JP2008047976A - Imaging apparatus and imaging method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase precision in face detection when capturing an image under a backlight environment. <P>SOLUTION: A face region is detected for an image signal obtained by converting object light photoelectrically. When imaging processing, such as autofocus and automatic exposure adjustment, is performed corresponding to the detected face region, the date and time in imaging are counted. The position in imaging is calculated. An orientation to the lens optical axis of an imaging apparatus is detected. The counted date and time information and the calculated current position information are used for calculating the position of the sun in imaging. When it is determined that the calculated position of the sun exists in the orientation on the lens optical axis, the gain of the image signal is amplified by a prescribed value. The face region is detected for the image signal, where the gain is amplified. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an imaging apparatus suitable for application to, for example, an apparatus that performs face detection and automatically adjusts exposure and focus, and an imaging method therefor.

  Generally, in a camera that performs automatic exposure adjustment (so-called AE (Automatic Exposure) camera), an appropriate exposure value is calculated based on the brightness of the subject, and the aperture and shutter speed are automatically adjusted based on the exposure value. Imaging is performed.

  However, when imaging is performed in a backlight environment, there is a problem that the exposure is adjusted based on the brightness of the background, and the subject is imaged darkly. For this reason, various methods have been devised so that appropriate exposure adjustment can be performed even in a backlight environment.

  In Patent Document 1, it is determined whether or not the backlight environment is determined by using GPS (Global Positioning System) positioning, an azimuth sensor, and date and time information. There is disclosure about performing exposure compensation.

Japanese Patent Application Laid-Open No. 2004-228561 discloses that imaging is performed by calculating the azimuth and altitude of the sun using GPS positioning and date / time information, and correcting the exposure value and the white balance value.
JP-A-8-95146 JP 2000-41800 A

  On the other hand, in recent years, when a subject is a person, a face portion of the person is detected, and focusing is performed around the detected face or white balance is adjusted. However, in a backlit environment, the face of the person who should perform face detection is picked up darkly, so the face detection rate decreases, and the phenomenon that the exposure cannot be adjusted to the face may occur. . As described above, since the face detection itself cannot be performed even if the automatic exposure adjustment function by the face detection is provided, there is a problem that the automatic exposure adjustment cannot actually be performed.

  The present invention has been made in view of this point, and an object thereof is to improve the accuracy of face detection when imaging is performed in a backlight environment.

  In the present invention, a face area is detected from an image signal obtained by photoelectrically converting subject light imaged through a lens, and image capturing is performed in accordance with the detected face area. Measure the date and time of the time, calculate the position at the time of shooting, detect the orientation with respect to the lens optical axis of the imaging device, and at the time of imaging using the time and date information and the calculated current position information When the position of the sun is calculated and it is determined that the calculated sun position is in the vicinity of the azimuth on the lens optical axis, the gain of the image signal is amplified by a predetermined amount, and the gain is amplified to the image signal. On the other hand, the face area is detected.

  By doing so, the gain of the image signal is amplified by a predetermined amount when it is determined that the position of the sun is in the azimuth on the lens optical axis of the imaging device, that is, when imaging is performed in a backlight environment. Therefore, the brightness of the entire captured image is improved.

  According to the present invention, when imaging is performed in a backlit environment, the gain of the image signal is amplified by a predetermined amount, so that the luminance of the entire captured image is improved and the luminance of the face portion is also improved.

  In this case, since face detection can be performed with the brightness of the face portion improved, the detection accuracy of face detection is improved.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 and 2.

  FIG. 1 is a block diagram illustrating a configuration example of a digital still camera according to the present embodiment. In the digital still camera 100 shown in FIG. 1, a lens 1 is disposed on the front surface of an image sensor 12 constituted by a solid-state image sensor using a charge-coupled device (CCD) or a complementary metal oxide silicon (CMOS). . The optical image of the subject is incident on a light receiving unit (not shown) of the image sensor 12 via the lens 1 and is subjected to photoelectric conversion. An aperture 2 is disposed in the optical path between the lens 1 and the image sensor 12, and the aperture amount is adjusted by the aperture drive unit 11. The amount of light incident on the image sensor 12 can be controlled by adjusting the aperture amount of the diaphragm 2 based on a command from the control unit 16 by driving by the diaphragm driving unit 11. Further, the focus lens in the lens 1 is configured such that the focus can be adjusted by the focus drive unit 10. The focus drive unit 10 varies the position of the focus lens in the lens 1 based on a command from the control unit 16. Adjust so that the focus is on the subject at the desired position.

  Each unit in the digital still camera 100 is controlled by the control unit 16. The control unit 16 is recorded in a non-volatile storage unit such as a built-in ROM (Read Only Memory) based on an operation signal obtained through a user operation on the operation unit 27, or a predetermined setting. In accordance with the computer program, predetermined calculation and control of each part constituting the digital camera 100 are performed.

  The imaging timing at the imaging element 12 is controlled by the timing generator 17. The timing generator 17 generates a pulse signal in synchronization with a clock signal supplied from a clock generation unit (not shown) of the control unit 16, and supplies the generated pulse signal to the image sensor 12. In the image sensor 12, the signal charge accumulated in the light receiving unit of the image sensor 12 is scanned in accordance with the pulse signal input from the timing generator 17 and output as an image signal.

  The output of the image sensor 12 is supplied to the analog signal processing unit 13. The analog signal processing unit 13 includes a correlated double sampling circuit, an AGC (Automatic Gain Control) circuit (both not shown), and the like, and the correlated double sampling circuit detects reset noise included in the input image signal. The AGC circuit amplifies the input image signal and controls it to a constant signal level. However, as will be described later, the amplification unit in the AGC circuit may perform amplification different from normal. The output of the analog signal processing unit 13 is supplied to the analog / digital conversion unit 14. The analog / digital conversion unit 14 converts the analog image signal input from the analog processing unit 13 into a digital image signal. The converted image signal is supplied to the image signal processing unit 15.

  The image signal processing unit 15 performs various signal processing on the image signal supplied from the analog / digital conversion unit 14 to generate an output image signal. For example, knee correction that compresses a certain level or higher of the image signal, γ correction that corrects the level of the image signal according to a preset γ curve, white clip processing that restricts the signal level of the image signal to be within a predetermined range, or black Perform clip processing. The image signal processing unit 15 performs an encoding process for converting the image signal into a JPEG (Joint Photographic Experts Group) system or an MPEG (Moving Picture Experts Group) system, and supplies the encoded image signal to the memory 25. Remember (record). Or you may make it perform the encoding process converted into the signals of standard television systems, such as NTSC (National Television System Committee) and PAL (Phase Alternating Line). The image signal to be displayed on the display unit 26 is also supplied from the image signal processing unit 15.

In addition, an AE detection unit 18, an AF (Auto Focus) detection unit 19, and a face detection unit 20 are provided as processing units that process the image signal processed by the image signal processing unit 15.
The AE detection unit 18 calculates luminance data of the subject from the image signal input from the analog / digital conversion unit 14 and calculates an aperture value and a shutter speed suitable for imaging. When adjustment of the gain for amplifying the image signal is necessary, the gain adjustment value (amplification amount) is also calculated. The brightness data is calculated by, for example, dividing one screen into a plurality of areas and integrating the brightness of each area after weighting each area or excluding the peak value of the brightness. Done. The luminance data obtained by the AE detection unit 18 is supplied to the control unit 16, and a command signal based on the value is generated by the control unit 16, and then the command signal is supplied to the aperture driving unit 11.

  An AF (Auto Focus) detection unit 19 extracts a high frequency component of the image signal and generates data obtained by integrating the high frequency component existing in a predetermined setting area on the screen. The integrated data is data indicating how much high-frequency components are present in the set area, and the level of contrast can be determined by using the integrated data. Generally, this data is called an evaluation value, and the control unit 16 drives the lens 1 by supplying a command signal to the focus driving unit 10 so that the evaluation value is maximized, that is, the contrast is maximized. By doing so, auto focus is realized.

  The face detection unit 20 performs feature point extraction and skin color region extraction on the digital signal input from the image signal processing unit 15, and patterns for main parts of the face registered in advance in the memory 25 and the like. The face area is detected by matching. The position and size of the detected face area are supplied to the control unit 16. If a plurality of faces are detected in the screen, a plurality of face detection result information is transmitted to the control unit 16.

  The processing unit that supplies data necessary for control by the control unit 16 includes an RTC (Real Time Clock) generation unit 21, a GPS (Global Positioning System) positioning unit 22, and an orientation sensor 24. The RTC generation unit 21 includes a clock oscillator and a counter, and measures the date and time by counting the time based on a signal generated by the clock oscillator.

  The GPS positioning unit 22 is connected to a GPS antenna 23 that receives satellite signals from GPS satellites, calculates the current position (latitude / longitude / altitude) from the satellite signals received by the GPS antenna 23, and the calculation result Is supplied to the controller 16. Based on the current position information input from the GPS positioning unit 22, the control unit 16 calculates the position of the sun at the imaging position at that date and time.

  The azimuth sensor 24 is a two-axis magnetic field sensor, and the two axes are composed of, for example, an X axis and a Y axis that are orthogonal to each other. The geomagnetism is output as an X-axis component and a Y-axis component, and the azimuth of the geomagnetic vector with respect to the X-axis and Y-axis is detected by taking the ratio. The direction of the detected geomagnetic vector is output to the control unit 16. In this example, when the geomagnetic vector direction with respect to the lens optical axis of the digital still camera 100 is detected and it is determined that the position of the sun is in the direction near the direction of the optical axis of the lens, the imaging environment is a backlight environment. Judge.

  The memory 25 is a storage medium that can be written to and read out under the control of the control unit 16. In addition to storing the above-described image signal, the memory 25 stores the current position information calculated by the GPS positioning unit 22 and the face detected by the face detection unit 20. Detection information, facial feature information necessary for face detection, orientation information by the orientation sensor 24, and the like are stored. The memory 25 is composed of, for example, a nonvolatile memory.

The display unit 26 drives a display (not shown) such as a liquid crystal panel based on the image signal input from the image signal processing unit 15 to display a captured image on the display.
In addition, the digital still camera 100 includes an operation unit 27. The operation unit 27 includes various operation keys such as a shutter button. A shutter button (not shown) is configured to operate in two stages of half-press and full-press. When the shutter button is half-pressed, an automatic adjustment function of exposure and focus works. When the shutter button is fully pressed, a captured image signal is displayed. An imaging operation to be stored in the memory 25 is performed. In this example, the shutter button is operated in two stages of half-press and full-press, but the operation of the shutter button is not limited to this.

  Further, in this example, it is assumed that a “face detection mode” for performing face detection accuracy improvement processing at a stage before imaging can be selected. The “face detection mode” is set by an operation on the menu screen displayed on the display unit 26, and the setting is stored in the control unit 16. The “face detection mode” may be selected by operating the shutter button. For example, as described above, the face detection may be performed by pressing the shutter button halfway to enter the “face detection mode”.

  Data transmission between the control unit 16, the image signal processing unit 15, the face detection unit 20, and the memory 25 is performed via a bus 28.

  Next, an example of the imaging process of this example will be described with reference to the flowchart of FIG. This example is an example for performing face detection accuracy improvement processing. The face detection accuracy improving process in this example is performed at a stage prior to normal imaging, and the “face detection mode” is selected in advance by the user, and an operation signal is input by an operation such as half-pressing the shutter button. This is performed when the control unit 16 detects this. First, in step S1, it is determined whether or not the backlight environment. That is, from the date and time information by the RTC generation unit 21 and the current position information by the GPS positioning unit 22, the position of the sun at the imaging position at the date and time is calculated by the control unit 16, and the control unit 16 digitally performs positioning by the direction sensor 24. When the lens optical axis of the still camera 100 is directed in the direction with the sun, it is determined that the environment is a backlight environment. When the lens optical axis is not directed in the direction with the sun, it is determined that the environment is not a backlight environment.

  If it is determined in step S1 that the environment is backlit, the analog gain of the image signal is amplified by the amplification unit in the analog signal processing unit 13 (step S2). As a result, the brightness of the entire captured image is increased, and the brightness of the face portion is improved at the same time, so that the accuracy of face detection in the face detection unit 20 is improved. Unlike the gain amplification of the image signal stored (recorded) in the memory 25 or the image signal displayed on the display unit 26, the gain amplification in this case is intended to increase the luminance to the extent that face detection is possible. Therefore, the amplification factor may be a preset value as a fixed value, or may be arbitrarily changed.

  In this state, face detection processing is performed by the face detection unit 20 (step S3), and autofocus control for focusing on the detected face position is performed (step S4). That is, a command signal is supplied from the control unit 16 to the focus driving unit 10 so that the evaluation value calculated by the AF detection unit 19 is maximized in the face detection area, and the lens 1 is received by the command signal from the focus driving unit 10. Is driven to adjust the focus to the face detection position.

  After focusing on the face detection position, automatic exposure control is performed around the detected face (step S5). In this case, the exposure control may be performed by the gain adjustment for the analog signal by the analog signal processing unit 13 or may be performed by the gain adjustment for the digital signal by the image signal processing unit 15. Alternatively, the electronic shutter speed may be adjusted. At the time of automatic exposure control here, gain amplification for face detection in step S2 is not performed, but gain amplification for properly storing (recording) and displaying is performed.

  As described above, when it is determined that the environment is a backlight environment, by amplifying the image signal itself, the overall luminance of the image is improved and the accuracy of face detection is increased. Then, after the face is detected, the exposure is adjusted again according to the detected face of the person, so that it is possible to take an image in a state where the exposure of the face of the person is appropriate.

  In the above-described embodiment, the analog signal processing unit 13 increases the analog gain to increase the detection rate of face detection. However, the image signal processing unit 15 can increase the digital gain in the same manner. The effect can be obtained. A processing example in this case will be described with reference to the flowchart of FIG.

  First, it is determined whether or not the backlight environment is present (step S11). That is, from the date and time information by the RTC generation unit 21 and the current position information by the GPS positioning unit 22, the position of the sun at the imaging position at that date and time is calculated by the control unit 16, and the lens of the digital still camera 100 is measured by the direction sensor 24. When it is determined that the optical axis is substantially directed in the direction with the sun, the control unit 16 determines that the environment is a backlight environment, and when the lens optical axis is not directed in the direction with the sun, the control unit 16 Judged not to be backlit.

  When it is determined in step S11 that the environment is a backlight environment, the digital gain of the image signal is amplified by the image signal processing unit 15 (step S12). As a result, the brightness of the entire captured image is increased, and the brightness of the face portion is also improved. Therefore, the accuracy of face detection in the face detection unit 20 is also improved. The gain adjustment rate in this case may be a rate set in advance as a fixed value, or may be arbitrarily changed.

  Next, face detection processing by the face detection unit 20 is performed (step S13), and autofocus control is performed according to the detected face (step S14). That is, a command signal is supplied from the control unit 16 to the focus driving unit 10 so that the evaluation value calculated by the AF detection unit 19 is maximized, and the lens 1 is driven by the command signal from the focus driving unit 10. The focus is adjusted to the face detection position.

  After focusing on the face detection position, automatic exposure control is performed around the detected face (step S15). In this case, the exposure control may be performed by the gain adjustment for the analog signal by the analog signal processing unit 13 or may be performed by the gain adjustment for the digital signal by the image signal processing unit 15. Alternatively, the automatic shutter speed may be adjusted.

  Further, as described above, when the face detection accuracy improving process is performed by digital gain amplification in the image signal processing unit 15, the gain amplification circuit in the image signal processing unit 15 is separated into two systems, and the face detection unit 20. The gain amplification is performed by the dedicated amplification unit for face detection only for the signal for use, and the normal gain amplification is performed for the image signal for storage (recording) and display by a different amplification unit. Also good. A configuration example in this case is shown in FIG. In FIG. 4, parts corresponding to those already described with reference to FIG.

  In FIG. 4, an image signal captured by the image sensor 12 and subjected to analog signal processing by the analog signal processing unit 13 is supplied to the analog / digital conversion unit 14. The image signal processing unit 15 includes a first digital gain circuit 30a and a second digital gain circuit 30b, and the first digital gain circuit 30a performs normal amplification for amplifying an image signal for storage (recording) or display. The second digital gain circuit 30b is provided as a dedicated amplification unit for face detection. The first digital gain circuit 30a provided as a normal amplifying unit performs normal gain adjustment for appropriately storing (recording) and displaying the image signal input from the A / D conversion unit 14. Then, the image signal after gain adjustment is transmitted to the memory 25 and the display unit 26 through the bus 28 as they are. On the other hand, in the second digital gain circuit 30b provided as an amplification unit for face detection, the luminance of the image signal input from the A / D conversion unit 14 is improved to such an extent that face detection is possible. Then, a certain amount of gain amplification is performed, and the image signal with the gain amplified is transmitted to the face detection unit 20.

  Thus, by dividing the processing system in the image signal processing unit 15 into two, normal gain amplification is performed on the image signal stored in the memory 25 and the image signal displayed on the display unit 26. Since a predetermined amount of gain amplification for increasing the detection rate of the face detection is performed only on the image signal transmitted to the face detection unit 20, the image displayed on the display unit 26 is the face detection signal. Therefore, it is not difficult to see an image by gain amplification. That is, only the gain of the image signal for face detection can be efficiently amplified. Further, since gain amplification for face detection and normal gain amplification for properly storing (recording) and displaying are performed in parallel, the entire processing time from imaging to recording or display is shortened. .

  In the above-described embodiment, an example in which the imaging apparatus according to the present invention is applied to a digital still camera has been described. However, the present invention is not limited to this, and for example, a video camera or other apparatus having a function equivalent thereto. It may be present and is widely applicable to various devices.

It is a block diagram which shows the structural example of the digital still camera by one embodiment of this invention. It is a flowchart which shows the example of a face detection accuracy improvement process by one embodiment of this invention. It is a flowchart which shows the example of a face detection accuracy improvement process by other embodiment of this invention. It is a block diagram which shows the structural example of the digital still camera by other embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Lens, 2 ... Diaphragm, 10 ... Focus drive part, 11 ... Diaphragm drive part, 12 ... Image sensor, 13 ... Analog signal processing part, 14 ... A / D conversion part, 15 ... Image signal processing part, 16 ... Control , 17 ... Timing generator, 18 ... AE detector, 19 ... AF detector, 20 ... Face detector, 21 ... RTC, 22 ... GPS, 23 ... GPS antenna, 24 ... Direction sensor, 25 ... Memory, 26 ... Display unit 27 ... Operation unit 28 28 Bus 30 Digital gain circuit 100 Digital still camera

Claims (5)

An imaging unit that photoelectrically converts subject light imaged through a lens to generate an image signal;
In an imaging apparatus that includes a face detection unit that detects a face area with respect to an image signal generated by the imaging unit, and that can perform an imaging process according to the face area detected by the face detection unit,
A sundial time unit for measuring the date and time at the time of imaging in the imaging unit;
A position calculation unit that calculates a position at the time of imaging in the imaging unit;
An azimuth detector that detects the azimuth of the lens relative to the optical axis;
An amplification unit for amplifying the image signal output by the imaging unit;
The sun position at the time of imaging is calculated using the date and time information timed by the sundial time unit and the position information calculated by the position calculating unit, and the calculated sun position is the azimuth detecting unit. Control for amplifying the gain of the image signal by a predetermined amount in the amplification unit and supplying the amplified image signal to the face detection unit when the amplification unit determines that the image signal is in the vicinity of the orientation on the lens optical axis An imaging apparatus comprising: a control unit that performs the above. The imaging device according to claim 1,
The imaging apparatus is characterized in that the imaging processing performs autofocus adjustment or exposure adjustment on an image signal with the gain amplified in accordance with a face area detected by the face detection unit. The imaging device according to claim 1,
The amplification of a predetermined amount in the amplification unit is performed only during a period in which face detection is performed from the image signal in the face detection unit,
An imaging apparatus characterized in that after the face detection process ends, a predetermined amount of amplification in the amplifying unit ends. The imaging device according to claim 1,
In addition to the face detection image signal amplification unit, a second image signal amplification unit that performs amplification processing on the recording or display image signal is provided.
An image pickup apparatus, wherein the second image signal amplifying unit performs amplification according to exposure adjustment of image pickup. In an imaging method in which a face area is detected for an image signal obtained by photoelectrically converting subject light imaged through a lens, and an imaging process is performed in accordance with the detected face area.
Measure the date and time at the time of imaging,
Calculate the position at the time of imaging,
Detecting the orientation of the lens with respect to the optical axis;
The sun position at the time of imaging is calculated using the timed date and time information and the calculated position information, and the calculated sun position is in the vicinity of the orientation on the optical axis of the lens. When it is determined, the imaging method is characterized in that a gain of the image signal is amplified by a predetermined amount, and a face area is detected from the image signal with the gain amplified.

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