JP2008164731A - Photographing device and its control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately decide an exposure value to be used for autofocus processing using AF auxiliary light concurrently in a short period of time. <P>SOLUTION: Subject luminance is detected from an image signal outputted from an image sensor 12 by an AE detection part 25. When a release button is half-depressed, exposure is performed while changing the exposure value, and the subject luminance is obtained from the image signal obtained in each exposure, then, shutter speed and an aperture value are decided when taking a still picture. If the subject luminance is lower than a fixed level, the AF auxiliary light is radiated to a subject from an auxiliary light radiation part 6. The exposure is performed at the exposure value obtained by shifting the exposure value to a positive side by a shift amount ΔEV further than the exposure value (shutter speed and aperture value) obtained to take the still picture, and the exposure value when AF processing is performed, is decided based on the image signal obtained from the exposure. The shift amount ΔEV is decided according to a subject distance estimated from the size of person's face specified from a photographic screen. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a photographing apparatus that takes an image with an image sensor and a control method thereof.

  2. Description of the Related Art In recent years, digital cameras that convert a subject image captured by an image sensor such as a CCD or MOS type into digital image data and record it on a recording medium such as a built-in memory or a memory card have become widespread. In many digital cameras, automatic exposure control (AE) processing and autofocus (AF) processing are performed with reference to an image signal obtained by an image sensor.

  In AE processing, subject brightness is detected from an image signal obtained by exposing a subject image with an image sensor, and a combination of shutter speed and aperture value, that is, an exposure value is set so that appropriate exposure is obtained according to the brightness level. I try to decide. In AF processing, a contrast detection method is often employed, and the integrated position of the high-frequency component of the image signal obtained by exposing the subject image is the maximum, that is, the in-focus position where the contrast of the subject image is the highest. And the lens position of the photographic lens is moved to the in-focus position.

  When the AF process is performed as described above, the contrast is evaluated while sequentially moving the lens position of the photographing lens, and control is performed so as to detect the in-focus position where the contrast is maximized. However, a sufficient contrast cannot be obtained from a subject image with a low luminance level as in the case of shooting in a dark room or the like. For this reason, for a subject image with a low luminance level, a digital camera is also known in which AF auxiliary light is emitted from a light source such as an LED toward the subject to increase the subject luminance and obtain sufficient contrast. ing.

  By the way, in the AF processing as described above, contrast detection is performed using an exposure value corresponding to the luminance level detected immediately before. However, if the luminance level is excessively increased by irradiation with AF auxiliary light, Since the overexposure is over, the in-focus position cannot be detected. In addition, even when AF auxiliary light is irradiated, a focus position may not be detected because sufficient light quantity and contrast cannot be obtained. In response to such a problem, Patent Document 1 determines whether or not to emit auxiliary light according to the contrast of a subject in a state in which no auxiliary light is irradiated when distance measurement is performed by a distance measuring sensor. Control is performed to prohibit photographing when the subject brightness exceeds a certain level when the auxiliary light is irradiated.

There is also known a digital camera that obtains a difference in subject luminance between before irradiation with AF auxiliary light and during irradiation with the maximum amount of light, and determines an optimum amount of AF auxiliary light from the difference (for example, Patent Document 2). reference). Furthermore, when performing strobe shooting, it is possible to determine the main subject and sub-subject on the shooting screen, and to perform appropriate shooting by performing exposure control based on their positions on the shooting screen and their mutual relationships. Such a camera is also known (see, for example, Patent Document 3).
JP 2002-341230 A JP 2003-114374 A JP 2005-055570 A

  In order to cope with the luminance change caused by the AF auxiliary light as described above, the subject luminance is measured in the state of the AF auxiliary light being applied, and the exposure value of the AF processing is determined based on the result. That's fine. However, since the image sensor has a small dynamic range and a narrow range of subject brightness that can be measured by one exposure, the subject brightness may not be measured accurately. Therefore, it is possible to measure the subject brightness with high accuracy by changing the shutter speed and the combination of the apertures, performing exposure at different exposure values, and performing multiple measurements with the measurable subject brightness range shifted. Although it is possible, in this case, it takes a considerable time to measure the subject brightness. For this reason, for example, in the case of performing still image exposure after performing AF processing in response to the operation of the release button, the subject brightness as described above is measured together with the AF processing immediately before exposure of the still image. There is a problem that the release time lag from the operation of the release button to the actual shooting of the still image increases.

  The present invention has been made in view of the above circumstances, and is capable of accurately determining an exposure value when performing autofocus processing by irradiating illumination light, and capable of performing autofocus processing with high accuracy. And a control method thereof.

  In order to achieve the above object, in the photographing apparatus according to claim 1, subject luminance for determining the first exposure value based on an image signal obtained by exposure of the image sensor in a state in which illumination light is not irradiated is set. In the autofocus process based on the image signal obtained by performing the first luminance detection to be detected and irradiating the illumination light and detecting the exposure of the image sensor under the second exposure value after the first luminance detection. Brightness detection means for performing second brightness detection for detecting subject brightness for determining the third exposure value, distance determination means for determining the subject distance to the subject, the amount of illumination light and the distance determination means Shift amount determining means for obtaining a shift amount to be the second exposure value optimum for the second luminance detection based on the subject distance determined by the first luminance value based on the first luminance detection. The And determining the second exposure value by shifting the first exposure value by the shift amount obtained by the shift amount determining means, and determining the third exposure value based on the second luminance detection. Exposure value determining means and exposure control means for executing exposure for second luminance detection using the second exposure value.

  The photographing apparatus according to claim 2, further comprising face detection means for specifying a human face area in the shooting screen based on an image signal from the image sensor, wherein the distance determination means is the person specified by the face detection means. The subject distance is determined from the size of the face. According to a third aspect of the present invention, the face detecting means specifies the center position of the face area specified together with the face area, and the shift amount determining means is the center of the face area in the shooting screen. The shift amount is reduced as the position is closer to the periphery of the shooting screen.

  According to a fourth aspect of the present invention, the face detecting means specifies the center position of the face area specified together with the face area, and the shift amount determining means is such that the subject distance is shorter than the normal shooting distance. Or when a macro mode for photographing a close subject is selected, based on the center position of the face area in the photographing screen, due to the deviation of the irradiation window that outputs the illumination light with respect to the position of the photographing lens The shift amount is corrected in consideration of unevenness in the amount of illumination light in the photographed screen.

  According to a fifth aspect of the present invention, a distance measuring sensor for measuring the distance to the subject is provided, and the distance determining means determines the distance to the subject based on the detection result of the distance measuring sensor.

  According to a sixth aspect of the present invention, there is provided a position detecting means for detecting the lens position of the photographing lens, and the distance judging means judges the subject distance based on the detected lens position. is there. In the photographing apparatus according to the seventh aspect, the focus control means determines whether or not the photographing lens is in a focus position with respect to the subject at a predetermined interval before operating the release button. If not, the photographic lens is driven so that the photographic lens is in the in-focus position, and the distance determining means is in the in-focus position immediately before determining the second exposure value. The subject distance is determined based on the lens position.

  According to another aspect of the present invention, the distance determining means is based on the lens position of the taking lens when the distance determining means is brought into the in-focus position by the autofocus process performed by the focus control means in response to the previous operation of the release button. Thus, the subject distance is determined. In the photographing apparatus according to claim 9, the distance determination means performs the release operation within a predetermined time from the previous release button operation, and the subject brightness measured in response to the previous release button operation. And the subject brightness measured in response to the current release button operation is less than a predetermined value, the autofocus process performed by the focus control means in response to the previous release button operation The subject distance is determined based on the lens position of the photographing lens when the focal position is set.

  According to a tenth aspect of the present invention, the apparatus includes a reflectance determination unit that determines the reflectance of the subject, and the shift amount determination unit further determines the shift amount using the reflectance obtained from the reflectance determination unit. Is.

  The imaging device according to claim 11, wherein the first luminance detection for detecting the subject luminance for determining the first exposure value based on an image signal obtained by exposure of the image sensor in a state where illumination light is not irradiated is performed. In addition, after the first luminance detection, the third exposure value in the autofocus process is determined based on an image signal obtained by irradiating illumination light and exposure of the image sensor under the second exposure value. Luminance detecting means for performing second luminance detection for detecting subject luminance, reflectance determining means for determining the reflectance of the subject, the amount of illumination light, and the reflectance determined by the reflectance determining means Shift amount determining means for determining the shift amount based on the first brightness value, determining the first exposure value based on the first luminance detection, and shifting the first exposure value by the shift amount determined by the shift amount determining means. Second An exposure value determining means for determining an exposure value and determining a third exposure value based on the second luminance detection, and an exposure for executing exposure for the second luminance detection using the second exposure value And a control means.

  In the photographing apparatus of the twelfth aspect, the reflectance determining means determines the color of the subject based on the image signal from the image sensor, and estimates the reflectance of the subject from the determined color.

  14. The photographing apparatus according to claim 13, wherein the first luminance detection is detection of subject luminance performed to determine an exposure value at the time of photographing a still image, and the luminance detection means responds to an operation of a release button. Thus, the first luminance detection is performed.

  In the photographing apparatus according to claim 14, the luminance detection means performs exposure by the image sensor using a plurality of different exposure values at the time of detecting the first luminance, thereby setting a range of subject luminance to be measured. The detection is performed by dividing into luminance ranges.

  According to a fifteenth aspect of the present invention, the image pickup apparatus includes a diaphragm unit that adjusts the amount of light incident on the image sensor, the image sensor has an electronic shutter function that controls a charge accumulation time, and the exposure control unit includes the second control unit. The aperture value used for luminance detection is the same as the aperture value used for autofocus processing, and the shutter speed of the electronic shutter function is determined so that the second exposure value and the third exposure value are obtained under this aperture value. Thus, the exposure at the time of the second luminance detection and the autofocus process is controlled.

  According to a sixteenth aspect of the present invention, the image pickup apparatus includes a diaphragm unit that adjusts the amount of light incident on the image sensor, the image sensor has an electronic shutter function for controlling a charge accumulation time, and the exposure control unit includes a second control unit. The aperture value used for luminance detection, the aperture value used during autofocus processing, and the aperture value used for still image shooting performed after autofocus processing are the same, and the shutter speed of the electronic shutter function is set under this aperture value. And the exposure at the time of second luminance detection, autofocus processing and still image shooting is controlled.

  In the photographing apparatus according to claim 17, when the shutter speed of the electronic shutter function to be used for the second luminance detection and the autofocus process is higher than a predetermined speed, the exposure control means uses the illumination light irradiation means. The illumination light is not irradiated, and the autofocus process is performed under the first exposure value immediately after the first luminance detection is performed by the luminance detection means.

  In the photographing apparatus according to claim 18, when the shutter speed of the electronic shutter function to be used for the second luminance detection and autofocus processing is out of a predetermined speed range, the exposure control means drives the diaphragm means. The aperture value is changed so that the shutter speed is within a predetermined speed range.

  The photographing apparatus according to claim 19, wherein the frame having the highest rate among the frame rates that can be operated at the shutter speed of the electronic shutter function determined according to the third exposure value during the autofocus process. 16. The photographing apparatus according to claim 12, further comprising a frame rate changing unit that selects a rate and drives the image sensor.

  In the photographing apparatus according to claim 20, the illumination light irradiating means is adapted to irradiate the illumination light when the subject brightness is lower than a certain level, and when the illumination light is not irradiated, the brightness detecting means first Immediately after the luminance detection is performed, autofocus processing is performed under the first exposure value.

  In the control method of the photographing apparatus according to claim 21, the second exposure value is determined based on the first exposure value determined based on the subject luminance measured before the illumination light is irradiated, and the illumination light is used. Exposure for measuring subject brightness for determining the third exposure value when performing autofocus processing in the irradiated state is performed by the image sensor using the second exposure value in the state of irradiating illumination light, and the subject And the second exposure value is determined by shifting the first exposure value by a shift amount corresponding to the subject distance and the amount of illumination light.

  According to a control method of a photographing apparatus according to a twenty-second aspect, the face of a person in the photographing screen is specified, and the subject distance is acquired from the size of the specified face of the person. According to a twenty-third aspect of the present invention, there is provided a method of controlling a photographing apparatus in which a distance measuring sensor for measuring a distance to a subject is used and the subject distance is acquired based on a detection result of the distance measuring sensor. Furthermore, in the control method of the photographing apparatus according to claim 24, the subject distance is obtained based on the lens position of the photographing lens. In the control method of the photographing apparatus according to claim 25, the reflectance of the subject is obtained. , And the shift amount is determined in consideration of the measured reflectance.

  In the control method of the photographing apparatus according to claim 26, the second exposure value is determined based on the first exposure value determined based on the subject brightness measured before the illumination light is irradiated, and the illumination light is used. The exposure for measuring the subject brightness for determining the third exposure value when performing the autofocus process in the irradiated state is performed by the image sensor using the second exposure value in the irradiated state. The second exposure value is determined by acquiring the reflectance of the subject and shifting the first exposure value by a shift amount corresponding to the reflectance of the subject and the amount of illumination light.

  In the control method of the photographing apparatus according to the twenty-seventh aspect, the color of the subject is determined based on the image signal from the image sensor, and the reflectance of the subject is estimated from the determined color.

  According to the present invention, the first exposure value determined based on the subject brightness measured before irradiating the illumination light is determined as the second exposure value for measuring the subject brightness in the state of illuminating the illumination light. The subject brightness based on the exposure result obtained by the image sensor in the state of illuminating the illumination light using the second exposure value and the exposure value shifted by the shift amount based on the subject distance and the reflectance of the subject. Is measured and the third exposure value for performing autofocus processing in the state where illumination light is irradiated from this subject brightness is determined. Therefore, illumination light can be accurately irradiated in a short time even if the dynamic range of the image sensor is narrow. In this state, the subject brightness can be measured, and the autofocus process is performed with the third exposure value. Therefore, the autofocus process can be performed with high accuracy.

  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 6a of an auxiliary light irradiation unit 6 as illumination light irradiation means 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. The in-focus position, which is a lens position that matches, is examined, and a preparatory process including an AF process in which the lens position of the photographing lens 4 is the in-focus position 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 pressed and fully pressed, the still image shutter speed and aperture value determined in the still image AE process are used while the AF process is in focus. To shoot a still image. A still image obtained by the still image shooting process is converted into image data and recorded on a removable memory card 9 (see FIG. 2).

  It should be noted that even when the release button 7 is fully pressed by a single pressing operation or when the release button 7 is pressed by one step, still image AE processing, AF AE processing, and AF processing 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 the AF auxiliary light from the irradiation window 6a toward the subject in order to ensure the brightness necessary for autofocus when the subject luminance is equal to or lower than a predetermined level during the AF processing.

  In this example, the auxiliary light irradiation unit 6 provided exclusively for the AF is used as the illumination light irradiation means for irradiating the illumination light toward the subject during the autofocus process, but as the illumination light irradiation means, However, the present invention is not limited to this, and a light source device provided for other purposes may be used as illumination light irradiation means. For example, a strobe device may emit light during autofocus processing, or a light source device that emits light for facilitating framing for a photographer in a dark place may be lit during autofocus 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 12 is arranged behind the photographic lens 4, and subject light transmitted through the photographic lens 4 is incident on 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 moves the focus lens 13a constituting the photographing lens 4 in the optical axis direction of the photographing lens 4 to perform focusing. In addition to the focus lens 13a, a motor, a motor driver, or the like that moves the focus lens 13a. Consists of. The aperture mechanism 14 includes an aperture blade 14a that forms an aperture opening on the optical axis of the photographic lens 4 and an actuator that drives the aperture blade 14a. Driving of the focus mechanism 13 and the diaphragm mechanism 14 is controlled by the system control unit 10.

  For example, a CCD type image sensor 12 is used, and a large number of light receiving elements are provided 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 by each light receiving element and accumulates them, converts the accumulated charges into an analog image signal, and outputs the analog image signal. Thus, the exposed subject image is converted into an electrical signal. The image sensor 12 is not limited to a CCD type.

  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 charge accumulated so far by the input of the electronic shutter pulse from the timing generator 16. By adjusting the input period during the period, the exposure time, that is, the shutter speed of the electronic shutter can be adjusted. In this example, the exposure exposure amount is adjusted by the shutter speed of the electronic shutter of the image sensor 12 and the aperture value of 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 electronic shutter of the image sensor 12 and the frame rate at which the image sensor 12 repeatedly stores and reads out charges 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 and an AMP circuit, and performs correlated double sampling and image signal amplification in synchronism with charge reading of the image sensor 12. The A / D converter 18 converts the image signal from the analog signal processing unit 17 into image data and outputs the image data.

  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 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, a VRAM 28, and a face detection unit 29. 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 the image data to be recorded on the memory card 9 in a predetermined compression format, for example, the JPEG format, and decompresses the image data read from the memory card 9.

  The AF detection unit 24 constitutes a focus control unit together with the system control unit 10 and the focus mechanism 13. In order to focus the photographing lens 4, the image data from the image input controller 19 is used to extract a high frequency component from the AF detection area set in the photographing screen, and an AF evaluation value obtained by integrating the high frequency component is used as a system. Output to the control unit 10. The system control unit 10 drives the focus mechanism 13 to move the focus lens 13a to an in-focus position where the AF evaluation value is maximum, that is, the contrast of the subject image in the AF detection area is maximum. Thereby, the focus of the photographing lens 4 is matched with the subject in the AF 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, and detects the luminance of the subject in the AE detection region based on the image data from the image input controller 19. . The detected subject luminance is sent to the system control unit 10 functioning as an exposure value determining unit and an exposure control unit. The system control unit 10 determines the shutter speed of the image sensor 12 and the aperture value of the aperture device 14 based on the subject brightness.

  As will be described later, when a face of a person is specified from the shooting screen by the face detection unit 29, the face region specified by the face detection unit 29 is assigned to the AF detection region and the AE detection region, respectively. When a person's face is not specified in the shooting screen, a predetermined initial detection area having an appropriate size in the center of the screen, for example, is assigned to each of the AF detection area and the AE detection area.

  The AF detection area for generating the AF evaluation value and the AE detection area for generating the subject luminance, that is, the area where the photographing lens 4 is in focus need not necessarily coincide with the area which is to be properly exposed. However, the AE detection area and the AF detection area in the AF AE process to be described later are made the same.

  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, and then sent to the media controller 26 and written to the memory card 9. At the time of reproduction, image data is read from the memory card 9 by the media controller 26, and data decompression is performed by the compression / decompression unit 23.

  In the internal memory 27, 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 that has undergone image processing is successively written into the VRAM 28. 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, whereby the captured image recorded on the memory card 9 is displayed on the LCD 8.

  The face detection unit 29 includes a face area specifying unit 29a, a center position calculating unit 29b, and an area calculating unit 29c, and performs face detection processing such as specifying a face area. As schematically shown in FIG. 3, the face area specifying unit 29 a checks the image data, specifies the face area A that is a part of the face of the person included in the shooting screen G, and shoots the face area A. The face area information indicating the range on the screen is output. The center position calculating means 29b obtains and outputs the face center position Ac on the shooting screen of the specified face area A, and the area calculating means 29c obtains the size (area) S of the specified face area A. Output.

  As described above, the face area A is used as an AF detection area and an AE detection area. Further, the face center position Ac and the size S of the face area A are sent to the system control unit 10 as a shift amount determining unit and a distance determining unit. When calculating the shift amount ΔEV, the system control unit 10 obtains a distance R (hereinafter referred to as a center-to-center distance) R from the photographing screen center Gc to the face center position Ac, and estimates it from the size S of the face region A. A subject distance from the digital camera 2 to the face (hereinafter referred to as an estimated subject distance) is obtained, and a shift amount ΔEV is calculated from these. The size of the face is not significantly different although there is a difference between individuals. Therefore, it is appropriate to use the size on the photographing screen, that is, the size S of the face area A and the focal length of the known photographing lens 4. The subject distance to the face can be estimated with accuracy.

  When the photographing lens 4 is a zoom type, the focal length may be detected and acquired when the estimated subject distance is obtained. In addition, when a plurality of human faces are included in the shooting screen, for example, the face as the main subject is specified, and the face area A, the face center position Ac, and the face size S are specified for the specified face. Find it. Various methods can be used to identify the main subject. For example, a face having a larger face on the shooting screen and closer to the center of the screen can be used as the face of the main subject. Also, a plurality of face areas may be specified and each process may be performed so as to be optimal for them.

  In FIG. 2, the strobe device 32 includes 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 circuit 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 to light the LED 33 with a constant brightness when the subject brightness is lower than a certain level. Light from the LED 33 is emitted toward the subject from the irradiation window 6a as AF auxiliary light.

Note that the irradiation area of the AF auxiliary light by the auxiliary light irradiation unit 6 is determined so as to cover almost the entire surface of the shooting screen, for example, with the center of the area being the center of the shooting screen. The reason why the almost entire surface of the shooting screen is covered is that the face area as the AF detection area is detected at an arbitrary position in the shooting screen. In addition, the constant level of the subject luminance that is a criterion for determining whether or not to irradiate AF auxiliary light is based on whether the contrast of the subject image can be detected with sufficient accuracy or whether the in-focus position can be accurately detected, for example. What is necessary is just to determine, and it is not necessary to make it the same as the standard which judges the necessity of strobe light.

  The above-described AE process for still image is a process for determining an exposure value (first exposure value) used when shooting a still image in response to the full press of the release button 7. Performed in response to half-press. In this still image AE process, in consideration of the narrow dynamic range of the image sensor 12, each measurement range is set to a range that can be measured by the image sensor 12, and various brightness ranges of the photographing scene are assumed. Is divided into a plurality of measurement ranges. For this measurement, the system control unit 10 performs control such that exposure by the image sensor 12 is performed for each range to be measured under a combination of a shutter speed and an aperture value corresponding to each range.

  The AF AE process is a process for determining an exposure value (third exposure value) for performing the AF process in a state where the AF auxiliary light is irradiated, and the subject luminance measured in the still image AE process is below a certain level. It is also executed when it is low. In this AF AE process, the AE detection unit 25 detects the subject brightness in the AE detection area from the image data obtained when the image sensor 12 is exposed while the AF auxiliary light is irradiated toward the subject. The shutter speed and aperture value corresponding to are determined.

  At the time of exposure of the image sensor 12 in the above-described AF AE process, it is expected that the subject luminance to be measured is increased by irradiating the AF auxiliary light. Therefore, the system control unit 10 performs exposure using an exposure value (second exposure value) obtained by shifting the exposure value obtained in the still image AE process to the plus side.

  As shown in FIG. 4, when the exposure value obtained by the AE process for still images is EV1, the subject brightness within a certain measurable range determined by the performance of the image sensor 12 with the set exposure value EV1 interposed therebetween. Is the actually measurable luminance range. In the AF AE process, the subject brightness to be measured is expected to increase due to the irradiation of the AF auxiliary light. Therefore, exposure is performed using the exposure value EV2 shifted by the shift amount ΔEV to the plus side of the exposure value EV1. Do. As a result, the measurable object luminance range in the AF AE process is shifted to the plus side by the shift amount ΔEV so as to be able to cope with the irradiation of the AF auxiliary light.

The shift amount ΔEV is determined by the system control unit 10 based on the amount of AF auxiliary light, the estimated subject distance, and the face center position Ac. In this example, as shown in FIG. 5, in consideration of the fact that the brightness increase due to the AF auxiliary light is smaller as the subject distance is shorter and further away from the center of the photographing screen, the estimated subject distance is shorter and the center-to-center distance is smaller. The shift amount ΔEV is obtained so that the smaller R is, the larger the value is. Factors that decrease the luminance increase as the distance from the center of the shooting screen decreases include a decrease in the peripheral light amount caused by the shooting lens 4 and a decrease in the light amount distribution of the AF auxiliary light toward the screen periphery.

  In this example, it is assumed that the face area A is specified at the center of the shooting screen, and an increase in subject luminance when the AF auxiliary light is irradiated under the condition is calculated. The amount of decrease in luminance according to the distance R is obtained as a correction amount, and the amount of shift ΔEV is obtained by correcting (subtracting) the increase amount using the correction amount.

  The method for calculating the shift amount ΔEV is not limited to this. For example, when the light amount distribution changes depending on the subject distance even if the center-to-center distance R is the same, the shift amount ΔEV calculated from the estimated subject distance is calculated between the centers. You may make it correct | amend with the fall of the brightness | luminance calculated | required by using the distance R and estimated object distance as a parameter. Further, the shift amount ΔEV may be obtained only from the estimated subject distance, or may be taken into account when determining the shift amount ΔEV by estimating the reflectance from the color of the face area, for example.

  When the face area is not specified by the face detection unit 29, a predetermined initial shift amount is used as the shift amount ΔEV. As the initial shift amount in this case, for example, the AF assist light is effectively irradiated, and the exposure value is shifted to the plus side by the increase in luminance when the AF assist light is irradiated to the subject at the normal subject distance. It has been decided to do. In consideration of the dynamic range of the image sensor 12, it is preferable to use an initial shift amount in which the subject luminance (EV1) measured by the still image AE process is within a measurable range when the exposure value EV2 is set. .

  In the AF process, the exposure value determined in the still image AE process is used when the AF auxiliary light is not irradiated, and the exposure value determined in the AF AE process is used when the AF auxiliary light is irradiated. Exposure is performed by the image sensor 12 while sequentially shifting the focus position, and an increase / decrease in contrast is determined with reference to the obtained AF evaluation value to obtain a lens position with the highest contrast. In this example, the lens position (in-focus position) that matches the focus is detected by a so-called hill climbing method, but the lens position that matches the focus is detected by another method based on the image signal from the image sensor 12. Also good.

  When the diaphragm mechanism 14 is driven, a time loss occurs until the diaphragm mechanism 14 is set to a predetermined diaphragm value. For this reason, the same aperture value is used in the AF AE process and the AF process, and time loss when shifting from the AF AE process to the AF process is eliminated. In addition, the aperture value used for still image shooting performed in response to the release button 7 being fully pressed, that is, the aperture value determined in the still image AE processing is used for AF processing, so that still image shooting from AF processing is performed. The time loss due to driving of the aperture mechanism 14 is eliminated when shifting to step (1). By doing so, the same aperture value used for the AF AE process is used, which is the same as that determined for the still image AE process and used for still image shooting.

  Specifically, after the aperture mechanism 14 is driven to the aperture value determined in 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. 6, 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 exposure value is obtained in the AF AE process. Is increased by the shift amount ΔEV, the shutter speed TV2 (= TV1 + ΔEV) is obtained by shifting the shutter speed to the high speed side by the shift amount ΔEV while the aperture value 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.

  Further, in order to speed up the AF process, the frame rate of the image sensor 12 in the AF process is switched according to the shutter speed determined in the still image AE process or the AF AE process. For example, three different frame rates are prepared for AF processing, and the system controller 10 selects the highest frame rate that can drive the image sensor 12 at the set shutter speed. Then, a parameter is set in the timing generator 16 so as to drive the image sensor 12 at the selected frame rate. As a result, the length of the frame period during the AF process is shortened to shorten the time required for focusing.

  In the AF process in this example, the lens position of the photographic lens 4 is moved during the period when the electronic shutter pulse is input to the image sensor 12, so that the lens position is moved and exposed during the same frame period. Thus, the frame rate is selected in consideration of the time required to move the lens position of the photographing lens 4.

  Although the shutter speed is changed while the aperture value is fixed, when the photographing sensitivity is variable, the photographing sensitivity may be changed in addition to the shutter speed. Further, the exposure value EV3 determined in the AF AE process and used in the AF process can be determined as a value with which the in-focus position can be detected satisfactorily in the AF process.

  Next, the operation of the above configuration will be described with reference to the flowcharts of FIGS. 7 and 8 and the timing charts of FIGS. FIG. 8 shows a timing chart when the AF auxiliary light is not irradiated, and FIG. 9 shows a timing chart when the AF auxiliary light is irradiated.

  As shown in FIG. 7, when the release button 7 is pressed halfway, the still image AE process is started in response. Assuming that the frame period immediately after the release button 7 is half-pressed is the first, during the first frame period, the image data obtained by the exposure of the image sensor 12 during the previous frame period is used. Face detection processing is performed by the face detection unit 29. Note that face detection processing may be performed using image data detected before that time or image data obtained by exposure after the release button 7 is half-pressed.

  For example, when a person's face is detected in the shooting screen, the face area A is identified and sent to the AF detection unit 24 and the AE detection unit 25 as face area information. The face area A indicated by the face area information is set as an AF detection area and an AE detection area. Further, the face center position Ac and the size S of the face area A are obtained, and these are sent to the system control unit 10.

  On the other hand, during the first frame period, parameters including the shutter speed of the first photometry of the still image AE process are set in the timing generator 16 by the system control unit 10. In the second frame period, while the electronic shutter pulse is being input from the beginning of the period, the aperture control mechanism 14 is driven by the system control unit 10 to obtain an aperture value for the first photometry. Thereafter, the input of the electronic shutter pulse is stopped, and exposure E01 by the image sensor 12 is performed. The shutter speed of this exposure E01 is based on parameters set in the timing generator 16 during the first frame period.

  When the third frame period comes after the completion of the exposure E01, transfer (reading) of each charge accumulated in the image sensor 12 by the exposure E01 is started 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 E01 is performed, a parameter including the shutter speed of the second photometry in which the exposure value is smaller than the first photometry is set in the timing generator 16, and the third In this frame period, the aperture mechanism 14 sets the aperture value for the second photometry, and then the exposure E02 by the image sensor 12 is performed. Then, in the fourth frame period, an image signal by the exposure E02 is output, and the image data is sent to the AE detection unit 25.

  Similarly, parameters such as a shutter speed for the third photometry are set in the third frame period during which exposure E02 is performed, and the aperture mechanism 14 performs the third photometry in the fourth frame period. Exposure E03 is performed after the aperture value is set to. Then, the image data of the exposure E03 is sent to the AE detection unit 25 in the fifth frame period.

  In the third photometry, since the aperture value is the smallest and susceptible to smear, smear detection is performed without changing the aperture after the third photometry. A setting for smear detection is performed on the timing generator 16 during the fourth frame period, and exposure E04 is performed during the fifth frame period. In this exposure E04, charges are accumulated at the same shutter speed as that of the exposure E03, but the accumulated charges are not moved to the vertical transfer path of the image sensor 12, but in the vertical and horizontal transfer paths during the sixth frame period. The driving is performed so that the electric charge at is transferred. As a result, only the smear component image data not including the subject image component is taken into the AE detector 25.

  When the input of the smear component image data is completed as described above, in the seventh frame period, the AE detection circuit 25 corrects the smear component from the image data of the exposure E03 based on the smear component image data. Done. Then, using the corrected image data and the image data obtained by the first and second photometry, the subject brightness in the AE detection area is obtained by the AE detection unit 25, and the subject brightness is determined by the system control unit. 10 is sent.

  When the subject brightness is input to the system control unit 10, an exposure value EV1 for capturing a still image is obtained from the subject brightness. Then, 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, the system control unit 10 determines whether or not the AF auxiliary light needs to be emitted from the subject luminance.

  For example, when the subject brightness is equal to or higher than a certain level, it is determined that AF auxiliary light is unnecessary. In this case, as shown in FIG. 9, AF processing is started following the still image AE processing. When the AF process is started in the eighth frame period, the aperture mechanism 14 is driven so as to achieve the aperture value AV1 as described above, and parameters including the shutter speed TV1 are set in the timing generator 16. The Further, in the ninth frame period following the eighth frame period, the focus lens 13a is moved to the initial lens position for detecting the in-focus position.

  When the movement to the initial lens position is completed and the tenth frame period is reached, the first exposure E11 for detecting the in-focus position is performed, and the result of the exposure E11 is used as an image signal in the eleventh frame period. Is output. Then, during the 12th frame period, the AF evaluation value of the AF detection area based on the exposure E11 is obtained by the AF detection unit 24 and sent to the system control unit 10.

  In the eleventh frame period, while the electronic shutter pulse is input to the image sensor 12, the focus lens 13a is moved to the next lens position, and the second exposure E12 is performed after the movement. The image signal of exposure E12 is output during the 12th frame period, and the AF evaluation value of the AF detection area is obtained by the AF detection unit 24 and sent to the system control unit 10 during the 13th frame period. Thereafter, in the same manner, exposure is sequentially performed while moving the focus lens 13a, and an in-focus position where the AF evaluation value is maximized is detected. When the in-focus position is detected, the focus lens 13a is moved to the in-focus position, and then a still image shooting process is started and a standby state is waited until the release button is fully pressed. .

  When the release button 7 is fully pressed during the standby state, the timing generator 16 is set with parameters for shooting a still image including the shutter speed TV1 determined by the AE processing for still images. During the frame period, exposure for a still image is performed at the aperture value AV1 and the shutter speed TV1. Image data obtained by this exposure is sent to the media controller 26 through image processing by the image processing unit 22 and data compression by the compression / decompression unit 23, and is recorded on the memory card 9.

  On the other hand, when the subject brightness is lower than a certain level, the system control unit 10 determines that AF auxiliary light is necessary, and calculates the shift amount ΔEV. As shown in FIG. 8, an estimated subject distance, which is an approximate distance to the face, is obtained from the size S of the face area A and the focal length of the photographing lens 2, and AF assist light is emitted from the estimated subject distance. The amount of increase in brightness is required. Subsequently, a face center distance R between the face center position Ac of the face area A and the center Gc of the photographing screen G is obtained, and unevenness in the light amount distribution of the AF auxiliary light is taken into account from the face center distance R. The amount of decrease in luminance with respect to the center of the screen is obtained, and the amount of increase in luminance is corrected thereby to obtain the shift amount ΔEV.

  When the shift amount ΔEV is obtained as described above, the shutter speed TV2 obtained by increasing the shutter speed TV1 determined by the still image AE process by the shift amount ΔEV is determined. As a result of shifting the shutter speed by the shift amount ΔEV as described above, if the shutter speed TV2 exceeds the fastest shutter speed TVmax of the image sensor 12, there is a certain level of brightness without using AF auxiliary light. As a matter of course, the same processing as in the case where the shift of the shutter speed is canceled and the AF auxiliary light is not irradiated is performed.

  If the shutter speed TV2 exceeds the fastest shutter speed TVmax of the image sensor 12 as a result of shifting the shutter speed by the shift amount ΔEV, the diaphragm mechanism 14 is driven so that the shutter speed TV2 is equal to or lower than the shutter speed TVmax. Then, narrowing down and AF AE processing and AF processing may be performed. In this case, the photographing sensitivity may be lowered instead of the aperture value.

  As shown in FIG. 10, the AF AE process is started in the eighth frame period, and the aperture mechanism 14 is driven so that the aperture value AV1 determined in the still image AE process is reached. Parameters including the shutter speed TV2 determined as described above are set in the timing generator 16. Further, the LED 33 is turned on and irradiation of AF auxiliary light is started.

  In the ninth frame period, the exposure E21 in the AF AE process is performed by the aperture value AV1 and the shutter speed TV2 set as described above, and the result of the exposure E21 is output as an image signal in the tenth frame period. The Then, during the eleventh frame period, the AE detection unit 25 obtains the subject brightness in the AE detection area from the image data of the exposure E21, and the subject brightness is sent to the system control unit 10. As a result, an appropriate exposure value EV3 is obtained for the subject brightness in the AF detection area when the AF process is performed while irradiating the AF auxiliary light, and is further used in the AF process from the exposure value EV3 and the aperture value AV1. The shutter speed TV3 is obtained by the system control unit 10.

  In this way, the subject luminance is not irradiated with AF auxiliary light, that is, with the AF auxiliary light irradiated using the exposure value EV2 obtained by increasing the exposure value EV1 of the still image AE process performed immediately before by the shift amount ΔEV. Therefore, it is possible to measure the subject brightness in the AF detection area used for AF processing with a single measurement with high accuracy, and to measure subject brightness faster than multiple exposures while changing the exposure value. It can be performed. Also, measurement errors due to overexposure can be prevented.

  When AF processing is started in the 12th frame period, parameters including the shutter speed TV3 for AF processing are set in the timing generator 16. At this time, the frame rate parameter having the highest frame rate at which the image sensor 12 can be driven at the shutter speed TV3 is set.

  In addition, during the twelfth frame period following the twelfth frame period, the focus lens 13a is moved to the initial lens position of the operation for detecting the in-focus position. Thereafter, the operation from the 13th frame period is the same as the AF process in the case where the AF auxiliary light is not irradiated. The exposure is sequentially performed while moving the focus lens 13a, and the AF evaluation value of the AF detection area becomes maximum. The focus position is detected, and the lens position is moved so as to be the focus position. At this time, since the image sensor 12 is exposed with the exposure value determined by the AF AE process, the in-focus position can be detected in a good state.

  When the AF process is completed, the LED 33 is turned off, and the camera enters a standby state for the still image shooting process. When the release button 7 is fully pressed during the standby state, the timing generator 16 is used to capture a still image. Parameters are set, and exposure for a still image is performed with an aperture value AV1 and a shutter speed TV1. At this time, since it is not necessary to drive the aperture mechanism 14, exposure for a still image can be started with a small time lag. Then, the image data obtained by this exposure and subjected to image processing and data compression are recorded in the memory card 9.

  If a human face is not detected in the shooting screen, the initial shift amount determined in advance as the shift amount ΔEV is set as the shift amount ΔEV, and an initial detection area of an appropriate size in the center of the screen is detected by AF. Processing is performed in the same procedure as the area and the AE detection area.

  FIG. 11 shows the position of the AF auxiliary light irradiation window position relative to the photographing lens position based on the face center position when it is determined that the subject distance is shorter than the normal photographing distance or when the macro mode is set. An example is shown in which the shift amount ΔEV is corrected in consideration of the light amount unevenness of the AF auxiliary light in the photographing screen caused by the shift. In addition, except being demonstrated below, it is the same as that of 1st embodiment, The same code | symbol is attached | subjected to the substantially same member, and the description is abbreviate | omitted.

  When calculating the shift amount ΔEV, the system control unit 10 is set to the macro mode in which the estimated subject distance obtained from the size S of the face region A is equal to or smaller than the threshold Lmin or close to the distance, The shift amount ΔEV obtained based on the estimated subject distance is corrected with the correction amount based on the positional relationship of the irradiation window 6a with respect to the photographing lens 4 and the face center position Ac. As a result, correction is performed on the shift ΔEV in consideration of unevenness in the amount of light caused by the difference in the position of the irradiation window 6a with respect to the photographing lens 4.

  For example, as shown in FIG. 1, when the front surface of the digital camera 2 is viewed from the subject side, the AF auxiliary light irradiation window 6a is located at the upper left position with respect to the photographing lens 4, as schematically shown in FIG. As shown specifically, the AF auxiliary light becomes stronger from the lower left of the shooting screen G toward the upper right of the shooting screen G through which the center of the AF auxiliary light beam passes, that is, the amount of light increases. In this case, correction is performed so that the correction amount (increase amount) of the shift amount ΔEV is increased as the face center position Ac is closer to the upper right side from the lower left side of the shooting screen G. The threshold value Lmin can be determined as the upper limit of the distance range that can be said to be substantially affected by the light amount unevenness of the AF auxiliary light.

  FIG. 13 shows an example in which a digital camera is provided with a distance measuring sensor for measuring the distance of a subject. In addition, except being demonstrated below, it is the same as that of 1st embodiment, The same code | symbol is attached | subjected to the substantially same member, and the description is abbreviate | omitted.

  The digital camera 2 includes a distance measuring sensor 41 and a distance calculating unit 42 that serves as a distance determining unit. As the distance measuring sensor 41, for example, a passive-type triangular distance measuring type is used. As shown in FIG. 14, the distance measuring sensor 41 is arranged at an interval of the base line length B, and has two lenses 41 a and 41 B having the same specification and parallel optical axes, and focal planes of the lenses 41 a and 41 b. And two line sensors (not shown) having resolution in the base line length direction. The distance calculation means 42 calculates the subject distance based on the amount of deviation of the luminance pattern imaged on the line sensor on the other lens 41b side with respect to the luminance pattern imaged on the line sensor on the one lens 41a side serving as the reference side. Ask.

  The reference side lens 41 a is arranged close to the photographing lens 4 in order to reduce the parallax with the photographing lens 4. The AF auxiliary light irradiation window 6a is provided in the vicinity of the reference side lens 41a. In the reference line length direction, the optical axis of the reference side lens 41a and the optical axis of the AF auxiliary light coincide with each other. It is provided as follows. As a result, as shown in FIG. 15, the centers of the AF auxiliary light irradiation area 44 and the distance measuring area 45 by the distance measuring sensor coincide with each other. The AE detection area and the AF detection area are determined so as to substantially coincide with the distance measurement area 45 by the distance measurement sensor 41.

  When the live view display is being performed, the system control unit 10 drives the photographic lens 4 based on the subject distance obtained by using the distance measuring sensor 41 and the distance calculating means 42 to perform approximate focusing, Thereafter, control is performed so that high-precision focusing is performed by a contrast detection method using the image sensor 12.

  When the release button 15 is half-pressed, as shown in FIG. 16, the system control unit 10 acquires the subject distance obtained from the distance measuring sensor 41 and the distance calculating means 42 at the time of half-pressing. When it is necessary to irradiate AF auxiliary light, a shift amount ΔEV suitable for the acquired subject distance is determined.

  As shown in FIG. 17, an AF auxiliary light irradiation window 6a is provided between the pair of lenses 46a and 46b of the distance measuring sensor 46 so that the distance between the lenses 46a and 46b, that is, the base line length is increased. Thus, the distance measurement sensor 46 and the AF auxiliary light irradiation window 6a may be unitized to save space while improving the distance measurement accuracy.

  The distance measuring sensor is not limited to the triangular distance measuring method as described above, and any of the passive type and active type distance measuring methods can be adopted, and the accuracy of determining the shift amount ΔEV is not limited. May not be too high.

  FIG. 18 shows an example in which the subject distance is determined from the lens position of the photographing lens. An encoder 48 is connected to the focus mechanism 13 of the photographing lens 4 as position detection means for specifying the position of the focus lens 13a, that is, the lens position. The system control unit 10 can acquire the subject distance of the subject in focus by specifying the lens position of the focus lens 13 a based on the signal from the encoder 48.

  When focusing by moving multiple lenses, the position of any lens that can detect the subject distance of the subject that is in focus or the position of the cam that drives it is detected as the lens position. May be. When focusing is performed by driving the photographing lens with a pulse motor, the position of the focus lens 13a may be specified based on the number of pulses supplied to the pulse motor.

  When the through image is displayed, the system control unit 10 slightly moves the focus lens 13a at an appropriate cycle to determine whether the contrast is maximized, and the contrast is maximized. If the focus lens 13a is not at the maximum, the focus lens 13a is moved to the focus position where the contrast is maximum.

  As shown in FIG. 19, when the release button 7 is half-pressed, the subject distance is acquired based on the lens position of the focus lens 13a at that time, and the subject when the AF auxiliary light is irradiated to the subject at the subject distance A shift amount ΔEV is obtained as the amount of increase in luminance. According to this, the subject distance can be determined in an extremely short time.

  When the subject distance is determined as described above, the position of the lens when the focus lens 13a is in the in-focus position immediately before the focus lens 13a during the minute movement or during the focusing operation is avoided. It is better to determine the subject distance from Further, in the case of manual focus, the shift amount ΔEV can be determined by acquiring the subject distance from the lens position when the photographer manually operates the photographing lens to perform focusing.

  In the above embodiment, the subject distance is acquired from the in-focus position of the photographing lens at the time when the release button is half-pressed or until immediately before, but as in the example shown in FIG. The subject distance may be acquired from the in-focus position determined by the AF process performed in response to the half press.

  As shown in FIG. 20, when the release button 7 is pressed halfway, the subject brightness is measured by the still image AE process. Whether or not AF auxiliary light is necessary is determined based on the subject luminance. If it is determined that the AF auxiliary light is necessary, the elapsed time from the time when the release button 7 is pressed halfway to the time when it is half-pressed next time is within a predetermined time, or the previous release button The difference between the subject brightness measured by the still image AE process in response to the half-press of 7 and the subject brightness measured in the still image AE process in response to the current half-press of the release button 7 is equal to or less than a predetermined value. Is investigated.

  When the elapsed time is within a predetermined time and the difference in subject brightness is less than or equal to a predetermined value, it is determined that the operation interval from when the release button 7 is pressed halfway down until it is pressed halfway is short, and there is almost no change in composition. Thus, the subject distance is obtained based on the in-focus position of the photographing lens 4 detected in the previous AF process, and the shift amount ΔEV is calculated using this subject distance. Then, an AF AE process is performed using the exposure value determined using the shift amount ΔEV, and then the AF process is performed. When the AF process is completed, the in-focus position (lens position) detected in the AF process and the subject brightness measured in the current still image AE process are stored in the internal memory 27, for example, and the stored in-focus position and The subject brightness is read and used next time the release button 7 is pressed halfway.

  FIG. 21 shows an example in which the shift amount ΔEV is determined based on the reflectance of the subject. When the release button 7 is pressed halfway, the system control unit 10 performs a process for acquiring the reflectance of the subject. Then, as conceptually shown in FIG. 22, the shift amount ΔEV is determined so that the higher the acquired reflectance is, the larger the value is. Note that the shift amount ΔEV may be corrected so that the value becomes larger as the reflectance is higher than the preset initial shift amount.

  Various methods can be adopted as a method for acquiring the reflectance of the subject. However, since the reflectance can be estimated with a certain degree of accuracy depending on the color of the subject, the release button 7 is half-pressed as shown in FIG. 23, for example. The color of the subject in the AF detection area is discriminated using the image data for one frame obtained at that time, the reflectance is estimated from the color, and this is obtained as the reflectance of the subject. Good

  In the example shown in FIG. 24, the reflectance of the subject is determined from the image pattern. The pattern recognition unit 51 uses the image data for one frame obtained when the release button 7 is half-pressed to check the shape of the subject, the composition / arrangement of the color, the ratio, etc., of the subject in the AF detection area. Pattern recognition specifying the type, color, etc. is performed, and the obtained information is sent to the system control unit 10. In the database memory 52, the assumed reflectance is written in correspondence with the type and color of the subject. Then, the system control unit 10 acquires the reflectance by reading the reflectance corresponding to the input information such as the type and color of the subject from the database memory 52.

  In FIG. 25, the database memory 53 stores the reflectance of the face in advance corresponding to, for example, the color of the skin of the face or the density of the color, and the system control unit 10 accesses the database memory 53, The reflectance corresponding to the face that most closely matches the face part specified by the face detection unit 29 is read out and obtained as the reflectance of the subject.

  In this example, when the reflectance is acquired as described above, the system control unit 10 determines the shift amount ΔEV based on the acquired reflectance and the estimated subject distance obtained from the size S of the face area A. As shown in FIG. 26, for example, the system control unit 10 assumes a subject having a predetermined reflectivity, and obtains the amount of increase in subject brightness when the AF auxiliary light is irradiated based on the estimated subject distance. After that, correction is performed so that the amount of increase in the subject brightness is the amount of increase when the acquired reflectance is obtained, and this is set as the shift amount ΔEV. In this case, as conceptually shown in FIG. 27, the subject luminance is inversely proportional to the square of the subject distance and proportional to the reflectance. Therefore, the subject luminance increases so that the value decreases as the estimated subject distance increases. If the obtained reflectance is smaller than the predetermined reflectance, the amount of increase is reduced, and if the acquired reflectance is greater than the predetermined reflectance, the amount of increase is increased. Correction may be performed so as to. Further, although the subject distance and the reflectance are obtained based on the face area, the subject distance and the reflectance may be obtained by other methods.

  In the above-described embodiment, several shift amounts ΔEV may be prepared in advance, and either one of them may be selected from the acquired subject distance and reflectance. In the example shown in FIG. 28, whether the distance to the subject is short, for example, a short distance corresponding to the macro mode, or more than that, whether the reflectance is high or low, that is, whether the reflectance is a certain value or more. Based on the determination result, one of set values set in advance as the shift amount ΔEV is set. As setting values, ΔEV1, ΔEV2, ΔEV3, and ΔEV4 are prepared in advance, and have a magnitude relationship of “ΔEV1 <, ΔEV2 <ΔEV3 <ΔEV4”.

  When the subject distance is short and the reflectance is high, the largest value ΔEV4 is set as the shift amount ΔEV, and when the subject distance is short but the reflectance is low, the second largest value is set. ΔEV3 is set as the shift amount ΔEV. On the other hand, when the subject distance is not a short distance, the smallest ΔEV1 is set as the shift amount ΔEV when the reflectance is low, and ΔEV2 is set as the shift amount ΔEV when the reflectance is high. In this way, by setting the shift amount ΔEV, the shift amount ΔEV is determined with priority on the subject distance that makes the reflected light amount of the subject smaller in inverse proportion to the square.

  In each of the above embodiments, a digital camera has been described as a photographing apparatus. However, the present invention is applied to various photographing apparatuses that detect a focus position and subject luminance based on an image signal from an image sensor and a control method thereof. can do. Further, the first exposure value is not limited to the one measured by operating the release button, but one that has been appropriately determined immediately before can be used.

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 explanatory drawing which shows the detection state by a face detection process. 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. It is explanatory drawing which shows notionally the magnitude | size of shift amount (DELTA) EV calculated | required from the size of a face, and face center distance. 6 is a graph showing an example of a relationship between an aperture value and shutter speed determined in still image AE and an aperture value and shutter speed used in AF AE processing and AF processing; It is a flowchart which shows the procedure of imaging | photography performed in response to operation of a release button. It is a flowchart which shows the procedure which determines shift amount (DELTA) EV. It is a timing chart which shows operation | movement of each part at the time of release half-pressing when not irradiating AF auxiliary light. It is a timing chart which shows operation | movement of each part at the time of release half-pressing in the case of irradiating AF auxiliary light. 10 is a flowchart illustrating an example of correcting a shift amount at a face center position in a short-distance shooting or macro shooting mode. It is explanatory drawing which shows the relationship between the light quantity nonuniformity of AF auxiliary light in the case of short distance photography, and a correction amount. It is a block diagram which shows the structure of the digital camera which provided the ranging sensor. It is explanatory drawing which shows an example of arrangement | positioning of each lens of a ranging sensor, and the irradiation window of AF auxiliary light. It is explanatory drawing which shows the relationship between the ranging area by a ranging sensor, and the irradiation area of AF auxiliary light. It is a flowchart which shows the process sequence at the time of using a ranging sensor. It is explanatory drawing which shows another example of arrangement | positioning of each lens of a ranging sensor, and the irradiation window of AF auxiliary light. It is a block diagram which shows the structure of the digital camera which shows the example which acquires a to-be-photographed object distance from the position of the focus lens of an imaging lens. It is a flowchart which shows the process sequence in the example which acquires a to-be-photographed object distance from the position of a focus lens. It is a flowchart which shows the process sequence in the example using the focus position by AF process responded to operation of the last release button. It is a flowchart which shows the process sequence in the example which determines shift amount (DELTA) EV from the reflectance of a to-be-photographed object. It is explanatory drawing which shows notionally the magnitude | size of shift amount (DELTA) EV calculated | required from a reflectance. It is a flowchart which shows the process sequence which acquires the reflectance of a to-be-photographed object from the color of a to-be-photographed object. It is a block diagram which shows the structure of the digital camera which shows the example which acquires a reflectance based on the result of having recognized the pattern of the to-be-photographed object. It is a block diagram which shows the structure of the digital camera which shows the example which acquires a reflectance from a person's face part. It is a flowchart which shows the example which determines shift amount (DELTA) EV from a to-be-photographed object distance and the reflectance of a to-be-photographed object. It is explanatory drawing which shows schematic relationship between a to-be-photographed object distance, a reflectance, and shift amount (DELTA) EV. 10 is a flowchart illustrating an example of selecting a predetermined shift amount ΔEV from the subject distance and the reflectance of the subject.

Explanation of symbols

2 Digital camera 6 Auxiliary light irradiation unit 6a Irradiation window 10 System control unit 12 Image sensor 13 Focus mechanism 14 Aperture mechanism 24 AF detection unit 25 AE detection unit 29 Face detection unit 41, 46 Distance sensor 51 Reflectance measurement unit

Claims (27)

An image sensor that receives the subject light from the photographic lens, converts the subject image into an electrical image signal, and outputs it. In response to the operation of the release button, the focus position is determined based on the image signal from the image sensor. In a photographing apparatus including a focus control unit that performs auto-focus processing to detect, and illumination light irradiation unit that irradiates illumination light toward a subject during auto-focus processing,
Based on an image signal obtained by exposure of the image sensor without illuminating illumination light, first luminance detection for detecting subject luminance for determining the first exposure value is performed, and first luminance detection is performed. Later, based on an image signal obtained by irradiating the illumination light and exposure of the image sensor under the second exposure value, subject brightness for determining the third exposure value in the autofocus process is determined. Brightness detection means for performing second brightness detection to be detected;
Distance determining means for determining the subject distance to the subject;
Shift amount determining means for obtaining a shift amount to be the second exposure value optimum for second luminance detection based on the amount of illumination light and the subject distance determined by the distance determining means;
The first exposure value is determined based on the first luminance detection, and the second exposure value is determined by shifting the first exposure value by the shift amount obtained by the shift amount determining means, and the second exposure value is determined. Exposure value determining means for determining a third exposure value based on the luminance detection of
An imaging apparatus comprising: an exposure control unit that executes exposure for second luminance detection using the second exposure value.   Face detecting means for specifying a face area of a person in a shooting screen based on an image signal from the image sensor, wherein the distance determining means is based on the face size of the person specified by the face detecting means. The photographing apparatus according to claim 1, wherein a subject distance is determined.   The face detection means specifies the center position of the specified face area together with the face area, and the shift amount determination means determines that the center position of the face area in the shooting screen is closer to the periphery of the shooting screen. The photographing apparatus according to claim 2, wherein the shift amount is reduced.   The face detection means specifies the center position of the face area specified together with the face area. When the macro mode for shooting is selected, based on the center position of the face area in the shooting screen, the shooting window in the shooting screen caused by the deviation of the irradiation window that outputs the illumination light with respect to the position of the shooting lens The photographing apparatus according to claim 2, wherein a shift amount is corrected in consideration of unevenness in the amount of illumination light.   The photographing apparatus according to claim 1, further comprising a distance measuring sensor that measures a distance to the subject, wherein the distance determining unit determines a distance to the subject based on a detection result of the distance measuring sensor.   2. The photographing apparatus according to claim 1, further comprising a position detecting unit for detecting a lens position of the photographing lens, wherein the distance determining unit determines a subject distance based on the detected lens position. .   The focus control means determines whether or not the photographing lens is in the in-focus position with respect to the subject at a predetermined interval before operating the release button. The photographic lens is driven so that the lens is in the in-focus position, and the distance determination unit is configured to subject the subject based on the lens position when the in-focus position is set immediately before determining the second exposure value. The photographing apparatus according to claim 6, wherein the distance is determined.   The distance determining means determines the subject distance based on the lens position of the taking lens when the in-focus position is obtained by the autofocus process performed by the focus control means in response to the previous release button operation. The imaging device according to claim 6.   The distance determining means performs the release operation within a predetermined time from the previous release button operation, and responds to the subject brightness measured in response to the previous release button operation and the current release button operation. When the brightness difference from the measured subject brightness is less than or equal to a predetermined value, the photographing lens when the in-focus position is obtained by the autofocus process performed by the focus control means in response to the previous release button operation. The photographing apparatus according to claim 6, wherein the subject distance is determined based on the lens position.   2. The apparatus according to claim 1, further comprising a reflectance determining unit that determines a reflectance of a subject, wherein the shift amount determining unit further determines the shift amount using a reflectance obtained from the reflectance determining unit. 10. The photographing device according to any one of 9 above. An image sensor that receives the subject light from the photographic lens, converts the subject image into an electrical image signal, and outputs it. In response to the operation of the release button, the focus position is determined based on the image signal from the image sensor. In a photographing apparatus including a focus control unit that performs auto-focus processing to detect, and illumination light irradiation unit that irradiates illumination light toward a subject during auto-focus processing,
Based on an image signal obtained by exposure of the image sensor without illuminating illumination light, first luminance detection for detecting subject luminance for determining the first exposure value is performed, and first luminance detection is performed. Later, based on an image signal obtained by irradiating the illumination light and exposure of the image sensor under the second exposure value, subject brightness for determining the third exposure value in the autofocus process is determined. Brightness detection means for performing second brightness detection to be detected;
Reflectance determination means for determining the reflectance of the subject;
Shift amount determining means for determining the shift amount based on the amount of illumination light and the reflectance determined by the reflectance determining means;
The first exposure value is determined based on the first luminance detection, and the second exposure value is determined by shifting the first exposure value by the shift amount obtained by the shift amount determining means, and the second exposure value is determined. Exposure value determining means for determining a third exposure value based on the luminance detection of
An imaging apparatus comprising: an exposure control unit that executes exposure for second luminance detection using the second exposure value.   12. The photographing apparatus according to claim 10, wherein the reflectance determination unit determines the color of a subject based on an image signal from the image sensor, and estimates the reflectance of the subject from the determined color.   The first luminance detection is subject luminance detection performed to determine an exposure value at the time of shooting a still image, and the luminance detection means responds to an operation of a release button in response to an operation of a release button. The imaging apparatus according to claim 1, wherein detection is performed.   The luminance detection means divides a range of subject luminance to be measured into a plurality of luminance ranges by performing exposure by the image sensor using a plurality of different exposure values at the time of the first luminance detection. The photographing apparatus according to claim 1, wherein the photographing apparatus is detected. The image sensor has an electronic shutter function that controls a charge accumulation time, and includes a diaphragm unit that adjusts the amount of light incident on the image sensor.
The exposure control means makes the aperture value used for the second luminance detection the same as the aperture value used in the autofocus process, and the second exposure value and the third exposure value are obtained under this aperture value. 15. The photographing apparatus according to claim 1, wherein a shutter speed of the electronic shutter function is determined to control exposure during the second luminance detection and autofocus processing. The image sensor has an electronic shutter function that controls a charge accumulation time, and includes a diaphragm unit that adjusts the amount of light incident on the image sensor.
The exposure control means makes the aperture value used for the second luminance detection equal to the aperture value used during autofocus processing and the aperture value used for still image shooting performed after the autofocus processing. The shutter speed of the electronic shutter function is determined below to control the second luminance detection, autofocus processing, and exposure during still image shooting. The photographing apparatus described.   The exposure control means irradiates illumination light from the illumination light irradiation means when the shutter speed of the electronic shutter function to be used for the second luminance detection and the autofocus process is higher than a predetermined speed. The photographing apparatus according to claim 15 or 16, wherein the autofocus processing is performed under the first exposure value immediately after the first luminance detection is performed by the luminance detection unit.   The exposure control unit drives the aperture unit to change the aperture value when the shutter speed of the electronic shutter function to be used for the second luminance detection and the autofocus process is out of a predetermined speed range. The photographing apparatus according to claim 15 or 16, wherein the shutter speed is within a predetermined speed range.   In the autofocus process, the image sensor is selected by selecting the frame rate having the highest rate from among the frame rates that can be operated at the shutter speed of the electronic shutter function determined according to the third exposure value. The photographing apparatus according to claim 15, further comprising a frame rate changing unit that drives the camera.   The illumination light irradiating means is adapted to irradiate illumination light when the subject brightness is lower than a certain level. When the illumination light is not irradiated, immediately after the first brightness detection is performed by the brightness detection means. The photographing apparatus according to claim 1, wherein the autofocus process is performed under a first exposure value. Based on the image signal obtained by receiving the subject light from the photographic lens with the image sensor, the brightness of the subject is measured and an autofocus process is performed to detect the in-focus position of the photographic lens. In a control method of a photographing apparatus provided with illumination light irradiation means for irradiating a subject with illumination light,
The second exposure value is determined based on the first exposure value determined based on the subject brightness measured before the illumination light is irradiated, and the autofocus process is performed when the illumination light is irradiated. The exposure for measuring the subject brightness for determining the exposure value of 3 is performed by the image sensor using the second exposure value in a state where the illumination light is irradiated, and the subject distance to the subject is acquired. A method for controlling a photographing apparatus, wherein the second exposure value is determined by shifting the first exposure value by a shift amount corresponding to the distance and the amount of illumination light.   The method of controlling a photographing apparatus according to claim 21, wherein the face of a person in the photographing screen is specified, and the subject distance is acquired from the size of the face of the specified person.     The method of controlling an imaging apparatus according to claim 21, wherein a distance sensor that measures the distance to the subject is used, and the subject distance is acquired based on a detection result of the distance sensor.   The method of controlling a photographing apparatus according to claim 21, wherein the subject distance is acquired based on a lens position of the photographing lens.   25. The method of controlling an imaging apparatus according to claim 21, wherein the reflectance of the subject is measured, and the shift amount is determined in consideration of the measured reflectance. Based on the image signal obtained by receiving the subject light from the photographic lens with the image sensor, the brightness of the subject is measured and an autofocus process is performed to detect the in-focus position of the photographic lens. In a control method of a photographing apparatus provided with illumination light irradiation means for irradiating a subject with illumination light,
The second exposure value is determined based on the first exposure value determined based on the subject brightness measured before the illumination light is irradiated, and the autofocus process is performed when the illumination light is irradiated. The exposure for measuring the subject brightness for determining the exposure value of 3 is performed by the image sensor using the second exposure value in a state of irradiating illumination light, and the reflectance of the subject is acquired. A method for controlling an imaging apparatus, wherein the second exposure value is determined by shifting the first exposure value by a shift amount corresponding to the reflectance and the amount of illumination light.   27. The method according to claim 25, wherein the color of the subject is determined based on an image signal from the image sensor, and the reflectance of the subject is estimated from the determined color.

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