JP2017009769A - Imaging device, focus control device and imaging method - Google Patents

Abstract

It takes time to focus a focus lens on a dark place where a peak of a contrast signal level is difficult to detect or a subject with a uniform color. A driving unit that drives a focus lens, an imaging unit that captures an optical image formed through the focus lens and outputs an imaging signal, and a subject of the subject when the captured subject is in focus When it is determined that the subject information associated with the distance and the first feature amount in the imaging region is stored for each zoom lens magnification and the subject being photographed cannot be focused, The second feature amount in the imaging area being acquired is obtained, and the similarity between the first feature amount and the second feature amount of the subject information at the magnification of the subject information is obtained. A control unit that selects subject information having the first characteristic amount that is the maximum, and the driving unit is configured to make the subject in a focused state based on the subject distance of the selected subject information. Four It is characterized by moving the slack lens. [Selection] Figure 13

Description

  The present invention relates to a focus control apparatus, an imaging apparatus, and a focus control method that perform autofocus control on a subject.

  Conventionally, many imaging apparatuses with a video recorder such as a surveillance camera and a DVD (Digital Versatile Disc) camera are equipped with an AF (Auto Focus) function for automatically adjusting the focus of a lens. As a focusing method in such an AF function, there is a contrast method in which the focus is adjusted by assuming that the position where the amplitude of the contrast signal of the captured image is the maximum value is the in-focus state.

  In the imaging apparatus, the captured image is brought into an out-of-focus state or in-focus state by moving the focus lens in the optical axis direction, and the amplitude of the contrast signal also changes accordingly. Therefore, in the basic contrast method, the focus lens is moved in the optical axis direction, the focus direction is detected based on the amplitude of the contrast signal before and after the movement, and the focus lens is moved in that direction. I'm singing. In the following description, the control for focusing the focus lens according to the AF function is referred to as “AF control”. A state in which the focus lens is moved by AF control or processing is performed to execute the AF function is referred to as “AF operation”. On the other hand, the state in which the AF function is being executed but the movement of the focus lens is stopped is called “AF standby”.

  By the way, the contrast strength to be noticed in this contrast method depends on the subject. Here, with reference to FIG. 15 and FIG. 15, a state when imaging a low-contrast subject will be described.

  FIG. 15 shows an example of a subject that is imaged in the imaging region by a conventional imaging device at night. This imaging area is substantially the same as the size of the output screen of the display device connected to the imaging device.

  FIG. 16 shows a contrast signal detected when the imaging apparatus images the low contrast subject 102.

  The conventional imaging apparatus detects the contrast signal of the low-contrast subject 102 (for example, a tower type building) inside the detection area 101 near the center of the imaging area 100. However, since the low-contrast subject 102 itself is dark and the background is black at night, the contour of the low-contrast subject 102 blends into the background.

  As shown in FIG. 16, the shape of the contrast signal level representing the degree of sharpness of the low-contrast subject 102 is gentle, and the in-focus point at which the peak of the contrast signal level is obtained even when the imaging device moves the focus lens in the optical axis direction. Hard to find. For this reason, the focus lens may cause hunting, or AF may stop without focusing.

  For this reason, in a surveillance camera using a contrast method for the AF function, it is difficult to focus on a building wall or sky with uniform colors, especially in a dark place as shown in FIG. Problems such as the infocus cannot be found are likely to occur. Therefore, when photographing a low-contrast subject, there has been a demand to suppress hunting and to quickly move the focus lens to near the in-focus point.

Japanese Patent Laid-Open No. 11-38309

  In Patent Document 1, when the subject currently being photographed can be measured, the current photographing is used as the past in-focus position for calculating the photographing distance mode value used in the subsequent AF operation. A predetermined number of distances to the subject being photographed are stored in a non-volatile memory for each magnification. If the subject currently being photographed cannot be measured, the mode of the shooting distance corresponding to the magnification is obtained from the average value of the distance to the stored subject and focused on the distance of the average value. Move the focus lens.

  In such a control method, in an environment where subjects with significantly different position information are photographed even at the same magnification, the focus distance mode is the average value, so the focus lens may stop at a position far from the focal point. Think enough. That is, the distance to be focused and the distance of the reference value are likely to deviate. In order to prevent this difference in value, it is necessary to focus using information correlated with the current subject rather than the recorded subject information.

  The present invention has been made in consideration of the above points, and an object thereof is to perform appropriate focus control on a low-contrast subject.

  In order to solve the above problems, the present invention provides a driving unit that drives a focus lens, an imaging unit that captures an optical image formed through the focus lens and outputs an imaging signal, and the captured subject is in focus. A storage unit that stores subject information associated with the subject distance of the subject and the first feature amount in the imaging region for each magnification of the zoom lens, and the subject being photographed cannot be focused. If it is determined, the second feature amount in the imaging region being photographed is acquired, and the first feature amount and the second feature amount of the subject information at the photographing magnification among the subject information are obtained. A control unit that obtains similarity and selects subject information having the first feature amount that maximizes the similarity, and the driving unit determines whether the subject is based on the subject distance included in the selected subject information. In focus The focus lens is moved so as to be in a state.

  According to the present invention, appropriate focus control can be performed on a low-contrast subject.

  Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

1 is a block diagram illustrating an overall configuration of an imaging apparatus according to an embodiment of the present invention. It is explanatory drawing which shows an example of the detection area | region in the imaging area which concerns on the example of 1 embodiment of this invention. It is explanatory drawing which shows an example of the 2nd detection area | region which concerns on the example of 1 embodiment of this invention. The state in which the subject is in focus is illustrated. FIG. 4A illustrates the time when the subject in FIG. 4A is in a defocused state. The example of the contrast signal level in a detection area | region is shown. The example of the to-be-photographed object in an imaging region is shown. The example of the contrast signal level in a detection area | region is shown. An example of the second detection region is shown. An example of a low-contrast subject in the imaging area is shown. The example of the contrast signal level in a detection area | region is shown. An example of the second detection region is shown. An example of a preliminary contrast subject in the imaging area is shown. The example of the contrast signal level in a detection area | region is shown. An example of the second detection region is shown. It is explanatory drawing which shows the 1st-3rd priority provided to the to-be-photographed object classified by the control part which concerns on the example of 1 embodiment of this invention. It is explanatory drawing which shows the structural example of the primary object information storage area | region which the memory which concerns on the example of 1 embodiment of this invention has, a to-be-photographed object information storage area, a distance information table, and each threshold value. It is explanatory drawing which shows the structural example of the to-be-photographed object information table which concerns on the example of 1 embodiment of this invention. It is explanatory drawing which shows the relationship between the 3rd threshold value referred in order that the control part which concerns on one embodiment of this invention stores the subject information stored in a subject information storage area, and a 4th threshold value. It is a 1st flowchart which shows the process example of AF operation | movement which the imaging device which concerns on one embodiment of this invention performs. It is a 2nd flowchart which shows the process example of AF operation | movement which the imaging device which concerns on one embodiment of this invention performs. It is a 3rd flowchart which shows the process example of AF operation | movement which the imaging device which concerns on one embodiment of this invention performs. It is explanatory drawing which shows the example of the to-be-photographed object which the conventional imaging device images in an imaging area at night. It is explanatory drawing which shows the contrast signal detected when the conventional imaging device imaged the low contrast subject.

  Hereinafter, an imaging device and a focus control device according to an embodiment of the present invention will be described with reference to the accompanying drawings.

  In the present specification and drawings, components having substantially the same function or configuration are denoted by the same reference numerals, and redundant description is omitted.

[(1) Configuration of Imaging Device According to this Embodiment]
FIG. 1 is a block diagram illustrating an overall configuration of an imaging apparatus 1 according to the present embodiment.

  The imaging device 1 includes a lens unit 2, an imaging device 8, a noise removal circuit 9, an automatic gain control circuit (AGC) 10, an analog / digital conversion circuit (A / D) 11, and an autofocus control device 12. . In addition, the imaging apparatus 1 includes motor driver circuits 41 to 43 and an electronic shutter 47. The imaging device 1 is used as, for example, a monitoring camera, but may be used as a personal camera or may be used in a portable terminal. In FIG. 1, the automatic gain control circuit 10 is described as AGC, and the analog / digital conversion circuit 11 is described as A / D.

  The lens unit 2 includes a variator lens group 3 that adjusts the zoom magnification by changing the magnification of the light beam received from the subject, a stop 4 for adjusting the amount of received light, and a focus lens group 5 that has a focus adjustment function (of the focus lens). An example). The lens unit 2 forms an optical image of a subject on a light receiving surface of an image sensor 8 formed using a CCD (Charge Coupled Device) or the like.

  In addition, the lens unit 2 includes a lens origin detector 6 and a temperature detector 7 that are composed of, for example, a photo interrupter. The lens origin detector 6 detects the absolute position (reference position) of the variator lens group 3 and the focus lens group 5 and uses the detection result as lens absolute position information to communicate with the control unit 30 or the imaging apparatus 1. Send to. In the following description, the position where the focus lens group 5 has moved relative to the absolute positions of the variator lens group 3 and the focus lens group 5 detected by the lens origin detector 6 is referred to as a “focus lens position”. The position of the focus lens group 5 focused on the subject is referred to as a “focus position”.

  The temperature detector 7 detects the temperature in the lens unit 2 and transmits the detection result as temperature information in the lens unit to the control unit 30 mounted on the imaging device 1 or an external system that can communicate with the imaging device 1. To do. The external system is configured by a control computer, for example, and can receive lens absolute position information or lens unit internal temperature information via the control unit 30.

  Further, the lens unit 2 includes motors 44 to 46 that drive the variator lens group 3, the diaphragm 4, and the focus lens group 5, respectively. The motors 44 to 46 are driven by motor control signals input from the motor driver circuits 41 to 43, respectively.

  The imaging device 8 (an example of an imaging unit) captures an optical image of a subject imaged in an imaging region on the light receiving surface through the focus lens group 5, photoelectrically converts the optical image, and obtains an electrical signal (imaging) Signal) is output to the noise removal circuit 9. The image pickup signal is subjected to a predetermined noise removal process in the noise removal circuit 9 and amplified to an optimum level in the automatic gain control circuit 10. The imaging signal is digitally converted by the analog / digital conversion circuit 11 and then output to the camera signal processing unit 13 as a digital imaging signal.

  The autofocus control device 12 includes a camera signal processing unit 13 and a control unit 30.

  The camera signal processing unit 13 includes a signal conversion processing circuit 14, a contrast signal generation unit 15, an AE (Auto Exposure) signal generation circuit 18, a subject information signal generation circuit 19, and an AG (Auto Gain) signal generation circuit 20.

  The signal conversion processing circuit 14 performs predetermined signal processing on the digital imaging signal input from the analog / digital conversion circuit 11. At this time, the signal conversion processing circuit 14 converts the digital imaging signal into a standard television signal conforming to a television system such as the NTSC (National Television Standards Committee) standard or the PAL (Phase Alternating Line) standard. Output to the outside. For example, the signal conversion processing circuit 14 transmits the television signal to an external system that communicates with the imaging device 1 via a network. In the external system, an image based on the television signal is displayed on the screen of the display device.

  Further, the camera signal processing unit 13 includes a contrast signal generation unit 15 (an example of a signal generation unit) including an HPF (High Pass Filter) circuit 16 and an integrator 17. The HPF circuit 16 can freely change the value of the cutoff frequency. Then, the HPF circuit 16 generates a signal higher than an arbitrary cutoff frequency and outputs the signal to the integrator 17. The integrator 17 sends a contrast signal VF obtained by integrating the signal input from the HPF circuit 16 to the control unit 30. Note that the contrast signal generation unit 15 including the HPF circuit 16 and the integrator 17 can acquire a value from an area of an arbitrary television signal. Each combination of the HPF circuit 16 and the integrator 17 is provided corresponding to each second detection region (an example of a plurality of detection regions) set in the imaging region of the imaging device 8 as shown in FIG. Also good.

  Here, with reference to FIG. 2 and FIG. 3, the detection area | region where the contrast signal generation part 15 produces | generates a contrast signal is demonstrated.

  FIG. 2 shows an example of the first detection area in the imaging area according to the present embodiment.

  The television signal output from the imaging device 1 is displayed on the output screen of the display device of the external system. An image captured in the imaging area 50 is displayed on the output screen. Near the center of the imaging region 50, a first detection region 51 having a rectangular frame is provided. The contrast signal generation unit 15 detects the contrast of the subject in the first detection area 51 and generates a contrast signal.

  FIG. 3 shows an example of the second detection area in the imaging area according to the present embodiment.

  For the nine second detection areas 52a to 52i (an example of a plurality of detection areas) set in the imaging area 50, the contrast signal generation unit 15 generates a contrast signal from the imaging signals corresponding to the respective detection areas. . And the control part 30 calculates | requires a contrast signal level for every 2nd detection area | region 52a-52i. As will be described later, the control unit 30 determines whether or not the subject is a low-contrast subject, and assigns a predetermined priority to the priority information of the subject. Used for. Then, the control unit 30 stores the subject information in the memory 32 according to the priority set in the subject information.

  Returning to the description of the configuration and operation of the imaging apparatus 1 in FIG.

  The contrast signal generator 15 uses the HPF circuit 16 to extract high-frequency components of the luminance signal in the first detection region 51 from the television signal (captured image) generated by the signal conversion processing circuit 14. The high-frequency component of the luminance signal in a certain detection region is, for example, the luminance signal (luminance value) output by a certain pixel in the detection region and the luminance signal output by an adjacent pixel or a pixel separated by a predetermined number of pixels. Extracted by taking the difference. This extraction process is performed for all pixels in the first detection region 51. Then, the camera signal processing unit 13 integrates the extracted high-frequency components of the luminance signals of all the pixels in the first detection region 51 by the integrator 17 to generate a contrast signal VF and send it to the control unit 30. To do.

  Based on the input television signal, the AE signal generation circuit 18 generates an auto iris signal AE having a signal level corresponding to the brightness of the current photographed image, the degree of opening of the aperture 4 of the lens unit 2, the gain of automatic gain control, and the like. It is generated and sent to the control unit 30.

  The subject information signal generation circuit 19 extracts a color signal or the like from the entire input television signal or an arbitrary region, and sends the subject information to the control unit 30. The subject information includes, for example, a subject contrast value, a color signal, a subject distance, and a luminance signal.

  The AG signal generation circuit 20 generates an AG signal for controlling the gain of the automatic gain control circuit 10 based on the input television signal, and sends it to the control unit 30.

  The control unit 30 includes information processing resources such as a CPU (Central Processing Unit) 31 that controls each unit of the imaging apparatus 1 and a nonvolatile memory 32 (an example of a storage unit). The memory 32 stores a program for realizing the functions according to the present embodiment, parameters used for the program, data generated by executing the program, and the like. For example, the memory 32 stores an auto iris data processing program (AEP) 33 and an autofocus data processing program (AFP) 34. The memory 32 stores each data shown in FIG. 9 described later. And the process which the control part 30 performs is implement | achieved when CPU31 reads a program, a parameter, data, etc. from the memory 32, and performs a predetermined process.

  Further, the control unit 30 receives a control command or the like from an external system connected via a communication interface (not shown). The memory 32 also has a function as a buffer memory that temporarily stores image data of captured images in units of frames. A buffer memory may be provided separately from the memory 32. The memory 32 may be provided outside the imaging device 1 and the focus control device 12.

  The control unit 30 calls the auto iris data processing program 33 from the memory 32, and obtains the brightness of the current captured video by the auto iris signal AE generated by the AE signal generation circuit 18. At the same time, the control unit 30 calls the autofocus data processing program 34 from the memory 32, and calculates an auto iris evaluation value that is an evaluation value for the degree of opening of the aperture 4, the gain of automatic gain control, and the like by the auto iris signal AE. In addition, the control unit 30 acquires an autofocus evaluation value that is a value of the contrast signal VF generated by the contrast signal generation unit 15.

  In addition, the control unit 30 instructs the contrast signal generation unit 15 to set the second detection regions 52 a to 52 i in the imaging region 50. Further, the control unit 30 adds the subject distance when the focus lens group 5 corresponding to the focus position is in focus to the subject information input from the subject information signal generation circuit 19 and stores the subject information in the memory 32. Run. Details of this processing will be described later.

  Then, the control unit 30 controls the drive unit based on the subject information read from the memory 32 to bring the focus lens group 5 into a focused state. For this purpose, the control unit 30 generates first and second motor control signals for controlling driving of the variator lens group 3 and the diaphragm 4 and outputs them to the motor driver circuits 41 and 42, respectively. The first and second motor control signals include an auto iris evaluation value, zoom magnification information indicating the current zoom magnification obtained based on lens absolute position information, lens unit temperature information, and trace curve data stored in the memory 32. And is generated based on The driving of the variator lens group 3 and the diaphragm 4 can be controlled using a known technique.

  The motor driver circuit 41 drives and controls a motor 44 that moves the variator lens group 3 of the lens unit 2 in the optical axis direction based on the input first motor control signal. The motor driver circuit 42 drives and controls the motor 45 that drives the diaphragm of the lens unit 2 based on the input second motor control signal. In this way, auto iris control is performed. When generating the first and second motor control signals, the accuracy of auto iris control can be improved by using the lens unit temperature information.

  Further, the control unit 30 controls the shutter speed of the electronic shutter 47 based on the auto iris evaluation value, thereby adjusting the light amount of the optical image of the subject formed on the light receiving surface of the image sensor 8. Further, the control unit 30 performs gain adjustment in the automatic gain control circuit 10 based on the auto iris evaluation value.

  Further, the control unit 30 detects the in-focus direction and the in-focus position based on the autofocus evaluation value, generates a third motor control signal, and sends this to the motor driver circuit 43 (an example of the drive unit). . The motor driver circuit 43 drives and controls a motor 46 (an example of a drive unit) that moves the focus lens group 5 of the lens unit 2 in the optical axis direction based on the third motor control signal. As described above, the motor driver circuit 43 and the motor 46 perform autofocus control for driving the focus lens group 5 in order to obtain an in-focus state with respect to the subject, and the subject can be focused during photographing. As these motors 44 to 46, for example, stepping motors are used.

[(2) AF Method for Low Contrast Subject Using Subject Information in Memory 32]
In conventional monitoring applications, many image pickup apparatuses can perform panning, tilting, and zoom operations. However, in most image pickup apparatuses, shooting conditions and types of subjects to be shot are determined. Therefore, the imaging apparatus can estimate the monitoring target based on the brightness around the object, the brightness of the object itself, the color, the contrast value, and the magnification.

  In utilizing the present invention, information advantageous for focusing on a low-contrast subject is stored in the memory 32 in advance. In the present invention, this subject information is used to focus on a subject that is originally considered to be in focus.

  In the description of the present invention, after a plurality of AF operations, the control unit 30 stores subject information up to a predetermined limit number in the memory 32 (subject information table shown in FIG. The process of selecting only subject information useful at the time of shooting and storing it in the memory 32 is called “optimization”.

<When the subject is determined to be a low-contrast subject during AF operation>
According to the AF operation of the present invention, when the subject being photographed is determined to be a low-contrast subject when focusing is performed based on the contrast AF operation, it is impossible to focus on a general contrast AF operation. The AF operation is suitable when it is determined, or when it is determined that ranging is impossible. Note that the method for determining that the subject being photographed during the AF operation is a low-contrast subject is, for example, a method in which the inclination of the contrast signal VF is equal to or less than a threshold value after the focus lens group 5 is moved more than a certain amount. .

  Hereinafter, the AF operation of the present invention will be described. When it is determined that the subject currently being photographed is a low-contrast subject, the control unit 30 performs subject focusing processing using the method according to the present invention.

  First, the control unit 30 selects subject information that is most similar to the subject that is currently photographed from a subject information table that stores subject information at the time of focusing in the past. Note that the subject information to be stored is not limited to subject information at the time of focusing in the past, and a value input and set in advance by a user or the like may be used. In the following description, a case in which subject information at the time of focusing in the past is stored will be described.

  First, the control unit 30 refers to the distance information table from the position of the variator lens group 3 and acquires the current magnification of the camera. Next, past subject information (OI_x) linked to the same magnification as the obtained magnification is selected as subject information (pI) from the subject information table.

  Then, the control unit 30 compares the color signal value from the subject information (pI) with the color signal value of the subject currently being photographed. In addition to the color information stored as the subject information, it may be a feature value such as a luminance signal value itself, which is the degree of tourism of the sensor, a motion vector, brightness, texture, and the like. Hereinafter, a case where a color signal value is used as an example of the feature amount will be described as an example.

  The processing for comparing the color signal values is as follows. First, subject information of the subject currently being photographed is acquired from the first detection region shown in FIG. Next, a color signal value is extracted from the acquired subject information, and a distance (d_I) on the data with the color signal value of the subject information (pI) is calculated using Equation (1).

  If the color of the output video is close, it is obvious that the size of the output color signal value is close. The fact that the magnitudes of the color signal values are close indicates that the distance in the data space between the color signal values to be compared is close. That is, it is possible to calculate the closeness of the color of the video, that is, the similarity of the color signal values, using an expression for obtaining a spatial distance such as Expression (1).

R ₀ , G ₀ , and B ₀ represent color signals of the subject currently being photographed, and Rn, Gn, and Bm represent color signals at the current camera magnification stored in the subject information table.

  Here, since the subject information (pI) in this embodiment detects the color signal in the size of the detection areas of the second detection areas 52a to 52i as shown in FIG. 2, the subject detection area of FIG. The size of the detection area currently being photographed is different. Therefore, the comparison by the absolute value causes the wrong object information to be selected, so that the color signal value is recalculated to a normalized value according to the size of each detection area in order to cancel the size difference. Is used to calculate the distance (d_I) on the data.

  Normalization is performed by, for example, integrating the color signal value for each color for each detection region from which a contrast signal or color signal is acquired, to determine the number of pixels for each detection region and the degree of sensitivity of the color signal obtained for each pixel. It is the value divided by the value obtained by multiplying the gradation. That is, assuming that the gradation at the time of obtaining the color signal value is S, the number of pixels for each detection region is P, and the value obtained by integrating the respective color signals is C_Value, each normalized color signal value (OC_Value) is Equation (2) is obtained.

  However, each color such as R (red), B (blue), and G (green) is entered in C.

  Then, the control unit 30 selects subject information (pI_m) that minimizes the distance (d_I) on the obtained subject information data from the subject information (pI). Then, subject distance information associated with the selected subject information (pI_m) is extracted. After that, the control unit 30 refers to the current position and distance information table of the variator lens group 3 and moves the focus lens group 5 to a position where the distance of the extracted subject distance information is in focus, thus completing the AF operation. Let

  Here, a process when there are a plurality of pieces of subject information having the smallest distance (d_I) on the data in the subject information (pI) will be described. In other words, a situation where the distance (d_I) on the data is minimized may occur when a plurality of pieces of information that are close in color to the subject currently being photographed are stored. In this case, since the imaging device often shoots the same subject, the in-focus position of the imaging device that has stopped the current AF operation can be close to the in-focus position for the subject being shot. It is thought that there is sex.

  Based on the above idea, when the subject information (pI_m) of the subject information that minimizes the data distance (d_I) is selected from the subject information (pI), and as a result, a plurality of subject information (pI_m) is selected. Then, the distance information table is referred from the current positions of the variator lens group 3 and the focus lens group 5 to calculate the currently focused subject distance. Thereafter, a difference between the calculated subject distance and the subject distance information associated with each of the subject information (pI_m) is obtained. Next, it is selected as information that refers to subject information (pI_m2) associated with subject distance information that is the smallest difference among the obtained differences.

  Thereafter, by referring to the current position and distance information table of the variator lens group 3, the focus lens group 5 is moved to a position where the distance of the extracted subject distance information is in focus, and the AF operation is terminated.

  Here, when there are a plurality of pieces of subject information that minimize the difference between the subject distance and the subject distance information associated with each of the subject information (pI_m), a plurality of pieces of subject information (pI_m2) are selected. It becomes. In this case, the most recent subject information in the subject information (pI_m2) is selected as information that is referred to, and the focus lens group 5 is moved to a position that focuses on the distance of the extracted subject distance information described above to perform the AF operation. Terminate.

  With these operations, the control unit 30 can use the optimized subject information table to focus on a low-contrast subject more accurately and quickly than the AF operation based on the contrast method.

  A specific example of the above algorithm will be described with reference to FIG.

  Further, it is assumed that subject information of the subject as shown in FIG. 6A is stored in the subject information table in this example as shown in FIG. As shown in FIG. 6A, the subject 54 is, for example, a tower-type building against the background of the daytime sky. In the first detection area 51, the sky and the building have colors and brightness. There is a difference. The subject can be focused by contrast AF. After the AF operation, the subject's magnification, the focusing distance, and the color signal value of the background sky feature amount, which is a low-contrast portion in the image, are stored as subject information in the subject by the subject information acquisition method described later. The Rukoto. For example, in the subject information table of FIG. 10, the above-described feature amount corresponds to a magnification of n and a number of 5. That is, in the subject information of the subject in the example, the information indicating the distance to the subject when focused (subject distance information) is D20, and the red, green, and blue signal values (color signal values (R ), Color signal value (G), and color signal value (B)) are R20, G20, and B20, respectively. Although details of priority information will be described later, this subject records information with a priority of 2.

  FIG. 4A shows a state where the camera is moved slightly to the left in the horizontal direction while being n times as large as the subject of FIG. 6 and the first detection area 51 at the center is imaged in the sky. Yes. FIG. 4B is an image in a state where the focus lens group 5 is moved and shifted from the in-focus position, that is, out of focus, when FIG. 4A is photographed. In the AF operation based on the contrast method, it is difficult to bring the in-focus state as shown in FIG. 4A from the out-of-focus state shown in FIG. In the case of the same color and brightness as in the sky, the shape of the contrast signal level is gentle as in the graph of FIG. 4C, and the imaging device moves the focus lens in the optical axis direction. This is because it is difficult to find the focal point at which the contrast signal level peaks.

  Here, a case will be described in which the present invention is used to focus with AF from a state in which a low-contrast subject is out of focus as shown in FIG.

  After receiving the AF start signal, the control unit 30 performs an AF operation based on the contrast method to drive the fixed distance focus lens group 5. At this time, even if the focus lens group 5 is moved, the contrast signal level is hardly changed, so that the subject currently photographed is determined to have low contrast. Then, AF based on the contrast method is stopped, and AF processing based on the present invention is executed.

  In the AF processing according to the present invention, first, color signal values (red = Rb, green = Gb, blue = Bb) are acquired from the first detection region 51 in FIG. The acquired color signal value is normalized by the above equation (2).

  Next, since the magnification of the current camera is n times, subject information associated with n times is extracted from the subject information table. Thereafter, the normalized color signal value and the color signal value of the subject information extracted based on the magnification are respectively compared using the formula (1), and selected as information for referring to the subject information having the smallest feature amount distance. To do.

  At this time, FIG. 4B is considered to be substantially the same color as the sky of FIG. 4A described above. Therefore, the acquired color signal values (Rb, Gb, Bb) substantially match the color signal values (R20, G20, B20) of the subject information in FIG. As a result, the subject information having the magnification n and number 5 is finally selected as reference information in the above processing.

  Then, D20 which is subject distance information linked to the selected magnification n and number 5 is extracted, and finally the focus lens group 5 is moved so as to focus on this distance (D20). Get focused on the sky.

  As described above, even if the subject is a low-contrast subject, the information obtained by estimating the current subject by comparing the information of the subject currently photographed and the subject focused on in the past from the feature amount. Thus, the camera can be brought into focus.

[(3) Method for optimizing subject information in the memory 32]
Hereinafter, a method for optimizing subject information in the memory 32 in performing the above-described AF operation will be described. By optimizing the subject information to be recorded by the following method, the effect of the present invention can be further exerted.

  As described above, the imaging apparatus can estimate the monitoring target based on the brightness around the object, the brightness of the object itself, the contrast value, and the magnification.

  In a subject information storage area shown in FIG. 9 described later, a plurality of past focusing histories are stored as subject information for each magnification. In this subject information storage area, information on a subject considered to have a high possibility of being in focus and considered to have low contrast is preferentially stored. This refers to subject information including past in-focus history when the imaging apparatus 1 focuses on a low-contrast subject that cannot be measured, when focusing on a low-contrast subject that can be measured. This is because it is preferable.

  For this reason, the control unit 30 divides the subject into the first low-contrast subject, the second low-contrast subject, and the preliminary subject using information obtained from the imaging signal at the time of focusing, and further, according to the type of subject, the priority order Add. Then, the control unit 30 stores the subject information in the subject information storage area according to the priority order.

  Here, the first low-contrast subject, the second low-contrast subject, and the preliminary contrast subject used in the present embodiment will be described with reference to FIGS. Each of the subjects shown in FIGS. 5 to 7 is taken by the imaging device 1 in the daytime.

  FIG. 5 shows an example of a first low-contrast subject. 5A shows an example of the subject 53, FIG. 5B shows an example of the contrast signal level in the first detection area 51, and FIG. 5C shows examples of the second detection areas 52a to 52i. The description of FIG. 5C will be described later.

  A subject 53 in the imaging region 50 shown in FIG. 5A is, for example, a wall surface of a building provided with a large number of windows, and changes in color and brightness in the first detection region 51 indicated by the contrast signal detection frame. It is a scarce subject. As shown in FIG. 5B, the level change of the contrast signal acquired by the control unit 30 from the contrast signal generation unit 15 is gentle. Such a subject 53 is referred to as a “first low contrast subject”. The control unit 30 can acquire a sufficient contrast signal from the first low-contrast subject in order to focus the focus lens group 5 in a bright environment. However, when a slight environmental change such as a change in brightness occurs, the control unit 30 can acquire from the first low-contrast subject only a contrast signal that is insufficient for the focus lens group 5 to focus, and the focus lens position. Is difficult to focus on. Therefore, although it is suitable as a low-contrast subject to be recorded, in some cases, when the imaging device 1 images the first low-contrast subject, it is based on subject information stored in the subject information storage area as will be described later. Therefore, it is necessary to perform AF control.

  FIG. 6 shows an example of a second low contrast subject. 6A shows an example of the subject 54, FIG. 6B shows an example of the contrast signal level in the first detection region 51, and FIG. 6C shows an example of the second detection regions 52a to 52i. The description of FIG. 6C will be described later.

  As shown in FIG. 6A, the subject 54 is, for example, a tower-type building against the background of the daytime sky. In the first detection area 51, the sky and the building are different in color and brightness. . Since the control unit 30 can obtain a sufficient contrast signal from the subject 54 captured near the center of the imaging region 50, the focus lens group 5 can be focused on the subject 54. However, the first detection region 51 includes the sky which is a low contrast portion in a wide range. At this time, as shown in FIG. 6B, the shape of the change in the contrast signal level is a peak of a low peak. Such a subject 54 is referred to as a “second low contrast subject”. Therefore, the control unit 30 extracts subject information of a low-contrast portion in the first detection region 51 by a method using second detection regions 52a to 52i, which will be described later, so that the in-focus position has low reliability. The subject information is stored in the subject information storage area.

  FIG. 7 shows an example of a preliminary contrast subject. 7A shows an example of the subject 55, FIG. 7B shows an example of the contrast signal level in the first detection area 51, and FIG. 7C shows examples of the second detection areas 52a to 52i. The description of FIG. 7C will be described later.

  As shown in FIG. 7A, the subject 55 is, for example, a tower-type building, building, or cloud against the background of the daytime sky, and in the first detection area 51, the color and brightness of the sky and the building There is a difference. As shown in FIG. 7C, the shape of the change in the contrast signal level is a high peak. Such a subject 55 is called a “preliminary contrast subject”. The range of the low-contrast portion in the first detection area 51 is narrow in the preliminary contrast subject, and the focus lens group 5 is easily focused in the contrast method. For this reason, the preliminary contrast subject is considered to be highly reliable with respect to the in-focus position of the focus lens group 5 although the degree of similarity with the first and second low-contrast subjects is relatively low. Therefore, the control unit 30 reserves information for assisting the adjustment of the focus lens position when neither subject information of the first and second low-contrast subjects is stored as a history in the subject information storage area of the memory 32. As a preliminary contrast object.

<Subject information recording method>
Next, a method by which the control unit 30 records subject information in the memory 32 will be described.

  The control unit 30 uses the determination that the focus lens group 5 is in an in-focus state as a trigger, and the focus lens group 5 is in focus during the AF operation as a numerical value indicating the possibility of being in focus when the AF operation is completed. Find the degree of confidence that represents the degree of The reliability is calculated by the control unit 30 based on the instruction history to the focus lens group 5 and the contrast signal level transmitted from the control unit 30 from the start of the AF operation to the stop of the AF operation. The process by which the control unit 30 calculates the reliability is known.

  Thereafter, the control unit 30 compares the calculated reliability with a reliability threshold (r_th) that is a reference value for determining whether or not the focus lens group 5 is in focus. If the calculated reliability is equal to or higher than the reliability threshold (r_th), the control unit 30 instructs the camera signal processing unit 13 to switch the first detection region 51 to the second detection regions 52a to 52i. A contrast signal and a color signal of each area are acquired from the camera signal processing unit 13.

  Next, how the control unit 30 classifies subjects using the second detection regions 52a to 52i in which the first detection region 51 is switched and gives priority to the subject information will be described.

  FIG. 8 shows an example of the first to third priorities given to the subject classified by the control unit 30.

  As described above, the control unit 30 classifies subjects whose reliability is greater than or equal to the reliability threshold (r_th) into first low-contrast subjects, second low-contrast subjects, and preliminary contrast subjects, and subject information on each subject. Is assigned one of the first to third priorities. In order for the control unit 30 to determine the first to third priorities, the number line in FIG. 8 includes a first threshold (d_th1) used as an example of a level threshold and a second threshold greater than the first threshold (d_th1). (D_th2) is provided.

  FIG. 9 shows a configuration example of a primary subject information storage area, a subject information storage area, a distance information table, and threshold values that the memory 32 has.

  The memory 32 includes a primary subject information storage area that temporarily stores subject information of a subject that is currently imaged by the imaging apparatus 1, a subject information storage area that stores a plurality of subject information of subject information captured in the past, and a distance information table. Have. In addition, the memory 32 stores a reliability threshold value and first to fourth threshold values. When the imaging device 1 images a subject, the control unit 30 stores new subject information (NI) acquired from the contrast signal generation unit 15 in the primary subject information storage area.

  On the other hand, in the subject information storage area, a subject information table (described later) that stores past subject information (OI_x: x = 1, 2, 3,... N) acquired by the control unit 30 from the contrast signal generation unit 15 in the past. (See FIG. 10). In the distance information table, the relationship between the position of the variator lens group 3 and the focus lens position is stored as distance information. The reliability threshold value is referred to in the process in which the control unit 30 determines whether the first detection region 51 can be switched. The first and second threshold values are referred to when the control unit 30 assigns any of the first to third priorities to the subject information. The third and fourth threshold values are determined by the control unit 30 as new subject information ( (NI) is referred to in the process for determining whether or not it can be stored in the subject information storage area.

  Returning to the description of the subject information recording method again.

  The control unit 30 obtains the difference (diff_pp) in the contrast signal level between the maximum contrast signal level (con_max) and the minimum contrast signal level (con_min) from the contrast signals acquired from the second detection regions 52a to 52i. The contrast signal level difference (diff_pp) may be a value including a positive or negative sign or may be an absolute value.

  Then, the control unit 30 gives high priority to the subject information if the difference in the contrast signal level is less than the level difference threshold, and lowers the subject information if the difference in the contrast signal level is equal to or greater than the level difference threshold. Give priority. Then, the control unit 30 preferentially stores the subject information to which the high priority is given in the memory 32.

  In the present embodiment, the control unit 30 compares the contrast signal level difference (diff_pp) with the first threshold value (d_th1) and the second threshold value (d_th1) as shown in FIG. If the difference (diff_pp) in the contrast signal level is less than the first threshold value (d_th1), the control unit 30 determines that there is no shading in the subject color or brightness. Such a subject is determined to be the first low-contrast subject because the contrast is uniform throughout the imaging region 50. For example, since the second detection areas 52a to 52i shown in FIG. 5C have the same contrast, the control unit 30 determines the subject 53 as the first low-contrast subject.

  When determining that the subject is the first low-contrast subject, the control unit 30 sets the priority information as the first priority (p_p1), and acquires distance information from the distance information table based on the focus lens position at the time of imaging. . Then, the control unit 30 temporarily stores new subject information (NI) including the color signal value of the region where the contrast signal level acquired from the contrast signal generation unit 15 is minimum, the acquired distance information, and priority information. Store in the subject information storage area.

  As shown in FIG. 8, if the difference (diff_pp) in the contrast signal level is equal to or greater than the second threshold (d_th2), there is a portion that is considered to have a certain level of contrast and a low contrast portion in the imaging region 50. Conceivable. Such a subject is determined as a second low-contrast subject by the control unit 30. For example, the second detection regions 52c, 52d, and 52g illustrated in FIG. 6C include sky, and these second detection regions have low contrast (con_min). However, the second detection areas 52a, 52b, 52e, 52f, 52h, and 52i include clouds or buildings, and any of the second detection areas has a high contrast (con_max). Therefore, the control unit 30 determines that the subject 54 is a second low contrast subject.

When the control unit 30 determines that the subject is the second low-contrast subject, the control unit 30 uses the second priority (p_p2) lower than the first priority (p_p1) as the priority information, and based on the focus lens position at the time of imaging. The distance information is acquired from the distance information table. Then, the control unit 30 stores new subject information (NI) including the color signal value of the region where the contrast signal level is minimum, the acquired distance information, and the priority information in the temporary subject information storage region. If the contrast signal level difference (diff_pp) is not less than the first threshold (d_th1) and less than the second threshold (d_th2) as shown in FIG. 8, it is considered that the contrast in the imaging region 50 is not uniform. Such a subject does not have the second detection areas 52a to 52i in which only a low contrast area exists. For example, any of the second detection areas 52a to 52i shown in FIG. 7C includes a building or a cloud that has a contrast with the sky, and there is no area that includes only the cloud or the sky. Therefore, the control unit 30 determines that the subject 55 is a preliminary contrast subject.

  When determining that the subject is a preliminary contrast subject, the control unit 30 uses the third priority (p_p3) lower than the second priority (p_p2) as the priority information, and determines the distance based on the focus lens position at the time of imaging. The distance information is acquired from the information table. Then, the control unit 30 stores new subject information (NI) including the color signal value of the region where the contrast signal level is minimum, the acquired distance information, and priority information in the temporary subject information storage region.

  Here, a configuration example of the subject information table will be described with reference to FIG.

  As described above, the memory 32 has a subject information storage area for storing subject information. The control unit 30 stores a plurality of past subject information (OI_x) acquired from the contrast signal generation unit 15 in the past in the subject information storage area in a table format. In the subject information storage area, a subject information table in which number information, distance information, color signal value information, and priority information are associated with each magnification is formed. The number information stores up to 5 numbers for each magnification. The distance information stores the subject distance, and the color signal value information stores color signal values corresponding to RGB. The priority information stores the priority given to each subject. In FIG. 10, the subject information (OI_x) having the magnification “1” and the number “1” is shown in a broken-line frame. There is an upper limit to the number of past subject information that can be stored in the subject information table. In the present embodiment, it is assumed that five past subject information can be stored for each magnification.

  It should be noted that until subject information is acquired by the control unit 30 and optimization in the subject information table is performed, the user of the imaging apparatus 1 can store arbitrary subject information in advance.

<Process for storing subject information in subject information storage area>
Next, a process performed by the control unit 30 when new subject information (NI) is stored in the temporary subject information storage area will be described.

  The reference for storing the subject information in the subject information storage area by the control unit 30 is to leave the subject information of the low-contrast subject in which the focus lens group 5 is focused. However, in the same environment, it is not always preferable to leave a plurality of similar subject information in the subject information storage area. This is because if similar subject information is continuously stored in the subject information storage area, the subject information stored in the subject information storage area lacks versatility. Therefore, the control unit 30 performs processing to leave subject information similar to the subject information already stored while leaving subject information of the low-contrast subject in the subject information storage area. In other words, when the new subject information read from the temporary subject information storage area is not similar to the past subject information read from the subject information storage area, the control unit 30 replaces the past subject information with a new subject information. The subject information is stored in the subject information storage area. In this process, the control unit 30 compares the new subject information (NI) and the past subject information (OI_x) as follows.

  First, when the new subject information (NI) is stored in the temporary subject information storage area, the control unit 30 sets the priority, distance information, color signal value, and all of the new subject information (NI) in the subject information storage area. The priorities, distance information, and color signal values of the past subject information (OI_x) are respectively compared. Then, the control unit 30 replaces the past subject information (OI_x) in the subject information storage area with new subject information (NI), or replaces the past subject information (OI_x) and does not replace the past subject information (OI_x). It is determined whether or not (NI) is deleted from the temporary subject information storage area.

  Here, the determination process performed by the control unit 30 will be specifically described with reference to FIG.

  FIG. 11 shows the relationship between the third threshold value (th_3) and the fourth threshold value (th_4) that the control unit 30 refers to in order to select subject information stored in the subject information storage area. In the following description, the third threshold value (th_3) is shown as an example of a distance threshold value, and the fourth threshold value (th_4) is shown as an example of a distance difference threshold value.

  First, the control unit 30 starts a calculation process triggered by the new subject information stored in the temporary subject information storage area. In this calculation process, the control unit 30 performs data processing on the data of the color signal value included in the new subject information (NI) and the color signal value included in the past subject information (OI_x) in the subject information storage area. The distance (d_I) (an example of the data distance) is obtained by the following equation (1).

  In Expression (1), Ry represents a red signal of the subject information, Gy represents a green signal of the subject information, and By represents a blue signal of the subject information. The subscript y is assigned n or o, respectively. n represents new subject information (NI) information, and o represents past subject information (OI_x) information.

<Processing when data distance (d_I) is greater than or equal to third threshold (th_3)>
Next, the control unit 30 selects past subject information (OI2_x) whose data distance (d_I) is equal to or greater than the third threshold value (th_3) from the subject information storage area. This selection process is represented by the upper number line shown in FIG. This number line shows subject information from the subject information storage area based on the distance (d_I) on the data between the color signal value of the new subject information (NI) and the color signal value of the past subject information (OI_x). A third threshold value (th_3) for selecting is shown. Thus, the process in which the control unit 30 selects the subject information (OI2_x) from the subject information storage area is to compare the similarity of the color features of the new subject information (NI) and the past subject information (OI_x). To be done.

  Then, the control unit 30 selects past subject information (OI3_x) from past subject information (OI2_x) based on the priority assigned to the selected past subject information (OI2_x). That is, it can be said that past subject information (OI2_x) includes past subject information (OI3_x). At this time, the control unit 30 acquires priority information from the past subject information (OI2_x) selected from the subject information storage area, and obtains the priority information priority of the new subject information (NI) and the past information. The priority of each priority information acquired from the subject information (OI2_x) is compared. As described above, since the priorities are higher in the order of the first priority, the second priority, and the third priority, the control unit 30 has assigned a priority less than the priority of the new subject information (NI). Subject information (OI3_x) is selected from past subject information (OI2_x). For example, if the priority of the new subject information (NI) is “2”, the past subject information (OI2_x) with the priorities “2” and “3” is used as the past subject information (OI3_x). 30.

  Next, the control unit 30 sets the new information (NI) whose priority assigned to the new subject information (NI) is equal to or higher than the priority assigned to the selected past subject information (OI3_x) as subject information. It is a target to be stored in the storage area. At this time, the control unit 30 stores new subject information (NI) in the subject information storage area instead of the past subject information (OI3_x) that minimizes the distance (d_I2) on the color signal value data. The distance (d_I2) on the data is calculated by the control unit 30 using the above equation (1). Then, the control unit 30 deletes the past subject information (OI3_x) that minimizes the data distance (d_I2) from the subject information storage area.

  Note that if the priority of the new subject information (NI) and the priorities of the past subject information (OI2_x) are all the same, the control unit 30 determines the new subject information from the temporary subject storage area. (NI) is deleted. In addition, when the control unit 30 determines that the priority of all past subject information (OI2_x) is higher than the priority of the new subject information (NI), the new subject information (from the temporary subject storage area ( NI).

  In this way, the control unit 30 compares the priorities of the new subject information (NI) and the past subject information (OI_x), and subjects the subject in the order of the first low-contrast subject, the second low-contrast subject, and the spare subject. Information can be stored in the subject information storage area.

<Processing when data distance (d_I) is less than third threshold (th_3)>
Next, a case is considered in which the distance (d_I) on the data of the color signal value of the past subject information (OI_x) with respect to the color signal value of the new subject information (NI) is less than the third threshold value (th_3). To do. At this time, the control unit 30 calculates the difference (diff_o) between the subject distance included in the new subject information (NI) and the subject distance included in the past subject information (OI_x).

  The lower number line shown in FIG. 11 shows subject information based on the subject distance difference (diff_o) from the past subject information (OI_x) whose data distance (d_I) is less than the third threshold (th_3). A fourth threshold value (th_4) for selecting (OI3_x) is set.

  Then, the control unit 30 selects past subject information (OI4_x) having a subject distance difference (diff_o) equal to or greater than the fourth threshold value (th_4) from the past subject information (OI_x). Thereby, the control unit 30 has a similar subject distance of the new subject information (NI) from the past subject information (OI_x) having color signal information similar to the color signal information of the new subject information (NI). Only past subject information (OI4_x) not to be selected can be selected from the subject information storage area.

  Then, the control unit 30 acquires the priority information from the past subject information (OI4_x), the priority included in the priority information of the past subject information (OI4_x), and the priority of the new subject information (NI). Each of the priority levels included in the degree information is compared. At this time, the control unit 30 selects subject information with a priority equal to or lower than the priority of the new subject information (NI) as subject information (OI5_x) from the past subject information (OI4_x).

  Then, the control unit 30 stores the new information (NI) in which the priority given to the new subject information (NI) is equal to or higher than the priority given to the selected past subject information (OI5_x). The target to be stored in the area. At this time, the control unit 30 replaces the selected subject information (OI5_x) with subject information (OI5_x) that minimizes the distance (d_I2) on the data of the color signal value obtained by the above equation (1). The new subject information (NI) is stored in the subject information storage area. Then, the control unit 30 deletes the past subject information (OI3_x) that minimizes the data distance (d_I2) from the subject information storage area.

  Note that if the priority of the new subject information (NI) and the priority of the past subject information (OI4_x) are all the same, the control unit 30 creates a new subject from the temporary subject storage area. Delete information (NI). Also, when the control unit 30 determines that the priority of all past subject information (OI4_x) is higher than the priority of the new subject information (NI), the new subject information from the temporary subject storage area. (NI) is deleted.

  Furthermore, the control unit 30 also newly adds the temporary subject storage area from the temporary subject storage area when the difference in subject distance between all past subject information (OI_x) and new subject information (NI) is less than the fourth threshold (th_4). Delete subject information (NI).

  Since the control unit 30 determines subject information to be left in the subject information storage area in accordance with such a rule, optimization is performed so that the subject information suitable for the imaging device 1 to capture a low-contrast subject is left in the subject information storage area. Processing can be performed. Therefore, the control unit 30 does not leave unnecessary subject information in the memory 32 when focusing on a subject that cannot be measured, that is, a low-contrast subject, as in the conventional method.

<Flow chart of AF operation>
12 to 14 are flowcharts illustrating an example of the AF operation performed by the imaging apparatus 1. This process represents a process sequence obtained by executing a program stored in the memory 32 by the control unit 30 in the imaging apparatus 1.

  The control unit 30 starts autofocus control processing when the power is turned on or the subject changes, and shifts to the AF operation state.

  First, the control unit 30 drives the electronic shutter 47 to expose the image sensor 8, thereby causing the image sensor 8 to capture an image signal (S1). Thereafter, the control unit 30 acquires the contrast signal level based on the contrast signal given from the camera signal processing unit 13 (S2).

  Next, the control unit 30 drives the focus lens group 5 based on the contrast signal obtained in step S2 (S3). At this time, based on the contrast signal acquired from the first detection area 51 shown in FIG. 2, the control unit 30 sets the subject currently being shot within the scope of application of the present invention, that is, the target of determination processing after step S5. It is determined whether or not (S4).

  When it is determined that the current object is a low-contrast object and it is determined that it is difficult to focus with the contrast AF operation, the process proceeds to the flow shown in FIG. The distance information table is referred to from the position of the variator lens group 3 to obtain the current camera magnification (S5).

  Next, subject information (pI) associated with the same magnification as the magnification obtained from the subject information table is extracted (S6).

  Here, the subject currently captured is subject information acquired in the first detection region of FIG. 2, but the information recorded in the memory 32 is subject information acquired in the second detection region of FIG. Therefore, the control unit 30 normalizes each acquired color signal value in order to eliminate the influence of the difference in the size of the detection regions in S7.

  Next, using the normalized color signal value, the distance (d_I) on the data is calculated by Equation (1) (S8). Then, subject information (pI_m) that minimizes the distance (d_I) on the data calculated in S9 is selected (S9), and then it is determined whether there are a plurality of subject information (pI_m) (S10). If the subject information that minimizes the distance (d_I) is unique (No in S10), subject distance information is extracted from the subject information (pI_m) (S11), and the distance of the extracted subject distance information is focused. Thus, the focus lens group 5 is moved (S17).

  On the other hand, when there are a plurality of pieces of subject information that minimize the data distance (d_I) in the determination of S10 (Yes in S10), the current focus is determined from the positions of the varifocal lens group 3 and the focus lens group 5. Subject distance information associated with each of the currently focused subject distance and the subject information (pI_m) among the subject information (pI_m) selected in S9. And subject information (pI_m2) having subject distance information that minimizes the difference is selected (S13). Note that the latest subject information may be selected (S15) from the subject information pI_m2 without performing the flow processing of S12 to S14.

  In S14, it is determined whether there is a plurality of subject information (pI_m2) selected in S13. If the subject information (pI_m2) is unique at this time, the subject distance associated with the subject information (pI_m2) in S16. Information is extracted, and the focus lens group 5 is moved to focus on the distance of the subject distance information (S17).

On the other hand, if it is determined in S14 that there are a plurality of subject information (pI_m2) selected in S13, the latest subject information in the selected subject information (pI_m2) is the final selected subject information. Then, the subject distance information associated with the subject information is extracted, and the focus lens group 5 is moved so as to focus on the distance of the subject distance information (S17).
After the focus lens group 5 is moved in S17, it finally shifts to the AF standby state (S40).
On the other hand, if the control unit 30 determines in step S4 that the subject is not to be subjected to the determination process in step S6 and subsequent steps, the control unit 30 continues the drive instruction for the focus lens group 5 in step S3. At this time, the control unit 30 instructs the focus lens group 5 to be driven based on the contrast AF method, and focuses the focus lens group 5 on the currently photographed subject (S15).

  In this case, the control unit 30 optimizes the subject information recorded / held in the memory 32 so as to be advantageous to the present invention.

  Based on the focus lens position and the contrast signal acquired from the camera signal processing unit 13, the control unit 30 determines whether the current focus lens group 5 is in focus, that is, the focus lens group 5 stops at the focus position. It is determined whether or not (S16). When determining that the focus lens group 5 is in focus, the control unit 30 calculates the reliability described above based on the current contrast signal level, the time until the focus lens group 5 stops at the focus position, and the like (S17). ). For example, if the time until the focus lens group 5 stops at the in-focus position is long, the control unit 30 has not found the peak of the contrast signal level, so the reliability becomes low.

  Next, the control unit 30 compares the reliability calculated in step S17 with the reliability threshold (r_th) read from the memory 32 (S18). When it is determined that the reliability is less than the reliability threshold (r_th), the control unit 30 shifts to the AF standby state (S40). In this AF standby state, the control unit 30 does not operate the AF until the subject information changes, and activates the AF when the subject information changes to enter the AF operation state.

  On the other hand, when the control unit 30 determines that the reliability is equal to or higher than the reliability threshold (r_th), an instruction to switch the first detection region 51 to the nine second detection regions 52a to 52i illustrated in FIG. This is performed on the contrast signal generator 15 via the signal processor 13 (S19). Then, the control unit 30 acquires the contrast signal and the color signal value of each of the second detection regions 52a to 52i from the contrast signal generation unit 15 (S20). Further, the control unit 30 acquires the current magnification based on the position of the variator lens group 3 at the time when the contrast signal and the color signal value are acquired in step S20 (S21).

  Next, the control unit 30 calculates a difference (diff_pp) in contrast signal levels (S22). The difference (diff_pp) in the contrast signal level is a value obtained by subtracting the minimum contrast signal level (con_min) from the maximum contrast signal level (con_max) in the second detection regions 52a to 52i.

  After that, as shown in FIG. 8, the control unit 30 compares the difference (diff_pp) in the contrast signal level with the first threshold value (d_th1) and the second threshold value (d_th2) (S23). The first threshold value (d_th1) is a numerical value smaller than the second threshold value (d_th2). When determining that the difference (diff_pp) in the contrast signal level is less than the first threshold (d_th1), the control unit 30 sets the priority information included in the subject information of the subject currently photographed as the first priority. Set (S24).

  If the control unit 30 determines that the contrast signal level difference (diff_pp) is greater than or equal to the second threshold (d_th2), the control unit 30 displays priority information included in the subject information of the subject currently being photographed. The second priority is set (S25). When the control unit 30 determines that the difference (diff_pp) in the contrast signal level is equal to or greater than the first threshold (d_th1) and the difference (diff_pp) is less than the second threshold (d_th2), the control unit 30 The priority information included in the subject information is set to the third priority (S26). Thereafter, the control unit 30 acquires the subject distance of the currently focused subject from the distance information table stored in the memory 32 based on the current focus lens position (S27).

  Here, the color signal value acquired in step S11, the priority information set in any of step S15, step S16, and step S17 and the subject distance acquired in step S18 are combined to obtain subject information. The control unit 30 stores the subject information in the temporary subject information storage area of the memory 32 (S28).

  Next, the control unit 30 refers to the subject information stored in the temporary subject information storage area as new subject information (NI) and compares it with past subject information (OI_x) already stored in the subject information storage area. . First, the color signal value is extracted from the new subject information (NI), the color signal value is further extracted from each past subject information (OI_x), and the data for each color signal is obtained using Equation (1). The upper distance (d_I) is calculated (S29). Then, the control unit 30 selects past subject information (OI2_x) in which the calculated distance (d_I) on the data is equal to or greater than the third threshold (d_th3) from the subject information storage area (S30). At this time, the control unit 30 determines whether or not there is past subject information (OI2_x) in which the distance (d_I) on the data is equal to or greater than the third threshold (d_th3) (S31).

  When the control unit 30 determines that past subject information (OI2_x) in which the data distance (d_I) is equal to or greater than the third threshold (d_th3) does not exist in the subject information storage area, the control unit 30 calculates the subject distance difference (diff_o) Calculate (S32). This difference in subject distance (diff_o) is calculated by subtracting the past subject information (OI_x) from the subject distance of the new subject information (NI). Then, the control unit 30 selects past subject information (OI4_x) in which the subject distance difference (diff_o) is equal to or greater than the fourth threshold value (d_th4) from the subject information storage area (S33). At this time, the control unit 30 determines whether or not there is past subject information (OI4_x) that is equal to or greater than the fourth threshold value (d_th4) (S34). When determining that the past subject information (OI4_x) does not exist in the subject information storage area, the control unit 30 deletes the new subject information (NI) stored in the temporary subject storage area (S39), Transition to the AF standby state (S40).

  The control unit 30 has subject information (OI2_x) in which the data distance (d_I) is equal to or greater than the third threshold (d_th3) in step S31, or is equal to or greater than the fourth threshold (d_th4) in step S34. When it is determined that the subject information (OI4_x) exists, the process proceeds to the next process. The control unit 30 compares the priority of the new subject information (NI) with the priority of the past subject information (OI2_x or OI4_x) in the next process that has been transferred (S35). Then, it is determined whether or not there is past subject information (OI2_x or OI4_x) with a priority lower than that of the new subject information (NI) (S36).

  If the control unit 30 determines in step S27 that there is no past subject information (OI2_x or OI4_x) with a priority equal to or lower than the priority of the new subject information (NI), it is stored in the temporary subject storage area. The new subject information is deleted (S39). And the control part 30 transfers to AF standby state (S40).

  On the other hand, when it is determined that there is past subject information (OI2_x or OI4_x) with a priority equal to or lower than the priority of the new subject information (NI), the control unit 30 performs the next process. In this process, the control unit 30 obtains past subject information (OI3_x or OI5_x) with a priority lower than the priority of the new subject information (NI) from the past subject information (OI2_x or OI4_x). elect. Then, the control unit 30 calculates a data distance (d_I2) between the color signal value of the new subject information (NI) and the color signal value of the selected past subject information (OI3_x or OI5_x) (S37). .

  Then, the control unit 30 deletes the past subject information (OI3_x or OI5_x) that minimizes the data space distance (d_I2) from the subject information storage area, and instead uses new subject information (NI) in the subject information storage area. Store (S38). Thereafter, the control unit 30 deletes the new subject information (NI) from the temporary storage area (S39), and finally shifts to the AF standby state (S40).

  The imaging apparatus 1 according to the embodiment described above can perform appropriate autofocus control when imaging a subject in a low contrast environment or when imaging a low contrast subject. For this reason, the imaging apparatus 1 can focus the subject by driving the focus lens position to an appropriate position even if the subject is difficult to measure.

  Here, the control unit 30 classifies the subjects based on the contrast signal levels respectively acquired from the plurality of second detection areas 52a to 52i after stopping the AF operation on the subjects that can be measured, and sets the subjects for each subject. Any one of the first to third priorities is assigned to the subject information. Since the first to third priorities indicate the priority order stored in the subject information storage area, subject information with a high priority is preferentially stored in the subject information storage area. For this reason, the imaging apparatus 1 can read out useful subject information from the subject information storage area and image a low-contrast subject at an appropriate focus lens position.

  In addition, when the subject information stored in the subject information storage area of the memory 32 exceeds the limit number, the control unit 30 optimizes the subject information storage area. In this optimization, if the new subject information stored in the temporary subject information storage area is similar to the past subject information stored in the subject information storage area, the new subject information is stored in the subject information storage area. Do not store. If the priority of the new subject information is the same as or lower than the priorities of the previous subject information, the new subject information is not stored in the subject information storage area. In this way, the number of past subject information stored in the subject information storage area is optimized, and unnecessary subject information can be prevented from being stored in the subject information storage area.

[(3) Other embodiments]
In the above-described embodiment, the case where the present invention is applied to the imaging apparatus 1 configured as shown in FIG. 1 has been described. However, the present invention is not limited to this, and various other configurations are also possible. The present invention can be widely applied to imaging devices having the same.

  For example, in the AF operation when the subject being photographed is determined to be a low-contrast subject during the AF operation, and it is determined that focusing cannot be performed in the contrast-type AF operation, the above-described exemplary embodiment In this case, subject information (pI) is selected from subject information closest to the current magnification. However, the subject information (pI) is not limited to the nearby magnification, but based on the entire subject information table, an arbitrary location on the subject information table, or a certain rule. May be elected.

  Further, when performing the AF operation of the present invention, the control unit 30 is not limited to the current color signal, but includes, for example, a region distribution (position, shape (moment of inertia)), a region area, a number of regions, and a defocus amount. Similarity can be similarly compared using (object distance), motion vector (difference data), hue (color component), saturation, lightness, and texture (pattern) or a combination of these features. Other feature amounts may be used instead of color signals in accordance with information recorded in past subject information, or similarities may be compared from feature amounts using a plurality of signal values. In that case, it is desirable to compare the degree of similarity by using a formula that compares the degree of similarity of the feature amount again.

  Further, the AF operation of the present invention described above is an AF operation suitable for focusing when it is determined that focusing is impossible in the AF operation based on the contrast method. If data of subject information other than the subject that cannot be focused in the AF operation based on the contrast method is held, the similarity of the above information is compared with other timing / subjects. The same effect can be obtained even when the AF operation is performed. In other words, by holding the data of the subject to be focused and calling the data at an arbitrary timing according to the type of the subject and performing the AF operation, the effect of improving the focusing accuracy similar to the present invention can be obtained. An AF operation suitable for such various subjects can be performed. For example, for a subject that includes a point light source instead of a low-contrast subject, the distance to the past subject, the brightness value, etc. are retained as feature quantities instead of color signal values, and it is determined that there is a point light source subject In this case, the AF operation may be performed by referring to the subject information using the above-described luminance value as a feature amount.

  Furthermore, the shape, position, and number of detection areas such as the contrast signal of the AF operation of the present invention are arbitrary, and it is not necessary to have one rectangle in the center. That is, the detection area can be arbitrarily set so that the difference between the color signal value and the contrast can be confirmed for a certain area. By setting the number, position, and size of detection areas according to conditions such as the type and size of the subject to be imaged and the position where the subject is expected to appear in the captured image, the detection area is more accurately set. It is possible to focus on the target subject.

  In the above embodiment, the AF operation is stopped when the focus lens is moved so as to focus on the distance of the referenced subject distance information. However, after the focus lens is moved, an arbitrary time contrast is obtained. An AF operation such as a method may be performed. By doing so, it is considered that even if there is a slight difference in subject distance that cannot be focused by simply performing the AF operation with reference to the subject distance information, the difference can be reduced.

  Also, when optimizing the subject information to be recorded, there are a plurality of contrast signal level peaks that can be in-focus in the detection region, and if the peaks are almost the same value, the difference in contrast signal level is small. The controller 30 may erroneously recognize this subject as the first low-contrast subject. In order to avoid such erroneous recognition, a level threshold is provided for the contrast signal level, and the control unit 30 determines that the subject is not a low-contrast subject if the contrast signal level of each peak is equal to or higher than the level threshold. To do. As a result, a subject with a high contrast signal level is not erroneously recognized as a low-contrast subject.

  In the subject information table of FIG. 10, five pieces of subject information are stored for each magnification, but the number of subject information stored in the subject information table may be arbitrary. Alternatively, only a certain range of magnifications may be specified, and a subject information table may be formed in which subject information corresponding to the magnifications within this range is shared.

  When the past subject information (OI_x) stored in the subject information storage area of the memory 32 exceeds the limit number, the control unit 30 has the lowest reference frequency among the past subject information (OI_x). Alternatively, the oldest information stored in the subject information storage area may be deleted. The control unit 30 may store new subject information (NI) in the subject information storage area instead of the deleted subject information.

  In addition to the subject distance, the focus lens position may be stored in the storage unit, and the focus lens may be driven based on the focus lens position of the selected subject information.

  The present invention is not limited to the above-described embodiments, and various other application examples and modifications can of course be taken without departing from the gist of the present invention described in the claims.

  For example, the above-described embodiment is a detailed and specific description of the configuration of the apparatus and the system in order to explain the present invention in an easy-to-understand manner. Absent. Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Moreover, it is also possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

  Further, the control lines and information lines indicate what is considered necessary for the explanation, and not all the control lines and information lines on the product are necessarily shown. Actually, it may be considered that almost all the components are connected to each other.

  DESCRIPTION OF SYMBOLS 1 ... Imaging device, 2 ... Lens unit, 5 ... Focus lens group, 8 ... Imaging element, 12 ... Autofocus control device, 13 ... Camera signal processing part, 14 ... Signal conversion processing circuit, 15 ... Contrast signal generation part, 16 ... HPF circuit, 17 ... integrator, 30 ... control unit, 31 ... CPU, 32 ... memory

Claims (7)

A drive unit for driving the focus lens;
An imaging unit that images an optical image formed through the focus lens and outputs an imaging signal;
A storage unit that stores subject information associated with the subject distance of the subject and the first feature amount in the imaging region when the captured subject is in focus, for each magnification of the zoom lens;
When it is determined that the subject being photographed cannot be focused, the second feature amount in the imaging region being photographed is acquired, and the subject information at the magnification at which the subject is photographed among the subject information is acquired. A controller that obtains the similarity between the feature quantity of 1 and the second feature quantity, and selects subject information having the first feature quantity that maximizes the similarity, and
The driving unit is an imaging apparatus that moves the focus lens so that a subject is in focus based on a subject distance included in the selected subject information.   The feature value is any one of a color signal that is a luminance signal that is a degree of photosensitivity of the sensor, a luminance signal value itself, a conversion value that is calculated based on the color signal or the luminance signal value. Imaging device.   The imaging device according to claim 1, wherein after the feature quantity of either the first feature quantity or the second feature quantity is normalized, the similarity of each feature quantity is obtained. When a plurality of pieces of subject information having the minimum similarity are selected, the control unit determines a difference between a subject distance associated with each of the plurality of subject information and a subject distance of a subject currently being photographed. Select subject information with information on subject distance that minimizes
The imaging apparatus according to claim 1, wherein the driving unit moves the focus lens so as to be in a focused state with respect to a subject distance associated with the selected subject information. The imaging device
The storage unit compares a contrast signal level difference between the calculated maximum contrast signal level and the minimum contrast signal level among a plurality of detection areas set in the imaging area with a level difference threshold value. The imaging apparatus according to claim 1, wherein priority is given to subject information of the subject based on a comparison result, and the subject information is stored according to the priority set in the subject information. A storage unit that stores subject information associated with the subject distance of the subject and the first feature amount in the imaging region when the subject is in focus for each magnification of the zoom lens;
When it is determined that the subject being photographed cannot be focused, the second feature amount in the imaging region being photographed is acquired, and the subject information at the magnification at which the subject is photographed among the subject information is acquired. A controller that obtains the similarity between the feature quantity of 1 and the second feature quantity, and selects subject information having the first feature quantity that maximizes the similarity, and
A focus control device that moves the focus lens so that the subject is in focus based on the subject distance in the selected subject information. When the subject is in focus, subject information associated with the subject distance of the subject and the first feature amount in the imaging region is stored for each zoom lens magnification,
When it is determined that the subject being photographed cannot be focused, the second feature amount in the imaging region being photographed is acquired, and the subject information at the magnification at which the subject is photographed among the subject information is acquired. Finding the similarity between the feature quantity of 1 and the second feature quantity, selecting subject information having the first feature quantity that maximizes the similarity,
A focus control method for moving the focus lens so that the subject is in focus based on the subject distance in the selected subject information.

Images