JP5159295B2 - Automatic focusing device and imaging device - Google Patents

Description

  The present invention relates to an automatic focus adjustment apparatus and an imaging apparatus that detect a high-frequency component in an image signal as a focus evaluation value and drive a focus lens based on the focus evaluation value to perform a focusing operation.

  In a digital camera using a CCD (Charge Coupled Device) as an image sensor, when a high brightness subject such as the sun or light is photographed, a band-like bright line is generated in the vertical direction of the photographing screen. This phenomenon is called “smear” and occurs when, for example, charges generated in a photoelectric conversion element in a portion with a large amount of incident light overflow to the transfer path when transferred and read.

  Also, in a digital camera using a CCD as an image sensor, a so-called contrast detection method that performs focus adjustment with a focus lens position at which a high frequency component (hereinafter referred to as a focus evaluation value) of a luminance signal of a subject image is maximized as a focus position Is often adopted.

  It is assumed that autofocus (AF) control using a contrast detection method is performed in a digital camera using a CCD as the image sensor. In this case, if smear occurs in the distance measurement area (AF area) where contrast detection is performed, the focus evaluation value becomes large due to the smear edge even at a focus lens position that is not in focus, resulting in erroneous distance measurement. was there.

To deal with this problem, for example, Patent Document 1 describes an automatic focus adjustment device configured to perform an AF operation (AF control) in an area without smear.
Japanese Patent No. 3563508

  However, in Patent Document 1, since the AF operation is performed based on the focus evaluation value of any region without smear, when smear occurs so as to overlap the desired subject, As a result, the focusing operation could not be performed.

(Object of invention)
An object of the present invention is to provide an automatic focus adjustment device and an imaging device capable of performing a focusing operation on a desired subject even when a smear occurs so as to overlap the desired subject. It is.

In order to achieve the above object, the present invention detects a high frequency component in an image signal captured by an image sensor as a focus evaluation value, and drives a focus lens based on the focus evaluation value to perform a focusing operation. Focusing means, distance measurement area setting means capable of setting a distance measurement area of an arbitrary size at an arbitrary position on the shooting screen, and smear detection means for detecting a smear occurrence area from the image signal An automatic focus adjustment device having face detection means for performing face detection using a captured image ,
The distance measurement area setting means is detected by the smear detection means at a face detection position detected by the face detection means when setting the distance measurement area based on a face detection result of the face detection means. The position and size of the ranging area and the number of the ranging areas are set while avoiding smear edges .

  According to the present invention, it is possible to provide an automatic focus adjustment device or an imaging device capable of performing a focusing operation on a desired subject even if smear occurs so as to overlap the desired subject. .

  The best mode for carrying out the present invention is as shown in the following examples.

  FIG. 1 is a block diagram illustrating a schematic configuration of a digital camera that is an imaging apparatus according to Embodiment 1 of the present invention.

  The digital camera according to the first embodiment includes an optical system 101 and a focus lens 102 as an imaging optical system. The light imaged by the imaging optical system is photoelectrically converted by the imaging device 103. Then, the signal digitized through the pre-processing circuit 104 including the CDS section and the nonlinear amplification section for removing output noise and the A / D converter 105 is stored in the memory 107 via the memory controller 106. In addition, the image processing unit 108 converts the image into an image and records it on the recording medium 109.

  Reference numeral 110 denotes an operation display unit that displays a shooting screen and a distance measurement area in addition to image display and camera state information display. Reference numeral 111 denotes a switch (hereinafter simply referred to as a switch SW1) for performing a shooting preparation operation. Reference numeral 112 denotes a photographing switch (hereinafter simply referred to as switch SW2) used when photographing after the operation of the switch SW1, and 120 denotes a main switch (hereinafter simply referred to as main SW) for turning on the system. . Shooting preparation operations such as AF are performed by operating the switch SW1, and shooting and image recording are performed by operating the switch SW2.

  The focus operation is controlled by the system control unit 113. First, the face detection circuit 115 detects the face position. A known method may be used for the face detection method. Here, it is assumed that the number of detected faces and the position and size information of each face are obtained. Next, a distance measurement area is set by the distance measurement area setting circuit 116, and the focus lens 102 is driven via the focus lens drive circuit 114. A focus evaluation value is calculated by a focus evaluation value calculation circuit 117 as will be described later using image signals taken at a plurality of focus lens positions. The focus position determination unit 118 determines the focus position of the focus lens 102 from the obtained focus evaluation value, drives the focus lens 102, and the focus detection area determination unit 119 determines the focus area (in focus range). The focus area is displayed on the operation display unit 110.

  The focus evaluation value is calculated by the focus evaluation value calculation circuit 117 as follows. A horizontal band pass filter is applied to each line of the image signal in the distance measurement area. Next, the line pass filter output signal having the largest absolute value is selected for each line. Integrate the selected signal vertically. With such a configuration, a signal having a large horizontal contrast is detected, and a signal with an improved signal-to-noise ratio is obtained by integrating in the vertical direction. This signal has the largest value in the focused state. When the defocus state is set, the signal becomes smaller. Therefore, an in-focus image can be obtained by detecting the position of the focus lens 102 where the signal has a maximum value and shooting at that position.

  A method for detecting and correcting the smear region will be briefly described with reference to FIGS. In FIG. 7A, reference numeral 701 denotes a smear area, and reference numeral 702 denotes a high luminance light source.

  The smear detection circuit 121 detects a smear generation region based on the luminance signal (see FIG. 7B) in the light-shielded optical black (OB) region. A region where the luminance signal is equal to or greater than a predetermined value is set as a smear region 701, and the luminance signal is detected as a differential signal (see FIG. 7C) by a band pass filter, and the position of the smear edge is detected. The smear correction circuit 122 corrects smear based on the smear detection information detected by the smear detection circuit 121. For the smear region 701, the smear is corrected by subtracting the luminance signal in the OB region from the luminance signal of the shooting screen.

  Hereinafter, the operation of the digital camera according to the first embodiment of the present invention will be described with reference to the flowchart of FIG.

  First, in step S201, the state of the main SW that powers on the system is detected. If it is ON, the process proceeds to step S202. In step S202, the remaining capacity of the recording medium 109 is checked. If the remaining capacity is 0, the process proceeds to step S203, and if not, the process proceeds to step S204. When the process proceeds to step S203, a warning is given that the remaining capacity of the recording medium 109 is 0, and the process returns to step S201. The warning may be displayed on the operation display unit 110, a warning sound may be emitted from a sound output unit (not shown), or both may be performed.

  If the remaining capacity of the recording medium 109 is not 0 in step S202 and the process proceeds to step S204, the smear detection circuit 121 performs smear detection, and the smear correction circuit 122 further performs smear correction. Here, the operation display unit 110 displays an image using the smear-corrected image signal. In the next step S205, face detection processing is executed by the face detection circuit 115 based on the image signal subjected to smear correction in step 204, and face detection information of the position and size of the face is acquired.

  In the next step S206, the state of the switch SW1 is checked. If it is ON, the process proceeds to step S208, and if not, the process proceeds to step S207. The function of the switch SW1 is to perform a shooting preparation operation such as AF (auto focus) or AE (auto exposure). If the switch SW1 is OFF and the process proceeds from step S206 to step S207, the state of the main SW is checked. If the switch SW1 is ON, the process returns to step S204. Otherwise, the process returns to step S201.

  If it is determined in step S206 that the switch SW1 is ON and the process proceeds to step S208, the system control unit 113 performs AE processing based on the image signal subjected to smear correction in step S204. In the next step S209, AF processing (details will be described later with reference to FIG. 3) is performed. Here, the AF processing is performed by the output signal of the image processing unit 108 that has not been subjected to smear correction. In the following step S210, the state of the switch SW2 is checked. If it is ON, the process proceeds to step S212. Otherwise, the process proceeds to step S211. The function of the switch SW2 is to start the photographing operation after the switch SW1 is operated.

  If the switch SW2 is OFF and the process proceeds to step S211, the state of the switch SW1 is checked here. If the switch SW1 is ON, the process returns to step S210. Otherwise, the process returns to step S204.

  If the switch SW2 is ON in step S210 and the process proceeds to step S212, a shooting operation (details will be described later with reference to FIG. 6) is performed. In the next step S213, the remaining capacity of the recording medium 109 is checked, and if the remaining capacity is 0, the process returns to step S203 for giving a warning. On the other hand, if the remaining capacity of the recording medium 109 is not 0, the process proceeds to step S214, and the state of the switch SW2 is checked.

  Next, the AF process executed in step S209 of FIG. 2 will be described using the flowchart of FIG. This control is performed by the system control unit 113.

  First, in step S301, the ranging area setting unit 116 performs ranging area setting reflecting the presence / absence of smear and the face detection result according to the flowchart of FIG. 4 described later. In the next step S302, the focus lens 102 is moved to the scan start position. In the first embodiment, the scan start position is set at one end of the set scan range. In subsequent step S303, the focus evaluation value of the distance measurement area set in step S301 and the position of the focus lens 102 are stored in a calculation memory (not shown) built in the system control unit 113.

  In the next step S304, it is checked whether or not the position of the focus lens 102 is at the scan end position. If it is the end position, the process proceeds to step S306. Otherwise, the process proceeds to step S305. The scan end position is set at the other end of the set scan range. If it is determined that the position of the focus lens 102 is not the scan end position and the process proceeds to step S305, the focus lens 102 is driven and moved in a predetermined direction by a predetermined amount. Then, the process returns to step S303.

  In step S304, assuming that the position of the focus lens 102 is the scan end position, the process proceeds to step S306. Then, it is checked whether the avoidance setting flag indicating that the distance measurement area has been set so as to avoid the position of the smear edge due to the occurrence of smear when the distance measurement area is set in step S301 is TRUE (true). If the result is TRUE, the process proceeds to step S307; otherwise, the process proceeds to step S308. If it is determined that the avoidance setting flag is TRUE and the process proceeds to step S307, correction calculation (addition) is performed for the focus evaluation value of the distance measurement area where avoidance is set. In the correction calculation, the focus evaluation values of the avoidance-set ranging areas obtained at the same focus lens position are added. Weighting addition may be performed on the basis of the area ratio or arrangement of distance measurement areas that are set to be avoided at the time of addition. Thereafter, the process proceeds to step S308.

  In the next step S308, based on the focus evaluation value stored in step S303 for each distance measurement area by the focus evaluation value calculation circuit 117 or the focus evaluation value calculated by correction in step S307, a peak value greater than or equal to a predetermined value is obtained. Focus determination is performed based on the presence or absence. In subsequent step S309, it is checked whether or not there is a focus detection area whose focus determination result in step S308 is in focus. If there is a focus detection area, the process proceeds to step S310. Otherwise, the process proceeds to step S311.

  If it is determined that there is a focused distance measurement area and the process proceeds to step S310, the position of the focus lens 102 when the focus position determination unit 118 indicates a peak value equal to or greater than the predetermined value for each focus distance measurement area, That is, the in-focus position is extracted. If there are a plurality of focus positions, the closest focus position is selected and the focus lens 102 is moved. Further, the focused area determination unit 119 displays the focused distance measurement area on the operation display unit 110.

  Further, if there is no in-focus range finding area, the process proceeds from step SS309 to step S311 because it is a case where a peak value equal to or greater than the predetermined value is not obtained, that is, because it is out of focus, it is called a fixed point beforehand. The focus lens 102 is moved to the set position.

  Next, distance measurement area setting will be described with reference to FIGS. 4 and 5. FIG. 4 is a flowchart showing the ranging area setting operation executed in step S301 of FIG. 3, and FIG. 5 is a diagram showing the ranging area setting that changes depending on the smear detection result and the face detection result. It is controlled by the ranging area setting unit 116.

  First, there are two basic ways of thinking in ranging area setting. First, when a face is detected, a ranging area is set at the face position, and when no face is detected, a plurality of ranging areas are set at the center of the shooting screen. Secondly, when the distance measurement area is set according to the first, if the smear edge is positioned within the distance measurement area to be set, the distance measurement area is set by avoiding the smear edge.

  Here, the ranging area setting that varies depending on the smear detection result and the face detection result shown in FIG. 5 will be described.

  First, as for the distance measurement area setting when a face is detected, as shown in FIG. 5A, a distance measurement area having the same size as that of the detected face is set at the detected face position. When a smear edge is detected at the face detection position, as shown in FIG. 5B, a distance measurement area is set avoiding the smear edge at the face detection position. As a specific setting method for avoiding the smear edge, there is a method of dividing and setting the distance measurement area inside and outside the smear area. If no smear edge is detected, one distance measurement area is set, and two or more distance measurement areas are set with the smear edge as a boundary.

  Next, as shown in FIG. 5C, the distance measurement area setting when neither smear nor face is detected is that the main subject is properly measured in many scenes and the background is in focus. The purpose is to prevent the omission phenomenon. Then, a plurality of distance measurement areas are set in a range of about 30% of the area ratio of the central portion of the photographing screen. Hereinafter, this is referred to as a smear / face detection area setting.

  In the distance measurement area setting shown in FIG. 5D, the face is not detected, and the smear / face undetected distance measurement area setting, that is, the smear edge is detected within the range of the distance measurement area setting in FIG. 5C. In this case, the distance measurement area is set in the same range while avoiding the smear edge.

  The ranging area setting shown in FIG. 5E is a ranging area setting when the detected smear area width is narrow. Here, as shown in FIG. 5B, when a distance measurement area is set inside the smear area, the distance measurement area corresponding to the smear area is shifted due to camera shake during distance measurement, and is affected by the smear edge. There is a risk of erroneous distance measurement due to the focus evaluation value. Therefore, in the distance measurement area setting shown in FIG. 5E, the distance measurement area is not set in the smear area and the distance measurement area is set on both outer sides of the smear area.

  Next, ranging area setting will be described with reference to the flowchart of FIG.

  First, in step S401, the smear detection circuit 121 checks whether there is a smear generation area. If there is a smear generation area, the process proceeds to step S404, and if not, the process proceeds to step S402. If it is determined that there is no smear generation area, the process proceeds to step S402. Here, the face detection circuit 115 checks whether a face is detected. If a face is detected, the process proceeds to step S412 described later. If no face is detected, the process proceeds to step S403, and a smear / face detection non-detection distance measurement area is set.

  When the process proceeds from step S401 to step S404 assuming that there is a smear generation region, the smear detection circuit 121 detects a smear edge position having a predetermined width and a luminance difference equal to or greater than a predetermined value. In step S405, it is checked whether the face is detected by the face detection circuit 115. If a face is detected, the process proceeds to step S410. Otherwise, the process proceeds to step S406.

  If it is determined that a face has not been detected and the process proceeds to step S406, it is checked whether a smear / edge position has been detected in the range of setting the ranging area when no smear / face is detected. If the smear edge position is detected in the next step S407, the process proceeds to step S408, and if not, the process proceeds to step S403. Proceeding to step S408, in the smear / face non-detection range-finding area setting range, as shown in FIG. 5D, a range-finding area is set avoiding the smear edge position, and in step S409, avoidance is performed. Set the setting flag to TRUE.

  On the other hand, if it is determined that a face has been detected and the process proceeds from step S405 to step S410, it is checked whether a smear edge position is detected at the face position detected by the face detection circuit 115. If the smear edge position is detected in the next step S411, the process proceeds to step S413. Otherwise, the process proceeds to step S412 to set a distance measurement area at the face position detected by the face detection circuit 115. If the smear edge position is detected and the process proceeds to step S413, the measurement is performed while avoiding the smear edge position at the face position detected by the face detection circuit 115 as shown in FIG. 5B or 5E. Set the distance area. In step S414, the avoidance setting flag is set to TRUE.

  Next, the photographing operation executed in step S212 in FIG. 2 will be described using the flowchart in FIG.

  First, in step S601, the subject brightness is measured. In the next step S602, the image sensor 103 is exposed according to the subject brightness measured in step S601. The image formed on the surface of the image sensor 103 is photoelectrically converted into an analog signal, which is sent to the A / D converter 105 in the next step S603, before output noise removal or nonlinear processing of the image sensor 103 is performed. After processing, it is converted into a digital signal.

  In the next step S604, the output signal from the A / D converter 105 is subjected to image processing such as smear correction and white balance adjustment by the image processing unit 108 to obtain an appropriate output image signal. In step S605, the output image signal is converted into an image format such as a JPEG format. In subsequent step S606, the output image signal is transferred to the recording medium 109 and stored therein.

  The automatic focus adjustment apparatus according to the present embodiment includes an image sensor 103 that captures a subject image formed by an imaging optical system. Further, a high frequency component in the captured image signal is detected as a focus evaluation value. Then, focusing means (system control unit 113, focus lens drive circuit 114, focus evaluation value calculation circuit 117, focus position determination unit 118, and the like, which drives the focus lens 102 based on the focus evaluation value and performs a focusing operation) A focusing area determination unit 119). Further, a distance measurement area setting means (a distance measurement area setting unit 116) capable of setting a distance measurement area of an arbitrary size at an arbitrary position on the shooting screen, and a smear generation area from the captured image signal. Smear detection means (smear detection circuit 121) for detection. The distance measurement area setting means sets the position and size of the distance measurement area and the number of distance measurement areas while avoiding the smear edge detected by the smear detection means.

  In addition, face detection means (face detection circuit 115) that performs face detection using the captured image is provided. The distance measurement area setting means avoids the smear edge detected by the smear detection means when setting the distance measurement area based on the face detection result of the face detection means, and the distance measurement area position and size, and The number of distance measuring areas is set.

  Further, a digital camera which is an image pickup apparatus including the automatic focus adjustment device has smear correction means (smear correction circuit 122) for correcting smear, and also has an electronic viewfinder function (EVF function) for displaying a subject image. . The smear correction means performs smear correction during the automatic exposure operation or EVF display operation, but does not perform smear correction during the focusing operation.

  As is apparent from the above, since the desired subject can be measured without being affected by smear, smear correction during the AF operation is not necessarily required. For this reason, since it is possible to skip the OB area necessary for smear correction, if the smear area detection information immediately before the start of the AF operation is stored, the AF operation can be speeded up by high-speed reading of the image sensor 103. Is possible.

  That is, it is possible to provide an automatic focus adjustment device that can perform AF control on a desired subject even if smear occurs so as to overlap the desired subject.

  Note that when displaying the subject on the operation display unit 110 even during the AF operation, smear correction may be performed in consideration of the appearance. In addition, although the focus evaluation value correction calculation is performed in step S307 in FIG. 3, for example, the distance measurement areas that are set to be avoided may be treated as independent distance measurement areas. Further, a method of obtaining the average focus position from the focus position of each distance measurement area is also conceivable, and the present invention is not limited to correction calculation.

  Further, in the case where the smear area width in FIG. 5E described above is narrow, no distance measurement area is set in the smear area. However, the focus evaluation value of the focus evaluation value is set by setting the distance measurement area in the smear area. It is also possible to perform acquisition and not use the distance measurement result of the distance measurement area according to the result. The distance between the smear edge position and the distance measurement area when setting the distance measurement area while avoiding the smear edge is the same as when the smear area is narrow, but the smear edge becomes a distance measurement area due to the effects of camera shake during distance measurement. There is a possibility of going in and out. For this reason, the interval setting may be changed according to the focal length or the like.

It is a block diagram which shows schematic structure of the digital camera which concerns on one Example of this invention. It is a flowchart which shows a series of operation | movement of the digital camera which concerns on one Example of this invention. It is a flowchart which shows AF operation performed in step S209 of FIG. It is a flowchart which shows the operation | movement of the ranging area setting performed in step S301 of FIG. It is a figure which shows the ranging area setting which changes with the smear detection result and face detection result which concern on one Example of this invention. It is a flowchart which shows the imaging | photography operation | movement performed in step S212 of FIG. It is explanatory drawing about general smear area | region detection.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Optical system 102 Focus lens 103 Image pick-up element 108 Image processing part 109 Recording medium 110 Operation display part 113 System control part 114 Focus lens drive circuit 115 Face detection circuit 116 Distance measurement area setting part 117 Focus evaluation value calculation part 118 Focus position determination 119 Focusing area determination unit 121 Smear detection circuit 122 Smear correction circuit

Claims (3)

A focus focusing unit that detects a high-frequency component in an image signal captured by an image sensor as a focus evaluation value, drives a focus lens based on the focus evaluation value, and performs a focusing operation; and an arbitrary position on a shooting screen A range-finding area setting unit capable of setting a range-finding area of any size, a smear detection unit for detecting a smear generation area from the image signal, and performing face detection using the captured image An automatic focus adjustment device having face detection means,
The distance measurement area setting means is detected by the smear detection means at a face detection position detected by the face detection means when setting the distance measurement area based on a face detection result of the face detection means. An automatic focusing apparatus, wherein a position and size of the distance measurement area and the number of distance measurement areas are set while avoiding smear edges. The automatic focus adjustment apparatus according to claim 1, further comprising smear correction means that corrects smear based on smear detection information detected by the smear detection means.   An imaging apparatus comprising the automatic focus adjustment apparatus according to claim 1.

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