JP2013142728A - Focal point adjustment apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an automatic focal point adjustment apparatus and method capable of improving stability in focusing, in an AF control using a detection function of a face etc., so as to relieve discomfort given to a photographer.SOLUTION: A focal point adjustment apparatus includes means 113 which generates a focal point evaluation value from an electric signal, which corresponds to a focal point detection area including a predetermined subject, of electric signals from an image pickup device 106, and control means 114 which adjusts a focus by a drive control of a focus lens 105. The control means has a first focus adjust operation mode using the focal point evaluation value of the focal point detection area, and a second focus adjust operation mode which is different from the first focus adjust operation mode in the drive control form of the lens and performs a tracking drive operation which corresponds to a distance change of the subject. When the subject is determined in a condition in which the second focus adjust operation mode can achieve stable focus adjustment, the second focus adjust operation mode is performed as the drive control of the focus lens, and when the subject is determined not to be in the condition, the second focus adjust operation mode is restricted.

Description

The present invention relates to an automatic focus adjustment apparatus and method in an imaging apparatus that detects a subject area in a shooting screen and performs focus adjustment based on the detection result when a subject such as a person is included in an imaging target. About.

In the auto focus (AF) control of an imaging apparatus such as a video camera, the following TV-AF method is the mainstream. In this method, an AF evaluation signal indicating the sharpness (contrast state) of the video signal generated using the image sensor is generated, and the position of the focus lens that maximizes the focus evaluation value in the AF evaluation signal is searched. In addition, an imaging apparatus having a face detection function is known in order to stably focus on a main person subject when shooting a person. For example, there has been proposed an imaging apparatus that performs focus detection by setting a focus detection area including a recognized face detection area (see Patent Document 1). In addition, an imaging apparatus that detects the eyes of a person and performs focus detection based on the eyes has been proposed (see Patent Document 2).

JP 2006-227080 A JP 2001-215403 A

In face AF control that detects a face from the above-mentioned shooting screen and performs AF control on the detected face, if the detected face is low contrast or dark due to backlight, it is mistaken as a blurred state, There is a possibility that the camera will be unstable because the focus is too big. In addition, the subject may turn sideways or rearward, making it impossible to detect the face and making it difficult to follow the intended face. In this case, for example, there is a possibility that the AF frame is erroneously moved to a low-contrast background, the focus is greatly fluctuated, and the face AF control becomes an unstable operation. As a result, particularly in the case of moving image shooting, this flicker may be recorded, which causes discomfort to the photographer.

Here, the following points can be cited as factors that make the focus appear to be largely flickering. That is, among the two types of operation modes of the TV-AF system described later (a micro-driving operation mode and a hill-climbing driving operation mode), the operation is performed in the hill-climbing driving operation mode despite being in focus. Because. This is because, when the contrast is low, it is difficult to obtain a change in the focus evaluation value, and it may be erroneously shifted to the hill-climbing drive operation mode without being distinguished from the blurred state. The minute driving operation mode is an operation mode in which the focus lens is finely reciprocated so as to prevent the out-of-focus blur and the stability is emphasized. On the other hand, the hill-climbing drive operation mode is an operation mode that emphasizes responsiveness such as moving the focus lens at a high speed in order to quickly move from the blurred position to the in-focus position. For this reason, if the hill-climbing drive operation mode is erroneously executed from the focused state, blurring will be noticeable. As described above, if the focus is greatly fluctuated from the point of focus, the photographer will be uncomfortable.

An object of the present invention is to provide an automatic focus adjustment apparatus and method that can improve the stability of AF control of a face or the like in view of the above-described situation.

An automatic focus adjustment apparatus according to the present invention includes an image sensor that photoelectrically converts light from a subject that has passed through an imaging optical system including a focus lens into an electric signal, and an electric signal output from the image sensor to capture an image on a shooting screen. Detecting means for detecting a predetermined subject, and generating means for generating a focus evaluation value from an electric signal corresponding to a focus detection region set including the predetermined subject among the electric signals output from the imaging device And a control means for controlling the focus by driving the focus lens. The control means performs a focus adjustment by driving and controlling the focus lens, and a first focus adjustment operation that emphasizes stability using a focus evaluation value obtained from a focus detection area set in the photographing screen. And the first focus adjustment operation mode has a second focus adjustment operation mode in which the driving control mode of the focus lens is different and the responsiveness for performing the follow-up drive operation corresponding to the change in the distance of the subject is emphasized. The second focus adjustment operation mode is executed as a focus lens drive control when it is determined that the subject condition allows stable focus adjustment in the second focus adjustment operation mode. If it is determined that the subject condition is not such that stable focus adjustment can be achieved by the second focus adjustment operation mode, the second focus adjustment operation mode is limited.

The automatic focus adjustment method of the present invention also includes an imaging step for photoelectrically converting light from a subject that has passed through an imaging optical system including a focus lens into an electrical signal, and imaging from the electrical signal output in the imaging step. A focus evaluation value is generated from an electrical signal corresponding to a focus detection area set including the predetermined subject among the electrical signals output in the detection step for detecting the predetermined subject in the screen and the imaging step. A generating step and a control step of performing focus adjustment by driving and controlling the focus lens. In the control step, when performing focus adjustment by driving and controlling the focus lens, a first focus adjustment operation that places importance on stability using a focus evaluation value obtained from a focus detection region set in the shooting screen. The first focus adjustment operation mode is different from the first focus adjustment operation mode, and the second focus adjustment operation mode emphasizing responsiveness for performing a follow-up drive operation corresponding to a change in the distance of the subject can be executed. And when it is determined that the subject condition can achieve stable focus adjustment in the second focus adjustment operation mode, the second focus adjustment operation mode is executed as focus lens drive control, and the second focus adjustment operation mode is executed. If it is determined that the subject condition is not able to achieve stable focus adjustment by the second focus adjustment operation mode, the second focus adjustment operation mode is controlled. To.

According to the present invention, this mode is restricted when it is determined that the subject condition is not capable of achieving stable focus adjustment in the second focus adjustment operation mode that emphasizes responsiveness. Therefore, it is possible to provide an automatic focus adjustment apparatus and method that can improve the stability of AF control of the face and the like and can reduce discomfort given to the photographer.

The block diagram which shows the structure of a video camera provided with the automatic focus adjustment apparatus of this invention. The flowchart which shows the face AF control process in one Example of this invention. The flowchart which shows the face AF stability availability determination process in one Example of this invention. The figure for demonstrating the micro drive operation mode in TV-AF process. The figure for demonstrating the hill-climbing drive operation mode in TV-AF process. The flowchart which shows the face AF control process in another Example. The flowchart which shows the face AF stability availability determination process in another Example. The figure which shows the example of a setting of a face frame and a normal frame.

The present invention is characterized by subject conditions that can achieve stable focus adjustment in the second focus adjustment operation mode that emphasizes responsiveness (subject detection results such as subject area size and darkness, subject tracking such as tracking of a specific subject, etc. In this case, this mode is executed as focus lens drive control, and the focus is stabilized by the second focus adjustment operation mode. When it is determined that the subject condition cannot be adjusted, the first focus adjustment operation mode in which stability is emphasized by limiting this mode is executed. Based on this concept, the focus adjustment apparatus and method of the present invention have the basic configuration as described in the section for solving the problems. As will be described later in the embodiment, the first focus adjustment operation mode that emphasizes stability using the focus evaluation value obtained from the focus detection area set in the photographing screen is, for example, a focus lens with a predetermined drive amount. This mode includes a minute driving operation in which focus adjustment is performed by reciprocally driving each time. Further, the second focus adjustment operation mode in which responsiveness is emphasized is, for example, a hill-climbing drive operation in which the focus lens is continuously driven in a predetermined direction at a higher speed than the first focus adjustment operation mode to perform focus adjustment. It is a mode to include.

Examples of the present invention will be described below. FIG. 1 shows a configuration of a video camera (image pickup apparatus) including an automatic focus adjustment apparatus according to an embodiment of the present invention. In the following embodiments, a video camera will be described, but the present invention can also be applied to other imaging devices such as a digital still camera.

<First embodiment>
In FIG. 1 showing the configuration of the main part of a video camera as an image pickup apparatus according to the first embodiment, 101 is a first fixed lens group, 102 is moved in the direction of the optical axis and zoomed to change the focal length. A variable magnification lens 103 can be made to stop. Reference numeral 104 denotes a second fixed lens group, and reference numeral 105 denotes a focus compensator lens (also referred to as a “focus lens”) having both a function of correcting the movement of the focal plane due to zooming and a focusing function. The first fixed lens group 101, the variable magnification lens 102, the stop 103, the second fixed lens group 104, and the focus lens 105 constitute an imaging optical system.

Reference numeral 106 denotes an image sensor as a photoelectric conversion element constituted by a CCD sensor or a CMOS sensor. The image sensor 106 captures a subject image formed by an imaging optical system including a focus lens and outputs an electrical signal by photoelectric conversion. Reference numeral 107 denotes a CDS / AGC circuit that samples the output of the image sensor 106 and adjusts the gain. A camera signal processing circuit 108 performs various image processing on the output signal from the CDS / AGC circuit 107 to generate a video signal. Reference numeral 109 denotes a monitor constituted by an LCD or the like, which displays a video signal from the camera signal processing circuit 108. A recording unit 115 records the video signal from the camera signal processing circuit 108 on a recording medium such as a magnetic tape, an optical disk, or a semiconductor memory.

Reference numeral 110 denotes a zoom drive source for moving the variable magnification lens 102. Reference numeral 111 denotes a focusing drive source for moving the focus lens 105. The zoom drive source 110 and the focusing drive source 111 are configured by actuators such as a stepping motor, a DC motor, a vibration motor, and a voice coil motor. Reference numeral 112 denotes an AF gate that passes only signals in an area used for focus detection (a focus detection area set to include a predetermined subject described later) in the output signals of all pixels from the CDS / AGC circuit 107. That is, the AF gate constitutes a generation unit together with the next AF signal processing circuit 113 and the like. The AF signal processing circuit 113 extracts a high frequency component, a luminance difference component, or a contrast maximum value (difference between the maximum value and the minimum value of the luminance level of the signal that has passed through the AF gate 112) from the signal that has passed through the AF gate 112. An AF evaluation signal is generated. That is, the AF signal processing circuit constitutes a generation unit that generates a focus evaluation value from an electrical signal corresponding to a focus detection area set including a predetermined subject among electrical signals output from the image sensor. The AF evaluation signal is output to a camera / AF microcomputer (also simply referred to as “microcomputer”) 114. The AF evaluation signal represents the sharpness (contrast state) of the video signal generated based on the output signal from the image sensor 106, but the sharpness varies depending on the focus state of the imaging optical system. The AF evaluation signal is a signal representing the focus state of the imaging optical system.

The microcomputer 114, which is a control means, controls the operation of the entire video camera, and performs AF control for controlling the focusing drive source 111 to drive and control the focus lens 105. That is, the control means also performs focus adjustment by driving and controlling the focus lens using the focus evaluation value obtained from the focus detection area set in the photographing screen. The microcomputer 114 performs AF control (also simply referred to as “TV-AF”) in the TV-AF method as AF control. The face detection unit 116 performs known face detection processing on the video signal, detects a human face (predetermined subject) in the shooting screen, and transmits the detection result to the microcomputer 114. Based on the detection result, the microcomputer 114 transmits information to the AF gate 112 so as to add a face frame to an area including the face in the shooting screen. Here, when the faces of a plurality of persons are detected by the face detection unit 116, there is a main face determination processing unit that prioritizes according to the position of the face, the size of the face, or an instruction from the photographer. The face determined to be the highest priority by the processing unit is set as the main face (main subject). For example, the face selected by the photographer's instruction has the highest priority, and the determination is performed such that the priority is higher as the face position is closer to the center of the screen and the face size is larger. However, this is not the case. As face detection processing, for example, there is a method of extracting a skin color region from the gradation color of each pixel represented by image data and detecting the face with a matching degree with a face contour plate prepared in advance. There is also a method of performing face detection by extracting facial feature points such as eyes, nose and mouth using a known pattern recognition technique. In the present embodiment, the face detection processing method is not limited to the above-described method, and any method may be used.

Next, face AF control processing executed by the microcomputer 114 will be described. FIG. 2 is a flowchart showing face AF control processing executed by the microcomputer 114 in FIG. This process is executed in accordance with a computer program stored in the microcomputer 114, and is repeatedly executed, for example, at the readout cycle of the imaging signal from the imaging device 106 for generating one field image. In FIG. 2, first, the result of performing face detection processing on the latest video signal is acquired from the face detection unit 116 (Step 201). Next, in Step 202, if a face exists as a result of Step 201, the process proceeds to Step 205, and if there is no face, the process proceeds to Step 203. In Step 203, an area (also referred to as “AF frame”) is set by the AF gate 112 at a predetermined fixed position on the screen, a hill climbing restriction flag described later is cleared (Step 204), and TV-AF control is executed (Step 204). Step 209). On the other hand, in Step 205, an AF frame (face frame) is set at the position of the main face from the result detected by the face detection unit 116. Further, a predetermined AF frame (normal frame) that includes the face frame and does not follow the subject is set.

Next, in face AF control, the subject included in the face frame may have low contrast, and it is determined whether or not the subject condition requires face AF control that emphasizes stability. Processing is executed (Step 206). This is a feature of the present invention described later. In response to the result, if the hill climbing restriction flag is set in Step 207, the hill climbing transition counter used for TV-AF control described later is cleared (Step 208), and the TV-AF control process (Step 209) is performed. Execute this to finish this process. When the hill climbing restriction flag is not set (No in Step 207), the TV-AF control process (Step 209) is executed. The TV-AF control processing is a method that combines a well-known minute driving operation mode and a hill-climbing driving operation mode, which will be described in detail later, and the focus lens is driven while driving the focus lens so that the focus evaluation value is maximized. This is a method of determining increase / decrease of the evaluation value and searching for a focal point.

Next, the face AF stability availability determination process in the first embodiment which is a feature of the invention will be described. FIG. 3 is a flowchart of face AF stability availability determination processing in the present embodiment. This face AF stability feasibility determination process is a process for determining whether or not the subject included in the face frame has a low contrast and it is difficult to execute a stable face AF control. . First, in Step 301, it is determined whether the face size is equal to or smaller than a predetermined size. Here, the predetermined size determines whether the face size is too small for a screen of less than 8% of the screen size. The microcomputer 114 of the control means includes a first focus adjustment operation mode, a second focus adjustment operation mode in which the drive control mode of the focus lens is different from this mode, and a follow-up drive operation corresponding to a change in the distance of the subject is performed. have. Then, the control means performs focus adjustment by driving and controlling the focus lens, and when it is determined that the subject condition can achieve stable focus adjustment by the second focus adjustment operation mode, this mode is set to focus. This is executed as lens drive control. On the other hand, if it is determined that the subject condition is not such that stable focus adjustment can be achieved by the second focus adjustment operation mode, the second focus adjustment operation mode is limited. Here, in order to make such a determination based on at least the size of the subject area obtained from the detection result by the detection means (here, the face size), the above steps are executed. .

When the face size is equal to or smaller than the predetermined size (Yes in Step 301), the focus degree of the normal frame is determined (Step 302). The normal frame is a frame that is set in a wider area than the face frame so as to include the face frame, and it is better to execute face AF control that emphasizes stability based on the focused state of the entire screen This is a frame that makes it easy to determine whether or not (subject condition). Here, the focus degree is a value obtained by dividing the maximum peak hold value (maximum value of the luminance signal) of the high-frequency component in the AF frame by the luminance difference component (maximum contrast value) (simple focus degree). Is used. When the subject is in focus, the maximum peak hold value is high and the luminance difference component is also high. When the focus is largely out of focus, the maximum peak hold value decreases, but the luminance difference component changes little. Therefore, the state of whether or not the subject is in focus can be roughly obtained by the simple focus degree. Empirically, the result of dividing the maximum peak hold value of the high-frequency component in the AF frame by the luminance difference component is 0.5 or more in focus, 0.25 or more and 0.5 or less is small blur, 0.25 The following is judged as a large blur. However, the method for determining the in-focus level is not limited to this, and it is only necessary to determine whether or not the in-focus state is achieved. If it is determined that the normal frame is in focus (Yes in Step 303), the hill climbing restriction flag is set (Step 304), and this process is terminated. When it is determined that the normal frame is not in focus (No in Step 303), the process proceeds to Step 305. The determination process described above is a feature of the present invention. When the face size is small, the resolution is lowered and the contrast tends to be lower than when the face is large. At that time, if the hill-climbing drive operation mode is entered even though the entire screen is in focus, the face AF control becomes unstable. Therefore, it is necessary to limit the hill-climbing drive operation mode. In the present embodiment, the AF signal processing circuit of the generating means obtains a focus evaluation value from an electrical signal corresponding to a first focus detection area including a predetermined subject and a second focus detection area larger than the focus detection area. Generate. Then, when the size of the subject area obtained from the detection result by the detection means is equal to or smaller than a predetermined size and the in-focus state of the second focus detection area is determined to be in-focus, The above steps are performed so that the two focus adjustment operation modes can be limited. Here, when the value calculated by dividing the maximum value of the luminance signal of the predetermined frequency component in the focus detection area by the luminance difference component is greater than or equal to the predetermined value, it is determined that the focus is achieved.

Next, when the face size is larger than the predetermined size (No in Step 301), a threshold value for determining whether the face frame is dark is set (Step 305). First, it is determined whether the peak luminance value of the face frame is equal to or less than a first predetermined value (Step 306). If the peak luminance value of the face frame is less than or equal to the first predetermined value (Yes in Step 306), it is determined whether or not the contrast value of the face frame is less than or equal to the second predetermined value (Step 307). If the contrast value of the face frame is equal to or smaller than the second predetermined value (Yes in Step 307), it is determined whether the peak value of the high frequency component of the face frame is equal to or smaller than the third predetermined value (Step 308). Here, the contrast value is a difference between the maximum value and the minimum value of the luminance signal level. When the peak value of the high frequency component of the face frame is equal to or smaller than the third predetermined value (Yes in Step 308), the hill climbing restriction flag is set (Step 310), and this process is terminated. Conversely, when each comparison value is greater than or equal to each predetermined value in Step 306, Step 307, and Step 308 (No in Step 306, No in Step 307, No in Step 308), the hill climbing restriction flag is cleared (Step 309). This determination process is a feature of the present invention, and when a scene of backlight or night scene is shot, the face becomes dark and the contrast tends to be low. At that time, if the mode shifts to the hill-climbing drive operation mode, the face AF control becomes unstable. Therefore, at least when the luminance value in the face frame is small and the contrast is low, it is necessary to limit the hill-climbing driving operation mode. Here, the first, second, and third predetermined values may be set to about 25%, about 20%, and about 10% of values that can be taken by each comparison value empirically. However, it is not limited to this because it is considered to change depending on the configuration of the lens and the imaging system. In this embodiment, the above steps are executed so that the second focus adjustment operation mode can be limited when it is determined that the subject detected by the detection means is darker than the predetermined darkness based on the focus evaluation value. To do. Here, in the focus evaluation value, at least the maximum value of the luminance signal of the predetermined frequency component in the focus detection region is smaller than the predetermined value, and the maximum difference between the brightest signal and the darkest signal of the luminance signal of each horizontal line When the contrast peak value (maximum contrast value), which is a value, is smaller than a predetermined value, it is determined that the subject is dark.

FIG. 4 is a diagram for explaining the minute driving operation mode of the focus lens 105 executed in Step 209 in the TV-AF process of FIG. In FIG. 4, the horizontal axis indicates time, and the vertical axis indicates the position of the focus lens 105. In the upper part of the figure, a vertical synchronizing signal of the video signal is shown. As shown in FIG. 4, the focus evaluation value EV _A for the electric charge (indicated by the slanted ellipse in the figure) accumulated in the image sensor 106 during the period _A is taken in at time T _A , and the image sensor during the period B A focus evaluation value EV _B for the charge accumulated in 106 is taken in at time T _B. The focal evaluation value EV _C for charge accumulated in the image sensor 106 during the period C is taken at time T _C. Then, at time _{T D,} the focus evaluation value _{EV A,} EV B, by comparing the EV _C, if EV A> EV _B and _EV C> EV _B, moves the driving (vibration) center of the minute drive. On the other hand, if EV _A <EV _B or EV _C <EV _B , the vibration center is not moved. As described above, the micro-driving operation mode is to determine the direction in which the focus evaluation value increases while moving the focus lens 105 or to search for the position (peak position) of the focus lens 105 where the focus evaluation value is the largest. is there. Note that the control for finely driving the focus lens 105 in order to determine whether or not the focus state is obtained from the change in the focus evaluation value can also be referred to as focus confirmation control. Further, the control for finely driving the focus lens 105 to determine the in-focus direction from the change in the focus evaluation value can also be referred to as in-focus direction discrimination control. The above mode is the first focus adjustment operation mode, which is a minute drive operation mode in which focus adjustment is performed by reciprocating the focus lens by a predetermined drive amount.

Next, the hill-climbing drive operation mode will be described with reference to FIG. In the hill-climbing drive operation mode, the focus lens 105 is driven at a high speed, and the peak position where the focus evaluation value obtained during that time reaches its peak or its vicinity is detected. FIG. 5 shows the relationship between the movement of the focus lens 105 and the change in the focus evaluation value in the hill-climbing drive operation mode. Here, in the movement of A, since the focus evaluation value decreases beyond the peak, the existence of the peak position (focusing position) can be confirmed, and the hill-climbing driving operation mode is terminated and the mode is shifted to the minute driving operation mode. On the other hand, since there is no peak in the movement of B and it decreases monotonously, it can be determined that the drive direction of the focus lens 105 is incorrect. In this case, the driving direction is reversed and the hill-climbing driving operation mode is continued. The above mode is the second focus adjustment operation mode, which is a hill-climbing drive operation mode in which the focus lens is continuously driven in a predetermined direction at a speed higher than that of the first focus adjustment operation mode. .

Then, the TV-AF process in Step 209 in FIG. 2 determines the in-focus direction by the minute driving operation mode, shifts to the hill-climbing driving operation mode, searches for the in-focus position by the hill-climbing driving operation mode, and again performs the minute driving operation mode. The process is shifted to and the focus confirmation is repeatedly executed. Here, the in-focus direction is determined in this minute driving operation mode, and it is determined whether or not the direction of moving the driving (vibration) center is continuously moving in the same direction when shifting to mountain climbing. That is, when the direction in which the drive center is moved is continuous, the count is incremented, and when the predetermined count value is exceeded, the hill-climbing drive operation mode is entered. This is the hill-climbing transition counter used in Step 208 in FIG. 2. By clearing this hill-climbing transition counter, it is possible to prohibit transition to the hill-climbing drive operation mode. In addition, the predetermined count value can be changed according to a simple degree of focus, and is 3 counts for large blur and 5 counts for small blur. The count value of increases. Here, in this embodiment, the transition to the hill-climbing driving operation mode is prohibited by clearing the hill-climbing transition counter, but even if the transition to the hill-climbing driving operation mode is restricted by increasing the predetermined count value described above, Good. For example, 5 counts for large blur and 10 counts for small blur.

Here, a setting example of the face frame and the normal frame will be described with reference to FIG. FIG. 8A shows an example in which a face frame A and a normal frame B are set in the imaging screen. The normal frame B is set around the center of the imaging screen, and the face frame A is set at the position where the face recognition is performed. In this embodiment, the focus evaluation value of the face frame A and the focus evaluation value of the normal frame B are added to perform TV-AF control. Thus, even when the face frame A has a low contrast, stable face AF control can be realized with the focus evaluation value of the normal frame B. However, when the hill climbing restriction flag is not set, the face AF control may be performed using only the face frame A. FIG. 8B shows an example in which TV-AF control is performed using only the normal frame set in Step 203. Here, when only the normal frame is set in the imaging screen, the face frame A is simply deleted from the state illustrated in FIG. 8A, and the focus evaluation value is detected using only the normal frame B, and TV-AF is performed. Control can be performed. However, the present invention is not limited to this, and in consideration of the fact that the photographer often places the subject in the center of the imaging screen, a normal frame C smaller than the normal frame B may be further set around the center of the screen. Good. In this case, the focus evaluation values acquired from the normal frame B and the normal frame C are added to perform TV-AF control.

<Second embodiment>
A face AF control process executed by the microcomputer 114 in the second embodiment will be described. FIG. 6 is a flowchart showing face AF control processing executed by the microcomputer 114 in FIG. Since this process is basically the same as the face AF control process in the first embodiment, the operations common to those in FIG. 2 will be described by replacing the last two digits with the same numerals as in FIG. To do. First, a face detection result is acquired (Step 601), and if a face exists (Yes in Step 602), a face presence flag and a face tracking permission flag described later are set (Step 610, Step 611). The face presence flag is a flag that is set when a face is detected, and indicates whether or not to continue AF control for the face frame when a face is no longer detected. Then, similarly to the first embodiment, an AF frame is set (Step 605), and the face AF stability feasibility determination process in the second embodiment described later is executed (Step 606). After the face AF stability availability determination process is executed, the process is the same as in the first embodiment.

Next, when the face does not exist (No in Step 602), it is determined whether the face presence flag is set (Step 612). When the face presence flag is not set (No in Step 612), since the AF control is not performed on the face frame, the AF frame is set at a predetermined position on the screen as in the first embodiment ( (Step 603), the mountain climbing restriction flag is cleared (Step 604), and the TV-AF control is executed (Step 609).

If the face presence flag is set (Yes in Step 612), it is determined whether or not the face tracking permission flag is set (Step 613). When the face tracking permission flag is set (Yes in Step 613), the face tracking process is executed (Step 617). When face tracking is being executed (Yes in Step 618), the process proceeds to Step 605 and the face AF control is continued. If face tracking is not executed (No in Step 618), the face tracking permission flag is cleared (Step 619), and the process proceeds to Step 614. Here, the face tracking process in Step 617 is a partial area in the imaging screen and is detected last when the detected face turns sideways and the face cannot be detected. This is a process for following a detected face by using a face detection area as a reference image and performing a known tracking process based on the reference image. As a result, even when the subject is moved, it becomes possible to focus and follow when the detection is temporarily impossible. In the face tracking process, for example, color difference data (color information), luminance, and the like of the reference image are acquired by a feature amount extraction unit, and a histogram is generated. It is stored as a template indicating the color characteristics of the subject to be tracked, and the cross-correlation (matching) with a histogram such as color difference data is calculated for neighboring search areas, and the area with a high correlation value detects the tracking target judge. This process is repeated. Then, when the correlation value becomes equal to or less than the predetermined value, it is determined that the tracking is not continued, and the tracking execution is stopped. The face frame is set based on the face tracking result during face tracking. The control means limits the second focus adjustment operation mode when it is determined that the specific subject in the imaging screen is being tracked. At this time, the control means uses the specific subject area immediately before the specific subject area cannot be specified as a reference image, extracts a feature amount in the reference image, and has a high cross-correlation with the feature amount. A region that is assumed to be a specific subject is tracked.

Next, when the face tracking permission flag is not set (No in Step 613), a face disappearance process is executed (Step 614). If the face disappearance process is being executed (Yes in Step 615), the process proceeds to Step 605 and the face AF control is continued. If the face disappearance process has not been executed (No in Step 615), the face presence flag is cleared (Step 616), and after proceeding to Step 603, if the face presence flag is not set (No in Step 612), the same processing is performed. Run.

Here, the face disappearance process in Step 614 is executed when a face cannot be detected after the face is detected or the face tracking process is completed, and a process for maintaining the face frame as it is for a predetermined period of time. It is. This is the following process. If the face cannot be detected temporarily or face tracking cannot be executed, the face may be detected again in the vicinity of the current face frame position. If the AF frame is set to a different position during that time, the subject will be focused but another subject such as the background will be focused, and when the face can be detected again, it will be refocused. As described above, focusing becomes unstable. In order to prevent this, face disappearance processing is performed. The predetermined period here may be about 5 frames empirically, but is not limited to this. During the face disappearance process, the face frame holds the current position. As described below, the control means limits the second focus adjustment operation mode when it is determined that the area of the specific subject has disappeared.

Next, face AF stability availability determination processing in the second embodiment which is a feature of the invention will be described. FIG. 7 is a flowchart of the face AF stability availability determination process in the present embodiment. First, it is determined whether or not face tracking is being executed (Step 701). If face tracking is being executed (Yes in Step 701), the hill climbing restriction flag is set (Step 704), and the process is terminated. If face tracking is not being executed (No in Step 701), it is determined whether or not a face disappearance process is in progress (Step 702). This is a feature of the present invention, and the face tracking process can enable focus tracking after a face cannot be detected. However, for example, when there is a subject having a similar color feature in the vicinity, there is a possibility that tracking may be erroneously performed. In this case, a face frame may be set for a subject that does not have a background contrast different from the intended subject, and face AF control may become unstable. In addition, if the subject distance change that causes the hill-climbing drive operation mode to occur during face tracking, it is considered that the reliability of tracking accuracy itself will be reduced because the pattern changes greatly. On the contrary, if the hill-climbing drive operation mode is executed, the picture may be greatly changed, and the tracking performance may be reduced. Therefore, it is necessary to prohibit the hill-climbing drive operation mode during face tracking.

Next, when the face disappearance process is in progress (Yes in Step 702), the hill climbing restriction flag is set (Step 704), and the process is terminated. If the face disappearing process is not in progress (No in Step 702), the hill climbing restriction flag is cleared (Step 703), and the process ends. This is a feature of the present invention, and the face disappearance process maintains the face frame for a predetermined period assuming that the face may be detected again in the vicinity of the current position. That is, the subject does not always exist at the position of the face frame. It may be a subject with no contrast. Because of such an unclear state, it is inappropriate to shift to mountain climbing. In addition, since it is assumed that the current state is maintained, the focus adjustment should not be executed with a large focus change. Therefore, it is necessary to prohibit the hill-climbing drive operation mode while the face is disappearing.

As described above, in the embodiment of the present invention, in the face AF control, the transition to the hill-climbing drive operation mode is prohibited in the shooting scene where the inside of the face frame has a low contrast or the control state of the face AF control. . Thus, stable face AF control can be realized, and the photographer's discomfort caused by fluff can be reduced.

The present invention also includes a case where a software program that realizes the functions of the above-described embodiments is supplied from a recording medium directly or using wired / wireless communication to a system or apparatus having a computer that can execute the program, and the program is executed. include. Accordingly, the program code itself supplied and installed in the computer in order to implement the functional processing of the present invention by the computer also realizes the present invention. That is, the computer program itself for realizing the functional processing of the present invention is also included in the present invention. In this case, the program may be in any form as long as it has a program function, such as an object code, a program executed by an interpreter, or script data supplied to the OS. As a recording medium for supplying the program, for example, a magnetic recording medium such as a hard disk or a magnetic tape, an optical / magneto-optical storage medium, or a nonvolatile semiconductor memory may be used. As a program supply method, a method in which a computer program constituting the present invention is stored in a server on a computer network, and a connected client computer downloads and programs the computer program is also conceivable.

The present invention has been described in detail based on the preferred embodiments thereof, but the present invention is not limited to these specific embodiments, and various forms within the scope of the present invention are also included in the present invention. included. A part of the above-described embodiments may be appropriately combined.

105: Focus lens, 106: CCD (imaging device), 113: AF signal processing circuit (generation means), 114: Camera / AF microcomputer (control means), 116: Face detection unit (detection means)

The present invention is characterized by subject conditions that can achieve stable focus adjustment in the second focus adjustment operation mode that emphasizes responsiveness (subject detection results such as subject area size and darkness, subject tracking such as tracking of a specific subject, etc. In this case, this mode is executed as focus lens drive control, and the focus is stabilized by the second focus adjustment operation mode. When it is determined that the subject condition cannot be adjusted, the first focus adjustment operation mode in which stability is emphasized by limiting this mode is executed. Based on this concept, the focus adjustment apparatus and method of the present invention have the basic configuration as described in the section for solving the problems. As will be described later in the embodiment, the first focus adjustment operation mode that emphasizes stability using the focus evaluation value obtained from the focus detection area set in the photographing screen is, for example, a focus lens with a predetermined drive amount. This mode includes a minute driving operation in which focus adjustment is performed by reciprocally driving each time. The second focus adjustment operation mode in which responsiveness is emphasized is, for example, a hill-climbing drive operation in which the focus lens is continuously driven in a predetermined direction at a higher speed than the first focus adjustment operation mode to perform focus adjustment. This mode is combined with the minute driving operation .

Claims (11)

An image sensor that photoelectrically converts light from a subject that has passed through an imaging optical system including a focus lens into an electrical signal;
Detecting means for detecting a predetermined subject in a photographing screen from an electrical signal output from the image sensor;
Generating means for generating a focus evaluation value from an electric signal corresponding to a focus detection region set including the predetermined subject among the electric signals output from the image sensor;
Control means for controlling the focus by driving the focus lens; and
An autofocus device having
The control means performs a focus adjustment by driving the focus lens to perform a focus adjustment, and a first focus adjustment operation mode that uses a focus evaluation value obtained from a focus detection area set in a photographing screen; The focus adjustment operation mode is different from the focus lens drive control mode, and has a second focus adjustment operation mode for performing a follow-up drive operation corresponding to a change in the distance of the subject, and is more stable by the second focus adjustment operation mode. When it is determined that the subject condition can achieve focus adjustment, the second focus adjustment operation mode is executed as focus lens drive control, and stable focus adjustment can be achieved by the second focus adjustment operation mode. An automatic focus adjustment device that restricts the second focus adjustment operation mode when it is determined that the subject condition is not met. The control means determines, based on at least the size of the subject area obtained from the detection result by the detection means, whether or not the subject condition allows stable focus adjustment in the second focus adjustment operation mode. The automatic focusing apparatus according to claim 1. The generation means generates a focus evaluation value from electrical signals corresponding to a first focus detection area including the predetermined subject and a second focus detection area larger than the first focus detection area, respectively.
The control means, when the size of the subject area obtained from the detection result by the detection means is equal to or less than a predetermined size and the in-focus state of the second focus detection area is determined to be in-focus, The automatic focus adjustment apparatus according to claim 2, wherein the second focus adjustment operation mode is limited. The control means determines to be in focus when a value calculated by dividing a maximum value of a luminance signal of a predetermined frequency component in the focus detection area by a maximum contrast value is a predetermined value or more. The automatic focusing apparatus according to claim 3, wherein The control means limits the second focus adjustment operation mode when it is determined that the subject detected by the detection means is darker than a predetermined darkness based on the focus evaluation value. Item 4. The automatic focusing apparatus according to Item 1. In the focus evaluation value, when the maximum value of a luminance signal of a predetermined frequency component in the focus detection area is smaller than a predetermined value and the maximum contrast value is smaller than a predetermined value, the control means 6. The automatic focusing apparatus according to claim 5, wherein the subject is determined to be dark. 2. The automatic control unit according to claim 1, wherein the control unit limits the second focus adjustment operation mode when it is determined that the specific subject in the imaging screen is being tracked. 3. Focus adjustment device. The control means uses the specific subject area immediately before the specific subject area cannot be specified as the reference image in the tracking state, extracts a feature amount in the reference image, and extracts the feature 8. The automatic focus adjustment apparatus according to claim 7, wherein a region which is assumed to be a specific subject having a high cross-correlation with the amount is tracked. 2. The automatic focus adjustment apparatus according to claim 1, wherein the control unit restricts the second focus adjustment operation mode when it is determined that the area of the specific subject has disappeared. 3. The first focus adjustment operation mode is a minute drive operation mode in which the focus lens is reciprocally driven by a predetermined drive amount to execute focus adjustment, and the second focus adjustment operation mode is a focus lens in a predetermined direction. The automatic focus according to any one of claims 1 to 9, wherein the autofocus is a hill-climbing drive operation mode in which focus adjustment is performed by driving at a higher speed than the first focus adjustment operation mode continuously. Adjusting device. An imaging step for photoelectrically converting light from a subject passing through an imaging optical system including a focus lens into an electrical signal;
A detection step of detecting a predetermined subject in the shooting screen from the electrical signal output in the imaging step;
A generation step of generating a focus evaluation value from an electric signal corresponding to a focus detection region set including the predetermined subject among the electric signals output in the imaging step;
A control step for driving and controlling the focus lens to adjust the focus;
An automatic focus adjustment method comprising:
In the control step, a first focus adjustment operation mode that uses a focus evaluation value obtained from a focus detection area set in the photographing screen when performing focus adjustment by driving and controlling the focus lens; A focus lens operation control mode is different from the focus adjustment operation mode, and a second focus adjustment operation mode that performs a follow-up driving operation corresponding to a change in the distance of the subject can be executed. When it is determined that the subject condition can achieve stable focus adjustment, the second focus adjustment operation mode is executed as drive control of the focus lens, and stable focus adjustment is performed by the second focus adjustment operation mode. An automatic focus adjustment method characterized by restricting the second focus adjustment operation mode when it is determined that the subject condition is not achievable.

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