JP5541671B2 - Imaging apparatus and focus control method - Google Patents

Description

  The present invention relates to an imaging apparatus and a focus control method.

  Patent Documents 1 and 2 have a phase difference detection type focus detection (hereinafter simply referred to as “phase difference AF”) means and a contrast detection type focus detection (hereinafter simply referred to as “TVAF”) means. Hybrid focus detection means (hereinafter simply referred to as “HBAF”) is disclosed. Patent Document 3 discloses an imaging apparatus in which an imaging pixel, a focus detection pixel, and a pupil dividing unit are provided in an imaging element to provide a phase difference AF (hereinafter simply referred to as “SAF”) function. Yes.

JP 2002-258147 A JP 2006-003428 A JP 2009-003122 A

  When HBAF is performed on a moving subject, a subject having a speed that can be followed by wobbling can be followed by TVAF, and a subject that changes rapidly like panning can be followed by phase difference AF. it can. However, in HBAF, TVAF cannot follow, but there is a problem that a moving object whose subject does not change as much as panning does not shift to phase difference AF unless it is once blurred.

  It is an exemplary object of the present invention to provide an imaging apparatus and a focus control method that can improve followability to a moving subject.

An imaging apparatus according to the present invention is an imaging apparatus capable of shooting a moving image, and performs focus detection by detecting a peak position of a contrast of an imaging signal obtained by photoelectric conversion of an optical image formed by a shooting lens. A first focus detection unit, a second focus detection unit that performs focus detection by acquiring information corresponding to a distance to a subject obtained from a phase difference between image signals of a pair of subject images, and the first focus A control unit capable of setting a first mode for adjusting the focus to the in-focus position detected by the detecting means or a second mode for adjusting the focus to the in-focus position detected by the second focus detecting means; The control unit determines whether the moving speed of the subject calculated based on the information corresponding to the distance is within a setting range, and the control unit sets the moving speed in the first mode. And it sets the second mode when in the circumference, when the second case the moving velocity is generated based on the imaging signal even if it set range in the mode degree is not in the target range The focus adjustment is performed in the second mode.

  ADVANTAGE OF THE INVENTION According to this invention, the imaging device and focus control method which can improve the followable | trackability to the to-be-photographed object can be provided.

It is a block diagram of the imaging device of a present Example. It is a block diagram of the AF signal processing circuit shown in FIG. 3 is a flowchart for explaining the operation of a CPU shown in FIG. 1. It is a flowchart of the phase difference detection process of S210 shown in FIG. It is a flowchart for demonstrating the detail of S230 shown in FIG.

  FIG. 1 is a block diagram of an imaging apparatus (digital camera, digital video camera) capable of moving image shooting according to this embodiment. The imaging apparatus includes a photographing lens, a phase difference AF unit, a TVAF unit, a face detection unit 115, and other components.

  The photographing lens includes a focus lens 105 that forms a subject image and is driven during automatic focus adjustment (AF) and a zoom lens (not shown) that moves in the optical axis direction to change the focal length of the photographing optical system.

  The phase difference AF means includes a distance information acquisition unit 101 that acquires information corresponding to the distance to the subject, a focus lens 105, a focus motor 106, a focus control circuit 110, and a CPU (control unit) 111.

  Note that it is possible to determine whether the subject is a moving object from the information on the change in distance to the subject obtained from the distance information acquisition unit 101, and it is possible to detect the moving speed of the subject when it is a moving object. .

  The distance information acquisition unit 101 includes a pupil dividing unit that guides a light beam that has passed through different pupil regions of the photographing lens, detects a shift amount (phase difference) between image signals of a pair of subject images formed by the light beam, and A distance signal D is generated by acquiring distance information from the phase difference. The distance information acquisition unit 101 is connected to the focus control circuit 110 and outputs a distance signal D representing information on the distance to the subject to the focus control circuit 110.

  The distance information acquisition unit 101 uses an external measurement system that performs measurement using light separate from the light from the photographing lens, and performs measurement using light through the photographing lens (that is, by the TTL method). Either measurement system may be used. The configuration of the external measurement system and the internal measurement system is not particularly limited.

  The external measurement system includes, for example, a pupil division optical system and a phase difference detection sensor. The pupil division optical system forms two subject images on the phase difference detection sensor. The phase difference detection sensor is composed of, for example, a line sensor, detects a phase difference between a pair of subject images, calculates a distance to the subject by a known triangulation method, and generates and outputs a distance signal D.

  The internal measurement system includes, for example, an imaging element 107 and an imaging signal processing circuit 108, and a pair of subjects formed on focus detection pixels embedded in the imaging element 107 by a light beam passing through a pair of pupil regions of the photographing lens. An image shift amount (phase difference) is detected (SAF method). SAF is known in Patent Document 3.

  The focus control circuit 110 moves the focus lens 105 in the direction of the optical axis via the focus motor 106 based on the distance signal D to focus. For this reason, the focus control circuit 110 functions as a focus detection unit (second focus detection unit) that performs focus detection by acquiring information on the distance to the subject obtained from the phase difference between the image signals of the pair of subject images. To do.

  The CPU 111 is composed of a processor, and controls the operation of each part of the phase difference AF means. The focus control circuit 110 and the CPU 111 are connected via a bus 117.

  The TVAF means includes a focus lens 105, a focus motor 106, an image sensor 107, an image signal processing circuit 108, an AF signal processing circuit 109, a focus control circuit 110, and a CPU 111.

  In TVAF, by detecting the peak position of the contrast value of an image signal (image signal) obtained from the output of the image sensor 107 while performing a scan that changes the relative position of the image sensor 107 and the focal position formed by the photographic lens. Focus detection. The TVAF of this embodiment detects a peak position (in-focus position) where the contrast value is maximized by reciprocating (wobbing) the focus lens 105 in the optical axis direction, and moves the focus lens 105 to that position. To focus on.

  The image pickup element 107 includes shooting pixels that photoelectrically convert a subject image (optical image) formed by the shooting lens to generate an image pickup signal (image signal), and includes a CCD or a CMOS sensor. The imaging element 107 is connected to the imaging signal processing circuit 108 and outputs an imaging signal to the imaging signal processing circuit 108.

  The image signal processing circuit 108 performs A / D conversion and other processes on the image signal from the image sensor 107. The imaging signal processing circuit 108 is connected to the AF signal processing circuit 109 and outputs an imaging signal to the AF signal processing circuit 109.

  Based on the image signal from the image signal processing circuit 108, an AF evaluation value (FV signal) corresponding to a contrast value and an IFA signal representing the degree of focus are generated for use in TVAF. The AF signal processing circuit 109 is connected to the focus control circuit 110 and outputs an FV signal and an IFA signal to the focus control circuit 110.

  FIG. 2 is a block diagram of the AF signal processing circuit 109. As shown in the figure, the AF signal processing circuit 109 includes one or a plurality of gates 109a, band pass filters (BPF) 109b, 109d, 109g, detectors (DET) 109c, 109e, 109h, and dividers (A / B). ) 109f.

  The gate 109a extracts a part of the screen of the image signal from the image signal processing circuit 108, and the BPF 109b extracts the high frequency component. The DET 109 c performs processing such as peak hold and integration on the high frequency component and outputs an FV signal to the focus control circuit 110.

  The BPFs 109d and 109g extract the high-frequency component of the imaging signal that has passed through the gate 401, and the DETs 109e and 109h perform processing such as peak hold and integration on the high-frequency component. The filter characteristic is set so that the frequency of the BPF 109d is higher than the frequency of the BPF 109g.

  The A / B 109f obtains (output of DET 109e) / (output of DET 109h), that is, the ratio of frequency components of the imaging signal, and generates an IFA signal for each focus detection frame. The focus detection frame is an area including a main subject for focus detection, and is set by a setting unit (not shown) or the face detection unit 115.

  When there are a plurality of gates 109a, the subsequent circuits are also a plurality, and the FV signal and the IFA signal are also a plurality of signals.

  The focus control circuit 110 moves the focus lens 105 in the direction of the optical axis via the focus motor 106 based on the FV signal and the IFA signal to focus. Therefore, the focus control circuit 110 detects the focus by detecting the peak position of the contrast of the imaging signal obtained by photoelectrically converting the optical image formed by the photographing lens (first focus detection means). ). The focus control circuit 110 selects from a plurality of signals according to conditions, and performs a focus operation based on the plurality of signals.

  The CPU 111 controls the operation of each part of the TVAF means.

  The CPU 111 performs hybrid AF (HBAF) having functions of automatic focus adjustment (phase difference AF) using a phase difference detection method and automatic focus adjustment (TVAF) using a contrast detection method.

  Further, the CPU 111 can set the first AF mode for automatically adjusting the focus position detected by the TVAF or the second AF mode for automatically adjusting the focus position detected by the phase difference AF.

  When the information corresponding to the distance to the subject does not change (when the subject is not a moving object), the CPU 111 moves the focus lens 105 to the vicinity of the focus position by phase difference AF, and from there, the focus lens is moved to the focus position by TVAF. Move to. More specifically, the CPU 111 performs AF control shown in FIG.

  The face detection unit 115 is an example of a subject detection unit that detects a subject having a specific shape. The face detection unit 115 compares the image with a database image stored in advance by template matching or the like. The face detection unit 115 is connected to the CPU 111 via the bus 117, and outputs to the CPU 111 the face position and size (face detection size), the number of faces, the reliability of the face (probability), and the like of a plurality of subjects.

  In addition, the imaging signal output from the imaging signal processing circuit 108 is temporarily stored in the memory 113, and then compressed by the codec 114 and recorded on the recording medium 112. The CPU 111 controls the operation of each part of the imaging system. In parallel with the compression and recording processing, the image signal stored in the memory 113 is subjected to image signal processing such as gamma correction and color gain correction in the image processing circuit 116, and is resized to an optimal size, such as a face frame. Are displayed in real time on a display unit (not shown). These components are connected to the CPU 111 via the bus 117.

  FIG. 3 is a flowchart for explaining the HBAF control operation (focus control method) during moving image shooting by the CPU 111, and “S” is an abbreviation of step. Note that the focus control circuit 110 may execute the operation shown in FIG. 3 instead of the CPU 111. Here, a case where the distance information acquisition unit 101 uses the above-described external measurement system is taken as an example. In the case of a lens unit that is detachably mounted on the camera body, the lens unit may be provided with a control unit that performs the control shown in FIG.

  First, the CPU 111 sets the first AF mode as the AF mode (S201). Next, the CPU 111 controls the imaging signal processing by the imaging signal processing circuit 108, the contrast signal processing by the AF signal processing circuit 109, and the phase difference detection processing by the phase difference detection sensor (S210).

  FIG. 4 is a flowchart of the phase difference detection process in S210.

  First, the CPU 111 performs A / D conversion on the value of the phase difference detection sensor (S211), and determines whether the A / D conversion has been performed a predetermined number of times (S212). When the CPU 111 determines that the A / D conversion has not been performed a predetermined number of times (N in S212), the flow returns to S211. When determining that the A / D conversion has been performed a predetermined number of times (Y in S212), the CPU 111 detects the phase difference between the pair of subject images (A image and B image) (S213), and calculates the distance from the phase difference ( S214), the moving speed of the subject is calculated from the distance change rate (S215).

  Next, the CPU 111 determines whether or not the subject has a speed within the set range from the detection result by the phase difference detection sensor (S220). The lower limit of the “setting range speed” is the maximum speed (the maximum speed of the scanning speed) that can be followed by TVAF wobbling, and is the maximum speed at which the subject image plane does not go out of the depth of focus due to the current focal length. The upper limit of the “setting range speed” is the minimum panning speed. The upper and lower limits of the setting range are stored in the memory 113 in advance.

  If the CPU 111 determines that the subject does not have the speed within the set range (N in S220), the in-focus position calculated from the result of the first AF mode (TVAF) and the in-focus position detected by the phase difference detection sensor It is determined whether or not the distance is greater than or equal to the threshold (S221).

  If the CPU 111 determines that the distance between the two in-focus positions is greater than or equal to the threshold (Y in S221), the CPU 111 sets the second AF mode as the AF mode (S222). If the CPU 111 determines that the distance between the two in-focus positions is less than the threshold (N in S221), the CPU 111 maintains the first AF mode (S223). Next, the CPU 111 moves the focus lens 105 according to the set AF mode (S224), and the flow returns to S201.

  As described above, in this embodiment, when the subject does not have the speed within the set range, AF is performed by TVAF unless the result of phase difference AF and the result of TVAF differ greatly. This can be done by TVAF when the subject is stationary or when the moving speed of the moving subject is less than the speed that can be followed by wobbling in the first mode, and the moving speed of the subject is higher than the panning speed. This is because the phase difference AF can be followed.

  On the other hand, if the CPU 111 determines that the subject has a speed within the set range (Y in S220), the CPU 111 determines whether there is a speed detection error (S230).

  FIG. 5 is a flowchart for explaining details of S230. First, the CPU 111 determines whether or not the variation amount of the AF evaluation value (FV signal) is equal to or greater than the threshold (S231). If the CPU 111 determines that the variation has occurred (Y in S231), the face detection size detected by the face detection unit 115 is detected. It is determined whether or not the fluctuation amount is greater than or equal to a threshold value (S232). If the CPU 111 determines that the variation amount of the face detection size is equal to or greater than the threshold (Y in S232), the CPU 111 determines that there is no speed detection error (S233). On the other hand, if the CPU 111 determines that the variation amount of the AF evaluation value is less than the threshold (N in S231) or the variation amount of the face detection size is less than the threshold (N in S232), the CPU 111 determines that there is a speed detection error. (S234).

  As described above, when the CPU 111 determines that the variation in the AF evaluation value is less than the threshold value (S231), the second AF mode is not set as the misfocus detection (Y in S230), so that the parallax of the phase difference AF sensor is set. Malfunction due to is unlikely to occur. If the CPU 111 determines that the variation in the face detection size detected by the face detection unit 115 is less than the threshold value (S232), the CPU 111 does not set the second AF mode for misfocus detection. Malfunction due to Lux is unlikely to occur.

  If the CPU 111 determines that there is a speed detection error (Y in S230), the flow proceeds to S221. On the other hand, when determining that there is no speed detection error (N in S230), the CPU 111 sets the AF mode to the second AF mode in which the result of the phase difference AF is prioritized (S240), and the result obtained by the phase difference AF is set. The focus lens 105 is moved to the focal position (S241).

  As described above, in this embodiment, in addition to the transition to the second mode (S222), the second mode is set when the information corresponding to the distance changes so that the subject has the speed within the setting range. (S240). The CPU 111 is faster than the speed at which focusing can be performed by TVAF, but for a moving object whose subject does not change as much as panning, the CPU 111 shifts to driving the focus lens 105 by phase difference AF without waiting for it to be blurred. effective.

  Next, the CPU 111 maintains the second AF mode (S242), controls to perform the same processing as S210 (S243), and then performs the same processing as S220 (S244).

  If the CPU 111 determines that the subject has a speed within the set range (Y in S244), the CPU 111 moves the lens to the in-focus position obtained by the phase difference AF (S245). Thereafter, the flow returns to S242.

On the other hand, when the CPU 111 determines that the subject does not have the speed within the set range (N in S244), the CPU 111 acquires an IFA signal (S246). Next, the CPU 111 determines whether or not the degree of focus acquired from the AF signal processing circuit 109 via the focus control circuit 110 is within the target range (S247). When CPU111 determines that the degree of focus is in the target range (N in S247), the flow returns to S201. On the other hand, if the CPU 111 determines that the focus level is not within the target range (Y in S247), the flow proceeds to S222.

  In the case of an imaging apparatus that uses SAF as the phase difference AF means, the distance focus detection by the image sensor 107 is TTL, so that no misfocus detection by parallax occurs. For this reason, S230 shown in FIG. 3 becomes unnecessary, and Y of S220 is directly connected to S240.

  In S220 of FIG. 3, the CPU 111 determines whether or not the moving object has a speed within the set range. However, the CPU 111 determines that the information corresponding to the distance to the subject has changed (that is, whether the moving object is a moving object). For example, you may move to S230 or S240 immediately. As a result, it is possible to improve followability to a moving subject.

  The flow shown in FIG. 3 can be stored in the memory 113 as a program as a focus control method to be executed by a processor mounted on the imaging apparatus.

  The imaging device can be applied to imaging a subject.

101 Distance information acquisition unit 105 Focus lens 107 Image sensor 109 AF signal processing circuit 111 CPU
115 Face detection unit

Claims (5)

An imaging device capable of video recording,
First focus detection means for performing focus detection by detecting a peak position of contrast of an imaging signal obtained by photoelectrically converting an optical image formed by the photographing lens;
Second focus detection means for performing focus detection by acquiring information corresponding to the distance to the subject obtained from the phase difference between the image signals of the pair of subject images;
A control unit capable of setting a first mode for adjusting the focus to the in-focus position detected by the first focus detection unit or a second mode for adjusting the focus to the in-focus position detected by the second focus detection unit; ,
Have
The controller determines whether or not the moving speed of the subject calculated based on the information corresponding to the distance is within a setting range;
The control unit sets the second mode when the moving speed is within a setting range in the first mode, and the imaging signal even when the moving speed is not within the setting range in the second mode. The focus adjustment is performed in the second mode when the degree of focus generated based on is not within the target range .   The control unit sets the second mode when the moving speed of the subject is higher than the speed that can be followed in the first mode, and the moving speed of the subject can follow in the first mode. The imaging apparatus according to claim 1, wherein the first mode is maintained when the speed is equal to or lower than the speed. In the first mode, when the moving speed is in a set range, the control unit is configured to change the amount of contrast representing the contrast value obtained from the first focus detection unit to be equal to or greater than a first threshold. When the second mode is set and the fluctuation amount is less than the first threshold, the in- focus position detected by the first focus detection unit and the second focus detection unit detect The imaging apparatus according to claim 1, wherein the first mode is maintained when a distance to the in-focus position is less than a second threshold value . It further has subject detection means for detecting a subject having a specific shape,
In the first mode, the control unit is configured such that the moving speed is within a set range, and the variation amount of the size of the specific shape of the subject detected by the subject detection unit is greater than or equal to a third threshold value. Is set to the second mode, and the variation amount is less than the third threshold value, and the in-focus position detected by the first focus detection means and the second focus detection means detect The imaging apparatus according to claim 1, wherein the first mode is maintained when a distance from the focused position is less than a second threshold . From the first focus detection means for detecting the focus by detecting the peak position of the contrast of the imaging signal obtained by photoelectrically converting the optical image formed by the taking lens, and the phase difference between the image signals of the pair of subject images A focus control method performed by a processor mounted on an imaging apparatus having a second focus detection unit that performs focus detection by acquiring information corresponding to the distance to the subject obtained. There,
Setting a first mode for adjusting the focus to the in-focus position detected by the first focus detection means;
Determining whether the moving speed of the subject calculated based on the information corresponding to the distance is within a set range;
Together with the said and the moving speed is determined to be in the set range second focus detection unit sets a second mode in which the focusing on the focus position detection while setting the first mode, the a step if focus level generated based on the image signal even when the moving speed in the second mode is determined not to set range is not in the target range for performing focus adjustment in the second mode ,
A focus control method characterized by comprising: