JP4979507B2 - Imaging apparatus and imaging method - Google Patents

Description

  The present invention relates to an imaging apparatus and an imaging method having an autofocus function for automatically focusing on a subject, and in particular, can accurately focus on a subject in a low brightness and low contrast environment. The present invention relates to an imaging device and an imaging method that can be used.

  A general imaging apparatus such as a digital still camera is equipped with an autofocus (hereinafter referred to as “AF”) device that automatically focuses on a subject. As an example of the AF control method used by the AF apparatus, a hill-climbing AF control method is known (see, for example, Patent Document 1). This hill-climbing AF control method is a method in which an integral value of a luminance difference between adjacent pixels is obtained from a video signal output from an image sensor, and this integral value is used as an AF evaluation value indicating the degree of focus. When the subject is in focus, the contour portion of the subject in the video signal is clear, so that the luminance difference between adjacent pixels in this video signal is large. That is, the AF evaluation value increases in the focused state. On the contrary, when the subject is out of focus, the contour portion of the subject is blurred, so that the luminance difference between adjacent pixels in this video signal becomes small. That is, the AF evaluation value is small in the out-of-focus state. The AF device acquires a video signal at the lens position at a predetermined timing while moving the lens, calculates an AF evaluation value, specifies a maximum value of the AF evaluation value (a peak position of the AF evaluation value), and performs AF By moving the lens to a position where the evaluation value is maximized and stopping it, the subject can be automatically focused. Thus, the hill-climbing AF control method can focus on the subject by detecting the peak position of the AF evaluation value.

Recently, AF control how to perform hill-climbing AF control method more accurately and faster have been proposed (e.g. see Patent Document 2). In the AF control method described in Patent Document 2, the AF evaluation value is sampled at a minute interval and the AF evaluation value is sampled at a rough interval until the focus position is approached. By selectively using the second mode in which AF evaluation values are sampled at appropriate intervals, the AF processing can be speeded up and the subject can be focused more quickly.

However, in the AF control method described in Patent Document 2, when the subject is in a low-luminance environment or a low-contrast environment, it takes time until the peak of the AF evaluation value is detected due to a large amount of noise included in the video signal. That is, since AF processing is repeatedly performed until the peak of the AF evaluation value is detected, a long time is required until focusing is achieved. Therefore, in order to solve the problem caused by the method described in Patent Document 2, a method has been proposed in which the filter used for the video signal is varied according to the luminance and the noise of the video signal is removed to reduce the variation in the AF evaluation value. (See, for example, Patent Document 3).
Japanese Examined Patent Publication No. 39-5265 Japanese Patent No. 3851027 JP 2006-145964 A

  On the other hand, image pickup devices (CCD) used in recent image pickup apparatuses have been increased in the number of pixels (densification), and the luminance difference between adjacent pixels has become smaller than the previous one. The difference in luminance between adjacent pixels in is small. For this reason, in the above-described conventional method, it is difficult to accurately and accurately specify the in-focus position due to variations in the AF evaluation value caused by noise included in the video signal.

  The present invention has been made in view of the above problems, and even when the luminance difference between adjacent pixels of a video signal is small, the maximum value of the AF evaluation value can be specified with high accuracy and more stable AF. An object of the present invention is to provide an imaging device capable of performing control.

The present invention, use an image sensor for receiving light of a subject that has passed through the photographic lens, and the lens moving means for moving the photographing lens, the AF evaluation value calculated by using the image data obtained from the shooting image element Shooting condition setting that can select multiple shooting conditions, including automatic focus detection means that determines the focus by smooth differential calculation , normal shooting mode for shooting at least a general subject, and macro mode for shooting a close subject And an imaging device comprising:
The automatic focus detection unit determines a total range of the AF evaluation values to be subjected to the smooth differential calculation according to a shooting condition set by the shooting condition setting unit, and the set shooting condition is the macro when set to mode, the normal than when it is set to shooting mode, the most important feature set narrow to Rukoto the total range of the AF evaluation value that is the calculation target of the smoothing differential operation And
The present invention also provides an image sensor that receives light from a subject that has passed through a photographic lens, a lens moving unit that moves the photographic lens, and an AF evaluation value that is calculated using image data obtained from the image sensor. And an automatic focus detection unit that determines a focus by using the smooth differential calculation, wherein the automatic focus detection unit determines a total range of the AF evaluation values to be calculated by the smooth differential calculation of the photographing lens. It is determined according to the focal length, and when the focal length is on the tele side, the total range of the AF evaluation values to be subjected to the smooth differential calculation is also set narrower than when the focal length is on the wide side. It is characterized by that.
The present invention also provides an image sensor that receives light from a subject that has passed through a photographic lens, a lens moving unit that moves the photographic lens, and an AF evaluation value that is calculated using image data obtained from the image sensor. And an automatic focus detection unit that determines a focus by the smooth differential calculation used. The automatic focus detection unit can vary a total range of the AF evaluation values to be calculated by the smooth differential calculation according to a shooting condition. The total range of the AF evaluation values which are determined according to the moving step amount of the photographing lens and are subject to the calculation of the smooth differential operation determined according to the first moving step amount is the first moving step. It is characterized by being narrower than the total range of the AF evaluation values to be calculated by the smooth differential calculation determined according to the second moving step amount smaller than the amount.

The present invention also provides an image sensor that receives light from a subject that has passed through a photographic lens, a lens moving unit that moves the photographic lens, and an AF evaluation value that is calculated using image data obtained from the image sensor. Shooting conditions that can be selected from a plurality of shooting conditions, including automatic focus detection means for determining the focus by the smooth differential calculation used, a normal shooting mode for shooting at least a general subject, and a macro mode for shooting a close subject In the imaging method executed by the imaging device having the setting unit, the automatic focus detection unit sets the total range of the AF evaluation values that are the calculation target of the smooth differential calculation by the shooting condition setting unit. The step of determining according to the conditions, and when the set shooting condition is the macro mode, the normal shooting mode is set Kiyori also and executes the steps of: setting narrow total range of the AF evaluation value that is the calculation target of the smoothing differential operation.
  The present invention also provides an image sensor that receives light from a subject that has passed through a photographic lens, a lens moving unit that moves the photographic lens, and an AF evaluation value that is calculated using image data obtained from the image sensor. In the imaging method executed by the imaging apparatus having an automatic focus detection means for determining a focus by the smooth differential calculation used, the automatic focus detection means is a total of the AF evaluation values to be calculated by the smooth differential calculation A step of determining a range according to a focal length of the photographing lens; and when the focal length is on a tele side, the AF evaluation that is a calculation target of the smooth differential calculation than when the focal length is on a wide side Performing a step of setting a total range of values to be narrow.
  The present invention also provides an image sensor that receives light from a subject that has passed through a photographic lens, a lens moving unit that moves the photographic lens, and an AF evaluation value that is calculated using image data obtained from the image sensor. In the imaging method executed by the imaging apparatus having an automatic focus detection means for determining a focus by the smooth differential calculation used, the automatic focus detection means is a total of the AF evaluation values to be calculated by the smooth differential calculation The step of determining the range according to the moving step amount of the photographing lens that varies according to the focal length of the photographing lens, and the smoothing differential calculation determined according to the first moving step amount The total range of AF evaluation values is a calculation target of the smooth differentiation calculation that is determined according to a second movement step amount smaller than the first movement step amount. And setting narrower than a total range of serial AF evaluation value, characterized by the execution.

  According to the present invention, a high-speed and high-precision autofocus function can be provided by detecting an in-focus point by performing smooth differentiation on an AF evaluation value calculated from image data of a subject in an imaging apparatus.

  In addition, according to the present invention, the range of the AF evaluation value used for the smooth differential calculation can be varied depending on the photographing mode and the focal length in the imaging apparatus, so that high-speed and high-precision automatic can be achieved while preventing false focusing. Focus function can be provided.

  Hereinafter, embodiments of an imaging apparatus according to the present invention will be described with reference to the drawings. 1 to 3 are views showing an example of the external configuration of an imaging apparatus according to the present invention. 1 is a front view, FIG. 2 is an upper plan view, and FIG. 3 is a rear view. In FIG. 1, a lens barrel unit 7 including a strobe light emitting unit 3, an optical finder 4, a remote control light receiving unit 6, and an imaging lens is disposed in front of a camera body CB which is a housing of the imaging apparatus. On one side surface, a memory card loading chamber and a battery loading chamber lid 2 are provided. 2, a release button (switch) SW1, a mode dial SW2, and a sub liquid crystal display (sub LCD) (hereinafter, “liquid crystal display” is referred to as “LCD”) 1 are arranged on the upper surface of the camera body CB. In FIG. 3, on the back of the camera body CB, there are an optical finder 4, an AF LED ("LED" is a light emitting diode) 8, a strobe LED 9, an LCD monitor 10, a power switch 13, a wide-angle zoom switch SW3, and a telephoto zoom. Switch SW4, Self-timer setting and release switch SW5, Menu switch SW6, Upward movement and strobe set switch SW7, Rightward movement switch SW8, Display switch SW9, Downward movement and macro switch SW10, Leftward movement and image confirmation switch SW11, OK switch SW12 and quick access switch SW13 are arranged.

  Next, functional blocks of the imaging apparatus according to the present invention will be described with reference to FIG. Various operations (processing) of the imaging apparatus according to the present invention are controlled by a digital still camera processor 104 (hereinafter simply referred to as “processor 104”) configured as a digital signal processing IC (integrated circuit) or the like. The processor 104 includes a first CCD (charge coupled device) signal processing block 104-1, a second CCD signal processing block 104-2, a CPU (central processing unit) block 104-3, a local SRAM (SRAM: static random access). Memory) 104-4, USB (universal serial bus) block 104-5, serial block 104-6, JPEG codec (CODEC) block 104-7, resize (RESIZE) block 104-8, TV signal display block 104-9 and A memory card controller block 104-10 is provided, and these blocks are connected to each other via a bus line.

  Outside the processor 104, an SDRAM (synchronous random access memory) 103 for storing RAW-RGB image data, YUV image data, and JPEG image data, a RAM 107, a built-in memory 120, and a ROM 108 storing a control program are arranged. And is connected to the processor 104 via a bus line.

  The lens barrel unit 7 includes a zoom optical system 7-1 having a zoom lens 7-1a, a focus optical system 7-2 having a focus lens 7-2a, an aperture unit 7-3 having an aperture 7-3a, and a mechanical shutter 7-. A mechanical shutter unit 7-4 having 4a is provided. The zoom optical system 7-1, the focus optical system 7-2, the aperture unit 7-3 and the mechanical shutter unit 7-4 are respectively a ZOOM motor 7-1b, a FOCUS motor 7-2b as a focus lens moving means, and an aperture motor 7-. 3b and mechanical shutter motor 7-4b. These ZOOM motor 7-1b, FOCUS motor 7-2b, aperture motor 7-3b, and mechanical shutter motor 7-4b are operated by a motor driver 7-5 controlled by the CPU block 104-3 of the processor 104. Be controlled.

  The zoom lens 7-1a and the focus lens 7-2a of the lens barrel unit 7 constitute an imaging lens for forming a subject optical image on the imaging surface of the CCD 101, which is an imaging element, and the CCD 101 includes the subject optical image. Is converted into an electrical image signal and input to an F / E-IC (front end IC) 102. The F / E-IC 102 includes a CDS (correlated double sampling unit) 102-1, an AGC (automatic gain control unit) 102-2, and an A / D (analog-digital) conversion unit 102-3. Each is subjected to predetermined processing, converted into a digital signal, and input to the first CCD signal processing block 104-1 of the processor 104. These signal processing operations are controlled by a VD / HD (vertical drive / horizontal drive) signal output from the first CCD signal processing block 104-1 of the processor 104 via a TG (timing generator) 102-4. The The first CCD signal processing block 104-1 performs signal processing such as white balance adjustment and γ adjustment on the digital image data input from the CCD solid-state imaging device 101 via the F / E-IC 102. VD signal and HD signal are output.

  The CPU block 104-3 of the processor 104 controls the sound recording operation by the sound recording circuit 115-1. The voice recording circuit 115-1 records the voice signal converted by the microphone 115-3 and amplified by the microphone amplifier 115-2 in accordance with a command from the CPU block 104-3. The CPU block 104-3 also controls the operation of the audio reproduction circuit 116-1. The audio reproduction circuit 116-1 amplifies an audio signal recorded in an appropriate memory by an audio amplifier 116-2 and inputs the audio signal to the speaker 116-3 in response to an instruction from the CPU block 104-3. Play audio. Further, the CPU block 104-3 controls the strobe circuit 114 to operate, thereby causing the strobe light emitting unit 3 to emit illumination light. The CPU block 104-3 also controls the operation of a distance measuring unit (not shown) that measures the subject distance.

  Note that the imaging apparatus according to the present invention performs AF control based on captured image data as will be described later. Therefore, it is not always necessary to measure the subject distance by the ranging unit. You can omit it. Further, measurement information of the subject distance by the distance measuring unit may be used for strobe light emission control in the strobe circuit 114. The subject distance measurement information obtained by the distance measuring unit may be used supplementarily for focusing control based on the captured image data.

  Further, the CPU block 104-3 is also coupled to a sub CPU 109 disposed outside the processor 104, and the sub CPU 109 controls display by the sub LCD 1 via the LCD driver 111. The sub CPU 109 is also coupled to the AF LED 8, the strobe LED 9, the remote control light receiving unit 6, the operation unit including the switches SW1 to SW13, and the buzzer 113, respectively.

  The USB block 104-5 is coupled to the USB connector 122, and the serial block 104-6 is coupled to the RS-232C connector via the serial driver circuit 123-1. The video signal display block 104-9 is coupled to the LCD monitor 10 via an LCD driver 117, and the TV signal display block 104-9 is also coupled to a video jack 119 via a video amplifier 118. . The memory card controller block 104-10 is coupled to the card contact of the memory card slot 121, and when the memory card is loaded into the memory card slot 121, the memory card controller block 104-10 comes into contact with and electrically connects to the memory card contact.

  Next, the operation of the imaging apparatus configured as described above will be described. By setting the mode dial SW2 shown in FIGS. 1 to 3 to the recording mode, the imaging apparatus is activated in the recording mode. The imaging apparatus has a plurality of recording modes, and these recording modes are collectively referred to as an imaging mode. The mode dial SW2 is set by the CPU block 104-3 detecting via the sub CPU 109 that the mode dial SW2 included in the operation key units (SW1 to SW13) in FIG. The driver 7-5 is controlled to move the lens barrel unit 7 to a position where it can be imaged. Further, power is turned on to the respective parts such as the CCD 101, the F / E-IC 102, and the LCD monitor 10 to start the operation. When the power of each part is turned on, the operation in the finder mode is started.

  In the finder mode, the light incident on the CCD 101 as the image sensor through the imaging lens of the lens barrel unit 7 is converted into an electrical signal and input to the CDS 102-1 as an RGB analog signal, and the A / It is sent to the D converter 102-3. The R, G, and B signals converted into digital signals by the A / D converter 102-3 are converted into YUV image data by YUV conversion means achieved by the second CCD signal processing block 104-2 in the processor 104. And is recorded in the SDRAM 103 as a frame memory. Note that the second CCD signal processing block 104-2 performs appropriate processing such as filtering processing on the RGB image data to convert it into YUV image data. The YUV image data is read out by the CPU block 104-3 and sent to the TV (television) via the video amplifier 118 and the video jack 119 via the video signal display block 104-9, or the LCD driver 117. To the LCD monitor 10 for display. This process is performed at intervals of 1/30 seconds, and a finder mode display updated every 1/30 seconds is obtained.

  When the release button SW1 of the operation unit is pressed, an AF evaluation value indicating the degree of focus in a predetermined at least part of the screen from the digital RGB image data captured in the first CCD signal processing block 104-1. Then, an AE evaluation value indicating the exposure state is calculated. The AF evaluation value is read as feature data to the CPU block 104-3 and used for AF processing that functions as an automatic focus detection unit.

  Since the edge of the subject in focus is clear, the high frequency component of the spatial frequency included in the image data is the highest. The AF evaluation value, which is the integrated value of the luminance difference between adjacent pixels of the pixels constituting the subject image data having a high spatial frequency, has a large value. Therefore, the displacement amount of the AF evaluation value acquired intermittently while moving the focus lens 7-2a becomes a value reflecting the high-frequency component included in the image data. Therefore, an image in which the AF evaluation value becomes a maximum value. The position of the focus lens 7-2a that has acquired the data is the in-focus position. That is, the focus position can be specified by detecting the peak position in the AF evaluation value. Also, taking into consideration that a plurality of local maximum points (peak positions) of the AF evaluation value appear, when there are a plurality of local maximum points (peak positions), the magnitude of the AF evaluation value at the peak position and the surrounding positions Considering the degree of decrease or increase of the AF evaluation value, AF processing is performed with the maximum point (peak position) estimated to be most reliable as the in-focus position.

  The AF evaluation value can be calculated from a specific range (AF processing area) in the digital RGB image data. FIG. 5 shows an image plane displayed on the LCD in the finder mode. In FIG. 5, the frame displayed at the center of the LCD 10 is an AF processing area in the imaging apparatus. In this AF processing area, for example, a range of 40% in the central horizontal direction and 30% in the vertical direction in the screen of RGB image data is set.

  The plurality of shooting modes provided in the imaging apparatus according to the present invention have different AF shooting ranges. For example, in the normal AF mode, the AF shooting range is from 1 m to infinity, and in the macro AF mode, the AF shooting range is from 1 cm to infinity. The AF mode is set by the mode dial SW2.

  An embodiment of an imaging method using an imaging apparatus according to the present invention will be described. The AF process in the imaging method according to the present invention acquires an AF evaluation value at a predetermined timing position of the moving focus lens 7-2a, performs a smooth differential calculation using the acquired AF evaluation value, and performs the smooth differential calculation. The result (smooth differential value) is used to determine the in-focus state and specify the in-focus position. First, the smooth evaluation process of the AF evaluation value will be described.

The AF evaluation value acquired based on the image data of the subject captured at a predetermined timing from the moving focus lens 7-2a is assumed to be X [0], and the AF evaluation value acquired a before the X [0]. X [−a], and the AF evaluation value acquired a after X [0] is X [a],
When the weighting coefficient for each AF evaluation value is b1, b2,..., The smooth differential value Y [0] is Y [0] = Σ [i = 0 → a] (X [i] −X [−i] ) × bi.

  A specific example of the above-described smooth differential equation will be shown. When obtaining the smooth differential value Y [0] using three evaluation values before and after the current AF evaluation value (X [0]), Y [0] = (X [1] −X [−1]) × 1 + ( X [2] −X [−2]) × 2 + (X [3] −X [−3]) × 3. Here, the weighting coefficient (bi = 1, 2, 3...) Is a distant AF evaluation value (for example, X [1]) close to the current AF evaluation value X [0]. For example, let X [3]) be a larger coefficient. That is, the smaller the degree of correlation with the current value (X [0]), the larger the value, and the specific coefficient value is not limited to the above example.

  As described above, the AF control method in the imaging method according to the present invention calculates the AF evaluation value by obtaining the smooth differential value based on the correlation of the AF evaluation value acquired corresponding to the movement of the focus lens 7-2a. The extreme value is specified and the in-focus position is detected.

  The above arithmetic expression performs smooth differentiation using three AF evaluation values before and after the current AF evaluation value X [0]. However, the number of AF evaluation values used for smooth differentiation is limited to this. Absent. The range in which smooth differential calculation is performed (hereinafter referred to as “smooth differential range”) can be varied as a parameter, and smooth differential calculation is performed using N number of AF evaluation values before and after using the number N specified by this parameter. It is desirable.

  In addition, a plurality of AF evaluation values are required to perform smooth differential calculation. For this reason, smooth differentiation cannot be performed immediately after the start of AF processing or at the AF evaluation value acquisition timing immediately before the driving end range of the focus lens 7-2a. Therefore, after the AF process is started, the smooth differentiation calculation process is started after waiting for the AF evaluation values for the number of times that can start the smooth differentiation calculation to be acquired. Alternatively, in order to compensate for the number of AF evaluation values necessary for the smooth differentiation calculation process, the smooth differentiation calculation process is started by estimating and interpolating using the already acquired AF evaluation values.

  Next, the relationship between the drive timing of the focus lens 7-2a and the AF evaluation value acquisition timing during AF processing will be described. The focus lens 7-2a is driven by a predetermined focus drive amount corresponding to one VD signal. For example, when the focus motor 7-2b is a pulse motor, the number of drive pulses corresponds to the focus drive amount. One focus lens drive is completed by driving the focus lens 7-2a by a predetermined number of drive pulses at a predetermined pulse rate corresponding to the falling edge of the pulse of the VD signal. Predetermined focus driving is performed again in response to the fall of the next VD signal pulse. In this way, the focus drive is synchronized with the VD signal (that is, the frame period).

  FIG. 6 is a timing chart showing the VD signal, the focus drive timing of the focus lens 7-2a, the charge sweep pulse (SUB) timing in the electronic shutter, and the exposure timing when image data is captured at a frame rate of 120 fps. . In FIG. 6, when one VD signal is generated, a pulse for driving the focus lens 7-2 a is generated a predetermined number of times as a trigger (twice in FIG. 6), and the drive amount corresponding to this drive pulse is focused. The lens 7-2a moves. Further, a charge sweep pulse is generated a predetermined number of times using the VD signal as a trigger, and the charge sweeping process of the CCD 101 is performed according to the number of SUBs. An exposure process is performed after the charge sweeping process is completed. Through exposure processing, the video of the subject is captured as image data, and an AF evaluation value is acquired using this image data. The number of drive pulses is variable and changes according to the focal length and the focus lens feed amount (focus drive range). Thus, the AF processing according to the present invention is performed within the drive range of the focus lens 7-2a in synchronization with the VD signal.

  The AF process using the smooth differentiation process will be described with reference to the flowchart of FIG. In FIG. 7, each operation step is expressed as S71, S72. Since the AF process is performed in synchronization with the VD signal as described with reference to FIG. 6, first, the process waits until the falling edge of the VD signal is detected (S71). After detecting the fall of the VD signal, the focus motor 7-2b is driven according to the predetermined number of pulses, and the focus lens 7-2a is moved (S72). After moving the focus lens 7-2a, a video signal is acquired, and an AF evaluation value is calculated from image data based on this video signal (S73). It is determined whether or not the number of AF evaluation values acquired is sufficient for smooth differentiation (whether or not the smooth differentiation range is satisfied) (S74). If the number of AF evaluation values acquired does not reach the smooth differentiation range, the process proceeds to S71. Return (NO in S74).

  If the acquired AF evaluation value has reached the smooth differential range (YES in S74), the smooth differential value is calculated using the above smooth differential calculation formula (S75). The above process is repeated until the driving range end position of the focus lens 7-2a is reached (NO in S76). When the focus lens 7-2a reaches the end position (YES in S76), the focus position detection process using the smooth differential value calculated above is performed (S77), and NG is determined based on the result of the focus position detection process. A determination process is performed (S78), the focus lens 7-2a is moved to the in-focus position set by the NG determination process, and the AF process ends (S79). Next, details of the focus position detection process (S77) and the NG determination process (S78) will be described.

  FIG. 8 is a flowchart showing a detailed process flow of the focus position detection process (S77 in FIG. 7). First, a value close to zero is searched from the calculated smooth differential value (S81). When there is no value close to zero in the smooth differential value (NO in S82), the in-focus position detection process is terminated as in-focus NG (S86). If there is a value close to zero in the smooth differential value (YES in S82), a peripheral value determination process (S83) is performed. The peripheral value determination process (S83) determines whether the smooth differential value around the smooth differential value close to zero is monotonically decreasing or increasing monotonously with respect to the smooth differential value close to zero. That is, the smooth differential value acquired before the smooth differential value close to zero is monotonically increased with respect to the smooth differential value close to zero, and the smooth differential value acquired after the smooth differential value close to zero is It is determined whether or not the smooth differential value close to zero is decreasing monotonously (S84). As a result of the determination, if it is monotonically descending and monotonically increasing (YES in S84), it is determined as in-focus OK (S85), otherwise (NO in S84), it is determined as in-focus NG (S86). The focal position detection process ends.

  FIG. 9 is a flowchart showing a detailed process flow of the NG determination process (S78 in FIG. 7). If focus is OK in the focus position detection process (S77 in FIG. 7) (YES in S91), the position of the focus lens 7-2a corresponding to the smooth differential value is determined as the focus position (S92). If it is in focus NG (No in S91), the NG position (for example, the hyperfocal distance) is determined as the focus position (S93).

  FIGS. 10 and 11 show examples of the AF evaluation value acquired in synchronization with the VD signal and the smooth differential value calculated based on the AF evaluation value in the AF processing described above. FIG. 10 is a graph showing an example of the displacement of the AF evaluation value calculated in an environment where the amount of light is different in the AF processing for the same subject. The vertical axis represents the magnitude of the AF evaluation value, and the horizontal axis The axis indicates the position of the focus lens 7-2a. FIG. 10A shows the case of LV10, and FIG. 10B shows the case of LV8. That is, FIG. 10B relates to an AF evaluation value acquired in an environment where the amount of light is smaller (darker) than in FIG. Therefore, since the luminance difference between adjacent pixels is very small, the influence of noise is large, and the AF evaluation value varies and a plurality of peak positions appear. If the peak position (maximum value) of the AF evaluation value is one as shown in FIG. 10A, it may be set as the in-focus position. However, as shown in FIG. If there is a position, it cannot be simply determined which position is the in-focus position.

  FIG. 11 is a graph showing the smooth differential value of the AF evaluation value shown in FIG. In FIG. 11, the horizontal axis indicates the position of the focus lens 7-2a as in FIG. 10, and the vertical axis indicates the magnitude of the smooth differential value. FIG. 11A shows a smooth differential value based on the displacement of the AF evaluation value shown in FIG. FIG. 11B shows a smooth differential value based on the displacement of the AF evaluation value shown in FIG. 11A and 11B, a predetermined number of AF evaluation values are acquired until the position of the focus lens 7-2a reaches “5” (until four or more smooth differential values can be acquired). If not, the smooth differential value is not calculated. The smooth differential value calculated after the predetermined number of AF evaluation values is acquired is displaced in the increasing direction as the focus lens 7-2a moves, and the sign is inverted from minus to plus at a certain point. . In FIG. 11, the smooth differential calculation is started when the position of the focus lens 7-2 a is 5, and the sign is inverted between 7 and 8. This inversion point corresponds to the maximum value of the AF evaluation value. As described above, the position where the sign of the smooth differential value calculated by the above-described arithmetic expression is inverted, that is, the position where the smooth differential value is zero is the maximum point of the AF evaluation value.

  As described above, the focus position can be identified by detecting the AF evaluation value acquisition position where the sign of the smooth differential value is inverted, and the focus lens 7-2a is moved to this focus position. Thus, AF processing can be performed.

  Next, another embodiment of an imaging method using the imaging apparatus according to the present invention will be described. Since the method for driving the focus lens 7-2a and the method for calculating the smooth differential value in this embodiment are the same as those in the first embodiment, different processing will be mainly described.

  FIG. 12 is a flowchart illustrating the flow of AF processing according to the second embodiment. Each operation step is expressed as S121, S122,. First, signal waiting processing is performed until the falling edge of the VD signal is detected (S121), the detection of the falling edge of the VD signal is used as a trigger to drive the focus motor 7-2b according to a predetermined pulse amount, and the focus lens 7- 2a is moved (S122). After moving the focus lens 7-2a, an exposure process is performed to acquire a video signal, and an AF evaluation value is calculated from image data based on the video signal (S123). It is determined whether or not the number of AF evaluation values acquired is sufficient for smooth differentiation (whether or not the smooth differentiation range is satisfied) (S124). If the number of AF evaluation values acquired does not reach the smooth differentiation range, the process proceeds to S121. Return (NO in S124).

  When a predetermined number of AF evaluation values have been acquired (YES in S124), a smooth differential value is calculated using the arithmetic expression already described (S125).

  A focus position detection process is performed based on the calculated smooth differential value, and it is determined whether or not a focus position is detected (S126). If the in-focus position is detected (YES in S126), the process proceeds to NG determination processing (S128). If the in-focus position is not detected (NO in S126), it is determined whether the focus lens has reached the drive range end position. If the focus lens has reached the end position (YES in S127), the process proceeds to NG determination processing (S128). If the focus lens has not reached the drive end position, the VD signal is waited (S121). Migrate to

  Next, the details of the in-focus position detection process (S126) and the NG determination process (S128) will be described. FIG. 13 is a flowchart showing a detailed process flow of the focus position detection process (S126 in FIG. 12). First, it is determined whether or not the calculated smooth differential value is substantially zero (S131). When the smooth differential value is not substantially zero (NO in S131), the process ends as in-focus NG (S135). If the calculated smooth differential value is substantially zero (YES in S131), a peripheral value determination process (S132) is performed. In the peripheral value determination process (S132), it is determined whether the smooth differential value around the substantially zero smooth differential value is monotonically decreasing or monotonically increasing with respect to the substantially zero smooth differential value. That is, whether or not the smooth differential value acquired before the substantially zero smooth differential value is monotonically increased with respect to the substantially zero smooth differential value, or the smooth smooth value acquired after the substantially zero smooth differential value. It is determined whether or not the differential value is monotonically decreasing with respect to the smooth differential value of substantially zero. If the result of the determination is monotonic decrease or monotonic increase (YES in S133), it is determined that the in-focus state is OK ( If the result of the determination is that there is no monotonic descent or monotonic increase (NO in S133), it is determined that the focus is NG (S135), and the focus position detection process is terminated.

  FIG. 14 is a flowchart showing a detailed process flow of the NG determination process (S128 in FIG. 12). If focus is OK in the focus position detection process (S126 in FIG. 12) (YES in S141), the position of the focus lens 7-2a corresponding to the smooth differential value is determined as the focus position (S142). If it is in focus NG (NO in S141), the NG position (for example, the hyperfocal distance) is determined as the focus position (S143).

  According to the second embodiment, since the focus position detection process is performed every time the smooth differential value is calculated, the AF process is terminated in the middle without driving the focus lens 7-2a to the lens drive end position. be able to.

  Next, still another embodiment of the imaging method using the imaging apparatus according to the present invention will be described. The present embodiment is characterized in that the smooth differentiation process is varied according to the photographing mode designated by the mode dial SW2. A description of the same parts as those in the first and second embodiments will be omitted, and different parts will be mainly described.

  First, AF processing according to the present embodiment will be described with reference to the flowchart of FIG. Each operation step is expressed as S150, S151,. First, processing for setting a smooth differential range is performed according to the current shooting mode (S150). After setting the smooth differential range, a wait process is performed until the falling edge of the VD signal is detected (S151). After detecting the fall of the VD signal, the focus motor 7-2b is driven according to the predetermined number of pulses, and the focus lens 7-2a is moved (S152). After moving the focus lens 7-2a, a video signal is acquired, and an AF evaluation value is calculated from image data based on this video signal (S153). It is determined whether or not the number of AF evaluation values acquired is sufficient for smooth differentiation (whether or not the smooth differentiation range is satisfied) (S154). If the number of AF evaluation values has not reached the smooth differentiation range, the process proceeds to S151. Return (NO in S154).

  If the acquired AF evaluation value has reached the smooth differential range (YES in S154), smooth differential calculation using the smooth differential calculation formula described in the first embodiment is performed using this smooth differential range (S155). The above processing is repeated until the driving range end position of the focus lens 7-2a is reached (NO in S156). When the focus lens 7-2a reaches the end position (YES in S156), the focus position detection process using the smooth differential value calculated above is performed (S157), and NG is determined based on the result of the focus position detection process. A determination process is performed (S158), the focus lens 7-2a is moved to the in-focus position set by the NG determination process, and the AF process ends (S159).

  As described above, in the AF process in the third embodiment, before performing the AD signal waiting process in the AF process in the first embodiment, the smooth differential range is set according to the photographing mode of the imaging apparatus, and the AF process is performed according to the set smooth differential range. It is characterized by performing smooth differential processing. Next, a detailed flow of the smooth differential parameter setting process (S150) will be described. The focus position detection process (S157) and the NG determination process (158) are the focus position detection processes ( S77) and the same process as the NG determination process (S78), and a detailed description thereof will be omitted.

  FIG. 16 is a flowchart showing a detailed process flow of the smooth differential parameter setting process (S150 in FIG. 15). First, the current shooting mode designated by the mode dial SW2 is acquired (S161). Next, it is determined whether or not the acquired shooting mode is the “normal AF mode” (S162). If the shooting mode is the normal AF mode (S162 is YES), the normal differential mode smooth differential range is set (here, the normal AF mode smooth differential range is 3). If the shooting mode is not the normal AF mode (NO in S162), since the imaging apparatus is set to the macro AF mode, a smooth differential range for the macro AF mode is set (here, the smooth differential range for the macro AF mode). Is 2). The AF process described above is performed using the smooth differential range set in this way.

  Next, the effect of changing the smooth differential range in different shooting modes as described above will be described. As already described, the focus lens 7-2a moves according to a predetermined drive amount of the focus motor 7-2b corresponding to one VD signal. Here, the focus motor 7-2b will be described as a pulse motor.

  The number of drive pulses (focus drive amount) corresponding to one VD signal is set larger in the macro AF mode than in the normal AF mode. For example, there are 2 pulses in the normal AF mode and 6 pulses in the macro AF mode. This is because, as shown in FIG. 20, the focus lens extension amount varies depending on the shooting mode. In FIG. 20, the focus lens extension amount in the normal AF mode is 30 pulses, and the focus lens extension amount in the macro AF mode is 200 pulses. Thus, since the amount of movement of the focus lens 7-2a corresponding to one VD signal is larger in the macro AF mode than in the normal AF mode, the displacement amount of the adjacent AF evaluation value is also greater. growing.

  Under such conditions, in the smooth differential calculation in the macro AF mode, if the same smooth differential range as the smooth differential calculation in the normal AF mode is set (for example, if the smooth differential range is 3), 18 pulses before and after Smooth differentiation is performed using the AF evaluation value corresponding to the minute, and the correlation between the AF evaluation values becomes too strong, and the displacement of the AF evaluation values is excessively averaged.

  This problem will be described with reference to FIGS. 18 and 19 are graphs showing the displacement (a) of the AF evaluation value acquired from the image data photographed under the same photographing conditions, and the displacement (b) of the smooth differential value using the AF evaluation value. FIG. 18 shows a case where the smooth differential range is “3”, and FIG. 19 shows a case where the smooth differential range is “2”. 18 and 19, the horizontal axis indicates the position of the focus lens 7-2a, and the vertical axis indicates the AF evaluation value (a) and the smooth differential value (b).

  When the in-focus position of the subject and the background are close, as shown in FIGS. 18A and 19A, the peak of the AF evaluation value is close. FIG. 18B shows a result obtained by performing the smooth differential calculation with the smooth differential range set to 3 in such a state. As shown in FIG. 18B, the extreme value (0 position) of the smooth differential value is detected not on the subject but on the background side. FIG. 19B is a diagram showing the result of performing the smooth differentiation operation on the same image data based on the displacement of the AF evaluation value and setting the smooth differentiation range to 2. FIG. As shown in FIG. 19B, the extreme value (0 position) of the smooth differential value can be detected for the subject.

  In the macro AF mode, as already described, since the focus drive amount is larger than that in the normal AF mode, the AF evaluation value peaks due to the subject and the background are likely to be close to each other. Therefore, as described above, by setting the smooth differential range for weakening the correlation of the AF evaluation values to 2 and setting it to be narrower than the smooth differential range in the normal AF mode, false focusing can be prevented.

  Next, still another embodiment based on Example 3 will be described. The AF processing, the driving method of the focus lens 7-2a, and the smooth differential value calculation method in the present embodiment are the same as those in the third embodiment. Here, different processes will be described.

  FIG. 17 is a flowchart showing another detailed process flow of the smooth differential parameter setting process (S70 in FIG. 15). First, the current shooting setting is acquired (S171). The shooting setting is a focal length that can be changed by SW3 and SW4. The neutral position is “mean”, the zoomed-in state is “Tele”, and the zoomed-out state is “Wide”.

  It is determined whether or not the acquired focal length is equal to or less than Mean (S172). When the focal length is equal to or less than Mean (YES in S172), the Wide-side smooth differential range is set (S173). Here, the Wide-side smooth differential range is 3. When the focal length is not less than Mean (when the focal length is long) (NO in S172), the Tele side smooth differential range is set (S174). Here, the above-described AF processing is performed using the smooth differential range set in this way, where the Tele side smooth differential range is 2.

  Next, the effect of changing the smooth differential range according to the difference in focal length will be described. As already described, the focus lens 7-2a moves in response to one VD signal by the focus motor 7-2b performing a predetermined drive. Here, the focus motor 7-2b will be described as a pulse motor.

  As shown in FIG. 21, the focus lens feed amount varies depending on the focal length, and the focal length ranges from 30 pulses to 350 pulses between the Wide side and the Tele side. The number of drive pulses (focus drive amount) corresponding to one VD signal is larger on the Tele side (longer focus than Mean) than on the Wide side (Mean or less). For example, on the Wide side, two pulses and on the Tele side 6 pulses are set.

  Thus, since the number of drive pulses is larger in the Tele side state than in the Wide side state, the amount of movement of the focus lens 7-2a corresponding to one VD signal is large. The amount of displacement of the AF evaluation value is also increased. Therefore, in the case of the Tele state, if the same smooth differential range as the state below mean is set (for example, the smooth differential range is 3) and the smooth differential operation is performed, AF evaluation values corresponding to 18 pulses before and after are obtained. The smooth differential calculation used is performed, the correlation between the AF evaluation values is too strong, the displacement of the AF evaluation value is averaged too much, and the extreme value (near 0) of the smooth differential value cannot be correctly detected, and the false match Burning occurs.

In order to prevent such false focusing, the smooth differential range is set to 2 in the Tele state where the AF evaluation value peaks of the subject and the background are close to reduce the correlation ratio between the AF evaluation values. In this embodiment, the use of the focus state by Focus feed amount as determined for varying the setting of the smooth differential range, the threshold focus movement amount, it is also possible to variably determine a smooth differential range is there.

  In addition, in both the first embodiment and the fourth embodiment, the example in which the same smooth differential calculation formula is used has been described. However, the smooth differential calculation formula is not limited to this, and other differential formulas are used. Replacement is possible. Further, in any configuration, since the vicinity of the extreme value of the AF evaluation value can be set as the in-focus position based on the result of the smooth differential calculation from the AF evaluation value, the AF evaluation value due to low luminance or low contrast can be set. A highly accurate AF process can be realized without being affected by variations.

  The present invention can also be applied to an imaging apparatus that can be mounted on a camera-equipped mobile device, an imaging method thereof, and the like.

It is a front view which shows the example of the imaging device which concerns on this invention. It is a top view which shows the example of the imaging device which concerns on this invention. It is a rear view which shows the example of the imaging device which concerns on this invention. It is a functional block diagram which shows the example of the imaging device which concerns on this invention. It is an image figure of AF processing area in the imaging device concerning the present invention. 6 is a timing chart showing AF evaluation value acquisition timing and the like of the imaging apparatus according to the present invention. 6 is a flowchart illustrating an example of AF processing performed using the imaging apparatus according to the present invention. It is a flowchart which shows the detailed process flow of the said AF process. It is a flowchart which shows the detailed process flow of the said AF process. It is a figure which shows the example of a displacement of AF evaluation value acquired in AF process of the imaging device which concerns on this invention. It is a figure which shows the example of a displacement of the smooth differential value calculated in AF process of the imaging device which concerns on this invention. It is a flowchart which shows another example of the AF process performed using the imaging device which concerns on this invention. It is a flowchart which shows the detailed process flow of the said AF process. It is a flowchart which shows the detailed process flow of the said AF process. It is a flowchart which shows another example of the AF process performed using the imaging device which concerns on this invention. It is a flowchart which shows the detailed process flow of the said AF process. It is a flowchart which shows the detailed process flow of the said AF process. It is a figure which shows the example of a displacement of AF evaluation value acquired in AF process of the imaging device which concerns on this invention, and a smooth differential value. It is a figure which shows the example of a displacement of AF evaluation value computed in AF process of the imaging device which concerns on this invention, and a smooth differential value. It is a figure which shows the relationship between the imaging | photography mode of the imaging device which concerns on this invention, and a focus lens extension amount. It is a figure which shows the relationship between the focal distance of the imaging device which concerns on this invention, and a focus lens extension amount.

Explanation of symbols

7-2a Focus lens 7-2b Focus motor 108 ROM

Claims (24)

An imaging device for receiving light of a subject having passed through the photographing lens, said lens moving means for moving the photographing lens, smooth differential operation using the AF evaluation value calculated by using the image data obtained from the shooting image element Automatic focus detection means for determining the focus by :
In an imaging apparatus having a shooting condition setting unit capable of selecting a plurality of shooting conditions including at least a normal shooting mode for shooting a general subject and a macro mode for shooting a close subject ,
The automatic focus detection means determines the total range of the AF evaluation values to be calculated by the smooth differential calculation according to the shooting conditions set by the shooting condition setting means,
When the set shooting condition is set to the macro mode, the total range of the AF evaluation values to be calculated by the smooth differential calculation is narrower than when the normal shooting mode is set. setting an imaging apparatus characterized that you.   By an image sensor that receives light of a subject that has passed through the photographic lens, a lens moving unit that moves the photographic lens, and a smooth differential operation using an AF evaluation value that is calculated using image data obtained from the image sensor. In an imaging apparatus having automatic focus detection means for determining a focus,
  The automatic focus detection means determines the total range of the AF evaluation values to be calculated by the smooth differential calculation according to the focal length of the photographing lens,
  An image pickup apparatus characterized in that when the focal length is on the tele side, the total range of the AF evaluation values to be subjected to the smooth differential calculation is set narrower than when the focal length is on the wide side.   By an image sensor that receives light of a subject that has passed through the photographic lens, a lens moving unit that moves the photographic lens, and a smooth differential operation using an AF evaluation value that is calculated using image data obtained from the image sensor. In an imaging apparatus having automatic focus detection means for determining a focus,
  The automatic focus detection means determines a total range of the AF evaluation values to be calculated by the smooth differential calculation according to a moving step amount of the photographing lens that varies according to photographing conditions,
  The total range of the AF evaluation values to be calculated in the smooth differential calculation determined according to the first movement step amount is determined according to a second movement step amount smaller than the first movement step amount. An imaging apparatus characterized by being narrower than a total range of the AF evaluation values to be calculated by the smooth differential calculation. The imaging apparatus according to claim 1, wherein the AF evaluation value is a value obtained by integrating a luminance difference between adjacent pixels constituting the image data. The imaging apparatus according to claim 1, wherein the smooth differential calculation is an operation of totaling a value obtained by multiplying a displacement amount of the AF evaluation value by a predetermined coefficient.   The imaging apparatus according to claim 1, wherein a coefficient used for the smooth differential calculation increases in accordance with a degree of deviation from the AF evaluation value at the time of obtaining a smooth differential value.   The imaging apparatus according to claim 1, wherein the smooth differential operation is to obtain a smooth differential value by the following equation.
  Y [0] = Σ [i = 0 → a] (X [i] −X [−i]) × bi
  However, Y [0] is a smooth differential value, i is a positive number, a is a total range, X [i] is an AF evaluation value, and bi is a weighting coefficient that increases in accordance with the degree of deviation from the AF evaluation value. The automatic focus detection means focuses the photographing lens position at the time of obtaining the AF evaluation value when the focal position determined by the smooth differential operation of the AF evaluation value is within the driving range of the photographing lens. The imaging apparatus according to claim 1 , wherein the imaging apparatus is determined as a position . The imaging apparatus according to claim 1, wherein the automatic focus detection unit performs a smooth differential calculation after obtaining an AF evaluation value within the photographing lens driving range, and determines a focus position. . The image pickup apparatus according to claim 1, wherein the automatic focus detection unit performs a smooth differential calculation while moving within the photographing lens driving range to determine a focus position . The automatic focus detecting means, if it can not determine the focal position within the driving range of the photographing lens, in any one of claims 1 to 8, characterized in that a focal position hyperfocal position of the photographing lens The imaging device described. The automatic focus detecting means, the imaging apparatus according to any one of claims 1 to 11, characterized in that moving the photographing lens to the focal position where the automatic focus detection means has determined.   By an image sensor that receives light of a subject that has passed through the photographic lens, a lens moving unit that moves the photographic lens, and a smooth differential operation using an AF evaluation value that is calculated using image data obtained from the image sensor. Automatic focus detection means for determining a focus, and shooting condition setting means capable of selecting a plurality of shooting conditions including at least a normal shooting mode for shooting a general subject and a macro mode for shooting a close subject. In the imaging method executed by the imaging device,
  The automatic focus detection means is
  Determining a total range of the AF evaluation values to be calculated by the smooth differential calculation according to the shooting conditions set by the shooting condition setting means;
When the set shooting condition is a macro mode, a step of setting a narrower total range of the AF evaluation values to be calculated by the smooth differential calculation than when the normal shooting mode is set; The imaging method characterized by performing these.   By an image sensor that receives light of a subject that has passed through the photographic lens, a lens moving unit that moves the photographic lens, and a smooth differential operation using an AF evaluation value that is calculated using image data obtained from the image sensor. In an imaging method executed by an imaging apparatus having automatic focus detection means for determining a focus,
  The automatic focus detection means is
  Determining a total range of the AF evaluation values to be calculated by the smooth differential calculation according to a focal length of the photographing lens;
  When the focal length is on the tele side, the step of setting a narrower total range of the AF evaluation values that are subject to the smooth differential calculation than when the focal length is on the wide side is performed. A characteristic imaging method.   By an image sensor that receives light of a subject that has passed through the photographic lens, a lens moving unit that moves the photographic lens, and a smooth differential operation using an AF evaluation value that is calculated using image data obtained from the image sensor. In an imaging method executed by an imaging apparatus having automatic focus detection means for determining a focus,
  The automatic focus detection means is
  Determining a total range of the AF evaluation values to be subjected to the smooth differential calculation according to a moving step amount of the photographing lens that varies according to photographing conditions;
  A total range of the AF evaluation values to be calculated in the smooth differential calculation determined according to the first movement step amount is determined according to a second movement step amount smaller than the first movement step amount. And a step of setting the AF evaluation value to be narrower than a total range of the AF evaluation values to be calculated by the smooth differential calculation. The imaging method according to any one of claims 13 to 15, wherein the AF evaluation value is a value obtained by integrating a luminance difference between adjacent pixels constituting the image data. The imaging method according to any one of claims 13 to 15, wherein the smooth differential operation is an operation of totaling a value obtained by multiplying a displacement amount of the AF evaluation value by a predetermined coefficient.   18. The imaging method according to claim 13, wherein a coefficient used for the smooth differential calculation is increased according to a degree of deviation from the AF evaluation value at the time of obtaining a smooth differential value.   The imaging method according to claim 13, wherein the smooth differential operation is to obtain a smooth differential value by the following equation.
  Y [0] = Σ [i = 0 → a] (X [i] −X [−i]) × bi
  However, Y [0] is a smooth differential value, i is a positive number, a is a total range, X [i] is an AF evaluation value, and bi is a weighting coefficient that increases in accordance with the degree of deviation from the AF evaluation value.   When the focus position determined by the result of smooth differential calculation of the AF evaluation value is within the driving range of the shooting lens, the automatic focus detection means determines the shooting lens position when the AF evaluation value is acquired as the focus position. The imaging method according to claim 13, wherein the imaging method is determined as follows.   21. The method according to claim 13, further comprising: a step of determining a focal position by performing a smooth differential calculation after the automatic focus detection unit acquires an AF evaluation value within the photographing lens driving range. Imaging method.   The imaging according to any one of claims 13 to 21, further comprising a step in which the automatic focus detection means performs a smooth differential calculation while the photographic lens is moving within a driving range to determine a focal position. Method.   23. The method according to claim 13, further comprising a step of setting the hyperfocal position of the photographing lens as the focal position when the automatic focus detection unit cannot determine the focal position within the moving range of the photographing lens. The imaging method described in 1.   24. The imaging method according to claim 13, further comprising a step of moving the photographic lens to the focal position determined by the automatic focus detection unit.

Images