JP2008076903A - Digital camera and control method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable a digital camera capable of controlling the emitted light amount of a flash by using the detected result of the face to always perform flash photographing, utilizing a proper emitted light amount, regardless of the number of faces detected. <P>SOLUTION: The flash control means 19 of the digital camera 1 regards only the region, corresponding to each of N (N is integer) detected faces as a region corresponding to the face and performs calculation, taking into consideration the face, for determining the temporary proper value Cfi (1≤i≤N) of the light amount emitted (S201 to S209). The proper emitted light amount Ch of the flash is determined, by performing an adjustment for setting the temporary proper values Cf1 to CfN as reference values. <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.

  Digital cameras usually take images before the shutter release button is pressed, and the images taken at that stage are used for exposure adjustment and focus adjustment, as well as dimming to determine the appropriate flash output. It's being used. 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. Japanese Patent Laid-Open No. 2004-228561 uses a form in which the amount of light emission is obtained using only data of the area corresponding to the face, or light emission using image data in which the weight of the area corresponding to the face is set higher than other areas. A method for determining the quantity is shown.
JP 2003-107567 A JP 2006-074164 A

  However, Patent Documents 1 and 2 merely exemplify a method for controlling the light emission amount in the case where one face is included in the shooting range, and a method for controlling the light emission amount when a plurality of faces are detected. There is no specific description. For example, it is possible to treat a plurality of areas as a single area by reducing the amount of light emission when the total area of the plurality of areas determined as faces exceeds a predetermined ratio. This method has a disadvantage that even if the amount of light reflected from each face is not so strong, if the total area of the face exceeds a predetermined ratio, the light emission amount is set to be weak. Further, a method of selecting any one face from a plurality of faces, such as a face closest to the center, and applying the methods of Patent Documents 1 and 2 to the face can be considered. In the case of the method, if the face in the center is small and the faces on both sides are large, or if the person in the center is dark black and the people on both sides are fair, there are inconveniences such as the faces on both sides are overexposed. is there. As described above, if the same method as that when there is only one face is simply applied when there are a plurality of faces, overexposure cannot be prevented for all the faces.

  In view of this problem, an object of the present invention is to provide a digital camera that can always perform flash photography with an appropriate light emission amount regardless of the number of detected faces.

  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 digital camera includes a calculation unit and a light emission amount determination unit for controlling the light emission amount of the flash using the detection result output from the face detection unit.

  The calculation means, for each of N (N is an integer) faces detected by the face area extraction means, considers only the faces as faces included in the image data, and performs the calculation considering the faces, thereby calculating the light emission amount. Is determined as a temporary appropriate value Cfi (1 ≦ i ≦ N). Here, the calculation considering the face means a process of using the detection result of the face in any form for the calculation for dimming. For example, the calculation means obtains the temporary appropriate value Cfi by using only data in an area corresponding to the i-th detected face in the image data. Alternatively, the data in the area corresponding to the i-th detected face is given higher weight than the data in other areas, and the light emission amount is obtained using the entire image data. As a result, the same number of the detected faces, that is, N provisional appropriate values Cf1 to CfN are obtained.

  The light emission amount determination means determines the appropriate light emission amount Ch of the flash by performing adjustment using the N temporary appropriate values Cf1 to CfN supplied from the calculation means as reference values. The adjustment using the temporary appropriate values Cf1 to CfN as the reference value means that the light emission amount is set to a value within a range that is estimated to be inconvenient from the reference value. The range of the light emission amount that is not inconvenient for each face can be estimated from the provisional appropriate value obtained for the face. Therefore, overexposure can be prevented for all faces if the light emission amount is set to a value that is inconvenient in any reference value.

  In one embodiment of the present invention, the temporary appropriate value Cfmin having the smallest value is selected from the temporary appropriate values Cfi (1 ≦ i ≦ N) supplied from the calculation means, and the minimum temporary appropriate value Cfmin is selected as the reference value. As a result, the appropriate light emission amount Ch is determined. The face whose calculated temporary appropriate value is the smallest is the face that is most likely to be out of the plurality of detected faces. Therefore, the flash light emission amount is determined so as not to greatly deviate from the temporary appropriate value Cfmin. If so, overexposure can be surely prevented.

  The method of the present invention is a method for controlling the amount of light emitted from the flash by the digital camera having the above-described configuration, and for each of N (N is an integer) faces detected by the face detection means, only the faces are used as the image data. A calculation step for obtaining a temporary appropriate value Cfi (1 ≦ i ≦ N) of the light emission amount by performing a calculation in consideration of the face as a face included in the face, and N temporary proper values Cf1 obtained in the calculation step A light emission amount determining step for determining an appropriate light emission amount Ch of the flash by performing adjustment using .about.CfN as a reference value.

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

[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. In addition to measuring the amount of reflected light, preliminary light emission has the purpose of preventing red eyes. The second light emission is a main light emission for obtaining a sufficient exposure amount. If the light emission amount of the main light emission is appropriate, an image with appropriate brightness 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 photographing mode set by the mode dial 3. 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 provided for each shooting scene, such as “priority auto”, “blur reduction”, “natural photo”, “person”, “landscape”, “night view”. The digital camera 1 set to the “AUTO” mode automatically pops up the built-in flash 4 when it is determined that flash photography is necessary, and causes the flash to emit light in conjunction with the operation of the shutter release button 2. On the other hand, since “natural photo” is a mode for performing flashless shooting, the built-in flash 4 does not operate in the digital camera 1 set to this mode even if the shutter release button 2 is operated. 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. When loading JPEG data, the reverse conversion is performed before loading the data 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.

  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.

  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. When a plurality of faces are detected by the face area extraction unit 24, the same number of area information as the number of detected faces is supplied. Then, by using the two types of images and area information, a calculation process described later is executed for each face to obtain and output temporary appropriate values Cf1 to CfN of the flash emission amount when the face is considered.

  The parameter α stored in the parameter storage unit 43 is a parameter that can be changed by setting, and is set by the face area extraction unit 24 and the camera shake detection unit 35. Alternatively, the overall control unit 30 receives the outputs of the face area extraction unit 24 and the camera shake detection unit 35 and sets the parameter α. When the face area extracting unit 24 sets parameters, one value is set for each extracted area. The camera shake detection unit 35 and the focus adjustment unit 20 set one value regardless of the number of regions extracted by the face region extraction unit 24.

  The light emission amount determination means 44 uses the temporary appropriate value Cn output from the first calculation means 41, the temporary appropriate values Cf1 to CfN output from the second calculation means, and the parameter α read from the parameter storage means 43. Thus, 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, the first calculation unit 41 calculates, for each region block (x, y), the difference Yd 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), and the amount of reflected light from which optimal exposure can be obtained. The amount of light emission 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 that does not depend on the face is performed, for example, by increasing the weight of the area block near the center of the image.

  FIG. 6 is a flowchart showing the processing of the second calculation means. Hereinafter, as illustrated in FIG. 4, the case where three areas 46 a, 46 b, and 46 c are extracted by the face area extracting unit 24 will be described. The second calculation means first initializes the value of the counter i to 1 (S201). Then, the area block group 47a corresponding to the area 46a indicated by the i-th (here, first) area information supplied from the face area extracting unit 24 is selected (S202). For example, the area of a range that overlaps the region 46a is calculated for each region block, and the block group 47a in which half or more of the area overlaps the region 46a is selected.

  Subsequently, the second calculation means obtains the luminance information Ya (p, q) of the selected area block for the non-light emitting image data (S203). Further, the luminance information Yb (p, q) of the selected area block is also acquired for the preliminary light emission image data (S204). In the example of FIG. 4, since the block group 47a selected for the region 46a includes 12 region blocks, luminance information Ya (p1, q1) to Ya (p12, q12) for 12 blocks and Yb (p1, q1) to Yb (p12, q12) are acquired.

  Subsequently, for each selected area block, the difference Yd (p, q) between the luminance information Yb (p, q) acquired in step S204 and the luminance information Ya (p, q) acquired in step S203 is calculated. (S205) Based on the difference Yd (p, q) obtained for the selected area block, an appropriate value (temporary appropriate value Cf1) of the flash emission amount when considering the face is determined (S206). In the example of FIG. 4, differences Yd (p1, q1) to Yd (p12, q12) for 12 blocks are obtained, and a provisional appropriate value Cf1 is determined based on these differences. For example, the amount of reflected light per unit light emission amount from the subject is estimated from the simple average of the differences Yd (p1, q1) to Yd (p12, q12), and the light emission amount to obtain the reflected light amount that provides the optimum exposure is obtained. Is a temporary appropriate value Cf1.

  The second calculating means 42 repeats the processing from step S202 to S206 until the counter value i matches the number N of detected faces (S207). In the example of FIG. 4, since there are three detected faces, the counter is counted up (S208), and the processing from steps S202 to S206 is performed for the region 46b and the block group 47b, and the region 46c and the block group 47c, respectively. Execute. When the above processing is completed for N regions (S207), the second calculation means 42 outputs the temporary appropriate values Cf1 to CfN obtained in step S206 (S209). In the example of FIG. 4, three provisional appropriate values Cf1, Cf2, and Cf3 are output.

  The light emission amount determining means 44 performs adjustment using the temporary appropriate value Cn output from the first calculating means 41 and the temporary appropriate values Cf1 to CfN output from the second calculating means 42 as reference values, thereby adjusting the appropriateness of the flash 11. The light emission amount 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 calculations based on the following equations (1) and (2).

Cf = minimum (Cf1, Cf2... CfN) (1)
Appropriate light emission amount Ch = Cn × (1−α) + Cf × α (2)
That is, for a plurality of faces, the one with the smallest value is selected from the calculated temporary appropriate values (Equation (1)), and the value Cf (Cfmin) and the temporary appropriate value Cn are used as a reference. By performing the adjustment, an appropriate light emission amount Ch is obtained (Equation (2)). The minimum appropriate value is used as the reference for adjustment because the face with the smallest appropriate amount of light emission is the face that is the most reflective and prone to overexposure. This is because if the amount is adjusted, overexposure can be prevented for all faces. For example, in the example of FIG. 4, the provisional appropriate value Cf1 of the light emission amount obtained for the largest face is the minimum value, so Cf = Cf1.

  As described above, the parameter α is set by the face area extraction unit 24, the camera shake detection unit 35, or the focus adjustment unit 20, and when set by the face area extraction unit 24, a value for each face is set. When parameter values are stored for each face, a value set for the face corresponding to the temporary appropriate value selected in equation (1) is selected as the value α used in equation (2). In the example of FIG. 4, three parameters α1, α2 and α3 are stored in the parameter storage means 43, but the value α used in the equation (2) is α1.

  Hereinafter, the parameter α setting process performed by the face area extraction unit 24 will be described. 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, there is a time lag of several tens of milliseconds between the detection of the face and the acquisition of image data at the time of non-light emission, or the acquisition of image data at the time of non-light emission and the acquisition of image data at the time of preliminary light emission. Therefore, if the subject moves during this time or if camera shake occurs, the image data used for each process may be different from each other.

  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 S202 of 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, even if the position of the face is slightly deviated from the time of face detection, most of the selected block group 47d is deviated. It corresponds to the back face (ellipse 49). Therefore, even if a deviation occurs, the luminance information of the selected block group 47d is worth reference when performing dimming. However, as shown in FIG. 8A and FIG. 8B, when the ratio of the face to the image is small and there is only one block corresponding to the face area 46e, the position of the face has shifted, The block 47e does not correspond to the face area 46e. In this case, the luminance information of the block 47e is no longer worth reference in the dimming process considering the face. This means that the reliability of the temporary appropriate value Cfi obtained 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 the present embodiment, the face area extraction unit 24 calculates, for each detected face, the ratio of the area extracted as the area corresponding to the face to the width of the image after the face extraction process is completed. To do. Then, the value of the parameter α is determined for each detected face by referring to a look-up table (LUT) that defines the correspondence between the face ratio and the parameter α. When N faces are detected, the face area extraction unit 24 determines N parameter values α1 to αN, and stores these values in the parameter storage unit 43 of the flash control unit 19. In the example of FIG. 4, the three parameters α1, α2, and α3 are stored in the parameter storage unit 43 as described above. Here, it goes without saying that instead of referring to the LUT, a circuit or 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. If the calculation process (2) is performed using the value set using this LUT, the influence of the temporary appropriate value Cf in the light emission amount adjustment is weakened when the proportion of the face in the image is small, and the subject moves or moves. Even if blurring occurs, the amount of light emission obtained by calculation does not greatly deviate from the appropriate range.

  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.

  There are various other LUTs used for determining the parameter α and for determining the parameter. For example, when a person's face is detected at the edge of the image, the person may not be a subject to be photographed. Therefore, in the LUT illustrated in FIG. 10, if the position of the extracted region is greater than or equal to Th3 and less than or equal to Th4 as the distance from the left end of the image, the value of the parameter α is set to the upper limit value αU, and When the position is other than that, that is, near the end of the image, the value of the parameter α is set to the lower limit value αL. If the calculation process (2) is performed using the value set using this LUT, when the detected face is located near the center, the influence of the temporary appropriate value Cf in the light emission amount adjustment is increased. When the position is located, the influence of the temporary appropriate value Cf in the light emission amount adjustment is weakened.

  Also, a method of determining the value of the parameter α depending on the detected face inclination (degree of neck tilt) and face orientation (front face, side face) is conceivable. In the face detection processing performed by the face area extraction unit 24, although depending on how it is learned, a face with a tilted neck or a face facing sideways has a higher probability of erroneous detection than a vertical front face. That is, the reliability of the temporary appropriate value Cf obtained by using the information on the face area is higher as the detected face inclination is vertical and closer to the front. Therefore, as shown in FIG. 11, when the horizontal axis is a face inclination and the face is inclined vertically or vertically, the value of the parameter α is set to the upper limit value αU, and the face inclination is set to a predetermined threshold Th6 or When Th7 is exceeded, the value of the parameter α is set to be smaller as the inclination is larger. When the inclination exceeds the next threshold values Th5 and Th8 and becomes horizontal or nearly horizontal, the value of the parameter α is set to the lower limit value αL. The LUT is defined as follows. Alternatively, a similar LUT is defined with the horizontal axis as the face orientation. If the calculation process (2) is performed using the values set using these LUTs, when the reliability of the temporary appropriate value Cf is high, the influence of the temporary appropriate value Cf in the light emission amount adjustment increases. When the reliability of the temporary appropriate value Cf is low, the influence of the temporary appropriate value Cf in the light emission amount adjustment is weakened.

  As described above, the parameter α may be set to a value corresponding to the amount of camera shake or the focal length. For example, when the detected camera shake amount exceeds a predetermined threshold, the value of the parameter α is set to the lower limit value αL. Alternatively, when the focal length is long, the effect of camera shake is likely to be strong, so when the focal length exceeds a predetermined threshold value, the value of the parameter α is set to the lower limit value αL. Since the amount of blur and the focal length are irrelevant to the detected face, when the parameter α is set based on the amount of blur or the focal length, any of the face-specific appropriate values Cf1 to CfN is set as the temporary appropriate value Cf. Regardless of whether or not is selected, the value stored in the parameter storage means 43 is used for the calculation.

  Note that which processing unit performs the setting of the parameter α or which LUT is used may be switched according to the setting of the shooting mode or the like, but the parameter storage unit 43 that simply stores the parameter. Instead of this, there may be provided means for receiving setting inputs from a plurality of processing units and newly obtaining an optimum parameter value using a plurality of input values.

  Further, according to the above configuration, when it is detected or predicted that there is a problem in performing dimming using the face detection result, it is possible to suppress the influence of the temporary appropriate value Cf in the light emission amount adjustment. However, in actual shooting, a problem that the digital camera cannot detect or predict in advance (for example, erroneous detection of a face) may occur. Therefore, a function for preventing the light emission amount determined by the light emission amount determination unit 44 from greatly deviating from the appropriate value may be provided even when the above problem occurs in the above configuration.

  For example, an appropriate value obtained when the light emission amount determining unit 44 performs dimming without considering the face, that is, the temporary appropriate value Cn output by the first calculating unit 41 is used as a reference, and the temporary appropriate value Cn is calculated. The appropriate light emission amount Ch is limited to a range that is considered appropriate based on the value. 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 determination means 44 is caused to execute processing based on the following equations (3) and (4) instead of the above equation (2).

Ck = Cn × (1−α) + Cf × α (3)

  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 obtained by the above equation (3) 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 (4). 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, in the digital camera according to the present embodiment, the light emission amount determination unit 44 uses the N temporary appropriate values Cf1 to CfN supplied from the second calculation unit 42 as reference values, and estimates from the reference values. Thus, since the light emission amount is set to a value within a range that is considered to be inconvenient, the light emission amount is determined to a value that is not inconvenient for any face. As a result, even when multiple faces are detected and the face size and brightness (skin color) are different for each face, flash photography is performed with an appropriate amount of light emission, and an image with no overexposure is obtained. be able to.

  In the present embodiment, as shown in the equations (2) and (3), the provisional appropriate value Cn obtained by the dimming without considering the face and the provisional appropriateness obtained by the dimming considering the face. Since the appropriate light emission amount Ch (or temporary appropriate light emission amount Ck) is obtained by calculating the 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 unit 44 is not limited to the processing based on the above equations (1) to (4), and other arithmetic expressions may be adopted. For example, the formulas (2) and (3) may calculate a mean square, a logarithmic average, etc. instead of a weighted average. 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. 12 shows the configuration and input / output data of the flash controller 19 in this embodiment. As shown in the figure, the flash control unit 19 includes a calculation unit 50, a light emission amount determination unit 51, and a weighting parameter setting unit 52.

  The arithmetic unit 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 obtains the temporary appropriate value Cn in the description of the first embodiment. The same process as the process of FIG. However, unlike the first calculation unit 41 of the first embodiment, the calculation unit 50 performs a calculation by assigning a weight to an area block corresponding to one face among the plurality of faces detected in step S104, and thereby calculating a temporary appropriate value. Cf1 to CfN are obtained. The weighting of each area block is set by the weighting parameter setting means 52.

  The weighting parameter setting unit 52 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 each area than for the area block corresponding to the area having no face. At this time, the weighting parameter setting means 51 does not uniformly set the weighting of the area block corresponding to the area from which the face is extracted, but sets the weighting higher as the face is larger. 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.

  For example, in the example shown in FIG. 4, the computing means 50 first increases the weight of the block group 47a corresponding to the area 46a, and sets the block groups corresponding to the area 46b and the area 46c to the same weight as the area having no face. Then, the arithmetic processing shown in FIG. 5 is executed to obtain a temporary appropriate value Cf1. Since the block group 47a corresponding to the area 46a includes 12 area blocks, the weights of the blocks at this time are as shown in FIG. 13A. Next, the calculation means 50 increases the weight of the block group 47b corresponding to the area 46b, and the block group corresponding to the area 46a and the area 46c has the same weight as the area having no face. To obtain a provisional appropriate value Cf2. Since the block group 47b corresponding to the area 46b includes two area blocks, the weights of the blocks at this time are as shown in FIG. 13B. Subsequently, the calculation means 50 increases the weight of the block group 47c corresponding to the region 46c, and the block group corresponding to the region 46a and the region 46b is weighted to the same weight as the region having no face, as shown in FIG. To obtain a provisional appropriate value Cf3. Since the block group 47c corresponding to the area 46c includes two area blocks, the weights of the blocks at this time are as shown in FIG. 13C.

  The light emission amount determining means 51 selects the one with the smallest value from the temporary appropriate values Cf1 to CfN obtained by the calculation means, and determines the appropriate light emission amount Ch of the flash to the minimum temporary appropriate value. Alternatively, the appropriate flash light emission amount Ch is determined to be a value obtained by adding or subtracting a predetermined value to the minimum provisional appropriate value. As a result, even when multiple faces are detected and the size and brightness (skin color) of the faces differ from face to face, flash photography is performed with an appropriate amount of light emission, and an image with no overexposure is obtained. Can do.

  Although the two embodiments have been described above as examples, the present invention is not limited to these embodiments. For example, if adjustment is performed using only the minimum value and the maximum value as reference values instead of adjusting only the minimum value among the temporary appropriate values Cf1 to CfN, it is possible not only to prevent overexposure but also brightness. The amount of light emission can be determined so that the insufficient face disappears. In addition to this, all methods and digital cameras that determine the appropriate amount of light for each face when multiple faces are detected and adjust the amount of light emitted using the appropriate amount of light for each face as a reference value are all available. It belongs to the technical scope of the 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 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) FIG. 10 is a diagram showing still another example of the LUT used for determining the parameter α. The figure which shows the structure and input / output data of the flash control part in other embodiment of this invention. Diagram showing examples of weighting parameter settings Diagram showing examples of weighting parameter settings Diagram showing examples of weighting parameter settings

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, 46a to 46e area indicated by area information,
47a to 47e area blocks corresponding to the area indicated by the area information,
48 Image data for face detection, 49 Actual face position during dimming

Claims (4)

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,
For each of N (N is an integer) faces detected by the face detection means, only the face is regarded as a face included in the image data, and calculation is performed in consideration of the face. Arithmetic means for obtaining an appropriate value Cfi (1 ≦ i ≦ N);
And a light emission amount determining means for determining the appropriate light emission amount Ch of the flash by performing adjustment using the N provisional appropriate values Cf1 to CfN supplied from the arithmetic means as reference values. camera.   The light emission amount determining means selects a temporary appropriate value having a minimum value from the N temporary appropriate values Cf1 to CfN supplied from the calculating means, and uses the minimum temporary appropriate value Cfmin as a reference value. The digital camera according to claim 1, wherein an appropriate light emission amount Ch of the flash is determined by performing adjustment. 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,
For each of the N faces (N is an integer) detected by the face area extraction unit, only the face is regarded as a face included in the image data, and the calculation considering the face is performed. A calculation step for obtaining a temporary appropriate value Cfi (1 ≦ i ≦ N);
And a light emission amount determining step for determining an appropriate light emission amount Ch of the flash by performing adjustment using the N temporary appropriate values Cf1 to CfN obtained in the calculation step as reference values. Camera control method.   In the light emission amount determining step, a temporary appropriate value having a minimum value is selected from the N temporary appropriate values Cf1 to CfN obtained in the calculating step, and the minimum temporary appropriate value Cfmin is used as a reference value. 4. The method of controlling a digital camera according to claim 3, wherein an appropriate light emission amount Ch of the flash is determined by performing adjustment.

Images