JP5322593B2 - Focus adjustment apparatus and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To avoid hunting when focusing a detected subject by detecting a preset subject by using a hybrid AF system that involves a phase difference AF. <P>SOLUTION: The focus adjusting device exerts focusing control selectively using a contrast AF system and a phase difference AF system. The face is detected from an input image supplied by an imaging element (S402). If a face is detected, the contrast AF system is used to drive a focus lens based on the contrast of a partial image showing the detected face (S406). If a face is not detected, the focus lens is driven using the contrast AF system (S403) or phase difference AF system (S405) according to a focusing state obtained based on the contrast of the input image or a phase difference (S404). <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a focus adjustment method and method used for an imaging apparatus such as a video camera, and more particularly to a focus adjustment method and method using both a contrast AF and a phase difference AF using a face detection function.

  A contrast AF method is generally used as an autofocus (AF) method mounted on an imaging apparatus such as a video camera. In the contrast AF method, a high-frequency component is extracted from a video signal obtained using an image sensor, and a so-called AF evaluation value signal, which is a signal indicating a focus state, is generated, and this AF evaluation value signal is maximized. In this way, the position of the focus lens is controlled.

  There has also been proposed an imaging apparatus that employs a so-called hybrid AF system that combines such a contrast AF system with a so-called external phase difference detection (hereinafter referred to as “phase difference AF”) system (for example, a patent). Reference 1). In the external phase difference AF method, light that does not pass through the imaging optical system is divided into two light beams, which are respectively received by sensors, and based on the phase difference of the received light that changes according to the distance to the subject, The position is controlled. The hybrid AF method can have both high-precision focusing performance by the contrast AF method and high-speed focusing performance by the external measurement phase difference AF method.

  On the other hand, a camera equipped with a face detection function is also actively developed. For example, as disclosed in Patent Document 2, based on the detected face area so as to focus on the detected face. A technique for designating an AF detection area is also introduced.

JP 2002-258147 A (paragraph 0085, FIG. 2, FIG. 3, etc.) JP 2007-279188 A

  In face-priority AF that focuses on the detected face area, the AF operation works to focus on the face in an image that contains a face, but the face is detected immediately after a new face is detected or conversely. Immediately after being stopped, the AF operation may become unstable. In particular, in the phase difference AF method, the phase difference of the subject image that changes according to the distance to the subject is directly detected by the sensor, and the focus lens is moved to the in-focus position obtained from the detected phase difference, so that the subject can be quickly moved. In response, the AF operation can be performed at high speed. However, detecting a face from the captured image takes various time since various image processing is performed, and after several times or more required for the phase difference AF, whether the face is present in the captured image or not is detected. If there is, it is possible to know the detection result of the face such as where it is.

  When face priority AF is performed using the hybrid AF method with phase difference AF1 in such a time delay, for example, the angle of view is changed by panning the camera in a state where no face is detected. If the following problem occurs. First, it is assumed that a subject that is not a person (face) is in the phase difference AF detection area, and that the person (face) is outside the phase difference AF detection area at a distance different from the distance to the subject. In this case, first, during the face detection, the AF operation is performed so that the subject in the detection area is focused by the phase difference AF. After a slight delay due to face detection, the focus operation is performed on the face by another method such as contrast AF for the area determined to be a face. From the viewpoint of the user, such an operation has a problem in that it appears that focus hunting occurs before and after face detection, which is very unpleasant.

  The present invention has been made in view of the above problems, and avoids hunting when a preset subject is detected using the hybrid AF method with phase difference AF and the detected subject is focused. The purpose is to do.

  Another object is to enable quicker focusing when a subject is detected and the detected subject is focused.

To achieve the above object, the focus adjustment apparatus of the present invention controls the first focus adjustment for controlling the focus lens to be driven in the direction of the in-focus position based on the contrast of the input image input from the image sensor. And a second focus adjustment method that controls the focus lens to be driven to the in-focus position based on the phase difference between a pair of images formed by light from the subject. Focus adjustment means for controlling the focus, and determination means for determining the positional relationship between the subject detection position obtained from the input image input from the image sensor and the phase difference detection area which is the phase difference detection area, said focusing means, the is determined in the determination means is the subject detection position above the phase difference detection area, when the size of the subject in the input image is a predetermined value or more, before The second focusing system to drive the focus lens, the is determined in the determination means is the subject detection position above the phase difference detection area, the size of the subject in the input image than the predetermined value Is smaller, the focus lens is driven by the first focus adjustment method, and the first focus is determined when the determination means determines that the subject detection position is below the phase difference detection region. The focus lens is driven by an adjustment method.

Also, a first focus adjustment method for controlling the focus lens to be driven in the direction of the in-focus position based on the contrast of the input image input from the image sensor, and a pair of images formed by light from the subject The focus adjustment method of the present invention that selectively uses the second focus adjustment method that controls the focus lens to be driven to the in-focus position based on the phase difference of A determination step of determining a positional relationship between a subject detection position obtained from an input image input from the image sensor and a phase difference detection region that is the detection region of the phase difference; and a focus adjustment unit in the determination step it is determined that there is the object detected position on an upper side of the phase difference detection area, when the size of the subject in the input image is a predetermined value or more, the by the second focusing method follower Drives Kasurenzu, the determination step in the subject detection position above the phase difference detection area is determined that, when the size of the subject in the input image is smaller than the predetermined value, the first focus of The focus lens is driven by an adjustment method, and when it is determined in the determination step that the subject detection position is below the phase difference detection region, the focus lens is driven by the first focus adjustment method. And a driving process.

  According to the present invention, it is possible to avoid hunting when a preset subject is detected using the hybrid AF method with phase difference AF and the detected subject is focused.

  Further, when the subject is detected and the detected subject is focused, the focus can be adjusted more quickly.

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

<First Embodiment>
Apparatus Configuration FIG. 1 is a block diagram showing a configuration of a video camera as an imaging apparatus according to the first embodiment including the focus adjustment apparatus of the present invention.

  In the figure, reference numeral 100 denotes a lens unit that houses an imaging optical system including a fixed lens 101, a variable power lens 102, a diaphragm 103, a fixed lens 104, and a focus lens 105 in order from the object side (subject side). Yes. Reference numeral 108 denotes a position encoder that detects the positions of the variable power lens 102, the diaphragm 103, and the focus lens 105.

  The zoom lens 102 is driven in the optical axis direction by the zoom motor 106, and the focus lens 105 is driven in the optical axis direction by the focus motor 107. The zoom motor 106 and the focus motor 107 operate by receiving drive signals from the zoom drive circuit 120 and the focus drive circuit 121, respectively.

  Reference numeral 109 denotes an image sensor formed by a CCD sensor, a CMOS sensor, or the like. The image sensor 109 photoelectrically converts an image of an object within the imaging range formed by light incident on the imaging optical system. The imaging signal processing circuit 119 performs various signal processing such as amplification processing, gamma correction processing, and white balance processing on the output signal from the imaging device 109, and converts it into an image signal of a predetermined video format. The obtained image signal is output to the monitor display 114 or recorded on an image recording medium 116 such as a semiconductor memory, an optical disk, or a hard disk.

  A main CPU 110 controls various operations and functions of the video camera. The operation switch group 115 includes a power switch, a switch for starting and stopping a recording operation and a reproduction operation, a switch for selecting an operation mode of the video camera, a zoom switch for changing the zoom state of the zoom lens 102, and the like. It has been. There is also provided a switch used for selecting an AF operation mode to be described later. When these switches are operated, a part of the computer program stored in the flash memory 113 is loaded into the RAM 112, and the main CPU 110 controls the operation of each unit according to the program loaded into the RAM 112.

  A face detection processing circuit 111 performs image processing on the image signal output from the imaging signal processing circuit 119, determines the presence or absence of a face, and when there is a face, the position of the face in the image and the face Detect size etc. The image processing performed by the face detection processing circuit 111 includes resizing processing for reducing the size of the original image signal for calculation, face contour detection processing, reliability determination processing for a face, and the like. For this reason, as will be described later, it takes several tens of milliseconds to several hundreds of milliseconds after receiving an image signal until a detection result is obtained.

  On the other hand, 131 is a line sensor for phase difference AF, and a plurality of light receiving elements are arranged in a line. The light from the subject reaches the line sensor 131 through the externally measured phase difference AF imaging lens 130 provided separately from the imaging optical system, that is, without passing through the lens unit 100. The light transmitted through the lens unit 100 can be divided into two, and an optical element capable of distributing the light to the image sensor 109 and the line sensor 131 can be inserted into the optical path, so that the camera can be configured.

● Principle of Phase Difference AF Method (Second Focus Adjustment Method) As shown in FIG. 2, the line sensor 131 in the first embodiment is added to the left and right with the position on the optical axis of the imaging lens 130 as the center. 200 light receiving elements are arranged side by side. Further, as shown in FIGS. 2A and 2B, the ratio of the size of the light receiving area of the line sensor 131 to the angle of view of the camera changes according to the zoom magnification. In FIG. 2, the light receiving area C is divided into a central light receiving area C and light receiving areas L 1, L 2, R 1 and R 2 arranged on the left and right sides thereof. Each light receiving area is composed of 40 light receiving elements.

  In this way, two line sensors 131 each including 200 light receiving elements are provided on the left and right. Then, a shift amount (phase difference) between a pair of images formed in the corresponding light receiving areas in these two line sensors 131 is detected. Since this deviation amount changes according to the distance to the subject, the signal output from the line sensor 131 is a signal according to the distance to the subject (or object). Needless to say, the number of light receiving elements constituting the line sensor 131 is not limited to 200.

  FIG. 3 shows the principle of the phase difference AF method using a line sensor. In FIG. 3, 201 is a subject, 202 is a first imaging lens, and 203 is a first line sensor. Reference numeral 204 denotes a second imaging lens, and 205 denotes a second line sensor. The pair of first and second imaging lenses 202 and 204 are in the imaging lens 130 shown in FIG. 1, and the pair of first and second line sensors 203 and 205 are in the line sensor 131 shown in FIG. Each corresponds. The first and second line sensors 203 and 205 are installed apart from each other by the baseline length B. Of the light from the subject 201, the light passing through the first imaging lens 202 forms an image on the first line sensor 203, and the light passing through the second imaging lens 204 is the second line sensor. An image is formed on 205.

An example of output signals (image signals) from the first and second line sensors 203 and 205 is shown in FIG. Since the first and second line sensors 203 and 205 are separated by the base line length B, the image signal from the first line sensor 203 and the image signal from the second line sensor 205 are shifted by the number of pixels X. Signal. Therefore, the phase difference X can be calculated by calculating the correlation between the two image signals while shifting the pixels and obtaining the pixel shift amount that maximizes the correlation. The phase difference X, the base line length B, the focal length f of the imaging lenses 202 and 204, and the distance L to the subject have the relationship of the following formula (1) based on the principle of triangulation.
L = B · f / X (1)

  That is, since the base line length B and the imaging lenses 202 and 204 are fixed values in each video camera, the phase difference X changes according to the distance L to the subject. Accordingly, based on the obtained phase difference X, the main CPU 110 obtains the distance L to the subject, and the position of the focus lens for focusing on the subject according to the obtained distance L (the current detected by the position encoder 108). The driving amount from the focus lens position) is calculated. This “calculation” is not only an operation using a calculation formula, but also a focus lens for a phase difference X or a distance L to a subject calculated based on the phase difference X stored in a memory (not shown) in advance. It also includes reading out the data of the position (in-focus position). Therefore, in the following description, it is described as “determining the focus lens position based on the phase difference” or the like, but the “phase difference” can be read as “the distance to the subject calculated from the phase difference”.

  By driving the focus lens 105 through the focus drive circuit 121 to the position of the focus lens thus obtained, a focused state can be obtained.

Principle of contrast AF method (first focus adjustment method) The imaging signal processing circuit 119 extracts a high-frequency component from the image signal obtained from the output of the imaging element 109 using a bandpass filter, and calculates an AF evaluation value. To do. The AF evaluation value is output to the main CPU 110. The AF evaluation value represents the sharpness (contrast state) of the image signal generated based on the output signal from the image sensor 109, but the sharpness varies depending on the focus state of the imaging optical system. The value represents the focus state of the imaging optical system.

  FIG. 5 shows the relationship between the focus lens position and the AF evaluation value. When the subject at a specific distance is imaged and the focus lens 105 is moved from the closest position to the infinite position, the evaluation value changes as shown in FIG. The focus lens position where the AF evaluation value is maximized is the focus position (focus point) for the subject.

  Therefore, the main CPU 110 can obtain the in-focus state by moving the focus lens 105 to monitor the change in the AF evaluation value and detecting the focus lens position where the AF evaluation value is maximized. Specifically, every time an AF evaluation value is calculated from the read image signal, it is compared with an AF evaluation value calculated in the past, and the drive direction of the focus lens 105 is determined based on the magnitude of the value. Then, after driving the focus lens 105 in the determined direction, the image signal is read again to calculate the AF evaluation value, and the process of driving the focus lens 105 in the determined direction is repeated. As a result, the focus lens 105 can be driven to a position where the AF evaluation value is maximized, and an in-focus state can be obtained.

AF Processing In the first embodiment, it is possible to select using the operation switch group 115 whether AF processing is performed without using the face detection result or AF processing is performed using the face detection result. . In the first embodiment, as the AF process that is performed without using the face detection result, the AF process is performed by a hybrid AF method that selectively uses the contrast AF method and the phase difference AF method. The AF process that does not use the face detection result is referred to herein as “normal mode”. Further, as will be described later in the first embodiment, “Face priority AF mode 1” and “Face priority AF mode 2” are provided as AF processing using the face detection result, and operation switch groups are similarly provided. 115 can be selected. First, the normal mode will be described, and then “face priority AF mode 1” and “face priority AF mode 2” will be described in order.

(I) Normal Mode In the video camera according to the first embodiment, as shown in FIG. 6, the focus lens 105 is driven at high speed using phase difference AF from a largely blurred state to the vicinity of the in-focus position. In order to obtain a more accurate in-focus state, the focus lens 105 is driven using contrast AF from the vicinity of the in-focus position to the in-focus position.

  FIG. 7 shows a flowchart of the AF process in the normal mode which is performed by the main CPU 110 and is unrelated to the face detection result. Note that the processing shown in this flowchart is repeatedly executed, for example, in the readout cycle of the image signal (input image) from the image sensor 109 for generating one field image. Hereinafter, this cycle is referred to as “V cycle”.

  First, in step S301, the main CPU 110 starts an AF process in the normal mode, triggered by turning on the power switch of the video camera or the like.

  In step S302, AF control by the above contrast AF method (hereinafter referred to as “contrast AF control”) is performed, an AF evaluation value is calculated from the read imaging signal (input image), and the calculated AF evaluation is performed. The focus lens is driven based on the value. In this contrast AF control, the focus lens 105 is moved by a predetermined amount in the direction obtained by comparing the AF evaluation value calculated this time with the AF evaluation value calculated in the past. In contrast AF control, in-focus state is maintained, for example, it is determined whether or not the AF evaluation value is lowered in order to determine whether or not the focus lens needs to be redriven. Processing is also included.

  In step S303, for the above-described AF control (phase difference AF) using the phase difference AF method, a pair of image signals output from the pair of line sensors 131 are acquired to obtain a phase difference between the image signals. In step S304, the focus position of the focus lens 105 is calculated based on the obtained phase difference.

  In step S305, the movement amount threshold th1 used in the next step S306 is set according to the position of the zoom lens 102 (focal length of the imaging optical system). The amount of movement here is the difference between the current position of the focus lens 105 detected by the position encoder 108 and the in-focus position obtained in step S304. The threshold th1 is set larger on the tele side than on the wide side.

  In step S306, the difference between the current focus lens position and the focus position obtained in step S304 is compared with a threshold value th1. The level of the focus state of the focus lens 105 can be determined by comparison with the threshold th1. If the difference between the current focus lens position and the in-focus position is larger than the threshold th1 (that is, the focus state is equal to or lower than a preset level), the process proceeds to step S307, and the in-focus position obtained from the phase difference in step S304. The focus lens 105 is moved. Then, the process returns to the contrast AF control in step S302.

  In step S306, if the difference between the current focus lens position and the in-focus position obtained in step S304 is smaller than the threshold th1, the process returns to the contrast AF control in step S302 as it is.

  As described above, during the AF process in which the contrast AF control is repeatedly performed, when the current focus lens position and the in-focus position obtained by the phase difference AF control are far apart from the threshold th1, that is, in the large blur state. The focus lens is driven by phase difference AF. Accordingly, it is possible to avoid frequent and discontinuous movement of the focus lens, and it is possible to take advantage of the favorable response of the phase difference AF and high-speed operation. Further, a highly accurate in-focus state can be obtained thereafter by contrast AF control.

(Ii) Face priority AF processing As described above, the video camera according to the first embodiment includes the face detection processing circuit 111 and detects a human face from an image captured by the image sensor 109. Specifically, after the image is read from the image sensor 109, the image is resized to an image smaller than the recorded image, and preprocessing is performed to facilitate face detection by pattern matching. Next, pattern matching is performed based on the outline of the face and the interval between eyes, and the face detection result in the image shows the position of the face, the size of the face, the interval between eyes, and the likelihood of being a face. The evaluation value shown is calculated. When a face is detected in one image, it is evaluated whether a face having a high correlation is detected continuously in time thereafter. As a result of these calculations and evaluations, a face detection result with reduced false detection can be obtained. As described above, after the image is read out from the image sensor 109, a face detection result is obtained after various processes are performed. Therefore, there is a considerable delay from the time when the image where the face is detected is captured. Although this delay time depends on the system specifications, it will be described below on the assumption that it takes 5 times (multiple times) of the V cycle and about 5V.

(Ii-1) Face priority AF mode 1
FIG. 8 is a flowchart showing an AF process procedure in the face priority AF mode 1. Note that the processing shown in this flowchart is repeatedly executed, for example, in a readout cycle (V cycle) of an image signal (input image) from the image sensor 109 for generating one field image.

  For example, when the face priority AF mode 1 is selected by user selection using the operation switch group 115, this process is started (step S401).

  In step S402, it is determined whether a face is detected from the read image. If no face is detected, the process proceeds to step S403, and the above-described normal contrast AF control is performed. On the other hand, when a face is detected, the process proceeds to step S406 to perform face frame contrast AF control. In the face frame contrast AF control performed in step S406, the AF evaluation value is calculated from the partial image signal of the area where the face is detected in the image signal read out from the image sensor 109, and the AF operation is performed to move to the vicinity of the face. It is control which performs focusing of.

  When AF processing is performed by face frame contrast AF control in step S406, the process returns to step S402 and the above-described processing is repeated.

  On the other hand, if a face is not detected and normal contrast AF control is performed in step S403, the process proceeds to step S404, and blur determination is performed using the obtained AF evaluation value. If it is determined that the blur is large (for example, if the AF evaluation value is equal to or less than a preset threshold value (level or less)), the process proceeds to step S405 to perform phase difference AF.

  As described above, in face priority AF mode 1, when a face is detected, AF processing is performed only by face frame contrast AF control without using phase difference AF. By controlling in this way, hunting can be reduced.

(Ii-1) Face priority AF mode 2
Next, the face priority AF mode 2 will be described with reference to the flowchart of FIG. Face priority AF mode 2 is a method that uses phase difference AF control even when a face is detected. Note that the processing shown in this flowchart is repeatedly executed, for example, in a readout cycle (V cycle) of an image signal (input image) from the image sensor 109 for generating one field image.

  First, the face frame, the angle of view of the camera, and the focus detection frame by the line sensor 131 will be described with reference to FIGS.

  In FIG. 10, a thick dotted line frame A is an angle of view of the camera, and B is a frame (a frame indicating a subject area) when a face is detected, and has various positions and sizes depending on the position of the subject and the orientation of the camera. Detected. A frame with a vertical line indicated by C corresponds to a phase difference detection frame (phase difference detection region) by the line sensor 131 with respect to the angle of view of the camera, and a pair of image signals obtained by subject light in this range is used. To detect the phase difference. As shown in FIG. 2, the phase difference detection frame changes in relative size with respect to the angle of view of the camera according to the zoom magnification. However, the amount of change of the frame according to the zoom magnification can be calculated simply. Can be sought.

  FIG. 11 shows the detection positions of four patterns of faces in the relationship between the angle of view A and the phase difference detection frame C of the camera shown in FIG. FIG. 11A shows a case where the face detection position is within the phase difference detection frame C of the line sensor 131. In such a state, phase difference AF using the line sensor 131 is performed to control the focus on the face. Is possible. In FIG. 11B, the face detection position is on the upper side of the phase difference detection frame C. In this case, in the phase difference AF, focus control is performed not on the face but on the body that is not shown and should be below the face. It is a state that can be considered. Therefore, even in such a positional relationship, it can be said that the face can be substantially focused using the phase difference AF control using the line sensor 131.

  However, even when the face detection position is above the phase difference detection frame C as shown in FIG. 11C, the possibility that the body is in the phase difference detection frame C is significantly reduced if the face size is small. become. Therefore, the phase difference obtained at this time cannot be relied on to use the phase difference AF for controlling the focus on the face. In the first embodiment, based on the fact that a person generally has about five heads and bodies, when the length of one side of the face detection frame B is L, the line sensor 131 starts from the lower end of the face detection frame B. When the length K to the lower end of the phase difference detection frame C is 4L or more (a predetermined multiple or more), the phase difference AF is not performed. On the other hand, in the state of FIG. 11D, since the face detection position is below the phase difference detection frame C, it is difficult to perform focus control by the phase difference AF.

  Next, the flow of processing in the face priority AF mode 2 will be described using the flowcharts of FIGS. 9A and 9B. Note that the processing shown in this flowchart is repeatedly executed, for example, in a readout cycle (V cycle) of an image signal (input image) from the image sensor 109 for generating one field image.

For example, when the face priority AF mode 2 is selected by user selection using the operation switch group 115, this process is started (step S501). In step S502, a pair of image signals output from the line sensor 131 for phase difference AF is acquired, and a phase difference L between the image signals is obtained. The time required to calculate the phase difference L varies depending on the brightness, and in order to synchronize with the period of the recorded image and face detection processing, the next step S503 waits for the timing of the V period. At the timing of the V cycle, the process proceeds to step S504, and the phase difference L obtained in step S502 is held. Here, in order to hold the value for a total of 6 cycles, that is, the latest 5V cycle related to face detection from the image signal and 1V cycle related to the accumulation of the image signal (that is, hold for 6V cycle). The data are sequentially stored in six memory spaces. That is, if the phase difference obtained at time T _n is L _n , the values of L _{n to} L _n−5 are held in the six memories, respectively. Although the calculation of the phase difference L is performed asynchronously with the V cycle, the phase difference L is held for 6 V in synchronization with the timing of the V cycle.

Then, it progresses to step S505 and it is judged whether the face was detected. When no face is detected, the process proceeds to step S506, and normal contrast AF control is performed. In the next step S507, the phase difference L _n−5 obtained in step S502 before the 5V period is read from the memory. In step S508, the difference between the in-focus position of the focus lens corresponding to the read phase difference L _n−5 and the current focus lens position controlled by contrast AF control is compared with a preset threshold th2. By doing so, the blur is determined. The level of the focus state of the focus lens 105 can be determined by comparison with the threshold th2. If the difference is within the threshold value th2, the process returns to step S502. If it is determined that there is a large blur (difference is greater than or equal to the threshold value th2) (that is, if the focus state is equal to or lower than a preset level), the process proceeds to step S509. Then, a focus position based on the latest phase difference L _n obtained in step S502, moves the focus lens to the determined focal position.

  On the other hand, if a face is detected in step S505, the process proceeds to step S510 in FIG. 9B. Here, a time difference T1 from the time when the previous face was detected to the time when the current face was detected is calculated. In step S511, if the time difference T1 is within 5V period, the process branches to step S515, and if it exceeds 5V period, the process branches to step S512. This is because if the face is detected within a predetermined time, the face can be detected stably and continuously, and the focus can be sufficiently tracked only by the face frame contrast AF control. (Step S515).

  On the other hand, the state that a face is detected at an interval exceeding a predetermined time can be considered when a face is detected for the first time after the camera is turned on or when a face is suddenly detected during shooting. For example, it is considered that there is a high possibility that the distance to the subject will change greatly, such as when a large change is made in the angle of view or when a person suddenly appears. Therefore, in such a case, the process proceeds to step S512, and it is determined whether or not the detected face position and size satisfy a predetermined selection condition at the angle of view of the camera. As described above with reference to FIG. 11, the face or the body of the subject becomes the phase difference detection frame of the line sensor 131 based on the relationship between the face detection position and the face size and the phase difference detection frame C of the line sensor 131. It is to determine whether it is included. When it is determined in step S512 that the predetermined selection condition is not satisfied, that is, the face and the body of the subject are outside the phase difference detection frame C of the line sensor 131 as shown in FIGS. In step S515, face frame contrast AF control is performed.

On the other hand, in step S512, it is determined that the predetermined selection condition is satisfied, that is, the face or the body of the subject is within the phase difference detection frame C of the line sensor 131 as shown in FIGS. If yes, the process proceeds to step S513. Then, the phase difference L _n−5 obtained in step S502 5 cycles before the time when the face is detected is read from the memory. In step S514, the focus position of the focus lens is obtained based on the read phase difference L _n−5 , and the focus lens 105 is moved to the obtained focus position. Thus, even when a face is detected, it is possible to focus more reliably and quickly using the phase difference AF.

  As described above, in the AF processing in the face priority mode 2, the phase difference is always obtained using the line sensor 131, and the obtained phase difference is held for the 5V period until the face detection result is obtained. Then, when the detected face position and size satisfy a preset condition, focus control is performed using the phase difference obtained 5 cycles before. As a result, phase difference AF can be performed while avoiding an inappropriate face AF operation even during face priority AF, and hunting can be reduced. Further, since the phase difference is not measured after the face detection result is known, but a value calculated in advance is used, it is possible to focus on the face quickly.

  As described above, according to the first embodiment, before the face detection result by the face detection processing circuit 111 is obtained, a restriction is imposed on performing the phase difference AF using the phase difference. , Hunting can be reduced. Further, at the same time when the face detection result by the face detection processing circuit is obtained, the phase difference AF can be performed immediately by using the phase difference acquired in advance, so that appropriate face priority AF can be executed quickly. As a result, the user's discomfort during face priority AF processing is reduced, and convenience is improved.

<Second Embodiment>
Next, a second embodiment of the present invention will be described.

  In the second embodiment, the AF operation of the camera in the still image shooting mode in the face priority AF process will be described. Since the configuration of the video camera and various AF operations are the same as those in the first embodiment, the description thereof will be omitted. Here, only the AF operation in the still image shooting mode will be described with reference to FIGS. I will explain.

  In the second embodiment, the phase difference AF control using the line sensor 131 shown in FIG. 13 is always performed at a preset cycle, but is performed asynchronously with a main face priority AF process described later.

  In FIG. 13, when processing is started in step S620, a phase difference is obtained from a pair of image signals obtained from the line sensor 131 in step S621, and the obtained phase difference is stored in a memory in step S622. For example, if the phase difference is acquired in a 1V cycle, 5 V cycles, that is, five phase differences are stored. If the phase difference is acquired in a 2V cycle, three phase differences are stored. The phase difference is saved. The time required to obtain this phase difference varies depending on the brightness of the subject and the system configuration.

  FIG. 12 is a flowchart showing face priority AF processing in the still image shooting mode. For example, when processing is started in step S601 due to selection of a still image shooting mode or the like, it is determined whether or not the shutter has been half-pressed in step S602. Until it is half-pressed, in step S603, the focus lens 105 is driven by obtaining the in-focus position based on the latest phase difference obtained in step S621 in FIG. In step S604, contrast AF control is performed.

  When the shutter is half-pressed in step S602 to instruct image recording preparation, the process proceeds to step S605 and the face detection process is started using the image signal from the image sensor 109 obtained at the next timing. . In the next step S606, contrast AF control is performed according to the procedure described in the first embodiment.

  When the shutter is fully pressed in step S607, the process proceeds to step S608, and photographing / recording is performed at the current focus lens position. After shooting, the process returns to step S602.

  On the other hand, if the shutter is not fully pressed, the process proceeds to step S610, and it is determined whether or not the result of face detection processing is output immediately after the shutter is half pressed. Here, as in the first embodiment described above, it is assumed that the face detection process takes a time corresponding to 5 V cycles. If no face detection result is output, the process returns to step S602. As described above, the focus lens 105 is not driven based on the phase difference and the AF operation is performed only by the contrast AF control until the face detection result is output after the preparation for photographing is instructed by half-pressing the shutter.

  If the face detection result is output (YES in step S610), the process proceeds to step S611 to determine whether a face has been detected. If a face is detected, the process proceeds to step S612, and it is determined whether the detected position and size of the face satisfy a predetermined selection condition at the angle of view of the camera. This determination is the same as the determination described with reference to FIG. 11 in step S512 of FIG. 9B in the first embodiment.

  If it is determined in step S612 that the predetermined selection condition is satisfied, the process proceeds to step S613. Then, the phase difference before the 5V period held in step S622 in FIG. 13 is read, and in the next step S616, the in-focus position of the focus lens 105 corresponding to the phase difference before the 5V period and the current focus lens position. The blur is determined from the difference. In this blur determination, for example, the obtained difference is compared with a preset threshold value, and if it is larger than the threshold value, it is determined that the blur is large. If it is determined that the blur is large, in step S617, the focus lens 105 is driven to the in-focus position corresponding to the read phase difference 5V before.

  On the other hand, other than the above, that is, when a face is not detected in step S611, and when the position and size of the face detected in step S612 do not satisfy a predetermined selection condition in the camera angle of view. The process proceeds to step S614. At this time, in step S614, the latest phase difference among the phase differences held by the processing of FIG. 13 is read out, and blur determination similar to step S616 is performed using the read out phase difference. If it is determined that the blur is large at this time, the focus lens 105 is driven to the in-focus position corresponding to the latest phase difference.

  If it is determined in step S615 or step S616 that the blur is small, the process returns to step S606, and the above-described operation is repeated while waiting for the shutter operation.

  As described above, according to the second embodiment of the present invention, at the time of still image shooting, the face detection result is awaited while performing AF operation only by contrast AF control with the shutter half-press as a trigger. Then, according to the face detection result, by appropriately determining which time point of the phase difference calculated and held in advance is used, the hunting operation or the face is out of focus, etc. The phenomenon can be suppressed.

  The first and second embodiments described above are merely examples, and in particular, the present invention can be implemented with parameters such as time setting such as a cycle being different depending on the system.

  Further, although face priority AF processing when a human face is detected has been described, the present invention is not limited to a human face. In other words, even if the detection target is replaced with various subjects that satisfy the preset detection conditions (for example, animals such as dogs and cats, specific characters, etc.) that can be detected when priority is given to focusing. It goes without saying that the invention can be implemented.

  Furthermore, although it demonstrated using the line sensor 131, the other method of detecting a focus by comparing two images can also be used instead.

It is a block diagram which shows schematic structure of the video camera in embodiment of this invention. It is a schematic diagram which shows the relationship between the angle of view of the camera in embodiment of this invention, and the light reception area | region of a line sensor. It is a figure which shows the principle of a phase difference AF system. It is a figure which shows the phase difference of the image signal by a phase difference AF system. It is a figure for demonstrating the principle of contrast AF system. It is a conceptual diagram which shows the division | segmentation of operation | movement with contrast AF and phase difference AF in embodiment of this invention. It is a flowchart which shows the AF process of the normal mode in the 1st Embodiment of this invention. It is a flowchart which shows the AF process of the face priority AF mode 1 in the 1st Embodiment of this invention. It is a flowchart which shows the AF process of the face priority AF mode 2 in the 1st Embodiment of this invention. It is a flowchart which shows the AF process of the face priority AF mode 2 in the 1st Embodiment of this invention. It is a figure which shows an example of an angle of view, the phase difference detection frame of a line sensor, and a face detection frame in the 1st Embodiment of this invention. It is a figure which shows the relationship between a view angle, the phase difference detection frame of a line sensor, and a face detection frame in the 1st Embodiment of this invention. It is a flowchart which shows the face priority AF process in the still image shooting mode in the 2nd Embodiment of this invention. It is a flowchart which shows the procedure of the phase difference in the 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Lens unit 101, 104 Fixed lens 102 Variable magnification lens 103 Aperture 105 Focus lens 106 Zoom motor 107 Focus motor 108 Position encoder 109 Image pick-up element 110 Main CPU
111 Face detection processing circuit 112 RAM
113 Flash memory 114 Monitor display 115 Operation switch group 116 Image recording medium 119 Imaging signal processing circuit 120 Zoom drive circuit 121 Focus drive circuit 131 Line sensor 130 Imaging lens

Claims (6)

Based on the contrast of the input image input from the image sensor, the first focus adjustment method for controlling the focus lens to drive in the direction of the in-focus position, and the position of the pair of images formed by the light from the subject A second focus adjustment method for controlling the focus lens to be driven to an in-focus position based on the phase difference, and a focus adjustment means for performing focus control selectively.
Determination means for determining a positional relationship between a subject detection position obtained from an input image input from the image sensor and a phase difference detection area which is the phase difference detection area;
The focus adjusting means determines that the subject detection position is above the phase difference detection area by the determination means, and the second adjustment is performed when the size of the subject in the input image is a predetermined value or more . When the focus lens is driven by a focus adjustment method, and the determination unit determines that the subject detection position is above the phase difference detection region, and the size of the subject in the input image is smaller than a predetermined value When the focus lens is driven by the first focus adjustment method and the determination unit determines that the subject detection position is below the phase difference detection region, the first focus adjustment method is used. A focus adjustment device for driving the focus lens. When the determination unit determines that the subject detection position is above the phase difference detection area and the size of the subject in the input image is equal to or greater than a predetermined value, the predetermined time is detected based on the time when the subject detection position is detected. a focusing position based on the detected phase difference to the previous period, if the amount of deviation between the current position of the focus lens Kere larger than the threshold value, the focus lens by the second focus adjustment method based on the phase difference The focus adjustment apparatus according to claim 1, wherein the focus adjustment apparatus is driven. When the determination unit determines that the subject detection position is below the phase difference detection region , or the determination unit determines that the subject detection position is above the phase difference detection region. Even if the size of the subject in the input image is smaller than a predetermined value , the focus position based on the latest phase difference detected by the second focus adjustment method and the current focus lens 3. The focus adjustment device according to claim 1, wherein if the amount of deviation from the position is larger than a threshold value, the focus lens is driven by the second focus adjustment method based on the latest phase difference. 4. . When a subject is not detected from the input image input from the image sensor and the focus state detected by the first focus adjustment method or the second focus adjustment method exceeds a preset level. driving the focus lens by said first focusing system, the focus state of claims 1 to 3, characterized in that to drive the focus lens by said in the following cases the level second focusing system The focus adjustment apparatus according to any one of the above. Focusing device according to any one of claims 1 to 4, characterized in that detects the face of a person as a subject from an input image input from the imaging element. Based on the contrast of the input image input from the image sensor, the first focus adjustment method for controlling the focus lens to drive in the direction of the in-focus position, and the position of the pair of images formed by the light from the subject A focus adjustment method for performing focus control selectively using a second focus adjustment method for controlling the focus lens to be driven to a focus position based on a phase difference, wherein a determination unit includes the imaging unit A determination step of determining a positional relationship between a subject detection position obtained from an input image input from an element and a phase difference detection area that is the phase difference detection area;
When it is determined in the determination step that the subject detection position is above the phase difference detection area and the size of the subject in the input image is greater than or equal to a predetermined value , the focus adjustment unit determines that the second focus When the focus lens is driven by an adjustment method, and it is determined in the determination step that the subject detection position is above the phase difference detection region, and the size of the subject in the input image is smaller than a predetermined value, When the focus lens is driven by the first focus adjustment method and it is determined in the determination step that the subject detection position is below the phase difference detection region, the first focus adjustment method And a driving process for driving the focus lens.

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