JP2008139683A - Imaging apparatus and autofocus control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To attain stable autofocus control by computing a greater focus evaluation value for photographic images that contain a facial region. <P>SOLUTION: The photographic image is divided to a plurality of divided regions and for each divided region, horizontal and vertical contrast components (C<SB>H</SB>[i, j]) and C<SB>V</SB>[i, j] are computed so as to compute a region evaluation value (α[i, j]) by weighting and adding them. When the face region is extracted from the photographic image and the region evaluation value of the divided region, corresponding to the face region is computed, weighting coefficient for the vertical contrast component is set higher. A focus evaluation value (AF evaluation value) is obtained, by integrating the region evaluation value of each divided region included in the focus-evaluation value region (AF evaluation region) and climbing control is performed so that the focus-evaluation value takes a maximum value. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an imaging apparatus and an autofocus control method used therefor.

  In an imaging apparatus such as a digital still camera or a digital video camera, autofocus control (hereinafter referred to as AF control) using a TTL (Through The Lends) type contrast detection method is generally used.

  In this AF control, an AF evaluation area (focus evaluation area) is set in a frame image (captured image), a high frequency component of a video signal in the AF evaluation area is extracted, and the extracted high frequency components are integrated. The value is calculated as an AF evaluation value (focus evaluation value). If the contrast amount in the AF evaluation area increases, the high frequency component of the video signal also increases. Therefore, this AF evaluation value is approximately proportional to the contrast amount in the AF evaluation area. Then, so-called hill-climbing control is used to drive and control the focus lens so that the AF evaluation value is maintained near the maximum value.

JP 2003-75713 A JP 2004-151608 A

  In general, when transmitting a video signal of each pixel forming a captured image, scanning is sequentially performed in the horizontal direction from the upper end to the lower end of the captured image, and the video signal of each pixel is transmitted in this scanning order. For this reason, normally, extraction of the high frequency component of the video signal is performed along the horizontal direction, and as a result, the AF evaluation value is a value representing the horizontal contrast of the image in the AF evaluation area. Therefore, when the contrast of the subject is high in the vertical direction but low in the horizontal direction (for example, a horizontal stripe pattern), there is a problem that the obtained AF evaluation value becomes small and focusing cannot be performed normally. It was.

  In order to solve this problem, AF control using vertical contrast detection has also been proposed. However, since the horizontal and vertical contrast components are usually mixed in the image, only the vertical contrast is considered. However, AF control is not stable.

  In various compositions, a person (especially a person's face) is often included in the subject. Therefore, it is important to perform AF control in consideration of this situation.

  SUMMARY An advantage of some aspects of the invention is that it provides an imaging apparatus and an autofocus control method that realize stable autofocus control. In particular, an object of the present invention is to provide an imaging apparatus and an autofocus control method that realize stable autofocus control when a human face is included in a subject.

  In order to achieve the above object, a first image pickup apparatus according to the present invention has an image pickup device and an optical system for forming an optical image corresponding to a subject on the image pickup device, and obtains a shot image by shooting. Imaging means, and focus evaluation value calculation means for calculating a focus evaluation value based on a video signal of a focus evaluation area provided in the captured image, and the optical so that the focus evaluation value takes an extreme value In an imaging apparatus that performs autofocus control by driving and controlling the system, the focus evaluation value calculation unit detects a horizontal contrast component and a vertical contrast component of an image in the focus evaluation region, and performs weighted addition of the detected components. The focus evaluation value is calculated by the following.

  Usually, since the contrast components in the horizontal and vertical directions are mixed in the image, it is possible to realize stable autofocus control for various subjects by configuring as described above. In addition, since a human face includes a relatively large amount of vertical contrast components, particularly stable autofocus control can be realized when the human face is included in the subject.

  For example, the first imaging apparatus further includes a face area extraction unit that extracts a face area from the captured image, and the focus evaluation value calculation unit determines whether the face evaluation area includes the face area. Accordingly, the degree of contribution of the vertical contrast component to the focus evaluation value is changed.

  Accordingly, when a human face is included in the subject, a relatively large focus evaluation value can be obtained, and stable autofocus control can be realized.

  Specifically, for example, the focus evaluation value calculating unit increases the contribution of the vertical contrast component to the focus evaluation value when the focus evaluation area includes the face area compared to when the face area is not included. .

  In addition, for example, the first imaging device further includes a face area extracting unit that extracts a face area from the captured image, and when the focus evaluation area includes the face area, the focus evaluation area is the face area. Is divided into a first region corresponding to a partial region inside or the entire region of the face region, and a second region obtained by removing the first region from the focus evaluation region, and the focus evaluation value calculating means includes: The first evaluation value corresponding to the weighted addition value of the horizontal contrast component and the vertical contrast component of the image in the first region, and the weighted addition value of the horizontal contrast component and the vertical contrast component of the image in the second region. The focus evaluation value is calculated from the sum of the second evaluation value and the contribution of the vertical contrast component of the image in the first area to the first evaluation value is within the second area with respect to the second evaluation value. Of images Greater than the contribution of the direct contrast component.

  Accordingly, when a human face is included in the subject, a relatively large focus evaluation value can be obtained, and stable autofocus control can be realized.

  In order to achieve the above object, a second image pickup apparatus according to the present invention has an image pickup device and an optical system for forming an optical image corresponding to a subject on the image pickup device. And a focus evaluation value calculating means for calculating a focus evaluation value based on a video signal of a focus evaluation area composed of a plurality of element areas provided in the captured image, and the focus evaluation value In the imaging apparatus that performs autofocus control by driving and controlling the optical system so as to take an extreme value, the focus evaluation value calculating unit detects a horizontal contrast component and a vertical contrast component of an image in each element region, For each element region, the horizontal contrast component and the vertical contrast component are compared to calculate an element region evaluation value from the larger contrast component, and each element region evaluation value is integrated or And calculates the focus evaluation value by disproportionation.

  Thereby, the obtained focus evaluation value is increased, and stable autofocus control can be realized. In addition, since a human face includes a relatively large amount of vertical contrast components, when a human face is included in a subject, an element area evaluation value for an element area corresponding to the face is calculated from the vertical contrast component. It becomes easy to be calculated. As a result, when a person's face is included in the subject, the focus evaluation value obtained is particularly large, and stable autofocus control can be realized.

  In order to achieve the above object, a first autofocus control method according to the present invention calculates a focus evaluation value based on a video signal in a focus evaluation area provided in a captured image, and the focus evaluation value is In an autofocus control method for performing autofocus control by driving and controlling an optical system in an imaging device so as to take extreme values, the horizontal contrast component and the vertical contrast component of an image in the focus evaluation region are detected, and those detected The focus evaluation value is calculated by weighting and adding.

  In order to achieve the above object, a second autofocus control method according to the present invention calculates a focus evaluation value based on a video signal in a focus evaluation area including a plurality of element areas provided in a captured image. In the autofocus control method for performing autofocus control by driving and controlling the optical system in the imaging apparatus so that the focus evaluation value takes an extreme value, the horizontal contrast component and the vertical contrast component of the image in each element region are Detecting, comparing the horizontal contrast component and the vertical contrast component for each element region, calculating an element region evaluation value from the larger contrast component, and integrating or averaging each element region evaluation value An evaluation value is calculated.

  According to the present invention, it is possible to provide an imaging apparatus and an autofocus control method that realize stable autofocus control.

  The significance or effect of the present invention will become more apparent from the following description of embodiments. However, the following embodiment is merely one embodiment of the present invention, and the meaning of the term of the present invention or each constituent element is not limited to that described in the following embodiment. .

  Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. In each of the drawings to be referred to, the same part is denoted by the same reference numeral, and redundant description regarding the same part is omitted in principle.

  FIG. 1 is an overall block diagram of an imaging apparatus 1 according to an embodiment of the present invention. The imaging device 1 is, for example, a digital video camera that can capture still images and moving images. However, the imaging apparatus 1 may be a digital still camera that can capture only a still image.

  The imaging apparatus 1 includes an imaging unit 11, an AFE (Analog Front End) 12, a video signal processing unit 13, a microphone 14, an audio signal processing unit 15, a compression processing unit 16, and an SDRAM as an example of an internal memory. (Synchronous Dynamic Random Access Memory) 17, memory card 18, decompression processing unit 19, video output circuit 20, audio output circuit 21, TG (timing generator) 22, CPU (Central Processing Unit) 23, A bus 24, a bus 25, an operation unit 26, a display unit 27, and a speaker 28 are provided. The operation unit 26 includes a recording button 26a, a shutter button 26b, an operation key 26c, and the like. Each part in the imaging apparatus 1 exchanges signals (data) between the parts via the bus 24 or 25.

  First, basic functions of the imaging device 1 and each part constituting the imaging device 1 will be described.

  The TG 22 generates a timing control signal for controlling the timing of each operation in the entire imaging apparatus 1, and provides the generated timing control signal to each unit in the imaging apparatus 1. Specifically, the timing control signal is given to the imaging unit 11, the video signal processing unit 13, the audio signal processing unit 15, the compression processing unit 16, the expansion processing unit 19, and the CPU 23. The timing control signal includes a vertical synchronization signal Vsync and a horizontal synchronization signal Hsync.

  The CPU 23 comprehensively controls the operation of each unit in the imaging apparatus 1. The operation unit 26 receives an operation by a user. The operation content given to the operation unit 26 is transmitted to the CPU 23. The SDRAM 17 functions as a frame memory. Each unit in the imaging apparatus 1 temporarily records various data (digital signals) in the SDRAM 17 during signal processing as necessary.

  The memory card 18 is an external recording medium, for example, an SD (Secure Digital) memory card. In this embodiment, the memory card 18 is illustrated as an external recording medium. However, the external recording medium is composed of one or a plurality of randomly accessible recording media (semiconductor memory, memory card, optical disk, magnetic disk, etc.). can do.

  FIG. 2 is an internal configuration diagram of the imaging unit 11 of FIG. By using a color filter or the like for the imaging unit 11, the imaging device 1 is configured to generate a color image by shooting.

  The imaging unit 11 in FIG. 2 includes an optical system 35, a diaphragm 32, an imaging element 33, and a driver 34. The optical system 35 includes a plurality of lenses including a zoom lens 30, a focus lens 31, and a correction lens 36. The zoom lens 30 and the focus lens 31 are movable in the optical axis direction, and the correction lens 36 is installed in the optical system 35 so as to be movable on a two-dimensional plane orthogonal to the optical axis.

  The driver 34 controls the movement of the zoom lens 30 and the focus lens 31 based on the control signal from the CPU 23, and controls the zoom magnification and focal length of the optical system 35. Further, the driver 34 controls the opening degree (size of the opening) of the diaphragm 32 based on a control signal from the CPU 23. Furthermore, the driver 34 controls the position of the correction lens 36 based on the camera shake correction control signal from the CPU 23 so that the blur of the optical image on the imaging surface of the image sensor 33 due to the camera shake is canceled.

  Incident light from the subject enters the image sensor 33 through the lenses and the diaphragm 32 constituting the optical system 35. Each lens constituting the optical system 35 forms an optical image of the subject on the image sensor 33. The TG 22 generates a drive pulse for driving the image sensor 33 in synchronization with the timing control signal, and applies the drive pulse to the image sensor 33.

  The image sensor 33 is composed of, for example, a CCD (Charge Coupled Devices), a CMOS (Complementary Metal Oxide Semiconductor) image sensor, or the like. The image sensor 33 photoelectrically converts an optical image incident through the optical system 35 and the diaphragm 32 and outputs an electrical signal obtained by the photoelectric conversion to the AFE 12. More specifically, the imaging device 33 includes a plurality of pixels (light receiving pixels; not shown) that are two-dimensionally arranged in a matrix, and in each photographing, each pixel receives a signal charge having a charge amount corresponding to the exposure time. store. The electrical signal from each pixel having a magnitude proportional to the amount of the stored signal charge is sequentially output to the subsequent AFE 12 in accordance with the drive pulse from the TG 22.

  The AFE 12 amplifies the analog signal output from the imaging unit 11 (image sensor 33), and converts the amplified analog signal into a digital signal. The AFE 12 sequentially outputs the digital signals to the video signal processing unit 13.

  The video signal processing unit 13 generates a video signal representing an image (hereinafter also referred to as “captured image” or “frame image”) captured by the imaging unit 11 based on the output signal of the AFE 12. The video signal is composed of a luminance signal Y representing the luminance of the photographed image and color difference signals U and V representing the color of the photographed image. The video signal generated by the video signal processing unit 13 is sent to the compression processing unit 16 and the video output circuit 20.

  FIG. 3 shows an internal block diagram of the video signal processing unit 13. The video signal processing unit 13 includes an AE evaluation unit 41, an AF evaluation unit 42, a face detection unit 43, and a motion detection unit 44.

  The AE evaluation unit 41 calculates an AE evaluation value corresponding to the brightness of the captured image. The CPU 23 adjusts the opening of the diaphragm 32 (and the amplification degree of signal amplification in the AFE 12 as necessary) via the driver 34 of FIG. 2 according to the AE evaluation value, thereby receiving the received light amount (brightness of the image). To control.

  The AF evaluation unit (focus evaluation value calculation means) 42 calculates an AF evaluation value (focus evaluation value) according to the contrast amount of the image in the AF evaluation area (focus evaluation area) provided in the captured image. The CPU 23 controls the position of the focus lens 31 via the driver 34 in FIG. 2 according to the AF evaluation value, thereby forming an optical image of the subject that falls within the AF evaluation area on the imaging surface of the image sensor 33. The function of the AF evaluation unit 42 will be described in detail later.

  The face detection unit 43 detects a human face from each captured image and extracts a face area including the face. Various methods are known as methods for detecting a face included in an image, and the face detection unit 43 can employ any method. For example, a face (face area) may be detected by extracting a skin color area from a photographed image as in the method described in Japanese Patent Application Laid-Open No. 2000-105819, or Japanese Patent Application Laid-Open No. 2006-21139 or Japanese Patent Application Laid-Open No. 2006. A face (face area) may be detected using the method described in Japanese Patent No. -72770.

  Typically, for example, the similarity between both images is determined by comparing the image of the region of interest set in the input image (that is, the captured image) with a reference face image having a predetermined image size. Based on this, it is detected whether or not a face is included in the region of interest (whether or not the region of interest is a face region). The similarity determination is performed by extracting a feature amount effective for identifying whether the face is a face. The feature amount is a horizontal edge, a vertical edge, a right diagonal edge, a left diagonal edge, or the like.

  In the input image, the region of interest is shifted in the horizontal direction or the vertical direction pixel by pixel. Then, the image of the region of interest after the shift is compared with the reference face image, the similarity between both images is determined again, and the same detection is performed. In this way, the region of interest is updated and set, for example, while being shifted pixel by pixel from the upper left to the lower right of the input image.

  Further, the input image (that is, the photographed image) is reduced at a certain rate, and the same face detection process is performed on the reduced image. By repeating such processing, a face of any size can be detected from the input image.

  The motion detection unit 44 uses, for example, a known image matching method (for example, a block matching method or a representative point matching method) and compares the video signals between the adjacent frame images, thereby moving the motion vector between the adjacent frame images. Is detected. This motion vector specifies the magnitude and direction of image motion between adjacent frame images. The CPU 23 performs camera shake correction by generating a camera shake correction control signal based on sequentially calculated motion vectors and controlling the position of the correction lens 36 in FIG.

  The microphone 14 in FIG. 1 converts audio (sound) given from the outside into an analog electric signal and outputs it. The audio signal processing unit 15 converts an electrical signal (audio analog signal) output from the microphone 14 into a digital signal. The digital signal obtained by this conversion is sent to the compression processing unit 16 as an audio signal representing the audio input to the microphone 14.

  The compression processing unit 16 compresses the video signal from the video signal processing unit 13 using a predetermined compression method. During video or still image shooting, the compressed video signal is sent to the memory card 18. The compression processing unit 16 compresses the audio signal from the audio signal processing unit 15 using a predetermined compression method. At the time of moving image shooting, the video signal from the video signal processing unit 13 and the audio signal from the audio signal processing unit 15 are compressed while being temporally related to each other by the compression processing unit 16, and after compression, they are stored in the memory card 18. Sent to.

  The recording button 26a is a push button switch for the user to instruct the start and end of shooting of a moving image (moving image), and the shutter button 26b is a button for the user to instruct shooting of a still image (still image). It is a button switch.

  The operation mode of the imaging apparatus 1 includes a shooting mode capable of shooting moving images and still images, and a playback mode for reproducing and displaying moving images or still images stored in the memory card 18 on the display unit 27. Transition between the modes is performed according to the operation on the operation key 26c.

  In the shooting mode, shooting is sequentially performed at a predetermined frame period (for example, 1/60 seconds). When the user presses the recording button 26a in the shooting mode, under the control of the CPU 23, the video signal of each frame after the pressing and the corresponding audio signal are sequentially recorded on the memory card 18 via the compression processing unit 16. Is done. When the recording button 26a is pressed again, the moving image shooting ends. That is, recording of the video signal and the audio signal to the memory card 18 is completed, and shooting of one moving image is completed.

  In the shooting mode, when the user presses the shutter button 26b, a still image is shot. Specifically, under the control of the CPU 23, the video signal of one frame after the depression is recorded on the memory card 18 via the compression processing unit 16 as a video signal representing a still image.

  When the user performs a predetermined operation on the operation key 26 c in the reproduction mode, a compressed video signal representing a moving image or a still image recorded on the memory card 18 is sent to the expansion processing unit 19. The decompression processing unit 19 decompresses the received video signal and sends it to the video output circuit 20. In the shooting mode, usually, the captured image is acquired by the imaging unit 11 and the video signal is generated by the video signal processing 13 regardless of whether the recording button 26a or the shutter button 26b is pressed. The video signal is sent to the video output circuit 20 for previewing.

  The video output circuit 20 converts a given digital video signal into a video signal (for example, an analog video signal) in a format that can be displayed on the display unit 27 and outputs the video signal. The display unit 27 is a display device such as a liquid crystal display, and displays an image corresponding to the video signal output from the video output circuit 20.

  When a moving image is reproduced in the reproduction mode, a compressed audio signal corresponding to the moving image recorded on the memory card 18 is also sent to the expansion processing unit 19. The decompression processing unit 19 decompresses the received audio signal and sends it to the audio output circuit 21. The audio output circuit 21 converts a given digital audio signal into an audio signal in a format that can be output by the speaker 28 (for example, an analog audio signal) and outputs the audio signal to the speaker 28. The speaker 28 outputs the sound signal from the sound output circuit 21 to the outside as sound (sound).

  The imaging apparatus 1 in FIG. 1 performs characteristic autofocus control (AF control). FIG. 4 is a partial block diagram of the imaging apparatus 1 corresponding to a part particularly related to AF control. FIG. 4 shows an internal configuration of the AF evaluation unit 42 of FIG.

  The AF evaluation unit 42 in FIG. 4 includes a horizontal contrast component detection unit 51, a vertical contrast component detection unit 52, a region evaluation value calculation unit 53, an integration unit 54, and an addition ratio control unit 55. The horizontal contrast component detection unit 51, the vertical contrast component detection unit 52, and the face detection unit 43 are provided with captured image data representing a captured image. The captured image data is formed by the video signal described above.

  In the AF evaluation unit 42, each captured image is captured by dividing it into M in the vertical direction and N in the horizontal direction. For this reason, each captured image is considered to be divided into (M × N) divided regions. M and N are each an integer of 2 or more. M and N may or may not match.

  FIG. 5 shows how each captured image is divided. The (M × N) divided areas are regarded as a matrix of M rows and N columns, and each divided area is represented by AR [i, j] with the origin O of the captured image as a reference. Here, i and j are integers that satisfy 1 ≦ i ≦ M and 1 ≦ j ≦ N. Divided areas AR [i, j] with the same i are composed of pixels on the same horizontal line, and divided areas AR [i, j] with the same j are composed of pixels on the same vertical line.

  The AF evaluation unit 42 calculates one AF evaluation value from one captured image, and sequentially transmits each AF evaluation value calculated for each captured image to the CPU 23 in order to realize AF control.

[AF evaluation value calculation method]
An operation for calculating one AF evaluation value from one taken image of interest will be described.

The horizontal contrast component detection unit 51 calculates a horizontal contrast component (hereinafter referred to as a horizontal contrast component) of the image in the divided area for each divided area forming the captured image. The horizontal contrast component calculated for the divided area AR [i, j] is represented by C _H [i, j].

For the divided area AR [i, j], the horizontal contrast component C _H [i, j] is calculated based on the video signal for the image in the divided area AR [i, j].

  FIG. 6A shows an example of an internal block diagram of the horizontal contrast component detection unit 51. The horizontal contrast component detection unit 51 in FIG. 6 includes an extraction unit 61, an HPF (high pass filter) 62, and an integration unit 63.

When calculating the horizontal contrast component C _H [1,1] for the divided area AR [1,1], the extraction unit 61 extracts the luminance signal in the divided area AR [1,1], and the HPF 62 A predetermined high-frequency component in the horizontal direction is extracted from the extracted luminance signal, and the integrating unit 63 integrates (or averages) the extracted high-frequency components, thereby obtaining a horizontal contrast component C _H [1. , 1]. For example, for example, the HPF 62 calculates the absolute value of the difference in luminance value between pixels adjacent in the horizontal direction, and the integration unit 63 integrates each absolute value calculated in the divided area AR [1, 1]. The horizontal contrast component C _H [1,1] is calculated by (or averaging). The same applies to the other divided areas AR [i, j]. Note that the luminance value is the value of the luminance signal. For a certain pixel, the luminance (brightness) of the pixel increases as the luminance value increases.

The calculated horizontal contrast component C _H [i, j] is approximately proportional to the horizontal contrast of the image in the divided area AR [i, j] and increases as the contrast increases.

The vertical contrast component detection unit 52 calculates a vertical contrast component (hereinafter referred to as a vertical contrast component) of the image in the divided area for each divided area forming the captured image. The vertical contrast component calculated for the divided area AR [i, j] is represented by C _V [i, j].

For the divided area AR [i, j], the vertical contrast component C _V [i, j] is calculated based on the video signal for the image in the divided area AR [i, j].

  FIG. 6B shows an example of an internal block diagram of the vertical contrast component detection unit 52. The vertical contrast component detection unit 52 in FIG. 6 includes an extraction unit 64, an HPF (high pass filter) 65, and an integration unit 66.

When calculating the vertical contrast component C _V [1,1] for the divided area AR [1,1], the extraction unit 64 extracts the luminance signal in the divided area AR [1,1], and the HPF 65 A predetermined high frequency component in the vertical direction is extracted from the extracted luminance signal, and the integrating unit 66 integrates (or averages) the extracted high frequency components, thereby obtaining a vertical contrast component C _V [1. , 1]. Simply, for example, the HPF 65 calculates the absolute value of the difference in luminance value between pixels adjacent in the vertical direction, and the integration unit 66 integrates each absolute value calculated in the divided area AR [1, 1]. The vertical contrast component C _V [1,1] is calculated by (or averaging). The same applies to the other divided areas AR [i, j].

The calculated vertical contrast component C _V [i, j] is approximately proportional to the contrast in the vertical direction of the image in the divided area AR [i, j], and increases as the contrast increases.

The horizontal contrast component (that is, C _H [i, j]) and the vertical contrast component (that is, C _V [i, j]) calculated for each divided region are sent to the region evaluation value calculation unit 53. The region evaluation value calculation unit 53 calculates a region evaluation value by performing weighted addition (weighted addition) of the horizontal contrast component and the vertical contrast component for each divided region. Assume that an area evaluation value calculated for the divided area AR [i, j] is represented by α [i, j]. Then, the region evaluation value α [i, j] is calculated according to the following formula (1).
α [i, j] = k _H [i, j] × C _H [i, j] + k _V [i, j] × C _V [i, j]
... (1)

Here, k _H [i, j] and k _V [i, j] are weighting coefficients calculated for each divided region by the addition ratio control unit 55, and when α [i, j] is generated by them. The addition ratio (contribution) of C _H [i, j] and C _V [i, j] is represented. A method for determining the weighting coefficients k _H [i, j] and k _V [i, j] will be described later.

  The integrating unit 54 calculates an AF evaluation value by integrating (or averaging) the area evaluation values α [i, j] for the divided areas in the designated AF evaluation area. For example, when the AF evaluation area matches the total area of the divided areas AR [5,5], AR [5,6], AR [6,5], and AR [6,6], the area evaluation value α [5 , 5], α [5, 6], α [6, 5] and α [6, 6] are calculated as AF evaluation values.

  The AF evaluation area is set based on the face area extracted by the face detection unit 43, for example. In this case, for example, when the face area overlaps with the divided areas AR [5,5], AR [5,6], AR [6,5] and AR [6,6], the divided area AR [5,5] , AR [5,6], AR [6,5] and AR [6,6] are set as AF evaluation areas, or an area including the total area is set as an AF evaluation area. Instead of this, for example, the AF evaluation area may be the entire area of the captured image or a predetermined partial area. Further, for example, the AF evaluation area may be arbitrarily set by a predetermined operation on the operation unit 26 in FIG.

[Method of determining weighting coefficient by addition ratio control unit]
A method for determining the weighting coefficients k _H [i, j] and k _V [i, j] by the weight ratio control unit 55 will be described.

  In AF control using a TTL (Through The Lends) type contrast detection method, only the horizontal contrast component is normally used. However, when the horizontal contrast component included in the photographed image is low, the subject can be correctly focused. There are cases where it is not possible. On the other hand, an image of face parts constituting a face such as eyes and mouth usually contains a lot of vertical contrast components. For example, when attention is paid to the periphery of the mouth, many components of change in the density of the image are included in the direction crossing the longitudinal direction of the mouth (that is, the vertical direction) (see FIG. 7A).

Focusing on this, in the present embodiment, the weighting coefficient k _V [i, j] for the divided area AR [i, j] corresponding to the face area is made relatively large.

A specific example is given. For the sake of concrete description, it is assumed that M = N = 8 and the AF evaluation area matches the entire area of the captured image. Then, as shown in FIG. 7A, in a certain captured image, the face area extracted by the face detection unit 43 is i _A = 2, 3, 4, 5, 6 or 7 and j _A = 2, 3 It is assumed that the total area 100 of the 36 divided areas AR [i _A , j _A ] in the case of 4, 5, 6 or 7 coincides. Further, as shown in FIG. 7A, the face area includes the entire face.

  The weight ratio control unit 55 determines the contribution of the vertical contrast component to the region evaluation value for each divided region AR [i, j] based on the position and size of the extracted face region (that is, the total region 100) on the image. A high vertical contribution region in which the degree is relatively large and a low vertical contribution region in which the contribution of the vertical contrast component to the region evaluation value is relatively small.

For example, a total of 36 divided areas AR [i _A , j _A ] forming the total area 100 are classified as high vertical contribution areas, and a total of 28 divided areas (AR [1,1] outside the total area 100 are included. ], AR [1,2], AR [2,1], etc.) are classified into low vertical contribution regions. Alternatively, as shown in FIG. 7B, only the divided areas forming the partial area 101 inside the face area are classified as high vertical contribution areas, and the other divided areas are classified as low vertical contribution areas. It may be. As a result, only a region having a particularly large vertical contrast component and concentrated facial parts such as eyes and mouth is classified as a high vertical contribution region. The partial area 101 is formed from a total of 16 divided areas AR [i _B , j _B ] when i _B = 3, 4, 5 or 6 and j _B = 3, 4, 5 or 6.

Then, the weighting coefficients k _H [i, j] and k _V [i, j] for each divided area AR [i, j] classified as the high vertical contribution area are set to k _H1 and k _V1 , respectively. The weighting coefficients k _H [i, j] and k _V [i, j] for each divided area AR [i, j] classified as the contribution area are k _H2 and k _V2 , respectively. Here, the inequality “k _V1 / (k _H1 + k _V1 )> k _V2 / (k _H2 + k _V2 )” holds (k _V1 , k _H1 , k _V2, and k _H2 are positive numbers).

Thereby, the contribution degree of the vertical contrast component (for example, C _V [3, 3]) to the region evaluation value (for example, α [3, 3]) of the divided region classified as the high vertical contribution region is set to the low vertical contribution. The degree of contribution of the vertical contrast component (for example, C _V [1,1]) to the region evaluation value (for example, α [1,1]) of the divided region classified as the region is larger. The former contribution (addition ratio) can be expressed by k _V1 / (k _H1 + k _V1 ), and the latter contribution (addition ratio) can be expressed by k _V2 / (k _H2 + k _V2 ). it can. As a result, the area evaluation value for the divided area corresponding to the face area increases.

Note that the weighting coefficients k _H [i, j] and k _V [i, j] may be different between the divided areas AR [i, j] classified as the high vertical contribution areas. That is, for example, when the divided areas AR [3, 3] and AR [3,4] are classified as high vertical contribution areas, k _H [3, 3] ≠ k _H [3,4], k _V [ Each of the weighting coefficients may be set such that 3, 3] ≠ k _V [3,4].

If no face area is included in the AF evaluation area, the weighting coefficients k _H [i, j] and k _V [i, j] for all the divided areas AR [i, j] are k _{H2, respectively.} And k _V2 . Therefore, as is clear from the above description, when the face area is included in the AF evaluation area, the degree of contribution of the vertical contrast component in the AF evaluation area to the AF evaluation value compared to the case where the face area is not included. Will grow.

[Operation flowchart]
Next, an operation flow of the imaging apparatus 1 focusing on still image shooting will be described. FIG. 8 is a flowchart showing this flow.

  First, when transitioning to the shooting mode, so-called preview is started in step S1. In the preview, a display image based on captured images sequentially captured at a predetermined frame period is updated and displayed on the display unit 27. Then, in the subsequent step S2, the hill climbing control is started (or executed). During the hill-climbing control, the position of the focus lens 31 (hereinafter referred to as “lens position”) is driven and controlled so that the AF evaluation value calculated for each captured image is maintained near the maximum value (or maximum value). The

  Next, in step S3, the CPU 23 checks whether the portrait setting is on. An operation for turning on the portrait setting is accepted by the operation unit 26. When the portrait setting is on, shooting and image processing suitable for shooting a person are performed. For this reason, the user often turns on the portrait setting when shooting a person.

  If the portrait setting is on, the face detection unit 43 in FIG. 4 detects the face area (step S4). If the portrait setting is not on, the face detection unit 43 detects the face. The area detection is suspended (step S5). In step S6, the CPU 23 confirms whether or not the shutter button 26b in FIG. 1 has been pressed. If the shutter button 26b is pressed, the process proceeds to step S7. If the shutter button 26b is not pressed, the process returns to step S2. Note that the processing of step S3 may be omitted, and the face area may always be detected.

  In the loop processing consisting of steps S7 to S12, AF evaluation values are sequentially obtained while moving the lens position from a predetermined reference position to a predetermined final position at predetermined intervals, and the AF evaluation value is maximum between the reference position and the final position. Is determined as the in-focus lens position.

  Specifically, in step S7, the lens position is moved to a predetermined reference position, and in step S8, an AF evaluation value for the current lens position is calculated. In step S9, it is determined whether or not the most recently calculated AF evaluation value is the maximum value among the AF evaluation values calculated so far in the loop processing. If the most recently calculated AF evaluation value is the maximum value, the process proceeds to step S10 and the current lens position is set to the in-focus lens position, and then the process proceeds to step S11. Otherwise, the process directly proceeds to step S11. To do. The in-focus lens position specified in step S10 can be updated to another lens position by repeating the loop process. For this reason, the focusing lens position specified in step S10 can be called a temporary focusing lens position.

  In step S11, it is determined whether or not the current lens position matches a predetermined final position. If the current lens position does not match the final position, the process proceeds to step S12 to move the lens position in the direction of the final position. Then, the process returns to step S8. On the other hand, if the current lens position coincides with the final position, the process proceeds to step S13, and finally the lens position is moved to the in-focus lens position specified in step S10, and then still image shooting is performed in step S14. To record the still image. That is, in the state where the focus lens 31 is finally located at the lens position specified as the focus lens position in the loop processing, one captured image is acquired, and the still image obtained by pressing the shutter button 26b is obtained. To the memory card 18. After the process of step S14, the process returns to step S1.

  As described above, the face area extraction result is referred to, and the vertical contrast component in the face area is largely reflected in the AF evaluation value. As a result, a larger AF evaluation value can be calculated for a captured image including a face area, compared to the conventional case, and stable AF control can be realized. Further, as the area evaluation value of the divided area corresponding to the face area increases, the degree of contribution to the AF evaluation value increases, and the face area is more accurately focused.

  If the extraction result of the face area is used, a weighting coefficient suitable for the face area is applied to the divided area AR [i, j] corresponding to the face area in the weighted addition process in the area evaluation value calculation unit 53 and non- Processing such as applying a weighting coefficient suitable for the non-face area to the divided area corresponding to the face area becomes possible.

For this reason, although it is preferable to use the face region extraction result, the same weighting coefficients k _H [i, j] and k _V [predetermined for all the divided regions AR [i, j] are used. i, j] can also be applied (in this case, the face detection unit 43 can be omitted). If this weighting coefficient is set appropriately (however, k _V [i, j]> 0), when a face area is included in the photographed image, an AF evaluation value is calculated based only on the horizontal contrast component. A larger AF evaluation value can be obtained than in the case. That is, as a result, a larger AF evaluation value can be calculated for a captured image including a face area, and stable AF control can be realized. Further, as the area evaluation value of the divided area corresponding to the face area increases, the degree of contribution to the AF evaluation value increases, and the face area is more accurately focused.

  Further, instead of calculating each region evaluation value by weighted addition, each region evaluation value can be calculated by the following calculation process (hereinafter referred to as “deformation calculation process”).

When this deformation calculation process is employed, the region evaluation value calculation unit 53 compares the horizontal contrast component and the vertical contrast component for each divided region and calculates a region evaluation value from the larger contrast component. For example, with respect to the divided area AR [1,1], when C _H [1,1]> C _V [1,1], α [1,1] is set to C _H [1,1], and C _H When [1,1] <C _V [1,1], α [1,1] is set as C _V [1,1]. The same applies to areas other than the divided area AR [1, 1]. The method for calculating the AF evaluation value by the integrating unit 54 based on each region evaluation value is as described above. When this deformation calculation process is employed, the face detection unit 43 and the addition ratio control unit 55 are omitted.

  As a result, a larger AF evaluation value can be obtained than when the AF evaluation value is calculated using only the horizontal contrast component or only the vertical contrast component, and stable AF control can be realized. Even if the face area is not extracted, the vertical contrast component is often larger than the horizontal contrast component for the divided areas corresponding to the face area. As a result, the area evaluation value is calculated from the vertical contrast component. It becomes easy. That is, as a result, a larger AF evaluation value can be calculated for a captured image including a face area, and stable AF control can be realized. Further, as the area evaluation value of the divided area corresponding to the face area increases, the degree of contribution to the AF evaluation value increases, and the face area is more accurately focused.

  Although the flow of the operation at the time of still image shooting has been described with reference to FIG. 8, the same effect can be obtained at the time of moving image shooting. At the time of moving image shooting, hill-climbing control is performed so that the AF evaluation value obtained sequentially is kept close to the maximum value (or maximum value). By calculating the AF evaluation value as described above, the face area is particularly determined. The effect of increasing the AF evaluation value is obtained for the captured image including the image, and stable AF control can be realized.

<< Deformation, etc. >>
As modifications or annotations of the above-described embodiment, notes 1 to 3 are described below. The contents described in each comment can be arbitrarily combined as long as there is no contradiction.

[Note 1]
The specific numerical values shown in the above description are merely examples, and as a matter of course, they can be changed to various numerical values.

[Note 2]
As can be seen from the above equation (1), the area evaluation value α [1,1] is weighted (weighted) by adding the horizontal contrast component C _H [1,1] and the vertical contrast component C _V [1,1]. If the weighting coefficient is selected so that the sum of k _H [1,1] and k _V [1,1] is 1, the region evaluation value α [1,1] can be obtained from the horizontal contrast component C. _H [1,1] and the vertical contrast component C _V [1,1] are weighted averages (the same applies to the other region evaluation values α [i, j]). Therefore, the weighted addition is a concept including a weighted average.

[Note 3]
The imaging apparatus 1 in FIG. 1 can be realized by hardware or a combination of hardware and software. In particular, the function of each part shown in FIG. 4 can be realized by hardware, software, or a combination of hardware and software.

  When the imaging apparatus 1 is configured using software, a block diagram of a part realized by software represents a functional block diagram of the part. Further, all or part of the functions of the respective parts shown in FIG. 4 and the functions of the CPU 23 involved in the AF control are described as a program, and the program is executed on a program execution device (for example, a computer) to execute them. You may make it implement | achieve all or one part of these functions.

1 is an overall block diagram of an imaging apparatus according to an embodiment of the present invention. It is an internal block diagram of the imaging part of FIG. FIG. 2 is an internal block diagram of a video signal processing unit in FIG. 1. FIG. 2 is a partial block diagram of the image pickup apparatus in FIG. 1 corresponding to a portion particularly related to AF control. It is a figure which shows each division area of the picked-up image defined in AF evaluation part of FIG. FIG. 5 is an internal block diagram (a) of the horizontal contrast component detection unit in FIG. 4 and an internal block diagram (b) of the vertical contrast component detection unit in FIG. 4. FIG. 5 is a diagram for describing a weighting coefficient determination method for weighted addition in the relationship with the face area extracted by the face detection unit in FIG. 4. 2 is a flowchart showing an operation flow of the imaging apparatus in FIG. 1 focusing on still image shooting.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Imaging device 11 Imaging part 13 Video signal processing part 23 CPU
DESCRIPTION OF SYMBOLS 31 Focus lens 33 Image pick-up element 35 Optical system 42 AF evaluation part 43 Face detection part 51 Horizontal contrast component detection part 52 Vertical contrast component detection part 53 Area evaluation value calculation part 54 Integration part 55 Addition ratio control part

Claims (7)

An imaging device having an imaging device and an optical system for forming an optical image corresponding to a subject on the imaging device, and obtaining a photographed image by photographing;
A focus evaluation value calculating means for calculating a focus evaluation value based on a video signal of a focus evaluation area provided in the photographed image,
In an imaging apparatus that performs autofocus control by driving and controlling the optical system so that the focus evaluation value takes an extreme value,
The focus evaluation value calculating means detects the horizontal contrast component and the vertical contrast component of an image in the focus evaluation region, and calculates the focus evaluation value by weighted addition of the detected components. . A face area extracting means for extracting a face area from the captured image;
The focus evaluation value calculating unit changes a contribution degree of the vertical contrast component to the focus evaluation value according to whether or not the face evaluation area includes the face area. The imaging device described. The focus evaluation value calculation unit increases the contribution of the vertical contrast component to the focus evaluation value when the face evaluation area includes the face region compared to when the face evaluation region is not included. Item 3. The imaging device according to Item 2. A face area extracting means for extracting a face area from the captured image;
When the face evaluation area includes the face area, the focus evaluation area includes a first area corresponding to a partial area inside the face area or the entire area of the face area, and the first area from the focus evaluation area. A second region excluding one region,
The focus evaluation value calculation means includes:
A first evaluation value corresponding to a weighted addition value of a horizontal contrast component and a vertical contrast component of an image in the first region;
Calculating the focus evaluation value from the sum of the second evaluation value corresponding to the weighted addition value of the horizontal contrast component and the vertical contrast component of the image in the second region;
The contribution of the vertical contrast component of the image in the first region to the first evaluation value is
The imaging apparatus according to claim 1, wherein a contribution degree of a vertical contrast component of an image in the second region to a second evaluation value is larger. An imaging device having an imaging device and an optical system for forming an optical image corresponding to a subject on the imaging device, and obtaining a photographed image by photographing;
A focus evaluation value calculating means for calculating a focus evaluation value based on a video signal of a focus evaluation area including a plurality of element areas provided in the captured image;
In an imaging apparatus that performs autofocus control by driving and controlling the optical system so that the focus evaluation value takes an extreme value,
The focus evaluation value calculation means detects a horizontal contrast component and a vertical contrast component of an image in each element region, compares the horizontal contrast component and the vertical contrast component for each element region, and determines the larger contrast component. An imaging apparatus characterized by calculating an element area evaluation value and calculating the focus evaluation value by integrating or averaging the element area evaluation values. A focus evaluation value is calculated based on a video signal in a focus evaluation area provided in the photographed image, and an auto system is controlled by driving and controlling an optical system in the imaging apparatus so that the focus evaluation value takes an extreme value. In the autofocus control method,
An autofocus control method, comprising: detecting a horizontal contrast component and a vertical contrast component of an image in the focus evaluation region, and calculating the focus evaluation value by weighted addition of the detected components. A focus evaluation value is calculated based on a video signal in a focus evaluation area including a plurality of element areas provided in a captured image, and the optical system in the imaging apparatus is driven and controlled so that the focus evaluation value takes an extreme value. In the autofocus control method for performing autofocus control,
The horizontal contrast component and the vertical contrast component of the image in each element region are detected, the horizontal contrast component and the vertical contrast component are compared for each element region, and the element region evaluation value is calculated from the larger contrast component, An autofocus control method, wherein the focus evaluation value is calculated by integrating or averaging each element region evaluation value.

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