JP2008104156A - Digital camera and control method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To emit a flash light with the proper quantity of light emission constantly even when a subject or a digital camera moves from face detection to light modulation control, in the digital camera which controls the quantity of flash light emission while utilizing a result of the face detection. <P>SOLUTION: A flash control means 19 of a digital camera 1 comprises a light emission quantity determining means 44 for determining the quantity of flash light emission by arithmetic processing in which a consideration degree of face in the determination of the quantity of light emission can be set as an arithmetic parameter; and parameter setting means (entire control unit 30, face area extraction unit 24 and the like) for acquiring index data indicating a degree of influences to be exerted upon the determination of the light emission quantity by movement of the digital camera or the subject, and setting a value of the arithmetic parameter to a value determined based on a value of the index data. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a digital camera having a function of controlling the amount of flash emission using face information included in a subject, and a method for controlling the amount of light emission.

  A digital camera normally captures an image before the shutter release button is pressed, and exposure adjustment and focus adjustment are performed using the image captured at that stage. Further, the image taken at that stage is also used to obtain the appropriate amount of light emitted from the flash. As a method of obtaining the flash emission amount, a method of obtaining an appropriate emission amount based on the brightness of the entire photographed image is generally used. However, in recent years, a human face is detected from the photographed image, and the face is detected. There has been proposed a method of varying the amount of flash emission depending on the presence or absence and the proportion of the face.

For example, Patent Document 1 discloses a method of reducing the amount of light emission when a human face is detected and the ratio of the face in the image is equal to or greater than a predetermined value. Further, in Patent Document 2, a form in which the amount of light emission is obtained using only data of a region corresponding to a face (first embodiment), and a weighting of a region corresponding to a face is set higher than other regions. A method (second embodiment) for obtaining a light emission amount using image data is shown.
JP 2003-107567 A JP 2006-074164 A

  In the methods disclosed in Patent Documents 1 and 2, if the content of the image data acquired for face detection is the same as the content of the image data acquired for dimming, the face portion is not overexposed. An image with appropriate brightness can be obtained without the face portion becoming dark. However, since there is usually a time difference of several tens of milliseconds or more between the acquisition time of the face detection image data and the acquisition time of the light control image data, the subject or the digital camera moves during this time. there is a possibility. That is, the content of the image data acquired for face detection and the content of the image data acquired for dimming are not always the same.

  If the face position is shifted from the time of face detection when dimming, the calculated amount of light emission is optimal even if the amount of light emission is calculated using the data of the area extracted as the area corresponding to the face. It is not a good value. In addition, depending on the target that was placed in the area where the face was detected as a result of the face shift, the amount of light emission may be more inappropriate than when the amount of light emission is calculated without considering the face. It may be set.

  In view of this problem, the present invention is a digital camera that can always perform flash light emission with an appropriate light emission amount even if the subject or the digital camera moves between the time when face detection is performed and the time when light control is performed. It is an object to provide a camera.

  The digital camera of the present invention includes an imaging unit that generates image data representing a subject, a light emitting unit that emits a flash, and a face detection unit that performs face detection processing on the image data generated by the imaging unit. The amount of light emitted from the flash is controlled using the detection result output by the face detection means. Then, as means for that, the light emission amount determining means for obtaining the light emission amount of the flash by a calculation process that can set the degree of consideration of the face in the determination of the light emission amount as a calculation parameter, and the movement of the digital camera or the subject determines the light emission amount. Parameter setting means for acquiring index data indicating the degree of influence and setting the value of the operation parameter to a value determined based on the value of the index data.

  The light emitting means may be a built-in flash or a removable external flash. Further, the face detection unit, the light emission amount determination unit, and the parameter setting unit may be implemented as independent circuits, or may be stored in a memory as a face detection program, a light emission amount determination program, and a parameter setting program, and follow the program. You may implement | achieve by making a CPU perform a process. The face detection means may output only the presence / absence of the face as a detection result, or may extract not only the presence / absence of the face but also an area corresponding to the face and output area information indicating the area. Also good.

  The method of the present invention is a method for controlling the amount of flash light emitted by the digital camera having the above-described configuration. Prior to the light emission amount determination step and the light emission amount determination step, index data indicating the degree to which the movement of the digital camera or subject influences the determination of the light emission amount is acquired, and the value of the calculation parameter is based on the value of the index data And a parameter setting step for setting to a determined value.

  Here, in many cases, the calculation process is estimated based on the detection result of the face detection process executed on one image data generated by the imaging unit and the other image data generated by the imaging unit. This is a process for obtaining the light emission amount based on the necessary light amount of the subject, that is, the light amount necessary for obtaining an exposure amount sufficient for obtaining an image of the subject. Therefore, as one embodiment of the present invention, the parameter setting means acquires, as the index data, data serving as an index of a time difference between the time when one image data is generated and the time when other image data is generated. When the time difference is at least within a predetermined range, the calculation parameter value may be set such that the greater the time difference, the lower the degree of consideration of the face.

  For example, the digital camera is provided with time measuring means for measuring the time difference, and the value of the calculation parameter is set based on the time difference measured by the time measuring means. The measurement of the time difference may be performed by accurately measuring the elapsed time from the time when the image data for face detection processing is generated to the time when the image data used for estimating the required light amount is generated. Measurement may be performed by detecting a time point according to the above. For example, the elapsed time from when the face is detected by the face detection process to when the necessary light amount is estimated may be measured.

  Alternatively, data indicating the shooting mode set for the digital camera or data indicating the state of the digital camera is acquired as the index data. Then, for example, the value of the calculation parameter is set so that the degree of consideration of the face becomes lower in the shooting mode and / or state in which the possibility of blurring is high. Alternatively, the value of the calculation parameter may be set so that the degree of consideration of the face becomes lower as the shooting mode and state have a longer estimated time difference. When accuracy is prioritized, parameters should be set based on the measured time. On the other hand, when it is desired to realize the above function with a simple mechanism without imposing a load on the digital camera, it is preferable to set a value according to the shooting mode and the camera state.

  In another embodiment of the present invention, the parameter setting means acquires data indicating the ratio of the face detected by the face detection means to the entire image as the index data. When the proportion of the entire face image is at least in a predetermined range, the value of the calculation parameter is set so that the degree of consideration of the face decreases as the proportion decreases. For example, when the proportion of the face is greater than or equal to a predetermined threshold, the degree of consideration of the face is set to the maximum value, and within the range from the threshold to 0%, the consideration degree of the face is set to be lower as the proportion is smaller. .

  In still another embodiment, the parameter setting unit acquires data indicating a focal length as the index data. Then, when the focal length is at least a predetermined range, the value of the calculation parameter is set so that the longer the focal length, the lower the degree of consideration of the face. In still another embodiment of the present invention, the digital camera includes camera shake detection means, and the parameter setting means acquires data indicating the amount of shake detected by the camera shake detection means as the index data. Then, when the blur amount is at least within a predetermined range, the value of the calculation parameter is set so that the greater the blur amount, the lower the degree of consideration of the face. In still another embodiment of the present invention, the parameter setting means acquires data indicating the distance to the subject measured by the distance measuring means as the index data. Then, when the distance is at least the length of the predetermined range, the value of the calculation parameter is set so that the longer the distance, the lower the degree of consideration of the face.

  In the configuration and procedure of the present invention described above, even when the face is misaligned from the time of face detection when performing dimming, if the misalignment has a large negative influence on the determination of the light emission amount, it corresponds to the face. The influence of the data of the region extracted as the region on the determination of the light emission amount can be suppressed low. Therefore, even if the face is shifted, at least the same level of dimming as when dimming is performed without considering the face, and even if not optimal, flash photography is performed with an appropriate amount of light emission.

  As specific processing, for example, a temporary appropriate value Cn of the light emission amount is obtained by performing an operation not using the detection result output by the face detection unit for the image data generated by the imaging unit, Thus, a temporary appropriate value Cn and a temporary appropriate value are obtained by performing a calculation using the detection result output from the face detecting means for the image data generated by the image pickup means. It is conceivable to perform an arithmetic process for obtaining an average with Cf, in which the influence of the temporary appropriate value Cf on the calculation result changes according to the parameter value set by the parameter setting means. Here, “average” means a process of balancing two values in some form of balance, and includes, in addition to simple average, square average, logarithmic average, weighted average, and the like. According to this calculation process, the degree of consideration of the face can be easily changed with one setting of the parameter α.

  In addition, as a calculation process in which the degree of consideration of the face in determining the light emission amount can be set as a calculation parameter, the light emission amount is calculated by setting different weights for each region on the image data generated by the imaging means. For example, a process for setting the weighting to an arbitrarily set operation parameter is also conceivable.

  The digital camera may include warning means for performing a predetermined warning operation when the degree of influence indicated by the index data exceeds a predetermined reference. When the degree of influence indicated by the index data exceeds a predetermined standard, the larger the value, the larger the degree of influence. If the index data exceeds the predetermined value, the smaller the value, the greater the degree of influence. If it is index data, it means when the index data falls below a predetermined value. The threshold value serving as a criterion for determining whether or not warning is required may be appropriately determined according to specifications and performance required by the user for the digital camera. By giving a warning before shooting, the user can perform shooting under better conditions. Also, by giving a warning after shooting, the user can redo the shooting after confirming the problem.

  The index data may be recorded on a recording medium in association with image data acquired by shooting with flash emission. Thereby, the information related to the determination of the light emission amount can be confirmed later together with the image.

  Hereinafter, as an embodiment of the present invention, a single-lens reflex digital camera having a flash photographing function and a method for controlling the flash emission amount of the digital camera will be described as an example.

[Embodiment 1]
1A, 1B, and 1C are views showing an external appearance of a digital camera 1 according to an embodiment of the present invention. As shown in FIG. 1A, a shutter release button 2, a mode dial 3 used for setting a shooting mode, a built-in flash 4, and a hot shoe 5 serving as an attachment port for accessories are provided on the top of the digital camera 1. ing.

  The shutter release button 2 has a structure in which two types of operations can be instructed by pressing in two steps. For example, in shooting using an automatic exposure adjustment function (AE: Auto Exposure) and an automatic focus adjustment function (AF: Auto Focus), the digital camera 1 has the shutter release button 2 lightly pressed (also referred to as half-press). Next, prepare for shooting such as exposure adjustment and focusing. In this state, when the shutter release button 2 is pressed down (also referred to as full pressing), the digital camera 1 starts exposure and records image data for one screen obtained by exposure on the memory card.

  The built-in flash 4 opens in the upper direction of the camera as shown in FIG. 1B by pressing a flash pop-up button 6 on the side (hereinafter referred to as a pop-up). Also, in some shooting modes, it may pop up automatically. The built-in flash 4 in the pop-up state emits light twice in conjunction with the second-stage pressing operation of the shutter release button 2. The first light emission is preliminary light emission for measuring the amount of reflected light from the subject, and the light emission amount is very small compared to normal light emission. The second light emission is a main light emission for supplying a sufficient amount of light to the subject for photographing (to obtain an appropriate exposure amount). If the light emission amount of the main light emission is appropriate, an appropriate brightness is obtained. An image can be obtained.

  The operation of the built-in flash 4 depends not only on the operation of the shutter release button 2 but also on the shooting mode set by the mode dial 3 and the flash emission mode set on the setting screen.

  Shooting modes include “AUTO” in which the camera automatically performs all settings related to shooting, “Manual” in which all settings related to shooting are manually performed by the user, “Program auto”, “Shutter priority auto”, “Aperture” Modes are prepared for each shooting scene, such as “priority auto”, “blur reduction”, “high sensitivity two-shot”, “natural photo”, “person”, “landscape”, and “night view”. As flash emission modes, modes such as “AUTO flash”, “forced flash”, “slow sync”, “red-eye reduction flash”, and “red-eye reduction flash + slow sync” are prepared.

  The digital camera 1 set to the shooting mode “AUTO” and the flash emission mode “AUTO flash” automatically pops up the built-in flash 4 when it is determined that flash shooting is necessary, and interlocks with the operation of the shutter release button 2. To fire the flash. On the other hand, since the shooting mode “natural photo” is a mode for performing flashless shooting, the built-in flash 4 does not operate even when the shutter release button 2 is operated in the digital camera 1 set to this mode. In addition, the digital camera 1 set to the flash emission mode “red-eye reduction emission” and “red-eye reduction emission + slow sync” has red-eye reduction emission for the purpose of preventing the occurrence of the red-eye phenomenon by constricting the pupil of the subject. I do. The digital camera 1 set to the photographing mode “person” also automatically emits red-eye reduction light when a predetermined condition is satisfied. In other modes, the operation of the built-in flash 4 is determined in accordance with the purpose of the mode.

  The digital camera 1 can also be used with an external flash 6 attached to a hot shoe 5 as shown in FIG. 1C. The external flash 7 is mechanically and electrically connected to the digital camera 1 by being attached to the hot shoe 5, so that, like the built-in flash 4, the shutter release button 2 according to the mode setting by the mode dial 3. The light emission operation is performed in conjunction with the second-stage pressing operation. In the following, the embodiment illustrated in FIGS. 1A and 1B will be mainly described. However, the present invention is applicable regardless of whether the flash is built-in or external.

  Next, an outline of the internal configuration of the digital camera 1 will be described with reference to FIG. As shown in FIG. 2, the digital camera 1 includes an imaging system including a lens 12, a lens driving unit 16, a diaphragm 13, a diaphragm driving unit 17, a CCD 14, and a timing generator (TG) 18. The lens 12 includes a plurality of functional lenses such as a focus lens for focusing on a subject and a zoom lens for realizing a zoom function. The lens driving unit 16 is a small motor such as a stepping motor, and adjusts the position of each functional lens so that the distance from the CCD 14 to each functional lens is a suitable distance for the purpose. The diaphragm 13 is composed of a plurality of diaphragm blades. The aperture drive unit 17 is a small motor such as a stepping motor, and adjusts the position of the aperture blades so that the aperture size of the aperture becomes a size suitable for the purpose. The CCD 14 is a CCD having 5 to 12 million pixels with a primary color filter, and discharges accumulated charges in response to an instruction signal from the timing generator 18. The timing generator 18 sends a signal to the CCD 14 so that charges are accumulated in the CCD 14 only for a desired time, thereby adjusting the shutter speed.

  The digital camera 1 also transfers an A / D converter 15 that converts the output signal of the CCD 14 into a digital signal, and image data output from the A / D converter 15 to another processing unit via the system bus 34. An image input control unit 23 and an SDRAM 22 for temporarily storing image data transferred from the image input control unit 23 are provided. The image data stored in the SDRAM 22 is RAW data.

  Further, the digital camera 1 includes a flash 11, a flash control unit 19 that controls the light emission timing and the light emission amount of the flash 11, a focus adjustment unit 20 that instructs the lens driving unit 16 to move the lens, and performs focusing. An aperture value and a shutter speed are determined, an exposure adjustment unit 21 that sends an instruction signal to the aperture drive unit 17 and the timing generator 18, and face detection processing is executed on the image data stored in the SDRAM 22. A face region extraction unit (face detection unit) 24 that outputs a value indicating presence / absence, and information (hereinafter, region information) indicating a region corresponding to the detected face when there is a face is provided. The flash control unit 19, the focus adjustment unit 20, and the exposure adjustment unit 21 may perform processing with reference to the result of detection processing executed by the face area extraction unit 24 in addition to the image data stored in the SDRAM 22. As a method for performing exposure adjustment with reference to the face detection result, for example, methods disclosed in Japanese Patent Laid-Open Nos. 2001-215404 and 2003-107555 can be used. As a method for performing focus adjustment with reference to the face detection result, for example, a method disclosed in Japanese Patent Application Laid-Open No. 2006-145629 can be used. Whether or not the flash control unit 19, the focus adjustment unit 20, and the exposure adjustment unit 21 refer to the detection result output from the face area extraction unit 24 depends on the shooting mode and other setting values.

  In addition, the digital camera 1 includes an image processing unit 25 that performs image processing on image data stored in the SDRAM 22. The image processing unit 25 enhances the appearance of the image, such as color tone correction and brightness correction for natural color and brightness of the image, and processing for correcting red eyes to black eyes when the image data includes red eyes. After various finishing processes for improving the quality, the processed image data is stored in the SDRAM 22 again.

  The digital camera 1 also includes a display control unit 26 that controls the output of image data stored in the SDRAM 22 to a liquid crystal monitor (LCD) 27. The display control unit 26 thins out the number of pixels of the image data stored in the SDRAM 22 so as to have a size suitable for display, and then outputs it to the liquid crystal monitor 27.

  The digital camera 1 also includes a recording / reading control unit 28 that controls writing of image data stored in the SDRAM 22 to the memory card 29 and loading of the image data recorded on the memory card 29 to the SDRAM 22. The recording / reading control unit 28 records the RAW data as it is or converted into JPEG data by compression encoding according to the setting of the user and then recorded on the memory card 29. Specifically, the recording / reading control unit 28 records an Exif (Exchangeable Image File Format) file in which the image data and the accompanying information of the image data are stored in the memory card 29. When loading image data, the image data extracted from the file is decoded and loaded into the SDRAM 22.

  The digital camera 1 also includes a camera shake detection unit 35 configured by a gyro sensor or the like. When the camera shake detection unit 35 detects a camera shake at the time of photographing, the camera shake detection unit 35 supplies information on the detected blur amount to the flash control unit 19, the exposure adjustment unit 21, and the image processing unit 25. The exposure adjustment unit 21 sets the shutter speed shorter when the camera shake is detected than when the camera shake is not detected, thereby reducing the influence of the camera shake on the acquired image. In addition, when camera shake is detected, the image processing unit 25 performs image processing for correcting the shake on the acquired image data.

  The digital camera 1 also has a distance measuring function that measures the distance from the digital camera 1 to the subject. Although the distance measuring function can be realized by providing a distance sensor on the front surface of the digital camera 1, in this embodiment, the distance to the subject is determined based on the position information of the focus lens and the number of driving pulses of the focus lens.

  In addition, the digital camera 1 includes a CPU (Central Processor Unit) 31, a RAM (Random Access Memory) 32 in which an operation / control program is stored, and an EEPROM (Electronically Erasable and Programmable Read Only Memory) in which various setting values are stored. An overall control unit 30 is provided. The overall control unit 30 detects various setting operations performed by the user including the setting of the shooting mode by the mode dial, and stores the set contents in the EEPROM 33. Then, when the setting operation is performed or when the photographing operation is performed, the flash control unit 19, the focus adjustment unit 20, the exposure adjustment unit 21, and the image input described above according to the setting values stored in the EEPROM. A signal for instructing the control unit 23, the face area extraction unit 24, the image processing unit 25, the display control unit 26, and the recording / reading control unit 29 via the system bus 34 and the execution timing of the processing. Is sent out.

  FIG. 3 shows the configuration of the flash control unit 19 and the input / output data of the flash control unit 19. As shown in the figure, the flash control unit 19 includes first calculation means 41, second calculation means 42, parameter storage means 43, and light emission amount determination means 44. The first calculation means 41, the second calculation means 42, and the light emission amount determination means 44 are calculation circuits that execute calculations described later, and the parameter storage means 43 is an EEPROM. However, the parameter storage unit 43 is not necessarily a component of the flash control unit 19. For example, the EEPROM 33 provided in the overall control unit 30 may be used as the parameter storage unit 43.

  The first calculation means 41 receives supply of non-light emission image data and preliminary light emission image data from the image input control unit 23 under the control of the overall control unit 30. Preliminary light emission image data is image data taken by the imaging unit in synchronization with preliminary light emission by the flash 11 under the control of the overall control unit 30. The non-light emitting image data is image data taken by the imaging unit immediately before or after the preliminary light emission. The first calculation means obtains and outputs a temporary appropriate value Cn of the flash light emission amount when the face is not taken into consideration by executing calculation processing described later using these two types of images. In the calculation process executed by the first calculation means, the area information output by the face area extraction unit 24 is not used.

  Similar to the first calculation means, the second calculation means 42 receives the non-light emission image data and the preliminary light emission image data from the image input control section 23 under the control of the overall control section 30. In addition, the second calculation means 42 receives supply of area information indicating an area corresponding to the face from the face area extracting unit 24. Then, a calculation process described later is performed using the two types of images and the region information, thereby obtaining and outputting a temporary appropriate value Cf of the flash emission amount in consideration of the face.

  The parameter α stored in the parameter storage unit 43 is a parameter that can be changed by setting, and is set by each processing unit including the face region extraction unit 24 and the camera shake detection unit 35. Alternatively, the overall control unit 30 receives the output of each processing unit and sets the parameter α.

  The light emission amount determining means 44 uses the temporary appropriate value Cn output from the first calculating means 41, the temporary appropriate value Cf output from the second calculating means, and the parameter α read from the parameter storage means 43. The light emission amount of the main light emission is determined, and the light emission amount of the flash 11 is controlled based on the determination.

  Hereinafter, the processing performed by the first calculation unit 41, the second calculation unit 42, and the light emission amount determination unit 44 will be further described. The first calculating means 41 and the second calculating means 42 divide the inputted non-light emitting image data and preliminary light emitting image data into a plurality of area blocks. FIG. 4 is a diagram showing an example of division into area blocks, and shows that image data 45 (non-light emission image data or preliminary light emission image data) is divided into n × m area blocks. . In the following description, region blocks having different positions are distinguished by reference numerals (1, 1) and (n, m) illustrated in the drawings.

  FIG. 5 is a flowchart showing the processing of the first calculation means. The first calculation means 41 acquires luminance information Ya (1, 1) to Ya (n, m) for each area block of the non-light emitting image data (S101). For example, RGB-YCC conversion is performed on non-light-emitting image data, the luminance value of each pixel is obtained, and the average value of each pixel luminance value for each region is obtained as luminance information Ya. With respect to the image data at the time of preliminary light emission, the luminance information Yb (1, 1) to Yb (n, m) of each area block is acquired in the same procedure (S102).

  Subsequently, for each region block, the first calculation unit 41 calculates the difference Yd (x, y) between the luminance information Yb (x, y) acquired in step S102 and the luminance information Ya (x, y) acquired in step S101. Is calculated (S103). Then, based on the differences Yd (1,1) to Yd (n, m) of all area blocks, an appropriate value (temporary appropriate value Cn) of the flash emission amount when the face is not considered is determined and output (S104). ). For example, the amount of reflected light per unit light emission amount from the subject is estimated from the simple average or weighted average of the differences Yd (1, 1) to Yd (n, m). Then, from the estimated amount of reflected light, the amount of emitted light that is the amount of reflected light that provides an optimum exposure, that is, the amount of emitted light that can supply light corresponding to the required amount of light of the subject is obtained, and this is set as a temporary appropriate value Cn. When calculating the weighted average of the differences Yd (1,1) to Yd (n, m), weighting independent of the face is performed, for example, increasing the weighting of the area block near the center of the image.

  FIG. 6 is a flowchart showing the processing of the second calculation means. As illustrated in FIG. 4, the second calculation unit 42 selects a region block group 47a corresponding to the region 46a indicated by the region information supplied from the face region extraction unit 24 (S201). For example, the area of a range that overlaps the region 46 a is calculated for each region block, and the block group 47 a in which half or more of the area overlaps the region 46 is selected. Subsequently, the luminance information Ya (p, q) of the selected area block of the non-light emitting image data is acquired (S202). Also, the luminance information Yb (p, q) of the selected area block of the preliminary light emission image data is acquired (S203).

  Subsequently, for each selected area block, the second calculation means 42 calculates the difference Yd (p) between the luminance information Yb (p, q) acquired in step S203 and the luminance information Ya (p, q) acquired in step S202. , Q) is calculated (S204). Then, based on the difference Yd (p, q) obtained for the selected area block, an appropriate value (temporary appropriate value Cf) of the flash emission amount when considering the face is determined and output (S205). For example, in the example of FIG. 4, since there are six selected blocks, the provisional appropriate value Cf is determined based on Yd (p1, q1) to Yd (p6, q6). For example, the amount of reflected light per unit light emission amount from the subject is estimated from a simple average of the differences Yd (p1, q1) to Yd (p6, q6). Then, a light emission amount that is a reflected light amount for obtaining an optimum exposure, that is, a light emission amount that can supply light corresponding to the required light amount of the subject to the subject is obtained, and this is set as a temporary appropriate value Cf.

The light emission amount determining means 44 performs an adjustment using the temporary appropriate value Cn output from the first calculating means 41 and the temporary appropriate value Cf output from the second calculating means 42 as a reference value, so that the appropriate light emission amount of the flash 11 is obtained. Ch is determined. In the present embodiment, the light emission amount is adjusted based on the parameter α stored in the parameter storage unit 43. Specifically, the light emission amount determining means 44 determines the appropriate light emission amount Ch by performing a calculation based on the following equation (1).
Appropriate light emission amount Ch = Cn × (1−α) + Cf × α (1)
In the calculation based on the equation (1), the value of the temporary appropriate value Cf greatly affects the determination of the appropriate value Ch as the parameter α increases.

  The dimming considering the face is based on the premise that the image data used for face detection and the image data used for dimming are the same. However, in actual shooting, as shown in the time chart of FIG. 7, there is a time difference t1 between the time point A at which the face detection image data is acquired and the time point B at which the non-light emitting image data is acquired. There is a time difference t2 between time point B at which the image data at the time of light emission is acquired and time point C at which the image data at the time of preliminary light emission is acquired. The total time difference T is usually several tens of milliseconds or more. During this time, the subject may move or camera shake may occur, so that the image data used for face detection and the image data used for dimming may differ from each other.

  When the image data used for face detection is different from the image data used for light control, the provisional appropriate value Cf output by the second calculation means is not necessarily an appropriate value. The greater the degree of difference (face position deviation) between the two types of image data, the lower the reliability of the temporary appropriate value Cf. In view of this, when the face position deviation (predicted deviation) between the two types of image data is large, the influence of the face detection result on the light emission amount control is suppressed by setting the parameter α to a small value. Specifically, the parameter α is set according to the policy, configuration, and procedure exemplified below.

  The digital camera of the present embodiment includes a plurality of parameter setting means for each policy exemplified below. More specifically, the overall control unit 30, the face area extraction unit 24, the camera shake detection unit 35, and the focal length adjustment unit (not shown) function as each function and also function as a parameter setting unit. Then, the parameter α in the parameter storage means 43 is set and updated stepwise by one parameter setting means selected based on the user's operation or setting or by a plurality of selected parameter setting means.

  First, the parameter setting function of the overall control unit 30 will be described. In general, the possibility that the image data used for dimming differs from the image data used for face detection increases as the time difference T or the time difference t1 shown in FIG. 7 increases. In other words, the greater the time difference, the lower the reliability of the temporary appropriate value Cf output by the second calculation means. Therefore, the overall control unit 30 as parameter setting means acquires information on this time difference as index data indicating the degree of influence of the movement of the digital camera or the subject on the determination of the light emission amount. When the time difference is large, the value of the parameter α is set small so that the value of the temporary appropriate value Cf does not greatly affect the determination of the appropriate value Ch.

  The overall control unit 30 acquires time difference information by measuring the real time with a software timer using the clock function of the CPU 31. Alternatively, a dedicated timer circuit may be provided instead of the software timer. The overall control unit 30 resets the timer when the image data for face detection is supplied from the image input control unit 23 to the face area extraction unit 24, and the light control unit 19 controls the light from the image input control unit 23 to the flash control unit 19. The timer value when the image data is supplied is recorded as a time difference. The image data for dimming includes non-light emission image data and preliminary light emission image data, and a value obtained when any one of the image data is supplied may be recorded.

  The RAM 32 of the overall control unit 30 stores a look-up table (LUT) that defines the association between the time difference and the parameter α. FIG. 8 shows an example of the LUT. The LUT is preferably defined so that the value of the parameter α decreases as the time difference increases. However, as illustrated in FIG. 8, a table may be used in which the value of the parameter α monotonously decreases when the time difference exceeds a predetermined value. That is, if the value of the parameter α is monotonously decreasing with respect to the time difference in a certain range, the parameter value may be constant in another range. The overall control unit 30 acquires a parameter value corresponding to the time difference measured by the timer by referring to the LUT. The acquired value is transferred to the flash control unit 19 and stored in the parameter storage unit.

  The flash control unit 19 may include the timer and the LUT. In this case, the flash control unit 19 resets the timer when the face detection result is supplied from the face area extraction unit 24 to the flash control unit 19, and the non-light-emitting image data or the preliminary light-emitting image data is stored in the flash control unit. 19 is recorded as a time difference. Although there is a slight time lag between the time when the image data for face detection is generated and the time when the face detection result is obtained, the measurement is based on the time when the face detection result is obtained. The obtained time difference is also sufficiently effective as index data. Further, if the timer is operated only when the face detection result is referred to and the region information is included, that is, when the face is detected, unnecessary time measurement is not performed. Therefore, the load on the digital camera can be reduced as compared with the case where time measurement is performed with the time of supplying image data for face detection as a base point.

  As described above, if the time difference is measured and the value of the parameter α corresponding to the time difference is set, the importance of the face in the light emission amount control can be adjusted by the reliability of the face detection result, and the light emission amount Can be controlled to an appropriate value.

  As another parameter setting method considering the time difference, there is a method of setting a value based on the camera state and the set photographing mode. The magnitude of the time difference depends on the camera state and the shooting mode. Therefore, the state of the camera and the shooting mode are also effective as index data indicating the degree of influence of the movement of the digital camera or the subject in determining the light emission amount. By setting the parameter α to be smaller in a state where the time difference tends to become large or in the shooting mode, it is possible to obtain the same effect as adjusting the parameter according to the measured time difference. Here, the “state” of the camera is a state distinguished inside the digital camera. For example, it can be said that the state before the predetermined operation is performed is different from the state after the predetermined operation is performed. In addition, it can be said that the state before the digital camera completes the predetermined operation and processing is different from the state after the completion.

  FIG. 9 shows an example of processing for setting the parameter α based on the camera state and the shooting mode. The overall control unit 30 initializes the value of the parameter α to the value α0 and initializes the value of the variable k to 1 (S301). When the processing unit that functions as the parameter setting means is only the overall control unit 30, the value α0 is 1. When a processing unit other than the overall control unit 30 is involved in parameter setting, the value α0 is set by reading the value previously set in the parameter storage unit 43 by another processing unit.

  When the initialization is completed, the overall control unit next adjusts the parameter α based on the state of the camera. In the example shown in the figure, it is determined whether or not the shutter release button 2 is half-pressed, that is, whether the operation is stopped when it is lightly pressed (S302). If the half-pressed state is not detected, the variable k is multiplied by a coefficient 0.7 (S303). On the other hand, when the half-pressed state is not detected, the value of the variable k is kept as it is, and the process proceeds to the next step.

  Hereinafter, the reason for determining the half-pressed state will be described. FIGS. 10A to 10C are diagrams showing the relationship between the operation of the shutter release button and the operation of the digital camera by arranging the processes of the digital camera from the left to the right in the drawing along with the flow of time. FIG. 10A and FIG. 10C show the digital camera 1 when the shutter release button 2 is pressed to the first stage (half-pressed), and after a while, it is pressed to the second stage (fully pressed). The operation is shown. On the other hand, FIG. 10B shows the operation of the digital camera 1 when the shutter release button 2 is pressed all the way to the second stage.

  As shown in FIG. 10A, the digital camera 1 of the present embodiment executes face detection processing before the shutter release button 2 is operated. When the half-pressing operation of the shutter release button 2 is detected, the face detection process is continuously executed until the full-pressing operation is detected. The flash emission amount is obtained in the process of light control after the full-press operation is detected. For the calculation of the light emission amount, the result of the face detection process performed immediately before dimming is used.

  On the other hand, as shown in FIG. 10B, when the shutter release button 2 is pressed all the way to the second stage, the face detection process is executed only before the shutter release button 2 is pressed. In addition, since the AE / AF process is executed after the shutter release button 2 is pressed, the time difference T (or t1) is larger than when the full-press operation is performed through the half-pressed state. In other words, determining whether or not the half-pressed state has passed in step S302 is substantially equivalent to determining whether or not the time difference is large.

  As another type of camera different from the digital camera 1, as shown in FIG. 10C, there is a type of camera that does not execute the face detection process after the shutter release button is pressed. In the case of a camera that performs the operation shown in FIG. 10C, the time difference T becomes larger when the camera is half-pressed, as is apparent from the comparison between FIG. 10C and FIG. 10B. Therefore, in the camera of the type illustrated in FIG. 10C, it is preferable to multiply the variable k by a coefficient less than 1 when a half-pressed state is detected, contrary to the process illustrated in FIG. 9.

  As is clear from the illustrations of FIGS. 10A and 10C, when adjusting the parameter α based on the state of the camera, the preferred adjustment method differs depending on the specifications and performance of the camera. The degree of parameter increase / decrease, that is, the value of the coefficient to be multiplied by the variable k is preferably determined according to the specifications and performance of the camera. Needless to say, the variable k may be adjusted by determining not only the half-pressed state but also other states in which the time difference tends to increase.

  When the adjustment of the variable k based on the camera state is completed, the overall control unit 30 subsequently refers to the EEPROM 33 and determines whether or not a predetermined shooting mode is set. In the example in the figure, determination is made regarding the red-eye reduction light emission mode and the high-sensitivity two-shot mode in which a time difference of 0.5 seconds or more is surely generated (S304, S306). When the red-eye reduction light emission mode is set, the overall control unit 30 multiplies the variable k by a coefficient 0.5 (S305). In the red-eye reduction light emission mode, light emission is performed for the purpose of constricting the pupil of the subject after the operation of the shutter release button 2 is detected. Become. Therefore, the value of the parameter α is reduced by performing the processing of steps S304 and S305.

  The overall control unit 30 also multiplies the variable k by a coefficient 0.5 even when the high-sensitivity two-shot mode is set (S107). The high-sensitivity two-shot mode is a mode in which non-flash shooting and flash shooting are automatically performed by one operation of the shutter release button. For this reason, the time difference T is larger than that in the other shooting modes because the non-flash shooting is performed. Therefore, the value of the parameter α is decreased by performing the processes of steps S306 and S307.

  In addition to this, if there is a shooting mode in which the time difference T inevitably increases or is likely to increase in order to achieve the purpose of the shooting mode, it is preferable to similarly decrease the value of the parameter α.

  In the process of FIG. 9, in step S303, S305, and S307, the variable k is multiplied by a coefficient stepwise. For example, when the shutter release button is pressed all at once in a state in which the red-eye reduction light emission mode is set, the value of the variable k in step S308 is 0.35.

  In step S308, the variable k determined in steps S301 to S307 is multiplied by the initial value α0 of the parameter α. The value of the parameter α thus determined is transferred to the flash controller 19 and stored in the parameter storage unit.

  As described above, if the parameters are adjusted based on the camera state and the shooting mode, it is possible to realize the light emission amount control in consideration of the reliability of the face detection result with a relatively simple process. .

  Note that when a digital camera performs a camera shake correction process on image data used for face detection processing or light control processing, the reliability of the face detection result is not necessarily low even if the time difference is large. Don't be. Therefore, the overall control unit 30 may determine whether the camera shake correction mode is on or off, and the process illustrated in FIG. 9 may be executed only when the camera shake correction mode is off.

  Here, the photographing mode can be determined before the shutter release button 2 is pressed. Therefore, the overall control unit 30 may determine the shooting mode regardless of the operation of the shutter release button 2 and perform a predetermined warning operation when the time difference is predicted to exceed the predetermined time. FIG. 11 shows an example of processing of the overall control unit 30 when a warning operation is performed. In the illustrated example, the overall control unit 30 determines whether or not the red-eye reduction light emission mode is set by referring to the EEPROM 33 (S401). Further, it is also determined whether or not the high-sensitivity two-shot mode is set (S402). When either one mode or two modes are set, a warning mark or a message indicating that the face is not regarded as important in the flash emission amount control is output to the liquid crystal monitor 27 via the display control unit 26. (S403). Alternatively, instead of output to the liquid crystal monitor 27, an LED lamp equipped in the digital camera may be blinked, or a warning sound may be emitted from a speaker.

  When the overall control unit 30 performs the warning operation, the user can have an opportunity to change the shooting mode setting. If the user gives priority to the light emission amount control with an emphasis on the face rather than the convenience of the mode setting, the user may take a picture after resetting the mode causing the warning to off.

  Note that the determination of the shooting mode may be performed based on not only information obtained from the EEPROM 33 but also a mode switching notification from another processing unit. For example, when the face area extraction unit 24 selectively executes a plurality of types of face detection processes with different detection accuracy, the time difference T tends to be long because the face detection process with high detection accuracy takes time. Therefore, the face area extraction unit 24 notifies the overall control unit 30 that the face detection processing has been switched as a kind of mode change. Accordingly, the overall control unit 30 can cause the digital camera 1 to perform a predetermined warning operation when a detection process with a long processing time is selected.

  Further, the warning operation may be performed after the pressing operation of the shutter release button 2. When measuring the time difference with a timer, the time difference cannot be estimated in advance. Therefore, after completion of the photographing, it is determined whether or not a warning is necessary based on whether or not the measured time difference exceeds a predetermined time, and a warning operation is performed. Also, when determining whether or not a warning is necessary based on the shooting mode, the processing illustrated in FIG. 11 may be executed after the shooting is completed. For example, when an image immediately after acquisition is displayed on a monitor for the purpose of confirming by the user, a warning mark or the like is displayed together with the image. Accordingly, the user can know the cause of the poor image quality of the acquired image, and can redo the shooting while changing the shooting conditions.

  Next, the parameter setting function of the face area extraction unit 24 will be described. FIG. 7A, FIG. 7B, FIG. 8A, and FIG. 8B are diagrams showing the relationship between the region indicated by the image data and the region information and the region block selected in step S201 in FIG. The image data 48 is image data used by the face area extraction unit 24 for face detection processing, and the image data 45 is image data used for light control by the flash control unit 19 (image data when no light is emitted or image data when preliminary light is emitted). It is. An ellipse 49 in FIGS. 7B and 8B indicates the position of the face during dimming.

  As shown in FIGS. 7A and 7B, when the proportion of the face in the image is relatively large, the selected block group 47b is used even if the face position at the time of light control is slightly shifted from the extracted area 46b. Corresponds to the face (ellipse 49) after being displaced. Therefore, even if a deviation occurs, the luminance information of the selected block group 47b is worth reference when performing dimming. However, as shown in FIGS. 8A and 8B, when the proportion of the face in the image is small and there is only one block corresponding to the face, the position of the face is shifted from the extracted region 46c. As a result, the block 47c does not correspond to the face. In this case, the luminance information of the block 47c is no longer worth reference in the dimming process considering the face. This means that the reliability of the temporary appropriate value Cf output by the second calculation means is higher as the ratio of the face in the image is larger and lower as the ratio of the face is smaller.

  Therefore, in this embodiment, the face area extraction unit 24 calculates the ratio of the extracted area to the horizontal width of the image after the face extraction process is completed. That is, data indicating the ratio of the face shown in the entire image is acquired as index data indicating the degree of influence of the movement of the digital camera or the subject in determining the light emission amount. Then, the value of the parameter α is determined by referring to a lookup table (LUT) that defines the correspondence between the ratio and the parameter α, and the α value is set in the parameter storage unit 43 of the flash control unit 19. To do. However, it goes without saying that instead of referring to the LUT, a circuit or a program for performing conversion equivalent to the LUT may be adopted.

  FIG. 9 shows an example of the LUT. According to this LUT, when the face ratio falls below a predetermined threshold value Th1, the parameter α is set to a predetermined lower limit value αL that is not zero. When the face ratio exceeds the predetermined threshold Th2, the parameter α is set to a predetermined upper limit value αU that is not 1. When the face ratio is greater than or equal to the threshold Th1 and less than or equal to the threshold Th2, the parameter α is set to a smaller value as the face ratio is smaller and larger as the face ratio is smaller in the range from the lower limit value αL to the upper limit value αU. As a result, when the ratio of the face to the image is small, the influence of the temporary appropriate value Cf in the light emission amount adjustment is weakened, and the light emission amount obtained by calculation increases the appropriate range even if the subject moves or shakes. It will not come off.

  In the above processing, the ratio of the width of the face to the width of the image is calculated. However, any value may be used as long as the value is an index of the ratio of the face to the image. . For example, the area of the extracted region, the number of pixels, the area ratio of the face to the area of the entire image, and the like may be calculated. Alternatively, since the width of the face and the interval between the two eyes are correlated, the eyes are detected to determine the interval between the eyes, and this is used as an index value indicating the ratio of the face in the image. Also good. That is, the parameter set as the horizontal axis of the LUT is not particularly limited as long as it meets the purpose of the above processing. In the LUT, the parameter value increases linearly in the range from the threshold Th1 to the threshold Th2, but may increase nonlinearly (the LUT draws a nonlinear curve). Further, since the threshold values Th1 and Th2 can be arbitrarily determined according to the design policy, in addition to the LUT in which the value of α increases monotonously only in a part of the range delimited by the threshold values as in the above example, the threshold values are set. An LUT in which the value of α is monotonically increased over the entire range without being provided may also be employed.

  Further, the face area extraction unit 24 sends a warning signal to the overall control unit 30 when the ratio of the face in the image falls below a predetermined reference. Receiving the warning signal, the overall control unit 30 performs the warning operation described above.

  Next, the parameter setting function of the camera shake detection unit 35 will be described. The fact that camera shake has been detected means that the state shown in FIG. 7B or FIG. 8B has occurred, and the reliability of the temporary appropriate value Cf becomes lower as the amount of shake increases. That is, the shake amount detected by the camera shake detection unit 35 itself can be index data indicating the influence of the movement of the digital camera or the subject in determining the light emission amount.

  The camera shake detection unit 35 also determines the parameter α using the LUT. FIG. 10 shows an example of the LUT used by the camera shake detection unit 35. The camera shake detector 35 not only detects the occurrence of camera shake, but also measures the amount of camera shake, so the horizontal axis of the LUT is the camera shake amount. According to this LUT, when the shake amount is 0, the value of the parameter α is set to the upper limit value αU, and thereafter, the value of the parameter α is set to be smaller as the shake amount increases, and when the shake amount exceeds a predetermined threshold Th9. The value of the parameter α is set to the lower limit value αL. Thereby, when the blur amount is large, the influence of the temporary appropriate value Cf in the light emission amount adjustment is weakened, and the light emission amount obtained by the calculation does not greatly deviate from the appropriate range.

  Further, the camera shake detection unit 35 sends a warning signal to the overall control unit 30 when the detected blur amount exceeds a predetermined reference. Receiving the warning signal, the overall control unit 30 performs the warning operation described above.

  Furthermore, other processing units may function as parameter setting means. For example, shooting using a lens with a long focal length, such as a telephoto lens, is more susceptible to camera shake than normal shooting because the angle of view is narrow. This means that the reliability of the temporary appropriate value Cf is not high when the focal length is long. Therefore, the overall control unit 30 that can detect the lens replacement operation or the focal length adjustment unit (not shown) that adjusts the zoom lens acquires focal length information as the index data, and corresponds to the focal length. A parameter value may be set. The LUT is, for example, a table that sets the value of the parameter α to the lower limit value αL when the focal length is longer than a predetermined threshold. As a result, when the focal length is long and susceptible to camera shake, the influence of the temporary appropriate value Cf in the light emission amount adjustment is weakened. Therefore, even if the subject moves or camera shake occurs, the cause is determined. The emitted light quantity does not deviate significantly from the appropriate range.

  The distance to the subject is also effective as index data indicating the degree of influence of the movement of the digital camera or the subject in determining the light emission amount. The distance to the subject is measured by the distance measuring function described above. Since there is a correlation between the distance from the digital camera to the subject (face) and the size of the face (ratio occupied by the face in the image), the parameter α may be set according to the distance to the subject. The same effect can be obtained as when the parameter α is set according to the ratio of the face in the image.

  Here, in the LUT illustrated in FIGS. 9 and 10, when the parameter value set on the horizontal axis is a value within a predetermined range, the parameter α on the vertical axis is linear with respect to the parameter on the horizontal axis. However, an LUT that increases nonlinearly, that is, a table that draws a nonlinear curve instead of a straight line may be adopted. Each threshold value can be arbitrarily determined according to the design policy.

  Note that which processing unit performs the setting of the parameter α or which LUT is used is switched according to the setting of the shooting mode and the like. Alternatively, instead of the parameter storage means 43 that merely stores parameters, input of parameter values or index data is accepted from a plurality of processing units, and a new optimum parameter value is obtained using the input values. Means for obtaining may be provided. For example, the parameter values output by the face area extraction unit 24, the camera shake detection unit 35, and other processing units are set as the initial value α0 in the processing of FIG. 9, and the parameter values are obtained by the processing illustrated in FIG. Alternatively, the index data output by each processing unit may be collected, and the parameter value may be determined based on a combination of a plurality of index data.

  In the present embodiment, the processing units involved in parameter setting each transfer information related to parameter setting to the recording / reading control unit 28. The information to be transferred includes index data. For example, data such as the measured time difference T (msec), the degree of importance of the face (%), the presence / absence of a warning, and the calculated appropriate light emission amount (Av) from the processing unit that determines each value to the recording / reading control unit 28. Forwarded to When recording the Exif file on the memory card 29, the recording / reading control unit 28 stores these pieces of information in a predetermined area of the file header. Alternatively, information related to parameter settings may be recorded in debug data accompanying the Exif file.

  The overall control unit 30 and the display control unit 26 display information related to the setting of the parameters together with the image when a confirmation display of the image taken by the user is requested. Thereby, the user can know the relationship between the photographing situation and the degree of consideration of the face in the light emission amount control.

  According to the above configuration, when there is a problem in performing dimming using the face detection result, the value of the parameter α is set to be small, and the influence of the temporary appropriate value Cf in determining the light emission amount is suppressed. be able to. However, the parameter α is set to an inappropriate value when incorrect index data is acquired due to a failure of the timer, erroneous face detection, or the like. Therefore, in the present embodiment, even if an unexpected situation occurs, adjustment is performed so that the light emission amount determined by the light emission amount determination unit 44 does not greatly deviate from the appropriate range.

  Specifically, the provisional proper value obtained when the light emission amount determining means 44 performs dimming without considering the face, that is, the provisional proper value Cn output by the first calculation means 41, is used as a reference. The appropriate light emission amount Ch is limited to a range that is considered to be appropriate based on the value Cn. That is, the appropriate light emission amount Ch is not limited to a fixed range, but is limited to a range determined based on the temporary appropriate value Cn.

Specifically, the light emission amount determining means 44 is caused to determine the appropriate light emission amount Ch by processing based on the following equations (2) and (3).
Ck = Cn × (1−α) + Cf × α (2)

  Here, Ck is a provisional appropriate light emission amount. UL is the maximum value that can be taken by the difference between the appropriate value Cf and the appropriate value Cn when the normal face detection is performed and the appropriate value Cf is larger than the appropriate value Cn. Further, LL is the maximum value that can be taken by the difference between the appropriate value Cf and the appropriate value Cn when the normal face detection is performed and the appropriate value Cf is smaller than the appropriate value Cn. The values of UL and LL are values obtained empirically by repeating dimming of a subject including a face.

  The provisional appropriate light emission amount Ck obtained by the equation (2) may be an extremely large value or an extremely small value when an unexpected situation occurs. However, even when such an extreme value is obtained, the appropriate light emission amount Ch is limited to a range from Cn−LL to Cn + UL by the calculation based on the above equation (3). Since the lower limit value of Cn−LL and the upper limit value of Cn + UL are values determined based on the appropriate value Cn, as long as the light emission amount is within this range, an image acquired by flash photography is an extremely failed image. Never become. In other words, even when an unexpected situation occurs, shooting is not wasted at all.

  The example described above is an example in which an upper limit value and a lower limit value are determined for the appropriate light emission amount Ch, but only an upper limit value or only a lower limit value is determined, and only when an extremely large value is obtained. Alternatively, the value may be limited only when the value becomes extremely small.

  As described above, according to the digital camera of the present embodiment, even when the face is detected and the position of the face is shifted when dimming, the shift has a negative effect on the determination of the light emission amount. When the influence of is large, the influence of the data of the area extracted as the area corresponding to the face on the determination of the light emission amount can be kept low. Therefore, even if the face is shifted, even if it is not optimal, flash photography is performed with an appropriate amount of light emission, and an image that is always worth viewing can be obtained.

  In the present embodiment, as shown in the equations (1) and (2), the provisional appropriate value Cn obtained by dimming without considering the face and the provisional appropriateness obtained by dimming with the face taken into account. Since the appropriate light emission amount Ch (or temporary appropriate light emission amount Ck) is obtained by calculating a weighted average with the value Cf, the influence of the temporary appropriate value Cf in the light emission amount adjustment can be determined with one setting of the parameter α. It can easily be strengthened or weakened. Since the 1st calculating means 41 and the 2nd calculating means 42 should just always perform the calculation based on the same calculating formula, compared with what uses a several calculating formula properly according to a light control policy, the 1st calculating means 41 and The circuit structure or program of the second calculation means 42 can be simplified.

  Note that the light emission amount adjustment method, that is, the processing of the light emission amount determination means 44 is not limited to the processing using the above formulas (1), (2), and (3), and the light emission amount is determined based on other arithmetic expressions. Also good. For example, instead of the weighted average, a square average, logarithmic average, or the like may be obtained. Further, for example, the adjustment amount from the reference value may be fixedly determined such that the value is closer to what percentage Cf than the intermediate value between the two reference values. Furthermore, an adjustment value determined after obtaining a weighted average or the like may be added or subtracted.

[Embodiment 2]
The digital camera to be described next has the same appearance and internal configuration as the digital camera of the first embodiment, but the processing performed by the flash control unit 19 is different from that of the first embodiment. FIG. 11 shows the configuration and input / output data of the flash controller 19 in this embodiment. The flash control unit 19 includes a light emission amount determining unit 50 and a weighting parameter setting unit 51 as shown in the figure.

  The light emission amount determining means 50 receives the non-light emission image data and the preliminary light emission image data from the image input control unit 23 under the control of the overall control unit 30, and uses the provisional appropriate value Cn in the description of the first embodiment. The amount of light emission is determined by executing the same processing as the processing of FIG. 5 described as the processing for obtaining. However, unlike the first calculation unit 41 of the first embodiment, the light emission amount determination unit 50 performs a calculation in which weight is applied to the area block corresponding to the face in step S104. The weighting of each area block is set by the weighting parameter setting means 51.

  The weighting parameter setting unit 51 is supplied with region information from the face region extraction unit 24 under the control of the overall control unit 30. Then, a higher weight is set for the area block corresponding to the area from which the face is extracted than for the area block corresponding to the area having no face. At this time, the weighting parameter setting means 51 does not set the weight of the area block corresponding to the area from which the face is extracted uniformly high, but weights the larger the face as exemplified in FIGS. 12A and 12B. Set high. For example, when the weight of an area having no face is set to 1, the weight is 3 if the number of blocks corresponding to the face is less than 3, the weight is 4 if the number of blocks is 3 to 6, and 7 to 10 If so, the weight is set to 5. If 11 or more, the weight is set to 6. As a result, if the ratio of the face to the image is large and the determination of the amount of light emission does not have much influence even if camera shake occurs, the value of the light emission amount is reflected from the region extracted as the region where the face is located. When the ratio of the face in the image is small and the determination of the amount of light emission is greatly affected when camera shake occurs, the value from the area extracted as a certain area The influence of the reflected light amount on the determination of the light emission amount can be kept low.

  Although the two embodiments have been described above as examples, the present invention is not limited to these embodiments. For example, the calculation parameters in the above embodiment are parameters that are large when the degree of considering the face is large and small when it is small, but are small enough to consider the face and large enough not to consider the face. The calculation parameter may be

  In the above embodiment, it is determined whether or not light corresponding to the required light amount of the subject can be supplied to the subject based on the reflected light amount obtained from the non-light emitting image data and the preliminary light emitting image data. The above determination may be made by measuring or estimating the distance to the subject, brightness, photographing sensitivity, and the like. In other words, the calculation process executed by the light emission amount determining unit is not limited to the above embodiment as long as it can set the degree of consideration of the face in the determination of the light emission amount as a calculation parameter. Furthermore, the index data is not limited to that exemplified in the above embodiment. In addition, calculation processing that can set the degree of consideration of the face as a calculation parameter is executed, and the value of the calculation parameter is based on the value of index data indicating the degree to which the movement of the digital camera or subject affects the determination of the light emission amount. All the methods and digital cameras that are set to the values determined by the method belong to the technical scope of the present invention.

Overview of digital camera according to an embodiment of the present invention (normal state) 1 is a schematic view of a digital camera according to an embodiment of the present invention (with a built-in flash popped up). 1 is a schematic view of a digital camera according to an embodiment of the present invention (with an external flash attached). Diagram showing the internal configuration of the digital camera Diagram showing configuration of flash controller and input / output data The figure which shows the example which divided | segmented image data into the area block The flowchart which shows the process of a 1st calculating means The flowchart which shows the process of a 2nd calculating means Diagram for explaining the time difference The figure which shows an example of LUT used for determination of parameter (alpha) The figure which shows an example of the process which sets a parameter based on the state and imaging | photography mode of a digital camera Diagram showing the relationship between digital camera status and time difference Diagram showing the relationship between digital camera status and time difference Diagram showing the relationship between digital camera status and time difference Diagram showing an example of warning processing Diagram showing the relationship between image data, face area, and area block (when face occupies a large percentage: during face detection processing) Diagram showing the relationship between image data, face area, and area block (when face occupies a large percentage: during dimming process) Diagram showing the relationship between image data, face area, and area block (when face ratio is small: during face detection processing) Diagram showing the relationship between image data, face area, and area block (when face ratio is small: during dimming process) The figure which shows an example of LUT used for determination of parameter (alpha) The figure which shows the other example of LUT used for determination of parameter (alpha) The figure which shows the structure and input / output data of the flash control part in other embodiment of this invention. A figure showing an example of setting weighting parameters (when the proportion of the face is large) Figure showing an example of setting weighting parameters (when the proportion of the face is small)

Explanation of symbols

1 Digital camera 2 Shutter release button 3 Mode dial
4 built-in flash, 5 hot shoe, 6 flash pop-up button,
7 External flash, 34 System bus,
45 image data for dimming, 46 area indicated by area information,
47 area block corresponding to the area indicated by the area information, 48 face detection image data,
49 Actual face position during dimming

Claims (26)

An imaging unit that generates image data representing a subject; a light emitting unit that emits flash; and a face detection unit that performs face detection processing on the image data generated by the imaging unit. A digital camera that controls the amount of light emitted from the flash using a detection result to be output,
A light emission amount determining means for obtaining a light emission amount of the flash by a calculation process capable of setting the degree of consideration of the face in the determination of the light emission amount as a calculation parameter;
Parameter setting means for acquiring index data indicating the degree to which the movement of the digital camera or the subject affects the determination of the light emission amount, and setting the value of the calculation parameter to a value determined based on the value of the index data. A digital camera characterized by that. The light emission amount determining means is based on the detection result of the face detection process executed on one image data generated by the imaging means and the other image data generated by the imaging means as the arithmetic processing. To calculate the amount of light emission based on the required amount of light of the subject estimated
The parameter setting means acquires, as the index data, data serving as an index of a time difference between the time when the one image data is generated and the time when the other image data is generated, and the time difference is at least within a predetermined range. 2. The digital camera according to claim 1, wherein the value of the calculation parameter is set such that the degree of consideration of the face decreases as the time difference increases.   The digital camera according to claim 2, wherein the parameter setting unit acquires, as the index data, data indicating a shooting mode set for the digital camera and / or a state of the digital camera.   The digital parameter according to claim 3, wherein the parameter setting means sets the value of the calculation parameter so that the degree of consideration of the face becomes lower in a shooting mode and / or state in which the possibility of blurring is high. camera.   The digital parameter according to claim 3, wherein the parameter setting unit sets the value of the calculation parameter so that the degree of consideration of the face becomes lower as the shooting mode and / or state has a longer estimated time difference. camera. It further comprises time measuring means for measuring the time difference,
The digital camera according to claim 2, wherein the parameter setting unit acquires data indicating the time difference by the time measuring unit.   When the parameter setting means acquires data indicating the ratio of the entire face image detected by the face detection means as the index data, and the ratio is at least within a predetermined range, the ratio is small. 2. The digital camera according to claim 1, wherein the value of the calculation parameter is set so that the degree of consideration of the face becomes lower.   The parameter setting means acquires data indicating a focal length as the index data, and when the focal length is at least a predetermined range, the longer the focal length, the lower the degree of consideration of the face. The digital camera according to claim 1, wherein a value of the calculation parameter is set. A camera shake detecting means;
When the parameter setting means acquires the blur amount data detected by the hand shake detection means as the index data, and the blur amount is at least within a predetermined range, the larger the blur amount, the more the face The digital camera according to claim 1, wherein the value of the calculation parameter is set so that the degree of consideration of the value becomes low. It further comprises distance measuring means for measuring the distance from the digital camera to the subject,
The parameter setting means acquires data indicating the distance measured by the distance measuring means as the index data, and when the distance is at least the length of a predetermined range, the longer the distance, the more the face is considered. 2. The digital camera according to claim 1, wherein the value of the calculation parameter is set so that the degree becomes low. First calculation means for obtaining a temporary appropriate value Cn of the light emission amount by performing calculation not using the detection result output by the face detection means for the image data generated by the imaging means;
A second calculating means for obtaining a temporary appropriate value Cf of the light emission amount by performing a calculation using the detection result output from the face detecting means for the image data generated by the imaging means;
The light emission amount determining means is a calculation process for obtaining an average of the temporary appropriate value Cn supplied from the first calculating means and the temporary appropriate value Cf supplied from the second calculating means, wherein the parameter setting 11. The digital camera according to claim 1, wherein a calculation process is performed in which the influence of the temporary appropriate value Cf on the calculation result varies depending on the parameter value set by the means.   The calculation process performed by the light emission amount determining unit is a process of performing calculation by setting different weights for each region of the image data generated by the imaging unit, and the calculation parameter is the weighting. The digital camera according to claim 1.   The digital camera according to any one of claims 1 to 12, further comprising a warning unit that performs a predetermined warning operation when the degree of influence indicated by the index data exceeds a predetermined reference.   14. The digital camera according to claim 1, further comprising a recording control unit that records the index data on a recording medium in association with image data acquired by photographing with flash emission. In a digital camera comprising an imaging unit that generates image data representing a subject, a light emitting unit that emits a flash, and a face detection unit that performs face detection processing on the image data generated by the imaging unit. A method for controlling the amount of light emitted from the flash using a detection result output by a face detection means,
A light emission amount determining step for obtaining the light emission amount of the flash by a calculation process capable of setting the degree of consideration of the face in the determination of the light emission amount as a calculation parameter;
Prior to the light emission amount determination step, index data indicating the degree to which the movement of the digital camera or the subject affects the determination of the light emission amount is acquired, and the value of the calculation parameter is set to a value determined based on the value of the index data. And a parameter setting step for setting. In the light emission amount determining step, based on the detection result of the face detection process executed on one image data generated by the imaging unit and the other image data generated by the imaging unit as the calculation process. To calculate the amount of light emission based on the required amount of light of the subject estimated
In the parameter setting step, as the index data, data serving as an index of a time difference between the time when the one image data is generated and the time when the other image data is generated is acquired, and the time difference is at least within a predetermined range. 16. The control method according to claim 15, wherein the value of the calculation parameter is set so that the degree of consideration of the face decreases as the time difference increases.   17. The control method according to claim 16, wherein, in the parameter setting step, data indicating a shooting mode set for the digital camera and / or a state of the digital camera is acquired as the index data.   18. The control according to claim 17, wherein, in the parameter setting step, the value of the calculation parameter is set so that the degree of consideration of a face becomes lower in a shooting mode and / or state in which a possibility of blurring is high. Method.   18. The control according to claim 17, wherein, in the parameter setting step, the value of the calculation parameter is set so that the degree of consideration of the face becomes lower as the shooting mode and / or state has a longer estimated time difference. Method. When the digital camera further comprises time measuring means for measuring a time difference,
17. The control method according to claim 16, wherein, in the parameter setting step, data indicating the time difference is acquired by the time measuring means.   In the parameter setting step, data indicating a ratio of the entire face image detected by the face detection unit is acquired as the index data, and when the ratio is at least a ratio in a predetermined range, the ratio is 16. The control method according to claim 15, wherein the value of the calculation parameter is set such that the smaller the value is, the lower the degree of consideration of the face is.   In the parameter setting step, data indicating a focal length is acquired as the index data, and when the focal length is at least a predetermined range, the longer the focal length, the lower the degree of consideration of the face. The control method according to claim 15, wherein a value of the calculation parameter is set. When the digital camera includes camera shake detection means,
In the parameter setting step, as the index data, data indicating a blur amount detected by a camera shake detection unit is acquired, and when the blur amount is at least a blur amount within a predetermined range, the larger the blur amount, the more the face The control method according to claim 15, wherein the value of the calculation parameter is set so that the degree of consideration of the value becomes low. When the digital camera is provided with distance measuring means for measuring the distance from the digital camera to the subject,
In the parameter setting step, data indicating the distance measured by the distance measuring means is acquired as the index data, and when the distance is at least a length of a predetermined range, the longer the distance is, the more the face is considered. The control method according to claim 15, wherein the value of the calculation parameter is set so that the degree is low.   The control method according to any one of claims 15 to 24, further comprising a warning step of performing a predetermined warning operation when the degree of influence indicated by the index data exceeds a predetermined reference.   The control method according to any one of claims 15 to 25, further comprising a recording step of recording the index data in a recording medium in association with image data acquired by photographing with flash emission.

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