JP4813439B2 - Imaging apparatus and control method thereof - Google Patents

Description

  The present invention relates to an imaging apparatus that performs imaging using an image sensor and a control method thereof, and more particularly, to an imaging apparatus having an illumination light (AF auxiliary light) irradiation function during autofocus and a control method thereof.

  In recent years, a digital camera that uses an image sensor made of a semiconductor element such as a CCD type or a MOS type, converts an image signal obtained by the image sensor into digital image data, and records it on a recording medium such as a built-in memory or a memory card. Imaging devices such as these are prevalent. Many digital cameras have automatic exposure control (AE) and autofocus (AF) functions, and the AE and AF are generally performed using image signals output from an image sensor.

  In the AE process, subject brightness is detected (photometry of subject brightness) based on an image signal output from the image sensor, and the shutter speed and aperture value are determined using the detected subject brightness as an exposure value. In AF processing, the integrated value of the high-frequency component (that is, the contrast value of the subject image) is obtained from the image signal output from the image sensor while changing the lens position of the focus lens, and the lens position at which this integrated value is maximized is matched. Determined as the focal position. This AF process is called so-called hill-climbing contrast detection AF, and is widely adopted.

  In contrast detection AF, when the subject brightness is low, such as when shooting in a dark room, it is difficult to obtain a difference in contrast value at each lens position. For this reason, a subject with a low luminance level is irradiated with illumination light (AF auxiliary light) from a light source such as an LED (light emitting diode) toward the subject to increase the subject brightness, thereby obtaining a sufficient contrast difference. Such a photographing apparatus is known.

However, even if the AF auxiliary light is irradiated as described above, the reach distance of the AF auxiliary light is limited, and sufficient luminance can be obtained even if the AF auxiliary light is irradiated toward a subject at a far distance. Since the level cannot be obtained and a sufficient contrast difference cannot be obtained, the operation accuracy of the focusing operation is lowered. For this reason, in Patent Document 1, a difference in subject brightness is detected between when the AF auxiliary light is irradiated and when it is not irradiated. When this difference is large, a normal AF operation is performed. When this difference is small, The focus lens is moved to the infinity end by determining that the subject is far away. Further, in Patent Document 2, a distance range (AF movement range) corresponding to the difference in subject brightness before and after the irradiation of AF auxiliary light is stored in advance, and the distance range corresponding to the actually obtained difference in subject brightness is set. Based on this, an AF operation is performed.
Japanese Patent No. 3673599 JP 2001-166200 A

  In the above Patent Documents 1 and 2, the exposure setting at each exposure performed when obtaining the difference in subject brightness before and after the irradiation of the AF auxiliary light is not described. For example, if the same exposure value is used before and after AF auxiliary light irradiation, the luminance level due to the presence or absence of AF auxiliary light will change, making the incident light quantity inappropriate (out of the dynamic range), and accurately detecting the subject luminance May not be.

  Image sensors such as CCD and MOS type generally have a small dynamic range and a narrow range of subject brightness that can be measured with a single exposure. Therefore, when trying to measure subject brightness with high accuracy, shutter speed and aperture value It is necessary to expand the subject luminance measurement range by performing multiple exposures while gradually changing the exposure value determined by the combination of the above. In this regard, in the Japanese Patent Application No. 2006-311610, the present applicant first detects the subject brightness accurately by performing exposure while changing the exposure value when the AF auxiliary light is not irradiated (still image AF processing). It is proposed that an exposure value at the time of AF auxiliary light irradiation is determined based on the subject brightness, and the subject brightness is detected based on the exposure value (AF AE process).

  However, in such a processing method, the AF AE process is started after the still image AF process is completed. Therefore, when the difference in subject luminance before and after the irradiation of the AF auxiliary light is obtained as described above. In other words, a time interval (time lag) of about several frame periods occurs between the two detection timings. For this reason, when camera shake or subject blur occurs during this timing lag, there is a problem that a brightness level change unrelated to the presence or absence of AF auxiliary light occurs, and the subject brightness difference cannot be obtained accurately.

  The present invention has been made in view of the above problems, and an imaging apparatus capable of accurately obtaining a difference in subject luminance before and after the irradiation of AF auxiliary light even when camera shake or subject blur occurs and its control It aims to provide a method.

  In order to achieve the above object, an imaging apparatus according to claim 1, wherein an imaging element that converts an electric charge obtained by exposure of subject light into an image signal and outputs the image signal, and subject light is imaged on a light receiving surface of the imaging means. A focus lens, an exposure setting unit that sets an exposure to the image sensor, a luminance detection unit that detects a subject luminance based on the image signal, and an illumination light that irradiates a focus illumination light toward the subject In an imaging apparatus including an irradiating unit and a focusing position detecting unit that detects a focusing position of the focus lens based on the image signal, exposure is performed by the imaging element in a state where illumination light is not irradiated. First brightness detection processing for detecting a first subject brightness, exposure setting with the first subject brightness as a first exposure value, and exposure by the imaging device in a state where illumination light is not irradiated The exposure is set by the second brightness detection process for detecting the second subject brightness and the second exposure value determined based on the first exposure value, and is exposed by the imaging device in a state where illumination light is irradiated. A third luminance detection process for detecting a third subject brightness, a difference calculation process for calculating a difference value between the second subject brightness and the third subject brightness, and the difference value based on the difference value High-speed autofocus processing for performing initial setting of the focus lens, setting the third subject brightness as a third exposure value, and detecting a focus position in a state where illumination light is irradiated, and the first exposure And a control unit that performs exposure setting based on a value and performs imaging processing for performing imaging with the image sensor. Since the third luminance detection process is not performed based on the result of the second luminance detection process, the third luminance detection process can be started before the end of the second luminance detection process, and the second subject for calculating the difference value It is possible to shorten the detection time interval between the luminance and the third subject luminance.

  In the photographing apparatus according to claim 2, the control unit causes the image sensor to perform a plurality of exposures while changing an exposure setting during the first luminance detection process, and the luminance detection unit The first object luminance is detected from the obtained image signal. Thereby, a luminance range exceeding the dynamic range of the image sensor can be measured.

  According to a third aspect of the present invention, the control means determines an initial position and a moving direction of the focus lens based on the difference value during the high-speed autofocus process. The distance of the subject can be determined based on the difference value, and the focusing operation can be speeded up.

In the photographing apparatus according to claim 4, the control unit sets the first exposure value with a shift amount based on the amount of illumination light emitted from the illumination light irradiation unit during the third luminance detection process. A value shifted to the plus side is determined as the second exposure value. Thereby, it is possible to prevent overexposure during illumination light irradiation.

The photographing apparatus according to claim 5 further includes camera shake detection means for detecting camera shake, and the control means does not execute the second luminance detection process when camera shake is not detected by the camera shake detection means. The difference calculation process calculates a difference value between the first subject brightness and the third subject brightness. As a result, it is possible to prevent unnecessary processing from being performed when camera shake cannot occur.

The imaging apparatus according to claim 6, further comprising subject blur detection means for detecting subject blur, wherein the control means detects the second luminance detection process when no subject blur is detected by the subject blur detection means. The difference calculation process calculates a difference value between the first subject brightness and the third subject brightness. Thereby, it is possible to prevent unnecessary processing from being executed when the subject is stationary.

The imaging apparatus according to claim 7, further comprising: a camera shake detection unit that detects camera shake; and an optical axis correction unit that corrects an optical axis of an imaging optical system including the focus lens, wherein the control unit includes the camera shake detection unit. When the camera shake is detected by the means and the detected camera shake angle is within a range that can be corrected by the optical axis correction means, the second luminance detection process is not executed, and the difference calculation process A difference value between one subject brightness and the third subject brightness is calculated. Thereby, the calculation accuracy of the difference value is further improved.

The imaging apparatus according to claim 8 further includes subject blur detection means for detecting subject blur and optical axis correction means for correcting an optical axis of a photographing optical system including the focus lens, wherein the control means includes When the subject blur is detected by the subject blur detection unit and the detected subject blur amount is within a range that can be corrected by the optical axis correction unit, the second luminance detection process is not performed and the difference calculation is performed. In the processing, a difference value between the first subject brightness and the third subject brightness is calculated. Thereby, the calculation accuracy of the difference value is further improved.

  The method for controlling an imaging apparatus according to claim 9 includes: an imaging element that converts an electric charge obtained by exposure of subject light into an image signal and outputs the image signal; and a focus lens that forms subject light on a light receiving surface of the imaging unit; Exposure setting means for setting exposure to the image sensor, brightness detection means for detecting subject brightness based on the image signal, illumination light irradiation means for irradiating focus illumination light toward the subject, And a focus position detection unit that detects a focus position of the focus lens based on the image signal, and performs exposure by the imaging element in a state in which illumination light is not irradiated. A first luminance detecting step for detecting one subject luminance, exposure is set by using the first subject luminance as a first exposure value, and exposure is performed by the imaging device in a state where illumination light is not irradiated. The exposure is set by the second brightness detection step for detecting the second subject brightness and the second exposure value determined based on the first exposure value, and the exposure is performed by the imaging device in the state of irradiating illumination light. A third luminance detecting step for detecting a third subject luminance, a difference calculating step for calculating a difference value between the second subject luminance and the third subject luminance, and based on the difference value A high-speed autofocus step for performing initial setting of the focus lens, setting the third subject brightness as a third exposure value, and detecting a focus position in a state where illumination light is irradiated, and the first exposure And an imaging step of setting exposure according to a value and performing imaging with the imaging device. Since the third luminance detection step is not performed based on the result of the second luminance detection step, the third luminance detection step can be started before the end of the second luminance detection step, and the second subject for calculating the difference value It is possible to shorten the detection time interval between the luminance and the third subject luminance.

  According to the present invention, it is possible to reduce the subject luminance detection time interval for calculating the difference in subject luminance before and after the irradiation of AF auxiliary light, and even when camera shake or subject blur occurs, AF auxiliary light The difference in subject brightness before and after irradiation can be obtained with high accuracy. Thereby, the operation accuracy of the focusing operation performed based on the difference in subject luminance before and after the irradiation of the AF auxiliary light is improved.

  An appearance of a digital camera embodying the present invention is shown in FIG. The digital camera 2 is provided with a photographing lens 4, a strobe light emitting unit 5, and an irradiation window 6 a for an auxiliary light irradiation unit (illumination light irradiation unit) 6 on the front surface of the camera body 3. Also, a release button 7 is provided on the upper surface, and various operation buttons and an LCD 8 (see FIG. 2) are provided on the rear surface.

  The release button 7 is a two-step operation of a half-press and a full-press that is further pressed from this half-press. Under the shooting mode, when the release button 7 is not pressed, a subject image within the shooting range is continuously displayed on the LCD 8, so-called through image display is performed.

  When the release button 7 is pressed halfway, the subject brightness is measured for still image shooting, and the still image AE process for determining the shutter speed and the aperture value according to the subject brightness, and the focus of the taking lens 4 on the subject. Preparation processing including AF processing for matching the two is performed. In addition, when AF processing is performed by irradiating AF auxiliary light from the irradiation window 6a, AF processing is performed after the AF AE processing is performed after the still image AE processing.

  After the preparation process, a still image shooting process is performed. In this still image shooting process, when the release button 7 is further pressed and fully pressed, still image shooting is performed using the still image shutter speed and aperture value determined in the still image AE process. The still image obtained by this still image shooting process is recorded as image data on a memory card 9 (see FIG. 2) that is detachably mounted.

  Even when the release button 7 is fully pressed by a single pressing operation or when the release button 7 is pressed by a single operation, the still image AE process, the AF AE process, and the AF process are sequentially performed. It can also be configured.

  The stroboscopic light emitting unit 5 emits stroboscopic light toward the subject in synchronism with the exposure of the still image when the subject luminance is insufficient. The auxiliary light irradiation unit 6 irradiates AF auxiliary light from the irradiation window 6a toward the subject in order to ensure the brightness necessary for the AF processing when the subject luminance is below a predetermined level.

  Although the auxiliary light irradiation unit 6 provided exclusively for AF is used as the illumination light irradiation means, the illumination light irradiation means is not limited to this, and a light source device provided for other purposes is used as the illumination light. You may use as an irradiation means. For example, the strobe device may emit light during AF processing, or the light source device that emits light for facilitating the framing of the photographer in a dark place may be turned on for AF processing.

  FIG. 2 shows the configuration of the digital camera 2. The system control unit 10 controls each unit of the digital camera 2 based on an operation signal from the operation unit 11 including the release button 7 and various operation buttons.

  An image sensor (imaging device) 12 is disposed behind the photographic lens (photographic optical system) 4, and subject light transmitted through the photographic lens 4 enters the light receiving surface of the image sensor 12. The photographing lens 4 incorporates a focus mechanism 13 for adjusting the focus and a diaphragm mechanism 14 for adjusting the amount of light incident on the image sensor 12.

  The focus mechanism 13 is included in the photographing lens 4 and includes a focus lens 13a that forms an image of subject light on the light receiving surface of the image sensor 12, and a motor or a motor driver that moves the focus lens 13a. By moving the lens 13 a in the optical axis direction of the photographing lens 4, the subject within the photographing distance range between the shortest photographing distance and infinity is brought into focus. The aperture mechanism 14 includes an aperture blade 14a that forms an aperture opening on the optical axis of the photographic lens 4, an actuator that drives the aperture blade, and the like. Adjust the amount of incident light.

  The image sensor 12 uses, for example, a CCD type single-plate color image sensor, and a large number of light receiving elements (photoelectric conversion elements) are two-dimensionally arranged on the light receiving surface thereof. The image sensor 12 is driven by various drive signals from the timing generator 16, converts the subject light into charges corresponding to the amount of light by each light receiving element and accumulates them, and the accumulated charges are voltage signals (image signals). Convert to and output. Thus, the exposed subject image is converted into an electrical signal. The imaging element is not limited to a CCD type image sensor, and a MOS type image sensor may be used.

  The image sensor 12 has an electronic shutter function for adjusting the charge accumulation time (exposure time). This electronic shutter function adjusts the charge accumulation time during the frame period by sweeping out and erasing the charges (unnecessary charges) accumulated so far by the input of the electronic shutter pulse input from the timing generator 16. . By adjusting the input period of the electronic shutter pulse during the frame period, the exposure time, that is, the shutter speed of the electronic shutter can be adjusted. The electronic shutter function and the aperture mechanism 14 constitute an exposure setting means, and the exposure value for the image sensor 12 is determined by the combination of the shutter speed by the electronic shutter function and the aperture value by the aperture mechanism 14.

  The timing generator 16 has various parameters for performing various operations at predetermined timings set by the system control unit 10, and generates a drive signal for driving the image sensor 12, a synchronization signal for synchronously operating each unit, and the like. To do. Depending on the parameters set in the timing generator 16, the shutter speed of the image sensor 12 and the frame rate at which the image sensor 12 repeatedly performs charge accumulation and charge readout can be changed. Note that the timing generator 16 in this example uses one whose setting contents become effective in the next frame period in which parameters are set.

  The image signal from the image sensor 12 is sent to the analog signal processing unit 17. The analog signal processing unit 17 includes a CDS circuit, an AMP circuit, and the like, and performs noise suppression by correlated double sampling, image signal amplification processing, and the like in synchronization with the charge reading operation of the image sensor 12. The A / D converter 18 converts the image signal output from the analog signal processing unit 17 into digital image data and outputs it.

  Image data from the A / D converter 18 is sent to the image input controller 19. The image input controller 19 controls input of image data to the bus 21. Connected to the bus 21 are a system control unit (control means) 10, an image processing unit 22, a compression / decompression unit 23, an AF detection unit 24, an AE detection unit 25, a media controller 26, an internal memory 27, and a VRAM 28. These units are controlled by the system control unit 10 via the bus 21 and can exchange data with each other.

  The image processing unit 22 performs predetermined image processing such as color interpolation, γ correction, white balance correction, and YC conversion on the image data. The compression / decompression unit 23 compresses image data to be recorded on the memory card 9 in a predetermined compression format (for example, JPEG format), and decompresses the image data read from the memory card 9.

  The AF detection unit 24 constitutes a focus position detection unit together with the system control unit 10. The AF detection unit 24 uses the image data from the image input controller 19 to focus the photographic lens 4 and extracts a high-frequency component from an AEAF detection area set in advance in the photographic screen. The AF evaluation value obtained by integrating the components is output to the system control unit 10. Based on the AF evaluation value, the system control unit 10 performs AF processing for matching the focus of the photographing lens 4 to the subject in the AEAF detection area.

  The AE detection unit 25 is a luminance detection unit that detects the luminance of the subject based on the image signal from the image sensor 12, and detects the luminance of the subject for the AEAF detection area based on the image data from the image input controller 19. Do. The detected subject brightness is sent to the system control unit 10. The system control unit 10 determines the shutter speed (TV value) of the image sensor 12 and the aperture value (AV value) of the aperture mechanism 14 based on the subject brightness.

  The media controller 26 controls writing and reading of data in the memory card 9. The image data to be recorded is subjected to various processes by the image processing unit 22 and the compression / decompression unit 23, then sent to the media controller 26, and written to the memory card 9. Further, at the time of reproduction, image data is read from the memory card 9 by the media controller 26, and data expansion processing is performed by the compression / expansion unit 23.

  The internal memory 27 is used as a work memory in which image data being processed by the image processing unit 22 is temporarily written. In addition, image data to be displayed on the LCD 8 is written in the VRAM 28. The D / A converter 31 displays the image based on the image data on the LCD 8 by reading out the image data on the VRAM 28 at a predetermined cycle.

  Under the shooting mode, exposure by the image sensor 12 is repeated, and image data subjected to image processing is written to the VRAM 28 one after another. Thereby, a through image is displayed on the LCD 8. Further, under the playback mode, the image data read from the memory card 9 and decompressed is written into the VRAM 28, so that the captured image recorded on the memory card 9 is displayed on the LCD 8.

  The strobe device 32 is composed of a strobe discharge tube incorporated in the strobe light emitting unit 5 and a circuit for causing it to emit light, and outputs strobe light under the control of the system control unit 10.

  The auxiliary light irradiation unit 6 includes an LED 33 as a light source and a drive circuit 34 that drives the LED 33. The drive circuit 34 is controlled by the system control unit 10 so that the LED 33 is lit at a constant brightness when the subject brightness is below a certain level. Light from the LED 33 is emitted toward the subject from the irradiation window 6a as AF auxiliary light.

  The AF auxiliary light is emitted so as to cover the AEAF detection area. In addition, the constant level of the subject brightness that is a criterion for determining whether or not to irradiate AF auxiliary light is, for example, whether the contrast of the subject image can be detected with sufficient accuracy, that is, whether the in-focus position can be detected with sufficient accuracy. It is not necessary to make the same as the standard for judging whether or not the strobe light is necessary.

  The still image AE process is a process for determining an exposure value used when shooting a still image, and is performed in response to a half-press of the release button 7. In this still image AE process, since the dynamic range of the image sensor 12 is narrow, the brightness range of various assumed shooting scenes is divided into a plurality of measurement ranges, and each measurement range can be measured by the image sensor 12. It is designed to be in a range.

  The AF AE process is a process for determining an exposure value for performing the AF process in a state where the AF auxiliary light is irradiated, and is executed when the subject luminance measured in the still image AE process is equal to or lower than a certain level. In the AF AE process, the subject brightness in the AEAF detection area is detected based on the image data obtained from the exposure of the image sensor 12 in a state where the AF auxiliary light is directed toward the subject, and the subject brightness is used as the exposure value. Determine the shutter speed and aperture value.

  In the AF AE process described above, it is expected that the subject brightness to be measured increases by irradiating the AF auxiliary light. For this reason, the system control unit 10 causes the exposure to be performed together with the irradiation of the AF auxiliary light by using the exposure value obtained by shifting the appropriate exposure value obtained in the AE processing for the still image to the plus side. In addition, the system control unit 10 uses the appropriate exposure value obtained in the AE processing for the still image, and executes exposure in a state where the AF auxiliary light is not irradiated before the AF auxiliary light is irradiated.

  As shown in FIG. 3, when the appropriate exposure value (subject brightness) obtained by the AE process for still images is EV1, a constant measurement determined by the performance of the image sensor 12 with the set exposure value EV1 sandwiched therebetween. The subject luminance within the possible range is a luminance range that can be actually measured. After the exposure is performed using the exposure value EV1, in the AF AE process, the exposure shifted by ΔEV to the plus side of the exposure value EV1 in consideration of the expected increase in subject brightness due to the irradiation of the AF auxiliary light. Exposure is performed using the value EV2. In this way, the measurable object luminance range during the AF AE process is shifted to the plus side by ΔEV so that it can cope with the irradiation of the AF auxiliary light. Further, by performing additional exposure again using the exposure value EV1 obtained by the still image AE process immediately before the AF auxiliary light irradiation, the difference in subject luminance before and after the AF auxiliary light irradiation is shortened. Make it available at time intervals.

  The shift amount ΔEV is determined in association with the amount of AF auxiliary light. For example, it may be determined that the exposure value is shifted to the plus side by an amount corresponding to an increase in luminance when the AF auxiliary light is effectively irradiated and the subject at the normally assumed shooting distance is irradiated with the AF auxiliary light. Also, since the range of the shooting distance where the focus position matches is determined according to the shooting lens and shooting mode, when the AF assist light is irradiated to the subject with the shortest shooting distance within the shooting distance range, It is also preferable to determine the shift amount ΔEV so that the luminance falls within the measurable range. Note that as the shooting distance is longer, the amount of increase in subject luminance due to the irradiation of the AF auxiliary light decreases. Therefore, in consideration of the dynamic range of the image sensor 12, it is preferable to determine the shift amount ΔEV so that the subject luminance (EV1) measured by the still image AE process is included in the measurable range related to the exposure value after the shift. .

  In the AF process, when the AF auxiliary light is not irradiated, the appropriate exposure value determined in the still image AE process is used. When the AF auxiliary light is irradiated, the exposure determined in the AF AE process is used. The focusing operation is performed using the value. As this focusing operation, an AF evaluation value (contrast value) is obtained from the image signal output from the image sensor 12 while changing the lens position of the focus lens 13a, and the lens position at which this integrated value is maximum is the focusing position. The above-described hill-climbing contrast detection AF is performed.

  By using the same aperture value in the AF AE process and the AF process, the time loss associated with the change in aperture value when shifting from the AF AE process to the AF process is eliminated. Further, by using the aperture value used for still image shooting, that is, the aperture value determined in the still image AE processing, for AF processing, time loss when shifting from AF processing to still image shooting is eliminated. By doing so, the aperture value used for still image shooting is used whenever the aperture value used for AF AE processing is used.

  Specifically, after the aperture mechanism 14 is driven to the aperture value determined by the still image AE process, in the AF AE process, exposure is performed by shifting the shutter speed to the high speed side by the shift amount ΔEV. Further, the exposure value determined by the AF AE process is also dealt with by changing the shutter speed.

  As shown in FIG. 4, when the shutter speed TV1 and the aperture value AV1 are determined by a predetermined program line PL with respect to the exposure value EV1 obtained in the still image AE process, the aperture value is determined in the AF AE process. The shutter speed TV2 (= TV1 + ΔEV) is obtained by shifting the shutter speed to the high speed side by the shift amount ΔEV while AV1 is fixed. If an appropriate exposure value for the subject luminance measured in the AF AE process is EV3, the AF speed uses a shutter speed TV3 (= EV3−AV1) that becomes the exposure value EV3 below the aperture value AV1. EV1 'indicates the subject brightness measured by performing additional exposure using the exposure value EV1 obtained by the AE process for still images immediately before the irradiation of the AF auxiliary light. The subject brightness EV1 'matches the exposure value EV1 under ideal shooting conditions in which camera shake, subject blur, and the like do not occur.

  As described above, the system control unit 10 performs the AF process for matching the focus of the photographing lens 4 to the subject in the AEAF detection area. This AF process includes a normal AF process performed when the AF auxiliary light is not irradiated and a high-speed AF process performed when the AF auxiliary light is irradiated. Furthermore, there are a first AF operation and a second AF operation in which the movement start position and the movement direction of the focus lens 13a are different as operations when detecting the focus position of the focus lens 13a that is in focus with the subject.

  As shown in FIG. 5A, the first AF operation is an operation of moving (stepping) the focus lens 13a from the short-distance side lens end toward the long-distance lens end. Further, as shown in FIG. 5B, the second AF operation is an operation of moving (stepping) the focus lens 13a from the long-distance side lens end toward the short-distance lens end. Note that the short-distance lens end is set closer to the short-distance side than the shortest lens position corresponding to the shortest shooting distance. Further, the far-end side lens end is set on the far side from the infinity lens position corresponding to infinity.

  In the normal AF process and the high-speed AF process, exposure is performed by the image sensor 12 every time the focus lens 13a is moved stepwise by the first AF operation or the second AF operation, an AF evaluation value is acquired, and the AF evaluation value is changed from increasing to decreasing. The lens position (peak position) is detected as the focus position, and immediately after the detection, the focus lens 13a is moved to the focus position and set.

  In the normal AF process, the focus position is detected using one of the first and second AF operations (for example, the first AF operation). In the high-speed AF process, in order to shorten the focusing time, one of the first and second AF operations is selected by estimating the distance to the subject from the difference in subject luminance before and after the start of the AF auxiliary light irradiation. The

  In the high-speed AF process, the system control unit 10 sets the above-described subject brightness EV1 ′ as the subject brightness before starting the AF auxiliary light irradiation, and sets the subject brightness EV3 measured by the AF AE process as the subject after the AF auxiliary light irradiation starts. The difference value δ (= EV3−EV1 ′) is calculated using the luminance. When the difference value δ is larger than the predetermined value Eth (δ> Eth), the system control unit 10 selects the first AF operation. This is because it is estimated that the subject in the AEAF detection area is located at a short distance where the luminance is increased by the irradiation of the AF auxiliary light. On the other hand, the system control unit 10 selects the second AF operation when the difference value δ is equal to or smaller than the predetermined value Eth (δ ≦ Eth). This is because it is estimated that the subject in the AEAF detection area is located at a long distance so that the luminance does not increase by the irradiation of the AF auxiliary light.

  It should be noted that the predetermined value Eth can be used to estimate the in-focus position at high speed by estimating the distance of the subject without being affected even if there is some variation in the brightness of each subject before and after the start of the AF auxiliary light irradiation. In consideration of the measurement accuracy of the subject brightness, it is set so that it can be performed. The predetermined value Eth is, for example, about 0.5 EV.

  Next, the operation of the above configuration will be described with reference to FIGS. 6 and 7, when the release button 7 is half-pressed, a still image AE process for measuring the subject brightness EV1 is started in response. Assuming that the frame period immediately after the release button 7 is half-pressed is the first, a parameter including the shutter speed of the first photometry is set in the timing generator 16 by the system control unit 10 during the first frame period. .

  When the second frame period is reached, the input of the electronic shutter pulse is started, and the input of the electronic shutter pulse is stopped after the aperture mechanism 14 is set to the aperture value (initial value) for the first photometry. Exposure Ea1 by the image sensor 12 is performed. The driving of the image sensor 12 at this time is performed based on parameters set in the timing generator 16 during the first frame period.

  In the third frame period, the charges accumulated in the respective light receiving elements of the image sensor 12 are transferred (read) by the exposure Ea1, and an image signal is output. This image signal is converted into image data via the analog signal processing unit 17 and the A / D converter 18 and then sent to the AE detection unit 25 via the image input controller 19.

  In the second frame period during which the exposure Ea1 is performed, a parameter for the second photometry that is different from the exposure value at the time of the first exposure Ea1 is set in the timing generator 16, and the third one is set. During the frame period, exposure Ea2 by the image sensor 12 is performed with an exposure value smaller than that during the first exposure Ea1 by changing the aperture value and the shutter speed. In the subsequent fourth frame period, an image signal by the exposure Ea2 is output, and the image data is sent to the AE detector 25.

  Similarly, in the third frame period during which the exposure Ea2 is performed, a parameter for the third photometry that is different from the exposure value in the second exposure Ea1 is set in the timing generator 16, and the fourth In this frame period, the exposure Ea3 by the image sensor 12 is performed with an exposure value smaller than that in the second exposure Ea2. In the subsequent fifth frame period, an image signal by the exposure Ea3 is output, and the image data is sent to the AE detector 25.

  In the fourth frame period during which exposure Ea3 is performed, parameters for the fourth photometry are set in the timing generator 16, and the aperture value and shutter speed are changed in the fifth frame period. First, exposure Ea4 for detecting the smear component is performed with the same exposure value as in the third exposure Ea3. During the subsequent sixth frame period, the transfer operation (vertical and horizontal transfer) of the image sensor 12 is performed without moving the charge accumulation of the light receiving element to the vertical transfer path, and the smear component does not include the subject image component. Only the image data is sent to the AE detector 25. Note that since the third exposure Ea3 has the smallest exposure value and is easily affected by smear, the smear component is acquired as the correction data.

  When the acquisition of each image data is completed as described above, the subject brightness EV1 (first subject brightness) of the AEAF detection area is set to AE in the subsequent seventh frame period based on the image data obtained by each photometry. The subject luminance EV1 obtained by the detection unit 25 is sent to the system control unit 10 as an exposure value EV1 for photographing a still image. When obtaining the subject brightness EV1, the image data obtained by the first and second exposures Ea1 and Ea2 and the image data obtained by exposing the exposure Ea3 are corrected based on the image data (smear component) obtained by the exposure Ea4. Done with.

  The exposure value EV1 is converted into a combination of the shutter speed TV1 and the aperture value AV1 based on a predetermined program line, and the aperture mechanism 14 is driven so as to become the aperture value AV1 in the subsequent eighth frame period. Further, in the eighth frame period, the system control unit 10 determines whether or not the AF auxiliary light needs to be emitted from the subject luminance EV1. For example, when the subject brightness EV1 is equal to or lower than a predetermined level, it is determined that AF auxiliary light is necessary, and the above-described shift amount ΔEV is calculated by the system control unit 10 from the amount of AF auxiliary light and a predetermined parameter.

  When the shutter speed TV1 is shifted based on the shift amount ΔEV, if the shutter speed TV2 (= TV1 + ΔEV) exceeds the fastest shutter speed TVmax of the image sensor 12, a certain amount of AF assistance light is not used. Assuming that there is brightness, the shutter speed is set to TV1, and the same processing (normal AF processing) as when AF auxiliary light is not irradiated is performed. In this case, the AF AE process may be continued after the aperture mechanism 14 is driven so that the shutter speed TV2 is equal to or lower than the shutter speed TVmax.

  When the subject brightness EV1 is higher than a predetermined level and AF auxiliary light needs to be emitted, AF assist is performed under the exposure settings of the shutter speed TV1 and the aperture value AV1 (first exposure value) when the ninth frame period is reached. In a state where light is not irradiated, exposure Eb (re-photometry) by the image sensor 12 is performed. In the subsequent tenth frame period, an image signal by the exposure Eb is output, and the image data is sent to the AE detector 25.

  In the ninth frame period during which exposure Eb is performed, a parameter including the shutter speed TV2 obtained by increasing the shutter speed TV1 determined by the still image AE process by the shift amount ΔEV is set in the timing generator 16. The Next, when the AF AE process is started in the 10th frame period, the LED 33 is turned on and the irradiation of the AF auxiliary light is started, and the aperture value AV1 and the shutter speed TV2 (second exposure value) are set. Under the exposure setting, exposure Ec by the image sensor 12 is performed. In the subsequent eleventh frame period, an image signal by the exposure Ec is output, and the image data is sent to the AE detection unit 25.

  Further, during the eleventh frame period, the subject brightness EV1 '(second subject brightness) when the AF auxiliary light is not irradiated is obtained from the image data of the exposure Eb by the AE detection unit 25. In addition, during the 12th frame period, the AE detection unit 25 obtains the subject brightness EV3 (third subject brightness) when the AF auxiliary light is irradiated from the image data of the exposure Ec. The subject brightness EV3 is an appropriate exposure value for the AEAF detection area in a state where the AF auxiliary light is irradiated.

  Further, during the 12th frame period, the shutter speed TV3 used in the AF process is obtained from the exposure value EV3 and the aperture value AV1, and the AF process is started in the 13th frame period. Then, parameters including the shutter speed TV3 are set in the timing generator 16. Further, during the 13th frame period, the difference value δ (= EV3−EV1 ′) is calculated by the system control unit 10.

  After the 14th frame period, the high-speed AF process shown in FIG. 8 is executed under the exposure settings of the aperture value AV1 and the shutter speed TV3 (third exposure value). When the high-speed AF process is started, the system control unit 10 compares the difference value δ with the predetermined value Eth. As a result of this comparison, the first AF operation is selected when the difference value δ is greater, and the second AF operation is selected when the difference value δ or less.

  When the first AF operation is selected, the focus lens 13a is moved to the near-end side lens end, and exposure is sequentially performed while moving the focus lens 13a toward the far-end side lens end step by step, thereby evaluating the AF evaluation value. Will continue to get. On the other hand, when the second AF operation is selected, the focus lens 13a is moved to the far side lens end, and the exposure is sequentially performed while moving the focus lens 13a toward the near side lens end step by step. Obtain evaluation values. Then, the lens position with the maximum AF evaluation value is detected as the in-focus position. The focus lens 13a is set at the in-focus position.

  When this high-speed AF process is completed, the LED 33 is turned off and the irradiation of the AF auxiliary light is stopped. Thereafter, the camera enters a standby state for still image shooting processing. When the release button 7 is fully pressed during this standby state, parameters for shooting a still image are set in the timing generator 16, and the aperture value AV1 and shutter speed are set. Exposure for a still image is performed with the exposure setting of TV1 (first exposure value). Then, the image data obtained by this exposure and subjected to image processing and data compression are recorded in the memory card 9.

  As described above, in this digital camera 2, the distance of the subject is estimated based on the difference value δ of the subject luminance before and after the AF auxiliary light irradiation is started, and the first AF operation / second AF operation is selected, that is, the focus lens 13a. Since the focus position is detected by selecting the movement start position and the movement direction, it is possible to detect the focus position with a small amount of movement.

  In the digital camera 2, exposure is performed again using the appropriate exposure value EV1 detected in the AE process for still image immediately before the AF AE process for irradiating AF auxiliary light, and the subject brightness obtained by this exposure is obtained. Since the difference value δ is calculated by using EV1 ′ and the subject brightness EV3 detected by the AF AE process, the subject brightness acquisition time interval before and after the AF auxiliary light irradiation is started is short, and it is caused by camera shake or subject shake. The influence can be prevented. In the above embodiment, the acquisition time interval of the subject luminances EV1 ′ and EV3 is set to one frame period (for example, 30 ms). However, this time interval is not limited to one frame period, and influences due to camera shake and subject shake are allowed. You may change suitably within the range.

  Next, a second embodiment of the present invention will be described. FIG. 9 shows a digital camera 40 according to the second embodiment. The digital camera 40 is different from the configuration of the digital camera 2 according to the first embodiment only in that it further includes a camera shake detection unit (camera shake detection unit) 41. The same components as those in the above embodiment are denoted by the same reference numerals, and description thereof is omitted.

  The camera shake detection unit 41 includes a known gyro sensor that detects an angular velocity, and detects camera shake within a predetermined time. As shown in FIG. 10, when the camera shake detected by the camera shake detection unit 41 during the AE processing for the still image is detected during the AF auxiliary light irradiation, the system control unit 10 re-exposes Eb described above. If no camera shake is detected, control is performed so that the AF AE process is performed without performing the re-exposure Eb.

  In the control flow of FIG. 10, when the shutter speed TV1 is shifted based on the shift amount ΔEV, until the determination of whether the shutter speed TV2 (= TV1 + ΔEV) exceeds the fastest shutter speed TVmax of the image sensor 12 or not. The flow is the same as that shown in FIG. When the shutter speed TV2 is equal to or lower than the shutter speed TVmax, it is determined whether or not the camera shake is detected by the camera shake detection unit 41 immediately before that.

  When camera shake is detected, the same processing as in the first embodiment, that is, re-exposure Eb is performed before the AF auxiliary light is irradiated, and the subject brightness EV1 'is calculated. Thereby, the acquisition time interval of the subject luminance difference is shortened, and the influence of camera shake is prevented. On the other hand, when no camera shake is detected, the influence of the camera shake can be ignored. Therefore, the re-exposure Eb is not performed before the AF auxiliary light irradiation, and the difference value δ is the subject brightness EV3 detected by the AF AE process. A value obtained by subtracting the subject brightness EV1 detected by the still image AE process from (δ = EV3−EV1). In this case, the ninth frame period shown in FIG. 8 becomes unnecessary, and the processing time is shortened accordingly.

  As described above, the configuration is such that the re-exposure Eb is selectively executed based on the camera shake detection result, so that when camera shake cannot occur as in shooting using a tripod, wasteful processing is executed. This can be prevented. In addition, as the determination of the camera shake detection by the system control unit 10, it is preferable to perform the determination by comparing the camera shake angle within a certain time detected by the camera shake detection unit 41 with a predetermined threshold value.

  Next, a third embodiment of the present invention will be described. FIG. 11 shows a digital camera 50 according to the third embodiment. The digital camera 50 is different from the configuration of the digital camera 50 according to the second embodiment only in that it includes a subject blur detection unit (subject blur detection unit) 51 instead of the camera shake detection unit 41. The same components as those in the above embodiment are denoted by the same reference numerals, and description thereof is omitted.

  The subject blur detection unit 51 includes a processing circuit that detects a motion vector of a subject by inter-frame calculation using a plurality of image data acquired in different frame periods. The subject blur detection unit 51 includes a subject within an AEAF detection area within a predetermined time. Detect shake. As shown in FIG. 12, the system control unit 10 performs the above-described re-exposure Eb when subject blur is detected by the subject blur detection unit 51 during the AE processing for still image when performing AF auxiliary light irradiation. If no subject blur is detected, control is performed so that the AF AE process is performed without performing the re-exposure Eb.

  As described above, by performing the re-exposure Eb selectively based on the subject blur detection result, similarly, it is possible to prevent unnecessary processing from being performed. In addition, as the determination of subject blur detection by the system control unit 10, it is preferable to perform the determination by comparing the subject blur amount (movement amount) within a predetermined time detected by the subject blur detection unit 51 with a predetermined threshold.

  Next, a fourth embodiment of the present invention will be described. FIG. 13 shows a digital camera 60 according to the fourth embodiment. The digital camera 60 only includes an optical axis correction mechanism (optical axis correction means) including a correction lens 61, an actuator 62, a driver 63, and a position detection unit 64 in addition to the camera shake detection unit 41. Is different from the configuration of the digital camera 40 according to the second embodiment. The same components as those in the above embodiment are denoted by the same reference numerals, and description thereof is omitted.

  The correction lens 61 is a lens for correcting the optical axis of the photographic lens 4, is disposed immediately before the image sensor 12, and is provided so as to be movable in a direction perpendicular to the optical axis of the photographic lens 4. The actuator 62 includes a voice coil motor (VCM) or the like, and moves the correction lens 61. The driver 63 drives the actuator 62 based on the control from the system control unit 10. The position detection unit 64 is a non-contact type position detection sensor including a magnet and a Hall element, and detects the position of the correction lens 61 and inputs a detection value to the system control unit 10.

  The system control unit 10 controls the driver 63 while monitoring the position information of the correction lens 61 from the position detection unit 64 based on the camera shake angle detected by the camera shake detection unit 41, and cancels the camera shake. 4 is corrected. As shown in FIG. 14, the system control unit 10, when performing AF auxiliary light irradiation, detects a camera shake angle even when a camera shake is detected by the camera shake detection unit 41 during AE processing for still images. If it is within a range that can be corrected by the optical axis correction mechanism (for example, within 0.3 °), control is executed so that AF AE processing is performed without performing re-exposure Eb.

  In this way, by providing the optical axis correction mechanism, it is possible to accurately detect the difference in subject brightness before and after the irradiation of the AF auxiliary light, and even when camera shake is detected, the optical axis correction can be performed. By configuring so that the re-exposure Eb is executed only when it is impossible, it is possible to prevent unnecessary processing from being executed when the amount of camera shake is small.

  Next, a fifth embodiment of the present invention will be described. FIG. 15 shows a digital camera 70 according to the fourth embodiment. The digital camera 70 differs from the configuration of the digital camera 60 according to the fourth embodiment only in that a subject blur detection unit 51 is provided instead of the camera shake detection unit 41. The same components as those in the above embodiment are denoted by the same reference numerals, and description thereof is omitted.

  Based on the subject blur amount (movement amount) detected by the subject blur detection unit 51, the system control unit 10 controls the driver 63 while monitoring the position information of the correction lens 61 from the position detection unit 64, and the subject blur is detected. The optical axis of the photographic lens 4 is corrected so as to cancel out. As shown in FIG. 16, the system control unit 10 detects the detected subject even when the subject blur is detected by the subject blur detection unit 51 during the AE processing for the still image when the AF auxiliary light is irradiated. If the shake amount is within a range that can be corrected by the optical axis correction mechanism (for example, within a movement range corresponding to a shake angle of 0.3 °), control is performed so that AF AE processing is performed without performing re-exposure Eb. To do.

  As described above, the re-exposure Eb is executed only when the optical axis correction is impossible even when the subject blur is detected, so that a wasteful process can be performed when the subject blur amount is small. Execution can be prevented.

  In each of the above embodiments, the still image AE process is executed when the release button 7 is half-pressed. However, the still image AE process is repeatedly executed before the release button 7 is half-pressed. In this case, the re-exposure Eb and AF AE processing may be executed when the release button 7 is half-pressed.

  In each of the above embodiments, a digital camera has been described as a photographing apparatus. However, a camera-equipped mobile phone or the like is provided as long as it has an AF / AE function based on an image signal from an image sensor and an illumination light irradiation function. The present invention can be applied to various types of imaging apparatuses.

It is a perspective view which shows the external appearance of the digital camera which implemented this invention. It is a block diagram which shows the structure of a digital camera. It is a graph which shows the relationship between the exposure value determined by the AE process for still images, and the exposure value used by the AE process for AF. 6 is a graph showing an example of a relationship between an aperture value and shutter speed determined by still image AE and an aperture value and shutter speed used in AF AE processing and AF processing; It is explanatory drawing which shows the movement start position and movement direction of a focus lens. It is a flowchart which shows the process sequence of imaging | photography performed in response to operation of a release button. It is a timing chart which shows operation | movement of each part at the time of half-pressing the release button in the case of irradiating AF auxiliary light. It is a flowchart which shows the procedure of the high-speed AF process performed when irradiating AF auxiliary light. It is a block diagram which shows the structure of the digital camera concerning the 2nd Embodiment of this invention. It is a flowchart which shows the imaging | photography process sequence of the digital camera concerning the 2nd Embodiment of this invention. It is a block diagram which shows the structure of the digital camera concerning the 3rd Embodiment of this invention. It is a flowchart which shows the imaging | photography process sequence of the digital camera concerning the 3rd Embodiment of this invention. It is a block diagram which shows the structure of the digital camera concerning the 4th Embodiment of this invention. It is a flowchart which shows the imaging | photography process sequence of the digital camera concerning the 4th Embodiment of this invention. It is a block diagram which shows the structure of the digital camera concerning the 5th Embodiment of this invention. It is a flowchart which shows the imaging | photography process sequence of the digital camera concerning the 5th Embodiment of this invention.

Explanation of symbols

2, 40, 50, 60, 70 Digital camera 4 Shooting lens 6 Auxiliary light irradiation unit 10 System control unit 12 Image sensor 13 Focus mechanism 14 Aperture mechanism 24 AF detection unit 25 AE detection unit 33 LED
41 Camera shake detection unit 51 Subject shake detection unit 61 Correction lens 62 Actuator 64 Position detection unit

Claims (9)

An image sensor that converts the electric charge obtained by exposure of the subject light into an image signal and outputs it, a focus lens that forms an image of the subject light on the light receiving surface of the imaging means, and an exposure setting that sets the exposure for the image sensor Means, brightness detecting means for detecting subject brightness based on the image signal, illumination light irradiating means for irradiating focusing illumination light toward the subject, and a focus position of the focus lens based on the image signal In a photographing apparatus provided with an in-focus position detecting means for detecting
A first luminance detection process for detecting a first subject luminance by performing exposure with the imaging element in a state where illumination light is not irradiated;
A second luminance detection process in which the first subject luminance is set as an exposure value and exposure is performed by the imaging element in a state where illumination light is not irradiated, and second subject luminance is detected;
A third luminance detection process in which exposure is set by a second exposure value determined based on the first exposure value, exposure is performed by the imaging element in a state in which illumination light is irradiated, and a third subject luminance is detected; ,
A difference calculation process for calculating a difference value between the second subject brightness and the third subject brightness;
A high-speed autofocus process that performs initial setting of the focus lens based on the difference value, sets the third subject brightness as an exposure value as a third exposure value, and detects a focus position in a state where illumination light is irradiated. When,
A shooting process for setting exposure according to the first exposure value and shooting with the image sensor;
An imaging apparatus comprising control means for executing   The control means causes the imaging device to execute a plurality of exposures while changing the exposure setting during the first brightness detection process, and the brightness detection means uses the image signal obtained by each exposure as a first subject. The photographing apparatus according to claim 1, wherein luminance is detected.   The photographing apparatus according to claim 1, wherein the control unit determines an initial position and a moving direction of the focus lens based on the difference value during the high-speed autofocus process. The control means, wherein the third time luminance detection process, the illumination light by a shift amount based on the amount of illumination light irradiated from the irradiation means, the first of said shift value to the positive side of the exposure value second The photographing apparatus according to any one of claims 1 to 3, wherein the exposure value is determined as an exposure value. The camera control unit further includes a camera shake detection unit that detects camera shake, and the control unit does not execute the second luminance detection process when the camera shake detection unit detects no camera shake. 5. The photographing apparatus according to claim 1, wherein a difference value between the subject brightness of the subject and the third subject brightness is calculated. Subject blur detection means for detecting subject blur is further provided, and the control means does not execute the second luminance detection process when the subject blur detection means does not detect the subject blur detection, and the difference calculation process The photographing apparatus according to claim 1, wherein a difference value between the first subject brightness and the third subject brightness is calculated. A camera shake detecting unit for detecting camera shake; and an optical axis correcting unit for correcting an optical axis of a photographing optical system including the focus lens, wherein the control unit detects and detects camera shake by the camera shake detecting unit. When the camera shake angle is within a range that can be corrected by the optical axis correction unit, the second luminance detection process is not executed, and the difference calculation process does not execute the second luminance detection process. 5. The photographing apparatus according to claim 1, wherein a difference value with respect to luminance is calculated. Further provided is a subject blur detection unit for detecting subject blur and an optical axis correction unit for correcting an optical axis of a photographing optical system including the focus lens, and the control unit detects the subject blur by the subject blur detection unit. When the detected subject shake amount is within a range that can be corrected by the optical axis correction unit, the second luminance detection process is not executed, and the difference calculation process calculates the first subject luminance and 5. The photographing apparatus according to claim 1, wherein a difference value with respect to the third subject brightness is calculated. An image sensor that converts the electric charge obtained by exposure of the subject light into an image signal and outputs it, a focus lens that forms an image of the subject light on the light receiving surface of the imaging means, and an exposure setting that sets the exposure for the image sensor Means, brightness detecting means for detecting subject brightness based on the image signal, illumination light irradiating means for irradiating focusing illumination light toward the subject, and a focus position of the focus lens based on the image signal In a focus position detection means for detecting a photographing device comprising:
A first luminance detection step of detecting a first subject luminance by performing exposure with the imaging element in a state where illumination light is not irradiated;
A second luminance detecting step of setting the first subject luminance as a first exposure value, performing exposure with the imaging element in a state in which illumination light is not irradiated, and detecting a second subject luminance;
A third luminance detecting step of setting exposure with a second exposure value determined based on the first exposure value, performing exposure with the imaging element in a state of irradiating illumination light, and detecting a third subject luminance; ,
A difference calculating step for calculating a difference value between the second subject brightness and the third subject brightness;
A high-speed autofocus step for performing initial setting of the focus lens based on the difference value, setting the third subject brightness as an exposure value as a third exposure value, and detecting a focus position in a state where illumination light is irradiated When,
A shooting step of setting an exposure with the first exposure value and shooting with the image sensor;
A method for controlling an imaging apparatus, comprising:

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