JP2008216763A - Auto-focus adjustment apparatus and imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an automatic focus adjustment apparatus that does not need to increase time required for an auto-focus operation, even when a quantity of emitted auxiliary light is controlled. <P>SOLUTION: The auto-focus adjustment apparatus includes: an auxiliary light means for irradiating a subject with auxiliary light when the subject is darker than specified brightness in the auto-focus operation; and an emitted light quantity control means for controlling the quantity of emitted auxiliary light. During the movement of a focus lens to a scan starting position, the emitted light quantity control means brings the auxiliary light into an emitted and non-emitted states to acquire the brightness of a focus detecting area and, from the acquired brightness, sets the emitted quantity of auxiliary light required for scanning (S301, S312 to S317, S306). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an automatic focusing apparatus suitable for an imaging apparatus and an imaging apparatus including the automatic focusing apparatus.

  In an image pickup apparatus, a focus adjustment is performed by detecting a position where a high-frequency component (hereinafter referred to as a focus evaluation value) of a luminance signal of a subject image formed on an image pickup element is maximized while moving a focus lens in an optical axis direction. Often, a focusing device is used. This method is called a contrast detection method, and an operation for detecting a position (focus position) at which the focus evaluation value is maximized while moving the focus lens in the optical axis direction is called a scanning operation. In this contrast detection method, the brightness of the subject image is low in a low-light environment and it becomes difficult to detect the contrast, so an auxiliary light source such as an LED (infrared light emitting diode) is provided to irradiate auxiliary light during scanning. There are many.

  The brightness required for the auxiliary light needs to be bright enough to identify the edge of the subject as contrast, but differs depending on the distance and reflectance of the subject and the exposure of the imaging device. Therefore, when the maximum light emission amount of the auxiliary light source is always irradiated, sufficient contrast may not be obtained due to saturation of the brightness of the captured image, and focusing may be impossible.

Therefore, in order to optimize the amount of auxiliary light, the amount of auxiliary light during scanning of the focus lens is determined according to the ratio of the brightness of the focus detection area when no auxiliary light is irradiated and the brightness of the focus detection area when auxiliary light is irradiated. An imaging device to be set has been proposed (Patent Document 1).
JP 2003-114374 A

  However, in Patent Document 1, in order to set the amount of auxiliary light, the brightness of the focus detection area is acquired by stopping and acquiring the auxiliary light when the auxiliary light is not irradiated and when the auxiliary light is irradiated, thereby increasing the time required for the autofocus operation. It had the problem that.

(Object of invention)
The object of the present invention is to achieve automatic focusing that does not increase the time required for the autofocus operation even when it is necessary to control the light emission amount of the auxiliary light because the brightness of the subject image is low and the contrast detection is difficult. An adjustment device and an imaging device are to be provided.

  In order to achieve the above object, the present invention provides a calculation means for calculating a focus signal corresponding to the contrast of a focus detection area based on an image signal from an image pickup means, a scan by moving a focus lens, and the focus signal. Autofocus means for performing an autofocus operation for positioning the focus lens at a focus position where the maximum is obtained, and in the autofocus operation, when the subject is darker than a predetermined brightness, the subject is irradiated with auxiliary light An auxiliary light unit; and a light emission amount control unit configured to control a light emission amount of the auxiliary light, and the light emission amount control unit emits the auxiliary light while the focus lens is moved to the scan start position. The brightness of the focus detection area is acquired in each of the non-light emitting states, and the brightness at the time of the scan is obtained from the acquired brightness. It is an automatic focusing device for setting the light emission amount of Johikari.

  In order to achieve the above object as well, the present invention is an imaging apparatus having the automatic focusing apparatus of the present invention.

  According to the present invention, even when it is necessary to control the light emission amount of the auxiliary light because the brightness of the subject image is low and it is difficult to detect the contrast, the autofocus that does not increase the time required for the autofocus operation is achieved. An adjustment device or an imaging device can be provided.

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

  FIG. 1 is a block diagram showing a schematic configuration of an imaging apparatus according to an embodiment of the present invention. In this embodiment, a person's face is used as a target of a specific subject whose estimated distance is obtained. As for the face detection method, it is assumed that the position and size information of the face can be obtained using a known method.

  In the present invention, “scan” refers to detecting the focus lens position where the focus evaluation value is maximized by moving the focus lens from the closest end to the infinite end direction in the optical axis direction, or vice versa. Say.

  The imaging apparatus according to the present embodiment has an optical system 101 and a focus lens 102. The imaged light is photoelectrically converted by the image sensor 103 and output as an image signal. This imaging signal is output to the memory controller 106 as a digitized signal through a pre-processing circuit 104 having a CDS circuit for removing output noise and a non-linear amplifier circuit, and an A / D converter 105. The memory controller 106 stores this imaging signal in the memory 107 and outputs it to the signal processing circuit 108. Then, the signal processing circuit 108 converts this imaging signal into an image and records it on the recording medium 109.

  Reference numeral 110 denotes an operation display unit that displays a live view image, various setting information of the imaging apparatus, a captured image, and the like. Reference numeral 111 denotes a switch for performing a shooting standby operation (hereinafter referred to as switch SW1), and 112 denotes a switch for performing shooting after operation of the switch SW1 (hereinafter referred to as switch SW2).

  The auto focus (also referred to as AF) operation is controlled by the system control unit 113. First, when the switch SW1 is operated, the focus lens 102 starts to move to the scan start position via the focus lens drive circuit 114. During movement until the focus lens 102 reaches the scan start position, the auxiliary light emission amount control unit 116 sets the light emission amount of the auxiliary light source 115 according to a flowchart described later.

  Next, a focus evaluation value calculation unit 117 calculates a focus evaluation value corresponding to the contrast of the image using image signals captured at a plurality of focus lens positions while moving the focus lens 102 in the optical axis direction. After the in-focus position is determined by the in-focus position determination unit 118, control is performed so that the focus lens 102 is driven to that position. A shooting standby operation such as an AF operation is performed by operating the switch SW1, and shooting and image recording are performed by operating the switch SW2. During the AF operation, the distance measurement range set by the distance measurement range setting unit 122 is scanned. The shooting condition analysis unit 119 and the shooting condition storage unit 120 are used for comparison of shooting conditions with the previous shooting as described later, and the face detection unit 121 is used to estimate the subject distance based on the detected face size. . These results are configured to reflect the light emission amount setting of the auxiliary light source 115 at the time of scanning in the AF operation.

  The focus evaluation value is calculated as follows. A horizontal band-pass filter is applied to each line of image data in a focus detection area (for example, provided on the left, center, and right on the screen, also referred to as a distance measurement frame). Next, the one having the largest absolute value of the bandpass output signal is selected for each line. Integrate the selected signal vertically. With the above configuration, a large contrast in the horizontal direction is detected, and a focus evaluation value with an improved S / N is obtained by integrating in the vertical direction. This focus evaluation value is the largest in the focused state, When defocused, the signal becomes smaller. Therefore, an in-focus image can be obtained by detecting the local maximum position of the focus evaluation value and shooting at that position.

  Hereinafter, a series of operations of the imaging apparatus according to the embodiment of the present invention will be described in detail with reference to FIG.

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

  If the remaining capacity of the recording medium 109 is not zero and the process proceeds to step S204, the state of the switch SW1 is checked. If it is ON, the process proceeds to step S206, and if not, the process proceeds to step S205. When the process proceeds to step S205, the state of the main switch (not shown) is checked. If it is ON, the process returns to step S204 where the state of the switch SW1 is checked, otherwise the process returns to step S201.

  If it is determined that the switch SW1 is ON and the process proceeds to step S206, an AE (automatic exposure) process is performed, and an AF operation is performed in the next step S207 according to the flowchart of FIG. In the following step S208, the state of the switch SW2 is checked. If it is ON, the process proceeds to step S210, and if not, the process proceeds to step S209. When the process proceeds to step S209, the state of the switch SW1 is checked. If it is ON, the process returns to step S208. Otherwise, the process returns to step S204 to check the state of the switch SW1.

  If the process proceeds to step S210 assuming that the switch SW2 is ON, the photographing operation is performed according to the flowchart of FIG. In step S211, the remaining capacity of the recording medium 109 is checked. If the remaining capacity is 0, the process returns to step S203, and if not, the process proceeds to step S212. When the process proceeds to step S212, the state of the switch SW2 is checked. If the switch SW2 is ON, the process waits at this step, and if it is OFF, the process proceeds to step S209 to check the state of the switch SW1.

  Next, the AF operation executed in step S207 will be described with reference to the flowchart of FIG.

  First, in step S301, it is checked whether or not it is a condition for emitting auxiliary light depending on the brightness of the subject. If the brightness is not less than the specified value, the process proceeds to step S302. The process proceeds to S303.

  When the process proceeds to step S302 assuming that the brightness of the subject is not less than the specified value, the focus lens 102 is scanned without emitting auxiliary light because the brightness is sufficient to detect the contrast of the subject. Thereafter, the process proceeds to step S318 described later.

  Further, when the process proceeds to step S303 on the assumption that the brightness of the subject is equal to or less than the specified value, whether or not the scene is the same as the previous shooting and is in focus in the previous shooting according to the flowchart of FIG. Determine whether. If it is determined that the same scene as the previous shooting is in focus and the previous shooting is in focus, the process proceeds to step S304; otherwise, the process proceeds to step S305. In step S304, scanning is performed without emitting auxiliary light if light was not emitted at the time of the previous shooting, and scanning is performed by emitting auxiliary light with the same amount of light if light was emitted. Thereafter, the process proceeds to step S318 described later.

  In step S305, the closest distance that can be measured in the distance measurement range set by the distance measurement range setting unit 122 is compared with the reference distance df. If the closest distance is shorter than the reference distance df, the process advances to step S307. If not, the process proceeds to step S306. Here, the reference distance df is set to be equivalent to the reach distance of the auxiliary light when the auxiliary light is set to full emission, and when the subject estimated distance is a long distance greater than or equal to the reference distance df, the auxiliary light is fully emitted. However, it can be determined that there is no harmful effect of being out of focus due to saturation. If it is determined that the closest distance is not closer than the reference distance df and the process proceeds to step S306, the auxiliary light is scanned with full light emission.

  If it is determined that the closest distance is closer than the reference distance df and the process proceeds to step S307, it is checked whether or not the face detection mode is set. If the face detection mode is set, the process proceeds to step S308. Proceed to When it is determined that the mode is the face detection mode and the process proceeds to step S308, the face detection unit 121 performs face detection. In step S309, if face detection is completed in step S308, the process proceeds to step S310. If face detection is not performed, the process proceeds to step S312.

If it is determined that face detection has been performed and the process proceeds to step S310, the estimated distance d to the subject is obtained from the detected face size as follows. Assuming that the actual standard face size is Lstd, the size of the face area detected on the image plane is L, and the focal length is f, the estimated distance d is d = f (1 + Lstd / L)
Can be obtained. In the next step S311, the estimated distance d obtained in step S310 is compared with the reference distance df. If the estimated distance d is shorter than the reference distance df, the process proceeds to step S312; The process proceeds to S306.

  In step S312, the focus lens 102 starts to move toward the scan start position (for example, the closest position). In the next step S313, during the movement until the focus lens 102 reaches the scan start position, the luminance value of the focus detection area is acquired without emitting auxiliary light. In the subsequent step S314, the auxiliary light is emitted with a predetermined light emission amount during the movement until the focus lens 102 reaches the scan start position, and the stabilization of the output is awaited. In the next step S315, the auxiliary light is emitted. The brightness value of the focus detection area in the light emission state is acquired. Note that the predetermined light emission amount set here is full light emission or a large light emission amount of about 80% in order to examine the influence of saturation when the auxiliary light is scanned as full light emission.

  Further, when the focus lens 102 has finished moving to the scan start position during the processing of steps S313 to S315, the following is performed. That is, when the movement time until the focus lens reaches the scan start position is short, the movement of the focus lens 102 is stopped when the focus lens 102 reaches the scan start position, and the luminance value of the focus detection region is Acquire.

  In the next step S316, it is checked whether or not there is a luminance difference of a certain value or more between the luminance value acquired without emitting auxiliary light in step S313 and the luminance value acquired in step S315 at a predetermined light emission amount. If there is no luminance difference greater than a certain value, the process proceeds to step S306, and if there is a luminance difference greater than a certain value, the process proceeds to step S317.

  If it is determined that there is no luminance difference of a predetermined value or more between the case where the auxiliary light is not emitted and the case where the auxiliary light is emitted, that is, it is determined that the reflection of the auxiliary light by the subject is small, the process proceeds from step S316 to step S306 as described above. In this case, since it can be determined that the adverse effect of being out of focus due to saturation is small even if the auxiliary light is set to full emission, scanning is performed with the auxiliary light set to full emission.

  On the other hand, if there is a luminance difference of a certain value or more between the case where the auxiliary light is not emitted and the case where the light is emitted, the process proceeds to step S317, where the auxiliary light is used because of a close subject or a highly reflective subject. Depending on the amount of emitted light, a problem of saturation and defocusing is assumed. Therefore, scanning is performed with the light emission amount of the auxiliary light as a specified small light emission amount. Thereafter, in either case, the process proceeds to step S308.

  In step S318, the focus evaluation value calculation unit 117 and the focus position determination unit 118 obtain a maximum value equal to or greater than a predetermined value from the focus evaluation value acquired during scanning. Then, the position of the focus lens 102 at that time is extracted, and the focus lens 102 is moved to the position where the focus evaluation value shows the maximum value, that is, the in-focus position. Here, when the maximum value of the focus evaluation value equal to or greater than the predetermined value is not obtained, that is, when out of focus, the focus lens 102 is moved to a preset position called a fixed point. Then, in the next step S319, the focus / non-focus distance measurement result is displayed on the operation display unit 110, and the current focus / non-focus distance measurement result and the setting of the imaging device such as the shooting mode are set. The shooting condition information such as the information and the brightness of the subject is stored in the shooting condition storage unit 120.

  Next, the operation mainly for determining the same scene in step S303 in FIG. 3 will be described with reference to the flowchart in FIG. Note that the information at the time of the previous shooting to be compared in the flowchart of FIG. 4 described below is the information stored in the shooting condition storage unit 120 in step S319 of FIG.

  In step S401, it is checked whether the previous shooting was in focus. If in focus, the process proceeds to step S402. Otherwise, the process proceeds to No. In step S402, the focal length is compared with that at the previous shooting, and if it is the same focal length, the process proceeds to step S403, and if not, the process proceeds to No. In step S403, the time elapsed since the previous photographing is checked. If it is within the predetermined elapsed time, the process proceeds to step S404, and if not, the process proceeds to No. In step S404, the shooting mode is compared with the previous shooting mode. If the shooting mode is the same, the process proceeds to step S405, and if not, the process proceeds to No.

  In step S405, the distance measurement range setting is compared with the previous shooting, and if it is the same distance measurement range setting, the process proceeds to step S406, otherwise the process proceeds to No. In step S406, the focus detection area setting is compared with the previous shooting, and if the focus detection area setting is the same, the process proceeds to step S407; otherwise, the process proceeds to No. In step S407, the brightness of the subject is compared with that at the previous shooting, and it is checked whether the difference amount (change amount) is within a predetermined value such as ± 1/3 step. If it is within the predetermined value, the process proceeds to step S408. Otherwise, go to No. In step S408, the white balance control value is compared with the previous photographing, and if it is equal to or smaller than the predetermined difference amount, the process proceeds to Yes, and if not, the process proceeds to No.

  Next, the photographing operation executed in step S210 of FIG. 2 will be described according to the flowchart of FIG.

  First, in step S501, the subject brightness is measured. In the next step S502, the image sensor 103 is exposed according to the subject luminance measured in step S501. The image formed on the image sensor surface is photoelectrically converted into an analog signal, which is sent to the A / D converter 105 in the next step S503, where preprocessing such as output noise removal and non-linear processing of the image sensor 103 is performed. Is converted into a digital signal. In step S504, the signal processing circuit 108 sets the output signal from the A / D converter 105 as an appropriate output image signal. In the subsequent step S505, the output image signal is converted into the JPEG format or the like, and in the next step S506, it is transferred to the recording medium 109 and stored.

  According to the above embodiment, while the focus lens is moved to the scan start position, the brightness of the focus detection area is acquired by setting the auxiliary light to the light emission and non-light emission states, and scanning is performed from the acquired brightness. The amount of the auxiliary light emitted at the time is set. For this reason, even in the case where the luminance of the subject image is low and the contrast detection is difficult due to the low illumination environment, even if the light emission amount control of the auxiliary light is performed, the time required for the AF operation is not increased. Adjustments can be made.

  In the above embodiment, the human face is used as the target of the specific subject for which the estimated distance d is obtained. However, the present invention is not limited to this. There may be a means for extracting the specific subject image, a means for detecting the size of the specific subject image on the shooting screen, and a means for obtaining the distance from the detected size to the specific subject. As a method for obtaining the estimated distance, if the above-described equation is used, it is sufficient if there is standard size information of the specific subject. Alternatively, information indicating the relationship between the size of the specific subject image, the focal length at the time of shooting, and the distance to the subject may be stored in advance in a storage circuit, and the distance may be obtained by referring to the information.

  In the above-described embodiment, there are three types of auxiliary light emission amounts that can be controlled, including non-light emission. A predetermined light emission amount may be set.

  In the above embodiment, the scene is determined to be the same as the previous shooting only when certain conditions for all the following items are satisfied. Each item includes a focal length at the time of shooting, shooting mode setting, distance measurement range setting, focus detection area setting, subject brightness, WB control value, and elapsed time from the previous shooting time. However, when an item including at least one of the items satisfies a predetermined condition, it may be determined that the scene is the same as the previous shooting. Moreover, the predetermined conditions to be satisfied for each item are not limited to the values shown above.

(Correspondence between the present invention and the embodiment)
In the present invention, the imaging means of the present invention is the imaging element 103, the computing means is the system control unit 113, the autofocus means is the system control means 113 and the focus lens driving circuit 114, and the auxiliary light means is the auxiliary light source 115. , Respectively. The focus signal corresponds to the focus evaluation value.

  Further, in the present invention of claim 1, the light emission amount control means corresponds to a part for executing the processes of steps S301, S312 to S317, S306 of FIG. Further, in the present invention of claim 3, the light emission amount control means is a part for executing the processing of steps S301 and S306 in FIG. 3, and in the present invention of claim 4, the light emission amount control means is in steps S305 and S316 of FIG. , S317, respectively, corresponding to the portions that execute the processing. Further, in the present invention of claim 5, the light emission amount control means is a part for executing the processes of steps S311, S316 and S317 in FIG. 3, and the focal length detection means is a part for executing the process of step S402 of FIG. , Respectively. Similarly, in the present invention of claim 5, the subject size detecting means for detecting the size of the specific subject in the shooting screen corresponds to step S308 in FIG. In the present invention of claim 6, the light emission amount control means corresponds to a part for executing the processing of steps S303 and S304 in FIG.

1 is a block diagram illustrating a configuration of an imaging apparatus according to an embodiment of the present invention. 6 is a flowchart illustrating an operation of the imaging apparatus according to the embodiment of the present invention. It is a flowchart which shows AF operation performed in step S207 of FIG. It is a flowchart which shows the detailed operation | movement of the same scene determination in step S303 of FIG. It is a flowchart which shows the imaging | photography operation | movement performed in step S210 of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Optical system 102 Focus lens 103 Image pick-up element 104 Pre-processing circuit 106 Memory controller 108 Signal processing circuit 109 Recording medium 110 Operation display part 113 System control part 114 Focus lens drive circuit 115 Auxiliary light source 116 Auxiliary light emission amount control part 117 Focus Evaluation value calculation unit 118 In-focus position determination unit 119 Imaging condition analysis unit 120 Imaging condition storage unit 121 Face detection unit 122 Distance measurement range setting unit

Claims (8)

A computing means for computing a focus signal corresponding to the contrast of the focus detection area based on the image signal from the imaging means;
An autofocus means for performing an autofocus operation for moving the focus lens to scan and positioning the focus lens at a focus position where the focus signal is maximized;
In the autofocus operation, when the subject is darker than a predetermined brightness, auxiliary light means for irradiating the subject with auxiliary light;
A light emission amount control means for controlling the light emission amount of the auxiliary light,
The light emission amount control means obtains the brightness of the focus detection area by setting the auxiliary light to each of the light emission state and the non-light emission state while the focus lens is moved to the scan start position. Then, the automatic focus adjustment apparatus is characterized in that the light emission amount of the auxiliary light at the time of the scan is set. The light emission amount control means has a short movement time until the focus lens reaches the scan start position, and the brightness of the focus detection area is acquired by setting the auxiliary light to light emission and non-light emission during the movement. If not, the focus lens is stopped at the scan start position to obtain the brightness of the focus detection area, and the light emission amount of the auxiliary light is set.
The automatic focus adjustment apparatus according to claim 1, wherein the scan of the focus lens is started after the light emission amount is set. The light emission amount control means sets the auxiliary light to a maximum light emission amount when the acquired brightness of the focus detection region is a specified value or less,
3. The automatic focus adjustment apparatus according to claim 1, wherein the scan of the focus lens is started after the light emission amount is set to a maximum. 4.   The light emission amount control means sets the light emission amount of the auxiliary light to be smaller than the maximum light emission amount when the closest distance that can be measured is closer than a reference distance. Item 4. The automatic focus adjustment device according to any one of Items 3 to 4. A focal length detection means for detecting a focal length at the time of shooting;
Subject size detecting means for detecting the size of the specific subject in the shooting screen,
The light emission amount control means maximizes the light emission amount of the auxiliary light when the estimated subject distance obtained from the focal length at the time of photographing and the size of the specific subject on the photographing screen is estimated to be closer than the reference distance. 4. The automatic focus adjustment apparatus according to claim 1, wherein the automatic focus adjustment apparatus is set to be smaller than a light emission amount.   At the time of shooting, if the current shooting conditions do not change with respect to the previous shooting conditions, and the result of the scan by emitting auxiliary light in the previous shooting is in focus, 6. The automatic focus adjustment apparatus according to claim 1, wherein the scan is performed with the same amount of auxiliary light emission as in the previous photographing.   The imaging condition includes at least one of a focal length, an imaging time, an imaging mode, a distance measurement range setting, a focus detection area setting, a subject brightness, and a white balance control value. The automatic focusing device as described.   An image pickup apparatus comprising the automatic focus adjustment apparatus according to claim 1.

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