification is performed. Here, the AF frame is an area for acquiring a focus evaluation value in the screen. The focus evaluation value is a value obtained by converting the analog video signal read from the image sensor 108 into a digital signal by the A / D converter 109 and extracting the high frequency component of the luminance signal from the output from the output. That is. Details of the AF frame setting for specifying the subject area will be described later with reference to FIG.

In S206, it is determined whether or not the subject specifying execution flag is TRUE. If it is TRUE, the subject area specifying AF scan in S208 is performed, and if it is FALSE, the process proceeds to continuous AF in S209. In S208, an AF scan for specifying a subject area is performed according to a procedure described later (see FIG. 8). In S209, continuous AF is performed according to the procedure described later (see FIG. 21). Here, without performing the continuous AF, a focusing operation is simply performed on the subject area that is specified only once, or only the subject area is specified, and the next second scanning operation is performed. It is also possible to take over. FIG. 9 is a diagram for explaining an example of AF frame setting in FIG.

In S210, the scene instability determination is performed according to the procedure described later (see FIG. 22). In S211, it is checked whether or not the shooting scene is determined to be unstable in S210. If it is unstable, the process proceeds to S201, and if it is not unstable, the process proceeds to S209. Here, the shooting scene is unstable means that the state of the subject to be shot and the state of the camera become unstable and are not suitable for shooting.

In S212, the focus degree determination flag is set to FALSE. In S213, photographing processing is performed according to a procedure described later (see FIG. 23).

In parallel with the operation described above, the AE processing unit 103 always controls the aperture and the shutter 102 based on the control signal from the CPU 115 so that the brightness of the image displayed on the operation display unit 117 is appropriate. An AE operation is performed.

FIG. 3 is a flowchart for explaining the scene stability determination of S202 in FIG. In S301, it is checked whether or not the camera movement amount detected by the angular velocity sensor unit 125 is equal to or less than a predetermined amount. If it is equal to or less than the predetermined amount, the process proceeds to S302, and if not, the process proceeds to S304. Here, it is determined whether the camera state is stable by checking that the camera operation amount is equal to or less than a predetermined amount.

In S302, it is checked whether or not the luminance change amount from the previous time is equal to or smaller than the predetermined amount. If the luminance change amount is equal to or smaller than the predetermined amount, the process proceeds to S303. Here, it is determined that the subject to be photographed has not changed by checking that the luminance change amount is not more than a predetermined value. In S303, it is determined that the shooting scene is in a stable state, and this process is terminated. In S304, it is determined that the shooting scene is not in a stable state, and this process is terminated.

FIG. 4 is a flowchart for explaining the face detection AF scan in S207 in FIG. In S401, AF frame setting is performed based on the face information (position / size) detected by the face detection module 123. In S402, the AF processing unit 105 moves the focus lens 104 to the scan start position. Here, the scan start position is determined based on the distance of the person estimated from the detected face size, for example. In S403, the CPU 115 stores the focus evaluation value at the current focus lens position in the DRAM 113. In S <b> 404, the current position of the focus lens 104 is acquired, and the CPU 115 stores the data of the position in the DRAM 113.

In S405, the CPU 115 determines the state (ON / OFF) of SW1 that instructs to prepare for photographing. If the state is ON, the process ends and the process proceeds to S212 shown in FIG. If so, the process proceeds to S406. In S406, scene change determination is performed according to a procedure described later (see FIG. 5). The scene change determination is a process for determining whether the scene to be photographed has changed from the state of the camera and the state of the subject.

In S407, the CPU 115 checks whether the current position of the focus lens 104 is equal to the scan end position. If both are equal, the process proceeds to S409, and if not, the process proceeds to S408. Here, the scan end position is determined based on, for example, the distance of the person estimated from the detected face size. In S408, the AF processing unit 105 moves the focus lens 104 by a predetermined amount in the scan end direction, and then returns to S403. In step S409, focus determination is performed according to a procedure described later (see FIG. 6).

In S410, it is checked whether or not the in-focus determination in S409 is “good”. If yes, the process proceeds to S411, and if not, the process proceeds to S414. Here, “◯” is a case where the contrast of the subject is sufficient and the subject exists within the scanned distance range.

In S411, an in-focus position where the focus evaluation value acquired in S403 reaches a peak is calculated. In S412, the AF processing unit 105 moves the focus lens 104 to the in-focus position calculated in S411. In S413, the peak detection flag is set to TRUE.

In S414, the determination is not “good”, that is, the contrast of the subject is insufficient, or the subject exists outside the scanned distance range, and the AF processing unit 105 stores the focus lens 104 in the DRAM 113 in advance (fixed point). Move to. Here, the fixed point is set to a distance with a high probability of existence of the subject. For example, if a face is detected, the distance of the person estimated from the size of the detected face is used.

FIG. 5 is a flowchart for explaining scene change determination in S406 of FIG. 4, S1105 of FIG. 11 described later, S1405 of FIG. 14, and S2107 of FIG. In S501, it is checked whether or not the face detection state detected by the face detection module 123 has changed. If the face detection state has changed, this determination process is terminated and the process returns to S201 shown in FIG. Proceed to Here, the face detection state is whether or not a face is detected. That is, if the face is detected at the previous scene change determination and the face is not detected at the current scene change determination, the face detection state has changed.

In S502, it is checked whether or not the camera movement amount detected by the angular velocity sensor unit 125 is equal to or greater than a predetermined amount. If it is equal to or larger than the predetermined amount, this determination process is terminated and the process returns to S201 in FIG. The process proceeds to S503.

In S503, it is checked whether or not continuous AF, which will be described later, is being performed. If continuous AF is being performed, the process proceeds to S504. In S504, it is determined whether the subject brightness difference is equal to or smaller than a predetermined value. The subject brightness difference is a difference between the subject brightness value acquired at the previous scene change determination and the subject brightness value detected at the current scene change determination. If the difference in the subject luminance values is large, it is determined that the scene has changed. If the subject luminance difference is equal to or smaller than the predetermined value, the determination process ends. If the subject luminance difference is larger than the predetermined value, the determination process ends and the process returns to S201 in FIG.

If it is not in continuous AF, the process proceeds to S505. In S505, it is checked whether or not the exposure time is equal to or longer than the predetermined time. If the exposure time is equal to or longer than the predetermined time, this determination process is terminated and the process returns to S201 in FIG. This is because when the exposure time is equal to or longer than the predetermined time, the interval for acquiring the focus evaluation value is extended, so that the AF accuracy cannot be ensured. Otherwise, the process proceeds to S506.

In S506, it is checked whether or not the state of the diaphragm 102 has changed. If the state has changed, the process proceeds to S507, and if not, this determination process ends. In this embodiment, the case of using the aperture control is described. However, when the exposure control is performed by the ND filter instead of the aperture control, a change in the state of the ND filter may be observed. This is because the peak position of the focus evaluation value changes when the state of the aperture or the ND filter changes.

In S507, it is checked whether or not the face is detected by the face detection module 123. If a face is detected, the determination process ends and the process proceeds to S402 in FIG. 4, otherwise the determination process ends. The process proceeds to S809 in FIG.

Next, the focus determination subroutine in step S409 in FIG. 4, step S1201 in FIG. 12 to be described later, and step S1501 in FIG. 15 will be described with reference to FIGS.

The focus evaluation value takes a mountain shape as shown in FIG. 7 when the horizontal axis represents the focus lens position and the vertical axis represents the focus evaluation value, except in the case of distance competition. Therefore, the shape of the mountain is judged from the difference between the maximum and minimum focus evaluation values, the length of the sloped portion with a slope greater than a certain value (Slope Thr), and the slope of the sloped portion. Therefore, it is possible to perform in-focus determination.

The determination result in the focus determination is output as “◯” or “×” as shown below.
○ Determination: The subject has sufficient contrast and the subject exists at a distance within the scanned distance range.
X: The subject contrast is insufficient or the subject is located at a distance outside the scanned distance range.

Further, in the x determination, a case where the subject is located outside the scanned distance range in the near side direction is determined as Δ determination.

The length L of the inclined part and the slope SL / L of the inclined part for judging the shape of the mountain will be described with reference to FIG. SL indicates the height of the sloped portion of the mountain. Points that are recognized to be inclined from the top of the mountain (point A) are defined as points D and E, and the width between points D and E is defined as the width L of the mountain. The range in which the inclination is recognized to be continued is a range in which a scan point having a focus evaluation value lowered from a point A by a predetermined amount (Slope Thr) or more continues. A scan point is a point at which a focus evaluation value is acquired while moving a focus lens continuously and moving from a scan start point to a scan end point. The sum SL1 + SL2 of the difference SL1 between the focus evaluation values of the points A and D and the difference SL2 of the focus evaluation values between the points A and E is defined as SL.

In the flowchart of FIG. 6, in S601, the maximum value and the minimum value of the focus evaluation value are obtained. Next, in S602, the scan point having the maximum focus evaluation value is obtained, and the process proceeds to S603. In S603, L and SL for determining the shape of the mountain are obtained from the scan point and the focus evaluation value, and the process proceeds to S604.

In S604, it is determined whether the mountain shape stops climbing on the near side. Judging that the closest side climb is stopped is when the following two conditions are satisfied. One condition is that the scan point with the maximum focus evaluation value is the closest end in the predetermined range in which scanning was performed. Another condition is that the difference between the focus evaluation value at the closest scan point and the focus evaluation value at a scan point that is one point away from infinity from the closest scan point is a predetermined value or more. That is. If it is determined that the near-side climb has stopped, the process proceeds to S609, and if not, the process proceeds to S605.

In S605, it is determined whether the mountain shape stops climbing on the infinity side. It is determined that the infinity side has stopped climbing when the following two conditions are satisfied. One condition is that the scan point having the maximum focus evaluation value is the infinity end in a predetermined range in which scanning is performed. Another condition is that the difference between the focus evaluation value at the infinity end scan point and the focus evaluation value at the scan point from the nearest end by one point from the infinity end scan point is greater than or equal to a predetermined value. . If it is determined that the infinity-side climb has stopped, the process proceeds to S608, and if not, the process proceeds to S606.

In step S606, the length L of the portion inclined at an inclination equal to or greater than a predetermined value is equal to or greater than the predetermined value, the average value SL / L of the inclination of the inclined portion is equal to or greater than the predetermined value, and the maximum focus evaluation value ( If the difference between Max) and the minimum value (Min) is greater than or equal to a predetermined value, the process proceeds to S607. Otherwise, the process proceeds to S608. In S607, the obtained focus evaluation value has a mountain shape, the subject has contrast, and the focus can be adjusted, so the determination result is “good”. In S608, since the obtained focus evaluation value is not mountain-shaped, the subject has no contrast, and focus adjustment is impossible, the determination result is x determination. In S609, the obtained focus evaluation value is not mountain-shaped, but it is in a state where it continues to climb in the close-up direction, and there is a possibility that a subject peak exists on the close-up side. The determination result is Δ. In-focus determination is performed as described above.

Next, subject area specifying AF frame setting processing in the present embodiment will be described with reference to the flowchart of FIG.

First, in S2701, it is checked whether or not the electronic zoom is performed. If the electronic zoom is performed, the process proceeds to S2705, and if not, the process proceeds to S2702. In S2705, AF frame setting for electronic zoom is performed. Here, the electronic zoom is to enlarge the center area of the screen and display it on the operation display unit 117. At this time, in order to enlarge a narrow area on the image sensor 108, the image displayed on the operation display unit 117 is generated from a smaller number of pixels than when electronic zooming is not performed. Therefore, when the AF frame is set so that the image displayed on the operation display unit 117 during the electronic zoom has the same ratio as when the electronic zoom is not performed, the number of pixels in the AF frame is smaller than when the electronic zoom is not performed. As a result, the S / N of the focus evaluation value decreases. For this reason, it is necessary to change the AF frame setting method between when the electronic zoom is performed and when the electronic zoom is not performed. In this embodiment, at the time of electronic zooming, one AF frame of a predetermined size is set near the center of the screen.

Next, in S2702, the current subject brightness is acquired. For convenience of explanation of the present embodiment, this value is assumed to be subject brightness B. The subject brightness itself is obtained as a result of the AE operation performed in parallel with the processing shown in FIG. 2, and is calculated by an AE processing unit including subject brightness detection means.

In step S2703, the previously acquired subject brightness B is compared with the low illuminance threshold 1. The low illuminance threshold value 1 is a threshold value indicating whether or not the subject is sufficiently bright. If this condition is satisfied, the process proceeds to S2706. In step S2706, N1 × N1 AF frame setting is performed. In this embodiment, as shown in FIG. 28A, in a high luminance situation, the size of the AF frame is set to 10% of the screen in both vertical and horizontal lengths, and N1 = 5 and 5 × 5 AF frame setting is performed. Shall be implemented. In step S2709, the subject area specifying execution flag is set to TRUE, and the process ends.

As described above with reference to FIG. 2, based on the state of the flag value, the subject area specifying scan in S208 in FIG. 2 or the continuous AF in S209 is switched.

On the other hand, if the subject brightness B is less than the low illuminance threshold 1, the process proceeds to S2704. In S2704, it is further determined whether or not the subject brightness B is less than the low illuminance threshold 1 and is equal to or greater than the low illuminance threshold 2. At this time, if the above condition is met, the process proceeds to S2707, and if not, the process proceeds to S2708. In S2707, N2 × N2 AF frame setting is performed. In this embodiment, as shown in FIG. 28 (b), in a certain dark situation, the size of the AF frame is 18% of the screen in both vertical and horizontal lengths, and N2 = 3 and 3 × 3 AF frame setting is performed. Shall be implemented. In step S2709, the subject area specifying execution flag is set to TRUE, and the process ends.

If the subject brightness B is less than the low illuminance threshold 2, the process proceeds to S2708. In S2708, as shown in FIG. 28C, at a brightness that makes it difficult to calculate the focus evaluation value, the size of the AF frame is set to 25% of the screen in both vertical and horizontal directions, and a 1 × 1 AF frame. Settings shall be implemented. Next, proceeding to S2710, the subject area specifying execution flag is set to FALSE, and the process ends.

As described above, the subject area specifying AF frame setting process in this embodiment is characterized in that the size of the AF frame used in the subject area specifying AF scan is switched based on the brightness of the subject. In general, when the subject is dark and the level of the video signal is low, using the video signal as it is does not have enough brightness, and it is difficult to obtain the original signal component of the focus evaluation value due to the noise of the image sensor . Therefore, by switching the number of pixels constituting the AF frame based on the brightness of the subject as in the present embodiment, it is possible to calculate an appropriate focus evaluation value even at low illuminance.

It should be noted that the present invention is not limited to this embodiment with respect to the size and number of AF frames. For example, the size of the AF frame may be set in consideration of the existence probability of the main subject in the screen, or may be set so that the number of AF frames is different between the horizontal direction and the vertical direction.

Next, FIG. 8 is a flowchart for explaining the subject area specifying AF scan of S208 in FIG. Here, AF scanning is performed to identify the area of the main subject in the screen.

First, in S801, a previous reference determination is performed according to a procedure described later (see FIG. 10). In S802, as a result of the previous reference determination in S801, if it is determined that the shooting scene does not change much from the previous time, the process proceeds to S803. Otherwise, the process proceeds to S806. In step S803, a previous reference AF scan is performed according to a procedure described later (see FIG. 11). In S804, it is checked whether or not the main subject area can be specified in the previous reference AF scan in S803. If it is desired to specify the main subject area, the process proceeds to S805.

In S805, the peak detection flag is set to TRUE. In step S806, zone AF scanning is performed according to a procedure described later (see FIG. 14). In S807, it is checked whether or not the main subject area can be specified in the zone AF scan in S806. In S808, uniform surface determination is performed according to the procedure described later (see FIG. 17). In S809, since the main subject area could not be specified in the zone AF scan of S806, an AF frame is set in a predetermined area set in advance on the screen. Here, the predetermined area is set to an area where the main subject is likely to exist, for example, one frame is set in the central area of the screen. In S810, focus drive is performed according to the procedure described later (see FIG. 20).

FIG. 10 is a flowchart for explaining the previous reference determination in S804 in FIG. Here, it is determined whether or not the photographic scene has changed much this time with respect to the photographic scene in which the previous AF scan was performed.

First, in S1001, it is checked whether or not the main subject area can be specified in the previous AF scan. If the main subject area can be specified, the process proceeds to S1002, and if not, the process proceeds to S1006. In S1002, it is checked whether or not the current position of the focus lens 104 is closer to the predetermined position. If it is closer, the process proceeds to S1003, and if not, the process proceeds to S1006. Here, it is determined whether or not it is closer to the predetermined position, but it may be determined whether or not it is on the infinity side from the predetermined position.

In S1003, it is checked whether or not the time difference between the previous AF scan and the current time is within a predetermined time. If it is within the predetermined time, the process proceeds to S1004. Otherwise, the process proceeds to S1006. In S1004, it is checked whether or not the camera direction is the same as that in the previous AF scan, and if it is the same, the process proceeds to S1005, and if not, the process proceeds to S1006. Here, the direction of the camera is, for example, the vertical and horizontal positions of the camera, and is detected by the angular velocity sensor unit 125. In S1005, it is determined that there is not much difference from the shooting scene in the previous AF scan, and this determination process ends. In S1006, it is determined that the shooting scene has changed significantly from the previous AF scan, and this determination process ends.

FIG. 11 is a flowchart for explaining the previous reference AF scan in S806 in FIG. First, in S1101, the scan range is set to the first range around the current position of the focus lens 104. Here, since it is determined that there is not much difference from the previous shooting scene, the first scan range is a narrow range. In step S1102, the focus lens 104 is moved to the scan start position. In S1103, the analog video signal read from the image sensor 108 is converted into a digital signal by the A / D conversion unit 109, and the image processing unit 110 extracts a high-frequency component of the luminance signal from the output, and the CPU 115 focuses on this. Store as an evaluation value. In S1104, the current position of the focus lens 104 is acquired, and the CPU 115 stores the data of the position.

In S1105, the CPU 115 determines the state (ON / OFF) of SW1 instructing to prepare for photographing. If the state is ON (on), the process is terminated, and the process proceeds to S212 in FIG. In this case, the process proceeds to S1106. In S1106, the scene change determination of FIG. 5 described above is performed. In S1107, the CPU 115 checks whether or not the current position of the focus lens 104 is equal to the scan end position. If the two are equal, the process proceeds to S1108; otherwise, the process proceeds to S1109. In step S1108, a main subject area determination described later is performed (see FIG. 12). In S1109, the AF processing unit 105 moves the focus lens 104 by a predetermined amount in the scan end direction, and then returns to S1103.

FIG. 12 is a flowchart for explaining main subject area determination in S1108 in FIG. 11 and S1411 in FIG. Here, it is determined whether or not the main subject area in the screen has been identified. FIG. 13 is a diagram for explaining an example of main subject area determination in FIG. In this example, the AF frame size is 10% of the screen, N = 5, the scan range is 0 to 500, and the predetermined depth range is ± 10. Note that the numerical values of the scan range and the predetermined depth range are numerical values representing the position of the focus lens 104. This corresponds to the number of pulses when a stepping motor is used as the driving motor for the focus lens 104 (not shown), and the larger value is the closest side.

First, in S1201, the above-described in-focus determination of FIG. 6 is performed for all the set AF frames. For example, it is assumed that the focus determination result as shown in FIG. In S1202, the peak position of the focus evaluation value (hereinafter referred to as PeakPos) in each AF frame is calculated and stored. For example, it is assumed that the peak position calculation result as shown in FIG. In S1203, it is checked whether or not the set AF frame is one frame. If the set AF frame is one frame, the process proceeds to S1214. Otherwise, the process proceeds to S1204.

In S1204, PeakPos of each AF frame of the center M × M frame is sorted in ascending order, and the sorted number is S. In the following description, M = 3. This is shown by a total of nine frames including three vertical frames and three horizontal frames surrounded by a thick line in FIG. Here, since the peak position cannot be calculated in the AF frame of X determination in the focus determination of S1201, it is not a sorting target. For example, in the case of FIG. 13B, the sort numbers 410, 400, 400, 400, 100, 100, 100, and 90 are sorted in the closest order, and the sort number S = 8.

In S1205, a counter P indicating the closest order of the peak positions in the M × M frame calculated in S1202 is set to 1. In S1206, the P-th PeakPos in the sort order is set as PeakPosP. For example, in the example of FIG. 13B, when P = 1, PeakPosP = 410. In step S1207, an AF frame “complex” is detected in the AF frame within the predetermined depth range with respect to the PeakPosP frame that is ○ in the M × M AF frames at the center, and the AF frames constituting the “cluster” are detected. The number and the position of each AF frame are stored. Here, “a lump” is, for example, a state in which AF frames satisfying a condition are adjacent vertically and horizontally. When there are a plurality of “chunks”, one of the “chunks” may be selected based on the number of AF frames constituting the “chunk” and the position of the “chunks”.

In S1208, in the center N × N AF frames, “○” is determined so that one or more frames in the center M × M AF frames are included, and “PeakPosP” is within a predetermined depth. Detect a “chunk”. Then, the number of AF frames constituting the “chunk” and the position of each AF frame are stored. For example, with respect to the determination results as shown in FIGS. 13A and 13B, a “chunk” as indicated by a gray frame in FIG. 13C is detected.

In S1209, it is checked whether or not the “chunk” detected in S1207 or S1208 is a “chunk” including the central frame. If the “chunk” includes the central frame, the process proceeds to S1215. Otherwise, the process proceeds to S1210. In S1210, it is checked whether or not the “chunk” detected in S1207 or S1208 is a “chunk” that includes at least a predetermined number of frames in the M × M frame. If so, the process proceeds to S1215, and if not, the process proceeds to S1211. In S1211, whether or not the “chunk” detected in S1207 or S1208 is a “chunk” that includes one frame of the central M × M frames and includes a predetermined number or more of the AF frames in the N × N frame. If yes, go to S1215. Otherwise, the process proceeds to S1212. In S1212, 1 is added to the counter P. In S1213, it is checked whether or not the counter P is larger than the sort number S. If the counter P is larger than the sort number S, the process proceeds to S1217. Otherwise, the process returns to S1206.

In S1214, it is checked whether or not the in-focus determination result in S1201 is ◯. If YES, the process proceeds to S1215. If not, the process proceeds to S1217. In S1215, it is determined that the main subject area has been identified. In S1216, each AF frame constituting the cluster is determined to be the main subject area and selected, and this determination process ends. If one AF frame is set here, that one frame is selected. In step S1217, it is determined that the main subject area has not been specified, and the determination process ends.

Next, FIG. 14 is a flowchart for explaining the zone AF scan of S809 in FIG. Here, the zone refers to each range when the focusable distance range is divided into a plurality of ranges.

First, in S1401, the focus lens 104 is moved to the scan start position. Here, the scan start position is, for example, the infinity end position. In S1402, the analog video signal read from the image sensor 108 is converted into a digital signal by the A / D conversion unit 109, and the image processing unit 110 extracts a high-frequency component of the luminance signal from the output, and the CPU 115 focuses on this. Store as an evaluation value. In S1403, the current position of the focus lens 104 is acquired, and the CPU 115 stores the data of the position.

In S1404, the CPU 115 determines the state (ON / OFF) of SW1 instructing to prepare for photographing. If the state is ON (on), the process is terminated and the process proceeds to S212 in FIG. In this case, the process proceeds to S1405. In S1405, the scene change determination of FIG. 5 described above is performed. In S1406, it is checked whether or not the focus lens 104 is at a preset zone boundary position. If so, the process proceeds to S1407; otherwise, the process proceeds to S1409. In S1407, zone update determination is performed according to the procedure described later (see FIG. 15). Here, zone update refers to scanning an adjacent zone after scanning a certain zone.

In S1408, whether or not it is determined to update the zone as a result of the determination in S1407 is checked. If it is determined to update the zone, the process proceeds to S1409, and if not, the process proceeds to S1411. In S1409, the CPU 115 checks whether or not the current position of the focus lens 104 is equal to the scan end position. If both are equal, the process proceeds to S1411. Otherwise, the process proceeds to S1410. In step S1410, the focus lens 104 is moved by a predetermined amount in the scan end direction, and then the process returns to step S1402. In S1411, the main subject area determination of FIG. 12 described above is performed.

FIG. 15 is a flowchart illustrating the zone update determination in S1407 in FIG. Here, it is determined whether or not the main subject is likely to exist ahead of the scanning direction, that is, whether or not to continue AF scanning. FIG. 16 is a diagram illustrating an example of zone update determination in FIG. In this example, the size of the AF frame is 10% of the screen, N = 5, and M = 3.

First, in S1501, the above-described in-focus determination in FIG. 6 is performed in all the set AF frames. For example, it is assumed that the focus determination result as shown in FIG. In S1502, it is checked whether or not scanning has been performed up to the final zone. If scanning has been performed up to the final zone, the process proceeds to S1512. Otherwise, the process proceeds to S1503. In S1503, it is checked whether or not there is a ○ determination frame. If there is a ○ determination frame, the process proceeds to S1504, and if not, the process proceeds to S1511.

In S1504, it is checked whether or not the center frame is Δ. If the center frame is Δ, the process proceeds to S1511. Otherwise, the process proceeds to S1505. In S1505, it is checked whether or not the Δ judgment frame is a “cluster” of the predetermined number of frames or more in the center M × M frame, and if it is, the process proceeds to S1511, and if not, the process proceeds to S1506. In FIG. 16, the predetermined number is 2 as an example. In S1506, it is checked whether or not the Δ judgment frame is a “cluster” of a predetermined number of frames or more in the AF frame of N × N frames so as to include one or more of the central M × M frames. The process proceeds to S1511. Otherwise, the process proceeds to S1507. In FIG. 16, the predetermined number is 4 as an example. In step S1507, it is checked whether or not the “O” determination frame is more than a predetermined number of “chunks” in the center M × M frame. If so, the process proceeds to step S1512. In FIG. 16, the predetermined number is 5 as an example.

In S1508, it is checked whether or not the center frame is X determination. If the center frame is X determination, the process proceeds to S1511. Otherwise, the process proceeds to S1509. In S1509, if the Δ determination frame or the × determination frame is a “cluster” of the predetermined number of frames or more in the center M × M frame, the process proceeds to S1511. Otherwise, the process proceeds to S1510. In FIG. 16, the predetermined number is 2 as an example. In S1510, it is checked whether or not there are more than a predetermined number of “chunks” of Δ judgment frames or X judgment frames in all of the N × N frames so as to include one or more of the central M × M frames. If so, the process proceeds to S1511. Otherwise, the process proceeds to S1512. In FIG. 16, the predetermined number is 4 as an example. In step S1511, it is determined that “the zone is to be updated”, and the determination process ends. In S1512, it is determined that “zone update is not performed”, and this determination process ends.

For example, when N = 5 and M = 3, the gray area shown in FIG. 16B becomes a “cluster”, and it is determined that the zone is to be updated.

FIG. 17 is a flowchart for explaining the uniform surface determination in S811 in FIG. Here, “a state that is a uniform surface” is a state in which there is no difference in brightness in the screen and there is no contrast, so that a focus evaluation value peak cannot be obtained sufficiently even when AF is performed. If the subject area specific AF scan of S208 in FIG. 2 is repeated every time the photographic scene is stabilized in the “uniform surface state”, the focus variation on the screen is repeated unnecessarily, which is troublesome. Therefore, in this uniform surface determination flow, when “a state of a uniform surface” is determined, an operation of stopping the focus lens 104 is performed until “a state of a uniform surface” is not determined.

First, in S1701, uniform surface determination is performed according to a procedure described later (see FIG. 18). In S1702, it is checked whether or not it is determined that the shooting scene is a uniform plane as a result of the determination in S1701, and if it is determined that it is a uniform plane, the process proceeds to S1703, and if not, this determination process ends. In step S1703, the AF processing unit 105 moves the focus lens 104 to a predetermined position. Here, the predetermined position is, for example, a hyperfocal distance including infinity on the infinity side of the depth of field.

In S1704, the CPU 115 determines the state (ON / OFF) of SW1 that instructs to prepare for photographing. If the state is ON (on), the process is terminated, and the process proceeds to S212 in FIG. In this case, the process proceeds to S1705. In S1705, the uniform surface determination described later is performed. In S1706, it is checked whether or not it is determined that the shooting scene is a uniform plane as a result of the determination in S1705. If it is determined that the shooting scene is a uniform plane, the process returns to S1704. Return to S201 of 2.

As described above, the focus lens 104 can be stopped until the “uniform surface” is not reached.

FIG. 18 is a flowchart for explaining uniform surface determination in S1701 and S1705 in FIG. Here, it is determined whether or not the state is a “uniform surface” based on the luminance information in the screen and the focus evaluation value. FIG. 19 illustrates the uniform surface determination of FIG. The [1] portion in FIG. 19A shows a “state that is a uniform surface”, and the [2] portion in FIG. 19A shows a “state that is not a uniform surface”.

First, in S1801, it is checked whether or not the set AF frame is one frame. If the set AF frame is one frame, the process proceeds to S1805. Otherwise, the process proceeds to S1802. In S1802, “difference in luminance integrated values between the screen center M × M frame and each of the four corner M × M frames in the entire screen N × N frame” is calculated. For example, assuming that the frame size is 10%, N = 5, and M = 3, when the area of [1] in the landscape of FIG. Is obtained by integrating the luminance values of the gray area indicated by A in FIG. Further, the luminance integral values of the four corner M × M frames in the entire screen N × N frame are obtained by integrating the luminance values of the gray areas shown in B, C, D, and E in FIG. Become. Assuming that the integrated luminance values are A, B, C, D, and E, the absolute values of AB, AC, AD, and AE are “the screen center M × M frame and the entire screen. The difference between the luminance integration values of the four corner M × M frames in the N × N frame ”.

In S1803, among the “differences between the integrated luminance values of the screen center M × M frame and the four corner M × M frames in the entire screen N × N frame” calculated in S1802, a luminance difference equal to or greater than a predetermined value is obtained. If there is, it proceeds to S1807. Otherwise, the process proceeds to S1804. In step S1804, the focus evaluation value of each AF frame of the center M × M frame is calculated as a new focus evaluation value. For example, addition is performed as a calculation method. In S1805, it is determined whether or not the focus evaluation value is equal to or greater than a predetermined value. If the focus evaluation value is equal to or greater than the predetermined value, the process proceeds to S1807, and if not, the process proceeds to S1806. In step S1806, it is determined that the shooting scene is “a uniform surface”, and the determination process ends. In step S1807, it is determined that the shooting scene is “not a uniform surface”, and the determination process ends.

Thereby, in the “state that is a uniform surface” like the [1] portion of FIG. 19A, it can be determined that it is “a uniform surface”, and the [2] portion of FIG. 19A. In such a “non-uniform surface” state, it can be determined that the surface is not a uniform surface.

FIG. 20 is a flowchart for explaining the focus drive in S813 in FIG. First, in S2001, it is checked whether or not the main subject area can be specified. If it can be specified, the process proceeds to S2002, and if not, the process proceeds to S2003. In S2002, the focus is driven to the closest position in the selected AF frame, and this process is terminated. In S2003, it is checked whether or not there is a ○ determination in the center M × M frame. If there is a ○ determination, the process proceeds to S2004, and if not, the process proceeds to S2005. In S2004, the focus is driven to the closest position among the ◯ determinations in the center M × M frame, and the process is terminated. In S2005, it moves to the position (fixed point) memorize | stored previously, and complete | finishes this process. Here, for example, the fixed point is set to a distance having a high probability of existence of the subject.

Next, FIG. 21 is a flowchart for explaining the continuous AF in S209 in FIG. First, in S2101, the focus degree determination flag is set to TRUE. In step S2102, the focus evaluation value is acquired for each set AF frame.

In step S2103, it is checked whether the set AF frame is one frame. If the set AF frame is one frame, the process proceeds to step S2105. Otherwise, the process proceeds to step S2104. In S2104, the evaluation value calculated using the focus evaluation value of the AF frame selected as the main subject region is reset as the focus evaluation value used in S2105 and thereafter. Thereby, even if the photographing scene changes and the main subject area in the screen changes, the focus evaluation value of the main subject area in the screen can always be calculated.

In S2105, the degree of focus is calculated based on the focus evaluation value. In this embodiment, the degree of focus is determined in three stages of high, medium, and low based on the focus evaluation value. In S2106, the CPU 115 determines the state (ON / OFF) of SW1 instructing to prepare for photographing. If the state is ON (on), the process is terminated and the process proceeds to S213 in FIG. If so, the process advances to step S2107. In step S2107, the scene change determination shown in FIG. 5 is performed.

In S2108, it is checked whether or not the peak detection flag is TRUE. If it is TRUE, the process proceeds to S2125, and if it is FALSE, the process proceeds to S2109. In step S2109, the current position of the focus lens 104 is acquired. In S2110, 1 is added to the acquisition counter for counting the acquisition of the focus evaluation value and the acquisition of the current position of the focus lens 104. This acquisition counter is set to 0 in advance in an initialization operation (not shown). In S2111, it is checked whether or not the value of the acquisition counter is 1. If the value of the acquisition counter is 1, the process proceeds to S2114. If the value of the acquisition counter is not 1, the process proceeds to S2112.

In S2112, it is checked whether or not “current focus evaluation value” is larger than “previous focus evaluation value”. If so, the process proceeds to S2113; otherwise, the process proceeds to S2120. In S2113, 1 is added to the increase counter. In S2114, the current focus evaluation value is stored as a maximum focus evaluation value in a calculation memory (not shown) built in the CPU 115. In step S2115, the current position of the focus lens 104 is stored in a calculation memory (not shown) built in the CPU 115 as the peak position of the focus evaluation value. In step S2116, the current focus evaluation value is stored as a previous focus evaluation value in a calculation memory (not shown) built in the CPU 115. In S2117, it is checked whether or not the current position of the focus lens 104 is at the end of the movement range. If so, the process proceeds to S2118; otherwise, the process proceeds to S2119. In S2118, the moving direction of the focus lens 104 is reversed. In step S2119, the focus lens 104 is moved by a predetermined amount.

In S2120, it is checked whether “the maximum value of the focus evaluation value—the current focus evaluation value” is greater than a predetermined amount. If “the maximum value of the focus evaluation value—the current focus evaluation value” is greater than the predetermined amount, the process proceeds to step S2121. If not, the process proceeds to step S2116. Here, if “the maximum value of the focus evaluation value−the current focus evaluation value” is larger than a predetermined amount, that is, if the predetermined value is decreased from the maximum value, the maximum value is regarded as a value at the focus peak position. In S2121, whether or not the increment counter is greater than 0 is checked. If it is greater than 0, the process proceeds to S2122, and if it is less than 0, the process proceeds to S2116. In S2122, the focus lens 104 is moved to the peak position where the focus evaluation value stored in S2115 is the maximum value. In S2123, the peak detection flag is set to TRUE. In S2124, the acquisition counter is set to zero.

In S2125, it is checked whether or not the current focus evaluation value has fluctuated by a predetermined ratio or more with respect to the maximum value of the focus evaluation value. If there has been a large fluctuation of a predetermined ratio or more, the process proceeds to S2127. move on. In step S2126, the position of the focus lens 104 is held as it is. In S2127, the peak detection flag is set to FALSE to reset the focus lens position at which the focus evaluation value is maximized, and the maximum focus evaluation value and the peak position are reset. In S2128, the increment counter is reset.

As described above, in the continuous AF operation, the focus lens is driven so that the main subject is always in focus.

FIG. 22 is a flowchart for explaining the scene instability determination of S211 in FIG. First, in S2201, it is checked whether or not the camera motion detected by the angular velocity sensor unit 125 is greater than or equal to a predetermined amount. If it is greater than or equal to the predetermined amount, the process proceeds to S2205; In S2202, it is checked whether or not the luminance change amount from the previous time is equal to or greater than a predetermined amount. If it is equal to or greater than the predetermined amount, the process proceeds to S2205; In S2203, it is checked whether or not the face detection state detected by the face detection module 123 has changed. If the face detection state has changed, the process proceeds to S2205; otherwise, the process proceeds to S2204. Here, the face detection state is, for example, whether or not a face is detected. That is, if the face is detected in the previous scene instability determination and the face is not detected in the current scene instability determination, the face detection state has changed. In step S2204, it is determined that the shooting scene has not changed (the scene is not unstable), and the process ends. In step S2205, it is determined that the shooting scene has changed (the scene is unstable), and the process ends.

Next, FIG. 23 is a flowchart for describing the photographing process of S213 in FIG. First, in S2301, the AE processing unit 103 performs AE processing for main exposure. In step S2302, AF for main exposure is performed according to the procedure described later (see FIG. 24). In S2303, the CPU 115 determines the state (ON / OFF) of the photographing switch SW2 (122). If the state is ON, the process proceeds to S2305. If the state is OFF, the process proceeds to S2304. In S2304, the state (ON / OFF) of SW1 instructing the preparation for photographing is determined. If the state is ON (on), the process proceeds to S2303. If the state is OFF (off), the process ends. In step S2305, the main exposure process is performed according to the procedure described later (see FIG. 26), and the process ends.

FIG. 24 is a flowchart for explaining the main-exposure AF in S2302 in FIG. First, in S2401, AF frame setting for main exposure is performed. The AF frame setting for the main exposure may be set with one frame having a predetermined size in the central region or may be set with a plurality of N × N frames. In S2402, it is checked whether or not the main subject detection flag is TRUE. If TRUE, the process proceeds to S2403, and if not, the process proceeds to S2409. In S2403, it is checked whether or not the focus degree calculated in S2105 in FIG. 21 is “high”. If the focus degree is “high”, the process proceeds to S2404; otherwise, the process proceeds to S2405.

In step S2404, the scan range is set to the first range (1) around the current position of the focus lens 104. Here, a narrow scan range is set by determining that the focus lens is positioned near the focus position where the main subject is substantially focused by the continuous AF operation, that is, near the focus position where the focus evaluation value shows a peak. In S2405, it is checked whether or not the degree of focus calculated in S2105 is “medium”. If the degree of focus is “medium”, the process proceeds to S2406, and if not, the process proceeds to S2407. In S2406, the scan range is set to the second range (2) around the current position of the focus lens 104. Here, the focus lens is positioned in the vicinity of the in-focus position by the continuous AF operation, but it is determined that the in-focus degree is not as high as the “high” state, and the narrow range is wider than the first scan range. To do. In S2407, it is checked whether or not the current position of the focus lens 104 is a macro area. If the current position is the macro area, the process proceeds to S2408; otherwise, the process proceeds to S2409. In S2408, the scan range which is a macro area stored in advance is set to the third range (3). In step S2409, the scan range is set to a fourth scan range (4) which is the entire focus detectable range stored in advance.

In step S2410, a main exposure AF scan is performed according to a procedure described later (see FIG. 25). In step S2411, the focus lens 104 is moved to the peak position calculated in step S2506 in FIG.

FIG. 25 is a flowchart for explaining the main-exposure AF scan in S2405 in FIG. First, in S2501, the focus lens 104 is moved to the scan start position. Here, the scan start position is the end position of the scan range set in S2404, S2406, S2408, or S2409 in FIG. In S2502, the analog video signal read from the image sensor 108 is converted into a digital signal by the A / D conversion unit 109, and the image processing unit 110 extracts a high-frequency component of the luminance signal from the output. Store as an evaluation value. In step S2503, the current position of the focus lens 104 is acquired, and the CPU 115 stores data on the position. In S2504, the CPU 115 checks whether or not the current position of the focus lens 104 is equal to the scan end position. If both are equal, the process proceeds to S2506, and if not, the process proceeds to S2505. In step S2505, the focus lens 104 is moved by a predetermined amount in the scan end direction, and the process returns to step S2502. In S2506, the peak position of the focus evaluation value is calculated from the focus evaluation value stored in S2502 and its lens position. In calculating the peak position of the focus evaluation value, when a plurality of AF frames are set, the calculation may be performed based on the closest peak position of the main subject area determined by the main subject area determination described in FIG. Alternatively, the peak position may be calculated in another way of determination.

FIG. 26 is a flowchart for explaining the main exposure processing in S2305 in FIG. First, after the exposure of the image sensor 108 in S2601, data accumulated in the image sensor 108 is read in S2602. In step S2603, the analog signal read from the image sensor 108 by the A / D converter 109 is converted into a digital signal. In step S2604, the image processing unit 110 performs various types of image processing on the digital signal output from the A / D conversion unit 109. In step S2605, the image processed in step S2604 is compressed according to a format such as JPEG under the control of the CPU 115. In step S2606, the CPU 115 performs control so that the data compressed in step S2605 is sent to the image recording unit 114 and recorded.

As described above, according to the present embodiment, it is possible to suppress a decrease in the detection performance of the main subject even when the shooting scene is low illuminance, and the main subject area is specified and focused before the shooting preparation instruction is given. Keep matching. This makes it possible to quickly focus on the main subject after the shooting preparation instruction.

Embodiment 2 of the present invention will be described with reference to the drawings. In the second embodiment, regarding the AF frame setting for subject identification in S205 of FIG. 2 in the first embodiment, the frequency band to be extracted when calculating the driving of the image sensor, the setting of the AF frame, and the focus evaluation value based on the subject luminance is set. Switch. This improves the calculation of the focus evaluation value at low illuminance.

The subject area specifying AF frame setting process in the present embodiment will be described with reference to the flowchart of FIG. First, in S2901, the current subject brightness is acquired. For convenience of explanation of the present embodiment, this value is assumed to be subject brightness B. The subject luminance itself is obtained as a result of the AE operation performed in parallel with the processing shown in FIG. 2, and is calculated by the AE processing unit.

Next, in S2902, the previously obtained subject luminance B and the low illuminance threshold 1 are compared. The low illuminance threshold value 1 is a threshold value indicating whether or not the subject is sufficiently bright. If this condition is satisfied, the process proceeds to S2904. In step S2904, the sensor driving mode is switched to A. This sensor drive A is a drive set so that the signal readout time from the sensor is prioritized and the number of lines in the vertical direction is reduced as compared to when the illumination is low.

In step S2907, the band pass filter is set to be the frequency band A to be extracted. This is because, in this embodiment, a high-frequency component of luminance in the horizontal direction is extracted to calculate a focus evaluation value, and components in an appropriate frequency band are extracted according to the number of pixels in the horizontal direction of the sensor drive A. It is.

Next, in S2910, it is checked whether or not the electronic zoom is performed. If the electronic zoom is performed, the process proceeds to S2912, and if not, the process proceeds to S2913. In step S2912, AF frame setting for electronic zoom is performed. Here, the electronic zoom is to enlarge the center area of the screen and display it on the operation display unit 117. Since the image is enlarged, the number of pixels of the image displayed on the operation display unit is smaller than when the electronic zoom is not performed. Therefore, when the AF frame is set so that the ratio of the image displayed on the operation display unit 117 during the electronic zoom is the same as when the electronic zoom is not performed, the number of pixels in the AF frame is smaller than when the electronic zoom is not performed. The S / N of the focus evaluation value decreases. For this reason, it is necessary to change the AF frame setting method between when the electronic zoom is performed and when the electronic zoom is not performed. In this embodiment, at the time of electronic zooming, one AF frame of a predetermined size is set near the center of the screen.

On the other hand, if it is not the electronic zoom, the process proceeds to S2913, where N × N AF frame setting is performed. In this embodiment, as shown in FIG. 30 (a), in a high luminance situation, the size of the AF frame is set to 10% of the screen in both vertical and horizontal lengths, and 5 × 5 AF frame setting is performed with N = 5. It shall be. In step S2918, the subject area specifying execution flag is set to TRUE, and the process ends.

If the subject brightness B is less than the low illuminance threshold 1, the process proceeds to S2903. In S2903, it is further determined whether or not the subject luminance B is less than the low illuminance threshold 1 and is equal to or higher than the low illuminance threshold 2. At this time, if the above condition is met, the process proceeds to S2905, and if not, the process proceeds to S2906.

In step S2905, the sensor driving B is switched. This sensor drive B is given priority to the improvement of S / N, and is a drive in which the number of lines in the vertical direction is set higher than that at the time of high luminance. In step S2908, the band pass filter is set to be the frequency band B to be extracted. In this way, the frequency band for sensor driving and extraction is determined according to the low luminance, and the S / N improvement at the time of low illuminance is achieved. The processing after S2910 is the same as described above. However, regarding the AF frame setting in S2913, the number of AF frames is the same as that in FIG. 30A when the luminance is high as shown in FIG. 30B, but the pixels constituting the AF frame are different due to the difference in sensor drive. The number is different. The same applies to the AF frame setting at the time of electronic zoom in S2912.

On the other hand, if the subject brightness B is less than the low illuminance threshold 2 in S2903, the process proceeds to S2906. In step S <b> 2906, the sensor driving is switched to B. This sensor drive B gives priority to the improvement of S / N, and is a drive in which the number of lines in the vertical direction is set larger than that at the time of high luminance. In step S2909, the band pass filter is set to be the frequency band B to be extracted. In S2911, it is checked whether or not electronic zooming is being performed. If electronic zooming is being performed, the process proceeds to S2915; otherwise, the process proceeds to S2914. In S2914, as shown in FIG. 30C, at a brightness that makes it difficult to calculate the focus evaluation value, the size of the AF frame is 25% of the screen both vertically and horizontally, and 1 × 1 AF Frame setting shall be performed.

On the other hand, when electronic zooming is performed, one AF frame having a predetermined size is set near the center of the screen in S2915. In S2916, the focus lens is moved to a predetermined position. In this embodiment, the hyperfocal distance is used.

In step S2917, the subject area specifying execution flag is set to FALSE. Thus, after subject area specifying AF frame setting processing, the subject area specifying AF scan of S208 in FIG. 2 is not executed, but the continuous AF of S209 is directly executed.

Next, proceeding to S2919, the peak detection flag is set to TRUE. This peak detection flag is a flag referred to in S2108 in FIG. 21. In this case, the peak detection flag is stopped at the current focus lens position, and the focus evaluation value obtained in S2102 in FIG. Changes in focus evaluation values will be monitored. In other words, as long as the brightness of the subject for which it is difficult to calculate the focus evaluation value continues, it is possible to prevent unnecessary focus adjustment thereafter.

In the present embodiment, the difference in sensor driving has been described as the difference in the number of pixels in the horizontal direction and the number of lines in the vertical direction on the premise of pixel thinning. However, the present embodiment is not limited to this. For example, a technique such as pixel addition in the sensor is known as a method for improving the S / N of the sensor. Switching may include such a combination of techniques.

As described above, according to the present embodiment, it is possible to suppress a decrease in the detection performance of the main subject even when the shooting scene is low illuminance, and the main subject area is specified and focused before the shooting preparation instruction is given. Keep matching. This makes it possible to quickly focus on the main subject after the shooting preparation instruction.

The focus adjustment apparatus and method of the present invention can be applied to an imaging apparatus such as an electronic still camera having a focus adjustment function.

101: photographing lens 102: aperture and shutter 103: AE processing unit 104: focus lens 105: AF processing unit 108: image sensor 109: A / D conversion unit 110: image processing unit 114: image recording unit 115: system control unit 120 : Main switch 121: Shooting standby switch 122: Shooting switch 123: Face detection module 124: Moving object detection unit 125: Angular velocity sensor unit

Claims (8)

Photoelectric conversion means for converting a subject image formed using a focus lens into an electrical signal;
Extraction means for extracting a signal component of a specific frequency band in a focus detection region from an output signal of the photoelectric conversion means;
Prior to photographing preparation, the focus lens is moved, and an object region to be focused is performed by performing an AF scan operation for acquiring an output signal of the extraction means in a set focus detection region in association with the position of the focus lens. A control means for performing a first operation for specifying the image and performing a second operation for performing a focusing operation by performing the AF scan operation at the time of shooting preparation;
Detecting means for detecting the brightness of the focus detection area;
The control means includes
When the brightness obtained by the detection means before preparation for photographing is less than a first threshold, control is performed so as to perform a third operation different from the first operation. . In the third operation, the subject region to be focused is specified by performing the AF scan operation in which the operation mode of the photoelectric conversion unit and the frequency band in the extraction unit are set different from the first operation. The focus adjustment apparatus according to claim 1, wherein the focus adjustment apparatus is an operation. The third operation is an operation for specifying a subject region to be focused by performing the AF scan operation in which the size of the focus detection region is set to be different from that of the first operation. The focus adjusting apparatus according to claim 1 or 2. The third operation is an operation for specifying a subject region to be focused by performing the AF scan operation in which the number of focus detection regions is set to be different from that of the first operation. Item 4. The focus adjustment apparatus according to any one of Items 1 to 3. In the third operation, when the brightness obtained by the detection unit is equal to or higher than a second threshold value that is darker than the first threshold value, the AF scan operation is performed to identify a subject area to be focused. 5. The operation according to claim 1, wherein the focus is fixed to a specific subject distance when the brightness obtained by the detection unit is less than the second threshold value. The focusing device according to item. In the third operation, when the brightness obtained by the detection unit is equal to or higher than a second threshold value that is darker than the first threshold value, the AF scan operation is performed to identify a subject area to be focused. And when the brightness obtained by the detection means is less than the second threshold value, the output signal of the extraction means extracted before moving the focus lens by a predetermined amount and the extraction extracted after the movement Based on the output signal of the means, the movement direction for the next movement of the focus lens is determined, the focus lens is moved in the movement direction, and the focus lens is extracted by repeating the movement operation. 5. The focus adjustment apparatus according to claim 1, wherein the focus adjustment apparatus is a continuous AF operation that moves to a peak position of the output signal of the means. In the third operation, when the brightness obtained by the detection unit is equal to or higher than a second threshold value that is darker than the first threshold value, the AF scan operation is performed to identify a subject area to be focused. If the brightness obtained by the detection means is less than the second threshold and greater than or equal to a third threshold that is darker than the second threshold, the focus lens is extracted before moving by a predetermined amount. Based on the output signal of the extraction means and the output signal of the extraction means extracted after movement, determine the movement direction when the focus lens is moved next, and move the focus lens in the movement direction; It is a continuous AF operation in which the focus lens is moved to the peak position of the output signal of the extraction unit by repeatedly performing the movement operation, and obtained by the detection unit 5. The focus fixing operation according to claim 1, wherein a focus fixing operation is performed so as to fix the focus to a specific subject distance when the threshold is less than the third threshold value. 6. Focus adjustment device. A photoelectric conversion unit that converts an object image formed using a focus lens into an electrical signal; an extraction unit that extracts a signal component in a specific frequency band in a focus detection region from an output signal of the photoelectric conversion unit; A focus adjustment method in an imaging apparatus, comprising: control means for controlling operation; and detection means for detecting brightness of the focus detection area,
Prior to shooting preparation, the focus lens is moved, and an AF scan operation is performed to acquire the output signal of the extraction means in the set focus detection area in association with the position of the focus lens, and the subject area to be focused is specified. A first step of performing a first operation;
A second step of performing a second operation different from the first operation by performing the AF scan operation and performing a focusing operation at the time of shooting preparation;
And a third step of performing a third operation different from the first operation when the brightness obtained by the detection means is less than a first threshold value before preparation for photographing. Focus adjustment method.

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