JP2008079158A - Digital camera and control method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a digital camera which utilizes the information of a detected face to control the light emission quantity of a flash and can execute flash photographing at a propter light emission quantity for an original subject (other than a person), even if a person unexpectedly comes into a photographing range. <P>SOLUTION: A flash control means 19 of the digital camera is provided with a first operating means 42 for obtaining a temporary proper value Cf of the light emission quantity by utilizing the information of the detected face, a second operating means 39 for obtaining a temporary proper value Cc by utilizing the information of the subject in a predetermined region such as a center, a range limiting means 40 for limiting a range of a value to be obtained by a proper light emission quantity Ch on the basis of the temporary proper value Cc, and a light emission quantity determining means 44 for executing adjustment using the temporary proper value Cf within the limited range to determine the proper light emission quantity Ch of the flash. <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

  In the methods disclosed in Patent Documents 1 and 2, when a subject including a face is flash-photographed, an image with appropriate brightness can be obtained without the face portion being overexposure and the face portion being darkened. it can. This is preferable for shooting with a person as a target, but is not necessarily preferable when an object other than a person is a shooting target. For example, a person who was about to shoot an animal or a building happened to have a person in the vicinity, so the flash intensity was adjusted according to the brightness of the person's face, and the original subject was white. This is because inconveniences such as skipping and appearing dark may occur.

  In view of this problem, the present invention is a digital camera capable of performing flash shooting with a light emission amount appropriate for an original shooting target (other than a person) even when a person unexpectedly enters the shooting range. It is an issue to provide.

  The digital camera of the present invention detects an image included in the image data generated by the imaging unit that generates image data representing the subject, a light emitting unit that emits flash, and the image unit, and an area corresponding to the face is detected. And a face area extraction unit that outputs area information to be displayed, and controls the amount of light emitted from the flash using the area information output by the face area extraction unit. The digital camera includes a first calculation unit that obtains a temporary appropriate value Cf of the light emission amount by performing calculation using region information output from the face region extraction unit for the image data generated by the imaging unit, and imaging Second calculation means for obtaining a temporary appropriate value Cc of the amount of light emission by performing an operation for distinguishing a predetermined area of the image data from an area other than the predetermined area for the image data generated by the means. . The second calculation means preferably obtains the provisional appropriate value Cc of the light emission amount by performing a calculation for distinguishing between the central portion of the image and the peripheral portion of the image, for example.

  Further, the digital camera includes a range limiting unit that limits a range of values that the appropriate light emission amount Ch can take based on the temporary appropriate value Cc supplied from the second calculation unit, and a range limited by the range limiting unit. And a light emission amount determining unit that performs adjustment using the provisional appropriate value Cf supplied from the first calculation unit as a reference value to determine the appropriate light emission amount Ch of the flash. For example, the range limiting unit determines an upper limit value and / or a lower limit value of the appropriate light emission amount Ch.

  It is desirable that the appropriate amount of light emitted from the flash is determined to be the amount of light that can illuminate the subject with the amount of light required by the subject, but the amount of light required by the subject depends on the reflectance of the subject, the brightness of the subject, It fluctuates according to the distance from the digital camera to the subject. In general, the farther the distance is, and the lower the reflectance of the subject, the less reflected light from the subject, and it is required to irradiate more light. Even when the subject is dark, a lot of light is required to fill the difference from the appropriate exposure. Therefore, even when the same range is photographed, the appropriate light emission amount obtained by the calculation varies depending on what is regarded as the main subject and the calculation is performed.

  In the above configuration, the calculation is performed in consideration of the face using the region information output by the face region extraction unit, but on the other hand, the calculation considering the possibility of the original subject such as the center subject is also performed. However, a certain restriction is imposed on the result of the calculation considering the face based on the result of the calculation considering the other. For this reason, even if the detected face is the main subject, the face is only included in the shooting range by chance, and there is no major inconvenience even if there is another main subject. The amount of light emission is determined.

  Further, the digital camera is further provided with a third calculation means for obtaining a temporary appropriate value Cn of the light emission amount without distinguishing a specific area for the image data generated by the image pickup means, and the range limiting means includes the appropriate light emission. The upper limit value and / or the lower limit value of the amount Ch may be determined as a value within a restricted range based on the provisional appropriate value Cn supplied from the third calculation means.

Thus, the upper limit value and the lower limit value of the appropriate light emission amount Ch are not set to excessive values, and the flash light emission amount is set to a value that is not inconvenient even when the center subject or the like is not actually considered. Is determined.

  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, and performs calculation using area information output from the face area extraction unit for image data generated by the imaging unit, thereby emitting light. A first calculation step for obtaining a temporary appropriate value Cf of the amount, and a calculation for distinguishing a predetermined region of the image data from a region other than the predetermined region with respect to the image data generated by the imaging means. The second calculation step for obtaining the appropriate value Cc, the range restriction step for restricting the range of values that the appropriate light emission amount Ch can take based on the temporary appropriate value Cc obtained in the second calculation step, and the range restriction step. The appropriate flash amount Ch of the flash is calculated by adjusting the temporary appropriate value Cf obtained in the first calculation step as a reference value within the range. It is characterized in that it has a light emission amount determination step of constant.

  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 area extraction unit 24 is provided that outputs a value indicating presence / absence, and information indicating the area corresponding to the detected face (hereinafter, area information) when there is a face. 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 a first computing means 42, a second computing means 39, a third computing means 41, a parameter storage means 43, a range limiting means 40, and a light emission amount determining means 44. The first calculation means 42, the second calculation means 39, the third calculation means 41, the range limiting means 40, 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 42 receives supply of non-light emitting image data and preliminary light emitting 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. In addition, the first 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 executed using the two types of images and the area information, thereby obtaining and outputting a temporary appropriate value Cf of the flash emission amount when the dimming is performed in consideration of the face.

  Similar to the first calculation means, the second calculation means 39 receives supply of non-light emission image data and preliminary light emission image data from the image input control section 23 under the control of the overall control section 30. The second calculation means uses these two types of images to execute a calculation process described later, whereby a temporary appropriate value of the flash emission amount when the light control is performed in consideration of the subject near the center of the image. Obtain and output Cc. The range limiting unit 40 determines an upper limit value U and a lower limit value L of the flash emission amount based on the temporary appropriate value Cc output by the second calculation unit. Alternatively, instead of determining the upper limit value and the lower limit value, some values (discrete values) allowed as the value of the light emission amount may be determined.

  Similar to the first calculation means, the third calculation means 41 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. The third calculation means obtains a temporary appropriate value Cn of the flash light emission amount when the dimming is performed in consideration of the entire image equally by executing calculation processing described later using these two types of images. ,Output.

  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.

  The light emission amount determining means 44 uses the temporary appropriate value Cf output from the first calculating means, the temporary appropriate value Cn output from the third calculating means 41, and the parameter α read from the parameter storage means 43. The amount of main light emission is obtained. At this time, the light emission amount determining means 44 determines the light emission amount as the upper limit value U if the light emission amount obtained by the calculation exceeds the upper limit value U determined by the range limit means 40. If the light emission amount obtained by the calculation is less than the lower limit value L determined by the range limit means 40, the light emission amount is determined as the lower limit value L. Alternatively, when the light emission amount obtained by the calculation becomes a value different from the specific value determined by the range limiting means 40, the light emission amount is determined to be a value closest to the value obtained by the calculation among the specific values. . Based on the determination, the light emission amount of the flash 11 is controlled.

  Hereinafter, the processing performed by the first calculation unit 42, the second calculation unit 39, the third calculation unit 41, the range limiting unit 40, and the light emission amount determination unit 44 will be further described. The first computing means 42, the second computing means 39, and the third computing means 41 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 42. Hereinafter, as illustrated in FIG. 4, the case where the region 46 a is extracted by the face region extraction unit 24 will be described as an example. The first calculation means 42 selects the area block group 47a corresponding to the area 46a indicated by the area information supplied from the face area extracting unit 24 (S101). 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 first calculation means obtains luminance information Ya (p, q) of the selected area block for the non-light emitting image data (S102). 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. Further, the luminance information Yb (p, q) of the selected area block is also acquired for the preliminary light emission image data (S103). In the example of FIG. 4, since the block group 47a selected for the region 46a includes two region blocks, luminance information Ya (p1, q1) to Ya (p2, q2) for two blocks and Yb (p1, q1) to Yb (p2, q2) are acquired.

  Subsequently, for each selected area block, the difference Yd (p, q) between the luminance information Yb (p, q) acquired in step S103 and the luminance information Ya (p, q) acquired in step S102 is calculated. (S104) 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 (S105). In the example of FIG. 4, the differences Yd (p1, q1) to Yd (p2, q2) for two blocks are obtained, and the temporary appropriate value Cf 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 (p2, q2), and the light emission amount to obtain the reflected light amount that provides the optimum exposure is obtained. Is output as a temporary appropriate value Cf.

  FIG. 6 is a flowchart showing the processing of the second calculation means 39. The second calculation means 39 acquires the luminance information Ya (u, v) of the area block near the center of the non-light emitting image data (S201). Further, the luminance information Yb (u, v) of the area block near the center of the non-light emitting image data is also acquired for the preliminary light emitting image data (S202). In the example of FIG. 4, the luminance information Ya (u1, v1) to Ya (u12, v12) and Yb (u1, v1) to Yb (u12, v12) for 12 blocks for the area block group 38 near the center. ) To get.

  Subsequently, for each area block, a difference Yd (u, v) between the luminance information Yb (u, v) acquired in step S202 and the luminance information Ya (u, v) acquired in step S201 is calculated (S203). Based on the obtained difference Yd (u, v), an appropriate value (temporary appropriate value Cc) of the flash emission amount when the light control is performed in consideration of the subject near the center is determined (S204). In the example of FIG. 4, the differences Yd (u1, v1) to Yd (u12, v12) for 12 blocks are obtained, and the temporary appropriate value Cc is determined based on these differences. For example, after increasing the weighting of the differences Yd (u1, v1) to Yd (u12, v12) obtained for the region block near the center, the weighted average of the differences Yd (1, 1) to Yd (n, m) is calculated. Ask. Then, the amount of reflected light per unit light emission amount from the subject is estimated based on the weighted average, and the light emission amount that gives the reflected light amount that provides the optimum exposure is obtained therefrom, and this is output as a temporary appropriate value Cc.

  FIG. 7 is a flowchart showing the processing of the third calculation means. The third calculation means 41 acquires the luminance information Ya (1, 1) to Ya (n, m) for each area block of the non-light emitting image data (S301). Also for 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 by the same procedure (S302). Subsequently, for each region block (x, y), a difference Yd between the luminance information Yb (x, y) acquired in step S302 and the luminance information Ya (x, y) acquired in step S301 is calculated (S103). . Then, based on the differences Yd (1,1) to Yd (n, m) of all the area blocks, an appropriate value (temporary appropriate value Cn) of the flash light emission amount when the light control is performed in consideration of the entire image uniformly. ) Is determined (S304). 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 (1,1) to Yd (n, m), and the light emission amount that provides the reflected light amount with which an optimum exposure can be obtained is obtained therefrom. This is output as a temporary appropriate value Cn.

  The range limiting unit 40 sets an upper limit value and a lower limit value for the appropriate light emission amount Ch determined by the light emission amount determination unit 44, thereby reducing the value of the appropriate light emission amount Ch output by the light emission amount determination unit 44 within a predetermined range. Limit to value. The range limiting means 40 is based on the appropriate light emission amount when the light is adjusted in consideration of the subject near the center of the image, that is, the temporary appropriate value Cc output from the second calculating means 39, and the temporary appropriate value Cc. The appropriate light emission amount Ch is limited to a range that seems to be appropriate based on the value of. That is, the appropriate light emission amount Ch is not limited to a fixed range, but as shown in FIG. 8, the range is based on the upper limit value U (Cc) and the lower limit value L (Cc) that vary according to the temporary appropriate value Cc. Limit. The upper limit value U (Cc) and the lower limit value L (Cc) are, for example, the maximum values that can be taken by the absolute value of the difference between the appropriate value Cc and the appropriate value Cn when the appropriate value Cc is larger than the appropriate value Cn. When A and the appropriate value Cc are smaller than the appropriate value Cn, the maximum value B that can be taken by the absolute value of the difference between the appropriate value Cc and the appropriate value Cn is adjusted in advance by dimming various subjects. Obtained empirically, the upper limit value U (Cc) of the appropriate light emission amount Ch is set to Cc + A, and the lower limit value L (Cc) is set to Cc−B.

  The light emission amount determining means 44 determines an appropriate light emission amount Ch based on the following equations (1) and (2). Here, Ck is a provisional appropriate light emission amount.

Ck = Cn × (1−α) + Cf × α (1)

  According to the formulas (1) and (2), the appropriate light emission amount Ch is affected by the face when a face is detected, but is appropriate when the center subject is considered instead of the face. It does not deviate greatly from the range of the light emission amount.

  The parameter α is set by the face area extraction unit 24, the camera shake detection unit 35, or the focus adjustment unit 20 as described above. 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. 9A, FIG. 9B, FIG. 10A, and FIG. 10B are diagrams showing the relationship between the region indicated by the image data and the region information and the region block selected in step S101 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. 9B and 10B indicates the position of the face during light control.

  As shown in FIGS. 9A and 9B, when the proportion of the face in the image is relatively large, most of the block group 47b corresponding to the face area 46b is not detected even when the face position is slightly different from the face detection time. , Corresponding 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. 10A and 10B, when the ratio of the face to the image is small and there is only one block corresponding to the face area 46c, the position of the face has shifted, Block 47c no longer corresponds to face area 46c. 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 obtained by the first 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. The value of the parameter α is determined by referring to a look-up table (LUT) that defines the correspondence between the face ratio and the parameter α. 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. 11 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 (1) is performed using the value set using this LUT, 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 subject moves or moves. Even if blurring occurs, the light emission amount 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. 12, 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 of (1) 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. 13, when the horizontal axis is the 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 (1) 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 by the camera shake detection unit 35 or the focus adjustment unit 20. 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.

  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.

  As described above, in the digital camera according to the present embodiment, the light control is performed using the face information detected by the first calculation unit, but on the other hand, the original photographing such as the center subject is performed by the second calculation unit. Dimming is performed in consideration of what is likely to be a target, and the output of the light emission amount determining means 44 is limited to a certain range based on the temporary appropriate value Cc output by the second calculating means. For this reason, even when a face of a person who is not an object to be photographed is detected and a calculation process that takes that face into consideration is executed at the time of light control, the flash emission amount finally determined is adjusted according to the center subject. The amount of light emitted when dimming is not greatly deviated. In other words, it is slightly higher or slightly lower than when dimming according to the subject in the center instead of the face, so the original subject to be shot out is dark or dark due to the face There is no excuse.

  Further, in the present embodiment, as shown in the equation (1), the weighting of the temporary appropriate value Cn obtained by the dimming without considering the face and the temporary appropriate value Cf obtained by the dimming considering the face Since the appropriate light emission amount Ch is obtained by calculating the average, the influence of the temporary appropriate value Cf in the light emission amount adjustment can be easily increased or decreased with one setting of the parameter α. Since the 1st calculating means 41, the 2nd calculating means 39, and the 3rd calculating means 41 should just have always performed the calculation based on the same calculation formula, compared with what uses a several calculation formula properly according to a light control policy, The circuit structure or program of each arithmetic means can be simplified.

[Embodiment 2]
The digital camera and the light emission amount control method according to the first embodiment are effective when the object in the center of the shooting range is the original shooting target, and the face in the vicinity is only a face included in the shooting range by chance. It is. However, in actual shooting, what is in the center is not necessarily the main subject, and in fact there are cases where the side face is the main subject. In such a case, if the one at the center is one that reflects light very well or does not reflect light compared to the surroundings, the value of the appropriate light emission amount Ch is set based on the temporary appropriate value Cc. It cannot be said that the restriction does not produce a negative result.

  Therefore, in the digital camera and the light emission amount control method of the present embodiment, the value of the appropriate light emission amount Ch is limited based on the temporary appropriate value Cc when the light is adjusted according to the center subject. The limit based on the provisional proper value Cc is further restricted based on the provisional proper value Cn output by the third calculation means so as not to overshoot.

  The digital camera of the present embodiment has the same external appearance and internal configuration as the digital camera of the first embodiment, but the range limiting means provided in the flash control unit 19 is different. FIG. 14 shows the configuration and input / output data of the flash controller 19 in this embodiment. In the present embodiment, the provisional appropriate value Cn output from the third calculating means is supplied to the range limiting means 37 in addition to the temporary appropriate value Cc output from the second calculating means 39.

  As with the range setting unit 40 of the first embodiment, the range setting unit 37 sets an upper limit value U (Cc) and a lower limit value L (Cc) that vary according to the temporary appropriate value Cc for the appropriate light emission amount Ch. The value of the appropriate light emission amount Ch output from the light emission amount determining means 44 is limited to a value within a predetermined range. However, in the present embodiment, the range setting unit 37 limits the settable range of the upper limit value as shown in FIG.

  As the minimum value LU and the maximum value UU within the settable range of the upper limit value, values that are considered to be reasonable are set based on experience from the provisional appropriate value Cn output by the third calculation means. A value that seems to be appropriate based on experience is, for example, an appropriate value as the upper limit of the flash light emission amount when the light is normally adjusted without considering the object and face in the center. A value obtained by adding a predetermined adjustment value to the appropriate value Cn is referred to as LU, and a value obtained by adding another adjustment value larger than the adjustment value to the temporary appropriate value Cn is referred to as UU. The adjustment value to be added to the temporary appropriate value Cn is acquired in advance by experience by repeating dimming for various subjects.

  For example, when there is an object that does not require a lot of light at the center of the imaging range (close, strong reflection, bright color, etc.), an upper limit value U (Cc) determined according to the provisional appropriate value CC. ) Is a relatively low value. However, in the present embodiment, when the upper limit value U (Cc) obtained by calculation (for example, U (Cc) = Cc + A) is equal to or less than the minimum value LU of the upper limit value as shown in FIG. 16A, the upper limit value is the minimum value. Set to LU. In this case, the appropriate light emission amount Ch is not limited to the value U (Cc), and can take a value in the range from the value L (Cc) to the value LU. Also, when there is an object that requires moderate light in the center of the shooting range (such as an object that is reasonably distant from the digital camera, the light reflection is normal, the color is neither bright nor dark) For this reason, the upper limit value U (Cc) determined according to the provisional appropriate value Cc is usually larger than the minimum value LU of the upper limit value and smaller than the maximum value UU. In this case, as shown in FIG. 16B, the obtained upper limit value U (Cc) is set as it is as the upper limit value of the appropriate light emission amount Ch, and the value that the appropriate light emission amount Ch can take is a value L (Cc). To a value U (Cc). Also, when there is something that requires a lot of light (one that is far from the digital camera, one that absorbs light, one that is darker than the surroundings, etc.) in the center of the shooting range The upper limit value U (Cc) determined according to the provisional appropriate value Cc is a relatively high value. However, in the present embodiment, when the upper limit value U (Cc) obtained by calculation is equal to or greater than the maximum value UU of the upper limit value, the upper limit value is set to the maximum value UU. In this case, the appropriate light emission amount Ch cannot take a value larger than UU.

  In the present embodiment, the amount of light required by the object in the center of the shooting range affects the determination of the flash emission amount, but does not influence too strongly. Therefore, even if the target near the center is not the original shooting target, and the face arranged in the peripheral part is not the original shooting target, there is no inconvenience in any case. Flash shooting is performed in quantity.

  In the present embodiment, even if there is a face in the center of the shooting range, the settable range of the upper limit value is limited, but the value is higher than the light emission amount Cc required for the subject (that is, the face) in the center. Even if the upper limit value is limited, there is no problem because the amount of light emission necessary for the face is not limited. The same applies whether the upper limit value U (Cc) is limited to the maximum value UU or the minimum value LU.

  In the illustrations of FIGS. 15 and 16A to 16C, only the settable range of the upper limit value U (Cc) is limited, but the settable range of the lower limit value L (Cc) is similarly limited. Needless to say, it is good.

  As described above, according to the present embodiment, no matter what the subject is or how much light the subject needs, it cannot be covered by image processing performed later, such as overexposure. Completely failed photos will disappear, and it will be possible to always obtain good quality images. In addition, the above explanation assumes that the main subject is completely unknown. For example, if the set shooting mode is the person mode, the person is likely to be the main subject. Therefore, the degree of effect may be adjusted by varying the UU and LU values for each shooting mode. One of the effects of the present embodiment is that the degree of effect can be easily adjusted simply by changing the set value.

  As described above, the two embodiments have been described as examples, but the present invention is not limited to these embodiments, and the light emission amount obtained by the calculation considering the face is determined based on a specific part of the shooting range (for example, the center). ) And a digital camera that limit to a predetermined range of values are all within 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 The flowchart which shows the process of a 3rd calculating means Diagram for explaining the range of light emission limit 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. The figure for explaining the restriction of the settable range of the upper limit value Diagram for explaining the upper limit value set in response to range restrictions Diagram for explaining the upper limit value set in response to range restrictions Diagram for explaining the upper limit value set in response to range restrictions

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

Claims (8)

An imaging unit that generates image data representing an object, a light emitting unit that emits flash, and a face that detects a face included in the image data generated by the imaging unit and outputs area information indicating an area corresponding to the face A digital camera comprising a region extraction unit, and controls the amount of light emitted from the flash using region information output by the face region extraction unit,
First calculation means for obtaining a temporary appropriate value Cf of the light emission amount by performing calculation using area information output by the face area extraction means for the image data generated by the imaging means;
Second computing means for obtaining a temporary appropriate value Cc of the light emission amount by performing computation for distinguishing between a predetermined area of the image data and an area other than the predetermined area for the image data generated by the imaging means;
Range limiting means for limiting the range of values that the appropriate light emission amount Ch can take based on the temporary appropriate value Cc supplied from the second calculating means;
A light emission amount determining means for performing an adjustment using the temporary appropriate value Cf supplied from the first calculation means as a reference value within a range limited by the range limiting means, and determining an appropriate light emission amount Ch of the flash; A digital camera characterized by comprising.   2. The digital camera according to claim 1, wherein the second calculation means obtains a temporary appropriate value Cc of the light emission amount by performing a calculation for distinguishing between a central portion of the image and a peripheral portion of the image.   The digital camera according to claim 1, wherein the range limiting unit determines an upper limit value and / or a lower limit value of the appropriate light emission amount Ch. A third operation means for obtaining a temporary appropriate value Cn of the light emission amount by performing an operation without distinguishing a specific area on the image data generated by the imaging means;
The range limiting means determines an upper limit value and / or a lower limit value of the appropriate light emission amount Ch to a value within a restricted range based on the value of the temporary appropriate value Cn supplied from the third calculation means. The digital camera according to claim 3. An imaging unit that generates image data representing an object, a light emitting unit that emits flash, and a face that detects a face included in the image data generated by the imaging unit and outputs area information indicating an area corresponding to the face In a digital camera provided with an area extracting means, a method for controlling the flash emission amount using area information output by the face area extracting means,
A first calculation step for obtaining a temporary appropriate value Cf of the light emission amount by performing a calculation using area information output from the face area extraction unit for the image data generated by the imaging unit;
A second calculation step of obtaining a temporary appropriate value Cc of the light emission amount by performing a calculation for distinguishing a predetermined region of the image data from a region other than the predetermined region for the image data generated by the imaging unit;
A range limiting step of limiting a range of values that the appropriate light emission amount Ch can take based on the temporary appropriate value Cc obtained in the second calculation step;
A light emission amount determination step for determining the appropriate light emission amount Ch of the flash by performing adjustment using the temporary appropriate value Cf obtained in the first calculation step as a reference value within the range limited in the range restriction step; A control method for a digital camera, comprising:   6. The control method according to claim 5, wherein, in the second calculation step, the provisional appropriate value Cc of the light emission amount is obtained by performing a calculation for distinguishing between a central portion of the image and a peripheral portion of the image.   The control method according to claim 5 or 6, wherein, in the range limiting step, an upper limit value and / or a lower limit value of the appropriate light emission amount Ch is determined. Performing a third calculation step for obtaining a temporary appropriate value Cn of the light emission amount by performing a calculation without distinguishing a specific area on the image data generated by the imaging means;
In the range limiting step, an upper limit value and / or a lower limit value of the appropriate light emission amount Ch is determined to be a value within a restricted range based on the value of the temporary appropriate value Cn obtained in the third calculation step. The control method according to claim 7.

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