JP5137343B2 - Imaging apparatus and imaging method - Google Patents

Description

  The present invention relates to an imaging apparatus such as a digital still camera and an imaging method, and more particularly to an imaging apparatus capable of shooting using a flash.

  In a conventional camera that controls light emission and non-light emission of a flash, normal sync shooting, slow sync shooting, or flash non-flash is automatically switched according to the luminance of the subject (see Patent Document 1).

  However, if flash emission / non-emission is controlled only by subject brightness, flash emission may occur when flash emission is not required, or a person's face may be captured darkly without flash emission in a backlight scene. Problems arise.

As a method for solving such a problem, a technique of detecting a person's face (face image) from an image signal, determining whether the light is backlit based on the brightness of the face image, and performing flash emission in the case of backlit Has been proposed (see Patent Document 2). According to this technique, when the main subject is a person, flash light emission is automatically performed in a backlight scene where the brightness of the face is dark, so that the person (face) can be photographed with an appropriate exposure.
Japanese Patent Laid-Open No. 7-20524 (paragraphs 0018 to 0035, FIGS. 4, 5 etc.) JP2003-92700 (paragraphs 0011 to 0015, FIG. 5 and the like)

  When the main subject is a person and it is desired to photograph the background together, it is necessary to obtain an appropriate exposure not only for the person but also for the background. However, since the technique disclosed in Patent Document 2 uses a face image to determine backlighting, an appropriate exposure can be obtained for a person's face, but so-called slow sync photography is automatically performed in a dark scene such as a night view. In this case, an image with a dark background is taken.

  An object of the present invention is to provide an imaging apparatus and an imaging method that can automatically perform photography with appropriate exposure for each of a person and a background.

An imaging apparatus according to one aspect of the present invention includes an imaging device that photoelectrically converts a subject image, a luminance determination unit that determines luminance of a subject region from an image signal obtained by using the imaging device, and a face from the image signal. Subject determination means for determining whether or not the subject is included in the subject and flash determination means for determining whether or not flash light reaches the subject. Then, the control means than a specified luminance object area by the brightness determination unit is determined to low luminance, and if a face is determined to be included in the subject by the subject determining means, slow-synchro photographing with flash The luminance determination unit determines that the subject area is lower than the specific luminance, the subject determination unit determines that the face is not included in the subject, and the flash determination unit flashes the subject area. If the light is determined to reach, and performs imaging control with flash shutter speed is relatively faster than slow synchro photographing.

The imaging apparatus control method according to another aspect of the present invention is applied to an imaging apparatus having an imaging element that photoelectrically converts a subject image. The control method includes a step of determining luminance of a subject area from an image signal obtained using an image sensor, a step of determining whether or not a face is included in the subject from the image signal, and a flash light on the subject. a step is equal to or reach, than the subject region specified luminance is determined that low intensity, and if a face is determined to be included in the subject, for slow sync shooting with flash and performing the photographing control, than the subject region specified luminance is determined that low luminance, when the face is determined to be not included in the subject, and is determined flash light reaches the subject, slow synchro And a step of performing photographing control with flash light emission having a relatively high shutter speed as compared with photographing.

According to the present invention, when the subject area has a brightness lower than the specific brightness and the face is included in the subject, the shooting control for the slow sync photography is automatically performed, while the subject area has the brightness lower than the specific brightness. In this case, the photographer will automatically control shooting with flash that is not slow sync shooting when the subject does not include a face and the flash light reaches the subject. Thus, it is possible to perform photographing with appropriate flash emission without requiring the above operation .

Embodiments of the present invention will be described below with reference to the drawings. First, the technology that is the premise of the third and fourth embodiments, which are embodiments of the present invention, will be described with reference to the first and second embodiments.

  FIG. 1 shows a configuration of a digital still camera as an image pickup apparatus that is Embodiment 1 of the present invention. The camera of this embodiment is a camera integrated with a photographing lens. However, the present invention can also be applied to a single-lens reflex camera in which a photographic lens (interchangeable lens) can be attached and detached.

  In FIG. 1, reference numeral 100 denotes a camera. Reference numeral 10 denotes a photographing lens, and reference numeral 12 denotes a shutter unit having an aperture function.

  Reference numeral 14 denotes an image sensor that converts an optical image formed by the taking lens 10 into an electrical signal, and is composed of a CCD sensor, a CMOS sensor, or the like. Reference numeral 120 denotes a gain amplifier that amplifies the analog signal output from the image sensor 14 and sets the photographing sensitivity.

  Reference numeral 16 denotes an A / D converter that converts an analog signal output from the image sensor 14 into a digital signal. A timing generation circuit 18 supplies a clock signal and a control signal to the image sensor 14, the A / D converter 16 and the D / A converter 26, and is controlled by the memory control circuit 22 and the system control circuit 50.

  Reference numeral 20 denotes an image processing circuit, which performs predetermined pixel interpolation processing and color conversion processing on the digital signal from the A / D converter 16 or the data from the memory control circuit 22 to generate image data. Furthermore, the image processing circuit 20 performs predetermined arithmetic processing using the image data.

  The system control circuit 50 controls the exposure control circuit 40 and the AF control circuit 42 based on the result of predetermined arithmetic processing performed by the image processing circuit 20. As a result, TTL (through the lens) AF (autofocus) processing, AE (automatic exposure) processing, and EF (flash pre-emission) processing are performed. Further, the image processing circuit 20 performs a TTL (through the lens) type AWB (auto white balance) process based on a result of a predetermined calculation process using the image data.

  A memory control circuit 22 controls the A / D converter 16, the timing generation circuit 18, the image processing circuit 20, the image display memory 24, the D / A converter 26, the memory 30, and the compression / decompression circuit 32.

  Data from the A / D converter 16 is written into the image display memory 24 or the memory 30 via the image processing circuit 20 and the memory control circuit 22 or via the memory control circuit 22.

  Reference numeral 24 denotes an image display memory, 26 denotes a D / A converter, and 28 denotes an image display unit constituted by a TFT-LCD or the like. The display image data written in the image display memory 24 is displayed by the image display unit 28 via the D / A converter 26. The electronic viewfinder function can be realized by sequentially displaying the image data generated by the output from the image sensor 14 using the image display unit 28.

  Further, the image display unit 28 can arbitrarily turn on / off the display according to an instruction from the system control circuit 50. When the display is turned off, the power consumption of the image processing apparatus 100 can be greatly reduced. Can do.

  Reference numeral 30 denotes a memory for storing still images and moving images, which are captured image data, and has a sufficient storage capacity for storing a predetermined number of still images and moving images for a predetermined time. This makes it possible to write a large amount of images to the memory 30 at high speed even in continuous shooting or panoramic shooting in which a plurality of still images are continuously shot. The memory 30 can also be used as a work area for the system control circuit 50.

  A compression / decompression circuit 32 compresses and decompresses image data by adaptive discrete cosine transform (ADCT) or the like, reads an image stored in the memory 30 and performs compression processing or decompression processing. Then, the processed data is written into the memory 30.

  Reference numeral 40 denotes an exposure control circuit for controlling the shutter unit 12. The exposure control circuit 40 performs AE (automatic exposure) processing based on the result of a predetermined calculation performed by the image processing circuit 20 using the captured image data. The exposure control circuit 40 also has a flash dimming function in cooperation with the flash unit 48.

  Reference numeral 42 denotes an AF control circuit, which performs AF (automatic focus adjustment) processing based on the result of a predetermined calculation performed by the image processing circuit 20 using photographed image data. A zoom control circuit 44 controls zooming of the imaging lens 10, and a barrier control circuit 46 controls the operation of the lens barrier 102.

  Reference numeral 48 denotes a flash unit that emits flash light to illuminate the subject, and has a flash light control function and also a AF auxiliary light projecting function.

  The exposure control circuit 40 and the AF control circuit 42 are controlled by the TTL method. The system control circuit 50 controls the exposure control circuit 40 and the AF control circuit 42 based on the result obtained by calculating the captured image data by the image processing circuit 20.

  The system control circuit 50 controls the entire camera 100. A memory 52 stores constants, variables, computer programs, and the like for operating the system control circuit 50.

  The system control circuit 50 includes a low luminance determination calculation unit 123, a backlight scene determination calculation unit 124, and a subject determination calculation unit 121.

  The low brightness determination calculation unit 123 calculates the brightness level of the subject area, that is, the shooting area photographed by the camera 100, from the image data obtained via the memory control circuit 22, and the subject area is more than the specific brightness. It is determined whether the brightness is low.

  The specific luminance is determined according to the set shooting mode and sensitivity. For example, if the shooting mode is set to the portrait mode, it is highly likely that the subject is a person. Therefore, the specific brightness may be set to be high so that the subject region is unlikely to be under. Also, if the sensitivity is set high, the subject area is unlikely to be under, so the specific brightness may be set low.

  The backlight scene determination calculation unit 124 calculates the luminance level of the subject area from the image data obtained via the memory control circuit 22. Then, it is determined whether or not the scene is a backlight scene depending on whether or not the person area determined by the center of the object area or the object determination calculation unit 121 described later is darker than the surrounding area.

  The subject determination calculation unit 121 performs calculation processing for detecting the characteristics of the main subject from the image data obtained via the image processing circuit 20, and whether or not the subject region includes a person, that is, whether the main subject is detected. It is determined whether or not it is a person (background). A method for determining whether or not the main subject is a person based on the image data is not particularly limited. For example, the determination can be made by detecting a representative silhouette of a person by a pattern matching method or detecting a skin color. Further, as shown in FIG. 1, a face determination calculation unit 122 is provided in the subject determination calculation unit 121, and information on a person's face (eyes, nose, mouth, ears, etc.) is obtained from image data using a pattern recognition technique or the like. By detecting, it can be more reliably determined that the main subject is a person.

  Note that the case where the main subject is a person is not assumed when an unspecified person is included in the background, and a person is included within a predetermined distance (for example, several meters). Is assumed. The distance to the person can be calculated based on the position of the zoom lens included in the photographing lens 10, the focus position of the focus lens, or the like, or can be obtained by using a distance measuring sensor.

  The system control circuit 50 controls the exposure control circuit 40 according to the determination results of the low brightness determination calculation unit 123, the backlight scene determination calculation unit 124, and the subject determination calculation unit 121. That is, shooting control of the camera is performed according to the determination result.

  Reference numeral 54 denotes a display unit including an LCD, an LED, and a speaker that output characters, images, sounds, and the like representing the operating state of the camera 100, messages, and the like in accordance with execution of a program in the system control circuit 50. The display unit 54 is disposed at a position where it is easy to visually recognize, such as in the vicinity of the operation switch. A part of the display unit 54 is installed in the optical viewfinder 104.

  Reference numeral 56 denotes a nonvolatile memory capable of electrically erasing and recording data, for example, an EEPROM.

  Reference numerals 60, 62, 64, 66, 68 and 70 are operation switches for inputting various operation instructions of the system control circuit 50, such as push switches, dials, touch panels, pointing devices based on visual line detection, voice recognition devices, and the like. Composed.

  Reference numeral 60 denotes a mode dial switch which is operated to turn on / off the power and select various shooting modes.

  Reference numeral 62 denotes a shooting preparation switch (SW1) which is turned on by a half-press operation (first stroke operation) of a shutter button (not shown). When the shooting preparation switch 62 is turned on, shooting preparation operations such as AF processing, AE processing, AWB processing, and EF (flash pre-flash) processing are started.

  Reference numeral 64 denotes a photographing switch (SW2) which is turned on when the shutter button is fully pressed (second stroke operation). When the photographing switch 64 is turned on, photographing processing is executed. In the photographing process, a signal read from the image sensor 14 is written into the memory 30 as image data via the A / D converter 16 and the memory control circuit 22. Further, development processing using calculation in the image processing circuit 20 and the memory control circuit 22 is also performed. Further, subsequent to the photographing process, image data is read from the memory 30 and a recording process for writing the image data compressed by the compression / decompression circuit 32 to the recording media 200 and 210 is also executed.

  Reference numeral 66 denotes an image display ON / OFF switch, which is a switch for setting ON / OFF of the image display unit 28.

  Reference numeral 68 denotes a quick review ON / OFF switch, which is a switch for setting ON / OFF of a quick review function for automatically reproducing captured image data immediately after shooting. In this embodiment, the quick review ON / OFF switch 68 is used to set ON / OFF of the quick review function when the image display unit 28 is OFF.

  An operation unit 70 includes a menu display button, a menu determination button, a flash setting button, an image playback button, an image quality selection button, an exposure correction button, a date / time setting button, and the like.

  Reference numeral 80 denotes a power supply control circuit that detects the presence / absence of the power supply 86 and the remaining capacity, controls the DC-DC converter based on the detection result and an instruction from the system control circuit 50, and supplies a necessary voltage for a necessary period. This is supplied to each block including the recording medium 200.

  82 is a connector on the power control circuit 80 side, and 84 is a connector on the power source side. A power source 86 includes a primary battery such as an alkaline battery or a lithium battery, a secondary battery such as a NiCd battery, a NiMH battery, or a Li battery, an AC adapter, or the like.

  Reference numerals 90 and 94 denote interfaces with recording media 200 and 210 such as a memory card and a hard disk. Reference numerals 92 and 96 denote connectors for connecting to the recording media 200 and 210. A recording medium detection circuit 98 detects whether or not the recording media 200 and 210 are attached to the camera 100.

  The camera of this embodiment has two systems of interfaces 90 and 94 and connectors 92 and 96 to which the recording media 200 and 210 are attached. However, one system or three or more systems may be provided. In addition, the standards of a plurality of systems of interfaces and connectors may be different.

  The lens barrier 102 is provided to cover the front surface of the photographing lens 10 and prevent the photographing lens 100 from being soiled or damaged when the camera 100 is not used.

  The optical viewfinder 104 is provided for observing a subject when the electronic viewfinder function of the image display unit 28 is not used.

  A communication circuit 110 has various communication functions such as RS232C, USB, IEEE1394, P1284, SCSI, modem, LAN, and wireless communication.

  Reference numeral 112 denotes a connector for connecting the camera 100 to another device by the communication circuit 110 or an antenna for wireless communication.

  The recording media 200 and 210 include recording units 202 and 212 configured by a semiconductor memory, a magnetic disk, and the like, interfaces 204 and 214 with the camera 100, and connectors 206 and 216 for connecting with the camera 100.

  FIG. 2 shows a photometric processing routine among the photographing processing routines in the camera 100 of the present embodiment. The imaging process is executed by the system control circuit 50 according to a computer program stored in the memory 52. In FIG. 2, “S” means a step. The same applies to other figures described later.

  When the photographing preparation switch SW1 is pressed by the photographer, the system control circuit 50 starts the photographing preparation operation described above. Thereby, the photometric calculation process is started.

  In step 100, the system control circuit 50 (low luminance determination calculation unit 123) determines whether or not the subject region has low luminance. If the brightness is not low (if the brightness is high), the process proceeds to step 103 to instruct the exposure control circuit 40 to perform shooting without flash emission (non-flash shooting), and the process is terminated.

  If it is determined in step 100 that the subject area has low luminance, the process proceeds to step 101 where the subject determination calculation unit 121 determines whether the main subject is a person. If the main subject is not a person, the process proceeds to step 103 where normal exposure is instructed to the exposure control circuit 40 and the process ends. If the main subject is a person, the process proceeds to step 102, where the exposure control circuit 40 is instructed to perform shooting with flash emission (flash shooting), and the process ends.

  The exposure control circuit 40 instructed to set the shooting sets the shutter speed, the aperture value, and the flash emission amount according to the instructed shooting and the photometry result, and waits for the shooting switch SW2 to be pressed for recording by AE control. Take a picture. This is the same in other embodiments described later.

  FIG. 3 shows a photometric processing routine in the case where the face determination calculation unit 122 is provided in the subject determination calculation unit 121.

  In step 100, the system control circuit 50 (low luminance determination calculation unit 123) determines whether or not the subject region has low luminance. If the brightness is not low (if the brightness is high), the process proceeds to step 103, the exposure control circuit 40 is instructed to perform non-flash photography, and the process is terminated.

  If it is determined in step 100 that the subject area has low luminance, the process proceeds to step 200 where the face discrimination calculation unit 122 performs processing for detecting a human face. If no person's face is detected, it is determined in step 203 that the main subject is the background, the process proceeds to step 103, the exposure control circuit 40 is instructed to perform normal shooting, and the process ends. If a person's face is detected, it is determined in step 201 that the main subject is a person, the process proceeds to step 202, the flash control for slow sync photography is instructed to the exposure control circuit 40, and the process ends.

  In slow sync photography, when taking a picture of a person against the background of a night scene, set the shutter time longer than usual, fire the flash at the beginning or end of the shutter time to make the person appear brighter, and the background also has an appropriate exposure. This is a shooting method. The flash emission amount may be lower than that in normal flash photography.

  In the conventional camera, it was necessary to set the slow sync mode (night view mode, etc.) by the photographer's operation in such a shooting scene, but the camera of this embodiment automatically performs slow sync shooting. Can do.

  FIG. 4 shows a photometric processing routine in which the face determination calculation unit 122 is provided in the subject determination calculation unit 121 and the shooting control is performed according to the reach distance of the flash light when the main subject is the background.

  In the present embodiment, as shown in parentheses in FIG. 1, a flash arrival determination unit 125 that compares the distance to the background with the arrival distance of the flash light is provided in the system control circuit 50. The distance information to the background can be obtained based on the position information of the zoom lens included in the photographing lens 10 and the focus position information of the focus lens. The reach distance of the flash light can be obtained based on the photographing sensitivity, the aperture value, and the light emission amount of the flash unit 48.

  In step 100, the system control circuit 50 (low luminance determination calculation unit 123) determines whether or not the subject region has low luminance. If the brightness is not low (if the brightness is high), the process proceeds to step 103, the exposure control circuit 40 is instructed to perform non-flash photography, and the process is terminated.

  If it is determined in step 100 that the subject area has low luminance, the process proceeds to step 200 where the face discrimination calculation unit 122 performs processing for detecting a human face. If no human face is detected, it is determined in step 203 that the main subject is the background, and the process proceeds to step 300.

  In step 300, the flash arrival determination unit 125 determines whether or not the distance to the background is shorter than the arrival distance of the flash light, that is, whether or not the background is within the flash light arrival range. When the distance to the background is shorter than the reach distance of the flash light, the process proceeds to step 301, where the exposure control circuit 40 is instructed to perform normal flash photography, and the process ends. On the other hand, if the distance to the background is longer than the reach distance of the flash light, the process proceeds to step 302 to instruct the exposure control circuit 40 to prohibit the flash emission, and the process ends.

  On the other hand, if a person's face is detected in step 200, it is determined in step 201 that the main subject is a person, and the process proceeds to step 202 to instruct the exposure control circuit 40 to perform flash photography for slow sync photography. To finish the process.

  In this embodiment, the distance information from the position information of the zoom lens and focus lens to the background is obtained, but the background is within the flash light reach based on the amount of reflected light from the background when the flash is emitted. It may be determined whether or not.

  FIG. 5 shows a photometric processing routine in the case where the backlight determination step is further provided in the third embodiment, and photographing control according to the result is performed.

  In step 100, the system control circuit 50 (low luminance determination calculation unit 123) determines whether or not the subject region has low luminance. If it is determined that the subject area has low brightness, the process proceeds to step 200 where the face discrimination calculation unit 122 performs processing for detecting a human face. If no human face is detected, it is determined in step 203 that the main subject is the background, and the process proceeds to step 300. The processing from step 300 to step 302 is as described in the third embodiment.

  On the other hand, if a person's face is detected in step 200, it is determined in step 201 that the main subject is a person, and the process proceeds to step 202 to instruct the exposure control circuit 40 to perform flash photography for slow sync photography. To finish the process.

  In step 100, if the subject area is not low brightness (if high brightness), the process proceeds to step 401, and the backlight scene determination calculation unit 124 determines whether the scene is a backlight scene. If it is determined that the scene is a backlight scene, the process proceeds to step 303, and a process of detecting a human face by the face discrimination calculation unit 122 is performed as in step 200. If no human face is detected, it is determined in step 306 that the main subject is the background, and the process proceeds to step 307. In step 307, the exposure control circuit 40 is instructed to perform non-flash photography, and the process ends.

  On the other hand, if a human face is detected in step 303, it is determined in step 304 that the main subject is a person, and the process proceeds to step 305 to instruct the exposure control circuit 40 to perform flash photography for daytime synchronized photography. To finish the process.

  Daytime synchronized shooting is a shooting method in which a flash is emitted to make the brightness of the subject equal to the background when the subject (person) is darker than the background in a backlight scene. In the conventional camera, in such a backlight scene, it was necessary to make a setting to force the flash to be emitted by the photographer's operation, but the camera of this embodiment automatically performs daytime synchro shooting. be able to.

  In each of the above embodiments, the case where the subject has a function of determining whether the subject is a person or the background has been described. In addition to this, if the face can be identified like a pet or a stuffed toy, it is used as the main subject. It is possible to provide a function of performing the same photographing process as when a person is determined as a main subject.

1 is a block diagram illustrating a configuration of a camera that is Embodiment 1 of the present invention. FIG. 3 is a flowchart showing a photographing process (photometry process) sequence in the camera of Embodiment 1; 9 is a flowchart showing a photographing process (photometry process) sequence in a camera that is Embodiment 2 of the present invention. 9 is a flowchart showing a photographing process (photometry process) sequence in a camera that is Embodiment 3 of the present invention. 9 is a flowchart showing a photographing process (photometry process) sequence in a camera that is Embodiment 4 of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Shooting lens 12 Shutter unit 14 Image pick-up element 20 Image processing circuit 40 Exposure control circuit 48 Flash unit 50 System control circuit 121 Subject determination calculation part 122 Face determination calculation part 123 Low brightness determination calculation part 124 Backlight scene determination calculation part 125 Flash arrival determination Part

Claims (2)

An image sensor that photoelectrically converts a subject image;
Brightness determination means for determining the brightness of the subject area from the image signal obtained using the image sensor;
Subject determination means for determining whether a face is included in the subject from the image signal;
Flash determination means for determining whether flash light reaches the subject;
Wherein said object area by the luminance determining means is determined to luminance lower than a certain intensity, and when the face by the object determination unit is determined to be included in the subject, for the slow-synchro photographing with flash Shooting control is performed, the luminance determination unit determines that the subject area is lower than the specific luminance, the subject determination unit determines that the face is not included in the subject, and the flash determination unit determines the subject And a control unit that performs shooting control with flash emission, which has a shutter speed relatively higher than that of the slow sync shooting when it is determined that the flash light reaches the camera. A method for controlling an imaging apparatus having an imaging element for photoelectrically converting a subject image,
Determining the luminance of the subject area from the image signal obtained using the imaging device;
Determining whether a face is included in the subject from the image signal;
Determining whether flash light reaches the subject;
When said than object area is specified luminance is determined that low luminance, and the face is determined to be included in the subject and performing shooting control for slow sync shooting with flash light,
Than said subject region is the specific brightness is determined that low luminance, when the face is determined to be not included in the subject, and a flash light is determined to reach the said object, the shutter compared to the slow-synchro photographing And a step of performing photographing control with flash light emission having a relatively high speed .