JP5110887B2 - Focus evaluation value detection device and digital camera - Google Patents

Description

  The present invention relates to a focus evaluation value detection device and a digital camera, and in particular, a focus evaluation value detection device that detects a focus evaluation value used for performing automatic focus control, and the focus evaluation value detection device. The present invention relates to a digital camera that performs focusing control using a camera.

  In recent years, with the increase in the resolution of solid-state imaging devices such as CCD (Charge Coupled Device) area sensors and CMOS (Complementary Metal Oxide Semiconductor) image sensors, digital electronic still cameras, digital video cameras, mobile phones, PDAs (Personal Digital) The demand for information devices having photographing functions such as assistants and portable information terminals is rapidly increasing. Note that information devices having the above photographing functions are collectively referred to as “digital cameras”.

  Also, this type of digital camera is generally equipped with an automatic focusing function (so-called autofocus function) for automatically focusing.

  There are various methods for this automatic focusing function, but focusing that indicates the level of contrast in a predetermined area to be focused based on luminance information obtained from an image signal obtained by imaging. A method (so-called contrast AF method) in which an evaluation value is derived and focused by controlling the imaging optical system so that the in-focus evaluation value is maximized is the mainstream. The region to be focused is also referred to as a focus area, a distance measurement area, or the like, but here referred to as an “evaluation region”.

  By the way, in the contrast AF method, generally, a high-pass filter (hereinafter also referred to as “HPF”) or a band-pass filter (Band Pass Filter, Hereinafter, it is also referred to as “BPF”) or the like, and a focus evaluation value is obtained by deriving an integrated value of the output corresponding to the evaluation region from the filter. Note that the focus evaluation value may be referred to as an AF evaluation value, a contrast evaluation value, or the like.

  Conventionally, when such a contrast AF method is applied, there is a case where a false peak occurs in the focus evaluation value due to a high-luminance portion in the subject image, resulting in erroneous focus.

  In order to solve this problem, Patent Documents 1 and 2 disclose a technique for accurately focusing by obtaining a focus evaluation value in an imaging region where a high-luminance portion does not exist.

  Further, Patent Document 3 weights each evaluation area in accordance with the area of a high-luminance subject existing in a plurality of evaluation areas, and adds the high-frequency component level after weighting of each evaluation area to perform focus evaluation. A technique for suppressing a pseudo peak in a high luminance part by deriving a value is disclosed.

Furthermore, Patent Document 4 discloses a technique for correcting a focus evaluation value based on a ratio of a high luminance image.
JP-A-6-14236 JP 2002-182106 A JP-A-8-321985 Japanese Patent Laying-Open No. 2005-122016

  However, in the technique for obtaining the focus evaluation value in the imaging area where the high-luminance portion does not exist, the focus evaluation value in the evaluation area is affected by the response characteristics of the HPF or BPF, and the focus is accurate. There was a problem that sometimes it was not possible. This will be described with reference to the drawings.

  FIG. 8 shows an example of an impulse response by an IIR (Infinite Impulse Response) type filter.

  As shown in the figure, the filter output in the case where an input signal (luminance information) corresponding to an image position with a high contrast is input has a relatively long vibration state due to the influence of the contrast. For this reason, in the subject image shown in FIG. 9 as an example, since the high brightness region exists in the upper left part, the influence of the high brightness region remains in the filter output in the evaluation region. As shown in FIG. 5, a false peak of the focus evaluation value is generated on the near side of the actual focus, and as a result, erroneous focus may occur.

  Further, the techniques disclosed in Patent Document 3 and Patent Document 4 have a problem in that it is necessary to derive the area and ratio of a high-luminance subject, and it is troublesome to derive a focus evaluation value.

  The present invention has been made in order to solve the above-described problems, and a focus evaluation value detection device and a digital device that can easily prevent the occurrence of false focus due to the occurrence of a pseudo peak in the focus evaluation value. The purpose is to provide a camera.

In order to achieve the above object, the focus evaluation value detection apparatus according to claim 1 receives luminance information obtained by imaging a subject and captures the subject based on switching instruction information from the outside. For the luminance information of the evaluation area to be evaluated for the in-focus state in the image, the first input luminance information is used as a reference value, and the reference value is obtained from each luminance information including the first input luminance information. A data offset unit that outputs luminance information in which a value that is initially output becomes zero by executing an offset to be subtracted, and outputs luminance information without performing offset processing on luminance information other than the evaluation region; The luminance information output from the data offset means is input, and components in a predetermined frequency band are extracted from the input luminance information in real time and output. And first and a filter output at a timing to be inputted is reset to substantially zero, the focus evaluation by integrating the outputted component from the filter as a target the evaluation region luminance information by a reset signal from the outside Detecting means for detecting a value; and outputting the switching signal for executing the offset processing to the data offset means at a timing when the luminance information in the evaluation area is input to the data offset means. And a means for controlling to execute the offset processing for each luminance information in the evaluation region, and outputting the reset signal to the filter at a timing when the luminance information subjected to the offset processing is input to the filter. Control means for controlling to reset the output of the filter, That.

According to the focus evaluation value detection device of claim 1, luminance information obtained by imaging the subject is input to the data offset unit, and in the captured image of the subject based on a switching signal from the outside. For the luminance information of the evaluation area to be evaluated in the focused state, an offset for subtracting the reference value from each piece of luminance information including the luminance information input first, with the luminance information input first as a reference value When the process is executed, luminance information whose value that is initially output becomes zero is output, and luminance information other than the evaluation region is output without performing offset processing. In the filter, the luminance information output from the data offset means is input, components of the predetermined frequency band from the brightness information which is input is output after being extracted in real time, and the luminance by a reset signal from the outside The output is reset to substantially zero at the timing when information is first input . The substantially zero means that it is basically zero, but is zero within a range that allows an error due to the electrical characteristics of the filter, a difference in use environment, and the like.

  Further, in the present invention, the focus evaluation value is obtained by integrating the components output from the filter for the evaluation region, which is a region to be evaluated for the focus state in the captured image of the subject, by the detection unit. Detected.

Here, in the present invention, the control means outputs the switching signal for executing the offset processing to the data offset means at a timing when the luminance information in the evaluation area is inputted to the data offset means, the controls as data offset means performs the offset processing for each luminance information of the evaluation area Rutotomoni, the reset signal to said filter at a timing offset processed the luminance information is input to the filter And the output of the filter is controlled to be reset .

As described above, according to the focus evaluation value detection apparatus of claim 1, luminance information in the evaluation area, which is an evaluation target area of the focus state in the captured image of the subject, is input to the data offset unit. The switching signal for executing the offset processing at a timing to output to the data offset means, and the data offset means is an offset at which the first output value for each luminance information in the evaluation area becomes zero Control to execute processing, and control to output the reset signal to the filter and reset the output of the filter to substantially zero at the timing when the luminance information subjected to the offset processing is input to the filter As a result, it is possible to prevent the occurrence of a pseudo peak in the in-focus evaluation value. It is possible to prevent the occurrence of factors to Ayamagoase in a simple manner.

  In the present invention, as in the invention described in claim 2, a plurality of the evaluation regions may be provided for one captured image. Thereby, generation | occurrence | production of the false peak of the focus evaluation value in a some evaluation area | region can be prevented, As a result, generation | occurrence | production of misfocusing can be prevented at a higher level.

  In the present invention, the filter may be an IIR type filter as in the invention described in claim 3. Thereby, the filter configuration can be simplified as compared with the case where an FIR (Finite Impulse Response) filter is applied as the filter.

  On the other hand, in order to achieve the above-mentioned object, a digital camera according to a fourth aspect of the present invention captures the subject with the focus evaluation value detection apparatus according to any one of the first to third aspects, and the subject. Imaging means for acquiring an image signal indicating the captured image; and generation means for generating the luminance information to be input to the filter of the focus evaluation value detection device based on the image signal acquired by the imaging means; An imaging optical system that forms the captured image in an imaging region of the imaging means, and the imaging optics so that the focus evaluation value detected by the detection means of the focus evaluation value detection device is maximized. Focusing control means for controlling the system.

  The digital camera according to claim 4 is provided with the focus evaluation value detection device of the present invention, and on the other hand, an image signal indicating the captured image is acquired by imaging the subject by the imaging unit, and the generation unit The luminance information to be input to the filter of the focus evaluation value detection device is generated based on the image signal acquired by the imaging means. The imaging means includes a solid-state imaging device such as a CCD area sensor or a CMOS image sensor.

  In the present invention, the captured image is placed in the imaging area of the imaging means so that the focus evaluation value detected by the detection means of the focus evaluation value detection device is maximized by the focus control means. An imaging optical system for imaging is controlled.

  Thus, according to the digital camera of the fourth aspect, the captured image is connected to the imaging region of the imaging unit so that the focus evaluation value detected by the focus evaluation value detection device of the present invention is maximized. Since the imaging optical system to be imaged is controlled, it is possible to easily prevent the occurrence of erroneous focusing due to the occurrence of a pseudo peak in the focusing evaluation value, as in the focusing evaluation value detecting device of the present invention. it can.

According to the focus evaluation value detection apparatus of the present invention, the offset process is performed at the timing when the luminance information in the evaluation area, which is the area to be evaluated for the focus state in the captured image of the subject, is input to the data offset means. The switching signal to be executed is output to the data offset means, and the data offset means is controlled to execute an offset process in which the first output value for each luminance information in the evaluation region is zero In addition, since the reset signal is output to the filter and the output of the filter is reset to substantially zero at the timing when the luminance information subjected to the offset processing is input to the filter, the focus is adjusted. As a result of preventing the occurrence of a false peak in the evaluation value, the occurrence of false focus caused by the occurrence of the false peak It is possible to prevent easily an advantage of being.

  In addition, according to the digital camera of the present invention, the imaging optical that forms the captured image on the imaging region of the imaging means so that the focus evaluation value detected by the focus evaluation value detecting device of the present invention is maximized. Since the system is controlled, similarly to the in-focus evaluation value detection device of the present invention, it is possible to easily prevent the occurrence of in-focus caused by the occurrence of a pseudo peak in the in-focus evaluation value. can get.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Here, a case where the present invention is applied to a digital electronic still camera (hereinafter referred to as “digital camera”) that captures a still image will be described.

  First, the configuration of the digital camera 10 according to the present embodiment will be described with reference to FIG.

  As shown in the figure, the digital camera 10 includes an imaging system 20 that performs processing for capturing an image of a subject, and a reproduction system 30 that performs processing for reproducing an object image captured by the imaging system 20. Is provided.

  The imaging system 20 includes an optical lens unit including a focus lens, an optical unit 22 that forms a subject image by the optical lens unit, and a CCD area sensor (located behind the optical axis of the optical unit 22). (Hereinafter referred to as “CCD”) 24, an analog signal processing unit 26 for performing various analog signal processing such as correlated double sampling processing on the input analog signal, and converting the input analog signal into digital data An analog / digital converter (hereinafter referred to as “A / D”) 28.

  The output end of the CCD 24 is an input end of the analog signal processing unit 26, the output end of the analog signal processing unit 26 is an input end of the A / D 28, and the output end of the A / D 28 is an input of an imaging circuit 32 described later of the reproduction system 30. Each is connected to the end. Accordingly, the analog signal indicating the subject image output from the CCD 24 is subjected to predetermined analog signal processing by the analog signal processing unit 26, converted into digital image data by the A / D 28, and then input to the reproduction system 30.

  Further, the imaging system 20 is provided with a motor drive unit 29 connected to a CPU (Central Processing Unit) 44, which will be described later, and the focus lens provided in the optical lens unit of the optical unit 22 is connected to the optical axis. The CPU 44 controls the driving of a focus adjusting motor (not shown) that changes the in-focus state by the focus lens by moving in the direction via the motor driving unit 29.

  On the other hand, the reproduction system 30 performs various digital signal processing on the digital image data input from the A / D 28, and then the digital image data and the digital image data corresponding to the evaluation area are described later. An image pickup circuit 32 that outputs a timing signal indicating the timing input to 34 is provided. Note that the imaging circuit 32 according to the present embodiment outputs the digital image data in pixel arrangement order in units of pixels.

  In addition, the reproduction system 30 has an input terminal connected to an output terminal that outputs digital image data of the imaging circuit 32, and performs offset processing described later on luminance information indicated by the digital image data input from the imaging circuit 32. A data offset unit 34, an input end connected to the output end of the data offset unit 34, a filter 36 for extracting a component in a predetermined frequency band from luminance information input from the data offset unit 34 in real time, and a filter 36 And an integration circuit 38 that generates and outputs a focus evaluation value by integrating the frequency components input from the filter 36. In the filter 36 according to the present embodiment, a band of 300 kHz or more is applied as the predetermined frequency band. However, the present invention is not limited to this, and any frequency band that can obtain a focused evaluation value as a result. Any band can be applied.

  Further, the reproduction system 30 has an input terminal connected to an output terminal for outputting the timing signal of the imaging circuit 32, and an output terminal connected to the data offset unit 34, the filter 36, and the integrating circuit 38. And an evaluation value integration area control unit 40 that controls the operation of the offset unit 34, the filter 36, and the integration circuit 38.

  The evaluation value integration area control unit 40 is based on the timing indicated by the timing signal input from the imaging circuit 32 (timing at which digital image data corresponding to the evaluation area is input to the data offset unit 34). On the other hand, a switching signal indicating that the offset processing described later is performed only on the luminance information corresponding to the evaluation region and the luminance information corresponding to the other region is output without any processing is performed as a data offset. Input to the unit 34. Further, the evaluation value integration area control unit 40 inputs a reset signal for resetting the filter 36 to the filter 36 based on the timing indicated by the timing signal. Furthermore, the evaluation value integration area control unit 40 inputs integration instruction information for instructing the integration circuit 38 to execute the integration of the frequency components input from the filter 36 based on the timing indicated by the timing signal.

  The playback system 30 also includes a CPU 44 that controls the overall operation of the digital camera 10 and a memory control unit 42 connected to a memory 50 for storing various types of information. The unit 42 is electrically connected via the system bus 60. Therefore, the CPU 44 can access the memory 50 via the memory control unit 42.

  Here, the output terminal of the integration circuit 38 described above is connected to the memory control unit 42, and the focus evaluation value obtained in the integration circuit 38 is stored in a predetermined area of the memory 50 via the memory control unit 42. .

  Note that the configuration shown in FIG. 1 shows only a portion particularly relevant to the present invention. In addition to these components, an LCD (liquid crystal display) that reproduces (displays) a photographed subject image is used. Configured display unit, release button that is pressed to perform shooting, various switches that are used to perform various settings such as shooting conditions and operation modes, and image data obtained by shooting (electronic) It goes without saying that other components necessary for the digital camera, such as a portable memory card for storing (file), are provided.

  The release button provided in the digital camera 10 according to the present embodiment is pressed down to an intermediate position (hereinafter referred to as “half-pressed state”) and pressed to a final pressed position beyond the intermediate position. The two-stage pressing operation, which is performed (hereinafter referred to as “fully pressed state”), is configured to be detectable.

  In the digital camera 10, the AE (Automatic Exposure) function is activated by pressing the release button halfway to set the exposure state (shutter speed, aperture state), and then AF (Auto Focus (automatic focus) function works to control the focus, and then exposure (photographing) is performed when it is fully pressed.

  The digital camera 10 according to the present embodiment employs the contrast AF method described above as the AF function, and the CPU 44 moves the focus lens provided in the optical unit 22 in the optical axis direction when the AF function is executed. , The focus lens position where the focus evaluation value obtained by the integration circuit 38 is maximized is specified, and the focus lens is positioned at the position, and focus control is performed by a so-called hill-climbing control method. .

  Next, the configuration of the filter 36 according to the present embodiment will be described with reference to FIG.

  As shown in the figure, the filter 36 includes four 2-input 1-output adders A1 to A4, five 1-input 1-output multipliers M1 to M5, and two delay circuits DL1 to DL2. ing. In the filter 36 according to the present embodiment, D-type flip-flops are applied as the delay circuits DL1 to DL2.

  One input terminal of the adder A1 is connected to the output terminal of the data offset unit 34, and the output terminal of the adder A1 is branched into two and connected to the input terminal of the multiplier M1 and the input terminal of the delay circuit DL1. Yes. The output terminal of the multiplier M1 is connected to one input terminal of the adder A2, and the output terminal of the adder A2 is connected to the input terminal of the integrating circuit 38.

  On the other hand, the output terminal of the delay circuit DL1 is branched into three and connected to the input terminals of the multiplier M2, the multiplier M3, and the delay circuit DL2. The output terminal of the delay circuit DL2 is branched into two and connected to the input terminals of the multiplier M4 and the multiplier M5. Further, the output terminal of the multiplier M2 is connected to one input terminal of the adder A3, the output terminal of the multiplier M4 is connected to the other input terminal of the adder A3, and the output terminal of the multiplier M3. Is connected to one input terminal of the adder A4, and the output terminal of the multiplier M5 is connected to the other output terminal of the adder A4. The output terminal of the adder A3 is connected to the other input terminal of the adder A1, and the output terminal of the adder A4 is connected to the other input terminal of the adder A2.

  Each reset input terminal of the delay circuit DL1 and the delay circuit DL2 is connected to an output terminal for outputting a reset signal of the evaluation value integration area control unit 40. Accordingly, by inputting the reset signal, the output signal of the filter 36 can be made substantially zero.

  Thus, the filter 36 according to the present embodiment is configured by an IIR filter. Since the IIR filter is conventionally known, further description of the configuration of the filter 36 is omitted.

  Next, with reference to FIG. 3, the operation when detecting the focus evaluation value in the digital camera 10 according to the present embodiment will be described. FIG. 3 shows an example of each of the luminance information indicated by the digital image data input to the data offset unit 34 at this time, the luminance information input from the data offset unit 34 to the filter 36, and the reset signal. It is a time chart.

  As described above, the evaluation value integration area control unit 40 performs the offset process only on the luminance information corresponding to the evaluation area, and outputs the luminance information corresponding to the other area without performing any process. The switching signal is input to the data offset unit 34.

  In response to this, the data offset unit 34, as shown in FIG. 3 as an example, takes luminance information in the evaluation region as a target and first inputs luminance information (in FIG. An offset process for offsetting each piece of luminance information is executed using the luminance information D2) as a reference value. Thus, in the example shown in the figure, the luminance information D2, D3, D4,..., Dk in the evaluation region is 0 (= D2-D2), D3-D2, D4-D2,. Dk-D2 is input to the filter 36.

  On the other hand, the evaluation value integration area control unit 40 inputs the reset signal to the filter 36 at the timing when the luminance information is first input to the filter 36 in the evaluation region. In response to this, the delay circuit DL1 and the delay circuit DL2 are reset, so that the output signal from the filter 36 once becomes substantially zero.

  When the offset processing for the luminance information as described above and the reset operation for the filter 36 are not performed, as shown in FIG. 4A as an example, the filter output corresponding to the evaluation region has a high contrast portion immediately before it. As a result, a high output value that should not exist is generated. On the other hand, when the offset process and the reset operation are performed, as shown in FIG. 4B as an example, the filter output corresponding to the evaluation region is subjected to the high contrast due to the influence of the high contrast portion immediately before it. There is no output value. As a result, as shown in FIG. 5 as an example, the occurrence of a false peak in the focus evaluation value as shown in FIG. 10 can be prevented, and the occurrence of erroneous focusing can be prevented.

  As described above in detail, in the present embodiment, the filter is reset at the timing when the luminance information is first input to the filter in the evaluation area that is the evaluation target area of the focused state in the captured image of the subject. At the same time, when luminance information in the evaluation area is input to the filter, an offset process is performed to offset each luminance information using the luminance information first input to the filter in the evaluation area as a reference value. Therefore, the occurrence of a false peak in the focus evaluation value can be prevented, and as a result, the occurrence of erroneous focusing due to the occurrence of the false peak can be easily prevented.

  In this embodiment, since the filter is an IIR filter, the filter configuration can be simplified as compared with the case where an FIR filter is applied as the filter.

  In the present embodiment, the case where only one evaluation area is provided for one captured image (subject image) has been described. However, the present invention is not limited to this, and is illustrated as an example, for example. As shown in FIG. 6, a plurality of evaluation areas may be provided (multi-point evaluation area) for one captured image (subject image). In this case, as shown in FIG. 7 as an example, the reset process and the offset process described above are executed for each evaluation region. Thereby, generation | occurrence | production of the false peak of the focus evaluation value in a some evaluation area | region can be prevented, As a result, generation | occurrence | production of misfocusing can be prevented at a higher level.

  In the present embodiment, the case where the IIR filter is applied as the filter of the present invention has been described. However, the present invention is not limited to this, and for example, an FIR filter may be applied. it can. Also in this case, the same effects as in the present embodiment can be obtained.

  In addition, the configuration of the digital camera 10 according to the present embodiment (see FIGS. 1 and 2) is merely an example, and unnecessary components are deleted or a new configuration is made without departing from the gist of the present invention. It goes without saying that elements can be added and the electrical connection state can be changed.

  Further, the time chart described in this embodiment (see FIG. 3) is also an example, and it is needless to say that the time chart can be changed without departing from the gist of the present invention.

  Further, in the present embodiment, the case where the present invention is applied to a digital electronic still camera has been described. However, the present invention is not limited to any information device having an AF function using a contrast AF method, such as a PDA or a mobile phone. But it goes without saying that it is applicable.

It is a block diagram which shows the principal part structure of the electric system of the digital camera which concerns on embodiment. It is a block diagram which shows the structure of the filter applied with the digital camera which concerns on embodiment. It is a time chart with which it uses for description of an effect | action of the digital camera concerning embodiment. It is a wave form diagram with which it uses for description of the effect of the digital camera which concerns on embodiment. It is a wave form diagram with which it uses for description of the effect of the digital camera which concerns on embodiment. It is the schematic which shows an example of the evaluation area | region used for description of the modification of the digital camera which concerns on embodiment. It is a wave form diagram with which it uses for description of the modification of the digital camera which concerns on embodiment. It is a figure with which it uses for description of the problem of a prior art, and is a wave form diagram which shows an example of the impulse response by an IIR type filter. FIG. 10 is a diagram for explaining a problem in the related art, and is a schematic diagram illustrating an example of a subject image having a high luminance region and an evaluation region. It is a figure with which it uses for description of the problem of a prior art, and is a wave form diagram which shows an example of the generation | occurrence | production state of a pseudo peak.

Explanation of symbols

10 Digital camera 22 Optical unit (imaging optical system)
24 CCD (imaging means)
34 Data offset part (generation means)
36 Filter 38 Integration circuit (detection means)
40 Evaluation value integration area control unit (control means)
44 CPU (focus control means)

Claims (4)

Luminance information obtained by imaging the subject is input, and based on the switching instruction information from the outside, the luminance information of the evaluation area to be evaluated for the focused state in the captured image of the subject is first Using the input luminance information as a reference value, by executing an offset that subtracts the reference value from each piece of luminance information including the first input luminance information, output the luminance information in which the first output value becomes zero And a data offset means for outputting luminance information without performing offset processing on luminance information other than the evaluation region;
Luminance information output from the data offset means is input, a predetermined frequency band component is extracted from the input luminance information in real time and output, and luminance information is input first by an external reset signal A filter whose output is reset to substantially zero at the timing of
Detecting means for detecting a focus evaluation value by integrating the components output from the filter for the evaluation region;
The switching instruction information for executing the offset processing is output to the offset unit at a timing when the luminance information in the evaluation region is input to the offset unit, and the offset unit outputs each luminance signal in the evaluation region. Control to execute the offset process on the filter, and to output the reset signal to the filter and reset the output of the filter at a timing when the luminance information subjected to the offset process is input to the filter. Control means to
An in-focus evaluation value detection device. The focus evaluation value detection apparatus according to claim 1, wherein a plurality of the evaluation areas are provided for one captured image. The focus evaluation value detection device according to claim 1, wherein the filter is an IIR type filter. A focus evaluation value detection device according to any one of claims 1 to 3,
Imaging means for acquiring an image signal indicating the captured image by imaging the subject;
Generating means for generating the luminance information to be input to the filter of the focus evaluation value detection device based on the image signal acquired by the imaging means;
An imaging optical system that forms an image of the captured image on an imaging region of the imaging means;
A focus control means for controlling the imaging optical system so that the focus evaluation value detected by the detection means of the focus evaluation value detection device is maximized;
Digital camera equipped with.